f ^K*^.*^^ ), MANUAL HUMAN MICEOSCOPICAL ANATOMY. MANUAL OF HUMAN MICROSCOPICAL ANATOMY, BY A. KOLLIKER, M PROFESSOR OF ANATOMY AND PHYSIOLOGY IN WUSZBURG. TRANSLATED BY GEORGE BUSK, F.R.S., AND THOMAS HUXLEY, F.R.S. EDITED, WITH NOTES AND ADDITIONS, BY J. DA COSTA, M.D. ILLUSTRATED BY THREE HUNDRED AND THIRTEEN ENGRAVINGS ON WOOD, PHILADELPHIA: LIPPINCOTT, GRAMBO & CO., vs- CONTENTS. INTRODUCTION. SECT. PAGE. 1. Historical Introduction, ....... 33 2. Present position of the Science, ..... 34 3. Aids to the Study (Literature, Microscope, Preparations), . . 36 GENERAL HISTOLOGY. I. OF THE ELEMENTARY PARTS, pp. 39, 40. 4. Simple and compound elementary parts, . . . . .39 5. Plastic fluid, fundamental substance, ..... 40 A. SIMPLE ELEMENTARY PARTS, pp. 41-70. 1. Elementary Granules, vesicles, nuclei 6 41 2. Of the Cells: 7. Composition, . . . . . . . .43 8. Form, chemical relations, nucleus, nucleolus, ... 44 9. Cell-formation, . . - . . . . .48 10. Free cell-formation, . . . . . . . 48 11. Endogenous cell-formation, . . . . . . .49 12. Multiplication of cells by division, ..... 54 13. Theory of cell-formation, ....... 56 14. Vital phenomena of cells, growth, ..... 59 15. Processes in the interior of the cells Absorption, . . .61 16. Excretive processes, ....... 67 17. Contractility of the cells, . . . . . . . 68 18. Metamorphoses of the cells, kinds of cells, .... 69 B. HIGHER ELEMENTARY PARTS, pp. 70-72. 19. .......... 70 II._OF THE TISSUES, ORGANS, AND SYSTEMS, pp. 72-119. 20. Enumeration of them, . . . . . . 72 21. Epidermic tissue, ....:... 74 XV111 CONTENTS. SECT. . PAGE 22. Cartilaginous tissue, ....... 78 23. Elastic tissue, . . . . . . . .81 24. Connective tissue, . . ..... 89 25. Osseous tissue, ........ 99 26. Tissue of the smooth muscles, ..... 102 27. Tissue of the striped muscles, ... ... 106 28. Nerve-tissue, . . . . . . . . 109 29. Tissue of the true glands, . " . .- . . . . 113 30. Tissue of the blood-vascular glands, . .- . . 116 SPECIAL HISTOLOGY. OF THE EXTERNAL INTEGUMENT, pp. 119-222. I. OF THE SKIN IN THE MORE RESTRICTED SENSE, pp. 119-159. A. CUTIS DERMA, pp. 119-139. 31. Parts of the common integument, . . ^ . . .119 32. Subcutaneous cellular tissue, . . - ; . . . ". . 119 33. Parts of the corium, tactile papillae, . . . . . 120 34. Connective tissue, elastic fibres, and muscles of the corium, . . . . 123 35. Fat-cells, . . . . ' . . '. .125 36. Vessels of the Skin, . ... ' .; ' . . . . ' 127 37. Nerves, . . . ., = OfiSI . . ', few 129 38. Development of the Cutis, . . . . . 134 39. Physiological remarks, . . : . , . : 135 B. CUTICLE OR EPIDERMIS, pp. 139-159. 40. Parts of the Epidermis, . . . . .' . .-> , ^ . I 39 41. Mucous layer, ......'. V 140 42. Horny layer, . . jjj -....': . 142 43. Colour of the Epidermis, . . i' . . .143 44. Thickness of the Epidermis, . . . . . 145 45. Physical and Chemical relations, ...... .. 146 46. Growth and regeneration, ..... 150 47. Development, . . . vO . .154 II. OF THE NAILS, pp. 159-171. 48. Parts of the Nail, . . . - - . 159 49. Structure of the Nail, . . . . . .161 50. Relation of the Nail to the epidermis, ... 164 51. Growth of the Nails, ....... 165 52. Development of the Nails, ...... 169 III. OF THE HAIRS, pp. 171-199. OF THE HAIRS IN THE MORE RESTRICTED SENSE. 53. Parts of the Hair, . . . . .171 CONTENTS. XIX SECT. PAGE 54. Disposition and size of the Hairs, . . . . . 171 55. External peculiarities, and Chemical composition of the Hairs, . . 172 56. Structure of the Hairs, cortical substance, .... 173 57. Medullary substance, ....... 177 58. Cuticular covering, ... .... 180 59. Hair-follicles, . . . . . . . .182 60. Hair-follicle in the more restricted sense, .... 182 61. Root-sheaths, ........ 184 62. Development of the Hair, . . . . . 186 63. Shedding of the Hair, . . . . . . .191 64. Physiological remarks, . . . . . . 193 IV.__OF THE CUTANEOUS GLANDS, pp. 199, 222. A. OF THE SUDORIPAROUS GLANDS, pp. 199-209. 65. Disposition, ........ 199 66. Structure, .- . . . . . . . .199 67. More intimate structure of the glandular coil, .... 200 68. Secretion of the sudoriparous glands, ..... 202 69. Sweat-Ducts, ........ 204 70. Development of the sudoriparous glands, ..... 205 B. OF THE CERUMINOUS GLANDS, pp. 209-212. 71. Structure, ........ 209 72. Secretion and development, ...... 210 C. OF THE SEBACEOUS GLANDS, pp. 212-222. 73. Structure, form, arid disposition, . . . . . 212 74. More intimate structure, ....... 216 75. Development, . . . . . , . . 218 OF THE MUSCULAR SYSTEM, pp. 222-266. 76. Definition of it, ........ 222 77. Structure of the muscular fibres, ..... 223 78. The mode in which they are associated, ..... 229 79. Connection with other parts, . . . . . . 231 80. Structure of the tendons, ....... 232 81. Connection of the tendons with other parts, .... 235 82. Accessory organs of the muscles and tendons, .... 238 83. Vessels of the muscles and accessory organs, .... 243 84. Nerves of the muscles, . . . . . . . 245 85. Chemical and physical relations of the muscles, . . . 250 86. Development of the muscles and tendons, ..... 253 87. Physiological remarks, ....... 259 OF THE OSSEOUS SYSTEM, pp. 266-345. 88. Definition, form, occurrence, ...... 266 89. Intimate structure of the osseous tissue, .... 267 XX CONTENTS. SECT. PAGE 90. Matrix of bone, ........ 270 91. Lacunse and canaliculi, ...... 275 92. Periosteum, ..... . 281 93. Marrow, ... . 282 94. Articulations of the bones : ( A.} Synarthrosis, .... 284 95. (#.) Movable articulation, Diarthrosis, . . . . 291 96. Articular capsules, ...... . 295 97. Physical and chemical properties of the bones and their accessory organs, 299 98. Vessels of the bones, &c., . .' . . . 301 99. Nerves of the osseous system, ..'... '''.'" 303 100. Development of the bones, \v .' . . :; '-. . 306 101. Primordial cartilaginous skeleton, . . . . . 306 102. Metamorphoses of the primordial cartilaginous skeleton, . . 310 103. Changes in the ossifying cartilage, . ' % 314 104. Ossification of the cartilage, . . . . .316 105. Elementary processes in the layers formed from the periosteum, . 324 106. Bones, not primarily cartilaginous, , f . . , 330 107. Growth of the secondary cranial bones, . . ' . . 330 108. Vital phenomena in the mature bones, . . . . .,, 336 OF THE NERVOUS SYSTEM, pp. 345-436. 109. Definition, division, ,. , ... .... . . 345 ELEMENTS OF THE NERVOUS SYSTEM, pp. 345-359. 110. Nerve-tubes or fibres,. ....... 345 111. Nerve-cells, . .... .... v , . . 356 CENTRAL NERVOUS SYSTEM, pp. 359-404. 112. Spinal cord, ........ 359 113. Conjectural course of the fibres in the spinal cord, . . . 369 114. Medulla oblongata and Pons Varolii, ..... 372 115. Cerebellum, . ' . : ...... 379 117. Ganglia of the cerebrum, ..... . ' 382 117. Hemispheres of the cerebrum, ..... 385 118. Membranes and vessels of the central nervous system, . . 392 PERIPHERAL NERVOUS SYSTEM, pp. 404-436. 119. Spinal nerves, ......... 404 120. Structure of the spinal ganglia, ...... 405 121. Further course of the spinal nerves, . . . . . 411 122. Cerebral nerves, . . . . . . . .416 123. Ganglionic nerves, . . . . . . . 418 124. Main trunk of the ganglionic nerves, ..... 418 125. Peripheral distribution of the ganglionic nerves, . . . 423 126. Development of the elements of the nervous system, . . . 426 127. Functions of the nervous system, . . . . . 431 CONTENTS. XXI OF THE DIGESTIVE ORGANS, pp. 436-568. OF THE INTESTINAL CANAL, pp. 436-528. SECT. PAGE 128. General structure, ... .... 436 OF THE ORAL CAVITY, pp. 436-499. A. OF THE MUCOUS MEMBRANE OF THE ORAL CAVITY, pp. 436-441. 129. Mucous membrane and submucous tissue, . . . 436 130. Epithelium of the cavity of the mouth, . . . 438 B. OF THE TONGUE, pp. 441-455. 131. Muscular structure of the tongue, ...... 441 132. Mucous membrane of the tongue. ..... 446 C. OF THE GLANDS OF THE ORAL CAVITY, pp. 455-467. 1. Mucous Glands: 133. Different kinds of glands, ....... 455 134. Their more intimate structure, ... . 456 2. Follicular Glands: 135. Simple follicles and Tonsils, . . 459 3. Salivary Glands: 136. :. . . . . . . . . .463 D. OF THE TEETH, pp. 467-499. 137. Constituent parts, ........ 467 138. Dentine (substantia eburned], ...... 468 139. Enamel (substantia vitrea], . . . . . .476 140. Cement (substantia osteoidea), . . . . . 480 141. Soft parts of the teeth, . . .. . . . 483 142. Development of the teeth, . . . . 484 143. Physiological conditions of the teeth, v .... 494 OF THE ORGANS OF DEGLUTITION, pp. 499-502. 1, THE PHARYNX. 144 .499 1. THE (ESOPHAGUS. 145. .......... 501 OF THE ALIMENTARY CANAL, pp. 502-528. 146. General conformation, . . . . . 502 147. Peritoneum, ........ 502 148. Muscular coat of the alimentary canal, .... 503 149. Mucous membrane of the stomach, ..... 505 XX11 CONTENTS. SECT. PAGE 150. Gastric glands, ..... .506 151. Other particulars of the mucous membrane, . . . . 509 152. Mucous membrane of the small intestine, . . . . 511 153. VHli of the small intestine, ...... 511 154. Glands of the small intestine, ...... 518 155. Closed follicles of the small intestine, ..... 520 156. Mucous Membrane of the large intestine, . . ' ., . 524 157. Development of the intestinal canal, .. . . , ; . 526 OF THE LIVER, pp. 528-549. 158. General structure, . . . . . . , ; .. f , ,, ,. 528 159. More intimate structure, ...... 528 160. Hepatic cells and cell networks, . . . '." .' . 532 161. Excretory ducts of the liver, . . . ... . . 537 162. Vessels and nerves of the liver, . -<. ^\'-- " . ..tf . . . 541 163. Development of the liver, . . .. . -.,,. .. -.,*> 546 OF THE PANCREAS, pp. 549-551. 164. .. ' .' '' $9 T-.'v'-J ^ :i- jio -.:. ,-?;. r, ^ ^ 549 OF THE SPLEEN, pp. 551-568. 165. General structure, . ., . ./: . ' .' :- r ;. 551 166. Coats and trabecular structure of the spleen, . . ., .-. . 551 167. Malpighian structure of the spleen, . . . . . 552 168. Red substance of the spleen, . . . "." ' ' . 556 169. Vessels and nerves of the spleen. .... -- v ? ">. . 562 170. Physiological remarks, *. ., . < . 567 OF THE RESPIRATORY ORGANS, pp. 568-595. 171. Enumeration of the respiratory organs, ; 568 OF THE LUNGS, pp. 568-585. 172. General structure, .'...... : . 568 173. Larynx, . ; . . . . . . 569 174. Trachea, ; \ . . . ... . . . 572 175. Lungs, . . . . . . . ; . 574 176. Air-vessels and cells, . . . . . y . 575 177. Minute structure of the bronchia, . . . ' ''' . 578 178. Vessels and nerves of the lungs, . . . . . 580 179. Development of the lungs, . .. * . . . . 583 OF THE THYROID GLAND, pp. 585-589. 180. General structure of the thyroid gland, . . . . 585 181. Minute structure, -......; 586 OF THE THYMUS, pp. 589-595. 182. General structure of the thymus, . . . . . .589 183. Minute structure, . . . . . . . 591 184. Development of the thymus, ...... 593 CONTENTS. XX111 OF THE URINARY ORGANS, pp. 595-613. PAGE 185. Enumeration of the urinary organs, ..... 595 186. Kidneys general structure of, . . . . . . 595 187. Composition of the renal substance, ..... 596 188. Tubuli uriniferi, ....... 598 189. Vessels and nerves of the kidneys, ..... 602 190. Urinary passages, ....... 607 191. Physiological remarks, . . . . . . .608 OF THE SUPRARENAL GLANDS, pp. 613-618. 192. General description of the suprarenal glands, . . . .613 193. Minute structure, . . . . . . . 613 194. Vessels and nerves, . . . . . . .615 1,95. Physiological remarks, . . . . . . 616 OF THE SEXUAL ORGANS, pp. 618-667. A. MALE SEXUAL ORGANS, pp. 618-640. 196. Enumeration of the male sexual organs, . . . . . 618 197. Testes, . . . . . . . . .618 198. Tubuli seminiferi, . ...... 621 199. Membranes, vessels and nerves of the testes, .... 626 200. Vasa deferentia, vesiculce seminales, and accessory glands, . . 627 201. Organ of copulation, ....... 630 202. Physiological remarks, . . . . . . 634 B. FEMALE SEXUAL ORGANS, pp. 640-660. 203. Enumeration of the female sexual organs, . . . . 640 204. Ovary, parovarium, . . . . . . . 640 205. Detachment and re-formation of the ova, ..... 643 206. Uterus and oviducts, . . . . . . 646 207. Changes in the uterus at the menstrual period and in pregnancy, . 649 208. Vagina and external genitals, ...... 654 209. Physiological remarks, ....... 656 C. OF THE LACTEAL GLANDS, 660-667. 210. Their structure, ....... 660 211. Physiological remarks, ....... 663 OF THE VASCULAR SYSTEM, pp. 66T-715. 212. Its elements, ........ 667 I. OF THE HEART, pp. 667-674. 213 667 II. OF THE BLOODVESSELS, pp. 674-693. 214. General structure of the bloodvessels, ..... 674 215. Arteries, ........ 678 216. Veins, ......... 684 217. Capillaries, . . . . . . . 689 XXIV CONTENTS. III. OF THE LYMPHATIC SYSTEM, pp. 693-699. SECT. PAGE 218. Lymphatic vessels, . . . . . . .693 219. Lymphatic glands, ....... 695 IV._OF THE BLOOD AND LYMPH, pp. 699-725. 220. Different kinds of fluids included in those terms, and their mode of occurrence, . . . ; . . . . 699 221. General structure of the morphological elements, . 5 . ' '. ' 700 222. Of the blood, . . . ... . .703 223. Physiological remarks, . IV.?' . . . "?/ 715 OF THE HIGHER ORGANS OF SENSE, pp. 725-785. I. OF THE ORGAN OF VISION, pp. 725-767. 224. Its parts, . . . . . . . . .725 A. OF THE EYEBALL, pp. 725-757. 225. Fibrous tunic of the eye, ; '' ' . 725 226. Vascular tunic, . . . .. , ' v | ' - . . 733 227. Nervous tunic, . . > ' \ ,. .. .. .,.-. 739 228. The lens, . ,. .. .. .. ;. . . . . 750 229. The vitreous humor, . ...^ ..,-, . N -.; .. , . ; 753 B. ACCESSORY ORGANS, pp. 757-760. 230. Eyelids, conjunctiva, lachrymal apparatus, .-, ..-. . . 757 231. Physiological remarks, . . . . 760 II. OF THE ORGAN OF HEARING, pp. 767-778. 232. -. . . -. -. -.-. -'y . , 767 233. External and middle ear, > -,' . ; -.'^ ;;> . . 767 234. The vestibule and semicircular canals, . . . .' 769 235. Cochlea, ..-'.; . . . . . 770 III. OF THE OLFACTORY ORGAN, pp. 778-785. 236. Its parts, . , . . . . . . . 778 APPENDIX. 1. Corpuscula tacttis and Pacinian bodies, . . . . . 785 2. Malpighian bodies of the spleen, . . . . . . 786 3. Corpora lutea, . .... ....... 787 4. Development -of the teeth, . . . . . . .^ 789 LIST OF ILLUSTRATIONS. FIG. PAGE 1. Nerve-cells of the Thalamus Opticus of Man, . . . . .44 2. Contents of a Malpighian Corpuscle of the Ox, .... 48 3. Cells from the Cephalic Cartilage of a Tadpole, . . . .50 4. Nuclei from the Ovum of an Ascaris dentata, .... 50 5. Ova of Ascarus nigrovenosa, ...... .51 6. Cartilage-cells from Articular Cartilage of the Condyle of the Femur of Man, 53 7. Cells from the Medullary Cavities of the Flat Bones of the Skull in Man, 53 8. Dividing Blood-corpuscles of the Chick, . . . . .54 9. Dentine Cells, from the Dog, ...... 55 10. Cartilage Cells of Man, ........ 60 11. Bone-cells from a Rachitic Bone, ...... 60 12. Plates of the Horny Layer of the Epidermis in Man, . . . .75 13. Epidermis of a two months' Human Embryo, ... 76 14. Epithelial Cells of the Bloodvessels, . . . . . .76 15. Epithelium of the Intestinal Villi of the Rabbit, .... 76 16. Ciliated cells from the finer Bronchise, .... .76 17. A simple Papilla with manifold Vessels and Epithelium from the Gums of a Child, 77 18. Ciliated Epithelium from the Trachea of Man, . . . .77 19. Portion of the Chorda Dorsalis of an Embryo Sheep, ... 80 20. Cartilage Cells from the White Layer of the Cricoid Cartilage, . . 80 21. Portion of a Human Epiglottis, . . . . . . . 81 22. Elastic Network from the Tunica Media of the Pulmonary Artery of a Horse, 81 23. Bundles of Connective Tissue from the Arachnoid of Man, . . 82 24. Network of Fine Elastic Fibres from the Peritoneum of a Child, . . 82 25. Elastic Membrane from the Tunica Media of the Carotid of a Horse, . 82 26. Formative Cells of Elastic Fibres, from the Tendo-Achillis, . . .83 27. Stellate Formative Cells of the Nucleus Fibres of Tendo-Achillis of a new- born Infant, . . . . . . . .83 28. Lax Connective Tissue with Fat-cells, from Man, .... 89 29. Formative Cells of the Connective Tissue from the Skin of a Sheep's Embryo, 90 80. Formative Cells of the Areolated Connective Tissue from the Allantois of a Sheep's Embryo, ........ 90 31. Perpendicular section of a Parietal Bone, ..... 99 32. Developing Bone-cells from a Rachitic Bone, . . . . .100 33. Muscular Fibre-cell from the Small Intestine of Man, . 103 34. Muscular Fibre-cell from the Investment of the Spleen of a Dog, . . 103 35. Muscular Fibres from Man, ...... 106 36. Primitive Fibrils from a Primitive Bundle of the Axolotl, . . .106 XXVI LIST OF ILLUSTRATIONS. FIG. PAGE 37. Tubular Nerve-fibres of Man, ...... 110 38. Nerve-cell of the Pike, . . . . . . . .110 39. Nerve-cells from the floor of the Fourth Ventricle in Man, . . Ill 40. Network of Hepatic Cells, . . . . . . .113 41. Two of the Smallest Lobes of the Lung from a new-born Child, . . 113 42. Gastric Gland from the Pylorus of the Dog, ..... 114 43. Glandular Vesicles from the Thyroid Gland of a Child, . . . 117 44. Malpighian Corpuscle from the Spleen of the Ox, . . . .117 45. Perpendicular section of the Skin of the Ball of the Thumb, . . 119 46. Compound Papillae of the Surface of the Hand, . . . .121 47. Horizontal Section of the Skin of the Heel, . . . . 121 48. Two Papillae of the Surface of the Hand, . . . . .122 49. Elastic Fibres from the Fascia Lata of Man, . . 123 50. Normal Fat-cells from the Breast, .... . . 125 51. Fat-cells with Crystals of Margarin, . . . . 125 52. Vessels of the Fat- cells; after Todd and Bowman, . . . .128 53. Vessels of the Papillae of the Cutis; after Berres, .... 128 54. Two Papilke from the extremities of the Fingers, with Axile-corpuscles, . 129 55. A. Surface of the Palm from within, .... --* 139 55. B. Perpendicular section of the Skin of the Negro, . . . . 140 56. Horny Epidermic Plates of Man, . . . . . . 142 57. Horny Plates boiled with Caustic Potassa, . . . * ;. .. . 148 58. Transverse section through the Body and Bed of the Nail, . .;. :. 159 59. Capillaries of the Bed of the Nail ; after Berres, . . ::./<* . 160 60. Longitudinal section through the Matrix of the Nail, . . . .; 161 61. Transverse section through the Body of the Nail, . . .-. . 162 62. Nail Plates boiled with Caustic Soda, . . . . ..163 63. Hair and Hair-sacs of middling size, ... . . -. .; .. .. . 171 64. Plates of the Cortical Substance of a Hair, . . . ,, 174 65. White Hair after treatment with Caustic Soda, . . . : , : ; .175 66. Cells from the Cortex of the Root of the Hair, .... 176 67. Cells from deepest part of Hair Bulb, . . . . . .176 68. Root of a dark Hair acted upon by Caustic Soda, .... 177 69. Medullary Cells of Hair, . . . . . . .178 70. Surface of the Shaft of a White Hair, . . . . .180 71. Portion of the transverse fibrous layer and structureless membrane of a Human Hair-sac, ......... 183 72. Elements of the inner Root-sheath, . . . .185 73. Rudiment of the Hair from the Brow of a Human Embryo, . . . 187 74. Rudiment of the Hair from the Eyebrow, ..... 189 75. Rudimental Hair from the Eyebrow, . . . . . .189 76. Eyelashes of a Child, ....... 191 77. Eyelashes with the Root-sheaths from a Child, . . . .191 78. A Sudoriparous Coil and its Vessels, ..... 199 79. Sweat-ducts, ......... 201 80. Perpendicular section through the Epidermis and outer surface of the Corium, . . . . . . . . . 204 81. Rudiment of a Sudoriparous Gland of a Human Embryo, . . . 206 82. Rudiment of a Sudoriparous Gland from a seven months' Foetus, . . 206 83. Perpendicular section through the Skin of the External Auditory Meatus, 210 84. Sebaceous Glands from the Nose, . . . . . .213 85. A Gland from the Nose, with Hair-sac opening into it, . . 213 86. Two Sebaceous Glands, ........ 215 87. A Glandular Vesicle of a common Sebaceous Gland, . . 216 LIST OF ILLUSTRATIONS. XXV11 FIG. PAGE 88. The development of the Sebaceous Glands in a six months' Foetus, . . 219 89. Primitive Fibrils from a primitive fasciculus of the Axolotl, . . 223 90. Transverse sections of Muscular Fibre, ..... 224 91. Human Muscular Fibre treated with Acetic Acid, . . . 224 92. A Primitive Fasciculus, separating transversely into discs ; after Bowman, 225 93. Primitive Fibres from a transversely striated Muscle of a Bug, . . 226 94. Transverse section of Rectus Capitis Anticus Major of Man, . . . 230 95. Transverse section of a Tendon of a Calf, ..... 96. Tendon of the Tibialis Posticus, .... . 234 97. A Primitive Fasciculus from Intercostal Muscle of Man, . . . 235 98. Disposition of Muscular Fibres at their insertion into the Tendon, . . 235 99. Insertion of the Tendo-Achillis into the Calcaneum, . . 237 100. Cartilage- cells from the Vaginal Ligaments surrounding the Tendons of the Poplitseus, . . . . - . . .241 101. Capillary Vessels in Muscle, ....... 243 102. Expansion of the Nerves in the Omo-hyoid muscle of Man, . . 246 103. Divisions of the Primitive Nerve-fibres in Muscle, .... 246 104. Divisions of Nerve-fibres in Thoracic Muscle of the Frog, . . 250 105. Primitive Fasciculi of a Human Embryo, ..... 254 106. Primitive Fibres of a Human Embryo, ..... 254 107. From the Tendo-Achillis of a New-born Child, . . . .256 108. Primitive Fibres from the Alar Muscles of the Dung-fly, . . . 259 109. Primitive Fasciculae of a Frog's Muscle in different degrees of Extension, . 264 110. Transverse section of Human Femur, ..... 268 111. Haversian Canals from Superficial Layer of Human Femur, . . . 268 112. Transverse section of Human Metacarpal Bone, .... 271 113. Transverse section of Shaft of Humerus, ..... 271 114. Perpendicular section of Parietal Bone, . . . . . 273 115. Transverse section of Shaft of Humerus, ..... 276 116. Section parallel with Surface of Human Femur, .... 276 117. Lacunae and Canaliculi of Parietal Bone, ..... 277 118. Surface of a Tibia of Calf, ...... 279 119. Bony Spicula) from Apophysis, ...... 280 120. Fat^cells from Marrow of Human Femur, . . 283 121. Transverse section of Ligamentum Nuchae of Ox, .... 285 122. Cells from Gelatinous Nucleus of the Lig. Intervertebralia, . . 286 123. Cartilaginous border of Human Symphysis, ..... 289 124. Human Cartilage Cells, ....... 290 125. Perpendicular section of Articular Cartilage of Human Metacarpal Bone, . 292 126. Diagram of Transverse Section of Phalangeal Articulation, . . 295 127. Synovial Membrane of Phalangeal Articulation, .... 297 128. Falciform Ligament of Knee, ...... 298 129. Cartilage Cells from Humerus of Embryo of Sheep, .... 308 130 Perpendicular section of Ossifying border of Shaft of Femur, . . 314 131. Femur of a Child, . . . . . . . .314 132. Femur of a Rachitic Child, ...... 317 133. Transverse section of Metatarsus of Calf, ..... 324 134. Diagram of Growth of Cylindrical Bone, ..... 327 135. Parietal Bone of Foetus, . . . . . . . . 331 136. Parietal Bone of new-born Child, ...... 331 137. Nerve Fibres of Man, . . . . . . . .346 138. Human Nerve-tubes, ....... 346 139. Nerve Fibres, . . . . . . . .348 140. Nerve-cells from Acoustic Nerve, . . . . . . 357 XXV111 LIST OF ILLUSTRATIONS. Fid. PAGE 141. Transverse section of Spinal cord, ...... 361 142. Cells from Gray Central Nucleus of Cord, .... 363 143. Nerve-cells from Anterior Cornua of Cord in Man, .... 364 144. Vertical section of Spinal Cord, ...... 366 145. Five transverse sections of Human Spinal Cord, .... 370 146. Transverse section through Human Medulla Oblongata, . . . 373 147. Nerve-cells of the Substantia Ferruginea, ..... 376 148. Large Cells of Cortical Substance of Human Cerebellum, . . 380 149. Internal portions of Gray Layer of Human Cerebral Convolutions, . . 387 150 Finest Nerve-tubes of Superficial White Substance of Human Cerebrum, 388 151. Ependyma in Man, ........ 397 152. Vessels of Cerebral Substance of Sheep, . . . -v . 400 153. Brain-sand from Pineal Gland, .... ... .,.!;< . 401 154. Lumbar Ganglion of Young Dog, . . ... . f. 405 155. Ganglion Globules from Gasserian Ganglion of Cat, . . :r . 407 156. Cells from Sheath of Nerve-cells of Spinal Ganglia in Man, , ,.- . . 407 157. Coccygeal Nerve, with an adherent Nerve-cell, . i ..- , . 408 158. Nerve-cell of the Pike, . . . . , , "... 409 159. A Pacinian Body in Man, . . . . ...... . 413 160. Transverse section of Ischiatic Nerve, . . . ; . . 414 161. Ganglion of Sympathetic Nerve of Rabbit, . . . ,. . 419 162. From the Sympathetic in Man, . . . . ;,, - . . , 419 163. Nerve-cells from the Cardiac Ganglion of the Frog, . -. ...... . 424 164. Nerve-cells from Spinal Ganglion of Human Embryo, . .-' * . . 427 165. Nerve-fibres from Ischiatic Nerve of Human Embryo, . -, .< . 427 166. Nerve from the Tail of a Tadpole, . . . . ... 428 167. Simple Papilla, with Vessels and Epithelium, . . . .- . 438 168. Epithelial cells in Oral Cavity of Man, . . . . . 439 169. Longitudinal section of Human Tongue, . 442 170. Transverse section of Human Tongue, .... v -; 443 171. Portion of longitudinal section of Human Tongue, . . : . . . 445 172. Branched Primitive Muscular Bundle from Tongue of Frog, . . 446 173. Two Papillse Filiformes of Man; after Todd and Bowman, . . .448 174. Papilla Fungiformis ; after Todd and Bowman, .... 448 175. Papilla Circuuavallata of Man, ...... 450 176. Epithelial Cells covered with Granular Matrix of Fungus, . . 451 177. Papilla Filiformis invested by a Fungus, ..... 452 178. Racemose Mucous Glands from the Floor of the Oral Cavity, . . 457 179. Diagram of two Ducts of a Lobe of a Mucous Gland, .... 457 180. Two. Glandular Vesicles of a racemose Mucous Gland of Man, . . 458 181. Follicular Gland from the root of the Tongue in Man, . . . 460 182. Vesicles of a few follicles from a Human Tonsil, . . . . 461 183. Human Molar Tooth, . . . . . . . .468 184. Transverse section of Dentinal Canals, ..... 469 185. Dentinal Tubules, . . . . . . . .470 186. Transverse section through the Dentinal Canal of a Human Tooth, . 470 187. Perpendicular section of the Apex of an Incisor Tooth, . . . 473 188. Dentine with Dentinal Globular and Interglobular Spaces, . . 473 189. Surface of Enamel from the Calf, . . . . . .478 190. Enamel Prisms from Man, ....... 478 191. Dentine and Enamel from Man, ...... 479 192. Dentine and Cement from Fang of Incisor Tooth, .... 481 193. Cement and Dentine of the Root of an old Tooth, .... 482 194. Lower Jaw of a Human Foetus, ...... 485 LIST OF ILLUSTRATIONS. XXIX FIG. PAGE 195. Diagram of the Development of a Milk-tooth ; after Goodsir, . . 485 196. Tooth-sac of Incisor of a Foetus, ...... 488 197. Surface of Dentinal Pulp of an Infant, ...... 489 198. Transverse section of Human (Esophagus, .... 501 199. Muscular-fibre Cells from (Esophageal Mucous Membrane, . . .501 200. Stomach of Man, . ....... 503 201. Muscular-fibre Cells from Small Intestine, ..... 504 202. Bloodvessels of Smooth Muscles of Intestine, . . . . 505 203. Perpendicular section through Tunics of Pig's Stomach, . . . 506 204. Mucous Gastric Gland of a Dog, ...... 507 205. Vessels of Large Intestine of a Dog, ...... 510 206. Section through the Walls of a Calf's Ileum, . . . .512 207. Intestinal Villus of a Young Kitten, . . . . . .512 208. Vessels of Villi of the Mouse; after Gerlach, .... 513 209. Villi without Epithelium and with a Lacteal, . . . . .513 210. Intestinal Villi of the Cat, ....... 514 211. Villi with the Epithelium, from the Rabbit, ..... 515 212. Lieberkuhnian Glands of the Pig, ...... 519 213. Peyer's Patch, in Man, . . . . . x .521 214. Portion of a Peyer's Patch of an Old Man, .... 521 215. Horizontal section from the middle of Peyer's Follicle of the Rabbit, . 522 210. Solitary Follicle from the Small Intestine; after Bohm, . 523 217. Solitary Follicle from the Colon of a Child, . . . . .525 218. Segment of a Pig's Liver, . . ..... 530 219. Portal Vessel of the Pig; after Kiernan, . . . . .530 220. Hepatic Cells of Man, ....... 532 221. Hepatic Cell-network, ........ 533 222. Hepatic Cell-network and its capillaries, ..... 542 223. Hepatic Veins of the Rabbit, . . . . . . .542 224. Arterial Network upon surface of a Child's Liver, . . . 545 225. Vessels f the Pancreas of a Rabbit, ...... 550 226. Section through the middle of the Spleen of an Ox, . . . 551 227. Fibres from the Pulp of Human Spleen, . . . ... 552 228. Artery covered with Malpighian Corpuscles from Spleen of Dog, . 553 229. Malpighian Corpuscles from Spleen of an Ox, ..... 554 230. Contents of a Malpighian Corpuscle, ..... 554 231. Blood-corpuscle-holding Cells and their Metamorphoses, . . . 559 232. Artery from the Spleen of a Pig, ...... 563 233. Ciliated Epithelium from the Human Trachea, . . . .571 234. Vertical Section through Anterior 'Wall of Human Trachea, . . 573 235. Lymphatics in the Tracheal Mucous Membrane of Man, . . . 574 236. Pulmonary Lobules from a Child, ...... 575 237. External Surface of the Lung of a Cow, ..... 577 238. Human Air-cell, ........ 579 239. Capillary plexus of Human Air-cell, ....... 581 240. Gland-vesicles from the Thyroid Gland of a Child, . . .586 241. Gland-vesicles of Thyroid filled with Colored Matter, . . . 587 242. Portion of Thymus of a Calf, ...... 590 243. Half of Human Thymus, . . . . . . .590 244. Section of an injected Lobule of Thymus of a Child, . . . 591 245. Vertical section of an injected Rabbit's Kidney, .... 597 246. Tubuli Uriniferi of Man, ....... 599 247. A Malpighian Corpuscle, ....... 599 248. From the Human Kidney ; after Bowman, .... 603 XXX LIST OP ILLUSTRATIONS. FIG. PAGE 249. Malpighian Corpuscle from Kidney of a Horse, .... 603 250. Transverse section through Cortical Tubules, ..... 606 251. Epithelium of Pelvis of Human Kidney, ..... 606 252. Vertical section through Suprarenal Capsule in Man, . . . 614 253. From the Suprarenal Capsule of Man, ..... 614 254. Section of Suprarenal Body of the Calf, . . . . .616 255. Section through Testis and its Tunics in Man, .... 619 256. Diagram of the Course of a Spermatic Tubule, . 619 257. Human Testis and Epididymis ; after Arnold, .... 619 258. Portion of a Spermatic Tube in Man, ...... 621 259. Human Spermatic Filaments, ...... 622 260. Development of the Spermatic Filaments in a Rabbit, . . . 622 261. Glands of a Littre, . . . . . . . .631 262. Arteries from Corpora Cavernosa Penis, . . . l -l' . 633 263. Section through the Ovary of a Woman, . . . * ... ...- ..-'" 640 264. Graafian Follicle of the Sow, . . . . :,. - . . 641 265. Human Ovulum, . . . . . ... 642 266. Two Corpora Lutea, .'.... . . . . 644 267. Muscular Elements from the Uterus in Pregnancy, . . ... 649 268. Muscular Fibre-cell from a Gravid Uterus, . . - * 650 269. Uterine Gland, ...... .- : . . 650 270. Muscular Fibre-cell of the Uterus, . . . . .652 271. Graafian Follicles from Ovary of a Newly-born Child, . . < 656 272. Lobules of the Lacteal Gland of a Puerperal Female, .. . . . 661 273. Development of Lacteal Gland, . . . . .... 663 274. Elementary Forms in Milk, . . . . . . . 664 275. Anastomosing Primitive Fasciculus from the Human Heart, ; , . . 668 276. Diagram showing the course of the Muscular Fibres of the Heart, . . 672 277. Elastic Membrane from the Tunica Media of the Popliteal Artery in Man, 675 278. Muscular Fibre-cells from the Human Arteries, .... 675 279. Artery and Vein from Mesentery of a Child, . . .*- . . . 679 280. Artery and Vein treated with Acetic Acid, . . . . 680 281. Transverse section of Art. Prof. Femoris of Man, . . . .. 681 282. Transverse section of Aorta, . . . . - . .. ... . 682 283. Muscular Fibre-cell from innermost layer of Axillary Artery, . . 683 284. Transverse section of the Saphena Vein, ..... 685 285. Muscular Fibre-cell from Renal Vein of Man, .... 686 286. Longitudinal section of Inferior Vena Cav a, ..... 688 287. Finest Vessels on the arterial side of the Capillaries, . . -:...' 691 288. Capillary Lymphatic from the tail of a Tadpole, . . .'..-.. .693 289. Transverse section of Human Thoracic Duct, . . -. . '. 695 290. Elements of the Chyle, . . . . . .700 291. Human Blood-globules, . . . .703 292. Colorless Blood-globules, . . . . . . .707 293. Blood-cells of the Frog and of the Pigeon, . . . . 713 294. Capillaries from the Tail of a Tadpole, . . . . .717 295. Blood-corpuscles of a Foetal Lamb, . . . . . 718 296. Transverse section of Eye, ....... 726 297. Capillaries and Lymphatics of Cornea of a Kitten, . . . 731 298. Nerves of the Cornea of a Rabbit, . . . . . .732 299. Cells from the Stroma of the Choroid, . ... . .734 300. Cells of the Pigmentum Nigrum of Man, ..... 735 301. Vessels of the Choroid and Iris of a Child ; after Arnold, . . 737 302. Vertical Transverse section of Human Retina, . . . .739 LIST OF ILLUSTRATIONS. XXxi 11 5 - PAGE 303. Elements of Human Retina, .;.... 740 304. Bacillar Layer of Retina, ....... 742 305. Nerve-cells from Retina of the Ox, ..... 743 306. Fibres of the Lens, from the Ox, . . . . . . 751 307. Human lens ; after Arnold, ...... 753 308. Transverse section of a Semicircular Canal, ..... 769 309. Vertical section of the Lamina Spiralis ; after Corti, . . . 771 310. Vestibular surface of the Lamina Spiralis Membranacea, . . . 771 311. Bipolar Ganglion-globule from Lamina Spiralis of a Pig; after Corti, . 774 312. From Nasal Mucous Membrane of the Sheep, .... 780 313. From the Olfactory Nerve of Man, ..... 782 INTRODUCTION. 1. THE doctrine of the elementary structure of Plants and Animals, belongs to the last two centuries, originating with Marcellus Malpighi (1628-94), and Anton van Leeuwenhoek (1632-1723), at the period when the assistance of magnifying glasses, powerful, though of very simple form, was first offered to observers. The ultimate constituents in respect of form, of organisms, were unknown to antiquity and to the middle ages, for although Aristotle and Galen speak of the homogeneous and heterogeneous parts of the body (partes similares et dissimilares), and Fallopius (1523-62) defined still more exactly the idea of " Tissues," and even attempted to classify them (' Tractatus quinque de partibus similaribus,' opera, torn. ii. Francof. 1600), yet the minuter structures were completely hidden from these investigators. Brilliant as were the first efforts of the young science under the guidance of these men and after- wards of a Ruysch, Swammerdam, and others, yet they were not adequate to acquire a safe footing for it, since, on the one hand, the philosophers were far too little masters of microscopic investigation to strive at once, with a clear insight, towards the true goal ; while, on the other, the deve- lopment of other branches of study, as of the grosser Anatomy, of Physio- logy, of Embryology, and of Comparative Anatomy, claimed too large a share of their attention. It thus happened that, with the exception of a few to some extent important works (Fontana, Muys, Lieberkuhn, Hewson, Prochaska), Histology made no considerable progress during the whole of the 18th century, and acquired no importance greater than that due to a disjointed collection of isolated observations. It was in the year 1801 that it first acquired a rank co-equal with that of its sister anatomical sciences by the genius of a man to whom indeed, Histo- logy owes no great discoveries, but who understood, as no one before him had done, so to arrange existing materials and so to connect them with Physiology and Medicine, that for the future its independence was assured. In fact, Bichat's ' Anatomic Generale' (Paris, 1801), was the first attempt to treat Histology scientifically, and on this ac- count merely, it constitutes an epoch ; but besides this, its importance 3 31 INTRODUCTION. was still greater, inasmuch as the tissues were not merely clearly defined and fully and logically treated of, but full account was taken of their physiological functions and morbid alterations. To this great internal progress, the present century has added an ever-increasing perfection of the external aids of the microscope, and a steadily increasing zeal in the investigation of nature, so that it is not to be wondered at, that in its five decades, it has left far behind all that was done in the century and a half of its earlier existence. In the last thirty years particularly, discoveries have so trodden upon one another's heels, that it must be considered truly fortunate that a bond of connection has arisen, and that Microscopical Anatomy has thus escaped the danger of becoming, as in earlier days, lost in minutiae. In the year 1838, in fact, the demonstration by Dr. Th. Schwann, of the originally perfectly identical cellular composition of all animal organisms, and of the origin of their higher structures from these elements, afforded the appropriate concep- tion which united all previous observations, and afforded a clue for further investigations. If Bichat founded histology more theoretically by constructing a system and carrying it out logically, Schwann has, by his investigations, afforded a basis of fact, and has thus won the second laurels in this field. What has been done in this science since Schwann, has been indeed of great importance to physiology and medi- cine, and in part of great value in a purely scientific point of view, inasmuch as a great deal which Schwann only indicated, or shortly adverted to, as the genesis of the cell, the import of the nucleus, the development of the higher tissues, their chemical relations, &c., has re- ceived a further development ; but all this has not amounted to a step so greatly in advance as to constitute a new epoch. If, without pre- tensions to prescience, it be permitted to speak of the future, this condition of Histology will last as long as no essential advance is made towards penetrating more deeply into organic structure, and becoming acquainted with those elements, of which that which we at present hold to be simple, is composed. If it be possible that the molecules which constitute cell-membranes, muscular fibrils, axile fibre of nerves, &c., should be discovered, and the laws of their apposition, and of the altera- tions which they undergo in the course of the origin, the growth, and the activity of the present so-called elementary parts, should be made out, then a new era will commence for Histology, and the discoverer of the law of cell genesis, or of a molecular theory, will be as much or more celebrated than the originator of the doctrine of the composition of all animal tissues out of cells. 2. In characterizing the present position of Histology and of its objects, we must by no means forget that, properly speaking, it con- siders only one of the three aspects which the elementary parts present INTRODUCTION. 35 to observation, namely, their form. Microscopical anatomy is concerned with the understanding of the microscopic forms, and with the laws of their structure and development, not with any general doctrine of the elementary parts. Composition and function are only involved, so far as they relate to the origin of forms and to their variety. Whatever else respecting the activity of the perfect elements and their chemical relations is to be found in Histology, is there either on practical grounds in order to give some useful application of the morphological conditions, or to complete them ; or from its intimate alliance with the subject, it is added only because physiology proper does not afford a due place for the functions of the elementary parts. If Histology is to attain the rank of a science, its first need is to have as broad and certain an objective basis as possible. To this end the minuter structural characters of animal organisms are to be examined on all sides, and not only in fully formed structures, but in all the earlier periods from their first development. When the morphological elements have been perfectly made out, the next object is to discover the laws according to which they arise, wherein one must not fail to have regard also to their relations of composition and function. In dis- covering these laws, here as in the experimental sciences generally, continual observation separates more and more, among the collective mass of scattered facts and observations, the occasional from the con- stant, the accidental from the essential, till at last a series of more and more general expressions of the facts arises, from which, in the end, mathematical expressions or formulae proceed, and thus the laws are enunciated. If we inquire how far Histology has satisfied these requirements, and what are its prospects in the immediate future, the answer must be a modest one. Not only does it not possess a single law, but the materials at hand from which such should be deduced, are as yet re- latively so scanty, that not even any considerable number of general propositions appear well founded. Not to speak of a complete know- ledge of the minuter structure of animals in general, we are not ac- quainted with the structure of a single creature throughout, not even of man, although he has been so frequently the object of investigation, and therefore it has hitherto been impossible to bring the science essentially any nearer its goal. It would, however, be unjust to over- look and depreciate what we do possess ; and it may at any rate be said that we have acquired a rich store of facts and a few more trustworthy general propositions. To indicate only the more important of the for- mer, it may be mentioned, that we have a very sufficient acquaintance with the perfect elementary parts of the higher animals, and that we also understand their development, with the exception of the elastic tissue, and of the elements of the teeth and bones. The mode in which 36 INTRODUCTION. these are united into organs has been less examined, yet on this head also, much has been added of late, especially in man, whose individual organs with the exception of the nervous system, the higher organs of sense, and a few glands (the liver, blood-vascular glands), have been almost exhaustively investigated. If the like progress continue to be made, the structure of the human body will in a few years be so clearly made out, that, except perhaps in the nervous system, nothing more of importance will remain to be done with our present modes of investiga- tion. With comparative Histology it is otherwise ; hardly commenced, not years but decades will be needed to carry out the necessary investi- gations. Whoever will do good work in this field must, by monographs of typical forms embracing their whole structure from the earliest periods of development,* obtain a general view of all the divisions of the ani- mal kingdom, and then, by the methods above described, strive to develop their laws. As regards the general propositions of Histology, the science has made no important progress since Schwann, however much has been attained by the confirmation of the broad outlines of his doctrines. The position that all the higher animals at one time consist wholly of cells and develop from these their higher elementary parts, stands firm, though it must not be understood as if cells, or their derivatives, were the sole possible or existing elements of animals. In the same way, Schwann's conception of the genesis of cells, though considerably modified and extended, has not been essentially changed, since the cell nucleus still remains as the principal factor of cell-development and of cell-multiplication. Least advance has been made in the laws which regulate the origin of cells and of the higher elements, and our acquain- tance with the elementary processes which take place during the for- mation of organs must be regarded as very slight. Yet the right track in clearing up these points has been entered upon ; and a logical inves- tigation of the chemical relations of the elementary parts and of their molecular forces, after the manner of Bonders, Ludwig, and others, com- bined with a more profound microscopical examination of them, such as has already taken place with regard to the muscles and nerves, further, a histological treatment of embryology, such as has been at- tempted by Reichert, Vogt, and myself, will assuredly raise the veil, and bring us, step by step, nearer to the desired though perhaps never to be reached, end. 8. The aids in studying Histology may here be best shortly ad- verted to. With respect to the literature of the subject, the more impor- * [See a very praiseworthy monograph of this kind by Leydig, Beitrage zur Mikrosko- pischen Anatomie und Entwickelungs-geschichte der Rochen u. Haie, 1852. (Microscopic Anatomy and Development of the Rays and Sharks.) TRS.] IKTRODUCTION. 37 tant monographic works are cited under their appropriate section, and here only those large independent works will be noticed, in which further instruction is to be found. It is right to head the list with Schwann's 1 Mikroskopische Untersuchungen liber die Uebereinstimmung in der Struktur und dem Wachsthumder Thiere und Pflanzen' (Berlin, 1839),* abstracted in Froriep's 'Neue Notizen' (1838), as the most fitting intro- duction to Histology. Beside this, we may name X. Bichat, 'Anatomie Ge'ne'rale,' Tom. iv. (Paris, 1801); E. H. Weber, 'Handbuchder Ana- tomie des Menschen von Hildebrandt,' Bd. 1, 'Algemeine Anatomie' (Braunschweig, 1830), a work distinguished in its day, and even now indispensably necessary, as a store of old literature [or Ed. 4 (Stuttgart, 1833)]; Brun's 'Lehrbuch der Allgemeinen Anatomie des Menschen' (Braunschweig, 1841), very clear, concise, and good ; Henle, ' Allgemeine Anatomie' (Leipzig, 1841), containing a classical account of Histo- logy in the year 1840, many original statements, and physiological, pathological, and historical remarks ; G. Valentin, article i Gewebe,' in R. Wagner's < Handworterbuch d. Physiologic,' Bd. i. (1842); R. B. Todd and W. Bowman, ' The Physiological Anatomy and Physiology of Man,' Parts i. ii. (London 1845-47), mostly based upon original observa- tions, very comprehensive and good [also Parts iii. iv. (184752)] ; Bendz, ' Haandbogiden almindelige Anatomie' (Kiobenhavn, 1846-47), with industriously collected historical data ; A. Kb'lliker, ' Mikrosko- pische Anatomie oder Gewebelehre des Menschen, Band II. Specielle Gewebelehre, 1, Halfte. u. 2 ; Halfte. 1 Abtheilung' (Leipzig, 1850-52), containing an exposition, as complete as possible, of the minute struc- ture of the organs and systems of man. With these are to be compared the yearly Reports of Henle, in Cannstatt's * Jahresbericht,' and those of Reichert, in Muller's ' Archiv,' in the latter of which, more objective views and an earlier appearance would be desirable. Useful figures are found in all the works above cited, with the excep- tion of those of Bichat, Weber, and Bruns; furthermore, the figures of injections in Berres' i Anatomie der Mikroskopischen Gebilde des men- schlichen Korpers,' Heft 1-12 (Wien, 1836-42), are for the most part excellent, as are the representations of tissues in R. Wagner's * Icones Physiologic^,' second edition, by A. Ecker. Those of Langen- beck, 4 Mikroskopisch-anatomische Abbildungen.' Lief. 1-4 (Gottingen, 1846-51) ; of A. H. Hassall, ' The Microscopic Anatomy of the Human Body' (London, 1846-49) ; and Mandl, ' Anatomie Microscopique' (Paris 1838-48), are middling ; while on the other hand, those given by Quekett, ' Catalogue of the Histological Series in the Museum of the Royal College of Surgeons of England' (London, 1850), are admirable. As regards Microscopes, I may express my opinion that of the more easily accessible, those of Plossl, Oberhauser, and Schiek, take the first * Translated for the Sydenham Society, 1847. 38 INTRODUCTION. rank. In Italy, Amici ; in England, Ross, Powell, and others, produce instruments quite equal to the above, but out of the question for Ger- many ; among small, cheap, but not particularly useful instruments for students and physicians, for 115 to 150 francs, George Oberhauser (Rue Dauphine, 19, Paris), furnishes the best. The much-famed instru- ments of Nachet are good, but inferior to those of Oberhauser ; on the other hand, the small ones of Schiek for 40 thalers [30 dollars], and those of Plossl for 70 to 100 Fl. [30 to 45 dollars], would be very serviceable if these artists were as productive as Oberhauser.* For the use of the mi- croscope I refer to J. Vogel, "Anleitung zum Gebrauche des Mikroskops" (Leipzig, 1841); H. von Mohl, "Mikrographie" (Tubingen, 1846); Hart- ing, " Het Mikroskoop deszelfs gebruik, geschiedenis en tegenwoordige toestand" (Utrecht, 1848-50), 3 Theile; Purkinje, article "Mikroskop," in Wagner's " Handworterbuch der Physiologic," Bd. 2, 1844; in which works, as well as in that of Quekett, " A Practical Treatise on the Use of the Microscope" (London, 1848, translated, by Hartmann, Weimar, 1850, [also Ed. 2, London, 1852)] ; and Robin, " Du Microscope et des Injections dans leurs applications a 1'Anatomie et a la Pathologic" (Paris, 1848), the preparation of microscopical objects is in part very elaborately treated of. A collection of microscopical preparations is indispensably necessary for a more exact study of Histology, especially sections of bones and teeth and injections. Every one may with a little trouble, form a mode- rate collection for himself, hints towards which he will find in the para- graphs standing at the end of each section of the special part, as well as in the works just cited. Microscopical preparations may also be exchanged with or purchased of Hyrtl, in Vienna ; Dr. Oschatz, in Berlin ; Topping, Smith, and Beck, Hett and others, in London ; and also in Paris. The largest private and public collections of microscopi- cal preparations exist in Vienna, with Hyrtl (injections) ; in Utrecht, with Harting and Schroder van der Kolk (injections, sections, muscles, nerves) ; in London, in the College of Surgeons (animal and vegetable tissues of all kinds) ; with Tomes (sections of bones and teeth) ; and with Carpenter (hard tissues of the lower animals). * [The opinion expressed in the above lines with regard to microscopes seems entirely too national. For clearness of definition of the object glasses and neatness of the stand, the instruments furnished by Ross, and Powell, and Lealand, are not only " quite equal/' but far superior to those of PlOssl, Oberhauser, or Schiek, the only objection to them being their high price. Of the cheaper microscopes, those most used at present in this country and in England are the small instruments of Nachet (Rue Serpente, Paris), the glasses of which are superior to those of PlOssl and Schiek, whilst the great convenience of the present stand, modelled according to the English style, renders them preferable to those of Oberhauser. In this country microscopes have been made by Mr. Spencer, of New York, the lenses of which are not inferior to the best glasses either of Ross, or of Powell and Lealand, but which are as yet too expensive to be introduced into general use. THE GENERAL ANATOMY OF THE TISSUES. I. OF THE ELEMENTARY PARTS. 4. IF the solid and fluid constituents of the human body be examined with the aid of strong magnifying powers, it appears at once that the smallest parts which they exhibit to the naked eye, as granules, fibres, tubes, membranes, &c., are not the ultimate elements in respect of form, but on the contrary, that all, in conjunction with a universally distri- buted, fluid, semi-fluid, or even solid, homogeneous, uniting substance, contain minute particles which differ in different organs but in the same organs have always a similar appearance. There are various kinds of these so-called elementary parts, simple and compound. The simplest are quite homogeneous, without any trace of their being com- posed of heterogeneous portions and are nearly allied to the inorganic forms, the crystalline granules and crystals, which also occur in the animal organism. Others already show that they have suffered a diffe- rentiation into an investment and determinate, though homogeneous contents : in others again, the contents present differences. The most important among all these forms, which may be comprehended under the general title of "simple elementary parts," are the cells, which not only form the starting-point of every animal and vegetable organism, but also, either as cells or after having undergone manifold metamorphoses, make up the body of the perfect animal, and in the simplest animal and vegetable formations (unicellular animals and plants), even enjoy an independent existence. Compared with cells, all other simple ele- mentary parts have quite a subordinate importance, so far as their direct participation in the formation of the tissues and organs is concerned ; while, from their being almost all contained in the interior of cells and from their being concerned in many and most important ways in the vital processes of these cells, their importance in other respects is very great. The simple elementary parts, which at first wholly comprise the com- mencing animal (or plant), often unite in the course of development in 40 GENERAL ANATOMY OF THE TISSUES. such a manner that they lose their independence and cease to exist as isolated elements. In this manner compound forms arise, each of which answers genetically to a whole series of simple ones, and which may most fittingly be called the " higher elementary parts." Such a coa- lescence has been observed with certainty only in cells, and from these most of the tubular and fibrous elements of the body are produced. 5. Formative and Nutritive Fluid Interstitial substance or matrix. While in plants the elementary parts in by far the majority of cases, unite directly with one another, in animals there is a very wide differ- ence ; a peculiar interstitial substance which combines them, and is ulti- mately derived from the blood, is always in a lower or more distant rela- tion therewith. If this take a direct share in the formation of the elemen- tary parts it is called " formative fluid," CytoUastema (Schleiden), from xt/fas, a vesicle, and /S^O-T^^ germ substance ; if it be present for their maintenance, it is called "nutritive fluid;" if it have nothing to do with either the one or the other of these functions, it is called the " ma- trix" or connecting substance. The cytoblastema is usually quite fluid, as in the blood, in the chyle, in many glandular secretions, in the con- tents of the glandular follicles, and in many embryonic organs; more rarely, viscid and like mucus, as in the gelatinous cellular tissue of embryos (vide infra), still more rarely solid, as the blastema from which the villi of the chorion arise and grow. The " nutritive fluid" takes the place of the formative fluid in all perfect organs ; and except when it is contained in special canals and cavities, as in bones, teeth, and perhaps in some cellular organs, is present in so small a quantity, that it cannot be directly observed. A matrix, lastly, is found in cartilages and bones as a solid, homogeneous, granular, or even fibrous substance connecting the cellular elements and for the most part arising from the blood, independently of them. The occurrence of a solid blastema, growing independently, in the villi of the chorion and of a solid matrix deposited directly out of the blood demonstrates that all parts of the body are not, as Schwann was disposed to believe, without exception developed from cells or in depen- dence upon cells. A few more recent authors, as Reichert, Donders, and Virchow, also consider that the connective tissue, excepting its elas- tic element, is to be reckoned among those tissues which are not at all, or not wholly, derived from cells ; but, as we shall see below, incorrectly. On the other hand, it is certain that in pathological formations such masses very frequently occur, fibrinous exudations becoming changed in great measure, without previous organization, i. e. cell formation into permanent tissues.* [* The Enamel and the Dentine of the teeth, and the so-called Cuticle of the hair (see 'O.i Hair and Teeth, and ' Quarterly Journal of Microscopical Science' for April, 1853), must ELEMENTARY GRANULES. 41 A. SIMPLE ELEMENTAKY PARTS. 1. ELEMENTARY GRANULES, ELEMENTARY VESICLES, NUCLEI. 6. In almost all animal fluids, whether contained in canals, or enclosed in cells, as well as in many more solid tissues, there are found and often in immense quantities, roundish corpuscles of very small, hardly mea- urable dimensions. Henle has called them "elementary granules," and has expressed the opinion that they are vesicular. This, however, is not always true, since it is demonstrable that many of these corpus- cles possess no investment. Such is the case with the fatty particles which occur in many cells and glandular secretiohs, with the granules of the black pigment of the eye and of other colored cells, the granular precipitates of biliary coloring matter, of different salts in the kidneys, and in the urine ; lastly, the protein granules (albuminous granules) which are found free in certain portions of the gray substance of the central nervous system and of the retina. Among the pathological but very common formations, we must enumerate here amorphous deposits, the colloid granules in the thyroid and elsewhere, and the corpuscula amylacea of the central nervous system, although these sometimes attain a very considerable size. All these granules want the properties ob- served in the higher elementary parts, such as endogenous growth, mul- tiplication, assimilation, and excretion, and so far incline towards the purely inorganic forms crystals; which are also found, though less commonly, in the organism, as for example in the spleen, in the lungs (black columns), in the ear, in the cells of the prseputial glands of the rat, in the blood-corpuscles of the dog and of fishes, in the fat-cells of man, arid in the cells of the chorion of the embryo of sheep. Elementary vesicles also occur very frequently, and are for the most part allied, physiologically, with the elementary granules, since, once formed they do not increase, and neither multiply by division nor by endogenous development. The milk-globules may with tolerable cer- tainty be arranged among these ; at first included within the cells of the nascent milk, they are subsequently found free, in enormous numbers, in the perfect secretion, and, as Henle first stated, consist of the fatty matter of the milk, with an investment of casein. The immeasurably small molecules of the chyle and of the blood, are also, according to H. Miiller's investigation, fat globules with a protein envelop, and similar vesicles may be found in most other fluids containing fat and albumen in abundance. In fact, since the discovery of Ascherson (Muller's ' Archiv,' 1840, p. 49), that whenever fluid fat and fluid albu- men are shaken together, the fat globules which are formed always certainly be regarded as structures which are not derived directly from the metamorphosis of cells. We are inclined also to believe, that the opinion of Reichert, Bonders, and Virchow, as to the nature of the connective tissue deserves much more attention than Professor Kolli- ker seems disposed to bestow on it. See on Connective and Elastic Tissues. TRS.] 42 GENERAL ANATOMY OF THE TISSUES. become surrounded by an albuminous coat, it is more than probable that whenever, in the body, fat and albumen in the fluid condition come into contact, similar vesicles are produced. A peculiar class of elementary vesicles is formed by the elements which occur in the yelk of certain animals. We are best acquainted with them in the yelk of the hen's egg,* in whose proper yelk-substance and yelk-cavity the globules which have been so long known are all vesi- cular, but have not the nature of cells. The membranes of these yelk- vesicles are excessively delicate and consist of a protein compound; the contents are fluid albumen, and, in the globules of the yelk-cavity, there is usually a large parietal fat globule, while in the others there are many smaller and larger ones. The development of these vesicles proceeds, in all probability, from the fat globules as in other elementary vesicles, from which, however, they are distinguished by the fact that they dis- tinctly possess the power of growth, during which their contents undergo metamorphosis, since in many the number of fat globules increases with age. Similar vesicles exist, also, in the yelk of fishes, Crustacea, and spiders, and here, as in birds, they have only a temporary importance, since they are not directly applied to the formation of the embryo, but only serve to nourish it. Lastly, free nuclei occur in many localities, either temporarily, where cells are formed immediately round nuclei, as in the chyle, the blood- vascular glands, the Peyerian patches; or permanently, as proper ele- ments of the tissue, in the wall of the thymus vesicles, in the rust-colored layer of the cerebellum, and in the granular layer of the retina. f Von Wittich ( cases, is certainly not so in all. In the corium the fat-cells are found more in the deeper part l>- round the hair-follicles and sebaceous glands, while they are wholly wanting in the pars papillaris. In persons in tole- FiG. 50. Normal fat-cells from the breast ; magnified 350 diameters: a, without reagents; 6, after being treated with ether, whereby the fat is exhausted, and the folded delicate membrane remains. FIG. 51. Fat-cells with crystals of margarin 5 magnified 350 diameters: a, cell with a star of crystalline needles, as they maybe found not uncommonly in normal fat; b, cell quite filled with crystals, from the white fat-lobules of an emaciated subject. 126 SPECIAL HISTOLOGY. rably good condition, the fat-cells are always rounded or oval, 0-01-0-06 of a line in diameter, with a dark border, filled with fluid, pale yellow fat, which forms a single drop and with a parietal nucleus which is not readily rendered visible (Fig. 50). In emaciated subjects, on the other hand, hardly any cells of this kind are met with, but instead, more or less abnormal forms : 1. Crranular cells, with numerous small fat- drops, forming whitish-yellow clustered lobules ; 2. Fat-cells containing serum, in yellow or reddish-brown minute lobular masses, which, to- gether with the fat (which has become more or less diminished in quan- tity, and usually appears as a single dark-colored globule), contain a clear fluid and a distinct nucleus, and are considerably smaller than the normal cells, 0-01-0-015 of a line; 3. Cells which contain no fat, but only serum, with a distinct nucleus, and having a delicate or thickened membrane ; they occur in more gelatinous fatty tissue, or mingled with the others ; they are also met with in oedema; 4. Lastly, Fat-cells containing crystals, either presenting 1 to 4 stars of acicular crystals (margarin), together with a drop of fat, or being completely filled with crystalline needles. The former occur among our normal cells, the latter only in the white, more isolated, fat-lobules. The nuclei in the fat-cells of the adult have not, as far as I am aware, yet been observed, excepting by Bendz (Almind. "Anat." p. 122, tab. I. fig. 4), who rarely, very rarely, noticed even two pale nuclei with nucleoli. It is true that Mulder (p. 601), states that they are furnished with one, rarely with two, nuclei, but Bonders and Moleschott (ib., p. 602, et seq.}, upon whom Mulder appears principally to rely, expressly say that they did not detect the nuclei; nor does Bonders (in the "Hol- land. Beitr.," I. pp. 57, 61), say anything about nuclei. I invariably find them when the fat has partially disappeared from the cell. In cells completely filled, I first distinctly noticed them, in some cases in the marrow, and in the fat-cells in the muscles; but I do not hesitate in the least to affirm their constant occurrence in all fat-cells, since no one can suppose that they are not formed until after the disappearance of the fatty contents. With respect to what Donders and Moleschott observe, as to the existence of two membranes in the fat-cells, the outer of which is said to be soluble in concentrated acetic acid, and in potass, and the inner not; the former, as Donders himself elsewhere supposes, can be regarded merely as connective tissue, which, in many instances, also penetrates between the separate cells and connects them together, or, pro- bably, is occasionally replaced by a homogeneous connective substance (modified cytoblastema). The crystals in the fat-cells are considered by Vogel to be margarin. As the forms of margarin and margaric acid are very similar, the question can be decided only on chemical grounds, and these appear to favor the latter. OF THE SKIN. 127 The pathological conditions of the fat-cells, although as yet but little investigated, corroborate my assertion of the constant occurrence of the nucleus. Without relying upon Schwann's observation, that the fat- cells of the subcutaneous cellular tissue of a rachitic child a year old, all contained a nucleus, I would more particularly adduce the condition of the fat-cells in cutaneous dropsy. In this affection, as long as the fat in the panniculus adiposus has not entirely disappeared, cells containing serum, and but a small quantity of fat, are extremely abundant, and exactly of the same form as those which are found in emaciated subjects, all with distinct nuclei ; and, besides these, there are numerous cells con- taining nothing but serum and also nucleated. In cases where the fat may be said to have altogether disappeared, and the colorless subcuta- neous cellular tissue is infiltrated throughout with water, I find the last- mentioned cells in greatly preponderating quantity, and associated with them, others of peculiar form. In the first place, fusiform or stellate cells, with from three to five irregular, oftea tolerably long processes, with a distinct nucleus, and mostly only scanty and minute dark fat- granules ; these, as the very numerous and various transitionary forms indicate, being developed from diminished cells containing serum, and from which the fat has been partially or wholly removed ; secondly, roundish or elongated minute cells (0-003-0-006 of a line) closely filled with dark granules, and without a visible nucleus, which, as is also easy to be perceived, owe their origin to a diminution of the fat-cells coincident with a change in their contents, and, on the other hand, are metamorphosed into the cellules with little or no fat, and containing serum, with which they are found associated. I may also mention that, in the inflamed medulla in the articular ends of the bones, as, according to Hasse, appears to be the case in rheumatism, I have seen the com- mon fat cells transformed into round and even fusiform cells, contain- ing serum and little fat, and occasionally furnished with nuclei. (From Kolliker, "Mikrosk. Anat.," Vol. II. p. 18.) 36. Vessels of the Skin. In the subcutaneous cellular tissue the arteries entering the skin give off many branches to the hair-follicles (see below), the fat-lobules and the smooth muscles, which, for the most part, form wide-rneshed networks of fine capillaries; more rarely, par- ticularly in the fat-lobules, the network is closer. More externally they supply the sudoriparous and sebaceous glands (see below), and also form terminal expansions in the inner part of the corium (pars reticularis), but not many : finally, they penetrate into the outermost part of the papillary layer, and into the papillce themselves, where they terminate in a close network of capillaries with narrow meshes. This consists, wherever there are papillce, of two portions ; firstly, of a horizontal 128 SPECIAL HISTOLOGY. plexus lying immediately under the surface covered by the epidermis, and which is composed of larger vessels (of O'Ol 0*005 of a line) with Fig. 52. 53 - wide, and of capillaries (of 0-003-0-005 of aline) with narrow meshes ; and secondly, of very many separate loops of the finest vessels (0-003 0'004 of a line) which are given off to the papillce. With cer- tain exceptions (v. 37) every papilla possesses its own capil- lary loop (Fig. 53),. (the branched papillce have many), which runs either' in the axis of the papilla or near the surface, almost as far as its apex. The larger trunks of the lym- phatic vessels are very easily recognizable in the subcutaneous cellular tissue, and are very numerous. In the corium itself different anatomists, Hasse, Lauth, Fohmann, &c., have demonstrated the lymphatics by in- jecting them with quicksilver. All agree in this, that they form an ex- cessively close network of fine vessels in its outermost part, according to Krause (1. c., p. Ill) of j 5 -^o of a line in diameter; the meshes of which become wider internally, and finally open by single trunks into the vessels of the subcutaneous cellular tissue. However, it is not by any means known, whether the vessels composing these plexuses are really the true commencement of the cutaneous lymphatics. FIG. 52. Vessels of the fat-cells. J$. Vessels of a small fat lobule ; a, artery ; b, vein. JB. Three fat-cells with their capillaries more magnified : after Todd and Bowman. Magni- fied 100 diameters. FiG. 53. Vessels of \\iepapillce of one entire and two half ridges of the cutis 5 after Berres. OF THE SKIN. 129 37. Nerves. The skin, in those parts of it which border upon the epidermis, particularly in some localities, is one of the structures most richly provided with nerves in the human organism, whilst in its deeper parts it is remarkable for their scantiness. In the panniculus adiposus, and in the fascia superficialis, as yet, no nerves are known besides those, which, giving off a succession of branches, traverse those parts to reach the corium, or to supply the hair-glands, smooth muscles, and Pacinian corpuscles, of which we shall speak further on. In the corium itself, the trunks which enter through the meshes of the deeper layers ascend by degrees, continually ramify- Fig. 54. ing, but without actually form- ing, terminal expansions, to- wards the pars papillaris. Here they anastomose frequently, and form rich terminal plexuses, in which deeper and more superfi- cial portions may be clearly dis- tinguished, the former consist- ing of fine branches still con- taining many primitive tubules, with wide meshes ; the second of fibres single or united in pairs, with narrow meshes. In this last or the fine terminal plexus, there also occur (whether in all the fibres is as yet undecided) in man and in ani- mals actual divisions of the primitive tubules, so that they divide, gene- rally at an acute angle, into two ; and from the plexus itself, the tubules finally enter the base of the papilla? in pairs, in order to run to their extremities, and there unite in a loop. The elements of the nerves of the skin exhibit no striking peculi- arities ; the diameter of some, in the trunks in the subcutaneous cellular tissue, is still as much as 0-005-0-006 of a line, and also in the deepest part of the corium, whilst they become finer and finer outwards. In the terminal plexus I find they vary according to the locality, from 0-003 to 0-0016, in the papilla from 0-0008-0-002 of a line. In the hand and foot the finest tubules vary between 0-0012-0-002 of a line; in the glans penis, in the lips and nose, on the other hand, only from, 0-0008-0-0012 of a line. R. Wagner has recently published some statements ("Allg. Zeitung," Jan., Feb., 1852; "Getting. Nachricht," Feb., 1852), according to- FIG. 54. Two papilla from the extremities of the fingers, without epithelium and with axile corpuscles, a, and nerves, b. A. Simple papilla, with four nerve-fibres and two termi- nal loops, c. B. Compound papilla, with two vascular points with capillary loops, d; and one nervous point with a terminal loop, e. 9 130 SPECIAL HISTOLOGY. which the relations of the nerves of the skin have hitherto been entirely misconceived. From the investigations of G. Meissner and himself, which were instituted upon the nerves of the palm of the hand, Wagner divides the papillce into nervous and vascular. The former are said to contain a peculiar oval corpuscle in their axis, which consists of super- imposed saccular or band-like laminae, resembling a fir-cone, and this structure is regarded by Wagner, as a peculiar sensory apparatus, and named by him " tactile corpuscle" (corpusculum tactus). Into these the nerves 1 to 3 fine dark-bordered tubules are said to enter from below, or from the side, and to terminate within them, either free, or perhaps divided into many delicate branches. Wagner found these corpuscles to be most abundant in the points of the fingers, and that they were more and more rare towards the wrist. I have considered it requisite to investigate these assertions, which are made with much confidence, particularly as Wagner grounds upon them great expecta- tions of the physiology of the sense of touch, and the following are the results at which I have arrived. Independently of the vessels and nerves, the papillae consist, in the main, of a sometimes more homogeneous, sometimes more distinctly fibrillated collagenous substance, which there is no reason to distinguish from connective tissue, and of fine elastic fibres in different stages of development, as fusiform cells (corpuscles of the connective tissue, of Virchow), cell networks, isolated fine elastic fibres and fibrous networks. These elements are so distributed, that in most papillce a cortical layer and an axile tract can be distinguished. In the former the fibrous elements are disposed longitudinally, and the connective tissue is often distinctly fibrillated, with the exception of the most superficial layer, which forms a clear, homogeneous but not separable margin. In the latter, on the other hand, the substance is more uniform and clear, and in many places is separated from the outer layer by transverse elastic fibres. When these latter, true elastic fibres, are not very closely dis- posed, no one would be led to consider that there is anything peculiar in this arrangement ; but undeveloped and very close together, as they are in Wagner's corpuscle, it is otherwise. These are, in fact nothing but the clear axis marked by transverse nuclei and nucleated fibres, which I have already described ; and, if no reagents be added, they pre- sent no other appearance than that which I have figured in my "Micro- scopic Anatomy," Fig. 4, or in Fig. 48 of this work. Dilute solution of soda, of which almost solely I have availed myself in investigating the course of the nerves in the papillae, often does not render their contour at all more distinct, and I therefore paid no fur- ther attention to their structure ; while, on the Other hand, acetic acid, which was also employed by Wagner and Meissner, brings out the axes of the papillae generally, though not always, as oval, or cylindrical, OF THE SKIN. 131 more sharply-defined bodies, to which the numerous transverse striae give a certain vague similarity to a fir-cone (Fig. 54). In its more inti- mate structure, such an " axile corpuscle," as I call it, does not con- sist of superimposed discs, as Wagner supposes, but of an internal mass of homogeneous connective tissue, which is most distinct in transverse sections, and when viewed from above ; and of an external generally single layer of undeveloped elastic tissue, which, in the form of fusi- form cells probably connected together and, more or less, drawn out into fine fibres, with shorter or longer nuclei (these last were also seen by Wagner), closely surrounds the internal substance in which here and there similar corpuscles also appear to be contained. Morphologi- cally, then, such a corpuscle is by no means peculiarly constructed, but resembles the axis of certain other papillae (e. g. of the sole of the foot), which are surrounded by true elastic fibres, particularly their often less- developed summits ; it is very similar, again, to the bundles of connec- tive tissue, with elastic fibres wound round them, such as are found in the corium; indeed, the difference consists principally in this, that the axis-corpuscles contain more undeveloped elastic tissue ; a circumstance easily comprehensible, since the papillce, as compared with the cutis itself, consist altogether of a tissue which is in a more embryonic state. With regard to their occurrence, axile corpuscles of the kind here de- scribed occur only in certain papillae ; arid, in fact, so far as my inves- tigations hitherto extend, only in those of the palm and surface of the hand, the red edges of the lips, and the tip of the tongue, not in those of the toes, thorax, back, glans penis, nymphse, and only rarely in those of the back of the hand and of the sole of the foot.* In the hand they * [I have recently succeeded in detecting these tactile corpuscles in the toes. They cor- respond exactly to the tactile corpuscles, as described by Wagner and Kolliker in other parts, only they were far less numerous than on the palm of the hand, or on the edges of the lip. I first discovered them in the papillae of the toe of an infant, and have twice since verified my observation. Their minute structure apparently consisted of superim- posed discs, such as described by Wagner. They may be most conveniently studied in fine transverse or perpendicular sections, which have been treated with acetic acid, or a dilute solution of soda. The nature of these so-called "tactile"' or "axile" corpuscles is as yet a matter of dispute. Most recent observers seem to entertain regarding them the same views as Kolliker (see Mr. Dalzell's, in the Edinburgh "Monthly Journal of Medical Science," March, 1853; also Mr. Huxley, "Quart. Journal of Micr. Sc.," Oct. 1853, and in Appendix to this work) ; yet Wagner, (in his reply to Kolliker, in "Miiller's Archiv. 1852,'') and more recently Meissner, ("Beitrage Zur Anatomic und Physiologie der Haut," Leipsig,1853) add additional observa- tions in confirmation of the nature of these "corpuscula tactus" as first described by them. Meissner has presented us with some very interesting researches on the relative frequency of their occurrence in the papillae in different parts of the body. Thus he found on a sur- face of 7 lines in length on the lips and apex of the tongue, only 4 or 5 ; on one square line comprising 400 papillae of the last joint of the index finger, 108, but only 40 on the second joint, 18 on the first. In the papillae at the root of the tongue, he was not able to discover any of these bodies. The tactile corpuscles are probably surrounded by a special membrane, since they can be isolated. They have as yet only been observed in Man, and in the Ape. DaC.] 132 SPECIAL HISTOLOGY. appear especially in the compound papilla, in particular cusps, one or two together, which may project more or less, and are sometimes shorter, frequently longer ; they occur more rarely in the simple papillae, as oval or cylindrical bodies, occupying J to f- the width of the summits of the papillae, and \ to J, or as much as f the length. In the points of the fingers, they occur in the proportion of 1 to every 2-4 papillce ; in the first phalanx, on the other hand, in the length of 1 line, only 2-6 are to be found, and in the palm they are still more rare. Fre- quently the axile corpuscles exhibit local constrictions, especially after the addition of acetic acid, are even spirally contorted, so tlfat they often have a certain similarity to a bundle of connective tissue treated in the same way, or with a spiral sudoriparous duct. Upon the back of the fingers and in the heel there appeared, in many individuals to be no axile corpuscles in the papillae ; in a small number, however, they were to be found even here, but scattered and small, in a few papillae. In the lips, I saw in two individuals axile corpuscles similar to those in the hand ; in one they were wanting. They existed only in that part of the red margin of the lip, which is visible when the mouth is closed ; they were very minute, and were placed partly in small projecting points of the larger papillae, partly in depressions between two of their pro- cesses. In the tongue, in which, according to Wagner, something similar to his corpuscles appears to exist, I met, in two cases, with no axile corpuscles ; whilst, in a third, I found them tolerably well deve- loped in the papillce fung if ormes of the point of the tongue (whether they are to be found in the posterior ones I know not), whilst they were wanting in the p. filif ormes and p. circumvallatw. In the p. fungif or- mes, one or many were situated in the point of the principal papilla, without extending into its simple processes, and therefore lay, as it were, at the bottom of a terminal pit, surrounded by the simple papillae. With regard to the course of the nerves of the skin, Wagner confirms the fact discovered by me, that even in man, the primitive tubules divide in the terminal plexuses (which I have recently also observed in the hand, the lips, and the tongue) ; and he further states that, in the palm at least, only those papillae contain nerves which possess the axile corpuscles, while they have no vessels. As regards the latter impor- tant circumstance, all those who have occupied themselves more parti- cularly with the investigation of the skin, must be aware that nerves are not to be found in all the papillae ; but seeing the difficulty of dis- covering the nerves in a dense organ like the skin, no one has thought it requisite on this account to depart from the old notion that every papilla contains a nerve, and is therefore a tactile process. Wagner having observed the sharply-defined axile corpuscles of the hand, ap- pears to have been surprised that they occurred only in certain papillae, and that these had nerves ; and struck with this circumstance, adopted OF THE SKIN. 133 the view referred to. As for myself, having again made long-continued investigations into the skin of the palm of the hand, I find that those points of the papillae, or those independent papilla, which contain axile corpuscles, do generally exhibit dark-bordered nerve-tubules very dis- tinctly ; but from this I should, for the present at any rate, by no means be led to conclude that the other papillae contain no nerves, but only vessels. If it be considered that dark-bordered nerve-tubules, though indeed rarely in proportion, are contained in vascular papillae without axile corpuscles, in the hand ; furthermore that in other places, as in the sole of the foot and the lips, such papillae are found ;*and finally, that the investigation of the cutaneous nerves is very difficult, it seems more judicious to suspend one's judgment upon this question, especially as it is possible, that pale, non-medullated, nerve-tubules, similar to those which I discovered in the skin of the Mouse, exist in man also. How- ever, I am by no means disinclined to agree with Wagner this far, that in the palm it is almost exclusively the papillae with axile corpuscles which contain dark-bordered nerves, for to say the least, it is very re- markable that in these papillae the nerves are so readily and satisfac- torily displayed. As to the possible existence of non-medullated fibres in the papillae without axile corpuscles, it is certainly too soon to express any definite opinion. With regard to the vessels, it is incorrect, uncon- ditionally to deny their existence in those papillae which contain nerves. In the compound papillae it is unquestionably true, that the cusps with axile corpuscles and nerves frequently contain no vessels ; at other times, however, even these contain a capillary loop, and this is still more fre- quently the case in the simple papillae with nerves. In the lip, the papillae containing nerves, whether they possess axile corpuscles or not contain vessels for the most part, if not always, and there are rela- tively very few papillae in which no nerves are visible. The tongue pos- sesses vessels and nerves in all the larger papillae ; on the other hand, I have as yet been unable to discover nerves in the simple papillae buried in the epithelium. It is yet to be ascertained how the nerves are dis- posed in other parts of the skin. It is surprising to me, that even in the sole of the foot, dark-bordered nerve-tubules can so rarely be perceived in the papillae, while in many situations they cannot be found at all. Further investigations are required to determine to what extent dark- bordered nerves are distributed in the papillae of the skin ; whether, perhaps, non-medullated fibres occur instead of them ; or whether, in certain situations, the nerves do not enter the papillae at all, but end in, the well-known superficial plexus at their base. With respect to the dark-bordered nerves in the papillae of the hand, Wagner is wrong in asserting that the nervous loops which I have figured are bloodvessels. He has only imperfectly seen the nerves of the papillae in question, perhaps on account of his having preferred the use of caustic soda, which more easily destroys them. Latterly, in making 134 SPECIAL HISTOLOGY. very delicate investigations, I have used only acetic acid, and have arrived at the following results: Each point of a papillae, or each papilla with an axile corpuscle, generally contains two, or as frequently happens at the points of the fingers four, dark-bordered tubules, which, surrounded by a neurilemma* which has escaped previous observers, pass upwards through the axis of the papilla to reach the base of the axile corpuscle, as a fine, convoluted nervous twig of 0-006--012 of a line in thickness. Here the nerve frequently becomes invisible, so that, as has happened to Wagner, one may be led to believe that it enters the cor- puscle, which is seatetl upon it, as upon a stalk, and there ends. How- ever, if a number of fresh preparations be treated with acetic acid and examined, the conviction is soon arrived at that this is merely apparent, the nervous tubules in reality proceeding along the outer surface of the corpuscle, either as far as its point, or very nearly so. In the mean- while they either remain together or take an isolated course. In both cases their neurilemma becomes excessively delicate, appearing finally to vanish entirely, while the nerves themselves surround the axile cor- puscle, passing round it either more directly, though in a slightly undu- lating course, or forming one or several spiral coils (Fig. 54, B}. As regards the actual termination of the nervous tubules, I retain the opi- nion I formerly expressed, inasmuch as, in at least six cases, I have again most distinctly seen loops (Fig. 54). It is, however, always difficult to observe them, and very frequently impossible, in spite of every exer- tion; and therefore, as we are all liable to error, I will blame no one for considering the termination of the nerves of the papillae to be unknown, or for believing in the existence of free ends, which perhaps also exist, and, at any rate, very frequently appear to exist. I only state what, according to my best belief, I have seen ; and while I have no prejudice in favor of loops, neither can I see anything alarming in their existence. This much, however, is certain, that Wagner has not traced the nerves in the papillae so far as they may be traced, and therefore, at present at all events, can lay no claim to a decisive voice in the matter. How the nerves in the papillae of the lips, tongue, and elsewhere, are disposed, I have not yet ascertained with certainty ; but with regard to the first of these, I believe I can also affirm, that they do not terminate in the axile corpuscles, but either merely pass by them or wind" round them. In the lips, in a single instance, I found well-marked nerve-coils in small papillae, or at the base of the large ones. 38. Development of the Outis. The following may be taken as a * [It is by no means easy to recognize this nenrilemma. Indeed, even its existence is ques- tioned by Meissner, who states that after the most careful observation, he has not been able to detect a neurilemma in one single instance. The nerve itself he thinks does not terminate in loops, as supposed by Kolliker, but penetrates into the tactile corpuscles. The cross-striae considered by Kolliker as elastic tissue, he justly describes as the termination of the dark- bordered nerve-tubules, for the action of soda on them proves them to be such. DaC.] OF THE SKIN. 135 general sketch of the development in the foetus, of the cutis in the broadest sense of the term. It consists at first of cells, which though not in man, yet in animals (the Frog, for instance) may be easily traced back to the earliest formative cells of the embryo. A considerable pro- portion of these cells are changed into connective tissue, becoming fusi- form, coalescing, and eventually being converted into bundles of fibrils; a process which appears to occur first in the fascia superficialis, the sub- cutaneous connective tissue, then in the pars reticularis of the corium, and finally in the papillary layer. Another portion of the cells are converted into vessels and nerves, as can be seen even in man, and very beautifully in the Batrachia (see my Memoir in the "Annales des Sciences Naturelles," 1846) ; while a third, growing and developing fat in its interior, becomes elastic fibres and fat-cells (vide supra, 23). The first foundations of all these parts having been laid, they continue to increase in a manner which is not yet exactly made out. The cutis ob- viously grows from within outwards (so that the papillae arise and are developed last of all), partly by the growth of its primitive elements, partly at the expense of cells, which are perhaps mostly of new forma- tion, and do not proceed from the original formative cells. The panni- culus adiposus also increases, partly by the increase of the cells of which it at first consists, partly by the subsequent development of others, as well as of connective tissue and vessels. In this manner, the skin grows for a long time after birth. In children below seven years of age, for example, the cutis is, according to Krause, only half as thick as in the adult, until at last, though at a time which is yet undetermined, the new development of cells ceases, as at a later period, perhaps, does the ex- tension of those elements, cells, fibres, &c., which are already formed. The fat-cells of adults, in which the process of growth is especially ob- vious, according to Harting, are in the orbit twice, in the palm three times as large as in the new-born infant ; whence it results that they in- crease in size in proportion to the parts of the body to which they belong. In embryos of two months the skin is 0'006-0*01 of a line thick, and wholly composed of cells. At the third month it is about 0-06 of a line, and already presents tolerably distinct connective tissue. In the fourth month the first lobules of fat appear, and the ridges of the hand and sole of the foot. From the seventh month onwards the panniculus adiposus is rapidly developed, and at birth it is relatively thicker than in the adult. 39. Physiological Remarks. If we attempt to harmonise the ana- tomical data here brought together, with the phenomena of sensation exhibited by the skin, we meet with considerable difficulties. The more intimate anatomy of the skin, as it is here detailed, fails to demonstrate nerves in all the papillae, or even in the majority of them ; and yet ex- 136 SPECIAL HISTOLOGY. periment teaches that though all points of the skin may not feel with the same delicacy, they are all nevertheless sensitive. I hoped to be able to submit Wagner's doctrine of the absence of nerves in many papillae to experimental proof, by examining the sensitiveness of various parts of the body with the finest possible English sewing needle. At first I really thought that I had found some places which were quite in- sensible, whilst in others the slightest touch produced sensation ; bat on carrying the investigation further, it appeared that the very same place was often sometimes sensible, sometimes not ; so that, finally, I came to the conclusion that the very smallest portions of the skin are sensitive. But since even in the palm of the hand the papillae containing nerves are widely dispersed, and in other places occur but rarely, or even not at all, it only remains either to assume the existence of non-medullated nerve-fibres in all the papillae, or to have recourse to the nervous plexus at the base of the papillae. I should unhesitatingly prefer the latter explanation, were it not : (1) that these plexuses are in many places so very scanty, and (2) that the slightest touch of the epidermis produces sensation ; for the present, therefore, I believe this must remain an open question. If we are not in a condition to understand how it is that every point of the skin is sensitive, still less are we competent to explain the different kinds of sensations. In this respect the following very general state- ment may be made. The excitement of the terminations of the nerves in the outermost parts of the cutis and the papillae is either direct or indirect. The former as it is produced, for example, when the cutis is laid bare, by penetrating instruments and by fluids, is much more intense than that which takes place through the mediation of the epidermis, one of the func- tions of the latter being to act as a defence against too violent impressions, and to blunt them according to its greater or less thickness. It can now be partly explained on anatomical grounds, why the delicacy and viva- city of the sense of touch are not everywhere equal, why they are less upon the hairy scalp, the back, the two upper divisions of the extremities, than on the face, on the genitalia, the hand and foot, the chest, and ab- domen. In the first place, where the tactile sense is delicate, the epi- dermis is in itself thin, as upon the eyelids and face, or has, at least a thin horny layer, as upon the penis and clitoris, whilst upon the back and extremities it is considerably thicker. Yet this circumstance is not a sufficient explanation, for parts with a thicker epidermis, as the palm of the hand and the sole of the foot are delicately sensitive, more so, in fact than others with a thinner covering, as the back of the hand and foot. Another condition must here obviously come into play, and it is, I think, that the skin is not equally well provided with nerves in all its parts. Sim- ple inspection teaches that the nerves upon the palm of the hand and OP THE SKIN. 137 the sole of the foot are more numerous than upon the back of the hand and foot ; upon the glans penis and clitoridis, the nipple, the face, they are more abundant than upon the abdomen, back, and thigh, &c. &c. ; and this is to some extent confirmed bj my measurement of the sensi- tive roots of the spinal nerves (vide "Mic. Anat.," p. 433). With the number of the nerves, is connected that of the actually demonstrable dark-contoured nerves in the papillae and the superficial nervous plexus, for nowhere is this more considerable than in the points of the fingers, the lips, the tip of the tongue, and the glans penis. As to the local sensibility of the skin, it is the province of anatomy, especially, to afford information, with regard to these two points : 1, how it is that we do not distinguish with the same clearness and exact- ness, in all parts of the body, the point at which a single irritation is applied : and 2, why two stimuli operating at the same time, under certain circumstances, appear double, under others single (Weber's experiment). I think that Weber's experiment cannot be explained by the mode of distribution of the peripheral nerves, but depends very pro- bably upon their central relations. It seems to me to be simplest to as- sume, that every peripheral end of a nerve is capable, when irritated, of producing a conscious sensation, but that, on account of the small num- ber of nervous fibres (in the cerebrum) which unite these with the seat of consciousness, if many contiguous, or even more distant, cutaneous nerves are excited, only a single conscious sensation results. In this case, the nerves of acutely sensitive parts must be connected with the seat of con- sciousness by more numerous intermediate fibres than those of other locali- ties, and at the ends of these fibres, also, we must suppose a sort of inter- lacement to take place. Upon this hypothesis, the former of the two points might be explained. A local irritation is, indeed, felt locally ; but, accord- ing as the nerves implicated are united with the brain by more or fewer conductors in the spinal cord, are we able to assign, more or less exactly, the precise spot ; so that, in some cases the limits of error will not exceed J-l line, while in others, they may extend to 1 or 1J inch and more. E. H. Weber has endeavored to demonstrate, in his last able Treatise upon the sense of touch, that it is only the termination of the nerves in the skin, not the fibres in the nervous trunks, which are the mediators of the sensations of pressure, warmth, and cold ; and he has expressed a supposition, that tactile organs as yet unknown may exist in the skin. R. Wagner believes that he has, in fact, found these organs in his so-called corpuscula tacttis, and he supposes that, composed as they are, accord- ing to him, of superimposed membranes, in the interspaces of which a very minute quantity of fluid is lodged, like elastic cushions, or a bladder filled with water, they are specially fitted to receive impressions from the epidermis at the extremity which is directed towards it, and to transmit them to the ends of the nerves which lie in and upon them. In my opinion, Weber's view of the greater sensibility of the termi- 138 SPECIAL HISTOLOGY. nations of the nerves in the skin, can hardly be doubted ; but, on the other hand, there is no obvious reason, a priori, why peculiar hitherto unknown organs should exist to that end ; nor why the condition to which I have already referred, the more isolated course of the fibres of the nervous tubules in the papillae and terminal plexuses, their fineness, superficial position, and the delicacy or absence of the neurilemma, may not abundantly suffice as an explanation. That Wagner's so-called cor- puscula tactus, my axile corpuscles, are not tactile organs in the sense intended by Weber, is easily demonstrable. Independently of the erro- neousness of his views of their structure, and of the fact that the nerves are not distributed in them, but only proceed along them, outside, in order, in many cases, to terminate even beyond them we find that all the essential functions of the skin are also performed without such cor- puscles. The feeling of warmth and cold, of orgasm, of tickling, of pressure, of pricking, of burning, of pain, are found partly over the whole surface of skin, partly in places where these corpuscles are cer- tainly absent, which sufficiently shows that they have not in the remotest degree the signification ascribed to them by Wagner. However, it is not likely that they exist for nothing in those particular localities, in which the sensibility to pressure is the greatest, and which we use especially as tactile organs, as the ends of the fingers, the point of the tongue, and the border of the lips ; and I consider them as parts, which in conse- quence of their being composed principally of dense, imperfectly -formed elastic tissue, confer a certain solidity upon the points of the papillse, and serve as a firm support for the nerves, in consequence of which, a pressure, which in other situations is not sufficient to affect the nerve, here takes effect. They would, in fact, be organs, like the nails and phalangeal bones, not essential and indispensable to the sense of touch, but only conferring upon it a greater acuteness than elsewhere. If, in this sense, they are to be called tactile corpuscles, I have nothing to say against the term, but then the phalanges and the nails, the " whiskers" of animals, &c., equally deserve the name of tactile organs. The contractility of the skin is exhibited in the wrinkling of the scrotum and of the skin of the penis, the erection of the nipple, and the occurrence of the so-called cutis anserina. It depends upon the smooth muscles of the skin already described, which, as Froriep and subse- quently Brown-Sequard and I have found, contract by electricity, inas- much as by this means, even in the living subject, the cutis anserina, the erection of the nipple, and, in recently-executed persons, a wrinkling of the scrotum can be produced. In the erection of the nipple by gentle mechanical irritation, the whole areola becomes diminished by the con- traction of its circular fibres, and thus protrudes the nipple whose mus- cular fibres, in this case, seem to be relaxed. Cold causes the areola and the nipple to contract, both becoming small and firm. The cutis anserina, which consists in wholly local contractions of the portions of OF THE SKIN. 139 the skin around the hair sacs by which their apertures are protruded conically, is explained simply by the existence of the muscles which I discovered, and which pass obliquely from the superficial part of the cutis down to the hair sacs, and when they act, extrude the sacs, and retract those portions of the skin whence they arise. The assumption of a contractile connective tissue in the skin, as well as in other parts, I must repudiate here, as I have already done (Mittheil. der Zuricher Gresellschaft, 1847, p. 27), because the smooth muscles, which can be microscopically demonstrated in the skin, and whose contraction by galvanism may be experimentally shown, sufficiently account for all the contractile phenomena which it exhibits. B. EPIDERMIS. 40. The corium is everywhere covered by a semitransparent mem- brane formed wholly of cells, and containing neither vessels nor nerves, the epidermis, which applies itself exactly to all the elevations and -6' depressions, and which accordingly upon its inner surface presents an exact cast of the outer surface of the corium^ the convexities and con- cavities of course being reversed. Upon its outer surface, also, the epidermis, to some extent, represents the form of the corium since the FIG. 55^2. Surface of the palm, from within: a, ridge answering to the groove between the ridges of the cutis ; 6, a similar one corresponding with the cleft between the rows of papillae; c, sweat ducts; d, broader points of insertion of these into the epidermis ; e, depres- sions for the simple and compound papillae. 140 SPECIAL HISTOLOGY. more marked elevations and depressions, such as the ridges of the palm of the hand and of the sole of the foot, the folds at the joints, muscular insertions, &c. are expressed in it, the latter even more strongly ; on the other hand, the papillae produce either no perceptible projection, or hardly any. The epidermis consists of two layers, chemically and morphologically distinct, and which are separated by a tolerably sharp line of demarca- tion, viz., the mucous layer and the horny layer. 41. The mucous layer, stratum Malpighii, rete or mucus Malpighii (rete mucosum), of many authors, is that part of the epidermis which lies immediately upon the corium, and almost everywhere appears undulated; in many places it is distinguishable even to the naked eye by its color, which is whitish or variously tinged with brown, and it is further cha- racterized by its small, soft, easily destroyed, peculiarly disposed cells. Fig. 555. The form of these cells and their dispo- sition are not the same in all localities. The innermost of them (Fig. 55 5), which, without interspersed free nuclei or semi- fluid substance, form a single layer resting immediately upon the free surface of the coriutn, are elongated, and not unfre- quently resemble the cells of cylinder- epithelium ; they are placed perpendicu- larly upon the corium ; their length is about from 0-0033-0-006, their breadth 0-0025-0-003 of a line. Upon these im- mediately follow in most places, elongated or even round cells of 0-003-0-004 of a line in many layers ; but in a few locali- ties, as in the hand and foot, at the free margin of the eyelids, in the mucous layer of the nails and hairs (vide infra), there are interposed here and there, between the rounded and elongated cells, one, two, or even three layers of similarly elongated and perpendicularly disposed elements, so that the mucous layer, on account of the numerous strata of perpendicular cells, has a striated appearance in its deepest part, under a low power. This character is the more striking, since the other elements of the mucous layer, the further they are followed from the first, round cells outwards, become thinner in another direction, i. e. become horizontally flattened (Fig. 55 c), and finally in the uppermost layers are transformed into thick vesicles, 0-006-0-016 of a line broad, and 0-002-0-008 of a line thick. At the FIG. 555. Perpendicular section of the skin of the Negro (from the leg), a a, cutis- papillse; b, deepest intensely-colored layer of perpendicularly elongated cells of the stratum mucosum; c, upper layer of the stratum mucosum: rf, horny layer. Magnified 250 diameters. OF THE SKIN. 141 same time, from their mutual pressure, they acquire a polygonal form which may even be recognized in isolated cells. All the cells of the mucous layer agree, in essential points, in their structure, and are nucleated vesicles distended with fluid. Their mem- brane is pale, often difficult of demonstration in the smallest, frequently quite distinct, always delicate, thicker in the larger ones, yet by no means to be compared to that of the cells in the horny layer. The contents are never quite fluid ; but also, excepting in the colored epi- dermis (vide infra), never normally contain larger particles, granules or fat-drops for example ; but are finely granulated, with more or less clearly-defined granules, w r hich invariably diminish in number in the more external cells. The nucleus, lastly, is small in the smallest cells, (0-0015-0-0025 of a line), in the large, of greater size (0-003-0-005 of a line) ; globular or lenticular in the round and flattened cells; elongated in the elongated cells. In the larger cells it appears obviously vesicular, often with a nucleolus, and lies centrally in the midst of the contents ; in the smaller it is apparently more homogeneous, without any visible nucleolus, and so disposed that it is not unfrequently in contact with one part or other of the cell-walls. [Most authors admit the existence of a special membrane between the cuticle and the corium. Krause (loc. cit. p. 112) describes on the upper surface of the corium a perfectly transparent, textureless, semi- fluid, tough mass of ^-J^th to -^50^ f a ^ ne i n thickness, which he be- lieves to be the cytoblastema of the epidermic cells, covered by a layer of free nuclei and real cells. Henle (loc. cit. p. 1010) considers the inferior layer of the cuticle as a continuous cytoblastema with inter- spersed nuclei, and calls it the "intermediate skin." Such free nuclei are admitted by Bruns (loc. cit. p. 358), by Gunther (loc. cit. p. 257), by Hyrtl (p. 379), by Hassall (loc. cit. p. 242), and others, whilst Reichert (Miiller's Archiv, 1845), denies their occurrence, and also that of the structureless membrane of Krause. Todd and Bowman (loc. cit. p. 413, Fig. 84), regard the lower portion of the epidermis as consisting of fully- developed cells (loc. cit. p. 404-411), and admit as the external border of the corium a simple homogeneous and transparent membrane, " basement membrane," which view Carpenter seems to share. My own observations lead me to believe with Reichert, that the lowest layers of the epidermis consist of fully-formed cells, as may be easily ascertained in most cases by the addition of acetic acid, or diluted alkalies to fine vertical sections. We are, therefore, not justified in drawing conclusions from those cases in which the cells are not distinct, which, it is true, does -not unfrequently occur ; for even then the regularity of distance separating the nuclei, the traces of cell-membranes observable as delicate stride between them, and the distinct limitation of the Malpighian stratum, as it approaches the corium, afford certain evidences of the existence of fully-formed cells. The homogeneous membrane of Krause, and the basement membrane of 142 SPECIAL HISTOLOGY. Fig. 56. the English authors, I believe to be identical. They are but the external portion of the corium, which appears, especially around and between the papillae, as a structureless and homogeneous membrane. A separation from the corium of this narrow, and on its under surface, by no means distinctly limited membrane, ought not to be attempted ; for although a distinct membrane in the embryo, it cannot be obtained as a special layer in the adult. (From Kolliker's Microsc. Anat. vol. ii. p. 47. DaC.)] 42. The horny layer (stratum corneum\ forms the external semi- transparent part of the epidermis, which in white people is colorless, and is composed almost wholly of uniform cells metamorphosed into plates. The deepest plates are still very similar to the uppermost cells of the stratum mucosum; but even in the second or third layer we find the widely different epidermic or horny plates. They (Fig. 56, 1, 2, 3) are, in fact, plates of moderate thickness, which in the lower and middle parts of the horny layer retain tolerably regular polygonal (4-5-6-sided) and smooth surfaces ; in the upper layers, on the other hand, they present more irregular outlines, are variously crooked and curved, and thence often appear to be wrinkled and folded. These plates must be regarded as cells, com- pletely flattened, and containing a very minute quantity of viscid fluid; and not, as might at first be imagined, as homogeneous lamellae, composed throughout of the same substance ; for by the addition of various reagents, espe- cially of acetic acid and potassa, they swell up and assume the form of vesicles (Fig. 57) ; at the same time, a rudimentary nucleus becomes obvious in a few, particularly in those from the middle and inner layers, but by no means in the majority of them, in the form of a flat, homogeneous, rounded or. elongated corpuscle, 0-003-0-004 of a line in length, and 0-002- 0-003 of a line in breadth, which, especially when seen from the side, is easily recognized by the dark contours which it then presents. The size of the plates of the ordinary horny layer varies from 0-008-0-016 of a line, and in the outer layer it is commonly somewhat FiG. 56. Horny plates of man: 1, without addition, viewed from the surface one with a nucleus; 2, from the side; 3, treated with water, granular and dark; 4, nucleated plate, such as occur on the outer surface of the labia minora and on the glans penis. Magnified 350 diameters. OF THE SKIN. 143 greater than in the inner. Upon the body of the penis the cells mea- sure 0-008-0-012 of a line; upon the glans, the largest are 0-016-0-02 of a line ; upon the outer side of the labia minora 0-012-0-02; on the labia major a 0-010-016 of a line. These last, larger cells, all possess distinct nuclei, and are almost identical with the epithelial plates, e. g. of the cavity of the mouth and of the vagina (Fig. 56, 4). Whilst the stratum Malpighii, except in its upper layer, is but indis- tinctly laminated, a clear lamination is obvious in the horny layer, inas- much as its plates applied together horizontally, form strata in number proportionate to the thickness of the horny layer (Fig. 55). It must not be imagined that these strata are distinctly defined from one another ; they are connected by their surfaces, and can only be detached and de- monstrated adhering together in numbers, by dissection, which is much facilitated by boiling or macerating the epidermis. The innermost, like the stratum Malpighii, taken together, exhibit a wavy course wher- ever papillae exist, projecting outwards over the points of the papillae, and following the depressions between them. This takes place in the most striking manner where very much developed papillae coexist with a moderately thick rete Malpighii, especially in the palm and in the sole of the foot, in which (see the figure in the section on the sudoriparous glands), the horny layer penetrates so deeply between the papillae, that its deepest cells are on a level with half their height : where the papillae are smaller, the horny layer sinks less deeply between them, or even lies quite flat upon the stratum Malpighii, as is the case where the papillae are absent. From this cause the boundary-line between the horny layer and the stratum mucosum in perpendicular sections, is sometimes straight, sometimes wavy, with smaller or greater elevations and depressions. The other parts of the horny layer take a more even course the further they are from the mucous layer ; yet not merely in the hand and foot, where, as is well known, the ridges of the corium are marked externally upon the epidermis, but in many other localities, a slightly wavy course of the uppermost layers may be perceived in perpendicular sections, and slight elevations indicate externally the points beneath which the papillae are seated. In the separate lamellae the plates are sometimes irregular, sometimes arranged circularly, as around the excretory ducts of the glands and hair-follicles, and also round the papillae on the palm of the hand and sole of the foot, as may be seen most readily at the apertures of the sudoriparous glands. 43. As regards the color of the epidermis, in the white races, as has been said, the horny layer is colorless and transparent or slightly yellowish, the mucous layer yellowish white or brownish. The color is deepest in the areola and in the nipple, passing even into blackish- brown, especially in women during pregnancy and after they have borne 144 SPECIAL HISTOLOGY. children ; it is less intense in the labia majora, the scrotum, and the penis, where for the rest it varies greatly, being sometimes almost entirely absent, sometimes very distinct, and is least considerable in the axilla and round the anus. Besides these situations, which in most individuals are more or less tinged, in the dark-complexioned more than in the fair, a lighter or more deeply colored, frequently very dark pigment is deposited in various other localities in the stratum MalpigJiii; in preg- nant women in the linea alba, and in the face (rhubarb-colored spots) ; in persons who are exposed to the sun, in the face, especially the brow, chin, and cheeks ; in the neck, the thorax, the back of the hands, the forearm ; and in dark persons over almost the whole body. These tints are not produced by special pigment cells, but are seated in the common cells of the mucous layer, round whose nuclei a finely granular or more homogeneous coloring matter or actual pigment granules are deposited. When the skin is only slightly colored, it is mostly only the neighborhood of the nuclei and in fact only of the lowermost layers of cells which is implicated, so that in perpendicular sections the papillse are seen to be surrounded by a yellowish fringe; darker shades are pro- duced by the extension of the color to two, three, four, and more layers of cells, and over the whole cell contents ; sometimes by a darker coloration of the deepest layer of cells ; the two conditions commonly coexisting. The horny layer also of the colored places of the skin, has according to Krause, its cell walls slightly tinged; this appears, however, only upon comparing them with those of uncolored parts of the skin, and only in the more deeply-tinged parts. In the negro, and the other colored human races, it is also only the epidermis which is colored, whilst the corium completely resembles that of Europeans. The pig- ment, however, is far darker and more abundant. In the Negro (Fig. 55), in whom, as regards the arrangement and size of the cells, the epi- dermis is precisely like that of the European, it is the perpendicular cells of the deepest part of the mucous layer which are darkest (dark brown or blackish-brown), and they form a sharply marked fringe con- trasted against the clear corium. To these succeed clearer but still brown cells, which are accumulated particularly in the depressions be- tween the papillae, but are also found on their points and lateral por- tions in many layers ; finally at the boundary close to the horny layer there follow brownish-yellow or yellow, often rather pale, more trans- parent layers. All these cells are colored throughout, with the excep- tion of their membranes, and especially the parts round the nuclei, which, in the internal layers, are by far the darkest portions of the cells.* The horny layer of the negro also inclines to yellow or brownish. * [The pigment in these cells seems of two kinds: a less intense yellowish pigment, and a dark granular pigment. The latter is irregularly dispersed throughout the contents of the cell, and in some parts it is conglomerated into small masses. It is generally especially OF THE SKIN. 145 In the yellowish skin of a Malay head in the anatomical collec- tion at Wurzburg, I find the same appearance as in a dark-colored European scrotum. It follows, then, that the epidermis of the colored races is, in no essential point, distinguishable from the colored regions in the white man, and it even agrees in nearly all respects with that of certain localities (the areola of the nipple, for instance). Pathological coloration of the epidermis (freckles, mothers' marks, &c.), according to Simon, Krause, Barensprung, and my own observa- tions, is produced exactly as the more intensely colored spots in the white man, and as the color of the negro's skin. Pigment deposits in the corium and in the papillae, such as may be seen in cicatrices, after chronic inflammation of the skin, and frequently as in ichthyosis and many ncevi, associated with a colored epidermis, in which the pigment is developed directly from the blood-corpuscles and their coloring mat- ter, must be carefully distinguished from the foregoing.* Numerous instances of partially or entirely white negroes and of black Europeans, not as a consequence of change of climate, but as a congenital or sub- sequently arising abnormal condition of the skin, have been noticed (see Hildebrandt. Weber, II. fig. 526 ; Flourens, Compt. rendus XVII.) But, for the future, it will have to be remembered, so far as the dark coloration of Europeans is concerned, that it may also arise from a de- position of the coloring matter of the bile. 44. The thickness of the epidermis as a whole, varies exceedingly, de- pending especially upon that of the horny layer. It measures : l-75th to l-50th of a line, upon the chin, the cheeks, and brow, in the external auditory passages, and upon the eyelids: l-50th to l-25th of a line, upon the bridge of the nose, on the breast and nipple of a female, on the back of the toes and fingers, upon the neck and back, on the inner and outer side of the thigh, on the scro- tum and the labia minor a : l-25th to 1-1 6th of a line, on the edge of the eyelids, on the male chest and nipple, the hairy scalp, the chin, penis, prepuce, and ylans penis : l-16th to l-10th of a line, on the red external parts of the lips, on the back of the hand : 1-1 Oth to l-7th of a line, on the flexor side of the fingers and toes : dense around the nucleus, which is itself but rarely recognizable, except by the aid of reagents, and does not seem to contain any of these darker granules. DaC.] * [A colored epidermis may also be produced by a parasitic vegetable growth, as in the disease called pityriasis versicolor, in which the yellowish color of the epidermis, is owing to layers of filaments and spores deposited under the epidermic cells. DaC.] 10 146 SPECIAL HISTOLOGY. 1-3 to 1-2 of a line, on the palm: and 3-4ths to IJd of a line, on the sole of the foot, in which tAvo latter localities the variations are greatest, independently of the circum- stance, that in the furrows and at the joints the skin is thinner than elsewhere. With regard to the proportionate thickness of the horny and mucous layers I find, in some localities, that the latter is constantly thicker than the former ; i. e., in all parts of the face, in the hairy scalp, in the penis, the glans, the scrotum, the nipple, and the skin of the thorax in man ; in the labia majora and minor a, on the back and neck. Here the mucous layer is 3-6 times, or 2-3 times as thick as the horny layer, according as its thickness is measured from the bases or from the points of the papillae. ; in a few of the localities mentioned, however, the stra- tum Malpighii is, in its thinnest parts, of the same thickness as the epidermis, as in the glans. In the rest of the body both layers are either equal in thickness, as in the external auditory passage, and here and there upon the flexor side of the first two sections of the extremities, or the horny layer is 2 to 5 times thicker than the mucous, and in the thickest places even 10 to 12 times as thick. The absolute thickness of the stratum MalpigJiii varies (at the base of the papilla?) between 0-007 and 0-16 of a line; where it is thicker than the horny layer, it measures in the mean 0-04 of a line, where it is thinner, 0*01 0-02 of a line. The horny layer by itself measures in many places only 0-005 of a line, in others 1 line or more ; when its thickness exceeds that of the stratum Malpigliii, it is generally about 0-1-04 of a line, when it is less, 0-01 of a line. 45. Pliysical and Vital Properties. The epidermis is but little elastic, flexible in the living condition and not easily frangible, softer in the deeper than in the superficial layers. The cells contain, neither in their membranes nor between them, any demonstrable pores (apart from the sudoriparous ducts and hair-sacs, which, in a manner, have their outermost portions hollowed out in the epidermis), and form a very solid, hardly a permeable substance. Many experiments, especially those of Krause, show, that the horny layer of the epidermis permits no fluids, except those which act chemically upon it, as the mineral acids and the caustic alkalies, to pass through it, either by pores or by imbibition, or by endosmose and exosmose, while it readily takes up gaseous matters, or easily vaporizable substances (alcohol, ether, acetic acid, ammonia, solutions of chloride of iron in ether, of acetate of lead in alcohol), and gives them off (cutaneous evaporation). This conclusion is not invalidated by the undeniable passage of water, liquid substances, ointments, and even solid matter (sulphur, cinnabar), through the unin- OF THE SKIN. 147 jured epidermis, since in these cases a mechanical intrusion of the sub- stances, in and through the sudoriparous ducts and hair-sacs, or their penetration into the sweat-ducts, and mingling with the sweat, explains their absorption. The mucous layer, at any rate, is easily penetrated by liquids, as is sufficiently shown by pathological anatomy (exudations which penetrate the mucous and raise up the horny layer into a vesicle the ready occurrence of absorption after the separation of the horny and the superficial portion of the muceus layer, by the action of vesi- cants). In their chemical relations, it is indeed well known how the cells and plates of the epidermis behave with regard to certain reagents, but there exists, at present, no perfectly satisfactory total analysis of the epidermis, with regard to its two layers which differ so widely ; and the organic combinations, also, which occur in it, are not sufficiently known. The so-called horn, which forms the membranes of the horny plates, is insoluble in water, easily soluble in concentrated al-kalies and con- centrated sulphuric acid, whence the skin, if wetted with these sub- stances, feels slippery and greasy ; there remains, however, a small residue insoluble in alkalies ; concentrated acetic acid, also, dissolves it, first rendering it gelatinous, by which it is distinguished from the protein compound of the hair. It contains less sulphur than the hair and nails, which is perhaps the reason why salts of lead, mercury, and bismuth, color the hair but not the epidermis. Besides these, Mulder finds in the horny layer a gelatinous matter, which is obtained by long boiling in water, and which would appear to be of a collagenous nature. The epidermis does not putrefy it melts in the fire without bending or swelling up, and burns with a clear flame. The behavior of the epidermis towards reagents is particularly of importance for the microscopist, on whose behoof I add the following account. After long maceration in water, the epidermis becomes detached in portions, and under moderate pressure is resolved into a white powder, consisting of the isolated horny plates, and the uppermost cell of the rete MalpigJiii. Boiled in water, pieces of the horny layer break up into their elements much more readily. Boiled in concentrated acetic acid from 15 to 25 minutes, all the horny plates become perfectly isola- ted, forming a cloudy, whitish deposit in the test tube ; they are ex- ceedingly pale, so that they are often hardly visible under a full illu- mination ; and are completely swollen up and changed into globular or elongated, distended, but always more or less flattened vesicles of 0-02- 0-032 of a line in breadth, and 0-006-0-01 of a line in thickness, the nuclei when they are present being also pale and hardly to be perceived. The 148 SPECIAL HISTOLOGY. Malpighian layer becomes pale under the action of cold, concentrated acetic acid, the cells and nuclei being rendered more distinct. The cell-contents are partially dissolved: by longer action the contours of the deepest layers of cells become invisible. The same thing occurs after boiling for four minutes. Caustic potass and soda act differently, according as the solutions used are concentrated or diluted. In the latter case, immediately after the addition of the reagent, the horny layer is rendered more clear, it swells up and changes in a short time into a beautiful tissue of pellucid, glo- bular vesicles, without nucleus or granules, and with sharp, moderately- thick contours, O02--032 of a line in breadth, and 0-016-0-02 of a line in thickness. If concentrated, solutions of the caustic alkalies render the plates at first smaller, so that they measure only 0-012-0-016 of a line, and are at the same time more wrinkled and pale, but with defined, dark contours ; in the course of an hour they swell up so as to appear as cells, but it takes two or three hours to give them the aspect of the plates which have been heated with dilute solutions. Boiled with these fluids, even the dry horny layer swells up, in an instant, into the most beautiful tissue of cells, without either granules or nuclei (Fig. 57), and at the same time the dissolving cell- contents mixed with the alkali, are collected in the cells, into greater and smaller granular masses ; after the action of the heat for five hours, all the cells disappear without leaving a trace, and yellowish and pale fat-drops in no great number, swim in the liquid. The cells of the Malpighian layer are still more acted upon by alkalies than those of the horny stratum : they swell up at once, and appear distinctly as deli- cate vesicles; these then dissolve, all but the uppermost two or three layers, which require a longer time, like those of the horny stratum, though less than the latter. The nuclei of all the cells withstand the operation of this reagent even less than the cells ; whilst, when the latter are dis- solved, a granular or striated substance remains behind, which is, pro- bably, partly fat. Concentrated sulphuric acid, in five minutes, causes the horny layer to swell up so much, that its elements, although still remaining flattened and irregular, appear quite distinctly to be vesicles; after half an hour they are somewhat more distended, and easily sepa- rable from one another. By boiling with this acid the plates swell up FIG. 57. Horny plates boiled with caustic potassa and distended ; the contents partially and wholly distended. Magnified 350 diameters. OF THE SKIN. 149 even in a minute, without exhibiting nuclei, and in two minutes they dis- appear without leaving any trace. Boiling in dilute sulphuric acid ren- ders the horny layer hard and transparent, and dissolves it wholly in 4-5 hours. The cells of the stratum Malpighii* are little altered by cold sulphuric acid : on boiling, their contours and nuclei at first become more distinct, but in about two minutes the whole is dissolved. Nitric acid colors the epidermis yellow, softens and changes it into xantho-proteic acid. The cells of the horny layers swell up somewhat, after a time, in the cold, and become granular ; the stratum Malpighii is rendered granular and indistinct, and sharply defined from the horny layer. Upon boiling, the whole epidermis is entirely dissolved in half a minute. Hydrochloric acid does not tinge the epidermis, and in the cold renders the cells of * [I have recently investigated the reaction of the pigmental cells in the Malpighian layer of the Negro, and with the following results. Macerated in water they remain unchanged. Caustic potassa renders the outline of the cell more distinct, but produces no effect on the enclosed pigment. After acting for three or four hours it dissolves the cell, and allows the dark pigment granules to escape. Boiled for ten minutes in a solution of caustic potassa, the cells become larger and more distinct; in many, nuclei and dark granules are visible ; and their color becomes changed to a yellowish brown. Prolonged boiling dissolves the cells, but does not act on the granular pigment ; caustic soda brings the pigment cells distinctly into view and causes them to swell up. Continued action for one or two hours, dissolves the cell and permits the unchanged black pigment to escape. Upon boiling for about four minutes in caustic soda, rupture of the cell-wall with escape of the contents ensues. Concentrated sulphuric acid has no effect on the Malpighian layer. When first added the cells are rendered more distinct ; after twenty-four hours no further effect is observable. Boiling in sulphuric acid produces no change on the cells; after a few minutes the whole epidermis is dissolved. Nitric acid when first added had no decided action ; but after a few hours it rendered the cells more indistinct, dissolving some, and staining the intermediate tissue yellow. Soaked for twenty-four hours in nitric acid, the whole pigmentary layer assumes a yellow color; the separate cells are scarcely recognizable. The rapidity with which the whole epidermis when boiled in nitric acid is dissolved, makes it difficult to determine its effect upon the Malpighian layer. Hydrochloric acid does not act as powerfully as nitric acid. At first its addition produces no effect on the cells; in the course of a few hours, they become more indistinct, but are not dissolved. The same result is obtained by allowing this acid to act for twenty-four hours. The cells are then indistinct, but of a black color; boiled for two minutes they swell up, enlarge, but are not rendered more distinct. More prolonged boiling (four or five minutes) dissolves the whole epidermis. Acetic acid causes the pigment-cells to be more easily dis- tinguished. In a preparation that had been placed for five weeks in concentrated acetic acid, the cells were very distinct; but not otherwise altered. No effect was produced upon the pigment. The action of Nitrate of silver, as it stains the horny tissue, cannot be well ascertained. In a preparation, that had been placed in a concentrated solution for twenty-four hours, the pigment cells, as far as they could be studied, were of a more intense color, but not otherwise altered. In alcohol and ether the epidermis is hardened and the pigment-cells of the Malpighian layer are well and distinctly seen, but these reagents exert no action on them. Boiled in ether the cells become distinct and of a lighter color. A solution of Iodine, colors the whole epidermis immediately, and thus prevents the study of its special action upon the pigmental cells of the Malpighian layer. DaC.] 150 SPECIAL HISTOLOGY. the horny layer somewhat more distinct than nitric acid. After boil- ing for a minute the horny layer becomes a beautiful cellular tissue, exactly as after the addition of dilute solution of potass. In carbonate of potass the epidermis is hardly changed at all. After seventeen weeks it is hardened and easily cut with a knife. Nitrate of silver colors it violet or brownish-black, by the formation of oxide of silver, of chloride of silver, and of black sulphuret of silver, in consequence of the chloride of sodium and sulphur which it contains. Investigated microscopically with the help of acetic acid, the tissue of the epider- mis is seen to remain quite unchanged, and minute dark granules are visible between its elements. Nitrate of mercury gives the epidermis a reddish-brown hue, sulphurets of the alkalies render it brown and black: many vegetable colors unite with it. In alcohol and ether it is insoluble, with the exception of a small quantity of fat which it contains. From all this, it results, with regard to the elementary parts of the epidermis, that they are cells, which, however, as the alkalies show, do not everywhere present the same characters. In the stratum mucosum they are actual vesicles and easily soluble in the horny layer, scarcely so ; and here, in fact, a distinction must be drawn between the resisting cell-membrane and the cell-contents, which swell up and disappear more readily; these, in the natural condition, form an apparently homogene- ous simple plate, but the difference between them may be readily ex- hibited by reagents. In what parts the small quantity of collagenous substance, which has been noticed, has its seat, is not clear ; perhaps it forms a portion of the contents, especially of the cells of the mucous layer, or belongs, it may be, to an intermediate substance between the cells, which, however, is not microscopically demonstrable. If the fat of the epidermis is not merely accidental, arising from the cutaneous secretions, it is most probably contained within the Malpighian cells. Cruns, Todd and Bowman, Valentin and Bruch, recommend the use of alkalies for the investigation of the epidermic tissues, but their full importance was first shown by Donders (Mulder's " Phys. Chemie," p. 257, et seq., and " Hollandische Beitrage," I. u. 11). They are now generally recognized as quite indispensable reagents for the investiga- tion of the horny tissues ; but, as Paulsen (" Obs. Microchem.," &c. Dorpat, 1848) and Reichert (Mull. "Arch," 1847, Jahresbericht.) ad- vise, it is well always to use only definite solutions. I may add, that a great saving of time is effected by the heating of the tissues to be inves- tigated in test tubes, with these and other reagents, as I have already done in examining those tissues of animals which contain cellulose ("Annales d. Sc.Nat.," 1846). 46. Gf-rowth and Regeneration. The epidermis possesses no power of continually active growth depending upon intrinsifc causes and founded OF THE SKIN. 151 upon the vital relations of its cells, or those which it has with the corium ; it is essentially a stable tissue, which does not change in its elementary parts, but, somewhat like a cartilage, has all its vital energies directed to its unchanged self-maintenance as a whole (thickness of the whole epidermis, proportion of the rete Malpighii to the horny layer), and in its separate parts. However, since a throwing-oif of the external layers, if not necessarily, yet accidentally, takes place almost con- tinually over the whole body to a greater or less extent, the epidermis is, so to speak, continually occupied in replacing what is lost, or in grow- ing, and thus exhibits its vegetative life in a more remarkable manner. Whichever takes place, it is the corium and its vessels from which the fluids required by the epidermis are derived. In every locality, we may suppose, that a certain determinate quantity of plasma, corresponding with the anatomical and physiological relations of the vessels of the corium and the thickness of the epidermis, permeates the latter, and, when it is not growing, simply fills its cells and plates (independently of that more watery fluid which subserves the cutaneous evaporation), maintaining their vital activity, and at the most causing temporary deposits of pig- ment in the rete Malpighii. If, on the other hand, its outer layers be removed, a certain amount of plasma becomes free and disposable, and then regeneration takes place, which, if it proceed continuously, may even be called growth. It is in this process that the vegetative life of the epidermis-cells is most distinctly evidenced, particularly in the rete Malpighii, where it is unquestionably most intense, exhibiting itself especially in the multiplication and growth of the cells, and in their chemical changes. In the horny stratum the phenomena are less strik- ing, though it must not be considered to be inactive even in the uppermost layer ; being by no means dead matter, as we evidently see, when under certain conditions, especially under abnormal states of the corium ' the source of its nutrition it sometimes becomes hypertrophied, some- times completely dies away. We have not as yet, however, attained to an exact insight into the vital manifestations of the epidermic cells, and are therefore not in a condition to decide which of the phenomena pre- sented by them are to be ascribed to their own activity, and which to the nature of the plasma which nourishes them. The latter is certainly of the greatest importance for the epidermis, and it is more than pro- bable that most of its peculiarities, as, for instance, its typically different thickness in different parts of the body, the different relations of the stratum Malpighii to the horny layer, and its pathological states, depend upon qualitative and quantitative differences in the plasma. Upon what condition, furthermore, it depends, that in the Malpighian layer, the changes of the cells are far more considerable than in the horny layer, whose elements all closely resemble one another, is as little obvious as 152 SPECIAL HISTOLOGY. the cause of the somewhat defined line of demarcation between the two layers, a condition which appears still more strikingly in the nails, and would lead one to suppose that, at the first formation, and in the course of the development of the epidermis and nails, a very considerable altera- tion suddenly takes place at one point in their cells, thus determining their separation into two layers. In the deep fold of the skin which surrounds the glans penis and clito- ridis, a continual desquamation and reproduction of the epidermic scales, which are here soft and nucleated, takes place, in consequence of which a peculiar secretion, the smegma preputii, is produced. Hitherto this secretion has been erroneously, but almost universally, supposed to be a sebaceous matter secreted by the preputial glands. The microscope shows : 1, that in the female, where the presence of smegma preputii is constant, neither sebaceous nor any other glands exist upon the pre- puce or glans clitoridis ; 2, that in the male, in whom such glands are indeed found, they are commonly but insignificant in relation to the quantity of smegma, and are often very few and scattered; 3, finally, that the smegma, in both sexes, consists principally of cells of the same form as those of the prepuce and glans penis and clitoridis ; whence, taking also into account the fact, that in the male it is generally dis- tinctly composed of superimposed layers covering the whole prepuce con- tinuously, whilst the sebaceous glands occur only isolated, it naturally follows that the smegma is principally constituted of desquamated epi- dermis. However, this does not exclude the preputial sebaceous matter in the male from also taking a share in proportion to the number and size of Tyson's glands, in the formation of what goes under the common name of smegma. There would in this locality then, really be a con- stant desquamation of the external, and a new development of the in- ternal layers of the epidermis, but here there are special purposes in view which elsewhere do not enter into consideration. The preputial fold, in fact, is to be compared to a gland ; and as the secretions of these are very often formed only by the continual casting off of the cells which line them (e. g. sebaceous glands), so is that of the prepuce. We must recollect that in many animals, e. g., the Weasel, the Beaver (E. H. Weber), without essentially changing the character which it possesses in man, the prepuce takes on a highly glandular nature, and that even in man it yields a secretion which differs considerably from common epi- dermis. According to Lehtnann, the yellow, fatty, strongly-odorous preputial smegma of man contains, when dried, in 100 parts : Ethereal extract, 52*8 ; alcoholic extract, 7*4; aqueous extract, 6*1; earthy salts, 9'7 ; albuminous substances soluble in dilute acetic acid, 5-6; insoluble residuum, 18'5. The ethereal extract contained saponifiable fat, choles- OF THE SKIN. 153 terin, a non-saponifiable and uncrystallizable fat and bilin (Gallenstoff). The smegma of the horse possessed nearly the same constituents ; and among the salts, oxalate of lime; while in man, ammonio-phosphate of magnesia occurred. The watery extract contained neither albumen nor casein. An extensive desquamation of the entire horny layer of the epidermis, such as takes place in the embryo and in many animals, does not occur in man except in certain morbid states. On the other hand, its power of regeneration is exhibited in other modes than those which have been mentioned. Excised portions of the epidermis, for instance, are very readily replaced, and with tolerable rapidity, so long as the corium be not injured ; and, in fact, not by the immediate deposition of epidermis in the wound, but only by the growing up of the whole epidermis from below. If the corium be injured as well, an epidermis is, indeed, formed upon the substance of the cicatrix, but without any of the previous ele- vations and depressions of the internal and external surface, because the new corium has neither papillae nor ridges. If the epidermis be raised up into a vesicle by acrid substances, e. g., Tartar emetic, a slight burn, &c., the wall of the vesicle, which consists of the horny layer and some few layers of cells of the mucous layer, never again becomes adhe- rent; but from the main substance of the mucous layer, which mostly remains lying upon the papillae, a new horny layer is by degrees deve- loped. If we inquire more minutely into the mode of regeneration of the epi- dermis, there can, in the first place, be no doubt that it takes place in the Malpighian layer, inasmuch as losses of substance of the horny layer, e. g. a piece cut out, are restored not by the formation of a new portion in the gap, but by the growth outwards of a horny layer from below (the wound remaining wholly unchanged), which gradually raises the bottom of the wound, and brings it to a level with the surrounding epi- dermis, the latter, in consequence of the pressure that it suffers from the growing portion, becoming everted and exfoliating. The reason of this phenomenon is to be sought, simply in this, that the non-vascular epider- mis draws the materials which it requires for its nutrition and regenera- tion from the superficial vessels of the corium. It is more difficult to ascertain from what portion of the Malpighian layer the regeneration proceeds. If a layer of cytoblastema and of free nuclei existed upon the surface of the corium, as many authors suppose, we might acquiesce in the view, that the epidermis grows by free cell-development in those innermost layers which rest immediately upon it ; but such a cytoblas- tema, as we have seen, does not exist, the stratum Malpighii being in- variably formed by perfect cells ; and thence nothing remains, but to suppose an endogenous cell-development around portions of contents in 154 SPECIAL HISTOLOGY. the deepest round cells, or a multiplication by division, for which latter view the occasional occurrence of two nuclei in some of the softer epidermic cells, seems to speak. It can be more easily made out, how, in the course of the growth of the epidermis, the youngest epidermic cells become changed into horny plates. The small and round vesicles of the deeper layers of the stratum Malpighii become larger and flatter the more they approach the surface, until at last they are completely converted into flattened plates. In the meanwhile their nuclei at first grow a little, and then, as a general rule, disappear wholly in the horny layers ; whilst the cell-contents, which are granular in the mucous layer, clearly distinct from the cell-membrane, and probably semi-fluid, become more solid and homogeneous in the horny layer, and finally coalesce with the cell-membranes. At the same time the latter are chemically altered, becoming less and less soluble in caustic alkalies. 47. Development of the Epidermis. The first layers of the epi- dermis are developed, in the Mammalia, by the metamorphosis of the most superficial of the original formative cells which compose the young embryo. When the rudiments of the stratum Malpighii *n& horny layer are once indicated, the former continues to increase in thickness, in con- sequence of the multiplication of its elements, whilst the horny layer, for the increase of its proper substance and to replace what it loses by desquamation, recruits itself from it exactly as in the adult. How the multiplication of the cells goes on in the rete Malpigliii has not been directly observed ; but it is certainly not by free cell-development, since in embryos of all ages the mucous layer consists wholly of cells, and free nuclei are altogether absent. As regards the horizontal extension of the epidermis, it appears, as Harting (" Rech. microme'tr," p. 47) justly ob- serves, from the circumstance that the epidermic scales of the foetus and of the adult differ very little in superficial size, that it can only in a very slight degree be ascribed to the growth of its elements. In fact the horny plates of the embryo of fifteen weeks already measure 0-009 -0-012, in the sixth month 0-01-0-012, in the seventh month 0-01- 0-014, in the new-born infant 0-012-0-016, in the adult 0-008-0-016 of a line. Since, however, keeping in mind the structure of the horny layer, it cannot well be supposed that new scales are continually inter- calated from below between its elements, and since a superficial multi- plication of the cells of the rete. which also do not increase in size, must certainly be granted, it seems impossible to admit any other conclusion than that, in agreement with the great superficial growth of the cutis and of the rete, and the small extensibility of the horny layers, a series of desquamations of the latter take place, which, if this view be correct, must likewise obtain after birth. OF THE SKIN. 155 In an embryo of five weeks I found, in the place of the epidermis, nothing but an external layer of polygonal cells of 0-012-0-02 of a line in diameter, and an internal layer of small cells of 0-003-0-004 of a line ; in embryos of fifteen weeks the epidermis is 0-01-0-012, of a line thick, and composed as before, only that the deep layer of cells answering to the stratum mucosum is often already double, and the external cells measure only 0-009-0-012 of a line. In the fifth month the epidermis in one instance measured on the heel and ball of the hand 0-02-0-024 of a line, over the ridges of the cutis 0-036-0-04, in the furrows between them on the back 0-02-0-024 of a line, of which thickness one-third may be regarded as belonging to the horny layer and two-thirds to the rete Malpigliii. In a somewhat older embryo it was, on the heel 0-06--064 of a line (mucous layer 0-05, horny layer 0-01-0-014), on the surface of the hand 0-05 of a line (mucous layer 0-04, horny layer 0*01), on the back 0-02-0-024 of a line (mucous and horny layers of equal thickness). The mucous layers consisted of many layers of smaller cells, the lowest of which were already elongated, and stood perpendicularly ; the horny layer, of at least two layers of polygonal flattened cells, with round nuclei. In the sixth month the epidermis upon the thorax measures 0*02 0-022, on the palm of the hand 0-06, on the sole of the foot 0*07 of a line, and everywhere it consists of many layers of cells. The outermost one or two are composed of horny plates without nuclei 0-01-0-14 of a line, perfectly similar to those of the external horny layer in adults ; then follow 3-4 layers of polygonal cells, the largest 0-01-0-012 of a line, with nuclei 0-004 of a line; finally a mucous layer, whose thickness equals about one-half or two-fifths that of the whole epidermis, with at least 3 or 4 layers of rounded cells of 0-003-0-004 of a line, the lowest of which are somewhat elongated, and are seated perpendicularly upon the cutis. In the seventh month, I found in one embryo, that the epidermis on the heel measured 0-12 of a line (mucous layer 0-072, horny layer 0-048), upon the back 0-07 of a line, (mucous layer 0-04 horny layer 0*03): in another it measured on the heel 0-120-14 of a line (mucous layer 0-05-0-06, horny layer 0-07-0-08), on the knee 0-046-0-064 of a line (mucous layer 0-016-0-024, horny layer 0-03-0-04). Both layers of the epidermis are as sharply separated from one another as in adults, and their elements similar to those of the perfect epidermis, especially the lowest parts of the stratum Malpighii and the plates of the horny layer, which have no nuclei, and measure 0-010*014 of a line in the uppermost layers. In the new-born infant, apart from the thickness of the epidermis, which in one case measured on the heel 0-10-11 of a line (mucous layer 0-04-0-05, horny layer 0-06), nothing particular is to be observed, 156 SPECIAL HISTOLOGY. except that by maceration, &c., it is much more easily separated from the corium than in the adult. The non-nucleated horny plates measured 0*012 '016, on the labia minora, where they possess nuclei 0*016 0*02 of a line. During embryonic life a desquamation of the epidermis occurs, which is perhaps repeated several times. Such is the fate, probably, of the layer of polygonal cells which arises first of all, and which in the second to the fourth months, becomes metamorphosed into an almost structure- less membrane, and is then no longer to be found ; perhaps also of the layer of epidermis, which covers the points of the hairs which have not yet appeared externally (vide infra Hairs); and in the second half of the foetal period it may be easily demonstrated as an actively occurring process. From the fifth month onwards, in fact, continually increasing desquamation of the external epidermic cells takes place, and these becoming in most parts mixed up with the sebaceous secretion of the skin, form the so-called vernix caseosa or smec/ma embryonum. This is a whitish or yellowish, viscid, inodorous material, which, especially from the sixth month onwards, covers the whole surface of the foetus with an often considerably thick and even laminated substance, which is most abundant upon the genitalia, on the flexor side of the joints (axilla, knee, nates), on the sole, the palm, the back, the ear, and on the head in large quantity, and when microscopically examined consists mainly of epidermic cells, but also contains sebaceous cells and fat globules. According to Davy ("Lond. Med. Gaz.," March, 1844) the vernix caseosa contains in 100 parts, 5*75 elain, 3*13 margarin (8*88 fat) ; the rest, 91*12 per cent., must be reckoned as epidermic scales, for since the vernix caseosa contains no free fluid, the 77*87 per cent, water and 13*25 solid substance found by Davy must be laid to the account of epidermic cells. This also holds good of Buck's analysis (" De Vernice caseosa," Halis, 1844) who found in 100 parts, 10*15 fat, 5*40 epithe- lium, and 84*45 water (so that there was 89*85 of epithelium) ; and also in two other cases, in which the water was not exactly determined, he found 14-80 and 9*31 per cent, of fat, and therefore 86*20 to 89*69 of moist epithelium. According to Buek, the fat of the vernix caseosa contains no cholesterin, as had been stated by Fromherz and Gugert, but oleic acid, and either stearic or margaric acid, which are probably not free, but combined with glycerine, a circumstance which also evidences its origin from the sebaceous glands, in which, normally, no cholesterin is formed. Lehmann found (1. c.) in the dry vernix caseosa of a nearly full-grown foetus, 47*5 per cent, of ethereal extract, 15*0 of alcoholic extract, 3*3 of watery extract, 4*0 of acetic acid extract (earthy phosphates and albuminous substances), epidermis and lanugo 23*7. In the ethereal extract the reaction of bilin was absent and the fresh vernix contained a large quantity of water, which in all probability had entered OF THE SKIN. 157 its cells from the liquor amnii. The smegma generally appears about the sixth month, varies greatly in quantity, and is, especially in newly- born infants, sometimes very greatly developed (as much as 3J drachms, Buek), sometimes wholly wanting ; in which latter case it either becomes mixed with the liquor amnii, which in fact often contains epidermic cells as well as fat (Mark, in Heller's " Archiv," 1845, p. 218), or may have been from the first, less developed. After birth the smegma is thrown off in the course of from two to three days, and the permanent epidermis appears, of whose further changes up to the adult state there is little to be said. In a child four months old the epidermis measured: Epidermis in toto. Rete Malp. Horny layer. On the heel, . . O26 of a line. 0-12 of a line. 0-14 of a line. On the back of the foot, O048-OOG of a line. 032-0-04 of a line. O'OlG-0'02 of a line. On the palm, . . 0-07-0' 1 " 0-04-0-07 " 0'03 On the back of the fingers, 0-050-0-07 0'04-0'05 O-OlG-0'02 " On comparing this with the adult, it is to be observed that the epidermis of the young child is disproportionately thick, and that this thickness depends especially upon the rete Malpigliii, whilst the horny layer exhibits only a slight development. The pigment of the rete Malpigliii arises, in the colored races, only after birth. P. Camper (" Kleinere Schriften," 1782, Bd. I. p. 24) saw a negro child, which at its birth was reddish, and hardly differed from that of a European, rapidly become tinged black at the edges of the nails and round the nipple. On the third day the genitalia became colored, and on the fifth and sixth the blackness spread over the whole body. In Europeans also, at birth, the pigment of the areola and of the other places which have been men- tioned, is not yet present: it is gradually developed in the course of the first year, so that in children of two or three months old it is only indi- cated. In investigating the skin, perpendicular and horizontal sections of fresh, dried, and boiled preparations are serviceable: they may be mois- tened with an indifferent fluid or with various reagents, the most impor- tant points in regard to whose effects have been noticed in the foregoing paragraphs. The epidermis is separated from the corium by maceration, by boiling, and where it is not thick, as on the genitalia, by acetic acid and soda, easily and in large flakes, so that its lower surface and the papillae of the corium become visible in the most beautiful manner, and the latter may be examined singly or in groups. In the fresh skin their position and number are quickly and easily to be recognized in horizon- tal sections, passing through the papillae and the deep layers of the epidermis. Its vessels are to be studied in thin parts of the skin (geni- talia, lips), in the fresh condition, or in injected preparations with those of the rest of the skin ; its nerves in perpendicular sections, in isolated 158 SPECIAL HISTOLOGY. papillae, or in thin portions of the skin (prepuce, glans, eyelids, conjunc- tiva bulbi) after the addition of acetic acid and dilute solution of caustic soda, or according to Gerber's and Krause's method. Gerber boils the skin until it is transparent, lays it a few hours in oil of turpentine until the nerves are white and glistening, and then examines them in fine perpendicular sections made with the double knife. According to Krause, the nerves are seen very well after treating the skin with nitric acid, if the right amount of action is hit upon. The elastic tissue of the skin comes out well under the action of acetic acid, soda, arid potassa. The smooth muscles may be readily isolated in the tunica dartos with more difficulty in the penis and in the areola, where it needs familiarity with them, in order in all cases, to recognize them with the naked eye. On the hair-sacs they are rendered visible microscopically, if a sac, with the sebaceous glands which appertain to it, be isolated, especially after the application of acetic acid, as small bundles near and in front of the sebaceous glands, but best and very easily in perpendicular sections of boiled skin (Henle). The examination of the fat-cells is especially in- structive in thin persons, in whom their membranes and nuclei are readily visible: in other cases their membranes are readily demonstrable by the aid of ether, which extracts the fat ; but the nuclei are seen with difficulty, though they may occasionally be discovered here and there even in full cells. The epidermis must, for its Malpighian layer espe- cially, be examined fresh, in fine perpendicular sections, to which acetic acid and dilute solution of soda may be added ; the horny layer, par- ticularly by the addition of alkalies, in perpendicular and horizontal sections ; however, mere maceration in water separates its elements from one another, and those who are practised can discover them in fresh preparations, when viewed both laterally arid from the surface. Literature. Gurlt, " Vergleichende Unters. liber die Haut des Men- schen u. d. Haus-saugethiere," &c., in Mull. " Archiv," 1835, p. 399 (good figures for the period) ; Raschkow, " Meletemata circa Mammal, dentium evolutionem," Vratisl, 1835 (first more complete description of the elements of the epidermis under Purkinje's guidance) ; Simon, "Ueber die Structur der Warzen u. liber Pigmentbildung in der Haut," Mull. "Arch.," 1840, p. 167 (pigment-cells in the rete of white persons) ; Krause, article "Haut," in Wagner's " Handworterbuch," II. 1844, p. 127 (a detailed and excellent treatise); Kolliker, " Zur Entwicklungs- geschichte der aussern Haut," in " Zeitschrift fur wiss. Zool.," Bd. II. p. 67 ; " Histological Observations," ibid. II. p. 118 ; Eylandt, " De musculis organicis in cute humana obviis," Dorp. Liv., 1850. Besides these refer particularly to the works of Simon (" Die Hautkrankheiten durch anatomische Untersuchungen erlautert," 2 Aufll., Berl., 1851); Yon Barensprung (" Beitrage zur Anat. u. Pathol. der menschlichen OF THE NAILS. 159 Haut," 1848); and Kramer ("Ueber Condylome u. Warzen," Getting. 1847). [Meissner, " Beitrage zur Anatomic und Physiologic der Haut ;" Leipzig, 1853.] Figures are given by R. Wagner, " Icon. phys. ;" Ber- res, tab. vi. vii. xxiv. (middling, with the exception of what regards the vessels) ; Arnold, " Icones org. sens.," tab. xi. (very pretty, but drawn with too low magnifying powers) ; Hassall, tab. xxiv. xxvi. xxvii. (among others, the skin of the negro also, and the areola of the white from within, colored); and myself, "Mikr. Anatomic," Taf. i. II. OF THE NAILS. 48. The nails, ungues, are nothing but peculiarly metamorphosed parts of the epidermis, and like it they consist of two layers, of a soft mucous, and a horny layer, or the proper nail. That part of the corium upon which the nail lies, or the bed of the nail, corresponds exactly in form with it, is elongated, quadrangular, arched in the middle, shelving off anteriorly and posteriorly, and espe- cially on the sides. When the nail is removed by maceration in con- nection with the epidermis, its anterior and middle parts are uncovered whilst its lateral edges and its posterior segment, on the other hand, are invested by a process of the cutis, the wall of the nail, which is anteriorly depressed and rounded off, posteriorly more acute and longer, and, taken together with the bed, forms a fold, the fold of the nail, which receives the lateral edges and the posterior (2-3 lines) portion of its root (Figs. 58, 60). The bed of the nail presents upon its surface peculiar ridges, similar to those of the palm and of the sole of the foot (Fig. 58 a). They begin at the bottom of the fold of the nail, at the posterior border of its bed, and, as Henle (p. 270) justly remarks, they run from, the mid- dle of it almost as from a pole. The middle ones pass directly for- wards ; the lateral at first describe an arc, which is the more convex FIG. 58. Transverse section through the 1 body and bed of the nail, a, bed of the nail, with its ridges (black) ; 6, corium of the lateral parts of the wall of the nail; c, stratum Mal- pighii of the nail with its ridges (white) ; e, horny layer on the wall of the nail ;/, horny layer of the nail, or proper nail substance, with short notches upon its under surface. Magnified 8 diameters. 1GO SPECIAL HISTOLOGY. the further out the ridges lie, and eventually are directed forwards like the others. At a distance of 2J to 3J lines from their origin, they all at once become more prominent, and take on the form of true laminae of 0-024 to 0-1 of a line in depth, which run directly almost to the anterior edge of the bed of the nail, and then end suddenly, as if truncated. The line of transition of the ridges into the lamince is convex anteriorly, and divides the bed of the nail into two sections, differing both in their extent and in their color : the posterior smaller one is nearly covered by the wall of the nail and underlies its root, the anterior and reddish- colored division underlying its body. The ridges and laminae of the bed of the nail, the number of which varies between 50 and 90, are, at their edges, beset with a series of short papillae of 0'008-0 - 016 of a line. In addition, I can confirm Henle"s statement that the bottom of the fold of the nail exhibits a few transverse ridges with larger papillae directed forwards ; further forwards where the lamince cease, there are also long isolated papillae. On the nail of the little toe, the papillae are frequently not seated upon ridges, but are more dispersed. The wall of the nail has no ridges upon its lower surface, and rarely a papilla here and there. These commence again upon its margin, where they are of some length, and are continued thence upon its upper surface, which is in no respect distinguishable from the cutis of the back of the fingers and toes. The corium of the wall and of the bed of the nail is dense, and for a considerable distance contains but little fat; in the ridges and laminae with their papillae, it is abundantly provided with fine elastic fibres. The vessels are particularly numerous in the anterior segment of the bed of the nail ; behind, where the root of the nail lies, and in the wall they are more scanty; their capillaries, 0'005 O'OOS of a line, form very distinct simple loops in the papillae, and single trunks often pass, even into many papillae. The nerves have the same relations below as in the skin, but I have hitherto been unable to detect their terminal loops or divisions in them. In the nail itself we may distinguish, the root, the body, and the free edge (Fig. 60). The soft root (Fig. 60 t) corresponds in its extent to the posterior ridged segment of the bed of the nail, and is either wholly hidden in the fold, or exposes a small semilunar surface, the lunula. The poste- rior edge is attenuated, slightly bent upwards, and is the thinnest and most flexible part of the nail. The hard body, which increases in thickness and breadth from behind forwards (&), lies for the most part with its upper sur- face uncovered; its somewhat sharp thin edges are hidden in the lateral FIG. 59. Capillaries of the bed of the nail, after Berres. OF THE NAILS. 161 parts of the fold, and its under surface reposes upon the anterior segment of the bed of the nail : lastly, the free edge (m) is, in cut nails, directed Fig. 60. /> \#, cutis of the bed of the nail ; jB, mucous layer of the nail ; C, horny layer of it, or proper nail substance ; a, layers of the bed of the nail ; 6, layers of the stratum Malpighii of the nail ; c, ridges of the proper substance of the nail ; d, deepest perpendicular cells of the mucous layer of the nail; e, upper flat cells of it; /, nuclei of the proper substance of the nail. * [With respect to Rainey's observations, Reichert, in his Report for 1849-50 (" Mull. Arch.," 1850-51) says, that the observation as to the follicles is quite correct, and that with Dr. Ammons, who had studied the growth and regeneration of the nails for some years, he had seen such capsules containing horny cells, with especial distinctness upon the bed of the nail of the great toe. TES.] OF THE NAILS. 163 transverse sections (Figs. 58, 61), as pointed processes of 0-01-0-02 of a line in length, which, as a rule, are most strongly developed at the edges of the nail, even to 0-040-06 of a line, and answer precisely in their number to the laminye of the under side of the stratum Malpighii. The upper surface of the substance of the nail is smooth, taken as a whole, yet sometimes even here, very distinct, parallel, longitudinal streaks appear as the last, almost effaced indications, of the inequalities of its bed. Usually, the thickness of this part of the nail continually increases from the root to near the free edge, so that the body of the nail is, an- teriorly, at least three times thicker (from 0-3 to 0-4 of a line) than the former ; at the free edge again, it becomes somewhat less. In its trans- verse diameter also, with the exception of the posterior edge of the root, the substance of the nail is not everywhere equally thick ; it thins con- siderably towards the lateral edges, so that at last the nails, where they lie in the fold, measure not more than 0-06-0-12 of a line, and finally terminate quite sharply. With regard to the structure of the proper substance of the nail, it can hardly be made out without the action of reagents. In perpen- dicular sections we see, particularly in the body, nothing but horizontal, fine, straight, or curved, closely-approximated lines, which one would be inclined to consider as the optical expression of delicate, superimposed lamellae, and between these, a multitude of elongated, horizontal, opaque or peculiar reddish-transparent striae, evidently nuclei. Only upon the most posterior part of the root, and on the under surface, where it meets the stratum Malpighii, do more or less distinctly flattened cells with nuclei appear disposed in layers. Horizontal sections show even less than the perpendicular ones ; exhibiting a pale transparent sub- stance, granular here and there, and mostly without indication of any structure whatsoever, occasionally with very indistinct contours of plates similar to those of the horny layer of the epidermis. Very different are < f the appearances presented after treating the nail with alkalies and certain acids. If the substance of the nail be boiled in dilute caustic soda, it be- comes changed upon the first bub- bling of the fluid into a beautiful cellular tissue (Fig. 62, J., B\ whose FIG. 62. Nail plates boiled with caustic soda. A, from the side; B, from the surface: a, membranes of the distended elements of the nail ; 6, their nuclei, from the surface ; c, from the side. Magnified 350 diameters. Fig. 62. 164 SPECIAL HISTOLOGY. polygonal elements all, without exception, the deep as well as the superficial, possess nuclei of 0-0030-0-0046 of a line in length and breadth, and 0-002 of a line in thickness, which, according as they turn their surfaces or their edges to the observer, appear as rounded, very pale, and finely-granulated discs, or as long, narrow, dark-con- toured rods ; it deserves further to be noted, that together with these, large and very pale nuclei of 0*006-0-01 of a line, and more, occur in considerable numbers, probably owing their existence to the excessive action of the reagent which has swollen them up. Caustic soda and potass also (which has a similar action upon the whole, though it acts more upon the nuclei) demonstrate the important fact, that the cells of the nail are flatter in the superficial than in the deeper layers. If, in fact, a fine perpendicular section be moistened with cold, or better, with hot solution of soda, we see the cellular structure of the nail appear almost at the very instant it becomes moistened, without any obvious enlargement of its elements ; and it is observable, at the same time, that its deepest cells are at least as thick again as the most superficial. If the soda solution acts longer, the section gradually swells up, in the under cells first, on account of their greater softness, and only sub- sequently in the flat and hard upper elements. By treating the nail with cold sulphuric and nitric acids, and also by boiling with hydro- chloric acid, its elements are isolated. Taking these facts, together with what we see in the unaltered nail, it results that its horny layer consists of closely united but not sharply defined lamellae; each lamella being composed of one or many layers of nucleated, polygonal, flat scales or plates, which, excepting their nuclei, are very similar to those of the horny layer of the epidermis, and in their deepest layers are thicker and somewhat less in circumference than in the upper and uppermost layers. Those of 0-0120*016 of a line, may be regarded as of an average size, as may be seen upon the addition of sulphuric acid, which otherwise exerts but little action, and at the commencement of the operation of soda and potass. i 50. With respect to the relation of the nail to the epidermis, I must especially refer to the perpendicular and transverse sections figured in Figs. 58 and 60. They show, in the first place, that the epidermis ap- plies itself upon the root, the posterior part of the body, and upon the margins of the nail, and that it meets it under the free edge and on the anterior parts of the lateral edges. This happens in such a manner, that whilst the mucous layer of the epidermis passes continuously, and without any line of demarcation, into that of the nail, the horny layer is, properly speaking, never continued directly into the actual substance of the nail, but partly applies itself with its lamellae parallel upon the nail, partly abuts upon it at various oblique angles. At the root, the horny layer passes more or less deeply into the fold of the nail, and at OF THE NAILS. 165 the same time runs, in a thin layer which becomes very fine anteriorly, upon the upper free part of the nail, as far as the end of the lunula or the beginning of the body. Anteriorly and posteriorly, in which latter region this layer not uncommonly reaches the posterior margin of the root, its cells lie parallel to the upper surface of the nail ; while in the middle, where it is thickest (Fig. 60 i), they are oblique or perpendicular to it. At the free edge of the nail the relations of the parts are similar, where the horny layer meeting the end of the under surface of the body of the nail, partly with more horizontal, partly with oblique lamellae, is perhaps also continued upon the commencement of the free edge. On the lateral edges, again, the horny layer passes anteriorly, in horizontal strata, under the nail ; more posteriorly it is arranged as upon the root, or simply rests against the edge of the nail. The horny layer thus forms a kind of sheath for the nail, which bears some resemblance to the sheath of the hair, though it is much more imperfect. If we com- pare the nail with the epidermis, we find, in the structure of its mucous layer, not the slightest peculiarity of any importance, while the horny layer is distinguished from that of the epidermis by its cells being nucleated, harder, and chemically different ; by their flattening and in- timate union. For the rest, the agreement of the two structures is so close, that the proper nail may justly be considered, as it has long been, a modified portion of the horny layer of the last joints of the fingers and toes. According to the chemical investigations of Scherer and Mulder, the nails agree very closely with the epidermis ; and, according to Mulder, they are distinguished from it, only by their somewhat greater propor- tion of sulphur and carbon. In his last essay, he considers them to be composed of protein + sulphamid (6'8 per cent, of the latter). This agrees with the observed action of reagents, with which the plates of the nail behave almost exactly like horny plates, only they are attacked with more difficulty and possess nuclei. According to Lauth, the nails contain more phosphate of lime than the epidermis, whence they derive their hardness : this may be correct, although, as Mulders tates ( a Phys. Chemie," p. 536), both yield about the same proportion of ash (1 per cent.). As regards the lamellar structure of the proper nail, it is to be re- garded in the same light as that of the horny layer of the epidermis ; but it is not so distinct, because the plates of the nail are more intimately connected than the elements of the epidermis. Reagents, however, render the lamellar structure very evident, and it is also clear in patho- logically thickened and curved nails. 51. G-rowth of the Nails. The nails grow continually, as long as they are cut ; on the other hand, if uncut, their growth is limited. In 166 SPECIAL HISTOLOGY. this case, as may be observed in those who are long confined to their beds by sickness, and in the Eastern Asiatics, the nails become 1J-2 inches long (in the Chinese, according to Hamilton, 2 inches), and to curve round the points of the fingers and toes. During the growth of the nail, the mucous layer does not change its position at all, but its horny layer is constantly being thrust forward. The formation of the latter goes on continually wherever it is in contact with the stratum Malpighii^ in other words upon its whole under sur- face, with the exception of the free anterior edge ; further, in many nails, upon a very small portion of the upper surface of the root, finally, at the posterior edge of the root itself. It is, however, the root portion which grows fastest, whilst the body of the nail is more slowly developed, which is demonstrated especially by the fact that it is not much thinner at the boundary between the root and the body than it is anteriorly upon the body itself, and that the transition of the cells of the stratum Malpighii into nail-cells is easily shown at the root, but with difficulty in the body. By the constant addition of new cells at the edge of the root, the nail grows forward ; by their addition to its under surface, it is thickened. The longitudinal growth exceeds that in thickness, because the first rounded cells, as they move from behind and below, forwards and up- wards, become more and more flattened and elongated. The mode in which the plates of the nail arise from the cells of the mucous layer, is easily demonstrable at the root of the nail. Here, in fact, the uppermost cells of the mucous layer are constructed very dif- ferently from the deeper ones ; they are more or less flattened, and closely resemble the cells of the epidermis, but they possess a nucleus, which, however, is only to be discovered by adding caustic soda, and then with difficulty. If we follow these cells, which form a layer of 0'06-0'12 of a line in thickness, toward the proper substance of the nail, we find that they become more and more flattened, and at last pass without any defined boundary into the latter, uniting together more closely, and taking on a more transparent appearance. In the body of the nail, the formation of nail substance is demonstrated with more difficulty, yet here, in opposition to Reichert, we must assume that it does take place, because the nail almost invariably increases in thickness even in the body, from behind forwards. However, there is unquestionably, in this part, a sharper demarcation between the two layers of the nail, than in the root ; but in fine sections it appears by no means so sharp as in those which are commonly examined, and I find, in fact, that the transition of the cells of the mucous layer into the plates upon the body of the nail, is demonstrable with tolerable readiness, par- ticularly on the addition of alkalies, where the ridges of the under sur- face of the proper nail are well developed. Between the ridges also, though no direct transition is recognizable, yet it may be observed that OF THE NAILS. 167 the plates of the proper nail which border upon the mucous layer are much less flattened than in the interior and on the surface, which also indicates that they are developed upon the spot. In conclusion I must add, in support of my view, that it is only in this way, that it becomes explicable why the under surface of the proper nail substance upon the root of the nail is almost smooth, while on the body of the nail it pre- sents more or less prominent ridges. The origin or increase of these ridges demonstrates clearly that nail-substance is also formed here. Corresponding with these ridges and with the grooves between them, we also find that the lowest layers of the nail plates, which are quite hori- zontal upon the root, run with an undulating course upon the body (Fig. 61). The general result then is, that whilst the formation of the nail goes on especially at its root, yet that plates are added to the body of the nail from below, though more slowly and scantily, thus producing the anterior thickening, or at least preventing the necessary thinning of the nail anteriorly. It is to be remarked further, that the development of nail-substance takes place in all parts of the middle line of the nail more rapidly than in the lateral portions, which, anteriorly, are almost as thin as in the root, though they possess longer processes below. But even there, substance must be added to the body of the nail, because it becomes broader anteriorly. The plates of the substance of the nail once formed, alter in certain respects, as they are pushed forwards and upwards by those which come after them. In the first place, their nature becomes altered in a man- ner which is little understood, the change consisting partly in the depo- sition of more phosphate of lime, partly in a solidification (conversion into horn) of their organic elements, particularly of the cell-mem- branes, in consequence of which, from being soft, as at the root and under surface of the nail, they become gradually harder and harder. In the second place, like the horny cells of the epidermis, they are very considerably flattened, and at the same time increase somewhat in their longitudinal and' transverse diameters ; finally, they coalesce more completely, so that they cannot be separately recognized, without the action of reagents, in the upper and anterior parts of the nail, which appear to be composed of nothing but a homogeneous substance which tears in all directions; whilst in the lower parts the separate nail- plates are, at least, indicated, and are occasionally tolerably distinct. On the other hand, the nuclei of the nail-plates do not disappear, and in this lies a characteristic distinction between the horny layer of the nail and that of the epidermis. They are to be seen in perpendicular sec- tions, of fresh nails, and after treatment with caustic soda, and even in the most superficial layers, though somewhat smaller and flatter than in the deep layer. It follows then, that certain metamorphoses go on in the proper substance of the nail, which as in the epidermis, are to be ascribed to a peculiar growth and vital process in the nail-cells them- 168 SPECIAL HISTOLOGY. selves. These seem to occur, however, almost solely in the lower and posterior parts of the nail, for if, as Schwann states (Fig. 91), two points be marked upon the posterior portion of the free surface of the nail, one behind the other, by piercing it with a needle and coloring with nitrate of silver, they in no wise alter their relative position in the course of the two or three months, during which they are moving towards the point of the nail. As to the pathological conditions of the nails, they are readily regene- rated when they have been detached, in consequence of crushing, burn- ing, freezing, cutaneous disorders (scarlet fever, &c.), inflammations, exudations, suppurations, and effusions of blood in the bed of the nail; in fact, as Pechlin (" Obs. Phys. Med.," p. 315) narrates, this regene- ration may take place periodically; in a boy, the nails, every autumn became bluish-black and desquamated, together with the epidermis (the horny layer ?), and were subsequently regenerated. In such a case, accord- ing to Lauth (" Me'm. sur divers points d'Anatomie," in the " Annales de la Socidte d'Histoire Naturelle de Strasbourg," t. i. 1834), and Hyrtl (" Anatomic," p. 382), the whole bed of the nail becomes covered by soft horny plates, which harden by degrees, grow into a regular nail, and eventually project with their free edges beyond the end of the finger. When the last joint of the finger has been lost, rudimentary nails fre- quently appear upon the back of the second and even of the first phalanx. The older cases are quoted in Pauli ("De vulneribus sanandis," Got- tingse, 1825, p. 98), more recently Hyrtl (1. c.) saw such a nail 2 lines long and 3 lines broad on the first phalanx of the thumb. As the for- mation of nail-substance depends upon the vessels of the bed of the nail, we may, with Henle, assume that varying conditions of the latter may frequently produce local thickening, thinning, or even detachment of the nail, and that their deformities in cyanosis and phthisis depend on these causes. The thickening and abnormal development of the nails, however, arise very frequently, as I have observed, from a partial obstruction of the capillaries of their bed. Thus in the lamellated nails of old people, greatly thickened and curved downwards in front, I find all the capillaries of the anterior segment of the bed of the nail closely filled with fat granules of different sizes, and wholly impermeable to the blood ; in such a case the development of nail-substance can take place only in small lamellae in the fold, which then, as may be readily under- stood, are raised up by those which are growing behind into a continu- ally more and more oblique position ; their posterior extremities forming, on the surface of the nail, transverse streaks one behind another at short intervals. After dividing the nervus ischiadicus, Steinriick (" De nervorum regeneratione," pp. 45-49) observed, in the Rabbit, that the nails and hair fell off, which is a result of the influence of the nerves upon the vessels. Finally, the shape of the bed of the nail also in- fluences its formation. It is thus explained, how (see Henle, 1. c.), after OF THE NAILS. 169 inflammation and closure of the fold of the nail, the formation of new nail at the posterior edge ceases, the nail no longer growing forwards, but at all its edges exactly covering its bed. 52. The development of the nail begins in the third month with the formation of the bed and fold, which are marked off from the surround- ing parts by the gradual growth of the skin into the wall of the nail. At first the bed of the nail is lined by the same cells as those which form the other parts of the epidermis (see 47), only that even in the third month the cells of the stratum Malpighii are distinguished by their elongated and polygonal form (length 0-004, breadth 0-001-0-0016 of a line). In the fourth month there arises between the stratum Mal- pighii and the horny layer of the bed of the nail, which latter is formed by a simple layer of polygonal clearly nucleated cells, a simple lamina of pale, flat, but also quadrangular and nucleated cells, 0*009 of a line in diameter, which are closely united together, and must be regarded as the first indication of the proper substance of the nail ; at the same time also, the stratum Malpighii under these cells become thickened so that it is certainly composed of, at least, two layers. The nail is therefore at first wholly included within the epidermis ; it is formed over the whole surface of the led of the nail as a quadrangular plate, and arises between the embryonic mucous layer and the horny layer, without doubt by a metamorphosis of the cells of the mucous layer, as is probable, especially from the minute size of the original cells of the nails. In the course of its further development, the nail is thickened by the addition of new cells from below (in the fifth month its thickness is about 0'024, in the sixth 0-04 of a line, of which in the latter 0'025 must be reckoned as proper nail-substance); it increases by the extension of its elements, and by the addition of new ones at its edges ; but it remains, even to the end of the fifth month, hidden under the horny layer of the epider- mis, until finally it becomes free, and in the seventh month, even begins to grow longitudinally, so that at this period, except in its greater softness and its smaller dimensions, it presents no essential difference from the perfect nail. With regard to the bed of the nail, its ridges are already indicated at the end of the fourth month, and in the fifth they are well-marked, 0-02-0-024 of a line deep, 0-004-0-005 of a line broad, and 0-008-0-014 of a line distant; these measurements also indicate the breadth of the laminae of the stratum Malpighii. At the sixth month they are somewhat larger and further apart. In the new-born infant, the whole nail is 0-3-0-34 of a line thick ; 0-16 of a line being proper nail-substance, 0-14-0-18 of a line stratum Malpighii. Its elements are still almost identical with those at the sixth month, and they appear with tolerable distinctness in the nail proper without any reagents, as elongated polygonal nucleated plates 0-002-0*28 of a line, as Schwann has already partly remarked. The free edge, 170 SPECIAL HISTOLOGY. projecting far forwards, which is presented in all nails, is worthy of remark. It is considerably thinner and narrower than the body, and is separated from it by a semilunar line ; it is rounded anteriorly, as much as 2 lines long, and is plainly nothing but the nail of an earlier period which has been thrust forward by the longitudinal growth of the nail in the course of its development. In fact it nearly corresponds in size with a nail of the sixth month. Soon after birth the long free edge of the nail of the new-born infant is cast off, at least once (according to Weber many times), in all pro- bability in consequence of external mechanical violence, which it is unable, owing to its delicacy, to resist. In the sixth and seventh months after birth, I find that the nails which the child brought into the world, are completely replaced by new ones, and in the second and third years the nail-plates are not distinguishable from those of the adult, whence it follows that the nail increases in thickness, less in consequence of any enlargement of its elements, than by the addition of new ones to its edges and under-surface. The investigation of the nail-cells and plates is best made in fine sections of recent nails, with and without the addition of reagents, especially caustic soda and sulphuric acid, concerning whose operation the most important points have already been noted. To examine the relations of the parts of the nail to one another, and to the epi- dermis, the nails must be separated from the cutis by maceration, or by boiling in water. It is then seen, that the nail is detached, with the cuticle, from the finger ; and in transverse and longitudinal sections, its mode of connection with the former is perceived. The bed of the nail also, its lamince and ridges, the fold and the lamince in the stratum Malpigliii of the nail, are easily seen, in this way. Since fine sections, in such a nail, are not readily made, precisely in the most important parts the margins and roots, it is necessary, for this purpose, to employ fresh nails separated from the bone with the cutis, and dried. These afford all the information required, portions of them swelling up readily in water, and exhibiting the structure of the different layers, with acetic acid and caustic soda, in the most distinct manner. Literature. A. Lauth, " Sur la disposition des ongles et des poils," Mem. de la Socie'te' d'hist. nat. de Strasbourg, 1830-4 ; Gurlt, " Ueber die hornigen Gebilde des Menschen u. der Haussaugethiere," Mull. "Arch.," 1836, p. 262; Reichert, in Mull. "Arch.," 1841, Jahresbe- richt; 0. Kohlrausch, "Recension von Henle's allgem. Anat.," in Get- ting. " Anzeigen," 1843, p. 24; Rainey, "On the structure and forma- tion of the nails of the fingers and toes," in "Trans, of Microsc. Society," March, 1849; Berthold, "Beobachtungen uber das quantitative Verhalt- niss der Nagel- u. Haarbildung beim Menschen," in Mull. "Arch.," 1850. OF THE HAIRS. 171 Fig. 63. III. OF THE HAIRS. 53. In every hair we distinguish the free part or shaft, scapus, with its tapering point, from the portion enclosed within the sac, the root, radix. In straight hairs the former is generally straight and rounded; in the wavy, undulated and somewhat flattened ; in the curly and woolly hairs, it is twisted spirally and quite flat or slightly ribbed. The root is always straight, tolerably cylindrical, and softer and thicker than the shaft, at least in its lower part ; in living hairs it ends in a still softer knob- like enlargement, 1|- to 3 times thicker than the shaft, the " bulb of the hair" ( fifi into elongated, rounded cells, with short nuclei, the fibrous structure becoming more and more obliterated, and these are finally continued without interruption into the elements of the lowest and thickest part of the hair, the bulb. They (Fig. 67) are nothing more than round cells of 0-003-0-006 of a line, which lie closely pressed together ; and like the cells of the mucous layer of the epidermis sometimes contain only colorless granules, sometimes are so full of dark pigment-granules, that they become true pigment- cells. It must be added, that the chemical relations of the cortex are altered in the lower half of the root, its elements becoming more sensitive to the action of acetic acid, which does not affect the plates of the shaft at all ; they swell up and dissolve in alkalies also, much more quickly than those of the shaft.* FiG. 66. Two cells from the cortex of the root of the hair (the finely-striated part of it immediately above the root), with distinct nuclei and a striated appearance; magnified 350 diameters. FiG. 67. Cells from the deepest part of the bulb of the hair; magnified 350 diameters: a, from a colored bulb, with pigment-granules and somewhat hidden nucleus; b, from a white hair with a distinct nucleus and few granules. *[Reichert ("Bericht"' for 1850, Mull. " Archiv," 1851) asserts that the cortical substance OF THE HAIRS. 177 The color of the cortical substance arises partly from spots of pigment, to some extent from air cavities, and partly from a coloring matter dif- fused through and combined with the substance of the cortical plates. The first or the granular pigment, exhibits all shades from clear yellow, through red and brown, to black; the diffused pigment is quite absent in white hairs, and is scanty in clear, fair hairs ; it is most abundant in the more opaque fair hairs, and in red as well as in dark hairs, in which it may by itself give rise to an intense red or brown color. The color of the cortex depends especially upon that of these two pigments, but sometimes the one, sometimes the other predominates, and it is only in the very light and in the very dark hairs that they are developed in about equal proportions. Fig. 68. S . 57. The medullary substance is a streak or cord which extends in the axis of the hair, from the neighborhood of the bulb nearly to the point (Figs. 65, 68). It is generally absent in the lanugo and colored hairs of the head, but if usually present in the thick, short hairs, and in the stronger long ones, as well as in the white hairs of the head. If white hairs be boiled with caustic soda until they swell and coil up, we can often, by the use of simple pressure, demonstrate without further trouble, the cellular structure of the medullary cylinder, which is then transparent for trans- FiG. 68. A portion of the root of a dark hair slightly acted upon by caustic soda ; a, medulla, still containing air, and with cells, which appear pretty distinct; 6, cortex with pigment spots; c, inner layer of the epidermis; d, outer layer of it ; e, inner layer of the inner root-sheath (Huxley's layer) ;/, outer fenestrated layer (Henle's layer). Magnified 250 diameters. of the hair is composed of superimposed lamina?, and recommends, in order to demonstrate the fact, that a hair should be treated with a solution of caustic potass of 10 per cent, and then submitted to pressure. Under these circumstances, u beautiful lamellae appear. The separate layers exhibit no trace of being composed of fut-ifmm cells; they appear finely striated, and in places, hyaline; sometimes elongated spots appear, of which it cannot be determined with certainty whether they are nuclei or perforations in the membrane." In some, there was no trace of these to be seen. Reichert considers the fibres of the cortex to be artificial products, and was unable to convince himself of the existence of nuclei in this part of the hair. TRS.] 12 178 SPECIAL HISTOLOGY. mitted light (Fig. 65 a). If a hair thus treated be carefully teased out, it is easy to isolate the medullary cells, either in aggregate masses, Fig. 69. or even completely separate (Fig. 69). They are rectangular or quadrangular, rarely rounded or fusiform of 0-007 0-01 of a line in diameter, occasionally containing dark, fat-like granules, and often when the alkali has not acted too strongly, a rounded clear spot of 0-0016-0-002 of a line, which is plainly the rudiment of a nucleus, and which also seems to swell up somewhat in soda. In fresh hairs, the medulla in the shaft is silvery white or dark, an appearance which, as many more favorable objects show, arises from rounded- angular, granular corpuscles, black (opaque) or of a brilliant white, according to the illumination, tolerably uniform in size, but varying according to the hairs, from 0'0002-0'002 of a line and occupying the medullary cells in great quantity (Fig. 68). These granules are not fat or pigment, as has been hitherto universally supposed, but air-vesicles, as may be readily demonstrated by boiling a white hair in ether or oil of turpentine, in both of which cases the medulla becomes quite clear and transparent. If such a hair, treated ^vith water, be dried between the fingers, it soon, often quite suddenly and visibly to the naked eye, assumes its previous white color, and if immediately after drying, it be placed under the microscope, without fluid, or with fluid at one end only, nothing is easier than to see the re-entrance of the air and the conse- quent darkening of the medulla. Not only in white hairs, but in dark ones also, the medulla contains air in the fresh state, only in this case it does not appear of a pure silvery white, but with a blonde, red or brown tinge ; this does not arise from any special pigment, which is only found occasionally in the medulla of dark hairs, but proceeds from its being seen through the colored cortical substance. A more careful investi- gation of the medullary cells shows, that while fresh they contain many small cavities in a viscid substance ; in these lie the air vesicles, which communicate to them the granular appearance above described. If we observe the air which has been expelled refilling the medulla of a dried hair, it seems as if all the cavities of one and the same cell communicated with one another, at least the air frequently passes in continuous winding streams from one cavity into the other ; indeed from the sudden manner in which the air sometimes fills the medulla, it might almost be believed that the cavities of contiguous cells were connected together. However this may be in certain cases, it is conceivable, that even if the cavities of the different cells are quite closed, and only separated from one another by delicate partitions, the air still may quickly fill the medulla under the appearances we have noted. For the rest, the vacuities of FIG. 69. Eight medullary cells, with pale nuclei, and fatty granules, from a hair treated with soda ; magnified 350 diameters. OF THE HAIRS. 179 the medullary cells, whether they are quite closed or not, are of different sizes, the aeriferous medulla appearing sometimes coarsely, sometimes finely granular. I have also seen cases in which the medullary cells obviously contained only a single large air-vesicle, and appeared almost like small fat-cells. Very frequently single larger or smaller spots may be observed in the medulla, which contain no air, and are thence pale, and this is constantly the case in the lowermost part of the medulla, close above the bulb. The medulla and the cortex are widely different if we compare the extreme forms of their elements ; in the one case we have rigid homo- geneous elongated plates, almost without contents, in the other rounded vesicles filled with fluid or air. If, however, we take into account all their conditions, we shall find that the limits are not so marked, and in fact are often hardly distinguishable. On the one hand, for instance, the medullary cells are not unfrequently of an elongated or short fusi- form figure, whilst on the other the plates of the cortex present a con- siderable cavity containing pigment. If such plates contain, instead of pigment or the smaller air-vesicles, air in a larger cavity, as occurs sometimes though not frequently, it is still more difficult to distinguish the two kinds of elements from one another, and the more so if, as in red hairs, the medulla and cortex are in places, or for considerable distances, not distinctly defined from one another, the superficial cells of the medulla being scattered and passing quite gradually into the plates of the cortex, which lie very close together and contain much air. It is not intended to imply, by this, that the medulla and the cortex are identical, but only that transitions exist, and that the differences which occur are less marked than is commonly supposed. The diameter of the medulla is generally, in proportion to that of the hair itself, as 1 : 3-5 ; relatively and absolutely, it is thickest in short thick hairs, thickest in the down and hairs of the head. In a transverse section it presents a round or flattened figure, and the cells which com- prise it are disposed in 1-5 or even more longitudinal series. The medullary substance, the cells in which were first accurately de- scribed by G. H. Meyer, varies most of all the constituents of the hair. In the down of the hairs of the head, it has been stated, by some, that it is wholly absent, which is to be corrected thus far, that it is certainly generally absent in the former, and frequently in the latter, perhaps more frequently, in certain individuals. In white hairs, even those of the head, of a tolerable length and thickness, I have never failed to find it always beautifully distinct. In rare cases the medullary tract is double throughout (Bruns, figure in Hassall), more frequently divided in places into two tracts, which soon unite again. In the lower part of the root, the medulla, which is here clear, is often thicker, and exhibits 180 SPECIAL HISTOLOGY. the nuclei of its cells very distinctly, especially after the addition of acetic acid. Steinlin and Eylandt assert of the medullary substance, that it does not belong to the proper hair, but to its papilla, and origi- nally represents a prolongation of this into the free part of the hair, which then dries up. This is incorrect. The papilla or germ of the hair is a part of the cutis, and has the same structure as the papillae, of the latter, whilst the medulla of the hair is composed of isolated cells, which by their resistance to alkalies, are in all respects allied to those of the epidermis. On the other hand, in animals, as has long been known, and as lately Brocker has especially shown, the papilla often projects far, even to the point of the hairs, bristles or spines, subse- quently drying up ; but in these instances, according to Brocker, it never, even after the action of potass, exhibits a cellular texture, whilst this is always obvious in the medullary substance, which is often present at the same time. Such an elongation of the papillae may occasionally be noticed even in man, to a certain extent ; thus Henle found it a few times prolonged into a short point. But any prolongation of this kind must be distinguished as decidedly from the cellular medullary substance, as in animals. 58. The cuticle of the Hair (cuticula\ is a very thin, transparent pellicle, which completely invests the hair, and is very closely united with the cortical substance. In its normal position, and observed in an unaltered hair, it is evidenced by hardly anything more than by nume- rous dark, reticulated, irregular or even jagged lines, which surround the hair at intervals 0*002 0*006 of a line from one another, and occa- sionally also by small serrations at its apparent edge (Fig. 70 A) ; if, on the other hand, a hair be treated with alkalies, the cuticle is raised in smaller or larger lamellae from the fibrous substance, and is even separated into its elements. These are quadrangular or rectangular flat plates without nuclei, generally pale and transparent (Fig. 70 B\ which do not swell up into vesi- cles by the action of any re- agent, and disposed in an im- bricated manner, form a simple membrane which completely surrounds the cortex of the hair in such a way, that the deeper or lower cells cover the upper ones. By sulphuric acid also the structure of the epidermis is readily made out ; the hair is, as it were, Fia. 70. A, surface of the shaft of a white hair ; magnified 1GO diameters. The curved lines mark the free edges of the epidermic plates: J5, epidermic plates from the surface, isolated by the action of caustic soda ; magnified 350 diameters. One or both of their longer edges are bent round, and so appear dark. OF THE HAIRS. 181 bristled at the edges with the erected plates and by scraping or rubbing, the cuticle is less easily obtained in large lamellae, but is readily enough reduced to its elementary parts. On the shaft of the hair the cuticle consists only of a single layer of plates 0-002-0-003 of a line thick, which measure 0-024-0-028 of a line in the transverse direction of the hair ; 0-016-0-02 in that of its length ; and are hardly more than 0-0005 of a line in thickness. The same structure exists also in the upper part of the root of th^ hair; of its lower part, on the other hand, so far as the inner root-sheath ex- tends, two layers of the epidermis constantly occur. The outer (Fig. (68 d is rendered especially obvious by the action of soda or potassa, and with a little pressure frequently comes away from the hair with the inner root-sheath, whilst the inner layer becoming undulated, remains lying upon the cortical substance, and may be easily studied, as well in the side view as upon its surface. In hairs that are torn out, this layer is found only where they are covered by the inner root-sheath, otherwise it remains behind in the hair-sac. Its elements also, are broad cells without nuclei, covering one another like tiles, which do not swell up in alkalies, ^and are soluble with great difficulty ; they are thicker than those of the other layer, and measure only 0-0020-004 of a line in the direction of the length of the hair. The whole outer layer measures 0-0016-0-002 of a line, whilst the inner layer upon the root has a thick- ness of 0-0025-0-0035 of a line. Upon the bulb of the hair, the two layers of cuticular plates pass with ja, tolerably defined margin into soft nucleated cells, which are broad in the transverse direction of the bulb, very short longitudinally, and somewhat longer in their third diameter, which stands perpendicularly or obliquely to the longitudinal axis of the hair. They are readily attacked by alkalies, or even by acetic acid, possess without exception transverse and longish nuclei, and finally pass, on the bulb, into the already described, round cells of which it is formed.* * [We cannot agree with Professor Kdlliker that the cuticle of the hair passes into the outer cells of the bulb. It may be worth devoting a little space to this matter, as the whole question of the homology of the hair essentially turns upon it. So far from being able to trace the two layers of the cuticle into the round cells of the bulb, we find that they cease somewhat suddenly when the shaft begins to expand, while its substance is fibrous-looking and contains only much elongated nuclei. Below this point, as Henle has correctly, figured in his " Allgemeine Anatomic," PI. I. Fig. 14, the transverse striations of the cuticle are absent ; and if the cuticular layer be viewed in section, it will be seen to be composed of a more transparent substance, which gradually becomes thinner until it is hardly distin- guishable as a distinct layer, and at the same time loses the oblique lamination, which it has above, where it is continuous with the two layers of the cuticle proper. The careful addition of caustic ammonia is particularly fitted to demonstrate the structure of this part. In the first place, it raises up the outer layer of the cuticle from the inner, and shows that the former, at any rate, is not continuous with any cells; and secondly, it dissolves and forces out the substance of the lower soft portion of the bulb, so that the lower part of the cuticle may be obtained as a transparent, colorless, and independent sheath, even from 182 SPECIAL HISTOLOGY. 59. The hair-sacs, folliculi pilorum, are flask-like follicles 1-3 lines long, which embrace the roots of the hair tolerably closely, and, in the lanugo, are lodged in the substance of the upper layers of the corium, while in the stronger or long hairs, they generally project into its deeper portion, and even extend for a greater or less distance into the subcu- taneous cellular tissue. These follicles are simply to be regarded as invo- lutions of the skin, with its two constituents, the corium and the epi- dermis^ and there may be distinguished, therefore, in each of them, an external fibrous, vascular part, the proper hair-sac, and a non-vascular cellular investment lining this, the epidermis of the hair-sac ; or, since it immediately surrounds the root of the hair, the "root-sheath" (vagina pili). 60. The proper hair-sac consists of two fibrous investments, an ex- ternal and an internal, and of a structureless membrane ; it is on an average 0-015-0-022 of a line thick, and contains in its lower part a peculiar structure, the papilla of the hair. The external fibrous membrane (Fig. 63 A), the thickest of the three layers of the hair-sac, determines its external form, and by its innermost layer is very closely connected with the corium. It consists of common connective tissue with longitudinal fibres, without any intermixture of elastic fibres, but with a considerable number of long fusiform nuclei ; it contains a tolerably close plexus of capillaries, and exhibits also a few nervous fibrils with occasional divisions. The internal fibrous membrane (Fig. 71 a) is much more delicate than the external ; bounded by smooth surfaces, and everywhere of equal thickness, it extends from the bottom of the hair-sac as far only as the entrance of the sebaceous glands. To all appearance, it contains neither vessels nor nerves, and is composed solely of a simple layer of transverse fibres, with a long narrow nuclei, which may be seen particularly well in the empty hair-sacs of both coarse and fine hairs, with or without the the very darkest hairs ; lastly, under favorable circumstances, this reagent raises up a definite basement membrane from the outer surface of the lowest part of the bulb, in immediate contact with the rounded " nuclei" of this part, and this basement membrane may be traced upwards into direct continuity with the homogeneous portion of the cuticle above-described. (In the " Edinburgh Monthly Journal of Medical Science/' for March, 1853, Mr. Dalzell states that the papilla of the hair has a basement membrane. Is it this structure to which he refers ?) In all cases in which, in man or in animals, we have isolated the hair-bulb from its sac, it seemed to have a definite limiting outer line down to the narrow neck by which it passes into the hair-sac, though it was not often easy to obtain evidence that this limiting line was the expression of a distinct basement membrane. However, the same difficulty would occur with any dermic papilla ; and it seems to us that there is sufficient evidence to show that the cuticle of the hair is not the product of any direct metamorphosis of cells, but represents a modified basement membrane with a subjacent layer of peculiarly altered blastema, corresponding precisely with the " Nasmyth's membrane" and the enamel of the teeth. Vide infra, on Teeth. TES.] OF THE HAIRS. 183 Fig. 71. addition of acetic acid. They resemble smooth muscular fibres, although they cannot be completely isolated and actually recognized as true fusi- form fibres with a single nucleus ; on which account, and especially as no contractions of the hair-sacs have in general been observed, I must for the present refrain from positively deciding upon their nature. The third layer, lastly (Fig. 71 6), is a transparent structureless mem- brane, which, when the hairs are torn out, invariably remains behind in the hair-sac, and extends from its base, though, as it would seem, without covering the papilla, as far as the inner root-sheath, and perhaps higher. In the uninjured hair-sac it appears only as a pale streak 0-001-0-0015, rarely 0-002 of a line thick, between the outer root-sheath and the trans- versely fibrous layer of the hair-sac ; by preparing an empty hair-sac, how- ever, it can readily be obtained in large shreds, and then appears smooth externally ; internally it is covered with very delicate, transverse, often anastomosing lines, which, like the membrane itself, remain unchanged in acids and alkalies. Neither acids nor alkalies bring out cells or nuclei in this membrane, and it therefore probably belongs to the category of true structureless membranes. The papilla of the hair (Fig. 63 i) also, less properly termed the hair- germ, pulpapili, belongs to the sac, and corresponds with a papilla of the cutis. It is generally seen but indistinctly, especially in dark hairs with a colored bulb, either appearing, only as a clear, indistinctly defined spot, or after the tearing out of the hair, remaining so covered by the cells of the bulb that nothing can be made out of it. It is only in the hair-sacs of white hairs, that its outlines can be more frequently distin- guished without wholly isolating it, especially by the help of a little pressure. Reagents, on the other hand, avail nothing, for they attack the papilla to about the same extent as the bulb, with the sole exception of a weak solution of caustic soda, in which it retains its outlines, for a Fio.71. A piece of the transverse fibrous layer, and of the structureless membrane (vitreous membrane) of a human hair-sac, treated with acetic acid ; magnified 300 diame- ters: a, transversely fibrous layer with elongated transverse nuclei ; 6, vitreous membrane in apparent section; c, its edges, where the sheath which it forms is torn; d, fine transverse partly anastomosing lines (fibres) on their inner surface. 184 SPECIAL HISTOLOGY. time at any rate, whilst the cells of the bulb are freed, and may be pressed out of the sac. The papilla is ovate or fungiform, J-^o of a line long, tT-sV of a line broad, and is connected with the layer of con- nective tissue of the sac, by a pedicle ; it has sharp contours and a per- fectly smooth surface, and in its structure completely agrees with the papillae of the cutis, consisting of an indistinctly fibrous connective tissue with scattered nuclei and fat granules, but not of cells. I have taken every pains to discover vessels and nerves in the isolated papilla, but in vain ; even acetic acid and dilute solution of caustic soda, which in general do such excellent service in these cases, have failed, and Hassall and Gunther met with the same results. It must not hence be concluded, that ihepapilla contains no vessels or nerves, for we know that in other places, where vessels do certainly exist, they often com- pletely escape the eye ; as, for example, in the dermal papilla? and in the villi; and with respect to the nerves, in the papillae of the cutis. In some animals the vessels may very readily be seen. 61. The root- sheath, or the epidermic investment of the hair-sac, is continuous with the epidermis around the aperture of the follicle, and may be divided into an external and an internal layer, which are dis- tinctly defined from one another. The external root-sheath is the continuation of the stratum Malpigliii of the epidermis, and lines the whole hair-sac, resting for its lower half on the transparent membrane above described; higher up, when this and the transverse fibres are absent, it lies directly upon the longitudi- nally fibrous layer. Its structure corresponds exactly with that of the stratum Malpighii, even in the having the outermost cells, which in the negro, according to Krause, are always brown, and in whites are so, at least in the hairs of the lalia majora, towards the upper part, arranged perpendicularly. At the bottom of the hair-sac, the outer root-sheath, its cells becoming gradually rounded, passes continuously, and without any sharp line of demarcation, into the round cells of the hair-bulb which cover the papilla. The outer root-sheath is generally about 3-5 times as thick as the inner ; but not unfrequently it becomes thinned towards its upper part, and below invariably passes into a very thin lamella. In the coarse hairs it measures in the middle of the root 0-018-0-03 of a line, and presents 5-12 layers of cells. The inner root-sheath (Fig. 68-e. g.) is a transparent membrane which extends from almost the very bottom of the hair-sac, over more than two-thirds of it, and then suddenly ceases. It is closely connected externally with the outer root-sheath, internally with the cuticle of the hair (its outer layer), so that normally there is no space between it arid the hair; further it is distinguished by its great density and elasticity, and it consists in all but its lowermost part, of two or even three layers OF THE HAT US. 185 of polygonal, elongated, transparent, and somewhat yellowish cells, all of which have their longitudinal axes parallel to that of the hair (Fig. 68). The outermost layer (Fig. 72, A\ which alone was formerly known, the inner root-sheath of Henle is formed of elongated cells without nuclei, 0-016-0-02 of a line in length, and 0-004-0-006 of a line in breadth, which are intimately connected, and in the ordinary mode of investiga- tion, after the addition of acetic acid, caustic soda, or potassa, which swell up the hair, or after the hair has been teased out, present elon- gated fissures between them, whence they appear like a fenestrated mem- brane. In quite recent hairs, however, if all reagents and mechanical injury have been avoided, we see hardly any trace of apertures in the upper half of the layer in question, and in the lowerh&lf (from the finely fibrous part of the cortex upwards), at most mere indications of them, in the form of striae, clear or dark, according as they are in or out of focus, and similar to those of the cortex of the shaft. We can hardly avoid supposing, therefore, that the openings as they are commonly seen (0-005-0-008 of a line in length, and 0-001-0-03 of a line in breadth), are produced artificially by the teasing out of the membrane. Secondly, cells also occur in the root-sheath, between which gaps are never visible. These (Fig. 72, B\ which form a simple or a double layer (Huxley's Fig. 72. layer), are constantly situated internal to the common, and as far as I have seen, always single, fenestrated layer of cells ; they are shorter and FIG. 72. Elements of the inner root-sheath ; magnified 350 diameters. ^?, from the outer layer, 1, its isolated plates; 2, the same in connection, from the 'uppermost parts of the layer in question, after treatment with caustic soda: a, apertures between the cells, b; 7>, cells of the inner not-perforated layer, with elongated and slightly notched nuclei; C, nucleated cells of the lowest part (single layer) of the inner sheath. 186 SPECIAL HISTOLOGY. broader than the cells which have already been described (0-014 to 0-018 of a line long, 0-006 to 0-009 of a line broad), but are also poly- gonal, and always possess, at least in the lower half of the root-sheath, distinct elongated nuclei, often prolonged into points of 0-004-0-006 of line. The diameter of the whole inner root-sheath is, upon the average, 0-006-0-015 of a line, whence it follows that its cells, of which there are never more than three layers, are at least 0-002-0-005 of a line thick. They are recognizable at once in their natural position, and by the teasing out of the root-sheath, and are readily isolated by the use of soda and potassa (Fig. 72), but without swelling up, a character which no less than their great resistance to alkalies altogether, distinguishes their cells, in common with the epidermic scales of the hairs, from all others. At the bottom of the hair-sac, the inner root-sheath consists only of a single layer of beautiful, large, polygonal, nucleated cells, without any intermediate openings (Fig. 72, (7), which becoming at last soft, delicate, and rounded, pass without defined limits into the outer layers of the round cells of the hair-bulb. Superiorly, this membrane not unfrequently becomes somewhat separated from the hair, and ends, not far from the apertures of the sebaceous glands in a sharp, notched edge, formed by its separate more or less projecting cells. Thence upwards, it is re- placed by a layer of cells, in some cases at first nucleated, but at other times not, which gradually approximates more and more, as it is traced higher up, to the horny layer of the epidermis, into which it passes con- tinuously ; it is not, however, any direct continuation of the inner root- sheath. 62. Development of the Hairs. The first rudiments of the hairs are flask-shaped, solid processes of the mucous layer of the epidermis formed by its growth inwards, in which the internal and external cells subse- quently become differentiated in such a manner, that the former, a gradual conversion into horn going on, are, in the axis of the rudiment, metamorphosed, in the first place into a small delicate hair, and secondly, around this into its internal sheath ; while the latter, undergoing less alteration and remaining soft, constitute the outer root-sheath and the soft cells of the hair-bulb. Hence the hairs and their sheaths arise at once in their totality. The former, as minute hairs with root, shaft, and point, and are therefore not developed point first, as the teeth are, with their crown first, and still less as Simon has supposed, from their root first. The elements of the youngest hairs are nothing but elongated cells similar to those of the cortex of the later hairs, which are deve- loped by the lengthening and chemical alteration of the innermost cells of the rudiments of the hairs. Medullary cells are entirely wanting, but the cuticle is clearly visible. The inner sheath is striated, presents no openings, and consists of elongated cells, which have been developed OF THE HAIRS. 187 from those lying between the hair and the outer sheath. The proper hair-sac is formed, in its fibrous layers, essentially in loco, out of the formative cells which surround the rudiment of the hair ; possibly, how- ever, they may be considered as an involution of the cutis, produced by the ingrowing process of the epidermis. Its structureless membrane, which appears very early, is, not improbably, closely related to the ex- ternal cells of the rudiment of the hair, answering to the outer hair- sheath, and formed by an excretion from them like the membranes pro- price of the glands ; as to the papilla, it is hardly possible to consider it as anything but an outgrowth of the fibrous layer of the hair-sac, analogous to the papillae of the cutis in general ; though the circumstance that it appears at a time when the hair-sac is hardly demonstrable as a whole, and that it may always be pulled out together with the rudiments of the hair and root-sheath, is apparently opposed to this view. The first rudiments of the downy hairs and of their sheaths, are found in the human embryo at the end of the third or at the beginning of the fourth month, upon the forehead and eyebrows. They consist of papilli- form masses of cells 0*02 of a line in diameter (Fig. 73) which are visible, even to the naked eye, as minute whitish spots separated by regular intervals. They are continuously connected with the rete Mal- pighii of the epidermis, and are nothing more than perfectly solid pro- cesses of it, which penetrate obliquely Fig. 73. into the corium, and here lie in the meshes of a delicate capillary network. These cells are spherical, 0-003-0-004 of a line in diameter, and consist of a clear granular substance and round nuclei of 0-002-0-003 of a line. Nothing was to be seen of any dermic rf * investment of these rudiments ; in other words, the foundation of what I have described as the proper hair-sac was not laid. In the fifteenth week the processes were already larger (0-025-0-03 of a line long, 0-013-0-02 of a line broad), flask-shaped, and surrounded by a thin structureless investment, which was continued into a delicate membrane lying between the cutis and the rete Malpighii, but united more closely with the latter. Besides this investment, which is, probably, only the structureless membrane which I have discovered in the perfect hair (see 60), another external layer of cells occurs on the hair-sacs, which can FIG. 73. Rudiment of the hair from the brow of a human embryo, sixteen weeks old; magnified 350 diameters: a, horny layer of the epidermis ; b, its mucous layer; t, structure- less membrane surrounding the rudiment of the hair and continued between the mucous layer and the corium ; m, roundish, partly-elongated cells, which especially compose the rudiment of the hair. 188 SPECIAL HISTOLOGY. generally be separated only in shreds with it, from the cutis, rarely al- together : this I regard as the first indication of the fibrous layers of the hair-sacs. In the sixteenth and seventeenth weeks, the processes of the mucous layer, which I will henceforward simply call " hair-rudi- ments," increase in size up to -004-0-06 of a line in length, and 0-03- 0-04 of a line in breadth, and acquire thicker coverings, but as yet ex- hibit no trace of a hair. In the eighteenth week these first appear in the eyebrows, as hair-rudiments of 0-1-0-2 of a line, their central cells becoming somewhat elongated, and arranging themselves with their lon- gitudinal axes parallel to that of the rudiment, whilst the peripheral cells are disposed with their now longer diameter transversely. A variety of shade in the hitherto homogeneous hair-rudiment arises in this manner, and a central substance, broad below, running above into a sharp point, becomes marked off from an outer portion, which is narrow below and thick above. When the rudiment has attained a length of 0-22 of a line, this marking off is still more distinct, the rather longer and especially broader, inner cone having a somewhat clearer appear- ance (Fig. 74). Finally, in rudiments of hair of 0'28 of a line, the inner cone is divided into two structures, a central portion somewhat darker, and an external, perfectly transparent and glassy, the hair and the inner root-sheath, whilst the peripheral cells which have re- mained opaque, constitute unmistakably the outer root-sheath (Fig. 75 A). At the same time the papilla, which was even before (Fig. 74) just traceable, becomes more distinct, and the proper hair-sac also more recognizable, as the cells which lie external to its structureless membrane begin to pass into fibres which may, even at this time, be known by their decussation. The hair-sacs and hairs arise, in other places, exactly in the same manner as in the eyebrows, except that their development takes place somewhat later. In the fifteenth week, no rudiments of hairs are visible, except on the forehead and eyebrows ; in the sixteenth and seventeenth week they appear all over the head, back, chest, and ab- domen ; and not till the twentieth week on the extremities. The hairs themselves never make their appearance earlier than 35 weeks after that of the rudiments ; in the nineteenth week, for example, the com- mencement of hairs is nowhere to be seen, except on the forehead and eyebrows ; and in the twenty-fourth week they are still absent upon the hand and foot, and partly on the forearm and leg. Once formed, the hairs and hair-sacs continue to grow. The former sometimes penetrate the epidermis immediately (eyebrows, eyelashes, Fig. 75), sometimes their points are insinuated between the horny layer and the stratum Malpighii, or among the elements of the horny layer itself, and grow for a time covered by the epidermis (chest, abdomen, back, extremities [?]), through which they eventually make their pas- sage. Involutions of the skin growing towards the hairs as they pass OF THE HAIRS. 189 out, never exist, and the supposition that they do, rests upon a wholly subjective foundation. Fig. 75. Fig. 74. The downy hairs, lanugo, the eruption of which is completed in the 23-25th week, are short fine hairs, whose peculiar arrangement has been noted above. They measure on the bulb 0-01, on the shaft 0-006, at the point 0-0012-0-002 of a line; are pale, or almost .colorless, and consist only of cortical substance and a cuticle. In man, the bulb is usually colorless, and often rests upon a very distinct papilla, arising in the ordinary manner from the bottom of the hair-sac. It has the same three layers as in the adult, and possesses a very well-developed epidermic investment, consisting of an external root-sheath of 0*004 0-012, and an inner sheath of 0-006-0-008 of a line, without openings. After their eruption, the downy hairs grow slowly to a length of J-J of a line, and in fact to a greater length in the head than elsewhere. Generally they remain to the end of foetal life, gradually acquiring a darker color, becoming in many cases, as on the head, even blackish ; another small portion falls off into the liquor amnii, is swallowed with FIG. 74. Rudiment of a hair from the eyebrow (O22 of a line in length), its inner cells forming a distinct cone, as yet without any hair, but with the papilla indicated : a, horny layer of the epidermis; 6, mucous layer; c, outer root-sheath of the subsequent sac; i, struc- tureless membrane upon its outer side ; A, papilla of the hair. Magnified 50 diameters. FIG. 75. jl, rudimental hair from the eyebrows, with just developed but not yet erupted hair, of O28 of a line in length. The inner root-sheath projects beyond the point of the hair somewhat at the upper part, and laterally at the neck of the sac; the first rudiments of the sebaceous glands appear in the form of two papillary outgrowths from the outer root-sheath. JB, hair-sac from the same, with its hair just erupted ; the inner root-sheath projects through the aperture of the hair-sac; the rudiments of sebaceous glands are as yet not developed; a. 6, c, /*, i, have the same signification as in Fig. 74 : e, hair-bulb; /, hair-shaft; g, hair-point; n, rudiments of the sebaceous glands. 190 SPECIAL HISTOLOGY. this by the foetus, and may afterwards be found in the meconium. A proper shedding of the hair does not take place at all in the foetus, so far as I can see, infants being born with the lanugo ; as little does any trace of a further formation of hair appear after its complete eruption. The question whether the point of the hair is first formed, or whether the latter is developed at once as a whole, is readily solved. Hairs which are just formed, have a bulb with soft cells, a horny point and an intermediate portion, in which the cells are converted into horn, and are partly found passing into the cells of the root, whence there can be no doubt that we have here a whole hair. That the horny part of this hair subsequently forms the point of a larger hair, is of no importance; and as little as the hairs of the head of a newly-born infant can be called points of hairs, because they subsequently become the points of larger hairs, can we so denominate these. Nor can it be said that the first foetal hair subsequently becomes, in totality, the point of a larger hair, since the hairs do not grow by the simple apposition of new ele- ments, like the bones, but by the multiplication of their lowest soft cells, some of which are always retained as a reserve for cells to be newly developed, whilst the others are converted into horn ; whence also it happens, that the cells even of a complete hair-bulb are to be regarded as the successors of those of the foetal hair.* * [From what has been said above (see note on the Cuticle) it is clear we do not share Professor Kolliker's view that the hair is an epidermic production. Reichert's view, on the other hand, that the hair results from the cornification of a dermic papilla or matrix, which drying up and becoming filled with air, remains as the medullary portion, seems to us to be nearer the truth. There can be no doubt of these two facts: 1, that no line of demarcation can be traced between the papilla of the hair and its shaft; and 2, that in many animals the papilla is vascular and nervous for a considerable distance into the shaft, and, therefore, is certainly a dermic structure. Whether Reichert's somewhat mechanical notion of the " drying up" of the matrix to form the medulla is correct, is not of much importance, so long as we keep in view the unques- tionable continuity of tissue and homological identity, of the medulla and cortex with the dermic papilla. For us, in fact, the Hair is homologous in all its parts with the Tooth. The substance of the shaft corresponds with the dentine, offering even rudimentary tubes in its aeriferous cavities ; the inner layer of the cuticle answers to the enamel, the outer to Nasmyth's mem- brane ; and whoever will compare these structures will be struck by the similarity even in their appearance. The sac answers to the dental capsule ; the outer root-sheath to the layer of epithelium (enamel organ) next the capsule ; the fenestrated membrane to the stellate tissue ; and what Professor Kolliker calls " Huxley's layer," to the columnar epithelial layer of the organon adamantines. The comparison may seem startling at first, but the examina- tion of the development of the teeth of an osseous fish, for example, will suffice, we believe, to afford full justification of it. With respect to the not very important question, as to the nature of the first rudiment of the hair-shaft, i. e. whether it is the point of a hair or a whole hair, we must confess that we should be tempted to arrive at the opposite conclusion to our author. Inasmuch as the por- tion of the hair which first appears becomes the point of the fully-grown hair, we should say that the hairs are formed like the teeth, point first. A hair, like a tooth, has a definite form to attain. As the latter has a peculiarly con- OF THE HAIRS. 191 63. Shedding of the Hair. After birth, a total shedding of the hairs takes place in consequence of the development of new hairs within the hair-sacs of the lanugo, which gradually force out the old ones. This shedding of the hairs, which I discovered in the eyelashes of a child of one year old, commences by an outgrowth of the soft round cells of the bulb and of the neighboring outer root-sheath, from the bottoms of the sacs of the lanugo, into long processes composed of cells, by which the Fig. 76. hair is raised from its papilla, whilst at the same time it becomes converted into horn even in its lowermost por- tion. When these processes have attained a length of 0*25 of a line, a differentiation of their outer and inner cells takes place, similar to that which has been already FIG. 76. The eyelashes of a child of one year old pulled out; magnified 20 diameters: Jl, one with a process of the bulb or of the outer root-sheath, of 0'25 of a line, in which the central cells are elongated (their pigment is not represented), and are clearly defined as a cone from the external ones; '.B, eyelash in whose process, of 0'3 of a line, the inner cone is metamorphosed into a hair and an inner root-sheath ; the old hair is pushed up. and like A and Fig. 75, possesses no inner root-sheath : a, outer; b, inner root-sheath of the young hair; c, pit for the papilla of the hair; c?, bulb; e, the shaft of the old hair; /, bulb; g, shaft; A, point of the young hair; t, sebaceous glands; 7c, three sudoriparous canals, which in A open into the upper part of the hair-sac; I, transition of the outer root-sheath into the rete mucosum of the epidermis. FIG. 77. An eyelash with the root-sheaths from a child one year old, with an old and a growing young hair, magnified 20 diameters : the young hair is wholly extruded, and now two hairs appear at one aperture. A sudoriparous canal opens into the hair-sac. The letters have the same signification as in Fig. 76. structed and narrowed root when complete, so has the hair when it has attained its full growth a peculiarly constructed bulb ; and it is not a perfect hair until this peculiar bulb is developed. Until it has attained this form it goes on growing; but once having reached it, it grows no more, but falls out and is replaced by a new hair (see following ). Tus.] 192 SPECIAL HISTOLOGY. described as occurring in those processes of the stratum Malpighii, in which the hairs of the lanugo are developed. The outer cells, in fact, remaining round and colorless, as they were before, the inner ones begin to develop pigment in their interior and to elongate, becoming distin- guished at the same time from the former, as a conical substance with its point directed upwards. At first (Fig. 76 A\ this central substance is quite soft, and like the layers of cells which surround it externally, dissolves readily in solution of caustic soda ; subsequently, however, when, together with the process which incloses it, it has elongated, its elements harden, and separate into two portions, an enternal dark pig- mented, and an external clear part, which are nothing else than a young hair, together with its inner sheath (Fig. 76 B). The young hair, whose point at first does not project beyond its inner root-sheath, now grows gradually, forcing its point through the aperture of the old sac, while at the same time its root-sheath elongates, and thrusts upwards the bulb of the old hair, until at last it passes completely out, and makes its appearance at the same opening with the old one, which is more and more pushed up. When the development of the hair has gone thus far, the last stage may be readily understood. The old hair, which has for a long time ceased. to grow, and to be connected with the bottom of the sac, being thus extruded, falls out, while the young hair becomes larger and stronger, and fills the gap left by the old one. The primary cause of the dying away and casting off of the old hair, I consider to be the development of the processes of the hair-bulb and outer sheath from the bottom of the sac, which has been described. As the sacs do not elongate to a corresponding extent, they push upwards all those parts which lie above them, and cause a continually increasing space to exist between the papilla and the proper hair, or the point at which the round cells of the bulb begin to elongate and undergo conversion into horny matter. The hair thus becomes in a manner detached from the source of its nourishment; it receives less and less blastema, at last ceasing to grow, and becoming converted into horn in its lowest part. The cells of the processes, on the other hand, which are connected with the papilla, are incessantly supplied from it with new formative material, which for the time they apply not to the formation of horny matter, but to their own growth. In this manner the processes continue to grow, and mechani- cally elevate the cornified root of the old hair with its sheaths, to the aperture of the sebaceous glands, where to all appearance a partial so- lution of the old sheaths takes place : this may be observed with cer- tainty in the inner sheath, and must be assumed to occur in the outer. All that has been said, holds good only with respect to the eyelashes. The hairs of the head, and the other hairs of the body of the child (al- most a year old) in question, never contained more than one hair, though Of THE HAIRS. 193 their bulbs presented processes without hairs like those which precede the shedding of the eyelashes ; such processes, in fact, being of very common occurrence in the hairs of children within the first year. I be- lieve I am not wrong, if from the presence of these processes I deduce the universal occurrence of a shedding of the hairs, particularly as it is certain that in many children within the first 2-6 months after birth, the hairs of the head fall out and are replaced by new ones. How- ever, further observation is necessary to determine what period is occu- pied by this first shedding of the hair, in what hairs it occurs, and whether perhaps the process is subsequently repeated. If we compare the shedding of the hairs with their first develop- ment, we find a great resemblance between the two processes. In both, elongated projections, wholly formed of round soft cells, shoot like buds from the stratum Malpighii^ in the one case of the skin itself, in the other of the hair-sacs and hairs. In both, a separation of the inner from the outer cells next takes place ; and while the latter are metamorphosed into the outer root-sheath, the former become the inner root-sheath and the hair. The latter arises, as is still more clear in the shedding of the hairs than in their first development, like the nail, with all its parts at once, as a small hair provided with point, shaft, and root, and which only subsequently begins to grow, in consequence of which it enlarges in all its parts, and finally reaches the surface. The differences between the two modes of development are very inconsiderable, and chiefly depend upon the rudimentary hair-processes, in the one case proceeding from the hairs themselves, but not in the other; and upon the circumstance that the young hairs, although in both cases they lie at first in a closed space, reach the surface more readily in the one case, than in the other. In the periodical shedding of the hair of animals, the observations of Heusinger and Kohlrausch, and lately those of Langer, Gegenbaur, and Steinlin, show that the new hairs are also developed in the sacs of the old ones; although, according to the last author, with whom how- ever Langer is not quite in accord, the process does not appear to be exactly the same as in man. 64. Physiological Observations. The hairs have a definite length, dependent upon locality and 'Sex, but if they are cut they grow again, and consequently exhibit the same conditions as the other horny textures. The place from whence the growth of the hair proceeds is unquestionably the bottom of the hair-sac. Here there arise around the papillae with the co-operation of a blastema formed out of its vessels or those of the hair-sac, new elements, by the continual multiplication of the existing cells, while those which are already present, somewhat higher up pass uninterruptedly, the middle ones into medullary cells, the next into cor- 13 194 SPECIAL HISTOLOGY. tical plates, the outermost into epidermic scales, and thus the horny part of the hair is continually forced from below upwards, and elongates. In the latter no formation of elementary parts takes place, but at most a certain metamorphosis of those which are already existent, which pro- duces a gradual thinning of the root from the bulb upwards, until it acquires the thickness of the shaft. Higher up still, these changes of the elementary parts cease, whence cut hairs, for example, do not produce new points. The root-sheaths and the outer layer of the epi- dermis take no part in the growth of the cut hairs. The complete hair, though non-vascular, is not a dead substance. Al- though the processes which go on in it are not at all understood, we may suppose that fluids are diffused through it which subserve its nu- trition and maintenance. These fluids are furnished from the vessels of the papilla and sac of the hair, in all probability ascend (particularly from the bulb) ; without any special canals through the cortex upwards, and thus reach all parts of the hair. Having served for the nutrition of the hair, they evaporate from its outer surface and are replaced by a fresh supply. Perhaps the hairs also absorb fluids from without, though of course only in the condition of vapor, like a hair used as a hygrometer ; on the other hand I cannot believe that, as many authors would seem to suppose, the secretion of the sebaceous glands passes from without into the hairs, since the perfectly closed cuticle is probably impervious to it. In the same way it seems to be in nowise proved that the hairs are pervaded by a peculiar oleaginous fluid (Laer), which might proceed from the medullary substance (Reichert), and which keeps it greasy, for such a fluid has not been demonstrated, and the greasiness of the hairs may be more simply explained by the externally adherent sebaceous matter, which is readily visible. The existence of hair in the medullary axis and in the cortex can only arise from a disproportion between the supply of fluid from the hair-sac and the amount evaporated ; it is owing as it were, to a drying-up of the hair, which, however, must not be sup- posed to go so far that the hair contains no fluid in its aeriferous portion. In any case, however, these portions are the most inactive, or relatively dead parts of the hair ; the cortex, on the other hand, which is also most readily altered by alkalies and acids, notwithstanding the apparent hardness and density of its elements, is the most rich in juices, and is that in which the nutritive process is most actively going on. Hence it follows, that the hair lives, and is to a certain extent dependent upon the collective organism, particularly on the skin, from whose vessels (i. e. those of the hair-sac) it derives the materials necessary for its maintenance. Therefore, as Henle well says, the condition of the hair is a sort of index of that of the activity of the skin ; if they are soft and shining, the skin is turgescent and transpires ; if they are dry, brittle, and rough, then it may be concluded that the surface of the body is in a collapsed condition. OF THE HAIRS. 195 The falling out of the hairs certainly depends, in many cases, when, for example, it takes place in the course of normal development, on nothing else than a want of the necessary nutritive material, which in the instance already explained, in speaking of the shedding of the hairs, depends on the detachment of the hair from its matrix by the abundant production of cells at the bottom of the hair-sac. In age, perhaps, it arises simply from the obliteration of the vessels of the hair-sacs. The whitening of the hairs, which chiefly depends upon a decoloration of the cortex, and less upon that of the almost colorless medulla, should probably be here considered, for its normal occurrence in old age gives it the significance of a retrogressive development. The frequent occurrence of cases, in which the hair grows gray first at its point or in the middle, and the well-established instances of its rapidly becoming white, are interesting, and strongly testify to the vitality of the hair ; but it has not yet been shown, what peculiar -pro- cesses in the elements of the hair produce the decoloration of its different pigments. As in youth hairs which are shed are replaced by others, so at a later age something similar appears to occur. It is quite certain that during the period of full health and activity, a continual replacement of the numerous hairs which fall out goes on ; furthermore that new hairs in great numbers spring up at the time of puberty in certain localities, but the manner in which this takes place is unknown. Inasmuch as even in adults we find hair-sacs with little processes downwards, whose proper hair has an abrupt clavate end, as in the child ; since further, in this case it not unfrequently happens that two hairs come out of one aper- ture, and even exist together in one sac ; and, finally, since in hairs which have fallen out spontaneously, we invariably find roots like those* which exist in the extruded hairs of the first shedding, it may be assumed that an actual shedding of the hairs occurs, even at a later period, in such a manner that the old hair-sacs produce new hairs while they throw off the old ones. I do not, however, intend to affirm by this, that an actual new formation of hairs does not occur after birth, but only this much, that in adults they are certainly regenerated from the already existing hair-sacs, especially if it be recollected that, accord- * [Henle (" Allg. Anat," p. 303) gives a very excellent description of this state of the hair-bulb: " Instead of the soft cellular hair-bulb, we find an inconsiderable clavate enlarge- ment, which is solid and fibrous, like the substance of the shaft, only more clear. From its outer surface, short and irregular processes project downwards, which are probably the notched lower edges of the outermost layers of the cortical substance ; they look like fibres connecting the hair with the inner wall of the sac. This kind of root is found in hairs which have fallen out spontaneously, and it is, therefore, probable that it belongs to a later stage of development of the hair, or rather marks the conclusion of its development. When the connection with the sac has ceased, which is the case in these clavate roots, the hair grows no longer 5 probably it is no longer nourished, but falls out." 196 SPECIAL HISTOLOGY. ing to Heusinger's observations, the whiskers of dogs, when pulled out, are produced from the same sacs in a few days, and also that during the shedding of the hair in adult animals, according to Kohlrausch, the young hairs are produced from the old sacs. Also, when the hairs which have fallen out after a severe illness, are replaced, it is more probable, since, according to E. H. Weber, the sacs of lost hairs remain for a long time, that they arise in the old sacs, than that new ones are developed.* The multiplication of the cells of the bulb of the hair during its growth takes place unquestionably, not by free cell-development, since no trace of anything of the kind is to be seen in any bulb, but either by endogenous cell-development round portions of contents, or by divi- sion. I do not think that all those hairs which possess a sharply-defined clav'ate bulb are on that account dead and ready to fall out. It is cer- tainly thus in many cases ; but in others this condition indicates nothing more than the normal termination of growth, whence of course, it does not follow that the nutrition also has ceased. In proof of the occurrence of a continual development of the hairs independently of the old hair- sacs, the hairs which lie spirally curled up under the epidermis and subsequently break through it, upon the forearm, leg, &c., are frequently cited. But I do not know that it would not be more correct to consider this, with many pathologists, rather as an abnormal process. In the first place this formation of the hairs by no means occurs in all per- sons ; and secondly, where it does, there are found together with those coiled-up hairs, which are apparently normally developed, others which are evidently abnormal, in great quantities. These, often in consider- able number (up to 9), with thick sheaths, lie in one sac and have rounded points, with irregular bulbs. With respect to their relations, it might for the present be wiser, so long as an actual, normal new development of hairs has not been demonstrated, not to assume it, and to consider that, even at a later period, the development of new hairs within the old sacs is the normal mode, especially since Dr. Langer has actually observed it to take place in many instances in the very same manner as that which I have described in children. The reason why the hairs grow continually, if they are cut, but not otherwise, is the same as I have already adduced, to account for the same occurrence in the * [Berthold (Mull " Archiv, " 1850) has communicated some curious statistics relative to the growth of Hairs. The hairs of the head of a female of from 16 to 24 years of age, grow at the rate of 7 lines a month. The growth of the hairs of the beard is quicker the oftener they are cut; shaved every 12 hours they would attain a length of from 5^-12 inches per annum ; every 24 hours, from 57^ inches; every 36 hours, from 4-6^ inches. They grow faster by A during the day than during the night; and in 18 days of summer, 0026 more than in 18 days of winter. TBS.] OF THE HAIRS. 197 nails. The vessels of the papilla excrete a certain quantity of nutritive fluid, just so much as is sufficient to keep the whole hair continually moist and in a state of vitality. If the hair be cut, more nutritive fluid is supplied than the hair can use, and therefore it grows by the aid of the superfluity until it has attained its typical length again, or. if it be continually cut, it as continually grows. Dzondi, Tieflfenbach ("Nonnullade regeneratione ettransplantatione," Herbip, 182*2) and Wiesemann (De coalitu partium, Lips. 1824) have succeeded in transplanting the hairs with their sacs. Hairs are deve- loped also in abnormal places, e. g. on mucous membranes, in encysted tumors, ovarian cysts, and in all these cases, even in the lungs (Mohr's case), possess sacs, root-sheaths, and an otherwise normal structure. No hairs are developed upon cicatrices of the skin. No satisfactory reason can be given for the excessive growth of the hairs, nor for their morbid universal falling out, together with their frequent reproduction in the same way ; probably the principal causes are to be found in increased or diminished exudations from the vessels of the papilla and of the hair-sac, and more remotely in the state of the skin and the organism in general. In other cases vegetable productions (fungi] in the interior of the hair itself (in Herpes tonsurans, the " Teigne tondante," Mahon), according to Gruby [" Gaz. Md.," 1844, No. 14], and Malmsten, (Mull. "Arch.," 1848, 1), or under the epidermis of the hair and around it (in the Porrigo decalvans of Willan according to Gruby), are con- cerned in the production of baldness, which then is limited (Alopecia cir cum script a). The process of becoming gray is also obscure, although grief, excessive intellectual activity, and nervous influences are sometimes evidently concerned in it. It is not until physiology and chemistry have approached these latter processes, that we can hope for a scientific pathology and treatment of the hair. Plica polonica, which, according to Bidder (1. c.), is a disease of the shaft of the hair, is said by Guens- burg and Walther (Miiller's " Archiv," 1844, p. 411, and 1845, p. 34), to arise from a fungus which is developed in the hairs (bulb, shaft), and partly destroys them ; whilst Munter (ibid., 1845, p. 42) could find no such fungus. This disease, as well as peculiar yellowish-white rings upon the human hairs, consisting of epithelial cells without nuclei (Svitzer, in u Fror. Notizen," 1848, No. 101), which appear to consist of an altered secretion of the sebaceous glands, are less interesting from a histological point of view, and therefore are but shortly adverted to here. For microscopic investigation, a white hair with its sac should be chosen in the first instance, subsequently colored ones. Transverse sections may be obtained, either by shaving twice at short intervals (Henle) or by cutting hair on a glass (H. Meyer), or in a bundle be- tween two cards (Bowman), or fixed in a cork (Hartin); longitudinal 198 SPECIAL HISTOLOGY. sections, by splicing a finer or splitting a coarser hair. The hair-sacs may be examined, both isolated and with the hair ; their different layers may be separated by preparations, and the nuclei of the external ones may be demonstrated by acetic acid. Concerning the papillae ^ all that is necessary has been said above; the whole upper part of the root-sheath generally follows the hair when it is torn out, and in the macerated skin it comes out very readily with the hair ; its cells may be made out with- out addition, or by a little acetic acid or caustic soda. The inner root- sheath is often to be found entire in torn out hairs, and may without further preparation, or by stripping off the outer sheath, be readily re- cognized in all its parts. Caustic soda and potassa acting for a short time, make it still more distinct. The cuticle must particularly be exa- mined with alkalies and sulphuric acid, like the hair itself. The most important details upon this point have already been given, and more may be found in Bonders (I. c.). I will only add that in this case also, the application of a high temperature (see above, in the section on the nails) saves much time. In investigating foetal hairs, in the very young state it is sufficient to tear off the epidermis, attached to which the rudi- ments of the hairs will be found. In older embryos, fine sections of the skin must be made ; or the epidermis and the corium may be stripped off together, in which case caustic soda is of assistance. Literature. Eble, " Die Lehre von den Haaren in der gesammten organischen Natur.," 2 Bde., Wein, 1831 ; Eschricht, " Ueber die Richtung der Haare am menschlichen Korper," in Mull. "Arch.," 1837, p. 37 ; V. Laer, " De structura, capill. hum. observationibus microscopicis illustr.," "Dissert, inaug.," Traject. ad Rhenurn, 1841, und " Annelin der Chemie u. Pharmacie," Bd. 45, No. 147 ; G. Simon, " Zur Entwick- lungsgeschchite der Haare," Miill. "Arch.," 1841, p. 361 ; Krause, article " Haut.," in Wagner's " Handworterbuch d. Phys." 1844, Bd. ii. p. 124 ; Kohlrausch, " Ueber innere Wurzelscheide und Epithelium des Haares," Miill. " Arch.," 1846, p. 300 ; Jasche, " De telis epithelialibus in genere et de iis vasorum in specie," Dorpat, 1847 ; Kb'lliker, " Ueber den Bau der Haarbalge und Haare," in the " Mitthiel d. ziirich., naturf.," Ges., 1847, p. 177; Hessling, " Vom Haare und seinen Scheiden in Froriep neue Notizen," 1848, No. 113; Langer, " Ueber den Haarwechsel, bei Thieren und beim Menschen," in den " Denkschr. d. Wien," Akad., 1850, Bd. i. The comparative anatomy of the hairs is treated of by Heusinger in Meckel's "Arch," 1822, 1823, und "System der Histio- logie ;" Erdl, in " Abh. d. Munch.," Akad., Bd. III. ii. ; Gegenbaur, in " Verhund d. phys. med. Gesellschaft zu Wurzburg," 1850; Steinlin, in " Zeitschrift, fiir rationellen Medizin," Bd. IX. The allied horny tis- sues are described in the "Dorpat. dissertations," by Brocker, " De textura et formatione spinarum," 1849 ; Hehn, "De text, et form, barbie Balsense," 1849; Schrenk, "De formatione pennre," 1849. OF THE GLANDS OF THE SKIN. 199 IV. OF THE GLANDS OF THE SKIN. Fig. 78. A. OF THE SUDORIPAROUS GLANDS. 65. The Sudoriparous Crlands consist of a single delicate, more or less convoluted tube, which secretes the sweat. They are formed over the whole surface of the skin, with the exception of the concave side of the concha of the ear, of the external auditory meatus, the glans penis, one lamella of the prepuce, and a few other localities ; and open upon it by numerous fine apertures. 66. In every sudoriparous gland (Fig. 45, Fig. 78), we may distin- guish, the glandular coil (Fig. 78 a, Fig. 75 g), or the proper gland, from the excretory duct or sudoriparous canal (Fig. 45 h, Fig. 78 b). The former is a rounded or elongated corpus- cle of a yellowish or transpa- rent yellowish-red color, which in general measures ^\ of a line ; but on the eyelids, the integument of the penis, scro- tum, nose, convex side of the concha of the ear, on the other hand, not more than iV-tjz of a line ; whilst on the areola of the nipple and in its neighborhood, at the root of the penis, and between the scrotum and perinseum, it attains as much as J a line, and in the hairy parts of the axilla reaches as much as J-1-1J line in thickness, and 13 lines in breadth. The sudoriparous glands, in most cases, are lodged in the meshes of the pars reticularis of the corium, sometimes more superficially, some- times deeper, surrounded by fat and loose connective tissue, together with or among hair-sacs. They occur more rarely in the subcuta- neous connective tissue, or at its boundaries, as for example in the axilla, to some extent in the areola mammce, in the eyelids, penis, and scrotum, the palm of the hand and sole of the foot. In the two last- named localities, they are disposed in rows under the ridges of the cutis, FIG. 78. A sudoriparous coil and its vessels; magnified 35 diameters: a, glandular coil; 6, excretory duct or sweat duct ; c, vessels of a glandular coil, according to Todd and Bow- man. C. " 200 SPECIAL HISTOLOGY. and at tolerably equal distances apart ; in other places they are met with, usually in a regular manner, singly or in pairs, in each mesh of the corium, although, according to Krause, spaces of J-J a line exist, where they are totally absent, or occur in groups of three or four close together. In the axilla, the glands form a connective layer under the corium. According to Krause, there occur on a square inch of the skin be- tween 400 and 600 glands on the back of the trunk, the cheeks, and the two superior segments of the lower extremities ; 924-1090 on the anterior part of the trunk, on the neck, brow, the forearm, back of the hand and foot ; 2685 on the sole of the foot ; and 2736 on the palm of the hand. The total number of the sudoriparous glands, without reck- oning those of the axilla, is estimated (somewhat too highly) by Krause at 2,381,248, and their collective volume (with those of the axilla) at 39,653 cubic inches. The vessels of the sudoriparous glands are particularly well seen in those of the axilla (Fig. 78) ; in others, the vessels may also be seen here and there (best in the penis, where, for example, glands of 0-36 of a line are supplied by the most delicate ramifications of an artery of 0-06 of a line, in their interior); and in successful injections of the skin, the glands appear as reddish corpuscles. Nerves have not hitherto been found in them. 67. Intimate Structure of the Glandular Coil. The sudoriparous glands, in general, consist of a single much convoluted canal (in one case, according to Krause, } of a line long), twined into a coil, which retains pretty nearly the same diameter throughout its length, and terminates, either upon the surface of the coil, or in its interior, in a slightly enlarged blind extremity. In the large glands of the axilla alone, the canal is usually divided, dichotomously, into branches, which subdivide, and sometimes, though rarely, anastomose ; and after giving off small caecal processes, each separate branch finally terminates in a blind extremity. The glandular canals have either thin or thick walls (Fig. 79). The former (Fig. 79 A) possess an external fibrous invest- ment, consisting of indistinctly fibrous connective tissue, with scattered elongated nuclei ; internally this is sharply limited, perhaps by a mem- brana propria, and is covered by a single, double, or multiple layer of polygonal cells of 0-005-0-007 of a line, which in their chemical rela- tions, and otherwise, correspond perfectly with the deep cells of pave- ment-epithelium, except that they almost invariably contain a few fatty granules, and still more frequently a small quantity of yellowish or brownish pigment-granules. The thick-coated sudoriparous glandular canals (Fig. 79 B] possess, besides the two layers just described, a middle layer of smooth muscles OP THE GLANDS OF THE SKIN. 201 running longitudinally, whose elements are easily separable, as muscu- lar fibre-cells of 0-015-0-04 of a line long, 0-002-0-005, or even 0-008 of a line broad, occasionally with a few pigment-granules, and each con- taining a roundish elongated nucleus. Whenever the glandular tubes con- rig. 79. tain only fluid, the epithelium is a single very distinct layer of polygo- nal cells of 0-006-0-015 of a line ; in the opposite case it can be seen only with difficulty or not at all. With respect to the occurrence of these two forms of glandular canals, the thick muscular walls are found, especially in the large glands of the axilla, whose cells all possess mus- cular walls, and thence acquire a very peculiar striated appearance. I have noticed a precisely similar structure only in the large glands of the root of the penis and of the nipple, although it is true that there is occasionally a muscular development, but slighter and only partial, in the glands of the palm, whose wide canals are distinguished by the thickness of their walls, and exhibit a muscular structure distinctly enough, though thinner than elsewhere. The same description applies to certain glands of the scrotum, and even of the back, of the labia majora, of the mons veneris, and of the neighborhood of the anus ; yet with this limitation, that often only a small part of the glandular tube, perhaps merely its caecal extremity, is provided with a muscular coat. The glands of the leg, of the penis, of the thorax (the areola excepted), of the eyelids, and the majority of those of the back and thigh, of the chest and abdomen, as well as of the two prominent segments of the upper extremity, are delicate and without muscles. The diameter of the glandular canals varies, in the smaller glands from 0-022-0-04 of a line, and is about 0-03 of a line on the average ; the FIG. 79. Sweat ducts ; magnified 350 diameters. A, one with thin walls and a central cavity without a muscular coat, from the hand : a, connective investment ; 6, epithelium ; r, cavity. JB, a portion of a canal without a cavity, and with a delicate muscular layer, from the scro- tum : a, connective tissue; 6, muscular layer; c, cells which fill the glandular canal with yellow granules among their contents. 202 SPECIAL HISTOLOGY. thickness of the walls, 0-002-0-003 ; of the epithelium, 0-006 ; of the cavity, 0'004 0-01 of a line. Among the axillary glands some have canals of 0-07-0-1, even 0-15 of a line, with walls 0-006 of a line in thickness, without the epithelium, and half of which is formed by the muscular layer ; others and in fact the largest glands, possess canals of 0*030-06, with walls of 0*004 of a line ; in the areola and the genitalia also, the dimensions of the larger glands vary, though within narrower limits. All the coils of the sudoriparous glands are penetrated by connec- tive tissue, interspersed with fat-cells, which supports the vessels and unites the separate convolutions of the tubes with one another ; some of them have an external fibrous covering investing the whole coil (of com- mon connective tissue with fusiform nuclei), which is particularly well developed in those more isolated coils which are lodged in the subcuta- neous cellular tissue (penis, axilla, &c.) 68. Secretion of the Sudoriparous Glands. All the smaller sudori- parous glands contain, as soon as any cavity is apparent in their canals, which, however, is by no means always the case, nothing but a clear, bright fluid, without any formed contents. In the axillary glands, on the other hand, the contents abound in formed particles, and appear either as a grayish, transparent, semi-fluid substance, with innumerable fine, pale granules, and often with solitary nuclei ; or as a whitish-yellow tolerably viscid matter, with a varying quantity of larger, opaque, colorless, or yellow granules, nuclei and cells, similar to the epithelial cells above described. That these cell contents, which, as I have found, contain much protein and fat, differ considerably from the common sweat, which is fluid and presents no formed elements, and probably rather approximate to the sebaceous secretion of the skin, is evident, on which account we might be induced to remove the glands of the axilla from the class of sudoriparous glands, and to regard their secretion as of a peculiar kind. These glands, however, sometimes afford a secre- tion containing but few granules, or even nothing but fluid ; and among the larger axillary glands smaller ones occur, which, so far as regards their contents, exhibit many transitions, on the one hand into the large, and on the other into common small glands.* If we further consider * [However true it may be that this secretion is sometimes fluid, and similar to that of sudoriparous glands in other situations, this is the exception, and by no means the rule. But it is not on account of their secretion, but mainly of their different structure, that these glands have been separated from the common sudoriparous glands. They differ from them by being united' into groups, and by their yellowish color. In size, too, they vary. Many are 5 or 6 times larger: some attain the size of 2 lines in diameter. The groups can be readily seen with the unassisted eye, if the adipose tissue adhering to a flap of skin from the axilla be removed. They then appear as small granulations of a reddish or rosy tint, and are soft and pulpy. The excretory ducts are not spirally wound as in the ordinary sudori- parous glands. In the Negro these axillary glands as first pointed out by Prof. Horner (American Journal OF THE GLANDS OF THE SKIN. 203 that, occasionally, the sudoriparous glands in other situations, as, for instance, in the areola of the nipple, contain a fluid abounding in granules, it is clear that it is unadvisable to distinguish the large axillary glands from the common kind, on account of the difference in their secretion ; and the more so, indeed, because we by no means know whether the latter, under certain circumstances, may not contain granules. As respects the origin of the granular contents, they must be referred to the cells which are developed in the glandular tubes. For we fre- quently meet in these with cells containing the same granules, which also occur free within the glandular canals ; and frequently may be said to constitute their whole contents. It sometimes happens, also, that in one and the same gland the ends of the glandular tubes contain nothing but cells, while the excretory duct exhibits hardly any trace of them, presenting merely granules and scattered free nuclei ; and in this case we can easily see that the cells, as they pass further upwards, become broken up to a greater and greater extent, thus setting free their nuclei and the granules in their interior. These cells plainly proceed from the epithelial cells lining the canal of the sudoriparous coil ; for, in the first place, the cells of the contents of the epithelium resemble one an- other in all respects ; and secondly, where cellular or granular contents are found in the glands themselves, the epithelium is for the most part completely absent, so that the former rests immediately upon the muscu- lar membrane. Now, since on the other hand, in those glands which contain only a clear fluid, the epithelium is always easily seen, and often presents many dark (even golden yellow) pigment granules in its cells, it may perhaps be assumed, that the cells in the contents are nothing but detached epithelium, and that the secretion mainly depends upon a growth and continual casting off of the epithelial cells. The examination of the secretion of the sudoriparous glands is neither chemically nor microscopically complete. As regards the former, the fact that the axillary glands secrete fat and a nitrogenous substance in large quantities, appear to me interesting, since from the obvious similarity in structure between these and the other sudoriparous glands, we may perhaps draw some conclusions as to the secretion of the latter. We already know that the ordinary perspiration contains nitrogenous matters (extractive) ; and as Krause (1. c., p. 146) has clearly shown, fat, also ; and it may be asked whether these substances do not perhaps in certain situations (e. g. hand, foot) occur more abundantly, or under certain conditions (local, adhesive, peculiarly odorous perspiration) increase in quantity. The so-called sweat-corpuscles of Henle (1. c., pp. 915 and 939), that is, structures similar to the mucus-corpuscles, I of Med. Science, 184G), are much larger than in the White. To the secretion of these large glands indeed, the peculiar smell of Negroes is attributed. In the groin sudoriparous glands very similar in their structure to these axillary glands are met with. DaC.] 204 SPECIAL HISTOLOGY. Fig. 80. have hitherto found neither in the sweat of man nor in the smaller glands ; but I may remark that almost constantly, even in the smaller sudoriparous glands, certain canals exist which present no cavity, but are wholly filled with epithelial cells. These appeared to me always to be near the blind end (Fig. 79, B\ whilst those which are nearer the excretory duct, almost invariably exhibit a cavity 0*004 0*1 of a line in diameter, I consider it therefore to be not impossible, that in the common sudoriparous glands, a cellular secretion is at times formed and excreted in the same manner as in the axillary glands ; for from what we see in the canals of the latter, it can hardly be doubted that granules, nuclei, and perhaps also remains of cells, occur in the sweat of the axilla. Whether the sweat in different individuals and races of men present notable differences is unknown, for it is not ascertained that the different odor of the cutaneous exhalation in the European and the Negro, for instance, depends on the sweat or the material of the per- spiration ; nor have its pathological relations been investigated, at all events not microscopically. 69. Sweat-Ducts. The excretory ducts of the sudoriparous glands, the sweat-ducts, or spiral canals (Figs. 45, 80), commence at the upper end of the glandular coil as simple canals, ascend with slight undulations vertically through the corium, and then penetrate between the papillce (never through their points), into the epider- mis. Here they begin to twist, and according to the thickness of the cuticle they perform from 2-16 closer, or more distant spiral turns, until even- tually they terminate by small, round, often funnel-shaped apertures, the so- called stveat-pores on the free surface of the epidermis. The length of the sweat-ducts de- pends on the situation of the glands and the thickness of the skin. The commencement of the duct is invaria- bly narrower than the canal in the coil itself, measuring 0-009-0-012 of a line ; it continues narrow up to its entrance into the stratum Malpighii FIG. 80. Perpendicular section through the epidermis and outer surface of the corium of the bulb of the thumb, transversely through two ridges, treated with acetic acid; a, horny layer of the epidermis; 6, mucous layer; c, cutis; d, simple papilla; e, compound papilla; /, epithelium of a sweat-duct passing into the mucous layer; g, cavity of it in the cutis; h, in the horny layer ; t, sweat-pore. Magnified 00 diameters. OF THE GLANDS OF THE SKIN. 205 where it dilates to about double the size, i. e., to 0-024-0-28 of a line (Fig. 80); retaining this breadth, it traverses the epidermis, and ter- minates in an aperture of 513^ of a line. In the axillary glands, the excretory duct measured in one case at the level of the sebaceous glands 0'06-0*09 of a line, immediately under the epidermis 0*03, in the epidermis itself 0'06 of a line. In the corium the sweat-ducts have always a distinct cavity, an external investment of connective tissue, with elongated nuclei (in the glands of the axilla, muscles also), at all events, inferiorly, and an epithelium composed of at least two layers of polygonal, nucleated cells without pigment granules. Where the ducts enter the epidermis, they lose their investment of connective tissue, which coalesces with the outermost layer of the corium, and henceforward they are bounded by nothing but layers of cells, which in the stratum Malpighii are nucleated, but in the horny layer are without nuclei. Chemically and morphologically they completely resemble the epidermic cells, with the sole exception that they are dis- posed more perpendicularly, particularly in the horny layer. The duct has often a distinct cavity in the epidermis, at other times there is a granular streak in the place of it, which is probably either a secretion or a deposit from the secretion. The sweat-pores, whose disposition, corresponding w T ith that of the glands, is sometimes very regular, at others more irregular, are distinguishable, even with the naked eye, in the palm of the hand and sole of the foot. In other localities they are visible only w r ith the aid of the microscope ; occasionally the excretory ducts of two glands unite into a single canal (Krause). 70. Development of the Sudoriparous Glands. The sudoriparous glands first appear in the fifth month of embryonic life, and are originally perfectly solid, slightly flask-shaped, processes of the stratum Malpighii of the epidermis, and are very similar to the first rudiments of the hair- sacs. In the earliest condition which I have observed, the processes measured in the sole of the foot 0-03 0*09 of a line in length, and 0-01 of a line in breadth at the neck, at the bottom 0-018-0-02 of a line, and even the very longest did not penetrate more than half through the cutis, which was 0-25 of a line thick. They were entirely composed of round cells, perfectly similar to those of the stratum Malpighii of the epidermis ; besides which, each process had a delicate investment, which was continuous with the boundary of the inner surface of the epidermis. No trace of sweat-pores or ducts was visible. At the beginning of the sixth month, the glands in the sole of the foot and palm of the hand extend as far as the middle and inner fourth of the cutis, measure at the clavate extremity 0-028-0-04 of a line, and 0-016-0-02 of a line in the duct which arises from them, are already slightly serpentine, and present a cavity, at all events partially in their narrow portion; they do not, however, penetrate the cuticle, or in any way open on the 206 SPECIAL HISTOLOGY. surface. It was not before the seventh month that I perceived, in the same situations, the first indications of the sweat-pores and ducts in the Fig. 81. - mm i.-.i epidermis, though as yet very indistinct, and the latter forming only half a spiral turn (Fig. 82, A) ; at the same time the part of the gland which projected into the corium was more considerably developed, reached as far as the innermost portion of that structure, and at its csecal extremity was bent into a hook or even slightly convoluted, so as to afford the first indication of a glandular coil of about 0-04 to 0-06 of a line. The canal arising from it usually presented several marked undulations, and measured in total thickness 0-015-0-022 of a line, with a cavity of 0-003-0-004 of a line, which frequently extended even to the terminal coil : like the latter it was composed of the original though thickened membrane continuous with the surface of the corium, and of an epithelium consisting of many layers of pale, polygonal, or rounded cells. The glands of the rest of the body about this period, appeared to me to be similarly constituted. I can say nothing as to their earlier condition, but even those of the axilla were in no wise distin- guished from the rest. From this time the development goes on very rapidly ; the end of the gland elongates more and more, and coils itself up (Fig. 82 B\ so that it assumes an appearance hardly different from that which it presents in the adult. In the new-born infant, the glan- dular coils in the heel measure 0-06-0-07 of a line (in a child of four months 0-06-0-1 of a line on the heel, in the hand 0-12 of a line), present FIG. 81. Rudiment of a sudoriparous gland of a human embryo at five months; magni- fied 3.50 diameters: a, horny layer of the epidermis; 5, mucous layer; c, corium; d, rudimen- tary glands, as yet without any cavity, and consisting of small round cells. FIG. 82. ^, rudiment of a sudoriparous gland from a seven months' foetus ; magnified 50 diameters. The letters a, 6, c?, as in Fig. 81. The cavity e is present throughout, only it does not extend quite so far as the end of the thicker part of the rudiment of the gland, which becomes converted into the glandular coils. The continuation of the canals into the epidermis and the sweat-pores,/, are present. J2, a coil of a sudoriparous gland, from a fcetus at the eighth month. OF THE GLANDS OF THE SKIN. f 207 much convoluted canals of 0-015-0-022 of a line, and traverse the epi- dermis with their already twisted ducts (in the corium of 0-008, in the rete MalpigUi of 0-022 of a line). It results from these facts that the sudoriparous glands are nothing else than involutions of the skin, and do not begin as hollow structures, but are at first a simple development of the stratum mucosum. By a continual process of cell-multiplication, the original rudiments grow deeper and deeper into the skin, acquire their peculiar spiral windings, and divide into the glandular coil and the sweat-duct ; while at the same time, either by liquefaction of their central part, which would thus, as it were, represent a first secretion, or by the excretion of a fluid between their cells, a cavity is produced. How the sweat-duct in the epidermis and the pore are formed is doubtful ; probably by a formative process in the epidermis itself. According to a few measurements which I have instituted (" Mikroscop. Anat.," II. i. 171), a development of sudoripa- rous glands appears to take place even after the fifth month, whilst the whole number appears to exist at birth. Little is known as to the pathological conditions of the sweat-glands. Kohlrausch (Muller's " Archiv," 1843, p. 866), -has found them of con- siderable size (J a line) in an ovarian cyst, together with hairs and sebaceous follicles. In Elephantiasis graecorum, G. Simon and Brii eke (Simon, " Hautkrank.," p. 268), noticed an increase in size of the sudo- riparous glands, and V. Barensprung observed the same thing in a kind of wart (1. c., p. 81) ; the latter also found that these glands were atro- phied in corns, and that the duct in the outer layers of the epidermis had disappeared. The condition of the several glands in old age, in cases where the secretion of sweat is altogether wanting, and in ab- normal perspirations, is not known. In a remarkable case of Ichtliyosis congenita (very similar to that mentioned by Steinhausen, only more marked) in a new-born infant, which was examined by Dr. H. Muller and myself, the sudoriparous glands were present ; their excretory ducts, so far as regards their course through the epidermis, which was thickened to 2 lines, were partly disposed as usual, partly they were placed, as in the sole of the foot, with their outer portions almost completely hori- zontal, and ran in some places for as much as 1J line in this manner, so that in superficial sections of the epidermis they appeared as parallel, at first sight altogether abnormal canals, with a cavity of 0-0025-0-003 of a line. The contents of the ducts were very peculiar, consisting in- variably of -a multitude of white oil drops. I observed sudoriparous glands also in the case described by Mohr, of a great cavity containing hairs in the lung ( a Berlin Med., Central-zeitung," 1839, No. 13), they were about 0-24 of a line in diameter, and were contained in- a panni- culus adiposuSj with common fat-cells ; and it may be remarked that the 208 % SPECIAL HISTOLOGY. wall of the cavity besides the panniculus also presented a corium with papillae, and an epidermis like the external integument. Method of Investigation. To examine the position of the sudoriparous glands and their excretory ducts, fine sections of fresh or slightly-dried skin of the palm or sole should be prepared, and made transparent by acetic acid or caustic soda. Gurlt used for this purpose skin hardened and rendered transparent in a solution of carbonate of potassa (liquor kali carbonici). Giraldes macerates the skin for twenty-four hours in dilute nitric acid (1 part acid, 2 parts water), and for twenty-four hours in water, a process which, according to Krause, is very useful, as the glands become yellow, and are readily distinguished. In macerated pieces of the skin, the cellular lining of the sweat-ducts may be drawn out of the corium, in the form of long tubes, with the epidermis ; in delicate parts of the skin I have, not unfrequently, succeeded in doing this after treatment with concentrated acetic acid. The investigation of the glandular coils themselves is very easy in the axillary glands ; in the others the skin must be prepared from within, and the glands sought for partly upon the inner surface of the cuts, partly in its meshes, a method which readily succeeds, with a little attention, particularly in the hand, foot, and nipple. The large glands of the ball of the foot of the Dog, described by Gurlt, are particularly well-fitted for demonstra- tion, and still more those of the prepuce and of the integuments of the udder of the Horse, which lie quite loose in the subcutaneous tissue. If it be desired to count the glands, their apertures may be sought for, or a piece of skin of determinate size may be treated according to Giraldes' method, and examined portion by portion (Krause). For the study of the development of the glands, sections of the fresh and dried skin of the heel and palm of embryos, may be made with the double knife or razor. In embryos preserved in spirit, if the sections be fine, the glands may also be very well seen, especially in the first moments of the action of caustic soda. Literature. Breschet et Roussel de Vauzeme, "Recherches ana- tomiques et physiologiques sur les appareils tegumentaires des animaux," in the " Annales des Sciences Nat.," 1834, pp. 167 and 321 (discovery of the sudoriparous glands) ; Gurlt, " Vergleichende Untersuchungen iiber die Haut des Menschen und der Haussaugethiere, besonders in Bezug auf die Absonderungsorgarie des Hauttalges und des Schweisses," in Muller's " Archiv," 1835, p. 399 (first good figures of the glands themselves). [Robin, " Note sur une espece particuliere des glandes de la peau de 1'homme," in the "Annales des Sciences Nat.," 1845; Homer, " On the Odoriferous Glands of the Negro," in American Journal of Med. Sciences, 1846.] Besides these, compare especially the general works of Todd and Bowman, Henle, Valentin, Hassall, and myself; the above-cited treatises of Krause, myself, Simon, Von Biirensprung, and Wilson ; further the figures of Berres, tab. XXIV. ; R. Wagner, "Icon. OF THE GLANDS OF THE SKIN. 209 Phys.," tab. XVI., fig. 9 ; F. Arnold, "Icon. Org. Sens.," tab. XL, and my own " Mikr. Anat.," tab. I. B. OF THE CERUMINOUS GLANDS. 71. The ceruminous glands of the Ear are brownish simple glands, in external appearance precisely'similar to the sudoriparous glands, which do not exist in the whole external auditory meatus, but only in its car- tilaginous portion, where they are situated between the lining membrane of the passage and the cartilage, or the fibrous substance which supplies its place, in a tough subcutaneous tissue, containing little fat. They form a connected yellowish-brown layer, visible enough to the naked eye, which is thickest in the inner half of the cartilaginous meatus, and becomes gradually thinner and more lax externally, extending, however, quite as far as the cartilaginous meatus itself. Each ceruminous gland consists of a glandular coil and an excretory duct. The former (Fig. 83 d), T\)-J-i f a li ne in g i ze > is formed by the multitudinous convolu- tions of a single canal of 0-03 O f 06 on the average 0-04-0*05 of a line in thickness, which occasionally, although not constantly, throws out little diverticula, and terminates in a blind slightly enlarged end. From the coil a short straight excretory duct, 0*017 0-024 of a line thick, passes perpendicularly upwards, penetrates the corium and epidermis of the auditory meatus, and usually opens independently in a circular pore of 0*044 of a line, or else into the upper part of a hair-sac. The following is the intimate structure of the ceruminous glands. The canals of the coil present a fibrous coat, and an epithelium, the former being 0-004-0-005, the latter 0-004 of a line in thickness. The fibrous covering presents exactly the same conditions as in the larger sudoriparous glands, that is, it consists of an internal longitudinal layer of smooth muscles, 0-0023-0-0026 of a line in diameter, and an external layer of connective tissue, with scattered nuclei, and occasionally very fine trans- verse nucleus-fibres. The epithelium rests immediately upon the mus- cular layer, and consists of polygonal cells of 0-006-0*01 of a line in a single layer, which contain a greater or smaller number of yellowish- brown pigment-granules, of immeasurable minuteness, insoluble in acids and alkalies in the cold, or whitish fat-globules up to 0-001 of a line in size, and which are so disposed that the whole lengths of a gland con- tain generally only one and the same kind of granules ; whence it arises that they appear either uniformly brownish or opaque (by reflected light whitish). The contents of the glandular canals are sometimes a clear fluid, sometimes a granular substance composed principally of cells ana- logous to those of the epithelium, whence it would seem that the same kind and mode of secretion occurs in them as in the sudoriparous glands. The excretory ducts possess a coat of connective tissue, and an epi- thelium consisting of several layers, and constituted of small nucleated 14 210 SPECIAL HISTOLOGY. cells, without fat or pigment-granules. In their cavity, which is, how- ever, riot always distinct, they sometimes contain a clear fluid ; some- times a small quantity of finely-granulated substance. Fig. 83. Ai. 72. The Cerumen of the ear is commonly considered to be the secretion of these glands, though this is only partially correct. If we examine the yellow or brownish, soft or more solid, viscid substance which is formed within the cartilaginous meatus, it is found to contain various constituents : independently of a few hairs, occasionally an Acarus folliculorum^ and epidermic cells in various numbers, there occur, 1. Very many cells completely filled with pale fatty matter of 0'009 0*02 of a line, usually of an oval, flattened, irregular shape ; in which, on the addition of water, or still better of caustic soda, the fat is separated in isolated, round, or irregular dark drops. 2. Much free fatty matter in the form of pale, small yellowish round drops, which, on the addition of water, appear as dark spherical granules, from an immeasurable minuteness up to 0-002 of a line and more ; and it is only upon this addition that they become quite distinct, but at the same time are decolorized. FIG. 83. Perpendicular section through the skin of the external auditory meatus ; a, corium ; 6, stratum Mulpighii; c, horny layer of the epidermis; d, coil of the ceruminons glands; c, their excretory ducts ; /, their apertures; g, hair-sacs ; A, sebaceous glands of the meatus ; i, masses of fat. Magnified 20 diameters. OF THE GLANDS OF THE SKIN. 211 3. Yellow or brownish granules, and masses of granules, free or rarely in cells, few upon the whole. 4. Lastly, when the secretion is more fluid, also a small quantity of a clear liquid. I consider that the first-named cells belong to the sebaceous secretion of the external meatus ; but that the remainder is the secretion of the ceruminous glands, which would, there- fore, eliminate oily fluid with scattered brown granules. This being the case, the analysis by Berzelius of the common ear-wax, a mixture of the sebaceous and proper ceruminous secretion, must only be admitted with caution. In my opinion, the brownish-yellow bitter substance, soluble in alcohol and water, found by him, and the pale yellow strong-tasted extractive matter, hardly soluble in water, and not at all in alcohol, must be attributed to the ceruminous glands ; the remaining fat, the horny matter, and probably also most of the albumen, to the sebaceous glands ; whilst the relations of the salts must, of course, be left undetermined. The vessels of the ceruminous glands are disposed like those of the sudoriparous ; in one case I noticed, in addition, a fine nervous fibre of 0-003 of a line in the midst of a gland. As to the development of these glands I can only say, that in a foetus of five months they had the form of straight, pale processes of the stratum Malpighii of the epidermis of the external auditory meatus, were entirely composed of nucleated cells, and ended by a slightly enlarged termination somewhat twisted upon its axis, in which the first indication of a glandular coil was presented. In other words, these rudimentary glands exactly resembled the sudoripa- rous glands at the same period ; and considering the great anatomical resemblance between the two structures, I do not doubt for a moment that the ceruminous glands, both in their first commencement and sub- sequently, go through the same phases as the former. According to all that I have seen of the ceruminous glands, I must consider them to be mere modifications of the sudoriparous. In speak- ing of these it has already been remarked, that their secretions are certainly not everywhere identical, being in one locality more aqueous, in another fatty and albuminous, with peculiar odorous ingredients. Even although the cerumen may, to some extent, contain peculiar sub- stances, e. #., the yellow bitter substance, which, however, according to Lehmann, is not bilin, nevertheless, taking into account the other cor- respondences (consider the almost constant and often very abundant yellow granules in the sudoriparous glands, which are also insoluble in acids and alkalies), we may associate the ceruminous glands with the sudoriparous, especially with the larger among the latter, which are both anatomically and physiologically most closely allied to them ; in fact, I am inclined, for my own part, to think, that the smallest pale ceruminous glands at the commencement of the meatus are hardly dis- tinguishable from common sudoriparous glands. Nothing is known of the pathological conditions of the ceruminous glands of the cerumen 212 SPECIAL HISTOLOGY. itself we know that it is often quite solid, at other times fluid, puriform, and pale colored. In the latter case, which is seen in congested condi- tions of the external meatus, it contains far more fluid and free fat than usual, and very beautiful cells containing fat.* With regard to the mode of examining the ceruminous glands, I must refer to the sudori- parous glands, with which they wholly agree in position, chemical rela- tion to acids, alkalies, &c. &c. Literature. R. Wagner, " Icones Phys.," tab. xvi. fig. 11, A, B ; Krause and Kohlrausch, in Muller's " Archiv," 1839, p. cxvi. ; Pappen- heim, " Beitrage zur Kentniss der Structur des gesunden Ohres," in Froriep's "Neue Notizen," 1838, No. 141, p. 131, and Specielle Gebe- lehre d. Gehororgans (Breslau, 1840); Henle, "Allg. Anat." pp. 915, 916, 934, 941 ; Huschke "Eingeweidelehre," p. 819; Hassall, "Microsc. Anatomy," &c., p. 427, pi. Ivii. ; Valentin, article " Gewebe," in Wagner's "Handw. d. Phys.," i. p. 755. C. OF THE SEBACEOUS GLANDS. 73. The Sebaceous Grlands are small whitish glands, which exist in almost every part of the skin, and which afford the cutaneous sebaceous or fatty secretion. In form they vary very considerably ; the simplest (Fig. 84, A) are short follicles of an elongated or pyriform shape ; in others the simple racemose glands two, three, or even more follicles or vesicles are united with a shorter or longer peduncle ; whilst in others, lastly (Figs. 84 B, 85), two, three, or more simple clusters of follicles communicate with a common duct, constituting an elegant compound racemose gland. Besides these three forms, which represent only the chief varieties, there are a good many intermediate ones, which do not require any detailed description. The sebaceous glands occur principally in the hairy parts of the body, opening, in common with the hair-sacs, upon the surface, whence they have also been termed the glands of the hair-sacs. In all the coarser hairs, the glands appear to be lateral appendages of the hair-sacs, and open by narrow excretory ducts into them (Figs. * [There is an occasional ingredient in the so-called cerumen which is worthy of notice, viz. a mucedinous fungus. Attention has been recently called to its occurrence by Dr. Inman (" Quarterly Journal of Micros. Science," January, 1853), who states that a pellet of ear-wax which he examined was composed of nothing but this fungus, with a minute por- tion of epithelium. However, Professor Mayer, of Bonn, so long ago as 1844 ("Beobach- tung Von Cysten mit Fadenpilzen aus dem aussern Gehorgange," &c., Muller's "Archiv," 1844, p. 404), described at length the structure of certain sacs containing fungi, which were extracted from the external auditory meatus of a girl eight years old, in whom they appear to have been at first accompanied by considerable deafness and irritation. The sacs were as large as a pea, and open atone end; externally they were composed of layers of epithe- lium scales, from which mucedinous threads, terminated by globular sporangia, projected into the cavity of the sac. These sacs appear to have been repeatedly formed and discharged, to a very considerable number. TRS ] OF THE GLANDS OF THE SKIN. 213 75, 76, 77, 83), whilst in the lanugo the ducts and the hair-sacs are often of about the same diameter (Fig. 84 _#), and open into a common canal, which may be regarded as a continuation of the one as much as of the other ; or the ducts may even be the larger (Fig. 85), the hairs bearing a subordinate relation to them, so that their sacs open into the glands, and the hairs come out through the glandular opening itself. In the hairless parts of the surface, sebaceous glands occur only in the labia minora (vide 54), and in the glans penis and prepuce, whilst they do not exist in the glans and prepuce of the clitoris. In general, the glands are situated close to the hair-sacs in the superficial layer of the corium, and are larger in the finer hairs than in the coarser ; in Fiff. 84. Fig. 85. particular cases, however, they present many differences. With respect to the glands of the larger hair-sacs, they are usually of the simple racemose kind, having an average size of JQ- T 3 ^ of a line, and are disposed around the sac to the number of from 2 to 5. The smallest, of 0-1-0*16 of a line, occur in pairs, attached to FIG. 84. Sebaceous glands from the nose; magnified 50 diameters. A, simple tubular gland without any hair ; _B, compound gland, which has a common opening, with a hair- sac : a, glandular epithelium, connected with 6, the stratum Malpighii of the epidermis c, contents of the glands, sebaceous cells, and free fat; d, the separate racemes of the compound gland ; e, hair-sacs (root-sheath), with the hair, /. FIG. 85. A large gland from the nose, with a little hair-sac opening into it ; magnified 50 diameters. The letters a-/ as in Fig. 84. 214 SPECIAL HISTOLOGY. each hair of the scalp; they are somewhat larger, 0-16-0-24 of a line in the hairs of the beard, and the longer hairs of the chest and axilla, in which situations several glands are usually disposed around the hair follicle ; the largest of all exist on the mons veneris, the labia majora, and the scrotum, where, at all events in the last-mentioned locality, they are found at the deepest boundary of the corium, and the glands, from four to eight being connected together, represent beautiful rosettes J-J -1 line broad. Attached to the sacs of the smaller coarse hairs, I find smaller sebaceous glands of 0-06-0-24 of a line, mostly in pairs; and also in the eyebrows, eyelids, and the hairs at the entrance of the nos- trils. The lanuginous hairs have generally larger glands, or aggrega- tions of glands of -1 of a line ; these are best displayed in the nose, the ear (concha, fossa scaplioidea\ the penis (anterior half), and the areola mammae, especially in the first of these situations, where the glands often attain a colossal size, and altogether peculiar forms (Fig. 85) ; the glands generally have a diameter of -*-J of a line on the caruncula lachrymalis, the lips, brow, thorax, and abdomen ; they are somewhat smaller, -*- J of a line, but almost always larger than in the hairs of the scalp, in the eyelids, cheeks, neck, back, and extremities. Of the glands which are not connected with hair-sacs, only a portion of those of the labia minora are of large size (0'14 0*5 of a line) and rosette-shaped, with an aperture of 0-083 of a line ; the others are for the most part simply tubular, and at most 0-12-0-16 of a line long, 0-04- 0-06 of a line broad. The glandular vesicles of the sebaceous glands are either round, or pyriform and flask-shaped, or even elongated or tubular. Their size varies exceedingly, from 0-060-16 of a line in length, 0-02-0-1 of a line in breadth, and is in the mean 0-04 of a line in the round ones ; 0-08 in length, and 0-03 of a line in breadth in the others. The excretory ducts also have very different dimensions, sometimes long, sometimes short, broad or narrow ; the principal excretory ducts measure in the nose and labia minora up to J of a line in length, y 5 -J of a line in breadth, and have an epithelium 0-015-0-03 of a line thick. The sebaceous glands on the glans penis, and on the inner lamella of the prepuce or " Tyson's glands," are very inconstant, occurring some- times only in a very small number, sometimes in hundreds. They are ordinary sebaceous glands, which are distinguished from those of other regions by their not being connected with hair-sacs, and by their open- ing independently on the surface of the skin. They may, generally, be perceived by the naked eye as small whitish points, which do not project above the skin ; and in sections of the skin treated with caustic soda or acetic acid, their peculiarities may be readily studied with the micro- scope. They appear to be sometimes tubular, at others, simply racemose ; the former present a round or pyriform follicle of 0-048-0-12 of a line in diameter, and a straight excretory duct of -^ of a line in length, and OF THE GLANDS OF THE SKIN. 215 Fig. 86. 0-024-0-035 of a line in breadth ; the latter have two to three, or at most five, terminal vesicles, and measure 0-080-18 of aline altogether. The apertures of both kinds of glands, \vhich have a diameter of 0-02-0-06 of a line, are easily seen. With re- gard to the position of the glands, I would remark that I have never failed in finding them, 10-50 and more, in number, on the inner la- mella of the prepuce, especially in the neighborhood of the frcenulum, and its anterior part ; while on the glans itself and its neck, they are sometimes totally absent, sometimes they occur on its anterior surface, and then generally in great numbers (up to 100). On the prepuce, the glands are for the most part racemose, in the penis more simple. Their contents exactly resemble those of the sebaceous glands, viz. cells containing fat, of which more will be said below. The sebaceous glands of the external sexual organs in the female, are found, generally in great numbers, on the inner and outer surface of the labia minor a, and some of them are as large as those belonging to the fine hairs on the labia majora, while some are smaller. I have never found sebaceous glands in the glans and inner -lamella of the prceputium clitoridis, although Burkhardt speaks of such in the corona clitoridis, but, in a few instances, I have met with them about the urethra and the entrance of the vagina. Resembling the sebaceous glands in all essential points, except their larger size, are the Meibomian glands in the eyelids, of which a more particular description will be given when we treat of the eye. According to E. H. Weber (Froriep, "Notiz.," Marz, 1849), the smegma prceputii of the Beaver, the " Castor" is not, in the main, a glandular secretion, since only a small portion of the pouch in which it is secreted is furnished with very simple, rounded, lenticular glandules, the largest measuring ^d of a line. The secretion, in individuals of both sexes, may rather be described as a laminated substance lining the entire " castor pouch," and consisting merely of epidermic cells and minute fatty globules. Leydig ("Zeitsch. f. w. Zool.," Bd. II., pp. 22, 31, et seq.), finds no glands at all in the " castor-pouch ;" and according FIG. 86. Two sebaceous glands; the larger, 1, from the inner lamella of the prepuce; the smaller, 2, from the glans penis: a, glandular epithelium continued into the stratum Malpighii of the skin; 6, c, contents of the gland, with scattered larger fat drops; g, horny layer of the epidermis, projecting somewhat into the duct. Magnified 50 diameters. 216 SPECIAL HISTOLOGY. Fig. 87. to him, the same is the case in the prseputial sac of the Weasel, whilst in the Rat and Mouse, the prepuce contains true sebaceous glands of a complicated structure. 74. The minute structure of the sebaceous glands may be described as follows : Each gland possesses an external delicate coat of connective tissue, continued from the hair-sac, or, in the case of free glands, from the corium, and containing masses of cells, which exhibit different con- ditions, according to the part of the gland. If we proceed from the excretory duct of one of them (Fig. 88 B\ we see, that not only the fibrous coat of the hair-sac, but a portion of its inner root-sheath, also, passes into the duct, and lines it with nucleated, rounded, or polygonal cells, disposed in several (two to six) layers. This cellular layer is con- tinued, becoming more and more delicate, into the remoter parts of the gland, and ultimately pene- trates into the proper glan- dular vesicles, clothing them with a single, rarely a double, layer. Internally to these f cells, which are distinguished by a greater or smaller number of fat granules from the epithelial cells above them, there immediately suc- ceed, in the glandular vesicles themselves, others (Fig. 8T B b) containing more fat ; and these finally pass into the innermost cells of the glandular vesicles, which are invariably larger (of 0-016-0-028 of a line) than the middle and outermost cells, are rounded or elongated in their form, and so filled with colorless fat that they might, not improperly, be termed sebaceous cells (Fig. 87 B). The fat contained in them appears either still to retain the form of dis- crete drops (55), as in the outer cells, or, as is indeed more frequently the case, under that of larger drops ; and in many cells there are but a few of them, or even only a single one, which quite fills the cell (d) ; in consequence of which these cells greatly resemble the fat-cells of the panniculus adiposus. If these innermost cells, which rarely exhibit any nucleus, are traced onward towards the excretory duct, nothing is FiG. 87. Jl, a glandular vesicle of a common sebaceous gland; magnified 250 diameters: a, epithelium sharply defined, but without any investing membrana propria, and passing continuously into the fat-cells, b (their contours are too indistinctly drawn), in the interior of the glandular tube. B, sebaceous cells from the glandular tube, and the cutaneous sebaceous matter; magnified 350 diameters: a, smaller nucleated cells, still more of an epithelial character, and containing but little fat; b, cells abounding in fat, without visible nucleus ; c, cell in which the fat is beginning to flow into one mass; d, cell with one fat-drop ; e,/, cells from which the fat has partially escaped. OF THE GLANDS OF THE SKIN. 217 more easy to observe than that similar cells, applied uninterruptedly one to the other, are continued into this also, i. e. into the canal lined by its epithelium ; then, entering the hair-sac, they occupy the space between the hair and the epidermis of the hair-sac, and are finally extruded. These cells are the sole sources of the cutaneous sebaceous matter, a substance which, when fresh and at the common temperature, is semi- fluid, but in the dead subject more consistent, like butter or soft cheese, whitish or whitish-yellow in color, sometimes viscid, at others friable. Its cells, in the fresh secretion, adhere together more or less closely, and are thence generally flattened and irregular in form ; their mem- brane is not recognizable, and their contents are quite homogeneous, and transparent, with a yellowish hue. If dilute alkalies, however, be added, they swell up after a short time into beautiful round or elongated vesicles, in which, in consequence of the penetration of the reagent, the fat divides into separate drops of various sizes, and into irregular masses ; at the same time the sebaceous matter becomes white, owing to the numerous minute fatty particles which are produced, and larger fat-drops are formed, probably in consequence of the solution of many cells. Besides that in the cells, the sebaceous matter also contains free fat, in larger or smaller quantity, and in some cases, perhaps, an exces- sively minute amount of a clear fluid. It appears, then, that the cutaneous sebaceous matter is a secretion, consisting, so to speak, only of formed elements, either cells containing fat alone, or cells together with drops of fat. These constituents are formed in the vesicular ends of the glands, in consequence of a produc- tion of cells, which, as in the epidermic tissues in general, proceeds en- tirely from the pre-existing cells, unaided by free cell-development, of which there is in this case no indication. By endogenous development round portions of contents, or by division, cells are continually produced at the bottom of the glandular vesicles. These are at first pale, and contain but few granules, like the epithelial cells from which they arise ; but as they are forced towards the interior by cells developed after them, they are very soon completely filled with moderately large, round, dark, fat-granules. They thus proceed towards the excretory ducts ; and the fat drops contained in them running more and more together, and the membranes themselves becoming rather more resistant, they eventually assume the form of the sebaceous cells above described. The free fatty matter in the sebaceous secretion is formed, in certain cases, by the solution of the cells whilst still in the interior of the glandular vesicles, for, in fact, in many glands, free fat, in smaller or larger, often very considerable drops (Fig. 86 B\ is met with, even in the terminal vesicles ; however, it is also, perhaps, produced in consequence of its draining from closed cells, a supposition which is not a little strengthened by the circumstance, that the fat-containing cells in the excreted seba- 218 SPECIAL HISTOLOGY. ceous matter are seldom filled to distension, but appear for the most part variously flattened, or even corrugated, and contain only a small quantity of fat. Understood in this way, the formation of the cutaneous sebaceous matter resembles in many respects that of the cuticle. The young, easily soluble cells at the bottom of the glandular follicles may be compared to the Malpighian cells of the epidermis, and the less soluble ones of the secretion filled with fat, to the horny plates, which seems the more appropriate, if we consider, 1, that the deep layer of the epidermis of the hair-sac is continued into the ducts of the glands, and even the outermost cells of the terminal vesicles; and 2, that the epidermis, in some situations being constantly detached, form secretions (I refer to the smegma iwceputii of the penis and clitoris), substances which are, more- over, to all appearance chemically allied to the sebaceous secretion ; for the latter, it may be remarked, according to an analysis of the contents of a distended gland by Esenbeck (Gmelin's " Handbuch der Chemie," Bd. ii.), contains principally, fat, 24-2 ; albumen and casein, 24*2 ; ex- tractive matters, 24 ; and phosphate of lime, 20 per cent. ; substances which are found, at all events in part, in the smegma. Of nerves, I have seen no indication in the sebaceous glands, nor of vessels distributed upon and between their lobules ; whilst numerous minute vessels and even capillaries, undoubtedly exist around the larger glands, most distinctly in the penis and scrotum, as well as in the ear. I would, moreover, refer to the smooth muscles described above, when speaking of the cutis, which are found in the neighborhood of the sebaceous glands, and whose contraction is, perhaps, not inoperative towards the emptying of their contents. 75. Development of the Sebaceous Grlands. The first formation of the sebaceous glands takes place at the end of the fourth and in the fifth month, and is intimately connected with that of the hair-sacs, since they make their appearance simultaneously with the hairs, or shortly after, as outgrowths of the hair-sacs ; whence they are not all formed at once, but those of the eyebrows, forehead, &c., first, those of the ex- tremities last. The mode of their development, more precisely described, is as follows : When the rudiments of the hair-sacs have attained a considerable development, and the first indication of the hair is visible in them (Fig. 75, A, B], there are perceptible, on their outer surface, small, indistinctly-bounded papillary processes (u, v), which consist of a cellular substance, solid throughout and continuous with the outer root- sheath, and of a delicate investment, which is continuous with that of the hair-sac. These processes of the external root-sheaths of the hair-sacs, as they may properly be called, at first of 0-02-0-03 of a line in length, and 0-01-0-016 of a line in thickness, now begin to grow in proportion to the hair-sacs, become globular, and finally, while they extend them- OF THE GLANDS OF THE SKIN. 219 selves and incline obliquely towards the bottom of the sac, pyriform and flask-shaped. A formation of fat in the internal cells now com- mences (Fig. 88, A\ which, beginning at the bottom of the pyriform pro- cesses, is continued, also, into their pedicles, and finally includes the cells of the outer root-sheath, until at last the fat cells reach as far as the canal of the hair-sac (Fig. 88, J9). The gland and its contents are Fig. 88. now complete, and it needs only that the cells at the bottom of the gland, or the glandular vesicles, should multiply, to force the sebaceous cells in the duct into the hair-sac, and fully to establish the secretion. The sebaceous glands, therefore, like the sudoriparous, are, at first, solid outgrowths of the Malpighian layer of the skin, for which an ex- ternal opening is not developed till afterwards, and the first cutaneous sebaceous matter is formed by a metamorphosis of the inner cells of the rudiment of the gland, while the space which these cells occupied be- comes the cavity of the gland, which, however, never appears empty, but is continually filled by successive generations of cells. The development of the glands, up to this point, proceeds pretty quickly. It may be stated generally, that so long as the hairs have not appeared externally, the rudiments of the glands are papillary, measure scarcely more than 0-03 of a line, and for the most part contain cells which are still quite pale ; after the hairs have made their appearance externally, we find larger pyriform rudiments with a thicker end, of 0-024-0-05 of a line, the cells of which are partly still pale, partly FIG. 88. To elucidate the development of the sebaceous glands in a six-months' fcetus : a, hair ; 6, inner root-sheath, here more closely resembling the horny layer of the epidermis ; c, outer root-sheath ; c?, rudiments of the sebaceous glands. A, flask-shaped rudiment of the gland, with fat developed in the central cells'; jB, larger rudiments; the development of fat has taken place also in their neck, and fatty cells have been excreted into the hair-sac, giving rise to the glandular cavity and the secretion. Magnified about 250 diameters. 220 SPECIAL HISTOLOGY. contain fat, and which now soon open into the hair-sac. In the fifth month, therefore, the secretion has already begun in many places, and in the sixth it is everywhere established. At the same time, however, it is to be observed that, together with the original glands, which occur, one or two together to each sac, in the sixth month, new rudiments are produced, which generally lie deeper, and taking on the same course as that which has been described, soon become secreting glands. The fatty cells of the newly-formed glands invariably contain many fat-globules, never a single large drop ; nuclei also occur in them, as in the pale cells which surround them. The further development of the sebaceous glands depends on the out- growth of the external fatless cells of the originally simple tubular gland, into solid processes, which by degrees become changed into glandular vesicles, in the same way as the first rudiments. By repeated budding of the primitive or secondary glandular vesicles, the larger clusters are formed, and from them the most complicated forms which are met with. The so-called glandular rosettes proceed, very often, from a single rudi- ment, which, growing rapidly, surrounds the hair-sac on all sides ; at other times, however, from two or more primary processes of the outer root-sheath. In the seven months' foetus, most of the glands are simple pedunculated follicles of 0-04-0-06 of a line in length, and 0-02-0-03 of a line in breadth, which are appended, singly or in pairs, to the hair- sacs ; in the ear alone, do four or five glands of the simplest kind sur- round a sac, and form rosettes of not more than 0*06 of a line in dia- meter ; in the nose, simple clusters of at most 0*1 of a line are presented. In the new-born infant, instead of the simple follicles, simple racemose- glands are found in all the above-mentioned situations, one, or more rarely two, to a sac 0-1-0-12 of a line in length, and only 0-04-0-06 of a line in breadth ; on the chest, the glands are rosette-like, also on the ear, temple, nose, nipple, labia majora, and scrotum, where they mea- sure 0-1, in the last four places even 0-4 of a line and more. From these data, it results, that after birth an increase in size takes place in most of the glands, and assuredly in the same manner as during the foetal period, a view which is favored by the occasional occurrence of pale, solid, glandular lobules, even in the adult ; certain glands arise only after birth, viz. those of the labia minora. Sebaceous glands also occur in abnormal localities ; thus Kohlrausch (Mull. "Arch.," 1843, p. 365), observed them in an ovarian cyst, and Von Barensprung (1. c., p. 104) in a subcutaneous cystic tumor of the brow ; in both places they were connected with hair-sacs, whence it may, perhaps, be concluded, that they are very frequently to be found in cysts which contain hair. In fact I met with very beautiful sebaceous glands, with a considerable amount of sebaceous matter, in the walls of OF THE GLANDS OF THE SKIN. 221 the cyst containing hair, mentioned above, from the lung (Mohr's case) ; Von Barensprung has, he believes, though rarely, observed a new de- velopment of sebaceous glands in cicatrices of some years' standing. When the hairs fall out, the sebaceous glands seem to disappear, at least I have repeatedly failed in finding them in bald places. Hyper- trophy* of the sebaceous glands takes place, according to E. H. Weber (Meckel's "Archiv," 1827, p. 207), in cutaneous cancer; ac- cording to Von Barensprung in akrothymion, or moist warts (1. c., p. 81), and in ncevus pilosus. The comedones also, among which I place Lichen pilaris, at least as Simon defines it (1. c., p. 334), are hair-sacs and sebaceous glands distended with sebaceous matter, which are especially frequent where the glands are distinguished by their large size, as on the nose, the lips, the chin, the ear, the areola, and the scrotum. They arise, either in consequence of the obstruc- tion of the apertures of the hair-sacs by impurities, or of the formation of a more viscid and consistent secretion ; and they contain, besides one or many hairs, which may also be wanting, fatty cells, like those of the normal cutaneous sebaceous matter, epidermic cells proceeding from the hair-sacs, free fat, often crystals of cholesterin and the Acarus folliculorum. Milium consists of small white spots on the eyelids, the root of the nose, the scrotum, and ear, which are formed, as Von Baren- sprung is certainly right in supposing, from the sebaceous glands also, by their distension alone, without the hair-sacs; in consequence of which, rounded prominences without any aperture are formed and raise up the skin : their secretion, similar to that of the comedones, may still frequently be pressed out through the hair-sacs. Finally, there can no longer be any doubt that the sebaceous cysts which lie in the corium itself (atheroma, steatoma, meliceris, and molluscum\ must also be re- garded as colossal hair-sacs with sebaceous glands. Further details may be found in the works cited. With respect to a little parasite, the Acarus folliculorum^ which resides in healthy and distended hair-sacs and sebaceous glands, I must refer to G. Simon (1. c., p. 287). In the case of Iclithyosis congenita above referred to, Dr. H. Muller and I found the excretory ducts of the sebaceous glands in the epidermis everywhere dilated to 0-02-0-06 of a line, with saccular diverticula, often lying many together one behind another, of 0-04-0-12 of a line, and quite full of sebaceous matter. Here and there a hair was found in one of these ducts, so that it appeared at the same time to be a hair-sac. In investigating the sebaceous glands, they should either be prepared from within, by cutting them with the hair-sacs which belong to them from the cutis, or perpendicular sections, not too fine, may be made. * [These glands, when hypertrophied, frequently lose their glandular structure, and are changed into yellowish granular masses. DaC.] 222 SPECIAL HISTOLOGY. The minuter structure may be best studied, at first in the glands of the scrotum and penis, or labia minora, as these can be isolated without any trouble ; to which end acetic acid, which renders the surrounding parts transparent, is very serviceable. With the others, so far as form, posi- tion, and size, are concerned, the use of alkalies, especially of caustic soda, is most advisable, inasmuch as they clear all the other parts, while they act but little on the glands on account of the quantity of fat they contain. If it be desired to study, not so much the investments, as the cells of the glands, obtaining at the same time a view of their whole figure, there is no plan better than maceration ; the hairs with their root-sheaths, and the cellular masses of the sebaceous glands, epithelium and contents, may then be drawn out altogether. Where the epidermis is thin (on the scrotum, labia majora, glans penis), the same end may be attained in a short time by the dropping on it concentrated acetic acid, and also by using caustic soda in the same manner, though with greater destruction of the glandular cells. To study development, the maceration of foetal skin, and the rendering it transparent by acetic acid, are of great use. The fat-cells in the interior of the glands are isolated with great ease by teasing out a large gland, and the secretion may be examined without addition, and also with water and caustic soda. Literature. Compare the works cited above under the head of " Skin," by Gurlt, p. 409 ; Krause, p. 126 ; G. Simon, p. 9 ; Valentin, p. 758 ; the " Essay on the Hairs," by Eschricht, which has been mentioned; then the general works by Henle, p. 899 ; Todd and Bowman, p. 424, fig. 92 ; Hassall (pi. liv. should be liii.), p. 401 ; Bruns, p. 349 ; Gerber, p. 75, figs. 40, 42, 43, 44, 45, 239 ; Arnold, part II., the figures of Wagner, "Icon. Phys.," tab. xvi., fig. 11, c; Arnold, "Icon. Anatom.," Ease. II., tab. xi., fig. 10, and Berres, tab. xxiv., besides that G. Simon, " Ueber die sogenannten Tyson'schen Dru'sen an der Eichel des mann- lichen Gliedes," in Muller's " Archiv," 1844, p. 1. OF THE MUSCULAR SYSTEM. 76. To this system belong all the transversely striped muscles, which, together with their accessory appendages, the tendons and fasciae, serve for the movements of the skeleton, of the proper organs of sense, and of the integuments. These muscles constitute a system situated between the integuments and the bones, and between the bones themselves, the individual parts of which are so associated and united by common membranes, that they may conveniently be regarded as a whole. 77. The proper elements of the muscles in question, visible even to THE MUSCULAR SYSTEM. 223 Fig. 89. the naked eye, the transversely striated (animal or voluntary) muscular fibres, or primitive fasciculi, are distinguished, especially by their size and the distinctness of their individual parts, from those of most of the striped muscles occurring in other situations (heart, large venous trunks, pharynx, oesophagus, larynx, urethra). With respect to this latter characteristic, it is to be remarked that the sheath of the primitive fasciculus, or the sarcolemma,* in every fasciculus without exception, especially on the addition of water, acetic acid, and alkalies, may at once be recognized as a perfectly structureless, transparent, elastic, smooth membrane, which in man, as in the mam- malia, is distinguished by its delicacy from the same tissue in the lower Vertebrata, and particularly in the naked Amphibia. The muscular or primitive fibrils may, though not without difficulty, be isolated, especially in muscles that have undergone slight maceration, or have been boiled, or immersed in alcohol or chromic acid. In general they are vari- cose, that is to say, present more or less distinct enlargements, at intervals of O'0004-O'OOl of a line ; in consequence of which arrangement, and owing to the circumstance that the thicker and thinner spaces, throughout the entire thickness of the fasciculus, are placed regularly on the same level, the latter for the most part appears to be marked with delicate trans- verse bands. Occasionally, moreover, in addition, a fine parallel striation is evident, or, more rarely, where the enlargements on the fibrils are less appa- rent or quite imperceptible, simply a longitudinal striation. In adults, the fibrils do not enclose any central space or canal (Jacquemin, Skey, Valentin), but, with the addition of a small quantity of a connecting interstitial substance, constitute perfectly compact fasciculi (Fig. 90). On the inner side of the sarcolemma^ FIG. 89. Primitive fibrils from a primitive fasciculus of the Axolotl (Siredon pisciformis) ; magnified 600 diameters : a, a small fascicular composed of them ; 6, an isolated fibril. * [It is greatly to be doubted whether the universality of the occurrence of this structure should be so strongly affirmed. We have been unable to detect it either in the muscular bundles of the heart, or in the great majority of those of the tongue, or in any of the muscles of a seven-months' foetus. In fact, the question of the existence of a sarcolemma as an independent structure very much resembles that of the existence of " fibrils." The sarco- lemma must be considered merely as the outer portion of the transparent, homogeneous matrix, in which the " sarcous elements" are imbedded (vide infra)] and the possibility of raising it up by artificial means, or of observing its optical expression, as a distinct structure, will depend upon the amount to which it is developed relatively to the various elements, and the extent of chemical differentiation which has gone on it as compared with the rest of the matrix. TRS.] 224 SPECIAL HISTOLOGY. numerous nuclei always exist, of a lenticular or fusiform shape, fre- quently with nucleoli) and from 0-003-0-005 of a line long. These nuclei are not placed with any regularity ; sometimes two or more at the same level, or in rows, or alternately one behind the other. Fatty, or yellowish pigment-granules, also, frequently occur around the nuclei and between the fibrils, chiefly, however, in muscular fibres which are not in a perfectly normal condition. The form of the muscular fasciculi is rounded-polygonal. In thick- ness they vary from 0-005-0-03 of a line, or more. In the trunk and extremities they are invariably thicker (0-016-0-03 of a line) than on the head, in which situation, especially in the facial muscles, they are Fig. 90. Fig. 91. distinguished by the smallness of their fibres (0-005-0-016 of a line) ; but, with respect to this, it is to be remarked that great differences not unfrequently exist in one and the same muscle. From all that is known, it would appear that there is no absolute difference in the size of the muscular fibre in man and in woman, or between weak and robust indi- viduals. On the other hand, it is not improbable that in one case one extreme, and in a second the other, may prevail. The thickness of the primitive fibrils, in man, amounts on the average to 0*0005 of a line; their number, in one of the larger fasciculi, must reach several hundreds, but is not accurately known. The distance between the transverse striae varies usually from 0-0004 to 0-001 of a line. Various controversial opinions still prevail with respect to the consti- tution of the muscular fibres. Several authors assert, or at all events consider it probable, that the primitive fibrils are produced artificially. FiG. 90. Transverse section of some muscular fibres or primitive fasciculi from the gastrocnemius of man ; magnified 300 diameters : a, sarcolemma and interstitial connective tissue ; ft, transverse section of the muscular fibrils, with the interstitial substance. FIG. 91. Portion of a muscular fibre of man. treated with acetic acid, magnified 450 diameters: a, sarcolemma; ft, a simple nucleus; c, double nucleus, surrounded with fatty molecules. THE MUSCULAR SYSTEM. 225 Fig. 92. This is the opinion entertained by Remak, who thinks a pre-existing division of the muscular cylinder still problematical ; of Briicke, who appears to regard the contents of the muscle-tubes during life as fluid ; of Du Bois-Reymond, and, above all, of Bowman. According to the latter, a division of the muscular fibres into " discs" (Fig. 92) is quite as natural, although not so frequent, as that into fibrils, and that they may be considered as columns composed of such discs, quite as correctly as bundles of fibrils. Were a muscular fibre completely divided in the direc- tion of both the transverse and longitudinal striae, rounded, angular, minute particles would be produced, which may be termed primitive particles, or " sarcous elements," In the fibre, these elementary particles are connected in both directions, the same particles in the one case constituting a "disc," and in the other a seg- ment or joint of the fibrils. The division into discs, upon which Bowman lays especial stress, would in my opinion have been of importance had it occurred as fre- quently as that into fibrils, and also, occasionally, in recent muscle ; but it is not so, for, in the first place, nothing of the sort can ever be seen in recent muscles of man and the higher animals ; and in the second place, even in mace- rated or otherwise manipulated fasciculi, the breaking up into discs is an extremely rare phenomenon ; whilst, on the other hand, the isolation and exhibition of the fibrils may be obtained, in almost every instance, by any one at all conversant with the subject. Moreover, in transverse sections of perfectly fresh living muscles, as, for instance, of the thigh of a Frog, made by means of the double-bladed knife, the transverse section of the fibrils is just as evident and distinct as in dried muscles, whilst, in precisely similar longitudinal sections, not a trace of the "discs" can be detected. This fact at once sets aside all those views, according to which the muscular fibres, during life, consist of a homo- geneous, solid, or fluid substance, or of minute particles, connected in two directions. To Bowman's opinion, moreover, is opposed the fact that his assumed "elementary particles," except in macerated muscles, where such a thing readily occurs, can only with difficulty be obtained in an isolated form, whilst, according to his view, such a disintegration, in cases where these particles do not cohere firmly, either in a longitu- dinal or transverse direction, would necessarily take place with equal FIG. 92. Jl, a primitive fasciculus, separating transversely into discs; magnified 350 diameters. It exhibits distinct transverse and fainter longitudinal striae. The discs, of which one more highly magnified is seen at B, are granular, and consist of the primitive particles (parcous elements) of Bowman, or segments of the fibrils according to other authors (after Bowman). 15 226 SPECIAL HISTOLOGY. Fig. 93. facility in either ; and in the second place, that, in the thoracic muscles of insects, the individual fibrils may be very distinctly and beautifully seen (Fig. 93) in the muscles, when quite fresh. When we consider the great similarity between the muscles of insects and of the higher animals, in every essential particular, this fact appears to me to be of a striking nature. I am, therefore, from this and the other reasons assigned, thoroughly convinced of the existence of fibrils during life, and believe that, where they do not so readily admit of being isolated, as in man and many animals, they are connected by a homogeneous, tenacious (albu- minous), interstitial substance, which is very evident in a transverse section, and in fact so firmly, that, under certain circumstances, transverse rupture of the fasciculi may take place, that is to say, in the direction of the thinner spaces of the fibrils ; as also occurs in other fibres ; for instance, in the elastic tissue, smooth muscles, and even in the corneous cells (internal root-sheath and cortex of the hair). With all this, it must not be sup- posed that fibrils exist in all muscular fibres of animals, either themselves striped or corresponding to the striped fibres here described. The study of development and of comparative anatomy much rather teaches that the muscular fibre occurs in various conditions, and, particularly, that it frequently exhibits more homogeneous contents, with or without transverse striation, and without fibrils. This, however, of course, affords no ground for the assumption of such a condition in man and the mammalia also ; and although such muscular fibres, in certain animals, readily break up into transverse segments (Leydig), still, it is not thereby proved that in the higher animals a similar division of the contents is to be regarded as natural, and that into fibrils as artificially produced. The diameter of the primitive fasciculi varies, not inconsiderably, in different muscles, or in one and the same muscle. Henle (who is fol- lowed by Gerlach), at an earlier period, assigned to them a diameter of 0-005-0-006, and at most of 0-017 of a line; but more lately (Stadelmann, " Sectiones transversse"), has declared that these measure- ments are not universally correct. I will here give some particulars upon which the measurements stated above, in the text, are founded. In a female, the fasciculi of the sacro-lumbalis measured '016 '028, the majority 0-020-0-022 of a line; in the pectoralis major, 0-01-0-03, most of them 0-02 of a line; deltoid, 0-016-0-026, the majority 0-02- 0-022 of a line; in the masseter, 0-006-0-02, the majority 0-01-0-018 FIG. 93. Primitive fibres from a quite recent transverseJy-striated muscle of a Bug; magnified 350 diameters. THE MUSCULAR SYSTEM. 227 of a line ; in the retrahens auricula?, 0-006-0-015, the greater part 0-008- 0-01 of a line. In a male, their diameter in the pectoralis amounted to 0-018-0-28 of a line, the greater number measuring 0-02-0-022 of a line ; in the deltoid, 0-012-0-024 for the largest, and for the smaller 0-016-0-02 of a line ; in the olliquus abdominis externus, 0-16-0*024 and 0-016-0-02 of a line; in the orbicularis oris, 0-008-0-016 and 0-01- 0-012 of a line ; in the/rcwteZw, 0-006-0-014 and 0-008-0-01 of a line. In a second individual, the pectoralis major contained fibres of 0-0068 0-024, most of them 0-018-0-02 of a line; the pyramidalis, some of 0-01-0-028, the majority 0-02 of a line. With respect to the nature of the primitive fibrils, much still remains to be cleared up. In general they must be regarded as solid ; and, in fact, there is nothing to indicate the existence of a cavity in them. It is fully ascertained that it is to them that the transverse striation of the primitive fasciculus is due. It is still doubtful, however, whence the appearance of transverse striation in the fibrils themselves arises; whether from their being spirally twisted (Arnold), from zigzag curva- tures (Will), or from varicosities. All that I have seen leads me to adopt the latter view, which is also that most generally entertained. I do not deny that, in the examination of numerous fibrils, appearances are occasionally met with, favorable to the other two views, and parti- cularly to that of Will ; but it is much more usual to find simple nodular enlargements. The large fibrils in the perennibranchiate Amphibia (Siren, Proteus, Menopoma), (Fig. 89), are above all others adapted for this investigation. In these animals, when they have been preserved in spirit, the fibrils become isolated in considerable numbers, and may be examined on all sides. It is the same with the muscles of the thorax in Insects. Quite lately Dr. Barry has propounded the view that each muscular fibril is constituted of two spirally convoluted filaments running in the same direction. I have seen nothing of the kind, and do not hesitate to describe the whole of Dr. Barry's exposition as nothing but a myth, and his figures as fantastical images. As regards the notion adopted by Bowman, Dobie, and others, that the fibrils &re constituted of still more minute particles (sarcous ele- ments), it may perhaps be stated, as the study of development shows, that the fibrils do, in fact, at first appear to consist of separate particles. But the question is whether in the adult such elementary particles con-* tinue to be evident, and this, at present, I am inclined to deny. The nuclei of the muscular fibres, in man, are situated, as I agree with Schwann in stating, only on the inner surface of the sarcolemma, and not within the fibrils ; that they are not placed externally on the fasciculi, as was formerly stated by Henle and Stadelmann, and more lately by Gerlach, is readily perceived, when the muscles are treated 228 SPECIAL HISTOLOGY. with alkalies. Under these circumstances the partially-swollen nuclei escape, together with the fibrils, in a state of solution, from the sheaths, which remain behind, and before they are dissolved may be easily exa- mined in an isolated state. In many muscles, even when there are no granules between the fibrils, larger or smaller fatty molecules occur around the nuclei.* * [With regard to the vexed question of the ultimate structure of striped muscle, we ques- tion if any real improvements have been made upon the description originally given by Mr. Bowman (" Phil. Trans.," 1840), viz., that it consists of minute, dark, subangular particles, the "sarcous elements," imbedded in a more transparent connecting substance or matrix; that neither discs nor fibrils can be said to exist in the normal state, the breaking up of the muscular bundle into either of these elements, resulting simply from the manner in which the lines of greatest cohesion are disposed, at the time when mechanical violence is applied to it. The assertion in the text that the fresh muscle of man and the mammalia does not break up into discs, is decidedly erroneous as we have seen it occur repeatedly. Nor can we grant the invisibility of the discs in longitudinal sections of muscle : what may be the case in such sections made with the double knife, we do not know, but in those accidental longitudinal fractures of the muscular bundles of man, mammals, and insects, which constantly occur, the edges of the discs are most distinct. Again, without making any section at all, the discs may, especially in insects, be traced, by altering the focus of the microscope, through the entire thickness of the bundles. The argument in the text, in fact, proves too much ; for if the fibrils are visible over the whole transverse section, their dark parts (discs) alternating with the light ones, must be as visible in a section, made in any longitudinal plane, as they are on the surface. However, that the appearance of discs should be absent in any longitudinal section of striped muscle is, to us, simply incomprehensible. With regard to the thoracic muscles of insects, it is to be observed, in the first place, that they do not represent ultimate fibrils, but non-fibrillatcd primitive bundles. Dr. Auber, in a valu- able paper in " Siebold and Kolliker's Zeitschrift" (H. 3 and 4, 1853), has already shown that there is no defined line of demarcation to be drawn between these and the ordinary muscles of insects, the two forms passing into one another by the peculiar flat bundles of the Libellulidae, though he still considers the thoracic muscles to represent ultimate fibrils. His sole argument, however, is their resemblance to the ultimate fibrils of the higher animals, which we think loses all force, when we consider a fact that he has overlooked, namely, that the muscles of the legs, &c., present a very beautiful, though very delicate fibrillation the fibrils being not more than JJJ^Q^ Ffijjfjs^ 1 f an ^ nc ^ i n diameter; that is, not more than from one-third to one-sixth the diameter of the thoracic muscles. Examined carefully with a high power (600), with a good definition, the edges of the discs, which under a lower power appeared very sharp and even, are seen to be distinctly granular, and to be composed of minute, somewhat fusiform or rounded particles, not more than ^oAuu tn ^ an inch in diameter, distinct from one another, and imbedded in the general transparent matrix, which is marked by fine longitudinal lines running between the rows of particles. Occa- sionally, the broad, dark discs appear to be separated by a delicate line, and this line, if carefully examined, is found to be composed of similar, but far more minute and paler particles. How- ever, this appearance, though very common, is not to be met with in all the bundles. Acetic acid swells the muscle up, and renders the sarcous elements still more distinct, though the whole becomes very pale. If dilute ammonia be added to such a bundle, so as to neutralize the acid, it resumes its original dimensions, and almost its original appearance, except that the sarcous elements have often a wonderful sharpness of outline. The thoracic fibres, treated with acetic acid, become exceedingly pale, and the distance between the discs is much increased. The latter often assume a granular appearance, but not so distinctly as in the former case; nor have we been able to detect any fibrillation of the intermediate substance, nor any minute sarcous elements, in them. They share the former character, however, no less than the latter, with multitudes of unquestionable mus- cular bundles so that taking into consideration the existence of fibrils very much minuter THE MUSCULAR SYSTEM. 229 78. The muscular fibres in the trunk and extremities are, in general, so associated, without the existence of any divisions, reticular connec- tion, or termination in the interior of the muscles, as to constitute con- tiguous prismatic bundles extending the entire length of the muscle. than the thoracic fibres in the muscles of insects, and the gradual transition of the latter into undoubted bundles, we do not hesitate to regard these thoracic fibres as homologous, not with primitive fibrils, but with primitive bundles; and therefore to neglect any argument which may be drawn from their existence, to that of primitive fibrils during life in the higher animals. The answer to the question, whether primitive fibrils exist during life or not, in fact, de- pends very much upon the meaning of the words. If it be meant that the muscular bundle is like a rope, the fibrils being the separate strands, united by " a homogeneous, tenacious substance," we should say that nothing of the kind exists during life. If, on the other hand, it be meant only that the molecules of the muscle are so arranged as to break up more readily and more frequently in the longitudinal direction than any other (just as a bar of wrought iron would tear into longitudinal fibres rather than in any other way, though it could by no means be said that it was composed of longitudinal fibres), why, there can be no question that such is the fact. The behavior of a muscular fasciculus, under the alter- nate action of acetic acid and ammonia, is as instructive with regard to this point, as that of bundles of connective tissue. The existence of varicosities of the fibrils must depend very much upon their state of ex- tension. Normally, they do not exist, unless, perhaps, the fibril has been split off from the very edge of a bundle, where the sarcous elements often project strongly. When very much stretched again, since the sarcous elements are more solid and resisting than the matrix, they will form knots, and the fibrils will appear more or less varicose. The great majority of in- stances in which the fibrils appear varicose, however, depend on imperfect definition and the same may be said of supposed zigzag bendings; while the spiral fancies, on the other hand, are more probably connected with an imperfect judgment. Recently, Drs. Sharpey (" Quain's Elements") and Carpenter (" Manual of Physiology") have advocated a view, the former, however, with some doubts (to which Professor Kolliker does not refer), founded upon an examination of the preparations of muscular fibrils, made by Mr. Lealand. They distinguish quadrilateral dark spaces in the fibrillae, each of which is set, as it were, in a transparent frame of the same shape; these joined together constitute the fibril, the lines of junction of the frames, or "cells" being indicated by a dark line. We have repeatedly seen the appearances which are thus described; but so far as we have been able to discover, they invariably arise from that peculiar interposition of rows of mi- nute paler sarcous elements, between the ordinary broad dark ones, to which we have re- ferred above in describing the muscles of insects. Very often, the finer sarcous elements are completely wanting, as in the thoracic muscles of Insects, in the muscles of the Frog, and in many of the bundles in Mammals; and in these cases there is, of course, no evidence at all of the existence of any such "cells." In conclusion, we may state the view which we are led to take of the structure of striped muscle, in a few words. In a homogeneous, transparent matrix, definite particles are im- bedded the sarcous elements, which are arranged side by side, in even transverse rows. In some cases the sarcous elements are all of one size; in others, they are alternately larger and smaller. The reason of this difference does not at present appear, but'it is very pos- sibly connected with the nutrition of the muscle. The matrix usually tends to break up into longitudinal bands the " fibrils," which have the diameter either of a single sarcous element, or of some multiple thereof; it likewise tends to break up in the transverse direc- tion, giving way between the pairs of rows (discs) of sarcous elements ; but these cleavage lines are no indication of the existence of discs or fibrils, as such in the unaltered muscle. The sarcolernma is simply the outer portion of the matrix, and its demonstrability as a sepa- rate structure depends upon the extent to which it is developed, and the amount of chemical change which it may have undergone relatively to the inner portion. TBS.] 230 SPECIAL HISTOLOGY. These secondary muscular fasciculi, as they are termed, are, each of them, enclosed by a special envelop of connective tissue, and, several together, united by stronger membranes into tertiary fasciculi, which, lastly, in a greater or less number, unite and constitute the separate bellies of the muscle, or muscles themselves. If the muscular fasciculi are placed in the same plane, they constitute the membranous or flat muscles ; and when disposed in a thick bundle, the elongated or columnar muscles. The muscles consequently are aggregations of numerous, larger and smaller secondary and tertiary fasciculi, the sheaths or perimysium of which constitute a connected system, in which that por- tion which surrounds the en- tire muscle, as the perimy- sium externum or muscular sheath (vagina muscularis), is to be distinguished from the more internal elements immediately surrounding the larger and smaller fasciculi and the muscular fibres the perimysium internum. The thickness of the secondary fasciculi varies from J to i a line ; that of the tertiary and still larger bundles, which are most evident in muscles with coarse fibres (glutceus maximus, deltoideus], is so various, and the division of the muscle in these more remote constitu- ents is so arbitrary, that there is nothing specially to be said with re- spect to them. The muscular sheaths or envelops, perimysium, composed of con- nective tissue, which are for the double purpose of conveying the vessels and nerves of the muscles, and of connecting the muscular fibres and supporting them when in action, vary in thickness according to the greater or less size of the groups of fasciculi surrounded by them. They are always, however, delicate, dull-white, non-glistening tunics, consisting of common connective tissue, and minute, isolated or anasto- mosing elastic fibres, of at most O001 of a line in thickness^ the latter occurring in greater number, especially in the perimysium externum, which may, consequently, very properly and conveniently, be regarded as a semi-elastic membrane, and its function estimated in accordance with this structure. In all muscles, especially in those of a more lax construction, a certain number of adipose cells of the usual kind (fre- FiO. 94. Transverse section from the redus capitis anticus major of Man, magnified 350 diameters: a, external perimysium; 6, perimysium internum; c, primitive fasciculus and secondary muscular fasciculus. THE MUSCULAR SYSTEM. 231 quently containing beautiful fat-crystals) occur, and in fat persons they are found quite in the interior. [It was formerly supposed that the primitive muscular fasciculi ran in a perfectly straight direction towards their insertions, without dividing or anastomosing ; but this is not correct. Recent investigations, made partly alone, partly with the assistance of Dr. Corti, have demonstrated the anastomosis of the fasciculi of striped muscles in the hearts probably of all Mammalia. We observed anastomosing fasciculi in Man, in the Rabbit, Dog, Cat, Calf, Frog, Heron, andLeydig has seen them in the Ruff. In the Mammalia, and in Man, they are frequent, and extremely delicate, and the anastomosis occurs by means of short transverse or oblique branches extending between parallel fasciculi. In the larynx, oesophagus, pharynx, and the tongue of the Rabbit, nothing similar to this was met with, but we found in the tongue of the Frog, immediately under the mucous membrane (which is readily removed in boiled preparations), the most delicate divi- sions, although no anastomoses. Fasciculi of 0*03 of a line or more, could be observed to form, by successively dividing at acute angles, large bundles of fine branches (the finest, 0-0012 to 0-0016 of a line), which were inserted into the mucous membrane of the tongue between its glands. I have seen, also, in the lymph-heart of frogs, an anastomosis of the striped muscles similar to that occurring in the heart, and Dr. Leydig (Zeitschrift fur Wissenschaftliche Zoologie, Bd. I. Heft 2, 3), has observed anastomoses in the muscles of Paludina virspara, which genetically correspond to the striped muscles. In the muscles of the trunk and extremities in Man and in the Mammalia, I have never been able to discover even the trace of an anastomosis, although it occa- sionally appeared to me, as if some fasciculi before or at their connec- tion with tendons, divided within a short space two or three times. I have certainly seen this division in the tails of batrachian-larvse, where single fibres at their insertion into tendons separated into from three to five conical branches. (From Kolliker's Micr. Anat., 1. 1, p. 210.) DaC.] 79. Connection of the Muscles with other parts. The muscular fibres are connected with the movable parts, the bones, cartilages, arti- cular capsules, the skin, &c., partly in a direct manner, partly with the intervention of fibrous elements, the tendons, fascice, certain forms of muscular ligaments and membranes (lig. interossece, membrance, obtura- torice). Those muscles which are attached either wholly, or at one or the other end without the intervention of tendons, constitute on the whole the smaller number. Where the muscular fibres arise directly from bone (obliqut, iliacus, psoas, glutsei, &c.) and cartilage (transversus abdominis, diaphragm), or rest immediately upon those structures (ser- rati, omohyoideus, sterno-hyoideus, aural muscles), they never extend 232 SPECIAL HISTOLOGY. further than to the periosteum or pericliondrium, terminating abruptly on those membranes, with the fibres of which they are not, in any way, continuous, nor do they come into immediate contact with the bone or cartilage. Where the muscles extend to the skin, they either expand immediately beneath, and without any connection with it, or radiate in it, in the form of larger or smaller divergent fasciculi (facial muscles) ; in which case they appear to be inserted, at all events occasionally, at once into the filamentary processes of connective tissue.* But the pre- cise mode of connection of these tissues has not yet been ascertained. 80. The sinews, tendons, are brilliant, white or yellowish structures, composed almost entirely of connective tissue. They are subdivided, according to their figure, into the rounded, cord-like, true tendons, and into membranous aponeuroses (centrum tendineum, galea, tendons of the abdominal muscles, latissimus dor si, cucullaris, &c.). The two forms, either in their external configuration or internal constitution, do not admit of definite distinction ; they consist of connective tissue, which is characterized by the parallelism of its elementary fibres, its consistence, and its poverty in elastic filaments. The elements of the connective tissue, the fibrillce, may be readily perceived, in fresh tendon, to be, as they are everywhere, extremely minute. In the cord-like tendons, they are slightly wavy in their course, all perfectly uniform in size, parallel to the long axis of the tendon, and in the recent state so closely approximated, that the demonstration of the existence of primi- tive fasciculi is not easy. Such fasciculi, however, do exist, having a breadth of 0*006 0*008 of a line, and a rounded polygonal figure, as may be seen, especially in transverse sections of dried tendons, particu- larly on the addition of alkalies. But in the natural state they are so firmly united that they cannot be isolated. On the other hand, in true tendons, in the recent state, secondary and tertiary fasciculi are very evident (Fig. 95). Delicate dissepiments, in fact, of loose connective tissue, penetrate the substance of the tendon, * [The insertion of muscles without the intermediation of tendons, directly into the con- nective tissue of the skin and mucous membranes, is seen very beautifully in the tongue and in the facial muscles of Mammals. The former case has been well-described by Dr. Salter (Todd's " Cyclopaedia," article " Tongue") ; the latter may be examined with great ease in the levator labii superioris of the Rat. Here the muscular bundles run in the subcutaneous connective tissue, keeping a pretty even diameter until they nearly reach their insertions. They then divide into many branches, each of which either tapers off to a conical extremity, or divides into a number of delicate pointed processes. In either case, the ends of the mus- cular fibre gradually or suddenly lose their striation, and pass directly into the irregular nucleated bands of the connective tissue. No sarcolemma can be demonstrated in the branched ends of the muscles, and the bands of the connective tissue are directly continuous with the matrix of the muscle; the change, from the one to the other, being evidenced merely by the appearance of the sarcous elements. Nothing can afford a more complete proof of the homology between the pseudo-fibril lated tissue of muscle and that of connective tissue, than what we find here. TRS.] THE MUSCULAR SYSTEM. 233 Fig. 95. and by their mutual connection form a continuous system of parallel tubes, thus dividing the tendinous fibrils or primitive fasciculi into numerous larger or smaller groups. Secondary fasciculi, mostly of a polygonal, or per- haps rounded or elongated figure, and having a diameter of 0-03-0-06 of a line, may be very readily distinguished ; and tertiary fasciculi, with poly- gonal contours, of 0-1-0-05 of a line, and more in diameter, and bounded by rather stronger dissepiments ; there are, also, generally apparent, still larger subdivisions, composed of nume- rous tertiary fasciculi, and which, being closely united in very various numbers and groups, by a common envelop of lax connective tissue, constitute the tendon itself. The aponeuroses are constituted either in the same way as the true tendons, and consist of several layers of parallel, secondary fasciculi, disposed contiguously in the same plane, or more resemble the fibrous membranes, and present primary and secondary fasciculi decussating in two or more directions (abdominal muscles, diaphragm). Fine elastic fibres (the so-termed nuclear fibres) occur in the secondary fasciculi of all tendons, in various conditions of development : sometimes as a series of slender fusiform cells connected by delicate processes ; sometimes as fully-formed fibres of uniform thickness, or as isolated fusiform cells. The arrangement of these elastic elements is uniform throughout, and they run at regular distances, parallel to, and among the fasciculi of connective tissue. - Consequently, in the transverse section of a tendon, the dark ends of the elastic fibres are apparent, distributed, at constant distances of 0-007-0-008 of a line apart, over the whole section. But, besides these stronger elastic filaments, mea- suring from 0-0005 0-001 of a line, there exist in most, perhaps in all tendons, extremely delicate fibrils of 0-0002-0-0004 of a line, connecting the former in various directions, so that in reality there is, in every ten- don, an elastic network, penetrating and entwining the fasciculi of con- FIG. 95. Transverse section of a tendon of the calf, magnified 20 diameters: a, secondary fasciculus; 6, tertiary ; c, nuclear fibres not quite in transverse section, but appearing as little streaks in the former ; d, interstitial connective tissue. 234 SPECIAL HISTOLOGY. nective tissue. These fibrils may also be distinguished on a transverse section, as minute dark points, or as lines radiating from the coarser points exhibited in the section (Fig. 96) ; and they are still more evident in longitudinal sections, in which, more especially, the whole of the fibrous system just described comes very readily into view. In such sections, also, it is evident that, in every case in which the formative cells of which the fibres are constituted still retain a certain degree of independence, very distinct elongated nu- clei exist in them. Besides these elastic fibres, the tendons, in certain situations, contain cartilage-cells (vid. infra), as well as common fat-cells, particu- larly in the more lax tendons, as in the tendinous fibres of the in- tercostal muscles, of the triangularis sterni, masseter, &c. The transversely banded aspect of the tendons, to which their glisten- ing appearance is due, depends simply upon the numerous curves of their fibrils, which correspond with each other throughout the fasciculus ; this appearance is destroyed when the tendon is forcibly stretched, and merely indicates its innate elasticity, which comes into play in the relaxed condition. The primary tendinous fasciculi, according to Bonders and Mole- schott, are seen in transverse sections treated with potass. This reagent, according to them, separates the secondary fasciculi into smaller ones, each of which consists of from 5 to 10 primitive fasciculi. In moistened transverse sections of dried tendon of man and the mammalia, I can very distinctly recognize the primitive fasciculi, although they have extremely delicate outlines. The appearance thus obtained affords an indistinct image of that presented in a transverse section of muscle. Even the very fibrils are, in this way, rendered distinct, a circumstance which appears to me of the greatest importance. When a transverse, not a longitudinal, section of tendon moistened with water or acetic acid is examined, there will be observed in all the secondary fasciculi, or in the primary when they can be distinguished, if not in all, yet in most cases, an extremely regular and minute punctation, nearly like that of the muscular fasciculi (Fig. 90), only not quite so distinct. The appa- rent granules are pale, round, of the same diameter as the tendinous fibrils which are obtained in other ways, and can be explained in no other manner than as being the transverse sections of such fibrils. FIG. 96. Tendon of the tibialis posticus (Man), magnified 60 diameters: a, secondary fas- ciculi ; 6, thicker nuclear fibres ; c, interstitial connective tissue. THE MUSCULAR SYSTEM. 235 These facts, better than any other, contradict Reichert's view, according to which the tendinous tissue is composed of a homogeneous substance. ( Vid. 24, note.) 81. Connections of the Tendons with other parts. The tendons are connected on the one side with the muscles, and on the other with the various parts moved by the muscles. Even by the naked eye, it may be seen that the former connection is effected in the one case in such a way that the tendon and muscle are continued into each other recti- linearly, and in the other so that the muscular fibres, with rounded extremities, join the borders and surfaces of the tendons and aponeuroses at an acute angle, as in the instance of the penniform muscles. The microscopic conditions in these two cases are widely different. In the former, the muscular fasciculi pass immediately into those of the tendon, in such a way that no sharply-defined limit exists between the two tissues, Fig. 97. and the entire fasciculus of muscular fibrils is con- tinuous with a nearly equal-sized bundle of tendinous fibrils (Fig. 97). Extraordinary as it may sound, I must say in order to describe the impression that this sort of conjunction of muscle and tendon gives me that it is that of a continuous connection of the muscular and tendinous fibrils. Where the muscular fasciculi join the tendons and aponeuroses at an acute angle, we find, in complete contrast with the condition just described, an abrupt limit between the muscle and tendon (Fig. 98). For, in this case, the fibres of the muscle really end, for the most part, obliquely truncated, with a slightly conical projecting terminal FIG. 97. A primitive fasciculus : a, from one of the internal intercostal muscles of Man, continuous into a tendinous fasciculus, 6, into which it passes without any defined limit. Magnified 350 diameters. FIG. 98. Disposition of the muscular fibres at their oblique insertion into the tendon of the gastrocnemius (Man): a, a portion of the tendon cut longitudinally; 6, muscular fibres with slightly conical or truncated extremities, affixed in small depressions on the inner aspect of the tendon, to the border of which the perimysium internum, c, is connected. Mag- nified 350 diameters. 236 SPECIAL HISTOLOGY. surface, or, more rarely, perceptibly attenuated, though always rounded, and are attached at a more or less acute angle to the surfaces of the tendons and aponeuroses, and on the borders of the former. Notwith- standing this, however, the connection between the two tissues is of the most intimate kind. The extremities of the primitive fasciculi are in- serted into minute pits in the surface of the tendon, whilst, at the same time, the connective tissue between them, the perimysium internum, is continuous with that on the surface of the tendon. These relations are best observed in muscles which have lain a long time in spirit, or been boiled ; in which, also, the sacciform blind extremity of the sarcolemma may occasionally be clearly seen. The last-described condition occurs whenever muscular fibres and tendons meet obliquely, consequently in all semiperiniform and penniform muscles ; in those whose tendons of inser- tion commence as membranous expansions (soleus, gastrocnemius, &c.), and which arise from the surfaces of fasciae, bones, and cartilages. Where, on the other hand, aponeuroses or tendons, with their elemen- tary tissues, join muscles in a straight line, a real transition, for the most part, takes place between the tendinous fasciculi and muscular fibres, but not always, for, even in such apparently rectilinear transition of muscles into tendons, there is frequently an oblique insertion of the former, with free extremities, though at very acute angles ; in such cases, for instance, as where tendons penetrate deeply into the substance of a muscle, and there divide into separate fasciculi. From what I have hitherto observed, there are many muscles in which all the fasciculi connected with tendons begin or terminate free, and indeed scarcely one in which this is not the case, with a greater or less number of fas- ciculi ; whence it may be deduced, as a general rule, that the tendons have for the most part a less diameter than the muscles. Besides muscles, tendons are connected with bones, cartilages, fibrous membranes (sclerotica, sheath of the optic nerve, tendinous fasciae), ligaments, and synovial membranes (subcruralis, &c.). With the first- named textures, the connection is either indirect, with the intervention of the periosteum and perichondrium, into the similarly constituted elements of which the tendinous fibres, for the most part, are continuous, or to the thickness of which they appear to add or direct. In the latter case (tendo Achillis, tendons of the quadriceps, pectoralis major, del- toideus, latissimus dor si, ilio-psoas, glutcei, &c.), the tendinous fasciculi rest, at an acute or right angle, on the surface of the bones, and become attached, without the intervention of the periosteum, which is wholly wanting in these situations, to all the elevations and depressions of the surface (Fig. 99). Close to the bones, the tendons frequently contain, throughout a certain extent, delicate, isolated cartilage cells, which are sometimes, however, contiguous and disposed in small rows. In exceptional cases, I have also seen the tendinous fibrils, at their extre- THE MUSCULAR SYSTEM. 23T mities next the bctae, entirely incrusted with calcareous salts, in the form of granules (ossified). In fibrous membranes, the tendons cease Fig. 99. quite imperceptibly, and without any interruption of continuity (tensor fascice, biceps humeri). In man, I must positively deny that the tendinous fasciculi are ever connected merely with the sarcolemma (Reichert). Nor could I satisfy myself that this is the case in the River-crab, in which the tendons, it may be remarked, consist of chitine. Whilst other animals have afforded indubitable evidence of the existence of the same conditions as in man, the Frog, in particular, presents evidence of this fact ; in the tadpole of which, owing to the sparing development of pigment in the tail, the transition of the extremities of the muscular fibres, which are frequently divided into three and five serrations, into the same number of minute tendons, may be very distinctly seen. In the caudal muscles, also, of the Cod, I noticed, very distinctly, the continuous connection of the tendons and muscles ; in this case, owing to the shortness of the muscles, many muscular fibres were even seen in their entire length, together with the tendinous fasciculi at each end.* FIG. 99. Insertion of the tendo JLchillis into the calcaneum of a Man sixty years old : #, bone with lacunse, a; canalli and fat-cells, 6; J3, tendon with tendinous fibrils and cartilage cells, c. Magnified 300 diameters. * [There can be no doubt that both the modes of connection between muscles and their tendons, described above, exist. Is it not possible that the gradual transition or the sharp 238 SPECIAL HISTOLOGY. 82. Accessory organs of the Muscles and Tendons. A. The mus- cular envelops or fascia? are fibrous membranes surrounding single muscles or entire groups of muscles, together with their tendons. They differ in structure according to the degree in which they partake of the character of tendons and ligaments, or of simple muscular sheaths; in the one case presenting that of tendons, and in the other of membranes composed of connective tissue and elastic fibres. In the former case they 'are white and glistening, and exhibit, in all respects, the structure of tendons and aponeuroses ; in the latter they frequently contain a larger quantity of fine elastic fibres in their connective tissue, and in some places may even assume the structure and dull-yellow aspect of the elastic membranes (via 1 . Fig. 49), and contain a close elastic network of the strongest kind. The fascia? are always of the tendinous character, where for some mechanical purpose a tough unyielding structure is requisite. They are of this kind, therefore: 1. At their origin from bones. 2. Where muscles arise from them, and they are of the nature of aponeuroses. 3. Where tendons radiate into them, and they them- selves act as terminal tendons. 4. Where thickened portions of them supply the place of ligaments. On the other hand, they are more or less elastic where they constitute a firm envelop to the muscles, but, at the same time, one which does not impede their changes in form. This is their character, especially in the middle of the limbs. [The membranes interosseoe (forearm, leg, foramen ovale\ which are not usually reckoned among the fasciae, are not apparently of the nature of ligaments of the bones, but rather of intermuscular ligaments. The plantar and palmar aponeuroses serve, in part, as tendons for the smaller muscles of the hand and foot, but chiefly as ligaments for the retention of the flexor tendons, in which respect they are analogous to the lig. cruci- atum carpi dorsale, &c. In them, even in the adult, the entire course of development of the nuclear fibres (minute elastic fibres), may be studied. Between the fasciculi of connective tissue, straight series of 10 to 20 and more, thickly placed, elliptical cells of 0-006 to 0-012 of aline, with round line of demarcation between the muscle and its tendon may have some connection with the age and completeness of the particular bundle examined? In the Frog, we have noticed that, among neighboring bundles, some exhibit transitions between the proper muscular tissue and the tendon, while others have the former very sharply defined ; and the exami- nation of the insertion of the triceps extensor cubiti of a seven-months' foetus has afforded us the most evident transitions from tendon into muscle, although the insertion of the bundles is here very oblique. The best way of expressing the mode of connection of muscles with their tendons, perhaps, would be to say that the matrix of the muscle and the matrix of the connective tissue, into which it is inserted, whether in the form of tendon or otherwise, are invariably continuous; the appearance of continuity or of discontinuity of the two tissues, arising solely from the sudden or gradual cessation of the deposit of the sarcous elements at their point of junction. The nature of the corpuscles which are to be found at the junction of tendons with bones and cartilages Professor Kolliker's "cartilage-corpuscles" has been adverted to in the note at p. 97. TRS.] THE MUSCULAR SYSTEM. 239 nuclei, and 2 to 6 minute opaque fat-granules, occasionally occur ; the cells afterwards disappear, and the nuclei, which, on the addition of acetic acid, appear a little yellowish, become more and more elongated, and transformed into long, slender, straight, or slightly-curved fibres, which are, finally, conjoined into long nuclear fibres; these fibres, how- ever, upon the whole are rare. The elongated nuclei are not always placed in a straight line, one behind the other, but frequently in an ob- lique, and in various other directions. In this way are produced serpen- tine nuclear fibres, which, even when fully formed, are still surrounded with isolated fat-granules, and lie as it were in vacant spaces in the con- nective, tissue. In this case, consequently, the nuclear fibres are not formed from the nuclei of the cells, from which the connective tissue is formed, but from special cells of a temporary nature; which circum- stance, were the fact of general application, would make it intelligible, that nuclear fibres may both surround the secondary fasciculi of connec- tive tissue, and also exist without any such tissue (membranous reticular expansions of nuclear fibres, "Micr. Anat.," II. 1, p. 226)]. B. Ligaments of the tendons. The tendons are retained in their posi- tions by various ligaments. Independently of certain ligamentous por- tions of the fasciae, which, being attached to the bones, form tubular processes around tendons, or otherwise confine them, there are the so- called tendinous sheaths (lig. vaginalia tendinum), as for instance on the flexor tendons of the fingers and toes, where they are formed of nume- rous successive narrow bands, which in these situations serve to strengthen the mucous sheaths. Other ligaments to be referred to this class, are the lig. carpi proprium, the trochlea, and the retinacula tendinum. 0. Mucous bursce and sheaths, bursar mucosce et vaginae synoviales. Where muscles or tendons, in their movements, rub upon hard parts (bones, cartilages), or on other muscles, tendons, and ligaments, there are found, between the parts in question, spaces filled with a slightly viscid fluid, which, according to Virchow (Wurzb. "Verb." II. 281), contain not mucus, but a material very similar to colloid matter, and which anatomists have been used to regard as lined with a special mem- brane, a synovial membrane. These spaces are said to constitute closed sacs of a rounded or elongated form, which either simply invest the opposed surfaces of bones and tendons, bones and muscles, &c., bursce mucosce; or in the form of double, although connected tubes, cover at the same time the surface of the tendons, and of the parts between which the tendons play, vagince synoviales. The truth of the matter is this, that it is only the smallest of these spaces which are lined with a continuous membrane; most of them are in many situations without such a lining. With respect to the mucous bursse, those appertaining to the muscles (psoas, iliacus, deltoid, &c.), are, eminently, to be consi- dered as continuous sacculi, whilst in those belonging to the tendons, a 240 SPECIAL HISTOLOGY. membrane can only be detached in parts, and is found to be almost wholly wanting exactly at the points where the mutually gliding parts are in contact. Precisely the same thing obtains in the synovial sheaths, among which the common sheaths of the flexor tendons of the fingers and toes, only in a certain measure, retain the form of a so-termed serous sac, although, even in this case, many parts of the surface of the tendons are without any such membranous lining. Whence it would appear, that in this case, as in many others, the old doctrine of the ex- istence of continuous serous sacs requires thorough emendation. In most of the synovial sheaths, and in many mucous bursse, are found occasionally, particularly in the retinacula, smaller or larger, reddish fimbriated processes, exactly resembling those of the joints, and which, in like manner, are nothing but vascular processes of the synovial mem- brane. D. Fibro-cartilages and sesamoid bones. The tendons of some muscles (tibialis posticus, peronceus longus], in those portions which run in the tendinous sheaths, contain, imbedded in their substance, dense semi-carti- laginous bodies, which are known under the name of sesamoid cartilages (fibro-eartilagines sesamoidece\ and when, as occasionally happens, they become ossified, of sesamoid bones (ossa sesamoidea) ; the latter occur normally, imbedded in the flexor tendons of the fingers and toes, pre- senting one surface towards an articulation. Respecting the more intimate structure of the last-mentioned parts, the following is to be remarked. The sesamoid bones consist of common, finely cancellated osseous substance, are on one side closely surrounded by tendinous or ligamentous tissue, and on the other, which is invested with a thin layer of cartilaginous substance, project into an articulation. The ligaments of tendons, in correspondence with their function, possess exactly the same firm structure as that of the tendinous portions of the fasciae and of the tendons themselves, and exhibit occasionally fine elas- tic fibres in process of development, or the round formative cells of such fibres disposed in rows. The retinacula tendinum have a more delicate structure ; their function being rather to convey vessels to the tendons, they consequently contain chiefly a more lax connective tissue, with fine elastic fibres, and also fat-cells. The mucous bursse, which are invariably thin-walled, consist, in as far as they possess a distinct membrane, of fasciculi of connective tissue, crossing each other in the most various directions, loosely connected, and in many places anastomosing, toge- ther with some fine elastic fibres. The mucous sheaths, on the other hand, in agreement with their double function, which in one respect is that of a mucous bursa, and in another that of ligaments confining the tendon or of tendinous sheaths, present in their thinner parts the struc- ture of bursce mucosce, and in the thicker, an unmixed, dense connective tissue, frequently with cells disposed in rows, which pass into elastic THE MUSCULAR SYSTEM. 241 fibres. Both of these kinds of sacs are lined, on the inner surface, to- gether with the parts contained in or otherwise bounding them, but only in places, with an epithelium, consisting for the most part of a simple layer of nucleated polygonal cells 0-004-0-007 of a line in diameter. The parts which are bare of epithelium, are : many portions of the mucous sheaths, and the tendons lying in them, and certain spots of the bursce mucosce themselves, which are distinguishable by their dull lustre and yellowish aspect, and which occur especially in those situations where the tendons and parts surrounding them are exposed to a greater degree of pressure. The common flexor sheath of the fingers is lined throughout with epi- thelium; and the same may be said of the mucous bursse, in which it is only certain loop-like ligaments, which beyond the limits of the bursae still surround the tendons, that do not present any cellular covering, as is the case, occasionally, in the subscapularis poplitceus, &c. All these bare places, which are uncovered by epithelium, invariably exhibit, almost throughout, the nature of fibre-cartilages, the dense con- nective tissue of which they are composed, and which for the most part is furnished with but few elastic elements, containing a greater or less, often a very considerable number of cartilage-cells" (Fig. 99), amongst which, the most frequent are rounded cells, with a dark contour, although by no means with thick walls, measuring 0-006-0-012 of a line, with a roundish nucleus of 0-003 of a line, and clear fluid, with or without some minute, opaque fatty granules. Besides these, there are, moreover, elongated cells, with one or two nuclei ; round, thin-walled cells, containing 1, 2-20 secondary cells, with thick walls, and dark contours ; the mother-cells measuring as much as 0-02-0-03 of a line ; and lastly, elongated cells, with concentric deposits, inclosing a nucleus, or nucleated secondary cell. In the tendons, the simpler forms of cells almost exclusively occur, and the cells, although frequently ex- tremely numerous, are for the most part isolated, or, at most, disposed in rows or groups of 2-6, which are contained in the connective tissue, both superficially and more deeply. In most cases, the common con- nective tissue alternates with one more resembling fibro-cartilage, so that the tendon, on a transverse section, presents a speckled, white and yellowish aspect; or it maybe, that the outer surface only of the tendon contains cartilage, the deeper portions retaining their usual condition. Where the deposition of the cartilage cells is most abundant, the tendons become thickened, or even studded, as it were, with distinct, fibro-carti- laginous masses (peroneus longus, tib. posticus). In the mucous bursse and the other parts above named, the cartilage cells are placed, not un- FIG. 100. Cartilage-cells from the vaginal ligaments surrounding the tendons of the poplit&us, magnified 350 diameters: a, cell with one; 6, with two nuclei; c, cell with one; rf, with two secondary cells, both of which have rather thick contents. 16 212 SPECIAL HISTOLOGY. frequently, in closer aggregation, or in longer rows of 5-10 cells or more, in which rows the terminal cells are invariably the smallest, and the middle ones the largest. On the cuboid bone, where the tendon of the peroneus longus passes over it, there is a layer of true cartilage J-J a line thick. The vascular processes of the tendinous sheaths and mucous bursse, correspond with those of the articulations, only that they are for the most part of smaller size. The synovial sacs of the muscular system are not mere meshes of connective tissue, like the subcutaneous mucous bursse, since they have, invariably, an epithelial lining in certain places ; they bear just as little resemblance, however, to the proper serous sacs (pleura, peritonaeum, &c.), because, with a few exceptions, their epithelium is never complete, and also because the cellular coat of the serous membrane is almost uni- versally wanting entirely in some spots. The synovial sacs of the mus- cular system, on the other hand, and the synovial capsules, which also never possess a complete epithelium, and frequently communicate with mucous bursse (quadriceps femoris, popliteus, subscapularis, &c.), belong to one and the same category, and diifer in some points from the serous sacs ; with respect to which, however, it must not be forgotten that transi- tionary forms between these two kinds of sacs exist. No one seems to have remarked upon the occurrence of cartilage cells in the various textures which go to the construction of the synovial sacs of the muscular system (except in the fibro-cartilages of the tendons); and the more so, because even Henle refers the fibro-cartilage of the tendinous sheaths to his interarticular cartilages (bandscheiben). It is quite true that the cartilage cells, while often occurring isolated in the connective tissue, or more frequently only in certain spots aggregated together, are not always readily seen ; they may, however, be recognized in sufficiently thin sections, and very distinctly on the addition of acetic acid. The cell-membranes are not in this case utterly destroyed, any more than they are in the cartilage cells of the interarticular ligaments, &c., and no doubt can be entertained as to their being true cartilage cells, W 7 hich, Almost without exception, exist, not as a tissue, but rather dispersed in the connective tissue. Those spots in which they exist in great quantity may be described as fibro-car- tilaginous places; but the distinction between these fibro-cartilages and those of true fibres not of the nature of cellular tissue (epiglottis, ossifying bones), must not be lost sight of. Genuine cartilage, as on the cuboid bone, I have never as yet met with in any other tendinous sheath; not even in the sulcus malleoli externi et interni ; in the sulcus of the heel ; nor in the sheath of the peronceus on the longus calcaneum ; in which situations, cartilage cells are, indeed, everywhere to be seen, but only scattered in the connective tissue. THE MUSCULAR SYSTEM. 243 With respect to the rows of cells which are met with in ligaments of the tendons, and in the tendinous sheaths, the nuclei of which, after the disappearance of the cell, continue to grow and arrange themselves together in the form of nuclear fibres, I cannot avoid remarking upon their close resemblance to the more simple cartilage cells of the ten- dinous sheaths and tendons, a resemblance so close, that I should almost be inclined to indicate it as marking their identity, if it did not sound altogether strange, to speak of a transition of the nuclei of cartilage cells into nuclear fibres. If not as identical, still they may be regarded as analogous formations ; and the rather so, because in almost every case where cartilage cells occur in the connective tissue, rows of cells of this kind, and their relation to elastic fibres may be shown to exist, as well as in the interarticular cartilages, or ligamentous discs of Henle, as they are termed, afterwards to be described. On the other hand, it is true, similar rows of cells are to be found in the palmar fascia, tendons and ligaments, although those structures possess no indubitable cartilage-cells. 83. Vessels of the Muscles and their accessory Organs. A. Blood- vessels. The ramifications of the larger vessels present little that is peculiar. The trunks reach the muscles in an oblique or transverse direction and then subdivide, running in the perimymum internum, in an arborescent manner, and at acute or obtuse angles, so that every part of the muscle is supplied by them. The minutest arteries and veins usually a . run parallel with the muscular fibres, between which they constitute a vas- cular plexus, so characteristic that, once seen, it can never be mistaken. The interstices of the plexus are rec- tangular, with the longer sides parallel to the longitudinal axis of the muscle, and it is of course composed of two ^ sets of vessels, one longitudinal, which, as is shown most conclusively in trans- verse sections of injected muscle, lie in the fissures between two muscular fasciculi, or in the irregular spaces left between several of them, and the other transverse, which -anastomosing in various ways with the former, surround the muscular fibres. Fig. 101. Thus FIG. 101. Capillary vessels in muscle, magnified 350 diameters: a, artery; 6, vein; c, capillary plexus. 244 SPECIAL HISTOLOGY. each separate primitive fasciculus is lodged, to a certain extent, in a plexus of capillaries, and being surrounded on all sides by them, is very abundantly supplied with blood. The capillaries of muscle are among the most minute in the human body, their diameter being often less than that of the blood-corpuscles themselves. In one of Hyrtl's preparations, they measure 0-0025-0-003 of a line; in the pectoralis major, when filled with blood, 0-002-0-003, and when empty 0-0016- 0-0020 of aline. The tendons may be reckoned amongst those parts of the body which are the most scantily supplied with blood-vessels. The smaller tendons, in the interior, present no trace of vessels, whilst externally, in the more lax connective tissue by which they are surrounded, there exists a wide- meshed capillary plexus. In the larger tendons, a few vessels occur in the superficial layers, and in the largest, by means of the microscope and injection, a scanty vascular network may also be rendered evident in the deeper layers ; but even in this case the innermost portions of the tendon are entirely without vessels. The tendon-ligaments present the same conditions as the tendons, only, that in them even still fewer ves- sels can be perceived. The thinner fascias, also, are altogether non- vascular ; sparing ramifications, exclusive of those in the lax connective tissue, amply supplied with blood-vessels, which covers their surface, are found in the thicker fasciae, such as the fascia lata. The synovial membranes of the muscular system, on the other hand, are very vascular, and especially their processes ;* with respect to these synovial mem- branes, however, since they agree in all respects with the synovial capsules of the osseous system, nothing further need be remarked in this place. B. The muscles are very scantily supplied with lymphatics ; the smaller muscles, in fact, such as the omohyoid, subcrural, &c., have none at all, either in their substance or on the surface ; and among the largest muscles, it is only in some, that solitary lymphatics, measuring J and J of a line are seen accompanying the blood-vessels. The deep or mus- cular blood-vessels in the extremities, it is true, are accompanied by lymphatics, but these are few in number ; and from the latter two circum- stances, it may be concluded, that even the larger muscles are but poorly supplied with these vessels. If they had not actually been observed in the fasciculi in certain cases, it might have been a question, whether muscles in general did possess lymphatics at all ; the occurrence of the deep lymphatic vessels proves nothing towards this, it being quite possible that the contents of these vessels, scanty as they are, might be derived from the skin (vola manus, planta pedis, &c.), from the joints, or perhaps from the bones. It may also be concluded, that if a few * [The vessels generally form loops, which communicate with each other by means of delicate branches, and which can readily be traced to the extremity of each process. DaC.] THE MUSCULAR SYSTEM. 245 lymphatics really exist in the larger muscles, they do not run among the secondary fasciculi, but only in the more vascular perimysium between the larger and more lax subdivisions, and especially where the latter contains adipose tissue, and is consequently soft, as, for instance, in the glutceus, and in the superficial layers of the muscles. Lymphatic vessels have never yet been noticed in tendons, fasciae, and the synovial capsules of the muscular system. At the same time, it cannot be said, at all events in the latter instance, that lymphatics may not, as in other serous membranes, be contained in the sub-serous connective tissue. 84. Nerves of Muscles. The distribution of the muscular nerves, with respect even to their coarser relations, presents considerable pecu- liarity, it being evident, in most muscles, that the nerves come in con- tact with their fibres only at a few limited points, and are by no means connected with them throughout their entire length. With respect to the ultimate termination of the nerves, it may be stated that in all muscles there exist anastomoses of the smaller branches, forming the so- termed "plexuses." These anastomoses among the larger branches are seen chiefly, if not altogether, where the entire ramification of the nerves takes place within an extremely limited compass (vid. note) ; elsewhere they rarely occur, or are wholly absent. Those between the smaller and smallest branches (terminal plexuses, Valentin), on the other hand, are very numerous everywhere, forming elongated roundish meshes, which run for the most part parallel with the longitudinal direction of the fasciculi. These terminal plexuses, composed, some- times of smaller, sometimes of larger, meshes, and formed principally by the ramules of one small branch, though not altogether isolated one from the other, proceed to form what are termed by Valentin the ter- minal loops; by which I understand nothing more than anastomoses of the ultimate twigs, effected by means of one or a few primitive fibres passing from one twig into another. It is consequently unimportant whether they follow a straight course, or are curved in a looplike form (Fig. 102). Whether, besides these loops, there are also free termina- tions of the nerve-fibres, such as are known to exist in the lower animals, and as I believed I once noticed in a Rabbit, is altogether doubtful ; whilst it is certain that, even in man, divisions of the nerve-fibres take place, although they are rare, and detected with difficulty, and their relation to the loops, it must be confessed, is still to be made out. The trunks entering the muscles are composed principally of thick nerve-fibres, about twelve of the finer ones occurring, on an average, among 100 of the larger (Volkmann). They become smaller in the interior of the muscle, so that the terminal plexus consists only of extremely minute fibrils, measuring 000-1-0-0025 of a line in diameter. 246 SPECIAL HISTOLOGY. In some cases, even, the gradual attenuation of the fibres may be directly observed, proving that the diminution in size does not take place, in this case at least, in consequence of division. Thus, in the Fig. 102. Fie. 103. omohyoid, I have noticed several nerve-fibres of 0-004-0-0053 of a line, derived from trunks measuring 0-05-0-07 of a line, become attenuated (within a distance of 0-15-0-2 of a line), to a diameter of 0-002-0-0026 of a line, and, after a further course of '.40*5 of a line, acquire that of the smallest fibrils, or 0-001 of a line. Simultaneously with this change in size, the nerve-fibres assumed in all respects the aspect of the so-termed sympathetic nerves, and ultimately became pale, with a simple contour line, and disposed to form varicosities ; at the same time that they appeared to lose every vestige of a coat composed of connective tissue, they still retained dark borders, and consequently were not non- medullated fibres (or free axis-cylinders), such as are seen in other ter- minations of nerves. Nervi vasorum (vascular nerves), accompanying the bundles of vessels, otfcur in all muscles, and, according to the size of the latter, form larger or smaller branches. They are composed only of the smallest fibres, and always follow the course of the large vessels, which can still FIG. 102. Ultimate expansion of the nerves in the omohyoid muscle of Man, magnified 350 diameters, and treated with soda: a, interstices of the terminal plexus; 6, terminal loops ; c, muscular fibres. FIG. 103. Divisions of the primitive nerve-fibres in muscle, magnified 350 diameters: ^4, double division from the omohyoid muscle in Man; a, neurilemma ; JS, division of a nerve from a facial muscle of the Rabbit into three apparently pointed twigs. THE MUSCULAR SYSTEM. 247 be recognized as arteries and veins. I have not seen how they termi- nate ; and this much only I know that they are never met with on the capillaries, and very frequently, also, are not to be found on the smallest arteries and veins. Occasionally, one or more fibrils from the terminal plexus of the muscular nerves may be seen to join these vessels ; a cir- cumstance quite in accordance with the demonstrable fact that the vas- cular nerves in many parts, for instance in the extremities, are derived from the spinal nerves. The smaller tendons contain no nerves, and the larger, such as the tendo Achillis and the tendon of the quadriceps femoris, only vascular nerves. The fascice and sheaths of tendons are also without nerves, as well as the synovial capsules of the muscular system, so far as I am at present aware. In many of the small muscles, the extent of space included in the distribution of the nerve is extremely limited, as for instance in the superior belly of the omohyoid, in a portion of which, three inches long, the space over which the nerves are distributed, does not exceed from five to eight lines in length. The trunk of the nerve entering in the middle of the transverse axis, divides into two equal primary branches, one passing towards the left, and the other towards the right, border of the muscle, and each giving rise to numerous anastomosing branches of all sizes, and thus supplying the entire thickness of the muscle from the most superficial to the deepest layers. Whilst this distribution of the nerve takes place at one point, a distribution not unlike that in an organ of sense, the rest of the muscle presents the utmost poverty, or even a complete deficiency, of nerves. In one case, which I examined closely, I was unable, besides the few vascular nerves in these portions, to detect more than three small nervous twigs of 0-021, 0-028, 0-042 of a line, which, though derived from the main nerves, differed from the other branches in their distribution. Two of them ran directly towards the lower, and one towards the upper, end of the belly of the muscle, giving off a few filaments composed of one or two primitive fibrils which passed through the muscle, and terminated, a little before reaching the intermediate and terminal tendons, in the most minute twigs and single nerve-fibrils. I found the same conditions of the nerves in the sub- cruralis, and in one of the costo-cervical muscles (arising from the first rib in the cervical fascia), as in the omohyoid; in the sternohyoid, sternothyroid, omohyoid (inferior belly), the same condition in some parts was noticed, whilst, in others, one apparently different existed, that is to say, the branches of the nerves frequently did not all divide at the same level, but were more widely spread. It was easily seen, however, that the above-described mode of division essentially obtained, also, in this case, viz. : that the separate portions of the muscles are in 248 SPECIAL HISTOLOGY. connection with the nervous plexuses, only at a point of limited extent. The proof of the existence of similar conditions in other small muscles was more difficult, as in those of the orbit, where the nerves reach the muscles at acute angles, follow a longer course in them, with their primary branches, and form their ultimate ramifications at various, more or less widely separated points ; yet even in this case it was tolerably well made out. It is easy to understand that, in the larger muscles, a microscopic examination, in toto, is impossible ; but it can be shown in other ways, as by the preparation and examination of minute flat fasciculi taken in their entire length, that conditions exist, at all events in some of them, similar to those which appear to be evidenced in the small muscles. It is thus seen, especially in muscles of lax structure, that each fasciculus presents precisely the same conditions as an entire smaller muscle. How the distribution of the nerves is effected in muscles with long fasciculi (sartorius, latissimus dorsi, &c.), I have not examined ; it is probable that in this case each primitive fasciculus is joined by the nerves at several points, widely apart. Valentin and Emmert, in the year 1836, simultaneously described the terminations of the primitive nerve-fibres in the muscles, to be in the form of loops, and the former maintained that the nerves of sensation termi- nated in a similar way. But Physiology having more recently shown that she does not well know what is to be done with these loops, and Microscopic Anatomy having distinctly demonstrated the existence, in many situations, of other modes of termination of the nerves (Pacinian bodies, &c.), the loops have fallen into such discredit, that the question now is, not as before, whether, besides the loops, there are other modes of termination, but rather, whether loops really exist anywhere ? With respect to the muscles especially, anatomists seem inclined to deny their existence altogether, since divisions and terminations of nerve-fibres have been discovered in them ; but this conclusion, from what has been re- marked above, would be incorrect. Henle also, in Canstatt's Jahresb. f. 1847, p. 63, says, that in his opinion the loops had been too rashly discarded; while on the other hand, Wagner, with reference to this ques- tion, places the analogy with what is seen in the Frog, &c., above direct observation, and denies the existence of loops. With respect to divisions of the nerves, Wagner ("Gott. Nach.," 1852, p. 27), finds them to be tolerably frequent in the muscles of the Mouse. I would, moreover, re- mark, that in one case, I think I noticed a minute ganglion with about five cells on a nervous twig in the omohyoid of man ; the observation, however, was not satisfactory, the muscle having been previously treated with soda. In the Invertebrata, many observers have long since described free terminations of the nerve fibrils, and their insertion with expanded ends into the muscular fibres, as Doyere in the Tardigrada, and Quatrefages THE MUSCULAR SYSTEM. 249 in Eolidina, and some Rotifera ( u Ann. d. Sc. K," 1843, p. 300, and pi. 11, fig. 12). I myself, in a larva of Chironomus (a dipterous insect), noticed a single nerve-fibre, proceeding to the two muscular fasciculi of the simple tarsus, bifurcate into two branches, which were implanted upon the surface of the muscle, with somewhat expanded terminations. In the Vertebrata, Muller and Briicke first described division of the nerves in the orbital muscles of the Pike (J. Muller, "Physiol.," 4th ed. vol. 1, p. 524), and in Amphioxus, Quatrefages noticed conditions precisely like those met with in the Invertebrata above mentioned. The observation is easily confirmed, as respects the orbital muscles of the Pike, in which, upon the teasing out of the fasciculus either of the fresh muscle as well as after it had been treated with corrosive sublimate, and rendered trans- parent by acetic acid, numerous divisions of the nerves are apparent. They are nevertheless not nearly so frequent in this case, as in the Frog, nor are the divisions more than bifid or trifid. Besides this, I was espe- cially struck with the glaring contrast that was presented, to what is seen in the Mammalia, in the enormous extent of space included in the dis- tribution of the nerve-fibres ; a distribution so extensive, that it is by no means easy to find a single primitive fasciculus which has not a nerve- fibre going to it; in many places even, the latter were seen in apposition with a fasciculus throughout a great extent, and surrounding it with loops, or with a variable number of spiral convolutions. A similar con- dition was observed by R.Wagner in the orbital muscles of the Torpedo, whilst in other muscles the nerves were very scantily supplied (" Gb'tt. Nach.," Oct., 1851). In the Amphibia, divisions and free terminations of the nerves have been described by Wagner. The former are remark- ably beautiful and numerous. They commence in nerve-fibres, measur- ing 0-004-0-006 of a line, in the smaller trunks and branches, and are several times repeated, with a gradual diminution of the fibres, until extremely minute filaments measuring 0-001-0-0015 of a line are formed. The divisions are for the most part di- or tri-chotomous, more rarely multiple; in one instance, however, Wagner noticed eight ramus- culi. The ultimate filaments are pale, and have a simple contour line. They never penetrate into the muscular fasciculus, but, after running a short distance, are either applied obliquely or transversely to it, or proceed for some distance in close contiguity and parallel with it; in either case, becoming attenuated to a sharp point, and frequently as fine as a fibril of connective tissue. All these conditions are best seen in the mylohyoi- deus (Wagner), and above all, in a delicate cutaneous muscle of the thorax, as was pointed out to me by Ecker, and in which the distribu- tion of the nerves has recently been very accurately described by Reichert. He observed in this case, as I had done in man, that only a small por- tion of the muscle was well supplied with nerves, which were but spar- ingly distributed to the other portions. The trunk of the nerve supply- 250 SPECIAL HISTOLOGY. ing the 160-180 fasciculi of this muscle, contains, according to Reichert, 7-10 fibres, and ultimately, by continual division, forms 290-340 Fig. 104. terminal filaments, so that there is more than one for each muscular fasciculus. 85. Chemical and Physical Relations of the Muscles. In 100 parts of fresh beef there are contained, according to Bibra, 72-56 74-45 parts of water. The solid constituents (25-55-27-44) in a man 59 years old, were composed of a residue insoluble in boiling water, alcohol, and ether, 16-83; soluble albumen and coloring matter, 1-75; substance affording gelatine, 1-92; extractive matter and salts, 2-80; fat, 4-24. The fat is derived chiefly from the blood, the fat-cells in the muscles and their nerves, and in part perhaps from the muscular fibres themselves, in which microscopic fat granules are, at all events occasion- ally, evident. The gelatine is derived from the perimysium, in smaller proportion also from the vessels and neurilemma; none, on the contrary, is afforded by the sarcolemma, which is still apparent in muscles com- pletely exhausted by boiling, whence (in opposition to Reichert) it is evident that the sarcolemma should not be referred to connective tissue. The inorganic salts and the albumen are principally afforded, probably by the muscular fibre itself, as are also and above all the salts described by Liebig and Scherer in the juice of muscles, of the lactic, acetic, bu- tyric, and formic acids, the free lactic acid, the creatin and creatinin, FIG. 104. Divisions of nerve-fibres, in a small twig from the cutaneous thoracic muscle of the Frog; magnified 350 diameters: a, bifurcation; b, threefold division. THE MUSCULAR SYSTEM. 251 the sugar of muscles or inosit, and the coloring matter, which substances, even the last-named, are lodged partly in the fibrils themselves, partly and chiefly, and this is the case especially with the albumen, in the in- terstitial substance, by which the fibrils are connected together. The 16*83 parts of insoluble residue belong in part to the elastic tissue in the vessels and perimysium, and to the smooth muscle in the vessels, but principally to the muscular fibrils themselves, which, as we have before seen ( 27), consist of a substance allied to fibrin. The sarcolemma is less affected by alkalies and acids than the fibrils, and approaches in its nature more nearly to the membrana propria of the glands, the walls of the capillaries, and the membrane of many cells. The coloring matter of the muscles (and the muscles themselves), like the blood, becomes bright red in the air, or still more in oxygen gas, and is rendered dark by sulphuretted hydrogen. It is extracted, and indeed readily, by water, but not by salts, in which circumstance, that is to say, in an altera- tion in the degree of concentration of the plasma with which the muscle is imbued, is perhaps to be sought the principal reason for the readiness with which the color of the muscles is altered in disease. The muscles, although softer and more easily torn than the tendons, possess, nevertheless, considerable tenacity, particularly during life, and they have a certain degree of elasticity. During life, as has been cor- rectly remarked by E. Weber, even when not under the influence of the nerves, they are not for the most part in their natural form, but stretched, or in a state of tension, and like harp-strings in the same condition, exert an elastic force. This is satisfactorily shown when the tendons of the extensor muscles in an animal's limb which is strongly flexed, are cut through, the nerves having been previously divided, whereupon the tendons are very considerably retracted (E. Weber). This tension of the muscles varies very much, according to the position of the limbs. It is very slight when the body is at rest with the limbs semiflexed, still less or even wholly absent when a muscle falls into a state of repose after it has acted powerfully upon the limb ; greater, and manifested in the greatest degree, when the antagonists of a muscle are acting with all their force. According to Weber, the living muscle, when in a state of inactivity, may be compared with caoutchouc, seeing that, like that substance, they possess a very great elastic extensibility ; or, in other words, a slight but very perfect elasticity,' as may be readily perceived in the muscles even of dead animals, which may be alternately stretched and allowed to retract. Owing to their elasticity, the muscles offer scarcely any hindrance to the movements of the limbs, arid in con- sequence of its perfect nature, they recover their previous form and length even after the greatest possible extension. This is exemplified in the stretching of the abdominal muscles in pregnancy and in certain pathological conditions. When the muscles are in a state of activity, 252 SPECIAL HISTOLOGY. their elasticity alters in a very remarkable manner : 1. During the con- traction they become more extensible or less elastic, on which account they exert a much less force by their contraction than would otherwise be the case, had their elasticity remained unchanged, and the same as in the inactive condition. 2. The elasticity of the active muscle, in one and the same muscle, is extremely variable ; it continues to diminish as long as it is in action, whence arise the phenomena of fatigue and loss of power in the muscles (E. Weber). In the dead muscle, according to the same observer, the elasticity is less perfect; that is to say, the dead muscle, when stretched, does not altogether resume its pristine form, and consequently is more readily torn, although such a muscle as the gracilis may still be capable of sup- porting a weight of eighty pounds without breaking. But at the same time it is also less extensible, more rigid, less flexible, or its elasticity is greater. The phenomena of fatigue in the muscles are consequently to be distinguished from those induced by death. In the former state, the diminution of elasticity occurs during the influence of the nerves and the contractions of the muscle itself, probably in consequence of changed conditions in the molecular nutrition of the muscle, and is con- sequently a vital phenomenon ; whilst in the latter case, innervation, nutrition, and contraction have ceased, and the increase of elasticity, which produces what is termed the rigor mortis, is a purely physical phenomenon, and not to be confounded with the increased tension, which, under the influence of life, takes place during the contraction of the muscles, simultaneously with a diminution of the elasticity. The tendons are very firm, and but slightly elastic ; and contain, according to Chevreuil, in 100 parts, only 62 03 of water, considerably less therefore than the muscles. They consist principally of a substance affording gelatin, although they are transformed with more difficulty than other parts into that principle. In my opinion the muscles are sometimes in a state of tension, some- times in their natural form, sometimes even compressed, and to all these three conditions vital contraction may be superadded. If a muscle in a state of extension contract, so as not to assume its natural form, it will still be in a state of tension after the remission of the contraction, arid if divided will retract. On the other hand, if a muscle in its natural form contract, it will, after the cessation of the nervous influence, immediately become extended ; as, for instance, the contracted heart, or an isolated muscle excited by galvanism. Consequently, when we speak of the elasticity of muscles, their tension, not only when they are extended, but also in the compressed condition, must be considered ; and this appears to me of some physiological importance, as in this way the extension of contracted muscles (heart), and of muscles whose THE MUSCULAR SYSTEM. 253 antagonists are paralyzed, becomes intelligible. With respect to the cadaveric rigidity, the important facts have quite recently come to light, that it may be arrested by the injection of blood (Brown-Se'quard); and also that it takes place even in the living animal, when the supply of blood to a group of muscles is entirely cut off (Stannius). In the latter case, the irritability of the nerves ceases at the same time, and on the restoration of the circulation the normal conditions in both muscles and nerves are also restored. By these facts, all hypotheses respecting the occurrence of the cadaveric rigidity, except that of Weber, are contra- dicted; even that of Briicke, which asserts that it is caused by the coagulation of the fibrin existing in the muscular fibre. But at the same time the question also arises, as to what is the proximate cause of the change in the elastic conditions of the muscles, whether it be due to the death or cessation of activity of the nerves, or to the deficient supply of blood to the muscles themselves ? Stannius decides in favor of the former supposition, and is consequently driven to the conclusion, that during life the motor nerves act upon the muscles, by reducing, during the state of repose, their natural amount of elasticity, whilst in the contraction of the muscle the influence of the nerves is momentarily relaxed. Thus, according to Stannius, the rigidity connected with con- traction, and vital contraction, would be identical, and nothing more than the condition of the muscle when freed from all nervous influence, and lasting until the nerve again puts the muscle into a state of rest, or its substance is decomposed. I must own that in this view, which moreover had already been proposed by Engel (" Zeitsch. der Wiener," Aerzte, 1849), I do not at present agree ; and in particular would remark, that the circumstance of the contractions which occur during life being much more considerable than those which attend the rigor mortis, appears to be opposed to it. 86. Development of the Muscles and Tendons. The rudiments of the muscles consist, originally, of the same formative cells as those of which the rest of the body of the embryo is constituted ; and it is not till afterwards that the muscles, tendons, &c., are gradually developed by a histological differentiation. In man, the muscles are not evident before the end of the second month ; at first, however, they cannot be detected by the unaided eye ; they are soft, pale, gelatinous, and not to be distinguished from their tendons. In the tenth and twelfth week they are more distinct, especially in specimens preserved in alcohol ; and at this time the tendons also may be distinguished as somewhat clearer, but at the same time transparent streaks. In the fourth month, both the muscles and tendons are still more distinct, the former being, on the trunk, of a light reddish color, the latter less transparent, and grayish, both retaining a soft consistence. 254 SPECIAL HISTOLOGY. Fig. 105. From this period, both textures acquire more and more of the configu- ration which they afterwards retain, so that at the maturity of the embryo, excepting that the muscles are still softer and paler, and the tendons more vascular and less white, they no longer present any difference worth notice. With respect to their intimate conditions, the primitive fasciculi, in the embryo, at the end of the second month, present the aspect of elon- gated bands (Fig. 105) 0-001 of a line broad, with nodular enlargements at different points, at which places are situated elongated nuclei ; the bands exhibit either a homogeneous or finely granular aspect, and but rarely an extremely faint indication of transverse striation. In their further development, these primitive muscular fasciculi, which, as com- parative histology teaches, originate in cells arranged in a linear series, continue to increase in breadth and length, and their contents, the original cell-contents, are developed into the muscular fibrils. In the fourth month (Fig. 106) they measure for the most part 0-00280-005, some even 0-006 of a line, whilst others do not exceed 0-0016, and 0-002 of a line. The larger ones are, still, always flattened, but of uniform width, and also considerably thicker than before, mostly with evident longitudinal and transverse striae, and even with fibrils, which admit of being isolated. It is partially evident, even in a longitudinal Fig. 106. view, but still better in a trans- verse section, that in many cases, the fibrils do not occupy the entire thickness of the pri- mitive tube, but that they are deposited around its periphery, the interior being as yet filled with a homogeneous substance as at first, and which now ap- pears like a canal within the fibrils. All the primitive tu- bules possess a sarcolemma (6), which on the application of acetic acid or soda, appears as a very delicate membrane, which by the imbibition of water, may occasionally be raised from the fibrils. The tubes, moreover, FiG. 105. Primitive fasciculi of an eight to nine weeks' human embryo ; magnified 350 diameters: 1, two fibres without transverse strise; 2, fibres presenting the first indications of transverse striation ; a, nuclei. FiG. 106. Primitive fibres of a four months' human embryo; magnified 350 diameters: 1, a fasciculus, with a clear, as yet, non-fibrillated substance in the interior: 2, fasciculus without such contents, with an indication of transverse striation ; a, nuclei ; b, sarcolemma. THE MUSCULAR SYSTEM. 255 as at first, present nuclei lying close upon the sarcolerama, and which frequently cause rounded elevations on the surface of the tube, and may be observed actively engaged in the process of multiplication. They are all vesicular, roundish or elongated, with very distinct, simple or double nucleoli measuring 0-0004-0*0008 of a line, and frequently with two secondary cells in the interior. They are much more numerous than previously, and most frequently disposed in pairs closely approxi- mated ; but often, also, in groups of three or four or even six, either contiguous or arranged serially. From this period to that of birth, no further important change takes place in the muscular fasciculi, except an increase in their size. In the new-born infant they measure 0*0056 -0-0063 of a line, are solid, rounded, polygonal, longitudinally or transversely striated, according to circumstances, as in the adult, with very readily isolated fibrils, and no longer any appearance of nuclei. From what has been remarked, it is clear that the sarcolemma repre- sents the sum of the membranes of the coalesced cells, and that the nuclei of the youngest fasciculi are the original cell-nuclei, whose descendants are represented in the nuclei of the older fibres, which have multiplied by an endogenous process. The muscular fibrils are the altered contents of the original tubes, become solid ; they appear, demonstrably in many instances, to be formed on the inner surface of the sarcolemma, from without to within, but in other cases probably in the whole of the tube at once. The growth of the entire muscle is chiefly to be referred to the in- crease, both longitudinal and in thickness, of the primitive fasciculi ; and the rudiments of all the future primitive fasciculi appear to be formed, probably even as early as the original rudiments of the muscle itself in every case at the middle period of foetal life. In the embryo, at the fourth or fifth month, they are perhaps five times as thick as in one at two months ; in the new-born infant they measure for the most part twice, occasionally even three and four times as much as in the fourth and fifth month, and in the adult their size is perhaps five times greater than in the new-born child. The number of fibrils must necessarily in- crease in proportion to the size of the fasciculus, because, according to Harting, they are but little thicker in the adult than in the foetus. The perimysium is developed, as I find in agreement with Valentin and Schwann, after the type of the common connective tissue, from fusiform, coalesced formative cells. The elementary parts of the tendons are, in no case, formed earlier than those of the muscles ; for, in embryos from the eighth to the ninth week, I have never been able to detect a trace of them, although at this time the muscular fibres are 'quite distinct. It is not till the third or fourth month, when, moreover, they become distinctly visible to the naked eye, that their elementary constituents can be made out, at this time presenting the appearance of long parallel bands with elongated 256 SPECIAL HISTOLOGY. nuclei, which, as the observations of Schwann and myself ( 24) on very young animals show, are formed by the coalescence of fusiform cells. As early as the fourth month they may be distinctly recognized as primi- tive fasciculi, which are wavy, and present, at intervals, elongated nuclei 0-0035-0-006 of a line long, and 0-0016 of a line broad, but are as yet without distinct fibrils, and not more than 0-0012-0-0016 of a line wide. Fig. 107. From this period up to the end of foetal life, the fasci- culi gradually increase in width, so that in the new- born infant they measure 0-002-0-0025 of a line; at the same time their fibrils are developed, as are also fine elastic filaments among the fasciculi, from special fusiform formative cells (vide 23). If these fasciculi be compared with those of the adult, measuring 0-006 -0-008 of a line, it is obvious, that the fasciculi of the tendons are continually acquiring an increase in thick- ness from their first origin, so that their proportional sizes in the four months' foetus, the new-born child, and the adult, are about as 1 : 1, 8 : 6 ; and, also, that in every case the growth of the tendons must in a great measure be referred to the increased thickness and elongation of their fasciculi. It would, moreover, appear, that subse- quent to the primary rudiments of the tendons, new fasciculi continue to be added during foetal life. Some controversial opinions are still entertained with respect to the development of the muscular fibres. Reichert and Hoist maintain that each fibril is the product of a single cell, and regard it as the equivalent of the smooth muscular fibre, or contractile fibre-cell. This view is er- roneous, as is readily shown by the examination of the mammalian and human embryo. Leydig's declaration, quite recently, in its favor (Beitr. p. 78), is explained by his having confounded the peculiar secon- dary muscular fasciculi in the plagiostomous fishes with the primitive fasciculi of the higher Vertebrata. In the Batrachia, according to Lebert and Remak, in the development of the muscles, elongated simple cells, with self-multiplying nuclei, are found, the contents of which cells undergo a metamorphosis similar to that occurring in the elongated muscular tubules formed of numerous cells, which, according to my ob- servations, also exist in these animals. The contractile part of the mus- cular fibre, whether it be transversely striped or not, and whether it presents fibrils or not, is generally developed from without to within, in the sarcolernma, forming a sort of tube w.hich does not become solid till afterwards ; less frequently it appears as a more solid cord on one side FIG. 107. From the tendo ^chillis of a new-born child, magnified 250 diameters, and treated with acetic acid, in order to show the formation of fine elastic fibres. THE MUSCULAR SYSTEM. 257 within the muscular fibre. In the former case, the nuclei and the original contents of the formative cells, which often contain a large quantity of fatty matter, are situated in the interior of the embryonic muscular tubule, or between it and the sarcolemma ; in the latter always close upon the sarcolemma. With respect to the pathological relations of these tissues, the follow- ing remarks may be offered : The substance of the striated muscles is not regenerated, and wounds of muscles heal simply with a tendinous callus. A new formation of them has been noticed by Rokitansky ("Zeitsch. der Wiener," Aerzte, 1849, p. 331), in a case of tumor of the testis in an individual 18 years old, and by Virchow (" Verh. der Wurzb.," Ges., I.) in an ovarian tumor. In the latter case, which came under my own observation, there were elongated, fusiform, transversely striated cells, each with a nucleus, similar to those described by Remak in the Tadpole. The state of the elementary parts in hypertrophy of the muscles is uncertain.* This condition, however, except in the tongue, heart, and certain respiratory muscles (Bardeleben), does not perhaps occur at all ; it is at all events extremely rare in the striped muscles. (Romberg, "Nervenkr.," p. 291, asserts, that such a condition ensues upon long-continued cramps, though it appears to me that this point is not yet sufficiently established.) Equally uncertain, also, is the intimate condition of the muscular elements in the increased development caused by exercise, and whether this depend upon the growth of the pre-exist- ing muscular fasciculi, or on the introduction of new ones the latter of which supposition may perhaps be affirmed without much chance of error, in the case of the extreme degrees of pathological hypertrophy. Atrophy of the muscles is very frequent, as in old age, paralysis, particularly of the tongue, and in cases of lead-poisoning, and in the development of cancer, fibrous tumors (consequent on inflammation), and of fat, &c., in the substance of the muscles. The processes, however, which are set up in these cases, have as yet been but little investigated. In extreme old age I find the fasciculi small, presenting occasionally a diameter of not more than 0-004-0-008 of a line, easily broken up, mostly without transverse stripes, and with the fibrils indistinct, whilst they frequently contain yellowish or brown granules, as much as 0-001 of a line in size, often in large quantity, and very many vesicular nuclei with nucleoli. * [Wedl has observed longitudinal rows of yellow or brownish granules in hypertro- phied as well as in atrophied muscle. These granules are not dissolved by acetic acid or alkalies; and seem deposited around the nuclei of the sarcolemma. In hypertrophied muscle, a peculiar gelatinous substance in the interstitial tissue is sometimes met with. This causes the primitive fasciculi to adhere to each other, and generally results in a com- plete softening and destruction of the sarcolemma, in the place of which we find a fine granular mass. The interstitial substance is sometimes found in an hypertrophied state. If this occur to any extent it produces an atrophy of the muscular fibre. DaC.] 17 258 SPECIAL HISTOLOGY. The nuclei often form continuous rows, or are accumulated on the inner surface of the sarcolemma, exhibiting in a peculiar manner the same distinct indications of an energetic multiplication by endogenous forma- tion, as are presented in the embryo (vide this , supra). In fatty de- generation^ the muscular fasciculi are, by degrees, replaced by connective tissue and fat cells which are developed between them ; whilst, at the same time, minute fatty molecules are developed in great number within them, in place of the fibrils, which gradually disappear. Paralyzed muscles were found by Reid (" On the relation between Muscular Contractility and the Nervous System," "Edinburgh Monthly Journal of Med.," 1841) to be thinner, softer, and paler; and Valentin ("Phys.," 2 ed. 2 Th., p. 62) noticed in such cases that the transverse stripes were indistinct, or had disappeared, and could no longer be pro- duced by water, alcohol, &c. ; the longitudinal stripes existed, but did not present their usual aspect, more resembling those of macerated muscle. Subsequently the altered fasciculi disappeared in part, and were to some extent replaced by fat. In a case of atrophy of the pec- toralis major caused by cancer, I noticed conditions similar to those I had observed in old age, viz. : destruction of the fibrils, the develop- ment of brownish granules, and the presence of numerous nuclei, to- gether with a clear fluid in the persistent sarcolemma ; and lastly a diminution of the fasciculi, which did not measure more than 0-002- 0*004 of a line in width. I also believe, that I noticed in many fasci- culi the development of larger, serially disposed cells, with very large and distinct nuclei, exactly like the so-termed cancer-cells. The condition of the muscles in emaciation is unknown. In an ema- ciated Frog, which had fasted for eight months, Bonders observed that the fasciculi were more slender, which he attributed chiefly to the removal of the interstitial substance between the fibrils. Paleness of the muscles is very common in dropsy, chlorosis, paralysis, lead-poison- ing, old age, &c. ; in which cases, probably the numerous brown or yellow granules are formed from a portion of the coloring matter. This condition is generally associated with softening, in which the fas- ciculi no longer exhibit any distinct transverse striae or fibrils, and readily break up into numerous particles, or even into a pultaceous matter. In tetanus, in which rupture of a muscle frequently occurs, Bowman ("Phil. Transact.," 1841, p. 69) observed on the fasciculi numerous nodular enlargements, in which the transverse strise were very closely approximated, and between them either actual rupture of the fibrils, or at all events a considerable stretching and disorganization of them, both of which states are clearly to be referred to a powerful and irregular contraction. The muscles sometimes contain concretions, particularly as the result of the cretification of pus, tubercles, and cys- ticercus-vesicles ; sometimes also true bones, such as are produced after prolonged exercise in the deltoid and other muscles (Exercirknochen). THE MUSCULAR SYSTEM. 259 Of parasites are to be noticed the not unfrequent Cysticercus cellulose? and Trichina spiralis ; and, besides these, in the Eel a nematoid worm, observed by Bowman (" Cyclop, of Anat." II. p. 512) alive, in the al- most empty sarcolemma. I met with something analogous to the latter, some years ago, in the abdominal muscles of the Rat (as have V. Sie- bold and Miescher also in the Mouse) ; that is to say white streaks 4-7 lines long, and 0*09 O'Ol of a line wide, which, on microscopic exa- mination, proved to be hollow primitive fasciculi, entirely filled with elliptical, slightly curved corpuscles, O004-0-005 of a line long, by 0*0019 of a line wide, and manifestly ova. The portions of the fas- ciculi thus transformed into pouches, had walls 0-009-0-01 of a line thick, with transverse stripes, and were continuous at either end with the perfectly normal fibre. 87. Physiological Remarks. The most remarkable peculiarity of the muscles is their contractility. In each contraction, the primitive fasciculi shorten themselves in a rectilinear direction, and at the same time become thicker ; they do not, however, undergo any considerable condensation. It is probable, that the contractions generally take place simultaneously in every part of a fasciculus, although at the same time it is not, of course, intended to be said that the contraction does not commence at the points where the terminations of the nerves occur, and that this contraction does not precede, though by a space of time immeasurably short, or at all events inappreciable by the eye, that of the other portions of the fasciculus. Under certain conditions, how- ever, successive, progressive, and partial contractions are observed. If during the contraction of a muscle, its longitudinal and transverse striae are noticed, it is diffi- cult to show that where the former exist, they disappear during the contraction, and give place to transverse markings ; and that the latter, where they were already present, become more distinct, and more closely approxi- mated. Moreover, in the easily isolated fibrils of the thoracic muscles of insects, it is easy to perceive that they exhibit very variable conditions in different ani- mals, and vary frequently in one and the same indivi- dual. Sometimes they are almost without transverse markings, and very pale ; sometimes darker, and with distinct transverse lines; sometimes, again, very dis- tinctly ringed ; and together with these varying condi- tions, does the thickness of the fibrils and the distance between the transverse striae, vary also ; so that the Fig. 108. Primitive fibres from the alar muscles of the " Dung-Fly :" a, slender fibril, with very distant delicate transverse striae ; 6, thicker fibre, with closer, alternately stronger and fainter striae; c, still thicker fibril, with the striae more closely approximated; rf, fibril with lateral, alternate elevations (they have come out too dark). Magnified 350 diameters. Fig. 108. 260 SPECIAL HISTOLOGY. fibrils which exhibit the most distinct striation, are almost as thick again as the others, and their transverse striae are placed almost twice as closely together. It may thence, perhaps, be allowable to con- clude, that in the act of contraction the principal phenomenon con- sists in the shortening and thickening of the fibrils, and also, that the changes in the fasciculus above noticed depend upon these changes in the fibrils. The further question now arises: how is this shortening of the fibrils effected ? and whence does the transverse striation arise ? Is the latter connected with the vital conditions of the muscle, or is it produced independently of these ? It is unnecessary to answer the latter query in the affirmative, for dead muscles exhibit transverse striae, and indeed, under the same conditions as the living. This is best shown in muscles successively subjected to various degrees of tension; and con- sequently, all notion of a merely partial contraction of the fibril, which arises on the first observation of these conditions, must be relinquished. The transverse striation is manifestly merely a physical, not a vital phenomenon. It arises, either because the fibrils are not homogeneous throughout their whole length, but divided into numerous small seg- ments^ some of which are possessed of greater elasticity than the others ; or, in the opposite case, it may depend upon the circumstance, that the fibrils are soft filaments, which, in shortening, become curved in a zig- zag or wavy manner, or varicose. Which of these two views is the correct one, cannot at present be determined ; and this much only can be said, that in favor of the former supposition, the fact can be adduced, that fibrils, after maceration, readily break up into minute particles (sarcous elements, Bowman), and possibly consist of a series of such elements connected by a heterogeneous interstitial substance ; whilst in favor of the second, are the conditions presented in the fibrils of con- nective tissue, which are undoubtedly homogeneous throughout, and yet when made to contract by the application of acetic acid, exhibit extreme- ly delicate transverse markings, in consequence of which, the fasciculi composed of them frequently offer a deceptive resemblance to those of striped muscle. It is difficult to say whether the sarcolemma partici- pates actively in the shortening of the fibrils, although, especially from the consideration of its chemical and physical properties, which ap- proach those of elastic tissue, I am rather inclined to the opinion, that its function, in the contraction of the fibre, is merely passive. The same may with greater certainty be affirmed of the albuminous fluid uniting the individual fibrils. Consequently, it is not the muscular fasciculus, in toto, but only the fibrils, which are to be regarded as the contractile elements ; a position which is not shaken by the circum- stance, that other conditions occur in the smooth muscles, and in many muscles in the Invertebrata (those that exhibit no fibrils). This is not the place to dilate upon the causes to which the contrac- THE MUSCULAR SYSTEM. 261 tions of the muscles are due, and by which they are necessarily produced, and I will merely offer the following remarks. There can be no doubt that the contractility of the muscular substance is a proper and inherent attribute, and only called into manifest action to a certain extent through the nerves; whilst it is equally certain, that there are no facts which conclusively demonstrate, that the striped muscles contract indepen- dently of a previous nervous influence. What the processes are which take place in the fibrils during the contraction is wholly doubtful; but it is to be hoped that the further investigation of the laws of the electric currents in the muscles, prosecuted in the way so successfully pursued by Du Bois Reymond (" Untersuchungen tiber thier. Electricitat," Ber- lin, 1848-49),* will throw some light upon this, as yet, obscure subject. It would be more than bold to hazard an assertion with respect to the nature and mode of action of the nerves upon the muscles, since we are quite as much in the dark as to the processes which take place in the nerves, as we are with regard to those occurring in the muscles them- selves. From the anatomical facts, which prove, that in many animals the motor nerve-fibres come in contact with each primitive muscular fasciculus only at a few points, and never penetrate into its interior, it is, however, rendered evident, that in the contraction of a muscle, the nervous influence must act from a certain distance. The muscles also possess sensibility, though of a rather peculiar kind, because punctures, burns, and incisions into their substance, excite scarcely any sensations worth naming, whilst every muscle, after long- continued activity, as well as when affected with cramps or spasms, be- comes painful and very sensitive to pressure. They are also endowed with an extremely delicate sense of feeling for their own state of con- traction, so that they are capable of estimating very minute variations in the force with which they act. The apparent contradiction between these facts is easily accounted for, by the consideration that the muscu- lar nerves contain but very few sensitive fibres, as is readily shown in the nerves of the orbital muscles, &c. These fibres, to which probably belong the few filaments above described, which are distributed over the whole muscle, though too scanty to render a muscle sensible to local im- pressions, nevertheless suffice, when implicated in the contraction of the entire muscular substance, to convey to the sensorium the degree of pressure to which they are subjected, and, when the organs are over- exerted, to induce pain, in consequence of the frequently-repeated irri- tation which they have undergone, or of the compression they endure from the rigidity of the muscle. The mechanical relations of the muscles have been excellently treated of in the article by E. Weber (1. c.), from which the following conclusions may be drawn. The extent of the shortening of the muscles amounts, * Translated by Dr. Jones, London, 1853. 262 SPECIAL HISTOLOGY. in experiments upon animals, on the average to fths, or in powerful muscles even to fths. The contractile force of a muscle does not de- pend, cceteris paribus, upon its length, but solely on its transverse sec- tional area; that is to say, on that of all its primitive fasciculi, so that a longer and a shorter muscle exert the same force, when the sum of the transverse sections of all the fasciculi is the same in both. According to the observations of Schwann and Weber, the elasticity of the muscles diminishes at each contraction, and consequently the molecular motions, called into play in them under the nervous influence, must be connected with a change in their substance of an altogether peculiar kind, which, however, can certainly only be regarded as a secondary effect. The degree of contraction differs according to the amount of antagonism with which it meets ; if the latter be sufficiently powerful, no true move- ment of the limb takes place, that is to say, the points of origin and insertion of a flexor muscle (for instance) do not approximate ; never- theless, the fibres themselves contract to a certain extent, in consequence of which the whole muscle becomes tense. This tension must be care- fully distinguished from that dependent upon the muscular elasticity, which is generally much less considerable. What has been termed the "tone" tonus of muscles, does not in most cases depend upon con- traction, but is an elastic tension ; I therefore hold, that the posture of the body and the occlusion of the transversely striated sphincters during sleep, has nothing to do with a contraction of the muscles, although such contraction is indubitably requisite to bring the body into this posture. In my opinion, during sleep, all the muscles (of course, with the excep- tion of the respiratory) are at rest, being held in a state of tension, and of antagonism to their opponents merely by their elastic force, and are consequently in the condition of a muscle when supported, in a person in the waking state. As for instance, a biceps, when the arm is bent, may immediately lose its tension if the arm be supported, so in the same way may all other voluntary muscles; only it must not be forgotten, that such a condition of muscular rest may ensue upon all conceivable degrees of contraction. Even the orbicularis oris, when contracted, may be at rest and lose its vital tension. The mouth, nevertheless, will re- main closed, for this reason, that although the elastic force, as always after a contraction, will not fail to exert a certain degree of extension upon it, it is unable to open the mouth, owing to its limited amount and inability to overcome the weight of the lips. I do not believe in any muscular "tone," if under that term be understood a long-continued involuntary contraction (though at first excited by the will) ; but am of opinion, that what has been mosj; generally described under this name, is merely an elastic tension, which has been confounded with the con- traction upon which it has ensued. Prom all we know, the nerves are incapable of exciting a long persistent contraction in the striped muscles, THE MUSCULAR SYSTEM. 263 but very capable of producing great effects, when the states of contrac- tion and of rest are duly alternated^ as for instance in walking, running, &c., and in the heart and respiratory muscles. The importance of this view of the nature of the muscular "tone," as regards the physiology of the nerves, is sufficiently obvious ; but in pathology also, it may be employed, in explanation of the retraction of divided muscles, and the shortening which takes place in muscles whose antagonists are paralyzed. The former, as correctly pointed out by E. Weber, depends upon the elastic force, and takes place, as far as I know, only in extended, tense muscles, but not in those which are in a state of contraction, which, on the contrary, when cut across, immediately be- come lengthened, as may be readily observed in the Frog. It is quite true, that contractions also take place in divided muscles, in conse- quence of nervous influence ; but these are never more than local, and cease without the production of any important effect on the form of the wound in the muscle. The shortening which occurs in the antagonists of paralyzed muscles, is not referable either to the elastic force of the non-paralyzed muscles, which is much too slight to influence the position of a limb, or to their persistent "tone," but depends simply upon the voluntary innervation of the muscles, which are still in an active condition, and which, no longer meeting with any opposition from their antagonists, draw the limb in their own direction. The persistence of the oblique position which now ensues, may be readily explained without our necessarily assuming the existence of a permanent contraction, when it is considered that muscles, the antagonists of which are paralyzed, never again become elastically tense. In lead-palsy, for instance, when the first contraction of the flexors, consequent upon the paralysis of the extensors, ceases, the former, even under the most favorable circumstances, become ex- tended only so far as to assume their natural form, a condition from which necessarily results the semiflexed position of the part affected. In accordance with this view, I regard the permanent condition of the unaffected side of the face, in one-sided paralysis of the facial nerve, and that of the upper eyelids in blepharoptosis, as produced, not by a per- sistent contraction, but as indicative of a state of perfect rest in the muscles, except when voluntary movements take place. The falling of the upper eyelid is explained by the paralysis of the levator, and the inability of the orbicularis, by its extension after a previous closure, to raise the eyelid beyond a certain point. In the same way the distortion of the face is produced, at first by the voluntary contraction consequent on the paralysis, upon the cessation of which it is impossible that the previous symmetry of the features should be restored, because the anta- gonist muscles on the opposite side are paralyzed, and their slight elastic force during life is insufficient, simply upon the cessation of the contrac- 264 SPECIAL HISTOLOGY. tion, to restore the pristine position of the lips, angle of the mouth, &c. An actual distortion, therefore, dependent upon persistent muscular contraction, can only take place in consequence of morbid conditions of the central organs. In the investigation of the muscles it is necessary that they should be studied in the fresh state, and with the aid of various reagents. The primitive fasciculi are most easily isolated in muscles which have been boiled or immersed in spirit, in which also, the transverse strise are for the most part very well displayed, as is also the case after treatment with corrosive sublimate or chromic acid. In the study of the transverse strise, it is above all indispensable that the muscles should be viewed in various degrees of extension and contraction (Fig. 109). The former conditions, which are well worth observation, are readily viewed, if long slender muscles, such as the hyoglossi of the Frog, &c., are examined on a wooden stage having a central opening filled in with glass. It will then be seen, when no exten- sion whatever is employed, that the transverse strise are narrow (about 0-0004 of a line) and very closely approximated, and that the fasciculus itself is broad; whilst, when it is extended to the utmost, the stripes are 0-0008 of a line wide, and placed at the same distance apart, and that the fasciculus is narrower. The contractions must be observed either in fresh muscles still quivering, and kept moist with serum, albumen, or vitreous humor; or in the way pro- posed by E. Weber, and which consists in the galvanizing, by means of the rotation apparatus, of the muscle to be examined, such, for in- stance, as the abdominal muscles and slender muscles of the extremities in the Frog, the diaphragm and cutaneous muscles of the smaller Mam- malia, &c. For this purpose the muscle must be placed upon a piece of looking-glass, from a small space in the middle of which the metallic coating has been removed. One of the conducting wires is brought through an opening in the stage, or else affixed to it so as to be im- movably in contact with one of the portions of tinfoil. If the muscle now be viewed under a magnifying power of 100 linear, whilst the second conducting wire is brought in contact with the other portion of tinfoil, the moment the circuit is completed, its fibres will be seen to contract in a rectilinear direction, and at the same time to become thicker, whilst the transverse striae are more closely approximated (vide Fig. 109, which represents both a contracted and an extended muscle). The muscular fibres remain in this condition so long as the galvanic influence is kept FIG. 109. A primitive fasciculus of a Frog's muscle in different degrees of extension : Jl, the fasciculus, stretched and slender, with broad distant transverse strice; J5, the same not extended, broader, and with narrower, closely approximated strise Magnified 350 diameters. THE MUSCULAR SYSTEM. 265 up, whilst when the circuit is broken they elongate themselves as rapidly as they contracted, and present zigzag flexures, when the muscle is lying free, but not when it is stretched by small weights attached to it by threads. From this it is evident, that if zigzag flexures take place during life, which is not yet known to occur, they can only arise when muscles in the quiescent condition are not in a state of tension ; as, for instance, in the case of a flexor muscle, which has come into a state of rest after it has produced its full effect upon the limb. The sarcolemma is readily seen in the muscles of Amphibia and Fishes, especially in specimens preserved in spirit, in which it frequently, but for the most part in places, appears at a distance from the fibrils. In the higher animals and in man, it is occasionally seen when the fasciculi are teased out ; and also in macerated and boiled muscles, and on the addition of acetic acid or alkalies. For this purpose I would especially recommend caustic soda, which in many cases renders the contents of the muscular tubules so fluid, that they escape in a continuous stream together with the nuclei, when the sheaths come very clearly into view. In no case, however, is the sarcolemma, in man, more beautifully exhibited than it is in softened, atrophied muscles which have undergone fatty or other de- generations ; and, in fact, the greater the degree of degeneration, the more distinctly is this structure exhibited. The muscular fibrils, in fresh muscles, are constantly visible only in a transverse section, and in the thoracic muscles of insects, elsewhere it is true they are occasionally seen, but more by chance than otherwise. They are easily isolated artificially in preparations preserved in spirit, particularly in the peren- nibranchiate Reptiles (Siredon, Proteus, &c.), by treatment with chromic acid (Hannover), by maceration for from 8 to 21 days, at a temperature of 18 R. in water, to which, for the prevention of putrefaction, some corrosive sublimate has been added (Schwann) ; maceration also in the fluids of the mouth (Henle) allows of their being readily exhibited ; whilst, according to Frerichs (Wagner, " Handworterb.," III. I. p. 814), in the stomach, the fasciculi break up into Bowman's discs. The nuclei of the fasciculi are best studied under the application of acetic acid ; by soda (vide supra) they may be isolated, and by potassa be made to swell considerably (Donders). On the subject of the effect of various reagents on the elementary tissues of muscle, the treatises of Donders (Holland. "Beitrage") and Paulsen (" Observ. michrochem.," Dorpat, 1849) may be consulted. The vessels of muscle are studied in fresh, thin muscles, and in injected preparations; the nerves in the smallest human muscles, in the muscles of the smaller Mammalia, in the cutaneous muscle on the thorax of the Frog, with or without the addition of soda. The perimysium, and the form and position of the muscular fibres, are very well shown in transverse sections of half-dried muscles; and the same observation holds good with respect to the elementary tissues of the tendons. The 266 SPECIAL HISTOLOGY. insertions of the latter into the bones, and their cartilage-cells in those situations are readily seen ; in the tendo Achillis, for instance, in vertical sections of dried preparations; with respect to their relation to the muscular fasciculi, vide supra, 81. In order to examine the cartilage- cells in tendons, thin horizontal sections are taken from the surface, which are treated with acetic acid, or a very dilute solution of soda. For the study of the development of muscle, the naked Amphibia must be placed in the first rank, and the Mammalia only in the second. Literature. Besides the memoirs, cited in 27, there are to be men- tioned: G. Valentin, article " Muscles," in the " Encyclopaedic Dictionary of the Medical Sciences," vol. xxiv. pp. 203-220, Berlin, 1840 ; H. R. Ficinus, "De fibrse muscularis form& et structure Diss. inaug.," Lips., 1836, 4, cum tab. ; F. Will, some remarks upon the origin of the trans- verse stripes of muscles, in Muller's "Archiv," 1843, p. 358 ; R. Remak, on the " Development of the Primitive muscular Fasciculi," in Froriep's "N. Notiz.," 1845, Nr. 768 ; Ed. Weber, art. "Muscular Motion," in R. Wagner's "Manual of Physiology," vol. iii. 2d division, 1846 ; Kol- liker, in "Ann. d. Sc. Nat.," 1846 ; Dobie, " Observations on the Minute Structure and Mode of Contraction of Voluntary muscular Fibre," in "Ann. Nat. Hist.," N. Ser. III. 1849; Lebert, " Recherches sur la For- mation des Muscles dans les Animaux vertebras, in Ann. d. Sc. N.," 1850, p. 205. OF THE OSSEOUS SYSTEM. 88. The Osseous System consists of a great number of hard organs, the Bones, of a peculiar, uniform structure, which are united either immediately or by means of other tissues, such as cartilage, ligaments, or articular capsules, into a connected whole the skeleton. The osseous tissue, in man, presents two principal forms the compact and spongy. The perfect solidity of the former, however, is only appa- rent, as, even to the naked eye, it is seen to be penetrated by narrow channels which run in various directions, and by a still greater number of similar but smaller canals, which are brought into view by the micro- scope. These vascular or Haversian canals (medullary canals of authors), may be said to be almost entirely absent in the spongy substance, in which they are represented by wider, rounded, or elongated spaces, visible to the unassisted eye, which are filled with marrow, in some bones occupied by veins or nerves (cochlea), and termed the medullary spaces or cells (cancelli, cellules medullares). These spaces all anasto- mose together, and are formed by the reticular arrangement of the small quantity of osseous tissue, which is disposed in the form of fibres, larninse, and small rods. When the spaces are of a larger size, the substance is THE OSSEOUS SYSTEM. 267 termed subst. cellularis, and when smaller, subst. reticularis. The latter, in some situations where the cavities are smaller, and the osseous parti- tions stronger, approaches in character the compact substance, although it does not actually become such ; and in others it passes without any defined limit, into compact tissue. This does not, however, prove that the two substances are identical, but as we learn from observation of their development, depends simply upon the circumstance that the spongy substance very frequently arises in a partial expansion of the compact. The share taken by the two substances in the formation of the different bones, and parts of bones, varies very considerably. It is only in a few situations that the compact substance is met with by itself without vascular canals as in the lamina papyracea of the ethmoid bone, some portions of the lachrymal and palate bones, &c. It occurs more frequently, however, with vascular canals, and without spongy substance as in many individuals in the thinnest portion of the scapula, ilium, acetabulum, cranial bones (ala magna, parva of the sphenoid, the orbital process of the frontal bone, &c.) Spongy substance with a thin compact cortex, without vascular canals, exists in the auditory bones, on the surfaces covered with cartilage of all bones, probably also in the smaller spongy bones. In all other cases, and consequently in most situations, the two substances are conjoined, but in such a way, that sometimes the spongy substance predominates (spongy bones and parts of bones), as in the vertebra?, carpal and tarsal bones ; sometimes the compact, as in the diaphyses of the long bones ; or the two are in equal proportions, as in the flat bones. 89. Intimate Structure of the Osseous* Tissue. The osseous tissue consists of a dense, for the most part indistinctly lamellar fundamental substance or matrix, penetrated by vascular canals and numerous minute microscopic spaces the bone-cells, or lacuna? (bone-corpuscles of authors), having very minute hollow processes, the lone-canaliculi. The vascular canals of the bones, or the Haversian canals (canaliculi medullares), are minute tubules, having an average diameter of -QI- C-OS of a line, and in the extremes one varying from 0*004 to 0-18 of a line, and which, except in the thinner parts of the facial bones, as above mentioned, exist universally in the compact substance, forming in it a wide network similar to that of the capillaries. In the long bones, and also in the ribs, clavicle, pubis, iscJiium, and lower jaw, they run chiefly in a direction parallel to the long axis of the bone, and, as shown in longitudinal sections, either parallel to the surface or perpendicular to it, at distances varying from 0*06 to 0'14 of a line apart. They are connected by transverse or oblique branches, which run in the direction both of the radius and of the tangents of a transverse section of the bone. Consequently, under a low magnifying power, in longitudinal 268 SPECIAL HISTOLOGY. sections of one of those bones, either parallel to the surface or perpen- dicular to it, closely approximated canals running parallel to each Ficr. 110. Fisr. 111. other, chiefly in a longitudinal direction, are seen, here and there with connecting branches, and thus forming a network, consisting of elon- gated, and most generally rectangular meshes (Fig. 111). And in a transverse section transverse sections of the canals, placed at tolerably defi- nite but small distances apart, are prin- cipally apparent (Fig. 112); which, more especially in younger bones, are occasionally connected by a tangential branch, and some anastomoses in the direction of the radius. In transverse sections of festal and undeveloped bone (in man even at the age of eighteen), scarcely any transverse canals occur, but chiefly those running horizontally FlG. 110. Segment of a transverse section from the shaft of the femur of an individual 18 years old: a, Haversian canals; 6, their openings internally; c, externally ; d, osseous sub- stance with lacunae. In this figure transverse sections of vascular canals and fundamental lamellae are not shown. Magnified 350 diameters. FlG. 111. Haversian canals from the superficial lamellae of the femur of an individual 18 years old, treated with hydrochloric acid : a, canals ; 6, osseous substance with lacunae. Magnified 60 diameters. THE OSSEOUS SYSTEM. 269 in the direction of the tangents and radius (Fig. 110), so that the bones appear to consist entirely of short thick lamellae, each of which, upon closer examination, is seen to belong to two canals, and exhibits a pale central line, indicating the division between the two constituent portions of which it is formed. In the jto bones, the greater number of the canals do not run in the direction of the thickness of the bone, but almost all, parallel with its surface, and indeed in lines which may be conceived as radiating from one point (tuber pariet ale, front ale, upper and anterior angle of the scapula, articular portion of the ilium) in a penicillar or stellate manner towards one or several sides ; or less frequently, as in the sternum, are all parallel to each other. In the short bones, lastly, there is most usually one predominant direction in which the canals run, as the ver- tical in the vertebrae, that of the long axis of the extremity in the carpal and tarsal bones, &c. ; it must be remarked, however, that the larger processes of these bones, as, for instance, the spinous processes of the vertebrae, differ in this respect from the rest of the bone, and, like those of other bones, such as the coracoid and styloid processes, exhibit the same disposition of the canals as that which exists in one of the shorter cylindrical bones. The lamellae, fibres, and bars of the spongy substance, occasionally present a few vascular canals, but only when they are of some thickness. As the Haversian canals are vascular channels, they open in certain situations : 1, externally, on the outer surface of the bone ; and, 2, internally, on the walls of the medullary cavities and spaces. In both situations, excessively fine and coarser pores may be everywhere per- ceived, partly visible to* the naked eye, and which are more numerous in proportion to the thickness of the cortex of the bone. But the rela- tion of the vascular canals in the compact substance to these canals thus proceeding from within and without, only partially resembles that between the branches and trunks of vessels, and only in the outermost and innermost lamellae of the cortical substance. In the interior of the cortical portion of a bone the canals are independent, and morphologi- cally may be most aptly compared to a capillary network, which* at its borders is in connection at many points with larger canals. Where the cortical substance rests upon the spongy substance, as in the interior of the ends of the diaphyses, and in the lateral periphery of the apopliyses, the vascular canals are continuous, sometimes abruptly, sometimes quite gradually, expanding in an infundibuliform manner, and frequently anastomosing, with smaller or larger medullary spaces, so that, very often, no definite limit is perceptible between them. I have never yet noticed caecal terminations of the vascular canals ; it is, however, certain that in many situations on the surface they must constitute, over exten- sive spaces, closed networks, especially where very few or no vessels 270 SPECIAL HISTOLOGY. enter the compact substance, as at the points of insertion of many tendons and ligaments, and beneath several muscles (temporal).* 90. The matrix of bone is lamellar, and the lamellae (Fig. 112) are apparent in thin sections, but are still better shown in bones from which the earthy matter has been removed, or which have been exposed to the weather or calcined, in which cases the lamellae exfoliate, and, in the cartilage of decalcified bones, may even be raised with the forceps. In the middle portions of the cylindrical bones they constitute two systems : one general, in which the lamellae are parallel with the external and internal surfaces of the bone, and numerous special ones, around the separate Haversian canals. These two systems are in some places in immediate connection, but, in most, merely in apposition, and on that account they may conveniently be regarded as of two kinds ; a view with respect to them which is in some degree supported by the pheno- mena presented in their development. The lamellce of the Haversian canals (Fig. 112 c, 113 5) surround those canals concentrically, in greater or less number. They consti- tute, as it were, the walls of the canal, and are intimately united to each * [A most valuable contribution to our knowledge of the structure and development of Bone has lately been made by Messrs. Tomes and De Morgan, in their " Observations on the Structure of Bone," read before the Royal Society in June, 1852, but not yet published. We are enabled, however, by the kindness of those gentlemen in allowing us to inspect many of their preparations, and in furnishing us with the proofs of their paper, to make some very important additions and corrections to the text. We may add, that although we do not always agree with Messrs. Tomes and De Morgan in the interpretation of the facts, differences which we shall duly note, our own investigations have led us to believe that their paper is by far the most accurate account of the process-of ossification which has yet appeared. These writers have pointed out the important fact, that, besides the well-known Haver- sian canals, other cavities exist in bone, which they denominate Haversian spaces. These have irregular outlines similar to that of the surface of exfoliations, while the boundaries of the Haversian canals are always more smooth and rounded. Again, in the latter, the laminae are more or less conformable with the canal ; while the walls of the spaces are formed by the unconformable edges and surfaces of the laminae of the adjacent Haversian canals, which have, as it were, been eaten away to form the space. In fact, bone, so far from being a permanent or stationary structure, is continually being deposited, and as con- stantly re-absorbed. The Haversian spaces are the result of the absorption of previously- existing osseous tissue ; but when this process has gone on to a certain extent, deposition commences in the spaces, and they are converted into Haversian canals. The calibre of these canals now becomes narrowed up to a certain point by the continual laminar deposi- tion of ossific matter, which, after a while, is traversed by new absorptive tunnels, or Haversian spaces, and is removed in its turn. The spaces are very numerous arid large in newly-formed bone situated near ossifying cartilage; while, in older bone, they are far less frequent and generally smaller. They are, however, never absent ; being found even in old subjects. They may be observed in various conditions in a series of sections. In one place the space will have attained a large size, while, in another part of the same section, its commencement will be seen extending from one side of an Haversian canal. One side of a space may be becoming the seat of a new system, while the opposite is undergoing further enlargement. TRS.] THE OSSEOUS SYSTEM. 271 other, much in the same way that the laminae of the walls of the larger vessels are continuous with each other. The number of lamellae belong- Fiff. 112. Fig. 113. ing to a canal, and the collective thickness of the system formed by them varies not inconsiderably, and bears no constant relation to the size of the canal, as is the case to some extent in the vessels ; small canals, therefore, are not unfrequently surrounded by numerous lamellae, and larger ones by but few.* In general, it may be said that the largest FIG. 112. Segment of a transverse section of a human metacarpal bone, treated with oil of turpentine : a, external surface of the bone, with the exterior fundamental lamellae ; 6, internal surface towards the medullary cavity, with the inner lamellae; c, Haversian canals in transverse section with their lamellar systems; d, interstitial lamellae ; e, lacunse and processes. Magnified 90 diameters. FIG. 113. Portion of a transverse section of the shaft of the humerus, magnified 350 dia- meters, treated with oil of turpentine : a, Haversian canals ; 6, their lamellar systems, each lamella presenting a more transparent and more opaque portion, with radiating striae in the latter; e, darker lines, which probably indicate greater intermissions in the deposition of the osseous substance ; d, lacunae without visible rays. From a preparation by Dr. H. Miiller. * [The "interstitial laminae" are the remains of Haversian systems, the larger parts of which have been removed by absorption to form new spaces. The irregular outline of the 272 SPECIAL HISTOLOGY. canals have thin walls, those of a middle size thick ones, and the most minute, again, walls of little thickness. The thinnest walls I have commonly noticed measure 0-008-0-02, and the thickest, 0*08-0*1 of a line. The thickness of the lamellae varies between 0-002 and 0-005 of a line, being on the average 0*003 to 0*004 of a line ; in number there are usually from eight to fifteen ; sometimes, however, no more than four or five, and occasionally as many as from eighteen to twenty- two. The lamellae of the Haversian canals, together with their canals, extend to the internal and external surfaces of the diaphyses, where they are connected with the general lamellae above mentioned, the fundamental lamellce (Fig. 111). The latter constitute an external and an internal layer, and penetrate also into the substance of the diapliysis, where they are interposed between the separate lamellar systems and the medullary canals. The two former layers, or the external and in- ternal fundamental lamellce, are parallel to the external and internal surfaces of the bone, and vary in thickness apparently without any definite rule, from 0*02 to 0*3, or even 0*4 of a line. The latter, or interstitial fundamental lamellce, are seen most clearly where the super- ficial fundamental laminae are developed, in partial connection and parallel with which they extend from without inwards, and from within outwards, some distance into the substance of the diapJiyses, where they are interposed, in masses varying in thickness from 0*02 to 0*12 of a line, between the other lamellae (Fig. 112 d). In the interior of the compact substance, on the other hand, in man, the Haversian systems are so closely crowded that there can be no question as to the non-exis- tence of lamellar groups between them, and it is evident that those lamellae, which in a transverse section appear in man to be parallel with the surface, almost all belong to horizontal canals ; and it is but rarely that distinct interstitial masses are seen, as is usually the case in other mammalia. The thickness of the separate lamellae just described is much the same as that of the lamellae of the Haversian canals, and their number varies from 10 to 100. We have hitherto considered only the diapliyses of the long bones. In their apophyses, the thin cortical layer of compact substance natu- rally presents only a few systems of Haversian canals, which, however, are constituted as elsewhere. The exterior fundamental lamellae are few in number, and internally, owing to the existence there of the spongy substance, they are wholly wanting. In the latter substance, the very few Haversian canals present lamellar systems as usual, except that they are thin, and the remainder, according to the condition of the osseous network, consists of a lamellated and fibrous tissue, which in outermost of the lamina of an Haversian^canal (see Fig. 113) results from its being the first deposition within the pre-formed irregular Haversian space. (Tomes and De Morgan, 1. c., p. 5.) TRS.] THE OSSEOUS SYSTEM. 273 general follows the contour of the medullary spaces and cells. The flat and short bones present a similar arrangement internally, whilst the cortical substance of these bones diifers from that of the cylindrical, only in the circumstance, that the fundamental lamellae, in the flat bones, form layers parallel with both surfaces of the bone. The thickness of the fundamental lamellae in the cranial bones (parietal), is sometimes the same in both aspects, and varies from 0'08 to 0-16 of a line, some- times they are wanting in vascular situations, and in places, wholly so, on the external aspect of the bone, in which case the Haversian lamellae reach almost to the surface. With respect to the intimate structure of the osseous lamellae, which is best studied in transverse sections, dried, polished, and sufficiently thin, there is usually evident, besides the bone-cells and canaliculi, in the generally not very distinct lamellae, an extremely fine though very distinct punctuated appearance, so that the whole osseous tissue appears granular, and to be composed as it were of separate, densely crowded, pale granules, measuring 0-0002 of a line (Fig. 114). If water or weak syrup, or albumen, be applied to a slice of bone, it assumes a condition probably similar to that which it possesses Flg during life. The lamellae, for the most part (both in transverse and perpen- dicular sections), become clearly visible, and their granular aspect is quite dis- tinct, although not so de- fined as before the bone was thus treated. For in the first place, together with the granules, there is exhibited a close, pale striation, referable to the canaliculi, which are filled with fluid and which, extending in various directions through the tissue, renders its delineation more complex ; there are also apparent in each lamella, as it were, two layers, one pale and more homogeneous, the other darker and granular, which latter chiefly is striated. When this condition is clearly displayed, an extremely delicate marking is produced, resembling that seen in transverse sections of certain urinary calculi (Fig. 113). When once seen in moistened sections, indications of this arrangement will occasionally be observed in dried preparations. In bone treated with hydrochloric acid, the granules and striae (dependent on the canaliculi), in sections both transverse and perpendicular to the FIG. 114. Portion of a perpendicular section of a parietal bone, magnified 300 diame- ters : a, lacunae, with pale, only partially-visible prolongations, filled with fluid as in the natural state : b, granular matrix. The striated places indicate the boundaries of the lamellae. 18 274 SPECIAL HISTOLOGY. surface, are less distinctly apparent, whilst the lamellar structure is very manifest, and most generally two layers may be noticed in each lamella, though by no means so clearly as shown in Fig. 113.* In sections parallel to the surface, the bone, in many situations, appears almost homogeneous throughout, presenting no trace of a granular structure, whilst in others a structure of that kind is obscurely visible, together with minute points (Deutsch), and besides these a longitudinal striation ; which last gives the whole a fibrous aspect. From this circumstance, many authors appear to have been led to describe the bone as composed of fibres, but quite incorrectly, for although the study of their develop- ment shows, that the ossifying parts are, to a certain extent, very dis- tinctly fibrous, it is impossible to demonstrate anything of the sort in perfect bone. On the other hand, there is no doubt that a coarsely fibrous appearance exists, and especially in the bone-cartilage of the compact substance, as has already been remarked by others, and which is probably due to the fibrous fasciculi of the original blastema; care however should be taken not to look upon longitudinal sections of lamellae as such fibres. f When bone is burnt and the fragments crushed, * [According to Tomes and De Morgan, the laminae, when well developed, are always constituted of two portions, an outer, highly granular,, often composed of a single line of large granules, and an inner, which is singularly clear and transparent, and to all appear- ance without granulation or any recognizable structure. This distinct separation into two layers, however, does not always exist; and in a complete Haversian canal, the innermost lamina of all is frequently clear, glassy, and structureless. The circumferential laminae are not so constantly present as is generally supposed, and they rarely entirely surround the shaft of a long bone, still more rarely the flat bones. In the fast-growing bones of young animals they are absent, while in adults they are usually well developed in some parts ; so that their presence seems to indicate that the bone is nearly stationary in its growth. In young, rapidly growing bone, the circumferential laminae are replaced by a series which may be called the undulating lamina. The surface of the bone sends off processes, formed of reduplicated lamina?, which eventually arch over and enclose those vessels of the periosteum which lie nearest them. The spaces thus formed become the seat of Haversian systems. Young growing bone, therefore, may be distinguished from that of adult animals, by its being composed of Haversian systems with intervening undulating laminae. (Tomes and De Morgan, b. c., pp. 4-6.) TRS.] t [Messrs. Tomes and De Morgan (1. c., pp. 13, 14) adduce very good reasons for believ- ing that the fibrous appearance which may often be detected in the laminaB of bone arises from imperfect illumination and definition, and express their belief that bone substance " is composed of granules or granular cells, imbedded in a more or less clear, homogeneous or subgranular matrix." They go on to say, " Thus as regards the basement, homogeneous tissue, it will be found that where lamination is highly developed, the laminaB have a trans- parent and structureless, and a more opaque and granular part, to which the former appears to be the matrix. The peripheral lamina of the Haversian systems is generally clear and free from granularity, and the internal lamina sometimes presents a similar structureless appearance. The matter which fills up the Haversian systems in the full-grown antlers of the Cervidae affords another and a very striking example of transparent structureless osseous tissue, which in this instance is the more distinct, from the absence of canaliculi in its sub- stance. Then, again, we have another instance in the clear tissue which is sometimes found between the superficial Haversian systems of ordinary bone. It has already been described as a non-laminated element found on the surface of certain bones. In the instances already cited, and no doubt in many others which may be found in the skeletons of the lower ver- THE OSSEOUS SYSTEM. 275 it affords, according to Tomes, minute angular granules, from -Jth to the diameter of the human blood corpuscle, and measuring, according to Todd and Bowman, gouoth-niosth of an inch, and which are also rendered evident when bone is boiled in a Papins' digester. From these particulars, and from the granular aspect of fresh bone, which has also been noticed by Tomes and by Todd and Bowman, and moreover from the pretty nearly equal size of the granules visible in it, with those described by Tomes, and lastly, from the circumstance that bone treated with hydrochloric acid, as well as when calcined, both present a perfectly homogeneous substance without vacuities, it may be assumed that the osseous tissue consists of an intimate mixture of inorganic and organic compounds, in the form of closely connected minute granules. 91. Bone Cavities or Cells, and Canaliculi (lacunce et canaliculi ossium). In dried sections of bone, there are visible, scattered through- out the entire osseous substance, in all the lamellae, microscopic melon- seed-shaped corpuscles, with numerous, fine, ramified, and partially anastomosing rays, whose opaque and white color (as viewed by direct light) is due, not to the deposition of calcareous salts, as was formerly supposed, and on which account they were termed " bone," or " calca- reous corpuscles," but simply to their being filled with air. In fresh bone, not yet deprived of its watery constituents, nothing can be seen in these bone-cells or lacunae but clear contents with a nucleus, which may best be described as the nutritive fluid of the bone, and conse- quently the designation above given to these cavities is the most suitable. The lacunce are elliptical, flattened cavities, having an average length of 0-01 of a line, 0-004 of a line wide, and 0-003 of a line thick, which give off both from the borders, and particularly from the surfaces, a great number of very fine canals, measuring 0-0005-0-0008 of a line in diameter the bone canaliculi above-mentioned (Figs. 115, 116, and 117) The lacunae are equally numerous in both of the lamellar systems before. tebrata, we have bone tissue without obvious granularity, and without obvious structure ; and although it forms but a small part of the general mass, yet from its constant presence at all ages and in all subjects, it must be regarded as an integral and normal part of mam- marial bone. The granular condition of bone tissue is tolerably obvious in all preparations, though it is much more marked in some specimens than in others. The amount of the component granules varies in different parts of the same specimen, and in specimens taken from different parts of the skeleton. Thus, in one situation, we may see laminae with a highly transparent part gradually merging into a transparent tissue, while in another the lamince may be granular throughout. Again, in young bone developed in cartilage, the part between the cells becomes highly granular, fragments of which may be found in certain adult bones, as in the petrous portion of the temporal bone. Bone near the articular surface frequently presents a well-marked granularity." We may remark, in addition to this very just account of the minute structure of bone, that of the lower vertebrata above referred to, the Skate offers one of the best examples of structureless bone, in those polygonal plates which are developed (not on the surface, as is commonly said, but) in the interior of the cartilaginous skeleton. TRS.] 276 SPECIAL HISTOLOGY. described, and are placed so close together, that, according to Harting (1. c., p. 78), from 709 to 1120, or, on the average, 910 of them occur within the space of a square millimeter. They lie for the most part within the lamellae, but also between them, and are in- variably placed with their broad sides parallel with the surfaces of the lamellae. The canaliculi proceeding from them are much branched, and penetrate the osseous substance in all directions, their course being irregular, and often actually curved. They proceed prin- cipally, however, in the first place, from both surfaces of the lacunae straight through the lamellae ; and secondly, parallel with the Ha- versian canals, from the two poles of the lacunae. It is only in certain limited spots that these canaliculi present ccecal termina- Fig. 115. ym?**- Fig. 116. tions ; everywhere else some of them anastomose in the most various ways with the canaliculi of the neighboring lacunae, whilst others FIG. 115. From a transverse section of the shaft of the humerus; magnified 300 diam.: a, Haversian canals; 6, lacunae with their canals, in the Haversian lamellae; c, lacunae of the interstitial lamellae ; d, lacunae with unilateral canaliculi proceeding to the surface of the Haversian system. FIG. 116. Section parallel with the surface from the shaft of a human femur magnified 100 diam. : a, vascular canals: 6, lacunae seen from the side, belonging to the lamellae of these canals ; c, lacunae viewed on the flat side, in lamellae which are cut horizontally. THE OSSEOUS SYSTEM. 277 communicate with the vascular canals, the medullary cavities, and the medullary spaces or cancelli of the spongy substance, or open on the surface of the bone. The entire osseous substance, therefore, is pene- trated ly a connected system of cavities and canaliculi, by means of which the nutritive juice secreted by the vessels is conveyed into its densest tissue. The lacunae and canaliculi do not exhibit precisely the same condi- tions in every part of the bones. In the lamellar systems of the Ha- versian canals, as seen in a transverse section, the elongated lacunae, by reason of their curvature, lie as it were concentric to the canal, and their excessively numerous pores or canaliculi necessarily produce a very close striation radiating from the vascular canal (Fig. 115). The lacunae are sometimes extremely numerous, sometimes more scanty; in the former case they are, for the most part, arranged in tolerably regular alternation, or one behind the other in the direction of the radius of the lamellar system ; but they are also frequently disposed very irregularly, either crowded together (vide the lower part of Fig. 115), or separated by wider interspaces. In horizontal and longitudinal sections of Haversian canals (Fig. 116), when the section has passed through the middle of a canal, the lacunae appear narrow and elongated, and disposed in rows one be- hind the other, and in numerous layers parallel with the canal ; and also furnished with numerous canaliculi, which proceed for the most part Fig. 117. directly inwards and outwards (consequently transversely through the lamellae), but partly in a direction parallel with the long axis of the FIG. 117. Lacunae viewed on the flat side, with the canaliculi, from the parietal bone; magnified 450 diam.: the spots on the lacuna? or between them belong to canaliculi, which are cut across, or are the openings of canaliculi into the lacunae ; a a a, groups of transverse sections of canaliculi, each group belonging to a lacuna which has been destroyed in the making of the section. 278 SPECIAL HISTOLOGY. canal. If the section strike the surface of a system, the superficial lacunas come into view, presenting very elegant forms, rounded or oval (Figs. 115 d, and 117), surrounded in an irregular manner by a complete tuft of canaliculi, which look directly towards the observer, and con- sequently appear more or less shortened, and by a smaller number of other canaliculi distributed on the surface of the lamellae. Occasion- ally, even in the thinnest parts of a section, there occurs a tuft of canali- culi, cut across transversely, and without the lacuna to which they belong, whence these portions of bone exhibit a sievelike aspect. All the canaliculi arising from the inner aspect of the innermost lacunae of an Haversian system, proceed towards the canal, with which they, by this means, communicate, as may be clearly seen in thin, perpendicular, and transverse sections of bones filled with air, and in the walls of medullary canals laid open longitudinally. From the borders and ex- ternal aspect of the same lacunae other canaliculi are given off, which per- haps occasionally terminate in blind extremities, but for the most part communicate with those of the neighboring, and particularly of the outer lacunae. The succeeding rows of lacunae are all mutually connected in a similar way, and thus the network of canaliculi and lacunae extends to the outermost lamellae of the system, where the lacunae either commuincate with those of the contiguous systems or of the interstitial lamellae, or terminate independently, in which latter case (Fig. 115 d) all the ca- naliculi, or at least most, and the longest of them, proceed inwards, that is to say, towards the vascular canal, from which they derive their nutritive fluid. In the interstitial osseous substance between the Haversian systems, when it exists in small quantity, the few lacunae, frequently not more than from 1 to 3 in number, are disposed more irregularly, and also present a rounded form (Fig. 115 e); when the interstitial substance is more abundant, and distinctly lamellar, the lacunae are also disposed more regularly, with their sides parallel to those of the lamellae. The canaliculi of these lacunae, in like manner, communicate with each other, and with those of the neighboring systems. In the outer and inner fundamental lamellae, lastly, the lacunae are all placed with their surfaces parallel with those of the lamellae, and consequently looking, for the most part, inwards and outwards, or towards the centre and periphery of the bone. In transverse sections they precisely resemble those of the Haversian systems, only that they are but little or not at all curved, except in the smallest cylindrical bones. In longitudinal sections, whether perpendicular or parallel to the surface, they present the conditions above described, with this limitation, however, that a larger number of lacunae, of course, are seen in the same space in the latter case than in the former, and also that the sievelike aspect described above is more frequently observed, giving the bone considerable resem- THE OSSEOUS SYSTEM. 279 blance to certain sections of teeth (Fig. 117). The canaliculi of these lamellae communicate, in part as usual with each other, in part open on the external and internal surfaces of the bone (Fig. 118). At the points of insertion of tendons and ligaments into the bones, the canaliculi of the outermost lacunae probably terminate in blind extremities ; a condition which obtains in every case, in those parts of bones which are covered with car- tilage (articular ends, ribs, surfaces of the bodies of the vertebrae, &c.) In I the rods, fibres, and plates of the 1 spongy substance, the lacunae are dis- fe posed in every possible direction, but for the' most part, with their long axis parallel to that of the fibres, bars, &c., and with their flat surfaces directed towards the cancelli. They anastomose also, in these situa- tions, by means of their canaliculi ; and the most superficial lacunae open freely into the cancelli. The size and shape of the lacunae, in man, upon the whole, vary but little. By far the greater number are melon-seed-shaped or lenticular, some, more fusiform or spherical. In sections of bone well filled with air, in which alone I have made my measurements, I find their average length to be 0-01-0-014 of a line, frequently under and above that size, or from 0-006 to 0-016, rarely 0-02 or even 0-024 of a line (cranial bones, lower jaw). The breadth, measured in horizontal sections, is 0-003-0-006 of a line; in transverse, it is usually somewhat greater, or as much as 0*008, or even 0*01 of a line, because the limits between the canaliculi and lacunae cannot always be accurately defined. Their thick- ness or depth, lastly, in the smallest lacunae, is 0-003-0-004, and in the larger 0-002-0-004 of a line. The diameter of the spherical lacunae is 0-006-0-008 of a line. The canaliculi are, on the average, 0-008-0-016 of a line long, seldom less or more, up to 0-02 and 0-024 of a line; in diameter they measure 0-0004 of a line ; at the finest extremities, 0-0005- 0-0008, on the average; 0-0008-0-001 of a line, at their origin from the lacunae. Their true distance apart, in horizontal sections, in which they appear as holes, is 0*0008-0-002 of a line; in transverse sections, in which they produce the radiating striae, in consequence of their being viewed in several planes, they appear to be somewhat closer together, or at distances varying from 0-0008-0-0012 of a line. The circumference FIG. 118. Portion of the surface of the tibia of the calf, viewed on the external aspect, , magnified 350 diam. : the numerous points are the openings of the canaliculi ; the dark, larger, indistinct spots indicate the lacunae to which these canaliculi belong, appearing from a greater depth. 280 SPECIAL HISTOLOGY. of a lacunas, together with the radiating canaliculi belonging to it, forms an imperfect sphere, having a diameter of from 0-02 to 0-034 of a line; with reference to which, however, it must not be forgotten, that individual canaliculi transgress the usual length of the others, as I have, in fact, measured anastomoses between two lacunas of the length of 0*04-0*045 of a line. The contents of the lacunce^ according to the later investigations of Bonders, Virchow, and myself, appear very closely to resemble those of the cells of cartilage during life ; that is to say, they are clear, probably viscid fluid, with a nucleus. If bone-cartilage be boiled in water or caustic soda for 1 or 2 minutes, these nuclei often show themselves very distinctly ; or opaque corpuscles make their appearance, which must be regarded as the contracted cell-contents including the nucleus, and analo- gous to the corpuscles in cartilage. A peculiar phenomenon is seen to occur, when bone is macerated in hydrochloric acid, which was first noticed by Virchow in a diseased, and afterwards in healthy bone, and by myself in the cementum of the horse's tooth, the lacunae become isolated, having longer or shorter processes, and appear like independent structures, or a sort of stellate cells. This phenomenon seems to depend simply upon the circumstance, that the tissue immediately sur- rounding the lacunae offers more resistance to the action of the acid than it does elsewhere. In the cementum of the horse's tooth, cells also enclosing the lacunae, and even Haversian ca- nals, may be isolated, the best proof, that everything which thus pre- sents itself in an isolated form, is not necessarily a morphological unity.* FIG. 119. A bone spicule from an apophysis, with distinct lacunae and nuclei. Boiled in water, and magnified 350 diameters. * [It is of very great importance in histology to keep in mind the caution expressed in the last paragraph of the text (see below, note 101), which applies as well to optical as to chemical distinctness. Tomes and De Morgan assert that both the lacuna and canaliculi have parietes, which are manifested by appearances similar to those observed in the dentinal tubes. They some- times found the lacunce and canaliculi filled up to a great extent with solid matter, so as to leave only a small space in the centre. An important modification of the lacunce, is described and figured by these authors (1. c., p. 8) in the circumferential laminae. Elongated tubes pass, in bundles or singly, more or less obliquely from the surface towards the interior of the bone. When long, they are sometimes bent once or twice at a sharp angle. They have parietes, and are connected laterally with the canaliculi. They occur irregularly in the circumferential lamina?, and in these only. [Similar tubes exist in the cementum of the Teeth.] We can confirm Messrs. Tomes and De Morgan's statement that the nuclei may be found without difficulty in recentjjone, and they may always be brought out with great distinctness by the action of dilute hydrochloric or strong acetic acid. This is especially the case in THE OSSEOUS SYSTEM. 281 92. The Periosteum. Among the soft tissues appertaining to bone, the periosteum is one of the most important. It is a more or less transparent, slightly glistening or whitish yellow, vascular, extensible membrane, investing a great part of the surface of bones, and contribut- ing most importantly to their nutrition, by the numerous vessels which it sends into their substance. The periosteum is not, everywhere, constituted alike. Opaque, thick, and for the most part with the glistening aspect of tendinous structures where it is covered only by the skin, or is connected -with fibrous parts, such as ligaments, tendons, fascice, and the dura mater cerebri, it is, on the other hand, thin and transparent in situations where muscular fibres arise directly from it without the intervention of tendon, and also on the diaphyses, where the muscles nearly rest upon the bone, as on the ex- ternal surface of the cranium (pericranium), in the vertebral canal, and in the orbit (periorbita). Where mucous membrane rests upon bone, the periosteum is, in most cases, very intimately united to it by the sub- mucous connective tissue, so that the two cannot be separated, and con- stitute a single membrane, which, as in the palate, alveolar processes, nares, &c., is of greater, or, as in the maxillary sinus, tympanum, ethmoid cells, &c., of less thickness. The connection of the periosteum with the bone itself is either more lax, consisting in simple apposition, and by more delicate vessels which penetrate the bone, or more intimate, taking place by means of larger vessels and nerves, and by numerous tendinous filaments. The former mode of connection is found especially where the periosteum is thin, and the osseous substance more compact, as in the diapJiyses, on the inner and outer surfaces, and in the sinuses of the cranium ; the latter, where the periosteum is thicker, and the compact substance thinner, as, for instance, in the apophyses, in the short bones, palate, and at the basis of the cranium. With respect to the intimate structure of the periosteum, it will be young bone. In old bone we have frequently been unable to discover them. Tomes and De Morgan, however, state that the nuclei are visible in sections of a fossil bone (supposed of a Pterodactyle) in their possession. Another peculiar condition of the " lacunal cells," described by these authors, is their ossi- fication. They found the light and spongy bones of old people to yield, if broken, a white powder, which was composed of large cells detached or united into masses. They are spherical, and contain a dark granular nucleus, which is surrounded by a thick transparent wall. Similar cells may be found adherent to the walls of the Haversian canals and can- celli; and in this case their nuclei have assumed the form of lacuna, and the canaliculi of adjacent lacuna advance into them. Similar cells may be found in most preparations of adult bone (1. c., p. 12). We must confess that we doubt the assumption of a lacunal form by the "nucleus" in these cases. We have repeatedly examined these bodies, but if the nucleus was visible at all, we found it unchanged, and often adhering to one side of the lacimce. Again, it is ques- tionable whether they may not rather be compared to the globules of dentine than to cells. TRS.] 282 SPECIAL HISTOLOGY. found to present, almost universally, excepting where muscles arise directly from it, two layers, which, although closely connected, differ, more or less distinctly, in their structure. The outer layer is composed chiefly of connective tissue, with occasional fat-cells, and is the principal seat of the true periosteal vessels and nerves, whilst in the inner layer, elastic fibres, commonly of the finer sort, constitute continuous, and often, very thick networks true elastic membranes superimposed one upon another, the connective tissue forming the less important element. Nerves and vessels occur in this layer also, but they do little more than merely pass through it, being destined for the bone itself. The parts of the surface of bones unprovided with periosteum are : 1. The articular extremities covered with cartilage, and all other places where the bone is covered with cartilage or fibro-cartilage. 2. Where ligaments and tendons are attached to the borders and surfaces of bones at a certain angle, as, for instance, at the insertions of the ligamenta flava, intervertebralia, iliosacra, interossea, teres ossis femoris, patellse, &c., of the tendons of the deltoid, coracobrachialis, popliteus, iliopsoas, triceps, sura?, quadriceps femoris, glutcei, &c. In all these situations, the tendons, ligaments, and cartilages, are attached directly to the bone, as has been already in part described, and not a trace of periosteum can be detected. 93. Marrow of the Bones. Almost all the larger cavities in the bones are occupied by a soft, trasparent, yellowish or reddish, highly vascular substance, the Marrow (medulla ossium). In the cylindrical bones, this substance is found in the medullary canal, and in the cancelli of the apophyses, whilst it is wanting in the compact substance, unless it be in the larger canals; the same is the case in the flat and short bones, the cancelli of which are filled with marrow ; but the diploe of the flat cranial bones, besides the marrow, also contains large veins, of which more will be said afterwards. In accordance with what has been re- marked, these venous spaces, the canales nutritii, Haversian canals, and the above described nerve-canals and air-cavities of the bones, contain no marrow. The marrow appears in two forms, one yellow, the other red. The former, as a semifluid substance, occurs principally in the long bones; and according to Berzelius, consists, in the humerus of the Ox, of 96*0 fat, 1-0 connective tissue and vessels, and 3-0 fluid with extractive matter, such as is found in muscle ; whilst the latter occurs in the apophyses, flat and short bones, above all in the bodies of the vertebra?, the basis cranii, the sternum, &c., and is distinguished not only by its reddish or red colour and less consistence, but also by its chemical composition ; for, according to Berzelius, this substance, in the diploe, contains 75-0 THE OSSEOUS SYSTEM. 283 water, 25-0 solid matters, such as albumen, fibrin, extractive matter, and salts, similar to those of muscle, and merely traces of fat. With respect to its structure, it presents, besides vessels and nerves, connective tissue, fat-cells, free fat, a fluid, together with, lastly, peculiar minute cells, marrow-cells. Connective tissue and fat are universally present, though in very various quantities. The former, on the surface of the larger medullary masses of the difapJiyses, is of rather firmer consistence, but cannot properly be described as a medullary membrane (endosteum, periosteum internum), because it does not admit of being separated as a continuous structure. In the interior of the marrow in the spongy bones, scarcely any connective tissue can be detected except in the larger masses of it, whilst in the diapJiyses, this tissue can be readily demon- strated as a very lax and delicate, areolated structure, containing the fat and supporting the vessels and nerves. Its elements correspond with those of the lax connective tissue (vide 24) ; although, as far as I have seen, it does not contain any elastic filaments. Fat-cells of 0-016-0-032 of a line, not unfrequently with a distinct nucleus, occur in large quanti- ties in the yellow, more dense marrow, quite as abundantly as in the panniculus adiposus, but for the most part not aggregated into distinct lobules. In the reddish marrow, when expressed, they are more rare; and in the red pulp of the bodies of the vertebrae and of the flat cranial bones, they occur only in very minute, scanty accumulations, or alto- gether isolated, to which circumstance, according to Berzelius, is owing the small quantity of fat in the diploe. In dropsical marrow these cells are frequently only half filled with fat, or with but one or more globules, containing, besides, a large quantity of serum ; and in hypersemia of the bones, they appear occa- sionally to be diminished in size, and occasionally elongated and fusiform. Free fat-globules, and a clear or yellowish fluid, are often met with in the softer kinds of marrow, and frequently in considerable quantity. That the former have not been set free from cells, in the preparation of the specimen, may be satisfactorily shown, but it must remain uncertain whether or not they are to be referred to cells that have ceased to exist. Lastly, there occur, together with some fluid, in all the red, or even only reddish marrow (never in the yellow), minute roundish, nucleated cells, exactly like those of the young medulla (vid. infra, fig. 132). These me- dulla-cells correspond in every particular with those, which Hasse and I (" Zeitsch. f. ration. Medicin," Bd. V.) found in the hypersemiated red marrow of the articular extremities of the cylindrical bones, but never- theless normally exist in the vertelrce, the true cranial bones, in the sternum, and in the ribs, whilst they are wanting in the long and short FIG. 120. Two fat-cells from the marrow of the human femur : a, nucleus; 6, cell-mem- brane ; c, oil ; magnified 300 diameters. 284 SPECIAL HISTOLOGY. bones of the extremities, and in the scapula and os innominatum, occur- ring apparently in variable number in the bones of the face.* 94. Connections of the Bones. A. synarthrosis, connection without articulation. 1. By suture. In this mode of connection, the bones are united by an extremely thin, membranous, whitish streak, to which authors have incorrectly given the name of sutural cartilage. It is composed merely of connective tissue, which, like that of the ligaments, extends, in short, parallel fasciculi, from the border of one bone to that of the other, and is characterized solely by the presence of numerous, short, unequal-sized, usually elongated nuclei. This sutural ligament, as it may be termed, is very evident as long as the cranial bones are still growing, at the same time, that it is softer and differently constituted (vide infra). As the growth of the cranium approaches its completion, this tissue gradually disappears, becomes firmer, and, in old age, seems, in many places, especially on the inner part of the sutures, and even before their com- plete obliteration, to be entirely removed. 2. Connection by ligament, syndesmosis, is effected by means of fibrous and elastic ligaments. The fibrous ligaments, constituting the majority of the ligaments, are white and glistening, corresponding in their struc- ture, partly with the aponeuroses and ligaments of the muscles, and partly with the true tendons. Elastic ligaments (Fig. 121), are, the ligamenta flava, between the arches of the vertebrae, and the ligamentum nuchse, which, however, is not nearly so well developed in man, as in some others of the Mammalia. The ligamenta flava are yellowish, highly elastic, strong ligaments, the elastic elements of which, in the form of roundish polygonal fibres, 0-0015 -0-004 of a line thick, united into a dense network, run parallel with the long axis of the vertebral column, and give the longitudinal, fibrillar aspect to the ligaments. Between these fibres, which are not collected either into fasciculi or lamellce, but are continuously connected through- out the entire thickness of each yellow ligament, there is interposed some connective tissue, upon the whole in small quantity, but demonstrable in every preparation, and occurring in the form of lax undulating fasciculi, * [These nucleated medulla-cells exist in great number in the superior maxillary bone of Man and of many of the Vertebrata. Several of them are sometimes enclosed in a common cell-wall, forming a variety of cell, frequently seen in pathological formations, viz. the parent-cell of the German authors, the plaque a noyaux multiples of Robin. The occurrence of nucleated cells in the normal medulla of the bones of the face has been mostly overlooked, and has hence given rise to many errors on the part of pathologists. In the description of morbid changes of the bones of the face, especially in those of the superior maxillary bone, representations are frequently given of small cancer-cells or nuclei, taken from the interior of the bone, which are but the normal nucleated cells of the medulla. Many tumors of the upper jaw have thus been pronounced cancerous, which were simply non-malignant hypertrophies of the bone. DaC.] THE OSSEOUS SYSTEM. 285 which are arranged parallel with the principal direction of the elastic fibres. According to Todd and Bow- Fig. 121. man (p. 72), the stylo-hyoid, and internal lateral ligament of the lower jaw, are, also, chiefly composed of strong elastic fibres. 3. By cartilage, synchondrosis. This mode of connection is effected either by cartilage alone, or 'asso- ciated with fibro-cartilaginous and fibrous tissue. The former condition is observed in the adult, only between the ribs and sternum, where, how- ever, properly speaking, a true syn- chondrosis exists only in the case of the first rib, the rest, from the second to the seventh, being connected with the sternum at the anterior extre- mity by articulation ; whilst the false ribs are either free at the ex- tremity, or are incurved one beneath the other. In the symphysis pubis, sacro-iliac synchondrosis, and the junctions of the bodies of the verte- brce, the surfaces of the bones are covered immediately by a layer of true cartilage, which, in the two former situations, is directly connected with the opposite layer, and in the latter by means of a fibro-cartilaginous tissue, and is externally encircled by fibro-cartilaginous, and fibrous, concentric layers. In the two former of these instances, there is, not unfrequently, a cavity in the interior of the connecting substance, so that the sacro-iliac sychondrosis, in particu- lar, may also be regarded as a sort of articulation (Zaglas). The intervertebral ligaments, or ligamentous discs, of the bodies of the vertebras, consist, 1, of exterior concentric layers of fibro-cartilage, and whitish connective tissue ; 2, of a central, principally fibro-cartila- ginous substance ; and 3, of two cartilaginous layers applied immedi- ately upon the bones. The concentric lamellae consist of alternate layers of connective tissue and of fibro-cartilage, which latter, even in fresh transverse sections, FIG. 121. A, a transverse section through a portion of the ligamentum nuchce of the Ox, magnified 350 diameters, and treated with soda : a, connective tissue, apparently homoge- neous; 6, transverse section of the elastic fibres (O004-001 of a line in diameter). J5, elastic fibres; a, from a human lig. subflavum, together with some connective tissue, 6, between them, magnified 450 diameters. 286 SPECIAL HISTOLOGY. may be recognized as dull yellow streaks, which become hard and trans- parent in water. The fibro-cartilage, on microscopic examination, pre- sents minute, elongated cartilage cells, disposed serially in a fibrous tissue, differing from connective tissue in its greater rigidity, the absence of distinct fibrils, its great resistance to alkalies and acetic acid, and the total absence of elastic fibres. The whitish layers of the outer laminae, although their fibrils are rather more rigid than those of the common ligaments and tendons, are less easily separated, and present 'but few fusiform cells, and frequently no elastic fibres whatever among them, must nevertheless, at present, be regarded as composed of connective tissue. These laminae are from J to j of a line and more in thickness, and form entire circles or segments of such, which, alternating with the somewhat thinner, and also fre- quently incomplete, rings of fibro-cartilage, with which they are closely connected, together with the latter constitute the larger half of the in- tervertebral ligaments. The general direction of the fibres of both sets of laminae is from above to below. They are, however, invariably oblique, so that those of the different layers cross each other. Besides which, it must be remarked, that the individual layers themselves also exhibit a more or less distinctly foliated structure, constituted in such a manner that the fine lamellae, in the portions composed of connective tissue, observe the same direction as the layers themselves, whilst in the fibre-cartilaginous portions they are disposed more in the direction of the radius of the ligamentous disc. The softer central substance of the intervertebral ligaments, or the gelatinous nucleus of authors, does not differ, essentially, from the por- tions above described ; for, even in this situation, layers of connective tissue occur, although they gradually diminish in proportion to the fibro-cartilage, and are less distinctly defined. The nearer we approach the centre, the less evident is any trace of an alternation of different 122 layers, and of a concentric ar- rangement of them ; the whole becomes transparent, soft, and, finally, almost homogeneous. The microscope shows the predomi- nance of fibro-cartilage, with large cells (0-012-0-024 of a line), frequently one within the other (Fig. 122) ; the uniformly thickened walls of which, composed of FiG. 122. Cells from the gelatinous nucleus of the lig. intervertebralia : 1, large parent cell, a, with a septum derived from two secondary cells of the first generation, and five secondary cells, 6, of the second generation ; with concentrically thickened walls and shrunken nuclei, c, in the small cell cavities: 2, parent cells, a, with two secondary cells, separated by a delicate septum, 6, and which, with uniformly thickened walls, contain a minute cavity and shrunken nucleus, c. THE OSSEOUS SYSTEM. 287 concentric layers, often enclose merely a minute cavity, with a shrunken nucleus; and besides these, smaller cells frequently in process of dissolu- tion, isolated or aggregated together ; and, lastly, an indistinctly fibrous or granular matrix, not unfrequently observed in a state of disintegra- tion, and a considerable quantity of fluid contained in larger or smaller areolar spaces in it. The more central portions of this fibrous substance gradually pass into a thin, hard, yellowish lamella of true cartilage, with thickened cells, not unfrequently beset with calcareous particles, which adheres to the bone not unlike an articular cartilage, though less firmly. More externally we find a cartilaginous substance, in the form of isola- ted, minute, discoid plates or particles, which appear to be in more im- mediate connection with the fibro-cartilaginous portions, and between these a connective tissue, with scattered cartilage-cells, as in the inser- tions of the tendons into the bones (vide 81). The more exterior por- tions of the surfaces of the bodies of the vertebrae, corresponding to these parts of the discoid-ligaments, are, in contradistinction to the more in- ternal portions, as it were porous, after the removal of the ligamentous layer ; the medullary cavities or cancelli then being exposed. The pores or cancelli are closed only by the cartilaginous substance of the disc, whilst the fibrous tissue, with its vertical fibres, is firmly connected with the interspaces between them. Between the sacrum and coccyx, and the individual coccygeal verte- brae, are interposed the so-called false intervertebral ligaments, consist- ing of a more uniform fibrous substance, without any gelatinous nucleus. The separate bones of the sacrum, at an early period, have true inter- vertebral ligaments between them, which afterwards become ossified from without to within, but in such a way, nevertheless, that even in the adult, traces of the ligament may still be perceived in the centre. With respect to the nature of the fibres of the intervertebral ligaments, Don- ders is inclined, especially from the consideration of their chemical re- lations, to regard almost all of them, not as connective tissue, but as analogous to the matrix of true cartilage, as is also H. Meyer (p. 300, et seq., and p. 310). This opinion may be correct, as regards the cen- tral, nuclear portion, and the fibro-cartilaginous laminae of the outer portions, but hardly so with respect to the purely fibrous parts of the latter. I believe, moreover, that it is not by chemistry, but by the study of the development of these tissues, that the question will be solved, because, although manifest, visible distinctions exist between the fibrils of connective tissue developed from cells, and the fibrous inter- cellular substance, viewed from a genetic point of view, chemistry pro- bably is not in a condition to distinguish one from the other.* The in- * [In our note on the connective tissue, we have already expressed the views we enter- tain of the homologies of the elements of cartilage and connective tissue ; and we need merely add that we know of no locality in which the transition of the matrix of cartilage 288 SPECIAL HISTOLOGY. tervertebral ligaments are liable to various forms of degeneration ; they may become ossified, from their cartilaginous lamellae outwards, the true fibrous substance probably at the same time disappearing ; and in this way anchylosis of two vertebrae frequently takes place. They may become atrophied, easily broken down, arid disintegrated, either in the nuclear portion, or elsewhere in circumscribed spots, into a dirty gru- mous matter. And lastly, it would appear that although in the normal state, they contain no vessels, vessels may, under certain morbid condi- tions, be developed in them ; at all events, extravasations of blood are not unfrequently met with, most generally close to the bones or in con- nection with them. In the sympJiysis pubis, the cartilaginous layer, which is thickest in the centre and anteriorly, and connected with the bones by a very un- even surface, consists, at the sides, where it is from J to 1 line thick, of true cartilage, with a homogeneous, finely granular matrix and sim- ple cells, measuring 0-01-0-024 of a line. In the centre, the matrix is softer and fibrous, and in this situation (more particularly, it would appear, in the female sex), there occasionally exists an irregular narrow cavity, with uneven walls, and containing a somewhat slimy fluid, origi- nating evidently in a solution of the innermost cartilaginous layers, and of which manifest traces may be perceived in the cartilaginous substance immediately enclosing it. The outer layers of the symphysis, which, as is well known, are most developed anteriorly and superiorly, do not arise, with the exception of the outermost lamellae composed of pure connective tissue, directly from the bones, but, properly speaking, unite only the outer portions of the above-described cartilaginous layers, and consist principally of a fibrous substance, to all appearance identical with connective tissue, and occasionally containing cartilage cells. The formation of the bone-corpuscles, as they are termed, may be traced perhaps more clearly in the symphysis than anywhere else, except in rachitic bone (Fig. 124). For at its osseous borders there are always to be found, either half projecting from, or entirely lodged in, the carti- lage, isolated, nucleated bone-corpuscles or cells, with homogeneous, and (from calcareous salts) granular walls, measuring 0-012-0-016 of a line with respect to which, from their development and from the considera- tion of the contiguous cartilage-cells, all of which present more or less thickened walls and rudiments of calcareous deposits, not the smallest doubt can be entertained. Well-characterized, half and wholly ossified parent cells of the same kind, with two secondary cells, and measuring 0*015-0-03 of a line, up to some including ten or twenty secondary cells into the pseudo-fibrillated collagenous portion of connective tissue is more unmistakably exhibited, than in the intervertebral cartilages of a young animal, e.g., a kitten. We have, in that note, endeavored to show that the notion of the existence of any real difference in the development of the fibrillated element in the different forms of connective tissue is un- founded. TRS.] THE OSSEOUS SYSTEM. 289 and having a length of 0'05 of a line, may be distinctly noticed in almost every preparation. Fig. 123. The sacro-iliac synchondrosis is effected by means of a flattened layer of cartilage, f-1 J- of a line in thickness, which is closely attached to the articular surfaces of the corresponding bones, between which it is inter- posed. The cartilage-cells close to the bone are flattened, with their surfaces directed towards it, and present beautiful transitionary forms into half and wholly isolated bone-cells, which exist on the border of the bone. In the interior of this cartilaginous layer, according to Zaglas, there is always a narrow cavity, which separates the cartilaginous layers of the two bones completely, or almost completely, from each other. It contains a synovia-like fluid, and is bounded by smooth and even walls, which differ from the rest of the cartilaginous substance in their greater hardness, as well as in their structure. The matrix of these cartila- ginous layers, in the direction of the surface, is finely fibrous; the cells are all of large size (as much as 0'035 of a line), with numerous secondary cells and uncommonly thick walls, so that the cavities, even of the se- condary cells, often appear extremely contracted ; but they do not exhi- bit any distinct indication of pore-canals or calcareous deposit. The costal cartilages are invested by a strong perichondrium, composed of connective tissue and numerous elastic elements, which commences at the sternal end in connection with the synovial membrane there existing, and at the other is continuous with the periosteum of the ribs. The cartilage, which is in connection with this membrane by a roughened surface, is of considerable firmness although elastic, pale, yellow, or in thin sections, exhibiting a transparent blue tint, internally almost always, FIG. 123. Cartilaginous border, towards the cartilage of the symphysis in Man; a, carti- lage cells with thickened walls; 6, the same undergoing ossification; c, cells nearly ossified, with homogeneous walls free in the matrix of the cartilage ; d, similar cells with calcareous granules: e, ossified cells at the border of the matrix of the bone containing calcareous gra- nules, and half projecting from it. Magnified 350 diameters. 19 290 SPECIAL HISTOLOGY. Fig. 124. in certain spots, of a yellowish-white color, with a silky lustre. Its matrix in the latter situations presents a fibrous structure, and elsewhere a finely granulated aspect. The outermost cells, to the depth of 0-06 0-1 of a line, are elongated, flattened, parallel to the surface, most usually small (sometimes not more than 0-006 of a line), but sometimes larger, and filled with one or even many secondary cells, one placed be- hind the other ; more internally, without entirely losing their flattened figure, they are larger (most of them 0-03-0-05 of a line), oval, and round, and lie with their surfaces towards the ends of the cartilage, and with their long axis for the most part in the direction of the radius of the transverse section of the rib ; in many cases, however, they are dis- posed more irregularly. The largest of these cells (measuring as much as 0-08 or, even 0-1 of a line), are found in the fibrous spots, and they, in common with all the interior cells, contain secondary cells, in varying, frequently in very considerable number (as many as 60 according to Ponders). The most remarkable characteristic of the elementary tissue of the costal cartilage is the large quantity of fat con- tained in it. In the adult, every cell, excepting the most superficial, contains, larger or smaller (from 0-0016-0-008 of a line), sometimes spherical, some- times more irregular fat- drops, which frequently so surround the nucleus as en- tirely to conceal it from view (Fig. 124 a, 5), whence it has been assumed, though not quite correctly, that the fat is seated in the latter. The cartilage on the greater cornu of the os hyoides, and between the body and the greater cornu, and the incon- stant cartilaginous appendage to the styloid process, differ in no respect from costal cartilage, only that the cartilage cells in those instances do not always contain large fat-globules. The costal cartilages frequently become ossified in old age ; but this ossification, as well as the fibrillation of the matrix, must not be re- garded as a normal process, nor be placed in the same category with the usual kind of ossification. The ossification is sometimes more limited, FiG. 124. Cartilage cells of Man, magnified 350 diameters: a, parent cell with three se- condary cells containing oil, from a costal cartilage; 6, two cells from the same situation in which the globule of oil is surrounded by a pale border; c, two cells with thickened walls from the cartilage of the greater cornu of the os hyoides, which together with the globule of oil also contain a distinct nucleus. THE OSSEOUS SYSTEM. 291 sometimes more extensive. In the former case, it does not proceed further than to the incrustation of the cartilage-cells, and of the matrix in which they are lodged, which has become fibrous ; in the latter, and frequently, also, in the former, the ossification is preceded by the forma- tion of hollow spaces in the cartilage, in which is deposited a cartilage- marrow, containing vessels, which are connected, in part with those of the perichondriwn, in part with those of the ribs ; and the osseous sub- stance is more that of normal bone, though almost always more opaque, less homogeneous, and with imperfectly formed lacunae, which frequently contain a calcareous deposit. Under the name of cartilage-marrow, are understood the medulla-cells, fat-cells, bundles of connective tissue and vessels which are presented instead of the detritus, afforded by the dis- integration of cartilage, and which may be said to correspond in all re- spects with those of developing foetal bone, and may be readily observed in ossifying costal and laryngeal cartilages. 95. B. Movable Articulation (Diarthrosis). The articular extremi- ties of the bones, or any other surfaces entering into the formation of a joint, are invariably invested with a thin layer of cartilage, which in the middle of the surfaces covered by it, is of tolerably uniform thickness, gradually thinning as it extends outwardly, and finally terminating with a very abrupt edge. This articular cartilage is closely applied to the bone with a rough, hollowed or raised surface, but is not united to it by any interposed substance ; and, on the opposite surface, it is in most joints usually quite bare, and directed towards the cavity of the articulation. Sometimes, however, it is invested with a special fibrous membrane, a perichondrium, which is an immediate prolongation of the periosteum, and extends most generally only over a small portion of the cartilage, gradually ceasing without any defined margin.* In some joints (shoulder, hip) the more secure lodgment of the articular head of the bone is in- sured by special cartilaginous lips. These are firm, yellowish-white, fibrous rings, attached, at the border of the articular cartilage, by a wider basis, immediately to the bone or partly to the cartilage. They thin off to an acute edge, and for the most part free and uncovered by the synovial membrane, or any epithelium, project into the articulation, being exteriorly in relation with the periosteum and synovial capsule. * [Reichert, who has paid particular attention to the question of the existence of an epi- thelium upon the articular cartilages, says, that in the foetal condition of Man and the domes- tic Mammalia, an epithelium exists over the whole surface of the synovial capsules, and, on the articular cartilage, lies in immediate contact with its substance. It resembles the epi- thelium of the vessels. In adults, on the other hand, he could discover an epithelium only on those parts of the articular capsules which are not subject to friction ; and here it had the same appearance as in the foetal condition. It was wanting upon the articular cartilages and their immediate neighborhood; but it was not uncommon to meet with fine desquamated flakes of cartilage in the synovia, which fell readily into folds, and thus resembled a fibro- cartilaginous tissue (Bericht, Mailer's " Archiv.," 1849, p. 16.) TRS.] 292 SPECIAL HISTOLOGY. Fig. 125. As regards the intimate structure of the parts just described, the articular cartilage, on completely formed bones (Fig. 125), and under normal conditions, presents throughout, a finely granular, in part almost homogeneous matrix, in which are lodged delicate cartilage- cells, which towards the surface of the carti- lage are numerous and flattened, and lie parallel to it; more deeply they are oval or rounded, more rare, and disposed in various directions; and lastly, close to the bone they are elongated, and placed vertically with respect to the surface of the bone. These cells all have distinct walls, easily dis- tinguished from the matrix by the use of acetic acid, clear, frequently granular con- tents, containing, however, but little fat, and a vesicular nucleus. They occur either isolated or in groups, and present very fre- quently two, four or even more secondary cells, which in the flat cells are placed close together, and in the elongated are disposed in rows. On the condyle of the lower jaw, as on the corresponding surface of the tem- poral bone, until the bone is completely formed, there is a thick layer of very dis- tinctly marked cartilage-cells, covered, to- wards the cavity of the articulation, by a layer of connective tissue. This cartilaginous layer disappears by de- grees, as the bone approaches its completion, and at last there remains beneath the layer of connective tissue, now become both relatively and absolutely thicker, merely an excessively thin and transparent lamina, the elements of which, although morphologically not true bone-cells, nor as yet ossified, still seem to resemble the latter more closely than cartilage- cells. % The cartilaginous lips of the joints consist principally of connective tissue, always containing, however, isolated cartilage-cells of a roundish or elongated form, with a moderately thick membrane, distinct nucleus, and occasionally fat-granules. I have not as yet noticed parent cells in FiG. 125. Articular cartilage of a human metacarpal bone, cut perpendicularly: a, most superficial, flattened cartilage cells; 6, middle round cells; c, innermost cells, disposed per- pendicularly in small rows; rf, outermost layer of the bone with ossified fibrous matrix and thick- walled cartilage cells, in this instance appearing dark from their containing air; e, true bone-substance; /, ends of the cancelli of the apophyses; g, one of the cancelli. Magnified 90 diameters. THE OSSEOUS SYSTEM. 293 this situation, whilst cells of the kind already described in the muscular system ( 82), arranged in series, are not unfrequently met with, and might perhaps be regarded as cartilage-cells, although their nuclei exhibit the most evident indications of a transition into nuclear fibres. The articular cartilages, moreover, during their development, which will be entered into more particularly afterwards, have no nerves or vessels, as is the case also with the cartilaginous lips.* The condition of the bone beneath the articular cartilages, requires special notice. It consists, in almost all joints, in immediate contiguity with the cartilage, of t a layer of incompletely formed bone-substance, and, more internally, of that tissue in its usual form (Fig. 125). The layer in question, which is 0*04 0*16, or on the average 0*12 of a line thick, is composed of a yellowish, mostly fibrous, hard, and truly ossified matrix, containing, however, not a trace of Haversian canals or medul- lary cavities, nor of any perfectly formed lacunae ; instead of which it presents roundish or elongated corpuscles, aggregated into little masses or rows, the larger of which are 0*016 0-024 of a line in length, and 0-006-0-008 of a line in breadth, and the smaller 0-006-0-008 of a line in length, and 0-004-0-005 of a line in breadth, which give thin sections of the bone a perfectly opaque aspect, and consequently might be regarded as bone-corpuscles (lacunae) filled with calcareous particles, as which they have lately been considered by H. Meyer (1. c., p. 325, 326). By the addition of spirit of turpentine, which, however, penetrates with difficulty, this error is dissipated, and it is found, that as in the case of the lacunae of dried bone, the opaque aspect is due only to the air con- tained in them, and that the bodies in question are nothing more than thick-walled cartilage-cells, retaining their contents (fat, nuclei), present- ing occasionally indications of canaliculi, and perhaps also partly calci- fied ; in other words, that they are undeveloped lacunae. The layer in which these cells are lodged, and which, towards the cartilage, is bounded by a straight line, occasionally dark from calcareous particles, and * [Besides the elements above mentioned, we find according to Dr. Leidy (see Am. Jour, of Med. Sc., April, 1849), numerous minute lacunoe, as an occasional peculiarity in the structure of articular cartilage. These lacunae are described by Dr. Leidy as existing in greatest abun- dance in the deeper part of the cartilage; but decreasing in number, as its free surface is ap- proached. They are lenticular in outline, and measure from l-1200th-l-3 120th of an inch; when well defined, they appear beneath the microscope more translucent than the cartilaginous matrix in which they are situated. When viewed a little within the focus of the instrument, they are of a deep black color, and oppose the transmission of all light. Another peculiarity de- scribed by Dr. Leidy is the penetrature of the structure of the cartilage by fibres or columns of bone. These fibres are quite uniform in shape and structure, being compressed and cylindrical ; in transverse sections they present an elliptical figure. They are not numerous, and vary from a size not exceeding a cell-group of 5 cells to the size of four or five such groups. They are concentrically laminated, and also present a radiated conformation, resem- bling somewhat the structure of an Haversian canal, but neither the canal nor the Purkin- jean corpuscles are discernible in them. DaC.] 294 SPECIAL HISTOLOGY. towards the true bone by a sinuous contour, in which the limits, as it were, of the individual lacunse are distinguishable, is not found either exclusively in bones not yet fully formed, as Gerlach believes, nor only at a more advanced age (from 30 upwards, and particularly in old men), as H. Meyer states, but, at all events as far as my observation extends, at all ages, from the complete development of the bone upwards, inva- riably in every articulation, except that of the lower jaw and those on the os hyoides.* The articular cartilage on the head of the femur, in a man 25 years old, measured 1 1J of a line in thickness ; on the condyles in the middle 1J-, on the margin, j-1 line ; in ihefovea patellce, IJ-lf of a line ; in the middle of the condyles of the tibia, 1 J of a line ; at the borders, J-f ths of a line; in the middle of the patella, 1J If ths of a line ; in the glenoid cavity of the tibia, J Jths of a line, on the body of the astragalus, on the upper side, f ths, on the under, J, on its head, f ths of a line ; at the base of the first metatarsal bone, ^ J, on its head Jd of a line, on the inner cuneiform bone, in front, J-J, behind, J-f ths of a line. In the foetus, about the middle period of uterine life, the vessels of the synovia! membrane, according to Toynbee ("Phil. Transact.," 1841), extend much further upon the articular cartilage ; of which fact, how- ever, I have been unable to satisfy myself in the humerus of a five or six month foetus, or in new-born infants. In pathological states endo- genous cell-formation is met with in an unusual degree of perfection, and more especially in all kinds of articular cartilages ; in which the parent cells, frequently of very considerable size, with one or two generations of secondary cells, and also containing fat, lie tolerably free in the fibrous matrix, and admit of being readily isolated (vide also Ecker in Rosera and Wunderlich's "Archiv," vol. II., 1843, p. 345). In the adult, the articular cartilages are non-vascular, although the vessels of the syno- vial membrane, at their border, often advance to some distance over them. What Liston ("Med. Chir. Transact.," 1840, pp. 93-4) describes as " vessels in the articular cartilage of several diseased joints, and as run- ning straight in parallel lines from the injected membrane of the bone into the cartilage, and as joining at their further extremities in that tissue, thus forming long loops," were certainly nothing more than the normal vessels of cartilage, which (vide infra) may be very beautifully displayed even in individuals 18 years old. There cannot, therefore, be any question of inflammation of the cartilages in the adult, though they doubtless suffer in morbid conditions of the bones upon which they rest, or in inflammation of the synovial membrane. They frequently assume a fibrous structure, a change which is often attended with a simultaneous * [This peculiarity of the bone beneath the articular cartilages was first pointed out by Dr. Sharpey (Quain and Sharpey, 5th ed., p. clviii.), and is particularly described by Tomes and De Morgan, 1. c., pp. 10, 11. TRS] THE OSSEOUS SYSTEM. 295 increase in thickness, Cruveilhier ("Diet, de He'd, et Cbir. prat." III., 514) having noticed fibres of this kind as much as 6 lines in length, thus far exceeding the normal thickness of articular cartilage. They some- times wear away rapidly, or even disappear altogether (in suppuration in the bone or in the articulation), so that the surface of the bone is left exposed; they also undergo partial loses of substance; when they exhibit ulcerous excavations, which may penetrate to the bone, or com- mence on the osteal surface of the cartilage. 96. The articular capsules (capsulce s. membranes synoviales] are not closed capsules, but short, wide tubular sacs, which are attached by two open ends to the borders of the articular surfaces of the bones, and thus connect them together. They are essentially more or less delicate, transparent membranes, but are in many situations so closely and com- pletely invested externally by fibrous layers the fibrous capsules as they are termed, as on cursory inspection to present the aspect of tolerably tough capsules. These fibrous coats are met with especially in situations where the articulation is either wholly unprotected, or but thinly covered by soft parts, or where a very firm connection is required (as in the hip- joint); they are absent for the most part, or are undeveloped, where muscles, tendons, and ligaments rest upon the articulation, or where, for special purposes, the synovial membrane is exposed to more considerable movements (as in the knee and elbow). The relation of the articular capsules to the bones and articular car- tilages, more precisely described, is as follows (Fig. 126) : The articular capsule is attached, either simply to the border of Fio . 126 . the cartilaginous surface, extending thence directly to the other bone (patella, amphiarthroses) ; or it may, in the first place, besides the border of the cartilage, also invest a larger or smaller extent of surface of the bone itself, and then pass to the second bone, with which it is connected in the one way or the other. In either of these cases the synovial membrane does not adhere immediately to the hard tissues subjacent to it, but is more or less closely connected with the periosteum and peri- chondrium, ultimately ceasing without any distinct margin, not far from the border of the articular cartilage, with the perichondrium of which it is inseparably united. With respect to the intimate structure of these tissues, the synovial FIG. 12G. Diagram of a transverse section of a phalangeal articulation, partly after Arnold : a, bones ; 6, articular cartilage ; c, periosteum continuous with the perichondrium of the articular cartilage; d, synovial membrane at the edge of the cartilage, connected at first with the perichondrium ; e, its epithelium. 296 SPECIAL HISTOLOGY. membranes, distinct from the fibrous capsules, as they are termed, which possess in all respects the structure of fibrous ligaments, consist : 1, of a layer of connective tissue, with not very numerous vessels and nerves ; and, 2, of an epithelium. The latter is composed of from one to four layers of large tessellated cells, measuring 0-005 0*008 of a line, with roundish nuclei of 0-002-0-003 of a line. The former, in its innermost part, is constituted of a layer of parallel fasciculi, with indis- tinct fibrils and elongated nuclei or fine elastic filaments ; more exter- nally of decussating bundles, with a fine elastic network, occasionally also of a network of bundles of connective tissue of very various thick- ness, with winding elastic fibres, exactly as in the arachnoid. Not unfrequently, common fat-cells occur, dispersed here and there in the meshes of the connective tissue, although upon the whole very rarely ; and also a few scattered cartilage-cells, with tolerably thick, opaque walls, and a distinct nucleus. The synovia! membranes possess neither glands nor papillge, whilst they present large adipose masses (plicce adi- posce) and vascular pirocesses (plicce vasculosce, plicce synoviales, liga- menta mucosa, of authors). The former, at one time erroneously termed " Haversian glands," are found principally in the hip- and knee-joints, in the form of yellow or yellowish-red soft processes or folds, and con- sist simply of large collections of fat-cells in vascular portions of the synovial membrane. The latter are met with in almost every joint, constituting, provided that the blood-vessels are filled, red, flattened projections of the synovial membrane, with an indented and plicated margin, and furnished with minute processes. These folds are usually placed close to the junction of the synovial membrane with the carti- lage, upon which they lie flat, thus forming, in many cases, a sort of coronal around it ; in others they are more isolated, and placed in other parts of the articulation. In their structure, they differ from the rest of the synovial membrane principally in their great vascularity, con- sisting as they do of little else than minute arteries and veins, and delicate capillaries forming wavy loops at the edge of the processes, and consequently they are very similar to the choroid plexuses in the ven- tricles of the brain. Besides the vessels, they present a matrix of, frequently, distinctly fibrous, connective tissue, the usual epithelium of the synovial membrane, occasionally solitary or numerous fat-cells, and, more rarely, isolated cartilage-cells. At the edge, they are almost invariably furnished with minute, foliated, conical, membranous pro- cesses of the most extraordinary forms (often resembling the stems of a cactus\ which also frequently contain vessels, but are for the most part constituted merely of an axis of indistinctly fibrous connective tissue, with occasional cartilage-cells, and an epithelium, very thick in places. The smaller ones frequently consist even of nothing but epithelium, or of little else than connective tissue. THE OSSEOUS SYSTEM. 297 In many joints there are firm, whitish-yellow, fibrous plates, the so-termed interarticular carti- lages or ligaments, which, either Fig. 127. projecting in pairs from the syno- vial capsule, are interposed be- tween the bones constituting the articulation (knee), or form a single diaphragm transversely across the joint (articulations of the jaw, clavicle, sternum, and wrist). These processes consist of a firm, fibrous tissue, the fibres of which usually cross each other in various directions, and are in all respects closely allied to con- nective tissue, but presenting less distinct fibrils ; and, besides this, of cartilage-cells and fine elastic fibres.* The cartilage-cells, in the most superficial layers, are more solitary, in the deeper, disposed more in rows and smaller, ultimately being replaced by fine elastic fibres, a certain number of which, at all events, appear to originate from cells resembling the cartilage-cells. The interarticular ligaments, which, from what has been said respecting them, must be enumerated among the fibro-cartilages, are not covered by synovial membrane, though they probably have an epithelial investment at the attached border, but only for a small extent, never over the entire surface. The articular liga- ments, with the exception of the softer ligamentum teres, are composed of the same firm connective tissue (in the costal ligaments containing cartilage-cells), as that of which the tendons and the fibrous ligaments, elsewhere, are constituted. The internal ligaments (lig. cruciatce), how- ever, present softer connective tissue, containing vessels, and covered with epithelium. FIG. 127. From the synovial membrane of a phalangeal articulation : ^f, two non- vascular appendages of the synovial processes, magnified 250 diameters : a, connective tissue in its axis ; 6, epithelium (in the peduncle of the larger process not distinctly cellular) continuous with that on the free borders of the process ; c, d, cartilage-cells ; 7?, four cells from the epithelium of the synovial membrane of the knee, one with two nuclei; magnified 350 dia- meters. * [These interarticular fibro-cartilages lose in old persons their distinct fibrous structure, and assume a yellow or brownish color. Yet they never, according to Virchow (Archiv. f. Path. Anat.), become entirely homogeneous, since a careful examination will always permit two directions of their fibres to be recognized, viz. : one parallel to the free edge, and the other running vertically towards it. DaC.] 298 SPECIAL HISTOLOGY. Fig. 128. Within the synovial capsules is contained, in small quantity, a clear yellowish fluid, which may be drawn out into threads, the synovia, and which, in its chemical composition, ap- pears very closely to resemble mucus, and particularly in its containing mucin in solu- tion. Examined under the microscope, in its normal condition, this secretion exhibits no- thing worthy of much remark, consisting simply of fluid which is rendered turbid by acetic acid, and very frequently contains epithelial cells, which have often undergone a fatty meta- morphosis, nuclei of such cells, and fat globules ; under conditions not quite normal, it may also contain blood- and lymph-corpuscles, detached portions of the synovial processes of the arti- cular cartilage, and a structureless gelatinous substance. The normal, healthy synovia, which in the Ox, according to Frerichs (Wagn. " Handb." III. 1), contains 91-8 water, 0*5 mucus and epithe- lium, O07 fat, 3-5 albumen and extractive matter, and 0'9 salts, is a secretion, not having essentially any formed elements in it, which simply exudes from the vessels of the synovial membrane with the inter- mediation of the epithelium ; and, in fact, from all its vascular processes, which are destined as it were for this special function, and always exist at the border of a cartilage requiring a lubricating covering. The non- vascular appendages of these processes give origin to the " loose carti- lages," as they are termed ; they do this by their increasing in size and solidity, and becoming detached from the vascular folds. These bodies are also met with in mucous bursae and the sheaths of tendons, which are also furnished with vascular folds (vid. sup. 82) ; they consist of connective tissue with elongated nuclei, coated with epithelium, and, though not always, contain a variable number of scattered fat- and true cartilage-cells ; and they are not developed externally to the synovial membrane, but from an outgrowth of that membrane itself. Similar solid bodies, moreover, may probably be produced in other ways ; Bidder ("Zeitsch. f. rat. Medicin," vol. Hi., p. 99, et seq.), at all events, and Virchow (" Med. Zeitung," 1846, Nos. 2 and 3) have observed similar bodies presenting no trace of organization. I am inclined, with Virchow, who has actually demonstrated the presence of fibrin in them, to regard them, in many cases, as fibrinous exudations, and in others as FIG. 128. From the falciform ligament of the knee: a, a filament of connective tissue with oval cells disposed in a series, and resembling cartilage-cells ; b, a similar filament with more elongated cells and nuclei. THE OSSEOUS SYSTEM. 299 solidified deposits from the synovia, which latter supposition is supported by the frequent occurrence of curdy, more or less consistent, structure- less masses, evidently inspissated synovia, in the tendinous sheaths of the hand. Portions of bone, also, detached from outgrowths at the cir- cumference of the articular ends of the bones, may find their way into the interior of the articulation. The plicce adiposce have perhaps less to do with the formation of the synovia than with the mechanism of the joint, serving the purpose of filling up hollows. 97. Physical and chemical properties of the Bones, and their acces- sory Organs. The bones are composed, besides a small quantity of water (3-78, according to Stark in the compact substance), and fat (2-3g Bibra), principally of a substance affording gelatine, and of inorganic elements. The latter, in the adult, constitute two-thirds (68-82 Bibra) of dry bone, and are nearly all left when the bone is calcined ; in which case, if due care be taken, the bone completely retains its external aspect, although it may be readily reduced to a white, opaque, friable, heavy powder, the so-termed u bone earth." This consists chiefly of 57-59J basic phosphate of lime (according to Heintz, 3 atoms base, 1 atom acid), of carbonate of lime (7-8 g) and traces of fluate of lime, phosphate of magnesia, silex (traces), arid alkaline salts. A small part of the salts of bone is also contained in the walls of the vessels and in the lacunae, and this part is dissolved in water. The collagenous sub- stance is the so-termed bone, formative, or ossifying cartilage. It is obtained when bone is treated at a low temperature with dilute hydro- chloric, or nitric acid, in the form of a soft, flexible, elastic, light-yel- lowish, cartilaginous, transparent substance, retaining accurately the shape of the bone. This bone-cartilage constitutes about J of the dry bone, putrefies when moist, and when dried, may be burnt away, leaving a small quantity of ash. It is dissolved by boiling, and from its com- bination with water is produced the gelatine, usually to the amount of 3 or 4 times its volume, and which may also be obtained directly by long boiling of the bone in a Papin's digester. With regard to the mode in which the principal constituent elements of the osseous tissue are combined, it is certain that the bone earth does not exist as a distinct deposit in any of the constituent parts of healthy, fully formed bone, but rather, although in a solid form, only in a very intimate union with the tissue. Since both the cartilage and the cal- cined bone retain the figure of the bone, in all its particulars, indepen- dently of each other, there can be no doubt, but that the most intimate union of the two substances exists throughout the entire bone, which, however, cannot be regarded as a chemical combination, principally for the reason, that the proportional relations between the collagenous sub- stance and the phosphate of lime are very variable ; and that, by simple 300 SPECIAL HISTOLOGY. boiling under an increased pressure, the gelatine is separated from the calcareous salts. The physical properties of the bones correspond with their composi- tion. Their hardness, density, and rigidity are due to the earthy, whilst their elasticity and flexibility depend upon the organic constitu- ents. In the normal bone of the adult, the two principal constituents are united in such proportions, that the bones, together with consider- able hardness and rigidity, have a certain degree of elasticity, though slight, so that they possess a considerable resisting power, and are broken, though not very readily, by the application of greater mechani- cal force. At an earlier age, when the cartilage is in greater relative proportion, the hardness of the bones is much less, their sustaining power consequently less considerable, and they are more liable to be bent ; whilst on the other hand, owing to their greater elasticity, they are much less liable to be broken. This is the case in a much higher degree in rachitis, in which morbid condition, the organic constituents amount to from 70 to 80 per cent. A condition the reverse of this is observed in old age, when the bones, though certainly harder, are more brittle, and therefore more readily fractured, to which liability, however, the rarefaction of the tissue which takes place in consequence of age, partly contributes. The inflammability of bone depends upon its organic basis, and its capability of resisting putrefaction to the inor- ganic constituents. The latter being so intimately combined with the animal tissues, serve as a protection to them, so that bones from ancient burial-places, and those of fossil animals still retain the full proportion of cartilage. The true cartilages, even in the foetus, contain, in their organic basis, from 50 to 75 per cent, of water, 3 to 4 per cent, of salts (chiefly of soda and carbonate of lime, and also some phosphate of lime and mag- nesia). The organic basis has been hitherto supposed to consist entirely of cJwndrin, a substance allied to gelatin, soluble in boiling water and gelatinising as it cools; but it was noticed by Bruns (p. 216), that the matrix and the cells of cartilage were not equally soluble in water, and Mulder and Donders have rendered it probable that the cliondrin, which had hitherto been investigated, is not a simple substance, and that the cartilages consist of several bodies of different natures, the matrix, and the membranes of the parent cells, their contents, and the secondary cells, of which the first is more soluble in water, potass, and sulphuric acid, than the others. The fibro-cartilages (cartilages containing connective tissue) have been, as yet, but little investigated. J. Muller, in the interarticular cartilages of the knee of the Sheep, found no chondrin ; whilst Donders, on the other hand, met with it in the intervertebral ligaments (" Holl. Beitr.," p. 264); he did not determine whether they also contained gelatin. According to Virchow, the gelatinous, nuclear portion of these THE OSSEOUS SYSTEM. 301 ligaments, in the new-born child, consists of a substance very nearly allied to that of "colloid" (Wurzb. " Verhandl.," II. 283). The liga- ments have the same chemical composition as the tendons. 98. Vessels of the Bones and their accessory Organs. A. Blood- vessels. The periosteum, besides the numerous vessels passing to the bone by which it is traversed, presents in its outer layer, composed of connective tissue, a tolerably close network of minute capillaries (0-005 of a line). The blood-vessels of the bone itself are very numerous, as may be seen in injected specimens, and also in recent bone full of blood. In the long bones, the marrow and the spongy substance of the articular ends are supplied by particular vessels, as is also the compact substance of the shaft. The former, or vasa nutritia, enter the bone through large special canals, one or two of which are found in the diaphyses, and many in the apophyses. These vessels, with the exception of a few twigs given off to the innermost Haversian canals of the compact sub- stance, and which possess all the tunics proper to the vessels elsewhere (even to the muscular), ramify in the marrow, where they form a true capillary plexus the vessels in which vary in size from 0-004 to 0-0052 of a line. The vessels of the compact substance arise, in great part, from those of the periosteum, very soon lose the muscular coat, and form, in the Haversian canals, which they either occupy by themselves, or together with some medullary substance, a network of wide canals, which from their structure, can only in the most trifling extent be re- ferred to the capillary system, most of them possessing a layer of con- nective tissue and an epithelium, and as it is only in the larger canals that fine capillaries co-exist with the main vessel. The venous blood is returned from all the long bones, in three ways : 1, by a large vein accompanying the nutritious artery, the ramifications of which it fol- lows ; 2, by numerous large and small veins at the articular extremities ; and, 3, lastly, by many small veins, which arise independently of each other from the compact substance of the diaphyses, in which their roots, as is correctly stated by Todd and Bowman, occupy the wider spaces and sinuses, or pouch-like excavations, which are very evident even in sections of bone. All the vessels of bone, the medullary vessels of the apophyses and of the diaphyses, as well as the vessels of the compact substance, communicate in a multiplicity of ways, so that the vascular system throughout the entire bone constitutes a continuous whole, in which it is possible for the blood from any one part to reach every other part ; for it was observed by Bichat (" Anat. Ge'ne'ral.," 1812, III. p. 37), in an injected tibia, the nutritious artery of which was obliterated, that the bifurcation of the vessel in the medullary canal was well injected, and that the nutrition of the marrow was evidently unaffected. 302 SPECIAL HISTOLOGY. In the short bones, the bloodvessels present pretty nearly the same conditions as they do in the apopliyses of the long bones ; the arteries and veins of larger and smaller size entering and quitting the bone at numerous points on the surface, and sometimes, as in the posterior aspect of the bodies of the vertebra?, in very large trunks, the vence basi-vertebrales of Breschet, furnishing a capillary plexus to the medulla, and also penetrating into the few Haversian canals of these bones. In the jto bones, such as the scapula and os innominatum, there are distinct nutritious foramina for the larger arteries and veins ; the com- pact substance receiving finer vessels from the periosteum, and the spongy substance being supplied by numerous and even large vessels, as in the neighborhood of the articular cavities. In the flat cranial bones, the arteries, for the most part, enter both the cortical and spongy substance from without, on both surfaces, presenting the usual conditions, whilst the vence diploeticce, as they are termed, have only their extremi- ties free in the medulla, as in other bones, their trunks, and larger and smaller branches running independently and generally unassociated with medullary substance in large, arborescent, special channels, the so- termed "canals of Breschet," which open at determinate points with large apertures (emissaria Santorini), and communicate freely with the veins of the dura mater, with respect to which relations, however, works on special anatomy must be consulted. The size and number of the veins in the cranial bones, is, moreover, extremely variable, and they are constantly becoming obliterated, particularly in old age, concomi- tantly with the frequent diminution of the diploe, on which account also the venous canals and their openings (emissaria) are of such variable dimensions. The articular and other cartilages of the osseous system, even the fibro-cartilages, in the adult, normally contain no vessels at all, except those of the perichondrium, which however in this respect is far inferior to the periosteum. But it may happen, that as in the costal cartilages in the middle period of life and afterwards, vessels make their appear- ance, in which case partial ossification frequently either precedes or follows. The fibrous ligaments are poorly supplied with vessels, and par- ticularly the elastic ligaments, and in this respect may be arranged with the tendons, whilst the synovial membranes are characterized by the considerable number of their bloodvessels. The above described synovial folds are especially rich in this respect, as is also the synovial membrane itself, which, everywhere beneath the epithelium, contains a pretty close plexus of canals, from 0-004-0-01 of a line in diameter. B. Lymphatics in bone, have been described by some older and more recent authors (vid. Mikrosk. " Anat.," II. 1, 336), but their existence is still not the less doubtful, and I have in vain endeavored to find such THE OSSEOUS SYSTEM. 303 vessels. With respect to the other parts of the osseous system, the only question can be, as to whether the periosteum and articular capsules possess lymphatics. In the former, they have not yet been observed, whilst in the latter their existence has been asserted by several authors, Cruveilhier, for example. It must be confessed, however, that it has not been by any means proved that they arise in these structures, at all events it appears to me to be very doubtful, whether the synovial mem- branes themselves contain vessels of this kind, whilst it is perhaps certain that lymphatics do exist in the loose connective tissue surrounding the articular capsules, and between them and the periosteum of the apophy- ses, particularly at the knee. 99. Nerves of the Osseous System. The periosteum is abundantly supplied with nerves, the majority of which, however, do not belong properly to it, but to the bone (vid. infra). With respect to the proper periosteal nerves, it appears that their number, on the whole, is not considerable, so that even in some places they may be entirely absent, as in the neck of the femur, and beneath certain muscles (glutceus minimus, peroncei, &c.) ; but there are perhaps but few bones in which they do not exist in one part or another. These nerves lie in the same layer as the vessels, sometimes along the larger branches, sometimes by themselves, arising, at all events in part, from the larger nerves of the bone itself, and are manifestly distributed over considerable spaces, although their ramifications and anastomoses are scanty. In the larger trunks of these nerves the primitive fibres measure, most generally 0-002 -0-004 of a line, though their size gradually lessens, partly owing to actual divisions, which I have seen with the utmost distinctness in the periosteum of the fossce infra-spinata, and iliaca in man, and J. N. Czermak in that of the frontal bone in the Dog ; and in part by a gradual attenuation, to a diameter of 0-0012-0-0016 of a line, many, and perhaps all, terminating with free extremities. On the articular ends of many bones, such as those of the elbow, knee, and knuckle-joints, I have noticed the nerves to be more abundant than elsewhere, ramify- ing and anastomosing in the vascular connective tissue covering the periosteum, and following principally the course of the blood-vessels 5 but in these situations, divisions and terminations of the primitive fibres did not come under my observation. The nerves of the bone itself, which, with the exception perhaps of the ossicula auditus and sesamoid bones, are universally present, do not exhibit exactly the same conditions in all bones. In the larger cylin- drical bones, they penetrate, in company with the nutrient vessels, in the form of one, or where two nutrient foramina exist, of two, pretty considerable trunks (measuring as much as 0*16 of a line), visible to the naked eye, directly into the medullary cavity, and are there distributed 304 SPECIAL HISTOLOGY. into the medulla, following the course of the vessels, though not always in apposition with them, towards the apophyses, and forming multifarious ramifications, but, at least as far as I have seen, only few anastomoses. In the second place, all these bones also present, in the apophyses, nu- merous finer nerves, accompanying the equally numerous blood-vessels directly into the spongy substance, and ramifying in the medulla ; and thirdly, extremely delicate filaments are sent even into the compact sub- stance of the diaphyses, in company with the minute arteries by which it is penetrated. There can be no doubt that these filaments are dis- tributed in the compact substance, although I have never succeeded in finding them within it. The smaller cylindrical bones of the hand and foot present the same conditions with respect to their nerves as the larger ones, except that in them, on account of the undeveloped con- dition of the medullary cavities, the numerous nerves are not so regu- larly divided into apophysal and diaphysal. Of the short bones, I have found the vertebra? to be the most abun- dantly supplied with nerves, and especially their bodies. The nerves enter posteriorly in company with the arteries and veins (vence basi-ver- tebrales), as well as anteriorly and on the sides, together with the vessels, arid are distributed in the marrow of the spongy substance. In the astragalus also, calcaneum, os naviculare, cuboideum, and Cuneiforms internum, I have noticed, in the larger, several, and in the smaller, at least one nervous filament. In the scapula and os innominatum, the nerves are very numerous, entering these bones chiefly at the points before indicated, with the larger vessels, sometimes on the expanded portion, sometimes in the neighborhood of the articular cavities. In the sternum also, and in the flat cranial bones, the existence of nerves is demonstrated without difficulty. In the latter, I have observed, even in the new-born infant, in the occipital and parietal bones, nerves entering through the fora- mina emissaria, which at this period also contain an artery ; and in the adult, there are found in the parietal, frontal, and occipital bones, although rarely, yet occasionally, microscopic filaments on the smaller arteries, which enter the compact substance from without, and probably penetrate as far as the diploe. From these observations, together with those of Kobelt, Beck, Engel, Luschka, &c., there can be no doubt that the bones are richly supplied with nerves. With respect to the origin of these nerves, they have already been traced by previous observers to the cerebral and spinal nerves, as for instance the nerves of the diaphyses of the femur, tibia and humerus, to the nn. cruralis, tibialis, ischiaticus, and perforans Casseri, as well as a nerve of the frontal bone to the n. supraorbitalis, which observations, as far as they relate to the tibial nerve, have been confirmed by my own, and by those of Luschka in the case of certain THE OSSEOUS SYSTEM. 305 of the cranial bones, and of the vertebrae. Nevertheless, the sympa- thetic participates in their formation, as Luschka, and before him, Kobelt have observed with respect to the vertebral nerves. Microsco- pical examination confirms this, inasmuch as the nerves of bone, in their trunks and terminations, resemble in every respect the sensitive branches of the spinal nerves, and contain, in the trunks, one-third of fibres, measuring 0-005-0-006 of a line; two-thirds measuring 0-002-0-004 of a line ; in the larger branches the majority of the fibres measure 0-002-0*003, but some as much as 0*006 of a line; and lastly, in the finest ramifications, fibres of not more than 0*00120-0016 of a line. The periosteal nerves, also, which may frequently be seen to be con- nected with the nerves of the bone, and may be traced to the nerves of the extremity, are derived, probably in the greater proportion, from the spinal nerves, although even in their case, perhaps, some participation of the sympathetic cannot be denied. How the nerves of bone terminate, I have not observed, and can only remark, that from the nerves in the marrow, extremely delicate branches, composed of neurilemrna and one or two fibrils, are ultimately developed; but as to what becomes of these I am ignorant. It is also, perhaps, worthy of notice, that in two situations, before their entrance into the bone, I have observed Pacinian bodies on the nerves ; viz. on the dia- physal nerve of the tibia, two lines before its entrance into the foramen, I noticed a single body, and two others on the largest nerve of the me- tatarsal bone of the great toe, also just before it entered the bone. I have never yet detected nerves in the ligaments, in Man (the liga- mentum nuchce of the Ox contains some fine nervous twigs, accompany- ing minute arteries ; the twigs measuring 0*004 of a line, with fine fibres of 0-012-0*0015 of a line), but have no doubt that they, like the tendons, inasmuch as that they contain vessels, are also furnished with a few scattered nerves. On the other hand, the interosseous membrane of the leg contains filaments derived from the interosseal nerve, which, formed of from one to three fibrils, measuring 0*003-0*004 of a line, present distinct ramifications and free terminations of the primitive fibrils. A nerve of 0-03 of a line, which together with an artery entered the fibrous external part of the symphysis pubis, may here be mentioned. With regard to the cartilages, I have as yet noticed only in the cartilage- canals in the septum narium of the Calf, together with vessels (arteries), very distinct, fine nervous twigs, measuring 0*0060*01 of a line, with fibres of 0-0012-0-0016 of a line thick. In the articular capsules nume- rous nerves exist, although they belong principally to the so-called fibrous capsules, and to the loose connective tissue external to the synovial membrane. In the knee I have seen nerves, even in the true synovial membrane, although in general they are rare, and are most distinct in the large vascular processes, which besides arteries, contain nerves of 20 306 SPECIAL HISTOLOGY. 0-007-0-008 of a line, with fine, also dividing filaments of 0-0008-0-002 of a line. I have also seen in the synovial membrane itself, close to the condyles of the femur, tolerably numerous nerves composed of delicate fibres. 100. Development of the Bones. In respect of their development, the bones fall into two groups, viz., into those which are preformed in a cartilaginous state (primary bones), and into those which from a small beginning are developed in a soft blastema (secondary bones). The former, while yet in the cartilaginous condition, present all their essential parts (diaphyses and apophyses, body, arches, and processes, &c.), and as far as their cartilaginous basis is concerned, originate like other cartilages, and continue to grow more or less in the same manner. They afterwards become ossified (in man, all of them) from within to without, transform- ing a portion of the cartilage completely into bone, so that what was the perichondrium becomes the periosteum, and afterwards attaining their ultimate figure, partly by means of the remaining cartilage, which con- tinuing to grow with them is successively ossified, and partly by means of a soft, ossifying blastema, which is deposited layer upon layer on the inner surface of the periosteum. In the second group, the bone is formed from a very limited, soft, non-cartilaginous basis, and continues to grow at the expense of that substance, which is continually developed anew, first at the margins only, but afterwards also on the surfaces. When these bones have attained a certain size, the blastema out of which they have hitherto been developed may become, partially, cartilaginous, in which case the cartilage stands in the same relation to the bone as it does in the former instance. The greatest part of their formative sub- stance, however, always remains in a soft condition, and from it, without its ever becoming cartilaginous, the principal bulk of the bone is produced. Frequently as the development of the osseous tissue has already been discussed, still, in a general point of view, the mode in which the bones, as organs, originate has hitherto been little considered, and I believe that I was the first, in my "Zootomical Report," Leipzig, 1849, to es- tablish the principal features of the process, and in my " Microscopical Anatomy," II. 1, p. 344, et seq., to trace it in its more particular details. H. Meyer (1. c.) agrees with me in most of the essential points, whilst Robin advances many different views, with which I do not accord, and has to some extent entirely misunderstood my statements. 101. The primary cartilaginous Skeleton of the human body, al- though less complete than the subsequent osseous framework, is still sufficiently extensive. We find as portions of it : 1. A complete verte- bral column, with as many cartilaginous, as there are afterwards osseous THE OSSEOUS SYSTEM. 307 vertebra, with cartilaginous processes, and with intervertebral ligaments. 2. Cartilaginous ribs, and a cartilaginous, entire sternum. 3. Wholly cartilaginous extremities, with as many and similarly formed pieces as there are afterwards bones, with the sole exception of the pelvic carti- lages, which constitute a single mass. 4. And lastly, an incomplete cartilaginous cranium. This primordial cranium, as it is termed ("Mikrosk. Anat.," tab. iii. figs. 1-3), forms originally a continuous cartilaginous substance, which corresponds, for the greater part, with the occipital bone (except the upper half of the expanded portion), the sphenoid (except the lamina externa of the pterygoid process), the mas- toid and petrous portions of the temporal bone, the ethmoid, the inferior turbinated bones, the ossicula auditus and the hyoid bone ; but it also presents some cartilaginous portions, which never become ossified, either remaining in the cartilaginous conditions during life, or afterwards disappearing; as for instance, Meckel's process, two cartilaginous la- mellae below the nasal bones, a narrow cartilaginous band connecting the styloid process with the os hyoides, and two others, one of which extends from the outer part of the ala parva laterally to the lamina cribrosa, whilst the other stretches upwards and forwards from the cartilaginous, mastoid, and petrous portions of the temporal bone. Consequently, in the cartilaginous cranium of man, the vault of the skull is totally want- ing, and almost all the lateral portions, as w r ell as nearly all of what afterwards becomes the facial bones ; nevertheless, at all events in the true cranium, the parts not formed of cartilage are closed by a fibrous membrane, representing in fact the further development of the soft, pri- mordial, cranial capsule, so that the cranium at this time, though only in part cartilaginous, is yet fully as complete!, as at an earlier period, and always corresponds to its original soft rudimental form. In other Mam- malia, as for instance, in the Pig, the cranium is much more completely cartilaginous ("Microskop. Anatomy," tab. iii. figs. 4, 5). The complete development of the primordial cartilage, considered liistologiealty, has not yet been accurately traced in all its stages, either in man or in mammalia. If we wish, therefore, to obtain anything like a sufficient idea of it, we must at present have recourse in a great measure to the lower Vertebrata. If the cartilage of the spinal column and of the head be examined in the latrachian larva, it is readily seen, that they are invariably constituted, while still in the soft state, of the same formative cells with vitelline corpuscles, as all the other organs. Before the development of the external branchiae, these cartilage-cells present the form of closely approximated spherical cells, 0-007 to 0-009 of a line in size, with nuclei measuring 0-0045-0-006 of a line, and filled with the well-known vitelline corpuscles; afterwards, when the branchiae have made their appearance, the granular contents of the cells begin to dis- appear, from within to without, whilst the nuclei become more distinct, 308 SPECIAL HISTOLOGY. lying in a clear fluid within them, and at the same time the cells slowly increase in size. When the branchise have disappeared, all the cartilage- cells are already quite transparent, with distinct nuclei and walls, and they now gradually increase to the size of 0-018-0-024 of a line, and the nuclei to that of 0-005 and 0-007 of a line ; the cells, from their mutual pressure, become polygonal, and constitute one of the most delicate cellular tissues possible. They now also begin to multiply by endogenous cell-formation around portions of the contents (Nageli), so that in each cell two secondary cells are formed around the two nuclei produced from the original nucleus, and entirely fill it; at the same time they again increase, though very slowly, particularly in certain carti- lages of the head, until they attain a size of 0-013-0-018 of a line, and in some places of not more than 0-0060-013 of a line; whilst between them, a thick interstitial substance is formed out of the coalesced walls of the different generations of cells. With respect to man and the mammalia, it can only be stated as a supposition, that the cartilage-cells originate in a modification of the primordial formative cells. This sup- position is favored by the circumstance, that in a human embryo of eight or nine weeks, the outer extremities of which were just developed, they presented scarcely a trace of formed cartilage, the innermost cells of the rudimentary extremities being hardly distinguishable from the outer. They were 0-004-0-006 of a line, in size, spherical, with grayish granular contents, and indistinct nuclei of 0-003 of a line, and formed a tissue of some consistence, without any appre- , ciable interstitial substance. The correspond- ing cells in the embryo of a sheep 6-7 lines in length were somewhat larger, although the embryo was smaller than the human foetus above noticed. In this case (Fig. 129) they measured for the most part, 0-006-0-01 of a line, had distinct walls, nuclei, and clear, aqueous, only slightly granular contents, and were lodged in a scanty homogeneous interstitial substance, so that they were only partially or not at all in contact with each other. The contents of only a very few cells were still in the opaque condition, and these were without any visible nucleus, others exhibited the commencement of transparency from the metamorphosis of their contents. The further development of the cartilage up to the end of foetal life, except in its ossification, presents these characteristics, viz.: (1.) That the cells pre- cisely like those in the batrachian larva, continually increase by endo- genous cell-formation, whilst precisely as in the same instance, there is no FiG. 129. Cartilage-cells from the humerus of an embryo of the Sheep, 6 lines long: a, cells with nucleus and clear contents (two cells retain remains of the earlier thick con- tents) ; 6, cells with consistent contents, without visible nucleus; c, intercellular substance. THE OSSEOUS SYSTEM. 309 indication whatever afforded, of the production of cells independently of those already in existence; and (2.) That the interstitial substance, which in this case is manifestly formed, for the greater part, indepen- dently of the cell membranes, is always increasing. With respect to the cells, they are in the second costal cartilage of a four-month foetus, according to Harting, 0*0036 of a line long, 0-0023 of a line wide, and consequently their aggregate bulk pretty nearly corresponds with that of the interstitial substance. In the embryo of the Pig, 3*5 lines long, the space occupied by the nucleated, clear, thin-walled cells, is, accord- ing to Schwann, thrice as great as that taken up by the interstitial sub- stance. In a five-months' human embryo, I have myself noticed the cartilage-cells, 0-003-0-008 of a line in diameter, with and without secondary cells, some with, and some without distinct walls, and sepa- rated from each other by a perfectly homogeneous substance, 0*002- 0*005 of a line thick. In the new-born child they measure, according to Harting, 0-032-0028 mm in length, and 0-0072 mm in breadth, and are three or four times as numerous as in the foetus at four months ; but on the other hand, they occupy considerably less space, proportionally, than the interstitial substance, the bulk constituted by which is more than double that of the cells. After birth, in the non-ossifying carti- lages, the interstitial substance and the cells increase in pretty nearly an equal ratio, so that their relative proportions in the adult are about the same as in the infant at birth. In the adult the cells are from 8 to 12 times larger than in the new-born child (Harting), but, according to him, their number is diminished, so that they amount to not more than half of what existed in the child, which is explained upon the supposition of a coalescence of the cells. The numbers given by Harting do not appear to rne to afford sufficient ground for the establishment of his posi- tion; and even should it be established, I cannot agree in the explana- tion offered, not being a-ware of a single fact in favor of the notion of a coalescence of cartilage cells.* * [We have deferred to this place the remarks we have to make with regard to the struc- ture of the cartilage, and its mode of growth; as a just conception upon this subject appears to us to be essentially necessary to a comprehension of the mode of development of Bone, in fact, we might say, to clear notions upon the structure of the tissue's generally ; for as we shall show more at length below, it was upon the structure of cartilage, and what he supposed to be its similarity to that of vegetable tissue, that Schwann based the whole nomenclature of his cell theory. Now we may so far anticipate what we shall have to show hereafter, as to premise that Schwann was misled upon two essential points, the first being the supposition that the histological elements of plants and animals are primarily independent cells ; the second, the notion that the " nucleus" of the animal, is homologous with the nucleus of the vegetable tissue. It is, we believe, from the inextricable confusion produced by these fundamental mistakes, which have been adopted by almost all Schwann's successors, that one-half of the controversies with respect to the structure of cartilage and the process of ossification have arisen. And yet to one who is free from them, nothing can be simpler. We have already (note p. 56) referred to the structure of foetal cartilage, but it may here 310 SPECIAL HISTOLOGY. 102. Metamorphoses of the primordial cartilaginous Skeleton. Of the primordial cartilages, one portion undergoes further development with the rest of the skeleton, constituting the permanent cartilages of be described more at length. We found the cartilage of the septum nasi of a four-months' human foetus to be composed of a homogeneous, soft matrix, without structure of any kind, in which lay imbedded, rounded or irregular vesicular bodies, varying in diameter from S0W~WW th of an inch ; tne commonest size, however, being ^i^-^-^th. These " corpuscles" frequently contained one or more granules, sometimes very small, sometimes larger, and of a distinctly fatty nature; such fatty granules, also, were sometimes to be found in the matrix around the corpuscles. The cavities in which they lay, were, for the most part, just large enough to contain them, and presented no walls or sharp lines of demarcation of any kind from the surrounding substance. When the corpuscles were as large as j^^th of an inch, they occasionally contained a round body of rather less than ^^g^th, as a " nucleus." The matrix was in some parts pale and indifferent ; but where the tissue had taken on its definitely cartilaginous nature, the chondrinous substance into which it was converted re- fracted the light much more strongly. In this part also, the cavities in which the corpuscles lay, were often of considerably larger dimensions than the latter, and their walls exhibited a sharp, dark line of definition from the surrounding substance, which was often brought out much more strongly by the action of acetic acid. It appeared, in fact, that the conversion into chondrin had not quite reached the inner surface of the cavities, and hence they were chemically and optically distinguished from the surrounding substance. Now, of course, it matters very little what names are given to these parts, so long as they are used only in one sense. Schwann considered the corpuscles to represent the " nuclei" of plants, and therefore gave them that name. Henle, Reichert, Kolliker, and nearly all their compatriots, Todd and Bowman, Leidy and Sharpey follow him. As a consequence, they consider the wall of the cavities to represent the cellulose "cell-wall'' in plants; and there has been much controversy as to how much of the matrix of the cartilage results from the union of these " cell-walls," how much from the development of an intercellular substance ; a controversy which has extended itself to the determination of the homolcgies of the ele- ments of every tissue. We must confess, it seems to us that the disputants have been fighting for a shadow. If, in fact, the youngest cartilage be composed of cells with distinct walls enclosing the cor- puscles, of course these cells may be united by an intermediate, " intercellular" substance ; and it will be an important question to determine in the further course of development what arises from the walls and what from the substance which unites them. But if, on the other hand, all this be pure hypothesis; if young cartilage be, as we have said, composed of nothing but a continuous, homogeneous matrix, in which the corpuscles are imbedded, but in which no other structure exists, what becomes of the controversy ? We believe that not merely will the account we have given, be found to be correct, by any one who will without prejudice examine into the subject, but it seems to result from the observations, even of those who have interpreted the facts otherwise. Schwann (" Mikros. Unters.," pp. 112, 113) describing the development of the cartilage of Pelobates, says : " The new cells arise in the cytoblastema (matrix nobis) We see at first mere cell-nuclei (corpuscles nobis), which are somewhat smaller than the nuclei of the full-grown cells, a, 6; partly nuclei, which are closely surrounded by a cell, c, c; in short, all transitional forms, from mere cell-nuclei and nuclei surrounded by small ells, to fully formed cells ; so that here, development takes place as in small cells, and the nucleus is their actual cytoblast The cell-membrane becomes distinct only in the full-grown state." In the next page, Schwann speaks of the free-swimming nucleated corpuscles which he obtained from the ossifying cartilage of a fcetal pig, and which he considers to be identical with the bodies already described in Pelobates. In reality, however, these bodies are not THE OSSEOUS SYSTEM. 311 the nose, joints, symphyses, and synchondroses ; a second disappears altogether in the course of development (certain cranial cartilages, vide cells in the same sense, being merely the nuclei of Schwann and the nucleated form of the corpuscles to which we have referred above. Whatever Schwann's words may indicate, then, his observations tend to precisely the same conclusion as our own. Henle (" Allg. Anat," pp. 803-808) follows Schwann, and equally fails to discriminate the cells in Pelobaies from the " cells" in the fostal pig. Reichert (in his admirable work, " Ueber das Bindegewebe," 1845) recognizes the fact that the cartilage-corpuscles are " nuclei" in Schwann's sense, and refers the appearance of a distinct wall in the cavities, to an optical delusion. He asserts that young cartilage is com- posed of distinct cells closely united together, without any measurable intercellular sub- stance ; as the cartilage grows, the latter increases, and eventually the cell-walls disappear. The only evidence of the existence of these cells and intercellular substance offered by Reichert, however, is the mode in which the tissue may be broken up ; a kind of evidence whose value the purport of the rest of his book is to reduce (and most successfully) to nothing. In effect, therefore, Reichert's observations come to the result already stated, that the festal cartilage is composed of a homogeneous matrix, in which the corpuscles are dis- persed. Robin (" Observations sur 1'Osteogenie") takes nearly the same view of the structure of cartilage as that we have indicated. " Cartilage is composed," he says, " of a homogeneous, amorphous, dense, elastic, hyaline basis (substance fondamentale], in which cavities are hollowed out, cartilage-cavities. In each of these cavities we find one or many (sometimes 20 to 30) cells, cartilage-cells^ whose parietes cannot be demonstrated to be distinct from their cavity. These cells are more or less granular, and have a nucleolated nucleus In the foetus, up to the age of four or five months, more or less, the cartilage cavities do not enclose one or more cells, but one or many masses of yellowish granulations, all of nearly the same size. These masses are more or less distinctly defined at their edges, in general indistinctly, and nearly reproduce the form of the cavity without ever filling it. They may be called carti- lage-corpuscles. Authors have not generally remarked this fact. By degrees the cells which replace these corpuscles are developed. These cells are formed all at once ; but the grades of the process as regards the commencing cell or the pre-existing granulations are as yet but little known Some authors wrongly call the cavities excavated in the fundamental substance, cartilage-cells ; and to the true cartilage-cells and masses of yellowish granulations or corpuscles, referred to above as existing in the fostal state alone, they give the name of contents.''' 1 Remak ( :{ Ueber die Entstehung des Bindegewebes und des Knorpels," Muller's " Archiv," 1851-2) appears to have been the first, definitely to recognize the cartilage-corpuscles, as the homologues of the primordial utricles of plants, a great step, and one which appears to us to lead to most important consequences. Like Schwann, however, led away by the gene- rally assumed anatomical independence of the vegetable cells, Remak interprets the struc- ture of cartilage in the same manner, and speaks of the secretion of the chondrinous wall by the primordial utricles, as " parietal-substance" within the primary cell-membranes. He adduces no evidence, however, that the facts are other than as we have stated them to be. Virchow (" Die Identitat von Knochen-, Knorpel-, und Bindegewebe-ktfrperchen so wie uber Schleirngewebe," " Verhandlung d. Phys. Med. Gesellschaft," 1852) is an important wit- ness in this matter. He says, " I have anew convinced myself that the so-called cartilage- corpuscles are actual cells which lie in a cavity of the basis (Grundsubstanz}, or in a cell- cavity presenting a double contour, and possess a membrane, granular contents, and a fre- quently nucleolated nucleus. In the neighborhood of the line of ossification, in growing cartilages, as well as in the young callus-cartilage of fractures, these cells are of very large size, clear, and round ; in the neighborhood of the articular extremities, excessively small, 312 SPECIAL HISTOLOGY. 101) ; the third and greatest part, ultimately becomes ossified, and constitutes all the bones of the trunk and extremities, and a great part of those of the cranium. All these bones are ossified, essentially in the compressed, and dark. Under favorable circumstances, the cells, in simple cartilage, may be isolated, and their peculiar relations with regard to acetic acid, which generally renders them darker and collapsed, may be exhibited. Water also causes them to collapse, and they thus occasionally form peculiar, jagged corpuscles, which one might be readily tempted to confound with branched cells. The larger the original cell was, so much the more branched does its collapsed mass appear." (p. 152.) "It might have been ex- pected that in the course of ossification of the cartilage, these cells would be seen to pass into the irregular, anastomosing bone-corpuscles ; but nothing of the kind is visible A point of difficult determination is, in general, the existence of actual cells in the small flat cavities of cartilage, e. g. towards the surface. Very frequently it would here seem as if the membrane of the cell had coalesced with the intercellular substance, and only the contents with the nucleus had remained behind. But on careful investigation especially under the prolonged operation of acetic acid, frequently after maceration in hydrochloric acid, we clearly see a complete cell with a nucleus and contents in the cavity" (p. 153). Virchow gives no figures, but the above passages furnish so accurate an account of what we have ourselves seen in young and in fully-formed cartilage, that we have thought we could not do better than cite them. The jagged appearance of the corpuscles to which he refers, is very common, and we have been led to suspect that it may arise from the same cause as the very similar appearance often exhibited by the colorless corpuscles of the blood, viz., a protean throwing out of processes. When Virchow, however, describes the passage of these " cells" into the branched or stellate corpuscles of fibro-cartilage, and considers the latter to be metamorphosed cartilage- corpuscles, he confounds together things which are essentially different. Careful examina- tion of foetal fibro-cartilage, e. g. the intervertebral fibro-cartilage of the Kitten, shows that the stellate body is the wall of the cartilage cavity, with processes which run out from it, the original corpuscle remaining in the interior of the cavity, either unchanged or becoming gradually lost, or fused into one mass with its walls. The account of the structure of cartilage given by Tomes and De Morgan (1. c., pp. 15, 16) in all essential points agrees with that of Virchow. They call the corpuscles, granular cartilage cells. To recapitulate : the facts contained in other observations, as apart from the interpretation, appear to agree perfectly with our own ; the result of which is, that in the fcetal state, car- tilage is composed of a homogeneous matrix, in which lie the corpuscles, in cavities which they just fill ; that their relation to the matrix is exactly that of the primordial utricles to the cellulose wall in plants, and that like this they may or may not develop a nucleus ; that with age they enlarge, but not so fast as the cavities, the walls of which become chemi- cally altered into chondrin, a change which often takes place in such a manner as to give rise to a lamination or to a difference in composition of the inner and outer portions. If the cartilage be converted into fibro-cartilage, the outer part becomes changed into collagen, while an alteration into a substance resembling elastic fibre, is effected in the inner portion, and in the direction of certain lines radiating from it, just as we have seen the elastic ele- ment to be developed in connective tissue (see on Connective Tissue). So much for the structure of cartilage: with regard to its development and multiplication we must equally demur to the statements in the text. It is, indeed, very true, that no new cartilage-cells arise independently of those which pre-exist: but in opposition to Professor Kolliker we must agree with Leydig, Robin, Remak, and Tomes and De Morgan, that the multiplication of the cartilage-cells invariably takes place by a process of division exactly analogous to that which occurs in plants. So far as we have seen (and in ossifying carti- lages, and in that of the Skate, it is easy to trace the process), the corpuscles first become con- stricted, being found occasionally of an hour-glass shape; and eventually divide. The matrix then grows in, so as to separate the two, and the process of fission is complete. TRS.] THE OSSEOUS SYSTEM. 313 same way. At one or more points (puncta ossificationis), in their inte- rior, a deposition of calcareous matter commences, simultaneously with a change in the cartilaginous elements ; which transformation proceeds on some or on all sides, continually converting additional portions of the cartilage into bone. Whilst this is going on, the cartilage, in most cases, ceases to grow in one direction, and, consequently, is there soon entirely converted into bone, whilst in others its growth continues, so that a new cartilaginous, plastic material is furnished for the progressive increase of the bone, which material, as in the epiphyses of the cylindrical bones, is sometimes developed into distinct ossific centres or nuclei. When the whole of the cartilage has been converted, and its perichondrium become periosteum, the bone does not cease to enlarge, but a new and peculiar mode of formation is now set up, in all these places, until its growth is completed. This consists in the ossification, from that surface which is in contact with the bone, of an organized, soft, plastic material, which is deposited on the inner surface of the highly vascular periosteum, and in proportion as this conversion into bone takes place on the one side, fresh, fluid materials for it are afforded by the periosteum on the other. 103. Changes in the ossifying Cartilage. The active vegetative process in the cartilage-cells when ossification is going on, depends upon this, that the cells which were hitherto of small size, and contained but few secondary cells, begin to grow, and successive generations of cells to be produced in them, as may, also, be seen at the ossifying margins of bones already existing, in which situation larger cells may be noticed close to the bone, and others, which are smaller in proportion to their distance from it. All the cells which are engaged in the incipient for- mation of the bone, present clearer and, less frequently, granular con- tents, a distinct, vesicular, round nucleus, with nucleolus and readily distinguishable walls ; they are very quickly altered, however, on the addition of water, acetic acid, alcohol, and by drying, &c., so that the contents contract around the nucleus, and form a roundish, elongated, irregular, even stellate, granular, opaque body (cartilage-corpuscle of authors). Their size and mode of grouping vary, not inconsiderably, according to age and situation. With respect to the former, they exhibit during embryonic life a constant increase, whilst after birth they appear to retain a uniform size ; and, as regards the latter, it may be stated as a law, that where the ossification of the cartilage proceeds in one direc- tion only, the cells, at the osseous border, are disposed in rows. This is most distinctly seen, as has been long well known, in the extremities of the diaphyses of the larger cylindrical bones, where the rows of cells are very prettily arranged in parallel lines close together, and are of con- siderable length ; it is also evident in the other long bones, as well as in 314 SPECIAL HISTOLOGY. many others where the cartilage ossifies only on one side, as in the con- necting surfaces of the vertebrce. Where, however, the ossific nuclei in the centre of a cartilage enlarge on all sides, the cartilage-cells are con- fusedly grouped in roundish, or oval, irregular little masses, as in the short bones at their first formation, and in the epiphyses. An accurate comparison of the cells which are closer to the ossifying margin, with those more remote from it, and of the groups formed by them, at once I Sg shows that their particular disposition is directly related to their mode of increase. Each individual group (or even two of them) corresponds, FIG. 130. Perpendicular section from the ossifying border of the shaft of the femur of a child a fortnight old : a, cartilage, in which the cells the nearer they are to the ossifying border are placed together in more extended longitudinal rows; 6, ossifying border, the dark streaks indicate the progressive ossification in the intercellular substance, the clearer lines the cartilage-cells which ossify subsequently; c, compact layer of bone near the ossifying border ; rf, the substantia spongiosa formed in the osseous substance by resorption, with can- celli, the contents of which are not shown. Magnified 20 diameters. FIG. 131. Femur of a child a fortnight old, natural size: a, substantia compacta of the shaft; 6, medullary cavity; c, substantia spongiosa of the shaft; d, cartilaginous epiphysis with vascular canals; e, osseous nucleus in the inferior epiphysis. THE OSSEOUS SYSTEM. 315 in a certain measure, with a single primordial cell, and represents all the descendants which in course of development have proceeded from it. In the one case, all these newly-formed cells are disposed, one behind the other, in a single or double linear series ; and in this way are produced, by their further increase, the rows of cells above described, whilst in the other they constitute a more globular mass. The primordial cells (first parent-cells) during this procedure, sometimes disappear as distinct or- ganisms, owing to the coalescence or fusion of their walls with the inter- stitial substance, sometimes not ; and the same holds good with those of the subsequent generations. The latter is usually the case in the rounded masses of cells, owing to their smaller size, and around them a contour line may for the most part be recognized, which is nothing more than the distended wall of the first cell ; whilst in the rows of cells, the walls of the original cells are not, usually, so merged in the intercellular sub- stance as to escape recognition. The entire matrix, in which the just- described, enlarged, and actively multiplying cells are enclosed, varies very considerably in thickness in the different cartilages ; scanty around the osseous nuclei in the epiphyses and short bones, it is J to J a line thick in the diapliyses. It is universally characterized by its yellowish, transparent color, and its streaky, apparently fibrous fundamental structure, from the other cartilaginous parts, which are, as usual, bluish- white, with a homogeneous or granular interstitial substance. The vessels met with in the ossifying cartilages constitute a phenome- non well worth attention ; from the middle of foetal life onwards, they occur in many situations, preceding by a shorter or longer time the appearance of the osseous nuclei, and accompanying their increase. I have observed them in the articular cartilage of the epiphyses of the long bones even in a person 18 years old. They entered the cartilage in great number, perpendicularly from the bone, ramifying and terminat- ing a little below its free surface. The cartilage-vessels invariably lie in wide canals (measuring, even in a five months' foetus, 0'02 0*04 of a line), excavated in the cartilage, and bounded by narrow, elongated cartilage-cells, the vascular canals of cartilage, or cartilage canals, which enter the cartilage from the perichondrium, and, when a vascular ossific nucleus exists (diaphysis), also from the border of the ossifying portion itself (though in less number, at all events at an earlier period), penetrate it in straight lines, in various directions, giving off a few branches, and, to all appearance without any anastomoses, or other kind of interconnection, end, for the most part, in blind, club-shaped dilata- tions. These canals are produced by a resolution of the elements of the cartilage, in the same way as the medullary cavities of the bone itself, originally contain a plastic material composed of minute rounded cells (cartilage-marrow), corresponding to the foetal cartilage- marrow, and develop in a short time out of this material, true sanguiferous vessels, 316 SPECIAL HISTOLOGY. and a wall composed of more or less developed connective tissue, and subsequently also of elastic fibrils. As concerns the vessels themselves, I have sometimes found, in a canal, only one large vessel (frequently very distinctly arterial, with muscular walls), sometimes two such, some- times capillaries in various numbers, but I am unable to explain how the circulation is carried on in these vessels. There must either be anasto- moses between the vessels of different canals, or if the latter be really closed, arteries and veins both probably exist in one and the same canal. The object of these vessels of cartilage appears to be one of a double cha- racter; in the first place, to convey the materials requisite for its growth and further development ; and secondly, to promote the ossification. The former of these functions is very manifestly carried out in the thick epiphysal cartilages, which grow to such a length before they become ossified, and even afterwards continue to enlarge ; and the latter is pro- bably effected principally in the short bones, which do not contain vessels until just before the commencement of ossification. Notwithstanding this, however, it is not intended to imply, that a cartilage cannot grow, nor become ossified without vessels ; but although the latter condition does in fact obtain in animals, and probably also in man, normally in certain situations (on the appearance of the first points of ossification of the embryo, those of the ossicula auditus, &c.), still, this does not prove that the vessels when existing have no concern in the processes adverted to ; and consequently it cannot be admitted, as lately supposed by- H. Meyer, that they are to be regarded in the light of accidental produc- tions, and as standing in no necessary relation with the development of the bone. 104. Ossification of the Cartilage. The ossification of the matrix generally precedes in some degree that of the cartilage-cells ; and, under normal conditions, is primarily effected by a granular deposition of calcareous salts (calcareous granules as they are termed). Where the cells are disposed in rows, at the ossifying border, this deposition of earthy matter always proceeds in the fibrous substance between the rows of cells, forming processes, which, in a longitudinal section, assume the appearance of pointed teeth, and surround the lowest portions of the rows of cells like short tubes. The same disposition, essentially, is also manifested in other situations, where the cartilage cells constitute more rounded groups, only, that in this case the ossifying matrix sur- rounds them more in a reticular manner. The calcareous granules or particles, the first visible deposit of the earthy salts of bones, are of a rounded angular figure, white by reflected, opaque by transmitted light, easily dissolved with effervescence in acids, and differing in size in different bones, from immeasurable minuteness up to O'OOl, or even 1-002 of a line; their size, however, does not appear to be regulated THE OSSEOUS SYSTEM. 317 Fig. 132. by period or situation, although there is no doubt that they are fre- quently, in one place, of uniform minuteness, and in others uniformly of coarser character, but rather by some change occurring in the supply of plastic material to the ossifying border. If this earthy deposit be traced in microscopical sections, from the margin of the ossification into the interior of the young bone, it will be apparent, that it is to it, for a certain distance, although with diminishing distinctness, that the granular and opaque aspect of the margin itself is due ; the substance gradually becomes more homogeneous, clearer, and more transparent, ultimately acquiring the aspect of perfect bone. According to all appearance, the primordial earthy granules or particles become gradu- ally fused together, and thus impregnate the whole tissue of the matrix of the cartilage, instead of, as before, separate portions, and thenceforth disappear as iso- lated, distinguishable parti- cles. With respect to the forma- tion of the bone-cells, I believe, that owing to the discovery of an excellent subject for their observation, viz., rachitic bone, I have put the matter, as regards the most essential particulars, in a clear point of view. The bone-cells are formed, as Schwann thought possible, and Henle supposed, from analogy with the ligni- fied vegetable cell with pores or dotted canals, from the cartilage-cells, by the thick- ening of their wall, with the simultaneous formation of canalicular vacuities in it, and its ossification. In the ossifying shaft of a rickety bone (Fig. 132) the morpho- logy of this process may be most beautifully observed. If the rows of FIG. 132. From the ossifying border of the condyle of the femur of a rachitic child, two years old, a, cartilage cells, simple and parent cells in series ; 6, more homogeneous j c, striated matrix between them; d, cartilage-cell.s at the commencement of their trans- formation into bone-cells ; e, the same further advanced, with very much thickened walls, indication of canaliculi, commencing deposition of calcareous matter in the walls, whence their darker color, though still with distinct nuclei ; /, bone-cells still more developed and more ossified, in an equally ossified, matrix. Magnified 300 diameters. 818 SPECIAL HISTOLOGY. cartilage-cells of the ossifying border, which in this case are of larger size, be traced from without to within, it will soon be found, that at the point where the deposition of calcareous salts (which takes place for the most part without the formation of the calcareous granules) commences, they exhibit, instead of a membrane indicated by a single, tolerably strong line, a thicker coat, which on the inner side presents delicate indentations. Even when the thickness of this membrane does not exceed 0*001 of a line (Fig. 132, d), it is obvious that the car- tilage-cells are about to be transformed into bone-cells ; and this be- comes still more evident, when, further on in the bone, the thickness of the membranes in question, together with the simultaneous diminu- tion of the cavity of the cell, is seen to be constantly increasing, the indentations of the interior contour line to become more and more marked, and, accompanying the progress of these changes, the walls to become more and more dark from the addition of calcareous matter (Fig. 132, e). The slow ossification of the matrix between the cells is very favorable to the observation of these changes, allowing not only of the accurate investigation of the first alterations in the cartilage-cells, but also of their subsequent conditions, at a time when they must be termed bone-cells and lacunce, being traced step by step. To this cir- cumstance alone is also due the establishment of the interesting fact, that cartilage-cells, enclosing secondary cells within them, are converted, as a whole, into a single, compound bone-cell. Cells of this kind -are very frequently met with, having two cavities, which cells, according to their degree of development, are sometimes wide and furnished with short prolongations, and sometimes from their contracted cavity and long canaliculi, resemble in all respects perfect bone-lacunae. Com- pound cells, with 3, 4, and 5 cavities, each with the remains of the original contents and nucleus, occur more rarely, though even such are occasionally to be found in almost every preparation. The cartilage- cells lying free, and inclose apposition, though in a non-ossified matrix, having thus evidently become transformed into bone-cells with nuclei and other contents, the ultimate changes now take place from which the rickety bone-substance acquires pretty nearly the nature of the sound tissue. These changes, in as far as they effect the bone-cells, chiefly depend, in the first place, upon the commencement of ossification in the matrix, but without any primary formation of calcareous particles ; and secondly, upon the continually increasing deposition of earthy mat- ter in it, and in the thickened cell-walls, owing to which, the new bone- substance, to the naked eye, becomes more and more white, and under the microscope appears more and more dark and transparent ; it now, also, becomes more homogeneous, and the abrupt limits of the bone-cells gradually less and less defined, till at last they appear, not as cellular organisms lodged in the matrix, but to be confused with it, being recog- THE OSSEOUS SYSTEM. 319 nizable only from their peculiar stellate cavities, the so-terined bone- corpuscles, or lacuna? and canaliculi. With the knowledge thus obtained of the formation of the lacunae in rachitic bone, the endeavor to arrive at an insight into the same process in normal bone, is no longer attended with as much difficulty as before, when the inquirer was involved in a maze of hypotheses of the most various kinds, and all without any certain foundation. The investigation of the conditions attending the development of bone, both in man and other animals, must nevertheless still be regarded as troublesome, and frequently little worth the pains bestowed upon it. It is, perhaps, cer- tainly manifest (vid. "Mik. Anat.," tab. iii. fig. 6), that the bone-cells, a little beyond the limit of ossification, become thickened, and, still presenting the remains of their cavity and the nucleus, beset with cal- careous particles ; and although such incrusted cells may even be isolated, yet the mode in which the changes are effected further on, is not, beyond a short distance, I must affirm, to be seen with anything like the dis- tinctness that it is in rachitic bone, because, more internally, the newly- formed medulla with its vessels, and the calcareous particles, render almost everything indistinct; and it is not till we get to the homogeneous and more transparent osseous tissue beyond, that distinct, but almost perfectly-formed lacunae come into view. Nevertheless, from all that we see, there cannot be the least doubt, but that the processes are essentially the same as in rachitis, only, that in the healthy bone the ossification of the thickened walls of the cartilage cells, presents two stages, instead of only one, as in the former case, inasmuch as they first appear granular from the deposition of the calcareous particles, and afterwards homogeneous. Moreover, even in perfectly normal bone, in the adult, I have met with places (some of which, independently of me, have also been lately described by H. Meyer (1. c.) ), such as the sym- physis pubis, the synchondroses of the vertebral, and those of the ilium, sacrum, and the points of insertion into the bones of certain tendons containing cartilage-cells. In all of these situations, at the line of junction between the cartilage or tendon and the bone, cartilage-cells of the most characteristic aspect may be seen, lying free in the cartilaginous matrix, and presenting the most various degrees of transformation into bone-cells ; some, in particular, having thickened walls, and a more or less copious deposit of calcareous particles ; while others are almost perfectly-formed bone-cells, with pores and a more homogeneous wall (Fig. 123) ; so that I am able to afford a certain support to the state- ment given above with respect to the mode of origin of the bone-cells, by the conditions presented in normal tissues also. In the last-named situations I have, likewise, very distinctly and very frequently noticed, half- or wholly-ossified parent-cells, containing from two to twelve secondary cells. 320 SPECIAL HISTOLOGY. There is another point in the development of the bone-cells still ob- scure, or at least that has not been directly observed, viz., how their pores or canaliculi become branched cavities, communicate with those of other cells and acquire open orifices in certain situations. All that is apparent in rachitic bone and elsewhere, is merely the circumstance, that the thickening of the ossifying cartilage-cells does not proceed with a straight but with an indented border, which is the case in fact from the beginning up to their completion, and that the bone-cells have, at first, more simple prolongations than afterwards. Observation teaches nothing beyond this. Now, as there can be no doubt that the canaliculi anastomose very freely, and also, that they frequently open on the outer surface of the bone, or into the cavities in its interior, I do not for a moment hesitate to express the opinion, that the canaliculi, arising as simple branches from the lacunce, are continued or further developed by absorption of the already -formed bone-substance. How such an absorp- tion takes place, cannot, it must be confessed, be explained ; but that affords no ground of objection to the opinion, because we see a similar process, though on a widely-different scale, take place in the formation of the medullary cavities and cancelli (vid. infra). It would appear to me, that currents of the nutritive fluid in the bone were chiefly concerned in this further development of the canaliculi; and the more so, because the first rudiments of the canaliculi, like the pore-canals of lignifying plant-cells, manifestly indicate nothing more than the points at which the ossifying cartilage-cells continue to admit and emit fluid; on which account, also, their direction is principally towards the internal and ex- ternal surfaces of the bone, from which the nutritive plasma is derived. It appears to me highly probable, that after the complete ossification of the cartilaginous tissue, the nutritive fluid derived from the blood-vessels of the periosteum and of the medullary cavities (1.) finds new ways for itself towards the lacuna? and their prolongations, which, as it may be said, alone are still open to it, and in this way effects their opening on the internal and external surfaces of the bone, and (2.) also burrows passages from the cavities lying nearest to it, and thus ultimately pro- duces a ramification of them, and brings about numerous communications between the different cavities. In accordance with which, a secondary formation of canaliculi must take place, not only in the region of the thickened walls of the original cells, but also in the osseous matrix, and this to a considerable extent, as is at once evident, when the distances between the anastomosing cavities are compared with the diameter of the original cartilage-cells. The development of the medullary spaces (cancelli) and of the medulla, is to a certain extent the last act in the transformation of cartilage into bone. The medullary spaces do not arise in a coalescence of the cartilage- cells, but from a solution of the more or less perfectly formed bone-sub- THE OSSEOUS SYSTEM. 321 stance, exactly like the large medullary cavities of the cylindrical bones. This is most distinctly and satisfactorily shown by the examination of the diaphyses of a sound or rachitic bone, but especially in the latter. At the limit of the ossification itself, the osseous tissue for a distance of about I to J of a line, is quite compact, without a trace of larger cavi- ties, and is composed in part of the ossified matrix, and in part of car- tilage cells, more or less advanced in their transformation into bone- cells ("Mik. Anat.," tab. iii.) ; beyond this part, however, cavities, at first small, and more internally, larger, come into view, the whole rela- tions of which show most convincingly that they do not originate in any development of the existing elements. They have an extremely irre- gular contour, are oval, or roundish and angular, and for the most part broader than the cartilage-cells, appearing to be eaten out, as it were, in the substance of the bone, and involving severally the compact tissue, matrix, and bone-cells. When the borders and limitary surfaces of these spaces are closely regarded, it is, in many instances, easy to notice bone- cells more or less removed, half projecting from, or buried in the wall, and between them projections of the ossified matrix, so that no doubt can any longer be entertained with respect to the origin of the cavities. It must be confessed that there is as little to be stated, in this case, as in that of the origin of the analogous cartilage-canals, and the further development of the canaliculi of the bone-cells, with respect to the mode in which this absorption takes place ; and the process is even still more inexplicable, because, allowing that it really does take place, there would then exist in the ossifying bone, at the same time and almost in immediate contiguity, a formation of bone and a resolution of the tissue, but very little less energetic. The above-described mode of formation of the cancelli) nevertheless, is a morphological fact, and consequently, the explanation of such a curious phenomenon becomes a problem to be solved by chemistry and physiology. As in the diaphyses, so in the ossification of all the other cartilages, medullary spaces are formed by the resorption of the inner portions of that part which is half ossified. But it must be stated, that these spaces do not present the same form, direction, and size in every bone ; though with respect to this, it is un- necessary to offer any special remarks, since the relations of this primitive spongy substance are, in the main, the same as they are after- wards. Still, it may be remarked, that in many bones, solitary spaces are apparently developed immediately from cartilage-canals, seeing that some at least of the latter, at the limit of ossification, communicate directly with the spaces in the bone ; and, moreover, that not unfre- quently, cartilaginous elements not yet wholly converted into bone-cells, are drawn into the process of resolution. The medullary cavities, however they arise, are filled with a soft, reddish substance foetal medulla. This substance at first consists of 21 322 SPECIAL HISTOLOGY. nothing but a small quantity of fluid and many rounded cells, with one or two nuclei and faintly-granular contents, of which I am unable to say how they originate, but only this much, that they are altogether new formations. In process of time these cells, which are in all respects identical with those which occur, in the adult, in certain bones (vid. supra), are developed in the usual way into connective tissue, blood- vessels, fat-cells, and nerves. The formation of bloodvessels proceeds with great rapidity, so that bones, very shortly after the development of the medullary spaces, exhibit bloodvessels in them ; that of the fat and nerves takes place more slowly, although the latter, at the period of birth, of course with fewer filaments than subsequently, may be very readily perceived in the large cylindrical bones, even more readily than in the adult, because at this time the medulla may be more easily washed away from them and the great vessels. The fat-cells at this period are but few in number ; the medulla, in man at least, being colored entirely red by the blood and the light reddish medulla-cells. After birth they gradually multiply, till at last, the marrow, in consequence of their great increase, and the disappearance of the medulla-cells, which are ulti- mately all transformed into the elementary tissues of the permanent medulla, acquires its subsequent color and consistence. In many of the primarily cartilaginous bones of Birds and Amphibia, the ossification of the cartilage commences, according to Rathke and Reichert (1. c.), on the outer aspect of the cartilage, so that at first a cylinder of bone is formed with cartilage internally and at the extremi- ties. The remainder of the internal cartilage then affords space to the medulla, whilst the epiphyses are formed out of that of the extremities. If the contents of the cartilage-cells, the "cartilage-corpuscles" of authors, be really surrounded by a membrane, as Yirchow supposes, it may be assumed that a similar tunic, analogous to the primordial utricle of the plant-cell (vid. sup. 8), exists also around the contents of the bone-cells, and that it takes an essential part, by its throwing out stel- late processes, in the first formation of the canaliculi, their further elon- gation and ultimate anastomoses. In this case, also, the stellate and readily isolated cartilage-cells from an enchondroma described by Vir- chow (Wurz. " Verh.," Bd. 1), around the internal portions of which the contours of rounded cells were visible, would be intelligible, and even the possibility of the isolation of stellate organisms from normal bone (vid. sup.) be explicable. My exposition of the formation of the lacunae in rachitic bone, is confirmed by Rokitansky and Virchow (Wurz. " Verh.," II.) ; whilst Robin declares that it is incorrect, giving a description of their formation which is, to me, unintelligible. I recommend to his notice rachitic bone, the cementum of the horse's tooth, and the symphy- ses ( 95), with which he is manifestly unacquainted, and hope that he THE OSSEOUS SYSTEM. 323 may then be induced no longer to regard Schwann's and my views as antiquated.* * [As we have already said, we must deny the existence of endogenous cell-development in ossifying, or any other cartilage. In fact, the process of multiplication of the corpuscles (nuclei (?) of Kolliker, granular cartilage-cells of Tomes and De Morgan) is so clear, that we are at a loss to comprehend how it can be mistaken. What is meant in the text by " contents," as distinct from the corpuscles, we do not know. Messrs. Tomes and Morgan describe the real changes which precede ossification, very exactly in a few words, thus : " Cartilage previous to its conversion into bone undergoes a rapid growth, which takes place principally in the direction of the long axis of the future bone. Each granular cell becomes divided into two, by segmentation transverse to the line of ossific advance. These are again divided and the process repeated from time to time, until in the place of a single granular cell we have a long line of cells extending from the unchanged cartilage to the point where ossification has taken place" (1. c., p. 16). "If attention be directed to the end of the line furthest from the bone, the cells will be found small in size, granular, and with a percepti- ble nucleus, but without an outer wall, distinguishable from the hyaline substance, which is abundant between the contiguous lines, but small in quantity between the cells composing the lines. But if the other end of the line be examined, very different conditions will be observed. The granular cells will be seen to have become rounded in form, to have in- creased to three times their original bulk, and to possess well-marked, circular nuclei. ..." -p. 17. So far, our own observations are in perfect accordance with those of Tomes and De Mor- gan. They go on, however, to observe, " in addition to which, each granular cell will have acquired a thick, pellucid, outer wall ;" and with this last statement we can by no means agree. Neither in Man, the Calf, the Rabbit, the Skate, nor in enchondroma, have we been able to see anything of the regular development of such an envelop- in fact, in the great majority of instances, we have convinced ourselves of the absence of anything of the kind there being nothing but a clear space between the corpuscle and the ossified wall of the cavity in which it lies. Bodies corresponding with the lacunal cells cartilage-corpuscles that is, invested by a thick coat of more or less granular, calcareous matter, may indeed often be obtained free; but they arise, like the corresponding bodies in rickety bone, simply from the deposition of calcareous matter in the cartilage-cavity before it has taken place in the matrix, or from a want of union between the two deposits ; and are therefore quite accidental. The lacuna, are developed, according to these authors, by the shooting out of the granular cells into processes, and their direct conversion into the lacuna, the nucleus of the granule- cell remaining as the nucleus of the lacuna. On this point also, we must differ from them, and agree with Virchow (1. c., note, 101) and Kolliker (supra, 104), that the development of the canaliculi is, by a process of resolution, quite independent of the corpuscles, which simply diminish in size, and either remain as the so-called " nuclei" of the lacunae or totally disappear. We can especially recommend the Skate (2) as a subject in which to trace the process of formation of lacunae, as the bone is homogeneous and transparent, and in conse- quence of being enclosed in a large mass of firm cartilage, may be cut with ease into very thin sections. We have observed it with great clearness also in enchondroma. There is one argument which seems to us conclusive on this point. Wherever the cana- liculi can be seen at all, however young the tissue, they are perfectly clear and transparent. If. however, they were formed by processes of the granular cells, they ought to be granular, and more or less opaque. Taking the same view of the structure of cartilage as Messrs. Tomes and De Morgan, then, our view of the nature of the lacunae, resulting from its ossification, agrees with that of Professor Kolliker. Cartilage becomes bone by the deposit of calcareous salts in the matrix and occasionally in its cavities. The lacunae are spaces left round the corpuscles, from which, by resorption, processes the canaliculi, are subsequently developed. If it be asked how it is that the lacunae may frequently be demonstrated both optically and chemically as 324 SPECIAL HISTOLOGY. Fig. 133. 105. Elementary processes in the Layers formed from the Perios- teum. The periosteum of the primarily cartilaginous bones, is propor- tionally very thick and vascular, consisting, as early as at the fifth month, of common connective tissue and fine elastic filaments, the latter of which in process of time become stronger and stronger, occasionally assuming the nature of elastic fibres. On the inner aspect of this fully formed periosteum, there is now deposited an ossijic blastema firmly ad- herent to the bone (Fig. 133, B) ; so that when the periosteum is re- moved, it generally remains upon it as a moderately thick, soft, whitish yellow lamella, in which, microscopic ex- amination shows the existence of a fibrous tissue, with a not particularly distinct fibrillar formation, something like imma- ture connective tissue, and granular, oval, or round nucleated cells, measuring 0*006 -0-01 of a line. When this lamella is raised from the bone, it is found to be very intimately connected with the most superficial layers, and on its internal sur- face a few little detached fragments of bone, and scattered masses of reddish, soft medulla, from the most su- perficial cancellar spaces, wrll be observed. The bone thus laid bare, when the removal of the periostea! layer has been carefully conducted, presents a rough, and as it were porous surface, with numerous medul- lary spaces, and remains, superficially, in spots of greater or less extent, quite soft, pale-yellow, and transparent, whilst more internally it becomes firmer and whiter, ultimately acquiring the usual appearance of perfect osseous tissue. When it is inquired, how the formation of bone, which indubitably takes place in this situation, is eifected, we refer to the blas- tema just described, the cells of which, scattered in the fibrillated con- nective tissue, have not the least resemblance to those of cartilage, but appear exactly like the foetal medulla-cells, or formative cells of the FIG. 133. Transverse section from the surface of the shaft of the metatarsus of the Calf; magnified 45 diam. : ^?, periosteum ; J3, ossifying blastema ; C, young layer of bone, with wide cavities, a, in which are lodged remains of the ossifying blastema, and reticular spi- culae, 6, which towards the blastema present a tolerably abrupt border; Z), more developed layer of bone, with Haversian canals, c, which are surrounded by their lamellae. distinct bodies, we must call to mind the fact already referred to, that in cartilage, the wall of the cavities have frequently undergone less change than, or a different change from, the surrounding matrix; and therefore appear both optically and chemically distinct, though they are by no means so, morphologically : and, therefore, that there is no difficulty in sup- posing the same thing to occur in bone. The chemical differentiation of the wall of the lacuna is, in fact, exactly comparable to that of the wall of the cavity which contains the " nucleus" in connective tissue, and in fibro-cartilage ; and which gives rise to the formation of the elastic element in those tissues. TRS.] THE OSSEOUS SYSTEM. 325 embryo. In fact, it is now, not difficult to show, that the outermost, still soft bone-lamellae pass into the blastema in question, with their separate spiculae and projections, and that (1.) the matrix of the bone arises from its fibrous tissue, by the simple uniform deposition of cal- careous salts, although usually, as it seems, without the previous ap- pearance of calcareous granules ; and (2.) that the bone-cells are formed out of the formative cells of the blastema. With respect to the latter, however, the transformation cannot be followed step by step, as in rachitic bones. This much, however, is always apparent, that the bone- cells at first present larger cavities, less developed rays, and more dis- tinct nuclei (the latter, as we know, remaining), and, as their occasion- ally visible outlines prove, correspond entirely in size with the cells just mentioned, so that I do not for a moment doubt, that they are formed in this situation exactly as they are elsewhere. With respect to the development of the ossifying blastema itself, it is at least clear, that it is derived from the numerous vessels of the foetal and young periosteum ; the origination of its fibres from fusiform cells, I have very frequently observed in man and in animals, but with respect to the cells, can only state that they occur of various sizes, and occasionally intermixed with free nuclei. The formation of bone in this blastema occurs wherever it is in con- nection with the bone ; it does not, however, take place in connected but in interrupted, reticular lamellce. The roundish or elongated spaces (Fig. 133, a\ which, from the first, remain between the layers of osseous tissue, and in the different layers communicate with each other, are no- thing else than the rudiments of the Haversian or vascular canals of the compact substance, and contain a soft, reddish medulla, which at first is obviously nothing more than the unossified portion of the ossific blastema, although it sometimes contains more formative cells than connective tissue. The cells of these spaces are very soon transformed into the usual, light-reddish medulla-cells, and partly into vessels which communicate with those of the interior of the bone, and in part also with those of the periosteum, with which, having once formed a junction, they remain continuous during the entire growth of the bone in thick- ness, so that the formation of the spaces in the bone is, at least after- wards, preindicated by those, which, in accordance with what has been said, proceed from the periosteum through the ossific blastema to the bone. Besides medulla-cells and vessels as well as some connective tissue, the bone-cavities of the periosteal layers also contain round, elongated, or dentate, flattened, faintly granular cellular corpuscles of Q'01-0'02 of a line, or more in size, with from 3 to 12 or more vesicu- lar nuclei and nucleoli, which are probably referable to the multiplica- tion of the medulla-cells (vid. 11). The periosteal layers, which, agreeably to what has been stated, are from the first deposited in the 326 SPECIAL HISTOLOGY. form of cribriform lamellae around the ossific-nuclei formed from carti- lage, continue to be produced so long as the general growth of the bone goes on, essentially in the same way, constituting the material by which it increases in thickness ; but at the same time, more or less important changes are set up in them ; the most considerable of which take place in the large cylindrical bones. In these, we find, more distinctly indeed after birth, that a large cavity is gradually formed in the interior, which at first contains foetal medulla-cells, and afterwards perfectly formed medulla. This medullary cavity is formed, in exact analogy with- the medullary spaces described in the preceding paragraphs, by the solution of the osseous tissue of the shaft; at first, only of that which is formed from the primitive cartilaginous rudiment, but soon, also of that deposi- ted from the periosteum upon the former, its development proceeding in a remarkable manner, as long as the general growth of the bone con- tinues. Whence it comes to pass, that, as at the ends of the diaphyses, so also on its surfaces, whilst new bone is continually deposited exte- riorly, that which is already formed is as continually absorbed in the interior ; and in fact these two processes are so combined, that the bone, during its development is, in a certain measure, several times regenera- ted, and, for instance in the humerus of the adult, does not contain an atom of the osseous tissue which existed at the time of birth, nor does the bone at that period contain any of the tissue of which it was con- stituted in the embryo at three months. These conditions will be rendered most distinctly intelligible, and especially with respect to the periosteal and cartilage layers, by means of a diagram (Fig. 134) which I have for a long time employed in my lectures. If, in this figure, we compare the primordial bone E E with the almost complete bone E 4 E 4 , it is apparent, that in the longitudinal growth of the diaphysis of the latter on both sides, at the expense of the continually growing epiphy- sal cartilage, an elongated cone of osseous substance, 1, 2, I 1 2 1 , and 3, 4, 8 1 , 4 1 , is produced, to which, ultimately, the epiphysal nuclei E 4 E 4 , also originating in the cartilage, are joined, whilst, to increase its thick- ness, the tubular layer P, P 1 , P 2 , P 3 , which are constantly increasing in length and, in the middle, in thickness, are applied to it. In a cylin- drical bone of this kind consequently, the entire portion formed from cartilage, presents a figure of a double cone with rounded bases ; and that formed from the periosteal layers, 1, '2, 3, 4, P 3 , and I 1 , 2 1 , 3 1 , 4 1 , P 3 , the form of an elongated tube thickest in the middle, and resem- bling an elongated vertebra of a Fish, with conically hollowed, terminal surfaces. The articular cartilage C, is the unossified portion of the epiphysal cartilage, and the medullary cavity which is not shown in the figure (it may be supposed to be indicated pretty nearly by the outlines of the fourth bone E 3 E 3 ), is formed by the resorption of the entire THE OSSEOUS SYSTEM. 327 osseous substance derived from the cartilage and periosteum of the younger bones ; in this case the first three, E E, E 1 E 1 , and E 2 E 2 . In the cylindrical bones, without a medullary cavity, and in all other bones containing nothing but spongy substance in the interior, the absoprtion does not proceed to nearly the same extent as it does in the above described cases, that is to say, only to the production of a looser spongy substance in the interior, and, consequently, we find, for instance in the vertebrae, more or less considerable re- mains even of the earlier bone-substance. In this situation also, the absorption al- ways affects not merely the osseous nu- cleus, formed from the cartilage, but like- wise the periosteal layers, the latest of which only remain more in their original form, as the substantia compacta. The Haversian canals do not originate, as is sufficiently apparent from what has been said, like the cancelli of the primary bone-substance, from a solution of a pre- existing tissue, but are nothing more than open cavities, left from the commence- ment, in the periosteal layers. They are relatively, of a considerable size at an early period (vid. also "Valentin. Entw." p. 262), measuring in the foetal humerus at five months 0-016-0-024 of a line in the femur at birth, according to Harting (p. 78), 0*10-0-024 of a line, just as in the most recently formed layers also of a later period. Their contents have been already described. The most important circumstance connected with them remaining to be no- ticed, is the mode in which their lamellar systems originate. These lamellse also are formed without the intervention of cartilage, and are nothing more than deposits from the contents of the canals, which sub- Fig. 134. Diagram of the growth of a cylindrical bone. JB, primary rudiment, the dia- physis ossified and the epiphyses cartilaginous: .4, the same bone in four stages of further advance, E'PPE 1 , E^P'E 2 , E 3 P 2 P 2 E 3 , E 4 F 3 P 3 E 4 ; P P'P 2 P 3 , periosteal layers of these four bones; the space contained within 1, 2, 3, 4, and I 1 , 2 1 , 3 1 , 4 1 , indicates the portion which in the largest bones is formed from cartilage ; E'E', cartilaginous epiphyses of the second bone; E 2 E 2 , epiphyses of the third bone, in one of which is an osseous nucleus ; E 3 E 3 , E 4 E 4 , epiphyses of the fourth and fifth bones, all with larger epiphysal nuclei: G, articular cartilage ; I, K, interstitial cartilage between the ossified epiphyses and diaphyses. 328 SPECIAL HISTOLOGY. stance, as has already been said, in respect of its fibres and cells, entirely corresponds with the ossific blastema beneath the periosteum, and, in a certain degree, is merely an originally unossified remainder of it. These conditions are easily observed in young bones, in which, the periosteal layers, before they have undergone any resolution, are rendered more and more compact by these new, secondary lamellae; but even at a later period a more or less ossified blastema (always without calcareous granules) may very frequently be perceived on the walls of the canals in question. Whilst the vascular canals are thus, on the one side, undergoing contraction by the deposition of these secondary layers, which, just as in the periosteum itself, appear laminated, either be- cause the ossific blastema itself is so constructed, or because the depo- sition of bone takes place with periodical pauses, they afterwards widen, or at least some of them, by absorption, as for instance, the canales nutritii, the great vascular openings in the apophyses, &c. ; and the compact substance, as has been already remarked, is also, in many places partially, and in some even entirely, absorbed. In what way the bone increases in thickness in the situations where tendons and ligaments, 'without the intervention of periosteum, are directly implanted into it has not yet been made out. From the cir- cumstance, that in the adult, in many of these situations, true cartilage- cells occur among the tendinous fibres, and also, that their passage into bone-cells may very clearly be observed, it might perhaps be concluded that a similar process may take place at an earlier period also. In fact, I have seen, even in young individuals, at the points of insertion of many tendons and ligaments (tendo Achillis, lig. calcaneo-cuboideum, aponeurosis plantaris, $c.) into the bone, cartilage-cells, and their meta- morphosis into bone-cells. Very frequently, also, tendons and ligaments are attached to portions of the bone which remain long in the cartilagi- nous condition, epiphyses, tuberositas calcanei, c., and the growth of these parts, of course, is simply to be referred to the cartilage. The formation of bone on the inner aspect of the periosteum is a fact long well known, although it has, hitherto, generally been thought, that in this situation also, it was preceded by a thin cartilaginous layer, until the contrary was shown by Sharpey and myself. Since the discovery by Duhamel ("Me'moires de 1'Academie de Paris," 1742, p. 384, and 1743, p. 138), that the bones of animals fed upon madder are colored red, a great number of experiments have been made with that substance, espe- cially by Flourens, in growing animals ; it being at first believed, that it only colored those parts of the bones which were formed after its administration. This method, however, has lost a good deal of its value since it has been shown by Rutherford (in " Robert! Blake, Hiberni, Dissert, inaugural, med. de dentium forrnatione et structura, in homine THE OSSEOUS SYSTEM. 329 et in variis aniraalibus," Edinb. 1780), Gibson ("Memoirs of the Lite- rary and Philosophical Society of Manchester," 2d series, vol. I. p. 146), Bibra (1. c.), Brulle' and Hugueny (1. c.), that when animals were fed upon madder, the whole of the growing bones, as well as the bones of adult animals, become colored, and especially so wherever they are in more immediate connection with the bloodvessels; for even the medulla is colored (Bibra). For which reason also, the innermost layers of the Haversian canals, the periosteal surfaces, and the vascular, young bone- substance, acquire a deeper color. There are, however, still some points worth investigating in this way, particularly with relation to the more recent statements of Brulle' and HugueVy, who, relying upon the circumstance, that, as they assert, the decoloration of growing, colored bones, is eifected merely by the absorption of the colored portions, believe they have found that the cylindrical bones also deposit osseous substance from within, particularly in the apophyses; whilst on the outer surface, absorption to the same extent takes place ; statements upon which I will not, at present, give any decided opinion, although at the same time I hold it as quite certain, that in many places an absorption does take place, on the exterior of the bone to a greater or less extent. It is only by such an absorption that the enlargement of the foramen mag- num from the sixth year upwards, at which time the portions of bone surrounding it are united, can be explained. And the same may be said with respect to the arches of the vertebrce, and numerous vascular and nerve-openings (foramen ovale and rotundum of the sphenoid bone, fora- mina inter transversaria, canalis caroticus, c. $c.\ Consequently, the law propounded by Serres (Meek. " Archiv," 1822, p. 455), that the openings in bone enlarge by the growth of the individual pieces by which they are bounded, is wholly incorrect, as applied to the openings and canals in the middle of bones ; as had been already, to some extent, de- clared by E. H. Weber and Henle; and even in other cases it holds good only for the earliest periods. The periosteal layers present a certain contrast to the osseous tissue developed from cartilage. The former constitute principally the firm cortex of the primarily cartilaginous bone, and are characterized by th'e occurrence of Haversian canals and their lamellar systems, whilst the latter produces the spongy substance, and contains no vascular canals. It must not, however, be forgotten that even the periosteal layers all have, at first, in a certain degree, a spongy structure, and in all these bones, without exception, contribute, and frequently very essentially, to the formation of the spongy substance; moreover, that in the cellular substance, which originates from the cartilage,. in the apophyscs for in- stance, secondary layers, similar to those of the Haversian canals, and of the spongy substance which is formed out of the periosteal layers, only not so much developed, appear to be formed. The morphological 330 SPECIAL HISTOLOGY. and chemical relations of the matrix of these two forms of osseous tissue have not as yet been determined. On the other hand the bone- laeunge of both kinds of tissue do not present the least difference. 106. Bones not primarily cartilaginous occur, in Man, only in the cranium. They originate outside the primordial cranium, between it and the muscular system, and thus within the structure constituting the vertebral system. They by no means exist as membranous and cartila- ginous capsules on the first appearance of the cranium, their formation not commencing till after that of the primordial cranium, from a secon- dary blastema, whence, in contradistinction to the other primary bones, the formative material of which exists prior to the commencement of ossification, they are termed secondary bones or, also, because in most places they are in contact with portions of the primordial cranium covering or overlaying bones (belegknochen). To this class belong, the upper half of the expanded portion of the occipital bone, the parietal, and frontal bones, the squamous portion and tympanic ring of the tem- poral bone, the nasal, lachrymal, malar, and palate bones, the upper and lower jaw, the vomer, and apparently, the internal lamella of the ptery- goid process of the sphenoid, and the cornua sphenoidalia. The blastema of these bones, which differs from that of the primary bones, in its being successively developed in a membranous matrix, simultaneously with the process of ossification, not existing previously in any considerable quan- tity, presents essentially, exactly the same conditions as that of the periosteal layers, and is also ossified in precisely the same way. The notion that certain cranial bones, in man and the Mammalia, are not developed from cartilage, is by no means new, although the morpho- logy of the question was first established by Rathke, Reichert, Jacobson, and myself; and its histology by Sharpey and myself. But with respect to the latter subject, a controversy still exists as to the true nature of the ossific blastema (as also, of that of the periosteal layers), whether it be a kind of connective tissue, as I believe, or a sort of cartilage, as Reichert and A. Bidder assert, with respect to which more will be found in my "Mikroskop. Anat." pp. 374, 375. 107. The secondary cranial bones, all, in the first instance com- mence in the form of a minute, elongated, or rounded, osseous nucleus, consisting of a portion of fundamental substance or matrix, with a few lacunae, and which is surrounded by a small quantity of soft blastema. How this nucleus originates has not yet been observed, although from the way in which its growth proceeds, it might be assumed with certainty, that shortly previous to its first appearance, a minute lamella of the soft blastema is formed in the situation of the future nucleus, which lamella spreading from a single point, becomes ossified by the addition THE OSSEOUS SYSTEM. 331 of earthy salts and the metamorphosis of its cells. The primary point of ossification having thus appeared, for instance in the parietal bone, its growth advances simultaneously with the horizontal extension of the membraniform blastema, in such a way that a delicate lamina composed of reticulated osseous spicules is shortly produced, from which, slender rays stretch out into the still unossified blastema (Fig. 135). If this formation be examined more closely, it will be observed, that the indi- vidual bone-spicules originate in the membranous blastema, by the ossification of its elements, and, that to a certain extent, the latter is absorbed in the spaces occupied by the spicules, remains of it being left in the interstices ; and moreover, that the formation of the osseous elements proceeds exactly in the same way, that it does in the periosteal layers ; the Fig. 135. Fig. 136. A ..t rays of bone as they extend further into the soft blastema becoming softer and paler, and containing less earthy matter, whilst their cells become more and more like the soft formative cells, till, at last, the spi- cules lose all distinct limitary outline, and are lost in the blastema. At first, the growth of these bones proceeds in a superficial plane only, the rays, as they extend and become connected by transverse branches con- Fig. 135. Parietal bone of a fourteen-weeks' old foetus; magnified 18 diameters. Fig. 136. From the inner surface of the parietal bone of a new-born child ; magnified 300 diameters: a, bone with lacunae, still pale-colored and soft; 6, border of the same; c, ossi- fying blastema with its fibres and cells. jB, three of these cells, magnified 350 diameters. 332 SPECIAL HISTOLOGY. tinuing to add to the size of the original, reticulated lamella, which, however, shortly begins to increase in thickness by the deposition of layers upon both sides of it ; the different portions, also, in proportion to their age becoming more and more compact. The formation of the thickening layers is to be referred to the periosteum, which is found on the surfaces of the secondary bones, very soon after their formation has begun, being developed either from their original blastema, or from the contiguous tissues (perichondrium of the primordial cranium, muscular and tendinous coverings), and proceeds exactly in the same way as in the periosteal layers of the primary bones ; that is to say, on the inner side of the periosteum, a soft blastema is deposited, which gradually ossifies, from the bone outwards, without its ever being cartilaginous (Fig. 136). In this way are now formed, chiefly on the outer, but also on the inner surface of the primary osseous lamella, arid proceeding outwardly from it, successive, new laminae, in consequence of which the rudimentary bone continually increases in thickness. All these new lamellae, like the primary one, are at first perforated by reticular open- ings, and the various sized, roundish or elongated interstices communi- cate with those of the previously and subsequently formed layers, so that the secondary osseous nuclei, like the periosteal layers, are from the first, penetrated by a network of canals, which, as in those layers, in part at least, soon present the appearance of Haversian canals. At first, filled only with a soft blastema, the remains of the plastic material of the various lamellae, these spaces, in consequence of the advance of ossification in their interior, which sometimes takes the form of bridges stretching across them, sometimes of a deposit on their walls, become more and more contracted. Ultimately, some are entirely closed, whilst others are converted into true vascular canals, the vessels being de- veloped from their contents, which are composed during the time of medulla-cells, and communicating with those of the periosteum. When the bone has arrived at this stage, its subsequent changes are readily followed. It continues to increase in breadth and thickness by the con- stant addition of new blastema on its edges and surfaces, until it has attained its typical form and size, and at the same time, by the solution of its compact substance, additional spongy tissue (or even large cavities), is formed in its interior, so that eventually, like bone developed from cartilage and periosteal layers, it presents, externally, compact sub- stance with Haversian canals ; and internally, medullary spaces (cancelli), although with distinct secondary deposits. The secondary cranial bones ossify, in part, earlier than the primary, and mostly with only a single nucleus. The soft blastema out of which they are formed, and which, so long as the bones continue to grow, is to be found on their surfaces and edges, does not, like carti- THE OSSEOUS SYSTEM. lage, grow independently with them, but is developed by degrees, from a plasma successively secreted from the vessels of the periosteum, the two lamellae of which are conjoined at the margin of the ossifying plate. The cells of this plasma, the metamorphosis of which, as in the periosteal layers, cannot be followed in every particular, are elongated, measuring in man, for the most part, 0-006-0-01 of a line, and pre- senting granular contents with oval nuclei of 0*0028 0*00-18 of a line. Such of these cells as are destined for the growth of the bone in thick- 'ness, with the exception of those of the glenoid cavity of the temporal bone, never present the slightest resemblance to cartilage-cells, and, together with their matrix, invariably ossify without the appearance of any calcareous particles ; those on the borders or extremities, on the contrary, may, as it appears, subsequently, take on the nature of true cartilage. The most striking example of this kind occurs in the con- dyle of the inferior maxilla, where, even during foetal life, a thick car- tilaginous layer is deposited, which so long as the growth of the bone continues, precedes its longitudinal growth, exactly like an epiphysal cartilage. I have noticed the same thing in the articular fossa of the temporal bone, where, however, the cartilage is less developed ; at the angle of the inferior maxilla (in the Calf), and at the anterior extremi- ties of each half of the same bone, which are connected by a semi- fibrous, semi-cartilaginous substance, corresponding very nearly with the symphysis. This fact loses much of the singularity which at first sight attaches to it, when we consider that all cartilage is at first soft, and consists of common formative cells. It is, consequently, only ne- cessary that the formative cells of the soft blastema of the secondary bones, should, at a certain period, pass through the same changes as those undergone by the formative cells of embryonic cartilage, in order to effect the production of cartilage in the bones. now in question. Further investigation is required to show, whether cartilage of this kind also occurs as a supplementary addition to other secondary bones, and to what extent, in animals. Still, it may be noticed, that in asserting as I have done, that all ossifications from a soft blastema take place without the deposition of calcareous granules, this statement is only in part correct, because it is quite true, in many cases, that this sort of deposition does occur in them, though never at an early period, and, generally speaking, but rarely. The ossifying margin, moreover, in these cases is never abrupt, as it is in ossifying cartilage. The ultimate changes of the secondary bones have not yet been closely investigated. Their mode of connection with each other, and also with primary bones by suture and coalescence, is tolerably well known. In the vault of the cranium, for instance, as the primary ossific points first appear in the situation of the tuberosities of the parietal and frontal bones, the bones are at first placed widely asunder, 334 SPECIAL HISTOLOGY. and are connected merely by a fibrous membrane, the continuation of the periosteal lamella of each, and which is united on the internal aspect with the remains of the membranous cranium of the embryo, and with the dura mater. The bones then continue to grow towards each other, and at last constantly advancing in the above-described continua- tion of the periosteum, come very nearly into contact at the frontal and sagittal sutures ; there remains, however, for a long time one large vacuity, in particular, between them, the anterior fontanelle, but which closes in the second year after birth ; whilst at the same time, the bones, which, up to this period, adjoined each other with a straight line of juncture, send out interdigitating tooth-like processes, till ultimately, when their blastema is wholly consumed, they continue united only by the remains of the periosteum (the sutural cartilage, as it is termed, or better, the sutural ligament), but which also is capable of becoming ossified sooner or later, and, indeed, invariably first on the inner aspect of the suture, where the tooth-like processes are very little developed. The changes of form in the entire bones during their development are very remarkable, and have hardly been attended to. If a parietal bone, for instance, of a foetus or new-born child, be compared with that of an adult, it will be found that the former is much more curved, and in no way at all represents a piece cut out of the middle of the latter. The adult parietal bone consequently must have undergone a very important alteration in the curvature of its surfaces, and this, as mechanical conditions are out of the question, can only have been effected by an unequal deposition of bone internally and externally, in the middle and at the borders ; or by deposition on the one side and absorption on the other. That unequal deposition does actually occur, is seen, for example, in the jug a cerebralia and impressiones digitatce, the sulci meningei, &c. ; but it appears to me, that the whole matter cannot be understood, unless we assume that local absorptions also take place in certain situations. How otherwise can be explained the in- crease in breadth of the superior orbital ridge, the increase of distance between the frontal eminences, even after the ossific union of the two portions of the frontal bone, the change of form of the lower jaw (the greater distance between the coronoid processes and the mental spine, the alteration in its curvature, the partial removal and renewal of the alveolce), &c.? We have already seen, that in the other bones, also, something of the kind must be presumed to take place, and, consequently, cannot hesitate to admit it in the present case, although the particulars of the process be unknown. That this process occurs in the interior of the secondary bones has been already mentioned. The formation of the diploe, which becomes more evident in the tenth year, is to be referred to it, as is also that of the frontal sinuses, and antrum Highmorianum, which however does not take place till a later period. THE OSSEOUS SYSTEM. 335 I would further remark, that the secondary bones, so long as they are in a growing state, are much more vascular than afterwards, even ex- ceeding, in this respect, the periosteal layers of the other bones; on which account their medulla, containing the multi-nuclear, enigmatical bodies, already referred to, is of a redder color. The vessels enter these bones at innumerable points on the surface, and, in the different bones, run in vertical or horizontal canals. The latter is the case in the flatter bones, in which the vascular channels run principally in the longitudinal direction of the osseous rays proceeding from the primary point of ossi- fication; and the former, in consequence of which the surface of the bone frequently presents an extremely delicate, millepore-like aspect, occurs in the thicker portions. A great many of these canals after- wards become obliterated, or, at all events, very much contracted, whence the surface of the bone is rendered smoother. In conclusion to these remarks on the development of the bones, I will add a few words regarding their conditions at different periods. Valentin noticed the cartilaginous rudiments of the ribs in a human embryo 6 lines long. That of the cranium is distinctly recognizable in the sixth or seventh week, as well as those of the vertebral zone and that of the extremities; those of the extremities proper do not appear till later (in the eighth or ninth week). Ossification commences as early as the second month, first in the clavicles and lower jaw (fifth to seventh week), then in the vertebrae, the hum er us, femur, ribs, and the cartilaginous por- tions of the lamina of the occipital bone. At the end of the second, and beginning of the third month, ossification is apparent in the frontal bone, scapulce, bones of the fore-arm and leg, and upper jaw ; in the third month, in the rest of the cranial bones, with few exceptions, the metacarpal and metatarsal bones, and phalanges ; in the fourth month, in the ilium and ossicula auditiis ; in the fourth or fifth month in the ethmoid, the turbi- nated bones, the sternum, pubis, and ischium; in the sixth to the seventh month, in the os calcis, and astragalus; in the eighth month, in the os hyoides. At birth, the epipliyses of all the cylindrical bones are still unossified, with the occasional exception of those at the lower extremity of the femur and upper end of the tibia ; and besides these all the carpal and the five smaller tarsal bones, the patella, sesamoid bones, and the last segment of the coccyx. After birth, up to the fourth year, the nuclei of these bones also make their appearance; but, in the os pisiforme, not till the twelfth year. The union of most of the epiphyses and pro- cesses, with the diapliyses takes place, in part at the time of puberty, in part towards the end of the period of growth.* * [Dr. Sharpey's discovery that certain bones of the skull are developed in the same man- ner as those layers which are formed under the periosteum in the long bones, has been a sort of apple of discord among histologists, and has produced a great variety of controversies not only among them, but among comparative anatomists ; controversies whose heat has 336 SPECIAL HISTOLOGY. 108. The vital phenomena exhibited in the mature bones are not, during the vigorous period of life, accompanied with any notable or active been somewhat increased, as we think, by a want of perception among the combatants, of the fact, that several totally distinct questions are involved. These questions seem to us to be the following, and we shall endeavor to consider them in detail. 1. Whether the tissue from which "secondary" bone proceeds is cartilage, or not? 2. Whether it is morphologically homologous with cartilage, or not? 3. Whether ossification takes place in it in the same manner as in cartilage, or not? And as the result of the answering these : 4. Whether the differences between the two tissues are sufficient to constitute the basis of a classification of the bones or not? 1. To answer this by saying with Meyer that every tissue which ossifies is cartilage, is simply to beg the whole question. Cartilage we hold to be distinguished from 'indifferent tissue, by the fact of its matrix containing chondrin. The substance which in the foetus con- tains no chondrin, but will subsequently become a cartilage though in common parlance it is very convenient to call it " foetal cartilage" is no more cartilage than the cartilaginous basis of a future bone, which might just as properly be called fostal bone, is osseous tissue. There can be no question then, we think, that Ko'lliker is in the right, as against Reichert, Meyer, and others, when he says that secondary bone is not developed from cartilage, and that, in this respect, it may be distinguished from primary bone. 2. Though this matrix of secondary bone, however, is assuredly not cartilage, it is another matter whether it is, or is not, morphologically homologous with cartilage. To arrive at any just conclusion on this head, it is necessary to understand the precise structure of this tissue, which Messrs. Tomes and De Morgan have been the first to point out : " If attention be directed to the part furthest removed from the bone, it will be seen that the membrane-like mass is composed of oval cells with slight prolongations from the extremities, which are frequently arranged in the form of bands of fibrous tissue. Dr. Sharpey has observed that the membrane into which the bone extends is like fibrous tissue in an early stage of develop- ment; and this observation is strictly true when confined to the part indicated, but the analogy ceases [?]as we extend our examination towards the bone. Here, in the place of cells with elongated processes, or cells arranged in fibre-like lines, we find cells aggre- gated into a mass, and so closely packed as to leave little room for intermediate tissue. The cells appear to have increased in size at the cost of the processes which existed at an early stage of development and formed a bond of union between them. Everywhere about growing bone, a careful examination will reveal cells attached to its surface, while the surface of the bone itself will present a series of similar bodies ossified. To those we propose to give the name of osteal cells, as distinguished from lacunal and other cells. In microscopic characters, the osteal cells closely resemble the granular cells of temporary cartilage ; so closely, indeed, that the latter, when detached from the cartilage, could not well be distinguished from them. They are, for the most part, spherical or oval in form, and lie on the surface of the growing bone in a crowded mass, held together by an intervening and apparently structureless matrix. Here and there we find a cell which has accumulated about itself an outer invest- ment of transparent tissue, and has, in fact, become developed into a lacunal cell destined to become a lacuna" (1. c. p. 23). The tissue, then, from which secondary bone immediately proceeds, is composed of a homogeneous matrix, in which corpuscles, identical with the cartilage-corpuscles, are imbedded: it is therefore identical, as Dr. Sharpey described it, with young connective tissue; and as we have seen above (note, 101), and as the authors state, with foetal carti- lage. Though not cartilage, therefore, it is homologous with it (as is, indeed, admitted by Professor Koiiiker) ; a fact which is still more strongly evidenced by the transition of carti- lage into a similar tissue, at its edges (Tomes andDe Morgan, 1. c. p. 24), which may readily enough be observed, and which has been particularly shown by Reichert to occur between the primary and secondary bones of the skull (" Zur Streitfrage fiber die Gebilde der Binde- substanz, ober die Spiralfaser und iiber den Primordial-Schadel," Muller's " Archiv," 1S53). Now it seems to us that a tissue which is identical with the embryonic form of cartilage, THE OSSEOUS SYSTEM. 337 morphological changes. It is true that, during this period, some of the processes above considered go on such as the enlargement of the sinuses in the cranial bones, of the points of insertion of muscles which passes into adult cartilage, and differs from cartilage only in the absence of chondrin (in/which respect ossified cartilage agrees with it), is in a morphological point of view homologous with cartilage. 3. With respect to the third question, Sharpey and Ko'lliker are of opinion that the deposit of calcareous matter and the formation of lacunas take place in the same manner as in cartilage, i. e. that the calcareous salts are deposited evenly through the matrix, leaving spaces round the corpuscles or " nuclei," from which the canaliculi are subsequently deve- loped by resorption. Messrs. Tomes and De Morgan, on the other hand (see passage cited above), maintain that secondary bone differs from primary, in so far as certain of the corpus- cles "osteal cells/' "arrange themselves side by side, and together with the transparent blastema in which they lie, become impregnated with ossific matter, and permanently fused with the bone-tissue with which they lie in contact. By the linear arrangement of these osteal cells, lamination is produced. In the case of new laminated bone, the cells are simply ossified without arrangement. Lying amongst the osteal cells will be seen some which have accumulated around them a quantity of tissue which forms a thick investment to them ; they then become granular, and take on in every respect the characters of a lacunal cell. These are found deposited at intervals along the line of ossification, and becoming blended with the general mass, the granular cell remaining as a lacuna, and sending out processes in all direc- tions" (" Abstract in Proceedings of Royal Society"). We must confess that all we have seen leads us to believe that the former of these accounts is correct. We have never been able to find evidence of any of the corpuscles becoming converted into "osteal cells," and we believe, for the following reasons, that this process does not take place. In examining the growing Haversian canals in Man, and par- ticularly in the Calf, we have very frequently found the innermost layer transparent, glassy, and structureless exhibiting nothing but the corpuscles (e?) lying in lacuna? without canali- culi. This layer would be as much as ^^thof an inch thick; in the layer (r) immediately external to it, however, the " osteal cells" were exceedingly well marked. The inner layer looked like smooth ice, and the outer like ice which had cracked into innumerable tolerably even portions but these cracks were by no means produced by the canaliculi, which, as yet, were hardly at all developed. Now it seems clear that if the " osteal cells" were pro- duced by the calcification of certain of the corpuscles, they ought to be more obvious in the young, inner layer, than in the outer ; whereas just the reverse occurs. The fact stated by Messrs. Tomes and De Morgan, that lamination is less obvious in young than in old bone, tends to exactly the same conclusion. Again, if the granular substance between the lacunae were composed of calcified corpuscles " osteal cells," the action of acids ought to bring them out as strongly as it does those of the lacuna? ; whereas neither in young bone nor in old can anything of the kind be seen. With respect to the lacunae, again, we have the same remarks to make as when speaking of cartilage. We have never been able to find any trace of the development of the corpus- cles (granular cells) into lacunae. As to the tissue which accumulates round them and forms an investment, we have frequently observed the appearance described ; but this investment was nothing but the clear, often homogeneous, calcareous matter, gradually encroaching on the matrix and enclosing the corpuscles. We consider, then, that the process of ossification in primary and secondary bone is iden- tical; the deposition of the calcareous matter in granules or as a homogeneous infiltration, being of no constancy or importance. In each case the deposit takes place in the matrix, and leaves spaces (lacunas) round the corpuscles (nuclei, granular cells). Subsequently, the canaliculi are developed in the matrix by a process of resorption ; while their walls and those of the lacuna? may or may not become chemically differentiated from it. At the same time, the matrix may or may not break up into lamina? and " osteal cells" or granules. Its 22 338 SPECIAL HISTOLOGY. and ligaments, and of the vascular channels; but a more exten- sive new formation of bone, "whether periosteal or in the Haversian systems, together with a simultaneous and more considerable absorption, never occurs in them. It was formerly believed that the coloration of the bones of adult animals by madder, proved that deposition of bone substance continued to take place even in them, it being assumed that newly forming osseous tissue only became colored ; but since it has been shown, that bones already formed were likewise colored by the same agent, and that colored bones in the adult did not lose their color (Brulle and Hugueny), this view becomes untenable. Whether in the perfect bone a change, if not of the elementary parts, but still of the atoms, takes place, the same external figure remaining, is another question, for the solution of which microscopy affords no facts. This much is certain, that the organization of bone is such, that notwithstand- ing the rigidity of their structure, they are in the most general and most intimate relation with the nutritive plasma of the blood. In every situ- ation where the osseous tissue is in connection with vessels, as on the external surface, in the walls of the medullary cavities and cancelli, and those of the Haversian canals, millions of closely crowded minute open- ings exist. These convey the blood-plasma, by means of the canaliculi, into the lacunae lying nearest to the surfaces mentioned, from which it is then conducted by wider canaliculi to the more distant lacunae, as far as the outermost layers of the Haversian lamellae, and those laminae of the great lamellar system which are most remote from the vessels. When the enormous number of the canaliculi and their multifarious anastomoses are considered, it must be allowed that no tissue in the human body is better provided for in respect of the distribution of the blood-plasma, whilst in scarcely any other is the direct conveyance of the fluid to the most minute particles more immediately necessary than in it. There can be no doubt that the fluids, which this " plasmatic vascular system" (Lessing) of the bones, obtains from the bloodvessels, probably some- what modified by the influence of the nucleus which, as I have before endeavored to show, is still retained in every lacunae, are most indis- pensably requisite for the maintenance of the bone ; for we see, that when the supply of blood to a bone is impeded by the destruction of the variability in this respect is neither more nor less remarkable than the greater or less fibril- lation of the corresponding element of connective tissue, or than the inconstancy of the dis- position of the cleavage lines of the same element in striped muscle. As little is any line of demarcation t to be drawn between primary and secondary bone as regards the tissues from which they proceed. Indifferent tissue, in which calcareous matter is deposited at once, is the basis of secondary bone ; an identical tissue in which to serve a temporary purpose chondrin is deposited, being subsequently withdrawn and replaced by calcareous salts is the basis of primary bone. And this paragraph may serve as an answer to the fourth question. If it be correct, we cannot imagine that any distinction of the bones into primary and secondary, upon the ground of their develop- ment or non-development from cartilage, can be other than arbitrary. TRS/] THE OSSEOUS SYSTEM. 339 periosteum or of the medulla, by ligature of the vessels of the limb, or by obliteration of the periosteal vessels by pressure from without (aneurism, tumors), necrosis of the parts involved certainly ensues, and can scarcely in any case be altogether obviated by the collateral circula- tion which actually exists also in the bones (vid. supra]. On the other hand we are scarcely, at present, in a condition to say, how the circula- tion of the plasma in the bones is carried on, though its movement to and from vessels (perhaps from the arterial, through several lamellar systems to the venous) must probably be assumed ; or what special changes in the course of the nutrition of bone take place ; with the latter in par- ticular we are unacquainted, because the chemical investigation of these changes, and especially of the organic products of decomposition, is still altogether imperfect. That the osseous tissue is in a state of constant, and indeed very energetic molecular change, is evidenced not only in its various morbid conditions, but also by the alterations it undergoes in old age. These alterations consist more especially in the disappearance of entire por- tions of the bones, either externally or internally ; of the former, an instance is afforded, in the entire removal of the alveolar processes of the jaws, and the latter is seen in the greater porosity and fragility of every kind of bone, such as the cylindrical bones and those of the cranium, in the enlargement of the vascular openings (vertebrae, apo- pliyses), and in the greater roughness of the surfaces of the bones. This senile atrophy of the bones may also be attended consecutively with an internal addition of bone-substance, a sclerosis, as it is termed, as in the flat bones of the cranium, in consequence of which, in direct contrast to the phenomena elsewhere presented by senile bone, the diploe disappears, its cancelli becoming filled up by new osseous tissue, whilst the venous spaces and foramina emissaria are obliterated and the entire bone rendered heavier. With this abundant vascular supply, and certainly not sluggish mole- cular change, it cannot be surprising that the bones should be so richly furnished with nerves, the principal function of which appears to me to consist in the regulation of the conditions of the vascular system, by their conveying to the central organ (spinal cord) through the sensitive fibres intelligence of the state of the vessels, of the quantity of nutri- tive fluid in the bone, and probably also of the modus of the molecular change going on in themselves, and by means of the motor elements their bringing a reflex influence from it, to the arteries and veins which are manifestly furnished with contractile fibres. These unconscious and involuntary alternations of influence of sensible and motor filaments, are, as it appears to me, the most important phenomena of the innerva- tion in bones, as well as in all other organs, the nerves of which are not constantly in relation with the external world, and make it intelli- gible, why it is, that no organ, containing nerves and vessels at all, 340 SPECIAL HISTOLOGY. possesses nerves of only one kind. It is not, however, by this, intended to imply that the nerves of bones do not convey conscious perceptions ; it is possible that, through them, we obtain a certain degree of know- ledge of the processes going on in the bones, of the degree of fulness of the vascular system, the mechanical influences to which they are exposed from without in the movements caused by the action of the muscles, the weight of the body, or of external objects, in lifting weights, mastication, &c. ; but in any case this knowledge would be very indeterminate, and the sensation excited not definitely localized, being confused in the general feelings of fatigue, effort, or relaxation. On the other hand, it is quite certain that the bones, in man, in many diseases, and in consequence of mechanical injury, afford pain, which latter fact has also been frequently noticed in animals, at all events, upon irritation of the larger nervous trunks of the diaphyses. In man the apophyseS) in particular, and the vertebral and cranial bones, seem readily to become painful, which is explained by the considerable number of nerves immediately in the spongy substance. The compact substance, on the other hand, might probably be regarded as scarcely obnoxious to pain ; as, for instance, in resections, but not so perhaps the periosteum, which less from its own nerves than as the vehicle of those of the bones before they enter their destination, must naturally be affected in the same way that they are. Whether the nerves of the bones through which, perhaps, the conscious perceptions, but in any case the painful impressions are conveyed, be identical with those through which the reflex actions, above referred to, are carried on, is not determined ; but, looking at the origin of most of the bone-nerves from the cerebro-spinal nerves, such an opinion might perhaps be maintained, it being premised that the connections of the nerves with the brain are to be regarded as less intimate than in the case, for instance, of the cutaneous nerves. I would, in addition, call attention to the remarkable occurrence of nerves in the cartilage of the septum narium in the Calf, although I am unable to say anything more with respect to their nature than with regard to that of the nerves of bone. On the subject of the numerous pathological changes which occur in the bones, only some brief remarks can here be made. Fractures readily unite, under but moderately favorable circumstances, by true bone-sub- stance, which, in the cylindrical bones of animals is preceded by the formation of a true cartilage, a fact of which I and others are satisfied ; whilst, according to Paget, this rarely appears to be the case in man. In the spongy bones, in fractures within the articular capsules, and under unfavorable circumstances, the fractured ends frequently unite merely by a fibrous callus, a sort of articulation being formed between them. After loss of substance the osseous tissue is readily regene- rated ; and it is the periosteum especially, which, in this case, as in THE OSSEOUS SYSTEM. 341 the growth of a bone in thickness, plays the principal part in the resto- ration ; of course by means of the exudation poured out from its vessels. In animals, entire bones of the extremities, and ribs are regenerated, pretty nearly in their original figure, not only when the periosteum has been saved, of which many examples are exhibited in Heine's collec- tion in Wurzburg, but even after entire excision with the periosteum, a rudiment of the bone is reproduced (Heine). In man also, a good many instances have been afforded of the reproduction of entire bones, such as the lower jaw, the ribs, the scapula (Chopart) ; and the cases of isolated, in some instances large, portions of bone being so regene- rated are very numerous. It is especially the diaphyses, which are readily replaced, when they have been lost in one way or another, less frequently the spongy bones and spongy parts of bones, and those of the cranium ; in the latter, however, openings made by the trephine are in many cases filled up, instead of fibrous membrane, with isolated patches of bone, or even with an entire piece of bone ; in fact, trephined portions of bone have united exactly in the same way as has been ob- served to take place with portions of bone half cut off (Pauli). Hyper- trophy of bone assumes the most various forms, all of which may be reduced under two principal types : 1, deposits on the surface, or ex- ternal Iiyperostoses, which are formed chiefly from the periosteum ; and 2, internal or scleroses, which consist in the filling up of the medullary cavities and Haversian canals with new bone, and these two forms may occur either separately or combined. The former takes place in inflam- mations of the periosteum, either idiopathic or in connection with cancer, arthritis, syphilis, &c., the latter not only consecutively in old age, but also in rachitis, osteomalacia, and syphilis. With respect to the micro- scopic conditions of these growths, Virchow deserves the credit of hav- ing distinctly indicated ("Archiv, f. Pathol. Anat. I.," p. 135), that the bony growths or osteophytes on the cranium are formed by a direct ossification of connective tissue without any preliminary development of cartilage, which is also undoubtedly the case in the filling up of the losses of substance in the cranium, in regeneration proceeding from the periosteum, and in most cases of sclerosis. The newly formed os- seous substance is sometimes like the normal (many exostoses), some- times more dense, with small vascular spaces and large irregular lacunae. Atrophy of the bones is shown in their disappearance in totality in consequence of chronic diseases, paralysis, anchylosis ; or in rarefaction of the osseous tissue analogous to senile atrophy, in syphilis, lepra, mercurial cachexy, paralysis, &c. Death of bone (necrosis) is observed in cases where the periosteum has been destroyed ; in inflammations of that membrane and of the bone, &c., for the most part attended with an excessive growth of the remaining sound parts.* Peculiar morbid conditions exist in osteomalacia and rachitis, but in neither of these * [In necrosed bone, the bone-corpuscles are generally but little changed; the inter-cor- puscular structure is granular and of a dark color. DaC.] 342 SPECIAL HISTOLOGY. diseases have microscopical researches afforded anything worth men- tion here, except what has been made known by H. Meyer and myself (11. cc.) with respect to ossification in rachitis. In this case I have found : 1, that in the disproportionately large epiphysal cartilages, the layer of the ossifying cartilage-cells (those disposed in rows), mea- sured, instead of J, 2 to 5 lines ; 2, that the ossifying border is toothed, owing to the circumstance that the cartilage and bone interlace in various ways ; 3, and lastly, that in decidedly rachitic bones, the de- position of calcareous granular particles is wanting, and the cartilage- cells almost invariably, shortly before the matrix, and also without any appearance of calcareous granules, are metamorphosed into bone- cells, on which account the formation of the latter can, in no case, be so well studied as in these bones (vid. supra}. Accidental cartilage- and bone-formations are very frequent. The former tissue is met with, notwithstanding that it is incapable of regeneration, and that wounds of it heal only with a fibrous tissue, more rarely with bone (ribs), in very many organs (bones, mammary glands, parotid, testicles, lungs, and skin) forming what is termed enchondroma ; moreover, as a new covering on the osseous growths, at the border of the worn articular ends of bones (Ecker). The latter is seen in ossifications of the per- manent cartilages (ribs, larynx, epiglottis, very rarely) of tendons (exercir-knochen, for example), in the dura mater and arachnoid (Mies- cher, Rokitansky), in the eye (Valentin), in the ovary, in fibrous membranes (membrana obturatoria), in enchondroma, in fibrous and carcinornatous growths, and in the lungs (Mohr's cysts containing hair). Even in these cases the osseous tissue does not essentially differ from the normal, and it is formed, sometimes from a cartilaginous, sometimes, and in fact mostly, from a soft blastema (Yirchow, 1. c. p. 137). In investigations relating to the structure of bone, good sections are, above all things, requisite. With a fine saw, thin slices are made, which are ground with water upon a smooth stone with the finger, or with a second smaller stone, for some minutes (5-10), until they are rendered uniformly transparent. The sections are then cleaned, and (the fat, if they contain any, being removed by ether) may be employed, being wetted with water, for the study of the Haversian canals and disposition of the lacunae ; and with turpentine, for that of the various lamellar systems. The lacunae and their prolongations, which, in sections, are dark and very distinct, owing to their being filled with air, are com- pletely filled by thin turpentine, so that the latter in great part, and also the former, are very frequently rendered invisible ; the same thing happens in water and thicker turpentine, though less rapidly, whence, before these agents have produced their effect throughout, many of the lacunae and canaliculi are beautifully shown. If it be desired to pre- serve the lacunae and canaliculi permanently visible, it is best to polish a thin section, by rubbing it between two glass plates. It may then be THE OSSEOUS SYSTEM. 343 examined without the addition of fluid, and presents as perfect figures as those represented in Figs. 115-117. The grinding of the bone with oil is not to be recommended, because the lacunae, then become filled with the oil, and even after thorough treatment with ether can seldom be rendered distinct. Next to sections of bone, the investigation of the bone-cartilage is the most worth while. This tissue is prepared by the treating of bone in the cold, with diluted hydrochloric acid (1 part acid, 10-20 water), until the fluid, which is to be frequently changed, no longer affords any precipitate with ammonia ; for which purpose, in small fragments of bone, some hours, in entire bones several days, are required. From the cartilage thus obtained, sections are now to be made with a sharp knife in all directions, suitable chiefly for the study of the Haversian canals and lamellae, which may even be raised from the surface. The lacunae, also, are still visible ; their prolongations or canaliculi appear as fine streaks, and their nuclei are seen without fur- ther trouble, especially also after treatment with potassa, or in cartilage which has been half dissolved by boiling in water. After long macera- tion in hydrochloric acid, the lacunae even become isolated, as stellate bodies with delicate walls, or, in the cementum of the horse's tooth, as structures corresponding to the former cartilage-cells. After long softening of bone-cartilage in water, the lamellar systems of the Haver- sian canals become more or less completely separated, presenting the appearance of short, coarse fibres among the larger lamellae (Gagliardi's claviculi). If bone be exposed in a platinum capsule to a strong white heat, the organic parts burn away, the bone becoming at first black, and ultimately perfectly white ; and, if due care be taken, the earthy constituents are left, completely retaining the original figure of the bone. Preparations of this kind are proper for the study of the lami- nated structure of the compact substance and of the lamellar systems of the Haversian canals, which, in this case also, sometimes appear isolated, as in macerated bone. For the microscopic examination of the inorganic constituents of bone, sections are subjected to heat on platinum foil, but they must be very thin, as they afterwards become more opaque, and, on account of their fragility, except in minute frag- ments, do not admit of being ground thinner (Bruns) ; or sections may be boiled in caustic potassa. In either case, the lacunae are seen dis- tinct, and empty, with the beginnings of the canaliculi, in a finely granular matrix. The natural condition of the lacunae is readily seen in perfectly recent bone, in thin sections or laminae ; as, for instance, in many parts of the bones of the face. In recent bone, also, the vessels may be studied, naturally injected, and with the microscope, being thus, far fitter for the purpose than when injections, which often fail, have been practised, and for the closer examination of which, more- over, the bones must afterwards be macerated in hydrochloric acid, and preserved in oil of turpentine. The nerves of the bones may be seen 344 SPECIAL HISTOLOGY. by the naked eye, on the nutritious arteries of the larger cylindrical bones, and readily, by the microscope, on the smaller vessels ; those of the periosteum must be studied after the membrane has been rendered transparent by caustic soda or acetic acid. The costal and articular cartilages are the most suitable for the study of cartilage, the membranes of the cartilage-cells being evident, sometimes without any addition, sometimes after that of acetic acid or soda, which render the matrix transparent. The development of bone may be investigated in a cylin- drical bone, and in the parietal bone ; the formation of the lacunae, in specie, in rachitic bones, and in the osseous surfaces of the symphyses and synclwndroses. * Literature. Besides the works cited in 22 and 25, are to be noticed, F. Bidder, " Zur Histogenese der Knochen" (" On the Histo- genesis of Bone"), in Muller's "Arch." 1849, p. 292; E. v. Bibra, " Chemische Untersuchungen Ub. die Knochen und Zahne des Menschen und der Wirbelthiere" ("Chemical Researches on the Bones and Teeth of Man and the Vertebrata") ; Schweinfurt, 1844; Votsch, "Die Hei- lung der Knochenbriiche per primam intentionem" (" Union of Frac- tures, &c.") ; Heidelberg, 1847; Kolliker, " Ueber Verknocherung bei Rachitis, u. Ub. den Bau der Synovialhaute" (" On Ossification in Rachitis, and on the Structure of the Synovia! Membranes"); "Mitth. der Zurich, nat. Gesellsch.," 1847, p. 93; Rokitansky, "Beitrage zur Kenntniss des Verknocherungsprocesses" (" Contributions to a knowledge of the process of Ossification"), in the " Zeitschrift der Wiener Aerzte," 1848, p. 1 ; A. Krukenberg, " Zur Lehre vom Rohrensysteme der Zahne und Knochen" (" On the Tubular Sys- tem of the Teeth and Bones"), in Muller's " Archiv.," 1849, p. 403; H. Meyer, "Der Knorpel u. seine Verknocherung" ("Cartilage and its Ossification"), in Mull. "Archiv.," 1849, p. 292; Virchow, in "Ver- handl. der Wurzb. phys. med. Ges.," vol. i. No. 13; Robin, " Observa- tions sur le developpement de la substance et du tissu des os," in " Me'm. de la Societd de Biologie," 1850, p. 179; Brulle and Hugwe'ny, "Ex- pediences sur la developpement des os dans les mammiferes et les oiseaux, Ann. d. Sc. Nat.," 1845, Nov. p. 283 ; Flourens, in "Ann. d. Sc. Nat.," 2 serie XIII. 103, ibid. XV. p. 202, ibid. 1845 ; Aout, p. 105, and D^c. p. 358 ; " Compt. rend.," T. XIX. p. 621 ; all his ob- servations collected in " Th^orie exp^rimentale de la formation des os," Paris, 1847-8, avec 7 pi. ; Beck, " Abb. Ub. ein. in Knochen verlau- fende Nerven," Freiburg, 1846; Kolliker, "Ueber die Nerven der Knocken" ("On the Nerves of Bone"), in Wurzb. "Verhandl.," I.; Luschka, "Die Nerven in der harten Hirnhaut" ("The Nerves in the Dura mater"), Tubingen, 1850: and " Die Nerven des Wirbelcanales und der Wirbel" ("Nerves of the vertebral Canal and of the Verte- brae"), Tub. 1850. THE NERVOUS SYSTEM. 345 OF THE NERVOUS SYSTEM. 109. The nervous system, regarded in the more general anatomical sense, constitutes a connected whole, consisting of two principal masses the spinal cord and brain, and of numerous cords nerves extending from them to almost all the organs of the body. The two former or the central nervous system, the central organs, are to be regarded not merely from an anatomical point of view, as affording origin to the nerves, but, also, in a physiological sense, as exciters of the movements, and seat of the sensations, as well as of the mental or psychical actions, and consequently as belonging to a higher or governing order of parts, whilst to the latter must be ascribed more of a ministerial office the communication of the contractions and sensations. This mode of regard- ing the two divisions of the nervous system, however, is only partially correct, because, in the first place, in the central organs, as in the nerves, very many subordinate parts exist ; and, secondly, because in the peripheral nervous system, the so-termed ganglia, physiologically and anatomically, represent central organs. The older division also of the nervous system into animal and vegetative, after the observations of recent times, can no longer be maintained ; and the latter, the sym- pathetic or ganglionic nervous system, can only be regarded as a por- tion of the peripheral system, though undoubtedly peculiarly consti- tuted. ELEMENTS OF THE NERVOUS SYSTEM. 110. The nerve-tubes or fibres (Figs. 137-139), also termed, primi- tive tubes, or primitive fibres of the nerves, are soft, fine, cylindrical filaments having a diameter of 0-0005-0-01 of a line ; they constitute the principal part of the nerves and of the white substance of the central organs, although they are not wanting in the greater part of the gray substance of the latter and in the ganglia. When examined in the re- cent state and by transmitted light (Fig. 137) they appear as clear as water, transparent, and with simple dark contours ; by reflected light glistening, opaline, like fat, in larger quantities together, white, and for the most part their appearance does not indicate that they are composed of different constituent parts. But it is readily seen upon the applica- tion of various methods, that they consist of three, entirely distinct, component structures, viz. : of a delicate coat, and a viscid fluid, in the centre of which is a soft but elastic fibre. The coat, or sheath of the nerve-fibres (limitary membrane, Valentin) (Fig. 139, 1, 2, 3, 4, a) is an excessively delicate, flexible, but elastic, perfectly structureless, and transparent membrane, which, in quite unaltered nerve-fibres, except in certain situations, is altogether invisible. But on the application of 346 SPECIAL HISTOLOGY. suitable reagents, at least in the thicker fibres of the nerves and of the central organs, it comes readily into view, corresponding in its chemical characters, in all essential particulars, with the sarcolemma of the mus- cular fibres. In the finest fibres of the peripheral, as well as of the central nervous system, the existence of this membrane has not yet been Fig. 138. demonstrated, and it must consequently for the present be left undecided whether these fibres possess sheaths or not. Within the structureless sheath, lies the nerve-medulla, or pulp, ("medullary sheath," Rosenthal and Purkinje, "white substance," Schwann), (Fig. 137, 3, 6, Fig. 139, 3, 4, b) in the form of a cylin- drical tube, closely and exactly surrounding the central fibre. In the recent nerve-fibre this substance is perfectly homogeneous, fluid, but viscid like a thick oil, and, according to the light by which it may be FiG. 137. Nerve-fibres, magnified 350 diameters. 1, from the Dog and Rabbit, in their natural condition; a, fine; 6, of medium thickness; c, coarse fibre from the peripheral nerves : 2, from the Frog, with the addition of serum ; a, drop of the contents expressed ; 6, axis-cylinder within the drop, continued into the tube : 3, from the spinal cord of Man, re- cent, with serum added; a, sheath; 6, medullary sheath with double contour; c, axis-cylin- der : 4, double-contoured fibre from the fourth ventricle in Man ; the axis-cylinder, a, pro- jecting and visible within the fibre : 5, two isolated axis-cylinders from the cord, one undu- lated, the other of unequal thickness, with some medullary substance attached to it. FJG. 138. Nerve-tubes of Man, magnified 300 diameters: four fine, two of which are varicose ; one of medium size with simple contours ; and four thick, two of which have double contours, and two, grumous contents. THE NERVOUS SYSTEM. 347 viewed, transparent and clear, or whitish and pearly, and it is obviously to it that the peculiar glistening appearance of the nerves is due. The nerve pulp is rapidly and invariably altered by the application of cold water, of most acids, and of many other reagents, the change consist- ing principally in a coagulation of it, which takes place gradually from without to within, sometimes involving the entire thickness, sometimes only its outermost layer. In the latter case, are produced the well- known nerve-fibres with double contour lines (Fig. 137, 2, 3, 4), or in which the medullary sheath is, externally, coagulated to a greater or less extent, remaining fluid internally ; in the former case, with the contents apparently wholly grumous and opaque (Fig. 138). The coagulated nerve- medulla, in fact, seldom appears homogeneous, but most generally gru- mous, granular, and as if composed of separate, irregular, larger and smaller masses, and, upon the application of acetic acid, as if formed of minute, separate, or reticularly united rods. The nerve-pulp is also altered very readily by pressure. It sometimes escapes from the ends of the tubes, or from hernial protrusions or ruptures of the sheath, form- ing larger or smaller drops of every imaginable shape, regularly spherical, clavate, fusiform, cylindrical, filamentary, or of the most bizarre figures, which likewise coagulate either on the surface merely, or throughout, and thence, like the nerves, appear with a double contour, or half or wholly grumous. But, within the fibres also, its structural conditions alter, for, instead of being continued through them as before, as a cylinder of uniform size, it accumulates in places into larger masses. In this way are produced the frequently described, varicose nerve-fibres (Fig. 138), in which the medullary sheath presents sometimes, minute moniliform enlargements, sometimes, various sized, irregularly distri- buted nodosities, or even, in places, complete interruptions. All these forms, in which the sheath frequently participates, but in which the cen- tral fibre takes no part, arise artificially, and are developed most readily in the finer fibres with more delicate sheaths, such as are found in the central organs. The central or axis-fibre of the nerve-tubes ("primitive band," Re- mak, cylinder axis, Purkinje, Fig. 137, 2, 3, 4, 5 ; 139, 1), is a cylin- drical or slightly flattened filament, which, in entire and unaltered nerve- fibres, is as little recognizable as the sheath, being surrounded by the pulp, and possessing the same refractive power, whilst it comes readily into view when the fibre is torn or treated with various reagents ; and it may thus be recognized as a constant structure, sometimes in the interior of the fibre, arid sometimes isolated. Under natural circumstances it is pale, most generally homogeneous, more rarely, finely granular or striated, bordered by straight or occasionally by irregular, pale contour lines, and it is, generally, everywhere of uniform thickness : it is distin- guished from the medullary sheath, especially by the circumstance, that 348 SPECIAL HISTOLOGY. Fig. 139. although soft and flexible, it is still, not fluid and viscous, but elastic and solid, something like coagulated albumen, with which it also ap- pears to agree in most of its chemical characters. This axis-cylinder exists in all nerve-fibres without exception, even in the finest, and invariably pre- i sents the same characters, except only, that it is sometimes thicker, sometimes more slender, according to the size of the fibre itself. The nerve-fibres, in which the three structures above described can be distinguished, and which we would designate as the medullated or dark- bordered, constitute, it is true, the greater proportion of those existing in the body, but besides these there are still some forms requiring more particular description. These are the nerve-fibres in which there exists no trace of a medullary sheath ; whilst they have an outer sheath and contents, sometimes identical with the axis-fibre of the other kind of nerves, sometimes similar but more clear. These non-medullated nerve-tubes occur, in the first place, as continuations to the other sort, where the latter are in connection with nerve-cells ; and also as more elongated, independent fibres, representing the so-termed processes of the nerve-cells of authors ; and lastly, at the terminations of the dark- bordered nerves. They may again be arranged in several subdivisions, distinguished respectively by their having or not having nuclei, and more or less transparent, more or less consistent contents. It must also be added, that the dark-bordered fibres differ extremely partly in respect to the delicacy or firmness of their structure, and partly in their diameter, which varies from 0-0005 to 0-01 of a line, or more, so that they may be distinguished into fine and coarse, delicate or firm fibres ; from which it is evident that the nerve-fibres, notwithstanding their general tubular character, still differ pretty widely from each other in various respects. The tunic or sheath of the nerve-fibres, discovered by Schwann, in most nerves is brought into view with some difficulty. It is only rarely, FIG. 139. Nerve-fibres, magnified 350 diameters. 1, from the Frog, boiled with alco- hol and acetic acid ; a, sheath ; 6, axis-cylinder ; c, crystals (fat T) : 2, isolated sheath of a Frog's nerve, boiled with soda : 3, from the floor of the fourth ventricle in Man, after treat- ment with soda ; o, sheath ; 6, medulla flowing out in drops, the axis-cylinder is wanting (having been drawn out in the preparation), and the pale streak is medulla : 4, from the root of the n. abducens of Man, treated with soda ; a, sheath ; b, medulla, axis-cylinder not visible. THE NERVOUS SYSTEM. 349 as in the roots of certain cerebral nerves (those of the muscles of the eye for instance), and of the spinal nerves that it appears distinct from the contents ; its presence however is, with certainty, and readily de- monstrated by the aid of chemical reagents. When the nerves are boiled in absolute alcohol, soon after the removal of a considerable part of the fatty matter of the pulp, the sheaths become tolerably dis- tinct, as dark boundary lines ; and they are rendered remarkably and beautifully so by a short boiling in acetic acid, during which, the remaining contents of the nerve-sheaths, with the exception of the central fibre, escape from them, whilst at the same time numerous (fat) crystals (Fig. 139, 1) are formed. When boiled in alcohol and treated in the cold with caustic soda, the nerve-fibres also exhibit the sheaths very beautifully, as pale, frequently undulating contours of the color- less, remaining contents ; and when such fibres are boiled for a moment in caustic soda, numerous, elongated fragments of perfectly empty, somewhat swollen nerve-sheaths, are detached, which, from their deli- cacy, present a striking resemblance to the empty tubules of the mem- brana propria, of the tubuli uriniferi (Fig. 139, 2). The sheaths, how- ever, are rendered most distinct by means of fuming nitric acid and the subsequent addition of caustic potassa. In this case the fatty matter of the medullary sheath escapes from the tubes in the form of color- less drops, the axis cylinder is dissolved, and the yellow sheaths are left empty, dilated and with swollen walls of 0-0004-0-0008 of a line in thickness. In nerves treated with corrosive sublimate, according to Czermaak(" Zeitsch. f. wissensch. Zoologie,"1850), the sheaths are, also, often very prettily shown. It has not yet been determined whether the finest nerve-fibres in the central organs, and in the peripheral nerves (under 0-001 of a line) possess a structureless sheath. Analogy with the coarser fibres is in favor of the existence of such sheaths, but on the other hand there are some facts which would seem to indicate that there are also, sheathless primitive nerve-fibres, both of the medullated and of the non-medullated kinds. I have already (in my " Microscopical Anatomy," II. 1, 396) remarked, that according to my observations in the Tadpole, several dark-bordered fibres are developed in one and the same structureless sheath formed by the coalescence of cell-membranes; and that a similar thing (at least from R. Wagner's figures) occurs in the electric organ of the Torpedo : in which cases special tunics can scarcely be supposed to exist around each separate fibre. And, quite recently, Stannius (" Gbtt. Nachr.," 1850) has found, in Petromyzon, that the nerve-fibres of the central organs possess neither membra- nous sheath nor pulp, and are, as it may be expressed, nothing more than free axis-fibres. When to this, it is also added, that the impossi- bility of demonstrating membranes, by no means certainly proves their non-existence, still, the facts stated are worthy of all consideration, 350 SPECIAL HISTOLOGY. and we must, in this question, for the present, abstain from all conclu- sions drawn from analogy. [Of the chemical nature of the sheath of the nerve-fibres but little is known. When boiled for about five minutes in concentra- ted acetic acid, it is not dissolved, scarcely changed. It resists boiling in caustic soda for a short time without altering, except that it swells up a little ; longer boiling dissolves it. It remains unchanged in water, alcohol or ether, even when boiled. Pettenkoffer's test for bilin (sugar and sulphuric acid) which reddens protein and elein, but according to Schulze, neither collagenous substances nor elastic tissue, does not color the nerve-sheath. Yet its action cannot be ascertained with the most desirable accuracy, since the nerve-medulla is simultane- ously reddened. Sulphuric acid and potaasa render the nerve-sheath yellow (xantho-proteinic acid), producing the same effect as they do, ac- cording to Paulsen, on elastic tissue. Hence it seems as if the nerve- sheath agrees in composition with elastic tissue, except that it is evidently less insoluble in alkalies. From Kolliker's Micr. Anat. II. 1. DaC.] In order to see the medullary sheath or nerve-pulp in its normal con- dition, a nerve of an animal just killed, without any addition, must be quickly brought under the microscope ; in which case some isolated fibres will always be seen quite unchanged, although, as the nerve dries, they are very rapidly altered. Besides this method, I would also recommend the examination of the nerves in the transparent parts of animals, either alive or just killed (nictitating membrane, mucous membrane of the Frog, tail of Tadpole, &c.), the observing of them on warmed pieces of glass (Stark.), and after treatment with chromic acid, which frequently preserves, particularly the cerebral fibres, quite uninjured. The nerve- pulp or medulla is obviously a viscid, fluid, extensible, glutinous sub- stance, to be compared in point of consistence with thick oil of turpen- tine, and which under pressure assumes all possible figures, appearing in the form of globules, filaments, and membranous masses, of very dif- ferent aspects, with pale or dark borders, and opaque or clear. In chemical composition it consists principally of fatty matter. The central filament of the nerve-fibres, which was perhaps seen as early as by Fontana, and with which we have become better acquainted under the name of " primitive band" given to it by Remak, or " cylinder- axis" as it has been termed by Rosenthal and Purkinje, is indisputably the most difficult of investigation, and the least known portion of the nerves. There is no microscopist who has not frequently seen this axis- fibre, but it may, without fear of contradiction, also be asserted, that there is none, not even excepting Remak himself, its discoverer, who can boast that he has studied and learned its relations in every particular. For this reason, but few, as Hannover and J. Muller, are unconditionally THE NERVOUS SYSTEM. 351 agreed with Remak and Purldnje in regarding the axis-cylinder as a constant element in recent nerve, whilst most observers have adopted the views of Valentin ("Repert." 1838, p. 76, 1839, p. 79), and Henle (" Allg. Anat."), who regard it as not always present, but rather as a secondary formation, which does not exist during life, and as the Tin- coagulated central portion of the contents of the nerve-fibre, which, during life, are homogeneous. I have endeavored to the utmost of my power to investigate the relations of this structure, and have arrived at the following results : 1. The axis-cylinder is constantly present in every nerve-fibre, both central and peripheral, in fine and in coarse fibres, and after death is apparent before the nerves are treated with any reagent whatsoever. In the human nerves, in the brain and spinal cord, as they are commonly obtained for examination, the axis-cylinder, when duly sought for, is everywhere and with certainty to be recognized ; and in fact by far the most easily in the central organs, where the absence of neurilemma and the delicacy of the nerve-sheaths oppose but little hindrance to the tearing asunder of the fibres. In these situations it may be seen in nearly the finest fibres. It always presents the aspect of a pale filament, which, together with a tolerable degree of consistence, is still very flexible and at the same time highly elastic, as may be readily observed on com- pression of small portions of the spinal cord (in which case very many axis -cylinders are stretched and torn, retracting considerably, and forming undulating curves). On the average it is about one-third as wide as its nerve-fibre, and consequently varies a good deal in diameter, is obviously quite solid, most generally homogeneous, but not unfre- quently also, faintly striated or very finely granular. It most usually follows a straight course, bordered by two parallel, pale contour lines, occasionally, however, it is, in parts, thicker or more slender, though it never presents varicosities like the nerve-fibres ; and it may, moreover, be curved or even slightly undulating, and also perhaps with an irre- gular, even jagged border. 2. When recent nerve-fibres of an animal just killed are treated with proper reagents, the axis-fibre instantaneously appears. If a thin cuta- neous nerve of the Frog, whilst under examination with a power mag- nifying 100 times be touched with a drop of glacial or concentrated acetic acid, the nerve retracts and there appear instantaneously, at each of the cut ends, large particles of the grumous nerve-pulp, and pale, clear fibres ; and the same thing happens if the nerve have been pre- viously teased out, and the fibres brought separately into view. The clear fibres are evidently the axis-fibres, as they may readily be traced into the projecting medullary sheaths and entire nerve-tubes, and in other respects, also, present all the characters of those fibres, only that they are much paler and broader (as much as 0*004 of a line, in the 352 SPECIAL HISTOLOGY. peripheral thick fibres) and evidently swollen ; they frequently, also, appear convoluted, or even spirally rolled, which is owing, simply to the shortening of the whole nerve caused by the acetic acid. The nerve- pulp itself is rendered grumous by the same reagent ; the grumous particles are sometimes granules, sometimes very short rods, like fat- crystals, which latter may be very often seen on the nerve-fibres, forming stellate, acicular groups (margaric acid) ; alcohol and ether also render the axis-cylinder very distinct, both, when recent nerves are treated with those reagents in the cold, in which case their action must be rather more prolonged, and when they are boiled in them. I can particularly recommend the boiling in absolute alcohol, by which means excellent preparations of the axis-fibres may be made, and in the shortest time. Under this treatment the nerves become firmer, but still admit of being readily torn into fibres, and always exhibit very numerous isolated central fibres of considerable length, which, contrasted with those brought into view by means of acetic acid, are, as it were, contracted (at most 0-002 of a line wide), yellowish, firmer, and often convoluted or twisted. Ether acts in the same manner. By both reagents the medullary sheaths are rendered paler and grumous, the grumous particles frequently appearing, as it were, to be united into a delicate network. When nerve-fibres are boiled, first in ether and afterwards in alcohol, they become quite pale, but the sheath and axis-cylinder perfectly distinct, the latter presenting precisely the same appearance as after treatment with alcohol alone. Consequently, it would seem, that the axis-fibres contain no trace of fatty matter ; at all events, except that they shrink a little, they are not altered by the action of ether and alcohol, and afterwards, also, again enlarge, under acetic acid, into broad pale bands. Besides the reagents above mentioned, the axis-fibres are particularly well displayed by chromic acid (Hannover), corrosive sublimate (Purkinje, Czermak), and gallic acid, but less readily in recent nerves, in which, it is true that they become instantaneously manifest, although it is never, except by accident, and rarely, that they can be isolated, than, especially after a more prolonged immersion in those. The nerve-fibres under these cir- cumstances appear contracted, the medullary sheath grumous, the axis- cylinder more opaque and somewhat diminished, in chromic acid yellow- ish, but in other respects exactly as above described. In the acoustic nerve of the Sturgeon, Czermak, by means of corrosive sublimate, has demonstrated in dividing nerve-fibres, the existence, also, of bifurcating axis-cylinders. Iodine also or iodine combined with aqueous hydri- odic acid (Lehmann) act very powerfully. In quite recent nerves it instantaneously renders the medullary sheath wholly grumous, and not only isolates numerous, somewhat shrunken axis- fibres, for a considerable length, but renders them in many nerve-fibres very distinct in situ^ and usually appearing convoluted or serpentine. Hydrochloric, sulphuric, THE NERVOUS SYSTEM. 353 and fuming nitric acids, in certain cases, also render the axis- cylinders apparent (Lehmann.)* 3. The axis-cylinder consists of a solid protein compound differing from common fibrin, and from the fibrin of the muscles. The chemical nature of the axis-cylinder is difficult of investigation, because it cannot be obtained in an isolated form in large quantity ; something, neverthe- less, may be learned from microchemical reaction as has been shown by Lehmann and myself. In concentrated acetic acid it swells up conside- rably, but is dissolved with difficulty, and even after it has been boiled continuously for several minutes, although pale, it always remains un- changed. When boiled for a longer time in acetic acid it dissolves, exactly like coagulated albumen, whilst the sheaths and some of the contents remain undissolved. Alkalies (potassa, soda, ammonia), in the cold, attack the axis-cylinder but slowly, though in soda it instantane- ously becomes very pale and swells up to 0'004-0'005 or even 0*006 of a line. Longer immersion in soda dissolves it, and the same thing takes place upon its being boiled, soon after the commencement of ebul- lition in the fluid. In fuming nitric acid, it disappears in a short time less than half a minute, exactly as is the case with coagulated albu- men. Treated with nitric acid and potassa the axis-cylinder is rendered yellow (xanthoproteinic acid) and may be seen spirally contracted, within the nerve-fibres, which are also shortened, but not to the same extent. On the other hand it is not colored by sugar and concentrated sulphuric acid, which redden coagulated albumen, at most acquiring a yellowish or pale-reddish hue. In water the axis-cylinder is unchanged, even when boiled, in which case it is readily isolated and appears somewhat con- tracted ; by ether and alcohol it is undissolved even by boiling, but shrinks to some extent. The latter effect is produced also by corrosive sublimate, chromic acid, iodine, and carbonate of potassa. Viewing all these reactions together, it might perhaps be stated with certainty, that the axis-cylinder is a coagulated protein compound which, however, dif- fers from fibrin, inasmuch as it is insoluble in carbonate of potassa and solution of nitre, and offers much greater resistance to acetic acid and caustic alkalies. On the other hand, it agrees with the substance of which the muscular fibres are composed, in its elasticity and insolubility in carbonate of potassa, differing from it in its insolubility in dilute hydrochloric acid, and difficult solubility in acetic acid. These are the most important facts connected with the axis-cylinder. The conclusion which may be drawn from them, appears to me, to be simply this, that the axis-cylinder is not an artificial product, but that it must be regarded as an essential constituent of the living nerves. * [I have always obtained the best preparations by soaking a nerve for six or twelve days in concentrated acetic acid. The axis-fibres can then be readily isolated; but are fragile and devoid of their elasticity. DaC.] 23 354 SPECIAL HISTOLOGY. The only objection which can be urged against this opinion consists in the circumstance, that the axis-fibre cannot be seen in living fresh nerves, and that it cannot generally be distinguished, as a special structure, in the interior of the nerve-tubes without the aid of reagents. But it must be remarked that it can also be brought into view in nerves that are still warm. Thus I find well-marked projecting axis-fibres at the roots of the cerebral nerves in Frogs just killed, which I have examined as quickly as possible, after the application of a solution of sugar, particularly in those of the optic, trigeminal, and vagus, also in the spinal nerves, for instance in the second. I see them under the same conditions in the peripheral nerves of the Frog that have been teased out, and, in these nerves, have on several occasions, even dis- tinctly noticed the axis-fibres in the form of convoluted filaments, in larger drops of the nerve-pulp expressed from the tubes (Fig. 137, 2). The only fact, therefore, that can be adduced in opposition, is this, that it is quite true that the axis-fibre cannot, with certainty, be perceived in the interior of the recent nerve-tubes themselves, except upon the application of some reagent ; but this circumstance obviously proves nothing at all, because neither can it be seen in the interior of tubes of less recent nerve-substance, all of which, as innumerable examples of isolated axis-fibres occurring in them, show, invariably contain such fibres. The axis-cylinder, possessing the same refractive power as the still fluid part of the medullary sheath, is necessarily indistinguishable from it, but from this circumstance we cannot conclude that it is absent, nor, equally, can such a conclusion be drawn from its invisibility in the recent nerve-fibril. Taking all these circumstances together, I am firmly convinced that a special, central structure exists even in recent nerves, which is distinguished from the more external portion, that is from the medullary sheath, not only by its chemical composition, as appears to me to have been placed beyond all doubt, but also by its consistence and elasticity, as well as by its possessing a determinate form. The condition in which we obtain the axis-fibre in the human nerves and central organs, by the addition of the serum of the blood, albumen, or vitreous humor, appears to me to represent its natural state ; on the other hand alcohol, ether, iodine, corrosive sublimate, gallic, and chromic acid render it more consistent than it is normally ; whilst acetic acid, dilute nitric acid, and alkalies exhibit it paler and more swollen. The nerve-pulp forms a semi-fluid cortex around the axis-fibre, and, though intimately connected, is not continuous with it. By pressure, therefore, the pulp may very frequently be expressed, by itself, from the ends of the tubes or from lateral rents of the sheath. The drops of pulp thus formed, usually coagulate on the surface, re- maining clear and transparent in the interior, like the central portion of the nerve-tubes. Many authors have described these bodies as por- THE NERVOUS SYSTEM. 355 tions of the whole contents of the nerve-tube, and have regarded their formation as a proof against the pre-existence of the axis-fibre, but incorrectly. They belong to the medullary sheath only, which, in the interior of all nerve-fibres with only a double contour, is still for some space perfectly clear and bright. An axis-fibre and a clear space, in fibres having a double contour, are therefore by no means identical, and it is not at all surprising, nor opposed to the existence of an axis-cylin- der, that a multitude of drops with a double contour and clear contents should be obtained from such fibres. The medullary sheath may also coagulate entirely, and then the axis-fibre remains evident, sometimes as a transparent streak of uniform breadth throughout ; sometimes, when the grumous particles are more numerous, it may be concealed by them, so that the entire contents of the nerve appear to be coagulated. They are so, however, only in appearance, the clear fibre always lying in the interior ; arid I have never yet seen it coagulated or grumous. Non- medullated nerve-fibres occur in many situations. I enumerate among them : 1, the pale fibres in the Pacinian bodies ; 2, the nucleated pale fibres in the terminations of the olfactory nerves ; 3, the per- fectly transparent, non-nucleated nerve-fibres in the cornea; 4, the pale, branched, and partially anastomosing terminations of the nerves in the electrical organ of the Torpedo and Ray (R. Wagner, Ecker) ; 5, the similarly constituted terminations of the nerves in the skin of the Mouse (vid. " Micr. Anat." 11); 6, the pale processes of the nerve-cells in the central organs and ganglia, even though they may not all pass into dark-bordered fibres. Of these fibres, those which occur at the extremities of nerves were, even by the earliest observers of them, unconditionally regarded as nerve-fibres ; and as respects the processes of the nerve-cells, I described this to be their nature as early as the year 1846 ; but these views could not be considered as fully es tablished, until the relation of the fibres with the elements presenting the dark borders was completely elucidated. But since it has been ascertained by Schwann, Ecker, and myself, that the nerve-fibres of the embryo are in precisely the same condition as the pale fibres now in question, and since, I, Wagner, Robin, and Bidder and Reichert, have shown that the pale processes of the nerve-cells pass into dark- bordered fibres, it has become more possible to arrive at positive conclusions on the subject. R. Wagner was the first to broach the supposition, that the pale fibres in the Pacinian bodies, and in the elec- tric organs, were nerve-sheaths, with axis-cylinders, and that the pro- cesses which pass into nerve-fibres, were themselves bare axis-cylinders, and, moreover, that the entire granular contents of a nerve-cell are nothing but an axis-cylinder enlarged into a globular form ; and after I had demonstrated the constant existence of the axis- cylinder in the living nerve, and that it was a structure distinct from the medullary 356 . SPECIAL HISTOLOGY. sheath, I considered myself fully justified in asserting that the dark- bordered nerve- fibres were in direct connection on the one side through the axis-cylinder, with the pale processes of the nerve- cells and the contents of those cells, and on the other, that they passed into the pale terminal nerves in the situations above mentioned. But this, by itself as I believe, affords no ground for the identification of the pale fibres in question, or the contents of the nerve-cells, with the axis-cylinders. This could only be established, if we knew with certainty that the medullary sheath of the dark-bordered nerve-fibres is superadded from without to the contents of the pale embryonic fibres during the development of the nerves, and is an entirely new formation between those contents and the membranous sheath. This is not the case, however, it being on the contrary more probable that the medullary sheath, which is also albu- minous, is developed merely from a metamorphosis of the outermost part of the embryonic nerve-contents, that is to say from the develop- ment of fat in it, and that the axis-cylinder is the unaltered innermost part of those contents. In this case all the structures, the nature of which we are now discussing, would represent, not bare axis-cylinders, but an entire embryonic nerve-tube, the contents of which were still homogeneous, or had not undergone differentiation, and would also be in continuous connection with all the parts of the dark-bordered fibres, a mode of explaining them to which, at all events at present, I am dis- posed to give the preference. In addition I would remark, that the pale nerve-fibres are also met ivith in different stages of development. The nucleated fibres in the olfactory membrane remain altogether in the stage of embryonic fibres, as also, to all appearance, do the pale rami- fications in the electric organ, and the contents of both these kinds of nerve-tubes would appear to have little agreement, in their consistence, with an axis-fibre ; in the Pacinian bodies the contents of the pale fibres in all respects, represent an axis-fibre, for it is probable that a sheath also exists in this situation ; in the cornea, the contents of the transparent terminal nerve-tubules are apparently more fluid ; and, lastly, with respect to the processes of the nerve-cells, they consist, whether they have a delicate sheath or not, of a substance often exactly resembling an axis-cylinder, but which is also frequently of softer consistence, cor- responding with the contents of the nerve-cell. The contents of the pale, non-medullated nerve-tubes, therefore, although genetically com- prehending more than an axis-fibre, still in all probability are capable pretty nearly of assuming its nature. 111. The nerve-cells (accessory corpuscles (Belegungskorper), nerve- corpuscles, Valentin), (Fig. 140), are nucleated cells, occurring in great numbers in the gray or colored substance of the central organs, in the ganglia, and occasionally also in the trunks, and peripheral expansions of the nerves (retina, cochlea, vestibule). The nerve-cells are covered THE NERVOUS SYSTEM. 357 externally by a delicate, structureless membrane, which in the cells of the ganglia (ganglion-cells, -globules, -corpuscles), may be demonstrated easily, but with great difficulty in those of the central organs ; the Fig. 140. application of reagents, however, will suffice to show, pretty distinctly, that the membrane exists around the larger cells, even in these situa- tions, whilst in the smallest, just as in the finest nerve-fibres, no mem- brane has yet been observed, although one probably exists. The contents of the nerve-cells are a soft, but tenacious, elastic substance, which be- sides the nucleus consists of two elements ; firstly, of a clear, homoge- neous, light-yellowish, or colorless matrix, upon which the physical properties of the contents depend, and which is a protein-compound ; and, secondly, of minute granules of different kinds. In the colorless nerve- cells these present the form of uniform, roundish, for the most part, minute and pale, more rarely, darker and larger corpuscles dispersed throughout the entire contents of the cells, and imbedded in the tena- cious matrix ; whilst in the colored cells, instead of these granules, more or less yellowish, brown or blackish corpuscles occur. The latter are most usually of a larger size, and are placed, closely aggregated, in a mass near the nucleus; in other instances, they nearly fill the entire cell, giving it the aspect, in all respects, of a brown or blackish pigment- cell. In the midst of these contents lies the nucleus, for the most part as a very clear, spherical vesicle with distinct walls, perfectly transpa- FIG. 140. Nerve cells, from the acoustic nerve, magnified 350 diameters : 1, nerve-cells with the origin of a fibre, from the anastomosis between the facial and auditory nerves, in the meatus audit, int. of the Ox ; a, membrane of the cell ; i, contents ; c, pigment ; rf, nucleus ; , continuation of the sheath upon the nerve-fibre; /, nerve-fibre : 2, two nerve-cells with fibres, from the n. ampull. infer, of the Ox ; a, sheath with nuclei ; 6, membrane of the cell j c, nucleus ; rf, the origin of a fibre with nucleated sheath : 3, isolated contents of a nerve- cell, with nucleus and two nucleoli. For these drawings I am indebted to Dr. Corti. 358 SPECIAL HISTOLOGY. rent contents, and one, or more rarely several, large opaque nucleoli, which occasionally exhibit a cavity. The size of the nerve-cells varies very much; like the fibres, they occur as large, small, and middle-sized. The extreme dimensions of the cells are 0-002-0-003, and 0-05-0-06 of a line. The nuclei, which for the most part are in proportion to the cells, measure from 0-00150-008 of a line; the nucleoli 0-0005-0-003 of a line. The nerve-cells, more- over, are distinguished according as they are : 1, thin or thick-walled, of which the former are found almost wholly in the spinal cord and brain ; and 2, as they are independent cells, or are furnished with pale processes, of which they may have one, two, or several (uni-, bi-, multi- polar cells), and which are frequently ramified, and the former, in many situations, continuous with dark-bordered nerve-fibres, and even having the nature of non-medullated nerve-fibres. Besides the nerve-cells, there also exist in the gray-substance of the higher central organs, as constant constituents, a finely granular pale substance, which has the greatest resemblance to the contents of the cells, and besides this, in places, large accumulations of free cell-nuclei. Similar elements are contained in the retina, and according to Wagner and Robin in the ganglia of the Plagiostomata. The nerve-cells are simple cells, as which they were understood even by Schwann ; this is clearly and manifestly shown by their form, their chemical composition, and their development. When Bidder, more lately (1. c.), relying upon the fact that the nerve-cells in many situa- tions are in connection at each end with dark-bordered nerve-fibres, pro- pounds the opinion that they are membraneless masses, imbedded in dilatations of the nerve-tubes, he has overlooked those cells from which no fibres are given off, which possess exactly the same membrane as those with processes ; and has not considered that there also exist nerve- cells with a single, and others with numerous processes, as applied to which, his view would be altogether unnatural ; and lastly, that the development of these bodies indicates that the nerve-cell is formed in toto, whether it possess processes or not, from a simple cell. It has not yet been determined whether the nerve-cells of the large central organs have membranes or not ; Stannius was unable to detect them in the Lamprey, and R. Wagner says the same of the nerve-corpuscles of the electric lobes of the Ray. I think I have seen a membrane in the large, many-rayed corpuscles in the spinal-cord and cerebellum of man, and occasionally, also, in others, but I freely acknowledge that no membrane can be detected in all the smaller cells, nor in the processes of the cen- tral cells in general. This does not, however, appear sufficient to justify the denial of the existence of membranes in these instances, and I believe, that in this case, as in that of the finest nerve-tubes, we must THE NERVOUS SYSTEM. 359 for the present abstain from any definite opinion. The processes of the nerve-cells, in the brain and spinal cord, which were first noticed by Purkinje, will be more minutely described when we come to speak of the central organs, and the question will there be discussed as to their relation to the central fibres. In the ganglia, there are no cells with branched processes, instead of which we find only those with one, two, rarely three or four, pale appendages, which are continuous with dark- bordered tubes. The nerve-cells consist, for the most part, of a coagu- lated, although soft protein-compound, which appears to correspond very closely with that of the axis-fibres. It has not been ascertained whether the membranes and nuclei differ essentially from it. The fatty matter, which has also been found in small quantity in the gray substance, con- stitutes in every case the opaque granules in the cells, and appears to exist in other conditions also, in their contents. When isolated nerve- cells are compressed, they become much flattened, resuming their pris- tine form when the pressure is removed. Their processes also are very elastic, and like the axis-fibres may be considerably extended, and after- wards again retract themselves. As our knowledge of the chemical composition of the gray and white substance still leaves much to be desired, I content myself with the fol- lowing statements. Lassaigne, in the brain of a lunatic, found Gray substance. White substance. Water 85'2 730 Albuminous matter 7-5 99 Colorless fat I'O 13'9 Red fat 3'7 0'9 Osmazome, lactates 1'4 I'O Phosphates 1'2 1'3 According to Fre*my (Comptes rendus, torn. ix. p. 703, "Ann. d. Chem. und Pharm. 1841," vol. xl. p. 69), the brain (both substances together) contains Water 80 Albumen 7 Fatty matter 5 Osmazome and salts 8 100 Which almost exactly agrees with Vauquelin's analysis, who more- over estimates the osmazome at 1-12, and the salts at 6'65; whilst it differs from that of Denis, who found much more fatty matter (12-40 in a man 20 years old, 13-3 in one aged 78), and less water (78 and 76{j). CENTRAL NERVOUS SYSTEM. 112. Spinal Cord. The nervous elements are so disposed in the spinal cord, that its external, white substance is constituted almost ex- 360 SPECIAL HISTOLOGY. clusively of nerve-fibres, whilst the gray nuclear portion with its pro- longations, the cornua, or horns, is formed, in almost equal proportions, of nerve- fibres and cells. The white substance of the spinal cord may, for the purpose of de- scription, be most conveniently, and in accordance with usage, divided into two halves, and each of these into three columns. The anterior columns (funiculi anteriores), are, towards the interior, almost com- pletely separated from each other by the anterior fissure (fissura ante- rior), which extends the whole length of the cord, and into which a vascular process of the pia mater penetrates. At the bottom of the fissure, however, the columns are united by the anterior or white com- missure (com. alba)', externally, they extend as far as the points of exit of the anterior roots of the nerves, or to the sulcus lateralis anterior, but are here inseparably connected with the lateral columns (funiculi laterales), which again, at the points of exit of the posterior roots, where the sulcus lateralis posterior is situate, are continuous, without any line of demarcation, with the posterior columns. The latter (funiculi pos- teriores) appear indeed as if they were in contact in the posterior mesial line, because the posterior longitudinal fissure described by many anato- mists, does not exist in man, except in the lumbar enlargement of the cord, and in the superior cervical region ; but they are nevertheless separated, to such a degree, throughout the whole length of the cord by very numerous vessels, which in the posterior mesial line penetrate as far as the gray nuclear portion, that the columns in most places are not even in contact, and even where they are, they are merely in juxta- position, and never by any means continuous into each other. Thus the white substance of the cord represents two halves, united only by the anterior white commissure, and each of which is divided more arti- ficially into three columns, which occupy the depressions left between. the projecting processes of the gray substance. The gray substance presents a central portion, more of a riband-like form, and four laminae projecting laterally from it, so that its transverse section forms a cross. The central portion or the gray commissure, in the adult, does not, normally, contain any canal, such as exists in the foetus, and consists of a central, cylindrical, or flattened tract, consti- tuted principally of nerve-cells, of a yellowish color the gray nucleus (subst. grisea. centralis), and of nerve-fibres running transversely, con- tinued beyond the nucleus, before and behind it the gray or posterior commissures. Of the laminae, in a transverse section also termed horns, the anterior are thicker, and shorter, of a uniform gray color, composed of larger and smaller nerve-cells, and of delicate nerve-fibres of me- dium fineness ; the posterior, longer and thinner, are constituted at their roots like the former, only most usually of smaller cells; but at the free edge are invested with a more transparent layer, containing THE NERVOUS SYSTEM. 861 a preponderance of smaller nerve-cells the substantia gelatinosa of Rolando. Of the roots of the spinal nerves, the anterior penetrate be- tween the anterior and lateral columns, di- rectly to the anterior horns, and the poste- rior are lost between the lateral and pos- terior columns, passing through the substan- tia gelatinosa into the posterior laminae or horns. With respect to the. intimate structure of the spinal cord, we have to distinguish in the white substance : 1, horizontal ; and 2, lon- gitudinal fibres. The latter, in all situations, except in the anterior commissure, are in great part altogether unmixed with horizon- tal fibres, and everywhere, both superficially and deeply, run parallel with each other, but they are never in- terlaced, nor do they ever constitute smaller fasciculi. The number diminishes from above downwards, because, as will be afterwards shown, they successively pass inwards towards the gray substance, presenting the general characters of the central nerve-fibres ; that is to say, the delicacy of sheath, disposition to the formation of vari- cosities, and to the breaking up into separate fragments, which are constituted either of all the elementary parts of the nerve-tubes, or consist of nothing more than an axis-fibre, or of the medullary sheath. Their diameter amounts to 0-0012-0-0048, on the average 0-002-0-003 of a linej and, in one and the same fibre is, evidently, always nearly the same, since, in the white substance, neither divisions nor any other kind of alteration in diameter of the fibres are found to exist. The transverse fibres occur : 1, in those portions of the lateral and pos- terior columns which adjoin the horns of the gray substance, and the description of which will be given afterwards with that of the gray substance ; 2, in the white commissure ; and, 3, at the points of entrance of the roots of the nerves. The white, or anterior commissure FIG. 141. Transverse section through the spinal cord in the superior lumbar region, mag- nified about 30 diameters, half diagrammatic : a, anterior column ; 6, lateral columns, motor portion; c, lateral columns, sensitive portion; d, posterior columns; e, anterior longitudinal fissure; /, posterior longitudinal fissure ; g, motor roots ; A, their internal fasciculus; i, their external fasciculus ; k, decussation of the anterior columns in the anterior commissure ; I, gray fibres of the lateral columns passing into the anterior gray commissure; w, gray cen- tral nucleus, here internally with two groups of somewhat darker cells ; , posterior gray commissure, with a vessel cut across; o, fibres of the posterior column passing into the gray commissure; p, fibres of the sensitive roots going off to the lateral columns; , from the cervical enlargement, 6| and 4| lines ; E, from the superior cervical portion, level with the second nerve, 6J and 4f lines. 6 THE NERVOUS SYSTEM. 371 the transverse sectional surfaces of all the nerves in square lines, and compared with them the transverse sectional area, taken with the utmost possible nicety, of the white substance of the spinal cord, at the level of the second cervical vertebra. It is quite true that there was now evident a very considerable diffe- rence against the spinal cord ; but when the very great attenuation of the nerve-fibres of the roots, at their entrance and in their further course in the cord, was brought into account, which was not done by Volkmann, the matter was entirely altered, and it became clear that the cord in the male subject contained more than sufficient fibres to furnish the peripheral ones, and in the female nearly sufficient, particularly when it is consi- dered, moreover, that in the entire enumeration, the numbers were stated rather in favor of the roots of the nerves (vid. the calculation in " Mikro- skop. Anatom.," II. 1, 116). It appears, therefore, scarcely to admit of doubt, that the notion of a termination of the peripheral nerves in the cord, has no support in mea- surements such as those which, following Volkmann, I have adduced ; . and that the latter, even when all due allowance is made for the uncer- tainty always incidental to such an inquiry, on the contrary indicate, at all events the probability, that the spinal nerves ascend to the cerebrum. They give no further information, however, and it depends upon other facts, whether such a central origin should be admitted or not, because it is even conceivable, that the peripheral nerves may end in the cord, and that the longitudinal fibres in the cord have a wholly different source. Since it is scarcely probable that the tracing of the nerve-fibres through the entire cord will be effected either at present or perhaps at any time, it is necessary to look round for other facts, which may possibly afford conclusive evidence on the subject ; and such facts do exist. In the first place, let us consider the course of the roots of the nerves in the cord, such as it has been described above. We found, that after they had all come, more or less, into contact with the gray substance, the greater number of them could be directly traced into connection with the longi- tudinal fibres of the anterior, lateral, and posterior columns. From this fact, together with my measurements, the passage of the greater part of the peripheral nerve-fibres into the cerebrum, will appear to many to be proved ; but, not to overlook anything, it may be further remarked, that the radical fibres, running longitudinally in the substance of the cord, may terminate in it, or after running in it may again enter the gray substance higher up. The former supposition is now, it must be con- fessed, but little probable, because in the first place, no one has yet seen the terminations of nerve-fibres in the white substance ; and in the second, because anything of the sort, for other reasons, would be very surprising, nerve-fibres being nowhere known to commence in the white substance ; and with respect to the latter, any re-entry of the roots of 372 SPECIAL HISTOLOGY. the nerves into the substance could not escape notice. Since the junction of the radical fibres with the anterior, posterior, and lateral columns, can be so well and so directly observed, the relation in question would necessarily be evident also ; and yet in the course of my perfectly unpre- judiced observations, I have never seen anything of the kind. Nothing, therefore, remains but to assume, that the great majority of the periphe- ral nerves really have a cerebral origin. Whether they all originate in the brain (where, we shall afterwards see) or in part, though, from my observations, but to a small extent, from the cord, cannot be determined, any more than the question can be decided, whether the white substance of the cord, besides the fibres derived from the peripheral nerves, also contains others passing from the brain to the cord. 114. The medulla oblongata and pons Varolii belong to the most complex parts of the central nervous system, containing white and gray substance, intermixed in very various modes. The white substance is, in part, a continuation of that of the cord, in part distinct from it, and is disposed in the following manner : the anterior columns of the spinal cord diverge from each other at the commencement of the medulla oblon- gata, allowing the decussating fibres of the corpora pyramidalia to appear. As they proceed, a smaller division joins the pyramids, form- ing their outer part, whilst the principal portion surrounding the olivary bodies, internally and externally, whence they are also termed the oli- vary columns, passes laterally, and then, divided into two bundles, proceeds above the second transverse layer of fibres, through the pons. One of these divisions constitutes the fillet (laqueus), which continued above the crura cerebelli ad cerebrum, enters the posterior corpora quad- rigemina, joining, within them, the corresponding division of the opposite side. The second division, or bundle, lies externally and inferiorly to the crura cerebelli, and enters the tegmentum of the cerebral peduncle. Besides this, the olivary columns, corresponding to the anterior columns of the cord, also, as it seems, give off fibres to the pedunculis cerebelli. The lateral columns of the spinal cord divide, on reaching the medulla oblongata, into three bundles ; one of which, ascending in a tolerably straight direction, is continuous with the fasciculus lateralis of the resti- form body, and with it enters for the most part into the peduncle of the cerebellum, and in small part into the tegmentum ; a second division penetrates forwards between the divergent anterior columns, decussates in two or three fasciculi with that of the other side (decussatio pyrami- dum), constituting the principal bulk of the pyramids ; a third division, lastly, appears between the posterior columns at the bottom of the rhomboid fossa, or fourth ventricle, as the eminentia teres. These latter are continued, on the floor of the fourth ventricle and applied to each other, into the tegmentum of the cerebral peduncles, whilst the pyra- THE NERVOUS SYSTEM. 373 mids, passing between the first and second transverse layers of fibres of the pons, are continued into the base of the cerebral peduncles. The posterior columns of the cord, lastly, chiefly constitute the fasciculi gra- ciles and cuneati, the latter of which, in great part, enter the pedunculi cerebelli, whilst the remainder, and the fasciculi graciles, situated exter- nally to the eminentice teretes, may be traced into the tegmentum of the crura cerebri. All these fasciculi consist, besides the gray substance, of parallel nerve-fibres of the same dimensions as those of the cord, that is to say, from 0'001-0'004 of a line, seldom more. Besides this white substance, the pons Varolii and medulla oblongata, omitting the roots of the nerves, present a system of mostly horizontal fibres. This system consists : 1, of the well-known transverse, arcuate fibres, external to the corpora pyramidalia and olivaria ; 2, of straight FIG. 146. Transverse section through the medulla oblongata in Man. P, pyramids; O, olivary bodies ; F.I, fasciculus lateralis; F.c, fasciculi cuneati ; F.g,fasc.graciles; H, root of hypoglossal nerve; F, root of n. vagus ; F.a,fissura anterior; F.p,fissura posterior in the floor of the fourth ventricle, or rhomboid fossa; R, raphe : "a, longitudinal fibres of the raphe ; 6, central gray layer with transverse fibres ; c, expansion of these fibres in the olivary column and body ; d, accessory olivary nucleus ; e, hypoglossal nucleus /, decussation of the hypo- glossal nerve ; g, nucleus of the vagus ; hhh, larger nerve-cells in the restiform bodies ; t, medullary mass in the interior of the olivary body, belonging to the internal transverse fibres; &, arcuate fibres external to the olivary body ; I, transverse fibres external to the pyramids; m, , o, gray nuclei in the pyramids and olivary columns. Magnified 15 diameters. 374 SPECIAL HISTOLOGY. fibres, which extend from before backwards, in the middle, through the medulla oblongata, contributing to the formation of the so-termed raphe (Stilling) ; 3, and lastly, of very numerous fibres proceeding from this raphe into the lateral halves of the medulla, following a more or less curved direction. These latter, the internal transverse fibres, commence behind the pyramids, and the anterior of them as a large mass, very minutely broken up by fine flattened fasciculi of the pyramidal and olivary columns, penetrate from within into the corpus dentatum olivce, the white substance of which is constituted by them ; they then expand in a brush-like form, and are continued through the gray substance of the corpus dentatum, ultimately turning backwards towards the fasciculus cuneatus [corpus restiforme] and lateralis. In this course, the fibres describe larger or smaller curves. The latter is the case with those which come out from the posterior part of the olivary nucleus [corpus dentatum], and which go almost directly backwards and outwards through the accessory olivary nucleus (Stilling), and the gray substance, containing large cells, situated on its exterior; the former condition obtains in the anterior fibres, which spread out in a radiating manner, passing at first forwards between the pyramids and olivary nucleus, and afterwards backwards in a sharp curve, superficially round the latter, into the lateral fasciculi. A second division of the internal transverse fibres goes behind the olivary nucleus with which it has no connection, directly from the raphe, through the posterior part of the olivary columns and the eminentice teretes, outwards and backwards, also into the restiform body. All these fibres, and most of them obviously so, are associated together, and appear to me to be continued from the restiform bodies and the peduncles of the cerebellum, into the anterior divisions of the medulla oblongata. With respect, however, to their more intimate relations, concerning which Stilling's work and my "Microscopical Anatomy" may be consulted, little is as yet known. The gray substance, in the medulla oblongata, is collected into larger masses, chiefly in three situations, viz., in the olivary and restiform bodies, and on the floor of the rhomboid fossa (fourth ventricle) : 1, the gray substance of the olivary bodies forms, as is well known, a folded lamella, constituting a capsule closed on all sides except the inner, which, although it occupies the situation of the anterior horns of the spinal cord, which are continued nearly to its inferior border, still has no direct connection with them ; appearing, also, to be otherwise isola- ted from all other gray substance. Within it, besides the very numer- ous nerve-fibres of the transverse fibre-system, which traverse it for the most part in straight lines, there occur in great numbers smaller nerve- cells, measuring 0-008-0-012 of a line in diameter, and of a rounded form, with 35 branching processes, and containing in the interior yel- lowish granules, to which the color of the olivary bodies is due. The THE NERVOUS SYSTEM. 375 closest observation has failed to afford me any indication of a connection between these cells and the fibres which run among them. On a level with the two upper thirds of the olivary body, is placed, behind the nucleus and wholly isolated from it, the body termed by Stilling the accessory olivary nucleus, in the form of a flattened, yellowish band, of exactly the same structure as the gray substance of the olivary body, and also traversed by horizontal nerve-fibres, and in fact by fibres which have for the most part already passed through the olivary body ; 2, in the restiform bodies, the gray substance (corpus s. nucleus cinereus) assumes the form of an ill-defined, elongated mass intermixed with very numerous nerve-fibres, and which occupies mainly the fasciculus late- ralis, but also extends into the fasciculi cuneatus and gracilis. This structure may be described as a continuation of the posterior horns of the spinal cord, even presenting, as Stilling correctly states, an indi- cation of the substantia gelatinosa of those processes, of which it may moreover be observed, that it is very remarkably developed in the upper- most portions of the cord, as far as the commencement of the decussa- tion of the pyramids, and has a position entirely lateral. The elements of the gray substance of the restiform bodies are, besides, numerous finer fibres, which appear to pass chiefly into the horizontal, internal fibre-system, and many, rather pale, but in part brownish nerve-cells with processes, pretty regularly disposed, and most of them of the same size as those of the olivary bodies ; 3, the gray substance on the floor of the fourth ventricle, is the continuation of the gray nucleus of the spinal cord, and forms a tolerably thick layer, extending from the calamus scriptorius as far as the aqueductus Sylvii. It contains throughout, numerous nerve-fibres, in part of very considerable diameter, up to 0-006, or even 0-008 of a line, in part of the finer and finest kinds, and besides these, nothing but caudate nerve-cells of all dimensions from 0-006, up to 0-03 of a line, and more. The largest of these are con- tained in the ala cinerea at the posterior extremity of the fourth ventri- cle, and in the subst. ferruginea s. locus cinereus (Fig. 147), in which latter situation, the cells also present well-marked pigmentary matter, and very numerous, delicately branched processes. The small multi- nuclear cells, which in the gray nucleus of the cord occur in the form of a compact structure, are here entirely wanting, not being found beyond the decussatio pyramidum. Besides these three masses of gray sub- stance, which can in part be referred to that of the spinal cord, there are found, in the medulla oUongata, some small collections of it, as in the pyramids near the olivary bodies, and in the olivary columns, exter- nal to the accessory nucleus, in all of which, as has been already stated by Stilling, are also to be seen in part larger cells, all caudate (in the latter situation measuring as much as 0-025 of a line), and finer nerve- tubes. One part of the gray substance just described, that namely of 376 SPECIAL HISTOLOGY. the anterior half of the fourth ventricle, belongs properly to the ports VaroliL It also contains, in its interior, besides the just described Fig. 147. elements, above the transverse fibre-layer, both in the middle as well as more laterally, many accumulations of gray substance, with larger and smaller (as much as O02 of a line and more) nerve-cells, all caudate, which are so irregularly imbedded among the longitudinal and transverse fibres, as to require no detailed description, and are connected on the one side with gray nuclei of the medulla oblongata, and on the other with the substantia nigra of the crura cerebri. The relations of the ten pairs of nerves which arise from the medulla oblongata, the pons, and the crura, constitute a very difficult question. But few inquirers have endeavored to solve it by other means than those usually employed, that is to say, by the tracing of the fibres, with the aid of the scalpel, which here goes no way at all. Among the excep- tions are E. Weber (Art. " Muscular Motion," in Wagner's " Handw. d. Phys." III. 2, pp. 2022), who made his examination in preparations, hardened by carbonate of potassa ; and Stilling, who pursued his by the microscopical examination of sections, similarly hardened by means of alcohol. My own results, obtained from preparations in chromic acid, which had been for the most part made transparent by soda, agree in almost every point with those of Stilling, which, at all events, among all observations on the subject, have gone most deeply into the matter. FIG. 147. Nerve-cells of the substantia ferruginea in the floor of the fourth ventricle or rhomboid fossa, of Man ; magnified 350 diameters. THE NERVOUS SYSTEM. 377 The nerves in question arise, without exception, not from the columns or fibrous substance, out of which they proceed, but all penetrate more or less deeply into the central parts, and all probably become connected, some not till they have decussated like the trochleares, with definite parts of the gray substance, which Stilling not inappropriately terms nerve nuclei (accessory nucleus, for instance). It is the floor of the fourth ventricle, and of the aqueduct of Sylvius, which are more par- ticularly concerned in this respect, since all the nerves above named, at least in part, extend to them. The more minute consideration of these relations may be seen in Stilling's Work, and in " Mikroskop. Anatomic," II. 1, pp. 458-462. Although a favorable judgment cannot be given upon Stilling and Wallach's work on the spinal cord, I am still very far from disposed to look down upon Stilling's anatomical writings in general, as would seem to have been the fashion for some time past. I am much rather of opinion, in which R. Wagner also coincides, that we have great reason to thank this author for his works on the medulla oblongata and pons Varolii ; for although there are some thfngs in them which cannot be maintained, and sufficient attention is not paid to the elementary con- stituents, still it cannot be denied that they contain a mass of important facts. I have tested, if not all, still the most important of Stilling's statements, and have found them almost all fully confirmed, and am, therefore, glad to take this opportunity of naming him, as the observer to whom we are indebted for the first accurate investigation of the course of the fibres in the central organs. I would also here, add : 1, that in further investigations of this kind, chromic acid, or chromate of potassa, is to be preferred to alcohol, particularly also when caustic soda is cautiously employed for the tracing of the course of the nerve- fibres in the gray substance thus rendered transparent; and, 2, that in conjunction with lower magnifying powers, the most powerful should be employed, and the relations of the elementary constituents should also be otherwise accurately investigated. The question as to the origin of the nerves in the medulla oblongata, presents itself as one of the most difficult nature. Most anatomists have hitherto been content to trace the roots of the nerves as far as one or the other column ; but this is not sufficient. All the nerves enter at least once, or even several times, into gray substance, in which, and no- where else, are their origins to be sought for. Now, it must be con- fessed, that through Stilling's great pains, the fruits of which I can, as it may be said, fully confirm all the ten pairs of nerves at present under consideration have been traced in their roots, as far as perfectly definite points of the gray substance ; but now comes for the first time the further question : do they commence in these situations, or do they 378 SPECIAL HISTOLOGY. proceed beyond them ? As true origins in the brain have never yet been seen with certainty by any one, there remains nothing but physio- logical analogies and reasons. As regards the former, we see in all the spinal nerves, that they first penetrate transversely as far as the gray substance, and then, only passing through this, join the white columns, and we may thence suppose that the cerebral nerves, which, in general, so closely resemble them, are in the same condition, and the more so, because these also at first penetrate transversely into the interior of the medulla, and the gray substance, with which they come in contact, corresponds with that of the cord. To this may be added also, that if we make the ten last cerebral nerves terminate in the gray substance, into which they may so readily be traced, the decussated influence of the parts above, upon them, which appears to be established by patho- logical phenomena, cannot be explained in the case of any one of them except the trochlearis, which decussates before it reaches its gray sub- stance. Now, in the accessorius and hypoglossus it is actually possible to see that the fibres come out from the gray substance, reached by them in the first instance, and afterwards decussate ; and the same thing is also at least probable* in the oculo-motorius ; so that I think it may be, that all the nerves now in question undergo decussation, and do not terminate in the so-termed nuclei of Stilling. Further investiga- tion will have to show whether this [decussation] takes place in the floor of the fourth ventricle, as would appear to be the case ; whether all the fibres of these nerves take part in it ; and where the fibres pro- ceed to after decussation. With respect to the latter, it may be sup- posed from analogy with the spinal nerves, that the true origin of the cerebral nerves is probably not in the medulla oblongata, but in the corpora striata and optic thalami. Of that portion of the portio major n. trigemini, which is continued into the restiform body, this may espe- cially be remarked, that it certainly does not originate in that part, but winds round it to somewhere above, as is the case also with the n. acces- sorius. However, in stating, in accordance with what has been said, that I do not consider it directly probable, that the sensitive and motor cere- bral nerves originate in the medulla oblongata and pons, it is by no means intended to imply that these parts may not, as central organs, exert some influence upon them and the more deeply placed nerves. If the medulla oblongata preside over the respiratory movements, if it and the pons be the agents of multiplied reflex motions, this may be the case, without its following that all the nerves called into action should terminate in them, and simply for the reason that the gray substance, so abundantly contained in them, influences the nerves which traverse it, exactly as must be supposed to be the case in the spinal cord. THE NERVOUS SYSTEM. 379 115. The cerebellum, with respect to the distribution of the ele- mentary tissues, exhibits tolerably simple conditions, gray substance occurring only on the surface of the convolutions, in the nucleus* den- tatus, and in the roof of the fourth ventricle ; all the remainder con- sists of white substance. The latter is wholly constituted of parallel, probably unbranched, dark-bordered nerve-fibres, possessing all the characters of central fibres (softness, proneness to become varicose, easy isolation of the axis-cylinder, &c.), are essentially alike in all situations, as far as their condition can be observed, and present a diameter of 0-0012-0-004 of a line in the extremes, and of 0.002 of a line in the mean. The gray substance occurs, in the first place, very scantily in the roof of the fourth ventricle above the velum medullare inferius, in the form of brown nerve-cells, measuring 0-02-0-03 of a line, scattered in the white substance, and recognizable by a sharp eye without further aid (the substantia ferruginea superior) ; and, secondly, in the nucleus dentatus, the grayish-red lamella of which contains a considerable number of yellowish pigment nerve-cells of a medium, size (0-008- 0-016 of a line) with four or five processes, and which have no direct connection with numerous nerve-fibres proceeding from the nucleus dentatus into the medullary substance of the hemispheres, which pass through among them. The relations of the gray substance on the surface of the convolutions of the cerebellum are more complex (vide " Mikr. Anat.," PL IV. fig. 4). It consists everywhere, as is well known, of a layer, internally of a rusty color, externally gray, which, except in the fissures, where the internal layer is most usually thicker, presents pretty nearly the same, but not everywhere an equal thickness. The internal ferruginous layer Contains nerve-fibres and large masses of free nuclei. The former arise, without exception, from the white substance, and run, in general, parallel to each other, although on a transverse section of any convolution slightly diverging in a penicillar manner, directly into the ferrugineous layer. Within this layer they also run from within to without as far as the gray layer, but are broken up into numerous, for the most part, fine fasciculi, which are much inter- laced, so that the whole ferrugineous layer is penetrated by a close but delicate network of nerve-fibres, which recalls in appearance the ter- minal plexuses in peripheral parts, as for instance, in the n. acusticus, in the follicles of the vibrissw, &c. In the meshes formed by these nerve-fibres lie a vast number of opaque, round corpuscles, measuring 0-002-0-004, in the mean 0-003 of a line, which are nothing else than free nuclei, and which frequently also exhibit a distinct nucleolus, and not unfrequently other granules. In their passage through the ferrugineous layer, the nerve-fibres of the white substance become gradually attenuated, most of them to a 380 SPECIAL HISTOLOGY. diameter of 0-0012 of a line, and in this state enter the external gray layer. This layer, although to outward appearance everywhere per- fectly homogeneous, consists of two not well-defined laminae, the inner of which contains nerve-fibres and very well-marked, large nerve-cells, whilst the outer presents nothing but a finely- granular, pale, light-yel- lowish substance, which is distributed generally throughout this gray layer, and contains no nerve-cells. The granular substance agrees chemically, morphologically, and physically in all respects with the already-described contents of the nerve-cell ; it is tenacious, elastic, rendered more opaque by acetic acid, and more transparent in caustic soda, in which it is, for the most part, dissolved, and exists in the purest form in the outer half of the gray layer, that is to say, next to the pia mater. The small nerve-cells, speaking generally, are very few in number and indistinct. They occur scattered throughout the gray layer, having a diameter of 0-004-0-008 of a line, more frequent towards the ferrugineous layer than more externally, and when successfully prepared, particularly by means of chromic acid, most of them exhibit delicate processes, which, however, can never be traced to any distance, and are frequently torn off close to the cells. Besides these cells, there also occur here and there, but on the whole rarely, nuclei of 0-002-0-0048 Fig. 148. of a line, which, to all appearance, are free, as they are met with even in the most carefully -made preparations. Entirely different from these smaller elements, and very peculiar, are the large cells of the gray layer (Fig. 148) discovered by Purkinje. These cells, measuring 0-016-0-03 of a line, and of a round pyriform or oval figure, with finely-granular, colorless contents, occur only in the innermost portions of the gray, FIG. 148. Large cells of the gray layer of the cortical substance of the human cere- bellum, magnified 350 diameters. THE NERVOUS SYSTEM. 381 close to the ferrugineous layer, and they are, not unfrequently, at least some of them, partly imbedded in its nuclei, in single or multiple layers, and presenting 2-3, rarely 1-4, long and much branched processes, directed particularly towards the outer surface of the convolutions, which are, almost without exception, at all events the strongest of them, given off from the sides of the cells which look from the ferrugineous layer. At their origin these processes are even 0-007, or as much as 0-008 of a line thick, and extremely finely granular or very delicately striped. As they proceed they become more homogeneous, and at the same time divide into very numerous and extremely slender branches, so that at last, from each process a large bundle of very fine filaments, having a diameter, in the finest, of scarcely 0-0002 of a line, is produced. A portion of these fibrils penetrate more horizontally into the gray layer, although most of them stretch directly outwards, and appear to extend nearly to the outer surface of the gray layer. That they extend very far is certain, for in preparations made with chromic acid, I have iso- lated some measuring 0*15-0-2 of a line, which were still not the finest ; and in successful perpendicular sections through the cortical layers of the convolutions, their principal branches appear as parallel, slightly undulating fibres in close contiguity, extending through more than two- thirds, or even three-fourths, of the gray layer, to which they give a peculiar striated aspect. Whilst the principal prolongations of the pro- cesses are, in this way, continued through the gray layer, they give off their branches at acute or right angles, whence not unfrequently a second striation is produced, crossing the one just described at a greater or less angle. In the innermost portion of the gray layer, among the large cells, there moreover exists some nerve-fibres ; but which, owing to their deli- cacy and the ease with which they are destroyed, it is very difficult to trace. Quitting the ferrugineous layer, and forming a continuous plexus, they are distributed in the inner third of the gray lamina among the large cells and their processes ; there mode of termination has escaped my observation, the result of which amounts only to this : 1, that they become finer and paler, decreasing from their original thickness of 0-0012, ultimately to one of 0-0006 and 0-0004 of a line, their dark outlines also being replaced by a paler contour ; 2, that they certainly do riot form terminal loops, such as Valentin and Hyrtl, who have pro- bably mistaken a fine plexus for such, think they have noticed ; but be- coming isolated, and running in a more straight direction, and almost as pale as the processes of the nerve-cells at the border of the inner third of the gray lamina, are lost towards the middle of it. The crura cerelelli are composed of nothing but parallel nerve-fibres, without any admixture of gray substance, corresponding with those of 382 SPECIAL HISTOLOGY. the medullary substance of the cerebellum itself, as a continuation of which they are to be regarded. 116. G-anglia of the Cerebrum. The three pairs of cerebral gan- glia, the corpora quadrigemina, optic thalami, and corpora siriata, all con- sist of bulky collections of gray substance, and of nerve-fibres ; the former of which are in part quite isolated (corpus striatum), in part mutually con- nected, and with more deeply lying portions of gray substance (thalami opticij corp. guadrigemind) ; the latter connect the ganglia, on the one hand with the cerebellum and medulla oblongata, and on the other with the hemispheres of the cerebrum. The corpus striatum contains two large gray nuclei, the nucleus caudatus anteriorly and superiorly, and the n. lenticularis posteriorly and inferiorly, which are, however, connected in front, constituting a single mass ; and besides these, the slender n. tceniceformis, with the amygdalce external to the lenticular nucleus, and is in connection prin- cipally with the basis of the cerebral peduncle or continuation of the pyramid which expands in it, forming numerous white fasciculi. The gray substance presents, as almost universally, nerve-cells and fine nerve- fibres. The former, which measure from 0-006-0-018 of a line, are, in part, colorless, and in part, contain pigment, as, especially, in the cau- date nucleus and third segment of the lenticular nucleus ; they are fur- nished with from two to five processes, and occur in greater numbers according to the depth of color of the gray substance. The nerve-fibres may be referred for the most part to those of the basis of the crura cerebri. They present the form of dark-bordered tubes from 0-0012-0-005, most of them from 0-002-0-004 of a line in size, which, running parallel and close together in a straight direc- tion, enter the first division of the lenticular nucleus, and the most anterior, thickest portion of the caudate nucleus. When traced further in the lenticular nucleus, it will be seen that they form larger and smaller fasciculi, decreasing somewhat in size (most of them measuring from 0-0012-0-003 of a line) and that, passing straight through the more scanty gray substance of the first divisions of the lenticular nucleus, they are all ultimately lost, spreading out in a penicillar form in its outermost and largest division. That is to say, white fasciculi mea- suring from 0-04-014 of a line, with fibres of 0-0012-0-002 'of a line, enter this division of the nucleus from the second ; and these fasciculi in close contiguity, slightly diverging and subdividing into smaller bun- dles, are continued further in a direction towards the outer border of the lenticular nucleus, before reaching which they disappear to the naked eye. If traced microscopically in preparations made with chromic acid, it is apparent, that the fasciculi proceed nearly to the outermost part of the lenticular nucleus, though gradually broken up THE NERVOUS SYSTEM. 383 into smaller bundles and separate fibres, and most intricately interlaced with each other. That these fibres terminate here, and do not proceed any further into the medullary substance of the hemispheres, may be considered as made out, not the faintest indication of any further con- tinuation being afforded, which, if it existed, could not escape being seen : on the other hand it is doubtful how they terminate here. All I have to state on the point is this : that the fibres of the nerve-fasciculi, entering the third division of the lenticular nucleus, as may be directly observed in a very great many instances, gradually become so much attenuated, as ultimately to measure not more than 0-0008, 0-0006, or even hardly 0-0004 of a line, and present an almost entirely pale aspect, so that they can scarcely any longer be distinguished from the finer processes of the nerve-cells ; with which in fact, unless everything is deceptive, they most probably are actually connected. All the fibres, also, which enter the caudate nucleus, present exactly the same condi- tions ; some of these enter the nucleus directly from the basis of the cerebral peduncle, others, which appear in its thinner portion, are manifestly derived from the lenticular nucleus, the first two divisions of which they traverse in the first instance ; in this case, also, there is no transition of the fibres into the medullary substance of the hemispheres, but a separation of the fasciculi into a plexus of the finest, almost non- medullated fibres takes place, and probably a connection between them and the cells. Besides the above described, in any case very numerous, nerve-fibres derived from the cerebral peduncles and terminating in the corpora striata, the nuclei of those bodies contain a considerable number of other fibres, whose origin it is, in part, difficult, and, in part, impossi- ble to assign. I think I can trace one set of these fibres to their source. In the most external part of the large nucleus of the corpus striatum, we find, on making various sections, a considerable number of moderately strong fasciculi, though not visible to the naked eye, which in their relative thickness and the diameter of their tubes (0-0012-0-002 of a line) differ from the fibres derived from the crus cerebri, which in this situation are reduced to the most extreme attenuation and dispersed in a plexiform manner. It is easily seen that all these fasciculi proceed from the medullary substance of the hemispheres ; and, as it appears, after they have run a certain distance parallel with the surface on the border of the nucleus of the corpus striatum, that they enter it. Many of these fibres are continued directly from the medullary substance into the ganglia, and, in this way, decussate, at right angles, with the former fibres. Assembled in fasciculi, these fibres penetrate more or less deeply into the gray substance of the corpus striatum, and of the third division of the lenticular nucleus ; and these terminate, as I think I have observed, without any considerable expansion, the formation of 384 SPECIAL HISTOLOGY. a plexus, or undergoing any farther decrease in size, their fibres form- ing loops with closely approximated sides. Although, speaking relatively, it is not difficult to make out the struc- ture of the corpus striatum, at all events, in its principal features, it is quite otherwise with the optic thalami and corpora quadrigemina, chiefly because the nerve-fibres in these situations are not so much assembled into fasciculi, but are more isolated and most intimately intermixed with the gray substance, on which account they cannot be traced to any great distance. The examination of the gray substance itself, however, is perfectly easy even in these bodies, arid its elements the nerve-cells present nothing peculiar, except that, in the optic thalami, they are for the most part more deeply colored, whilst those in the corpora quadrige- mina are paler. With respect to the nerve-fibres, it is quite certain that the superior portion of the crura cerebri, that is to say, the crura cerebelli ad corpora quadrigemina^ the continuations of the olivary columns, portions of the corpora restiformia, and the eminentice teretes, pass into the ganglia now under consideration, although I have not as yet succeeded in eliciting anything determinate as to the course they take. But I think it may be stated, that the fibrous masses above named, in great part at least, are not continued into the medullary sub- stance of the hemispheres, because, on the one hand, most of their fibres decrease from the original diameter of 0*0012 0'004 of a line down to the smallest, or less than 0-001 of a line ; and on the other, because no such passage of the fibres can be perceived on that side of the optic thalamus, which looks towards the medullary substance of the hemi- spheres. The superficial white investment, however, of the ganglia in question, must be excepted, which in any case may eifect a relation between them and the hemispheres, as its fibres, measuring 0'001-0'003 of a line, or even more, disposed in fasciculi, and crossing each other ' horizontally in various directions, do not appear to terminate in it. Neither is the relation of the optic thalami to the corpora quadrigemina, and that of the fornix to the latter, by any means clear, so that it is pleasing, at all events, to find that another important question admits of a more satisfactory solution. When the external portion of the optic thalamus is examined, it will be found that it adjoins a considerable mass of white substance, which at first sight appears to be a continuation of the basis of the cerebral peduncles passing below and external to the optic thalamus, between the lenticular and caudate nuclei of the corpus stria- turn, to enter directly into the medullary substance of the hemispheres. Closer observation renders it obvious, that this white substance, as has been said before, in part enters the corpus striatum, particularly the lenticular nucleus, and in part radiates from without inwards, from the hemisphere into the optic thalamus. That is to say, very numerous white fasciculi, visible even to the naked eye, coming from the hemi- THE NERVOUS SYSTEM. 385 sphere throughout the entire height of the thalamus, enter the latter, run towards the superior surface to the superior and internal border, and the pulvinar, being ultimately lost exactly in the same way as are the fibres continued from the cms cerebri into the corpus striatum ; that is, these fasciculi, the elementary fibres of which originally measure 0-0012-0-0025 of a line, ultimately subdivide into extremely close plex- uses composed of fibres of the most extreme fineness, 0-0004-0-0008 of a line, the terminations of which cannot be traced. I will just notice the constitution of some structures connected with the above-described ganglia. The substantia nigra of the cms cerebri presents pigment-cells precisely similar to those of the substantia fer~ ruginea, except that they are for the most part rather smaller, and have fewer processes, surrounded with nerve-fibres of the finest, and also of the stronger kind. The commissura mollis contains smaller cells, with 1, 2, 3, and more processes, and light-colored pigmentary contents; and besides these, very many, plexiform, vertical, and horizontal, fine fibres of 0-0012-0-0016 of a line, with some still finer, less than 0-001, and a few stronger measuring as much as 0-004 of a line. The pineal gland exhibits pale, rounded cells, without any processes, and scattered nerve-fibres of 0-001-0*002 of a line, and also, generally, a considerable quantity of sabulous matter (brain-sand) (vid. 118). Its peduncles, their anterior prolongations, and the commissura posterior, contain fibres measuring 0-001-0-003 of a line, and are composed in part also of the finest fibres. The floor of the third ventricle presents, immediately beneath and behind the anterior commissure, extremely large, and smaller, colorless cells, with from one to four, occasionally very thick processes. These are lodged in great number in a close plexus of fine fibres of 0-0004-0-0012 of a line; and cells, in other respects exactly similar, though not quite of the same size, also exist in the corpus mam- millare, likewise intermixed with very numerous fibres of the finest sort; there are other still smaller cells of 0-008-0-012 of a line, for the most part with only two processes, in the tuber cinereum. The hypophysis cerebri contains, in its anterior, reddish lobe, no nervous elements ; but rather, according to Ecker (art. " Blood-vascular Glands," in Wagner, " Handw. d. Physiol."), the elementary tissues of blood-vascular glands ; that is to say, a vascular stroma of connective tissue, in the interstices of which, lie vesicles (cells?) measuring 0-030-0*090 mm , containing sometimes only nuclei, and a fine granular substance, sometimes distinct cells, in older persons also colloid-like masses. The posterior, smaller lobe consists of a fine granular substance, with nuclei and bloodvessels, and also contains fine, varicose nerve-fibres, which, like the vessels, descend from the infundibulum. 117. Hemispheres of the Cerebrum. The white substance of the 25 SPECIAL HISTOLOGY. hemispheres of the brain consists entirely of nerve-fibres, of 0-00012- 0-003, on the average 0-002 of a line in size, without any admixture of gray substance. These fibres, of whose special course, we, as yet, know extremely little, never form plexiform interlacements or fasci- culi, but all run in parallel, and most generally, straight lines, and undoubtedly proceed from the corpus callosum and ganglia of the cere- brum as far as the superficial gray substance, whilst it must remain undetermined whether, in their course, they divide or not. But besides these fibres, omitting also the commissura anterior, ihefornix, and the origin of the optic nerves, the hemispheres contain others crossing the former at right angles. I have found these fibres, in the first place, on the outer side of the corpus striatum, in which situation they are to be referred, in part, to the fibres which enter the corpus striatum from the hemispheres and terminate in it ; perhaps, also, in part, to the expan- sion of the corpus callosum in the inferior lobes ; and secondly, in the most superficial layer of the white substance, near the gray cortical sub- stance, where they occur in not inconsiderable numbers, and running, in part, obliquely ; but of their origin nothing satisfactory could be ascer- tained. Whether there are still other, and what traces of fibres, the future must show. The more intimate structure of the gray substance of the convolutions is tolerably manifest (vid. "Mikroskop. Anatomie," PL IV. fig. 2). It is most conveniently divided into three layers, an external, white ; a middle, pure gray ; and an internal, yellowish red. The latter, in thick- ness almost equal to the other two, usually presents, on its outermost border, a clear, frequently white streak, and occasionally, more inter- nally, a second, thinner and less white layer, so that there are in fact four or even six successive laminse ; 1, a yellowish-red layer (inner part) ; 2, the first white streak ; 3, yellowish-red layer (outer part) ; 4, second white streak ; 5, the gray layer ; 6, superficial white layer. The gray substance contains, in its whole thickness, both nerve-cells and nerve- fibres ; and besides these, much granular matrix-substance, exactly like that of the cerebellum. The nerve-cells are not easily investigated, except in preparations in chromic acid, and in all the three layers they agree in this respect, that by far the greater number of them are fur- nished with from one to six processes, which give off numerous branches, and ultimately form extremely fine, pale fibrils of about 0-0004 of a line in diameter, differing, however, in respect of size, number, &c. In the superficial white layer the cells are few, small (0-004-0-008 of a line), with one or two processes, and scattered in an abundant, finely granular matrix. The middle or pure gray layer, most abounds in cells, which in it, are closely aggregated also in a granular matrix. Their size varies very considerably, some being very small (0-0030*005 of a line), frequently appearing as little more than nuclei, whilst there are many THE NERVOUS SYSTEM. 387 others of larger dimensions, up to 0-016 and 0-02 of a line (Fig. 149). Their figure is pyriform or fusiform, tri- or multangular, also perhaps more rounded, by far the greater number having from one to six pro- cesses, usually three, four, or five ; and where this is not the case, they may have been torn off in the preparation, since stumps of them may be very readily noticed in the cells, which are altogether very delicate. In the innermost yellowish-red layer, lastly, the cells are again rather more scanty, though still extremely abundant, otherwise presenting the same characters as those in the gray substance, having sometimes pale, sometimes pigmentary contents ; the latter in the inner layers more particularly, and in old persons. The nerve-fibres of the gray substance of the convolutions, arise, as it is easy to demonstrate, from the medullary substance of the hemispheres, Fig. 149. and penetrate, bundle after bundle, directly, and all parallel, into the yellowish-red layer. Arrived here, many fibres separate from the rest, and penetrate the yellowish-red layer in all directions, but more espe- cially parallel to the surface, and consequently crossing the main fasci- culi. When these horizontal fibres are more closely aggregated, they produce the above-described whiter or clearer streaks in this layer, the outer of which streaks is situated exactly at the point, where the fasciculi which enter the gray substance, are lost. In fact, as these proceed more outwardly, they constantly decrease in size, owing to their giving off lateral FIG. 149. From the internal portions of the gray layer of the convolutions of the human cerebrum, magnified 350 diameters. Nerve-cells: a, larger; 6, smaller; c, nerve-fibres with axis-cylinder. . 388 SPECIAL HISTOLOGY. fibres, and to the attenuation and separation of their elements, until, when they have reached the gray layer, they become lost to sight, although if more closely traced they may still be perceived as intricately interlaced fibrils of the utmost fineness, and with scarcely any appearance of dark contours, only that there are a certain, though smaller number of fibres, which, upon reaching the gray layer, do not lose their breadth and dark contours, but are continued in a straight or oblique course through it, extending horizontally to a further distance, in the outer white layer. In this layer, consequently, we find a considerable number of finer, and of the very finest fibres (Fig. 150), crossing each other in various directions, and in - 15 - several superimposed layers, which, are obviously, as to their origin, to be referred to those arising from the reddish-gray layer ; and which probably also, as Remak has assumed, are derived, at the basis of the cerebrum, from the anterior extremity (knee) of the cor- pus callosum. How these fibres are related to the cells in the white layer is doubt- ful, although this much is certain, that many of them return into the gray-red substance from which they arose, or in other words from loops, which were first described by Valentin, and which I have very frequently and distinctly noticed in chromic acid preparations treated with caustic soda. I have also observed, in the gray-red substance, isolated loops with closely ap- proximated sides, and also with their convexity looking towards the surface of the brain. The fasciculi of the gray-red substance contain fibres which, at first, measure 00012-0-003 of a line, but almost all of which ultimately decrease in size down to 0-001, and, in the gray substance, acquire the diameter of the smallest nerve-tubes, 0'0004 O'OOOS of a line. The fibres given off from these fasciculi, within the gray-red layer are, in part, of the same size as those in the fasciculi, which is the case particularly with those of the thicker white streak, in part finer. The fibres which proceed from these fasciculi into the superficial white substance, are also, usually, of greater size, up FIG. 150. Finest nerve-tubes of the superficial white substance of the human cerebrum; magnified 350 diameters. THE NERVOUS SYSTEM. 389 to 0*003 of a line, many of which form loops ; there are, however, in this layer together with these, some of the finest fibrils, measuring 0*0004 of a line. Notwithstanding all my endeavors, I have been unable to discover any connection between the nerve-cells and fibres, in the cortical portion of the cerebrum ; but the existence of such a connection would appear to me to be nowhere so probable as here, where the nerve- fibres, especially in the pure gray layer, assume so much the appearance of processes of the cells, as almost to deceive the observer, and where, in any case, they terminate. There are in this situation an immense number of nerve-fibres, so fine and pale that they could scarcely be regarded as such, were they not straighter than the processes, and did they not, particularly when treated with soda, exhibit minute varicosi- ties. If anywhere in the central organs, an origination of nerve-fibres exists here, although it is quite intelligible that it should not yet have been observed, when we consider the delicacies of the structures con- cerned. The corpus callosum presents, in the anterior portions of its body above the septum pellucidum, the fornix, and the corpora striata, dull gray streaks, scattered in the white substance, in which the microscope discovers no cells, but only clear vesicles of 0-003-0-004 of a line, with nuclei, in the midst of numerous nerve-tubes, similar to what are met with in certain fasciculi of fibres of the corpus striatum. Besides this, Valentin (" Nervenl.," p. 244) occasionally noticed on the surface of the corpus callosum, between the raphe and the strice obtectce, a delicate gray investment with clear nerve-cells, which appears to be identical with the fasciola cinerea, which is continued into the fascia dentata of the pes hippocampi major (vid. Arnold. " Bemerk," p. 87) ; otherwise the corpus callosum is wholly composed of white medullary substance with parallel nerve-fibres of exactly the same aspect and diameter as those of the medullary substance of the hemispheres. The same may be said, also, of the commissura anterior and fornix, which latter, however, comes in contact with gray substance in very many ways, as in the optic thalamus, from the tuberculum anterius of which its radix descendens arises ; in the corpus mammillare (vid. sup. 116) ; at the commence- ment of the radix ascendens ; in the floor of the third ventricle, to- wards which some delicate fasciculi of the radix ascendens are given off; and at its point of junction with the septum pellucidum, which latter, together with a common thick coat presenting much connective tissue and corpuscula am.ylacea (vid. 118), exhibits numerous plexuses of the finest kind of nerve-fibres and nerve-cells, exactly as does the tuber cinereum. The fibres of the fornix measure, in its white portions 0-0008-0-005, mostly 0-002-0-003 of a line; in the optic thalamus (upper part), and in the corpus mammillare^ the fibres are only of the finest sort, measuring 0-0004-0-001 of a line. The cornu ammonis, and the calcar 890 SPECIAL HISTOLOGY. avis (pes hippocampi minor), present nearly the same conditions as those of the cerebral convolutions ; in the gray substance of the former, however, there is a peculiar sort of streak, containing chiefly round cells without processes, and closely aggregated. Lastly, we have to consider the origin of the first two pairs of nerves. The olfactory nerve contains, in the white portion of the tractus olfacto- rius, fine nerve-fibres, of 0-0004, or at most 0-002 of a line, the finest, pale-bordered, and apparently non-meclullated ; and besides these, also some gray substance, with fine granular structure, and cells of 0-007- 0-008 of a line. These cells, with some still smaller, down to a diameter of 0-003 of a line, many with branched processes, constitute the bulbus n. olfactorii, intermixed with numerous fine fibres, the relation of which to the cells and to the true nerves of smell cannot be made out. The optic nerve arises, with its tractus divided into two crura, from the corpora geniculata, and the corpora quadrigemina and optic thalami ; besides which, it is also in connection with the crura cerebri, the sub- stantia perforata antica, the tuber cinereum, and the lamina terminalis. The precise origin of its fibres, dark-bordered tubes of 0-002 of a line, is in Man unknown, but to draw conclusions from experiments in ani- mals, it exists principally in the corpora quadrigemina, whilst we know that they partially decussate in the chiasma (commissure). In this body, however, there are, as stated by Arnold, Todd and Bowman, &c. : 1, fibres which do not decussate, but are continued from the tractus into the optic nerve of the same side ; and 2, commissural fibres, which may indeed be divided into an anterior and posterior set, the latter constituting a commissure between the two points of origin of the optic nerves, whilst the anterior could only unite the two retince. The existence of the first-named fibres is certain, although they are much more scanty than the decussating elements; but that of the others also can hardly be denied. Speaking physiologically, a commissure of the optic thalami and corpora quadrigemina may perhaps be explained, but a commissure also of the retince does not appear to be altogether impossible, because we know that the retina contains gray substance, and in it, nerve-cells with branched processes. With respect to the origin of the nerve-fibres in the brain and higher central organs, in general, it is several years since I first observed the origin of dark-bordered fine fibres from the processes of the nerve-cells in the spinal cord of the Frog ("Zeitsch. f. wiss. Zool.," vol. I. p. 144, tab. xi. Fig. 7). In man I have not as yet been so fortunate as to per- ceive anything of the sort with certainty, though I do not myself doubt that similar conditions obtain in this case also. In fact, R. Wagner and Leuckart think they have seen, in man, the processes of the many-rayed cells in the substantia ferruginea, passing into nerve-tubes (" Gott. An- THE NERVOUS SYSTEM. 391 zeig.," 1850, No. 43); as has Prof. Domrich, in the cortical substance of the cerebellum, according to a communication to me by letter. R. Wagner again (" Grb'tt. Nachr.," Oct. 1851), has, recently, also found in the electric lobes of the Ray, that from the many-rayed ganglion-globules or nerve-cells, one or more, rarely two, unbranched processes are con- tinued into dark-bordered fibres. He now explains this transition, in the same way as before, saying that the processes were continued as axis-cylinders into the dark-bordered tubes, in which Leydig, who has observed the same transition in the cerebellum of the "Hammer-headed Shark," agrees with him, as does Stannius, in the case of Petromyzon. Nevertheless, it is still not quite evident to me, that any condition should exist in this case, different from that which obtains in the ganglia, where the processes of the nerve-cells are not simply axis-cylinders, but also have a coat, which investing the medullary matter of the nerve, is con- tinuous with the sheath of the dark-bordered tubes ; although, seeing that the presence of tunics on the nerve-corpuscles of the central organs, and their processes, in general, is still a disputed point, I am prepared to admit that the fact may be otherwise. These researches have opened the way, and I have no doubt, as I have already said in rny Microsco- pical Anatomy, that in time we shall succeed in demonstrating the origin of dark-bordered tubes in many other situations in the central organs, in man, and other animals. On the other hand, however, supported by repeated investigation of the human brain, I must assert, that it is in the highest degree probable that in many places it will be altogether impossible to demonstrate the origin of fibres from nerve-cells, because very many nerve-tubes, particularly those of the cortical substance of the cerebellum and cerebrum, ultimately become so pale and slender, as not to allow of their being distinguished from the processes of nerve- cells. Whether the loops which distinctly exist in the convolutions of the cerebrum, and which I have also seen in the corpora striata, are ter- minations, or whether free prolongations of nerve-tubes exist, we know not, and the less so because it cannot even be asserted that certain fibres really so terminate. It may fairly be assumed that the fibres of the corpus callosum and the commissural fibres in general, commence in the one hemisphere in connection with cells and terminate in the other, and that the fibres which proceed from the surface of the convolutions to the optic thalami and corpora striata terminate in the latter, but to assert, that it is so, is impossible, notwithstanding the visible loops, for it may be that these latter are not terminations at all, and that the fibres in question are all in the one place and the other in connection with nerve- cells. That nerve-fibres should originate independently of any connec- tion with cells would be contrary to all analogy, but in such an obscure subject we must always be prepared for much that is new, and be careful not wholly to reject any possibility, simply from d priori considerations. 392 SPECIAL HISTOLOGY. Several authors have noticed divisions of the nerve-tubes in the central organs, such as, among the older ones, Ehrenberg, Volkmann, E. H. Weber, and more lately also, Hessling ( u Fror. N. Notiz.," Ap. 1849, Jenaische, Ann. I. p. 283), E. Earless (ibid., p. 284), and Schaffner (" Zeits. f. rat. Med.," IX.) in the brain of various vertebrate animals, especially at the junction of the white and gray substance. I am not inclined to doubt these statements, especially the latter, but I cannot avoid the remark, that in the human brain, I have, hitherto, in vain sought for divisions of this kind, and have had many hundreds of fibres from the gray substance before me, under the most favorable circum- stances, which presented no indications of the sort, whilst I have inva- riably found such divisions in the spinal cord (vid. supra). The many- rayed nerve-cells with branched processes are not as yet fully known in all their relations. I have described their processes (as will be univer- sally allowed, correctly), as a sort of pale, non-medullated nerve-tubes, and have isolated them occasionally to the extent of J and J of a line, without being able to notice anything more with regard to their termination, than the fact of their ultimately assuming an extreme de- gree of fineness. R. Wagner states, that those processes, which do not pass into dark-bordered nerve-tubes, serve to connect the separate nerve- cells together, but in so doing he manifestly says more than actual observation warrants, as he has, hitherto, seen such a connection, only in the electric lobes of the Ray. In the present state of neural Anatomy there is nothing which should be more carefully avoided than the general application of isolated observations, and I am therefore of opinion that this question must as yet be regarded as an open one. It may indeed be very consonant with physiological considerations, to explain the reflex and alternating actions of separate sections of nerves by such connec- tions between the cells, but it is precisely for that reason, that we should be the more careful, and the more so because less obvious theories explain the conditions just as well. I conclude, therefore, from the observations hitherto made, only this much, that nerve-cells may anastomose, leaving it to future inquiries to decide, whether they do so universally and with all their processes, or whether in certain situations the latter do not stretch out without any attachment, exerting a mutual influence and affecting the nerve-fibres simply by juxtaposition, as appears to be the case in the large nerve-cells of the cord and the roots of the spinal nerves. 118. Membranes and Vessels of the central Nervous System. A. MEMBRANES. 1. Spinal cord. The dura mater *. meninx fibrosa is a whitish yellow, occasionally glistening, firm, tolerably elastic membrane, consisting of parallel and mostly longitudinal fasciculi of connective tis- sue, and of a fine, elastic, fibrous network in almost equal proportions. THE NERVOUS SYSTEM. 393 The outer surface of the dura mater is, in front, where the membrane is always at least as thin again as behind, pretty closely united to the fas- cia longitudinalis posterior of the spinal column, free posteriorly and on the sides, and separated from the arches of the vertebrae and their peri- osteum by a space, occupied by a lax connective tissue with anastomosing fasciculi scarcely more than 0-004-0-005 of a line thick (reticular con- nective tissue), containing a few elastic fibrils (convoluted and longitu- dinal), and round, fusiform and stellate nucleated cells, similar to the formative cells of the connective tissue, and besides these with larger or smaller aggregations of frequently gelatiniform, transparent fat with cells containing serous fluid. The vessels of this space are in part the well-known plexus venosi, in part finer vessels, and also a network of the finest capillaries in the lax connective tissue itself. The internal sur- face of the dura mater would appear, from what is generally stated, to be lined with an outer lamella of the arachnoid ; nothing, however, is to be seen but an epithelium, composed of polygonal, flattened, nucleated cells, on the innermost layer of the dura mater, and not a trace of any special substratum. The ligamentum denticulatum has no epithelium, and like the thickened processes of the pia mater, to which it is attached, presents, in all respects, a structure similar to that of the dura mater. The arachnoid membrane is constituted, not of an external and inter- nal lamella, the former of which is united to the dura mater, the latter free, but of a single layer corresponding to the internal lamella of authors. It is an extremely delicate, transparent membrane, exactly correspond- ing in extent and relations to the dura mater. Its outer surface, in the posterior mesial line of the cervical portion, is connected with the dura mater, above, by tolerably strong processes, lower down, by delicate fibrils, elsewhere it is perfectly smooth and glistening, which appearance depends upon an epithelium precisely like that of the dura mater, and it is merely in apposition with that membrane, as the pulmonary pleura is with the costal. The internal surface of the arachnoid is also smooth, though without epithelium ; it is separated from the spinal cord, and cauda equina by a large interspace, the subaracJmoid space, affording, however, numerous slender processes to the pia mater and the roots of the nerves, which processes not only accompany the vessels and nerves, but occur, especially in the posterior mesial line, arranged in a consecu- tive series, and occasionally, particularly in the cervical region, form a perforated or complete septum. As regards its intimate structure, the arachnoid contains, chiefly, reticularly anastomosing bundles of con- nective tissue of 0-001-0-004 of a line, which are so united as to form lamellae, some external with more slender, and some internal with stronger fasciculi, and which are usually so surrounded by fine elastic fibres, as to present a moniliform appearance when swollen by the appli- cation of acetic acid (Fig. 23). In many fasciculi, these fibres are very 394 SPECIAL HISTOLOGY. fine or wanting, others again, in addition, contain elastic fibres also in the interior. The vascular membrane, pia mater, very closely invests the spinal cord and the gray substance of the filum terminale, penetrating on the one hand into the anterior and posterior fissures, where it appears within the spinal cord in the form of slender processes, and affording, on the other, delicate sheaths to the roots of the nerves. It contains for the most part common connective tissue with straight fibres, and, more rarely, anastomosing bundles ; and besides these a good many nuclei often of a lenticular form, with a few elastic fibrils. Here and there are met with in the pia mater bright yellow or brown pigment-cells, of an irregular, fusiform figure with fine prolonged ends and measuring 0-04-0-05 of a line in length, which in the cervical region, owing to their greater num- ber, give the membrane, not unfrequently, a brown or even blackish color. 2. Brain. The membranes of the brain, though corresponding, in. general, with those of the spinal cord, yet present some differences. The dura mater, in this situation, consisting of the true fibrous membrane of that name and of the internal periosteum of the cranial bones, which, as the immediate continuations of the corresponding membranes of the spinal canal, become consolidated together at the level of the atlas, is, in general, thicker and also whiter than in the spinal cord. Its external or periosteal lamella, of a whitish-yellow color and rough, is attached more or less firmly to the bones, supports the larger vasa meningea, and is also otherwise more richly supplied with vessels than the internal proper dura mater, with which, at an earlier period, it was more laxly united, and from which, except where the sinuses are contained, it may not unfrequently be separated even in the adult. The internal lamella is less vascular, whiter, presenting in many places a glistening tendinous aspect, and on its surface is quite smooth and for the most part even. The processes of the dura mater, the greater and less falciform processes, and the tentorium, appear as prolongations of this internal lamella ; and between the two lamellge are situated, with few exceptions, the venous canals or sinuses of the dura mater. Both lamellae contain con- nective tissue of the same form as that in the tendons and ligaments, with, for the most part, indistinct bundles, and parallel fibrils, which either extend of a uniform size for considerable distances in it, or, espe- cially as in the sinuses, form small, tendinous bands, crossing each other in various directions, and containing among them a good many fine elastic fibres. The internal surface of the dura mater is lined with a single (according to Henle with more than one) layer of tessellated epithelial cells, of 0-005-0-006 of a line in size, with rounded or elongated nuclei measuring 0-002 0*004 of a line ; possessing no other covering which might be described as a parietal lamella of the arachnoid (vid. Luschka, Serose Haute, p. 64). THE NERVOUS SYSTEM. 395 The arachnoid membrane of the brain differs from that of the spinal cord, not so much in its structure as in its disposition. It is true, that in this situation also, there is but one lamella demonstrable as a mem- brane composed of connective tissue, which corresponds with the so- termed visceral layer of the arachnoid of authors, and is also very closely applied to the inner surface of the dura mater, but the arachnoid mem- brane here is in much more intimate relation to the pia mater. That is to say, instead of its being united with the latter, as in the cord, by scat- tered fibres and lamellae, it is, in the brain, in many situations, as on all the convolutions, and the projecting parts at the base of the brain, adherent to and coalescent with it, and, elsewhere, where this is not the case, united to it by numerous processes. For this reason, there exists, in the brain, no continuous subarachnoid space, but numerous, larger and smaller spaces, which only partially communicate. The larger of these spaces between the cerebellum and medulla oblongata, and under the pons Varolii, the crura cerebri, the fossa Sylvii, &c., open directly into the subarachnoid space of the spinal cord, whilst the smaller, corre- sponding to the sulci, and over which the membrane composed of connec- tive tissue is stretched, are perhaps partially in communication with each other, but, at all events most of them, not with the larger spaces just mentioned. The arachnoid, as has been correctly stated by Henle, is nowhere in connection with the lining membranes of the cerebral ven- tricles. The structure of the membrane is the same as in the spinal cord, except that the anastomosing fasciculi and spiral elastic fibres are for the most part thicker, measuring as much as 0*01 or even 0-02 of a line ; and the former frequently present, as it were, special and more homogeneous sheaths of connective tissue, beneath which, fat- and pig- ment-granules are often deposited. The outer surface is covered with an epithelium in all respects like that of the dura mater. The pia mater cerebri is more vascular but more delicate than that of the spinal cord, and covers all the elevations and depressions on the surface of the brain, if not very closely yet quite exactly, with the single exception of the floor of the fourth ventricle, above which it is stretched across from the calamus scriptorius, as far as the nodulus, the free border of the vela medullaria inferiora and the flocculi, forming the tela chorioidea inferior, from which points it proceeds to invest the under surface of the inferior vermiform process and of the tonsillce. The pia mater penetrates into the interior of the brain only at one point, viz., at the transverse fissure of the cerebrum, where it passes beneath the splenium corporis callosi, investing the vena maana G-aleni, as well as the pineal gland, forming the tela chorioidea superior, with the plexus chorioideus ventriculi tertii; and passing beneath thefornix, also constitutes the vascular plexuses of the lateral ventricles, which 396 SPECIAL HISTOLOGY. are continuous with the pia mater at the base of the brain, between the cms cerebri and the inferior lobe. With respect to its intimate struc- ture, the cerebral pia mater contains so many vessels, that in parts the connective tissue which forms the matrix appears as a subordinate con- stituent. It is rarely, as in the spinal cord, distinctly fibrous, for the most part more homogeneous, approaching in character " Reichert's mem- branes," or immature connective tissue, with a few nuclei and without elastic fibres. Occasionally, however, the pia mater also contains reticular connective tissue, as around the vena Craleni, the pineal gland, the larger vessels, and also on the cerebellum. Fusiform pigment-cells also occur here, as in the spinal cord, particularly on the medulla ob- longata, arid pons Varolii, but also, more anteriorly, at the base of the brain as far as within the fissure of Sylvius, in which situation I have noticed them even in the m. adventitia of smaller arteries. Those portions of the pia mater which are in relation with the ven- tricles, the telce chorioidece and plexus chorioidei, do not differ in their structure from other portions of the membrane, except that, especially in the plexus, they are composed almost wholly of vessels, and are fur- nished with an epithelium at those points where they are not adherent to the walls of the ventricles. This epithelium consists of a single layer of roundish polygonal cells, 0-008-0-01 of a line in diameter, and 0-003-0-004 of a line in thickness, and usually containing together with the rounded nucleus, yellowish granules, often in great numbers, and one or two, dark, round oil-drops of 0'001-0*002 of a line in size. Ac- cording to Henle, almost all these cells send out, from the angles towards the layer of connective tissue of the plexus, short, slender, acuminate, transparent, -and colorless processes, like spines ; and according to Valentin ("Physiol.," 2d ed., part 2, p. 22), in the Mammalia they also support cilia. The epithelium is succeeded by a thin layer of apparently homogeneous, connective tissue, beneath which is a very close inter- lacement of larger and smaller vessels, between which no formed con- nective tissue can be perceived, but only a clear, homogeneous, inter- stitial substance. All the portions of the ventricles which are not lined by the con- tinuations of the pia mater, that is to say, the floor of the fourth ventricle, the aqueductus Sylvii, the floor and the sides of the third ventricle, the ventriculus septi lucidi, the roof of the lateral ventricles, the anterior and the posterior cornua, and a considerable part of the descending cornu, in the embryo also the cavity in the olfactory bulb, and the canal in the spinal cord, have a special lining membrane, the so-termed ependyma ventriculorum (Fig. 151). This is a simple tessel- lated epithelium, which, according to Purkinje and Valentin (Mull. "Arch.," 1836; Val. "Repert.," 1836, p. 156), is said to exhibit ciliary THE NERVOUS SYSTEM. 397 motion, a statement, however, which Virchow and I have not been able to confirm in the case of an executed criminal. It lies, normally, immediately upon the nerve- substance, but there is so frequently developed beneath it, especially in the for nix, the stria cornea, and the septum lucidum, a filamentous layer, resembling connective tissue, 0-01-0-05 of a line thick, that its occurrence at a certain age might almost be described as constant, as a in fact it is by Virchow. The epithelium sometimes presents, particularly as in the third ventricle, large cells of 0-008-0-012 of a line, with pigment-granules and masses, together with nuclei, measuring 0*003 of a line; in other situations, as in the lateral ventricles, the cells are not more than 0-005-0-007 of a line in size, but almost as thick as wide, with roundish nuclei and a good many yellowish granules, which are generally crowded in the interior.* The vessels of the membranes just described present very various conditions. In the first place, in the dura mater of the cord, if we ex- cept those on the external surface and the numerous arteries and veins of the cord by which it is perforated the vessels are very few in num- ber, and in this respect the membrane presents more of the conditions of a muscular fascia or tendinous expansion. On the other hand, there exist in this situation, between the dura mater and periosteum of the vertebral canal, the well-known venous plexuses, as well as finer ramifi- cations in the adipose tissue, which do not demand any further descrip- tion. In the cranium, on the contrary, the entire dura mater is vascu- lar, but especially in its external periosteal layer, which, partly for its own supply, partly for that of the cranial bones, to which it gives off numerous branches, supports the arterice meningece, and also conveys through its veins a portion of the blood returned from the bones. Besides this, in the cerebral dura mater are lodged the venous sinuses, FIG. 151. Ependyma in man. A, from the cm-pus striatum 1, from the surface: 2, from the side; a, epithelial cells; b, nerve-fibres lying beneath ; B, epithelium cells from the com- missura mollis. Magnified 350 diameters. * [According to the recent researches of Virchow, the spinal ependyma differs some- what from that lining the ventricles of the brain. It is more gelatinous and resistant, and contains cells which are much larger than those of the cerebral ependyma. It lies in the middle of the gray matter, in the exact situation where the spinal cord exists in the foatus, and forms a continuous filament, extending to ihefilum terminate. The ependyma is prolonged without distinct boundaries, between the nervous elements. Virchow has found a continuous layer of a similar substance in the interior of the higher nerves of sense. He has quite recently also discovered in its deeper layers peculiar granules, with the chemical reaction of cellulose. (Vide 118, infra.) DaC.] 398 SPECIAL HISTOLOGY. which are simple excavations in it, for the conveyance of blood and lined with an epithelium ; and most of which are obviously situated between the periosteal lamella and the proper dura mater, thus, in their position, corresponding with the plexus venosi spinales. The arachnoid membrane, either of the spinal cord or of the brain, contains no proper vessels (vid. Luschka, 1. c., p. 71), whilst the pia mater in both situa- tions supports not only the very copious ramifications of the vessels of the nervous substance itself, but is also supplied, with a tolerably rich, proper capillary plexus of its own. In one portion of the pia mater, viz., in the vascular plexuses, the vessels are distributed solely in the membrane itself, the branches entering the nervous substance being of subordinate importance. Lymphatics it is said have recently been in- jected with air and quicksilver by Fohmann and Arnold, (vid. " Anat." II. p. 618) both in the pia mater on the surface of the cerebrum and cerebellum, as well as in the choroid plexus, but this observation appears to me very much to demand confirmation. The membranes of the central nervous system, also contain nerves, at all events in part. In the dura mater of the cerebrum they run in the periosteal lamella of the membrane, following pretty nearly the course of the meningeal arteries, and are especially distinct on the a. meningea media, which is accompained, not only by twigs of the nervi molles, but also by a special nerve first noticed by Arnold (n. spinosus, Luschka), which, according to Luschka, is derived from the third branch of the n. trigeminus, the former of which are distributed with the vessels, and the latter appears to be destined principally for the bones. Besides these, Purkinje has noticed nerves on the anterior and posterior menin- geal arteries, and Arnold long ago described the well-known n. tentorii cerebelli, proceeding from the fifth pair, which, as has been lately shown, particularly by Pappenheim and Luschka (1. c.), goes to the larger sinuses of the dura mater. The elements of this white-looking nerve and of the n. spinosus of Luschka, are those of the n. trigeminus, those of the others, fine fibres, and in both situations they present divisions. In the dura mater of the spinal cord, I, as well as Purkinje, have been unable to detect any nerves ; they occur, however, as has been already mentioned, in the periosteum of the vertebral canal, and on the arteries going to the vertebrse and cord, as well as in the sinuses and lax adipose tissue of the canal (Luschka, 1. c.). In the arachnoid itself I have never noticed any nerves, but on the vessels by which it is penetrated, and in the processes connecting it with the pia mater, they may perhaps be seen, especially at the base of the brain to which nerves, those seen by Luschka (Serose Haute, p. 70), notwithstanding the divisions observed in them, appear tome to belong. Bochdalek (1. i. c.) has lately described nerves of the cerebral arachnoid, THE NERVOUS SYSTEM. 399 derived from the n. accessorius, iheportio minor trigemini, and the facial nerve, but fails to show that they terminate in the membrane. When the same author also finds extremely numerous nerves in the arachnoid covering the cauda equina, he falls into the same error, as Rainey had previously encountered in regarding connective tissue, disposed in the more rare reticular form, as nerves. In the cauda equina, I am acquainted with nerves only on the filum terminate, accompanying the vessels, and nowhere else ; not even in the dura mater, into which Boch- dalek equally supposes he has traced them. The nerves discovered by Purkinje in the pia mater of the Ox, also exist in man, in whom the pia mater of the cord, including the filum terminate, is richly supplied with plexuses of fine nerves, measuring 0*0015-0-003 of a line, which throughout do little more than accom- pany the vessels. At the base of the brain, many similar plexuses occur on the arteries of the circle of Willis, which, in twigs, at most 0-03 of a line in diameter, are distributed through the entire pia mater of the brain, accompanying and always following the course of the various vessels, with the exception of those of the cerebellum ; their terminations, however, can nowhere be perceived. It is certain that they do not accompany the arteries into the cerebral substance, and that no nerves exist in the vascular plexuses ; whether there are any or not on the vena Cf-aleni, I have not yet inquired. The origin of these nerves has been ascertained by Remak to be in the posterior roots, each of which, as I have satisfied myself, in many situations, and as it appears to me more frequently in the cervical portion of the cord, from the fibres in closest contiguity to each other, sends out fine fibrils across the subarachnoid space into the pia mater. As in this case, so also in the cerebrum, besides the sympathetic nerves (plexus caroticus internus, plexus vertebralis), the cerebral nerves may participate in the supplying of the pia mater, since Bochdalek has noticed numerous fine twigs, given off from the roots of many of the cerebral nerves, of the same structure as the roots themselves, joining the nervous plexuses of the arteries at the base of the brain and of the pia mater of that region, and of the cerebellum, as well as in the plexus chorioideus ventric. quart. (?). He also found that isolated fine filaments entered the pia mater, directly from the medulla ollongata, the pans Varolii, and crura cerebri, which were not previously conjoined with the neighboring ner- vous trunks. B. Vessels of the central nervous system. With respect to the dis- tribution and condition of the bloodvessels the brain and spinal cord agree almost entirely. After ramifying to a considerable extent in the pia mater, the arteries enter the nervous substance, except in a few situations (substantice perforator, pons), as fine, though still distinct, 400 SPECIAL HISTOLOGY. Fig. 152. arterial vessels, and ultimately subdivide, by continuous ramification, for the most part at acute angles into a rather wide network of very fine capil- laries, from which again the venous radicles arise, joining so as to form the well-known trunks, both on the surface and in the interior (Fig. 152). The gray substance is invariably much more richly supplied with vessels than the white, the plexus formed by them being closer, and the capillary vessels themselves of less calibre, to which its color is in some respect due. Accord- ing to E. H. Weber, the interstices of the capillaries in the medullary sub- stance, measure 0*0142 of a line in width and 0-025 of a line in length ; in an injected preparation by Gerlach of the sheep's brain, the breadth of the interstices in the gray substance was three or four times less than in the white. In the spinal cord, the disposition of the entering trunks is sometimes very regularly in series. Two series of vessels of this kind exist in the bottom of the anterior fissure, which, from the processes of the pia mater, pene- trate the gray substance on the right and left; whilst a third series corre- sponds to the posterior fissure, and others not unfrequently also to the roots and the processes of the ligamentum denticulum. All these vessels enter the gray substance without undergoing any direct or considerable decrease in size, and there find their ultimate distribution. In the brain very delicate parallel vessels are met with in the gray substance of the cerebellum, less distinctly in the cerebrum and other parts. The structure of the vessels is, in general, the same as elsewhere. The arteries, upon their entrance into the nervous substance, possess three coats the tunica adventitia, though resistant, is a thin and apparently quite homo- geneous membrane ; the t. media is purely muscular ; and the t. intima formed of nothing but a very delicate elastic membrane, with openings, and well-marked fusiform epithelial cells. One after another of these coats is gradually lost, till before the capillaries are reached, we find nothing but the t. adventitia, and scattered, transversely placed, elon- gated cells, with transverse nuclei and an epithelium ; with which class of vessels are soon associated capillaries with a structureless membrane and few or more nuclei, sometimes of great minuteness, the finest FIG. 152. Vessels of the cerebral substance of the Sheep, from one of Gerlach's injec- tions : a, of the gray ; b, of the white substance. THE NERVOUS SYSTEM. 401 measuring in the cord, 0-0022, in the brain 0-002 of a line. Of the veins, the largest, for the most part, do not present a trace of smooth muscle, exhibiting nothing but connective tissue with nuclei, or fine elastic filaments and epithelium ; in the smaller ones I have, occasion- ally, though very rarely, observed contractile elements. In the ventricles of the brain there exists, under normal conditions, an extremely small quantity of clear serous fluid, which is manifestly secreted by the arterial plexuses, and which, probably aided by the ciliary movements, assists in the nutrition of the walls of the cavities. A second fluid, the liquor cerebro-spinalis is contained in the suba- rachnoid spaces above described, which according to Luschka, are lined by an epithelium, and from the largest of which, extending from the base of the brain to the termination of the canal of the dura mater medullas, the fluid in question may be readily obtained. It is alkaline, contains of water 98*56 albumen and extractive matter 0-55 salts 0-84 per cent., principally chloride of sodium. Its principal function appears to be to conduce to the more free motion of the central nervous system, and to act as a regulator in varying degrees of fulness of the vascular system. A few pathological points may here be referred to. The ependyma ventriculorum presents not only, as above mentioned, almost constantly in places, a thin fibrous substratum, but is frequently, especially in dropsy of the ventricles, and in old age, very much thickened by a layer of that kind. In either case it invariably contains, as was first mentioned by Purkinje, yellowish bodies, with con- centric striae of a round or biscuit shape, and not unlike starch granules. They are scarcely affected by acids, whilst in caustic alkali they become pale and gradually dissolve. I find these corpuscula amylacea (Fig. 153), almost always on the fornix, the stria cornea, and septum pellucidum, and also elsewhere in the walls of the ventricles, as well as in the cortical substance of the brain, in the medul- lary substance of the cord, and in the filum termi- nate ; in the first-mentioned situations they frequently occur in incredible quantity, close together, in the newly formed connective tissue, or between the ner- vous elements. That these bodies are a pathological product is certain, but not so of what they consist, or how they are formed, although everything indicates a nitrogenous FIG. 153. 1, " Brain-sand" from the pineal gland, in bundles of connective tissue: 2 f corpuscula amylacea from the ependyma of Man ; magnified 350 diameters. 26 402 SPECIAL HISTOLOGY. substance, and a formation from successive deposits.* In the plexus chorioidei, in the pineal gland, occasionally in the pia mater and * [The recent investigations of these corpora amylacea by Virchow, (see Archiv. f. path. Anat. Sept. 1853) have led him to the important discovery of their true nature, viz. : that they are composed of a substance, resembling the cellulose in plants. The fact that in the animal kingdom, starchy substances had only been found in a low class of the invertebrated animals, induced Virchow to examine all starch-like bodies occurring in the higher classes of the animal kingdom, and thus the exact composition of the corpora amylacea was ascer- tained. As this discovery is of great importance, I shall quote the author's own words. " In a histological point of view, it has often occurred to me, that the umbilical cord in Man possessed a great similarity in its structure to the cellulose in the Ascidians. (See Wiirzb. Verhandl. 1851, Vol. II. p. 161, note.) And I was the more confirmed in this idea by Schacht's observations, so that ever since my researches have been more carefully directed to this subject. But in most instances I searched in vain, as in the ova of amphibia and fishes, the peculiar yelk-plates of which I described. (Zeitschrift fur Wiss. Zoologie. 1852, Vol. IV. p. 240.) I was more successful, however, recently, when I directed my attention to the so-called " corpora amylacea " of the brain, of the exact nature of which, as compared with the other starch-like bodies in man, I had not been able to form any very definite conclusions. I soon found that on the application of iodine, they assumed a bluish tint, and upon subsequently adding sulphuric acid, the exquisite violet color, which is known to be- long to cellulose, and which appeared the more intense, as it formed a distinct contrast to the surrounding yellow or brown nitrogenous substances. " I have so frequently repeated these investigations, and with so many precautions, that I consider the results as perfectly certain. For I have instituted comparative researches not only in different human bodies, and in the most different situations, but I have allowed the reagents employed to act under all possible conditions." The best manner, Virchow continues, to obtain this reaction is to allow an hydrated solution of iodine to act on the bodies in question, and then to add a little diluted sulphu- ric acid. Care should be taken not to add too much iodine at once, and to allow the sulphuric acid to act very slowly. The most beautiful preparations were obtained by adding a drop of sulphuric acid to the edge of the thin glass covering a preparation, and allowing it then to remain undisturbed from twelve to twenty-four hours. Every precaution having been taken against an accidental admixture of starch or cellulose, the following results were obtained : "The corpora amylacea are chemically different from the concentric spherical corpuscles of which the brain-sand is composed, and with which they have hitherto been confounded. The organic basis of these brain sand-granules, is evidently nitrogenous ; iodine and sul- phuric acid color it an intense yellow. The same is true not only of the sandy matter in the pineal gland, and the choroid plexuses, but also of that of the Pacchionian granulations and of the dura mater, as well as of the dentated plates in the spinal arachnoid. In all these parts, except in a few spots in the pineal gland, I have never obtained the characte- ristic blue reaction. It would, therefore, be henceforth advisable to restrict the term ' cor- pora amylacea' to these cellulose corpuscles. " The cellulose granules seem to be connected with the presence of the ependyma sub- stance in certain quantities, and might not improperly be considered as a part of it. But how they are produced from it, it was impossible to recognize. They are usually minute, scarcely corresponding in size to the nuclei of the ependyma. Can they originate from these 1 ? The larger they are, the more distinctly laminated they appear. But they do not exhibit anywhere a nitrogenous admixture, distinguishable by its yellow color. Their centre is generally of a darker blue, and hence, perhaps, denser than their border. " The supposition, of these bodies being introduced from without, is the less probable because a similar substance is nowhere else known. The cellulose in plants exhibits a number of varieties, but this animal cellulose is distinguishable above all by its slight resis- tance towards reagents; for concentrated acids and alkalies act on it more powerfully than on vegetable cellulose." THE NERVOUS SYSTEM. 403 arachnoid (also in the cord), and although rarely, also in the walls of the ventricles, there is furthermore met with, as a constant, though pathological production, the gritty matter of the brain (brain- sand). It consists of roundish, simple or mulberry-shaped, opaque, mostly concentrically striated globules of 0*005-0*05 of a line, and together with them of angular bodies, of a stalactitic, clavate, or other irregular figure, with an uneven, botryoidal, scaly surface ; and also in the form of simple, cylindrical, rigid fibres, either branched or reticular, and of fine particles. The brain-sand contains principally carbonate of lime, but also phosphate of lime and magnesia, and an organic substance, which after the salts have been removed, for the most part perfectly retains the figure of the concretion, that is to say, of a concentrically laminated pale body, or as clear fibres. It is quite certain that this brain-sand, when it assumes the form of elongated, branched, reticular bodies, is simply developed in the bundles of connective tissue (Fig. 153), as, not unfrequently, in the pineal gland and in the membranes of the brain ; in other cases it appears to be an independent incrusta- tion on fibrinous concretions. Whilst cells impregnated with calcareous matter, which Remak (" Obs.," p. 26) supposed them to be, according to Harless (Mull. "Arch.," 1845, p. 354), do not exist. Lastly, also, may be mentioned the Pacchionian granulations of the pia mater, and ossifications of the membranes. The former, which are situated prin- cipally on both sides of the falx major, on the flocculi, in the choroid plexuses, &c., consist chiefly of a tough fibrous substance, not unlike immature connective tissue, containing also undeveloped elastic tissue, and corpuscula amylacea. The latter, which are true osseous plates, occur sometimes on the inner surface of the cerebral dura mater, some- times on the arachnoid, particularly of the cauda equina. The cellulose corpuscles were found only in the substance of the ependyma of the ventricles and its prolongations, including the transparent substance in the spinal marrow de- scribed by KoMliker as the " substantia grisea centralis," but not in the cortical layer of the brain, or in the interior of the cerebral substance. Neither was Virchow able to detect them in the brain of a child, or, as Bernard's experiments might lead us to suppose, in the brain of a Rabbit, and he is, therefore, inclined to attribute to them a pathological import. Similar bodies have been found, by Rokitansky in the optic nerve, by Kolliker in the retina, by Luschka in the ganglion of Gasser. The exact chemical nature of these bodies has not, as yet, been satisfactorily ascertained. They have not the pure reaction of vegetable cellulose, nor, as Donders supposes them 'to have, that of starch, and they might, perhaps, at present, be more properly called "amy- loid" corpuscles. If boiled in water they are dissolved. This discovery of Virchow's is of great importance, not only with regard to the anatomy of the corpora amylacea, but as establishing as an undoubted fact the existence of vegetable matter as a part of the animal economy. Whether this be a pathological formation or not, it is at present impossible to decide, the former is, however, highly probable, since corpuscles with the same reaction have been found in certain abnormal conditions of the spleen. (Vid. 170, Spleen). DaC.] 404 SPECIAL HISTOLOGY. PERIPHERAL NERVOUS SYSTEM. 119. Spinal nerves. The thirty-one pairs of nerves springing from the spinal cord, arise, with few exceptions, by anterior and pos- terior roots. Receiving a delicate tunic from the pia mater, they con- verge, and are continued across the subarachnoid space, to perforate, independently of each other, the arachnoid and dura mater, from the latter of which they obtain a firmer coat. Proceeding further, the pos- terior root forms its ganglion, by the deposition around and among its nerve-fibres, of ganglion-cells, which, to all appearance, give origin to special nerve-tubes, the ganglionie fibres of the spinal-nerves, each for the most part arising from a cell, and which have no further connection with the fibres of the posterior root passing through the ganglion, than that, in their invariably peripheral course, they are in apposition, and intermingled with the latter. The motor root never acquires ganglion- cells, merely passing by the ganglion, in more or less close apposition with it. Beyond the ganglion, the two roots are united in such a man- ner that their elements are very intimately commingled, and a common nervous trunk formed, containing in all its divisions sensitive and motor elements. It is usually connected with the neighboring nerves above and below it, in the formation of the well-known plexuses, afterwards giving off its terminal branches to the muscles, integument, vessels of the trunk and extremities, articular capsules, tendons, and bones. As in the roots, so also in the branches of the common trunk, it is seen that the motor twigs contain principally thick fibres, and those destined for the integument and other organs ab.ove named, finer ones ; ultimately, however, in the terminal ramifications, all the fibres are of uniform size. The fibres of all the spinal nerves appear to run quite distinct from each other, and to present no divisions in the trunks and branches, whilst, in the terminal ramifications of them, divisions frequently occur, and, at all events in certain animals (Mouse, batrachian larva), also reticular anastomoses. They terminate either in loops, or in free prolongations, the latter being the case, particularly, in the Pacinian bodies, which are structures composed of numerous concentric capsules separated by fluid, of an oval form, and measuring J-2 lines, found principally in the hand and foot, and which usually contain the termination of a nerve- fibre. In the first and last pairs of spinal nerves occasionally only a single root can be perceived, in the former case the motor, and in the latter the sensitive. I have communicated the diameters of aril the anterior and posterior roots on the left side in a male and female body, in the " Verh. d. Wurzb. phys. med.," Gesellsch. 1850, Heft II. and the transverse sectional areas deduced from these observations are given in TUB NERVOUS SYSTEM. 405 my "Microscopical Anatomy," 116. The roots are furnished with a delicate neurilemma, derived from the pia mater, and presenting a simi- lar structure, which forms both an external sheath 0-002 of a line in diameter, as well as internal septa to the individual fasciculi. The con- tiguous roots frequently anastomose, and this is. much more usually the case with the sensitive roots ; in the cervical nerves in Man in parti- cular, it is found to take place constantly in one or other of the nerves. 120. The structure of the spinal ganglia, in the Mammalia, is a difficult subject of investigation, but I think the following may be stated with certainty respecting them. Fig. 154. The sensitive roots, so far as I have hitherto been able to make out, enter into no connection with the nerve-cells in the gan- glion, but forming one, or, in the larger ganglia, several, or even numerous fasciculi, which in the latter case anastomose, simply traverse it, to be reunited be- low the ganglion into a single trunk, which is then immediate- ly blended with the motor root. Most of the nerve-cells them- selves appear to be in connec- tion with the nerve-fibres, giv- ing off either one or two, or more rarely, several. These fibres, which I term ganglion- fibres, proceed in a prepon- derating majority perhaps all of them peripherally, joining and strengthening the perfora- ting root-fibres ; so that each ganglion is to be regarded as a source of new nerve- fibres.* FIG. 154. 'A lumbar ganglion of a young Dog, treated with soda, and magnified 45 diameters: S, sensitive roots; AT, motor roots; R.a, anterior branch of the spinal nerve; R.p, posterior branch ; in both their composition from both roots is manifest ; r, ganglion, with the cells and ganglion-fibres, which assist in the strengthening of the sensitive roots travers- ing the ganglion. * [The new "ganglion-fibres" join differently the nerve-fibres on which the ganglion is seated, or by which it is perforated. In the large ganglia the new fibres penetrate in 406 SPECIAL HISTOLOGY. The structure of the spinal ganglia (Fig. 154) is a difficult subject for investigation, in Man. No complete results can be obtained from the larger of them, but more may be made out in the smaller or smallest, as in those of the fifth sacral nerve and n. eoccygeus, which are to be sought within the sac of the dura mater, also perhaps in the fourth sacral and first cervical nerves. If a comparative examination be instituted, of the spinal ganglia of the smaller Mammalia (Rabbit, Puppy, Mole, Mouse, Rat), and if not only the scalpel and needle be employed, but if the entire ganglia be examined after the application of acetic acid, and above all, of a dilute solution of soda, with the aid of the compressorium, a satisfactory insight into their structure may be obtained. The fibres of the roots of the nerves while passing through the ganglia present nothing at all peculiar, that is to say, no change in size ; nor have I ever observed any divisions of them, and I think it may be positively asserted, that such an occurrence, if it take place at all, must be extremely rare, as, notwithstanding that I have specially sought for it, and have been able, in the lower Mammalia, to trace numerous nerve-fibres through the entire ganglion, I have never noticed anything of the sort. The principal constituents of the ganglia the ganglion-globules or -cells [nerve-cells] (Figs. 155 and 157), have a distinct outer coat, are for the most part roundish, elongated, or pyriform, usually a little flattened,and measure from 0-012 to 0-036, or even 0-04 of a line; on the average 0-02-0 03 of a line. The contents are through- out finely granular, and not unfrequently exhibit, in the vicinity of the nucleus, an accumulation of yellow, or yellowish-brown, larger pigment granules, which increases in age, and to which the gan- glia are chiefly indebted for their yellow color. The nuclei measure fasciculi between the perforating nerve-fibres ; in the smaller ganglia they either wind around the nerve-fibres, or run along the side of the nerve on which the ganglion is situated. This depends mainly on the exact position of the ganglion. If it be placed in the middle of the nerve, the former occurs, whilst if it be situated on one side of it, the latter is the more frequent. The new ganglion-fibres mostly proceed peripherally, but according to a recent observer, Axmann (Beitrilge zur Anatom. u. Phys. des Gangl. Syst., Berlin, 1853) this is not the case with all of them. From many careful dissections he satisfied himself that whilst, as stated by Kolliker and others, most of the new fibres, proceeding from every spinal ganglion, run in a peripheral direction, and are distributed along with the cerebro-spinal nerve-fibres, to the tissues subjected to will and sensation, some are connected through the rami communic antes with the sympathetic system. He also found that a small number of the ganglion-fibres penetrate through the roots of the cerebro-spinal nerves into the spinal column and brain, where, he states, they have been frequently mistaken for attenuated cerebro-spinal nerve- fibres. He adds, further, that he has been able to trace their connection with the spinal ganglia in the Frog, Mouse, and Pike, and also in a human foetus of six months. It is, how- ever, difficult to understand how Axmann was able to determine that these fibres proceeded from the ganglia to the spinal marrow, since they might be as readily supposed to have been minute fibres proceeding from the ganglia of the spinal marrow towards the external ganglia. DaC.] THE NERVOUS SYSTEM. 407 These nerve-cells Fig. 155. 0-004-0-008, the nucleoli 0-0008-0-002 of a line, are situated, in the first place, in larger numbers on the surface of the ganglion, be- tween the neurilemraa and the perforating radical fibres ; and secondly, at all events in Man, in the interior, where they occupy the interstices of the plexus formed by the nerve- fibres. The individual cells are retained in their situations by a special tissue, which also separates them from the contiguous cells and from the nerve-fibres. This tissue ap- pears on isolated cells, as if it formed a spe- cial coat to them, and is consequently termed their external sheath, but in fact it repre- sents a system of small septa, connected in a complex manner, and pervading the entire ganglion, receiving the separate cells in its meshes, and only more rarely appearing as a definitely bounded coat on individual cells. This structure is evidently to be referred to connective tissue ; it presents, however, several forms, which have been, in part, already, properly dis- tinguished by Valentin (Mull. "Arch." 1839, p. 143), viz. 1, in the form of a sometimes homogeneous, sometimes more fibrous substance, with scattered, flattened, roundish nuclei of 0-002-0-003 of a line ; and, 2, in that of isolated elongated, triangular or fusiform cells, measuring 0-003-0-005 of a line, with nuclei as above, and which sometimes may be supposed to resemble epithelial cells, although, as is evident from a comparison of their different forms, they rather cor- respond with the developmental cells of connective, or of elastic tissue (Fig. 156). Besides these two forms, the former of which occurs everywhere, and the latter principally in the larger ganglia, certain intermediate types are met with in Man, which consist, as it were, of nucleated "fibres of Remak," as they are termed (vid. infra), or, at all events, in the preparation, break up into such. From by far the greatest number of the nerve-cells, in Man and the Mammalia, are given off pale processes, 0-0015-0-0025 of a line, in all respects corresponding to those of the central cells, but furnished with a special sheath, and which, as I discovered in the year 1844 (" Selbst. u. FIG. 155. Ganglion-globules (nerve-cells) from the Gasserian ganglion of the Cat, mag- nified 350 diam. : 1, cell with a short, pale process, showing the origin of a fibre, a; sheath of the cell and nerve-tube, containing nuclei; 6, cell-membrane of the nerve-cell; 2, cell with the origin of a fibre, without sheath; 6, cell-membrane of the nerve-cell; 3, nerve-cell, deprived, in the preparation of it, of its membrane and external sheath. FIG. 1 56. Cells from the sheath of the nerve-cells of the spinal ganglia in Man, mag- nified 350 diameters. Fig. 156. 408 SPECIAL HISTOLOGY. Fig.157. Abh. des Symp. Nerv.," Zurich, 1844, p. 22), are each of them con- tinued into a dark-bordered nerve tube (Figs. 155, 157). The cells observed by me had but one process, the so-termed uni- polar-cells, and I at first thought that such only ex- isted in the spinal ganglia. It now appears, however, from more recent re- searches, especially from those of Stannius, that they also contain cells with two processes, one of which may again divide ; fresh and more extended in- vestigations therefore are required to show how the matter really stands. At present I think the following should be remarked : 1, in Man and the Mammalia I have certainly established the fact of the existence of unipolar-cells, and think it may also be asserted that they are very nu- merous ; 2, quite lately I have myself, although rarely, noticed cells with two, pale processes, and I am willing to admit the possibility that such cells frequently occur, as it is certain that many processes must be torn off in the comparatively rude methods necessarily employed to isolate the cells ; 3, when Stannius very recently noticed in a human foetus, and in a foetal Calf, together with unipolar and apolar cells, in the latter numerous bipolar cells, it should be inquired whether the lat- ter were not cells which afterwards divide ? because divisions of the nerve-cells undoubtedly take place (vid. infra), and in this way become unipolar ; 4, whether the cells give off one or two fibres, one of the latter does not go towards the centre and the other towards the peri- phery, but both proceed in the latter direction ; at all events, in the examination of all small ganglia, only such ganglion-fibres are visible. Stannius, in bipolar cells of this kind from the Calf, also found the two processes closely approximated ; 5, it is difficult to determine whether cells without processes also occur in the spinal ganglia, seeing that the processes are very readily detached, and that cells thus truncated may very easily be regarded as apolar cells. In small ganglia in the Mam- malia a fibre may be traced to each cell, whilst in the smallest spinal ganglia in Man, and in the inconstant ganglia of the posterior roots (vid. seq.\ cells are not unfrequently met with, to which no fibre is at- tached, "and, consequently, I would, at present, merely state that, in any case, fibres arise from the majority of the cells. In order to examine these conditions, either the larger ganglia in Man are selected, which FiG. 157. Twigs of the coccygeal nerve within the dura maler, with an adherent, pedun- culated nerve-cell in its nucleated sheath, from which the derivation of a fibre is very distinctly seen ; magnified 350 diameters. From Man. THE NERVOUS SYSTEM. 409 Fig. 158. are torn into fibres as carefully as possible under a simple microscope, until the fibres are traced to their origin, which may be done with a little trouble in almost every ganglion, or the small ganglia of the fifth sacral and coccygeal nerves are taken for the purpose. In these gan- glia, in almost every individual, solitary and completely isolated, pedun- culated, ganglion-globules are met with, close to or in the neighborhood of the ganglia, each in its special sheath, which in this case appears to be homogeneous (Fig. 157), and in many cases, the simple, dark nerve- fibres lying in the peduncle of the globule, and frequently also its con- nection with the cell, by means of a pale process, may be distinctly perceived. In the ganglia aberrantia also of Hyrtl, that is to say the inconstant, larger or smaller collections of nerve-cells, which are found in every subject upon the posterior roots of the larger nerves, the simple origins of fibres may occasionally be distinctly noticed. The dark- colored fibres, arising from the nerve-cells, simply constitute the continuation of the pale processes of the cells, so that the membranes and contents of each part pass continuously into each other, and thus also the membrane and the contents of the cells are connected with the sheath of the nerve-tubes, the medullary sheath, and the axis-cylinder. In older nerve- cells, or by the operation of reagents (ar- senious acid, chromic acid, iodine), the con- tents of the cell become detached from the membrane, and the axis-cylinder appears as a direct continuation of the former (Fig. 158), as was first shown by Harting (vid. also Stannius in and Leydig, 1. c. is the best proof that the contents of the nerve-cells cannot be understood as contained in a dilated nerve-tube.* e "Gott. Anzeig.," 1850, Tab. 1, Fig. 9), which FIG. 158. Nerve-cell of the Pike (bipolar, as they are termed), which is continued at each end into dark-bordered nerve-tubes, treated with arsenious acid : a, sheath of the nerve-cell j 6, sheath of nerve ; c, nerve-medulla ; rf, axis-cylinder continuous with the contents of the nerve-cell ; e, which have shrunk away from the sheath. Magnified 350 diameters. * [The axis-cylinder is supposed by some observers not to be, as above stated, a continua- tion of the contents of the cell, but rather of its nucleus. This continuation of the nucleus into the. axis-cylinder is best seen in ganglia, which have been kept for some days in diluted acetic acid. We are thus, according to Axmann (I. c.) not only able to see the connection of the axis-cylinder with the nucleus, but also to isolate the nucleus with a portion of the axis- cylinder attached to it. This continuation of the nucleus of the ganglion cell into the axis- cylinder has been observed in all classes of animals. It was first described by Harless in the ganglion corpuscles of the electric lobes of the Torpedo Galvani. DaC.] 410 SPECIAL HISTOLOGY. The nerve-tubes or ganglion-fibres thus originating, which frequently arch round or embrace the cells with several circular turns, are at first fine, measuring 0-0015-0-0025 of a line, but (not continuing so as I formerly supposed, when I was acquainted only with their origin), they all very soon increase in size, as may be very readily observed in many fibres, whilst still within the ganglion, up to 0*003 arid 0*004, many even to as much as 0*005 and 0-006 of a line; becoming, consequently, medium- sized, and thick nerve-fibres. The processes of the cells and the nerve-fibres springing from them are also furnished with nucleated sheaths like the cells themselves, the vaginal processes, as they are termed, which they lose, however, at the point where they join the emergent trunk, obtaining instead of it, as a coat, the common neurilemma of the nerves. The description I have above given of the conditions observable in the spinal-ganglia in Man and the Mammalia, differs very considerably from what was found by Bidder, Reichert, R. Wagner, and Robin, to be the case in Fishes. The chief difference consists in this, that whilst in the Mammalia, from all we know, the roots of the nerves have no direct connection with the nerve-cells, and merely pass through the ganglion, in Fishes, all the radical fibres are connected with the cells, so that each fibre is interrupted by a bipolar cell, and independent ganglion-fibres are wholly wanting. R. Wagner has thought, that what obtains in the Fish might be applied, unconditionally, to all the Vertebrata, and asserts, that the occurrence of bipolar cells in the course of the posterior radical fibres is in accordance with Bell's doctrine, and a necessary contingent in the mechanism of the sensitive fibres ; and moreover, that in this case the highly important and long-sought distinction between sensitive and motor primitive fibres, has been discovered. In opposition to this I have expressed the opinion, that it is not a necessary postulate, that what is found in the Fish should be applied to Man, and that the interruption of a sensitive fibre by a nerve-cell does not distinguish it from a motor fibre. Although Wagner has very recently characterized this opinion of mine as unphysiological, he will not, at the same time, convince any one that the spinal ganglia of the Mammalia are constructed as he thinks, and I shall therefore wait to see whether further observations will con- firm my observations or not. In order to complete them, I will more- over mention, that direct measurement of the sensitive roots above and below the ganglia, shows a not inconsiderable difference in favor of the latter situation (vid. " Mikroskop. Anat.," II. p. 509), which as diffe- rences in the thickness of the entering and emergent nerve-fibres, and divisions of them within the ganglion do not exist, can only be referred to the fibres which originate in the ganglion and proceed towards the periphery, a view which is also confirmed by direct observation (Fig. THE NERVOUS SYSTEM. 411 154). With respect to the interesting observations on the structure of the spinal ganglia of the lower animals, and particularly of Fishes, I would refer especially to the works of R. Wagner, Bidder, Robin, and Stannius, cited below. 121. Further course and termination of the Spinal Nerves. Below the spinal ganglion, the sensitive and motor roots unite to form a common trunk, their fibres being intermixed in diverse ways, as may be very distinctly perceived in small animals. All the subsequent branches, both of the anterior and posterior main divisions, as well as their fur- ther continuations, are consequently of a mixed nature, formed of por- tions derived from both roots ; a condition which they retain up to their ultimate distribution. Here, however, an alteration takes place, the motor fibres going off in by far the larger proportion into the muscular branches, and the sensitive chiefly to the cutaneous. Where the gan- glion-fibres which arise in the spinal ganglia are distributed, cannot be ascertained anatomically.* When their physiological relations, how- ever, are considered, it would appear as by far the most probable sup- position, that they do not, as at first sight one would be inclined to suppose, join the sympathetic in the rami communic antes, but, that ac- companying the spinal nerves, they are continued chiefly into the vascular branches, and consequently are distributed in the integuments, muscles, bones, joints, tendons, and membranes (periosteum, pia mater, &c.), but also, perhaps, to the glands and involuntary muscles of the skin. The nerve-fibres in the main trunks of the spinal nerves present the same diameter as in the roots, that is to say, there are finer and thicker tubes, and a certain number of intermediate forms ; but, as they pro- ceed, the fibres separate, the thicker going more to the muscular branches, and the thinner into the cutaneous nerves. According to the statements of Bidder and Volkmann, the proportion of the fine to the thick fibres is, in man, as 1. 1 : 1, in the muscular nerves as 0. 1-0*33 : 1 ; statements which I can but confirm, adding to them, that the nerves of the bones contain, in the trunks, one-third of thick and two-thirds of fine, whilst those of the articulations, tendons, and membranes, exhibit a great preponderance of fine fibres. In my opinion, most of the fine fibres contained in the branches of the spinal nerves must be regarded as derived from the spinal cord, and as being, in their function, quite of equal importance with the thick fibres, and at present, the only thing that remains unascertained, is whether they all ascend to the brain, or perhaps in part arise in the spinal cord ; upon which point reference may be made to 112. The spinal nerves are composed in general of parallel tubes, for the * [Vid. note, 120. DaC.] 412 SPECIAL HISTOLOGY. most part undulating, upon which circumstance their transversely banded aspect depends ; they exhibit, however, in their course, very frequent anastomoses, in which way the various larger and smaller plexuses with decussating fibres are formed. The formation of these plexuses is due to an interchange of entire fasciculi or fibres, never to a connection be- tween the individual primitive fibres, and in a microscopical point of view affords no point worthy of remark. Divisions of the nerve-fibres do not occur, according to our present experience, in the trunks and larger branches of the spinal nerves of the Mammalia [in Fishes, Stannius noticed numerous divisions in the trunks of the motor and mixed nerves (" Archiv fiir phys.," Heilk. 1850, p. 77)], nor do they exhibit any considerable change in their diameter ; but in the ultimate ramifications, on the other hand, it is certain that such divisions do take place, even in Man, accompanied by a very con- siderable diminution in the size of the fibres ;* with respect to which con- ditions, and the terminations in the skin, muscles, bones, and membranes in general, reference may be made to the detailed descriptions given in the proper places. One kind, only, of termination of the spinal nerves, is still to be noticed here, that in the Pacinian bodies. The small bodies, so named by Henle and myself (" Ueber die Pacin. Korperehen des Menschen und der Thiere," Zurich, 1844), were first accurately described by the Italian, Pacini ("Nuovi organi scoperti nel corpo umano," Pistoja, 1840), espe- cially in the nerves of the palm of the hand and sole of the foot, and, in fact, as Langer of Vienna afterwards showed, had been previously noticed by A. Yater (J.G. Lehmann, " De consensu partium corp. hum.," Vitembergse, 1741), although their nature had riot been recognized. These organs are of an elliptical or pyriform shape, of a whitish trans- parent color, with whiter streaks internally, and measure J-2 lines in size ; in Man, they are constantly found on the cutaneous nerves of the palm of the hand and sole of the foot, in the subcutaneous connective tissue itself, and most numerously in the fingers and toes, particularly on the third phalanx, according to Herbst ("Die Pacin. Korperchen und ihre Bedeutung," Gott., 1847), there are about 600 in the hand and not quite so many in the foot; besides which, it must here also be stated, that they are invariably found on the great sympathetic plexus, in front of, and close to the abdominal aorta, behind the peritoneum, particularly near the pancreas, frequently also in the mesentery, close to the intestine ; and also occasionally on other nerves, such as the * [The ultimate ramifications are supposed by Axmann (I.e.), to be merely axis-cylinders surrounded by the sheaths of the nerves, the granular contents of the nerve-tubes having gradually disappeared. DaC.] THE NERVOUS SYSTEM. 413 Fig. 159. ...0 ...4 n. pudendus communis, on the glans penis (Fick) and bulb of the ure- thra, on the intercostal nerves, sacral plexus, cutaneous nerves of the upper- and fore- arm, on the dorsum of the hand and foot, and the cutaneous nerves of the neck. The structure of the Pacinian bodies is, upon the whole, simple (Fig. 159). Each of them consists of very numerous (20-60) concentric layers of connective tissue, of which layers the external are separated by wider, and the internal by narrower inter- spaces, in which is contained a clear serous moisture, which is collected in larger quan- tity in an elongated central cavity, bounded by the innermost lamella. Each body pre- sents a rounded peduncle, formed from the continuation of its lamellae, and connected with a nervous twig, and in which a dark nerve-fibre, 0-006-0-068 of a line (in the Cat, 0-0044-0-0077 of a line) thick, runs to the Pacinian body. This fibre enters the central cavity from the penduncle, where it becomes 0-006 of a line wide and 0-004 of a line thick, pale, non-medullated, almost like an axis-cylinder, and terminates in the upper part of the cavity, in a free, slightly granular tubercle, the extremity being fre- quently bifid or trifid. Further observa- tions, and comparative anatomical details with regard to these bodies, which are also found in great number in many Mammalia, as well as in Birds, in the skin, beak, and tongue (Herbst, Will), and with respect to which physio- logy is still wholly in the dark, will be found in the works above quoted, and also in Reichert (" Bindegewebe," p. 65), Herbst (" Gott. gel. Anz.," 1848, Nos. 162, 163, 1850; " Nachr. v. d. Univ.," p. 204, 1851, p. 161), Will ("Sitzungsber. d. Wiener Acad.," Feb., 1850), Osann("Bericht ttber d. zoot. Anst. in Wurzb.," 1849), Strahl (Miiller's " Arch.," 1848, p. 163), and Pappenheim (" Comptes rendus," xxiii. p. 68). [Todd and Bowman, " Physiol. Anatomy," Part II., p. 395, figs. 74, 75, 76; and Bowman, art. "Pacinian Bodies," " Cyc. of Anat. and Phys."] FIG. 159. A Pacinian body in Man, magnified 350 diam. : a, its peduncle ; b, nerve- fibre in it ; c, external ; d, internal layer of the sheath ; e, pale nerve-fibre in the cen- tral cavity ; /, divisions and terminations of the same. 414 SPECIAL HISTOLOGY. The spinal nerves, from their point of exit through the dura mater, are enclosed by a firm sheath of connective tissue the nerve-sheath, or neurilemma which also sends finer prolongations into the interior of the nerves, and, as in the muscles, forms boundaries to larger or smaller fasciculi, as well as extremely delicate septa between the individual tubules (Fig. 160). In the ultimate ramifications, where isolated primi- tive fibres, or some few of them, still often re- tain an external coat, the neurilemma presents the aspect of a homogeneous membrane, with elongated nuclei of 0*003 of a line ; and it presents this character also in the smaller twigs of the cutaneous and muscular nerves, only that gradually the substance begins to split, in a longitudinal direction, into fibres, the nuclei become longer (0-005-0-008 of a line), frequently almost like those in smooth muscles, and elastic fibres also make their appearance, which are not unfre- quently entwined around whole fasciculi. The larger nerves, lastly present common connective tissue, with distinct longitudinal fibrils, as in fibrous membranes, intermixed with numerous reticulated elastic fila- ments ; they still, however, exhibit, especially in the interior, immature forms of connective tissue. All the larger nerves contain vessels, although not in great number ; they run principally in a longitudinal direction, and form a loose plexus of minute capillaries of 0-002-0*004 of a line, with elongated inter- stices, which invests the fasciculus, and, in fact, penetrates between its elements ; never, however, surrounding individual primitive fibres, but only entire divisions of them. The ganglia contain a delicate capillary plexus, in the form of a network, so that each nerve-cell is surrounded by special vessels. The Pacinian bodies also contain vessels, which even penetrate as far as the central cavity (Todd and Bowman, II. p. 397, Fig. 75, and p. 399, Fig. 76 ; Herbst, Tab. IV. Figs. 1 and 2). On the subject of the condition of the cutaneous nerves of animals, I would here add a few remarks. In the skin of the tail of batrachian larvae (Rana, Bvifo, Triton, Bombinator^ Alytes\ I have described the very delicate ramifications and plexuses of the embryonic pale nerve- fibres ; and moreover, quite evident loops of the fully formed dark nerve- tubes, and isolated divisions of the latter ("Ann. des S. Nat.," 1846, p. 102, pi. 6, 7). In the full-grown Frog, according to Czerm&k (Mull. "Archiv," 1849, p. 252), the nerves destined to the skin, form, on its inner aspect, a wide network, already described by Burdach, from which FiG. 160. Transverse section of the ischiatic nerve, magnified 15 diam.: a, general sheath of the nerve; b, neurilemma of the tertiary fasciculi; c, secondary nervous fasciculi, in part with special sheaths. From the Calf. THE NERVOUS SYSTEM. 415 again numerous fasciculi are given off, penetrate the derma perpendicu- larly, and, having reached the superficial glandular layer of the skin, form a superficial nervous-plexus between the glands. With respect to the true termination of the nerve-fibres, Czermdk arrived at no definite results, but made the interesting discovery that thick and thin nerve- fibres of the deeper plexus divide dichotomously very frequently and repeatedly, and thus spread themselves over larger surfaces; of which divisions I have most fully satisfied myself from preparations furnished by Czermdk. Similar conditions were found by Leydig (" Zeitsch. f. wissen. Zool.," III.) in the skin of Fishes; where also exist superficial and deeper plexuses, with numerous divisions of finer and thicker tubes, all of which on the surface ultimately become quite fine, pale, and finally invisible. In the Invertebrata, as appears from Leydig's researches in Argulus, and especially in Carinaria, conditions are met with perfectly analogous to those described by me in the nerves of the Tadpole ; and I cannot agree with Leydig, when he describes the nucleated enlarge- ments as nerve-cells. On the other hand, the conditions observed in Artemia and Corethra are perhaps, peculiar, because in these instances larger branches of the cutaneous nerves are, at their extremities, in con- nection with numerous roundish vesicles, which might have the function of nerve-cells (" Zeitsch. f. wiss. Zool.," vol. I. iii.). In the integuments of the Mammalia and of Man, except in the Paci- nian bodies, until a short time since, no one had seen anything of divi- sions in the nerve-tubes ; all observers rather agreeing that terminal loops existed there, especially in the papillae. But it now appears, from the researches of myself, J. N. Czermdk, and C. Gegenbaur, that pro- bably loops and divisions, and occasionally even free terminations, all exist in that situation. That in Man, terminal loops occur in the papillae, and divisions in the terminal plexuses, I have already men- tioned ; the latter are especially well shown in the conjunctiva scleroticce, where free terminations also appear to exist, and where peculiar convo- lutions of nerves (nerven-knauel), similar to those formerly described by Gerber* (vide " Micr. Anat.," II. i. p. 31, Fig. 13 J., 3), present them- selves. Czermak, moreover, observed divisions of the cutaneous nerves in the Mouse, and I myself a transition of the dark-bordered nerves into pale anastomosing filaments, of 0'001-0 f 0005 of a line, exactly resem- bling the embryonic fibres in the Tadpole (" Micr. Anat.," II. i. p. 24) ; lastly, Gegenbaur has noticed numerous divisions in the expansion of the nerves of the tactile hairs in the Mammalia. Further experience will have to show in what relative proportions the loops, divisions, and free terminations, stand with respect to each other, and whether in the diffe- rent Mammalia, notwithstanding any apparent difference, some corre- spondence obtains or not. * [" General Anatomy," translated by G. Gulliver, p. 263, pi. 19, Figs. 99, 100. TBS.] 416 SPECIAL HISTOLOGY. 122. Cerebral Nerves. The sensitive and motor nerves arising in the brain, correspond in most particulars so closely with the spinal nerves, that a short description of them will suffice ; and with respect to the higher nerves of sense, they will be afterwards described, more fully, in connection with the organs to which they belong. The motor cerebral nerves, the third, fourth, sixth, seventh, and twelfth pairs, with respect both to their roots and to their course and distribution, present exactly the same conditions as the motor roots and muscular branches of the spinal nerves, with the sole exception, that by all these nerves, from their anastomosing with sensitive nerves, some sensitive fibres are conveyed to the muscles. It deserves remark : 1, that according to Rosenthal and Purkinje, nerve-cells exist in the trunk of the oculo-motorius in the Ox, which, however, Bidder (p. 32) was unable to find ; 2, that the facial nerve, in its gangliform enlargement, presents a number of larger nerve-cells, through which, however, accord- ing to Remak, only part of the fibres pass (Mull. "Archiv." l%tl); 3, that according to Volkmann (in Bidder's " Ganglien-korper," p. 68), the small root of the hypoglossal nerve in the Calf, which is furnished with a ganglion, produces motor effects. What is the significance of this occurrence of nerve-cells in motor nerves has not been ascertained. Probably simple fibres having a peripheral destination arise from them, exactly as in the spinal ganglia. In any case it shows that ganglia are not necessarily placed only on sensitive nerves. The fifth, ninth, and tenth pairs, resemble the spinal nerves, inasmuch as that they all con- tain motor and sensitive elements. In the irigeminus the small root exhibits a preponderance of thick fibres ; the larger, numerous fine fibres. The Gasserian ganglion, as well as the smaller ganglionic body seated upon it, contains many larger and smaller nerve-cells of 0-008- 0-030 of a line, with nucleated sheaths, and presents the same conditions, according to my observations, in small Mammalia and in Man, as a spi- nal ganglion, that is to say, it is simply traversed by the fibres of the greater root, and, from unipolar cells, gives origin to numerous nerve- fibres of medium size, which go to join the emergent branches. Bipolar cells also occur, but, as it appears, in less quantity, and anything that can be said about apolar cells is as applicable here as in the case of the spinal ganglia. The ultimate distribution of the n. trigeminus is for the most part similar to that of the cutaneous nerves, and, in particular, the existence of divisions of the nerve-tubes may be distinctly demonstrated in the mucous membranes, as in the conjunctiva at the edge of the cor- nea, in the ciliary ligament, in the tooth-pulp, and in the papillae of the tongue. Terminal loops and free terminations appear to exist in the papillae of the mucous membrane of the mouth and tongue, and in the conjunctiva, whilst in the cornea, the extremities of the nerves are quite THE NERVOUS SYSTEM. 417 transparent and pale, and constitute a wide-meshed plexus without any divisions. With respect to the ganglia, which are placed on the n. trigeminus (ganglion ciliare, oticum, sphenopalatinum, linguale, supra- maxillare), I find their structure more to resemble that of the sympa- thetic ganglia, only that they contain a considerable number of larger nerve-cells. The glossopharyngeus, although endowed with motor pro- perties, still, according to Volkmann (Mull. "Arch.," 1840, p. 488), has no fibres which do not pass through one or other of its ganglia. In its roots, which contain numerous fine fibres, there are, according to Bidder (1. c. p. 30), in the Mammalia, not unfrequently, isolated nerve- cells, often placed free upon it, in which, as in similar cells, on the roots of the n. vagus, the giving off of two middle-sized fibres, it is said, may occasionally be readily perceived. The ganglia of the glossopharyngeus present the same conditions as the spinal ganglia, that is to say, the radical fibres simply traverse them, and, within the ganglion, fibres arise from cells, which are for the most part unipolar ; its ultimate ramifica- tion in the tympanic cavity and in the tongue, contains small ganglia, and otherwise corresponds with that of the n. trigeminus (p. major). In Man, all the roots of the n. vagus enter the jugular ganglion, whilst in some of the Mammalia Dog, Cat, Rabbit, according to Remak (in Fro- riep's "Not.," 1837, No. 54), in the Dog and Sheep, according to Volk- mann (Mailer's "Arch.," 1840, p. 491), but not in the Calf, in which nerve-cells occur in the apparently motor root, it has also a primary fasciculus, which has no connection with the ganglion. In the ganglion jugulare and in the intumescentia ganglioformis of the facial nerve, I have not been able to find anything different from the spinal ganglia, only, that the nerve-cells measure occasionally no more than 0-009 of a line, although it is true that there are also a great many as large as 0-03 of a line. The ultimate distribution of the nerve exhibits, as Bidder and Volkmann correctly state, a constant kind of separation of thicker and more slender fibres, so that the branches to the oesophagus, heart, and stomach, are composed almost entirely of fine fibres, whilst in those going to the lungs, and in the laryngeus superior, the fine are to the thick fibres as 2 to 1 ; and in the laryngeus inferior and the rami pha~ ryngei, as 1 to 6-10. All these fine fibres are very far from being derived from the sympathetic, as they occur in preponderating quantity even in the roots of the vagus, and are also numerous in the laryngeus superior. Many of them, moreover, may be nothing more than attenu- ated or originally finer ganglion-fibres, as they are termed, arising in the ganglia of the vagus itself, and which likewise I should not refer to the sympathetic. With respect to the terminations of the vagus, reference must be made below to the proper places. The n. accessorius Willisii, although perhaps also in part sensitive, has no nerve-cells, and in its 27 418 SPECIAL HISTOLOGY. distribution and termination, so far as is known, presents nothing peculiar. Terminal loops within the trunks of nerves had been already noticed by Gerber, and have lately been described by Valentin in the vagus (pectoral portion) of the Mouse and Shrew-mouse, but without their expressing any opinion with respect to their signification. Still more mysterious are the nervous filaments seen by Remak and Bochdalek, coming out from, and again re-entering the brain. 123. Granglionic Nerves. Under this name, perhaps, is most suitably designated the n. sympathicus, as it is termed, the sympa- thetic or vegetative nervous system, as it presupposes no physiological hypothesis, but simply expresses the fact, which, anatomically, is most apparent to the eye. The ganglionic nerves are neither a wholly inde- pendent part of the nervous system (Reil, Bichat), nor a mere section of the cerebro-spinal nerves ; but on the one hand, from the very numerous fine nerve-fibres originating in their ganglia ganglion-fibres of the sym- pathetic, form an independent system ; whilst on the other, they are also connected with the spinal cord and brain, owing to their receiving a smaller number of fibres of the other nerves. Upon comparing the ganglionic nerves with the cerebro-spinal, we find, that the former, as they are constituted from a double source, in a certain respect undoubt- edly resemble the latter, which are also formed from ganglionic fibres of the spinal ganglia, and from others proceeding from the cord ; but they differ, particularly in this respect, that they possess a much greater number of independent elements, of ganglia and ganglionic fibres, and enter into much more numerous anastomoses with each other. Conse- quently, although we appear to be justified from an anatomical point of view, in considering the ganglionic nerves by themselves, still they must not be regarded as something altogether peculiar, seeing that, essentially, every nerve exhibits the same principal elements, and some cerebral nerves, vagus, glossopharyngeus, possess even numerous peripheral ganglia ; and moreover, because comparative Anatomy shows that they are produced from the spinal nerves, and Physiology the absence of peculiar functions in them. 124. The principal trunk of the ganglionic nerves (nervus sympa- thicus). The n. sympathicus in man appears as a whitish, or white nerve, the dark-bordered fibres of which usually run parallel with each other, without divisions or anastomoses, some measuring 0-0025-0-006 of a line or even more, and others not more than 0-0012-0-0025 of a THE NERVOUS SYSTEM. 419 line. These finer and coarser fibres are partially intermixed, partly Fig. 161. Vs. disposed more in a fascicular manner, the latter being the case near the ganglia of the main trunk and in that part itself. The structure of the ganglia is, in the main, similar to that of the spinal ganglia. Each of them consists : 1, of perforating nerve-fibres, proceeding from one part of the trunk to the other ; 2, of a certain number of finer tubules originating in the ganglion ; and 3, of numerous nerve-cells; besides these the rami communicantes also enter the ganglia, and a certain num- ber of peripheral branches are given off from it. The nerve-cells in the sympathetic (Fig. 162 B), present, in all essential particulars, precisely the same conditions as those in the spinal ganglia, only that they are, on an average, smaller, measuring 0*006-0'018, 0-008-0-01 of a line in the mean, with less and paler pigment, or even colorless and usually pretty uniformly rounded. As respects the origin of the nerve-fibres of the main trunk, it is, in the first place, evident, that they are in great part derived from the rami communicantes which arise immediately below the spinal ganglia from the trunks of the spinal nerves ; that they are in general formed like the sensitive roots of those nerves (that is, contain a preponderance of finer fibres), and, whether simple or com- pound, that they are manifestly connected with both roots. From all that has hitherto been made out, the fibres of these connecting branches are derived chiefly from the spinal cord and from the spinal ganglia, FIG. 161.- Sixth thoracic ganglion, on the left side, of the sympathetic nerve of the Rabbit, viewed from behind, treated with soda, and magnified 40 diam. : T. 2, trunk of the sympa- thetic; R. c. R. c, rami communicantes, each dividing into two branches; Spl., n. splanc hnicus ; S, twigs of the ganglion with two stronger fibres and finer filaments, probably going to vessels ; G, nerve-cells, and ganglion-fibres joining the main trunk. FIG. 162. From the sympathetic in Man, magnified 350 diam. : j$, a portion of a gray nerve treated with acetic acid ; a, fine nerve-tubes ; 6, nuclei of the fibres of Remak. B+ Three nerve-cells, one with a pale process. 420 SPECIAL HISTOLOGY. and are consequently roots of the sympathetic ; in a smaller proportion, however, they might be derived from the sympathetic, and joining them- selves to the spinal nerves are further distributed peripherally together with them. Having entered the main trunk of the sympathetic, the rami communicantes, so far as they are derived from the spinal nerves, almost invariably run, dividing into two or several branches upwards and downwards in it, towards its cephalic and pelvic extremities, being in apposition with the longitudinal fibres of the trunk. In the Rabbit, the- fibres of a given ramus communicans may very frequently be traced as far as the nearest ganglion and beyond it, in separate peripheral branches, but, in general, the course of the individual fasciculi very soon escapes the eye. It may nevertheless be asserted with great cer- tainty, that they all gradually go off in the peripheral branches of the main trunk, for in the first place all these branches frequently contain, in considerable quantity, the same dark-bordered thicker fibres, as those which are contained in the rami communicantes, and secondly their ter- mination or origin is never observed in the main trunk itself; which circumstance is also the principal reason why the rami communic antes can be regarded not as branches of the sympathetic, but only as its roots. Besides the fine and coarser fibres of the rami communicantes, the main trunk of the sympathetic contains other fibres in very great numbers, which are dark-bordered, but pale, finest nerve-tubes measur- ing 0'0012-0*002 of a line, with respect to which I unhesitatingly assert, that they originate in it, and are in no way continuations of the rami communicanteSj as has been quite recently supposed, since the discovery of the bipolar ganglion-cells in Fishes. In the Mammalia it is, in fact, extremely easy to prove, by the examination of entire sympathetic ganglia under the careful application of dilute soda and compression, that the great majority of the fibres of the rami communicantes have not the slightest connection with the ganglion-cells, but much rather that they simply pass through the ganglia, and ultimately go off in the peripheral branches. Now, as, besides these fibres in the main trunk, numerous other fibres of the finest kind exist, which can in no way be assigned to the rami communic antes ^ it is clear, that they must be struc- tures of entirely new formation. This conclusion appears to be the more legitimate, when it is added, that it is not, as I first and many since have shown, by any means so difficult to demonstrate simple origins of fibres in the sympathetic ganglia of the Mammalia and Amphibia, and that, in the ganglia a considerable portion of fine fibres assume the aspect of so-called convoluted fibres, that is to say, of fibres winding about in various directions through the mass of cells. From what I have seen in the Mammalia and man, the sympathetic ganglia correspond so far with those of the spinal nerves, that they contain a THE NERVOUS SYSTEM. 421 preponderance of unipolar, rarely of bipolar cells, differing, however, in this respect, that apolar cells certainly exist in them in more consider- able quantity, and the ganglion fibres arising in them are invariably of the finest kind, occurring in the peripheral nerves, and probably in most cases, quit the ganglia in various directions. As for a topographical tracing of the various fibres in the main trunk of the sympathetic, with reference to their origin from particular rami communic antes and ganglia, and their continuation into particular peripheral branches, if more be required than what has already been stated it is not by any means at present to be thought of, but must be reserved for future in- vestigation. It has-been asserted, that the smaller cells in the ganglia of the sympathetic are different from the larger cells in the spinal ganglia, for instance ; and also that they are connected only with fine nerve-tubes (Robin), but this is not correct, as is apparent in part from the observa- tions of Wagner and Stannius ; for we find : 1, in the ganglia of the cerebral and spinal nerves of the Mammalia and of man, all intermediate sizes between larger and smaller nerve-cells, and also, occasionally, though rarely, larger cells, measuring as much as 0-03 of a line in the sympathetic ganglia ; and we may also be convinced, 2, that the diame- ter of the nerve-fibres originating in the first-named ganglia, is not at all regulated by that of the cells, all their ganglion-fibres being pretty nearly of the same size, and which is confirmed also by the bipolar cells of Fishes, where the one fibre arising from the cell is often considerably thicker than the other ; in Petromyzon, according to Stannius, even six times. Should it be at all supposed that the small cells are peculiar to the sympathetic nerve alone, I must, as above, with respect to the nerve-fibres, remark, that not to mention the ganglia of the roots of the cerebral and spinal nerves, small nerve-cells also occur in situations where there can be no question about the sympathetic, as in the spinal cord and brain, and, if instances of the same kind in the peripheral nerves be desired in the retina and cochlea. At all events, this much is certain, that the ganglia of the ganglionic system of nerves constantly present smaller nerve-cells, and that the fibres arising from them are of the fine kind only. Bidder and Volkmann have shown, in the Frog, that the greater part of the fibres of the rami communicantes are distributed peripherally, with the spinal nerves, and that only a small portion of them, which moreover are derived from the spinal ganglia, should be regarded as roots of the sympathetic. But I think I have noticed in the Babbit and in Man, that the rami communicantes have chiefly a central des- tination. Still, in man, fibres also occur very frequently according to Luschka always, which must be regarded as branches of the sympa- 422 SPECIAL HISTOLOGY. thetic going to the peripheral distribution of the spinal nerves, from which again twigs are given off to nerves of the vertebrae ; with respect to which conditions the more detailed observations given in my " Mikr. Anat.," II. p. 525, and particularly those of Luschka (" Nerven des Wirbelcanals," p. 10 et seq.) may be consulted. With regard to the question, whence the fibres are derived which join the main trunk of the sympathetic from the spinal nerves, it is certain that that portion of the rami communicantes, which arises from the motor root, and which, according to Luschka, is always a white filament, takes its origin from the cord (or brain) itself, but as regards the other, proceeding from the sensitive root, it may be formed, in part or wholly, from fibres origi- nating in the ganglion. The latter, however, appears to be improbable, for two reasons : 1, because in that case, the existence of conscious sensations from parts supplied by the sympathetic would scarcely be conceivable ; and 2, because the fibres originating in the spinal ganglia are of medium size, whilst, in the rami communicantes, upon the whole, only a few of that kind occur, and these, moreover, must be referred to the motor root. We may here offer a few remarks upon the fine fibres of the gan- glionic nerves. It has been long known, that the sympathetic contains a larger proportion of finer nerve-fibres than the cerebro-spinal nerves, but it was not till 1842 that Bidder and Volkmann labored to show, that these fibres are not only smaller, but also, in other respects, ana- tomically different ; on which account in contradistinction to the thick fibres of the cerebro-spinal nerves, they termed them sympathetic nerve- fibres. In opposition to this, Valentin (" Rep.," 1843, p. 103) and I (" Sympath.," p. 10 et seq.) have endeavored to prove, that the fine fibres in the sympathetic do not constitute a special class, and in this I think we were tolerably successful. The principal reasons are as fol- lows : 1. Fine and thick nerve-fibres do not differ intrinsically in any essential respect except in size, and present the most numerous interme- diate dimensions. 2. Fine nerve-fibres having exactly the same charac- ters as those of the so-termed sympathetic exist in many other situations, as for instance, in Man and the Mammalia, in the posterior roots of the spinal nerves and of the sensitive cerebral nerves, in which situations, as I have already shown, there can be no question whatever as to a derivation of the fibres from the sympathetic, and where we have pre- sented to us, nothing but fine cerebro-spinal fibres ; similar fibres are contained by thousands in the spinal cord and brain, as well as in the two higher nerves of sense. 3. All thick nerve-fibres decrease in size in their ultimate ramifications, owing to divisions, or direct diminution, so that ultimately they acquire the diameter and nature of the fine, and finest kinds of fibres. 4. All thick nerve-fibres in the course of their development are, at one time, exactly in the condition of the so- THE NERVOUS SYSTEM. 423 termed sympathetic fibres. From these facts it would appear certainly evident, that it is impossible to regard the fine fibres of the sympathetic as altogether of a special nature, and peculiar to it alone, and that it will not do, in the anatomical point of view, to classify the fibres accord- ing to their size, very many in fact, in their course, assuming all possi- ble degrees of thickness. Allowing that the great number of very fine pale fibres in the sympathetic is a prominent anatomical fact, as is also indeed the case in the higher nerves of sense and in the gray substance, still, speaking physiologically, I am by no means of opinion that the fineness of the fibres in the sympathetic indicates anything of a special nature in them, and which does not exist elsewhere, but perhaps, that where this condition does exist both in them and in other situations, it is connected with a distinct kind of function. 125. Peripheral distribution of the ganglionic Nerves. From the main trunk of the sympathetic arise the branches proceeding to the periphery, which without exception, receive finer and thick fibres from it, but besides these, in part at least, contain other special elements, to which is due their varied aspect. Some of them, for instance, are white, as is the main trunk in most situations, such are the n. splanch- nici ; others grayish white, as the nervi intestinales, the nerves of the unimpregnated uterus (Remak, "Darmnerven System," p. 30); others again gray, and at the same time less firm to the feel, as the n. caroti- cus, internus, the nn. carotid externi s. molles, the nn. cardiaci, the vascular branches in general, the branches connecting the large ganglia and plexuses in the abdomen, those which enter the glands, and the pelvic plexuses. The peculiar condition of the latter nerves depends, in part, upon the paler color of the fine fibres of the sympathetic itself, but in great measure upon the presence of the fibres, named after their discoverer, the fibres of Remak ("gelatinous fibres " of Henle), which were at first regarded as a kind of nerve-tubes, and of which, even now, some cannot be convinced that they are only a sort of connective tissue. They are sometimes more readily isolated, sometimes more united into a compact substance resembling homogeneous connective tissue. In the former case they present the aspect of flat, pale fibres, 0*0015-0-0025 of a line broad, and 0-0006 of a line thick, of an indistinctly striated, granular, or more homogeneous substance ; and which, under the action of dilute organic acids, exhibit precisely the same conditions as connec- tive tissue, and from point to point are furnished with, mostly elongated, or fusiform nuclei, 0-003-0-007 of a line long, 0-002-0-003 of a line broad. These fibres, again, are found in almost all the gray portions of the ganglionic nerves I cannot find them in many parts of the pelvic plexuses in Man, where they are replaced by a non-nucleated abundant connective tissue, though they are said by Remak to abound 424 SPECIAL HISTOLOGY. in the nerves of the impregnated uterus ( u Darmnervensyst," p. 30) in very great quantity, so that they amount to from three to ten times the number of the dark-bordered true nerve-fibres. They constitute the main part of the proper basis of these trunks, and the dark-bor- dered tubes extend through them, sometimes more isolated, sometimes assembled in larger or smaller fasciculi ; more rarely, and only in the neighborhood of the ganglia themselves, do they appear to form sheaths to individual tubes of the finest kind. Besides these " fibres of Remak," the peripheral ramifications of the sympathetic are, above all, distin- guished by a great number of ganglia. These bodies, of a larger or less size, some even microscopic, are placed on the branches or terminations, and, indeed, the microscopic ganglia, so far as is hitherto known, on the nervi carotid, in the pharyngeal plexus, in the heart, at the root of the lungs and in the lungs, on the suprarenal capsules, in the lymphatic glands, in the kidneys of Man occasionally, on the posterior wall of the bladder, in the muscular substance of the neck of the uterus in the Sow, in the plexus cavernosi, and with respect to their distribution, will be further adverted to when we come to speak of the viscera. I will here remark in general, concerning them that with respect to the size and figure of the nerve-cells, and the origination of fine fibres, they present precisely the same conditions as the ganglia of the main trunk. As regards the last point, it may be especially noticed, that in one situa- tion the origin of nerve-fibres from unipolar cells, and the rarity of the double origin of fibres, is particularly well displayed, viz. in the septum of the heart in the Frog (Fig. 163), where R. Wagner has also described their occurrence. These ganglia, therefore, are also sources of nerve-fibres, and the emergent branches always contain more than the roots, on the supposition that the fibres come out only in one direction, which perhaps in most places may be the case. In the same situation also, it is most readily and satisfactorily seen that many of the cells are apolar and without any processes (Fig. 163); as is also most plainly shown in the cardiac ganglia and small ganglia, t>n the wall of the urinary bladder in Bombinator, in which ganglia, as well as in the similar ganglia in the Frog, the conditions described are as manifest as possible. How the fibres arising from these various localities, from the rami communicantes, the ganglia of the main trunk, and the peripheral gan- glia, are disposed in their ultimate distribution, is as yet very doubtful. Many peripheral branches anastomose with other nerves, and thus escape all further research, as the nn. carotid externi and internus, the latter of which, containing scarcely anything but fine fibres and numerous FIG. 163. Nerve-cells from the cardiac ganglia of the Frog, magnified 350 diam.: one with the origin of a nerve-tube. THE NERVOUS SYSTEM. 425 "fibres of Remak," I do not look upon in the common sense as a root, but as a branch, arising from the superior cervical ganglion, and pro- bably the other cervical ganglia ; as well as the rami communicantes, seeing that individual fibres of them, actually join peripherally the spinal nerves ; and the rami cardiaci, pulmonales, &c. Other branches in the parenchyma of the organs become so fine, that it is impossible to trace them. What has been as yet established respecting their ultimate course, is as follows : 1. Divisions occur in the branches and terminal ramifications of the sympathetic, as in the nerves of the spleen, the Pacinian bodies in the mesentery, in the nerves accompanying the mesenteric vessels in the Frog, in those which exist temporarily in the uterus of the Rodentia, of the lungs and stomach of the Frog and Rabbit, of the dura mater on the meningeal arteries, in branches of the sympathetic of the Sturgeon, in the cardiac nerves of the Amphibia, and in those of the urinary bladder in the Rabbit and Mouse. 2. There are free terminations of the nerves, as in the Pacinian bodies and on the mesenteric vessels in the Frog. 3. The thicker fibres of the sympathetic ultimately so decrease in size as to become of the fine kind; as may be readily seen in the rami intestinales, lineales, and hepatici, which, indeed, even in the interior of the organs in question, contain some coarser nerve-fibres, but ultimately lose them. The actual terminations, how- ever, in the organs themselves, in the heart, lungs, stomach, intestine, kidneys, spleen, liver, uterus, &c., are as yet quite unknown ; although from the impossibility of finding any dark-bordered fibres in the ultimate ramifications of these nerves, it may be supposed that they terminate, almost everywhere, in non-rnedullated, embryonic fibres. In fact, I have, at all events hitherto, in vain endeavored to find a trace of them. Schaffner says, that in the heart of Bombinator he has seen the passage of the dark-bordered fibres into pale, anastomosing fibrils of the finest kind, whilst Pappenheim (1. c.) describes loops in the nerves of the kidney. As regards the nature of the "fibres of Remak," most recent ob- servers incline to the opinion first advanced by Valentin (" Repert.," 1838, p. 72; Muller's "Archiv," 1839, p. 107), that they are not nerve- fibres at all, but to be referred to the connective tissue of the nerves ; whilst Remak still thinks himself obliged to adhere to his previous opinion, that they are, or may be, in part at least, nerve-fibres ("Darm. nervensyst.," p. 30). As for myself, I freely acknowledge the force of the reasons adduced by the latter observer, which are based chiefly upon the similarity of the fibres in question to the pale embryonic nerve- fibres, inasmuch as that even in the adult, nucleated nerve-fibres are met with in the olfactory nerve ; but I am compelled, nevertheless, as before, fully to concur with Valentin, as do also Bidder and Volkmann, and 426 SPECIAL HISTOLOGY. many others. My reasons are the following : 1. The " fibres of Remak," as may be easily shown, arise from the sheath of the nerve-cells of the sympathetic ganglia, and are continued in the nervous trunks, surround- ing the nerve-fibres arising from the ganglia. Now as it is certain that these sheaths are a sort of connective tissue, as is apparent also from the spinal ganglia, where they occur in precisely a similar way, only more scantily and without their being continued into the nerves, it fol- lows that the "fibres of Remak" can scarcely be anything else. 2. The finest twigs of the spinal nerves also exhibit nucleated fibres, in all re- spects like those of Remak, as for instance, those going to the skin, &c. ; with respect to which, as they are wanting in the trunks of the nerves, there can be no question at all of their not being nerve-fibres. 3. The quantity of the "fibres of Remak" always diminishes towards the finest ramifications, which could not be the case were they nerves. It is not, indeed, altogether correct, as stated by Valentin, that they are not to be found in the finer intestinal nerves, for there can be no doubt that they do exist there, though much more rarely than in the trunks of the nerves, and are only to be brought into view by compression. According to Remak (Mull. " Arch.," 1844, p. 464), they also exist in the cardiac nerves of the Mammalia ; although as far as I can perceive, only in the immediate neighborhood of the ganglia. Relying upon these reasons, I continue in the firm persuasion that the nucleated fibres in the sympa- thetic nerve of adult Mammalia are a form of the neurilemma; but I will not omit to remark, that I consider it quite impossible to determine, in undeveloped nerves, what is neurilemma and what young nerve-fibres. Thus in the Rabbit, 2-6 months old, in the n. caroticus internus, not a single developed nerve-fibre is to be met with, and apparently nothing but "fibres of Remak," although it is quite certain thattogether with them, there must also exist the rudiments of numerous dark-bordered fibres. In the nerves of the spleen, in the Calf, in like manner, nume- rous nucleated fibres are met with, though in the terminations (vide " Cyclopaedia of Anatomy," III. p. 795, figs. 539 and 540), which, pro- bably, afterwards become nerve-fibres. In young animals, consequently, we must not look for a decision of the question; whilst in older ones, it is quite otherwise. In them, a nucleated fibre can only be regarded as a nerve when it can be traced into a dark-bordered fibre, or to a true process of a nerve-cell ; and this, as we have seen, is not the case in those of the sympathetic system. It may, however, be remarked, that " fibres of Remak" also occur in the ganglia of the main sympathetic trunk, but that they do not, for the most part, extend to any distance beyond them, so that usually but few are contained in the trunk of the nerve itself, 126. Development of the elements of the Nervous System. The THE NERVOUS SYSTEM. 427 nerve-cells, wherever they may occur, are nothing else than transforma- tions of the so-called embryonic-cells; some of which simply enlarge, whilst others throw out a varying number of processes, and are, at all events in part, connected with nerve-fibres. Many nerve-cells also appear, at a subsequent period, to increase by division ; at all events, I do not know how otherwise to explain the fre- quent occurrence of two nuclei in the nerve-cells of young animals, especially in the ganglia ; and the cells connected by communicating filaments, which have been noticed by various observers. Fig. 164. The peripheral nerve-fibres all originate on the spot, but their subse- quent development proceeds in such a way that the central extremities always precede the peripheral. With the exception of the extremi- ties of the nerves, they are developed from fusiform nucleated cells, which are nothing else than modifications of the primordial formative cells of the embryo, and are conjoined into pale, flattened, elongated, nucleated tubules or fibres 0-001-0-003 of a line, broad. Now, at first the nerves consist only of fibres of this kind, and of the rudiment of the neurilemma, being gray or dull white, like the sympathetic filaments ; subsequently, in the human embryo at the fourth or fifth month, they always assume a whiter color, and the proper white or medullary sub- stance continues to be more and more developed in them. Of the three possible modes of development of this substance propounded by Schwann, one only, in the present state of things, can come into question, that namely, as to whether the medullary sheath is a structure deposited between the membrane and the contents of the embryonic nucleated fibres; in which case the contents of the latter would become the axis- fibre. But besides this, the medullary sheath may originate in what did FIG. 164. Nerve-cell from a spinal ganglion of a sixteen weeks' human embryo : a, nucleus in the pale process of the cell; 2, self-developing nerve-tubes from the brain of a two-months' human embryo ; 3, cells from the gray cerebral substance of the same embryo. FIG. 165. 1, two nerve-fibres from the ischiatic nerve of a sixteen- weeks' embryo; 2, nerve-tubes from a newly-littered Rabbit; a, their sheath ; 6, nucleus; c, medullary sheath ; 3, nerve-fibre from the tail of the Tadpole ; a, 6, c, as before ; at y the most careful investigation. The third hypo- thesis is indeed conceivable, but in opposition to it, we find that pores and canals exist even in the youngest and softest dentine, when the de- velopment of the tooth is at all advanced, and therefore, that they can hardly be regarded as secondary formations. In favor of the first sup- position, on the other hand, it may be said, that it would, if true, indi- cate a close agreement between dentine and osseous tissue, structures which are in every case nearly allied, inasmuch as the dentinal tubules would be homologous with long and narrow, simple or possibly coalesced, osseous lacunce. Certain objections may be urged, which are not, per- haps, so important as they at first appear. These are, in the first place, that the dentinal canals have special walls and may be isolated as tubes, which might be regarded as demonstrative evidence that they are deve- loped out of peculiar vesicular structures, either nuclei or cells; and secondly, that upon this supposition, the filamentous appendages to the dentinal cells are not so readily interpreted. But as regards the former, we have recently learnt that the osseous lacunce and canaliculi may also 492 SPECIAL HISTOLOGY. be isolated, with special walls which are not those of the original cells, and the same is true of the Haversian canals, whence it would be con- ceivable that the walls of the dentinal canals also, although originally and genetically not special structures, might eventually become so. Since, again, the processes of the dentinal cells may be nothing else than the still soft part of the cells in which ossification is commencing, this first hypothesis may be regarded as having a certain claim to con- sideration, the more so as the osseous lacunce in the teeth frequently as- sume forms resembling those of the dentinal canals, often communicate with them, and, at least in animals, are interposed among them. To sum up, it may be said, that in any case, the matrix of the dentine proceeds from the cylindrical cells investing the pulp of the tooth, which undergo a greater or less elongation, coalesce and ossify. The dentinal canals either arise from the nuclei of these cells, or are, and this at present appears to me to be more probable, the remains of the cavities of the cells, whose boundaries have undergone a greater consolidation, arid therefore correspond with osseous lacunce. The divisions of the canals are explained, if we conceive, either that the dentinal cells divide longitudinally from time to time, as I believe I have actually observed, or that a cell coalesces with two of its predecessors. As to the more delicate ramifications, we can only suppose that they are formed by a secondary process of resorption in already formed dentine, like that which must be assumed to occur in the osseous lacunce, to account for the anastomoses of their canaliculi, and their communication with Haversian canals ; at least, I see no possibility, whatever view we take, of explaining their formation in any other way, without coming into opposition with well-ascertained facts. No such process as the thicken- ing and ossification of dentinal cells accompanied by the formation of pore-canals can be observed, so that the fine lateral branches appear to be entirely of secondary origin. In the course of the ossification of the dentine, at least in man, we find that the deposition of calcareous salts in the recently-formed, structurally characterized, though only slightly hardened dentine, takes place in such a manner that the whole appears to consist of isolated globules. These globules, which are visible not only at later periods, but in the earliest cap of dentine, and are best seen at the edge of the root of a large tooth viewed externally, eventually disappear if develop- ment proceed normally, calcareous matter being deposited between them, so that the dentine becomes quite homogeneous and clear; in the opposite case, they persist in greater or less number, and the spaces between them, which are nothing but the interglobular spaces above described, contain unossified dentine. According to my observations, the development of the cement takes place from that portion of the dental sac which lies between the pulp THE TEETH. 493 and the enamel organ, and commences, even before the eruption of the teeth, contemporaneously with the formation of their fangs. About this time the dental sac elongates inferiorly, applies itself to the grow- ing fang, yields, from its abundant vascular network, a soft blastema, in which nucleated cells are developed, and then ossification takes place. The cement, therefore, is not formed by the ossification of the sac itself. I met with the first traces of it in newly-born infants, in the form of isolated, elongated, or rounded scales, which were firmly attached to the dentine of the, as yet, very short fang, and looked exactly like the developing osseous substance in the cranial bones ; the smallest exhi- bited distinct osseous lacunce and a faint yellow tinge, but were quite soft and transparent, passing at their edges into a clear cellular blas- tema ; in the larger ones, the margins were similar, but the centre was darker and firmer, and in this way every stage of transition to actual bone was presented, without any granular deposit of calcareous matter. With the elongation of the fang, new osseous scales of this kind were formed and gradually coalesced from above downwards into a single layer, to which continual additions were made from without, until the whole thickness of the cement was produced. I am unacquainted with the manner in which the Nasmyth's mem- brane is produced. No structureless layer exists upon the enamel organ, by the ossification of which it might be supposed to be formed, and therefore I should be inclined to regard it as a calcified, amorphous exudation secreted from the enamel organ immediately after the ossifi- cation of the last enamel cells, which glues together and protects the ends of the prisms of the enamel. If we now, in conclusion, take a general view of the different struc- tures in the teeth and their mutual relations, we perceive that although they agree in certain respects, yet they cannot be brought under one class. Dentine and cement are much more closely allied to one ano- ther, than to enamel, and should it prove to be correct that the den- tinal canals are formed by the coalescence of the cavities of thickened, elongated cells, the dentine will correspond with an osseous tissue, whose matrix is constituted only by the thickened walls of the original cells, and whose lacunce are all directly connected. Cement, or bone and dentine, often have a very close external resemblance to one another, particularly, on the one hand, when the latter is traversed by numerous Haversian canals, and, as Retzius believes he has observed, contains osseous lacunse ; and, on the other hand, when, in bone, the lacunae are either greatly elongated, with numerous canaliculi, vascular canals also existing ; or when with few lacunce, the canaliculi are numerous and parallel, like dentinal canals. This much is certain, that the two sub- stances never become exactly alike, and it is probable that their develop- ment is always to a certain extent different. 494 SPECIAL HISTOLOGY. The enamel may be best compared with a dentine whose cells are ossified throughout, and which, therefore presents no canals, like that in the outermost layers of fishes' teeth; at least the two substances agree in this, that they are entirely composed of elongated cells without any connecting matrix. When canals occur in the enamel, it acquires a very great similarity to dentine ; but these canals probably have a to- tally different import to those in the dentine, viz. that of cavities which proceed from absorption. With the cement, the enamel has, in general, no analogy, though there is a kind of homogeneous cement with an indistinct transverse striation which, at least externally, looks some- what like enamel, but has hardly, like the latter, arisen from elongated cells. If we consider the nature of the parts from which the various substances are developed, the dentine, formed from the vascular part of the mucous membrane of the mouth, is a true product of the homologue of the derma (schleimhaut-productiori), the enamel an epithelial structure, and the cement an investing substance, afforded by the mucous membrane. 143. The substance of the perfect tooth, though hard, is by no means incapable of molecular change, as its various diseases best show. The functions of the lacunce and their canaliculi in the bones are here performed by the dentinal canals with their ramifications, the lacunce and canaliculi in the cement, and the fissures between the prisms of the enamel. All these cavities, during life, contain a fluid, derived on the one side, from the vessel of the pulp, on the other, from those of the alveolar periosteum, and permit of changes in the substance, though they may be slow. Nothing definite, however, is known about the latter, but from the circumstance that perfect dentine is not colored wh'en an animal is fed with madder (Hunter, Flourens, and others : compare Henle, p. 878), it may be concluded, that they are far less active than in the bones, and perhaps take place in such a manner that the calcareous matters are not at all or only very slowly renewed. The dentine is un- doubtedly best provided with fluid supplies, from its being penetrated by very numerous and frequently anastomosing canals. We can as little .suppose any regular circulation in it as in the bones ; but it may be .assumed that a certain movement takes place, proportionate to the :amount of the exudative and absorptive processes in the pulp, of the waste in the tooth itself, and of the supply afforded to the enamel and >cement and probably given off from the latter tissues externally. Though the enamel is not impermeable, it permits of the passage of fluids with difficulty, as is best shown by the circumstance that the nerves of the dental pulp are not affected by acids, so long as the coating of enamel is entire, but readily enough, when, as in the incisors, the dentine is ex- tposed. The enamel, again, is the hardest dental tissue, possesses scarcely -any organic matrix and no constant systems of canals. Nasmyth's THE TEETH. 495 membrane, which is attacked with so much difficulty by chemical reagents, is, very probably, still more impenetrable than the enamel itself, and hence these two substances serve admirably to protect the teeth. The sensibility of the teeth arises from the nerves of their pulp ; they are affected by contact, heat, cold, and chemical agents. Slight mechanical influence can only act by the vibrations which they may communicate to the substance of the tooth and thence to the pulp ; it is therefore the more remarkable that the teeth have a certain sense of locality, so that it is possible to distinguish whether they are touched internally or externally, above or below, on the right or on the left side. The sensibility of the teeth is indeed tolerably delicate, especially on the masticating surface, where the smallest foreign bodies, as hairs, grains of sand, &c., are perceived when these surfaces are rubbed against one another ; and as regards its acuteness, it is, in disease at least, excessive, which is sufficiently explained by the considerable num- ber of nerves in the pulp and the readiness with which they may be compressed within their hard receptacle. With age the teeth become denser ; the pulp cavity is filled with a kind of irregular dentine and may be totally obliterated, which is, per- haps, the normal cause of their falling out. In certain cases observed by Tomes, the fangs in old age were quite transparent, like horn. The following remarks may be made upon the pathology of the teeth. Permanent teeth which have fallen out are sometimes replaced by a third dentition ; but it must not be forgotten that the milk teeth occasionally remain beyond their time, and care must be taken not to confound a second tooth, late in its eruption, with a third. Teeth which have been extracted may be replaced (in fifteen months a canine tooth which had been extracted from the upper jaw was perfectly firm again). An abnor- mal development of the teeth takes place particularly in the ovarium, but also elsewhere. Fractures of the teeth may be reunited when they occur within the alveoli, by imperfect dentine or cement. Regeneration of the worn down parts takes place only in animals (Rodents, e.g.] in which the teeth constantly grow. Hypertrophy of the cement (the so-called exostosis\ deposits of dentine in the walls of the pulp cavity and ossification of the pulp itself, are exceedingly common, and result from chronic inflammation of the periosteum and pulp.* A partial dis- * [Wedl in his recent work (Grundziige der path. Histol.) has added some very inte- resting observations to our knowledge of the structural changes occurring in the different parts of teeth. In hypertrophy of the cement he observed the canaliculi dilated, so as to form Haversian canals, and agrees with Kolliker (vid. 140 supra) as to the frequency of the hypertrophy of the entire cement in old teeth. In partial hypertrophies of the cement he detected numerous dentinal globules, bounded by irregular fissures, and on their external border many bone-corpuscles. These latter were separated from each other by a yellowish intercorpuscular substance, and in many instances by peculiar simlous cavities, which traversed the lamella? of the osseous substance. 496 SPECIAL HISTOLOGY. appearance of the fang is not uncommon. Necrosis of the teeth takes place when the periosteum has been stripped off, or the pulp has died. The teeth become rough and dark, even black, and finally fall out. The nature and causes of dental caries are doubtful. It attacks living and false teeth (Tomes), and always begins on the exterior, from Nasmyth's membrane (Ficinus), whence the fluids of the mouth have been supposed to have considerable influence upon it ; it does not follow, however, that one living tooth may not be more disposed to it than another, being ren- dered less capable of resistance either by its chemical composition, or by the mode of its nutrition. Caries, however, is assuredly not a simple solution of the salts by the oral fluids, but a solution accompanied by a putrefactive decomposition of the organic elements of the tooth, which becomes covered with infusoria and fungi ; in fact, according to Ficinus's observations, the latter growths would appear to play the more impor- tant part, inasmuch as the decay of the teeth usually commences in those localities in which undisturbed opportunity is given to these organisms to develop, as in the cracks and pits of the enamel, in the depressions of the molar teeth, in the clefts between the teeth, but not where the dentine is otherwise exposed, as on the masticating surface, in filed places, &c. The usual course of caries is, that the discolored spots of the cuticle of the enamel, covered with living and growing organisms (infu- sorial animalcules, similar to a Vibrio, which Ficinus calls Denticola, mucedinous fungi (Erdl, Klenke, Tomes), similar to those which are found upon the tongue, and which Ficinus wrongly refers to the Denti- colce) first lose their calcareous salts, and then break up into angular, cellular pieces, as if they had been treated with hydrochloric acid. The decay then penetrates through the enamel to the dentine, always first softening it, so that it yields not more than 10 per cent, of ash (Ficinus), and then decomposing it. The dentine is more affected by this process than the enamel, its canal first becoming filled with the fluids proceeding from its decomposition, which may reach the pulp and give rise to pain, unless, as Tomes found, the dentinal canals in the neighboring healthy The deposits of dentine in the walls of the pulp-cavity, the " osteo-dentine" of Owen, he regards as mainly originating from the dentinal globules, which to him are protein-bodies. This osteo-dentine partakes in some instances more of the nature of bone, than of dentine, but consists generally of a central substance and of tubules radiating from it; it frequently appears to be formed of concentric layers. The centraF substance Wedl describes as con- sisting either of hyaline dentinal globules, of a grayish, amorphous mass, or of distinct bone-corpuscles of varying shapes, separated by spaces resembling Haversian canals. The newly-formed tubules run from this central mass towards the dentine of the tooth, with the canals of which they communicate. Sometimes they are intersected in their course by the presence of many dentinal globules, or by irregular lacuna?. In all instances of these formations, that he has examined, the dentinal globules existed in great abundance. The dark color of the globules, wherever met with, Wedl is disposed to attribute to their retro- gressive metamorphosis, whilst he regards the dark color of the interglobular spaces as dependent on a deposit of brown pigment in their interior. DaC.] THE TEETH. 497 portions become obliterated by deposits, or the pulp is protected by new masses of dentine developed in the cavity* (Ficinus, Tomes). Eventually a brownish deposit takes place in the tubules and then the intermediate substance becomes completely broken up. In this manner the process of decomposition extends further and further, until at last the crown collapses, the root also becoming dissolved and finally falling out. In jaundice, the teeth not uncommonly assume a yellow color, which is occasionally almost as intense as in the skin, and in asphyxiated per- sons they are said frequently to be red ; both facts being explicable only by the supposition that the coloring matter of the bile and of the blood transudes into the dentinal tubuli. In rachitis the teeth remain unaf- fected. In the mucus upon the teeth, an abundant growth of the muce- dinous fungi which have been mentioned, is always to be met with in a finely granular matrix, surrounding mucus- or epithelium-corpuscles ; besides which we find the infusoria of carious teeth and the earthy deposits of the oral fluids. If this mucus accumulates, it hardens and forms the tartar of the teeth, which consists, according to Berzelius, of earthy phosphates 79-0, mucus 12-5, ptyalin 1*0, organic matter, soluble in hydrochloric acid, 7 '5. The best mode of examination of the teeth is by making fine sections and preparations softened in hydrochloric acid. To obtain good speci- mens of the former it is necessary to employ only young and fresh teeth, as the enamel otherwise readily breaks off. A longitudinal or trans- verse slice should be first taken off with a fine saw, and may then be rubbed down, first upon a coarser and then upon a finer stone, as thin as possible ; the section should then be cleaned and polished between two glass plates, until its surface is as smooth and shining as it can be made, and finally washed with ether in order to remove any impurities it may have contracted. When well polished and dried, all the dentinal canals and lacuna? will be filled with air, and the section may be pre- served without further addition under a glass plate, cemented by some thick and quickly solidifying varnish. Such polished sections are pre- ferable to any others, which, on account of their irregular surface, re- quire to be covered with different fluids, as Canada balsam, oil of tur- pentine, &c., in order to be examined by high magnifying powers. It almost always happens, in fact, that some portion of these fluids enters the dentinal tubules, which then become quite clear and indistinct and invisible in their finer ramifications. A very viscid varnish alone is of any service. In preparing these sections of the teeth, the slices may * [" It is worthy of mention, also, that in the teeth of the hare, the sow, and the stag, especially in the molars, stony masses are constantly found. They are semi-transparent, for the most part oval and rounded bodies, situated in the axis of the dental pulp, towards its apex, in irregular rows, never extending the whole length of the dental pulp, but only to a greater or less distance from the coronal extremity." Raschkow, Meletemata, &c., cited and translated in Nasmyth's "Researches" (1839), p. 139. TRS.] 32 498 SPECIAL HISTOLOGY. also first be affixed to pieces of glass with Canada balsam, and then be rubbed down with a file and polished, on one side first, and then by warming the balsam and turning the section round, upon the other. When such a section has been washed with ether and dried, it is as good as one prepared with water only. Two sections made perpendicu- larly to one another through the middle of the crown and fang of a tooth, from before backwards, and from right to left, are sufficient to exhibit the most important features of the teeth ; but sections ought also to be prepared, showing the surface of the pulp cavity and that of the enamel ; and also different oblique and transverse sections through the commencement of the dentinal canals of the fangs, to exhibit the anastomoses of their branches. The dental cartilage is easily demon- strable by maceration in hydrochloric acid, a process which requires a longer or shorter time according to the concentration of the acid and its more or less frequent renewal, taking 3-4 days in strong acid and in dilute, from 5-8. If it be desired to soften the tooth so much that the tubules may be isolated, it must be left for about eight days in con- centrated hydrochloric acid ; in thin sections of dental cartilage 12-24 hours' treatment with sulphuric and hydrochloric acid, and a few hours with dilute solutions of caustic potassa and soda, are sufficient for this purpose. It is very instructive also to macerate thin sections of teeth in acid and to examine them upon glass plates at intervals, until they entirely break up. The enamel prisms are readily isolated in develop- ing enamel ; the transverse lines are seen best when the object is mois- tened with hydrochloric acid, and the transverse sections of the prisms are seen exceedingly well in longitudinal sections, in some layers. The early development may be studied in embryos of two, three or four months with the simple microscope and in transverse sections of parts hardened in spirit ; the structure of the dental sac, and the development of the dental tissues in foetuses of four, five, and six months, and in new-born infants, both in fresh subjects and, if it be desired to recognise the relations of the enamel organ, in spirit-preparations also, in which its structure is very well retained. The pulp of mature teeth is obtained by breaking them in a vice, and their nerves are best seen on the addi- tion of dilute solution of caustic soda. Literature of the Teeth. L. Frankel, " De penitiori dentium human- orum structur^ observationes," Vratislav, 1835 ; and Retzius, " Be- merkungen tiber den innern Bau der Zahnen," in Mull. " Arch.," 1837 ; J. Tomes, " A Course of Lectures on Dental Physiology and Surgery," London, 1848; R. Owen, " Odontography," London, 1840-45, 1 vol., with atlas of 150 plates; and article "Teeth," in "Cyclopaedia of Anatomy," IV. p. 864 ; Krukenberg, " Zur Lehre vom Rohrensysteme der Zahne und Knochen," in Mull. " Archiv," 1849, p. 403 ; J. Czer- mak, " Beitrage zur mikroskopischen Anatomie der menschlichen Zahne, THE PHARYNX. 499 in Zeitschr. fur. wiss. Zool." 1850, bd. II. p. 295; Arnold, in " der Salzblirger med. Zeitung," 1831, p. 236 ; Raschkow, " Meletematacirca dentium mammalium evolutionem," Yratisl. 1835 ; Goodsir, in " Edinb. Med. and Surg. Journal," 1838, No. XXXI. 1; and Froriep's " Neue Notizen," Nos. 199, 200, 202, 203; Marcusen, " Ueber die Entwick- lung der Zahne der Saugethiere," aus dem " Bulletin Phys. Math." VIIL, No 20, Petersburgh, 1850. On Dental Caries consult Erdl. in " Allg. Zeitung fiir Chirurgie von Rohatzsch," 1843, No. 19 ; Ficinus, in "Journal fiir Chirurgie von Walther and Ammon," 1846, p. 1 ; Klenke, "Die Verderbniss der Zahne," Leipsig, 1850. The Comparative Anatomy of the teeth is treated of microscopically in the works of Owen and Retzius above cited; also by Erdl, in the " Abhandlungen der Math. Phys. Klasse, der Konigl. Bayer. Akad." bd. III. Abth. 2 ; Tomes, in the "Phil. Trans." 1849-50 (Marsupialia and Rodentia) ; Agassiz, in the "Poissons fossiles ;" Henle and J. Muller, " Syst. Beschreibung der Plagiostomen," 1838. [To these should be added: Blake, "Essay," &c., 1801; Hunter, "Treatise on the Natural History and Diseases of the Human Teeth," edited by Thomas Bell (Works by Palmer, 1835, vol. ii.) ; Tomes, "On the Structure of the Teeth, the Vascularity of those Organs, and their relation to Bone," Proceedings of the Royal Society, June, 1838 ; Owen, " On the Structure of the Teeth, and the resemblance of Ivory to Bone," British Association Reports, 1838 ; Nasmyth, " Medico-Chirurgical Transactions," 1839 ; "Proceedings of the British Association," 1839; " Researches on the Development, Structure, and Diseases of the Teeth," 1849 ; Huxley, " On the Development of the Teeth," " Quarterly Journal of Micr. Science," 1853; Salter, "On certain appearances occurring in Dentine," ibid. 1853. TRS.] OF THE ORGANS OF DEGLUTITION. I. THE PHARYNX. 144. The alimentary canal assumes a greater independence in the pharynx, acquiring a special investment of transversely striated muscles, the constrictores and levatores, which, however, do not entirely surround it and arise for the most part from bones. The thickness of the walls of the pharynx is about 2 lines on an average, depending principally upon this muscular layer, external to which there is a tense fibrous mem- brane, composed of connective tissue and elastic fibres, while internally it is separated by a layer of submucous connective tissue from the mucous membrane. The latter is paler than that of the oral cavity and its structure in the upper half of the pharynx differs considerably from that in the lower half. In the latter locality, that is, below the pha- ryngo-palatine arches, or in the region through which the food passes, it possesses a tessellated epithelium similar in structure and thickness to 500 SPECIAL HISTOLOGY. that of the oral cavity ; above them, on the other hand, that is, on the posterior surface of the soft palate from its free edge, upon the upper surface of the uvula, in the region of the choance and Eustachian tubes, and upon the vault of the pharynx, there is a ciliated epithelium like that in the nasal cavity and larynx, to the description of which, below, the reader may be referred. In this upper or respiratory section, the mucous membrane is also redder, thicker, and more glandular than in the lower division, otherwise, however, its structure is pretty much the same, with the exception that it presents no papillae, which, however, in some parts of the lower division are very little developed and rare, and would even appear to be entirely wanting. Compared with that of the oral cavity I find the mucous membrane of the pharynx to possess much more and much stronger elastic tissue, which, in the deeper layers, forms connected, very dense, elastic membranes. The pharynx contains two sorts of glands ; 1, racemose mucous glands (vide supra, 134), and, 2, follicular glands. The former J-l line in diameter, have distinct apertures and abound more particularly in the upper portions of the pharynx, where they form a perfectly continuous layer on the posterior wall, in the neighborhood of the pharyngeal open- ing of the Eustachian tubes, and upon the posterior surface of the velum, diminishing in number lower down. Follicular glands, simple as well as compound, analogous to the tonsils, are met with in the vault of the pharynx, where the mucous membrane is closely attached to the base of the skull. Here a glandular mass, stretching from one Eustachian open- ing to the other, and from one to four lines thick, may constantly be met with ; it is, upon the whole, smaller, but otherwise its structure resem- bles, in all essential respects, that of the tonsils ( 135). Besides this mass, whose largest sacculations are situated in the middle of the roof of the pharynx, and in the recesses behind the Eustachian apertures, and which, in aged persons, frequently present enlarged cavities, filled with puriform masses, there occur round the apertures of the tubes, and upon them, towards the choana?, on the posterior surface of the velum palati, and on the lateral walls of the pharynx, as far as the level of the epiglottis, more or less numerous, smaller and larger fol- licles, whose size is too great for apertures of the mucous glands, and which have in all probability the same structure as the simple follicles of the root of the tongue, and receive the excretory ducts of the mucous glands. The mucous membrane of the pharynx is rich in bloodvessels and lymphatics. The former constitute superficially a network with elon- gated meshes, sending short loops into the rudimentary papillae. The nerves are very numerous, form superficial and deep plexuses, the former with fine fibres of 0*001-'0015 of a line, which occasionally divide, and whose ultimate terminations escape the eye. THE (ESOPHAGUS. 501 II. THE OESOPHAGUS. 145. The wall of the oesophagus, 1 J-lf lines thick, consists, exter- nally, of a fibrous membrane composed of connective tissue, with exceed- ingly beautiful elastic fibres. To this succeeds a muscular membrane f-1 line thick, composed of an external, longitudinally fibrous layer, having a thickness of 0*5 of a line, and of an internal, circularly fibrous layer of 0*24 0-3 of a line, which are in close apposition. From the pharynx, where the longitudinal fibres arise in two bundles from the constrictor infimus, united with a third from the cricoid cartilage, they extend as far as the stomach, with whose muscles they are partly con- tinuous. In the upper third of the oesophagus, as far as its entrance into the thorax, transversely striated muscles alone are found, arranged in bundles of 0-04-0-24 of a line, which sometimes distinctly anastomose. Further downwards smooth muscles of the same structure as those in the intestine (infra) make their appearance, in the first place in the cir- cular layer, and subsequently, among the longitudinal fibres ; the pro- rig. 198. Fig. 199. 4 -y .f portion of these gradually increases, until at last, in the lower fourth, smooth muscle altogether predomi- nates. Isolated, transversely-stri- ated muscles, however, are, accord- ing to Ficinus, to be met with as far as the cardia. Most internally we find, separated from the muscular coat by a white, soft layer of sub- mucous connective tissue (tunica nervea of the ancients), the pale-red mucous membrane, which below takes on a whitish tint. Its total thick- Fia. 198. Transverse section from the middle of the resophagus (Man), magnified 1-2 diameters: a, fibrous investment; 6, longitudinal muscles ; c, transverse muscles ; d, tunica nervea e, longitudinal muscles of the mucous membrane ; /, papillae ; g, epithelium ; h, aper- ture of a mucous gland ; i, mass of fat. Fia. 199. Muscular-fibre cells from the tssophageal mucous membrane of the Pig, after being treated with nitric acid of 20 per cent.; magnified 15 diameters. 502 SPECIAL HISTOLOGY. ness of 0-36-0-45 of a line is due, to the extent of about 0-1-0-12 of a line, to its laminated, tessellated epithelium, which presents the same structure as in the oral cavity, with the exception, however, that the actual epithe- lial plates constitute about a moiety of the whole, and, after a short mace- ration, or, as frequently happens in the dead subject, spontaneously, may be readily stripped off in large white sheets, either alone, or accom- panied by adherent portions of the deeper layers. The proper mucous membrane, measuring on the average O3 of a line, possesses numerous conical papillae of 0-04-0-05 of a line in length, and consists of ordinary connective tissue, with fine elastic fibres, among which, however, as Brucke and I have ascertained, a great quantity of longitudinal bundles of smooth muscles, and in addition, more isolated groups of ordinary fat cells and small racemose mucous glands, may be observed. The oesophagus is moderately provided with lymphatics and blood- vessels ; the latter send loops into the papillae and form at their bases, a not very wide network, like that in the pharynx. Nerves may also be met with in considerable numbers in the mucous membrane, contain- ing fine fibres of 0*0012-0-0015 of a line, but I have not yet succeeded in tracing them into the papillae, nor in observing divisions, nor the modes in which they terminate. Literature. C. Th. Tourtual, "Neue Untersuchungen iiber den Bau des Menschlichen Schlund-und Kehlkopfes," Leipzig, 1846. OF THE ALIMENTARY CANAL. 146. Those parts which constitute what may, more strictly speaking, be called the alimentary canal, are the least fixed of all which compose the alimentary tract and are almost invariably attached by special mem- branous bands the mesenteria in the great cavity of the abdomen, lined by the peritonaeum. With the exception of a small portion of the rectum, the walls of the alimentary canal consist everywhere of three tunics: a serous the peritonaeum; a muscular consisting of two or even three layers ; and a mucous membrane, the latter containing a great number of glandular structures, which may be divided into three groups, racemose mucous glands, tubular glands, and closed follicles. 147. The peritonaeum is much thicker in its external or parietal, than in its internal or visceral layer (in the former case 0-04-0-06, in the latter 0-02-0-03 of a line), though its structure is essentially the same in each locality. It consists principally of connective tissue with distinct, variously interwoven bundles, and abundant reticulated elastic fibres, which are coarser in the parietal lamina. A loose subserous con- nective tissue, containing more or less fat, unites the peritonaeum with the other organs, or, as in the mesenteric folds, connects its layers together ; under the visceral lamina, however, it is very little developed except in certain localities (colon, appendices epiploicce], and in certain THE ALIMENTARY CANAL. 503 folds of the peritonceum, it does not exist at all. The free surface of both lamellae of the peritonceum is lined by a simple tessellated epithe- lium, whose slightly flattened, polygonal, nucleated cells measure, on the average, 0-01 of a line, they are so closely united and so constantly kept moist, that the free serous surface appears perfectly smooth and shining. The peritonceum is, in general, but scantily supplied with vessels ; they are most abundant in the omenta, in the visceral layer and in the sub- serous tissue, in which last alone, lymphatics have as yet been found. The nerves are also but few, and are especially to be met with in the omentum, the mesenteria, and hepatic ligaments, where they accompany the arteries. 148. Muscular tunic of tlie alimentary canal. The whole alimen- tary tract, from the stomach to the rectum, possesses a special muscular coat, which, however, does not everywhere present the same conditions. In the stomach the muscular tunic varies in thickness; at the fundus it is thin (J-J of a line) ; in the middle, it has a thickness of about \ a line : in the pyloric region, finally, about f or even 1 line. It consists of three incomplete layers : 1, most externally, longitudinal fibres, especially at the cardia, where they arise from the ex- pansion of a part of the lon- gitudinal fibres of the oesopha- gus ; and also at the pylorus and in the pars pylorica, whence, tensely stretched, they are continued upon the duo- denum ; 2, circular muscles, in the middle region, from the fundus to the pylorus ; where they are accumulated, consti- tuting the so-called sphincter of the pylorus ; 3, most internally, oblique fibres, which, in connection with the circular fibres, embrace the fundus as in a sling, and run ob- liquely upon the anterior and posterior walls of the stomach, towards its greater curvature, where they terminate upon the outer surface of the mucous membrane or unite together. In the small intestine, the muscular coat is somewhat thicker in the duodenum and the upper portions, than in the lower ; it has, in general, a thickness of J-J of a line, and is composed only of longitudinal and transverse fibres. The former are always less developed and do not * FIG. 200. Stomach of Man, reduced: a, (Esophagus, with the longitudinal fibres ; tr, transverse fibres (second layer), for the most part dissected off; tj j , transverse fibres of the fundus; o,fibr& obliqua p, pylorus d, duodenum. 504 SPECIAL HISTOLOGY. form a continuous layer, since they are very few or entirely absent along the attachment of the mesentery ; they are usually most distinct upon the free border, though even here they may be readily torn away with the serous membrane, so as, at once, to leave the second layer exposed. The latter is complete and continuous, consisting of circular bundles, which not uncommonly anastomose at very acute angles. In the large intestine, the longitudinal fibres are reduced to the three ligamenta coli, muscular bands of 4-6, or even 8 lines broad, and -J-J line thick, which commencing upon the caecum are united upon the sigmoid flexure, into a single longitudinally fibrous layer, which is con- tinued upon the rectum. Beneath these bands there lies a continuous, circularly fibrous layer, thinner than in the small intestines and more especially developed in the duplicatures, which are known under the name of the plicae sigmoidece. Fig. 201. The rectum possesses a muscular layer of 1 line and more thick, in which the more abundant longitudinal fibres lie ex- ternal to the circular. The ultimate, somewhat thickened ex- tremity of the circular fibres is the sphincter ani internus, with which the transversely striated sphincter externus and levator ani are conjoined. In their elementary structure, all the muscles of the proper alimentary canal belong to the so-called smooth or non-striated (vegetative, organic) muscles (see 26). Their elements, the fibre-cells, are fusiform, on the average 0-002-0*003 of a line broad, and O'06-O'l of a line long, pale, flattened, and homo- geneous, and provided with a nucleus 0-006-0-012 of a line long, and 0-001-0-0028 of a line broad. Many of the fibres present knot-like enlargements and fre- quently zigzag flexures, which produce the transversely striated appearance of the entire bundles of such muscles so frequently met with in spirit preparations. The arrangement of the fibre-cells in the different strata is simply this ; mutually applied in their length and breadth and coherent, they are united into thin muscular bands, which then, invested with a coating of connective tissue and, frequently, also united into secondary bundles, constitute the thinner or thicker muscular tunics of the different regions ; which, again, are surrounded and separated from the contiguous parts, by considerable layers of connective tissue. Bloodvessels are very abundant in the smooth muscles ; and their capillaries, of 0-003-0-004 of a line, constitute a charac- teristic* network with rectangular meshes. FIG. 201. Muscular fibre cell from the small intestine (human). * [Hardly characteristic ; the vessels are arranged in precisely the same way in the fascial aponeuroses; e. g., the/ascia lata of the thigh. TRS.] THE STOMACH. 505 Nothing is known about the lymphatics ; nor are the relations of the nerves yet ascertained, except that Ecker has observed the division of Fig. 202. fine nervous tubules in the muscular tunics of the stomach of the Frog and Rabbit. MUCOUS MEMBRANE OF THE STOMACH. 149. The gastric mucous membrane is soft and loose in texture ; and its color, during digestion, is reddish-gray or bright red, at other times grayish. When the stomach is empty, the inner surface is thrown into longitudinal folds, which disappear in its distended state. Further- more, it presents, especially in the pyloric region, around the apertures of the tubular or gastric glands, little reticulated folds or even isolated villi* (plicae villosce, Krause) of 0-024-0-048 or even 0-1 of a line, (A-s'u Krause). Not unfrequently, also, the mucous membrane is marked out especially upon the right side, by little shallow depressions, into slightly raised polygonal areas of J-2 lines, the so-called " etat mamelonne"' of pathologists, which, however, is also exhibited by per- fectly healthy stomachs. The mucous membrane is thinnest (J J of a line), at the cardia, in the middle it becomes thickened to J a line, and in the FIG. 202. Bloodvessels of the smooth muscles of the intestine, magnified 45 diameters. * [These gastric villi have been recently accurately described and depicted by Dr. Neill, (vid. Amer. Journ. of Med. Sc., Jan. 1851.) By the aid of minute injections, Dr. Neill found that the ridges between the orifices of the tubuli, formed of convoluted capillaries, become larger and more elevated in the antrum pylori, and that as the pyloric orifice is approached, distinct, conical villi make their appearance, which he thinks, have not been previously described as constant by any of the writers on the subject. These villi are not as large as those of the small intestines, but, otherwise, similar in appearance. They are mainly composed of capillaries closely united by a basement membrane, and are covered with a cylinder-epithelium. In the antrum pylori, alveoli of different shapes exist in the interstices and at their bases. Whether they contain lacteals or not is doubtful. The uses of these gastric villi have not as yet been ascertained. Dr. Neill (1. c.) suggests, that they may be connected with the absorption of solutions of albuminous compounds. DaC.J 506 SPECIAL HISTOLOGY. Fig. 203. pyloric region to f or 1 line, which depends entirely upon the glandular layer, since the epithelium and muscular layer everywhere possess the same thickness. The submucous tissue is abundant and, as throughout the whole intestine, contains occasional fat-cells. 150. The gastric glands. The gastric glands the most important part of the mucous membrane are tubular glands which, set close together, pass straight through the entire thickness of the mucous membrane to its muscular layer, and therefore vary, in the different regions of the stomach, from -J- to f , or even 1 line, but are on the average J a line in length. Each of them commences as a cylindrical tube, of 0-03-0-04 of aline in diameter, at the surface of the mucous membrane, diminishes inferiorly to as little as 0-014-0-02 of a line, and terminates by a clavate or flask-shaped enlargement of 0-02-0-026-0-036 of a line. The lower third of the glands is usually undulated or even twisted into a corkscrew shape, espe- cially at the pylorus ; occasionally it gives off a shorter or longer csecal branch before its termination. Every gastric gland is sur- rounded by a delicate membrana propria and possesses in its upper third, a cylindrical epithelium continuous with that of the surface of the stomach ; for the inferior three-fourths of its extent, on the other hand, it presents pale, finely granular, polygonal nucleated cells of 0-006-0-01 of a line, which probably never constitute a distinct epithelium, but appear completely to fill the tubes.* FIG. 203. Perpendicular section through the tunics of the Pig's stomach, from the pylorus, magnified 30 diameters: a, glands; 6, muscular layer of the mucous membrane; c, submu- cous tissue (tunica nerved), with divided vessels ; d, transverse layer of muscles ; e, longitudi- nal layer of muscles; /, serous membrane. * [Professor Kolliker (" Verhandlungen der. Phys. Med. Gesellsch. zu Wiirzb." vol. IV. 1, p. 52), has recently had the opportunity, in a case of suicide by drowning, of examining the human gastric mucous membrane in a fresh and normal state. He directed par- ticular attention to the glandular apparatus, and found that the gastric glands are not as uniform in structure as above-described, but present three distinct types. 1. Simple tubular glands with peptic cells, 1 (Lab-zellen). 2. Compound tubular glands with peptic cells. 3. Compound tubular glands with cylinder epithelium. The first are the most common ; they occur in the middle zone of the stomach, and are generally simple tubular glands, some of which at their termination, give off short csecal branches. The compound tubular glands with peptic cells occur in the narrow cardiac zone. They commence by a tube of 0-04 to OOS mm long, 03 to 04 mm broad, lined with cylinders. This divides first into two or three, and then into four or seven equally long cylindrical tubules, which 1 Vid. p. 508. THE STOMACH. 507 In animals, the gastric glands are more complicated than in man, frequently presenting dichotomous divisions and subdivisions of their FIG. 204. A, mucous gastric gland of a Dog, from the pylorus, with cylinder epithelium : a, wide cavity of the gland ; 6, its caeca! appendages. 12, peptic gastric gland from the middle of the stomach : a, common trunk of the gland ; b, its chief branches ; c, terminal caeca. Magnified 60 diameters. C, a portion of the cceca, magnified 350 diameters, and viewed longitudinally. 7), the same viewed in transverse section : a, membrana propria b, large cells close to it; c, small epithelium round the cavity. are lined by rounded or oval cells (peptic-cells), and which run side by side to the base of the mucous membrane. In these cells minute oil-globules are frequently observed. The terminal tubules have a peculiar twisted appearance, which is dependent on numerous lateral dilatations. In this part of the stomach no racemose glands exist, although they are found in the lower part of the oesophagus. Between both these forms of " peptic gastric glands," (Magensaftdriisen) Professor Ko'lli- ker observed, fasciculi of contractile fibre-cells, but he denies the existence of the spiral fibre-cells investing the glands, as described by Ecker. The compound tubular glands with cylinder-epithelium occur in the pyloric zone, and resem- ble the last-described variety, with the exception, that the tubules are larger and devoid of the rounded finely granulated peptic cells. Neither simple glands, nor racemose glands, as stated by Ecker, are here observable. These investigations of Professor Kolliker confirm the opinion of Bonders, as to the exis- tence of two varieties of glands in the human stomach, viz.: the proper gastric glands (called by Kolliker from their secretion "peptic" gastric glands) and the simple mucous glands. These two distinct forms have been previously described in the stomach of Mam- malia by Kolliker (Vid. 150, infra and " Mikroscopische Anatomic" II. 2, p. 240), but in Man their existence has hitherto not been satisfactorily ascertained. DaCJ 508 SPECIAL HISTOLOGY. free ends; in many genera, they are of two very distinct kinds, the mucou-s gastric glands, with a cylinder epithelium and the peptic gastric glands (Magensaftdriisen) with cells similar to those which exist in man. A more detailed description of some forms will be found in my " Mikro- skop. Anatomic" (II. 2, p. 140) ; and I here subjoin figures (p. 507) of the two forms of the glands in the dog, merely to render my meaning intelligible. The secretion of the gastric glands has not been so completely exa- mined in man, that we can say with certainty whether they all secrete gastric juice or not. A few experiments which I instituted with regard to this point, tend to show that here, as in animals, it is only particular glands those in fact of the middle of the stomach which yield the proper, active secretion ; however, further observations must be made on stomachs in the freshest and most normal state, to confirm this result. In any case, the secretion of the glands is for the most part a fluid, though in the mucus, a small quantity of which usually covers the mucous membrane, we not only meet with half-destroyed cylinder epithelium, but almost invariably, with a certain quantity of proper glandular cells ; and it is impossible to say whether these are essential, or only accidental constituents of the glandular secretion. In many animals there are two secretions ivitli different properties corresponding with the two forms of gastric glands, a fact to which Bischoff and Wasmann first drew attention, and which I can confirm. In the Dog, glands with cylinder epithelium exist in the pylorus; those with round cells in the remainder of the stomach ; there is the same arrangement in Ruminants and in the Rabbit ; whilst in the Pig, it is only the middle of the stomach and especially the great curvature, which presents the latter glands. A series of experiments on artificial digestion, which were carried out by Dr. Goll, of Zurich, and myself, principally with the pig's stomach, afforded the distinct result, that, so far as their solvent powers are concerned, the glands present very different relations ; those with round cells act upon protein compounds which have been coagulated by acids in a very short time, while those with cylinder epithelium, either have no action at all or take a long time to produce a slight effect. Furthermore a well-marked acid reaction is presented by that region of the stomach only in which the former glands are situated. The active organic substance, pepsin, is not contained in the gastric mucus, which consisting of detached epithelium cylinders, often form a thick covering over the mucous membrane, but in the finely granulated, rounded cells of the peptic gastric glands, to which there- fore the term peptic cells (Labzellen, Frerichs)* may well be applied. According to my observations, however, these peptic cells do not neces- sarily become thrown off, nor take any direct share in digestion, but * [Literally, "rennet-cells." TRS.] THE STOMACH. 509 frequently exert their action simply by pouring the juice which they prepare into the glands. 151. We have seen, that beside the glands, only a very scanty tis- sue enters into the mucous membrane. Around their extremities alone, do we find a dense, continuous, reddish layer 0-022-0-044 of a line in thickness (Briicke), the muscular layer of the mucous membrane, con- sisting of bundles of common connective tissue and of smooth muscles, interwoven, the latter of which cross one another principally in two directions, and, in the Pig, even pass between the glands and into the plicce villosce. In man, we meet only with vessels, and an amorphous connective tissue, without elastic fibrils, interposed between the glands, forming at the surface of the mucous membrane, a clear, perfectly homogeneous stratum, the structureless membrane of authors, which is continuous with the membrane proprice of the separate glandular tubes, but cannot, like them, be isolated. The whole internal surface of the stomach from the cardia (where the tessellated epithelium of the oesophagus terminates by a sharp notched edge), possesses a simple covering of cylindrical cells, about 0-01 of a line long on the average, which lie immediately upon the outermost homogeneous portion of the mucous membrane, without any interposed substance. During life, this cylinder epithelium whose other relations will be treated of below, in describing the small intes- tine, where a layer of exactly similar nature is to be met with is closely united with the mucous membrane, though not so intimately, but that its elements are, at times, detached to a larger or smaller amount by the mechanical violence to which it is necessarily occasionally sub- jected in the stomach. After death this takes place so readily, that the cells can be seen in situ, in man, only under very favorable circum- stances. Perhaps, also, detachment of the epithelium to a certain ex- tent may take place normally, in one way or another, during digestion; at least, in animals the quantity of loose epithelial cells is often very great and they frequently almost entirely constitute the mucous coating which covers the surface of the stomach. Besides the tubular glands, the stomach also contains, though they are inconstant and vary very much in number, closed follicles the so- called lenticular glands, which are identical in structure with the soli- tary follicles of the small intestine, and therefore need not be further described in this place.* * [" Although it may be that the lenticular glands of the stomach are always present in children, they are certainly inconstant in adults, since in many cases no trace whatever can be discovered of them. In other instances they are exceedingly numerous, covering the whole surface of the stomach, but in this case, the invariably diseased state of the alimen- tary tract, suggests the idea, that they stand in some connection with it. In many mammalia no trace of such structure is to be found, while, according to Bischoff (Mull. Arch. 1838), 510 SPECIAL HISTOLOGY. The bloodvessels of the gastric mucous membrane are very numerous, and their distribution is quite characteristic (compare Fig. 205, repre- Fi