TEXT-BOOK or ANATOMY HEI Third 848 II THl AT Professc Third and 12 MEMCAL .SCIHKDOL K*v«o« ewritten. .0 pages. ^7.00 net :iNE )SIS dents 'hysician to sd Plates i^iotn,^^56^; i.eainerx)rTiarmvioracco, $6.50 net P. BLAKISTON'S SON & CO., Publishers and Booksellers 1012 WALNUT STREET, PHILADELPHIA 5-27-05 CLINICAL HEMATOLOGY A PRACTICAL GUIDE TO THE EXAMINATION OF THE BLOOD BY CLINICAL METHODS, WITH REFERENCE TO THE DIAGNOSIS OF DISEASE By JOHN C. DA COSTA. Jr.. M.D. Demonstrator of Clinical Medicine, Jeffei son Medical College; Chief of Medical Clinic and Assistant Visiting Physician, Jefferson Medical College Hospital ; Hematologist, German Hospital, Philadelphia Second Edition, Revised. Enlarged by 117 pages. With 9 Full-page Plates in Colors, representing the subjects, as closely as possible, as they appear to the eye ; 3 Charts, and 64 other Illustrations. Octavo ; 591 pages. Cloth, $5.00 net A Text-Book of HUMAN PHYSIOLOGY INCLUDING HISTOLOGY AND MICROSCOPICAL ANATOMY, WITH SPECIAL REFERENCE TO THE REQUIRE- MENTS OF PRACTICAL MEDICINE By DR. L. LANDOIS Professor of Physiology and Director of th^ Physiological Institute in the University of Greifswald Tenth Edition^ Revised^ Enlarged. Translated and Edited by A. P. BRUBAKBR. M.D. and AUGUSTUS A. E:SHNE:r. M.D. Professor of Physiology at Jefferson Professor of Clinical Medicine, Philadelphia Medical College, Philadelphia, etc. Polyclinic, etc. Tenth Edition, Revised and Enlarged. With 394 Illustrations. Octavo ; 1027 pages. Cloth, ^7.00; Leather, ^8.00 w^/ DISEASES OF THE SKIN THEIR DESCRIPTION, PATHOLOGY, DIAGNOSIS AND TREAT- MENT, WITH SPECIAL REFERENCE TO THE SKIN ERUPTIONS OF CHILDREN, AND AN ANALYSIS OF 15,000 CASES OF SKIN DISEASE By H. RADCLirrE CROCKER. M.D.. r.R.C.P. Physician for Diseases of the Skin, University College Hospital, etc. Third Edition, Thoroughly Revised. 112 Illustrations. Octavo; 1400 pages. Cloth, ^5.00; Sheep, ^6.00 net P. BLAKiSTON'S SON d, CO., Publishers and Booksellers 1012 Walnut Street, Philadelphia «9> BASED ON RECENT MEDICAL LITERATURE. Gould's The standard Medical /yigQI^Q 1 Reference Books. Dictionaries. 185,000 HAVE BEEN SOLD. BY GEORGE M. GOULD, A.M., M.D., Editor of American Medicine. THE ILLUSTRATED DICTIONARY OF MEDICINE, BI- OLOGY, AND ALLIED SCIENCES, including the pro- nunciation, ACCENTUATION, DERIVATION, AND DEFINITION OF THE TERMS USED IN MEDICINE AND THOSE SCIENCES COLLATERAL TO IT: BIOLOGY (ZOOLOGY AND BOTANY), CHEMISTRY, DENTISTRY, PHARMA- COLOGY, MICROSCOPY, ETC. With many Useful Tables and numerous Fine Illustrations. Large Square Octavo. 1 633 pages. Fifth Edition now ready. Full Sheep,' or Half Dark-Green Leather, net, ;^lo.oo; With Thumb Index, net, ^ll.oo; Half Russia, Thumb Index, net, $12.00 THE STUDENT'S MEDICAL DICTIONARY, including all THE WORDS AND PHRASES GENERALLY USED IN MEDICINE, WITH THEIR PROPER PRONUNCIATION AND DEFINITIONS, BASED ON RECENT MEDICAL LITERATURE. With Tables of the Bacilli, Micrococci, Leuko- mains, Ptomains, etc., of the Arteries, Muscles, Nerves, Ganglia, and Plexuses ; Mineral Springs of the U. S., etc. Eleventh Edition, Illustrated. Revised, Enlarged by over 150 pages. Small Square Octavo. Half Dark Leather, «^/, ^2.50; with Thumb Index, net, ^3.00 The illustrations in this book, of which there are about 300, are ex- tremely practical. Those of the Bones, Muscles, Nerves, etc., when taken together with the Anatomical Tables which they illustrate, will be found particularly useful for reference and memorizing. There are 41 cuts of Bones, 34 of Muscles, 21 of Nerves, l8of Joints, 3 of the Heart, 10 of Ligaments, 1 2 of Pelves, a plate of the Skeleton, a plate of Veins, a plate of Arteries, 31 cuts of Bandages, 20 of Urinary Sediments, lo of Postures, 6 of Motor Points, 6 of Surgical Knots, 8 of Hernia, 21 of Sutures, 2 of the Tongue, 4 of the Brain, and many others. Altogether the student will find ** Gould's Student's Dictionary" a most valuable book, not only as a dictionary but also as an atlas illustrative of many subjects which need pictures to thoroughly explain their details. . THE POCKET PRONOUNCING MEDICAL LEXICON. 30,000 words pronounced and defined. Containing all the Words, their Definition and Pronunciation that the Student generally comes in contact with ; also elaborate Tables of the Arteries, Muscles, Nerves, Bacilli, etc. , etc. ; a Dose List in both English and Metric Systems, etc. , arranged in a most convenient form for reference and memorizing. Fourth Edition, 837 pages. 64mo. Full Limp Leather, Gilt Edges, net, ;^l.oo; Thumb Index, net^ ls.25 Digitized by the Internet Archive in 2007 with funding from IVIicrosoft Corporation http://www.archive.org/details/compendofhistoloOOradarich % /ppt.^t!C^^ ^ HISTOLOGY RADASCH From The Southern Clinic. "We know of no series of books issued by any house that so fully meets our approval as these ?Quiz-Gpmpends;/. .\ They are well arranged, full, and concise, and are really ^e best llfte of text-tiooks , that could be found for either student or practitioner.'^ ■ ^■' tk 'i BLAKISTON'S ? QUIZ=COMPENDS ? The Best Series of Manuals for the Use of Students Price of each, Cloth $1.00 net. Interleaved, for taking: Notes, $1.25 net. tnT" These Compends are based on the most popular text-books and the lectures of prominent professors, and are kept constantly revised, so that they may thor- oughly represent the present state of the subjects upon which they treat. [C^The authors have had large experience as Quiz-Masters and attaches of colleges, and are well acquainted with the wants of students. I[:::?'They are arranged in the most approved form, thorough and concise, con- taining over 600 fine illustrations, inserted wherever they could be used to ad- vantage. [C^Can be used by students of any college. fC^They contain information nowhere else collected in such a condensed, practical shape. Illustrated Circular Free. POTTER'S ANATOMY. Seventh Revised and Enlarged Edition. Includ- ing Visceral Anatomy. Can be used with either Morris' or Gray's Anatomy. 117 Illustrations and 16 Lithographic Plates of Nerves and Arteries, with Ex- planatory Tables, etc. BRUBAKER. PHYSIOLOGY. Eleventh Edition, with new Illustrations and a Table of Physiological Constants. Enlarged and Revised. LANDIS. OBSTETRICS. Eighth Edition. Revised and Edited by Wm. H. Wells, M.D., Instructor Jefferson Medical College, Philadelphia. 47 Illustrations. POTTER. MATERIA MEDICA, THERAPEUTICS, AND PRESCRIPTION WRITING. Sixth Revised Edition. WELLS. GYNECOLOGY. Third Edition. With many Illustrations. GOULD and PYLE. DISEASES OF THE EYE AND REFRACTION. In- cluding Treatment and Operations and a Section on Local Therapeutics. With Formulae and 109 Illustrations, several of which are in colors. Third Edition. HORWITZ'S SURGERY, Minor Surgery, and Bandaging. Fifth Edition. Enlarged and Improved. With 98 Formulae and 167 Illustrations. LEFFMANN. CHEMISTRY. Inorganic and Organic. Fourth Edition. In- cluding Urinalysis, Animal Chemistry, Chemistry of Milk, Blood, Tissues, the Secretions, etc. STEWART. PHARMACY. Fifth Edition. Based upon Prof. Remington's Text-Book of Pharmacy. BALLOU. VETERINARY ANATOMY AND PHYSIOLOGY. With 29 graphic Illustrations. WARREN. DENTAL PATHOLOGY AND DENTAL MEDICINE. Fourth Edition. Illustrated. Containing all the most noteworthy points of interest to the Dental Student, and a Section on Emergencies. HATFIELD. DISEASES OF CHILDREN. Colored Plate. Third Edition. Revised and Enlarged. SCHAMBERG. DISEASES OF THE SKIN. Fourth Edition. Illustrated. RADASCH. HISTOLOGY. With 98 Illustrations. THAYER. SPECIAL PATHOLOGY. With 34 Illustrations. KYLE. NOSE, THROAT AND EAR. Illustrated. Price, each, $1.00 net. Interleaved, for taking Notes, $1.25 net. P. BLAKISTON'S SON & COMPANY, Publishers PHILADELPHIA FQUIZ-COMPENDS? A COMPEND OF HISTOLOGY HENRY ERDMANNJRADASCH, M.S., M.D. ASSOCIATE IN HISTOLOGY AND EMBRYOLOGY IN THE JEFFERSON MEDICAL college; FORMERLY FELLOW IN CHEMISTRY IN THE UNIVER- SITY OF IOWA (1895-6) ; FORMERLY LECTURER ON CHEMISTRY AND DIRECTOR OF THE CHEMICAL LABORATORIES IN THE COLLEGE OF PHYSICIANS AND SURGEONS KEOKUK^ IOWA (1897-8). Wxtii Ntnrtg-nglit SfUuBtrattona qtv\55\ Philadelphia : P. BLAKISTON'S SON & CO. 1012 Walnut Street. 1905. A7 4\A Copyright, 1905, by P. Blakiston's Son & Co. PRESS OF REPORT PUBLISHING CO. Lebanon, Pa. TO THIS VOLUME IS AFFECTIONATELY DEDICATED 524 \^ P.R£FA:e^E It has been the author's purpose to supply a volume more complete than the existing compends, and yet not so volum- inous as a Text-book. An effort has been made to present the matter in a clear and concise manner, and as up-to-date as possible. The subject of Embryology has been touched upon only in so far as it bears directly upon the Histology. The chapter on Technic has been made as complete as is necessary for routine histologic and pathologic work. The Connective Tissues have been grouped in what seems a simple and also characteristic manner. The Blood Cells have also been arranged in a simple and readily-compre- hended form. The chapter on Placenta and Umbilical Cord has, how- ever, been written somewhat in detail, as the embryology of these organs is essential for a thorough knowledge of their structure. The illustrations are from the works of Prof. Minot, to whom the writer is indebted for their use. The forty-seven new cuts were prepared under the direc- tion of Dr. H. H. Cushing. Of these, twenty-seven are from slides, while the remainder represent modifications of current Text-book figures. The writer desires to thank Dr. R. C. Rosenberger for his assistance in proof-reading and suggestions, and the publishers for their many kindnesses and courtesies. 914 South Forty-seventh Street, Philadelphia. August, 1905. vu. CONTENTS. ' PAGE. CHAPTER I. Technic i CHAPTER n. The Cell 28 CHAPTER HI. The Tissues — Epithelial Tissues 41 CHAPTER IV. Connective Tissues 53 CHAPTER V. Muscular Tissues 72 CHAPTER VI. Nervous Tissues 78 CHAPTER VII. Circulatory System 88 CHAPTER VIII. Lymphatic System ICXD CHAPTER IX. Alimentary Tract 106 CHAPTER X. Digestive Glands 132 CHAPTER XI. Respiratory System and Thyroid Body 142 ix. X. CONTENTS. PAGE. CHAPTER XII. Urinary System and Adrenal 154 • CHAPTER XIII. Male Genital System 169 CHAPTER XIV. Female Genital System 182 CHAPTER XV. Placenta and Umbilical Cord 198 CHAPTER XVI. Skin and Its Appendages 211 CHAPTER XVII. Nervous System 226 CHAPTER XVIII. Eyeball and Lacrimal Apparatus 245 CHAPTER XIX. The Ear 2(i^ CHAPTER XX. The Senses of Smell, Taste and Touch 280 LIST OF ILLUSTRATIONS FIG. PAGE. 1. The Cell 29 2. Karyokinesis, Close Coil 32 3. Karyokinesis, Loose Coil 33 4. Karyokinesis, Equatorial Plate 34 5. Karyokinesis, Nuclear Spindle 35 6. Karyokinesis, Daughter Stars 36 7. Karyokinesis, Daughter Cells ^6 8. The Ovum 38 9. Simple Squamous and Cuboidal Epithelial Cells 42 10. Squamous Cell of Frog's Skin (surface view) 42 11. Squamous Cell, Isolated 42 12. Stratified Squamous Epithelium 42 13. Simple Columnar, Ciliated and Goblet Cells 43 14. Isolated Columnar and Ciliated Cells ; Goblet Cells in Various Stages 43 15. Pseudostratified Cells 44 16. Stratified Columnar, Ciliated and Goblet Cells 45 17. Transitional Cells 45 18. Various Forms of Endothelial Cells 47 19. Simple Tubular Gland from Large Intestine 49 20. Diagram of Tubular Glands 51 21. Diagram of Alveolo-tubular Glands 51 22. Diagram of Alveolar Glands 52 23. Varieties of Connective Tissue. ' 54 24. White Fibrous Tissue 56 25. Varieties of Cartilage 6z 26. Cross-section of Compact Bone 65 27. Cross-section of Developing Bone 70 28. Varieties of Muscular Tissue 74 29. Nerve Cells and Fibres 81 30. Tactile Cells 83 31. Corpuscle of Meissner 84 32. Pacinian Body 85 ^2,- Motor Nerve-endings 86 34. Tendon-spindle 87 xi. Xll. LIST OF ILLUSTRATIONS. FIG. PAGE. 35. Cross-section of a Medium-sized Artery.... 91 ^6. Cross-section of a Vein 93 Z7. Forms of Blood Cells 95 38. White Blood Cells 96 39. Hemin Crystals 98 40. Hemoglobin Crystals 98 41. Section of a Human Lymph Node loi 42. Section of the Spleen 103 43. Section of the Thymus Body 105 44. Longitudinal Section of a Tooth 108 45. Cross-section of the Tongue 112 46. Vertical Section of a Human Tonsil 114 47. Cross-section of a Human Esophagus 116 48. Section of the Cardiac End of the Stomach 119 49. Section of the Pyloric End of the Stomach 121 50. Section of the Duodenum 123 51. Longitudinal Section of a Villus 124 52. Cross-section of the Ileum 125 SZ' Cross-section of the Colon 127 54. Cross-section of the Human Appendix 129 55. Section of Pig's Liver 133 56. Section of Human Pancreas 140 57. Section of the Submaxillary Gland of a Fox 141 58. Cross-section of Trachea 145 59. Section of Human Lung 147 60. Section of Human Thyroid Body 152 61. Section of Human Kidney 155 62. Section of Injected Kidney 159 6^. Sections of Human Ureter and Bladder 162 64. Section of Human Adrenal 167 65. Section of Human Testicle -. 170 66. Human Spermatozoa 176 67. Section of a Human Prostate 178 68. Cross-section of an Ovary of a Cat 183 69. Ovum of a Cow 185 70. Cross-section of a Human Fallopian Tube 189 71. Resting Uterine Mucosa 191 72. Cross-section of a Human Vagina 194 7^. Diagram of Development of Primates 199 LIST OF ILLUSTRATIONS. XUl. FIG. PAGE. 74. Diagram of Development of Primates 200 75. Diagram of Development of Primates 202 yd. Semi-diagrammatic Outline of Uterus and Embryo 204 TJ. Human Placenta at Term 206 . 78. Cross-section of the Human Umbilical Cord 208 79. Cross-section of the Skin of the Sole of the Foot ..... 213 80. Section of Scalp Hair 216 81. Cross-section of a Nail 219 82. Section of a Lactating Human Mammary Gland 222 83. Vertical Section of Human Cerebral Cortex 228 84. Vertical Section of Human Cerebellar Cortex 233 85. Cross-section of Human Spinal Cord 239 86. Corneo-Scleral Junction of Man 248 87. Vertical Section of the Retina of a Rabbit 252 88. Cells from the Retina of an Ape 255 89. Vessels of the Eye 260 90. Section of the Eyelid 263 91. Horizontal Section of the Internal Ear of a Kitten 273 92. Scheme of the Structure of the Tympanic Wall 274 93. Corti's Organ 276 94. Diagram of Olfactory Mucosa 280 95. Isolated Cells of Olfactory Mucosa 281 96. Taste-Bud from the Papilla Foliata of a Rabbit 282 97. Corpuscle of Wagner 283 98. Pacinian Body 284 CHAPTER I. TECHNIC. For a thorough understanding of Histology a knowledge of Technic is requisite, as sections for study must be properly prepared, and this requires skill and care. The various steps necessary to prepare a piece of tissue for sectioning are Fixation, Dehydration, Clearing and In- filtration. FIXATION. Fixation is the process by which the intercellular sub- stance and the protoplasm of the cells are coagulated by the aid of solutions thereby keeping them as nearly like normal as possible. Such solutions are fixing fluids, of which there are a great many combinations. Simple fixatives which are not numerous, will be given first, and under each, its combinations. 1. Heidenhain's Solution consists of a saturated solu- tion of bichlorid of mercury in a normal salt solution. Bichlorid of mercury 112 gms. Sodium chlorid 5 gms. Water 1000 c.c. Add the bichlorid to the hot salt solution and when dis- solved set aside to cool. The excess of bichlorid will crys- tallize and keep the solution saturated. Three to five per cent, of glacial acetic acid aids the pene- tration of the bichlorid and assures more thorough fixation. This solution requires from two to four hours to fix one- half-inch cubes. 2. Potassium Bichromate. — This salt in a solution of three and one-half per cent, strength is a good fixative and 2 TECH NIC. hardener. The strength is gradually increased one-half of one per cent, by frequent renewal, to sir per cent., in the course of six weeks. It will not injure tissues left in it for a longer time. It is not often used alone but in combina- tions mentioned below. a. Zenker's Fluid is a mixture of Miiller's fluid and bichlorid of mercury. Miiller's fluid looo c.c. Corrosive sublimate 112 gms. Mix and add before use Glacial acetic acid 50 c.c. This solution requires from twelve to twenty-four hours to act and should be freshly prepared each time before using. b. Tellyesnicky's Fluid consists of a three per cent, so- lution of potassium bichromate to which is added five per cent, of glacial acetic acid (5 c. c. per 100). It is allowed to act twelve to twenty-four hours and then the tissues are thoroughly washed and dehydrated. Nuclei are better pre- served by this solution than by the usual bichromate mix- tures. c. Miiller's Fluid depends upon potassium bichromate for its action. Penetration is aided by sodium sulphate. Potassium bichromate 60 gms. Sodium sulphate 30 gms. Water 3000 c.c. This solution requires from three to six weeks for fixing, but a longer time does not injure the tissues. It is commonly used in the dark, and renewed as often as it becomes cloudy. d. Kopsch's Fluid is a combination of potassium bichro- mate and formalin. Potassium bichromate (3.5%) . . . . .80 parts. Formalin (40%) 20 parts. FIXING SOLUTIONS. 3 The tissue remains in this sohition for about twenty-four hours, and is then transferred to a 3.5 per cent, solution of potassium bichromate for three or four days. It should then be thoroughly washed and dehydrated. This solution is especially adapted to the nervous system. Other combinations of this class are Orth's, Erlicki's and Bensley's solutions. 3. Chromic Acid is generally used in .1 to .5 per cent, solutions, and should be allowed to act one to eight days, as it penetrates slowly. It is especially adapted to connective tissues and where mitotic figures are to be studied. 4. Osmic Acid. — This reagent is used in .1 to i per cent, solutions as well as in combination with others. It is a spe- cific reagent for adipose tissue but if turpentine or alcohol- ether is used for clearing the osmicated fat will be removed. The time for fixation depends upon the strength, usually from twelve to twenty-four hours for i per cent, solutions. a. Flemming's Solution: Osmic acid (2% solution) 2 c.c. Chromic acid (1% solution) 45 c.c. Glacial acetic acid 3 c.c. This solution which fixes the tissues in from one to two days, although a longer time will not injure them, should be changed at least once. The tissues are then thoroughly washed and dehydrated. This fluid, which is good for the study of mitotic figures, should be prepared just before using, as it does not keep. b. Golgi's Solution: Osmic acid (2% solution) 3 c.c. Potassium bichromate (3.5% solution) ... 25 c.c. Fix three, five or seven days and transfer to silver nitrate. This is used especially in the Nervous System. The details of the process will be described under Silver Staining. 4 TECHNIC. 5. Formalin is a saturated solution of Formaldehyde Gas in water. It is not used in full strength, but usually as a 4 to 10 per cent, solution. A 4 per cent, solution is pre- pared as follows : Formalin 10 c.c. Sodium chlorid (.5% solution) 90 c.c. This requires from twelve to twenty-four hours for its action, and is especially useful in the nervous system. It may be used with potassium bichromate as above given. 6. Nitric Acid is used as a j per cent, soliiiion, and small pieces of tissue are allowed to remain therein from one-half to one hour. Large specimens (embryos) require from four to eight hours. After fixation the tissues are immediately transferred to 70 per cent, alcohol. It is especially adapted to connective tissues, ova and embryos. 7. Alcohol. — There are several strengths of alcohol suit- able for fixation. Besides acting as fixatives they at the same time dehydrate. a. Absolute Alcohol. — This should be of at least 99.2 per cent, strength. It acts very rapidly and thoroughly but its expense prevents its routine use. It must be changed several times. After twenty-four to forty-eight hours the tissues are ready to be cleared. b. Ninety-five Per Cent. Alcohol acts in the same way as the above, but some (Mallory and Wright) hold that shrinkage results if any solution weaker than the absolute alcohol is used. This strength has however yielded good results in the nervous system. It must be frequently renewed Tissues that have been fixed in solutions containing either osmic acid or chromium salts must he thoroughly washed be- fore dehydration. Golgi's method of staining is an excep- tion as will be seen when its steps are considered. DEHYDRATION. 5 Blood spreads are readily fixed in a solution of equal parts of absolute alcohol and ether, in which they are al- lowed to remain from twenty minutes to an hour. Another good fixative is absolute alcohol, nine parts, and formalin, one part. The time for fixing is about the same. The blood spreads may be subjected to a temperature of 120° C. for twenty m'inutes. Ehrlich prefers this method of fixation to the above. DEHYDRATION. After the tissues have been fixed in one of the above solu- tions and washed, they are ready for the second step, that of Dehydration. Dehydration, or Hardening, is the removal of the water from the tissues, and is accomplished by alcohols of ascend- ing strengths. The tissues are transferred to a fifty per CENT, solution for six to twenty-four hours, unless other- wise directed. This is followed by immersion in a seventy PER CENT, solution for the same time, and then in a ninety- five PER CENT, solution for at least twenty-four hours. Dur- ing this time, the last should be changed once. To in- sure perfect dehydration, the specimens, after being drained, may be placed in absolute alcohol for twelve to twenty-four hours. If the following steps are not to be carried out immediately the tissues shall be transferred to a solution of seventy or eighty per cent, alcohol in which they may remain in- definitely. CLEARING. After dehydration is completed the tissues are ready for the clearing agents. Clearing is the process by which the alcohol is removed and an agent that will mix with the infiltration medium sub- 6 TECHNIC. stituted. If paraffin is to be used an oil, or fluid miscible with both alcohol and paraffin is necessary ; if celloidin in- filtration is to follow, then a mixture of alcohol and ether is used. For the paraffin method the tissues are removed from the alcohol, drained a few minutes and then transferred usually to an oil, for twenty-four hours. The oil penetrates the tissues, removes the alcohol and remains in its place. Chloroform, xylol, and various oils may be employed, among them being turpentine, which usually requires twenty-four hours for half-inch cubes. Xylol requires from six to twenty-four hours, or until the tissue is transparent. Cedar oil is used as follows : The tissues are first placed in a mixture of equal parts of cedar oil and absolute alcohol for twenty-four hours. They are then drained and placed in pure cedar oil for the same length of time. If pure oil alone is used, it is changed several times until the tissues are trans- parent, which usually requires twenty-four to forty-eight hours. INFILTRATION. After clearing, the tissues are ready for Infiltration. Infiltration is the process by which the interstices of the tissue are filled with an agent that hardens and allows the tissue to be cut without distortion. There are two impor- tant agents. Paraffin and Celloidin. Gum may be used for special purposes. The paraffin method will first be con- sidered. After clearing, the tissues are drained, blotted with tissue paper, and then placed in a tube of melted paraffin, at a tem- perature a little above the melting point, usually 50° to 55° C. This is called Paraffin No. i, and its object is the removal of the bulk of the oil. After twenty-four hours the tissues INFILTRATION. 7 are removed to a tube of fresh paraffin and allowed to re- main the same length of time. This is Paraffin No. 2, and the remainder of the oil is removed and pure paraffin left in the tissues. The tissues are then ready to be blocked. By the use of chloroform, infiltration with paraffin can be accomplished, to great extent, in the cold. The tissues are completely dehydrated with absolute alcohol and then placed in PURE CHLOROFORM to replace the alcohol. This is ac- complished when the tissues become submerged, usually four to eight hours. They are then transferred to a warm, satur- ated solution of paraffin in chloroform, for two to four hours, and then to pure melted paraffin until all the chloroform has disappeared (two to twelve hours). If delicate structures are to be infiltrated they may be cleared slowly by adding toluol, or benzol, drop by drop to the specimen in absolute alcohol and mixing after each ad- dition. By this method, 2 c.c. of oil can be added to the same amount of absolute alcohol in four to six hours and no shrinkage result. The specimens may then be transferred to a mixture of absolute alcohol (i part) and toluol (3 parts) for one to three hours. They may then be placed in pure toluol from one to four hours, the time depending upon the size, one-eighth to one-fourth inch in diameter. From this it may be transferred to a solution of paraffin in toluol for two to four hours, after which more paraffin is added, and the tube transferred to the paraffin-bath, where it remains for an hour or two, and is then cast. Blocking may be accomplished by the use of leaden angles, paper boxes, or zi/ooden blocks. The leaden angles are of various sizes and are used in connection with brass plates. These are all cooled in ice water, quickly dried and the angles put into place. A small layer of paraffin is then run into the mold, and the tissue placed therein, and oriented. 8 TECHNIC. The mold is then filled with melted paraffin, and as scK)n as a scum is formed, the whole is immersed in ice-water, and the angles cautiously removed, so that the water can act upon all sides except the bottom. Unless this is done, the paraffin, in cooling rapidly and contracting, will enclose water bubbles that are unnecessary and annoying. A little skill is required to cast successfully. Usually, by this method, the paraffin remains clear, a condition much to be desired. A cup is pre- pared upon the end of a block, by wrapping a strip of news- paper, five inches long and two inches wide, tightly around one end of the block, and sealing with paraffin. If BLOCKS are used, these should be preferably of oak, an inch and a quarter long, by seven-eighths square. The end is carefully and tightly wrapped with a strip of thin paper, forming a cup one-half to one inch deep. The specimen is then quickly oriented upon a thin layer of paraffin, and the cup filled with paraffin. It is then set aside and allowed to cool. The enclosed air-bubbles rise. The paraffin is usually not clear by this method, but is made so by placing the block, for several days, upon the paraffin bath. The warmth clears the paraffin. After casting, the blocks are trimmed, and are then ready to be cut with the microtome. For the celloidin infiltration method, fixation and DEHYDRATION are carried out in the same manner as for par- affin, but a different clearing agent is used. A mixture of equal parts of absolute alcohol and ether will clear tissues in twenty-four hours, at the end of which time they are ready for the celloidin. Celloidin, or pyroxylin is used in two different solutions — thick and thin. The thick solu-tion is prepared by dissolv- ing one ounce of the celloidin in a mixture of 150 c.c. each of absolute alcohol and ether. It is best to soften the celloidin INFILTRATION. 9 for some hours in the absolute alcohol, and then add the ether. Preserve in a magnesium citrate bottle. The thin celloidin is made by diluting the thick with an equal part of the alcohol and ether mixture. After clearing, the tissues are drained for a few seconds, and then transferred to the thin celloidin for one to four days, and then to the thick for four to seven days. They are then ready to be cast. The tissues may be blocked, as in the paraffin method, by placing the specimen in a paper cup, as above, upon a wooden, vulcanite, composition, or glass block, and covering with thick celloidin. They are then set aside until a thin scum forms, due to the contact with the air, after which they are placed in eighty per cent alcohol to harden the celloidin. In twenty-four to forty-eight hours, they are ready to cut. Another way to cast is to place the tissues in low Stender dishes, cover well with very thick celloidin, and orient imme- diately. When a scum has formed, the dishes are lowered into another containing the alcohol for hardening. Still another way is to place the tissues with thick celloidin in stoppered paraffin tubes, and, after several days, loosen the stopper and allow the alcohol and ether to gradually es- cape. When the celloidin has retracted from the sides, the mold is lifted out and placed in the alcohol. If the celloidin is not hard enough, the blocks may be placed, for twenty-four to forty-eight hours, in eighty per cent, alcohol, containing i to 5 per cent, glycerin. Gum. This infiltration medium is prepared as follows : Cane Sugar 28.5 gms Water 30 c.c. Syrup i Cane Sugar 28.5 gms. Water 30 c.c. ( Gum Acacia 57 gms. Gum < .^. ^ 1 Water 310 c.c, lO TECIINIC. Mix together four parts of the syrup, five parts of the gum and to this add nine parts of a saturated solution of boric acid. Filter through muslin. The tissues are thoroughly washed, free of any trace of alcohol, and are then placed in the above solution, and al- lowed to remain until penetrated, which requires at least twenty-four hours, if half-inch cubes are used. A longer time is better. The process is aided by allowing the jar with the tissues to stand in a warm place. Tissues infiltrated with gum must be frozen and cut in a freezing microtome. After the above steps have been finished, the tissues are ready to be sectioned. Paraffin blocks are aU dry, the knife of the microtome being placed so that it meets the block squarely. When large objects are cut, it is sometimes necessary to place the knife obliquely. Very thin sections may be straightened for mounting by floating them in warm water. The slide pre- pared with Mayer's albumen (See p. 25) is then dipped be- neath them, and if carefully lifted, the section rests smoothly in place thereon. Celloidin blocks are treated differently. The knife is placed obliquely and kept moist with 80 per cent, alcohol. The block likewise is kept moist, and as the sections are cut, they are transferred, by means of a large sable brush, to a dish of the same alcohol, and allowed to remain there until required. If the celloidin is too soft, the sections will be quite thick. This may be remedied by hardening the blocks in alcohol contain- ing I to 5 per cent of glycerin. Celloidin answers very well for the nervous system, but where thin sections are desired, the paraffin method is preferable. DECALCIFICATION. II DECALCIFICATION. Bone and teeth may be ground for study. If sections are desired, the inorganic matter must be removed, by means of acids. This process is Decalcification. Whole teeth and small pieces of bone are fixed and hard- ened in solutions containing a salt of chromium, and are al- lowed to remain as long as required. After being thoroughly washed and dehydrated as above, they are ready for the de- calcifying agent, of which large quantities are to be used. The solutions given below are the most important. I. Phloroglucin-Nitric Acid is no doubt the best. It consists of Phloroglucin * . . . i gm. Nitric acid (concentrated) 5 c.c. Alcohol (70 per cent.) 100 c.c. The phloroglucin is dissolved in the nitric acid, and al- lowed to stand until the fumes have disappeared (about twenty-four hours). The alcohol is then added, and the so- lution is ready for use. The teeth or bone are placed therein until readily penetrated by a needle or cut with a scalpel. The tissues are then transferred to alcohol and dehydrated in the manner already stated. Celloidin is the better infiltrating agent, as heat tends to harden osseous tissues. Additional nitric acid may be added if desired, but not over 20 per cent. Mayer's Solution is a 5 per cent, solution of nitric acid in 95 per cent, alcohol. It acts very well. The alcohol is sup- posed to prevent swelling of the tissues. Trichloracetic Acid. A 5 per cent, solution of this is used. It is slower than the nitric acid, but the treatment is the same. Staining. In order to study the various portions of a cell, they must be differently stained. Two stains are gen- erally used — NUCLEAR, or basic; and, protoplasmic, or 12 TECHNIC. ACID. The NUCLEAR stain is used first, followed by the acid ; this is called counter-staining. Gruebler's products are recommended. Basic Stains. The most important of the basic stains are HEMATOXYLIN and the anilin dyes. There are several ways to prepare the hematoxylin. The most rapid is the Harris method. Hematoxylin (harris). Hematoxylin I gm. Absolute alcohol lO c.c. Potassium alum (sat. aq. sol.) . . . . . 200 c.c. Dissolve the hematoxylin in the alcohol and add it to the alum solution. When this is brought to a boil, add i gm. of mercuric oxid, and cool the solution rapidly. The oxygen liberated ripens the solution immediately, and the stain is ready for use when cool. It should be filtered and diluted with three to four times the quantity of water, when ready, and will require three to five minutes to stain. Delafield's hematoxylin is prepared as follows : Hematoxylin 4 gms. Alcohol 25 c.c. Ammonium alum (sat. aq. sol.) 400 c.c. Dissolve the hematoxylin in the alcohol, and add this solu- tion, drop by drop, to the alum solution. Expose this to the light and air for a week or more, and then filter. To the filtrate add Glycerin 100 c.c. Methyl alcohol 100 c.c. Expose again for a long time, and filter. This solution must be diluted three to four times, like Harris'. STAINS. 13 Acid hematoxylin is made up as follows : Hematoxylin I gm. . Absolute alcohol 30 c.c. Glycerin 60 c.c. \ Saturated Water 60 c.c. \ with alum. Glacial acetic acid 3 c.c. Add the glycerin and water to the hematoxylin, dissolved in the alcohol ; then add the acid. This solution must be ex- posed to the light for three weeks, when it becomes bluish. Sections stained in it are at first not dark, but when exposed to the light, they become bluish. Most of the ANiLiN DYES are not stable, but fade when ex- posed to the light. Methylene blue is used in connection with the nervous system. Methyl green is used for organs and tissues containing mucin, and in blood stains. Safranin is used for the study of karyokinesis. It should be used upon tissues hardened in Flemming's solution. Safranin * i gm. Absolute alcohol ......... 100 c.c. Water 200 c.c. Sections may remain in this solution from two to twenty- four hours, and even longer. They are then washed in plain alcohol, or carefully differentiated in acid alcohol, and then only the chromatin retains the stain. BiSMARK BROWN. — This Stain is not very soluble in water. A saturated solution is made by boiling the stain in water, and then filtering. This gives a 3 to 4 per cent, solution, which is diluted by adding one-third volume of absolute alco- hol. This stains rapidly, but does not overstain. It is usea to advantage in contrast with hematoxylin, hi connective tissues and cerebellum. It answers well in staining the acid 14 TECHNIC. cells of the stomach. The sections should first be deeply stained with hematoxylin, and then subjected, five minutes, to the above stain. The acid cells are distinctly brown, while the peptic cells have a bluish cast. Acid Stains. — The more comimon acid stains are eosin, PICRIC ACID, VAN GIESON and ORANGE. EosiN is commonly used as a one per cent, aqueous, or al- coholic solution. It requires one to two minutes, and should be washed ofif with water, if an aqueous solution has been used ; otherwise, with alcohol. Picric acid. — A saturated aqueous solution is used for 15 to 30 seconds. It is then washed quickly with 95 per cent alcohol. Van GIESON consists of picric acid and acid fuchsin. Picric acid (sat. aq. sol.) 100 c.c. Acid fuchsin (i per cent, sol.) 5 c.c. Stain from one to three minutes, and wash with alcohol. A little stronger solution is used for the nervous system. Orange, is used as a one per cent, solution, and is em- ployed as a blood stain. There are stains that affect both nucleus and protoplasm sufficiently to differentiate each well. Such are carmin and CARMiNic ACID COMBINATIONS. They are used chiefly in BULK STAINING, especially for entire embryos. Borax carmin consists of carmin boiled in a solution OF BORAX. Carmin 2 gms. Borax (2 per cent. aq. sol.) 200 c.c. Boil, and then add a few drops of a five per cent, solution of acetic acid and 100 c.c. of 70 per cent, alcohol. After a few hours filter, and to the filtrate add a small piece of thymol or menthol, to preserve. STAINS. 15 Allow the solution to stain sections for 15 to 20 minutes, and then differentiate with acid alcohol, prepared as follows : Hydrochloric acid (concentrated) i cc. Water 29 cc. Alcohol (95 per cent.) 70 cc. This stain is also used for hulk staining. 2. Alum carmin. — This is prepared by boiling one GRAM OF Cx\RMIN with IOC CC. OF A FIVE PER CENT. SOLUTION OF AMMONIUM ALUM. This is filtered when cool, and pre- served as above. It also requires the same time for staining. 3. PiCRO-CARMiN is a DOUBLE STAIN, and its preparation is not so simple. It consists of the following : Carmin . 4 gms. Ammonia (concentrated) 10 cc Water 200 cc Dissolve the carmin in the ammonia, to which a little water has been added. Then add the water, and, after 24 hours, filter. Allow the solution to stand until most of the am- monia has evaporated and add an aqueous saturated solution of picric acid until precipitation occurs. The solution must be stirr€d all the time. Set it aside to crystallize and to evap- orate to one-third of its bulk. Pour off the liquid and evap- orate it to dryness. Dissolve the first crystals and evaporate to dryness. This residue, as a one per cent, solution in water, is a very good double stain. Paracarmin consists of carminic acid^ aluminum CHLORID, CALCIUM CHLORID and JO PER CENT. ALCOHOL. Carminic acid i gm. Aluminum chlorid 0.5 gm. Calcium chlorid 4 gms. Alcohol (70 per cent.) 100 cc Dissolve and filter. l6 TECHNIC. This stain is especially useful in embryology, as it does not overstain, and may be used again and again. It is a good contrast stain to Weigert"s elastica stain, in sections. Ehrlich-biondi-heidenhain stain. — This stain is used especially in blood zvork or those tissues containing many leukocytes. It is composed of : Orange (saturated aq. sol.) lOO c.c. Acid fuchsin (saturated aq. sol.) 20 c.c. Methyl green (saturated aq. sol.) .... 50 c.c. This solution is diluted to make a solution of i-ioo, which, upon the addition of acetic acid, must be bright red. It is difficult to prepare, and so is better bought ready for use. Organs should be fixed in corrosive sublimate, and stained for 12 to 24 hours, washed with 90 per cent, alcohol, and dehydrated with absolute alcohol, cleared and mounted in balsam. Besides these, there are special stains, by means of which, certain structures are brought out. Among these, the most important are the Gold, Silver, Myelin and Elastica Stains. The Gold Stain, used for lymphatic spaces and nerve end- ings, is not always successful ; but when it succeeds, the re- sults are beautiful and gratifying. There are a number of ways of preparing the solution, but the best is the boiling method. Eight c.c. of a one per cent, solution of gold chlorid are mixed with two c.c. of formic acid, and brought to a boil, and cooled. This is repeated three times, and it is then ready for use. Small strips (3 to 5 mm. thick) are placed in it for one hour, and the container kept in the dark. They are then washed in distilled water, and exposed to the light in a solu- tion of formic acid (loc.c. of acid to 40 c.c. of water) for one SPECIAL STAINS. 1 7 or two days. They are then dehydrated in 70 per cent, al- cohol, and left there for 4 to 8 days or longer. Silver Nitrate. — Pieces of the nervous system are fixed in the Golgi solution (see Fixatives, p. 3) and then placed in silver nitrate. The steps are as follows : Half-inch cubes of the nervous system are fixed in the dark for three, five and seven days in Golgi's solution, which is to be renewed once after the first two or three hours. The tissues are then washed, for one minute, in distilled water, blotted between filter paper and transferred to a 0.75 per cent, solution of silver nitrate for two to four days. While in this solution, they are exposed to the light. They are then removed to absolute alcohol for two to three hours, dried for one minute between filter-paper, cleared in toluol, cast in parafiin and, when cold, cut with a flooded knife, as in the celloidin technic. The results seem as good if the dehydration be prolonged to six or eight hours and the tissues then cleared, over night, in pure cedar oil, and finally infiltrated, for six to eight hours^ in the parafiin bath. The blocks cut much better, and they may be preserved indefinitely. By using 3, 5 and 7 days for fixation, dififerent blocks are prepared, of which some will be successful. Silver nitrate is used chiefly for nervous tissues. It may also be injected into the blood vessels to stain the en- dothelium, and into the lymphatics to outline the small chan- nels. It has also been used in the liver, to outline the bile capillaries. Myelin Stain. — This is w^eigert's hematoxylin stain FOR myelin sheaths. The tissues are fixed in bichromate, though this is not absolutely necessary. Celloidin infiltration is usually the best. l8 TECHNIC. After the sections have been cut, they are placed, for twenty-four hours, in the following solution : Potassium bichromate 5 gms. Chrom alnm 2 gms. Water 100 c.c. They are then washed thoroughly, and transferred to the following solution, for twenty-four hours : Copper acetate 5 gms. Acetic acid (36 per cent.) 5 c.c. Chrom alum 2.5 gms. Water 100 c.c. This solution is a mordant. The sections are carefully washed and carried into the following solution : Hematoxylin i gm. Absolute alcohol 10 c.c. Lithium carborate (sat. aq. sol.) i c.c. Water .90 c.c. The sections are stained, from fifteen minutes to two or four hours, in this solution, and then washed until the wash- ings are clear. They are then differentiated in the following : Potassium ferricyanid 5 gms. Borax 4 gms. Water 200 c.c. In this solution they must remain vmtil the gray matter becomes yellowish. This change must be watched under the microscope. The sections are immediately transferred to water, which is frequently renewed. They are then dehy- drated, cleared and mounted in balsam. The myelin sheaths will be bluish black. CLEARING AGENTS. I9 Weigert's Elastica Stain is used to demonstrate the elas- tic TISSUE in organs and tissues, and is prepared as follows : Fuchsin ... 2 gms. Resorcin 4 gms. Water 200 c.c. This mixture is brought to a boil, and then 25 c.c. of a solu- tion of liquor ferri sesquichlorati added, the mixture stirred and boiled for 3 to 5 minutes. When cool, it is filtered, and the precipitate dissolved upon the filter, in 200 c.c. of 95 per cent, alcohol. This is stirred and boiled until the precipitate is entirely dissolved. The solution is then cooled and brought up to 200 c.c. with 95 p^r cent, alcohol and 4 c.c. of hydro- chloric acid added. Sections should be stained, from 20 minutes to an hour, in this solution, washed well in 95 per cent, alcohol, cleared and mounted. CLEARING AGENTS FOR SECTIONS. After staining and dehydrating, the sections are to be CLEARED (See Slide Technic, p. 27). The clearing agent removes the alcohol and prepares the section for the final step of mounting. These agents differ from those used in block technic. When balsam or dammar is to be used, the sections are cleared with an oil. Of these, the following are the most important: Creosote (beechwood) is one of the commonest and the best for general laboratory use. Oil of origanum is also a very useful clearing agent, and is especially adapted for celloidin sections and those stained with van Gieson's stain. It neither dissolves the celloidin nor renders it stiff. Oil of cloves acts rapidly, but dissolves celloidin and re- 20 TECH NIC. moves anilin dyes. It does not evaporate, but renders the section hard and becomes yellow with age. Cedar-wood oil clears slowly, but has the advantage of not abstracting the anilin dyes. Oil of bergamot is very good, but has the disadvantage of removing eosin. Xylol, toluol, benzol all act very rapidly, and require dehydration with absolute alcohol. They are useful with anilin stains, and are readily applicable as solvents of balsam. They, however, render celloidin stif¥ and hard. Carbol-xylol is a mixture of xylol and carbolic acid. Xylol I part. Carbolic acid - - 3 parts. It acts very rapidly, and is best for hematoxylin and carmin stains ; it does not stiffen celloidin. Anilin oil-xylol consists of anilin oil, tzvo parts, and XYLOL, one part. It is more commonly used than the pre- ceding. Most of the oils require about ^ve minutes to act. The sec- tions are set aside during this time. In the case of rapidly- acting agents, the slides are retained in the hand and rocked back and forth until the section is clear. This is usually ac- complished in a minute or so. After clearing, the sections are ready for the final step, that of MOUNTING. There are a number of mounting media. such as BALSAM, DAMMAR, FARRANt's SOLUTION and GLYCER- IN JELLY. Balsam. — Sections to be mounted in balsam must be thoroughly dehydrated and cleared in an oil. The oil is then removed by blotting, a small drop of balsam placed upon the specimen and a clean cover-glass applied. INJECTION 21 The balsam is soluble in chloroform, Hirpentine, benzol or xylol. The latter agent is the best. Sections mounted in this medium are permanent. Dammar is more complex. It consists of the following: Gum dammar i^ oz. Gum mastic ^ oz. Turpentine 2 oz. Chloroform 2 oz. The dammar is to be dissolved in the turpentine, and the mastic in the chloroform. Each is to be filtered, the filtrates mixed and the mixture filtered. This is to be kept in a well- stoppered bottle, to prevent the evaporation of. the chloro- form. Farrant's solution. — Sections to be mounted in this medium are neither dehydrated nor cleared, but washed with water and mounted in this solution. It is prepared by adding gum-arabic to a mixture of equal parts of water, glycerin and a saturated solution of arsenious acid. The solution must be filtered after the gum is dissolved, and should have the consistence of a thick syrup. Preparations mounted in this medium may be made per- manent by ringing. This is done by running a ring of ce- ment around the edge of the cover-glass. Glycerin Jelly. — This medium must be warmed before it can be used. A drop is placed upon the specimen, and the cover-glass quickly applied, as this medium sets rapidly. It is used for special purposes, as for isolated cells, urinary caists, crystals, etc. Neither dehydration nor clearing is necessary. INJECTION. Injection masses. — In order to study the circulatory system, the vessels must be injected with a substance that will outline them. For this purpose, either an aqueous sohi- tion of Berlin blue, or gelatin masses are used. 22 TECHNIC. Berlin blue is used in water, one part to 20, and this is injected with a hand syringe or by continuous air pressure. It gives very good results. The GELATIN MASSES may be either carmin or Prussian BLUE. The CARMIN mass consists of the following: Carmin 2 gms. Water. Ammonia. . Stir the carmin in a little water, and add strong ammonia, drop by drop, until the carmin is entirely dissolved. Filter the solution and add it carefully to the melted gelatin. The latter is prepared by soaking gelatin in double its quantity of water, and melting. The mixture is stirred and then neu- tralized with dilute acetic acid. If too acid, the carmin will be precipitated, and if the ammonia is not neutralized and the gelatin is quite alkalin, the stain will not be limited to the injected vessels, but will be diffused into the surrounding tissues. This mass should be filtered while hot, and preserved with a little camphor. The PRUSSIAN BLUE mass is somewhat similar. Four gms. of the Prussian blue are stirred into 80 c.c. of water, and the mixture added to gelatin prepared as above. The solu- tion is filtered while hot, and preserved with camphor, or covered with methyl alcohol. The entire body, or individual organs, may be injected. When the hand syringe is used, great care must be exercised that the pressure be not too great, as the vessels will rupture and the mass extravasate. The continuous air pressure method is the better. The mass must be melted and the ani- mal kept warm by immersion in warm water. As soon as the injection is complete, the animal or organ is immersed BLOOD. 23 in ice- water, so that the gelatin may set immediately. When the body is cooled, the organs are cut into blocks, and trans- ferred to 80 per cent alcohol, where they remain until thor- oughly hardened, which takes from one to three days. They are then treated with 95 per cent, alcohol to dehydrate, cleared and infiltrated like any other tissue. Blood is drawn from the finger tip or lobe of the ear. The part is thoroughly cleansed and finally washed with alcohol. A sterilized needle is then plunged to a depth of about one- eight of an inch, and the blood allowed to flow. The part should not he squeezed, as this dilutes the blood with lymph, and causes errors in accurate work. Blood spreads are obtained by touching a drop of blood with a cover-glass, and immediately placing this upon a second glass. The two are then slid apart, so that a thin Hhn of blood is present upon each. If the glasses are lifted apart, the cells are greatly distorted and useless for study. The spreads are allowed to dry in the air, and then fixed by (i) heat, (2) alcohol-ether mixture, or (3) the alcohol-formalin solution. If HEAT is used, the spreads are placed in an oven, and kept at a temperature of 120° C. for twenty minutes. The ALCOHOL-ETHER MIXTURE consists of equal parts of absolute alcohol and ether. This fixes the spreads in twenty minutes. Results with this fixative are very good. The ALCOHOL-FORMALIN MIXTURE consists of ninc parts of absolute alcohol and one part of formalin. Spreads are fixed in twenty minutes. After fixation, the spreads are allowed to dry, and may then be stained like any other tissue. Hematoxylin and eosin give a good result. Among special stains is the ehrlich-biondi-heidenhain stain. For its composition, see Stains, p. 16. 24 TECHNIC. Wright's blood stain is one of the most satisfactory, and is prepared in the following manner : Steam 1.5 grams of methylene blue in 150 ex. of a one per cent, aqueous solution of sodium bicarbonate for one hour, in a sterilizer. Add a one-tenth per cent, aqueous solution of yellowish eosin to 100 c.c. of the methylene blue solution until the mixture turns purple, and a yellowish metallic scum forms upon the surface, and a blackish precipitate appears ; about 500 c.c. of eosin solution will be required, and it should be added slowly, while constantly stirring. The solu- tion is then filtered, the precipitate dried and made into a saturated solution with methyl alcohol. This solution is filtered and 80 c.c. of the filtrate are diluted with 20 c.c. of methyl alcohol. Dried spreads are stained, for one minute, with this solu- tion, and the stain then diluted upon the glass, with water, until the stain is semi-transparent. After two or three min- utes, the spreads are thoroughly washed with distilled water, dried quickly and mounted. The acidophilic granules are reddish lilac and red, while the basophilic granules are deep blue, or even black. This solution both Hxes and stains the cells. Eosin and methylene blue give good' results. The spreads are stained in a one-half per cent, alcoholic solution of eosin for two or three minutes, using gentle heat. Then they are placed in a saturated aqueous solution of methylene blue for two or three minutes. The spreads are then thor- oughly washed, dried and mounted in balsam. As a rule, the granules of the leukocytes are well stained. In order to obtain the hell-sMped red cells, the finger should be thoroughly cleansed, and the blood drawn as usual. The first drop should be wiped off and a drop of one per cent, osmic acid solution placed over the puncture. The blood then SLIDE TECHNIC. 2^ flows into the osmic acid, which acts as a fixative, and pre- vents contact with the air until fixation is complete. If this drop be examined under the microscope, the bell-shaped cells will be seen in great numbers. Blood platelets may also be stained in the above way. Erythroblasts of the spleen may be studied in spreads made by drawing thin pieces of the organ over cover-glasses. These are then fixed in the following : Mercuric chlorid 78 gm. Sodium chlorid .28 gm. Water 30 c.c. This solution should be filtered, and spreads fixed in it for one minute. They should then be washed and stained one- half hour with aqueous hematoxylin, washed and covered with a 3 per cent, solution of eosin, for two to three minutes. They are then washed, dried and mounted. Spreads may be stained, for three minutes, with eosin, and one-half minute with five per cent, methylene blue, then washed, dried and mounted. Slide Technic. — The preparation of sections for micro- scopic study requires skill and care. Paraffin sections are made to adhere to the slide by means of Mayer's albumen. This is prepared by mixing, thor- oughly, white of egg and glycerin in equal parts, and filter- ing. A very thin film is all that is necessary. The following desk reagents are sufficient for all ordinary work: Coplin staining jar, containing lodin. Coplin staining jar, containing Kerosene. Coplin staining jars, containing Alcohol, Nos. i and 2. One Barnes bottle, containing Hematoxylin. One Barnes bottle, containing Van Gieson's stain. One Barnes bottle, containing Eosin. 26 TECHNIC. One Barnes bottle, containing Alcohol. One Barnes bottle containing Water. One Barnes bottle containing, Acid Alcohol. One Barnes bottle, containing Creosoie. One Barnes bottle, containing Albumen. One Barnes bottle, containing Picric Acid. The method of procedure for staining is given in detail below : 1. Cover a clean slide with a thin film of albumen. 2. Add a few drops of water, and float on this the cut paraffin section. 3. Warm gently over a flame, so as to spread the section, but be careful not to melt the paraffin. 4. Drain and set aside, or in an oven, for six to twenty- four hours. The slide must be perfectly dry before the other step can be carried out. Put on the slide an identification label. 5. Place in the kerosene for five to fifteen minutes, to remove the paraffin. 6. Wash with alcohol, to remove the kerosene, and place in the jar of iodin, five to ten minutes, to remove the crystals of bichlorid of the fixing agent. 7. Remove the excess iodin from the slide with tissue paper, wash with alcohol and place in the iirst alcohol jar for fifteen minutes, to remove the remainder of the iodin. 8. Drain the section, wash with water, cover with hema- toxylin for three to five minutes, and wash with water to deepen the color. 9. Counter-stain. Eosin one to two minutes, wash with water and then alcohol, to remove excess stain ; or, Van Gieson one-half to one minute, wash with water and then alcohol, as above ; or. Picric acid fifteen seconds and wash with alcohol. SLIDE TECHNIC. 2^ Carmin may be used alone for fifteen minutes, or followed by picric acid, as in the preceding. . ID. After washing with alcohol, dehydrate in the second jar of alcohol. Allow sections to remain about five minutes. 11. Clean the slide carefully without allozmng the sec- tion to dry. Blot with tissue paper. 12. Cover with a drop or two of creosote for five min- utes. This removes the alcohol, renders the specimen trans- parent, and allows the use of balsam. This is sectional clear- ing. 13. Drain off the creosote, hlot, add a drop of balsam and cover with a clean cover-glass. 14. Remove the identification Label, apply a clean one, and write the name thereon. After the paraffin has been removed, the specimen should never he allowed to dry. The above technic will answer for all ordinary histologic and pathologic work, and, if strictly adhered to, there will not be the slightest trouble in making excellent preparations. CHAPTER II. HISTOLOGY, Histology is the science that treats of the minute structure of normal tissues and organs. Although to the naked eye tissues may have an apparent structure that seems ultimate, when examined under the microscope this structure is seen to be but gross. Each section studied will be found to be composed of minute elements, more or less regular, and definitely grouped and arranged. These elements are Cells. A Cell is a small mass of protoplasm containing a nucleus. It is the histologic basis of the body, and has a ^ A/^ complex structure. Certain parts are absolutely essential ^5-%/^ for the proper performance of its various functions, while others are accessories, which most cells possess. The parts of a typic cell are : 1. Cell-body. 2. Nucleus. ^ 3. Centrosome. 4. Nucleolus. 5. Cell-wall. I. The Cell-body, or Protoplasm, or Cytoplasm is a granular, semi-solid substance that constitutes the bulk of the cell. It may or may not be limited by a cell-wall. It consists of two main parts, the Spongioplasm, or Filar-mass, and the Hyaloplasm, or Interfilar-mass. The Spongioplasm, as its name indicates, is a frame- work of comparatively solid structure, in the meshes of which is found the semi-fluid hyaloplasm. The elasticity of the spongioplasm is said to give rise to ameboid movements. In the protoplasm are to be seen small darkly-staining bodies, the microsomes, and paler masses, the plastids. 28 THE CELL 29 At the outer margin of the cell-body is a narrow, peripheral zone, containing no microsomes, known as the Exoplasm. At times, there are other structures present, as fat globules, glycogen, secretion granules, vacuoles and pigment. The cell-body has affinity for acid, or protoplasmic, stains, such as eosin, picric acid, carmin, orange, etc. Fig. 1. — Scheme of a Cell. Microsomes and spongioplasm only partly sketched {St6hr's Histology). 1. Spongioplasm ; 2. hyaloplasm ; 3. microsomes ; 4. exoplasm ; 5. chroma- tin ; 6. achromatin ; 7. linin ; 8. chromatic knots ; 9. nuclear mem- brane ; 10. centrosome ; 11. nucleolus ; 12, cell-membrane ; 13. in- clusions. 2. The Nucleus is usually a darkly-staining body having a sharp outline, and occupying, as a rule, a central position. In glandular cells, its location varies with the stage of secre- tory activity. Its structure resembles that of the protoplasm, to a certain extent. It consists of a network and semi-fluid substance, surrounded by a distinct membrane or wall. 30 HISTOLOGY. The network is called the chromatin, or nuclear fibrils, and the semi-solid substance, the nuclear matrix, sap, or ACHROMATIN. Chromatin is the part of the nucleus that responds to the stains. It is arranged as an irregular network of anastomos- ing fibrils, each consisting of a delicate central thread, the linin, upon which the real chromatin substance is arranged, in the form of granules. It is the most important portion of the nucleus during the process of cell-division. Achromatin is the semi-fluid substance that fills the meshes of the chromatin. It reacts but faintly to stains, and is not of the same importance as the above. The nuclear membrane is the wall that limits the nucle- us. It is present in nearly all nuclei, and stains readily. It consists of amphipyrenin. Of the above sfructures, the chromatin persists throughout all the stages of reproduction, while the remainder of the nuclear constituents disappear. 3. The Centrosome is a small, darkly-staining structure, which, owing to its small size, has been found in but few of the cells of the human body. It is readily seen and studied in the ova of some of the lower animals, especially those of ascaris megalocephala. It lies, usually, just outside of the nucleus, in a small, clear field called the attraction sphere, within which are seen delicate lines that radiate from the centrosome. The attraction sphere and the centrosome con- stitute the astrosphere. Besides being the center of cell- division, the centrosome seems to play an important part during the resting stage. In pigrnent cells and white blood corpuscles, it seems to preside over the movements of the whole cell, and in ciliated and flag- ellated cells over the action of these processes. 4. The Nucleolus is a small body found within the CELL PROPERTIES 3 1 nucleus. It is not always present, and more than one may be found. In nerve cells and ova it is unusually large and readily stained, while in others it is scarcely noticeable. Its importance is doubtful, as no definite function has as yet been found. It consists of pyrenin, and disappears during cell-division. .; -tutc--^ %'- '- ^tr-^l-M^kyOc- 5. The Cell-wall is a more or less prominent m-embrane that limits cells. It is not present in all animal cells, though Lfejrl some hold that even the wandering cells possess a delicate membrane. In some instances, it consists of the differenti- ated, peripheral protoplasm, and in others, is a secretory pro- duct of the protoplasm. Of the above structures, the Cytoplasm, Nucleus and Centrosome are the essential parts, when the important functions of the cell are considered. In red blood cells, the nucleus is absent, and as a consequence, these cannot repro- duce themselves. Cells differ greatly in form and size ; the nucleus conforms somewhat to the shape of the cell. Usually, but one is pres- ^ ent, but in giant cells and voluntary striated muscle, many are to be found. [J^m-o^ uJe limited to only a portion of the cell, as to hair-like '^^ , processes called cilia. '''''• ■ • ^ Irritability is the property of response to surrounding in- fluences or stimuli. This is more pronounced in the individu- CCUlL ^€^^-X'i^L ^1 cells of such animals that possess no nervous system. Here ^j, j'- It is practically a primary change in the cell. When a nerv- /y,,/' ous system is present, this presides over such changes, which / ak*e then secondary, ^if**** /^'AReproduction is the process by means of which a cell or CELL-DIVISION. 33 an organism propagates itself and continues its life history. Without this or an analogous process, life would soon cease to exist. It is of two varieties, direct, amitosis or budding and indirect, mitosis or karyokinesis. Of these, the latter is the more common. In Amitosis, the cell-body is m.arked by a constriction that gradually deepens and is imparted to the nucleus. As this deepens, the protoplasm and nucleus are finally divided Central spindle. Fig. 3. — Scheme of the Loose Coil and Separation of the Centrosomes {i^tohf's Histology). into two small but practically equal cells, which have the same structure as the parent cell. By growth, these cells, which are called daughter cells, increase in size, until that of the parent, or mother, cell is attained. Mitosis is a very complex process, in which the nucleus plays a very important part. The protoplasm is almost pass- ive until the late stages of the process. The various stages are the prophase, metaphase, anaphase and telophase. These are not absolutely separable from one another. The changes that occur may be grouped under three heads — nuclear, centrosomic and protoplasmic. 34 HISTOLOGY. Prophase. — The nuclear changes are quite complex. Whereas the chromatin is ordinarily arranged as an irregular network, when division begins the irregular twigs of the net- work gradually become smooth, and form, usually, a single thin closely-convoluted thread, called the close spirem, or SKEIN. The thread becomes thicker and shorter, and the coil looser, and this constitutes the loose spirem, or SKEIN. The thread then separates into a number of segments called CHROMOSOMES. This sometimes occurs before the Polar radiation. Central spindle. ,«k*W^^^ Fig. 4. — Scheme of the Mother StAr, or Equatorial Plate. ( Stohr's His to logy. ) loose spirem is formed. The chromosomes become U or V- shaped, and arrange themselves along the equator of the cell, with the closed ends directed toward a common center, called the polar Held. This arrangement is termed the equatorial PLATE^ or monaster, and practically ends the chromatin changes during the prophase. The chromosomes are always even in number, and the same number is always formed in each cell of the same species. In man, the number is said to be sixteen. The nuclear membrane, during these changes, has gradu- ally become more and more hazy, and finally disappears. The ackromatin is released, and mixes with the protoplasm. KARYOKINESIS. 35 The nucleolus likewise gradually fades and disappears. The centrosome is the dynamic center of the cell. It di- vides into two portions (if within the nucleus, it passes first into the protoplasm), each oi which becomes surrounded by its own attraction sphere. These centrosomes gradually move apart, through an arc of 90°, to opposite poles of the cell. During this change, the intervening rays remain in contact, forming a spindle of delicate threads, which is com- plete when the centrosomes reach their polar position. This Fig. 5. — Scheme of Metakinesis, Showing the Nuclear. Spindle. (Stohr's Histology.) is the CENTRAL, or ACHROMATIC SPINDLE, and the threads are of the utmost importance, and become attached to the chromosomes of the equatorial plate. With the formation of the equatorial plate and central spindle, the prophase ends. Variations, too numerous to de- scribe, occur, but the above is the usual course in this stage of mitosis. Metaphase. This is the stage during which the chromo- somes divide and separate. It concerns the chromatin chiefly. The chromosome divide longitudinally into two equal por- tions. This cleavage occurs at the closed end first, and as it proceeds, the daughter chromosomes become separated, one- 36 HISTOLOGY. half being drawn toward the one centrosome, and the other toward the second. This gives rise to a second spindle, the NUCLEAR, or CHROMATIC SPINDLE. The Separation is affected by the traction exerted upon the daughter chromosomes hy the threads of the central spindle. Anaphase. This is the stage of complete separation of the chromosomes. The latter collect around their respective centrosome, and remain connected to the opposite set, for some time, by the central spindle threads. The figures thus formed are the diasters, or daughter stars. Fig. 6. — Scheme of the Daughter Stars. {8t6hr's Fig. 7. — fecuEME of Division of THE Protoplasm Forming Daughter Cells. Histology.) Telophase. This stage is concerned with the protoplas- mic changes and the formation of a resting nucleus. Up to this time, the protoplasm has been practically quiescent. The chromosomes collect around the centrosomes, and unite to form a close skein. Lateral twigs are developed that anastomose to form the nuclear network, a nuclear mem- brane is formed and a micleolus appears. The hitherto inert protoplasm shows changes. A double row of vaculoes appears at the equator of the cell, and separa- tion occurs in the intervening space until two separate masses are formed ; these are the daughter cells. MATURATION. 37 The above changes are usually succeeded by a period of rest. ^tc^ Although apparently a long process, only about one-half '■/•" hour is consumed in the division of human cells, but the cells . of lower animals require a longer period. yii^ivl In the case of giant cells, the nucleus divides and redivides, ^*^i while the protoplasm remains unchanged. They may also be formed by the fusion of the protoplasm of a number of cells with the retention of the individuality of the nuclei. As all cells are developed from preexisting elements, it is but natural that the original cell of the body, the Ovum, should be of greatest interest. It is the most characteristic cell of the body, and is secreted by the ovary. It is the largest cell, and illustrates the individual parts well. The Ovum consists of a limiting wall, the vitelline mem- brane, that is well developed. Within this, is the protoplasm, vitellus, which consists of two parts — the deutoplasm, or NUTRITIVE YOLK, and the animal protoplasm, or forma- tive YOLK. This is of importance, embryo logic ally. Within the vitellus is found the nucleus, or germinal vesicle, which contains a deeply stained nucleolus, or germinal spot. In what might be termed an embryologic ovnm, there are two layers external to the vitelline membrane, the zona pellu- ciDA and the corona radiata. Of these, the former is the more important, because of the part which it plays in the early stages of development. There are a number of processes that occur in the ovum before it can develop into an offspring. Of these, the most important are MATURATION and FERTILIZATION. The former occurs, usually, in the ovary, and the latter, as a rule, in the Fallopian tube. Maturation is the process by which part of the chromatin and a small portion of the protoplasm are ex- 38 HISTOLOGY. traded in the form of two minute structures called polar BODIES. It is a modified karyokinesis, and its object is un- known. All ova must pass through this process before they can be fertilized. Fertilization is the process in which the male and female elements unite to form a complete and perfect cell, which, by division, gives rise to the cells that ultimately form the whole body. Ovum from a Cow. Corona radiata ; 2. zona pellucida : 3. vitellus ; 4. germinal vesicle; 5. germinal spot (Stohr's Histology). The male element, or spermatozoon consists of head, MIDDLE-PIECE and TAIL. Of thcsc the HEAD and middle- piece, representing the nucleus and centrosome, respec- tively, of a cell of the testicle, enter the ovum and form eight chromosomes. The chromatin of the germinal vesicle of the ovum also forms eight. By longitudinal cleavage thirty- two are formed of which sixteen enter into each diaster and, consequently, each daughter cell. By this process the de- DERIVATIVES OF THE TRIPLOBLAST. 39 scendants of the fertilized ovum contain double the number of chromosomes that existed in either of the original cells before fertilization. After fertilization the ovum divides and redivides forming an irregular mass of cells called the Morula, or Mulberry Mass. Certain of these cells form a complete layer that sur- rounds the remainder, which constitutes an irregular mass. The layer is the Outer Cell-mass and the latter the Inner Cell-mass. This structure constitutes the Blastula, or one- layered vesicle. Of these two structures the inner is the more important as it persists and forms the whole body while the outer disappears. The Inner Cell-mass forms two layers, an outer, several cells in thickness, the Ectoderm, or Epiblast, and an inner, composed of but a single layer, the Entoderm, or Hypo- blast This is the Gastrula, or Diploblast. The ecto- derm and entoderm each set aside a number of cells which by multiplication form a third layer, the Mesoderm, or Me- SOBLAST, that lies between the two. This structure receives the name of Blastodermic Vesicle, or Triploblast. From these three primitive layers all the organs and tis- sues of the body are formed as follows : Ectoderm. The nervous system (cerebro-spinal and sympathetic) the retina, the bulk of the crystalline lens, the epithelium of the cornea and conjunctiva, the epithelium of the internal ear and of the olfactory organ. The epithelial lining of the anterior portion of the male urethra, the vestibule and labia of the female and the glands leading thereto. The epithelial lining of the mouth and salivary glands, the enamel of the teeth, the cells of the nasal tract, to the pharynx, and its glands and the lining of the anus. 40 HISTOLOGY. The epidermis and appendages of the skin. Entoderm. The epithehal lining of the bladder, of the first portion of the male and entire female urethra and the prostate. The epithelium of the tongue, thymus and thyroid bodies of the parathyroids, middle ear and Eustachian tube. The epithelium of the alimentary and respiratory tracts from the mouth and posterior nares down and the epithelium of all glands opening into these structures. Mesoderm. The vascular system. The lymphatic system including the large serous cavities, spleen and thymus body (except the corpuscle^ of Hassal). The muscular system (except the muscles of the sweat- glands). The connective tissues. Testicle, vas, seminal vesicles, ejactulatory duct, ovary, Fallopian tubes, uterus and vagina. Kidneys and ureters. CHAPTER III. THE TISSUES. From the preceding table it will be seen that all tissues are developed from the three layers of the triploblast. These tissues are grouped, histologicallyj under four classes, Epi- thelial, Connective, Muscular and Nervous. A Tissue consists of similarly differentiated cells held to- gether by intercellular cement, " and performing a definite function. The intercellular substance varies with the differ- ent tissues. The cells of a tissue may be so arranged as to form an organ or merely a supporting structure. EPITHELIUM. The Epithelial Tissues are characterized by the small amount of the intercellular cement. The cellular elements are usually prominent, and rich in granular protoplasm. They are found lining cavities that communicate normally with the air and usually secrete, although they may also have a protective function. The cells vary in size, form and arrangement, as will be seen later. For convenience of description, the cells are classified as ows: .i:f:^ I. Squamous. 4. Prickle cells. a. Simple. 5. Goblet cells. b. Stratified. 6. Trasitional cells. 2. Columnar. 7. Pigmented. c. Simple. Specialized. d. Stratified. 8. Neuro-epithelial. Modified. 9- Glandular. 3. Ciliated. e. Simple. f. Stratified. 41 42 THE TISSUES. I. Squamous, a. The simple squamous cells consist of a single layer of flattened elements, each containing a large nucleus. This is usually in the center, and has an oval, >] 9\ ®\ (&[ &\ Fig. 9. a. Simple squamous cells. ft. Simple cuboidal cells. or round form. They occur in the descending limb of Henle's loop, the capsule of Bowman in the kidney, the alveoli of the lungs, and in parts of the ventricles of the brain. b. The stratified squamous variety consists of many layers of cells that are unlike in form. The lowest layer, Fig. 10. — Surface View of Squam- ous Cells of Frog^s Skin. Fig. 11. — Squamous Cell Isolated. Fig. 12. — Stratified Squamous Epithelium. the germinal stratum, is columnar, while those cells just above are polygonal. The succeeding cells become more and more flattened, forming the squames, or scales, from which EPITHELIAL CELLS. 43 this variety receives its name. It is found covering the body as the epidermis, Hning the mouth, pharynx, esophagus, epi- glottis, vocal cords and the anus and vagina. 2. Columnar, c. Simple columnar cells are tall, cylindric elements arranged in a single layer. The nucleus is <2^ /^ o Fig. 13. a. Simple Columnar showing Cuticular Border, h. Simple Ciliated Cells, c. Simple Columnar and Goblet Cells. usually oval, and found nearer the base than the center of the cell. The variety is found in the stomach and intestinal tract, the penile portion of the urethra and in many gland ducts. Low columnars are often called cuboidal. PsEUDOSTRATiFiED cclls are simple columnar, or ciliated, cells, in which the nuclei are not all basal, but occupy differ- FiG. 14. a. Isolated Columnar Cells, h. Isolated Ciliated Cells, c. Three Stages of Goblet Cells. ent levels, thus giving the appearance of several layers of cells, where, in reality, but a single layer exists. d. Stratified columnar cells consist of a number of layers of columnar elements superimposed upon one another. 44 THE TISSUES. The cells are not as large as the preceding. They occur in the vas deferens, seminal vesicles, membranous urethra and the ducts of some glands. 3. Ciliated cells, e. Simple ciliated cells are simple columnar elements, which bear, upon their exposed surface, a varying number of hair-like processes called cilia. These possess a motion that is directed toward the outlet of the organ in which these cells are found. They line the oviducts, uterus, smaller bronchioles, spinal canal, accessory spaces of the nasal fossae and the ventricles of the brain. Fig. 15. — Pseudostratified Cells. f. The stratified ciliated cells are practically stratified columnar cells, of which the exposed layer alone possesses cilia. They are found in the epididymis, first part of the vas, middle ear. Eustachian tube, upper part of the pharynx, in the larynx, trachea and nasal tract. 4. Prickle cells are polygonal elements that possess little spines, which project from the sides of the cells. These, meeting the spines of other cells, prevent the cell-bodies from touching. In this way, a series of intercellular bridges and spaces is formed. These cells are found in the epidermis, just above the genetic layer. 5. Goblet cells are cells of the cylindric type, distended with a peculiar secretion called mucin. When filled, they re- semble a goblet, hence the name. When the secretion has been discharged, the cells are long and slender, the part con- taining the nucleus projecting on either side. Such cells are met with in the gastro-intestinal and respiratory tracts. EPITHELIAL CELLS. 45 6. Transitional cells are peculiar stratified elements that are neither columnar nor squamous. They occupy an inter- mediate position, as all the cells are polygonal. They occur in the pelvis of the kidney, in the ureter, bladder, the first Fig. 16. a. Stratified Columnar Ceils. &. Stratif.ed Ciliated Cells, c. Stratified Columnar Cells showing Goblet Cells. portion of the male and the greater portion of the female urethra. 7. Pigmented cells are polygonal or columnar cells, in which the protoplasm contains a varying number of pigment Fig. 17. — Transitional Cells. granules. The former shape is found in the epidermis of colored races, and around the nipple and genitals of Cau- casians ; the latter occurs in the retina of the eye, and the pig- ment granules obscure the various parts of the cell. 46 THE TISSUES. 8. Neuro-epithelial cells are epithelial cells that have be- come so differentiated as to perform a nervous function (special sense). They differ according to location, and will be described under each special sense. They occur in the retina (rods and cones), in the internal ear (hair and pillar- cells), in the olfactory mucous membrane and in the taste- buds. 9. Glandular cells also vary according to the nature of the gland in which they are found, as in the liver, pancreas, etc. Mucous membranes. The epithelial surfaces within the body are termicd Mucous membranes. Glands, which are evaginations of such surfaces, are also classed with mucous membranes. Such membranes are complexes of all four varieties of tissues. They are lined by epithelial cells, of any of the varieties above mentioned, that rest upon a deli- cate BASEMENT MEMBRANE, beneath which is found a layer of fibro-elastic tissue called the tunica propria. The struct- ure is limited, peripherally, by a layer of involuntary, non- striated muscle tissue, the muscularis mucosae. The latter is not always present, as will be seen when the various organs are studied in detail. These membranes line cavities that communicate normally zvith the air and usually secrele. As some writers classify Endothelial cells as epithelial, it is well to consider them at this time, so as to contrast them. Endothelial, or, better, Mesothelial, cells are thin, flat- tened elements possessing a large projecting nucleus. They are irregular in outline, and are held together by intercellu- lar cement. They never occur in more than a single layer, and form, with fibro-elastic supportive tissue, the subendo- thelial connective tissue, a Serous Membrane. A Serous Membrane possesses neither basement membrane nor mus- MUCOUS AND SEROUS MEMBRANES. 47 cularis mucosae, and lines cavities that do not communicate normally with the air and never secretes. Such membranes are smooth, moist, glistening and transparent, and subject to inflammations different from those of the foregoing. Openings called stomata are said to exist, but these are now considered artifacts. B & D Fig. 18. -Abdominal Endothelium, a. Endothelial cell : h. nucleus of cell ; c. cell boundary ; d. stigmata ; e. endothelial cells of stomata ; f. sto- mata. B. — Mesenteric Endothelium. C. — Arterial Endothelium. D. — Perivascular Lymphatics, a. Endothelial cells of lymphatics ; h. bloodvessel (arteriole). Serous membranes are found lining joint-cavities, the cir- culatory and lymphatic systems and the larger serous cavi- ties, the pleural, peritoneal and pericardial. 48 THE TISSUES. CHARACTERISTICS. MUCOUS MEMBRANES. SEROUS MEMBRANES. Where found Lining cavities that In cavities that do not communicate normal- normally communi- ly with the air. cate with the air (fe- male peritoneal cav- ity excepted). Lined by Epithelial cells of any Endothelial ( M e s o- variety. thelial) Cells, one layer. Secrete. . . . With few exceptions. Epithelial cells, base- Do not Structure Endothelial cells, sub- ment membrane, tu- endothelial connec- nica propria, muscu- tive tissue. laris mucosae. Represents All four varieties of But three varieties (no tissue. muscular tissue). A description of epithelial tissues would not be complete without a consideration of Glands. A Gland is an evagina- tion of a mucous surface, consists of epithelial cells, ar- ranged in definite groups, and performs a physiologic func- tion. These groups are the secretory units of the organ. As these units are of different shapes, a classification of glands is necessary, to understand and separate them. Tubular Glands. Simple. Branched. Coiled. Compound. Tubulo-Alveolar Glands. Alveolar, or Racemose Glands. Simple. Compound. GLANDS. 49 Tubular. Simple tubular glands are mere cylindric depressions in the mucous membrane. They are Hned, usual- FiG. 19. — Gland of Lieberkuehn from a Section of the Large Intestine. a. Lumen ; h. secretion of cells ; c. nucleus and protoplasm of cell ; d. fun- dus cells at the beginning of secretion ; e, f. goblet cells in later stages; g, dying goblet cells {Stdhr's Histology). ly, by simple columnar cells. They occur in the cardiac end of the stomach, and in the small and large intestines. 50 THE TISSUES. The branched tubular are like the above, except that the lower end is divided into two or more secretory units. The lining cells may be columnar, or ciliated, as in the uterus. These glands are found in the fundus and pyloric portion of the stomach, in the duodenum (Brunner's glands), in the uterus, and in the prostate. Coiled tubular glands are really simple tubes, the secre- tory portion of which has become coiled and convoluted to occupy as small a space as possible. The lining cells are columnar or cuboidal (low columnar.) Examples are the sweat and ceruminous glands. Compound tubular glands are those in which the primi- tive tubules have divided and redivided until an enormous number of divisions has resulted. Pure examples of this variety are the liver (also called reticular), testicle, kidney, thyroid, lacrimal and serous glands of the mucous mem- branes. Tubulo-alveolar glands are those in which the terminal tubules possess sac-like evaginations along the walls. Such glands are the submaxillary, sublingual, prostate, Brunner's, mammary and the lungs. Alveolar. The simple alveolar, or saccular, glands are sac-like depressions extending from the free surface. They are comparatively few in number, and occur as the smallest sebaceous glands. The COMPOUND RACEMOSE glauds are like the compound tubular, except that the terminal portions are saccular, in- stead of tubular. Such glands are the pancreas, parotid, and the large sebaceous glands. As a rule, all glands, at some period in their development, are connected with the mucous surface by a tube called a duct. This connection, in most instances, persists, but where it disappears, the gland becomes isolated, and the term duct- GLANDS St less gland is applied. Such are the adrenals, pituitary and thyroid bodies, parathyroid, carotid and coccygeal glands, the ovary and the areas of Langerhans in the pancreas. These form an internal secretion that is absorbed by the circulatory or lymphatic system. Fig. 20.- Diagrams op Tubular Glands (Stohr's Histology). A. Simple tubular ; B. branched tubular : a. excretory duct ; C. compound tubular. Fig. 21. — Alveolo-Tubular Glands (Stohr's Histology). 1. Branched alveolo-tubular ; 2. compound alveolo-tubular ; a. excretory duct. The function of a gland is to give rise to a substance to be used by the body in some of its many processes. This sub- stance is called a secretion, and it may be liquid or cellular. (ovum). The liquid secretions may be serous, mucous, or mixed. These terms apply to the respective glands as well. Serous glands are those which form a thin albuminous 52 THE TISSUES. secretion. The glandular cells respond well to stains. The parotid and pancreas belong to this class. Mucous glands are those that give rise to a thick viscid substance. The cells here stain but lightly with the ordinary stains. Such are the small glands found in the mouth, esophagus, trachea and the sublingual, according to some writers. ihhh "^''W^ Fig. 22. — Alveolar Glands (Stohr's Histology). 1. Alveolar system ; 2. alveolar compound gland ; a. excretory duct. Mixed glands are those in which both varieties of secre- tion are formed. The secretory areas are stained darkly or lightly, according to whether they are serous or mucous. The sublingual and submaxillary glands are examples, and of these, the latter is the more characteristic. The minute structure of glands will be considered under the Alimentary Tract. The excretory glands are the kidneys, lungs and sweat glands. Each will be considered in detail, under its re- spective system. CHAPTER IV. CONNECTIVE TISSUES, The Connective Tissues are the supportive tissues of the body. They are characterized by the predominance of the inter celhdar substance over the cellular elements. This intercellular substance varies in the different forms, as will be seen when each is considered. For the convenience of description, this class has been subdivided into the following varieties : Fibrous. Modified. I. White. 6. Adipose. a. Loose. 7. Adenoid. h. Dense. 8. Cartilage. 2. Yellow elastic. 9- Bone. 3. Mucous. 10. Dentin. 4- Retiform. II. Blood. 5. Mixed. The Fibrous varieties are characterized by the fibrous or semi-solid intercellular substance. The cellular elements are comparatively feziu, and are found scattered among the fibrils. There are several varieties of cells found in con- nective tissues. These are the true, or fixed, the wandering and the plasma cells. The true, or fixed, connective tis- sue cell is a flattened, stellate element with many processes that extend in all directions, and anastomose with those of other cells. Within the network thus formed lies the inter^ cellular substance. In young tissue, the cells are not all of the above form. Some are round, others are spindle-shaped ; these gradually become converted into the stellate variety. The WANDERING Cell passes into the tissue from the blood- 53 Fig. 23. -Mucous Connective Tissue, a. Spindle cells ; h. stellate cell ; c. inter- cellular substance. B. — Cross Section of Tendon, a. Epitendineum ; h. peritendineum ; c. tendon fasciculi : d. interfascicular space. C. — Part of B, highly magnified, a. Epitendineum; b. cell in a; c. peri- tendineum ; d. tendon fasciculus ; e. interfascicular space. D. — Ten- don Cells from Interfascicular Spaces. E, — Elastic Tissue Cross- section of Ligamentum Nuchae. a. Elastic fibres ; b. white fibrous supportive tissue. F. — E highly magnified, a. Elastic fibres ; b. white fibrous supportive tissue. G. — Areolar Tissue, a. White fibre bundles : b. elastic fibres ; c. spindle cell ; d. granule cell ; e. plasma cell ; f. stellate cell. H. — Adipose Tissue, a. Interlobular connective tissue : b. fat cells ; c. nucleus and protoplasm of the cell. I. — H highly magnified, a. Fat cell ; b. protoplasm and nucleus of cell. K. — Lymphoid Tissue, a. Leukocytes ; b. stellate connective tissue cells ; c. reticulum. L. — Pigmented Connective Tissue Cell trom a Pike. WHITE FIBROUS TISSUE 55 vessels. It may return, or remain and become a fixed, or true connective tissue cell. Plasma cells are large granular fixed elements, especially noticeable in areolar tissue. They are at first oval or ob- long, and later change to the stellate type. The INTERCELLULAR substaucc is soft, and, in most varie- ties, fibrous. These fibrils react characteristically to certain stains, as will be pointed out later. They vary in thickness, and are arranged in bundles which may be parallel, or may interlace. These bundles lie in a more or less homogenous ground substance that varies in quantity in the different varieties. The origin of the intercellular substance is still in dispute. Two theories are advanced. According to some writers, it is of intracellular origin, while others claim it to be inter- cellular in derivation; in other words, it is formed in the homogeneous, semi-solid intercellular or ground substance, which exists before the fibrils appear. The real origin is probably by a combination of these two processes. It seems that the intercellular substance is formed from the peripheral protoplasm of the cell, which becomes fibrillar in character. This small amount of differentiated protoplasm is then sup- posed to increase itself, and so give rise to the remainder of the fibrils. The origin of the elastic fibres is not so plain, both of the above views being held in regard to them. In elastic carti- lage, they are of intercellular origin, but still the intracellular formation must not be lost sight of. I. White fibrous tissue consists of fine or coarse bundles of inelastic fibrils, either parallel or forming a deli- cate meshwork. Its two subdivisions are, a, loose, and b, dense. a. Loose fibrous connective tissue is a minute network 56 CONNECTIVE TISSUES. of small bundles of fibrils formed for the support of capillary blood-vessels. The cellular elements are of the types named above, and are few in number. Upon boiling, it yields gela- tin, and is digested by pancreatin. Fig. 24. — Intermuscular Connective Tissue Bundles op Man. a. Fat drop ; 6. fat cells ; c. bundles of white fibres ; d. nucleus of a cell ; e. elastic fibres {Stdhr's Histology). It forms the capsules of organs, and is found as the tunica propria and submucosa of the alimentary and respiratory tracts. b. In the dense variety, the fibrils are coarser, and ar- ranged in larger bundles, which are usually parallel. Tendons are dense white fibrous tissue, in which all the fibril bundles have a parallel course. The whole structure is surrounded by a sheath of looser tissue, called the epiten- dineum, from the inner surface of which septa are sent in that divide the tendon fibres into large secondary bundles. ELASTIC AND MUCOUS TISSUES. 57 These latter are further subdivided into primary bundles, each of which is surrounded by a minute sheath, the peri- tendineum. Between the individual bundles, lie the peculiar tendon cells. These are flattened, rectangular elements ar- ranged end to end upon the tendon bundles. The nuclei are peculiarly arranged. In two adjoining cells they will be seen near the line of junction, but in the cells on either side of these, they are separated by nearly the length of the two cells. In FASCiA^, the bundles are large, dense, and closely packed. 2. Elastic tissue, as its name indicates, has the peculiar property of elasticity. The fibres are yellow in color, refractile, and coarser than those of the white variety. In areolar tissue, they are branched, while in other places bands and even membranes are formed (arteries). When separated and ruptured, the torn ends curl. This occurs in no other tissue. This variety occurs in the ligamentum nuchae, where the fibres are very heavy, and are surrounded by white inelastic fibres, in the ligamentum su'bflava, in blood-vessels, and in the true skin. Elastic tissue is digested by pancreatin, and, upon boiling, yields elastin. 3. Mucous, or Embryonic, connective tissue is that variety in which the intercellular substance is semi-fluid. The cellular elements are mostly of the spindle-shaped variety, although numerous stellate cells are present. Round cells are also frequently seen. The intercellular substance is semi-solid in the youngest tissue, and takes a peculiar homogeneous stain. As the tissue becomes older fibrils begin to develop, and of these, the white are formed into bundles, while the elastic are usually individual. S8 CONNECTIVE TISSUES. Mucous connective tissue is found in the umbilical cord, in embryos and in the vitreous humor of the eye. 4. Retiform connective tissues, or reticulum is the supportive tissue of glands and gland-like organs. It con- sists of delicate bundles of fibrils forming a network, in the meshes of which are found the functionating cells of the organ. The cells are chiefly stellate in form, and their pro- cesses anastomose around the fibril bundles. This tissue is more resistant to those reagents that dissolve the white variety (hydrochloric acid and potassium hydrate) and yields neither elastin nor gelatin upon boiling, nor is it digested by pancreatin. 5. MiXED_, or AREOLAR Connective tissue is a combination of the white and elastic varieties. The white tissue is present in the form of delicate bundles, and these form a loose network with the elastic fibres, which are usually thin and branched. The stellate and wandering cells are well represented, but the plasma cells are more numerous than in any other variety of tissue. This variety is found binding the skin to the fascia be- neath and between muscles. Modified. In these varieties of connective tissue, the intercellular substance varies from liquid (blood) to the hard, unyielding material found in bone and dentin. The cellular elements also differ, as will be seen when each variety is discussed. 6. Adipose tissue, or fat, is white fibrous tissue, in whirh the cells have become repositories for fat globules. These cells are quite numerous, but the stellate shape is lost. The minute globules unite to form a single large drop that distends the delicate cell-membrane. By this coalescence, the protoplasm and nucleus of the cell are forced to one side, and are seen as a thin hand, or crescent. The nucleus may contain vacuoles. LYMPHOID TISSUE. 59 Fat cells are spherical, when not closely packed, as the fat is liquid at the body temperature. After death, margarin crystals are seen in the protoplasm. The cells are collected into groups called lobules, and these form larger masses called lobes. Blood-vessels, nerve and lymphatics are present in considerable number. The first named are especialh numerous, as there is a close relation between fat deposition and the vascularity of the part. According to some writers, fat cells are specialized con- nective cells that exist in no other form. This seems doubt- ful, however, as experiments have shown that when animals are starved, the spherical, fat-containing cells return to the stellate form as the fat is removed. From this, it would seem that these cells act merely as storage cells. When adipose tissue is studied, after ordinary preparation, merely a network of fibres and cell boundaries is seen. This is due to the fact that the fat has been removed by the alco- hol leaving the insoluble white fibrous supportive tissue. In such sections, the nucleated crescents of protoplasm are read- ily observable. In sections of osmicated fat, the peripheral cells are circular in outline, while the deeper ones are irregu- lar and black, due to the action of the osmic acid, which is a characteristic reagent for fat. Sitdan III, also used as a test for fat, stains the globules dark red. Adipose tissue is found widely distributed over the body, except in the penis, scrotum, ear and eyelid. From the orbit and around the kidneys it never entirely disappears, though death be due to starvation. 7. Adenoid, or lymphoid tissue is a special form of the connective variety consisting of a network of reticulum, in the meshes of which are found lymphocytes, or zvhite blood cells. These cells are usually the small lymphocytes, although 6o CONNECTIVE TISSUES. varying numbers of the large lymphocytes (hyalin cells) and poly nuclear cells are to be seen. For a description of these cells, see blood (p. 95). For readiness of comprehension, lymphoid tissue is di- vided into four varieties: a. diffuse; b. solitary follicle; c. peyer's patch, or agminated follicle; and d. lymph node, or GLAND. a. Diffuse adenoid tissue is an indefinite collection of leukocytes in an organ. The cells are not especially arranged, neither is there a special supportive tissue present, as in the last two varieties. It is found in the tunica propria of the alimentary and respiratory tracts, and the cells are merely scattered be- tween the bundles of white fibrous tissue. It forms the medulla of the thymus body, and the bulk of the tonsil and spleen, and is transient in character. b. Solitary follicles are small, dense collections of leukocytes in white fibrous tissue, as above. There is no special supportive tissue present; although the outline may be slightly irregular, it is sharp. Each follicle usually shows a lighter center in which the cells are fewer and younger. This is called the germinal center, and here the new cells are formed by karyokinetic division. Solitary follicles are found in the alimentary and respira- tory tracts, the spleen and tonsil. They, like the diffuse variety, are transient structures. (See Fig. 42, page 103.) c. A PEYER^s PATCH is a morc or less regular collection of solitary follicles sharply outlined from the surrounding tissue. Each patch consists of ten to sixty solitary follicles, each of which usually shows a germinal center. (See Fig. 52, p. I2S). Peyer's patches are found in the ileum. d. Lymph nodes (Lymph Glands) are small, bean- shaped bodies interposed in the pathways of the lymphatic CARTILAGE 6l vessels. As they are closely related to the Lymphatic System, their structure will be there considered. 8. The CARTILAGES are characterized by a solid intercellu- lar substance. The cellular elements also differ from those previously described. Three varieties are found in man: the hyalin, white FiBRO and YELLOW elastic. The general structure will first be considered, under peri- chondrhim, cells and intercellular substance. The perichondrium is a fibrous sheath that surrounds cartilage and gives rise to its cellular elements. It is composed of white fibrous tissue, and is divided, functionally, into two parts. This division is not apparent under the microscope, as the layers fade into each other. The outer part is the fibrous layer, and contains few cells. The inner portion, or chondro genetic layer, is rich in cells that are not of the stellate type, but flattened and elongated, or spindle-shaped. These are the chondroblasts, which be- come cartilage cells. Blood-vessels also are present. The cartilage cells, or chrondroblasts, vary in the different portions of the cartilage. Just beneath the perichondrium, they are flat and thin, indicating an early stage. Toward the center, they gradually become broader until, finally, they are oval or round in form. Each cell is rich in protoplasm, which contains one or more vacuoles. The nucleus is usual- ly prominent. The cell is sharply outlined from the sur- rounding substance by a thick wall, the capsule. This is a product of secretion of the cell, and it is cast off, as a rule, every time the cell divides. Each cell may be individual, or several may be seen within one capsule, which is due to the fact that the new cells did not form capsules for themselves. This is seen especially in ossification of cartilage. Between the cell and the capsule is usually a space called the lacuna. 62 CONNECTIVE TISSUES. The intercellular substance varies. In the hyalin variety, it is apparently homogeneous ; in zirJiite iihro, it is composed mainly of white fibrous tissue, while in the yellow Hhro it consists of yellow elastic fibres. Hyalin cartilage is a peculiar bluish or pearly tissue, which is elastic, and readily cut with a knife. The cellular elements are as above. They are quite numer- ous, and close just beneath the perichondrium. Further down, a number are usually found within one lacuna and capsule. The intercellular substance or matrix, is apparently homo- geneous. Upon very careful study, and treatment with spe- cial reagents, it shows a fibrillar character, in the meshes of which is seen the ground substance, which is homogeneous. This ground substance is formed by a fusion of the castoff capsules, and responds very well to hematoxylin, showing a peculiar bluish color. This variety of cartilage is found covering articular sur- faces, lining joint-cavities, as the costal, tracheal and most of the laryngeal cartilages. It precedes, with a few excep- tions, all the bones of the body, and may ossify in old age. White fibro cartilage consists of islands of the hyaiir. variety, separated by an intercellular substance made up of delicate bundles of white Hbrous tissue. This form may ossify or calcify in old age. It is not very abundant, and is found deepening joint- cavities, as inter-articular fibro-cartilages, and as the inter- vertebral discs. Yellow fibro, or elastic cartilage is that variety in which the intercellular substance is composed of elastic fibres. It is practically /lya/m cartilage in which the hyalin matrix has been replaced by elastic tissue. The cartilage cells are CARTILAGE 63 found in small groups, surrounded by only a small amount of the hyalin substance. This variety never ossifies or calci- fies, and is to be looked for in regions where elasticity is re- quired, as in the epiglottis, ear. Eustachian tube and small laryngeal cartilages. ' * m •'■* I r A i3 C Fig. 25.- Sections of Cartilage. — Hyalin Cartilage, a. P^ibrous layer of perichondrium ; h. genetic layer of pericliondrium ; c. youngest chondroblasts ; d. older chon- droblasts ; e. capsule ; f. cells ; g. lacuna. B. — Elastic Cartilage. C. — White Fibro-cartilage. Cartilage contains no bloodvessels, except in the perichon- drium, and during the developing stage. Lymph channels are said to be absent, so that its nutrition is not of a very high order. 9. Bone is the most highly differentiated of the connect- ive tissues. It is characterized by the presence of a very 64 CONNECTIVE TISSUES. hard, unyielding intercellular substance *that has a character- istic arrangement. Bones, like cartilage, are surrounded by a fibrous sheath, the periosteum, beneath which is the hone substance proper ; the latter consists of cells and intercellular substance. The periosteum is composed of two layers — outer, or fibrous, and inner, or genetic. The outer layer consists of white fibrous tissue, support- ing a large number of bloodvessels, and containing but few cells. The inner, or genetic, layer is rich in cells and capil- laries. These cells are the future osteoblasts that secrete the osseous tissue. From its inner surface, it sends in bundles of fibres that pierce the layers of bone at right angles, and bind them together. These are Sharpey's fibres. The cells are all of the irregular stellate type, and consist of flattened bodies and short processes that extend into small canals, to be described later. The protoplasm is not very abundant, and the nuclei are oval, and often vesicular. The intercellular substance is hard and resistant. It con- sists of osseous material that is secreted by the cells, and is peculiarly arranged in the compact variety. It contains spaces, or lacunae, from which extend minute canals, or canaliculi. Beside these, there are a great number of canals that vary in length and diameter. These are the Haversian carnals. Bone is comiposed of inorganic and organic salts; the former are soluble in mineral acids, by which they may be removed and the tissue cut. The latter are removed by burning , after which process the inorganic substance re- mains as a porous mold of the bone. There are two varieties — cancellous, or spongy, and COMPACT, or solid. Cancellous bone consists of spicules forming a network BONE. 65 resembling a sponge. These spicules have a fibrillar struct- ure, and contain little spaces, called lacunae. In the living condition, these lacunae are occupied by bone-making cells, termed osteoblasts. This variety is found around the medullary cavity and in the heads of the long bones, and forming the central portion of the flat bones. The meshes of the network are filled with marrow. Fjg. 26. — Cross-section of Human Compact Bone. a. Periosteum ; Jj. peripheral lamellae : c. Ilaversian canals ; d. lacunae ; 6. interstitial lamellae ; f. perimedullary lamellae ; g. marrow ; h. Haversian lamellae {Stohr's Histologi/). Compact bone has a characteristic structure. The osse- ous matter is arranged in layers, or lamellae, between which lie the lacunae. There are four varieties of lamellae : a. Peri- osteal, peripheral, or circumferential; b. Haversian, or con- centric-; c. Intermediate, ground, or irregular ; and d. Peri medullary, or Internal. a. The peripheral, periosteal, or external lamellae arc those formed directly from the periosteum. They are few in number, and several are required to complete the circum- ference. Between them are a number of irregular spaces, 66 CONNECTIVE TISSUES. lacunae, from which Httle canals extend, the canaliculi. The external layer has a number of small depressions called Howship's foveae, or lacunae. These are occupied by large bone destroying cells called osteoclasts. Haversian canals are not present, but larger canals, containing blood-vessels from the periosteum, are seen. These are Volkmanns canals. b. The Haversian lamellae, which are probably the most numerous, are thin layers circularly arranged around a small central canal called the Haversian canal. These layers are separated by the lacunae, and pierced by the canaliculi. The lamellae of a system are parallel to one another, but the different systems usually run at various angles. An Haversian system consists of the lamellae, canal, lacunae and canaliculi. The canals are occupied by blood-vessels, nerves and lymphatics. Those nearest the marrow cavity contain mar- row. The canals are generally parallel to the long axis of the bone, and anastomose freely with one another. c. The intermediate, interstitial, or irregular lamellae lie between the Haversian systems, and are irregular in size and form. They are the remains of Haversian and periosteal lamellae, altered by the growth of the bone in diameter. No canals are found here, but lacunae and canaliculi are present between the lamellae. d. The perimedullary, or internal lamellae are not very regular, and are found surrounding the medullary, or mar- row cavity. The lacunae are small, irregular spaces found between the various lamellae throughout the bone, and occupy a portion of each of the adjacent lamellae, and do not lie in one alone. These spaces are said to be lined by a delicate membrane. They contain the osteoblasts. BONE-MARROW. 67 Extending in all directions, are small canals, or canaliculi. that communicate with those of other lacunae, so that a series of intercommunicating spaces results. Those lacunae lying nearest the Haversian canals, communicate with them, but the peripheral ones of a system do not communicate, to any great extent, with those of the interstitial lacunae. The canaliculi serve as supports for the processes of the osteo- blasts. The MEDULLARY CAVITY, which Contains the nutrient mar- row, is a large space, in the shafts of the long bones. The MARROW is of two varieties, red and yellow. The red is found in young persons, while the yellow occurs in those above the prime of life. The difference is due to the pres- ence of a great deal of fat in the yellow, whereby the color becomes changed. Marrow consists of a delicate network of reticulum, sup- porting a close capillary plexus and a number of different cells. These cells are : myelocytes, or marrow cells ; nu- cleated RED BLOOD CELLS, Or ERYTHROBLASTS, WHITE BLOOD CELLS, or LEUKOCYTES, and MYELOPLAXES. Myelocytes are large nucleated masses of granular proto- plasm. The nucleus is usually round, and the granules fine. The latter usually react to the acid stain. These cells may show ameboid movements, and are found in the blood in certain diseases. Erythroblasts, or nucleated red cells. These cells differ from the ordinary red cells in possessing a nucleus, and may show mitotic figures. They vary somewhat in size, but are seldom over 9.5 microns in diameter. By a loss of the nucleus, these cells become the erythrocytes^ or normal red cells. The LEUKOCYTES are usually the Unely and coarsely granu- lar eosinophils, and the basophils. H The I 68 CONNECTIVE TISSUES. Myeloplaxes, or osteoclasts, are very large, irregular cells. The protoplasm is abundant, and a number of nuclei may be seen. These cells are of great importance in bone destruction, from which the term osteoclast is derived. They may be capable of ameboid movements. Bones are nourished by blood-vessels that enter through the nutrient foramen and pass to the marrov^ cavity. From here, branches are sent to the various parts by way of the Haversian canals. Other vessels, derived from the perios- teum, lie in Volkmann's canals, which are found in the cir- cumferential lamellae. Nerves and lymphatics accompany the blood-vessels. Development of Bone. — Bone is not a primary, but a secondary tissue. It is preceded by cartilage or by fibrous tissue. Bone developed from hyalin cartilage is called en- dochondral, while that developed in fibrous tissue is re- ferred to as INTRA-MEMBRANOUS boUC. Endochondral bone formation is the process by which the hyalin cartilage is converted into spongy bone. It is, in reality, a combined process, for so soon as the spongy bone is formed, this is changed to the compact variety by the intra-membranous, or periosteal method. When ossification begins, the cartilage cells in that vi- cinity begin to multiply rapidly, and arrange themselves in rows parallel with the long axis of the bone. Multiplication is most rapid in the center of the area, and, as a result, the new cells are unable to form new capsules for themselves ; in consquence, a large number are seen in one space called a primary areola, or marrozv space. In the cartilage between these spaces, calcareous matter is deposited, and the cells above and below arrange themselves into parallel rows. The cells within the areolae either disappear, become osteoblasts, or osteoclasts; the latter dissolve the cartilaginous and cal- BONE DEVELOPMENT. 69 careous partitions between the spaces. As a result of the latter, larger spaces are formed, and these are the secondary areolae. Those cells that become osteoblasts, lay down a thin layer of osseous tissue upon the remaining par- titions, so that, at first, these consist of a core of calcific ma- terial covered by a thin veneer of true bone. As the process continues, the calcareous matter is entirely removed, and is replaced by bone. While these changes have been in progress, the perichon- drium has become the periosteum, which now forms osteo- blasts. These, with trabeculae of the periosteum and blood- vessels, pass inward toward the center of ossification, and enter the areolae. This vascularization forms the first mar- row. The blood-vessels pass uprward and downward from the center, following the process of calcification. Gradu- ally, the delicate rod of cartilage is converted into a rod of spongy bone. The articular portions are separated from the shaft by an interposed disc, the epiphyseal cartilage. Periosteal bone formation now begins. The inner surface of the periosteum becomes converted into a thin layer of osseous tissue, and the osteoblasts remain surrounded by a small space that is continued along its processes. This space and its continuations are the lacunae and canaliculi. As the inner surface is changed to bone, the outer surface has a corresponding amount added to it, so that the thickness of the periosteum is proportionately the same. With the formation of periosteal bone, the various lamellae are formed. The peripheral are merely the converted perios- teum. The Haversian systems and lamellae are formed in the following manner. From the inner surface of the peri- osteal layer, projections are formed at various angles. These meet other projections, thereby enclosing a small space, the primitive Haversian canal. Osteoclasts gain access and make 70 CONNECTIVE TISSUES. this Space regular and larger. Then osteoblasts lay down layer upon layer of osseous matter until only a small channel, Fig. 27. — Cross-section of a Developing Bone of a Human Fetus of Four Months. o. Periosteum ; h. boundary between endochondral and periosteal bone ; c. perichondral bone ; d. remains of area of calcification ; e. endo- chondral bone; f, f. blood-vessel; g, g'. developing Haversian spaces; h. marrow; i. blood-vessel (Stohr's Histology). the Haversian canal, is left. The remains of the peripheral lamellae between the various systems go to make up the interstitial lamellae. BONE DEVELOPMENT 71 With the formation of the peripheral lamellae, the net- work of spongy bone is removed from the center by osteo- clasis. This leads to the formation of a marrow cavity. As the bone increases in size, the cavity increases in proportion, by the destruction of the surrounding bone. During the prime of life, hone formation exceeds cavity formation, but in old age, the reverse is the case, sc that the shaft becomes thinner, and the cavity larger. The bone increases in diameter by the continued addition of peripheral lamellae, as a tree grows in thickness. It grozvs in length by the interposition of a disc of cartilage between the shaft and head of the bone. In this disc, new cartilage is formed as rapidly as ossification occurs. This is the cam- bium layer, and should it ossify, that end of the bone would no longer increase in length. This change occurs normally when full height is reached. This method of bone formation occurs in all bones except those of the face and of the vault of the cranium. Intra-membranous bone formation is the process whereby white fibrous tissue becomes converted into bone. Two peri- osteal layers are present, and between these, the bone is formed. Upon the fibrous bundles connecting them, osteo- blasts deposit osseous material until all are converted at the same time the formation of Haversian systems occurs. Such bones increase, in thickness, as above, and laterally, by the maintenance of a layer of fibrous tissue at its edges. This is the cambium layer, and when full growth is attained, this layer ossifies, and union occurs between the various bones. ID. Dentin will be considered under the teeth. II. Blood is the only liquid connective tissue. As it is part of the circulatory system, it will be considered when that is described. CHAPTER V. MUSCULAR TISSUES. Muscular tissues are those which produce the various movements of the body, whether voluntary or involuntary. Like epithelial tissues, they consist chiefly of cellular ele- ments, the intercellular substance being small in amount. The varieties are voluntary striated, involuntary non- striated and involuntary striated. Voluntary striated muscles are characterized by being under the control of the will. Each MUSCLE consists of a large number of tmits called fibres, bound together by white fibrous tissue. Each fibre, or cell, is a narrow cylinder. It varies from one to ^\t inches in length, and exhibits cross and longitudi- nal striations. It is composed of a large number of fibrillae, which are surrounded by a membrane called the sarcolemma, and separated from one another by sarcoplasm. Many peri- pherally located nuclei are present. The fibrillae consist of sarcous elements which stain darkly and are doubly refractile, or anisotropic. The sarcoplasm is a palely staining, semi-solid substance that lies between the fibrillae, and is singly refractile, or isotropic. The longitudinal striations are formed by the alteration of the fibrillae and the sarcoplasm, and are usually not as dis- tinct as the cross, though at times the reverse is the case. The cross striations .are due to the alternation of light and dark discs, or bands. The dark bands, or Brueckers lines, are composed of rows of parallel sarcous elements, separ- ated by the sarcoplasm. These sarcous elements are cylin- drical, except at the ends, where they are cone-shaped. The ends form part of the light disc. Each dim band is divided transversely by a less refractile line, called Hensen's disc. 72 VOLUNTARY MUSCLE. 73 The light discs are subdivided into three portions, an intcrmediaie and tzi^o lateral. The intermediate disc con- sists of a single row of small globules, interposed between the apices of the cones. These are Dobie's globules, or the membrane of Kranse. The lateral discs are merely the cone- shaped continuations of the sarcous elements. They are- a little dimmer than the intermediate disc. It will be seen from the figure that the main portion of this light disc consists of the refractile sarcoplasm. The nuclei are numerous, and are found beneath the sar- colemma, but external to the muscle substance. They are long and rather narrow, but respond well to the stain. The SARCOLEMMA is a delicate fibrous sheath that lies close to the fibre. It is not seen, as a rule, except by special preparation. If a fresh muscle fibre be treated with water, the muscle substance ruptures, and the delicate membrane is shown spanning the interval. Upon cross-section, the fibres show a sharp outline, and the peripheral nuclei are readily distinguished. Upon care- ful observation, the fibrillae are seen collected into groupS; constituting Cohnheim's fields. Contractility is an inherent quality of the sarcous ele- ments, but the sarcoplasm does not possess it. Occasionally, among the tongue muscles are found some fibres that branch. Such fibres are numerous in the tongue of the frog. Muscles.— Fibres are collected into definite groups called Muscles. Each muscle is surrounded by a sheath of white fibrous tissue called the epimysium. From its inner surface, septa are sent in that divide the muscle into a number of large secondary bundles. These secondary bundles are further subdivided into primary bundles^ or fascicvdi, which are invested by a sheath, the perimysium. This sends in fibres that pass between the individual fibres, and these rep- 74 MUSCULAR TISSUES. ^Si^^' ,'«■ -\ ">'v ^7 ♦ a— r '^fp ■■-A ^^■^^ Fig. 28. A. — Longitudinal section of smootli muscle fibres — a. muscle fibre ; 6. nu- cleus ; c. fibrous tissue between fibres. B. — Cross-section of smooth muscle fibres — a. perimysial connective tissue ; h. blood-vessel ; c. nu- cleated fibre ; d. nonnucleated fibre. C. — Longitudinal section of vol- untary muscle fibres. — a. sarcolemma ; b. nucleus ; b Fig. 36. — Portion of a Cross-section of a Human Vein. A. Intima ; B. Media ; C. Adventitia — a. internal elastic lamina ; &. smooth muscle fibres ; c. white fibrous connective tissue ; d. smooth muscle fibres in the adventitia {^tohr's Histology). present, it is not prominent. At intervals, this coat is thrown into folds called valves. These are duplications of the intima, and are usually arranged in pairs. At the place in which they are located, the vessels are usually slightly dilated. Valves occur only in the veins of the lower e;c- tremities. The MEDIA contains a very small amount of muscle tissue, but is reinforced by fibro-elastic tissue. In some veins, the 94 CIRCULATORY SYSTEM. muscle tissue is entirely wanting (brain and bones), while in oth-ers, longitudinal fibres are present in this coat. The lack of muscle tissue accounts for the collapsibxlity of these vessels. The ADVENTiTiA is the most prominent coat, and may pos- sess longitudinal muscle fibres. It is similar, in structure, to the arteries. .Blood-vessels are nourished by vessels that pierce the ad- ventiti-a and send branches to the media, the vasa vasorum. The intima is nourished by the blood that flows over it. The NERVES are chiefly sympathetic, and are distributed to the media and adventitia. They are the nervi vasorum. Vessels are often the centers of extensive lymphatic chan- nels that lie in the adventitia. The Blood is the only liquid connective tissue. It is com- posed of CELLULAR ELEMENTS, the CORPUSCLES, and the INTERCELLULAR SUBSTANCE, the LIQUOR SANGUINIS. The CELLULAR ELEMENTS are of three varieties, the red CELLS, WHITE CELLS and PLATELETS. *The RED CELLS, or ERYTHROCYTES, are nonnucleated, bj- .;* > concave discs averaging 7.5 to 8.5 microns in diameter. ^^ Under the microscope, they are pale straw colored or green- ish. Each cell consists of a framework, the stroma, that con- tains the hemoglobin. The latter carries the oxygen. Some cells average from 5.5 to 7.5 microns, and are called microcytes, while those over 8.5 microns are macrocytes. In normal blood, the cells tend to form rolls, or rouleaux. Under the same condition, 5,000,000 corpuscles are found, per cubic mm., in the male, and about 4,500,000 in the female. ♦According to Lewis of Harvard, the normal red cells are hell-shaped and the biconcavity is due to collapse that occurs upon exposure to the air. Rouleaux are readily formed by these cells fitting into one another. RED BLOOD CELLS. 95 Nucleated red cells, or erythroblasts, are found in the fetus, in bone-marrow and the spleen. The cell of average size is called a normoblast, the smaller, a microhlast, and the larger, a macrohlast. In Ushes, repiiles, birds and amphib- ians, the red cells are nucleated. In all mammals, they are circular, except in the camel family, in which they are oval. In the frog, the red cells are very large, oval, biconcave, nu- cleated discs that are far larger than the same cells in man. F Fig. 37.— Blood-cells. A. Platelets ; B. Leukocytes : C. Leukocytes in motion : C\ Leukocyte at rest; D. Red cells of frog, lateral view. 1. Red cells of man at close focus; 2. at distant focus; 3. lateral view of red cells (rouleaux). F. Crenated red cells of man; 4, 5, 6. red cells of frog {Stohr's His- tology). The size of the red cell is by no means proportionate to that of the animal. The musk deer possesses one of the smallest (2.4 microns), while the proteus has about the largest (62.5 microns). That of the elephant is but 9.2 microns in diam- eter, and beside it stands that of the humming bird, with' a diameter of nearly 9.4 microns. The red cells are more numerous in carnivorous than in herbivorous animals, while in birds they are larger in size. 96 . CIRCULATORY SYSTEM. In the amphibians, where the size is great, the number is small. White blood cells, or leukocytes, are large, pale cells readily distinguished from the above. About 5,000 to 8,000 are found in each cubic mm. of blood, and some of the varieties have the powers of motion and phagocytosis. They are classified as follows : 1. Lymphocytes (small lymphocytes). 2. Hyalin cells (large lymphocytes). 3. Polynuclear, polymorphonuclear leukocytes, or FINELY GRANULAR OXYPHILS {Formerly n^eutrophil). 4. Coarsely granular oxyphils (Formerly acidophil), 5. Finely granular basophils. 6. Coarsely granular basophils. Fig. 38. — White Blood-cells of Man. a. Lymphocyte : b. poiymorplionuclear cells ; c. finely granular oxyphil. X 600 {Stohr's Histology). 1. The LYMPHOCYTES average 5 to 7 microns. Each con- sists of a large darkly staining nucleus surrounded by a narrow rim of faintly stained protoplasm. It is neither ameboid nor phagocytic (though this is now in doubt), and constitutes about 15 to 30 per cent, of all the white cells. 2. The HYALIN CELL averages 11 to 15 microns. Both nucleus and protoplasm stain but faintly, hence the name. It is actively ameboid and phagocytic. It represents 2 to 6 per cent, of the white cells. 3. POLYNUCLEAR, POLYMORPHONUCLEAR LEUKOCYTES, Or FINELY GRANULAR OXYPHILS, ACIDOPHILS, Or EOSINOPHILS, I WHITE BLOOD CELLS. 97 average 7.5 to 11 microns. The nucleus has many shapes, as U, V, W, etc., and may even be divided in a num- ber of segments (polynuclear). The protoplasm contains a number of fine granules that take the acid stain deeply. These granules were at one time regarded as neutrophilic, and the cells were called neutrophils. They are actively ame- boid and phagocytic, and represent 60 to y2 per cent, of all leukocytes. 4. The COARSELY GRANULAR OXYPHIL, ACIDOPHIL, Or EOSINOPHIL, is about 7 to TO microns in diameter. The proto- plasm contains a few Large granules that take the acid stain deeply. It was form-erly called acidophil, or eosinophil, and is actively ameboid, but not phagocytic. It represents .1 to 4 per cent, of the leukocytes. 5. The FINELY GRANULAR BASOPHIL reSCmblcS GROUP 3, except that the granules take a basic stain, and are present to the extent of .i to i per cent. 6. The COARSELY GRANULAR BASOPHIL is Said to be absent from normal blood. It is a relatively large cell, and is also called the mast cell. Another cell that is usually described among the leukocytes is the myelocyte, or marrow cell. This cell is not a normal constituent of the blood, but is found there in certain blood diseases. The BLOOD PLATELETS are small (2 to 4 microns), oval or circular discs, capable of ameboid movement. They number about 200,000 to 300,000 per cubic mm. Their function and origin are unknown. The INTERCELLULAR SUBSTANCE, Or LIQUOR SANGUINIS, contains the salts of the blood. Its density is such that the cells retain their normal shape. If, however, solutions are added that differ in density, the action upon the cells is char- eteristic. h 98 CIRCULATORY SYSTEM. Upon the addition of salt solution, the cells become irregu- lar in outline, and are crenated. If water be added, it dis- solves the hemoglobin, and the cells swell and become spheri- cal, but, as a rule, are not destroyed. The action of acetic acid is important. The addition of a .3 per cent, solution decolori:;es the red cells and renders the white cells more distinct. This is made use of in Hematology for the purpose of counting the white cells, in a fresh condition. When blood clots, fibrin is precipitated, and this entangles the corpuscles. 1. Hemin crystals of man (x 560) ; 2. crystals of common salt : 3. hematoid crystals of man (Stohr^s Histology). 40. — Hemoglo- Crystals of a Dog (x 100) ; a crystal Separating into fibres (Stohr's Histology). Hemoglobin is an organic compound of iron, and, as it - exists in the blood, it cannot be readily studied. Its conver- sion into the crystallin state is not difficult. Hemoglobin crystals will be formed if a drop of de- fibrinated blood be mixed with a drop of Canada balsam, or clove oil, and covered with a cover-glass. They are large, red, tetrahedral crystals. Hemin crystals may be prepared by adding a small crystal of salt and two drops of glacial acetic acid to a little dried blood, and heating until the mixture boils. During this process, it should be covered. When cool, small brownish crystals will be found. These may be single or grouped in HEMAL GLANDS 99 the form of rosettes, and are known as Teichmann's crystals. Among the blood-making organs are placed the coccygeal and CAROTID glands. The former, luschka^s gland, is found in front of the coccyx, and is joined to the middle sacral artery. It is sur- rounded by a fibrous sheath, which sends in septa that divide the organ irregularly into areas, or compartments. The latter contain groups of polyhedral cells surrounded by dense plexuses of capillaries. Nonmedullated nerve fibres are numerous. The CAROTID GLAND is fouud at the bifurcation of the com- mon carotid artery, and its structure is the same as that of Luschka's gland. CHAPTER VIII. THE LYMPHATIC SYSTEM. The Lymphatic System includes the lymphatic and thoracic ducts, capillaries and intermediate vessels, and a number of organs, Lymph Node (Lymphatic Gland), Spleen and Thymus Body. The ducts resemble veins more than arteries. Their walls are thin, and they possess valves. The arrangement of the muscle, and the distribution of the nerves, are like those of an artery. Lymph capillaries are much larger than those of the vascular system, measuring 30 to 60 microns in diamiCter. Lymphoid tissue is arranged in four ways, diffuse, SOLITARY FOLLICLES, AGMINATED FOLLICLES and LYMPH NODES, or LYMPHATIC GLANDS. The first three have been considered under Adenoid Tissue. (See Connective Tis- sues, p. 59). Lymph Nodes, or Glands, are small, bean-shaped organs, surrounded by a capsule, and composed of cortex, me- dulla and HiLus. The capsule consists of white fibrous tissue, and is ar- ranged in two layers, enclosing a lymph space. From its inner surface, traheculae are ^ent into the cortex, and these divide the latter into a number of masses called secondary follicles, or nodules. The lymph space continues along the traheculae. The CORTEX contains the secondary nodules and traheculae. The former consist of dense adenoid tissue, and contain a germinal center. The cells are chiefly lymphocytes, which are arranged in concentric layers around the periphery. Other cells of the hyalin variety are found in the central por- LYMPH NODE. lOI tion. During gestation, nucleated red cells may be present. The follicles continue into the center of the node as the me- dullary cords. The irabcc III a e sepd.v Site the follicles from one another, and pass into the medulla surrounded by the lymph space. The MEDULLA consists of the medullary cords and trabeculae. Z^:^'" - (; I Fig. 41. — Longitudinal Section of a Lymph Node. a. Hilus ; b. arteriole ; c. venous sinuses ; d. adipose tissue ; e. secondary nodule of cortex ; /". vein medulla ; g. subcapsular lymph sinus : li. germinal center of secondary nodule ; i, i. trabeculae ; k. capsule ; I. lymph sinus ; m. medullary cord. The cords are the band-like continuations of the secondary follicles, and are separated from the trabeculae by the lymph spaces that accompany the latter. They consist of dense adenoid tissue, supported by reticulum. At the hilus, the edulla comes to the surface. The HILUS is a scar-like depression at one side, where the vessels enter and leave. At this place, the secondary ^nodules are wanting, and the medulla comes to the surface. I02 THE LYMPHATIC SYSTEM. The arterial vessels, to a great extent, enter at the peri- phery of the node. Their branches continue into the trabe- culae, and then pass into the folHcles. Those that enter at the hilus, also follow the trabeculae, and bridge the sinuses to enter the lymphoid tissue. The venous radicals all pass toward the hilus, where one or more vessels may be formed that carry all the blood away The afferent lymph vessels pierce the capsule at different points, and empty into the capsular sinus. The lymph passes down along the trabeculae, and filters through the organ. All the lymph is collected into one or more afferent vessels that leave at the hilus. Lymph nodes, or glands, are the highest form of lymphoid tissue. They are scattered throughout the lymphatic system, in the pathways of the vessels. They are often collected into groups, as in the axillary, inguinal and femoral regions Lymphatic glands are uncertain structures, as they may disappear early, or change from place to place. They make the white blood cells, filter the lymph, are the centers of cell destruction, and may possibly give rise to red blood cells. SPLEEN. The Spleen is a lymphoid structure, surrounded by a capsule of dense white fibrous tissue that contains involun- tary nonstriated muscle fibres, and limits the splenic sub- stance. The capsule sends in trabeculae that divide the organ ir- regularly into compartments. At one side, is a depression, the HILUS, at which the vessels enter and leave. The splenic substance consists of two main portions, the PULP and MALPIGHIAN CORPUSCLES. The PULP is composed of diffuse adenoid tissue, broken down red cells, nucleated red cells and some large polynu- SPLEEN 103 clear elements. To the red cells the peculiar color is due, and the organ has been called the "grave-yard of the red cells." The cells are supported by retiform connective tissue. The MALPiGHiAN CORPUSCLES are solitary follicles and consist of dense adenoid tissue. They differ from the ordi- nary follicle in possessing an eccentrically-placed arteriole. ^ ^ -!*~>'rLrt, ^'^i^c- Fig. 42. — Section of Spleen. a. Capsule ; b. trabeculae longitudinal section ; c. pulp ; d. Malpighian corpuscle ; e. germinal center of corpuscle ; jf. eccentric arteriole in corpuscle ; g. trabecula cross section ; U. blood-vessel. This adenoid tissue is held to be in the adventitial sheath of the arteriole, and forms a spherical mass at the bifurcation of the vessel. These follicles usually show germinal centers. The circulatory system of the spleen is peculiar in being an open one. Capillaries, as such, do not exist, and the arterioles and venules are connected by blood spaces, or ampullae. I04 THE LYMPHATIC SYSTEM. The splenic artery enters at the hilus, and breaks into branches that follow the trabeculae. Of these, some quickly pass into the pulp, while others follow the trabeculae to their smallest divisions. The spleen is divided into lobules, about one mm. in diameter, each one of which is further subdivided into histologic units, one for each terminal artery, or am- pulla. These terminal vessels are covered by a lymphatic sheath, the ellipsoidal sheaths. The terminal ampullae are porous, and continue as veins. The spleen is subject to rhythmic contractions, one per minute, and about i8 per cent, of its volume is lost at each contraction. These are produced by the involuntary muscle in the capsule and trabeculae. When the cardiac impulse sends the blood into the arteries, the blood passes into the ampullae, and through the porous walls into the pulp. When the rhythmic contractions occur, the blood is forced into the veins, and, at the same time, the arteries are closed. This shows an open circulation (Mall). Lymphatics occur in the capsule and trabeculae only. THYMUS BODY. The Thymus Body is essentially a lymphoid structure, though it undergoes peculiar changes in its life's history. It originates as a true gland (epithelial organ), but soon leukocytes infiltrate it, and cause the disappearance of the epithelium, except small islands. After the sixth year, it generally undergoes further change. The lymphoid tissue is gradually replaced by adipose tissue, so that an old thymus will show but little adenoid tissue. This organ is surrounded by a capsule of white fibrous tissue that sends in septa, which divides the organ into LOBES and lobules. Each lobule consists of cortex and medulla. THYMUS BODY 105 The CORTEX is composed of dense lyiuplioid tissue, and stains deeply, owing to the large number of leukocytes pres- ent. The MEDULLA consists of diffuse adenoid tissue, and takes, therefore, a lighter stain. The supportive tissue is retieulinii. In the medulla, are found small, peculiar bodies, consisting of concentrically arranged epithelial cells ; these are the cor- Ftg. 43. — Section of the Thymus Body of a Child. a. Capsule ; h. interlobular connective tissue ; c, c. adipose tissue ; d. blood- vessels in interlobular tissue ; e. cortex ; f. medulla ; g. blood-vessel in lobule; h, h. corpuscle of Hassal ; *. corpuscle of Ilassal magnified. piiscles of Hassal. They are supposed to represent the re- mains of the epithelium, though some hold that they repre- sent endothelium of blood-vessels. These bodies are encap- sulated, and may be compound. The blood-vessels pierce the capsule, and form branches in the interlobular connective tissue. From these, capillaries enter the lobules and are distributed to the adenoid tissue. CHAPTER IX. ALIMENTARY TRACT. The Alimentary Tract starts at the Hps, and extends to the anus. It receives the food, digests it and casts off that which is undigested. The various portions perform different functions, and the lining cells differ accordingly. The inner coat is a mucous membrane that gives rise to glands, which are devices of nature for increasing the secretory sur- face. The absorptive surface is increased by prolongations of the mucosa into the lumen of the organ (villi of the small intestine). The Lip is covered externally by skin^ and internally by MUCOUS MEMBRANE. Between these, are found connective tissue and muscle. The SKIN consists of two portions, the epithelial, or epi- dermis, and the connective tissue portion, or derma. The epidermis is composed of stratified squamous cells, of which two layers, the stratum corneum and stratum Mal- pighii are distinct. The stratum corneum is the outer, and consists of nonnucleated scales; the stratum Malpighii is the genetic portion. Its lowest cells rest upon a basement membrane, and are columnar in shape. Those above are polyhedral ; the latter become more flattened as the corneum is approached. The derma consists of white fibrous connect- ive tissue supporting blood-vessels, nerves and lymphatics. Beneath, the epithelium it is thrown into waves called •papillae. The mucous surface is also lined by stratified squamous cells, that differ from the outer, however, in being larger and less readily stained. The cells rest upon a basement membrane, beneath which is the tunica propria, composed of papillated, delicate white fibrous tissue. io6 TEETH. 107 Between the tunica propria and skin, are found connective tissue and voluntary striated muscle. Near the tunica pro- pria, are to be seen small, compound tubular glands that open upon the mucous surface. At the margin of the lip these two surfaces join, and this is the miico-ciiiancous junc- tion; here the epithelial layer is quite thick, and the cells are larger and bladder-like, resembling the epitrichial cells of the fetus. Blood-vessels are found in great abundance, and form dense plexuses, especially around the glands. The Mouth is Hned by a mucous membrane, consisting of siratiiled squamous cells resting upon a basement mem- brane and tunica propria. Here and there are found small glands of the sam.e nature as those found in the lips. THE TEETH. The Teeth have a peculiar structure. Each consists of a portion that extends beyond the gum, the crown; and a por- tion passing into the jaw, the root, or fang. Between these, is a narrow part covered by the gum, the neck. The fang is covered by a fibrous membrane, the periodontal membrane. Within the tooth, is a space called the pulp cavity. The CROWN is the exposed portion, and is covered by the enamel, which is thinnest at the neck, but increases in thick- ness as the summit is reached. The enamel is composed of peculiarly modified epithelial cells, the adamantoblasts, or amelioblasts that have become changed to the hardest sub- stance in the body. Each cell is columnar, and becomes con- verted into enamel from within outward, assuming the shape of a prism. These prisms are thinner at their inner ends, and are arranged in bundles that are perpendicular to the surface of the dentin beneath. The various bundles are, however, not parallel to one another. io8 ALIMENTARY TRACT. The CEMENTUM, or CRUSTA PETROSA, extends from the enamel to the base of the tooth. It is a narrow layer of bonv ■ 5 Fig. 44. — Longitudinal Section of an Incisor Tooth. A. Crown; B. Neck; C. Fang; 1. enamel; 2. dentin; 3. pulp-cavity; 4. ce- mentum ; 5. root-canal {after Stohr's Histology). substance, thickest at the base, and containing, here and there, quite a number of laaifiae, canaliculi and osteoblasts. i TEETH. 109 The basal portion is pierced by a small canal, root canal, through which the nerve and vessels enter the tooth. The DENTIN is found beneath the enamel and cementum, and forms the bulk and shape of the tooth. It is an ivory- like substance, formed by the odontoblasts, and consists of a great number of tubules that extend from the pulp cavity to the enamel and cementum. Each tubule consists of more compact material than the intervening portions, and for this reason are called dentinal tubules, or sheaths; the inter- vening portions are the intertubular dentin. The canals within the tubules have a greater diameter near the pulp cavity than peripherally, and, as they pass outward, give off branches that communicate with the other tubules. The canals contain processes of the odontoblasts that extend out- ward as the dentinal fibres. Beneath the enamel these canals pass through spaces, in which dentin failed to form but which are filled by a soft substance, and are known as the interglobular spaces. At the cementum, the canals end blindly. Here are found a series of smaller spaces called Tomes' granular layer. The inter Uibular dentin has a fibril- lar structure. The dentin may be looked upon as a modified bone, in which cell-spaces, or lacunae, are absent, but in which the canaliculi are represented by the dentinal canals. Enamel and dentin start to form at the same line, but while the enamel is formed from within, outward, the dentin is laid down from without, inward. The PULP CAVITY is a space within the tooth that has not been encroached upon by the dentin. In the living condi- tion, it is filled by the pulp. This is a highly sensitive vas- cular tissue, composed chiefly of the white fibrous variety, which supports the vessels and nerves that penetrate through the root canal. Separating it from the dentin, is a row of DONTOBLASTS^ which are modified pulp cells. no ALIMENTARY TRACT. The ODONTOBLASTS are very tall columnar, or pyramidal cells whose bases are closely applied to the dentin. From the bases, the dentinal -fibres pass into the canals. The apex usually receives a branch of a nerve fibre. Separating the tooth from the bony socket, is a thick membrane, the periodontal, or alveolar membrane. . This is practically a periosteum, as upon both surfaces osteoblasts are present. Those upon the tooth side form the cementum, while those upon the socket surface aid in forming the jaw. The intervening portion consists of white fibrous connective tissue, of which many fibres have a transverse course. These correspond to Sharpey's fibres, as they pass into the cement- um and the jaw. The membrane is continuous with the tunica propria of the gum. THE TONGUE. The Tongue, like the Teeth, occupies part of the mouth cavity. It is covered by a mucous membrane that consists of stratified squamous cells, basement membrane and tunica propria, which, along the sides and base, is papillated. The upper surface, or dorsum, is characteristic. Its anterior two- thirds is covered by minute projections, called papillae; of these there are three varieties, filiform, fungiform and circumvallate. The central portion consists chiefly of voluntary striated muscle. The FILIFORM PAPILLAE are cone-shaped projections of the tunica propria, covered by the stratified squamous cells, the outer ones of which are hard and horny. The central part of a papilla consists of white fibrous tissue, which is thrown into small secondary papillae that are not visible ex- ternally These papillae are the most numerous, and are scattered over the whole of the anterior two-thirds. They are directed backward, and are the ones that produce the TONGUE. Ill scratching sensation when the hand is Hcked by a lower animal. The FUNGIFORM PAPiLLiAE are flat-topped, table-like structures, in which the sides are parallel. They have sec- ondary papillae, and are scattered like the filiform variety, but are less numerous. The ciRCUMVALLATE PAPILLAE are the most important. While the top is flat, the sides usually converge and give this variety a narrow base, secondary papillae are found only on the upper portion. Each papilla is surrounded by a little vallum, or ditch, hence the name. These papillae are the least numerous, and are found only in one area. Ten to fifteen arrange themselves like a letter V, with the apex at the foramen cecum, a little de- pression that lies at the boundary of the anterior two-thirds and posterior one-third of the tongue. These papillae con- tain TASTE-BUDS along their sides. The TASTE-BUDS are the end organs of taste, lie in the epithelial portion of the sides, and have a definite structure. They are barrel- shaped, and open at the exposed ends. Each consists of two kinds of cells, outer (stave-like), the susten- tacular, or supporting cells, and the inner, neuro-epithelial elements. The SUSTENTACULAR cclls are flat and stave-like elements possessing a prominent nucleus. The neuro-epithelial ele- ments are spindle-shaped, and each ends in a minute, hair- like process, the gustatory hair, that projects through an opening in the barrel, the gustatory pore. The nerve fibre that extends to each bud forms branches, one of which is sup- plied to each neuro-epithelial cell. Beneath the mucosa is found the musculature of the tongue. This consists of the voluntary striated variety, ar- ranged longitudinally, vertically and transversely. The IT2 Ai:iMKNTARY TRACT. "'W' k/r* ist^giii^ Fig. 45. — Cross-section of Tongue. a. Stratifiec: squamous cells : h. basement membrane : c. tunica propria ; d. serous glands : e. mucous glands ; f. venule : g. longitudinal muscle fibres ; h. vertical muscle fibres ; i. transverse muscle fibres ; I. sep- tum : m. filiform papilla ; n. secondary papillae ; r. adipose tissue. A. Filiform papilla. B. Fungiform papilla. (". D. (^ircumvallate papillae — m, m. taste buds ; n, n. glands. E. Taste bud — o. nucleus of neuro-epithelial cell ; r. nerve fibre ; s. gustatory hair ; t susten- tacular cell ; v. neuro-epithelial cell. TONSILS 113 longitudinal fibres are arranged in bundles that lie beneath the tunica propria and extend around the tongue. They are separated by small bundles of vertical fihres. In the center, the fibres are vertical, oblique and transverse, and are separ- ated in the middle line by a little partition, or septum. This consists of white fibrous tissue, and arises at the base, but does not reach the tip. It varies in height, being higher in the middle than at either end. In the muscular portion, small glands are often found. Occasionally, branched muscle fibres are fotmd. The true hose of the tongue, the posterior one-third, pos- sesses no papillae. It contains small salivary^ glands and collections of adenoid tissue called the lingual tonsils' The blood-vessels are quite numerous; the capillaries ex- tend into the papillae and between the muscle fibres and form plexuses around the glands. The lymphatics are in the base, and are found quite numer- ous in the tunica propria, where they receive branches from the papillae. THE TONSILS. The Tonsils are found just between the mouth and pharynx, and are essentially lymphoid structures. They are covered, upon their exposed surface, by strati- fied squamous cells that dip down into the organ in the form of irregular tubes called the tonsillar crypts. The organ is separated from the surrounding tissue by a layer of white fibrous tissue, the capsule, that sends in trabeculae, which form the main frame-work of the organ. The bulk of the tonsil consists of adenoid tissue, in the form of the diffuse variety and solitary follicles. The latter show germinal cen- ters, and are found chiefly around the crypts. The support- ive tissue is of the retiform variety. Leukocytes may be 114 ALIMENTARY TRACT. seen on their way to the crypts, where they become the sal- ivary corpuscles. Blood-vessels, and especially lymphatics, are numerous. The vascular capillaries ramify the adenoid tissue, while the ^^: i:^'?::!!^^^^^^ l^- ' Fig. 46. — Vertical Section of Human Tonsil. a. Stratified squamous epithelium ; ft. basement membrane ; c. tunica pro- pria ; d. trabeculae ; e. diffuse adenoid tissue ; f. adipose tissue ; h. capsule ; i. glands ; k. muscle ; I. blood-vessel ; m. epithelium of crypts ; q, q. crypts. lymph channels surround the follicles and form a peripheral vessel beneath the fibrous capsule. THE PHARYNX. The Pharynx is a musculo-membranous bag that con- nects the mouth cavity and the esophagus. It has three coats, MUCOUS, FIBROUS and muscular. The MUCOUS coat is lined, in the lower, or alimentary, portion, by stratified squamous cells, The upper, or respira- ESOPHAGUS. 115 tory, part is lined by stratiHed ciliated cells. These all rest upon a basement membrane, beneath which is the tunica propria, that is thrown into waves or papillae. The tunica propria contains a considerable amount of diffuse adenoid tissue. The FIBROUS COAT is composed of large bundles of white fibrous tissue, and serves as a support to the larger vessels and the small pharyngeal glands. It also serves as an attach- ment for the muscle fibres. The MUSCULAR COAT consists of voluntary striated muscle, surrounded externally by loose areolar tissue. The blood-vessels and lymphatics are numerous. The cap- illaries are found in the mucous and muscular coats, around the glands and between the muscle fibres. ESOPHAGUS. The remainder of the Alimentary Tract is tubular, and possesses four coats, mucous, submucous, muscular and FIBROUS. The MUCOSA is further subdivided into four layers, epithelium, basement membrane, tunica propria and muscu- laris mucosae. In the Esophagus, the mucous coat is lined by stratiHed squamous cells. These rest upon the basement membrane, beneath which is the papillated tunica propria. The latter consists of yellow elastic and white fibrous tissues, in which the capillary vessels form a delicate network beneath the epithelium ; the ducts of the glands pass through this layer on their way to the surface. The mujcularis muco sae co n- sist s of in voluntary, nonstriated miiscle fibres^, ok^cularl^L-and longitudinally arranged. In the upper portion of the esopha- gus, this layer is often wanting, but in the lower part it is always present. In the relaxed condition, the mucous and submucous coats are thrown into longitudinal folds. ^K ii6 ALIMENTARY TRACT. The SUBMUCOUS coat is composed of coarser bundles of white fibrous tissue, which forms a loose network for the support of the large blood-vessel trunks. In this coat are seen a number of glandular structures, the esophageal %( 6 '4 Fig. 47. — Cross-section Esophagus. a. Stratified squamous epithelium ; Z>. basement membrane ; c. tunic pro- pria ; d. muscularis mucosae ; e. esophageal gland ; f. blood-vessel ; (J. submucosa : fc. outer longitudinal muscle ; I. fibrous coat ; n. inner circular muscle. glands, which are apparently mucous, as they stain lightly They send their ducts through the mucous coat. As the stomach is approached, these glands become more numerous, and may even be found in the mucosa. STOMACH 11/ The MUSCULAR COAT consists of muscle fibre, arranged in two layers, inner circular and outer longitudinal. In the upper third, these fibres are of'the voluntary striated y?^^^^ in the lower third, smooth, ^xvd in the middle portion, mixed. The involuntary variety continues throughout the remainder of the tract. The FIBROUS COAT consists of fibro-elastic tissues, and con- nects the organ with the surrounding tissues. It sends in bundles between the muscle bundles, of which they are said to form the perimysium. The blood-vessels pass directly to the submucosa, where branches are formed, and sent to the mucous and muscu- lar coats. Here they form longitudinal plexuses. The lymphatics follow the same general course, ^u^^^ Mu^ *M!! is found in the epididymis. It consists of a number of tubules, in which the lining cells are low columnar, or even ciliated. The tubules are closed, and are separated from one another by vascular connective tissue. The cells that line the various portions of the male genital tract are as follows : Testicle. 'Spermatogonia ) ^ c, ^ , 1 y Basal layer. Sustentacular j Seminiferous Tubule \ Spermatocytes, or mother cells. Second layer. Daughter cells, Third layer. .Spermatids, Fourth layer. TuBULi Recti Cuboidal or squamous, Rete Testis Cuboidal or squamous. Vasa Efferentia Columnar or ciliated. Epidydimis Stratified ciliated. Stratified columnar. Stratified ciliated (some). Seminal Vesicles Simple or pseudositratified columnar. Ejaculatory Duct Simple columnar. Vas Deferens I \ CHAPTER XIV. THE FEMALE GENITAL SYSTEM. This system consists of the Ovary, Oviduct, Uterus, Vagina, Glands of Bartholin and Genitalia. The Ovary, the distinctive female organ, Hes upon the posterior surface of the broad Hgament and projects into the pelvic cavity. It is surrounded by a capsule of white fibrous connective tissue called the tunica albuginea. This is not so prominent as that of the testicle. The free surface of the capsule is covered by low columnar cells called the GERMINAL EPITHELIUM. The organ consists of Cortex and Medulla. The Cortex is the outer part, and surrounds the medulla, except at one point, at which the vessels enter and leave ; this is the HiLUM, and here the medulla comes to the surface. The cortex is the glandular portion, where the cellular ele- ments of the secretion, the ova, are formed. It consists of a delicate reticulum, the stroma, in which the Graafian FOLLICLES are found, and occasionally groups of large, polygonal epithelial cells, called the interstitial cells. The free surface of the stroma is covered by the modified mesothelial cells, the germinal epithelium, from which the ova are derived. These cells are low columnar elements. The Graafian follicles are characteristic structures. They vary in size; the smallest are just beneath the tunica albu- ginea, the medium-sized near the medulla, and the largest extend from the medulla to the capsule, and cause a projec- tion upon the surface of the organ. Externally the follicle is covered by a layer of condensed stroma called the t heca j^olliculi ; the outer portion of this is called the tunica fibros.\, and the inner the tuni ca vas - '182 ^^^ "^ ' OVARY. 183 CUL OSA. The THECA is lined by a number of layers of gran- UTarcells termed the zona c.ra nulqsAi^ within which is a space, the antrum, filled by a liquid, the ljouor folliculi. At one point, the granule layer projects into the antrum, and this mass contains the ovum. This projection is called I Big. 68. — Cross-section of Ovary op a Cat. The Graafian follicles are so numerous that but little of the medulla is seen. a. Germinal epithelium ; h. tunica albuginea ; c. immature Graafian fol- licle : d. ovum; e. cortical stroma: f. interstitial cells; (j. theca fol- liculi ; h. zona granulosa ; i. antrum containing liquor folliculi ; k. discus proligerus : I. corona radiata : m. zona pellucida ; n. vitellus: o. germinal vesicle ; p. follicle without ovum ; r. hilum ; s. medulla showing the tubules of the parovarium ; t. arteriole ; u. venule. the DISCUS PROLIGERUS, or CUMULUS oviGERUs. Just withiu the granule cells ot the discus is seen a layer of long columnar cells, the corona radiata. These cells rest upon a thick homogeneous membrane called the zona pellucida, which is separated from the ovum by a small space, called the 184 THE FEMALE GENITAL SYSTEM. PERiviTELLiNE SPACE. This Space is disputed by some writers. The corona is supposed to give rise to the zona pel- lucida. The ovum that Hes just within the space consists of a cell-wall, the vitelline membrane, and cell-body, the viTELLUS. In the vitellus is seen the nucleus, or germinal VESICLE, which contains the prominent nucleolus, or germi- nal SPOT. The Ovum is the most characteristic and largest cell in the body. Its diameter varies from .2 to .3 mm. The zona pellucida that surrounds it is quite thick, measuring from 7 to 10 microns. The protoplasm consists of yolk granules, the nutritive yolk, or deutoplasm, and the formative YOLK. The nucleus averages about 30 microns, is eccen- trically placed and sharply outlined by a membrane that pos- sesses a double contour. The chromatin is rather scant, but the nucleolus is quite large and prominent. The Graafian follicles, of which there are about 36,000 in each ovary, are developed during intrauterine life, and all are usually present at birth. Not all of these develop, by any means. The smallest consist of the ovum^ surrounded closely by a few layers of small granule cells and a delicate theca. They lie just beneath the tunica albuginea, and show no antrum. The medium-sized follicles lie near the medulla, and pre- sent an antrum. The granule cells are more numerous, and the ovum larger. The fully-developed fol- licles extend from the medulla through the cortex beyond the original surface level, projecting varying distances. The FOLLICULAR CELLs_are derived from the germinal epi- thelium, and grow into the stroma in long columns during the developmental period, as the egg-tubes of PfluegeRj^ In such a column, will be found several large, and a great number of small, cells. These columns become OVARY. 185 separated into a number of groups of cells consisting of one or more large, and many small, cells. The large are the O OGENETIC ^ and the small the granule, cells. Gradually, the large cells fuse to form a single mass of protoplasm, and all the nuclei, except one, disintegrate. The single cell re- sulting is called the oocyte. The egg-tubes are separated into these groups by the stroma that grows into the columns. '^■<^^m^ Fig. 69. — Ovum from a Cow. 1. Corona radiata ; 2. zona pellucida ; 3. vitellus ; 4. germinal vesicle ; 5. germinal spot. I This stroma further condenses around each group to form the primitive theca. Toward the age of puberty, these follicles begin to develop, though they may start sooner. The granule cells increase rapidly in number, and some of the more central ones (iisappear by disintegration or lique- faction. This gives rise to the space, or antrum, which be- comes filled by a liquid, the liquor folliculi. The latter is probably derived from the blood-vessels. l: l86 THE FEMALE GENITAL SYSTEM. As the follicle develops and is about to rupture, the ovum (oocyte) undergoes a process called Maturation. Maturation is the process by which the polar bodies are formed and extruded. The germinal vesicle migrates toward the periphery, and undergoes mitotic change. When the nuclear spindle is formed parallel to one of the radii, the peripheral half^ surrounded by a small amount of protoplasm, is thrust out of the cell. This is the first polar body. Without rest, the remaining chromosomes immediately undergo division again, and the extrusion process is repeated. This is the second polar body. The remaining chromosomes form a new nucleus called the germ-nucleus. By this change, the number of chromosomes is reduced from twenty-four, in the oocyte, to twelve, in the matured ovum. The first polar body often divides into two, and as a result of maturation, four cells are formed. Of these four, the ovum is the only one capable of producing an offspring. The three polar bodies disintegrate and disappear. This is entirely different from the change in the testicle. In that organ, the sperma- tocyte gives rise to four cells, each of which becomes a spermatozoon, capable of fertilization. As the follicle increases in size, it approaches the tunica albuginea, and causes it to protrude. The stroma interven- ing between the ovum and the tunica gradually diminishes until merely the tunica remains. As the follicle increases, and the pressure within becomes greater, the tunica becomes progressively thinner, until it is no longer able to withstand the pressure. Then it ruptures, and the liquor folliculi and the ovum, surrounded by the granule cells, are cast out of the ovary. The vessels of the tunica vasculosa rupture, and the follicle fills with blood. When this occurs, the body is called the corpus h emorrhagicum . _The cells of the theca penetrate the clot, and cause this to organize. In addition OVULATION. 187 to these cells, there are certain other large cells that possess a yellowish pigment. These are the lutein cells, and their function is unknown. They are derived from the theca. If the ovum has not been fertilized, this body is called a CORPUS LUTEUM SPUR IUM^ which rapidly undergoes atrophy; in a few weeks, it leaves a white scar called the corpus albi- cans^ If fertilization has occurred, then the body persists until near the end of pregnancy, and is termed the corpus LUTEUM_\^ERUM. The corpus luteum seems to be a gland of short duration. It seems to secrete a substance that causes the second suc- ceeding menstrual How. Experimental study upon animals, in which the follicles were destroyed, showed an almost in- variable absence of the second succeeding period. The pre- ceding flow was caused by the follicle preceding the experi- ment. This secretion also stimulates the uterus, and aids the implantation of the ovum in the uterine mucosa, provid- ing fertilization has occurred. (Frankel). Of all the follicles formed, but few are ever fertilized. A great number atrophy; in the remiainder, maturation oc- curs. Of these ova, there are those which are cast into the abdominal cavity and absorbed by the peritoneum; those in which the ovum passes down the genital tract and is cast out, or disintegrates, and lastly, those that become fertilized. Ovulation includes the delivery of the ovum from the follicle and its passage through the genital apparatus. In the lower animals, in which the young are developed from eggs outside of the body (oviparous), this process is evinced by the 'laying of the egg" In the viviparous ani- mals, or those in which the offspring is developed within the mother, this process is not accompanied by any outward signs or manifestations. In the temperate climate, it begins at about the twelfth to the fifteenth year, and continues until l88 THE FEMALE GENITAL SYSTEM. about the forty-fifth to the fiftieth year. At that time it ceases, and fertihzatioii cannot occur thereafter. The Medulla consists of a loose network formed by large, coarse bundles of white fibrous tissue, in which strands of SMoaTH MUSCLE TISSUE are found. These latter are limited to the medulla. In the meshes of the stroma are seen the INTERSTITIAL CELLS^ which are more numerous than in the cortex. In this part of the ovary are found the large blood- vessel trunks, which are very numerous. The vessels enter the ovary at the hilus, and fonn a large number of branches in the medulla. From these, smaller ones are sent to the corte:^:, some passing to the follicles, where they form a dense surrounding plexus, while others pass to the tunica vasculosa of the tunica albuginea. The lymphatics follow the vessels closely. Nerve fibres accompany the vessels, and surround the follicles. Ganglia occur in the medulla. The Parovarium, or Epoophoron, lies near the hilus of the ovary, and consists of a number of short vertical tubules united to a single horizontal tube. The vertical tubules are short, and are lined by low columnar cells. The horizontal tubule has a larger diameter than the preceding, and is lined by the same variety of cells. It often lies deep in the broad ligament. The Paroophoron lies in the broad ligament, between the ovary and uterus, and consists of a number of short, closed tubules lined by low columnar cells. The tubes re- semble the vertical tubes of the epoophoron. THE FALLOPIAN TUBE. Although the ovary possesses no excretory apparatus like other glands, the Oviduct, or Fallopian Tube, acts as such. The Fallopian Tube consists of the outer fimbriated END, the middle, or ampulla, and the inner uterine end, or FALLOPIAN TUBE. 189 ISTHMUS. It has three coats, mucous, muscular and FIBROUS. The mucous coat consists of simple ciliated cells that lie upon a basement membrane and tunica propria. A muscii- laris mucosae is absent. The tunica propria is thrown into Fig. 70. — Cross-section of the Human Fallopian Tube. a. Epithelium ; h. tunica propria : c, villi ; d. muscular coat, inner circular layer ; e. muscular coat, outer longitudinal layer ; f. blood-vessels in the fibrous coat ; g. blood-vessels in villus ; h. fibrous coat ; k. epi- thelium of fimbria ; I. tunica propria of fimbria. longitudinal folds that are high in the fimbriated end, but diminish in heighth as the uterus is approached. These folds are the^iLLi, which possess a very narrow base, but the part lying in the lumen of the tube is greatly branched. The tunica propria consists of white fibrous and yellow elastic tissues, in which diffuse adenoid tissue is found. 190 THE FEMALE GENITAL SYSTEM. The MUSCULAR coat consists of involuntary nonstriated muscle tissue arranged in inner circular and outer longitudi- nal layerj. Near the uterine end, an inner longitudinal layer is added. This corresponds to a muscularis mucosae. The FIBROUS coat consists of white fibrous tissue, and is surrounded by peritoneum. The blood-vessels lie in the deeper portion of the tunica propria. From these, smaller ones are sent into the villi, and into the muscular and fibrous coats. The vessels are usually quite tortuous. The lymphatics accompany the blood-vessels. The nerves are both medulla-ted and nonmedullated. They accompany the blood-vessels, which they supply, and then pass to the mucosa, where they end in relation with the cells. THE UTERUS. The Uterus is a flattened, pear-shaped organ that con- sists of BODY and cervix. It is an important organ, as within it develops the offspring, in viviparous animals. All parts consist of MUCOUS, muscular and fibrous coats. The MUCOUS coat of the body is about i mm. in thickness, and is composed of simple ciliated cells, basement mem- brane and tunica propria. Within the latter are found a rich capillary plexus and diffuse lymphoid tissue. The sur- face is not smooth, but is broken by the formation of GLANDS. These are tube-like depressions lined by the simple ciliated cells, and are of the branched tubular variety. They are the uterine glands and extend to the muscular coat, but do not penetrate it. They are often so long, that, when they reach the muscular coat, they turn and run parallel to it for some distance. The MUCOSA of the cervix is a little different. The uter- ine end is lined by simple ciliated cells, and glands are pres- UTERUS. 191 ent. The vaginal end is lined by stratified squamous cells, and gland-like depressions are present. The orifices often close, causing them to become distended with secretion. In this condition, they produce globular projections called the ovuLi Nabothi. The cervical mucosa is thrown into folds iS^^SSis^^^^^^D Fig. 71. — Resting Uterine Mucosa. a. Mucosa ; b. epithelium ; c. gland tubule {Stohr's Histology, after Bohm and Davidoff). called the plicae palmatae. The vaginal portion of the cervix is covered by stratified squamous cells. H| The MUSCULAR coat consists of three layers of smooth ^" muscle, inner longitudinal, middle circular and outer longi- tudinal The inner longitudinal represents an hypertrophied 192 THE FEMALE GENITAL SYSTEM. muscuiarts mucosae. It is- separated from the middle layer by a very thin layer of connective tissue. This muscle layer is called the stratum mucosum. The middle layer is the thickest, and contains the large vessels. It is called the stratum vasculare. The outer longitudinal layer lies just beneath the fibrous coat, and is often called the stratum SUPRA vasculare. _ In the CERVIX, the circular fibres are more pronounced, forming a dense band or ring. The muscle fibres average 50 to 60 microns in length ; but, during pregnancy, they lengthen to from 300 to 600 microns. The FIBROUS, or serous, coat is quite thin. It is com- pletely invested by peritoneum in the body. Menstruation is the periodic change that occurs in the uterine mucosa, every twenty-eight days, during the child- bearing period (13th to 50th year). It is divided into stages, the HYPERTROPHIC, DESQUAMATIVE, REPARATIVE and RESTING stages. During the hypertrophic, or constructive stage, the mucosa increases to 2 or 3 mm. in thickness, and the surface becomes irregular. This is due to the increase in size and number of the blood-vessels, and to cell proliferation in the tunica propria. The glands become broader, deeper and more tortuous. This change requires four to six days, and is succeeded by the desquamative, or destructive stage. The DESQUAMATIVE, or DESTRUCTIVE, Stage is characterized by the appearance of the flow, or flux. It is caused by the diapedesis of some of the blood from the capillaries of the tunica propria. The blood passes into this layer be- neath the epithelium, and cuts ofT the nutrition of the over- lying cells, causing them to undergo a fatty degeneration. These cells then disintegrate, exposing the vessels, which VAGINA. 193 rupture and allow the blood to pass into the uterine cavity. The surface is thus left without an epithelial covering, and the thickness of the mucosa becomes reduced. This stage, lasting three to five days, is followed by repair. The REPARATIVE Stage is that in which the mucosa re- turns to the normal condition. The hyperemia disappears, and the disintegrated epithelium is replaced by epithelial cells from the glands. This stage requires about five to eight days. The RESTING stage constitutes the remaining twelve to fourteen days of the period. During this stage, the uterine mucosa is quiescent. Should fertilization occur at the time of the constructive stage, the other three stages may not take place. The blood-vessels are important. Two arteries, the uter- ine and ovarian, supply the organ. T he^ ma in branches of these^ arteries pass to th^ middle circular layer of rnuscle,- which plays the part of submucosa. Smaller branches are sent into the mucosa, and there form plexuses around the glands. The large trunks are very tortuous, to allow for the increase in the size of the uterus during pregnancy. The lymphatics originate in the mucosa; these vessels empty into a set of larger vessels in the middle layer of the muscular coat. From here, the vessels pass into the serous coat. The nerve Hhres are both medullated and nonmedullated. The former pass into the mucosa, some ending in the epi- thelial layer. The latter pass chiefly to the muscular tissue. THE VAGINA. The coats of the Vagina are the same as those of the uterus. The MUCOUS coat consists of stratified squamous cells, supported by a basement membrane and tunica propria. The 194 THE FEMALE GENITAL SYSTEM. subepithelial portion of the tunica propria is papillated. Tht* deeper portion contains many large elastic fibres and con- siderable diffuse lymphoid tissue. Occasionally, some simple -^- 'lpwim'^%mi^-^ji^^v'm:m^m^i Fig. 72. — Cross-section of Segment of Human Vagina. a. Stratiflecl squamous epithelium: h. tunica propria; c. inner circular muscle fibres ; d outer mixed muscle fibres. tubular glands are met with, and the lining cells arc of ihi simple ciliated variety. The MUSCULAR coat varies in thickness, that nearer the outlet being the thicker. The layers are not shari;ly separ- ated from one another, but the general direction is inner cir- GENITALIA I9S cular and outer longitudinal The mucous and muscular coats are thrown into folds that are ca lled rugae. The FIBROUS coat consists of dense fibrous tissue, and serves to connect the vagina with the surrounding tissues and organs. The larger vessels lie in the deeper portion of the mucosa, and send branches into the mucosa and muscularis. The capillaries of the mucosa pass chiefly to the papillae. The veins form dense plexuses beneath the fibrous coat. Large vessels occur in the lower part of the mucosa, causing it to resemble cavernous tissue. The lymphatics follow the same course as the blood- vessels. The nerves are both nonmedullated and medullated. Geni- tal corpuscles may be found in the mucosa. THE GENITALIA. The VAGINAL ORIFICE is guarded by a delicate annular, or crescentic membrane called the Hymen. This consists of white fibrous tissue covered upon its external and internal surfaces by stratified squamous cells. Occasionally, it is very vascular. Just outside of this fold, the primitive uro-genital sinus spreads to form the Vestibule of the vagina. This is a triangular space, with the apex formed by the junction of the labia minora, the sides by these folds and the base by the vaginal orifice. It contains the opening of the urethra. This space is lined by stratified sqnanvons cells. In the tunica propria, are found a great many elastic fibres and mucous and sebaceous glands, especially near the opening of the urethra. The lower portion of the tunica propria contains so many large venous channels that it is practically erectile TISSUE. Opening into the vestibule upon each side is a gland, the 196 THE FEMALE GENITAL SYSTEM. analog of the gland of Cowper of the male. This is the gland OF Bartholin,, which is a compound racemose gland, and the acini are lined by large, clear, mucous cells. The ducts are lined by low columnar cells. Covering the vaginal orifice, to a greater or less extent, are seen the Labia Minora, or Nymphae. These consist of a central mass of loose connective tissue, in which the blood-vessels are abundant, especially the veins. In the tis- sue between the veins, smooth muscle tissue exists, and this with the vascularity, forms to erectile tissue. The folds are covered, upon both sides, by stratified squamous cells that rest upon a papillated tunica propria. In these papillae, capillary plexuses are seen. Sebaceous glands are numerous, but hairs and sweat-glands are absent. The Glans Clitoris lies in the tissue formed by the junc- tion of the labia minora. It is covered by stratified squam- ous cells. The central part consists of erectile tissue, and many large and small vascular papillae are present. Geni- tal corpuscles and sebaceous glands are found. The Glans is covered by a fold of skin, the prepuce, in which the sebaceous glands are quite numerous. The Labia Majora are merely folds, or pouches of skin. Their outer surfaces are covered by ordinary skin. In the subcutaneous tissue ar^ seen numerous vessels, nerves, glands, bundles of smooth muscle and an abundance of adi- pose tissue. Along a median line, they come in contact with each other, and the skin surface is somewhat modified. Here elasic and muscle tissues are abundant, but adipose tissue is wanting. The skin of the labia majora is somewhat darker than that in the immediate neighborhood, owing to the pres- ence of pigment in the epithelial layers. Over the pubis, the two labia meet and form a prominent mass, the Mons Veneris. CELLS LINING FEMALE GENITAL TRACT. I97 The various portions of the female genital tract are lined by the following cells : Fallopian Tube Simple ciliated. Uterus. Body Simple ciliated. Cervix, Uterine end Simple ciliated. Vaginal end Stratified squamous. Vagina Stratified squamous. Vestibule Stratified squamous. Labia Stratified squamous. CHAPTER XV. THE PLACENTA AND UMBILICAL CORD. A description of the formation of the Placenta and Cord must be given, in order to understand their structure at term. Should the ovum become fertilized, it is passed down the Fallopian tube by the ciliated cells, as fertilization usually occurs in this portion of the genital system. It is surrounded by the zona pelliicida and corona, or !:ona radiata. The mucous membrane of the uterus becomes thickened, as for menstruation, and the ovum becomes lodged, usually in the fundus. The mucosa of the uterus is divided into regions ; that immediately beneath the ovum is the placental decidua, or DECiDUA SEROTiNA ; the ovum becomes covered by a portion called the ovular, or reflex decidua ; the remainder is the UTERINE DECIDUA, or DECIDUA VERA. The ovum divides and redivides, and passes down the Fallopian tube towards the uterus. These cells form an ir- regular mass, the morula. The outer cells of this mass ar- range themselves beneath the zona pellucida as the sub- zonal ECTODERM, or OUTER CELL MASS, while the remainder constitute the inner cell mass. The entire structure grows rapidly, and, as a result, a cavity is formed around the inner mass, except at one point, where it is attached to the sub- zonal layer. The cavity is filled with liquid, under pressure. This mass is called the blastula, or one-layered vesicle. The point of attachment is called the embryonic' area. In this condition, the ovum usually reaches the uterus. The outer mass, at the point of union with the inner mass, 198 TRIPOBLAST. I99 becomes greatly thickened, its upper portion being called the TROPHODERM (Minot), and its under portion the ectoderm. The trophoderm extends all around the zona pellucida, and is closely applied to it. The innermost cells of the inner MASS then arrange themselves as a single layer of cuboidal cells that extend into the cavity of the blastula and form, by meeting, a little vesicle, the entodermal vesicle. By this formation, the gastrula, or diptoblast, in which two dis- tinct layers, ectoderm and entoderm, are seen, is completed. From these two layers, the mesoderm is derived. This con- stitutes the TRIPLOBLAST, or THREE-LAYERED VESICLE. The Fig. 73. — Diagram of Supposed Development of Primates {Minot). Tro. Trophoderm ; Ec. ectoderm ; Mes. mesoderm ; Ent. entoderm ; Coe. coelom. mesoderm lies between the ectoderm and entoderm, and where these layers separate, it splits into two layers, one of which accompanies the ectoderm around the diploblast to form the somatopleure, and the other accompanies the en- toderm to form the splanchnopleure. The mass increases in size, and the trophoderm in the embryonic area thickens greatly. At the same time, the cells at the junction of tropho- derm and ectoderm disappear, leaving a space, the amniotic CAVITY. This cavity is now bounded by trophoderm above and the combined ectoderm, micsoderm and entoderm be- neath, these latter constituting the embryonic shield. At 200 THE PLACENTA AND UMBILICAL CORD. the edges of the cavity, the mesoderm continues with the trophoderm, forming the prochorion. At what are to be the cephalad and caudad regions of the future embryo, transverse depressions appear in the somatopleure (one at each end) ; these are called the head and tail folds of the amnion, respectively. The lateral folds appear on each side in the same manner. All these grooves deepen, and the somatopleure extends ventrally from all di- rections (less from caudad) to form the body-wall; its re- FiG. 74. — Diagram of Early Development op Primates. Later Stage of 73 iMinot). a. Amniotic cavity; b. ectoderm; c and d. mesoderm; e. entoderm. turn folds pass dorsally over the embryo to unite, forming an inner membrane next to the embryo, the true amnion, and an outer above the embryo, the false amnion, or primitive CHORION. The prochorion consists of trophoderm (ecto- derm) and mesoderm ; the amnion, of mesoderm and ecto- derm, and the body-wall of ectoderm and mesoderm, re- spectively. At all points, like layers are opposed to like layers. In the formation of the body-wall and amnion, the SPLANCHNOPLEURE has been pushed before the somatopleure ALLANTOIS. 201 to form a tube within the body, the gut-tract and a sac out- side, the YOLK SAC and vitelline duct. In the formation of the amnion, the embryo loses its con- nection with the chorion at all points, except caudally, where the mesoderm and ectoderm of the two are continuous, form- ing the BELLY-STALK. By this time, the ovum has become lodged in the uterine mucosa. This process is accomplished by the aid of the trophodermal cells, that have the power of phagocytosis (de- struction of tissue) and erode the superficial tissues of the mucosa, forming a cavity into which the ovum sinks. The epithelium of the uterus is lost in this region and also in the glands and the superficial vessels exposed. The trophoderm becomes thrown into little processes, or villi, (present as early as the fifth day, Peters) due to actual growth and the disappearance of cells in the trophodermal layer. As a re- sult, there are formed a series of intercommunicating spaces. The villi are composed of trophoderm and mesoderm. When the vessels of the mucosa are exposed, they rupture into the glandular spaces, and from these, the maternal blood gains access to the trophodermal lacunae, or spaces. Thus does the embryo receive nourishment from the mother, before the umbilical vessels are present. The area of the ovum left uncovered when the ovum becomes lodged, is covered by mucosa that is reflected from the lining at the sides of the ovum. This is, therefore, called decidua reflexa, or ovu- lar DECIDUA. We must rememiber that the belly-stalk connects the em- bryo with the prochorion. This belly-stalk is of importance, because into it grows an evagination of the caudal end of the guttract, near its cloacal end. This evagination grows out of the body before the body-wall is formed in the caudal region, and is called the allantois. In some animals, the 202 THE PLACENTA AND UMBILICAL CORD. OVIPAROUS, the allantois loses connection zmth the belly-stalk, and is free. It remains as a dilated sac, and serves as a receptacle for urine. In the viviparous animals, it remains connected with the belly-stalk, and connects permanently the embryo with the uterus, becoming the organ of nutrition and respiration. Its outer ends spread along the inner surface, carrying splanchnic mesoderm to the villi of the avascular Fig. 75. — Diagram of Early Development of I'rimates. Later than Fis. 74 (Minot). a. Amnion ; 6. chorion ; c. embryo ; d. yolk-sac ; e. body-stalk ; f. allantois ; g. entodermal cavity of embryo ; h. entoderm ; i. chorionic villi. prochorion, and with the latter structure it forms the true CHORION. In this mesoderm, four main vessels develop, tzvo arteries and tzvo veins. The two veins enter the body and proceed towards the heart, while the other two pass into the body, and connect with the aorta. The distal ends of all the vessels pass into the chorion, and divide to supply all the villi. These villi are still covered by the trophodenn, consisting CHORION. 203 usually of two layers. Of these, the outer becomes converted into a thin layer of protoplasm, in which the original nuclei remain. This protoplasm constitutes the syncytium. The villi do not long remain simple, but branch and re- branch ; the vessels follow these branches, and penetrate to the very ends. Some of the villi enter the uterine glands, in which the epithelium becomes denuded by about the sixth week, and the surface cells by the fourth week, and are the floating villi; others become attached, and form the Hxed villi. When the epithelium of the uterus is lost, the en- gorged superficial capillaries of the placental decidua become connected with the glands, and the blood enters these, and then the trophodermal spaces. These channels are the later interznllous spaces. From these cavities, the blood is re- turned to the venous channels of the mucosa, but no direct connection is established betzveen vhe fetns and the mother. These villi are very abundant, and may be scattered all over the ovum, or be limited to the equator of the mass. Up to this time, all are equal in size. Soon a difference is noted in size, those at the place of attachment of the ovum increase in number and size, forming the chorion frondo- sum, while the remainder disappear and constitute the chorion laeve. At about the fifth month, a villus has the following ap- pearance. Of the trophodermal cells, the outer do not re- main large, distinct elements, but become flattened, and rep- resent a mere layer of nucleated protoplasm that covers the villi ; this is the syncytium, and it is the covering of the em- bryonic connective tissue that constitutes the core of the villi and supports the vessels. In the inner layer, the cells re- main distinctly outlined, and persist, for a short time, as the cell-layer of Langhans. From the fifth month on, they disappear so that ultimately only the syncytium remains. 204 THE PLACENTA AND UMBILICAL CORD. Here and there in the villi are seen groups of cells that rep- resent collections of syncytial cells, the cell knots. These, like the other syncytium, contain nuclei that are small, but stain deeply. The protoplasm responds well to the acid Fig. 76. — Semi-Diagrammatic Outline of an Antero-Posterior Section OF A Human Uterus Containing an Embryo of About Five Weeks. a. Anterior ; p. posterior surface ; g. outer limit of decidua ; s, s. limits of the decidua serotina ; ch. chorion, within which is the embryo en- closed by the amnion, and attached to the chorion by the umbilical cord ; from the cord hangs the pedunculated yolk-sac ; r, r. decidua reflexa (Minot). Stains. The Langhans cells, however, contain large nuclei, but neither these nor the protoplasm respond well to stains. After the third month, the number of villi that becomes attached to the mucosa rapidly increases, so that after that PLACENTA. 205 time, the fetal and maternal portions become more and more fixed to each other. This is the beginning of the formation of the placenta, such as it is seen at birth. The villi branch repeatedly, and the whole structure grows rapidly, causing the child to do the same. Any disturbance that will retard the growth of the placenta will also retard the growth of the fetus in great • er proportion. The difference between the placenta at the fourth or fifth month, and at birth, is merely in size. This is due to the increase in number and branches of the villi The villi are separated into groups by connective tissue septa that are derived from the uterine tunica propria. These are the placental sepfae. At birth, the Placenta is a flesh-like, saucer-shaped mass, the attached surface of which is divided into lobes, or cotyle- dons. The fetal surface is covered by the amnion, a con- tinuation of the sac in which the fetus lies, and shows the vessels as they enter and leave the organ ; the opposite sur- face is divided inco lobes, or cotyledons, covered by the de- cidua serotina. The weight of the placenta is about one-sixth that of the child. It consists of two portions, the fetal and maternal. This organ consists of a fleshy miass lying between two membranes. Upon the fetal surface, we find the amnion and CHORION. The amnion consists of a single layer of cuboidal epithelial cells that rest upon the mesodermal tis- sue. These epithelial cells possess prominent, deeply-stain- ing nuclei, but the protoplasm does not react well to the stain. The mesodermal tissue is somewhat fibrillar, and few cells are present. It is avascular. The chorion is comiposed of mesodermal tissue, in which the fibrils are more or less distinct. From the side opposite to the amnion are seen projections. These may vary from 2o6 THE PLACENTA AND UMBILICAL CORD. small simple villi, to those resembling a tree possessing an enormous number of twigs. Along this surface of the chor- ion, may be seen masses of a fibrillar substance that are Fig. 77. — Human Placenta at Term. A. Vertical section at margin ; D. decidua : Cho. chorion ; Fih. fibrin : Vi. placental villi ; Si. marginal sinus ; vi. aborted extra-placental villi ; J), decidual tissue. B. Portion of decidual tissue at b highly magnified ; V. blood-vesseis ; d. deciuual cells with one nucleus ; d'. multinucle- ated decidual cells (Minot). called canalized Hhrin. The bulk of the placenta consists of villi. These form a reddish, spongy mass, divided into masses called cotyledons. The main stems contain two or MEMBRANES. ' 20/ more vessels surrounded by mesodermal tissue. Peripheral- ly, each villus is covered by a thin layer of nucleated proto- plasm, the syncythun. The small twigs consist of a core of mucous connective tissue supporting several small capil- laries. The syncytium surrounds each twig. In places are seen collections of nuclei representing the cell-knots. The cavities between the villi are the intervillous spaces contain- ing the maternal blood and, at times, canalized fibrin. From this, it is readily seen that the fetal and maternal blood currents do not intermingle. They are separated from each other, the endothelium of the fetal capillaries on the one hand, and the syncytium of the villi on the other. The maternal side of the placenta is covered by the DECIDUA SEROTINA, Or the STRATUM COMPACTUM of the mu- cosa. It is less than a millimeter thick, and possesses a number of short, oblique channels. These are the remains of the uterine glands ; they now represent blood sinuses, which contain maternal blood. The serotina extends into the fetal portion as the placental septae, and divides it into the cotyledons. At the edge of the placenta, it becomes attached to the chorion, and con- tinues as the DECIDUA vera. At this junction, there is a con- siderable space that extends all around the edge of the pla- centa. This is the marginal 'sinus, and is prominent be- cause few, or no, villi have developed here. The MEMBRANES consist of the amnion and the uterine lining, or the stratum compactum. The latter is thin, and contains neither glands nor epithelium. When the fetus in- creases in size and causes a dilatation of the uterus, the amniotic sac is forced against the uterine lining, and causes an atrophy of the glands and cells of the stratum compact- um. As a result, a mere fibrinous membrane, that has a loose connection with the amnion, is produced, due entirely to pressure. 208 ' THE PLACENTA AND UMBILICAL CORD. The Umbilical Cord is the connecting link between the fetus and the placenta, and represents the early allantoic stalk. It is surrounded by one or more layers of cuboidal epi- theHal cells continuous on the one hand with epithelium of the amnion, and on the other, with the ectodermal cells of the body, supported by a little subepithelial fibrous tissue. Within this covering is the pecuHar tissue called Wharton's jelly. Fig. 78. — Cross-section of Human Umbilical Cord (Miriot). A, A'. Umbilical arteries ; V. umbilical vein ; Y. remains of allantois. This is embryonic connective tissue in which the cells are chiefly spindle-shaped; some round and stellate cells, however, are seen. The intercellular substance is semi-solid, and takes a peculiar homogeneous stain. During the early months of pregnancy, the intercellular substance contains a great deal of water, and the cellular elements are few. At the end of pregnancy, the intercellular substance is more or less fibrillar, though the semi-solid portion predominates. At this time, the cells are mostly of the stellate type, but not numerous. At the body end, occasionally, traces of allan- toic cavity and yolk sac are found. The VESSELS contained are the single umbilical vein and two UMBILICAL ARTERIES. Thesc are thick-walled and well developed, and the muscle fibres run both circularly and FETAL CIRCULATION. 20g longitudinally. The wall of the arteries is thicker than that of the vein. The insertion of the cord into the placenta is usually eccentric, and, at this point, the vessels branch rapid- ly, and spread out in all directions. The circulation of the placenta is a closed one. The blood is carried from the iliac arteries to the umbilicus through the hypogastric arteries, which continue in the cord as the um- bilical arteries. These branch to follow the villi, and, ulti- mately, terminate in tufts of capillaries in the terminal vil- lous twigs. The blood at this point receives the oxygen and nutritive matter from the maternal blood that circulates in the intervillous spaces in which the villi lie. There is no direct communication between the fetal and mxiternal blood, for they are separated from each other by the endothelium of the capillaries, and the syncytium covering the villi. As the oxygen and nutritious substances pass into the fetal blood, the effete matter and gases pass out into the maternal blood. The principle is the same as in the lung, where the blood is oxygenated. Red cells never pass from one systeni to another, but leukocytes that have the power of ameboid motion may. The blood is collected by the radicals of the mnbilical vein, and carried into the body to the under surface of the liver, where the greater portion enters the portal vein, through the continuation of the umbilical vein, and the remainder is carried to the inferior cava by the ductus ven- osus. The blood passes to the right auricle, then through the foramen ovale to the left auricle, from which it passes, through the auriculo-ventricular orifice, into the left ven- tricle. The blood then passes into the aorta chiefly to the upper extremities and head, is collected by the radicals of the superior vena cava, and emptied into the right auricle. From this chamber, it passes through the auriculo-ventricu- lar orifice into the right ventricle, from which it passes into the pulmonary artery towards the lungs. As these organs 2IO THE PLACENTA AND UMBILICAL CORD. do not functionate at this time, most of the blood is sent to the aorta through the ductus arteriosus. The blood then passes towards the lower extremities, and, as it reaches the internal iliac arteries, most of it is sent to the placenta through the arterial trunks, which, inside of the body, are called the hypogastric arteries, and in the cord the umbilical arteries. CHAPTER XVI. THE SKIN AND ITS APPENDAGES. The Skin covers the external surface of the body, and is its most extensive organ. It consists of two portions, the Epidermis, or Cuticle, and the Cutis Vera, or Corium. The Epidermis is the epithelial portion of which appen- dages are modifications. It consists of stratified squamous cells, which, over the general body surface, are divisible into tzvo layers, stratum Malpighii and stratum corneum. The STRATUM Malpighii, or rete mucosum, is composed of a number of layers of cells. The basal part consists of columnar elements, and is called the genetic layer. The cells stain deeply, and under certain conditions show pigment granules. The layer is uneven in its course, as it conforms to the waves of the corium. The upper cells of the stratum Malpighii are large, polyhedral elements that do not touch one another, but are separated by intercellular spaces. Each cell is provided with a number of delicate spines, or prickles, that meet those of other cells, and thus prevent the cell- bodies from coming in contact with one another. These are the prickle cells. As the upper part of this stratum is ap- proached, the cells becom.e flattened, and have an even course. The STRATUM CORNEUM ordinarily forms a thin layer. Its cells are very thin and scale-like, and usually possess no nuclei. They are derived from the cells beneath, but differ from them in consisting of keratin that gives them their hard and horny characteristic. These cells are constantly cast off, and the cells below increase to replace them. Be- tween these two layers an irregular stratum granulosum is often seen. 211 212 THE SKIN AND ITS APPENDAGES. In certain parts of the body, sole and palm, the stratum GRANULOSUM and another, the stratum lucidum, are well developed. The STRATUM GRANULOSUM lies jiist above the stratum Malpighii, and is composed of two or three layers of flattened, spindle-shaped cells that contain a deeply-staining nucleus and coarsely granular protoplasm. The granules are kcra- tohyalin, that, later, form the horny matter of the stratum corneum. These granules are quite large and prominent, and respond well to hematoxylin. They seem to be modified protoplasm, but some hold that they represent products of the degenerating nucleus. The STRATUM LUCiDUM lies just above the stratum granu- losum, and separates this from the stratum corneum. It forms a narrow, glistening band of cells, two or three layers broad, in which the keratohyalin granules have fused to form a homogeneous substance, called the eleidin. This substance reacts well to eosin. The nuclei are not prominent, nor are the cell-bodies distinct. The Derma, True Skin, or Cutis Vera, is composed of connective tissue arranged in two more or less distinctly- separated layers. These are the stratum papillare, or upper, and the stratum reticulars, or lower. The stratum papillare consists of delicate bundles of small white fibrils forming a "close network with elastic fibres. The upper portion of this stratum is thrown into small waves called the papillae, to which the stratum Malpighii conforms. Over the general skin surface, these papillae do not extend through the stratum Malpighii, but in the palmar and plantar regions they are visible externally, and cause the peculiar markings seen in these areas. These papillae are important, as they contain either capillary plexuses, or spe- DERMA. 213 cial sensory nerve endings. The lower portion of the papil- lare consists of a looser network, in which the vessels form plexuses parallel with the surface. It gradually passes into the STRATUM RETICULARE. Fig. 79. — Cross-section of Skin of Sole of Foot. Stratum corneum ; h. stratum lucidum ; c. stratum granulosum ; d. stra- tum Malpighii ; e. derma ; f. panniculus adiposis ; g. duct of sweat gland : h. prickle cells : i. genetic layer ; k. cross-section of a smooth muscle fibre ; I. duct of sweat gland ; m. Pacinian body ; n. secretory portion of sweat gland ; 0. muscle of tubule ; p. blood-vessel ; q. adi- pose tissue. The STRATUM RETICULARE is not distinctly separable from the preceding. It is composed of larger bundles of coarser fibrils of white fibrous tissue, and contains some yellow elas- tic tissue, as will be seen below. Here are found the larger 214 THE SKIN AND ITS APPENDAGES. blood-vessels and the appendages and special sensory nerve endings. In the corium of the scrotum, penis and nipple, smooth muscle fibres are found. When these bundles con- tract, "goose-flesh" is produced. The elastica is often separated into layers, of which there are four, the subepithelial, papillary, reticular and subcutan- eous elastic layers. Beneath the stratum reticulare is usually a layer of adi- pose tissue that separates the skin from the fascia. This is the PANNicuLus ADiPOSUS, and it varies in thickness in the different regions. The color of the skin is due to the presence of pigment granules in the lower layers of the stratum Malpighii. Such granules have been found even in the corium. In the white races, this pigmentation is limited to the nipple and genital region. Whether the pigment is due to the vital activity of the cells, or whether it is brought here and deposited, is not definitely settled. The former seems to be the origin of that of the retinal cells. The skin is the protective organ, and varies in thickness in the different regions. It is thinner on the less exposed sur- faces, as the inner surfaces of the thighs and arms, and thicker on the exposed regions, as back, sole and palm. The blood-vessels of the skin vary in size and number, according to the location ; in the gluteal, plantar and palmar regions, they are greater, whil^in the most movable parts they are most branched. The larger trunks lie in the reticu- lare, parallel to the surface, and form a capillary plexus in the papillare. From this plexus, capillary tufts enter the various papillae. The latter vessels continue as venous cap- illaries, that form a plexus just beneath the papillae. This empties into another in the lower portion of the derma that communicates with a subdermal plexus ; the latter lies be- APPENDAGES. 215 twcen the derma and the panniculus adiposus, and its ves- sels possess valves. The long nerve trunks are found in the reticulare, and from these branches form a suhpapillary plexus. Medul- lated fibres extend towards the surface, and form the special endings. The nerve endings are very numerous in the skin. These comprise the free endings, or those in which the naked axis cylinder pierce the epithelial layer, branch and send these divisions between epithelial cells. The higher forms of end- ings comprise tactile corpuscles of Meissner, most numerous in the palmar and plantar skin of the fingers and toes ; end bulbs of the conjunctiva and gentalia; Pacinian bodies espe- cially in the palms and soles ; and the organs of RufUni, re- sembling the neuro-muscular endings. For a detailed de- scription, see Nerve Endings (p. 82). In addition, there is the usual nerve supply to the blood-vessels. The lymplmtics of the skin consist of superficial, or papil- lary plexus, which receives the lymph from the spaces in the papillae, and a deeper, or subcutaneous plexus that con- sists of larger trunks, that anastomose with the above, and communicate with the special plexuses of the appendages. THE APPENDAGES. The Appendages of the skin are the Hairs, Nails, Se- baceous, Sweat and Mammary Glands. These are all de- rived from the epidermis. THE HAIRS. The Hairs are protective organs limited to certain por- tions of the body. Each consists of a root, that portion with- in the skin, and a shaft, that part seen above the surface. The ROOT is somewhat flask-shaped, the lower end being enlarged to form the iiair-bulb. This, on its under surface, 2l6 THE SKIN AND ITS APPENDAGES. is indented and invaginated by a little mass of connective tissue, the hair papilla, that contains a small tuft of capil- laries, upon which the nourishment of the hair solely de- pends. The root is surrounded by a condensation of the derma, in which the connective tissue bundles are arranged into two layers. Fig. 80. — From Section of Scalp {Stohr's Histology). 1. Hair-shaft ; 2. hair-root ; 3. sebaceous gland ; 4. arrector pili muscle ; 5. root-sheaths ; 6. follicular sheath ; 7. hair-bulb ; 8. papilla ; 9. fat cells. In the outer, the fibres have a longitudinal course, while in the inner, they run circularly. Within this circular layer is a prominent homogeneous band, the glassy membrane. This represents a greatly hypertrophied Z^a^^m^n^ mem- brane. These layers constitute the follicular sheath. Internal to it are found the epithelial cells, which are contin- HAIRS. 217 nous with the epidermis. These are arranged into layers that are the root sheaths, of which there are two, outer and INNER. The OUTER root sheath is the direct continuation of the stratum Malpighii. These cells are the same as elsewhere, and continue to the bottom of the root, where they blend with those of the inner root sheath. Throughout the greater part of the follicle, this layer consists of several rows of cells. Toward the bulb, it gradually becomes reduced to a single layer. The inner root sheath begins at the lower edge of the orifice of the sebaceous gland that opens into the hair fol- licle. Above the duct, it is replaced by the stratum corneum. This sheath consists of two portions, the outer of which is called the layer of Henle. This lies next to the outer root sheath, and is composed of a single layer of flattened cells. Within this lawyer is the sheath, or layer of Huxley, which consists of two or three layers of large irregular cells. In the bulb, all of these layers, including the outer root sheath, are inseparable, and gradually pass over into the hair itself. The Hair occupies the central portion of the follicle, and is composed of three parts, cuticle, cortex and medulla. The cuticle is composed of ai single layer of irregular, nonnucleated scales. These are very thin, and overlap. With- in the follicle, they lie closely applied to the layer of Huxley. The cortex consists of a great many layers of long, spindle- shaped elements. The nuclei are rod-shaped. The me- dulla, when present, is composed of several rows of cu- boidal cells that do not extend the length of the hair. They contain granules of keratohyalin, and frequently have a dark appearance; this is due to the presence of small air- bubbles. 2l8 THE SKIN AND ITS APPENDAGES. The heaviest hairs are found on the scalp and pubis, in the axilla, and upon the face of males. Delicate hairs occur taJl over the body surface, and these are like the lanugo HAIRS of the fetus. The color of the hair is due to pigment granules in the cortex. These cells may even contain pigment in solution. Diffuse pigment is abundant in dark and red hairs, but ab- sent in white. Opening into the hair follicles are the sebaceous glands. This is usually upon the side toward which the hair leans, and here is also seen the muscle of the hair follicle, the arrector pili muscle. This is smooth muscle, and is at- tached above to the derma, just beneath the stratum Mal- pighii, and below to the hair bulb. When it contracts, it causes the hair to ''stand on end." THE NAILS. The Nails are peculiar appendages that serve for the protection of the ends of the fingers and toes, and consist of the ROOT and the nail-body. The ROOT is the proximal end at which the organ grows. Here the epithelial cells are transformed into the hard sub- stance that gives the nail its character. Along the sides, the nail is protected by an overhanging ledge of skin, which constitutes, at the root, the nail-fold^ and at the sides, the NAIL-3YALL. The angle formeS by the nail and wall is the nail-groove. The stratum corneum continues into the angle over the edge of the nail as the eponychium. The NAIL-BODY consists of the nail proper and the nail- bed upon which the nail rests. The nail represents a greatly-hypertrophied stratum lu- cidum. The cells are flattened elements, in which the nuclei are indistinct, and the protoplasm clear. At the proximal end is the root, and at this place alone the nail grows. It is GLANDS. 219 marked by a white area, the lunula. Here the epithelial layer is so thick that the underlying capillaries are invisible. The cells also are said to contain keratohyalin granules. At the distal end, the nail projects as the free edge. The NAIL-BED consists of the stratum Malpighii and the corium. The stratum Malpighii resembles that of the skin surface, and rests upon the papillated corium. That portion beneath the lunula is termed the matrix. The corium is composed of bundles of white fibrous and yellow elastic tis- sues that have a general longitudinal direction. Between Fig. 81. — Cross-section of Nail. 1. Nail; 2. corium; 3. epithelium; 4. nail-wall; 5. nail groove; 6. bone of phalanx ; 7. eponychium. the bundles are vertical fibres that pass from the periosteum towards the nail. The papillae of the bed are not like those of the skin, but consist of long ridges that extend from the root to the end of the nail. They are small beneath the root, but increase in height as the free edge is approached, and end abruptly at that point. THE GLANDS. The Glands comprise the Sweat, Sebaceous and Mam- mary Glands. The Sweat-Glands are of the coiled tubular variety. Each consists of a secretory portion, that lies in the stratum reticu- 220 THE SKIN AND ITS APPENDAGES. lare, and an excretory duct, that passes up through the derma and cuticle to open upon the surface. The SECRETORY PORTION coiisists of a single layer of cu- hoidal cells lining the tubule. These are separated from the basement membrane by a layer of smooth muscle fibres. The protoplasm is granular, and ma-y contain pigment gran- ules and fat globules. The nucleus is usually quite distinct. The secretory tubule is coiled upon itself, and the various convolutions are separated from one another by interstitial tissue that corresponds to the tunica propria. The DUCT that leads from the secretory part to the sur- face has, usually, one-half the diameter of the secretory tubule, and is lined by iwo layers of cells that rest upon a basement membrane and tunica propria. In the epidermis, its course is spiral, and no separate wall is present, the epi- thelial cells of the epidermis acting in this capacity. The diameter of this portion is greater than that of the corium. Its opening upon the surface is large and trumpet-shaped, and is called the sweat-pore. These glands are generally distributed, except on the mar- gins of the lips, glans penis and inner surface of the pre- puce. T hey' a^i"e rhbst numerous in the palm, and largest in the axilla. The average diameter is i mm., but in the latter region, they may attain a size of 3 or 4 mm. In this region, the secretory tubule may be branched. The normal secretion is an oil that keeps the skin soft and pliable. When the innervation becomes disturbed, the se- cretion becomes thin and watery, and is then termed szveat. The GLANDS OF MoLL, of the eyelid, and the ceruminous GLANDS of the external ear, are coiled tubular "glands that secrete oil alone. The Sebaceous Glands are lacemose structures. They are usually found in connection with the hair follicles ; the MAMMARY GLAND. 221 largest hairs possess small glands, while the smallest hairs are appendages of the attached sebaceous glands. Each is surrounded by a capsule of white fibrous tissue that forms the supportive structure. The ALVEOLI are lined by cells that are a continuation of the cells of the stratum Malpighii, and which rest upon a basement membrane and tunica propria. These cells are very large, and completely fill the ailveolus. Those in the center, where the lumen should be, are further advanced in changes than the basal cells. The entire protoplasm^ becomes converted into oil, which constitutes the secretion, and is called SEBUM. The death of the cell is necessary to the formation of this secretion. The transformed cell is imme- diately replaced by another. The excretory duct is lined by several layers of cells that do not ta-ke part in the secre- tory activity, and are derived from the outer root sheath of the hair follicle. Sebaceous glands are found in regions devoid of hairs, as in the margins of the lips, glans penis, prepuce, glans clitoris and labia^ minora. THE MAMMARY GLAND. The Mammary Gland is an alveolo-tubular organ. Ac- cording to some writers, it is a modiUed sweat-gland, while others hold it to be a modified sebaceous structure. It is a compound organ, if such a term may be used, as it is composed of from fifteen to twenty individual compound glands. Eaich of these possesses its own excretory duct, that has its own opening in the nipple. The entire organ is covered by skin. Each gland consists of lobes and lobules separated and supported by white fibrous and adipose tissues. All of the individual glands are further bound together in the same 2.22 THE SKIN AND ITS APPENDAGES. manner. The ducts converge and end in the nipple, which forms a small projecting mass. Each lobule consists of a number of acini, which are tubu- lar or alveolar in structure. The numiber of these depends upon the state of activity. In the gland of pregnancy, the E^li# !;■ PC Fig. 82. — Section op Lactating Human Mammary Gland (Stohr's Histology), a. Alveolo-tubule ; 6. tubule ; c. duct ; d. connective tissue. acini are very numerous, and are lined by simple columnar, or cuhoidal cells, in which are accumulated the fat globules that form the important constituent of the milk. These cells rest upon a basement membrane, but in places are sep- arated therefrom by peculiar elements called basket cells, which are compared to the smooth muscle tissue of the sweat MILK. 223 glands. The ducts are lined by simple columnar cells that rest upon a basement membrane, outside of which circular bundles of white fibrous tissue are to be found. These ducts unite to form the main secretory duct of the individ- ual glands ; each m-ain duct dilates to form a small ampulla, or SINUS LACTIFEROUS, before the nipple is reached. The nonlactating gland consists chiefly of white fibrous and adipose tissues, in which are seen a number of ducts, but few acini. The bulk of the organ consists of the fibrous and adipose tissues. When pregnancy occurs, the ducts divide and redivide, and the terminal portions dilate to form the acini. This increase in the glandular part causes the in- crease in the size of the organ, and the tingling sensation that occurs at that time. After lactation has ceaised, most of the acini undergo retro- gression, atrophy, and disappear. Some of the ducts under- go the same change. As a result, the gland becomes some- what smaller and flabby. In old age, or after the child-bear- ing period bas passed, the glandular and ductular portions retrograde and disappear in the same manner, until, in old age, they may be entirely absent. The glands are then rep- resented by fibrous and adipose tissues. Milk consists of minute globules of fat, o.i to 0.5 mm. in diameter, surrounded by a thin layer of casein. This pre- vents them from coalescing. They are formed in the proto- plasm of the cells of the acini, but the cell, after discharging them, does not die, as formerly supposed. At first, col- ostrum is present in the glands ; this consists of fat and colostrum corpuscles, which are either degenerated gland cells, or leukocytes. The nipple, or mammilla, consists of an outer covering of pigmented skin, and within it the individual ducts are found. These are separated from one another by fibrous 224 THE SKIN AND ITS APPENDAGES. tissue and involuntary nonstriated muscle. The muscle tis- sue is arranged circularly and vertically, extending to the apex of the mammilla. By its contraction, an erection is pro- duced. Such tissue is called false erectile tissue. At the base of the nipple is a pigmented area called the areola, which contains a ring of sebaceous glands called the glands OF MONTGOMMERY. In addition to the general blood-vessels, the various ap- pendages have special supplies. From the suhpapillary ar- terial plexus, branches pass to the hair follicles, to form one plexus beneath the hyalin membrane, and another in the papilla. The venous radicals formed, empty into suhpapil- lary plexus of veins. Around the sebaceous and sweat glands, the subpapilbry arterial plexus forms a close net- work of capillaries, which form venous branches that empty into the suhpapillary venous plexus. The blood-vessels of the mammary gland converge to- wards it, and pass into the organ in the partitions between the lobules. From these vessels, branches extend into the lobules, and form close plexuses around the acini. The appendages are supplied with nerves from both sym- pathetic and cerebro-spinal systems. The hair follicles re- ceive medullated fibres that branch freely, and end in spoon- shaped masses upon the glassy membrane. The sweat-glands are supplied with sympathetic fibres, that form a close net- work beneath the basement membrane, which they pierce, to end upon the gland cells. The mammary gland has both varieties of nerves. The sympathetic are the more numer- ous ; these pass to the blood-vessels on the one hand, and to the acini on the other. In the latter, they form a plexus beneath the basement membrane, and from this plexus, branches end upon the gland cells. The nerve-endings in the nipple are numerous. NERVES OF MAMMARY GLAND. 225 The glands and hair folHcles are surrounded by separate lymplmtic plexuses that empty into the subcutaneous ves- sels. In the mammary gland, plexuses are found between the individual lobes, around the ampullae and in the nipple. These empty into the axillary lymphatics. CHAPTER XVII. THE NERVOUS SYSTEM. The Nervous System consists of the Cerebrum, Cere- bellum, Pons, Medulla and Spinal Cord. It is surrounded by three membranes, the Dura, Arachnoid and Pia. The Dura is a tough membrane composed of interlacing bundles of white fibrous and yellow elastic tissues that con- tain lymph spaces between them. Within the skull, it forms the inner periosteum of the cranium, which relation ceases at the foramen magnum, the entrance into the vertebral canal. In the latter, it is not. connected with the bone, but- hangs like a bag and contains the spinad cord. This mem- brane is lined by endothelial cells, and forms the outer boun- dry of the subdural lymph space. It is quite vascular, and a few nerves, that pass to the blood spaces, are found. The Arachnoid is a thin, delicate membrane made by loosely interwoven bundles of white fibrous tissue. It lies closely applied to the dura, and is separated from the pia by the SUBARACHNOIDEAN LYMPH SPACE. This space is also lined by endothelial cells. It forms the Pacchionian BODIES and villi, but contains neither blood-vessels nor nerves. The Pia is the vascular membrane. Its outer portion contains the bulk of the vessels, while the inner enters into close relation with the nervous tissue. Its blood-vessels lie in the fibro-elaistic network, surrounded by perivascular lymphatics. Its arachnoidean surface is covered by endo- thelial cells. Only a few nerve fibres are present. The pia is the only one of these membranes that follows the fissures and depressions of the nervous system. The Nervous System consists of Gray and White Matter. 226 THE CEREBRUM. 22/ The Gray Matter consists of nerve cells, their proces- ses and NEUROGLIA. The NERVE cells are of various forms, unipolar, bipolar and multipolar. The first possess but one process, the second, tzi^o, and the third, three or more.- The cell-body may be of any shape, and consists of granular protoplasm that has a fibrillar structure. The nucleus is usually large, but does not take a deep stain. The nucleolus is very large, and stains deeply. The PROCESSES are dendritic and axis cylinder. The DENDRITES are minor processes that are subdivided into a great many smaller processes, the tele dendrites. The axis- cylinder process, or neurit, is the main process. In cells of the FIRST TYPE, or Deiter cells, the neurit leaves the gray matter to become the center of a nerve fibre. In those of the SECOND TYPE, or GoLGi CELLS, the axis-cylinder never leaves the gray matter. The NEUROGLIA consists of neuroglia, or glia cells, and a fibrillar intercellular substance. The cells are either spider or mossy. For a detailed description of these, see the chapter on Nervous Tissues (p. 79). The White Matter consists of medullated nerve fibres held together by neuroglia and white fibrous connective tissue. In the Cerebrum and Cerebellum, the Gray Matter is extenml, and constitutes the cortex. The White Matter is internal, and is called the Medulla. In the Spinal Cord, the Gray Matter is surrounded by the White Matter. In the Medulla and Pons, there is no distinct arrangement. CEREBRUM. Beside the Cerebrum, there are other masses of nervous tissue to be considered here. These are the Olfactory Lobes, the Pituitary and Pineal Bodies. 228 THE NERVOUS SYSTEM. The GRAY MATTER, or Cortcx of the Cerebrum, is divided into layers that are not sharply limited from one another. In or-j V 1% \.y. FIG. 83. — Vertical Section of Human Cerebral Cortex. a. Pia mater ; h. molecular layer ; c. small pyramidal cells ; d. large pyra- 'mydal cells; e. layer of polymorphous cells; f. layer Oi. fusiform cells; g. medulla ; In. radial bundles of medullated fibres in cortex ; i. pial process ; fc. large pyramidal cell. some regions, five can be nrade out, in others three, while four form the average number. The Cortex is made irregu- lar by the formation of fissures and convolutions. The THE CEREBRUM. 229 latter consist of a central mass of white matter, Medulla, covered by the gray matter, or cortex. The CORTICAL LAYERS are, from without inward, the MOLECULAR, SMALL PYRAMIDAL, LARGE PYRAMIDAL and MIXED, or POLYMORPHOUS LAYERS. The MOLECULAR layer consists mainly of neuroglia and cell-processes. The latter are derived from the next two layers, and are chiefly dendrites. The neuroglia forms a network within which the dendrites and medullated nerve fibres lie. The latter run parallel to the surface, and are therefore called tangential fibres. Among the cellular elements are some of the second type, or Golgi cells. The nms-cylinders of these cells remain in the gray matter. They are polygonal, stellate and spindle- shaped cells, in which the dendrites run parallel to the sur- face, and are called the cells of Cajal. The LAYER OF SMALL PYRAMIDAL cclls is composcd of Sev- eral layers of cells, the dendrites of which extend into the molecular layer, while some of the axis cylinders partially pass to the molecular layer (second type) and others pass into the medulk) (first type, or Deiter cell). In the latter case, the axis cylinders give off branches called collaterals The CELLS themselves are small, measuring lo to 12 microns in diameter, and triangular in outline. The dendrites arise from the angles, while the axis-cylinder, or neurit, has its origin at the middle of the base. The LAYER OF LARGE PYRAMIDAL Cclls COUStitutCS the widest and most important layer. The cells are usually 20 to 50 microns in diameter, though some may exceed this. The dendrites pass to the molecular layer, while the neurit becomes a medullated nerve fibre. These cells are, therefore, cells of the first type. Their outline is triangular, and the nucleus is large and prominent. 230 THE NERVOUS SYSTEM. The LAYER OF POLYMORPHOUS cells coiitaiiis cells of vari- ous shapes ; these are large and small pyramidal, spindle- shaped, oval and polygonal. The latter predominate. The DENDRITES pass to the upper layers of the cortex, while the AXIS-CYLINDERS, in some instances, remain in the cortex, and in others pass into the medulla. In the last three layers, bundles of medullated nerve fibres, having a radial course, are seen. They begin in the small pyramidal layer, increase in number as they approach the medulla, and contain, beside those fibres derived from the immediate cortical cells, others whose origin is not definite. The Medulla consists of medullated nerve fibres from various sources ; those that pass to the periphery of the body from the pyramidal and polymorphous cells ; others from the pyramidal cells that pass from one hemisphere to the other ; those that connect different areas of the same side (pyra- midal cells), and whose axis cylinders are "T" branched, and pass into the cortex sooner .or later ; lastly, fibres that come from distant parts of the same or the other hemisphere, or other parts of the nervous system. OLFACTORY LOBE. The Olfactory Lobe, that portion of the nervous system devoted to the sense of smell, is comparatively small in mati. There are Uve layers present, which are best marked in the central part of the organ. These are the layer of peripher- al FIBRES, the glomerular layer, the molecular layer, the LAYER OF mitral CELLS and the granule layer. The layer of peripheral fibres consists of a plexus formed by the fibres of the olfactory nerve. The glomerular layer lies beneath the above, and is made up of peculiar round, or oval, bodies 100 to 300 THE PITUITARY BODY. 23 T microns in diameter. They are said to be masses of inter- lacing tclodendria of the olfactory and mitral cells. The MOLECULAR LAYER is made up of large and small spindle-shaped ganglion cells whose dendrites end in the glomeruli, and whose axis-cylinders pass to the fifth, or GRANULAR, LAYER. The LAYER OF MITRAL CELLS consists mainly of large pyramidal cells varying in size from 30 to 50 microns. Their dendrites pass to the glomeruli and the axis-cylinders to the granule layer. The GRANULE LAYER consists of uervc cells and fibres. The cells are stellate ganglion elements, and peculiar gran- ule cells ; the latter appear to have no axis-cylinders. Some of the nerve fibres are derive.d from the mitral cells, some from the molecular layer, and others from the outside. The deeper bundles enclose granule and stellate cells. THE PITUITARY BODY. The Pituitary Body, or Hypophysis, is a small organ consisting of a nervous, or posterior lobe, and an epithel- ial, or ANTERIOR LOBE. Both are surrounded by a common capsule of fibrous tissue. Although the posterior lobe has a nervous origin, its structure, in man, in no way resembles that of the ner\ous system. Fibrous tissue predominates, a'nd the spindle-shaped cells are comparatively few and pigmented. The anterior lobe, however, is divided into a number of tubular alveoli, lined by polygonal epithelial cells. These cells are of two varieties, acidophilic and basophilic ; the latter are the more numerous. These are irregularly arranged so that a small lumen remains. This may contain colloid substance. The nuclei are large and oval. The interstitial tissue in both lobes is quite vascular. 232 THE NERVOUS SYSTEM: THE PINEAL BODY. The Pineal Body, or Epiphysis, is a small, apparently un- important organ in man. In some lower animals, it is a visual organ. This rudimentary structure consists of a number of tubules lined by polygonal cells supported by fibrous tissue and neuroglia in the lower part. These tubules contain the brain sand, or acervulus cerebri, pe- culiar concretions of phosphate and carbonate of magnesium, ammonium and calcium, which are not limited to this body, however, but may be found in other portions of the nervous system. CEREBELLUM. The Cerebellum, or' Little Brain, has a characteristic gross appearance, when sectioned. Its Cortex and Medulla are so colored and arranged as to give the appearance of a TREE, called the arbor vitae, or tree of life. The Cortex consists of three sharply-marked layers, the MOLECULAR, the GANGLIONIC and GRANULE LAYERS, from without inward. The MOLECULAR LAYER consists of a network of neuroglia, in which the dendritic branches of the cells of the lower layers are found. They are mostly those of the ganglionic CELLS. In addition, there are small and large multipolar cells ; the axis cylinders of the former remain in this layer, while those of the latter pass toward the second layer and form a network of branches around the ganglionic cells. They are thereupon called the basket cells. Fibres from the MEDULLA pass into this layer and break into a great number of delicate terminal twigs. The GANGLIONIC LAYER, Or LAYER OF PuRKINJE CELLS, is very characteristic. The bodies of these cells are very big, measuring 30 to 70 microns. A large nucleus and a distinct THE CEREBELLUM, ^?>?> nucleolus are present. The protoplasm is fibrillar, but con- tains no pigment granules. Two main processes extend from the body ; the lower, or neurit, passes to the medulla ...y ^— ' Fig. 84. — Vertical Section of the Human Cerebellum. A. Cerebellum, low power ; B. cerebellum highly magnified ; a. molecular and ganglionic layers ; ft. granule layer ; c. medulla ; d. pia matter ; e. cell of Purkinje ; f. cell of molecular layer ; g. cells of the granule layer ; C. Cell of Purkinje. and becomes a medullated nerve fibre. The upper, or den- dritic, quickly breaks into two, that run at right angles to the main stem. From the upper sides of these two 234 THE NERVOUS SYSTEM. branches, an immense number of small, delicate branches are formed. These cells are called antler cells, from their appearance. The cells are more numerous at the top than at the bottom of the convolutions. The GRANULE LAYER is composed of great and small GRANULE CELLS. The SMALL cells possess large nuclei and a small amount of protoplasm. The dendritic processes re- main mostly in this layer, while the neurit passes to the molecular layer, forming ''T" branches that run parallel to the surface. The larger cells resemble the cells of the ganglionic layer, but the axis-cylinder forms a net- work of branches, being a cell of the second type. Beside the neuroglia present, there are some fibres of the medullated variety. This layer is thicker at the summit of the convolu- tion, and diminishes as the base is reached. The Medulla consists of medullated nerve fibres, support- ed by neuroglia and connective tissue ; of these fibres, some form the inferior peduncles; others the middle ( pontine )y and the remainder the superior peduncles, which connect the cerebellum with the corpora quadrigemina. THE PONS. The Pons has not the definite arrangement of the cere- brum or spinal cord. Its nerve fibres are collected into large bundles, and the gray matter is found in masses called nuclei. It is divided into ventral and dorsal portions. The VENTRAL part is made up chiefly of iransverse fibres that connect the cerebellar hemispheres ; to these are added certain fibres that pass from the cerebral cortex to the me- dulla (anterior pyramids). These transverse fibres are sub- divided into a venlral, or superficial; dorsal, or deep; and middle, or penetrating layers. The pyramidal fibres lie in two groups, one on each side of the midline, as they pass THE MEDULLA. 235 towards the cerebrum from the lower part of the pons, these pyramids becomie separated into numerous bundles by the penetrating transverse, or middle fibres. In the spaces be- tween the fibres, is found gray matter composed of small multipolar ganglion cells. The DORSAL portion of the pons consists of the continua- tion of the dorsal tracts of gray matter, and the formatio reticularis. The latter consists of fibres that form a coarse network in which gray matter is distributed. The upper portion of the fourth ventricle is within the pons. Its floor is covered by a layer of gray matter, and here certain nerves (fifth, sixth, seventh and eighth) have their origin. Here also are found nerve cells whose pig- mentation and grouping make them visible to the naked eye. THE MEDULLA. The Medulla connects the central system with the spinal cord. It resembles the cord more than other portions, and consists of the continuation of its tracts and gray matter, though somewhat dififerently arranged. Most of the motor fibres, as they pass to the spinal cord, dcciissaie, or cross to the opposite side from which they originate. This decussation occurs in the medulla, and is the cause of the derangement of the gray matter, especially of the ventral horns. The GRAY MATTER COUsistS of the VENTRAL and DORSAL HORNS. The decussating fibres, in passing to the opposite side, take an oblique course ; in so doing, they cut the horns of gray matter so that the ventral mass becomes separated from the basal portion. The former is pushed to the side and dorsally, by these fibres, thereby forming the olivary BODIES. This mass of gray matter is now called the lateral NUCLEUS. The BASAL portion of the horns lies as a nucleus 236 THE NERVOUS SYSTEM. by the side of the central canal. The transverse and longi- tudinal fibres entering the medulla form a loose network, the FORMATio RETICULARIS, which is filled with gray matter. The DORSAL columns of white matter (Goll and BuR- dach), increasing in size by the addition of two gray masses, affect the dorsal horns of gray matter, gradually forcing these nearer to the ventral horns. These gray masses re- ferred to are the nucleus gracilis and the nucleus cun- EATUS. It is in these nuclei that the fibres of the dorsal col- umns end. The nerve cells in these nuclei send their axis cylinders to the cerebellum of the same and opposite sides, and to higher portions. The latter fibres constitute the in- ternal ARCUATE FIBRES. They are sensory, and form a second decussation above that of the motor fibres. The in- ternal ARCUATE FIBRES pass to the ccrebrum, and in passing to their destination, have a longitudinal course. The fibres that pass to the cerebellum are seen ventrally in relation to anterior pyramids, and enter into the inferior peduncles of the cerebellum. These form the anterior external arcu- ate FIBRES. Fibres from the posterior funiculi also enter these peduncles, and they constitute the posterior internal FIBRES. The INFERIOR OLIVARY BODY COUtaiuS the DENTATE NU- CLEUS. This consists of an irregular band of gray matter open toward the midline, at which place the fibres enter and leave. These fibres are the olivary peduncles, which pa'ss through the gray matter and then through the restiform bodies to the cerebellum. Near this gray mass are found two other collections of gray matter, the outer dorsal and the INNER (mesial) accessory olivary nuclei. The medulla contains the lower half of the fourth ven- tricle. In the gray matter of its floor, is a collection of ganglion cells, the hypoglossal nucleus, which is the point THE SPINAL CORD. 237 of origin of the hypoglossal nerve. Near this collection, and at first dorsal, then lateral, is a collection constituting the NUCLEUS of the tenth and ninth nerves. The ANTERIOR PYRAMID of the medulla is made up of the fibres of the direct pyramidal tract of the cord, and also some of the fibres from' the cross pyramidal tract. The LATERAL TRACT consists of fibres of the ground bundle, and fibres not included in the direct cerebellar and cross pyramidal tracts. The former enter into the formation of the formatio reticularis, while the sensory -fibres continue to the cerebrum. The RESTIFORM BODIES, Or INFERIOR PEDUNCLES of the cerebellum, contain fibres from the medulla and cord, and some from the pons. The POSTERIOR PYRAMIDAL TRACT is formed by the con- tinuation of the dorsal columns of the cord. THE SPINAL CORD. This portion of the nervous system is the longest. It is characterized by possessing the gray matter internally and the white matter externally. Its form varies in the different regions ; in the cervical and lumbar areas, it is enlarged, and these enlargements are termed the intumescentia cervi- CALis and lumbalis, respectively. The outline in the cer- vical region is oval, in the thoracic region almost circular, and in the lumbar portion oval. The cord ends in the neighborhood of the second lumbar vertebra, and its termination is cone-shaped. This is called the CONUS medullaris. Owing to the fact that the cord is shorter than the vertebral canal, the lower lumbar, the sacral and coccygeal nerves pass down for varying distances be- fore reaching their respective foramina. This produces a mass of fibres, in the lower part of the canal, called the 238 THE NERVOUS SYSTEM. CAUDA EQUINA. In the center of the latter is a fibrous band that extends toward the end of the canal. It is the filum TERMINALE. The Cord consists of two hemispheres separated ve-ntrally by the anterior, or ventral median fissure, in which is seen a process of the pia. Dorsally, no fissure exists, but a septum is present. This is the posterior, or dorsal medi- um SEPTUM, or raphe. The gray matter of the cord is arranged in the form of a letter H, the two side bars constituting the horns, and the cross-bar the gray, or posterior commissure. The horns are further subdivided into ventral, or anterior, and DORSAL, or posterior. The VENTRAL HORNS are large and blunt, and do not ex- tend to the periphery. In them are found collections of lairge, multipolar ganglion cells having a motor function. The axis-cylinders of these cells pass out of the ventral portion of the cord as the ventral root of the spinal NERVE. These cells average 60 to 120 microns, and are quite numerous. Each is surrounded by a distinct lymph space. They are collected into three groups, antero-med- lAN, ANTERO-LATERAL and POSTERO-LATERAL. Those of the ANTERO-MEDiAN group do not cxist in the lumbar region w^hile the postero-lateral cells are present only in those portions of the cord that are well developed. The DORSAL, or posterior horns are sharp amd pointed, and usually extend to the edge of the cord. The cells here are small in number and size, averaging from 15 to 20 mi- crons, and are scattered along the external margin. They comprise marginal cells whose axis cylinders pass into the lateral columns after passing through the substantia gelatin- osa ; spindle-shaped cells, the neurits of which pass into the dorsal columns; stellate cells, the axis cylinders of which pass into the dorsal columns of Burdach. THE SPINAL CORD. 239 II TO Fig. 85. — Cross-section of Human Spinal Cord at Lower Cervical Region. From Decapitated Criminal (Dr. H. H. Cushing). 1. Anterior spinal artery : 2. pial process in ventral fissure : 3. dura ; 4. nerve fibres from ventral horn (motor root fibres) ; 5. stellate cells of ventral Jiorn ; 6. ventral horn : 7. dorsal horn : 8. nerve fibres to dorsal horn (sensory root fibres) : 9. dorsal septum; 10. dor- sal spinal artery and vein (arteria et vena fissurae posterioris) : n. fibres of the column of Goll ; 12. tissue separating the columns of Goll and Purdach : 1.^. column of Burdach ; 14. traces of tLe lateral horn: 15. fibres of the lateral columns: 17. central canal in the gray comm ssure : 18. ventral, or white commissure: 19. fibres of the ventral columns : 20. arteria et vena fissurae anterioris. 240 THE NERVOUS SYSTEM. Along the median edge of the horn, near its junction with the gray commissure, lies a group of cells that expends from the cervical to the mid-lumbar region. This is the vesicular COLUMN OF Clark. A similar collection, though less dis- tinct, is seen in the lower lumbar region, the nucleus of Stilling. The neurits of these cells of the dorsal horns pass into the DORSAL columns; those of the vesicular column of Clark pass into the direct cerebellar tract, on the same side and into the ventral (anterior) commissure. In the dorsal horn is the substantia gelatinosa Rolandi, which consists of cells of the second type (Golgi). The GRAY COMMISSURE consists of medullated and non- medullated commissural fibres separated into ventral (smaller) and dorsal (larger) bands by the central canal of the cord. The ventral portion is called the ventral, or anterior gray COMMISSURE, while the other receives the name of dorsal, or posterior gray commissure. The whole is the GRAY, or posterior commissure, in contradistinction to the anterior, or white commissure. The CANAL of the cord is the remains of the embryonal cavity within this portion of the nervous system. In child- hood, it is lined by simple ciliated elements, the ependymal CELLS. Above, it communicates with the fourth ventricle, and its form varies in the different portions of the cord. It becomes more or less obliterated with increasing age, par- tially by increased growth of the lining ependymal cells and partially by the ingrowth of neurogliar processes. Besides the nerve cells, processes and fibres, the gray matter contains that peculiar supportive tissue found only in the nervous system, called neuroglia. This substance is ectodermal in origin. THE SPINAL CORD. 24I Neuroglia consists of two varieties of cells, spider and MOSSY. The spider cells are composed of thin, flat bodies from which extend large slender processes. The mossy cells have short, heavy processes. In addition to these, there are some cells that possess large bodies and few pro- cesses. Fibres that, apparently, have no connection with any cell, are seen passing over or under cell bodies. These processes all interlace to form a network for the support of the nerve cells and their processes. This substance is the SUBSTANTIA SPONGIOSA. Around the central canal of the cord, the substantia spongiosis becomes more modified, and is called the substantia gelatinosa centralis. The net- work is much closer in this region. Around the dorsal horns, it forms a homogeneous, striated mass, in which a few nerve cells are found. This is the substantia gelatinosa Ro- LANDI. The WHITE MATTER cousists of mcdullatcd nerve fibres, connective tissue, and neuroglia. Spider cells are especially numerous here. The nerve fibres possess no neurilemma, and are grouped into columns. Ventrally, they aire separated by the fissure, and dorsally, by the septum, into the hemi- spheres. Ventrally, they are connected by a band of white matter that lies between the bottom of the fissure and the gray commissure. This is the white, or ventral (anter- ior) commissure. The motor fibres are usually large, meas- uring 15 to 20 microns in diameter. The sensory are smaller. The columns are as follows : The ventro-medium columns that lie between the ventro- median fissure and the ventral roots of the spinal nerves ; the LATERAL, that lie between the ventral and dorsal roots, and are subdivided into antero-lateral, or those ventral to the transverse midline, and the postero-lateral, or those q 242 THE NERVOUS SYSTEM. behind the same line. The dorso-median columns that lie between the septum and the dorsal roots of the spinal nerves. These areas are further subdivided into individual columns. In the VENTRO-MEDiAN region, there are several groups, the DIRECT PYRAMIDAL TRACT (Turck). This is a uarrow band of fibres that lies along the fissure, and represents the non- decussating fibres from the motor regions of the brain. The remainder of this region constitutes the anterior ground BUNDLE. Along the periphery of the ventro-lateral region is a narrow column called the tract of Gower, or the ascend- ing antero-lateral tract. Next to the gray matter in the entire lateral region is the mixed lateral column; this contains both motor and sensory fibres. Between these two lies the descending antero-lateral columiu, or lateral GROUND bundle. In the postero-lateral region, along the periphery, is the DIRECT cerebellar tract. This is composed of fibres derived from the vesicular columns of Clark. Just within this is the large crossed pyramidal tract, which consists of the motor fibres that decussated in the medulla. Just in front of the dorsal roots is a smiaill tract, made up of fibres from the posterior roots, the bundle of Lissauer. The dorso-median region consists of two columns, the column of Burdach, funiculus cuneatus, and the col- umn OF GOLL, FUNICULUS GRACILIS. The COLUMN OF BUR- dach lies next to the gray matter of the dorsal horn, and is the outer of the columns. The column of Goll lies along the septum, and usually does not extend in to the gray commis- sure. These columns consist of sensory fibres that pass up to the brain, and also of short fibres that connect the various segments of the cord. Capping the dorsal root is a collection of nerve fibres from the lateral part of the dorsal root. This THE SPINAL CORD. 243 is the COLUMN of Lissauer. The cells of these fibres all lie in the spinal ganglia, and the fibres pass to the higher levels of the cord. The SPINAL NERVES consist of VENTRAL, OT MOTOR, and DORSAL, or SENSORY ROOTS. Before these unite to form the nerve, a mass of gray matter is seen upon the dorsal root. This is the spinal ganglion. The fibres of the dorsal root are derived from the cells that lie in the ganglia, and where they enter the cord, a distinct depression is noted. The ven- tral ROOT is made up of fibres derived from the cells in the ventral horn, and where they emerge, only a slight incurving of the surface is seen. The circulaiion of the nervous system is carried on chiefly by the vessels in the pia. In the cerebrum, the vessels of the cortex enter vertically, and form a close plexus of capil- laries most plentiful where the cells are. Those intended for the medulla are larger, and, passing through the cortex, form capillary networks between the fibres and parallel to them. In the CEREBELLUM, the capillaries are few in the outer portion of the molecular layer, but in the granule layer and around the cells of Purkinje, close meshes are formed. In the spinal cord, there are two sets of vessels, those that enter at all points of the periphery and supply chiefly the white matter, and those derived from the artery lying in the ventro-median fissure ; the latter set goes to the gray matter. The smaller peripheral vessels remain in the white matter, and run parallel to the fibres, while the larger pene- trate the gray matter and supply the outer part. The artery in the fissure sends branches into the gray commissure; these divide right and left, and form dense plexuses in the gray substance. 244 THE NERVOUS SYSTEM. The blood is collected by venous radicals that have the same general course. The SUBARACHNOIDEAN LYMPH SPACE continues as the PERIVASCULAR LYMPHATICS that accompauy the blood- vessels. CHAPTER XVIII. THE EYEBALL AND LACRIMAL SYSTEM. The Eyeball is one of the most important organs of the special senses. It is composed of three coats, and contains FOUR REFRACTIVE MEDIA. The COATS are the External, or Corneo-scleral ; the Middle, or Choroid, Ciliary Body and Iris ; and the Internal, or Retina. The REFRACTIVE MEDIA are the cornea, the aqueous and VITREOUS HUMORS and the lens. Of these, the cornea and lens alone are of importance. The Corneo-sclera is the protective and transparent coat of the eyeball. The Sclera constitutes about five-sixths of this coat. It is composed of coarse bundles of white fibrous tissue that interlace to form a dense, tough coat. These bundles are arranged chiefly longitudinally and transversely. Between the bundles are spaces that contain large, stellate cells. These spaces communicate with the lymph spaces within the cornea. On its external surface, the sclera is in relation with the CAPSULE OF Tenon, and, anteriorly, the conjunctiva. To it are attached the ocular muscles. Between the sclera and choroid is ai lymph space called the SUBSCLERAL SPACE. Here the tissue is loosely arranged and lined by endothelial cells. At the entrance of the optic nerve, the sclera is pierced by the nerve fibres so as to form a sieve-like area, the lamina cribrosa. Pigmentation oc- curs here, as well as at the corneo-scleral junction. Its pres- ence in the subscleral tissue gives rise to the lamina fusca. The Cornea is a specialized portion of the sclera modified for the transmission of light. It consists of five layers : 245 246 THE EYEBALL AND LACRIMAL SYSTEM. ANTERIOR EPITHELIUM,, ANTERIOR LIMITING MEMBRANE, SUBSTANTIA PROPRIA, POSTERIOR LIMITING MEMBRANE, and, POSTERIOR ENDOTHELIUM. The ANTERIOR EPITHELIUM is a Continuation of the epi- thehum of the conjunctiva. This is of the stratified squam- ous variety, and the tunica propria beneath is not papilla ted. The layers of cells are more numerous at the corneo-scleral junction thao in the center. The basal cells are long and columnar, and possess processes that extend into the an- terior elastic lamina, while the external cells are squamous. The middle layers are prickle-cells, and the spaces between are lymph channels. The ANTERIOR ELASTIC LAMINA, Or BOWMANS MEM- BRANE, is a clear, prominent bamd serving as a basement membrane to the epithelial cells. Although called elastic, it does not consi'st of elastic tissue. It is thickest in the center, and becomes thinner as the junction is approached, where it disappears entirely. The SUBSTANTIA PROPRIA forms the bulk of the cornea, and consists of a number of layers (about sixty) of white fibrous tissue arranged parallel to one another. It is due to this arrangement that this organ is transparent. In addi- tion to these fibres, there are others that penetrate the organ at a right angle to the layers, and bind all together. These are the perforating fibres. Between the various layers are a large number of irregular spaces called the corneal la- cunae. These contain large stellate cells that are the origi- nal connective tissue cells of the organ. They are the cor- neal CORPUSCLES. The spaces communicate with one an- other by means of little canals called canaliculi, into which their processes extend. These spaces are readily shown by the gold chlorid method of staining. The POSTERIOR LIMITING MEMBRANE, Or MEMBRANE OF Descemet, is analagous to the anterior membrane; unlike THE CHOROII). 247 this one, however, it is thicker peripherally than centrally; and seems more independent of the substantia propria than the anterior. It docs not respond to the clastica stain, and, consequently, is not made up of elastic tissue, as its name would seem to indicate. It becomes the pectinate ligament. The ENDOTHELIAL LAYER cousists of a single layer of well- defined regular cells, which cover the posterior surface of this organ, and continues over the anterior surface of the iris. These cells are hexagonal, and possess a fibrillar pro- toplasm that seems to extend through several layers. The cornea possesses blood-vessels during the develop- mental period ; these, however, disappear before birth, so that none are then present. Lymph, which circulates through the many spaces and canaliculi, nourishes the cornea. The sclera possesses but few vessels, and these are found chiefly at the corneo-scleral junction, where a circular net- work is formed. The nerves are sensory; at the corneo-scleral junction, a circular plexus is formed, from which fibres pass into the substantia propria, while others penetrate the anterior elastic lamina to pass into the epithelial layer. Some of these fibres extend almost to the surface. The Middle Coat, or tunic, also called the Uveal Tract, is the vascular coat. It contains the main vessels of the eyeball, except the central artery of the retina, and consists of the Choroid, Ciliary Body and Iris. The Choroid is the vascular portion, and is divided into three layers, the stroma layer, the chorio-capillaris, and the glassy membrane. The stroma layer is sometimes referred to as the layer of large vessels, as they are found only in this portion. It consists, externally, of delicate fibres that connect with those of the subscleral tissue and form a complete space the supra- 248 THE EYEBALL AND LACRIMAL SYSTEM. CHOROIDAL, or SUBSCLERAL LYMPH SPACE. Ill this tisSUe are found pigmented connective tissue cells, and it has re- ceived the name of lamina suprachroidea. The main por- tion of the stroma layer consists of bundles that are closely arranged. The network formed by these are the venous trunks, externally, and the arterial trunks, internally ; the latter are accompanied by bundles of muscle tissue. Pig- mented cells exist between the bundles. «— ES Fig. 86. — CoRNEO- Scleral Junction of Man. 1. Epithelium ; 2. connective tissue of conjunctiva ; 3. sclera ; 4, 5, 6, 7 and 8. ciliary body ; 4. meridional ; 5. radial ; 6. circular fibres of ciliary muscle ; 7. ciliary process ; 8. pars ciliaris retinae ; 9. pars iridica retinae ; 10. stroma of iris ; 11. posterior elastic lamina of cornea : 12. substantia propria : 13. epithelium : 14. canal of Schlemm ; 15. angle of iris, or infiltration angle {Stohr's Histology). The inner portion of this layer is called the boundary zone; the bundles are arranged into several layers in herb ivorous animals, so as to give a peculiar metallic reflex, and is called the tapetum fibrosum. This area is usually free from pigment cells. In the carnivorous animals, the fibres are replaced by distinct cells that contain crystals. The metallic reflex, however, is the same. This constitutes the tapetum cellulosum. CILIARY BODY AND PROCESSES. 249 The CHORio-CAPiLLARis coiitaiiis little stroma, and is com- posed chiefly of a dense capillary plexus. No pigment cells are seen. The capillaries are most numerous around the macula latea. The GLASSY MEMBRANE lies at the inner boundary of the choroid, and consists of refractile homogeneous tissue. It is a very thick basement membrane, and supports the pig- mented cells of the retina. The choroid extends to the ora serrata, a peculiar, ser- rated line, at which the nervous portion of the retina ceases. At this point, the choroid continues as the Ciliary Body. The Ciliary Body is composed of three main portions, the Ciliary Ring, the Ciliary Process and the Ciliary Muscle. It is thicker than the choroid, which is due espe- cially to the addition of the muscle tissue. The Ciliary Ring is practically the continuation of the stroma layer of the choroid and the boundary membrane, and consists of dense white fibrous tissue, which forms a circular band about 4 mm. in breadth. The vessels have a longi- tudinal course. The Ciliary Processes are projections of the stroma, cov- ered by pigmented epithelial cells, from 60 to 80 in number. They arise at the junction with the choroid, and extend toward the iris, increasing in height, ending abruptly at that point. At this place, they are about i mm. in height. Each process consists of a core of stroma (connective tissue) supporting blood-vessels and covered by the pigmented epi- thelial cells of the retina, the pars ciliaris retinae. These cells rest upon a continuation of the glassy membrane. There are two layers, the outer of which consists of low columnar or cuboidal elements that are the continuation of the true pigmented cells of the retina. The inner layer is composed of cells that are columnar, possess little or no pigment, and are the representative of the optical portion of the retina. 250 THE EYEBALL AND LACRIMAL SYSTEM. The Ciliary Muscle is of the nonstriated variety, and Hes external to the ciHary ring, just beneath the sclera. The fibres are arranged in meridional, radial and circular sets. The meridional are the outermost, and extend from the canal of Schlemm, in the corneo-scleral junction, to the ciliary ring. These are the tensor muscles of the choroid. The radial fibres, which compose the middle layer, extend peripherally, and, spreading fan-like, are inserted into the ciliary ring and processes. The circular fibres are the inner ones, and their direction is equatorial. They consti- tute Muller's ring-muscle. The ciliary region is indicated, externally, by a band about one-fourth of an inch broad, starting at the corneo-scleral junction. It is called the danger zone of the eyeball, as in- juries here usually result fatally to sight. The Iris is the continuation of the stroma layer and glassy membrane of the choroid. It receives, also, the posterior lamina and the endothelium of the cornea, and consists of the anterior endothelium, stroma layer, posterior lam- ina and PIGMENT layers. The anterior endothelium is a continuation of that of the cornea, and covers the anterior surface of the iris. The cells are neither so regular nor distinct as those of the cornea. The STROMA LAYER is composcd chiefly of a coarse net- work of white fibrous tissue, some of which is circularly ar- ranged around the blood-vessels, which possess no muscular coat. Anteriorly, this stroma is very much reticulated, and forms a support for the endothelial cells. According to some authors, this portion constitutes an anterior limiiing mem- brane. In the stroma layer, pigment cells are found in vary- ing quantities ; in gray eyes, very few are seen ; as the color passes to blue, brown and black, the number increases, the last possessing the most. In albino eyes, not only are the THE CORNEO-SCLERAL JUNCTION. 25I pigmented connective cells of the stroma layer absent, but the pigment that is usually present in the posterior epithelial cells continued from the retina, is also absent. As a result of this, the retinal blood-vessels cause a peculiar red reflex, the retinal reflex. In the other eyes the pigment obscures it. In the stroma, is found muscle tissue of the involuntary non-striated variety. This is arranged circularly and RADIALLY. The CIRCULAR fibres are near the anterior part of the iris, and contract the pupil, when stimulated ; these form the SPHINCTER pupillae muscle. The radial fibres lie near the posterior part, and when they contract, the pupil is di- lated ; they constitute the dilator pupillae muscle. The posterior limiting membrane, or membrane of Bruch, is a continuation of the glassy membrane. It sup- ports the pigmented cells, the pars iridica retinae. The pigmented layer, a continuation of the pars ciliar- is retinae, and called the pars iridica retinae, is usually pigmented, and consists of two layers of cells. It continues to the anterior margin of the pupil. The PUPIL is the aperture in the iris. Its size is regulated, autom.atically, by the amount of light entering. The Corneo-scleral junction is the region in which cornea, sclera, ciliary body and iris come together. The sclera passes over into the cornea, but the line of transition is not abrupt, but gradual, and forms an oblique line that extends from before, backward and inward. Beneath the posterior margin, usually within the sclera, is a circular canal, the canal of Schlemm, which extends around the corneo-scleral junction. In this region, the membrane of Descemet is seen to divide into a large number of fibres that extend to the base of the iris. Between the fibres are a large number of intercommunicating spaces called the SPACES OF FoNTANA. Thcsc spaccs lie around the angle 252 THE EYEBALL AND LACRIMAL SYSTEM. formed by the cornea and iris, called the infiltration ANGLE, and communicate with the anterior chamber and thi: canal of Schlemm. The network is called the pectinate LIGAMENT, and is lined by endothelial cells. THE RETINA. The Retina forms the internal, or nervous, coat of the eyeball. It may be divided into two portions, the pars OPTICA, that portion capable of vision, and the pars ceca, or the blind part, possessing no nervous elements. The latter portion is further subdivided into pars ciliaris and pars Fig. 87. — Vertical Section op Retina op a Rabbit {Stdhr's Histology). 1. Pigment layer ; 2. rods and cones ; 3. external limiting membrane ; 4. outer granule layer ; 5. outer reticular layer ; 6. inner granule layer ; 7. inner reticular layer ; 8. ganglion-cell layer ; 9. nerve fibre layer ; 10. inner limiting membrane ; a. expanded base of a Mtiller fibre ; h. nucleated portion of same. IRIDICA RETINAE. The simplest division of the retina, how- ever, is PARS OPTICA, PARS CILIARIS and pars IRIDICA RETINAE. The PARS OPTICA lines almost the entire optic cup, and ex • tends forw^ard to the end of the choroid. Here the nervous portion ceases, and the coat becomes abruptly thinner, and forms an irregular serrated line, the ora serrata. From this point, the last two portions of the retina continue. THE RETINA. 253 The Optical portion consists of eleven layers, counting the pigmented layer. These layers are classed as neuro-epi- THELIAL and CEREBRAL. The NEURO-EPITHELIAL pOrtion consists of the first five layers within the pigment layer, and the CEREBRAL portion the remaining divisions. The pig- mented part is derived from the outer layer of the optic cup, and the the other parts from the inner layer. Optic Vesicle. Retinal Layer. Classes. Outer Layer. Pigmented Layer PIGMENT LAYER. /Layer of rods and cones. j External limiting membrane NEURO-EPITHELIAL I Outer granular layer. LAYER. ] Henle's fibre layer. T T / Outer RETICULAR (molecular) Inner Layer \ \ ' ] Outer ganglionic (inner granule). /Inner reticular (molecular). CEREBRAL. I Inner ganglionic. \ Nerve fibres. ^Internal limiting membrane. The PIGMENT LAYER consists of polyhedral cells contain- ing a black, granular, mobile pigment. The position occu- pied by this pigment depends upon the presence or absence of the light. The nonpigmented nuclei occupy the basal por- tion of the cell. These cells continue over the ciliary body and iris as the pars ciliaris and iridica retinae. In the iris, both layers are pigmented, but not in the ciliary region. This layer is derived from the outer layer of the optic cup. The nervous structures are supported by neuroglia, of which a great deal is present, and unevenly distributed. The LAYER OF RODS AND CONES is the most important por- tion of the retina. The CONES consist of cell-body and cone-fibre. The (iELL-BODY is about 30 microns in length, and is divided into 254 THE EYEBALL AND LACRIMAL SYSTEM. two segments, cuter and inner. The outer is conical, may be striated, rests upon the Hmiting membrane, and is ap- parently composed of discs. The inner segment is striated and flask-shaped. At its junction with the outer segment, it is granular, and the other part is fibrillar. The cone-fibre ends in the outer reticular layer, and has a nucleus near its junction with the body. The RODS are longer than the cones, averaging about 50 microns. They have, somewhat, the same structure as the preceding and are alm.ost uniform in size. The different seg- ments react differently to stains. The outer segment pos- sesses prominent cross and faint longitudinal striations. In this portion of the cell, the rhodopsin, or visual purple, is located. The ij'iner segment is spindle-shaped, granu- lar, and fibrillar like the above. The rod-Hhres terminate in the outer reticular layer, where they are enlarged. The nuclei lie in the outer granular layer. They may be ir- regularly placed, and in lower animals, may even be striated. Usually, three or four rods are seen to each cone. In the central portion of the yellow spot, the cones alone are present. The EXTERNAL LIMITING MEMBRANE COUsistS of the OUtcr ends of the fibres of Miiller. These run radia-lly, and ex- tend through almost the entire thickness of the retina. The outer ends of these fibres are enlarged, and lie so close to- gether that they form a membrane, the outer limiting MEMBRANE. Thcsc fibres do not penetrate the rod and cone layer, but give branches to all of the other layers. Each fibre possesses a nucleus that lies in the inner nuclear layer. At their internal ends, they are again enlarged, and form the INTERNAL LIMITING MEMBRANE. GHa cclls are also present. The OUTER GRANULE, or NUCLEAR LAYER consists of sev- eral layers of oval nuclei, which are the granules. These are TPIE RETINA. 255 the nuclei of the rod and cone-fibres. The former are the more numerous. Henle's fibre layer is best developed in the macular region, from which area it diminishes peripherally. It is made up of the inner segments of the rod and cone-fibres. The OUTER MOLECULAR, Or RETICULAR LAYER is COmpOScd of the inner ends of the rod and cone cells, which are branched, and fibrillar, and proceed from the inner nuclear layer. A y^ Y Fig. 88. — Cells from Retina of an Ape (Stohr's Histology). 1. Cell of ganglion of optic nerve. 2. Cells of inner granule layer. 3. Rod- cells : a. outer segment ; b. inner segment : A:, rod-granule ; x. fibre- apparatus. Below are rod-cells and fragments, 4. Cone-visual cells ; a. outer segment; i. inner segment: k. cone-granule; f. cone-fibre; X. fibre apparatus. 5. Radial fibre, Miiller's fibre : k. nucleus ; r. pyra- midal base. The INNER GRANULAR, or OUTER GANGLIONIC/ LAYER is made up of several varieties of closely packed cells, the most numerous of which are oval, bipolar elements. These are placed vertically, and the smiall amount of protoplasm present continues as an inner process that passes to the inner molecular layer ; here it breaks into many branches that form a network around the ganglion cells. The outer process of these oval cells surround the ends of the rod-fibres in the form of a delicate rete, or mesh of fibrillae. Other cell- processes pass to the cone-fibres and to the inner molecular layer. 256 THE EYEBALL AND LACRIMAL SYSTEM. Another kind of cell is present, the amakrine cell, which forms a layer near the inner boundary of this nuclear layer. These cells possess no axis-cylinders, but other processes extend into the inner molecular layer. A third variety possesses a cell-body, the long diameter of which lies parallel to the surface of the retina. The pro- cesses pass into the outer molecular layer. Some connect with the rod-fibres ; these are larger, and lie internally, while the others that pass to the cone-fibres are smialler, and have an external position. In addition to the above, there are some cells present in this layer that send their axis cylinders into the optic nerve. The nuclei of Miiller's fibres lie in this layer. The INNER RETICULAR, Or MOLECULAR, LAYER COUsistS of fibrils of cells of the preceding layer and from cells of the inner ganglionic layers. The fibres lie at dififerent levels, which gives them a striated appearance. The GANGLIONIC (inner) layer is composed of a single layer of multipolar ganglion cells. The cell-bodies are flask- shaped, .and the axis cylinders pass into the layers of nerve fibres. The dendritic processes extend into the inner mole- cular layer at different levels, and, supposedly, do not com- municate with those of other cells. In the region of the macula lutea, these cells become increased in number, form- ing, often, eight layers. The LAYER OF nerve fibres is the expanded optic nerve. These fibres pierce all the layers, except the internal limit- ing membrane. They enter the eyeball through the cribri- form LAMINA of the sclera, ^t which point the medullary sheaths are lost, and when the layer of nerve fibres is reached, these nonmedullated fibres diverge. As most of the fibres pass from the ganglion cells toward the brain, it would be better to say that they converge at the optic nerve THE OPTIC NERVE. 257 entrance, where the layer of nerve fiijres is thickest, and decreases as the ora serrata is approached. The INTERNAL LIMITING MEMBRANE is formed by the fusion of the inner ends of Miiller's fibres. There are three important areas in the retina, i. the optic NERVE ENTRANCE, OPTIC PAPILLA, or BLIND SPOT, 2, the MA- CULA LUTEA, or YELLOW SPOT, and, 3, the ora serrata. 1. In the BLIND spot, only the layer of nerve fibres is pres- ent. It lies about one-eighth of an inch to the nasal side, and about one-tenth of an inch below the optic axis. In the center is usually -a shallow depression ; around the edge, it is raised, and forms the papilla nervi optica. 2. The YELLOW SPOT is in the direct visual axis. The color is due to the presence of a diffuse yellow pigment. Its edge is raised, owing to the great thickness of the inner ganglion- ic layer. From the edge to the center, all the layers de- crease and disappear, so that in the center, the fovea cen- tralis, the cones alone are pt^es^nt. H^re vision is most acnte. 3. At the ORA SERRATA, all of the nervous layers end ab- ruptly, and are continued as a single layer of cuboidal or columnar cells. Beyond this point, there is no vision. The light rays falling upon the retina are not transmitted to the brain by a direct route. The impressions are received by the rods and cones, which send impulses to the cells of the outer reticular layer; these cells communicate with the ganglion cells, and the impulses are carried to the brain by the axis-cylinders of these cells, as they form the optic nerve. The Optic Nerve consists of a single bundle of nerve fibres that possess no neurilemma. It is surrounded by the dura, arachnoid, and pia, continued from the brain. The lymph spaces included within these, communicate with those of the eyeball. The dura and pia pass over into the sclera. 258 THE EYEBALL AND LACRIMAL SYSTEM. but the arachnoid, as such, is lost before this occurs ; as a result, the two lymph spaces between these three layers be- come one. The nerve fibres penetrate the sclera through the LAMINA CRiBROSA. As they pass through this coat, they lose the medullary sheath, so that they become nonmedullated fibres when they enter the retina. VITREOUS BODY AND LENS. Of the REFRACTIVE MEDIA of the eyeball, the Vitreous and Aqueous Humors and the Lens are yet to be described. The Vitreous Humor, or Body, occupies the optic cup, or VITREOUS CHAMBER. This body consists of a fine limiting membrane, the hyaloid membrane, a delicate homogene- ous structure enclosing the substance of the organ, which is composed of about 98 per cent water and 2 per cent, solid elements. The latter comprise connective tissues and wan- dering cell, and some fibrils. This organ is traversed by a small canal, called the canal OF Stilling, or hyaloid canal. This extends from the optic nerve to the lens, and in intra-uterine life is occupied by a branch of the retinal artery, the hyaloid artery, that passes to the lens. The Aqueous Humor is practically lymph. It occupies the anterior and posterior chambers, and as a refractive medium, is unimportant. The Crystalline Lens is a solid body, and the most im- portant refractive medium of the eyeball. It possesses two curvatures, of which the anterior is the greater. It lies in a depression of the vitreous humor, called the patellar fossa, and is held in position by the suspensory ligaments. The LENS consists of a capsule, within which lies the Jens substance. The capsule is composed of delicate white fibrous tissue, and to it are attached the ligaments. This is thicker anteriorly, and seems composed of layers. THE CHAMBERS OF THE EYEBALL. 259 The SUBSTANCE OF THE LENS is of epithelial origin, and consists of LENS FIBRES that are greatly elongated cells. Upon the anterior surface, just beneath the capsule, is a single layer of cuboidal cells called the lens epithelium. At the equator of the lens, these cells lengthen, forming the LENS FIBRES, which are hexagonal, nucleated structures. The nuclei are large and oval, and lie near the middle of the fibres. Peripherally, the fibres are harder than those of the center. The Suspensory Ligament of the lens is really a con- tinuation of the hyaloid membrane, and is composed of a large number of fibres that pass from, the anterior and poster- ior layers of the capsule. Those from the anterior layer pass into the depressions between the ciliary processes, while those from' the posterior layer are attached to the summits of the proce^sses. Between these two layers of fibres is a small space, the canal of Petit. This region constitutes the ZONE OF ZiNN. The Chambers of the eyeball are Anterior, Posterior and Vitreous. The Anterior lies between the iris and cornea the Posterior between the lens and vitreous humor, and the Vitreous is occupied by the vitreous body. These are large lymph spaces, and are connected with one another, and with the other spaces of the eyeball. The circulation of the eyeball is carried on by the central ARTERY OF THE RETINA, the LONG and SHORT POSTERIOR and the ANTERIOR CILIARY ARTERIES. The RETINAL ARTERY passcs into the eyeball through the center of the optic nerve, and forms a zi^horl of branches upon its entrance. These vessels extend to the ora serrata. The layer of rods and cones and the macula lutea possess no blood-vessels. The blood is collected by venous stems, which form the central vein of the retina that has a course parallel to the artery. 26o Cornea. THE EYEBALL AND LACRIMAL SYSTEM. ^: 'i^'J'l^JX-^j^ ^ Anterior ciliary artery. ^^ Anterior ciliary vein. o connection with circulus ' major. y Connection with chorio-capillaris. d Arterial episcleral branches. 8' Venous episcleral branches. ^ Arterial conjunctival branches. £ Venous conjunctival branches. ^ Arterial branches to corneal junction. ^y Venous branches to corneal junction. V Venae vorticosae. S Venous sinus of sclera. Fig. 89. — ^Vessels of the Eye. External tunic, stippled ; middle tunic, white ; internal tunic and optic nerve, stippled criss-cross ; arteries, light ; veins, dark. Central vessels of retina : a. artery ; a', vein ; b, c, d. anastomoses wth vessels of sheath, short posterior ciliary arteries and choroidal ves- sels, respectively. A, Inner, B, outer sheath vessels ; i. short posterior ciliary artery ; i'. vein ; II. episcleral artery ; II'. veins ; III. capillaries of chorio-capillaris. 1. long posterior ciliary artery : 2. circulus iridicus major ; 3. branches to ciliary body; 4. to iris {StOhr's Histology), THE CIRCULATION OF THE EYEBALL. 261 The SHORT POSTERIOR CILIARY arteries are about twenty in number. They pierce the sclera near the entrance of the optic nerve, and pass into the choroid. As they pass through the sclera, they give off branches that supply the posterior half of this coat. In the choroid, these vessels form the chorio-capillaris. Their branches anastomose with branches of all others, including those of the central artery of the retina. The LONG POSTERIOR CILIARY arteries pierce the sclera near the optic nerve, and pass to the ciliary region between the choroid and sclera. At the base of the iris, they form a circle of vessels, the circulus arteriosus iridicus MAjOR^, which sends branches to the ciliary processes, the choroid and the iris ; the latter branches pass to the pupillary region, where they form the circulus iridicus minor. The ANTERIOR ciliary arteries are derived from the ves- sels of the recti muscles. These penetrate the sclera near the corneo-scleral junction. Their branches nourish the an- terior half of the sclera, the conjunctiva, the ciliary muscle, and the anterior half of the choroid; they connect with the circulus iridicus major, and form a network of capillaries at the corneo-scleral junction. Around the optic nerve, there is some anastomosis between the branches of the ciliary arteries. The blood is returned by the venae vorticosae, which are four to six in number. These run a course entirely different from that of the arteries. Each is formed by a whorl of veins, and passes through the sclera to empty into the oph • thalmic veins. The blood from the anterior ciliary arteries is carried by the anterior ciliary veins that run parallel to the arteries. These also receive the blood from the episcleral spaces. The lymphatics are extensive, and form a series of inter- communicating spaces. 262 THE EYEBALL AND LACRIMAL SYSTEM. Anteriorly, the spaces in the cornea communicate with those of the sclera, and with the canal of Schlemm and the anterior chamber, by means of the spaces of Fontana. The ANTERIOR CHAMBER communicatcs with the posterior chamber, and through this, with the canal of Petit. Posteriorly, the lymphatics of the optic nerve communi- cate with the subarachnoidean space, on the one hand, and the hyaloid canal and perivascular spaces of the retina, on the other. The space of Tenon lies external to the sclera, and re- ceives lymph from the subscleral space, directly, and by way of the channels around the venae vorticosae; the lymph is sent to the spaces around the optic nerve. The latter communicate with those of the central nervous system. The nerves, long and short ciliary, supply the choroid and pass between it and the sclera; at the ciliary body, they form the ciliary ganglion plexus, that supplies the ciliary muscle, iris and cornea and vessels. Those of the iris form a circular plexus. The nerves of the cornea have been considered. THE APPENDAGES OF THE EYEBALL. The Appendages are the Eyelids, Conjunctiva and the Caruncle. The Eyelid consists of a double fold of skin, the under surface of which has become modified to form a mucous MEMBRANE. This is the conjunctiva, which is composed of stratified columnar cells that rest upon a basement mem- brane and tunica propria. Among the epithelial cells, some goblet cells are seen. Over its greater extent, the conjunc- tiva is smooth, but toward the region opposite to the free edge, folds are formed. Beneath the tunica propria, is found a dense plate of white fibrous tissue called the tarsal plate (incorrectly called THE EYELID. 263 cartilage). This is wedge-shaped, with its thicker edge at the marg-in of the Hd. It extends a Httle over one-half the Fig. 90. — Sagittal Section of Eyelid of a Child Six Months Old {Stohr^s Histology). 1. Skin : E. epidermis ; C. derma ; 8c. subcutaneous tissue ; Hb. lanugo hairs ; K. sweat-glands ; W. eyelash ; Eh. developing lash ; W, W". portions of follicle of eyelashes ; M. portion of a ciliary gland. 2. Or- bicularis palpebrarum muscle ; O. transverse section of same ; McR. tarsal muscle. 3. Tendon of levator palpebrarum superior ; mps. superior levator muscle. 4. Conjunctival portion; e. epithelium; tp. tunica propria ; at. accessory tear gland ; *. tarsus ; m. tarsal gland (Meibomian) ; a. arcus tarseus externus ; 5. margin of eyelid. height of the lid, and at its end, an accessory tear gland is found, the gland of Krause. It contains a number of 264 THE EYEBALL AND LACRIMAL SYSTEM. compound racemose glands y the ducts of which open upon the free margin. These are the Meiboml\n, or tarsal, GLANDS, and number about thirty in the upper, and a few less in the lower, lid. They resemble sebaceous glands, and the ducts are lined by stratified squamous cells. At the margin of the lid, mmscle fibres .are seen to surround the ducts. These glands secrete an oily substance that lubricates the edges of the lids, prevents them from uniting, and ordi- narily keeps the tears from overflowing. Between the tarsal plate and the upper skin surface, is found the subcutaneous fibrous tissue. In this layer is the muscle of the eyelid, which is chiefly of the voluntary variety, although some smooth muscle is present. Some voluntary muscle fibres are found between the cilia and Meibomian gland ; these constitute the marginal muscle. In the tarsal connective tissue are found smooth muscle fibres constituting the lid-muscle of Mueller. The SKIN covers the outer surface. Its structure is the same as in other places, and it contains many sebaceous and sweat-glands and fine hairs. Pigmented cells are found in the corium. Very little fat is found in the loose subcutan- eous tissue. At the edge of the lid, are seen two rows of heavy hairs, the CILIA, or eyelashes. They pass deeply into the corium, and last about four months. Between the cilia and the ducts of the Meibomian glands, are some coiled tubular structures called the glands of Moll. These are ceruminous glands, and resemble those of the external ear. Their ducts, at times, are seen to open into the follicles of the cilia. The skin at the conjunctival margin forms an acute angle, while above the ciliary region, the angle is obtuse. This serves to distinguish these two margins. The Conjunctiva lines the under surface of the eyelid, and is then reflected over the eyeball from the insertion of the THE LACRIMAL APPARATUS. 265 muscles to the cornea. Here the stratified cells alone con- tinue upon this organ. It consists of stratified columnar cells, basement membrane and tunica propria. In the latter, lymphoid tissue is often present in abundance. At the inner angle, or canthus^ of the lids is seen, in lower animals, a third eyelid. This is called the plica SEMILUNARIS, Or MEMBRANA NICTITANS. In lowcr foHTlS, a distinct tarsal plate is present, which is seldom present in man. Here it is usually a small fold, covered by stratified squamous cells, in which some glands may be found. The Caruncle is a little patch of skin at the inner canthus. It contains hair follicles, sweat-glands, adipose and muscular tissues within its corium, and is covered by stratified squam- ous cells. A little voluntary striated and some smooth muscle tissue are present. Within the eyelid, tmo arterial arches are formed, one at the upper edge of the tarsus, the external, and the other at the edge of the lid, the internal. These arches are pro- duced by the vessels coming from the inner and outer canthi. The smaller branches pass to the glands and conjunctiva of the lid, where they form delicate plexuses. The lymphatics form a close, delicate plexus beneath the conjunctiva, and a loose set at the upper margin of the lid, that communicate with each other. The branches of the lat- ter possess valves. The nerves give off branches to the muscles and skin, and then form a plexus beneath the conjunctiva. The latter supplies the glands, cilia and conjuncti'va, forming, in the latter, a subepithelial plexus .and special endings, such as CONJUNCTIVAL CORPUSCLES and END-BULBS. THE LACRIMAL APPARATUS. The Lacrimal Apparatus consists of the Lacrimal Gland, the Canaliculi, the Lacrimal Sac and the Naso- lacrimal Duct. 266 THE EYEBALL AND LACRIMAL SYSTEM. The Lacrimal Gland is a compound tubular organ of a serous character. . Like the mammary gland, it is a com- pjDund gland, as it is composed of six or seven individual glands merely bound into one mass. Each has its own duct that opens upon the conjunctival surface. Each Gland is covered by a delicate capsule of white fibrous tissue that divides it into lobes and lobules. The LOBULES consist of the tubular acini, which are lined by simple cuhoidal cells. The protoplasm of these is granular, and the nuclei have a basal position. These cells rest upon a basement membrane, which is suported by interstitial con- nective tissue of a fibro-elastic nature. The ducts are lined by simple columnar cells. The blood-vessels are numerous, and form close capillary plexuses around the tubular acini. The nerves form a subepithelial plexus, but the exact mode of ending is not known. Each Canaliculus has a lining of stratified squamous cells that rest upon the tunica propria and fibro-elastic layer. Out- side of the tunica propria is seen some voluntary striated muscle, chiefly longitudinally arranged. The opening of the canaliculus is called the puncta, and at this point, some of the muscle fibres are circularly disposed, forming sphincter muscles. The Sac and Duct are lined by stratified columnar cells. In the tunica propria, considerable diffuse adenoid tissue is found. Occasionally, in the lower end of the duct, cilia\ted epithelial cells are present. Within the orbit, the eyeball is surrounded by a serous membrane called the capsule of Tenon. The space enclosed is the space of Tenon, or the episcleral lymph space. This space aids in the movement of the eyeball. CHAPTER XIX. THE EAR. The Ear is made up of three parts, the External, Middle and Internal. The EXTERNAL EAR receives the sound waves and conducts them to the middle ear. The vibrations of the drum are carried across the middle ear and conducted into the in- ternal EAR, where they are translated into the proper im- pressions. The External Ear consists of the Pinna and a short Canal, the External Auditory Canal. The Pinna is covered, upon both sides, by skin, and, in its center, possesses a mass of elastic cartilage. It is very irregular, but adapted to catch sound waves. The skin possesses hair follicles and sebaceous glands. The lobe, the lower soft portion, contains no cartilage, and is very vas- cular. The External Auditory Canal consists of outer, car- tilaginous and inner, bony portions. The outer part is lined by skin, in the corium of which are found cerumin- ous GLANDS. Thcsc are coiled tubular organs that form the wax. Hairs are very abundant here. In the inner, or osseous, portion, hairs and glands are absent, and the tunica propria is closely attached to the periosteum of the bone. The Tympanic Membrane, or Drum, separates the middle from the external ear. Externally, it is covered by stratified squamous cells continued from the skin. In this location, the stratum corneum is nucleated, and the corium is thin, except in the region of the handle of the malleus. The middle portion consists of white fibrous tissues arranged as radial, or external, and circular, or internal fibres. 267 268 THE EAR. The former becomes thinner toward the center of the tympanum and disappears entirely. The circular fibres are more numerous externally, and become thinner toward the handle of the malleus, where they disappear. Between these two layers, is a small amount of loose connective tis- sue. Peripherally, the fibrous layer becomes thickened to form the annulus fibrosus. The internal surface is cov- ered by simple squamioiis, or columnar, cells that rest upon a basement membrane. In the flaccid area of the drum, the middle layer is absent, so that the internal and external lay- ers touch each other. The Middle Ear, or Tympanum, is an irregular cavity within the bone, and is connected with the pharynx by the Eustachian Tube. This maintains an equal pressure upon both sides of the membrane. The mucous membrane lining these portions is covered by pseudo stratified ciliated epi- thelium. The cilia are absent upon the ear bones, liga- ments and MEMBRANA TYMPANi. Small mucous glands are found in the tunica propria. The antrum and mastoid CELLS are lined by low polygonal cells. The Ear Bones are the malleus, incus and stapes. These are small masses of osseous tissue, by means of which the sound waves are transmitted from the drum to the in- ternal ear. In the thickest portions, they possess Haversian systems. Their articular surfaces are covered by hyalin cartilage. The stapes alone possess a marrow cavity. The MEMBRANE clo'sing the fenestra rotunda, that leads to the internal ear, consists of connective tissue. Its middle ear surface is covered by nonciliated cells, while that which lies in the internal ear is covered by endothelial cells. The OSSEOUS portion of the Eustachian tube is lined by a thin mucous membrane that is closely adherent to the periosteum. The lining cells are pseiido-stratiiied ciliated THE INTERNAL EAR. 269 elements. Glands are absent. In the cartilaginous por- tion, the mucosa is thicker, and is lined by straiiHed ciliated cells, among which there are a large number of goblet cells. In the tunica propria, mucous glands and diffuse lymphoid tissue are seen, and the latter may be formed into solitary follicles near the pharyngeal end. The hlood supply to the tympanic membrane is important. Its external surface is supplied by capillaries derived from the vessels of the external canal, while the inner surface receives vessels from those of the middle ear. The mucosa of the Eustachian tube receives blood from both the middle ear and pharyngeal vessels. Lymphatic vessels follow those of the circulatory system.. Those of the external surface of the membrana tympani empty into those of the external canal, while those of the inner surface empty into those of the tympanum. The latter lie in the deeper portions of the tunica propria, and, at intervals, possess dilatations. The nerves of the external surface of the tympanic mem- brane are derived from the auriculo-temporal ; in addition to these, fibres enter at the edge. Both form a close plexus. This supplies the external surface by a subepithelial plexus. The inner surface is supplied by the tympanic plexus, which sends branches to the epithelial layer. Occasionally, minute ganglia are present. The Eustachian tube receives fibres from the tympanic, as well as from the pharyngeal plexuses. THE INTERNAL EAR. The Internal Ear, or Labyrinth, consists oi Sacculus, Utriculus, Semicircular Canals and Cochlea. The Labyrinth consists of the osseous and membran- ous portions, which are separated from each other by a 270 THE EAR. lymph space. The bony labyrinth surrounds the mem- branous portion, and is separated from it by the perilymph. Within the membranous part is the endolymph. SACCULUS AND UTRICULUS. ' The Sacculus and Utriculus are two cavities of unequal size, which do not communicate with each other directly, but with the ductus endolymphaticus by two small canals. The Sacculus is the smaller, and lies anterior to the utricu- lus. The Utriculus is connected to the semi-circular canals, while the sacculus communicates with the cochlear portion of the membranous labyrinth, by means of the ductus re- uniens. The bony walls are covered by periosteum, which is lined by a layer of endothelial cells continued over the trabeculae, that extend from the periosteum to the membranous laby- rinth. From this point, the endothelium continues over the external surface. The walls of the saccule and utricle are composed of bundles of white fibrous tissue arranged into two layers of variable thickness, 5 to 15 microns. The thickest portions are where the nerve fibres enter the maculae acusticae and maculae cribrosae. The cells lining these vesicles consist of simple polygonal epithelium, 3 to 4 microns in height, except over the maculae acusticae, where they are of the neuro-epithelial variety. Upon approaching these areas, the polygonal change to cuhoidal and become progressively higher until a height of 30 microns is reached. These cells are of two varieties, sustentacular, or supportive, and SPECIAL, NEURO-EPITHELIAL, Or HAIR-CELLS. The susTENTACULAR cclls are very long, irregular col- umns, the basal portions of which are branched. The large nuclei, located at various levels in the inner half of the cell. THE SEMICIRCULAR CANALS. 27I produce a bulging of the cell-body. The granular proto- plasm possesses pigment granules of a yellowish color. The special^ or hair-cells, are also columnar, but not as long as the preceding, and extend through only one-half of that layer. The basal portion of these cells is broad, and contains large, round nucleus. The distal end is rounded, and possesses a cuticular border, the cupola, from which projects a conical cilium 120 microns long. This ex- tends into the endolymph. Closer examination shows that the cilium consists of many finer hairs. The protoplasm of these cells is granular, and contains a yellowish pigment. The Otoliths are small, prismatic calcium carbonate crys- tals, I to 15 microns long, occurring in the vesicles, and im- bedded in a gelatinous substance, the otolith membrane, that covers the neuro-epithelial cells. This otolith mcfii- hrane contains many of these prisms. The Ductus Endolymphaticus and its dilated extremity, the Sacculus, have the same structure as saccule and utricle. A plexus of nerve fibres is found benea.th the neuro-epi- thelium. The fibres extend into the epithelial layer, and as they pierce the basement membrane, the medullary sheath blends therewith, and leaves the axis cylinder free. These latter form fibrillae that pass to the neuro-epithelial (hair) cells ; some pass higher between the supportive cells. In these areas, the capillary plexuses are especially numerous. THE SEMICIRCULAR CANALS. The Membranous Semicircular Canals are united to the periosteum by trabeculae, as in the preceding, and the endothelial ceils pursue the same course in this lymph space. The epithelium resembles that of the saccule and utricle, being polygonal, but slightly larger, varying from 2^2. THE EAR. 12 to i6 microns. Specialized areas, cristas acusticae, are found in the floor of the ampullae (dilated portions at the junctions of the canals). Here the thickened fibrous wall forms the transverse septum. The specialized areas resemble those of the saccule and utricle. The hairs of the neuro-epithelial cells are unusually long*, some reaching to the middle of the lumen. They are called the auditory HAIRS, and arise from the cupola of the cdls. The nerve fibres pass to the thick transverse septum, and form a plexus from which finer fibres follow the same course as in the saccule and utricle. The blood-vessels are distributed in the same manner. THE COCHLEA. The Cochlea consists of a spiral bony canal that winds around the central, vertical axis, or modiolis. The bony canal is separa.ted into an upper, the scala vestibuli, and a lower, the SCALA tympani. These divisions are further separated by a central shelf of bone called the lamina spir- alis. This extends about half of the way across, and the BASILAR MEMBRANE Completes the partition. At the upper end of the cochlea, these canals communicate with each other; both contain the perilymph. The Ductus Cochlearis, or Scala Media, is a delicate, triangular canal that lies in the scala vestibuli; its outer basal angle is attached, externally, to the outer wall, and the inner ang^le, internally, to the lamina spiralis. It contains the endolymph, and has an important epitheHal lining. The BASILAR MEMBRANE Separates it from the scala tympani. and the membrane of Reissner from the scala vestibuli. The latter membrane is quite thin, about 3 microns, and extends from the lamina spiralis (internal to the crista) to the bony wall of the scala vestibuli at an angle of about 45 THE COCHLEA. nz degrees Upon its VESTIBULAR WALL, it is covered by a layer of pigmented endothelial cells which rest upon the middle connective tissue layer, in which capillaries are found. The epithelial lining of its inner surface consists of a single layer of polygonal cells. The outer wall of the scala media, for about two-thirds of its distance from the upper angle, is covered by ciihoidal cells, within which there are quite a Fig. 91. — Horizontal Section through Petrous Bone of a Kitten {Stohr's Histology), 1. Ganglion spirale ; 2. macula ; 3. ganglion vestibulare : 4. meatus acus- ticus internus; o. vestibular, and 6. cochlear divisions, respectively, of the acoustic nerve ; 7. scala tympani ; 8. scala vestibuli ; 9. bone ; 10. modiolus. number of capillaries, a very unusual conditian. This is the stria vascularis. At the lower margin of the latter is a small projection, the prominentia spiralis; this, with the lower part of the outer wall, is covered by flattened cells that become columnar as the basilar membrane is reached. The tissue external to these cells is quite thick, and extends over the vestibular wall above the attachment of Reissner's. 274 THE EAR. membrane, and below the attachment of the basilar mem- brane. This is the ligamentum spirals. At the attach- ment of the basilar membrane, this ligament forms a pro- jection called the crista basilaris. The FLOOR of the ductus cochlearis (tympanic side) con- f g Fig. 92. — Scheme of the Structure of the Tympanic Wall of the Duct of the Cochlea {Stdhr^s Histology), A. Side view ; B. surface view. a. auditory teeth ; b. epitlielium of sulcus spiralis ; c. inner hair cells ; d. inner head plates ; e. outer head plates ; f. phalanges ; g. outer hair cells ; h. cells of Hensen ; i. cells of Claudius. 1. Nerve ; 2. first spiral cord ; 3. inner pillar cells ; 4. vas spirale ; 5. tunnel ; 6. outer pillar cells ; 7. Nuel's spaces ; 8. Deiter's cells ; 9. membrana bisilaris ; 10. tympanal lamella. sists of the basilar membrane that unites the spiral promi- nence to the spiral lamina; this is completed by the ltmbus that extends from the end of the spiral lamina to the attach- ment of Reissner's membrane. The outer portion of the limbus is thicker near the mem- brane, due to an increase in the periosteum. This portion THE ORGAN OF CORTI. 275 contains clefts and depressions that deepen toward the inner half, at which point the cleft is quite deep, and little projec- tions, separated by lateral clefts, give rise to the auditory TEETH, which number about 2,500. These teeth and pro- jecting areas are covered by simple polygonal cells, while the CLEFTS are lined by columnar elements. The inner half of the LiMBUS consists of a slightly projecting mass, the SUPERIOR LIP, due to the sudden decrease in thickness, and a lower portion that continues over the bony lamina toward the basilar membrane ; the latter is the inferior lip. Be- tween these, lies a little space, the sulcus spiralis, due to the sudden decrease in thickness of the periosteum. The sulcus is lined by flat cells. The BASILAR MEMBRANE is covcrcd, on its tympanic sur- face, by the tympanic lamella, made up of spindle-shaped cells and delicate fibres, representing an incomplete change to endothelial cells. This is continuous with the periosteum of the scala tympani. Above this layer is the membrana propria, that represents a greatly hypertrophied basement membrane and seems to support the epithelium upon its upper surface. The outer end of the basilar membrane is covered by the cells of Claudius that continue toward the outer wall and pass into the columnar and flattened elements that are found upon the basilar crest. These cells possess spherical nuclei embedded in a slightly granular and pig- mented protoplasm; they represent a continuation of the CELLS OF Hensen. Between the limbus and the cells of Claudius, lies the organ of Corti, composed of neuro-epi- thelial and sustentacular cells. This organ is divided into an inner portion, the membrana tectoria, and an outer part, the zona pectinata. The CELLS of the Organ of Corti are the pillar, hair and sustentacular cells. 276 THE EAR. The PILLAR CELLS are peculiar, S-shaped elements pos- sessing a striated body, surrounded by a narrow band of protoplasm. The latter is thickened at the base (tunnel side), and in this part is seen the nucleus. The lower end rests upon the basilar membrane, and is expanded to form \ P Fig. 93. — Cokti's Organ, x Tunnel of Corti traversed by nerve fibres {St6hr's Histology). a. Labium vestibulare ; 6. sulcus spiralis ; c. membrana tectoria ; d. inner hair cells ; e. outer hair cells ; /. cells of Hensen : g. cells of Claudius ; h. capillaries of stria ; i. nerve bundle ; k. labium tympanicum : I. in- ner pillar cells : ni. outer pillar cells ; n. cells of Deiter ; o. membrane basilaris ; p. tympanal lamella. the FOOT ; the upper end likewise undergoes an expansion, termed the head. These cells form two rows, inner and outer; they articulate above, and form a triangular canal called CoRTi's tunnel. This contains a semi-solid inter- cellular substance. The inner cell, being shorter, is more THE ORGAN OF CORTI. 2/7 nearly vertical, and its head bears an articular surface for the reception of the articular head of the outer cell. The inner cells are more numerous and thinner than the outer, about 3,850 to 3,600, respectively. The head process of both cells continues externally as a thin, shelf-like process called the head plate. Of these, the inner head plates lie above, but are shorter than the outer. The outer are called the phlangeal processes, and by their union with the cells OF Deiter, form the membrana reticularis. The NEURO-EPiTHELiAL CELLS are distributed upon the inner and outer surfaces of the pillar cells. They are the HAIR CELLS, and of these there are two rows, inner and OUTER. Like the hair cells of the preceding, and the neuro- epithelial cells of the nasal mucous membrane, they are about half the length of the sustentacular, or pillar cells, and are columnar elements containing a granular protoplasm and an oval nucleus. The outer end has a cuticular border, from which about twenty hairs extend. The outer cells are longer and narrower than the inner, and more numerous. Usually, one hair cell is present for each two pillar cells. The outer hair cells are found in three or four rows, which are sep- arated by the ends or phalanges of Deiter's cells and the membrana reticularis. The inner row rests upon the outer pillar cells ; the cells of the next row lie opposite to the rods, and the third row alternates, producing a peculiar checker- board appearance, the ends of the hair cells being separated from one another by the ends of the Deiter cells. The SUSTENTACULAR, or Deiter, cells are internal and EXTERNAL. Each ccll consists of a thin pyramidal process and a large basal part that contains the nucleus. The in- tercellular SPACES OF NuEL, between the cells of the organ of Corti, contain a substance like that in the tunnel of Corti. Internally, Deiter's cells pass through the entire layer, and are continuous with the cells of the sulcus. Externally, 278 THE EAR. they form the phalanges that help produce the membrana reticularis. A surface view will show both sustentacular and neuro-epithelium ; a basal view, however, will show only sustentacular elements. Just external to the Deiter cells are other sustentacular elements, the cells of Hensen. These extend to and continue with those of Claudius. Extending over the organ of Corti, and arising from the upper lip of the limbus, is a membrane composed of delicate fibres and interfibrillar substance. This is the membrana tectoria^ or CoRTi's MEMBRANE. ^At One time, this was part of the cells beneath, those of the sulcus and auditory teeth; it represents a cuticular border. The branches of the auditory nerve are vestibular and cochlear. The vestibular supplies the sacculus, utriculus, maculae and the semicircular canals (cristae). The coch- lear branch passes to the cochlea, and is made up as follows : In a little bony canal in the lamina spirale is a strip of gray matter that is called the ganglion spirale. This con- sists of bipolar cells, one branch of which passes outward into the organ of Corti, while the other, the axis-cylinder, passes through a minute canal in the axis to the central canal, where it meets other fibres from different levels. These pass to the base and to the internal auditory meatus, as the COCHLEAR BRANCH, and then to the medulla. The dendritic branches of these ganglion cells form a plexus in the minute canal of the spiral s'helf. Toward the organ of Corti, the lamina is pierced by many canals called the for- amina NERVOSA, through which numerous fibres pass, along its inner epithelium, to the organ of Corti. Upon entering these canals, the medullary sheaths and neurilemmae are lost, and the naked axis-cylinders, in bundles, continue. Each bundle separates into two, one of which remains at the inner surface, and the other passes along the outer side of the pillar cells. The latter lies in the tunnel. Other fibres cross THE CIRCULATION OF THE EAR. 279 the tunnel and pass to the outer side of the outer pillar cells and form several bundles between the Deiter cells. From these, various bundles, fibrillae end upon the hair cells. The blood-vessels follow the nerves, those of the utriculus and sacculus follow the vestibular branch, and those of the cochlea the cochlear division. After giving off branches to the first turn, the main trunk enters the canal of the axis, from which the branches form the peculiar glomeruli COCHLEAE. Branches of the latter penetrate the scala vesti- buli, and supply the limbus and neighboring tissues. Other branches continue over the vestibule to the ligamentum spirale, the stria vasculare, and basillar membrane surround- ing the scala vestibuli. The veins -surround the scala tym- pani and form a trunk below the spiral ganglion. CHAPTER XX. THE SENSES OF SMELL, TASTE AND TOUCH. THE ORGAN OF SMELL. The Nasal Mucosa is divided into respiratory and ol- factory portions. The lowF^r portion of the respiratory area, called the vestibule^ is lined by stratified squamous cells to the inferior turbinate bone. Here a great many hairs, sebaceous and mucous glands that extend for a short distance, are encountered. Above the turbinate, the epithel- ium is of the stratified ciliated variety, and many goblet cells are present. The tunica propria contains much adenoid tis- sue and a large venous plexus. Mucous and serous glands are also present in great numbers in the region of the inferior turbinate and nasal septum. The mucosa is 4 mm. thick in this area. The OLFACTORY mucosa is usually prominent on account of its yellow color, but this does not indicate the entire ol- factory membrane. It is very thick, and ciliated cells no longer exist. The epithelium is of the neuro-epithelial var- iety, and two kinds are present, the sustentacular and NERVOUS elements. The SUSTENTACULAR cells are irregular, and possess an OUTER SEGMENT which is Cylindrical, and an inner that is narrow and irregular. The outer segments form a row of columnar elements. The oval nuclei form a regular band or row. The protoplasm contains granules and pigment near the inner end, the former being arranged in rows. A cuticular border is present, and forms the membrana lim- 280 THE NASAL MUCOSA. 281 ITANS OLFACTORiA. The inner segments are irregular, and usually branch at their internal ends. The NERVOUS ELEMENTS, GT neuro-epithelial cells proper, consist of a peculiar, inconspicuous strips of protoplasm pos- sessing an enlargement near the middle, in which lies a large, round nucleus. The latter form a band or zone of spherical elements. The outer end-s of the rods extend to the free surface, between the supportive cells, while the inner ends pass to the basement membrane. Pig. 94. — Diagram of Olfactory Mucosa. a. Sustentacular cells ; &. neuro-epithelial elements ; c. basal cells ; d, base- ment membrane. The BASAL cells are small and irregular elements that send processes between the upper layers and, internally, rest upon the basement membrane. The tunica propria consists of a loose network of fibro- elastic tissue. This supports the mucous (Bowman's) glands, whose functionating epithelium possesses a brownish pigment. These glands are numerous, forming a continuous layer. The Accessory Cavities possess a lining of ciliated cells. The mucosa is very thin, .02 mm., and it is firmly attached to the perio'Steum. Glands are very few in the mucosa of these cavities. 282 THE SENSE OF SMELL. The blood-vessels are numerous. The arterial branches form a dense subepitheHal plexus, including a network around the glands. The veins are large in number and size, especially upon the inferior turbinate. The lymphatics lie in the lower part of the tunica propria ; in the olfactory area, an extra set of vessels occurs in the superficial portion. These communicate with the channels around the nerves. fis Fig. 95. — Isolated Elements of the Olfactory Mucosa. a. Neuro-epltlielial cell ; &. sustentacular cells showing cuticular border. The nerves are those of ordinary and special sensation. The former are derived from the trigeminus, and do not pass to the cells. The tatter are derived from the olfactory nerve. The fibres of the olfactory nerve are nonmedullated, and are sent from branches that lie between the mucosa and the bony wall. These pass to the epithelial layer, and are sur- rounded by perineural lymphatic sheaths. When the epi- thelium is approached, the fibres break into ultimate fibrillae that pass directly to the neuro-epithelial cells. The central ends of these fibres are in relation with the glomerular cells of the olfactorv lobe. THE SENSE OF TASTE. 283 THE SENSE OF TASTE. The Sense of Taste is clue to the Taste-buds. These are not restricted to the circitmvallate papillae of the tongue, but are found in the papillae foliatae, in the posterior surface of the epiglottis, at times in the fungiform papillae and in the soft palate and uvula. The organs are barrel-shaped, and consist of two varieties of cells, the sustentacular and the neuro-epithelial. The sustentacular cells are the outer, and are com- posed of a cell-body and a pointed end. The latter, with its 2, __;.., ~;a;vC-l- Fig. 96. — Taste-bud from a Papilla Foliata of a Rabbit. 1. Epithelium ; 2. tunica propria ; a. taste-bud ; b. gustatory hairs ; c. gustatory pore. neighbors, forms an opening at the exposed end of the organ called the gustatory pore. The cell-body varies in its thick- ness and the enlargement may be central or proximal. In this enlargement is seen, the large nucleus. The NEURO-EPITHELIAL elements are peculiar, long, spindle-shaped cells possessing a nuclear enlargement. This is more pronounced than that of the preceding. The peri- pheral end of each cell is continued as a hair-like projection through the gustatory pore; this projection is the gustatory HAIR. The GLOSSO-PHARYNGEAL NERVE forms a plexus in the tunica propria, and from this, a subepithelial plexus arises. 284 THE SENSE OF TOUCH. From the latter, fibres pass to the taste-buds, some to enter and others to surround this Httle organ. Those that enter, surround the gustatory cells in a deHcate plexus, and end as little enlargements upon the cells. The other fibres form branches in the epithelium between the taste-buds, termi- nating in end-bulbs. THE SENSE OF TOUCH. The Sense of Touch is not limited to any special region, but it is best developed in certain areas, as the palm and SOLE. It is restricted to the skin, and represents a modifi- FiG. 97. — Corpuscle of Meissner from Great Toe of Man. n. Medullatea nerve Gbre ; n. connective tissue sheath ; e. varicosities. The nuclei are invisible {Stohr^s Histology). cation of general sensibility. In the papillae of the skin, especially that of the sole and palm, are found the tactile CORPUSCLES OF MeISSNER. These are elongated structures, about 50 by 150 microns, and possess transverse striations that seem due to cells with transversely placed nuclei. These are encapsulated by white fibrous tissue, and are pierced, at the lower end, by nerve fibres whose medullary sheaths blend with the capsule. The axis cylinders run spirally, branch within the organ and in- PACINIAN BODIES. 285 terlace. These branches are irregular, and possess enlarge- ments, at intervals. The corpuscles of Vater, or Pacinian bodies, are very large, oval structures. Each consists of a capsule, an inneu BULB and an end-knob. The CAPSULE consists of many layers of white fibrous tis- sue, each separated from its neighbor by a lymph space lined Fig. 98. — Pacinian Body from Mesentery op a Cat. 1. Fat cells ; 2. artery ; 3. nerve fibre ; 4. inner bulb ; 5. axis-cylinder ; 6. layers of the capsule {Stohr's Histology). by endothelial cells. These lamellae are held together by an INTRA-CAPSULAR LIGAMENT that pierces all. The inner- bulb is a cylindric mass of almost homogeneous protoplasm possessing nuclei. Through this, the axis cylinder passes to terminate in a slight enlargement called the end-knob. The conjunctival corpuscles, or corpuscle of Krause, are also tactile corpuscles. These are surrounded by a deli- cate fibrous capsule, which is surrounded and lined by 286 THE SENSE OF TOUCH. endothelium. The center of the corpuscle seems occupied by the divisions of the axis cylinder that passes to it, and by lymph. Such corpuscles are found in the conjunctiva, edges of the eyelids, in the lips, epiglottis, and in the glans penis and glans clitoris. The GENITAL CORPUSCLES are more complex than the pre- ceding. They may resemble the Pacinian body, or may be composed of several simple corpuscles fused into one. INDEX. A. Accessory cavities, 281 Acervulus cerebri, 232 Achromatic spindle, 35 Achromatin, 30 Acid cells, 14, 119 Acidophil, see Eosinophil Acrosome, 173 Adamantoblasts, 107 Adelomorphous cells, 118 Adenoid tissue, 59 Adipose tissue, 58 Adrenal, 166 Adventitia of artery, 90 of vein, 94 Agminated follicles, 60, 126 Air-sacs, 149 Albumen, Mayer's, 25 Alcohol for clearing, absolute and ether, 8 for fixation, absolute, 4 absolute and ether, 5 absolute and formalin, 5 ninety-five per cent., 4 Alimentary tract, 106 Allantois, 201 Alum carmin, 15 Alvei, 147 Alveolar ducts, 148 membrane, no Alveoli of lungs, 149 Alveolo-tubular glands, 50 Amakrine cell, 256 Ameboid motion of leukocytes, 96 Amelioblasts, 107 Amitosis, 33 Ammion, false, 200 true, 205 Ammiotic cavity, 199 folds, 200 Amphipyrenin, 30 Ampullae capillary, 92 of ear, 272 of oviduct, 188 of spleen, 103 Amyloid bodies, 175 Anabolism, 31 Anaphase, 36 Anastomoses, 93 Angle of infiltration, 252 Angles, leaden, 7 Anilin oil-xylol, 20 Anisotropic disc, ^2 Annuli fibrosi, 88 Annulus fibrosus, 268 Antrum of follicle, 183 Appendix, follicles of, 128 glands of, 128 occlusion of, 129 Aqueous humor, 258 287 Arantii, corpus, 89 Arachnoid, 226 Arcuate fibres of the cornea, 246 of the pons, 236 Arcus tarseus externus, 265 internus, 265 Area of Langerhans, 134 Areola, 224 Areolar tissue, 58 Arrectores pilorum, 218 Arteries, large, 91 medium, 90 small, 92 Astrosphere, 30 Atria, 149 Attraction sphere, 30 Auditory cells, 2Tj hairs, 2^^ nerve, 278 ossicles, 268 teethj 275 Auerbach, plexus of, 130 Axial fibre, 173 Axis-cylinder, 78 Axilemma, 80 B. Basal border, 128 Balsam, 20 Basement membrane, 46 Basic stains, 12 Basilar membrane, 2T2 Basket cells, 22,2 Basophil, 97 Belly-stalk, 201 Bensley's solution, 3 Benzol, 7, 20 Berlin blue. 22 Bertini, columns of, 157 Bile capillaries, 133 Biondi-Heidenhain stain, 16 Bipolar cells, 79 Bismark brown, 13 Bladder, 163 Blastodermic vesicle, 39 Blastula, 39, 198 Blind spot, 257 Blocking, 7 Blood cells of, erythroblasts, 25, 95, 102 erythrocytes, 94 leukocytes, 96 platelets, 25, 97 crystals, 98 films, 23 fixation, 5 hemoglobin, 98 platelets, 25, 97 technic, fixation, 2^ spreads, 23 stains, 2^, 24 288 INDEX. Blood-forming organs carotid gland, 99 coccygeal gland, 99 marrow, 67 Blood-vessels arteries, 90 capillaries, 92 heart, 89 nerves of, 94 veins, 93 Bone canaliculi, dy cells, 64 compact, 65 composition, 64 corpuscles, 65 decalcification, 64 development endochondral, 68 intramenbranous, 71 growth, 71 Haversian canal, dd lamellae, dd system, dd Lacunae, dd Howships, 66 lamellae, 65 lymphatics of, 68 marrow cavity, 67 cells, 68 red, dy yellow, 67 nerves of, 68 osteoblasts, 65 osteoclasts, 65 perichondral, 69 periosteum, 64 Sharpey's, fibres of, 64 structure of, 65 Volkmann's canals, dd vessels of, 68 Bone-cells, 64 Bone-marrow cells of, 67 red, dy, 68 serous, 67 yellow, 67 Bones of ear, 268 Bony cochlea, 2^2 labyrinth, 269 Borax carmin, 14 Boundary zone of choroid, 248 Boundary zone of kidney, 159 Bowman's capsule, 156 glands, 281 membrane, 246 Brain, see Cerebrum Brain sand, 22,2 Bronchi, 146 Bronchiole respiratory, 148 terminal, 148 Bruecker's lines, 72 Brunner's glands, 126 Bulb, hair, 215 Bulbus oculi, see Eyeball Burdach's columns, 242 C. Cecum, foramen, 1 1 1 Cajal, cells of, 229 Calcification of cartilage, 69 Calyces, renal, 161 Cambium layer, 71 Canada balsam, 20 Canal, hyaloid, 258 of Petit, 259 of Schlemm, 251 of Stilling, 258 of spinal cord, 240 semicircular, 271 Canaliculi, of bone, dy of eyelid, 266 Canalized fibrin, 206 Capillaries, bile, 133 blood, 92 lymph, 100 secretory of acid cells, 120 of demilunes, 140 of hepatic cells, 134 of parotid, 139 Capsule of Bowman, 156 of cartilage cells, 261 of Glisson, 132 of lens, 258 of Tenon, 266 suprarenal, 166 Carbol-xylol, 20 Cardia, 118 Cardiac muscle, 76 Carmin, borax, 14 alum, 15 injection mass, 22 Carminic acid, 15 Carotid gland, 99 Cartilage calcification of, 69 capsule, 62 cells, 61 chrondroblasts, 61 costal, 62 elastic, 62 fibro, d2 hyalin, 62 ossification of, 69 perichondrium, 61 vessels of, 63 Caruncle, lacrimal, 265 Cedar oil, 5, 20 Cellodin infiltration, 8 Cells acid, 14, 119 acidophilic, 96 adelomorphous, 118 amakrine, 256 auditory, 2t^ basket, 232 basophilic, 97 bipolar, 79 blood red, 94 white, 96 bone, dte, 67, 97 Myeloplaxes, 67 Myocardium, 89 N. Nabothi, ovuli, 191 Nails bed, 219 body, 218 eponychium, 218 fold, 218 groove, 218 lunula, 219 matrix, 219 root, 2i8 wall, 218 Nares, 142 Nasal mucosa blood-vessels of, 282 Bowman's glands, 281 lymphatics, 282 nerves of, 282 olfactory area, 280 respiratory portion, 280 Nerve cells axis-cylinder, 78 bipolar, 79 Deiter's, 79 dendrites, 78 first type, 79 Golgi's, 79 multipolar, 79 neurit, 78 neuron, 78 second type, 79 structure, 78 telodendrites, 79 unipolar, 79 Nerve-endings classification, 82 conjunctival, 83 corpuscles of Meissner, 83, 284 of Vater, 84, 285 of Wagner, 83, 284 end-bulbs, 83 genital, 83 Nerve-endings (continued) in epithelium, 82 smooth muscle, 85 voluntary muscle, 85 motor, 85 neuromuscular, 86 neuro-tendinous, 87 Pacinian body, 84, 285 Ruffini, 86 sensory, 82 tactile cells, 83 corpuscles, 83 Nerve fibre axis-cylinder, 80 internode, 80 medullary sheath, 80 medullated, 80 myelin, 80 neurilemma, 80 nodes of Ranvier, 80 nonmedullated, 80 sheath of Schwann, 80 white substance of Schwann, 80 Nerve trunk blood-vessels of, 82 endoneurium, 82 epineurium, 82 lymphatics, 82 myelin, 80 perineurium, 82 sympathetic, 80 Nervi nervorum, 82 vasorum, 94 Nervous system, 226 tissues, 78 Neurilemma, 80 Neuro-epithelium of ear, 271, 277 of eye, 254 of nose, 281 of retina, 254 ' uds, 283 of taste bud Neurofibrils, 78 Neuroglia, 79 cells of, 79 fibres, 79 Neuron, 78 Neutrophil, 97 Nissl's bodies, 78 Nitric acid, 4 Nodes of Ranvier, 80 Nodules cortical, 100 lymph, 60, 100 secondary, 100 solitary, 60, 100, 122, 127 Normoblasts, 95 Nuclear division, 34 matrix, 29 , membrane, 29 ; sap, 29 spindle, 36 Nucleolus, 30 Nucleus achromatin, 30 chromatin, 30 cuneatus, 236 INDEX. 299 Nucleus (continued) daughter, 36 gracillis, 236 resting, 29 Stilling, 240 Nuel, spaces of, 27 ^ Nutritive yolk, 184 Nymphae, 196 O. Odontoblasts, 109 Oils for clearing anilin, 20 anilin-xylol, 20 bergamot, 20 benzol of, 20 cedar-wood, 20, 6 clove, 19 creosote, 19 origanum, 19 turpentine, 6 toluol, 7, 20 xylol, 6, 20 Olfactory lobe glomerular layer, 230 granular layer, 231 mitral cells, 231 molecular layer, 231 peripheral fibres, 230 Olfactory mucosa blood-vessels of, 282 cells of, 280 glands of, 281 Olivary bodies, 230 oocyte, 185 Optic nerve, 257 papilla, 257 Orange, 14 Ora serrata, 257 Oral cavity, 107 Organ of Corti, 275 Orth's solution, 3 Osmic acid fixative, 3 stain for fat, 59 Osteoblasts, 65 Osteoclasts, 65 Ossicles, auditory, 268 Ossification endochondral, 68 intra-membranous, 71 Otolith membrane, 271 Otoliths, 271 Outer cell-mass, 198 Ovary antrum of follicle, 183 blood-vessels of, 188 corpus albicans, 187 hemorrhagicum, .186 luteum, 187 cortex, 182 egg tubes of Pflueger, 184 germinal epithelum, 182 Graafian follicle, 182 hilus, 182 interstitial cells, 188 lymphatics, 188 medulla, 188 muscle tissue of, 188 nerves of, 188 tunica albuginea, 182 Oviduct, 188 Ovulation, 187 Ovuli Nabothi, 191 Ovum dentoplasm, 38, 184 escape of, 187 fertilization, 38 formative yolk, 38, 184 maturation, ■^'j, 186 nutritive yolk, 38, 184 segmentation, 39 structure, 37 Oxyntic cell, 118 Oxyphil, see Eosinophil r. Pacchonian bodies, 226 villi, 226 Pacinian bodies, 84, 285 Palatine tonsils, 113 Pancreas areas of Langerhans, 139 blood-vessels of, 139 cells of, 139 centro-acinar cells, 139 ducts, 139 nerves of, 139 zymogen granules, 139 Pancreatic duct, 139 Panniculus adiposus, 213 Papilla circumvallate, in filliform, no foliate, 283 fungiform, in hair, 216 of mucosa of tongue, in esophagus, 115 optic, 257 tactile, 196, 212 vascular, 196, 212 Paracarmin, 15 Paradidymis, 181 Paraffin fixation of, sections, 25, 26 infiltration, 6 removal from sections, 20 sectioning, 10 Parathyroids, 152 Paroophoron, 188 Parotid gland, 139 Parovarium, 188 Pars ciliaris retinae, 249 iridica retinae, 251 optica retinae, 252 Pectinate ligament, 252 Pelvis of kidney, 157 Penis arteries of, 180 corpora cavernosa, 180 corpus spongiosum, 180 emissary veins, 180 erectile tissue, 180 glands of Tyson, 180 glans, 179, 180 helicine arteries, 180 nerves, 181 tunica albuginea, 179 veins, 180 300 INDEX. Peptic cells, 14, ii8 glands, 118 Perforating fibres of cornea, 246 of Sharpey, 65 Pericardium, 89 Perichondrium, 61 Periodontal membrane, no Perimysium, tz Perineurium, 82 Periosteal lamellae, 65 Periosteum, 65 Peripheral nerve endings, 82 Peritendineum, 57 Peri vitelline space, 184 Petit's canal, 259 Peyer's patches, 60, 126 Pflueger's ^%,z tubes, 184 Phagocytes, 96 Phlangeal plates, zyj process, zTy Pharynx, 114 Phloroglucin — nitric acid, 1 1 Pia mater. 226 Picric acid stain, 114 Picro-carmin, 1 5 Picro-fuchsin, 14 Pigment cells, 45 of hair, 218 of iris, 250 of retina, 253 of skin, 213 Pig's liver, 132 Pillar cells, zTd Pineal body, 232 Pinna, 267 Pits, gastric, 117 Pituitary body, 231 Placenta canalized fibrin, 206 cell-knots, 207 chorion, 205 decidua, 201 development of, 198 intervillous spaces, 207 septa of, 205 syncytium, 207 villi of, 207 Plasma cells, 55 Plastids, 28 Platelets of blood, 97 Pleura, 146 Plexus of Auerbach, 130 of Meissner, 130 Plica circulares, 125 palmatae, 191 semilunaris, 265 Polar bodies, 186 field, 34 Polynuclear cells, 96 Pons, 234 Portal circulation, 134 system, 134 vein, 134 Potassium bichromate, i Precapillary vessels, 92 Prepuce, 180 Prickle cells, 44, 211 I Primary marrow cells, 68 spaces, 68 Prochorion, 200 Prominentia spiralis, ztz Prophase, 34 Prostate blood-vessels, 179 capsule, 177 glands, 178 nerves, 179 Prostatic bodies, 178 Protoplasm, 28 Prussian blue, 22 Pseudostratified cells, 43 Pulp cavity, 109 splenic, 102 tooth, 109 Pupil, 251 Purkinje cells, 22,2 Pyramidal cells of cerebrum, 228 columns, direct, 242 crossed, 242 Pyramids Malpighian, 1 56 medullary, 156 of Ferrein, 154 Pyrenin, 31 R. Ranvier, nodes of, 80 Receptaculum chyli, 130 Rectum, 127 valves of, 127 Red blood cells, 94 bone marrow, (i7 Reissner's membrane, 2^2 Remak's fibres, 80 Renal corpuscles, 156 pelvis, 157 Reproduction, 32 Respiratory bronchiole, 148 organs, 142 region, 142 Restiform bodies, 22,7 Rete Malpighii, 211 testis, 172 Retia mirabilia, 92 Reticular connective tissue, 58 gland, 50 Reticulum, 58 Retina amakrine cells, 256 blind spot, 257 blood-vessels, 259 central artery, 259 cone-cells, 253 cone-fibres, 253 fovea centralis, 257 ganglion cells, 256 Henle's fibre layer, 255 limiting membrane, inner, 254 outer, 254 macula lutea, 257 molecular layer, inner, 256 outer, 255 nerve fibre layer, 256 optic, 257 INDEX 3o> Retina (continued) optic nerve papilla, 257 ora serrata, 257 pars ciliaris, 249 iridica, 251 optica, 252 pigment layer, 253 rhodopsin, 254 rod-cells, 254 fibres, 254 visual purple, 254 Rod-cells, 254 fibres, 254 Rolandi, substantia gelatinosa, 240 Root sheaths, 217 Rouleaux, 94 Ruffini, end-organs of, 87 S. Sacculations of colon, 127 Sacculus, 270 Safranin, 13 Salivary corpuscles, 1 14 glands, 137 Sarcolemma, yz Sarcoplasm, yz Scala media, z-j^ tympani, 272 vestibuli, zyz Schlemm's canal, 251 Schwann, .sheath of, 80 white substance of, 80 Sclera, 245 _ Scleral conjunctiva, 245 Sebaceous glands, 220 Sebum, 221 Secondary marrow spaces, 68 Secretion, 31, 151 Secretory canals, 140 Sectioning celloidin, 10 paraffin, 10 Sections, staining of, 26 Semen, 175 Semi-circular canals, 271 Seminiferous tubules, 170, 171 Seminal vesicles, 177 Sense of smell, 283 taste, 283 touch, 284 Sensory endings, 82 Septa, placental, 205 Septum linguali, 113 posterior median, 238 Serous glands, 51, 138 membranes, 46 Sertoli's columns, 171 Sharpey's fibres, 64 Sheath Henle's, 217 Huxley's, 217 medullary, 80 myelin, 80 Silver staining blood-vessels, 17 lymphatics, 17 nervous tissue, 17 Sinus lactiferous, 223 marginal, 207 lymph, 10 1 of kidney, 154 Sinusoids, 92 Skein, daughter, 36 dense, 34 loose, 34 mother, 34 Skin appendages, 215 arrector pili muscle, 218 blood-vessels of, 214 color of, 214 corium, 212 derma, 212 epidermis, 211 glands, 219 layers of, 211 lymphatics, 215 panniculus adiposus, 214 pigment, 214 Slides, 2(i Small intestine, 122 Smell, 283 Smooth muscle, 75 Sole-plate, 85 Solitary follicles, 60, 122, 128 Somatopleure, 199 Spaces of Fontana, 251 of Nuel, 2Ty Spermatid, 174 Spermatoblast, 175 Spermatocyte, 174 Spermatogenesis, 174 Spermatogonia, 171, 174 SpermatozoSn, 38, 173 Spider cell, 79 Spinal cord blood-vessels of, 241 canal, 240 cells, 248 commissures, 240 columns, 241 fissure, 238 gray substance, 238 horns, 38 membranes of, 226 septum, 238 white matter, 241 Spindle, central, 35 nuclear, 36 Spinal ganglion, 24^5 Spirem, 34 Splanchnopleure, 199 Spleen capsule, 102 circulation, 103 corpuscles, 103 lobules, 104 Malpighian corpuscles, 103 pulp, 102 trabeculae, 102 Spongioplasm, 28 Spongy bone, 64 Spot, germinal, 37, 184 Staining of sections, 26 302 INDEX. Stains acid, 14 acid hematoxylin, 13 alum carmin, 15 anilin dyes, 13 basic, 12 bismark brown, 13 borax carmin, 14 carmin, 14 Delafield's hematoxylin, 12 Ehrlich-Biondi-Heidenhain, 16 elastica, 19 eosin, 14 eosin-methylene blue, 24 for adipose tissue, 59 fold, 16 [arris* hematoxylin, 12 hematoxylin acid, 14 Delafield's, 12 Harris', 12 methylene blue-cosin, 24 methyl green, 13 myelin, 17 nuclear, 12 orange, 14 osmic acid for fat, 59 paracarmin, 15 picric acid, 14 picro-carmin, 15 protoplasmic, 14 silver, 17 safranin, 13 Sudan III for fat, 59 Van Gieson, 14 Weigert's elastica, 19 myelin, 17 Wright's blood, 24 Stars, daughter, 36 mother, 34 Stellate cells, 53 Steno's duct, 139 Stomach acid cells, 119 blood-vessels, 121 cardiac end, 118 coats, 117 glands, 118 lymphatics, 121 mucous membrane, 117 nerves, 122 peptic cells, 118 pyloric end, 112 Stratum corneum, 211 germinativum, 211 granulosum, 212 of ovary, 183 lucidum, 212 Malpighii, 211 mucosum, 192 papillare, 212 reticulare, 213 supra vasculare, 192 vasculare, 192 Stria vascularis, 273 Stilling canal of, 258 nucleus of, 240 Subarachnoid space, 226 Subdural space, 226 Subscleral, 245 Sublingual gland, 139 Submaxillary gland, 14 Substantia gelatinosa, 240 grisea contralis, 240 propria, 246 spongiosa, 241 Succus entericus, 126 Sudan III, 59 Sudoriparous glands, 219 Sulcus spiralis, 275 Suprarenal body blood-vessels, 167 cells, 166 cortex, 166 medulla, 166 nerves, 168 zones, 166 Suspensory ligaments of lens, 259 Sustentacular cells, iii, 254, 270, 277, 280, 283 Sweat-glands blood-vessels, 220 cells of, 220 lymphatics, 220 modified, 220 nerves, 220 pore, 220 Sweat-pore, 220 Syncytum, 203 T. Tactile cells, 83 corpuscles, 83, 284 menisci, 83 papillae, 196, 212 Taenia coli, 127 Tapetum cellulosum, 248 fibrosum, 248 Tarsal glands, 264 plates, 262 Taste-buds, iii, 142, 283 pore, III, 283 Tear gland, 266 accessory, 263 Technic general, 1 slide, 25 Teeth auditory, 27 f^ cementum, 108 crown, 107 dentin, 107 enamel 107. fang 107. nerves 109. pulp 109. root 107. root canal 109 vessels of 109 Teichmann's crystals, 92 Tellyesnicky's solution, 2 Telophase, 36 Tendon 56 cells 57 Tenon capsule of 266. space of 266. Terminal bronchioles 148. INDEX. 303 Testicle blood-vessels, 173 excretory tubules, 171, 172 interstitial cells 172. lobules of 170. lymphatics 173 mediastinum, 169 nerves 173. seminiferous tubules, 170 tunica albuginea, 169 vaginalis 169. Theca folliculi, 182 Third eyelid, 265 Thymus blood-vessels, 105 changes in 104 corpuscles of Hassal 105 cortex 105 medulla 105. Thyroid body blood-vessels, 152 colloid substance 151. lymphatics 152. Tigroid bodies 78. Tissue areolar, 58 adipose 58. connective 53. definition of 41. elastic 56. embryonic 57. epithelial, 41 erectile 180, 195, fibrous 55. lymphoid 59. mucous, 57 muscular cardiac 76. smooth 75. voluntary ^2. nervous 78 retiform 58. Toluol 7, 20. Tome's granular layer, 109 Tongue blood-vessels, 113 glands, 113 lymphoid tissue 113. muscle III. papillae, no taste-buds 1 1 1. Tonsil crypts of, 113 lingual 113. palatine 113. Touch 284. Trachea 144. Transitional cells, 45 Trichloracetic acid, 11 Trigonum vesicae, 166 Triploblast, 39 Trophoderm, 199 Trophodermal lacunae, 201 Tubular glands coiled 50 compound 50 branched 50 Tubular glands (continued) reticular 50 simple 49 Tubules dentinal 109 intercalated, 138 intermediate, 138 secretory 138. seminiferous 170. uriniferous, 157 Tubuli recti 171. Tubulo-alveolar glands, 50 Tunica adventitia, 90 Tunica albuginea ovary, 182 pelvis, 180 testicle 169. externa artery 90 eye 245. vein 94 interna artery 90 eye 245 vein 94. media artery 90 eye 245. vein 94 propria 46 vaginalis 169 Tunica vasculosa, 182 Tunnel of Corti, 276 Turpentine 6. Tympanic cavity 268. lamella 275 membrane 267 Tympanum 268. Tyson's glands 180. U. Umbilical cord 208. Units functionating, 138 secreting 138. structural 138. Ureter 162 Urethra female 164 male 164 Urinary bladder, 163 organs 154. Uriniferous tubule, 157 Uterus blood-vessels of, 193 cervix 190. glands 190. lymphatics 193. menstrual changes 192 mucosa 190. nerves 193. ovuli Nabothi 191. Utriculus, 270 Uveal tract, 247 Vacuoles 29. Vagina 194 Valves of heart 88. veins 93. Valvulae conniventes, 125 Van Gilson's stain, 14 . 304 INDEX. Vasa efiferentia, 172 Vasa vasorum 94. Vascular papillae 196, 212. Vas deferens, 176 Vater-Pacinian body, 84, 285 Veins central 132 coats of 93. portal, 134 valves of 93. Venae archiformes, 160 rectae, 160 stellatae, 160 vorticosae, 201 Ventricles of larynx 143. Vermiform appendix, 127 Vesicle blastodermic 39 entodermal 199 germinal 37, 184. seminal 177. Vestibule of vagina 195. Villi chorionic, 203 of oviduct, 189 of placenta 207. of small intestine 123. Visual cells, 254 Visual purple, 254 Vital phenomena 31. Vitelline membrane, 37, 184 Vitellus 37, 184 Vitreous humor, 258 Vocal cords 143 Volkmann's canals, 66 Voluntary muscle T2. W. Wagner, corpuscles of, 83, 284 Wandering cells 53. Wei'^ert's elastica stain, 17 Weigert's myelin stain, 19 Wharton's duct 141. jelly 208. White blood cells 96 commissure, 240 fibrous tissue 55 matter 80, 22T. substance of Schwann, 80 Wirsung's duct 139 Wright's blood stain 24. X. Xylol 6, 20. Xylol, anilin oil, 20 Xylol balsam, 20 Xylol, carbol, 20 Y. Yellow bone marrow 67. elastic tissue 57. fibro-cartilage 62. spot 257. Yolk formative 184. nutritive 184. Z. Zenker's fluid 2 Zinn, zone of 259. 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