5RARY MEDICAL LIBRARY . ' THE LIBRARY SAN DIEGO COUNTY MEDICAL SOCIETY UJL. DATE DUE 3 RtC'fl BRARY Library by members OEMCO NO. 38-298 -?ting Saturdays, Sun- ~>e loaned to members 4. All other books and periodicals may be taken out lor i4 days, renewable by telephone or otherwise, for the same period, provided they be not wanted by other members. 5. Weekly periodicals of the current month, monthly periodicals of the current quarter, and last number of quarterlies, may not be taken out unless there be duplicates. 6. The above privileges of taking books from the rooms shall not extend to such books, periodicals or anatomical plates, as are of exceptional value or rarity. 7. Books may be obtained from other libraries for members only. 8. A fine of five cents a day will be assessed upon a member for each book that he retains beyond the time allowed. He shall, moreover, be de- barred the borrowing of other books until the previous ones are re- turned, and his fines are paid. 9. All injuries to books beyond a reasonable wear and all losses shall be made good to the satisfaction of the librarian. BRAIN AND SPINAL CORD A MANUAL FOR THE STUDY OF THE MORPHOLOGY AND FIBRE-TRACTS OF THE CENTRAL NERVOUS SYSTEM BY DR. MED. EMIL VILLIGER PRIVATDOZENT IN NEUROLOGY AND NEUROPATHOLOGY IN THE UNIVERSITY OF BASEL TRANSLATED BY GEORGE A. PIERSOL, M.D., Sc.D. PROFESSOR OF ANATOMY IN THE UNIVERSITY OF PENNSYLVANIA FROM THE THIRD GERMAN EDITION WITH 232 ILLUSTRATIONS PHILADELPHIA & LONDON J. B. LIPPINCOTT COMPANY a,, Copyright, 1912, by J. B. LIPPINCOTT Co. 3C, 36"~ TRANSLATOR'S NOTE THE increasing attention given to the study of the Central Nervous System has emphasized the need of a suitable guide for laboratory exercises. The usefulness of Dr. Villiger's excellent manual has been greatly increased by the addition of Part III, illustrating the architecture of the brain-stem by series of consecutive sections, which first appeared in the second edition. While of much assistance to the student in identi- fying details under the microscope, the series so well represents the actual preparations, that close study of the illustrations alone will amply repay where satisfactory specimens are inaccessible. The translator has respected the author's desire to retain the brevity and clearness which characterize the book ; he has refrained, therefore, from amplifying the text, which appears, with slight changes, as in the original. Through the courtesy of the firm of Wilhelm Engelmann, of Leipzig, in supplying advance proofs, it has been pos- sible to include the new figures, which have been added to the third German edition. The selected bibliography, appended by the translator, will be of service, it is hoped, to those desirous of consulting the original papers or the more comprehensive works pertaining to the Central Nervous System. PHILADELPHIA, September, 1912. PREFACE TO THE THIRD EDITION THE cordial reception accorded the second edition has rendered necessary, within a short time, issuing a new edition. Radical changes or amplifications, notably the desired additions to the series of microscopical representations of brain sections, could not be undertaken. Notwithstanding the first intention to print the edition without alterations, the hearty cooperation of the publishers has made it possible to introduce, particularly in t Part II, some new figures, to which I wish to direct especial attention. E. VILLIGER. BASEL, April, 1912. AUTHOR'S PREFACE THE second edition presents substantial changes. While some sections, pertaining to morphology as well as to fibre-tracts, have been simplified and made clearer, others have been treated with greater completeness. Certain figures have been replaced by better ones, and many new ones, relating to the paths of conduction, have been added. The chief change, however, lies in the addition of Part III, in which I have attempted to meet the often expressed wish, that the conduction-paths be represented not only by diagrams, but also by microscopical pictures. I am well aware that this third part presents considerable gaps. Unfortunately at the time only vertical sections through the brain-stem were at my disposal ; further, the drawing of the new and especially the microscopical illustrations made such claims upon me, that it was impossible to satisfy all desires. Nevertheless, I indulge the hope that the study of the fibre-tracts will be facilitated by the microscopical representations now given and by the newly added schematic figures. Moreover, I wish particularly to emphasize, that this second edition remains a manual and as such is designed primarily to assist the student, with all possible con- ciseness and clearness, in the study of the anatomy of the central nervous system. It is my privilege to take this opportunity of expressing my sincerest thanks to Professors J. Kollmann and N. K. Corning for their kindness in placing at my disposal numerous microscopical preparations. My especial acknowledgment is due the firm of Wilhelm Engelmann, of Leipzig, whose cordial cooperation enabled me to carry out the radical changes made necessary by the introduction of larger figures, particularly the microscopical illustrations. E. VILLIGER. vii CONTENTS PART I. MORPHOLOGY. Subdivision of the Central Nervous System . . 3 Development of the Brain 4 Development of the Spinal Cord 8 Form, Size and Weight of the Brain 9 General Consideration of the Brain n Telencephalon End-Brain 17 Pallium Cerebral Mantle 18 Rhinencephalon Olfactory Brain 25 1. Lobus olfactorius 26 A. Lobus olfactorius anterior 27 B. Lobus olfactorius posterior. ... 29 2. Gyrus fornicatus 30 3. Hippocampus 32 4. Gyrus dentatus 32 5. Uncus Gyrus uncinatus. Gyrus intralimbicus. Gyrus fascio- laris 35 6. Gyri Andreae Retzii 36 Pars optica hypothalami 37 Internal Configuration 38 Gray Masses and Nuclei 46 Summary of Telencephalon 50 Diencephalon Inter-Brain 52 Thalamus opticus 54 Pars mamillaris hypothalami 56 Ventriculus tertius 57 The Nuclei of the Diencephalon 58 Summary 63 Mesencephalon Mid-Brain Lamina quadrigemina Pedunculi cerebri Aquaeductus cerebri (Sylvii) Gray Masses of the Mid-Brain Summary Isthmus rhombencephali Metencephalon Pons Varolii Cerebellum A. Lobus superior B. Lobus posterior c. Lobus inferior Myelencephalon Medulla oblongata. . Ventriculus quartus Fossa rhomboidea Gray Masses of the Rhombencephalon. Summary of the Rhombencephalon. . . . Brain-Membranes Meninges Dura Mater Arachnoidea Pia Mater Spinal Cord Medulla spinalis External Configuration Internal Configuration Membranes of the Spinal Cord Dura mater spinalis Arachnoidea spinalis Pia mater spinalis PAGE . 66 . 66 66 68 . 68 69 70 89 89 90 93 95 93 93 PART II. FIBRE-TRACTS. Methods of Investigating the Fibre-Tracts .... 97 Histogenesis of the Nervous System 102 Development of the Ependyma and Neu- roglia Cells 103 Development of the Nerve-Cells 105 Development of the Cells of the Cerebro- Spinal Ganglia and of the Sympathetic Ganglia 105 The Formed Elements of the Nervous System 106 A. The Support-Cells 106 B. The Nerve-Cells 107 Microscopical Structure of the Cerebral Cortex 114 I. Cortex of the Pallium 114 II. Rhinencephalon Bulbus olfactorius Gyrus fornicatus Hippocampus and Gyrus dentatus. , Hippocampus ... Gyrus dentatus Cerebral Localization The Motor Centre The Sensory Centres Sense-Centres . The Speech Centres General Division of the Paths of Conduction. Conduction Paths of the Telencephalon 1. Association Fibres 2. Commissural Fibres 3. Projection Fibres 118 118 119 120 121 122 123 124 126 128 131 134 134 135 135 CONTENTS. A. Short Paths 135 B. Long Paths 137 Radiatio corporis striati M4 Connections of the Corpus Striatum 144 Fibre-Tracts of the Rhinencephalon 144 1. Peripheral Tract 144 2. Central Tract 145 A. Connection of the bulbus olfac- torius with the primary centres 145 B. Connection of the primary centres with the secondary or cortical centres 145 3. Connection of the two primary centres 149 4. Further connections of the primary centres 149 5. Connection of the two cortical centres 149 6. Further connections of the cortical centres 149 Conduction Paths of the Diencephalon 150 Conduction Paths of the Mesencephalon 151 Conduction Paths of the Metencephalon 154 Microscopical structure of the Cerebellar Cortex and Fibre-Tracts 154 Spinal Cord 159 The Gray Matter 159 The White Matter... .. 160 PAGE 1. Paths of the Anterior Column .... 161 2. Paths of the Lateral Column 161 3. Paths of the Posterior Column 163 Medulla Oblongata 166 Origin of the Cerebral Nerves 172 Nervus olfactorius 172 Nervus opticus 172 Nervus oculomotorius 175 Nervus trochlearis 176 Nervus abducens 176 Nervus trigeminus 176 Nervus facialis and Nervus intermedius Wrisbergi 178 Nervus acusticus 179 1. Nervus cochleae 179 2. Nervus vestibuli 181 Nervus glossopharyngeus and vagus 184 Nervus accessorius 185 Nervus hypoglossus 186 General Survey of the Principal Paths 186 A. Projection Paths 186 I. Centripetal Paths 186 1. Ascending sensory spinal paths 186 2. Sensory paths of the cerebral nerves 188 II. Centrifugal Paths 191 B. Reflex Paths 192 c. Association Paths 197 PART III. SERIAL SECTIONS OF THE BRAIN-STEM. A. From ( the anterior end of the corpus cal- losum to the quadrigeminal region 205 B. From the caudal part of the medulla oblon- gata to the quadrigeminal region 235 PART I. MORPHOLOGY. BRAIN AND SPINAL CORD MORPHOLOGY Medullary plate Cuticle-plate Chorda Medullary groove Medullary ridge The brain and the spinal cord together constitute the central nervous system (sy ' sterna nervorum centrale~). The brain (encephalori) is that part of the central nervous system lodged within the cranial case ; the spinal cord (medulla spinalis} is that part within the vertebral canal. The boundary between the two is neither macroscopically nor microscopically sharply defined. The lowest segment of the brain corresponds perfectly in form and structure with the uppermost one of the spinal cord and is called, therefore, medulla oblongata the length- ened marrow. An approximate coarse boundary line is supplied by the lowest bundle of the so-called pyramidal decussation, or by the highest root-bundle of the first cervical nerve. A further separation of the brain into different segments is best accomplished by embryology. The nervous system develops from a broad axial stripe of the outer germ-layer, .the ectoderm, that imme- diately overlies the chorda dorsalis or noto cord. Within this stripe, the cells of the outer germ-layer grow into elongated cylindrical or spindle-form elements, while those within the adjoining ectoderm become flat- tened. In this manner the outer germ-layer differ- entiates into two zones : ( i ) the thinned out cuticle plate and (2) the thicker axially placed neural or medullary plate. The two zones soon become more sharply defined from each other; the medullary plate curves ventrally and at its margins rises above the surface of the germ. In this manner arise the medullary ridges, which include between them the broad, and at first shallow, medullary groove. The ridges are simple folds of the outer germ-layer, along the juncture of the medullary and cuticle plates. 3 Medullary tube Central canal FiG. I. Schematic representation of the formation of the medullary tube from the outer germ-layer. 4 MORPHOLOGY. The medullary plates are converted into the medullary tube very early. This tube is formed by a typical folding process. The medullary ridges progressively rise above the dorsal surface of the embryo, bend medially and grow towards each other until their summits meet and later fuse. As the medullary ridges rise above the surface of the embryonic area, they draw along the cuticle-plate ; the latter, however, does not come into relation with the nervous system, but becomes the epithelial covering of the body. In the medullary tube, which encloses a cleft-like space, the central canal (can- alis centralis}, filled with primary lymph, we distinguish the brain-tube and the spinal tube ; from the former develops the brain and from the latter the spinal cord. Anterior brain-vesicle (Prosencephalon) Middle brain-vesicle (Mesencephalon) Posterior brain-vesicle (Rhombencephalon) Hind-brai vesicle Mid-brain vesicle FIG. 2. Schematic representation of the three primary brain-vesicles. DEVELOPMENT OF THE BRAIN. The fundamental form is the simple brain-tube. In consequence of increased growth in certain parts and diminished growth in others, the brain-tube early exhibits a segmentation. At first it consists of three dilatations, the primary brain-vesicles, separated by two annu- lar constrictions, the vesicles being desig- nated as anterior, mid- dle and posterior. From these three brain-vesi- cles later arise the three chief divisions : the Fore-brain or Prosen- cephalon, the Mid-brain or Mesencephalon and the Hind-brain or Rhombencephalon. The three primary vesicles subsequently give rise to five secondary brain-vesicles, since the fore-brain differen- tiates into the telencephalon and the diencephalon, while the hind-brain divides into the metencephalon and the myelen- cephalon. The hind-brain is sepa- rated from the mid-brain by a narrow constricted segment, the isthmus (isthmus rhombencephalt} . The mye- lencephalon is continuous with the spinal cord. The primitive brain- tube, therefore, differentiates into six ^^=^^=^// ^-~~ Metencephaio divisions (Fig. 3) : the telencephalon, the diencephalon, the mesencephalon, the isthmus, the metencephalon and the myelencephalon. In the later stages, the devel- opment of the nervous substance is especially vigorous in the two lateral walls of the neural tube, while the median areas of its floor and roof (the floor- and roof-plates'} for the most part remain thin and epithelioid. The different divisions of the brain-tube participate in the further development in very Telencephalot, Mesencephalon Myelencephalon FIG. 3. The five secondary brain -vesicles. DEVELOPMENT OF BRAIN. 5 unlike degree. Certain segments remain far behind, while others far outstrip their sur- roundings in consequence of their vigorous growth. Along with the displacement ot ^ Maencephalon Telencephalon. jjp_ FIG. 4. Brain of human embryo of five weeks. After a model by His. certain brain-segments induced by unequal growth, other processes contribute to the efface- ment of the original fundamental plan of the whole. Among such factors belong partic- FIG. 5. Brain of human embryo of the third month. After a model by His. ularly the appearance of robust cross-fibres (corpus callosum, pons). Consequently it is impossible to mark off superficially the individual segments on the brain of the adult. 6 MORPHOLOGY. The developmental relations of the parts of the brain to the individual brain-vesicles is best explained by the accompanying" table after His. It will serve as guide in the con- sideration of the morphology. (Compare also Figs. 5, 6, 7, 8, 9.) Telencefhalc FIG. 6. Diagram showing the further development of the five secondary brain-vesicles. (His.) The prosencephalon and the mesencephalon together are also designated the cere- brum or great brain. The brain-stem (truncus cerebri) embraces the so-called the brain- FIG. 7. Median sagittal section through the adult brain. Telencephalon is ye'.low; diencephalon red; mesencephalon blue; metencephalon green; myelencephalon violet. ganglia; it consists of the stem of the end-brain, the inter-brain, the mid-brain, the isthmus, the pons and the medulla oblongata. SUBDIVISIONS OF THE BRAIN. Telencephalon Prosencephalon Fore-Brain Mese f Pallium Hemisphaerium .j Rhinencephalon [ Stem of End- Brain Pars optica Hypothalami Pars mamillaris Hypothalami :ncephalon Mid-Brain Diencephalon { Thalamus 1 Thalamencephalon ventricle | * The cavities of the embryonal brain-vesicles likewise change their form under the influence of the various growth-processes. The central canal of the spinal cord is continued into the hind- part of the myelencephalon. The cavity of the fore -part of the myelencephalon and that of the entire metencephalon become the fourth ventricle. The cavity of the mid-brain remains as the aquaeductus cerebri or Sylvian aqueduct. The cavity of the dien- cephalon or inter -brain becomes the third ventricle, which communicates with the lateral ventricles the cav- ities of the hemisphere - vesicles by means of the Y-like foramen of Monro (Joramen interventriculare'} . All these spaces are filled with a fluid, the liquor cerebro-spinalis. Aguaeduct. cerebri (Sylvii) IV. Ventricle Central canal FIG. 10. Diagram showing the brain-ventricles. DEVELOPMENT OF THE SPINAL CORD. The part of the neural tube that becomes the spinal cord appears of oval form on transverse section. The central canal forms a dorso-ventrally directed cleft, which is bounded laterally b^ the thickened walls of the medullary tube, but dorsally and ven- trally by thinner parts of the same ; therefore, a separation into a right and left half is Floor platt FIG. ii. Cross-section of spinal cord of a human embryo of four and one-half weeks. (Hit.) FIG. 12. Cross-section of spinal cord of a hu- man embryo of three months. (His.) easily recognizable. The thinner dorsal and ventral walls appear as commissures behind and before, the dorsal or posterior commissure being called the roof-plate and the ventral or anterior commissure the floor-plate. During the further development, these plates grow relatively little, while both lateral halves continue to thicken, their growth being especially marked ventrally. In this locality on each side appears a ventral projection. Consequently, the floor-plate is pushed farther from the surface and, finally, a median longitudinal cleft, the fissura mediana anterior, is formed in front. A similar change THE SPINAL CORD. 9 occurs in the dorsal region, the roof-plate being likewise pushed in and disappearing at the bottom of the sulcus medianus posterior. The spinal cord now consists of two robust lateral halves, separated from each other by an anterior fissure and a posterior sulcus. During this further development also the central canal has changed its form, since the dorsal part of the original dorso-ventrally directed cleft becomes closed in consequence of the apposition of the lateral walls. At first the spinal cord extends the entire length of the vertebral canal with a fairly constant volume. The lower end of the cord becomes rudimentary and defined from the preceding part, assumes a conical form and becomes the conus medullaris. A fur- ther alteration in the extension of the spinal cord is brought about by the inequality between its growth and that of the surrounding vertebral canal. The latter constantly increases in length, the lower segment of the spine developing with especial vigor. Since the growth of the cord fails to keep pace with that of the spine, the cord apparently shortens and no longer extends the entire length of the vertebral canal. The conus medullaris is drawn up from the sacral canal and enters the lumbar region, until, finally, it is found opposite the first or second lumbar vertebra. During this ascensus medullae spinalis the end of the conus medullaris is drawn out into a thin thread, which extends as far as the coccygeal region and is known as the filum terminate. A further consequence of this ascensus is a change in the course of the nerves emerging from the spinal cord. In the cervical region the course of the nerves is still horizontal ; in the thoracic region it is more and more oblique ; while in the lumbar region, and, still more in the sacral, the nerves are directed downward. The nerve-trunks emerging from the last part of the cord lie, therefore, for a long distance within the vertebral canal before they leave the latter. They surround the conus medullaris and the filum terminale and in this manner lead to the formation of the so-called horse-tail or cauda equina. In completion, the spinal cord undergoes some further changes in its form. Gradually two segments acquire greater development, the one in the cervical portion and the other in the upper part of the lumbar region. They are known as the cervical enlargement (intumescentia cervicalis} and the lumbar enlargement (intumescentia lumbalis} respectively. FIG. 13. Anterior aspect of spinal cord. Schematic. FORM, SIZE AND WEIGHT OF THE BRAIN. The brain possesses in a general way the form of the cranial cavity. It is applied so closely to the inner wall of the skull, that a cast of the cranial cavity repeats to a considerable degree the form of the brain. Corresponding to the numerous variations in the configuration of the skull, sometimes the brain is more spherical and at other times more ellipsoidal in form. Its dorsal surface is arched, its ventral one flattened. io MORPHOLOGY. The length of the brain is, on an average, between 160-170 mm. and its greatest transverse diameter 140 mm. The female brain is usually somewhat shorter than the male. The weight of the brain has long been the subject of numerous investigations. The average brain-weight of the adult man has been found to be 1375 grams, that of the adult woman 1245 grams. The minimal weight of the male brain has been placed at 960 grams, that of the female brain at 800 grams. As maximal weights, 2000 grams and over, 1900 grams, 1861 grams and 1807 grams have been specified. The difficulty of determining the average brain-weight lies in the fact that various factors exert a substantial influence. In this connection age plays a prominent r61e. Observations show that the mean brain-weight in both sexes reaches its maximum towards the twentieth year, remains stationary between the twentieth and fiftieth years, and then gradually decreases. Further influences are body-weight and body-length. In general, heavier individuals possess a heavier brain and with increase in height is asso- ciated increase in brain-weight ; small individuals, however, possess a relatively heavier brain than large ones. In relation to the form of the skull, a higher average brain- weight has been found in the broad-headed type than in the long-headed. Many obser- vations regarding the influence of race exist, with the following results : Grams. Caucasian race : average brain-weight, 1 335 Chinese: average brain-weight, 1332 Sandwich Islander: average brain- weight, 1303 Malay and Indian : average brain-weight, 1266 Negro : average brain-weight, 1 244 Australian: average brain-weight, 1185 Definite differences in the brain-weight among the European nations have been recorded: Grams. German : average brain-weight, 1425 English : average brain-weight, 1346 French : average brain-weight, 1280 Among all peoples, the female sex shows a smaller average brain-weight. Further, the influence of culture is to be noted. According to the measurements of P. Broca, among the cultured nations the brain-mass probably gains somewhat in the course of time. Based on the measurements of Egyptian skulls, E. Schmidt found that nations, which have regressed from a higher culture, exhibit a smaller cranial capacity than that possessed by them during the period of their cultural bloom. Finally, pathological conditions must also be considered, since sometimes they in- duce an increase and at other times a decrease of the brain-weight. Of great interest has always been the question, to what extent do the absolute and relative proportions of the brain indicate the favored position which man enjoys in com- parison with other animals. It has long been known, that man does not possess abso- lutely the heaviest brain. The brain-weight of the elephant reaches 4000 grams and more, while that of certain cetaceans may be 3000 grams. It is, however, clear that, BRAIN-WEIGHT. n in proportion to body-weight, these animals possess relatively a smaller brain-mass than does man. On the other hand, several investigators have shown that man does not possess relatively the heaviest brain, since in this respect he is surpassed by certain song- birds, apes and mice. If, however, one compares, as did Ranke, the weight of the spinal cord with that of the brain, man is found to possess the heaviest brain. While this proportion in the adult human subject is approximately 2 per cent., in the anthro- poid apes this ratio increases to about 6 per cent, and among the other mammals it rises to from 23 to 47 per cent. It is particularly difficult to establish a definite relation between brain-weight and intelligence. The comparison of many brains shows, that it is not permissible to esti- mate the intellectual capacity of an individual merely according to his brain-weight. The following data exist regarding the weights of the brains of distinguished men: Turgenjeff : 2012 Broca: 1484 Cuvier : 1861 Dupuytren : 1437 Byron : 1807 Dante : 1420 Kant: 1600 Liebig : 1352 Schiller: 1580 Tiedemann : 1254 Gauss: H9 2 Dollinger: 1207 This comparison shows, that while the majority of these brains exceeded the average weight of 1375 grams, there are also men of eminent intellect who possess a relatively low brain-weight. Moreover, there are records of notable brain- weights (2028 and 1900 grams) among individuals of insignificant mentality. Remarkably lo-v brain- weights (300 grams and less) occur among idiots. According to the present investigations, the conclusion is justified, that psychic functions can proceed normally only where the brain-weight has passed a certain mini- mum. According to Obersteiner, the lowest level to which the brain-weight may sink without noticeable impairment of the intellectual faculties is for the male brain 1000 grams and for the female 900. It is to be noted, that weighing the entire brain supplies only an uncertain index of the psychic capability, for the reason that the individual parts of the brain, so varying in structure and function, do not undergo uniform increase or diminution in size and weight. An accurate knowledge of the weights of the individual parts of the brain would be of great importance, especially art exact determination of the weight of the gray substance of the end-brain, the cerebral cortex, with which particularly the higher psychic functions are associated. Even then we would fail to reach a positive result, since, in addition to the weight, other relations must be considered, especially the finer structure. GENERAL INSPECTION OF THE BRAIN. Let us first examine the dorsal surface of the brain. This is strongly arched in the sagittal as well as in the frontal direction -fades convexa cerebri (Fig. 14). A deep median vertical cleft (Jlssura longitudinalis cerebri} divides the whole into two 12 MORPHOLOGY. Fissura longitudinalis cerebri symmetrical halves, the hemispheres of the end-brain. On probing to the bottom of the fissure, one learns that the separation is not complete, since in the middle of the cleft the two halves are united by a broad hori- zontal commissure, the corpus callosum. In front of the latter, the fissure passes to the ventral surface of the brain ; behind the commissure, the fissure likewise penetrates deeply and ends in a large transverse cleft (fissura transversa cerebri}, which separates the hemispheres from the subjacent cere- bellum. The surface of the hemispheres ex- hibits clefts and furrows of varying depths and the intervening convolutions. The ventral surface of the brain, known as the basis cerebri, is much more com- plexly modelled. In the first place, we per- ceive to what extent the hemispheres occupy also the base of the brain. In the anterior part, the fissura longitudinalis cerebri runs in the mid-line, as far backward as an X- FIG. 14. Brain viewed from above; frontal pole below, shaped Structure, the chiasmd QptlCUm. On Bulbus olfact. Tract, olfact UN. glossophar. and vagus N. accesso rit, Diagonal band ' N. optiCHS Chiasma optic. Tract, optic. Corpus . peduncnlaris (SuM. Per/, post) Pans and Sale. ' oasilaris pontit N. abducens Pyramis Oliva N. kypoglotn Cerebell Jncisura Medulla Sulc. cerebtlli Post oblongata. lateral, ant. FIG. is. Basal aspect of the brain. BASAL ASPECT OF BRAIN. 13 folding the chiasma slightly backward, one sees a thin gray and easily torn lamella stretching from the front border of the chiasma into the depth of the fissura longitudi- nalis cerebri ; this is the lamina terminalis. Forwards from the chiasma lead the nerves of sight (nervi optici}, while posteriorly and laterally, on each side, extends the visual path, the tractus optici. Lateral from the chiasma and the optic tract lies a gray field, penetrated by larger and smaller openings, the substantia perforata anterior. The anterior boundary of this field presents a triangular area, the trigonum olfactorium, from whose front point a narrow white-stripe, the tractus olfactorius, leads forward to end in the broadened terminal bulbus olfactorius. The olfactory nerve-fibres (fila olfactoria} extend from the ventral surface of the bulb as delicate white thread-like strands, that have been torn in removing the brain. Bulbus olfactorius, tractus olfactorius, trigonum olfactorium, substantia perforata anterior are all parts of the rhinencephalon. These will be more closely considered in connection with the rhinencephalon. Behind the chiasma opticum rises a gray hump, the tuber cinereum, that tapers to the infundibidum bearing a bean-shaped gray body, the hypophysis or pituitary body. The hypophysis lies in the sella turcica of the body of the sphenoid and may readily become separated in consequence of the tearing of the thin infundibulum, when the brain is taken out, so that only the conical pointed part of the infundibulum presents^ while the hypophysis remains within the sella turcica. Laterally, the tuber cine- reum is bounded by the tractus optici, whose further course is over the forward and outwardly coursing cerebral stalks, the pedunculi cerebri, and then to pass deeply. Behind the tuber cinereum, rise two white pyriform structures, the corpora mamil- laria or candicantia. Behind these and between the pedunculi cerebri lies the fossa interpeduncularis, which is prolonged backward into the recessus posterior and forward into the recessus anterior. The floor of this depression is formed by the substantia perforata posterior, a % gray surface modelled by numerous apertures and divided into halves by a median furrow. Towards the cerebral peduncle it is bounded by a groove, the sulcus nervi oculomotorii, from which emerge the fibres of the oculo- motor nerve. Behind these deeply sunken structures, appears a white, broad, transverse bridge, the pons Varolii, which in front and behind is sharply bounded, in the middle is impressed by a broad median furrow, the sulcus basilaris, and at the sides narrows and then extends laterally and backward to sink into the cerebellum. Behind the pons lies the tapering bulb, the medulla oblongata, which is prolonged into the spinal cord. It presents the median longitudinal furrow, the fissura mediana anterior, that is bounded on each side by a white strand, the pyramid or pyramis. Beyond the pyramidal tract, the sidcus lateralis anterior extends as a shallow groove, beyond which, in turn, lies an elongated egg-shaped elevation, the oliva or olivary eminence. The medulla covers the median part of. the cerebellum, occupying a broad furrow, known as the vallecula cerebelli, behind which appears the strongly arched ventral surface of the cerebellum. A deep median cleft, the incisura cerebelli posterior, separates the two halves of the little brain, the hemisphaeria cerebelli, which exhibit numerous, more or less parallel narrow tracts, the folia. On slightly raising the cerebellum, the fissura transversa cerebri appears as a deep cross cleft, separating the cerebellum from the cerebrum and opening into the fissura longitudinalis cerebri. i 4 MORPHOLOGY. Closer examination of the base of the brain leads further to the location of the exits of the individual cerebral nerves from the brain, concerning which the following table may afford explanation. The exits of these nerves from the skull are also noted. Nerve Exit from the Brain Exit from Skull I. Fila olfactoria II. N. opticus III. N. oculomotoris IV. N. trochlearis V. N. trigeminus VI. N. abducens VII. N. facialis VIII. N. acusticus IX. N. glosso- pharyngeus X. N. vagus XI. N. accessorius XII. N. hypoglossus Bulbus olfactorius Chiasma opticum Suicus nervi oculomotorii, close in front of pons, on medial edge of cerebral peduncle Dorsal, behind the corp. quadrigemina, lateral to frenulum veli medullaris an- terioris. Course around the cerebral peduncle Front border of pons, lateral, near the entrance of middle cerebellar peduncle into the cerebellum Hind border of pons, in the groove between the latter and the medulla (pyramid) Lateral to N. abducens, on hind border of pons. in front of and lateral to olive Lateral to N. facialis, on hind border of pons, lateral to olive Behind the N. facialis and N. acusticus, in upper part of furrow behind olive Behind the N, glossopharyngeus, in the furrow behind the olive Upper root -fibres (cerebral portion): behind N. vagus, in the furrow behind the olive Lower root-fibres (spinal portion) : be- tween the front and hind roots of the cervical nerves, as far as 5th or 6th. Suicus lateralis anterior, between pyra- mid and olive Lamina cribrosa Foramen opticum Fissura orbitalis superior Fissura orbitalis superior R. ophthalmicus: Fis. orbit, sup. R. maxillaris: Foram. rotundum R. mandibularis: Foram. ovale Fissura orbitalis superior Porus acusticus internus Meatus acusticus mternus Canalis facialis Foramen stylo-mastoideum Porus acusticus Foramen jugulare Foramen jugulare Foramen jugulare Canalis hypoglossi N. I, II and VIII are sensory nerves, N. V, VII, IX and X are mixed nerves, N. III. IV, VI, XI and XII are motor nerves. Let us now examine a median sagittal section through the brain. In the first place, we recognize the brain-mass belonging to the hemisphere, with its fissures and convolutions, and, further, the corpus callosum, the large commissure connecting the CORPUS CALLOSUM. 15 two cerebral hemispheres. The middle part of the bridge is the body (truncus corporis callosi) ; behind, the commissure thickens to form the splenium; while in front, it bends sharply downward and forms the knee, genu corporis callosi, that tapers into the beak- like rostrum corporis callosi. The latter is prolonged as a short thin white lamella, the Corpus callosum ( Truncus) Sept. pellncidnm Corpus callosum (Genu) Foramen Monroi Fermi* Lam. terminal!: Recessus opticus Chiasma optic. Infiindibiilntn and Hypophysis /- /undi- Tn6. Corp. bull ciner. mamillare FIG. 16. Median sagittal section through the brain. Spleninm Corp. callis Corpus pineaU Corpora quadrigemin Pedunculus cerebri Cerebellum Pans Medulla oblongata FIG. 17. Median sagittal section through the adult brain. lamina rostralis, which is continuous with the attenuated lamina terminalis that extends to the front surface of the chiasma opticum. Behind the corpus callosum, covered by the hinder part of the hemisphere, lies the cerebellum ; the deep fissura transversa cerebri is plainly seen separating the hemisphere and cerebellum. 1 6 MORPHOLOGY. Let us examine the parts of the brain lying beneath the corpus callosum. Closely attached to the under surface of the latter, a lamella of white matter extends forward from the place where the splenium joins the body or trunk of the corpus callosum. The structure gradually leaves the corpus callosum, arches downward with forwardly directed curve until close behind the lamina rostralis, and then sinks deeply into the brain-sub- stance, just behind a transversely cut white bundle of fibres, the anterior commissure or commissura anterior. This white lamella belongs to the fornix. Between the fornix, on the one hand, and the truncus, genu, rostrum and lamina rostralis of the corpus callosum, on the other, extends a thin white sheet, the septum pellucidum. Beneath the Cyrus subcallosus" J Area, parolfactoria. (Broca's field) Massa intermedia Commissura habe- quadri- posterior Corpus ma.milla.re FIG. 18. Median sagittal section through the adult brain; subcallosal region. fornix and the hind part of the corpus callosum is situated the thalamus, between whose fore-end and the descending fornix lies an opening, the foramen interventriculare or foramen of Monro. At the posterior end of the thalamus, beneath the splenium corporis callosi, lies the pineal body, the corpus pineale. The cleft, which penetrates the pineal body in front, is called the recessus pinealis. Immediately beneath is found the cross-section of the commissura posterior cerebri, with which are joined, proceeding backward, the lamina quadrigemina, the velum medullare anterius and the cerebellum. On the median surface of the thalamus, behind the foramen interventriculare, lies the cross-section of the middle commissure or massa intermedia, by means of which the opposed surfaces of the two thalami are connected. The sulcus hypothalamicus {Monroi} is a furrow that extends backward from the foramen interventriculare, beneath the massa intermedia, towards the commissura posterior TELENCEPHALON. 17 and separates the region of the thalamus from the more dependent hypothalamus. On examining this region more closely, we note again parts that have been mentioned in connection with ihe base of the brain : in front the lamina terminalis that joins the anterior surface of the chiasma opticum, the recessus options between the lamina and the chiasma and behind the latter, the recessus infundibuli, the infundibulum with the hypoph- ysis, the tuber cinereum, the corpus mamillare, and the substantia perforata posterior, forming the floor of the fossa interpeduncularis ( Tarini). Continuing backward, the cerebral peduncle, the pons and the medulla oblongata are seen in cross-section. The sulcus hypothalamicus, running backward from the foramen interventriculare, opens into the aquaeductus cerebri, or aqueduct of Sylvius, which extends beneath the quadrigeminal plate and joins the fourth ventricle that under- lies the cerebellum (Figs. 16, 17, and 18). TELENCEPHALON. The telencephalon or end-brain includes : The hemisphaerium, The pars optica hypothalami. To the hemisphaerium belong: The pallium or cerebral mantle, The rhinencephalon, The stem of the telencephalon the gray nuclei of the end-brain. To the pars optica hypothalami belong : The lamina terminalis, The chiasma opticum, The tuber cinereum, The infundibulum, The hypophysis. The hemisphaerium contributes the chief mass of the end-brain. In order to study the morphology of the telencephalon to the best advantage, one proceeds in the following manner : the brain is placed on the dorsal surface, with the base upward ; the pons, cerebellum and medulla oblongata, all connected, are completely separated from the brain by a transverse cut passing through the front border of the pons. A second cut, sagittal and in the mid-line, divides the two hemispheres from each other. In the first place, let us examine a hemisphere in general. Each hemisphere presents three surfaces : a convexly arched dorso-lateral surface, a flat median surface, and a basal surface, which is subdivided by a deep incision into a smaller anterior and a larger posterior part. We distinguish further an anterior frontal pole (pohis frontalis}, a posterior pole (polus occipitalis) and a temporal pole {polus temporalis}, the latter representing the fore-end of the posterior division of the basal surface. A dorsal border marks the transition of the lateral to the median surface ; its medial continuation forms the base to the basal border. The lateral border corresponds to the transition of the lateral at the basal surface. i8 MORPHOLOGY. PALLIUM CEREBRAL MANTLE. The surface of the pallium or cerebral mantle is subdivided into definite lobes (lobi) by definite and usually deep clefts and furrows, the fissures and sulci. Of such divisions or lobi cerebri are recognized : Lobus frontalis, Lobus parietalis, Lobus temporalis, Lobus occipitalis. An additional special lobe, the insula or island of Reil, lies hidden at the bottom of the lateral or Sylvian fissure. Each lobe further exhibits convolutions (gyri cerebri), which, while bounded by the fissures, are often connected at the bottom of the fissures Sulc. frontal. Suit med. ont, \Suh. jrae- Sulc. centralis Sulc. post- Sulc. praecentral. Sulc. frontal, inf. Sulc. reidiat. Polia frontalis Ram. ant. ascend. Ram. ant. hori- Truncus fissurae lateral. Fissur, lateral. (Ram. post.) poralis Ic. interpariet. Sulc. pariet. transfers. Sulc. intermed. Primus Fissura parieto- occipit. Sulc. intermed. secund. Snlc occipit. transvers. Sulci occipitalet superiores et later. Polus occipitalis ura praeoccipital. FIG. 19. Dorso-lateral cerebral surface. Fissures and convolutions. by deep convolutions (gyri profundi). The short superficial or sunken convolutions that connect two longer gyri are called annectant convolutions (gyri transitivt). The secondary fissures (incisura) are superficial aberrant furrows, usually uncertain in their course and springing from deeper sulci, that cut into the convolutions and in certain cases cause doubling of the gyri. LOBES AND GYRI OF THE DORSO-LATERAL SURFACE. Turning again to the basal aspect of the hemisphere, the vallecula Sylvii (fossa cerebri lateralis} appears as a deep cleft, lateral to the substantia perforata anterior, that separates the basis cerebri into an anterior and posterior division. From the valley the fissura cerebri lateralis, or Sylvian fissure, extends outward, at first as the truncus fissurae lateralis, toward the dorso-lateral surface of the hemisphere. On reaching the latter, the fissure divides into three branches : ( i ) the short ramus anterior horizontalis ; running horizontally forward, (2) the ramus anterior ascendens, also short and directed almost vertically upward, and (3) the long ramus posterior, which continues the direction of the FISSURES AND CONVOLUTIONS. 19 anterior horizontal limb backward and somewhat obliquely upward and at its end usually divides in a Y-like manner into a ramus ascendens and a ramus descendens. Approxi- mately from the middle of the dorsal border of the hemisphere, the sulcus centralis or fissure of Roland, runs obliquely downward and forward toward the posterior ramus of the fissura cerebri lateralis. As a rule, this furrow exhibits two knee-like bends, one at the junction of the upper and middle thirds, the other at the transition of the second and lower thirds ; the fissure, moreover, usually crosses the upper border of the hemisphere. Lobus frontalis. The frontal lobe lies above the fissure cerebri lateralis and in front of the central fissure, and presents the following fissures and convolutions. The sulcus praecentralis superior begins somewhat below the upper border of the hemisphere and runs more or less parallel with the sulcus centralis. Somewhat lower, the sulcus praecentralis inferior continues in the same direction and below penetrates between the ramus anterior ascendens fissurae cerebri lateralis and the lower end of the sulcus cen- tralis. The upper end of the inferior precentral sulcus almost constantly lies in advance of the lower end of the superior fissure. As variations, the precentral fissures may con- nect with the central fissure and the lower precentral may join the fissura cerebri lateralis. The sulcus frontalis superior extends forward from the superior precentral sulcus, approaching the upper border of the hemisphere in front. At times the fissure cuts through the sulcus praecentralis superior towards the central fissure, thereby producing the cruciform type of precentral furrow. In many cases the superior frontal sulcus is interrupted by two or three annectant convolutions. The fissure may also be doubled. The sulcus frontalis inferior likewise extends forward, from the inferior precntral fissure, but more arched and downward. The fissure is usually clearly marked, but it may present very variable forms and be interrupted by deep or superficial annectant convolutions. Ordinarily a short furrow, the sulcus radiatus, extends downward from the inferior frontal between the anterior horizontal and ascending rami of the fissura cerebri lateralis. The small sulcus frontalis medius is generally to be seen between the superior and inferior frontal fissures. This sulcus is often readily identified, but it may exhibit the most diverse forms, since it may be displaced or effaced by annectant convolutions. At times the fissure is clearly recognizable as a continuous and deep furrow. The foregoing fissures bound the following convolutions. The gyrus centralis anterior lies between the superior and inferior precental fissures in front and the central fissure behind. The gyrus frontalis siiperior is bounded by the superior frontal fissure below and the superior prefrontal fissure behind. Between the superior and inferior frontal fissures extends the gyrus frontalis medius, which is subdivided by the median frontal sulcus into a pars superior and a pars inferior. The gyrus frontalis inferior lies below the inferior frontal fissure. This convolution, also known as Brocd 's convolution on the left side, includes three subdivisions: The pars opercularis, between the lower end of the inferior precentral fissure and the anterior ascending ramus of the fissura cerebri lateralis; The pars triangularis, between the anterior ascending and horizontal rami of the lateral fissure ; and The pars orbitalis, between the anterior horizontal ramus and the trunk of (he lateral fissure. 20 MORPHOLOGY. Behind the sulcus centralis, or fissure of Rolando, and above the ramus posterior of the fissure of Sylvius, stretches the parietal lobe, while below the last named fissure lies the temporal lobe. Posteriorly, both lobes pass into the occipital lobe without a definite boundary. As a conventional boundary, we may adopt a line that unites the dorsal end of the parieto-occipital fissure, which incises the upper border of the hemi- sphere, with the incisura praeoccipitalis. The fissura parieto-occipitalis is a deep cleft on the hind part of the median surface of the hemisphere (Fig. 22), which incises the upper border of the hemisphere and extends a short distance on its dorso-lateral aspect. It is readily identified as a deep incision on the upper border of the hemisphere about midway between the central fissure and the occipital pole, rather nearer the latter. The incisura praeoccipitalis appears as a slight notch on the lateral border of the hemisphere, approximately at the junction of the middle and posterior thirds (Fig. 19). Lobus parietalis. The sulcus postcentralis extends behind and more or less parallel with the central fissure. This furrow is sometimes continuous, and sometimes Gyr. centr. posterior Lobulus parietalis superior Pars opercul. Gyr. fron- I p ars trianpt- talis { lari. inft rs. orbital. Gyr. frontalls superior Gyr. centralis ant Gyr. descendens ( Ecktr ) Gyr. temporalis Gyr. temp. Gyr. temporalis inferior superior medivs FIG. 20. Dorso-lateral cerebral surface. Fissures and convolutions. subdivided into two parts, the sulcus postcentralis superior and inferior. Each sub- division may retain its individuality, or at the same time join the sulcus interparietalis. When the superior postcentral fissure is independent, it usually exhibits variations in form and size, sometimes being unbranched and paralleling the central fissure, but often forming a three- or four-limbed furrow. As does the precentral, so the postcentral fissure at times anastomoses with the central fissure ; the inferior postcentral fissure, moreover, may connect with the Sylvian fissure. The sulcus interparietalis begins, mostly with a bifurcation, behind the upper end of the inferior postparietal fissure. By the junction of this sulcus with one or other of the postcentral fissures, a veritable vortex of furrows, a fissure-star, is formed. The sulcus interparietalis pursues an arched course backward, beneath the dorso-lateral end of the parieto-occipital fissure, and usually opens out into the sulcus occipitalis transversus. Occasionally the interparietal fissure passes across the transverse occipital furrow and continues backward as the sulcus occipitalis superior. The interparietal fissure is often made up of several parts ; during its course isolated fissures are given off upward as FISSURES AND CONVOLUTIONS. 21 well as downward. A short furrow, known as the sulcus parietalis transversus (Bris- saud), extends upward, towards the border of the hemisphere, from in front of the dorsal end of the parieto-occipital fissure. Often two furrows pass downward. One sulcus runs behind the ascending end-branch of the ramus posterior of the Sylvian fissure and is called the sulcus intermedius primus (Jensen). It often extends as a continuation of the upper transverse parietal fissure, but may be strongly developed and, indeed, may establish a connection between the interparietal fissure and the ascending end of the superior temporal fissure. The other sulcus is given off farther backward, runs behind the ascending end of the superior temporal fissure and is known as the sulcus intermedius secundus (Eberstaller). Both of these sulci intermedii may also exist as independent fissures. By means of the foregoing fissures the following convolutions are defined : the gyrus centralis posterior lies behind the sulcus centralis, bounded below by the fissura cerebri lateralis and behind by the fissura postcentralis. Above the sulcus interpari- etalis lies the lobulus parietalis superior, while beneath this fissure extends the lobulus parietalis inferior. This lower parietal lobule presents two special convolutions, the gyrus supramarginalis and the gyrus angularis. The gyrus supramarginalis encloses the ascending terminal stem of the ramus posterior of the Sylvian fissure and is bounded by the sulcus intermedius primus behind. The gyrus angularis surrounds the ascending end of the superior temporal fissure, and is bounded in front by the sulcus intermedius primus and behind by the sulcus intermedius secundus. Lobus temporalis. One of the most constant fissures is the sulcus temporalis superior. It begins in front at the temporal pole, extends backward and upward parallel to the fissura cerebri lateralis and ends, as a rule, in the gyrus angularis by running upward behind the ascending terminal branch of the fissura cerebri lateralis. At times one finds a forking into an ascending and a descending branch. The sulcus temporalis medius runs below the superior temporal fissure. The fissure is seldom continuous, usually being made up of several parts. Below the middle temporal fissure, and on the basal surface, extends the sulcus temporalis inferior. The three temporal convolutions are defined by these fissures. The gyrus temporalis superior extends below the sulcus cerebri lateralis and above the superior temporal fissure ; the gyrus temporalis medius lies between the superior and middle temporal sulci ; and the gyrus temporalis inferior is located below the inferior temporal fissure. The surface of the upper temporal con- volution facing the Sylvian fissure presents the gyri temporales transversi, also known as the convolutions of Heschl, which are weakly developed in the front half and more strongly behind. Lobus occipitalis. The anterior bound- Sulc. centra /it ittsvlae ary of the lobus occipitalis is formed in part FlG 2I ._ Fissures and convolutions of the insuia. by the sulcus occipitalis transversus, a sulcus liable to many variations respecting its position, length and direction. In addition, there are the sulci occipitales superiorcs and the sulci occipitalcs lateralcs. By means of these fissures the gyri occipitales superiores and the gyri occipitales laterales are defined. Towards the oc- cipital pole, the convolutions join a vertical gyrus, known as the gyrus descendens (Ecker). 22 MORPHOLOGY. Insula. On penetrating the depth of the fissura cerebri lateralis, by drawing apart the edges of the bounding lobes, one comes to a deep depression, the fossa cerebri lateralis {SylviC), at the bottom of which lies the insula, also known as the basic lobe (Stammlappen). Those parts of the lobes bounding the Sylvian fissure, which cover- in the island, together constitute the operculum. Since the frontal, parietal and temporal lobes participate in its production, we distinguish a pars frontalis, a pars parietalis and a pars temporalis of the operculum. The surface of the temporal lobe directed towards the insula presents the sulci and gyri temporales transversi. Similar fissures and con- volutions exist also upon the surfaces of the parietal and frontal opercula facing the island. The insula appears in the form of an irregular conical projection, a three-sided pyramid whose apex the island-pole is directed forward and outward. The island is Looulus Sitlcns paracentralis paractntr. Sulcus centralis Corpus callosunt Sulcus carports callosi Sulcvs cinguli Gyr frontal s Lobus quadrangulans < _ ( Dechve ) ( Pars posterior The lingula lies deeply placed in the incisura cerebelli anterior and consists ot from four to six or eight small lamellae, which rest upon and are fused with the velum medullare anterius. Lateral from the posterior lamellae, the vinicula lingulae extend toward the middle cerebral peduncle. Behind the lingula, and separated from it by the sulcus praecentralis, follows the lobulus centralis, which overhangs the lingula and laterally sends out its lamellae, the aloe lobuli centralis. The monticulus, the largest segment of the superior worm, lies behind the lobulus centralis, separated from the latter by the' sulcus postcentralis. It includes the culmen and the declive and corresponds to the hemisphere-segment of the lobulus quadrangularis. The latter is subdivided by the sulcus superior anterior into a pars anterior and a pars posterior, corresponding to the culmen and declive respectively. B. Lobus Posterior. The lobus posterior includes the hind part of the upper surface and the posterior half of the under surface of the cerebellum. It is separated Stile, praepyramidalis Stile, postpyramidalis Sulc inf. ant. Sitlc inf. fast.- us gracilis Lobulns semiliinari inferior FIG. 77. Lower surface of the cerebellum. from the lobus superior by the sulcus superior posterior, and from the lobus inferior by the sulcus postpyramidalis in the worm and by the sulcus inferior anterior in the hemi- sphere. The sulcus inferior anterior may be readily identified if the course of the sulcus superior posterior be followed. It begins at the side, on the front border of the hemi- 74 MORPHOLOGY. sphere, in the sulcus horizontalis cerebelli at the place where the sulcus superior posterior opens, thence runs in a curve toward the worm, where it ends in the deeply pene- trating sulcus postpyramidalis. By means of the sulcus horizontalis and the sulcus inferior posterior, the posterior lobe of the hemisphere is subdivided into three parts, which correspond with two segments of the worm. HEMISPHERE Lobulus semilunaris superior Lobulus semilunaris inferior Lobulus gracilis WORM Folium vermis . . Tuber vermis . . The folium vermis lies in the incisura cerebelli posterior, forms a single stout lamella and connects the two upper crescentic lobules, the lobuli semilunares superiores. The tuber vermis or tuber valvulae corresponds to the lobulus semilunaris inferior and the lobulus gracilis. The lobulus semilunaris inferior is broad medially and narrow laterally, and often separated into two parts, an anterior and a posterior, by a lateral fissure that runs into the sulcus horizontalis. The anterior and smaller part maintains approximately the same width throughout and at the side is applied to the lateral end of the lobulus gracilis. The posterior and larger part exhibits usually two or three small lobules, often two crescentic segments, of which one begins medially at the worm with the thicker end and ends laterally in a point, and the other begins broad at the side and becomes pointed toward the worm. The lobulus gracilis lies in front of the lobulus semilunaris inferior, maintains a more or less constant thickness throughout, and is separated from the lobulus semilunaris inferior by the sulcus inferior posterior and from the lobus inferior by the sulcus inferior anterior. C. Lobus Inferior. This lobe includes the following parts : WORM HEMISPHERE Pyramis Lobulus biventer Uvula Tonsilla Nodulus FIOCCUIUS Velum medullare jost. Nodulus Flocculus Lotulus gracilis s temilunaris inferior PIG. 78. Cerebellum viewed from below and in front. The pyramid, separated from the tuber vermis by the sulcus postpyramidalis ; connects the biventral lobule of the one side with that of the other. A fissure splits each lobulus biventer into two portions, an anterior medial and a posterior lateral. THE CEREBELLUM. 75 Pyramis Uvula Lobulus cent The tonsilla is embraced by a medially concave curve described by the sulcus praepyramidalis, which separates the pyramis from the uvula. In advance of the uvula lies a small conical structure, the nodulus. Immediately in front of the latter is a thin white sheet, the velum medullare posterius, that continues laterally on each side as the pedunculi flocculi to join the flocculus. Lateral to the latter, between the lobulus quadrangularis of the superior lobes and the lobulus Declive Fol!nm verm - Tnber vermit biventer is seen the accessory flocculus, flocculus secundarius. On removing the tonsil, a broad lamella, the ala uvulae, or the furrowed band, is seen pass- ing outward from the uvula. The posterior margin of this band is free, its anterior one is continuous with the posterior medullary ve- lum. The deep recess, whose floor is formed by the ala uvulae and the velum medullare posterius, lodges the tonsil and is called the nidus avis. Its lateral wall is contributed by the lobulus biventer and the pedunculus flocculi, while it is bounded medially by the uvula and behind by the pyramid. The lobulus biventer forms the lateral, the tonsil the medial and the flocculus the anterior part of the lobus inferior. The foregoing relations are recapitulated in the following table: Lingulai-^^ IV. Ventricul-us Pans' FIG. 79. Median sagittal section through the worm of the cerebellum. Lobus superior Lobus posterior Lobus inferior VERMIS Lingula , , Sulcus praecentralis Lobulus centralis Sulcus postcentralis HEMISPHAERIUM Vinculum lingulae Monticulus Culmen Declive Ala lobuli centralis Lobulus quadran- gularis Pars anterior Sulc. sup. ant. Pars posterior Folium vermis. . Tuber vermis. Sulcus postpyramidalis Pyramis Sulcus praepyramidalis Uvula Nodulus . . . Sulcus superior posterior Lobulus semilunaris superior Sulcus horizontalis cerebelli Lobulus semilunaris inferior Sulcus inferior posterior Lobulus gracilis Sulcus inferior anterior Lobulus biventer Tonsilla Flocculus (Flocculus secundarius) On sectioning the cerebellum, we recognize the internally situated white medullary substance, the corpus medullare, and the substantia corticalis, which invests the periphery as a thin continuous band of gray matter. The medullary substance of the cerebellum 76 MORPHOLOGY. is composed of that of the hemispheres and of the worm, which are continuous medially. Stout tracts of medullary substance, the laminae medullares, pass outward from the medullary centre and send off, mostly at acute angles, secondary medullary laminae, The latter, in turn, give off still smaller sheets, which finally are enclosed by gray substance and represent the cerebellar convolutions or folia, the gyri 4 cerebelli. This structure, when viewed in sagittal sections, is known as the arbor medullaris, on account of the tree-like branching. In sagittal sections through the worm, where this delicate figure is particularly well seen, it is called the arbor vitae vermis. The medulla of the hemispheres is con- nected with neighboring parts of the brain by masses of nerve fibres. These masses constitute more or less robust columns, which are termed the peduncles, crura or brachia of the cerebellum and serve to connect it with the pons, the mid-brain and the medulla oblongata. The brachia pontis, middle cerebellar peduncles, or crura cerebelli ad pontem, emerge on each side from the horizontal sulcus at the anterior border, between the FIG. 80. Schematic representation of the crura cerebelli. Blue, superior peduncle; green, middle peduncle; yellow, inferior peduncle. FIG. 81. Superior cerebellar peduncles, also termed crura cerebelli ad corpora quadrigemina and bract Portion of the cerebellum has been removed to expose the dentate nuclei. lobulus quadrangularis, tonsilla and flocculus, and pass convergingly forward, to blend with the pons. The crura cerebelli ad cerebrum or superior cerebellar peduncles, also known as the crura cerebelli ad corpora quadrigemina and the brachia conjunctiva cerebelli, lie MEDULLA OBLONGATA. 77 in front of the pontile crura, pass as flattened cylindrical columns convergingly forward and disappear beneath the quadrigeminal bodies. The velum medullare anterius stretches out between them. Tractus cerebro-splnalis \\~ FIG. 82. Brachia pontis or middle cerebellar peduncles and corpora restiforme or inferior cerebellar peduncles. The crura cerebelli ad medullam oblongatam or inferior cerebellar peduncles, also often called the corpora restiformia, pass out between the foregoing cerebellar arms and turn sharply backward and downward into the medulla oblongata. MYELENCEPHALON. MEDULLA OBLONGATA. The upper boundary of the medulla oblongata is marked ventrally by the inferior edge of the pons and dorsally by the striae acusticae in the floor of the fourth ventricle ; the lower boundary is indicated by the attachment of the upper root-bundles of the first cervical nerves, or, ventrally, by the lower limit of the pyramidal decussation. Let us first examine the ventral surface of the medulla (Fig. 75). In the mid- line runs the fissura mediana anterior, which is prolonged into the fissure of the spinal cord bearing the same name, but separated from it by the crossing fibre-bundles of the pyramidal decussation, decussatio pyramidum. Toward the lower edge of the pons, the fissure widens into a small depression, the foramen caecum. On both sides the median fissure is bordered by the pyramid, a slightly convex tapering column, broad above and narrow toward the spinal cord, which appears to pass into the anterior column of the cord. Only a small part of the pyramidal fibres, however, actually maintains a course along the anterior median fissure in the anterior column of the spinal cord, since the greater part crosses the rnid-line in the decussatio pyramidum and continues within the lateral column of the cord of the opposite side. The part which continues within the anterior column is known as the anterior pyramidal tract, that within the opposite lateral column as the lateral pyramidal tract. These will receive more detailed attention in the consideration of the fibre-paths (page 161). MORPHOLOGY. The pyramid is bounded on the outer side by the sulcus lateralis anterior, from which emerge the root-bundles of the hypoglossal nerve. Lateral to the sulcus lateralis and adjoining the pyramid is seen the oliva, an ovoid eminence whose thicker end reaches as far as the pons and which narrows below. The sulcus lateralis anterior may be marked, especially in its lower part, by transversely arching strands of fibres, known as the fibrae arcuatae. Turning now to the dorsal aspect of the medulla (Fig. 83), we note, in the lower part, the sulcus medianus posterior, which above is soon closed by a thin medullary sheet, the obex. At this point, beneath the obex, the central canal of the cord opens Fovea superior, Area. acustica\. Taenia ventricnli uarti Ventricul. Arantii Obex post. termed, post. Funie. gracilis Fun. cuneat. Fun. lateralis Sulc. lateral, post. FIG. 83. Fossa rhomboidea, showing details of the floor of the fourth ventricle. into the fourth ventricle. Lateral to the sulcus medianus, next comes the sulcus inter- medius posterior, which in the upper part of the medulla runs laterally and then disappears. Farther outward is the less distinct sulcus lateralis posterior, which likewise turns out- ward and may be followed to about the level of the middle of the olive. Between the median and lateral posterior sulci, the posterior column, funiculus posterior, represents the upward prolongation of the corresponding column of the spinal cord. By means of the sulcus intermedius posterior the funiculus is subdivided into two special tracts. On each side of the posterior median fissure, between the latter and the posterior interme- diate fissure, lies the fasciculus gracilis, or Golfs column, continued upward from the cord. In the upper part it broadens into the clava and then, again narrowing, proceeds laterally and upward. Between the lateral and intermediate posterior sulci runs the fasciculus cuneatus, the upward prolongation of BurdacK s column, which at the level of THE FOURTH VENTRICLE. 79 the clava expands into the tuberculum cuneatum and higher up also bends outward. Lateral to the sulcus lateralis posterior, between it and the sulcus lateralis anterior, the lateral column, funiculus lateralis, ascends from the spinal cord. After reaching the lower end of the olive, the column passes laterally and dorsally, close to the olive, almost as far as the pons. It is separated into a dorsal and a ventral part by a slight furrow, along which emerge the delicate root-fibres of the accessory, vagus and glossopharyngeal nerves. The dorsal part of the funiculus lateralis broadens above and, in the region behind the tuberculum cuneatum, swells into the tuberculum cinereum. Farther above, it passes laterally in company with the upper ends of the column of Goll and of Burdach. These upward and laterally directed portions of the column of Goll and of Burdach and the dorsal segment of the funiculus lateralis collectively constitute the corpus restiforme or inferior cerebellar peduncle, also called the cms cerebelli ad medullam oblongatam, that passes to the cerebellum. Medially, the corpus restiforme borders the lateral margin of the fourth ventricle. The fossa rhomboidea, which forms the floor of the fourth ventricle, overlies the dorsal surface of the preceding parts. VENTRICULUS QUARTUS. Isthmus, metencephalon and myelencephalon together surround the fourth ventricle, a cavity filled with a small amount of cerebro-spinal fluid, which below passes into the central canal of the spinal cord and above is continuous with the Sylvian aqueduct. Three segments are distinguished, the pars inferior, the pars intermedia and the pars superior ventriculi quarti. The pars inferior belongs to the medulla oblongata and is embraced by the cor- pora restiformia. The pars intermedia forms the middle and broadest portion and continues above into the region between the pontile crura. The pars superior belongs to the isthmus rhombencephali, its dorsal boundary being formed by the brachia conjunctiva cerebelli and the velum medullare anterius. The floor of the fourth ventricle is formed by the fossa rhomboidea and its roof by the anterior medullary velum, the superior cerebellar peduncles or brachia conjunctiva, the posterior medullary velum and the tela chorioidea. The posterior medullary velum and the tela chorioidea together constitute the legmen fossae rhomboideae, the roof in the limited sense. The edge along which the anterior and posterior medullary vela meet is known as the fastigium; at this place the fourth ventricle projects into the medullary substance of the cerebellum, forming the tent-like recessus tecti. The pars intermedia extends laterally on each side into the recessus lateralis ventriculi quarti. Originally the fourth ventricle is a closed cavity, except above where it communicates with the third ventricle by means of the aquaeductus cerebri and below where it is continuous with the central canal of the spinal cord. Its floor and roof are clothed with epithelium, the epen- dyma. On the roof this epithelium lines the anterior and posterior medullary vela and then continues as the thin lamina chorioidea epithelialis, which is attached to the tela chorioidea ventriculi quarti and thence is prolonged onto the borders of the abutting parts of the brain. If the ventricle be forcibly opened behind from above, as when the tela chorioidea is removed, the thin epithelial lamina is likewise torn. The separation takes place where the lamina passed onto the more robust surrounding parts of the brain, only 8o MORPHOLOGY. a thin white edge, the taenia ventriculi quarti, remaining along the borders of the tear. The taenia of the fourth ventricle begins at the obex, thence passes onto the corpus resti- forme, there forms the posterior border of the recessus lateralis and continues along the peduncle of the flocculus and the posterior medullary velum. The tela chorioidea of the fourth ventricle represents that part of the pia mater cerebri that projects between the ven- tral surface of the cerebellum, more particularly the uvula and the tonsilla, and the dorsal surface of the medulla oblongata (Fig. 84). The two pial sheets are united by subarachnoidal tissue. The tela chorioidea has the form of an equilateral triangle, whose anteriorly directed base is attached in the middle to the nodulus and at the sides along the posteripr medullary velum and the flocculus, and whose apex is directed posteriorly toward the hind end of the fourth ventricle. It pushes into the ventricle villiform proc- esses that constitute the plexus chorioideus ventriculi quarti, subdivided into medial and Velum medullare anterius Corpora quadrigetnina IV. Ventriatlus Arachnoidia Velum medullare Post. Tela chorioidea Cisterna cerebello-mednllaris Afertura medialis Medulla oblongata FIG. 84. Sagittal section through fourth ventricle, showing relations of the tela chorioidea. Ependyma, red; pia mater, blue. lateral portions. The medial plexus consists of two thin stripes that pass in the mid-line, close together, from behind forward to the nodulus. From the latter, the lateral plexus continues, on each side, outward into the recessus lateralis ventriculi quarti. In the early condition, the tela chorioidea, with the lamina chorioidea epithelialis, completely closes the posterior part of the fourth ventricle. Later, however, openings are formed at those places, at which the tela chorioidea and the lamina epithelialis are broken through. Such an opening is the apertura medialis ventriculi quarti or the foramen of Magendi, situated in the posterior part of the tela chorioidea immediately in front of the obex. At the sides, in each lateral recess, is found the apertura laleralis ventriculi quarti (Key-Retzii) or the foramen of Luschka. Through these three openings the ends of the medial and lateral parts of the choroid plexus of the fourth ventricle pass and project into the sub- arachnoid space, communication between the ventricle and the subarachnoid space being in this manner established. The villi which protrude through the apertura lateralis are readily found, since they lie medial to the flocculus, between the latter, the lobulus biventer and the tonsilla. FLOOR OF THE FOURTH VENTRICLE. Si Fossa Rhomboidea. The floor of the fourth ventricle, the fossa rhomboidea, is, as indicated by its name, rhomboidal in outline. Its posterior part, bordered by the corpora restiformia, belongs to the myelencephalon ; its middle part lies in the metencephalon ; and its anterior part belongs to the isthmus. By means of a longitudinal furrow, sulcus medianus fossae rhomboideae ', it is divided into symmetrical halves. Transversely coursing white bands, the striae medullares or striae acusticae, which run from the lateral recesses toward the mid-line, separate the pars superior from the pars inferior fossae rhomboideae. The part of the fossa included between the medullary striae constitutes the pars intermedia. The striae medullares present many variations in their course and develop- ment. They may be wanting or many, but are seldom identical in development Fossa mediana Fovea superior Taenia ventriculi guarti Ventricvl. Arantii Tuberc. cinerevm Fvnic. gracilis Fun. cjmeat. Fnn. lateralit FIG. 85. Dorsal surface of the medulla oblongata. Fossa rhomboidea. Obex Stile, median, post. Sulc. intermed. post Sulc. lateral, post. and course on the two sides. Often they run obliquely outward and upward from the sulcus medianus. The pars inferior of the ventricle deepens in its lower portion, presents several fields defined by furrows and, on account of its peculiar shape, is called the calamus scriptorius. At the lower border of the pars inferior lies the obex, a thin white medullary sheet from which the taeniae ventriculi quarti pass laterally. Immediately in front of the obex, where the sulcus medianus sinks into the central canal of the spinal cord, is a small depression, the ventriculus Arantii. In the pars superior, the median sulcus widens into the fossa mediana. On each side of the median furrow, a flat ridge, the eminentia medialis, extends the entire length of the ventricular floor. This ridge is narrow in its lower part and forms 6 82 MORPHOLOGY. a triangular field, the trigonum nervi hypoglossi, whose base is above at the striae medul- lares and apex below, directed toward the ventriculus Arantii. On careful inspection, two special divisions of this field are recognized, an outer broader part, the area plumiformis (Retzius), and an inner narrower one, the area medialis trigoni nervi hypoglossi (Retzius). At the border between those two fields are to be seen mostly short, obliquely coursing delicate furrows and folds, and likewise a thin feathery band. Such markings are often visible also at the lateral border of the trigonum hypoglossi. Retzius, therefore, named this lateral and broader field, "area plumiformis. ' ' In the upper part of the ventricular floor, the eminentia medialis is broader and pro- jects more into the ventricle. The elevation is termed the colliculus facialis. Laterally, the eminentia medialis is defined by the sulcus limitans, which in the pars superior widens into the fovea superior, and in the pars inferior into the fovea inferior. Below the fovea inferior, and lateral to the trigonum hypoglossi, is seen a gray oblique triangular field, known as the a/a cinerea, which begins pointed at the fovea inferior and broadens toward the lower border of the fossa rhomboidea. In front of the posterior border of the fossa and behind the ala cinerea, lies a small gray mammillated field, the area postrema, that extends from the mid-line along the lower border of the ventricle forward and outward. A light narrow band, known as the funiciilus separans, runs from the opening central canal outward and forward, between the area postrema and the ala cinerea. The fovea superior is accompanied laterally by a bluish colored area, the locus caeru- leus. The latter and the superior fovea exhibit small furrows and folds, rugae loci caerulei et foveae superioris, which may often be followed, for a considerable distance, for- ward toward the isthmus and backward toward the recessus lateralis. To the outer side of the sulcus limitans, lateral to the fovea superior, the fovea inferior and the ala cinerea, the area acustica is seen as a flat elevation, which toward the recessus lateralis presents the tuberculum acusticum. The funiculus separans, above noted, courses toward the lower inner end of the area acustica and there disappears. THE GRAY MASSES OF THE RHOMBENCEPHALON. In the floor of the trigonum lemnisci, in the isthmus, lies the nucleus lemnisci. The pons includes a larger ventral portion, the pars basilaris pontis, and a smaller dorsal one, the pars dorsalis pontis. These two divisions are readily seen in a cross- section. The basal part exhibits numerous transversely coursing white fibre-strands that continue laterally into the pontile crura or middle cerebellar peduncles. In the lower part of the basilar division, between the thin white fibre-bundles, grayish lamellae repre- sent the cross-sections of the tracts of fibres, which descend from the cerebral peduncles, pass through the entire pons and continue to the medulla oblongata and the spinal cord. These are the pyramidal tracts, the fasciculi longitudinales pyramidales. The fibrae pontis superficiales are seen as transversely coursing fibres that pass ventral to the pyram- idal tracts, while the Jibrae pontis profundae run dorsal to or partly through the pyramidal strands. The pontile nuclei, nuclei pontis, are small masses of gray substance lying scattered between the bundles of fibres. nervi cochleae, NUCLEI OF THE HIND-BRAIN. 83 The pars dorsalis pontis, also termed the tegmentum pontis, appears gray in transverse sections. It contains the following nuclei : The nucleus nervi abducentis, within the colliculus facialis, The nucleus nervi facialis, The nucleus motorius et sensibilis nervi trigemini, The nucleus tractus spinalis nervi trigemini, The nuclei nervi acustici, within the area acustica, embracing : Nucleus medialis Nucleus dorsalis Nucleus medialis Nucleus lateralis (Deiters) Nucleus superior (Bechterew) Nucleus n. vestibularis spinalis The nucleus olivaris superior, The nucleus corporis trapezoidei, The nuclei reticulares tegmenti. 'Within the cerebellum (Fig. 87), in addition to the cortex or substantia cortl- calis covering the entire surface, special gray masses are found within the corpus nervi vestibuli, Tegmentum pontis N. trigemin and sensory trigeminus nuclei Stratum profnndit pantis Pyramidal tracts __ Stratum superficial^ pontis FIG. 86. Cross-section of brain-stem in region of pons. medullare. In the medial part of the hemisphere lies the nucleus dentattis, which appears as a much plicated lamella of gray substance with a medially directed opening, the hilus nuclei dcntati. Within the worm, the roof-nucleus, nucleus fastigii or nucleus tecti, lies on each side of the mid-line. Between the nucleus fastigii and the nucleus dentatus, two additional centres are found, the nuclei globosi, small gray masses lateral to the roof-nucleus, and the nucleus emboliformis, medial to the dentate nucleus. 8 4 MORPHOLOGY. Nucleus fastigii Nuclei globosi Nucl. embolifortnis Nucleus dentatiis Within the medulla oblongata, in the fasciculus gracilis within the clava, lies the nucleus fasciculi gracilis, while in the fasciculus cuneatus, in its position correspond- ing to the tuberculum cuneatum, lies the nucleus fasciculi cuneati, The tuberculum cinereum corre- sponds to the nucleus tractus spi- nalis nervi trigemini. Within the olive are found the nucleus oliva- ris inferior, with the nuclei of the two accessory olives, the nucleus olivaris accessorius ventralis and dorsalis. The nuclei arcuati lie ventral to the pyramidal tracts, while within the lateral columns are ^ e nuclei PIG. 87. Horizontal section of the cerebellum, exposing the internal nuclei. Posterior column nuclei FIG. 88. Diagram of the brain-stem, dorsal aspect, showing the location of the nuclei of the cerebral nerves. Motor nuclei are red, sensory nuclei are blue. The floor of the trigonum hypoglossi contains the nucleus nervi hypoglossi. Close to the latter but within the floor of the ala cinerea, is the sensory nucleus of the vagus SUMMARY OF RHOMBENCEPHALON. 85 nerve, which anteriorly is continuous with the like nucleus of the glossopharyngeal nerve. In this region, medial to the ala cinerea, the motor nucleus dorsalis of the glossopharyn- geal and vagus nerves appears as a small group of cells. The nucleus tractus solitarii occupies the elongation of the sensory nucleus of the glossopharyngeal and vagus nerves. Somewhat lateral, but more deeply placed, lies the nucleus ventralis or nucleus ambiguus of the ninth and tenth nerves. The caudal prolongation of the nucleus ambiguus con- FiG. 89. Diagram of brain-stem, lateral aspect, showing location of nuclei of cerebral nerves. Motor nuclei are red, sensory nuclei are blue. tains the elongated nucleus nervi accessorii, whose spinal part reaches into the ventral horn of the spinal cord. The nerve-cells within the formatio reticularis, occurring scattered or in small groups, constitute the micleus of the formatio reticularis. The more important of these nuclei are discussed at greater length in connection with the Fibre-Tracts. The positions of the nuclei of the cerebral nerves are diagram- matically shown in Figs. 88 and 89. SUMMARY OF THE RHOMBENCEPHALON. To the rhombencephalon or hind-brain belong : The isthmus rhombencephali, The metencephalon, The myelencephalon. It encloses the fourth ventricle. To the isthmus rhombencephali belong : Dorsal The brachia conjunctiva cerebelli, The velum medullare anterius, The trigonum lemnisci ; Ventral The crura cerebri. To the metencephalon belong : The pons and the cerebellum. 86 MORPHOLOGY. The cerebellum is subdivided into the worm and the hemispheres. More or less deeply penetrating fissures separate the lobes of the hemispheres from one another. The chief segments are the lobus superior, the lobus posterior and the lobus inferior, each of which is made up of lobules. The individual lobes and lobules of the hemispheres corre- spond to definite divisions of the worm. The myelencephalon, or the medulla oblongata, has as its upper boundary, ventrally the lower border of the pons, dorsally the striae medullares fossae rhomboideae. Below, the medulla passes into the spinal cord, its ventral boundary being the lower end of the pyramidal decussation. Dorsal, behind the rhomboid fossa, are the dorsal and lateral columns, with their tubercula, and the restiform bodies. Ventral, lie the pyramids and the olives. The fourth ventricle has as its roof the velum medullare anterius, the brachia conjunctiva cerebelli, the velum medullare posterius and the tela chorioidea ; as its floor, the fossa rhomboidea. It is connected with the third ventricle by means of the aquae- ductus cerebri, below is continuous with the central canal of the spinal cord, and com- municates with the subarachnoid space by means of the apertura mediana (foramen Magendii) and the aperturae laterales (foramina Luschkae). The most important masses of gray substance within the rhombencephalon are : The nucleus lemnisci, The nucleus pontis, The substantia corticalis cerebelli, The nucleus dentatus The nucleus fastigii ~, i . r cerebelli, The nucleus globosi The nucleus emboliformis The nucleus gracilis, The nucleus cuneatus, The nucleus lateralis, The nucleus arcuatus, The nucleus olivaris inferioris, The nuclei nervorum, within the floor of the fourth ventricle. THE MENINGES. The membranes investing the brain are three : the dura mater, the arachnoid and the pia mater. The dura mater forms the outermost covering of the brain. Beneath it lies the arachnoid, a delicate transparent membrane that is separated from the dura by the sub- dural space. The innermost covering is the pia mater, separated from the arachnoid by the subarachnoidal space. The arachnoid and the pia have been also regarded as the outer and inner layers of the soft-brain membrane, the leptomeninx, in contrast to the hard brain-membrane, the pachymeninx, represented by the dura. BRAIN-MEMBRANES. 87 DURA MATER. The dura mater consists of two lamellae. The outer lamella, which lies against the bone and serves as the inner periosteum of the cranial case, consists of soft, loose vascular connective tissue. The inner lamella is denser, made up of fibrous connective tissue, and contains few blood-vessels. While the outer layer appears as periosteum and is prolonged on the cerebral nerves as robust sheaths, the inner layer comes into closer relation with the brain, since it sends processes between the larger divisions of the brain. Such processes are : i. The falx cerebri, or falx cerebri major, which, penetrating between the hemi- spheres, begins in front at the crista galli, attached by its convex upper border to the sides of the sulcus sagittalis of the cranial vault, and extends backward as far as the protuberantia occipitalis interna. Between the outer and inner lamellae, along the upper convex border of the falx, is a blood-space, which is triangular in cros§ion and known as the sinus sagittalis superior. The lower concave border of the sickle-like falx is free and encloses the smaller sinus sagittalis inferior. From the internal occipital protuberance Sinus sagittalis superior 'ilationts Pacchioni Cranium Spatinm epidural. Dura rnater Spatinm snbdural. Arachnoidea Spatinm snbarach. Pia mater Substantia corticalis cerebri Falx cerebri FIG. 90. Schematic section through the skull and the meninges. forward, the falx is attached to the tent-like tentorium cerebelli, the line of junction being the tent-edge, while the border attached to the crista galli is the crest-edge. In front, the falx only incompletely separates the two frontal lobes, but behind its height is so increased, that it penetrates almost, but not quite, to the upper surface of the corpus callosum. 2. The falx cerebelli, or falx cerebri minor, which forms a small sagittal pro- longation of the large falx, penetrates between the cerebellar hemispheres and descends from the internal occipital protuberance to the foramen magnum. The convex border encloses the sinus occipitalis and is attached along the crista occipitalis. Corresponding to the terminal limits of the crest, the cerebellar falx divides into two diverging arms, which enclose the continuations of the sinus occipitalis. 3. The tentorium cerebelli, which forms a dorsally arched transverse partition between the basal surface of the occipital lobes of the cerebrum and the dorsal surface of the cerebellum. The outer convex margin is attached, on each side, along the lineae transversae of the occipital and parietal bones, where it encloses the sinus transversus, and along the dorsal edge of the petrous portion of the temporal bone, where it conveys the sinus petrosus superior. Thence the attachment of the tentorium passes to the pro- 88 MORPHOLOGY. cessus clinoides anterior. In front, the free inner margin of the tentorium meets the outer one and then extends backward and slightly upward to unite with the lower edge of the falx cerebri. Along this line of union lies the sinus rectus, which in front receives the vena cerebri magna Galeni (Fig. 55) and behind opens into the confluens simium or the torcular Herophili. 4. The diaphragma sellae turcicae, which forms a bridge of dural tissue over this depression in the sphenoid bone. Between the basal and dorsal lamellae of the diaphragma sellae turcicae lies the hypophysis or pituitary body. An opening in the middle of the membrane, the foramen diaphragmatis, affords passage to the infundibulum. ARACHNOIDEA. This delicate transparent membrane consists of connective tissue and is devoid of blood-vessels. It is separated from the dura by the subdural space and connected with the pia by strands of connective tissue. These strands form the subarachnoidal tissue, and the cleft between the arachnoid and the pia is the subarachnoidal space. The latter is traversed by the connective tissue trabeculae and plates of the subarachnoidal tissue and contains a fluid, the liquor cerebro-spinalis, in considerable quantity. The subarach- noidal space communicates with the ventricles by means of the foramen Magendii and the foramina Luschkae (page 80). Over the cerebral convolutions the subarachnoidal tissue is scanty, in these localities the arachnoid and the pia being fused into a common membrane. Over the cerebral fissures, on the contrary, the space between the two membranes is larger, since the pia penetrates into the fissures. The large spaces are found principally at the base of the brain and where the latter passes into the spinal cord ; in these locations, at certain places, the arachnoid is widely separated from the pia, resulting in the formation of the cisternae subarachnoideales. Such spaces are : The cisterna cerebello-medullaris ; between the posterior border of the cerebellum and the medulla oblongata ; The cisterna fossae Sylvii, over the Sylvian fossa ; The cisterna chiasmatis, surrounding the optic chiasm ; The cisterna interpeduncularis , between the cerebral crura ; The cisterna ambiens, ascending laterally from the cerebral peduncles to the corpora quadrigemina ; The cisterna corporis callosi, along the convex dorsal surface of the callosum. In certain places, as on both sides of the sinus sagittalis superior or along the sinus transversus, villous projections from the outer surface of the arachnoid push before them the thin dura mater and encroach on the venous sinuses. Such elevations are called the arachnoidal villi or Pacchonian granulations (Fig. 90). According to the investigations of Key and Retzius, these structures facilitate the passage of serous fluid into the venous spaces. PIA MATER. The innermost brain-membrane consists of delicate bundles of connective tissue, con- tains numerous blood-vessels, and directly invests the surface of the brain, penetrating to the bottom of all the fissures. By means of the subarachnoidal tissue, the pia is attached to the arachnoid. Between the pia and the surface of the brain, there exists only a very narrow cleft, the subpial or epicerebral space. THE SPINAL CORD. 89 Pyramit THE SPINAL CORD. The spinal cord or medulla spinalis presents a compressed cylindrical column, some- what more flattened in front than behind, that is enclosed within its protecting membranes and only incompletely fills the vertebral canal. Above, it passes into the medulla oblongata, the upper limit corre- sponding to the lower end of the pyramidal decussation. Below, the spinal cord reaches to the level of the first or second lumbar vertebra. It is not everywhere of equal thickness, but in two places exhibits spindle-shaped enlargements (Fig. 91) : a. In the cervical region of the spine the cervical enlargement, intumescentia cervicalis, from the third cervical to the second thoracic vertebra ; b. In the lower part of the thoracic spine the lumbar enlargement, intumescentia lumbalis, from the ninth thoracic to the second lumbar vertebra. Both enlargements correspond to the regions in which the large limb-nerves arise. The lumbar enlargement below passes over into a short conical segment, the conus medullaris or conus terminalis, from which proceeds a long delicate thread-like process, the Jilum terminale. The average length of the spinal cord is 45 cm. in men, and from 41-42 cm. in women. In accordance with the pairs of spinal nerves given off from the cord, we recog- nize a pars cervicalis, from which the cervical nerves emerge ; a pars thoracalis, from which the thoracic nerves arise, and a pars lumbalis, from which the lumbar and the sacral nerves are derived. EXTERNAL CONFIGURATION. The anterior or ventral surface of the spinal cord is cleft in the mid-line by a deep longitudinal furrow, ihejissura mediana anterior ; the posterior or dorsal surface is modelled by a superficial longitu- dinal groove, the sulcus medianus posterior. By Radix posterior ~^C\ \* f /^^s^ Sulcus lateralis posterior Cornu postering ^ -Formatio retlcularis Funiculus lateral. Intumescent, lumbalis Conns medullarit Filum terminale FIG. 91. Front view of the spinal cord. Schematic. Funiculus posterior Sulc. med. Fasciculus gradlis post. Sulcus intermedius posterior Pasc. cune v. Radix antei Colu Corn* anterius Sulc. lat. anterior Fissura mediana anterior Funiculus anterior FIG. 92. Transverse section of the spinal cord. means of these two fur- rows the spinal cord is divided into symmetrical halves. Lateral to the posterior median sulcus, in each half runs the sulcus lateralis posterior, along which the pos- terior root-bundles enter. MORPHOLOGY. Lateral to the anterior median fissure, on each side extends the sulcus lateralis anterior, which is not a continuous furrow, unless the emerging anterior root-fibres are torn away. In the upper thoracic and the cervical region, an additional delicate longi- tudinal groove, the sulcus intermedius posterior, is distinguishable between the median and lateral posterior sulci. The anterior root-fibres that emerge along the anterior lateral sulcus form individual bundles, the radices anteriores, sepa- rated from one another by intervals. The posterior root- fibres, which enter along the posterior lateral sulcus in an unbroken row, likewise form outwardly converging bundles, the radices posteriores. Each pair of anterior and posterior ant. Radix post. FIG. 93. Schematic representation of the formation of the spinal nerves. root-bundles passes to a defi- nite foramen intervertebrale (Fig. 93). Here, the posterior root presents a small fusiform swelling, the ganglion spinale, and then unites in its fur- ther course with the corresponding anterior root, thereby forming the spinal nerve, which latter divides into an anterior and posterior division. The emerging root-bundles run not only outward, but at the same time caudalward, and, indeed, the more so the nearer to the caudal end of the spinal cord they emerge. In the lumbar region, the course of the nerve-roots within the vertebral canal is nearly parallel with the long axis of the cord, so that the conus medullaris and the filum terminale lie in the midst of a generous bundle of nerve-roots, which, on account of the supposed resemblance to a horse's tail, is designated the caiida . equina. By means of the longitudinal furrows, the spinal cord is subdivided into the following columns : The funiculus anterior, between the anterior median fissure and the anterior lateral sulcus ; The funiculus lateralis, between the anterior and posterior lateral sulci ; The fumculus posterior, between the posterior median fissure and the posterior lateral sulcus. The posterior column is separated by the sulcus intermedius posterior into a medial and a lateral division, the medial one being known as the fasciculus gracilis, or GoW s column, and the lateral one as the fasciculus cuneatus, or Burdock's column. INTERNAL CONFIGURATION. Even with the unaided eye, one can readily distinguish gray and white substance in a transverse section of the spinal cord. When cut across, the centrally situated gray substance appears H-form in outline. The bridge of gray substance connecting the two limbs of the H, encloses the central canal, canalis centralis, which is immediately sur- rounded by the substantia gelatinosa centralis and lined with ependyma. Above, the central canal widens at the transition of the spinal cord into the medulla oblongata and THE SPINAL CORD. 91 passes over into the fourth ventricle. Below, at the lower end of the conus terminalis, it expands into the ventriculus terminalis (Krause), becomes again narrow at the transition into the filum terminale and, finally, ends blindly. The part of the gray bridge that passes behind the central canal is known as the commissura posterior, that which lies in front is the commissura grisea anterior. In front of the latter, between it and the bottom of the anterior median fissure, is the commissura alba anterior. The gray substance, in each half of the spinal cord, presents in front a thick swelling, the anterior horn or cornu anterius, and behind a more slender part, the poste- rior horn or cornu posterius. Since the gray substance extends continuously throughout the entire length of the cord, the anterior and posterior horns appear in longitudinal sections as columns ; they are called also, therefore, the columnae griseae. The lateral L'ssmter's z Formatio reticnlaris Clarke's column Ant I \ , ^4 Coiiuiiisstirn alba Anterior root FIG. 94. Transverse section of the spinal cord. part of the gray substance, in the lower cervical and the upper thoracic regions of the cord, becomes more independent and there forms the lateral horn or columna later alis. In the entire cervical and upper thoracic cord, the gray substance extends into the white matter as a network of gray trabeculae and strands, which occupy the angle between the lateral and posterior horns and constitute the formatio reticularis. The posterior cornu begins ventrally as the base, then becomes narrower and forms the neck, cervix columnae posterioris ; dorsally follow the head of the horn, caput columnae, and the point, apex columnae posterioris, which latter embraces a crescentic field, the substantia gelatinosa Rolandi, and the dorsally situated marginal zone. Medial to the neck of the posterior cornu and close to the posterior commissure, one finds the nucleus dorsalis or Clarke's column as a small group of cells within the gray substance of the upper lumbar, the entire thoracic and the lower cervical regions. The white substance surrounds the gray and is subdivided, as already noted, into three tracts the anterior column, between the anterior median fissure and the anterior roots, the posterior column, between the posterior median fissure and the posterior roots, 9 2 MORPHOLOGY. and the lateral column, between the anterior and posterior roots. The posterior column is further divided by the sulcus intermedius posterior into the medially situated fasciculus gracilis or Goll's column, and the laterally placed fasciculus cuneatus or Burdach's column. In the essentials, the make-up of the spinal cord is the same in its various segments, the central gray substance in the characteristic H being everywhere enclosed by the white matter. The size and form of the cord in cross-sections, as well as the proportions of the gray and white substance, however, vary in the individual regions. In regard to size, the stronger development in the cervical and lumbar enlargements is at once noticeable. So far as the form is concerned, transverse sections are so charac- teristic in the different regions that, within certain limits, the region from which a section has been taken can be determined from such data alone. Thus, cross-sections of the cord in the cervical region, particularly at the level of the IV-VIII nerve, and in part TA-a LI FIG. 95- Transverse sections of the s-pinal cord at different nerve-levels. C, cervical; Th, thoracic; L, lumbar; 5, sacral. also in the highest thoracic segments are transversely oval ; in the thoracic region the cross-section is almost circular ; while in the lumbar region it is more quadrate, with more marked ventral flattening. The quadrate form is especially evident in the sacral and likewise in the coccygeal cord, where, however, in contrast to the lumbar region, the strongest flattening is dorsal with coincident ventral narrowing. Regarding the proportion of the gray and the white substance, it is readily seen that the gray substance is most abundant in those segments from which the large limb- nerves arise, that is in the cervical and lumbar enlargements. In these segments the great development of the anterior horns is particularly evident. The gray substance in the dorsal cord, on the contrary, is poorly developed, the H-form being here seen to best advantage. The white substance exhibits a robust development in the cervical, as well as the thoracic region. Towards the lumbar cord it progressively decreases in amount and, in the sacral region and toward the conus medullaris, the white matter forms only a thin peripheral zone surrounding the gray matter, which at these levels con- siderably exceeds in amount the white. SPINAL MENINGES. 93 THE MEMBRANES OF THE SPINAL CORD. As is the brain, so also the spinal cord is surrounded by three envelopes the dura mater, the arachnoid and the pia mater. Dura mater spinalis. This membrane forms a strong fibrous investment consist- ing of two layers, the outer, which fuses with the periosteum of the vertebrae, and an inner, which is the spinal dura proper. The space between these two layers is filled with loose connective tissue, contains the large venous plexus and is traversed by lymph- spaces ; it is the cavum interdurale or cavum epidurale. The dura extends as a long FIG. 96. Schematic representation showing relations of the spinal meninges to one another and to the vertebral canal. Dura is yellow; arachnoid, green; pia, with ligamentum denticulatum, blue. wide sac over the conus medullaris, narrows at the level of the second or third sacral vertebrae, thence, as the filum durae matris spinalis, clothes the filum terminale and finally passes into the periosteum of the coccyx. Arachnoidea spinalis. This is a delicate vascularless membrane, separated from the dura mater by the cavum subdurale and from the pia mater by the cavum subarachnoi- deale. It is connected with the subarachnoidal fibres, which are particulary robust and numerous toward the sulcus medianus posterior ; in the lower cervical and in the thoracic region, they form a special partition, the septum subarachnoideale or septum cevicale intermedum. Within the subarachnoidal space the liquor cerebro-spinalis circulates. Pia mater spinalis. This membrane encloses the spinal cord as a delicate vas- cular envelope and forms, by penetrating within the anterior median fissure, the septum anterius. The pia is connected with the dura mater by means of the ligamentum dentic- ulatum. The latter consists of from 1923 small triangular processes, with their bases attached to the pia, which extend outward from the lateral surface of the cord between the anterior and posterior roots of the spinal nerves, to be attached by their points to the dura mater. The ligamentum denticulatum serves as a suspensory band that holds the spinal cord in position. PART II. THE FIBRE-TRACTS. THE FIBRE-TRACTS. METHODS OF STUDYING THE FIBRE-TRACTS. The older anatomists contented themselves with the task of describing the brain simply from the exterior and, in a sense, without further leading conceptions. In this period originated the terminology that owes its existence to merely purely superficial and accidental resemblances. As examples, one recalls the designation of the corpora quadri- gemina as the "nates" and "testes," the suggested resemblance of the corpora mamil- laria to the female breasts, of the calcar avis to the cock's comb, of the lyra Davidis to a harp, or of the fornix to an arch. In order to render more exact investigation possible, the pioneer observers first sought to overcome the softness of the central nervous substance, and to that end employed various chemical agents, as alcohol, corrosive sublimate and salt solutions. Cold was also used to give the brain greater consistence, and, indeed, Gennari and Reil made their observations on frozen brains. In this manner, in 'a purely morphological way, began the foundation of the study of the internal- connection of the individual brain-segments and. until the middle of the nineteenth century, the method of direct mechanical dissociation of the alcohol-hardened brain was employed to demonstrate the chief fibre-tracts (Gall and Spurzheim, Burdach, Reil, Arnold, Foville). A distinct advance in brain-anatomy was made when the structure of the central nervous system began to be studied from the standpoint of development. In this Tiedemann and Reichert were pioneers. In the introduction to his ' ' Anatomic und Bildungsgeschichte des Gehirns," Tiedemann observes that the origin and development of the brain were an almost totally neglected part of anatomy and physiology. He mentioned the law formu- lated by Harvey, that the embryo of man and of the animals does not appear in a com- pleted and only diminished form, but that it begins with a simpler form, successively passes through lower formative stages and finally reaches a higher stage of development. Why, says Tiedemann, should not a similar progression from a simpler to a more complex structure also occur in the construction of the brain of the embryo and of the foetus ; and, further, should not this process supply explanations concerning the form and struc- ture of the brain, so intricate in its completed condition? Tiedemann busied himself for several years with the construction of the embryonal and foetal brain. The pure mor- phology of the brain, however, reached high-water mark with the embryological method of examination followed by C. B. Reichert. Through the work of Schmidt, Mihalkovics, Kolliker, His and others, this method has led to a strict scientific division of the brain and to the establishing of a comprehensive morphological basis. 7 97 98 THE FIBRE-TRACTS. By these " embryological " methods much was gained, but by no means all. Embryology taught us to understand the development of the form, but told us nothing concerning the intimate connection of the parts, a clear insight into which alone leads to a comprehension of the function of the central nervous system. The question of the intimate connection of the parts, however, is nothing but the question of the fibre-tracts and there- with we enter a new phase of brain-investigation. We may designate this phase as the physiological in contrast to the pure morphological, since the extraordinarily difficult and laborious endeavors of the later investigators to unravel the intricate fibre-complex of the central nervous system are all undertaken from the physiological standpoint and with a physiological aim. After Helmholtz had shown for the invertebrates and Remak for the vertebrates, that the nerve-fibres proceed from the nerve-cells, it became evident that the simple method of dissociation no longer sufficed. What neurology had then to attempt was not merely the accurate description of the external form, but, before all else, the estab- lishing and the tracing of the intricate paths which the nerve-fibres pursue, and the definite establishment of all the numerous connections joining centre with centre within the interior of the central nervous system and bringing the latter into relation with the periphery. Although tracing these fibre-paths even within the peripheral nerves is by no means easy because of the peculiar plexus-formation and anastomoses of certain nerves, such task is especially difficult within the brain and spinal cord, since here often within a small space the most diverse paths run side by side and, further, decussations and interfeltings of the nerve-fibres make the direct tracing of the nerve-tracts impossible. A method of fundamental importance for following the nerve-paths through longer stretches was now introduced, namely, the method by series of consecutive sections, introduced by Benedikt Stilling. The necessity of cutting the brain and spinal cord into thin segments for the accurate investigation of their finer structure, even the older inves- tigators recognized and suggested means by which to accomplish this end. As early as 1824, Rolando made thin cross-sections of hardened spinal cord with a razor and examined them with a hand-lens. But the segments cut by Rolando were not sufficiently thin to be used with higher amplification ; moreover, they were made without system. In 1836 Valentin examined microscopically the spinal cord of freshly-killed sheep and pigeons, by cutting the cord, under water, with a pointed two-bladed knife, into the thinnest possible lamellae and then carefully compressing the sections while being observed. In this manner Valentin studied the spinal cord layer by layer, from without inward, in longitudinal sections, and expressed the opinion, that for the correct understanding of the structure of the spinal cord examination by strata is the only proper way. Four years later, Hannover advanced along this line even farther than Valentin. He employed a brain and spinal cord hardened in chromic acid, which he cut into thin sections with a sharp knife, and examined the relations of these lamellae piece by piece. Shortly after the appearance of Hannover's paper, the great doctor of Cassel, Benedikt Stilling, began in 1841 his investigations concerning the structure of the spinal cord. Stilling was the first to cut a spinal cord into many consecutive sections, as thin and transparent as possible, and then to study in each section the distribution of the white and gray substance. He traced progressively from section to section the changes in the picture, and finally, by reproducing the individual pictures, gained, at least to a METHODS OF INVESTIGATION. 99 certain degree, a clear conception of the internal structure of the cord. This method by series of consecutive sections, which Stilling designated as "investigation layer by layer," is even to-day the one most employed in the examination of the central nervous system. During the continual use of so productive a method, it was inevitable that the original technique of Stilling should undergo many alterations and improvements. The employ- ment of the method was facilitated by better hardening of the organs. Already in 1832, Ludwig Jacobson recommended potassium chromate as a preservative for anatomical preparations. Hannover first put Jacobson' s discovery to use for histological investigation. Later chromic acid was displaced from the technique by one of its salts. At any rate, no one has rendered greater service than Heinrich Miiller by the introduction of potas- sium bichromate, now so universally serviceable. From him came also the classic Miiller' s fluid, which, indeed, even to-day is much used in its original composition. Later followed many new hardening reagents. One of these, formalin or formol, must be especially mentioned, since in recent years its many advantages have brought it into universal use. Formol was introduced in histological technique by Blum in 1893. The -method of consecutive sections was further facilitated by the introduction of the microtome, by which exact cutting and large regular sections are made possible, so that an entire brain may be laid into a series of thin sections without losing one. We may mark the sections in their proper sequence, determine in each the topography of the gray substance and of the fibre-tracts, and, by means of the series, from these isolated data construct a composite picture of the principles of construction of the part of the brain under discussion. The application of Stilling' s mode of investigation was materially facilitated by the methods of staining. For a long time Gerlach's carmine staining was dominant. An important advance was gained by Weigert's admirable hematoxylin-method. At present we have at our disposal a quite considerable number of different dyes, which may be used with advantage in investigating fibre-paths. But neither the Weigert stain, nor any other of the procedures so far recommended and used, is capable of solving the question, the answer to which has always been most sought for the correct understanding of the structure of the nervous system. Continually was asked : In what manner are the nerve-fibres related to the nerve-cells? In what manner are the nerve-cells related to one another? How do the nerve-fibres in the brain and spinal cord arise and how do they end? In this connection, two methods were epoch-making Ehrlich's methylene blue method and Golgi's silver-method. Ehrlich's procedure, which was introduced in 1886 and depends on the coloring of the living nerves by means of methylene blue, was subse- quently improved by Retzius, Apathy, Bethe and others. Golgi's method is older. A number of years before, the Italian investigator had obtained preparations, in which the nerve- cells and their processes stood out with great sharpness as dark figures, by treating the brain-substance with the chromic acid salts and with silver nitrate. Golgi described his method as early as 1873, but at first his observations were little known. Not until the publication of an elaborate paper in 1886, did Golgi excite widespread attention and his results and methods become the starting point of an energetic examination of the central nervous system. For example, the Spanish savant, Ram6n y Cajal, was able, by the use of the Golgi method on embryos and young animals, to arrive at results that partly solved many of the dominant questions, or placed them in a new light. At first ioo THE FIBRE-TRACTS. through the labors of this investigator, soon also through those of others, especially of Kolliker, Lenhosse"k, van Gehuchten and Retzius, a clear picture took the place of the previous schemata. The most important findings of these researches are, that the nerve- fibres are nothing more than extraordinarily long processes of the nerve-cells, that every nerve-fibre, from beginning to end, is to be regarded as a part of a single nerve-cell, and that every nerve-cell, with the nerve-fibres proceeding from it, represents an histo- logical individuality or nervous unit. Waldeyer christened such anatomical unit, neurone, and therewith founded the neurone-theory. The method of Stilling enables us to trace a nerve-tract through a long stretch. The identity, however, is possible and certain only so long as the fibre-bundles compos- ing the tract do not suffer interruption, or so long as they are not deflected from the plane of the section, or do not separate into widely diverging fibres. The accurate iden- tification and tracing of the fibre-tracts, even when they branch in the most diverse directions or resolve, have necessitated the search for new methods. One of these additional methods is the pathologico-anatomical one, based on the inves- tigation of secondary degenerations. Rokitansky announced in the first edition of his Pathological Anatomy (1847), that atrophy of the brain following apoplexy and inflam- mation leads to atrophy of different fibre-paths, when extensive, indeed, to the disap- pearance of an entire hemisphere and the related fundamental tracts. This communica- tion for a time remained unnoticed. In 1850 Ludwig Tiirck described more closely such secondary degenerations and inferred from his findings, that in those cases of cross-section of the spinal cord, in which the direction of physiological conductivity and that of the degeneration were identical in the secondarily degenerating cord-paths, the degeneration itself was caused by the disturbance of functions. Notwithstanding these exceedingly important results, at first only few investigators followed Tiirck along this line of investi- gation. In later years, however, this method has been universally employed and to it we are indebted for the many papers by which our knowledge of the fibre-paths of the central nervous system has been materially extended. The method depends upon the principle, that every nerve-fibre in its function is dependent upon the related nerve-cell. Destruction of the latter, or separation of the nerve-fibre from its cell, results in degenera- tion of the related fibre. Let us assume that a descending tract of the spinal cord has been destroyed in some part of its course. What happens ? The portions of the nerve- fibres below the injury are separated from their trophic centre ; they therefore die. This destruction or secondary degeneration within the spinal cord proceeds downward. On examining a cross-section of the cord passing below the seat of injury and comparing it with a corresponding section of a normal spinal cord, the seat of the degeneration is readily located and the involved tracts may be accurately followed by means of serial sections. This method of investigation by secondary degeneration is closely related to the physiological method or the method of vivisection. Certain nerve-centres or nerve-fibres of an animal may be directly stimulated or destroyed, and from the resulting symptoms conclusions drawn as to the relations of the nerve-centres or nerve-tracts to the peripheral parts ; thereby a functional differentiation of the nerve-fibres is also possible. The pathological method is based on a principle similar to that of the vivisection procedures. Here also the destruction of parts of the central nervous system is con- cerned, but these mutilations are not experimental but caused by the establishing of METHODS OF INVESTIGATION. 101 diseased processes. In this relation, the study of the pathological changes in certain affections of the spinal cord is of primary importance. By means of the experimental method, which has been used on animals with such great success, we are able to follow and to study the course of the fibre-bundles by degenerations. This method, employed only under certain conditions, was introduced by Gudden and his pupils and is the atrophy-method, or the method of developmental arrest. Gudden' s method is distinguished from other experimental procedures in that it is directed against the young animal. The chief difference consists therein, that, follow- ing an experimental impression on the new-born animal, the entire process proceeds much more rapidly and completely than in the adult. The absorption of the disintegration products from the elementary parts destroyed goes on much more rapidly and com- pletely in the new-born, so that scarcely a trace of the fibres and only few remains of the cells are left. In addition, the technique is relatively easy, while a further distinct advantage, as Gudden himself pointed out, is the almost incredibly rapid and admirable healing of the injury without disturbing secondary processes. In 1852 Waller showed, that the peripheral stump of a cross-sectioned peripheral nerve undergoes degeneration. For a long time it was believed, that the peripheral segment alone degenerated, and that the central one remained unaffected by such changes. Since the study of Ranvier on degeneration and regeneration of sectioned nerves, how- ever, we know that also the central segment suffers important modifications. Ranvier showed, that in the central segment of the axis-cylinder new fibrillae were formed, which became new nerves, using the sheath of the degenerating peripheral segment as a sup- port to reach the periphery. The nerve reassumes its function it is regenerated. If, however, from any cause the developing nerve fails to secure such support, its further development is arrested and a nervous tumor, a neuroma, is formed, as seen in amputation- stumps. But in these cases, especially when of long standing, a certain grade of atrophy of the nerves, as well as a diminution in the number of the corresponding nerve- cells, may be observed. These changes are exceptionally rapid and marked so soon as the interference occurs in young individuals, particularly in the new-born. If in a new-born animal a motor nerve is removed, a certain region of the cerebral cortex destroyed, or the spinal cord partially cut through, not only is always a degeneration of the fibres in the separated peripheral stump to be observed, but also atrophy and indeed complete disappearance of the cells of origin. Gudden believed at first, that this differ- ence from the Wallerian degeneration was attributable to the lesion being in the new- born animal. Later, he recognized that it was not the age, but the position that exer- cised the influence. Then, too, Forel proved, that the death of the cell after destruction of the related fibre occurred in the adult, as well as in the new-born animal. Death of the cell depends alone on the place where the fibre is sectioned. Section of a motor nerve at the periphery is followed by only a slow impairment and diminution in the size of the cells and fibres of the central stump. Section of the same nerve at its point of emergence from the brain, results in the death of the central root, as well as of all the cells of origin within the nucleus of the nerve. The method of Gudden has been rich in results. In 1872-74 Gudden proved, by extirpation of the cortical motor zone in dogs, that the pyramidal tracts run direct from the cerebral cortex* to the spinal cord. Other important results are the establishing of the nuclei of origin of almost all the 102 THE FIBRE-TRACTS. motor cerebral nerves, the course of the medial fillet and the termination of the optic tract. Closely connected with the method of Gudden are the pathological cases of early lesion and consequent atrophy of certain parts of the central nervous system, as well as the cases of congenital malformation involving the cerebro-spinal axis. Our knowledge concerning the fibre-tracts, moreover, has been especially advanced by the embryological method introduced by Flechsig, based on the study of the develop- ment of the nerve-fibres. This method rests on the fact, that the different fibre-systems within the central nervous system acquire the medullary substance at a definite time, which, however, varies for the individual systems. On examining the infantile brain, it is found that certain fibres are already medullated, while others have not yet acquired this sheath. This difference between the medullated and non-medullated fibres is readily appreciable microscopically and, therefore, the examination of the nervous system in its various develop- mental stages affords the possibility of delimiting and tracing certain fibre-systems. An additional means, which has contributed much not only to the morphology but also especially to the accurate investigation of the fibre-tracts, is the comparative anatom- ical method. Since in the different classes of animals this or that part of the brain is varyingly developed, in correspondence with different functional development, the investi- gations in the domain of comparative anatomy have supplied numerous explanations con- cerning the many-sided connections of individual parts of the central nervous system. Finally, a combination of these various methods has been attempted. Edinger united the comparative anatomical method and that of Flechsig. Bechterew combined vivisection with the study of development and created the embryologico-physiological method. Admirable results were also achieved by Bechterew with his pathologico-physio- logical method, which consisted in studying secondary degenerations with simultaneous stimulation of the degenerated parts by means of the electrical current. HISTOGENESIS OF THE NERVOUS SYSTEM. The elements of the nervous system are developed from the outer germ-layer or the ectoderm. As we have already seen, the brain and the spinal cord arise from a broad medial strip of ectoderm. Here the medullary plate is formed, which is bounded exter- nally by the cuticle-plate. The medullary plate sinks and, at the same time, projects with its edges above the level of the embry- onic area ; in this way is formed the medullary groove, bounded by the med- ullary ridges. The medullary groove closes and becomes the medullary or neural tube. The medullary tube, the direct successor of the medullary plate, consists FIG. 97. Dorsal half of neural tube, overlaid by the ectoderm; epithelial and two dividing (so-called germ-) cells. (His.) at first of closely pressed epithelial Cells, each of which extends the entire thick- ness of the layer. The wall of the entire tube, therefore, originally exhibits the character of a single-layered columnar epithelium, whose cells are bounded by the membrana limitans externa on the one "side, and by the membrana limitans interna on the other (Fig. 97). Each epithelial cell encloses a large nucleus. In the inner zone, other large cells are irregu- DEVELOPMENT OF NEUROGLIA. 103 larly scattered between the epithelial elements, from which they are clearly distinguished by their round form and transparent homogeneous protoplasm. His designated these as the germ-cells. The epithelial cells multiply rapidly and, consequently, become laterally compressed and elongated. Their nuclei lie at different heights and give rise to the appearance of a three- to six-celled layer. In reality, however, the cells completely retain the character of a single-layered columnar epithelium. Some of the epithelial cells are early transformed. They grow into the spongio- blasts of His, from which are developed the supporting elements, the ependyma and neuroglia cells. Others of the epithelial cells change to pear-shaped elements and become the neuro- blasts, which are transformed into the nerve-cells. Both kinds of cells, the spongioblasts and the neuroblasts, therefore, are derivatives from the original ectodermic elements of the medullary plate. The above mentioned "germ-cells" of His are nothing more than cells of the primary medullary area under- going mitosis and represent elements, whose division supplies the material for the increase of the indifferent ectodermal cells, on the one hand, and of their derivatives, the spongio- blasts and the neuroblasts, on the other. DEVELOPMENT OF THE EPENDYMA AND THE NEUROGLIA CELLS. The ependyma cells maintain in the foetal stage the character of an epithelium and the relations to the membrana limitans externa and interna. In the brain, as in the spinal cord, the ependyma cells extend from the inner to the outer surface of the neural wall, the length of the cells keeping pace with the increase in the tube. The inner portion of the cell, nearer the central canal, retains more the character of a cell-body ependyma cell, while the outer portion gradually diminishes to a delicate fibre, which as an ependyma fibre radially traverses the neural wall. The entire arrangement constitutes the ependyma system or the ependymium. On examining this ependymal framework more closely, a distinctive disposition of the ependyma cells is seen in the spinal ... . PIG. 98. Transverse sec- cord. In a cross-section of the medullary tube of a 3-4 day t i 0n of neural tube of a four- chick embryo (Fig. 98), we recognize how the ependyma fibres ^ e - fe c ) hick embryo ' (Len ' traverse the wall of the tube, at the sides passing almost parallel from the central canal and ventrally and dorsally diverging radially. In conse- quence of the coming together of the nucleus-bearing portions of the cells, there appears within the medullary tube, in the vicinity of the central canal, a broad, richly nucleated zone, the inner layer of His or the ependymal nuclei-zone of Len- hosse"k. In a general way, this zone corresponds to the later epitheiulm of the central canal. The ependyma fibres of the later anterior commissure present a rough appearance, being heavy and beset with spines ; they also emphasize the already slight meridional disposition of the more laterally situated ependyma fibres. In a somewhat later stage, the ependyma fibres exhibit varicosities, particularly in their inner portions; in addition, in their outer portions they undergo a subdivision into several branches, all of which extend to the periphery, where they end in small triangular expansions. 104 THE FIBRE-TRACTS. Subsequent stunting of the lateral parts of the ependyma framework is most marked in the spinal cord of the higher forms. In the other parts of the central nervous system, the ependyma cells and fibres retain their embryonal form, even after completed growth. The ependyma cells are, therefore, phylogenetically as well ontogenetically, the oldest cells of the supporting framework, arising directly from the ectoderm cells, or, indeed, being in a modified way these themselves. During later stages, the elements, particularly the ependyma fibres, are curtailed in varying degrees ; a part of the epen- dyma cells later migrate and become the neuroglia cells. The neuroglia cells arise only after the formation of the ependyma framework. On examining the spinal cord of a ten-day chick, one finds a number of elements which closely re- semble the ependyma cells, their fibres likewise extending to the periphery and there ending in conical thickenings. They differ from the ependyma cells proper, however, in that their cell- bodies no longer lie at the central canal, but farther outward. At first such cells are encountered only in the vicinity of the central canal and in meagre number ; later, however, they are more numerous and occur also in the peripheral zone. This is explained by the manner in which the neuroglia cells arise. Originally these cells lie, as do the ependyma cells, at the central canal ; then the cell-bodies migrate FIG. 99. Transverse section of the spinal cord of a human embryo, 14 cm. long, showing ependymal framework. (Lenhossek.) FIG. too. Development of the neu- roglia cells. Spinal cord of a ten-day chick. (Lenhossik.) FIG. 101. Neuroglia cells from the white substance of the spinal cord of an embryo of 30 cm. in length. (Lenhossek.) from the region of the epithelium, part of the cell-body becoming a thin fibrilla, that later disappears. Small spines and branches appear on the former smooth cell-bodies, as well as similar thorny outgrowths for a short distance along the process stretching from the cell-bodies to the periphery. At first such migrated cells are present only in sparing number ; later, however, their number materially increases and the cells are dis- tributed more or less uniformly throughout the entire cross-section of the spinal cord. DEVELOPMENT OF NERVE-CELLS. 105 This radiating sustentacular apparatus constitutes in man and the higher mammals an embryonal feature. Subsequently, the picture changes. The radial type disappears and the shape of the cells alters. The minute spicules and branches develop very markedly, while the peripherally directed processes atrophy. The cells become the true spider or neuroglia cells. The latter, therefore, pass through various developmental stages ; at first they are ependyma cells, then radial sustenacular cells, from which arise the neurog- lia cells. DEVELOPMENT OF THE NERVE-CELLS. The neuroblasts, from which the nerve-cells arise, are developed in the innermost layer of the medullary tube, bordering the central canal. Thence they migrate outward through the inner layer and localize within a dorso-ventrally expanding region, that is bounded medially by the inner layer and laterally by the marginal zone. On examining a cross-section of the medullary tube of a four- weeks human embryo (Fig. 102), the cleft- like central canal is seen in the middle, bordered by the inner plate, outside of which lies the stratum of neuroblasts, broad ventrally and thinner dorsally. Follow- ing His, we call this stratum the mantle layer. Peripheralward, the latter joins the marginal zone the Randschleier of His. The neuroblasts are pear- shaped cells, with oval nuclei, which send out a peripherally di- rected process that bears at its end a characteristic thickening, the growth-wedge of Cajal. This process is nothing less than the later nerve-fibre. While the rapidly growing fibres endeavor to reach their objective point, the cells change their form. On the surface appear small humps and jagged protuberances. These projections later elongate and become compact branches beset with small knobs. By the further development of the knobs and the manifold division of the outgrowths, the later protoplasmic processes or dendrites of the cells arise. In this manner the nerve-cell, or rather the neurone, is formed as an independent individual. It includes the cell-body and the outgrowing protoplasmic processes or dendrites and sends out the delicate neive-process or neurite, which in its later development becomes the nerve-fibre. DEVELOPMENT OF THE CELLS OF THE CEREBRO-SPINAL GANGLIA AND THE SYMPATHETIC GANGLIA. The spinal ganglia are developed from a band of ectodermic cells located where the medullary plate passes into the cuticle-layer. In the stage of the medullary groove, this ganglion-strand occupies, on each side, the prominent ridge of the medullary plate and, as the medullary tube separates from the overlying ectoderm, unites temporarily with the strand of the other side to form a common medial cord. In consequence of the formation of the medul- PiG. 102. Transverse sec- tion of the spinal cord of a four-weeks human embryo. Differentiation into the inner layer, next the lumen of the canal, the middle or mantle layer, containing the neuro- blasts, and the outer periph- eral layer. (His.) FIG. 103. Further development of the neuroblasts. On the right, two neuroblasts exhibit processes bearing growth-wedges. Spinal ganglion Cuticle-plate Medullary tube FlG. 104. Development of the ganglion-strand. Schematic. io6 THE FIBRE-TRACTS. lary tube, the elements of the ganglion-strand, the ganglioblasts, are displaced laterally and form, on each side of the medullary tube, segmentally arranged cell-groups. The latter are the anlagen of the future spinal ganglia. During their migration along the medullary tube, the ganglioblasts become spindle-shaped. This form becomes subse- quently still more pronounced, each of the two pointed ends gradually growing out into a nerve-fibre, the centrally directed one growing into the dorsal portion of the Posterior root Spinal ganglion Peripheral nerve IG. 105. Neurobl nd ganglioblasts. cord as a posterior root-fibre, and the other, as the peripherally directed sensory fibre, traversing the body to its termination. The bipolarity of the ganglion-cells later disappears, the cells becoming unipolar elements. This unipolarity is manifested not only by the cells of the spinal ganglia, since the cells of the corresponding ganglia of the cerebral nerves are also unipolar elements. The ganglion acustici alone contains permanently bipolar cells. The sympathetic ganglia originate from the cerebro-spinal ganglia. According to the younger His, this development is accomplished by an actual migration of cellular elements from the spinal ganglia. THE FORMED ELEMENTS OF THE NERVOUS SYSTEM. The formed elements of the nervous system are the support- cells and the nerve-cells. A. THE SUPPORT-CELLS. These include the ependyma cells and the neuroglia cells. The former constitute the epithelial lining, the ependyma, of the central canal and its prolongations the fourth ventricle, the aquaeductus cerebri, the third ventricle and the lateral ventricles. The neuroglia cells, the spider 'cells or astrocytes, are present in all parts of the gray and white substance and form, by means of their numerous processes, the framework proper, the astropilemma or spongiopilemma. As chief forms, we dis- tinguish the short-rayed and the long-rayed neuroglia cells. They all possess numerous processes, which, however, are seldom uniformly distributed around the circumference of the l \e?uma N n e ^etai C coi S tex rom cell-body, but usually emerge in separate close tufts, like bun- dles of rays. The processes are delicate, mostly of the same thickness, from beginning to end of uniform width and end free. While in the majority of cells they proceed in all directions, there are also astrocytes in which the processes exhibit a one-sided development, or arise from the two poles of the cell. THE NERVE-CELLS. 107 For a long time the supporting tissue proper of the nervous system, or the neu- roglia, as distinguished from connective tissue, blood-vessels and lymphatics, was regarded as a sort of ground-substance in which the nerve-cells and nerve-fibres were embedded. The chief role therein was played by a kind of cement-substance, the glia, to which be- longed special cells and fibrous elements, the glia cells and glia fibres. In 1811 Keuffel first succeeded in demonstrating a definite meshwork in cross-sections of the spinal cord, by brushing out the nervous substance, and believed that this reticulum represented noth- ing more than the prolongations of the pia mater. Arnold and Virchow termed the neu- roglia a granular ground-substance, but, as early as 1853, Virchow demonstrated round or fusiform cells within this ground-mass and regarded the tissue as of nervous character, believing that the nerve-cells were developed from the neuroglia. Bidder went somewhat further and spoke of fibrillae and stellate cells with processes. In 1863 Kolliker pointed out that the supporting tissue of the nervous system consisted of nothing else than a complex of anastomosing stellate cells, which by their union formed a reticulum for the nervous elements. He still assumed, however, an anastomosis between the processes of the cells. It remained for Deiters, by means of isolation, to represent the neuroglia cells in their correct form. The greatest service, however, was rendered by Golgi. Through his investigations, it became clear that the neuroglia is not a special issue, but that it is represented by certain elements the neuroglia cells, spider cells or astrocytes. B. THE NERVE-CELLS. The first accurate description of the nerve-cell was given by Remak in 1838. Thirteen years later, R. Wagner discovered in the nerve-cells of the electrical lobes in the brain of torpedo, that of the processes passing out from the cells only a single one is connected with a nerve-fibre. In 1854 Remak communicated similar results in his studies on the nerve-cells of the gray ventral columns of the spinal cord of the ox. These observations of Wagner and of Remak were confirmed, in 1865, by Deiters' in- vestigations on the human brain and spinal cord. Deiters found that among the many processes passing from a nerve-cell always one ran unbranched, while the others under- went repeated division. The unbranched process he named the nerve-process or axis- cylinder process, and the branched ones the protoplasmic processes. In his investigations Deiters employed the method of isolation, this teasing method being subsequently long used to demonstrate the nerve-cells. It is evident, however, that with such technique, by which the cells were torn from all their relations, other investigators could achieve little more than Deiters had already done, and that the most diverse statements concern- ing the conception of the relations of adjacent elements to each other were inevitable. Thus, a direct union of neighboring cells with each other was accepted by many investi- gators as an undoubted fact. Sometimes it concerned broad connecting bridges or anas- tomoses, sometimes the passage of delicate end-fibres into each other. According to other investigators, all nerve-cells possessed more than a single typical nerve-process. Gerlach's work merits the greatest consideration. Gerlach succeeded in demonstrating an exceptionally rich felt-work of the most delicate nerve-fibres in all parts of the gray substance. He extended the observations of Deiters, who had seen the protoplasmic processes repeatedly branch and also the most delicate of these ramifications still further subdivide, in that he held, that the finest ramifications of the protoplasmic processes io8 THE FIBRE-TRACTS. eventually formed a delicate ' ' nerve-fibre reticulum. ' ' This Gerlach regarded as the most important constituent of the gray substance. According to Gerlach, the divisions of the delicate protoplasmic processes observed by Deiters were only the beginning of the ner- vous reticulum. Gerlach, however, went still further. He assumed that from this net- work of nerve-fibres, by the gradual confluence of the minute branches, broader nerve- fibres were again formed, which emerged from the gray substance. Accordingly, the nerve-fibres had a two-fold origin, on the one hand, directly from the cells as nerve- processes or axis-cylinder processes, and, on the other, indirectly from the cells through the medium of the reticulum of nerve-fibres resulting from the branching of the proto- plasmic processes. Gerlach supposed, therefore, that the end-twigs of the sensory fibres entered the delicate network, which, on the other side, received the branched protoplas- mic processes of the motor nerve-cells. Gerlach' s fibre-reticulum can be best pictured by comparing it with the capillary network of the blood-vessels ; the sensory fibre is the artery, which is resolved into the capillary network ; the protoplasmic processes of the cells form the beginnings of the venous reticulum, from which proceeds the nerve-process representing the vein. This nerve-fibre reticulum of Gerlach enjoyed for a long time general acceptance. With the improvements in the methods of investigation, however, a powerful revulsion took place. In this, the chief r61e was played by the silver-method of Golgi. This investigator made the important discovery, that the nerve-processes of the cells, regarded as unbranched, may give off delicate collateral branches. Moreover, that there are many cells in the brain and spinal cord whose nerve-processes are not continued as medullated nerve-fibres, as in the case of the other cells and in conformity with the general law announced by Deiters, but resolve into their ultimate end-twigs immediately after emerg- ing from the cells or after a short course. Golgi divided, therefore, the nerve-cells of the brain and the spinal-cord into two classes : Type I, cells with long nerve-processes, which latter are directly prolonged into nerve- fibres ; Type II, cells with short nerve-processes, which after a short course, almost immediately after exit from the cells, break up into their terminal branches. Later, the two varieties were described as the types of Deiters and of Golgi. Also functionally these two cell-types differ. Golgi regarded the Deiters cells as motor and the others as sensory elements. He interpreted the protoplasmic processes as merely the nutritive organ of the nerve-cell and questioned their nervous significance. Of most importance, however, is the hypothesis advanced by Golgi and his pupils concerning the internal connection of the central nervous apparatus. Golgi denied anastomoses of the protoplasmic processes with one another and, consequently, a connection between the cells in the sense of Gerlach, although suggesting a view somewhat similar. He cham- pioned the existence of a "general nervous network," which, on the one hand, arises from the delicate collateral branches of the long nerve-processes and from the terminal subdi- visions of the nerve-processes of cells assumed by him to be sensory elements, and, on the other hand, receives additional constituents, such as the end-twigs of the nerve-fibres which enter the gray substance. This network he believes to exist throughout the entire gray substance of the spinal cord and of the brain. Opposed to this ' ' nervous network' ' are the important considerations of His and of Forel. As early as 1883, based upon embryological investigations, His had shown THE NERVE-CELLS. 109 Dendritei Collateral the independence of the nerve-cells from one another ; while in 1887, chiefly upon pathological experiences with Gudden's atrophy-method, Forel opposed the acceptance of a general network. What he, for the first time, especially emphasized, was the principle of contact instead of continuous reticular connection. There was still wanting, however, the histological proof, and this proof was supplied by the Spanish savant, Ram6n y Cajal. By means of his investigations, it was established that every nerve-cell, with its emerg- ing nerve-fibres, represented an histological as well as a neurological entity a neurone, and that the entire nervous system is built up of such nervous units. Closer examination of such a nervous unit or neurone (Fig. 107), shows that two kinds of processes leave the cell-body : (a) the branching protoplasmic processes or the dendrites and () the axis-cylinder process, also called the nerve-process, axone or neurite. The nerve-process is distinguished by its uniform diameter and smooth, regular structure. During its course it gives off many secondary twigs, the collaterals or paraxones, and ends by forming a terminal arborization or telodendrion. All these parts the cell with its dendrites and the axone with its telodendrion constitute collectively a nervous unit or a netirone. Concerning the function of the individual parts of the neurone, the cell-body with its dendrites forms the perceptive and impulse-giving element, while the nerve- process with its collaterals and the end-arborization, is the organ of transmission, carrying the impulse from the nerve-cell to other elements. The protoplasmic proc- esses or dendrites, therefore, conduct cellulipetally , receiving the impulse and' carrying the same to their own cell-body ; the nerve-process or neurite conduct cellulifugally, receiving the nervous stream from its own cell-body and conducting it to other cells. The manner in which the transference from one neurone to the other occurs is not definitely known. According to certain investigators, the chaining together of the nervous units is effected by the nerve-process of one cell, split into the delicate fibres of its end-arborization, being closely applied to or overlying the dendrites and cell-body of another cell, whereby the transference of the impulse is accomplished. The opponents of the theory of mere contact hold that there exists not only a simple application, but also a continuous connection between the nervous substance of the nerve- processes and of the protoplasmic parts in the form of an extremely delicate nervous network. Even if definite proof were supplied as to the connection of the individual neurones with one another by means of such a network, it remains none the less certain, that the nerve-cells with their processes are the essential elements for the entire nervous activity and that they must be regarded as the elements of the nervous system, which anatomically, trophically and as regards specific function, enjoy a certain degree of indepen- dence. We are, therefore, justified in designating them as nervous units or neurones. FIG. 107. Schematic representation of a neurone. no THE FIBRE-TRACTS. The nerve-cells are found chiefly in the central nervous system ; further, in the ganglia, the sense-organs and in the course of the cerebro-spinal and the sympathetic nerves. They are of variable size (4 to 135/0 an< ^ of manifold shape. The chief charac- teristic of every nerve-cell consists in its always possessing processes. Nerve- cells with- out processes, the so-called apolar cells, are never found in the nervous system of the adult. Such cells are either immature forms and found only during the earliest period of embryonic development, as the germ-cells of His, or they are artificial products, arising from the tearing off of the processes during isolation. According to the number of the processes, unipolar, bipolar and multipolar cells are distinguished. . FIG. 1 08. Nerve-cells of different types, a, unipolar cells; 6, bipolar cells; c, pyramidal cell; d, Purkinje cell. Unipolar Cells. These are numerous during embryonic development, as the neuroblasts ; much less frequently they are encountered in the nervous system of the adult, as in the retina and in the mesencephalon on each side of the aquaeductus cerebri as the cells of origin of the upper motor root of the nervus trigeminus. The nerve- cells of the cerebro-spinal ganglia are apparently unipolar, with the exception of the cells of the ganglion spirale and of the ganglion Scarpae ; in their embryonic condition, how- ever, these elements are bipolar, only later becoming unipolar, when their nerve-processes divide, at a certain distance from the cell-bodies, into a central and a peripheral branch. Bipolar Cells. These elements are found almost exclusively in the peripheral sensory nervous system, as in the epithelium of the olfactory mucous membrane, in the retina and in the spinal and vestibular ganglia. Multipolar Cells. These are the most numerously represented and the most impor- tant elements of the nervous centres. Connected with these are two kinds of processes the nerve-process, axis-cylinder or neurite, and the protoplasmic processes or dendrites. THE NERVE-CELLS. in Dendrites FIG. 109. Nerve-cell from spinal cord of a new- born cat. The nerve-process or neurite is usually single, although cells with several nerve- processes occur within the central cortex, as the cells of Cajal. To this category belong also the multipolar cells of the sympatheticus described by different authors. The neurite leaves the cell by means of a small conical elevation, the implantation cone ; the origin may be either from the cell, or, as is very often the case, from one of the protoplasmic processes, near or at some distance from the cell-body. Its smooth regular quality and uniform diameter throughout its entire course are characteristic of the nerve-process. The protoplasmic processes or the dendrites are broad and dense at their origin from the cell-body, become gradually thinner and repeatedly undergo antler-like division to form often an arborization of extraordinary richness, the finest twigs of which end free. Their irregular course and knobbed condition are characteristic of the dendrites, which are often beset with numerous knots, thorns or spines. According to the behavior of their nerve, processes, nerve-cells are grouped into two classes. i. Cells with long nerve -processes, Deiters' cell-type (Fig. 109), in which the neurite is ex- tremely long and becomes the axis-cylinder of a cen- tral or peripheral nerve- fibre. 2. Cells with short nerve-processes, Golgi's cell-type (Fig. no), in which the short neurite does not become a nerve- fibre, but, close to the cell, undergoes repeated division and resolves into its end-arborization. These elements are conveniently designated as Golgi cells, or cells of Golgi's Type II, as distinguished from the cells of Golgi's Type I, or the cells with long neurites. According to the behavior of the protoplasmic processes, are distinguished: a. Stellate cells, the dendrites of which arise separately from the entire circumfer- ence of the cell-body and extend in all directions, as the motor anterior horn-cells and the tract-cells of the spinal cord. b. Cells with a chief dendrite, in which a robust protoplasmic process arises, along with other dendrites, gives off lateral branches and ends arborized, as the pyramidal cells of the cerebral cortex and the mitral cells of the bulbus olfactorius. c. Cells with polar dendrites, in which the cell-body is mostly fusiform and gives off from opposite sides a basal and an apical dendrite. The basal dendrite forms a tuft resembling the roots of a tree, while the apical dendrite springs from a chief protoplasmic process, which eventually likewise resolves into numerous branches. The nerve-process springs from a basal dendrite, as in the pyramidal cells of the hippocampus. d. Cells with monopolar dendrites, in which usually several chief dendrites arise from one pole of the cell-body and soon break-up, after repeated division, into a wide arborization. The nerve-process arises from the other pole, as in the Purkinje cells of the cerebellum, or in the granule cells in the gyrus dentatus. FIG. no. Nerve-cell with short axone or nerve- process; cerebral cortex. 112 THE FIBRE-TRACTS. With regard to their intimate structure, the nerve-cells may be divided into two chief groups, in accordance with the behavior of their protoplasm towards the basic anilin dyes. Following Nissl, we distinguish somatochromic and karyochromic cells ; in the former both nucleus and protoplasm stain, in the latter only the nucleus. After staining with basic anilin colors, such as methylene blue or thionin, the protoplasm of the somatochromic cells exhibits a part taking the dye, the chromophilic substance, and a part remaining uncolored, the chromophobic substance. The stainable part appears as a multitude of deeply colored bodies having the form of spherical granules, threads, flakes, spindles or jagged particles, which also extend into the dendrites, but do not invade the axis-cylinder process. These are known as Nissl bodies or granules. On PIG. in. Structural details of nerve-cells, a, pyramidal cell from adult human motor cortex, showing neurofibrillar network; 6, pyramidal cell from adult human visual cortex; c, anterior horn-cell from human spinal cord showing Nissl bodies; d, Golgi-Holmgren canals in pyramidal cell of rabbit; e, ending of nerve-fibres on nerve-cells; /, pericellular or Golgi network, (a, b, d, e, and / after Cajal; c, after Schmaus.) account of the mottled appearance of the cell-body conferred by the staining substance, von Lenhossk calls the latter tigroid. The arrangement of the chromophilic substance is variable, the granules sometimes being irregularly scattered, at other times disposed in concentric layers, or, as in the case of fusiform cells, grouped as a sort of cap at each pole of the cell-nucleus. A conical mass of the chromophilic substance is usually found at the points of division of the dendrite-stems. Concerning the chromophilic part of the protoplasm, the nerve -fibrillae or neurojibrillae deserve first notice. These occur within the cell-body, as well as within the processes, and constitute a more or less ex- tensive reticulum, the fibrillar network. In Fig. in, a and b, such intracellular networks are represented. The figures e and / show, further, how nerve-fibres, after resolving into delicate arborizations, end at the cells and how the finest fibres form a delicate network over the surface of the cell-body and the dendrites, this constituting the external network of Golgi. THE NERVE-CELLS. 113 The chromophilic and the chromophobic substance differ also in their functional relations. The chromophilic substance is wanting in the protoplasm of a large number of nerve-cells and, therefore, does not represent a vital element of the nerve-cell. It accumulates during the resting condition, is sometimes notably reduced during the period of activity and disappears in lesions of the neurone, to reappear in generous quantity, however, after temporary injury and recovery of the cell. These characteristics seem to prove, that the chromophilic substance exercises a nutritive rather than a nervous function. The chromophobic substance seems to represent the element possessing the function of conducting the nervous stream, the fibrillae and the perifibrillar substance probably sharing in this conduction. In addition to the Nissl bodies, the protoplasm of many cells contains pigment granules, which are usually disposed in groups of variable size. The pigment is com- monly not uniformly distributed within the cell, but arranged at the base of one of the dendrites. It is wanting during early life and increases with age. Marinesco regards the pigment granules as regression- and age-products of the nerve-cells. Claim- ing mention are, further, the fine channels, the canals of Holmgren, which lie within the interior of the cell and communicate with the lymph-canals situated outside the nerve-cell. The nucleus of the nerve-cells appears as a clear spherical vesicle, possesses a distinct nuclear membrane and lies most frequently in the middle of the cell. Within the nucleus are found one or several deeply staining nucleoli, which often contain still smaller bodies, the nudeololi. The remaining interior of the nucleus is traversed by a meagre sup- porting substance, the linin framework, on which rests the chromatin, as well as against the nuclear membrane. Concerning the relations of the cells to the surrounding tissue, it should be noted, that the cells are enclosed within cavities, the pericellular spaces, which communicate with the perivascular lymph-channels of the central nervous system. The envelopes of the nerve-cells are, according to Cajal, of two kinds, (a) The cell-membrane proper, the membrana fundamental, which invests every cell of the gray substance as an extremely delicate, homogeneous, elastic cuticle, and () a connective tissue envelope, a delicate nucleated membrane, which surrounds all the peripheral cells ganglion cells and the cells of the sympathetic with the exception of the cells of the retina and of the olfactory mucous membrane. The ependyma and the neuroglia cells are sustentacular elements and together form the supporting framework of the nervous system. The nerve-cells are usually closely placed in larger or smaller groups and consti- tute the essential components of the gray masses of the nervous system ; exceptionally they occur singly, scattered within the white substance. The nerve-fibres are the axis-cylinder processes or nerve-processes of the nerve- cells, and, while everywhere encountered within the gray masses, constitute the chief components of the white substance of the nervous system. They serve to establish rela- tions of the nerve-cells with one another, whether the relations be between neighboring or widely separated cells of one and the same region of gray substance, as between the various regions of the cerebral cortex; whether the relations be between the cells of a certain region and those of one far remote, as between the central cortex and the n 4 THE FIBRE-TRACTS. deeper placed gray masses (thalamus, pons, medulla oblongata and spinal cord); or whether the relations be between the central and the peripheral nervous system. The nerve-cells are, therefore, the specific function-bearing elements. They are the force-sources or the transposition-apparatus of the various forms of nervous activity and, at the same time, also the nutritive organs, the trophic or nutritive centres, of the nerve- fibres which pass from the cells. A nerve-fibre separated from its nutritive centre loses its function and no longer conducts. A nerve-cell with its protoplasmic processes, or dendrites, and its nerve-process, or neurite, constitutes a nervous unit, or a neurone. The protoplasmic process conducts cellulipetally ; the nerve-process conducts cellulifugally and through it, by means of its end-arborization, as well as of its collaterals, occurs the transference of the impulse from one neurone to the other. Cells of the same function usually lie together, closely packed, and constitute a region, a centre, a ganglion or a nucleus. In like manner fibres of the same function usually lie together, closely placed, and form a path of conduction or a fibre-system. MICROSCOPIC STRUCTURE OF THE CEREBRAL CORTEX. I. CORTEX OF THE PALLIUM. Based on the arrangement of the nerve-cells, the following six strata or layers are distinguished. i. The molecular layer. This constitutes the most superficial stratum and is a dense feltwork, composed principally of fibres running mostly parallel to the surface ; hence, I. Molecular layer II. Outer granule / .;";>. ///. Layer of small and -medium pyramidal cells IV. Inner granule layer V. Layer of large pyramidal cells VI. Layer of poly- morphic cells White substance FIG. 112. Schematic representation of the structure of the cerebral cortex. STRUCTURE OF CEREBRAL CORTEX. 115 it is also designated as the layer of tangential fibres or the tangential fibre-layer. In addition to numerous neuroglia cells, this layer contains the terminal ramifications of the dendrites of the more deeply lying pyramidal cells and the end-arborizations of the nerve-fibres coming 'from the white substance and ending in the cortex. Further, it con- tains certain cells, including medium sized polygonal elements, with from four to six dendrites and a nerve-process arborizing within the molecular layer, and fusiform or tri- angular cells, with few more or less horizontally coursing dendrites and two or several nerve-processes, that also run horizontally and end within the molecular layer. The ele- ments with several neurites encountered within the tangential fibre-layer, are known as Cajal cells. 2. The outer granule layer, a stratum of small pyramidal cells. 3. The layer of small and medium sized pyramidal cells. 4. The inner granule layer, a stratum of small pyramidal cells. 5. The layer of large pyramidal cells. The cell-body of the pyramidal cells is pyramidal in form, the base presenting towards the white substance and the apex directed towards the molecular layer. The apex is prolonged into a robust protoplasmic process, the primordial branch, which gives off lateral twigs at right angles, runs toward the molecular layer and there ends after repeated division. The basal dendrites pass off from the base of the cell-body, radiating laterally, or towards the white matter. The nerve- process springs from the base of the cell, or from a basal dendrite close to the cell-body, and runs towards the white substance ; during its course through the gray substance, the nerve-process gives off fine collaterals, that run horizontally or obliquely and end after a number of branchings. 6. The layer of polymorphic cells. Here are found cells, ovoid, fusiform, triangular or polygonal in form, which often exhibit a robust protoplasmic process, directed towards the molecular layer. Each cell sends off a nerve-process that passes to the white substance, after giving off a number of collaterals. Additional cells, with short nerve-processes or of Golgi's II type, are encountered, not only in this layer, but also within the strata of small and large pyramidal cells. Finally, the so-called cells of Martinotti occur as fusiform or triangular elements', whose distinguishing characteristic consists therein, that the nerve-process traverses the layer of the pyramidal cells to reach the molecular stratum, where it ends. Regarding the disposition of the nerve-fibres, thicker or thinner parallel bundles of fibres enter the cortex from the white substance, proceed towards the periph- ery, and, gradually diminishing in thickness, towards the layer of the small pyramidal cells resolve into their component fibres. These bundles are known as the medullary rays or radii and consist of the nerve-processes of the pyramidal and of the polymorphic cells, which are passing from the cortex, and of the nerve-fibres, which enter from the white substance and end within the cortex; these last are also called the terminal fibres. Between the individual medullary rays are narrow interspaces containing delicate horizon- tally coursing fibres, which form the interradial feltwork. The latter are somewhat denser where the medullary radii break up into their individual fibres and thereby pro- duce the stripe of Baillarger. The fibres of the interradial feltwork are the collaterals of the nerve-processes of the pyramidal cells. Towards the periphery, beyond the inter- radial feltwork where the radii resolve into their component fibres, lies the supraradial ii6 THE FIBRE-TRACTS. feltwork, which marks the ending of the terminal fibres and, farther outward, joins the layer of tangential fibres. The cerebral cortex does not, however, present the same structure in all regions. Local variations occur, in relation to the arrangement of the several cell-layers, as well as in regard to the behavior of the fibre-layers. There exists a cyto- and a myelo- PiG. 113. Structure of the cerebral cortex in different regions. A, cortex of precentral convolution; B, postcen- tral convolution ; C, superior temporal convolution (auditory cortex); D, surrounding the calcarine fissure (visual cortex). (Cajal.) architectonic differentiation, the recent investigations of Brodmann and of Vogt having shown that the entire cerebral cortex may be subdivided into numerous histologically different cortical fields. While it is impracticable here to discuss in detail the differ- ences, Fig. 113 presents these relations, so far as the make-up of the cell-layers is con- cerned, in the precentral and postcentral convolutions and in the auditory and visual cortical areas, according to the earlier studies of Ramon y Cajal. The preponderance of CORTICAL AREAS. 117 the large and giant pyramidal cells in the precentral convolution is to be noted in contrast to the peculiar structure of the visual cortex, in which the original six-layered type is PIG. 114. Lateral surface of hemisphere, with cytoarchitectonic cortical areas. (Brodmann.) FIG. 115. Mesial surface of hemisphere, with cytoarchitectonic cortical areas. (Brodmann.) transformed into one of nine layers, by the introduction of special layers of stellate cells (Fig. 113, D 4 and 5). THE FIBRE-TRACTS. Mitral cells II. RHINENCEPHALON. Microscopic structure of the bulbus olfactorius, the gyrus fornicatus, the hippocampus and the gyrus dentatus. BULBUS OLFACTORIUS. The bulbus olfactorius exhibits the following layers : i. The layer of the superficial nerve-fibres. This, the fibre-layer, is formed by the nerve-fibres coming from the olfactory epithelium (Fig. 116). Within the epithelium of the olfactory mucous membrane, the bipolar nerve-cells lie among the sus- tentacular cells. They are elongated narrow fusiform or irregular elements, with a thick peripherally directed process, Fibres ending in Mius Granule cells Golgi cells that ends within the epithelium, and a delicate centrally di- rected process, beset with varicosities, that traverses the tunica propria undivided. United into small bundles, the fila olfactoria, the central fibres pass through the apertures of the lamina cribrosa, enter the bulbus olfactorius and there form a close feltwork of crossing fibres, the fibre-layer. 2. The glomerular lay- er. Joining the stratum of nerve-fibres, the layer of glom- eruli olfactorii follows. Here the end-arborizations of the fibres from the fibre-layer meet those of the dendrites of certain cells, namely, the brush and mitral cells. In consequence of the close intermingling of these delicate terminal twigs, small round or ovoid structures, the glomeruli olfactorii, are formed. The olfactory fibres com- posing the fibre-layer divide often into two, or indeed into three, twigs, which enter the glomeruli ; in this manner, such ramifications may penetrate into two different glomeruli. 3. The molecular layer. This layer, also known as the stratum gelatinosum of Clarke, forms a stratum comparable to the layer of small pyramidal cells of the cerebral cortex. Within it, along with traversing and branching fibres, are found large and small brush-cells. 4. The layer of mitral cells. When compared with the cerebral cortex, it rep- resents the layer of the large pyramidal cells. The component mitral cells are of quite characteristic form. The cell-body is large, exhibits the form of a triangle or a mitre, and resembles that of the Purkinje cells of the cerebellar cortex. The protoplasmic processes are of two kinds, the ordinary dendritic stems and the so-called olfactory brushes, the penicilli olfactorii. The former pass obliquely from the cells, then run more Gtanvle layer Layer of mitral alls Molecular layer Glomerular layer Nerve-fibre layer La,. ribrosa Tunica profiria \ Epithelium FIG. 116. Olfactory mucous membrane and bulbus olfactorius. Schematic. GYRUS FORNICATUS. 119 horizontally, branch once, and end, usually after a long course, free, forming a feltwork within the deepest part of the molecular layer. The olfactory brushes traverse the molecular layer and assist in forming the glomeruli with their elaborate varicose end- arborizations. The nerve-processes of the mitral cells extend towards the granule-layer, bend sagittally at various levels and continue within the tractus olfactorius. During their course they give off collaterals, which end in free branches within the superficial and deep strata of the molecular layer. The brush-cells are often spindle-form in shape and horizontally placed. The larger cells are found within the molecular layer, external to the mitral cells, which latter they in general resemble in giving off the two kinds of dendrites and in sending their nerve- processes to the granule-layer. The small brush-cells, also known as the peripheral brush- cells, lie close beneath and between the glomeruli. They likewise send one dendrite to the glomerulus, the nerve-processes behaving like those of the large brush-cells. 5. The granule-layer. Within this stratum are found the granule cells or granula, peculiar small elements with long processes. These granula also penetrate between the mitral cells and, beyond these, into the molecular layer as far as the glom- eruli. The granule cells are triangular, resembling the pyramidal cells, or fusiform or pear-shaped, all being placed vertically. An outwardly directed process, mostly single but rarely double, divides repeatedly after a longer or shorter course, usually close beneath the mitral cells, to form a brush-like terminal arborization, that ends within the most superficial region of the molecular layer at the glomeruli in delicate filaments. In the opposite direction, that is inward, the granules exhibit several processes, which are usually smooth and slightly branched and end free after a short course. As yet, a nerve-process has not been discovered. In addition to the granules, this layer contains cells of Golgi's II type multipolar elements with fusiform or polygonal cell-body and a nerve-process that breaks up within the granule-layer. The nerve-fibres running within the granule-layer are partly the nerve-processes of the mitral and brush cells ; further, fibres enter the bulbus to end some within the granule-layer, and some within the molec- ular layer in the vicinity of the glomeruli, after having penetrated the layer of mitral cells. The nerve-processes of the mitral and brush cells, that pass to the tractus olfacto- rius, end within the cortex of the tractus and of the tuberculum olfactorium and within the olfactory area of the substantia perforata anterior and the adjoining parts of the sep- tum pellucidum. These end-stations exhibit the structure of a modified cerebral cortex. GYRUS FORNICATUS. The structure of the cortex of the gyrus fornicatus deviates from the typical make-up of the cerebral cortex chiefly in relation to the layer of the large pyramidal cells. Within the gyrus cinguli, this stratum contains, in the outer half, few small pyramid cells and, in the inner half, those of medium size. The latter, almost all of uniform diameter, lie deeply placed and together, in consequence of which disposition the middle portion of the layer appears poor in cells and, on account of the ascending primordial branches of the pyramidal cells, is called the stratum radiatum. Towards the corpus callosum, all layers suffer diminution fn thickness and in the size of the cells. The cortex of the gyrus hippocampi bears, in many respects, a close resemblance to that of the gyrus cin- guli. That part of the gyrus hippocampi which borders the fissura collateralis and rhinica, 120 THE FIBRE-TRACTS. however, exhibits slight deviation from the common type. Towards the fissura hippo- campi, the molecular layer is broader. Within the layer of small pyramidal cells, the cells are irregularly arranged in chains of hillocks, while within the third layer are found larger pyramidal cells with very long primordial branches ; moreover, of these cells the largest are very deeply placed, whereby the conspicuous radial striation, the stratum radiatum, is produced. The layer of polymorphic cells contains almost exclusively small irregular cells, that are embedded within a close network of nerve-fibres. HIPPOCAMPUS AND GYRUS DENTATUS. The hippocampus, or cornu Ammonis, and the gyrus dentatus represent two spe- cial convolutions. On following the gyrus hippocampi dorsally, one reaches the subin- culum, that constitutes that part of the hippocampal convolution in which gradually begins a change in the structure of the cerebral cortex, leading finally to the typical structure of the hippocampus. The white substance splits into two layers : the one passes to the free surface of the hippocampus and constitutes the alveus> the other passes to the lateral wall and roof of the inferior horn of the lateral ventricle. The alveus is Layer of polymorphic cells Layer of pyramidal cells Molecular layer KIG. 117. Hippocampus or cornu Ammonis and gyrus dentatus in transverse section. Schematic. THE HIPPOCAMPUS. 121 continuous with the fimbria. The uppermost layer of the gray substance, the substantia reticularis alba, corresponding to the molecular layer of the typical cortex, divides into a superficial and a deep stratum. The superficial layer adjoins the molecular layer of the gyrus dentatus and forms the lamina medullaris circumvoluta. The deep layer forms the stratum lacunosum, that arches around and embraces the lamina medullaris and ends in a recurved hook at the medial side of the cell-layer of the gyrus dentatus. Between the lamina medullaris circumvoluta and the stratum lacunosum, lies the stratum moleculare. The pyramidal cells of the subinculum gradually collect into a single layer of cells as they approach the hippocampus. At first the arrangement of the cells is still irregular, towards the gyrus dentatus the cells form a single thick layer, but within the terminal sheet of the hippocampus they once more are irregularly disposed. In this way two special zones are produced, a deep layer of pyramidal cells, the stratum lucidum, and, between the latter and the stratum lacunosum, the stratum radiatum, so called on account of the traversing long primordial stems of the pyramidal cells. The layer of polymorphic cells is known as the stratum oriens. The gyrus dentatus exhibits three strata : the molec- ular layer, the granule-layer or the stratum granulosum, and the layer of polymorphic cells. The relations between the strata of the modified cortex of the special convolutions and those of the typical cerebral cortex are shown in the following table and Fig. 117: Cerebral Cortex Hippocampus Gyrus dentatus c Lamina medullaris circumvoluta \ Molecular layer < Stratum moleculare > Molecular layer I Stratum lacunosum ) i i i 11 f Stratum radiatum ) Granule-layer or stratum Layer of pyramidal cells edimci -* * tteral pyramidal tract Area of tr. rubro-spikalis -__^ j ( }'^^^^~^^^^^'( ^\\ ^Tractus spino-cerebellaris dor- salts (Flechsig) Lateral boundary layer ' fTT ^B HMO ^B^ Ml Tractus spino-cerebellaris ven- '- tralis (Cowers) Tract, spino-thalamicus " \T .^^^ f{( \^\ ^gg*^f3- Tract** sfino-olivaris (Hel-weg) Anterior root ^ " U Anterior ground bundle ' \ ^^ Fasciculus Tract, vestibulo-spinalis svlco-marginaHs Anterior pyramidal tract s. Tract, tecto-spinalis FIG. 149. Fibre-systems of the white substance of the spinal cord. At the ventral bordedie anterior column, fibres are found which come from Deiters' nucleus and constitu^^^B tractus vestibulo-spinalis anterior or the anterior mar- ginal bundle. Lastly, as an addironal descending path within the anterior column, the posterior longitudinal bundle, or the fasciculus longitudinalis media/is, must be noted. The remaining part of the anterior column constitutes the anterior ground bundle or fasciculus anterior proprius. Within this field longitudinally course the endogenous fibres, which serve to unite different segments of the spinal cord. 2. TRACTS OF THE LATERAL COLUMN. The tractus cerebro-spinalis lateralis or the lateral pyramidal tract extends as a robust bundle in the dorsal part of the lateral column. The termination of the fibres is in the anterior horn of the same side of the cord. The tractus spino-cerebellaris dorsalis or direct eerebellar tract lies at the periphery, lateral to the pyramidal tract. The fibres arise from the cells of Clarke's column, extend upward within the lateral column and pass, as a constituent of the restiform body, to the cerebellum, where they end within the anterior superior worm. The tractus spino-cerebellaris ventralis or Cowers* tract also lies at the periphery of the lateral column, in front of the direct cerebellar tract, and likewise ends within the 162 THE FIBRE-TRACTS. cerebellum. The fibres take their origin from cells, on the same and the opposite side, which lie in the lateral part of the anterior horn and in the central field of the gray substance. They ascend at first with the direct cerebellar tract, do not, however, enter the restiform body, but continue as far as the pons, then enter the superior cerebellar peduncle and pass backward to the cerebellum, where they end within the anterior part of the superior worm (Fig. 74, fibrae arciformes). The tractus spino-olivaris or triangular bundle of Helweg is an additional small tract, which lies at the periphery of the lateral column, ventral to Gowers' bundle, and establishes relations between the spinal cord and the inferior olivary nucleus in the Fibres of lateral bundle Fibres of - medial bundle FIG. 150. Diagram of the tracts of the posterior column. medulla oblongata. The source of the fibres has not been positively determined. They form, perhaps, an ascending tract, arising within the gray substance of the cord and ending in the olive; according to other views, the bundle conveys both ascending and descending fibres. The entire area of the lateral column included between the foregoing tracts and the gray substance, belongs to the lateral ground bundle or fasciculus lateralis proprius. Within this again appear numerous endogenous fibres, long and short associ- ation fibres, which bind together various higher and lower lying segments of the spinal cord. The short fibres lie close to the gray substance and form the lateral boundary zone. In addition, within the lateral ground bundle are found the following sets of fibres: *Jie tractus rubro-spinalis or Monakow's bundle, whose fibres descend from the nucleus ruber of the opposite side and lie within the cord medial to the direct cerebellar and ventral to the lateral pyramidal tract, partly within the field of the latter. The tractus PATHS OF THE SPINAL CORD. 163 Golfs colttr, 'i r Jack's column vestibulo-spinalis lateralis, from Deiters' nucleus, passes somewhat more ventral. Medial to Gowers' bundle lies the tractus spino-thalamicus. The fibres of this path are the axones of the commissure- cells of the cord, which pass through the anterior commissure to the opposite lateral column and there turn upward. The termination of the path is in the thalamus. The tractus spino-tectalis consists of a fibre-strand, that accompanies the spino-thalamic tract and ends in the region of the corpora quadrigemina. The entire path is, therefore, also called the tractus spino-tectalis et thalamicus. Approximately within the same field, the tractus tecto-spinalis lateralis descends from the quadrigeminal region; likewise, in the vicinity of the spino-thalamic fibres, the tractus thalamo-spinalis descends as a path from the thalamus. 3. TRACTS OF THE POSTERIOR COLUMN. The posterior column is composed, in largest part, of the continuations of the sensory posterior root-fibres, that proceed from the spinal ganglia (Fig. 150). The cells of the latter give off a nerve-process, which soon divides into two branches, one passing peripheral- ward and the other centralward. The- centrally coursing branches enter the spinal cord, as the pos- terior root, as two more or less distinct bundles. One of these is made up of fine fibres, lies lateral and passes toward the substantia gelatinosa Ro- landi; the other consists of coarse fibres, lies medial and passes toward the posterior column. The en- trance zone of the lateral bundle, between the apex of the posterior horn and the periphery of the cord, is known as Lissauer's marginal zone; that of the medial bundle, to the inner side of the posterior horn, is called the radicular zone. Immediately upon entering the spinal cord, the fibres of both bundles undergo a Y-form branching. Both result- ing branches assume a longitudinal direction and during their course, respectively up or down, give off numerous collaterals to the gray substance of the cord. The descending branch is the thinner and ends, after a short course, within the gray substance. According to their length, the ascending fibres are short, medium or long. The short fibres pass into the gray substance after a very limited course; those of medium length proceed farther upward, but like- wise end within the cord by bending over into the gray substance; while the long fibres ascend to the medulla oblongata, where they end within the poste- rior column nuclei, the nucleus gracilis and cuneatus. The fibres entering the cord below are dis- FIG. 151. Diagram illustrating the gradual i i i , , . , ,. , , medial displacement of the long tracts of the placed more and more towards the mid-line by the posteri0 r column. i6 4 THE FIBRE-TRACTS. fibres entering at higher levels ; those fibres, therefore, that on entering the cord occupy the lateral part of the posterior column, as they ascend soon collectively constitute the middle and, finally, the innermost part of the column. Hence, as already noted, the posterior column exhibits in the cervical region of the cord, a subdivision into the medial fasciculus gracilis Tract, cerebro-spinalis ant. Tract, tecto-spinalh _ Tract. vi$tibnlo-spinalis anterior / . Tract, vestibulo-spinalis lateralls Tract, nilro-spinalis Tract, cerebro-spinalis lateralis FIG. 152. The chief tracts descending to the spinal cord. or Golfs column and the lateral fasciculus cuneatus or Burdock 's column a demarcation not emphasized in the lower part of the cord. Coil's column consists essentially of fibres that come from the lower segments of the cord and is nothing more than the continuation of the laterally situated fibres of the lower segments, which during their ascent have been pushed toward the mid-line by the new increments of fibres entering at higher levels. Or, we may PATHS OF THE SPINAL CORD. 165 say, in the cervical region of the cord, Coil's column is composed of fibres which ascend from the lower parts of the cord and conveys sensory fibres from the lower extremities and the lower half of the trunk, while Burdach's column carries sensory fibres that enter the spinal cord from the upper half of the trunk and the upper extremities (Fig. 151). Nuclei fnnic. post. - - - Tract, splno thalatiiicus Tractus spino cerebellares dor- saiis et vtntralis FIG. 153. The chief tracts ascending from the spinal cord. The terminal arborization of the ascending fibres and of the collaterals occurs in almost all parts of the gray substance of the same side of the cord ; a small part of the fibres passes, by way of the posterior commissure, to the opposite side to end within the posterior horn. The short fibres and the collaterals of the lateral bundle, in particular, end within the homolateral posterior horn and also within the central field ; the main fibies 166 THE FIBRE-TRACTS. and collaterals of the median bundle, which end within the cord, arborize around the cells of Clarke's column, the cells of the intermediate zone and the anterior horn cells. The collaterals from the posterior column, which break up around the anterior horn cells, constitute the reflex collaterals. The descending branches of the fibres of the posterior column, entering the root- zone medial to the posterior horn, caudalward form a bundle that in cross-section appears comma-shaped. The fibres of this field, the comma bundle of Schultze, after a short course enter the gray substance. In addition to the chief fibres, within the posterior column are others which arise in the posterior horns of the cord, as the axones of association-cells. They course within the ventral part of the posterior column and in cross-section appear as the ventral field (Fig. 149). Finally to be noted are fibres that extend from the cervical region as far as the conus terminalis. In the upper regions, they lie dorsally at the periphery of the poste- rior column, more within the area of Coil's column ; farther below, they migrate toward the septum posterius and, within the sacral region, in cross-section appear as a small medial oval field. This part has been termed the oval bundle of the posterior column. It corresponds to the bandelette m6diale of Gombault and Philippe, the dorso-medial sacral field of Obersteiner and the tractus cervico-lumbalis dorsalis of Edinger. The chief tracts descending to and ascending from the spinal cord are represented in Figs. 152 and 153. THE MEDULLA OBLONGATA. The medulla oblongata forms the transition from the spinal cord to the brain. The intimate make-up, relatively simple within the spinal cord, at the same time undergoes manifold modifications. Not only does the gray substance change its form, but new masses, large and small nuclei, appear. Coincidentally, a rearrangement of certain systems of the white substance occurs, certain tracts of fibres are suppressed and new ones make their appearance. Almost each cross-section presents a different picture. It would carry us too far to follow accurately at this place the structure of the medulla oblongata in its topographical relations, as shown in transverse sections. The study of the fibre- tracts in the brain and spinal cord, without the use of serial sections, is impossible ; and especially the study of the fibre-tracts in the medulla oblongata offers difficulties as nowhere else. The reader is particularly referred, therefore, to Part III of this book, in which, by means of the drawings of serial sections, the most important tracts may be followed through the entire brain-stem. By means of these microscopical pictures and the assist- ance of the following diagrammatic figures, the reader will be able to find his way. In the consideration of the morphology, the most important gray masses of the medulla oblongata have been mentioned ; we may limit ourselves, therefore, to the pres- entation of the connection of these gray masses with other parts of the central nervous system. Then, as supplementary, the origin of the cerebral nerves will be more closely considered, since, as pointed out in the morphological section, the nuclei of most of the cerebral nerves are situated along the floor of the fourth ventricle. PATHS OF THE MEDULLA OBLONGATA. 167 We proceed most advantageously, if we trace upward the fibre-systems of the white substance of the cord, which were described in the preceding section. At the same time, we will ignore the fibre-systems, which come from the brain and descend in the cord and have been mentioned repeatedly in previous sections. Let us first follow the tract of the posterior column. The fibres of Burdach's and of Coil's column end in the nuclei of the posterior column, that is, within the nucleus fasciculi cunati and the nucleus fasciculi gracilis. From these nuclei further tracts are developed, of which one in particular, the tract establishing relations between the pos- Lemniscus medialis Tractus spino-thalamicws Nucl. funic. post. FlG. 154. Posterior column tract, medial fillet and tegmental tract. terior column nuclei and the thalamus, now concerns us. The fibres pass, as the axones of the cells within the cuneate and gracile nuclei, in ventrally directed courses, the fibrae arcuatae internae, toward the mid-line, where by decussation they form the raphe. After crossing, the fibres assemble close to the mid-line and, turning upward, pass longitudinally to higher levels. The field so formed is known as the interolivary stratum, on account of its position between the two inferior olivary nuclei. The fibre-bundles can be traced through the pons and the mid-brain as far as the thalamus, where they end in the nucleus lateralis and in the centrum medianum. This is the path usually called the medial fillet or lemniscus medialis ; it is also known as the tractus bulbo- thalamicus. 1 68 THE FIBRE-TRACTS. Tractits spino-thalamicus . Fasc. grac. et cuneat. ^^ FIG. 155. Course of the medial fillet. THE MEDIAL FILLET. 169 The medial fillet is not composed exclusively of fibres which come from the nuclei of the posterior columns. During its course through the medulla oblongata, the fillet-tract is augmented by the fibres from the spinal cord, which we have studied as the tractus N.ruber Tractus cerebello-tegmentallt ' ' Fibrae arcitatae externae dorsales Niicl. gracilis et cuneatus - Fibrae arcuatae internae, continued as fibrae arcuatae venttales externae Tract, spino-cerebellaris dorsalis (Flechsig) PIG. 156. Formation of the restiform body. spino-thalamicus. In addition, as will be pointed out later, fibres come from the terminal nuclei of the cranial nerves. All these contributions collectively constitute the medial fillet, which ends within the thalamus. Still other tracts arise from the posterior column nuclei and unite the latter with the cerebellum. Some of these fibres pass, as do the above-mentioned fibrae arcuatae 1 70 THE FIBRE-TRACTS. internae, first towards the mid-line and there cross. They course, however, not longitu- dinally within the interolivary stratum, but pass ventrally along the raphe as far as the anterior medial fissure, then around the pyramids and the olives as the fibrae arcuatae extemae ventrales, and continue as constituents of the restiform bodies to the cerebellum. Other fibres issue dorsally from the posterior column nuclei and pass directly to the corpus restiforme as the fibrae arcuatae externae dorsales (Fig. 156). Perhaps these are joined by direct fibres from the posterior column tracts. The constitution of the corpus restiforme, or the inferior cerebellar peduncle, may now be considered. Although the tracts ascending to the cerebellum from the spinal cord and the medulla are the principal factors in its make-up, additional paths of especial importance are contributed to the restiform body by the fibre-bundles from the vestibular nerve and its end-nucleus. The restiform body consists of two chief parts, a lateral and a medial division. The lateral division is formed by the following fibre-bundles: a. The tractus spino-cerebellaris dorsalis or direct cerebellar tract. Although the tractus spino-cerebellaris ventralis or Gowers' bundle likewise passes to the cerebellum, it reaches the latter, not by way of the restiform body, but, farther above, in conjunction with the superior cerebellar peduncle (Figs. 157 and 178). b. The fibres from the nucleus gracilis and cuneatus of the same and of the opposite side: fibrae arcuatae externae dorsales et ventrales, as well as direct fibres from the posterior column. c. A few fibres from the nuclei arcuati or pyramidal nuclei, d. Fibres from the lateral column nuclei. e. Fibres from the inferior olivary nucleus. The last fibres tractus olivo-cerebellaris contribute the chief bulk of the lateral division of the peduncle. They arise in largest part from the contralateral olive, a few fibres coming also from the olive of the same side, and end, as do the other fibres _ , .. / N _ of the lateral division, within the cortex Tractus spino- I \ Tractus spino- of th e worm. The medial division consists of two chief varieties of fibres: a. One set of fibres is the sensory root-fibres of certain cerebral nerves, as the trigeminus and the vestibular, which pass FIG. 157. Schematic representation of the course of ,. , , n . . , the tractus spino-cerebellaris dorsalis and ventralis. dlrect tO the Cerebellum and Constitute the direct sensory cerebellar tract of Edinger. b. The other fibres connect the nuclei of the sensory cerebral nerves with the cere- bellum; among these connections, those of the vestibular nucleus with the cerebellum deserve special notice. The termination of the fibres of both sets is, in largest part, within the nucleus tegmenti of the cerebellum. Fibres pass also in the opposite direction from the nucleus tegmenti or roof nucleus to the end-nuclei of the sensory nerves, Deiters' and Bechterew's THE RESTIFORM BODY. 171 nuclei especially receiving such fibres. These bundles, that bring the nuclei of the sensory cerebral nerves into relation with the cerebellum, constitute the tractus nucleo-cerebellaris. The latter forms an indirect sensory cerebellar tract, in contrast to the above-mentioned direct one. Fibres from the cerebellum also pass caudally to the medulla oblongata by way of the restiform body.' The tractus cerebello-bulbaris or fastigio-bulbaris is a descending bundle, which proceeds especially from the nucleus tecti of the opposite side and, perhaps, also from the nucleus dentatus. The bundle is known also as the tractus uncinatus (Russel-Thomas). The fibres pass above the superior cerebellar peduncle and, in their farther course, reach the medial division of the restiform body. Their termination is partly within Deiters' nucleus and partly, .farther caudalward, within certain nuclei of the medulla oblongata, along with collaterals to the motor nuclei of cerebral nerves V, VII and X. Atten- tion has been called to these paths, as the tractus cerebello-tegmentales bulbi, when considering the chief connections of the cerebellum. Such cerebellofugal tracts proceed from the restiform body, with the fibrae arcuatae externae ventrales, to the olive and the pyramid and ascend within the raphe to the formatio reticularis of the medulla oblongata. The inferior olivary nucleus, as we have seen, gives off a robust fibre-bundle, which passes to the corpus restiforme of the opposite side and, thence, to the cerebellum. A small number of fibres, on the other hand, arise within the cerebellar cortex and descend to the opposite olive. The olivary nucleus possesses still further connections. Thus, from the ascending tractus spino-cerebellares collaterals are sent to the inferior olivary nucleus, while other fibres are received from the tractus spino-olivaris or Helweg's tri- angular tract, as well as from the tractus thalamo-olivaris. By means of the last-mentioned path, impulses from the thalamus, and also from the cerebral cortex by way of the thalamus, are carried to the inferior olive and, by way of the olivo-cerebellar tract, to the cerebellum (Fig. 145). The medial fillet or interolivary stratum appears in cross-sections of the medulla as a field, that lies between the two olives at the sides of the raphe (see Part III). Dorsally, as the apex of this field, the posterior longitudinal bundle or the fasciculus longitudinalis medialis is seen as a small bundle of longitudinally coursing fibres. It will be considered more fully in connection with the vestibular nerve (page 182). Lateral to the interolivary stratum and dorsal to the olive, a field spreads out which, in addition to numerous scattered nerve-cells, contains longitudinally coursing nerve-fibres. This area, the upward continuation of the formatio reticularis of the spinal cord, is known as the association field of the medulla oblongata. The formatio reticularis extends far up into the mid-brain and contains numerous connecting paths, of longer or shorter course, by which manifold relations are established between certain nerve-nuclei. It is probable that within this formatio reticularis run those association fibres which unite the nuclei of the vagus, facial and phrenic nerves for coordinated activity during respiration. Repeated mention has been made of tracts, coming from other parts of the brain, which have their ending within this formatio reticularis. The reader should refer to the section on the Reflex Tracts (page 192), as well as to the microscopical illustrations in Part III. I 7 2 THE FIBRE-TRACTS. THE CEREBRAL NERVES. NERVUS OLFACTORIUS. The first member of the conventional series of twelve cranial nerves, the nervus olfactorius, is represented by the short peripheral paths, the fila olfactoria, connecting the olfactory mucous membrane with the glomeruli within the bulbus olfactorius. Since the structures formerly described as the first cerebral nerve, the olfactory bulb and tract, are parts of the rhinencephalon, their consideration falls properly with that of the brain. They have been discussed under the Fibre-Paths of the Rhinencephalon (page 144), to which the reader, therefore, is referred. Right NERVUS OPTICUS. The fibres of the optic nerve arise within the retina and are the axones of the ganglion cells located within the ganglion-cell layer of the nervous tunic of the eye, They extend to the chiasm. Here, one part of the fibres passes to the tractus opticus of the opposite side, the other part passes direct to the tract of the same side. The fibres end within the corpus geniculatum laterale, the pulvinar and the superior colliculus ; these end-stations constitute primary visual centres. From the lateral geniculate body and the pulvinar, fibres pass through the hindmost part of the posterior limb of the capsula interna to the secondary or cortical visual centres within the cortex of the cuneus, thereby forming the optic radiation of Gratiolet. Fibres also pass in the opposite direction from the cortical visual centre to the primary centres. It must be noted fur- ther, that fibres exist, which arise within the primary centres and end within the retina. The visual fibres proper terminate FIG. 138. The path of visual impulses. within the corpus geniculatum laterale and the pulvinar thalami and probably do not invade the superior colliculus of the corpus quadrigeminum, at least in the higher vertebrates. The optic fibres which pass to the superior colliculus are concerned with a special duty. Stimuli carried by these fibres to the superior colliculus are transferred to the deeper lying oculomotor nucleus, resulting in the liberation of the pupillary reflex. These optic fibres ending in the superior colliculus are known, therefore, as pupillary fibres. CEREBRAL NERVES. 173 The pupillary reflex consists in a contraction of the pupil in response to the entrance of light. The reaction is exhibited by both eyes ; that is, when the light falls on only one eye, the contraction occurs not only in the stimulated eye (direct reaction), but also in the other eye (consensual reaction). FIG. 159- The course of the visual path. The intercentral paths of the pupillary reflex are not positively established, although it may be regarded as certain, that the entire reflex-tract is made up of a sequence including several neurones. It may be assumed that the stimulus passes : a . From the retina to the superior colliculus ; b. From the superior colliculus to the nucleus of the oculomotor nerve ; c. From the oculomotor nucleus to the ciliary ganglion ; d. From the ganglion ciliare to the sphincter pupillae muscle. Since the illumination of one eye causes uniform contraction of both pupils, the re- flex being, therefore, homo- and heterolateral, it follows that the impulse from one colliculus must be transferred to both oculomotor nuclei, or one nucleus must be able to stimulate '74 THE FIBRE-TRACTS. both the right and left sphincter pupillae muscles. The particular fibre-bundle, by means of which the impulse is transferred from the superior colliculus to the oculomotor nucleus, is not definitely determined. In Fig. 160, the reflex path is schematically represented, with the as- sumption, that the fibres proceeding from the superior colliculus reach both oculomotor nuclei. A knowledge of the course of the fibres of the optic nerve, particularly their semi- decussation, supplies the explanation of one of the most important disturbances of vision hemiopia (half seen) or hemianopsia (half not seen). If the conduction of one optic tract, for example the left, be interrupted by a lesion, the stimuli coming from the left retinal halves of the two eyes can no longer be transmitted to the cortical centres in the left hemisphere, the right halves of the visual fields are lost and only the left halves of fixed objects are still seen (Fig. 158). This condition is spoken of as homolateral or homony- mous hemianopsia or hemiopia. Lesion of the left tractus leads to right-sided homonymous hemianopsia or to left-sided hemiopia ; lesion of the right tract leads to left-sided homonymous hemianopsia or to right-sided hemiopia. Homonymous hemianopsia follows, of course, not only lesion of the tractus opticus, but also lesion of the secondary paths connecting the primary and sec- ondary centres, that is within the optic radiation, or lesion of the cortical centre. In relation to the diagnosis of the seat of the lesion, the pupillary reaction pos- sesses a certain significance. If in ho- monymous hemianopsia the light-reflex is lost when the insensitive half of the retina is illuminated, the seat of the lesion is the tractus (Wernicke's hemianopsic pupillary rigidity or hemiopic pupillary reaction). If, on the contrary, the light-reflex of the pupil is intact, then the lesion lies higher, for example, in the internal capsule or in the cerebral cortex. In the majority of cases of homonymous hemian- opsia, we have to do with tumors of the occipital lobe, more rarely with lesions of the tractus opticus. Complications associated with hemianopsia, such as hemiplegia, hemiparesis, con- tractions and aphasic disturbances (with right-sided hemianopsia), must also be borne in mind. The same-sided or homonymous hemianopsia is the opposite of the heteronymous hemianopsia, which occurs more rarely than the homonymous. When the temporal halves of both visual fields are wanting, such heteronymous hemianopsia is known as temporal hemianopsia. In such cases, the lesion is situated within the chiasm, either in the middle or in the anterior or the posterior angle of the chiasm, whereby the decussating fibres are involved. Temporal hemianopsia is observed, for example, in acromegaly, in which the enlargement of the hypophysis cerebri concurrently affects the chiasm. When the nasal halves of both visual fields are wanting, the condition is spoken of as nasal hemianopsia and is produced by involvement of the uncrossed fibres, as when the chiasm is subject to pressure on both sides in the lateral angle by enlarged carotids. Cortex (visual centre) N. oculomotorius FIG. 160. The pupillary reflex path. Cortex (visual centre) CEREBRAL NERVES. 175 NERVUS OCULOMOTORIUS. The oculomotor nerve arises in the nucleus nervi oculomotorii, which lies in the region of the superior colliculus, ventral to the aquaeductus Sylvii, within the floor of the central gray substance (Figs. 88 and 89). The nucleus consists of a medially placed medial nucleus and FIG. 161. The deep origins of the motor cerebral nerves. a pair of large-celled lateral nuclei. The nerve conveys fibres which originate within the me- dial nucleus and the lateral nucleus of the same and, in part, of the opposite side. The fibres pass ventrally in laterally convex curves and emerge from the brain-stem along the sulcus nervi oculomotorii on the medial surface of the pedunculus cerebri. The voluntary innervation of the nucleus proceeds, as in the case of all the motor cere- bral nerves, from the cerebral cortex. The entire path of conduction includes: Accomtnodatio a. The central neurone cerebral cortex to nucleus; b. The peripheral neurone nucleus, peripheral nerve, muscle. Uvatorpaipebrae Retfus superior ctlrt infernub Obliquus inferior Recrus inferior MIC. . trochlearis PIG. 162. Subsidiary nuclei of the ocu- lomotor nucleus. (Bernheimer.) It must be pointed out, however, that the course of the central path is not yet known; probably the path is composed of several neurones. Likewise, uncertainty exists regarding the location of the cortical centres, which have been variously assumed as lying within the gyrus angularis, the occipital lobe or the frontal lobe. The centre for voluntary eye-movements, however, is quite generally regarded as including the posterior part of the second or middle frontal convolution. Investigations have shown, that the entire oculomotor nucleus is made up of certain groups of cells, of which a particular group always gives origin to the fibres for a particular muscle. Con- cerning these special subdivisions of the nucleus, however, we shall not enter more fully, for the reason that these relations, as yet, have been by no means definitely established. Fig. 162 I 7 6 THE FIBRE-TRACTS. represents the individual cell-groups, according to the investigations of Bernheimer on monkeys. In the middle is the medial chief nucleus, on either side the lateral chief nucleus with its various subdivisions, and, medial from the latter, the small lateral nucleus, which is also known as the nucleus of Edinger- Westphal. NERVUS TROCHLEARIS. The trochlear nerve has its origin in the nucleus nervi trochlearis, which is located in the caudal prolongation of the oculomotor nucleus in the region of the inferior colliculus. The fibres of the fourth nerve pass dorsally, cross in the velum medullare anterius and emerge from the brain-stem behind the quadrigeminal bodies, on either side of the frenu- lum veli medullaris anterioris. As in the case of the oculomotor nervi, the path includes: a. The central neurone from cerebral cortex to nucleus; b. The peripheral neurone nucleus, peripheral nerve, muscle. NERVUS ABDUCENS. The nucleus of the abducens nerve lies in the floor of the fourth ventricle and in the colliculus facialis. The emergent fibres of the sixth nerve pass ventrally and leave the brain-stem at the posterior border of the pons. The path includes: a. The central neurone from cerebral cortex to nucleus; b. The peripheral neurone nucleus, peripheral nerve, muscle. NERVUS TRIGEMINUS. Here a motor part and a sensory part are to be distinguished (Figs. 163 and 164). I. Motor Portion. The central neurone takes origin in the cerebral cortex of the lower third of the central convolutions, passes with the pyramidal tracts downward and Nucleus radicis descendentis N. trlgemtnt lens n. trigem. sory nucleus . trigem. FIG. 163. Course of the trigeminus, vagus and glossopharyngeus within the brain-stem. CEREBRAL NERVES. 177 ends in the chief motor nucleus, within the dorso-lateral part of the tegmentum of the pons. The peripheral neurone arises within this motor nucleus, the motor root of the nerve receiving also fibres from the nucleus of the opposite side. The fibres emerge from the pons as the portio minor nervi trigemini and pass to the muscles. A small part of the motor root arises from small cells, which lie lateral to the Sylvian aqueduct within the region of the corpora quadrigemina and constitute the nucleus radicis descendentis Central trigeminal tract - Motor nucleus ^ Sensory terminal nucleus Descending- sensory trigeminal root and its ending in sensory nucleus FIG. 164. Course and relations of the root-fibres of the trigeminal nerve. nervi trigemini. This group of cells joins caudally the cell-area of the locus caerulus. The -fibres arising from these cells, after giving off collaterals to the chief motor nucleus, pass outward with the other peripherally directed processes of the motor neurones. 2. Sensory Portion. The origin of the sensory part of the trifacial nerve lies within the ganglion Gasseri. The axones of the unipolar ganglion cells of this ganglion divide into two branches. One of these extends peripherally as the peripheral nerve, the other passes centrally, enters the pons as the portio major nervi trigemini, and runs to the sensory end-nucleus of the trigeminus, close to the motor nucleus. Here each 178 THE FIBRE-TRACTS. fibre divides into an ascending and a descending branch. The ascending branch ends within the sensory nucleus within the pontile tegmentum. The descending branch ends, after giving off numerous collaterals, in a nucleus that is nothing more than the caudal prolongation of the sensory nucleus. The descending branches form collectively the tractus spinalis nervi trigemini; the gray substance in which this path ends, constitutes the nucleus tractus nervi trigemini. The descending tract, as well as the nucleus, can be followed downward as far as the cervical cord, the nucleus being identical with the substantia gelatinosa Rolandi capping the posterior horn. From the sensory end-nucleus arises the // neurone. The fibres pass towards the mid-line, giving off collaterals to the nucleus of the facial nerve, cross to the fillet-tract of the opposite side, there turn upward and run forward (partly within the medial fillet and partly as a more laterally placed special ascending bundle), and later enter the thalamus with the medial fillet. Finally, a /// neurone succeeds the second one, thus linking the thalamus with the cortical sensory area. Still to be mentioned are sensory fibres, which pass direct to the cerebellum as constituents of the direct sensory cerebellar tract; further, fibres which pass from the sensory end-nucleus to the cerebellum as constituents of the tractus nucleo-cerebellaris. NERVUS FACIALIS AND NERVUS INTERMEDIUS WRISBERGI. The facial nerve arises in the nucleus nervi facialis, which lies within the ventral area of the pontile tegmentum, ventro-lateral to the abducent nucleus. The fibres spring- ing from the nucleus first proceed dorsally, pass around the nucleus of the abducent nerve the facial knee and the colliculus facialis then course ventrally and emerge from the brain-stem at the posterior border of the pons, lateral to the olive. The volun- tary innervation of the nucleus is effected by fibres, which start from the lower third of the precentral convolution, pass through the internal capsule (knee), then through the cerebral peduncle to the pons, and, finally, to the homo- and the contralateral facial nucleus. The path includes, as in the case of the other motor nerves: a. The central neurone from cerebral cortex to nucleus; b. The peripheral neurone nucleus, peripheral nerve, muscle. The facial nucleus resembles the oculomotor nucleus in including a number of different groups of cells, in which, in the first place, we distinguish two chief groups, an upper and a lower facial nucleus. The upper contains cells, whose axones form collec- tively the superior facial branch; the lower, cells whose axones form the inferior facial branch. Moreover, the superior facial nucleus receives its innervation from the motor centres of both hemispheres, a fact of clinical significance. This bilateral innervation explains why, in central facial paralysis, the muscles supplied by the upper facial division are not involved in the paralysis, since innervation is still provided by the unaffected central neurones of the other hemisphere. In peripheral facial palsy, on the contrary, all the muscles supplied by both the upper and lower facial are paralyzed. The nervus intermedius Wrisbergi (the nerve of Sapolini, by whom it was regarded as the thirteenth cerebral nerve) is a mixed nerve, which accompanies the facial and continues as the chorda tympani. The motor fibres take origin in a small cell- group lying dorso-medial to the facial nucleus. The sensory fibres arise within the gan- glion geniculi. The axones arising from the cells of this ganglion divide into two branches. CEREBRAL NERVES. 179 One of these passes peripherally and forms, after joining the motor fibres, the peripheral nervus intermedius, that continues as the chorda tympani. The other branch passes centrally, enters the brain-stem and ends within the nucleus tractus solitarii as part of the gustatory path (page 189). - NERVUS ACUSTICUS. The acoustic nerve consists of two parts, the nervus cochleae and the nervus vestibuli. Cortex (auditory centre) Corpus genicular. medial* Corpus quadrigemin. post. Nuc. lemnis. lot. i. NERVUS COCHLEAE. This nerve takes origin within the ganglion spirale cochleae. The peripherally directed fibres of these bipolar' ganglion cells run to the auditory cells within the organ of Corti; the centrally directed fibres enter the brain-stem and end in two nuclei. The latter are the nucleus ventralis nervi cochleae, situated ventral and lateral to the corpus restiforme, and the nucleus dorsalis nervi cochleae, or tuberculum acusticum, which lies dorsally, although connected with the ventral nucleus. The impulses carried by these peripheral neu- rones are conveyed to the higher levels by the central path including: a. Neurones passing from the nucleus ventralis to the mid-line, forming the corpus trapezoides. The path is augmented by fibres from the superior olive and from the nucleus of the corpus trapezoides. After crossingthe mid-line, some fibres end within the superior olivary nucleus, while others are joined by fibres from the nucleus of the corpus trapezoides and from the superior olive of the side on which the path now runs. The fibres form collectively the lateral fillet or lemniscus later- alis, which ends within the corpus geniculatum mediale and, chiefly by collaterals, within the inferior colliculus. Some fibres extend as far as the superior colliculus. The lateral fillet receives additional fibres from a group of cells lying in the midst of the tract, known as the nucleus lemnisci lateralis. b. Neurones passing from the nucleus dorsalis or tuberculum acusticum over the corpus restiforme and, as the superficial striae acusticae, toward the mid-line; thence cours- ing deeply to cross the raphe and reach the opposite superior olive, they join the lateral fillet and finally end within the corpus geniculatum mediale. c. Neurones arising within the lateral geniculate body and passing to the auditory centre within the cortex of the gyrus temporalis superior. Fibres also run in the opposite direction, from the auditory centre to the medial geniculate body and to the inferior colliculus. 01 iva superior Nvc. corf or. trapes. PIG. 165. The auditory path. 1 8o THE FIBRE-TRACTS. fn M- / V N. cochleae FIG. 166. Course followed by the auditory impulses. CEREBRAL NERVES. 181 2. NERVUS VESTIBULI. The vestibular division of the auditory nerve arises within the ganglion vestibulare or Scarpds ganglion, located at the bottom of the internal auditory canal. The periph- erally directed processes or fibres of these ganglion cells run to the ampullae, the utricle and saccule of the internal ear; the centrally directed fibres enter the brain-stem and divide into ascending and descending branches. The descending branches form a descending vestibular root and end within the nucleus nervi vestibularis spinalis, which extends as far as the posterior column nuclei. The ascending branches end within the nucleus medialis, as well as within the lateral Deiters 1 nucleus and the upper Bechterew* s nucleus. From these end-nuclei, fibres pass to the cerebellar worm as constituents of the tractus nucleo-cerebellaris. A part of the vestibular fibres pass direct to the roof-nucleus Direct sensory cerebellar tract Nucleus FIG. 167. Path of the impulses from the vestibular nerve. of the cerebellum as constituents of the direct sensory cerebellar tract, the fibres giving off collaterals to Deiters' nucleus. The medial nucleus is brought into relation with the superior olive by means of fibres. Perhaps fibres pass also to the formatio reticularis and to the thalamus. In view of its importance, the system of Deiters' nucleus claims closer attention. This nucleus receives, on the one hand, fibres from the roof-nucleus of the cerebellum ; on the other hand, as we have seen, Deiters' nucleus gives origin to a fibre-bundle that, as the tractus vestibulo-spinalis, passes to the spinal cord. Within the same nucleus, moreover, also another path, the posterior longitudinal bundle or the fasciculus longitudinalis medians, takes its origin. The fibres pass from Deiters' nucleus toward the mid-line, some crossing the latter and then dividing into ascending and descending branches. The ascending branches can be followed upward as far as the oculomotor nucleus ; the descending branches pass to the anterior column of the 182 THE FIBRE-TRACTS. spinal cord. The posterior longitudinal bundle, however, does not consist exclusively of fibres from Deiters' nucleus. Other fibres take origin in the common nucleus of the commissura posterior and of the fasciculus longitudinalis medialis within the forepart of tibuti \ ~. - Tract, vestibulo-spinalis Pic. 168. Origin and course of the posterior longitudinal bundle. the mid-brain, in front of the oculomotor nucleus. The posterior longitudinal bundle may be traced from its nucleus through the mid-brain, the pons and the medulla oblongata into the spinal cord, during its course giving off numerous collaterals to the nuclei of the CEREBRAL NERVES. 183 nerves supplying the ocular muscles. This bundle is of great importance. It establishes relations of the nuclei of the eye-muscles to one another, among which that of the abducens to the oculomotorius nucleus deserves particular attention. Of especial impor- tance is the connection of the abducent nucleus with those cells of the oculomotor nucleus, from which pass the fibres for the rectus internus, since the synergic function of the Cortex of auditory ctntre Fate, longitud. mediate FIG. 169. Course of the auditory path. Connection of the superior olive with the nucleus of the abducens (VI) and, by means of the posterior longitudinal bundle, with the nuclei of the other nerves (III, IV) to the ocular muscles. rectus externus and internus, which consists in the conjugate deflection of the eyes toward one side, can be explained only by the existence of a direct or an indirect connection between these nuclei. Fig. 168 represents the manner in which the coordinate action of the two muscles may be explained upon an anatomical basis. Connection of the abducens nucleus with that of the oculomotorius, by means of the posterior longitudinal bundle, is 1 84 THE FIBRE-TRACTS. positively established. Further, that the nerve-fibres for the rectus internus arise, in greater part, from the cells of the oculomotor nucleus of the opposite side. On the other hand, it is still undecided, whether the efferent paths from the cortical centre for synergic eye-movements are first interrupted in a special centre within the quadrigeminal region, or pass directly into the posterior longitudinal bundle. In any event, this tract undergoes a total or partial decussation before it enters the posterior longitudinal bundle. In Fig. 1 68, the path from the cortex to the nucleus of the bundle is represented as crossed. In tnis way, the explanation for the following phenomena is supplied. When a cortical centre for eye-movements is stimulated, the left one for example, deviation of both eyes toward the right occurs. On the other hand, in left-sided disease of the cerebral cortex, followed by paralysis of the right half of the body, deflection of both eyes toward the side of the lesion, that is the left, is frequently observed, since, under these conditions, the eye-muscle nerves of the left side functionally predominate. "In lesions of the hemi- spheres, if there is conjugate deviation of the eyes, the patient looks toward the injured hemisphere when there is paralysis, or the limbs are contorted during a convulsion" (Grasset). The diagram explains, further, the deviation of the eyes, toward the side opposite to the seat of the lesion, frequently observed in diseases of the pons. For example, if a lesion of the posterior longitudinal bundle lies in the vicinity of the right abducens nucleus, deviation of the eyes toward the right occurs in consequence of the mastery by the nerves controlling the left eye-muscles. The posterior longitudinal bundle possesses further importance, since it brings the vestibular apparatus and the cerebellum into relation with the nuclei of the eye-muscles and the spinal cord, by means of the fibres arising within Deiters' nucleus. It unites, therefore, the centres concerned in maintaining equilibrium and orientation in space. It is to be noted, that, since a connection between the superior olive and the abducens nucleus exists, relations of the acoustic nerve, that is of the auditory path, with the abducens, and, by means of the posterior longitudinal bundle, with the other nuclei of the eye-muscle nerves may also be established. These connections explain the occur- rence of reflex ocular movements in response to auditory impressions (Fig. 169). NERVUS GLOSSOPHARYNGEUS AND VAGUS. i. Motor Portion. The efferent fibres arise partly within the nucleus motorius dorsalis nervi vagi et glossopharyngei, which lies in the floor of the fourth ventricle lateral to the hypoglossal nucleus and medial to the nucleus alae cinereae ; the larger part of the fibres, however, arises from the cells of the nucleus -ventralis or ambiguus, which lies within the formatio reticularis dorsal to the dorsal accessory olive. Since the voluntary innervation of the nucleus proceeds from the cerebral cortex, the path includes : a. The central neurone from the cerebral cortex to nucleus; b. The peripheral neurone nucleus, peripheral nerve, muscle. The root-bundles passing out from the dorsal nucleus are the equivalents of motor preganglionic sympathetic fibres destined for the innervation of involuntary muscle ; this nucleus, therefore, is also designated as the sympathetic motor nucleus. The fibres pro- ceeding from the nucleus ambiguus, on the contrary, are for the voluntary muscle"; this nucleus, therefore, is known as the somatic motor nucleus. The latter consists of several CEREBRAL NERVES. 185 groups of nerve-cells, the individual groups representing centres for the particular groups of muscles innervated by the vagus. The positions of these centres within the nucleus, however, are not yet sufficiently determined. 2. Sensory Portion. The efferent fibres arise within the ganglion superius et petrosum nervi glossopharyngei and ganglion jugulare et nodosum nervi vagi respectively. The peripherally directed branches form the peripheral sensory nerves ; the centrally directed branches enter the brain-stem as the sensory root-fibres and pass to the end- nuclei. One part of the fibres ends within the nucleus aloe cinereae, while another part Ala cinerea Trigonnm hypoglossi Lemn. medial. Oliva N. XII FIG. 170. Transverse section of the medulla ob- longata. Origin of the IX and X (motor part) and of the XII nerve. Nucleus tractus solitarii Tract, solitaritts FIG. 171. Origin of ths IX and X nerves, sensory part. forms a descending root, the tractus solitarius, and ends within the accompanying tract of gray substance, the nucleus tractus solitarii. The central neurones arise within the end-nuclei. The fibres emerging from the end-nuclei pass toward the mid-line and the interolivary layer, thence with the medial fillet to the thalamus. Within the latter, the third neurone takes origin and ends within the cerebral cortex. The sensory end-nuclei are also connected with the cerebellum, by means of the tractus nucleo-cerebellaris. Further, all of the centrally coursing sensory root-fibres do not terminate within the end-nuclei of the glossopharyngeus and vagus, since some of them join the descending tractus spinalis of the trigeminus nerve. NERVUS ACCESSORIUS. The spinal accessory nerve presents a cerebral and a spinal portion. The fibres of the cerebral part arise from a nucleus, situated within the caudal prolongation of the nucleus ambiguus ; further, from a small dorsal nucleus, which represents the caudal prolongation of the dorsal motor vagus nucleus. The fibres of the spinal portion of the accessorius take origin from cells situated in the base of the lateral horn and in the dorsolateral part of the anterior horn of the spinal cord, as far down as the fifth, or even seventh, cervical segment of the cord. The path includes: a. The central neurone from cerebral cortex to the nucleus; b. The peripheral neurone nucleus, peripheral nerve, muscle. As well known, the accessorius supplies the sterno-cleido-mastoideus and trapezius muscles. These fibres include the spinal portion of the nerve and constitute the ramus externus, while the fibres of the cerebral portion, as the ramus internus, pass to the vagus, as a part of which they are to be regarded. 1 86 THE FIBRE-TRACTS. NERVUS HYPOGLOSSUS. The nucleus of the hypoglossal nerve lies in the floor of the fourth ventricle, within the trigonum nervi hypoglossi. The efferent fibres pass from the nucleus, proceed ventrally and emerge from the brain-stem between the pyramid and the olivary eminence. The path includes: a. The central -neurone from cerebral cortex (lower third of the precentral convolu- tion), knee of internal capsule, nucleus. b. The peripheral neurone nucleus, peripheral nerve, muscle. SUMMARY OF THE CHIEF TRACTS. A. PROJECTION TRACTS. The entire sensory projection path from the sense-surfaces (skin, retina, labyrinth, etc. ) to the sensory region of the cerebral cortex, as well as the entire motor projection path from the motor region of the cerebral cortex to the muscles, is made up of several paths of conduc- tion or projection systems. I. CENTRIPETAL TRACTS, i. Ascending sensory tracts from the spinal cord. a. The path for the conduction of impulses of touch, temperature and pain from the trunk and the extremities. Neurone I: The impulse is conveyed from the periphery to the ganglion-cells within the spinal ganglion and thence to the spinal cord by the posterior roots. The latter enter the spinal cord and end within the gray substance. Neurone II: Origin within the gray substance of the spinal cord. The fibres pass, as the axones of commissure-cells, by way of the anterior gray commissure to the opposite lateral column and form the tractus spino-thalamicus, which higher up joins the medial fillet and with it ends within the thalamus. Neurone III: Origin* within the thalamus. Course to the cerebral cortex, in part direct by way of the internal capsule, and in part after traversing the lenticular nucleus. Cortical ending within the area of somatic sensibility. The conduction of impulses of contact or tactile sensibility is not limited to the spino-thalamic tract, but takes place also through the long tracts of the posterior columns. b. The path for the conduction of the muscle-sense from the trunk and the extremities. Neurone I: The impulse is conveyed, as in the case of those of touch, temperature and pain, first to the spinal cord. The fibres enter as posterior roots, do not, however, end within the gray substance of the spinal cord, but ascend within the posterior column to the medulla oblongata, where they first find their ending within the nucleus gracilis and cuneatus. Neurone II: Origin within the posterior column nuclei; course, after decussation, as medial fillet to thalamus and there end. Neurone III: Origin within the thalamus. Course to cortical somatic sensory area. The conduction of muscle-sense is not only by way of the posterior column nuclei and the medial fillet, but also shares the tracts passing to the cortex by way of the cerebellum, that is by CENTRIPETAL PATHS. 187 the tractus spino-cerebellaris ventralis et dorsalis. From the cerebellum, the conduction passes through the superior cerebellar peduncle to the thalamus and thence to the cerebral cortex. It is to be noted, that tracts lead to the cerebellum also from the posterior column nuclei. The partly uncrossed (muscle-sense or deep sensibility) and partly crossed (pain and temperature) conduction of sensibility within the spinal cord, explains the peculiar disturbances of sensibility in hemilesions of the cord, as manifested in the Brown-Se"quard symptom-complex. In hemilateral lesions of the spinal cord, we find, on the same side Tractus spino-thalamicus N. IX, X Nnc. grac. et cuneat. FIG. 172. The sensory tract. as the lesion, paralysis in consequence of interruption of the descending motor paths, and disturbances of the deep sensibility or muscle-sense in consequence of the involvement of the ascending paths of the posterior column and of the spino-cerebellar tracts ; while, on the side opposite the lesion, are found disturbances of superficial sensibility, pain and temperature impulses in consequence of the crossed path of the tractus spino-thalamicus. Further, the fact that the conduction of sensibility, especially of muscle-sense, also takes place by way of the cerebellum, supplies the explanation of those pathological dis- turbances, which we designate as ataxia or errors of coordination, since the impulses proceeding from the muscles and articulations are no longer transmitted to the cerebellum in consequence of the lesion of the posterior column tracts. 188 THE FIBRE-TRACTS. 2. Sensory Tracts of the Cerebral Nerves. a. The path for the impulses of touch, temperature and pain from the integument of the head (with the exception of the occipital region and certain areas of the external ear supplied respectively by the occipital and great auricular nerves), further, from the conjunctiva, the mucous membranes of the nasal fossae, of the mouth and tongue, of the palate, of the pharynx, etc., lies in the trigeminus, the glossopharyngeus, or the vagus. b. The path for the impulses of orientation and movement muscle-sense from the face lies probably in the trigeminus; that from the larynx probably in the vagus. Pcstertor column tracts spino-cerebellaris dorsalis et ventralis Tractns ipino- thalamicus FIG. 173. Ascending tracts from the spinal cord, a + b = conduction of muscle-sense; c = conduction of impulses 01 pain and temperature; a + c = conduction of tactile sensibility. The impulse is carried from the periphery to the ganglion of the corresponding nerve, and thence to the end-nucleus within the brain-stem. To the peripheral neurone I is added the central neurone II. The latter arises within the sensory end-nucleus, its axone, the efferent nerve-fibre, passes upward with the medial fillet and ends within the thalamus. From here the neurone III extends to the cerebral cortex. c. The path for the visceral impulses, from the lungs, heart, oesophagus, stomach, etc., lies in the vagus and the sympathetic. d. The path for the equilibrium impulses lies in the vestibular nerve, supple- mented by spinal fibres. The path leads to the cerebellum, thence by way of the superior cerebellar peduncle to the nucleus ruber and the thalamus, and then to the cerebral cortex. CENTRIPETAL PATHS. 189 and ino-cerebeltaris dorsalis (FUchsig) FIG. 178. Spino-cerebellar and cerebellofugal tracts. Vestibulo-cerebellar tract-system of Deiters' nucleus. oblongata the fibres arising within the nucleus gracilis and cuneatus. An indirect con- duction from the spinal cord is perhaps effected by the tractus spino-olivaris or Helweg's triangular tract, which ends within the inferior olivary nucleus, and thence by the tractus olivo-cerebellaris to the cerebellum, by way of the restiform body. The direct and the indirect sensory cerebellar tract, as well as the tracts from the quadrigeminal region, are also included among the centripetal paths. By means of the cerebellofugal tracts, impulses may be carried from the cerebellum to other paths and by means of the latter, in turn, be transferred to motor paths. The chief cerebellofugal tracts proceed from Deiters' nucleus and from the nucleus dentatus. From Deiters' nucleus arise the tractus vestibule- I 9 4 THE FIBRE-TRACTS. spinalis and the posterior longitudinal bundle, the last-named system coming into relation with the spinal cord and with the nuclei of the nerves supplying the ocular muscles Pyramidal (red) and cortico-pontile tracts Tract from pans to trebellum (middle peduncle) Tracts of pat, column Tract, rutro-spinalis Tract, spino-cerebtllaris FIG. 179. Cerebellopetal and cerebellofugal tracts. that is, binding together the centres concerned in maintaining equilibrium and relations to space. From the nucleus dentatus arises the superior cerebellar peduncle, whose fibres end within the nucleus ruber, whence the tractus rubro-spinalis passes to the spinal cord. REFLEX PATHS. 195 It is to be noted, that the relations of the cerebellar hemispheres with the spinal cord are homolateral or of the same side. Additional cerebellofugal paths are those which, as the tractus tegmentalis pontis et bulbi, run within the tegmental region of the pons and medulla oblongata, whereby transference to motor nuclei may in turn be effected. If the maintenance of equilibrium be adjusted to a voluntary movement, the cere- bellum is also direcdy stimulated from the cerebral cortex. The paths for such impulses Tracts coming: from higher respiratory centres to nucleus respiratorius Central (nucleo-cortical) tract of vagns Sensory end-nucleus of vagut Sanguis Plex. brachial. ' Nn.f-horacales FIG. 180. Schematic representation of the tracts chiefly concerned in respiration. are the frontal and the temporo-occipital cortico-pontile tracts, which end in the pontile nuclei, whence the conduction to the cerebellum is by the middle cerebellar peduncle. In addition, the pontile nuclei are under the influence of the pyramidal tract, from which, within the pons, collaterals are given off to the nuclei. By means of the superior cerebellar peduncle (cerebellum-nucleus ruber thalamus cortex), the cerebellum sends impulses to the cerebral cortex and thereby influences conscious innervation (Figs. 145 and 147). Besides the cerebellum, other organs that preside over reflex activity call for mention. Such organs, in the first place, are the thalamus and the corpora quadrigemina. i 9 6 THE FIBRE-TRACTS. The centripetal paths of the thalamus are: the ascending tract of the medial fillet, the fibres of the optic tract ending within the pulvinar, the fibres from the olfactory centres and the fibres from the cerebellum by way of the superior peduncle. The thalamofugal paths lie within the tractus thalamo-spinalis, the tractus rubro-spinalis and the central tegmental tract. By means of the connections between the thalamus and the cerebral cortex, impulses coming from the periphery are carried to the cortex and, in reversed direction, activities occurring within the cerebrum are transferred to lower lying centres. The centripetal path of the superior colliculus lies within the tractus opticus and partly within the lateral fillet ; that of the inferior colliculus within the lateral fillet. A centripetal path of the corpora quadrigemina is afforded also by the ascending tractus spino-tectalis, associated with the tractus spino-thalamicus. Fibres pass from the quadri- geminal region to the cerebellum and an important descending path forms the tractus tecto-spinalis, the path from the quadrigeminal bodies to the spinal cord. Since fibres from the optic and acoustic nerves end within the quadrigeminal region and the path effects the transference of impulses of these nerves to the spinal cord, the tecto-spinal tract is also known as the visuo-auditory reflex path. The foregoing by no means completes the enumeration of the reflex paths, since throughout the brain-stem course numerous additional tracts, which serve to unite func- tionally related centres. In this connection, it is only necessary to recall the complex mechanism of the medulla oblongata, in which different nuclei are brought into the most varied relations, whereby numerous simple, as well as the most complex, reflex proc- esses are effected. While it is impracticable here to consider all such reflex paths, in order to obtain some notion of such complicated mechanisms, we may represent, by means of a simple diagram, the centres and tracts chiefly concerned in respiration. Respiration is maintained by the stimulus carried to the respiratory centre through the circulation. In addition, the reflexes transmitted by the vagus also come into con- sideration. In Fig. 1 80, the respiratory centre is represented by the nucleus respiratorius within the formatio reticularis. This nucleus stands in close relation with the sensory end-nucleus of the vagus, since impulses are conveyed to it by the collaterals given off from the central vagus-tract. Moreover, as indicated in the figure, the nucleus respira- torius is also under the influence of the higher lying respiratory centres. By means of the paths passing from the respiratory nucleus, as well as by the farther connecting neurones, the impulse is transferred to the motor nuclei of certain cerebral nerves and the gray substance of the spinal cord and, thence, is carried by the motor fibres to the muscles concerned in respiration. Thus, the impulse is carried by the phrenic nerve to the diaphragm; by the thoracic nerves to the intercostales and levatores costarum; by the cervical plexus to the scalene, sterno-hyoid and sterno-thyroid muscles (depression of the larynx); by the brachial plexus to the rhomboidei and pectoralis minor; by the accessorius to the sterno-cleido-mastoid and trapezius; by the vagus to the crico-arytaenoideus posticus and thyero-arytaenoideus (widening of the vocal cleft) and the levatores veli palatini et uvulae (elevation of the soft palate and the uvula); the facial nerve to the facial muscles (widening of the nasal apertures and the oral cavity). The paths passing from the nucleus respiratorius course in the medulla oblongata within the formatio reticularis, and, as shown in the accompanying diagram, numerous motor nuclei are brought into common activity by means of these association tracts (Fig. 220). ASSOCIATION PATHS. 197 C. ASSOCIATION TRACTS. When discussing cerebral localization, it was pointed out, that the various divisions of the brain were 'divided in a general way, according to their function, into higher and lower parts. Functionally the highest division is the cerebrum, with the cerebral cortex; the lower divisions intervene between the spinal cord and the cerebrum and include the medulla oblongata, the pons and the cerebellum, the mid-brain and the diencephalon or inter-brain. All nerve tracts, which convey to the central nervous system the most varied impulses from the individual sense-organs and the various organs within the body, find their immediate ending within the lower brain-centres; within these lower centres arise efferent paths, by means of which the stimuli received are again projected towards the periphery and transferred to the organs of movement. In this manner are brought about all those movements that we designate as simple and complex reflexes, which occur without participation of our consciousness. The impulses conveyed to the central nervous system, however, are not confined to the subcortical centres, but are carried by other paths to the cerebral cortex, where, in the appropriate sensory centres, impulses are called forth which psychically correspond to what we designate as sensation. This impulse within the sensory cortical centres continues, so long as the stimulus continues. With the stimulus, the impulse disappears and therewith the sensation also ceases. We are able, however, to picture an object, even when we no longer perceive it, or to recognize it when it again appears. Therefore, on its first appearance, the stimulus must have called forth a permanent impulse, in addition to the vanishing sensory impulse; the latter is designated the concept impulse. The retention of this impulse makes possible the recognition, the proving, or the representation of the object; that is, there remain per- sistent traces of previous sensory or motor impulses, the so-called latent dispositions. These latent dispositions or subconscious impressions, when later awakened by new impulses, render possible the conscious memory or conception of sensation and movement. The ability to call into activity and to convert the latent dispositions or impressions into conceptions is what we call thought. In addition to this mnemonic function, the cerebrum possesses the associative function. One conception can awaken others by reason of the linking together of the latent dis- positions. By union of partial conceptions (visual, gustatory, olfactory, tactile and other sensations), the complete conception is attained; by the blending of the complete con- ceptions, the general conceptions are formed. In this way are "reproduced" entire complexes of conceptions, which are definitely connected and, as it were, lie prepared; it may be, however, that certain complexes of conception are arranged in other and new sequences, new conceptions being thereby "produced." The associative function consists, therefore, in the reproduction and production of conceptions, and on this possibility of a definite sequence of conceptions depends the exercise of the higher psychic processes, that is, thought. By means of these associative processes, the individual cortical areas within the same projection and memory fields, as well as the different projection and memory fields, are brought into connection with one another. Such connection between the dispositions I 9 8 Ski* PIG. 181. Schematic representation of the physiologically different conductions. Red, centrifugal tracts; blue, centrip- etal tracts; black, intercentral tracts. ASSOCIATION PATHS. 199 or residues of the same kind exists everywhere within the corresponding cortical areas. The association between residues of different kinds, as well as the connection of projection areas with memory centres and of the various projection and memory centres with one another, is established by means of the association fibres, which as short and long fibres unite adjoining convolutions and remote regions respectively. Since, however, the widely different processes of the outer world and of the body proper give rise to the formation of manifold < impressions and to the exercise of the most simple as well as the highest psychic processes, something further always occurs. The influences taken up by the organism react outwardly, since they always find expres- sion in the various movements of the . organs. While the purely reflex reactions are carried out unconsciously, through the agency of the lower -brain-centres and without the participation of the cerebrum, the voluntary movements, our conduct and voluntary acts are dependent upon the activity of the cerebral cortex, every action, indeed, being determined by conceptions and, in the final analysis, by kinaesthetic or motor concepts. These relations will be best understood, if, in conclusion, we consider more closely those most important movements concerned in speech, by means of which our entire sensations, conceptions and thoughts find expression. When discussing cerebral localization, it was pointed out, that in right-handed, therefore, in the majority of individuals, the speech-zone, with its different centres, was located within the left hemisphere. The chief centres include (Fig. 182): the sensory speech-centre (A~), within the posterior third of the superior temporal convolution, where the memory-pictures of the heard words are deposited the centre, therefore, for the memory of word-tones and the motor speech-centre (M}, within the posterior third of the inferior frontal convolution, in whose cells the memory-pictures of the spoken words lie and on whose integrity depends the ability to carry out the coordinated movements of certain muscles necessary for speech. These two speech-centres, the sensory and the motor, stand in close relation with each other, the latter dependent upon the former, since speech is acquired by repetition of the word-sounds heard. On observing the development of speech in the child, we find in the connection of these two centres the basis for the possibility of pronouncing by repeating but without understanding. The development of speech teaches, moreover, that speech proper, that is, the intelligent utterance of sounds, in contrast to their mere repeat- ing, is preceded by an understanding of speech without speaking a stage of ' ' normal deaf-mutism. ' ' The child understands much, but speaks little or nothing of what it understands ; it is, for the time, deaf-mute. Therefore, an intimate connection is early established between the memory of the word-sound or the acoustic word (A} and the idea (.#). In Fig. 182, this close connection, as well as that between the sensory and motor speech-centres, is represented by the double line, A B. In this relation it should be emphasized, that the idea-centre (.#) is represented as a definitely bounded cortical area only as a schematic expedient, and that, as a matter of fact, we must con- ceive the formation of the idea as a complex process involving, more or less, the entire cerebral cortex. From this speech-comprehension without speaking (a 1 a 2 a A B} and the first mere repeating of spoken words (a 1 a 2 a A Mm m l nt 2 ), later comes the repeating of words with the understanding of speech; that is, speech proper. The 200 THE FIBRE-TRACTS. Vision Speech Writing Fig. 182. Scheme of spoken and written speech. B, conception centre; M, motor speech-centre (Broca); A, sensory speech-centre (Wernicke); O, visual letter-centre; m, motor centre (facial, lingual and laryngeal musculature); a, auditory centre; o, visual centre: H, motor centre for hand; m> m* fc> h* - cortico-muscular tracts for speaking and writing; * On Fig. 182, we may trace the following paths : Speech comprehension : a 1 a 2 a A B ; Repeating words : a 1 a 2 a A M m m l m 2 ; Spontaneous speech : B A M m m 1 m 2 B - M- m-m l -m 2 Reading : o 1 - o 2 - o - O - A or M B; Reading aloud : o l o 2 o OA or M B M mm l m z ; Spontaneous writing : B A or M O H k l h 2 ; Copying : o 1 - o 2 - o - O - H- h l -h 2 ; Dictated writing : a 1 a 2 a A or M O H h 1 h 2 . At the same time, the diagram explains the different types of the disturbances of speech or aphasia. A lesion of the speech-centre, M, leads to cortical motor aphasia. The patient can neither speak spontaneously, nor repeat; moreover, since reading and writing depend upon the integrity of the sensory as well as of the motor speech-centre, reading, spon- taneous writing and dictated writing are also impaired. On the other hand, the patient understands what is spoken, since A is intact, and can copy writing. ASSOCIATION PATHS. 203 A lesion of the sensory speech-centre, A, leads to cortical sensory aphasia. In the first place, comprehension of speech is lost; further, repetition, reading and dictation writing are suspended, while spontaneous writing and copying, as well as speech, are retained. In speaking, however, the patient manifests the symptoms of paraphasia, that is, the interpolation of incorrect words and exchange and mutilation of words. Destruction of both chief centres, the motor and the sensory, leads to total aphasia. When the efferent path from the motor speech-centre, M, is interrupted by a sub- cortical effusion, the clinical picture of subcortical motor aphasia or word-dumbness appears; when the lesion involves the path to the sensory speech-centre, subcortical sen- sory aphasia follows. These subcortical aphasias leave inward speech intact, and the ability to read and write are retained. On the other hand, in subcortical motor aphasia, voluntary speech, repeating and reading aloud, are suspended or involved; in subcortical sensory aphasia, speech-comprehension, repeating and dictation writing are wanting or impaired. If the path from the idea-centre to the motor speech-centre (BM*) be interrupted, the patient is said to be affected with transcortical motor aphasia, with loss of voluntary speech and writing; if the path from the sensory centre to the idea-centre be broken, the resulting condition is termed transcortical sensory aphasia, with loss of the compre- hension of speech and of writing. An interruption of the path uniting the sensory and motor speech-centres (AM} leads to the so-called conduction aphasia. The ability of repeating words is impaired ; speech and comprehension of writing and the ability to copy are retained, as well as spontaneous speech and writing; the performance of these functions, however, is attended with the manifestations of paraphasia and paragraphia. PART III. SERIAL SECTIONS THROUGH THE BRAIN-STEM OF A FOUR-YEAR-OLD CHILD FROM THE ANTERIOR END OF THE CORPUS CALLOSUM TO THE QUADRIGEMINAL REGION FROM CORPUS CALLOSUM TO QUADRIGEMINAL REGION. 207 g 3 208 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM CORPUS CALLOSUM TO QUADRIGEMINAL REGION. 209 210 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM CORPUS CALLOSUM TO QUADRIGEMINAL REGION. 211 212 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM CORPUS CALLOSUM TO QUADRIGEMINAL REGION. 213 214 SERIAL SECTIONS THROUGH THE BRAIN-STEM. e .2 FROM CORPUS CALLOSUM TO QUADRIGEMINAL REGION. 215 216 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM CORPUS CALLOSUM TO QUADRIGEMINAL REGION. 217 218 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM CORPUS CALLOSUM TO QUADRIGEMINAL REGION. 219 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM CORPUS CALLOSUM TO QUADRIGEMINAL REGION. 221 222 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM CORPUS CALLOSUM TO QUADRIGEMINAL REGION. 223 224 SERIAL SECTIONS THROUGH THE BRAIN-STEM. r^ 1 i i t 21 i i ,'sy x I ! j i i i 1 inantillo-thalamicus "V Vicg d'Azyr) \ 'i 1 ! **L | i J i iS J * o i i ; i ^ 1^*1 ^ J3 O i|-a| J 3 FROM CORPUS CALLOSUM TO QUADRIGEMINAL REGION. 225 226 SERIAL SECTIONS THROUGH THE BRAIN-STEM. If! FROM CORPUS CALLOSUM TO QUADRIGEMINAL REGION. 227 228 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM CORPUS CALLOSUM TO QUADRIGEMINAL REGION. 229 * ! It 3 1 i s i * u ^* i* 3 s ' 1 1 1 a 230 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM CORPUS CALLOSUM TO QUADRIGEMINAL REGION. 231 I HI S3 2.32 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM CORPUS CALLOSUM TO QUADRIGEMINAL REGION. 233 SERIAL SECTIONS THROUGH THE BRAIN-STEM. B FROM THE CAUDAL END OF THE MEDULLA OBLONGATA TO THE QUADRIGEMINAL REGION \ 236 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM MEDULLA OBLONGATA TO QUADRIGEMINAL REGION. 237 rif];JJfJ12HlJ 9 1 Us a 4 I :l|1 6 " - & I III III! !|! - 238 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM MEDULLA OBLONGATA TO QUADRIGEMINAL REGION. 239 *3 52 a >. C -r 3 S * o a "3 E g 3 C S "8 2 S **iJ g fl S: * . S 3 l 2 o o o ^ 2 o s ; ^ ^ g 1 2 * S 5 1 i j i d i : 3 * fl S 9 g : g I|| i! !!fl iiilliS 1 1 jg J2 - . 2 5 5 2 Q | 'S^^ 1 K ^ ^ 8 B 111 s Millll 1 1 i 1 1 ! - 1 i 1 53-no rt^S-3 s s i i i i 1 1 1 1 1 ! ! 1U ? 1 * 1 1 i J s C o s s ^ 1 3 _ w 2 i S 1 1 - 1 1 1 i I; ! ^ o I f - * $ 1 ! ' 1 1 J ^*r 1* 1 I 1 1 1 1 1 1^ 1 1 1 : | * J 1 1 1 1 a 2 H Jjlj'li ailni 248 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM MEDULLA OBLONGATA TO QUADRIGEMINAL REGION. 249 urn iPiii S -s ~ !:.^s II 250 SERIAL SECTIONS THROUGH THE BRAIN-STEM. t j S t! i* 1 j FROM MEDULLA OBLONGATA TO QUADRIGEMINAL REGION. 251 l ! iff 252 SERIAL SECTIONS THROUGH THE BRAIN-STEM, FROM MEDULLA OBLONGATA TO QUADRIGEMINAL REGION. 253 Ut * 5 Jl iHlifll J! !- 3 , I 1 1 < VwoJ7^i-i.r OTW ** llli is * 6 UHll! ^ <5 c g -S .S * M I N -3 5 i i| S ill H co P Cfl (M co W *d ISlliiitl 5 I 4 a I 3 1 1 3 | t.s5i M &n I ! s ? i 1 1 1 8 | s i : s 5 s ; lllllls^.f fi S & jjH I ll^l l*1.li *^ rt X ^ N.* cd ^ w "d C3 -U irts ~ I _ - * 1 J JM S 2 ^^ < So'S : 3H ilHl'lI'i {Jfiillii iHniiiii 1 ^ 1 1 1 1 1 1 1 Bjfili l h i^fiiii'i * 2 * -3 1 : . s 5 8 J * 1 3 * a j "S 5 " -4-> ^ S I 5 1 e 1 ! - 8 0*0 ^S .^^o^w * 3 M?^^ >3"" g M C?fJ-g T 3-oc'' I II 1 1 1 ! i I I ^urtg^^^-go^ i i 1 1 1 1 ^ - s R a 'a a * Hljflll.. -8 -s I 8 ^ .2 5 . I S -S * - 14-4 1 1 1 1 flfl lilt] ! fe i :* ; : :| i -: 1 1 * I s i ; ii^l^ls! ! 2-54 SERIAL SECTIONS THROUGH THE BRAIN-STEM. 1 FROM MEDULLA OBLONGATA TO QUADRIGEMINAL REGION. 255 * i ! e 1 ; | 1 I jiili II 1 l!l!P!!!!!!!l!i I'iiitlilflli*! 1 i! iltl! illllli 1 1 1 ". 3 8 5 I i 3 1 s 8 J o-^^ & I j E .g H ~ ;: S ~ .8 51 > . 1 1 1 1 til 1 1 a s l 'iimitniiiiii 3-?-Ss2--^i*'^^g-Ss^ l!iit|ii!iii*U! I R S ? S s II 1 1 M I si m ! t * i U.f * n f 4 I 1 1 1 s *lB !**xJoJi-TiB_ - 1 i!!jiM llSli H s^^^^-o^Ss^^iS&sl 256 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM MEDULLA OBLONGATA TO QUADRIGEMINAL REGION. 257 U " 1 1 1 1 1 5 1 1 1 ^ i ! 1 1 * I a Sl2gsg:3'3|iSG| J ,t. 8 1 S I ! 3 ] 1 1 1 ! 1 1 1 s ! I ^ll 1 !!! 2 1*1 : e * 5 & i i * ^ 5 ,5 - o -O -a "eSSa^-SSi^S ^" ^=og. S 2^rt^ c c-S i S u ,' r ' i: e-S'3SS Slu 2rt 6 ^ I ^ N s i ! 2 1 1 ! i i i tJ " ^ 5a^**5raJI* 8 ! y: -*-. *c w fi- lo l5aXjai UM itii tilii & | "3 S 2 & S I - ^ fi "- ^ ' S * ^ " i?lS**ii!'f-felltlH? l!l^^ll^5^s&s| SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM MEDULLA OBLONGATA TO QUADRIGEMINAL REGION. 259 1 1 s 1 1 1 1 ; i. 260 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM MEDULLA OBLONGATA TO QUADRIGEMINAL REGION. 261 4 .2 3 ill I I 1 1 III s 'b -o - 2 11 . - - 266 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM MEDULLA OBLONGATA TO QUADRIGEMINAL REGION. 267 i i i 1 1 ~ 1 1 s i f 1 i H i 3 * . i ! - 1 & I ! I H S M & u ^ "e w Hi m 1 * " -5 i s s 1 g 1 if i a * i 1 1 * flit mill 2 s s i i ;. J 5 1 1 S 5 ^ J j I |:a J I ii -s > - $ f J is? slf i i 1 1 1 1 1 i J lit lil^iif J3rt.rtl3-' J '0.2 MV * - g-^i^flS-gjg^ c>;u'8Guci~+3 JHSiilJU > fe .*j n, O _n S || g-| ||||S * ff k. '1 ->0 g^8S58|^2| i 1 2 1 1 1 1 1 i r S J I a " 1 1 1 1 S ! iiiiPjiM II I ;l |ll|l | | ^ | S 5 IS i 5 liiijl!!!! hlllliSii f f * f I f 1 1 Illlllll 268 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM MEDULLA OBLONGATA TO QUADRIGEMINAL REGION. . 269 * * ? 1 j 1 .4 1 1 i 1*1 "flail iitiiJili I jjTSuo.S'u 05 => -^ r 3 ^s^- 2 ^ HjHijjJj j'il!*!!! U* 'Iff ill SJiflSd! 8 1 3 1 * -a s S 1 I !' S ' * * '{' I ' J 5 ! i f 1 1 1 j i i Kis^; S H i i 2 ^ - 583 ! 1 1 1 1 1 1 1 i i "^".^Ss 3 ^^- ^feSoo. G S., 2 3 hj ^SoBg.0^- 3 l^ljjill ft 5 ^ C > ^ B I ^ 2 2 g o ' * 1 1 1 tf^i % S I g I 5 o ^>Co*O aT^aJ U > Mfltll'BaJS < i n n 1 1 > i I s^ s^s i g-g b i I 5 t5 S sS^^^d^* ^ H?j i! s s a I I S 1 1 a | | s i | s a Miliiliii] ? 1 5 1 1 5 1 ! i ! s is i 8 & .s ft^ 270 SERIAL SECTIONS THROUGH THE BRAIN-STEM. FROM MEDULLA OBLONGATA TO QUADRIGEMINAL REGION. 271 n 11* 1 4 1 1 * 11 1 - 1 1 -i * l Jli 5 .-S-c-S^SsiS-o S = ** - S 1 5 = = 1 1 1 1 1 1 1 1 1 1 1 H 1 1 1 |i 1 1 1 a H I ^ I E I s ^ | S V I1 1 * I i 1 * ! * I ~ ~ =3 6 * 8 -g 1 i i * | I ^a||'||.||_2o| s 8 I ' ~ j 8 J H ! ! ? 1 1 s I i -s i I ! liillMill 1 ! ! ! ! * ! 1 ^ i * S i 1 1 t -3 1 1 1 * s s 1 ^ - 5 - a I i 4 -> i -i^i ^ i i 1 1 O XI g~a|Soi3 ^CrtO)*r'^ria)'-iS5fe g^g&8'3fi8&fi ^lililill^^!! Il^l2li8|52l i ^ i " r. 274 FROM MEDULLA OBLONGATA TO QUADRIGEMINAL REGION. 275 3 1 1 1, 1 1 1 1 1 1 M 1 1 i If I * s : s : ! .s : i ^ 1 1 : s * * s l 11 ili 5 ! < > .o -s i 1 1 1 1 : 1 ! i I o . B S 1 * .= = B 3 s s -% : - 1 1 3 I I 'a lip!-! I 1 1 I 1 * 1 I . t i I -9 3 iti'jS Jti 8" *. 1- * 1 8 ; *; *J ' 2 . 1 -g D-j,^^ 2 J3 g i j. -JS . * ^ I S 2- -I *'!? 3 I 3 S "8 a I ilijlillil 8 1 1 ; 2 i a & -g Pli^lliil hiiilllii g 1 1 1 1 s ^ -I I III S - I] I* M * 1 1. i r 1 S T - ST f^l 3 i i - 1 -1 3 I If || 1 1 8 .| |i 1 1 1 1 1 1 ! I il I M 1 j i M 1 1 i oj3 u xg .g.n o x.2 .- M*l!iiifinU! i|!|ii?iii!iiill iliillJlMfliill 1 1 * ] I I I 7. a e 1 8 - i 8 I a a f- ' lilifilllilHJl SELECTED REFERENCES. The following list includes important books and monographs relating to the anatomy of the Central Nervous System, which the student may consult with advantage. Extended bib- liographies will be found in Obersteiner and in the year-books of Anatomy and Neurology. BARKER, L. F. The Nervous System and its Constituent Neurones. 1899. BECHTEREW, W. Die Leitungsbahnen im Gehirn und Ruckenmark. 1899. BRODMANN, K. Die Cortexgliederung des Menschen. Jour. f. Psychol. u. Neurol., Bd. X., 1907. BRODMANN, K. Die feinere Anatomic des Grosshirns. Lewandowsky's Handbuch der Neurologic, 1910. CAJAL, S. RAMON Y. El systema nervioso del Hombre e de los Vertebrados. 1902. CHARPY, A. Systeme Nerveux. In Poirier's Traite" d' Anatomic Humaine, Tome III., 1899. CUNNINGHAM, D. J. Surface Anatomy of the Cerebral Hemispheres. 1892. DALTON, J. C. Topographical Anatomy of the Brain. Atlas. 1885. DEJERINE, J. Anatomie des Centres Nerveux. 1901. DOGIEL, A. S. Der Bau der Spinalganglien des Menschen und der Saugethiere. 1908. DONALDSON AND DAVIS. Areas of Cross-Sections of the Spinal Cord at the Level of each Spinal Nerve. Journal of Comparative Neurology, Vol. XIII., 1903. EDINGER, L. Vorlesungen ueber den Bau der nervosen Zentralorgane. 1908. FLECHSIG, P. Die Leitungsbahnen im Gehirn und Ruckenmark. 1876. GEHUCHTEN, VAN A. Anatomie du Systeme Nerveux del'Homme. 1906. HABERLIN, C. Zur Topographic der Hirnventrikel. Arch. f. Anat. u. Entwick. 1909. HELD, H. Die Enstehung des Nervengewebes. 1909. His, W. Die Formentwickelung des menschlichen Vorderhirns. 1889. His, W. Die Entwickelung des menschlichen Gehirns. 1904. HORSLEY, V. The Cerebellum : Its Relation to Spacial Orientation and to Loco- motion. Boyle Lecture. 1905. JACOBSOHN, L. Ueber die Kerne des menschlichen Hirnstamms. Akademie der Wissenschaften, Berlin. 1911. JAKOB, C. Vom Tierhirn zum Menschenhirn. Atlas. 1911. JOHNSTON, J. B. The Nervous System of Vertebrates. 1906. JOHNSTON, J. B. The Morphology of the Fore-Brain Vesicle in Vertebrates. Journal of Comparative Neurology and Psychology. Vol. XIX., 1909. 279 2 8o SELECTED REFERENCES. KAES, T. Die Grosshirnrinde des Menschen in ihren Massen u. in ihrem Faserge- halt. 1907. KOELLIKER, A. Handbuch der Gewebelehre. Band II., 1896. KUPFFER, K. Die Morphologic des Central nervensystems. In Hertwig's Handbuch der Entwickelungslehre. Bd. II., Th. 3., 1906. LENHOSSEK, M. Der feinere Bau des Nervensystems. 1895. LEWANDOWSKY, M. Handbuch der Neurologic. I. Allgemeine Neurologic. 1910. MALONE, E. Ueber die Kerne des menschlichen Diencephalon. Akademie der Wissen- schaften, Berlin. 1910. MARBURG, O. Mikroskopisch-topographischer Atlas des menschlichen Zentralnervensys- tems. 1910. MONAKOW, C. Der rothe Kern, die Haube u. die Regio subthalamica bei einige Sauge- thieren u. bei Menschen. Arbeiten a. d. Hirnanatomischen Institut in Zurich. Bd. III., 1909. NEBELTHAU, E. Schnitte durch das menschliche Gehirn. 1898. NEUMAYER, L. Histo- und Morphogenese des peripheren Nervensystems, der Spinal - ganglien und des Nervus sympathicus. In Hertwig's Handbuch der Entwickel- ungslehre. Bd. II., Th. 3, 1906. OBERSTEINER, H. Anleitung beim Studium des Baues der nervosen Centralorgane. 1912. PARKER, G. H. The Phylogenetic Origin of the Nervous System. Anatom. Record, Vol. IV., 1910. RETZIUS, G. Das Menschenhirn. 1896. Atlas of special regions. SACHS, E. On the Structure and Functional Relations of the Optic Thalamus. Brain, Vol. CXXVL, 1909. SABIN, F. R. Atlas of the Medulla and Midbrain. 1901. SCHAFER AND SYMINGTON. Neurology. In Quain's Anatomy, Vol. III., 1908. SMITH, E. A new Topographical Survey of the Human Cerebral Cortex. Jour, of Anatomy and Physiology, Vol. XLL, 1907. STREETER, G. L. Die Entwickelung des Nervensystems. In Keibel and Mall's Hand- buch d. Entwickelungsgeschichte d. Menschen. Bd. II., 1911. TILNEY, F. Contribution to the Study of the Hypophysis Cerebri, with Especial Refer- ence to Its Comparative Histology. 1911. VOGT, C. La myeloarchitecture du thalamus du cercopitheque. Jour. f. Psychol. u. Neurol, Bd. XII., 1909. WERNICKE, C. Atlas des Gehirns. 1897. ZIEHEN, T. Die Morphologic des Centralnervensystems der Saugetiere. In Hertwig's Handbuch der Entwickelungslehre. Bd. II., Th. 3, 1906. ZIEHEN, T. Die Histogenese von Hirn- und Riickenmark. In Hertwig's Handbuch der Entwickelungslehre. Bd. II., Th. 3, 1906. ZIEHEN, T. Nervensystem. In Bardeleben's Handbuch der Anatomic. 1899. INDEX Abducens, 176 Accessorius, 185 Acervulus, 56 Acusticus, 179 Ala cinerea, 82 lobuli centralis, 73 uvulae, 75 Alveus, 45, 120 Angulus gyri olfact. lat, 28 Ansa lenticularis, 144, 219 peduncularis, 144, 219 Anterior column, 90 tracts, 161 commissure, 135 ground bundle, 161 Apertura medialis ventric. quarti (Magendii), 80 lateralis ventric. quarti (Luschkae), 80 Aphasia, 202 Apraxia, 130 Aquaeduct. cerebri Sylvii, 68 Arachnoidea cerebri, 88 spinalis, 93 Arachnoidal villi (Pacchioni), 88 Arbor medullaris, 76 vermis vitae, 76 Arcuate fibres, 167, 170 nucleus, 84, 170 Area acustica, 82 medial, trigoni N. XII., 82 parolfactoria (Broca), 27 plumiformis, 82 postrema, 82 Ascensus medullae spinalis, 9 Association cells, 160 area, 171 centres (Flechsig), 127 conduction, 133 fibres, 134 tracts, 197 Astrocytes, 106 Astropilemma, 106 Auditory centre, 126 path, 190 Axis-cylinder, in process, 109 Axone, 109 Baillarger's stripe, 39, 115 Band of Giacomini, 34 Bandelette mediale (Gombault-Philippe), 166 Basal ganglia, 46 Basket cells, 154 Basis cerebri, 12 pedunculi, 67 Bechterew's nucleus, 181 Bipolar cells, 109 Brachia cerebelli, 76, 156 ad cerebrum, 76 ad corp. quadrig., 76 ad medullam, 76 ad pontem, 76, 155 conjunctiva, 70, 76, 156 corp. mamillar., 57 pontis, 76, 155 quadrigemina, 66 Brain development, 4 form, 9 membranes, 86 morphology, 3 size, 10 weight, 10 Brain-sand, 56 Brain-stem, 6 Brain-vesicles, 4 Broca's callosal stalks, 30 centre, 128 convolution, 20 diagonal band, 30 field, 27 Bulbus cornu post., 43 olfactorius, 27, 118 Burdach's column, 78, 164 Cajal's cells, in, 115 Calamus scriptorius, 81 Calcar avis, 43 Callosal convolutions, 36 radiations, 40 Calloso-marginal fissure, 23 Capsula externa, 48, 135 extrema, 50, 136 interna, 48, 61, 142 Cauda equina, 9 Cavum epidufale, 93 interdurale, 93 psalterii, 44 septi pellucidi, 41 subdurale, 93 281 282 INDEX. Central tegmental tract, 151 Centrifugal tracts, 131, 191 Centripetal tracts, 131, 186 Centrum medianum (Luys), 60, 228 semiovale (Vieussens), 39 Cerebellar cortex, 154 falx, 87 peduncles, inferior, 76, 170 middle, 76, 157 superior, 76, 156 tent, 76 tracts, 155 Cerebellum, 72, 152 Cerebral cortex, 39 crura, 66 ganglia, 46 mantle, 18 nerves, 172 nerves, table, 14 peduncles, 66 Cerebro-spinal fluid, 88 Cerebrum, II Chiasma opticum, 37, 174 Cingulum, 135, 149 Cisterna ambiens, 88 cerebello'-medullaris, 88 chiasmatis, 88 corporis callosi, 88 fossae Sylvii, 88 interpeduncularis, 88 Clarke's column, 90, 159 Claustrum, 50 Clava, 78 Climbing fibres, 155 Cochlearis, 179 Colliculus facialis, 82, 178 subpinealis, 66 Column-cells, 160 Columna fornicis, 44 Columnae griseae, 91 Comma bundle of Schultze, 166 Commissura anterior, 16, 135 alba, 91 grisea, 91 cerebri magna, 40 habenularum, 55 hippocampi, 44, 135, 146 posterior cerebri, 56 medullae, 90 supramamillaris, 225 Commissure-cells, 160 fibres, 135 Confluens sinuum, 88 Conus medullaris, 9, 89 terminalis, 89 Convolutions, see Gyri Cornu Ammonis, 45, 120 Cornua ventriculi lat, 40, 41, 42 Corona radiata, 135 Corpora candicantia, 56, 147 geniculata, 56 mamillaria, 56, 147 restiformia, 77, 170 Corpus album subrotund., 59 callosum, 14, 40 fornicis, 44 geniculatum, 56 Luys, 61 mamillare, 56, 147 medullare cerebelli, 75 parabigeminum, 271 patellare (Tschish), 60 pineale, 55 resti forme, 77, 170 striatum, 41, 48, 144 subthalamicum, 61, 224 trapezoides, 179 Cortical cells, 39 Cortico-bulbar tract, 138 Cortico-spinal tract, 138 Crura cerebelli, 76, 155 ad cerebrum, 76 ad corp. quadrig., 76 cerebelli ad medullam, 77 ad pontem, 76 fornicis, 44 Crus fornicis, 44 Culmen cerebelli, 73 Cuneus, 24 Cuticle-plate, 3 Declive cerebelli, 73 Decussation, cerebellar peduncles, 156 fillet, 167 Forel's, 274 Meynert's, 274 motor, 77, 138 pyramidal, 77, 138 ^ sensory, 167 Deiters' cells, in nucleus, 181 Dendrites, in Development, brain, 4 ependyma cells, 103 nerve-cells, 105 neuralgia, 104 spinal cord, 8 spinal ganglia, 105 Diagonal band of Broca, 30 Diaphragma sellae turcicae, 88 Diencephalon, 52, 150 summary, 63 Digitationes hippocampi, 43 Direct cerebellar tract, 161 Direct sensory cerebellar tract, 170 INDEX. 283 Dura mater cerebri, 87 spinalis, 93 Edinger-Westphal nucleus, 176 Embolus, 83 Eminentia collaterale, 43 medialis, 81 pyramidalis, 71 saccularis, 38 Encephalon, 3 End-brain, 4, 17, 134 Endogenous fibres, 160 End-plate, 37 Ependyma cells, 103 nuclear zone, 103 f Ependymium, 103 Epicerebral space, 88 Eyes, movements of, 184 Facialis, 178 Facial knee, 178 nucleus, 178 Falx cerebelli, 87 cerebri, 87 major, 87 minor, 87 Fascia dentata (Tarini), 32 Fasciculus ant. propr., 161 arcuatus, 135 (Foville), 71 cerebro-spinalis ant., 139 lateralis, 139 cuneatus, 77, 90, 164 fronto-occipitalis, 135, 207 gracilis, 77, 90, 164 lateral, propr., 162 lenticularis (Forel), 222 longitudinal, dorsal. (Schutz), 148, 151 inferior, 135 medialis, 148, 153, 182 superior, 135 praedorsalis, 153 mamillaris princeps, 147 mamillo-tegmentalis, 147 mamillo-thalamicus, 147 obliquus pontis, 71 pyramidalis, 82, 138 retroflexus (Meynert), 148 solitarius, 185 sulco-marginalis, 161 tegmento-mamillaris, 147 thalamicus, 224 thalamo-mamillaris, 147 uncinatus, 135 Vicq d'Azyr, 147 Fasciola cinerea, 33 Fastigium, 79 Fibra pontis, 71 Fibrae arci formes, 70, 155 arcuatae, 78, 167 ext. dor sales, 170, 247 ext. ventrales, 170, 247 internae, 167, 242 pontis profundae, 82 superficiales, 82 propriae, 134 terminates, 115 Fibrillar network, 112 Fila lateralia pontis, 71 olfactoria, 27, 118, 144 Fillet, lateral, 179 mesial, 167 Filum terminale, 9, 89 Fimbria, 33, 44 Fissura calcarina, 24 cerebri lat., 18 longitud., ii transversa, 12 chorioidea, 42 collateralis, 24 hippocampi, 24 longitudinalis cerebri, n mediana ant., 77, 89 parieto-occipital., 20, 24 prima (His), 26 rhinica, 24 Rolandi, 19 transversa cerebri, 12 Flechsig's association centre, 127 direct cerebellar tract, 161, 170 Feltwork, interradial, 115 supraradial, 115 Flocculus, 75 accessory, 75 peduncle of, 75 Folium vermis, 74 Foramen caecum, 77 diaphragmatis, 88 interventriculare, 8, 43 Luschkae, 80 Magendii, 80 Monroi, 8, 43 Forceps, 40 Fore-brain, derivatives, 65 Forel's tegmental decussation, 274 Formatio reticularis, 85 Fornix, 44, 137, 146 longus (Forel), 146 periphericus (Arnold), 135, 149 pillars of, 44 transversus, 44, 146 Fossa cerebri lateralis (Sylvii), 18 interpeduncularis (Tarini), 68 mediana, 81 rhomboidea, 81 Fountain decussation, 273 2 8 4 INDEX. Frenulum veli medullaris, 70 Frontal pontile tract, 137 lobe, 19 Funiculus anterior, 90, 161 lateralis, 90, 161 posterior, 90, 163 separans, 82 Fourth ventricle, 79 Ganglioblasts, 106 Ganglion-strand, 105 Ganglion ectomamillare, 68 habenulae, 61, 148 interpedunculare (Gudden), 69, 148 profund. mesencephali, 69 tegmenti dorsale, 69, 147 Gennari's stripe, 39 Germ-cells, 103 Giacomini's band, 34 Globus pallidus, 48 Glomeruli olfactorii, 118 Glomus chorioideum, 44 Glossopharyngeus, 184 Golgi-Holmgren canals, 113 Golgi's network, 112 cells, in Coil's column, 90, 164 Cowers' tract, 161, 170 Granule layer, cerebellum, 154 olf. bulb, 119 Gratiolet's optic radiation, 136, 172 Gubler's paralysis, 143 Gudden's tegmental bundle, 147 Gustatory centre, 126 paths, 190 Cyrus, or Gyri, ambiens, 27 Andreae Retzii, 36 angularis, 21 centralis ant., 19 post, 21 cerebelli, 76 cinguli, 30 dentatus, 32, 121, 122 descendens (Eckar), 21 diagonalis, 30 digitati externi, 35 epicallosus, 34 fasciolaris, 34, 35 fornicatus, 25, 30, 119 frontalis,. 20 fusiformis, 24 hippocampi, 32 insulae, 22 intralimbicus, 35 lingualis, 24 occipitales, 21 olfactorio-orbitalis, 29 Gyrus olfact. lateral., 27 medial., 27 orbitales, 25 perforatus, 29 profundi, 18 rectus, 25 rhinenceph.-fusiform., 32 rhinenceph.-lingual., 32 rhinenceph.-temporales, 32 semilunaris, 27 subcallosus (Zuckerkandl), 30 subsplenialis, 34 supramarginalis, 21 temporales, 21 transversi, 21 transitivi, 18 uncinatus, 35 Habenula, 55 Hearing, cortical centre, 126 Helweg's triangular tract, 162, 171 Hemianopsia, 174 Hemiopia, 174 Hemiplegia alternans oculomot, 143 facial., 143 completa, 142 cruciata, 144 incompleta, 142 Hemisphaerium, 17 Heschl's convolutions, 21 Hind-brain, 85 Hippocampus (cornu Ammonis), 45, 120 Hypoglossus, 185 Hypophysis, 38 Hypothalamus, 64 Incisura praeoccipitalis, 20 temporalis (Schwalbe), 24 Indirect sensory cerebellar tract, 171 Induseum griseum, 33, 123 inferius, 34 Infundibulum, 37 Insula, 22 Intermedius Wrisbergi, 178 Inter-brain, 52 Internal capsule, 48 Interolivary stratum, 117 Interradial feltwork, 115 Intumescentia cervicalis, 89 lumbalre, 89 Island of Reil, 22 Isthmus gyri fornicati, 30, 31 rhombencephali, 4, 70 Lamina affixa, 41 chorioidea ventric. lat, 41 ventric. quarti, 79 ventric. tertii, 57 INDEX. 285 Lamina medullaris circumvoluta, 121 praecommissuralis, 30 quadrigemina, 66 rostralis, 15 septi pellucidi, 41 terminalis, 15, 37 Laminae medullares cerebelli, 76 thalami, 60 Lancisi's striae, 33 Lateral column, 90, 161 ground bundle, 162 nuclei, 85, 170 pyramidal tract, 161 tracts, go, 161 ventricle, 40 Lattice layer of thalamus, 59, 227 Lemniscus lateralis, 179, 190 medialis, 167, 187 Leptomeninx, 86 Ligamentum denticulatum, 94 Limbic lobe, 25 Limbus Giacomini, 34 Limen insulae, 28 Lingula cerebelli, 73 Liquor cerebro-spinalis, 8 Lissauer's marginal zone, 163 Lobi cerebelli, 72, 73, 74 insulae, 22 Lobuli cerebelli, 72, 73 Lobulus paracentralis, 24 Lobus frontalis, 19 occipitalis, 21 olfactorius, 26 olfact. ant., 27 post., 29 parietalis, 20 temporalis. 21 Locus caeruleus, 82, 177 Luys' body, 60, 228 Lyra Davidis, 44, 135 Mammillary bodies, 61 Mantle layer, 105 Marginal zone, 91 Martinotti cells, 115 Massa intermedia, 55 Medial fillet, 149, 167, 187 Medulla oblongata, 77, 166 spinalis, 89, 159 Medullary groove, 3 plate, 3 ridge, 3 tube, 4 Membrana limitans, 102 Meninges, 86 Mesencephalon, 4, 66 summary, 69 Metathalamus, 63 Metencephalon, 4, 77 Meynert's fountain decussation, 153, 273 Mid-brain, 66 Middle commissure, 55 Mitral cells, 118 Molecular layer, 114, 121, 122, 154 Monakow's nucleus, 243 bundle, 153, 162 Monoplegia, 145 Monticulus cerebelli, 73 Moss fibres, 155 Motor tract, 131, 138, 151, 191 centre, 124 Multipolar cells, no Myelencephalon, 4, 77, 166 Nerve process, 108 cells, 106 Nervus abducens, 176 accessorius, 185 acusticus, 179 cochleae, 179 facialis, 178 glossopharyngeus, 184 hypoglossus, 186 intermedius (Wrisbergi), 178 oculomotorius, 175 . olfactorius, 172 opticus, 172 Sapolini, 178 trigeminus, 176 trochlearis, 176 vagus, 184 vestibuli, 181 Wrisbergi, 178 Neural or medullary tube, 102 Neurite, 109 Neuroblasts, 103 Neurofibrillae, 112 Neuroglia, 103 Neuroglia cells, 103, 106 Neurone, 109 Nidus avis, 75 Nissl's bodies, 112 Nodulus, 75 Nucleus alae cinereae, 85, 185 ambiguus, 85, 184 amygdalae, 50, 145, 219 arcuati, 84, 170 caudatus, 47, 144 corpor. geniculati, 61 mamillaris, 61, 147 trapezoides, 83, 179 dentatus cerebelli, 83 dorsalis (Clarkii), 91, 157 emboliformis, 83 eminentiae teretis, 263 fastigii, 83 286 INDEX. Nucl. funiculi cuneati, 84, 167 gracilis, 84, 167 globosi, 84 habenulae, 61, 148 hypothalamicus, 61 intercalatus Staderini, 251 laterales, 84, 170 lemnisci, 70, 82, 179 lenticularis, 48 lentiformis, 48, 144 nervorum, see Cerebral Nerves, 172 olivaris accessor., 84 inferior, 84, 170 superior, 179 pontis, 82 praepositus XII, 255 respiratorius, 196 reticularis lateralis, 243 tegmenti, 83, 155 Roller, 251 ruber, 69, 137, ISS, 227 salivatorius, 257 semilunaris (Flechsig), 60, 227 tecti, 83 thalami, 58, 59 Obex, 78 Occipital lobe, 21 Oculomotorius, 175 Olfactory bulb, 27, 118 bundle, basal, 149 centre, 126, 149 nerve, 118, 172 path, 190 tract, 27, 145 tubercle, 27 Oliva inferior, 84, 170 superior, 83, 179 Operculum, 22 Optic radiation, 172 tract, 172 Optico-acoustic reflex tract, 153 Opticus, 172 Oval bundle, 166 Pacchionian granulations, 88 Pachymeninx, 86 Pallium, 18 Paraplegia, 143 Parietal lobe, 20 Pars mamillaris hypothalami, 56 optica hypothalami, 37 Pedunculi cerebri, 66 Pedunculus corpor. mamillaris, 147 flocculi, 75 Penicilli olfactorii, 118 Pia mater cerebri, 88 spinalis, 93 Pineal body, 55 Pituitary body, 38 Plexus chorioideus ventric. lat, 42 ventric. quarti, 8u ventric. tertii, 58 Pons Varolii, 71 Pontile nuclei, 82 tegmentum, 83 tracts, 137 Posterior column, 163 comma bundle, 166 nuclei, 167 oval bundle, 166 triangular bundle, 166 ventral field, 166 Posterior horn cells, 159 Post, longitudinal bundle, 148, 153, 182 of Schiitz, 148, 153, 182 Praecuneus, 24 Projection fibres, 131, 135, 186 Prosencephalon, 4 Protoplasmic processes, 109 Psalterium, 44 Pulvinar, 55 Pupillary reflex, 173 Purkinje cells, 154 Putamen, 48 Pyramidal nuclei, 170 tracts, 137, 161, 191 Pyramids, decussation, 77 Pyramis cerebelli, 74 Quadrate lobule, 24 Radiatio corpor. callosi, 40 striati, 144 strio-subthalamica, 144 strio-thalamica, 144 Radicular zone of cord, 163 Radii, cortical fibres, 116 Randschleier, 105 Recessus anterior, 68 infundibuli, 38 lateral, ventric. quarti, 79 opticus, 17 pinealis, 55 posterior, 68 suprapinealis, 56 tecti, 79 triangularis, 58 Reflex collaterals, 131, 166, 192 Reflex conduction, 131, 191 Regio subthalamica, 61 Restiform body, 158, 170 Rhinencephalon, 25, 144 Rhombencephalon, 4, 70 Roof-nucleus, 83 Rostrum, 15 Rugae loci caerulei, 82 INDEX. 287 Saccus vasculosus, 38 Sapolini's nerve, 178 Schultze's comma bundle, 166 Schutz's longitudinal bundle, 148, 153 Sensory centres, 126 cerebellar tracts, 170 speech centre, 199 tracts, 186 Septum anterius, 93 cervicale intermed., 93 pellucidum, 16, 41 subarachnoideale, 93 Sinus occipitalis, 87 petros. sup., 87 rectus, 88 sagittal., 87 transversus, 87 Smell, cortical centre, 126 Speech centres, 199 disturbance, 202 path, 200 Spinal cord, 159 cells, 160 development, 8 membranes, 93 tracts, 161 Spongioblasts, 103 Spongiopilemma, 106 Stratum gelatinosum, 118 granulosum, 115, 119, 122, 154 griseum centrale, 68, 225 colliculi sup., 69 lacunosum, 121 lucidum, 121 moleculare, 114, 118, 121, 122, 154 oriens, 121 radiatum, 121 reticulare, 60, 227 zonale, 54 Stria alba tuberis (Lenhossek), 57, 146 cornea, 41 medullaris, 54, 148 olfactoria lat, 29, 145 med., 27, 145 terminalis, 41 Striae acusticae, 81, 179 Lancisii, 33, 40, 145 longitudinales (corp. callosi), 40 medullares or acusticae, 81, 179 Stripe of Baillarger, 39 sennari, 39 Vicq d'Azyr, 39 Subarachnoidal space, 86, 88 tissue, 88 Subdural space, 86 Subiculum, 45 Subpial space, 88 Substantia cortical, cerebelli, 83, 154 cerebri, 38, 114 gelatinosa centralis, 91 Rolandi, 91 nigra (Sommering), 67 perforata ant., 29, 145 post., 68 reticularis alba, 247 (Arnold), 32, 121 grisea, 241, 247 Sulcus or sulci arcuat. rhinencephali, basilaris (pontis), 71 centralis insulae, 22 Rolandi, 19 cerebelli, 72, 73, 74, 75 chorioideus, 54 cinguli, 23 circularis (Reili), 22 corpor. callosi, 23 dentato-fasciolaris, 34 digitati externi, 35 fimbrio-dentat., 33 frontales, 19 hypothalamicus (Monroi), 16, 55 interdigitales, 43 intermedius, 41 post., 90 primus (Jensen), 21 secundus (Eberstaller), 21 interparietalis, 20 lateralis ant., 89 post., 89 limitans, 82 median, fornicis, 44 fossae rhomboid., 81 post., 89 mesencephali lat, 68 med., 68 Monroi, 16, 55 nervi oculomotorii, 67 occipitales, 21 occipitalis transvers., 20, 21 olfactorius, 25 orbitales, 25 paracentralis, 23 parietal, transvers. (Brissaud), 21 parolfact. ant, 27 post., 26 postcentralis, 20 praecentralis, 19 radiatus, 19 semiannularis, 28 subcallos. med., 30 subparietal., 23 supraorbital. (Broca), 23 temporales, 21 Supraradial feltwork, 116 Sylvian aqueduct, 68 288 INDEX. Sylvian fissure, 18 fossa, 18 valley, 18 System of Belters' nucleus, 181 Taenia chorioidea, 42 fimbriae, 44 fornicis, 42 pontis, 71 semicircularis, 146, 214 tecta, 33. 4O thalami, 58 ventriculi quarti, 80 Taeniae, 42 Tapetutn, 43 Taste, cortical centre, 126 paths, 189 Tegmen fossae rhomboid., 79 Tegmental decussation, 153, 273 tract, central, 151 Tegmentum, 67 pontis, 83 ' Tela chorioidea ventric. quarti, 79 ventric. tertii, 52, 57 Telencephalon, 17, 134 internal configuration, 38 Telodendrion, 109 Temporal lobe, 21 Tentorium cerebelli, 87 Thalamencephalon, 54 Thalamus, 54, 58 Third ventricle, 57 Tigroid, 112 Tonsilla, 75 Torcular Herophili, 88 Tracts, projection, 186 Tract, bulbo-thalamicus, 151, 167 cerebello-bulbaris, 170 cerebello-tegmentalis, 150, 156 cerebro-spinalis, 138, 161 cervico-lumbalis dorsal., 166 corticis ad pontem, 137 cortico-habenularis, 146, 148 cortico-mamillaris, 146 cortico-tectales, 153 cortico-tegmentalis, 136 cortico-thalamici, 150 fastigio-bulbaris, 171, 259 habenulo-peduncularis, 148 mamillo-tegmentalis, 147 mamillo-thalamicus, 147 nucleo-cerebellaris, 170, 181 olfacto'-ammonicus, 215 olfacto-habenularis, 148 olfacto-mesencephalic., 149 olfactorius, 27, 145 olivo-cerebellaris, 170 Tract, opticus, 13, 172 peduncularis transvers., 68 ponto-cerebellares, 137, 155 rubro-reticularis, 153 rubro-spinalis (Monakow), 153, 162 rubro-thalamicus, 151 solitarius, 185 spinalis N. V., 178 spino-cerebellaris dorsal. (Flechsig), 161, 170 ventral. (Cowers), 70, 161, 170 spino-olivaris (Helweg), 162, 170 spino-tectalis, 153, 163 spino-thalamicus, 151, 163, 169, 186 tecto-bulbaris, 153 tecto-cerebellares, 153 tecto-pontinus (Miinzer), 153, 269 tecto-reticularis (Pavlow), 153 tecto-spinalis, 153, 161, 163 tegmento-mamillaris, 147 thalamo-corticales, 135, 150 thalamo-habenularis, 148 thalamo-mamillaris, 147 thalamo-olivaris, 151, 171 thalamo-spinalis, 151, 163 uncinatus, 171, 259 vestibulo-spinalis, 161, 163, 181 Trigeminus, 176 Trigonum collaterale, 43 habenulae, 55 lemnisci, 70 nervi hypoglossi, 82 olfactorium, 27 praecommissurale, 30 subpineale, 66 Trochlearis, 176 Truncus cerebri, 8 Tuber cinereum, 37 valvulae, 74 vermis, 74 Tuberculum acusticum, 82, 179 cinereum, 79 cuneatum, 79 mamillare laterale, 57 olfactorium, 27 thalami ant., 59 Uncus, 35 Unipolar cells, no Uvula, 75 Vagus, 184 Vallecula cerebelli, 72 lateralis, 18 Velum interpositum, 57 Velum medullare ant., 70 post., 75 terminale (Abbey), 34, 44 INDEX. 289 Vena cerebri interna, 58 magna (Galeni), 58 chorioidea, 58 septi pellucidi, 58 terminalis, 58 Ventral field of cord, 166 Ventriculus Arantii, 81 lateralis, 40 quartus, 79 terminalis (Krause), 91 tertius, 57 Verga's ventricle, 44 Vermis cerebelli, 72 Verrucae gyri hippocampi, 32 Vestibularis, 181 Vicq d'Azyr's stripe, 40 bundle, 147 Vinculum lingulae, 73 Visual centre, 127 path, 191 Visuo-auditory path, 196 Weber's paralysis, 143 Wernekink's commissure, 271 Wernicke's centre, 129 field, 60, 229 pupillary reaction, 174 Wrisberg's nerve, 178 Writing centres, 202 Zona incerta, 224, 225 SAN DIEGO MEDICAL LIBRARY D 000 781 608 5 \ SAN