c. LIBRARY THE ANATOMY OF THE CENTRAL NERVOUS ORGANS 3n Ibcaltb anb in E)i6ca0C. /^ DR HEINRICH OBEKSTEINEE, Professor (ext.) at the University of Vienna. TRANSLATED, WITH ANNOTATIONS AND ADDITIONS, BT ALEX HILL, M.A., M.D., M.R.C.S., MASTER OF DOWNING COLLEGE, CAMBRIDGE ; EXAMINER IN ANATOMY TO THE UNIVERSITIES OF CAMBRIDGE AND GLASGOW. Mltb lOS JUusttations* LONDON: CHARLES GRIFFIN & COMPANY, EXETER STREET, STRAND. 1890. [All Rights Reserved.] 46"/ Mo Digitized by the Internet Archive in 2010 with funding from Open Knowledge Commons (for the Medical Heritage Library project) http://www.archive.org/details/anatomyofcentralOOober IIHFACE TO THE ENGLISH EDITION. No apology is necessary for placing before the English student of neurology Professor Obersteiner's exact and impartial account of the anatomy of the central nervous system. The labour of selecting from the mass of literature, with which the subject is every year enriched, the facts of greatest importance, and the theories which harmonise most with one another, must have been immense. It would only be right that the students of all countries should be allowed to participate in the result. In giving an English dress to Professor Obersteiner's text, we have attempted to transpose its forms of expression into the Enorlish mode. The translator has always held that to transform a book from one language into another needs the collaboration of members of both nationalities, and he wishes to express his indebtedness to Fraiilein Kloss for having read through the whole of the German text with him. He has also been in constant communication with Professor Obersteiner, who has not only explained obscure passages, but has also added much new matter and made numerous alterations, which <-dve to the Enoflish version the value of a new edition. All additions to the text made by the translator are included in square brackets [ ]. He is also responsible for all footnotes, for the introduction of figs. 2, 3, 4, 5, oa, 6, 8, 19a, 34, 57, 149, 150, 151, 15G, 157, 192, 193, 194, 195, 196, 197, 198, and for the Appendix. In going through Professor Obersteiner's work, care has been taken to check the references in the text, and in the footnotes to the figures, where they have been re-arranged alphabetically. Some trouble has also been spent upon the Index, into which the terms used in the German edition have b VI PREFACE TO THE ENGLISH EDITION. been introduced, in order that the reader, who is acquainted with such terms in their German dress — and some of them have not hitherto made their appearance in English — may have the opportunity of looking up the structures which they desig- nate in this text-book. When doing this it seemed worth while to give the commoner synonyms and French equivalents. Not that the glossary has any pretentions to lexicographical com- pleteness — it is merely the translator's working vocabulary. No attempt has been made to keep step with the German edition in typography. Capital letters are used to call attention to the sections, while Italics are restricted to the names of observers quoted as authorities ; personal names which are used as the appellations of structures or methods are printed in ordinary type. The spelling of the word "neurogleia" will probably attract the attention of the reader. Neurogloea would undoubtedly be more correct, but would affect the pronunciation. In German the spelling "neuroglia" is perhaps unexceptionable, but it makes a terrible word when pronounced in the English fashion. Not only the spelling of the term but also its application is, however, open to discussion. It appears to the translator to be a useful term when applied to the connective-tissue of the central nervous system, which differs from other forms of connective- tissue in its origin from epiblast; whereas, when restricted to the "matrix" it gives an undesirable definiteness to what is, after all, a hypothetical substance. Downing College Lodge, March, 1890. rPiEFACE TO TIIM (WAIMX^ EDITIOX. Some decades ago our knowledge of the intimate structure of the central nervous system was still very insufficient — so insufficient, indeed, that pathology was able to make little use of it. Hence we can understand how, of the little that was known, the practi- tioners of the time, with very few exceptions, made use of the most striking facts only, and had to be content with an extreme poverty of data. Since then, however, a succession of distinguished observers, supported by the improvements made in method, have, with surprising rapidity, successively thrown more light into the chaos of manifold nerve-paths and their nodal points ; and there- fore it had to be acknowledged in practical medicine that the brain- and spinal cord-anatomy (until now so contemptuously set aside) — despite their difficulty — are worthy of the most exhaustive consideration. Nay more, regions which seem to stand far enough away from nerve-pathology — ophthalmology, osteology, and even dermatology — have come to feel the need of a fundamental orientation of the central nervous organs. To meet this want we possess now, especially in German, a number of most excellent anatomical text-books. But as no part of anatomy (least of all, perhaps, the anatomy of the nervous system) can be learnt from books, students and physicians seek' out the laboratories where opportunity is offered them of making themselves familiar with the structure of the brain and spinal cord. Certainly, the establishment of ideally-equipped labora- tories for the study of brain anatomy, such as His wanted at the meeting of the Berlin Association of Naturalists of 1SS6^ Vlll PREFACE TO THE GERMAN EDITION. will long remain pium desiderium. At present, teachers and students must be content with the incomplete commencements of such institutions as already exist in some of the larger universities. Experience has now taught me what are the justifiable claims which a beginner, who does not yet wish to become a specialist in the subject, may make upon a text-book. Especially must I assert that while, on the one hand, it is superfluous to go into incompletely established details (a course which is likel}", indeed, to produce a depressing and confusing effect), yet, on the other hand, some information with regard to pathological processes should most certainly be given. In the following pages I have tried to provide the student with a trustworthy and reliable guide, with which, in the absence of any other teacher, he may undertake the troublesome journey through the several regions of the central nervous system. Hence, I have continually introduced directions for making preparations : the numerous illustrations, although they are true to nature (with the exception of those which are purely diagram- matic), are only meant to facilitate the study of original prepara- tions — not to replace them. Any one who has the opportunity of visiting a laboratory with a good collection of ready-made preparations can with advantage use these, and so save himself much expenditure of time and patience in making a set of sections for himself When, however, circumstances allow, working with the knife not only gives the dexterity necessary for undertaking independent investigations, but anatomical relations imprint themselves much more firmly upon the memory when one makes the sections for oneself, and, in especial, one obtains a clearer view of the situation of the sevei'al elements relatively to one another. Good drawings and cleverly executed models facilitate the comprehension of difficult anatomical relations. With regard to models, however, it must be said that as yet we do not possess PREFACE TO THE GERMAN EDITION. IX any that are completely satisfactory. Of the very artistic, but also very expensive, model of Aeby, Ills says, most truly, that although when wc have it before us it seems very clear and transparent, it does not stand the test so soon as the eyes are removed from it. The work under discussion, therefore, differs in many respects from existing text-books of brain-anatomy. First, as to the manner in which the material is presented, the strictly didactic standpoint is maintained ; whether the student makes preparations for himself or not, he can follow the route prescribed for him in the book. The more detailed histological relations are treated separately. The attempt has been made, while not overlooking any of the more important facts concern- ing the central nervous system, to avoid such minute details as should be left for special research. The introduction of pathologico-anatomical observations, espe- cially of the pathological changes in the elements, will prepare the road for the comprehension of the processes of disease in the central nervous system without its being in the least intended to work out an exhaustive pathological anatomy of these organs. That a special value has been attributed to numerous and good illustnitions has been already mentioned. In the choice of illustrations, which have been throughout executed in the xylographic establishment of V. Eder of Vienna in the most satisfactory way from original drawings, it is to be understood that a certain restraint had to be imposed to prevent the price of the book from becoming excessive. On this account, especially for drawings 118 to 136, the question had to be discussed whether the preparations chosen should be stained with carmine or accord- ing to AVeigert's method. When I chose the former, I did so on the ground that I wished the illustrations to be true reproductions of the original preparations. Successful Weigert's-preparations from the adult are hardly to be made sufficiently instructive with low magnification ; whereas preparations from the embryo were X PREFACE TO THE GERMAN EDITION. to be avoided on account of the difficulty which the student would find in getting the material. I suppose I need not point out that the presentation of the material rests throughout upon autoptic observations ; when facts are stated on the ground of the observations of other authors, this is in every case noted. The usefulness of this book is further increased by the addition of an index. HEINRICH OBERSTEINER. ViENXA, October, 1887. CONTENTS. Introdcctiok, . Methods of Examinatiox, Deli be ring, Sectionsories, Celloidin, . Staining of nuclei, „ of medullary sheath by Weiytrrs and other methods, ,, of the axis-cylinder, Impregnation by GoUjVs and other methods, Embryological methods, . Study of degenerations, . Comparative method, Physiological method, Morphology of the Central Xervocs System, Histogeny, , . . . Morphogeny, .... Gross anatomy of the spinal cord, ,, medulla oblongata, ,, ,, cerebellum, ,, its medullary centres Floor of the fourth ventricle Koof ,, ,, ,, ,, mid-brain, ,, ,, 'tween-brain, Optic thalamus. Floor of the third ventricle, ,, ,, cerebrum. Nucleus caudatus, Nucleus lenticularis, Nucleus amygdaleus, White matter. Corpus callosum, Fornix, Anterior commissure, Base of the fore-brain, Ventricles, Margin of the cortex, Surface of the hemispheres, Lobation , , Mesial surface ,, Anomalies of convolution. Physiological meaning of the convolutions, I'AOK 1 4 4 8 U 12 16 16 IS 10 24 24 26 28 34 38 42 47 55 55 59 60 63 63 64 65 65 67 68 68 70 73 74 75 77 81 84 89 98 102 104 Xll CONTENTS. Histological Elements of the Nervous System, Nervous elements — Nerve-fibres, ,, pathological changes, Nerve-cells, .... ,, pathological changes, . Non-nervous elements — Blood-vessels, ,, pathological changes, . Epithelium, .... Connective-tissue, ,, pathological changes, Neurogleia, .... Fat-granule-cells, amyloid bodies, &c., Arrangement of Elements in the Nervous System, Schemes of the nervous system — Luijs, Meynert, Hill, . Aeby, Fleclisig, Topography of the Spinal Cord, Cross-section of its several areas Minute anatomy, Course of fibres, . Blood-vessels, Pathological anatomy. Topography of the Brain, . Examination by cross-section. Medulla, Pons, . Mid-brain, 'Tween-brain and fore-brain Course and Connections of Nerve-Fibres, Tracts of the spinal cord. Decussation of the pyramidal tracts. Constituents of the crusta, . ,, ,, internal capsule, Fillet, .... Cerebellar connections, Gowers' tract, Cranial nerves, .... Olfactory, .... Anterior commissure, . Cortical centres of olfaction, PAGE 107 107 118 121 131 135 140 148 149 152 153 155 158 168 168 169 169 169 170 177 178 187 200 203 209 210 212 225 235 244 249 249 250 253 254 257 260 263 265 265 274 275 CONTENTS. xiri tXHK Optic nerve, ........ STl* The chiasm, 2:9 Corticiil centres of vision, 2S4 Posterior commissure, . 2SS Corpora quadrigemina, 2S4 Oculomotor, .... 2S7 Trochlear, .... 290 Abducent, .... 292 Trigeminal, ..... 293 Cortical connections, 2'J<; Facial, .... 297 Auditor)', .... 29» Corpus trapezoides, 3(X> Superior olive, . 3Wi Cortical connections. 3(/7 Glossopharj'ngeal, .... 30S Serial homology of cranial nerves, . 309 Vagus, .... 312 Spinal accessory, . 312 Hypoglossal, . 314 Connections of the cerebellum, . 315 Central nuclei. 315^ Medullar)- substance, . 317 Connections with other parts, 321 Cortex cerebelli. 323 Blood-vessels, . 333 Pathological anatomy, 333 Connections of the cerebrum. 3.35 Ganglia at the base. 336 Optic thalamus. - 336 Nuclei caudatus et lenticularis. . 340 Corpus subthalamicum. . 343 Substantia nigra. . .344 MeduUary substance, . 344 Corona radiata, . 344 Fornix, .... . 345 Corpus mammillare. 345 Corpus caUosum, . 347 Anterior conrniissure, . . 34S Intrahemispheral fibres, . 348 Cortex cerebri. . 350 Local peculiarities of structure. . 360 Comu Ammonis, . . 362 Conarium, .... . 369 Hypophysis, . 370 Blood-vessels of the great brain, . 371 Pathological anatomy. . 37i XIV CONTENTS. Meninges, Dura mater, Pathological changes Araclinoifl, Pathological changes Pia mater, Pathological changes TelEe choroidese, . The Great Vessels of the Brain, Their diseases, Appendix : Rotation of the Gp.eat Brain, Olossarial Index, . . • • PAGE 377 378 381 383 385 386 387 387 388 393 395 405 LIST OF ILLUSTRATIONS. 1. Scheme illustrating the nutrition of a ner\-e-fibre (after Sckwalhe), 2, 3. Transverse sections, showing the formation of the sensory root-ganglia (after Beard), ...••••• 4. The epiblast involuted to form the central nervous system wiiilc still single layer (after //'>>•), ...••• 5. A group of spongioblasts (after //w), . . . • 5rt. More advanced stage, showing neuroblasts with axis-cylinder processes 6. Transverse section of the spinal cord of a trout-embryo (after His), 7. The cerebx'al vesicles, ....•• 8. Diagram showing the connection of the nucleus caudatus with the cortex cerebri (after Wernicke), , 9. Caudal end of spinal cord from ventral surface, . 10. Cervical enlargement of the spinal cord from the dorsal side, 11. The base of the brain as far as the optic tracts (dorsal view), 12. Same as fig. 11, viewed laterally, . . . . • 13. llind-brain, mid-brain, and 'tween-brain, from the dorsal surface, 14. Cerebellum, dorsal view, . . . • • • 15. Cerebellum, from the ventral side, .... IC. Sagittal section through the brain in the median lino (right half), 17. Frontal section through the medulla oblongata and cerebellum of an ape 18. Hind-brain, mid-brain, and 'tween-brain, from the dorsal side, . 19. Transverse section through the anterior corpora quadrigemina, . 19«. Diagram to show the cortical relations of the nucleus caudatus (after Wernicke), ...•••• Section through the 'tween-l)rain and the neighbouring part of the fore brain, half a centimeter beneath the upper surface of the optic thalamus and nucleus caudatus, ...••• Horizontal section of same, one centimeter deeper than in fig. 20, 22. Frontal section through the human cerebral hemisphere, 23. Sagittal section through the brain in the median line, . 24. Part of a median section through the great brain, 25. Left hemisphere of the brain in front of the optic chiasm, 26. Diagram of the cerebral ventricles and the plexus choroideus, . 27. Frontal section through the right cerebral hemisphere, behuul th sjilenium corporis callosi, . . . • • 28. Frontal section through tlie right hemisphere behind the uncus, 29. Portion of a median section of the cerebrum, 30. Left hemisphere from the side, .... 31. Left hemisphere of a human embryo at the fifth month, . 32. Left hemisphere from above, .... 33. Left hemisphere, mesial surface, .... 34. Diagram showing the lobation of the cerebrum, . 20. 21. PACE 19 28 29 30 30 31 35 38 39 39 40 42 44,45 47 48 50,51 54 56, 57 62 €6 67 69 71 72, 73 75 76 77 80 82 83 86 87 88 90 91 XVI LIST OF ILLUSTRATIONS. FIG. 35. Left hemisphere from the base, ..... 36. Left hemisphere, mesial surface, ..... 37. Cross-section of a small portion of the anterior columns of the spinal cord 38. Medullated peripheral fibre, ..... 39. Peripheral nerve-tibres of the frog, .... 40. Axis-cylinder of a fibre from the white substance of the spinal cord, 41. A fresh medullated nerve-fibre from the sciatic of the frog, 42. Nerve-fibre from the sciatic of the frog, .... 43. A short piece of a thin peripheral nerve, showing nodes of Ranvier, 44. An isolated medullated fibre, ..... 45. Remak's fibres from the sympathetic of the neck of a rabbit, 46. Central medullated nerve-fibre from the brain, . 47. Very fine varicose axis-cylinders from the bulbus olfactorius of the dog, 48. Peripheral nerve-fibre from a new-born puppy, partially surrounded with myelin, ........ 49. Two fibres from the anterior roots springing from a softened spinal cord, 50. Several forms of hypertrophic varicosity of axis-cylinder from softened foci in the spinal cord, ...... 5L A cell from the anterior horn of the spinal cord of the pike, 52. A cell from the anterior horn of the human spinal coid, . 53. A pigmented cell from the substiuitia ferruginea (human brain), 54. Two shrunken cells from a human spinal ganglion, 55. Pyramidal cell from the cortex of human cerebrum, 56. Granules from the cortex of the cerebellum, 57. Diagram designed to show the homology of the granules of the olfactory bulb and retina and the cells of the spinal ganglia, 58. Simple atrophy of a nerve-cell from the oculomotor nucleus (human), 59. Commencing atrophy of a cell from the anterior horn of the spinal cord Degeneration of the nucleus ..... 60. Fatty-pigmentary degeneration of a pyramidal cell of the cortex cerebri 61. Granular deterioration of a cell of the anterior horn in myelitis, 62. Cell of anterior horn with ten vacuoles in myelitis, 63. Colloid degeneration of a cell of the anterior horn in myelitis, . 64. Calcified nerve-cells from the cortex cerebri beneath an apo}ilexy, 65. A cortical cell divided into a number of pieces, . 66. A middle-sized artery of the brain so torn as to expose each of its coats 67. A small artery from the brain, with clumps of pigment, . 68. A small vein from the brain-substance, .... 69. An artery from the cortex cerebri, .... 70. Section from the cornu Ammonis, showing perivascular and pericellula lymph spaces, ....... 71. Isolated capillaries from the cerebral cortex, 72. Cells with hrematoidiu-crystals from the walls of an old apoplectic clot, 73. A moderate-sized artery from the corpora striata, with numerous pig ment cells, ....... 74. Capillary vessel from a case of melanasmia, 75. Fatty degeneration of the muscular coat of a cerebral artery, 76. Calcification of the muscular coat of a vessel of the brain, 77. Calcification of an artery of the brain affecting the adventitia as well as its other coats, .....••• FACE 94 100 108 109 110 110 110 113 113 113 115 115 115 117 119 120 122 122 122 124 124 127 128 131 131 131 1.32 132 132 134 134 136 136 136 1.38 1.38 139 141 141 141 142 142 142 LIST Ol' ILLUSTRATIONS. xvii FW- I-A 92. 93. Scheme of a simple primitive nervous system, . . . 102 94. Scheme of a commissure and of a decussation, . . . .163 95. Diagram of motor nerve-roots, . . . . . .104 96. Diagram of sensory nerve-roots, . . . . . . I(i4 97. Transverse section through the human spinal cord : at the level of the third cervical nerves, . . . . . . .172 98. Transverse section through the human spinal cord : at the level of the sixth cervical nerves, . . . . . . .172 99. Transverse section through the human spinal cord : at the level of the third dorsal nerves, ....... 172 100. Transverse section through the human spinal cord : at the level of the twelfth dorsal nerves, . . . . . . .173 101. Transverse section through the human spinal cord : at the level of the fifth lumbar nerves, . . . . . . .173 102. Transverse section through the human spinal cord: at the level of the third sacral nerves, ....... 173 103. Transverse section through the human spinal cord : through the in- ferior part of the conus meduUaris at the origin of the nervus coccygeus, . . . . . . . .173 104. Cross-section of the anterior column of the spinal cord, . .178 105. Jimction of the anterior root-bundle with the anterior horn, lumbar region, . . . . . . . . .LSI 106. A nerve-cell from the anterior horn of the human spinal cord, . . 181 107. A nerve-cell from Clarke's column as seen in longitudinal section, . 185 108. Diagram showing the course of fibres in the spinal cord, . .188 109. Diagram showing the subdivisions of the white columns of the cord, . 194 110. Descending degeneration of the spinal cord after a one-sided lesion of the brain, ........ 197 111. Ascending degeneration in the cervical swelling, . . . 197 112. Semidiagrammatic representation of the arteries in the interior of the spinal cord, ........ 202 113. So-called combined systemic disease of the spinal cord, . . 2(i5 114. Chronic transverse diffuse myelitis, ..... 206 XVlll LIST OF ILLUSTRATIONS. FIG. 115. Syringo-myelia, ..... 116. Disseminated sclerosis in the cervical cord, 117. Figure to show the level of the dorsal portions of the cross-sections represented in figs. 118-130, 132-136, . 118. Section of. the medulla oblongata (at a, fig. 117), 119. Section of the medulla oblongata (at b, fig. 117), 120. Section of the medulla oblongata (at c, fig. 117), 121. Section of the medulla oblongata (at (/, fig. 117), 122. Cross-section of the medulla oblongata (at e, fig. 117), 123. Cross-section of the medulla oblongata (at/, fig. 117), 124. Transverse section of the medulla oblongata (at (/, fig. 117), 125. Transverse section of the after-brain (at h, fig. 117), 126. Cross-section of the after-brain (at i, fig. 117), . 127. Transverse section of the after-brain (at k, fig. 117), 128. Transverse section of the after-brain (at I, fig. 117), 129. Transverse section of the after-brain (at m, fig. 117), 130. Transverse section of the after-brain (at n, fig. 117), 131. Frontal section through the cerebellum and medulla oblongata of monkey, ...... 132. Transverse section of the mid-brain (at o, fig. 117), 1.33. Transverse section of the mid brain (at }y, fig. 117), 134. Transverse section of the mid-brain (at q, fig. 117), 135. Transverse section of the mid-brain (at r, fig. 117), 136. Transverse section of the mid-brain (at s, fig. 117). 137. Frontal section through brain of monkey, 138. Frontal section through brain of monkey, passing through the middle of the optic thalamus, .... 139. Frontal section through monkey's brain at level of front of thalamus, 140. Scheme of pyramidal tracts, 141. Diagram showing the constitution of the crus cerebri 142. Horizontal section through the internal capsule. Plan of the central connections of the posterior columns Left hemisphere in front of the optic chiasm (base). Sagittal section of the bulbus olfactorius of the dog, Portion of the same, .... Transverse section of the human olfactory tract. Scheme of the central apparatus of smell. Outline of the brain of a dog. Outline of the brain of a cat. Outline of the brain of an otter, . Scheme of the central apparatus of vision. Scheme of the central origin of the trigeminal nerve. Schematic projection of the medulla oblongata, . Scheme of the central auditory apparatus, 157. Diagrammatic sections of the spinal cord and medulla showing the relative positions of the roots of a spinal and segmental cranial nerve, ........ Diagram showing the disposition of the nervus accessorius "Willisii cross-section, ....... 159. Same, in longitudinal section, ...... 143. 144. 145. 146. 147. 148. 149. 150. 151. 152. 153. 154. 155. 156, 158. PACK 206 206 210 212 213 214 215 217 218 22a 222 224 227 229 23a 232 234 235 236 239 240 243 244 246 247 250 253 254 259 267 268 268 273 274 278 278 278 289 294 297 301 311 313 313 LIST OF ILLUSTRATIONS. XIX no. IGO. Sa.fijittal section through the cerebellum some millimeters to one side of the nii 38J> 396 398 400 402 402 402 40J INTRODUCTION. An investigation of the complicated characters wliich distinguisli the line structure of the brain and spinal cord is impossible witliout a previous acquaintance with the more obvious features of their external configuration. Details of fine structure are often difficult to grasp, and their comprehension is facilitated by filling them into a mental outline of the organ to which they belong. Therefore, as soon as the first section (devoted to methods of study most in vogue) is disposed of, we shall give an account of the more obvious microscopical features of the cerebro-spinal axis, especially its external mouldings, and of such details presented by cross-sections through the brain at various levels as can be recognised without further preparation (SGCOnd section — morphology). Before commencing the microscopical investigation of the central nervous system by means of transparent sections, acquaintance must be made with the characters of the histological elements of which it is made up. In the third section an account is given of the more important nervous and non-nervous constituents of the system in health, and also of the changes to which they are subject in disease. Next, the spinal cord is described as being relatively the simplest part of the central nervous organs (fourth section). After this, we suppose (fifth section) that a number of cross- sections, not constituting an unbroken series, but useful for micro- scopical investigation, are made through the spinal cord and brain. During the preparation of such sections and their necessary examina- tion with an ordinary magnify in g-glass, one becomes acquainted with many facts concerning their organisation, especially as one can trace from section to section the changes in topographical distribution which their constituents undergo. The same routine must be followed by any one who investigates a series of sections which he has not cut for himself. He ought first to make a general survey of his prepara- tions with a magnifying-glass, and try to obtain a stereoscopic picture of their more important features. This done, we shall attempt, on the ground work of knowledge thus obtained, to follow individual bundles, trace their divisions and con- 2 INTKODUCTION. nections, and determine their end-points. This is the object of the sixth section, which treats fii'st of the fibre-routes in the spinal cord, and then of the cranial nerves. Their finer relations are rendered intelligible by a study of the structure of the cerebellum and cerebrum. The concluding section (the seventh) is devoted to the cavities of the central nervous system, which stand in such close anatomical and physiological relation to the brain and cord as to deserve a special description. SECTION I.— METHODS. TiiK anatomical study of the central nervous system is fraught with difiieulties such as are never met with in investigating other organs. The account of the structure of the brain and spinal cord about to be given, which goes somewhat further than the mere outlines of the subject, is based upon the most recent results of research in this field. The causes of the diflSculty are not far to seek. It might be anticipated that the structure of the organ to which the most various and complicated, and at the same time highest and noblest, functions are allotted, would obviously correspond in complexity to its work. It is also to be understood that this organ of relatively small size but complicated structure, made up as it is of minute nerve tracts and other parts, and composed of a delicate, soft, and destructible tissue, will hardly admit of investigation by the ordinary anatomical methods. Such reflections alone suffice to account for the fact, that only since the introduction of special methods has this "book sealed with seven seals" been opened and its characters so difficult to read been forced to yield their meaning. The methods in use up to the present, most of which are required for the investigation of the varying situation and connections of the elements rather than their structure, although very different in prin- ciple, yet support and complete one another. Excluding simple anatomical inspection, we can arrange our methods in five groups, as follows : — 1. The teasing out of the fibres of a properly -prepared central nervous system. 2. The preparation of an uninterrupted series of sections through the normal organ. 3. The study of organs, the several parts of which either develop at dift'erent periods, or else have sustained retrogressive metamor- phosis. 4. The comparison of homologous parts of the central nervous system in difierent animals. 5. The experimental observation of action, from which structure 4 DEFIBERING. may be inferred, or the study of localised disease of the central nervous system associated with functional anomalies. Other methods of more limited application, but none the less valuable on this account, will be detailed in their proper places. 1. DEFIBERING. Since the central nervous system when fresh presents a consistence which precludes the separation of fibres, it must, if this method is to be used, be subject to a preparation which, while hardening the bundles of fibres, softens the connective tissue binding them together. Such a result has not hitherto been satisfactorily obtained. Simple hardening in alcohol to which saltpetre or hydrochloric acid (used by Ruysch and Vicq cTAzyr) or potash {Reil) is added has been known for a long time. Hardening in chromates with subsequent hardening in alcohol is better. External configuration is best studied after hardening in bichromate of potassium and subsequently in alcohol. J. Stilling places pieces of brain in Miiller's fluid, dehydrates in spirit, and then leaves them in absolute alcohol until they attain a firm consistence. After this they are macerated in artificial wood-vinegar (200 grms. acetic acid, 800 grms. water, 20 drops of creosote). In this they remain, as a rule, for several weeks (it is impossible, however, to fix the time, for it can only be determined by experience); if the preparations become too soft they are placed for several days in crude wood-vinegar. We can with the help of forceps separate certain tracts of fibres in such pieces of brain and preserve them in Canada balsam, after treatment, in a watch-glass, with oil of cloves. In all well-hardened spirit and chromic preparations, every artificial break in the white matter, and for the most part also in the grey masses of the brain, shows the course of fibres. It must, however, be understood that all methods of defibering, especially when the preparation contains fibres crossing one another in difterent directions, are apt to yield misleading results. 2. THE PREPARATION OF SECTION-SERIES. To Stilling belongs the merit of having introduced this most useful method into brain-anatomy. If we imagine a piece of brain cut into such a series of sections as would, if put together again, completely reproduce the original structure, we shall see that it ought to be possible, were it not for special difiiculties which present themselves, to follow any trans- versely cut band of fibres through the whole length of the series. SECTIONS. 5 Although tills idoiil is not .-ilways uttalnablo, it is only since the introtluction of tliis nu'tliod of making continuous series of sections tliat notable progress in the anatomy of the brain has been made. Further histological methods can be applied to any of the sections. The reconstruction of an organ from the observation of a series of transparont sections presents no little difFiculty, and the conception of structure which we gain by this method needs to be checked by seeing the object itself as exposed by dissection. When such a scries is to be made, the central nervous system must first be hardened. Attempts to freeze the tissue and cut it when fresh have not been successful, for the natural brain-substance suffers too much in the process. The freezing method is, however, useful for tumours. Amongst hardening fluids, solutions of chromic salts stand first, and are to be preferred to simple chi'omic acid. Bichromate of potassium is most used. Fresh pieces of the central nervous system are placed in a 1 per cent, solution of this salt. The fluid is repeatedly changed for the first few days, and is rendered gradually stronger, until it is brought up to 2 or 3 per cent., at which strength the pieces are left until they are sufiiciently hard. The time needed averages six to eight weeks, but depends on various circumstances, on the temperature of the room for example (it requires less time in summer than in winter); small pieces, too, take a shorter time than large ones. In an incubator, in which the temperature is maintained at from 35° to 40" 0., it is possible to harden the tissue sufficiently for cutting in from eight days to a fortnight. The time required depends upon the particular part of the central nex'vous system under treatment. The hardening of spinal cord in chrome-salts requires especial care. After the preparations are ready for cutting, they can still remain for some months in the chromic solution without injury; if they are to be preserved still longer they must be transferred to a weak solution (O'l per cent.) of the salt, in which they can be kept for years. The formation of mould is no sign that the preparations are spoilt. The addition of a little carbolic acid does not prevent the formation of fungi, but checks their growth. The hardening is hastened by adding to the bichromate of potassium a little free chromic acid (20 or 30 drops of a 1 per cent, solution of chromic acid to 500 grms. of the bichromate solution). Even though the pieces are not thoroughly hardened in chrome- salts, they can still bear the subsequent hardening in alcohol. This is accomplished usually by washing them out first for several days in water [it is not, as a rule, however, advisable to place them directly in water, but to transfer them from the solution of chromates to 25 6 HARDENING. or 30 per cent, spirit, which is changed every day until the liquor drawn off is almost colourless], and then for a like time in 50 per cent, alcohol, after which they are transferred to strong (95 per cent.) alcohol. To prevent precipitation it is recommended that the vessels should be kept in the dark {H. Virchoio). A long maceration in alcohol renders such preparations easier to cut, but destroys certain details of structure. Owing to a partial solution of the myelin by the alcohol, various spots, spaces, and so forth are artificially produced. If we desire to stain the myelin-sheath (in osmic acid or by certain other methods) the dehydration by alcohol must be omitted. The preparations in this case are only washed in water. The use of alcohol from the commencement of hardening is to be avoided, except in certain cases in which one wishes to study details in the structure of nerve-cells (JVissl, Trehinslci). Mutter's fluid consists of 10 parts bichromate of potassium, 5 parts sul^jhate of soda, and 500 parts water. Erlitzk'ijs fluid is made by mixing 5 parts bichromate of potassium, 1 part sulphate of copper, 200 parts water. It hardens more quickly than Mailer's fluid or bichromate of ammonia (which is apt to make the preparation too hard), but sometimes produces dark precipitates in the preparation, which have already led to mistakes. With some practice one can tell by touching, or gently pressing, a preparation, whether it has reached the proper consistence for cutting ; the safest thing ;to do is to try it with the razor. It may comfort inexperienced persons to know that it sometimes happens that the preparation proves to be unfit to cut, although one cannot account for this mishap. When it is desired to prepare very small pieces of brain or cord for cutting in a condition in which the most minute details of structure, as for example the nuclear figures, may be visible, it is necessary to take the pieces quite fresh from the living or recently-killed animal, and treat them with one of the so-called fixing" media. FoVs modification of Fleinming's fluid is the best of all the fixing media yet pi'oposed ; it consists of — 1 per cent, solution of perosmic acid, . 2 parts by vol. 1 „ „ chromic acid, . 25 ,, 2 ,, ,, acetic acid, . 8 ,, Water, . . .... 68 „ It does not do to be economical with this fluid. It should be changed as soon as it appears cloudy. After some hours (even up to twenty-four or more) the preparation is carefully washed until all traces of the hardening fluid are removed, and then preserved in 80 per cent, alcohol. MICROTOMES. 7 The preparation of sections, which need often to be of very hirge size, used to require a skilful steady hand ; but the difliculties are now very much reduced by the introduction of the miCPOtome. Out of all tliose which have been introduced in recent ycurs, only such microtomes as answer our purpose need be mentioned. In its simplest form the microtome consists of a hollow metal cylinder closed below with a movable floor, which is pushed up and down without rotation on its axis by a fine micrometer-screw. The preparation is fi.xed in the cylinder by means of an embedding mass, A perfectly flat broad glass or metal ring is fixed to the free edge of the tube. The prepara- tion is raised by means of the screw through the required thickness of the section. The knife, which should be broad and light, with a biconcave or plano-concave surface, is kept wet with water or, better still, with alcohol as it is pushed over the smooth i-ing or plate. Gndden's microtome is made on this principle. It must be placed so that its upper part is immersed in a vessel of water under the surface of which the sections are cut. It is intended for preparing large sections which swim away in the water as they are cut, and hence are preserved from traction. Some skill is required in using the knife in this microtome if faultless sections are to be obtained. It is made by Katseh of Munich. The simplest embedding mass is made by melting wax and oil together and pouring them while hot into the tube of the microtome, usually a mixture of three parts wax and two parts oil suffices ; but the proportions of the two substances must be regulated by the hard- ness of the tissue. Other substances also, such as stearin, paraffin, tallow, &c., can be employed in a similar way. It is necessary to clear away the embedding mass from the margin of the preparation, so that the knife passes through little besides the tissue. The knife needs frequent stropping, and must be cleansed after each cut. When the section is large and perishable it is caught up out of the water on a piece of filter paper and at once covered by another piece of wet paper. The section remains in its envelope of paper throughout the procedui-e about to be described. Each envelope should be marked with a number. Excellent results can also be obtained with other microtomes, parti- cularly the so-called sledge-microtomes, in which the knife is carried on a sledge, while knife and preparation alike are kept moist with alcohol dropped from a wash-bottle. We especially recommend the sledge-microtome of Reichert of Vienna, with its automatic arrange- ment for lifting the sections. Weigert^s modification of the " diving- microtome" of Schanze of Leipsic is useful for large preparations. It makes it possible to cut sections under alcohol. 8 CELLOIDIN. [For general laboratory purposes the most convenient form of micro- tome is undoubtedly one whicli allows the tissue to be cut frozen. In some cases a piece of tissue can be frozen, cut, stained, and mounted in glycerin and water for hasty examination in the j)Ost-morlem room. If the tissue has been hardened in spirit it is necessary to throw a piece of suitable size and shape into water until all spirit is removed. This takes, as a rule, about an hour ; but if the piece sinks (as does not usually occur with nervous tissue) this may be accepted as a sign that most of the spirit has diffused out into the water. It is then dipped in gum and placed on the freezing-plate of the microtome. If ether is used as a freezing agent a few minutes only are required to bring the tissue into a suitable condition of hardness, which means, for some tissues, the most complete freezing possible, for others, a condition of partial thaw. Nervous tissue, when frozen hard, is, as a rule, too brittle to cut. The surface may be partially thawed by touching it with a wet camel's-hair brush. No microtome is more suitable for cutting frozen nervous tissue than Boys; the extremely oblique position of the razor and the circular movement enable one to avoid breaking the section transversely, as is very apt to happen when a knife is driven straight forwards through the extremely friable frozen nervous tissue. The sections are lifted from the razor into salt solution with a lax'ge wet camel's-hair brush.] The tissues can be embedded for cutting with the sledge-microtome in pasteboard or metal boxes filled with wax and oil, or, if they are of no great depth, they may even be stuck on a piece of cork. If they are to be cut on cork they must be placed with the cork in a thick solution of gum, out of which both are lifted together into absolute alcohol in which they remain for twenty-four hours ; or else they are placed in thick solution of celloidin, subsequently set by immersion in alcohol of 80 per cent. The alcohol commonly used in the laboratory is about 95 per cent.* It may be let down to the required strength by mixing with distilled water in the proportion of 9 to 1 -5. Stronger alcohol, and especially absolute alcohol, dissolves celloidin. When the tissues are unfit to cut in other ways, owing to the hardening being improperly carried out, or else owing to the tissue, softened by disease perhaps, being incapable of hardening, they may yet be made into excellent sections by adopting the celloidin method. Pieces of spinal cord about 1 centimeter thick, are placed for two or three days in common alcohol. They are then completely dehydrated in absolute alcohol, and subsequently placed in a thin solution of celloidin in equal parts of sulphuric ether and absolu e \* Methylated spirit if free from resins, as shown hy its giving a clear mixture with water, is equally useful.'] CELLOIDIN. alcDhol. In tl.is tlicy niniiiii lor a V!iri:iM(^ time, according to thick- ness (usually thrc(! or four clays). Next they are transferred to a syrupy solution of celloidin, in which tliey renuiin a few days. After this a piece is lifted with adhering celloidin on to a cork, exposed under a glass until it is almost set, and then cork and preparation together are placed in 80 per cent, alcohol. This method of em- bedding in celloidin is indispensable for very friable pr(;parations, or for preparations which are with difficulty held together, or which present cavities in their interior, [The nuthod of embedding in celloidin which we have adopted for the last six years is the same in principle with that described by Barrett* Its usefulness for all purposes depends upon the replace- ment by water of the alcohol in the celloidin-mass. Owing to the tissue-like permeability of celloidin, this is effected without perceptible alteration in form. The embedded preparation can afterwards be cut on a freezing-microtome. So simple is the procedure that it is well as a matter of routine to apply it invariably in investigations into the structure of the central nervous system. The tissue, either stained en hlocq or left for staining after it is cut, is placed in absolute alcohol. This is replaced by a mixture of absolute alcohol 3 parts, ether 1 part. When this has soaked into the tissue a small piece of Sherinffs dry celloidin is placed in the vessel. The celloidin dissolves very slowly, and the gradually concentrating solution permeates the tissue far more thoroughly than even the weakest ready-made solution would do. Fresh pieces, or, to hasten the process, pieces of waste celloidin-jelly, are added daily until the solution flows with difficulty. It is then poured out with the tissue in its centre into a flat-bottomed glass dish. The dish is covered with a plate of smooth glass. By this arrangement a very slow evaporation is allowed, and the celloidin when°set will be found to be of uniform consistency, and not prone to curl when cut. If it is important to save time, the celloidin is poured into a paper boat which is immersed in chloroform, which sets the celloidin in a few hours without measurable alteration in bulk {Caldwell). When set somewhat firmly, the tissue with a convenient bed is cut out with a knife, and the block thrown into water for an hour (or if saturated with chloroform, into spirit and then into water). When all the alcohol is replaced by water, the block can be frozen and cut with a facility quite unattainable in spirit-set celloidin. There is no pleasanter material to cut than frozen celloidin. In some cases it is desirable to embed the tissue in celloidin, even before cutting into series of sections in paraffin. If this is desired, the chloroform- * Journal of Anatomy and Physiolo'jij, vol. xix., p. 94, 1885. lO CARMINE-STAINING. saturated block, or even the alcohol block, can be placed in melted paraffin.] The investigation of the constitution of the central nervous system by means of sections only reached its full development when Gerlach showed us how the use of staining" agents reacting difier- ently to the several tissue-elements allow us to make a differentiation in the preparation. Ammonia-carmine, the stain which happened to be employed first, has not only yielded the most abundant results, but is still one of the best reagents. The best carmine which can be bought, and it is not always possible to obtain a good specimen, is mixed in a beaker with ammonia into a soft pap, to which so much distilled water is added as will yield a dark black-red solution. The solution is filtered, and exposed to the air until the surplus ammonia has evaporated. The solution improves on keeping. The fluid can always be filtered back into the bottle after use, and may be employed for years. Alcohol preparations are very quickly coloured in this solution j a few minutes only being needed. Chromic preparations take a varying time, increasing with the time the prepai-ation has been kept j it may vary from an hour to several days, and each case must be treated on its own merits. When it is desired to accomplish the staining quickly, the watch-glass containing the preparation should be placed on a wire net over a vessel of boiling water ; three to five minutes usually suffices under these circumstances. In the incubator the time depends upon the temperature. For slight magnification the sections are cut thick and slightly stained ; for use with high powers, deep staining is necessary. The stained sections are washed in distilled water (the addition of a few drops of acetic acid makes the nuclei more conspicuous), they are then placed for a quarter of an hour in common, and for a similar time in absolute, alcohol. From absolute alcohol they are transferred to clove-oil, in which they remain until transparent. Celloidin prepara- tions can bear neither absolute nor clove-oil ; they must be cleared in oil of thyme (origanum) [or oil of bergamot] or creosote ; clove-oil dissolves celloidin. Creosote is expensive, but has the advantage that the dehydration with alcohol need not be so complete. Cedar- oil is not good for celloidin preparations as it makes them opaque, but otherwise it is a good clearing medium. Turpentine may be used by itself. Finally the section is spread out on a slide, the surplus oil is sucked up with blotting-paper, dammar varnish [or Canada balsam] is dropped on to it, and it is covered with a cover-slip. Sections enclosed between two pieces of paper are placed with their envelope in the clove-oil. From this they are lifted with forceps on to the slide, and it is now easily possible to detach the upper paper. NUCLKAK STAINS. II The other pu'cc of i)apc'r is then seized witli the forceps and turned over, so that the section comes to lie upon the j^lass. Tlio second paper is then easily removed, provided the surplus clove-oil has been dried off with a number of layers of blotting-paper. Ammonia-carmine stains the axis-cylinders and all cells non-nervous as well as nervous [but especially their nucha]. Uoyers dry ammonia-carmine is useful for some purposes, since the common ])reparation is apt to become suddenly useless owing either to the formation of a bright-red precipitate, or else to the growth of fungus in the fluid. A freshly-prepared solution of the powder affords a useful substitute for the liquid ammonia-carmine. Picro- carmine is often recommended instead of ammonia-carmine. A good picro-cai-miue for colouring the central nervous system is prepared by L'Oicenthal in the following way : — In 100 grms. water, 0-05 grm. of caustic soda is dissolved, to this is added 0-4 grm. carmine; the mixture is then boiled for ten or fifteen minutes, and diluted to 200 cc. To this fluid is added just sufficient of a 1 per cent, watery solution of picric acid to redissolve the precipitate first formed. It then stands for two or three hours when it is filtered several times through the same filter-paper. After some weeks or months the solution is apt to become dim. Beside the carmine-staining we use also — 1, nuclear stains; 2, stains for medullary sheaths ; 3, stains for the axis-cylinders alone. A. NUCLEAR STAINS. Alum-hsematoxylin is the most used. As much htematoxylin as will lie on a three-penny bit, and the same quantity of alum are placed in a test-tube two-thirds full of distilled water, and boiled until they dissolve ; the resulting claret-coloured fluid is then filtered. The solution will not stain until after it has been kept for some days. It is advisable to filter off the precipitates as they form. Colouring occurs very quickly, and it is often necessary to use the solution in a considerably diluted condition. The section, after it is washed, should only appear grey-blue, but all nuclei and amyloid bodies (when they occur) will be found strongly stained. All the rest of the section ought to be left almost or quite uncoloured. Various other preparations of hsematoxylin act in a similar manner. If the section is overstained it can in some cases be set right by weak salt solution. Nuclear staining gives beautiful results in sections already stained in carmine or picro-carmine. The further treatment is the same as for carmine preparations; alcohol, clove-oil (thyme-oil), dammar varnish. 12 OSMIC ACID. Csokor's carmine stains nuclei well. 50 grms. powdered cochineal and 5 grms. alum are dissolved in .500 grms. of water, and the solution reduced to two-thirds its bulk by boiling. A few drops of carbolic acid are added to prevent the formation of moulds. Numerous other nuclear stains are useful in their place — e.g., a watery solution of Bismarck-brown (1 to 300), Grenadier's carmine solution, nigrosin, &c., &c. B. MEDULLARY-SIIEATH STAINS. 1. Exner's Perosmic Acid Method. — Quite small pieces of nerve-tissue (at the outside not more than a centimetre thick) are placed in a sufficient quantity of 1 per cent, perosmic acid solution. In two days the solution is changed. In five to ten days the pieces are darkly coloured, but they may remain for a longer time in the solvition. [Good results are often obtained in twelve to twenty -four hours; the prepara- tion should, while in the osmic acid, be kept in the dark.] The prepara- tion is then washed [a quarter to half an hour in running water is by no means too long to remove all traces of dissolved osmic acid and prevent subsequent precipitation on the addition of alcohol], placed for a few seconds in alcohol, embedded and cut. The sections, which must be very thin, are cleared in glycerin, lifted with adhering glycerin into a slide, on which a drop of strong ammonia-water has previously been placed, and covered with a cover-glass after exposure to the air for a few minutes. Even the finest meduUated fibres are stained black. The fault of this excellent method is that the preparations quickly degenerate and are often useless in a few days. [Permanent preparations, although with some faults incidental to the solution of the fat, are obtained by mounting the section after the usual dehydration, in Canada balsam.] The method can only be applied to very small pieces of tissue. 2. Palladium and Gold. — Alcohol is to be avoided in preparing the sections which are placed for five minutes in a watery solution of palladium chloride (about 1 in 2000). They are washed in distilled water, placed in a very weak solution of gold chloride (1 in 5000) made acid with hydrochloric acid, and exposed for twenty -four hours to a moderate light by which time the fibre-tracts assume a violet colour. After repeated washing in water they are treated with alcohol, clove-oil, and dammar varnish. The preparations are only to be used with a low power, but they give good general results, as only the coarser fibres are stained. 3. Weigeris Hcematoxylin-method. — The tissue must be hardened in chromic salts ; but it can be transferred through alcohol into celloidin, WEIGEKTS STAIN. 1 3 although it is dosiralilc th;it it should not bo washed out iu water. Fair results may 1)0 ohtaiiiod with this method after washing out with water, and the tissue may v.vm he cut under water on a Oudden's microtome, hut the hest results of which the method is capable are only possible when washing out in water has been avoided. The block of tissue is fastened on to cork with celloidin in the manner already described, and after being immersed for several hours in 80 per cent, alcohol it is placed in neutral solution of copper acetate (made by mix- ing equal parts of saturated copper acetate solution and water). In this it remains in an incubator at 35° to 40° 0. for one or two days. The sections are then cut and placed in alcohol, from which they are lifted into a solution of hiematoxylin, prepared by dissolving 1 part h.-ematoxylin in 10 parts alcohol and 90 parts water. The solution is not fit to use for one or two weeks. Addition of 1 per cent, of a cold saturated solution of lithium carbonate ripens the fluid sooner. In this solution the sections remain a longer or shorter time (from two to twenty-four hours), according to the degree of colouration required — spinal-cord requires a shorter time, brain-cortex a longer time. The sections, now quite black, are washed in water, and then placed in a decolourising solution composed of borax 2 parts, ferridcyanide of potassium 2-5 parts, water 100 parts. Here the section remains until a difi"erentiation between the nerve-fibres and grey matter is distinctly visible, the time necessary varying from a quarter of an hour to twenty-four hours. Owing to their blue-black colour the medullated fibres stand out sharply on a brown field. Often the decolourising fluid works too strongly, and it is advisable to thin it, even with fifty times its volume of water in the case of peripheral nerves (Gelpke). Since the sections which are cut after the tissue has been treated with copper-acetate are not amenable to staining with carmine it is frequently convenient to prepare a number of sections from the hardened tissue, and to submit only those to which it is desired to apply Weigert's method to the copper-acetate. Sections do not require to stay so long in the incubator as directed for the block of tissue. The sections should be rinsed in weak alcohol before they are transferred to the hjematoxylin. In cases in which staining of the finest fibres is not necessary, it is possible to dispense with the copper solution, provided the colouring is conducted in the incubator. It is some- times impossible when the sections are thick to efiect a sufficient decolourising in the ferridcyanide solutions; after remaining, however, for twenty-four hours in alcohol the section can be again treated with ferridcyanide with better eflect. The preparation of an uninterrupted series Of sectionS from tissue embedded in celloidin with subsequent staining in Weigert's 14 CELLOIDIX-SERIES. hsematoxylin is rendered possible by the following metliod recom- mended by this histologist. One or more glass-plates are carefully cleansed and covered with collodion as if for photography, next strips of tissue-paper are cut a little broader than the sections and a little longer than the glass-plate. The sections are taken off the razor ■with these strips in such a way that, by using a gentle traction, they are rotated on their axes, and arranged in the direction in which the series is proceeding. The strip travelling from right to left, each succeeding section is received on the right side of the one before, and the strips of sections when complete are kept in the same order. It is important to keep the section damp during the cutting, and until it is transferred to the glass-plate. This is accomplished by having near the microtome a shallow dish containing a number of layers of blotting- paper soaked in 80 per cent, alcohol, with a single sheet of tissue-paper on the top. The strips of paper bearing the sections are laid on this damp bed, the sections being on the upper surface. The collodion (solution of celloidin) on the glass-plates being now dry the strips of sections are inverted on to the plates, and being gently pressed the sections adhere to the celloidin. Usually two rows of sections can be laid side by side on the same plate. All superfluous alcohol being now removed without the sections being actually dried, a second film of collodion is quickly poured over them. As soon as this layer is dry on the surface the preparation can be marked with methyl-blue in such manner as to remind one of their orientation. The glass-plate is now either set aside in 80 per cent, alcohol, or at once (before it is really dry) transferred to the hajmatoxylin-solution. In this, especially if placed in an incubator, the strips of celloidin detach themselves easily from the glass. They must be carefully washed. The strips can be cut into convenient pieces, washed in alcohol of 90 to 95 per cent, (but not absolute), cleared in creosote or in a mixture of three parts xylol to one part of anhydrous carbolic acid and mounted in dammar varnish. Oil of thyme and oil of cloves are to be avoided. [It is perhaps desirable to mount in xylol balsam or in dammar varnish without a cover-slip.] Formerly Weigert introduced a method for staining medullated nerves in acid fuchsin ; but this has now been superseded by the easy, and in every way excellent, hjematoxylin-method, which is of inestimable value for studying degeneration of medullated nerves. Since its introduction numerous modifications which cannot all be described here have been proposed. PaVs method deserves descrip- tions in detail, as it gives excellent results. Its value consists in the complete decolourisation of the tissue between the medullated nerves and the opportunity of subsequently staining it, which is not allowed PALS STAINING. I 5 by Wrigort's method. Pieces of tissue arc liardened in Miiller's fluid. If this reagent lias been completely washf^d out, or if the tissue has assumed a green colour, it must be put for a few hours into 0-5 per cent, chromic acid, or for a longer time in a 2 per cent, to 3 per cent, solution of bicliromate of potassium before proceeding further. The sections are put for twenty-four to forty-eight hours in Weigert's hsema- toxylin-solution (part of the time, if need be, in an incubator at 35"^ to 45" C); washed in water, to which, if tlie sections are not already stained deep-blue, some lithium carbonate solution is added ; and then placed for 20 to 30 seconds or longer, until the section looks as if decolourised by Weigert's method, in a ^ per cent, watery solution of permanganate of potash, after a previous washing in the following solution for a few seconds — 1 part pure oxalic acid, 1 part sulphide of potassium, 200 parts distilled water. Everything except the medullated nerves is completely decolourised by the permanganate of potash. After careful washing, the sections can be further stained in various dyes (particularly picro-carmine). Dehydrate and clear in the usual way. This method is excellent for a collodion-series. The nerve-fibres are very sharply marked off by Pal's method ; and other tissues can be defined with proper staining. Brown patches are unavoidable in some sections, but they do no harm. Other tissues besides the nerve-fibres are apt to be darkly stained by Weigert's method (or Pal's modification). The contents of blood-vessels especially stain ; in some cases the colourisation affects the corpuscles, in other cases the plasma. Sometimes this staining only affects the vessels in a defined region, as, for instance, in the deepest layer of the cortex. At times coagulation-products, stained intensely dark, are seen in these vessels, and easily mistaken, when thread-like in form, for medullated nerves. Calcified vessels and nerve-cells also stain. Within the nerve- cells the pigment assumes a darker colour. Especially after de- colourisation with ferridcyanide we notice that all nerve-cells have not reacted in the same way to the colouring agents ; an attempt has been made, as we shall show later on, to make use of this diflerence for the classification of nerve-cells, the difference being supposed to be associated with a difference in function. 1 6 SUBLIMATE-METHOD. C. AXIS-CYLINDER STAINS. The axis-cylinders of nerves stain very distinctly with carmine ; at the same time, however, owing to the staining of tlie connective tissue they are often unrecognisable, and it is of importance to find a method which, while staining the axis-cylinders and so rendering them conspicuous, leaves the connective tissue uncoloured. This is desirable, for instance, in the patches of disseminated sclerosis. Freuds method of gold-staining answers the purpose, although occasionally the medullated sheath is stained. Sections from tissues hardened in chrome-salts are placed in 1 per cent, solution of gold chloride mixed with an equal volume of 95 per cent, alcohol. After four to six hours they are washed in distilled water and then placed in caustic soda (1 part to 5 or 6 of water). After two to five minutes, the sections are lifted out, drained, and put in 10 per cent, solution of potassic iodide; in five to ten minutes the sections, having acquired the proper colour, are washed in water and alcohol. To prevent swelling and crinkling, delicate sections, as soon as they leave the potassic iodide, need to be put on to a slide and dried with pieces of blotting-paper. The results yielded by this method, which allows of the highest magnification, are excellent, although the method is a little trouble- some. The nerve-fibres appear black, dark-blue or dark-red, according to the nature of the specimen. OTHER METHODS OF COLOURING, IMPREGNATING WITH METALS, &c. Of the principal methods of colouring by impregnation only a few of the chief need be mentioned. The Sublimate Colouring of Golgi. — Little pieces of the central nervous system are, after thorough hardening in bichromate of potassium, placed in a 0-2.5 per cent, watery solution of corrosive sublimate. The fluid is renewed as often as it becomes coloured yellow, and the concentration of the solution may be raised to 0-5 or even 1 per cent. Small pieces are saturated in eight to ten days, but the longer they are left the more thoroughly are they permeated; and they may remain in the solution without harm for years. The pieces are now cut, and despite their very favourable consistence the sections need not be made very thin; they must be well washed, however, else after some weeks numerous acicular crystals of corrosive sublimates will be seen. Subsequent treatment as usual. SAFFRANIN-STAINING. 1 7 Witli low and mndcciitc; mngnification certain nerve and connective- tissue eells, l)ut never all, as well as connective-tissue (ihres jipix-ar intensely blaek. This colour is due to a fine crystalline precipitation, opaque to transmitted light, in the tissue spaces [oi- lymph spaces] around the tissue-elements. No other method shows in such a conspicuous manner the continuity of the spaces around the cells and their branches. Its principal fault is its uncertainty, for in one preparation not more than a tenth part of the nerve-cells and probably fewer connective-tissue cells are stained, while another shows numerous connective-tissue cells but no nerve-cells. A similar method is also given by Golgi for impreg- nating with nitrate of silver, but it offers no special advantages. Pal has invented an improved sublimate-method. It consists in treating the sections with sodic sulphide (Na2S), which gives more precise figures, black even with a high power. 10 grms. of caustic soda are dissolved in 1000 grms. of water; half of this is saturated with sulphuretted hydrodgen, mixed with the other half and kept in a well stoppered bottle. The sections are carefully lifted from the sublimate solution into this fluid, and remain there until the spots, at first white, become black. Subsequent treatment as usual. Golgi's staining is especially successful when the brain has been hardened in the following manner : — A 2-5 per cent, solution of bichromate of potassium is injected into the carotids of an animal just killed, for the purpose of rinsing the brain; small pieces are then placed in Miiller's fluid, which is frequently changed during eight to ten days ; then for twenty-four hours in a mixture of 4 parts Miiller's fluid to 1 part 1 per cent, solution of perosmic acid. The pieces may now be placed in the sublimate or silver solution. The preparations are supposed to keep better if not covered with a cover-slip [owing to the balsam, in the absence of the cover-slip, being allowed to dry]. Adamkieicicz' Staining in Saffranin. — The sections are placed in water weakly acidified with nitric acid. After a short time they are placed in the colouring solution (a deep burgundy-red watery solution of saftranin). Here they lie until they are overstained, when they are washed first in common, and then in absolute alcohol, which also is made acid with nitric acid. Lastly, they are placed in clove-oil when the red stain decreases ; and mounted in Canada balsam. The nerve medulla is stained orange or red, the nuclei of the connective tissue violet. Degenerated parts come out very distinctly. Thicker sections may be left unstained and mounted in glycerin, when a very clear general view is obtained, especially with the medulla oblongata ; degenerated spots in the spinal cord are clearly 9 1 8 MYELINATION. distinguished from nerve-fibres. Such preparations mounted in glycerin are best ringed round with paraffin. Lastly, it must be remarked that in many preparations in which nerve-fibres cross one another, by placing the plane mirror of the microscope in such a position that the light traverses the section obliquely, some sets of fibres are left dark, while others show up distinctly. This does not succeed with preparations made according to Weigert's method. Flesch, also, has proposed the use of COlOUPed light ; where it is a matter of slight difierence in colour in difierent parts of the section this artifice can be sometimes employed successfully. 3. THE INVESTIGATION OF THE CENTRAL NERVOUS SYSTEM IN EMBRYONIC AND PATHOLOGICAL CONDITIONS. The methods arrange themselves in three groups : — (a.) In the early periods of foetal life all nerve-fibres are destitute of medullary sheaths, so that to the unaided eye the central nervous system appears almost uniformly transparent, and of a red-grey colour. During further development all nerve-fibres are not suiTounded simul- taneously with medullary sheaths. White patches appear at difierent periods, owing to the successive acquisition by the nerves of their medullaiy sheaths, which occurs first in peripheral nerves and later in the central system ; the ground-tissue remains grey. Flechsig was the first to show that the protection of the nerves with myelin does not take place at hap-hazard, but according to determined laws ; hence important conclusions as to the structure and development of the system may be drawn from an observation of this process. By making use of this method of inspection it is possible to pick out and follow definite groups of fibres which later on are lost in the chaos of tracts. It is also possible by this method to distinguish in an apparently uniform nerve-tract constituents which, developing at difierent periods, must have separate functions. The conclusion, too, which may be safely accepted, that the fibres which first attain to a full development are the first to come into use is of the highest physiological import- ance. The particular stages at which they acquire their structural completeness must be noted. Weigert's hsematoxylin-method with its certainty and simplicity has greatly helped in the investigation of the time of myelination of nerves. It is sometimes taken for granted that a nerve-fibre, no matter how long (reaching, it may be, from the brain to the lumbar cord), gets its myelin-sheath throughout its whole length at one time. This proposi- tion is not proved, and it is well in using Flechsig's method to bear in SECONDARY DEUENERATION. 19 O^ -co mind the possibility of a sliglit diirerenco in time in the accjuisitiou of myelin by dillereut parts of the nerve. It is also believed by many that a nerve acquires its myelin in the direction in which it subsequently conducts. (6.) When a nerve is cut through, its peripheral end degenerates quickly. It is similarly the case that if a certain part of the white or grey substance of the cerebro-spinal axis is destroyed, by a tumour or hremorrhage, for example, individual groups of fibres atrophy. The laws of this secondary degeneration — as this form of atrophy is called — are only partially known. We suppose, without being able to advance irrefutable proof, that every nerve-fibre is nourished by the cell with which it is connected — its trophic centre. If the trophic centre is destroyed, or if the nerve-fibre is severed from it, the nerve necessarily dies. When a nerve-route in the central system is cut through the part severed from its trophic centre degenerates. For most nerve-tracts, we cannot say for all, it is proved that degeneration progresses in the direction in which the impulses are in the habit of travelling along the fibre. RokitansTcy first, in 1847, pointed out this secondary degeneration, and TiircJc so thoroughly worked at it that we have to thank him for a large part of the anatomical knowledge which we have acquii-ed by this method, at any rate so far as the spinal cord is concerned. All injuries to the whole cross-section of the spinal cord result in the degeneration of certain fibre-tracts upwards from the seat of the disease, while others degenerate downwards. A third set of fibre-tracts remain apparently normal both above and below the injury. The first set of fibres have their nutrient centres below the injury, the second set above, while one ought to allow, with regard to the third set, that they are nourished Fig. 1. — Scheme il- from both sides. A more exact observation shows, lustrating the however, that most of these fibres do not remain intact, but a small part of each of them, be it above or below the injury, does degenerate, and since we discover that the fibres of this portion of the cord have their trophic centres hard by the seat of injury, no matter where it occurs, we must conclude that the course of each individual fibre is a short one. From this example we see in what manner secondary degeneration can yield information with regard to the course of fibres in the -i -J 6^ nutrition of a nen^e-fibre from two sides, after Schwalbe. 20 HISTOGENY. nervous system. We must, however, at the same time clearly be careful in making use of this class of evidence until the con- ditions of the degenerative process are better known. Schicalbe calls attention to possible sources of error. It is not inconceivable that a nerve-fibre wliicli is connected at either end with a nerve-cell [a combination, the existence of which is only hypothetical] is influenced in its nuti'ition in such a way that the action of A in the direction B, diminishes the action of B in the direction of A. He believes that in the middle at i an indifl:erent point is to be found, at which the fibres can be cut through without resulting in secondary degenera- tion. If the fibre is cut through at a, the fibre dies from a to i, where the nutritive influence of B begins ; and contrariwise when it is cut through at h. It is to be noticed, however, that such a diminishing nutrient influence is not proved ; whereas we do know of cases in which fibres atrophy throughout the whole length of the central nervous system when their trophic centres are destroyed. [Recent investigations into the histogeny of the nervous system have determined, almost with certainty, that the essential nerve- fibre, the axis-cylinder, is from origin to termination a process of a nerve-cell. The nerve-cells are united with one another by many branching processes. The central system consists of a plexus offering a variety of alternative routes to the afferent impulse. The nodal points of this meshwork are formed by cells which are for the most part small. Wherever a long efferent fibre starts from tlie plexus, the cell of which it is a process and from which it grows out, is found to present a size proportional to that of the fibre to which it gives origin, and over the nutrition of which it permanently presides. At its distal end, the fibre branches for the purpose of establishing a con- nection with the region towards which it grows out. No nutriment is received from this dendritic termination backwards along the fibre, but throughout its whole length the fibre depends for its vitality upon its connection with the cell from which it sprang. The nerve- fibre DIES WHEN CUT OFF FEOil THE CELL OF WHICH IT IS A PROCESS. From this account of the growth of nerve-fibres, it will be under- stood that within the cerebro-spinal axis, motor (descending) fibres degenerate below the level of section ; sensory (ascending) fibres degenerate above this level. The portions of the white columns, in the immediate vicinity of the grey matter, consist of fibres which connect together neighbouring regions of the plexus, and it is conse- quently very difiicult to obtain evidence as to the direction in which they die ; for the fibres which the lesion destroys are so short, that even in a section taken a little way above or below the lesion, the same situation in the axis is already occupied by other sets of fibres. NUTlllTION Ol" NEItVK. 21 "Wlu'ii an ;int('ri()r spinal iicrvc-root i.s cut, tlio lilircs ImIow the section dii', na shown by Waller. The distal portion of tlio root degenerates completely, as do also all the fibres which the anterior root yields to the mixed nerve. When the posterior root is cut proxinially to its ganglion, all its fibres die between the section and the spinal cord ; all the fibres between the section and the ganglion live. ITntil recently it was thought that if the posterior root is cut on the distal side of the ganglion, all the fibres between the section and the ganglion live, while all those which the section severs from the ganglion die. This lias been shown by Max Josej^h not to be quite correct ; the greater number of the fibres of the posterior root depend for their nutrition upon the cells of the spinal ganglion, but a certain small proportion of them have their nutritive centres nearer to the periphery. So at least we may infer from the fact that some fibres die right through those portions of the root which are still attached to the ganglion on both its proximal and distal sides. The undegenerated fibres which should be found in the peripheral nerve have not been recognised as yet however. The difference between the fibres of the anterior and posterior roots, as regards their be- haviour to section, has only been intelligible since His, Froriep, and Beard have shown us that while anterior roots grow out from the sjiinal cord, the spinal ganglia are formed from epiblastic thick- enings outside and independent of the primitive neural plate, the cells of which give off" processes which, growing inwards towards the cord and outwards towards the periphery, constitute the posterior roots and sensory nerves respectively. If the degeneration-method is to be made \ise of, it is desirable that the alteration in appearance presented by the dying nerves, and the time of onset of the successive phases in these alterations should be understood. In this investigation it is of the highest importance to bear in mind that, while the axis-cylinder is the process of a cell in the central plexus, the myelin-sheath by which it is surrounded is formed from many cells which have an independent, although epiblastic, origin. Section of a nerve results in the death of its axis-cylinder. It seems, however, that as long as it lives the axis-cylinder exercises a restraining influence upon the nutrition of the myelin-cells by which it is surrounded ; their tendency to form additional protoplasm, to grow and multiply is maintained at a minimum ; their fatty metabolite, upon the existence of which depends their usefulness, is present in maximum quantity. When the axis-cylinder dies the myelin-cells enjoy a sudden exaltation of nutritive activity, their protoplasm accumu- lates, their fatty metabolite is absorbed ; their nuclei increase in size, 22 SECONDARY DEGENERATION. develop regular active chromatin skeins and initiate cell-division. This condition of sur-activity soon begins to wane, accumulation of protoplasm ceases, the cells shrink and assume a stable form. Fimilly, the degenerated nerve comes to resemble a cord of connective tissue. A nerve-fibre has essentially the same structure whether it occurs within or without the axis. It consists of the real fibre, the cell- process or axis-cylinder, invested by myelin-cells, each of which is a hollow cylinder filled with phosphatic fat. While within the axis fibre and myelin-cells are supported by a neurogleia-sheath. When running through mesoblastic tissues, they are invested with a connective-tissue sheath, the sheath of Schwann. A peripheral nerve completely loses its irritability (in a warm- blooded animal) within forty-eight hours after section. Even by this time a distinct change is visible to the naked eye. Owing to the already-commencing accumulation of protoplasm in the medullary sheath, at first about the nuclei, with coincident absorption of myelin, the fibre looks less solidly white, and glistening. In about twenty days (Banvier) the myelin only remains in drops, which here and there distend the sheath of Schwann. Within the fresh cord a degenerated area is recognisable by the fifth week after injury as a milky patcli. In three or four months it becomes less white, then grey, transparent and gelatinous in appear- ance (Sherrington). Finally, it is indistinguishable until after harden- ing of the cord. In the cord, hardened in bichromate of potassium, the degenerated area is visible at an earlier stage than in the fresh cord (in the cervical and dorsal regions in nine days — Sherrington) as an area lighter in colour and yellower than the surrounding white matter. For about the first six months after injury the distinctness of the degenerated tract increases. After this time it begins to shrink. In sections stained with carmine or acid fuchsin degenerative changes can be recognised in about a week (in the posterior columns in three days, in the lateral pyramidal tract in five, in the direct cerebellar tract in seven- — Homen). At first the axis-cylinder appears thicker than normal and granular, and stains less darkly with carmine and more darkly than normal with acid fuchsin. The myelin-sheath begins to stain, especially at its inner part, more distinctly with carmine and less distinctly with acid fuchsin or Weigert's hfematoxylin. Absorption of fat and proliferation of the myelin and neurogleia cells then ensues, in the same manner as already described for peripheral nerves. In a carmine-stained section the degenerated area is recog- nisable for a long period with a low power as a dark-red patch, although its power of staining gradually diminishes.*] * For further details see Langley, ' ' Critical Digest, " Brain, April, 1886. gudden's method. 23 It is self-t'viileut tliat the same ellt'cts, which result from disease, will follow injviry produced by the oxpcriinentcr's knife; while in the latter case, it is possible to limit the injury to a single well-defined bundle. This method of artificially-produced secondary degeneration was first used by Waller for the purpose of following fibre-tracts. Information obtained by experiment upon animals can only be applied with qualifications to the human brain. (c.) Essentially different to the methods we have just been describ- ing is the plan introduced by Gudden, which also has yielded imi)or- tant results. There are points of similarity certainly between this method and the method of secondary degeneration ; but in Gudden's method lesions are produced only on new-born animals (rabbits, puppies, and kittens). In such subjects the nervous system is still in a partly-embryonic condition, and we have, therefore, arrested development as well as secondary degeneration combined in the results of the injuiy. The still-growing cell-groups stand in quite a different relation to the destroyed conducting paths to that in which they would stand to a fully-developed functional organ which had already obtained a certain stability of structure. An advantage not to be overlooked in this method of Gudden is the focility with which operative interference can be undertaken. The animals are easily handled. The readier coagulation of blood causes the bleeding to stop soon, even when large vessels are cut. The wounds heal quickly without supuration ; a few catgut sutures, which are absorbed, alone are necessary. The slight covering of hair to the new-born animal is even a help. The animal is given back to the parent's care after the operation. It may be allowed to live for six or eight weeks, the longer the better, as a rule, and then it is killed and its central nervous system examined. We may expect to deduce the most far reaching conclusions as to the structure of the nervous system from the results of this method. The laws, according to which the results of these experimental injuries to new-born animals are obtained, are not sufficiently well established to enable us to use the method without precautions. It cannot be certainly said how far the degeneration (an unsatis- factory term in this case) proceeds. From numerous examples it is determined that when a peripheral nerve is destroyed in a young animal, the groups of nerve-cells from which it takes its origin do not assume their proper form, but whether other routes springing from these cells on the opposite side suffer the same fate is an open question. Whether the degeneration is pathological or artificially set up, it is in 24 VARIATIONS IN DEVELOPMENT. all cases observed in the central system that it stops short at the nerve-cells in which the destroyed route terminates. 4. THE COMPARATIVE METHOD. Since we can take for granted that the functional importance of an organ keeps pace with its anatomical prominence, we may expect many important disclosures from the comparative method. First, we must study the system in the lower animals, in the hope that in them it will present a simpler organisation, and one, therefore, easier to understand them in man. Further, one may take into con- sideration the fact that certain functions, and the organs to which they belong, are not equally developed throughout the animal kingdom; the sense of smell is as deficient in man, for instance, as the sense of sight in the mole. The central organs associated with the senses above- named must show a corresponding feebleness. Edinger has successfully combined the comparative and historical methods by examining the embryos of lower vertebrates. Animals which have strongly developed hind-legs (jumpers) can be compared with animals with large fore-legs (diggers), and also with others, such as the whale, in which the limbs are rudimentary. Meynert first attributed to this kind of observation its proper merit. There are many obvious differences in the relative importance of the several parts of the central nervous system in different animals, which we cannot yet bring into accord with their functional peculiarities. 5. PHYSIOLOGICAL METHOD. All the methods by which injury is intentionally inflicted on animals might be included under this head ; they have, however, been grouped with the injuries of disease. In the methods now under considera- tion we have to do with excitation or paralysis of muscles, resulting respectively from irritation and ablation of the brain or cord. For example, when a certain spot on the surface of the brain is stimulated, movement of a defined muscle-group results ; or a particular region being excised, a sense organ is thrown out of gear. "We may conclude that the part of the brain injured was in each case related to the organ over which it has lost its influence. Xo method, however, needs to be used with greater care, or leads more easily to mistakes. The stimulation and the destruction of a part of the brain is apt to call into evidence, not the part especially implicated, but some neighbouring region sympathetically set in action ; or, again, unless the stimulus is appropriate it is apt to be ineffective. This is not, STAINING LIVING NERVES. 25 however, th.« plucc to point out all tlu- mistakes which have occurred; ^vc must content oursolv.^s with showing that the value of physiologi- cal experiments must only he estimated in careful association with anatomical data. Porhaps the condition of clectrotonus may he used for anatomical ^"ThTsame results which we are able to produce in the central nervous system experimentally follow injury and disease; by the action of tumors, luvmorrhages, inflammation, etc., localised irntation and paralysis are induced, and the phenomena which resu t show the connection of the several parts of the system to one another. Lven more caution is necessary in interpreting these results than in the case of injuries induced experimentally. By the aid of the methods above-mentioned, wc have been able recently to throw much light upon the structure, hithei-to but little understood, of the highest organs of the body. New methods are still wanted, however, to enable us to unravel the tangle of conducting paths. It is due to Tiirck, Gerlach, Stilling, 3feynert, Flechsig, Gudden, Weigert to point out the advances in the subject which the introduction of the methods which bear their names have produced. So important is the differentiation which staining affords that one would expect useful results from staining the tissues of the living animal. Mrlich has taken the first step by injecting methyl-blue into the circulation. It stains the endings of centripetal nerves and (for some minutes only) the ends of some centrifugal fibres. After- treatment with iodide of potassium {Pal) or biniodide of potassium (Smirnow) renders the preparations more durable Any method which would so fix the staining intra vitam as to make it available for study after death would be especially valuable. The fixing methods already mentioned make some progress towards this goal. _ None of the methods at present in use will stand a strict criticism and the same want may be anticipated in the case of methods devised in future If it is recognised that no single method is suflicient in itself, but that all must be used in conjunction, a thorough exploration of the nerve paths may be finally counted on. 26 SECTION II.— MORPHOLOGY OF THE CENTRAL NERVOUS SYSTEM. In fresh preparations the difference in colour between the grey and white substances is sufficiently marked for anatoruical purposes. Previous hardening in alcohol gives to the soft nerve-mass a con- sistence which facilitates its handling, and, at the same time, brings out certain minute details in configuration. Lenhossek recommends that the specimens reqiiired for demonstrations should be furnished with a coating of celloidin. When'-this has been done they may be left exposed to the air for two hours or so without injury. They must be put away in spirit. The great disadvantage of alcohol- preparations is the loss of the natural colour. Artificial staining may be used to remedy this defect. No method is quite satisfactory, but if a section of an alcohol-hardened-brain is put in caustic potash the grey substance becomes much darker again. Soaking in such aniline colours as fuchsin or methyl-violet and subsequent washing does not afford durable preparations, but the staining is distinct at first. [The following method of bringing out the grey and white matter in strong contrast is sometimes useful for class demonstrations : — Slices of spirit-brains, complete coronal sections for example, ai-e placed in a watery solution of tannin or gallic acid; they are then washed for about an hour in running water, after which they are immersed in a solution of ferrous sulphate for a few minutes, and again washed. The large quantities of proteids in the grey matter fix the gallic acid, which subsequently combines with the iron. Very striking diflerentia- tion is thus obtained, but the black staining is seldom restricted to the grey matter; it is apt to sink into such bundles of fibres as are transversely cut.j Brains hardened in bichromate of potassium, and subsequently, after the chrome-salt is washed out in water, placed in alcohol, are useful for macroscopic work. The chrome-salts efiect a staining which varies with the direction and thickness of the nerve-fibres. During the process of hardening the brain, all pressure or traction upon the tissue must be prevented by careful support with cotton-wool and by the use of vessels of suitable form. DRV BRAINS. 27 The difroroncos in colour are made most visible if ilu; preparations, after a month's liardeiiing in ]\1 idler's fluid, are placed in alcohol, to which 1 per cent, of hydrochloric acid is added. Pieces so treated preserve for a long time in <,dycerin their characteristic staining {Ageno and Beisso). The various discomforts attending the use of wet preparations, such as the smell, the fumes of alcohol, the wetting of the fingers in handling them, have led to the introduction of dry methods, which are iiseful at least for the study of external form. The following amongst these methods may be mentioned : — The brain is hardened in alcohol or bichromate of potassium and alcohol, or it is put fresh into an almost concentrated solution of chloride of zinc, in which it remains until it sinks ; after which it is placed in alcohol, changed several times, and left usually for about a fortnight. From alcohol, the brain is put in glycerin, where it remains until saturated ; this takes from a fortnight to a month according to the size of the preparation. The brain is then lifted out of the glycerin and placed where it can drain and dry in the air {Giacomini). When dry it can be varnished. Different regions on its surface can then be painted. Whole human brains are best hardened in chloride of zinc, as the centre is apt to become rotten if they are placed whole in bichromate of potassium. In the case of such thick pieces of tissue as the human brain-stem the central portions, in the pons especially, are apt to soften. The elastic feeling of the preparation shows when this is the case. Schwalbe's method of preparing dry brains is to be recommended. They are hardened in zinc-chloride or spirit (if in zinc-chloride they must be thoroughly washed), dehydrated in strong alcohol (96-97 per cent.), placed in turpentine for about eight days, then in melted paraffin. The best paraffin for the purpose melts at from 45° to 50° C. They lie in the paraffin in an incubator for from five to eight days, by which time they are thoroughly soaked. The paraffin is allowed to drain off, and the preparation to cool in the position which best prevents distortion. In the following account the terms "outer, inner, above, below, anterior, posterior" will only be employed in cases in which the use of the terms has become so universal as to be unavoidable without ambiguity; for instance, the "anterior" and " posterior nerve-roots." The brain being looked upon as the centre we shall speak of pro- ceeding towards it as proceeding brainwards or proximally, and away from it as travelling caudalwards or distally. The terms dorsal, 25 MEDULLARY CANAL. ventral, lateral, and mesial (nearer to the middle line), and median (in the middle line) need no explanation. DEVELOPMENT. ^The portion of the epiblast which is marked out as the seat of origin of the central nervous system constitutes the floor and sides of the medullary groove. It is not simply a uniform plate, but the central portion, out of which the spinal cord will be formed, is distinct from a row of thickenings which lies on either side of the large main fossa. It is these lateral thickenings of the epiblast which develop into the spinal ganglia {His). The medullary folds grow up until meeting in the mid-dorsal line, they convert the medullary groove into a canal. Closure occurs in the neck-region first, and spreads rapidly forwards over the head and more ^a.. Figs. 2 and 3. — Transverse sections through a developing chick, showing the forma- tion of the sensory root-ganglia (after Beard). — ga, Ganglia; dp., epiblast; liy, hypoblast ; m.j), medullary plate ; n, notochord ; net, neuro-epithelial tube ; c. c, central canaL slowly backwards through the dorsal, lumbar, and sacral regions. The rudiments of the sensory ganglia (both cranial and spinal) are formed by delamination from the lateral thickenings just described {Beard'' GANGLIONIC lirDIMICNTS. 29 When the medullax'y plates meet in the mid-dorsal lino these thicken- ings are loft outsido the neural canal, or rather, to define their situation more accurately, they arc just caught within the approacliing lips of the medullary plate and rest upon the dorsal surface of the neural tube. Afterwards they sink down into their permanent positions on either side of the cerebro-spinal axis. The whole of the central nervous system is formed from epiblast, and as the rest of this layer becomes the skin and sense organs, the portion of it which is set aside for the nervous system may be distinguislied as neuro-epithelium. The layer of neuro-epithelium is at first only one cell thick, later on it becomes many layered, owing to proliferation of its cells; but it is particularly noticeable in sections which are stained, so as to bring out the chromatin figures of the nuclei, that these exhibit the changes which usher in cell division only in the cells which lie next to the central canal of the spinal coi'd, and in the case of the brain near its surface (cortex) as well as next to the ventricles. In his recent researches, His has shown that even at the time when the neuro-epithelium constitutes but a single layer, the cells compos- Fig. 4. — The epiblast involuted to form the central nervous system while still a single layer, rabbit (after Hlsi). A round germ-cell lies between the proximal ends of two supporting cells. ing it are distinguishable into two classes. Although they all belong to the same layer, they exhibit from the first a distinction into the more important cells, " germ-cells," which develop into nerve-cells and the "spongioblasts" or supporting cells. The spongioblasts are elongated, palisade-like cells, the oval nuclei of which lie at some distance form the central canal. The germ-cells are round protoplasmic cells which lie amongst the inner non-nucleated segments of the spongioblast (figs. 4, 5, 5a). As the spongioblasts become more elongated, their nuclei sheer over one another, but the supporting tissue of the system is formed by cells which reach throughout its whole thickness. The substance of these cells is not homogeneous, but consists of a formed part disposed in filaments and a soft transpai-ent substance in which the filaments are ^o NEUROBLASTS AND SPONGIOBLASTS. embedded. The fibrillar elements are disposed so as to form a membrane, the " internal limiting " membrane which supports the epi- thelium of the central canal, and they also constitute the scaffolding for both grey and white matter. Throughout the grey matter the spongio- blasts are disposed radially with tangential or oblique connecting bands. "When they reach the outside of the grey matter, they break up into a close irregular plexus, the " border veil," as His has called it, an expression which may be Latinised as "velum confine," because . «p Fig. 5. — A group of spongioblasts, the basal ends of which form the internal limiting membrane (after His). — g, Germ-cell ; tr, cells transitional between germ-cells and neuroblasts; sp, spongioblasts. Fig. 5a. — Similar to 5, but somewhat more advanced. The neuroblasts (nb) are giving off axis-cylinder processes. it prevents the migration farther outwards of the neuroblasts while it gives passage to thin processes. It is along this close outer net- work that the longitudinally-running fibres are directed, and it con- sequently becomes the scaffolding of the white matter also. The nerve-cells, on the other hand, are formed by the division of the germ-cells, the daughter-cells of which, becoming pyriform, are termed "neuroblasts." For some considerable time the neuroblasts have one process only, the axis-cylinder process, which is directed outwards towards the anterior roots of the nerves. Subsequently the neuroblasts develop lateral dendritic processes. POSTEIIIOK KO(yr. 31 In tho earlier fitaj^os (jf dov(4oi.in.-nt tlxf ccrcbro-spinal axis is altogether occupicil in forniing nictor-eells and 6bres. Its neuroblasts take no part in the formation of sensory n(Tves. The fibrc^s of the posterior root arise as outgrowths of the cells of the ganglia. Those cells arc at first bipolar; one of their processes extending outwards into the sensory nerve, the oth.-r inwards to the cord. Subsequently •y^r. %. ■wc. '/ J , / I » jL mU-K Ficr. 6. -Transverse section of half the spinal cord of a trout-embryo (after l^ts). ° — c c Central canal ; mli, membrana limitans interna ; g, germ-cell ; sp, spongioblast; nb, neuroblast; loc, white columns, of which the supportmg tissue is a close net-work formed from the ramifications of the outer segments of the spongioblasts. the centripetal and centrifugal processes are placed in direct continuity by the cell body withdrawing itself away from them at right angles. Thus while the cells continue to provide for their nutrition through the vertical limb of the T, the passage of the afferent impulses through its body is rendered unnecessary. The account of the early stages in the histogeny of the ceUs gijen by His still leaves some points unsettled, as, for instance, the ongin of such nerve-cells as have no axis-cylinder processes, or of the 32 MYELIN-CELLS. neurogleia-cells of Deiters, unless these are all derived from spongio- blasts. A similar obscurity enshrouds the origin of the myelin-cells that invest the axis-cylinder processes of the neuroblasts. The origin of the neurogleia-cells has been much debated. By some they have been considered as immigrant-cells, white blood corpuscles, or cells of connective-tissue rank, but Vignal concludes from his observations that they, like the nerve-cells, are epithelial derivatives. In the spinal cord, motor nerve-cells are recognisable as such, at the tenth week of intra-uterine life. They make their appearance in two principal groups corresponding to the anterior and lateral horns. As already remarked, the fibres of the posterior root are outgrowths of cells which lie in the sensory ganglia outside the cerebro-spinal axis. Although dilated at its anterior end into the brain, the grey- matter which borders the central canal is formed in the same manner throughout its whole length. Beneath the lining epithelium lies the layer of cells, which, as shown by the form and prominence of the chromatin-skeins in their nuclei, are undergoing active proliferation into nerve-cells. From the nerve-cells fibres extend outwards as motor nerves. It seems pretty certain that these fibres (axis-cylinders) extend without a break from the nerve-cells in the axis in which they take origin to the striated muscle which they innervate; the fibres destined for involuntary m\iscle, on the other hand, reach, in the first instance, to cells of sympathetic ganglia only, and are by means of these broken up into a number of finer filaments. Inside the cerebro-spinal axis, as well as throughout their peripheral course, the fibres are supported by myelin-cells, which, wrapping themselves round the axis-cylinder, develop in their substance a special phosphatic fat, and in this way constitute protecting and insulating tubes. Whether the myelin-cells arise from epiblastic or mesoblastic elements has not as yet been made out. While within the central nervous system the axis-cylinders and their myelin-sheaths are supported by the neurogleia, and it is almost necessary to point out that the origin of the myelin-sheath of intra- axial fibres is far from clear, for, according to Boveri, it is not broken up into segments. ScMeffer decker, on the other hand, asserts that " nodes of Eanvier" are to be found within as well as without the cerebro-spinal axis. The white columns appear later than the grey matter. Their origin has not as yet been satisfactorily made out. Probably the motor fibres grow downwards from cells of the cortex, while sensory fibres originate in cells of the cord and grow upwards. The anterior end of the involuted tiibe of epiblast is dilated into DEVELOPMENT OK IlKAIX. 33 the cerebral vesicles (fig. G). From the anterior vesicle the cerebrum grows out as a secondary fore-brain. At first this n(;\v vesicle is single, but it soon divides into two, each conmiunicating with tho primary fore-brain by an aperture, the foramen of Monro. The formation of grey matter within the secondary vesicles is confined to the posterior and inferior parts of tlie wall of the ventricle. Here, however, it occurs extensively as the corpus striatum, which bulges into the ventricle, and is divided into two parts by a deep groove. The optic thalamus and corpus striatum are, therefore, widely separate in their origin, the former being a local development of the grey matter bordering the primary fore-brain, while the latter is formed in the wall of the secondary vesicle. But little remains to be said with regard to the further development of the central grey matter — the formation of neuroblasts from the cells of its inner layer — their migration outwards — the radiation of their processes towards the pori})hery — the investment of the grey matter with a sheath of longitudinal fibres occur throughout its whole length. In the case of the brain, on the other hand, the seat of the chief formative activity is transferred to the surface of the vesicles where the neuroblasts, which are afterwards to become the cells of the cortex of the cerebrum, corpora quadrigemina and cerebellum, commence their existence. To follow all the changes in the walls of the cerebral vesicles by which the formation of the brain is accomplished would require a special treatise on embryology, nor can the task be attempted at present owing to the incompleteness of our knowledge, but certain points which have the most important influence upon our conception of the fundamental structure of the central nervous system may be briefly referred to. The cranial nerves are formed in the same way as the spinal nerves, their motor fibres being outgrowths from cells of the central grey matter, the sensory fibres originating in cells of the sensory ganglia, and growing inw^ards into the central grey matter and outwards to the surface. To this descx-iption the olfactory and optic nerves do not seem, at first sight, to correspond, for both these cranial nerves, or rather the " tracts," by means of which their connection with the brain is established, appear as hollow outgrowths from the brain ; the optic vesicles being diverticula of the fore-brain ; the olfactory vesicles being, apparently, diverticula of the hemispheres of the secondary fore- brain. In the case of the olfactory tracts, an earlier stage, in which they were connected with the dorsal wall of the primary fore-brain in the same manner as other sensory nerves, has been described by Marshall. The relation of the first two cranial nerves to the central 3 34 VELUM INTERPOSITUM. system is, however, complicated by the fact that elements, which else- where lie in the sensory ganglia and cerebro-spinal axis, viz., bipolar cells, " gelatinous " substance, and multipolar cells, are situate in the olfactory bulb and retina in immediate juxtaposition with the epithelium of the sense organs. There appears to be this great phylogeri,etic difference between the nose and eye and other sense organs that, owing to their situation at the anterior end of the body and consequent advantages for obtaining information, they very early became highly specialised, and the portion of nerve plexus which lay beneath them was so intimately united to them that its subsequent withdrawal into the axial system, as in the case of other segmental sense organs, was impracticable. The roofs of the anterior cerebral vesicle and the back part of the posterior cerebral vesicle (fig. 7, Zh and Nh) remain undeveloped. The ventricular epithelium is simply supported by pia mater, in which ramify the vessels of the choroid plexus. The roof of the anterior vesicle is a flat plate, triangular in shape, the " velum interpositum." The hemispheres of the cerebrum project backwards, and press up against the sides of the anterior vesicle. Where they touch the margins of the velum interpositum this membrane grows out side- ways, pushing the wall of the secondaiy fore-brain in front of it, and so involuting it into its ventricle, where it rests as a free fold upon the corpus striatum. In this way a choroid plexus is carried into the lateral ventricles, the velum interpositum being grasped by the wall of the cerebral hemisphere from the back of the foramen of Monro to the uncus. By the subsequent downward growth of the hemisphere, as well as the increase in thickness of the crus cerebri, the postero- external angle of the velum interpositum is carried downwards and forwards round the crus. If the finger were placed beneath the wing of a butterfly to represent the crus cerebri and the back of the wing were then bent downwards I'ound the finger, the form of the velum interjiositum would be accurately represented. The margin of the curved slit, through which it pushes its way into the lateral ventricle, is thickened by longitudinal fibres. The bundle on the convexity of the slit is the fornix. The bundle in its concavity is the stria cornea. The pineal gland arises as a hollow outgrowth from the back of the roof of the fore-brain ; the pituitary body as a hollow downgrowth from its floor which applies itself to the back of a diverticulum from the buccal cavity, which comes up through the hole in the floor of the pituitary fossa of the sphenoid bone. The corpus callosum is, in its full development, a secondary growth which breaks through the wall of the hemisphere, sweeping away the greater part of the arcuate convolution of Arnold. Its anterior CEllEllRAL VESICLES. 35 end is first, fonard iiiiil <,'n)\vlli pioi-ccils from before Imckwjirds. Tho remiiina of tho arcuato convolution aro seen in the wtriie nieduUares seu obtectio, or nerves of Lancisi, and in the subcallosal convolution. Tho portion of the wall of the heniisphcre, which is intercepted between tho cori)US callosnni and the fornix, rcnnains undeveloped as the septum pelluciduni or wall of the so-called lifth ventricle.*] ms DIVISIONS OF THE CENTRAL NERVOUS SYSTEM. From the earliest time the system has been described as the elongated spinal COrd (med\illa sinnalis), and the more massive and globular brain (cerebrum in its wider sense or encephalon). Anatomically the brain and spinal cord are not sharply divided, and it has, there- fore, been necessary to call the contents of the spinal canal the spinal cord, and to consider it as separated from the brain by a }»lanc parallel to the antei'ior surface of the atlas. The brain is again subdivided into great brain (cei-ebrum), small brain (cerebel- lum), and medulla oblongata. Usually the medulla oblongata is regarded as the segment between the proximal end of the spinal cord and the pons varolii, the latter being looked upon as belonging to the cerebellum. Some people {e.g., Jlerkel) include the pons with the medulla oblongata. The part in front of the pons belongs to the great brain. The division most widely accepted nowadays is based upon developmental study. In the embryo, the nervous system forms a tube closed anteriorly. This tube is swollen out into several smooth vesicles which divide it into, at first, three, and subsequently four portions, lying one behind the other. The divisions are named from before backwards, the anterior, middle, and posterior cerebral vesicles. From the anterior vesicle grows out the secondary anterior vesicle. At first this is single, but soon it * For a more detailed account of the development of the brain see Quain'a Anatomy, Ninth Edition, vol. ii., pp. S18-S50. Fig. 7. — The cerebral vesicles. — SVh, Secondary fore-brain; Zh, 'tween-brain ; Mh, mid- brain ; Hh, hind-brain ; Nh, after-brain ; mx, longitudinal fissure; FM, foramen of Monro; MR, central canal. 36 CENTRAL AND PERIPHERAL GREY TUBES. is divided by the downgrowth of the falx into the two cerebi-al hemispheres. The sevei'al portions of the brain are developed from one or other of these five divisions. 1 . Secondary anterior cerebral vesicle {Svh) forms the cere- brum with its cortex, corpus callosum, fornix and anterior commissure, nucleus lenticularis, and nucleus caudatus. 2. Primary cerebral vesicle (■Zh), or 'tween-brain, includes the optic thalami, infundibulum, optic commissure, and corpora albicantia. 3. Middle cerebral vesicle (JZ/O forms the mid-brain ; corpora quadrigemina and peduncles of great brain. 4. The anterior of the two hinder vesicles (Hh) forms the hind-brain ; cerebellum with its peduncles and the pons. 5. Posterior of the two hinder vesicles (-A'A) forms the after- brain or medulla oblongata. All the structures developed from the secondary anterior vesicles belong to the cortex or brain-mantle, while the structures to which the remaining four vesicles give rise constitute, with the exception of the cerebellum, the brain-stem (caudex). The nuclei lenticularis et caudatus are included, for the most part, in the description of the brain-stem, leaving only the cortex of the great brain for the mantle- formation ; recently, however, it has been shown that the nucleus caudatus, as well as the lateral part [and perhaps the central part too] of the nucleus lenticularis, ought to be included amongst cortex- formations. [The morphological relations of the cortex to the rest of the cerebro- spinal axis, is a matter of the greatest importance, involving, as it does, the question of the primary constitution of the nervous system. The brain is distinguished from the spinal cord by the possession of an envelope, not complete, but covering the greater part of the surface of its three vesicles, as the cortex or mantle-formation. Throughout the whole system the " axis " consists of a tube of grey matter bordering the central canal, invested by a sheath of longitudinally running white fibres. 2Ieynert recognised the continuity of the grey matter bordering the central canal, and termed it " centrales Hohlengrau," withovxt, however, giving to the term any strict morphological or anatomical limitations. From the translator's point of view, all the gi'ey matter of the lower system, including therein the optic thalami, constitutes the central grey tube. This receives sensory, and gives origin to motor nerves, none of which appear to pass through its plexus without joining with it, but each nerve terminates in, or springs from, the portion of the grey matter belong- ing to the metamer which the nerve supplies. In its fore part the CORPUS STKIATl'.M. 37 nt'rvous system is dilated into (lie vesicles already descrilxHl, and here a marked dillei-euce iu anatomical arrani,'eineiit is seen. The; white matter which invests the central grey tuhe is in turn surrounded hy a layer of grey matter of altogether ditferent constitution. This second investment constitutes the cortex (»f the cerebellum, corpora quadrigemina, and cc^rebral hemispheres. In the lowest vertebrates the cerebellum is, as a rule, small ; although, even amongst fishes, it may attain, as in the shark for instance, a considerable size and com- plex structure. The corpora bigemina are larger proportionally in lower vertebrates than they are in man. The cortex of the cereljrum is, however, a late development ; only in mammals does it constitute an important layer. In reptiles and birds the mass of the cerebral hemisphere consists of what in mammals we know as corpus striatum. Does the corpus striatum belong to the central or the peripheral grey tube ? It does not, like the optic thalamus, contain the primary centres of any sensory nerves. The nucleus caudatus is intimately connected with the cortex, for its head, as shown in the accompanying diagram after Wernicke, rests on the anterior perforated space, its tail is continuous with the cortex of the temporal lobe. Fig. 8. — Diagram representing the counectiou of the nucleus caudatus with the cortex of the frontal and temporo-sphenoidal lobes. Nucleus caudatus, nucleus amygdaleus, and claustrum are continuous at their temporal extremities. The nucleus lenticularis is sunk more deeply beneath the cortex, and completely invested in white matter. In structure and development, however, the lenticular and caudate nuclei strongly resemble one another, and all the evidence we at present possess is in favour of assigning them both to the same position in the system, as parts of the peripheral grey tube. The optic thalamus, on the other hand, is to be regarded as the anterior extremity of the central grey tube.] The entrance into the lateral vesicles from the fore-brain constitutes eventually the foramen of INIonro ; the cavities of the brain vesicles remain as the permanent ventPicles. 38 SPINAL CORD. The cavity of the secondary fore-brain becomes the lateral ventricle. ,, „ primary fore-brain ,, the third ventricle. „ ,, mid-brain „ the aqueduct of Sylvius. ,, ,, hind-brain ,, the fourth ventricle. ,, ,, medullary canal ,, the central canal. The several divisions of the central nervous system indicated in the account just given will be briefly passed in review in this section. A. THE SPINAL CORD. The human spinal cord (figs. 9 and 10) forms a cylindrical column of 40 to 50 cm. (18 inches) in length, reaching in the upright position from the first cervical to the first or second lumbar vertebra. In the child it reaches farther [the third lumbar at birth]. In the fcetus farther still. When the body is bent sharply forwards the lower end of the cord in the adult only reaches to the twelfth dorsal vertebra. Eeger determined that when the body is strongly bent the spinal cord is stretched by 6"8 per cent, of its length. The thickness of the cord varies but little in diflTerent individuals ; treating its cross-section as a complete circle, one finds that its diameter above the cervical swelling varies from 8 to 11 mm. ; in the dorsal cord, between the two swellings, from 6 to 9 mm. In two situations it presents spindle-shaped swellings, due almost entirely to an increase in its transverse diameter. The first of these, the cervical swelling, has at the level of the fifth or sixth cervical vertebra a breadth of 15 mm., the lumbar enlargement lying at the level of the lower dorsal vertebrae attains a breadth of 11 to 12 mm. The antero-posterior diameter increases in these sitviations by 1 to 2 mm. only. The lumbar swelling (intumescentia lumbalis) terminates directly in the conus medullaris. The latter forms the end of the cord. To it, however, is attached a thin thread of some 25 cm. in length, the filum terminale. Flesch has shown that the cord is so constituted as to present — after the removal of the pressure of the vertebrfe — the curves which are seen in it when in situ,. In the middle line of both dorsal and ventral surfaces it presents a fissure, the posterior and anterior longitudinal fissures. The former is distinct at the surface only, the latter shallow but broad. The dorsal roots originate in an almost uninterrupted line 2 to 3 mm. laterally to the posterior fissure. "When they have been cut away, the place of their origin is still indicated by a furrow, the dorse- SPINAL CORD. 39 lateral groove. It is slmllow for the most part but somewhat (hcply cut into the conl in the cervical region. The anterior roots arise in iTi^ Rar-iJj/ I'/M Fnl If • ''^r-Fslp Jl iifiiw RpcS-p- Gsp<^, Jc V -Fnp -Fnl BpdSy ft J }[d Ce Fi". 9.— Caiidal end of spinal cord from ventral surface {natural size). — //, Lumbar enlargement ; Cm, conusmedul- laris ; Ft, filum terminale. The anterior nerve-roots on the left side are removed, on the right side [Ua] they enter into the formation of the caiida equina (Ce). Fsla, fissura longitudinalis ant. ; Slv, sulcus lateralis ventralis ; Fna, funiculus anterior ; Fl, funiculus lateralis. Fig. 10. — Cervical enlargement of the spinal cord from the dorsal side (natural size). Besides the cervical enlargement (Jc) a portion of the dorsal cord is also visible {Md). All the posterior roots are cut away on the right side, and on the left side the sixth and seventh cer\-ical (Epc 6 and 7) and the third dorsal (/?/-(/ 3) are left as far as the spinal gangUa (Gap). [The division of the posterior roots into fasciculi, as shown in the picture, is hardly true to nature.] — Fslp, Fissura longitudinalis post. ; Spd, sulcus paramedianus dor- salis; Sid, sulcus lateralis dorsalis ; Fnp, funiculus posterior ; Fnl, funi- culus lateralis ; Fng, funiculus gracilis ; Fnc, funiculus cuneatus. many separate bundles spread out transversely as well as longi- tudinally. The furrow left after their removal (the so-called antero- 40 SPINAL NERVE-ROOTS. lateral groove) is very indistinct. The roots incline on leaving the cord caudally as well as laterally, the inclination downwards being sharper the lower their situation on the cord. By the time the lumbar swelling is reached the roots lie almost parallel with the Fig. 11. — The base of the brain, as far as the optic tracts. Tlie cei-ebellum is almost completely removed ; the secondary fore-brain and all structures which lie in front of the optic tracts are cut away ; on the left side the nerve- roots are retained ; on the right side they are, witli few exceptions, removed. //, Nervus opticus ; ///, nex'vus oculomotorius ; ///', lateral accessory portion of oculomotorius ; V, nervus trigeminus ; VI, nervus abducens ; VII, nervus facialis ; VIII, nervus acusticus ; IX, nervus glossopharyngeus ; X, nervus vagus ; XI, nervus accessorius Willisii ; XII, nervus hypoglossus ; Cgl, corpus geniculatum laterale ; Ch, chiasma nervorum opticorum ; Cm, corpus mammilare ; Fna, funiculus anterior ; Fnl, funiculus lateralis ; Fob, fasciculus obliquus pontis ; Focp, foramen caecum posterius ; Fsla, fissura longitudinalis anterior meduUse ; Jf, infundibulum ; LmP, tract connecting lemniscus and pedunculus cerebri ; Oi, inferior olive ; Pp, pes pedunculi cerebri ; Po, pons ; Py, pyramid ; Eac 1, anterior root of the first cervical nerve ; Shpp, substantia perforata postei'ior ; SI III, sulcus oculomotorii ; Slpp, sulcus substantive perf. post. ; Stv, sulcus hateralis ventralis ; Spo, sulcus postolivaris ; Sppy, sulcus parapyramidalis ; Til, tractus nervi optici ; Tbc, tuber ciuereum ; Trie, trigonum intercrui'ale ; Vm, motor trigeminal root ; Vs, sensory ditto. TMKIK I'lIYSIOLOGY. 4I cord ; the conus incduUjiris and filum terininale lie in the middle of a considerable Imndlo of nerves, t\w whole constituting the Cauda equina. On account of the obliquity of the roots one can tell in any detached piece of cord which is its proximal and which its distal end. This, again, is of great use in helping us to distinguish the left side from the right in cases of unilateral lesion. In the cervical cord a still more distinct furrow is to be seen about 1 mm. laterally to the posterior longitudinal fissure, becoming more distinct as we travel cerebralwards, the sulcus paramedianus dorsalis seu intermedins posterior, Spil. The cord is divided by these furrows into several longitudinal columns distinct from one another on the surface. 1. Anterior column, Fna, lying between the anterior fissure and the line of exit of the anterior roots. 2. Lateral column, Fnl, on the outer side of the anterior column, between this and the posterolateral sulcus. 3. Posterior column, Fnp, between the posterior longitudinal and dorsolateral sulci. In those regions in which a paramedian sulcus is visible, the posterior column is again divided into two, Burdach's column, File (funiculus cuneatus) ; and Goll's column (funiculus gracilis), Fng. Usually 31 pairs of spinal nerves are reckoned, viz., 8 cervical, 12 dorsal, 5 lumbar, 5 sacral, and 1 pair of coxygeal nerves. One or two microscopical coxygeal nerves may be usually found, however, in the filum terminale (Hanber). The separate groups of anterior roots with the muscles which they innervate constitute not so much anatomical as physiological associa- tions. Ferrier and Teo have shown that stimulating a particular root in the ape's cord gives rise to a definite complex action corresponding to the habits of the animal. For example, stimulation of the first dorsal root, results in such a movement as in picking a fruit ; the eighth cervical, the scalptor ani action ; seventh cervical, a movement as if the body were drawn up on a branch clasped with the hands; sixth cervical, the hand is moved to the mouth. 42 B. THE BRAIN. 1. THE AFTER-BRAIN. The cross-section of the system increases very rapidly in its trans- verse diameter in front of the first cervical nerve. The spinal cord forms into the medulla Oblongata. This reaches to the back of 31v Fna jSpoFba Fig. 12. — A preparation similar to tliat iu fig. 11, seen from the left side. Natural size. Nerve roots are for the most part cut away. — //, Nervus opticus ; IV, trochlearis ; VIII, acusticus; Alp, ala pontis ; Brc, brachium conjuncti\'Tim (superior cerebellar peduncle) ; Brqa, anterior brachium ; Brqp, posterior brachium ; Cfjm, corpus geuiculatum mediale ; Cgl, corpus geniculatum laterale ; Ch, chiasma nervorum opticorum ; Crd, corpus restiforme ; Fba, fibrte arcuatre; Fna, funiculus anterior ; Fnl, funiculus lateralis ; Fnp, funiculus posterior ; Fob, funiculus obliquus ; Glp, glandula pinealis ; Lm, lemniscus or fillet ; 01, inferior olive ; Po, pons, cut across at Po-\- ; Pp, pes pedunculi ; Pu, pulvinar thalami; Py, pyramid; Qa, corpus quadrigeminum anterior; Qp, corpus quadrigeminum posterior; Sid, sulcus lateralis dorsalis; Sim, sulcus lateralis mesencephali ; Slv, sulcus lateralis ventralis ; Spo, sulcus postolivaris ; Spt, sulcus corp. quad, transversus ; T II, tractus opticus ; TcE, tuberculum cinereum Eolandi ; Tpo, taenia pontis ; Tpt, tractus peduncularis transversus ; Tho, thalamus opticus, cut at Tho + . SULCI OF MEDULLA OBLONGATA. 43 the groat cross-fibres of the pons. It attains a length of about .J cm. On tho surface of the medulla several details in moulding are to bo noticed. We will describe the furrows first. For the most part the furrows are longitudinal, and continue upwards the sulci of the cervical cord. Tho anterior fissure, Fla (fig. 11), extends on the ventral surface as far as the back of tho pons ; it is very shallow in tho distal part, but deepens in front, and ends at last, where the pons fibres cross, in a blind hole, foramen ca;cum posterius, Focp. A rather shallow fissure forms an acute angle with the anterior fissure at the hinder cud of the medulla, and extends forwards as far as the border of the pons, sulcus parapyramidalis, Sppy. The furrow corresponding to the anterior roots, hardly to bo seen in the cord, is more distinct in some parts of the medulla oblongata, sulcus lateralis ventralis {seic intei-nus oliva;), Slv. Here and there, however, it is obliterated by crossing fibres. The following sulci belong to the dorsal surface (figs. 12 and 13) : — 1, Sulcus lateralis dorsalis, Sid; 2, sulcus paramedianus dorsalis, Spd; 3, in the middle line, posterior longitudinal or dorsal fissure, Fslp. The first two incline laterally up the medulla, the sulcus lateralis can be followed to the pons, the sulcus paramedianus soon disappears. The fissura long. dors, ends suddenly where the central canal opens out into the fourth ventricle, and the posterior columns diverge to the two sides. In the proximal part of the medulla appears a sharply marked fissure more than 1 cm. long, the sulcus postolivaris. It extends from the margin of the pons to the sulcus lat. vent, which it joins. In the rest of its extent, it lies between this fissure and the sulcus lat. dors. The swellings which these furrows throw into relief are not equally prominent in all brains. The anterior columns of the cord are pushed aside by the pointed extremities of the pyramids (fig. 11), Py. Passing up beneath the ])yi'amids they disappear from the surface. A very prominent swelling, the inferior olive (eminentia olivaris), 6 to 7 mm. broad by 12 to 14 mm. long lies between the sulci ventralis lateralis et postolivaris. A bundle of fibres, fibra; arciformes, Fba, can invariably be seen arching round the hinder end of the olive and, to a certain extent, spread over it. It is not, as a rule, raised much above the surface. Especially in children's bi-ains, a little rounded eminence, tuberculum cinereum Rolandi, TcR, is to be seen laterally to the olive near its distal end. The funiculi siliquas are minute longitudinal columns occasionally described on the mesial or lateral side of the olive. 44 Fig. 13. — Hind-brain, mid-brain, and 'tvveen-brain from the dorsal surface {natural size). The greater part of the secondary fore-braia is removed by four sections, one horizontal, one frontal, and two sagittal. Most of the nerve- roots are cut away. — IV, N. trochlearis ; VII, nervus facialis ; VIII, nervus acusticus ; Ac, ala cinerea ; Bix, brachium cerebelli ad corp. quad, cut at Brc + ; Brqa, brachium corp. quad, anterior ; Brqp, brachium corp. quad, posterior ; Cgm, corpus geniculatum mediale ; CI, clava ; Goa, commissura anterior ; Com, commissura mollis ; Crst, corpus restifomie ; Cscr, calamus scriptorius ; Et, eminentia teres ; Fcl, columnse fornicis ; Fnc, f imiculus cuneatus ; Fng, fimiculus gracilis ; Fnl, f imiculus lateralis ; Foa, fovea anterior ; Frv, frenulum veli anterioris ; Fslp, fissura longitud. posterior ; Gcc, genu corporis callosi ; Gli, ganglion habenulae ; Glji, glandula pinealis ; K, conductor sonorus vel tractus auditorius; Lc, locus coeruleus; %, lingula; Lm, lemniscus or fillet ; M, situation of foramen of Monro ; Nc, nucleus caudatus ; Pile, pedunculus conarii ; Po, pons at Po + cut across ; Pp, pedimculus cerebri ; 45 -Thcf Pu, puhinar ; Qa, corp. quad, anteriora ; Qp, corp. quad, posteriora ; Slch, sulcus choroideus ; Sid, sulcus lateralis dorsalis ; Sim, sulcus longitudinalis mesencophali ; Slmd, sulcus longitudinalis medianus ventriculi quarti ; Spd, sidcus paramedianus dors. ; Spl, septum pellucidum ; Sql, sulcus corp. quadrig. longitudinalis ; Sqt, sidcus coi'p. quadr. transversus ; Stc, stria cornea ; Stm, striaj meduUares acusticaj ; Tac, trigonum acustici ; Tha, tuberculum an- terius; The, tuberculum cuneatum; Th, trigonum hypoglossi; Thos, thalamus opticus ; Trh, trigonum habenulai ; TvS, trenia ventriculi tertii ; Via, anterior horn of lateral ventricle ; Vma, velum medullare anterius ; Vspl, ventriculus septi pellucidi. The part of the medulla which lies between the sulcus lat. dors, and the fourth ventricle, is named the restiform body (corpus restiforme, 46 SURFACE OF MEDULLA. inferior peduncle of the cerebellum, brachium cerebelli ad medullam oblongatam), Crst. Looked at from the surface merely, the corpus restiforme appears as if it were the continuation upwards of the posterior column of the cord. Both constituents of the posterior column swell out somewhat in the region of the calamus scriptorius. The swelling of the funiculus gracilis, which is known here as the clava, CI (or posterior pyramid), is more distinct than that of the funiculus cuneatus (tuberculum cuneatum), Tbc. A number of nerves arise from the medulla. The origin of the first cervical nerve, Rac. i, is also prolonged upwards into this region. Between the pyramid and the olive, and extending almost the whole length of the latter, come out the root^fibres of the hypoglossus (fig. 11), XII. Between the olive and the corpus restiforme, an uninterrupted series of roots take exit to join the n. accessorius Willisii, XI, the vagus, X, and the glossopharyngeal, IX. The larger part of the n. accessorius arises in the spinal cord; the root-fibres which pass out through the lateral column extend as far downwards as the fifth pair of nerves. It is impossible to distinguish with certainty the upper roots of the n. accessorius which are attached to the medulla in the region of the olive from those of the vagus, or the vagus fibres from those of the glossopharyngeal. All one can do is to assign the more distal fibres to the accessorius, the more proximal to the glossopharyngeal. In the furrow between the pons and the pyramid, 2 mm. from the median line, the n. abducens arises in several bundles, quickly uniting togethei', which pass out in the transverse furrow between the pyramid and the pons. Bundles of fibres, Stm (fig. 13), take origin in the floor of the fourth ventricle, and, encircling the corpus restiforme, just before it sinks into the cerebellum, join with another bundle, VIII (fig. 11), which comes out from the corpus restiforme itself, to form the n. acusticus. A little swelling at the edge of the fourth ventricle, the taeniola or fasciola cinerea, corresponds to one of the centres from which the eighth nerve takes origin (its accessory nucleus). Mesially to the auditory nerve and rather close to its ventral side the facial nerve takes exit in a strong bundle. 2. THE HIND-BRAIN. The pons, Po, comprises an immense tract of crossing fibres, measuring about 3 cm. from before backwards, and 4 cm. from side to side. At either side the pons constitutes a more rounded column, the middle cerebellar peduncle (brachium cerebelli ad pontem), fig. 13, Po -r , which passes dorsally into the cerebellum. This closes the CEREBELLUM. 47 ring through whiih llio columns of the hiiul-hniiii must pass on their road forwards. The cerebellum, looked at from al)ov(! (dorsally), presents a deep notch, ineisura niarsupialis, Jm. On its ventral or under margin is a shallower, broader notch, ineisura semilunaris, Isl. The former contains the process of the dura mater known as the falx cerebelli, while the latter is fdled u}) with a portion of the mid-brain. On the dorsal surface a ridge extends from the one notch to the other, from which (as from the roof-tree of a house) the two surfaces of the cere- bellum slope away. On either side of this ridge a shallow groove, sulcus longitudinalis superior cerebelli, Slsji, marks ofi" the superior vermis, Vrsp, from the lateral lobes. The dorsal surface of the cerebellum is completely covered in cortex- substance. spm Fig. 14. — CerebeUum, dorsal view. Natural size. The mid-brain is cut across behind the corpora qnadrigemina at J//t. — Al, Lateral angle of hemisphere ; II, hemispheres of cerebellum, de.dera ct sinistra; Jm, ineisura marsupialis ; Jsl, ineisura semihuiaris ; Lg^ lingula ; Lsa, lobus superior anterior ; Lsm, lobus superior medius ; Lsjy, lobus superior posterior ; Shm, sulcus horizon- talis magniis ; Ssa, sulcus superior anterior ; Ssp, sulcus superior posterior ; Vrsp, vermis superior ; | cer, pointing brainwards ; and J, spin, spine- wards. The ventral side of the cerebellum can only be seen by cutting through the massive columns which unite it with the rest of the hind-bi'ain. On this side the median part or vermis inferior, Vrif, is sharply cut off by deep furrows, sulci longitudinales inferiores, from 48 CEEEBELLUM. the lateral hemisphere. The great lateral hemispheres arch over and hide the vermis inferior, shutting it up in the vallecula. It can only be brought into view by pressing the hemispheres aside. The anterior part of the vermis inferior does not reach into the incisura semilunaris. A layer of white substance extends brain- wards in front of it, the velum meduUare anterius or roof of the front part of the fourth ventricle ; on this is borne a recurved part of the superior vermis. It follows from this that the superior vermis is much longer than the inferior. The ventral surface of the cerebellum is not entirely covered with grey matter. cep Jsl \7tlCi Fig. 15. — Cerebellum from the ventral side. Nat. size. The cerebellar peduncles are cut at x . The anterior lamina tectoria is cut away from its attachment to the mid-brain. The lobus anterior inferior is broken away from the left hemisphere. — Al, Angulus lateralis; Fl, flocculus; Fist, pedunculus flocculi; Hdex, right hemisphere ; Hsin, left hemisphere ; Jm, incisura marsupialis ; Jsl, incisura semilimaris ; Lc, lobulus centralis ; Lia, lobus inferior ant.; Lim, lobus inf. med.; Lip, lobus inf. post.; Lsa, lobus sup. ant.; Lsm, lobus sup. med.; Lsp, lobus sup. post.; No, nodulus ; Pyc, pyramid; Sjl, sulcus flocculi; Shm, sulcus horizontalis magnus ; Sla, sulcus inf. ant.; Sip, sulcus inf. post.; Slif, svdcus longitudinalis inf.; Ssa, sulcus sup. ant.; Ssp, sulcus sup. post.; Uv, uvula; Vma, velum meduUare anterius; Vmp, velum meduUare posterius ; Vrif, vermis inferior. The surface of the cerebellum is broken up in a characteristic way by a large number of fuPPOWS. They are not, as a superficial exami- nation would lead one to think, of anything like equal depth. If the FISSUIIKS OF CEREIJELLUM. 49 cerebellum is cut at right angles to the direction which these furrows assume, it will be sinni that some of them extend so much deeper than others as to make it possible to divide the organ into lobes (tig- IG). There is no uuil'uriaity in the classilication of these lobes and their nomenclature. The lobes are divided by secondary furrows into lobules, which again l)ear convolutions. The greatest fissure is the sulcus horizoutalis magnus, Shm, which divides the cerebellum into an upper [in lower animals anterior] and lower [or posterior] part. This deepest and most constant of the fissures of the cerebellum originates at the middle peduncle, and extends around the cerebellum almost parallel to its border. At first it lies a little on the under surface, it then extends over the border, and for a short distance before its termination belongs to the ujiper surface (fig. 14). The fissures on the upper surface are thickly set. They form arches parallel to the hinder border of the cerebellum and the incisura semi- lunaris, the centre of their curvature being situate in the region of the corpora quadrigemina. Two of these are fairly constant and important ; they divide the upper surface into three divisions. They are named sulci cerebelli superiores anterior, Ssa, et posterior, Ss}). The anterior fissure (fig. 15) commences on the middle peduncle and crosses the vermis to join the fissure on the opposite side. The upper surface of the vermis is divided by it into two almost equal segments (tig. 14). The posterior fissui-e commences in the great hoi-izontal sulcus, a little in front of the postero-external angle of the cerebellum. Crossing the upper surface it almost i-eaches the horizontal sulcus again at the spot where the latter passes on to the vermis, without, however, actually joining it. The fissures on the under surface of the cerebellum present the same want of regularity. Two principal fissures are, however, again to be recognised, sulci cerebelli inferiores. anterior et posterioi', Sia and Sip. Another short but deep fissure leaves the great horizontal fissure in a gentle cui-ve directed backwards, and ends in the groove between the cerebellum and the medulla, SJl. The anterior inferior sulcus does not commence as does the posterior inferior in the great horizontal sulcus, but in the floccular sulcus. The disposition of the sulci on the vermis is best seen in a median sagittal section (fig. 16). Both its superior and inferior surfaces are crossed by three chief fissures which are too short to need separate names. As a rule, no distinct furrow separates the upper from the under vermis ; the continuation across the middle line of the great horizontal fissure may be used for this purpose. The above-named fissures divide the surface of the cerebellum into 4 50 LOBES OF CEREBELLUM. lobes and lobules. On the under surface at any rate they are not sufficiently constant to allow of a uniform nomenclature. The hGmisphePes are divided into — on the upper surface : — Anterior lobG, Lsa, seu lunatus anterior, ) T..-.JJT r 4- ■ > Lobus quadrangulus. Middle „ Lsm, „ „ posterior, J ^ * Posterior „ Ls]^, „ semilunaris superior. On the under surface : — Anterior lobe, Lia, seu amygdala, seu tonsil. Middle „ Lim, „ \ S^^^^^^^- ^ , • ^ ( cuneiiormis, setc biventer. Posterior ,, Lip, „ semilunaris infez'ior. Pig. 16. — Sagittal section through the brain in the median line. Eight half. Hat. size. Of the cortex of the cerebrum only a part of the frontal region is drawn. — IT, Nervus opticus; ///, nervus occulomotorius ; AAS, aditus ad aquse- ductum Sylvii ; AS, aquteductus Sylvii ; Cc, canalis centralis ; Cell, corpus callosum ; Ch, chiasma nervorum opticorum ; Cm, corpus mammillare ; Coa, commissura anterior ; Coha, commissura baseos alba ; Com, commissura mollis; Cop, commissura posterior; Cscr, calamus scriptorius; Cu, culmen; Dc, declive ; Fee, folium cacuminis ; Fel, columna fornicis cut across at + ; Fna, fimiculus ant. med. spinalis ; Fnp, funiculus post. med. spin. ; Foca, foramen caecum ant. ; Focp, foramen csecum post. ; Gee, genu ; Gh, ganglion habenulse ; Gl}), glandula pinealis ; Hy, hypophysis ; Lc, lobulus centralis ; Lg, lingula ; Lia, lobus inf. ant. ; Lim, lobus inf. med. ; Lip, lobus inf. post. ; Lsm, lobus sup. med. ; Lsp, lobus sup. post. ; Ll, lamina terminalis ; FLOCCULUS. The three upper as well as the two posterior lobes on the unth;r •surliifi' have a i)run()Uiiceil semilunar form. Only the anterior lobe or tonsil, which i)ushes itself in towards the middle line, has a more compliciitod shape. The two tonsils from oi)posite sides meet in the middle line above the medulla obloni,'ata. The floccular sulcus cuts oft' a small, but very conspicuous, lobe, the flocculus or lobus vagi, Fl, which occupies the commencement of the great horizontal fissure resting on the middle peduncle. Some small accessory lobules, which lie beside the flocculus on the middle peduncles, are known as accessory flocculi. Proceeding from the front of the vermis backwards along its upper surface, and continuing our course along its under surface (fig. 16), we find : — ...Cell M, situation of ioramen of Monro ; Nc, nucleus cauclatus ; No, noclulus ; Nt, nucleus tecti ; Po, pons ; Pp, pes pedunculi ; PspJ, pedunculus septi pellucicU cut at + ; Pu, pulvinar thalami ; I'yc, pyramis cerebelli; Qa, corpus quadrigeminum anterius ; Qp, corpus quadrigeminum posterius ; Rcc, rostrum ; Rh, ramus meduUaris horizontalis ; Rif, infundibulum ; Rip, recessus infrapinealis ; Ro, recessus opticus ; Rtrc, rima transversa cerebri ; Hv, ramus medullaris verticalis ; Shm, sulcus horizontalis magnus ; Sia, sulcus inf. ant. ; Sip, sulcus inf. post. ; SIM, sulcus Monroi ; Spec, splenium ; Sqt, sulcus Corp. quad, transversus ; Ssa, sulcus sup. ant. ; Ssp, sulcus sup. post. ; Stc, stria cornea ; The, tuber cinereum ; Thorn, thalamus opticus, mesial surface ; Thos, thalamus opticus, upper surface ; Tv, tuber valvulae ; Tv3, ta?nia ventriculi tertii ; Uv, uvula ; Vma, velum medullare ant. ; F4, fourth ventricle. 52 VERMIS. 1. The lingula, Lg, a tiny tongue-shaped lobule, made up of from five to eight minute convolutions, lying on the velum medullare anterius, Yma. Sometimes its under surface is free from the velum, in which case it also is marked by transverse convolutions. The lingula extends on either side in a little leaflet, the frenulum lingulse, which represents an atrophied portion of the lateral hemisphere. 2. The central lobe, Zc, projects forwards until it touches the back of the corpora quadrigemina. To this piece of the vermis again belongs an inconspicuous portion of the hemisphere, the ala lobi centralis. 3. The upper lobe of the vermis (or monticulus) comprises by far the largest part of the vermis. It is again divided into two — (a) culmen (apex), Gu, reaching as far backwards as the union of the anterior superior sulci of the two sides, Ssa ; (6) declive, Be, reaching thence backwards to the posterior superior fissure ('S'sp), belongs both to the upper and the under vermis. 4. The posterior lobe of the vermis ; divided again into (a) the little folium cacuminis. Fee, a single convolution bounded by the posterior superior and the great horizontal sulci ; (6) the tuber valvule, Tv. 5. The pyramis, Pye, is the next section of the vermis, consisting ot from five to eight folia. It attains to its greatest breadth behind the amygdalae. 6. The part of the inferior vermis in front of the pyramis is narrow and shaped like a steep house-roof. It is called, on account of its situation with regard to the tonsils, the uvula, XJv ; it presents six to ten free transverse folia. 7. Lastly, in front of the uvula projects a little knob, the nodulus, No. [The importance of these names is somewhat diminished by the fact that, as can be seen in fig. 16, they do not exhaust the lobes of the vermis, and also by a doubt as to their morphological value. No serious attempt has yet been made to trace the lobation of the cerebellum throughout the vertebrata.] The medullary centre of the cerebellum consists of two egg-shaped masses of white substance belonging to the hemispheres, and united to- gether by the medullary substance of the vermis. The white substance is, in the main, a repetition in miniature of the whole cerebellum ; but the portion belonging to the vermis is not relatively so large as the rest. Portions of the medullary centre are prolonged into the lobes and lobules, dividing repeatedly, and occupying the centres of all the folia. A special description of these divisions of the medullary substance is, therefore, unnecessary. Those of the vermis, as they are represented in fig. 16, may be mentioned. The central white substance of the ARBOR VIT.K. 53 vermis, called corpus trapezoides (a name which has given rise to mistakes), gives off two principal branches. One of these, the vertical branch, Kv, projects upwards into the monticulus. The other, or horizontal branch, lih, is directed backwards into the central mass of the hinder lobes ; quite near its origin this horizontal limb gives a considerable branch downwards into the pyramid. A less important branch passes in front of the vertical ramus into the central lobe, while another is continued in front of the horizontal one into the uvula. A still smaller branch enters the nodule, whilst the most minute of all forms the medullary substance of the lingula. The branches of the vermis taken together constitute, with their cortical covering, the ai-bor vitae. In connection with the cerebellum, although not really belonging to it, for it forms rather the embryonal roof of the fourth ventricle, the velum medullare posterius Tarini {seu valvula semilunaris), Vmp, must occrtpy our attention. To exhibit this structure it is necessary to cut otf the medulla oblongata at the level of the hinder border of the pons, and then to break oft' the tonsils of the cerebellum. Fig. 15 shows the left velum medullare posterius on the right hand side of the picture. Each tonsil is now seen lying with its upper surface in a hemispherical depression, the floor of which is not formed by the substance of the cerebellum but by a delicate transpai-ent membrane, which stretches from the uvula and nodule on either side as a semi- lunar leaflet attached along its posterior convex border to the cere- bellum, but presenting a free concave border directed forwards. It is comparable in appearance to one of the semilunar aortic valves. Laterally the free edge is prolonged into a bundle of nerve-fibres, which can be followed as far as the flocculus, Fist; stalk of the flocculus. Grey matter is also to be found in the medullary centre of the cerebellum. It can be shown by cutting the cerebellum horizontally, the section following the sulcus horizontalis magnus, or by making at right angles to this sulcus a section inclining obliquely outwards and backwards from the incisura semilunaris. In either case the corpus dentatum cerebelli, Ndt, appears as a narrow grey zigzag band. The corpus dentatum, Kdt, fig. 17 (seu nucleus dentatus seu fimbri- atus seu lenticulatus, corpus ciliare seu rhomboideum), is a puckered up bag of grey substance, the open mouth of which looks a little mesially and ventrally. It lies in the mesial half of the hemisphere, and so close to the ventricle that it is only separated from it by a thin layer of white substance. Its longest antero-posterior diameter (converging somewhat with that of the opposite side) is about 2 cm. The corpus dentatum is not seen in its greatest extension in a frontal section. 54 NUCLEUS OF ROOF. Another not well-definecl, light-grey or brownish mass, oval in shape, appears between the two corpora dentata in a frontal section. This is Stilling's roof-nucleus, n't (nucleus tecti sen fastigii, substantia ferru- ginea superior). Between the corpus dentatum and the nucleus of the roof are some little scattered clumps of grey matter which Stilling names the nuclei emboliformis et globosus. 2Ieynert calls them both the nuclei subdentati (gezackte nebenkerne). In fig. 17, taken from the brain of the monkey, these nuclei are not visible. The presence of these nuclei inside the cerebellum depends iipon the fact that from three directions lai^ge white bundles stream into this organ on either side. One of these bundles, the corpus restiforme, which skirts the margin of the fourth ventricle, has been already noticed, Grst. The middle and largest peduncles of the cerebellum, which unite it with the pons, have also been noticed. They belong altogether to the hind-brain. Henle may be followed in considering the line joining the points of exit of the trigeminal and facial nerves (fig. 11) as the ^ \^^J^ Fig. 17. — Frontal section through the medulla oblongata and cerebellum of an ape. • Ticice 7iatwal size. — VIII, ±^erxus acusticus ; f^////;, chief auditory nucleus ; IX, nerrus glossopharjTigeus ; Co + , superior commissm-e (and decussation) ; C7'st, corpus restiforme ; Flp, fasciculus longitudinalis post. ; H, hemisphere of cerebellum ; A^dt, nucleus dentatus ; No, nucleus olivaris ; Nt, nucleus tecti ; Py, anterior pyramid of the medulla ; Ba, raphe ; V4, ventriculus quartus ; Va, ascending root of trigeminus ; Vrsp, vermis superior. division between the middle peduncle and the pons proper. The greater number of fibres in the pons are directed transversely {Foville compares their appeai-ance as seen from the mid-ventral line to a head of hair parted in the middle) ; a broad band of fibres is, however, conspicuous in the anterior half of the pons, which, starting in the usual direction, subsequently inclines backwards and outwards CEIIEHELLAK I'EDUNCLES. 55 over the surface of the others towards the point of exit of the facial nerve. It is called the fasciculus obliquus (rubau fibroux obliijuc of Foville), fig. 11, Fuh. A bundle of fibres, the ponticulus, Pol, is usually to be seen along the hinder border of the pons, si)reading over th(! pyramid. The third pair of cerebellar peduncles, which have not yet been mentioned, pass from this organ towards the great Ijrain converging in this direction much in the same way as the posterior peduncles con- verge spinewards. They and the posterior peduncles together bound a rhomboidal space; sinus rhomboidalis (or fourth ventricle). They look as if they went to the corpoi'a quadrigemina, and hence have been named by mistake the processus cerebelli ad corpora quadri- gemina. They are also named the brachia conjunctiva [seu conjunc- toria, processus cerebelli ad cerebrum) ; compare figs. 12 and 18, Brc. Between the mesial edges of the anterior peduncles lies a thin tongue-shaped membrane with its point turned brainwards, the velum medullare anterius, Vma, already described; on it lies the lingula, Lg. The lateral borders of the anterior peduncles are not really visible, for as they converge forwards to slip under the posterior tubercles of the corpora quadrigemina they are overlapped, even from the moment that they leave the pons, by two other white tracts, the lemnisci, which converge more quickly than the anterior peduncles, and almost reach the middle line in front of the point of the velum medullare. The lemniscus (fillet, laqueus, ruban de Reil), Lm, has a triangular form, and is usually divided into two parts by a shallow furrow, which also runs bi'ainwards and mesially. An isolated bundle can almost always be seen lying in the furrow between the anterior border of the pons and the superior cerebellar peduncles; passing on round the cerebral peduncles it sinks at last into the fissure between them. This bundle, the taenia pontis, Tpo (fig. 12), can some- times be lifted up for a considerable distance as a free cord. It has already been mentioned that the great fifth nerve takes its exit from the pons near its anterior border. The motor-root is attached in front of the larger sensory one, fig. 11, Vm and Vs. The floor of the fourth ventricle (sinus sive fossa rhomboidalis) is exposed by cutting the cerebellum from all its connections with the rest of the brain. It is longest in its antero-posterior diameter (about 3 cm.). Its greatest breadth (about 2 cm.) is in the line connecting the attachments of the auditory nerves. The margins of the sinus rhomboidalis are formed in front by the superior cerebellar peduncles, and by the corpora restiformia behind. Of the two diagonals of the sinus, the longitudinal is marked by 56 Fig. IS.— Hind-brain, mid -brain, and 'tweeu-brain from tlie dorsal side. Nat. size. Tlie greater part of the secondary fore-brain is removed by three cuts made in the horizontal, sagittal, and frontal planes respectively. — IV, Nervus trochlearis; VII, nerviis facialis; VI 11, nervus acusticus; Ac, ala cinerea; Brc, brachium cerebelli ad corpus quadrigeminum ; Brqa, brachium anterius ; Brqp, brachium posterius ; Cgm, corpus geniculatum mediale ; C'l, clava ; Coa, commissura anterior ; Com, commissura mollis ; Crst, corpus restiforme ; Cscr, calamus scriptorius ; Et, eminentia teres ; Fcl, columnse fornicis ; Fnc, funiculus cuneatus; Fng, funiculus gracilis; Fnl, funiculus lateralis; Foa, fovea anterior ; Frv, frenulum veli anterioris ; Fslp, fissura longitudinalis posterior ; Gcc, genu corporis callosi ; gh, ganglion habenulse ; Glp, glaudula pinealis ; K, conductor sonorus ; Lc, locus coeruleus ; Lg, lingula ; Lm, lemniscus ; M, situation of foramen of Monro ; Nc, nucleus caudatus ; Pdc, 57 This RJ-p pedunculus conarii ; Po, pons cut across at + ; Pp, pes pedunculi cerebri ; Pu, puh-inar; Qa, anterior corpora quadrigemiua ; Qp, posterior coqjora cjuad- rigemina ; Slch, sulcus choroideus ; Sid, sulcus lateralis dorsalis ; Sim, sulcus longitudinalis mesencephali ; Sbnd, sulcus longitudinalis medianus ventriculi quarti; Spd, sulcus paramedianus ; Spl, septum pellucidum ; Sql, sulcus corp. quadrig. longitudinalis; Sqt, sulcus corp. quadr. transversus ; Stc, stria cornea ; Stm, stria? meduUares sexi acusticse ; Tac, trigonum acustici ; Tba, tuberculum anterius ; The, tuberculum cuneatum ; Th, trigonum hypoglossi ; Thos, thalamus opticus; Trh, trigonum habenulte ; TvS, ta-nia ventriculi tertii ; Via, anterior horn of the lateral ventricle ; Vma, velum meduUare anterius; Vspl, ventriculus septi pellucidi, seu quintus ; V3, ventriculus tertius. 58 SINUS RHOMBOID ALIS. a conspicuous fissure (sulcus medianus longitudinalis sinus rliom- boidalis), Slmd, while transverse bundles of fibres (striae medullares, seu acusticaj), Stm, starting in the middle line, pass outwards to encircle the corpora restiformia, and join the auditory nerve. These striae acusticee are subject to great individual variations. They may in exceptional cases be absent on one side, or even on both sides. Occasionally they are very strongly developed. Sometimes individual bundles cross over one another during their course. Bundles lying quite free, not fused with the floor, may also be met with. Besides the usual tracts which cross the tseniola cinerea to join the auditory nerve, other bundles of white fibres are also generally to be met with in the floor of the fourth ventricles, such a bundle [the conductor sonorus seu tractus acusticus] or " Klangstab " of Bergmann, fig. 24, K, is often to be found originating in the median fissure, near the striae medullares, and passing obliquely outwards and forwards towards the anterior cerebellar peduncles. Three divisions can be recognised in the posterior half of the sinus rhomboidalis on either side of the middle line. The most mesial of these forms a right-angled triangle with the right angle bounded on one side by the median fissure, on the other by the striae acusticae. This triangular region is covered with white substance ; it corresponds in the main with the nucleus of the hypoglossal nerve, and may, therefore, be named the trigonum hypoglossi, Th. Laterally to this triangle lies another with its apex against the striae acusticae. Its surface is a little depressed below the rest of the floor of the fourth ventricle and is grey in colour. Since it corresponds very closely to the nuclei of the vagus (and glossopharyngeus) it may be called the trigonum vagi (it is more often named ala cinerea, hence the lettering Ac). The lateral portion of the posterior half of the floor of the fourth ventricle is raised above the general surface. It extends beyond the striae acusticae, brainwards, and there attains its greatest development. It is termed the tuberculum acusticum [a well-marked swelling in the child's medulla], since it corresponds to a group of nerve-cells which many regard as the nucleus of this nerve. The proximal [anterior] half of the floor of the fourth ventricle is distinguished from the distal half by having a complete covering, albeit a thin one, of white substance, which gives to its lateral boundary a sharper definition than is exhibited by the distal half. A cylindrical eminence, about 4 mm. broad, lies on either side the middle line. Commencing, as the continuation upwards of the trigonum hypoglossi, it extends to the front of the fourth ventricle beneath the corpora quadrigemina ; at their \;pper part, owing to VELA MEDULLAIMA. 59 •the (h-awing together of the superior cerebellar peduncles, these cininonces, Jil einiuentia} teretes (wrongly calk'd funiculi terctes), are somewhat contracted. Laterally to the eminentia teres a depressed spot is visiljle, the fovea anterior, Foa, distinguished, as a rule, by the presence of a fairly large superficial vein. Lastly, in the front of the floor, near the lateral angle, is to be noticed a dark-brown or bluish space, stretching forwards for from 4 to 6 mm. as far as the corpora quadrigemina, locus cceruleus, Lc. Its colour, which is not always visible until the surface has been scratched, is due to a strongly pigmented group of nerve-cells, sub- stantia ferruginea, which shows through the upper layer of the medulla. At its proximal extremity the ventricle has a breadth of .'^ mm. Beneath the corpora quadrigemina it sinks into the aquseductus Sylvii, Qp- The cerebellum cannot be looked upon as a portion of the roof of the hind-brain. It is a secondary formation which grows later from the two sides and arches over the fourth ventricle. The following structures cover in the venti'icle : — L The front is covered by the velum medullare anterius. 2. The middle part by the vela medullaria posteriora. 3. The vooi of the hinder part of the ventricle is formed by a thin vascular membrane, reduced for the greater part of its extent to a triangular layer of epithelium and pia mater, tela choroidea inferior ventriculi quarti. This is continuous in front with the vela posteriora. It is shown when the back of the cerebellum is lifted up from the medulla oblongata. Some other small and unimportant developments (little plates of white matter) are found in this part of th6 ventricle, namely, the obex (often absent) which fills in the angle between the diverging funiculi graciles and the taeniae ventriculi quarti, Aljy (ligulae, alse pontis, ponticulus), fig. 12, which skirt the outer margin of the ventricle as far forwards as the strise acusticae. These little plates of white matter are very delicate and easily torn off" with the membranous roof of the venti'icle with which they are intimately connected; in fig. 13 they are only partly visible. The base of the triangular membrane con-esponds to the vermis, and fuses with its pia mater. [In a section which cuts through the front of the fourth ventricle this group of pigmented cells appears as a round black spot on either side. It is as well to restrict the name substantia ferruginea to this clump of pigmented cells, which, although small, is as dark as the substantia nigra, and to use the term locus cceruleus for the grey-blue 6o FORAMEN OF MAGENDIE. appearance whicli the flooi' of the foiarth ventricle presents over the region beneath which the substantia ferruginea lies.] A peculiar shaggy plexus of vessels, the plexus choroideus cerebelli medialis, hangs to the under surface of the tela choroidea on either side of the middle line. The depending fringes commence at the calamus scriptorius, and take a sagittal direction as far forwards as the back of the velum medullare posterius. Here they turn outwards, and lying on the under side of the cerebellum, run along the stalks of the flocculi to meet the auditory nerves, where they form a somewhat larger coil, the plexus choroideus cerebelli lateralis (ala, plexus nervi vagi). In the part of the roof of the ventricle, which is thinned out as the tela choroidea, three gaps are formed during the course of development, the only communications, perhaps, between the brain- ventricles and the pericerebral space. Between the two plexus choroidei mediales, and just in front of the calamus scriptorius, a large hole is pierced in the roof, easy to demonstrate although at one time its existence was much doubted, the foramen Magendii (apertura inferior ventriculi quarti, orifice commun des cavites de I'encephale). There are also always to be found, as Key and Retzius have proved, two other openings, which lie at the lateral angles (recessus laterales ventriculi quarti) of the tela choroidea, just where the plexus choroideus lateralis comes out, apertures laterales ventriculi quarti. According to Merhel and Mierzejewshy, communications between the lateral ventricles of the great brain and the surface are also to be found in the form of elongated clefts above the gyri hippocampi. 3. THE MID-BRAIN. Proceeding forwards we reach the mid-brain, or region in which the corpora quadrigemina are included. In connection with this region it will be necessary to describe structures which, although they belong properly speaking to the 'tween-brain, press themselves backwards into the mid-brain region. The mid-brain is not more than a centimeter in length and is divided by a furrow, the sulcus lateralis mesencephali, Sim, (figs. 12, 18, and 19), into two easily distinguishable parts ; the ventral (basal) and dorsal portions of the mid-brain. The sulcus lateralis is seen whether the brain-stem is looked at from above or from the side. It commences at the front of the pons and bounds the structure already described under the name of fillet. The great cerebral peduncle (pes pedunculi cerebri), P/> (figs. 11, 12, and 13), lies on the ventral side of this furrow, and projects, laterally, somewhat beyond it. As it comes out from the pons it INTERPEDUNCULAR SPACE. 6 I has a In-cadth of 12 to 20 mm., which is increased during its short superficial course. Passing beneath the optic tract, TI/, it disappears {i\)iu view in the interior of the great brain. It consists of Ininrlles of fibres visible as separate bundles from the surface, not folhjwing its main direction, but giving it the appearance of a twisted cord. Those which are most mesially placed as it leaves the pons, pass so abruptly to the outer side that they have an almost transverse course. These are the fibres, LmP, from the fillet to the peduncle, so called for reasons which will be presently explained. Each peduncle runs not straight forwards, but diverging from its fellow at an angle of 70° to 80^; a triangular space is thus left between the two, trigonum intercrurale, Trie (fossa interpeduncularis [interpeduncular space] ). A deep furrow, from which the fibres of the oculomotor nerve emerge (sulcus oculomotorius), SlIII, marks the boundary between the pes pedunculi and the trigonum intercrurale. In the mid-line of the fossa is another well-mai-ked furrow, sulcus substantise perforatte posterioris, Slpp. The medial portion of the fossa, broad in front and pointed behind, constitutes the floor of the third ventricle. It is pierced by numerous blood-vessels, and hence is termed the substantia perforata posterior, Shj^jx The perfoi-ated space is bounded on either side by elongated swellings which really belong to the dorsal portion (the tegment) of the peduncle. They can only be seen when the peduncles are pushed aside, and hence are not visible in fig. 11. The part of the mid-brain lying dorsally to the lateral sulcus presents two rounded swellings, the corpora quadi-igemina (or in submammalian orders, bigemina), Qa and Qp. A median fissure rising abruptly from the velum medullare, and opening out in front into a little shallow triangular fossa, lodges the pineal gland, Glp, and separates the tubei'cles of the corpora quadrigemina of one side, from those of the other. The triangular fossa, just mentioned (trigonum subpineale), often presents a slight elevation in the centre (coUiculus subpinealis of Schwalhe). At the back, where it sinks on to the valve of Vieusscns, the fissure is bounded on either side by a little ridge of white substance (sometimes the two ridges are fused together), frenulum veli medullaris antici, Frv. A transverse sulcus, sulcus corp. quad, transversus {seu frontalis), Sqt, crosses the median fissure at right angles, dividing the anterior pair of tubercles from the posterior. It is shallowest near the middle line. The anterior tubercles, Qa, measure in the sagittal direction 8 mm., in the frontal direction 12 mm. The posterior tubercles, Qp, measure 6 mm. by 8 mm. The latter are distinguished by the abruptness of their posterior surfaces. 62 MID-BRAIN. From each of the corpora quadrigemina a white bundle passes ventrally, laterally, and Lrainwards. These are the peduncles of the corpora quadrigemina (brachia conjunctiva). On each >side the two brachia are separated by a continuation of the transverse furrow, which might well be called in this part of its course the sulcus inter- brachialis. The posterior brachium is soon divided into two by a shallow furrow. The posterior of these two divisions disappears in the sulcus lateralis. The anterior joins a spindle-shaped elevation of about 1 cm. in length, the internal geniculate body, Cgm (ganglion seu corpus geniculatum mediale seu internum) which is squeezed into the sulcus interbrachialis. It must be looked upon as a part of the 'tween-brain. The anterior brachium, Brqa, continues its course, covered by the overhanging optic thalamus, almost to the optic tract. It is broadest where it comes out from the anterior tubercle, but loses a considerable portion of its substance beneath the lateral geniculate body. A thin nerve tract, which is very visible in many aninials but rarely distinctly seen in man, proceeds from in front of the anterior tubercles downwards, outwards, and backwards across the brachia, and then on across the pedunculus cerebri, tractus peduncularis transversus, fig. 12, Tjjt. Its termination is never distinctly seen. Fig. 19.— Transverse section througli the anterior corpora quadrigemina (semi- diagrammatic).— /1 5', Aquaiductus Sylvii; Brqp, brachium posterius corporum quadr. ; Pp, pes pedunculi ; Q, region of the corpora quadrigemina; Qa, anterior corpora quadrigemina ; Sim, sulcus lateralis mesencephali ; SS, sub- stantia nigra Soemmeriugi ; T(j, tegmentum. When the mid-brain is cut across at right angles to its long axis (fig. 19) the proximal continuation of the fourth ventricle, aqueeductus Sylvii, is to be seen in the middle line. In the substance of this part of the brain-stem several strata are distinguishable : — 1. The region of the corpora quadrigemina is limited by a line drawn transversely through the aqueduct, Q. 2. A region of mixed grey and white substance, the tegment, Tg. OPTIC THALAMUS. 63 3. A stratum which is at once distinguished ])y its colour, duo to the iutonsoly bluck pigmentation of the cells of which it is composed, stnvtuin nigrum, *S'6' (substantia nigra Soemmeringi, stratum inter- medium). 4. Lastly, the lowest portion of the picture is occupied by the semi- lunar section of the pes pedunculi or crusta. Pp. The attachment of the oculomotor nerve, fig. 11, ///, has been already mentioned. Most of it comes out of the sulcus oculomotorius; detached bundles, however, pierce the mesial surface of the crusta. Not infre(|uently a detached portion of the nerve, isolated from the main bundle by a blood-vessel, takes exit from the peduncle con- siderably further outwards, ///'. The trochlear nerve, figs. 12 and 13, IV, arises as a thin thread, or in some cases as two separate roots, from the lateral angle of the velum medullare. It lies usually in the furrow between the posterior tubercles of the corpora quadrigemina and the superior cerebellar peduncles. 4. THE 'TWEEN-BRAIN. It is very difficult to fix the boundaries between this portion of the brain and the parts in front of and behind it, namely, the secondary fore-brain and the mid-brain. The most important structures which it includes are the optic thalami, Tho, with the two corpora geniculata, Cgl and Cgm, the optic tracts, Til, and the corpora mammillaria, Cm (figs. 11, 12, and 13). By some people the outer part of the thalamus is looked upon as belonging to the secondary fore-brain ; an opinion based upon phylo- genetic considerations, an explanation of which would lead us too far. One part of the optic thalamus, the pulvinar, Pu, has already been shown to press backwards against the corpora quadrigemina. If all the rest of the great brain which lies superficial to the thalami is cut away so that these are left uncovered, a view into the ventricles of the great brain is obtained. We will content ourselves, in the first place, with a description of the external appearances of the parts included in the 'tween-brain, reserving the study of their intimate structure until sections through the whole of the great brain are under discussion. The OPTIC THALAMUS (couche optique), fig. 18, is a large oval body which lies upon the pedunculus cerebri, with its long axis inclined forwards and inwards. Its lateral portion, which is continued into the optic tract (fig. 13), arches outwai-ds over the peduncle towards the base of the brain. The upper surface of the thalamus, Thos^ 64 INFUNDIBULUM. appears white owing to a thin covering of fibres (stratum zonale), while its mesial sui"face is grey. The two are separated by an angular border. The fairly flat mesial surfaces (fig. 16) of the two thalami are very near together, and at one part are actually fused in the middle line forming the [soft, grey, or] middle commissure, Com (commissura mollis, trabecula cinerea). It is a short band, usually flattened from above downwards, and easily broken. This commissure is not seldom completely wanting. In some cases, on the other hand, it is double. In hydrocephalous distension of the ventricle, it may be di-awn out to a considerable length (17 mm. — Anton). The cavity of the 'tween-brain is named the middle or third ventricle, VS. The aqueduct of Sylvius opens oiit on reaching its oblique posterior wall into the aditus ad aquteductum Sylvii, fig. 16, A AS. From this a fissure runs along the middle of the posterior wall and floor of the ventricle. In the floor it opens out into a funnel- shaped depression, recessus infundibuli, Eif. This recess produces a grey conical swelling on the surface of the basis cerebri projecting behind the optic chiasm, tuber cinereum (fig. 11), The. To the point of the infundibulum. If, hangs an ellipsoidal body, the hypophysis cerebri [pituitary body], Hy. The upper surface of the thalamus is bounded laterally by a furrow (fig. 21) which contains a large vein, as well as a thickened ridge of ependyma. At the bottom of the furrow there lies also a bundle of fibres. Thickened ependyma and fibres together make the stria cornea, Stc (stria terminalis, taenia cornea), figs. 16, 18, and 20. The furrow begins at the front of the thalamus, runs outwards and backwards, and can be followed into the inferior horn of the lateral ventricle. In addition to the general rounding of its upper surface the optic thalamus presents certain minor elevations (fig. 18). A distinct rounded elevation, about as large as a bean, constitutes its anterior end, tuberculum anterius, Tha. A shallow furrow, sulcus choroideus, Slch, starts at the back of this tubercle, and divides the rest of the surface into a mesial and a lateral portion. The back of the thalamus is elevated into the considerable rounded pulvinar, Pu. Beyond this the thalamus bends downwards and outwards, and narrows into a swelling, somewhat smaller than a bean, corpus geniculatum laterale {seu externum), in which the optic tract terminates. The optic tract encircles the peduncle, and meets on the basis cerebri with the tract of the opposite side in the chiasma nervorum opticorum, Ch. The lateral corpus geniculatum does not lie immediately on the peduncle, for the mesial portion of the optic tract, which is directed towards the mesial geniculate body, insinuates itself between the two. A white tract, (JANCLION IIAIJKNL'L.K, 65 which unites the two gcuii-ulutc l)odie.s together, and is best seen in the new-born chikl, is named by Rauher, ansa intergenicularis. The boundary between the upper and mesial surfaces of the thalamus is rendered more evident by a ledge of white matter which is generally continued into a plate of gelatinous substance projecting towards the middle line, tfenia thalami (T. ventriculi tertii) figs. 16 and 18, I'vS. This overhanging ledge swells just in front of the trigonum subpineale into a club-shaped body, the ganglion habenulaj, Gh. Between this and the back of the thalamus lies a small triangular region, the trigonum habenulje, Trh. Provided the membranes of the brain have not been dragged oft' roughly, a little conical body, the glandula pinealis (conarium), Glp, is seen lying in the horizontal fissure between the corpora quadrigemina. It is 8 to 12 mm. long. Short peduncles pass from the anterior end of the pineal gland, which forms part of the posterior wall of the third ventricle, to the ganglion habenulje on either side, pedunculi habenulse, Pdc. The postei-ior part of the third ventricle presents a little pit beneath the pineal body, recessus infra- pinealis (ventriculus conarii), Rijy (fig. IG). Below this a well-formed tract of white matter, visible when the pineal gland has been removed, crosses above the anterior opening of the aqueduct of Sylvius, the posterior commissure, fig. 16, Cop. It bounds the trigonum subpinealis in front. We are already acquainted with most of the structures which are found on the ventral surface of the 'tween-brain. First comes the optic chiasm, Ch (fig. 11), with the tuber cinereiim, The, in the angle made by the posterior edges of the optic tracts. Behind this again lie two white rounded eminences about the size of peas, corpora mam- millaria {seu candicantia), Cm. They form the proper anterior border of the trigonum interpedunculare. 5. THE GREAT BRAIN. The total fore-brain is split by the great longitudinal fissure (see fig. 7) into two equal halves, the hemispheres. The surface of the hemispheres is almost everywhere covered with grey matter, the cortex. It is depressed into fissures and raised into convolutions, but certain grey masses found in the interior of the great brain will be referred to first. If the method recommended for exhibiting the optic thalamus has been followed, a rounded swelling freely projecting into the ventricle, the caudate nucleus (corpus striatum, intra-ventricular portion of the corpus striatum), Nc (fig. 20), is seen to its outer side and separated from it by the stria cornea. It is largest in front of the thalamus, and thins 5 66 NUCLEUS CAUDATUS. away behind into a narrow riband. This riband, or tail of the nucleus, lies parallel to the stria cornea. It curves backwards, downwards, and, finally, forwards, and can be followed as far as the tip of the temporo- sphenoidal lobe (fig. 19«). It thus comes about that tlie nucleus Fig. 19a. — Diagram to show the cortical relations of the nucleus caudatus, nc {after Wernicke). The head of the caudate nucleus is in continuity with the cortex of the frontal lobe, the extremity of the tail with that of the temporal lobe. caudatus describes an arch, the anterior limb of which is formed by the massive head, the posterior limb by the tail. The latter part of the caudate nucleus lies in that portion of the ventricle called the descending horn. If a horizontal section is made through the hemisphere parallel to the surface of the optic thalamus and nucleus caudatus, and only cutting off their domes, a rounded body, about half a centimeter in transverse diameter and projecting (as a rule) backwards into a point, is seen in the anterior part of the thalamus. It is the anterior nucleus (upper nucleus, centre anterieur), JVa. The fairly-distinct capsule which in- vests the anterior nucleus is prolonged backwards as a plate of white substance, lamina medullaris medialis thalami optici, Lmm. This lamina, therefore, divides the thalamus into two pieces of almost equal breadth. The lateral nucleus, M, projects beyond the mesial nucleus (nucleus internus), Ifm, both in front and behind. The lateral boundary of the thalamus is marked by a white lamella, lamina medullaris lateralis thalami, Lml. If a second horizontal section is made through the hemisphere about J cm. below the surface of the head of the nucleus caudatus (fig. 21), an idea is obtained of the depth to which this grey mass reaches. The nucleus anterior of the thalamus is no longer visible, but the lamina medullaris medialis, Lm77i, and the nucleus lateralis, JVl, are clearly distinguished. The lateral boundary of the thalamus is formed by the feebly-developed lamina lateralis, Lml. Another grey mass appears in this section which nowhere reaches to the surface, but is embedded in white matter, the lenticulaP NUCLEUS LENTICULAR IS. 67 nucleus (nucleus lonticularis, extra-ventricular portion of the corpus striutuni), Nlf. It lies like a blunt wedge with its angular border thrust in between the nucleus caudatus and optic thalamus, separated from each of these by the white substance of the internal cajjsule, Ci. -^Z.==^4la! Fig. 20. — Section through the 'tween-bram and the neighbouring part of the fore- brain half a centimeter beneath the upper surface of the optic thalamus and nucleus caudatus. Ned. size. Only the thalamus, the nucleus caudatus, and the parts immediatelj- surrounding them are represented. — Com, Commissura mollis ; Fd, columna fornicis ; Fcr, crus fornicis ; Gcc, genu corporis callosi ; gh, ganglion habenulie ; Glp, glandula pinealis ; Lml, lamina meduUaris lateralis ; Lmm, lamina meduUaris mediahs ; Na, nucleus anterior ; Nc, nucleus caudatus; Nl, nucleus lateralis; Nm, nucleus medialis ; Pdc, pedun- culus pinealis ; Qa, anterior corpora quadrigemina ; Qp, posterior corpora quadrigemina ; Spec, splenium corporis callosi ; Spl, septum pellucidum ; Stc, stria" cornea ; Via, anterior horn of lateral ventricle ; Vli, descending horn of lateral ventricle ; Vlp, posterior horn of lateral ventricle ; Vspl, ventriculus^septi pellucidi ; V3. third ventricle. Two thin w^hite lamina? traverse the nucleus lenticularis, dividing its substance into three segments, which may be named, proceeding from the inner angle outwards, the first, second, and third pieces of the 68 NUCLEUS AMYGDALEUS. nucleus lenticularis, Nlf^, Nlf^, Nlfo. The mesial and second segments (which togethei" constitute the globus pallidus) of the lenticular nucleus are pale, like the thalamus, while the outer segment or putamen is as dark as the nucleus caudatus. The lateral surftice of the nucleus lenticularis corresponds in situa- tion to the portion of the cortex of the great brain called the island of Reil, /, The nucleus and the cortex are separated by one grey and two white layers. Next to the nucleus lenticularis comes a thin layer of white matter, the outer capsule (capsula externa), Ce, to the outer side of which is applied the grey sheet of the claustrum (nucleus tseniaeformis seu lateralis), CI. Between the claustrum and the cortex of the island of Eeil lies the sheet of white matter termed lamina fossse Sylvii (capsula extrema). The mesial surface of the claustrum corresponds to the outer surface of the nucleus lenticularis, its lateral surface adapts itself to a certain extent to the cortex of the island of Heil, exhibiting similar small elevations and depressions. The anterior angle of the nucleus lenticularis is situate somewhat farther back than the front of the nucleus caudatus. The posterior angle lies a little behind the thalamus. To get a complete picture of the nucleus lenticularis, a frontal (transverse vertical) section must be made through the hemisphere at the level of the front of the thalamus (fig. 22). It now appears as a wedge, with its convex base resting on the cortex of the island of Reil, its angle — more acute than in a horizontal section — is directed beneath the thalamus. Between the nucleus and the cortex is again, seen the claustrum shut in between the external capsule and the lamina fossae Sylvii. The region which lies below the thalamus (regio subthalamica), seen in this section, and sections carried more posteriorly, contains both grey and white matter; and can only be treated of when we are dealing with the minute structure of the brain. If a section is carried a little farther forward than in J&g. 22, so that it traverses the optic chiasm, the lateral segment of the nucleus lenticularis is seen, better than in. this section, to be in direct relation to another grey mass, the nucleus amygdaleus (nucleus amygdaliformis). Am. This nucleus is understood to be a thickened portion of the cortex of the temporo-sphenoidal lobe. [The claustrum also is fused at its anterior end with the nucleus amygdaleus.] The tractus opticus, //, in its course around the cerebral peduncle pushes itself in between the nucleus lenticularis and nucleus amygdaleus. The white matter of the hemisphere reaches its greatest development above the central ganglia (or basal ganglia, a term 69 /' %m. Fir,. 21.— Horizontal section, one centimeter deeper than in fig. 20. Nat. size. The operculum, which had been detached from its connections by the section, is removed.— iJ/v/a, Brachium anterius; Brqp, brachium posterius; Ce, capsula 70 INTERNAL CAPSULE. externa ; Cm, capsula interna, anterior limb ; Cip, capsiila interna, posterior limb; CI, claustrum; Coa, commissura anterior; F, fimbria; f^ frontal lobe; Fcl, columna fornicis ; Fd, fascia dentata ; Fov, fasciculus occipitalis verticalis of Wernicke ; frv, frenulum veli anterioris ; G, genu capsulse interna ; Gcc, genu corporis callosi ; H, gyrus hijjpocampi ; /, island of Reil ; Lml, lamina meduUaris tlialami lateralis ; Lmm, lamina medullaris tbalami medialis ; M, great longitudinal fissure ; Nc, nucleus caudatus (head) ; Nc', nucleus caudatus (tail) ; Nl, nucleus lateralis tlialami ; NJf, nucleus lenticularis ; Nlf 1 and 2, globus pallidus; Nlf 3, putamen; Nm, nucleus medialis tbalami; Ntg, nucleus tegmenti ruber ; Q occipital lobe ; P parietal lobe ; Pu, pulvinar ; Qa, anterior corpora quadrigemina ; Qp, posterior corpora quadrigemina ; Spl, septum pellucidum ; Ss, sagittal fibres of occipital lobe ; Tx>, tapetum ; Tt, gyrus temporalis transversus; VA, Vicq d'Azyr's bundle ; Via, anterior horn of lateral ventricle ; Vli, inferior horn of lateral ventricle ; Vspl, ventriculus septi pellucidi ; V3, ventriculus tertius. comprehending nuclei caudatus et lenticularis and the optic thalamus). In a horizontal section parallel to, but above, the upper surface of the corpus callosum, the whole central mass of the hemisphere appears white (centrum semiovale Vieussenii). Such a section is not figured, but a frontal section of the centi'um is seen in fig. 22, CsV. In deeper sections, which pass through the included grey masses (fig. 21), the •white matter is seen to be broken up into limited tracts, which invest the lenticular nucleus, as the internal and external capsules. The former is seen in a horizontal section to consist of two segments meeting one another at an oblique angle, the knee (genu) of the internal capsule, G. The two segments are distinguished as the anterior limb, Cia, compi*essed between the nucleus lenticularis and the nucleus caudatus, and the posterior limb, Cijy, between the nucleus lenticularis and the optic thalamus. Certain special masses of white matter — the corpus callosum, fornix, and anterior commissure — must now be described. («.) The Corpus Callosum. — If the two hemispheres are pressed apart, a white structure of from 7 to 9 cm. in sagittal diameter is seen crossing the bottom of the longitudinal fissure. Its fibres exhibit a transverse arrangement. Cell. In addition to the transverse fibering, some distinct bundles of longitudinal fibres lie on its upper surface, strise longitudinales mediales (nervi Lancisii), NL (fig. 25), and between them a furrow, the raphe (sutura corporis callosi). From that portion of the corpus callosum seen at the bottom of the fissure, its substance radiates outwards on either side into the hemispheres (radiatio corporis callosi). Above the corpora quadrigemina, the posterior edge of the corpus callosum is, as seen in a sagittal section, roundly thickened and rolled over, splenium corporis callosi, Spec. In front it turns over in the knee (genu corporis 71 Mm Luna r .. -- Fig. 22.— Frontal section tlirough the human cereljral hemisphere. Left side, posterior portion. Natural size.— IT, Tractus opticus ; al, situation of ansa lenticularis ; Ain, amygdala ; C, central fissure ; Ca, gyrus centralis anterior; cAm, anterior end of cornu Annnonis ; Cell, cori^us callosum ; Ce, capsula externa ; Ci, capsula interna ; cl, claustrum ; dim, sulcus calloso-marginalis ; Cng, gyrus foruicatus ; Coa, commissura anterior ; Cp, g>'rus centralis pos- terior ; csth, corpus subthalamicmn ; CsV, centrum semiovale Vieussenii ; f, frontal lobe ; Fcl, anterior pillar of fornix ; Fs, gyrus frontalis superior ; /, island of Reil ; Lmm, Lml, lamma meduUaris medialis et lateralis ; J\/f^ great horizontal fissure ; Na, Njti, Nl, nucleus anterior, medialis et lateralis, thalami optici ; JVc, nucleus caudatus (tail) ; NlfS, 2, 1, the three portions of the nucleus lenticularis ; OpP, opercular portion of mferior parietal lobule ; oti, sulcus occipito-temporalis inf. ; Otl, gyrus occipito-temporalis lateralis ; Pp, pes pedunculi ; pros, sulcus prajcentralis, pars superior ; 2J*rain). This coinniissure makes its appearance at an early stage in the development of the brain. It appears to be Fig. 24.— Part of a median section through the great brain. The optic thalamuslis broken away ; the parts of tlie temporal lobe are somewhat separated from one another, jyatural sizc.—BW, Gyrus subcaliosus; CAm, cornu Ammonis ; Cell, corpus callosum; cell, sulcus corporis callosi ; dc, fissura calcarina; C'n(/, gyrus ciuguli; Coa, commissura anterior; Cu, cuneus ; Fc/, columna fornicis ; Fcp, corpus fornicis ; Fcr, crus fornicis ; Fd, fascia dentata ; Fi, fimbria ; Gcc, genu cor])oris callosi; //, gyrus l)ypocami)i; I, isthmus gyri foruicati; oti, sulcus occipito-temporalis inferior ; PCa, pedunculus cuuei ; poc, fissura parieto-occipi- talis ; Fee, rostrum corporis callosi ; shp, sulcus subparietalis ; Spec, spleniiun corporis callosi; Splc, septum pelucidum ; Stlm, stria longitudinal is medialis ; Tf, tuberculum fascise dentatije. present in all vertebrates, attaining a greater relative importance amongst the lower members of the sub-kingdom, in which the cortex of the great brain and its special commissm-e, the corpus callosum, are rudimentary, than in Man.] The part of the base of the fOPe-brain, which lies in front of the optic chiasm, must now be treated of in further detail. The lateral and mesial portions of this surface will be separately described. On either side lies a light grey area, bounded behind by the optic tract, in front by the frontal convolutions, and laterally by the temporo-sphenoidal lobe, T; this is known as the substantia perforata anterior (lamina cribrosa), tig. 25, Spa. N'umerous apertures for vessels are seen in this region, especially in its antero-lateral portion. It is these holes which have given the area its name. Separate white bundles, emerging from the side of the temporo-sphenoidal lobe, cross this area, 76 GREY FLOOE-COMMISSURE. as well as the transverse orbital convolution, to reacli the free white column of the olfactory tract, Trol. The olfactory tract passes forwards and slightly inwards for a distance of about 3 5 cm. At its anterior end it bears a yellowish grey swelling, the olfactory bulb (bulbus nervi olfactorii), Bol. The median portion of this part of the base of the brain, in front of the optic chiasm, is narrower than the substantia Pspl — Sim...- Coa Tbc % J ■>--=s^ ^'^inv I Fig. 25. — Part of the base of the brain, the left hemisphere in front of the optic chiasm. The apex of the temporal lobe is cut away. — //, Nervus opticus ; Am, nucleus amygdaleus ; Bol, bulbus olfactorius ; ch, chiasma ; Cm, corpus mammillare ; Coa, elevation in the grey commissure of the floor of the third ventricle caused by the underlying anterior commissure; F, fi'outal lobe; Gcc, genu corp. callosi ; Lt, lamina terminalis ; M, lougitudinal fissure ; NL, nervus Lancisii ; Pjj, pes pedunculi ; Pspl, pedunculus septi pellucidi ; Rcc, rostrum corporis callosi ; Sim, sulcus medius subst. perf. ant.; Sp)a, substantia perforata anterior ; T, temporal lobe ; Tbc, tuber cinereum ; Trol, tractus olfactorius ; Til, tractus opticas ; U, uncus. perforata, but reaches farther forwards; it constitutes the most anterior portion of the floor of the third ventricle (or grey floor-commissure). The part which lies immediately in front of the chiasm is very VENTKK'I.KS. 77 easily torn, it is named the huniiui tei-niinalis, Ll, fig. 25 (see also fig. 23). A slight elevation is produced by the anterior commissure, here covered by a thin layer of grey matter. In front of this grey elevation is seen a furrow, sulcus medius sul>- stantiaj perforatte anterioris, Sim, which extends to the rostrum corporis aillosi, Rcc. On either side of the median furrow is seen a thin longitudinal swelling which emerges from under the rostrum; pedunculus septi pellucidi, Pspl. Its hinder end turns outwards towards the perforated space ou which it is lost. M TcllS \ Spell fjie Fig. 26. — Diagram of the cerebral ventricles and the plexus choroideus. — cell. Corpus callosum; com, comraissura mollis; F, fornix; Gf, gj'rus fomicatus; M, great longitudinal fissure ; Nc, nucleus caudatus ; Plchl, plexus choroideus lateralis ; PlcJnn, plexus choroideus medialis ; Ps, psalterium ; slch, sulcus choroideus ; alM, sulcus Monroi ; Spch, suprachoroidal space ; stc, stria cornea ; Tchs, tela choroidea superior ; Tito, thalamus opticus ; VI, ventri- culus lateralis ; Vncst, vena strite corneal ; VS, third ventricle ; VSh, its horizontal portion; V3v, its ventricle portion ; V3v', the same portion below the grey commissure ; V V, Verga's ventricle. 6. THE VENTRICLES OF THE GREAT BRAIN. Although the anatomical disposition of the ventricles of the great brain seems simple, their morphological relations to the nervous sub- stance are only to be made out by careful ontogenetic study. yS VELUM INTERPOSITUM. The ventricles of the brain can be entered from behind beneath the splenium corporis callosi. However much the transverse slit which here exists (fissura transversa cerebri anterior, rima transversa) is closed up by the membranes of the brain, it yet affords this opening. The first thing which meets the view when one removes the back of the brain, with the corpus callosum and body of the fornix (on one side at any rate the fornix should be left for further study) is not the optic thalamvis but a vascular membranous fold which covers it. Seen in its whole extent at once this fold has the form of an equ.ilateral triangle. The base of the triangle corresponds with the transverse fissure ; its apex reaches the anterior pillars of the fornix ; its antero-lateral borders lie parallel to the stride cornere and somewhat mesial to them, and are attached to the surface of the thalamus (fig. 26), this fold of membrane is the tela choroidea superior (velum triangulare [seit interpositum]), Tchs. The lateral margin of the tela choroidea carries a convoluted system of blood-vessels, more extensive behind than in front, the choroid plexus of the great brain, PlcJil. At the junction of the lateral and posterior borders of the tela choroidea, the plexus attains its greatest development swelling into the so-called glomus. Fi'om this angle of the tela the choroid plexus is continued downwards, and finally forwards [around the cerebral pedv;ncle], following the course of the crus fornicis as far as the anterior point of that portion of the lateral ventricle, which we shall learn presently to call the descending horn. If the fornix, F, has not been removed one notices that its sharp lateral border is attached to the tela choroidea along a line parallel to, but slightly on the mesial side of, the stria cornea and the line of attachment of the tela to the thalamus. The situation of the choroid plexus is marked on the thalamus by a shallow groove, sulcus choroideus, slch (figs. IS and 26). On the under side of the tela choroidea, near the middle line, are attached two narrow strips of choroidal plexus, plexus choroidei medii, Plchm. They extend from the anterior angle of the tela to its base. The whole hollow space in the interior of the great brain is divided into three portions by the attachments of the tela to the thalami, a middle, VS, and two symmetrical lateral ventricles, T7. Another space is left between the fornix with the psalterium, and the tela (below Verga's ventricle therefore), spatium supra-choroideum, Spch. On the diagram (fig. 26) its extent is purposely exaggerated. The third (or middle) ventricle is made up of two portions, one vertical, the other horizontal, united as seen in cross-section in a T. The vertical limb of the T, bounded by the mesial surfaces of the thalami, is the principal portion of the ventricle (fig. 26, V3v and CUMMLMCATIU-NS UF THE VENTRICLES. 79 V3v\ and figs. 20, 21, and 22). At its hinder end tlie aqujeductus Sylvii opens into the ventricle at the aditus ad aquieductum, A AS (fig. 23). From this spot its floor sinks downwards somewhat quickly to the apex of the infundibulum. The anterior wall is formed by the lamina cinerea terminalis, Lt, already described. The lowest ])art of this surface is so pushed into the ventricle by the optic chiasm, that a pouch is formed above the chiasm, recessus chiasmatis (seu opticus), Ho. The upper edge of this vertical portion of the ventricle is formed by the stria meduUaris thalami, to which, for the most part by tlie intervention of the tjenia ventriculi tertii, 2\-3, the plexus choroideus medius is attached. In front, where the stria medullaris approaches quite close to the anterior pillar of the fornix, a space, foxamen of Monro, J/, is left between the thalamus and the fornix. The plexus choroideus lateralis with a vein passes out of the lateral ventricle into the third ventricle through this hole, and bends backwards in the plexus choroideus medius. The foramen of Monro constitutes the only direct connection between the middle and lateral ventricles (see also fig. 7). A shallow groove is to be noticed on the mesial face of the thalamus, which passes in a gentle curve beneath the commissura mollis, from the foramen of Monro to the aditus ad aquaeductum Sylvii, sulcus Monroi, SIJI. (fig. 23). The horizontal portion of the third ventricle, VSh (not always included in the third ventricle in descriptions of this part of the "brain), comprises that portion of the ventricle which is shut in between the tela choroidea and the upper surface of the optic thalamus. It extends fi'om the stria medullaris outwards to the line of attachment of the tela choroidea. This cleft narrows towards the front, where it ends in a point. It corresponds obviously to the tela choroidea media in form. The paired lateral ventricles (ventriculi laterales seu tricornes), VI, lie in the interior of each hemisphere, and communicate through the foramen of Monro with the middle ventricle ; they are not directly in connection with one another. Just as the whole hemisphere is to be looked upon as presenting an arch open in front with a posterior prolongation, the occipital lobe, so the cavity which it contains is an arched space with a special occipital prolongation backward. In each lateral ventricle (figs. 18, 20, and 21) is distinguished a central or principal part (cella media), from which a horn (anterior horn. Via) passes forwards, a diverticulum is continued backwards (posterior horn, VIp), and, lastly, the ventricle ends in the inferior limb of the arch, the inferior [or descending] horn, Vli. 8o LATERAL VENTRICLE. The anterior horn is the part of the lateral ventricle which corresponds to the head of the nucleus caudatus, and reaches still farther forwards into the frontal lobe. Its mesial wall is formed by the septum pellucidum. The corpus callosum constitutes its front wall and roof. The cella media begins at about the level of the foramen of Monro. Its roof is formed by the middle portion of the body of the corpus callosum. In the floor of the ca-vdty lie, in order from without inwai'ds, the tail of the nucleus caudatus, the stria cornea, the lateral portion of the optic thalamus, and the plexus choroideus lateralis (figs. 18 and 26). The upper surface of the fornix may also be included in the floor of the cella media, since this structure lies with only its mesial edge resting against the corpus callosum. The posterior horn of the lateral ventricle (fig. 27) begins at about the level of the splenium corporis callosi, and reaches usually nearly to Fig. 27. — Frontal section through the right cert! .J hemisphere, behind the splenium corporis callosi. Posterior segment. Natural size. — M, Mesial surface of the hemisphere ; dc, fissura calcarina ; Vlp, posterior horn of the lateral ventricle ; Bcp, bulbus cornu posterioris ; Phmn, pes hippocampi minor ; Fli, fasciculus longitudinalis inf. ; Tp, tapetum. the occipital pole of the hemisphere. For upper and outer walls the posterior horn has the continuation of the corpus callosum or tapetum, Tp. The mesial and lower wall is formed, as shown in a frontal section, by three distinct elongated elevations. The upper corresponds to the margin of the corpus callosum, forceps posterior corporis callosi HIPPOCAMPUS. 8 1 (biilbus cornu posterioris), Hep. The iniy a fissure (fissura calcarina), clc, which, cutting deeply into the mesial surface of the hemisphere, pushes in front of it tlic wall of the ventricle. In some Vjrains in wliich this swelling is strongly developed, its surface is somewhat indented transversely, faintly recalling a bird's claw. The lowest of the three swellings is produced by a thickening in the mass of longitu- dinal white fibres, fasciculus longitudinalis inferior, Fit. The choroid plexus does not enter the posterior horn. The inferior (descending-) horn (fig. 28), VU, extends far for- wards into the temporal lolie, but terminates about 2 cm. behind its pole. It is apparently open to the mesial surface through the hippocampal fissure (fissura cornu Ammonis, h). For the greater part of its extent the inferior horn is roofed in by the tapetum ; the tail of the caudate nucleus and the stria cornea also extend to the front of this horn. Near the anterior end of the cornu Ammonis the tail of the caudate nucleus, which by this time is reduced to a thin grey band, begins to swell suddenly, and passes over into the nucleus amygdaleus (figs. 22 and 25). Let ns enter the inferior horn from the mesial side through the fissure hippocampi, h, with a view to explore its inferior wall. A succession of structures are met with all arranged longitudinally; first, a broad convolution, gyrus hippocampi (subiculum cornu Am- monis), £f, on the surface of which, in the fresh brain, a reticulated white layer is recognisable, substantia reticularis Arnoldi ; secondly, a frequently notched grey cord, almost hidden at the bottom of a furrow, fascia dentata, /d; thirdly, a flattened white triangular column, the fimbria, Fi, covering up the fascia dentata, which is only distinctly visible after the fimbria has been pushed aside; fourthly, a considerable white swelling, the pes hippocampi majoris (cornu Ammonis, CAm), which is greatly enlarged and distinctly indented in front ; fifthly, in the depth of the inferior horn is to be found not infrequently a swelling, eminentia collateralis Meckelii, FcM, which, like the pes hippocampi minoris of the posterior horn, is simply due to the deep indentation of the surface by a fissure (fissura collateralis sew occipito-temporalis inferior), oti. The eminentia collateralis is separated from the cornu Ammonis by a furrow, which I will call the fissura subiculi interna, so deep that it almost splits the subiculum. It is not distinctly marked off from the tapetum on the outer side. Of the several structures just mentioned, the subiculum and fascia dentata, as well as part of the fimbria, lie outside the inferior horn proper. The fimbria presents a sharp edge, to which the plexus 82 INDUSIUM GRISEUM. choroideus latei'alis, Pc, is attached. Only the portion of the fimbria which lies laterally to this edge enters the inferior horn. The cornu Ammonis and eminentia collateralis properly form its floor. Followed back to the splenium corporis callosi, one sees that the subiculum cornu Ammonis is continued over the corpus callosum as the gyrus fornicatus {seit gyrus cinguli, Cng); also, that the fascia dentata is the termination of the free edse of the cortex. Above the Fig. 28. — Frontal section through the right hemisphere behind the imcus. Anterior segment. Tlie upper part is not represented. — //, Tractus opticus; CAm, cornu Ammonis ; Cell, corpus callosum ; cell, sulcus corporis callosi ; C'gl, corpus geniculatum laterale ; Cgm, corpus geniculatum mediale; Cng, cin- gulum ; EcM, eminentia collateralis Meckelii ; F, fornix ; fd, fascia dentata ; Fi, fimbria ; h, fissura hippocampi ; H, gyrus hippocampi ; Ne, nucleus caudatus ; Op, operculum; ot'i, sulcus occipito-temporalis inferior; Otl, Otm, gyri occipito-temporalis lateralis et raedialis ; Pc, plexus choroideus lateralis ; Pp, pes pedunculi ; S, fissura Sylvii ; Ste, stria cornea ; Tho, thalamus opticus ; Tp, tapetum ; Ts, Tm, Ti, gyri temporalis superior, medius et inferior ; ts, tm, tc, sulci temporalis sup. med. et inf.; Tt, gyrus temporalis transversus; U, uncus ; 17(, inferior horn of the lateral ventricle. corpus callosum it constitutes a thin layer of grey substance hardly distinguishable from the cortex of the gyrus fornicatus, indusium griseum. The free mesial edge of the indusium is thickened, and forms (without other addition) certain recognisable longitudinal strife, striae longitudinales mediales {sei'. nervi Lancisii, Stlm — figs. 25 and 29). Just before the fascia dentata, having reached the splenium corporis callosi, begins (much diminished in size) to ascend on to its upper side, it swells out into a tubercle looking as if the great splenium pressed it down, tuberculum fasciae dentatse (Zuckerkandl), Tf. CONNECTTOX OF T-ATETJAI, VKXTRK T,E WTTII S( l:i .\( K. 83 Between this tul)crculuin and tlio uscondin;^ gyrus hiitpocjimpi lie certain minute convolutions, bettor seen in many animals than in Man, whicli ZiickerkaiuU calls callosal convolutions, liW. Excep- tionally in Man, these convolutions form a cord-like body, which stretches on to the upper surface of the corpus callosum beneath the gyrus fornicatus. The fimbria becomes the cms fornicis. The splenium corporis callosi squeezes itself in between the crus and the continuation ■"^^m. Fig. 29. — Portion of a median section of the cerebrum. The optic thalamus has been pulled away. The structures of the temporo-sphenoidal lobe are a little separated from one another. Natural size. — B W, Gyrus corporis callosi ; CAm, cornu Ammonis ; Cell, corpus callosum ; cell, sulcus corporis callosi ; clc, fissura calcarina ; Cng, gyrus cinguli ; Coa, commissura anterior ; Cu, cuneus ; Fcl, columna fornicis ; Fcp, corpus fornicis ; Fcr, crus fornicis ; Fd, fascia dentata ; Fi, fimbria ; Gcc, genu corporis callosi ; H, gyrus hippocampi ; /, isthmus gj'ri fomicati ; oti, sulcus occipito-temporalis inferior ; PCu, pedunculus cunei ; poc, fissura parieto-occipitalis ; Rcc, rostrum corporis callosi ; shp, sulcus sub- parietalis ; Spec, sjilenium corporis callosi ; Splc, septum j)ellucidum ; Stlm, stria longitudmalis medialis ; Tf, tuberculum fasciae dentata? ; U, uncus. upwards of the fascia dentata. Between these two structures and the corpus callosum a triangular area is left. Starting at the foramen of Monro and travelling along the concave border of the fornix, the plexus choroideus finds entrance from the mesial surface into the lateral ventricle through a curved cleft (figs. 26 and 28). Development teaches us, however, that no true gap in the brain-wall exists, for the foi'amen of Monro is all that is left of a much larger passage from the primary to the secondary fore- brain found in the foetus. The velum interpositum, which springs 84 TRANSVERSE FISSURE. from the primitive falx cerebx-i, is, with its choroid plexus, developed early in fcetal life. By its further growth on either side the velum interpositum pushes the inner walls of the primitive prosencephalic (cerebral) vesicles before its margin into their cavities (the future lateral ventricles), and so makes in each of them a cleft which extends backwards from the foramen of Monro ; the transverse fissure of the cerebrum (fissura choroidea seu transversa cerebri). The involuted portion of the wall of the ventricle is thinned down to a mere layer of epithelium, which covers the choroid plexus, but still, along the whole extent of the transverse fissure, closes the ventricle in. In fig. 26 the space between the lateral margin of the fornix and the line along which the tela choroidea is fixed to the thalamus, corresponds to the transverse fissure. Through this gap the choroid plexus advances into the lateral ventricle. [It is not common in English text-books to extend the use of the term " transverse fissure " to all jjarts of the cleft through which the velum interpositum gains admittance to the lateral ventricles, but the custom is rather to limit the term to the "transverse fissure of Bichat" or incisura pallii. See Macalister's Anatomy, p. 702.] Fig. 28 shows the plexus choroideus, Fc, in two situations, one in the inferior horn and the other beneath the corpus callosum. In this latter situation the pitting in of the wall of the ventricle by the plexus is also to be seen. 7. THE FISSURES AND CONVOLUTIONS ON THE SURFACE OF THE GREAT BRAIN. The great brain may be regarded as a single almost globular body, divided by the great longitudinal fissure into two hemispheres, each of which presents a convex outer (lateral) and a flat mesial surface, which meet at an edge, sharp for the greater part of its extent. On the surface of the adult brain a large, although variable, number of fissures are visible. Between them the surface is raised into con- volutions. It must be allowed that the fissures and convolutions of the cortex are not constant in arrangement ; most of them, however, follow a definite type, and much trouble has been taken to determine the laws of their topographical distribution. We cannot yet regard the investigations into their developmental history and arrangement in difierent animals as complete. In the following account, Ucker's nomenclature will be adopted on the ground that, being accepted by most anatomists, and being under- FISSUKKS AND ("ON V( H,r'l"l( iNS. 85 stood in all laiuls, liis classiticatiou has come, in a sense, to be an international one. The (jucstion is often discussed whether greater attention should be paid to the convolutions or the fissures. The proper way to look at the matter is to regard the fissures as cut into the surface of the brain, the convolutions as the portion of tissue left between adjoining fissures. If an embryonic human brain is examined at the fifth or sixth month, or if we look at the brain of a rodent animal, certain fissures are seen cutting into the flat surface in regions where no convolutions have yet appeared ; the latter only make their appearance as the fissures become numerous and approach near together. Fissures may be arranged in order of importance in the three following groups : — 1. Principal or total fissures (fissurte, scissura;, sulci primarii). 2. Typical or secondary fissures (sulci secundarii). 3. Atypical or tertiary fissures (sulci tertiarii). The chief fissures are the first to appear and permanently the deepest. They are called total fissures, because in early embryonic life, when the wall of the ventricle is thin, they involute it into the ventricular cavity. An example of this condition persists in the adult Ijrain in the posterior horn of the ventricle, the calcar avis, Phmn, being formed in this way (fig. 27). The later subsidiary fissures sink into the surface only ; they are divisible into those which are present in every normal brain (secondary fissures), and those which are subject to individual variations in number and direction (tertiary fissures). The portions of the brain marked otT by fissures are distinguished as lobes, lobules, and gyii. The chief divisions are distinguished as lobes. This delimitation applies not to the cortex only, but also to the underlying mass of the brain. Each lobe comprises convolutions of which some in ordinary parlance are termed lobules. Typical convolutions, it goes without saying, are those bounded by typical fissures. Atypical fissures bound atypical convolutions. We only recognise as convolutions those which appear on the surface, and often forget that little convolutions are to be found in the bottom of certain fissures ; deep or bridging convolutions. The superficial connections between adjoining convolutions are named by Merkel, gyri transitori [annectant convolu- tions]. The amount of cortex hidden away in the fissures is in the human brain about double that which appears on the surface. Chief FisSUPeS. — 1. Fissura Sylvii (fossa Sylvii,* fissura lateralis), * [A term better restricted to the open depression on the fwtal lirain, which precedes the closed-in fissure of Sylvius.] 86 SYLVIAN FISSURE. fig. 30. It is essentially distinguished from all other fissures by the manner of its origin. Its appearance is due to the fact that the great brain, during its growtli, curves round its central stem-connec- tion, making on its surface an arch open in front and below, which closes in an area, at first oval and later triangular in form, the " island." Fig. 30. — Left hemisphere from the side. Half natural size. — Anrj, Gyrus angularis; c, central fissure ; Ca, gyrus centralis anterior ; dim, sulcus calloso-margin- alis ; Cp, gyrus centralis posterior ; fi, sulcus frontalis inferior ; Fi, gyrus frontalis inferior; Fm, gyrus front, medius ; Fs, gyrus frontalis superior; fs, sulcus frontalis superior ; ip, fissura interparietalis ; Oi, gyrus occipitalis I inferior ; o/, sulcus occipitalis lateralis ; Om, gyrus occipitalis medius ; Op, operculum ; Os, gyrus occipitalis superior ; otr, sulcus occipitalis transversus ; PF, frontal pole ; Pi, lobulus parietalis inferior ; PO, occipital pole ; poc, fissura parieto-occipitalis, pars lateralis ; Pop, pars opercularis ; Porb, pars orbitalis ; pre, sulcus prsecentralis inferior ; pros, sulcus prsecentralis superior ; Ps, lobulus parietalis superior ; pstc, sulcus postcentralis, a constant little side branch of the interparietal fissure in front of the parieto-occipital fissure ; PT, temporal pole ; Ptr, pars triangularis ; raa, ramus anterior ascendens ; rah, ramus anterior horizontalis ; sh, pars horizontalis ; Sm, gyrus supra- marginalis ; Ti, gyrus temporalis inferior ; tin, sulcus temporalis medius ; Tm, gyrus temporalis medius ; trs, truncus fissurae Sylvii ; Ts, gyrus tem- poralis superior; ts, sulcus temporalis superior; Tt, gyrus temper, transversus. The boundaries between the four lobes when not made by fissures are marked with dotted lines. During the further growth of the brain, the island is, in a sense, fixed to the stem portion of the hemisphere, while the rest of the great brain is free; hence surrounding parts bulge over the island, CENTRAL FISSURE. 87 and, closing it in fVoiii thnc sidos (from ilw. IVoiit, fVoiu alcove;, and from below), leave it lying at the bottom of a [V-shaped] cleft, the fissura Sylvii. The island is seen only after the neighbouring con- volutions ha\e been i)ulled aside. Tht> form of the Sylvian fissure is determined by this growth of the hemisphere from three sides. It consists of a short commencing portion, trs (truncus fissurte Sylvii), which ascends abruptly from the substantia perforata anterior on to the lateral surface of the hemisphere, and then bends over into the principal or horizontal portion of the fissure, sh (ramus horizontalis posterior) ; this ramus runs, slightly ascending, far l)ackwards. Two short lateral fissures usually ascend from the anterior portion of the hori/.ontal ramus ; of these, the first runs horizontally forwards, rah (ramus anterior horizontalis) ; the other ascends vertically, raa (ramus anterior ascendens). Fig. 31.— Left hemisphere of a human embryo at the fifth month. — F, Frontal ; F, parietal ; 0, occipital ; 7\ temporal lobes ; /, island of Reil. 2. Sulcus centralis (sulcus Rolandi, fissura transversalis, scissura pei'pendicularis), c. This fissure also runs its course on the convex surface. It begins at about the level of the centre of the mesial cortex-border, but without quite reaching the edge, and is thence directed obliquely forwards and downwards towards the horizontal limb of the Sylvian fissure, into which, however, it seldom extends. Its lower end lies not quite 3 cm. behind the ramus ascendens of the Sylvian fissure. Since the central fissure does not cut deeply enough into the surface to produce a bulging of the ventricle wall, it ought not, strictly speaking, to be treated as a chief fissure, but its early origin, depth, and constancy, justify us in assigning this rank to it. 3. Fissura parieto-occipitalis (fissura occipitalis, f. occipitalis per- pendicularis), poc, belongs in its principal part to the mesial, in its smaller part to the lateral surface. Hence two divisions are distinguished, and often called by separate names. A mesial portion (fissura perpendicularis interna), fig. 33, and a lateral portion (upper 88 OCCIPITO-PARIETAL FISSURE. part or fissura perpendicularis externa), fig. 32. The fissure on the mesial surface is distinguished by its depth and extent. Commencing Fig. 32. — Left hemisphere from above. Half nat. size. — a, Side branch of the intraparietal fissure in front of the parieto-occipital ; Ang, gyrus angularis ; c, central fissure (fissure of Rolando) ; Ca, gyrus centralis ant. ; dim, sulcus calloso-marginalis ; Op, gyrus centralis posterior ; fi, sulcus frontalis inf. ; -^<> gyrus frontalis inf. ; Fm. gyrus frontalis medius ; Fs, gyrus frontalis sup. ; fs, sulcus frontalis sup. ; ip, fissura intraparietalis ; Om, gyrus occipitalis medius ; Os, gyrus occipitalis superior ; otr, sulcus occipitalis transversus ; PF, frontal pole ; Pi, lobulus parietalis inf. ; PO, occipital pole ; poc, fissura parieto-occipitalis ; pre, sulcus prsecentralis inferior ; prcs, sulcus prscentraUs superior ; Ps, lobulus parietalis sup. ; pstc, sulcus centralis post. ; S, fissura Sylvii ; Sm, gyrus supramarginalis ; ts, sulcus temporalis superior. The antero-posterior diameter of the corpus callosum, as it lies in the great longitudinal fissure, is indicated by the distance between m and n. at the cortex-border some 4 or 5 cm. in front of its posterior angle, it runs downwards and sharply forwards, joining another fissure LOBKS OF CKUEBIUM. 89 (tissuni (.■alcariiia, about to bo (lcscril)ctl) at an acvito aiiglo. Ah already int'utioned, tliu parieto-occipital fissuro extends over the border, and runs a short course (1 to 2 cm.) nii woiiKl bo necessary. The gyrus forni- catus is sometimes looked upon, as we shall presently see, as a special lobe. By some {Ebcrstaller especially) it is denied that the occipital lobo reaches on the convex surface so far downwards and forwards as we have described. It must not be forgotten that any division of the hemispheres into lobes is artificial, valual)le only as a help to localising spots on its surface ; we can easily overlook the faults which are inseparable from any method of delimitation. [Although the classification of the lobes of the brain just discussed is highly ai'tificial, and like all other attempts at mapping out the brain into lobes, has no object other than to enable one to indicate with precision localities upon its surface, it yet appears to the Fig. 34.— Diagram showing the lobation of the cerebrum. — F, Frontal lobe; R, Rolandic lobe ; 0, occipital lobe ; T, temporal lobe ; /, island of Keil ; Py, pyriform lobe (uncinate gyrus) ; OB, olfactory bulb. translator that the brain during: its growth exhibits a well-marked tendency to bulge into defined lobes. A survey of all accessible mammalian brains leads him to the conclusion that these natural lobes have a distinct mor])hological, and, therefore, presumably also a distinct physiological significance. As shown in the accompanying diagram, the anterior end of the cerebral hemisphere is the part which has the appeai'ance of greatest stability. The appearance of the fossa of Sylvius on the outer surface seems to be due to an intimate relation which exists between the nucleus lenticularis and the overlying cortex, whereby a portion of the surface, afterwards known as the island of Reil, is fixed and prevented from participating in the free growth of the rest of the hemisphere. The result of this fixation of •92 FRONTAL LOBE. the floor of the fossa of Sylvius is a bvalging of the general surface of the hemisphere over the fossa, by which it comes at last to be covered in at the bottom of the "fissure" of Sylvius. In its overgrowth the sur- face exhibits a lobar conformation. The frontal lobe swells backwards ; but the erowth of this region is less exuberant than that of the rest of the convex surface. The portion of the brain which surrounds the crucial or central (Rolandic) sulcus — the sigmoid gyrus of animals — the ascending frontal and parietal convolutions or operculum of Man, con- stitutes the most distinct of all the lobes of the brain. Examination of a large number of brains leads to the conviction that the crucial and central sulci are homologous ; but the marking out of the lobe is not affected by the view taken upon this question. The sigmoid gyrus, or operculum, as it may well be called, grows downwards as a lappet which overhangs the fossa of Sylvius. The development of this lobe varies distinctly as the force, rapidity, and specialisation of movement exhibited by the animal. The inferior and posterior part of the hemi- sphere bulges forwards as the temporo-sphenoidal lobe, across or below the fossa of Sylvius, its position depending upon the extent to which this fossa is overhung by the lobes already mentioned. The pro- longation backwards of the posterior and superior pax't of the hemi- sphere as a natural lobe is obvious in many animals. In the rabbit, for ■example, it assumes a rounded form, the surface between the lobe and the rest of the brain being somewhat depressed. In this respect the brain of the rabbit contrasts remarkably with that of the mole. These four bulgings, frontal, opercular, occipital, and temporo-sphenoidal, are the largest and most distinct, but they include other less obvious elevations. It is very difficult to say how that portion of the surface which lies behind the Rolandic and tempoi'o-sphenoidal and in front of the occipital lobe should be allocated, although there are sufficient indications of the existence upon it of other less pronounced swellings. Doubtless each region of the cortex, in which a variable function is localised, is liable to variations in size {cf. figs. 149, 150, 151)]. 1. Frontal Lobe. — Three surfaces are to be distinguished — lateral,, mesial, and basal. Since the basal surface lies on the roof of the orbit, it is often termed "orbital." Three constant fissures are found on the lateral surface — (1) Sulcus prsecentralis, iprc + pros, fig. 30 (vertical frontal fissure, sulcus prferolandicus), lies in front of and almost parallel with the central fissure. (2) Sulcus frontalis superior, ./s; and (3) Sulcus frontalis inferior, fi, runs forwards from the pr?ecentral sulcus, parallel with the inner border of the hemisphere. The prjecentral sulcus, which begins a short distance above the KTJONTAT, I.OllK. 93 Sylvian fissuro, doos not, as a rule, nnich so far as tlw posterior end of the superior frontal fissure; ; a short fissure, ])rcs, runnin;^ in the same direction is, however, always to brt found at the hin