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The gross and minute anatomy of the cent
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THE GROSS AND MINUTE
ANATOMY OF THE CENTRAL
NERVOUS SYSTEM
GORDINIER
THE GROSS AND MINUTE
ANATOMY OF THE CENTRAL
NERVOUS SYSTEM
H. C. GORD1NIER, A.M., M.D.
PROFESSOR OF PHYSIOLOGY AND OF THE ANATOMY OF THE NERVOUS SYSTEM IN THE
ALBANY MEDICAL COLLEGE; MEMBER AMERICAN NEUROLOGICAL ASSOCIATION
wattb 48 ifulUpage plates anb 213 ©tber illustrations
MANY OF WHICH ARE PRINTED IN COLORS, A
LARGE NUMBER BEING FROM ORIGINAL SOURCES
PHILADELPHIA
P. BLAKISTON'S SON & CO.
IOI2 WALNUT STREET
1899
LX ' Copyright, 1899, by P. Blakiston's Son & Co.
Press of Wm, F. Fell & Co.,
1220-24 Sansom St.,
philadelphia.
TO
professor m. alien Starr,
IN GRATEFUL ACKNOWLEDGMENT OF MANY KINDNESSES,
THIS BOOK IS SINCERELY DEDICATED BY
ONE OF HIS FORMER PUPILS.
PREFACE.
The absence of a complete work in English on the Anatomy
of the Central Nervous System has convinced the author of the
necessity for the preparation of a systematic text-book which shall
present this most difficult subject in a concise but comprehensive
manner — a book that will meet the needs of medical students
and at the same time be of service to the clinician in associ-
ating symptoms of nervous diseases with anatomic facts. This
work consists essentially of the lectures which the author has
been accustomed to deliver to his students, amplified, rearranged,
and illustrated with many cuts, both original and borrowed.
The writer desires to acknowledge his indebtedness to the
o
magnificent works of Cajal, Edinger, Flatau, Dejerine, His,
Jakob, Koelliker, Lenhossek, Quain, Retzius, Starr, Van Gehuch-
ten, Wernicke, and others.
It is a pleasurable duty to testify to the help in this work from
the interest of many pupils and from the investigations set on
foot by the intelligent questions of many of those young seekers
after truth in successive years. With the earnest hope that the
author's labors will be helpful to some, and may perhaps clear
up some obscure questions here and there, this work is sub-
mitted to the students of medicine.
The writer owes a debt of gratitude to his former students,
Drs. James T. McKenna and Edgar R. Stillman, for assistance
rendered in the preparation of this work, and to Mr. E. N.
Reed for assistance in reading proof-sheets ; to Wait H. Still-
man and Joseph McKay, of Troy, N. Y., for the preparation
of photographs and microphotographs, and to Dr. Thomas W.
Salmon for the execution of several of the original drawings.
Hermon C. Gordinier.
Troy, N. Y., June 2, iSgg.
CONTENTS.
CHAPTER I.
The Histologic Elements of the Nervous System 17
Histology of the Nerve-cell, 17
Forms or Varieties of Nerve-cells, 24
Purkinje Cell, . 25
The Basket Cell of the Cerebellum, 28
Pyramidal Cells of the Cortex, 28
Cell-processes and Nerve -fibers, 30
The Axis-cylinder, }i
Nerve-fibers, 31
Non-medullated Fibers, 35
The Peripheral Nerve Terminations, 37
The Terminations of Sensory Nerves, 38
The End Bulbs of Krause, 40
The Tactile Menisques 42
The Corpuscles of Golgi, 43
The Muscle Spindle, 43
The Terminations of the Motor Nerves, 45
Neurone or Neurodendron, . . . 47
The Neuraxone or Axone, 49
The Neuroglia, 52
Blood-vessels and Lymphatics, .... 58
The Tunica Adventitia, 58
Tunica Media, . 59
Tunica Intima, 59
Veins, .... 60
Capillaries, 60
Lymphatics, 6l
The Adventitial Lymph-space, 63
Pericellular Lymph-spaces, 63
CHAPTER II.
Spinal Cord, 64
The Nerve-cells of the Cord 76
The Course of Fibers in the Sensory Tracts of the Cord, 95
The Course of the Fibers of the Dorsal Funiculi or Posterior Columns, . . 97
The Column of Goll, 99
The Columns of Burdach, 99
The Cornu Commissural and Septomarginal Descending Tracts, 100
The Cornu Commissural Tract, 101
The Septomarginal Tract, 102
Cowers' Anterolateral Ascending Tract — Fasciculus Ventrolateral is Super-
ficialis, 103
The Anterolateral Descending Tract of Marchi and Lowenthal, 104
The Olivary Tract of Bechterew, 105
A Long Sensory Tract in the Gray Matter (Ciaglinski), 106
Lissauer's Tract, 106
Anterior Ground Bundles, 107
The Ground Bundles of the Lateral Columns, or the Lateral Limiting Layers, 107
The Spinal Nerves, 108
Spinal Ganglia, 109
The Anterior or Motor Nerve-roots 112
x CONTENTS.
Spinal Cord (Continued) — Page
The Posterior or Sensory Nerve-roots, . . 113
The Appearances of Transverse Sections of the Cord at Different Levels, . . 114
Neuroglia of the Spinal Cord, 117
The Subpial Neuroglia Layer, the Rindenschicht of the Germans, , . . 119
Posterior Horns, .... . . 122
The Substantia Gelatinosa Rolandi, . .... 122
The Region of the Central Canal, . . . 122
The Blood-supply of the Spinal Cord, . . 122
Veins of Spinal Cord, .... ... 124
CHAPTER III.
The Medulla Oblongata or Bulb . . . . 125
The Fourth Ventricle, . . . . 131
A Transverse Section of the Medulla at the Level of the First Cervical Nerve. . 137
A Section at the Level of the Motor Crossway, 140
The Raphe, ...... . . 146
The Formatio Reticularis, . . . . . . 146
Connections of the Hypoglossal Nuclei, ... .... 152
The Vagus and Glossopharyngeal Nerves, . 155
The Olivary Bodies, . 159
The Central Tegmental Tracts of Bechterew and Flechsig, . 163
Section through the Middle of the Olivary Bodies, . 163
A Transverse Section of the Medulla near its Junction with the Pons, . . 166
The Abducens Nerve, ... 166
The Facial Nerve, .... ... 168
Connections of the Facial Nerve, . . . 171
The Auditory Nerve, .... . 171
The Cochlear Nerve, .... . 171
The Vestibular Nerve, . 1 72
Connections of the Auditory Nerve, . . . 175
The Superior Olivary Body, . . ... . . 176
Connections of the Vestibular Nerve, . 176
With the Cerebellum, . . . 176
With the Lateral Fillet, ... 177
With the Internal or Mesial Fillet, . . . . 177
With the Nuclei of the Sixth Nerve, 177
With the Olivary Body and the Lateral Column of the Same Side, 177
The Pons Varolii, ... . . 1 78
A Transverse Section of the Pons, . . 179
The Nuclei of Origin of the Trigeminal Nerve, 182
The Cerebral Connections of the Trigeminal Nerve, ... . 185
CHAPTER IV.
The Cerebellum or Epencephalon, .... . . . . . 186
The Vermis or Worm,
Superior Surface, .... ...
Inferior Surface, . . .
Lobules of the Superior or Dorsal Surface of the Cerebellar Hemisphere, . . 190
Lobules of the Inferior Surface of the Cerebellar Hemisphere, . . . . 190
Minute Anatomy of the Cerebellum, .... . . 193
The Cortex of the Cerebellum, ... ....
The Cells of Purkinje, ... 200
The Cerebellar Peduncles, . 202
The Middle Peduncles, ... 203
The Inferior Cerebellar Peduncles, or Corpora Restiformia, 203
CHAPTER
The Region of the Mid-brain, . . .
The Corpora Quadrigemina,
Minute Anatomy, . . .
The Cerebral Peduncles, .
The Mesial Fillet, or Lemniscus,
The Superior Cerebellar Peduncles, .
210
210
212
220
223
229
CONTENTS. xi
The Region of the Mid-brain {Continued) — Page
The Superior Longitudinal Bundle, ' 230
The Motor Oculi, or Third Pair of Cranial Nerves 235
The Connections of the Oculomotor Nucleus 23S
The Fourth Pair of Cranial Nerves, 240
The Superior or Accessory Nucleus of the Fifth or Trigeminal Nerve 240
CHAPTER VI.
Region of the Third Ventricle, 234
The Third Ventricle 244
The Pineal Gland, or Conarium, , 246
The Posterior Commissure, 248
The Optic Thalami, 24S
The Ganglion Habenulse, 2S7
Connections of the Opiic Thalamus, 25S
The Subthalamic Region, or Stratum Intermedium, 259
The Red or Tegmental Nucleus of Stilling, . 261
The Connections of the Red Nucleus, 262
The Substantia Nigra (Locus Niger; Intercallatum of Spitzka), .... 263
Retina, 263
The Layer of Optic Nerve-fibers, . ... . 264
The Layer of Ganglionic Cells, 264
The Inner Molecular Layer, 265
The Inner Nuclear Layer, 265
The Outer or External Molecular Layer, 266
The Outer Nuclear Layer, 266
The Layer of Rods and Cones, . 266
The Pigment-Layer, 267
The Course of the Optic Nerves and Tracts, 268
The Connections of the Optic Tracts, 273
The Optic Chiasm, 274
The Pituitary Body, 276
The Tuber Cinereum, 279
The Infundibulum, 279
CHAPTER VII.
The Membranes of the Brain, 280
Dura Mater, 280
Processes of the Cerebral Dura Mater, 281
The Falx Cerebri, or Processus Falciformis Major, 281
The Tentorium Cerebelli, . . 281
The Falx Cerebelli, or Processus Falciformis Minor, 282
The Arachnoid Membrane, 284
Subarachnoid Spaces, 285
The Pacchionian Glands, or the Arachnoid Villi, 287
The Pia Mater, 288
The Velum Interpositum and Choroid Plexuses, 288
The Tela Choroidea Inferior and Choroid Plexuses of the Fourth Ventricle, 291
Choroid Plexuses of the Fourth Ventric'e, 291
CHAPTER VIII.
Fore-brain or Prosencephalon, 293
Fissures 294
The Fissures of the External Surface of Each Hemisphere, 294
The Longitudinal Fissure, 294
The Transverse Fissure, 294
The Fissure of Sylvius 298
The Fissure of Rolando 299
The Parieto-occipital Fissure, 299
The Intraparietal or Interparietal Fissure 300
The Calcarine Fissure, . 300
The Collateral Fissure, 300
The Callosomarginal Fissure 303
xii CONTENTS.
Fore-brain or Prosencephalon {Continued) — Page
The Convolutions, Gyri, or Lobules, 3°3
The Frontal Lobe, 3°3
The Parietal Lobe, 3°°
The Ascending Parietal or Posterior Central Gyrus 306
The Superior Parietal Convolution, 307
The Inferior Parietal Convolution, 308
The Occipital Lobe, 3° 8
The Occipital Convolutions, 309
The Insula, or Island of Reil, 3 10
The Temporosphenoid Lobe, 3 J 3
The First or Superior Temporal Convolution, 313
The Second or Middle Temporal Convolution, 314
The Third or Inferior Temporal Convolution, 314
Convolutions of the Mesial Surface, 315
The Marginal Convolution, 215
The Gyrus Fornicatus, 316
The Quadrate Lobe, or Precuneus, 316
The Cuneus 3 l6
The Lingual Lobule, 316
The Limbic or Falciform Lobe, 317
The Gyrus Hippocampus, or Subiculum Cornu Ammonis 317
The Dentate Gyrus, or Fascia Dentata, 31S
The Base of the Cerebral Hemispheres, 318
The Inferior Longitudinal Fissure, 3 J 9
The Olfactory Bulb, 319
The Olfactory Tract, 319
The Corpus Callosum, 319
The Anterior Perforated Spaces 320
The Sylvian Fissure, 320
The Optic Chiasm or Decussation, 320
The Interpeduncular Space, 323
The Tuber Cinereum, 323
The Infundibulum, 323
The Pituitary Body, or Hypophysis Cerebri, 323
The Corpora Albicantia or Mammillaria, 324
Posterior Perforated Space, 324
The Crura Cerebri, or Peduncles of the Cerebrum, 325
Olfactory Lobe, Bulb, Nerves, and Tracts, 326
The Olfactory Nerves, 326
Olfactory Bulb : Its Minute Anatomy, 328
The Outer Layer, or Layer of Olfactory Nerve-fibers, .... 328
The Layer of Olfactory Glomeruli ; the Stratum Glomerulo-
rum 329
The Molecular Layer, or Stratum Gelatinosum, 330
The Layer of Central Nerve-fibers, 332
The Olfactory Tracts, 332
The Trigonum Olfactorium and Space of Broca, 335
The Anterior Commissure, 336
CHAPTER IX.
Histology of the Cerebral Cortex, together with the Minute Anatomy
of the Centrum Ovale, 338
The Histology of the Cerebral Cortex, 338
Layers of Cortical Cells and Fibers, 343
Superficial, Molecular, or Outer Cortical Layer, 343
Layer of Small Pyramidal Cells, 345
Layer of Large Pyramidal Cells 346
Layer of Polymorphous Cells, 350
The Anatomy of the Cornu Ammonis, or Hippocampus Major, and the Gyrus
Dentatus, . 350
Gyrus or Fascia Dentata, 359
The Centrum Ovale, 362
The Association Fibers, 364
Fibne ArcuaUe Propria, 364
CONTENTS. xiii
Histology of the Cerebral Cortex, together with the Minute Anatomy page
of the Centrum Ovale {Continued ) —
The Cingulum, or Bundle of the Gyrus Fornicatus, 364
The Fasciculus Arcuatus, 364
The Fasciculus Uncinatus, 368
The Superior Longitudinal Fasciculus, or Fasciculus Arcuatus of Burdach, 368
The Inferior Longitudinal Bundle 368
Fasciculus Occipitofrontalis (Forel and Onufrowicz), 369
The Perpendicular Fasciculus of Wernicke, 370
The Projection System of Fibers, 373
CHAPTER X.
General Anatomy of the Interior of the Cerebral Hemisphere 387
Corpus Callosum, 3&J
The Lateral Ventricles, 393
Eminentia Collaterals 394
The Corpora Striata, 398
The Lenticular Loop, or Ansa Lenticularis, 402
The Tractus Striothalamicus (Edinger), . 403
The Taenia Semicircularis 404
The Internal Capsule, 407
The Fornix, 413
The Septum Lucidum, 414
The Fifth Ventricle, 414
CHAPTER XI.
The Blood-vessels of the Brain, 416
Carotid Arteries, 4 I 8
The Anterior Cerebral Arteries, 421
The Middle Cerebral or Sylvian Artery, 422
The Central or Ganglionic Branches of the Middle Cerebral, . . . 423
Posterior Communicating Artery, 424
The Anterior Choroid Artery, 424
The Vertebral Arteries, 4 2 5
The Basilar Artery, 4 2 5
The Posterior Cerebral Arteries 425
The Circle of Willis, 428
Blood-vessels of the Cerebellum, 430
Arterial Supply to the Pons Varolii and Medulla Oblongata, 432
The Venous Systems of the Brain, 435
Characteristics of the Veins and the Venous Circulation, 435
The Cerebral Veins, 435
The Superficial Veins, 43 6
The Deep Cerebral Veins, 44°
Veins of the Cerebellum, 44°
The Venous Sinuses, 44 2
The Emissary Veins, 447
CHAPTER XII.
Cerebral Localization, 448
The Cortical Centers for General Sensations, ' 454
The Centers of Vision, 457
Retinal Representation in the Occipital Cortex, 462
Color-vision, 462
The Auditory Centers, 462
The Centers for Language, 4°5
The Center for the Reception of Heard Words, 466
The Center for the Reception of Memories of the Appearance of Objects
Seen and for the Appearance of Words as Written or Printed, 469
The Center for the Reception of the Appearance of Objects Gained through
the Sense of Touch, 47°
The Motor Speech-center, or Center for the Reception of the Muscular
Memories Necessary to Produce Speech, 47 1
The Cortical Center for Writing, 475
Sensory Center for Writing 479
xiv CONTEXTS.
Cerebral Localization (Continued) — Page
The Centers which Preside over the Higher Intellectual Faculties, 480
The Cortical Center for the Special Sense of Taste, 482
The Cortical Center for the Special Sense of Smell, 483
The Localization of Lesions in the Centrum Ovale, 484
Lesions of the Centrum Semiovale beneath the Motor Area 485
Centrum Ovale of the Temporal Lobe, 486
Localization of Lesions in the Centrum Ovale of the Parietal Lobe, .... 486
Centrum Semiovale of the Occipital Lobe 487
Lesions of the Corpus Callosum, 487
Localization of Lesions of the Internal Capsule 488
Basal Ganglia, 488
Localization of Lesions of the Corpora Quadrigemina, 488
Localization of Lesions in the Crura Cerebri, 489
Localization of Lesions in the Pons Varolii, 490
Localization of Cerebellar Lesions, 493
Lesions of the Middle Lobe, or Worm .493
Lesions of the Cerebellar Hemisphere, 494
Lesions of the Middle Cerebellar Peduncle, 495
Localization of Lesions in the Medulla Oblongata, 496
Localization of Spinal-cord Lesions, 499
The Divisions of the Cerebral Cortex According to Flechsig, 506
CHAPTER XIII.
The Embryology of the Central Nervous System, 508
The Development of the Spinal Cord, 5 I 3
Development of the Medulla Oblongata, 525
Cerebellum and Pons, 5 2 ^
Corpora Quadrigemina, Crura Cerebri, and Aqueduct of Sylvius, 530
The Third Cerebral Vesicle (Second Primitive Vesicle), Mesencephalon,
or Mid-brain, 53°
Optic Thalami, Infundibulum, Pituitary Body, Pineal Gland, Corpora Mammillaria,
and Optic Chiasm, 53 1
Development of the Cerebral Hemispheres, 539
Development of the Commissural System of the Cerebral Hemispheres, . . 543
The Evolution of the Fissures of the Cerebral Hemisphere 545
The Callosomarginal Fissure, 545
The Fissure of Rolando, 545
The Precentral Sulcus or Fissure, 546
The Fissures or Sulci of the Island of Reil, 546
The Various Fissures of the Frontal, Parietal, Temporal, and Occipital
Lobes, 546
Development of the Cranial Nerves, 547
Development of the Olfactory Lobe, 550
Development of the Retina and Optic Nerves, 552
The Retina, . 556
The Optic Nerve, 557
CHAPTER XIV.
Technic of the Macroscopic and Microscopic Examination of the Brain and
Spjxal Cord, 559
Virchow's Method, 560
Pitres' Method, 561
The Removal of the Spinal Cord, 563
Differential Stains for the Various Elements of the Nervous System, 563
Staining of Nerve-cells after the Method of Nissl, 564
To Stain Nerve-cells with Thionin 564
Method of Bevan Lewis, 565
Modification of Kronthal's Method, 565
Golgi's Method, for Staining Nerve-cells and Their Processes 566
Golgi's Rapid Method, 566
Golgi's Slow Method, 566
Berkley's Method of Impregnation 566
CONTENTS. xv
Technic of the Macroscopic and Microscopic Examination of the Brain and
Spinal Cord (Co>itinu,-J) — Page
Cox's Modification of the Golgi Sublimate Method, 567
Weigert's Method of Staining the Myelin Sheaths, 568
Marchi's Method 569
Neuroglia Stains, 569
Differential Stains for Neuroglia Fibers. — Method of Mallory, . . . 569
Mallory's Phosphotungstic-acid Hematoxylin Method for
Staining Neuroglia, 570
Stains for Axis-cylinder Processes, 571
Neutral Carmin, 571
Nigrosin, 571
Van Gieson's Method, 571
Stains for End Organs, Terminations of Nerves, and Collateral Branches, . 572
Method of Gerlach, 572
Method of Freud, 572
Method of S. Ramon y Cajal, 572
Ehrlich's Vital Methylene -blue Method (Modified by SemiMeyer), . 573
General Stains 573
Hematoxylin, , 573
INDEX, 575
ILLUSTRATIONS.
Fig. Page
i. A Group of Multipolar Nerve-cells from an Anterior Horn of the Spinal Cord. Show-
ing Nissl granules and pigment [Colored), , ' 19
2. Multipolar Nerve-cells from the Spinal Cord of an Ox. Stained with methylene-blue
and showing striation of cell-bodies and their processes (Colored), 21
3. A Ganglion Cell from an Anterior Horn of the Spinal Cord of an Ox. Showing the
arrangement of the Nissl granules and the ramification of the dendrites (Colored), 22
4. Section of Posterior Spinal Ganglion of Embryo Chick. Illustrating bipolar cells.
[After Van Gehuchten) , 24
5. Microphotograph of a Group of Multipolar Nerve-cells from the Anterior Horn of
the Human Spinal Cord. Stained with the Cox-Golgi method, 25
6. Microphotograph showing Purkinje Cell, 26
7. A Frontal Section through an Olfactory Bulb of a Six-weeks'-old Cat. Showing
layer of granular cells. (After Koelliker), 27
8. Microphotograph of Small Pyramidal Cells, 28
9. Microphotograph of Large Pyramidal Cells. 29
10. A Group of Large Pyramidal Cells from the Motor Area of the Human Brain.
Stained after the method of Bevan Lewis, 30
11. Nerve-fibers from the Muscle of a Frog Injected with Methylene-blue. Showing the
dark stained axis-cylinders, the nodes of Ranvier, and the separation of the terminal
axones into several primitive fibrillar. (After Koelliker), 32
■ 12. Medullated Nerve-fibers Blackened by Osmic Acid. (Landois and Stirling), . . . 33
13. Medullated Nerve-fibers (with Osmic Acid). (Landois and Stirling) , 33
14. A Bundle of Nerve -fibers Stained with Nitrate of Silver. Showing the outlines of
epithelial cells of the perineurium. (After Ranvier), 34
15. Remak's Fiber from Vagus of Dog. (Landois and Stirling), 36
16. Transverse Section of a Nerve (Median). (Landois and Stirling), 37
17. Termination of Sensory Nerves in Stratified Squamous Epithelium. Golgi Stain.
(After Retzius), 38
18. Vertical Section of the Skin of the Palm of the Hand. (Landois and Stirling), . . 38
19. Wagner's Touch Corpuscle from the Palm, Treated with Gold Chlorid. (Landois
and Stirling), ^8
20. Cylindric End Bulbs from the Conjunctiva of the Calf. (Merkel), 39
21. End Bulb of the Human Conjunctiva, Treated with a Mixture of Acetic and Osmic
Acids. ( W. Krause), 40
22. Articular Corpuscle from Phalangeal Joint in Man. (IV. Krause), ....... 40
23. A Microphotograph of Two Pacinian Corpuscles from the Mesentery of a Cat, ... 41
24. Tactile Menisque from the Nose of a Guinea-pig. (Ranvier), 42
25. Organ of Golgi from the Human Tendo Achillis, Chlorid of Gold Preparation.
(After Ciaccio), 43
26. Muscular Fibers with Motorial End Plates. (Landois and Stirling), 45
27. Motor Terminations in a Lizard, Stained by Methylene-blue. (Landois and Stirling)
(Colored), 46
28. A Large Cell of the Second Type of Golgi from the Granular Layer of the Cere-
bellum. (After Koelliker) (Colored), 51
29. Three Cajal Cells from the Cortex of the Gyrus Fornicatus of a Dog. (After Koel-
liker), 5 2
30. Motor and Sensory Neurones. ( fakob's Atlas) (Colored), 53
31. Microphotograph of Neuroglia Cells. Showing the relation they bear to the capil-
lary blood vessels. Stained after the Cox-Golgi method, 55
32. Three Neuroglia Cells (Astrocytes). Showing the relation the neuroglia processes
bear to the cell-body. (After Weigert) (Colored), 57
xvu
xviii ILLUSTRATIONS.
Fig. Page
33. Neuroglia Cells from the Cerebral Cortex of a Dog's Brain. Showing their connec-
tion with blood-vessels. {After Jvoelliker), 59
34. A Capillary Blood-vessel from the Gray Matter of the Spinal Cord of an Ox. Stained
with methylene-blue and magnified 400 diameters (Colored), 61
35. A Camera Lucida Drawing of a Part of the Gray Matter of the Anterior Horn.
Showing pericellular and perivascular lymph channels (Colored), ... . . 62
36. View from Behind of the Lower End of the Spinal Cord with the Cauda Equina
and Dural Sheath. (Allen Thomson), 66
37. Photograph of Human Spinal Cord 67
38. Diagram Showing the Relative Size and Form of Different Segments of the Coccy-
geal, Sacral, Lumbar, Dorsal, and Cervical Cord. (After Gowers), 70
39. A Transverse Section of the Human Spinal Cord through the Mid-lumbar Region to
Show its General Topography. Weigert's stain, .... 71
40. Transverse Section of the Human Spinal Cord at the Level of the Eighth Dorsal
Vertebra. X 10 - (Landois and Stirling), 73
41. Section of the Isthmus of the Lumbar Cord. Showing the central canal in the mid-
dle, surrounded by the substantia gelatinosa centralis. (After E. A. Schafer,
from Quoin), . 75
42. A Group of Multipolar Nerve-cells from an Anterior Horn of the Spinal Cord.
Showing Nissl granules and pigment (Colored), 77
43. Section of the Lumbar Cord of an Adult. Showing the anteromedian and postero-
lateral groups of cells (Colored), 79
44. Camera Lucida Drawing of a part of an Anterior Horn with Adjacent White Matter
of the Lateral Column. Showing nerve-fibers coming from that column and
coursing between and around the motor nerve-cells. Stained after method of
Weigert-Pal, 80
45. Diagram of a Transverse Section of the Spinal Cord. (After Starr), 81
46. Microphotograph of Transverse Section of Cord. Showing nerve-fibers cut across, . 85
47. Microphotograph of a Partial Transverse Section of the White Matter of the Spinal
Cord of an Ox, 87
48. Schematic Representation of the Situation of the Various Tracts of Fibers in the
Spinal Cord, ... . 88
49. Diagram Indicating the Course of the Motor and Sensory Fibers of the Spinal Cord
and Medulla (Colored), 93
50. Posterior Cornu and Column at the Last Dorsal Segment. (After Gowers), ... 97
51. Longitudinal Section of the Cord in the Cervical Region of a Sheep's Embryo,
Twenty-two Centimeters long. Showing the division of the posterior nerve-fibers
after entering the cord. (Landois and Stirling), 98
52. Lateral Column of a New-born Rabbit, 98
53. Transverse Section of the Spinal Cord at the Level of the First Sacral Segment.
(After Alexander Bruce) 101
54. Course and Termination of Gowers' Tract. (According to Hoche) 103
55. Transverse Section through a Posterior Spinal Ganglion. Stained after the method
of Weigert 109
56. A Group of Cells from a Human Posterior Spinal Ganglion. Stained after the
method of Nissl, no
57. Schematic Representation to Show the Origin and Relations of the Anterior and
Posterior Spinal Nerve-roots, Ill
58. A Section through the Spinal Cord of a New-born Mouse. Showing reflex collat-
erals from posterior nerve-roots terminating about the nerve-cells of the anterior
horn. (After Lenhossek), 113
59. Diagram Showing the Relative Size and Form of Different Segments of the Coc-
cygeal, Sacral, Lumbar, Dorsal, and Cervical Cord. (After Gowers), 1 15
60. Transverse Section through a Sacral Segment of the Spinal Cord. Weigert preparation, 116
61. A Section through the Spinal Cord of a Human Fetus, Twenty-three Centimeters in
Length. Showing the central canal with its substantia gelatinosa centralis and
ependymal cells. (After Lenhossek), IlS
62. Transverse Section of the Spinal Cord of a Human Embryo, Fourteen Centimeters in
Length. Illustrating the distribution of neuroglia. (After Lenhossek), 119
63. A Transverse Section through a Segment of the Dorsal Cord, to Show the General
Arrangement of Neuroglia. Nigrosin stain (Colored), 120
64. A Camera Lucida Drawing of a Field of the Lateral Column of Figure 63. Nigrosin
stain (Colored), 121
65. Scheme to Show the Course and Distribution of the Terminal Branches of the Arte-
rial Plexus of the Pia Mater. (After Van Gehuchten) 123
ILLUSTRATIONS. xix
Fig. Page
66. View from Before of the Medulla Oblongata, Pons Varolii, Crura Cerebri, and Other
Central Portions of the Encephalon ^Natural size). [At/en Thomson.) — [Front.
Quain' 's " Anatomy ") , 127
67. View of the Medulla Oblongata, Pons Varolii, Crura Cerebri, and Central Parts of
the Encephalon from the Right Side. (Quoin's " Anatomy.") — (Allen Thomson), 129
68. Posterior and Lateral View of the Medulla Oblongata, Fourth Ventricle, and Mesen-
cephalon (Natural size). (£. A. S.) — (Front Quain's '' Anatomy "), 133
69. Transverse Section through the Medulla Oblongata at the Beginning of the Motor
Decussaiion. (After Koelliker), 137
70. Diagram of the Structure of the Medulla Oblongata. (From Gotvers' "Diseases of.
the Nervous System"), 138
71. Transverse Section of the Medulla Oblongata through the Motor Decussation.
(After Henle), 141
72. Transverse Section of the Medulla at the Beginning of Hypoglossal Nerves. The
pyramidal or motor decussation is complete. (After Henle), 142
73. Section of the Medulla Oblongata at About the Middle of the Olivary Body. (After
Schwalbe.) — (Front Quain's Li Anatomy"), 143
74. Section of Medulla Oblongata at Level of Sensory Crossway. Weigert-Pal preparation, 145
75. Diagram Indicating the Course of the Motor and Sensory Fibers of the Spinal Cord
and Medulla (Colored), 147
76. Section Through Formatio Reticularis of the Medulla Oblongata. Method of Wei-
gert-Pal • 150
77. Microphotograph from a Seven-months' Human Fetus of Section of Formatio Retic-
ularis Grisea. The cells with their decussating axones are seen, 15 1
7S. Transverse Section through the Hypoglossal Nucleus. Method of Weigert-Pal
(Colored) 153
79. Medulla Oblongata from a Human Embryo of Eight Months. (After Koelliker), . 156
80. Transverse Section through the Medulla of a Mouse at the Level of the Commissural
Nucleus. (After Ramon y Cajal), 157
Si. Microphotograph Showing Multipolar Cells of Inferior Olivary Body, 159
82. Hemisection of Medulla to Show Olivary Body. Method of Weigert-Pal, .... 161
83. The Cerebello-olivary Tract. (After Edinger), . 165
84. Transverse Section through the Pons Varolii. Illustrating the origin of the sixth
and seventh cranial nerves, 167
85. Lateral View of the Medulla Oblongata with the Schematic Representation of the Nu-
clei and the Intramedullary Course of the Cranial Nerves. (From faiob's Atlas)
(Colored), 169
86. Transverse Section through the Distal Part of the Pons of an Eight-months' Hu-
man Embryo. [After Koelliker), . 172
87. Microphotograph Showing Cells of Ventral Auditory Nucleus. Method of Golgi, . 173
88. Dorsal Part of a Transverse Section of the Medulla Oblongata from a Human Em-
bryo of Six Months. (After Koelliker), 174
89. Transverse Section through Upper Part of Pons Varolii. Method of Weigert-Pal, . 178
90. Transverse Section through the Pons, in the Region of the Crossing of the Fourth
Nerve in the Dorsal Medullary Velum. (After Koelliker) 181
91. Lateral Sagittal Section through the Pons and Cerebellum of a Fetal Mouse. (After
Ramon y Cajal), 1S3
92. Section through Medulla of a Human Fetus of Seven Months. Showing axones and
collaterals of the trigeminal nerve entering the enlarged caput posterioris, .... 1S4
93. Figure Showing the Three Pairs of Cerebellar Peduncles. (After Hirschfeld and
Leveilli, from Sappey), . 187
94. Superior Surface of the Cerebellum, 191
95. Inferior Surface of the Cerebellum, ' 191
96. Microphotograph of Cerebellar Cortex. Showing the molecular and granular lay-
ers and the arrangement of the arbor vitse, 193
97. Section through Cerebellum to Show the Dentate Nuclei and White Matter of the
Hemispheres, 195
98. Microphotograph of a Section through the Corpus Dentatum of the Human Cerebel-
lum. Containing three large (multipolar) polygonal cells. Method of Berkley, . 195
99. Microphotograph Showing Basket Cells and Fibers Surrounding the Bodies of Two
Purkinje Cells (Human Cerebellum). Cox-Golgi method, 197
100. Granular Cells of the Inner Layer, with Ascending Neuraxones branching J-shaped
to Form the Horizontal Fibers of the Molecular Layer. (After Van Gehuchten), . 198
101. Microphotograph Showing the Moss-like Fibers of the Cerebellum. Cox-Golgi
Method, 199
xx ILLUSTRATIONS.
Fig. Page
102. Microphotograph of Purkinje Cell, 201
103. Scheme of the Fibers Passing to and from the Cerebellum, 205
104. Schematic Representation of the Different Constituents of the Cortical Gray Matter of
the Cerebellum. [After Van Gehuchten), 208
105. Lateral view of Mesencephalon, Pons, and Medulla. (Gegeulumer), 211
106. Metencephalon, Mesencephalon, and Thalamencephalon, from the Dorsal Surface.
(After Obersteiner), 212
107. Microphotograph of a Transverse Section through the Corpora Quadrigemina of a
Sheep. Showing layer of superficial cells. Method of Berkley, 213
108. A Characteristic Cell from the Third (Gray) Layer of the Optic Lobe of an Eigh-
teen day-old Chicken. Golgi's method. (After Koelliker), . . 215
109. Schematic Representation of the Essential Histologic Elements of the Optic Lobe
of a Bird. Showing the probable route taken by visual impressions to reach the
cerebral (occipital) cortex. (After Koeliiker) (Colored), 217
no. Transverse Section through the Corpora Quadrigemina from an Eight-months'
Human Fetus. (After Koelliker) • 219
111. Transverse Section through the Mid-brain of an Adult. Weigert's method, . . . . 221
112. Diagram of Section of the Crus. (Modified- from Wernicke, from Gowers), . . . . 222
113. Diagram Indicating the Course of the Motor and Sensory Fibers of the Spinal Cord
and Medulla (Colored), 225
114. Transverse Section through the Spinal End of the Posterior Corpora Quadrigemina of
a Cat. Weigert preparation. (Ajter Koelliker), 227
115. Horizontal Section through the Cerebellum, 229
116. Microphotograph through the Red Nuclei of the Mid-brain of a Young Sheep. Show-
ing decussation of the fibers of the superior cerebellar peduncles. Method of
Golgi, 231
117. Microphotograph of a Section through the Red or Tegmental Nucleus of a Young
Sheep. Showing seven of its characteristic, cells. Golgi method, 231
118. Course and Termination of Gowers' Tract. (According to Hoche) 234
1 19. Microphotograph through the Nucleus of Origin of the Motor Oculi Nerve. Show-
ing the multipolar cells of this nucleus. Golgi preparation, 236
120. A Camera Lucida Drawing through the Nuclei of Origin of the Third or Motor
Oculi Nerves. Showing the location of the nuclei and their cells, together with the
descending axones from those cells which go to form the nerve-roots (Colored), . 237
121. Diagram of the Groups of Cells Forming the Nuclei of the Third and Fourth Cranial
Nerves. (After Perlia, from Quain), 238
122. Transverse Section through the Mid-brain at the Level of the Posterior Corpora
Quadrigemina. Weigert preparation . 239
123. Schematic Representation of the Origin of the Trigeminal Nerve. (After Edinger), 241
124. Horizontal Section through the Cerebral Hemispheres to Show the Region of the
Third Ventricle, 245
125. Section through the Superior Part of One of the Superior Corpora Quadrigemina and
the Adjacent Part of the Optic Thalamus. (After Meynert.) — (From Quoin's
"Anatomy"), 250
126. Frontal Section through Basal Ganglia to Show the Nuclei of the Optic Thalamus.
(After von Monakow.) — (Front Starr' s "Atlas") 151
127. Microphotograph through Optic Thalamus Showing Busch Cells. Golgi method, . 252
128. Microphotograph through Optic Thalamus Showing Stellate Cells. Method of Golgi, 255
129. Microphotograph through Optic Thalamus with a Single Large Polygonal Cell.
Method of Berkley 255
130. A Perpendicular Section through the Brain of a Rabbit Lateral to the Corpus Mam-
millare. (After Koelliker) 257
131. Section of Corpora Quadrigemina. Showing cells of red nucleus. Cox-Golgi
method, 261
132. Diagrammatic Section of the Human Retina. (Schultze.) — (After Quain), .... 264
133. Section through the Retina of a Mammal to Show Layer of Horizontal Cells of the
External Molecular Layer and the Spongioblasts of the Internal Molecular Layer.
(After Ramon y Cajal), 265
134. The Essential Elements in the Retina of a Dog. (After Van Gehuchten), .... 267
135. The Origin and Relation of the Optic Tract. (G. D. Thane.) — (From Quain), . 268
136. Microphotograph through Optic Thalamus of a Sheep. Showing fibers from optic
nerve terminating about stellate cells. Method of Berkley, 269
137. Diagram of the Corpora Quadrigemina Anterior, 27 1
138. Horizontal Section through the Optic Chiasm of a Child. (After Koelliker), . . . 274
139. Frontal Section through the Interbrain. (After Koelliker) 275
ILLUSTRATIONS. xxi
Fl <5- Page
140. Sagittal Section of the Pituitary Body and Infundibulum with Adjoining Part of
Third Ventricle. {Schivalbe, from Quain) 277
141. Examples of Some of the Various Forms of Pyramidal Cells Found in the Ventral
Part of the Posterior Lobe of the Pituitary Body. {After Berkley), 278
142. Medisection of Brain, Showing Important Sinuses 282
143. Section of the Posterior and Lower Parts of the Brain within the Skull to Exhibit
the Subarachnoid Space and Its Relation to the Ventricles. {After Key and Ret-
zius.) — {From Quain), 286
144. Coronal Section through the Great Longitudinal Fissure, Showing the Meninges.
{Key and Retzius) , . 287
145. Vertical Section of the Cortex Cerebri and its Membranes. X 2 /^- {After Landois
and Stirling) , ' 289
146. View of the Upper Surface of the Velum Interpositum, Choroid Plexuses, and Cor-
pora Striata. {From Sappey, after Vuq d'Azyr), 290
147. Photograph of the Superior Surface of the Cerebrum, 295
148. Photograph of the External Surface of the Brain, 297
149. Photograph of the Median Surface, of the Brain, 301
150. Vertical Section through Frontal Lobe 301
151. Diagrammatic Representation of the Lobes of the Cerebrum, 305
152. Frontal Section through Parietal, Temporal, and Occipital Lobes, Together with the
Cerebellum, 307
153. Photograph of the Superior Surface of the Cerebrum, 311
154. Longitudinal Section through Cerebral Hemisphere to show the Centrum Semiovale
of the Frontal, Parietal, Occipital, and Temporal Lobes, 313
155. "Convolutions of the Mesial Surface of the Cerebrum, 315
156. Section through Left Gyrus Hippocampus. Showing the formation of the hippo-
campus major. Method of Weigert-Pal, 317
157' Photograph of the Base of the Human Brain, 321
158. Olfactory Lobe of the Human Brain. {His.) — {After Quain), 327
159. A Schematic Representation of the Principal Elements of the Olfactory Bulb of a
Mammal. ( Van Gehuchten), 329
160. Mitral Cells from a Mouse Twenty-four Days Old. {After Koelliktr), 331
161. A Frontal Section through an Olfactory Bulb of a Six-weeks' -old Cat. Showing
layer of granular cells. {After Koelliker) 333
162. Sections of Cerebral Convolutions. {After Baillarger, from Quain) 339
163. A Scheme of the Distribution of the Nerve-fibers of the Cerebral Cortex. According
» to the views of Meynert, Obersteiner, Edinger, and Dejerine. {After Dejerine), . 340
164. A Scheme Showing the Development of our Knowledge of the Different Cell-layers
of the Human Cerebral Cortex from the Time of Vicq d'Azyr, in 1790, to the time
of Cajal,in 1890. {After Dejerine) {Colored), . . , 3.41
165. A Cajal Cell in Course of Development from Section of Ascending Frontal Gyrus of
a Human Fetus at Eight Months. (After Retzius) 344
166. Microphotograph of Small Pyramidal Cells, 345
167. Microphotograph of Large Pyramidal Cells, 347
168. Cells with Ascending Axones from the Cortex of the Gyrus Fornicatus of a Six-
days' -old Mouse. {After Koelliker) , 348
169. Microphotograph of Polygonal Cell of the Fourth Layer of the Cerebral Cortex of a
Mouse's Brain, 349
170. Diagram of the Cells of the Cerebral Cortex. {After Starr), . . 351
171. Section through Left Gyrus Hippocampus. Showing the formation of the hippo-
campus major. Method of Weigert-Pal, 353
172. Microphotograph of a Frontal Section through the Brain of a Mouse. Showing the
peculiar involution of the gyrus hippocampus as it forms the cornu ammonis, . . . 354
173. Microphotograph of Cornu Ammonis of a Dog's Brain. Showing contour and for-
mation of cornu ammonis, 355
174. Microphotograph of Cornu Ammonis of a Rat's Brain. Showing three large
pyramidal cells, . 357
175. Microphotograph through Cornu Ammotiis. Showing the deep part of the superfi-
cial layer, or stratum lacunosum, 358
176. Microphotograph of Section through Cornu Ammonis and Gyrus Dentatus (Rat's
Brain). Showing a group of small pyramidal cells of the gyrus dentatus 360
177. Microphotograph of Small Pyramidal Cells of the Gyrus Dentatus and their Axones,
Forming the Moss-like Fibers 361
178. Horizontal Section of the Cerebrum above the Corpus Callosum to Show the Cen-
trum Ovale. {After Van Gehuchten), 363
xxii ILLUSTRATIONS.
Fig. Page
179. Cortex of Human Brain. Showing the nerve-fiber systems and plexuses. Weigert's
and Golgi's method combined. (After Andricn, from Starr's "Atlas"), . . . 365
1S0. Diagram of the Association-fibers of the Cerebral Hemisphere. [E. A. S., after
Meynert,from Quain), _ 367
1 Si. Semidiagrammatic Representation to Show the Fasciculus Occipitofrontalis, the Taenia
Semicircularis, and the Fasciculus Uncinatus. {After Bejerine), 369
1S2. A Scheme to Show the Origin and Termination of the Fibers of the Corpus Callo-
sum. [After Van Gehuchten), 370
1 S3. Microphotograph Showing the Radiation of the Fibers Composing the Corona Radi-
ata of a Rat's Brain. Method of Golgi 372
1S4. Diagrammatic Arrangement of the Projection Tracts Connecting the Cerebral Cortex
with the Lower Xerve-centers. {After Stan'), 374
185. Diagram to Show the Relative Position of the Several Motor Tracts in Their Course
from the Cortex to the Crus. [After Gowers), 375
186. Diagram of the Course of the Motor Tract as Shown in a Diagrammatic Horizontal
Section through the Cerebral Hemisphere, Pons, and Medulla. [After Gowers), . 377
187. Diagram Indicating the Course of the Motor and Sensory Fibers of the Spinal Cord
and Medulla [Colored'), 379
iSS. Diagram of the Course of the Pyramidal or Motor Tract of the Right Hemisphere.
[After Gowers) 381
189. [After Sachs). I. Sensory Tract. II. Horizontal Section of Cord. III. Relation
of Motor Tract to Nuclei of Cranial Nerves. (After Flat au) [Colored ), .... 383
190. Horizontal Section of Cerebrum above the Corpus Callosum to Show the Centrum
Ovale. [After Van Gehuchtcn) 388
191. Portion of a Median Section of the Brain, 389
192. View of the Corpus Callosum from Above. [From Sappey, after Foville, from Quain), 390
193. Photograph of Horizontal Section through Cerebrum to Show Lateral Ventricles, . 391
194. View from Above and the Side of the Whole Left Lateral Ventricle. Natural size.
[E. A. S. and G. D. T., from Quain), 395
195. Two Views of a Plaster Cast of the Cavities of the Cerebral Ventricles. (After
XVelckcr, from Quain), 397
196. Photograph of a Section through the Frontal and Tip of Temporal Lobes, .... 398
197. Photograph of Sagittal (Longitudinal) Section through a Cerebral Hemisphere, . . 400
198. Microphotograph of Large Rectangular Cells of Corpora Striata. Golgi method.
[After Starr), ... 401
199. Diagram of a Section through the Crus, etc., in Front of the Corpora Quadrigemina.
[Modified from Wernicke) 402
200. Scheme Showing the Tractus Striothalamicus. [After Edinger), 404
201. Photograph of a Longitudinal Section through a Cerebral Hemisphere to Show
the Ganglia of the Hemisphere, 405
202. Photograph of a Horizontal Section Through a Cerebral Hemisphere to Show
Relations of Internal Capsule, 409
203. Horizontal Section through the Right Hemisphere of a Man. [After von Monaktm>)
[Colored), 411
204. Distribution of Arteries in the Cerebral Cortex. [After Buret), 417
205. The Arteries of the Base of the Cerebrum. [G.B. T., after Buret, and from Nature,
from Quain) [Colored), 419
206. Cortical Distribution of the Middle Cerebral Artery (Diagrammatic). [G.B. T. ,
after Charcot, from Quain) [Colored), 422
207. Diagram of the Blood-supply to the Central Ganglia bythe Lenticulostriate Arteries,
External [E) and Internal (/). [After Buret), 423
208. Diagram Showing the Areas of Cortical Distribution of the Anterior, Middle, and
Posterior Cerebral Arteries Respectively. [E. A . S. , from Quiin) 426,427
209. Arteries of the Anterior Surface of the Pons and Medulla. [After Buret) 429
210. Arteries of the Posterior Surface of the Medulla. (After Buret) 430
211. Anterior and Posterior Median Arteries of the Pons and Medulla. [After Buret), . 433
212. Diagram to Show Plan of Distribution of the Arteries of the Medulla. (After
Buret) * _ _ 434
213. Superficial Veins of the Base of the Brain. (After Testut), .......... 436
214. Superficial Veins of the Internal Surface of the Left Hemisphere. [After Testut), . 437
215. Superficial Veins of the External Surface of the Left Hemisphere. [After Testut), 438
216. Veins of Galen, or the Deep Cerebral Veins. [After Van Gehuchten), . ... 439
217. Diagram Showing Communications Existing between the Lateral and Cavernous Sin-
uses and the External Veins, indicated in Figure by *. [After Leube)—[From
Loomis and Thompson," Practice of Medicine"), .'. 441
ILLUSTRATIONS. xxiii
F 'G- Page
219. Plan Showing the Relative Position of the Structures in the Right Cavernous Sinus,
Viewed from Behind, (After Gray), 446
218. Medisection of Brain, Showing Important Sinuses, 444
220. Diagram of the Motor Areas N on the Outer Surface of a Monkey's Brain. (HorsUy
and Sehdfer, from Landois and Stirling), 449
221. Diagram of the Motor Areas on the Marginal Convolution of a Monkey's Brain.
(Horsley and Sehdfer, from Landois and Stirling) 450
222. A Drawing of the Left Cerebral Hemisphere (Human) [Colored), 451
223. A Drawing of the Right Cerebral Hemisphere (Human) [Colored), 452
224. Position of the Arm-center. (After Cowers) 453
225. Position of the Center for the Face and Tongue. (After Gcrwers), 453
220. Cortical Visual Centers on the Outer Surface of the Hemisphere. (After Cowers), . 45s
227. Inner Aspect of the Right Hemisphere. (After Cowers) 458
228. Diagram of Course of Optic Nerve-fibers from the Cortex to the Retina. (After
Sahli, Modified and Extended, from Tyson), 459
229. Situation of Lesions Causing Word-deafness Only. (From Starr), 467
230. Situation of Lesions Causing Word-blindness Only. (From Starr), 469
231. Situations of Lesions Causing Aphasia. (After Starr, from Tyson), 472
232. Diagram Showing Location of Tumorwhich Produced Complete Agraphia (Author's
Case) 475
233. View from Before of the Medulla Oblongata, Pons Varolii, Crura Cerebri, and Other
Central Portions of the Encepbalon (Natural size). (Allen Thomson) — (From
Quain' s "Anatomy "), 491
234A. Diagram of Skin Areas Corresponding to Definite Spinal Segments. (From Tyson,
after Starr), 497
234B. Diagram of Skin Areas Corresponding to Different Spinal Segments. (From Tyson,
after Starr), 498
235. Diagram (Framed from an Original Investigation) Showing the Relation of the A^er-
tebral Spines to Their Bodies and to the Origin of the Several Nerve-roots. (After
Cowers), 5 00
236. Diagram of Lesions Showing Brown-Sequard's Paralysis. (After Starr, from Tyson), 503
237. Schema Showing Chief Symptoms in Left Unilateral Lesion of the Dorsal Cord.
(After Erb,from Tyson), 5°3
238. Sections Showing Stages in the Conversion of the Medullary Groove into the Neural
Canal. (E. A. S.,from Quain), 509
239. Longitudinal Section of Head of a Four-and-a-half-day Chick. (After Von Mihal-
kovics,from Edinger), S 11
240. Fore-part of the Embryo Viewed from the Dorsal Side. (After Koelliker, from
Quain), _ 5 Z 4
241. Myelospongium from Spinal Cord of Three-and-half-weeks' Human Embryo. (His,
from Quain) - 5*5
242. Inner Ends of Spongioblasts with Germinal Cells between Them. (His, from
Quain), 5 J 5
243. Inner Ends of Spongioblasts. (His, from Quain), 515
244. Three Neuroblasts, Each with a Nerve-fiber Process Growing out Beyond the Base-
ment Membrane of the Embryonic Spinal Cord. (His, from Quain), 515
245. Ependymal Fiber of Marrow of a Seven-days'-old Embryo of a ChickeD. (After
Golgi), 517
246. Lower End of the Spinal Cord of a Human Embryo of Three Months. (From
Minot), 5 l8
247. Section of Spinal Cord of Four Weeks' Human Embryo. (His, from Quain), ... 519
248. Transverse Section of the Cervical Part of the Spinal Cord of a Human Embryo of
Six Weeks. (After Koelliker, from Quain), 519
249. Transverse Section of the Spinal Cord from the Upper Dorsal Region of a
Human Embryo of Six Weeks. (After His, from Minot), .......... 521
250. Sections across the Region of the Calamus Scriptorius of the Brain. (His, from
Quain), 5 2 3
251. Sections across the Fourth Ventricle of a Somewhat Older Embryo. (His, from
Quain), ■ • - - ■ 5 2 3
252. Sections across the Lower Half of the Fourth Ventricle of a still Older Embryo.
(His, from Quain), 5 2 3
253. Transverse Section of the Medulla Oblongata of His' Embryo Ru. (After W. His,
from Minot) 5 2 &
254. Transverse Section of the Medulla Oblongata of His' Embryo Mr. (After W. His,
from Minot) , 5 2 7
xxiv ILLUSTRATIONS.
Fig. Page
255. Median Section through the Brain of a Two-and-a-half-months' Fetus, {//is, from
Qnaiit) 529
256. Fetal Brain of the Third Month. [His, from Quain), 531
257. Transverse Sections through the Brain of a Sheep's Embryo of 2.7 Centimeters in
Length. (After Koelliker, from Quain), 533
258. Brain of a Chick Embryo, Fourth Day. (After Duval, from Minot), 535
259. Three Sections through the Fore-brain of a Four-and-a-half-weeks' Embryo, (//is,
from Quain), 537
260. The Surface of the Fetal Brain at Six Months. (R. Wagner, from Quain), . . , 540
261. Brain of a Human Embryo of about Three Months (According to Marchand, four
months). (After F. Marchand, from Minot), 541
262. Fetal Brain of the Beginning of the Eighth Month. (Mihalkovics,from Quain), , 544
263. Sections across the Hind-brain of a Human Embryo, 10 mm. Long. (His, from Quain), 548
264. Section from the Same Embryo at the Exit of the Facial Nerve. (//is, from
Quain), 549
265. Cranial Nerves of a Human Embryo, 10.2 mm. Long. (His, from Quain) 550
266A. Brain of Chick of Second Day, viewed from below, to show the formation of the
optic vesicles by outgrowth of the side of the fore-brain, and at the same time by
the folding over of the enlarged part, the production of a grooving or cupping of the
vesicles. (His, from Quain. ) B. Brain of Human Embryo of Three Weeks.
Showing the primary optic vesicles as outgrowths from the fore-brain. (His, from
Quain), 553
267. Side View of Anterior Part of Brain of More Advanced Human Embryo. Showing
the primary optic vesicle folded and tucked. (His, from Quain) 553
268. Side View of the Same Part of the Brain in a still more Advanced Embryo, the Eye
Having Been Cut Away. (His, from Quain), 553
269. Rabbit Embryo of Ten and One-half Days ; Section of the Lens Anlage. (From
Minot), .' 555
270. Vertical Section of the Eye of a Chick Embryo of the Third Day. (From A/inot), . 555
271. Rabbit Embryo of Thirteen Days; Section of the Eye. (From Minot), 556
INTRODUCTION.
That the comprehension of the normal and abnormal activities
of an organ must be based upon an understanding of its structure
is a truth as old as Galen, and certainly there can be no doubt
that a knowledge of the anatomy of the nervous system is
absolutely essential to a clear understanding of its diseases.
While teachers of the diseases of other organs have usually
been content to refer their students to the general anatomic
course for details of the anatomy of those organs, teachers
of the diseases of the nervous system have almost universally
included, both in their text-books and in their lectures, a more or
less complete account of the anatomy of the brain and spinal
cord ; not alone because the symptoms of nervous diseases
can only be explained by constant reference to the anatomy of
the nervous organs, but also because in the general anatomic
course the finer details of the peculiarly complex anatomy of
the nervous system are neither sufficiently described nor demon-
strated.
With one or two exceptions the text-books on nervous dis-
eases continue to present, along with the pathology, more or
less of the anatomy of the nervous system ; but many of the
teachers of this subject have of late years confined themselves
rather strictly to its pathology, and have not attempted to com-
bine with this, within the limits of a single course of lectures,
the large mass of facts and theories in regard to the anatomy
of the central nervous organs which has increased so rapidly
during the past few decads. In a well-arranged college course
students should have acquired and digested this anatomic
knowledge before commencing the study of nervous diseases.
It is most desirable, it seems to me, that this change which
xxvi INTRODUCTION.
has partially taken place in the medical colleges should occur
also in the text-books, so that these last may devote their
entire space to pathology, as their title implies, and not be
burdened by a necessarily somewhat cursory description of the
anatomy of the central nervous organs, the importance of which
is so great that every student of neurology should possess a
book devoted exclusively to its harmonious and complete expo-
sition. There seems, therefore, to be room for an English work
which shall present the anatomy of the central nervous organs
systematically and thoroughly ; which shall begin with the
simplest elements and proceed to their most complex combina-
tion in these intricate organs without getting beyond the grasp
of the undergraduate student, and yet shall be complete enough
to satisfy the demands of the neurologist.
Since the separation in the teaching of the anatomy and of
the pathology of the nervous system took place in the Albany
Medical College, Doctor Gordinier has been in full charge of
the instruction in the anatomic part of the subject, and this
book is the fruit of years of teaching, and, therefore, should,
and I believe does, possess the two characteristics so desirable
in teaching — clearness of style and profuseness of illustration.
Henry Hun.
Alrany, June 6, rSgg.
THE
GROSS AND MINUTE ANATOMY
OF THE
CENTRAL NERVOUS SYSTEM.
CHAPTER I.
THE HISTOLOGIC ELEMENTS OF THE NERVOUS
SYSTEM.
The histologic elements comprise nerve-cells, nerve-fibers, and
end organs, neuroglia tissue, blood- and lymphatic vessels, and
lymph-spaces.
HISTOLOGY OF THE NERVE-CELL.
The nerve-cell — known also under the various names of nerve
vesicle, corpuscle, or ganglion cell — is the beginning of a nerve
unit, or neurone.
This unit, or neurone, consists of a cell-body with its various
protoplasmic branches, one of which becomes a central or per-
ipheral nerve.
The nerve-cell is a granular protoplasmic body containing a
large, usually centrally placed, clear nucleus, in which lie one or
more nucleoli. The nucleus is surrounded by a delicate mem-
brane, and consists of a network which, because of its affinity
for staining with different reagents, is called chromoplasm, and
of a more fluid material in the meshes of the network called
karyoplasm. Many of the cells in the sympathetic system
contain two or more nuclei. During life the nucleolus is
2 17
IS CENTRAL NERVOUS SYSTEM.
usually angular, provided with processes, and capable of motion.
After death the nucleolus is highly refractive, and assumes a
spheric form. The cells of the central nervous system have no
enveloping membrane or capsule, but many of the cells of the
peripheral sympathetic ganglia, and the ganglia of the posterior
spinal nerve-roots, have membranous envelopes continuous with
the sheaths of the nerves.
If a nerve-cell is stained after the method of Nissl, — i.e., with
methylene-blue or magenta red, — and is examined with a high
power of the microscope ( T V oil immersion), the protoplasm sur-
rounding the nucleus will be seen to consist of' a stainable and
an unstainable portion. The stainable portion, which stains very
intensely, is composed of a number of granular bodies separated
from one another by parts of the clear unstainable portion, which
appears as a matrix in which these granular bodies rest. Each
Nissl body consists of a number of very fine chromatic granules,
held together by a very delicate coagulable achromatic substance
of unknown nature. These bodies are somewhat irregular, and
differ as to size and shape : some are oval or round, others
assume the form of a wedge or spindle, while others are rod-like.
The nucleus is frequently covered at each end or pole by
granular masses of like nature, called nuclear caps. These
granular bodies are often called the granules of Nissl, because
this observer discovered a very unique method of staining them,
by means of which they can easily be recognized and studied.
They have the appearance of being arranged somewhat concen-
trically in layers, starting from the center and growing more
numerous as they approach the periphery. They are called
protoplasmic or chromophyllic granules, because of their affinity
for the basic anilin dyes.*
Nissl, from the study of the relation that the nerve-cell body
bears to its nucleus, has divided nerve-cells into two chief
groups. The first group comprises the somatochrome nerve-
cells, or those cells whose protoplasm completely surrounds the
* These chromophyllic bodies also exist in the dendritic or protoplasmic processes of the cell,
where they are lengthened and appear rod-like, presenting a faint longitudinal striation. The
axone, or axis-cylinder, and the adjacent portion of the cell-body from which the axone springs,
called the axone hillock, is entirely free from these granules.
Y^^Psw""
>«-
ih'/C, spotted, from the spotted appearance they give to the cell.
THE HISTOLOGIC ELEMENTS OF THE NERVOUS SYSTEM. 23
states that in no other cells of the body do granules exist having
the foregoing- characteristics.
Benda does not support this statement of Lenhossek. He
says that similar bodies exist in gland-cells, liver-cells, cells of
the pancreas, and in the cells of some sarcomatous tumors.
In nearly all of the cells of the spinal cord and in many of the
cortical brain-cells, particularly the large ganglion cells of the
latter, exist granular masses of yellowish pigment. These
masses of pigment are frequently found close to the giving off
of the axis-cylinder, and sometimes extend into that process
and rarely into some of the dendritic branches of the cell. This
pigment, although apparently consisting of small granules, must
differ chemically from the chromophyllic bodies of the cell,
because it does not ordinarily take any staining reagent which
stains the protoplasmic granules. When, however, structural
alterations in the cell occur, the pigment is increased in amount
and will stain a deep black with osmic acid.
Max Schultze, about thirty years ago, discovered that each axis-
cylinder of a nerve-cell was made up of a number of longitudinal
fibrillae, which were continuous with the fibrillar that exist in the
nerve-cell and in its protoplasmic branches. This observation of
Schultze has been entirely ignored, until verified by the recent
histologic studies of Becker, Flemming, Benda, Marinesco,
Dogiel, Nissl, and Lugaro. These observers have found that in
the unstainable portion of the cell-body exist numbers of fine
fibrillae, which extend into and terminate in the ultimate ramifi-
cations of the dendritic processes and are continuous with the
fibrillae of the axis-cylinder.*
* Cowers' theory of the conduction of nervous impulses is based upon the recent concep-
tion of the neurone and upon the histologic construction of nerve-cells and fibers as described
long ago by Alexander Schultze and recently confirmed by Becker, Flemming, Marinesco, and
Dogiel. He believes that the fibrillae, which have their origin in the terminal ramifications of
the dendrites and which pass uninterruptedly through the cell, conduct nerve impulses through
that body, the impulses having come from the surrounding collaterals or axones, through the
matrix or ground substance in which the cell and its dendrites rest. According to this theory
the nerve impulses are merely in transit, the cell taking no part in their production. Whether
or not the matrix in which the cell-body and dendrites rest, and in which the terminations of
collaterals and axones occur, simply transfers impulses from nerve terminals to the fibrils in the
dendrites of the cell, or whether it has anything to do with the excitation of nerve impulses,
is still an open question. The only function assigned to the cell is trophic in character, the
nutrition of the cell processes being dependent on the cell-body, this nutritional influence prob-
ably coming from the nucleus of the cell.
24
CENTRAL NERVOUS SYSTEM.
FORMS OR VARIETIES OF NERVE-CELLS.
The bipolar cells are found in the ganglia of the sympathetic
system, in the posterior spinal ganglia, and ganglia of the sen-
sory cranial nerves in embryonic life, and in the molecular layer
of the. cerebral cortex. They are spindle or pyriform in shape,
and have a single fine axone springing from each pole.
The multipolar nerve-cells
are very irregular masses of
protoplasm having a variety
of shapes : stellate, angular,
pyramidal, caudate, polygo-
nal, and the like. They
are the largest of all the
cells of the nervous sys-
tem, varying in diameter
from eight to one hundred
and twenty /*, the largest
being about sixteen times
the size of a red blood-
corpuscle. They possess a
large, clear nucleus with a
nucleolus, and they usually
contain masses of yellowish
pigment. They give off from
various angles of the cell-
body numerous fine, tubular
protoplasmic processes or
dendrites, which divide and
subdivide like the branches
of a tree. They are found
throughout the entire nervous system, but predominate in the
following localities — viz., in the anterior horns of the spinal cord,
in the medulla oblongata, in the cortex cerebri, basal ganglia,
and in the peripheral ganglia of the sympathetic.
There exist other forms of nerve-cells, probably transitional
in character, among which may be mentioned the so-called gran-
ular cells, which form a distinct variety in many situations; as for
Fig. 4. — Section of Posterior Spinal Gang
lion of Embryo Chick. Illustrating bi
polar cells. — {Afttr Van Gehuckten.')
THE HISTOLOGIC ELEMENTS OF THE NERVOUS SYSTEM.
25
example : the cells of the substantia gelatinosa Rolandi of the
posterior horns of the spinal cord, in the retina, olfactory bulb
(the character of the small cells which compose the granular
layer of the olfactory bulb is still much in dispute ; Cajal believes
them to be nerve-cells, while Van Gehuchten and Koelliker think
they are neuroglia), and in the cerebellum, where they form a
distinct layer. Their protoplasm is scant, and their processes
are very difficult to discern with the ordinary methods of stain-
ing. They are probably bipolar cells.
J? IG . q. MlCROPHOTOGRAPH 01' A GROUP OP MULTIPOLAR NERVE-CELLS FROM THE ANTE-
RIOR Horn OF the Human Spinal Cord. Stained with the Cox-Golgi method.
PURKINJE CELL.
Another characteristic form of nerve-cell is the so-called
Purkinje cell, found in the cortex of the cerebellum, where they
form a distinct layer. They are quite regular in outline, some-
what flattened, and distinctly flask-shaped. They are from thirty
to seventy ,,. in their longest diameter, and contain a large,
spheric nucleus, "ten to fifteen ,,. in diameter," with a distinct
26
CENTRAL NERVOUS SYSTEM.
nucleolus. They are situated in the cortex of the cerebellum,
between the external or molecular layer and the internal or
granular layer. From their basal surface proceeds a distinct
slender axis-cylinder process of great length, which continues
downward through the granular layer into the medullary por-
tion or white matter, where it becomes a medullated nerve-fiber.
In its course it gives off collaterals which curve upward and ter-
m *
■ - ' >',«s
<&
\f ) T - ■■' .iff ..?,:•' JUa>
FIG. 6. — MlCROPHOTOGRAPH SHOWING PURKINJE CELL.
minate in the external or molecular layer. From the opposite
or cortical end of the cell-body spring two processes, or den-
drites, or a single process which soon divides into two, and this
dichotomous division continues until an enormous tree-like mass
of fibers is produced, which covers a considerable extent ot sur-
face and is always distinct from the branching processes of other
cells.
THE HISTOLOGIC ELEMENTS OF THE NERVOUS SYSTEM.
NF
MZ
01
Fig. 7. — A Frontal Section through an Olfactory Bulb ok a Six-weeks' -old Cat.
Showing layer of granular cells. — [After Ifoelliker.)
Ep. Ependyma. Gl. Glomerule. Kz. Layer of granular cells. M. Molecular layer. MF.
Layer of medullated fibers. MZ. Layer of mitral cells. Sir. gr. Granular zone (stratum
granulosum).
2S
CENTRAL NERVOUS SYSTEM.
THE BASKET CELL OF THE CEREBELLUM.
This is a cell peculiar to the cerebellar cortex, the axone or
nerve process of which has a horizontal course, and continually
gives oft descending collateral branches which terminate in
brushes of fibrils about the bodies of the Purkinje cells, giving
them the appearance of resting in a basket of fine fibrils.
■ -~!
!$*
f
\Wm
m
Fig. N. — Microphotograph of Small Pyramidal Cells.
PYRAMIDAL CELLS OF THE CORTEX.
The pyramidal cells of the cerebral cortex are so numerous
and of such anatomic ami physiologic importance that the)' may
well be described separately. They properly belong to the
multipolar variety of cells, are triangular or pyramidal in shape,
ami possess a fine apical dendrite or process which gradually
tapers as it extends toward the superficial layer of the cortex.
Many ot these apical processes bifurcate close to their cortical
ending. Delicate protoplasmic processes or dendrites project
THE HISTOLOGIC ELEMENTS OF THE NERVOUS SYSTEM.
29
from all parts ot the cell-bod)', while from each corner of the
base springs a dendrite which extends obliquely to the plane of
the vertical fibers of the cortex, and divides into numerous
irregular branching filaments, all of which are studded in their
course by minute protoplasmic offshoots, the so-called gemmules
or buds. These buds or gemmules are minute in diameter
where they join the dendritic branch, grow larger, and terminate
in a beaded extremity. They are also found on the apical
branches of the cell. They probably serve to convey nerve
Fig. 9. — Microphotograph of Large Pyramidal Cells.
impulses from one dendrite to another, or receive impulses from
the intracortical end-apparatus (Berkley). The axis-cylinder
process generally springs from the middle of the basal portion
of the cell-body, passes vertically downward, is usually of great
length, smooth, less in diameter than the dendrites, and gives off at
right angles collateral branches. Each cell contains an oval nu-
cleus with well-defined nucleolus, and varies from eight to twelve
u in diameter. The larger ones are called the giant pyramidal
cells (Betz),and are probably motor in function. Some of these
CENTRAL NERVOUS SYSTEM.
cells, according to Bevan Lewis, measure thirty to ninety-six p in
length and twelve to forty-five jj. in breadth. This variety of
cell nearly always contains an abundance of yellowish pigment.
^V
/ \ ""*v
tt ■}.
Fig. io. — A Grout of Large Pyramidal Cells from the Motor Area of the
Human Brain. Stained after the method of Bevan Lewis.
CELL PROCESSES AND NERVE-FIBERS.
The protoplasmic body of the cell gives off from projections
on its surface a number of processes which branch out, tree-
like, in all directions and divide into filaments of extreme fine-
THE HISTOLOGIC ELEMENTS OK THE NERVOUS SYSTEM. 31
ness. Some of them are very long, while others are short and
thick. These branches, or dendrites, as they are termed, do not
anastomose with one another or with adjacent or distant cell
branches, but may influence other dendrites or nerve processes
by near approximation or slight contact.
By connecting with blood-vessels and lymphatics, they may
serve a nutritional function (Golgi). Most observers, however,
believe that they have a nervous function, collecting nerve im-
pulses from nerve-cell processes and conveying them to their
own cell-body.
The Axis-cylinder. — The most important process of the
cell is the axis-cylinder process, known also under the name
of neuraxone, axone, or nervous process. Along this process
travel nervous impulses to or from the cell-body. It is, there-
fore, the conducting medium for nervous impulses originating
irom the periphery and passing centrally, or vice versa. This
process is always single except from the cells in the uppermost
cortical layer of the cerebrum and in the cells of the spinal
and sympathetic ganglia and ganglia of the sensory cranial
nerves. The cells of the posterior spinal ganglia in man have
been incorrectly described by many authors as belonging to the
bipolar type. This description is true insomuch as it applies to
the lower vertebrates. In man, however, this bipolar type is
seen only in fetal life. As development goes on, the two axones
either become fused in their entirety, forming one axone, which
branches T-shaped, or, what seems more probable, there is an
unequal development of the cell-body to form a protoplasmic
pedicle from which the branching axone takes its origin. The
axone starts as a delicate single strand of protoplasm, variable in
length, which frequently gives off a few lateral branches (collat-
erals). In most cases it receives, soon after leaving the cell-
body, a layer of myelin, and becomes a medullated nerve-fiber.
NERVE-FIBERS.
There are two chief forms of nerve-fibers, the white and the
gray — the medullated and the non-medullated.
The white or the medullated nerve-fibers form the white sub-
3^
CENTRAL NERVOUS SYSTEM.
stance of the cerebrospinal system and the greater part of the
peripheral nerves, and give to them their characteristic micro-
scopic and macroscopic appearance. Each fiber consists of a
central portion or core, — the axis-cylinder of Purkinje, which is
Fig. ii. — Nerve-fibers from the Muscle of a Frog Injected with Methylene-
blue. Showing the dark stained axis-cylinders, the nodes of Ranvier, and the separation
of the terminal axones into several primitive fibrillae. — {After Koi-lliker.)
the essential part of the nerve and conducts nervous impulses.
This axis-cylinder is longitudinally striated, due to the fact that
it consists of a number of exceedingly fine fibrillar, which are
arranged longitudinally and are held together by a very deli-
THE HISTOLOGIC ELEMENTS OF THE NERVOUS SYSTEM.
33
cate stroma or network called by Koelliker "neuroplasm," and
by Waldeyer "axioplasm." At
the termination of a nerve-fiber
the axis-cylinder often separates
into a number of terminal fila- «— ^
ments, which are termed the primi-
tive fibrillse of Max Schultze (Fig.
n).* Near the nodes of Ranvier
it is not uncommon to find trans-
verse markings in the axis-cylin-
der. These are the so-called lines
ofFrohmann. Each axis-cylinder
B IS
S-
Fig. 12. — Medullated Nerve-fibers
Blackened by Osmic Acid. — [Lan-
dois and Stirling.)
fs. Ranvier's node. sch. Schwann's
sheath.
Fig. 13. — Medullated Nerve-fibers
(with Osmic AcidJ. — (Landois and
Stirling. )
a. Axis-cylinder. s. Sheath of Schwann.
n. Nucleus. /, /. Granular substance at
the poles of the nucleus, r, -, . Ranvier's
nodes, where the medullary sheath is
interrupted and the axis-cylinder appears.
/, i. Incisures of Schmidt.
is the prolonged axone of a nerve-cell, and remains uninter-
*The fibrils composing the axone consist of a conduciing medium called by Hansen " hya-
loplasm," and a granular material called " spongioplasm." Gowers calls the terminal fila-
ments of the axis-cylinder "axites."
3
34
CENTRAL NERVOUS SYSTEM.
rupted throughout its course. It is surrounded by a delicate
sheath composed of a substance similar to horny material, hence
called neurokeratin. This sheath is called the axilemma. Sur-
rounding the axis-cylinder is a layer of semifluid fatty material
which stains deep black with osmic acid, called myelin ; or, from
its discoverer, the white substance of Schwann. The myelin
has an inner and an outer layer of neuro-
keratin, with an intervening network of
the same material, in the meshes of
which exist the droplets of semifluid
myelin. Owing to its peculiarity of re-
fraction the myelin gives to the nerve-
fiber as seen with transmitted light its
double contour (Figs. 12 and 13).
The myelin, or white substance of
Schwann, apart from giving to the nerve-
fiber its contour, is a protective to the
axis-cylinder, and possibly may act as
a non-conducting medium to prevent
nerve impulses from being deflected from
their intended course. It does not form
a continuous envelop for the axis-cylin-
der, but at rather regular intervals it is
interrupted, leaving gaps or constrictions
called Ranvier's nodes. The nerve seg-
ment between two nodes is called an
interan nular or internodal segment. The
internodes are united within the sheath
of Schwann by the constricting bands
of Ranvier, a sort of annular ring formed
of an albuminous-like material. This
material stains readily with silver nitrate, which agent also
stains the axis-cylinder at the nodes, producing the so-called
crosses of Frohmann (Fig. 14). Each internodal segment con-
tains just below its middle an oval-shaped nucleus situated
beneath the covering of the myelin or neurilemma in a depres-
sion of the myelin. The nodes of Ranvier are supposed to
subserve a nutritive function, permitting the passage of blood
Fig. 14. — A Bundle of
Nerve-fibers Stained
with Nitrate of Silver.
— [After Ranvier.')
Showing the outlines of epi-
thelial cells of the perineu-
rium. The dark crosses of
Frohmann on the nerve-fibers
at the nodes of Ranvier are
due to the staining of the
axis-cylinder and of a band
of intercellular substance
which encircles the axis-cyl-
inder at the node.
THE HISTOLOGIC ELEMENTS OF THE NERVOUS SYSTEM. 35
plasma into the axis-cylinder. Certain incisures can be seen
in the myelin which extend obliquely across it. These are
named, from their discoverers, the incisures of Schmidt or
Lantermann. By many, and particularly Koelliker, they are
considered as artifacts, the latter observer never having found
them in living nerves.
It has been shown that the layer of myelin which surrounds
most of the nerve-fibers of the central nervous system appears
for the various tracts at different periods of fetal development.
Flechsig has shown that fibers which have the same function
develop simultaneously, and in the direction in which they con-
duct impulses.
Surrounding the myelin, or white substance of Schwann,
is a closely investing, delicate, almost structureless membrane,
called the neurilemma, primitive or tubular sheath of Schwann.
This sheath is continuous and uninterrupted throughout,
although it presents constrictions which correspond to the
nodes of Ranvier, which dip down almost to the axis-cylinder.
Some medullated fibers lack this sheath of Schwann, or neuri-
lemma, being simply inclosed in myelin ; as, for example,
the white fibers of the brain and columns of the spinal cord.
The size of medullated fibers varies very much, this being due
mainly to the amount of myelin surrounding them, although
the axis-cylinders also vary in diameter. The diameter of the
axis-cylinder depends somewhat upon the cell from which it
springs and upon the length of its course, the large cells usually
giving off nervous processes of greater diameter and length
than those from smaller cells. The medullated nerves vary
from 2 to 2.5 /i, or rrin> to rsW of an inch, in diameter.
Non-medullated Fibers. — These fibers occur chiefly in the
sympathetic system, and are sometimes called sympathetic or
Remak's fibers. These non-medullated fibers differ in form.
First, simple nerve strands presenting globose swellings are
found, occurring near the termination of nerve-fibers, being
formed by the splitting-up of their axis-cylinder processes — as,
for example, the optic nerve layer of the retina, the ramifications
of the olfactory nerves, and as is often seen among the fibers of
the spinal cord and brain. Secondly, as naked axis-cylinders,
36
CENTRAL NERVOUS SYSTEM.
fit^o
which are primitive fibers held together by a cement substance —
as, for example, the axis-cylinder processes of many nerve-cells.
Thirdly, axis-cylinders surrounded by a very delicate sheath,
which corresponds to the neurilemma or
Schwann's sheath of medullated nerves.
These fibers bear the name of Remak, their
discoverer, and are commonly described as
the non-medullated fibers of the sympathetic
system, or the fibers of Remak (Fig. 15).
They contain nuclei situated at intervals in
each fiber lying between the axis-cylinder and
neurilemma, and are faintly striated.
This form is found in the sympathetic sys-
tem and in some of the cranial nerves. All
nerves of the embryo up to a certain period
of development are also of this kind.
The size of the non-medullated fibers
varies, these being in general about half the
size of the medullated fibers ; but some — as,
for example, those of the olfactory bulb —
are many times the size of the medullated
fibers.
The nerve-fibers are joined into fasciculi
or bundles by a connective-tissue sheath.
These bundles are in turn united to other
bundles, to form a peripheral nerve. The
sheath which unites and covers the nerve
bundles or fasciculi is called the epineurium
(Fig. 16). It serves to convey to the nerve
bundles blood-vessels, lymphatics, and nerves.
The connective-tissue sheath which encircles
each individual bundle or fasciculus is covered
by epithelium, and from its position is called
the perineurium. The delicate sheath which is
between the fibers of each single fasciculus is termed the endo-
neurium. It serves to give support to the nerves and blood-ves-
sels, and communicates by channels with the lymphatics of the
perineurium. The nerve trunks themselves are supplied by
Fig. 15. — Remak's Fi-
ber from Vagus of
Dog. — [Landois and
Stirling. )
b. Fibrils. n. Nucleus.
p. Protoplasm sur-
rounding it.
THE HISTOLOGIC ELEMENTS OF THE NERVOUS SYSTEM.
37
nerve-fibers which extend through the epineurium, terminating
in end bulbs. These are the nerves of the nerve, or the nervi
nervorum.
The nerve centers of the cerebrospinal axis are supported by
connective-tissue envelopes, connective tissue about the blood-
vessels, and, most important of all, a neuroglia tissue matrix.
THE PERIPHERAL NERVE TERMINATIONS.
The peripheral nerves, which contain mixed motor and sensory
Fig. 16. — Transverse Section oe a Nerve (Median). — (Landois and Stirlir,
ep. Epineurium. pe. Perineurium, ed. Endoneurium.
fibers, terminate in one of three ways. First, in interepithelial
arborizations ; second, in specialized end organs or tactile cor-
puscles ; and third, in the motorial end plates. The first two
methods of termination belong to the sensory nerves only, while
the last method belongs to the sensorimotor nerves of the
voluntary muscles. There are six chief forms of specialized end
organs — namely, the tactile corpuscles of Meissner and Wagner,
the end bulbs of Krause, the Pacinian or Vater's corpuscles,
the tactile menisques, the. corpuscles of Golgi, and the so-called
muscle spindles.
3«
CENTRAL NERVOUS SYSTEM.
THE TERMINATIONS OF SENSORY NERVES.
First, the interepithelial arborizations. This is the usual mode
of ending for a large number of sensory nerves. They termi-
Fig. 17. — Termination of Sensory Nerves in Stratified Squamous Epithelium.
Golgi Stain. — {After Rclzius.)
d
Fig. 18. — Vertical Section of the Skin of the Palm
of THE Hand. — (Landois and Stirling.)
a. Blood-vessels, b. Papilla of the cutis vera. c. Capillary.
d. Nerve-fiber passing to a touch corpuscle, f. Nerve-
fiber divided transversely, e. Wagner's touch corpuscle.
g. Cells of the Malpighian layer of the skin.
Fig. 19. — Wagner's Touch
Corpuscle from the
Palm, Treated with
Gold Chlorid. — {Landois
and Stirling.)
n. Nerve-fibers, a, a. Groups
of glomeruli.
THE HISTOLOGIC ELEMENTS OF THE NERVOUS SYSTEM.
39
nate in the skin and mucous membranes, as well as in the hair
bulbs, the teeth, the tendons of muscles, and many of the glands
of the body. As the nerve-fiber approaches the surface of
the skin or the mucous membrane it loses its myelin and neuri-
lemma. The naked axis-cylinder then repeatedly divides, form-
ing a ramified plexus of fine fibrils, which terminate by passing
among the epithelial cells of the skin and mucous membrane
(Fig. 17).
Secondly, the tactile corpuscles of Meissner and Wagner.
These touch corpuscles are most numerous where the sense of
touch is best developed, — that is, in the palms of the hands and
Fig. 20. — Cylindric End Bulbs from the Conjunctiva of the Calf. — [Merkel.)
A. Longitudinal section. B. Transverse section. n. Entering nerve-fiber. c. Nucleated
capsule.
soles of the feet, especially in the ends of the fingers and toes, —
more sparingly in the tip of the tongue, skin, and lips, back of
the hands and feet, skin of the nipples, and in the conjunctiva.
They are oval or elliptic in shape, about seventy p. or tbtt of an
inch in length, and thirty p or tbtt of an inch in thickness (Figs. 1 7
and 18). They are composed of connective tissue consisting of
a capsule which sends numerous trabecular into its interior, which
serve to support the nerve-fibers in their spiral or convoluted
course. Several medullated nerve-fibers pass to the base of each
capsule and surround it in a spiral manner ; they then enter the
capsule and pursue a spiral course, supported by the trabecular,
and terminate in globular enlargements close to the capsule.
4 o
CENTRAL NERVOUS SYSTEM.
THE END BULBS OF KRAUSE.
These are very small cylindric or oval-shaped corpuscles,
and are slightly bent near their base. They are from 0.075 to
0.14 mm. in diameter. They consist of a nucleated connective-
tissue capsule, in the interior of which is a core of soft protoplasm
containing numerous polyhedral cells, in which rests the naked
axis-cylinder, the myelin being lost when the latter enters the base
of the capsule (Figs. 20, 21, and 22). The neurilemma continues
Fig. 21. — End Bulk of the Human Conjunc-
tiva, Treated with a Mixture of Acetic
and Osmic Acids. — ( W. Krause.)
n. Two medullated nerve-fibers entering cor-
puscle.
Fig. 22. — Articular Corpuscle from
Phalangeal Joint in Man. — ( IV.
A'rause.)
inward with the axis-cylinder, and forms a lining to the capsule
and a covering for the central protoplasmic core. The axis-
cylinder usually terminates near the extremity of the capsule in an
elongated globular expansion. Rarely the nerve-fiber separates
into two or three parts which become twisted before terminating.
These corpuscles are found in the mucous membranes of the
mouth, lips, nose, and conjunctiva, in the papillae of the tongue,
in the mucous membrane of the glans penis and vagina, and in
the synovial membranes of the joints of the fingers, in which
latter place they are often called articular end bulbs.
THE HISTOLOGIC ELEMENTS OF THE NERVOUS SYSTEM.
41
The Pacinian or Vater's corpuscles are irregularly oval-shaped
bodies situated on some of the cerebrospinal and sympathetic
nerves, and are from ?\ to tV of an inch in length and from ? V
to yV of an inch in breadth. Each corpuscle incloses the termi-
flg. 23. — a mlcrophotograph of two pacinian corpuscles from the mesentery
of a Cat.
nation of a single nerve-fiber, which, with its connective-tissue
sheath and blood-vessel, forms a pedicle by which the corpuscle
is attached to the main nerve. These bodies consist of a lami-
nated connective-tissue capsule composed of from forty to fifty
tunics or lamellse. Each tunic decreases in thickness from with-
42 CENTRAL NERVOUS SYSTEM.
out inward, and the several tunics are arranged similarly to the
coats of an onion. Each lamella consists of white connective-
tissue fibers arranged transversely, and of elastic fibers which
pass in a variety of ways. The lamellae are lined with endothelial
cells, and are slightly separated from one another by a transparent
fluid, probably lymph (Fig. 23). In the central part or axis of
each corpuscle is the core, made of a soft material (protoplasm)
through which passes the prolongation of the nerve-fiber. A
single medullated nerve-fiber passes into each corpuscle, the
sheath of Schwann uniting with the capsule. The myelin is lost
and the naked axis-cylinder proceeds through the soft central
core, to terminate near the extremity of the capsule in a vari-
cosity. Sometimes the fiber forks, each division terminating in
Fig. 24. — Tactile Menisque from the Nose of a Guinea pig. — [Ranvier.)
n. Nerve-fiber, a. Tactile cells, m. Tactile discs, e. Epithelial cells.
an oval expansion. These corpuscles are found in the subcuta-
neous tissue on the nerves of the fingers and toes in the neigh-
borhood of joints, on the intercostal nerves, the nerves of the
arms and of the neck, on those of the nipples, on those of the
external genitalia of both sexes, on the nerves of the abdominal
sympathetic, and particularly on the nerves of the mesentery.
They are very abundant on the nerves of the mesentery of the
cat, where they are often so large that they may be seen with
the naked eye.
THE TACTILE MENISQUES.
Another form of termination of the sensory nerve-fibers is
that of the tactile menisques of Ranvier (Fig. 24). They occur
THE HISTOLOGIC ELEMENTS OF THE NERVOUS SYSTEM.
43
in both the superficial and deep layers of the skin, and consist of
plexuses of nerve-fibers which form arborizations whose branches
become flattened, resembling leaves in shape.
THE CORPUSCLES OF GOLGI.
A special form of muscle nerve-ending has been described by
Golgi and Rollett, and occurs in tendons, particularly near the
point of junction of the tendon with the muscle. At that point
the bundles of fibers composing the tendon become somewhat
enlarged, and medullated nerve-fibers, after losing their myelin,
penetrate the fibers composing the tendon. They then, as naked
Fig. 25. — Organ of Golgi from the Human Tendo Achillis, Chlorid of Gold
Preparation. — {After Ciaccio.)
m. Muscular fibers, t. Tendon muscles. G. Golgi's organ. «. Nerve-fibers.
axis-cylinders, break up into a number of fibrils, which form
terminal arborizations, somewhat spindle shaped. This enlarge-
ment of the fibers of the tendon, with the terminal arborizations,
forms the so-called corpuscles of Golgi (Fig. 25).
THE MUSCLE SPINDLE.
These bodies have been found in nearly all the skeletal
muscles, but are especially abundant in the biceps of the arms
and in the small muscles of the hands. They are found more
abundantly in the belly of the muscle than in the tendon, and are
44 CENTRAL NERVOUS SYSTEM.
most easy of demonstration in atrophied muscles. They do
not occur or else are very uncommon in the muscles of the
eye, the diaphragm, and intrinsic muscles of the tongue. They
vary from 2 to 4 mm. in length and 0.15 to 0.4 mm. in breadth.
These bodies, as their name implies, are spindle shaped. They
are often found lying parallel to the nerve which supplies
them ; frequently two spindles will be found in the same plane,
lying end to end.
The muscle spindle consists of muscle-fibers, nerves and
their endings, a connective-tissue sheath, blood-vessels, and
lymphatics.
One or more muscle-fibers, somewhat diminished in size, enter
either the distal or proximal pole of the muscle spindle and
pass toward the center of the spindle, where they usually divide
into several smaller fibers ; they then begin to lose their trans-
verse markings, and become nucleated, the nuclei completely
filling the muscle-fiber. These nuclei exist for a short distance
in the muscle-fiber at the equatorial region of the spindle, after
which the fiber again becomes striated. Each spindle is usually
supplied by two nerves, one of which enters the spindle at the
distal or proximal end, and one entering the spindle at its cen-
tral part. The nerve-fiber which enters the spindle at its center
is the larger, and probably terminates about the nuclei of the
muscle-fiber. The other nerve-fiber forms a plexus of fibrils
beneath or in the sheath of the spindle, or else terminates in
bulbous extremities. The nerve sheaths blend with those of
the muscle spindle on entering the latter.
The sheath of the spindle consists of several laminae, which
have, on cross-section, the appearance of an onion. At the
center of the spindle there are from eight to ten laminae, but at
the poles they become less in number and blend with the
sheaths of the muscle. The sheath of the spindle sends many
septa into the interior of the spindle, which pass between the
muscle-fibers and nerves. The blood-vessels of the spindle
usually enter and leave at the opening for the central nerve.
A lymphatic space exists in the center of each spindle, occupy-
ing about its middle third. The function of the muscle spindle
is not positively known, but from the situation and important
THE HISTOLOGIC ELEMENTS OF THE NERVOUS SYSTEM.
45
nerve connection, it is supposed to be concerned in the produc-
tion and conveyance of muscle-sense impressions.
THE TERMINATIONS OF THE MOTOR NERVES.
The motor nerves terminate both in voluntary and involuntary
muscles. In the former the nerves are all medullated and have
their origin in the cerebrospinal system, while in the latter they
are non-medullated and belong to the sympathetic system. The
motor nerves to the voluntary muscles terminate chiefly in
special expansions which have received the various names of
motor nerve plates or organs, motor sprays, or fields of inner-
End plate
Muscle nucleus
Fig. 26. — Muscular-fibers with Motorial End Plates. — {Landois and Stirling.)
vations of Kuhne, or the eminences of Doyere. These end
organs or plates are located beneath the sarcolemma of the
primitive muscle-fibers, and are continuous with their sarcous
substance. They are flattened or slightly elevated masses of
granular protoplasm having an irregularly spheric or oblong
shape, and contain cells with investing envelopes and clear oval
nuclei and nucleoli.
In mammals each individual muscle-fiber usually has but one
end organ and receives but one nerve-fiber. If the muscle-
fiber be especially long, more than one nerve-fiber may enter it.
In reptiles, however, two or more end organs are frequently
found in a single muscle-fiber. Each motor nerve-fiber as it
passes into the muscle repeatedly divides at the nodes of Ranvier
4 6
CENTRAL NERVOUS SYSTEM.
into a number of branches, the courses of which are both ascend-
ing and descending. These in turn give off a number of fine
forked branchlets, each of which pursues mostly an oblique or
transverse course between the muscle-fibers, forming an intra-
muscular nerve plexus. Each primitive nerve fibril still medul-
lated passes to a muscle-fiber, having divided just before reaching
it. As it enters the fiber it loses its myelin, and the neurilemma
sheath becomes continuous with the sarcolemma of the muscle-
fiber. The naked axis-cylinder then passes beneath the sarco-
lemma resting upon the motorial end plate, when it divides into
two or three primary branches, which further subdivide into a
Fig. 27. — Motor Terminations in a Lizard, Stained by Methylene-blue. — [Landois
and Stirling.')
a. Muscular fibers, b, A nerve trunk which splits up into small branches, c, containing a few
medullated fibers, d. The medullated fibers, d, end in motorial end plates, e.
number of ultimate flat twigs expanding at their ends into minute
bulbs. The nerve termination is then a distinct arborization,
each branchlet retaining its individuality and not anastomosing,
the whole figure resting upon the motorial end plate, which in
turn is continuous with the sarcous element of the muscle-fiber.
It is probable that the contractile wave of the muscle has its
point of origin in the motorial end plate.
The motor nerves for the non-striated or involuntary muscles
are non-medullated, and come mostly from the sympathetic
system. Near their termini they ramify and form close net-
works or plexuses of fibers. In the angles formed by the cross-
THE HISTOLOGIC ELEMENTS OF THE NERVOUS SYSTEM. 47
ing of the fine fibrils composing these plexuses ganglion cells
are found. From these ganglionic plexuses fibrillae arise which
pass between the muscle-fibers and continue parallel with them.
They frequently bifurcate in their course, each division giving
off small branches which terminate in varicose or bulbous ex-
tremities opposite the nuclei of the muscle-cells, without passing
into them. According to Arnold and others, however, these
terminal fibrillae pass into the muscle-cells and end in their
nuclei.
NEURONE OR NEURODENDRON.
The nervous system is known to consist of a great number of
anatomic units variously arranged, which, after the development
of their protoplasmic processes, remain absolutely independent
bodies. These anatomic units have been designated neurones,
or nerve units, by Waldeyer, and neurodendrons, or nerve trees,
byKoelliker. They are the essential elements of nervous tissue
and possess peculiar physiologic, chemic, psychic, and trophic
properties.
The neurone, or nerve unit, is made up of three parts : the
nerve-cell body, the protoplasmic processes of Deiter, or, as they
are now called after His dendrites, with their terminal ramifica-
tions, and lastly, the so-called axis-cylinder process, axone, or
neuraxone, with its collateral branches and terminal end brushes
(telodendrons).
The neurones are arranged in certain localities in distinct
groups — viz., in the cortex of the brain and cerebellum they exist
in several thin layers ; in the medulla oblongata or bulb and
spinal cord they occur in vertical columns ; in the central ganglia
they are arranged in distinct masses. In many locations they
occur singly or in slight groups.
The neurone, then, is a unit, an individual entity, consisting of
cell-body, dendritic processes, neuraxone, collaterals, and term-
inal arborizations.
The cell-bodies, or neurocytes, present a variety of forms, the
most generally distributed one being the irregular, large or small
multipolar form. The form of cells have been sufficiently dis-
cussed, page 25.
4 S CENTRAL NERVOUS SYSTEM.
The dendrites, or the protoplasmic processes which arise from
the irregularities of the surface of the cell-body, branch in various
directions, dividing and subdividing like the branches of a tree,
not anastomosing with one another or with adjacent or distant
dendritic processes of other cells. They are variable in length,
some branches being quite long, whereas others are very short.
Their thickness also varies, some of the short branches being
rather thick, while the longer branches are quite thin. They
frequently present along their course varicose-like swellings.*
They are variable as to number, some cells possessing but one
or two dendrites, while others possess from five to seven. If the
finer dendritic processes be observed with a moderately high
power of the microscope, say with a 1 or { of an inch objective,
there will be seen numerous minute protoplasmic buds jutting
from their sides. They are somewhat club-shaped and are very
minute in diameter, close to the parent stem, but become longer
and larger to end in bead-like extremities. These lateral buds
have been termed gemmules. They are very abundant on the
dendritic branches of the cortical cells of the cerebrum or of the
Purkinje cells of the cerebellar cortex. Owing to the fact that
these lateral buds have until very recently been observed only
in specimens stained after the method of Golgi, they have been
considered by some authors as artifacts, but Ramon y'Cajal has
shown that they may be beautifully demonstrated in specimens
stained by the intravital method of Ehrlich.
The function of the dendrites is not positively known, and
much of our knowledge is as yet hypothetical. They probably
convey nerve impulses to the cell-body from which they spring,
influencing nerve terminations or filaments and other dendrites
by contiguity of surface or possibly by contact through the
gemmules. From the extent of surface occupied by the den-
drites and their ramifications one would believe that they may
serve a nutritional function, aiding the nutrition of the cells of
which they are a part.
The belief of Golgi that they were connected with the blood-
* These tuber-like or varicose swellings that are seen on the dendrites of specimens pre-
pared after the method of Golgi are due to local collections of chromophyllic granules (Len-
hossek).
THE HISTOLOGIC ELEMENTS OF THE NERVOUS SYSTEM. 49
vessels, and that the nutritive plasma was carried by them to
the cell-body has been disproven by various observers.
Lenhossek states that after carefully examining many Golgi
sections he failed to find any connection between the dendrites
and the blood-vessels. He further showed that they were devel-
oped long before the blood-vessels. He believes that they
absorb nutritive plasma from all parts of their surface, the plasma
coming from the lymph-spaces which, surround the dendrites,
which spaces exist in great abundance throughout the central
nervous system. There is probably a much greater circulation
and absorption of nutritive plasma in the gray than in the white
matter, because of the abundant blood supply from the enormous
number of capillaries and the liberal lymphatic distribution about
the blood-vessels, nerve-cells, and processes in the former.
Berkley states that in the cerebral cortex the dendrites are
surrounded by a mass of nerve-fibers which give off at frequent
intervals collaterals which divide and subdivide, ending in little
bulbs, which constitute the intracortical end apparatus of these
nerve-fibers. These little bulbar endings come into close ap-
proximation with the globular endings of the gemmules, and
he states that it is exceedingly probable that the nervous im-
pulses pass from cell to cell, or those impulses arising from the
periphery and passing brainward, pass across from the bulbous
endings of the nerve-fibers to the gemmules and through the
dendrites to the cell-bodies, thus exciting the cells into activity.
Berkley also states that in many diseased conditions — "intoxi-
cations " — these lateral buds are the first part of the neurone to
become affected ; and he believes that the early symptoms of
dementia paralytica may be explained by their destruction and
consequent loss of function as conductors of nervous impulses.
THE NEURAXONE OR AXONE.
The most important of the protoplasmic processes is the one
which in most cases is destined to become, after receiving a
covering of .myelin, a medullated nerve-fiber. This process
is the so-called axis-cylinder process, neuraxone, or simply
axone. The neuraxones are smooth throughout, and are usu-
4
50 CENTRAL NERVOUS SYSTEM.
ally variable as to the length of their course, some having
a short course, while the course of others is very long. They
are of extreme fineness, and give off, at varying distances, side
branches called collaterals (paraxonen). These collaterals may
be seen issuing nearly at right angles from many of the nerve-
fibers composing the columns of the spinal cord or the medulla.
The collaterals frequently branch, and these in turn give off deli-
cate branches, all of which end in fine brushes of fibers or arbori-
zations about the dendrites of nerve-cells. The collaterals are
usually finer than the neuraxones from which they issue, and
often become medullated. The nerve-fibers, which are simply
medullated axis-cylinders, frequently divide toward the end of
their course into two or three branches, each one retaining its
individuality.
Both the axis-cylinder process, or axone, and its collaterals
(paraxonen) terminate or end about nerve-cells in brush-like
expansions or tree-like arborizations, each little branchlet either
ending free or in a minute bulbous expansion. These terminals
are termed the telodendrons. As a rule, to which there are
but few exceptions, the neurones throughout the cerebrospinal
system possess but one neuraxone, the exceptions being found
in the cells of the posterior spinal ganglia, which often possess
two axones, one passing centrally, dividing T-shaped in the
spinal cord, one division passing vertically upward, the other
downward, each giving off at right angles numerous collaterals
which enter the gray matter of the cord. The other, a periph-
eral axone, passes peripherally to terminate in a sensory end
organ. The cells of the ganglia connected with the sensory
cranial nerves have somewhat similar connections, possessing
two axones, one central and one peripheral.
The Cajal cells in the outer or molecular layer of the cerebral
cortex are known to possess two or more axones. They form
a distinct type of neurone (Fig. 29).
Some of the cells of the visceral sympathetic ganglia have
many axones or axis-cylinder processes.
Neurones may be classified into three chief types: (1) Those
whose axones are very long, giving off collaterals, but retaining
their individuality. They pass directly into the white matter
THE HISTOLOGIC ELEMENTS OF THE NERVOUS SYSTEM.
51
and become medullated nerve-fibers, ending in near or distant
parts of the nervous system, or in peripheral end organs.
Because the cells of the anterior horns of the spinal cord,
whose functions are known to be motor, all possess so long a
neuraxone Golgi termed this first type of neurone " motor."
We know positively, however, that long axones are possessed
not only by motor neurones, but by sensory ones as well — as,
for example, the neurones of the multipolar cells of the ves-
Fig. 28. — A Large Cell of the Second Type of Golgi from the Granular Layer
of the Cerebellum. — (After Koelliker.)
icular column of Clarke, which pass across through the white
matter of the cord and become vertical in the direct cerebellar
tract, thence passing upward to terminate in the cerebellum.
Another example of long axones may be mentioned, the
ascending branches of the posterior nerve-roots, many of which
continue throughout the whole length of the posterior columns
and terminate in the medulla about the cells of the nuclei of the
posterior columns.
5-
CENTRAL NERVOUS SYSTEM.
AS
In the neurones of the second type, or
second type of Golgi, the neuraxones, after a
short course, break up into innumerable fine
filaments which form networks, thus losing
their individuality. Because of their abund-
ance in the gray matter adjacent to the pos-
terior horns, which is presumably sensory in
function, Golgi concluded that this type of
neurones was also sensory in character. It
may be stated here that the axones of this
second type of neurone rarely, if ever, leave
the gray matter, and their function is that
of association. Cajal denies their sensory
character and states that cells with short
axones are distributed throughout the cen-
tral nervous system (Fig. 28).
The third type of neurones are those
which have been recently described by
Ramon y' Cajal, and hence are often called
the Cajal cells. They have only been found
in the molecular or outer layer of the cortex.
They consist of small cells, which are varia-
ble as to shape, the spindle shape being the
type. The axones from these cells have a
horizontal course and are constantly giving
off ascending collaterals which terminate in
the outermost part of the molecular layer in
minute bulbous expansions (Fig. 29).
Neurones are also divided according to
their functions into three general classes :
motor, sensory, and associative.
Fir.. 29. — Three Cajal
Cells from the C< >r-
TEX OF THE GYRUS
FORNICATUS OF A
Doc. — (After Koelli-
ker. )
THE NEUROGLIA.
This is the name applied to the tissue
which forms the supporting framework of
the central nervous system. So closely does
it resemble connective tissue in appearance
fV 9 2
Fi 9 3
Fig. 30. — Motor and Sensory Neurones. — [Jacob's Atlas.)
Fig. 1. — A large motor or pyramidal cell from the cortex of the cerebrum, with its apical tree-
like branching protoplasmic processes or dendrites possessing numerous lateral buds or gem-
mules. This cell possesses a single long slender basal process, ax, or axone (axis-cylinder
process), which gives off at right angles collateral branches, b. This cell with its processes
forms a central motor neurone.
Fig. 2. — Represents a single motor or ganglionic cell from an anterior horn of the spinal cord,
with its numerous dendrites and a single axone, ax, which axone terminates in a motor end
plate, the whole forming a peripheral motor neurone.
Fig. 3. — Indicates schematically the relationship between the cortical and peripheral motor neu-
rones and between the peripheral and central sensory neurones.
53
THE HISTOLOGIC ELEMENTS OF THE NERVOUS SYSTEM.
55
and function that, until within a recent period, it was con-
sidered by most anatomists identical to that tissue. Virchow,
however, as far back as 1846, discovered its true nature
from the histologic study of sections of the brain beneath the
ependyma of the ventricles. He discovered a structureless
membrane which he believed differed from true nerve-cells and
fibers and was perfectly satisfied that this tissue, which in 1853
Fig. 31. Microphotograph of Neuroglia Cells. Showing the relation they bear to the
capillary blood-vessels. Stained after the Cox-Golgi method.
he named neuroglia, differed decidedly from connective tissue.
He also observed that neuroglia tissue did not occur in the
peripheral nerves, and that the blood-vessels of the nervous
system were surrounded by it. Owing to the embryologic
researches of His and the histologic studies of Golgi, Ramon y'-
Cajal, Beneke, Weigert, and Mallory, and the publication by
the last two authors of their selective methods of staining, we
are enabled to understand more accurately than ever before the
56 CENTRAL NERVOUS SYSTEM.
origin and histologic structure of neuroglia tissue. This tissue,
which is epiblastic in origin, is composed of cells and their
processes, which cells bear the various names of spider cells of
Deiter, glia cells, neuroglia cells, and stellate cells or astrocytes.
They are of two chief forms — large and small spheric. The
cell-body is somewhat irregular in outline, is composed of pro-
toplasm and contains a nucleus large in size and spheric in
shape. These cells vary from six to thirteen /■* in diameter.
The large spheric cells contain granular chromatin, while the
chromatin in the small spheric cells appears as a dark homo-
geneous mass. By another classification the cells are divided
according as their processes are long or short. In the former —
/'. e., those having long processes — delicate filaments are given
off in a radiating manner from all parts of the cell-body ; these
processes are very fine, of uniform thickness, and occasionally
bifurcate near their extremities, usually, however, remain-
ing entire to their ends. They do not anastomose with each
other, have no varicosities, and are solid and smooth throughout.
A few of these cells have brush-like processes springing from
one or both ends. The neuroglia cells with long processes
exist mostly in the white matter.
In the cells of the second form, those with short processes,
the filaments are not so long, are more irregular, and somewhat
thicker than are those of the first form. These cells are found
with but few exceptions in the gray matter, and resemble very
closely some of the small forms of multipolar nerve-cells, from
which they are with difficulty differentiated. The fibers vary in
size from those of extreme fineness to those of fifteen a in
thickness. The latter fibers are only found where pathologic
changes produce complete or incomplete destruction of nervous
tissue, when they are in reality hypertrophied.
It is a remarkable fact that when degeneration changes occur
in the central nervous system, the place of the destroyed tissue
becomes in large part occupied by an increase of neuroglia
tissue. It should be remembered that while neuroglia tissue
resembles very closely connective tissue in function, it differs
decidedly from it in development, the former being epiblastic
while the latter is mesoblastic in origin.
THE HISTOLOGIC ELEMENTS OF THE NERVl IL'S SYSTEM.
57
In discussing the question as to the relation of the processes
to the neuroglia cells, Weigert states that while in embryonic
life they are parts of the cell, later the processes are lost to the
cell-bodies, and the latter exist free in the network of neuroglia
fibers. He bases his conclusions on the facts that the fibers
are no longer of the same chemic composition as the proto-
plasm of the cell-bodies, and that the fibers react to his recent
differential stain unlike protoplasm. He also believes that the
Fig. 32. — Three Neuroglia Cells (Astrocytes). Showing the relation the neuroglia
processes bear to the cell-body. — {After Weigert.)
neuroglia cells and fibers, while epiblastic in development,
differ decidedly from the true nervous tissue, his reasons being
that neuroglia tissue proliferates when the nervous system
becomes diseased, and that with his new neuroglia stain, true
nervous tissue remains unstained, while neuroglia tissue stains
blue. In gliomatous tumors, which are made up almost entirely
of neuroglia fibers and cells, it is quite common to find in cer-
tain parts of the growth neuroglia cells- with processes lying in
CENTRAL NERVOUS SYSTEM.
a meshwork ot differentiated fibers, while in other localities
neuroglia cells, with processes radiating from all surfaces of the
cell-body, or else coming from either pole, may be observed.
BLOOD-VESSELS AND LYMPHATICS.
The blood-vessels of the central nervous system differ some-
what from those in the other parts of the body ; it will therefore
be necessary to give a brief description of them here.
The arteries of the brain and cord, like similar vessels else-
where in the body, possess three distinct coats, but the inner
coat is subdivided so that the larger arteries may be said to
possess four coats — viz., an outer coat, or tunica adventitia ; a
middle or muscular coat, the tunica media ; and an inner coat,
the tunica intima, which is further subdivided into two layers,
an outer or elastic lamina, the membrana fenestra, and an inner
or endothelial layer.
The Tunica Adventitia. — The tunica adventitia of the
larger arteries is composed of connective tissue continuous with
the pia mater. In the smaller arteries this adventitial coat con-
sists of a delicate membranous investment, lightly striated,
containing connective-tissue cells, stellate or fusiform in shape,
and possessing round or oval-shaped nuclei. This coat is fre-
quently pigmented and often contains fat granules. While this
outer coat is loosely applied to the middle coat, or tunica media,
there exists between them a distinct space filled with lymph,
which presents ampullar dilatations in the angles formed by
the branching of vessels. This space is termed the adventitial
lymph-space, or Virchow-Robin space. If sections of hardened
brain-tissue are examined microscopically, distinct spaces will
be found outside of the adventitial coat, which are so much
larger than the diameter of the vessels that they form distinct
channels in which the vessels rest ; these are the perivascular
lymph canals or spaces of His. They possess no endothelial
lining. These channels communicate with the epicerebral space
located between the outer surface of the cortex and the pia
mater.
All the vessels of the central nervous system have a strong
THE HISTOLOGIC ELEMENTS UF THE NERVOUS SYSTEM.
59
protective coat of neuroglia tissue, which may have the func-
tion of preventing injury to the brain tissue from too great arte-
rial pressure.
Tunica Media. — The tunica media consists of smooth, non-
striated muscle-fibers arranged transversely to the long axis of
the vessel, thus placing the spindle muscle-cells at right angles
to the vessel wall, the muscle nuclei and those of the endothe-
Fig. 33. — Neuroglia Cells from the Cerebral Cortex of a Dog's Brain. Showing
their connection with blood-vessels. — [After A'oelliker.)
lium of the inner coat appearing to cross one another. In the
small cerebral vessels this tunic differs from vessels of a corre-
sponding size among the systemic arteries in that it contains
a single layer of circularly arranged muscle-fibers.
Tunica Intima. — The tunica intima consists of an inner or
endothelial layer, which is merely a tube of squamous endothe-
lial cells United at their margins by cementine and pos-
sessing oval nuclei, which are arranged longitudinally, having
60 CENTRAL NERVOUS SYSTEM.
their longest diameter in the direction of the vessel's length.
The outer or elastic layer is a delicate elastic membrane which,
for the smaller arteries, has no definite structure. It gives to the
larger arteries an appearance of longitudinal striation. The
presence of this layer in the smaller arteries is doubted by many
histologists.
VEINS.
The veins have three coats similar to those of the arteries.
The tunica media, however, differs from that of the arteries in
that it consists wholly of connective tissue, being devoid of
muscle-fibers, and is, in the smaller vessels, destitute of elastic
fibers. In consequence of these changes in the media the cali-
ber of the veins is larger, the vessel wall thinner and more lax.
They contain no valves.
CAPILLARIES.
The capillaries of the cerebrospinal system are exceedingly
minute, some of them being smaller than the average diameter
of a red blood-corpuscle. They vary from four to eight m in
diameter (about Tinnr of an inch). It is possible that various
hardening reagents narrow the diameter of the capillaries, and
that in the living state they are not so small, their lumen per-
mitting the passage of the red cells. It is, however, perfectly
possible for the red corpuscles, owing to their elasticity, to circu-
late through capillaries whose diameter is less .than the diameter
of the corpuscles. The capillaries may be distinguished micro-
scopically by the disappearance of the muscular coat and the
continuation of a vessel as a simple tube consisting only of an
endothelial lining and having a slight adventitial sheath. The
former is a continuation of the endothelium of the smaller
arteries, and consists of elongated fusiform cells, which stain
beautifully with silver nitrate, with oval nuclei ; the nuclei are
well stained with a saturated solution of methylene-blue. The
slight adventitial layer is the remains of the tunica adventitia of
the larger vessels, and its presence is indicated by a few round
or oval nuclei, with a few nucleated connective-tissue cells ar-
ranged in a longitudinal manner outside of the endothelial layer.
THE HISTOLOGIC ELEMENTS OF THE NERVOUS SYSTEM.
61
LYMPHATICS.
The lymphatics oi the central nervous system are confined to
certain spaces about the blood-vessels and nerve-cells and to
channels which appear as if tunneled out of the nervous sub-
stance. True lymphatic vessels or lymph-glands have never
been discovered within the cranial cavity or in the spinal canal.
i^ \<\ Ln
1
Fig. 34.— A Capillary Blood-vessel from the Gray Matter of the Spinal Cord
of an Ox. Stained with methylene-blue and magnified 400 diameters.
The lymph-spaces, which are very abundant throughout the
nervous system, communicate at the surface of the brain and cord
with the subarachnoid space. This latter space in the brain com-
municates, according to Key and Retzius, with the venous sinuses
by means of the Pacchionian bodies, which bodies may be consid-
ered as outlets for the subarachnoid (cerebrospinal) fluid. The
62 CENTRAL NERVOUS SYSTEM.
spinal and cranial nerves, as they pass out through their respective
foramina, receive prolongations in the form of tubular sheaths
from the dura, pia, and arachnoid membranes. The spaces
between these sheaths are lymphatic in nature and communicate
with the subdural and subarachnoid spaces. These perineural
spaces are considered by many observers as outlets for the sub-
Fig. 35. — A Camera Lucida Drawing of a part of the Gray Matter of the
Anterior Horn. Showing pericellular and perivascular lymph channels.
arachnoid fluid. This seems proven for the optic nerve and for
some of the spinal nerves. The sheaths that surround the
optic nerve remain distinct from one another, so that the peri-
neural spaces may be injected through the subdural and sub-
arachnoid cavities. William Browning has proven that the peri-
neural spaces about the lumbar and sacral nerves may be
injected through the subarachnoid cavity in lower animals at all
THE HISTOLOGIC ELEMENTS OK THE NERVOUS SYSTEM. 63
ages, but in man only during fetal life, as the spaces become
obliterated shortly after birth. Hence these spaces may be
considered as outlets for the subarachnoid fluid in the lower
animals, but in the human body only during the intra-uterine life.
THE ADVENTITIAL LYMPH-SPACE.
In describing the histology of the blood-vessels of the nervous
system mention was made of a space which exists between the
tunica media and tunica adventitia ; this space is very narrow,
save in the angle formed by the branching of the vessel where it
presents ampullar dilatations. These spaces are continued
around the smaller arteries and capillaries throughout the central
nervous system. Those of the brain pass out of the cranial
cavity with the carotid and vertebral arteries and terminate in
the deep cervical glands.
In addition to the adventitial lymph-spaces, small channels
exist in which the small blood-vessels and capillaries rest ; they
appear as if tunneled out of the nervous tissue, and are called
the perivascular lymph-canals of His. They do not possess a
lining membrane ; the adventitial sheath of the blood-vessel,
however, is closely applied to the walls of the canal. In the
walls of these channels exists a matrix of neuroglia, processes of
which pass across each space and become connected with the
adventitial sheath of the contained vessel. Whether these neu-
roglia processes aid in the absorption of lymph is as yet unknown.
PERICELLULAR LYMPH-SPACES.
Surrounding the nerve-cells of the cerebrospinal nervous
system exist numerous oval, round, or polygonal-shaped spaces,
which in hardened specimens at least are much greater in
diameter than are the nerve-cells which rest within them. These
pericellular spaces are continuous with the adventitial lymph-
spaces into which they drain.
CHAPTER II.
SPINAL CORD.
The spinal cord, or medulla spinalis, is located in the vertebral
canal, and is enveloped by three membranes — viz., the outer, or
dura mater ; the middle, or arachnoidean membrane ; and the
inner, or pia mater. These membranes protect the cord and
give support to its nutrient vessels. The dura (so called from
the Latin durus, hard) is a strong fibrous membrane continuous
with the dura of the brain. It surrounds the cord and the plexus
of nerves called the cauda equina in a loose, sac-like manner,
and is separated from the bony canal of the vertebra? by loose
areolar tissue and by a plexus of veins — the vertebral plexus.
This space between the bone and the dura is called the epidural
space. The dura is attached above to the circumference of the
foramen magnum, and below to the third sacral vertebra, from
which it extends as a fibrous cord to the periosteum of the
coccyx. Double openings exist opposite the intervertebral
foramina for the transmission of the spinal nerves ; processes
of this membrane surrounding these nerves at their exit forming
tubular sheaths. The dura of the cord differs from that of the
brain in several respects — /.
SsfcSfr'
Fig. 42. — A Group of Multipolar Nerve-cells from an Anterior Horn of the
Spinal Cord. Showing Nissl granules and pigment.
77
SPINAL CORD.
79
anterior horn of each side. This cell group extends throughout
the entire cord. It is particularly well marked in quadrupeds
whose dorsal muscles are well developed, and therefore has
been termed by Kaiser the nucleus for the back muscles. The
fourth group is found along the lateral periphery of the anterior
horn, having a vertical extent from the fourth cervical to the upper
part of the second dorsal segment. This is the area from which
the nerves of the brachial plexus are derived. This group has
been called by Kaiser the cell group for the upper extremity.
Fig. 43. — Section of the Lumbar Cord of an Adult. Showing the anteromedian and
posterolateral groups of cells.
All these cells are motor in function, innervating the muscles
to which the anterior nerve-roots are destined. They also have
a very important bearing upon the nutrition of the anterior
nerve-roots and the muscles which those nerves innervate.
Any acute pathologic change in the cells is followed by motor
paralysis, partial or complete, degeneration of the motor nerve-
fibers, and rapid wasting of the muscles to which they are dis-
tributed. They are, therefore, trophic as well as motor in func-
tion. These cells are functionally grouped, according to certain
definite movements associating groups of muscles.
8o
CENTRAL NERVOUS SYSTEM.
The intrinsic cells are found distributed throughout that part
of the gray matter located between the anterior and posterior
cornua, the so-called middle zone. The neuraxones of the intrinsic
cells pass into the white columns of the same and opposite sides,
as long and short fibers, where they divide T-shaped, one branch
passing upward, the other downward. The long fibers are doubt-
less sensory. The short fibers are probably associative in func-
tion, passing upward and downward in the white columns of the
A- "" Tu-'
Fig. 44. — Camera Lucida Drawing of a Part of an Anterior Horn with Adjacent
White Matter of the Lateral Column. Showing nerve-fibers coming from that
column and coursing between and. around the motor nerve-cells. Stained after method of
Weigert-Pal.
cord, giving off collaterals which reenter the cord at higher and
lower levels, ending in brush-like expansions about the intrinsic
cells of those levels. A group of intrinsic cells exists near the
base of each anterior horn, the neuraxones of which pass ob-
liquely across the gray and white matter, becoming vertical near
the periphery of the opposite side of the cord, forming the antero-
lateral ascending tract of Gowers. This tract is probably sen-
sory in function, transmitting to the brain impulses of pain and
temperature. A second group of these cells is located at the
Fig. 45. — Diagram of a Transverse Section of the Spinal Cord. — {After Stan-.)
On the right side the columns of the cord are shown, and the fibers entering the gray matter
from these columns. I. Anterior median column. II. Anterolateral column. III.
Lateral limiting layer. IV. Ascending anterolateral tract of Gowers. V. Direct cerebellar
column. VI. Crossed pyramidal column. VII. Lissauer's column. VIII. Column of
Burdach. IX. Column of Goll.
The posterior nerve-roots are shown on the right side of the diagram, and their various methods
of termination in the gray matter : I. Fiber entering Lissauer's tract. 2. Fiber entering
posterior horn. 3. Fiber terminating deep within posterior horn. 4. Fiber entering
column of Burdach. 5- Fiber passing to root zone of column of Burdach, and sending
the collateral fiber to the anterior horn. 6. Fiber entering root zone, and sending collateral
to the Clarke column of cells. 7. Fiber entering root^zone and passing by way of the gray
commissure to the opposite side of the cord.
On the left side the various cells of the gray matter are shown : a. Motor cells, with motor
nerve-roots passing out of the cord. b. Intrinsic cells of the posterior horns ; the one on
the margin is a " border-cell "; the other lies deep within the horn; they send neuraxones
into the posterior and lateral columns respectively, c. Intrinsic cell of the posterior horn ;
Golgi's second type. d. Cell of the column of Clarke, with its axone passing to the direct
cerebellar column, e. Intrinsic cells of the intermediate gray matter, with their axones
passing into the anterolateral column, f. Intrinsic cell in median gray matter, with its
axone passing to Gowers' tract, g. Commissural cells in the median gray matter, their
axones passing to the opposite side of the cord. h. Sensory cell sending its axone to
opposite column of Gowers.
6 • 81
SPINAL CORD. 83
base of the posterior horn, near its inner side, close to the
posterior commissure. They are of large size, multipolar, and
sensory in function. Spread about them exist the end brushes
of collaterals and axones from the posterior nerve-roots, which
conduct impressions of equilibrium from the trunk muscles to
these cells. From this group of cells neuraxones pass horizon-
tally across the gray and white matter of the same side, becoming
vertical along the periphery of the cord, where they form the
direct cerebellar tract, or column of Flechsig. They extend from
the third lumbar to the seventh cervical nerve. This entire
group of cells forms the vesicular column of Lochart Clarke.
Cells of a like character exist in the same location throughout
the sacral region, and have been termed the sacral nucleus of
Stilling. Among the intrinsic cells may be mentioned a group
of cells on each side located near the median surface of the base
of the anterior horns — the so-called commissural cells. They
possess axones which have both a short and long course, those of
short course passing in curves through the anterior commissure
into the opposite anterior cornu, where each axone terminates
by breaking up into two or three fine filaments. They probably
associate in function the two anterior cornua. The axones having
a long course pass via the anterior commissure through the
gray matter into the anterolateral area of the cord. They may
conduct sensory impressions to the opposite side of the cord.
The remaining cells belong to the second type of Golgi ; they
are small, spheric or triangular, and exist mostly in the posterior
horns. Their axones are short and do not leave the gray
matter; they divide dichotomously, breaking up into a network
of fine filaments. They may possibly serve a reflex function.
The white matter of the cord surrounds the gray matter on
all sides except where the posterior horns reach the dorsal peri-
phery of the cord. Macroscopically, it consists of a homogeneous
white mass, which, when examined with a low power of the
microscope, resolves itself into masses of cut-off, medullated
nerve-fibers arranged vertically. These nerve-fibers differ very
much as to size, and have no neurilemma or sheath of Schwann.
Between the nerve-fibers exists neuroglia tissue and many
fine collaterals. A mantel of neuroglia, the subpial neuroglia
!SS\
84 CENTRAL NERVOUS SYSTEM.
layer, surrounds the periphery of the cord. The neuroglia
gives support to the nerve-fibers and to the numerous blood-
vessels which are given off from all portions of the periphery
and ramify toward the center of the cord.
The fibers are variable in size, usually corresponding in
diameter to the length of the tracts to which they belong.
The white substance is divided anatomically into three primary
columns for each side — an anterior or ventral, a lateral, and a
posterior or dorsal. The anterior column lies between the
anterior cornua and ventral nerve-roots. The lateral columns
are between the exit of the anterior and posterior nerve-roots.
The posterior columns are situated between the posterior cornua
and nerve-roots, being separated from each other by the dorsal
median septum. They are subdivided by the intermediate
neuroglia septum into two smaller columns — an inner or
median one, adjacent to the posterior median fissure, called
the column of Goll, and an outer or external one, located
between the septum and the posterior horn, called the column
of Burdach or the posterior root zone. It is to be noted that
this intermediate septum is only well marked in the cervical
region, but the columns are distinct throuehout the cord.
These various columns are further subdivided into a number of
tracts or fasciculi of nerve-fibers, long and short, whose ana-
tomic and physiologic relations have been made known by
pathologic and embryologic research. The fibers which com-
pose these tracts spring from four different sources : First, from
the posterior nerve-roots and spinal ganglia, having a centri-
petal course ; second, fibers from the motor area of the brain,
centrifugal in their course ; third, fibers which pass into the white
matter of the cord from the intrinsic cells of the gray matter,
which form long and short tracts, the long tracts being doubt-
less sensory in character, while the short tracts are supposed
to associate different levels of the gray matter ; and fourth,
fibers having a descending course : the neuraxones from the
Purkinje cells of the cerebellar cortex.
We have thus found that the white matter which appeared to
the naked eye as a homogeneous mass may be resolved into
vertical fibers grouped into tracts whose course may be long or
Fig. 46.— Microphotograph of Transverse Section of Cord.
cut across.
Showing nerve-fibers
85
SPINAL CORD.
87
short. Our knowledge in regard to the exact location of the
different systems of these tracts has been greatly aided by the
study of secondary degeneration, the result of experimental or
pathologic destruction of partial or total transverse sections
of the cord. This study was undertaken by Turck, who inves-
tigated the after-effects of such sections of the cord. He found
that when the cord was completely destroyed transversely by a
fig. 47- mlcrophotograph of a partial transverse section of the white
Matter of the Spinal Cord of an Ox.
lesion, — such as transverse myelitis, hemorrhage, or the like, —
certain definite tracts or systems of fibers degenerate upward
or centripetally, while others degenerate downward or centri-
fugally. The study of secondary degeneration was long ago
carried out by Waller, who showed that if a nerve were severed
from its mother cell, it would degenerate throughout its whole
extent, the degeneration usually being in the direction in which
the nerve-fiber conducted impulses. For example, if an anterior
88 CENTRAL NERVOUS SYSTEM.'
nerve-root be severed from its connection with its trophic cell
in the anterior horn of the spinal cord, that nerve degenerates
peripherally to its termination in the muscle which it innervates,
the muscle sharing in the resulting atrophy. Also on section
of a posterior or sensory root, ventrad to its ganglion, which
contains its trophic cell, that nerve degenerates centrally or in
the direction in which it conducts impulses. On the contrary,
XII XIII
Fig. 4S. — Schematic Representation of the Situation of the Various Tracts of
Fibers in the Spinal Cord.
I. Direct pyramidal tract. II. Descending tract of Marchi and Lowenthal. III. Olivary or
triangular tract. IV. Anterolateral ground bundles of fibers. V. Anterolateral ascending
tract of Gowers. VI. Lateral limiting layer. VII. Direct cerebellar tract. VIII. Crossed
pyramidal tract. IX. Lissauer's tract. X. Middle root zone. XI. Posterior root zone.
XII. Postero-internal or column of Goll. XIII. Septomarginal tract. XIV. Comma tract
of Schultze. XV. Anterior root zone. XVI. Cornu commissural tract.
if a section be made dorsal to the ganglion, the nerve degener-
ates peripherally throughout its whole extent in a direction
opposite to that in which impulses are conducted. A careful
study has shown that the following tracts in the spinal cord
undergo secondary degeneration — viz., the direct and crossed
motor tracts, the tracts of the columns of Burdach and Goll, the
direct cerebellar, the anterolateral ascending tract of Gowers,
and the descending tract of Marchi and Lowenthal. It is in-
SPINAL CORD. 89
teresting to note that the embryologic studies of Flechsig,
Bechterew, Edinger, and Kahler have confirmed the separate
existence of these tracts and have proved that other tracts also
are found in the cord. Flechsig has shown that the different
tracts of the white matter receive their myelin at certain
definite periods of embryonic development. In early embryonic
life that part of the cord which afterward consists of white
matter is composed entirely of naked axis-cylinders, which gives
to a section a dark gray appearance. Later, as the tracts be-
come medullated, they can easily be distinguished by the white
appearance which each tract assumes. By this method, the
following tracts or systems of fibers have been differentiated —
viz., the ground bundles of the anterior columns, ground bundles
of the posterior columns, the anterolateral mixed zones, the
lateral limiting layers, the columns of Goll, the direct cerebellar
tracts, the direct and crossed pyramidal tracts, the anterolateral
ascending tracts of Gowers.*
In order to render clearer the anatomic relations of the sep-
arate tracts, it will be necessary to accurately describe the rela-
tive positions of these tracts as seen on transverse section.
The anterior or direct pyramidal tracts or columns of Turck
form narrow columns of nerve-fibers bordering on each side of
the anterior median fissure. These tracts extend downward in
the cord, gradually decreasing in size, and usually terminate at
the mid-dorsal region. In rare instances, when a larger per-
centage than normal of the motor-fibers take this direct course,
* I. The ground bundles of the anterior columns receive their myelin when the fetus is from
30 to 32 cm. long. About the sixth month.
2. The ground bundles of the posterior columns, when the fetus is 25 cm. in length. About
the fifth month.
3. The anterolateral mixed zone, when the fetus is 25 to 35 cm. long. Fifth to seventh
month.
4. Lateral limiting layer, when the fetus is 32 cm. long. About the sixth month.
5. The fasciculi of the columns of Goll receive their myelin when the embryo is between
six and seven months old.
6. The direct cerebellar tracts receive their white substance about the seventh month of
fetal life.
7. The fibers of the direct and crossed pyramidal tracts become enveloped in myelin at
about the ninth month.
8. The anterolateral ascending tracts of Gowers become medullated at the eighth month
of embryonic life.
90 CENTRAL NERVOUS SYSTEM.
they continue downward as far as the lumbar or sacral region,
and extend from the white commissure to the periphery of the
cord, causing slight bulgings on each side of the anterior median
fissure. On the other hand, when the columns contain less than
the normal number of fibers, they terminate about the middle of
the cervical region.
The anterior ground bundles of Flechsig comprise all that
part of the anterior columns outside of the direct pyramidal
tracts. They extend throughout the entire length of the cord,
and consist chiefly of fibers having a short course, which fibers
doubtless connect different levels of the anterior cornua.
The anterolateral mixed zone, one on each side, is bounded
on its inner side by the gray matter ; externally, by Gowers'
tract and the crossed pyramidal tract. The posterior portions
of these columns bordering upon the intermediate gray matter
and the posterior horns are called the lateral limiting layers.
This zone is composed of association fibers which probably con-
nect different levels of the gray matter.
The anterolateral ascending tracts of Gowers occupy rather
long, narrow, crescentic areas along the anterolateral periphery
of the cord in front of the direct cerebellar and crossed pyra-
midal tracts, and are found throughout the cord as low down as
the lumbar enlargement.
The anterolateral descending tracts of Marchi and Lowen-
thal comprise a small area in Gowers' column of each side, close
to the periphery of the cord. These areas were discovered by
Marchi and Lowenthal. They have been found to extend
throughout nearly the entire length of the cord.
The direct cerebellar tract, — also called the column of Flech-
sig, — one for each side, exists along the periphery of the
lateral column, posterior to the tract of Gowers and external to
the crossed pyramidal tract. In the upper cervical region its
posterior part is separated from the periphery of the cord by
the crossed pyramidal tract. It originates as low down as the
first lumbar nerve, and has its greatest s [ ze where the cells ol
Lockhart Clarke, whose neuraxones form the greater portion of
this tract, are best developed — namely, in the dorsal region.
The crossed motor or pyramidal tracts — the fasciculi cerebro-
SPINAL CORD. 91
spinalis lateralis — occupy a large area in the posterior part of the
lateral columns of each side. They extend throughout the
entire length of the cord, some of their fibers terminating in the
conus medullaris. Through the greater part of the cervical and
dorsal regions these tracts are separated from the periphery of
the cord by the cerebellar tracts. In the upper cervical and lower
dorsal regions, owing to a movement ventrad of the direct
cerebellar tracts, the motor tracts are permitted to reach the
periphery of the cord, which position they retain throughout the
lumbar region. Their posterior surfaces are in contact with the
posterior horns ; their anterior portion, with the tracts of
Gowers and the lateral limiting layers.
The posterior columns contain two chief systems of fibers or
tracts, which extend throughout the cord, being separated from
each other in the dorsal and cervical regions by a process of
neuroglia called the intermediate septum. On each side the
outer area, which borders on the posterior horn, is called the
column of Burdach, posterior ground bundle of Flechsig, or the
posterior root zone of Charcot. The inner fasciculus or bundle
of fibers, which borders upon the. posterior median fissure, is
called the column of Goll, or postero-internal column.
The origin and partial course of the fibers which compose the
various tracts of the cord will be described in the order of their
relative importance from a clinical and physiologic standpoint.
The Crossed and Direct Pyramidal Tracts. — The motor fibers
of the cord which are located in the direct and crossed pyra-
midal tracts arise from the motor areas of the brain, and repre-
sent the neuraxones of the large pyramidal cells, which are
abundantly found in the third layer of the cortex. Their
course from the cerebral cortex to the medulla will be de-
scribed later. When they reach the medulla they occupy a
large area on each side of the anterior median fissure, and at the
first or second cervical nerves large bundles of fibers or axones,
representing about eighty per cent, of the whole number, pass
obliquely across to the opposite side, entering the posterior part
of the lateral column of the cord ; hence the name " crossed
pyramidal tract." These crossed fibers become vertical and
extend downward, gradually decreasing in size until they reach
92 CENTRAL NERVOUS SYSTEM.
their termination, at the level of the third or fourth sacral nerve,
a small number of fibers continuing downward to terminate in
the filum terminale. The neuraxones which do not cross,
representing about twenty per cent, of the motor fibers, pass
downward in the area of the cord adjacent to the anterior
median fissure on the same side ; hence they are called the
direct or uncrossed pyramidal tract. They usually cease about
the level of the mid-dorsal region. The motor neuraxones, like
most of the long fibers of the columns of the cord,, give off at
different levels side branches or collaterals which leave the
parent stem at right angles. The axones, with the collaterals
composing the crossed pyramidal tract of each side, pass for-
ward and inward, entering the gray matter, where they break
up about the motor nerve-cells into innumerable fine filaments
or arborizations.
The neuraxones and collaterals of the direct pyramidal tract
end, according to Lenhossek, in fine brush-like expansions about
the motor nerve-cells of the anterior horn of the same side.
On the contrary, undoubted clinical and experimental evidence
is at hand to prove that the greater portion of fibers cross over
through the anterior commissure to end about the motor cells
existing in the opposite anterior cornu. Most of the fibers of
the direct pyramidal tract seem destined to the arm ; hence the
relation of the arm is almost exclusively with the cerebral hemi-
sphere of the opposite side.* The fibers of the motor tracts,
direct and crossed, conduct impulses of voluntary motion from the
motor areas of the brain to the muscles. If the fibers of the motor
tract be destroyed by severing their connection with the cells of
the motor area of the brain, there will result a motor paralysis
of the opposite side of the body and a descending degenera-
tion from the point of lesion throughout the entire extent
of the tract. In the cord the degenerated areas will be
the direct pyramidal tract of the same, and the crossed pyra-
midal tract of the opposite side. This degeneration is com-
plete, involving the termination of the axones and collaterals
* W. H. B. Stoddart has proven by experimental division of an anterior pyramid in a
number of dogs that nearly all the fibers of the direct pyramidal tract ultimately cross to the
opposite side of the cord.
Fig,
49. — Diagram Indicating the Course of the Motor and Sensory Fibers
of the Spinal Cord and Medulla.
a, a. Motor cells of the cerebral cortex, b, b. Arborizations of the fibers of the sensory tract
in the cerebral cortex, c. Nucleus of the column of Burdach, showing terminal arboriza-
tions of the long sensory fibers of the cord. d. Nucleus of the column of Goll, showing
terminal arborizations of the long sensory fibers of the cord. e. Section of the medulla,
showing sensory decussation, f. Section of medulla, showing motor or pyramidal decus-
sation, g, g. Motorial end plates, h. Section through the cervical region of the cord,
showing termination in the anterior horn of the motor fibers of the direct pyramidal tract
after they have crossed in the anterior commissure ; also fiber of crossed pyramidal tract end-
ing about anterior horn cell of same side, i, i. Posterior spinal ganglia, j, k. Sensory fibers
of short course. /. Sensory fibers of long course, terminating in medulla, vi, m, m. Sen-
sory end organs. «. Section through lumbar cord.
93
SPINAL CORD. 95
about the nerve-cells of the anterior cornua, and is due to
the loss of trophic or nutritional influence which results from
the severance of the nerve-fibers from their mother cells in
the motor areas of the cortex. The peripheral portion of the
tract, on the contrary, remains normal, because its nutrition is
dependent upon the motor cells of the anterior cornu, whose
neuraxones form the peripheral portion of the tract.*
THE COURSE OF FIBERS IN THE SENSORY TRACTS
OF THE CORD.
The sensory portion of the cord may be divided into four
chief areas for each side — that is, the direct cerebellar tracts, the
columns of Burdach and Goll, and Gowers' anterolateral ascend-
ing tracts.
The direct cerebellar tract, or the fasciculus cerebellospinalis,
owes its origin to neuraxones from the cells of the vesicular
column of Clarke.f These cells, which are multipolar, exist at
the base of the posterior horn near its inner side, and form a
distinct column, vertical in extent from the seventh cervical to
the third lumbar segment. It should be noticed, however, that
Stilling has called attention to a number of cells in a correspond-
ing portion of the cord in the upper cervical and lower lumbar
regions, which cells probably perform a similar function, so that
in reality the column may be said to extend throughout the
cord. From this column of cells numerous neuraxones pass
rather obliquely across the white matter of the lateral column,
reaching the circumference of the cord, dorsad to Gowers' tract,
* In many of the lower animals — i. e., in the dog, cat, rabbit, etc. — there is an apparent total
decussation of the motor fibers, the latter, after decussating, occupying the posterior part of the
lateral columns. The experiments of Marchi, Moeli, Lowenthal, and Sherrington seem to have
established the fact that about twenty-five per cent, of the fibers which were formerly believed
to decussate in the medulla to form a part of the crossed pyramidal tract do not, but trend back-
ward to pass downward in the posterior part of the lateral columns of the same side and termi-
nate about the nerve-cells of the anterior cornu of that side. This view is supported clinically
by the fact that in many hemiplegias there is also present a paresis of the side of the lesion
involving particularly the lower extremity.
f According to Tooth, the fibers of the direct cerebellar tracts come directly from the
posterior nerve-roots.
9 6 CENTRAL NERVOUS SYSTEM.
where they bifurcate, the long branches passing upward, the
short branches downward. (See Fig. 50.)
The long branches continue upward and pass by way of the
restiform body to end about the cells in the cortex of the superior
vermis of the cerebellum of the same and opposite sides.* No
collaterals from the axones of the central portion of this tract have
been discovered. No axones from the cells of Clarke's column
pass into the posterior columns. The peripheral portion of this
tract consists of fibers and collaterals from the posterior nerve-
roots of the same side which pass through the white matter of
the postero-external column and then enter the base of the
posterior horn to end in brush-like expansions about the cells
of Clarke and Stilling. These fibers probably serve to conduct
sensations of equilibrium to the cells of Clarke and Stilling,
whence they are further conveyed via the direct cerebellar tract
to the cerebellum.
The direct cerebellar tract receives its myelin at the seventh
month of fetal life. Experimental division of the cord in the
lower animals has shown that the long branches of the axones
of this tract degenerate in an ascending or centripetal direction,
which defeneration ends in the worm of the cerebellum. The
short branches of the axones of this tract degenerate downward
for a short distance. Their function is unknown. The trophic
influence of the central portion of this tract comes from the cells
of Clarke and Stilling. The peripheral portion as well, according
to Edinger, receives its trophic influence from the same source.
This statement of Edinger is merely hypothetic. It is more
probable that the peripheral portion of this tract consists of
collaterals from the posterior nerve-roots, which roots consist of
the central axones of the cells of the posterior spinal ganglia.
* According to Alexander Bruce, the'direct cerebellar tract, after entering the middle portion of
the restiform body, ascends in front of the nucleus dentatus of the cerebellum, at the upper mar-
gin of which it passes backward along the convex margin of the superior cerebellar peduncle,
immediately after that structure has emerged from the hilum of the dentate nucleus. At the
posterior margin of the peduncle the direct cerebellar tract bends inward toward the superior
worm, terminating on both sides of the central, monticulate, and lingual lobules. A majority
of the fibers terminate in the same side of these lobules, but a considerable number cross over
to the same-named lobules of the opposite side via the ventral cerebellar commissure of
Stilling.
SPINAL CORD. 97
THE COURSE OF THE FIBERS OF THE DORSAL FUNICULI OR
POSTERIOR COLUMNS.
As before mentioned, the posterior columns are separated into
two divisions : an inner portion, or column of Goll, or funic-
ulus gracilis ; 'and an outer one, the column of Burdach, wedge-
shaped column, posterior root zone, or the funiculus cuneatus.
Throughout the cervical and part of the dorsal regions these
' 1 -':■■'>
■rM ■■}'':. ■■'■■■■:■ h V^i-!^v£ "■ v ; •':.. X^-
:.V 1 ':-':. ■.•■•/••■:'.■••.- :,•':■■..■:)::•'.•■■.•■-.■■■:■■ ''•■'■■ --WiSrM-
■.■.■■'.•' ".'■'.'.'•'■ . '. : •','.■'•'•'■<:'/:.' '.:' :.■':: • : ■'.'■: •""•■:. a
Fig. 50. — Posterior Cornu and Column at the Last Dorsal Segment. — [After Gou-ers.)
p. M. C. Posteromedian column. P. E. c. Postero-external column. P. M. S. Posterior median
septum. P. C. Posterior commissure, v. Commissure vein. p. V. c. Posterior vesicular
column, c. C. Caput cornu. P. R. Posterior root. a. An artery, d, d, d. Adjacent to a
strip of the lateral column, indicate the tracts of fibers passing from the vicinity and interior
of the posterior vesicular column along the septa of the lateral column, to form the direct
cerebellar tract, x, x. Tracts of fibers passing from the neck of the horn, hear the poste-
rior vesicular column, to the postmedian column.
columns are separated by the postero-intermediate septum.
That these columns are distinct from each other and contain
separate systems of fibers seems proved by two facts : first,
that the separate systems of fibers' receive their myelin at differ-
ent periods of embryonic life ; secondly, from the study of the
pathologic appearances of secondary degenerations in this area.
In the lumbar and sacral regions it is not possible to separate
the component fibers of the posterior columns into a postero-
7
CENTRAL NERVOUS SYSTEM.
internal, or column of Goll, and a postero-external, or column of
Burdach. This is owing to two facts : first, the long fibers
which arise from the lower spinal ganglia have not reached the
position which they occupy in the dorsal region adjacent to the
posteromedian septum ; second, a number of short and long
fibers exist in both regions which do not take their origin from
the spinal ganglia, but originate from the intrinsic cells of the
gray matter of the cord.
Fig. 51. — Longitudinal Section of
the Cord in the Cervical Re-
gion of a Sheep's Embryo, 22
cm. long. Showing the division of
the posterior nerve-fibers after enter-
ing the cord. — [Lamlois and Stir-
ling.)
Fig. 52. — Lateral Column of a New-born
Rabbit.
c. Collateral fibers, el. Bending rounding of the
longitudinal fibers to end in the gray matter.
//. Axis-cylinder process of a nerve-cell bend-
ing in among the longitudinal fibers of the
white column. /, /, /. Longitudinal fibers of
different lengths.
With the exception of fibers which come from the intrinsic
cells at the base of the posterior horns, — which form in the lumbar
and sacral regions two distinct tracts, the cornu commissural
and septomarginal, — the fibers of which these columns are com-
posed are derived from the posterior nerve-roots, which repre-
sent the central neuraxones of the cells of the posterior spinal
ganglia. The posterior nerve-roots enter the posterior columns
just outside of the posterior horns, in the region of the sub-
spinal cord. 99
stantia gelatinosa Rolandi, where they bifurcate, both divisions
having a vertical course, one upward, the other downward.
Both give off collaterals nearly at right angles, which enter the
gray matter and break up into fine filaments about the intrinsic
nerve-cells, or the motor cells of the anterior cornua.
The branches which continue downward after pursuing a
short course enter the gray matter in curves and end about
the nerve-cells of the posterior horns. The branches which
continue upward may be divided into those having a short and
those having a long course. The former pass upward a variable
distance, and finally pass into the posterior horns, to end about
the cells in the gray matter. Those of long course pass upward,
and when they reach the medulla they curve slightly forward
and end in free arborizations about the cells of the nucleus
cuneatus, or nucleus of the column of Burdach, and nucleus
gracilis, or nucleus of the column of Gobi.
The Column of Goll. — These columns, also termed the
postero-internal columns, consist of long fibers only of the pos-
terior nerve-roots from the various levels of the sacral, lumbar,
and dorsal regions of the cord, which fibers end in the medulla,
about the cells of the nucleus gracilis, or nucleus of the column
of Goll, of the same side. These fibers probably have the func-
tion of conducting impressions from the sensory muscle nerves.
The Columns of Burdach. — These columns contain fibers
of short and long course, with their collaterals. The fibers
bifurcate, one division passing downward, the other upward.
Most of the fibers whose course is downward are said by Schultze,
Flatau, and Lenhossek to occupy a comma-shaped area in the
ventral and median portion of this column, known as the comma-
shaped bundle of Schultze.* Hoche has shown that the fibers of
the comma-shaped bundle pass in curves into the gray matter of
the cord. In addition, the median portion of this column, in the
* The comma-shaped bundle, or tract of Schultze, was formerly believed to have but a short
course and to consist entirely of the short descending axones from the posterior nerve-roots.
Hoche has followed descending degeneration of this tract through ten spinal segments, and
believes the tract to have a long course. Zapfer believes the fibers of this tract to come from
cells in the gray matter (endogenous fibers), and also from the posterior nerve-roots (exogenous
fibers). Gombault, Philipe, and Tooth believe that this tract consists of fibers coming only
from cells of the dorsal part of the gray matter.
ioo CENTRAL NERVOUS SYSTEM.
cervical region contains long branches, which pass upward and
end in arborizations about the cells of the nucleus of the column
of Burdach. The posterior portion of this column, or posterior
root zone, which borders on the posterior horn, contains fibers
with collaterals from the posterior roots, which, after a short
course, enter the posterior horns. Many fibers from the column
of Burdach pass into the column of Goll, as is shown by the
study of secondary degeneration.*
The majority of the fibers from both of these columns depend
for their nutrition upon the cells of the posterior spinal ganglia.
The fibers degenerate in the direction in which they pass. The
fibers which degenerate downward occupy three areas : first, the
comma-shaped area in Burdach's column ; second, the area of
the septomarginal tract ; and third, the area of the cornu com-
missural tract. A complete transverse section of the nerves
composing the cauda equina results in a complete degeneration
of the root-fibers that enter into the formation of the posterior
columns at the point where the cauda equina merges into the
cord. Just above this area where new fibers enter, the degen-
erated area now occupies the entire column of Goll, with a
portion only of Burdach's column. Higher up the cord this
degenerated area is confined to the column of Goll, and passes
upward to terminate about the cells of the nucleus of that column
in the medulla.
THE CORNU COMMISSURAL AND SEPTOMARGINAL DESCENDING
TRACTS.
That the fibers of which both of these tracts are composed
have their origin from the intrinsic cells of the posterior part of
the gray matter of the cord seems proved from the fact that
they are not found degenerated when the posterior nerve-roots
* Flechsig and Bechterew, on embryologic grounds, have divided the fibers of which the
columns of Burdach are composed into three root zones— an anterior, a middle, and a posterior.
The anterior root zone lies between the posterior commissure, base of posterior horn, and
posterior median fissure. The middle root zone lies between the anterior and posterior root
zones, being bounded on the inner side by Goll's column, and on the outer side by the posterior
horn. The posterior root zone occupies the dorsal part of Burdach's column, and rests against
the dorsal periphery of the cord.
SPINAL CORD.
are experimentally divided, or when they are atrophied, the
result of disease. In locomotor ataxia, a disease which is now
universally regarded as due to sclerosis of the posterior nerve-
roots, the fibers of these two tracts remain undegenerated, and
are in striking contrast to the degenerated fibers in the pos-
terior column from the posterior nerve-roots. The fibers of
these two fasciculi degenerate downward when the diseased
process destroys the intrinsic cells existing in the posterior part
of the gray matter of the cord, such degeneration having been
observed by Hoche in two cases of compression myelitis. Other
observers have found them degenerated in cases of syringo-
Fig. 53. — Transverse Section ok the Spinal Cord at the Level of the First
Sacral Segment. — {After Alexander Bruce.)
S. M. Septomarginal tract. C. C. Cornu commissural tract.
myelia, which is a gliosis affecting at first the gray matter sur-
rounding the central canal and then gradually extending in all
directions from that point (Fig. 53).
The Cornu Commissural Tract. — This tract lies in the
anterior part of the posterior column, adjacent to the posterior
commissure, posterior cornu, and the posterior median septum.
It attains its greatest size in the lower lumbar region, and dimin-
ishes in size both above and below this level. This tract extends
throughout the lumbar and sacral regions of the cord, originating
as high as the eleventh dorsal segment and terminating at the
fifth sacral segment.
102 CENTRAL XERV( >US SYSTEM.
The Septomarginal Tract. — This tract, as its name denotes,
is located along- the margin of the posterior median septum. It
attains its greatest size in the sacral and lumbar regions. It
consists of a narrow strip of fibers located alongside the median
septum, extending in the sacral region as far forward as the
cornu commissural tract, with which its fibers commingle, and
reaching backward to the periphery of the cord, where it expands
into an oval-shaped area. At the level of the fifth lumbar seg-
ment this tract is much reduced in size, extending ventrally to
about one-half the length of the septum, and being entirely
distinct from the cornu commissural tract. Above this level it
rapidly diminishes in size, until at the level of the third lumbar
segment it occupies a slight triangular field bordering on the
posterior part of the septum and the adjoining part of the per-
iphery of the cord. At the level of the twelfth dorsal segment
it is entirely displaced from its position along the septum, and
comes to occupy a small area along the dorsolateral periphery
of the posterior column. Hoche has proved that this tract may
originate as high as the lowest cervical segment, and that its
fibers continue downward into the filum terminale.
In the cervical region, owing to the fact that the nerves
coming from the lower extremity occupy the column of Goll
and those of the upper extremity are confined to Burdach's
column, a section of the cervical nerves at this level produces
an ascending degeneration, confined to Burdach's column, which
degeneration passes upward, terminating about the cells of the
nucleus of this column in the medulla. Thus, the study of sec-
ondary degeneration proves that the entering posterior nerve-
roots are located close to the posterior horns, and that the fibers
which enter the cord at higher levels displace inward, toward
the column of Goll, those that have entered below, so that in
the cervical region the fibers from the lower extremities occupy
almost entirely the columns of Goll, while most of those from
the arms are located in the columns of Burdach.
GOWERS'
SI'tXAL CORD.
ANTEROLATERAL ASCENDING TRACT— FASCICULUS
VENTROLATERALS SUPERFICIALIS.
This tract consists of neuraxones from the intrinsic cells of
the intermediate gray matter, and from cells at the base of the
anterior horns. This origin has been positively proved by the
experiments of Mott, who found that when the posterior nerve-
roots only were severed Gowers' tract remained undegene-
rated, but, on the other hand, when the intermediate gray matter
was injured or destroyed, this tract was found degenerated
throughout its entire extent. The axones from these intrinsic
Fig. 54. — Course and Termination ok Gowers' Tract. — {JoivJihg to Hoche.)
cells doubtless decussate in the anterior commissure of the cord,
and pass obliquely across the white matter of the anterolateral
area of the cord, where they occupy a broadly comma-shaped
area, situated midway between the periphery and gray matter, in
front of the direct cerebellar and crossed pyramidal tracts, and
extending as far forward as the anterior nerve-roots, being sepa-
rated from the periphery of the cord by the anterolateral de-
scendino- tract of Marchi and Lowenthal. This tract increases
in size from below upward, and passes into the anterolateral
field of the formatio reticularis of the medulla oblongata, in which
104 CENTRAL NERVOUS SYSTEM.
region some of the fibers may be connected with the cells of the
lateral nucleus. This bundle then continues onward through
the medulla and pons as far as the root of the trigeminal nerve,
beyond which point its course is in much dispute. According
to Hoche, :;: the terminal course of Gowers' tract is as follows :
At the level of the upper half of the olivary body the direct
cerebellar tract turns backward into the restiform body, while
Gowers' tract continues upward through the medulla and pons
to the region of the trigeminal or fifth nerve, around which nerve
it curves, and passes into the cerebellum by means of the velum
medullare anticum and superior cerebellar peduncle.
Mott, however, after studying the course of Gowers' tract in
monkeys, believes it to consist of two afferent bundles — axones
from the gray matter of the cord : one, the ventral cerebellar
tract, occupying the most peripheral part of this area, which, on
reaching the pons, forms a loop over the fifth nerve to join the
superior cerebellar peduncle, and then descends on its posterior
aspect to the middle lobe or vermis of the cerebellum. The
remaining bundle, which he terms the crossed afferent tract of
Gowers and Edinger, continues upward through the cord, the
medulla, and the pons, beyond which it lies outside of the lateral
fillet or lemniscus, and terminates in the corpora quadrigemina,
some fibers continuing to the optic thalamus.
Bechterew has shown that the constituent fibers of this tract
receive their myelin at the eighth fetal month.
The function of this tract, accordine to Gowers, is to conduct
sensations of pain and temperature, and the very interesting
case recently reported by Henry Hun is confirmatory of the
same fact.f
THE ANTEROLATERAL DESCENDING CEREBELLAR TRACT OF
MARCHI AND LOWENTHAL.
This tract of fibers, discovered by Lowenthal, is located ventrad
* Hoche's case is the only one in man in which Gowers' tract has been completely traced.
See original article in " Archives fiir Psychiatrie und Nervenkrankheiten," 1896, p. 510.
•f "New York Medical Journal" for April 17, May I and S, 1897': "Analgesia, Thermic
Anesthesia ami Ataxia. "
SPINAL CORD. 105
to the crossed pyramidal tract, and extends along the antero-
lateral periphery of the cord as far forward as the anterior
median fissure, some of its fibers beings commineled with those
of Gowers' tract. That this tract is distinct from the motor
tracts seems proved by the fact that it has never been found
degenerated after disease or ablation of the motor area of the
brain. While the exact position of the anterolateral descending
tract in the cord is well known, the source and distribution of
its component fibers still remains in much doubt. The experi-
ments of Marchi and Biedl seem to prove that the fibers of this
tract have their origin in the cerebellum. Marchi found that,
after hemi-extirpation of the cerebellum, a secondary descend-
ing degeneration occurred in the spinal cord, the degenerated
area corresponding exactly to the known anatomic position ot
this tract. Biedl also found, on experimental division of the
restiform body, a similar degeneration, thus confirming the
earlier experiments of Marchi. Ferrier, Turner, and Risien
Russel, on the contrary, found the anterolateral descending
tract degenerated after destruction of Deiter's nucleus, the
cerebellum and restiform body being intact. According to
Risien Russel, this tract of fibers occupies a position in the for-
matio reticularis between the descending root of the fifth nerve
and the raphe ; the fibers pass downward between the inferior
olivary body and the lateral nucleus, occupying the anterolateral
periphery of the cord as far forward as the anterior median
fissure. The anterolateral descending tract extends through-
out the cord, but decreases in size from above downward. The
fibers of which it is composed may enter the anterior horns at
different levels, to terminate about their nerve-cells.
THE OLIVARY TRACT OF BECHTEREW.
The olivary fasciculus, or the triangular bundle of Helweg,
appears on transverse section as a small triangular area of
fibers located in the ventral part of the anterolateral portion
of the spinal cord, with its base resting against the periphery of
the cord. The most lateral fibers of the anterior nerve-roots
frequently pass through this triangular area. At the beginning
106 CENTRAL NERVOUS SYSTEM.
of the motor decussation the olivary tract becomes spread out
and loses its triangular shape. Just above the motor crossway
the fibers of this tract occupy an oblong field along the ventral
periphery of the medulla, adjacent to the anterior pyramid. At
the beginning of the inferior olivary body the tract becomes
much reduced in size, and again assumes a triangular form, the
base of which caps the inferior part of the olive. At a higher
level the tract appears to have joined the olivary body. It is
possible, as suggested by Bechterew, that the fibers of which
this tract is composed are axones from cells of the olivary body.
The fibers of this tract, according to Bechterew, become medul-
lated after birth, hence they are entirely distinct from the motor
tracts or from the ground bundles of fibers. Because the fibers
of the olivary tract become medullated at about the same time
as those of the central tegmental tract of the medulla, Bechterew
believes that both tracts form a functionally continuous system
of fibers.
A LONG SENSORY TRACT IN THE CRAY MATTER (CIAGLINSKI ).
In connection with the sensory tracts of the cord, mention may
be made of a long sensory tract of fibers in the gray matter of the
cord, discovered in 1 896 by Adam Ciaglinski. This tract of fibers
is somewhat pyramidal in shape on transverse section, and is
located, according to Ciaglinski, in the gray commissure between
the ventral border of the posterior columns and the central canal.
It has been traced from the lumbar cord to the cervical enlarge-
ment. Ciaglinski believes its fibers to come from the posterior
nerve-roots, and thinks that it may conduct sensations of pain
and temperature. Further clinical and experimental evidence
must be at hand before any positive statements regarding this
tract can be made.
LISSAUER'S TRACT.
This comprises an area which surrounds the tip of the posterior
horns, extending in part into the lateral column and in part into
the column of Burdach. It is composed more particularly of
SPINAL CORD.
107
fibers from the lateral division of the posterior nerve-roots.
These fibers soon divide, passing up and down and giving off
collaterals, which, with the axones, enter the posterior horns and
finally terminate in brush-like expansions about the cells existing
in those horns.
ANTERIOR GROUND BUNDLES.
The anterior ground bundles occupy all of the anterior
columns of each side save the direct pyramidal tract, the fibers
of Gowers' tract, and those of Marchi and Lowenthal. They
are collections of fibers which extend throughout the entire
length of the cord, and consist of neuraxones from the intrinsic
cells of the gray matter which lie near the base of the anterior
horns. These neuraxones mostly cross in the anterior white
commissure, although some fibers of the same side enter the
anterior ground bundle of that side. After entering these
columns the axones branch T-shaped, one branch passing upward,
the other downward, both branches having only a short course.
They give off collaterals at right angles. The branches, with
their collaterals, reenter the gray matter at higher and lower
levels, and end in brush-like expansions among the motor and
intrinsic cells of the anterior cornua.
At the point of the motor crossing in the medulla, part of the
fibers of the ground bundles are pressed backward into the
posterior part of the formatio reticularis, where they continue
upward as a distinct bundle of nerve-fibers on each side of the
raphe, and from this point on are called the posterior longitudinal
bundles.
One of the functions of this system of fibers is to associate
different levels of the anterior cornua, thus bringing into harmony
the action of the motor-cells of various levels.
THE GROUND BUNDLES OF THE LATERAL COLUMNS, OR THE
LATERAL LIMITING LAYERS.
These bundles of fibers occupy areas adjacent to the gray
matter of the cord between the anterior nerve-roots and base of
10S CENTRAL NERVOUS SYSTEM.
the posterior horns of each side. They are composed of neur-
axones from the intrinsic cells of the intermediate gray matter
of the same and opposite sides. The axones pass into the white
matter and bifurcate, passing, after a short course, upward and
downward; with their collaterals, reenter the gray matter at
higher and lower levels, where they divide into fine filaments
about the intrinsic nerve-cells. These bundles are traversed by
many fibers from the cells of the gray matter passing across the
lateral columns, and also by fibers entering the gray matter
from the crossed pyramidal tract. They may serve to associate
different levels of the gray matter. Experimental evidence
seems to prove that the fibers of the ventral portion of the
lateral limiting layer associate different levels of the anterior
cornu of the same side, while the fibers of the dorsal portion
probably associate different levels of the posterior cornu of the
same side.
THE SPINAL NERVES.
There are thirty-three pairs of spinal nerves in man, each
pair corresponding to a spinal segment.* According to the region
from which they issue, they are termed cervical, dorsal, lumbar,
sacral, and coccygeal nerves, there being eight cervical, twelve
dorsal, five lumbar, five sacral, and three coccygeal nerves.
These nerves — each possessing an anterior and a posterior root
— emerge from the cord at regular intervals. The anterior roots,
which leave the cord, arise from the multipolar cells of the ante-
rior horns and pass out through the anterolateral columns of
the cord. The posterior roots, which enter the cord, have their
point of entrance at the posterolateral sulci.
These nerve-roots are made up of filaments, — from five to ten
in number for each root, — the posterior roots having their fila-
ments associated into two bundles. The posterior sensory roots
are of greater size than the anterior or motor roots, and have
connected with them the posterior spinal ganglia.
* Most anatomists only enumerate thirty-one pairs of spinal nerves; this is owing to the fact
that the two lowest pairs of coccygeal nerves are rudimentary, and hence without special
function.
SPINAL CORD.
109
SPINAL GANGLIA.
The spinal ganglia are in general located in the epidural space,
just in front ot or within the intervertebral foramina. The ganglia
connected with the sacral nerves, however, are contained within
the subdural space of the spinal canal. The spinal ganglia are
oval, usually bilobate, the lobes corresponding to the two bundles
of filaments into which each sensory nerve-root is divided. Each
ganglia is made up of a large number of cells, chiefly unipolar,
spheric, or slightly pyriform in shape, and between 60 to So u
Fig. 55. — Transverse Section through a Posterior Spinal Ganglion. Stained after
the method of Weigert.
in diameter ; great variations in size occur, the largest being as
much as 170 fi in diameter, and the smallest as low as 25 i_i in
diameter (Figs. 55 and 56).
Each cell is surrounded by a distinct connective-tissue capsule,
which is continuous with Henle's sheath of the corresponding
axis-cylinder, and is lined with a layer of epithelium. Beneath
this capsule, surrounding the protoplasm of the cell, exists a
small, clear, homogeneous, unstainable space devoid of granules.
This seems to indicate that the protoplasm does not entirely
no CENTRAL NERVOUS SYSTEM.
occupy the capsule ; at least Lenhossek says that this clear space
is not an artifact, due to the shrinking of the protoplasm during
the process of hardening. The protoplasm is made up chiefly
of chromophyllic granules. These granules are very fine
throughout the body of the cell, but around the periphery there
exists a layer of much coarser granules. The construction of
the matrix in which these granules are embedded is still in
dispute. By some it is considered to be composed of a number
Fig. 56. — A Group of Cells from a Human Posterior Spinal Ganglion. Stained
after the method of Nissl.
of fine fibrillar, continuous with the fibrillar composing the
axones, while others assert that no such fibrillar exist. These
latter believe that the matrix is simply a homogeneous ground
substance in which the granules are embedded. Most of the
cells of the posterior spinal ganglia are very deeply pigmented,
the pigmentation being limited to the protoplasm, and occurs
most often near the point of exit of the axone.
These cells contain a large spheric nucleus, surrounded by
SPINAL CORD.
a distant nuclear membrane. It is centrally located, contains a
small nucleolus, and is made up of very fine granules. By far
the greater number of these cells are monopolar, and hence
give off but one axone. This axone, at a short distance
from the cell-body, bifurcates T-shaped, one branch passing
peripherally to terminate in a sensory end organ, while the
f xlik"
Fig. 57. — Schematic Representation to show the Origin and Relations of the
Anterior and Posterior Spinal Nerve-roots.
A. Anterior or motor nerve-roots. B. Posterior or sensory nerve-roots. D. Posterior spinal
F. Central, E, peripheral, axones of the posterior spinal ganglia.
Other continues centrally to arborize about nerve-cells in the
spinal cord or medulla oblongata.
A few of these cells are bipolar, giving off two axones, one
from each pole, one of which is peripheral as above and the
other central. According to Dogiel, there exists in the posterior
spinal ganglia numerous small cells which he calls spinal ganglion
cells of the second type. These cells might be very properly
termed the intrinsic cells of the posterior spinal ganglia. The
H2 CENTRAL NERVOUS SYSTEM.
chief axone of each cell terminates, after losing its myelin sheath,
in an arborization about and within the capsule of a chief spinal
ganglion cell, forming an extra- and intra-capsular network.
Dogqel further asserts that these intrinsic cells are in turn sur-
rounded by the termination of sympathetic nerve-fibers.
The function of these posterior spinal ganglia is doubtless
trophic, since on section of the nerve-roots posterior to their
ganglia the fibers degenerate to their peripheral destination,
while if they are divided anterior to their ganglia, there is an
ascending degeneration of the fibers which continues as far
as they extend, the short fibers to the posterior horns, the long
fibers to their nuclei in the medulla. According to Edinger,
the sensory fibers, carrying impressions of equilibrium to the
cells of Clarke and Stilling, are dependent on these cells for
their nutrition and not upon the cells of the spinal ganglion,
merely passing between them in their course. The anterior and
posterior nerve-roots become continuous in the intervertebral
foramina, and continue peripherally as mixed nerves, having
both motor and sensory functions. (See Fig. 57.)
THE ANTERIOR OR MOTOR NERVE-ROOTS.
The anterior nerve-roots, which consist of both coarse and fine
fibers and are distributed to the voluntary muscles,* are the
neuraxones of the motor cells of the anterior cornua of the
spinal cord. The multipolar cells of large size give off axones
which are greater in diameter than are those from the multi-
polar cells of smaller size. There are three distinct bundles of
these axones, which form the anterior nerve-roots : first, a lateral
bundle, coming from the lateral cell group ; second, a median
bundle, arising from the median cell group ; and lastly, an inner
bundle, springing from the anterior cell group.
These axones give off a few collaterals, the termination of
which remains unknown. The anterior nerve-roots pass out of
the anterolateral area of the cord in curves, and take mostly a
* According to Gaskell and Mott, the fine fibers join the sympathetic system and are distributed
to the involuntary muscles of the internal organs.
SPINAL CORD. 113
downward direction. The curvature of the anterior nerve-roots
gradually increases from above downward, so that while in the
cervical region they are given off almost at right angles, with
exception of the first cervical nerve, which ascends slightly, to pass
between the atlas and occipital bone. In the dorsal region they
fljggTTWW
Fig. 58. A Section through the Spinal Cord of a New-born Mouse. Showing
reflex collaterals from posterior nerve-roots terminating about the nerve-cells of the anterior
horn. — {After Lenhossek.)
are oblique, and in the lumbar and sacral regions their course is
almost vertical.
THE POSTERIOR OR SENSORY NERVE-ROOTS.
These roots, on entering the cord, are arranged into two
bundles — a lateral and a mesial. The former is composed of
fibers of small size, which, near the tip of the posterior horn,
ii 4 CENTRAL NERVOUS SYSTEM.
enter the substantia gelatinosa, become vertical, and form the
boundary zone or column of Lissauer. The mesial bundle
consists of fibers, some of which pass into the column of Burdach,
while others pass through that column into the column of Goll.
All these root-fibers bifurcate on entering the cord, one process
passing upward, the other downward. Both divisions are con-
stantly giving off collaterals at varying distances. Many of the
fibers having a downward course unite to form a comma-shaped
fasciculus or tract in the median portion of Burdach's column.
Those fibers which pass upward, with the exception of those
which reenter the gray matter (see posterior column), end
about the cells of the nuclei of the columns of Burdach and Goll
in the medulla. The collaterals from these longitudinal fibers
all pass into the gray matter, and may, in general, be divided into
three sets : First, collaterals which pass across the intermediate
gray matter to end in brush-like expansions about the motor
nerve-cells of the same side ; these are called sensorimotor
or reflex collaterals ; second, collaterals which end in arboriza-
tions about the cells of Clarke and Stilling and the intrinsic cells
of the gray matter ; these collaterals come largely from the
middle region of Burdach's column ; third, collaterals which
pass across in the posterior or gray commissure and end among
cells in the fine network of fibers of the substantia gelatinosa
of the posterior horn of the opposite side.* (See Figs. 45 and 59.)
THE APPEARANCES OF TRANSVERSE SECTIONS OF
THE CORD AT DIFFERENT LEVELS.
In the sacral region there is a preponderance of gray matter,
there being only a thin layer of white matter, the most of which
exists in the posterior columns. In general, the anterior and
* According to Morat and Bonne, there are present in the posterior nerve-roots a few
centrifugal elements. They proved this fact by observing that, on stimulation of the peripheral
end of a severed posterior nerve-root, there occurred vasomotor phenomena in the area of distri-
bution of the nerve. They also found that, on section of the posterior nerve-roots of the last
lumbar and first sacral segments central to the ganglia, on the central side of the section the
great majority of the fibers degenerated, while a few remained normal. In the peripheral end,
on the contrary, most of the fibers remained normal, while a few degenerated, thus proving that
a few fibers degenerated downward and receive their nutrition higher up in the cord or in the
brain stem. These facts remain (<> lie corroborated by future observations.
SPINAL CORD.
J «5
posterior horns resemble each other in size and thickness. The
lateral horns are well marked. The commissure is very broad.
The conns terminalis on transection resembles closely similar
sections of the lower sacral part of the cord, the gray matter
Fig. 59.— Diagram showing the Relative Size and Form of Different Segments
of the Coccygeal, Sacral, Lumbar, Dorsal, and Cervical Cord.— [After Gowers.)
preponderating, while the white matter consists of a very thin
margin, most evident in the lateral columns.
In the lumbar region the outline of the cord is circular, the
anterior horns are much broader and thicker than the posterior.
There exist in the anterior horns well-defined groups of motor
nerve-cells, which give exit to a large number of motor nerves
n6 CENTRAL NERVOUS SYSTEM.
which are distributed to the lower extremities. The lateral
horns are distinct only in the lower segments. The white
matter preponderates, owing to the great number of nerve-
fibers received from the lower extremities.
In the dorsal or thoracic region the gray matter consists of
two narrow crescentic bodies united by means of a band of gray
Fig. 60. — Transverse Section through a Sacral Segment of the Spinal Cord.
Weigert preparation.
a. Pia mater, b. Arachnoid, c. Dura mater. (/, d. Severed descending nerve-roots. I.
Anterior column. 2. Lateral column. 3. Posterior column. 4, 4. Cell groups of Stilling.
and white matter — the commissures. The lateral horns are well
seen only in the upper segments. The anterior and posterior
horns are about equal in thickness, but the anterior horn is
much shorter, and contains, in this region, very few ganglionic
cells. In the upper part, at the base of the posterior horn, is
the group of the cells of Clarke. The great amount of white
matter is the striking feature of transverse sections of this
SPINAL CORD. n 7
region. In the upper part is found the beginning of the postero-
intermediate septum, which is the dividing-line between the
columns of Goll and Burdach.
In the cervical region there is a general increase in the size
of the cord, which affects the gray as well as the white matter.
This is due to the fact that this region receives the fibers from
the upper extremities as well as the long and short tracts from
below. The cord is flattened anteroposteriorly, hence loses its
cylindric form. The lateral horns are very prominent, and in
the upper segment exists a cell-group at the base of these
horns, which group gives origin to the spinal accessory or
eleventh pair of cranial nerves. The processus reticularis is
prominent on the outer side of the gray matter between the
anterior and posterior horns. The anterior horns are short and
broad and appear of large size, which is due somewhat to the
lateral extension of gray matter forming the lateral horns.
The posterior horns are long and slender and gently diverge,
the divergence increasing as the segments gradually approach
the medulla. At the same time the central canal trends back-
ward and assumes a somewhat flattened appearance. The
nerve-roots leave the cord at nearly right angles.
NEUROGLIA OF THE SPINAL CORD.
The neuroglia of the cord, as elsewhere throughout the central
nervous system, consists of large numbers of neuroglia cells
(astrocytes) with their processes, which latter pass between the
nerve-fibers and cells and around the blood-vessels, forming a
supporting framework, ground substance, or stroma, in which
the elements of the cord are embedded. In addition to the
neuroglia cells described under head of histologic elements,
there occurs lining the central canal of the cord, as well as the
ventricles of the brain, a supporting framework similar in func-
tion to neuroglia tissue, but made up of the so-called ependymal
cells and processes. In the cord during embryonic life these
cells are oval or fusiform in shape, and are arranged around the
central canal in a radiating manner. They possess two pro-
cesses, one short and thick, extending to the cavity of the central
nS
CENTRAL NERVOUS SYSTEM.
canal, then being prolonged into its lumen as a very fine ciliated
process ; the other, or peripheral process, extends transversely
through the gray and white matter, to end just beneath the pia
in a club-shaped enlargement. As this process nears the pia
it frequently divides into two or more branches, which end as
Fig. 6i. — A Section through the Spinal Cord of a Human Fetus, 23 Cm. in Length.
Showing the central canal with its substantia gelatinosa centralis and ependymal cells. —
{After Lenhossek.)
above described. As age advances this typical arrangement of
the ependymal cells becomes lost by atrophy of its processes
and the probable transformation of the ependymal cells into
adult neuroglia cells.
In the following locations the neuroglia of the cord is much
increased in amount: (1) Around the entire periphery of the
SPINAL CORD.
119
cord, where it forms a distinct mantle ; (2) in the anterior
horns ; and (3) in the region of the central canal.
THE SUBPIAL NEUROGLIA LAYER, THE RINDENSCHICHT OF
THE GERMANS.
This layer consists of a thick, closely-meshed network of
neuroglia fibers, having interspersed among them large num-
Fig. 62. — Transverse Section of the Spinal Cord of a Human Embryo, 14 Cm, in
Length. Illustrating the distribution of neuroglia. On the right are seen the ependymal
cells. On the left, the neuroglia cells. — {After Lefihossek.')
bers of neuroglia cells. It forms a covering- or mantel for the
cord, which varies in thickness from 0.0 1 to 0.06 mm. This
layer is entirely distinct from the pia mater. It is thickest in
the region about the anterior and posterior nerve-roots, and
gives off fine parallel coursing bundles of fibers, which accom-
pany the nerve-roots for a short distance. It is also quite thick
at the entrance of the posterior median fissure, where a
process, the posterior median septum, extends into that fissure
120 CENTRAL NERVOUS SYSTEM.
and serves to divide the posterior columns into symmetric
halves, and conducts blood-vessels into the cord. A distinct
process of neuroglia exists in the cervical region, the posterior
intermediate septum, which separates the columns of Goll and
Burdach from each other. The cells of this layer all possess
long fibers, and are stellate in shape. The subpial neuroglia
Fig. 63. — A Transverse Section through a Segment of the Dorsal Cord to
show the General Arrangement of Neuroglia. Nigrosin stain.
I, I, 2, 2. Short and long neuroglia septa. 3. Postero-intermediate septum. 4, 4. Subpial
neuroglia layer.
layer sends into the white matter of the cord numerous pro-
cesses having a radial course, the glia septa, which accompany
the blood-vessels ; these processes surround the vessels and
form for them canal-like channels. The neuroglia of the white
matter of the cord consists only of cells with long processes.
The fibers of the white matter, apart from being separated by
SPINAL CORD. 121
the glia septa into many bundles, are separated from one another
by a_ delicate cribriform framework of neuroglia, so arranged
that each individual nerve-fiber is surrounded by a neuroglia
process. In the posterior columns this neuroglia framework is
much increased in amount. No ordinary connective tissue
exists in the cord save that which forms the adventitia of the
blood-vessels, and the pia process extending into the anterior
median fissure.
Fig. 64. — A Camera Lucida Drawing of a Field of the Lateral Column of
Figure 63. Nigrosin stain.
a. Subpial neuroglia layer with septa, b. Cribriform framework of neuroglia, d. Severed
nerve tubes, c. Stellate neuroglia cells.
The neuroglia of the gray matter differs from that of the
white matter in containing both varieties of cell. The antero-
lateral horns contain an abundance of neuroglia cells and fibers,
and according to Lenhossek, the cells with short processes pre-
dominate. These horns possess a rich network of very fine
neuroglia fibers, in addition to coarse fibers which have a hori-
zontal course, and are arranged in bundles which become nar-
122 CENTRAL NERVOUS SYSTEM.
rowed as they pass out with the anterior nerve-roots, while the
central ends spread out in the interior of the cornua.
Posterior Horns. — The tip of the posterior horn and Lis-
sauer's columns contain a rich plexus of neuroglia fibers, while
the substantia spongiosa is very much less rich in neuroglia.
The Substantia Gelatinosa Rolandi. — This region of the
posterior horn, contrary to the usually accepted opinion, is,
according to Weigert, very poor in neuroglia, the few neuroglia
fibers being found there having a radial arrangement.
The region of the central canal is rich in neuroglia cells
and fibers. These are chiefly arranged in the form of a circular
network just beneath and around the central canal. In front
and behind the central canal the fibers display a commissural-
like arrangement ; laterally they are continuous with the fibers
of the anterior horns (Fig. 61).
THE BLOOD SUPPLY OF THE SPINAL CORD.
The arteries which nourish the cord are the following: First,
lateral spinal branches from the subclavian, from the thoracic
intercostals of the aorta, from the lumbar, and from the internal
iliac arteries. Second, the anterior and posterior spinal branches
of the vertebrals. The anterior are two in number, and arise
from the vertebrals a little below their junction to form the
basilar, and at the level of the foramen magnum they unite into
one vessel, the anterior median artery, which extends down-
ward, throughout the entire length of the cord, receiving
branches of reinforcement from the lateral spinal arteries. This
vessel lies in the pia mater, which it supplies, and it also gives
off branches to the substance of the cord.
The posterior spinal arteries, two in number, usually arise from
the vertebrals at the sides of the medulla and pass backward
to the dorsal portion of the medulla, where they take a descend-
ing course behind the line of attachment of the posterior nerve-
roots, extending downward to the cauda equina.* These ves-
* The posterior spinal arteries occasionally have their origin from the posterior inferior
cerebellar arteries (Duret).
Sl'INAL CORD.
123
sels receive reinforcements from the lateral spinal arteries
through the intervertebral foramina. The lateral spinal arteries
after entering the cord are designated root arteries. They
pierce the dura mater, and send branches to the anterior and
posterior nerve-roots. The anterior root arteries, of which there
are about eight, are about twice as large as the posterior root
arteries, but only one-half as numerous. The more minute
arterial divisions which supply the substance of the cord may
Fig. 65. — Scheme to show the Course and Distribution of the Terminal Branches
of the Arterial Plexus of the Pia Mater. — {After Van Gehnchten.)
a. spin. post. Posterior spinal arteries, a. spin. ant. Anterior spinal arteries, a. sil. Anterior
median fissure, rite. ant. Anterior root arteries.
be divided into two sets : first, a centrifugal set, which is
composed of a series of arterioles, about 250 in number, which
come from the anterior spinal artery into the anterior median
fissure, penetrating the anterior commissure, then dividing into
a right and a left branch, which soon subdivide into smaller
arteries and capillaries for the central part of the gray matter.
Ascending and descending branches are given off for anasto-
mosis with the corresponding vessels at different levels. The
centripetal set have a radial arrangement, coming in from all
I2 4 CENTRAL NERVOUS SYSTEM.
parts of the periphery. They consist of short and long branches,
the short branches supplying the outer portion of the white
matter of the cord, the long branches penetrating the gray matter
and supplying the parts not supplied by the centrifugal vessels.
The posterior horns, as well as the adjacent white matter and
cells of Clarke, are supplied by a small median artery, the inter-
funiculate, which passes between the posterior columns of each
side to the posterior commissure and then divides, entering the
before-mentioned regions. The posterior fissural artery passes
ventrally through the posterior median fissure to supply the
columns of Goll.
VEINS OF SPIXAL CORD.
These have no valves. They issue from the interior of the
cord alongside of the anterior and posterior nerve-roots —
hence they are often called root-veins. Of these, there are
from forty to fifty in number — twenty-five to thirty anterior, the
remainder posterior. They pass into the pia mater, where
they form plexuses which cover the entire surface of the cord,
emerging chiefly from the anterior and posterior median fissures,
where they join the anterior and posterior longitudinal median
veins. Near the base of the skull two or three small branches
are formed, which communicate with the vertebral veins and then
terminate in the inferior cerebellar veins, or in the inferior
petrosal sinuses.
CHAPTER III.
THE MEDULLA OBLONGATA, OR BULB.
The medulla oblongata extends from the lower border of the
transverse fibers of the pons Varolii above to the foramen
magnum below, and gradually decreases in size from above
downward. It is somewhat rhomboid in shape, and i's continu-
ous below with the spinal cord. Its anterior surface rests in the
basilar groove of the occipital bone, while its posterior surface
is continuous above with that of the pons Varolii, and lies be-
tween the hemispheres of the cerebellum, in a fossa called the
vallecula, or little valley. Issuing from it are the lower six
pairs of cranial nerves.
The medulla is divided into symmetric halves by the ex-
tension upward of the anterior and posterior median fissures of
the cord. The anterior median fissure contains a fold of pia
mater, and continues upward to just below the pons, where it
ends in a small fossa, the foramen caecum. It is interrupted
below by the motor or pyramidal decussation. The posterior
fissure is a deep but narrow fissure, and continues upward to
about the middle of the medulla, where, owing to the diverg-
ence of the posterior columns, it becomes lost on the floor of
the fourth ventricle.
The medulla may be divided into anterior, lateral, and pos-
terior columns, which are continuations upward of the corre-
sponding columns of the spinal cord. The columns, together
with special deposits of nervous matter peculiar to the medulla,
give to it its outward configuration. The anterior columns, or,
more properly, the anterior pyramids of the medulla, lie between
the anterior median fissure and the exit of the hypoglossal or
twelfth pair of cranial nerves below, and the exit of the sixth
pair above. The exact line of division between the anterior
125
126 CENTRAL NERVOUS SYSTEM.
pyramids and the lateral columns is the ventrolateral groove,
which is the direct continuation upward of the line of emergence
of the anterior nerve-roots of the spinal cord. The anterior col-
umns of the cord are continued upward into the medulla in the
same relative position on each side of the anterior median
fissure. They form only a small number of the fibers present
at or above the motor or pyramidal crossing.
In the spinal cord were noted two distinct divisions of the
motor or pyramidal tracts, one coming down in the anterior
column, adjacent to the anterior median fissure, known as the
direct pyramidal or motor tract ; the other, much greater in
size, occupying a large area in the posterior part of the lateral
column of the cord, known as the crossed pyramidal or motor
tract because of having crossed in the medulla. These two
bundles, direct and crossed motor tracts, form the anterior col-
umns or pyramids of the medulla.
The lateral columns, or lateral areas of the medulla, lie between
the exit of the hypoglossal nerves or the ventrolateral grooves in
front and the exit of the spinal accessory, pneumogastric, and
glossopharyngeal nerves behind, which nerves issue from the
dorsolateral grooves, which are the continuation upward of like-
named grooves existing in the cord. The olivary bodies are
embedded in the upper part of the lateral area. The lateral
columns are continuations upward of the corresponding columns
of the cord, but the latter are not preserved as such in their
entirety, owing to the fact that the fibers of the crossed pyramidal
tracts leave their position to form the motor decussation, and the
direct cerebellar tracts or columns of Flechsig gradually trend
backward and unite with the restiform bodies to pass into the
cerebellum.
The posterior area of the medulla is a continuation upward
of the posterior columns of the spinal cord, which have gradually
increased in size from below upward. This area is subdivided
by a neuroglia process — the postero-intermediate septum — into
the inner or column of Goll, and the outer or column of Burdach,
which in turn are separated from the lateral area of the medulla by
the dorsolateral groove. The former passes upward, the fibers
of which it is composed ending about a collection of ganglionic
Fig. 66. — View from Before <>k the Medulla Oblongata, Pons Varolii, Crura
Cerebri, and other Central Portions of the Encephalon (Natural size). —
[Allen Thomson.*) — [From Quavi's "Anatomy.")
On the right side the convolutions of the central lobe, or island of Reil, have been left, together
with a small part of the anterior cerebral convolutions ; on the left side these have been
removed by an incision carried between the thalamus opticus and the cerebral hemisphere.
I'. The olfactory tract cut short and lying in its groove. II. The left optic nerve in front of the
commissure. II / . The right optic tract. Th. The cut surface of the left thalamus opticus.
C. The central lobe or island of Reil. Sy. Fissure of Sylvius. XX- Anterior perforated
space. . Pyramid. XII Bundle of
hypoglossal nerve emerging from the surface ; at b it is seen coursing between the pyramid
and the olivary nucleus, 0. f.a.e. External arciform fibers. n.I. Nucleus lateralis, a.
Arciform fibers passing toward restiform body partly through the substantia gelatinosa, g. ,
partly superficial to the ascending root of the fifth nerve, a. V. X. Bundle of vagus root,
emerging, f.r. Formatio reticularis. C.r. Corpus restiforme, beginning to be formed,
chiefly by arciform libers, superficial and deep. n.c. Nucleus cuneatus. n.g. Nucleus
gracilis. /. Attachment of the ligula. f.s. Funiculus solitarius. n.X.,n.X'. Two parts
of the vagus nucleus. n.XIL Hypoglossal nucleus. )i.t. Nucleus of the funiculus teres.
71. am. Nucleus ambiguus. r. Raphe. A. Continuation of anterior column of cord. (/.,
o /r . Accessory olivary nuclei, p.o.l. Pedunculus oliv^e.
the lateral nuclei. These collections of nerve-cells are composed
in part of cell groups from the anterior horns, with the addition
of special deposits of nerve-cells found in this area. The direct
cerebellar tracts, or columns of Flechsig, occupy the same rela-
tive position in the lateral periphery of the medulla as in the
spinal cord, being situated in front of the crescentic bundle of
i 4 4 CENTRAL NERVOUS SYSTEM.
fibers, the descending root of the fifth nerve. Here also the
posterior columns continue to diverge, the central canal and
gray matter broaden out, and, after trending backward, the
canal opens into the fourth ventricle, thus exposing the central
gray matter of the medulla as part of the floor of that ventricle.
Most of the fibers of the posterior columns have ended in
their respective nuclei — namely, in an inner, club-shaped mass
next to the median line, the nucleus of the column of Goll, or
nucleus gracilis, and an outer broad swelling, the nucleus of the
column of Burdach, or nucleus cuneatus. Both gray masses
contain multipolar nerve-cells, about which the fibers of the
columns, or funiculi graciles and cuneati, end. From the cells
of these two nuclei new axones stream out, forming bundles of
curved fibers, — the so-called internal arcuate fibers, — which pass
anteriorly through the gray matter, decussate in the raphe with
those coming from the opposite side, and become located just
posterior to the anterior pyramids, between the olivary bodies,
whence they assume a longitudinal course. Edinger has proved
by embryologic studies that many of these fibers surround and
pass through the olivary bodies without becoming connected
with their nerve-cells, and locate themselves in the above-
described area. To these bundles of fibers of each side the
name mesial fillet or lemniscus has been given, and the decus-
sation has been called the sensory decussation, or the posterior
pyramidal decussation, and from its position between the olivary
bodies it is often called the interolivary decussation. This
system of fibers — the fillet or lemniscus — forms a long tract,
which terminates in the sensory area of the cerebral cortex.
The higher the sections of the medulla, the smaller the poste-
rior nuclei become, because nearly all their fibers are lost in the
arciform fibers of the fillet, their place being gradually usurped
by the appearance of the broad rope-like bands, — the restiform
bodies, or the inferior cerebellar peduncles, — which at this level
have attained considerable size.
The head of each posterior horn is severed from its narrow
cervix by the internal arcuate fibers and by fibers of the lateral
area passing into the formatio reticularis. The cervix is finally
lost in this latter structure.
Fig. 74. — Section of Medulla Oblongata at Level of Sensory Crossway.
Weigert-Pal preparation.
Anterior pyramid or motor tract, b. Inferior olivary body. c. Restiform body or inferior
cerebellar peduncle, d. Internal arcuate fibers from nuclei of columns of Burdach and
Goll passing ventrally to decussate between the olivary bodies (sensory decussation). .. e.
Postero-external arcuate fibers, f. Nucleus of column of Burdach. g . Nucleus of column
of Goll. h. Fourth ventricle, i. Hypoglossal nerve-roots, j. Raphe, k. Interolivary
bundle, median fillet, or lemniscus.
10 145
"\
146 CENTRAL NERVOUS SYSTEM.
Owing to these two decussations, the fibers of the ground
bundles of the anterior columns are displaced dorsally, so that
in cross-sections a little farther brainward they come to occupy
a position in the posterior part of the formatio reticularis on
each side of the raphe.
THE RAPHE.
The raphe, or median septum, is the middle line of the medulla
seen on transverse section. It extends from the bottom of the
anterior fissure to the gray matter of the floor of the fourth
ventricle. Here the various fine nerve-fibers decussate with
their fellows of the opposite side. They consist largely of the
fibers coming from the nuclei of the posterior columns, known
as the internal arcuate fibers, with a small number of external
arcuate fibers from the same source and fibers from the various
cranial nerve nuclei. Scattered among the various decussating
fibers of the raphe exist a number of multipolar nerve-cells
belonging to the formatio reticularis alba.
THE FORMATIO RETICULARIS.
As its name implies, this is a reticulated meshwork of hori-
zontal, longitudinal, and oblique fibers, crossing one another at
various angles and having interspersed between them many
multipolar nerve-cells, which cells collectively are called the
nucleus reticularis tegmenti (Bechterew). These cells of the
formatio reticularis are doubtless in part intrinsic and associative
in character, combining the various complex acts which are per-
formed by the medulla oblongata.
This formation lies between the olivary bodies and the nuclei
of the posterior columns, and is bounded laterally by the direct
cerebellar tracts. The area is subdivided into two regions, a
lateral and a mesial. The former borders on the direct cerebellar
tract of the medulla, and contains a large number of ganglionic
cells derived in part from the remains of the. anterior horns.
This lateral region is called the formatio reticularis grisea. The
mesial area is located between the raphe and the hypoglossal
Fig. 75. — Diagram Indicating the Course of the Motor and Sensory Fibers
of the Spinal Cord and Medulla.
a, a. Motor cells of the cerebral cortex. b\ b. Arborizations of the fibers of the sensory tract
in the cerebral cortex, c. Nucleus of the column of Burdach* showing terminal arboriza-
tions of the long sensory fibers of the cord. d. Nucleus of the column of Goll, showing
terminal arborizations of the long sensory fibers of the cord. e. Section of the medulla,
showing sensory decussation, f. Section of medulla, showing motor or pyramidal decus-
sation, g, g. Motorial end plates, h. Section through the cervical region of the cord,
showing termination in the anterior horn of the motor fibers of the direct pyramidal tract
after they have crossed in the anterior commissure ; also fiber of crossed pyramidal tract end-
ing about anterior horn cell of same side. i, i. Posterior spinal ganglia. J, k. Sensory fibers
of short course. /. Sensory fibers of long course, terminating in medulla, m, m, m. Sen-
sory end organs, n. Section through lumbar cord.
147
THE MEDULLA OBLONGATA, OR BULB. 149
nerve-roots, and because it is composed mainly of nerve-fibers,
with only a few cells, this area is called the formatio reticularis
alba.
The fibers of the formatio reticularis are arranged as follows :
First, the horizontal fibers belongingr to the fillet or lemniscus.
Second, those fibers which have come from the anterior ground
bundles of the spinal cord and have trended backward to form the
posterior longitudinal bundles, and which appear on transverse
section as two distinct bundles of nerve-fibers, more or less tri-
angular in shape, on each side of the raphe, just below the floor
of the ventricle, and continue to occupy the same relative position
beneath the aqueduct of Sylvius until they reach the neighborhood
of the nucleus of the oculomotor or third pair of cranial nerves,
beneath the anterior corpora quadrigemina. In their course they
give off collaterals to the nuclei of several of the cranial nerves,
especially those concerned in the movement of the eyeballs. Some
of the fibers of the posterior longitudinal bundles end in arbori-
zations about the cells of the formatio reticularis grisea from the
upper part of the pons Varolii to the anterior corpora quadrigem-
ina. These collections of cells in the formatio reticularis of each
side have been called by Koelliker the nucleus magnocellularis
diffusus. Third, fibers from the remains of the lateral columns
which pass into this area. These in part probably consist of the
fibers of the ground bundles of the lateral columns. These fibers
are connected with the cells of the nucleus reticularis tegmenti,
and continue brainward to the region of the posterior corpora
quadrigemina. Fourth, it is positive that Gowers' anterolateral
ascending tract, which is located lateral and slightly dorsal to the
olivary body, passes into the formatio reticularis grisea, and
thence upward to the pons, where, according to Hoche, it joins
the superior cerebellar peduncle and passes to the cerebellum.
Lastly, are found the before-mentioned internal arcuate fibers,
too-ether with the axones and collaterals from some of the
cranial nerves and those from the cells of the nucleus reticularis
tegmenti. The cells of the formatio reticularis are rather large
multipolar cells possessing long, thick, branching dendritic pro-
cesses with strong axis-cylinders, which pursue different courses.
Their common course is inward to the raphe, where they decus-
ISO
CENTRAL NERVOUS SYSTEM.
sate and pass into the ventral or dorsal parts of the formatio
reticularis. After a short course they become longitudinal and
gfive off numerous collaterals, which often bifurcate, one branch
^mli^egl:
mmm^^^
Fig. 76. — Section through Formatio Reticularis of the Medulla Oblongata.
Method of Weigert-Pal.
passing upward, the other downward, both branches probably
ending by arborizing about the cells of the formatio reticularis
at higher and lower levels.
Sections at this level — that is, at the sensory decussation — show
THE MEDULLA OBLONGATA, OR BULB.
LSI
the interposition of several of the cranial nerve nuclei — namely,
the twelfth, or hypoglossal, the ninth, or glossopharyngeal, and
the tenth, or pneumogastric.
The nuclei ol origin of the twelfth pair are found on each
side ot the median line, beneath the floor of the fourth ventricle
and close to the aforesaid spinal canal, and consist of large
groups of multipolar nerve-cells, which vary from 25 to 70 //
in diameter. Their protoplasmic processes, or dendrites, are
very numerous, and pursue a rather long course. According to
***< ..5
■
Fig. 77. — Microphotograph from a Seven-months' Human Fetus op Section of
Eormatio Reticularis Grisea. The cells with their decussating axones arc seen.
Van Gehuchten, many of the dendrites cross the median line and
ramify about the hypoglossal nerve-cells of the opposite side,
forming a protoplasmic commissure. The axis-cylinder pro-
cesses pass in slight curves ventrally, and emerge from the
medulla, between the olivary bodies and the pyramids, in the
anterolateral groove. Some of the axones, however, frequently
pass through the mesial portion of the olivary bodies and
between the fibers of the anterior pyramids, having their point
of exit in a slight sulcus on the ventral aspect of the pyramid of
152 CENTRAL NERVOUS SYSTEM.
each side. These axis-cylinders, or root-fibers, from the hypo-
glossal nuclei form a sharp boundary-line between the formatio
reticularis alba and grisea. The group of cells from which these
nerve-fibers arise corresponds to the cells which, in the spinal
cord, are located at the base of the anterior horns. But owing
to the previously described changes, they first occupy a position
ventrolateral to the spinal canal, and when the canal opens into
the fourth ventricle, they come to lie on the floor of the ventricle,
on each side of the median line. This group of nerve-cells,
on transverse section, occupies a somewhat triangular field, just
beneath the ependyma of the fourth ventricle on each side of
the raphe (Fig. 78).
Ventral to the chief nucleus of the hypoglossal nerve exists,
in the formatio reticularis, slight groups of small multipolar
nerve-cells, which surround the root-fibers of the hypoglossal
nerve. These collections of cells form the hypoglossal nucleus
of Roller.
It is highly improbable, at least in man, that the axones from
these small cells take any share in the formation of the root-
fibers of the hypoglossal nerve.
CONNECTK )NS OF THE HYPOGLOSSAL NUCLEI.
Surrounding this nucleus, and passing between its nerve-
cells, exist large numbers of very fine, and also coarse, medul-
lated nerve-fibers, which fibers give to this nucleus the appear-
ance of a stratum zonale.
These fibers arborize about the nerve-cells of the hypoglossal
nucleus, and probably form the means of connection of this
nucleus with the rest of the nervous system. Their source is as
follows :
1. Fibers from the motor tract (central motor tract of the
hypoglossal nerve), which occupy the middle part of the
motor tract and, becoming longitudinal at the level of this
nucleus, pass diagonally, and crossing in the raphe, terminate
about the hypoglossal nerve-cells of the opposite side.
2. Fibers enter this nucleus from the posterior longitudinal
bundle.
— -- f i ^s^'i;
'-J-'^s'iftVfA^
mMMM&m
Fig. 78.-
>\ •
-Transverse Section through the Hypoglossal Nucleus. Method of
Weigert-Pal.
'S3
THE MEDULLA OBLONGATA, OR BULIi. 155
3. Collaterals from the sensory end nuclei ot the vagus,
glossopharyngeal, and trigeminal nerves terminate about the
cells of this nucleus.
4. Large numbers of radial coursing fibers, which appear
to come from the olivary bodies, but may in part be motor
fibers Irom the pyramidal tract, enter this nucleus (Koelliker).
5. The hypoglossal nuclei are united with each other by com-
missural fibers which cross in the raphe.
THE VAGUS AND GLOSSOPHARYNGEAL NERVES.
The vagus and glossopharyngeal are mixed motor and
sensory nerves, and are connected in the medulla through three
nuclei. The motor nerve-root of each of these nerves consists
of the axones from the cells of the nucleus ambiguus. The com-
bined sensory nerve-roots represent the axones from the mono-
polar cells of the jugular and petrosal ganglia. The sensory
axones, on entering the medulla, do not immediately bifurcate,
but pass dorsally between the descending trigeminal roots, to
terminate after bifurcating among the cells of two distinct gray
masses located in the dorsal part of the medulla. On approach-
ing their end nuclei, they give off collaterals which, with their
axones, arborize about the cells existing in those nuclei.
There are thus two sensory end nuclei, among the cells of
which these sensory nerve filaments terminate. The first of
these is the so-called sensory nucleus of origin, and is located
dorsolateral to the nucleus of origin of the hypoglossal nerve,
producing on each side of the floor of the fourth ventricle the
gray prominence, the ala cinerea, or trigonum vagi, which ex-
tends upward to the fovea inferior. These nuclei, one for each
side, are composed of small spindle- or club-shaped cells about
30 to 40 [i long and 12 to 20 /.t wide. The cell groups of these
nuclei correspond in the spinal cord to cells which exist at the
base of the posterior horns. The cells of the upper portion of
these nuclei are connected with the sensory axones of the glosso-
pharyngeal nerves, while the cells of the lower part of them are
in relation with the axones of the pneumogastric nerves. The
second end nucleus consists of axones, collaterals, and nerve-
cells, and is called the vertical nucleus of Ramon y Cajal, the
i 5 6
CENTRAL NERVOUS SYSTEM.
fasciculus solitarius of Lenhossek, or the combined descending
root of the vagus and glossopharyngeal nerves ; also called the
respirator)/ bundle (Meynert, Gierke, Krause). This combined
descending root ot the vagus and glossopharyngeal nerve is
»=r«
Fig. 79.— Medulla Oblongata from a Human Embryo of Eight Months. — [After
ICoeiliker.)
P. Anterior pyramid whose fibers are not medullatecl. O. Olivary and accessory olivary
bodies. OC. Cerebello-olivary tract. PC. Cerebellar peduncle. Pi. Pontic ulus or
ligulce. IX, X. Glossopharyngeal and pneumogastric nerve-roots. X 1 . Combined sen-
sory end nuclei for vagus and glossopharyngeal nerves. Ps. Fasciculus solitarius with de-
scending fibers. Xm. Motor root-fibers of vagus and glossopharyngeal. A'''. Nucleus
ambiguus. V. Descending sensory trigeminal nerve. Villa. Descending vestibular
tract. Fid. Posterior longitudinal bundle. S. Median. S 1 . Lateral fillet or lemniscus.
S 2 . Interolivary bundle. PC. Direct cerebellar tract. XII. 1 hypoglossal nucleus and
root- libers.
located in the formatio reticularis on each side, a little ventro-
lateral to the first sensory end nucleus. It extends brainward
nearly as high as the superior end of the interior olivary body,
THE MEDULLA OBLONGATA, OR BULB.
157
and as far spinalward, according to Krause and Cajal, as the
eighth cervical nerve, there being located near the base of each
posterior horn. It has its greatest size just above the calamus
scriptorius, and gradually decreases in size from above down-
ward, and trends backward and inward. According to Koelliker,
the fasciculi become lost among the fibers of the funiculi cuneati,
but Cajal states that farther below they again become prominent
Fig. 80. — Transverse Section through the Medulla of a Mouse at the Level of
the Commissural Nucleus. — {After Ramon y Cajal.)
A. Commissural nucleus. B. Nucleus of the hypoglossal. C. Crossing of the fibers of median
fillet or lemniscus. D. Transverse section of solitary fasciculus, a. Cells of the com-
missural nucleus. b, c. End fibers of the pneumogastric and glossopharyngeal. d.
Decussation of collaterals from the hypoglossal nerve-cells, g, f. Sensory collaterals
terminating about the cells of the hypoglossal nucleus.
near the base of the posterior horns. These fasciculi, one for
each side, consist of fine axones, collaterals, and end brushes,
with, in several places, deposits of gray matter, which gray mat-
ter is usually located mesial to the nerve bundles. In their
upward course the fasciculi solitarii, deep beneath the epen-
dyma of the fourth ventricle, approach the raphe, and the gray
masses unite into an oval, somewhat saddle-shaped nucleus — the
158 CENTRAL NERVOUS SYSTEM.
commissural nucleus of Cajal. According to this observer, the
fibers of the solitary bundles lie in the lateral portion of this
nucleus. About three-quarters of them pass the middle line,
decussate with their fellows, and then arborize about the cells
existing in the opposite side of this nucleus. The cells of this
nucleus are small, oval, spindle, or angular, having very fine
neuraxones, which pass anteriorly across the raphe, forming
bundles of fibers which enter the lemniscus or fillet, which is
probably the central sensory tract for these nerves. This res-
piratory bundle may associate, through collaterals, the nuclei
controlling the various respiratory muscles (Figs. 79 and 80).
The A I o tor Nucleus of the Vagus and Glossopharyngeal Nerves.
— The motor root-fibers of the vagus and glossopharyngeal
nerves are the axones from collections of multipolar cells
located in the posterolateral portion of the formatio reticu-
laris of each side deep beneath the floor of the fourth ven-
tricle and mesial to the detached posterior horns. These
cells form on each side a distinct nucleus, somewhat pear-
shaped, which is prolonged upward to near the superior end of
the inferior olive and downward to the beginning of the sensory
crossway. It has received the name of nucleus ambiguus.
The axones of the cells from the upper portion of this nucleus
go to form the motor root-fibers of the glossopharyngeal,
while those of the lower portion form the root-fibers of the
pneumogastric and accessory portion of the spinal accessory
nerve. About the cells of this nucleus exist fine end brushes,
probably in part collaterals, from the descending root of the
trigeminal nerve, thus establishing a connection between the fifth
nerve and the motor division of the vagus and glossopharyn-
geal nerves. Collaterals also from the formatio reticularis grisea
arborize about the cells of this nucleus. No collaterals have as
yet been discovered connecting the sensory nerve filaments of
the vagus and glossopharyngeal with their motor nerve-cells,
although it is highly probable that such a connection exists. The
axones from the cells of these nuclei pass dorsally to a point
near the sensory end nuclei ; then they form distinct curves and
pass anterolaterally through the formatio reticularis and along-
side of the sensory fibers from their respective ganglia. In
THE MEDULLA OBLONGATA, OR BULB
159
their course they give off a few collaterals, which decussate in
the raphe with their fellows of the opposite side.
THE OLIVARY BODIES.
The olivary bodies, one on each side, are embedded in the
lateral part of the medulla just behind the anterior pyramids,
from which they are separated by the emerging hypoglossal
nerve-roots. Posteriorly, they are separated from the restiform
bodies by the dorsolateral groove for the exit of the spinal
■^■/W, Hi\i
■
a i - . ■*
.% •
X
v. ■ ' J
Fig. 81. — Micrdphotograph showing Multipolar Cells of Inferior Olivary Body.
accessory, pneumogastric, and glossopharyngeal nerves. A
short, deep, transverse groove exists between these bodies and
the pons Varolii above. The olivary bodies produce externally
two large, oval-shaped elevations, with their long axes arranged
longitudinally. Numerous fibers may be seen passing across
them to join the restiform bodies. They are about 16 or
17 mm. long, and consist of a mass of white, medullated
nerve-fibers, surrounded by a capsule of gray matter which
presents a wavy, sinuous outline. This capsule is closed at
160 CENTRAL NERVOUS SYSTEM. .
either end, but presents on its median surface an opening
— the hilum. On transverse section the capsule may be seen
to consist of two blades or laminae : an anterior or ventral,
and a posterior or dorsal. The anterior blade is shorter and
its direction almost transverse, while the dorsal or posterior
lamina is longer, and has an oblique direction, backward and
inward. The laminae are perforated on all sides by bundles of
fine, medullated nerve-fibers ; part of these fibers are rearranged
within, pass out of the hilum, decussating in the raphe, and end
in arborizations about the nerve-cells of the opposite olivary
body. This bundle of fibers on each side forms a system, — the
cerebello-olivary tract, — which will soon be described. The
remaining fibers, fibriae arcuatae, simply pass through the olivary
bodies entering the formatio reticularis grisea ; while those
which pass through the anterior or ventral lamina probably are
external arcuate fibers. Microscopically, the olivary bodies are
composed of a neuroglia network, in the meshes of which
exist a great many small multipolar cells, which are roundish
or pear-shaped, contain a yellowish pigment, and are from
1 8 to 26 11. in diameter. Each cell has from three to five
dendrites, and a long, fine neuraxone, the destination of
which is unknown, although Koelliker believes that it passes
into the lateral columns, and ends about the motor cells of the
cord. Cajal states that some of these neuraxones become trans-
verse, cross the median line, pass through the opposite olivary
body, and enter the white matter, while others pass out of the
olivafy body without decussating and are lost among the anterior
external arcuate fibers. These bodies, in addition, contain a vast
number of fine nerve-fibers, which end in brush-like expansions
about the cells. They are probably arborizations from the
neuraxones of the cells of Purkinje, from which, according to
Koelliker, the cerebello-olivary tract arises (Fig. 82).
In addition to the olivary bodies, two other gray masses exist,
having about the same histologic construction, which, because of
their proximity to the former, are called accessory olivary bodies.
They are divisible into a median or inner accessory olivary
body and a dorsal or posterior accessory olivary body on each
side. The inner one is located in the lemniscus, just dorsal to
Fig. 82 — Hemisection of Medulla to Show Olivary Body. Method of Weigert-Pal.
a. Median accessory olivary body. b. Anterior median fissure, c. Anterior pyramid, d.
Nucleus arciformis. e. Olivary body. f. Dorsal accessory olivary body, which also in-
cludes gray mass at the extremity of the dorsal lamina of olivary body. g. Cerebello-oli-
vary tract.
11 161
THE MEDULLA OBLONGATA, OR BULB. i6j
the pyramids and ventrolateral to the anterior lamina of the
olivary body. Because of their relation to the anterior pyramids,
they are sometimes called the pyramidal nuclei. The dorsal or
posterior accessory body is found just dorsal to the inner portion
of the posterior blade of the olivary body of each side. These
accessory bodies are traversed by the internal arcuate fibers ;
usually, however, the root-fibers of the hypoglossal nerves pass
between them and the main olivary bodies. In the ventral part
of each pyramid among the external arcuate fibers exists a tri-
angular-shaped mass of gray matter called the nucleus arciformis.
THE CENTRAL TEGMENTAL TRACT OF BECHTEREW AND
FLECHSIG.
The central tegmental tract consists of a small bundle of
fibers, which probably take their origin from the olivary body of
the same side. This bundle is located in the formatio reticularis,
dorsal to the olivary body, which position it retains until it
reaches the level of the lower border of the pons Varolii, where
it becomes located dorsal to the corpus trapezoides in the space
between the superior olivary body and the lemniscus ; at a
higher level in the pons it occupies a position in the central part
of the tegmentum, hence its name. Still higher up, this bundle
of fibers passes between the crossing fibers of the . superior
cerebellar peduncle, and then takes a position lateral to the pos-
terior longitudinal bundle, and terminates, according to Bech-
terew, in the region of the third ventricle. Flechsig states, how-
ever, that the fibers of this tract continue brainward and end in
the globus pallidus of the lenticular nucleus. Helweg asserts
that the fibers of this tract pass in part into the lenticular loop
and in part into the posterior commissure. :;:
SECTION THROUGH THE MIDDLE OF THE OLIVARY BODIES.
Here the motor and sensory decussations are completed ; the
restiform bodies occupy the lateral periphery of the section, and
* It is probable that the olivary tract of Bechterew or the triangular bundle of Helweg and
the central tegmental tract form a functionally continuous bundle of fibers which connect the
spinal cord and olivary body with the mid-brain.
104 CENTRAL NERVOUS SYSTEM.
have attained considerable size. The gray matter is broadened ;
the anterior and posterior horns still exist, severed from their
connection with the gray matter. The olivary bodies, with
their accessory nuclei, are seen with their wealth of cells and
fibers.
At this level exists another system or tract, consisting of
fibers which decussate in the raphe and pass into the opposite
olivary body ; it is known as the cerebello-olivary tract. Take,
for example, the right cerebello-olivary tract: Its fibers come,
according to Koelliker, from the cells of Purkinje, in the cere-
bellar cortex of the same side, and pass downward in the lateral
portion of the restiform body until they reach the medulla, when
they move inward, and occupy the middle portion of the resti-
form body ; they then pass to the neighborhood of the right
olivary body in curves, "arcuate fibers," where they spread
out and almost completely surround that body ; they then pass
through its laminae into its interior, where the fibers are re-
arranged, forming a compact bundle, which passes out at the
hilum ; the fibers decussating with their fellows of the opposite
side, entering the hilum of the opposite olivary bod)', and ending
in arborizations about the cells of that body.* The axones of the
cells of the olivary bodies then pass outward into the lateral
column, where they curve downward and inward to terminate
about the motor cells in the anterior cornu of the left side.
The fibers which compose this tract degenerate downward.
This fact has been proved by experimental destruction of a
cerebellar hemisphere of a young animal, when there followed
complete atrophy of this tract and of the opposite olivary body.
The same condition has been observed in man after extensive
disease of a cerebellar hemisphere.
The restiform bodies, which at this level have attained a large
size, are composed of. the following systems of fibers:
First, the direct cerebellar tract, which has passed backward
into the restiform body of the same side ; it terminates in the
cortex of the superior worm of the cerebellum.
* Bechterew, i>n the contrary, believes that the majority of the fibers of this tract come from
the cells in the corpus dentattim, only a few coming from the cerebellar cortex.
THE MEDULLA OBLONGATA, OR BULB.
1 6 5
Second, a few fibers pass from the cells of the nuclei gra-
ciles et cuneati around the outer posterior surface of the
medulla, reaching the restiform body of the same side. They
are called the postero-external arcuate fibers.
Third, fibers from the nuclei of the posterior columns, which
are continuations of the interolivary tracts. After decussating,
they pass around the external surface of the opposite anterior
pyramid and olivary body and join the restiform body of the
opposite side. These are the antero-external arcuate fibers.
The posterior external arcuate fibers come from the posterior
Fig. 83. — The Cerefello-olivary Tract. — {After Edinger.")
nuclei of the same side, while the anterior external arcuate
fibers come from the posterior nuclei of the opposite side.
The majority of these fibers pass to the cortex of the superior
worm of the cerebellum. A few probably go to the corpus
dentatum.
Fourth, fibers pass to the restiform body from the lateral
nucleus of the same side.
Fifth, the descending tracts of Marchi and Lowenthal. They
may have their origin in the cerebellar cortex and pass down-
ward into the restiform bodies ; thence into the anterolateral
areas of the cord. They probably end in the median gray matter
of the cord.
1 66 CENTRAL NERVOUS SYSTEM.
Sixth, the direct sensory cerebellar tract passes into the resti-
form body and thence to the cerebellar cortex, thus establishing
a connection between the nucleus vestibularis of the auditory
nerve and the cerebellar hemisphere.
Seventh, the large bundle of fibers of the cerebello-olivary
tracts already described.
A TRANSVERSE SECTION OF THE MEDULLA NEAR ITS
JUNCTION WITH THE PONS.
The restiform bodies here are very large, and are gradually
passing into the cerebellum. The olivary bodies are greatly
diminished in size. The crescentic bundles of fibers of the fifth
pair of nerves may be seen internal to the restiform bodies.
Dorsal and slightly medianward to the restiform body, lying
between it and the dorsal nucleus of the auditory nerve, exists
on each side an oblong area of longitudinal fibers, known as the
acusticocerebellar or the direct sensory cerebellar tract. This tract
extends downward as far as the posterior columns of the cord,
and contains fibers which connect the cells of Deiter's nucleus
with the cerebellar cortex. According to Edinger, this tract
comes from the cerebellum, and is, in reality, the fasciculus solita-
rius, or the combined descending vagoglossopharyngeal root.
Koelliker believes that it is connected with the sensory nuclei
of the trigeminal, vagus, and glossopharyngeal nerves and ter-
minates in the posterior columns.*
Three nerve nuclei occur in this region — namely, the sixth or
abducens, the seventh or facial, and the eighth or auditory.
The abducens or sixth pair of cranial nerves represent the
axones from a collection of multipolar nerve-cells, 40 to 50 /i
in diameter, located just beneath the floor of the fourth ventricle,
external to the posterior longitudinal bundles and below the
striae acousticse. The nucleus of each side is inclosed in the
loop ot the facial nerve. According to Obersteiner, the root-
fibers of this nerve receive an accession of fibers from the oppo-
site nucleus, they having crossed in the raphe. The root-fibers
* Ferrier and Turner believe the direct sensory cerebellar tract to be an efferent bundle of
fibers from the middle lobe of the cerebellum to Deiter's nucleus.
THE MEDULLA OBLONGATA, OR BULB.
167
then pass anteriorly through the gray and white matter, and
emerge in a depression existing at the junction of the pons with
the medulla, just external to the fibers of the anterior pyramid.
The innermost fibers of this nerve frequently pierce the anterior
pyramid ; the nerve is then directed upward and forward upon
the anterior surface of the pons Varolii.
The nuclei of the abducens are connected with the posterior
longitudinal bundles by fibers which, it is believed, pass to the
Fig. 84. — Transverse Section through the Pons Varolii. Illustrating the origin cf
the sixth and seventh cranial nerves.
The nucleus of the seventh is not shown, but its fibers can be seen, a, arching over the nucleus
of the sixth nerve, b. Raphe. .:. Fibers of the abducens nerve, d. Deep transverse
pontine fibers, e. Pyramidal tract, f. Superficial transverse pontine fibers.
opposite oculomotor nucleus, thus permitting the associative
movements of the eyeballs. These nuclei are also connected by
fibers with the superior olivary bodies. (See p. 176.) These
bodies are in relation with fibers from the auditory nuclei, and
owing to the connection of these latter nuclei with the cerebellum,
there is established an association between the motor nerves of
the eyes, the auditory nerves, and the cerebellar cortex. This
ii,S CENTRAL NERVOUS SYSTEM.
association may be of great service in enabling us to judge of
our position in space.
The facial nerve is a mixed motor and sensory nerve, consist-
ing of a large motor and a small sensory root. The sensory
root comes from the cells of the geniculate ganglion, and is
called the nerve of Wrisberg, while the motor root represents
the axones from a nucleus in the pons at its junction with the
medulla. The motor nucleus is located deep in the lateral por-
tion of the formatio reticularis, is about four millimeters long, and
presents on transverse section a roundish or slightly oblong
form. It consists of a group of large, mostly pigmented, multi-
polar nerve-cells, which are surrounded by a fine meshwork of
fibers. This nucleus is probably the upward continuation of
the nucleus ambiguus, which at a lower level gave origin to the
motor fibers of the vagus and glossopharyngeal nerves. Some
authors claim this nucleus to be the upward continuation of part
of the cell group of the severed anterior horn. The axones from
the cells of this nucleus pass at first dorsomesially to reach the
floor of the fourth ventricle, where they form a distinct elevation
— the eminentia teres, or the tuberculum nervi facialis. At this
point the fibers are located just external to the posterior longi-
tudinal bundle ; they then make a sudden bend and pass ventro-
laterally between the facial nucleus and the sensory trigeminal
nerve-roots to their point of emergence — the upper end of the
medulla at its junction with the pons, in a depression between
the olivary and restiform bodies. Inclosed in the loop or genu
formed by the two curves of this nerve is the nucleus of the sixth
or abducens nerve. Just as the fibers of the facial are about to
become horizontal beneath the ependyma of the fourth ventricle
they give off collaterals, which cross the median line and end
about the cells of the facial nucleus of the opposite side. It is
a well-known fact that in facial paralysis the result of a central
lesion, the lower branches only are affected, and the orbicularis
palpebrarum and frontalis muscles remain normal ; it is possible,
as suggested by Mendel, that those muscles are supplied with
fibers that join the facial through the motor oculi nerve. They
probably pass in the posterior longitudinal bundle and join the
facial at its genu. The nerve of Wrisberg, or the sensory
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THE MEDULLA OBLONGATA, OR BULB. 171
division of the facial, represents the axone from the cells of the
geniculate ganglion (P. Martin). These axones possess both a
peripheral and a central division ; the central division passes into
the medulla to the region of the fasciculus solitarius or the com-
bined descending vagus and glossopharyngeal roots. The
peripheral fibers join the facial, and, according to Duval, are
probably those which go to form the chorda tympani nerve, and
are concerned with the special sense of taste.
CONNECTIONS OF THE FACIAL NERVE.
The facial nuclei are connected with the motor tracts by col-
laterals which pass from these tracts dorsally, decussate in the
raphe near the bottom of the ventral fissure, and then course
dorsolaterally to end about the cells of the facial nuclei.
The facial nerve is also connected with the sensory trigeminal
nerve by four or five bundles of fibers, which are collaterals
from the descending trigeminal nerve-roots.
This nucleus is indirectly connected with the cochlear division
of the auditory nerve by fibers from the corpus trapezoides and
superior olivary body.
THE AUDITORY NERVE.
The auditory nerve, or the nerve of the special sense of hear-
ing, possesses two roots, which differ both in their anatomic
relation and physiologic functions. The first, which is called the
cochlear nerve, presides over the function of hearing ; the
second root, or vestibular nerve, is concerned in the maintenance
of equilibrium. The cochlear nerve is also termed the lateral,
posterior, or dorsal root; the vestibular, the ventral, anterior, or
mesial root.
The cochlear nerve represents the axones from the cells
of the spiral ganglion located in the bony wall of the cochlea
which forms the anterior part of the labyrinth. The periph-
eral axones from the cells of this ganglion end about the
ciliated cells of the organ of Corti in the cochlear duct. The
central axones as they exist in the internal auditory meatus
1 7 2
CENTRAL NERVnUS SYSTEM.
resemble in their position the posterior root of a spinal nerve.
The cochlear nerve in its centripetal course then enters the
lowermost part of the pons, external or lateral to the resti-
form body, and, without decussating, terminates in an end
nucleus — the ventral acoustic nucleus.
The vestibular nerve represents the axones from a swelling
or ganglion in the auditory meatus called the vestibular gan-
glion, or the intumescentia gangliformis of Scarpa. The per-
^g
Fig. 86. — Transverse Section through the Distal Part of the Pons of an Eight-
months' Human Embryo. — [After Kodtiker.)
P. Superficial pontine fibers (non-medullated). Pv. Anterior pyramid. VIII' 1 , Ventral audi-
tory nucleus from which the medullated fibers of the corpus trapezoides arise. VIII' 1 .
Dorsal auditory nucleus. iVv. Nervus vestibuli. / II 2 . Emerging tacial nerve-roots.
/ '//. Nucleus of the facial nerve. /'/. Abducens nerve, L. Lemniscus. 17. Posterior
longitudinal bundle. F.arc.i. Interna! arcuate fibers. Nc. Cochlear nerve. Pc. Cere-
bellar peduncle. An. Descending auditory root. fgr. Substantia reticularis grisea, I.
Descending trigeminal nerve-roots. / ] . End nucleus of trigeminal nerve.
ipheral axones are distributed to the fusiform cells ot the
semicircular canals. The centra] axones of the vestibular nerve
take a course internal to tin: ventral acoustic nucleus and resti-
form hod)', being located between the latter and the sensory
bundle of the filth nerve. In their course dorsally they bifur-
cate, the branches, with their collaterals, ending about the cells
of I )e-iter's nucleus and the chief auditory nucleus. The cells
of both spiral and vestibular ganglia are bipolar.
THE MEDULLA OBLONGATA, OR BULB.
'7 ■
Both divisions of the auditory nerve are connected in the
medulla and pons with three end nuclei : first, the anterior, ven-
tral, or lateral acoustic nucleus ; second, the clorsomesial, or
chief auditor)' nucleus ; and third, the dorsolateral, or nucleus of
Deiter. The anterior nucleus is an oval collection ot nerve-cells
wedged in between the cerebellum in front and the restiform
body behind. It produces on the outer surface ot the medulla
'.*->■..
f J
'-li
*
•
*■ '■ *
v ■£Z%3k***&Sf Ti
w*-'H^'^
JT IG . gy. MlCROPHOTOGRAPH SHOWING CELLS OF VENTRAL AUDITORY NUCLEUS. Method
of Golgi.
an enlargement known as the tuberculum acousticum. The
anteroposterior diameter of this nucleus is about three milli-
meters, and its transverse about two millimeters. It consists in
man of two portions — dorsal and ventral. The ventral portion,
often called the nucleus accessorius, consists of many rather
small, roundish cells, 25 to 35 a in size, which resemble
closely those of the posterior spinal ganglia. They are sur-
rounded by a great number of fine nerve terminals. The
174
CENTRAL NERVOUS SYSTEM.
dorsal portion, or tuberculum acousticum, which is located
between the cerebellum and the pons, consists of two forms of
cells — small, round ones, and large, somewhat cylindric-shaped
cells ; these are fewer in number than those of the anterior por-
tion. Hie clorsomesial, or chief nucleus of the auditory, or
nucleus vestibularis, occupies a large triangular area just beneath
the Boor of the fourth ventricle, external to the combined sensor)'
Fig. 88. — Dorsal Part of a Transverse Section of the Medulla Oblongata from
a Human Embryo ok Six Months.— [After Koelliker.)
/■'/. Posterior longitudinal bundle. VI. Abducens nerve. J'/ ] . Nucleus of abducens. /"//.
Facial nucleus. VII 1 . Ascending axones from cells of facial nucleus. VII 1 . Knee of
facial nerve. VII s . Emerging facial fibers. 'Jr. Corpus trapezoides. Oo. Superior
olivary body. .Vr\ Vestibular nerve. I'll I. Ventral auditory nucleus. VIII 1 . Descend-
ing vestibular root. D. Nucleus of Deiter. V. Sensory trigeminal nerve-root. F.rh.
Fovea of the fourth ventricle.
nucleus of the vagus and glossopharyngeal nerves and postero-
internal to the restiform body. This nucleus consists mainly of
small multipolar nerve-cells, about 20 u in diameter. The
dorsolateral, or large-celled nucleus of Deiter, is located poste-
rior to the restiform body and dorsolateral to the chief auditory
nucleus, embedded in the held of hbers which form the direct
sensor\' cerebellar tract. This nucleus ma)' easily be distin-
mushed from the former nucleus by the larg-e size of its cells,
THE MEDULLA OBLONGATA, OR BULB. 175
which are multipolar, and are from 40 to 100 fi in diameter. It
increases in size from below upward. At the point where the
fibers of the restiform body pass into the cerebellum it is more
dorsally located, and has its greatest size. This part of the
nucleus is called the nucleus of Bechterew, or nucleus vestibu-
laris of Flechsig.
The fine fibers of which the cochlear nerve is composed are
related to the cells of both divisions of the ventral or lateral
auditory nucleus. On entering the nucleus they divide Y-shape,
one division passing upward, the other downward, each division
giving off several collaterals ; these divisions, with their collater-
als, further subdivide into fine plexuses about the cells of this
nucleus. The rather coarse fibers of the vestibular nerve pass
dorsolaterally through the medulla, internal to the ventral audi-
tory nucleus and restiform body, and when the}' approach their
end nuclei, the chief auditory nucleus, and the nucleus of Deiter,
they divide Y-shaped, giving off at the same time numerous col-
laterals, one division passing brainward, the other spinalward.
The former ends about the cells of these two end nuclei, while
the latter branches, forming the so-called descending division of
the vestibular nerve. These latter fibers, with their collaterals,
end in fine end brushes about a group of cells which continue
downward on both sides as far as the cuneate nuclei. Some of
the cells of this group are large, while others are small.
Monakow and Koelliker believe these cell groups to be a
continuation downward of the nuclei of Deiter. They may be
considered as the descending nuclei of the vestibular nerves.
Connections of the Auditory Nerve. — The axones from the
cells of the accessory division of the ventral auditory nucleus pro-
ceed toward the raphe, producing transverse bundles of fibers
which are located just posterior to the anterior pyramids called
the corpora trapezoidea. Among the fibers of each corpus trape-
zoideum exist numbers of large, spindle-shaped, multipolar nerve-
cells, whose axones pass anteriorly, and then bend at an angle
and assist in the formation of the corpus trapezoideum by forming
transverse fibers. The fibers pass in part into the superior olivary
body of the same side, while the remainder decussate in the raphe
and pass to the superior olivary body of the opposite side.
*\
i 7 6 CENTRAL NERVOUS SYSTEM.
THE SUPERIOR OLIVARY BODIES.
These are cylindric masses of gray matter, consisting
of neuroglia fibers, fine nerve terminations, and numerous
pear- or spindle-shaped cells, which possess a single axis-
cylinder and numerous dendritic branches. These cells begin
at about the level where the nuclei of the facial nerves are first
observed, and are located anterior and slightly internal to them.
They are surrounded by the fibers of the corpora trapezoidea,
which fibers end about their nerve-cells. A few axones of the
cells of the superior olivary bodies pass dorsally to end about
the nuclei of the abducens nerve. The majority of the axones
of the superior olivary bodies pass dorsolaterally, decussate
in the raphe, and form the lateral fillet of the opposite side.
This fact seems to be proved by the experiment of Baginski,
which showed that after the destruction of the cochlea in a
young animal there followed an atrophy of the ventral auditory
nucleus, the corpus trapezoideum, the superior olivary body,
all of the same side, and of the lateral fillet of the opposite side.
Most of the axones from the cells of the tuberculum acousticum
and a few from the nucleus accessorius pass around the resti-
form body of each side, then proceed just beneath the ependyma
of the ventricle, where they are known as the striae acousticae,
until they approach the raphe ; they then pass ventrolaterally,
decussate in the raphe, and enter the lateral fillet of the opposite
side. A few fibers do not decussate, but go to the fillet of the
same side. Monakow found that the destruction of the lateral
fillet close to the corpus quadrigeminum was followed by an
atrophy of the striae acousticae of the opposite side. The nucleus
of the lateral fillet or lemniscus is the upward continuation of
the cells of the superior olive of each side. This group of cells
continues from the upper end of the superior olive to near the
point where the fillet fibers join the posterior corpus quadrige :
minum.
CONNECTIONS OF THE VESTIBULAR NERVE.
i. Willi the Cerebellum. — The nucleus of Deiter is connected
with the cerebellum, first, by a large bundle of fibers — the acous-
THE MEDULLA OBLONGATA, OR BULIi. 177
tico-cerebellar tract; also called the direct sensory cerebellar
tract (Edinger). Much doubt still exists in regard to the source
of the fibers of which this tract is composed. Some observers
(Russel, Ferrier, and Turner) believe it to be an efferent tract
connecting the middle lobe of the cerebellum with Deiter's
nucleus, while Koelliker believes, from embryologic study, that
the tract consists chiefly of axones from the cells of Deiter's
nucleus, a few coming from the cells of the chief auditory nucleus.
The fibers passing into the middle portion of the restiform body
and proceeding to the region of the roof nuclei of the cerebellum,
between which nuclei they decussate with their fellows from the
opposite side, to end in the opposite roof nucleus.
2. With the Lateral Fillet. — The second connection is by
fibers from the nuclei of Deiter and the chief nuclei, which
course ventrolateral^ into the formatio reticularis, cross over
in the raphe, and pass to the dorsal surfaces of the superior
olivary bodies, where they assist in the formation of the lateral
fillet of each side.
3. With the Internal or Mesial Fillet. — The third connection
is by axones proceeding from the cells of Deiter's nucleus and
coursing ventromesially between the root-fibers of the vestib-
ular branch and the mesial nerve, and turn upward, probably
entering the internal fillet or lemniscus.
4. With the Nuclei of the Sixth Nerve. — The fourth connec-
tion is formed by fibers from both end nuclei of the vestibular
nerve to the abducens nuclei.
5. With the Olivary Body and the Lateral Column of the
Same Side. — The fifth connection is by the descending vestibular
olivary tract and the descending vestibular spinal tract (Van
Gieson). The vestibular olivary tract passes ventromesially
through the lateral field of the formatio reticularis and ends in
the olivary body of the same side. The descending vestibular
spinal tract passes through the periphery of the lateral field of
the formatio reticularis and descends in the lateral column of
the spinal cord. Its ultimate distribution is unknown.
178
CENTRAL NERVOUS SYSTEM.
THE PONS VAROLII.
The pons lies between the brain stem, or crura cerebri, above,
the medulla below, and the cerebellum behind. It serves to
connect the cerebrum with the cerebellum and the cerebellar
hemispheres with each other by means of broad, transverse
bundles of fibers. It permits most of the long tracts of the
a
Fig. 89. — Transverse Section through Upper Part of Pons Varolii. Method of
Weigert-Pal.
a. Aqueduct of Sylvius, b. Posterior corpus quadrigeminum. c. Posterior longitudinal bundle.
d. Beginning decussation of superior cerebellar peduncles, e. Lateral fillet or lemniscus.
f. Median fillet or lemniscus, h, It. Deep transverse pontine fibers, g, g. Fasciculi of
pyramidal tract, i. Superficial transverse pontine fibers.
medulla to continue brainward without any special change ol
relative position. It contains a few special gray deposits, whose
cells give origin to the auditory, facial, abducens, and trigeminal
nerves. The auditory and facial nerves come out lateral to the
abducens at the junction of the pons with the medulla. The
abducens comes out at the junction of the pons with the
THE MEDULLA OBLONGATA, OR BULB. 179
medulla, close to the median surface of the pons in the upper
end of the ventrolateral groove. The fifth pair, or trigeminal
nerves, emerge from the lateral part of the ventral surface of the
pons, just above its central portion. The anterior surface of the
pons is convex, and rests in the sphenobasilar groove. This
surface is contracted laterally, owing to the convergence of the
broad bundles of transversely arranged fibers, which fibers form
a commissural-like arch between the hemispheres of the cere-
bellum. The above fibers form the middle peduncles of the
cerebellum. They are divided into a superficial and a deep set
by the passage through them of the anterior pyramids, or great
motor tracts. Along the middle of the ventral surface, running
from before backward, is a groove in which the basilar artery
rests. The dorsal surface forms the upper half of the floor of
the fourth ventricle. Its middle part is somewhat flattened,
while its sides are elevated, due to two broad bands of white
fibers, — the superior peduncles of the cerebellum, — which have
come from the neighborhood of the corpora quadrigemina.
They form the upper and outer boundary of the fourth ventricle,
which at this point is gradually narrowing into the aqueduct of
Sylvius, which serves to connect the fourth ventricle with the
ventricle above, or the third ventricle. The superior portion of
the pons arches over the crura cerebri.
A TRANSVERSE SECTION OF THE PONS.
The pyramids, which occupy a position anteriorly, are no longer
free, as they were in the medulla, being concealed between the
superficial and deep transverse fibers, but they still remain as
two distinct bundles of fibers, while above the middle of the pons
they are separated into a number of fasciculi. Between the trans-
verse fibers of the pons exists, on each side, a large number of small,
multipolar nerve-cells, forming groups called the nucleus pontis.
According to Cajal, the fibers of the corticocerebellar tracts end
in brush-like expansions about these cells, and are further con-
tinued by the axones of these cells, which pass as transverse
fibers to the cortex of the cerebellum. Koelliker believes that
many of these transverse fibers conduct impulses centrifugally,
and are the axones from the cells of Purkinje, which end in
180 CENTRAL NERVOUS SYSTEM.
arborizations about the cells of the nuclei pontis of the same
and opposite side. Posterior to the transverse fibers is the
formatio reticularis, which is an upward continuation of the
same formation in the medulla ; and, as in the medulla, it
contains two fields — an inner and an outer. The former is
located between the nerve-roots of the sixth pair of cranial
nerves, they continuing anteriorly, as do the hypoglossal
nerves. From the scanty supply of nerve-cells and conse-
quent lack of color, this area is called the formatio reticularis
alba. The outer field is located between the nerve-roots of
the sixth and seventh pairs of cranial nerves. As it is rich in
nerve-cells, it is called the formatio reticularis grisea. The raphe
exists in the pons as in the medulla, but extends anteriorly only
to its transverse fibers. In the formatio reticularis exist cell
groups, continuations of like groups in the medulla, for the
origin of the facial, abducens, and in part of the trigeminal
nerves, and just posterior to the pyramids are the tracts of fibers
— the corpora trapezoidea — already described.
In the anterior part of the formatio reticularis, surrounded by
these fibers, exist the superior olivary bodies. The two divi-
sions of the fillet or lemniscus occupy a large part of the antero-
lateral field of the formatio reticularis, the lateral fillet being
located along the outer periphery and meeting the mesial fillet,
which is located dorsal to the deep transverse fibers of the pons,
at almost a right angle. Thus the fillet is seen to occupy a large
part of the anterolateral region of the tegmentum, as the space
occupied by the formatio reticularis is called. The fillet is di-
vided into two distinct bundles of fibers, — a mesial fillet and a
lateral fillet, — the anatomic and physiologic relations of which
are entirely distinct. The mesial fillet represents the combined
axones from the cells of the nuclei cuneati et gracilis an d from
the cells of the sensory end nuclei of all the cranial nerves of
the opposite side except the auditory, the axones having decus-
sated in the raphe. Some of the axones and collaterals of the
mesial fillet that have come from the nucleus cuneatus end about
the cells of the formatio reticularis of the pons and those of the
anterior and posterior corpus quadrigeminum ; other fibers pass
to the lenticular nucleus of the same and of the opposite side, while
many reach the parietal lobe of the brain through the posterior
THE MEDULLA OBLONGATA, OR BULB. 1S1
division ot the internal capsule. The fibers from the nucleus
gracilis and end nuclei of the sensory cranial nerves end in the
ventral part of the optic thalamus (Monakow). From the cells
ot the optic thalmus axones pass through the posterior limb of
the internal capsule and radiate toward the parietal lobe.
The lateral fillet or lemniscus is the central auditory tract,
Fig. 90. — Transverse Section through the Pons, in the Region of the Crossing
of the Fourth Nerve in the Dorsal Medullary Velum. — {After Koelliker.)
Br.C. Superior cerebellar peduncles. Vd. Descending cerebral root of fifth nerve. lVd.
Fourth nerve of right side. Fl. Posterior longitudinal bundle. Tg. Tegmentum or sub-
stantia reticularis. LM. Median lemniscus or fillet. LI. Lateral lemniscus or lillet. P.
Pyramidal fibers between the superficial and deep transverse pons fibers.
being composed of axones from the end nuclei of the auditory
nerve and the superior olivary body ; it then passes to the pos-
terior corpus quadrigeminum, and thence, by means of its
brachium posterioris, through the extreme posterior part of the
posterior limb of the internal capsule, and radiates, via the corona
radiata, to the first and second temporosphenoid gyri.
1S2 CENTRAL NERVOUS SYSTEM.
On each side of the median line in the posterior part of the
reticular formation is the triangular area of longitudinal fibers —
the posterior longitudinal bundles. Beneath the ependyma of
the fourth ventricle, and lateral to these bundles, exist a number
of highly pigmented nerve-cells, called the substantia ferruginea.
Just external to the posterior longitudinal bundle of fibers, in the
loop formed by the bends of the facial nerve, is a collection of
large multipolar nerve-cells, which give origin to the abducens
or sixth pair of cranial nerves.
Slightly dorsolateral to the nucleus of the abducens is the
dorsal or chief auditory nucleus, which occupies a large field.
External and a little dorsal to this nucleus is the nucleus of
Deiter and Bechterew, which has already been described. In
front, and at the side of Deiter's nucleus, is the lar^e bundle
of fibers of the restiform body, or the inferior cerebellar
peduncle.
THE NUCLEI OF ORIGIN OF THE TRIGEMINAL NERVE.
This nerve has two roots on each side — an anterior or motor,
the smaller, and a posterior, the sensory. Both roots appear at
the side of the pons, just above its middle. The motor root
consists of the axones from the cells of the motor nucleus of this
nerve in the pons. The sensory root is made up of the axones
of the monopolar cells of the Gasserian ganglion, which is
located in a fossa near the apex of the petrous portion of the
temporal bone. The axones of these monopolar cells each
divide into two divisions, one of which passes peripherally, form-
ing the great sensory nerve of the face, while the other passes
centrally, entering the pons, where it bifurcates, one division
passing slightly upward, the other downward, both giving off
very fine collaterals. The former, those which pass upward,
enter the enlarged termination of the substantia gelatinosa of the
posterior horn, ending about the small nerve-cells therein con-
tained, and thus this termination may be considered as the end
nucleus of this set of fibers. The latter, the descending branches
(spinal portion of this nerve), pass downward as far as the
beginning of the motor crossway or the upper level of the first
cervical segment. They form crescentic bundles, one for each
THE MEDULLA OBLONGATA, OR BULB.
183
side, which are located just external and slightly lateral to the
substantia gelatinosa of the posterior horns, occupying about
the same relative position to the heads of the posterior horns as
do the tracts of Lissauer in the spinal cord. These bundles of
fibers gradually diminish in size from above downward. In
their course they give off, nearly at right angles, a large number
of fine collaterals. The main branches, with many of their col-
Fig. 91. — Lateral Sagittal Section through the Pons and Cerebellum of a
Fetal Mouse. — [After Ramon y Cajal.)
. Sensory root of the fifth nerve divided into (a) ascending and descending (b) branches. C.
Terminal ramifications of the ascending branch, d. Root-fibers passing downward, e.
Posterior part of the descending sensory root. B. Bifurcation of the vestibular nerve,
whose ascending branch (g) goes to the cerebellum, and whose descending branch (f) goes
to the medulla. G. Superior cerebellar peduncle. D. Descending cerebellar fibers. E.
Corpus restiforme (inferior cerebellar peduncle). F. Lateral fillet or lemniscus. Ff.
Corpus trapezoides. O. Corpus dentatum.
laterals, end in fine, brush-like expansions about the multipolar
nerve-cells existing in the substantia gelatinosa of the posterior
horns, which latter may be considered as continuous end nuclei
for these descending branches, hence explaining the reason for
the statement above, that these bundles gradually diminish in
size from above downward. Other collaterals from the descend-
IS 4
CENTRAL NERVOUS SYSTEM.
ing branches, probably comprising all the remainder, presumably
reflex in function, end in fine arborizations about the cells of the
motor nuclei of the hypoglossal, facial, and trigeminal nerves.
The axones trom the cells of the sensory end nuclei of the tri-
geminal nerves pass in curves (internal arcuate fibers), decussate
in the raphe, and pass as longitudinal fibers into the mesial fillet
or lemniscus of each side, thus forming the central sensory
tracts of these nerves. These longitudinal fibers give off in
their course collaterals, which end about the large multipolar
nerve-cells of the formatio reticularis.
Fig. 02. — Microphotograph of a Section through the Medulla of a Human Fetus
of Seven Months.
Showing axones and collaterals of the trigeminal nerve entering the enlarged caput posterioris.
The motor root, also called the nervus masticatorius, be-
cause it ennervates the muscles of mastication, comes chiefly
from the motor nucleus in the pons, but it receives an accession
of fibers from a nucleus which is located beneath and lateral
to the aqueduct of Sylvius.
The chief motor nucleus of each side is a collection of multi-
polar nerve-cells located slightly backward and a little external
to the sensory end nucleus in the pons, and also slightly dorsal
THE MEDULLA OBLONGATA, OR BUL1!. 1S5
to the nucleus of the facial, of which it is probably an upward
termination. The axones of these cells pass ventrolaterally, and
issue from the side of the pons as a small bundle of fibers, just
ventral to the sensory root, the two roots being separated from
each other by a small bundle of transverse pontine fibers. A
few axones from the cells of the median part of this nucleus
pass dorsally in curves across the median line or raphe, and
unite with the motor roots of the opposite side ; hence each
motor root receives a small number of fibers from the nucleus
of the opposite side.
The accessory nucleus, the cells of which give origin to the
descending trigeminal or cerebral root-fibers, consists of a col-
lection of large, somewhat spheric or pear-shaped cells, which
are probably multipolar in character, although it is usual to
describe them as unipolar nerve-cells. No dendrites can be
discovered coming from these cells after they have been stained
with silver nitrate. In carmin-stained specimens, however, den-
drites canusually be seen. They are located deep beneath, and
lateral to, the aqueduct of Sylvius, extending as far brainward
as the corpus quadrigeminum. The cells of this nucleus give
off single thick axis-cylinders, which course downward until they
reach the neighborhood of the chief motor nucleus, where they
branch, one branch ending in a plexus of fibers about a motor
cell of the chief nucleus (Lugaro, Ramon y Cajal), the other
branch joining the root-fibers from the same nucleus.
The Cerebral Connections of the Trigeminal Nerve. —
The sensory end nucleus of the trigeminal nerve is connected
with the opposite sensorimotor area by means of axones which
leave this nucleus and cross in the raphe to pass brainward
in the mesial fillet of the opposite side.
The motor area for the masticatory muscles, which is located
probably in the lower part of the ascending frontal gyrus, is
related with the motor nucleus of the opposite side by fibers
which leave this area and join the pyramidal tract. According
to some observers, fibers from the sensory trigeminal roots pass
dorsolaterally, enter the lateral part of the restiform body,
where they commingle with fibers of the direct sensory cere-
bellar tract, and pass to the cerebellum. This cerebellar con-
nection of the trigeminal nerve is denied by Bechterew.
CHAPTER IV.
THE CEREBELLUM OR EPENCEPHALON.
The cerebellum, or little brain, is located in the inferior
occipital fossa. Above it are the occipital lobes, separated from
it by a strong process of dura mater — the tentorium cerebelli.
In form the cerebellum is irregularly oval or oblong, its greatest
diameter, 7.5 to 10 cm. (three to four inches), being from side
to side. It measures 5 to 5^ cm. (2 to 2^ inches) antero-
posteriorly. Its greatest thickness is at its ventral portion,
where it is about five cm., or two inches. Toward the periphery
of the hemispheres it becomes quite thin, being at the periphery
only about one cm., or five lines, in thickness. Its average
weight in the adult is about 170 gm., or 5^ ounces. In the
infant it is much smaller in proportion to the entire encephalon
than in the adult. It is composed of two hemispheres, joined
by a middle portion or lobe, which, from its shape and from the
appearance given to it by numerous transverse ridges upon it,
is called the worm, vermis, or vermiform process. This division
into hemispheres is much more apparent on the under surface,
owing to a broad, shallow depression or sulcus, — the vallecula, or
little valley, — which, running anteroposteriorly, separates them.
The vallecula lodges the posterior part of the medulla oblon-
gata, and from it projects the inferior part of the middle lobe or
worm, called the inferior vermiform process. The latter forms,
in a general way, the roof of the fourth ventricle, and lies behind
and below the corpora quadrigemina. The cerebellum has on
its anterior and posterior surfaces deep depressions, — the ante-
rior and posterior incised notches, — which are continuous with
the vallecula. In the anterior notch, which is broader, rests the
posterior corpora quadrigemina, while the posterior notch, which
is shallower, contains the falx cerebelli. The bottom of these
THE CEREBELLUM OR EPENCEPHALON.
187
notches is formed by the worm, while the sides are composed of
the cerebellar hemispheres. The cerebellum is divided into an
upper and a lower surface by a great horizontal fissure, which
begins at its anterior margin and extends circumferentially to
the median line behind.
The upper surface is convex at its middle portion and grad-
ually slopes toward its periphery. It consists of two hemi-
spheres connected by a convex median lobe, the superior vermis
Fig. 93. — Figure Showing the Three Pairs of Cerebellar Peduncles. — [After
Hirschfeld and Leveille, from Sapper. )
On the left side the three cerebellar peduncles have been cut short ; on the right side the hemi-
sphere has been cut obliquely to show its connection with the superior and inferior
peduncles. I. Median groove of the fourth ventricle. 2. The same groove at the place
where the auditory stria; emerge from it to cross tire floor of the ventricle. 3. Inferior or
restiform bod}-. 4. Funiculus gracilis. 5, 5. Superior peduncle.
On the right side the dissection shows the superior and inferior peduncles crossing each other as
they pass into the white center of the cerebellum. 7, 7. Lateral grooves of the crura cerebri.
S. Corpora quadrigemina.
or worm. The latter is of great physiologic importance, since
its experimental removal in lower animals and pathologic
changes in it in man, such as a tumor, hemorrhage, injuries, etc.,
produce disturbances of coordinated movements and difficulty
in the maintenance of equilibrium. This proves that this central
portion or worm is principally concerned in the adjustment of.
coordinated movements and the maintenance of equilibrium.
The cerebellum is connected with the remainder of the cerebro-
iSS CENTRAL NERVOUS SYSTEM.
spinal axis by three large bundles of nerve-fibers — the superior,
middle, and inferior cerebellar peduncles. The superior pedun-
cles (processus ad cerebrum) appear to come from the region
just beneath the corpora quadrigemina, where they decussate,
extending from one cerebral hemisphere to the opposite cere-
bellar hemisphere. In their course they run outward and back-
ward, and before entering the cerebellum they diverge, forming
the lateral boundaries of the upper half of the fourth ventricle,
and are united by the valve of Yieussens, or the superior medul-
lary velum. They then appear to pass into the nucleus den-
tatum of the cerebellum of each side. The superior cerebellar
peduncles connect the cerebellum with the cerebrum.*
The middle peduncles (processus ad pontem) consist of the
before-mentioned superficial and deep sets of transverse fibers,
some of which pass from the pons to the cerebellar cortex and
some from the cerebellar cortex to the pons, forming the great
transverse commissure of the cerebellum. These are located
external and anterior to the superior peduncles.
The inferior peduncles (corpora restiformia ; processus ad
medullam) serve to connect the medulla and the spinal cord to
the cerebellum by means of long tracts of fibers. As they pass
upward and backward on their way to the cerebellum they
diverge, and assist in forming the lateral boundaries of the lower
part of the fourth ventricle. They end chiefly in the cortex of
the superior worm of the cerebellum.
THE VERMIS, OR WORM.
SUPERIOR SURFACE.
This surface presents a transversely ridged appearance, and
has, from before backward, the following lobules : First, the lin-
gula is most anterior, between the superior peduncles of the cere-
bellum, resting upon the superior medullary velum. It consists
of a tongue-shaped process composed of four or five transverse
lamina;, which latter are prolonged over the superior peduncles,
* While the course of the superior cerebellar peduncles appears to extend as above described,
yet most of the fibers have been proved to have an opposite course — i. e., from the corpus den-
tatum toward the cerebrum.
THE CEREBELLUM OR EPENCEPHALON. 189
and are called the fraenulum lingular. Its basal part is con-
tinuous with the lobus centralis. Next is the lobus centralis,
which is just back of the lingula, being separated from it by an
interlobular fissure, the precentral ; it is in front of the culmen,
which overlaps it. This lobule, with the lingula, forms the
bottom of the anterior incised notch. The next lobule is the
monticulus cerebelli, which forms the greater part of the con-
vexity of the worm, its anterior portion being called the culmen,
or height, the posterior part, the declive. The monticulus is
separated from the central lobe by the postcentral fissure. The
culmen must be lifted in order to expose the central lobe, and
the declive, when raised, exposes a lobule just posterior to it,
the folium cacuminis, which is a small lobule next in size to the
lingula, and continuous laterally with the posterior superior or
semilunar lobes.
THE INFERIOR SURFACE.
This surface, from before backward, presents the following
lobules : First, the nodulus, which bears the same relation to the
inferior vermiform process as does the lingula to the superior.
It occupies the anterior extremity of the vermis, and is com-
posed of a few transverse laminae separated by slight fissures.
It is the smallest lobule of the inferior worm. The lateral part
of the inferior medullary velum is continued on each side of
the nodule as a thin white band which serves to connect the
nodulus with the flocculus.
Second, the uvula, located just dorsal to the nodulus, forms
the greater part of this surface of the worm. It increases in
size from before backward, and attains its greatest size close to
the pyramid ; it is separated from the hemispheres by a deep
fissure, — the sulcus valleculas, — and is connected with the amyg-
dalae, or tonsils, which exist on each side, by a corrugated
grayish ridge, the furrowed band, which crosses the sulcus valle-
cula;. Its surface is marked by three or four transverse intra-
lobular fissures.
Third, the pyramid. The posterior portion of the inferior
worm is called the pyramid. It is a large, conic projection
190 CENTRAL NERVOUS SYSTEM.
consisting of three or four transverse laminae, separated by fis-
sures ; the sulcus vallecula? separating it from the hemispheres.
It is connected with the digastric lobule by a narrow ridge of
gray matter at the bottom of the sulcus valleculas ; from the
inferior surface of the pyramid, extending anteriorly over the
superior surface, is a process called the tuber valvulae. The
right and left sulci vallecula? are the deep anteroposterior
grooves on the inferior surface of the cerebellum which sepa-
rate the inferior worm from the cerebellar hemispheres.
LOBULES OF THE SUPERIOR OR DORSAL SURFACE
OF THE CEREBELLAR HEMISPHERE.
First, the lobulus quadratus, or square lobe, is located on
each side of the monticulus.
Second, the posterior superior semilunar lobe occupies the
posterolateral part of the dorsal surface. It is connected with
its fellow of the opposite side by the folium cacuminis.
LOBULES OF THE INFERIOR SURFACE OF THE
CEREBELLAR HEMISPHERE.
First, the flocculus, situated on each side of the nodulus below
the middle peduncles and posterior to the sensory nuclei of the
pneumogastric nerves.
Second, the amygdalum, or tonsil, is located on each side of
the uvula. It is connected with the uvula and projects into
the fourth ventricle.
Third, the cuneate or diagastric lobule is a large, somewhat
wedge-shaped or triangular area, located just external to the
amygdalum and pyramid, being attached to the latter by a grayish
ridofe crossing the bottom of the sulcus vallecula?. Its lamina?
are curved, with their concavity forward and inward. It is sepa-
rated from the tonsil on each side by a fissure in front of the
pyramid, called the prepyramidal fissure. The tonsil when re-
moved leaves a hollow depression on the mesial surface of this
lobule, which, because of its resemblance to a bird's nest, is
called the nidus avis.
Fig. 94. — Superior Surface of the Cerebellum.
A.I.N. Anterior incised notch. L.C. Central lobe. C. Culmen. M. Monticulus. D. De-
clive. P.I.N. Posterior incised notch. L.I.S. Inferior semilunar lobe. H.F. Great
horizontal fissure. L. S.S. Superior semilunar lobe. L. Quad. Quadrate lobe.
Fig. 95. — Inferior Surface of the Cerebellum.
A.I.N. Anterior incised notch. F. Flocculus. L.Q. I.obus quadratus. N. Nodulus.
U. Uvula. P. Pyramid. P.I.N. Posterior incised notch. T. Tonsil. L.C. Lobus
cuneatis. L.G. Lobus gracilis. L.I.S. Lobus inferioris semilunaris.
191
THE CEREBELLUM OR EPENCEPHALON.
'93
Fourth, the lobus gracilis, or slender lobe, is just external to
the cuneate lobe, around the periphery of which lobe it extends.
It is also connected with the pyramid. It has along its periphery
the inferior semilunar lobule.
MINUTE ANATOMY OF THE CEREBELLUM.
The cerebellum consists of gray and white matter, the former
surrounding the latter and forming its cortex. The gray matter
FlG. 96. — MlCROPHOTOGRAPH OF CEREBELLAR Cortex. Showing the molecular and granu-
lar layers and the arrangement of the arbor vitas.
consists of foliated lamina;, each one of which has a central core
of white matter, and is formed of secondary and tertiary folia,
which arrangement gives to sections of the cerebellum the char-
acteristic arbor vita; appearance. The gray matter clips into the
various fissures and sulci, and is thus spread over a large extent
of surface, which surface is nearly as great as that covered by
the cortex of the cerebrum. The white matter is more abundant
13
194 CENTRAL NERVOUS SYSTEM.
in the hemispheres than in the vermis. In the former it is irreg-
ular in contour and is somewhat oblong-. In the latter it is
scant and arranged in a quadrangular shape ; hence the name
corpus trapezoideus. From the central white stem of the vermis
a thin extension of white matter passes out which bridges across
the superior peduncles and forms the roof of the upper part of
the fourth ventricle, upon which the lingula rests. This ex-
tension is the before-mentioned superior medullary velum, or
valve of Vieussens. Below, a similar process of white matter
extends from the cerebellum and forms, with a process of pia
mater, the tela choroidea inferior, the roof of the lower part of
the fourth ventricle, and is called the inferior medullary velum.
The white matter consists of medullated nerve-fibers, which form
short and long tracts, which will be described later. Deep
in the central part of the white matter of each hemisphere and
reaching below, nearly to the fourth ventricle, is embedded a
nucleus — the corpus dentatum, or ciliare. Each dentate body
consists of a convoluted, sinuous bag of gray matter, having a
dorsal and a ventral lamina, with an opening or hilum on its
ventral and mesial surface. It contains a rich plexus of nerve-
fibers with a large number of multipolar nerve-cells in their
meshes.* These cells vary from 30 to 40 ft in diameter, and
possess numerous dendritic processes which come off chiefly
from the inner portion of the cell-body. The neuraxones from
these cells, after giving off within the corpus dentatum one or
two collaterals, pass out of the hilum into the superior cerebellar
peduncles, of which they form the great bulk. The dentate
bodies resemble very closely the inferior olivary bodies. This
resemblance is heightened by the fact that three smaller nuclei
lie close to each — namely, the roof nucleus of Stilling, or tegmental
nucleus, the micleus embolliformis, and the nucleus globosus. The
roof or tegmental nucleus belongs properly to the worm. It is
about 10 mm. long, and is an oblong mass of gray matter
on each side of the middle line, just above the ependyma
of the fourth ventricle, from which it is separated by a thin
* It is probable that many of the fibers which form the network within the corpora dentata
are the terminations of the axones coming from the cells of the nuclei rubri.
mmgmatm
■*;;co ,^n
WM -^W"' ,^|
v 1 * \ ira
W-
- v- * w ' . '"^VjSiL- '
' ■-
! ™^PP^" ^.. _J^f"
v -r&$gr^
Fig. 97. — Section Through Cerebellum to Show the Dentate Nuclei and White
Matter of the Hemispheres.
CO. Dentate nucleus. N. Nodule. T. Tonsil. W.M. White matter ot cerebellar hemi-
sphere.
M
X
Wti
fcf y 'fc*
ftMttVs « ■ * 1 ■*****# /**- 1 lit'. ',■■' . •■
& '"
I
^Jasp
Fig. 98. Mickophotograph of a Section through the Corpus Dentatum of the
Human Cerebellum. Containing three large (multipolar) polygonal cells. Method of
Berkley.
195
THE CEREBELLUM OR EPENCEPHALON.
197
layer ot white matter. The nucleus embolliformis is a small,
clavate mass of gray matter located mesial to the hilum of
the dentate body. Beneath and on the inner side of this nucleus
is the nucleus globosus. The fibers which surround the dentate
bodies are called extracapsular or extraciliary fibers. From
the intricate network of these fibers, resembling the hairs ot
wool, the term fleece is applied to this portion. These fibers
doubtless come from the cerebellar cortex, being the axis-cylin-
«- •..'•,'- >'■'■: *• ■■'■ -^ jb~
■W
\i -
Fig. 99. — Microphotograph Showing Basket Cells and Fibers Surrounding the
Bodies of two Purkinje Cells (Human Cerebellum). Cox-Golgi method.
ders of the cells of Purkinje. Some of them pierce the dentate
body of each side and issue at the hilum, assisting in the forma-
tion of the superior peduncles, while most of them surround
the dentate bodies and are probably those descending fibers
which o-o to form the so-called cerebello-olivary tracts, and tracts
of Marchi and Lowenthal, of the corpora restiformia. Others
doubtless pass as pontine fibers, assisting in the formation of the
middle peduncles.
ioS CENTRAL NERVOUS SYSTEM.
THE CORTEX OF THE CEREBELLUM.
The cerebellar cortex is divided into two distinct layers,
between which are the characteristic cells of the cerebellum, the
cells of Purkinje. The first or outer layer is termed the molecu-
lar layer, and the other the internal granular or, from its
appearance, the rust-colored layer. The molecular layer con-
tains two chief forms of cells — outer, small, stellate cells, and
inner, basket cells, or " Korbzellen " of the Germans. The stel-
late cells are small, multipolar cells, 10 or 15 fi in diameter, each
Fig. 100. — Granular Cells of the Inner Layer, with Ascending Neuraxones
Branching T-shaped to Form the Horizontal Fibers of the Molecular Layer.
— {After Van Gehuchten.)
possessing several short dendrites which repeatedly ramify,
many of them assuming a horizontal course. Their axis-cylinders,
or neuraxones, are delicate processes of considerable length,
and possess several collateral branches. The axones pass ver-
tically, entering the upper part of the molecular layer, forming
there an intricate maze of fibers. Their final destination has not
been traced. The basket cells, which are the innermost of the
molecular layer, are slightly larger than the stellate cells, being
from 11 to 20 11 in diameter, and multipolar in form. Each cell
possesses several dendrites which ramify in the innermost part of
THE CEREBELLUM OR EPENCEPHALON.
199
the molecular layer, and a long, thick neuraxone. It is of
interest to note that these axones start from the cell-bodies as
very fine, horizontal processes which increase in size until they
become two, three, or even four times their original thickness.
Each neuraxone passes out horizontally from the cell-body and
gives oft, at varying distances, numerous branching collaterals,
which pass vertically downward until they reach close to the
Fig. ioi. — Microphotograph Showing the Moss-like Fibers of the Cerebellum.
Cox-Golgi method.
bodies of the Purkinje cells, where the fibers end in tuft-like
expansions, forming a basket-like network about each Purkinje
cell ; hence their name, " basket cells " (Fig. 99).
The inner or rust-colored layer is made up of a large number
of closely arranged, granular, multipolar cells, each possessing
a large nucleus and nucleolus. They are from 5 to 10 ,« in
diameter, and give off a large number of branching, dendritic
processes and fine neuraxones, which often start from one of
the short, dendritic processes. These neuraxones, according to
CENTRAL NERVOUS SYSTEM.
Ramon y Cajal, pass into the molecular layer, where they divide
in a T-shaped manner, there forming horizontal fibers. It is
thought by Cajal that these branches end about the dendritic pro-
cesses of the cells of Purkinje. In addition to the before-men-
tioned cells, there exist large, multipolar cells, which belong to the
second type of Golgi — that is, possessing short, stOut, dendritic
branches which occupy parts of the lower molecular and upper
granular layers. The axis-cylinders of these cells repeatedly
ramify in the granular layer, forming fine interlacements. It is
not known whether or not they are connected with fibers of the
underlying white matter. Cajal describes a large number of
centripetal fibers which, on entering the granular and molecular
layers, branch and show in their course, at their points of branch-
ing and at their terminations, irregular, moss-like thickenings.
This appearance occurs mainly in the fibers of the granular layer.
He believes .that they conduct impulses to the granular cells of
this layer. He describes other centripetal fibers entering the
molecular layer, there branching tree-like, among the dendritic
ramifications of the cells of Purkinje (Fig. 102).
THE CELLS OF PURKINJE.
These cells exist between the two previously-described layers,
and are the characteristic cells of the cerebellum. Thev are of
great physiologic importance because of their supposed function,
which is to originate impulses which serve to coordinate the
muscles of the body, and thus maintain equilibrium. They are
oval, roundish, or flask-shaped bodies, 35 to 70 fi in diameter, pos-
sessing a nucleus and nucleolus. From their cortical surface are
given off at first horizontal or oblique, stout, protoplasmic pro-
cesses, one or two in number, which soon send out, nearly at right
angles, many radiating processes, each branching like a tree,
and further subdividing into many smaller branches. These
dendrites are covered with minute, club-like protuberances — the
gemmules, or buds. From its resemblance to a tree, this rami-
fication bears the name arborization. These dendrites almost
entirely occupy the molecular layer, each dendrite ending in
a free extremity, which often curves upon itself near the
THE CEREBELLUM OR EPENCEPII ALON. 201
margin ot the cortex. The Purkinje cells possess very long,
delicate axis-cylinders, which pass through the granular layer,
enter the white matter, and form the chief cortical system of
fibers. In their course they give off numerous collaterals,
which pass upward through the granular layer, enter the mole-
cular layer, and, according to Cajal, come into contact with
the dendritic processes of these cells. He believes, by this
connection of collaterals and dendrites, the simultaneous action
IP
Fig. 102. — Microphotograph of Purkinje Celt,.
of many of these cells of Purkinje is secured. It is interesting
to note that the axis-cylinders of these cells are developed much
earlier than the dendritic processes.
The fibers of the cerebellum comprise the short and the long.
The former, or association fibers, are delicate bundles of fibers
lying just beneath the cortex, serving to unite adjacent areas of
the same hemisphere. The long or projection fibers consist of
two sets centrifugal and centripetal. The former represent
2oz CENTRAL NERVOUS SYSTEM.
the axones from the cells of Purkinje and the cells of the
nuclei dentata. The centripetal fibers are those which proceed
to the cerebellum from the various parts of the cerebrospinal
axis. The projection fibers as a whole are the before-mentioned
peduncular system of fibers, which serve to bring the cerebellum
into relation with all the other parts of the central nervous sys-
tem. There are three cerebellar peduncles — superior, middle,
and inferior.
THE CEREBELLAR PEDUNCLES.
The superior peduncles, also called the brachia conjunctiva,
consist of bundles of nerve-fibers which have their chief origin
in the cells of the dentate bodies, and are the before-mentioned
intraciliary fibers. They receive in addition fibers from the cells
of Purkinje. They then pass from the cerebellum brainward to
the region of the posterior corpora quadrigemina, beneath which
is located on each side the nucleus ruber, or red nucleus, of the
tegmentum. Below and close to each nucleus the majority of
the fibers of each peduncle decussate with their fellows of the
opposite side and pass to the opposite nucleus, ending about its
nerve-cells. A few fibers, however, do not decussate, but pass
to the nucleus ruber of the same side. Thus each corpus
dentatum is connected with both nuclei rubri, but chiefly with
the nucleus of the opposite side. Gudden, Forel, and Marchi
have shown, by the study of secondary degeneration, that the
fibers of these peduncles pass chiefly to the cells in the posterior
part of the nuclei rubri. Many of them, however, pass antero-
laterally, and end in the ventral part of the optic thalami. From
the cells of each thalamus new neuraxones pass out through the
posterior part of the internal capsule, and radiate toward the
cerebral cortex, to terminate probably in the cortex of the
parietal and central convolutions, thus establishing a connection
between the cerebellar hemisphere of one side and the opposite
cerebral hemisphere. The superior peduncles contain, in addi-
tion to these ascending fibers, some which degenerate downward,
and these latter are probably the axones from the cells of the
nuclei rubri. They pass to the corpora dentata, and end about
the cells therein contained.
THE CEREBELLUM OR EPENCEPHALON. 203
THE MIDDLE PEDUNCLES.
The fibers which form the middle peduncles consist in part of the
axones from the cells of Purkinje, which pass from the cerebellar
cortex in a transverse manner, ending about the cells of the
nuclei pontis, some of the same, others of the opposite side.
Other fibers from the same source end in a similar manner
about the cells of the formatio reticularis of both sides, thus,
according to Bechterew, establishing a connection between the
cerebellum and the remains of the anterolateral ground-bundles
of fibers, which also pass into the formatio reticularis. The re-
maining fibers of the middle peduncles come chiefly from the
cells of the nuclei pontis, being their axis-cylinders, and, after
decussating in the raphe, pass to the cortex of the opposite
cerebellar hemisphere.
These peduncles establish a connection chiefly between the
frontal, temporal, and occipital lobes of each side and the opposite
cerebellar hemisphere, owing to the fact that fibers from these
lobes end about the cells of the nucleus pontis of the same side,
and the axones of these latter cells pass to the opposite cerebellar
hemisphere, forming continuous paths of conduction — the so-
called frontocerebellar and temporo-occipital cerebellar tracts.
THE INFERIOR CEREBELLAR PEDUNCLES, OR CORPORA
RESTIFORMIA.
These contain fasciculi of fibers which come from several
sources. Those which have been most thoroughly studied are
the following :
First, the direct cerebellar tracts, or columns of Flechsig,
whose fibers are the neuraxones from the cells of Clarke and
Stilling, and have their greatest development in the upper lumbar
and lower dorsal segments ; they proceed upward along the
posterolateral periphery of the cord, and on reaching the
medulla, gradually trend backward into the corpora restiformia ;
they then pass medianward to the corpora dentata, and termi-
nate, according to Bechterew and von Monakow, without de-
cussation, in the cortex of the superior worm.
204 CENTRAL NERVOUS SYSTEM.
Second, two small bundles of fibers pass to the cerebellum
from the nuclei of the columns of Goll and Burdach. The first,
or the posterior external arcuate fibers, pass around the poste-
rior periphery of the cord, and reach the restiform body of the
same side. The second bundle, which comes from the nuclei of
the posterior columns, after crossing in the raphe (interolivary
fibers), passes around the periphery of the anterior pyramids and
olivary bodies and joins the restiform body of the opposite side.
These are the anterior external arcuate fibers. According to'
Bechterew, these fibers pass lateral to the corpora dentata and
end in the cortex of the superior worm.
Third, fibers pass to the corpus restiforme from the lateral
nucleus of the medulla of the same side. They pass to the
superior worm.
Fourth, the descending cerebellar tracts of Marchi and Lowen-
thal, which probably have their origin in the cerebellar cortex,
and are the axones from the cells of Purkinje. They degenerate
P'ig. 103. — Scheme ok the Fibers Passing to and from the Cerebellum.
The fibers of the superior peduncles are indicated by Roman numerals, the middle peduncles by
letters, and the inferior peduncles by Arabic numerals. For convenience, both ends of the
fibers are marked.
Inferior Cerebellar Peduncle. — I. Direct cerebellar tract. 2. Anterolateral descending tract
of Lowenthal and Marchi. 3. Fiber from posterior nerve-root decussating in anterior
commissure and ending about a cell of origin of Gowers' tract. 4. Postero-external arcuate
fibers passing from the nucleus gracilis and cuneatus of the same side via the restiform
body to the cerebellar cortex. 5. Internal arcuate fibers from the nucleus gracilis and
cuneatus of the opposite side, decussating in the raphe, and passing around the opposite
anterior pyramid to join the restiform body opposite to their origin. 6. Cerebello-olivary
tract passing from the cerebellar cortex to the opposite olivary body, whence the tract is
continued downward by axones from the cells of the olivary body in the lateral column to
terminate about the cells of the spinal cord at various levels. 7. The vestibulocerebellar
tract passing from the auditory nucleus to the cortex of the superior worm.
Middle Cerebellar Peduncle. — A, B. Fibers from cells of Purkinje passing to the formatio retic-
ularis of the same and opposite sides. C. Fiber from nucleus pontis passing to cerebellar
cortex of opposite side. D, E. Fibers from cells of Purkinje to nucleus pontis of same
and opposite sides.
Stiperior Cerebellar Peduncles. — I. Fiber from corpus dentatum passing to optic thalamus of
same side. II, IV. Fibers from corpus dentatum passing to red nucleus of the same and
opposite sides. Ill, V. Fiber from red nucleus passing to corpus dentatum. VI. Fiber
from red nucleus to optic thalamus. VII. Fiber of Gowers' tract passing through formatio
reticularis, arching over the root of the fifth nerve, and reaching the superior cerebellar
peduncle, passing the corpus dentatum of the same side and sending a collateral branch
to the cerebellar cortex.
Th. Optic thalamus ; Ours, crus cerebri; Pons, pons Varolii ; Med, medulla oblongata; S.
C, spinal cord.
Fig. 103.— Scheme of the Fibers Passing to and from the Cerebellum.
205
THE CEREBELLUM OR EPENCEPHALON. 207
downward and have been traced into the anterolateral area of
the cord, they probably end in the median gray matter.
Fifth, the direct sensory cerebellar tract — better called the
acousticocerebellar tract — joins the restiform body and pro-
ceeds, after decussating, to the opposite roof or tegmental
nucleus and nucleus globosus. This tract conveys centripetal
axones from Deiters' nucleus, thus establishing a connection
between the nucleus vestibularis of the auditory nerve and the
cerebellar hemisphere of the opposite side. This tract also
contains descending fibers, axones of the cells of Purkinje, which,
according to Koelliker, end about the cells of the nuclei of the
posterior columns, and probably give fibers and collaterals to
Deiters' nucleus and the nucleus of the trigeminal, pneumogas-
tric, and glossopharyngeal nerves.*
Sixth, the large tract of centrifugal or efferent fibers, known
as the cerebello-olivary tract, whose fibers are the axones of the
cells of Purkinje of the same side, and, after having decussated
in the raphe, end about the cells of the opposite olivary body.f
In addition to the previously-mentioned peduncular system of
fibers, the cerebellar hemispheres are connected by means of
two commissures which exist in the worm — an anterior and a
posterior. The anterior commissure of .Stilling is ventral to the
roof nucleus, being separated from the latter by a narrow band
of fibers. A fasciculus from this commissure passes between
the roof nuclei, there decussating, and then, taking a direct
downward course, is continuous upon each side with the vertical
and horizontal branches of the arbor vitse. According to Ober-
steiner, a fasciculus from this commissure passes between the
roof nuclei, there decussating, and then assuming a sagittal
* According to J. S. Risien Russel, the direct sensory cerebellar tract of Edinger is a struc-
ture entirely separate and distinct from the restiform body, and ought to be so regarded.
Anatomically they stand out clearly and distinctly as two definite structures, having little if any
resemblance, and having connections totally distinct from each other. Embryologically it has
been found that the fibers of the direct sensory cerebellar tract receive their myelin at a dif-
ferent period to the fibers of the restiform body.
t According to von Bechterew, each restiform body, or inferior cerebellar peduncle, con-
tains a tract of centripetal or afferent fibers, which originate from cells in the opposite olivary
body and terminate chiefly in the corpus dentatum, a few fibers passing to the cerebellar cortex.
Koelliker states that no such afferent cerebello-olivary tract exists, the olivary fibers being the
axones of the cells of Purkinje from the opposite side.
20$
CENTRAL NERVOUS SYSTEM.
course. The posterior commissure is located ventral to the
fibers of the corpora dentata and is continuous on each side
with branches of the arbor vitae.
A system of short fibers of association connect the different
cerebellar folia ; they are located just beneath the cortex, and are
called, from their general arrangement, the garlanddike fasciculi.
The fibers of the before-mentioned systems may be divided,
Fig. 104. — Schematic Representation of the Different Constituents of the Cor-
tical Gray Matter of the Cerebellum. — (After Van Gehuchten.)
according to the manner in which impressions are conducted,
into two sets — those which conduct impressions peripherally,
and, secondly, those which conduct them centrally. The former
fibers, with the exception of those which pass out of the dentate
bodies, are the axones from the cells of Purkinje. The latter ter-
minate, according to Cajal, in two ways — first, as moss-like fibers,
so called because, on entering the granular and molecular layers,
THE CEREBELLUM OR EPENCEPHALON. 209
they show, in their course, at their points of branching and at
their terminations, irregular, moss-like thickenings. These
fibers terminate mostly about the cells of the granular layer ; a
few, however, end in the molecular layer. The second set of
fibers enter the molecular layer and terminate in arborizations
about the dendritic ramifications of the cells of Purkinje. Ac-
cording to Koelliker, however, these last-described fibers do not
terminate about the cells of Purkinje, but about the basket cells
and possibly about the small, stellate cells of the outer mole-
cular layer. In the previous description of the cortex of the
cerebellum, it was described as consisting of two layers — a mole-
cular and a granular. However, as in the cerebral cortex, we
find in the cerebellum five distinct layers of cortical cells : First,
the small, stellate cells ; second, the large cells with basket ter-
minations ; third, the Purkinje cells ; fourth, the small, granular
cells; and, lastly, the large, granular cells, or those of the second
type of Golgi. All of these cells, save those of the third layer,
are possibly concerned in the reception and conveyance of cen-
tripetal sensory impulses to the cells of Purkinje. The latter
are supposedly concerned in the orderly arrangement of such
impulses, and in originating impulses of coordination for the
maintenance of equilibrium. This connection between the cells
of Purkinje and the other sets of cells may be thus explained.
The axones of the small granular cells form horizontal branches
which terminate about the dendrites of the cells of Purkinje,
after receiving the mosslike terminals. The collaterals of the
basket cells terminate in the tuft-like expansions in the same
way, only about the cell-bodies. The small, stellate cells, owing
to their connection with centripetal fibers, presumably influence
these cells in the same manner. The collaterals from the
axones of Purkinje's cells pass upward, and probably associate
the functions of many Purkinje cells. The action of the large,
granular cells is thought to be associate, but their function is
not definitely known.
14
CHAPTER V.
THE REGION OF THE MID-BRAIN.
From the middle cerebral vesicle are developed the parts
which afterward form the mid-brain, or mesencephalon. In
adult life the cavity of the middle cerebral vesicle has become
extremely narrowed, leaving only a mere channel or passage of
communication between the third ventricle or cavity of the
primitive fore-brain and the fourth ventricle or cavity of the
hind-brain. This canal, owing to this fact, is often called
the iter a tertio ad quartum ventriculum, or the aqueduct
of Sylvius, and in reality forms the ventricle of the mid-brain.
It is about two centimeters (nine lines) long, is lined by ciliated,
columnar epithelium, which is surrounded by a thick layer ol
gray matter, continuous with that of the fourth ventricle. On trans-
verse section near the fourth ventricle, the aqueduct is T-shaped,
becomes shield-shaped until near the third ventricle, when it
becomes triangular. Just beneath the posterior commissure it
expands into the third ventricle. This region of the mid-brain
is a means of connection between the pons, medulla, and cere-
bellum below, and the inter-brain, or thalamencephalon, and
the cerebral hemispheres above. This region includes the
corpora quadrigemina, the crura cerebri, the Sylvian aqueduct,
and adjoining gray matter which contains the nuclei of origin of
the third and fourth and the descending root of the fifth pair
of cranial nerves.
THE CORPORA QUADRIGEMINA.
The corpora quadrigemina are four rounded eminences which
are developed from the dorsal wall or roof of the mid-brain.
They are separated by two grooves, a median longitudinal and
THE REGION OF THE MID-BRAIN. 211
a transverse, the latter separating- them into a ventral or
superior pair and a dorsal or inferior pair. The former
groove, in conjunction with the transverse, separates them from
one another. They are located just behind the optic thalami,
third ventricle, and posterior commissure, and beneath the pos-
terior extremity ot the corpus callosum. They are above the
crura cerebri, and rest upon the lamina quadrigeminum, beneath
which is the aqueduct of Sylvius. The anterior or superior
pair, much the larger, are termed the nates ; the dorsal or inferior
pair, the testes. They have, extending from the external surface
CORPUS GENICULATUM
EXTERNUM
PONS
OLIVARY BODY
PULVINAR OF OPTIC
THALAMUS
'EAL BODY
iPUS GENICULA TUM
INTERNUM
CORPOR. I
Q UADRIGEMINA
MIDDLE CEREBELLAR
PEDUNCLE
INFERIOR CEREBELLAR
PEDUNCLE
Fig, 105. — Lateral View of Mesencephalon, Pons, and Medulla. — [Gegenbauer.')
of each side, large bundles of fibers, termed their brachia, or arms,
which are separated by a groove into an anterior pair, continu-
ous with the anterior corpora quadrigemina, and a posterior
pair, continuous with the posterior corpora. The brachium
coming from the side of each anterior corpus passes outward
under cover of the pulvinar of the optic thalamus, and between
it and the internal geniculate body, to enter the external gen-
iculate body and the optic tract, of which it is in great part a
prolongation. The posterior brachia are very short and divide
into two fasciculi, one of which joins the internal geniculate body
CENTRAL NERVOUS SYSTEM.
and the other disappears beneath that body and probably passes
through the posterior limb of the internal capsule, and thence
to the cortex of the temporosphenoid lobe.
ANTERIOR CORNU
OF LATERAL
VENTRICLE
FIFTH VENTRICLE
SEPTUM L VCID UM
ANTERIOR PIL-
LARS OF FORNIX
TAENIA SEMI-
CIRCULAR1S
ANTERIOR
COMMISSURE
THIRD VENTRICLE
MIDDLE
COMMISSURE
SULCUS
CHOROIDEUS
NA TES
CORPUS GEh'ICU-
LA TUM INTERNUM
LATERAL GROOVE
OF
MESENCEPHA LON
PONS
CONDUCTOR
SONORUS
SULCUS LONGITUDINALIS
MEDIANUS
TRIGONUM HYPOGLOSSI
CORPUS RESTIFORME
CLA VA
POSTERIOR FISSURE
SULCUS PARAMEDIANUS
DORSALIS
SULCUS LA TERALIS DORSALIS
CORPUS CALLOSUM
CAUDATE
NUCLEUS
FORAMEN OF
MONRO
OPTIC THALAMUS
STRIA PINEALIS
PEDUNCULUS
CONARII
PINEAL BODY
SULCUS CORP.
QUAD. LONGI-
TUDINALIS
TESTIS
FRENULUM VELI
LINGULA
EMINENTIA TERES
TUBERCUr.UM
ACUSTICUM
ALA CINEREA
TUBERCULUM CUNEATUil
FUNICULUS GRACILIS
FUNICUL US CUNEA TVS
LATERAL COLUMN
Fig. 106. — Metencephalon, Mesencephalon, and Thalamencephalon, from the
Dorsal Surface. — {After Obersteiner.)
MINUTE ANATOMY.
If a transverse section be made through the anterior or supe-
rior corpora quadrigemina of any mammal, the naked eye will
discern that the gray and the white matter composing them are
arranged in successive layers. If the section then be observed
THE REGION Of THE MID-BRAIN.
213
with a low power of the microscope, six distinct layers can be
recognized — viz. :
First, a narrow, outer layer, consisting of neuroglia cells and
fibers, the cells being of the stellate variety.
Second, a superficial layer of medullated nerve-fibers, forming
a stratum zonale, they being composed almost entirely of fibers
from the optic tract, which are the axones from the multipolar
cells of the retina, they arborize about the dendrites of the cells
of the underlying third layer.
«- ? .s *
A'
-- - »> J ,-
^■i
*/
***
FlG. I07. — MlCROPHOTOGRAPH OF A TRANSVERSE SECTION THROUGH THE CORPORA QUAD-
rigemina OF A Sheep. Showing layer of superficial cells. Method of Berkley.
Third, a superficial layer of gray matter, consisting of an
outer, lighter-colored portion of optic fibers and an inner, dark
portion about which these fibers end. There are two chief
forms of cells in this superficial gray layer — an outer layer of
spindle-cells, and an inner layer of small, polygonal cells. Some
of the former resemble the small, pyramidal cells of the second
layer of the cerebral cortex. In the sheep these cells fre-
quently give off four dendrites, two basal and two apical, the
214 CENTRAL NERVOUS SYSTEM.
former being short, seldom branching, and are finer than the
latter. The apical dendrites continue upward until they reach
the layer of superficial, medullated fibers, where they frequently
bifurcate, ending free or in a roundish swelling. Many of them
have but one apical dendrite, which is thick and forks after a
short course, each branch proceeding to the superficial layer
and ending free.
All these dendrites possess tuberous excrescences, which give
a peculiar, beaded appearance to the layer. Their axones are
difficult to follow, owing to the tangle of fibers occurring in this
layer. Most of them come from the base of the cell-body, while
some are given off from the main apical dendrite. They course
forward and outward toward the optic fibers. The small, tri-
angular or polygonal cells possess from two to four dendrites,
which come off from angles of the cell-body. These branches
are moderately thick, pursue mostly an oblique or a horizontal
course, branch frequently at a distance from the cell-body, and
terminate in free ends about cells of a like nature. Starr states
that the axones of these cells enter the optic tract and pass to
the occipital cortex.
The fourth layer consists of inner medullated nerve-fibers,
which have a longitudinal course, and enter both the superficial
and deep layers of gray matter. This layer contains axones
from the cells of the outer gray layer, passing to the occipital
cortex, to end about the pyramidal cells there, and axones pass-
ing in an opposite direction from the occipital cortex to the
outer gray layer previously described (von Monakow).
The fifth or deep layer of gray matter contains a number of
large, multipolar, triangular and polygonal cells, resembling
closely the cells of the anterior cornua of the spinal cord, poss-
essing from two to six very stout and long dendrites, which
become attenuated in their course, branch frequently, and ter-
minate free in a Y-shaped end. The axones come off usually
from the base of the cell, or from one of the main dendrites,
and have a mesial or dorsal course toward the fillet. Some of
them probably pass to the red nucleus and to the nucleus of the
oculomotor nerves.
The sixth layer consists of the central gray matter sur-
Fig. 108. — A Characteristic Cell from the Third (Gray) Layer of the Optic Lobe
of an Eighteen-day-old Chicken. Golgi's method. — (After Koelliker.)
N. The neuraxone from the cell-body with its numerous collaterals.
215
C.O.T.
Fig. 109. — Schematic Representation of the Essential Histologic Elements of
the Optic Lobe of a Bird. Showing the probable route taken by visual impressions
to reach the cerebral (occipital) cortex. — (After Koelliker.)
C.R.F. Centripetal retinal fibers with terminal arborizations, e, e, e. a&ndsfi.c. Spindle-shaped
cells of the second layer with descending axones. b. Pyramidal-shaped cell of the third
layer with a descending axone coming from the chief apical dendrite, c, c. Triangular-
shaped cells also with descending axones. The axones from the above-named cells form
C.O.T., or the cerebral oplic tract, d. Spindle-shaped cell of third layer whose axone
ascends and forms a centrifugal optic fiber which probably terminates in the retina.
217
k
THE REGION OF THE MID-BRAIN.
219
rounding the aqueduct of Sylvius. It is from two to three
millimeters thick, and is composed of a homogeneous mass of
neuroglia tissue, chiefly made up of spheric or slightly oblong
neuroglia cells, with innumerable long, slender processes radi-
ating from all parts of the cell-body. Embedded in this neuroglia
mass exists a number of small and large multipolar nerve-cells,
the small cells, triangular in shape, being scattered throughout
the inner portion of the neuroglia layer, and each possessing
four to eight dendrites and a fine long neuraxone, whose course
is ventrolateral or mesial. The collaterals from these axones
form the arch-like fibers of this layer. The large cells belong
Fig. iio. — Transverse Section Through the Corpora Quadrigemina from an Eight-
months' Human Fetus. — (After Koelliker.)
In the region of the aqueduct of Sylvius and between the arching fibers are to be seen the char-
acteristic multipolar cells of the gray matter of this region.
to the nuclei of origin of the third, fourth, and upper or descend-
ing root of the fifth nerve. They are located ventral to and on
each side of the aqueduct of Sylvius (Fig. no).
The posterior quadrigeminal bodies possess small (15 to
20 fj) and large (30 to 50/*) multipolar nerve-cells, similar to
those which exist in the anterior corpora quadrigemina. The
course of their axones is dorsal, mesial, or lateral, and they prob-
ably enter the lateral fillet or lemniscus or the posterior brachia.
The cells of the posterior corpora quadrigemina are connected
with the auditory apparatus by means of the lateral fillet, the
fibers of which end in part about these cells, and in part about
2:o CENTRAL NERVOUS SYSTEM.
the cells of the lateral tegmental nucleus. From these cells
new axones start out and, entering the posterior brachium,
radiate, after passing through the extreme posterior end of the
internal capsule, through the centrum ovale, terminating about
the cells of the first and second temporosphenoid lobes. The
axones of the cortical cells of the temporosphenoid lobe pass
centrifugally via the posterior brachium, and end about the cells
of the posterior corpora quadrigemina, thus forming a double
connection between these bodies and the cortex of the temporo-
sphenoid lobe.
THE CEREBRAL PEDUNCLES.
These peduncles, or crura cerebri, consist chiefly of longi-
tudinal tracts or fasciculi of fibers which have both a cen-
trifugal and a centripetal course. They serve to connect
the cerebral cortex and basal ganglia with the pons, medulla,
cerebellum, and the spinal cord. Each peduncle is separated
into a ventral convex portion, called the crusta, or "Fuss"
(German), and a dorsal, slightly concave portion, the teg-
mentum, by the crescentic gray area of dark pigmented nerve-
cells, the substantia nigra, which area extends from the upper
margin of the pons Varolii to the posterior border of the
corpora mammillaria, and reaches the surface on both the
inner and outer sides of the peduncle. On its inner side is
a groove, the sulcus oculomotorius, through which passes the
third nerve. On the outer side another groove exists — the
sulcus lateralis.
The ventral portion or crusta, also called pes pedunculi, con-
sists of the following systems of longitudinal fibers : First, the
motor or pyramidal tract ; second, a tract connecting the tem-
poral and occipital lobes with the pons, and thence with the
opposite cerebellar hemisphere ; third, the frontocerebellar tract ;
fourth, a fasciculus of fibers located above the pyramidal tract,
between it and the substantia nigra ; fifth, a small bundle of
fibers on the inner side of the crusta, joining the fillet.
First, the pyramidal or motor tract of each side forms in the
medulla the anterior pyramids, which, on reaching the inferior
THE REGION OF THE MID-BRAIN. 221
border of the pons, separate into distinct bundles which lie
between the superficial and deep transverse pontine fibers. On
emerging from the superior border of the pons they are again
collected into two bundles, which occupy the middle two-fifths
ot each cms. They then course upward until they reach the
internal capsule, where they form the anterior two-thirds of the
posterior limb ol the internal capsule, and radiate to the region
about the fissure ot Rolando, known as the motor area of the
cerebral cortex. The reason for tracing the course of the motor
I
Fig. hi. — Transverse Section Through the Mid-brain of an Adult. Weigert's
method.
A.C.Q. Anterior corpus quadrigeminum. A.S. Aqueduct of Sylvius. C.G.M. Central gray
matter. F.D.O.T. Fountain-like decussation of tegmentum (Meynert's). L.F. Lateral
fillet or lemniscus. M.F. Mesial fillet or lemniscus. III. Root-fibers of the third
(oculomotor) nerves. R.N. Red or tegmental nucleus. P. Pulvinar of optic thalamus.
S.N. Substantia nigra. P.P. Pes pedunculi or cerebral peduncles.
tract in a direction opposite to the development and conduction
of its component fibers is given on page 141, section Medulla
Oblongata.
The second is a tract which connects the occipital and temporal
lobes with both cerebellar hemispheres, but chiefly with the one
of the opposite side. The fibers of this tract proceed from the
pyramidal cells of the cortex of the occipital and temporal lobes.
The tract passes beneath the lenticular nucleus, and between its
posterior extremity and the external geniculate body, and forms a
222 CENTRAL NERVOUS SYSTEM.
fasciculus which continues downward in the outer side of the
crusta, occupying about one-fifth of its bulk. It extends into
the pons, where the individual fibers arborize about the cells of
the nucleus pontis, which nucleus continues this tract, by way of
the middle cerebellar peduncle, to both cerebellar hemispheres,
but chiefly to that of the opposite side.
Third, the pontocerebellar tract occupies rather more than
the inner fifth of the crusta. The fibers of this tract come from
the prefrontal lobe, and pass between the lenticular and cau-
date nuclei, occupying a large part of the anterior limb of the
Fig. 112. — Diagram of Section of the Crus. — {Modified from Wernicke, from Gowers.)
L F, U F. Upper and lower fillet. CQA. Anterior corpora quadrigemina. Aq. Aqueduct.
III. Nucleus of third nerve (3). PH. Posterior horizontal fibers, c p. Brachium of the
posterior corpora quadrigemina. R N. Red nucleus. S N. Substantia nigra. CGI.
Internal geniculate body. T O C. Temporo-occipital cerebellar fibers. Py. Pyramidal
fibers. F C. Frontocerebellar fibers. . C C. Caudate cerebellar fibers, t. Inner fibers of
crusta to tegmentum.
internal capsule, and course downward on the inner side of
the pyramidal tract, ending in the ventral portion of the pons
Varolii about the nerve-cells of the nucleus pontis of the same
side. The cells of the nucleus pontis of each side are joined by
fibers from the cortex of both cerebellar hemispheres, chiefly,
however, with the cerebellar hemisphere of the opposite side.
The fibers are the axones of the cells of Purkinje of the same
and the opposite side, the latter fibers having crossed in the
raphe, thus establishing a connection between the frontal lobe of
one side and both cerebellar hemispheres, but chiefly with the
cerebellar hemisphere of the opposite side.
THE REGION OF THE MID-BRAIN. 223
Fourth, a rather broad but thin layer of fibers, which in the
crusta is located above the pyramidal tract, and between it and
the substantia nigra. This bundle of fibers, according to Flech-
sig, arises from the cells of the corpus striatum, and continues
downward through the crusta to the cells of the nucleus pontis.
These latter cells may continue this tract by their axones to the
cortex of the same and opposite cerebellar hemisphere, establish-
ing a cross-connection between the corpus striatum of one side
and the cerebellar hemisphere of'the same and the opposite side.
Fifth, the small bundle of fibers which occupies the most mesial
portion of the crusta is said to join the fillet. According to
Spitzka, this bundle of fibers contains the central sensory tracts
for the cranial nerves.
The tegmentum or dorsal part of the crura cerebri is con-
tinuous anteriorly with the tegmental region beneath the optic
thalami, and below with the tegmental region of the pons and
medulla. It contains longitudinal tracts of fibers, — continuations
of tracts proceeding upward from the medulla, cerebellum, and
pons, — in addition to several fasciculi of arched fibers, having
among them several scattered collections of gray matter. The
tegmentum is divided into a right and a left half by the upward
continuation of the raphe, at which point the various decussa-
tions take place. The following longitudinal tracts of fibers
are to be found in the tegmentum : First, the mesial fillet, or
mesial lemniscus ; second, the lateral fillet, or lateral lemniscus ;
third, the superior cerebellar peduncles ; fourth, the superior lon-
gitudinal bundles ; fifth, the remaining longitudinal tracts of the
formatio reticularis. It will be proper at this point to trace these
various systems of fibers not only through the tegmentum of
each crus, but to their termination, either in the basal ganglia
or in the cerebral cortex (Figs. 1 1 1 and 112).
THE MESIAL FILLET, OR LEMNISCUS.
This is a continuation brainward of the axones of the cells of
the nucleus gracilis and nucleus cuneatus. In describing the
course of the long tracts of fibers in the posterior columns of
the cord, it was found that they terminated about the cells of
22 4 CENTRAL NERVOUS SYSTEM.
the previously-mentioned nuclei, and that most of the axones of
these cells on each side passed ventromesially as internal
arcuate fibers to decussate in the raphe between the olivary
bodies, forming the so-called interolivary or superior sensory
decussation. They then continue their course just back of the
anterior pyramid of the opposite side in the same relative posi-
tion through the pons, occupying the ventral portion of the
formatio reticularis. On transverse section, each mesial fillet
forms an oblong area on both sides of the raphe, just dorsal to
the deep, transverse, pontine fibers. In the crus it occupies the
ventral portion of the tegmentum, and becomes continuous lat-
terly with the lateral fillet, or lateral lemniscus, which here occu-
pies a somewhat triangular area in the outer side of the tegmen-
tum, the two thus forming a sickel or crescentic mass of fibers.
On its course brainward the mesial fillet receives an accession
of fibers from the anterolateral columns and from the cells of
the various end nuclei of the sensory cranial nerves of the
opposite side, save the auditory, forming for those nerves cen-
tral, sensory tracts. The mesial fillet gives off both axones and
collaterals to the cells of both the median and lateral fields
of the formatio reticularis.
The mesial fillet then continues brainward in the tegmentum
of the crus to the subthalamic region, where, according to
Bechterew, the fibers from the cells of the nucleus gracilis, and
those from the nucleus cuneatus, pursue different courses.
Some fibers from the cuneate nucleus pass to the anterior
corpus quadrigeminum, giving off on their way a few fibers and
collaterals to the nucleus of the lateral fillet, or lemniscus. The
main bundle, however, continues upward to the outer side of
Luy's body, to form two fasciculi, one joining the lenticular
loop and the other Meynert's commissure.
The first of these fasciculi passes to the globus pallidus of the
lenticular nucleus of the same side, while the remaining fascic-
ulus passes to the lenticular nucleus of the opposite side by
way of Meynert's commissure. The fibers of both fasciculi end
about the intrinsic cells of these nuclei, whence new axones start
out and radiate to the cortex of the central and parietal convolu-
tions, thus establishing a connection between the nucleus cuneatus
Fig. 113. — Diagram Indicating the Course of the Motor and Sensory Fibers
of the Spinal Cord and Medulla.
a. Motor cells of the cerebral cortex, b, b. Arborizations of the fibers of the sensor)' tract
in the cerebral cortex, c. Nucleus of the column of Burdach, showing terminal arboriza-
tions of the long sensory fibers of the cord. d. Nucleus of the column of Goll, showing
terminal arborizations of the long sensory fibers of the cord. e. Section of the medulla,
showing sensory decussation, f. Section of medulla, showing motor or pyramidal decus-
sation, gj g. Motorial end plates, h. Section through the cervical region of the cord,
showing termination in the anterior horn of the motor fibers of the direct pyramidal tract
after they have crossed in the anterior commissure ; also fiber of crossed pyramidal tract end-
ing about anterior horn cell of same side, i, i. Posterior spinal ganglia. /, /■. Sensory fibers
of short course. /. Sensory fibers of long course, terminating in medulla, m, m } m. Sen-
sory end organs. ;/. Section through lumbar cord.
15 225
THE REGION OF THE MID-BRAIN.
227
and the cortex of the central and parietal lobes. The portion of
the fillet whose fibers are the axones of the cells of the nucleus
gracilis course mesially to the fibers from the nucleus cuneatus.and
give off collaterals which join the anterior corpus quadrigeminum,
ending- probably about the cells of the fifth layer. The main
bundle ot fibers continues forward to end, according to von Mon-
LAI
LAI
Fig. 114. — Transverse Section Through the Spinal End of the Posterior Cor-
pora Quadrigemina OF A Cat. Weigert preparation. — [After Koelliker.)
Be. Brachium conjunctivum (superior cerebellar peduncle). C. Commissure. Fid. Posterior
longitudinal bundle. G. Fibers from lateral fillet passing medianward as fibrce arcuate.
LL Fibers of the lateral fillet or lemniscus terminating about the cells of the posterior corpus
quadrigeminum. LAI, LAI. Median fillet or lemniscus. NqJ. Nucleus of the posterior
corpus quadrigeminum. P. Superficial pons fibers. Pyr. Pyramidal bundles of fibers.
R. Raphe. Sr. Substantia reticularis. A. Aqueduct of Sylvius.
akow, Schlesinger, and Mott, about the cells of the ventral
nucleus of the optic thalamus, where, by means of the axones
from the cells of this nucleus, this tract, now called the cortical
fillet, is further continued through the posterior division of the
internal capsule, and through the centrum semiovale, to termi-
nate in the region of the central convolutions, chiefly the post-
central and parietal gyri. The mesial fillet contains a tract of
228 CENTRAL NERVOUS SYSTEM.
fibers which have been found to degenerate downward after
lesions of the central ganglia, especially after destruction of the
optic thalamus ; this degeneration extends downward toward the
nuclei of the posterior columns* (Figs, in, 112, and 113).
The lateral fillet, or lateral lemniscus, is the chief central
auditory tract. It forms an area somewhat triangular on the
outer side of the pons. It is composed, first, of axones from the
cells of the ventral auditory nucleus, chiefly of the opposite side;
second, axones from the cells of the ventral auditory nucleus, pass-
ing dorsally around the restiform body and beneath the ependyma
of the fourth ventricle (striae acousticse), decussating with their
fellows in the raphe, and proceeding ventrolaterally to join the
lateral fillet of the opposite side, a few fibers passing without
decussating into the lateral fillet of the same side ; third, axones
from the cells of the superior olivary body, which, after decus-
sating in the raphe, pass to the opposite lateral fillet, a few fibers
passing to the lateral fillet of the same side ; fourth, axones
from the cells of the nucleus of the lateral fillet ; fifth, fibers joining
the lateral fillet in the region of the corpora quadrigemina, which
come from the ventral tegmental decussation. The lateral fillet
occupies, in the ventrolateral part of the tegmentum of the crus,
a triangular area which is continuous on the inner side with the
mesial fillet. It continues brainward in the same position until
it reaches the region of the posterior corpus quadrigeminum,
where most of the fibers terminate about its cells, while some
terminate about the cells of the internal geniculate body and
posterior nucleus of the optic thalamus. According to Koel-
liker, some of the fibers terminate also about the cells of the
upper portion of the lateral nucleus of the lemniscus. A small
bundle of fibers from the lateral fillet ends about the cells of the
anterior corpus quadrigeminum, some axones of which are con-
nected with the nuclei of the third and fourth nerves, and
whose cells are also connected with the terminal fibers of the
optic nerve. This connection may serve a common reflex pur-
pose, by means of which movements of the eyeballs may be
excited, owing to auditory or optic impressions.
* Such eases have been recorded by Bruce, Campbell, Jacob, and Mahaim.
THE REGION OF THE MID-BRAIN.
229
From the cells of the posterior corpora quadrigemina, internal
geniculate body, and posterior nucleus oi the optic thalamus,
axones pass out by way oi the posterior arm, or brachium,
through the extreme posterior end oi the internal capsule, and
thence radiate through the centrum semiovale to the pyramidal
cells ot the superior and middle temporosphenoid lobes.
f
Fig. 115. — Horizontal Section Through the Cerebellum.
A.C.Q. Anterior corpora quadrigemina. P.C.Q. Posterior corpora quadregemina. CD. Cor-
pus dentatum. M.C.P. Middle cerebellar peduncle. S.C.P. Superior cerebellar peduncle.
I.C. P. Inferior cerebellar peduncle. F.V. Fourth ventricle.
THE SUPERIOR CEREBELLAR PEDUNCLES.
The centripetal fibers, of which each peduncle is composed,
have their chief origin from the cells of the dentate nucleus oi
the cerebellum. A few centripetal fibers join the peduncles
from the cortex of the worm, being the axis-cylinders from the
cells of Purkinje. These peduncles make two compact bundles,
one on each side of the upper part of the fourth ventricle, form-
ing its outer boundaries, and having between them the superior
medullary velum. In their course brainward they converge and
become located in the roof of the fourth ventricle and on each
side of the aqueduct of Sylvius, where they form two long
230 CENTRAL NERVOUS SYSTEM.
bundles of fibers, crescentic on transverse section, which occupy
a large part of the dorsolateral periphery of the tegmentum.
As they approach the region of the posterior corpora quadri-
gemina they are more ventrally located, just posterior to the
red or tegmental nuclei ; the greater part of the fibers of each
bundle decussate with their fellows of the opposite side, and ter-
minate about the cells of the posterior portion of the nucleus
ruber of the opposite side. A number of fibers do not decus-
sate, but pass to the nucleus ruber of the same side. Some of
the fibers of the superior cerebellar peduncles pass through the
nuclei rubri into the optic thalami, where they terminate. Many
fibers, probably axones from the cells of the nucleus ruber, con-
tinue onward to end about the ventral portion of the optic thal-
amus, from the cells of which new fibers start out to pass through
the posterior portion of the internal capsule, and thence radiate
to the region of the central gyri and parietal lobe. Some of
these fibers may terminate in the lenticular nucleus. Some
anatomists do not agree with this description of the cortical
termination of this tract. There is also included in each superior
cerebellar peduncle a centrifugal tract of fibers, which arises from
the cells of the opposite red nucleus, and probably terminates
among the cells of the dentate nucleus of the cerebellum.
THE SUPERIOR LONGITUDINAL BUNDLE.
Each bundle appears on cross-section as a somewhat triangular-
shaped area of longitudinal fibers, located on one side of the
raphe beneath the gray matter of the fourth ventricle and that
of the aqueduct of Sylvius. Each bundle extends upward to a
collection of cells in the central gray matter of the third ventricle,
at the beginning of the aqueduct of Sylvius and ventral to the
oculomotor nucleus. This is Edinger's nucleus, or the nucleus
of the posterior longitudinal bundle, where, according to Cajal,
a large part of the fibers terminate, the rest continuing onward
to end in the optic thalamus. Inferioriy, they are continuous
with the fibers of the anterior ground bundles of the spinal cord,
being, in reality, their upward extensions. In the medulla,
owing to the motor and sensory decussations and the interposi-
Fig. 116. — Micropkotograph Through the Red Nuclei of the Mid-israin ok a
Young Sheep. Showing decussation of the fibers of the superior cerebellar peduncles.
Method of Golgi.
Fig. 117. — Microphotograph of a Section through the Red or Tegmental Nu-
cleus of a Young Sheep. Showing seven of its characteristic cells. Golgi method.
231
THE REGION OF THE MID-BRAIN. 233
tion of many fibers and cells, these ground bundles become dis-
placed dorsally, and come to occupy a position on each side of
the raphe, in the dorsal part of the formatio reticularis. In their
course the posterior longitudinal bundles of fibers give off col-
laterals to the motor nerves concerned in the movements of the
eyeballs (III, IV, and VI), and probably to all the motor cranial
nerves. These collaterals pass in the raphe to the nuclei of the
opposite side, although a few pass to the nuclei of the same
side. It is probable that collaterals and axones from these
bundles also terminate about the cells of the substantia reticu-
laris grisea. According to Cajal, the posterior longitudinal
bundle of fibers receives accessions of fibers from the auditory
nucleus of Deiter, which have an ascending course and give off
numerous collaterals to the motor nerves of the eyeballs, and,
secondly, from the sensory trigeminal nuclei, and from the cells
of the formatio reticularis alba.
Despite much clinical and experimental research, doubt still
exists with regard to the exact course and termination of the
two remaining tracts of the formatio reticularis — namely, the
anterolateral ascending tract of Cowers and Bechterew and the
lateral ground bundle of fibers. The former, which occupies, in
the cord, a triangular or broadly comma-shaped area along its
anterolateral periphery, ventral to the direct cerebellar and
cross-pyramidal tracts, ascends to the medulla, where, according
to Gowers and Bechterew, the fibers may be, in part or totally,
intercepted by the cells of the lateral nucleus, and the tract is
further continued, by means of the axones from these latter cells,
which enter the lateral field of the formatio reticularis, occupying
a position in the medulla dorsolateral to the lower olivary body,
and continuing in the same relative position through the pons
and brain-stem, to pass with the fibers of the mesial fillet through
the posterior division of the internal capsule, and radiating
through the centrum ovale, to terminate in the cortex of the
parietal lobe. On the other hand, the studies of Auerbach,
Lowenthal, and Patrick on lower animals, and of Hoche in
man, would seem to prove that this tract, after reaching the
pons, passes into the cerebellum.
v In the description of Gowers' tract, contained in the section
2 34
CENTRAL NERVOUS SYSTEM.
on the spinal cord, the termination of the tract was given ac-
cording to the latest view advanced by Hoche. From a clinical
standpoint, however, this description seems inadequate, because
lesions of the parietal cortex have been followed by a loss
of sensation of temperature and pain. Therefore, if we must
assume that Gowers' tract conducts such sensations, a part at
least of the fibers must be in relation with the parietal lobe, a
connection which Hoche's case does not take into account. It
would seem that the view of Mott must be the more correct
one, since he has shown that a part of the fibers of this tract
Fig. 118. — Course and Termination of Gowers' Tract. — [According to Hoche.')
(crossed afferent tract of Gowers and Edinger) terminates in
the optic thalamus, which we know is in connection with the
parietal lobe.
The ground bundles of the lateral columns enter the formatio
reticularis of each side, chiefly the lateral portions. Many of
the fibers end about the collections of cells therein (nucleus
reticularis tegmenti). The remainder, according to Bechterew,
continue brainward to the region of the posterior corpus quad-
rigeminum, where the fibers end in a special collection of nerve-
cells for each side in the central part of the formatio reticularis,
named by Bechterew the superior central nucleus. The remain-
THE REGION OF THE MID-BRAIN. 235
ing tracts of fibers, of short course, are probably the axones of
the cells of the formatio reticularis, whose chief function is to
connect the different levels of the medulla, pons, and brain-stem.
In Golgi specimens it will be found that most of the axones,
after a short course, decussate in the raphe, then fork, one
division passing upward, the other downward, and they prob-
ably arborize about cells of a like character at higher and lower
levels. Some of the axones do not decussate, but after a short
course bifurcate in the same manner.
THE MOTOR OCULI, OR THIRD PAIR OF CRANIAL
NERVES.
This is the common motor nerve of the eyeball and innervates
all the external muscles of the eye save the superior oblique
and external rectus. \t also supplies the sphincter pupillse and
the ciliary muscle, through its connection with the ciliary gan-
glion. The origin of this nerve, on each side, is from a nucleus
situated between the anterior corpora quadrigemina and beneath
the floor of the ventral portion of the aqueduct of Sylvius, just
outside of or lateral to the raphe. It extends ventrally as far as
the posterior portion of the third ventricle and dorsally to
beneath the middle of the posterior corpus quadrigeminum,
where it becomes continuous with the nucleus of origin of the
trochlearis or patheticus nerve, this latter nucleus being simply
the posterior continuation of the former. The oculomotor
nucleus is composed of large and small multipolar nerve-cells,
containing a yellowish pigment and arranged on each side into
an anterior, posterior, and median group. The anterior group
is located in the wall of the posterior part of the third ventricle,
and consists of a group of small, multipolar nerve-cells whose
axones pass dorsally. Posterior to this group exists the main
part of this nucleus, called the posterior group, the axones of
the median cells of which pass inward, decussate with their fellows
of the opposite side, and join the opposite oculomotor nerve,
while the axones of the other cells of this group pass out on the
same side without decussation. The median cell-group is just
beneath the aqueduct of Sylvius and between the main divisions
236
CENTRAL NERVOUS SYSTEM.
of the two posterior groups, and its axones pass on each side
toward the oculomotor nerve-roots of that side. Just anterior to
the median cell group exists on each side two nuclei, united an-
teriorly and forming an imperfect, crescent-shaped mass. The
cells of this group are small, and are embedded in a dense
tangle of fibers. It is not at present known whether this
nucleus on each side is connected with the nucleus of the oculo-
motor nerve or whether it is independent. It was discovered
by Edinger and Westphal, and receives the joint names of both.
^¥^f
$*.
FlG. II9. — MlCROPHOTOGRAPH THROUGH THE NUCLEUS OF ORIGIN OF THE MOTOR OCULI
Nerve. Showing the multipolar cells of this nucleus. Golgi preparation.
The experiments of Hensen and Voelkers on dogs, and the
clinical observations of Pick, Kahler, Oppenheim, Starr, and
others, lend support to the theory that the oculomotor nucleus
consists of a series of centers arranged from before backward,
which are presumably as follows, in order from before backward :
First, a group of cells concerned in accommodation ; second,
those presiding over the reflex action of the iris to light ; then
cells for the innervation of the following- muscles — internal rec-
tus, superior rectus, levator palpebral superioris, inferior rectus,
THE REGION OF THE MID-11RA1N. 2 37
inferior oblique, and superior oblique, the latter muscle being
supplied by the patheticus, or fourth nerve.
The axones from these various cell groups pass ventrally
through the tegmentum, some between and others through the
mesial portion of the red nuclei, to reach the base of the brain,
Fig. 120. — A Camera Lucida Drawing through the Nuclei of Origin of the Third
or Motor Oculi Nerves. Showing the location of the nuclei and their cells, together
with the descending axones from those cells which go to form the nerve-roots.
where they emerge from a groove — the sulcus oculomotorius —
as two thick, roundish nerves, which become located in the inter-
peduncular space close to the inner side of each peduncle and
just above the pons Varolii. They then pass between the supe-
rior cerebellar peduncle and posterior cerebral artery, forward
to the outer side of the posterior clinoid process, just anterior to
2 3 8
CENTRAL NERVOUS SYSTEM.
which they pierce the dura mater, forming the outer boundary
of the cavernous sinus, and continuing forward they enter the
sphenoid fissures, where each nerve divides into two bundles,
a superior and an inferior, which enter the orbit between the
heads of the external rectus muscle. The superior bundle
passes over the optic nerve to supply the superior rectus and
levator palpebrae superioris muscles. The inferior bundle
divides into three parts — one for the internal rectus, one for the
inferior rectus, and the third, the longest, for the superior
NUCL. LAT. ANT
[OARKSCHCWITSCH)
NUCL.OORS.I.(ANT.)/
H UCL.VEMT, I. (aNT.)
nucl.dors.ii-Cposx)
(V.GVDOENj
NUCL.CE4TRAUS-
NUOt.V|ENT.II.(POST.}
Fig. 121. — Diagram of the Groups of Cells Forming the Nuclei of the Third and
Fourth Cranial Nerves. — {After Prrlia from Quain.)
oblique. This latter branch is also connected with the ciliary
ganglion, and contains fibers for the ciliary muscle and sphincter
of the pupil.
THE CONNECTIONS OF THE OCULOMOTOR NUCLEUS.
First, with the motor or pyramidal tract, by collaterals which,
after decussating, arborize about the cells of the nucleus of the
third nerve of the opposite side ; second, with the posterior longi-
tudinal bundle. This bundle is chiefly connected with the oculo-
THE REGION OF THE MID-BRAIN.
239
motor nucleus of the opposite side, although a few fibers pass
to the nucleus of the same side. We may here recall the fact
that the posterior longitudinal bundle is also connected with the
nuclei of the fourth and sixth nerves. Owing to the latter con-
nection, the conjugate or associative movements of the eyeballs
may take place ; thus, if both eyes are turned to the right, the
right eye turns to the right by virtue of a contraction of the right
external muscle, innervated by the right abducens or sixth nerve j
while the left eye deviates to the right owing to a contraction of
D.P.N
L.&
Fig. 122. — Transverse Section Through the Mid-brain at the Level of the
Posterior Corpora Quadrigemina. Weigert preparation.
D.P.N. Decussation of the patheticus or fourth pair of cranial nerves. P.C.N. Posterior cor-
pora quadrigemina. P.L.B. Posterior longitudinal bundle, showing its relation to the root
fibers of the third nerve.
the left internal rectus, innervated by the left motor oculi nerve ;
hence, both eyes are moved conjointly to the right by the activity
of the two chief motor nerves of the eye, associated through the
posterior longitudinal bundle. The third connection is with the
optic tract, possibly through cells in the anterior corpus quadri-
o-eminum, whose axones and collaterals arborize about the cells
of this nucleus (Koelliker). According to Darschewitsch, how-
ever, this connection is made by a small bundle of fibers leaving
the mesial portion of the optic tract to pierce the optic thalamus
2 4 o CENTRAL NERVOUS SYSTEM.
and to reach the oculomotor nucleus through the posterior com-
missure. This connection completes the reflex arc, by means
of which the pupillary reflexes are subserved.
THE FOURTH PAIR OF CRANIAL NERVES.
This pair, called on each side the patheticus, or trochlearis,
arises from a collection of medium-sized (40 to 50 /x) multi-
polar nerve-cells located beneath the anterior part of the infe-
rior or posterior corpus quadrigeminum, in the ventral gray
matter of the aqueduct of Sylvius, and internal to the descend-
ing root of the fifth nerve. This group of cells is continuous
anteriorly with the oculomotor nucleus, and is in reality the
dorsal continuation of that nucleus. The axones from the cells
of this nucleus pass downward toward the pons Varolii, then
curve dorsally around the lower part of the Sylvian aqueduct to
enter the superior medullary velum, there to completely decus-
sate with their fellows of the opposite side. The two nerves
emerge just below the inferior quadrigeminal bodies, and, pass-
ing downward across the superior peduncles of the cerebellum,
wind around the outer side of each crus cerebri, where they are
to be seen. Each nerve then pierces the dura mater behind the
posterior clinoid process, and runs forward in the wall of the
cavernous sinus lying against the ophthalmic nerve, and then,
crossing the third nerve obliquely, enters the sphenoid fissure
and ramifies on the superior oblique muscle (Figs. 121 and 122).
THE SUPERIOR OR ACCESSORY NUCLEUS OF THE
FIFTH OR TRIGEMINAL NERVE.
This nucleus * consists of a collection of multipolar cells
slightly crescent-shaped, located in the central gray matter, at
the lateral border of the aqueduct of Sylvius, and beneath the
posterior corpus quadrigeminum. A few cells of this nucleus
frequently extend forward as far as the beginning of the ante-
*The cells of the superior or accessory trigeminal nucleus are believed to be multipolar by
Koelliker and Obersteiner, while Ram6n y Cajal, Lugaro, and Golgi think they are without
dendrites, and are pear-shaped, unipolar cells.
Fig. 123. — Schematic Representation of the Origin of the Trigeminal Nerve. —
[After E dinger. )
16 241
THE REGION OF THE MID-BRAIN. 243
rior corpus quadrigeminum. The nucleus probably extends
caudad to the anterior extremity of the fourth ventricle, where it
is continuous on each side with the darkly pigmented cells of
the substantia ferruginea, which are grouped on each side of
the ventricle, lateral to the posterior longitudinal bundles and
beneath the ependyma, and are covered by a bluish-gray area,
— the locus cceruleus, — through which this dark group of cells
may be seen. This group may be considered as part of the
nucleus, since Mendel found them wasted in a case of progres-
sive facial atrophy where the fibers of the trigeminal nerve of
that side were degenerated. The axones from the cells of the
accessory trigeminal nucleus join the portiominor or motor divi-
sion of the fifth nerve ; they are probably motor in function,
although Merkel believes they may have a trophic function,
while Huguenin thinks they have a vasomotor function.
CHAPTER VI.
REGION OF THE THIRD VENTRICLE.
From the primary cerebral vesicle is developed the 'tween
brain, called also interbrain, or thalamencephalon ; this includes
the third ventricle, pineal body or gland, optic thalami, optic
tracts, infundibulum and pituitary body, middle and posterior
commissures, posterior perforated spaces, corpora albicantia or
mammillaria, tuber cinereum, and lamina cinerea. This region
is between the secondary fore-brain (cerebral hemispheres and
contained ganglia) anteriorly and superiorly and the mid-brain,
consisting of the corpora quadrigemina and crura cerebri, pos-
teriorly and inferiorly. It is connected anterolaterally with the
cerebral hemispheres, and they rest upon its superior surface
with only pia mater intervening. Posteriorly it is connected with
the corpora quadrigemina.
THE THIRD VENTRICLE.
This ventricle is the remains of the primary cerebral vesicle.
It is a deep but narrow cavity, placed between the optic thalami
and extending to the base of the brain. Above it exists the
fornix and corpus callosum. It has for its roof the velum inter-
positum lined with epithelium, from which are suspended the
choroid plexuses for this ventricle. Its floor is composed of
the parts which exist in the interpeduncular space, which are,
from before backward, the lamina cinerea, tuber cinereum, in-
fundibulum, corpora albicantia, posterior perforated space,
and part of the tegmentum. Its lateral boundary is, in reality,
the surrounding central gray matter, although anatomists
generally state that this boundary is the optic thalamus. The
optic thalami lie very close to each other just anterior to
244
REGION OF THE THIRD VENTRICLE.
245
the middle part of the ventricle, and are connected by a trans-
verse bundle of fibers — the middle or soft commissure. This
commissure is the result of the union of the mesial surfaces of
the thalami, which occurs at about the fifth month of fetal life.
Fig. 124. — Horizontal Section through the Cfrf.krai. Hemispheres to Show the
Region of the Third Ventricle.
A.M.F. Anterior median fissure. A.M. Anterior horn of lateral ventricle. A P. F. Anterior
pillar of fornix. H.C.N. Head of caudate nucleus. A.C. Anterior commissure. M.C.
Middle or soft commissure. 3rd.V. Third ventricle. O.T. Optic thalamus. P.PG.
Peduncle of pineal gland. T.C.N. Tail of caudate nucleus. P.G. Pineal gland.
A.C.Q. Anterior corpora quadrigemina. P.C.Q. Posterior corpora quadrigemina. C.P.L.V.
Choroid plexus of lateral ventricle. F. Fornix. C.P.3rd.V. Choroid plexus of third ven-
tricle. P.H. Posterior horn. D.H. Descending horn. P. O.T. Pulvinar of optic thala-
mus. P.C. Posterior commissure. V.C.S. Vena corpora striati. C.C. Corpus callosum.
It is frequently absent, and is so soft that, unless great care be
used in removing or manipulating the brain, it will be torn.
The anterior part of the floor of the ventricle is separated from
its lateral walls by the prominent anterior pillars or columns of the
fornix, which are lined at this point by the central gray matter of
246 CENTRAL NERVOUS SYSTEM.
the ventricle. Just anterior to the fornix passes the anterior com-
missure ; between the anterior pillars of the fornix and the ven-
tral part of each optic thalamus exists an aperture which leads
into the lateral ventricle on each side. This is the foramen of
Monro, which is the only means of connection between the third
and lateral ventricles. The peduncles of the pineal gland run
along on each side of the superior part of the margin of the
lateral walls of the ventricle. This cavity is limited posteriorly
by the entrance or opening of the aqueduct of Sylvius, by the
posterior commissure, and by a reflection of epithelium from the
upper surface of the pineal gland upon the under surface of the
velum interpositum. The cavity of the ventricle is more shallow
behind than in front. The deep anterior portion of it passes to
a conic termination, which lies above the optic commissure,
called the optic recess ; behind this recess is another depression,
the infundibulum, which leads to the pituitary body or hypoph-
ysis cerebri. At the posterior extremity of the cavity, above
the entrance of the Sylvian aqueduct, is a depression which
extends backward to the stalk of the pineal gland, or conarium.
The third ventricle has four openings — viz., those of the foramen
of Monro, one on each side, communicating with the lateral
ventricles, the opening of the aqueduct of Sylvius, which com-
municates with the fourth ventricle, and that of the infundibulum.
This cavity is lined with ciliated epithelium, which fills in all its
inequalities, is reflected over the mesial surfaces of the optic
thalami and upon the velum interpositum and choroid plexuses.
The epithelium rests upon a thin layer of ependymal tissue, be-
neath which is the central gray matter, which is continuous with
that lining the aqueduct of Sylvius — a prolongation of the gray
matter of the fourth ventricle. It extends upon the mesial
surfaces of the optic thalami and rests posteriorly upon the
tegmentum. In front and below, it comes to the surface as the
posterior perforated space and tuber cinereum.
THE PINEAL GLAND, OR CONARIUM.
The pineal gland, also termed epiphysis cerebri, receives its
name because of its supposed resemblance to a fir-cone, the
REGION OF THE THIRD VENTRICLE. 247
Latin term pinus being the generic name for a class of the cone-
bearing trees. It is a small, reddish-gray body about the size
of a bean, but conic in form. It is dorsal to the posterior
commissure, with which it is connected, and lies a little ventral
to and between the superior or anterior corpora quadrigemina.
It is retained in place by a duplicature of pia mater from the
under surface of the velum interpositum. It is, according to
Schwalbe, twelve millimeters in its anteroposterior, eight in its
transverse, and four in its vertical diameter. It is connected
with the rest of the cerebrum by a broad, flat bundle of white
fibers, which bundle is separated by the pineal recess into a
dorsal, or superior, and ventral, or inferior, lamina. The upper
or dorsal lamina (pedunculus conarii) sends a bundle of fibers
to the right and left into each optic thalamus. This lamina is
also continuous on each side with the trigonum habenulae, and
its anterior portion continues forward as the peduncle of the
pineal gland, along the margin of the third ventricle, and passes
into the ganglion habenulae. The lower or ventral lamina
passes into the posterior commissure. These fibers are derived
probably from the optic tract, and pass into the opposite oculo-
motor nucleus. The pineal gland is covered by pia mater,
which sends into its interior a number of vascular connective-
tissue processes, which divide the gland into a number of
spheric or tubular spaces called follicles, which latter are lined
with epithelium similar to that, of the lymph-glands. These
follicles are filled with calcareous granules composed of the
phosphates and carbonates of the alkaline earths, which gran-
ules bear the name of the acervulus cerebri, or brain-sand.
The gland is a hollow outgrowth of the medullary wall of the
roof of the primary fore-brain vesicle, which latter afterward
forms the third ventricle. The gland becomes separated from the
ventricular cavity, after which numerous small processes bud out
from its inner walls and coalesce, forming its crypts. Cajal
has shown that nerve-fibers and cells are found in this gland.
These nerve-fibers belong to the sympathetic system, and ac-
company the large vessels into the gland ; they then leave the
vessels, pass between the ^follicles, and repeatedly branch and
unite with each other, forming an interstitial plexus ; they end
248 CENTRAL NERVOUS SYSTEM.
free in varicose-like arborizations or club-shaped thickenings.
The nerve-cells lie between the follicles ; they are small sphe-
roid or irregular-shaped cells, with two to four dendrites, which
vary as to length, some being rather short, while others are
moderately long. They terminate with thickened free extremi-
ties.
THE POSTERIOR COMMISSURE.
This is a fasciculus of medullated fibers, mostly transverse,
which overlies the entrance of the aqueduct of Sylvius into the
third ventricle. It is located in the posterior wall of the latter
cavity. The pineal gland is just above and slightly dorsal to
it. A part of the fibers of the ventral portion of this commis-
sure originate in the ganglia subthalami, deep in the inter-
brain on each side of the raphe. These fibers proceed dorsally
to reach the region just back of the corpora quadrigemina, where
they decussate with their fellows of the opposite side and
pass into the tegmental region of that side, close to the poste-
rior longitudinal bundle, possibly being associated with that
bundle. They then continue downward to the medulla. Dark-
schewitch asserts that the median fibers of this bundle pass into
the nucleus of the oculomotor nerve, and that the dorsal bundle
of the commissure passes into the corona radiata of the hemi-
sphere connecting it with the opposite superior corpus quadri-
geminum. According to Meynert, most of the fibers of this
commissure are continuations of the fibers of the fillet, which,
after decussating, pass through the optic thalamus into the
corona radiata of the opposite side.
THE OPTIC THALAMI.
These are two large, oblong masses, chiefly of gray matter,
appearing to be wedged in between the corpora striata and to
rest upon the crura cerebri. Their superior or dorsal surfaces
are covered by a thin mantle of white fibers — the stratum
zonale. They are developed from the lateral walls of the inter-
brain. On the outer side of each thalamus is the posterior limb
of the internal capsule. Their internal surfaces form, with the
REGION OF THE THIRD VENTRICLE. 249
central gray matter, the outer boundaries or walls of the third
ventricle. A small part of each thalamus assists in forming the
floor of the lateral ventricle. Above exists the fornix, separated
from the optic thalamus by the velum interpositum. Each optic
thalamus has four distinct surfaces — superior or dorsal, inferior
or ventral, internal or mesial, and external or lateral. The
superior surface is separated from the nucleus caudatus by a
groove, which contains the vena corpora striata and a fasciculus
of fibers — the taenia cornea or semicircularis, or the stria
terminalis. This surface is divided by a slight longitud-
inal depression corresponding to the thickness of the fornix,
which lies above it, called the sulcus choroideus, dividing it
into a mesial and a lateral portion. The lateral portion of this
depression is found in the floor of the body of the lateral ven-
tricle, and is covered with epithelium common to the lateral
ventricle. Anteriorly this portion grows into a distinct promi-
nence, called the anterior tubercle. The surface internal or
mesial to the sulcus is covered by the velum interpositum. It
is separated from the inner or mesial surface by the peduncles
of the pineal gland. At the posterior and inner part of this
area exists a large and important prominence — the pulvinar.
It overlaps the brachia of the corpora quadrigemina. Between
the pulvinar and the beginning of the peduncle of the pineal
gland on each side exists a depressed area of gray matter,
called the trigonum habenulce. Ventral to the trigonum exists
a small, club-shaped swelling — the ganglion habenula.
The internal or mesial surface of each thalamus is almost flat,
and forms the outer boundary of the third ventricle. It is cov-
ered by the ventricular epithelium, which rests upon a very thin
layer of ependyma, which gives to the surface a pale-gray color.
It is united with its fellow of the opposite side by the middle or soft
commissure. The external and lateral surface forms the inner
boundary of the posterior limb of the internal capsule. This limb
of the capsule separates the thalamus from the lenticular nucleus.
This area extends from the anterior extremity of the thalamus
backward to the pulvinar, and is called the lateral nucleus. Both
extremities are somewhat rounded ; the posterior extremity is
composed almost entirely of the prominence called the pulvinar,
250
CENTRAL NERVOUS SYSTEM.
which latter is made up principally of gray matter — and is con-
nected both with the optic tract and occipital lobe ; on the posterior
and inferior surfaces of the pulvinar exist two elevations of gray
matter — the internal and external geniculate bodies. The in-
ternal geniculate body is an oval elevation, located on the inferior
and inner side of the pulvinar between the brachia of the corpora
quadrigemina. Below and external to it, and continuous ante-
Fig. 125. — Section through the Superior Part of One of the Superior Corpora
Quadrigemina and the Adjacent Part of the Optic Thalamus. — (After Mey-
nert.) — (From Qaain's "Anatomy.")
s. Aqueduct of Sylvius, gr. Gray matter of the aqueduct, c.q.s. Quadrigeminal eminence,
consisting of: /. Stratum lemnisci. 0. Stratum opticum. c. Stratum cinereum. 77/.
Thalamus (pulvinar). c.g.i, c.g.t. Internal and external geniculate bodies, br.s, br.i.
Superior and inferior brachia. f. Upper fillet, p. I. Posterior longitudinal bundle, r.
Raphe. /TV. Third nerve ; n. Ill; its nucleus. I. p.p. Posterior perforated space, s.n.
Substantia nigra. Above this is the tegmentum with its nucleus, the latter being indicated
by the circular area. cr. Crusta. //. Optic tract. M. Medullary center of the hemi-
sphere, n.c. nucleus caudatus. st. Stria terminalis.
riorly with the optic tract, is a small, club-shaped body, about the
size of a bean, called the external or lateral geniculate body.
The internal geniculate body is covered with a layer of white
fibers, and contains a number of small, multipolar nerve-cells,
each from 20 to 25 fi in diameter, and is connected on each side
with the auditory tract.
The external or lateral geniculate body is of a yellowish-gray
REGION OF THE THIRD VENTRICLE. 251
color, — owing to the preponderance of gray matter, — contains
multipolar nerve-cells of from 30 to 40 u in diameter, possessing
many dendrites radiating from all parts of the cell-body. This
body receives fibers from the optic tract, axones from the multi-
polar cells of the retina.
Both these bodies are connected with the corpora quadrigem-
ina, the internal being connected with the posterior or inferior
Fig. 126. — Frontal Section through Basal Ganglia to show the Nuclei of the
Optic Thalamus. — (After von Monakow.) — (From Starr's "Atlas.")
B. Section at junction of middle and anterior two-thirds of the thalamus. OT. Optic thalamus.
lot. Lateral nucleus. med. Median nucleus. vent. Ventral nucleus. ta. Anterior
nucleus. Int. Cap. Internal capsule. LN. Lenticular nucleus. /. Lenticular loop.
corpus quadrigeminum and the external with the anterior or
superior corpus quadrigeminum.
The optic thalami have a double connection with all parts of
the cerebral cortex : first, by bundles of fibers from the different
nuclei of the thalami (von Monakow), called the projection fibers
of these bodies ; and, secondly, by axones from the pyramidal
cells of all parts of the cortex. In a general way, according to
von Monakow, the thalami are anatomically related with the cere-
2_S-
CENTRAL NERVOUS SYSTEM.
bral cortex, as follows : The anterior and mesial portions of the
thalami are in relation with the frontal lobes ; the lateral area or
ganglion with the parietal lobe ; the ventral ganglion with the
operculum ; the posterior ganglion, corpus geniculatum exter-
num, and pulvinar with the gyri of the occipital lobe ; the corpus
geniculatum internum and posterior ganglion with the temporal
lobe. This projection system of fibers passes through the in-
ternal capsule in bundles, which have been termed laminse
medullares, or peduncles of the optic thalamus. They divide
FlG. I27. — MlCROPHOTOGRAPH THROUGH OPTIC THALAMUS SHOWING BUSCH CELLS.
Go]gi method.
each thalamus, according to von Monakow, into the following: nu-
clei : the anterior or tuberculum anterius, the median, the lateral,
the ventral, the posterior, and the pulvinar. The geniculate
bodies and the ganglion habenulae are so closely associated with
the optic thalamus that they will be described with that body.
The anterior nucleus, or tuberculum anterius, is the promi-
nence on the anterior portion of the dorsal surface of the
thalamus, lateral to its sulcus choroideus. It is surrounded on
all sides by the white substance, and its free surface is covered
REGION OF THE THIRD VENTRICLE. 253
by the fibers called the stratum zonale. Some axones from the
cells of this nucleus pass downward to the base of the brain,
ending in the corpus albicans or mammillare, forming the
bundle of Vicq d'Azyr or fasciculus thalamomammillaris, thus
establishing a connection between the optic thalamus, the gyrus
hippocampus, uncinate gyrus, and cornu ammonis. The cells
of this latter region give origin to the fornix fibers, which end in
the corpus mammillare. Von Monakow found in several cases
where these regions were diseased an atrophy of the fimbria, of
the anterior pillar of the fornix, and of the corpus mammillare of
the same side.
The median nucleus is posterior and inferior to the anterior
nucleus. It has been divided by von Monakow into a median and
a lateral portion. It extends backward to the trigonum habenulse.
External to it is the lateral nucleus, while below and adjacent is
the ventral nucleus. It is connected with the island of Reil and
the second and third frontal gyri. The lateral nucleus occupies
the entire lateral surface of the thalamus, resting against the
internal capsule. It is the largest of the nuclei, and extends
from the anterior extremity of the thalamus posteriorly to the
pulvinar. It receives from the cerebral cortex numerous fibers,
which come from the region of the central convolutions.
The ventral nucleus is located beneath the median and lateral
nuclei, and occupies the entire Ventral surface of the thalamus.
It lies close to the lower portion of the internal capsule. Accord-
ing to von Monakow, the anterior portion of this nucleus is in
relation anatomically with the frontal lobe, the remainder being
in relation with the parts of the cerebral cortex about the fissure
of Sylvius — viz., the operculum, central gyri, and the supra-
marginal gyrus.
The posterior nucleus is located beneath the pulvinar and
between the geniculate bodies ; it is in anatomic relation
with that part of the cortex located between the occipital and
temporal lobes.
The pulvinar, which occupies the posterior portion of the
optic thalamus, has been described on page 249. It is in relation
with the optic tract and occipital lobe.
The nuclei of the optic thalamus contain three distinct forms
254 CENTRAL NERVOUS SYSTEM.
of nerve-cells: first, stellate, or " Strahlenzellen "; second, the
cells with brush-like processes (" Buschzellen " of Koelliker) ;
third, the polygonal cells, first described by Starr.
The first variety exists throughout the optic thalamus, but is
principally found in the lateral and median nuclei. They have
been called by Starr stellate, and are identical with the cells
described by Koelliker as the Strahlenzellen. They are spindle,
spheric, or triangular in shape, 35 to 50 (i in diameter, and
give off from four to ten dendrites, which, with their many
branching processes, radiate in all directions from the cell-body
— hence their name. A few of the dendrites are very long, but
the majority are short. They seldom possess granules, and
their branches do not form brushes of fibers. The axone comes
off from the cell-body and gives off a few collaterals. Its course
can be traced a short distance only. It is probable, however, as
suggested by Starr, that many of the axones from these cells
pass into the internal capsule.
The Buschzellen, or the cells whose dendritic processes are
arranged in brush-like expansions, were discovered by Koel-
liker. They are round, spindle, or triangular-shaped cells, from
25 to 40 u in diameter, with six to eight dendrites, each of
which repeatedly divides into a brush of very fine fibrils.
Koelliker has shown that in preparations after the Golgi method
the main stem of each dendrite is granular, and stains deep
black, while the brush of fine fibrils takes the stain less readily,
and is lighter in color. The axones of these cells resemble
those of the first variety. These cells are located in the dorsal
half of the optic thalamus, also in the corpus geniculatum lateralis
of each side and in the gray matter about the third ventricle.
The polygonal cells occur only — according to Starr, who dis-
covered them — in the ventral or anterior nucleus of the thalamus.
They are large cells, from 50 to 60 (i in diameter, polygonal in
shape, and give off from the cell-body a number of very long,
slender dendrites studded with gemmules. The course of the
dendrites is tortuous, but they do not possess as many branches
as do those from the stellate cells. The axone comes from the
body of the cell, gives off a few collaterals, and, according to
Starr, has no uniform direction.
Fig. 128. — Microphotograph through Optic Thalamus showing Stellate Cells
Method of Golgi.
»t*"-1 _.JC* / *'_
Fig. 129.— Microphotograph through Optic Thalamus with a Single Large
Polygonal Cell. Method of Berkley.
255
REGION OF THE THIRD VENTRICLE.
257
THE GANGLION HABENUL.-K.
This is a small swelling- on the anterior portion of the mesial
surface of the optic thalamus. It is united with its fellow of the
opposite side by a commissural band — the dorsal thalamic com-
missure. From the cells of this ganglion a few fibers pass
backward to the pineal gland (Starr). It receives fibers from
f/Ju* ft
I, in.
Fig. 130. — A Perpendicular Section through the Brain of a Rabbit Lateral to
the Corpus Mammii.lare. — [After Koelliker.)
CA. Cornu ammonis. Cf. Columna fornicis. Cp. Commissura posterior. Cqa, Ctjp. Corpora
quadrigemina. D Brc. Decussation of the superior cerebellar peduncles. Fl. Fornix.
FM. Fasciculus retronexus (Meynert). Ft. Fasciculus tegmenti. Fthm. Fasciculus
thalamomammillaris (Vicq d'Azyr). Gb. Basal ganglion. C/i. Ganglion habenula?.
GI. Lateral ganglion of corpus mammillare. Lm. Median lemniscus or fillet. Lo. Lobus
olfactorius. O. Optic tract. P. Pons. Pan. Pedunculis corporis mammillaris. Ps.
Psalterium. Sp. Septum pellucidum. St A'. Head of caudate nucleus. Strm. Stria
medullaris. Strm 1 . Connection of the same with the columna fornicis. Vm a. Anterior
medullary velum. V iv. Fourth ventricle. ///. Oculomotor nerve-roots. X . Radiation
of the fibers of the peduncle of the corpus mammillare.
the peduncles of that gland. The cells of this ganglion give
off axones which form a bundle of fibers — the fasciculus retro-
flexus, or Meynert's bundle.* This fasciculus of fibers passes
downward throueh the teo;mentum, between the red nucleus and
posterior longitudinal bundle, giving off, according to Meynert,
* After destruction of the ganglion habenulre, the fasciculus retroflexus of Meynert degenerates
to its termination in the interpeduncular ganglion.
•17
25S CENTRAL NERVOUS SYSTEM.
a few fibers to that nucleus ; then the main bundle bends nearly at
a right angle, and proceeds downward into the tegmentum of the
pons and medulla.* According to Forel, Gudden, and Edinger,
however, this bundle of fibers curves through the tegmentum,
between the red nucleus and posterior longitudinal bundle, and
ends, after decussating with its fellow, among a collection of
nerve-cells existing in the back part of the posterior perforated
space between the crura cerebri, called the interpeduncular
ganglion (Fig. 130).
CONNECTIONS OF THE OPTIC THALAMUS.
First, each thalamus has a double connection with all parts of
the cerebral cortex, both by axones from the cells of the various
nuclei of which it is composed (projection system of the thala-
mus) and by axones from the pyramidal cells of all parts of
the cerebral cortex. Second, it is connected with the primary
or first division of the optic tract by fibers (axones of the
ganglionic cell layer of the retina) which end about the cells of
the pulvinar and external geniculate body. Third, it has a
double connection with the occipital lobe by axones from the
cells of the pulvinar (optic radiation), which end about the
pyramidal cells of the cortex of the occipital lobe, and by axones
from the pyramidal cells of that lobe, which end about the cells
of the pulvinar. Fourth, the anterior nucleus of each thalamus
is connected with the corpus albicans by the fasciculus thalamo-
mammillaris, or bundle of Yicq d'Azyr, bringing this nucleus
into anatomic relation, through the fornix fibers, with the
hippocampal and uncinate gyri. Fifth, the fibers of the len-
ticular loop end chiefly in the optic thalamus, and connect the
lenticular nucleus (putamen chiefly) with the optic thalamus.
Sixth, the cells of the ganglion habenulae give rise to fibers
which form the fasciculus retronexus of Meynert. This con-
nects the thalamus with the interpeduncular ganglia. Seventh,
*It is very probable that the fibers of the fasciculus retrorlexus terminate in arborizations
about the cells existing in the interpeduncular ganglion, and that the descending part of the tract
which descends in the tegmentum to the pons and medulla is the axones from the interpedun-
cular ganglion cells.
REGION OF THE THIRD VENTRICLE. 259
von Monakow has shown that the chief part of the median fillet or
lemniscus (interolivary bundle from the nuclei of Goll and
Burdach) ends about the cells of the ventral and lateral nuclei
of the thalamus, and that axones from these latter cells pass
through the posterior part of the internal capsule and radiate
toward the parietal lobe, forming the cortical fillet or lemniscus.
Eighth, the thalamus is connected with fibers which originate
from the cells of the nucleus ruber and fibers from the superior
cerebellar peduncles ; this establishes a connection between
the optic thalamus and the opposite cerebellar hemisphere.
Ninth, each optic thalamus is connected with the caudate nucleus
by a fasciculus of fibers — the stria thalamica.
THE SUBTHALAMIC REGION, OR STRATUM
INTERMEDIUM.
This, is a region on each side located beneath the optic
thalamus, above the peduncles of the cerebrum, and internal to
the posterior portion of the internal capsule. This region con-
tains an intricate maze of nerve-fibers, — the zona incerta, — which
come from the lenticular nucleus, the internal capsule, and the
optic thalamus on their way to the ganglia located in this region,
which ganglia appear wedged in between the extreme posterior
limb of the internal capsule and the inferior portion of the
optic thalamus. These ganglia are the nucleus ruber, or teg-
mental nucleus ; the subthalamic nucleus, or Luys' body ; and the
substantia nigra, or locus niger. The red nucleus appears, on
transverse section, as a spheric shaped body located beneath
the inner portion of the optic thalamus, internal to Luys' body
and above and slightly internal to the substantia nigra. The
subthalamic nucleus, Luys' body, is a lenticular gray mass
resting above and a little internal to the crusta ; it is external to
the red nucleus and between the inferior border of the thalamus
and the substantia nigra. The substantia nigra is located just
above the cms cerebri, and continues into the peduncle of the
brain, there forming an intermediate stratum, which serves to
separate the peduncle into a ventral portion, or crusta, and a
dorsal portion, or tegmentum.
260 CENTRAL NERVOUS SYSTEM.
The nucleus hypothalamicus, subthalamicum, or Luys' body,
is of a dark brownish color, lenticular in form, and spindle-shaped
on transverse section. It is, according to Koelliker, 9 to 10 mm.
in its transverse, 3 to 5 mm. in its dorsoventral, diameter. It
is inclosed, save at its mesial surface, by a capsule of fine
medullated nerve-fibers, consisting of a ventral and a dorsal
lamina. The nucleus proper consists of fine medullated
nerve-fibers, having in their meshes a number of angular or
spindle-shaped cells containing much granular pigment and
possessing many protoplasmic processes. This body is very
rich in capillary blood-vessels. According to Stilling and
Koelliker, some of the fibers from the optic tract (perforating
fibers), after having passed through the crus cerebri, end among
the nerve-cells of this body. It is quite probable that these
fibers belong either to Gudden's or Meynert's commissure, and
are not an essential part of the optic tract. This statement
seems proved by an observation of von Monakow, in one of
whose cases there was complete degeneration of the entire
optic tract while Luys' body remained absolutely normal.
According to this observer, many of the axones from the cells
of Luys' body pass through the crus cerebri and enter the
corpus striatum, to end chiefly about the cells of the outer
division of the lenticular nucleus or putamen, thus establishing
a connection between this body and the lenticular nucleus. A
commissure exists between the subthalamic nuclei, or Luys'
bodies, consisting of nerve-fibers from two sources : First, fibers
which originate in the subthalamic nucleus of one side, which
probably pass, after decussating, into the subthalamic nucleus
of the opposite side ; second, a bundle of fibers, first described
by Forel, existing in the tegmentum, lateral to the red nucleus.
This bundle, according to Forel, consists of two fasciculi — a
ventral and a dorsal. The ventral fasciculus (bundle H 2 of
Forel) consists of fibers which probably originate in the corpus
mammillare of the same side and then course upward and along
the lateral border of Luys' body, into which some of the fibers
enter, while the majority pass through the crusta into the in-
ternal capsule. The fibers of the dorsal fasciculus (bundle H'
of Forel) pass into the basal part of the optic thalamus.
REGION OF THE THIRD VENTRICLE.
261
THE RED OR TEGMENTAL NUCLEUS OF STILLING.
This has received its name because of the reddish appear-
ance it presents in sections of fresh brain, this color being- due
to its great vascularity. On transverse section it appears
round, while in sagittal sections it has an elongated oval ap-
pearance. The root-fibers of the third nerves pass vertically
Fig. 131. — Section of Corpora Quadrigemina. Showing cells of red nucleus.
Cox-Golgi method.
through the inner portion of these nuclei, which are located
deep beneath and on each side of the aqueduct of Sylvius,
above the substantia nigra and below the inner portion of the
thalami. These nuclei are surrounded by a large number of
medullated nerve-fibers, which form for them a sort of mantle,
and come chiefly from the cerebellar peduncles. Each red
nucleus is seen to be composed microscopically of a very thick
tangle or plexus of nerve-fibers and collaterals, having inter-
262 CENTRAL NERVOUS SYSTEM.
spersed among them a number of triangular multipolar nerve-
cells, which often attain a very great size — 20 to 70 /j. in diam-
eter. In the sheep these cells are possessed of from two to six,
rarely more, very strong dendritic processes of great length.
They frequently fork, and are only slightly beaded, terminating
free or in a bulbous expansion. The axones usually come off
from the body of the cells, although occasionally they may be
seen to arise from the base of one of the primary dendritic
trunks. They give off a few collaterals, which pursue a course
dorsolateral}}' toward the dorsal tegmental decussation.
The Connections of the Red Nucleus. — First, with the
superior cerebellar peduncles. The experiments of Forel and
Gudden prove that a large number of fibers from the superior
cerebellar peduncle of one side end about the cells located in
the posterior portion of the nucleus ruber of the opposite side.
Forel made a section of the right superior cerebellar peduncle
of a rabbit, and found resulting, a complete atrophy of the fibers
of the peduncle beyond its decussation and a corresponding
atrophy of the posterior portion of the nucleus ruber. Gudden's
experiment differed from the above only in that he removed the
entire left cerebellar hemisphere. When the rabbit matured, a
complete atrophy was found of the left superior cerebellar
peduncle and posterior portion of the right nucleus ruber.
Mahaim has proved that the axones from the cells of the
middle and anterior portion of the nucleus ruber pass, after
decussating, into the opposite cerebellar peduncle, and thence
to the cerebellum. This nucleus, according to Cajal, receives
collaterals from the descending tegmental bundle, which bundle
is composed of axones from a group of multipolar cells located
in the lateral portion of the superior layer of the anterior corpus
quadrigeminum. They descend in curves, decussate in the
middle line, and form the dorsal or fountain-like decussation of
the tegmentum (Meynert). They then continue downward on
the inner side of the lateral fillet. A few collaterals and axones
from Gudden's commissure pass in and arborize about this
nucleus. It is connected also by fibers with the optic thalamus
and lenticular nucleus, the latter fibers passing through the
internal capsule.
REGION OF THE THIRD VENTRICLE. 263
THE SUBSTANTIA NIGRA (LOCUS NIGER; INTERCALLATUM
OF SPITZKA).
If a transverse section through the cerebral peduncles is made
at any point beyond the ventral border of the pons, a dark-gray
mass of increasing size, having an irregular crescentic outline,
will be seen. It is rather thicker on its inner than on its outer
border, and consists of fine nerve-fibers and numerous multi-
polar nerve-cells of a spindle shape containing granules of dark
pigment ; hence its name. This mass serves to divide each
peduncle into a ventral and a dorsal portion. The former, which
makes up about one-third of the bulk of each peduncle, receives
the name crusta ; the dorsal part, occupying the remaining two-
thirds, is called the tegmentum.
RETINA.
In order fully to appreciate the relation between the integral
parts of the retina and the optic paths, and the course taken by
light impressions, it will be needful to precede the description of
the optic nerves and tracts by a brief description of the histo-
logic formation of the retina. The retina is developed embryo-
logically from the ventral wall of the optic cup by a multipli-
cation of its cells. It is, therefore, an outward expansion or
growth of the wall of the primary forebrain. On vertical sec-
tion the retina consists, microscopically, according to Schultze,
of eight distinct layers, which are, from within outward, as
follows :
1. The layer of the optic nerve-fibers.
2. The layer of ganglionic nerve-cells.
3. The inner molecular layer.
4. The inner nuclear layer.
5. The outer molecular layer.
6. The outer nuclear layer.
7. The layer of rods and cones.
8. The pigment layer.
The retina is bounded on its inner side by a very delicate
membrane — the membrana limitans interna. A similar mem-
264
CENTRAL NERVOUS SYSTEM.
brane exists, lying between the outer nuclear layer and the layer
of rods and cones — the external limiting membrane.
1 . The Layer of Optic Nerve-fibers. — This layer consists of a
large number of nerve-fibers, mostly axones from the gangli-
onic cells of the layer above, and whose course is centripetal,
Outer or choroid surface.
.•& Layer of pigment cells.
7, Layer of rods and cones.
j .* Membrana limitans externa.
6. Outer nuclear layer.
5. Outer molecular layer.
.» 4. Inner nuclear layer.
nner molecular layer.
^ Layer of nerve- cells.
1 . Layer of nerve-fibers.
. . Membrana limitans interna.
Inner or vitreous surface.
Fig. 132. — Diagrammatic Section of the Human Retina. — (Schultze.) — (After Quain.)
forming a large part of the fibers of the optic nerve. Some of
the fibers of this layer course (centrifugally) through the gang-
lionic cell layer, and terminate either in the inner molecular
layer or in the fourth or inner nuclear layer, among the bipolar
cells.
2. The Layer of Ganglionic Cells. — The ganglionic cell layer
REGION OF THE THIRD VENTRICLE.
265
is located just external to the layer of optic nerve-fibers. It
consists, save in the region of the macula, of a single stratum
of multipolar nerve-cells. Each cell has a single axis-cylinder
process, or axone, whose course is central, and these axones,
with others, proceed inward to form most of the fibers of the
optic nerve. The peripheral process or dendrite becomes
branched, and terminates in the inner molecular layer, there
Rods and cones
Visual cells
Layer of gangli-
onic cells
Layer of optic
nerve-fibers
Fig. 133. — Section through the Retina of a Mammal to show Layer of Hori-
zontal Cells of the External Molecular Layer and the Spongioblasts of
the Internal Molecular Layer. — {After Ramon y Cajal.)
commingling with the central processes of the bipolar cells
of the inner nuclear layer.
3. The Inner Molecular Layer. — This layer consists chiefly
of the dendrites of the ganglionic cells of the second layer,
together with the arborizations of the central processes of the
bipolar cells of the inner nuclear layer. This layer contains, in
addition, a number of cells which resemble young neuroglia
cells (spongioblasts), but which, according to Ramon y Cajal,
are nerve-cells. Owing to the inability to find axis-cylinder
processes, he calls them amacrine cells.
4. The inner nuclear layer is made up mainly of round or
266 CENTRAL NERVOUS SYSTEM.
oval-shaped cells, each with two processes — a central and a per-
ipheral. The peripheral process or axone, which is exceedingly
fine, courses inward to the inner molecular layer, where it
terminates in an arborization about a dendritic process of a
ganglionic cell. The peripheral process or dendrite of these
bipolar cells is quite thick, and continues outward into the outer
molecular layer, where it breaks up into several fine branches,
producing an arborization which comes in contact with an
arborization from a central process or axone of a visual cell
existing in the outer nuclear layer.
5. The outer or external molecular layer is not nearly so thick
as the inner molecular layer, and consists almost entirely of the
arborizations of the axones of the visual cells of the outer
nuclear layer, together with the termination of the dendrites of
the bipolar cells of the inner nuclear layer and the horizontal
cells.*
6. The Outer Nuclear Layer. — This is the layer of visual
cells (Van Gehuchten). These cells are oval or round in shape,
and are bipolar. Their central processes or axones proceed
inward, and terminate, either in arborizations or in enlarged or
thickened extremities, in the outer molecular layer about the
dendrites of the bipolar cells of the inner nuclear layer. The
peripheral processes of these cells are the rods and cones of the
retina, which may be likened to the dendrites of other nerve-
cells. The axones of the visual cells whose dendrites form the
rods, end in slight thickenings or in clubbed extremities, while
the axones of the cells whose dendrites form the cones terminate
in arborizations.
7. The Layer of Rods and Cones. — The rods and cones are
the peripheral processes or dendrites of the visual cells ; they
are arranged in a palisade-like manner throughout the whole
extent of the retina, between the external limiting membrane
and the pigment layer. The rods are much more numerous
than the cones, and are cylindric in form. The cones are conic
* These horizontal cells, according to Van Gehuchten, are found in the external molecular
layer. Their protoplasmic processes (dendrites) are in relation with the axones of the visual
cells, while their axis-cylinders pass horizontally through the molecular layer to end in fine
ramifications about the axones of visual cells at variable distances.
REGION OF THE THIRD VENTRICLE.
267
in shape, and are shorter and broader than the rods. Both
the rods and cones are divisible into outer and inner segments.
In the case of the rods, this division is at about the middle of its
length, while in the cones it is at the junction of the tapering
point with the expanded part. The outer segments of the rods
are cylindric, and are transversely and longitudinally striated ;
they terminate in the pigment or outer layer. The outer seg-
ments of the rods are supposed to occasion the purplish-red
Layer of rods and cones.
External granular layer with
visual cells.
External molecular layer.
Internal granular layer of
bipolar cells.
Interna] molecular layer.
Layer of ganglionic cells.
Layer of optic nerve-fibers.
Fig. 134. — The Essential Elements in the Retina of a Dog. — {After run Gekuclttm.)
color of the retina. The outer segments of the cones are
spindle-shaped, and taper to a blunt point, which also ends in the
pigment layer ; they are only striated transversely. The inner
segments of both the rods and cones are continuous, through
the membrana limitans externa, with the peripheral processes of
the visual cells.
8. The Pigment Layer of the Retina. — This, the outer layer
of the retina, is composed of a single layer of hexagonal cells
268 CENTRAL NERVOUS SYSTEM.
separated by a distinct amount of intercellular substance. The
outer surface of these cells is slightly convex, and is in contact
with the inner layer of the choroid. Their inner surface rests
against the layer of rods and cones with which these cells come
in contact, either by sending out slight protoplasmic processes,
which pass between the rods and cones, or by contact with the
inner surface of their cell-body. Each of these cells possesses
an outer clear zone containing an unpigmented nucleus, and an
inner zone filled with dark pigment granules (Figs. 132, 133,
and 134).
ini.aetv, b, sup. brnch.
pulvinar \ I nf. brack.
eUp. mmd.b «
tania, semio.
ea:t.(fen.b. — j
inf. tju«.<£. b.
opt. tract
ant. pert: sp.
opt.fomwv.
opt. rune
Fig. 135. — The Origin and Relation of the Optic Tract. — (G. D. Thane.) —
[From Quain.")
The parts are viewed from below the mid-brain, having been divided transversely immediately
above the pons, and the pons, cerebellum, and medulla oblongata are removed.
THE COURSE OF THE OPTIC NERVES AND TRACTS.
The optic nerve is protected by a strong outer sheath of
dura mater, which is continuous with the sclerotic coat of the
eyeball. A process of pia mater closely invests the nerve
internally, and between the two exists the arachnoid membrane,
the outer surface of which is adherent to the dura. The space
between the arachnoid communicates with the general sub-
arachnoid space. The individual nerve-fibers of which the optic
nerve consists are not surrounded by a sheath of Schwann.
Each optic nerve contains an enormous number of nerve-
fibers (400,000 to 450,000 Salzer), which may ' be divisible
into centripetal and centrifugal tracts of fibers. The cen-
REGION OF THE THIRD VENTRICLE.
269
tripetal fibers oi the optic nerve are the central processes
or axones of the multipolar or ganglionic cells of the second
layer of the retina. The peripheral processes or dendrites
of these cells, as we have seen, arborize about the axones
ot the bipolar cells of the retina ; the dendrites of these
latter cells terminate about the axones of the visual cells, whose
peripheral processes are the rods and cones. There is thus
established a conducting medium through the retina continuous
o c>
Fig. 136. — Micro-photograph through Optic Thalamus of a Sheep.
from optic nerve terminating about stellate cells. Method of Berkl
Showing fibers
with the optic nerve ; each optic nerve then passes backward
and slightly inward through the optic foramen to the region
immediately in front of the tuber cinereum, where it unites with
its fellow to form the optic commissure or chiasm. The greater
part of the fibers of each nerve decussate with those of the
opposite side to join the opposite optic tract, but the remainder
continue backward in the lateral portion of the chiasm without
decussating, passing into the optic tract of the same side. The
2 7 o CENTRAL NERVOUS SYSTEM.
crossed fibers come from the cells of the nasal half of each
retina, while the uncrossed come from the cells of the temporal
half of each retina.
Each optic nerve contains a fasciculus of fibers which take
their origin from the region of the macula of the retina and
pass into the optic tract of the same and opposite sides. The
fibers of this fasciculus which pass into the optic tract of the
same side probably come from the temporal side of the macula,
while those that decussate and pass into the optic tract of the
opposite side doubtless come from the nasal side of the
macula. This bundle of fibers is triangular on transection, and
occupies, at first, the inferior portion of the optic nerve ; as the
nerve passes through the optic foramen, it becomes more cen-
trally located ; just before reaching the optic chiasm it occupies
the dorsomesial part of the nerve. In the optic tract it is again
centrally placed. Each optic tract, then, contains the fibers
from the nasal half of the retina of the opposite eye and from
the temporal half of the retina of the same eye. The optic
tract then continues backward under the cover of the temporal
lobe, passing around the crus cerebri, where it is separated by a
groove into two distinct fasciculi or bundles — a lateral or ex-
ternal, and a mesial or internal. The mesial or internal fascic-
ulus is not concerned with vision, but is connected with the
internal geniculate body and posterior corpus quadrigeminum,
Fig. 137. — Diagram of the Corpora Quadrigemina Anterior, CQA, showing
their Connections. — (Af/er M. A. Starr.)
On the right of the figure the superficial and deep masses of gray matter are shown, pidv.
Pulvinar of the optic thalamus, pn. Posterior nucleus of the optic thalamus lying between
the corpus geniculatum externum, cge, and the corpus geniculatum internum, cgi. I C.
Internal capsule. F. Fillet. K X. Red nucleus of tegmentum. FED. Peduncle of
cerebrum, sn. Substantia nigra. O T. Optic tract. -V. Optic chiasm. II. Optic nerve.
I, 2. Fibers from retina to pulvinar of optic thalamus (I, centripetal) (2, centrifugal).
7 and 8. Fibers between the optic thalamus and occipital cortex. 3 and 4. Fibers between
the retina and the corpus geniculatum externum. 9 and IO. Corresponding fibers to
occipital lobe. 5 and 6. Fibers between the retina and corpus quadrigeminum anterior. II
and 12. Corresponding fibers to the occipital cortex. 13. Cell of the superficial gray
matter of the C Q A sending fiber to the nucleus of the third nerve, 16. 14. Cell of the
deep gray matter of C Q A sending fiber to third nerve nucleus. 15. Cell of the deep gray
matter of C Q A sending fiber to fillet. 17. Fiber from the red nucleus terminating about
14. 18. Fiber from fillet terminating about 13. O L. Occipital lobe of the brain, with
its cortex, containing both cells and terminal brushes of the visual tract.
Fig. 137. — Diagram of the Corpora Quadrigemina Anterior.
REGION OF THE THIRD VENTRICLE. 273
and is a part of Gudden's commissure. The lateral bundle is
the true optic tract, and passes into the primary optic ganglia,
which are the external geniculate body, the pulvinar of the optic
thalamus, and the anterior or superior corpus quadrigeminum,
entering the latter by way of its arm or brachium. The fibers
of the optic tract terminate in fine end brushes about the nerve-
cells of the superficial and deep layers of the lateral or external
geniculate body.* In the optic thalamus they terminate chiefly
about the nerve-cells of the posterior portion (pulvinar). In the
anterior corpus quadrigeminum they form the superficial layer
of white fibers, terminating free or in brush-like expansions about
its nerve-cells. From the cells of the primary optic ganglia
new axones arise which issue from the outer side of the
thalamus and pass through the extreme posterior end of the
internal capsule ; they then curve backward around the posterior
horn of the lateral ventricle and radiate through the centrum
semiovale (optic radiation of Gratiolet) to the cortex of the
occipital lobe, ending chiefly in the cuneus and the parts ad-
jacent to the calcarine fissure.
The centrifugal fibers of the first division of the optic nerve
come from the cells of the primary optic ganglia and pass to
the retina. The centrifugal fibers for the second division of the
optic tract are the axones of the pyramidal cells of the occipital
cortex. They end about the cells of the primary optic ganglia.
There is thus established a continuous centrifugal fasciculus of
fibers for the optic tract from the occipital cortex to the retina
(von Monakow).
THE CONNECTIONS OF THE OPTIC TRACT.
Although the exact path of connection between this tract and
the nuclei of the motor nerves of the eye is not definitely known,
it is probable that it may be through the axone of the cells of
the anterior corpus quadrigeminum on each side, which, pro-
ceding downward, join the posterior longitudinal bundle, and
thus reach the region of the nuclei of the third, fourth, and sixth
* The external geniculate bodies receive exclusively the fibers coming from the macula
lutea.
18
274 CENTRAL NERVOUS SYSTEM.
nerves. According to Koelliker, the axones from these cells
pass directly or by their collaterals to the central gray matter
around the Sylvian aqueduct, and there arborize about the cells
of the third nerve nuclei. According to Darkschewitsch, a
bundle of fibers leaves the mesial portion of the optic tract,
pierces the thalamus, and reaches the oculomotor nucleus through
the ventral portion of the posterior commissure. This bundle,
he believes, may complete the reflex arc by which a connection
is made between the retina and the ventral portion of the
MMMMMMM'
mm
MmWSi&MmMm
. :•■ ~'iS&h :■';-'>.:.■>{ >&!".>?
111
CM
1
Fig. 138. — Horizontal Section through the Optic Chiasm of a Child. — {After
Koelliker. )
CM. Meynert's commissure. No. Optic nerve. Tr.o. Optic tract, v. Ventral concavity of
chiasm.
third nerve nucleus, which, according to Kahler and Pick, govern
the contraction of the pupil. The optic nerves are probably con-
nected through their primary ganglion, by means of the median
fillet or lemniscus, with the medulla oblongata and the spinal cord.
(See Fig. 137.)
THE OPTIC CHIASM.
This commissure is oblong in shape, its longest diameter being
from 10 to 12 mm.; it rests in the optic groove of the sphenoid
bone. On each side the anterior perforated space and internal
REGION OF THE THIRL) VENTRICLE.
275
carotid artery are located. A little above, and anteriorly, lies
the lamina cinerea ; posteriorly, is the tuber cinereum, with the
intundibulum. The middle portion of the chiasm is occupied by
fibers of the optic nerves, which decussate and pass to the oppo-
site sides. Its lateral portions are occupied by those fibers of
the optic nerves which do not decussate. Hie posterior portion
ot the chiasm is occupied by the so-called "inferior commissure
of Gudden." :|: This commissure consists of a bundle of fibers
tor each side, which bundle, after decussating, joins the optic
tract, forming- its mesial portion. It then passes to the internal
Fig. 139. — Frontal Section through the Interdrain. — [After Koelliker.)
Ch. Commissure of the hypothalamic nuclei. Fm, Fasciculus thalmomammillaris Vicq d' Azyr.
Th.o. Optic thalamus, dm. Stratum zonale of hypothalamic nuclei. J7 1 . Field I of
Forel. L>ul. Lateral medullary lamina of optic thalamus. C.i. Internal capsule. I, If
and ///. The three divisions of the lenticular nucleus. Tr.o. Optic tract. Pp. Pes
peduncli. // 2 . Field 2 of Forel. CL. Luys' body. Z.i. Zona incerta of Forel. Cm.
Corpus mammillaria.
geniculate body. According to some authors, it continues by way
of the posterior arm or brachium into the posterior corpus quad-
rigeminum. According to Obersteiner, part of this bundle
passes by way of the lenticular loop (ansa lenticularis) into the
lenticular nucleus, thus forming a crossed connection between
that nucleus and the internal geniculate body.
Gudden's commissure also contains a fasciculus of fibers
* Hannover believes that a fasciculus of fibers exists on each side which is located in the
most ventral part of the optic chiasm, and that they form a commissure whose function is to
associate both retina' together.
276 CENTRAL NERVOUS SYSTEM.
occupying its innermost part which join the outermost part of the
cms cerebri. These fibers probably come from the cortex of
the occipital and temporal lobes. This commissure was dis-
covered by Gudden, who enucleated the eyes in very young
animals and, as a result, found that while both optic nerves and
the primary optic ganglia were completely degenerated, the
internal geniculate bodies and a fasciculus of fibers occupying the
posterior portion of the chiasm, which showed no degenerative
changes, remained, and hence could have no connection with
vision.
Dorsal to Gudden's commissure is a fasciculus of fibers called
Meynert's commissure. It has no connection with the optic
tract, and is not concerned with vision. Its supposed origin is
from collections of spindle cells located on each side of the
tuber cinereum. These collections of cells form the basal optic
ganglia. The axones of the cells pass in curves into the cms
cerebri, and probably terminate about the cells of the subthalamic
or Luys' nucleus (Fig. 138).
THE PITUITARY BODY.
This gland, also called hypophysis cerebri, has been described
on page 323. It is divided into two portions or lobes : an ante-
terior or glandular portion, -which is the larger, partially sur-
rounding the posterior, which is called the infundibular lobe.
Between the two lobes is a closed canal, lined with epithelium.
The glandular portion is developed from the ectoderm of the
buccal cavity. The posterior or infundibular lobe is continuous
with the infundibulum, and, like that body, is developed as an
outgrowth from the floor of the third ventricle. According to
Berkley, who has made an exhaustive study of the anatomy of
this gland, the anterior portion contains nerves which belong to
the sympathetic system only. Some are fine varicose fibers,
with numerous ramifications coming off from the main stem at
right or slightly obtuse angles. Others follow the course of
the arteries, and give off from the main stem branches which
course irregularly through the gland substance, crossing over or
accompanying the large venous channels in the septa, to be
REGION OF THE THIRD VENTRICLE.
277
distributed upon the coils of the epithelial cells of the follicles,
there terminating in clubbed extremities. No nerve-cells are
found in the anterior portion of the gland. In the infundibular
or posterior lobe of this gland are three distinct parts : First,
an outer lamina of ependymal cells, arranged in several layers,
which are separated by delicate connective-tissue trabecular
from the surrounding capsule. Secondly, an
inner layer of epithelial cells of a secretory type,
often arranged into distinct acini, which latter
are separated by connective-tissue bands carry-
ing blood-vessels. The acini occasionally coal-
esce, forming small cavities, which sometimes
contain colloid material. Thirdly, a central re-
gion containing small round and polygonal cells
separated by connective tissue, together with a
few spindle or pear-shaped cells. The nerve-
cells are found only in the ventral portion of the
posterior lobe. They are divided into cells pos-
sessing one neuraxone (of which there are two
forms — a large and a small oval or pyramidal)
and a second form — those which possess two or
more neuraxones. The large pyramidal cells
of the first class possess many strong branching
dendrites, which terminate in beautiful feathery
tufts. The axones give off, close to the cell-
bodies, a few collaterals, and terminate by
breaking up into a number of fine branches,
some of which are lost about other nerve-cells,
while others end in networks among the epi-
thelial cells along the border of the lobe.
The small pyramidal cells differ from those
just described, in that they possess dendrites,
all of which, save one, are short and have hair-like processes on
the main stem close to the cell-body, and terminate free in
clubbed extremities. The cells of the second group are chiefly
flask-shaped, and are widely distributed. They each possess
from three to four dendrites, which grow gradually finer and
terminate free. These cells possess from two to four very fine
Fig. 140. — Sagittal
Section of the
Pituitary Body
and infundibu-
lum with Adjoin-
ing Part of
Third Ventricle.
— (Schwnlbe, from
Quain.)
a. Anterior lobe. a'.
A projection from it
toward the front of
the infundibulum.
b. Posterior lobe
connected by a stalk
with the infundibu-
lum, i. I.e. Lamina
cinerea. 0. Right
optic nerve. eh.
Section of optic
chiasm, r.o. Recess
of ventricle above
the chiasma. an.
Corpus mammillare.
2 7 8
CENTRAL NERVOUS SYSTEM.
axis-cylinders, which apparently terminate about similar cells.
In addition, there are several forms of cells found in various
parts of the gland, such as small flask-shaped and pyramidal
cells found in the central part of the gland, small spheric cells
possessing dendritic processes which cover a large space, and
Fig. 141. — Examples of Some of the Various Forms of Pyramidal Cells Found
in the Ventral Part of the Posterior Lobe of the Pituitary Body. — (After
Berkley. )
5 and 6. Irregularly pyramidal or oval cells with numerous dendrites terminating in feathery
arborizations and a single neuraxone. II. Pyramidal cell with very long apical dendrite.
12. Pyramidal cell with dendrites terminating in feathery tufts.
spheric cells whose processes end in tufts of fine filaments.
Most of the axones from these various cells course upward
toward the infundibulum, but Berkley was unable to follow any
of the fibers into that body (Figs. 140 and 141).
REGION OF THE THIRD VENTRICLE. 279
THE TUBER CINEREUM.
The tuber cinereum is an elevation of gray matter between
the corpora mammillaria behind, and the optic commissure
in front, to which it is attached. It is continuous anteriorly with
the lamina cinerea. From its middle portion extends down-
ward and slightly forward a conic process, — the infundibulum, —
which is connected with the posterior lobe of the pituitary body.
The tuber and infundibulum correspond to a recess in the middle
portion of the third ventricle.
THE INFUNDIBULUM.
Berkley has shown that the infundibular walls are very rich in
neuroglia elements. These cells consist of two chief varieties :
Elongate or slightly pyramidal forms, which begin just beneath
the ventricular surface and extend almost through the wall to
near its outer margin ; they break up into a few fine branches,
which are occasionally clubbed. The second type is a large
spheric neuroglia cell with processes radiating from all parts of
the cell-body. This form is found throughout the infundibular
wall, but is more abundant on its inner portion. The nerve-cells
are all multipolar, mostly pyramidal in shape, and possses one
or more neuraxones, which are sparse in comparison with the
neuroglia elements.
CHAPTER VII.
THE MEMBRANES OF THE BRAIN.
The membranes that surround the brain are three in number :
(i) An external fibrous membrane — the dura mater; (2) an in-
ternal vascular membrane — the pia mater ; (3) a very delicate
membrane situated between the pia and dura — the arachnoid
membrane.
DURA MATER.
The cerebral dura mater is a tough, rather thick, inelastic
membrane, possessing a rough external or periosteal surface,
and a smooth, glistening, internal surface lined with flattened
endothelium. The fibrous tissue of which the dura mater is
composed consists of two layers or laminse, an outer and an inner,
which are inseparable for the greater part of their extent ; but in
certain localities they separate, forming channels which consti-
tute the venous sinuses. These channels are lined with endo-
thelium continuous with that of the inner coats of the veins.
The external or outer surface of the dura forms the periosteum
(endocranium) of the internal surface of the skull. In the adult
the dura is rather loosely attached to the bones of the cranial
vault, save along the line of the sutures, where it is intimately
adherent by many small fibrous processes and blood-vessels
which penetrate the bones. It is also firmly attached at the base
of the skull, and gives off tubular, fibrous prolongations which
blend with areolar sheaths of the cranial nerves as they pass
through the various basal foramina, forming for these nerves
tough, fibrous envelopes, which are continuous with the peri-
cranium. On the outer side of each cavernous sinus the Gas-
serian ganglion is located, in a space between the dural laminae,
called the cavum Meckelii. The dura is closely adherent around
280
THE MEMBRANES OF THE BRAIN.
the margin of the foramen magnum, and becomes continuous
through this foramen with the dura mater surrounding the
spinal cord.
PROCESSES OF THE CEREBRAL DURA MATER.
The dura mater sends the following processes into the
interior of the skull : the falx cerebri, the tentorium cerebelli,
and the falx cerebelli.
The falx cerebri, or processus falciformis major, is a
strong, curved process of dura mater, sickle-like in shape, which
is located in the great longitudinal fissure, the convexity being
above, the concavity below. Its narrow anterior part is attached
to the crista galli of the ethmoid bone ; its broad posterior part
is connected with the middle of the upper surface of the ten-
torium cerebelli, along which line of attachment the straight
sinus runs. Its convex superior surface has a rather broad
attachment along the middle line of the under surface of the
frontal, parietal, and occipital bones as far back as the internal
occipital protuberance. Between the laminae of this process
exists a large venous space — the superior longitudinal sinus.
Its inferior concave surface is free, and lodges the inferior
longitudinal sinus ; behind, it approaches the corpus callosum.
The Tentorium Cerebelli. — The tentorium cerebelli is a
transverse arched process of the dura mater located between
the inferior surface of the occipital lobes and the superior
surface of the cerebellum, which latter surface it covers. The
occipital lobes are supported by it, being thus prevented
from exerting pressure on the cerebellum. The tentorium is
decidedly convex along its median portion, forming a ridge to
which is attached the posterior border of the falx cerebelli.
This process gradually inclines downward in all directions
toward its circumference, following the form of the superior
surface of the cerebellum, and forming over it a roof-like
structure. The convex posterior border of the tentorium is
attached to the transverse ridges of the inner surface of the
occipital bone, and here separates to form the lateral sinuses.
In front it is united to the superior borders of the petrous por-
282 CENTRAL NERVOUS SYSTEM.
tions of the temporal bones, inclosing the superior petrosal
sinuses. At the apex of the petrous portion of the temporal
bone the external and internal borders meet, forming two
processes, which cross each other, the former passing inward to
the posterior, the latter forward to the anterior, clinoid pro-
cesses. The free internal border is concave, and bounds a
Fig. 142. — Medisection of Brain, showing Important Sinuses.
Falx cerebri. 2, 2. Its convex border, with the great longitudinal sinus. 3. Its concave
border. 4, 4. Inferior longitudinal sinus. 5. Base of falx cerebri. 6. Straight sinus.
7. Apex of falx cerebri. 8. Right half of the tentorium, seen from below. 9. Right
lateral sinus. 10. Superior petrosal sinus. 11. Inferior petrosal sinus. 12. Posterior
occipital sinus. 13. Falx cerebelli. 14. Optic nerve. 15. Motor oculi. 16. Pathetic.
17. Trigeminus. 18. Abducens. 19. Facial and auditory nerves. 20. Glossopharyngeal,
pneumogastric, and spinal accessory nerves. 21. Hypoglossal nerve. 22. First cervical
nerve. 23. Second cervical nerve. 24,24. Upper extremity of ligamentum denticulatum.
triangular opening, within which are found the corpora quadri-
gemina and the crura cerebri.
The Falx Cerebelli, or Processus Falciformis Minor —
This somewhat triangular-shaped process of dura mater ex-
tends downward, between the cerebellar hemispheres in the
posterior incised cerebellar notch, from the middle of the pos-
THE MEMBRANES OF THE BRAIN. 283
terior border of the tentorium cerebelli, to which it is attached.
Its posterior margin is united to the internal occipital crest, and
as it approaches the foramen magnum it often divides into two
small folds, which are lost on the sides of this foramen.
At the base of the skull the dura gives off a shelf-like process
which forms a roof for the pituitary fossa and has a central
opening through which passes the infundibulum. This process
is called the diaphragma sellse.
The dura mater is composed of white fibrous and elastic
tissue, arranged in bundles, which cross each other rather
obliquely, save in the falx and tentorium, where they have a
radial arrangement. The inner surface of the dura is lined with
flattened endothelium, as are the parts of the outer surface not
attached to the bones. The dura mater is traversed by a system
of connective-tissue spaces which are located between the bun-
dles of connective tissue. These spaces are in reality lymphatic
canals, and communicate with the subdural space. Within them
exist large, flattened, connective-tissue cells. They can be in-
jected by inserting a cannula directly into the membrane, when
the injected material will escape into the subdural space. This
fact is very important from a surgical point of view, because it
readily explains how micro-organisms gain entrance through the
dura and infect the meninges, producing abscess or extensive
leptomeningitis. In the dura, on each side of the superior
longitudinal sinus, exist small diverticula or venous spaces
(lacunae venosae laterales), in which the middle meningeal veins
frequently terminate ; these spaces communicate both with the
diploic veins and the longitudinal sinus.
The arteries which supply the dura mater are derived chiefly
from the anterior, middle, and posterior meningeal. These
vessels are very abundant, and, in general, course between the
dura and the internal table of the skull, where they subdivide
into a large number of small twigs, which penetrate the
internal table of the skull, conveying nourishment to the bones.
These so-called meningeal arteries are mainly distributed to
the bones of the skull, the only one of the meninges which they
supply being the dura mater, hence this term meningeal is
somewhat misleading.
284 CENTRAL NERVOUS SYSTEM.
The arteries of the dura mater are accompanied by veins
which receive blood from the dura and the cranial bones ; after
anastomosing with the diploic veins they empty into the various
sinuses, with the exception of the veins which accompany the
middle meningeal arteries, which leave the skull through the
foramen spinosum to reach the internal maxillary vein.
The nerve supply of the dura is mainly by filaments from the
fourth, the fifth, and twelfth cranial nerves, and from the sym-
pathetic.
THE ARACHNOID MEMBRANE.
The arachnoid is an exceedingly thin membrane, made up of
delicate bundles of fibrous tissue, and is covered both onits inner
and outer surface with endothelium. It is located between the
pia and dura mater, being separated from the former by the
subarachnoid space and from the latter by the subdural space.
This membrane passes over the various convolutions and
fissures of the cerebrum and cerebellum without dipping into
the fissures, with the exception of those that contain processes
of dura mater. It also forms tubular sheaths, which accompany
the nerve-fibers through their foramina. This membrane is
easily demonstrated by simply injecting air beneath it by means
of a small blow-pipe. Between the arachnoid and the pia exists
a loose connective tissue, the subarachnoid tissue, which consists
of numerous fibrous bands or trabeculae lined by endothelium,
which pass from the under surface of the arachnoid to the pia
mater, the meshes between the trabeculae forming spaces which
differ as to size ; these spaces in the subarachnoid tissue con-
tain a large part of the cerebrospinal fluid, and are called sub-
arachnoid spaces. It may be mentioned, however, that over
some parts of the convexity and sides of the hemispheres
the subarachnoid space is partially or completely obliterated,
owing to the fusion of the arachnoid and pia, they being insepar-
ably blended. Over the posterior two-thirds of the base there is
a broad separation or space left between these two membranes,
which interval forms the very large subarachnoid space. The
arachnoid has but a limited blood supply, and, so far as I am
aware, no nerve supply, although nerve filaments have been
THE MEMBRANES OF THE BRAIN. 285
found in the arachnoid of ruminants by Volkmann, Bochdalek,
and Luschka. These come, according to Bochdalek, from the
motor division of the trigeminus, from the facial, and from the
spinal accessory nerves.
SUBARACHNOID SPACES.
Over the convexity of the cerebral convolutions only a slight
separation exists between the arachnoid and the pia mater ;
hence the arachnoid space is very shallow ; but over the base,
especially the posterior two-thirds, a wide separation exists
between these two membranes, so that very large spaces exist
in the exceedingly loose meshwork of the subarachnoid tissue,
which contain most of the cerebrospinal fluid. These spaces
are continuous in front and behind with the subarachnoid
spaces of the spinal cord. Two large subarachnoid spaces
exist at the base of the brain : the subarachnoid space of the
cerebellum and medulla oblongata (the " cisterna magna cere-
bellomedullaris ") and the basal subarachnoid space.
The former, the space of the cerebellum and medulla, is
situated between the dorsal surface of the medulla and the
inferior surface of the cerebellum. It is separated in front from
the cavity of the fourth ventricle by a process of pia mater, — the
tela choroidea inferior, — which forms the roof of the lower part
of this ventricle ; above, it passes over the inferior surface of the
vermis, extending laterally over the amygdalar lobes. This
space is continuous below with the posterior arachnoid space of
the spinal cord. It is in communication with the cavity of the
fourth ventricle by an opening in the middle of the tela choroidea
inferior, called the foramen of Magendie. Laterally, this space
communicates with the cavity of the ventricle by two openings in
the pia at the extremities of the lateral recesses, which are called
the foramina of Key and Retzius.
The basal subarachnoid space extends in front of the medulla,
pons, interpeduncular space, and crura cerebri, as far forward
as the optic chiasm, and laterally to the margins of the temporal
lobes. This large space is continuous with the anterior sub-
arachnoid space of the cord, and, above, communicates with
286
CENTRAL NERVOUS SYSTEM.
several small spaces — one in front of the optic chiasm, one in
each fossa Sylvii, and a space over the corpus callosum ; pos-
teriorly, it is continuous with the space of the cerebellum and
medulla.
The cerebrospinal fluid which occupies the subarachnoid
space is continuous with that within the cerebral ventricles
Fig. 143. — Section of the Posterior and Lower Parts of the Brain Within the
Skui.l to Exhibit the Subarachnoid Space and Its Relation to the Ventricles.
— [After Key and Rrf-Jus. ) [From Quain. )
I, I/. Atlas vertebra. 2. Odontoid process of the axis. 2', 3. Third ventricle. 4. Fourth
ventricle. C.C. Corpus callosum. C. Gyrus fornicatus. C. Cerebellum. /.Tentorium.
p. Pituitary body. c.c. Central canal of the cord. /M, in the cerebellomedullary part
of the subarachnoid space, is close to the foramen of Magendie, by which that space com-
municates with the fourth ventricle.
through openings in the pia mater of the medulla oblongata
(foramina of Magendie, Key, and Retzius). It is also continu-
ous with the fluid in the perineural and perivascular spaces.
The cerebrospinal fluid forms a perfect water-bed, which pro-
tects and supports all that part of the base of the cerebrum,
except the orbital part of the frontal lobes and the basal surface
of the apices of the temporal lobes, which rest on membranes
covering bone. This fluid also forms a bed for the pons, cere-
bellum, and medulla (Fig. 143).
THE MEMBRANES OF THE BRAIN.
287
THE PACCHIONIAN GLANDS, OR THE ARACHNOID VILLI.
These glandular-like bodies are collections of whitish oranula-
tions of variable size which begin to appear about the seventh
year of lite, and continue to grow as age advances. They are
found in the following situations: (1) Along the superior longi-
tudinal sinus, where they perforate the dura and become lodged
into irregular pits or depressions in the calvarium ; (2) pro-
jecting from the inner surface of the dura into the superior
longitudinal sinus; (3) along the margin of the fissure of
Sylvius ; (4) on the surface of the pia near the
hemisphere.
margin 01
the
SUBARACHNOID SPACE
Superior longitudinal sinus
PA CCHIOXIA N BOD Y
— — CORPUS CALLOSUM
F10. 141. — Coronal Section Through the Great Longitudinal Fissure, Showing
the Meninges. — (Key and Retzins.)
The Pacchionian bodies are not glandular in structure.
Luschka has shown that they are the arachnoid villi, which have
enlarged and in their growth have passed through small openings
existing in the inner layer of the dura, which openings commu-
nicate with large venous spaces in that membrane on each side
of the longitudinal fissure. In their growth outward they
invaginate the outer layer of the dura, and by pressure cause
the absorption of bone which produces the irregular pits in the
calvarium in which they are lodged.
These bodies consist of a spongy network of connective
2SS CENTRAL NERVOUS SYSTEM.
tissue, similar to and continuous with the subarachnoid tissue.
They are covered by the outer layer of the dura and the arach-
noid, and may serve for the outflow of lymph from the subdural
and subarachnoid spaces into the sinuses of the dura mater,
especially the superior longitudinal sinus (Fig. 144).
THE PIA MATER.
The pia mater of the brain is a very vascular membrane
applied to the entire cortical surface of the cerebrum and cere-
bellum, and dips down into their various fissures and sulci. It
sends a reduplication or fold into the ventricles of the brain,
which forms the velum interpositum and choroid plexuses.
Great numbers of small vessels which penetrate the cortex of
the brain are given off from the inner surface of the pia mater.
At the base of the brain the pia is much thickened, and invests
the crura cerebri, pons, and medulla, and gives off to the central
ganglia a number of long straight vessels which perforate the
brain substance, forming the anterior and posterior perforated
spaces. The pia mater consists of rich plexuses of blood-vessels,
derived from the internal carotid and vertebral arteries, which
are supported by delicate fibrous connective tissue, which tissue
surrounds the blood-vessels and gives off tubular prolongations
to the vessels which pass into the brain substance, forming for
them loose perivascular sheaths, the spaces of which are con-
tinuous with the subarachnoid spaces.
The nerves distributed to the pia accompany the blood-vessels
and are derived from the third, fifth, sixth, facial, glossopharyn-
geal, pneumogastric, spinal accessory, and sympathetic.
THE VELUM INTERPOSITUM AND CHOROID PLEXUSES.
The velum interpositum, or tela choroidea superior, is a dupli-
cature or fold of pia mater, triangular in shape, which has
extended into the ventricles of the brain after passing through
the transverse fissure of Bichat. This fold, the velum interposi-
tum, consists of two lamellae, a dorsal and a ventral, between
which exists subarachnoid tissue. It lies beneath the fornix and
THE MEMBRANES OF THE BRAIN.
289
splenium of the corpus callosum, its dorsal lamella being united
with the ventral surface of these bodies, and above the optic
thalami and corpora quadrigemina, its ventral lamella uniting
with the optic thalami.
It overlies the body of the third ventricle, forming for it a
membranous roof, and extends over each optic thalamus as far
as the oblique grooves on its superior surface. The posterior
part or base of this triangular fold of pia mater is continuous
with the pia mater covering the inferior surface of the occipital
lobes and the superior surface of the cerebellum. The apex of
the fold is bifid, each division terminating just dorsal to the ante-
Fig. 145. — Vertical Section of the Cortex Cerebri and Its Membranes. X -Yz-
— {After Landois and Stirling.)
co. Cortex cerebri, p. Intima pke dipping into the sulci, a. Arachnoid, connected with p
by means of the loose subarachnoid trabecule in the subarachnoid space, sa. v, v. Blood-
vessels, d. Dura, sd. Subdural space.
rior pillar of the fornix. Its lateral margin consists of a convo-
luted mass of highly vascular processes — the choroid plexuses
of the lateral ventricles. These processes on each side pass
through the choroid fissure into the descending horn of the
lateral ventricles to their extremities, and they gradually con-
verge anteriorly, and between the foramina oi Monro they
become continuous with each other. From this junction of the
choroid plexuses of the lateral ventricles two small plexuses
pass backward along the middle of the under surface of the
velum interpositum, and descend into the cavity of the third
ventricle to form the choroid plexus of that ventricle. The
2go
CENTRAL NERVOUS SYSTEM.
choroid plexuses of both the lateral and third ventricles are
covered by the ventricular epithelium, as is that part of the
velum interpositum which covers the third ventricle.
The choroid plexus is made up of small processes of pia
Fig. 146. — View of the Upper Surface of the Velum Interpositum, Choroid
Plexuses, and Corpora Striata. — {From Sappey, after Vicqd'Azyr.)
. Fore-part of the tela choroidea or velum interpositum. 2, 2. Choroid plexus. 3, 3. Left
vein of Galen partly covered by the right. 4. Anterior pillars of the fornix divided in
front of the foramen of Monro ; on either side are seen small veins from the front of the
corpus callosum and the septum lucidum. 5. Vein of the corpus striatum. 6. Convoluted
marginal vein of the choroid plexus. 7. Vein rising from the thalamus opticus and corpus
striatum. 8. Vein proceeding from the inferior cornu and hippocampus major. 9. One
from the posterior cornu. 11. Fornix divided near its middle and turned backward.
12. Lyra. 13. Posterior pillar of the fornix. 14. The splenium of the corpus callosum.
mater, which consist principally of the ramifications of great
numbers of small blood-vessels arranged in the form of glom-
eruli and held together by a delicate connective-tissue stroma,
producing a villous-like appearance. These processes are cov-
THE MEMBRANES OF THE BRAIN. 291
ered by cubic epithelial cells, which in the new born are ciliated;
they usually contain a yellowish pigment or minute droplets of
fat. The choroid plexuses are supplied by the anterior and poste-
rior choroid arteries. The choroid veins return the blood from
these plexuses, and at the foramen of Monro join the veins of
the corpora striati, to form the veins of Galen (Fig. 146).
THE TELA CHOROIDEA INFERIOR AND CHOROID PLEXUSES
OF THE FOURTH VENTRICLE.
The tela choroidea inferior is a process of pia mater analogous
to the velum interpositum. It consists of two lamellae separated
by subarachnoid tissue, within which courses the posterior infe-
rior cerebellar artery. The ventral lamella is prolonged from
the medulla oblongata, and overlies the lower half of the fourth
ventricle, forming, with the inferior medullary velum, a roof for
that part of this ventricle. This portion of the ventral lamella
is somewhat triangular in shape, its base being reflected over
the inferior margin of the velum medullare inferioris, and its
apex extending just below the obex. The dorsal lamella is
reflected upon the inferior vermis and the amygdala of the cere-
bellum, where it becomes continuous with the pia mater. Both
lamellae are covered by epithelium.
CHOROID PLEXUSES OF THE FOURTH VENTRICLE.
From the inferior surface of the ventral lamella projects a
series of small, vascular, villous tufts, covered by the epithelium
lining the roof of the ventricle ; these are the choroid plexuses
of the fourth ventricle. They consist of a middle and a lateral
set for each side, which are continuous with each other in front,
and are called the middle and lateral choroid plexuses. The
middle set is located on each side of the middle line of the
ventral or inferior lamella, extending from the foramen of
Magendie forward to the margin of the inferior medullary velum,
over which margin the ventral lamella is reflected. Here the
292 CENTRAL NERVOUS SYSTEM.
two sets unite in the form of a letter T, the vertical part cor-
responding to the middle sets, while the horizontal part cor-
responds to the lateral sets. The lateral set of each side
continues along the margin of the inferior medullary velum into
the lateral recesses of the ventricle, terminating at the lateral
openings in the pia mater.
CHAPTER VIII.
FORE-BRAIN OR PROSENCEPHALON.
The cerebrum is the largest part of the encephalon. It rests
in front, in the anterior and middle fossa of the skull. It is
supported behind by the tentorium cerebelli, which serves to
separate it from the cerebellum. In man it forms about three-
fifths of the entire encephalon. Its upper surface is ovoid and
convex, narrow in front and broad behind. Its anteroposterior
diameter is about eighteen cm. (seven inches), and its great-
est transverse diameter, which corresponds to the parietal
protuberances, is about thirteen cm. (five inches). Its under
surface is somewhat irregular. In front the frontal lobe is seen
resting in the anterior fossa, the temporal lobe occupying the
middle fossa, and the occipital lobe resting upon the tentorium
cerebelli. The cerebrum is divided into two hemispheres, right
and left, by a deep cleft the longitudinal fissure. This great
fissure extends to the base of the brain in front and behind, but
is bridged at its middle by a broad band of fibers running
transversely, — the corpus callosum, which is the great commis-
sure of the cerebrum. This commissure forms a sort of floor
for the superior division of this fissure, and lodges a long pro-
cess of dura mater — the falx cerebri. Each hemisphere is con-
vex on its outer surface, to rest against the concavity of the
cranial vault. It is narrowed anteriorly, broadened posteriorly,
and presents a flattened median surface, which forms the outer
boundary or side of the great longitudinal fissure. The cere-
brum is composed of both gray and white matter, the former
entirely surrounding the latter. The surface of the gray invest-
ing matter presents various infoldings or depressions and ele-
vations of different size. The elevations bear the name of gyri
or convolutions ; the depressions, of fissures or sulci. The
293
294 CENTRAL NERVOUS SYSTEM.
effect of the fissures and convolutions is to increase enormously
the surface extent of gray matter, — the extent of surface in the
fissures being double that of the convexity of the gyri, — upon
the amount of which gray matter the higher intellectual attri-
butes depend. As we descend in the scale of animal life, the
convolutions become more simple and flattened, the fissures
less deep and the cerebrum is greatly reduced in size.
4
FISSURES.
The fissures serve to divide the cerebrum into its lobes, and
form its important anatomic landmarks. They are divided into
the primary or interlobar fissures, and the secondary or intralobar
fissures. The former are of great depth (twenty-five mm. —
almost an inch ; exceptionally, an inch or more), are constant, and,
with slight variation have a uniform size, location, and direction.
They are as follows : The great longitudinal fissure, subdivided
into a superior and an inferior portion ; the transverse or fissure
of Bichat; the fissure of Sylvius; the fissure of Rolando; the
parieto-occipital ; the inter- or intraparietal ; the callosomargi-
nal ; the calcarine ; and the collateral.
The secondary fissures — often called sulci for the sake of dis-
tinction — are short and shallow, and do not present the typical
marks as given above. They are numerous and complicated,
and present many variations. The important ones will be men-
tioned in describing the lobes.
THE FISSURES OF THE EXTERNAL SURFACE OF EACH
HEMISPHERE.
The longitudinal fissure separates the cerebrum into its
hemispheres, completely dividing the anterior portion of the
frontal lobe and the entire occipital lobe, the middle portion of
the fissure being interrupted by the bridge of cross fibers — the
corpus callosum.
The transverse fissure, in form like the letter U, separates
the cerebrum above from the cerebellum below. This fissure is
continuous on each side with the choroid fissure, which is
m
G "t '
Fig. 147. — Photograph of the Superior Surface of the Cerebrum.
A.M.F. Anterior median fissure (longitudinal). Mar. Gyr. Marginal gyrus. S.F.C. Superior
frontal gyrus. S.F.Fis. Superior frontal fissure. M.F.G. Middle frontal gyrus. Pre.
Sul. Precentral sulcus. I.F.Fis. Inferior frontal fissure. Asc.F.G. Ascending frontal
gyrus. Intra. P.Fis. Intraparietal fissure. Supra. M.G. Supramarginal gyrus. S.P.C.
Superior parietal convolution. Ang. G. Angular gyrus. M.O.G. Middle occipital
gyrus. I.O.G. Inferior occipital gyrus. S.O.G. Superior occipital gyrus. Fxt. P.O.F.
External parieto-occipital fissure. R. Cerebellar H. Right cerebellar hemisphere. S.
Vermis. Superior vermis. P.I.N. Posterior incised cerebellar notch. L. Cerebellar II.
Left cerebellar hemisphere. I.F.G. Inferior frontal gyms.
295
FORE-BRAIN OR PROSENCEPHALON.
297
really a prolongation of the transverse fissure. The choroid
fissure is due to an infolding of the median surface of the
hemisphere wall, producing an arch-like groove between the
tornix and the optic thalamus. It is closed by an invagina-
Fig. 148. — Photograph of the External Surface of the Brain.
I.F.S. Inferior frontal sulcus or fissure. I.F.G. Inferior frontal gyrus. M.F.G. Middle
frontal gyrus. S.F.S. Superior frontal sulcus. S.F.G. Superior frontal gyrus. Pr.S.
Precentral sulcus. Acs.F. Ascending frontal gyrus. R.F. Rolandic fissure. Asc.P.
Ascending parietal convolution. Intra. P. F. Intraparietal fissure. S.P.G. Superior parie-
tal gyrus. Intra.P.F.H. (Horizontal limb) Intraparietal fissure. S.M.G. Supramar-
ginal gyrus. Ang.G. Angular gyrus. E.P.O. External parieto-occipital fissure. S.O.S.
Superior occipital sulcus. S.O.C. Superior occipital convolution. M.O.C. Middle occi-
pital convolution. I.O.S. Inferior occipital sulcus. I.O.C, Inferior occipital convolution.
I.T.C. Inferior temporal convolution. M.T.S. Middle temporal sulcus. Par.F. Parallel
fissure. C. Cerebellum. M.T.S. Middle temporal sulcus. M.T.C. Middle temporal
convolution. I.T.C. Inferior temporal convolution. S.T.C. Superior temporal convolu-
tion. T.P.G. Temporoparietal annectant gyri. T.T.G. Transverse temporal gyrus.
P.L.S. Posterior limiting sulcus. G.L.I. Gyrus longus insula. G.B.I. Gyrus brevis
insula. S.C.I. Sulcus centralis insuke.
tion of a process of pia mater (the choroid plexus) covered
with ventricular epithelium. In order to expose this fissure,
this process of pia mater must be rather forcibly removed,
when a curved fissure will be seen on each side, extending" from
29S CENTRAL NERVOUS SYSTEM.
the beoinninof of the descending- horn of the lateral ventricle to
the corresponding foramen of Monro. These fissures together
form the great transverse fissure, which emerges between the
corpora quadrigemina and the inferior surface of the occipital
lobes above and the superior surface of the cerebellum below.
The fissure of Sylvius is the largest of the primary fissures,
and the first one to be developed, appearing at about the third
month of fetal life. It is in reality not a mere cleft, as are
most of the other external fissures, but it is formed by the
folding together of the hemisphere into an arch, the concavity
being downward near the brain-stem. The wide space thus
formed is termed the fossa or vallecula Sylvii. This fossa
may be recognized in the human embryo as early as the fifth
week. At the sixth fetal month this fossa diminishes in size
and takes on a triangular form. This is due to the rapid
growth of the frontal, parietal, and temporal lobes, their margins
coming in contact with one another and overlapping the fossa
to form opercula, or lids. The island of Reil is developed from
the bottom of the original fossa, and is covered by the above-
mentioned opercula, thus narrowing the fossa into the fissure of
Sylvius. This fissure starts at the base of the brain, a little
lateral to the anterior perforated space.* It passes outward
and forward and reaches the external surface of the cerebrum,
where it turns upward and backward, dividing into two limbs : a
short anterior limb, which passes vertically upward into the lower
frontal convolution, where it ends ; and a long or horizontal limb,
which passes backward and gradually upward to end in the
division of the parietal lobe, called the supramarginal gyrus.
It is common for this fissure to bifurcate at its termination.
Deep in this fissure, hidden by the overlapping of the lower
frontal and parietal lobes and the point of the temporal lobe,
are a few small convolutions or gyri, called the island of Reil.
This overlapping of the lobules is called the operculum, or cover.
The Sylvian fissure separates the frontal and parietal lobes
above from the temporal below.
*The anterior limb of the Sylvian fissure often gives oft a short horizontal branch, which
passes into the lower frontal gyrus, where it terminates.
FORE-BRAIN OR PROSENCEPHALON. 299
The fissure of Rolando, or central fissure, is one of the
most important anatomic landmarks on the external surface of
the hemisphere. It is always present in man and the higher
mammalia, develops toward the close of the fifth month of fetal
life, and appears as two distinct primitive grooves, separated by
a slightly elevated portion, which later becomes hollowed out,
thus bringing about the junction of the two primitive fissures to
form the fissure of Rolando. The Rolandic fissure is of great
depth, — often an inch or more, — and is located near the middle
of the hemisphere. It usually starts as a distinct notch on the
median surface of the hemisphere in the paracentral lobule.
Thence it takes an oblique course downward and slightly for-
ward, and most often terminates just above and close to the
horizontal limb of the Sylvian fissure ; occasionally, however, it
communicates with the latter fissure. The slope of this fissure
makes an angle of about sixty-seven degrees with the superior
margin of the hemisphere. It lies between two important con-
volutions, which have an ascending direction, — hence their name,
ascending gyri, — and forms the boundary between the frontal
lobe in front and the parietal lobe behind. The anterior
ascending gyrus, which forms the anterior boundary of this
fissure, is called the ascending frontal gyrus ; the posterior one,
the ascending parietal gyrus. These two gyri together, be-
cause of their position midway between the frontal and
parietal lobes, have received the name of the central gyri or
convolutions.
Theparieto-occipital fissure (occipital of Wilder), developed
at the fourth fetal month, is best marked on the median surface
of the hemisphere ; it is, however, seen on the outer surface as
a deep and oftentimes wide notch, which separates the parietal
lobe in front and the occipital behind. The external or outer
portion of this cleft, which is called the external parieto-occipital
fissure, forms an anatomic landmark second only in importance
to the fissure of Rolando. The main portion of this fissure is
to be found on the median surface of the hemisphere, where it
is seen as a deep cleft passing obliquely downward and forward
to unite with a fissure — the calcarine — soon to be described. This
union produces a large Y-shaped junction, which incloses a very
3 oo CENTRAL NERVOUS SYSTEM.
important little wedge-shaped gyrus, the cuneus, which is the
half-vision center.
The intra- or interparietal fissure serves to separate the
parietal lobes into a superior and an inferior division. It develops
at the sixth month of fetal life as two distinct sulci, one parallel
to the fissure of Rolando, the other having a longitudinal course
close to the margin of the hemisphere ; they unite at the eighth
or ninth month, producing a continuous fissure. This fissure
starts near the horizontal limb of the Sylvian fissure, runs verti-
cally upward, parallel to the Rolandic fissure, giving off a slight
vertical sulcus, which continues upward. This is the so-called
postcentral sulcus. The intraparietal fissure then makes an
abrupt curve upward and backward, to terminate beyond the
external parieto-occipital fissure. It is separated from the latter
fissure by the superior occipital gyrus, and often joins the ante-
rior occipital fissure. On its vertical course it forms the posterior
boundary of the ascending parietal gyrus, and gives off the above-
mentioned ascending branch just before it passes backward,
called the postcentral sulcus. This fissure occasionally extends
into the Sylvian.
The calcarine fissure, which unites with the median branch
of the parieto-occipital fissure, branches in a T-shape from the
posterior extremity of the occipital lobe, which is its point of
origin. From this point it extends forward on the median sur-
face, and unites with the parieto-occipital fissure, making with
that fissure an acute angle, then passing forward and slightly
downward, to terminate near the middle of the median surface
of the temporal lobe. Its anterior portion, which is a deep
cleft, produces in the posterior horn of the lateral ventricle a
prominence known as the hippocampus minor, or calcar avis.
The collateral fissure is seen on the median surface of
the temporal lobe ; it is below the calcarine and runs parallel
with it. It passes forward to near the commencement of the
Sylvian fissure and ends in the tip of the temporal lobe. Be-
tween this fissure and the calcarine exists the lingual or middle
occipitotemporal gyrus. The middle portion of this fissure pro-
duces a projection in the lateral ventricle called the eminentia
collate ralis.
Fig. 149. — Photograph of the Median Surface of the Brain.
M.G. Marginal gyrus. C.M.F. Callosonaarginal fissure. Forn.G. Gyrus fornicatus. 1'ara.
S. Paracentral sulcus. Para. Paracentral lobule. R.F. Kolanclic fissure. Quad.L.
Quadrale lobe. I.P.O.F. Internal parieto-occipital fis,sure. C. Cuneus. C.A.F. Ante-
rior calcarine fissure. L.L. Lingual lobule or gyrus. Col.F. Collateral fissure. C.P.F.
Posterior calcarine fissure. I.T.G. Inferior temporal gyrus. S.C.C. Splenium corpus
callosum. For. Fornix. C.C. Corpus callosum. R.C.C. Rostrum of corpus callosum.
G.C.C. Genu of corpus callosum.
Fig. 150. — Vertical Section Through Frontal Lobe.
FORE-BRAIN OR PROSENCEPHALON. 303
The callosomarginal is a very long and somewhat tortu-
ous fissure, located on the median surface of the hemisphere,
and becomes developed at about the middle of the fifth month
of fetal life. It begins in front, below the rostrum of the corpus
callosum, near the anterior perforated space, passes upward,
outward, and forward, pursuing a course parallel to the corpus
callosum, then, turning backward, ends near the margin of
the hemisphere, a little back of the fissure of Rolando.* It
separates the marginal convolution above from the gyrus forni-
catus below, and forms the anterior boundary of the quadrate
lobe (Figs. 147, 148, and 149).
THE CONVOLUTIONS, GYRI, OR LOBULES.
The fissures — the Sylvian, Rolandic, and external parieto-
occipital — are the great anatomic landmarks which serve to
separate the external surface of the cerebral hemisphere into
five lobes — viz., the frontal, parietal, temporosphenoid, occipi-
tal, and the central lobe, or island of Reil.
THE FRONTAL LOBE.
The frontal lobe in man constitutes about one-third of the
whole cerebral hemisphere. It presents on transverse section
the outline of a spheric triangle. That portion which rests on
the orbital plate of the frontal bone is termed the orbital lobe.
The entire frontal lobe is bounded posteriorly by the fissure of
Rolando, which separates it from the parietal lobe. Its inferior
boundary is the Sylvian fissure. Above, it forms part of the
margin of the longitudinal fissure. Its external surface, which
is convex, presents several convolutions or gyri, separated by
sulci or secondary fissures. The three following gyri have a
general direction from before upward and backward : The first
or superior frontal gyrus, the longest of the three, runs parallel
with the margin of the hemisphere of which it is a part, and is
* In many brains a fissure is prolonged backward from the main one through the quadrate
obe, terminating near the internal parieto-occipital fissure.
304 CENTRAL NERVOUS SYSTEM.
continuous with the marginal gyrus on the median surface, the
latter being only the mesial surface of the first frontal gyrus.
In front it reaches the apex of the frontal lobe ; behind, it is
often continuous with the ascending frontal gyrus, or it may be
separated from the latter by the superior portion of the pre-
central sulcus. From the gyrus below it is separated by the
superior frontal sulcus, a long, shallow fissure, running forward
and downward. The middle or second frontal gyrus is much
shorter but broader than its fellow above, runs from below up-
ward and backward, and at its upper part is often made con-
tinuous with the ascending frontal convolution by a small annec-
tant gyrus. The inferior part of the dorsal portion of this
lobule is prevented from coming into contact with the ascending
frontal by a vertical sulcus, which arises just above the fissure
of Sylvius and runs parallel to the fissure of Rolando. This is
the precenlral sulcus above referred to. It is deeper than most
of the sulci, and sometimes becomes continuous with the calloso-
marginal fissure (Schwalbe). It forms the anterior boundary of
the ascending frontal or central gyrus, separating it from the
second and third frontal gyri. This sulcus often presents an
anterior limb, which is continuous with the inferior frontal fissure.
The main sulcus, usually continuous, is, however, often sepa-
rated into two or three divisions by small annectant gyri, which
serve to connect the frontal gyri with the anterior central or
ascending frontal gyrus. In the posterior part of the middle
frontal gyrus of the left side exists the center in which are
stored the muscular memories used in writing ; hence, when
destroyed agraphia occurs. The third or inferior frontal
gyrus is the smallest of the three. It passes from the inferior
portion of the ascending frontal anteriorly to the end of the
frontal lobe. It forms the anterior operculum, which, together
with the superior and inferior opercula, forms a roof for the island
of Reil. It curves around both limbs of the Sylvian fissure, which
produces indentations on the gyrus, and thus divides it into
three parts. According to Broca, this gyrus is more developed
in man on the left side, because of the fact that in its posterior
area exists the motor speech center. It is separated from the
second frontal gyrus by the inferior frontal sulcus, which starts
FORE-BRAIN OR PROSENCEPHALON.
30S
from about the middle of the precentral sulcus and passes for-
ward to the frontal lobe, where it bifurcates. It is continuous
below with the orbital lobe.
A very important part of the frontal lobe lies between the
precentral fissure and the fissure of Rolando. This is the
before-mentioned ascending frontal gyrus, also called the anterior
central convolution. It begins below at the Sylvian fissure, where
it is connected with the ascending parietal gyrus, passes upward,
and unites on the median surface of the hemisphere with the
ascending parietal gyrus, the junction being termed the paracen-
tral lobule. Below, this convolution forms part of the superior
First occipital cu;ir
Second occipital conv.
Th ird occipital conv.
Fig. 151. — Diagrammatic Representation of the Lobes of the Cerebrum.
boundary of the fissure of Sylvius. It is connected with the
three frontal lobules by small annectant gyri. That part of the
frontal lobe anterior to the ascending frontal or anterior cen-
tral gyrus is often called the prefrontal region or lobe.
The inferior surface of the frontal lobe, which rests upon
the orbital plate of the frontal bone, is termed the orbital
lobe. It is slightly concave, and has the form of a triangle, the
base being directed anteriorly, the narrow portion or apex
pointing posteriorly. It has near its median surface a well-
marked sulcus or groove, which forms the lateral boundary of
the basal portion of the superior frontal gyrus, or, as it is called
3 o6 CENTRAL NERVOUS SYSTEM.
here, from its straight course, the gyrus rectus. In this groove
rests the olfactory bulb and tract, and hence it is also called
the olfactory sulcus. The margin of the lobe forms part of the
marginal gyrus of the median surface. The orbital lobe is
subdivided by the orbital or triradiate sulcus into three gyri.
This sulcus is irregularly H-shaped, and might almost be called
compound, being made up of a number of smaller sulci. Its
posterior part curves laterally around from the Sylvian fissure,
to end near the root of the olfactory tract. Three or four
sulci, running from before backward, communicate with this
branch. The divisions of the orbital lobe are the internal,
anterior, and posterior gyri, which are the basal portions re-
spectively of the superior, middle, and inferior frontal convolu-
tions (Fig. 157).
THE PARIETAL LOBE.
This lobe occupies a large extent of a cerebral hemisphere.
Its upper and outer surface is convex ; its median surface is flat,
forming part of the boundary of the superior longitudinal fissure,
and is termed the quadrate lobe. The parietal lobe is located
dorsal to the frontal, above the temporal, and ventral to the
occipital lobes. Its anterior boundary is the fissure of Rolando,
which separates it from the frontal lobe ; its posterior boundary
is the external parieto-occipital fissure, which is between it and
the occipital lobe. Its lower boundary is the horizontal limb of
the Sylvian fissure, which separates it from the temporosphenoid
lobe. The intraparietal fissure separates this lobe into three
convolutions — the ascending parietal and the superior and infe-
rior parietal.
The ascending parietal or posterior central gyrus is
between the fissure of Rolando in front and the ascending or
vertical division of the intraparietal fissure behind. It ascends
to the median surface, where it is continuous with the ascending
frontal, the union of the two forming the paracentral lobule. It
is separated from the superior parietal lobule by the postcentral
sulcus, which is only a continuation or a branch of the intra-
parietal fissure. Below, it is also continuous with the ascending
frontal or anterior central gyrus. This gyrus, with its fellow of
FORE-BRAIN OR PROSENCEPHALON.
307
the frontal lobe, forms two very important gyri, which, from their
central position, are termed the central convolutions (anterior
and posterior), and from their important relation to the oreat
motor tract they are termed the motor convolutions. From
this extensive area the fibers arise which form the motor tract,
Fig. 152. — Frontal Section through Parietal, Temporal, and Occipital Lobes,
Together with the Cerebellum.
P. O. F. Parietooccipital fissure. P. L. Parietal lobe. S. T. G. Superior temporal gyrus.
C. Cuneus. C. F. Calcarine fissure. T. T. G. Middle temporal gyrus. L. L. Lingual
lobule. I. T. G. Inferior temporal gyrus. C. D. Corpus dentatum. T. Tonsil. N.
Nodule.
and into this and the adjacent parietal area pass the fibers of the
sensory tracts.
The superior parietal convolution or lobule lies above
the horizontal division of the intraparietal fissure, along the
3 o8 CENTRAL NERVOUS SYSTEM.
margin of the hemisphere. It is dorsal to the upper part of the
ascending parietal gyrus, being separated from it by the post-
central sulcus. It extends backward to the occipital lobe, the
dividing-line being the external parieto-occipital fissure.
The inferior parietal convolution is below the superior,
being separated from it by the intraparietal fissure. It is con-
tinuous behind with the occipital lobe and in front with the lower
part of the ascending parietal. Below, it is separated from the
temporal lobe by the horizontal limb of the Sylvian fissure. It
is made up of the supramarginal, angular, and postparietal
convolutions, their principal direction being downward and
arching around the end of the Sylvian and first temporal fis-
sures. The supramarginal gyrus lies below and posterior to
the intraparietal fissure, and between the inferior part of the
ascending parietal lobule and the upper end of the horizontal
limb of the Sylvian fissure, which it encircles. It is continuous
behind with the angular and below with the first temporo-
sphenoid gyri. The angular gyrus is just back of the supra-
marginal, with which it is continuous. Above, it is bounded by
the intraparietal fissure ; below, by the first temporal or parallel
fissure, which it surrounds. It -is connected posteriorly with the
middle occipital gyrus by a small annectant convolution. The
angular gyrus of the left side is of considerable clinical and
physiologic interest, because in man it is the center for the
visual memories of written language, and in the lower animals
it is the center for the memories of objects seen. The post-
parietal gyrus is that part of the inferior parietal lobule which
surrounds the end of the second temporal fissure.
THE OCCIPITAL LOBE.
The occipital lobe is pyramidal in shape, forms the posterior
extremity of the hemisphere, rests upon the tentorium cerebelli,
is situated behind the parietal lobe, and above and behind the
temporosphenoid. It is connected with these two latter by
small annectant gyri. It is separated in front from the parietal
lobe by the external parieto-occipital fissure ; below, it is con-
FORE-BRAIN OR PROSENCEPHALON. 309
nected with the posterior part of the temporosphenoid lobe.
Its median surface forms the posterior margin of the superior
longitudinal fissure, and it is separated in front from the quad-
rate lobe by the internal parieto-occipital fissure, and behind
from the temporal lobe by the calcarine fissure. The occipital
lobe is subdivided into three smaller convolutions or gyri by
two constant sulci — the anterior superior or vertical occipital
sulcus, and the lateral or inferior occipital sulcus. The former
begins near the end of the lateral sulcus, from which it is
separated by the inferior parietal annectant gyrus. It passes
upward and forward, and ends just back of the external parieto-
occipital fissure. Occasionally this fissure is joined by the pos-
terior limb of the intraparietal fissure. Frequently, it becomes
continuous with the end of the horizontal part of the intra-
parietal fissure. This sulcus separates the first or superior
occipital convolution from the second. The lateral or inferior
occipital sulcus runs obliquely upward and backward, where it
branches Y-shaped, one branch passing to the extreme end of
the occipital lobe ; the other passes downward toward the cal-
carine fissirre, where it ceases. This sulcus separates the second
from the third occipital convolution.
The Occipital Convolutions. — The first or superior occip-
ital gyrus is superior and mesial to the anterior occipital
sulcus. Its general direction is from below upward. It brings
the occipital lobe into relation with the parietal by means of
the first annectant gyrus. The second or middle occipital is
beneath the superior gyrus and between the anterior and in-
ferior occipital sulci. It is much broader than the one above,
and is somewhat quadrangular in outline. It is connected with
the angular gyrus by the second annectant convolution, and
with the middle temporal by the third annectant convolution.
The third or inferior occipital convolution is situated below and
behind the middle, from which it is separated by the inferior
occipital sulcus. It forms the extreme posterior and inferior
portion of the occipital lobe. It is connected with the lower
temporosphenoid convolution by the fourth annectant gyrus.
310 CENTRAL NERVOUS SYSTEM.
THE INSULA, OR ISLAND OF REEL.
Deep in the Sylvian fissure, on the side of the cerebrum and
near its base, is a group of small convolutions which were in
embryonic life a part of the cortex, but now appear subcortical,
being entirely concealed from view by the margins of the Sylvian
fissure — the operculum. This small group of convolutions is
called the insula, or island of Reil, because of its being isolated
from the rest of the cerebral cortex, it being covered over by
the opercula which are formed by the following parts — viz., the
posterior margin of the third frontal forming the anterior
operculum ; the lower margin of the central convolutions, the
superior operculum ; and the apex of the temporosphenoid lobe,
the inferior operculum. In a general way, when the operculum
is referred to, the superior operculum is meant.
The gyri which compose the insula can only be seen when
the margins of the Sylvian fissure are spread apart or cut
away. They originate in the Sylvian fossa, a little outside of
the anterior perforated space, and appear as a triangular area of
gray matter, the base of which is upward and the apex down-
ward and inward. The apex is distinctly elevated, and separates
the fossa from the fissura Sylvii. This area is separated from the
opercula by a fissure, — the sulcus limitans insulae, — and is beset
with several small, shallow sulci, which radiate fan-shaped from
the apex to the base. One is deeper than the rest, and serves to
subdivide this region into two divisions — a precentral and a post-
central lobule. This is the central sulcus, or sulcus centralis
insulae, which has a direction much like the overlying fissure
of Rolando, and is developed at the same time. The insula
consists of a cluster of from five to seven small gyri — the gyri
operti ; their general direction is similar to the direction taken
by the small sulci — namely, upward and forward. The more
centrally located gyri have a vertical course. Within the fissure
of Sylvius, and posterior to the insula, exist two or three small
gyri which connect the superior temporal convolution with the
inferior parietal lobe ; these have been called the temporo-
parietal convolutions.
Fig. 153. — Photograph of the Superior Surface of the Cerebrum.
A.M.F. Anterior median fissure (longitudinal). Mar. Gyr. Marginal gyrus. S.F.G. Superior
frontal gyrus. S.F.Fis. Superior frontal fissure. M.F.G. Middle frontal gyrus. Pre.
Sul. Precentral sulcus. I.F.Fis. Inferior frontal fissure. Asc.F.G. Ascending frontal
gyrus. Intra. P.Fis. Intraparietal fissure. Supra. M.G. Supramarginal gyrus. S.P.C.
Superior parietal convolution. Ang. G. Angular gyrus. M.O.G. Middle occipital
gyrus. I.O.G. Inferior occipital gyrus. S.O.G. Superior occipital gyrus. Ext. P.O.F.
External parieto-occipital fissure. R. Cerebellar H. Right cerebellar hemisphere. S.
Vermis. Superior vermis. P.I.N. Posterior incised cerebellar notch. L. Cerebellar II.
Lett cerebellar hemisphere. I.F.G. Inferior frontal gyrus.
3 11
FORE-BRAIN OR PROSENCEPHALON.
ii-,
THE TEMPOROSPHENOID LOBE.
The temporosphenoid lobe is the portion of the cerebrum
which is located in the middle fossa of the skull. It lies at a
deeper level than either the frontal or occipital lobes, and is
more circumscribed. It is bounded above and in front by the
Sylvian fissure, which completely separates it from the irontal lobe
and partially from the anterior part of the parietal lobe, being
Fig. 154. — Longitudinal Section through Cerebral Hemisphere to Show the
Centrum Semiovale of the Frontal, Parietal, Occipital, and Temporal Lobes.
C. O. F. Centrum semiovale of the frontal lobe. C. 0. P. Centrum semiovale of the parietal
lobe. S. L. S. Superior limiting sulcus. C. O. O. Centrum semiovale of the occipital
lobe. C. O. T. Centrum semiovale of the temporal lobe. I. C. A. Internal carotid artery.
A. T. L. Anterior extremity of temporal lobe. F. S. Sylvian fissure. A. L. S. Anterior
limiting sulcus.
connected behind and above with the latter lobe. It blends
behind with the occipital lobe, being partially separated from
it by the inferior occipital fissure. The area in which both are
blended is called the occipitotemporal region. Its external
surface presents three gyri — the first or superior, the second
or middle, and the third or inferior temporal.
The first or superior convolution is between the horizontal
limb of the Sylvian fissure above, forming the inferior boundary
of the latter fissure, and the superior temporal sulcus below.
ji 4 CENTRAL NERVOUS SYSTEM.
This gyrus runs upward and backward, and is continuous behind
with the supramarginal and angular gyri. The superior temporal
sulcus — called also the parallel fissure, because of its position with
respect to the Sylvian fissure — runs from before backward, then
upward, and ends in the angular gyrus, which surrounds it.
This sulcus separates the first from the second temporal convo-
lution.
The second or middle temporal gyrus is between the second
and superior temporal sulci, passes from before backward and
upward, and is continuous with the lower part of the angular
and the middle occipital gyri. The second temporal sulcus runs
parallel to the one above, but is not so long or deep.
The third or inferior temporal convolution is below the middle
temporal sulcus, and is separated from the occipitotemporal
gyrus by the inferior occipital sulcus. It is connected with the
occipital lobe by an annectant gyrus.* The posterior portion
of the left superior and middle temporal gyri contains the
sensory receptive center for the auditory memories of spoken
language.
The median surface of the cerebral hemispheres presents six
lobes, separated by five main fissures. The lobes are the mar-
ginal, gyrus fornicatus or the convolution of the corpus callo-
sum, the quadrate or precuneus, the cuneate, lingual, uncinate, or
gyrus hippocampus. The fissures are the callosomarginal, the
internal parieto-occipital, the calcarine, collateral, dentate, or hip-
pocampal fissure. Besides the convolutions and fissures, the
median surface also presents the following structures : First,
the divided transverse fibers of the corpus callosum. The
anterior portion of this body is distinctly curved, and hence is
called the genu, or knee. The enlarged posterior part is called
the splenium, or pad. Between the two surfaces exists the
body. Below, and connected with the under surface at the pos-
terior extremity, exists the fornix, whose anterior part is sepa-
rated from the corpus callosum by a thin triangular blade of white
matter, — the septum lucidum, — which blends above with the
* A fourth temporal gyrus can be seen on the under surface of the temporal lobe, separated
from the gyrus above the third temporal by the third temporal sulcus ; below, this lobule is
bounded by the collateral fissure.
FORE-BRAIN OR PROSENCEPHALON.
3>5
anterior part of the corpus callosum and below with the fornix.
Beneath the fornix is situated the outer surface of one of the
central ganglia, called the optic thalamus. In the center of the
thalamus is a bundle of transverse fibers, which brings the optic
thalami into relation with each other. This transverse bundle
of fibers is known as the middle commissure. Ventral to the
fornix exists the anterior commissure.
CONVOLUTIONS OF THE MESIAL SURFACE.
The marginal gyrus or convolution is the median surface
of the frontal and central gyri. It forms a large part of the
Af^ r*v Paracentral kbulf
Fig. 155. — Convolutions of the Mesial Surface of the Cerebrum.
boundary of the longitudinal fissure, and is the most extensive
convolution of the median surface of the hemisphere. It is sepa-
rated from the underlying convolution — the gyrus fornicatus —
by the callosomarginal fissure, which also separates it from the
precuneus or quadrate lobe, which lobe forms really the poste-
rior marginal gyrus. In front of the upturned end of the
callosomarginal sulcus, anterior to the quadrate lobe or pre-
cuneus, exists the paracentral lobule, it being the junction on the
median surface of the hemisphere of the two central convolutions.
It presents on its upper surface a deep and distinct notch, the
316 CENTRAL NERVOUS SYSTEM.
beginning of the fissure of Rolando. This lobule is limited in
front by the paracentral sulcus, behind and below by the calloso-
marginal fissure. The marginal gyrus begins at the base of the
brain just in front of the anterior perforated space, takes a
course upward, forward, and then bends backward along the
margin of the longitudinal fissure, ending at the termination of
the callosomarginal fissure.
The gyrus fornicatus, or convolution of the corpus callosum,
also called gyrus cinguli, is archdike, and is situated between
the marginal gyrus above and the corpus callosum below. Pos-
teriorly, it is connected with the precuneus or quadrate lobe.
It is a very extensive convolution, beginning below at the base
of the brain, in the anterior perforated space. It then takes a
curve upward and backward around the genu of the corpus
callosum, forming a complete arch around that body. It then
passes backward and curves downward, becoming narrowed at
the isthmus of the gyrus fornicatus, and taking a direction for-
ward, ends near the tip of the inferior part of the median surface
of the temporal lobe.
The quadrate lobe, or precuneus, is somewhat square-
shaped, and situated along the margin of the hemisphere,
between the upturned end of the callosomarginal fissure in
front and the internal parieto-occipital fissure behind, which
latter fissure separates it from the cuneus. It is continuous
above with the superior parietal lobule, being in reality its
median surface; below, it is continuous with the gyrus fornicatus.
The cuneus is that very important little wedge-shaped or
triangular lobule whose apex is downward and forward, and
whose base broadens out along the margin of the hemisphere.
It is situated between the internal parieto-occipital fissure in
front and above and the calcarine below. When this region is
destroyed on either side, there occurs a paralysis of the opposite
halves of the visual fields ; hence it is the half-vision center,
each cuneus receiving visual impulses from the corresponding
half of each retina.
The lingual lobule, also called the median occipitotemporal
gyrus, is bounded above by the calcarine fissure, which separates
it from the cuneus, and below by the collateral or occipitotem-
FORE-BRAIN OR PROSENCEPHALON. 317
poral fissure, which separates it from the fourth temporal gyrus.
Anteriorly, it is continuous with the gyrus hippocampus.
The limbic or falciform lobe is bounded above by the
callosomarginal fissure, below by the anterior part of the col-
lateral fissure, and posteriorly by the postlimbic sulcus, which
is only a slight vertical branch of the callosomarginal fissure.
The fissures which serve to separate the limbic lobe are together
called the limbic fissure. This area includes the gyrus forni-
catus, the gyrus hippocampus, the dentate lobe, the septum
lucidum, fornix, the anterior commissure, the peduncles of the
corpus callosum, the nerves of Lancisi, or the strise longitu-
dinales, which form a rudimentary supracallosal gyrus, and a
Fig. 156. — Section through Left Gyrus Hippocampus. Showing .the formation of the
hippocampus major. Method of Weigert-Pal.
rudimentary gyrus beneath the corpus callosum, the gyrus infra-
callosus, or gyrus fornicis.
The slender extension of the gyrus fornicatus into the temporal
lobe has received the name of gyrus hippocampus, or subicu-
lum cornu ammonis. It embraces the lateral aspect of the crus
cerebri, and is separated above from the optic thalamus by the
dentate or hippocampal fissure, which fissure extends from the
splenium of the corpus callosum downward and forward to the
uncinate gyrus. It produces in the descending horn of the lateral
ventricle an elevation called the hippocampus major, or cornu
ammonis. Before reaching the tip of the temporal lobe the
hippocampal gyrus becomes considerably thickened, and then
3 i8 CENTRAL NERVOUS SYSTEM.
forms a recurved portion, which looks backward and inward,
and is continuous with the fimbria of the fornix and the dentate
gyrus. This recurved portion is called the uncinate gyrus, or
simply uncus. Posteriorly, the gyrus hippocampus is continuous
with the gyrus fornicatus and the lingual gyrus of the occipital
lobe.
The dentate gyrus, or fascia dentata, is a narrow convolu-
tion with a toothed or notched appearance, — hence its name, —
located between the fimbria and the gyrus hippocampus and
being overlapped by the former. It starts just above the
splenium of the corpus callosum, between it and the gyrus
fornicatus, by a curved lamina, — the fasciola cinerea, — which is
continuous with the lateral and mesial longitudinal striae. It
then extends forward and downward, and is separated from the
gyrus hippocampus ; it coalesces with the uncinate gyrus. The
fimbria is a narrow layer of white matter, belonging to the
cerebral hemisphere, alongside the dentate gyrus. It is con-
tinuous with the zone of horizontal fibers beneath the ependyma
of the cornu ammonis, called the alveus, from which it receives
an accession of fibers. It is continuous above with the posterior
pillar of the fornix, being in part formed of its fibers. The
fimbria overlaps the dentate gyrus, and presents on its mesial
portion a hooked prolongation continuous with the choroid
plexus. This gyrus is connected with the fornix and the gyrus
fornicis, or gyrus infracallosus.
The above-described parts of the median surface of the
cerebral hemisphere, which together constitute the limbic lobe,
are in man not well developed, but in some of the lower ani-
mals whose sense of smell is very acute (osmatics) they are
greatly developed, and have been termed, together with the
olfactory bulb, the rhinencephalon.
THE BASE OF THE CEREBRAL HEMISPHERES.
This region consists of the bases of the anterior, middle, and
posterior lobes. The anterior, which is the basal surface of the
frontal lobe, rests upon the convexity of the orbit. It is sepa-
rated from the middle or temporosphenoid lobe by the Sylvian
FORE-BRAIN OR PROSENCEPHALON. 319
fissure. The middle lobe is die basal surface of the temporo-
sphenoid, and rests in the middle fossa of the base of the
skull. The posterior is the basal surface of the occipital lobe,
and rests upon the tentorium cerebelli. The following ana-
tomic points are to be observed upon the base of the brain,
from before backward — viz., the longitudinal fissure, the orbital
lobe, the olfactory bulb and tract of each side, the corpus cal-
losum and its peduncles, the anterior perforated space of each
side, the Sylvian fissure, the optic chiasm, nerves and tracts on
each side, the lamina cinerea, the tuber cinereum, the infundib-
ulum, the pituitary body, the corpora albicantia, the posterior
perforated space, the third and fourth pair of cranial nerves,
and the crura cerebri.
The inferior longitudinal fissure divides the anterior por-
tion of the frontal lobe and the entire occipital lobe.
The olfactory bulb is, in man, a small, rather club-shaped
swelling of gray matter which, with the olfactory tract, lies on
the orbital surface of the frontal lobe and is lodged in the sulcus
olfactorius. The bulb presents on its under surface several
small, roundish elevations, which are the transversely divided
olfactory nerves which have come from the rod-shaped cells of
the olfactory mucous membrane of the upper nasal chamber
after having passed through the foramina in the cribriform plate
of the ethmoid bone. The olfactory bulb contains many nerve-
cells, about the dendrites of which these peripheral olfactory
nerve-fibers end.
The olfactory tract passes backward from the bulb and pre-
sents an inner or mesial and an outer or external root. The
triangular area seen between the diverging roots of the
olfactory tract is known as the trigonum olfactorium. The
base of this cortical area is backward toward the anterior per-
forated space, the apex forward toward the junction of the two
roots of the olfactory tract. Externally, it is continuous with
the orbital lobe.
The corpus callosum terminates at the base of the brain as
a narrow concave portion which is connected with the tuber
cinereum by a thin band of gray matter — the lamina cinerea. It
gives off two peduncles, which may be observed by raising and
3 2o CENTRAL NERVOUS SYSTEM.
pushing the optic chiasm backward. They run obliquely across
the outer part of the anterior perforated space of each side, and
probably end near the apex of the temporal lobes. Anteriorly,
they pass around the genu of the corpus callosum and are con-
tinuous with the striae longitudinales, or nerves of Lancisi.
• The anterior perforated spaces, one on each side, are
gray in color, and are formed by the lenticular nuclei of the
corpora striati, — which have come to the surface of the base at
this point, — are triangular in shape, and are perforated by
numerous large and small blood-vessels, which pass from the
middle cerebral arteries into the corpora striati. Each space is
bounded in front by the orbital part of the frontal lobe and
olfactory tract ; behind, by the optic tract ; externally, by the
frontal and temporosphenoid lobes and by the beginning of
the fossae Sylvii. Internally, it is continuous with the lamina
cinerea.
The Sylvian Fissure. — This begins at the base of the brain,
in the anterior perforated space. Here it separates the frontal
from the temporosphenoid lobe. This part of the fissure is
called the fossa or vallecula Sylvii. It lodges the middle cere-
bral or Sylvian artery. On separating the margins of the
temporosphenoid and frontal lobes which form the boundaries
of this fissure, the prominent cluster of small gyri — the insula,
or island of Reil — may be seen.
The Optic Chiasm or Decussation. — This is the junction
of the two optic nerves. They form an incomplete decussation.
The fibers coming from the inner or nasal halves of the two
retinae, which supply the outer or temporal halves of the field
of vision, decussate, and pass to the opposite optic tract. The
fibers coming from the outer or frontal halves of the retinae do
not decussate, but pass directly backward on the same side, to
unite with the nasal fibers from the opposite sides of the retinae,
they having decussated in the chiasm. The optic chiasm is
located in the median! portion of the base of the brain, in front
of the tuber cinereum and behind the lamina cinerea, which
latter is a thin blade of gray matter extending from the termi-
nation of the corpus callosum to the tuber cinereum, and is con-
tinuous on each side with the anterior perforated space. From
Fig. 157. — Photograph of the Base of the Human Brain.
L. F. Inferior longitudinal fissure. G. R. Gyrus rectus. 0. B. Olfactory bulb. O. T.
Olfactory tract. Optic N. Optic nerve. F. L, Base of frontal lobe. Orbital L. Orbital
lobe. S. F. Sylvian fissure. A. P. S. Anterior perforated space. S. A. Sylvian artery.
Op. T. Optic tract. C. M. Corpora mammillaria. T. L. Temporal lobe. Crus C. Crus
cerebri. 3rd X. Third nerve. 4th X. Fourth nerve. Pons. Pons Varolii. 6th N. Sixth
nerve. 0. L. Occipital lobe. 8th X. Fighth nerve. Oliv. B. Olivary body. V. A.
Vertebral artery. T. V. Tuber valvule. S. C. Spinal cord. Tonsil. Amygdalum or
tonsil. I. P. L. Inferior posterior lobe of cerebellum. S. L. Slender lobe. D. L. Digas-
tric or cuneate lobe. Floe. Flocculus. B. A. Basilar artery. Post. C. A. Posterior
cerebral artery. I. P. S. Interpeduncular space. P. C. A. Posterior communicating artery.
T. C. Tuber cinereum. I. C. A. Internal carotid artery. Tri. S. Triradiate sulcus or
fissure. Opt. C. Optic chiasm.
321
FORE-BRAIN OR PROSENCEPHALON. 323
the optic chiasm on each side the optic tracts pass backward and
outward toward the occipital lobe.
The interpeduncular space is a lozenge-shaped space situ-
ated behind the optic tracts, which form its anterolateral boun-
dary, and in front of the crura cerebri, — the diverging peduncles
of the cerebrum, — which form its posterolateral boundary. In
this space exist, from before backward, the tuber cinereum, the
infundibulum, the pituitary body, the corpora albicantia or
mammillaria, the posterior perforated space, and the motor
oculi, or third pair of cranial nerves.
The tuber cinereum is an elevation of gray matter extending
from the corpora albicantia behind to the optic chiasm in front,
to which it is attached. It is continuous with the lamina cinerea,
and forms part of the floor of the third ventricle.
Passing downward and forward from its middle portion is a
hollow, cone-shaped process, the infundibulum, which has
attached to it the posterior lobe of the pituitary body. This
funnel-shaped canal communicates with the cavity of the third
ventricle, and is two or three lines in length.
The pituitary body, or hypophysis cerebri, is a reddish,
vascular mass of an oval shape. It is situated in the sella
turcica, in which it is retained by a process of dura mater
derived from the inner wall of the cavernous sinus. It consists
of two divisions or lobes — anterior and posterior. They differ
in their development, the anterior lobe being developed from a
tubular process of the ectoderm of the buccal cavity. This
lobe is of a yellowish-gray color, and is made up of a number
of slightly convoluted tubules or alveoli, which are lined by
columnar epithelium, often bearing cilia. The tubules are
united by a stroma of connective tissue, which conveys to the
gland an abundant blood and lymphatic supply. It resembles
very closely in structure the thyroid gland, and, like the latter,
often contains colloid material. It is surrounded by a connec-
tive-tissue capsule. The posterior lobe is an outgrowth from
the embryonic cavity, which soon becomes that of the third
ventricle. This ventricle communicates with the pituitary body,
during fetal life, by means of the infundibulum. In the adult
the infundibulum is impervious, and is made up of a meshwork
3 2 4 CENTRAL NERVOUS SYSTEM.
of connective tissue containing spindle-shaped and branched
cells, some of which are pigmented. A very interesting clinical
fact is that in the disease recently described by Marie, of Paris,
and named by him acromegalia, — and which is characterized by
a great increase in the size of the head, the lower jaw, the
hands and feet, and frequently of other bones, such as the
scapula, clavicle, sternum, and ribs, the chest being often of
enormous proportions and the spine being curved, — after
death, in nearly all instances, an enlargement has been found
of the pituitary body which varies in size, sometimes being as
large as a Tangerine orange. The function of this body is
absolutely unknown. Although it is in man a ductless gland,
it must, however, lend to the economy an internal secretion
which is conveyed to the blood by means of its lymph capil-
laries. In some manner, yet unknown, it probably assists in
the maintenance of nutrition of the osseous system.
The Corpora Albicantia or Mammillaria. — These are
two small, round eminences of white and gray matter, about the
size of a pea, situated between the crura cerebri, behind the
tuber cinereum and in front of the posterior perforated space.
The white matter is arranged superficially in the form of a
mantle (stratum zonale), and is formed chiefly by the anterior
pillars or crura of the fornix, which, descending to the base of
the brain, are reflected upon themselves and form for each body
a covering of white matter. The fibers of these crura termi-
nate among the nerve-cells within the albicantia. Each of these
bodies is brought into relation with the optic thalamus by a
bundle of fibers (bundles of Vicq d'Azyr, axones from the
ventral nucleus of the thalamus), which pass downward and end
among the nerve-cells of the albicantia. Both of the above-
mentioned bundles produce a continuous conducting tract on
each side between the ventral nucleus of the optic thalamus and
the gyrus hippocampus (cornu ammonis). The interiors of the
corpora albicantia contain two groups of nerve-cells, mesial and
lateral, called their nuclei.
The posterior perforated space is a whitish-gray area
located between the corpora mammillaria in front and the pons
Varolii behind. Laterally this space is continuous on each side
FORE-BRAIN OR PROSENCEPHALON. 325
with the substantia nigra of the tegmentum of the crura cerebri.
It forms the back part of the floor of the third ventricle, and
is perforated by numerous small vessels, — branches of the
posterior cerebral and communicating arteries, — which pass
into the interior to supply the interior part of the optic thalamus
and walls of the third ventricle. The third nerves may be seen
issuing from the interpeduncular space on each side, then pass-
ing forward around the crura cerebri.
The crura cerebri, or peduncles of the cerebrum, are seen
on each side of the interpeduncular space, forming the outer
boundary. Below, they are lost among the fibers of the pons.
Above, they break up into numerous tracts, which radiate toward
the cerebral cortex and the central ganglia. They are two very
thick cylindric masses about three centimeters in length, and
composed of large bundles of medullated nerve-fibers. They
diverge in their course from below upward, and before entering
the hemisphere they are crossed by the optic tracts. The fourth
nerves may be seen winding around their outer parts, almost
meeting the third nerves near their median surface, as the latter
nerves curve around their inner parts. The crura cerebri enter
the inner side of each hemisphere, and their fibers spread out
between the optic thalamus and caudate nucleus on the inside
and the lenticular nucleus on the outside, forming the internal
capsule. Then they spread out fan-shaped, forming the corona
radiata, and proceed to all parts of the cerebral cortex. A
peduncle on transverse section consists of two parts of longi-
tudinal fibers separated by an intermediate stratum of dark
gray matter in which is embedded a large number of dark pig-
mented nerve-cells ; hence its name — the locus niger, or sub-
stantia nigra. The superficial or ventral layer is called the
crusta ; the deeper or dorsal, the tegmentum, which is a continua-
tion upward of the fillet and the formatio reticularis. These two
layers of longitudinal fibers — superficial, or crustal, and deep, or
tegmental — are made up of numerous long tracts of centripetal
and centrifugal fibers. The former pass into the subthalamic
region, central ganglia, and cerebral cortex ; the latter, proceed-
ing from the cerebral cortex and central ganglia, pass downward
to enter the pons, cerebellum, medulla, and spinal cord.
j26 CENTRAL NERVOUS SYSTEM.
OLFACTORY LOBE, BULB, NERVES, AND .TRACTS.
The olfactory apparatus includes the regio-olfactoria, the
olfactory nerves, the olfactory lobe or bulb, the trigonum olfac-
torium, the olfactory tracts, and the anterior commissure.
The regio-olfactoria, or olfactory region, consists of the upper
part of the nasal septum, the root of the nose, and the upper
and a part of the middle turbinated bones.
This region is covered by the olfactory mucous membrane,
being thicker than is the Schneiderian mucous membrane,
covering the parts below, which later is the true respiratory
region, and is lined with stratified epithelium bearing cilia. The
olfactory mucous membrane contains two chief forms of cells —
columnar, non-ciliated, strongly pigmented, epithelial cells, the
pigment giving to the olfactory mucous membrane a brownish-
yellow color ; and true olfactory nerve-cells, spindle or rod-like
in shape, containing spheric nuclei. These olfactory nerve-
cells are situated between the columnar cells, and are bipolar in
form, their short, thick peripheral processes terminating on the
surface of the mucous membrane, where they spread out in the
form of a network, while their long, slender central ones (the fila
olfactoria) pass beneath the epithelial cell-layer, to form the true
olfactory nerves.
The Olfactory Nerves. — The olfactory nerves, twenty in
number, consist of bundles of fine fibers (the fila olfactoria),
which are the central coursing axones of the rod-shaped olfac-
tory nerve-cells of the regio-olfactoria. They are non-medul-
lated fibers, which course vertically upward and enter the cranial
cavity through the foramina in the cribriform plate of the ethmoid
bone, to reach the inferior surface or ventral part of the olfactory
bulb, where they terminate in arborizations about the dendrites
of the mitral cells within the olfactory glomeruli. These bipolar
cells resemble closely the cells of a posterior spinal ganglion,
possessing a peripheral axone which terminates free on the sur-
face of the olfactory mucous membrane, and a central axone
which terminates in the olfactory bulb. These cells, with their
axones and terminals, form the peripheral or olfactory neurones
of the first order.
FORE-BRAIN OR PROSENCEPHALON.
3 2 7
The olfactory lobe is a hollow protrusion or fold which extends
forward from the under surface of the wall of the cavity of the
cerebral hemisphere. It forms a distinct ridge along the basal
part ol the hemisphere, from which it soon separates, being
converted into a blind, tubular-like diverticulum, which com-
municates posteriorly with the cavity of the lateral ventricle.
This diverticulum is early separated by a groove (the primary
Fig. 158. — Olfactory Lobe of the Human Brain. — [Bis.) — [After Quain.)
Bit. Olfactory bulb. T. Tract. Tr.o. Trigone. R. Rostrum of corpus callosura. /.
Peduncle of corpus callosum, passing into G.s., gyrus subcallosus (diagonal tract, Broca).
Br. Broca's area. F.p. Fissura prima. F.s. Fissura serotina. C.a. Position of anterior
commissure. L.t. Lamina terminals. C/t. Optic cbiasma. T.o. Optic tract, p.olf.
Posterior olfactory lobule (or anterior perforated space), m.r. Mesial root. l.r. Lateral
root of tract.
fissure of His) into an anterior and a posterior part. From the
anterior part is developed the olfactory tract and bulb, and the
trigonum olfactorium. From the posterior part is developed the
posterior olfactory lobe, which comprises the peduncles of the
corpus callosum, the inner and outer olfactory roots, and the
anterior perforated space.
The olfactory lobe, which in many animals (osmatics) attains
a very large size, is in man rudimentary, the anterior olfactory
328 CENTRAL NERVOUS SYSTEM.
lobe being represented by the olfactory tract and bulb and
trigonum olfactorium, while the posterior lobe comprises the
gray matter of the anterior perforated space.
The olfactory lobe contains, in most of the lower animals, a
narrow, central cavity (the olfactory ventricle) lined with ciliated
epithelium, which rests on a neuroglia basis and communicates
with the anterior cornu of the lateral ventricle. In man no such
cavity exists, it having been obliterated by an overgrowth of
neuroglia.
The olfactory bulb, although a part of the cerebral cortex,
presents certain peculiarities of structure which differ from it.
It is an oval or club-shaped mass of gray matter, which forms a
sort of elongated cap for the ventral portion of the olfactory
tract. The bulb and tract are situated in the olfactory sulcus
on the orbital surface of the frontal lobe. The inferior surface
of the bulb rests on the cribriform plate of the ethmoid bone,
through the foramina of which it is connected with the olfactory
nerves.
Olfactory Bulb : Its Minute Anatomy. — The minute
structure of the olfactory bulb can be best studied by making
sagittal sections through it, after being stained by the method
of Golgi. It will be found to consist of four well-defined layers ;
these are from without inward:
i. The layer of olfactory nerve-fibers.
2. The layer of olfactory glomeruli — stratum glomerulorum.
3. The molecular layer, or stratum gelatinosum.
4. The layer of central nerve-fibers.
1 . The outer layer, or layer of olfactory nerve-fibers, consists
of a thin, superficial layer of non-medullated nerve-fibers, which
forms for the ventral portion of the bulb a slight stratum
zonale, each individual fibril being the central axone of a rod-
shaped nerve-cell from the olfactory mucous membrane. The
fibers of the olfactory nerves pass into the underlying glomeruli.
Each fibril, just before entering a glomerulus, separates into two
or three divisions, which usually enter a single glomerulus ; but,
occasionally, they may pass into two glomeruli. Within the
glomerulus the terminal divisions of the olfactory fibril frequently
branch, forming antler-like terminations, which come into con-
FORE-BRAIN OR PROSENCEPHALON.
3 2 9
tact with an olfactory end brush of an apical dendrite of a
mitral cell.
2. The Layer of Olfactory Glomeruli ; the Stratum Glomerulo-
rum. — This layer contains many small, roundish bodies, from
30 to 50 p in diameter, which are arranged alongside of one
another, forming a continuous row beneath the layer of olfactory
nerve fibers and above the molecular layer.
Layer of ependymal
cells.
Layer of central olfac-
tory fibers.
Layer of mitral cells.
Layer of olfactory
fibrils (the fila
olfactoria).
Layer of olfactory
nerve-cells from
the regio olfac-
toria.
Fig. 159.— A Schematic Representation of the Principal Elements of the
Olfactory Bulb of a Mammal.— {Van Gehuchten.)
Each glomerulus consists of the terminal arborization of an
olfactory nerve-fiber, together with olfactory end brushes from
the apical dendrites of mitral cells. These two forms of termi-
nals produce an interlacing network or tuft of fibrils, which
assume a spheric form. The glomeruli are nourished by a
rich capillary plexus of vessels, which have descended from the
overlying pia mater.
33o CENTRAL NERVOUS SYSTEM.
3. The Molecular Layer, or Stratum Gelatinosum. — In the outer
part of the molecular layer may be seen numerous vertically
ascending fibers, a part of which are lost in this layer ; the
remainder continue upward and surround the glomeruli by
passing between them. This layer also contains the apical
dendrites of the large and small mitral cells, as well as the
terminal branches of the dendrites of the deeper-lying granular
cells.
The inner part of the molecular layer contains two chief forms
of cell — the deep and the superficial layers of mitral cells, which
correspond to the large and small pyramidal cells of other parts
of the cerebral cortex.
According to Ramon y Cajal, the apical dendrites of the large
mitral cells possess from eighteen to twenty olfactory end
brushes, which are distributed to as many glomeruli.
The large mitral or pyramidal cells are mostly triangular in
shape, and from 30 to 50 ^ in diameter ; they are usually ar-
ranged in a single row or layer, although Koelliker states that it
is common to find two or three layers of these cells. They give
off two sets of dendrites, apical and lateral. The apical den-
drites are, with rare exceptions, single in man, and they do not
branch until they reach the interior of the olfactory glomeruli,
each glomerulus receiving but a single apical dendrite. Within
each glomerulus the dendrite terminates by breaking up into a
globular-shaped, interwoven mass of fibers, to form an olfactory
brush of fibers, — pennicilli olfactorii, (Koelliker), — each olfactory
brush of fibers coming into contact with the terminal arboriza-
tion of an olfactory nerve-fiber. The lateral dendrites of the
mitral cells, two or three in number, spring from the lateral
angles of the cell-body, and pursue a rather long, horizontal
course parallel to the row of mitral cells, and terminate free.
They form a layer of fibers which separates the deepest part of
the molecular from the fourth or internal layer.
The axis-cylinder or axone of the large mitral cells springs
from the angle at the base of the cell-body. It is a strong, thick
process which descends vertically through the molecular layer,
and between the granular cells to the inner part of the fourth
layer, where it bends at a right angle and pursues a horizontal
FORE-BRAIN OR PROSENCEPHALON.
331
course inward (centrally), passing into the olfactory tract. The
collaterals from the axones of the large mitral cells pursue an
upward course and terminate free in the deep or superficial part
of the molecular layer.
The Superficial Layer of Medium and Small-sized Mitral
Cells. — These cells are spindle or triangular in shape and
resemble very closely the large mitral cells, save that they are
smaller in size and their apical dendrites are much shorter.
Fig. 160.— Mitral Cells from a Mouse Twenty-four Days Old.— (Afwr Koelliker.)
D. Dendrites from mitral cells forming horizontal fibers. M. Deep layer of mitral cells.
M 1 . Superficial layer of mitral cells, n. Axones of deep mitral cells. Rp. Arborizations
of apical dendrites of the mitral cells forming brushes of olfactory fibrils.
They possess both
dendrites pursue an
Each apical dendrite
within an olfactory g
fibers. The axis-cyl
same course as do
into the fourth layer,
axones of these cell
which have mostly a
lateral and apical dendrites. The lateral
oblique or horizontal course, ending free.
, like that of the large mitral cell, terminates
lomerulus, there breaking up into a tuft of
inder processes of these cells pursue the
those from the large mitral cells, passing
where they take a horizontal course. The
s give off in their course fine collaterals,
horizontal direction.
332 CENTRAL NERVOUS SYSTEM.
The Fourth Layer, or Layer of Central Nerve-fibers. — The
outer part of this layer is occupied by a large number of very
small granular cells arranged in rows, between which pass the
descending axones of the mitral cells. These granular bodies
are triangular, pyramidal, or spindle-shaped ; they possess short,
central branches or dendrites, and a single, long, delicate, per-
ipheral or apical dendrite, which latter, toward its termination,
frequently forks and ends in a brush of fine fibrils in the region
of the glomeruli. Both the central and peripheral processes
are studded with gemmules. No axis-cylinder processes have
thus far been discovered coming from these cells. Cajal con-
siders them to be nerve-cells whose axis-cylinders probably pass
downward. Van Gehuchten thinks they are misplaced epen-
dymal cells, while Koelliker believes they are neuroglia cells.
The inner part of this layer is mostly occupied by medullated
nerve-fibers and collaterals ; the former have both a centrifugal
and a centripetal course. These fibers pass both in a horizontal
and vertical or radial direction. The vertical fibers have several
sources : first, terminal commissural fibers from the anterior
commissure, which end about the olfactory glomeruli — these are
the centrifugal fibers ; second, ascending collaterals from the
large mitral cells ; third, descending axones from the large,
medium, and small mitral cells.
The horizontal fibers are separable into those which are a part
of the anterior commissure (hence called commissural) and those
which form the olfactory tracts. The commissural bundles of
fibers are located in the deepest part of this layer, adjacent to
the olfactory ventricle. The fibers which together form the
olfactory tract are more superficially located, consisting of the
axones of the mitral cells. The inner border of the fourth
layer is lined with ependymal cells.
The Olfactory Tracts. — The nerve-fibers of the olfactory
bulbs collect at their posterior extremities as two well-marked
bundles of fibers — the olfactory tracts.
Each olfactory tract forms for the bulb a distinct stalk or
pedicle, which is narrowed at its point of emergence from the
bulb and grows slightly broader as it courses backward. It is
flattened on its ventral or inferior surface and ridged or convex
xp~
HF
MZ
Fig. 161. — A Frontal Section through an Olfactory Bulb of a Six-weeks'-old
Cat. Showing layer of granular cells. — [After Koelliker.)
Rp. Ependyma. Gl. Glomerule. Kz. Layer of granular cells. M. Molecular layer. MF.
Layer of medullated fibers. MZ. Layer of mitral cells. Str.gr. Granular zone (stratum
granulosum).
333
FORE-BRAIN OR PROSENCEPHALON. 335
along the middle of its superior or dorsal surface ; hence it is
prismatic or triangular on transverse section. The olfactory
tract and bulb is lodged in the olfactory sulcus of the orbital
lobe, where some of its fibers become continuous along the
inner side of the sulcus with the cortex of the frontal lobe.
The olfactory tract contains two systems of fibers — the olfactory
fibers proper (the axones of the mitral cells) and the commis-
sural fibers from the anterior commissure. The former (true
olfactory fibers) form the ventral part of the tract, while the
commissural fibers occupy its dorsal part. The ventral bundle
(true olfactory tract) separates posteriorly into two roots — an
inner or mesial and an outer or lateral ; these roots diverge
from each other and inclose a triangular space of gray cortex
— the trigonum olfactorium.
The Trigonum Olfactorium and Space of Broca. — These
two areas form a part of the cortical gray matter of the base of
the anterior olfactory lobe, which lobe is bounded internally and
posteriorly by the primary fissure of His. This fissure sepa-
rates it from the anterior part of the peduncle of the corpus
callosum on its inner aspect, and from the posterior olfactory
lobe (anterior perforated space) behind. This area has travers-
ing it from before backward the diverging roots of the olfactory
tract. That part of the area located between the olfactory roots
is known as the trigonum olfactorium ; it receives many fibers
from the dorsal part of the tract, and forms the middle or dorsal
root which comes from the anterior commissure. The portion
of gray matter located between the internal root and the
peduncle of the corpus callosum is called the Area of Broca ; it
receives fibers from the mesial or inner root.
The course of the root-fibers of the olfactory tract in man :
The external, outer, or lateral root passes obliquely across the
outer part of the anterior perforated space into the fossa Sylvii,
where its fibers come into relation with the gyrus hippocampus,
the uncinate gyrus, the cornu ammonis, and probably the
amygdaloid nucleus. The inner or mesial root passes back-
ward, inward, and upward around the area of Broca, to which it
lends fibers and then passes in to the anterior extremity of the
gyrus fornicatus, its fibers probably terminating among the
336 CENTRAL NERVOUS SYSTEM.
pyramidal cells of the cortex of this entire lobe. It will thus be
seen that the olfactory tract and bulb have a connection both
with the beginning and termination of the limbic or falciform
lobe. This connection of the olfactory bulb and tract with the
limbic lobe Broca aptly compares to a tennis-racquet, the
olfactory tract corresponding to the handle and the limbic lobe
to the circumference of the blade. Some of the fibers of the
mesial root pass posteriorly beneath the gyrus fornicatus to the
septum lucidum and fornix, and thence are continued into the
white matter of the cornu ammonis.*
The dorsal or middle root is composed of commissural fibers
from the anterior commissure which have decussated in the
median line and pass into the olfactory tract through the trigo-
num olfactorium, terminating in the olfactory bulb about the
glomeruli and mitral cells. This centrifugal tract of fibers forms
an olfactory commissure and connects the olfactory bulb of one
side with the hippocampal and uncinate region of the opposite
side. Meynert believes that this root also contains fibers joining
the two olfactory bulbs, and thus forms an olfactory chiasm.
THE ANTERIOR COMMISSURE.
The anterior commissure belongs to the cerebral hemisphere
and associates in function those parts which are not united by
the corpus callosum — i. . Visual tract from optic
thalamus (OT) to the occipital lobe. E. Central auditory tract. F. Superior cerebellar
peduncle. G. Middle cerebellar peduncle. IT. Inferior cerebellar peduncle. CN.
Caudate nucleus. CQ. Corpora quadrigemina. Vt. Fourth ventricle. The numerals
refer to the cranial nerves. J. Eighth nerve nucleus.
The long tracts of the projection system of fibers pass through
the internal capsule into the crura cerebri, where they become
separated into fasciculi, one body of these occupying the ventral
part, or crusta, and the other the dorsal part, or tegmentum of
each peduncle. The former are the prolongations of the axis-
cylinder processes, or axones, of the pyramidal cells of the cortex.
The following bundles occupy in the peduncle its anterior por-
THE CENTRUM OVALE.
375
tion — foot, orcrusta: The frontocerebellar tract, the motor tract,
and a tract connecting the occipital and temporal lobes with both
cerebellar hemispheres, but chiefly with the cerebellar hemi-
sphere of the opposite side.
The frontocerebellar tract is composed of axones from the
pyramidal cells of the prefrontal lobes ; from this wide area of
origin the fibers from this tract converge as they proceed down-
Fig. 185. — Diagram to show the Relative Position of the Several Motor Tracts
in their Course from the Cortex to the Crus. — (After Gowers.)
The section through the convolutions is vertical ; that through the internal capsule, I C, hori-
zontal ; that through the crus is again vertical. CN. Caudate nucleus. O TH. Optic
thalamus. L2 and L3. The middle and outer parts of the lenticular nucleus, f, a, I.
! Face, arm, and leg fibers. The words in italics indicate the corresponding cortical centers.
ward, backward, and inward, through the centrum semiovale
and between the caudate and lenticular nuclei, occupying the
anterior division or limb of the internal capsule ; thence descend-
ing in the innermost part of the crusta, or foot of the crus
cerebri, to the ventral part of the pons Varolii, ending about the
cells of the nucleus pontis of the same side. The cells of the
nucleus pontis are joined by fibers from both cerebellar hemi-
376 CENTRAL NERVOUS SYSTEM.
spheres ; chiefly, however, from the cerebellar hemisphere of the
opposite side. These latter fibers are theaxones from the cells of
Purkinje of the same and of the opposite side, the fibers having
decussated in the raphe. It will thus be seen that the prefrontal
lobe is in anatomie connection with both cerebellar hemi-
spheres, but chiefly with the cerebellar hemisphere of the oppo-
site side.
The motor tracts consist of two divisions or neurones — a cen-
tral and a peripheral. The fibers of which the central division
of these tracts are composed take their origin from the motor
area of the cerebral cortex, and are the axis-cylinder processes,
or axones, of the large pyramidal or motor cells of the third
layer of the cortex. The motor area of each hemisphere in-
cludes the posterior part of the prefrontal lobe, the anterior
and posterior central, or, from their course, the ascending
frontal and parietal gyri, with their union on the median surface
of the hemisphere, called the paracentral lobule. It may be
stated, in a general way, that the upper third of the motor area,
including the paracentral lobule, innervates the muscles of the
trunk and lower extremity, the middle third those of the upper
extremity, while the lower third functionates the muscles of the
face, tongue, mouth, and larynx — all of the opposite side. The
posterior part of the left third frontal gyrus contains the mem-
ories necessary to innervate the motor speech processes. From
this very extensive cortical area the axones of the motor cells
pass through the centrum semiovale of Vieussens, converging
as they proceed until they reach the internal capsule, where
they are collected into distinct bundles which occupy the an-
terior two-thirds of the posterior division of the internal capsule,
the posterior part of this division of the capsule being occupied
by the sensory, optic, and auditory tracts. It will be remem-
bered that the motor centers for the muscles of the face, tongue,
mouth, and larynx occupy the lowest part of the motor area ;
hence the fibers which proceed from the facial center have a
course directly inward, while those from the centers located
above — namely, the arm, leg, and trunk — have a course down-
ward and inward ; thus the fibers from the face become located
in the extreme anterior division of the posterior limb of the in-
THE CENTRUM OVALE.
377
ternal capsule, while the fibers from the arm, leg, and trunk
areas are located just back of the facial fibers, in the order herein
mentioned. In the left internal capsule the fibers that innervate
the motor speech center pass a little anterior to those of the
Fig. 186. — Diagram of the Course of the Motor Tract as shown in a Diagram-
matic Horizontal Section through the Cerebral Hemisphere, Pons, and
Medulla. — {After Gowers.)
Fr. Frontal lobe. Oc. Occipital lobe. A F. Ascending frontal, and A P, ascending parietal
convolutions. P C F. Precentral fissure in front of the ascending frontal convolution.
I P F. Interparietal fissure. A section of the crura is lettered on the left side. S N.
Substantia nigra. Py. Region occupied by the pyramidal fibers (motor tract), which on
the right are shown as continuous lines, converging in the white substance of the hemi-
sphere, to pass through the posterior limb of I C, the internal capsule (the elbow of which
is shown at *) — through the crus and pons, and to divide in the medulla into the decussat-
ing lateral pyramidal tract [Ipt) and the direct anterior pyramidal tract {apt). FC. Fronto-
cerebellar tract. Py. Pyramidal tract. TOC. Temporo-occipital cerebellar tract.
face. The fibers of each motor tract then enter the ventral por-
tion or foot of the crus cerebri, occupying the middle two-fifths
of its anterior surface ; the tract then continuing spineward,
reaches the ventral portion of the pons Varolii, where each tract
378 CENTRAL NERVOUS SYSTEM.
separates into several fasciculi, which lie between the superficial
and deep transverse pontine fibers. On emerging from the in-
ferior border of the pons, these fasciculi are again collected into a
distinct bundle, one for each side, which form the fleshy columns
seen on each side of the ventral fissure of the medulla ob-
longata — the anterior pyramids. These continue to the inferior
portion of the medulla ; at this point — namely, in the region of
the first and second cervical nerves — there occurs an incomplete
decussation, the so-called pyramidal or motor crossway. Here
the majority of the fibers decussate and pass to the opposite
side, while the minority do not cross, but pass down on the same
side.
The crossed fibers descend throughout the entire length of
the spinal cord, and occupy an extensive area in the posterior
part of the lateral column ; in the cord this crossed bundle of
fibers receives the name of the crossed motor or pyramidal
tract. This tract decreases in size from above downward, owing
to the fact that many of its axones and their collaterals are con-
stantly bending forward and inward to enter the gray matter of
the anterior horn of the same side, there terminating in arbori-
zations about the motor cells. The fibers of the direct pyr-
amidal tract— also called uncrossed motor tract — continue down-
ward on the same side, occupying a small area adjacent to the
anterior median fissure. This bundle of fibers is called the
column of Turck. It usually ceases at the level of the mid-dorsal
region, although in exceptional cases it passes down to the lum-
bar region ; in its descent its axones and collaterals pass, by
means of the anterior commissure, to the anterior horn of the
opposite side, ending at various levels about the motor cells
therein contained.
It will thus be seen that the central division of the motor tract
consists of collections of central motor neurones — the pyramidal
cells, with their dendrites and axones, the course of the latter
continuing without interruption until they end by arborizing
about the motor cells contained in the anterior cornu of the side
opposite to their origin. The central division of the motor
tract also contains the central tracts for the various motor cranial
nerves, which are as follows : The oculomotor, or tliird pair ; the
Fig. 1S7. — Diagram Indicating the Course of the Motor and Sensory Fibers
of the Spinal Cord and Medulla.
<7, a. Motor cells of the cerebral cortex. t>, b. Arborizations of the fibers of the sensory tract
in the cerebral cortex, c. Nucleus of the column of Burdach, showing terminal arboriza-
tions of the long sensory fibers of the cord. d. Nucleus of the column of Goll, showing
terminal arborizations of the long sensory fibers of the cord. e. Section of the medulla,
showing sensory decussation, f. Section of medulla, showing motor or pyramidal decus-
sation, g, g. Motorial end plates, h. Section through the cervical region of the cord,
showing termination in the anterior horn of the motor fibers of the direct pyramidal tract
after they have crossed in the anterior commissure ; also fiber of crossed pyramidal tract end-
ing about anterior horn cell of same side, i, i. Posterior spinal ganglia. /, /-. Sensory fibers
of short course. /. Sensory fibers of long course, terminating in medulla. ;;/, m, m. Sen-
sory end organs, n. Section through lumbar cord.
379
THE CENTRUM, OVALE.
38l
trochlearis, or fourth ; the motor division of the fifth, or trigem-
inus ; the abducens, or sixth pair ; the seventh, or facial ; the
combined motor divisions of the glossopharyngeal and pneumo-
gastnc, or ninth and ^//z pairs ; the spinal accessory, or eleventh ;
and the hypoglossal, or twelfth pair. The exact cortical areas
from which the various central cranial nerve
tracts arise is only positively known for the
facial, motor division of the trigeminal, and the
hypoglossal ; these all take their origin from the
cortex of the lowest third of the central convo-
lutions. These various tracts occupy the knee
of the internal capsule, and in the crus cerebri
they are located on the inner side of the pyr-
amidal tract ; they continue downward in the
crus, pons, and medulla, until they reach the
level of their respective nuclei, — whose cells
give origin to the peripheral divisions of these
nerves, — when they decussate with their fellows
and pass to the nuclei of the opposite side, end-
ing about their nerve-cells. It is very probable,
owing to the fact that many of the motor
cranial nerves innervate bilaterally acting mus-
cles, that some of the fibers do not decussate,
but end about the motor cells of the same side.
The partial course of the peripheral division of
the motor cranial nerves has been discussed else-
where. The peripheral portion of each motor
tract consists of the motor cells of the anterior
cornu, with their axis-cylinder processes, which
latter form the anterior spinal nerve-roots.
They terminate in the motor end organs of the
various skeletal muscles.
This corhbination of motor nerve-cells, with
their axones and dendrites and their terminal endings in the
muscles, form the peripheral motor neurones. There is thus
formed by these two groups of neurones, central and peripheral,
a functionally continuous tract from the motor cortical region
of one cerebral hemisphere to the muscles of the opposite side
of the body.
MLDUL
CO RO
Fig. 188. — Diagram
of the Course of
the Pyramidal
or Motor Tract
of the Right
Hemisphere. —
[After Gowers.)
382 CENTRAL NERVOUS SYSTEM.
The occipital and temporal lobes are connected by a tract with
the opposite cerebellar hemisphere and slightly with the cerebel-
lar hemisphere of the same side. The fibers of this tract are
the axones from the pyramidal cells of the cortex of the occipital
and temporal lobes. It was formerly thought that this fasciculus
of fibers, after passing through the centrum semiovale, entered
the extreme posterior part of the internal capsule, but Flechsig
has proven that this is incorrect, and has shown that they course
in part beneath the lenticular nucleus and in part between that
nucleus and the external geniculate body, whence they enter the
outer part of the foot, or crusta, of the cerebral peduncle and
continue downward to the pons Varolii of the same side, where
the individual fibers terminate about the cells of the nucleus
pontis. The tract is further continued to the cortex of the
opposite cerebellar hemisphere by means of the axones of the
cells of Purkinje, which also terminate about the same cells of
the nucleus pontis after having decussated in the raphe. This
tract also communicates with the cerebellar hemisphere of the
same side, owing to the fact that a few axones from the cells of
Purkinje of that side terminate without decussating.
The Sensory Tract. — This tract conducts centripetally impres-
sions of touch, pain, temperature, and muscular sense via the
spinal cord, medulla, pons, brain-stem, and basal ganglia to the
cerebral cortex, where the impressions are received as conscious
perceptions. It forms the chief portion of the projection system
of fibers existing in the dorsal part or tegmentum of the crus
cerebri.
The fibers which compose this tract have their origin in the
cells of the posterior spinal ganglia. Each ganglion cell gives
off a single axone, which soon divides, Y-shaped, the thicker
branch passing out to form a peripheral sensory nerve and to
terminate in a sensory end organ, and the finer branch, as a
posterior nerve-root, passing into the spinal cord just dorsal to
the substantia gelatinosa Rolandi, where it divides into an
ascending and descending branch.
The descending branches of the posterior nerve-roots have
but a short longitudinal course in the posterior columns, when
they curve inward and terminate in arborizations about the cells
Fig. i
■{After SaMs.)
Fig. I, Sensory tract, a, b. Cells of spinal ganglia, one fiber,/, forming part of sensory nerve
the other fiber, c, entering a posterior root, fibers of the latter dividing into ascending and
descending (I, 2, 3, 4) branches. Of the ascending branches, some (4) terminate with
" end-brushes " in the nucleus cuneatus, and nucleus gracilis, col. Collateral fibers enter-
ing gray matter. 8. Fibers forming anterior ground bundle. 5,6. Fibers forming lateral
ground bundle. 10. Fib;rs forming Gowers' tract. 7. Fibers forming direct cerebellar
tract.
Fig. II. r.a. Anterior root. r.p. Posterior root. LR. Lissauer's marginal zone. 1. Direct
pyramidal tract. 2. Anterior ground bundle. 3. Lateral ground bundle. 4. Gowers'
anterolateral tract. 5. Crossed pyramidal tract. 6. Direct cerebellar tract. 7. Column
of Burdach. 8. Column of Goll. 9. Posterior longitudinal septum. 10. Anterior longi-
tudinal fissure. 11. Anterior median group of cells. 12. Posterolateral group. 13.
Column of Clarke.
Fig. III. Relation of motor tract to nuclei of cranial nerves. — {After F/atau.)
383
THE CENTRUM OVALE. 385
of the gray matter of the cord. The ascending branches con-
sist of two divisions — those which pursue a rather short longi-
tudinal course and those which pursue a long course. The
former enter the gray matter in curves, and terminate as do the
descending branches. Some of the branches of long- course
pass upward into the postero-external column, or column of
Burdach ; while the greater number pursue a similar course in
the postero-internal column, or column of Goll. All these fibers
of long course continue upward until they reach the lower dor-
sal region of the medulla, where they bend nearly at right
angles and terminate in brushes of fibrils about the nerve-cells
of the nucleus cuneatus and nucleus gracilis. Both ascending
and descending branches are constantly giving off in their course
collaterals, which enter the gray matter and terminate about the
intrinsic cells of the posterior horns and intermediate gray
matter about the motor cells of the anterior horns (reflex col-
laterals) and about the cells of Clarke's column.
Gowers tract, which is supposed to conduct sensations of
temperature and pain, consists of axones which arise from the
intrinsic cells located in the intermediate gray matter near the
base of the anterior horn, around which cells collaterals from
the posterior nerve-roots terminate. The axones from this
group of intrinsic cells pass across the gray matter, probably in
the anterior commissure, to the opposite side of the cord, where
they turn upward and become located in the anterolateral per-
iphery of the cord, ventral to the direct cerebellar and crossed
pyramidal tracts. These fibers course upward until they reach
the medulla oblongata, where some may be intercepted by the
cells of the lateral nucleus. The tract then continues upward in
the formatio reticularis, where it occupies a position dorso-
lateral to the olivary body. At about the middle of the pons
Varolii, according to Hoche, this bundle makes a distinct curve
over the fifth nerve and enters the cerebellum by means of the
superior cerebellar peduncle and velum medullare anticum. It
is extremely probable that a part of the fibers of this tract con-
tinue brainward in the formatio reticularis, and terminate in
part in the corpus quadrigeminum, and in part in the optic thal-
amus. The cortical termination of this part of the tract is prob-
25
3 86 CENTRAL NERVOUS SYSTEM.
ably in the parietal lobe, the fibers passing with those of the
mesial fillet.
The largest portion of the sensory tract, whose axones have
terminated about the cells of the nuclei cuneati and gracili, is
farther continued by the axones from the cells of these nuclei,
which axones pass ventromesially (internal arcuate fibers) to
the region between the olivary bodies, where they decussate,
forming the interolivary or superior sensory decussation. Each
tract then turns upward just dorsal to the anterior pyramids, and
is now termed the mesial fillet, lemniscus, or interolivary tract.
In the pons it occupies the ventral portion of the formatio retic-
ularis, and continues brainward through the ventral part of the
tegmentum of the cms cerebri to the subthalamic region, where
a small part of the fibers from the cells of the nucleus cuneatus
terminate in the anterior corpus quadrigeminum. The main
bundle of fibers from this nucleus passes to the outer side of
Luys' body, and joins both the lenticular loop and Meynert's
commissure. The first part of the bundle passes by way of the
lenticular loop to the globus pallidus of the lenticular nucleus of
the same side, while the remaining fasciculus passes to the len-
ticular nucleus of the opposite side by way of Meynert's com-
missure. The fasciculus of fibers of the fillet or lemniscus, which
are the axones from the nucleus gracilis, give off collaterals which
join the anterior corpus quadrigeminum, ending about the cells of
the fifth layer. The main bundle of fibers of this fasciculus, how-
ever, continues ventrad, and terminates in arborizations about
the cells of the ventral nucleus of the optic thalamus of the same
side (von Monakow), the axones of which cells continue this tract
through the posterior third of the posterior division of the in-
ternal capsule, whence they radiate through the centrum semi-
ovale to the cortex of the postcentral and parietal lobes. The
sensory tract receives in its course axones and collaterals from
the various sensory end nuclei of the cranial nerves of the
opposite side, with the exception of those from the auditory.
These fibers form the central sensory tracts for the cranial nerves
from whose end nuclei they originate.
CHAPTER X.
GENERAL ANATOMY OF THE INTERIOR OF THE
CEREBRAL HEMISPHERES.
Horizontal or sagittal sections through a cerebral hemisphere
show it to be made up entirely of gray and white matter, the
former completely surrounding the latter, forming for it a con-
voluted mantle of a thickness nearly uniform. The white mat-
ter appears as a homogeneous white mass, presenting an
irregularly oblong or oval shape, and is called, for each hemi-
sphere, the centrum semiovale (Yieussens). The white matter,
as seen on complete horizontal section of the entire cerebrum,
is called the centrum ovale major. Sections of the centrum
ovale present a number of small hemorrhagic points, which are
the cross-sections of small blood-vessels. These points are
called the puncta vasculosa (Fig. 190).
CORPUS CALLOSUM.
On separating the hemispheres, a broad band of transversely
arranged fibers appears at the bottom of the longitudinal fissure.
This is the corpus callosum, or the great transverse commissure
of the cerebrum, connecting corresponding areas of the frontal,
parietal, and occipital lobes. It is narrower in front than be-
hind, is 7 to 8 cm. (about 2,% inches) in length on its superior
surface, and is from 5 to 6 cm. (about 2 y^ inches) on its inferior
surface, and extends farther forward than backward, reaching to
a point within 3 cm. {1% inches) of the anterior, and within
5 cm. (2 inches) of the posterior end of the hemispheres. It
presents a gentle curve from before backward, its upper surface
being convex, its lower, concave. Both ends are more thick-
387
CENTRAL NERVOUS SYSTEM.
ened than the intermediate portion, or body. The posterior
extremity terminates free, and is rolled upon itself, forming an
expanded portion called the splenium, or pad. The anterior
extremity curves downward and backward between the frontal
lobes, making a bend called the genu, or knee, It then con-
Fig. 190.— Horizontal Section of Cerebrum above the Corpus Callosum to show
the Cenirum Ovale. — [After Van Gehuchten.)
tinues downward and backward, and at the base of the brain it
blends with the lamina cinerea. This latter portion, the re-
flected part, is called the rostrum.
Two distinct white bands are given off at the termination of
the corpus callosum, and are called its peduncles, one for each
side. These peduncles diverge, pass across the posterior por-
ANATOMY OF INTERIOR OF CEREBRAL HEMISPHERES.
3S9
tion of the anterior perforated space, and enter, each on its own
side, the fossa of Sylvius. Thence they pass to the apices of
the temporal lobes, where they terminate, possibly uniting with
the inner olfactory roots.
On the upper surface of the corpus callosum are a number of
minute transverse depressions, which indicate the course taken
by most of its component fibers. A longitudinal furrow exists
in the middle, and has on each side two small, white bundles of
for.Mon.
ept. luc. \
fornl
branev.fiis.
pineal gtrui
post, comm..
pineal body
\ aplenium
CTCT. Sljlu.
central lobe
monKculu3
/
pU.boau/
corp. alh,
tub. ualv.
Fig. 191. — PORTION of a Median Section of the Brain. Showing the corpus callosum,
third ventricle, aqueduct of Sylvius, fourth ventricle, pons, cerebellum, etc.
fibers — the nerves of Lancisi. They are continuous anteriorly
with the peduncles of the corpus callosum. Laterally, near the
margins, are seen other fibers having a longitudinal course,
called the striae longitudinales laterales. Both the median and
lateral striae pass backward into the dentate gyrus. The
median portion of the under surface of the corpus callosum is
connected in front with the septum lucidum, and behind with
the fornix. The transverse fibers of the corpus callosum are
continuous with the white fibers of the centrum ovale, and inter-
390
CENTRAL NERVOUS SYSTEM.
lace with the various projection systems of fibers and continue
to the cortex of each hemisphere. The main mass of the trans-
verse fibers was formerly called the tapetum. The term tape-
turn is now applied to the association bundle of fibers described
Fig. 192. — View of the Corpus Cali.osum from Above. — (From Sappey after Foville,
from Quain.)
The upper surface of the corpus callosum has been fully exposed by separating the cerebral
hemispheres and throwing them to the side. The gyrus fornicatus has been partly detached
and the transverse fibers of the corpus callosum traced for some distance into the cerebral
medullary substance.
1. The upper surface of the corpus callosum. 2. Median furrow or raphe. 3. Longitudinal
stride bounding the furrow. 4. Swelling formed by the transverse bands as they pass into
the cerebrum, arching over the side of the lateral ventricle. 5. Anterior extremity or knee
of the corpus callosum. 6. Posterior extremity. 7. Anterior, and 8, posterior, fibers pro-
ceeding from the corpus callosum into the frontal and occipital lobes respectively. 9.
Margin of the swelling. 10. Anterior part of the gyrus fornicatus. II. Fissure between
the corpus callosum and this convolution opened out. Outside 12, is the termination of the
callosomarginal fissure, and before 13 is the parieto-occipital fissure. 13. Upper surface of
the cerebellum.
by Forel and Onufrowicz. The fibers of the corpus callosum,
which pass iorward into the frontal lobes, above the anterior
cornu on each side, are termed the forceps minor ; while those
that come from the splenium, and curve backward into the
occipital lobes, above the posterior cornua, are called the forceps
Fig. 193. — Photograph of Horizontal Section through Cerebrum to Show
Lateral Ventricles.
S.L.F. Superior longitudinal fissure. CO. M. Centrum ovale minor. F.M. Foramen of
Monro. A.P.F. Anterior pillar of fornix. F. Body of fornix. D.P.F. Descending or
posterior pillar of fornix. P.I.N. Posterior incised cerebellar notch. C.C. Corpus
callosum. P.C.L. Posterior cornu of lateral ventricle. Em.C. Eminence due to calcarine
fissure called calcar avis or hippocampus minor. II. M. Hippocampus major. D.C.L.
Descending cornu of lateral ventricle. F.F. Corpus rlmbriatum. C.P.L. Choroid plexus
of lateral ventricle. O.T. Optic thalamus. T.C.N. Tail of caudate nucleus. T.S.
Trenia semicircularis. V.C.S. Vena corpora striata. S.S. Sulcus semilunaris. II. C.N.
Head of caudate nucleus. A.C.L. Anterior cornu of lateral ventricle. S.L. Septum
lucidum.
391
ANATOMY OF INTERIOR OF CEREBRAL HEMISPHERES. 393
major. The median surfaces of the hemispheres, which overlap
the corpus callosum, are called the labia cerebri. The space
between them and the superior surface of the corpus callosum
is frequently called the ventricle of the corpus callosum.
THE LATERAL VENTRICLES.
In order to expose the lateral ventricles, a horizontal section
through the cerebrum should be made at a level with the corpus
callosum, and then a longitudinal incision should be made through
the corpus callosum on each side of its middle line or raphe, when
the ventricular cavities will be exposed, the corpus callosum form-
ing their roof. The lateral ventricles are the cavities of the second-
ary fore-brain and belong entirely to the hemispheres. They
are situated deep in the centrum ovale, and do not communicate
with each other, but communicate with the cavity of the primary
fore-brain, the third ventricle, by an opening on each side, the
foramen of Monro, which is the remains of a much larger pas-
sage, communicating in the fetus with the primary and the second-
ary fore-brain. The ventricular cavities are lined with ciliated
epithelium of the columnar variety, which rests on a neuroglia
basis — the ependyma. They contain normally a small amount of
serum. Each ventricle consists of a middle portion or body
with three extensions or cornua : the anterior, the middle, often
called the lateral, or descending cornu, and the posterior cornu.
The body of the ventricle lies between the foramen of Monro and
the posterior extremity of the corpus callosum. Internally it is
separated from its fellow by a thin blade of white matter, the
septum lucidurn, which septum is connected above with the under
surface of the corpus callosum and below with the fornix. The
ventricle has for its floor, from before backward, the intraven-
tricular portion of the corpus striatum, or caudate nucleus, the
taenia semicircularis, the optic thalamus, the choroid plexus, and
one-half of the body of the fornix. The anterior cornu curves
around the anterior extremity of the corpus striatum to reach
the frontal lobe. It has for its front wall and roof the corpus
callosum. On the inner side is the septum lucidurn. On the
outer side is the head of the caudate nucleus. The middle or
394 CENTRAL NERVOUS SYSTEM.
descending cornu is the largest and longest of the three. It
passes at first backward and outward, then downward and for-
ward, forming in its course a great curve around the back of the
optic thalamus and crus cerebri. It then proceeds forward and
inward to terminate near the apex of the temporal lobe close to
the amygdalum. This cornu is roofed by the body of the corpus
callosum and tapetum, and has prolonged into it the caudate
nucleus, the corpus striatum, the taenia semicircularis, and a small
part of the optic thalamus. It has for its floor the hippocampus
major, or cornu ammonis, the pes hippocampus, the eminentia
collateralis, and the fimbria of the fornix. The hippocampus
major, or cornu ammonis, — so called because of its resemblance
to a ram's horn, — is a curved eminence extending along the entire
length of the floor of the descending horn. It is the ventricular
portion of the gyrus hippocampus, and is due to the extension
inward of the dentate or hippocampal sulcus of the mesial sur-
face of the temporal lobe, the gray matter of which is separated
from the cornu ammonis by a thin layer of white matter covered
by ependymal tissue, called the alveus. This cornu, as it
descends and approaches its termination, becomes enlarged and
presents along its edges a number of digitations, which, from
their resemblance to the paw of an animal, give it the name
pes hippocampus.
EMINENTIA COLLATERALIS.
This is a white eminence between the cornu ammonis and the
outer wall of the descending horn of the lateral ventricle, and is
due to the extension inward of the collateral fissure. The tri-
gonum ventriculi is the space between the eminentia collateralis
and the cornu ammonis.
The fimbria, often called the corpus fimbriatum, is the pro-
longed posterior pillar of the fornix, which extends into the de-
scending cornu, and can be traced forward to the uncinate
gyrus. It is attached by its inner margin to the hippocampus
major, while its outer border is free, and lies on the upper sur-
face ol the hippocampus.
The posterior cornu begins at the splenium of the corpus
Fig. 194. — View from Above and the Side of the Whole Left Lateral Ventricle.
Natural size. — {E. A. S. and G. D. T., from Quain.)
The insula has been sliced away and the middle or descending cornu, c.i., exposed. Within
this are seen the following parts : c.i. Entrance to cornu inferius. h. The hippocampus
major, coll. The eminentia collateralis. ft. Fimbria, continued from the fornix, tri.
Trigonum ventriculi. calcar. Calcar avis. c.p. Cor»u posterius. c.a. Cornu anterius
of ventricle, f. Fornix, ff Its anterior pillar, f. M. Foramen Monroi. c,c. Corpus
callosum. th.opt. Thalamus opticus, anterior tubercle, pick. Plexus choroides. /.via.
Forceps major.
395
ANATOMY OF INTERIOR OF CEREBRAL HEMISPHERES.
397
callosum and curves backward and inward into the occipital lobe.
It has for its upper and outer walls the tapetum. Its inner and
lower walls have three projections. The upper is the marginal
bundle of fibers of the corpus callosum, called the forceps pos-
terioris. The middle projection is due to the calcarine fissure,
which extends deep into the margin of the hemisphere and
pushes before it the wall of this cornu, producing an eminence
Fig. 195. — Two Views of a Plaster Cast of the Cavities of the Cerebral Ven-
tricles. — {After Welder, from Quain.)
A. From above: I. Nucleus caudatus. 2. Middle cornu. 3. Fourth ventricle. 4. Calcar
avis. 5. Third ventricle. 6. Middle or soft commissure. 7. Sylvian aqueduct. 8. Re-
cessus lateralis. B. From the side: I. Nucleus caudatus. 2. Middle commissure. 3.
Optic thalamus. 4. Recessus suprapinealis. 5. Recessus pinealis. 6. Aqueduct of Syl-
vius. 7. Posterior cornu. 8. Fourth ventricle. 9. Recessus lateralis. 10. Middle or
descending cornu. II. Chiasm. 12. Anterior commissure. 13. Anterior cornu. The
projections into the cavities of the structures which bound the ventricles are seen as impres-
sions upon the cast.
called the hippocampus minor, or calcar avis. The lowermost
projection is a thickening due to a bundle of white fibers — the
inferior longitudinal fasciculus.
The floor of the body of the lateral ventricle contains the fol-
lowing bodies : the corpus striatum, the taenia semicircularis,
the optic thalamus, and the choroid plexus. The latter will be
described later.
3'.»S
CENTRAL NERVOUS SYSTEM.
THE CORPORA STRIATA.
The corpora striata, together with the claustral and amygda-
loid nuclei, are the ganglia of the cerebral hemispheres. The
corpora striata are situated deep in the cerebral hemispheres,
ventrolateral to the optic thalami, being separated from the
u:
J U U.'
, ^.. V
'JEMP)d
IL^
m *8g
r°
x
l,v> .
W^, JSJp'i)
*^
l-ClaasTrum
i ^^rg
wL/*j
su( a
%b r ^3 ^
i O.N. ^Bjti..
^m^tr^c
Fig. 196. — Photograph of a Section through the Frontal and Tip of Temporal
Lobes.
S.T.F. Superior longitudinal fissure. CO Corpus callosum. A.P.F. Anterior pillar ot fornix.
S.F.G. Superior frontal gyrus. L.V. Lateral ventricle. H.C.N. Head of caudate nu-
cleus. T.C. Internal capsule. M.F.G. Middle frontal gyrus. F.C. External capsule.
L.N. Lenticular nucleus. I. E.G. Inferior frontal gyrus. A.C. Anterior commissure.
T.L. Temporal lobe. O.N. Optic nerve.
latter bodies by the taenia semicircularis, or striae corneae. They
are so named because of their streaked appearance on trans-
verse section, this appearance being clue to the passage through
them ot the fasciculi of white fibers which compose the internal
capsule. Each corpus may be described as an oval mass of
ANATOMY OF INTERIOR OF CEREBRAL HEMISPHERES. 399
gray and white matter, located deep in the hemisphere, and con-
sists of two parts — an extraventricular, or nucleus lenticularis,
which is entirely embedded in the white matter, and an intra-
ventricular portion, or caudate nucleus, which is within the
lateral ventricle. This division of each corpus striatum is due
to bundles of fibers from all parts of the cerebral cortex, which,
converging, pass through this ganglion on their way to the crus
cerebri. These fibers do not produce a complete separation of
the lenticular from the caudate nucleus, as they are united an-
teriorly and posteriorly by slender tracts of fibers. The extra-
ventricular or lenticular nucleus is bounded internally by the
internal capsule, externally by the external capsule, which sepa-
rates it from the claustrum, a thin layer of gray matter with a
wavy margin. Inferiorly, it is bounded by the lenticular loop.
Its horizontal section has the shape of a double convex lens ;
hence its name. On vertical section it is triangular in shape.
It is separated into three zones by two laminse of white fibers
from the internal capsule, and by axones of its own cells on
their way to the lenticular loop. The outer or larger part is
called the putamen ; the inner two zones, from their pale color,
are called the globus pallidus. The intraventricular or caudate
nucleus is pyriform in shape, and consists of an anterior ex-
panded portion, or head, and a narrow posterior portion, or
tail. The head forms the outer wall and part of the floor of the
anterior cornu. The tail extends backward along the outer
part of the floor of the lateral ventricle, then passes downward
and forward into the descending cornu, terminating near its
end in the amygdaloid nucleus or tubercle. It is covered by
ependymal tissue, upon which rests the ciliated epithelium com-
mon to the ventricles. On its outer side is the internal capsule,
which separates it from the lenticular nucleus. The caudate
nucleus, with the optic thalamus, forms the inner boundary of
the internal capsule. The two nuclei are continuous anteriorly
with each other by small bands of gray matter in the ventral
portion of the anterior limb of the capsule. The head of the
caudate nucleus is continuous inferiorly with the anterior per-
forated space, which, in turn, is also connected with the anterior
inferior extremity of the lenticular nucleus. Through the ventral
4O0
CENTRAL NERVOUS SYSTEM.
and basal portion of the lenticular and caudate nuclei passes a
compact bundle of fibers — the anterior commissure. From the
posterior end of the putamen, or the outer division of the lentic-
ular nucleus, passes a process oi gray matter into the roof of
the descending- horn of the lateral ventricle, which joins the tail
of the caudate nucleus, thus uniting- these two nuclei posteriorly.
Microscopic examination of these two nuclei shows that they
contain two chief forms of multipolar cells — large rectangular and
Fie;. 197. — Photograph of Sagittal (Longitudinal) Section through a Cerebral
Hemisphere,
C.O.F. Centrum ovale of frontal lobe. C.R. Corona radiata. CO. P. Centrum ovale of
parietal lobe. C.O.O. Centrum ovale of occipital lobe. D.H.L. Descending or middle
born of lateral ventricle. C.A. Cornu ammonis. N.L. Nucleus lenticularis. C.O.T.
Centrum ovale of temporal lobe.
small triangular, polygonal, or spindle-shaped cells. The former
are found, according to Koelliker, almost exclusively in the
putamen, while the smaller cells are found throughout the globus
pallidus and the caudate nucleus. According to Starr, both vari-
eties are scattered indifferently throughout the gray matter, and
are never associated into groups. The large cells have a slen-
der body, from 36 to 70 fi long, and give off from each end one
or two, occasionally three to five, very long dendrites, which
ANATOMY OF INTERIOR OF CEREBRAL HEMISPHERES.
401
soon turn, nearly at right angles to the long axis of the cell-body.
They have a very long course, and do not branch more than
twice. Just prior to reaching their destination they fork. The
axones come off either from a projection from the cell-body or
FlG. 198. — MlCROFHOTOGRAPH OF LARGE RECTANGULAR CELLS OF CORPORA STRIATI.
Golgi method. — {After Starr.)
from the base of one of the dendrites. The cells of the globus
pallidus and of the nucleus caudatus are practically the same in
appearance, save that in the former they are smaller. They are
from 20 to 40 11 in diameter, possessing, from all sides of the
cell-body, many branching dendritic processes studded with
26
402 CENTRAL NERVOUS SYSTEM.
getnmules. The axones come from the cell-body, but their
course is difficult to trace. Those from the large cells of the
putamen pass either through the globus pallidus and enter the
internal capsule to pass into the crus cerebri, or the greater
number may pass by way of the lenticular loop (ansa lenticu-
laris), to be described.
THE LENTICULAR LOOP, OR ANSA LENTICULARIS.
The lenticular loop is a rather large fasciculus of fibers which
proceeds from the medullary laminae between the divisions of
OP. th: ^-jK©lSIIii
-t
V'
Wt
"M.
%$£. ^' : '.; :f ^
r7n
m -
® ^u-r-o^ & urn
^VN.
CKUSTft-
Fig. 199. — Diagram of a Section through the Crus, etc.. in Front of the
Corpora QuadRIGEMINA. — {Modified from Wernicke.)
P C. Posterior commissure. Aq. Aqueduct ot Sylvius. P L. Posterior longitudinal fibers
III. Third nerve. LB. I.uys'body. OP T. Optic tract. O.P.T.H. Optic thalamus. Int.
Cap. Internal capsule. Lent. Loop. Lenticular loop. R.N. Red nucleus. Lent. N. Lentic-
ular nucleus.
the lenticular nucleus. These fibers have their origin chiefly from
the cells of the outer division of the lenticular nucleus (the puta-
men), and, according to some observers, the loop receives acces-
sions of fibers from the caudate nucleus and the cerebral cortex.
This tract courses mesially beneath the globus pallidus, from
which point the course and termination of its component fibers
is much in dispute.
Von Monakow believes that the fibers of this tract are
arranged into three distinct bundles — two anterior and one pos-
ANATOMY OF INTERIOR OF CEREBRAL HEMISPHERES. 403
terior. The two anterior bundles pierce the internal capsule
and crus cerebri in curves at the level of Luys' body, both bun-
dles passing into that body ; the most ventral bundle passes
into the ventral surface of the body, terminating about its nerve-
cells, while most of the fibers of the more dorsally placed bundle
pass into the body through its dorsal portion ; the remaining fibers
unite with fibers of an unknown origin to pass forward and in-
ward to the region of the tuber cinereum, where they terminate.
The posterior bundle — the largest of the three, and the one
commonly called the lenticular loop — does not pierce the crus
cerebri, but courses between the crus cerebri and the anterior
pillar of the fornix, and then curves upward and inward to end
in the gray matter beneath the ependyma of the third ventricle
and in the optic thalamus.
According to von Bechterew, the lenticular loop also contains
centripetally coursing fibers from the mesial fillet or lemniscus.
These fibers are the axones from the cells of the nucleus cune-
atus of the opposite side. They probably terminate about the
cells of the globus pallidus. From these cells new fibers start
out and pass upward through the centrum semiovale to arborize
about the cells of the cortex of the central and parietal lobes.
These cortical (sensory) neurones probably form the tegmental
radiation of Edinger.
The axones from the cells of the caudate nucleus pass into
the internal capsule ; thence downward toward the base of the
brain, where they curve backward to enter the optic thalamus
and adjacent nuclei. A few axones from the cells of the cau-
date nucleus pass dorsolaterally through the internal capsule
and globus pallidus to enter the lenticular loop.
THE TRACTUS STRIOTHALAMICUS (Edinger).
Edinger has discovered a tract of fibers which exists in all
vertebrates, and takes its origin from the cells of the head of
the caudate nucleus and from those of the putamen. These
fibers form a distinct bundle, which passes downward through the
anterior limb of the internal capsule to the base of the brain,
whence they curve dorsally to reach the optic thalamus, where
4 o 4 CENTRAL NERVOUS SYSTEM.
most of them terminate ; a few fibers, however, continue back-
ward beneath the optic thalamus and end in the posterior corpus
quadrigeminum and in the substantia nigra (Fig. 200).
THE TAENIA SEMICIRCULARIS.
The taenia, also called stria corneae and stria terminalis, is a
fasciculus of white fibers which forms the boundary between
the nucleus caudatus of the corpus striatum and the optic thal-
amus. It is placed superficially in the side of a depression — the
sulcus semilunaris — between the nucleus caudatus and optic
Fig. 200. — Scheme Showing the Tractus Striothai.amicus. — {After Edinger.)
thalamus. Beneath this bundle, occupying the bottom of the
depression, is the vena corporis striati, which receives a number
of superficial veins from the corpus striatum and optic thalamus
and joins the vena Galeni. The anterior portion of the taenia
descends, in front, between the anterior extremity of the optic
thalamus and head of the caudate nucleus. Some of its fibers
join the anterior commissure, and the remainder continue to the
base of the brain and terminate in the gray matter of the ante-
rior perforated space. Schwalbe, however, states that the
taenia divides into two parts anteriorly, one of which is con-
tinuous with the anterior pillar of the fornix ; the other passes
in front of the anterior commissure, to become lost in the gray
Fig. 201. — Photograph of a Longitudinal Section through a Cerebral Hemi-
sphere to show the Ganglia of the Hemisphere.
S.F.G. Superior frontal gyrus. M.F.G. Middle frontal gyrus. I.F.G. Inferior frontal gyrus.
Ex.C. External capsule. Cls. Claustrum. I.R, Insula or island of Reil. N.A. Nucleus
amygdala. G.P. Globus pallidus of lenticular nucleus. Int.C Internal capsule. C.N.
Caudate nucleus.
4°5
ANATOMY OB' INTERIOR OF CEREBRAL HEMISPHERES. 407
matter between the septum lucidum and head of the caudate
nucleus. Posteriorly, it passes, in conjunction with the tail ot
the caudate nucleus, into the descending cornu of the lateral
ventricle, both terminating in the nucleus amygdala. The
nucleus amygdala is a thickening of the cortex near the apex
of the temporal lobe, producing a bulging in the roof of the de-
scending cornu called the amygdaloid tubercle. It is dorsal to
the nucleus lenticularis, with which it is probably continuous.
The claustrum is a thin, wavy sheet of gray matter, having on
its inner side a narrow strip of white matter — the external cap-
sule — and on its outer side the cortex of the insula or island of
Reil. Anteriorly, it blends with the nucleus amygdala (Ober-
steiner).
THE INTERNAL CAPSULE.
This receives its name because it bounds the lenticular
nucleus internally, and is one of the most important parts,
anatomically, of the whole nervous system. It is composed of
a number of important tracts of medullated nerve-fibers, whose
function is to bring the cerebral cortex into anatomic and
physiologic relation with parts below — namely, the pons, cere-
bellum, medulla, and spinal cord. Hence, it must contain both
centripetal and centrifugal tracts of fibers. The clearest type
of its topography can be obtained from horizontal sections
through the hemisphere and basal ganglia. It is a broad, homo-
geneous band of white matter (fasciculi cut across) between
the lenticular nucleus on its outer and the caudate nucleus and
optic thalamus on its inner side. It consists of two divisions
or limbs, — an anterior and a posterior, — united with each other
at an angle, which is called the knee or elbow of the capsule.
The anterior portion or limb, which is the shorter, is between
the lenticular nucleus on the outer side and the caudate
nucleus on the inner side ; and the posterior portion or limb
is between the lenticular nucleus on the outside and the optic
thalamus on the inside. Anteriorly, posteriorly, and superiorly
it blends with the centrum semiovale. The fibers of which it is
composed radiate fan-shaped toward all parts of the cortex,
forming the corona radiata of Reil. Below, the internal capsule
4 o8 CENTRAL NERVOUS SYSTEM.
is continuous with the crus cerebri. Experiments on animals,
and clinical observations verified by pathologic researches in
man, prove that the anterior limb of the capsule is composed of
a tract of projection fibers going to the optic thalamus and of a
tract of fibers connecting that portion of the frontal lobes which
is in front of the central convolutions (the prefrontal lobe) with
the opposite cerebellar hemisphere. This is the frontocerebellar
tract. In the anterior two-thirds of the posterior limb is the
great motor tract; the posterior third contains the tracts which
convey touch, temperature, and muscle sense, as well as the
optic and auditory tracts, and a tract of projection fibers con-
necting the temporal and occipital lobes with the opposite cere-
bellar hemisphere. Apart from the above-mentioned systems of
fibers, the capsule contains, in addition, projection fibers which
unite all parts of the cerebral cortex with each optic thalamus.
The exact location of the different tracts of which the internal
capsule is composed is as follows: In the anterior limb are two
tracts of fibers, the ventral of which is a projection bundle of
fibers to the optic thalamus from the frontal lobe. It is of no
great clinical importance. The dorsal bundle is a large fascicu-
lus (frontocerebellar) collecting its fibers from all parts of the
frontal lobe, and thence passing to the opposite cerebellar hemi-
sphere via the nucleus pontis, a few fibers being connected with
the cerebellar hemisphere of the same side.
The posterior limb contains the motor and sensory tracts.
The motor tract, which occupies the anterior two-thirds of this
limb, may be divided into the following fasciculi of fibers, enu-
merated from before backward : The most anterior bundle is
made up of fibers conveying motor impulses to the facial mus-
cles ; it is located just ventral to the knee of the capsule.
Posterior to the facial fibers, fibers come from before backward —
the motor fibers to the hypoglossal nerve, to the arm, the leg,
and the trunk, in regular order, as indicated by the diagram
(Fig. 203).
Just dorsal to the motor or pyramidal part, occupying the
posterior third of the capsule, is the sensory tract. The extreme
posterior part of the posterior limb of the capsule contains the
optic and auditory tracts, the latter being external to the former.
Fig. 202.— Photograph of a Horizontal Section through a Cerebral Hemisphere
to Relations of Internal Capsule.
O.T. Optic thalamus. P.L.I. C. Posterior limb of internal capsule. K.I.C. Knee of internal
capsule. A.L.I.C. Anterior limb of internal capsule. H.C.N. Head of caudate nucleus.
Ex.C. External capsule. L.N. Lenticular nucleus. F.S. Fissure of Sylvius. Ins.
Insula. Cls. Claustrum.
409
Jfypog/ossu.s
-f PhonaticnsKcnu
Sensor.Biitide.
Sehstrah/ung
JLcvJicushiindel
Fig. 203. — Horizontal Section through the Right Hemisphere of a Man.
— (After von Monakow.')
The important parts of the internal capsule are colored red.
B.Kn. Knee of corpus callosum. I7i. Anterior horn of lateral ventricle. F 3 . Inferior o
third frontal convolution. / stric. lenticulostriate division of internal capsule. Knie ic.
Knee of internal capsule. I optic. Lenticulo-optic division of internal capsule. Th. Optic
thalamus. J. Insular island of Reil. CI. Claustrum. Operc. Operculum. T v First tem-
poral convolution, rlic. Retrolenticular region of internal capsule. CA. Ammonis horn.
calc. Calcarine fissure. Hh. Posterior horn of lateral ventricle, ss. Optic radiation of
Gratiolet. T 2 . Second temporal convolution. Facialis. Position in capsule of facial bundle
of fibers. Hypoglossus. Position of hypoglossal fibers. Arm. Position of arm fibers. Bein.
Position of fibers for leg. Sensor, bilndel. Sensory fibers. Sehstrahlitng. Optic tract.
Acusticusbiindel. Auditory tract.
411
ANATOMY OF INTERIOR OF CEREBRAL HEMISPHERES. 413
In addition to the before-mentioned tracts, the posterior limb of
the capsule contains a fasciculus of fibers connecting the occip-
ital and temporal lobes with the opposite cerebellar hemisphere,
as well as projection fibers from the same source to the optic
thalamus.
THE FORNIX.
The fornix is composed of longitudinally arched bundles of
fibers consisting of symmetric halves — one for each hemisphere.
It has a body and two pillars or columns for each side, one
anterior and one posterior. It is located beneath the corpus
callosum, with which it is continuous behind, being separated
from it in front by the septum lucidum. The body of the fornix
rests upon the velum interpositum, which separates it from the
optic thalamus and third ventricle below. It is triangular in
shape ; broad behind, narrow in front. Its lateral surfaces form
part of the floor of the body of each lateral ventricle. The
anterior pillars, or columnae fornicis, are two roundish bundles
of nerve-fibers which descend through the gray matter of the
third ventricle, behind the anterior commissure and in front of
the foramen of Monro on each side, forming its anterior boun-
dary. As they descend they diverge, leaving an interval which
is occupied by the septum lucidum. They receive a few fibers
from the taenia semicircularis, the crura of the pineal gland, and the
septum lucidum. According to Koelliker, the taeniae semicir-
cularis do not unite with these pillars ; on reaching the base
of the brain they curve backward and upward, around the cor-
pora albicantia, forming loops which make the white portion, or
stratum zonale, of these bodies. They end in arborizations about
the inner cell-groups of these bodies. These cell-groups also
have terminating about them a fasciculus of fibers (axones from
the cells of the ventral nucleus of the optic thalamus) which is
called the bundle of Yicq d'Azyr, or fasciculus thalamomam-
millaris.
The posterior pillars of the fornix are two flattened bands —
prolongations from the sides of the body of the fornix. At their
commencement their upper surfaces are adherent to the under
4 i4 CENTRAL NERVOUS SYSTEM.
surface of the corpus callosum. Between these diverging crura
and the splenium of the corpus callosum exists a triangular area
of white matter, the psalterium, which presents on its surface a
number of transverse oblique and longitudinal lines. From
the fancied resemblance these bear to the strings of a harp, this
area is also called the lyra. The psalterium is a commissure
between the cornua ammonis. Each crus curves downward and
outward around the pulvinar of the optic thalamus, then enters
the descending cornu of the lateral ventricle, giving off some
fibers to the hippocampus major, while the rest continue along
the inner border of the cornu to end in the gyrus hippocampus
and uncinate gyrus. The latter fibers form the before-mentioned
fimbria. The study of secondary degenerations proves that the
fibers of the fornix really proceed from the cornu ammonis and
region of the gyrus hippocampus and pass to the corpus mam-
millare.
THE SEPTUM LUCIDUM.
The septum lucidum forms the inner boundary of the lateral
ventricles, and is united in front with the anterior portion (the
genu) and the descending portion (the rostrum) of the corpus cal-
losum. Posteriorly and inferiorly it unites with the fornix and its
anterior peduncles. It is a triangular area of white matter, con-
sisting of two very thin laminae separated by a narrow closed
space which contains a little fluid. This interval or space is
termed the ventricle of the septum lucidum, or the fifth ventricle.
THE FIFTH VENTRICLE.
This ventricle does not communicate with the other ventricular
cavities. It was originally a part of the great longitudinal fis-
sure, but owing to the union of the hemispheres by the develop-
ment of the corpus callosum above and the fornix below, that
space which had been a part of the longitudinal fissure became
a distinct cavity with walls of its own — the laminee of the septum
lucidum. These laminae are formed of the mesial wall of the
ANATOMY OF INTERIOR OF CEREBRAL HEMISPHERES. 415
hemispheres, and are thus composed of an internal layer of gray
matter, covered with pia mater, similar to the cortex but much
more delicate in structure ; a middle layer of white matter ; and
an external layer of ependymal tissue, covered by an epithelial
layer continuous with that lining the lateral ventricle.
CHAPTER XL
THE BLOOD-VESSELS OF THE BRAIN.
An accurate acquaintance with the exact distribution of the
blood-vessels that nourish the brain is of great importance, be-
cause of the fact that very many cerebral affections are due to
their rupture or to obstruction by emboli or thrombi, all of which
conditions are more frequent in the brain than in any other
organ of the body. This is due to the large size of its main
trunks of supply, as well as to their direct course in the blood
stream. For this reason emboli are more easily swept into the
vessels of the brain than into those of the other organs. Owina
o o
to the high arterial tension to which these vessels are more
or less constantly subjected, they often early present degenerative
changes in their walls, which increase's the chance of rupture or
of the formation of thrombi.
The cerebral blood-vessels are arranged in two systems — the
cortical and the central or ganglionic. The former are for the
nutrition of the convolutions and underlying white matter, and
are distributed in the pia mater. They consist of two sets, —
long and short, — which enter the cortex at right angles to its
surface.
The long arteries, which supply a considerable part of the
centrum semiovale, pass through the gray matter, penetrate the
white matter for an inch or more, following the course of its
nerve fasciculi, and communicate with each other by very fine
capillary branches, which form elongated plexuses. Most of the
shorter ones are distributed to the cortex only, although some
of the longer branches reach the white matter just beneath the
cortex. They anastomose very freely, forming distinct plexuses
in the gray matter.
The central or ganglionic vessels nourish the central ganglia
416
BLOOD-VESSELS OF THE BRAIN.
417
and adjacent parts, and are terminal end arteries, there existing
no anastomosis between them and the cortical vessels. While
the terminal cortical vessels anastomose slightly with one an-
other, this is insufficient, in case of their obstruction, to pre-
vent a local necrosis of the areas which they nourish. Hence,
the general statement may be made that the majority of the
arteries of the brain are physiologically end vessels.*
Fig. 204. — Distribution of Arteries in the Cerebral Cortex. — {After Dttret.)
I, I. Medullary arteries. i', 1 '. In groups between the convolutions, l". Commissural
arteries. 2, 2. Arteries of the cortex cerebri, a. Large meshed plexus in first layer. /'.
Closer plexus in middle layer. c. Opener plexus in the gray matter next the white sub-
stance, with its vessels ({/).
The arterial supply to the cerebrum comes from two sources
— the internal carotids and the vertebrals.
"'Physiologically considered, end arteries are such as are found in the brain or the
heart, obstruction of which causes local death of the part they nourish. These arteries may
not be strictly end arteries in the sense Cohnheim intended, for many of them anastomose with
other terminal branches, but the collateral circulation thus established is insufficient of itself to
maintain the nutrition of the part thus supplied wdien either terminal vessel is obstructed, their
plugging, either by emboli or thrombi, always resulting in local areas of necrosis or softening,
which usually give rise to definite localizing symptoms.
27
418 CENTRAL NERVOUS SYSTEM.
CAROTID ARTERIES.
The right internal carotid artery arises from the innominate
artery, while the left has its origin from the highest point of the
arch of the aorta, both carotids dividing at the upper border of
the thyroid cartilage into external and internal branches, called
respectively the external and internal carotid arteries.
The internal carotid of each side, continuing upward, reaches
the cavity of the skull through the middle lacerated foramen,
having passed through the carotid canal in the petrous portion
of the temporal bone. It then passes through the cavernous
sinus until it reaches the anterior clinoid process, where it pierces
the dura mater and reaches the base of the brain' at the begin-
ning of the fissure of Sylvius. The vertebral arteries, which
have their origin from the subclavian arteries, pass through all
the foramina in the transverse processes of the vertebrae above
the fifth cervical ; during this course they give off several lateral
spinal arteries, whose medullary branches pass with the spinal
nerves to the spinal cord, supplying it and its membranes. They
then pierce the dura mater and reach the interior of the skull
through the foramen magnum. It is interesting to note that,
owing to the direct course of the blood-stream in the left carotid
artery, — it being continuous with that in the aorta, — emboli, which
are frequently dislodged from diseased cardiac valves, more
frequently pass into this vessel than into the right, because the
latter artery arises from the innominate, which is given off from
the aortic arch at an angle with the course of the blood-stream.
This fact remains true for the vertebrals : the right has its origin
from the subclavian after the latter vessel becomes horizontal,
while the left arises from the subclavian in its upward course,
and hence is in direct line of the blood-stream.
The internal carotid artery, after reaching the base of the
brain, rests on the anterior perforated space at the inner portion
of the Sylvian fissure, between the optic and oculomotor nerves.
It terminates in the following branches : the anterior and middle
cerebral, the posterior communicating, and the anterior choroid
arteries.
-{G. D. T., after Duvet, ana
Fig. 205. — The Arteries of the Base of the Cerebrum. -
from nature, from Quaiu.)
On the left side of the brain the temporal lobe is cut away so as to open the inferior and poste-
rior horns of the lateral ventricle. The mid-brain is divided close above the pons and the
posterior cerebral arteries are cut at their origin from the basilar.
Central arteries (to the basal ganglia) : am. Anteromesial group arising from the anterior cere-
bral, al. Anterolateral group, from the middle cerebral, pm>pl (on the optic thalamus).
Posteromesial and posterolateral groups, from the posterior cerebral.
Choroid arteries : a ch. Anterior, from the internal carotid, f ch (on the splenium). Posterior,
from the posterior cerebral.
Peripheral arteries ; I, I. Inferior internal frontal, from the anterior cerebral. 2. Inferior ex-
ternal frontal. 3. Ascending frontal. 4. Ascending parietal, and 5? temporoparietal,
trom the middle cerebral. 6. Anterior temporal, 7, posterior temporal, and 8, occipital,
trom the posterior cerebral.
419
BLOOD-VESSELS OF THE BRAIN. 421
THE ANTERIOR CEREBRAL ARTERY.
The anterior cerebral artery passes forward and inward across
the anterior perforated space to reach the inferior longitudinal
fissure between the frontal lobes, where it lies close to its fellow
of the opposite side, and gives off a branch of communication
with that vessel called the anterior communicating artery. It
then passes forward around the genu of the corpus callosum,
reaching its superior portion, and after giving off its cortical
branches, it courses backward to terminate with the posterior
cerebral artery.
The branches of the anterior cerebral artery are the anterior
communicating, the central or ganglionic, the commissural, and
the cortical. The anterior communicating artery is a small,
transverse branch, about two lines in length, which connects the
two anterior cerebral arteries. This communicating- branch
gives off two or three of the anteromedian arteries, which pass
to the head of the caudate nucleus. The central or gang-
lionic branches are the anteromedian group of vessels, most of
which come from the anterior cerebral, while a few come from
the anterior communicating. They pass through the anterior
perforated space and lamina cinerea to be distributed to the
head of the caudate nucleus.
The commissural branches supply the corpus callosum. The
cortical branches are the orbital, the marginofrontal, the calloso-
marginal, and the quadrate. The orbital branches supply the
inner part of the orbital lobe and the olfactory bulb. The
marginofrontal artery, which comes from the anterior cerebral
as it rests on the corpus callosum, supplies the marginal gyrus,
the convex surface of the superior and middle frontal gyri, and
the superior portion of the ascending frontal convolution. The
callosomarginal branch is distributed to the gyrus fornicatus.
The quadrate artery nourishes the quadrate lobe, or precuneus.
It will thus be seen that the cortical branches of the anterior
cerebral artery supply the entire median portion of the cere-
bral hemisphere as far back as the cuneus, the first and second
frontal, the upper part of the ascending frontal, together with
the orbital lobe and olfactory bulb.
4--
CENTRAL NERVOUS SYSTEM.
THE MIDDLE CEREBRAL OR SYLVIAN ARTERY.
The middle cerebral or Sylvian artery, the largest terminal
branch of the internal carotid, lies in the Sylvian fissure. Its course
is forward and outward until it reaches the island of Reil, where
it divides into five cortical branches, which lie in the sulci of the
insula ; these branches are then continued on to the convex sur-
face of the hemisphere, to supply a part of the frontal, most of
the central, and the parietal convolutions, as well as a large part
of the temporal lobe. The cortical branches of the Sylvian are the
Fig. 206. — Cortical Distribution of the Middle Cerebral Artery (Diagrammatic).
— (G. D. T. after Chai'cot, from Quain.)
CENT. Anterolateral group of central arteries. I. Inferior external frontal artery. 2. Ascend-
ing frontal artery. 3. Ascending parietal artery. 4. Parietotemporal artery.
inferior frontal, the ascending frontal, the ascending parietal, the
parietotemporal, and the sphenoid.
The first or inferior frontal artery is distributed to the convex
surface of the inferior frontal convolution. ; The second or
ascending frontal supplies the lower two-thirds of the ascending
frontal and the root of the second frontal, the upper third of the
ascending frontal being supplied by the marginofrontal branch
of the anterior cerebral artery. The third or ascending parietal
artery is distributed to the whole of the ascending parietal, the
superior parietal, and that part of the inferior parietal lobule
BLOOD-VESSELS OF THE BRAIN.
423
adjacent to the ascending parietal gyrus. The fourth, the
parietotemporal artery, supplies the supramarginal, the angular,
the posterior part of the inferior parietal, and the first and second
temporal gyri. The fifth or sphenoid artery supplies the an-
terior part of the first and most of the second temporal convo-
lutions.
The Central or Ganglionic Branches of the Middle
Cerebral. — These branches arise from the middle cerebral
close to its origin. They consist, first, of two small vessels
which pass through the inner part of the floor of the Sylvian
fissure to the head of the caudate nucleus ; and, second, of
numerous small vessels — the anterolateral arteries — which come
Fig. 207. — Diagram of the Blood-supply to the Central Ganglia by the Lentic-
ULOSTRIATE ARTERIES, EXTERNAL (£) AND INTERNAL (/). — {After Buret.)
Ill V. Third ventricle. PP. Pillars of the fornix. Mid. C. Middle cerebral artery.
off from the Sylvianat right angles and pass through the anterior
perforated space to be distributed to the caudate nucleus, except
its head, to the lenticular nucleus, the internal capsule, the ex-
ternal capsule, and a part of the optic thalamus.
These central or ganglionic branches of the Sylvian artery
are grouped by Duret into internal and external branches.
The internal branches pass through the inner segments of the
lenticular nucleus and are distributed to that nucleus and to the
internal capsule. The external vessels, which are divisible into an
anterior and a posterior set, pass upward outside of the lenticu-
lar nucleus, pierce the third segment of the lenticular nucleus, and
pass to the internal capsule. The anterior branches are called the
424 CENTRAL NERVOUS SYSTEM.
lenticulostriate arteries ; they pass to the lenticular and caudate
nuclei, except the head of the latter. The posterior branches,
or the lenticulo-optic arteries, supply the posterior parts of the
internal capsule and the anterior and inner parts of the optic
thalamus. The largest of the lenticulostriate arteries, which
passes between the lenticular nucleus and the external capsule,
and terminates in the caudate nucleus, is called, from its ten-
dency to rupture, " the artery of cerebral hemorrhage "
(Charcot).
POSTERIOR COMMUNICATING ARTERY.
The posterior communicating artery arises from the back
part of the internal carotid before that vessel divides into the
anterior and middle cerebral arteries. Occasionally it arises
from this latter vessel. The communicating artery passes back-
ward over the optic tract and crus cerebri, and joins the poste-
rior cerebral, a branch of the basilar. In its course it gives oft
small branches of supply to the dorsal portion of the optic
chiasm, to crus cerebri, infundibulum, and pituitary body, and to
the corpora mammillaria. From the posterior part of this com-
municating branch a few small vessels are given off, which, with
similar vessels from the posterior cerebral, form the postero-
median ganglionic branches.
THE ANTERIOR CHOROID ARTERY.
The anterior choroid artery is a small, slender branch from
the back part of the internal carotid, just external to the poste-
rior communicating ; it courses backward on to the optic tract
and crus cerebri, then passes beneath the uncinate gyrus,
enters the transverse fissure at the lower part of the descend-
ing horn of the lateral ventricle, and supplies the hippocampus
major, or cornu ammonis, the corpus fimbriatum, and the cho-
roid plexus.
BLOOD-VESSELS OF THE BRAIN. 425
THE VERTEBRAL ARTERIES.
The vertebral arteries, after reaching the cranial cavity-
through the foramen magnum, course along the ventral portion
of the medulla oblongata until they approach the lower border
of the pons Varolii, where they unite to form the basilar artery,
which is a mere prolongation of them. In their intracranial
course each vessel gives off the following branches : the poste-
rior meningeal, the anterior and posterior spinal, and the
posterior inferior cerebellar artery. The posterior meningeal is
a small vessel which leaves the vertebral at the foramen mas:-
o
num ; it supplies the falx cerebelli and the bone and dura mater
of the posterior fossa of the skull. The anterior and posterior
spinal arteries are described in connection with the blood-supply
of the spinal cord. The posterior inferior cerebellar arteries
are to be considered with the description of the nutrient vessels
of the cerebellum, pons, and medulla.
THE BASILAR ARTERY.
The basilar artery, a short but large vessel, is formed by the
union of the two vertebrals. It rests in the median groove on
the ventral surface of the pons, and extends from its inferior to
its upper border, where it terminates by dividing into two
branches — the posterior cerebral arteries. The branches of the
basilar are the transverse or pontal, the internal auditory, the
anterior cerebellar, the superior cerebellar, and the posterior
cerebral. The pontal as well as the cerebellar branches will be
described in connection with the blood-supply to the cerebellum,
pons, and medulla. The internal auditory artery passes with
the auditory nerve into the internal auditory meatus and is dis-
tributed to the internal ear (Fig. 209).
THE POSTERIOR CEREBRAL ARTERIES.
The posterior cerebral arteries, the terminal branches of the
basilar, wind around the crura cerebri, and after receiving the
posterior communicating branches from the internal carotids,
426
CENTRAL NERVOUS SYSTEM.
pass backward to reach the under surface of the cerebral hemi-
spheres, and terminate in three branches, which are distributed
to the occipital and temporal lobes. The branches of the pos-
terior cerebral are the central, or ganglionic, and the cortical, or
terminal. The central, or ganglionic, consist of the postero-
median, the posterior choroid, and the posterolateral. The
posteromedian arteries consist of several small vessels which
arise from the posterior cerebral close to its origin. These
vessels, in connection with a few bearing the same name from
the posterior communicating, pass through the posterior perfor-
ated space to supply the inner part of the optic thalamus and
walls of the third ventricle. The posterior choroid branch,
which supplies the velum interpositum and choroid plexus,
passes through the transverse fissure. The posterolateral
vessels take their origin from the posterior cerebral after it has
passed around the eras cerebri ; they give branches to the cms
cerebri, corpora quadrigemina, and posterior part of the optic
thalamus. The cortical or terminal branches, three in number,
are distributed as follows: (1) A branch to the uncinate con-
volution ; (2) a branch to the superior part of the temporal
lobe ; (3) the temporo-occipital branch to the cuneus, the
lingual gyrus, and the outer surface of the occipital lobe.
Fig. 208. — Diagram Showing the Areas of Cortical Distribution of the Anterior,
Middle, and Posterior Cerebral Arteries Respectively. — (£. A. S.,from Quain.)
A. Lateral aspect (see opposite page). B. Mesial aspect. C. Basal aspect. The area supplied
by the middle cerebral frequently extends to the upper border of the hemisphere in the
region of the parietal lobe, and therefore somewhat further than is represented in A.
427
BLOOD-VESSELS OF THE BRAIN.
429
THE CIRCLE OF WILLIS.
The branches of the internal carotids and vertebrals form at
the base of the brain a remarkable anastomosis, called the circle
ot Willis. This circle is completed anteriorly by the anterior
cerebral arteries and their branch of communication, the anterior
•5 tcreb post .
a. Co ei>.
a.cuzrc&
a , o&Teb. u
Fig. 209. — Arteries of the Anterior Surface of the Pons and Medulla. — [Aftei
Buret. )
a. cereb. post. Posterior cerebral artery. a. cereb. sup. Superior cerebellar artery, a. cereb.
moyen. Middle cerebellar artery, a. cereb. inf. Inferior cerebellar artery.
/. Root-arteries of spinal accessory nerve. 2. Anterior spinal artery, j. Root-arteries of pneu-
mogastric nerve. 4. Root-arteries of glossopharyngeal nerve. 5. Root-arteries of the oculo-
motor nerve. 6. Root-arteries of the facial and acoustic nerves. 7. Root-arteries of the
trigeminus nerve. 8. Root arteries of hypoglossal nerve.
communicating ; posteriorly, by the posterior cerebrals and point
of the basilar ; and laterally, by the internal carotids and pos-
terior communicating arteries. This circle of anastomosis
serves to equalize the blood-flow to the brain, and is the only
means of communication between the cortical and central or
43°
CENTRAL NERVOUS SYSTEM.
ganglionic blood-vessels. If either of the main trunks (carotids
or vertebrals) are obstructed, the nutrition of the parts of the
brain supplied by the branches of the obstructed vessels is not
interfered with, because they are supplied through the circle of
Willis by the remaining vessels, which are pervious.
The cerebellum, the pons Varolii, and the medulla oblongata
are supplied with branches from the vertebrals and basilar
arteries.
■eb. uT-f
- U- . Spt-7-l jOost ,
Fig. 210. — Arteries of the Posterior Surface of the Medulla. — (After Duret.)
a. cereb. inf. Inferior cerebellar artery, a. spin. post. Posterior spinal artery.
BLOOD-VESSELS OF THE CEREBELLUM.
The blood-supply to the cerebellum is derived from three ves-
sels — the superior, the middle, and the inferior cerebellar arteries.
The superior cerebellar arteries take their origin from the basilar
close to its point ot division into the posterior cerebral arteries.
Each vessel courses backward and outward over the pons
Varolii, being separated from the posterior cerebral artery,
BLOOD-VESSELS OF THE BRAIN. 431
whose course it resembles, by the motor oculi, or third cranial
nerve. It then courses around the crus cerebri, parallel with
the fourth cranial nerve, and reaches the upper surface of the
cerebellum, where it divides into an internal or superior vermi-
form branch, and an external or hemispheral branch. The
former vessel passes backward along the superior vermiform
process, anastomoses with the artery of the opposite side, and
when it reaches the posterior notch of the cerebellum it joins
the inferior vermiform artery, a branch of the posterior inferior
cerebellar artery. The external or hemispheral branch runs
backward over the superior surface of the cerebellum, supplying
it, and terminates near the posterior part of this surface, where
it anastomoses with the terminal hemispheral branch of the pos-
terior inferior cerebellar artery. This artery also supplies
branches to the velum interpositum, the superior medullary
velum, or valve of Vieussens, the corpora quadrigemina, and the
pineal gland.
The middle cerebellar — also called the anterior inferior cere-
bellar — arteries are branches of the basilar, and originate from
that vessel just above the inferior border of the pons ; their
course is downward and outward across the pons to the anterior
portion of the under surface of the cerebellum, which they sup-
ply. They anastomose with the posterior inferior cerebellar
artery. This vessel, at the beginning of its course, is crossed
by the abducens or sixth cranial nerve, and just as it passes
upon the inferior surface of the cerebellum, it lies close to the
facial and auditory nerves. In its course across the pons it
gives off several rather large vessels for the supply of the middle
cerebellar peduncles.
The inferior cerebellar arteries are also known as the pos-
terior inferior cerebellar. This latter name serves to distinguish
them from the middle cerebellar, which have, unfortunately, been
named the anterior inferior cerebellar arteries. These two ves-
sels are the largest branches of the vertebrals, and have their
origin from them opposite the lateral surfaces of the medulla
near its middle portion. Each vessel passes outward and back-
ward across the restiform body and between the pneumogastric
and hypoglossal nerve-roots ; it then goes to the under surface
432 CENTRAL NERVOUS SYSTEM.
of the cerebellum, where it divides into two branches — an in-
ternal, or inferior vermiform, and an external, or hemispheral.
The inferior vermiform branch passes backward between the
vermiform process and the cerebellar hemisphere, supplies the
vermiform process, and anastomoses with the vessels of the oppo-
site side and the superior vermiform, a branch of the superior
cerebellar artery. The external or hemispheral branch is dis-
tributed to the under surface of the cerebellum, and anastomoses
along its outer margin with the middle and superior cerebellar
arteries. This vessel also gives branches of supply to the choroid
plexus of the fourth ventricle and to the restiform bodies.
ARTERIAL SUPPLY TO THE PONS VAROLII AND
MEDULLA OBLONGATA.
The pons Varolii and medulla oblongata receive their arterial
supply from a series of small vessels which come off directly
from the basilar and vertebral arteries and from their branches
— the anterior and posterior spinal and the inferior cerebellar
arteries. The branches of the above-mentioned arteries which
reach the interior of the pons and medulla have been divided
by Duret into the three following sets :
First Set, the Median Arteries. — These are small vessels which
pass parallel to one another through the median plane of the
pons and medulla to reach the floor of the fourth ventricle, where
they terminate by dividing into fine capillary plexuses for the
supply of the cranial nerve nuclei and the beginning of their
nerve-roots.
The second set, or root arteries, pass in a transverse manner
around the outer portion of the pons and medulla to reach the
point of emergence of the roots of the cranial nerves, where they
divide into two branches — central and peripheral. The central
branch continues with the nerve to its nucleus of origin, sub-
dividing into a few parallel branches which terminate into a
capillary plexus about the nucleus, inosculating with small twigs
from the median arteries. The peripheral branch is distributed
along the nerve-roots.
The third or lateral set of vessels continue around the lateral
BLOOD-VESSELS OF THE BRAIN.
433
and anterior columns of the medulla to be distributed to the
restiform and olivary bodies as well as to the anterior pyramids.
The median arteries to the pons consist of a large number of
parallel coursing vessels, which come off directly from the basilar
,a oe-rcb.joosb.
'a..cere&.sup_
■a.cerejp.
'1-LOlfC/ZJlc
bcLsilcur
fe£&?t^?&f'&? y ' } jVc*cs//t:
-^iiiii^7
fit'i^/
'Jttr/ht- Optic 7ierre
-Riyht' Optic tract-
Fig. 228. — Diagram of Course of Optic Nerve-fibers, from the Cortex to the
Retina. — {After Sahli, Modified and Extended, from Tyson.)
459
CEREBRAL LOCALIZATION. 4 6i
all show that lesions of that part of the mesial surface of the
occipital and adjacent part of the temporal lobe bordering on
the calcarine fissure are invariably attended by partial or com-
plete bilateral homonymous hemianopsia — that is, a paralysis of
the fields of vision opposite to the lesion. Hence, this area
may be termed the half-vision center. The visual area may be
affected by irritative or destructive lesions. In the former case
the patient suffers from periodic nervous discharges, resulting in
visual hallucinations, such as a sudden flash of light, frequently
followed by temporary blindness in the opposite halves of the
visual fields. Destruction of this area on one side produces the
characteristic visual loss known as bilateral homonymous hemi-
anopsia, while destruction of the visual areas of both sides pro-
duces total blindness. It will thus be seen that hallucinations
of vision and bilateral homonymous hemianopsia are as charac-
teristic for irritative or destructive lesions of the visual area as
are partial unilateral convulsions and motor paralysis for lesions
of the motor region. In order to understand the peculiar form
of visual defect known as homonymous hemianopsia, it will be
necessary to recall to mind the course of the optic tract. The
fibers of this tract, which have their origin from the cells of the
temporal half of each retina, do not decussate in the optic
chiasm, but pass backward on the same side ; while those that
proceed from the cells of the nasal half of each retina cross
over in the chiasm to join the fibers from the temporal half of
the opposite retina, thus forming the optic tract of that side.
The fibers then continue backward to terminate about the cells
of the external geniculate body, the pulvinar of the optic thala-
mus, and the anterior corpus quadrigeminum. From the cells
of these primary optic centers new fibers start out, which pass
through the extreme end of the posterior division of the internal
capsule and thence radiate through the centrum semiovale, to
terminate about the cortical cells of the occipital lobe, chiefly
the cuneus and lingual gyrus ; thus, for example, the right oc-
cipital lobe has, terminating about its cortical cells, the fibers from
the temporal half of the right retina and those from the nasal
half of the left retina. It may be stated that the temporal
halves of the retinae receive impulse from the nasal halves of
4 f>2 CENTRAL NERVOUS SYSTEM.
the visual fields, and the nasal halves of the retinae receive im-
pulses from the temporal halves of the visual fields. Therefore,
a lesion involving the right visual area in the occipital lobe will
cause, owing to the fact that the right optic tract contains the
fibers from the temporal half of the right and the nasal half of
the left retina, a paralysis of the left halves of the visual field,
because of a loss of function of the right halves of each retina.
This defect is called bilateral homonymous hemianopsia.
• RETINAL REPRESENTATION IN THE OCCIPITAL CORTEX.
The very interesting case reported by Henry Hun, in connec-
tion with others collated by Seguin and Henschen, seem to
prove that the different quadrants of the retinse are represented
by different areas of the median surface of the occipital cortex.
In Hun's case there was a defect in the lower left quadrant
of each field of vision, with a corresponding atrophy of the
lower half of the rigiit cuneus. Henschen locates the cortical
center for the lower quadrant of each retina in the superior
part of the lingual gyrus.
COLOR VISION.
In regard to a cortical center for the representation of color
vision, nothing positive is known. Gowers believes it may be
located in the anterior division of the occipital lobe, while Hen-
schen places it in the vicinity of the calcarine fissure.
THE AUDITORY CENTERS.
Apart from the results of the experiments of Schafer and
Brown, physiologists and clinicians agree in locating the centers
for audition in the temporal lobes. The above-mentioned physi-
ologists experimented by destroying, on each side, the superior
temporal lobes of six monkeys, and in one animal the entire
temporal lobe was removed without producing the slightest loss
of hearing, even of a temporary character. The experiments
CEREBRAL LOCALIZATION. 463
of Ferrier, both those before and those undertaken since the
publication of the results of the work of Schafer and Brown, do
not bear out the conclusions of these latter observers. Ferrier
locates the auditory centers in the posterior part of the superior
or first temporosphenoid convolution on each side. Electric
excitation of this area on either side invariably produced in the
monkey retraction or picking up of the opposite ear, associated
with the opening of the eyes and dilatation of the pupils, with
turning of the head and eyes to the opposite side. He further
states that he placed a monkey on a table, and while all was
still he made a shrill whistle close to the animal's right ear ; im-
mediately the ear was retracted and the animal turned with a
look of intense surprise, with eyes widely opened and pupils
dilated, toward the side from which the sound proceeded, thus
proving that the stimulus of an external sound to a normal ani-
mal produced exactly the same phenomena as resulted from
electric stimulation of the auditory center. The similar result
in both cases is due to reflex action, in the former case to a
stimulus (electiic) applied directly to the auditory center, and
in the latter case is due to stimuli carried to the same center by
way of the auditory tract. These experiments, with others, on
animals whose sense of hearing is very acute has led Ferrier to
state that irritation of the superior temporosphenoid convolu-
tion of one side excites subjective auditory sensations of the
ear of the opposite side, such as pricking of the ear and turning
of the head and eyes toward the side. The destruction of this
area on either side caused an absence of the usual reaction to
the auditory stimuli coming from the ear opposite to the lesion
after the ear on the side operated on was carefully plugged.
Destruction of both superior temporal gyri caused complete
absence of the response to auditory stimuli, which invariably
attracted the attention of a normal animal. This seems con-
clusive proof that in the monkey there are two centers of hear-
ing, one in each superior temporal gyrus, the destruction of one
producing deafness in the opposite ear, and the destruction of
both producing total deafness.
In man the centers of audition are located in the same parts
of the temporal lobes as Ferrier has located them in the mon-
464 CENTRAL NERVOUS SYSTEM.
key. This has been proven by a few well-recorded cases with
autopsies. These cases show that lesions of the superior tem-
poral gyri give rise to two sets of symptoms — i, .m
D.ir
jj.v
J). vi
JD.VE
D.VM
2>.XI
DJCU.
CV2
Fig. 234 B,
-Diagram of Skin Areas Corresponding to Different Spinal
MENTS. — (Front Tyson , after Starr.)
49S
Seg-
CEREBRAL LOCALIZATION. 49g
frequently regurgitated through the nose. As a result of the
involvement of the nuclei of the spinal accessory nerves, laryn-
geal symptoms supervene, such as weakness of the voice, diffi-
culty in coughing, and marked difficulty in phonation. Because
of the paralysis of the epiglottis, particles of food frequently
lodge in the larynx or bronchi, often giving rise to insufflation
pneumonia.
There is a rare lorm of bulbar paralysis acute in onset, prob-
ably of an infectious nature, accompanied by the same symp-
toms as previously described, only being much more rapid in their
development, death usually resulting within a few weeks. This
affection resembles acute poliomyelitis of children, but the prog-
nosis is much more grave.
In many cases of tumor involving the medulla oblongata dia-
betes mellitus, polyuria, bradycardia, tachycardia, and Cheyne-
Stokes respiration have been observed, in addition to the before-
mentioned symptoms.
LOCALIZATION OF SPINAL-CORD LESIONS.
The symptoms available for diagnosis and localization of
spinal-cord diseases may be divided into two great groups, —
motor and sensory, — corresponding in a general way to the
ventral and dorsal parts of the cord.
The motor symptoms may be due to affections of the upper
(corticospinal) or lower (spinomuscular) motor neurones, each
of which produces a perfectly distinct and classic type of par-
alysis. If the upper motor neurones are separated at any part
of their course from their trophic cells in the motor area of the
cerebral cortex, there results a secondary degeneration down-
ward, involving the direct and crossed pyramidal or motor tracts,
which gives rise to a type of paralysis having the following
characters : All the muscles are equally involved, though the
limbs are incompletely paralyzed. The muscles are usually not
wasted, save from disuse, and they are continually in a state of
partial or complete tonic contraction, giving rise to stiffness and
rigidity. The electric reactions are normal ; muscular irritability
500
CENTRAL NERVOUS SYSTEM.
a
a
is greatly increased, the slightest tap producing prompt muscular
contraction ; the reflexes, both superficial and deep, are greatly
exaggerated, ankle- and knee-clonus
being usually present. As a result of
this form of paralysis, locomotion is
much interfered with and a character-
istic spastic gait is developed. The
patient assists himself with two canes ;
his chest is bent forward ; the legs
move forward very stiffly by the aid of
the trunk-muscles, the toes scraping
the ground, and the knees frequently
interlocking — cross-legged progression.
Very rarely cases occur in which a
primary degeneration of the motor
tracts in the cord (spinal part of the
corticospinal tracts) has been found
with symptoms identical in character
with those previously described. This
very chronic disease was first described
by Erb in 1875, and is generally known
as Erb 's palsy, primary lateral sclerosis,
or spasmodic paralysis.
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512
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM. 513
brain. The subjoined table, from Dejerine, indicates the differ-
ent parts of the cerebrospinal system derived from each en-
cephalic vesicle.
THE DEVELOPMENT OF THE SPINAL CORD.
That part of the neural tube not concerned in the formation
of the cerebral vesicles is converted into the spinal cord. This
tube is oval on cross-section, and can very early be differen-
tiated into a right and a left half by a thickening due to cell-
growth or multiplication of its lateral walls. The upper and
lower walls, or the roof and floor, remain very thin and form
later the commissures, the former forming the posterior or dor-
sal commissure, while the latter forms the anterior or ventral
commissure.
The cells of which the walls of the neural tube are composed
consist at first of a single layer of cells having a distinctly epi-
thelial character. They are very long, extend in a radial man-
ner throughout the entire thickness of the walls, and lie very
close to each other, thus having a palisade-like appearance.
While the epithelial character of the cells is preserved, there
may be distinguished an inner and an outer clear zone without
nuclei, the middle zone containing all the nuclei, which are in-
creased in numbers as development progresses. Between the
inner clear zones of these epithelial cells and toward the central
cavity there appears at the fourth or fifth week, in the human
embryo, a number of cells spheric in shape, 10 to 14 p in diam-
eter, with nuclei, which present one or another stage of karyo-
kinesis. These are the p-erminatino- cells or "Keimzellen" of His.
They are early transformed into neuroblasts, or primitive nerve-
cells, by a lengthening out of their cell-body and the formation
of a single protoplasmic stalk, or axis-cylinder, which forms a
nerve-fiber. Along with the growth of the walls of the neural
tube, the epithelial cells increase in length, become vacuolated ,
lose their definite cell-boundary, and their protoplasm becomes
filled with perforations. The individual cell appears as if pos-
sessed of branching processes united with those from adjacent
cells, and thus forms a network which extends throughout the
33
5 H
CENTRAL NERVOUS SYSTEM.
entire thickness of the embryonic cord. This network has been
termed by His myelospongium, or neurospongium, and the cells
from which it is formed are called spongioblasts, they being the
primitive neuroglia cells. They are at this stage elongated and
oblong in form, and have oval nuclei. Each spongioblast pos-
sesses two main processes — an outer and an inner, or peripheral
Fig. 240. — Fore-part of the Embryo Viewed from tfie Dorsal Side. — (After
A'ot'liiker, from Quain.)
/'. Fore-brain, e. Ocular vesicles. M. Mid-brain. //. Hind-brain, h. Fart of the heart
seen bulging to the right side. Vom, Omphalomesenteric or vitelline veins entering the
heart posteriorly. Mr. Medullary canal, spinal part. p. Protovertebral somites.
and central. The inner or central processes course inward to
the inner boundary, where they break up into fine branches,
which unite to form a close network called the internal limiting
membrane. The outer or peripheral processes branch and form
a network, which is most distinct in the outer layer. At a later
stage these spongioblasts become thickened near the position
ol their nuclei ; the nuclei proliferate rapidly and then migrate,
Fig. 241. — Myelospongium from Spinal Cord of Thsee-and-.
Embryo. — [His, from Quain. )
-Half-Weeks' Human
ifili
Fig. 242. — Inner Ends of Spon-
gioblasts (sp) with Germinal
Cells, g, Betweenthem. From
spinal cord of human embryo. —
[His, from Quain.)
Fig. 243. — Inner Ends
of Spongioblasts
(Sp). A germinal cell
Ig) and two transi-
tional cells ( Tr) from
spinal cord of human
embryo. — (His, from
Quain. )
Fin. 244. — Three Neu-
roblasts, Each with
a Nerve-fiber Pro-
cess Growing out
Beyond the Base-
ment Membrane of
the Embryonic Spi-
nal Cord. — (His,
from Quain. )
515
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM.
517
accumulating about the central canal and along the periphery
of the medullary wall of the neural tube. Many of the cells
lose their central processes, the outer process alone remaining ;
soon this process is also lost, and lateral branches having devel-
oped, the elongated configuration of the cells is lost, the cells
being transformed into the spheric neuroglia or stellate cells of
Deiter.
Other spongioblasts which have accumulated about the cen-
tral canal form for it its epithelial lining, or ependyma. These
ependymal cells have fine radiating processes which pass through
the entire thickness of the gray and white matter of the embry-
Fig. 245. — Ependymal Fiber of Marrow of a Seven-days'-old Embryo of a
Chicken. — {After Golgi.)
onic cord. About the fifth week of embryonic life their free
surfaces develop cilia, which extend into the central cavity.
These ependymal cells are identical in character with neuroglia
cells. At a period when the neuroblasts, or nerve-cells, can be
well differentiated, the medullary wall of the neural tube may
be divided into three layers: First, the outer neuroglia layer,
or the Randschleier of His, in which location the white matter
is developed. Second, the middle or mantle layer, the habitat
for the neuroblasts, or the region of the gray matter. Third,
the inner layer of ependymal cells.
The researches of His have shown that both the spongio-
5 i8 CENTRAL NERVOUS SYSTEM.
blasts from which the neuroglia cells are developed and the
neuroblasts from which the nerve-cells and fibers are developed
are formed from cells of the epiblast, which are identical in
character. This observation of His has recently been confirmed
by Ramon y Cajal, who states that cells which, from their form
and position, would be classed as spongioblasts, frequently alter
their shape and, throwing out axis-cylinder processes, become
converted into nerve-cells and fibers. The neuroblasts of the
primitive nerve-cells are pear-shaped, owing to the development
from each of an elongated protoplasmic process which becomes
the axone of the future nerve-cell. The cells at this period do
not possess dendrites, they being developed much later. The
neuroblasts are capable of motion and frequently alter their
position.
s n
Fig. 246. — Lower End of the Spinal Cord of a Human Embryo of Three Months.
— [From Jfino/.)
Epy. Ependymal layer, n. Neuroblast layer. R. Outer neuroglia layer, or Randschleier.
The study of a transverse section of the human embryonic
cord at the fourth week shows it to be composed of an outer
neuroglia layer, the Randschleier, in the meshes of which the
white matter is developed ; of a middle or mantle layer, occu-
pied by neuroblasts, from which the gray matter is developed ;
and, lastly, an inner layer of ependymal cells.
The neuroblasts found distributed throughout the middle
layer tend to collect into two large groups, which are located in
the outer and ventral part of this layer and constitute in the
human embryo of six weeks the chief portion of each half of
the cord. The more ventral portions of these groups form the
anterior horns or cornua, the cells being motor in function. The
axones of these cells pass, in slight curves, through the ventral
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM.
519
portion of the outer layer, to form the primitive anterior spinal
nerve-roots. The processes of the more dorsally located neuro-
blasts do not leave the embryonic cord, but pass into the meshes
of the myelospongium, where, according to His, they meet re-
sistance, and hence their direction is changed into an upward
Fig. 247. — Section of Spinal Cord of Four
Weeks' Human Embryo. — {His, from Quaiu.)
The posterior roots are continued within the cord into
a small longitudinal bundle which is the rudiment
of the posterior white column. The anterior roots
are formed by the convergence of the processes of
the neuroblasts. The latter, along with the elon-
gated cells of the myelospongium, compose the gray
matter. The external layer of the cord is traversed
by radiating fibers which are the outer ends of the
spongioblasts. The anterior commissure is begin-
ning to appear. This figure is much more magni-
fied than the next one.
Fig. 248. — Transverse Section
of the Cervical Part of
the Spinal Cord of a Human
Embryoof Six Weeks. — {After
Koelliker,from Quain.)
c. Central canal, e. Its epithelial
lining. e ; (superiorly). The orig-
inal place of closure of the canal.
a. The white substance of the an-
terior columns. g. Gray sub-
stance of anterolateral horn. p.
Posterior column, ar. Anterior
roots, pr. Posterior roots.
and downward course. These neuroblasts, with their processes,
form the intrinsic cells and fibers of the cord.
A cross-section of the cord at the sixth or eighth week shows
the central canal elongated ventrodorsally and presenting, near
its middle on each side, a lateral extension which cuts deeply
into each lateral wall of the medullary tube, thus dividing the
primitive cord into the ventral and dorsal zones of His. At
520 CENTRAL NERVOUS SYSTEM.
this stage can be seen issuing from the neuroblasts of the ventral
zones fibers proceeding ventrally to reach the outside of the
cord forming the anterior or motor nerve-roots. Entering the
dorsal zones, fibers may be seen which are the axones of the
embryonic posterior spinal ganglia. At a later period in devel-
opment the central cavity decreases in size until about the tenth
week, when its walls almost coalesce between the dorsal zones,
leaving only a small triangular-shaped opening in its most dorsal
extremity. Still later all traces of the cavity are obliterated,
there remaining only the central canal.
At the sixth week no trace exists of the anterior and posterior
longitudinal fissures. The former is due to an arrest of devel-
opment of the floor of the central cavity, and a corresponding
rapid development of the ventral zones resulting in two bulg-
ings which never coalesce, but become approximated in the
median line, leaving a fissure between them. In this fissure is
found a process of connective tissue from the pia. The so-
called posterior fissure is doubtless the remains of the dorsal
part of the central cavity, being indicated as a mere slit, which
contains a process of neuroglia from the ependymal cells of its
dorsal w r all. This process was named the posterior longitudinal
fissure by early anatomists, from its resemblance to the anterior
fissure, and the probability of its containing a process of pia,
and, although later anatomists have proved the falsity of this
view, it is still, owing to long usage, convenient to retain the old
name, and hence in the description of the spinal cord it is so
recognized.
The anterior horns depend, for their growth, upon the con-
version of the germinating cells of the mantle layer into neuro-
blasts, and the subsequent growth of the latter into complete
motor neurones.
The cells of the posterior horns are probably derived from
the dorsal part of the mantle layer. The cervix of each poste-
rior horn is formed by the narrow part of the gray matter con-
necting the dorsal and ventral zones and located opposite the
central furrow or groove.
The white matter of the cord is developed in the outer layer,
or Randschleier of His. This layer forms a complete covering
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM.
5-i
for the mantle layer, or gray matter. In the dorsal zone on each
side exists an oval projection of the Randschleier, called the oval
bundle of His, which extends from the entrance of the most
ventrally placed posterior root to near the mid-dorsal line, and
contains longitudinally coursing fibers from the embryonic pos-
terior spinal ganglia. Increasing- in size, each bundle extends
backward to the arch formed by the union of the dorsal zones
with the roof of the medullary tube. This arch gives rise to
the columns of Goll, which become united, owing- to the oblit-
eration of the small triangular opening, this being the remains
Rscb
Fig. 249. — Transverse Section of the Spinal Cord from the Upper Dorsal
Region of a Human Embryo of Six Weeks. — {After His , from Minot.)
d.pl. Deck-plate, ov.b. Oval bundle of dorsal zone. D.R. Dorsal root. Rsch. Randschleier
of ventral zone. b. Floor-plate. V.R. Ventral root.
of the dorsal periphery of the central cavity, which lies between
them. The oval bundle continues to grow dorsomesially and,
becoming situated between Goll's columns and the gray matter,
unites with its fellow of the opposite side to form the columns
of Burdach. This oval bundle is connected with the dorsal
part of the outer layer, or Randschleier, which forms a covering
for the ventral zone by a narrow portion located at the bottom
of a sulcus, called the central groove. This narrow portion
begins to grow rapidly, and completely obliterates the central
groove. At this point on each side are developed the lateral
522 CENTRAL NERVOUS SYSTEM.
pyramidal tracts. In that part of the outer layer, or Randschleier,
located between the ventral fissure and the exit of the axones
of the neuroblasts of the ventral zone (anterior horns) are formed
the anterior columns of the cord, while that portion located be-
tween the oval bundle and the exit of the same nerve-fibers
gives rise to the lateral columns.
The posterior spinal ganglia take their origin from cells of
the epiblast located just external to the medullary ridges of each
side, and when these ridges meet at the mid-dorsal line to form
the neural tube, these groups of cells also unite at the median
line to form a slightly elevated portion of the epiblast, which is
termed the neural crest. At regular intervals along each side
of this crest corresponding to the middle of the mesoblastic
somites, or provertebra, lateral projections, or outgrowths of
cells appear, which separate from the neural crest to form the
primitive posterior spinal ganglia.
The embryonic cells of the spinal ganglia are bipolar in form,
each cell possessing both a central and a peripheral axone. The
former enter the dorsal columns of the cord and form the sen-
sory nerve-roots, while the latter have a peripheral course, and
are destined to terminate in sensory end organs. Toward the
end of embryonic life most of these cells become unipolar, either
by fusion of their protoplasmic processes or, what is more prob-
able, by an outgrowth of a protoplasmic stalk. This stalk or
pedicle divides T-shaped, one division passing into the dorsal
part of the cord as a posterior spinal nerve-root, where it again
divides into a long ascending and a short descending branch.
The other process passes peripherally as a periphery sensory
nerve-fiber and terminates in a sensory end organ.
The fibers of the columns of the cord have their origin from
the various parts of the brain, as well as from the spinal cord
and posterior spinal ganglia. They are simply the lengthened-
out axis-cylinder processes of the cells of these regions which
have grown in the direction in which they convey impulses.
These fibers are at first all non-medullated, but receive their
myelin sheaths at later periods of development. Flechsig has
shown that the fibers of the different columns of the cord re-
ceive their myelin at certain definite periods of embryonic life,
Fig. 250.— Sections Across the Region of the Calamus Scriptorius of the Brain.
— {His, from Quain.)
A. Region of the glossopharyngeal ganglion. B. Of the auditory facial ganglion.
Fig. 251. — Sections Across the Fourth Ventricle of a Somewhat Older
Embryo. — ( His, from Quain . )
A. Section taken through the lower part. B. Across the widest part (trigeminus region).
Through upper part (cerebellar region), r. Roof of neural canal, al. Alar lamina.
Basal lamina, v. Ventral border.
Fig. 252.— Sections Across the Lower Half of the Fourth Ventricle of a Still
Older Embryo. Showing gradual opening out of the neural canal and the commencing
folding over of the alar lamina (at/). — (His, from Quain.)
v. Ventral border, t. Tenia, ot. Otic vesicle, rl. Recessus labyrinthi.
In the succeeding stage (not here represented) the angle at v has almost disappeared, the fold/
has extended over the alar lamina, and the two thickened halves are in the same horizontal
plane, covered by a greatly expanded and thinned-out roof.
523
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM. 525
so that the location and course of the various tracts can be
easily demonstrated.
The embryonic cord completely fills the cavity of the spinal
canal up to the beginning of the fourth month, but at birth,
owing to a more rapid development of the spinal canal, the lower-
most part of the cord (coccygeal portion) reaches only to the
level of the third lumbar vertebra, and in the adult to the lower
part of the first lumbar. This apparent ascent of the cord alters
the course of the nerve-roots running out of it. At first these
roots leave the cord nearly at right angles, but later, owing to
the before-described changes, these fibers have an oblique or
a nearly longitudinal course within the spinal canal. In the
lumbar and sacral parts of the cord these descending fibers form
the cauda equina. The cervical and lumbar enlargements are
well differentiated at the fourth month of fetal life.
The membranes and the blood-vessels of the cord are both
derived from the mesoblast, which has formed a canal around
the neural tube.
DEVELOPMENT OF THE MEDULLA OBLONGATA.
The medulla oblongata is developed from the fifth or after-
brain vesicle — the metencephalon. Although the medulla differs
in shape from the spinal cord, its development is essentially the
same. Early in the growth of the after-brain vesicle there is to
be distinguished a floor (Bodenplatte), lateral walls, and a roof
(Deckplatte). From thickenings of the floor and lateral walls
are developed (third month) the anterior and lateral columns,
continuous with those of the cord. From the roof no nerve-
cells are developed, and it retains its epithelial character and
becomes spread out over quite an extensive surface, forming a
covering to the cavity of the metencephalon, or fourth ventricle.
Later, this covering becomes blended with the under surface of
the pia, which is very vascular, the vessels being arranged into
two rows of villous processes which grow into the cavity of the
after-brain vesicle, to form the choroid plexuses of the fourth
ventricle, or tela choroidea inferior.
Transverse section of the metencephalon in an embryo of
526
CENTRAL NERVOUS SYSTEM.
about three weeks shows the primitive medulla to be more or
less shield shaped, with a triangular medullary cavity. This
appearance is due to the growth laterally of the thin dorsal wall
or roof which forms the base, while the dorsal halves of the
lateral walls are spread widely apart ; their ventral halves, which
meet the dorsal at a distinct angle, gradually converge and join
the floor of the medullary wall in the median line. The angle
of junction of the dorsal and ventral parts of each lateral wall
serves to separate the medullary walls into the dorsal and ventral
zones of His. Owing to the widening of the medullary tube
and the expansion of the roof, the dorsal and ventral zones are
brought nearly into one plane. Along the edge of the dorsal
zone a fold, by which the edge is arched outward and downward,
Fig. 253. — Transverse Section of the Medulla Oblongata of His' Embryo Ru
(Length of Back, 9.1 mm.). — [After W. His, from Minot.)
RL. Rhomboid lip. Ts. Tractus solitarius. X. Vagus nerve. XII. Hypoglossal nerve.
is formed and is separated from the dorsal zone by an external
notch. This fold has been called the fold of the rhomboid
fossa — the Rautenlippe.
The walls of the metencephalon, as well as those of the rest
of the cerebral vesicles, may be early differentiated, owing to an
orderly arrangement of the spongio- and neuroblasts, into three
distinct layers — an outer neuroglia or white matter (the Rand-
schleier), the middle mantle or gray matter, and the inner or
ependymal layer.
The lower boundary of the dorsal zones is indicated by an
oval-shaped area on each side containing longitudinal nerve-
fibers, axones, and collaterals from the cerebral ganglia : these
are the solitary bundles or tracts. They are homologous with
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM.
5 2 7
the oval bundles of the Randschleier of the spinal cord. The
ventral zones are separated from each other above by a median
groove, which begins at a point where the central canal widens
and extends to the aqueduct of Sylvius. On each side of this
groove is developed an eminence which later is called the
eminentia teres. The ventral zones are separated laterally
from the dorsal by a less prominent groove, the remains of which
are indicated in the adult by the fovea anterior and posterior.
The fold, or Rautenlippe, on each side grows downward and
unites with the main fold of the dorsal zone ; by so doing it
surrounds the solitary bundle, displacing it inward, so that it
comes to occupy a deeper position. At this stage the dorsal
Fig. 254. — Transverse Section of the Medulla Oblongata of His' Embryo Mr.
—{After W. His, from Minot.)
T. Tractus solitarius. RL. Secondary rhomboid lip. F.r. Funiculus restiformis. a.Tr. As-
cending trigeminal tract.
and ventral zones are in about the same plane, the groove sepa-
rating them being nearly obliterated. In the dorsal zone are
developed the restiform body, the clava, the solitary bundle, and
the descending trigeminal nucleus and tract. The nucleus of
Burdach's column is probably derived from the Rautenlippe.
The neuroblasts of the dorsal zone that are developed during
the fourth week form the arcuate fibers. The neuroblasts of
this zone which are formed later migrate in tracts, both within
and outside of the solitary bundle, into the lower part of the
ventral zone, where, with other neuroblasts, they form the olivary
body.
The raphe, which is a neuroglia partition between the ven-
52S CENTRAL NERVOUS SYSTEM.
tral zones, arises from a thickening of the floor of the medullary
wall. It is the place of crossing of fibers from one side of the
medulla to the opposite ; no neuroblasts can migrate across this
partition.
The neuroblasts of the gray matter (mantle layer) of the
ventral zone enter chiefly into the production of the formatio
reticularis ; those that have migrated from the dorsal zone form
the main and accessory olivary bodies. The layer of neuro-
blasts beneath the ependyma gives rise to the motor cranial nuclei
in this region. In the outer layer (neuroglia), or Randschleier,
are developed the white columns of the medulla. This outer
layer is divided by the exits of the ventral nerve-roots (hypo-
glossal) into a median or ventral and lateral regions corre-
sponding to the anterior and lateral columns of the cord. In
the dorsal part of the median region are developed longitudinal
fibers which collect into bundles and form the posterior longi-
tudinal bundles. At the fourth month large numbers of longi-
tudinal fibers appear in the ventral parts of the median region ;
these fibers form the anterior pyramids. The lateral region of
each side contains the fibers of the restiform body, some arcuate
fibers, descending trigeminal nerve-fibers, solitary bundle, and
nucleus of Burdach's columns.
CEREBELLUM AND PONS.
The cerebellum and pons Varolii are developed from the
fourth cerebral vesicle, or epencephalon. This vesicle is con-
tinuous behind with the metencephalon, or fifth vesicle, the two
together forming the elongated, somewhat boat-shaped cavity —
the embryonic fourth ventricle. The epencephalon is separated
from the metencephalon, or mid-brain, by a narrow constricted
part of the neural tube, called by His the isthmus. The cere-
bellum grows out from the dorsal wall or roof of the fourth
cerebral vesicle, and becomes located between the medulla
oblongata and the isthmus. From the floor of this vesicle the
pons Varolii becomes developed. As early as the third month
the transverse fibers so characteristic of the pons may be dis-
tinguished. The growth of the pons is very rapid, and proceeds
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM.
529
pari passu with that of the cerebellum. The lateral walls »ive
rise to the middle cerebellar peduncles. The cerebellum
appears at first as a budding forward of the dorsal wall of the
epencephalon, which, as it grows, forms a distinct transverse
thickening or ridge overhanging the thin roof of the medulla
oblongata. At about the third month of embryonic life the
middle portion of this ridge increases in size, and becomes
Fig. 255. — Median Section through the Brain of a Two and a Half Months'
Fetus. — (His, from Qitain.)
The mesial surface of the left cerebral hemisphere is seen in the upper and right-hand part of
the figure ; the large cavity of the third ventricle is bounded above and in front by a thin
lamina; below is seen the infundihulum and pituitary body. Filling the upper part of the
cavity is the thalamus opticus ; in front and below this is the slit-like foramen of Monro.
Behind the thalamus is seen another slit-like opening which leads into the still hollow ex-
ternal geniculate body.
olf. Olfactory lobe. p. Pituitary body. e.g. Corpora quadrigemina. cb. Cerebellum. 7/1.0.
Medulla oblongata.
differentiated from the lateral parts by the development of four
rather deep transverse grooves or fissures, which serve to divide
it into three permanent lobes. The middle portion or lobe is
called the worm, or vermis. From now on the lateral parts
increase greatly in size, growing outward on each side to form
the cerebellar hemispheres, right and left. The cerebellum, or
expanded roof of the fourth cerebral vesicle, is connected in
front with that of the mid-brain, and behind with the choroid
34
53Q CENTRAL NERVOUS SYSTEM.
plexus of the after-brain vesicle, or fourth ventricle, by two
lamellae of white matter — the anterior and posterior or superior
and inferior medullary velum (Figs. 255 and 256).
CORPORA QUADRIGEMINA, CRURA CEREBRI, AND
AQUEDUCT OF SYLVIUS.
THE THIRD CEREBRAL VESICLE (SECOND PRIMITIVE VESICLE),
MESENCEPHALON, OR MID-BRAIN.
This part of the embryonic neural tube develops very rapidly,
and, in consequence of the cephalic curvatures of the medullary
tube, it at first occupies the summit of the brain vesicles. In
front it is continuous with the fore-brain, and behind with the
hind-brain. Owing to the much more rapid development of the
hemispheric vesicles, together with that of the cerebellum, the
mid-brain is completely covered in. In man only a small part
of the brain is developed from this vesicle. Its walls become
uniformly thickened, thus narrowing the cavity into a small per-
manent canal, which communicates above with the third ven-
tricle, or ventricle of the inter-brain, and below with the fourth
ventricle, or ventricle of the hind-brain. This narrowed canal
is called the aqueduct of Sylvius. From the thickened anterior
wall (floor) the peduncles of the cerebrum (crura cerebri) are
developed ; these appear at the third month as two rounded,
longitudinal ridges on each side of the median line. It is prob-
able that a large part of the posterior perforated space is also
developed from this same area, and appears in the adult as a
triangular gray lamina between the crura cerebri. The dorsal
region or roof of the mid-brain becomes much thickened, and is
divided at the third month into two lateral halves by the develop-
ment of a median groove, and these halves are again separated
at the fifth month by the appearance of a transverse groove,
into four parts, two ventral and two dorsal ; these are the
corpora quadrigemina.
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM.
53'
OPTIC THALAMI, INFUNDIBULUM, PITUITARY BODY,
PINEAL GLAND, CORPORA MAMMILLARIA, AND
OPTIC CHIASM.
The first primitive cerebral vesicle, or fore-brain, owing to the
development by a process of budding out of its ventral wall of
a secondary vesicle whose growth is exceedingly rapid, becomes
located between this fully developed secondary fore-brain, or
m.o.
Fig. 256. — Fetal Bkain of the Third Month — (His, from Quain.)
The brain is represented in profile, but the external wall of the right hemisphere has been re-
moved to show the interior of the lateral ventricle with the corpus striatum curving around
the bend of the fossa of Sylvius. The curved projections above the corpus striatum are
infoldings of the mesial wall of the hemisphere vesicle. The lettering is the same as in
figure 255.
prosencephalon, and the mid-brain ; hence its name, dienceph-
alon, inter-brain or between-brain. The inter-brain at the fifth
week is oblong in shape, distinctly narrowed at its anterior
extremity where it joins the cerebral hemispheres, less so at its
posterior extremity, which is attached to the mid-brain. From
its walls grow out on each side at a very early period two hollow
protrusions, the primary optic vesicles, the details of which will
be considered later. Its cavity (third ventricle) communicates
with the cavities of the cerebral hemispheres (lateral ventricles)
532 CENTRAL NERVOUS SYSTEM.
by an opening on each side which at first is very large, but later
becomes exceedingly narrowed, owing to the growth of the
cerebral hemispheres. These openings of communication are
termed the foramina of Monro. Posteriorly, the cavity com-
municates with the cavity of the hind-brain (fourth ventricle) by
means of the central canal of the mid-brain (aqueduct of
Sylvius).
Each optic thalamus is formed by a marked thickening of
the lateral walls, which grow gradually inward into the cavity of
the inter-brain, converting it into a narrow cleft, which is perma-
nent, and located between the convex surfaces of the optic
thalami. This cleft is called the third ventricle. The inner
convex surfaces of the optic thalami meet across the middle of
this space, their union forming the middle or soft commissure.
At the beginning of the fourth week the floor of the inter-
brain cavity is prolonged downward, forming a funnel-shaped
diverticulum, which remains throughout life, and is called the
infundibulum. Connected with the apex of the infundibulum
is the pituitary body, or hypophysis cerebri. The roof of this
cavity resembles that of the hind-brain, from the fact that it per-
sists as a simple epithelial layer which unites with the under
surface of the pia mater, the two together forming a fold which
is deflected into the cavity, and from which are suspended the
choroid plexus (tela choroidea superior) of the third ventricle.
In connection with the growth of the inter-brain mention
must be made of the evolution of two as yet functionally un-
known parts — the pineal gland, or epiphysis cerebri, and the
pituitary body, or hypophysis cerebri. The former takes its
origin from the roof; the latter from the floor of the inter-brain.
The pineal gland develops in man at about the sixth week
as a median dorsal budding or outgrowth from the roof of the
inter-brain at a point where it becomes continuous with the
roof of the mid-brain. It has at first a tubular shape resem-
bling somewhat the finger of a glove. In all vertebrates except
man it is directed forward in its growth, and is retained in that
position, but in man it develops in an opposite direction, coming
to lie on the mid-brain roof.
It terminates blind, but its cavity is at first continuous with
Fig. 257. — Transverse Sections through the Brain of a Sheet's Embryo of 2.7
cm. IN Length. — (After Koettiker, from Qiiain.)
In A, the section passes through the foramina of Monro ; in B, through the third and lateral ven-
tricles somewhat further back. st. Corpus striatum. th. Optic thalamus, t. Third ven-
tricle, c, c' ' . Rudiment of internal capsule and corona radiata. /. Lateral ventricle with
choroid plexus, pi. h. Hippocampus major, f. Primitive falx. a. Orbitosphenoid. sa.
Presphenoid. /. Pharynx, ch. Chiasma. 0. Optic nerve, m, 111. Foramina of Monro.
to. Optic tract, ink. Meckel's cartilage.
533
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM. 535
that of the third ventricle. Later in its development, budding
processes appear from thickenings of its walls, which divide the
cavity of the gland into a number of compartments or follicles
which are lined with cylindric ciliated epithelium. In man the
follicles tend to become solid and contain deposits of calcareous
matter. In the roof of the inter-brain, just dorsal to the pineal
gland, fibers appear having a transverse course, connecting
the posterior parts of the optic thalami. They form the
posterior commissure. In reptiles, according to Spencer, the
pineal gland remains as a long stalk whose distal or periph-
eral end lies beneath the epidermis, having passed through an
Fig. 258.— Brain of a Chick Embryo, Fourth Day.— -{After Duval, from Minot.)
I. First, II, second, cerebral vesicle. Ep. Epiphysis or pineal gland. H. Cerebral hemisphere.
L. Lens, surrounded by the optic vesicle, ot. Otocyst. Md. Hind-brain.
opening in the roof of the skull (parietal bone), called the
parietal foramen. This portion of the sac enlarges into a hol-
low globe, which soon becomes flattened. The wall next to the
epidermis thickens to form a lens-like structure, while the oppo-
site part of the wall to which the stalk, is attached has a retina-
like construction.
In the region of the retina nucleated cells, together with pig-
ment, have been observed, and in the stalk, nerve-fibers are
found. The development of this body in reptiles, the forma-
tion of a lens- and retina-like structure, together with the pres-
ence of cells and pigment in the latter, and the presence of
536 CENTRAL NERVOUS SYSTEM.
nerve-cells in the stalk, all indicate that it must be a true but
rudimentary eye.
The pituitary body, or hypophysis cerebri, has a double
origin from the epiblast, it being developed in part from the
oral cleft and in part from the floor of the inter-brain. In man
at the sixth week there is developed from the oral cleft a hollow
protrusion upward and backward toward the inter-brain. This
protrusion is called the pouch of Rathke, or the pocket of the
hypophysis. This pouch becomes constricted at its origin, but re-
mains connected for a long time with the oral cavity by a narrow
canal or duct, which eventually becomes obliterated. At about
the same time a somewhat similar protrusion forms from the
floor of the inter-brain (infundibulum), which enlarges downward
and backward toward the hypophysis, the end of which subse-
quently becomes fused with the posterior wall of the hypoph-
ysis, there being no communication between either cavity.
The sac of the hypophysis toward the end of the second month
(His) develops a number of projecting processes or buds which
increase in size and branch, and have developed between them
numerous blood-vessels. Ultimately, these processes become
separated from the parent sac and, continuing to grow, form
with that sac a distinct lobe, to the posterior wall of which is
applied the end of the infundibulum, the latter resting in a
slight depression between two lateral thickenings of the lobe.
The ventral portion of the pituitary body is termed the glandu-
lar portion, while the dorsal part is called the infundibular por-
tion. In both divisions of the gland nerve-fibers exist, but in
the glandular portion they belong only to the sympathetic sys-
tem. From the floor of the inter-brain are developed, in addi-
tion to the infundibulum, the corpora mammillaria, tuber
cinereum, ventral part of the posterior perforated space, and
the optic chiasm.
The corpora mammillaria, or albicantia, appear at first as
a roundish elevation of the floor in the median line, which later
become divided by a median depression into two permanent
tubercles. The small, elevated portion of the floor which slopes
toward the infundibulum is known as the tuber cinereum. Its
development is but imperfectly understood.
Fig. 259. — Three Sections through the Fore-brain of a Four and a Half
Weeks' Embryo. — [His, /ram Quaiti.)
A. Through the lower anterior part of the fore-brain. S. Falx. Sf. Fold of roof passing below
falx toward the third ventricle. Bf. Fold forming the sulcus ammonis. v. HI., h.Rl.
Anterior and posterior parts of olfactory lobe. Cs. Corpus striatum. O. IV. Groove con-
tinuous with optic stalk. P.s. Pars subthalamica. T.c. Tuber cinereum.
B. Section a little further back. Sf 'is replaced by a less prominent but broader fold of the roof,
Ad, which subsequently receives the choroid vessels, and is, therefore, the choroid fold.
Hs. Hemisphere vesicle. Th. Thalamus. S.M. Sulcus of Monro, below and behind the
thalamus.
C. Still further back. Ad. Choroid fold here projecting into lateral ventricles, but still free from
mesoblast and blood-vessels. Ma. Mammillary tubercle. The other lettering as before.
537
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM. 539
The Optic Chiasm. — From the ventral part of the floor of
the inter-brain there is formed a transverse ridge-like thickening
through which later the fibers of the optic nerves pass ; this is
primitive optic chiasm.
DEVELOPMENT OF THE CEREBRAL HEMISPHERES.
The secondary fore-brain, or prosencephalon, develops at first
as a single vesicle from the ventral wall of the primary fore-
brain. This vesicle soon enlarges forward and upward and
becomes divided by an infolding of the medullary wall in the
median line in front, and above into two hemispheral vesicles,
right and left. The groove produced as a result of the deep
infolding of the medullary wall carries a process of connective
tissue from the mesoblast, which becomes the falx cerebri, and
the groove is called the longitudinal fissure. The median walls
of each hemisphere come close together, being only separated
by the falx cerebri lodged in the longitudinal groove ; owing to
this fact the median surfaces become flattened. Just in front of
the ventral wall (lamina terminalis of His) of the cavity of the
inter-brain (third ventricle), the median walls of the hemispheres
are not separated by the falx cerebri, but form a solid septum
somewhat triangular in shape, continuous behind with the lamina
terminalis, in front with the corpus callosum, and below with the
corpora striata. Within this septum in man is found a closed
cavity which does not communicate with the general ventricular
cavities ; it is termed the fifth ventricle. The walls of the hemi-
spheral vesicles are at first very thin, each inclosing a very large
cavity — the lateral ventricle. The lateral ventricles communicate
with the cavity of the inter-brain (third ventricle) by very large
openings on each side — the foramina of Monro. These foramina
gradually decrease in size, owing to an increase in growth of
their walls, until they are converted into mere slit-like openings.
In connection with the study of the further development of
the cerebral hemispheres must be considered, first, its extraor-
dinary growth ; second, the infolding of its thin walls to form a
few deep primary fissures with corresponding projections into
the ventricular cavities ; third, the development of the commis-
54°
CENTRAL NERVOUS SYSTEM.
sures through which each hemisphere is brought into functional
relation with the other ; fourth, the development of numerous
other infoldings or fissures varying in depth, but without corre-
sponding internal' projections.
The hemispheral vesicles grow very rapidly at first, forward,
upward and outward, and then backward, so that at the third
month they cover the region of the inter-brain (optic thalami),
at the end of the fourth month they reach the mid-brain (corpora
quadrigemina), and at the beginning of the sixth month they
have completely covered the corpora quadrigemina and the
Fig. 260. — The Surface of the Fetal Brain at Six Months. — [R. Wagner, from
Qttain.)
This figure shows the formation of the principal fissures. A. From above. B. From the left
side. F. Frontal lobe. P. Parietal. O. Occipital. T. Temporal. a, a, a. Slight
appearance of sulci in the frontal lobe. s. Sylvian fissure. s / . Its anterior division.
Within it, C, the central lobe. r. Rolandic sulcus, p. Parieto-occipital fissure.
greater part of the cerebellum, beyond which they project at
the seventh month. (See Figs. 257, 259, and 260.)
The Fossa or Fissure of Sylvius. — This is the first pri-
mary sulcus to appear. It may be recognized as early as the
fifth week of fetal life. It is at first discernible as a broad,
shallow depression, which becomes gradually deeper, being due
to an infolding of the convex walls of the hemispheral vesicle
at the middle of its lower margin. The inner part of the wall
of the depression becomes very much thickened, and forms an
elevation which extends along the whole length of the floor of
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM. 541
the hemisphere, and projects into the cavity of the lateral
ventricle. This is the primitive corpus striatum, and the
thickening of which it is a part is continuous posteriorly with
that part of the inter-brain which forms the optic thalamus.
(See Fig. 257.) A part of this thickening on each side con-
tinuous with the outer part of the optic thalamus assists in the
formation of the cerebral peduncles. The outer part of the
hemispheral wall, which forms the floor of the fossa of Sylvius,
afterward becomes the insula, or island of Reil, which at the
ninth month is converted into a number of small gyri (gyri
breves insula) by the formation of several small sulci. At the
Fig. 261. — Brain of a Human Embryo of about Three Months (According to
Marchaxd, Four Months). — (After F. Marchatid, from Mi net.)
th. Optic thalamus, bf. Bogenfurche. c.c. Corpus callosura. Sp. Septum lucidum. c.a.
Anterior commissure. 01. Olfactory lobe. Chi. Optic chiasma. inf. Infundibulum.
Pons. Pons Varolii, cbl. Cerebellum, mb. Mid-brain, pin. Pineal gland.
fifth month the fossa of Sylvius becomes much deeper, of greater
length, and has an oblique direction. The margins of the fossa,
increasing in size, approach each other and completely conceal
from view the island of Reil, forming for it an operculum, thus
converting the fossa into the fissure of Sylvius. The anterior
limb of the fissure is formed by an infolding of the wall just in
front of the fossa of Sylvius. Owing to the formation of the fossa
of Sylvius each hemisphere is divided into two primary lobes,
one ventral, the other dorsal, to the fossa. The ventral one is
called the frontal lobe, while the dorsal receives the name of the
542 CENTRAL NERVOUS SYSTEM.
temporal lobe. A part of this latter lobe develops backward
toward the cerebellum and forms the occipital lobe (Fig. 260).
The lateral ventricles, because of the before-mentioned
changes, are much reduced in size, and conform more or less
to the shape of the hemisphere, being somewhat arched or
ring-like in shape. That part of the lateral ventricle remaining
in the frontal lobe is termed the anterior cornu, the portion
which descends into the temporal lobe is called the middle or
descending cornu, while the part which extends backward and
inward into the occipital lobes is the posterior cornu.
Along the median line of the hemisphere is developed a fold
which produces an external groove and a corresponding internal
ridge. This groove is the primary fissure, or Bogenfurche
of His. It begins in front at the olfactory lobe, which it divides
into an anterior and a posterior part, and continuing backward
in a curved direction joins a corresponding groove, the hippo-
campal sulcus, which is also the result of an infolding of the
median wall of the temporal lobe. There is thus formed a long,
arched fissure; hence its name, arcuate fissure, "Bogenfurche."
The posterior end of this groove or fissure branches and forms
the internal parieto-occipital and calcarine fissures. This pri-
mary fissure and the fissure of Sylvius are the only ones formed
by an infolding of the hemisphere walls, all others being
simple depressions of these walls. The internal ridge corre-
sponding to the primary fissure or groove has the same arched
course. The posterior half of the ridge forms the hippocampus
major, or cornu ammonis, and that part of the ridge which
corresponds to the branch known as the calcarine fissure
develops the hippocampus minor, or calcar avis. Nothing is
known of the further development of the anterior half of this
ridge. The narrow portion of the hemisphere wall located just
below this ridge is called the Randbogen, or gyrus arcuatus, a
large part of which is occupied by the corpus callosum. The
part of the Randbogen just dorsal to the corpus callosum is
beset with a number of small, transverse ridges, and forms the
dentate lobe ; the posterior end becomes bent upon itself, form-
ing the uncinate gyrus (Figs. 260 and 261).
The Choroid Fissure. — There appears in man at about
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM. 543
the fifth week of embryonic life an infolding into the lateral-
ventricle of the dorsal margin of the median surface of each
hemispheral wall, which occasions an arch-like groove — the
choroid fissure. This fissure extends from ' the foramen of
Monro to the apex of the temporal lobe. It embraces the
upper convex part of the corpus striatum and carries into the
lateral ventricle a fold of vascular pia. The median wall which
takes part in the formation of this fissure does not become
thickened, but remains very thin, consisting only of a single
layer of epithelium which becomes ultimately adherent to the
outer surface of the pia, forming a covering for it. The very
vascular pia now grows rapidly within the lateral ventricle, and
consists of a number of villous tufts which at first quite fill the
cavity of the ventricle, but later there is a considerable free
space about them. These vascular folds on each side form the
choroid plexuses of the lateral ventricle, and are continuous
with the choroid plexus of the third ventricle by means of the
foramen of Monro. In adult life the choroid plexus of each
lateral ventricle becomes confined to the body and descending
cornu of this ventricle.
DEVELOPMENT OF THE COMMISSURAL SYSTEM OF THE
CEREBRAL HEMISPHERES.
At about the third month of fetal life fusion occurs between
the median walls of the cerebral hemisphere in front of the
terminal lamina, and forms a triangular septum continuous
behind with the lamina and below with the corpora striata.
The fusion of the walls occurs only at the periphery of this
area, no union occurring in the middle portion. This middle
portion, which forms the largest part of the area, is the septum
lucidum and contains a closed cavity — the fifth ventricle. From
this triangular area the anterior commissure, the corpus callo-
sum, fornix, and septum lucidum take their origin. The
anterior commissure is first made manifest by a local thicken-
ing just beneath the Bogenfurche and in front of the foramen of
Monro, and consists of a few transverse fibers.
The genu of the corpus callosum is formed from the anterior
544
CENTRAL NERVOUS SYSTEM.
part of the triangular area ; the pillars of the fornix from the
posterior part, the intermediate or larger portion located
between the fornix and genu of the corpus callosum, forms the
septum lucidum.
Between the fifth and sixth months the union of the hemi-
par.occ
all. mar.
Fig. 262. — Fetal Brain of the Beginning of the Eighth Month. — [Mikalkovics,
from Qua in.)
A. From above. B. From the side. C. Mesial surface. J\o. Rolandic sulcus. Sy. Sylvian
fissure. par.otc. Parietooccipital. calc. Calcarine. pr.c. Precentral. pll. Parallel.
int. par. Intraparietal. call. mar. Callosomarginal. itnc. uncus.
spheres has extended backward, and involves that part oi the
hemispheral walls between the Bogenfurche above and the
choroid fissure below, and is called the marginal arch, gyrus arcu-
atus, or Randbogen. From the anterior part of this curved ridge
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM. 545
originates the body and splenium of the corpus callosum and
the fornix. The curved groove located above the body of the
corpus callosum is the remains of the anterior part of the
Bogenfurche, and is termed the fissure of the corpus callosum.
The posterior part,, located in the temporal lobes, forms the
hippocampal fissure.
THE EVOLUTION OF THE FISSURES OF THE CEREBRAL
* . HEMISPHERE.
The primary fissures are all formed by involutions of the
hemispheral walls, with the production of corresponding eleva-
tions within the lateral ventricles. The secondary fissures are
mere indentations or grooves of the surface of the brain with-
out the production of internal ridges within the lateral ventricles.
The primary fissures have already been described in connection
with the general growth of the hemispheral vesicle. They
comprise the fossa and fissure of Sylvius ; the arcuate fissure, or
Bogenfurche ; the hippocampal, the parieto-occipital, and the
calcarine fissures.
The secondary fissures are the callosomarginal, the fissure
of Rolando, precentral, and the various other fissures of the
frontal, parietal, and occipital lobes, together with those of the
island of Reil.
The callosomarginal fissure takes its origin at the fifth
month of fetal life in front and above the corpus callosum, by the
union of two or three smaller fissures. Posteriorly, this fissure
is prolonged backward and upward by joining a few shorter
sulci, terminating just dorsal to the fissure of Rolando. That
part of the hemispheral mantle between the callosomarginal fis-
sure and the corpus callosum is called the gyrus fornicatus.
The Fissure of Rolando. — This fissure usually develops
toward the end of the fifth month, and appears as two distinct
limbs or grooves — an upper and a lower. The lower groove,
much the larger, has a slight oblique direction, and when fully
developed, forms the lower two-thirds of the fissure. It reaches
downward almost to the fissure of Sylvius. Above, it is sepa-
rated from the upper groove by an elevation of the cerebral
35
546 CENTRAL NERVOUS SYSTEM.
cortex (mantle). The upper groove or limb is much shorter
and deeper than the lower, and is separated from the margin of
the hemisphere by a narrow strip or cortex. The two limbs at
first ununited soon join by the formation of a groove which runs
over the summit of the intervening elevated portion of the cor-
tex. Later in the course of development this fissure becomes
much deeper and the elevated portion is displaced to the bot-
tom of it, where it remains as a permanent elevation, indicating
the point of junction between the two primitive grooves of
which this fissure is composed. The fissure of Rolando forms
the anatomic division between the frontal and parietal lobes.
The precentral sulcus or fissure originates at the end of the
sixth fetal month in two distinct portions located in front of the
fissure of Rolando. These portions usually remain entirely dis-
tinct from each other, although they occasionally unite. Be-
tween this sulcus and the fissure of Rolando develops the
ascending frontal or anterior central convolution.
The fissures or sulci of the island of Reil are developed
during the fifth and sixth months of embryonic life, and consist
of three vertical sulci named from before backward — the pre-
central, the central, and the postcentral. The precentral sulcus
appears as if continuous with its precentral fissure, the central
sulcus with the fissure of Rolando, and the postcentral with the
intraparietal fissure.
The various fissures of the frontal, parietal, temporal,
.and occipital lobes are formed about the sixth month of fetal
life. In the frontal and temporal lobes their course is chiefly
longitudinal, while in the parietal and occipital lobes their course
is either oblique or vertical. These fissures serve to separate
the above-mentioned lobes into gyri or lobules.
The development of the interior intraparietal and collateral
fissures are worthy of separate description.
The inter- or intraparietal fissure appears at the sixth month as
two distinct limbs — one dorsal to the fissure of Rolando and run-
ning parallel to it ; the other has horizontal course below the mar-
gin of the hemisphere. The two sulci join during the eighth month,
to form the main fissure. The intraparietal fissure separates the
parietal lobe into a superior and an inferior parietal lobule.
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM. 547
The collateral or occipitotemporal fissure is formed at the sixth
month. It consists of a deep, long, horizontal fissure located on
the median surface of the temporal lobe near its lower margin,
and produces an eminence in the descending horn of the lateral
ventricle, known as the eminentia collateralis, or pes acces-
sorius. By many this fissure is considered to be an infolding of
the hemispheral wall, and should be classified with the primary
fissures.
DEVELOPMENT OF THE CRANIAL NERVES.
The cranial nerve-roots are arranged into ventral or motor
and dorsal or sensory. They are developed in a manner entirely
similar to the spinal nerves. The neuroblasts in the upper
cervical region of the cord form on each side two distinct lonei-
tudinal columns of cells, which are continued brainward along
the floor of the cerebral vesicles, as far forward as the ventral
part of the mid-brain. These two columns of neuroblasts
correspond, in the fully developed cord, to the cell-groups exist-
ing in the ventral and lateral horns, and hence are distinguished
as the ventral and lateral columns of (neuroblasts) cells. The
neuroblasts of the ventral columns give origin to the following
pairs of motor cranial nerves — viz. : hypoglossal, abducens,
patheticus, and motor oculi. The neuroblasts of the lateral
columns form the spinal accessory, motor divisions of the
glossopharyngeal and pneumogastric (nucleus ambiguus), the
facial and the motor division (portio minor) of the fifth or tri-
geminus.
The sensory fibers of the cranial nerves, with the exception
of the optic and olfactory, are developed before the complete
closure of the neural tube, from an outgrowth on each side
called the neural bands, which serve to connect the dorsal part
of the medullary ridges with the external epiblast. Soon this
connection with the external epiblast is lost, and the two neural
bands become united just dorsal to the point of junction of the
medullary ridges, to form the neural canal. There is thus formed
a neural crest, which extends along the mid-dorsal part of the
neural tube as far brainward as the ventral part of the mid-brain
543
CENTRAL NERVOUS SYSTEM.
roof. This crest posteriorly is continuous with the neural crest
of the spinal cord. From the paired outgrowths of the neural
crest are developed the sensory ganglia of the cranial nerves,
the fibers of which nerves represent the peripheral and central
processes of the cells of these ganglia. These ganglia are in
order, from below upward, the jugular, the petrosal, the genicu-
late, the auditory, and the Gasserian. They give origin, respect-
Fig. 263. — Sections Across the Hind-brain of a Human Emuryo, 10 mm. Long. —
{His, from Quain.)
In A, the origin of the spinal accessory and hypoglossal nerves is shown, the fibers of both aris-
ing from groups of neuroblasts in the basal lamina of the neural tube. In B, one of the
roots of the hypoglossal is still seen, and, in addition, the root of the vagus nerve. This is
represented as in part arising like that of the spinal accessory in A, from a group of neuro-
blasts in the basal lamina, and in part from a bundle of longitudinally coursing fibers placed
at the periphery of the alar lamina, and corresponding in situation to the commencing pos-
terior white columns.
ively, to the sensory divisions of the pneumogastric, the glosso-
pharyngeal, the facial, the auditory, and the trigeminal nerves.
The ganglia, which are connected with the sensory cranial
nerves, have the same histologic formation as do the posterior
spinal ganglia. As development goes on, these ganglia shift
their position and become more ventrally located.*
* All cells of the cerebral ganglia, with the exception of those of the auditory ganglia,
become, later in development, unipolar.
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM.
549
The primitive cerebral ganglia contain embryonic cells bi-
polar in shape, each cell possessing a central and a peripheral
axone. The central axones enter the cephalic part of the neural
tube as sensory cranial nerve-fibers, and terminate about certain
special collections of nerve-cells in the dorsal zones of different
Mc.v.
* -;
Fig. 264. — Section from the same Embryo at the Exit of the Facial Ner\e.
(Several sections have been combined to form this figure.) — (His, from Quain.)
VI. Fibers of sixth nerve taking origin from group of neuroblasts in basal lamina. 1'II.G.g.
Ganglion geniculi of the facial. VIII.G.i.c. Intracranial ganglion of auditory. V/II.G.v.
Ganglion vestibuli. VIII. G.c. Ganglion cochlefe.
segments of the neural tube. These groups of cells form for
the central axones (sensory nerve-fibers) terminal end nuclei
(formerly called the nuclei of origin for those nerves) ; the per-
iphery (sensory) axones grow outward and join sensory end
organs.
Central sensory axones from the cells of the ganglia connected
with the pneumogastric and glossopharyngeal nerves penetrate
550 CENTRAL NERVOUS SYSTEM.
the medulla, and, curving downward, form on each side two oval
bundles of descending fibers — the solitary bundles. These
bundles at first are superficially located, but later become dis-
placed rather deeply inward, and may be seen as roundish
bundles, one on each side, slightly ventrolateral to the sensory
end nuclei of the pneumogastric and glossopharyngeal nerves.
Fig. 265. — Cranial Nerves OF a Human Embryo, 10.2 mm. Long. — {His, from Quain.)
The cranial nerves are indicated by Roman, the spinal nerves by Arabic, numerals.
c.h. Cerebral hemisphere, th, Thalamencephalon. m.b. Mid-brain. Mx. Maxillary process.
JMn. Mandibular arch. Hy. Ilyoid arch. The facial nerve is seen to send a branch
(chorda tympani) across the hyomandibular cleft. G.g. Gasserian ganglion, e.g. Ciliary
ganglion, v. Vestibular, and e, cochlear, part of auditory, g.fi. Ganglion petrosum of
glossopharyngeal, g.j. Ganglion jugulare of vagus. An anastomosis is seen between
these, gJf- Ganglion trunci of vagus. F. Ganglion described by Froriep as belonging
to the hypoglossal, r.d. Ramus descendens of hypoglossal. ot. Otic vesicle. The eye
is also represented, and a part of the heart.
DEVELOPMENT OF THE OLFACTORY LOBE.
The olfactory lobe is formed about the fourth week of
embryonic life as a hollow protrusion or fold of the hemi-
spheral wall, extending forward from the ventral part of the
under surface of the hemispheric vesicle, to form a distinct
longitudinal ridge, separated by an internal groove. This pro-
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM. 55I
trusion soon partially separates from the hemisphere, to form a
blind, tubular-like process which is only connected at its base or
posterior part with the hemispheral wall, its cavity communicat- '
ing with the lateral ventricle, of which it is a part. The primitive
olfactory lobe is crossed by the primary fissure, or Bogenfurche
of His, which divides it into a ventral and a dorsal part. The
ventral part gives origin to the olfactory tract and bulb and the
trigonum olfactorium ; from the dorsal part is developed the inner
and outer olfactory roots, the peduncles of the corpus callosum,
and the anterior perforated space.
The first process in the development of the olfactory nerves
is the separation of the olfactory plates, which are the thickened
parts of the epiblast united to the walls of the fore-brain vesicle.
This takes place by an ingrowth of a process of the mesoblast.
The second stage is the formation, by karyokinesis, of neuro-
blasts from the ectodermal cells of the olfactory plates. These
neuroblasts soon assume a bipolar shape, and together form on
each side a ganglion which lies between the epiblast (olfactory
plate) and the olfactory lobe. At the end of the fifth week
this ganglion grows upward and backward, and becomes located
in a groove just dorsal to the anterior division of the olfactory
lobe. It then grows ventrally, and surrounding the olfactory
bulb, becomes fused with it, thus forming a superficial layer
around it. The exact development of the peripheral olfactory
nerves is not at present known. According to His, the bipolar
cells of the above-described ganglia lengthen at each pole into
centripetal or central olfactory nerve-fibers, and centrifugal or
peripheral olfactory nerve-fibers, the latter being distributed to
the olfactory mucous membrane. It seems more reasonable to
believe that this ganglionic mass which forms the superficial
gray layer, capping the ventral half of the olfactory bulb, gives
origin to the mitral cells, whose axones form the central olfac-
tory nerve-fibers and whose dendrites assist in the formation of
the olfactory glomeruli, the peripheral olfactory apparatus con-
sisting of the olfactory cells of the Schneiderian mucous mem-
brane with their processes. (See page 325.)
552 CENTRAL NERVOUS SYSTEM.
DEVELOPMENT OF THE RETINA AND OPTIC NERVES.
The optic vesicles are developed as hollow protrusions, one
from each side wall of the primary fore-brain. It will be
remembered that the ventral wall of the fore-brain expands,
and growing rapidly, forms the cerebral hemispheres, thus
changing the position of the fore-brain so that it becomes
located between the prosencephalon and the mid-brain, and is
called the inter- or between-brain. Hence, the optic vesicles
are attached on each side to the ventral wall of the inter-brain,
just in front of the infundibular region. The distal part of each
optic vesicle enlarges upward and outward, while the proximal
hollow part becomes narrowed and is connected with the ven-
tral wall of the brain. This narrow part is called the stalk, or
pedicle of the optic vesicle, and is the rudiment of the optic
nerve. The most prominent part of the optic vesicle joins the
adjacent external epiblast, which becomes thickened and is
thrust inward, pushing before it a part of the front wall and
pedicle of the optic vesicle. The front wall of the optic vesicle
is so completely invaginated that it nearly meets the posterior
wall, and causes an almost complete obliteration of the cavity
of the optic vesicle. The concavity thus formed, containing the
involuted epiblast, is called the optic cup. The anterior or
inner wall of this cup becomes much thickened, to form the
retina, while the posterior or outer wall remains thin, and has
deposited within its epithelial cells pigment, forming the pig-
ment layer of the choroid. This hollow involuted portion of
the epiblast forms the rudiment of the lens and becomes
separated from the adjacent external epiblast by the closure ot
its mouth,, remaining within the cavity of the optic cup close to
its anterior wall. Later, owing to the more rapid growth of the
walls of the optic cup and the slow growth of the lens, it becomes
displaced forward and occupies the mouth of the cup, and has
developed between it and the thickened anterior wall of the cup
or retina, the vitreous humor.
During the time of the invagination of the epiblast to form
the lens, a groove is formed along the lower border of the optic
vesicle, extending backward from the epiblast to the stalk of the
A
Fig. 266, A. — Brain of Chick of Second
Day, Viewed from Below, to Show
the Formation of the Optic Vesicles
by Outgrowth of the Side of the
Fore-brain, and at the Same Time by
the Folding Over of the Enlarged
Part, the Production of a Grooving
or Cupping of the Vesicles. — {His,
from Quain.)
1, 4, 5. Fore-, mid-, and hind- brain. 2. Optic vesicle
Fig. 266, B.— Brain of Human Embryo
of Three Weeks. Showing the primary
optic vesicles as outgrowths from the fore-
brain. — (His, from Quain. )
3. Infundibulum.
Fig. 267. — Side View of Anterior
Part of Brain of More Ad-
vanced Human Embryo. Showing
the primary optic vesicle folded and
cupped. — (His, from Quain.)
I. Cerebral hemisphere (part of). 2.
Olfactory lobe. 3. Optic cup.
Fig. 268. — Side View of the Same Part of
the Brain in a still more Advanced Em-
bryo, the Eye Having Been Cut Away. —
(His, from Quain.)
. Cerebral hemisphere. 2. Anterior part of the olfac-
tory lobe. 3. Cut end of optic stalk, showing the
manner in which it is folded. 4. Tuber cinereum.
553
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM. 555
vesicle, whose walls do not coalesce, there remaining a cleft or
fissure which receives the name of the choroid fissure; through
this fissure a portion of vascular mesoblastic tissue surround-
ing the optic vesicle gains entrance to the cavity of the optic
cup behind the lens, and forms the vitreous humor. This
choroid fissure soon becomes obliterated by the coalescence of
its walls, and thus the cavity of the optic vesicle is completely
walled in, and is filled with the vitreous humor.
Fig. 269. — Rabbit Embryo of Ten and
One-half Days; Section of the Lens
Anlage. — (From Minot.)
mes. Mesoderm. P. Pigment layer. R.
Retina. L. Lens. Ec. Ectoderm.
'°°° Mes.
Fig. 270. — Vertical Section of the Eye
of a Chick Embryo of the Third
Day. — (From Miuot.)
Ec. Ectoderm. L. Lens. Ret. Retina. Clio.
Choroid layer. Md. Wall of brain. Mes.
Mesenchyma. X I2 ^ diam.
The closure of this fissure begins in front and gradually pro-
ceeds backward toward the retina ; a small portion remains open,
through which passes the arteria centralis retina, which courses
inward to the concavity of the retina, where it branches, some
branches passing through the vitreous, and being distributed to
the posterior surface of the lens, producing the tunica vasculosa.
The mesoblast which surrounds the optic cup, owing to increase
in size of the latter, becomes condensed and forms for it a dis-
555
CENTRAL NERVOUS SYSTEM.
tinct investment, this being the outline of the eyeball. The
portion of this investment within the cavity of the optic cup and
close to the retina forms the choroid, while the external portion
.develops into the sclerotic coat.
The process of mesoblast which grows in between the lens
and the external epiblast has developed within it a cavity which
separates the mesoblastic process into two layers, an anterior
R ...■■•••.f.'it
tu.v
Fig. 271. — Rabbit Embryo of Thirteen Days; Section of the Eye. — [From Minot.)
N. Optic nerve. P. Pigment layer. R. Retina. Ec. Epidermis. L. Lens. tu.v. Tunica
vasculosa. mes. Mesenchyma.
and a posterior. From the anterior is developed the cornea,
with the exception of its epithelium, while the posterior layer
forms the iris. The cavity, at first between the two layers, but
now located between the cornea and lens, is called the anterior
chamber, and contains the aqueous humor.
The retina is developed from the inner (really the anterior)
wall of the optic cup. The external (outer or posterior) wall
EMBRYOLOGY OF THE CENTRAL NERVOUS SYSTEM. 557
becomes thinned, has pigment deposited within its cells, and
forms the pigment layer of the retina (choroid). Separating the
retina proper from the pigment layer is the membrana limitans
externa. The construction of the retina is not unlike that of the
wall of the embryonal brain, consisting at first of several layers
of elongated, nucleated spindle cells, which are transformed
partly into nerve-cells and fibers, and partly into neuroglia cells
and fibers, the latter forming the so-called sustentacular or sup-
porting tissue. The retina grows rapidly in thickness ; this is
due to a multiplication of its cells, which become arranged into
three layers, corresponding to similar layers in the walls of the
embryonal nervous system. These are the ependymal layer or
outer part, the mantel or intermediate layer, and the Rand 1
schleier or layer of nerve-fibers. The layer of nerve-fibers is
separated from the vitreous by the membrana limitans interna.
The cells of the ependymal layer, which are located next the
membrana limitans externa, form the outer nuclear layer, the
layer of rods and cones, and possibly the molecular layer and
the inner nuclear layer. The cells corresponding to the middle
or mantel layer give origin to the inner molecular layer and the
layer of ganglionic nerve-cells. The inner layer, or Rand-
schleier, is the layer of nerve-fibers. The rods and cones are
developed from elongated sensory cells in the outer nuclear
layer.
The rods and cones of the retina are developed in man at
birth, but in all animals that are born blind they are probably
not developed until after birth. They first appear as small and
large roundish projections over the surface of the external limit-
ing membrane, the small projections being the cones, the large
ones, the rods. Each of these projections is an outgrowth of
cells which form the outer nuclear layer of the retina. They
become elongated and penetrate the pigment layer, in which
their tips become embedded.
The Optic Nerves. — The hollow optic stalks, or peduncles,
of the optic vesicles which are attached to the ventral part of
the inter-brain become solid by the growth of their walls and the
consequent obliteration of their cavities. Each optic stalk is
continuous anteriorly with the retina, and receives from the cells
558 CENTRAL NERVOUS SYSTEM.
of its ganglionic layer many axones which grow inward (cen-
tripetal fibers) into the optic stalk, and finally reach the primary
optic ganglia of the same and the opposite side, terminating in
arborizations about their nerve-cells. The crossed fibers form
a chiasm (optic chiasm) in front of the infundibulum by passing
through a f idge formed between the roots of the optic stalks. In
many of the lower animals this decussation is complete, but in
man it is incomplete. The optic stalk also contains fibers,
axones of the cells of the primary optic ganglia, which grow
outward (centrifugal fibers) through the optic stalk and ulti-
mately terminate about the cells of the retina.
The solid optic stalks contain, at the time of the obliteration
of their cavities, radially placed neuroglia cells whose processes
form a meshwork through which the previously-mentioned
nerve-fibers pass.
CHAPTER XIV.
TECHNIC OF THE MACROSCOPIC AND MICRO-
SCOPIC EXAMINATION OF THE BRAIN AND
SPINAL CORD.
In order to expose the brain, an incision through the scalp
should be made, extending from one mastoid process to the
other. Use a short scalpel, and cut from within outward to
prevent injury to the hair. If this is found very heavy, as in
some women, it is wise to part it at a line across the vertex,
from mastoid to mastoid, and then braid each fold, one for-
ward, the other backward, protecting them from soiling by
covering with gauze. Dissect the anterior flap free from the
temporal muscles and carry it forward nearly to the margin of
the orbit. The posterior flap should be dissected back as far as
the occipital protuberance.
The bone should now be bared of the temporal muscles and
pericranium along the line of incision, which extends in a circu-
lar manner across the frontal bones behind the orbital ridges,
thence downward and backward across the temporal and
occipital bones to the occipital protuberance. Care should be
taken not to saw through the inner table for fear of injuring
the brain-tissue. The incision can be finished by severing the
inner table with the chisel and mallet. When the calvaria
is nearly free, it may be removed by inserting into the anterior
part of the incision a blunt hook and pulling sharply backward.
With a blunt-pointed scissors cut through the dura along the
lines corresponding to the incision, and fold each side of the
dura inward, thus exposing the hemispheres ; next, separate
the falx cerebri from the crista galli by passing a knife down-
ward on the left side to the falx, and then cut to the right until
it gives way, pull the dura gently backward and let it hang.
559
560 CENTRAL NERVOUS SYSTEM.
The brain being- exposed, with one hand push backward the
frontal lobes and cut the exposed cranial nerves and carotid
arteries close to their foramina. Then lift each temporal lobe
in order, and cut through the tentorium cerebelli close to its
attachment to the petrous bone. Supporting the convexity with
the palm of one hand, tilt the brain backward, separating it from
the cord as low down as possible, after having severed the
cranial nerves from their points of attachment to the pons and
medulla. The brain now being free, can be lifted gently out of
the skull.
Of the several methods in use for sectioning the fresh brain,
those described by Virchow and Pitres are all that could be
desired to determine the location and extent of cerebral lesions.
The method of Dejerine, while not so commonly used, is better
for preserving fresh sections for subsequent microscopic study.*
VIRCHOW'S METHOD.
In this method the brain is placed on a flat surface, with its
base down ; the hemispheres are then carefully spread apart so
as to expose the corpus callosum. A longitudinal incision is
now made, close to the margin of the hemisphere, through the
corpus callosum, into the body of the lateral ventricle, care being
taken not to injure the basal ganglia ; the incision is then
extended forward and backward so as to expose the whole
length of the ventricle with its anterior and posterior cornua.
A second longitudinal incision is made outside of the basal
ganglia, from one end of the hemisphere to the other. Incisions
of a like character are to be made in the hemisphere of the
opposite side. As many more longitudinal incisions through
each hemisphere can be made as seems desirable, care being
taken not to cut through the pia, as this membrane serves to
* Method of Dejerine. — The brain, resting on its upper surface , is first sectioned by a com-
plete transverse incision through it, the incision starting through the ventral part of the pons
just in front of the trigeminal nerves. The occipital and frontal lobes are separated by trans-
verse incisions beginning at each extremity of the corpus callosum. A horizontal cut through
each hemisphere is now made just above the caudate nucleus. If it is desirable to separate the
attached cerebral hemispheres, this may be done by an incision through the corpus callosum and
middle of the interpeduncular space.
EXAMINATION OF THE BRAIN AND SPINAL CORD— TECHNIC. 561
hold the sections together, so that after the brain is sectioned
they can be properly replaced. The remains of the corpus
callosum and fornix are next cut through and reflected backward
by passing the knife through the foramina of Monro, thus
exposing the velum interpositum and choroid plexuses. By
pulling back the velum interpositum, the third ventricle is
brought into view. The corpora quadrigemina may be seen by
cutting through the posterior pillars of the fornix. Frontal or
transverse sections are now made from before backward through
the basal ganglia. A longitudinal section is next made through
the pineal gland, corpora quadrigemina, and worm (vermis) of
the cerebellum, exposing the aqueduct of Sylvius and the fourth
ventricle. The cerebellum is further divided by making median
horizontal sections radiating from its peduncles. The brain is
now turned over and the pons and medulla are divided into
sections by several transverse incisions.
This method of Virchow is not suitable for further microscopic
study, because the brain is already too much cut up. The fol-
lowing method of Pitres is well adapted for the gross and micro-
scopic study of the sections :
PITRES' METHOD.
In this method the lateral ventricles are exposed in the same
manner as in Virchow's method.
The pons, medulla, and cerebellum are separated from the
hemispheres by cutting transversely through the crura cerebri,
and may be sectioned in the same manner indicated in Vir-
chow's method. The cerebral hemispheres are detached from
one another by a longitudinal incision through the third ven-
tricle. Each hemisphere is further, divided into the following
six sections by incisions made parallel to the fissure of Ro-
lando and extending completely through the gray and white
matter :
1. Prefrontal Section. — This section is made through the
frontal lobe, five centimeters ventral to the fissure of Rolando.
It shows the gray and white matter of that lobe.
2. The pediculofrontal section passes through the foot or base
36
562 CENTRAL NERVOUS SYSTEM.
of the three frontal convolutions, showing the ventral parts of
the insula or island of Reil, the lenticular and caudate nuclei, and
the internal capsule.
5. The frontal section is through the ascending frontal convo-
lution, and shows the optic thalamus and lenticular and caudate
nuclei, the internal and external capsules, the claustrum,' the
descending horn of the lateral ventricle, and the insula.
4. The parietal section passes through the ascending parietal
convolution, and shows, in addition to the parts shown in the
frontal section, the hippocampus major divided transversely.
5. The pediculoparietal section is made through the parietal
lobe, three centimeters dorsal to the fissure of Rolando, and
shows the tail of the caudate nucleus and the dorsal part of
the optic thalamus.
6. The occipital section is through the occipital lobe, one cen-
timeter anterior to the external parieto-occipital fissure, and
shows the gray and white matter of the occipital lobe.
If it is not advisable to section the brain in its fresh state, it
may be permitted to harden in a ten per cent, solution of forma-
lin for a week or ten days, when it can be divided into a series
of frontal or sagittal sections.
This method is particularly useful for the study of the gross
or microscopic appearance and situation of lesions. It preserves
the normal difference in color between the gray and white mat-
ter, and permits of staining by the methods of Weigert, Golgi,
Nissl, and Van Gieson. Another solution which will be found
useful to harden the cerebrospinal axis entire is Orth's fluid.
It may be changed each day for three days. At the expiration
of three weeks the hardening is complete, when it may be
transferred to alcohol. This method permits of staining after
the before-mentioned methods, save Nissl's. An excellent and
well-known preservative solution for hardening the brain or
spinal cord is Miiller's fluid. This fluid consists of potassium
bichromate 2 to 2^ parts, sodium sulphate 1 part, water 100
parts. This fluid should be renewed each day for a week ; it
takes from six weeks to three months to harden properly.
Specimens are then transferred directly into alcohol. This
method of hardening is particularly useful for staining, by
EXAMINATION OF THE BRAIN AND SPINAL CORD— TECHNIC. 563
Weigert's method, the Cox-Golgi, or by Berkley's modification
of the Golgi method.
Orth's Fluid.
Potassium bichromate, 2 to 2. 5 parts
Sodium sulphate I part
Water, 100 parts
Formaldehyd (forty per cent, solution), 10 parts.
THE REMOVAL OF THE SPINAL CORD.
To remove the spinal cord, the body is placed with the face
downward, the head projecting over the end of the table, with
the chest elevated by placing a block beneath it. An incision
is now made over the spinous processes of the vertebra to the
bone extending from the occipital protuberance to the sacrum.
The soft parts covering the vertebral lamina are dissected away
from each side. The vertebral lamina are sawed through or
cut, by means of a chisel, from the upper cervical to the lower
lumbar. The lamina being free, the cervical arches are cut
through with a chisel and the spinal processes of the lumbar
vertebra are freed from their ligaments in the same manner.
The dorsal portion of the spine with its processes can now be
stripped away its whole length. The nerve-roots are severed
on each side with a narrow-bladed knife. The membranes and
cord are cut across high in the cervical region ; the cord is then
lifted from its position by taking hold of the dura with the
forceps and separating it from above downward with a scissors
and the handle of a scalpel. After the cord is removed, the
dura is cut through longitudinally both in front and behind.
The cord being supported by the fingers, is divided by a sharp
scalpel into a number of transverse sections two centimeters
apart.
DIFFERENTIAL STAINS FOR THE VARIOUS ELE-
MENTS OF THE NERVOUS SYSTEM.
In this description mention will be made of some of the
methods which have been found particularly useful in staining
564 CENTRAL NERVOUS SYSTEM.
the elements of the nervous system. If the student is desirous
of becoming familiar with all the methods now in use, he should
consult the excellent works of V. Kahlden, B. Pollack, Mallory
and Wright. The differential stains may be divided into those
useful for staining nerve-cells and their protoplasmic granules,
those for delineating the contour of cell-bodies and their proto-
plasmic processes, those for myelin sheaths, and those for
neuroglia tissue. These do not include certain general stains to
be described hereafter, which are not considered differential in
character.
Staining of Nerve-cells after the Method of Nissl. —
Small cubes of fresh nervous tissue i to \ x / 2 centimeters in
diameter, after having been hardened in ninety-six per cent,
alcohol, are fastened to blocks by dipping the base of each cube
into thick celloidin. Sections are cut very thin and placed into
ninety-six per cent, alcohol. They are stained for about five
minutes in the following solution of methylene-blue, which has
been previously heated over a flame until it bubbles :
Methylene-blue (B. patent), 3.75
Venetian soap, 1.75
Aquadestillata, IOOO
They are next differentiated in anilin oil 10 parts, alcohol
(ninety-six per cent.) 90 parts, until the color ceases to be dis-
charged in coarse clouds. Each section is now placed on a
glass slide and thoroughly and carefully dried with filter-paper,
and then cleared in oil of cajuput, again dried and washed with
a little benzine ; lastly, add a few drops of benzine collophonium,
and pass slide through a flame to drive off excess of benzine ;
this ignites the benzine, which should be immediately blown out.
This process should be repeated a few times until all the ben-
zine is evaporated ; heat the slide, and cover with a thin cover-
glass. By this method the cell-body with its protoplasmic gran-
ules are beautifully stained.
To Stain Nerve-cells with Thionin. — (1) Harden in ninety
per cent, alcohol, then in absolute alcohol, or in formalin followed
by alcohol ; (2) embed specimens in celloidin or paraffin ; (3)
stain sections for five minutes in concentrated solution of
thionin; (4) wash quickly in water ; (5) differentiate in anilin
EXAMINATION OF THE BRAIN AND SPINAL CORD-TEC1 INIC. 565
oil i part, absolute alcohol 9 parts ; (6) clear in oil cajuput ;
(7) then in xylol; (S) xylol balsam.
Method of Bevan Lewis. — This method is well adapted
for the study of the different cell-layers of the cortex as they
normally exist. The nerve-cells, with their protoplasmic pro-
cesses retaining their original size and shape, not having been
altered by hardening reagents. This method also stains the
axis-cylinder processes, neuroglia tissue, pia mater, and the
connective tissue about blood-vessels.
A piece of brain-tissue about one inch in length and three-
fourths of an inch thick is removed, care being taken to include
the entire cortex and the overlying pia mater. It is then cut
into fine sections by means of a freezing microtome. These
sections are conveyed on the blade of the microtome knife to
distilled water, and then immediately floated on to glass slides,
the superfluous water being permitted to drain away. The sec-
tions are then covered for a few seconds with a one-fourth of
one per cent, solution of osmic acid. This short contact with
osmic acid simply fixes the myelin without producing a distinct
osmic acid staining-- The sections are now washed in distilled
water for five or ten minutes. Each section is again floated on
to a glass slide, the excess of water being drained off. They
are stained on the slide for from a half to one hour with a one
fourth of one per cent, solution of anilin blue-black. They are
then washed in water and again floated on glass slides, where
they are permitted to dry by exposure to the atmosphere.
When thoroughly dry, they are mounted in Canada balsam.
The nerve-cells and fibers are stained a bluish-gray color.
The following method, a modification of Kronthal's, is a
very useful one, not only to show the nerve cell-body and its
protoplasmic granules, but stains the axone and the dendritic
processes, as well as the neuroglia. It stains capillary blood-
vessels very beautifully. Fresh nervous tissue (brain or cord)
is obtained, and a small bit of the gray matter is placed on a
cover-glass, and is covered by another cover-glass. The two
cover-slips are pressed together so as to spread the tissue out
into as thin a layer as possible. The separated covers are per-
mitted to dry in the air, and are stained for forty minutes in a
50t> CENTRAL NERVOUS SYSTEM.
saturated solution of methylene-blue, then washed in water for
a minute or two, dried in the air, and mounted in Canada
balsam.
Golgi's Method for Staining Nerve-cells and Their
Processes. — This method depends for its efficacy upon the
precipitation of silver or mercury salts in the protoplasm of the
nervous tissue. It was by this method discovered that the
nervous system was made up of a multitude of units or neu-
rones, which are perfectly independent anatomically and physio-
logically of each other.
Golgi's Rapid Method. — Harden small specimens (i to
1^2 cm.) of young, fresh, nervous tissue in ten or more
volumes of three per cent, bichromate of potash solution 4
parts, one per cent, osmic acid solution 1 part, in the dark
for from two to eight days, depending upon what particular
part of the nervous tissue you desire to impregnate. For neu-
roglia it must remain from two to three days ; for nerve-cells,
three to five days ; for nerve-fibers, five to seven days.
The specimen, after having hardened, should be washed in
three-fourths of one per cent, solution of silver nitrate and then
placed for one or two days in one per cent, solution of silver
nitrate. The section is next dehydrated for thirty minutes in
ninety-six per cent, alcohol, and then cut without embedding be-
tween hardened liver, or by dipping it into thick celloidin and
fastening it to a block, which is placed in chloroform to secure
immediate hardening of the celloidin. The sections, not cut too
thin, are dehydrated in absolute alcohol for a short time and
cleared in cedar, clove, or bereamot oil, and mounted in Canada
balsam with or without cover-slip.
Golgi's Slow Method. — Small cubes of fresh nervous tissue
are placed in a recently prepared two per cent, solution of bi-
chromate of potassium at room temperature for two to six
weeks, or until sufficiently hard. They are then placed in 0.75
per cent, solution of silver nitrate for from one to four days, or
in 0.5 per cent, solution of corrosive sublimate for two or three
weeks. Proceed as in rapid method.
Berkley's Method of Impregnation. — The brain or cord
is hardened in Miiller's fluid until it is sufficiently hard to admit
EXAMINATION OF THE BRAIN AND SPINAL CORD— TECIINIC. 567
of thin sections not more than three mm. in thickness. These are
immersed in a mixture of a three per cent, solution of potassium
bichromate and one per cent, osmic acid, in the proportion of
one hundred parts of the former to twenty of the latter. In this
mixture the pieces remain for three or five days ; they are then
removed from the fluid, dried slightly on filter-paper to remove
any superfluous bichromate. They are next washed for a few
minutes in a weak solution of silver nitrate, and then are placed
into the staining mixture, which consists of two drops often per
cent, solution of phosphomolybdic acid to each sixty cubic centi-
meters of a one per cent, solution of silver nitrate in distilled
water. This mixture should be made fresh each time. Speci-
mens remain in this solution from three to five days. Cut and
mount as for Golgi specimens.
Cox's Modification of the Golgi Sublimate Method. —
This method, because of its simplicity, is particularly useful for
beginners. It stains all the elements.
A small tube of fresh tissue is permitted to remain for six
weeks in summer and for three weeks in winter in the follow-
ing: mixture :
Five per cent, solution of potassium bichromate, ... 20
Five per cent, solution of corrosive sublimate, .... 20
Five per cent, solution of potassium chromate, ... 16
Aqua destillata, 40
Sections are cut and mounted, as in the Golgi rapid method.
Tissue previously hardened in Muller's fluid can be impreg-
nated by this method. Bevan Lewis has recently modified this
method by adding to the sections on a slide, after having come
out of alcohol, a few drops of liquor potassse and immediately
washing off with a little distilled water. The addition of the
liquor potassae has the effect of bringing out the elements with
intense blackness.
Weigert's Method of Staining the Myelin Sheaths.—
To Weigert is due the credit of discovering a unique method of
staining the myelin sheaths, which has become classic. It
depends upon the fixation of the myelin with chrome salts so
that it can not be dissolved by alcohol or ether, and acts as
568 CENTRAL NERVOUS SYSTEM.
a distinct mordant, permitting the myelin to stain very deeply
with hematoxylin.
i. Harden the tissue in Midler's or Erlitzky's fluid.
2. Transfer specimens from hardening fluid immediately into
ninety-six per cent, alcohol ; then embed in celloidin.
3. Sections should be cut very thin and placed into equal
parts of water and a saturated neutral solution of copper acetate
for twenty-four hours.*
4. Stain for from thirty minutes to twenty-four hours in the
following solution of hematoxylin :
Hematoxylin (Gruber's or Merck's), ........ I
Alcohol absolute, IO
Lithium carbonate, . . I
Aqua destillata, ad IOO
5. Wash in water and differentiate for a few minutes to half
hour in —
Borax, 2
Potassium ferricyanid, 2.5
Aqua destillata, 100
6. Wash immediately in water, dehydrate in alcohol, clear in
xylol or origanum oil, and mount in Canada balsam.
Of the many modifications of Weigert's original method, the
one devised by Pal is most generally used and gives very satis-
factory results :
1. Harden specimens as for Weigert's method.
2. Place section for overnight in three per cent, solution
potassium bichromate, or for several hours in a one-half per
cent, solution of chromic acid.
3. Stain sections in Weigert's hematoxylin for twenty-four to
forty-eight hours.
4. Wash in water plus four per cent, of a saturated solution
of lithium carbonate, until sections appear of a uniform deep-blue
color.
* Weigert now recommends instead of this solution :
Copper acetate 5
Acetic acid, 36 per cent, solution 5
Chrome alum, 2.5
Water ad 100 M.
EXAMINATION OF THE BRAIN AND SPINAL CORD— TECHNIC. 569
5. Differentiate in a freshly prepared one-third per cent, solu-
tion of potassium permanganate, until gray matter appears
yellowish brown, about half a minute.
6. Continue differentiation in the following; solution until the
gray matter appears white and the white matter is of a dark-
blue color :
Oxalic acid, t
Potassium sulphite, I
Distilled water, 200
If sections do not differentiate quickly, transfer them again to
permanganate solution for a few seconds and then repeat step 6.
7. Wash thoroughly in water, dehydrate in ninety-five per
cent, alcohol, clear in xylol or origanum oil, and mount in Can-
ada balsam.
Erlitzky's Fluid.
Potas?ium bichromate, 25
Cuprum sulphate, 5
Aqua, 1 00.0
Specimens harden at room temperature in from, ten to four-
teen days.
Marchi's Method. — i. Fix small pieces (2-3 mm.) of ner-
vous tissue for eight to fourteen days in Miiller's fluid.
2. Transfer to a mixture composed of equal parts of Miiller's
fluid and one per cent, solution of osmic acid for six to twelve
days.
3. Wash in running water for twenty-four hours.
4. Harden in alcohol, embed in celloidin, cut, and mount in
Canada balsam containing no chloroform.
This method is very useful in studying secondary degenera-
tions.
NEUROGLIA STAINS.
Differential Stain for Neuroglia Fibers. — Method of
Mallory. — 1. Fix very fresh human nervous tissue in a four per
cent, aqueous solution of formaldehyd for four or more days.
2. Place in a saturated aqueous solution of picric acid four to
eight days.
3. Transfer to a five per cent, aqueous solution of bichromate
570 CENTRAL NERVOUS SYSTEM.
of ammonia for four to six days in the incubator at t,j° C, or for
three to four weeks at room temperature ; change solution on
the second day.
4. Place directly into alcohol.
5. Embed in celloidin.
6. Fasten sections to slide by means of ether vapor.
7. Stain in anilin-gentian violet fifteen to twenty minutes.
8. Wash off with normal salt solution.
9. Iodin solution 1:2: 100 for one minute, or a stronger
solution for a few seconds.
10. Wash thoroughly with water.
11. Dry with filter-paper.
12. Decolorize in equal parts of anilin oil and xylol.
13. Wash off thoroughly with xylol.
14. Mount in xylol balsam.
The neuroglia, nuclei, and to some extent red blood-corpuscles
are stained blue. The other tissue elements are colorless.
Mallorys Phosphotungstic-acid Hematoxylin Method for
Staining A T euroglia. — 1. Fix in four per cent, aqueous solution
of formaldehyd four days.
2. Saturated aqueous solution of picric acid four days.
3. Five per cent, aqueous solution of bichromate of am-
monium four days to six days in incubator, or three or four
weeks at room temperature.
4. Stain sections in phosphotungstic-acid hematoxylin four to
twenty-four hours.
5. Wash in water.
6. Alcohol.
7. Clear in oleum origani cretici.
8. Mount in xylol balsam.
Neuroglia fibers and nuclei are stained blue, connective tissue
deep pink, axis-cylinders light pink, myelin sheaths yellow,
protoplasm of ganglia cells and dendrites purplish or bluish
gray. Mallory recommends staining sections at first lightly in
Van Gieson's mixture, which stains the axis-cylinders a deep-red
color.
EXAMINATION OF THE BRAIN AND SPINAL CORD— TECHKIC. 571
STAINS FOR AXIS-CYLINDER PROCESSES.
Neutral carmin is an excellent stain for axis-cylinders, also
stains nerve-cells very well. Sections should remain in it for
twenty-four hours, when they should be thoroughly washed in
water, dehydrated in alcohol, cleared in clove oil, and mounted
in Canada balsam. To prepare neutral carmin, dissolve
without heat one gram of carmin in 50 c.c. of aqua destil-
lata, plus 5 c.c. aqua ammonia. Expose the mixture to the
air until no ammoniacal odor exists ; filter, and keep tightly
corked.
To stain axis-cylinders with nigrosin proceed as follows :
1. Stain sections for five or ten minutes in a saturated watery
solution of nigrosin.
2. Decolorize in dilute alcohol, then in absolute alcohol.
3. Clear in oil of origanum ; mount in Canada balsam.
This very simple method gives beautiful results. It stains
well the ganglion cells and their protoplasmic processes. De-
generated areas are stained a bluish black.
Van Gieson's Method. — 1. Specimens should be hard-
ened in Miiller's fluid or alcohol.
2. Stain for from five minutes to one-half an hour in alum
hematoxylin.
3. Wash thoroughly in water.
4. Stain for three to five minutes in Van Gieson's solution,
which consists of one per cent, aqueous solution of acid fuchsin,
15 c.c. saturated aqueous solution of picric acid, 50 c.c. aqua
destillata.
5. Wash in water for a short time.
6. Dehydrate in alcohol ; clear in clove oil ; mount in Canada
balsam.
The axis-cylinders and ganglion cells are deep red, myelin
sheaths yellow, neuroglia red, nuclei lilac.
572 CENTRAL NERVOUS SYSTEM.
STAINS FOR END ORGANS, TERMINATIONS OF NERVES, AND
COLLATERAL BRANCHES.
Method of Gerlach. — i. Tissue should be hardened in one
or two per cent, solution of ammonium bichromate for three
weeks ; when specimen is sufficiently hard, it should be sectioned
under water without the use of alcohol. Put sections in a y^
per cent, solution of chlorid of gold and potassium.
2. Acidulate with a few drops of hydrochloric acid for twelve
hours, or until they become of a slight violet color.
3. Wash in a very weak solution of hydrochloric acid, 1 : 2000.
4. Put sections in a yV per cent, solution of hydrochloric acid,
and in sixty per cent, alcohol for ten minutes.
5. Absolute alcohol ; clear in clove oil ; mount in Canada
balsam.
Method of Freud. — 1. Harden specimens at first in Er-
litzky's or Miiller's fluid, then in alcohol.
2. Embed in celloidin, cut sections and place them in a one
per cent, solution of chlorid of gold for three to five hours.
3. Wash in water and bring sections for reduction in a solu-
tion composed of sodium hydrate 1, aqua destillata 5, for three
minutes.
4. Wash in water and place sections for from five to fifteen
minutes in ten per cent, solution of potassium iodid, until sections
appear reddish violet.
5. Wash in water, dehydrate in alcohol, clear in xylol, and
mount in Canada balsam.
Method of S. Ramon y Cajal to show the collaterals. —
1. Rather thin sections of fresh rabbit's brain are brushed over
with a saturated solution of methylene-blue (B. Gruber), or
methylene-blue in a powder is dusted over the sections ; after
three-quarters of an hour the sections are washed in weak saline
solution.
2. Fix in solution of —
Ammonium molybdate, IO
Distilled water, 100
Hydrochloric acid IO drops
for two or three hours.
EXAMINATION OF THE BRAIN AND SPINAL CORD— TECHNIC. 573
3. Wash in water to remove excess of ammonium molyb-
date, and harden for three to four hours in —
Formalin 40
Distilled water, 60
One per cent, solution platinum chlorid, 5
4. Wash quickly to remove the formalin for several minutes
in a three per cent, alcoholic solution of platinum chlorid.
Embed in paraffin.
5. Thick sections are dehydrated in alcohol absolute with the
addition of l ^ per cent, platinum chlorid; clear in xylol; mount
in Canada balsam.
Ehrlich's Vital Methylene-blue Method {Modified by
SemiMeyef). — i. Hypodermic injection of methylene-blue BX
solution (saturated at 37 C), 2 c.c. at intervals of fifteen to
thirty minutes. Ready after three to six injections.
2. Brain to be cut into two or three pieces and put into the
following solution for twenty-four hours at a temperature of
32° R:
Ammonium molybdate IO
Distilled water ioo
Hydrochloric acid, cone, 10 drops.
3. Wash in running water for two hours.
4. Place specimens in eighty per cent, alcohol for one-half to
one hour, then in ninety-five per cent, alcohol for same length
of time, and then into several changes of absolute alcohol.
All No. 4 at ice temperature (32 F.).
5. Xylol (several times to be renewed) ; embed in paraffin.
6. Cut, clear in xylol, and mount in Canada balsam.
GENERAL STAINS.
Hematoxylin is the most useful of the general stains. It
stains the nuclei and connective tissue, and stains quite well the
ganglion cells and processes. The following formulae contain
hematoxylin as the base, and will be found useful in staining
nervous tissue :
• Phosphomolybdic-acid Hematoxylin (Mallory).
Hematoxylin crystals, 1-75 g rams
One-half per cent, aqueous solution of phosphomolybdic
acid, 200 c.c.
574 CENTRAL NERVOUS SYSTEM.
Expose solution to light in a bottle plugged with absorbent
cotton ; it will be ready for use in six weeks.
i. Stain section from twenty minutes to one hour.
2. Wash in two or three changes of fifty per cent, alcohol until
celloidin becomes completely decolorized.
3. Dehydrate in ninety-five per cent, alcohol, clear in clove oil,
and mount in balsam.
Ehklich's Acid Hematoxylin.
Hematoxylin crystals, 2 grams.
Alcohol, absolute, 60 c.c.
Acetic acid (glacial), 3 c.c. -v
Water, 60 c.c. Satura| ed with
ammonia alum.
Glycerin, 60 c.c. /
This solution is exposed to the light for three weeks, when it
is ready for use. Specimens are stained for a few minutes,
washed in water, dehydrated in alcohol, cleared in xylol or oil,
and mounted in Canada balsam.
Aqueous Alum Hematoxylin Solution.
Hematoxylin crystals, I
Saturated aqueous solution of ammonia alum IOO
Water 300
Thymol, a few crystals.
The solution should be exposed to the light for about two
weeks, when it is ready for use. The author prefers this solu-
tion to Delafield's. Excellent contrast stains are eosin and
anilin blue-black ; the latter stains the axis-cylinders and proto-
plasmic processes.
Stain with alum hematoxylin for a few minutes, then place
sections in watery solution of eosin until sections are stained
red, wash in water, dehydrate quickly in alcohol, clear in clove
oil, and mount in Canada balsam.
Stain with alum hematoxylin for a few minutes, then place
sections direct in a five per cent, watery solution of anilin blue-
black for a few seconds, wash, clear, and mount as above. The
nerve-cells are stained bluish, while the neuroglia cells are
stained a lilac.
INDEX.
A.
Abducens nerve, 166
Accessory nucleus, 76, 185
Acervulus cerebri, 247
Acoustic nucleus, anterior, 173
ventral, 172
Acousticocerebellar tract, 166, 177, 207
Adventitial lymph-space, 58, 63
Agraphia, 472
Ala cinerea, 135
Alexia, 470
Alternate hemiplegia, 490
Alveus, 318, 354, 356, 394
Amacrine cells, 265
Amnesic aphasia, 468
Amygdaloid nucleus, 399
Amygdalum, 190
Amyotrophic lateral sclerosis, 501
Anastomotic vein, great, 439
posterior, 439
Angular gyrus, 308
Ansa lenticularis, 402
Anterior cerebral artery, 422
choroid artery, 424
commissure of spinal cord, 74
communicating artery, 421
inferior cerebellar arteries, 431
Anterolateral arteries, 423
Aphasia, amnesic, 468
motor, 472
of conduction, 486
tactile, 471
verbal, 468
Apices cornuum posteriores, 74
Aqueduct of Sylvius, 210
development of, 530
Sylvian, 132
Arachnoid, cerebral, 284
spinal, 65
villi, 287
Arantius, ventricle of, 135, 136
Arborization, 200
Arborizations, interepithelial, ^8
Arcuate fibers, 164
anterior external, 204
antero-external, 165
external, 204
internal, 144
postero-external, 165
Area of Broca, 335
posterior, of medulla, 126
Areas, lateral, of medulla, 126
Arkyostichochronie nerve-cells, 21
Arm-area of cerebral cortex, 451, 452
Arnold, substantia reticularis of, 355
Arterial supply of cerebrum, 417
to medulla oblongata, 432
to pons Varolii, 432
Arteries, anterior inferior cerebellar, 431
anterolateral, 423
carotid, 418
inferior cerebellar, 431
lenticulo-optic, 424
lenticulostriate, 424
long, of brain, 416
middle cerebellar, 431
of brain and cord, 58
of cerebral dura mater, 283
posterior cerebral, 425
superior cerebellar, 430
vertebral, 425
Artery, anterior cerebral, 421
choroid, 424
communicating, 421
ascending frontal, 422
parietal, 422
basilar, 425
inferior frontal, 422
internal auditory, 425
marginofrontal, 421
middle cerebral, 422
of cerebral hemorrhage, 424
parietotemporal, 423
posterior communicating, 424
meningeal, 425
quadrate, 421
sphenoid, 423
Sylvian, 422
Articular end bulbs, 40
Ascending frontal artery, 422
parietal artery, 422
Association, centers of, of cerebral cortex,
507
fibers of centrum ovale, 364
zones of, of cerebral cortex, 507
Astrocytes, 56
Ataxic paraplegia, 503
Atrophy, progressive muscular, 501
575
576
INDEX.
Auditor)' artery, internal, 425
centers, 462
nerve, 171
connections of, 175
dorsomesial nucleus of, 174
nucleus, anterior, 173
dorsolateral, 174
dorsomesial, 174
sphere of cerebral cortex, 507
Axilemma, 34
Axioplasm, 33
Axis-cylinder, 31
nigrosin for staining, 571
of Purkinje, 32
process, 47, 49
processes, stains for, 57 r
Axone, 31, 47, 49
B.
Back-muscles, nucleus for, 79
Baillarger, outer line of, 339
Basal ganglia, lesions of, 488
Basilar artery, 425
sinus, 444
vein, 437
Basket cell of cerebellum, 28
cells, 199
Becliterew and Flechsig, central tegmental
tract of, 152
nucleus of, 175, 1S2
olivary tract of, 105
Berkley's method of impregnation, 566
Bipolar nerve-cells, 24
Blood-supply of spinal cord, 122
Blood-vessels, cortical, 416
of brain, 416
of central nervous system, 58
of cerebellum, 430
Bodenplatte, 525
Bodies, olivary, 126
restiform, 164
Body, Luys', 259, 260
Nissl, 18
pituitary, 276
Bogenfurche of His, 542
Boundary zone, 114
Brachia conjunctiva, 202
Brachial enlargement of spinal cord, 69
Brain, blood-vessels of, 416
central vessels of, 4 1 <>
ganglionic vessels of, 416
long arteries of, 416
membranes of, 280
motor area of, 449
technic of microscopic and macroscopic
examination of, 559
venous systems of, 435
Brain-sand, 247
Broca, area of, 335, 471
space of, 335
Brown-Sequard's paralysis, 504
Buds, 200
Bulb, 69, 125
of internal jugular vein, 445
olfactory, 319, 328
fourth layer of, 332
Bulb, olfactory, large mitral cells of, 330
layer of central nerve-fibers
of, 33 2
molecular layer of, 330
outer layer of, 328
pyramidal cells of, 330
superficial layer of medium
and small-sized cells of, 331
Bulbar paralysis, acute, 499
Bundle, comma-shaped, 99
hemispheral, 337
inferior longitudinal, 368
Meynert's, 257
of gyrus fornicatus, 364
of Vicq d'Azyr, 253, 324, 413
posterior, 337
longitudinal, 82
nucleus of, 230
superior longitudinal, 230
triangular, 105
Burdach, column of, 84, 91, 99, 126
nucleus of, 144
fasciculus arcuatus of, 368
Buschzellen, 254
C.
Cajal cells, 50, 52, 343
varieties of, 344
commissural nucleus of, 158
method of staining, 572
Calamus scriptorius, 132, 136
Calcar avis, 300, 397
Calcarine fissure, 3C0
Callosomarginal fissure, 303, 545
Canal, central, of spinal cord, 74, 122
neural, 508
Capillaries of nervous system, 60
Caps, nuclear, 18
Capsule, internal, 399, 407
localization of lesions of,
488
Caput cornu, 72
Carmin, neutral, for staining axis-cylinders
and nerve cells, 571
Carotid arteries, 418
Cauda equina, 69
Caudate nucleus, 399
Cavernous sinuses, 446
Cavum Meckelii, 280
Cell-bodies, 47
Cell-group for upper extremity, 79
Cell-processes, 30
Center for ideas, 467
reception of appearance of objects
gained through sense
of touch, 470
of heard words, 466
of memories for appear-
ance of objects seen
and of words written
or printed, 469
of muscular memories
necessary to produce
speech, 471
retraction of angle of mouth, 453
INDEX.
577
Center for smell, 483
for taste, 482
for writing, sensory, 479
half-vision, 461
olfactory, 483
Centers, auditory, 462
cortical, for general sensations, 454
for writing, 475
for language, 465
of association of cerebral cortex, 507
of vision, 457
which preside over higher intellectual
faculties, 480
Central canal of spinal cord, 74, 122
convolutions, 307
anterior, 305
gyrus, posterior, 306
sulcus, 310
vessels of brain, 416
Centrum ovale, association fibers of, 364
localization of lesions in, 484
minute anatomy of, 338, 362
of parietal lobe, lesions of,
486
semiovale, lesions of, beneath motor
area, 485
of occipital lobe, 487
of temporal lobe, lesions
of, 486
Cerebellar arteries, inferior, 431
middle, 431
superior, 430
commissures, 207
hemisphere, lobules of inferior sur-
face of, 190
lobules of superior or
dorsal surface of, 190
hemispheres, lesions of, 494
tract connecting oc-
cipital and temporal
lobes with, 221
lesions, localization of, 493
peduncle, inferior, 182, 203
middle, lesions of, 495
peduncles, 202
middle, 203
superior, 202, 229
tract, anterolateral descending, 104
descending, 204
direct, 90, 95, 143, 204
sensory, 166, 1 77J
tracts, direct, 203
sensory, 207
veins, inferior, 441
superior, 440
Cerebello-olivary tract, 160, 1 64, 207
Cerebellum, 186
anterior commissure of, 207
basket cell of, 28
blood-vessels of, 430
connections of, 187
of vestibular nerve
with, 176
cortex of, 198
development of, 528
inferior peduncles of, 188
37
Cerebellum, inferior vermiform process of,
186
lesions of middle lobe of, 493
of worm of, 493
middle lobe of, 186
peduncles of, 1 88
minute anatomy of, 193
peduncles of, 188
posterior commissure of, 208
superior peduncles of, 1 88
upper surface of, 187
veins of, 440
vermiform process of, 186
worm of, 186, 188
Cerebral arachnoid, 284
arteries, posterior, 425
artery, anterior, 421
middle, 422
central branches of,
423
ganglionic branches
of, 423
cortex, auditory sphere of, 507
centers of association of, 507
connection of optic thalamus
with, 251
divisions of, according to
Flechsig, 506
histology of, 338
layers of, 338
olfactory sphere of, 5°7
projection spheres of, 507
sensory spheres of, 507
stratum zonale of, 338
tangential fibers of, 339
visual sphere of, 507
zones of association of, 507
dura mater, 280
hemisphere, development of commis-
sural system of, 543
evolution of fissures of,
545
primary fissures of, 545
secondary fissures of, 545
hemispheres, base of, 318
development of, 538
general anatomy of in-
terior of, 387
hemorrhage, artery of, 424
localization, 448
peduncles, 220
pia mater, 288
vein, anterior, 437
middle, 437
veins, 435
deep, 440
superficial, 436
vesicles, primary, 508
secondary, 5 1 1
Cerebrospinal fluid, 286
Cerebrum, 293
anterior commissure of, 336
arterial supply of, 41 7
central fissure of, 299
choroid fissure of, 297
convolutions of, 303
S7S
INDEX.
Cerebrum, convolutions of mesial surface of,
3'5
fissures of, 294
of external surface of, 294
gyri of, 303
inferior longitudinal fissure of,
3»9
lobules of, 303
longitudinal fissure of, 293, 294
peduncles of, 325
secondary fissures of, 294
transverse fissure of, 294
Cervical enlargement of spinal cord, 69
region of spinal cord, 1 17
Cervix cornu, 72
Charcot, posterior root-zone of, 91
Chiasm, optic, 274
development of, 539
Choroid artery, anterior, 424
fissure of, 54 2
of cerebrum, 297
plexuses, 288
of fourth ventricle, 291
vein, 440
Chromophyllic granules, 18
Chromoplasm, 17
Ciaglinski, long sensory tract of, 106
Cingulum, 364
Circle of Willis, 429
Circular sinus, 444
Cisterna magna cerebellomedullaris, 285
Clarke, Lockhart, vesicular column of, 83
Claustrum, 407
Clava, 131
Cochlear nerve, 171
Collateral branches, stains for, 572
fissure, 547
Collaterals, 50
Color-vision, 462
Column, anterior, of spinal cord, 84
lateral, connections of vestibular
nerve with, 177
of Burdach, 84, 91, 99, 126
nucleus of, 144
of Flechsig, 83, 90, 143, 203
of Goll, 84, 91, 99, 126
nucleus of, 131, 144
of Lissauer, 114
postero-internal, of spinal cord, 91
vesicular, 83
Columns, anterior, of medulla, 126
lateral, ground bundles of, 107
nuclei of, 143
of medulla, 126
of spinal cord, 84
of Tiirck, 89
posterior, course of fibers of, 97
of spinal cord, 84
Comma-shaped bundle, 99
fasciculus, 114
Commissural cells of spinal cord, 83
nucleus of Cajal, 158
system of cerebral hemisphere,
development of, 543
Commissure, anterior, 372, 400
of cerebellum, 207
Commissure, anterior, of cerebrum, 336
of spinal cord, 74
gray, of spinal cord, 74, 75
inferior, of Gudden, 275
Meynert's, 276
middle, of third ventricle, 245
posterior, of cerebellum, 208
of pineal gland, 248
of spinal cord, 74, 75
soft, of third ventricle, 245
white, of spinal cord, 74
Commissures, cerebellar, 207
of spinal cord, 71
Communicating artery, anterior, 421
posterior, 424
Conarium, 246
Conduction, aphasia of, 486
Conus medullaris, 69
terminalis, 115
Convolution, anterior central, 305
first temporal, 313
inferior parietal, 308
temporal, 314
marginal, 315
middle temporal, 314
of corpus callosum, 316
second temporal, 314
superior temporal, 313
third temporal, 314
Convolutions, central, 307
motor, 307
occipital, 309
of Cerebrum, 303
of mesial surface of cerebrum,
315
superior parietal, 307
temporoparietal, 310
veins of, 438
Cord, central ligament of, 69
dorsal, 69
spinal, 64
Cornu ammonis, 353,394
anatomy of, 350
commissural tract, 100, 101
Cornua, anterior, of spinal cord, 72
of lateral ventricle, 393
of spinal cord, 72
Corpora albicantia, 324
development of, 536
mammillaria, 324
development of, 536
quadrigemina, 210
development of, 53°
lesions of, 488
restiformia, 188, 203
striata, 398
trapezoidea. 175, 180
Corpus callosum, 293, 319, 371, 387
convolution of, 316
genu of, 414
lesions of, 487
peduncles of, 388
ventricle of, 393
ciliare, 194
dentatum, 194
limbriatum, 394
INDEX.
579
Corpus striatum, vein of, 440
trapezoideus, 194
Corpuscles of Golgi, 43
Pacinian, 41
tactile, 39
Vater's, 41
Cortex, cerebral, auditory sphere of, 507
centers of association of, 507
divisions of, according to
Flechsig, 506
histology of, 338
layers of, 33S
olfactory sphere of, 507
projection spheres of, 507
sensory spheres of, 507
tangential fibers of, 339
visual sphere of, 507
zones of association of, 507
of cerebellum, 198
pyramidal cells of, 28
stratum zonale of, 338
Cortical area for muscles of trunk and spine,
4 53 . .
governing motion, 449
blood-vessels, 416
cells, layers of, 343
center for general sensations, 454
for smell, 483
for taste, 482
for writing, 475
fibers, layers of, 343
layer, molecular, 343
outer, 343
superficial, 343
Cox's modification of the Golgi sublimate
method of staining, 567
Cranial nerve, fifth, superior or accessory nu-
cleus of, 240
nerves, development of, 547
eleventh pair of, 139
fourth pair of, 240
sensory fibers of, 547
third pair of, 235
twelfth pair of, nuclei of origin
of, 151
Crossed paralysis, 490
Crosses of Frohmann, 34
Cross-legged progression, 500
Crura cerebri, 325
development of, 530
lesions of, 489
Crusta, 220, 325
Culmen, 189
Cuneate lobule, 190
Cuneus, 316
Cup, optic, 552
Cytochrome nerve-cells, 22
Decussation, pyramidal, 140
sensory, 144
superior sensory, 224
Degeneration, secondary, 87
Deiter, large-celled nucleus of, 174
nucleus of, 182
protoplasmic processes of, 47
spider-cells of, 56
Dejerine's method of sectioning brain, 560
Dendrites, 47, 48
function of, 48
number of, 48
Dentate gyrus, 318
ligament, 66
Diaphragma selliv, 283
Diencephalon, 511
Digastric lobule, 190
Dorsal cord, 69
funiculi, course of fibers of, 97
region of spinal cord, 116
Doyere, eminences of, 45
Dura, 64
mater, cerebral, 280
arteries of, 283
nerve-supply of, 284
processes of, 281
E.
Edinger, tegmental radiation of, 403
Edinger's nucleus, 230
Ehrlich's vital methylene-blue method of
staining, 573
Eleventh pair of cranial nerves, 1 39
Embryology of central nervous system, 508
Eminences of Doyere, 45
Eminentia cinerea, 135
collateralis, 300, 394
teres, 168
Emissary veins, 447
End bulbs, articular, 40
of Krause, 40
Endocranium, 280
Endoneurium, 36
End-organs, stains for, 572
Enlargement, brachial, of spinal cord, 69
cervical, of spinal cord, 69
lumbar, of spinal cord, 69
Epencephalon, 186
Ependyma, 135, 354, 393
Epidural space, 64
Epineurium, 36
Epiphysis cerebri, 246
Erb's palsy, 500
Eyelids, elevation of, center for, 453
D.
Deckplatte, 525
Declive, 189
Decussation, interolivary, 144, 224
motor, 140
optic, 320
posterior pyramidal, 144
Face-area of cerebral cortex, 45 1, 452
Facial nerve, 168
connections of, 17 1
Falciform lobe, 317
sinus, 442
vein, 443
Falx cerebelli, 282
580
INDEX.
Falx cerebri, 281
Fascia dentata, 318, 359
Fasciculi cerebrospinalis lateralis, 90
garland-like, 208
teretes, 135
Fasciculus arcuatus, 364, 368
cerebellospinalis, 75
inferior longitudinal, 39
occipitofrontalis, 369
olivary, 105
perpendicular, 370
retroflexus, 257
superior longitudinal, 368
thalamomammillaris,253, 413
uncinatus, 368
ventrolateralis superficialis, 103
Fasciola cinerea, 318
Fibers, projection-system of, 373
Fibrae arcuate propria, 364
Fibrillse, primitive, 33
Fields of innervation, 45
Fifth cranial nerve, superior or accessory
nucleus of, 240
ventricle, 414
Fila olfactoria, 326
Fillet, internal or mesial, connections of vesti-
bular nerve with, 177
lateral, 18 r, 228
connections of vestibular nerve
with, 177
mesial, 144, 180, 223
Filum terminale, 69, 92
Fimbria, 318, 394
Fissure, anterior longitudinal, of spinal cord,
71
calcarine, 300
callosomarginal, 303, 545
central, of cerebrum, 299
choroid, 542
of cerebrum, 297
collateral, 547
dorsal, of spinal cord, 71, 72
inferior longitudinal, of cerebrum, 319
interparietal, 300,546
intraparietal, 300, 546
lateral, 300
longitudinal, of cerebrum, 293, 294
occipital, 299
occipitotemporal, 547
of Rolando, 299, 545
of Sylvius, 298
development of, 540
parieto-occipital, 299
posterior longitudinal, of spinal cord,
71
of spinal cord, 72
postero-intermediate, of spinal cord,
72
precentral, 546
prepyramidal, 190
primary, 542
Sylvian, 320
transverse, of cerebrum, 294
ventral, of spinal cord, 71
Fissures of cerebral hemisphere, evolution of,
545
Fissures of cerebrum, 294
of external surface of cerebrum, 294
of frontal lobe, 546
of island of Reil, 546
of occipital lobe, 546
of parietal lobe, 546
of temporal lobe, 546
primary, of cerebral hemisphere, 545
secondary, of cerebral hemisphere, 545
of cerebrum, 294
Flechsig, anterior ground-bundles of, 90
columns of, 83, 90, 143, 203
nucleus vestibularis of, 175
posterior ground-bundle of, 91
Fleece, 197
Flocculus, 190
Fluid, cerebrospinal, 286
Folds, medullary, 508
Foramen caecum, 125
of Magendie, 132, 285
of Monro, 246
Foramina of Key and Retzius, 285
Forceps major, 393
minor, 390
posterioris, 397
Fore-brain, 293
Formatio reticularis, 146, 180
alba, 14S, 180
grisea, 146, 180
Fornix, 249, 373, 413
Fossa of Sylvius, development of, 54°
Sylvii, 298
Fourth pair of cranial nerves, 240
Fovea inferior, 135
superior, 135
Frcenulum lingular, 189
Freud, method of staining of, 572
Frohmann, crosses of, 34
lines of, 33
Frontal artery, ascending, 422
inferior, 422
gyrus, ascending, 305
first, 303
inferior, 304
middle, 304
second, 304
inferior part of dorsal
portion of, 304
superior, 303
third, 304
lobe, 303
fissures of, 546
Frontocerebellar tract, 222, 353
Funiculi, dorsal, course of fibers of, 97
teretes, 135
Fuss, 220
Galen, veins of, 440
Ganglia, basal, lesions of, 488
of sensory cranial nerves, 548
spinal, 109
Ganglion cell, 17
habenulse, 249, 257
interpeduncular, 258
INDEX.
5Si
Ganglion, spinal, posterior, 71
Ganglionic cells of retina, 264
vessels of brain, 416
Garland-like fasciculi, 208
Gemmules, 48, 200
Geniculate body, external, 250
internal, 250
lateral, 250
Genu of corpus callosum, 414
Gerlach, method of staining of, 572
Giant pyramidal cells, 29
Glands, Pacchionian, 287
Glia-cells, 56
Globus pallidus, 399
Glomeruli, olfactory, layer of, 329
Glossopharyngeal nerve, 155
motor nucleus of, 158
Golgi, corpuscles of, 43
Golgi's method for sta'ning nerve-cells and
their processes, 566
rapid method of staining, 566
slow method of staining, 566
Goll, column of, 84, 91, 99, 126
nucleus of. 131, 144
Gowers and Bechterew, anterolateral ascend-
ing tract of, 233
anterolateral ascending tract of, 80,
90, 103
Gowers' tract, 385
Granular nerve-cells, 24
Granules, chromophyllic, 18
of Nissl, 18
protoplasmic, 18
Gray commissure, 74, 75
matter of spinal cord, 71
neuroglia of, 121
substance, intermediate, 74
Groove, medullary, 508
posterolateral, of spinal cord, 72
Ground bundle of fibers, lateral, 233
posterior, 91
bundles, anterior, 107
function of, 107
of Flechsig, 90
of lateral columns, 107, 234
Gudden, inferior commissure of, 275
Gyri of cerebrum, 303
Gyrochrome nerve-cells, 22
Gyrus, angular, 308
ascending frontal, 305
parietal, 306
cinguli, 316
dentatus, 359
anatomy of, 350
first frontal, 303
occipital, 309
fornicatus, 316
bundle of, 364
hippocampal, 350
hippocampus, 31 7
inferior frontal, 304
occipital, 309
lingual, 300
marginal, 315
middle frontal, 304
occipital, 309
Gyrus, occipitotemporal, middle, 300
posterior central, 306
postparietal, 308
rectus, 306
second frontal, 304
occipital, 309
superior frontal, 303
occipital, 309
supramarginal, 308
third frontal, 304
occipital, 309
uncinate, ?iS
H.
Half-vision center, 461
Helweg, triangular bundle of, 105
Hematoxylin as a general stain, 573
Hemiplegia, alternate, 490
Hemispheral bundle, 337
Hemisphere, cerebral, development of com-
missural system of,
543.
evolution of fissures
of, 545
primary fissures of, 545
secondary fissures of,
545
Hemispheres, cerebral, base of, 318
development of, 539
general anatomy of
interior of, 387
Hilum of olivary body, 160
Hippocampal gyrus, 350
Hippocampus major, 394
anatomy of, 350
minor, 300, 397
His, Bogenfurche of, 542
spaces of, 58
Horn of spinal cord, head of, 82
neck of, 72
Horns, anterior, of spinal cord, 72
lateral, of spinal cord, 72
posterior, of spinal cord, 72, 122
Hypoglossal nuclei, connections of, 15 2
nucleus of Roller, 152
Hypophysis cerebri, 246, 276, 323
I.
Ideas, center for, 467
Incisures of Lantermann, 35
of Schmidt, 35
Infantile spinal paralysis, 501
Inferior cerebellar arteries, 43 1
frontal artery, 422
Infundibulum, 246, 279, 323
development of, 532
Innervation, fields of, 45
Insula, 310
Intellectual faculties, higher, centers which
preside over, 480
Interannular segment, 34
Interbrain, 244, 511
Intercallatum, 263
5 S2
INDEX.
Intermediate gray substance, 74
Internal auditory artery, 425
capsule, 399, 407
localization of lesions of, 48S
Internodal segment, 34
Interolivary decussation, 144, 224
Interparietal fissure, 300, 546
Interpeduncular ganglion, 251, 258
space, 323
Intraparietal fissure, 300, 546
Intrinsic cells of spinal cord, 80
Island of Reil, 310
Iter a tertio ad quartum ventriculum, 211
J-
Jugular vein, internal, bulb of, 445
K.
Karyochrome nerve-cells, 22
Karyoplasm, 17
Keimzellen, 513
Key, 131
and Retzius, foramina of, 285
Krause, end bulbs of, 40
ventriculus terminalis of, 74
Kronthal's method of staining, modification
of, 565
Kiihne, fields of innervation of, 45
L.
Labbe, posterior anastomotic vein of, 439
Labia cerebri, 393
Lacunre venose lateralis, 283, 442
Lamina medullaris circumvoluta, 355
involuta, 359
Lamina? medullares, 252
Lancisi, nerves of, 389
Language, centers for, 465
Lantermann, incisures of, 35
Laryngeal muscles, center for, 453
Lateral arteries of pons and medulla, 432, 434
columns, nuclei of, 143
fissure, 300
limiting layers, 90, 107
nuclei, 143
sinuses, 445
ventricles, 393
Leg-area of cerebral cortex, 45 1, 45 2
Lemniscus, lateral, 181, 228
mesial, 144, 223
Lenticular loop, 399, 402
nucleus, 399
Lenticulo-optic arteries, 424
Lenticulostriate arteries, 424
Lewis, Eevan, method of staining of, 565
Ligamentum denticulatum, 66
Ligula, 132
Limbic lobe, 317
Lines of Frohmann, 33
Lingual gyrus, 300
lobule, 316
Lingula, 188
Lissauer, column of, 114
Lissauer's tract, 106
Lobe, falciform, 3 1 7
frontal, 303
limbic, 317
occipital, 308
olfactory, 327
development of, 550
orbital, 305
parietal, 306
quadrate, 306, 316
slender, 193
temporosphenoid, 313
Lobule, cuneate, 190
diagastric, 190
inferior semilunar, 193
lingual, 316
paracentral, 305
postcentral, 310
precentral, 310
Lobules of cerebrum, 303
of inferior surface of cerebellar hemi-
sphere, 190
of superior or dorsal surface of cere-
bellar hemisphere, 190
Lobus centralis, 189
gracilis, 193
quadratus, 190
Localization, cerebral, 448
Locomotor ataxia, 502
Locus cceruleus, 243
niger, 263, 325
Long arteries of brain, 416
Longitudinal sinus, inferior, 443
superior, 442
Loop, lenticular, 399, 402
Lumbar enlargement of spinal cord, 69
region of spinal cord, 115
Luys' body, 259, 260
Lymphatics of nervous system, 58, 61
Lymph-canals, perivascular, 58
Lymph-space, adventitial, 58, 63
Lymph-spaces, pericellular, 63
Lyra, 414
M.
Magendie, foramen of, 132, 2S5
Mallory, method of, for staining neuroglia
fibers, 569
Mallory's phosphotungstic-acid hematoxylin
for staining neuroglia, 570
Marchi and Lowenthal, anterolateral descend-
ing tracts of, 90. 104, 204
Marchi's method of staining, 569
Marginal convolution, 315
gyrus, 315
sinus, 443
Marginofrontal artery, 421
Martinotti, cells of, 349
Median arteries of pons and medulla, 432, 433
Medulla, anterior columns of, 126
pyramids of, 1 26
lateral areas of, 126
columns of, 126
INDEX.
S«3
Medulla, median septum of, 146
oblongata, 69, 125
arterial supply to, 432
development of, 525
lesions of, 496
posterior area of, 126
raphe of, 146
spinalis, 64
transverse section of, at level of first
cervical nerve, 137
transverse section of, at level of
motor crossway, 140
transverse section of, near junction
with pons, 166
Medullary folds, 508
groove, 508
plate, 508
ridges, 508
velum, inferior, 132, 194
superior, 131, 194
Medullated nerve-fiber, 49
nerve-fibers, 31
Membrana limitans interna of retina, 263
Membrane, external limiting, of retina, 264
Membranes of brain, 280
Meningeal artery, posterior, 425
Menisques, tactile, 42
Mesencephalon, 210, 530
Methylene-blue method of staining, Ehrlich's
vital, 573
Meynert's bundle, 257
commissure, 276
Mid-brain, 530
minute anatomy of, 212
region of,'2Io
Middle cerebellar arteries, 431
cerebral artery, 422
zone of spinal cord, 74
Mind-blindness, 469
Mitral cells, large, of olfactory bulb, 330
of olfactory bulb, superficial layer
of medium and small - sized,
331
Molecular cortical layer, 343
layer of olfactory bulb, 330
of retina, external, 266
inner, 265
Monro, foramen of, 246
Monticulus cerebelli, 189
Motion, cortical area governing, 449
Motor aphasia, 471
area, lesions of centrum semiovale be-
neath, 485
of brain, 449
cells of spinal cord, 76
convolutions, 307
decussation, 140
nerve-organs, 45
nerve-plates, 45
nerve-roots, 112
nerves, terminations of, 45
neurones, peripheral, 76
nucleus of vagus and glossopharyngeal
nerve, 158
oculi nerve, 235
speech-center, 471
Motor sprays, 45
tract, 220, 408
tracts, 376
Mouth, angle of, center for retraction of, 453
Miiller"s fluid, 562
Multipolar nerve-cells, 24
Muscle-spindle, 43
Muscular atrophy, progressive, 501
Myelin, 34
sheath, Weigert's method of staining,
567
Myelospongium, 514
N.
Naming center, 468
Nates, 211
Nerve cell-bodies, 47
Nerve-cells, arkyostichochrome, 21
bipolar, 24
cytochrome, 22
forms or varieties of, 24
Golgi's method for staining, 566
granular, 24
gyrochrome, 22
histology of, 17
karyochrome, 22
multipolar, 24
of Purkinje, 25
of spinal cord, 76
somatochrome, 18
staining of, after the method of
Nissl, 564
with thionin, 564
stichochrome, 21
corpuscle, 17
fiber, medullated, 49
fibers, 30, 31
medullated, 31
non-medullated, 31, 35
olfactory, layer of, 320
Remak's 35
sympathetic, 35
organs, motor, 45
plates, motor, 45
roots, 70
anterior, 112
motor, 112
posterior, 113
sensory, 113
Nerves, cranial, development of, 547
motor, terminations of, 45
of Lancisi, 389
olfactory, 326
sensory, terminations of, 38
spinal, 108
terminations of, stains for, 572
Nerve-supply of cerebral dura mater, 284
Nerve-terminations, peripheral, 37
Nerve-trees, 47
Nerve-unit, 17, 47
Nerve-vesicle, 17
Nervi nervorum, 37
Nervous process, 31
system, central, embryology of, 508
5 S 4
INDEX.
Nervous system, differential stains for various
elements of, 563
Nervus masticatorius, 184
Neural canal, 508
tube, 508
Neuraxone, 31, 47>49
Neurilemma, 35
Neurocytes, 47
Neurodendron, 47
Neuroglia, 52
cells, 56
fibers, differential stains for, 569
of gray matter of spinal cord, 121
of spinal cord, 117
stains. 569
subpial, of spinal cord, 83
Neurokeratin, 34
Neurone, 17, 47
motor, 51
of second type, 52
Neurones, classification of, 50
long, 5°
motor, peripheral, 76
of the first order, 76
Neuroplasm, ^^
Neurospongium, 514
Neutral carmin, for staining axis-cylinders and
nerve-cells, 571
Nidus avis, 190
Nigrosin for staining axis-cylinders, 57 1
Nissl body, 18
granules of, 1 8
method of, staining of nerve-cells after,
564
Nodes, Ranvier's, 34
Nodulus, 189
Non-medullated nerve-fibers, 3 1, 35
Nuclear caps, 18
layer of retina, inner, 265
outer, 266
Nucleus accessorius, 173
ambiguus, 158
amygdala, 407
amygdaloid ,399
arciformis, 163
caudate, 399
cuneatus, 131, 144
embolliformis, 194
for the back-muscles, 79
globosus, 194
gracilis, 131, 144
hypothalamicus, 260
lenticularis, 399
magnocellularis diffusus, 149
pontis, 179
reticularis tegmenti, 146, 234
sacral, S^
subthalamicum, 260
vestibularis, 174, 175
Obex, 132
Occipital convolutions, 309
cortex, retinal representation in, 462
fissure, 299
Occipital gyrus, first, 309
inferior, 309
middle, 309
second, 309
superior, 309
third, 309
lobe, 308
fissures of, 546
lesions of centrum semiovale
of, 48 7
sinus, 443
sulcus, anterior superior, 309
inferior, 309
lateral, 309
vertical, 309
Occipito-cerebellar tract, 221
Occipito-temporal fissure, 547
gyrus, middle, 300
Oculomotor nucleus, connections of, 238
Olfactory bulb, 319, 328
fourth layer of, 332
large mitral cells of, 330
layer of central nerve-fibers of,
33 2
molecular layer of, 330
outer layer of, 328
pyramidal cells of, 330
superficial layer of medium
and small-sized mitral cells
of- 331
center, 483
glomeruli, layer of, 329
lobe, 327
development of, 55°
nerve-fibers, layer of, 328
nerves, 326
region, 326
sphere of cerebral cortex, 507
sulcus, 306
tract, 319, 332
roots of, 335
Olivary bodies, 126, 159
accessory, 160
superior, 176, 180
body, 143
connections of vestibular nerve
with, 177
hilum of, 160
fasciculus, 105
tract, 105
Operculum, anterior, 304
Optic chiasm, 274, 320
development of, 539
cup, 552
decussation, 520
nerve-fibers of retina, 264
nerves, course of, 268
development of, 55 2 > 557
recess, 246
thalami, 248
connection of, with cerebral
cortex, 251
thalamus, 249
anterior nucleus of, 252
tubercle of, 249
connections of, 258
INDEX.
585
Optic thalamus, development of, 532
lateral nucleus of, 249, 253
median nucleus of, 253
peduncles of, 252
posterior nucleus of, 253
surfaces of, 249
' ventral nucleus of, 253
tract, connections of, 273
tracts, course of, 268
vesicle, pedicle of, 552
stalk of, 552
Orbital lobe, 305
Orth's fluid, 563
P.
Pacchionian glands, 287
Pacinian corpuscles, 41
Palsy, Erb's, 500
Paracentral lobule, 305
Paralysis, acute bulbar, 499
Brown-Sequard's, 504
crossed, 490
infantile spinal, 501
spasmodic, 500
Paraphasia, 486
Paraplegia, ataxic, 503
Paraxones, 50
Parietal artery, ascending, 422
convolution, inferior, 308
superior, 307
gyrus, ascending, 306
lobe, 306
fissures of, 546
lesions of centrum ovale of, <
Parieto-occipital fissure, 299
Parietotemporal artery, 423
Pars olfactoria, 337
Pathetic nerve, 240
Pedicle of optic vesicle, 552
Peduncle, inferior cerebellar, 182
Peduncles, cerebellar, 202
superior, 229
cerebral, 220
of cerebellum, 188
of cerebrum, 325
of corpus callosum, 388
of optic thalamus, 252
of pineal gland, 246
Pedunculus conarii, 247
Pennicilli olfactorii, 330
Perforated space, posterior, 324
spaces, anterior, 320
Pericellular lymph-spaces, 63
Perineurium, 36
Peripheral nerve terminations, 37
Perivascular lymph canals, 58
Perpendicular fasciculus, 370
Pes hippocampus, 394
pedunculi, 220
Petrosal sinuses, inferior, 445
superior, 445
Pia mater, 65
cerebral, 288
nerves of, 288
Pigment-layer of retina, 267
Pineal gland, 246
development of, 532
peduncles of, 246
posterior commissure of, 248
Pitres' method of sectioning brain, 561
Pituitary body, 267, 276, 323
development of, 536
Plate, medullary, 508
Plexuses, choroid, 288, 289
Poliomyelitis anterior acuta, 501
Polygonal cells, 254
Polymorphous cells, layer of, 350
Pons, development of, 528
transverse section of, 179
Varolii, 178
arterial supply to, 432
lesions of, 490
Postcentral lobule, 310
sulcus, 300
Posterior cerebral arteries, 425
communicating artery, 424
meningeal artery, 425
Postparietal gyrus, 308
Precentral fissure, 546
lobule, 310
sulcus, 304, 546
Precuneus, 316
Prepyramidal fissure, 190
Primary fissure, 542
Primitive fibrillar, ^^
sheath, 35
Processus ad cerebrum, 188
ad medullam, 188
ad pontem, 188
falciformis major, 281
minor, 282
reticularis, 74
Progression, cross-legged, 500
Progressive muscular atrophy, 501
Projection spheres of cerebral cortex, 507
system of fibers, 373
Prosencephalon, 293, 511
Protoplasmic buds, 48
granules, 18
processes, 48
of Deiter, 47
Psalterium, 373, 414
Pulvinar, 249, 253
Purkinje, axis-cylinder of, 32
cells of, 200
nerve-cells, 25
Putamen, 399
Pyramid, 1 89
Pyramidal cells, giant, 29
large, layer of, 346
of cortex, 28
of olfactory bulb, 330
small, layer of, 345
decussation, 140
posterior, 144
nuclei, 163
tract, 220
tracts, anterior, 89
crossed, 91
direct, 89, 92 '
Pyramids, anterior, 140
5 86
INDEX.
Pyramids, anterior, of medulla, 126
posterior, 131
Q-
Quadrate artery, 421
lobe, 306, 316
R.
Radiation, tegmental, 403
Ranvier, tactile menisques of, 42
Ranvier's nodes, 34
Raphe, 527
of medulla, 146
Rautenlippe, 5 2 ^
Recess, optic, 246
Red nucleus, 259, 261
connections of, 262
Regio olfactoria, 326
Reil, fasciculus uncinatus of, 368
island of, 310
fissures of, 546
sulci of, 546
Remak's nerve-fibers, 35
Restiform bodies, 131, 164
Retina, 263
development of, 552, 556
external limiting membrane of, 264
molecular layer of, 266
ganglionic cells of, 264
inner molecular layer of, 265
nuclear layer of, 265
membrana limitans interna of, 263
optic nerve-fibers of, 264
outer nuclear layer of, 266
pigment layer of, 267
rods and cones of, 266, 557
Retinal representation in the occipital cortex,
462
Ridges, medullary, 508
Rindenschicht, 119
Rods and canes of retina, 266, 557
Rolando, fissure of, 299, 545
substantia gelatinosa of, 73
tubercle of, 137
Roller, hypoglossal nucleus of, 152
Roof nucleus of Stilling, 194
Root arteries, 123
anterior, 1 23
of pons and medulla, 432, 434
posterior, 123
zone, posterior, of spinal cord, S4, 91
Roots, anterior, of spinal nerves, 108
posterior, of spinal nerves, 108
Rostrum, 414
Sacral nucleus, 83
Sagittal sinus, 442
Schmidt, incisures of, 35
Schultze, comma-shaped bundle of, 99
Schwann, white substance of, 34
Sclerosis, amyotrophic lateral, 501
Sclerosis, primary lateral, 500
Secondary degeneration, 87
Segment, interannular, 34
internodal, 34
Semilunar lobe, posterior superior, 190
lobule, inferior, 193
Sensations, general, cortical center for, 454
Sensory center for writing, 479
cerebellar tract, direct, 166, 177, 207
cranial nerves, ganglia of, 548
decussation, 144
fibers of cranial nerves, 547
nerve-roots, 1 13
nerves, terminations of, 38
spheres of cerebral cortex, 507
tract, 382, 408
long, in gray matter, 106
tracts of the spinal cord, 95
Septomarginal descending tract, 100, 102
Septum, intermediate, 91
lucidum, 414
vein of, 440
median, of medulla, 146
postero-intermediate, 126
ventral, of spinal cord, 71
Sheath, primitive, 35
tubular, 35
Sinus, basilar, 444
circular, 444
confluens, 442
falciform, 442
inferior, longitudinal, 443
jugularis, 445
marginal, 443
occipital, 443
sagittal, 442
sphenoparietal, 446
straight, 443
superior longitudinal, 442
transverse, 444
Sinuses, cavernous, 446
inferior petrosal, 445
lateral, 445
superior petrosal, 445
venous, 442
Sixth nerve, nuclei of, connections of vestibular
nerve with, 177
Slender lobe, 193
Slit, anterolateral, of spinal cord, 72
Smell, cortical center for, 483
Somatochrome nerve-cells, 18
Space, interpeduncular, 323
of Broca, 335
posterior perforated, 324
Virchow-Robin, 58
Spaces, anterior perforated, 320
subarachnoid, 285
Spasmodic paralysis, 5 00
Speech-center, motor, 471
Sphenoid artery, 423
Sphenoparietal sinus, 446
Spider-cells of Deiter, 56
Spinal accessory nerve, 139
arteries, anterior, 122
lateral, 123
posterior, 122
INDEX.
587
Spinal cord, 64
accessory nucleus of, 76
^ anterior column of, 84
commissure of, 74
cornua of, 72
horns of, 72
longitudinal fissure of, 71
anterolateral mixed zone of, 90
slit of, 72
blood-supply of, 122
central canal of, 74, 122
cervical enlargement of, 69
region of, 117
commissural cells of, 83
commissures of, 71
complete transverse lesions of,
504
cornua of, 72
development of, 513
dorsal enlargement of, 69
fissure of, 71, 72
region of, 116
extent of, 66
gray matter of, 7 1
head of, horns of, 72
intrinsic cells of, 80
lateral columns of, 84
horns of, 72
lesions, localization of, 499
lumbar enlargement of, 69
region of, 115
middle zone of, 74
motor cells of, 76
neck of, horns of, 72
nerve-cells of, 76
neuroglia of, 117
posterior columns of, 84
commissure of, 74, 75
fissure of, 72
horns of, 72, 122
longitudinal fissure of,
71
root-zone of, 84, 91
postero-intermediate fissure of,
72
postero-internal column of, 91
posterolateral groove of, 72
removal of, 563
sensory tracts of, 95
subpial neuroglia of, 83
technic of macroscopic and micro-
scopic examination of, 559
thoracic region of, 116
transverse section of, at different
levels, 114
veins of, 124
ventral fissure of, J l
septum of, 71
white commissure of, 74
matter of, 71, 83
ganglia, 109
posterior, function of, 112
ganglion, posterior, 71
nerves, 108
posterior roots of, 108
Spitzka, intercallatum of, 263
Spongioblasts, 265, 514
Sprays, motor, 45
Stains, differential, for various elements of
nervous system, 573
for axis-cylinder processes, 571
for collateral branches, 572
for end organs, 512
for terminations of nerves, 572
general, 573
neuroglia, 569
Stalk of optic vesicle, 552
Stellate cells, 56, 254
Stichochrome nerve-cells, 21
Stilling, red nucleus of, 261
roof nucleus of, 194
sacral nucleus of, 83
substantia gelatinosa centralis of, 74
tegmental nucleus of, 261
Strahlenzellen, 254
Straight sinus, 443
Stratum gelatinosum, 330
glomerulorum, 329
granulosum, 360
intermedium, 259
lacunosum, 355, 356, 357, 359
moleculare, 355,359
oriens, 354, 356
radiatum, 357
zonale, 248, 324, 355, 359
of cerebral cortex, 338
Stria terminalis, 249, 404
Strise acusticte, 135
corner, 398, 404
Subarachnoid space, 65
spaces, 285
Subiculum cornu ammonis, 317, 350
Subpial neuroglia layer, 119
of spinal cord, S^
Substantia ferruginea, 1S2
gelatinosa centralis, 74
of Rolando, 73
Rolandi, 122
nigra, 220, 259, 263, 325
reticularis alba, 355
Subthalamic region, 259
Sulci, 294
of isjand of Reil, 546
Sulcus, anterior superior occipital, 309
centralis insulte, 310
choroideus, 249
inferior occipital, 309
lateral occipital, 309
lateralis, 220
limitans insuke, 310
oculomotorius, 220, 237
olfactory, 306
postcentral, 300
precentral, 304, 54°
vertical occipital, 309
Superior cerebellar arteries, 430
Supramarginal gyrus, 308
Sylvian aqueduct, 132
artery, 422
fissure, 320
Sylvius, aqueduct of, 210
development of, 53°
58S
INDEX.
Sylvius, fissure of, 298
development of, 540
fossa of, development of, 540
Sympathetic nerve-fibers, 35
Syringomyelia, 503
T.
Tactile aphasia, 471
corpuscles, 39
menisques, 42
Taenia cornu, 249
semicircularis, 249, 398, 404
Tangential fibers of cerebral cortex, 339
Tapetum, 390
Taste, cortical centers for, 482
Tegmental nucleus, 194, 261
radiation, 403
tract, central, 163
Tegmentum, 220, 223, 325
Tela choroidea inferior, 285, 291
Telodendrons, 47, 50
Temporal convolution, first, 313
inferior, 314
middle, 314
second, 314
superior, 313
third, 314
lobe, fissures of, 546
lesions of centrum semiovale,
486
Temporocerebellar tract, 221
Temporoparietal convolutions, 310
Temporosphenoid lobe, 313
Tenia, 132
Tentorium cerebelli, 186, 281
Testes, 211
Thalamencephalon, 244, 511
Thionin, staining of nerve-cells with, 564
Third pair of crania] nerves, 235
Thoracic region of spinal cord, 116
Tonsil, 190
Torcular Herophili, 442
Tract, acousticocerebellar, 166, 1 77 , 207
anterolateral ascending, 80, 193, 233
function of, 104
descending cerebellar, 104
central tegmental, 163
cerebello-olivary, 160, 164, 207
connecting occipital and temporal lobes
%vith cerebellar hemispheres, 221
cornu commissural, 100, 101
descending cerebellar, 204
direct cerebellar, 83, 95
pyramidal, 92
sensory cerebellar, 166, 177
frontocerebellar, 222, 375
Gowers', 385
Lissauer's, 106
long sensory, in gray matter, 106
motor, 108, 220
occipitocerebellar, 221
olfactory, 319
roots of, 335
olivary, 105
Tract, pyramidal, 220
sensory, 382, 408
septomarginal, descending, 100, 102
temporocerebellar, 221
uncrossed pyramidal, 92
Tracts, anterior pyramidal, 89
anterolateral ascending, of Gowers, 90
descending, 90
crossed motor, 90
pyramidal, 90, 91
direct cerebellar, 90, 143, 203
pyramidal, 89, 91
sensory cerebellar, 207
motor, 376
olfactory, 332
sensory, of the spinal cord, 95
Tractus striothalamicus, 403
Transverse sinus, 444
Triangular bundle, 105
Trigeminal nerve, accessory nucleus of, 240
cerebral connections of, 185
motor root of, 182, 184
nuclei of origin of, 182
sensory root of, 182
Trigonum habenulre, 249
olfactorium, 335
ventriculi, 394
Trochlear nerve, 240
Trolard, great anastomotic vein of, 439
Trunk and spine, muscles of, cortical area for,
453
Tube, neural, 5°8
Tuber cinereum, 279, 323
valvule, 190
Tubercle, 399
anterior, of optic thalamus, 249
of Rolando, 131, 137
Tuberculum acusticum, 1 73, 174
anterius, 252
nervi facialis, 168
Tubular sheath, 35
Tunica adventitia of arteries, 58
intima of arteries, 59
media of arteries, 59
Tiirck, columns of, 89
Twelfth pair of cranial nerves, nuclei of, 151
U.
Uncinate gyrus, 31S
Uncus, 318
Upper extremity, cell-group for, 79
Uvula, 189
Vagus, 155
motor nucleus of, 158
Vallecula, 1S6
Sylvii, 298
Valve of Vieussens, 132, 194
Van Gieson's method of staining, 571
Vater's corpuscles, 41
Vein, anterior cerebral, 437
basilar, 437
INDEX.
589
Vein, choroid, 440
falciform, 443
great anastomotic, 439
middle cerebral, 437
of corpus striatum, 440
of septum lucidum, 440
posterior anastomotic, 439
Veins, cerebral, 435
deep cerebral, 440
emissary, 447
inferior cerebellar, 441
of cerebellum, 440
of convolutions, 438
of Galen, 440
of nervous system, 60
of spinal cord, 124
superficial cerebral, 436
superior cerebellar, 440
Velum interpositum, 288
medullary, inferior, 132, "194
superior, 131, 194
Venous sinuses, 442
systems of brain, 435
Ventral septum of spinal cord, 71
Ventricle, fifth, 414
fourth, 131
choroid plexuses of, 291
of Arantius, 125, 136
of corpus callosum, 393
third, middle commissure of, 245
region of, 244
soft commissure of, 245
Ventricles, lateral, 393
cornua of, 393
Ventriculus terminalis, 74
Verbal aphasia, 468
Vermiform process of cerebellum, 186
inferior, 1 8
Vermis, 186, 187, 188
inferior surface of, 189
superior surface of, 188
Vertebral arteries, 425
Vesicle, second primitive, 530
third cerebral, 530
Vesicles, primary cerebral, 508
secondary cerebral, 511
Vesicular column, 83
Vestibular nerve, 171, 172
Vestibular nerve, connections of, 176
of, with cerebel-
lum, 176
of, with internal
or mesial fillet,
177
of, with lateral
column, 177
of, with lateral
fillet, 177
of, with nuclei
of sixth nerve,
177
of, with olivary
body, 177
Vicq d' Azyr, bundle of, 253, 324, 413
white layer of, 339
Vieussens, valve of, 132, 194
Villi, arachnoid, 287
Virchow-Robin space, 58
Virchow's method of sectioning brain, 560
Vision, centers of, 457
Visual sphere of cerebral cortex, 507
W.
Wedge, 131
Weigert's method of staining the myelin
sheath, 567
Wernicke, perpendicular fasciculus of, 370
White matter of spinal cord, 71, 83
substance of Schwann, 34
Wilder, occipital fissure of, 299
Willis, circle of, 429
Word-blindness, 470
Worm of cerebellum, 186, 188
superior, 187
Wrisberg, nerve of, 168
Writing, cortical center for, 475
sensory center for, 479
Z.
Zona incerta, 259
Zone, anterolateral mixed, of spinal cord, 90
middle, of spinal cord, 74
Zones of association of cerebral cortex, 507