CORNELL UNIVERSITY LIBRARY FROM The Estate of S.Simpson RETURN TO ALBERT R. MANN LIBRARY ITHACA, N. Y. Cornell University Library QP 376.F38 1886 The functions of the brain / 3 1924 003 167 040 The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924003167040 THE BEAIN THE FUNCTIONS OF THE BRAIN DAVID FEEEIEE, M.D., LL.D., F.E.S. FELLOW OF THE ROYAL COLLEGE OF PHYSICIANS PROFESSOR OF FORENSIC MEDICINE, KING'S COLLEGE, LONDON PHYSICIAN TO KING'S COLLEGE HOSPITAL, AND TO THE NATIONAL HOSPITAL FOR THE PARALYSED AND EPILEPTIC SECOND EDITION, RE-WRITTEN AND ENLARGED iitji ntraunras fllnstatiiras NEW YORK G. P. PUTNAM'S SONS 27 & 29 WEST 23 rf STREET 1886 'INDEED EVERY DISCbVERY IS A VERIFIED HYPOTHESIS! AND THERE IS NO DISCOVERY UNTIL VERIFICATION HAS BEEN GAINED: UP TO THIS POINT IT WAS A GUESS, WHICH MIGHT HAVE BEEN ERRONEOUS' G. H. Lewes, The Physical Basis of Mind, p. 224 TO DE HUGHLINGS JACKSON WHO FROM A CLINICAL AND PATHOLOGICAL STANDPOINT ANTICIPATED MANY OF THE MOKE IMPORTANT RESULTS OF RECENT EXPERIMENTAL INVESTIGATION INTO THE FUNCTIONS OF THE CEREBRAL HEMISPHERES is fflutk is JteMcafcir AS A MARK OF THE AUTHOR'S ESTEEM AND ADMIRATION PBEEACE THE SECOND EDITION. While my primary object in this edition has been, as before, to give a detailed account of my own investigations, I have endeavoured to present to the reader a systematic exposition of the functions of the brain and central nervous system in accordance with what seem to me, after extensive and critical survey, the best established facts of recent physiological and pathological research. The book has been almost entirely re- written; a good deal has been added ; and not a few modifications have been made, chiefly in matters of detail and methods of explanation. The principal doctrines formerly advocated in respect to the localisation of cerebral functions are maintained in all essentials unchanged. In the preparation of this edition my grateful acknow- ledgments are due to Dr. Bevan Lewis, of the West Biding Asylum, for many beautiful sections and drawings illustrative of the structure of the brain and spinal cord ; and to my colleague Dr. C. E. Beevor for much valuable assistance in general. 34 Cavendish Square : October 1886. PREFACE TO THE FIRST EDITION. My chief object in this book has been to present to the student of physiology and psychology a systematic exposition of the bearing of my own experiments on the functions of the brain. To do this satisfactorily I have thought it necessary to consider the functions of the cerebro-spinal system in general, with the view more especially of pointing out the mutual relations between the higher and the lower nerve centres. Throughout I have aimed at a concise digest rather than an encyclopaedic account of the various researches by which our knowledge of the brain and spinal cord has been built up. 16 Upper Berkeley Street, Portman Square, W. : October 1876. CONTENTS. PAGE INTBODUCTOEY xxi CHAPTEE I. STEUCTUBE OF THE CEEEBEO-SPINAL CENTEES. § 1. Methods of investigation — § 2. The spinal nerves — § 3. Grey matter of the spinal cord — § 4. White matter of the spinal cord, and roots of the spinal nerves — § 5. Medulla oblongata — § 6. Nuclei of the cranial nerves — § 7. Pons Varolii — § 8. Corpora quadrigemina — § 9. Crura cerebri — § 10. Cerebellum — § 11. Optic thalami — § 12. Corpora striata — § 13. Internal capsule and corona radiata — § 14. Cerebral hemispheres — § 15. Cerebral convolutions — § 16. Cortex cerebri — § 17. Belations of the in- ternal capsule — § 18. Belations of the basal ganglia — § 19. Corpus callosum and fornix — § 20. Anterior commissure — § 21. Optic nerves and tracts — § 22. Olfactory bulbs and tracts CHAPTEE II. FUNCTIONS OF THE SPINAL COED. § 1. General 51 Part I. — The Cord, as a Conductor. § 2. Hemisection of the spinal cord — § 3. Excitability of the spinal cord — § 4. Experiments of Ludwig and Woroschiloff as to the sensory and motor tracts — § 5. Centrifugal paths — lines of secon- dary degeneration — § 6. Centripetal paths— lines of secondary degeneration — § 7. Columns of Burdach and columns of Goll — § 8. Specific sensory paths discussed — § 9. Muscular sensibility — § 10. The muscular sense 51 xii CONTENTS Part II. — The Spinal Cord as an Independent Centre. PAGE § 11. Simple nerve centres — § 12. Conditions of reflex action — § 13. Inhibition of reflex action — § 14. Laws of reflex action — § 15. Characters of reflex actions — § 16. Eeflex action and feeling — ■ § 17. Spinal co-ordination — functions of the plexuses — § 18. Special spinal centres — § 19. Cilio-spinal centre and dilator nerve of the iris — § 20. Eelations of the spinal to higher centres — § 21. Tone of muscles — so-called tendon reflexes — § 22. Tone of blood-vessels — secretory nerves — § 23. Trophic influence of the spinal cord — § 24. Relation of nerve centres to heat-production — § 25. Eelations of the spinal to the sympathetic nervous system . 60 CHAPTEE III. FUNCTIONS OP THE MEDULLA OBLONGATA. § 1. Motor paths — § 2. Sensory paths — § 3. The medulla oblongata as an independent centre— § 4. Centres of deglutition — § 5. Centres of articulation — § 6. Eespiratory centres — § 7. Cardiac centres — § 8. Vaso-motor centres — § 9. Yaso-constrictors and vaso-dilators— Gaskell on the visceral nerves — § 10. Eelations of the cardiac and vaso-motor centres — pathological phenomena . 90 CHAPTEE IV. FUNCTIONS OF THE MESENCEPHALON AND CEKEBELLUM — GENEKAL. § 1. Eemoval of the cerebral hemispheres — § 2. Experiments on frogs — § 3. Experiments on fishes — § 4. Experiments on pigeons — § 5. Experiments on mammals — § 6. Explanation of the phe- nomena — § 7. Eesponsive actions, nature, and classification . . 108 I. Maintenance of Equilibrium. § 8. Goltz's balancing experiment — factors of equilibration — § 9. In- fluence of tactile impressions — § 10. Influence of visual impres- sions — § 11. Influence of labyrinthine impressions — the labyrinth — effects of section of the semicircular canals — § 12. Meniere's disease — lesions of the auditory nerves — § 13. Explanation, of the phenomena— Goltz's hypothesis — § 14. Mechanism of laby- rinthine impressions — § 15. Sense of rotation — Crum-Brown's experiments — experiments on deaf-mutes 121 CONTENTS xiii T , I'AUE II. Co-ormnation of Locomotion. § 16. Phenomena and mechanism— § 17. Locomotor ataxy — § 18. Pathology of ataxy 139 III. Emotional Expression. § 19. Phenomena and mechanism 146 CHAPTER V. FUNCTIONS OF THE OPTIC LOBES OR COEPOEA QUADEIGEMINA. § 1. Anatomy and structure of the optic lobes — § 2. Ocular relations — experiments of Hensen and Volkers— § 3. The optic tracts and their relations — § 4. Irido-motor reactions — § 5. Comparative development of the optic lobes — § 6. Effects of lesions of the optic lobes — § 7. Goltz's croaking experiment — § 8. Excitability of the optic lobes — phenomena of irritation— § 9. Explanation of the phenomena — § 10. Effects on the pupils — § 11. Effects on respi- ration and other organic functions — general conclusions . . 149 CHAPTEE VI. FUNCTIONS OF THE CEEEBELLUM. 1. Effects of lesions of the cerebellum — Flourens' experiments — § 2. Experiments of Vulpian, Eenzi, Dickinson, &c. — § 3. Dura- tion of the effects — experiments of Dalton, Weir-Mitchell, Luciani — § 4. Symptoms of cerebellar disease and atrophy — irritative and destructive lesions — § 5. Effects of localised lesions — Magendie's experiment — § 6. Excitability of the cerebellum — § 7. Phenomena of electrical irritation — in monkeys — § . 8. Ocular and other movements — § 9. Experiments on rabbits — § 10. Ex- periments on dogs and cats — § 11. Experiments on pigeons — § 12. Galvanisation of the head — Purkinje's and Hitzig's experi- ments — § 13. Objective and subjective effects of galvanisation — § 14. Relative development of the cerebellum— § 15. Mechanism of cerebellar co-ordination — § 16. Recovery from cerebellar lesions — § 17. Afferent relations of the cerebellum — relations to sensory tracts — § 18. Relations to the labyrinth — § 19. Special relations to the semicircular canals — § 20. Irritation and destruc- tion — § 21. Relations to the eyes— § 22. Superior and inferior cerebellar peduncles— § 23. Efferent relations of the cerebellum — middle cerebellar peduncles — relations to the hemispheres — § 24. Visceral relations of the cerebellum — general conclusions . 174 xiv CONTENTS CHAPTBE VII. FUNCTIONS OF THE CEEEBEUM. Introductory — Method of Investigation. PAGE § 1. Flourens' views — § 2. Views of Hughlings Jackson — experiments of Fritsch and Hitzig — excitability of the cerebral hemispheres — § 3. Methods of stimulation — galvanisation and faradisation — § 4. Conduction of electrical currents — views of Dupuy, &c. — § 5. Excitability of the cortex and medullary fibres compared . 220 CHAPTEE VIII. PHENOMENA OF ELECTEICAL IEEITATION OF THE CEEEBEAL HEMISPHEEES. § 1. Experiments on Monkeys — cerebral topography — § 2. Ex- citable areas — § 3. Experiments on dogs — § 4. Experiments on jackals — §5. Experiments on cats — §6. Experiments on rabbits * — § 7. Experiments on guinea-pigs — § 8. Experiments on rats — § 9. Experiments on pigeons — § 10. Experiments on frogs — § 11. Experiments on fishes — § 12. Experiments on the corpora striata — § 13. Experiments on the optic thalami 235 CHAPTEE IX. the hemispheees consideeed physiologically. The Sensoey Centres. • § 1. Methods of investigation 268 Part I. The Visual Centre. § 2. Indications from electrical irritation — § 3. Extent of the visual centre — § 4. Effects of lesions of the occipital lobes — § 5. Effects of lesions of the angular gyri — § 6. Munk's experiments on the angular gyri — § 7. Lesions of the angular gyrus and occipital lobe — § 8. Cortical relations of the optic tracts — amblyopia and hemiopia — § 9. Clinical investigations — § 10. Visual centre in dogs — § 11. Experiments of Munk and Loeb, &c. — § 12. Visual centre in cats and rabbits — § 13. Visual centre in pigeons — § 14. Indications from secondary degeneration — researches of Gudden, Monakow, &c 270 CONTENTS xv Part II. The Auditory Centre. PAGF. § 15. Indications from electrical irritation — § 16. Experimental determination of the auditory centre — § 17. Munk's experiments. 305 Part III. Olfactory and Gustatory Centres. § 18. Indications from anatomy — Broca's anatomical researches — § 19. The anterior commissure — § 20. Indications from electrical irritation — § 21. Indications from destructive lesions — § 22. Clinical investigations ......... 312 Part IV. The Tactile Centre. § 23. Anatomy of the sensory tract — cerebral hemiansesthesia — § 24. Connection of the sensory tract — § 25. Earlier experiments on the hippocampal region — § 26. Later experiments on the hip- pocampal region — § 27. Experiments of Horsley and Schafer — lesions of the gyrus fornicatus — general conclusions as to the tactile centre 323 OHAPTEE X. the hemispheees consideked physiologically. The Motoe Centres. § 1. Indications from electrical irritation — § 2. Indications from destructive lesions — § 3. Permanent results and secondary de- generations — § 4. Clinical observations — § 5. Differentiation of the pyramidal tracts of the corona radiata — § 6. Psycho-motor paralysis in lower mammals — § 7. Psycho-motorparalysisindogs — § 8. Analysis of the symptoms — § 9. Comparative organisation of the cortical motor centres — § 10. Associated and bilateral move- ments — § 11. Theories as to functional compensation — § 12. Functional compensation and specific localisation considered — . § 13. Views of Schiff as to the effects of cortical lesions — § 14. Questions as to affections of sensation. — § 15. Examination of clinical data — § 16. Views of Hitzig and Nothnagel as to the muscular sense — § 17. Views of Bastian — § 18. Views of Bain and Wundt as to the sense of effort — § 19. Arguments considered — the sense of effort shown to be of centripetal origin — § 20. Ex- periments of Weir-Mitchell on the nerves of amputated limbs — § 21. Experiments on muscular discrimination without volitional effort— § 22. The frontal motor centres — indications from elec- trical irritation— § 23. Effects of destructive lesions — § 24. The prefrontal and postfrontal centres — § 25. Anatomical connections and secondary degenerations— § 26. Experiments of Munk, Hitzig, Goltz, and Kriworotow— § 27. Psychical symptoms and lesions of the frontal lobes 346 xvi CONTENTS CHAPTEE XI. FUNCTIONS OF THE BASAL GANGLIA. PAGE s 1. Anatomical relations — the corpora striata — § 2. Eelations of the optic thalami — § 3. Indications from electrical irritation — § 4. Lesions of the corpora striata and internal capsule in man — § 5. Experimental lesions — Nothnagel's experiments on rabbits— experiments of Carville and Duret on dogs — § 6. Diseases and experimental lesions of the optic thalami — § 7. Eelations of the optic thalamus to the optic tract — § 8. Analysis of the clinical and experimental data— § 9. Special relations of the optic thalamus — Monakow's researches — § 10. General conclusions 404 CHAPTEE XII. THE HEMISPHEEES CONSIDEEED PSYCHOLOGICALLY . § 1. Brain and mind — general — § 2. Duality of the hemispheres — § 3. Conditions of sensation and perception — § 4. Memory — § 5. Feelings and emotions — § 6. Appetites and desires — § 7. Motives to volition — § 8. Volition and ideation — § 9. Conflict of motives — § 10. Acquisition of speech and writing — § 11. Centres of articu- » lation and registration — § 12. Aphasia, pathology of — § 13. Analysis of the symptoms — § 14. Eelations to the left hemi- sphere — § 15. Sensory aphasia — word-blindness — § 16. Word- deafness — § 17. Control of ideation — § 18. Attention — § 19. Sub- strata of attention — comparative development of the frontal lobes 424 CHAPTEE XIII. CEEEBEAL AND CEANIO-CEEEBEAL TOPOGEAPHY. § 1. Physiological homologies between the human and simian brain — experiments of Bartholow and Sciamanna — § 2. Ana- tomical homologies — § 3. Fissures and sulci — § 4. Frontal lobe — § 5. Parietal lobe — § 6. Temporo-sphenoidal lobe — § 7. Occipital lobe — § 8. Internal aspect of hemisphere — § 9. Central lobe — § 10. Excitable areas of human and simian brain — § 11. Cranio- cerebral topography — researches of Fer6, Ecker, Hefftler — § 12. Turner's cranial areas — § 13. Position of the fissures — § 14. Frontal area — § 15. Upper antero-parietal area — § 16. Lower . antero -parietal area — § 17. Upper postero-parietal area — § 18. Lower postero-parietal area — § 19. Occipital area — § 20. Squamoso-temporal area — § 21. Ali-sphenoid area — § 22. Prac- tical rules for surgical purposes — Eeid's researches . . . 459 INDEX 493 LIST OF ILLUSTRATIONS. With the exception of fig. 6, fig. 42, figs. 102 and 123, and figs. 136, 137, which are from electros kindly given me by Dr. James Ross, Professor Huxley, Dr. Duret, and Dr. Beid respectively, and several figures originally prepared for the ' Transactions of the Royal Society,' the following illus- trations, originals and copies, have been specially engraved for this wor by Mr. T. P. Collings :— FIGURE. PASS 1. Diagram of the cerebrospinal and sympathetic nerves (modified from Quain) 3 2. Boots of the spinal nerves (Quain) 4 3. Section of the spinal cord of monkey — lumbar region . . 6 4. „ „ „ dorsal region . . . 6 5. „ „ „ cervical region . . 6 6. Section of spinal cord of human embryo at five months (Ross) 9 7. Medulla oblongata, pons, and crura cerebri (after Quain) . . 13 8. View of the fourth ventricle (Sappey) 14 9. Dorso-lateral view of the medulla oblongata of monkey . . 15 10. Section of the medulla oblongata of monkey at the decussation of the pyramids 16 11. Section of the medulla oblongata of monkey at the middle of the olivary bodies 17 12. Diagram of the nuclei of the cranial nerves — posterior aspect (after Erb) 20 13. Diagram of the nuclei of the cranial nerves — lateral aspect (after Erb) 20 14. Section of the medulla oblongata of monkey at the origin of the auditory nerve 21 15. Section of the medulla oblongata of monkey at the origin of the abducens nerve 22 16. Section of the pons of monkey in the region of the valve of Vieussens 24 17. View of the base of the brain 26 18. Brain of monkey — exposing the interior of the lateral ventricles, &c 27 19. Section of the corpora quadrigemina of monkey . . . . 28 20. View of the fourth ventricle (Sappey) Jf 31 a LIST OF ILLUSTRATIONS FIGURE. PAaE 21. Cortex of the cerebellum (Beevor) 32 22. Brain of dog — exposing the interior of the lateral ven- tricles 23. Frontal section of brain of monkey— showing the internal capsule and lenticular nucleus . . . . . . 24. Frontal section of brain of monkey through the anterior com- missure ....... 25. Horizontal section of left hemisphere of monkey 26. Brain of rabbit ~^f. Brain of monkey'. 28. Cortex cerebri of monkey — frontal lobe . 29. „ „ „ motor area 30. „ „ „ temporal lobe 31. „ ,, „ occipital lobe . 32. „ „ „ cornu Ammonis . 33. „ „ „ gyrus hippocampi . 34. Sagittal section of hemisphere of monkey 35. Horizontal section of brain of mole, showing the anterior com- missure (after Ganser) ....... 36. Frontal section of hemisphere of monkey, showing the nucleus amygdala? 37. Medulla oblongata, pons, and crura cerebri (after Quain) . . 38. Sagittal section of the olfactory tract and bulb of monkey 39. Hemisection of spinal cord of monkey 40. Section of spinal cord of human embryo at five months (Ross) 41. Nervous system of an ascidian (Carpenter) .... 42. Nervous system of the crayfish (Huxley) 43. Brain of frog . ' 109 44. Brain of fish (carp) 110 45. Brain of pigeon Ill 46. Brain of rabbit 113 47. Semicircular canals of turkey . . . . • . . . 128 48. Interior of the labyrinth with the membranous semicircular canals and nerves (Breschet) 49. Frontal section of the nates (corp. quad.) of rat — after enucleation of the right eye (after Ganser) 50. Sagittal section of encephalon of dog — showing the position of the oculo-motor nuclei (after Hensen and Volkers) . . 153 51. Atrophy of the cerebellum — Shuttle worth's case . . . 181 52. Lesion of median lobe of cerebellum of monkey . . . . 184 53. Lesion of left lateral lobe of cerebellum of monkey . . 187 54. Cerebellum of monkey — upper and posterior aspect . . . 188 55. „ „ lateral aspect 188 56. # „ rabbit — upper and posterior aspect . . . 191 57. „ „ anterior aspect 191 58. „ dog— upper and posterior aspect . . . 193 33 35 36 37 39 40 41 41 41 42 42 42 43 40 47 48 50 52 59 67 67 128 150 70. 71. 72. 73. 74. LIST OF ILLUSTBATIONS xix FIGURE. . PAGE 59. Cerebellum of dog — lateral aspect 193 60. „ cat — upper and posterior aspect . . . . 194 61. „ „ lateral aspect 194 62. Brain of pigeon 195 63. Brain of carp 195 64. Atrophy of the motor region of the left hemisphere . . . 216 65. Base of the same brain — showing atrophy of the right lobe of the cerebellum ........ 216 66. A. Section of cortex of the normal lobe of the cerebellum of fig. 65 217 B. Section of cortex of the atrophied lobe . . ... 217 67> Left hemisphere of brain of monkey 236 68. Mesial aspect of right hemisphere of monkey . . . . 238 69. Excitable areas of brain of monkey — upper aspect . . . 240 „ „ lateral aspect . . . 240 „ „ base of brain . . . 244 „ „ mesial aspect . . . 245 dog 247 „ „ according to Fritsch and Hitzig 248 75. Excitable areas of brain of jackal 255 76. Brain of cat — upper aspect 257 77. Excitable areas of brain of cat — lateral aspect . . . 257 78. „ „ „ rabbit 259 79. „ „ „ guinea-pig 261 80. ,, „ „ rat — upper aspect . . . . 262 81. „ „ „ „ lateral aspect . . . 262 82. Brain of pigeon 262 83. Brain of frog 262 84. Brain of fish (carp) 262 Bight hemisphere, and left hemisphere of brain of monkey — showing bilateral lesion, causing complete and permanent blindness 272 87. Bemoval of both occipital lobes 274 88. Bemoval of occipital and prefrontal lobes .... 275 89. Destruction of left angular gyrus 276 90. I Destruction of both angular gyri 277 Jl. i 92. Charcot's scheme of the optic tracts 289 93. Scheme of the optic tracts and visual centres .... 292 94. Visual sphere of the brain of dog, according to Munk . . . 298 95. I Bilateral destruction of the superior temporo-sphenoidal con- 96. I volution 308 97- 1 Bilateral destruction of the auditory centre .... 309 98. I 99. Horizontal section of the brain of mole (after Ganser) . . < f - J 85. , 86.} xx LIST OF ILLUSTRATIONS VIQUKE. AGE ' [ Bilateral lesion — causing loss of smell and taste . . . 319 102. Lesion of brain of dog — causing hemiansesthesia (Carville and Duret) 324 1 <1R ) ' > Lesion of the left hippocampal region 328 105. Lesion of the right hippocampal region 329 106. Natural appearance of the brain represented in figs. 103, 104 . 331 107. A., B. Natural appearance of posterior half, and under surface of brain represented in fig. 106 331 108. Frontal section of fig. 107 B 331 109. I Lateral and basal aspect of left hemisphere, in which the hippo- 110. i campal region had been destroyed 338 111. Lesion of the motor area of right hemisphere . . . . 349 112. Lesion causing paralysis of right limbs, &c 350 113. Lesion of centre of biceps, &e. 351 114. Lesion of leg centre 352 115. Section of spinal cord in cervical region — showing secondary de- generation consecutive to the lesion represented in fig. 114 353 116. Section of the same cord in the lumbar region . . . 353 117. Lesion of the motor zone of the left hemisphere . . . 355* 118. Section of the sphial cord in the cervical region 119. „ „ „ dorsal „ 120. „ „ „ lumbar „ showing J. 357 secondary degeneration consecutive to the lesion repre- sented in fig. 117 121. Lesion of prefrontal region 396 122. Frontal section of brain represented in fig. 121, showing secon- dary degeneration of the mesial fibres of the internal capsule 398 123. Lesion of brain of dog, causing hemiplegia (Carville and Duret) 412 124. Lesion of cortex with penetration of the optic thalamus . . 416 125. Horizontal section of the optic thalami of the rabbit — showing the various nuclei (after Monakow) .... 420 126. Convolutions of the human brain — lateral aspect (Ecker) . . 472 127. „ „ simian brain 473 128. „ „ human brain — median aspect (Ecker) . . 476 129. „ „ simian „ ,,„... 477 130. Excitable areas of human brain — lateral aspect . . . , 478 131. „ „ simian „ „ „ ... 479 132. „ „ human brain — upper aspect . . . . 480 133. „ „ simian „ „ „ ... -181 134. Cranial areas — according to Turner . . . . . . 433 135. Relations of convolutions to skull (Turner) . . . . - 86 i.36. Relations of fissures to skull (Eeid) 490 J.J7. Relations of convolutions to skull (Beid) .... ^91 INTEODUCTOBY. There is, perhaps, no subject in physiology of greater import- ance and general interest than the functions of the brain, and there are few which present to experimental investigation con- ditions of greater intricacy and complexity. No one who has attentively studied the results of the labours of the numerous investigators in this field of research can help being struck by the want of harmony, and even positive contradictions, among the conclusions which apparently the same experiments and the same facts have led to in different hands. And when the seemingly well-established facts of experimentation on the brains of the lower animals are compared with those of clinical observation and morbid anatomy in man, the discord between them is frequently so great as to lead many to the opinion that physiological investigation on the lower animals is little calculated to throw true ight on the functions of the human brain. These discrepancies appear less unaccountable when the methods of experimentation and the subjects of experiment are taken into consideration. Up to quite a recent date, the principal method pursued- by investigators into the functions of the brain consisted in observing the results following the destruction, by various means, of different parts of the encephalon. The serious nature of the operations necessary to expose the bra'n for purposes of experiment, and the fact that the xxii INTRODUCTORY various parts of the encephalon, though anatomically distinct, are yet so intimately combined and related to each other as to form a complex whole, make it natural to suppose that the establishment of lesions of greater or less extent in any one part should produce such general perturbation of the functions of the organ as a whole, as to render it at least highly difficult to trace any uncomplicated connection between the symptoms produced and the lesion as such. Moreover, the degree of evolution of the central nervous system, from the simplest re- flex mechanism up to the highest encephalic centres, and the differences as regards the relative independence or subordina- tion of the lower to the higher centres, according as we ascend or descend the animal scale, introduce other complications, and render the application of the results of experiment on the brain of a frog, or a pigeon, or a rabbit, without due qualification, to the physiology of the human brain, very questionable ; or even lead to conclusions seriously at variance with well-established facts of clinical and pathological observation. Notwithstand- ing these difficulties and discrepancies, many of which will be found, on careful examination, to be more apparent than real, experiments on animals, under conditions selected and varied at the will of the experimenter, are alone capable of fur- nishing precise data for sound inductions as to the functions of the brain and its various parts ; the experiments performed for us by nature, in the form of diseased conditions, being rarely limited, or free from such complications as render analysis and the discovery of cause and effect extremely difficult, and in many cases practically impossible. The dis- covery of new methods of investigation opens up new fields of inquiry, and leads to the discovery of new truths. The dis- covery of the electric excitability of the brain by Fritsch and Hitzig has given a fresh impetus to researches on the functions of the brain, and thrown a new light on many obscure points in cerebral physiology and pathology. Though great advances INTRODUCTORY xxiii have been made within the last ten years, much, however, still remains to be done. We are still only on the threshold of the inquiry, and it may be questioned whether the time has even yet arrived for an attempt to explain the mechanism of the brain and its functions. To thoughtful minds the time may seem as far off as ever ; yet it is sometimes useful to re- view and systematise the knowledge we have so far acquired, if for no other reason than to show how much still remains to be conquered. STRUCTURE OP THE BEAIN AND SPINAL COED. CHAPTEE I. STRUCTURE OF THE CEREBRO- SPINAL CENTRES. § 1. The following sketch of the anatomy of the cerebro- spinal system is intended mainly to facilitate the exposition of the details of the physiological and pathological investigations by which the functions of the brain and spinal cord have as yet been determined. The minute anatomy of the brain and spinal cord is still in many respects exceedingly obscure. Some' great facts have been firmly established by a concurrence of anatomical, physiological, and pathological research, but many others, founded merely on histological examination, partake more of the character of hypotheses than of demonstrated fact, and cannot be safely relied on either in support of or in opposition to the results of physiological or pathological experiments. The difficulties of cerebro-spinal histology are enormous, and many connections and relations which are des3ribed by one set of investigators as real are found by others, equally competent, as merely apparent. Of the various ambitious and all too premature schemes of the minute structural relations I of the cerebral and spinal tracts and centres proposed for our/ acceptance no two agree even in fundamental particulars. Especially fruitful in reliable results of recent years, and likely to. yield many more in years to come, has been the 2 STRUCTURE OF THE CEREBROSPINAL CENTRES Wallerian method of determining the structural and func- tional relations of the cerebro-spinal centres and tracts, by a study of the position and direction of the lines of degenera- tion induced by artificial or pathological lesions of certain parts of the brain and cord. In relation with this, also, facts of great value, but more open to varieties of interpretation, have been ascertained by embryological investigation of the respective periods and mode of development of the several cerebral and spinal tracts, -which we owe mainly to Flechsig. 1 But as yet both methods have established comparatively little with any degree of certainty, and the great bulk of minute cerebro-spinal anatomy is in the most unsatisfactory state. § 2. The cerebro-spinal centres consist of the brain, or encephalon, contained within the skull, and the spinal cord, contained within the vertebral canal. The brain is in relation more or less direct with the periphery, by which is meant all the organs of receptivity and activity, by means of thirty-one pairs of spinal, and twelve (or, according to English anatomy, nine) pairs of cranial nerves. These nerves are separable into two great divisions, according to the nature of the func- tions which they subserve. The one set carry impressions from the periphery to the cord and brain, and are therefore called afferent nerves ; while the other convey impulses from the brain and cord to the periphery, and are therefore termed efferent. The most prominent functions performed by these nerves being the conveyance of sensory impressions and motor stimuli respectively, the restricted terms sensory and motor are commonly employed in lieu of the wider terms afferent and efferent. The spinal nerves are connected with the cord by two roots; the one of which, the efferent or motor (a, fig. 2), arises from the anterior or ventral aspect ; the other, the afferent or sen- sory (6, fig. 2), from the posterior or dorsal aspect of the cord. The two roots remain separate for a short distance, during which the posterior passes through a ganglion (6', fig. 2) or collection of nerve cells, and then unite to form one trunk (7, fig. 2), which is therefore a mixed nerve, composed both of afferent and efferent fibres. 1 Die Leitungsbahnen im Gehim unci Rtlckenmark, 1876. THE SPINAL NEBVES Fig. 1.— Diagram of the Cere- brospinal and Sympathetic Kerves. This diagram, composed and modified after figures by Quain, represents the spinal cord as seen from before. The spinal nerves are indi- cated by the Roman nume- rals : — CI-YUI being the cer- vical nerves ; lu-xir, the dorsal ; Li-V, the lumbar, and the rest, not specially numbered, the sacral nerves. The plexiform arrangement of the nerves is seen on the left side. The brachial plexus is seen to be composed of branches from CV to di, with some communicating branches from civ and dii ; the lumbo- sacral plexus is seen to de- rive branches from li to siv inclusive. The individual branches of these plexuses are indicated by letters and small numerals, but are not here named in detail. The sympathetic cord ami ganglia are seen on the right side, with their junctions ■with the spinal nerves, a, the superior cervical gan- glion ; b, the middle cervical ganglion ; cd, the inferior cer- vical' ganglion, united with the first dorsal ganglion ; sp u the great splanchnic nerve ; $p„ the lesser splanch- nic nerve; d', the eleventh dorsal ganglion ; $$, the upper sacral ganglion. B 2 4 STBUCTUBE OF THE CEREBROSPINAL CENTRES Shortly after their exit from the intervertebral foramina the spinal nerves enter into communication with the gangliated cords of the sympathetic nervous system (fig. 1, a, b, c, d, &c.) which lie on each side of the vertebral column. This system of nerves and nerve centres, more or less independent of the cerebro-spinal system, specially innervates the walls of the viscera and blood-vessels. The spinal nerves, in their course to the periphery, in many cases form junctions or anastomoses with each other, whereby nerve trunks are formed composed of nerves derived from different roots, and these again form subsidiary divisions Fie. 2. -Spinal Cord (Quain).— In a the anterior surface of the cord is shown, toe anterior nerve root being divided on the right. In B a transverse section of the cord is exhibited, showing the crescentic shape of the grey matter in the interior. 1, the anterior median fissure. 2, posterior median fissure. 3, anterior lateral de- pression over which the anterior nerve roots are seen to spread. 4, posterior lateral groove into which the posterior roots are seen to sink. The anterior column is included between 1 and 3 ; the lateral column between 3 and 4 ; and the posterior column between 4 and 2. 5. The anterior root. 5' in A = thc anterior root divided. 6, the posterior roots, the fibres of which pass into the ganglion 0'. 7, the united or compound nerve. and junctions ; so that a complicated plexus is the result, in which it is impossible anatomically to trace the fibres of the individual roots from which they spring. Two of these plexuses require special consideration ; viz. the brachial plexus (fig. 1, cv-di), from which the nerves of the upper extremity are derived ; and the lumbo-sacral plexus (fig. 1, li-siv), from which come the nerves of the lower extremity. The plexiform arrangements of the nerves have important functional significations, some of which will be considered below. THE SPINAL. COBD 5 § 3. The spinal cord, which in man extends from the upper border of the atlas to the second lumbar vertebra, where it tapers to a point (filum terminate), is uniformly cylindrical in shape except at the points of origin of the roots Arming the brachial and lumbo-sacral plexuses. Here the diameters are increased, giving rise to the cervical and lumbar enlargements respectively (fig. 1). The cord is divided into two symmetrical halves by the anterior and posterior longitudinal fissures (a/, Pf> fig 8 - 3, 4, 5), and the two halves are connected together by a commissure, which is seen on cross section to be formed by an anterior portion, situated at the bottom of the anterior fissure, and termed the white commissure (a c, fig. 3), and a grey portion, the grey commissure (p c), in which there is a more or less distinct canal, the central canal (c c), which is the remnant of the hollow tube from which both cord and brain were developed. The cord is composed of grey and white matter. The grey matter has the appearance of a double crescent united by the commissure. The horns of the crescent are termed the anterior (a) and posterior (p) horns respectively. The shape of the horns varies at different parts of the cord (figs. 3, 4, 5), but in general the anterior horns are clubbed, and do not reach the surface, while the posterior horns are prolonged to the groove into which the posterior roots enter. The grey matter of the anterior horns contains large multi- polar nerve cells arranged in groups (ae, ai, in figs. 3, 4, 5), embedded in a dense spongy network composed largely of nerve fibres and fine processes of the nerve cells. Of the numerous branches of the multipolar cells one is continued as the axis cylinder of one of the fibres of the anterior roots. The others — the protoplasmic processes — help to form the dense network, of which the grey matter is largely composed, which connects together different cell groups, and probably forms the medium of communication between the cells and the various tracts with which they are in relation. The grey matter of the posterior horns contains also some multipolar cells of smaller size and more spindle shape than those of the anterior horns. They are also much less numerous 1 , *K p J™ ff pr.. ll Fig. 3.— Transverse Section of Spinal Cord of Monkey. Lumbar region. (From preparation and drawing by Bevan Lewis.) Fig. 4.— Transverse Section of Spinal Cord of Mod key. Dorsal region. (From preparation and drawing by Bevan Lewis.) Description applicable to Fiefs. 3, 4, and 5. A, anterior cornn. r, posterior corrm, a, anterior column. I, lateral column p, posterior column, ae, anterior com- missure, ae, external cell group! and cti, internal cell groups of anterior cornn. uj\ anterior median fissure, or, anterior roots, cc, central canal fr, formatio reticularis, it, cells of tractns intermedio -lateralis. Clarke's vesicular column, pc, pos terior commissure, pf, posterior me- dian fissure, pm, posterior median column (column of Goll). pv, pos- terior roots, sg, substantia gelatv nosa. GL Of Fig. 5. — Transverse Section of Spinal Cord of Monkey. Cervical region. (From preparation and drawing by Bevan Lewis.) TSE SPINAL COBD 7 and are not aggregated in groups. These cells also possess axis cylinder, and protoplasmic, processes. But whether the axis cylinder processes are directly connected with posterior nerve roots, as Deiters supposes, or pass in the direction of the anterior horns, as G-erlach holds, is not definitely deter- mined, though certain facts in some of the lower vertebrates would support Deiters' view. The apex of the posterior horns is covered by grey matter similar to that which surrounds the central canal, . and is termed the substantia gelatinosa (sg, figs. 4, 5) ; but though this contains nerve elements it would seem, from the researches of Kuhhe, to consist mainly of a substance allied to keratin. Besides the cells of the anterior and posterior horns proper other cell groups have received special designations. One of these, situated laterally to the anterior horn but more or less fused with it in the cervical and lumbar enlargements, is termed the postero-lateral, or intermedio-lateral group (i I, figs. 3, 5), and 1 consists of cells of a spindle shape, and much smaller than those of the anterior horns generally. The other group, which is situated at the inner side of the base of the posterior horns, is termed Clarke's vesicular column (vc, fig. 4), and consists of. multipolar cells, also considerably smaller than those of the anterior horns. The grey matter viewed longitudinally forms a double column extending through the whole length of the cord. The width is not uniform. As has already been mentioned, there are special enlargements in the lumbar and cervical regions, and these are due mainly to the greater amount of grey matter in these situations. But throughout the whole cord the grey matter, more particularly of the anterior horns, is specially abundant at the junctions of the spinal nerves, so that a necklace arrangement is visible. This is seen much more distinctly in some of the lower vertebrates, and is an indication of the formation of the spinal cord of segments, more or less fused together, corresponding to the ventral ganglionic chain of the invertebrata (see fig. 41) . The cells of certain groups do not extend the whole length of the cord. Those of Clarke's vesicular column are found most distinctly in the region extending between the ninth 8 STBUCTUBE OF THE CEREBROSPINAL CENTRES dorsal and third lumbar nerves. They are found continuously as high as the seventh cervical nerve. But homologous groups, more or less detached from the continuous column, are de- scribed as occurring as low as the origin of the second or third sacral nerve, and as high as the third cervical (Stilling). Boss ' traces their homologues also in the cells forming the nucleus of the vagus, and Gaskell 2 arrives at the same con- clusion. § 4. The white matter of the cord consists of tracts or columns of nerve fibres, which have received special names according to their position and connections. The general term anterior column (a, figs. 3, 4, 5) is given to that tract which lies between the anterior median fissure and the point of emergence of the anterior roots. Between this point and the attachment of the posterior roots lies the lateral column (I, figs. 3, 4, 5), and between this and the posterior median fissure lies the posterior column (p). But the Waller ian method, and the respective periods a.t which the nerve fibres of different tracts become invested with* a medullary sheath, show that the columns are susceptible of further differentiation and specialisation. The Pyramidal Tracts (fig. 6, p, p'). — These tiaets, which are so called because they are continuous with the anterior pyramids of the medulla oblongata (fig. 7, pa), consist of two divisions, (1) the direct pyramidal tract, and (2) the lateral or crossed pyramidal tract. The direct tract, which is con- tinuous with the pyramid of the same side, occupies the region of the anterior column immediately adjoining the anterior median fissure. It is also termed the anterior median column (fig. 6, t), or the column of Tiirck. The lateral pyramidal tract (fig. 6, p), wbich is continuous with the opposite pyramid, occupies the posterior portion of the lateral column external to the posterior cornu. The pyramidal tracts diminish in size from above down- wards, the direct tract ceasing about the middle of the cfbrsal region, while the lateral tract extends to the lower extremity 1 Diseases of the Nervous System, 1881. 2 ' The Structure, Distribution, and Function of the Nerves which innervate the Visceral and Vascular System,' Journal of Physiology, vol. vii. No. 1. THE SPINAL COED 9 of the lumbar enlargement where it comes to the surface external to the apex of the posterior horn. The pyramidal tracts are connected with the anterior horns of the spinal cord ; the lateral or crossed tracts with the anterior horns on the same side on which they are situated, and the direct tracts with the same after crossing in the an- terior commissure. Hence it would appear that the portions of the pyramid which do not decussate at the decussation of the pyramids of the medulla oblongata cross ultimately through the anterior commissure on their way downwards. Fig. 6.— Transverse Section of Spinal Cord of Human Embryo at five months (Ross). ah, ah', anterior horns of grey substance. ; h, / h', posterior horns, ar, ar', anterior rout zones, pr, pi', posterior root zones. }■, I' 1 , pyramidal fibres of lateral columns. T, columns of Turck. G, columns of Goll. dc, dd, direct cerebellar tracts, c, anterior commissure. The decussation is completed by the middle of the dorsal region, where the direct tracts cease generally to be visible. The Direct Cerebellar Tracts (fig. 6, dc).— On the surface of the lateral pyramidal tract there is a flattened strand or column, first described by Foville, but more minutely investi- gated t>y Flechsig, which is traceable from the region of the second or third lumbar nerve up to the inferior peduncle of the cerebellum (fig. 9, d c). This tract receives fibres from the cells of Clarke's vesicular column (fig. 4, v c), and thus serves to connect these cells with the cerebellum. 10 STRUCTURE OF THE CEREBROSPINAL CENTRES The Anterior Root Zones (fig. 6, ar). — The anterolateral columns which remain after elimination of the pyramidal and direct cerebellar tracts constitute the anterior root zones. In these an anterior portion and a lateral portion are differen- tiated, separated more or less by the lateral anterior roots, and also a portion which intervenes between the lateral pyramidal tract and the grey matter, termed by Flechsig the lateral limiting zone (fig. 3, fr). The anterior root zones do not increase steadily from below upwards, like the tracts formerly described, but vary in size with the spinal segments, and the number and size of the anterior roots of the spinal nerves. They appear to belong to the fundamental spinal system proper, and serve to connect the different segments with each other, not merely those on the same side, but in part also those of the other side by means of the anterior commissure. This is more particularly true of the anterior division of the anterior root zones, but the relations of the lateral portion are somewhat more complicated. The lateral limiting zone consists of smaller fibres than the others, and probably they increase in number from below upwards. The Posterior Median Columns {Columns of Goll) (figs. 3, 4, 5,pm; and fig. 6, g). — Immediately bounding the posterior ' median fissure are two columns* one on each side, of a wedge shape — the apex directed towards the posterior commissure — which extend as distinct columns from the medulla oblongata to the middle of the dorsal region. Farther downwards they are not traceable as distinct columns in man, but in the monkey are distinct as far as the lumbar region (fig. 3, pm). These columns increase in size from below upwards. The exact relations of theBe columns to the posterior roots and posterior horns are not in all respects agreed upon, but the experiments of Singer 1 would seem to demonstrate a direct continuity of some at least of the posterior rootsJn the column of Goll ; for after section of the posterior roots of the upper sacral and lower lumbar nerves in a dog on the left side, he found a tract of degeneration in the posterior median 1 SiUungsber. d. h. Acad. d. Wissensch., Bd. lxxxiv. Atth. iii. 1881. THE SPINAL COBD 11 column ascending all the way up to the medulla oblongata on the same side. Posterior Root Zones (Burdach's Columns) (fig. 6, pr). — These are the portions of the posterior columns which remain after separation of the posterior median columns. The dimensions of these columns vary with the number and size of the posterior roots of the spinal nerves. They appear to be formed mainly by the fibres of the posterior roots which enter them, but again leave them, after a longer or shorter course, to join the grey matter of the cord. The Roots of the Spinal Nerves. — The most conflicting views still exist as to the course and connections of the anterior and posterior roots. With respect to the anterior roots it appears well estab- lished that the majority, if not all (Laura), terminate primarily in the multipolar cells of one or other of the cell groups of the anterior horns through the axis-cylinder processes of these cells. From the cells of the anterior horn fibres pass into the lateral column of the same side, some also into the anterior column of the same side, and a considerable number through the anterior commissure to the anterior column of the opposite side. A passage of nerve roots to the median group of cells of the anterior horn -of the opposite side has been described by Mayser, but this is not confirmed by the researches of Laura. 1 Of the posterior root fibres some — the lateral division (see fig. 5) — enter the apex of the posterior horn, and penetrating the substantia gelatinosa diverge, brush fashion, horizontally in the direction of the anterior horns, as well as upwards and downwards into the substantia spongiosa. Others — the median division (see fig. 5) — enter the posterior columns and ascend in these a considerable distance before penetrating the grey matter. Some of the fibres, as would appear from the experiments of Singer above mentioned, ascend directly in the posterior median column, or column of Goll. Connec- tions have been described between the posterior roots and the cells of Clarke's vesicular column, also with the solitary cells 1 ' Sur la Structure de la Moelle Epiniere,' Archives Italiennes de Biologic, tome i. faso. ii. 1882. 12 STBUCTUBE OF THE CEBEBBO-SPINAL CENTBE8 of the posterior cornu, and with the lateral group of nerve cells of the anterior cornu. From the cells of Clarke's column fibres pass into the direct cerebellar tract, as has been before mentioned. The connections between the other cells, in which the posterior roots terminate, and the columns of the spinal cord, have been so differently described by Laura and others that nothing definite can be regarded as demonstrated. But it is probable, from physiological experiment, that the tracts of sensation decussate in the posterior commissure, and ascend in the opposite side of the cord, either in the posterior horns, or in the lateral tracts immediately adjacent to them. § 5. The Medulla Oblongata. — At the upper border of the atlas the spinal cord passes into the medulla oblongata, which extends from this point to the lower border of the pons Varolii (fig. 7, pv). The course and relations of the spinal centres and tracts here become exceedingly complex, owing to the intercalation of other centres, and multiple connections between , the cerebellum and other encephalic centres. The anterior longitudinal fissure of the spinal cord is con- tinuous with a. similar fissure on the anterior or ventral aspect of the medulla oblongata (fig. 7, d). On each side of this are two pyramidal shaped columns, termed the anterior pyramids (fig. 7, pa), which decussate with each other more or less completely at the lower extremity of the fissure — the decussation of the pyramids. These tracts are continuous with the pyramidal tracts of the spinal cord. The greater portion of each pyramid is continuous with the lateral or crossed tract of the opposite side of the cord, while the smaller portion is continuous with the anterior median tract or column of Tiirck on the same side. But, as Flechsig has shown, the respective proportion of crossed and direct fibres in individual cases is liable to great variation ; and in some rare cases there is no decuss ation at a ll, each pyramid passing directly into the anterior median column of the same side. The rest of the anterior and lateral columns, or anterior root zones, are thrust out of their original position by the pyramids, and disappear beneath and around the olivary, THE MEDULLA OBLONGATA 13 hodij, which stands out with well-defined prominence on the anterolateral aspect of the medulla oblongata (fig. 7, o). The posterior median fissure of the spinal cord ceases abruptly at the lower posterior aspect of the medulla oblongata, by the opening up of the central canal of the spinal cord into the fourth ventricle, the sides of which constitute in a general r, ' < Pig. 7,— View from beforeof the Medulla Oblongata, Vans Varolii, Crura Cerebri, &c. (after Quain).— On the right side the convolutions of the central lobe, or Island of Re-il, bare been left. ; on tKe leftthe incision has been carried between the optic thalamus and the cerebral hemisphere, i', the olfactory tract cut short. II, the left optic nerve in front of the commissure, n', the right optic tract. Th. The cut surface of the left optic thalamus, c, the Island of Reil. Stj, the fissure of Sylvius, xx, locus perforatus anticus. e, the external, and i the internal corpus genieulatum. h, the hypophysis cerebri, or pituitary body, tr, tuber cinereum and infundibulurn. a, one of the corpora albicantia. r, the peduncle, or cms cerebri, in, close to the left oculo-motor nerve, x y the locus perforatus posticus. J'V, Pons Varolii, v, the greater root of the fi[tb nerve. +, the lesser or motor root ; on the right side this is placed on the Gasserian ganglion. 1, 2, 3, the divisions of the fifth nerve. Vi, the sixth nerve. Vila, the facial. VII&, the auditory, vin, the pneumogastric. Vin a, the glosso -pharyngeal. VIII b, the spinal accessory, jx, the hypoglossal. Jf, the flocculus, pa, the anterior pyramid, o, the olivary body. r, the restiforrn body, d, the anterior median fissure of the spinal cord, above which is the decussa- tion of the pyramids, ca, the anterior column, cl, the lateral column of the spinal cord. sense the restiforrn tracts or inferior peduncles of the cere- bellum. The point where the posterior median columns diverge is termed the calamus scriptorius. The columns which are the continuation of the columns of Goll are here called the 14 STRUCTURE OF THE CEREBROSPINAL CENTRES funiculi f/raciles, and they are seen to swell at the calamus into a club shape, owing to the development in each of a nucleus termed the clavate nucleus (fig. 8, 4). Immediately external to the funiculi graciles are the columns which are continuous with the columns of Burdach, and are here called the funiculi euneati. These also contain each a special nucleus of grey matter termed the cuneate nucleus (fig. 9, n c). External to the cuneate fasciculus and nucleus another column is capable of differentiation ; a column which is cou- Fie. 8.— The Fourth Ventricle exposed by Division of the Cerebellum (Sappeyl.— On the left side the cerebellar peduncles haye been cut short; on the right the middle peduncle has been cut short, while the superior and inferior retain their connec- tions. 1, Median groove of the med. obi. bounded on each side by the fasciculi tej-etes. 2, stria; acusticaa. 3, inferior cerebellar peduncle or restiform body. 4, clavate nucleus. 5, superior cerebellar peduncle, or processus a cerebello ad cerebrum. G, fillet. 1, crura cerebri. 8, corpora quadrigeinina. tinuous with the posterior horn of the spinal cord, but here considerably enlarged. The column is termed the column of Eolando, and the grey matter, the tubercle of Rolando (fig. 9,«b). Into the restiform tract passes also a special division of the lateral column — the direct cerebellar tract (fig. 9, d c). Other fibres are seen to proceed from the lateral aspect of the upper extremity of the restiform tract, and to cross the surface of the olivary body and pyramid to the middle line. THE MEDULLA OBLONGATA 15 A special bundle of these arcuate fibres, which crosses be- neath the lower margin of the olivary body, has received the name of the arciform band of Solly (fig. 9, fa). Of these various columns and tracts the course of the anterior pyramids is alone clear. They ascend in the same relative position upwards through the pons to the crura cerebri (fig. 7, p). When a transverse section is made of the medulla oblon- gata at the decussation of the pyramids (fig. 10) it is seen that, in consequence of the passage of the fibres from the lateral tracts to the pyramid of the opposite side, the anterior horns are detached from the central grey matter and pushed j- i( j, 9.— Dorso-lateral View of Medulla Oblongata of Monkey fnat. size).— c, cerebellum divided and partially dissected so as to show the middle peduncle, cp, middle peduncle, rfc, direct cerebellar tract, fa, arciform fibres. /, lateral column. y/c, nucleus cuneatus. 0, olivary body, p, pyramid. / n, tubercle of Rolando. /, trapezium. V, fifth nerve. VIII, eighth or auditory nerve. out laterally. The posterior horns also become much modi- fied. While the basal portion adjacent to the central grey substance maintains its original position, the neck is pro- longed out laterally, and the apex swells into a head, which is the beginning of the tubercle of Rolando (fig. 10, c p). Posteriorly the grey matter of the funiculi graciles and funiculi cuneati begins to appear as offshoots from the basal portion of the posterior horns (fig. 10, Nf/, and nc). Higher up, where the central canal opens into the fourth ventricle, the basal portion of the grey matter forms a ring round the central canal, of which the ventral portion is the representative of the anterior horns, and the dorsal of the posterior. The detached portion of the anterior horns is represented only by collections 16 STRUCTURE OF THE CEREBROSPINAL CENTRES of cells laterally situated in an area which, owing to its aspect, is termed the reticular formation. When a section is made at a level with the middle of the olivary bodies (fig. 11) the central canal is fully opened up, and the grey matter which formed the dorsal aspect of the central canal is spread out laterally on the floor of the fourth ventricle, while the ventral, or nuclei of the motor nerves, remains close to the middle line. Fig. 1 0.— Section of the Medulla Oblongata of Monkey at the Decussation of the Pyramids. (From preparation and drawing by Bevan Lewis). — ca, anterior cornu, with cell frroups. cp, posterior cornu, with fibres of the posterior roots of the first cervical nerve, cc, central canal. D decussation of pyramids. F" supposes, may be really derived from the posterior columns through the inter- olivary layer. § 6. From the grey matter of the posterior aspect (teg- mentum) of the medulla oblongata, and its upward continuation into the pons, spring the cranial nerves from the twelfth (ninth) to the fifth inclusive. Some of these— the twelfth (hypoglossal), the eleventh (accessory), the seventh (facial), the sixth (abducens oculi) — are purely motor; the eighth (auditory) purely sensory ; the tenth (vagus), the ninth (glosso- pharyngeal), and fifth (trigeminal) mixed or sensori-motor nerves. The exact relations and connections of the nuclei of origin of these nerves would require a more elaborate descrip- tion than can be included in the limits of this sketch, and it will suffice to indicate the general relations. In the accom- panying figures (figs. 12 and 13) these are indicated in a diagrammatic manner. Just before the opening up of the central canal into the fourth ventricle, the central grey substance which forms the basal portion of the anterior and posterior horns surrounds the canal. The ventral portion forms the nucleus of the hypoglossal nerve (figs. 11 and 12, xn), which emerges from the medulla between the olive and pyramid ; while the dorsal position forms the nucleus of the accessory-vagus nerve (fig. 12, xi). A spinal nucleus of this nerve, which supplies the sterno-mastoid and trapezius muscles, is traceable to the lateral cells of the anterior horn of the spinal cord for some con- siderable distance below (fig. 12, xi). With the opening of the central canal the ventral portion of the grey matter, or motor column, remains close to the middle line, while the dorsal portion is spread out laterally on the floor of the fourth ventricle, and forms a column which gives origin to the vagus and.glosso-pharyngeal nerves (figs. 11, 12, x and xi). On the lateral ventral aspect of the nucleus of the vagus a strand of fibres is men— funiculus solitarius—(fig. 11, fs), which can be followed downwards in the cervical portion of 1 Neurolog. Centralblatt, No. 4, 1885. c 2 20 STBUCTUBE OF TEE CEBEBBO-SPINAL CENTBE8 the cord. It is supposed to consist of fibres connecting the vago-accessorius and glosso-pharyngeal nuclei with the origin of the phrenic nerve, and hence called the respiratory bundle (Krause). In the region of the striae acusticas a third collection of nerve cells appears, which are regarded as forming the nuclei of origin of the eighth or auditory nerve. The innermost of Pig. 12. — Diagram of the posterior aspect of the Medulla Oblongata, showing the position of the Nuclei of the Cranial Nerves. (After Erb.) V, motor nucleus, v', middle, and v", inferior sensory nucleus of the fifth nerve, vx, abdu- oens nucleus, vn, facial nucleus, viii, inner, and vm', outer auditory nucleus, vin" and viii'", divisions of the anterior auditory nucleus, rx, glosso-pharyngeal nucleus. X, vagus nucleus, xi, acces- sorius nucleus, xn, hypoglossal nu- cleus. 1, middle cerebellar peduncle. 2, superior cerebellar peduncle. 3, inferior cerebellar peduncle. 4, emi- nentia teres. 5, striae acusticse. 6, ala cinerea. v-xii, the respective cra- nial nerve roots. FiG. 13. — Diagrammatic representation of the Nuclei of the Cranial Nerves, as seen in section. The left half is supposed removed, and the nuclei nearer the median line are shaded darker than the others. (After Erb.) vy, pyramidal tracts, py kt, decussation of the pyra- mids, o, olivary body, o*, upper oli- vary body, v, motor, v'. middle sen- sory, and v", lower sensory nucleus of the fifth nerve, vi, abducens nucleus. G/, knee of the facial nerve, vn, facial nucleus, vm, inner auditory nucleus, ix, glosso-pharyngeal nucleus, x, vagus nucleus, xi, accessorius nucleus, xii, b-ypoglossal nucleus, kz, clavate nu- cleus, rt, roots of fifth nerve, bvi, roots of sixth or abducens. nvn, roots of facial. this group is termed the posterior median or internal nucleus (figs. 12, 13, viii; fig. 14, vm 2 ). . External to this, and in close relation to the cerebellar peduncle, is another collection of cells, the lateral median or external nucleus, or Deiters' nucleus (fig. 14, s). Though it has been generally supposed that the auditory nerve is con- nected with this nucleus, this is disputed by Laura, and, as THE CRANIAL NERVES 21 before stated, Monakow considers that this nucleus is in rela- tion with the cuneate fascicle. The later experiments of Vegas 1 do not, however, support Monakow's view. But that the cells of Deiters' nucleus are not related to the auditory nerve would appear to be proved by investigations of Onufrowicz,' 2 which show that they undergo no atrophy after destruction of the auditory nerve or labyrinth. This author thinks that the relation of the posterior median nucleus (which Laura regards vm st Cr -0 C 0f" 7— /TTIpgir 1 ■'■'■;, Flo. 14. — Medulla Oblongata of Monkey. — Section through the region of the striffi acus- tie.se. (From preparation and drawing by Bevan Lewis). — cr, restiform body. F/\ formatio reticularis. H, upper extremity of hypoglossal nucleus. L. lateral column near the termination of the olivary body. N a , anterior auditory nucleus. Nr, nerve cells of roots of auditory nerve, o, superior olivary body. P, pyramid, s, internal division of inferior cerebellar peduncle, Deiters' nucleus. Bt, stria? acustica?. T, lowest fasciculi of trapezium. V, ascending root of fifth nerve. VIII, roots of auditory nerve. VIII-, region of internal auditory nucleus. as the principal nucleus) to the auditory nerve is doubtful, and his researches lead him to believe that the true origin of the auditory nerve is the semilunar shaped mass covering the origin of the inferior cerebellar peduncle, and corresponding with the tuberculum acusticum of some of the lower verte- brates (fig. 14, st). The stria?, acustica?, which look like the direct continuations of the posterior roots of the auditory 1 Archiv f. Psycliialrie, Bd. XVI. Heft 1. 2 Ibid. Bd. XVI. Heft 3. Mil 22 STRUCTURE OF THE CEREBROSPINAL CENTRES nerve, have no such direct relations. Perhaps they may be indirect paths or connections through the tuberculum acusti- cum, though, as they are sometimes wanting, even this is doubtful. Another group of cells included in what is generally termed the anterior nucleus (fig. 12, Tin", vni'" ; and fig. 14, n 8 , n r), Fig. 15. — Section through Medulla Oblongata af Monkey at emergence of Sixtlx Xerve. ( From preparation and drawing by Bevan Lewis). — A, anterior column. F<7, genu of facial nerve. G, substantia gela'tinosa. 1„ lateral column. L/>, posterior longitu- dinal bundle. 0, superior olivary body. I', pyramid. R, raphe. IV, fourth ventricle. v, ascending roots of fifth nerve. Yl, root of abducens. nvi, abducens nucleus. Vil, roots of facial. and apparently specially related to some of the fibres of the auditory nerve, forming what is usually termed the anterior root, is regarded by Onufrowicz as really a formation homo- logous with the ganglia of the posterior spinal roots. The real origin of the anterior division (the vestibular nerve) is in the vermis cerebelli or in the grey matter of the fourth ' THE CBANIAL NEBVES 23 ventricle, ventral to the superior cerebellar peduncle. The auditory nerve proper, the cochlear or posterior division, arises mainly from the tuberculum acusticum, but its connection with higher centres is not known with any degree of accuracy. The sixth nerve (abducens oculi) springs from a nucleus close to the middle line, which is practically a prolongation upwards of the motor column, which gives origin to the hypo- glossal (figs. 12 and 13, vi ; and fig. 15, n vi). The seventh nerve, however (the facial), though a purely motor nerve does not spring from the ventral column, but from a nucleus occupying a position which corresponds to the detached cells of the anterior horn in the formatio reticularis. To reach this nucleus the fibres of the seventh nerve make an acute bend (knee) round the nucleus of the sixth (fig. 13, of), with which, it has been supposed, also the seventh enters into relation. From a similar group of cells above the facial nucleus springs the motor root of the fifth or trigeminal nerve (fig. 12, v). This column extends from the nucleus of the facial as high up as the entrance of the aqueduct of Sylvius. The sensory root of the fifth is in part derived from a nucleus which lies laterally to the motor root (fig. 12, v'), but mainly from the caput cornu posterioris, extending from the tubercle of Eolando for a considerable distance down the cervical region, as far as the second or third segment (figs. 12, 13, v"; and figs. 11, 14, and 15, v). Some sensory roots have also been traced into the cerebellum. A considerable centre of origin of the fifth nerve is a group of large vesicular cells" which surround the aqueduct of Sylvius (fig. 16, v). The roots derived from this nucleus have been described by Meynert and others as sensory,' but Henle and Porel consider that they belong to the portio minor or motor division of the fifth. The various nuclei described are connected commissurally, and with strands, crossing in their ascent, proceeding to the cerebrum. But the various paths have not been ascertained with any degree of certainty. A relationship of special im- portance, however, has been ascertained by Duval and Laborde. A direct connection exists between the nucleus of the sixth and certain fibres of the third and fourth cranial nerves of the oppo- site side. This is established through specially differentiated 24 STRUCTURE OF THE CEREBROSPINAL CENTRES tracts, which occupy the dorsal aspect of the formatio reticu- laris, and are termed the posterior longitudinal bundles (figs. 15, -Lp, 16, l). In these bundles also probably run fibres which associate other motor nuclei with each other, as they maintain a constant relation to the ventral, or motor, column of the grey matter of the fourth ventricle, and its continuation upwards in the pons. § 7. In the pons A r arolii the ascending longitudinal tracts are traversed by the fibres of the middle peduncles of the „V JV A C , CT ; TB -P - X r' -JF £ -C Fig. 10. — Section of Pons of Monkey in the region of the valve of Yieussens. (From preparation and drawing by Bevan Lewis). — a, aqueduct of Sylvius, c, pyramidal tracts, ex 1 , roots of fourth nerve ascending to its nucleus. CT S , the same seen in transverse section. D, decussation of the fourth nerves. F\ inferior lamina of fillet (pes). F% median lamina of fillet, a, central grey substance. L, posterior longitudinal bundles, p, superior cerebellar peduncle decussating with its fellow at x. t, portion of testis, iv, fourth nerve, v, descending root of fifth nerve. cerebellum, which form a suj^erficial and deep layer, inter- weaving in the median line or raphe. The pyramidal strands are divided into separate groups or locularuents by the trans- verse fibres, and numbers of large multipolar cells occupy the interstices (fig. 1G, c). In some animals the deep fibres of the pons are visible at the upper border of the pyramids, con- stituting what is called the trapezium (fig. 9, t). It is evident, from the greater sectional area of the pyramidal tracts in the pons, than in the medulla oblongata, that they here receive a PONS VABOLII 25 large accession of fibres, derived both from the nuclei of this region and from the cerebellum. It is doubtful whether there is any direct passage of cerebellar fibres into the pyramidal tracts. It is probable that the connection between the cere- bellar peduncles and the pyramidal strands is established indirectly through the multipolar cells of the pons (nucleus pontis) . ■ The anatomical investigations of Meynert, confirmed by pathology, show that the connection between the pyramids and cerebellar peduncles is a crossed one, i.e. the left peduncle being related to the right pyramid, and the right peduncle to the left pyramid. Hence the cerebellar lobes are in relation with the pyramidal tracts on the same side of the spinal cord, see- ing that the pyramidal tracts decussate more or less completely at the lower aspect of the medulla oblongata. Numerous other arcuate fibres exist in the pons in addition to those above mentioned, but their relations are still very imperfectly determined. § 8. Leaving for the present the posterior region or teg- mentum, and following the course of the pyramidal tracts, we find that from the anterior aspect of the great transverse system of the pons, they emerge in the base or foot of the cerebral peduncles, or crura cerebri (fig. 7, p). The crura cerebri diverge from each other slightly in their course upwards, and disappear into the base of the cere- bral hemispheres (fig. 17). On the posterior aspect of the crura cerebri, and immediately in front of the cerebellum, are situated the corpora quadrigemina (in mammals) or corpora bigemina or optic lobes (in birds, frogs, and fishes) (figs. 43-45 b). The anterior pair of tubercles are termed the nates, and the posterior pair the testes (fig. 18, n and t). These ganglia lie between the cerebellum and the optic thalami with which they appear to be respectively connected. The connection with the cerebellum is through the superior peduncles of the cerebellum or processus a cerebello ad testes (fig. 8, 5; fig. 18, ps). They extend superficially between the anterior aspect of the cerebellum and the posterior margin of the testes, and between the two is a thin transverse lamina called the valve of Vieussens (fig. 18, vv). 20 STBUCTURE OF THE CEREBROSPINAL CENTRES The superior cerebellar peduncles in reality pass under- neath the ganglia of the corpora quadrigeinina, and converge and decussate through a group of cells lying on each" side of the middle line underneath the anterior tubercles of the corpora quadrigemina. These cell groups constitute each the red nucleus or nucleus tegmenti (fig. 19, en). The red nucleus seems to be the primary terminus of the superior cerebellar Fig. 17. — Ease of the Brain. 1, superior longitudinal fissure. 2, the fissure of the left olfactory tract, which is cut. 2', the orbital lobe. 3, 3, 3, the fissure of Sylvias. 4, the gyrus hippocampi, .i, the subiculum cornu Ammonis. 5, the occipital lobe. 6, the anterior pyramid of the medulla oblongata. 7, the amygdaloid lobule of the cerebellum. 8, the biventral lobe. 9, the slender lobe. ID, the posterior inferior lobe. The Roman numerals I to IX indicate the respective cranial nerves ; x is the first spinal nerve. peduncle, but beyond this the fibres have been variously traced. Flechsig traces them to the lenticular nucleus (fig. 23), and also through the optic thalamas into the corona radiata. Passing into the base of the corpora quadrigemina between the superior and middle peduncles of the cerebellum a tract of fibres is seen (fig. 7, c), whose course is almost transverse to the longitudinal strands of the crus. This is the fillet or CORPORA QUADRIGEMINA 27 lemniscus. These fibres come from a tract -which on cross section of the pons (fig. 16, f 1 , f-) is seen to form the ventral aspect of the reticular formation posterior to the pyramidal tracts. This more or less differentiated layer of the reticular formation is a continuation of the anterior and lateral root zones of the spinal cord. The relations of the fibres forming the fillet have been differently described by different anatomists. Fig. 18. — Brain of Monkey, the Cerebral Hemispheres being pushed upwards and forwards and drawn asunder, so as to expose the basal ganglia. (From a drawing by F. Lemaistre). — ha, brachium anterius. bp, braehium posterius. c, cerebellum divided in the middle line, re, corpus callosum. cge, corpus geniculatum exter- num, cgi, corpus geniculatum internum. 2 36 STRUCTURE OF THE CEREBROSPINAL CENTRES tion. The pyramidal tract proper occupies the middle third or half of the ems (fig. 19, c). The outer third has been regarded by Meynert and Huguenin as the continuation of the posterior columns of the spinal cord (see p. 18), but this is denied by Fleehsig. Flech- sig considers them to be continuous with certain dorso-lateral tracts of the pons, but their further relations are not clear. He thinks they are continued into the cerebellum, but, as will be afterwards shown, this cannot be accepted. The inner third of the foot of the crus — the accessory pyramidal tract — contains the fibres which probabby have the same relation to the motor nuclei of the medulla, pons, &c. as the pyramidal tract to the anterior horns of the spinal cord. cc '^^' Fig. 24. — Frontal Section of Brain of Monkey at right angles to the crura cerebri, in the region of the anterior commissure (nat. size).— ac, anterior commissure, cc. corpus callosum. cl, claustrum. ec, external capsule. /', pillars of fornix, ic, internal capsule, in, island of Reil. nc, nucleus caudatus. id, nucleus lenticularis. Certain fibres which are in immediate relation with the lccus niger ascend with the other fibres of the foot of the crus into the internal capsule. The lenticular nucleus has a triangular shape, the base directed outwards towards the island of Reil. It consists of three divisions, separated by medullary lamina? (fig. 23, n I). The basal division is separated from the cortex and medul- lary fibres of the island of Reil by a thin strip of grey matter, the claustrum (fig. 23, cl), and by a thin layer of fibres termed the external capsule (fig. 23, e c). Beneath the optic thalamus, and embraced in the con- cavity of the internal capsule, is the subthalamic region, in which is a cell group which bears the same relation to the internal capsule as the locus niger to the foot of the crus. THE INTERNAL CAPSULE 37 This group of cells constitutes Luys' body, or corpw rvbtha- lamicum (rig. 23, l c). Frontal sections in this region show only the tail of the nucleus caudatus (fig. 23, n c) lying at the upper external aspect of the optic thalamus, separated from the lenticular nucleus by the internal capsule. But in sections farther forwards (fig. 24) the area of the caudate nucleus increases, while that of the lenticular nucleus diminishes, until at the anterior extremity the internal capsule is seen to be embraced by the two divisions of the corpus striatum, more or less fused with each other, showing that the lenticular and caudate nuclei are merely divisions of essentially one ganglion. When a horizontal section is made through the middle of the basal ganglia (fig. 25) the relations of the internal capsule to the corpus striatum and optic thalamus are displayed in a different aspect. The internal capsule with its fellow of the oppo- site side has an X- shaped appearance — the anterior half, situated between the nucleus caudatus and nu- cleus lenticularis, forming, with the posterior half, situated between the optic thalamus and nucleus len- ticularis, a sharp angle or knee (fig. 25, i e). The other structures visible in frontal sections are readily recognisable in their same relative positions. Into the lenticular nu- cleus of the corpus striatum pass certain tracts of the foot of the eras, besides many from the tegmentum, included in what is termed the lenticular loop til Pig. 25. —Horizontal Section of Left Hemisphere of Monkey — on a level with the anterior commissure (nat. size). — ac, anterior commissure, ca, cornu Ammonis. cl, claustrum. eg, corpora quaclrige- mina. ec, external capsule, ic, internal capsule. ill, island of Eeil. /', anterior or descending (Mey- nert) pillar of fornix. J', ascending fibres, or Vieq d'Azyr's bundle, fni, Meynert'sfaseiculus. fa, fissure of Sylvius, nc, nucleus caudatus. nl, nucleus lenticularis. or, optic radiations (G-ratiolet). P, pulTinar. p, posterior commissure. 38 STRUCTURE OF THE CEREBROSPINAL CENTRES (ansa lenticularis), which cross the ascending tracts of the in- ternal capsule. The internal capsule containing all the fibres of the foot of the crus, except those ending in the lenticular nucleus, and reinforced by fibres from the optic thalamus and subthalamic region, emerges from between the lenticular nucleus and tail of the caudate nucleus as the corona radiata, which spreads out in the form of a hollow fan towards* the cortex of the hemisphere. § 14. Each hemisphere forms a kind of hollow shell enclosing and overlapping the basal ganglia. The central cavities — the lateral ventricles — communicate with each other and with the third ventricle, and through this with the rest of the cerebro-spinal canal. These relations are best seen in the embryonic brain. At first the cerebrum is merely a vesicular protrusion from the anterior cerebral vesicle, which ultimately forms the optic thalami with the third ventricle. The originally single vesicle becomes constricted along the middle line, so as to form two vesicles, each with a central cavity — the lateral ventricle, communicating with its fellow by a small opening, the fora- men of Monro. The walls of the vesicles develop into the corpora striata and cerebral hemispheres, and obscure the primitive form; but it remains more or less distinctly traceable, and explains the significance of structures and relations otherwise unintel- ligible. The outline of the cerebral vesicles may be traced from the walls of the third ventricle. Here they are very thin, and form in man the septum lucidum, the two layers sepa- rated by an interspace termed the fifth ventricle, which, how- ever, has none^fJ^ej2hara^ters_of the other divisions of the cerebro-spinal tube, and has no communication with them. The walls of the septum lucidum are much thicker relatively in other animals, and show the essential structure of the rest of the' hemispherical wall (fig. 22, in front of 10). From the septum lucidum the wall of the hemisphere may be traced continuously all round and back again to the extremity of the temporo-sphenoidal lobe, where it fuses with the substantia THE CEREBRAL HEMISPHERES 8U innominata of the anterior perforated space which is continu- ous with the central grey matter of the cerebro-spinal tube (fig. 7, xx, and fig. 17). The fully developed hemisphere has the shape of an irregular spherical triangle, the convexity of which is directed outwards. The flattened mesial aspects approach each other in the longitudinal fissure, at the bottom of which is the corpus callosum (fig. 18, cc), or great transverse commissure, which connects the two hemispheres together. Division of this commissure exposes the interior of the hemispheres (fig. 22, n). The cavity of each hemisphere has the general form of the exterior. The anterior extremity, which extends into the frontal region, is called the anterior horn of the lateral ven- tricle ; the posterior extremity, which extends into the occipital region, is termed the posterior horn ; and the prolongation, which dips in the direction of the temporal region, is termed the descending horn of the lateral ventricle. § 15. The external surface of the hemispheres is in many of the lower animals smooth (fig. 26, a), or only obscurely marked by fissures or folds, but in all the higher animals, and specially in man, the surface is disposed in folds or convolutions separated by primary and secondary fissures, or sulci, which have a definite position and relation to each other (see Chap. VIII.) At present it will suffice to indicate some of these and the great divisions which are usually made of the hemispheres. The first and most important fissure is the fissure of Sylvius (fig. 27, a), which runs obliquely upwards and backwards from the anterior perforated space. If the edges of this fissure are drawn asunder a portion of the cortex is displayed, which is moulded over the lenticular nucleus of the corpus striatum (tig. 25). This is termed the central lobe, or island of Reil (fig. 25, i k ; fig. 1, c). a. 26.— Brain of Rabbit.— A, smooth cerebral hemi- sphere, c, oerebellum. <>, olfactory bulb. V 40 STBUCTUBE OF THE CEBEBBO-SPINAL CENTRES The hemisphere may be considered as having been sharply bent round the upper extremity of the fissure of Sylvius into two great divisions. Above and in front of it are the frontal lobe (fig. 27, f l), and the parietal lobe (fig. 27, pi), separated from each other by the fissure of Eolando (fig. 27, b), or central fissure. Behind and below it are the occipital lobe (fig. 27, o l), separated from the parietal lobe by the parieto-occipital fissure (fig. 27, c), and the temporal, or temporo-sphenoidal lobe (fig. 27, t s l), which is directed downwards and upwards. These names are derived from the relations which these portions of the brain have to the frontal, parietal, occipital, TSL Fig. 27. — Left Hemisphere of Brain of Monkey (Macaque). temporal, and sphenoidal bones of the skull. Each lobe is divided into numerous secondary and. tertiary divisions, which will be detailed subsequently (see fig. 67 with description). § 16. The surface of the ridges and depths of -the sulci is formed by the grey matter. The nerve cells of the grey matter are of different kinds and variously grouped, viz. small roundish and angular cells scattered almost throughout the whole cortex ; spindle cells, most occurring towards the medul- lary aspect of the cortex ; and pyramidal cells, some of which are of great size (giant cells). These elements are variously arranged and grouped in different regions of the cerebral hemispheres (see figs. 28-33). The medullary fibres penetrate the cortical grey substance to a certain depth, but the exact Fig. 28.— Cortex of Frontal Lobe of Monkey. ( x 147, Bevan Lewis.) — 1, first or peripheral layer. 2, second layer, small angular cells. 3, third layer, large pyramidal cells. 4, fourth layer, ganglionic cells. 5, fifth layer, spindle cells. •v&' • V4> V,- « ' Puffer FPfti-ftSi-- Mtf Jite Fig. 29.— Cortex of Motor Area of Brain of Monkey. ( x 147, Bevan Lewis.)— 1, first or peri- pheral layer. 2, second layer, small angular cells. 3, third layer, large pyramidal cells. 4, fourth layer, ganglionic cells and 'cell clusters.' 5, fifth layer, spindle cells. f*^^r~'- ■-*=* ^?£^ J®Ksft * < .» r.. . ;,* 2 AV n< *M Pig. 31. —Cortex of Occipital Lobe, (x 145, Bevan Lewis.)— 1, first or peripheral layer, 2, second layer, small angular cells. 3, third layer, pyramidal cells. 4, fourth layer, angular and gra- nule cells. 5, fifth layer, pyra- midal cells. 6, sixth layer, gra- nules and ganglionic cells. 7, seventh layer,spiud!e cells. #-*l*iP*« ... fc *M< IB t- '•■•< - : Fig. 32. — Cornu Ammonisof Mon- key. ( x 147, Bevan Lewis.) — 1, granular stratum of fascia dentata. 2, nuclear lamina. 3, stratum lacunosum. 4, stratum radiatum. 5, ganglionic layer. 6, molecular stratum. 7, alvcus. *'*.t'u.VI» i ft ■.'Tf; i ! • /+- hll' {. f'< ■• Fig. 33.— Cortex of Gyrus Hippo- campi, fx 145, Bevan Lewis.) — 1, First or peripheral layer. 2, second layer, aggregated pyramidal cells. 3, third layer, large pyramidal cells. THE CEREBRAL CORTEX 43 relations of the various layers to the medullary fibres and to each other have not been as yet determined. It is supposed that the basal processes at least of the large pyramidal cells become each directly continuous with a medullary fibre, like the axis cylinder processes of the multipolar cells of the anterior horns of the spinal cord. The grey matter of the cortex at the inner margin of the temporal lobe is folded inwards, so as to form a ridge in the descending cornu of the lateral ventricle (fig. 25, ca). This inve rted convolution is, owing to its shape, termed the hippo- campus major, or cornu Ammunis. It follows the course of -e.c C.A Fig. 34. — Sagittal Section of Hemisphere of Monkey fnat. size).— A, nucleus amygdalae oc, termination of anterior commissure. CA, cornu Ammonis. eg, corpus genicu- latum externum, cf, claustrum. ec, external capsule, is, internal capsule. m\ tail of nucleus eaudatus. nl, nucleus lcnticularis. pc, posterior cornu of lateral ventricle. the descending cornu to its lower or anterior extremity (fig. 34). At this point the cortex of the temporal lobe is con- siderably thickened, so that on section it looks like an almond- shaped tubercle, and is termed the nucleus amygdala (fig. 34, a ; fig. 36, a). § 17. Reverting again to the basal ganglia and internal capsule we have seen that certain of the tracts followed up from the foot of the cms terminated in the corpora striata, but that the rest of the fibres of the internal capsule passed through between the divisions of tins ganglion on towards the cortex (fig. 34, ic). The pyramidal tract ascends in that portion of the internal capsule immediately posterior to the 'knee,' as seen in horizontal section (fig. 25, ic), forming the anterior third of the posterior division, and is distributed to 44 STBUCTUBE OF THE CEBEBBO-SPINAL CENTBES the cortical regions bounding the fissure of Eolando (see Chap. X.). There is thus a direct continuity between certain regions of the cortex and the pyramidal tracts of the spinal cord. The portion of the internal capsule situated anterior to the knee or the anterior division contains those fibres of the foot of the crus situated mesially to the pyramidal tracts, and which are distributed to the frontal regions of the cortex (see Chap. X. § 24). The fibres of the outer division of the crus cerebri ascend in the posterior division of the internal capsule and bend outwards and downwards to the region of the hip- pocampus (Flechsig). With these ascend fibres derived from the optic tracts and their connections with the corpora geni- culata, optic thalamus, and corpora quadrigemina, which spread themselves towards the posterior or occipital regions, constituting the 'optic radiations' of Gratiolet (fig. 25, or). In addition to the fibres derived from the foot of the crus and the optic tracts, the internal capsule receives fibres from the optic thalamus and subthalamic region, which, according to Flechsig, are distributed to regions tying posterior to the pyramidal tracts (Haubenstrahlung). The corona radiata is composed, in addition to the fibres of the internal capsule, of fibres connecting the cortex with the optic thalamus, and, according to some anatomists, also with the divisions of the corpus striatum. § 18. Of the fibres from the optic thalamus a tract has been traced by Meynert from the anterior extremity towards the frontal regions. Another tract descends from the anterior extremity on its internal aspect and then passes outwards beneath the lenticular nucleus towards the regions of the island of Eeil. Some of these fibres appear to be continuous with the external capsule (fig. 28, e c). The corpus striatum was regarded by Meynert as a ' ganglion of interruption ' of the fibres connecting the cerebral cortex with the periphery. From the base of the lenticular nucleus he traced fibres of the corona radiata ascending into the frontal and parietal regions, and similarly a set of fibres connecting the cortex with the upper lateral aspect of the nucleus caudatus. This view of the relations of the corpora striata to the hemispheres, THE CORPUS CALLOSUM 45 though recently defended by Kowaleski, 1 has, however, been contested by Henle, Wernicke, and others, who maintain that neither the nucleus caudatus nor nucleus lenticularis is con- nected with the cortex through the corona radiata, but that these ganglia are themselves terminal stations of certain tracts of the cerebral peduncle, and are in fact only modified portions of the hemisphere, co-ordinate with, but not subordinate to, the grey matter of the cortex. This view seems to be more in harmony with the anatomical appearances than that advo- cated by Meynert, though we cannot regard the point as yet definitely settled. § 19. The cerebral hemispheres are connected together by a great system of commissural fibres, the corpus callosum (fig. 18, cc), which forms the floor of the longitudinal fissure and roof of the cerebral ventricles. The fibres of this system are in the middle mainly transverse, but as they enter the hemispheres they diverge in various directions— forwards, transversely, backwards, and downwards — so as to reach all the parts of the hemispheres to which the corona radiata is distributed. Owing to the appearances thus presented, it has by some been errone- ously supposed that the corona radiata is merely the terminal distribution of the fibres of the corpus callosum decussating with each other in the middle line ; a view which is utterly at variance with the physiology and pathology of the cerebral hemispheres. 2 Underneath the corpus callosum and more or less fused with it (fig. 18, p) posteriorly there is another system of fibres — the fornix — which connects the hippocampi with each other and 1 Centralblatt f. Nervenheilkunde (abstract), No. 3, 1883. 2 . The theory that the corpus callosum is a decussation of the fibres of the internal capsule, originally advanced by Foville, has been recently revived and more or less modified by Hamilton (Proc. Roy. Soc. vol. xxxvi. 1884), on the strength of the appearances presented by sections prepared and enlarged by a special method of his own (Brain, vol. vi. 1884). The method of investigation adopted by Hamilton— mere naked-eye appearances or lens amplification— is not competent to distinguish between apparent and real continuity of fibres and tracts with each other ; and it has been shown by Beevor (Brain, Oct. 1885) that in sections stained (Weigert's method) so as to display the medullary fibres, and properly examined by the microscope, the fibres of the internal capsule and corpus callosum interweave with each other in proceeding to the grey matter of the cortex. There is no direct continuity between the two sets of fibres. 4G STRUCTUEE OF THE CEREBROSPINAL CENTRES with the optic tbalami. The fibres of this system spring, as the posterior pillars, or fimbria?, from the free surface of the cormi Ammonis on each side. These ascend and converge and form the body of the fornix. Here many of the fibres have an almost transverse direction, constituting the appearance termed the lyra of the fornix. From the body other fibres continue forwards, gradually converging, and descend as the anterior pillars immediately behind the anterior commissure. z. r-.cl ht Fig. 35. — Horizontal Section of the Brain of the Mole on a level with the anterior commissure ( x 4). (After G-anser. ) — < frc, anterior commissure, dividing into po y pars olfactoria, and pt, pars temporalis, ci, internal capsule. /', fimbria, fit, anterior pillar of fornix, fd, fascia deutata. /m, Meynert's fasciculus, gl.ol, glo- meruli olfactorii. hi, posterior longitudinal fasciculus. k\ granular layer of olfac- tory bulb, mp, middle peduncle of cerebellum, na, nucleus amygdalse. nc, nucleus caudatus. nl, nucleus lenticularis. p, pyramidal tract, rn, red nucleus. r.ol, roots of the olfactory nerve. rs t regio subthalamic a. s, septum lucidum, sa, substantia alba, sp t superior cerebellar peduncles, st, stria terminalis. t.ol, tractus olfactorius. These descend as far as the corpora mammillaria (fig. 7, a), and here twisting on themselves reascend to the anterior tubercles of the optic thalamic 1 It is, however, supposed by Gudden, Forel, and others that there is no direct continuity between the descending and ascending fibres. What are here termed, with Meynert, the descending and ascending pillars are sometimes spoken of in a reverse manner, as if the corpora mammillaria were the starting- pont of the fornix. The descending pillars are therefore termed the ascending, and the ascending fibres the descending. Owing to the direct continuity of these THE ANTERIOR COMMISSURE 47 § 20. The anterior commissure, which appears to connect the corpora striata with each other, has in reality no connec- tion with these ganglia. The anterior commissure is composed of two divisions, which are best seen in animals which have highly developed olfactory bulbs (see fig. 35, ac). The anterior division (pars olfactoria, p o, fig. 35) consists of fibres which connect, the olfactory bulbs with each other. This portion of the anterior commissure is by far the larger in those animals which have large olfactory bulbs, and is in- conspicuous in the monkey and man . But in these there may be seen also fibres of this division passing from the anterior commissure downwards and forwards in the direction of the point where the inner root of the olfac- tory tract joins the hemisphere (fig. 24, ac). The posterior division {pars temporalis, p t, fig. 35), which varies much in size in different animals, passes outwards and downwards with a curve backwards, beneath the lenticular nu- cleus, towards the nucleus amygdalse and hippocampal lobule, in the me- dullary fibres of which it spreads out in the form of a pencil (figs, 35, 36). The whole of the fibres terminate in this region in front of the descending cornu of the lateral ventricle (see figi 34, ac). No fibres pass to the occipital re- lflf; M ,_ ProntaI ;>ct , m of Mgllt gion, as Meynert has supposed. K&S^g&^SSft : Besides these commissural or as- X u £ Ie o£ ZH^ol^e. sociating fibres others have been de- ^tT*nif ' 2S2<££. scribed as connecting different con- ^j™ °» &£?*« volutions and different regions of the £nS a rir datus ' ** nucleM cortex with each other. Some of these are more or less hypothetical and artificial ; others, such as the longitudinal system of the gyrus fornicatus and gyrus hippocampi, appear to come under the category of associating fibres. § 21. The roots of the optic tracts have already been traced. two sets of fibres being disputed, the fibres here termed the ascending have been termed by Forel Vic% d'Azyr's fasciculus. 48 STRUCTURE OF THE CEREBROSPINAL CENTRES The tracts wind round the crura cerebri and unite to form the chiasma, whence spring the optic or second cranial nerves (rig. 37, ii). The constitution and mode of disposition of the respective tracts in the optic nerves are subjects on which much has been written, and will bo discussed further in con- nection with experimental data (Chap. V.). Fig. 37.— View from before of the Medulla Oblongata, Pons Varolii, Crura Cerebri, &c. ( After Quain). — On the right side the convolutions of the central lobe, or Island of Reil, have been left ; on the left the incision has been carried between the optic thalamus ami the cerebral hemisphere, i', the olfactory tract cut short, n, the left optic nerve in front of the commissure, n', the right optic tract. Th. The cut surface of the left optic thalamus, c, the Island of Reil. Sy, the fissure of Sylvius, xx, locus perforates anticus. e, the external, and i the internal corpus geniculatum. A, the hypophysis cerebri, or pituitary body, tc, tuber cinereum and iufundibulum. «, one of the corpora albicautia. r, the peduncle, or cms cerebri, in, close to the left oculo-motor nerve. ,t, the locus perforatus posticus. PV, Pons Varolii, v, the greater root of the fifth nerve. +, the lesser or motor root ; on the right side this is placed on the Gasserian ganglion. 1, 2, 3, the divisions of the fifth nerve, vi, the sixth nerve. VII ff, the facial, vnft, the auditory, vin, the pnenmo gastric. Vina, the glossopharyngeal, viii/j, the spinal accessory, ix, the hypoglossal. .//, the flocculus, pa, the anterior pyramid, o, the olivary body. /■, the restiform body, d, the anterior median fissure r>f the spinal cord, above which is the decussa- tion of the pyramids, at, the anterior column, el, the lateral column of the spinal cord. In regard to the tracts, it would appear, from the researches of Gudden on the effects of extirpation of the eyeballs, that the roots of the optic tracts which spring from the corpora geni- culata interna have no real connection with vision, as they do not undergo atrophy, like the other roots, when the eyes are THE OLFACTORY TRACTS 49 destroyed. They are regarded by Gudden as forming a com- missure in the posterior angle of the chiasma — the inferior commissure. The true roots of the optic tract are those which pass to the corpus geniculatum externum, pulvinar, and ante- rior brachium of the corpora quadrigemina. Stilling derives a root also from the corpus subthalamicum, or Luys' body, but this is not substantiated by the researches of Monakow. § 22. The olfactory or first pair of cranial nerves spring from the olfactory bulbs, which lie on the cribriform plates of the ethmoid bone. The olfactory bulbs were primarily pro- trusions of the cerebral vesicles, the cavity continuous with the lateral ventricles, a condition still seen in the rhinen- cephalon of the frog (fig. 43). In process of development the cavity becomes more or less obliterated, and the walls of the protrusion become converted into the olfactory bulb and olfac- tory tract, intervening between it and the hemisphere. The olfactory tract (fig. 37, i') is joined to the hemisphere by two apparent roots, an inner and an outer root, separated by a triangular interval in the anterior perforated space {trigonum olfactorium) . Between the two roots the junction with the anterior per- forated space is sometimes described as a third root. The inner root joins the mesial aspect of the anterior extremity of the gyrus fornicatus, while the outer root passes outwards across the fossa Sylvii to the extremity of the temporo-sphenoidal lobe, where it fuses with the anterior extremity of the gyrus hippocampi, subiculum cornu Ammonis, or hippocampal lobule. The termination of this root is not so evident in the monkey as in animals with very highly developed bulbs (figs. 73, 78). In these this portion of the hemisphere forms a distinct lobe or protuberance, the natiform protuberance (Owen), or pyriform lobe (Gudden), or hippo- campal lobule. The olfactory tract consists mainly of the medullary fibres of the original rhinencephalon, from which the grey matter has almost entirely disappeared, together with the fibres of the anterior division (pars olfactoria) of the anterior commissure. The grey matter, however, remains covering the anterior and lower, and in monkeys also the upper, aspect of the tract, form- 50 STSUCTUBE OF THE CEREBROSPINAL CENTRES ing the olfactory bulb. This exhibits certain peculiarities of structure, differing from the rest of the cortex (tig. 38). The medullary fibres, in the centre of which is the remnant of the original cavity (fig. 38, ■>), are covered by a layer of granules embedded in a fine plexus of nerve fibres (fig. 38, 3). This is succeeded by a layer of nerve cells resembling tbe pyramidal cells of the cortex, the basal processes of which are supposed to be continuous with the fibres of the tract. These cells send branching processes outwards towards the periphery (tig. 38, i). Fm. 38.— Sagittal Section of the Olfactory Bulb and Tract of the Monkey. (From a preparation anil drawing by Beevor.) — 1, olfactory tract. 2, central grey substance. 3, granular layer. 4, ganglionic cellular layer. 5, gelatinous layer. 6, glomerular laver. 7, olfactory nerYe fibres. The ganglionic cellular layer is succeeded by a gelatinous layer, similar to the external layer of the cortex cerebri, in which are scattered cells similar to those of the ganglionic layer (fig. 38, 5). The gelatinous layer is succeeded by a layer of peculiar roundish or oval structures termed the glomeruli olfactorii (fig. 38, 6), the exact constitution of which is not agreed on, but which are undoubtedly the primary origin of the olfactory nerves, which, collecting on the surface (fig. 38, 7) of the glomerular layer, descend through the foramina of tbe cribriform plate to the nasal mucous membrane. 51 CHAPTEE II. FUNCTIONS OF THE SPINAL COED. § 1. When the spinal cord is severed transversely at any point, either experimentally or as the result of disease, all the parts below the seat of injury are paralysed, both as regards sensation and voluntary motion. But though sensation proper and volitional control are abolished, yet a number of functional manifestations of greater or less complexity are still possible both in the domain of organic and animal life — functions which are in their turn entirely annihilated when the cord itself is disorganised. From this it is evident that the spinal cord is not merely the medium of communication between the periphery and the centres of sensation and volition, but also an independent centre, or group of centres. We have therefore to consider the functions of the cord — first as a conductor, and second as an independent centre. Paet I. — The Cord as a Conductor. § 2. When a hemisection of the cord is made, paralysis of voluntary motion occurs on the side of lesion, and paralysis of sensation on the opposite side. The following experiment 1 which I made on a monkey illustrates these propositions. The cord was cut on the left side, between the seventh and eighth dorsal nerves, to the extent indicated in the accompanying figure, which is after a microphotograph of the first slice from the cord above the incision. The cord, except at the region of' the lesion, was . otherwise intact (fig. 39). 1 See Brain, April 1884, ' Hemisection of the Spinal Cord.' e 2 52 FUNCTIONS OF THF SPINAL COED Directly after this injury, and till death, eighteen days subsequently, there was, on the side of lesion, absolute paralysis of motion, and perfect retention of sensibility, not apparently heightened, to every form of stimulation, tactile and painful. The animal's attention was immediately excited by a touch anywhere on the same side below the lesion, and put its hand to, or rubbed, the part touched or pinched. On the opposite side voluntary motion was unimpaired, and the animal was able to use its right leg freely and forcibly with perfect precision. There was, however, absolute insensi- bility to every form of sensory stimulation, such as contact, Fig. 39. — Hemisection of Spinal Cord of Monkey (microphotogrnph x 12). (Experiment described in text.; pinching of the toes and muscles, and a degree of heat which excited lively manifestations of uneasiness and pain in the left leg or in the hands. It was observed also that, though the animal could move its right leg for volitional purposes with perfect precision when the eyes were open, it could not do so when the eyes were blindfolded, being evidently unaware of the position of its leg, and unable to extricate it from any obstruction. This, how- ever, it readily effected when the eyes were freed. With the exception of certain statements made in refer- ence to the muscular sense, which will be considered more at HEMISECTION OF THE SPINAL COED 53 length subsequently, the results of this experiment agree with those obtained by Brown- Sequard, and with the facts of disease or injury of one-half of the spinal cord in man. It has usually been found by other experimenters, and also in cases of unilateral disease of the cord, that on the side of lesion there is a hypersensitiveness to sensory impressions ; but this was not apparent in the experiment above recorded. What the cause of this hyperesthesia so frequently observed may be is not quite clear ; but it does not appear to be an essential feature of a lesion capable of inducing total anaesthesia of the opposite side. It is probable, from the results obtained by other physiologists, that the sensory paths are not so entirely crossed in many of the lower animals as they appear to be in the monkey and man, and that the paths of voluntary motor impulse are not exclusively direct, or confined to the same side of the spinal cord. Apart, however, from certain differences in degree, the general rule prevails, that the motor paths are on the same side, and the paths of sensation on the opposite side. § 3. But when we come to the exact differentiation of the sensory and motor tracts opinions become exceedingly divergent. Nor is this greatly to be wondered at. The methods of investigation so successful in determining the functions of nerves, viz. the complementary methods of ex- citation and section, are here most difficult of application, and the sources of error numerous. Owing to the small area in which the various tracts are compressed, it is difficult to employ electrical stimulation to excite one part without risk of extrapolar conduction, and consequent irritation of other parts. It has, indeed, been asserted by Van Deen and Schiff that, with the exception of the posterior columns, none of the rest- of the spinal cord is excitable by electricity or any other form of stimulus. That this is erroneous has been satisfac- torily shown by the experiments of Fick, 1 who obtained move- ments by electrical irritation of the anterior columns after removal of the posterior roots and posterior columns of the cord. These results have been confirmed by Mendelssohn, 2 1 Pfluger's Archiv f. Physiologie, Bd. II. 2 Du Bois-Eeymond's Archiv f. Physiologie, 1883, Heft 2 and 3. 54 FUNCTIONS OF THE SPINAL COBD who has also shown that the muscular contractions which result from irritation of the anterior columns are not reflex, as they occur sooner than when irritation is applied directly to the posterior columns, the time lost being that necessary to excite reflex action through the grey matter. The experiments of Ludwig and Woroschiloff, mentioned below, also prove the excitability of the columns of the spinal cord. And the more recent experiments of Horsley, as well as similar facts observed by myself, show that stimulation of the lateral columns of the spinal cord induces movements in parts below the section. But, owing to the difficulty of preventing diffusion, the method of stimulation by the electric current is liable to too many fallacies to be altogether reliable. Nor is the method of section of particular tracts free from complication, and the extent of injury really inflicted has not always been deter- mined with that degree of accuracy necessary to ensure con- fidence in the results arrived at. Besides these difficulties there are others which complicate the question. In experi- menting on the lower animals it is often extremely difficult, if not impossible, to discriminate between mere reflex action, which ensues on stimulation of sensory nerves, and sensation proper. The occurrence of reactions above the section, on stimulation of sensory nerves below the section, does not necessarily indicate that the paths of true sensation have not been interrupted. Such facts prove only the conveyance of afferent impressions to higher regions — a fact of great importance, but requiring interpretation in relation with the results of other methods. § 4. The careful and varied experiments of Ludwig and Woroschiloff ' have shown that motor impulses may be trans- mitted downwards, and sensory impulses conveyed upwards, without any apparent disturbance of the normal order, when the whole of the anterior and posterior columns, and also the grey matter, have been severed, and when, therefore, only the lateral columns of the cord remain intact. By diverse sections of one or both lateral columns, or parts 1 Der Verlauf der motorischen und sensiblen Batmen durch das Lenden- mark des Kaninchens, 1874. EXPEBIMENTS OF LUDWIG AND WOBOSCHILOFF 55 of them, they found that when only one lateral column re- mained, movements of the arms and anterior part of the body could be readily excited by irritation of the opposite leg behind the section, but only with difficulty by irritation of the leg on the same side. In order that impressions on the opposite leg should readily call forth movements in the anterior part of the body it was found, that that portion of the lateral column should remain intact, which lies in the area bounded by the prolongation outwards of the anterior and posterior commis- sures — the middle third. Slight movements could, however, be excited in the anterior part of the body if only the anterior or posterior third of the lateral column remained. In respect to motor impulses their experiments showed that by sensory stimulation of parts above the lesion — the ears, &c. — movements could be excited only in the leg on the side of which at least a portion of the lateral column remained in- tact. If the lateral column were entirely destroyed on one side, no reflex movements whatever occurred in the leg of that side by sensory stimulation above the lesion. For the convey- ance of reflex motor impulses to the leg of the same side at least the anterior half of the lateral column must remain intact. The co-ordinated movements of the leg such as are required for sitting, springing, &c. require the integrity of the middle third of the lateral column. Elestrical irritation of the cut surface of the cord, severed below the calamus scriptorius, was able to excite co-ordi- nated movements of the leg only on the side on which the middk third of the lateral column was uninjured. But tetanic contraction of the muscles of the other leg could also be inducjd, though the lateral column on this side was entirely severad. H thus appears that the sensory impulses which excite movements in parts above the section are conveyed mainly in the opposite lateral column, and specially in the middle third of Ms column ; and that the centrifugal impulses which excite such movements as are characteristic of purposive co- ordination are conveyed in the lateral column of the same side, and specially in the middle third of this column. The relative facility with which sensory impressions on the leg on the side 56 FUNCTIONS OF THE SPINAL CORD of lesion evoke movements in the anterior part of the body is termed by Ludwig and Woroschiloff cross hyperaesthesia ; and they give a hypothetical explanation of this by assuming that on the side of lesion certain inhibitory fibres have been divided. It does not appear to me that either the term or the explanation is at all necessary. The hyperaesthesia on the side of lesion is only a sign by contrast of the diminished sensibility on the other side, and as a matter of fapt ceases when the other lateral column is similarly divided, and both legs are reduced to the same level of sensibility. As regards purely local reflexes, i.e. the movements of the limbs below the lesion, they found that the excitability of the limb on tlje side of lesion was equal to that on the opposite side to minimal stimuli; but, as the stimulation increased, the movements of the leg on the sound side became more active, unaccompaiiied, how- ever, by general movements in the parts above the lesion ; while the reverse was the case on the leg on the side of lesion. While doubts may be entertained as to how far theae experi- ments, taken by themselves, indicate the paths of sensation and volition, as distinct from mere reflexes more or less general, yet when they are viewed in connection with the results of hemisection of the cord in the monkey, and the symptoms of unilateral disease or injury of the cord in man, therd seems no reason for doubt that the lateral columns contain the paths of sensation and voluntary motion ; and that it is the division of these tracts mainly, if not exclusively, that causes oss of sensation on the opposite side, and loss of voluntary molpn on the same side. Ludwig and Woroschiloff have not been able to differentiate the sensory from the motor tracts of the lateral columns, and believe that they are more or less mingled together. But the facts of human and experimental pathology indicate thatlthey are, to a large extent at least, distinctly separable from each other. § 5. When the motor centres of the cerebral hemispheres, (Chap. X.) are destroyed, or the tracts leading from them are severed, degeneration ensues and changes occur (sclerolis) which render .the position of the ■ degenerated tracts readily distinguishable from the normal tissue. CENTRIFUGAL PATHS 57 Investigations of this nature show conclusively that when the motor centres, or voluntary motor tracts, are destroyed, degeneration proceeds downwards exclusively in the pyramidal tracts in a well-defined area of the cord. The path of degeneration coincides exactly with the tracts, which the embryological researches of Flechsig have shown to be developed in relation with the cerebral hemispheres, and at a later period than the fundamental spinal tracts. We have thus a concurrence of experimental, pathological, and anatomical evidence determining the paths of voluntary motor impulse in the spinal cord. The pyramidal tracts, as already described, descend from the cortex through the internal capsule, foot of the crus and pons, and, decussating more or less com- pletely at the lower anterior aspect of the medulla oblongata, proceed mainly in the opposite lateral column ; while some, which do not decussate there, proceed down the anterior median column of the same side for some distance before crossing to the opposite side. When a transverse section is made of the spinal cord it- self the descending degeneration affects the same tracts, but, in addition, also certain others. These are the anterior root zones. In these, however, the degeneration proceeds downwards only a short distance ; a fact which shows that the anterior root zones are not long paths of conduction from the encephalic centres, but merely centrifugal paths between higher and kwer spinal segments. That they are motor is clearly shown by the direction of the degeneration, but they are motor in a different sense from the pyramidal tracts, and belong to the fundamental spinal system. As these tracts are apparently continuous with the reticular formation of the tegmentum, it would appear that the anterior root zones are the paths of conduction of motor impulses from centres distinct from those of voluntary motion proper. The completeness of the degeneration which ensues in the pyramidal tracts when the cord is severed, or the cerebral motor centres destroyed, shows that the sensory tracts of the spinal cord, though apparently in the same region of the cord, are not confusedly mingled with those of voluntary motion. Nor when the pyramidal tracts are densely sclerosed primarily 58 FUNCTIONS OF THE SPINAL COBD (primary lateral sclerosis), or secondarily to cerebral lesion, is sensation impaired. It is therefore impossible to avoid the conclusion, in opposition to the hypothesis of Ludwig and Woroschiloff, that the tracts of sensation are distinctly defined and separable from those of voluntary motion. It has not, however, been found that any tracts in the postero-lateral columns degenerate upwards when the cord is severed at any point. 1 There are certain facts which render it probable that the sensory paths lie in the lateral limiting zone 2 of Flechsig (see fig. 6) in the angle formed by the anterior and posterior horns. - This region has been found quite free from degeneration when the pyramidal tracts proper have been found densely sclerosed, either as the result of degeneration secondary to cerebral lesion, or primarily in cases of lateral sclerosis with spastic paraplegia. Why, how- ever, in this case these tracts should not degenerate upwards when they are divided is not clear, unless we assume that they maintain a continuous relation and connection with the cells of the posterior horns ; and this is extremely probable. § 6. But while the existence of sensory paths in the lateral 1 Gowers (Diagnosis of Diseases of the Spinal Cord) figures a tract (fig. 3) in the antero-lateral column of the. dorsal region, which he ascribes to ascend- ing degeneration in a case in which the lower part of the cord was crushed, and which he thinks may be the sensory path. Somewhat similar appearances, found in a case of compression of the spinal cord by a tumour, are ascribed by Westphal (Archiv f. Psychiatrie, Bd. x. Heft 3) to foci of multiple degene- ration. Hadden has published (Trams. Patholog. Society, 1882) a description of a cord, in which there were symmetrical tracts of degeneration in a some- what similar position to those of Gowers' case, in the upper cervical region and lower portion of the medulla oblongata. But there was no clinical history further than that the specimen was from that of a patient affected with loco- motor ataxy. The true nature and significance of the degeneration is there- fore only a matter of speculation. [Since this was in type H. Tooth (St. Bart. Hosp. Hep. vol. xxi.) has published a case in which there was a tract of degene- ration, similar to that in Gowers' case, in the cervical region after injury of the cord in the mid-dorsal region. But as at the level of the first cervical root it merged with the direct cerebellar tract it seems probably to belong to this system.] 2 These remain intact in a case reported by Schultze (Archi/o f. Psychiatric, Bd. xiv. 359, Case V.), in which, in consequence of solution of continuity of the lower cervical region, there was secondary degeneration of the pyramidal tracts, and also of the lateral columns and anterior root zones. The internal division of the lateral columns, the columns immediately in contact with the anterior horns and the limiting layer, were entirely free from degeneration. CENTRIPETAL PATHS 50 columns is not clearly indicated by the facts of secondary degeneration, this method of research shows very conclusively that when the cord is divided ascending degeneration takes place in the direct cerebellar tracts (fig. 6, dc), the posterior root zones (columns of Burdach (fig. 6, pr), and posterior median columns (columns of Goll) (fig. 6, g). Degeneration in the direct cerebellar tracts has been followed up to the restiform bodies and thence into the superior vermiform process of the cerebellum. The posterior root zones degenerate upwards only for a Pig. 40.— Transverse Section of Spinal Cord of Human Embryo at fire months (Ross). (th, ah', anterior horns of grey substance. ph,ph', posterior horns, ar, , superior vertical canal, fo, fenestra ovalia. into the vestibule by five apertures, two of the tubes uniting into one (fig. 47). The canals form each two-thirds of a circle, and at one end each presents a dilatation, or ampulla. Fin. 4ft. — The Interior of the Rijrht Labyrinth with its Membranous Canals and Xerves (Breschet).— a, tin- outer wall ol the In my labyrinth is removed so as to display the membranous parts within. 1, commencement of the spiral tube ot tlie cochlea.. 2, po-terior semicircular canal, partly opened. 3, external ur horizontal canal. 4, superior canal. 5, utriculus. 6, sacculus. 7, lamina spiralis. 7'. sr;d:i t\mpani. ft, ampulla of the superior membranous canal, it, ampulla of the horizontal. 10, ampulla of thi' posterior semicircular canal. -B, membranous labyrinth and nerves detacbed. 1, facial nerve in the internal auditory meatus. 2, anterior division of the auditory nerve, giving branches to 5. ft, and 9. the utricle and the ampulla? of the superior and horizontal canals. 3, posterior division of the auditory nerve, giving branches to the surulus < 6 ) and posterior ampulla CIO), and cochlea ( 4 ). 7. united part of the superior and posterior canals. 11, posterior extremity of the horizontal canal. The canals are termed respectively, according to their posi- tion and relation to each other, the superior vertical (rig. 47, c s ; fig. 4H, a 4) ; the posterior vertical (fig. 47, cp ; fig. 48, a 2) ; and the horizontal (fig. 47, c h ; fig. 48, a a). THE SEMICIBCULAB CANALS 129 Within these bony tubes are membranous canals of the same shape as the bony canals (fig. 48) but of less diameter and separated from the osseous walls by a liquid termed the perilymph. Each canal has a dilatation or ampulla situated in the corresponding dilatation of the bony tube, and all com- municate with a common sinus situated in the vestibule and termed the utricle (fig. 48, a 5). The membranous canals are filled with a liquid termed the endolymph. On the ampullary dilatations of the membranous canals are distributed respec- tively three branches of the vestibular division of the auditory nerve (fig. 48, b). The ultimate terminations of this nerve consist of fusiform cells furnished with hair-like processes, which project from the epithelial surface of the ampullae. Embedded in the epithelial lining of the sinus and ampullae are certain calcareous crystals, varying in form and size in different animals, termed otoliths or otoconia, which are intimately connected with the nerve terminations, and probably play an important part in their excitation. The canals, being embedded in bone, and in close relation with a lobule of the cerebellum, are not easily isolated for purposes of experimentation, but in some animals the opera- tion is easier than in others. An ingenious method has been adopted by Vulpian, viz. administering madder to the animals for some time previously, which causes the canals to become bright red in the midst of osseous tissue of a paler hue. When the membranous canals are injured very remarkable disturbances of equilibrium ensue, which vary, as Flourens first pointed out, with the seat of lesion. This has been amply confirmed by the experiments of Cyon, 1 Spamer, 2 Hogyes, 3 and others. According to the observations of Flourens and Cyon on pigeons, when the horizontal canal is divided on one side, the head is thrown into a series of oscil- lations in a horizontal plane round the vertical axis. These cease in a short time, but on section of the corresponding canal on the other side they reappear with greater intensity and the animal is unable to maintain its equilibrium, falling, 1 Cyon, Sur Us Fonctions des Canaux Semicirculaires. ThJse, Paris, 1878. 2 Spamer, PflUger's Archiv, Bd. xxi. 1880. 3 Hogyes, Idem, Bd. xxvi. 1881. 130 MAINTENANCE OF EQUILIBRIUM or turning on a vertical axis, or circling round and round. Flight is difficult or altogether impossible. After the lapse of eight to ten days, however, all the disturbances may have so subsided that except for some maladresse, especially visible in flight, the animal seems quite normal. When the posterior vertical canals are divided the disturb- ances of equilibrium are of a similar character, but more violent. In this case the movements of the head are in a vertical plane, round a horizontal axis. Instead of spinning round a vertical axis, the animal tends to execute a somersault '- head over heels. These disturbances may all subside within a fortnight, leaving only a certain brusquerie in the move- ments and almost complete inability to fly. Section of the posterior vertical canals causes movements of the head from behind forwards, and from right to left, or vice versa. There is profound disturbance of equilibration, and the animal tends constantly to turn somersaults heels over head. The plane of the movements of the head in this case is diagonally round a horizontal axis. An analysis of the movements consequent on section of the respective canals shows that they take place in the plane of the canals operated on. The effects of section of the semicircular canals in rabbits are of essentially the same character as those seen in pigeons. But they are more enduring, and in particular, as Cyon shows, the oscillations affect the eyeballs more than the head or trunk. When one of the horizontal canals is injured there is a tendency to movements of manege; when one of the vertical canals is injured the animal turns on its longitudinal axis. The eyeballs deviate and are thrown into a state of nystagmus, the plane of the oscillations varying with the canal injured. The oscillations of the eyeballs are more or less independent of movements of the head, and in fact are most pronounced when the head is fixed. The direction of the eyeballs will be the subject of future consideration (seep. 209). In frogs also section of the semicircular canals causes very marked disorders of equilibrium, varying with the canals in- jured, the head turning on the longitudinal axis of the body, the animal falling to one side, on leaping, when the horizontal LESIONS OF THE SEMICIBCULAB CANALS 131 canals are cut ; falling on its back when the posterior vertical canals are cut ; turning complete somersaults and exhibiting the utmost disorder of movement when the other vertical canals are divided. In a frog with the superior vertical canals divided, attempts at swimming are compared by Cyon to movements of waltzing in the water, the animal maintaining an upright position and pivoting round and round. It has been observed that the disturbances of equilibrium after section of one or more of the canals, on one or both sides, are of comparatively short duration. When the whole of the semicircular canals on one side are destroyed the dis- turbances of equilibrium are also transitory. Equilibration is at first very uncertain, and flight is impossible. There is a tendency to fall towards the side injured, and in particular the leg of this side is observed frequently to give way suddenly as if it were broken. In many animals also the head assumes an unnatural position, the occiput being directed towards the side of injury, and the beak towards the opposite side. This condition has been specially described by Spamer, 1 and attri- buted by him to secondary implication of the cerebellum ; but in a pigeon described by Munk, 2 in which the semicircular canals of the right side were deficient, the same distortion of ' the head was observed, apart from affection of the cerebellum or intracranial centres. When the whole of the canals are destroyed on both sides the disturbances of equilibrium are of the most pronounced and almost indescribable character. Goltz 3 describes a pigeon so treated which always kept its head with the occiput touching the breast, the vertex directed downwards, with the right eye looking to the left, and the left looking to the right, the head being almost incessantly swung in this position in a pendulum- like manner. Cyon 4 says it is impossible to give an idea of the perpetual movements to which the animal is subject. It can neither stand, nor lie still, nor fly, nor maintain any fixed attitude. It executes violent somersaults now forwards, now backwards, rolls round and round, or springs in the air 1 Hogyes, PflUger's ArcMv, Bd. xxvi. 1881. 2 Munk, Du Bois-Reymond's Archiv, 1878, p. 347. 3 Goltz, PflUger's Archiv, 1876. * Cyon, op. cit. K 2 132 MAINTENANCE OF EQUILIBBIUM and falls back to recommence anew. It is necessary to en- velop the animals in some soft covering to prevent their dashing themselves to pieces by the violence of their move- ments, and even then not always with success. The extreme agitation is manifest only during the first few days following the operation, and the animal may then be set free without danger, but it is still unable to stand or walk, and tumultuous movements come on from the slightest disturbance. But after the lapse of a fortnight it is able to maintain its upright position with some support, and to pre- serve any attitude given it, if not in any way disturbed, and gradually it begins to gain steadiness. At this stage it re- sembles an animal painfully learning to stand and walk. In this it relies mainly on its vision, and it is only necessary to cover the eyes with a hood to dispel all the fruits of this, new education, and cause the reappearance of all the motor dis- orders. It is only after the lapse of months that the animal again approaches a normal appearance. Even then its movements axe all uncertain and insecure. Its march is slow, and it seems to be carefully feeling the ground. Flight is altogether impossible. By preference it remains in some obscure corner, as if anxious to avoid all disturbance or agitation. When it is suddenly startled it exhibits all the former confusion and tumbles about helplessly. § 12. Some physiologists (Bottcher, 1 Baginsky, 2 &c.) have endeavoured to explain away the phenomena observed after section of the semicircular canals on the assumption that the operations involve mechanical disturbance, or anatomical lesions in the cerebellar peduncles or other portions of the brain. But the experiments of Goltz, Cyon, Spamer, Hogyes, and Laborde prove that the disturbances of equilibrium occur after methods of procedure which entirely exclude either mechanical or other lesion of the intracranial centres ; and, apart from all other evidence, the undoubted fact that the disturbances vary with the canal injured completely disposes of such an hypothesis. Lesions of the cerebellum and neigh- 1 ArehivfU/r Ohrenheilkunde, Bd. ix. 1875. z Du Bois-Eeymond's ArcMv, 1881, Heft 3 und 4. LESIONS OF THE SEMICIBCULAB CANALS 133 bouring parts are apt to ensue some time subsequently to the operation, from secondary inflammatory changes sot up by the wounds, but the symptoms which result from irritation or destruction of the semicircular canals in the first instance are entirely separate from such secondary complications. In what relation, then, do injuries of the semicircular canals stand to the disorders of equilibration observed ? The first supposition which suggests itself is that the phe- nomena are related to disturbance of the sense of hearing, seeing that the lesions affect the mechanism of the ear. This, however, is not the case ; for Flourens and many other experi- menters have sho-wn that animals in which the semicircular canals alone have been destroyed retain their sense of hearing, so far at least as regards aerial vibrations. When the cochlea alone is destroyed animals lose their sense of hearing, but do not lose their faculty of equilibration. - It has also been proved anatomically that the division of the auditory nerve which supplies the vestibule and ampullae of the semicircular canals is a distinct branch from that which supplies the cochlea. 1 Whether the double origin of the auditory nerve corresponds to the two terminal subdivisions, as Cyon and Laborde assume, is not certainly established. The connection of the anterior root of the auditory nerve with the inferior peduncle of the cerebellum is probable, but the anatomical researches of Laura, and the experimental researches of Monakow 2 and Onufrowicz, 3 throw at least great doubt on the connection between this root and the so-called lateral nucleus of Clarke. But it is an interesting fact that, as we descend the animal scale, the cochlea dwindles and disappears, while the semi- circular canals remain well developed. The lamprey has only one saccule and two semicircular canals in its internal ear, and no external auditory meatus. Cyon found that though these animals gave no indications of hearing the loudest sounds, yet they exhibited the most profound disorders of equilibration when their semicircular canals were injured. 1 This is so in all the lower animals, but Ketzius states that in man the ampulla of the posterior eanal is supplied by a division of the cochlear nerve. * Archiv filr Psychiatric, Bd. xiv. Heft 1. 1883. 3 Ibid. Bd. xvi. Heft 3. 134 MAINTENANCE OF EQUILIBRIUM They were unable to maintain their normal attitude, circled round and round when attempting to swim, or rotated round the axis of their bodies. It is undoubtedly true that in the great majority of cases of Meniere's disease, which is characterised by attacks of vertigo and disturbance of equilibrium, and which is dependent on disease of the internal ear, hearing is impaired. This, however, is easily accounted for on the supposition that the cochlea is also implicated in the disease. But we may have all the phenomena of Meniere's disease without impairment of the sense of hearing, so far as relates to aerial vibrations. I have reported a case of this kind. 1 Eesults similar to those induced by injuries of the semicircular canals are caused by section of the auditory nerve itself. Goltz has shown that when the auditory nerve has been divided on both sides in the frog, the animal loses its power of maintaining its equi- librium when submitted to the balancing experiment already described. If its leg is irritated the animal jumps as before,., but instead of alighting on its feet it falls on its back, or in some other irregular fashion, and rolls over and over before it can regain its normal position. More recently Bechterew 2 has described similar effects of section of the auditory nerve in dogs. The animals roll round towards the side of operation, and exhibit a skew deviation of the eyes — that on the side of section looking downwards and outwards, the other upwards and inwards, and oscillating in the opposite direction. The rolling is most marked during the first few days after the operation, being then almost in- cessant. When not. rolling on its axis the animal lies on the side of section, with this side of the head downwards, the other upwards. The legs on the side of section are doubled up close to the trunk, but flaccid, while those on the opposite are rigidly extended outwards. If the animal, however, is placed in any other position than on its side, all the stiffness of the limbs ceases to be manifest. The disturbances of equilibrium gradually become less pronounced ; but for many weeks after the operation the animal is very unsteady. This 1 ' Labyrinthine Vertigo,' West Riding Asylum Reports, vol. v. 1875. 2 Pfliiger's Archiv f. Physiologic, Bd. xxx. 1883. LESIONS OF THE SEMICIRCULAR CANALS 135 is greatly increased by covering the eyes, and a loud sound frequently causes the animal to fall on its side — the side of section — or roll round once or twice. When both auditory nerves are cut the animal can neither stand nor walk. There is no paralysis of the limbs whatever, but all the movements are irregular and purposeless. The head and eyes oscillate, but the eyes oscillate in a horizontal plane, and there is no skew deviation as when only one nerve is divided. These results might be ascribed to injury of some part of the brain in the attempt to divide the auditory nerve within the skull, but both Goltz and Bechterew give satisfactory evidence against this view. Goltz has shown that when that portion of the skull of the frog which contains the internal ear is detached from the rest, without opening the intracranial cavity, the results are still the same, thereby excluding the possibility, of intracranial lesion. § 13. The disturbances are attributed by some (Vulpian, Brown- Sequard, &c.) to reflex motor reaction, excited by the irritation consequent on the operative procedure. But, though this may explain some of the first effects of the lesions, it is evidently not all ; for, as Goltz observes, the phenomena con- tinue long after the Wounds have entirely healed up. Nor are they explicable on the supposition of an auditory vertigo, or psychical confusion, occasioned by a disharmony between conscious impressions and ideas ; for it has been shown by Flourens, Lowenberg, and Bechterew that the disorders occur in animals in which the cerebral hemispheres have been removed or functionally annihilated. But that psychical con- fusion does play some part in the disorders is evident from the fact that they are more marked, and come on spontane- ously in animals retaining their hemispheres, while some external stimulation is necessary to excite them after destruc- tion of the hemispheres. But this psychical confusion and panic are only the subjective side of the disturbance of a mechanism which is essentially reflex in character. The in- tensification of the disturbances by the emotions of fear and dread is merely an illustration of a fact familiar in human experience under similar circumstances. 136 MAINTENANCE OF EQUILIBBIUM There can, I think, be no room for doubt that the disturb- ances of equilibrium above described are in direct causal relationship with the lesions of the semicircular canals or auditory nerves as such, apart from all mechanical or organic lesion of the intracranial centres. But there is room for dis- cussion as to whether the disturbances are due to irritation or destruction of the nerves, or their peripheral expansions in the labyrinth — a point which I reserve for consideration in a subsequent chapter (see Chapter VI. § 19). But, whether we attribute them to irritation or destruction, or both, the phenomena observed in connection with lesions of the semicircular canals clearly point to these organs as the source of impressions which are necessary for the maintenance of the equilibrium, and without which optic and tactile im- pressions alone barely suffice even after prolonged education. The hypothesis, originated by Goltz, that the semicircular canals constitute an afferent apparatus for the maintenance of the equilibrium of the head, and with it of the body in general, is perhaps too narrow ; for, as has been seen, move-* ments of the eyeballs, and also of the trunk and limbs, are in relation with the canals as well as movements of the head. As Cyon observes, the head is affected specially only in pigeons ; whereas in frogs it is the trunk, and in rabbits the eyeballs ; to which may be added, that in dogs, according to Bechterew's experiments, head, eyes, trunk, and limbs are all involved. These facts indicate, therefore, that the semicir- cular canals are in relation with all the movements which are concerned in equilibration in different animals. § 14. The exact mode of origination of the labyrinthine im- pressions has been much discussed, and it would be premature to say that the point is definitively determined. The hypo- thesis advanced by Goltz, and supported in all essential points by the investigations of Mach, 1 Breuer, 2 and Crum-Brown, 3 is that the impressions are conditioned by the degree, and rela- tive variations, of pressure exerted by the endolymph upon the ampullary dilatations of the membranous canals on which the 1 Sitzungsberich. d. Wien. Acad., Bd. lxviii. 1873. 2 Wien. Med. JahrbUcher, 1874 and 1875. " Journal of Anatomy and Physiology, vol. viii. 1874. MECHANISM OF LABYBWTHINE IMPBESSIONS 137 vestibular nerves are spread. This hypothesis has, however, been contested by Cyon and others, on the ground that varia- tions in pressure in the canals, experimentally induced, do not cause disturbances of equilibrium. Cyon's hypothesis is that vibrations of the otoliths, conditioned by movements of the head and undulations of the endolymph, are the immediate excitants of the ampullary nerves. 1 But, whether it is tension or otolithic vibration, we may assume, with Goltz, that each variation in the position of the head will excite irritation of the ampullary nerves according to the plane in which the movement takes place. If it is pressure, inclination of the head to the right side will cause the endolymph to flow from the right ampulla and to the left, and vice versa if the head is inclined to the left. These symmetrical plus and minus variations may be supposed to excite the centres of equilibra- tion to action appropriate to the position of the head and body associated therewith. When the conditions are perverted, by lesions of the canals, disturbances of equilibrium are the necessary result ; and these will vary according to the seat of lesion. § 15. It is by means of the semicircular canals that we are aware, according to Crum-Brown, of the axis, rate, and direc- tion of rotation of the head and body, apart from all other channels of perception. If a person be placed on a revolving disc, with his eyes shut, he is still able to determine the sense and extent of the angle through which his body has been revolved. When rotation has been kept up for some time the rate gradually appears to diminish, and after a longer time all sense of rotation entirely disappears. When the rotation is stopped the individual feels as if he were being whirled round 1 Sewall (Journal of Physiology, Feb. 1884, vol. iv. No. 6) finds that in sharks and skates destruction of the semicircular canals is often entirely nega- tive as regards disturbances of equilibrium. When disorders of equilibrium did occur they were more particularly observed in connection with injuries of the vestibular sacs, particularly the saccules, rather than of the ampullse. Lacera- tion of the saccules and removal of the otoliths seem to have been most effective in inducing disturbances. During this process nystagmus was always very marked, and frequently vomiting occurred even when equilibrium was not affected afterwards. 138 MAINTENANCE OF EQUILIBBIUM in the opposite direction. If at this period he opens his eyes a distressing sense of vertigo comes on, explicable by the dis- cord between his visual, tactile, and labyrinthine impressions. The bypothesis is that rotation in a plane perpendicular to any of the canals causes the endolymph, on account of its inertia, to press in the reverse direction against the ampullary nerves. This gradually ceases as the movements of the liquid and bony canals become equalised, and so the rotation ceases to be felt. On stoppage of the rotation, however, the endo- lymph continues to move on, and an impression of rotation in the reverse direction is occasioned. This also ceases after a time, owing to friction, and the phenomena subside. ' Each canal,' as Crum-Brown argues, 'has an ampulla at one end only, and there is thus a physical difference between rotation with the ampulla first and rotation with the ampulla last ; and we can easily suppose the action to be such that only one of these rotations (say with the ampulla first, in which case, of course, there is a flow from the ampulla into the canal) will affect the nerve termination at all. One canal can, therefore, on this supposition, be affected by and transmit the sensation of rotation about one axis in one direction only, and for complete perception of rotation in any direction about any axis six semicircular canals are required, in three pairs, each pair having its two canals parallel (or in the same plane), and with their ampullar turned opposite ways. Each pair would thus be sensitive to any rotation about a line at right angles to its plane or planes, the one canal being influenced by rotation in the one direction, the other by rotation in the opposite direction.' These conditions are fulfilled by the fact that the two horizontal canals are on the same plane, and the superior vertical canal on the one side is in the same plane as the posterior vertical canal on the other, and vice versa (see fig. 47). Thus in each case there is one canal — the horizontal — at right angles to the mesial plane, and two other canals — the superior and posterior vertical — equally inclined to the mesial plane. Though, as has been stated, there are some difficulties in the way of accepting the hypothesis of variations in tension, yet that the ampullary nerves receive stimulation respectively under such conditions as described by Crum-Brown, Mach, and MECHANISM OF LABYRINTHINE IMPRESSIONS 139 Breuer is in the highest degree probable ; and we can thus furnish an explanation of facts otherwise inexplicable. Important confirmation of these views is afforded both by experiments on animals and also on deaf mutes, especially those who have become so from disease. Breuer ' affirms that vertigo cannot be induced by rotation in pigeons whose semi- circular canals have been destroyed ; and Hogyes 2 states that the same is true of rabbits whose membranous canals have been extracted. James 3 found that a large proportion of deaf mutes (186 in 519) were totally insusceptible of being made dizzy by rapid rotation ; while in two hundred normal indi- viduals only one remained exempt. In a note appended to the memoir one observer reports that out of twenty cases, half of whom had been born deaf, and the other half had lost their hearing from disease, the latter could not be made dizzy by rotation, whereas in the former a few seconds' spinning were sufficient to excite vertigo. It is no valid argument against the functions ascribed to the semicircular canals to assert that, as the disturbances are only temporary, therefore the phenomena are due purely to reflex irritation. If the semicircular canals were stated to be the only afferent organs of equilibration the argument would have weight ; but the organs themselves are double, and in their entire absence compensation is possible through the agency of visual and tactile impressions. The fact that closure of the eyes intensifies the disorders, and renews them when they have almost ceased, shows how much the recovery is dependent on the functional compensation effected by the other factors of the afferent consensus. II. Co-OEDINATION OF LOCOMOTION. § 16. Animals deprived of their cerebral hemispheres, be- sides being able to maintain their equilibrium, are also capable of locomotion in their usual manner. Fishes balance them- selves with their fins, and by alternate lateral strokes of the ■ Op. tit. 2 Op. tit. 3 ' The Sense of Dizziness in Deaf Mutes,' American Journal of Otology, Oct. 1882. 140 CO-OBDINATION OF LOCOMOTION tail swim forward with the same precision as before ; frogs leap on land, or swim when thrown into the water ; birds, if urged, walk forward, or fly if thrown into the air; rabbits bound away in their characteristic mode of progression, in response to appropriate external stimuli. For reasons above stated it is impossible, in the higher animals, to demonstrate, experimentally, the retention of the faculty of co-ordinated locomotion in the centres situ- ated below the hemispheres, but we are able to arrive at the same conclusion in another way. It is a fact of every-day observation that the function of locomotion, once set in action, is carried on with all regularity and precision, without attention and apparently without consciousness, while the cerebral hemispheres are practically detached and engaged in other directions. From the homology subsisting between the mesencephalic and cerebellar centres of man and the lower vertebrates we argue the homology of function, and what we have seen to be true of the lower animals is to be regarded as more or less true of man. It may be, but we have no means of determining with exactitude, that this function is, in the lower animals, primarily or hereditarily inherent in the con- stitution of their nerve centres, and that in the higher it is rather, as Carpenter expresses it, a secondary reflex or auto- matic action, i.e. the result of previous experience and con- scious action. Whichever way we look at it, the result is the same, viz. that, whether primarily or secondarily developed, the co-ordination of movements of locomotion is a function of the lower centres. It is manifestly impossible to draw a hard and fast line between the functions of equilibration and of locomotor co- ordination, for without equilibration locomotion becomes im- practicable, and the same afferent factors are concerned in both. In discussing the function of equilibration I have frequently spoken of the two together ; but, theoretically, the two functions are capable of differentiation from each other. We can conceive an animal possessed of the power of main- taining its bodily equilibrium, and of the necessary muscular adjustments to this end in loco, but unable to move out of its position. Therefore, even though we may not be able to FACTOBS CONCEBNED IN CO-OBDINATION 141 separate them practically, or localise the two functions in clearly differentiated centres, it is convenient to consider them apart. The mechanism of co-ordinated locomotion, like the me- chanism of equilibration, consists of — 1, an afferent system ; 2, a co-ordinating centre ; 3, an efferent or motor system, by which the centre is brought into relation with the muscles of the trunk and limbs. That which excites the centre to action, in the first in- stance, may be various. In the animal deprived of its hemi- spheres it can only come from without, and is generally some form of tactile stimulus. The central apparatus of locomotion, once set into activity, continues to functionate (to use a convenient expression) in a rhythmical manner. The duration of this activity coincides with the degree of, intensity or continuance of the primary stimulus, and the vitality of the nervo-muscular apparatus. The fish in the water is under continual stimulation of its body surface by contact with the mobile waterj and, therefore, it continues to swim till arrested by some obstacle or by fatigue. The rhythmical strokes of the tail would appear to be in a great measure conditioned by each other, the one stroke exciting the opposing stroke in regular succession. So the frog, when thrown into the water, is impelled to swim by the same kind of stimulus which acts on the body of the fish. The leaping movements on land are kept up in rhythmical succession by the successive impressions of contact with the ground after each leap. The pigeon makes bilateral rhythmical movements of the wings ; quadrupeds either leap or walk, in the latter case usually with diagonally co-ordinated action of the fore and hind limbs ; while man progresses principally by alternate pendulum-like swings of the lower extremities — the rhythmical succession being kept up by the alternate impressions of con- tact with the ground, which the sole of the foot receives after each step. Though in man the upper extremities have become differentiated away from purely locomotive purposes, yet it may be observed that they are co-ordinated with the lower extremities in the same diagonal manner as in quadrupeds ; the right hand swinging with the left leg, and vice versa. The 142 CO-OBDINATION OF LOCOMOTION upper extremities are likewise co-ordinated with the other bodily movements, in the adjustments necessary to the main- tenance of equilibrium. § 17. Locomotion involves a vast complexity of motor adjustments of the head, trunk, and limbs beyond the simple synergic combinations of the muscles of the limbs which are co-ordinated in the spinal cord, and are capable of being called forth by stimulation of the anterior roots (see Chapter II. § 17). The centre of gravity is continually varying, and each move- ment of the active limbs necessitates graduated adjustment of the trunk and apparently passive limbs, in order that the movements d' ensemble may be carried out in even simultaneity and succession without abruptness, and in harmonious re- lation with each other. By stimulation of the cord below the calamus scriptorius, the limbs of rabbits, as Ludwig and Woroscbiloff have shown, may be thrown into co-ordinated and alternating action such as are seen in running and leaping ; and similar co-ordinated actions of the limbs may be called forth reflexly in animals deprived of all centres above the spinal cord. But the spinal centres alone are unable to provide for the execution of these movements in relation to the body as a whole, and its surroundings, which are implied in locomotion from place to place. These necessitate the presence and activity also of the mesencephalic and cerebellar centres. During the acquisition of all movements of any degree of complexity, not already organised, or, if so, insufficiently developed, the learner directs his movements in large measure by the aid of vision, and plants his body and limbs in the position he sees best adapted for carrying out the end desired ; and he is guided also, and the energy of his motor adjustments regulated and graduated, by the sensations and impressions arising in connection with muscular action. When facility has been acquired, neither vision nor the sense of muscular action seems necessary, and the most complex co-ordinations can be effected with the utmost precision without attention, and even without consciousness. What was at one time a conscious effort becomes an organised reflex, provided for in the mechanism of the lower nerve centres; and it is only under certain abnormal conditions that the conscious factors LOCOMOTOB ATAXY 143 formerly at work, again assume importance. This is ex- emplified, and the conditions necessary to locomotor co-ordi- nation illustrated, in tabes dorsalis, or locomotor ataxy. In this affection, which is due to disease of the posterior columns of the spinal cord, there is a remarkable combination of dis- orders of station and locomotion. The individual so affected stands with difficulty, and totters and stumbles in his gait, and the movements of his limbs are characterised by an ex- cessive energy, brusquerie, and irregularity, altogether striking and pathognomonic. The disorderly energy and uncertainty are manifested mainly in the lower extremities, but they may occur also in the upper extremities, and in some cases also in the muscles of articulation. All the disorders of the limbs are intensified when the eyes are shut or the patient is in the dark. In the recumbent posture he can move his limbs freely in all directions and with energy ; and in this position can co-ordinate his limbs for volitional purposes without appreciable unsteadiness, even when his gait is already profoundly ataxic. Mention has already (p. 124) been made of the difficulty of maintaining the balance ; a symptom which is most marked in those cases in which there is impaired sensibility in the soles of the feet. So long as the eyes are open the patient is able to maintain his equilibrium, but in the dark, and when the eyes are shut, he oscillates greatly, and is in danger of falling if unsupported. In the great majority of ataxics tactile sensibility is perverted. The individual suffers from severe lancinating pains, there is numbness of the feet, retardation of sensation, and various other indications of sensory impairment. There is want of tone in the muscles, and the so-called tendon reflexes are abolished. § 18. There is considerable diversity of opinion as to the explanation of the disorders characteristic of ataxy. Some (Erb, &c), who hold that the spinal cord itself is not a centre of co-ordination attribute the symptoms to disease of hypo- thetical centrifugal co-ordinating tracts. But we have already seen that synergic co-ordination is a function of the spinal centres themselves ; and we have no reason for assuming that there exist centrifugal tracts other than those of the anterior 144 CO-OBDINATION OF LOCOMOTION and lateral columns, which call into play the spinal centres. The morbid anatomy of the disease shows beyond all doubt that all the symptoms characteristic of ataxy may be mani- fested in the entire absence of any abnormality in the antero- lateral tracts and anterior roots. The disease affects tracts which are essentially centripetal, as shown by the direction of secondary degeneration. But, though centripetal, they are not the paths of sensation proper, except in so far as that the posterior roots run for a certain distance in the posterior root zones before entering the grey matter and reaching the opposite side of the cord. Though in a large proportion of cases there is impairment of tactile and general sensibility, yet in others, in which ataxy has existed in a marked degree, this has not been found ; and there appears to be no constant relation between the degree of ataxy and the extent of impair- ment of tactile, muscular, or general sensibility. There may be the most profound ansesthesia without ataxy. This is the case in anesthesia of cerebral origin, in which the centres or tracts of sensory perception are destroyed. And there is a remarkable case on record ' of total anaesthesia of spinal origin in which there was complete retention of motor power without ataxy. The patient had no sense of his limbs or of the energy of his movements ; but, though he could not stand with his eyes shut, yet with his eyes open he could walk and co-ordinate all his movements with fair precision, and without any of the abruptness and irregularity seen in ataxy. Even with his eyes shut he could will and carry out a desired movement without any greater uncertainty or vacil- lation than characterises the actions of perfectly normal in- dividuals under similar conditions. This case proves beyond doubt that sensation, cutaneous or muscular, is not indis- pensable to motor co-ordination. However necessary it may be as a guide to the acquisition of complex movements in the first instance, the power, once acquired, can be exercised with- out the aid of any sense of movement actually effected. But, though there may be total anaesthesia without ataxy, it is quite possible, as has been insisted on by Leyden, 2 that there 1 Sohiippel, Arehiv d. Heilkunde, Bd. xv. 1874. 2 Tabes Dorsualis, art. Eulenburg's Real-Encyclopadie, 1883. LOCOMOTOB ATAXY 145 may be disorders of sensibility in ataxics, not readily deter- mined by ordinary methods of examination, which exercise a positive disturbing influence, and lead to false judgments as to the energy and graduation of the various motor adjustments. In ataxy sensation is more frequently perverted, and the rate of transmission retarded, than actually abolished. The posi- tive disturbing influence of such conditions cannot be con- sidered as disproved by the occurrence of a total anaesthesia ■without ataxy ; but it is not necessary that we should assume that they are invariably present. There is reason for believing that ataxy may exist apart from false sensations, or erroneous judgments founded on them. I am not aware that any case has been actually reported, but the probability is that in sclerosis of the posterior columns, conjoined with cerebral hemianaesthesia, ataxy would be just as pronounced on the one side as the other ; though, from the nature of the lesion, any disturbances of sensation proper would be entirely elimi- nated. As the posterior root zones — disease of which is the essen- tial cause of ataxy (Charcot and Pierret) — belong to the fundamental spinal system, and vary with the development of the spinal segments, it is probable that they contain fibres which, independently of sensation, and in a purely reflex manner, serve to secure, in harmonious and graduated relation to each other, the synergic combinations organised in the spinal centres, the stimulus to each being supplied by the activity of that with which it is immediately associated. The more complex the combinations, the greater the necessity of such a system of fibres. Hence locomotion, which involves the graduated activity of so many centres, is more likely to suffer than the more simple synergic combinations of the muscles concerned in any individual movement of the limb, when the posterior root zones are invaded by disease. Simple acts of volition might still be carried out with a fair amount of precision when locomotion would be difficult or altogether impossible. Such is the condition actually seen in ataxy, and it is only in the extreme stages, when the lesions are more diffuse, that co-ordination in general has the same abrupt and tumultuous character as that of locomotion. With the aid of 146 INSTINCTIVE OB EMOTIONAL EXPRESSION vision an ataxic is able to overcome to a large "extent the un- certainty and irregularity of his movements, which otherwise would be very evident ; but this involves considerable strain, and his efforts to compensate by volitional action for the defects of a self-adjusting mechanism speedily induce exhaus- tion and fatigue. So long also as sensation is not seriously impaired, the sense of muscular action enables him, to some extent, to guide his movements and graduate his motor inner- vation irrespective of vision, and in some degree to repress the disorderly tendency of his limbs. Bat no conscious efforts can ever entirely make up for the defects of the self-adjusting mechanism of motor co-ordination ; and, from the complete retention of all motor co-ordination in animals deprived of their cerebral hemispheres, we may conclude that this is provided for and organised in the centres situated below those of consciousness and volition. III. Instinctive ok Emotional Expkession. § 19. Animals deprived of their cerebral hemispheres are still capable of exhibiting, in response to various forms of sensory stimulation special and general, reactions, more or less complex, which do not at all differ in character from those which we associate with feeling or emotion. They start at sounds, flinch at light thrown in their eyes, or even direct their movements in relation with retinal impressions ; respond by movements expressive of disgust or discomfort at unplea- sant nasal or gustatory stimuli, and make the most varied reactions to stimulation of the nerves of common sensation. Frogs croak, as if from pleasure, when their backs are gently stroked ; and rabbits scream piteously, and exhibit the various signs of agitation characteristic of intense pain, if their toes are pinched, or any sensory nerve severely stimulated. The outward manifestation of feeling is a purely instinctive or reflex act, over which we have little or no control, and which we can simulate only so far as those movements are concerned which are also under volitional control. But the changes in the pupils, the affections of the secretions, of the rhythm of the heart, and the visceral concomitants of feeling are beyond INSTINCTIVE OB EMOTIONAL EXPBESSION 147 our control, and manifest themselves only in relation with the actual existence of the exciting cause, and in spite of all attempts to suppress them. But the physical embodiment, or outward expression of feeling, does not necessarily imply the existence of pain or feeling as a state of consciousness. As all the physical mani- festations of feeling are capable of being called forth in animals deprived of their cerebral hemispheres, which alone are the substrata of consciousness, we must regard them as merely the reflex or instinctive response of- centres in which "sensory impressions are correlated with the motor, vasomotor, and secretory apparatus. The phenomena observed in animals deprived of their cerebral hemispheres are in all respects analogous to those observed in human beings under the influence of chloroform. Chloroform, as proved by actual experiment, first annihilates the excitability of the hemispheres — a condition coinciding with the abolition of consciousness — but the mesencephalic and lower centres retain their excitability long after this point has been reached. Hence impressions which under normal condi- tions would excite pain, as well as groans, cries, and the other physical expressions of pain, merely excite the physical mani- festations without any painful sensation proper. These are no more expressive of conscious suffering than the notes elicited by striking the keys of a pianoforte are indicative of pleasure or pain on the part of the instrument (Crichton-Browne). The centres of emotional expression are therefore situated below the centres of conscious activity and ideation, and must necessarily be in relation with every form of centripetal and centrifugal impulse through which signs of feeling may be induced or manifested. These conditions are not furnished below the mesencephalic centres. With these, however, as the experiments of Vulpian and others have shown, every form of reaction, excepting perhaps the reactions special to the olfac- tory nerve, may be elicited in response to appropriate peri- pheral stimulation, in all respects like those of the unmutilated animal. But, though the facts above related prove that in the absence of the cerebral hemispheres acts of extraordinary L 2 148 INSTINCTIVE OB EMOTIONAL EXPRESSION complexity— equlibration, co-ordinated locomotion, adaptive reactions, and signs of feeling in response to sensory stimula- tion — are capable of being carried out, it is a problem of sur- passing difficulty to analyse the mechanism of the various manifestations, and specialise the centres in which they are individually localised. In the following chapters an attempt will be made to determine the functions of the different centres; though, at the outset, I would remark that the cerebellar, mesencephalic, and spinal centres cannot possibly be detached or considered apart from each other. 149 CHAPTEE V-. FUNCTIONS OF THE OPTIC LOBES OR COEPOEA QUADRIGEMINA. § 1. The optic lobes, or corpora bigeniina of fishes (fig. 44, b), batrachians (fig. 43, b), and birds (fig. 45, b) are structu- rally homologous with the corpora quadrigemina of mammals. The general anatomical relations of these ganglia have already been mentioned (Chapter I. § 8) . They were seen to be con- nected with the reticular formation and antero-lateral tracts of the spinal cord through the upper and lower fillet on the one hand, and with the corpora geniculata, optic tracts, and cerebral hemispheres on the other. In the ventral and ven- trolateral aspect of the central grey substance of the aque- duct of Sylvius the nuclei of the third, fourth, and portion of the fifth cranial nerves were seen to be situated (fig. 19). The superficial origin of the optic tracts from the optic lobes is at once apparent in the lower vertebrates, and from the anterior tubercles or nates in many mammals, such as the rabbit. The connection is less direct in monkeys and man, but on careful exposure of the parts it is clearly evident that the anterior brachium is continuous with the optic tract through the corpus geniculatum laterale (fig. 18, cge). The testes, or posterior tubercles, seem to have no direct relation with the optic tracts in the lower mammals. In the monkey and man their arms, or brachia, pass into the corpora geniculata media (fig. 18, cgi). From these tubercles are traceable certain portions of the optic tracts, which, however, form a commissure in the chiasma (the inferior commissure), and do not appear to enter into the composition of the optic nerves (Gudden). The testes consist of a superficial stratum of fibres, con- stituting the origin of the posterior brachia, and a lenticular 150 FUNCTIONS OF THE, OPTIC LOBES mass of grey matter, consisting mostly of small multipolar nerve cells, into which radiate fibres of the brachia from the surface, and also fibres from the lower fillet, which, partially at least, decussate with those of their fellows on the opposite side. Meynert regards the brachium of one side as directly related to the fillet of the opposite side ; but it is more prob- able that the relations between the brachia and the fibres of the fillet are only indirectly established through the grey matter. The valve of Vieussens connects the upper vermiform process of the cerebellum with the testes. The anterior tubercles or nates have a greyer tint than the testes, and have on the surface a superficial or zonal stratum of fibres continuous with the anterior brachia or optic tracts. FIG. 49.— Frontal Section of the Nates (Corpora Qnadrigemina) of the Rat. The right eye had been enucleated, x 12. ( After Q-anser. ) *. 57. — Anterior aspect of Cerebellum of Babbit, e is on the cut surface of the pons Varolii. The signifi- cation of tlie numerals is given iu the text. Fi«. 56. —Upper Surface of Cerebrum and Cerebellum of Rabbit. The signification of the numerals is given in the text. § 9. Electrisation of the Cerebellum of Rabbits. The following results were detailed in the ' West Elding Asylum Reports,' vol. hi. 1873. The cerebellum of the rabbit is divided into a number of lobules, more distinctly differentiated from each other than in the case of the monkey and other higher animals. I do not attempt a homological nomenclature, but simply describe the results in reference to the position of the electrodes, as indi- cated in the accompanying figures (figs. 56 and 57). 192 FUNCTIONS OF THE CEBEBELLUM Median Lobe. Upper part (1). — Both eyes move to the right in a horizontal plane. Middle part (2). — )Both eyes move to the left in a horizontal Lower part (3). — J plane. From these results it would appear that the various divi- sions of the middle lobe differ in action as regards the lateral movements of the eyes. There is, however, no differentiation in the corresponding part of the brain of the monkey, the movement to the right or left depending on whether the elec- trodes were applied to the right or left side. I have not again verified these results on the rabbit, and therefore it is not im- probable that these differences may be partly, if not entirely, due to the position of the electrodes as regards the middle line, a point the importance of which has been more parti- cularly brought out in subsequent experiments. The essential fact, however, is the plane of the ocular movements. Lateral Lobe. — Left side. Upper Lobule (4). — Upwards with inward rotation of "left eye ; downwards with outward rotation of right eye. Middle Lobule (5). — Upwards and rotation outwards of left eye ; downwards and rotation inwards of right eye. Lower Lobule (6). — Both eyes rotate to the right on their antero-posterior axes. Anterior Lower Lobule (7). — Apparently the reverse rota- tion to that described under (6). (One observation only.) (8). — Anterior part of the Cerebellum. (Position not exactly denned.) (One observation only.) Both eyes moved upwards, and then oscillated upwards and downwards. Besides these ocular movements, protrusion of the eyeballs and increased convexity of the cornea were noted, and also some dilatation of the nostrils. Another recent experiment, without attempt at definite localisation, confirmed the fact of ocular movements, and also showed that movements of the limbs occurred on the same side as irritation. Twitching of the ears was also observed to occur during stimulation. The general fact of movements of the eyes, limbs, nostrils, and ears was also noted in some experiments on the cere- ELECTRISATION OF THE CEREBELLUM IN DOCS 193 helium of rats. Localisation experiments were not, however, carried out on these animals. I have also instituted experiments on the cerebellum of the cat and dog ; several unsuccessfully, but in a few with a con- siderable degree of success as regards the extent of exploration and definiteness of the results. § 10. Electrisation of the Cerebellum of Dogs. Median Lobe. 1. Pyramid (fig. 58, i). a. Left side. — Both eyes move to the left. b. Eight side. — Both eyes more to the right. Fi G , 58.— Cerebellum of the Dog, seen from behind and above. 1, pyramid of the middle lobe. 2, posterior extremity or declive of the superior vermiform process. 3, montieu- lns. 4. postero-snperior lobule of the lateral lobe of the cerebellum. Fir,. 5*9.— Right side of Cerebellum of Dog 5, the flocculus. Upper Vermiform Process. 2. Posterior Extremity (declive) (fig. 58, 2). a. Middle. — Both, eyes move doitmwards. b. Left side.— Both eyes move doivnwards and to the left. c. Right side.— Both eyes move downwards and to the right. 3. Lateral Lobe. 4. Postero-superior Lobule (right) (fig. 58, 4). Both eyes move upwards and to the right, rotating on their axes. This movement resulted from irritation applied to various points on this lobe. 5. Floccular Region (right) (fig. 59, ft). Rotation of the eyeballs on their anteroposterior ares, some- times to the" right, sometimes to the left, according to the o 104 FUNCTIONS OF THE CEREBELLUM application of the electrodes on various points in this region, but the situation could not be determined with accuracy. In the dog, also, I have observed movements of the limbs, nostrils, and ears during irritation of the cerebellum. Owing to the head being fixed, movements, if any, which might be caused were rendered impossible. Experiments on the cerebellum of the cat led to essentially the same results from stimulation of corresponding regions, as will be seen by the following : — Electrisation of the Cerebellum of Cats. Median Lobe. 1. Pyramid (here curved in the form of an S) (fig. GO, 1 a, l b). a. Eight curve. — Both eyes more to the right, h. Left curve. — Both eyes more to the left. Fir. 60.— Cerebellum of Cat, postero-superlor Fig. CI.— Loft side of Cerebellum of Cat Surface. 1, S-curyed pyramid of middle 5, floccular region. lobe. 2, deelive. 3, anterior extremity of median lobe (montieulus). 4, postero- superior lobule. 2. Upper Vermiform Process. Posterior Extremity (deelive) (fig. CO, 2). a. Middle. — Both eyes move doirnwards. h. Left side. — Both eyes more downwards and to tlie left, e. Eight side. — Both eyes more downwards and to the right. Lettered Lobe (fig. GO, 4). 3. Postero-superior Lobule— various points. Left. — Both eyes more upward and to the left. Eight. — Both eyes more upward and to the right. Besides these movements of the eyeballs, it was observed ELECTRISATION OF THE CEREBELLUM IN PIGEONS 195 that on irritation of the left side of the cerebellum the left pupil became contracted, and the left limbs were thrown into action. Movements of the head, if any, were not noted. Both in the cat and dog the cerebellum is difficult to reach, and, owing to the proximity of large venous sinuses, great and often fatal hemorrhage results from attempts at complete exposure; hence, I have not succeeded in arriving at trustworthy conclusions in reference to the irritation of other regions. These results, though incomplete, serve more particularly to indicate the homology of function between the cerebellum of the cat and dog and that of the monkey and rabbit, which were more fully and more frequently explored. For the purpose of comparison some experiments were made on the cerebellum of pigeons and fishes (carp). Fig. 62. — Brain of Pigeon, c, the cerebellum. Fig. 63.— Brain of Carp, o, the cerebellum. § 11. Electrisation of the Cerebellum of Pigeons (fig. 62, c). Irritation of the cerebellum of pigeons causes no move- ments of the eyeballs, but, according as the electrodes are applied to the right or left side, the head is jerked backwards and to the same side, and frequently the wing of the same side is flapped and the leg drawn up. Electrisation of the Cerebellum of Fishes {Carp) (fig. 63, c). Irritation of the right side causes the eye on the same side to be jerked forwards, the tail to be bent to the right, and the fins spread out. Irritation of the left side causes exactly the same manifestations on the left side, while irritation on the middle of the cerebellum causes the eyes to be jerked for- o 2 196 FUNCTIONS OF THE CEBEBELLUM wards, the tail to be bent up towards the head, and the fins to be spread out — a state of opisthotonus. § 12. The experiments on the cerebellum of mammals re- ceive a remarkable confirmation from, and confer an important significance on, the phenomena which are observed in man when a galvanic current is passed transversely through the skull in the cerebellar region. These phenomena were first described by Purkinje, 1 and more recently they have been very fully investigated by Hitzig. 2 When a galvanic current of moderate intensity is passed through the head by placing the poles of the battery in the mastoid fossas just behind the ears, the individual experiences a feeling of vertigo, in which the relation of his body to surrounding objects seems to be, or is, actually disturbed ; or external objects seem to alter their relation to him. The direction in which the equilibrium is disturbed, or in which external objects seem to move, de- pends on the direction of the current through the head. When the positive pole, or anode, is placed in the right mastoid fossa, and the negative pole, or kathode, in the left, so that the current passes from right to left, at the moment when the circuit is closed, the head and body suddenly sink cowards the anode, while external objects seem to whirl to the left. The direction in which external objects seem to move is compared by Purkinje to the motion of the tire of a wheel, standing parallel to the face, from right to left. When the eyes are closed the appearance of motion is transferred to the individual himself, who feels as if he were suddenly whirled from right to left, or as if the basis of support on the left side bad been suddenly withdrawn. The direction is exactly re- versed when the positive pole is placed on the left and the negative on the right side ; or, while the electrodes maintain their former position, when the circuit is broken. It has been found by Hitzig that at the moment when the head inclines towards the anode the eyeballs also move in the same direction, and then undergo oscillations, or strain towards the side of the cathode. The ocular deviations are a combination of lateral and rotal^ry movements. 1 Bust's Magazin, 1827. 1 Untersuch. ii. das Gehirn, p. 198 et seq. GALVANISATION OF THE HEAD 197 In the objective effects of the galvanic current directed through the head in this manner we see, on the side of the anode, essentially the same phenomena as result from the direct application of the electrodes to the same side of the cerebellum ; for, as is shown by the foregoing experiments, the predominant direction of the head and eyes is to the same side, with some degree of diagonal or rotatory motion. This gives us strong grounds for attributing the phenomena to irritation of the cerebellum on the side of the anode. And this would agree with the law of galvanic stimulation of the cere- bral hemispheres, in which, as Hitzig found, the anode is the more effective. On what this important variation from the usual law of galvanic stimulation of nerve structures depends is not quite clear ; but it is probable, as De Watteville * has pointed out, in connection with the unipolar excitation of nerves, that the real excitant is the virtual cathode established in the deeper tissues by the application of the anode on the surface. It is in accordance with the law of electrotonus that breaking the circuit reverses the conditions of irritation ; hence at the interruption of the current the other half of the cere- bellum becomes stimulated, and all the objective phenomena, viz. the inclination of the head and eyes, occur towards the opposite side. § 13. But simultaneously with these objective effects there occur certain modifications of consciousness or subjective sensations, which have an important bearing on the true significance of the cerebellar movements. Modifications of consciousness must, however, be regarded as coincident only, and not correlated with cerebellar action as such. The fact that removal of the cerebral hemispheres annihilates con- sciousness and volition, while it does not affect the function of equilibration, shows that the co-ordination of sensory impres- sions with special motor adjustments is an independent re- sponsive mechanism. Hence it seems to me a radical error to account for the objective phenomena by any sensations experienced by the individual, such as a feeling of vertigo or a, feeling as if the body were Wddenly left unsupported on the one side or the other. The subjective phenomena are only 1 De Watteville, L' Electrotonus des Nerfs chez V Homme, 1883. 198 FUNCTIONS OF THE CEBEBELLUM simultaneous accompaniments of the objective, and depend, not on the cerebellum, but on the cerebral hemispheres, just as reflex action may be and often is accompanied by conscious- ness, though consciousness is not essential to the mechanism itself. Keeping these distinctions in mind, we shall be better able to interpret the relation between the objective and sub- jective phenomena observed on irritation of the cerebellum. At the moment when the head and eyes incline to the side of the anode, external objects appear to be whirling to the opposite side. If, on the other hand, the eyes be kept shut, the individual himself feels as if he were being whirled in the same direction as the objects seemed to take when the eyes were kept open. The movement of external objects to the left coincides, as Hitzig has correctly shown, with the ocular movements to the right when the anode is placed in the right mastoid fossa, and the current closed. Now this is precisely the direction in which objects seem to move when the eyes are suddenly deviated to the right. If the right eye is fixed on some object, and the inner side of the eyeball pressed on, the object appears to move to the left. In like manner, if the eyeball is pushed to the left, the object will appear to move to the right ; and so it will seem to move up or down, according as the eyeball is pushed downwards or upwards respectively. Further, if the body be whirled rapidly on a vertical axis in the direction from right to left, external objects will appear to revolve from left to right ; an appearance which continues for some time after the rotation has stopped, owing to the persistence of retinal impressions. A feeling of giddiness or insecurity comes on if external objects seem to revolve, and the compensatory action necessary for maintaining the equi- librium is, in the case of rotation to the left, inclination of the head and body to the right side, and deviation of the eyes to the right, in order to keep the objects in view, and thus prevent their passing out of the field of vision. The direction of the eye to the right by voluntary effort, when, the body has been whirled from right to left, is sufficient to stop the apparent movement of objects which ccHinues after the rotation has ceased. From these facts it appears that the effect of irritation of MECHANISM OF CEBEBELLAB CO-ORDINATION 199 the right side of the cerebellum is the natural compensatory action which coincides with a feeling of being revolved from right to left ; and this is shown very conclusively by the fact that when the eyes are shut the feeling of rotation to the left is the only senstion experienced, and that, too, even when the body is actually inclining to the right side. The right side of the cerebellum, therefore, co-ordinates the muscular mechanism which prevents the displacement of equilibrium towards the opposite side, and this involves move- ments of the head, eyes, and limbs on the right side. These are the actual results of the direct application of the electrical stimulus to the cerebellum itself. In like manner, the move- ments which result from irritation of the anterior part of the middle lobe of the cerebellum, viz. the backward movement of the head and extension of the trunk and limbs, together with the upward movement of the eyes, are to be regarded as the natural compensatory efforts to counteract a seeming rota- tion forward on a horizontal axis. "We may suppose, there- fore, that the subjective side of these objective phenomena is a feeling of being revolved like a wheel from behind forwards on a horizontal axis. Similarly the forward movements of the head and downward direction of the eyes, resulting from irritation of the posterior part of the median lobe, are the compensatory or antagonistic actions to counteract a disturb- ance of the equilibrium in the opposite direction, i.e. from before backwards. Hence we may suppose that irritation of this part coincides with the sensation of rotation like a wheel on a horizontal axis from before backwards. The cerebellum would, therefore, seem to be a complex arrangement of individually differentiated centres, which in associated action regulate the various muscular adjustments necessary to maintain equilibrium and steadiness of the body ; each tendency to the displacement of the equilibrium round a horizontal, vertical, or intermediate axis acting as a stimulus to the special centre which calls into play the antagonistic or compensatory action. We should, therefore, e^ct to find that a lesion which annihilates the functional activity of any of the individual cerebellar centres should manifest itself in a tendency to the 200 FUNCTIONS OF TEE CEBEBELLUM overthrow of the balance in the direction naturally opposed by this centre. This also is in accordance with the facts of experiment. We have seen that stimulation of the anterior part of the middle lobe excites the muscular combinations which would counteract a tendency to fall forwards. Hence destruction of this part shows itself in a tendency to fall forwards. In this we see both the negative effect caused by the removal of the one centre, and the positive effect exerted by the unopposed and antagonistic centres. In like manner, stimulation of the posterior part of the middle lobe calls into play the muscular adjustments necessary to counteract a backward displacement of the equilibrium ; and hence, as we have seen, destruction of this region mani- fests itself in a tendency to fall backwards. The lateral lobes of the cerebellum contain centres for complex adjustments against lateral, combined with diagonal and rotatory displacements to the opposite side ; and hence, as has been found by experiment, lesions of the lateral lobes exhibit themselves in disturbances of the equilibrium, either laterally, to the side opposite the lesion, or as the resultant of lateral and rotatory displacement in rolling over to the side of lesion. The effects of lesion of the lateral lobes may there- fore vary— a fact which may account for some of the discre- pancies among the results obtained by different experimenters* § 14. Every form of active muscular exertion necessitates the simultaneous co-operation of an immense assemblage of synergic movements throughout the body to secure steadiness and maintain the general equilibrium ; and on the hypothesis that the cerebellum is the centre of these unconscious adjust- ments we should expect the cerebellum to be developed in proportion to the variety and complexity of the motor activities of which the animal is capable. The facts of comparative anatomy and development are entirely in harmony with this hypothesis. In the reptilia and amphibia, whose movements are grovelling , and sluggish, or of the simplest combination, the cerebellum is of the most rudimentary character ; while in mammals it is richly lamin^d, and the lateral lobes highly developed in proportion to the motor capabilities repre- sented in the motor zone of the cerebral hemispheres. RELATIVE DEVELOPMENT OF THE CEBEBELLUM 201 If we compare the relative development of the cerebellum in the several orders of the same class of animals we find it highest in those which have the most active and varied motor capacities, irrespective of the grade of organisation otherwise ; ' a,nd the cerebellum of the adult is, relatively to the cerebrum, much more highly developed than that of the new-born infant ■ — a relation which evidently coincides with the growth and development of the muscular system. § 15. The mechanism of cerebellar co-ordination is essen- tially independent of consciousness and volition, and is an example of responsive or aesthetiko-kinetic action. But while we may theoretically in all animals, and practically in many, abolish consciousness and volition by removal of the cerebral hemispheres, and still leave the mechanism of equilibration intact, yet in the normal state cerebellar activity is associated With that of the hemispheres ; an association which serves to explain many of the facts which might seem to oppose the view we have taken of the functions of the cerebellum as a whole and of its individual parts. The displacement of equilibrium in any direction not only 1 ' If, on the other hand, we compare the cyclostome and plagiostome cartilaginous fishes, in reference to their modes and powers of locomotion, we shall find a contrast which directly accords with that in their cerebellar development. The myxine commonly passes its life as the internal parasite ,of some higher organised fish; the lamprey adheres by its suctorial mouth to a stone, and seldom moves far from its place : neither fish possesses pectoral or ventral fins. The shark, on the contrary-, unaided by an air-bladder, sustains itself at the surface of the sea by vigorous muscular exertion of well-developed pectoral and caudal fins, soars, as it were, in the upper regions of the atmo- sphere, is proverbial for the rapidity of its course, and subsists, like the eagle, by pursuing and devouring a living prey ; it is the fish in which the instru- ments of voluntary motion are best developed, and in which the cerebellum presents its largest size and most complex structure. And this structure cannot be the mere concomitant of a general advance of the organisation to a higher type, for the sluggish rays that grovel at the bottom, though they copulate, and have in most other respects the same grade and type of structure as the more active squaloid plagiostomes, yet have a much smaller cere- bellum, with a mere crucial indentation instead of transverse lamina. . . . Finally, amongst the normal osseous fishes, the largest and highest organised cerebellum has been found in the tuafcy, whose muscular system approaches,' in some of its physical characters, most nearly to that of the warm-blooded classes.'— Owen, Comparative Anatomy and Physiology of the Vertebrates, vol. i. p. 287 et seq. 202 FUNCTIONS OF THE CEBEBELLUM calls into play by reflex or responsive action the compensa- tory motor adjustments, but also induces conscious or volun- tary efforts of a similar antagonistic or compensatory nature. Thus a tendency to fall forwards, while reflexly calling into action the muscular combinations which pull' the body back- wards, may also excite consciousness and cause voluntary effort in the same direction. The same muscular adjustments which are capable of being effected by the cerebellum are also under the control of the will, and may be carried out by the cerebral hemispheres independently of the cerebellum. Hence it is that lesions of the cerebellum, while interfering with the mechanical adjustments against disturbance of the bodily equilibrium, do not cause paralysis of voluntary motion of the muscles which are concerned in these actions. This is an exceedingly important fact, which, though disputed by some, seems to be established experimentally beyond all question. During the wildest reeling and tumbling of pigeons and other animals, in which the cerebellum has been destroyed, there is no sign of muscular paralysis or diminution of the energy of muscular contractions ; and I have carefully investigated the condition of the muscular system in monkeys, in which lesion of the cerebellum had caused such disorders of the equilibrium that locomotion was impossible, and have found that voluntary movements of the head, trunk, and limbs were freely carried out in the recumbent position. The facts on which the state- ment has been founded that lesions of the cerebellum produce paralysis of motion on the opposite side of the body are susceptible of quite a different interpretation. It has been ob- served that tumours, or apoplectic extravasations into one half of the cerebellum, frequently coincide with hemiplegia of the opposite side of the body. But in these cases, as Vulpian has rightly indicated, the hemiplegia is not the result of the cerebellar lesion as such, but of compression or interference with the subjacent tracts of the pons and medulla. As these decussate in the medulla oblongata, the effect of compression by a tumour of the lateral lobe of the cerebellum is paralysis on the opposite side' of the body* Lesions of the cerebellum which do not exert such an in- fluence on the subjacent tracts do not cause hemiplegia on BECOVEBY FBOM CEBEBELLAB LESIONS 203 the opposite side. The lateral lobe co-ordinates muscular adjustments mainly on the same side of the body, but as these are called into action by reflex stimulation, it is only this form of co-ordination which is suspended by lesions of the cere- bellum ; a condition, however, which is essentially distinct from paralysis of voluntary motion. The effect, whatever name it may be best designated by, is direct and not crossed. In terming the effect of cerebellar lesion a paralysis of reflex adjustment I do not thereby imply a paralysis of reflex action. This, which would result from spinal lesion, must necessarily coincide with paralysis of voluntary motion, as the path from the hemispheres would thereby be interrupted. What is implied is that the same combinations of muscular action which are co-ordinated in the cerebellum for the main- tenance of the equilibrium are capable of being called into voluntary action by the cerebral hemispheres. Hence, though lesions of the cerebellum destroy the self-adjusting co-ordina- tion of muscular combinations necessary to maintain the equilibrium, they do not cause paralysis of voluntary motion in the same muscles. So, conversely, by removal of the cere- bral hemispheres we cause paralysis of voluntary motion, but do not affect the independent mechanism of cerebellar co- ordination. When we make this necessary distinction we are enabled to understand how limited lesions of the cerebellum may produce only transient effects, and how even complete destruction of the cerebellum may ultimately be recovered from. § 16. The disturbance of equilibrium is always most marked immediately after the infliction of injury to the cerebellum. This, which has been by many looked upon as a sign of irrita- tion, is to be accounted for by the sudden derangement of the self-adjusting mechanism on which the maintenance of the equilibrium mainly depends. As, however, the animal may supplement the loss of this mechanism by conscious effort, in process of time it acquires the power of voluntary adapta- tion, and thus is enabled to maintain its equilibrium, though perhaps with a less degree of security than before. The more extensive the lesion, the greater the disturbance of the mechanism, and the greater the difficulty of effecting 204 FUNCTIONS OF THE CEREBELLUM through conscious effort all the muscular adjustments neces- sary to 'maintain the balance. The disturbances of equilibrium are therefore of a more enduring character, and it is only by a long process of training that volitional acquisition can replace a mechanism essentially independent of consciousness. Even should this point be reached, the constant attention necessary to preserve steadiness of movement, and prevent displacement of equilibrium, would be a heavy strain on the animal's powers ; and it would be in accordance with this condition that pro- longed or varied muscular exertion should cause great apparent exhaustion. Such, in fact, was observed by Weir Mitchell l to be the case in some pigeons in which he had inflicted con- siderable injuries on the cerebellum. In one of these, four months after the operation, no other abnormality could be detected except that when pursued about the room it gave out sooner than its fellows, and often quite suddenly. The last sign of awkwardness was a certain want of power to direct its beak. % A similar feebleness and incapacity for prolonged exertion was observed by Luciani in the dogs which have been referred to above (p. 178). But these facts do not necessitate the hypothesis originally advocated by Luys, and supported by Weir Mitchell and Lu- ciani, that the cerebellum is a reservoir of energy for the rein- forcement of movements throughout the economy. There is no diminution in the force of muscular contractions after cerebellar lesions. By sparing higher centres the cerebellum may in one sense be regarded as a source of energy, but the real cause of the apparent fatigue exhibited by animals after cerebellar lesions is the fact that all their motor adjustments, formerly easy and automatic, are now performed under a laborious sense of strained attention and conscious effort. The cerebral hemispheres have to perform the work formerly done by the cerebellum, and there can be little doubt that the removal also of the cerebral hemispheres would render the animal absolutely helpless. This is in a measure verified by the condition of Luciani's dog in which the sigmoid gyri were also destroyed (p. 179). 1 Amer. Joum. Med. Set., 1869. AFFEBENT BEL AT ION 8 OF THE CEBEBELLUM 205 A similar mode of explanation is applicable to those cases of atrophy or disease of the cerebellum which have run a latent, or almost latent, course during life. A congenital defect, or slowly progressive lesion, would be the most favour- able condition for the supplementation by conscious effort of a self-adaptive mechanism which is more or less entirely wanting, or gradually undergoing degeneration. But congeni- tal defects or lesions in early life have been found associated with very tardy acquisition of stability of locomotion, and it is questionable whether in man perfect substitution is possible, a want of precision and energy, and a continual tendency to reel or fall being generally observable. § 17. In a previous chapter (Chapter IV.) the maintenance of equilibrium waa shown to be an example of adaptive or responsive action depending on the co-ordination, in some central organ, of certain afferent impressions with the requisite motor adjustments. The afferent factors of this mechanism were found to be mainly of three kinds; viz. tactile, visual, and labyrinthine impressions ; and it was seen that marked disturbances of equilibrium resulted from perversion or inter- ference with any part of this afferent system. The foregoing experiments on the cerebellum justify the conclusion that the cerebellum is the great central organ of this co-ordination. This view is further confirmed by a comparison of the disturb- ances of equilibrium, consequent on lesions of the cerebellum, with those resulting from morbid affections of the afferent apparatus, as well as by a consideration of the anatomical relations of the cerebellum itself. The afferent impressions conveyed to and calling forth the action of the cerebellar centres were regarded as physical in contradistinction to psychical modifications; and though under normal conditions these may be coincident with modifications of consciousness, consciousness 'is neither essential nor is it a correlative of cerebellar action as such. We should not expect, therefore, that lesions of the cere- bellum would cause any affection or paralysis of either tactile, visual, or auditory sensation, properly so called, even though a direct connection of these nerves with the cerebellum should be anatomically demonstrated. 206 FUNCTIONS OF THE CEBEBELLUM The cerebellum was regarded by many of the older writers as the seat of common sensibility. This opinion was founded chiefly on the continuity of the posterior columns of the spinal cord with the restiform tracts or inferior peduncles of the cerebellum. That the restiform bodies are mediately related with the posterior columns, through the olivary bodies, has been established by the researches of Meynert and other anatomists, the relation being mainly cross, i.e. the restiform body on the one side being related to the opposite posterior column. The posterior columns being regarded as the path of com- mon or tactile sensation, the opinion that the cerebellum was the seat of common sensibility seemed well founded. But we have seen that the more recent investigations into the sensory paths of the spinal cord do not support this view of the func- tions of the posterior columns ; for tactile sensibility is cer- tainly not abolished by section of these tracts (see Chap. II. § 6). Brown- Sequard has also shown by direct experiment that section of the restiform bodies does not cause loss of tactile sensation. These facts, in conjunction with the results of experimental lesions and disease of the cerebellum, afford overwhelming evidence against the view that the cerebellum is the seat of common sensation. Neither Flourens, Vulpian, Luciani, nor other recent experimenters have ever observed cutaneous anesthesia in animals deprived of their cerebellum, nor have I in monkey? or human beings observed any indica- tions of cutaneous anaesthesia after extensive lesions or disease of this organ. Lussana l endeavours to show that cerebellar inco-ordina- tion is due to loss of the muscular sense. But this is a pure assumption, and he supplies no tangible evidence of the actual impairment of this so-called sense. It is extremely difficult to test the muscular sense in the lower animals, but I have observed monkeys which, owing to lesion of the cerebellum, were unable to maintain their equilibrium handle and grasp objects with as great precision and firmness as before. The best evidence on this head is furnished by the facts of disease 1 ' Sur les Fonctions du Cervelet,' Journ. de la Physiologie, tome v. 1862, and tome vi. 1863. BELATIONS TO COMMON SEN80BY TBACTS 207 in man, and these prove beyond all doubt that the muscular sense may be entirely unaffected in cases in which the charac- teristic titubation is most pronounced. These considerations, however, though sufficient to dispose of the view that sensation proper in any of its forms is affected by cerebellar lesions, by no means oppose the view that through the restiform bodies and their connections with the posterior columns of the spinal cord the cerebellum is brought into re- lation with certain centripetal impressions, which with others serve to call forth the muscular adjustments requisite for equilibration. As a matter of fact, injuries of the restiform tracts induce the most turbulent disorders, similar to those caused by lesion of the semicircular canals. 1 Whether this is due to lesion of the root of the vestibular nerve which joins the restiform tract, or to injury of other afferent tracts, or to both, is not easy to determine. But the experiments of Bechterew 2 on the olivary bodies show that lesions of these structures induce also disturbances of equilibrium, with rolling or manege, forced movements, and deviation of the optic axes similar to those caused by lesion of the middle cerebellar peduncles. These facts render it probable that it is through the medium of the olivary bodies that the impressions con- veyed by the posterior columns of the cord ascend to the cerebellum through the restiform tracts, and that it is the interruption of these connections which lead to the disorders of equilibrium which ensue. The restiform bodies are also related, as has been already described (Chapter I. § 5) to the direct cerebellar tracts derived from the cells of Clarke's vesicular column, and the portion of the spinal roots which enter them. What is the true function of these centripetal tracts has not been definitely determined, and we can only speculate on the subject (see below, p. 218). But that it is through the restiform tracts that the tactile impressions are conveyed, which form such an important factor in the con- sensus of afferent impressions which excite and regulate cere- bellar co-ordination, seems to be fairly well established. 1 Laborde, Comptes Bendus de la Soctiti de Biologie, June 1882. 2 Ueber den Olivenktirper der Med. Oblong. Wratsch, 1882, No. 35. Abstract in Neurolog. Centralbl., Dec. 1, 1882. 208 FUNCTIONS OF THE CEBEBELLUM § 18. Another important factor in the mechanism is the connection between the auditory nerve, or a portion of it, and the cerebellum. A division of the auditory nerve, the anterior, which is in especial relation with the ampullae of the semi- circular canals, appears to ascend directly into the cerebellum by the restiform tract, and is considered by some anatomists also to have connections with a nucleus (Deiter's nucleus) situated in the restiform tract, and through this indirectly with the cerebellum. But, as has been seen, this connection cannot be looked upon as at all satisfactorily established. The central connections of the auditory nerve are still obscure, but there can be no doubt that certain of the fibres ascend directly to the cerebrum without entering the cerebellum. Meynert's view, that the whole of the roots of the auditory nerve pa3S into the cerebellum in the first instance, and only indirectly into the cerebrum, possibly through the valve of Vieussens or superior peduncles, is clearly untenable. Lesions of the cerebellum do not impair the sense of hearing in animals, nor do diseases of the cerebellum in man cause deafness, except in such cases as lead to direct implication, by pressure or the like, on the auditory nerves themselves. We have already seen, however, the enormous influence exercised by the semicircular canals on the faculty of equili- bration, and we have the anatomical foundation of this rela- tion in the connection which exists between the labyrinth and the cerebellum. There is further a remarkable and significant similarity between lesion of the individual semicircular canals and injury of certain regions of the cerebellum, and also between direct irritation of the canals and electrical irritation of different portions of the cerebellar cortex. It has been seen that section of the superior vertical canals causes displacement of equilibrium forwards, or diagonally round a horizontal axis — an effect which corresponds with lesion of the anterior part of the middle lobe of the cerebel- lum. Section of the posterior vertical canals causes a ten- dency to fall backwards or describe a somersault backwards round a horizontal axis — an effect which corresponds with injury of the posterior part of the median lobe. Section of the horizontal canals causes lateral or rotatory displacements BELATIONS TO TEE LABYBINTE 209 round a vertical axis — an effect which corresponds with injury of the lateral lobes. The experiments of Mach and Crum-Brown already re- ferred to (Chapter IV. § 14) show that rotation backwards round a horizontal axis is calculated to cause irritation of the nerve- endings in the ampullae of the superior vertical canals, perhaps by increased tension, or otolithic vibration, in these rela- tively to that in the opposed posterior vertical canals. Eota- tion forwards round a horizontal axis causes a reversal of these conditions, leading to increased irritation of the posterior vertical as compared with the superior vertical canals. Eota- tion round a vertical axis causes increased tension or irritation of the ampullary nerves of the horizontal canal on the side from which the rotation takes place. From previous considerations we may assume that the ampullary irritation acts as the stimulus to the motor adjust- ments calculated to oppose the displacement of the equilibrium in the direction which coincides with this irritation. As- suming the seat of irritation to be correctly indicated by Crum-Brown, we should regard the superior vertical canal as the afferent of the posterior cerebellar centres, the posterior vertical canal as the afferent of the anterior cerebellar centres, and the horizontal canal as the afferent of the corresponding lateral centres. If these conclusions are well founded, we should expect that carefully localised irritation of the several ampullae should excite movements of the eyes, head, and trunk, harmonising with those resulting from direct irritation of the correlated cerebellar regions. § 19. As a matter of fact, the experiments of Cyon, Hogyes, and others on animals, and the results of irritation of the labyrinth in man, strongly confirm the above hypothesis both generally and in detail. Localised irritation of the individual canals is, however, surrounded with numerous difficulties, and especially electrical irritation, on account of the complications induced by extrapolar diffusion. But apart from the possible complications caused by the operative procedure, no valid objection can be made against the experiments of Cyon and Hogyes, in which the canals were irritated by the slight touch of as ponge or a bristle. In a memoir presented to the p 210 FUNCTIONS OF TBE CEREBELLUM Academie des Sciences in 1877 ' Cyon described a series of ocular movements and oscillations which he observed on mechanical irritation of the semicircular canals in rabbits. The great feature of these ocular movements was that the direction was determined by the canal irritated. ' Each semi- circular canal has a special influence on the ocular movements. Excitation of the horizontal canal in the rabbit produces a rotation of the eye on the same side in such a manner that the pupil becomes directed backwards and downwards ; excita- tion of the posterior vertical canal causes a deviation of the eye so that the pupil looks forwards and slightly upwards ; while irritation of the superior vertical canal causes a deviation backwards and downwards. The excitation of each canal always causes movements of both eyes, but the movements of the opposite eye are contrary to those of the side irritated. The pupil contracts on the side irritated and becomes dilated on the opposite. Cyon, however, in his thesis 2 makes some modification of his statements as to the direction of the ocular movements, particularly as regards those depending on irritation of the horizontal and posterior vertical canals. Irritation of the horizontal canal, he says, causes the globe to be directed forwards and downwards ; of the posterior vertical canal, backwards and upwards ; and of the superior vertical canal, backwards and downwards. In the other eye the direction is contrary, viz. backwards and upwards, forwards and down- wards, and forwards and upwards, on irritation of the hori- zontal, posterior, and superior vertical canal respectively. This discrepancy is doubtless due to the fact that the nystag- mus which comes on after the first deviation, which is almost tetanic in character, is apt to mix itself up with the direct effects of irritation, and to reverse the really primary move- ment. The results first obtained by Cyon seem to me more in accordance with other facts than his later ones. Hogyes 3 finds that touching the horizontal canal or ampulla, causes the eyes to turn to the same side, and induces nystagmus in the same plane. With the nystagmus are 1 ' Les Organes PSripheriques du Sens de l'Espaoe,' Comptes Rendus, 1877. 2 Thfese : Sur les Fonctions des Canaux Semkirculaires, 1878. s Op. cit. BELATIONS TO THE LABYBINTH 211 associated also movements of the head and body. Irritation of the left vestibular nerve generally causes the eye of the same side to move upwards and outwards, and rotate inwards ; while the opposite eye moves downwards and inwards, and rotates outwards. Irritation of the right vestibular nerve exactly reverses these movements in the two eyes. Spamer's experiments with faradic and galvanic stimulation possess so little uniformity that the methods must be regarded as un- satisfactory. Of a similar nature to the irritation induced by actual touching of the canals is that observed in man by the injection of air or liquids into the ear in cases of rupture of the mem- brana tympani. In a case of this kind Lucae ' observed that injection into the left ear caused the eyes to turn to the left, accompanied by a subjective appearance of objects moving suddenly to the right and a feeling of vertigo ; while injection into the right ear exactly reversed the phenomena. § 20. The results of direct irritation of the semicircular canals, though in some respects in need of revision, and perhaps modification, are essentially similar to those of direct irritation of the cerebellum itself in different regions. The predominant direction of the ocular and other movements is in some axis inclining to the side of irritation. Under normal conditions there would appear to be a balance of opposing forces, so that overaction in any one direction is calculated to call into play the antagonistic adjustment. Hence the primary ocular deviation is always followed by a reflux oscillation in the reverse direction. Should, however, the one limb of the mechanism act in excess of the other, either as the result of abnormal irritation of the ampulla or the correlated cerebellar centre, or as the result of destructive lesion of the same parts, the balance will be overthrown in the direction of the pre- dominant or unopposed force. But the direction of the over- throw in cases of irritation ought to be exactly the reverse of that in cases where the lesion is purely destructive. In ex- perimental lesions both factors may be at work and not easily separable, but we need not assume, as some have done, that the effects of lesion of the semicircular canals are only phe- 1 Archiv f. Ohrenheilkunde, Bd. vii. Heft iv. 1881. v 2 212 FUNCTIONS OF THE CEBEBELLUM nomena of irritation. The tendency in simple and uncom- plicated irritation seems to be overthrow of the balance towards the side of irritation, or in some axis inclining in this direction. This frequently occurs in Meniere's disease, in which there seems to occur paroxysmal irritation of the semicircular cauals, accompanied by hissing or ringing in the affected ear and a distressing sense of vertigo. But the direction in which the balance is overthrown is not always towards the side of irrita- tion, for I have observed it in several patients clearly towards the opposite side. This is probably due to over- compensation. The sense of falling to one side causes active volitional effort on the part of the individual, so that he falls in reality towards the opposite side. It is the presence of the hemispheres, and the intervention of conscious and volitional efforts, which complicate all the properly reflex phenomena of cerebellar adjustments. Hence it is that irritation of one side of the cerebellum causes the feeling of rotation towards, or loss of support on the other side, because, as the action which is called forth is in reality the adjustment to counteract such displacement, the two become indissolubly associated in con- sciousness, and the one effect invariably calls up the other. The feeling of loss of support on the opposite side of the body may be regarded as analogous to the apparent vanishing of objects in the same direction. When the various factors concerned in the mechanism of equilibration appear out of harmony, or contradictory to each other, a distressing sense of insecurity and faintness is the inevitable result. This is merely the psychical side of motor disturbances, which, apart from the cerebral hemispheres, would occur without any such accompaniments. § 21. While the anatomical as well as the physiological connection of the cerebellum with the auditory nerve is suf- ficiently clear, we cannot say the same of the relation between the cerebellum and the eyes. That destruction of the cere- bellum does not affect the sense of sight is amply demonstrated by the experiments of Flourens and other physiologists. Animals in which the cerebellum has been destroyed evidently see and appreciate threats, and endeavour to escape, but their efforts to do so only end in turbulent confusion. The sense RELATIONS TO THE EYES 213 of sight is a function of the cerebral hemispheres. Blindness does not occur in cases of atrophy of the cerebellum in man, but it is not an infrequent result of tumours situated in the cerebellum, as elsewhere. Loss of vision from intracranial tumours is caused by the secondary changes induced in the optic nerves, purely by indirect action, and has no special relation to the situation of the tumour. But, though the cerebellum is not essential to the sense of sight, yet that it has intimate relations with the optic and oculo-motor nerves is shown by the importance of visual impressions in the mechanism of equilibration, and by the relation between oculo-motor and general motor adjustments, which has been demonstrated by the above recorded experiments. We have yet much to learn respecting the constitution and connections of the superior cerebellar peduncles and valve of Vieussens, and respecting the relations between the red nuclei and the optic and oculo-motor nerves. That we have in these ana- tomical connections between the cerebellum and the eyes is, on many grounds, highly probable. The superior cerebellar peduncles, as has been seen (Chapter I. § 7), decussate into the red nuclei, but their further relations are highly obscure. A case of great importance in this relation has recently been carefully examined and put on record by Mendel. 1 In this case there was, apparently in consequence of primary lesion (a hemorrhagic focus) in the pulvinar of the left optic thalamus, atrophy of the left red nucleus, and a tract of secondary degeneration in the right superior cerebellar peduncle, trace- able as far as the nucleus dentatus. Mendel suggests, with great probability, that this may be the medium of communi- cation of optical impressions with the centres of equilibration. By the decussation of the superior peduncles the optic tracts would thus be in cross relation with the cerebellar hemispheres, and, owing to the decussation in the optic chiasma, the eyes would be mainly in direct relation with them. This would be in harmony with the fact observed on electrical irritation of the cerebellum, viz. that the pupil on the same side became contracted. Lesions of the superior peduncles of the cerebellum, as 1 ' Secondare Degeneration im Bindearm,' Neurolog. Centralb., No. 11, 1882. 214 FUNCTIONS OF TEE CEREBELLUM well as of the structures with which they are in relation, produce marked disturbances of equilibrium, for such disturb- ances must necessarily ensue upon lesions of any part of the mechanism, whether central, afferent, or efferent. Lesions of the optic lobes, or of the connections between the optic or oculo-motor nerves, would naturally have this effect. To interruption of the connections of the superior peduncles, or to direct injury of the oculo-motor nuclei, or both, are doubtless due the very marked disorders of equilibrium observed by Bechterew 1 in connection with lesions of the walls of the third ventricle and neighbourhood of the aque- duct of Sylvius ; disorders which have all the characters of those which result from lesions of the semicircular canals or olivary bodies of the medulla oblongata. § 22. Whether in the' inferior and superior peduncles there are efferent as well as afferent cerebellar tracts is a question on which we have little or no definite information. I have found both in rabbits and in monkeys that electrical irritation of the restiform tract causes movements of the head, trunk, and limbs, with a tendency to pleurosthotonus on the same side. These might be merely reflex phenomena, but the fact that, after deep transverse section, irritation of the part below the cut produces precisely the same action as before, while irritation above the cut is absolutely negative, rather favours the idea that the restiform body may contain efferent motor tracts. But the question is one which requires further in- vestigation. Bespecting the superior peduncles it is stated by Albertoni and Michieli 2 that electrical irritation or puncture causes pleurosthotonus towards the side opposite the irrita- tion. They are disposed to regard these phenomena as direct rather than reflex on the ground that they occur when the sensibility has been entirely exhausted. 1 ' Die Function der eentralen grauen Substanz des dritten Hirnventrikels,' Pfliiger's Archiv f. Physiologie, Bd. xxxi. July 1883. — The hypothesis advanced by Bechterew, that the grey matter of the -walls of the third ventricle acts- as a peripheral organ to the centres of equilibration — similar to the semicircular canals — impressions in which are conditioned by varying degrees of pressure of the contained cerebro-spinal fluid caused by movements of the head and of the eyeballs, has at least the merit of originality. « ' Sui Centri Cerebrali di Movimento,' Lo Sperimentale, 1876. EFFERENT RELATIONS OF TEE CEREBELLUM 215 § 23. The middle peduncles of the cerebellum form the great medium of connection between the lateral lobes of the cerebellum and the pyramidal motor tracts. These peduncles, I as has been shown by Meynert, decussate in the pons and! enter into intimate relations with the opposite pyramidal tracts) through the cells of the nucleus pontis. A direct connection between the peduncular and pyramidal tracts is doubtful.! The cross relations between the peduncular and pyramidal^ tracts in the pons bring the lateral lobes of the cerebellum in relation with the motor tracts on the same side, owing to the / decussation of the pyramidal tracts at the lower aspect of the medulla oblongata. These anatomical facts are in harmony with the effects of electrical irritation of the cerebellum, by which, as has been seen, movements are excited on the same side of the body. The functional relationship to the two sides of the body is therefore cross in the case of the cerebral hemi- spheres and direct in the case of the cerebellar lobes ; and thus each cerebral hemisphere acts in combination with the opposite cerebellar lobe. That this is so, and that the cerebellum acts in subordination to the cerebrum, is shown by the fact that in many cases of long-standing disease of one cerebral hemisphere, atrophy ensues in the opposite lobe of the cerebellum. In a case of this kind which I have recorded ' there was marked atrophy of the right lobe of the cerebellum consecutive to destruction of the anterior or motor region of the left hemi- sphere (figs. 64 and 65). The pyramidal tract of the left side had undergone second- ary degeneration, and, with it, the right middle peduncle and right lobe of the cerebellum had become greatly re- duced. An examination of the cortex of the right lobe of the cere- bellum proved also that this had undergone extreme degenera- 1 'Brain of a Criminal Lunatic,' Brain, April 1882.— The patient was a woman who, after the age of thirty, became suddenly aphasic and hemiplegic on the right side. She became insane, murdered her two children, and was committed to Broadmoor Asylum, where she died twelve years after the occur- rence of the paralysis. The whole of the cortex in the region indicated in the figure, together with the corpus striatum, had entirely disappeared, and been converted into a cyst full of fluid. For further details reference may be made to the original paper cited. 210 FUNCTIONS OF THE CEREBELLUM tion, and that the cells of Purkinje had in many parts entirely disappeared (fig. 66, b). Pig. 64.- Side view of Brain, in which the anterior half of the left hemisphere hart 'become atrophied in consequence of disease, c, upper extremity of the fissure of Rolando of right hemisphere, p, interparietal fissure, s'. extremity of horizontal limb oi fissure of Sylvius, oc, parietooccipital fissure. Fui. 65. —Under Surface of same Brain (Fig. 64). showing Atrophy of the right lobe of the Cerebellum. § 24. It is a question whether, along with tactile or common sensory, visual, and labyrinthine impressions, other sensory RELATIONS TO THE CEBEBBUM 217 impressions are correlated in the cerebellum with the motor adjustments necessary for stability and equilibration. On a former occasion ' I ventured to suggest that possibly visceral Pig. 66.— a, Section of a Leaflet of the left lobe of the Cerebellum (normal), b, Section of a Leaflet of the right lobe, showing disappearance of Purkinje's cells and atrophy of the granular layer. (Prom preparations and drawings by J. A. Scott.) or organic sensory impressions were represented in the cere- bellum, mainly on the ground of the very intimate mutual 1 First edition of this work, § 26. 218 FUNCTIONS OF THE CEBEBELLUM reactions between states of the viscera and the exercise of equi- libration. I instanced among other things the very pronounced disturbances of equilibrium and vertiginous sensations which are experienced in connection with certain visceral derange- ments, and the influence which mechanical displacement of the viscera, such as occurs in the rising and falling of a vessel at sea, seems to have in the production of sea-sickness. The almost invariable expression of vertigo in a .peculiarly distress- ing sensation in the region of the epigastrium, with or without actual nausea or vomiting, shows that there is a very close relation between the centres of equilibration and the organic sensibilities. In connection with these speculations it is per- missible to suggest that the direct cerebellar tracts may form the afferent paths between the viscera and the cerebellum. These tracts, as has been seen, connect the cells of Clarke's vesicular columns with certain cortical cerebellar regions. These columns exist almost exclusively in the dorsal region of the cord, and are absent from those regions — the lumbar and cervical enlargements — which are specially related to the animal powers and sensibilities. Eoss's ' suggestion that they are therefore specially concerned in visceral innervation has much probability, and this is further supported by the homo- logy which he traees between Clarke's columns and those which give origin to the accessorio-vagus. 2 The hypothesis that the cerebellum presides over the func- tions of organic life was first propounded by Willis, and was founded mainly on false anatomical views as to the origin and connections of the pneumogastric nerve. There is, indeed, little or no evidence that the cerebellum is essential to the due performance of the functions of organic or vegetative life. 1 Diseases of the Nervous System, 1881. 2 These speculations have been amply confirmed by the researches of Gaskell, previously referred to (Chap. III., p . 103, note), which have shown that the appearance of the cells of Clarke's vesicular column ooinoid.es with that of the fine medullated nerves which constitute the visceral spinal system. 'Although as yet the fine medullated fibreB which constitute the rami vis- cerales have not been directly traced into the cells of the columns vesiculares, the connection of these fibres with this column of cells is, to my mind, proved conclusively by the fact that the cells of Clarke's column are confined to those regions of the central nervous system which give origin to the rami viscerales.' — Gaskell, op. cit. p. 56. VISCEBAL BELATIONS OF THE CEBEBELLUM 219 Willis's hypothesis has been, however, revived by Luciani 1 on what appear to be most slender and unsatisfactory grounds. In one of the dogs before mentioned (p. 178), from which he had removed the greater portion of the cerebellum, general malnutrition and marasmus occurred in the later months of its survival. But as the animal had attained a state of good health and nutrition after the primary effects of the operation had subsided, and as coincident with the marasmus and mal- nutrition there were signs of purulent otitis and catarrhal conjunctivitis, it is much more likely that the marasmus was caused by the suppuration and its attendant constitutional disturbance, than that any of these effects depended on the destruction of the cerebellum as such. The condition of the second dog at the end of a much longer period of survival is quite sufficient to dispose of Luciani's hypothesis, founded as it was on the results only of the first experiment. In the second animal the state as regards nutrition was altogether excellent. The committee of investigation reported : ' The weight was 4*900 grams ; the body was well nourished, and the adipose tissue was abundant.' Notwithstanding the large amount of research that has been expended on the cerebellum there are many points in its anatomy and physiology on which we are as yet devoid of precise information, and the opinion of Vulpian, writing in 1866 — ' that the problem of the functions of the cerebellum is still far from being definitely solved ' — will still apply to the present state of our knowledge. But, though the exact formula of cerebellar function may yet have to be found, the effects of injury and disease of this organ have been fairly well ascer- tained ; and these show that the functions of the cerebellum I are outside the sphere of mind proper, as expressed in sensa- 1| tion, emotion, volition, and intellect. 1 Fisiologia del Cervelletto, 1884. 220 CHAPTEE VII. FUNCTIONS OF THE CEBEBRUM. Introductory — Method of Investigation. § 1. In the preceding chapters we have seen that, notwith- standing the complete removal of the cerebral hemispheres, animals, in proportion to their lowness in the scale, still remain capable of a great variety of most complex and adaptive forms of activity, little if at all differing in character from those .prompted by intelligence. On more detailed investigation of these forms of activity, however, the conclusion was arrived^at that they were nothing more than responsive actions called into play, through the primary or acquired organisation of the nerve centres, by certain forms of peripherical stimulation, independ- ently of any intelligent adaptation of means to ends on the part of the animal itself. From the facts of human physiology and pathology, by which alone the question can be answered, it was concluded that consciousness was inseparable from the activity of the cerebral hemispheres, and that, therefore, however much the responsive actions of the lower ganglia might resemble con- scious actions, they did not come within the sphere of truly psychical phenomena. The destruction of the cerebral hemispheres, by annihilating sensation, ideation, volition, and intelligence in general, reduces the animal to the condition of a complex machine, the activity of which is the immediate or direct result of certain forms of ' ento-' or ' epi-peripherical ' stimulation. But though the functions of" the cerebrum have thus been negatively indicated, the whole mechanism of cerebral activity still remains to be investigated. Though it is by means of the cerebrum that we feel and think and will, the question is whether, by physiological or pathological investigation, we can FLOURENS' VIEWS 221 throw a light on psychological manifestations ; whether the cere- brum, as a whole and in each and every part, contains within itself, in some mysterious manner inexplicable by experimental research, the possibilities of every variety of mental activity, or whether certain parts of the brain have determinate functions. Up to a comparatively recent date, if we except the cum- brous cross-divisions and fanciful localisation of ' faculties ' of the phrenological system, the results of experimental physio- logy and human pathology had been considered as opposed to the localisation of special functions in distinct regions of the cerebral hemispheres. The experiments of Flourens, the great pioneer in cerebral physiology, led him to the following conclusions with regard to the question of localisation of function : — ' Ainsi 1°, on peut retrancher, soit par devant, soit par derriere, soit par en haut, soit par le cote, une portion assez etendue des lobes cerebraux, sans que leurs fonctions soient perdues. Une portion assez restrainte de ces lobes suffit done a Vexercice de leurs fonctions. ' 2°. A mesure que ce retranchement s'opere, toutes les fonctions s'affaiblissent et s'eteignent graduellement ; et passe certaines limites, elles sont tout-a-fait eteintes. Les lobes cerebraux concourent done par tout leur ensemble a l'exercice plein et entier de leurs fonctions. ' 3°. Enfin, des qu'une perception est perdue, toutes le sont; des qu'une faculte disparait, toutes disparaissent. II n'y a done point de sieges divers ni pour les diverses facultes, ni pour les diverses perceptions. La faculte de percevoir, de juger, de vouloir une chose reside dans le meme lieu que celle d'en percevoir, d'en juger, d'en vouloir une autre ; et conse- quemment cette faculte, essentiellement une, reside essentielle- ment dans un seule organe.' ' The doctrines of Flourens met with very general acceptance as being in accord with at least many well-established facts of clinical medicine, such as the occurrence of extensive disease or injury of brain substance without any appreciable physio- logical or psychological defect. 2 And there are not wanting 1 Systirne Nerveux, 1842, p. 99. 2 On this see the author's Localisation of Cerebral Disease, 1878. 222 FUNCTIONS OF THE CEBEBBUM some, even at the present day, notably Brown- Sequard, 1 who hold that there is no constant relation between the locality of the lesion and the symptoms which may be manifested :— the same lesion causing most diverse symptoms, and the same symptom occurring in connection with the most diverse lesions. But to certain careful observers, Bouillaud, 2 Andral, 3 and others, there were many unquestionable facts of clinical medi- cine, such as limited paralysis in connection with limited cere- bral lesions, which appeared wholly inexplicable except on the hypothesis of a differentiation of function in the cerebral hemispheres. And the, in more recent times, established coincidence of aphasia, or loss of speech, with disease of a certain region in the left hemisphere served still further to render the theory of functional equivalence doubtful ; though what aphasia really meant in physiological terms, or why in practically symmetrical hemispheres a faculty should be local- ised in the one, to the exclusion of the other, remained a matter of mystery and dispute. § 2. Hughlings Jackson, from a minute and careful study of the phenomena of unilateral and limited epileptiform convul- sions, arrived at the conclusion that they were due to irritation, or discharge, of certain convolutions of the opposite cerebral hemisphere functionally related to the corpus striatum and muscular movements. Though he furnished many arguments in favour of his hypothesis, since verified, his views were regarded merely as ingenious speculations, and devoid of any actual proof that the grey matter of the convolutions was really excitable. Experimental physiologists had all failed to obtain evidence of the susceptibility of the cerebral cortex to any of the ordinary stimuli of nerves, mechanical, chemical, thermal, or even electrical. This apparent inexcitability of the cerebral cortex greatly retarded the progress of cerebral physiology. The complementary methods of excitation and destruction, which rendered the study of the functions of the peripheral nervous system a matter of comparative ease, were 1 ' Comptes Eendus de la Societe de Biologie,' 1876 et sea., the Lancet, 1876. 2 Traiti de I'Encephalite, p. 279. ■ Clinique Midicale, tome v. p. 569. EXCITABILITY OF THE CEBEBBAL COBTEX 223 not available in the case of the central nervous system, and the determination of the functions of the hemispheres and of their different parts had to be founded only on the results of vaguely established experimental lesions in the lower animals, or on the complex assemblage of phenomena met with in connection with the fortuitous and indefinite experiments of dise ase in man. Everywhere doubt and discrepancy prevailed. I A new era in cerebral physiology was inaugurated by the discovery by Fritsch and Hitzig in 1870 J that the application of the galvanic current to the surface of the cerebral hemi- sphere in dogs gave rise to movements on the opposite side of the body — movements which varied with the position of the electr odes) Subsequently, 2 in the course of experiments under- taken primarily in order to test the views of Hughlings Jack- son in reference to the causation of unilateral epileptiform convulsions, I verified and extended the facts first indicated by Fritsch and Hitzig. These have led to much repetition, variation, and controversy, and the results have been that the indications furnished by the electrical irritation of the hemi- spheres have so guided and directed experimental and clinical research, that the physiology of the brain has made greater advances during, the last ten years than in all the previous yea rs qf-p hysinlogy and pathology together. ^3. The method principally followed by Fritsch and Hitzig in their researches consisted in applying directly to the surface of the hemispheres, by means of a pair of blunted electrodes, the stimulus of the closing, opening, or commutation of the current of a galvanic pile, of sufficient intensity to cause a distinct sensation when applied to the tip of the tongue^ The method employed by myself was the similar application of the electrodes, of the secondary spiral of Du Bois-Eeymond's in- duction coil, connected with a cell of the mean electro-motive power of 1 Daniell. The resistance in the primary coil was such as to give a current of the maximum of 1*9 absolute unit, as estimated for me by my colleague Professor Adams. The induced current generated in the secondary coil at 8 cm. 1 Eeichert u. Du Bois-Eeymond's Archiv, 1870. 1 'Exp. Besearches in Cereb. Physiology and Pathology,' West Biding Lunatic Asylum Reports, 1873. 224 FUNCTIONS OF THE CEBEBBUM distance from the primary spiral was of a strength sufficient to cause a pungent, but quite bearable, sensation when the electrodes were placed on the tip of the tongue. The measure- ment by the tongue is the most convenient practical test of the intensity of the current, and the best means of regulating the degree of stimulation. In long-continued experiments the failure of battery power may require closer approximation of the secondary to the primary coil, in order to produce the same sensation on the tongue as at first. Owing to my having given the distance of the secondary from the primary alone in the record of my first experiments, without specially calling attention to this circumstance, it has been concluded by Hitzig and others that, in order to produce the effects I have described, I employed currents of enormous intensity, sufficient to cause structural lesions and unlimited conduction to neighbouring and subjacent parts. I have found by repeated experimenta- tion that, with a uniformly acting cell, and the secondary coil at 8 cm., all the effects I have described are easily reproducible. Absolute uniformity, however, cannot be secured, on account of the conditions which modify the excitability of the hemi- spheres. That which will cause intense and indefinite action in an animal non-narcotised, will excite only moderate and definite action in an animal sufficiently narcotised to abolish all sense of pain, and no effect at all on an animal deeply anaesthetised. Other conditions also mentioned by Hitzig, e.g. the state of the circulation in the brain, greatly modify its excitability, hemorrhage lowering it in a marked degree. Considerable differences 'also exist in different animals with respect to the excitability of the hemispheres; and it is only rarely that a complete exploration of the brain can be successfully carried out in any one animal, the excitability of the brain rapidly becoming exhausted during the operations necessary to reach the more concealed and deep-seated regions. The skill with which the operations are made considerably affects the degree of success attainable. In consequence of these various modifying conditions it is impossible to fix any arbitrary standard, founded on the mini- mum strength of current necessary to excite any one part in METHODS OF STIMULATION 225 any given subject of experiment. Various regions of the brain differ in regard to their degree of excitability. A current suf- ficient to cause decided contraction of the orbiculari s oculi w ill frequently fail to produce any movement of the limbsX Byarbi- trarily fixing a standard of stimulation which they thought suf- ficient, Fritsch and Hitzig failed to elicit most important positive results of deep significance in regions of the brain which they choose to call inexcitable. There is no reason to suppose that one part of the brain is excitable and another not. The ques- tion is, how the stimulation manifests itself^ Though it is obviously advisable to use no stronger current than is sufficient to produce a definite result, the measure, of the intensity of the stimulus to he employed in each case is the degree of definite and decided localisation of effects uniformly attainable. It is also necessary to guard against conduction to neighbouring structures, by insulation of the electrodes, and careful removal of the fluid which is apt to collect on the surface. The mean strength I have found to be given by the fixation of the secondary coil at 8 cm., though frequently less and occa- sionally some increase is required. The chief object being to secure efficient stimulation, to call forth in a decided and distinct manner the functional activity of the part to which the electrodes are applied, it would matter little whether we used the galvanic or faradic stimulus, provided they were both equally suitable for this purpose. But this is not the case. Not only a certain intensity, but a certain duration of the stimulus, is necessary to produce the characteristic effect. The closing or opening shock of the galvanic current, applied to the region of the brain, from which movements of the limbs are capable of being excited, causes only a sudden contraction in certain groups of muscles, but fails to call forth the definite purposive combination of muscular contractions, which is the very essence of the reaction, and key to its interpretation. rPrrtsch and Hitzig, in their description of the results of their experiments with the galvanic stimulus, did not, in my opinion, sufficiently define the true character of the move- ments. If the galvanic current is applied for a longer period Q 226 FUNCTIONS OF THE CEBEBBUM than that necessary to cause the momentary closing or opening shock, electrolytic decomposition of the brain substance ensues at the points of contact with the electrodes ; an objection from which the faradic stimulus is entirely free. I have in my possession the brains of monkeys and other animals, on which experimentation by the induced current was maintained for many hours, which, with the exception of some degree of hyperemia consequent on exposure as much as stimulation, are entirely free from structural lesion. The following experiment will show the comparative ef- ficiency of the galvanic and faradic methods of stimulation : — Having exposed the brain of a monkey in the region in which I had previously localised the centre of the biceps, excitation of which causes supination and flexion of the fore- arm, I sought to determine the exact strength of the induced current necessary to produce this definite action, and to com- pare its effect with that of the galvanic current. With the single cell already mentioned, and secondary coil at 13 cm., no result followed ; secondary at 12 cm., likewise without effect ; secondary at 11 cm., slight appearance of out- ward rotation of the wrist ; secondary at 10 cm., faint supi- nation of the hand ; secondary at 9 cm., gentle and slow supination and flexion of the forearm ; secondary at 8 cm., distinct and decided supination and flexion of the forearm, without any complication with other movements. The galvanic current was then employed from six cells (small Smee's elements) of Weiss' battery. During closure of the current no result followed, nor when the current was slowly interrupted. With eight cells and slowly repeated interruption spasmodic and sudden jerks of the hand and forearm were observed, but no definite supination or flexion. With ten cells and slowly repeated interruption similar spas- modic movements were caused ; but only when the current was rapidly closed and opened did the spasmodic jerks be- come converted into the continuous action of supination and flexion of the forearm. To the tongue the sensation communicated by this stimulus was certainly as strong, if not more pungent, than that of the induced current, and at the point of contact of the electrodes CONDUCTION OF ELECTRICAL CURRENTS 227 active electrolytic decomposition and evolution of gas began to manifest itself. This experiment shows that it is not every degree of in- tensity or every degree of duration of stimulus that is sufficient to excite the due activity of the hemispheres, and that the galvanic method of stimulation is in all respects inferior to that of faradisation. It will be seen also that the intensity of current derived from the secondary coil at 8 cm. is not beyond that requisite for the production of distinct and definite reaction. § 4. Though the effects of localised destructive lesions, strictly parallel to those of localised irritation, are of them- selves sufficient to dispose of the objections raised, on the score of diffusion of currents, against the view maintained by Hitzig and myself, that the phenomena of electrical irritation are significant of functional excitation of cortical centres as such, yet an examination of the conditions of electrical irrita- tion alone shows how little weight these objections possess. It has been contended by Dupuy, 1 and others that the movements which are excited by the application of the elec- trodes to the surface of the hemisphere, are in reality due to conduction of the currents to the real motor centres situated at the base of the brain. He argues that it is impossible to localise the action of the electrical current in the region in- cluded within the electrodes, inasmuch as it can be shown that extrapolar conduction extends through the brain sub- stance to a considerable distance. By placing the sciatic nerve of the galvanoscopic frog preparation on the posterior part of the brain, and applying the electrodes to the anterior part of the hemisphere, he found that active contraction of the gastrocnemius muscle resulted, showing that the current had traversed the whole extent of the hemisphere. The same fact of extrapolar diffusion through the brain substance was also demonstrated, and more accurately by Carville and Duret. 2 By placing non-polarisable electrodes on the hemisphere at a distance from the exciting electrodes, and connecting them with a galvanometer, they found that a 1 Examen de Quelques Points de la Physiologie du Cerveau, 1873. 2 Sur les Fonctions des Himispheres C&ribraux, 1875. Q 2 228 FUNCTIONS OF THE CEBEBBUM decided deflection of the needle occurred at the moment of stimulation. Extrapolar conduction through the brain sub- stance is thus proved ; but it is no more than what the ordinary laws of conduction through animal tissues would have led one to expect. This, however, is a very different thing from the conclusion which Dupuy and those who follow him would draw, viz. that it is only to conduction to the basal ganglia that the move- ments in question are due. Mere vague statements as to the supposed result of irritation of the basal ganglia cannot be allowed to weigh against the actual results of irritation directly applied to them. Irritation of the ventricular aspect of the corpus striatum causes general contraction of the muscles of the opposite side of the body; and it is impos- sible by applying the electrodes to the surface of this ganglion to produce differentiated contraction in any one muscle or muscular group. Irritation of the optic thalamus produces no movements of any kind, and irritation of the corpora quadri- gemina produces dilatation of the pupils and a combination of muscular movements of the head, trunk, and limbs, such as has been already described. We know, therefore, by direct experiment, what irritation of the basal ganglia should pro- duce ; but the phenomena of irritation of the cortex are of a very different order. The phenomena of localised and uni- lateral convulsive movements attributed by Hughlings Jackson to vital irritation of certain regions of the cortex are precisely of the same nature as those induced by electrical irritation of the same regions, and, as has been shown by Franck and Pitres, 1 may be induced by mere mechanical stimulation when the cortex is in a state of inflammatory irritability. It would be absurd to suppose that mechanical irritation under such conditions acts only by conduction to the basal ganglia. The great and significant feature of the reactions produced by electrical excitation of the cortex is that they are definite and predictable, 2 and vary with the position of the electrodes. 1 Progris Midical, Jan. 5, 1878. 2 This is unquestionable, and may be made the subject of lecture demon- stration, under the degree of narcotisation necessary to eliminate all spon- taneous movements. The experiences of Couty (' Sur le Cerveau Moteur,' CONDUCTION OF ELECTBICAL CUBBENTS 229 As -will be seen in the following chapter, areas in close proxi- mity to each other, separated by only a few millimetres or less, react to the electrical current in a totally different manner. If there were no functional differentiation of the areas under stimulation the diverse effects would be absolutely incompre- hensible on any theory of mere physical conduction, which would, under the circumstances, be practically to the same point in all eases. Movements of the limbs can only be excited from certain points, all others being ineffective. No current applied to the prefrontal or oecipital regions will cause move- ments of the limbs, and yet physical conduction to supposed motor centres and tracts at the base is just as easy from these points as from the parietal regions, which react invariably and uniformly. The supposition that it is mere conduction to the corpus striatum and motor tracts which accounts for the movements is further absolutely contradicted by the simple experiment of placing the electrodes on the island of Eeil, which immediately overlies the lenticular nucleus. Here we get in nearest proximity to the corpus striatum and internal capsule, and yet no reaction whatever can be induced by currents which are highly effective when applied to the more distant parietal regions. An interesting observation was made by Carville and Duret during their experiments, which affords another among the numerous proofs that electrisation of the cortex does not act merely by conduction to subjacent ganglia or tracts. In a dog on which they were operating they failed to produce movements by the application of even the strongest currents to regions which in other dogs they had uniformly found readily excitable. The cause of this proved on examination to be the existence of a large cavity, filled with fluid, occupying the medullary substance of the hemisphere between the cortex and the corpus striatum. Physical conduction from the cortex to the corpus striatum was thus in nowise impeded, and the Archives de Physiologie, Oct. 1883) to the contrary are doubtless due to his radically vicious method of operating without anesthetics : ' Les animaux dont je me suis servi ont ete presque toujours laisses normaux, sans ames- thesie, sans immobilisation ' (p. 267). Besults obtained under such conditions do not require further consideration. 230 FUNCTIONS OF THE OEBEBBUM connections between the corpus striatum and cerebral peduncle were intact ; yet, owing to the destruction of the medullary fibres, the cortical centres could not transmit any impulse downwards, however strongly excited. It is impossible, there- fore, to explain away the results of electrical irritation of the cortex by mere conduction to subjacent ganglia or motor tracts, even though a certain amount of extrapolar diffusion is de- monstrable. But mere physical diffusion is not equivalent to diffuse stimulation. I have shown that it is not any or every degree of stimulation which is sufficient . to excite the activity of the cortex. A strength of current capable of inducing the most violent tetanic spasm if applied to a motor nerve has no appreciable action on the cerebral centres. Hence, though physical conduction may occur in the brain substance, effective stimulation will only occur at the point where the current reaches the necessary intensity, and that is in the intrapolar region. Bisks of diffusion, however, must always be borne in mind as a possible source of error, but they can be eliminated by frequent repetition of the experiments, working with the minimum effective current and similar obvious precautions, which all competent investigators naturally take. § 5. It would be a matter of indifference, as regards the great question of differentiation of function in the cerebral cortex, if it should appear that it is not the grey matter of the cortical regions which is really excitable, but the cone of subjacent medullary fibres distributed to them. For, if the medullary fibres are differentiated in function, the regions to which they are distributed must be similarly differentiated, unless we are to suppose that the grey matter is merely so much inert stuff; a supposition which, however absurd, is, nevertheless, the logical outcome of the views propounded by some writers on this question. That the medullary fibres are excitable has been proved, but the excitability of the cor- responding cortical regions is not thereby excluded ; and as a matter of fact, as will be seen, is capable of satisfactory de- monstration. It was first shown by Burdon Sanderson > that, after re- moval of the cortex, electrical stimulation of the medullary 1 Proceed. Royal Soc, June 1874. EXCITABILITY OF THE MEDULLABY FIBRES 231 fibres thus laid bare caused movements like those resulting from the application of the electrodes to the respective regions of the cortex themselves. This has been confirmed by the experiments of Braun, 1 Putnam, 2 Carville and Duret, 3 Alber- toni and Michieli, 4 Franck and Pitres, 5 Eichet, 6 and others ; so that we may regard it as satisfactorily established that the medullary fibres are functionally differentiated paths of com- munication between the cortex and the periphery. They stand to the cortical matter precisely in the same relation as the anterior spinal roots do to the anterior horns of the spinal cord. When the anterior horns are diseased (as in anterior polio-myelitis), or the anterior roots divided, the motor nerves in the course of four to five days entirely lose their excitability and undergo complete degeneration. This important fact was first demonstrated by Albertoni and Michieli, who found that after removal of the grey matter of the cortex the medullary fibres, at first excitable, ceased after an interval of from four to five days to respond to the strongest electrical currents. And it has now been established that after purely cortical lesions 7 degeneration occurs in the corona radiata and pyramidal tracts down the whole extent of their course in the spinal cord. Though the direct excitability of the anterior horns may be questionable, no one doubts the excitability of the anterior roots. But no one doubts the motor functions of the anterior horns on that account. Yet among other ridiculous objections to the motor functions assigned to certain cortical regions it has been argued that they ought to conform to the same laws as regulate the excitability of motor nerves. The excitability of nerve centres and nerve tracts is not only not necessarily the same, but, in reality, it is the very point of 1 Centralblatt f. d. med. Wissensch., 1874. 2 Boston Med. and Surg. Journal, 1874. 3 ' Sur les Fonctions des Hemispheres Cerebraux,' Archives de Physiologic 1875. 4 ' Sui Centri Cerebrali di Movimento,' Lo Spenmentale, 1876. s Soc. de Biologie, 1877. 6 Sur les Circonvolutions Oiribrales, 1878. i See the facts and experiments by the author and Professor G. Yeo, Trans. Intern. Med. Congress, 1881, vol. i. ; Discussion on Localisation, p. 231 ; and ' On the Effects of Lesions of Different Eegions of the Cerebral Hemispheres,' Philosoph. Trans., Part II. 1884. 232 FUNCTIONS OF THE CEBEBBUM difference by which the direct excitability of the cortical grey matter can be established. Putnam found that a stronger current was necessary to excite the medullary fibres than the corresponding cortical centre. On replacing the removed cortical lamina, and apply- ing the formerly effective current, no action whatever resulted. It is possible, however, as Carville and Duret have contended, that the necessity of intensifying the current when the cortex has been removed is due to the haemorrhage that occurs, and the consequent tendency to diffusion when the electrodes are placed on the oozing surface. Franck and Pitres likewise find in non-narcotised animals that the excitability of the cortical centres is greater than that of the corresponding medullary fibres ; but Eichet states that in narcotised animals the medullary fibres are more excitable than the cortical centres. The experiments of Bubnoff and Heidenhain ' confirm those of Eichet, and show that during the narcosis produced by morphia the medullary fibres are more readily excitable than the corresponding cortical centres. It is possible that this may be the explanation of the fact, signalised by Hitzig, that the anodal closure was more effec- tive than the cathodal closure in his experiments with the galvanic current. The stimulus in this case would proceed from the virtual cathode established in the deeper and more excitable subcortical regions (see p. 197). Deep narcosis, however, abolishes the excitability both of the grey matter and the subjacent medullary fibres, so that no reaction what- ever occurs on the application of currents otherwise effective. It has, however, been asserted by Marcacci 2 — whose experi- ences in this and many other respects appear altogether unique — that, even after freezing the cortex, electrical stimula- tion is still effective, and causes the same movements as be- fore. This assertion has been completely refuted by Varigny, 3 who found after refrigeration of a given region that no ordinary stimulation was capable of exciting the movements formerly readily excitable ; and that, when the current was intensified 1 Pfluger's Archiv f. Physiologie, 1881. 2 Archives Italiennes de Biologie, tome i., 1882. 3 L'ExcitabilMA Electrique des Girconvolutions Ciribrales, 1884. EXCITABILITY OF THE COBTEX 233 beyond all limits of localised irritation, general agitation ■was produced everywhere except in the parts governed, and ordinarily alone thrown into action, by stimulation of the region in question. Besides the differences which appear to exist in respect to the relative excitability of the grey matter and medullary fibres, there are others of greater importance which clearly establish and differentiate the independent excitability of the cortex from that of the medullary fibres. It was first shown by Franck and Pitres that between the moment of excitation and the resulting movement there elapses an interval, capable of exact measurement. This interval, after deducting the time necessary for the transmission of the impulse through the spinal cord and motor nerves, indicates a retardation in the cortex of 0-045 second. When the grey matter is removed, and the stimulus is applied to the medullary fibres, the period of retardation diminishes to 0"03 second, or about one-third less. They have further shown — and their observations have been confirmed by Eichet, Bubnoff and Heidenhain, Varigny, &c. — that the grey matter of the cortex, like nerve centres in general, is capable of storing up, and responding to a succes- sion of stimuli individually insufficient to excite action. Irri- tation of the cortex frequently responds in a succession of discharges of an epileptiform nature — a phenomenon which never occurs when the medullary fibres alone are stimulated. The duration of the effect in the latter case is strictly propor- tional to the duration of the electrical excitation. Bubnoff and Heidenhain have further demonstrated a characteristic difference between the muscular curves registered by stimu- lation of the cortex and medullary fibres respectively. In the latter case the curve rises abruptly, and is of short duration ; while in the former it rises more gradually, and is much more prolonged. These differences conclusively prove the in- dependent excitability of the cortex as such. But, as before remarked, it was not necessary to prove this, qua the question of differentiation of function in the cortex. For the admitted differentiation of the medullary fibres, and the dependence of their functional vitality on the integrity of the corresponding cortical centres, necessarily implies a corresponding differen- 234 FUNCTIONS OF THE CFBEBBUM tiation in the regions to which they are distributed. In addition to the various facts above mentioned, which show that the cortex as such is excitable, and that it is not merely on physical conduction to the excitable medullary fibres that the movements depend, we may adduce the interesting experi- ments of Soltmann l on new-born dogs. In these it is not "possible to excite movements of the limbs from the cortex before the tenth day, at which time the foreleg is generally capable of being stimulated to action. Yet several days before this, it is easy, by comparatively weak currents, to ex- cite the same movement by irritation directly applied to the subjacent medullary fibres. That the cortex is not merely a physical conductor of the electrical current to the excitable medullary fibres is thus clearly apparent. With these considerations on the methods of investigation I propose in the next chapter to describe the phenomena observed on electrical irritation of the cerebral hemispheres in different orders of animals, and in the next place to en- deavour to interpret them in the light of the complementary method of destruction. The details of individual experiments are spared, except on points of uncertainty or dispute. For fuller data on which the statements and views maintained by the author are based reference is made to the undermen- tioned papers and memoirs. 2 1 Jahrbuch filr Kinderheilkunde, 1876. On this see further Chap. VIII. §3. 2 (1) ' Experimental Researches in Cerebral Physiology and Pathology,' West Biding Lunatic Asylum Reports, vol. iii. 1873. (2) ' Experiments on the Brain of Monkeys,' First Series, Proceedings of the Boyal Society, No. 161, 1875 ; ibid. Second Series, Philosoph. Transactions, vol. ii. 1875 ; ' On the Effects of Lesions of Different Regions of the Cerebral Hemispheres ' (in conjunction with Professor G. Yeo), Philosoph. Transactions, Part II. 1884. 235 CHAPTEE VIII. PHENOMENA OF ELECTRICAL IRRITATION OF THE CEREBRAL HEMISPHERES. Part I. — Experiments on Monkeys. § 1. The surface of the cerebral hemispheres in macaques, the species of monkeys usually employed in these experiments, is divided into certain lobes and convolutions by certain pri- mary and secondary fissures or sulci (figs. 67, 68). Different systems of nomenclature have been adopted by different writers, and different views have been expressed in reference to the homologies of the various sulci and convolutions. As it is not necessary for mere topographical description to enter into questions of homology, I have in the following references mainly followed the nomenclature of G-ratiolet, with the addi- tion of such synonyms as are in most common use among writers on cerebral topography. Of the primary fissures there are three readily distinguish- able on the convex aspect, the fissure of Sylvius (fig. 67, a), the fissure of Rolando, or central fissure' (fig. 67, b), and the parieto- occipital or perpendicular fissure (fig. 67, c), also called the simian fissure. The frontal lobe (fig. 67, f l) includes all in front of the fissure of Eolando, or central fissure. This is divided by secondary fissures, one of which anterior to and almost parallel with the fissure of Eolando is termed the antero-parietal (Huxley) or pracentral sulcus (Ecker) (fig. 67, ap), and two others running almost at right angles to this. The upper one (fig. 67, sf), which is a mere prolonga- tion forwards of the prsecentral sulcus, is the supero-frontal sulcus ; the lower ^fig. 67, if) is the infero-frontal sulcus. •230 ELECTRISATION OF THE CEREBRAL HEMISPHERES The convolution included between the central and prffi- central sulci is termed the ascending frontal, or y>ri the Cut. l;. the- ecu ial sulcus. , the super; ir external external c involution. lutiun. iv, tut: fourth Fig. 76.— Upper Surface of the Hemi- spheres of the Cat.— 1J, the crucial sulcus. Retraction and adduction of the opposite fore-leg. The movement performed rapidly, as it frequently is on stimula- tion, exactly resembles that of striking a ball with the paw. (5). On the sigmoid gyrus anteriorly. Elevation of the shoulder, with flexion of the forearm andpaw. It would seem as if (0) and (6) in the brain of the monkey were both combined in this region. (a). On the rounded frontal extremity of the joint second and third external convolutions. 258 ELECTBISATION OF THE CEBEBBAL HEMISPHEBE8 Clutching or grasping action of the paw, with protrusion of the claws. This, which is one of the most characteristic actions of the cat's paw, is always very readily induced if the brain is at all excitable. (7) . Gn the frontal division of the second external (coronal) convolution. Elevation of the angle of the mouth and cheek, loith closure of the eye. Movements of the eyeballs were occasionally noted here both by myself and Hitzig. (8). On the frontal division of the third external (super- Sylvian) convolution. Retraction with some degree of elevation of the angle of the mouth, and drawing dowmvard and forward of the ear. Occasionally only the movement of the ear was observed. (9). On the conjoint orbital extremity of the third and fourth (super- Sylvian and Sylvian) convolutions. Opening of the mouth and movements ofthettongue. Frequently this was associated with vocalisation and othei signs of emotional expression, such as spitting and lashing the tail as if in rage. I have not been able to differentiate any point exactly corresponding to (11) in the dog. It seems to be included in the action of (8). Nor have I found any point correspoJ&ing to (12) in the dog and jackal. Stimulation of the point marked ( + ) just posterior to the ansate fissure, which anatomically would seem to correspond with the tail centre of the dog, was either negative or, when the current was strong, was followed by movements of the eyes and head to the opposite side, such as occurred on stimulation of (13), the next region, due probably to diffusion. (13). Various points on the parietal division of the second external convolution. The eyeballs move to the opposite side, and frequently also the head moves in the same direction. The pupils were occa- sionally seen to contract. (14) . On the posterior division of the third external (super- Sylvian) convolution. Pricking of the ear, and head and eyes turn to the opposite side. Sometimes only the movement of the ear occurred ; and EXPERIMENTS ON EODENTS 259 in some cases, 'when the excitability of the brain was exhausted or in deep narcosis, no result whatever occurred. (15). The tip of the uncinate gyrus. Elevation of the Up and torsion of the nostril on the same side. (i6). On the frontal extremity of the Sylvian convolution. Divergence of the lips, so as partially to open the mouth, which becomes fully opened when the stimulation is kept up. In my earlier experiments I observed sudden retraction of the head on stimulation of the prefrontal regions ; effects which I think are due merely to conduction of the current to the olfactory bulbs, which are in such close proximity. Irritation of the posterior limb of the Sylvian convolution was very often associated with movements of the jaws, gene- Eio. 78.— Left Hemisphere o f the Brain of Babbit.— 0, the olfactory bulb, x, parallel sulcus. ThT^TgTTrn^ation of the circles ami numerals is given in the test. rally closure. Some doubts arise as to the real nature of these movements, owing to the possible conduction of the current to the cut surface of the temporal muscle, which recraires to lie reflected in order to reach this region. In some experiments, just as in dogs and jackals, stimu- lation of the recurved portions of the first or uppermost ex- ternal convolution gave rise to movements such as might be caused by painful irritation of the opposite extremities. Part IV. — Experiments on Rabbits. § 6. The brain of the rabbit being devoid of convolutions, it is more difficult to define the exact points of stimulation. The position of the various centres was fixed in the accompany- ing figure by careful comparison with the dead brain during the process of experimentation (fig. 78). s 2 2C0 ELECTBISATION OF THE CEBEBBAL HEMI8PHEBE8 A shallow sulcus (x) running parallel with the longitudinal fissure may be regarded as homologous with that marking off the superior external convolution in the dog and cat. The position of the fissure of Sylvius is indicated by a shallow depression between the narrow frontal and the broad posterior lobe, from the lower extremity of which the olfactory tract (o) is seen to spring. (1). A point which is situated at the anterior extremity of the shallow sulcus, parallel to the longitudinal fissure. Advance of the opposite hind leg from an extended position. (4). Retraction with adduction of the opposite fore limb. (5) . Elevation of the shoulder and extension forward of the fore limb, as in the act of stepping forwards. (7). Covering a large extent of the frontal aspect of the hemisphere. Retraction and elevation of the angle of the mouth, with frequently repeated chumping or munching action of the jaws, while the head becomes gradually turned to the opposite side. (8). Just posterior to the above mentioned. Closure of the opposite eye, combined with elevation of the cheek and angle of the mouth, and occasionally with some undefined movement of the ear. (9). On the orbital aspect of the frontal region. Opening of the mouth, ivith movements of the tongue. (t) . I have not been able to differentiate any centres corre- sponding to (11) and (12) in the monkey or dog. (13). On the parietal region. Generally a forward movement of the opposite eye, and occasionally turning of the head to the opposite side. In one or two instances the pupil appeared to contract, though this was regarded as doubtful. (14) Sudden retraction and elevation or pricking of the opposite ear — this occasionally coinciding with a sudden start, apparently as if the animal were about to bound forward. (15). Torsion or closure of the nostril, generally on both sides. Occasionally this was associated with the movement of the ear described under (14), doubtless from conjoint stimulation of the two centres. EXPERIMENTS ON RODENTS 21 U Stimulation of other parts of the brain gave no definite results, though in one case, on slipping the electrodes just within the longitudinal fissure posteriorly, a sudden spasmodic extension of the opposite hind leg and general shudder were produced. Experiments on Guinea-pigs. § 7. The brain of the guinea-pig (fig. 79) is almost an exact copy of that of the rabbit. The results of electrical irritation are essentially the same. The numerals have the same signification as those on the brain of the rabbit. (1). Advance of the hind leg. (■0). The fore paw is lifted as if to step forward, and then Fie. 79. — Left Hemisphere of the Brain of the Guinea-pig. — o, the olfactory bulb. The signification of the circled and numerals is given in the text. rapidly withdrawn and adducted. The two movements of (4) and {■',) in the rabbit could not be separately differentiated. (7). As in the rabbit, retraction and deration of the angle of the mouth, grinding movements of the jaws, and ultimately dragging of the head to the opposite side. (S). Closure of the eye and elevation of the cheek. (9). Mouth opened. (n). Pricking of the opposite ear. Experiments on Eats. § 8. Several experiments were made on albino rats. The results obtained were essentially the same as those in guinea- pigs and rabbits. The centres for the movements of the limbs, however, are situated nearer the frontal extremity of the hemisphere than in rabbits and guinea-pigs. The accom- 2G2 ELECTRISATION OF THE CEREBRAL HEMISPHERES panying figures (figs. 80, 81) indicate by the same numerals the centres corresponding to those of the rabbit and guinea- pig, a separate individual description being unnecessary. FIO. 80.— Upper Sur- face'of the Brain of the 1-iat. — o, the ol- factory bulb. Pig. 81. — Hight Hemisphere of the Brain of the Rat. — o, the olfactory bulb. The signification ot the circles and numerals is giyen in the text. Part Y. — Experiments on Pigeons. § 9. The brain of the pigeon (fig. 82), as well as of the common fowl, on which I have also made experiments, though apparently constructed on the same type as the brain of rodents, differs from these in the fact that electrical irritation fails to excite analogous movements. In my first experiments l-'io. 82.— Brain ot the Pigeon. FIG. 83.— Brain of the Prog. (Enlarged x 2.) PIG. 81.— Brain of the Carp. I had observed no result whatever on irritation of the hemi- sphere in any part ; but in subsequent experiments I found I had missed a very definite and constant reaction, observable in connection with stimulation of a region marked on the ac- companying figure (fig. 82 x ). Irritation of this point, which is situated in the upper parietal region, causes intense con- EXPEBIMENTS ON FBOGS, ETC. 203 traction of the opposite pupil, occasionally associated with turning of the head to the opposite side. In a few cases I have also observed, from stimulation of the region below this, turning of the head to the opposite side without contraction of the pupil. Beyond these effects the results of stimulation were entirely negative. Experiments on Frogs. § 10. Owing to the small size of the cerebral hemispheres of the frog (fig. 83, a), it is scarcely possible to ensure localised irritation by means of the electric current, or to avoid risks of conduction to neighbouring structures. I found, however, that the application of closely approximated fine needle elec- trodes to the hemisphere induced movements of the opposite limbs, but I could not differentiate regions for each limb respectively. Langendorff, 1 who has repeated and confirmed my obser- vations, finds that it is only from the parietal region of the hemisphere that movements can be induced by weak currents, stimulation of the other regions being ineffectual in this respect. Experiments on Fishes. § 11. In fishes also the cerebral hemispheres (fig. 84, a) are relatively and absolutely of very small size, and limitation of electric stimulation correspondingly difficult. My experi- ments have been made on carp. I have found it comparatively easy to expose the brain and keep the animals alive during experimentation by the following method. The body of the fish was secured by a clamp fixed in a stand in such a manner as to keep the mouth just below the surface of a trough kept at a constant level by a running stream of water. Free play was allowed to the tail and fins without any alteration of position. Irritation of the hemisphere caused the tail to be struck vigorously to the opposite side, and the pectoral, anal, and dorsal fins to be thrown into action ; but their movements 1 Centralblatt f. d. med. Wissensch., 1876. 264 ELECTRISATION OF THE BASAL GANGLIA seemed too complex to admit of exact description. Generally, also, along with the movements of the tail and fins, the eye- balls moved forwards or inwards. Part VI. — Electrical Stimulation of the Basal Ganglia. Corpus Striatum. § 12. I have found that electrieal stimulation applied to the surface of the ventricular nucleus of the corpus striatum in the monkey, cat, dog, jackal, and rabbit causes precisely the same results, viz. a condition of pleurosthotonus, or general muscular contraction on the opposite side of the body. The head is drawn strongly to the side, and the body bent in the form of an arch, with the concavity to the opposite side ; the facial muscles are thrown into spasmodic contraction, and the limbs are rigid in the position of equilibrium between the flexors and extensors, the flexors predominating. In the rabbit the tonic spasm is not so rigid as in the other animals, and the jaws are ground together during the maintenance of the irritation. There is no differentiation of movement from any point of the ventricular aspect of the ganglion, all the actions differen- tiated in the cortical centres being simultaneously called into play. These results have been confirmed by the experiments of Garville and Duret l who have found with me that general muscular contraction of the opposite side of the body occurs on the application of the electrodes to the corpus striatum. It has, however, been asserted by Franck and Pitres 2 that neither from the corpus striatum nor from the optic thalamus is it possible to excite movements even with currents ' les plus intenses ' when the electrodes are placed exactly on the ganglia themselves, whereas general muscular contraction of a tetanic character is readily induced by irritation directly applied to the internal capsule. I have, however, so often and in so many orders of animals proved the positive influence of irritation 1 ' Sur les Fonotions cles Hemispheres Cerebraux,' Archives de Physiologie, 2eme S6rie, vol. i. 2 ' Convulsions d'Origine Cortioale,' Archives de Physiologie, 3eme Serie, vol. ii. COBPUS STBIATUM 2G5 of the corpus striatum, and the negative influence of the same strength of current when applied to the optic thalamus, that I cannot admit the accuracy of the statements made by these physiologists. I have recently re-investigated the sub- ject, and arrived at the same results as before on monkeys and rabbits. But in order that the results should be trustworthy it is necessary that the cerebral ventricles be exposed in such a manner as to avoid shock and haemorrhage, otherwise no re- action will be obtained from irritation of the corpus striatum, any more than from the optic thalamus. I have generally reached the interior of the ventricles after piecemeal exposure of the hemisphere, so that sudden shock and haemorrhage were avoided. In one instructive experiment which I recently made on a monkey I found, contrary to my usual experiences, that irritation of the corpus striatum was entirely without effect. I found, however, on further investigation, that this was due to general exhaustion of excitability, inasmuch as the corpora quadrigemina also — which usually are so readily excitable — barely reacted to an altogether disproportionate strength of current. I am convinced that to such and similar conditions may be attributed the failure on the part of Franck and Pitres to obtain evidence of the reaction of the corpus striatum to electrical irritation. It has, however, been proved beyond all question that the medullary fibres of the cortical motor centres are readily excitable and functionally differentiated like the centres with which they are connected. Franck and Pitres ' have further ascertained that, on horizontal sections of the internal capsule in dogs, movements of the facial muscles, fore and hind limbs, and of the ear, can be individually elicited by stimulation of points echelonned respectively from before backwards. It is therefore not an unreasonable supposition to attribute the apparent motor excitability of the corpus striatum to actual irritation of the internal capsule by conducted currents. This mode of explanation, however, is inconsistent with other facts. If it were a mere question of conduction to the internal cap- sule, the same reaction should occur from the optic thalamus, 1 Soc. de Biologie, Dec. 30, 1877. 2G0 ELECTRISATION OF THE BASAL GANGLIA between which and the lenticular nucleus the motor division of the internal capsule is situated. Conduction to the internal capsule is quite as easy in the one case as the other. But, as a matter of fact, the same current which when applied to the intraventricular nucleus of the corpus striatum produces marked pleurosthotonus is entirely without effect when the electrodes are shifted on to the optic thalamus. I have veri- fied this repeatedly. And a statement made by Franck and Pitres themselves is sufficient to dispose of their hypothesis that the motor reactions are due to irritation of the internal capsule. They state that not even strong currents were effecr tive when the electrodes were applied directly to the corpus striatum, while at the same time the fibres of the internal cap- sule were readily excitable by a current of much less intensity. But inasmuch as in my own hands, as well as in those of Carville and Duret, and Minor, 1 electrical irritation of the nucleus caudatus did not fail to cause general muscular con- traction on the opposite side, it is obvious conduction to the internal capsule cannot explain the results, otherwise they should have occurred under the strong stimulation employed by Franck and Pitres. The effects can only be explained on the hypothesis of direct excitability of the corpus striatum itself. Minor, however, states that after destruction of the cortical motor centres, when after the lapse of time secondary degeneration had occurred in the pyramidal tracts, he found that irritation of the corpus striatum on that side failed to excite the usual reactions ; and he therefore doubts the excita- bility of the corpus striatum as such. But it is more probable that the tracts through which the corpus striatum acts were also involved in the degeneration, or that in the experiment in question the corpus striatum had lost its usual excitability by the operations necessary to expose it. Optic Thalamus. § 13. I have not observed in the monkey, cat, dog, or jackal any outward manifestation on irritation of the ventri- 1 ' Zur Frage ii. d. Bedeutung des Corpus Striatum ' (Netvrolog. Centralbl. June 1883). OPTIC THALAMUS 267 cular aspect of the optic thalamus with a current sufficient to excite the most marked pleurosthotonus when applied to the ventricular aspect of the corpus striatum. The same negative result was obtained by Carville and Duret. In one monkey I observed, however, a spasmodic extension of the legs on the application of the electrodes on the third- ventricular aspect of the optic thalamus in the region of the soft commissure. In rabbits the effect of irritation of the surface of the optic thalamus was also in general without obvious result. In one case, however, I observed movements of the eyeballs, twitching of the opposite ear, shuddering and spasmodic movements of the limbs, and general restlessness during irritation of the optic thalamus ; phenomena which might be manifested in connection with general sensory irritation. On no occasion did irritation of the optic thalamus, in any of the animals ex- perimented on, cause the utterance of any sounds expressive of pain or emotion of any kind. Bechterew, 1 however, states that he has excited emotional utterance in pigeons, fowls, and dogs by mechanical as well as by electrical irritation of the optic thalami. He seems to have applied electrical irritation only by insulated needles thrust through the substance of the hemisphere to the optic thalamus. As no such phenomena ever occurred in my own experi- ments in which the optic thalami were clearly exposed, I cannot accept Bechterew's statements as an accurate repre- sentation of the facts as regards irritation strictly confined to the ganglion itself. 1 ' Die Function der Sehhiigel,' Neurolog. Cmtralblatt, No. 4, 1883. 208 CHAPTEE IX. the hemispheres considered physiologically. The Sensory Centres. § 1. In the preceding chapter only a bare description has been given of the phenomena of electrical irritation of the various regions of the cerebral hemispheres in different orders of animals, similar regions being designated by the same numerals for purposes of comparison. It is apparent that, with certain individual differences, peculiar to and character- istic of, the different orders of animals, there are fundamental . resemblances which have an important bearing on questions of homology. Though many of the movements described are evidently such as may be termed purposive, or combinations employed habitually for volitional purposes, there are others whose signification is not so clear ; and it has still to be determined what is the real relation between excitation of a given part of the cortex and the resulting motor reactions. The mere fact of motion following stimulation of a given area does not neces- sarily signify a motor region. The movements may be the result of some modification of consciousness incapable of being expressed in physiological terms, or they may be reflex ; or they may be truly motor in the sense of being due to irritation of a part in direct connection with the motor strands of the crus cerebri and spinal cord. The method of stimulation is by itself incompetent to decide these questions, and requires as a complement the strictly localised destruction of those areas stimulation of which gives rise to definite motor mani- festations. Here, however, difficulties begin and discrepancies arise, often of the most extraordinary character. It is not such an easy matter to ensure the strict limitation of the THE SENSORY CENTRES 269 influence of a destructive lesion to the part immediately de- stroyed. For the functions of the whole nervous system, the different portions of which form a complex solidarity, may be deranged by a lesion at any part; and even if this should not be the case, there is at least great risk that the parts more immediately in relation with the lesion may be damaged temporarily or permanently. The former risk is, as a matter of fact, in experimental lesions carefully established of a very trivial character, for in the vast majority of cases the animals I have mainly experimented on, viz. monkeys, exhibit such undoubted signs of general well-being almost directly after the operation that the idea of general prostration and rever- beration through the whole system requires mention only to be dismissed. The latter risk is, however, of much greater moment and reality if the animals survive the operations for many hours. Unless the primary lesions are established in such a manner as to prevent their becoming the foci of secondary inflammatory processes, more or less diffuse, no ceitainty can be arrived at in respect to the direct effect of the lesions, how- ever well anatomically circumscribed in the first instance ; and thus errors of the most grievous description are apt to arise in reference to the delimitation of the respective cortical centres. The vast majority of the experiments made on this head by many physiologists, such as Munk, are vitiated by the almost universal occurrence of secondary encephalitis, with indefinite extension of the primary lesions. This, however, can be entirely obviated by the application of the Listerian principles of antiseptic surgery, such as my colleague Professor Yeo and myself have employed in our researches, 1 and adopted also by Horsley and Schafer. By this method the absolute limitation of the primary destructive lesions can be secured without risk of secondary encephalitis or meningitis, and by this method alone is an exact delimitation of the cortical centres possible. The destructive lesions may be made with the scalpel or by means of the actual cautery, and, if the anti- septic precautions are strictly carried out, remain as exactly defined as when originally established, however long the 1 Brit. Med. Journal, 1880 ; Phil. Trans. 1885. 270 THE SENSOBY CENTBE8 animal may survive. A careful post-mortem examination is imperatively required in all cases, and no reliance is to be placed in merely vague statements as to the position of the primary lesion, which so many physiologists' seem to think sufficient in the accounts they furnish of their experiments. In addition to the results of physiological experiment, particularly on monkeys, which of all others have the most direct bearing on the organisation of the human brain, some reference is made in the following chapters to the facts furnished by the experiments of disease in man. These, however, require to be handled with the utmost caution, otherwise they may be made to support almost any doctrine however absurd. Almost every form of disturbance of the cerebral functions has been manifested in conjunction with anatomical lesions of the utmost diversity as to character, size, and position ; and likewise without any visible or de- monstrable lesion whatever. In the absence of any exact means of discrimination between the direct and indirect effects, of pathological lesions, or of the relation between functional disturbance and structural alteration, little reliance can be placed on localisation of function founded on the positive facts of cerebral disease alone. 1 Clinical cases are mainly valuable as confirmatory of physiological experiments, and more es- pecially as supplying negative instances. A case — however otherwise complicated — of total destruction of a region in which a certain function is supposed to be localised, without loss or impairment of the function assigned to it, outweighs a thousand positive instances in which a causal relationship seems to be established between the particular region and the function in question. Paet I. — The Visual Centre. § 2. The results of electrical stimulation of the occipital lobe and angular gyrus have already been recorded. No 1 Exner's work, Localisation der Functionem in der Grosshirnrinde, 1881, is in many respects a typical example of the fallacies of induction per enumera- tionem swvplicem. His tables and figures of ' negative instances ' are, however, of great value. THE VISUAL CENTRE 271 appreciable manifestation was observed in connection with irritation strictly confined to the convexity of the occipital lobe, . while irritation of the angular gyrus was invariably associated with movements of the eyeballs, and occasionally of the head, to the opposite side ; and very frequently with - contraction of the pupils. The corresponding region in the brain of the cat, dog, and jackal is the parietal^aspect of the / second external convolution, the posterior extremity of'ihis being similar to the occipital lobe of the monkey in not re- sponding outwardly to the electrical stimulus. In the brain of the rabbit the corresponding region (fig. 78, 13) likewise occupies the parietal region ; and in the brain of the pigeon the centre for the contraction of the pupil (fig. 82, x ) occupies a similar position. The phenomena of electrical irritation appeared to me indicative of the excitation of subjective visual sensation, and, acting on this hypothesis, I arrived, by the complementary method of destructive lesions, at the first delimitation of the cortical centre of vision. In my earlier experiments, owing to the complications almost invariably resulting from secondary extension of the primary lesions, if the animals were allowed to survive any length of time, I contented myself with obser- vation of the animals for only short periods ; and therefore questions were left undetermined as to the degree of perma- nency of the symptoms produced in the first instance. Anti- septic surgery has, however, removed the difficulties and com- plications formerly experienced, and the results of experiments under this method which I have since made in conjunction with my colleague, Professor G. Yeo, 1 as well as the results obtained by other physiologists, have necessitated consider- able modification of the views I formerly entertained respecting the extent of the visual centres and their relations to the eyes, though the facts on which my former views were founded have been completely confirmed by my later researches. Formerly I localised the visual centres in the angular gyri, to the exclusion of the occipital lobes. This, being only a partial truth, is an error ; for the visual centres embrace not ' See ' On the Effects of Lesions of Different Regions of the Cerebral Hemi- spheres.' By Professors Ferrier and Yeo. Philosoph. Trans., Pt. II., 1884. 272 THE SENSORY CENTRES only the angular gyri, but also the occipital lobes, which together I term the occipito-angular regions. There is, how- ever, as will be seen, a remarkable difference between the angular gyri and the occipital lobes in their relations to the eyes. But in order to cause complete and permanent loss of vision in both eyes it is necessary completely to extirpate both angular gyri and both occipital lobes. Fig. 85. — Right Hemisphere. (From a photograph.) Fig. 86. — Left Hemisphere. (Prom a photograph.) Bilateral Lesion causing Total Blindness. § 3. In the following experiment 1 (figs. 85, 86) this opera- tion was successfully carried out, and, as proved by careful post- mortem examination, without any secondary inflammation or extension of the primary lesion. The result of this lesion was complete and permanent blindness— for the eleven months which the animal lived — followed by atrophy of the optic discs 1 Experiment 12*, ibid. THE VISUAL CENTRE 273 and fixity of the pupils — all other sensory faculties and the motor powers remaining absolutely unimpaired from first to last. At first the animal was unwilling to move spontaneously, as it knocked its head against every obstacle in its way. Food had to be put in its hands, as it could not find anything by itself ; but it learnt to find its food by groping, and gradually gained sufficient confidence to wander about its cage and in its confines, guided by touch and hearing, which were evidently acute and perfect. It walked about with a somnambulistic air, looking apparently in the distance, and picked its way very carefully, unless startled, when it would bounce in full career against any obstacle in its way. Judging by the signs of satisfaction which it exhibited when certain articles of food— oranges, &c. — were given it, it enjoyed the sense of taste; and the manner in which it smelt at its food before eating showed that the sense of smell was retained intact. With the exception of blindness, which was from the first absolute, the animal was in complete possession of all its other faculties. That the lesion in this case did not invade a larger area than that devoted to vision will become manifest as we proceed. § 4. Though the occipital lobes are included in the visual centres, it is nevertheless a remarkable fact that they can be injured, or cut off bodily, almost up to the parieto-occipital fissure, on one or both sides simultaneously, without the slightest appreciable impairment of vision. This fact, which I had already observed in my former experiments, has been completely confirmed by Professor Yeo and myself, and also by Professors Horsley and Schafer. The statements of Munk, 1 that lesion of one occipital lobe causes hemianopsy towards the opposite side, by paralysis of both retinse on the side of lesion, and that bilateral lesion causes complete blindness, are entirely erroneous, and depend on direct implication or secondary extension of the lesion into the angular gyri. In two cases 2 I removed the greater portion of both occipital lobes at the same time without causing the slightest appre- 1 Die Functionen der Grosshwnrinde, 1877-1880, Berlin, 1881. * Experiments XXII. and XXIII., Philosoph. Trans, vol. clxv. Part II., 1875 (figs. 29-34). 274 THE SENSORY CENTRES ciable impairment of vision. One of these animals (fig. 87) within two hours of the operation was able to run about freely, avoiding obstacles, to pick up such a minute object as a raisin without the slightest hesitation or want of precision, and to act in accordance with its visual experience in a perfectly normal manner. In another animal ' in which (fig. 88) both occipital lobes had been likewise removed, and which survived for nearly a month when the prefrontal lobes were also removed, there was from the first some slight visual disturbance, evidenced by Pig. 87.— Lesion of both Occipital Lobes. (Roy. Soc.) some want of precision in laying hold of things offered it ; but it was found on post-mortem examination that the right angular gyrus was injured as well as both occipital lobes. In another experiment, 2 in which both occipital lobes and both angular gyri were implicated, blindness was observed during the two days which the animal survived. In all cases in which there was impairment of vision the lesions invaded also the angular gyrus on one or both sides. 1 Experiment XXIV., Phil. Trans, vol. clxv. Part II. figs. 35- 37. 2 Experiment XXI., ibid. figs. 26-28. THE VISUAL CENTRE 275 Among the monkeys operated upon by Dr. Yeo and myself one ' had the left occipital lobe severed and removed closely behind the parieto-occipital fissure without any perceptible affection of vision to the one side or the other, the animal being able to see and seize things both to right and left. In another, 2 both occipital lobes were deeply incised and broken up without the slightest impairment of vision. And in a third 3 both occipital lobes were removed so extensively as only to leave a triangular portion of each behind the upper extremity of the parieto-occipital fissure. Fig. 88.— Removal of Occipital and Prefrontal Lobes. (Boy. Soo.) Yet this animal within two hours after the operation was able to run about freely, pick up minute objects, and in gene- ral, from this time onwards, to behave as if nothing whatever had occurred to it. Its powers of vision showed no signs of impairment, and it exhibited no defect as regards general intelligence. 1 Experiment 1 *, Phil. Trans. Part II., 1884, fig. 1. » Experiment 2 *, ibid. figs. 2 and 3. 3 Experiment 9 *, ibid. fig. 15. t 2 276 THE- SENSORY CENTRES Horsley and Schafer inform me ' that the results of removal of the occipital lobes in their experiments entirely harmonise with mine as to the completely negative effect of this operation on the animal's visual and other faculties. We can therefore dismiss Munk's statements as to the effects of lesions of the occipital lobes as being unfounded and erroneous. § 5. But when we turn to the effects of destructive lesions of the angular gyrus unilaterally and bilaterally, and to these in combination with lesions of the occipital lobes, very remark- able relations are found to exist. I had found in my earlier experiments that a destructive lesion of one angular gyrus caused temporary loss of vision in Fig. 89.— Destruction of Lett Angular Gyrus, causing temporary blindness of the right eye. (Boy. Soc.) the opposite eye. In one animal 2 the left angular gyrus was destroyed (fig. 89), and the left eye securely closed. After recovery from the chloroform stupor the animal began to grope about a little, but would not budge, from its position, though it was evidently on the alert and in full possession of its other faculties. It did not flinch at light flashed in its eye/. After it had remained in this condition for an hour the bandage was re- moved from the left eye, whereupon the animal nimbly made off, and ran through the open door of its cage to join its com- 1 Private communication. ! Experiment VII., Phil. Trans, vol. clxv. Part II., 1875, fig. 9. THE VISUAL CENTBE 277 panions. Next day when the left eye was again bandaged no affection of vision could be discovered in the right eye. In another case ' in which previously the motor centres of the left hemisphere had been destroyed, with the effect of causing right hemiplegia, the angular gyrus was destroyed. This was followed by temporary total loss of vision in the right eye, so that the animal, when obliged to move, which it Pigs. 90 and 91— Bilateral Lesion, causing temporary complete loss of vision. did very unwillingly, ran its head fuU tilt against everything that came in its way. The removal of the bandage which had been put on the left eye was followed by an instantaneous transformation, and the animal began to run about and act as if suddenly restored to the enjoyment of sight. In a third 2 similar experiment the results were exactly the same. In a ' Experiment VIII., op. tit. fig. 10. ■ Experiment IX., op. cit. 278 THE SENSOBY CENTBES fourth experiment ' the angular gyrus was exposed and accu- rately destroyed with the galvanic cautery in both hemispheres. Before this was done the animal had been allowed fully to recover from the narcosis under which the operations of ex- posing the angular gyri had been effected. When it had been satisfactorily determined that vision was perfect, the angular gyri were seared with the cautery without further narcotisa- tion, and without the slightest sign of pain or discomfort on the part of the animal. It was at once let loose, but appeared scared, and would not stir from its place. It was therefore for some hours impossible to obtain any satisfactory informa- tion as to its powers of vision. The pupils were contractile to light, and a light flashed in the eyes caused some wincing. When a piece of apple was dropped near it, so as to come in contact with its hand, it took it up, smelt it, and ate it with signs of satisfaction. Hearing was acute, and it turned its head and replied when called to by name. With the exception of the reluctance to move from its position, arising evidently, from a sense of insecurity, there was nothing to indicate de- cisively that the animal was blind. But I had found that this animal was very fond of sweet tea, and would run anywhere after it. I therefore brought a cup of sweet tea and placed it to its lips, when it drank eagerly. The cup was then with- drawn and placed in front of it, a little distance, but the animal, though from its gestures intensely eager to drink ifurther, was unable to find the cup, though its eyes were looking straight into it. This test was repeated several times, and with exactly the same result. At last, on the cup being placed to its lips, it plunged its head in, and continued to drink till every drop was exhausted, while the cup was lowered and drawn half-way across the room. Next day the animal still continued blind, and paid no attention to threats, grimaces, or other means of appeal to its sense of vision. The animal was then killed in order that the position and extent of the lesions might be accurately determined before secondary inflammatory processes could have advanced. These had already begun, but were confined to the angular gyri, which were somewhat swollen and raised, and to the adjoining anterior margin of the occipi- 1 Experiment X., op. cit. THE VISUAL CENTRE 279 tal lobes, and with slight implication of the posterior margin of the left ascending parietal convolution. The destruction was purely cortical, the grey matter alone being disorganised, and in the angular gyri exclusively (figs. 90, 91). These facts seemed to justify the opinion I expressed that the angular gyri were the centres of vision, each being in complete cross relation with the opposite eye, since the effect of unilateral extirpation was evidently for the time total blind- ness of the opposite eye, and not hemiopia. And it further seemed as if the rapid recovery from unilateral lesion were due to the compensatory action of the other gyrus, inasmuch as bilateral destruction caused total blindness in both eyes of a more enduring and, as I ventured to suppose, probably per- manent nature. But further investigation, on animals which have been permitted to survive for much longer periods than were compatible with exact experiments under old surgical methods, has shown that the visual centres of the cortex are of a much more extensive character. In my first experiments antiseptics were not used, and hence some degree of innamr matory action and consequent disturbance of the grey matter immediately in relation with the actual lesion were unavoid- able, even though not obviously perceptible to the eye for some hours after the operation. In my later researches with Professor Yeo, in which stringent antiseptic precautions were employed, secondary extension of the primary lesions was entirely prevented, and the duratiori of the total loss of vision in the opposite eye after lesion of the angular gyrus, if the lesion were superficial, was found in several instances to be even more transient than I had previously found to be the case ; while the effects of bilateral lesions were found to vary according to whether they were established simultaneously or successively. In one case ' destruction of the convexity of the right angular gyrus was found to cause some imperfection of vision shown in an incorrect appreciation of the distance of objects when both eyes were open— which proved, on the right eye being bandaged, to be due to total blindness in the left eye, so that the animal refused to stir, or, if it did so on compul- 1 Experiment 3 *, Phil. Trans., vol. ii. 1884. fig. 4. 280 THE SENSOBY CENT BE 8 sion, ran against every obstacle in its path. On the bandage being removed from the right eye, after a short period of ob- servation, the animal speedily showed that it was able to direct its movements with perfect precision. These observa- tions were made within the first two or three hours after the operation, and next day no trace could be discovered of the symptoms. Though it has been urged by some, against the validity of this and other experiments to be reoorded, that the observa- tions were made while the animals were still in a state of stupor or shock following the operation, this is false, for no observations were made until the animals clearly showed perfect possession of all their other faculties. The period of reliable observation is not to be measured by the mere time that has elapsed since the operation, for the period of recovery is most variable, many animals being up and active almost before their wounds have been dressed. Those who do not take advantage of the earlier opportunities of observation miss^ important facts which are beyond all possibility of question. In another animal, 1 destruction of the convexity of the left angular gyrus was followed by total blindness of the right eye, so that for the three hours it was observed after full recovery of all its other faculties it ran against every obstacle right and left, and failed to respond to any test of vision that could be devised. Next day, the left eye being still bandaged, it showed to all appearance the possession of perfect vision with the eye which was totally blind the day before. Three weeks subsequently the right angular gyrus was similarly destroyed by the cautery, whereupon the animal became for a time totally blind in both eyes ; being unable to move about without knocking against obstacles, and paying no attention to signs and tests, which would certainly have called forth re- sponse in a normal animal. At the end of two or three hours it began to give some indications of returning vision, and next day appeared quite well and in full enjoyment of its visual faculties. In this case the destruction of the other angular gyrus had re-induced the blindness in the eye, which had apparently 1 Experiment 5*, Phil. Trans., vol. ii. 1881, fig. 7. TEE VISUAL CENTRES 281 quite recovered its powers, indicating a bilateral relation between each angular gyrus and the eyes. In another case ] destruction of the convexity of the left angular gyrus was followed by similar temporary total blind- ness in the right eye, which next day had entirely disappeared ; but on lesion of the right angular gyrus three weeks after- wards vision became temporarily impaired in the right eye, the one which had been affected previously, while no apparent defect could be discovered in the opposite eye. This occur- rence was unusual, and careful examination was made as to whether the defect was of a hemiopic nature, but it was per- fectly clear to rigid tests that neither after the first nor second operation was the defect to one side or the other, but purely of an amblyopic character. The lesion of the right angular gyrus was less extensive than that of the left. Yet the con- dition was such as to show again a bilateral relation of the angular gyrus, the second operation showing itself mainly, if not entirely, in the eye which had already been blind tem- porarily by reason of destruction of the opposite angular gyrus. In this animal, at a subsequent date, the lesions of both angular gyri were extended backwards in a third operation into the anterior margins of the occipital lobes across the parieto- occipital fissures. This operation was so entirely negative that the animal was found running about the room as if nothing had happened to it within fifteen minutes after the completion of the operation. It continued in perfect health and in full enjoyment of all its faculties till it was killed by chloroform four months afterwards ; a striking example of the safety of even repeated operations on the brain and its mem- branes under strictly antiseptic precautions. In another animal 2 in addition to the destruction of the convexity of the left angular gyrus, the corpus callosum was torn through posteriorly, with a view to determine whether the rapidity of compensation of a unilateral lesion depended on the integrity of the corpus callosum. It had already been determined by a special experiment 3 that division of the 1 Experiment 4*, fig. 4, Phil. Trans., vol. ii. 1884. ' 2 Experiment 7*, figs. 9-11, ibid. ■ ' Experiment 6*, fig. 8, ibid. 282 THE 8EN80BY CENTRES corpus callosum had no paralysing effect either on the motor or sensory faculties. After the lesion in question the right eye was totally blind for several hours, but next day the animal was able to run about in every direction with perfect vision on all sides in the eye which had been totally blind the day before. The lesion of the corpus callosum had therefore no influence on the rapidity of compensation. When five Weeks subsequently the right angular gyrus was injured, but to a less extent than the left, total obscuration of vision in both eyes occurred, but of the most transient duration. On the right eye being bandaged, marked impairment of vision was evident in the left eye on all sides ; but this also speedily disappeared, and the animal remained perfectly well, and in full enjoyment of vision and all its other faculties. In another animal ' both angular gyri were cauterised very thoroughly, so as to destroy the grey matter of the sulci as well as the convexity. Total blindness ensued in both eyes without other defect, sensory or motor. The total blind; ness continued, however, only for three days. On the fourth day some indications of returning vision were observed, but the animal never during the whole period of its survival — over two months — regained perfect vision, but always exhibited some uncertainty or want of precision in its endeavours to seize things offered it, or to pick up minute articles of food from the floor, such as currants or grains of corn. After death it was found that the angular gyri had been completely obliterated ; but the occipital lobes and the optic radiations (fig. 25, or) passing backwards into them were uninjured. A suggestion has been made that injuries of the angular gyrus affect vision only by reason of implication of the optic radiations of the occipital lobes; but this has no foundation in actual fact. Nor, if it were, would the result be cross amblyopia, but homonymous hemiopia towards the opposite side, in case of unilateral lesion, and total and per- manent blindness in case of bilateral destruction of the tracts in question. The above-mentioned experiments show that lesion of the angular gyrus in all cases causes impairment of vision more or less transient according to the extent of the 1 Experiment 8*, figs. 12-14, PHI. Tram., Part II., 1884. THE VISUAL CENT BE 283 injury. The affection is not of a hemiopic nature, but shows itself in total blindness or amblyopia of the opposite eye. But the rapidity of compensation, and the fact that subsequent destruction of the other gyrus affects the clearness of vision in both eyes, indicate that each angular gyrus has relations with both eyes, though the cross relation is the only perceptible one on unilateral lesion. The last-mentioned experiment ren- ders it doubtful whether complete clearness of vision is ever regained after total extirpation of both angular gyri. § 6. As to other effects of lesion of the angular gyrus I have never seen, either on unilateral or bilateral destruction, the slightest appearance of ptosis or paralysis of the ocular muscles ; and, in direct contradiction to Munk, I have found the sensibility of the conjunctiva and the reflex closure of the eyelids as distinct as in the normal condition. If one may utilise Munk's own data, the account he gives of the effects of lesion of the angular gyrus demonstrates the absurdity of his notion that the angular gyrus is the sensory centre of the eyeball, and confirms the account above given of its rela- tion to vision. 1 After destruction of the left angular gyrus he found that brusque approximation of the finger to the left eye invariably caused winking, but the same action against the right eye only caused winking when the eyelids were actually touched ; a clear proof of the sensibility of the eye, and the non-perception of the threatened danger at a distance. This absence of winking at threatened danger he admits to be characteristic also of true blindness ; but inasmuch, says he, as this animal could not be blind, presumably because its occipital lobe was intact, ' therefore the absence of winking could only be due to the inability of the cortex to act on the sphincter palpebrarum.' This exquisite specimen of petitio principii needs no further comment. Further, he says that after destruction of the left angular gyrus, and closure of the left eye, the animal often fails to seize things offered it, or thrown down before it, especially when the objects are small— another clear indication of defective vision. Lastly, he says that on bilateral extirpation of the angular gyrus he has ob- served that monkeys ' after incomplete restitution ' — whatever 1 Munk, Die Functionen der Grosshirnrinde, p. 64. 284 THE SENSORY CENTRES this may mean — are unable, like normal monkeys, to take things offered them delicately with the fingers, but instead make grabs at them with the whole palm. This is only a further illustration of the same imperfection of vision observed in the last-mentioned experiment, which consisted in a want of precision in prehension, and a continual tendency to place the hand over, to the side, or short of, the object wished for, instead of directly on it at once. § 7. We have seen that the occipital lobes may be re- moved without any appreciable impairment of the faculty of clear vision ; that unilateral destruction of the angular gyrus produces only transient loss of vision in the opposite eye ; and that even bilateral destruction of the angular gyrus does not cause permanent total loss of vision. When, however, the angular gyrus and occipital lobe are together destroyed in the one hemisphere, as in the following experiment, transient amblyopia occurs in the opposite eye, and more or less enduring hemiopia in both eyes towards the side opposite the lesion, by reason of paralysis of both retina on the side cor- responding to the lesion. This condition of hemiopia, first pointed out by Munk, has been erroneously attributed by him to lesion of the occipital lobe alone, owing to the imperfection of his experimental methods. In the case in question ] the convexity of the left angular gyrus, together with the whole convex aspect of the left occipital lobe, was destroyed with the galvanic cautery. Transient total blindness occurred in the right eye, so that the animal continued for an hour to knock its head against every obstacle, and to be irresponsive to every test of vision. Subsequently, however, it was found, on examination of the right and left eye respectively, that there was loss of vision towards the right side. The animal knocked the right side of its head when moving among obstacles, and took things offered it, or picked up objects from the floor, only towards the left. In this animal, however, the hemiopia was not permanent, and within the short space of a fortnight all traces of the defect, formerly so evident, had disappeared. In this case, however, portions of the angular gyrus and a considerable portion of 1 Experiment 10*. fig. 17, Phil. Trans., Part II., 1884. THE VISUAL CENTBE 285 the mesial and inferior aspect of the occipital lobe remained intact. In another animal 1 a kind of diagonal experiment was performed. The convexity of the left angular gyrus was firs^ destroyed. Vision in the left eye appeared unimpaired. Vision with the right eye was lost, or impaired ; , but within an hour and a half the animal could see sufficiently well with this eye as to be able to pick up small articles of food on either side indifferently. Four months subsequently — the animal in the meantime being in all respects perfectly well — the right angular gyrus was cauterised, and the right occipital lobe removed bodily. The result of the second experiment was hemiopia towards the left. Eepeated tests of the range of vision in the right and left eye respectively proved that the limitation of vision was much greater in the left than in the right eye, the animal with the left eye closed being able to see well to the right, and also considerably to the left of the median line; while with the right eye closed vision to the left of the middle line appeared completely lost. As time went on, the range of vision to the left gradually increased, until, within a month after the second operation, it was impossible to discover in the manner in which the animal used its hands and eyes any sign of the hemiopic defect previously so manifest. In this case post-mortem examination proved that the left angular gyrus was merely superficially eroded, while the occipital lobe was intact; while on the right the convexity only of the angular gyrus was destroyed, but the occipital -lobe was obliterated. Yet, notwithstanding this extensive bilateral destruction of the visual centres, vision was ultimately regained to such an extent that no appreciable defect could be dis- covered in the animal's powers of visual perception and ideation. A somewhat similar diagonal bilateral lesion was made in the case of a monkey previously referred to (p. 275) . 2 Both occipital lobes had been extensively destroyed without any perceptible impairment of vision. Six weeks subsequently > Experiment 11*, fig. 16, Phil. Trans., Part II., 1884. 2 Experiment 9*, ibid. 286 THE SENSORY CENTRES the left angular gyrus was cauterised on the convexity, with the effect of causing temporary blindness in the right eye. This within a few hours had so far disappeared that the animal was able to guide its movements and pick up grains of oats from the floor with precision towards the left, but with some uncertainty towards the right. Next day clear vision to the right as well as to the left was fully established ; and from this time onwards no defect could be discovered. The animal continued active, vivacious, and intelligent, and maintained the leadership of its companion monkeys, which it had pre- viously assumed. Though, therefore, after extensive destruction of the oc- cipito-angular region in one hemisphere, the temporary ambly- opia of the opposite eye leaves a more enduring homonymous lateral hemiopia to the opposite side, yet unless the destruction of the cortex in this region is absolutely complete (and in none of the above-recorded experiments was this the case) restoration occurs, to such an extent at least that the defect ceases to be perceptible by any tests applicable to the lower animals. Whether exact perimetric exploration, such as can be carried out on human beings, would reveal some defect of visual acuity towards the opposite side is not improbable ; but the facts show beyond doubt that the previous total hemi- opia gives place to such a restoration of vision that the animal becomes again able to direct its actions with intelli- gence and precision accordingly. Luciani and Tamburini 1 have also found that the hemiopia, at first evident after de- struction of the angular gyrus and portion of the occipital lobe, is only of temporary duration. But there are reasons for believing that the restoration is due to incomplete destruction of the visual centres on the one side, and that hemiopia persists if every portion of the centres is removed or destroyed. It is, however, extremely difficult thoroughly to destroy a given centre, if at all exten- sively convoluted, by pure decortication, apart from secondary inflammatory action. Complete obliteration can be effected more readily, though without precision, by the secondary encephalitis usually following lesions established without anti- f ' Ski Centri Psico-sensori Corticali, 1879. THE VISUAL CENTRE 287 septic precautions ; and particularly by lesions implicating the medullary fibres of the given centre before they bave radiated to their ultimate cortical terminations. It is under the latter conditions, both in man and animals, that permanent hemiopia has been mainly, if not exclusively, observed in connection with lesions of the occipito-angular region. In one animal, 1 while endeavouring to destroy the hippo- campal region, I inflicted considerable injury on the medullary fibres and cortex of the left occipito-angular region. This resulted in some degree of right hemiopia, which, however, soon disappeared. The subsequent more extensive destruc- tion of the optic radiations of the occipito-angular region of the right hemisphere gave rise to left hemiopia, which at the end of three months was as absolute as at first, and showed no indications of retrogression. In this case the damage to the visual centres of the left hemisphere may have prevented their compensating for the lesion in the right hemisphere, if that were possible ; but the facts of clinical medicine are suf- ficient to prove that similar lesions confined to the one hemi- sphere are capable of causing permanent paralysis of the corresponding sides of both retinse. § 8. The various facts above narrated show that each hemisphere is in relation with the corresponding half of both retinse, and that the semidecussation of the optic tracts, pre- viously demonstrated (Chapter V. § 3) is maintained in the cortical centres. But the retinal relations of each hemisphere are somewhat more complex than a simple division of the retinal fields into two correlated halves projected on the cor- responding side of each hemisphere. For we have seen that unilateral lesion of the angular gyrus produces a temporary blindness, or amblyopia, of the opposite eye, which bas none of the characters of hemiopia ; and bilateral destruction induces a more or less permanent impairment of visual acuity on both sides. Certain facts recorded serve to show that each angu- lar gyrus has relations with both eyes, inasmuch as injury of the second, some time subsequently to the apparent entire disappearance of the effects of the first lesion, induces defect ' Experiment 26, figs. 117-124, Phil. Trans., Part II., 1884. 288 THE SENSORY CENTRES in both eyes. The cross action is, however, the only one which is capable of being detected in the lower animals from unilateral lesion ; though this does not exclude the possibility of a slighter impairment of vision in the eye of the same side not perceptible to ordinary tests. It appears to me, therefore, that, in addition to the repre- sentation of the correlated halves of both retinas in the corre- sponding occipito-angular region, the angular gyrus is the special region of clear or central vision of the opposite eye, and perhaps to some extent also of the eye on the same side. We have seen that the removal of the occipital lobes does not appreciably impair the faculty of vision, but that in all cases disturbances of vision, however temporary, resulted from lesions of the angular gyri alone. With these facts also should be taken the results of electrical exploration of the visual centres. While irritation of the angular gyrus invariably caused movement of the eyeballs to the opposite side, irritation of the occipital lobe was uniformly negative. 1 As these as well as certain other movements above described (Chapter VIII., § 6) are most probably merely associated movements, indicative of subjective visual sensations, their excitation from the angular gyrus alone would support the view that this is the centre of clearest vision. Before satisfactory evidence had been adduced to prove that hemiopia might occur in man in connection with cortical or subcortical lesions in the posterior lobe, Charcot, founding mainly on the facts of hysterical hemianeesthesia, had come to the conclusion that lesions of the "hemisphere, or of the posterior division of the internal capsule, produced only cross blindness or amblyopia of the opposite eye. In order to ac- count for this phenomenon, and at the same time to explain the hemiopia resulting from direct lesion of the optic tract, he propounded the following scheme of the constitution and relations of the optic tracts (fig. 92, with description). Among the fibres of the chiasma. are some [b' a) which cross to the opposite eye, and others (a' b) which pass to the 1 Luciani and Tamburini (op. cit.) have observed similar movements also from irritation of the occipital lobe. In reference to this I can only say that my explorations on at least ten separate animals gave no such phenomena SCHEMES OF THE OPTIC TRACTS 289 eye of the same side. The latter lie externally, while the former occupy a more central position in the optic tracts. Each tract in fact contains fibres for each eye, the external for the eye on the same side, the internal for the correspond- ing half of the opposite eye. Hence lesion of the left side of the chiasma, or of the left optie tract (k), will cause hemiopia of both eyes, paralysing the left side of both retinse. The external fibres, or those which do not decussate in the chiasma, decussate with their fellows in the corpora quadri- gemina (t q) , and so reach the opposite hemisphere ; while the fibres which decussate in the chiasma do not again decussate in these ganglia, but pass di- rectly through the corpora geni- culata (c g) into the hemisphere (l o g, l o d) . In consequence of this arrangement all the fibres of the right eye reach the left hemisphere, and all those of the left eye the right hemisphere. Hence lesion of the cerebral centre causes complete blind- ness of the opposite eye ; while lesions lower down, whether in the corpora quadrigemina, corpora geniculata, or optic tracts, affecting the two sets of fibres before they have run their complete course, cause partial blindness, or hemiopia of each eye. It cannot, however, be doubted that this scheme is un- satisfactory, and in contradiction with now well-established clinical as well as experimental, facts, which prove that hemi- opia may result from cortical and subcortical lesions of the posterior lobe, not affecting the optic tracts. Landolt ' has also shown that, even in those cases in which apparently only 1 La France Midicale, Feb. 3, 187,7. U Flo. 92. — Scheme of the Decussation of the Optic Tracts, according to Charcot. — T, semi- decussation in the optic chiasma. tq. de- cussation posterior to the corpora genicu' ata. CG, corpora geniculata. «'&, fibres which do not decussate in the chiasma. &'a, fibres which undergo decussation in the chiasma. &'a", fibres coming from the right eye which meet in the left hemisphere LOft. LOD, right hemisphere. K, lesion of the left optic tract, producing right lateral hemiopia. log, a lesion at this point, producing right ambly- opia. T, lesion producing temporal hemi- opia. ks, lesion producing nasal hemiopia. 290 THE SENSOBY CENTEES the opposite eye is affected, there is also some contraction of the visual field in the eye of the same side ; a condition which is not accounted for in Charcot's scheme. Those on the other hand are equally wrong who, like v. Grafe 1 and Fere, 2 in the scheme they propound of the cortical relations of the optic tracts, allow only for homonymous hemiopia as a consequence of lesion of the hemisphere or internal capsule. Some of the writers 3 who adopt this scheme boldly deny the existence of any well-authenticated case in which lesion of one hemisphere has caused blindness in the opposite eye. This is perfectly true as against any assertion of permanent monocular blind- ness, but no such assertion is made by those who contend that a cross cerebral amblyopia is both possible and proved. Apart altogether from hysterical hemiansesthesia, respecting the true nature of which doubts may be entertained, 4 there are on record 5 several carefully investigated cases of hemianesthesia, due to organic disease, in which, with some degree of "contraction of the visual field of the eye on the same side, there has been almost complete blindness, or very great impairment of vision, in the opposite eye. 6 1 Gas. Hebdomad. 1860. 2 L' Hemianopsie, 1882. 3 Mauthner, Vorbrttge a. d. Gesammtgebiete der Augenheilkunde, 1881 ; Starr, ' The Visual Area in the Brain, &c. Amer. Joum. Med. Sci., 1884. 4 A hypothesis of, in my opinion, a very far-fetched character has been propounded by Priestley Smith ('Keflex Amblyopia,' Ophthal. Review, May 1884) in explanation of the amblyopia met with in hysterical hemiansesthesia. This is to the effect that the amblyopia is due to reflex contraction of the vessels which nourish the retina. Though a general ischsemia exists on the hemiansesthetic side, tfiis is only one of an assemblage of correlated pheno- mena ; and to make it the cause of all the others, and to attribute to a degree of ischsemia, which is not discoverable by the ophthalmoscope, not only the amblyopia, but also the deafness, loss of taste and smell, loss of motor power, and the profound hemiansssthesia which exists in these cases, is a very large assumption, and without parallel elsewhere in the whole range of pathology. Our author attempts to account for the amblyopia, which I have described in connection with lesion of the angular gyrus, by a reflex contraction of the retinal vessels, caused by the cerebral injury. A reflex action from irritation of an insensitive surface would be a further novelty in physiology and patho- logy. And even if it could be admitted, the fact that it only occurs from lesion of the angular gyrus would show that this region has a special relation to the eye of the opposite side. s Grasset, Montpellier Midical, 1883 ; Ferrier, ' Cerebral Amblyopia and Hemiopia,' Brain, Part XII., 1881. 6 Sharkey (Medico-Chir. Transactions, vol. lxvii. 1884) has recorded a case SCHEMES OF THE OPTIC TRACTS 291 To such conditions the term hemiopia is altogether in- applicable, and the schemes of the constitution and relations of the optic tracts constructed by v. Grafe and his followers fail to explain them satisfactorily. 1 Of the various diagrams representing the relations of the optic tracts the one suggested by Sharkey 2 most nearly accords with experimental and clinical facts ; but it fails to account of great importance in this relation. The patient, a woman, aged 41, died in St. Thomas's Hospital of cardiac and pulmonary disease. Seven years pre- viously she was admitted as a patient into Guy's Hospital suffering from left hemiplegia and herniansesthesia. At this time there was dimness of vision in the left eye almost amounting to complete blindness. Four weeks after the- onset of the attack vision in the left eye had greatly improved, along with the other forms of sensation of the left side ; and, after less than three weeks more, vision in the left eye was completely restored. From this time till her death some degree of left hemiplegia continued, but the hemianassthesia had disappeared, and vision with the left eye was perfectly normal, there being no hemiopia or colour-blindness. The cause of the left hemiplegia and antesthesia was an embolism of the right middle cerebral artery, leading to softening and absorption of a considerable area of the left hemisphere, including the angular gyrus. But the occipital lobe was intact and in nowise reduced as compared with the right. Though, in this case, the lesion was too extensive to allow of accurate localisation, and though there appears to have been no accurate perimetric investigation of the field of vision in both eyes, there can be little doubt that the affection of vision was mainly of the nature of a crossed amblyopia, such as results from lesion of the angular gyrus in the monkey. And it is further noteworthy that the occipital lobe was uninjured. It is quite true that patients affected with hemiopia complain mainly, not exclusively, of loss of vision in the eye on the hemiopic side. Thus an individual with loss of vision towards the right, owing to homonymous defect in the left side of both retinas, attributes his symptoms to the right eye alone. In the absence of careful investigation, therefore, the mere statement of a patient is not to be accepted as satisfactory proof that only one eye is affected. But this case is not of that nature, having been investigated by competent physicians, and is in perfect harmony with other similar cases, in which a careful perimetric exploration has shown that the eye opposite the cerebral lesion has alone appreciably suffered. 1 A scheme suggested by Grasset (MontpeUier Medical, 1883), in which the fibres from the outer side of both retinue are made to decussate twice— once in the corpora quadrigemina, and again in the corpus callosum— before reaching their ultimate termination in the cortex, though it explains the possibility of mon- ocular blindness by lesion of the internal capsule, and of hemiopia by lesion of the occipital lobe, is highly artificial, and also not in accordance with the facts of experimental lesion of the angular gyrus apart from lesion of the internal * ' Case of Homonymous Hemianopia,' Trans. Ophth. Soc, vol. iv. 1883. it 2 292 THE SENSOBY CENTRES for the partially bilateral relations of the angular gyrus. The accompanying scheme (fig. 93) more completely fulfils the various requirements, though it is to be regarded as a mere diagram, and not as an actual anatomieal picture. Each occipital lobe is in relation with the half of each retina on its own side, while each angular gyrus is in relation with the centre of the opposite eye, partly by fibres which are supposed to cross in the chiasma, and partly by fibres which reach it after decussation in the lower visual centres — possibly the corpora quadrigemina. At the same time also a partial intermingling in the chiasma of the fibres from the centre of each eye brings each angular gyrus to some extent also in Fig. 93. — Scheme of the Optic Tracts and Visual Centres.— A, the right, and A' the left angular gyrus, c, optic chiasma. E, the right, and b', the left eye. n, the right and n', the left optic nerve, o, the right, and 0', the left occipital lobe. T, the right, and T 1 , the left optic tract. The thin continuous line represents the retinal relations of o. The thick continuous line _ represents the retinal rela- tions of o'. The interrupted line — _ _ indicates the retinal relations of A, and the dotted line .... the retinal relations of A'. The relations of A and a' ■with the eye on the same side are indicated by finer interrupted and dotted lines respectively. relation with the eye on the same side (see fig. 93, with description). The relations indicated in the scheme would account for the greater affection of the opposite eye from destructive lesion of the one angular gyrus, and the bilateral amblyopia from destruction of both angular gyri. The exact extent of retinal field in relation to each angular gyrus is only a matter of SCHEMES OF THE OPTIC TRACTS 293 speculation; but, inasmuch as bilateral destruction of the occipital lobes in the monkey does not appreciably affect the range of vision, the angular gyri must maintain relations with the full area of clear vision, and as a matter of course specially with the maculae luteae. Though the destruction of one occi- pital lobe does not appear to cause any hemiopic defect so long as the angular gyrus is intact, yet when the angular gyrus is destroyed the removal also of the occipital lobe leads to paralysis of the corresponding side of both retinae. In such case we should still expect to find a small area of central vision on all sides of the fixation point, innervated by the undestroyed angular gyrus of the opposite side, and the ex- tent of the visual field will be greater on the side of lesion than on the opposite. As a matter of fact this is the condition actually demonstrated by accurate perimetric observation in a large proportion of the cases of hemiopia which have been observed in man. 1 § 9. But the clinical records at present existing 2 in regard to the position of the fixation point, and the condition as to central vision in cases of hemiopia, are so often marked by such laxity and imperfectness of perimetric investigation, that little reliance can be placed upon them in this relation, and the whole subject is in need of careful revision. In a case of hemiopia, from the symptoms undoubtedly of cortical origin, reported by Sharkey, 3 there was in the eye opposite the lesion an area of normal vision extending to from 15°-55° from the fixation point, and in the eye of the same side a similar area extending from 15°-70° from the fixation point. On the other hand, Nettleship 4 has recorded a case in 1 Wilbrand (Hemianopsie, Berlin, 1881) gives the proportion as thirty-three in fifty-six cases reported by various authors. Hirsehberg, from his examina- tion of oases of hemiopia, regards it as the rule that the vertical line diverges towards the defective side so as to leave an area of central vision of from 3° to 5° in extent. ' 2 See on this subject Nothnagel, Topische Diagnostik der Gehimkranklieiten, 1879 P- 586 et seq. ; Bellouard, L' Himianopsie, 1880 ; Wilbrand, Hemian- opsie 1881 ; Mauthner, Vortrage a. d. Gesammtgeb. d. Augenheilkunde, 1881 ; Starr ' The Visual Area in the Brain, &o.' Amer. Journ. Med. Sci., 1884 (a brochure, however, characterised by numerous gross inaccuracies). » Trans. Ophth. Soc, Oct. 1883. * Nettleship, Trans. Ophth. Soc, Oct. 1883. 294 THE SENSOBY CENTRES which, from lesion of the optic tract, there was hemiopia in the eye of the same side (the other being completely blind from destruction of the optic nerve) divided exactly by a line passing through the fixation point. Other cases have been reported of hemiopia due to lesion of the optic tract, proved post mortem,' 1 in which, though in some respects lacking in precision, the line dividing the normal and defective retinal halves appears to have been vertical through the fixation point. Inasmuch as in some cases of hemiopia it has been proved by exact perimetric investigation that the vertical line dividing the normal from the defective retinal halves has passed through the fixation point, and in others has swerved to a greater or less extent away from this point towards the defective side, and unsymmetrically in each eye, it is clear that there must be difference in causation in the two cases ; and the facts and considerations which have gone before render it most probable that the differences depend on whether the optic tract itself is affected, directly or indirectly, in any. part of its course as far as the primary optic nuclei, or whether the lesion is strictly cerebral. There is not on record a single case of cortical lesion limited to the occipital lobe in which hemiopia has occurred. On the other hand many cases have been reported 2 of lesion of one or both occipital lobes without any discoverable symptoms. It might be said of the cases of unilateral lesion that hemiopia may have existed and been overlooked ; but this would be impossible in a case of bilateral lesion, for then the patients ought to have been blind, if lesions of the occipital lobes alone really caused hemiopia. In most of the instances of hemiopia, which have been examined after death, in which the optic tracts, optic thalami, or corpora geniculata have not been obviously diseased, the lesions have been found in the medullary fibres of the posterior region, vaguely and inaccurately called the occipital lobe ; or if the cortex has been mainly affected, the lesions have been multiple and diffuse, and not confined to the occipital region ; and in addition to hemiopia there have been hemiplegia, hemiansesthesia, aphasia, or other symptoms of extensive im- 1 See Wilbrand, Hemianopsie, p. 93. 2 See the author's Localisation of Cerebral Disease, 1878. THE VISUAL CENTRE 295 plication of the cerebral tracts and centres beyond those of the occipito-angular region. It is impossible, therefore, to found on such material any accurate inductions as to the limits and relations of the visual centres. We may interpret the clinical facts in the light of experimental research, but of themselves they are altogether insufficient to establish any rigid conclusions as to the limits of the visual area, and certainly do not establish any relation between hemiopia and lesion of the occipital lobe as such, apart from the angular gyrus. § 10. The visual centres in the lower mammals, especially those of dogs, have been the subject of numerous investiga- tions of recent years. Among the more important of these are the researches of Munk, 1 Luciani and Tamburini, 2 Dalton, 3 Bianchi, 4 and Loeb. 5 Those of Loeb, 6 conducted under the auspices of Goltz, are specially worthy of trust. In none of the researches by these different experimenters, however, have the exact limits of the visual sphere in dogs been determined with any degree of accuracy or harmony. In all cases the lesions causing temporary, or enduring, dis- turbances of vision have involved the posterior division of the second external eonvolution (fig. 73, (13)) ; the region which, from the homology of the electrical reactions, I have indicated as the visual centre. But none of the authors have sufficiently defined by accurate post-mortem examination the exact extent of cortex destroyed, either primarily or by secondary inflammatory processes, in ' Die Fwnctionen der Grosshimrinde, 1881. 2 ' Sui Centri Psioo-sensori Cerebrali ' (Bivist. Speriment. 1879) ; and Luciani, in Brain, July 1884. s ' Centres of Vision in the Cerebral Hemispheres,' New York Med. Rec, 1881. 4 ' Sulle Compensazioni Funzionali della Corteoeia Cerebrale,' Rivist. Speriment. 1883. 5 ' Die Sehstorungen naoh Verletzung der Grosshimrinde,' Pfluger's Archiv, Bd. xxxiv. 1884. « This writer, however, while thoroughly exposing the falsity and absurdity of the statements of Munk, is, by reason of some strange intellectual blindness, unable to see that the very experiments on the basis of which he wages a feeble and futile polemic against cerebral localisation in reality support the truth of this doctrine in the strongest possible manner. 296 THE SENSOBY CENTBES those cases in which the visual disorders remained permanent —the only condition which can satisfy the requirements of scientific evidence as to the true boundaries of the visual area. In some cases the disturbances of vision from unilateral lesion have been merely temporary, in others they appear to have lasted indefinitely or permanently. Until the question has been determined, how much of the cortex it is necessary to destroy in order to produce the latter effect, it is absurd to argue that because experimenters are not agreed on this point therefore there is no fixed and determinate visual area in the hemisphere. It is also premature, until, this has been satisfactorily determined, to propound hypotheses as to com- pensation by other parts of the same hemisphere or by the other. For, so long as any portion of a centre remains, its specific function is capable of being manifested to a greater or less degree. Similarly in reference to bilateral lesions. In some cases the blindness, at first complete in both eyes, has not been permanent. But in others, as in one of Munk's . experiments, 1 complete and permanent blindness in both eyes, without any other defect either as regards sensory or motor power, appears to have been produced. Such a fact shows that the recovery of vision, which others have observed even after bilateral destruction of the same region, is due merely to less complete extirpation. Differences of this kind depend in all probability on the varying extent of secondary softening in the hands of the different experimenters. It was found by Hitzig and by Goltz that the affection of vision from unilateral lesion of the cortex manifested itself exclusively in the opposite eye. Munk 2 in his first experi- ments arrived at the same conclusion. Lesion at the point a (fig. 94) he found caused visual disturbances only in the opposite eye. 3 Dalton also found that the opposite eye alone was rendered * Munk, op. cit. p. 99. 5 Further on this subject, and on the presentative and re-presentative rela- tions of the cortical centres, see Chapter XII. 8 In what is obviously merely temporary impairment of visual perception, due to only partial lesion of the visual sphere, Munk assumes the existence of what he absurdly terms ' psychical blindness' (Seelenblindheit), in contradis- tinction to ' cortical blindness ' (Bindenblindheit). THE VISUAL CENTRE 297 blind, and to all appearance permanently so, when the cortex was destroyed in the region of the posterior division of the second external convolution, which he terms the angular convolution. 1 Luciani and Tamburini, on the other hand, found that destruction of the second external convolution, more par- ticularly of its median or parietal portion, caused blindness of the opposite eye, and also some degree of amblyopia of the eye on the same side. § 11. The further experiments of Munk, however, as well as those of Loeb, and also later experiments by Luciani 2 have shown that, though in dogs each visual sphere is mainly in relation with the opposite eye, it is also in relation with the outer quadrant of the eye on the same side ; so that destruction of the visual centre in one hemisphere paralyses the inner three-fourths of the opposite retina, and the outer fourth of the eye on the same side. The condition, therefore — at least the enduring one— is that of homonymous hemiopia towards the opposite side, the defect in the eye opposite the lesion greatly exceeding that of the eye on the same side. But the facts recorded by Luciani and Tamburini seem to show be- yond doubt that, for a short time at least, after the destruction of the middle portion of the second external convolution, there is complete blindness in the opposite eye. There is, however, no real discrepancy, between these results, and we appear to have in dogs relations of the visual sphere similar to those obtaining in monkeys in the angular gyrus and occipital lobe respectively. The middle portion of the second external convolution is 1 Loeb makes an egregious blunder in calling the Sylvian convolution (see his figure, op. cit.) the angular convolution, and attributing to Dalton the localisation of the visual sphere in this region. Dalton expressly defines his angular convolution as the posterior division of the second external convolution. He describes two experiments : in the one case the lesion extended also into the convolution above and behind it, and in the other the lesion involved also the two convolutions between this and the fissure of Sylvius. The latter state- ment, as well as the figures illustrating the paper, should, one would think, have 'been sufficient to prevent such a blunder on the part of one otherwise so careful. ■' < Sensor. Local, in the Cortex Cerebri,' Brain, July 1884. 298 THE SENSORY CENTRES that which corresponds in its electrical reactions with the angular gyrus, and we may regard the posterior portion as the homologue of the occipital lobe. The region which Munk defines as the visual sphere em- braces a considerable extent of the posterior extremity of the hemisphere, chiefly the posterior division of the first and second external convolutions (fig. 94, a, a). The point a u situated chiefly in the posterior division of Fig. 94. — A, A the Visual Area in the Brain of the Dog, according to Munk. the second external convolution, which he first regarded as especially the depository of the visual pictures (Erinnerungs- bilder) of the opposite eye, and the destruction of which caused 'psychical blindness' (Seelenblindheit) — in contradistinction to ' cortical blindness ' (Rindenblindheit) , to produce which it was necessary also to destroy the whole of the area marked a — he subsequently defined as the centre of clear vision in the opposite eye. Further, the mesial portion of the visual sphere, adjoining the falx, is the centre for the inner half ; THE VISUAL CENTBE 299 the anterior portion, for the upper half; and the posterior portion, for the lower half, of the opposite retina. The lateral portion he regards as the centre for the outer quadrant of the eye on the same side. Destruction of each portion induces blindness in the re- spective region of the eye on the opposite or the same side accordingly, and it is only by eccentric fixation of the eyes, or by practice, that the animal is able to overcome the defects so induced. These statements, for which the evidence adduced by Munk appears ridiculously insufficient, have been conclusively refuted by Loeb. Loeb has shown by carefully devised ex- periments — in many of which he first enucleated one of the eyeballs, where it was necessary that it should be entirely eliminated — that there is no single portion of the region included within the visual zone by various authors, which may not be injured without causing any visual defect per- ceptible on the day after the operation, nfunk's assertion that lesion of the point a, (fig. 94) causes uefect in the point of clear vision is especially erroneous, as it is precisely this point which is least affected when visual disturbances do occu^l When visual disturbances do ensue — which is the rule, and as the records of the various experiments show, particularly when secondary extension of the primary lesion occurs, cr when the operations are repeated — they are in- variably of the character of hemiopia or hemiamblyopia. There is no foundation whatever for the statements made by Munk that particular regions of the retina are in special relation with particular regions of the visual zone.] "When defect of vision occurs from lesion of the posterioTTobe, it is always of the same hemiopic character, whatever region is specially injured. The lateral portion of the sphere defined by Munk is not specially in relation with the outer quadrant of the eye on the same side, nor any portion more in relation with one part of the opposite retina than another. In par- ticular, as remarked, central vision is precisely that which is least affected in all cases, whether of unilateral or bilateral lesion of the visual zone as defined by Munk. There is never any eccentric or abnormal fixation of the 300 THE SENSORY CENTRES eyeballs when the special regions indicated by Munk are destroyed, such as would necessarily result if particular por- tions of the retina were paralysed. Nor is the recovery of vision, after partial lesions of the visual zone, due to practice and the acquisition of new visual experience ; inasmuch as recovery takes place when the animal is kept absolutely in the dark, and prevented from exercising its visual faculties. 1 The results obtained by Loeb are in perfect harmony with the strict localisation of a visual sphere in the hemisphere. Partial lesions produce only transient effects, which may not be perceptible on the day after the operation. But to argue, as this physiologist does, that there is no definite visual sphere in the hemisphere because the limits may not have been correctly assigned by any of the experimenters, and because unfounded assertions have been made by Munk, is in the highest degree illogical ; and he is contradicted by his own experiments, in which it is clearly shown that the degree and duration of the hemiopia varied with the degree of destruction „ of the occipital region, and in some cases remained permanent without any appreciable defect otherwise in the animal's powers and capacities. On grounds of homology we have every reason for con- cluding that the region (fig. 73, (13)) from which electrical re- actions are obtained, similar to those of the angular gyrus in monkeys, is the extreme anterior limit of the visual zone ; while the posterior limits are not exactly defined, though the posterior or occipital .division of the second external convolu- tion appears to be the most important part of the visual sphere. § 12. The limits of the visual area in cats have not been the subject of much experimental research, but the anatomical disposition and electrical- reactions of the parieto-occipital division of the second external convolution (fig. 77, (13)) indicate without doubt that this region is homologous with the visual zone of the dog's brain. That in cats also each centre is in relation with the corresponding side of both retinse, as in dogs, 1 That practice is of no importance, however, is not denied. The great fact is that it is not essential. ' Indess will ich nicht in Abrede stellen, dass auch die Uebung sich bei erstoperirten Thieren von Vortheil erwiesen mag ' (op. cit. p. 60). THE VISUAL CENTBE 301 is more than probable. The researches of Gudden ' and others on the constitution of the optic chiasma in cats show that, as in dogs, there is a semi-decussation of the optic tracts ; and Nicati 2 found experimentally that division of the chiasma in the antero-posterior or sagittal diameter did not cause complete loss of vision in either eye ; a ' fact explicable Only on the theory of semi-decussation of the optic tracts. In one experiment which I made on a cat I observed that, after destruction of the visual zone of the left hemisphere, (fig. 77, (13)), there appeared to be complete blindness of the opposite eye, and that the animal — the left eye being closed — • knocked against every obstacle in its path. On the left eye being unclosed the animal walked with greater freedom, but still occasionally knocked the side of its head. This I attri- buted 3 to blindness still existing in the right eye ; but on again examining into the facts of the case, I am inclined to think that the true explanation was a hemiopic defect in both eyes, continuing after the temporary total blindness of the eye opposite the lesion. As regards rodents the visual centre would, according to the homology of the electrical reactions, occupy the parieto- posterior region of the hemisphere (fig. 78, (13)), a region anatomically corresponding with (13) in the brains of the gyrencephalous animals. The exact limits of the visual zone in these animals do not appear to have as yet been experi- mentally determined by any inquirer, but lesion of the hemi- sphere of the rabbit involving the region indicated has been found by Moeli i to cause loss of vision in the opposite eye of a more or less temporary character. The total loss of vision in the opposite eye observed by Moeli seems to accord with the results of sagittal section of the optic chiasma in this animal and the guinea-pig obtained by Brown- Sequard. 5 As a consequence of this operation there 1 Archiv f. Ophthalmologic, Bd. xx. 1874. 2 Archives de Physiohgie, Ser. II. tome v. 1878. 3 First edition, p. 170. • ' Versuche an der Grosshirnrinde des Kaninchens,' Virchow's Archiv Bd. lxxvi. 1879. 5 ' Sur les Communications de la Betine avec l'Encephale,' Archives de Physiologic, 1871-72. 302 THE SENSORY CENTRES was total blindness in both eyes. Gudden ' also, in his first researches on this point, was of opinion that there was total decussation of optic tracts in the rabbit, and that enucleation of the eyeball, or destruction of the optic tract or centres on one side, led to complete atrophy of the opposite tract or nerve respectively. But in his later researches 2 he arrived at the conclusion that there was a small fascicle of uncrossed or direct fibres also in this animal, similar to the arrangement obtaining in the higher animals. This being the case, it would be more probable that in the rabbit also each hemi- sphere would have relations, to some extent at least, with the eye on the same as well as on the opposite side. Some ex- periments made by Munk 3 support this view, but the question is one which cannot as yet be regarded as definitively deter- mined. § 13. As regards pigeons and birds generally there is a region (fig. 82, x ) , electrical irritation of which causes reactions homologous with those of (13) in the brain of higher animals* The region in question occupies the parieto-posterior aspect of the hemisphere, where the cortex forms a thin lamina over the central ganglion, and corresponds anatomically with the visual zone of the gyrencephalous animals. McKendrick 4 found that destruction of this region caused blindness in the opposite eye ; whereas removal of the anterior part of the hemisphere had no effect on vision, nor removal of the posterior extremity of the hemisphere. Similar results have been obtained by Jastrowitz. 5 Blaschko, 6 however, found that vision did not seem entirely abolished in the opposite eye by destruction of the cortex in the region indicated ; and Munk, 7 continuing his researches, came to the conclusion that, though vision seems at first to be entirely abolished in the opposite eye, yet after a time it 1 Archiv f. Ojohthalmologie, Bd. xx. 1874. « Ibid. Bd. xxv. 1879. 8 TJeber die centralen Organe fur das Sehen u. d. Horen bei den Wirbet- thieren, 1883. 4 ' Observations and Experiments on the Corpora Striata and Cerebral Hemispheres of Pigeons,' Trans. Boy. Soc. of Edinburgh, January 1873. b Archiv filr Psychiatrie, Bd. vi, 1876. 5 Inaugural Dissertation, Berlin, 1880. . ' Memoir cit. sup. THE VISUAL CENTRE 303 appears that the extreme outer or lateral region of the retina is not paralysed ; indicating that each hemisphere, as in the higher animals, is partially in relation with both eyes. It is usually stated that in pigeons a complete decussation of the optic tracts occurs in the chiasma; hut Gudden, 1 who at first regarded this as beyond all doubt, questions whether there may not be some uncrossed fibres in these animals as well as in rabbits. That even in the pigeon, with its widely separated and laterally placed eyes, a certain amount of binocular vision is possible was indicated by Miiller, 2 who found, in addition to the usual fovea centralis, another fovea, situated nearer the temporal region of the retina. The outer fovesB would serve for binocular, and the central fovese for monocular vision. Muller's statements as to the existence of two fovea have been confirmed by Hirschberg 3 by ophthalmoscopic examina- tion. These observations have been quoted by Munk in corroboration of his experimental results, to which, if correct, they undoubtedly lend considerable support. § 14. That the visual area of the cortex is not merely a functionally differentiated region capable of being replaced by some other portion of the hemisphere, but anatomically the central expansion of the optic radiations, and therefore struc- turally distinct from all other centres, is proved by the atrophy which ensues in the primary optic centres, tracts, and nerves when the visual zone proper is destroyed, and by the atrophy occurring in, and strictly confined to, the region included within the visual zone when the optic radiations are severed. That atrophy occurs in the primary centres, tracts, and nerves from lesion of the visual zone of the cortex, altogether apart from direct injury to these structures, has been abun- dantly proved. In one of the experiments above related, in which the animal was rendered completely and permanently blind, the gradual evolution of atrophy of the optic discs was distinctly traced during life ; and after death the optic nerves, tracts, and primary centres were found to be greatly reduced 1 Archiv fur Ophthalmologie, Bd. xxv. 1879. 5 Heinrioh Miiller, Gesammelte Schriften (by Becker), 1872, p. 143. »•' Zur vergleichende Ophthalmoscopic,' Du Bois-Beymond's Archiv, 1882. 304 THE SENSORY CENTBES in size as compared with those of a normal brain. Similar facts have been recorded in connection with lesions or defects in the occipito-angular region in man. 1 Gudden 2 found that destruction of the cortex in the left parieto-occipital region in a new-born puppy led to atrophy of the left corpus geniculatum externum, left anterior tubercle of the corpora quadrigemina, the left optic tract, and to some extent of the right optic nerve. Monakow 3 observed similar results in rabbits on destruc- tion of the occipital region ; and Ganser 4 the same in cats on destruction of the cortex, involving the parieto-occipital region. Monakow has further shown that the atrophic changes, con- secutive to destruction of the cortical visual centres, affect special tracts and structures, viz. the optic radiations, median medullary layer (fig. 49, m m) of anterior tubercle, and the cells of the corpus geniculatum externum and pulvinar ; whereas when the eyeball is enucleated the atrophic changes occur in the gelatinous ground-substance of the corpus geniculatum exter- num, pulvinar, and anterior tubercle of the corpora quadri- gemina, and in the last also in the cells of the superficial grey layer. It thus appears that of the structures composing the pri- mary optic nuclei some are more immediately related to the cortical centres, others to the optic tracts ; and that between these two connections exist, which serve to establish an in- direct relationship between the eyes and the cortical visual sphere. But while destruction of the cortical centres leads indirectly to atrophy of the optic tracts, it has not been satis- factorily established that enucleation of the eyeball leads to atrophy extending beyond the primary centres. Neither Gudden, nor Ganser, nor Monakow has been able to discover any indubitable cortical atrophy after enucleation of the eyeball in cats, dogs, or rabbits. Hence, though such an occurrence 1 See Sharkey's case, already referred to, p. 290. Monakow (Archiv f. Psychiatrie, Bd. xiv. 1883) has minutely investigated a similar case of atrophy of the optic tracts in connection with porencephalic defect of the occipito- angular regions. Dr. Cobbold, of Earlswood, has submitted to me for examina- tion the brain of an idiot in which the same condition existed. 2 Archiv f. Ophthalmologic, Bd. xxi. 1875. s Archiv f. Psychiatrie, Bd. xii. 1881, * Ibid. Bd. xiii. 1882. THE AUDITOBY CENTBE 305 is theoretically possible, especially in cases of congenital absence of the organ of vision, or removal before it can have been employed to any extent as a channel of perception, the statements of some authors that they have observed secondary atrophy of the visual zone consecutive to the enucleation of the eye or eyes, must be viewed with considerable caution. The atrophic changes seem to be arrested in the primary centres. But when the optic radiations themselves are severed, as in certain experiments on rabbits made by Monakow, atrophy extends both centrally and peripherically. In the latter case the atrophic changes are exactly such as result from destruction of the cortical visual area itself. In the former the atrophy becomes manifest in the region em- braced in the visual zone (parieto-occipital region), and par- ticularly affects the third and fifth layers of the cortex — viz. the layer of granules and large pyramidal cells, and the layer of multipolar cells immediately external to the medullary layer, which is also remarkably reduced. Monakow therefore concludes that the optic radiations are specially connected with the third and fifth layers of the cortex in the visual area. A further confirmation of these interesting and important observations is eminently desirable. But it follows from the various facts recorded that the localisation of a special area of visual perception in the cortex is based on structural as well as functional relations with the eyes ; so that a functional equivalence or indifferentism of the various regions of the cortex and the theory of one region compensating for the loss of another are assumptions which involve anatomical impossibilities. Paet II. — The Auditory Centre. § 15. Among the reactions consequent on electrical irrita- tion of the hemisphere there is one the significance of which might almost be deduced a priori. The reaction in question is that which occurs on electrical irritation of the superior temporo-sphenoidal convolution, viz. pricking of the opposite ear, associated with wide opening of the eyes, dilatation of the pupils, and turning the head and eyes to the opposite side. 806 THE SENSORY CENTRES These phenomena are just such as occur when a. loud sound is made in immediate proximity to the opposite ear. Taking a monkey I placed it on a table, and while all was still I made a shrill whistle close to the animal's right ear. Imme- diately the ear was pricked, and the animal turned with a look of intense surprise, with eyes widely opened and pupils dilated, to the direction from which the sound proceeded. On repetition of the experiment several times, though the pricking of the ear and turning of the head and eyes in the direction of the sound invariably occurred, the look of sur- prise and dilatation of the pupils ceased to be manifested. From the mere character of the reactions, therefore, it might be fairly concluded that irritation of the superior temporo- sphenoidal convolution arouses subjective auditory sensations, of which the pricking of the ear, and attitude of surprise, or ■excited attention, are merely the outward physical manifesta- tion. Equally, if not more characteristic, are the effects observed On stimulation of the homologous region in the brains of the lower animals, whose habits are such as to make their safety largely dependent on the acuteness of their hearing. In the cat, dog, and jackal this region is embraced in the posterior division of the third external or supra- Sylvian convolution (figs. 73, 75, 77, (h)). In all these pricking of the opposite ear was invariably seen, but the rest of the associated reactions varied in intensity. In the brain of the rabbit stimulation of the corresponding region (fig. 78, (i+)) caused also pricking of the opposite ear, frequently associated with turning the head and eyes in the supposed direction of the sound. But in the wild jackal and timid rabbit there was not only the reflex pricking of the ear, but the quick start or bound, as if to escape from danger, such as might be indicated by loud or unusual sounds. In the pigeon the absence of the auricle renders it more difficult to fix on any simple movement as the associated expression of auditory sensation, but in this animal also the occasional turning of the head to the opposite side, on stimulation of the parietal region below and behind the visual centre, is in all probability of the same nature as the foregoing. THE AUDIT OBY CENTRE 307 But in addition to the strong presumption furnished by the character of the electrical reactions that the superior temporo- sphenoidal convolution in the monkey (or its homo- logues in the brain of the. lower animals) is the centre of hearing, the results of localised destruction of this convolution are such as to prove this beyond all doubt. To test the sense of hearing in the lower animals, and to distinguish between mere reflex reaction to auditory impres- sions and auditory sensation proper, is a matter of some difficulty ; and it is especially difficult to determine the exist- ence of unilateral deafness, on account of the impossibility of absolutely restricting sonorous vibrations of any intensity to one side alone. By plugging the one ear this may in a measure be overcome, if the test sounds are not of great intensity ; but the possibility of conveyance of sonorous vibra- tions through the skull, apart from the tympanic apparatus, must always be taken into account. § 16. In several preliminary experiments 1 on the temporo- sphenoidal lobe the lesion was not confined to the superior temporo-sphenoidal convolution, but when this was involved on the one side there was absence of the usual reaction to auditory stimuli proper when the ear of the same side was securely plugged. When the lesion was bilateral there was total absence of response to auditory stimuli, which usually excite active reaction and signs of attention. In one experiment 2 the left angular gyrus had been pre- viously cauterised the day before, and all effects had passed off. ' The superior temporo-sphenoidal convolution was then exposed on both sides and each accurately destroyed (figs. 95, 96). Bepeated tests indicated retention of tactile sensibility, taste, smell, and vision, and complete volitional motor power. But hearing was to all appearance entirely abolished. As the animal was keenly on the alert, it was not easy to devise an entirely satisfactory test without arousing its attention otherwise. In order to avoid attracting its attention by sight, I retired into another room, and watched the animal through 1 Experiments XI., XII., XIII., XIV., Phil. Trans, vol. olxv., Part II. 2 Exp. 'XV., ibid. x 2 308 THE SENSORY CENTRES a chink in the door. While it sat comfortably before the fire it paid no attention whatever to loud calls, shrill sounds, or whistling. For purposes of comparison another monkey, whose powers of hearing were undoubted, was placed with it as a companion, and the tests repeated as before. The differ- ence in the behaviour of the two was most striking. While the normal monkey became startled at each sound, and peered Fi<:s. 05 ami 90. — The shading In these figures indicates the position of the lesions of the cortex in the hemispheres of the monkey, causing loss of hearing in both ears and temporary loss of sight in the right eye. The dotted line indicates the extent of the surface exposed by removal of the skull. (Roy. Soc.) about curiously to ascertain its origin, the other appeared altogether unconcerned. By repeated and otherwise varied tests it was clearly established that the animal was perfectly indifferent to sounds which in other monkeys excite lively re- action, while in all other respects it was quick and keenly responsive. Beyond this, as a proof of deafness, it seems im- possible to go in the lower animals. The same result is THE AUDIT OBY CENTRE 309 further conclusively demonstrated in the following experiment, in which also the permanency of the symptoms is satisfactorily shown. In this animal l the superior temporo-sphenoidal convolu- tion was cauterised in both hemispheres ; and, as was found on careful examination, 2 the lesions were accurately confined to this convolution in both hemispheres, without inflammation or secondary extension. The animal was allowed to survive Figs. 97 and 98. — Destruction of Superior Temporo-sphenoidal Convolution on both sides, causing complete deafness. (From photographs.) for more than a year, during which time, from the beginning till the end, it enjoyed perfect, health and the full enjoyment of all its faculties and powers, with the single exception of hearing. No sign of hearing, or even twitching of the ears, could be elicited by sounds which invariably attracted the 1 Experiment 13*, Phil. Trans. Part II. 1884. 2 See the series of photographs of sections illustrating the text, Plate 22 (figs. 23-38). S10 THE SENSORY CENTRES attention of other monkeys which were its companions, or which were subjected to the same conditions. Six weeks after the operation the animal was exhibited before the physiological section of the International Medical Congress in London, 1881, 1 along with another monkey affected with right hemiplegia from lesion of the motor area of the left hemisphere. While it was climbing about, and disporting itself before the audience, a percussion cap was exploded; causing the hemiplegic monkey to start suddenly, while this one remained perfectly unconcerned, and gave not the slightest indication of having heard anything. All present admitted that the animal was undoubtedly deaf; it was defective in no other respect. As time went on tests were continually repeated and varied. Occasionally a doubt was raised as to whether the absence of reaction to sounds was absolute. But careful examination, and elimination of mere coincidences of movement in an animal keenly alert to all its surroundings, established clearly that the condition of total deafness re- mained unchanged during the whole period of survival. Further proofs of the localisation of the auditory centres in the superior temporo-sphenoidal convolutions are almost superfluous. In all experiments on the temporo-sphenoidal lobe in which there was any evidence of impairment or loss of hearing, the superior temporo-sphenoidal convolution was involved in the lesion. On the other hand hearing is not impaired by destruction of any other portion of the temporo- sphenoidal lobe. In at least a dozen cases in which I have established the most extensive lesions in, or entirely removed the whole of, the temporo-sphenoidal lobe, with the exception of the superior temporo-sphenoidal convolution, on one or both sides, I have obtained clear indications of the continu- ance of signs of perception of auditory stimuli, indicated by twitching of the ear and turning to the origin of slight sounds, such as tapping, scratching, or whispering close to the ear. My results have been entirely confirmed by Horsley and Schafer, who have informed me that their experiments have shown that it is only when the superior temporo-sphenoidal 1 See Transactions of the International Medical Congress, 1881, vol. i. p. 237. THE AUDITORY CENTRE 311 convolution is destroyed that hearing is impaired or abolished, and that no such effect is produced by entire removal of the rest of the temporo-sphenoidal lobe. § 17. As to the position of the auditory centre in dogs and the other lower mammals we should, even without further experimental demonstration, have good reason for localising it in the region which reacts similarly to that of the monkey on electrical excitation (see area (14), figs. 73, 75, 77, 78). Munk states l that a destructive lesion in both hemispheres, established primarily towards the lower extremity of the third external convolution, and involving also the adjacent ex- tremity of the second external convolution, causes temporary impairment of hearing, which, as in the case of vision, he calls ' psychical deafness.' This, however, in the course of a few weeks entirely disappears, so that at the end of this time no difference from the normal can be detected. At first, how- ever, before the disturbances induced by the primary lesion have subsided, the animal appears to be totally deaf, and exhibits no reaction to the loudest sounds. In order to secure total and enduring deafness — absurdly termed by him ' cortical ' (Bindentaubheit) in contradistinction to 'psychical' deafness (Seelentaubheit) — Munk states that destruction not merely of the posterior division of the third external convolution, but also of the posterior divisions of the first and second convolutions, is necessary. His experiments on this point are, however, exceedingly unsatisfactory; and that his conclusions are erroneous has been demonstrated by Luciani and Tamburini 2 who have found that bilateral de- struction of the posterior division of the third external con- volution alone produces total deafness ; while destruction of the posterior division of the second external convolutions has no effect on the sense of hearing whatever. Munk's primary lesion destroys only a portion of the true auditory centre j and the secondary disturbances which are set up by the lesion functionally annihilate the whole for the time being. For the time, therefore, the animal appears wholly deaf But when the secondary disturbances have subsided, the uninjured 1 Op. cit. p. 40. 2 Sui Centri Psico-sensori Corticali, 1879. 312 THE SENSOBY CENTBES portion of the auditory centre is able to resume its functions, and the animal recovers its hearing. In order that deafness should be permanent the whole of the posterior division of the third external convolutions must be destroyed, and it is not necessary that the lesion should extend beyond these. Though similar experiments have not as yet been carried out on other mammals, we have every reason to believe that destruction of the regions homologous in their electrical re- actions will yield results as regards the sense of hearing en- tirely in accordance with those obtained in monkeys and dogs. From these it is apparent that the posterior division of the Sylvian convolution in the dog is not the homologue of the first or superior temporo-sphenoidal convolution in the monkey, as has been assumed by Meynert. 1 The homology lies between the superior temporo-sphenoidal and the posterior division of the supra- Sylvian or third external convolution. Though anatomically the posterior division of the Sylvian convolution appears to correspond with the superior temporo- sphenoidal, the resemblance is only superficial, and is con- ditioned by the shallowness of the fissure of Sylvius in the dog, as compared with that of the monkey. In all probability the Sylvian convolution of the dog is represented within the lips of the fissure of Sylvius in the brain of the monkey, overlapping and concealing the deeply seated insular lobule, or island of Eeil. Paet III. — The Olfactory and Gustatory Centres. § 18. The position of the olfactory centre may with great probability be inferred from anatomical considerations alone, apart from actual experiment. We have already seen (Chapter I. § 21) that the olfac- tory bulb and tract are the modified remnants of a hernia- like protrusion of the cerebral vesicle anteriorly, such as permanently characterises the rhinencephalon of the frog. 1 ' Die Windungen der convexen Oberfliiche des Vorder Hirns,' Archiv f. Psychiatrie, Bd. yii. 1877. THE OLFACTOBY AND GUSTATOBY CENTBES 313 The anterior portion of the protrusion becomes the olfactory- bulb, while the rest of the walls coalesce to form the olfac- tory tract, the original cavity becoming obliterated, so that only traces remain. The roots of the tract, or remnants of the lateral walls of the rhinencephalon, diverging from the point where the original cavity becomes shut off from the anterior cornu (trigonum olfactorium) , are continuous re- spectively with the anterior and posterior or lower extremi- ties of the great limbic or falciform lobe, which, bent round the corpus callosum, constitutes the internal margin of the hemisphere. Broca l aptly compares the connections of the olfactory bulb and tract with the falciform lobe to a tennis racquet, of which the olfactory tract forms the handle, and the falciform lobe the circumference. The inner root fuses with the anterior extremity of the gyrus fornicatus or callosal convolution, while the outer root fuses with the ■ anterior extremity of the hippocampal convolution or hippocampal lobule (uncus, subiculum, pyriform lobule, &c.) The region of the trigonum olfactorium is considered by Broca to constitute a third root (the grey root), containing fibres which connect the tract with the cortex at the base of the orbital convolutions (the anterior olfactory centre). According to the degree of development of the sense of smell in different animals, the structures above described, or certain portions of them, vary enormously; so that Broca divides all animals into ' osmatics ' (including the great majority of mammals) and ' anosmatics,' in which the sense of smell is relatively feebly developed (primates, amphibious carnivora) ; rudimentary (balaenidse) ; or altogether wanting (delphinidse) . In the osmatics (cat, dog, rabbit, &c.) the olfactory bulbs and tracts are very large, and the hippocampal lobule in particular of all other cerebral regions attains remarkable proportions, so that in these animals it forms a distinct pro- tuberance in the lower temporo-sphenoidal region (fig. 73). In the anosmatics, on the other hand, the hippocampal lobule is small, though distinct, in those — such as the monkey and 1 Revue d' Anthropohgie, 1878; Anat. Comp. des Circonvolutions Ciribrales ; Becherches sur les Centres Olfactifs; Ibid. 1879. 314 THE SENSORY CENTRES man — in which smell is good, but secondary to other sensory faculties ; while in the balssnidsB ' it is greatly reduced, and in the dolphin quite rudimentary. Though there appears also to be a relation in the osmatics between the size of the internal root and the anterior portion of the callosal convolu- tion — where Broca supposes a superior olfactory centre to exist — yet that there is no real concomitance between the two is shown conclusively by the brain of the cetaceans, in which, z. r.cl «c '\ I 9 r.oC 4-44 net- FIG. 99.— Horizontal Section of the Brain of the Mole on a level with the anterior commissure (x 4). (Alter Cfanser. )—«<•, anterior commissure, dividing into pit, pars olfactoria, and pt, pars temporalis, ci, internal capsule. f, fimbria, fa, anterior pillar of fornix, fd, fascia dentata. /M, Meynert's fasciculus, i/l.ol, glo- meruli olfactorii. hi, posterior longitudinal fasciculus. /.-, granular layer of olfac- tory bulb. mp, middle peduncle of cerebellum, wa, nucleus amygdalse. nc, nucleus caudatus. nl, nucleus lenticularis. r, pyramidal tract, rn, red nucleus, r.ol, roots of the olfactory nerve, rs, regio subthalamica. », septum Ineidnm. so, substantia alba. .s^>, superior cerebellar peduncles, si, stria torminalis. t.ol, tractus olfactorius. though the sense of smell is rudimentary or absent, the anterior portion of the callosal convolution is specially well developed; a fact which Broca himself admits to be appa- rently in flagrant contradiction to his hypothesis. Not only is the callosal convolution large, but it is moreover much 1 ' Sur l'Enc6phale des Balffinidw,' by Beauregard, Joum.de VAiuit. ct dc la PJiysiologie, tome xix. 1883. THE OLFACTOBY AND GUSTATOBY CENTBES 315 more richly convoluted than is the case in the great majority of mammals. Hence it is obvious that we cannot regard the relationship which Broca would seek to establish between the internal or superior olfactory root and the callosal convolution as at all justified on anatomical grounds. The only relationship which undoubtedly exists is between the size of the olfactory bulb and the hippocampal lobule or anterior third of the hippocampal convolution. That the rest of the falciform lobe is related to other functions than the sense of smell is a conclusion clearly indicated by comparative anatomy, and demonstrable, as will be shown subsequently, by physiological experiment (§ 25). § 19. The anatomy and connections of the anterior com- missure (fig. 99, a c) are further of great significance as to the position of the olfactory centres. This commissure, as has been described above (Chapter I. § 18), consists of two divisions, an anterior and posterior. The anterior division is the com- missure between the olfactory bulbs, and varies in size with these. The posterior division is traceable outwards to the region of the hippocampal lobule and nucleus amygdalae (Luy's ganglion olfactif), and is obviously a commissure of centres related to the olfactory organs. Ganser, 1 however, has pointed out that the size of the posterior or temporal division does not vary simply with the size of the pyriform lobule. Thus in the dog, whose pyriform lobule is seven times as large as that of the rabbit, the tem- poral division of the anterior commissure is a third smaller. What may be the significance of this fact is not quite clear, though it is probably an index of the degree of association of the two centres with each other. Cateris paribus, the smaller the temporal division, the greater the independence of the respective centre in each hemisphere. § 20. Passing next the results of electrical irritation of the hippocampal lobule, we obtain very significant indications of subjective olfactory sensation. As above described (Chapter VIII.) irritation of this region in the monkey, cat, dog, and rabbit was attended by 1 ' Ueber die vordere Hirnoommissur der Saugethiere,' Archiv filr Psy- chiatrie, Bd. ix. 1879. 316 THE SENSOBY CENTRES essentially the same reaction in all, viz. a peculiar torsion of the lip and nostril on the same side. This reaction is pre- cisely the same as is induced in these animals by the direct application of some strong or disagreeable odour to the nostril, and is evidently the outward, or associated, expression of ex- cited olfactory sensation. The reaction in this case is on the same side as the irritation, and is thus unlike all the other re- actions which ensue on irritation of the hemisphere elsewhere. Only occasionally was the reaction bilateral, except in the rabbit, where this occurred as the rule. The direct or uncrossed reaction of the hippocampal lobule is what we should naturally expect from the anatomical dis- position of the olfactory tracts. Each olfactory tract is con- nected only with the hemisphere on the same side — the inner root with the anterior or superior extremity of the falciform lobe, the outer with the posterior or inferior extremity of the same. Though, as has been mentioned, Broca was of opinion that the connection of the inner or superior root indicated the existence of an olfactory centre in the anterior part of the callosal convolution, yet the brain of the cetacese does not support this view ; and it is more probable that the inner root is, in reality, connected by the longitudinal fibres of the callosal convolution with the hippocampal lobule. Two separate olfactory centres in one hemisphere, to say nothing of a third centre, which Broca also supposes to exist at the base of the orbital convolutions, cannot be regarded as probable or justified by mere anatomical appearances alone. But in any ease all the connections of the olfactory tract are with the hemisphere of the same side. Meynert assumes the existence of a decussation of the olfactory tracts in the anterior commissure ; but the investigations of Gudden and Ganser are entirely opposed to this hypothesis. Anatomically there are no appearances of decussation of the olfactory and temporal divisions of the anterior commissure; and when one olfactory bulb is removed, the whole of the olfactory division disappears on both sides ; while the temporal division remains intact and unchanged. These results are altogether opposed to the theory of decussation, and we may regard it as esta- blished that the anterior commissure is not an olfactory THE OLFACTOBY AND GUSTATORY CENTRES 317 chiasma in the same sense as the optic commissure. There is therefore no anatomical basis of connection between the olfactory tract and the opposite cerebral hemisphere. § 21. There is considerable difficulty in determining the effects of destructive lesions of the hippocampal lobule. Apart from the difficulties of testing the sensibility to odours proper in the lower animals, as distinguished from mere irritants of the Schneiderian membrane, it is practically impossible to establish lesions in the hippocampal lobule without injury to neighbouring regions. Hence the accurate determination of the centre of smell by destructive lesions involves considerable complications. But by processes of exclusion, and by the various considerations above mentioned, the localisation of the olfactory centre seems capable of being arrived at with a con- siderable degree of precision. In the first experiment 1 made in reference to this question the left temporo-sphenoidal lobe was deeply divided trans- versely in a line coinciding with the anterior prolongation of the inferior occipital sulcus, and the greater portion of the superior, middle, and inferior temporo-sphenoidal convolutions disorganised and scooped out. The lower extremity of these convolutions remained uninjured superficially, though almost entirely severed from their connections above. The hippo- campal convolution, however, was not severed. As the result of this lesion it was observed that hearing was diminished, or abolished, on the right side, in relation with the lesion of the superior temporo-sphenoidal convolution. Owing to the difficulty of preventing diffusion to both sides of the mouth, no accurate determination could be made as to the sense of taste, though there appeared to be less sensi- tiveness to acid on the right side of the tongue. The vapour of acetic acid, however, caused distinctly less reaction in the left nostril than in the right. In this case also some defect of tactile sensibility was observed on the right side. There was thus a complex assemblage of phenomena, some of which — the deafness on the right side — are explicable by previous experiments, while others — the defect of tactile sen- sibility on the right side — will be further elucidated below 1 Experiment XI., fig. 13, Phil. Trans, vol. clxv. Part II. 1875. 318 THE SENSORY CENTRES (§ 25). The symptoms also indicated that- the centres of smell on the same side, and taste on the opposite, were in- volved in the lesion. In a second experiment l a similar lesion was established in the left hemisphere, but passing more deeply into the hippocampal region, and more completely severing the lower portion of the temporo-sphenoidal lobe from the rest. Hearing was impaired or abolished on the right side, the superior temporo-sphenoidal convolution being destroyed. Sight was unaffected. Tactile sensibility was at first impaired, and ultimately on the third day almost completely abolished on the right side. Smell appeared defective or lost on the left side, as judged by the following facts. The animal took a piece of apple offered it, and after 'smelling it began to eat. The right nostril was then stopped up, and when a piece of apple was again offered the animal seized it, and held it to its nostrils repeatedly, as if it had difficulty in making out the nature of the object by its sense of smell. In a third experiment 2 both temporo-sphenoidal lobes were broken up and disorganised— on the left side more com- pletely than on the right. Sight was unimpaired, but hearing was entirely abolished on both sides, no response being elicited by the loudest sounds. Tactile sensibility was at first somewhat defective on the right side, and next day, as the process of softening advanced, very considerably diminished on this side. Acetic acid caused no reaction when held before the nostrils or placed in the mouth. Only when the acid was placed within the nostrils did any reaction occur ; an effect evidently due to irritation of the nerves of common sensation in the nostrils, and more marked on the left than on the right side, on which there was some defect of tactile sensibility. In this case, therefore, in which the lower portion of the temporo-sphenoidal lobes was disorganised smell and taste seemed abolished. In a fourth experiment 3 the lower extremity of the 1 Experiment XII., figs. 14 and 15, op. cit. 2 Experiment XIII., figs. 16 and 17, op. cit. 3 Experiment XIV., figs. 18 and 19, op. cit. THE OLFACTOBY AND GUSTATOBY CENTBE8 319 temporo-sphenoidal lobe was thoroughly disorganised on both sides, the lesion on the left side destroying also the hippo- campal region very extensively. As the result of this bilateral lesion, tactile sensibility was abolished on the right side. Neither aloes nor colocynth, nor citric acid, which in ordinary conditions excite lively indications of sensation, caused the Figs. 100 and 101. — Lesions of the Eight and Left Hemisphere, causing loss of taste and smell. (Roy. Soo.) In the right hemisphere (100) the shading indicates the extent of destruction of the grey matter. In the left (101) the dark shading indicates the superficial extent of the wound ; and the dotted lines the extent of internal de- struction of the lower portijn of the temporo-sphenoidal lobe. slightest reaction when placed on the tongue. The vapour of acetic acid held close to the nostrils caused no reaction. When it was introduced within the nostrils, a remarkable difference was observed between the reactions of the right and left respectively. On the right side, which was also devoid of common sensibility, acetic acid caused no reaction whatever. S20 THE SEN80BT CENTBES On the left side copious lacrymation ensued — from the left eye particularly. Not merely was there entire insensibility to sapid stimuli on the tongue, but there appeared also an abolition of common sensibility ; so that the tongue could be pricked or touched with a heated wire without exciting any motor reaction. The facts of this experiment indicate abolition of smell, taste, and tactile sensibility on both sides of the tongue, and of tactile sensibility on the right side of the body. The re- action of the left nostril to acetic acid, viz. the copious lacry- mation, was evidently due to mere irritation of the nerves of common sensation of the nasal mucous membrane. As has been already observed, the lesions described, im- plicating as they do a considerable portion of the temporo- sphenoidal lobe, do not of themselves indicate with precision the respective centres of the various forms of sensibility, general and special, which were observed to be affected. But we have already seen that affections of hearing are to b$ ascribed to destruction of the superior temporo-sphenoidal convolution ; and it will be shown in the next section that the affections of tactile or common sensibility are to be referred to destruction of the hippocampal region. Excluding these, the affections of smell and taste are evidently related to lesions of the hippocampal lobule and the neighbouring regions. The facts of comparative anatomy and the phenomena of electrical irritation show beyond all doubt that the hippo- campal lobule is the centre specially related to the sense of smell. Munk ' considers the hippocampal gyrus as the centre of smell from the facts he observed in the case of a dog which had been rendered blind by bilateral lesion of its occipital regions. This animal seemed to be unable, like other dogs, to detect by smell pieces of meat laid before it. After death it was found that the hippocampal gyri had been secondarily almost entirely converted into cysts distended with fluid. Though Munk adduces this case to show that the hippocampal gyri are the centres of smell, yet, inasmuch as the hippo- campal lobules were implicated in the lesion, the case is evidently as merely another confirmation of the facts above 1 Die Functionen der Grosshirnrinde, p. 130. THE OLFACTORY AND GUSTATORY CENTRES 321 related in favour of the localisation of the olfactory centres in the hippocampal lobules proper. . § 22. As to the sense of taste I have not succeeded in differentiating any special region related to this faculty, but that it is in close relation with the olfactory centre is probable from the facts described. It was noted in connection with electrical irritation of the lower extremity of the temporo- sphenoidal convolutions in the monkey, and of the same region in the brain of the cat, that movements of the lips, tongue, cheek-pouches, and jaws were occasionally induced — pheno- mena which might be regarded as indications of the excitation of gustatory sensation. This interpretation receives support from the above-described results of destructive lesions ; and we have, therefore, reasonable grounds for concluding that the gustatory centres are situated at the lower extremity of the temporo-sphenoidal lobes, in close relation with those of smell. This would enable us to explain the occasional occurrence in man of anosmia and ageusia as the result of severe blows on the head, especially the vertex. A blow in this region causes counterstroke of the base of the brain, particularly in the region of the olfactory centres. No doubt many of the cases of so-called loss of taste and smell are merely cases of loss of smell only, the impairment of taste extending only to the per- ception of flavours, which, as is well known, are compounded of taste and smell together. But there are cases in which both smell and taste proper are impaired or abolished by cranial injuries, 1 and it is permissible to suppose that this may be caused by concussion and contusion of the lower ex- tremities of the temporo-sphenoidal lobes, where the olfactory centres certainly, and the gustatory centres in all probability, are situated. Both anatomy and experimental physiology show that the olfactory centre is situated on the same side as the cor- responding peripheral organ — unlike the other sensory centres of the cerebral hemisphere. Cases have been reported by W. Ogle, 2 Fletcher and 1 See Localisation of Cerebral Disease, 1878, p. 138. 2 ' Anosmia,' Med.-Chir. Trans. 1870, Cases 8, 9, and another mentioned in to note p. 275. T 322 THE SENSOBY CENTBES Bansome, 1 of the occurrence of loss of smell in the left nostril, with right hemiplegia and aphasia. Though the exact locality of the lesion in such cases may not be considered as satisfactorily established, yet, as the symptoms were such as are known to be associated with embolism of the middle cerebral artery, we have reason to regard the anosmia as in all probability due to softening of the region of the hippocampal lobule. But there are certain facts in human pathology which would seem at variance with these results. In the condition termed cerebral hemianesthesia — hysterical or alcoholic — smell appears to be impaired or lost on the same side as the other faculties of sense, general and special. Different inter- pretations have been given of the pathology of hysterical hemianesthesia ; but, assuming that it depends on some affec- tion of the opposite cerebral hemisphere, the apparent loss of smell is explicable by the anaesthetic condition of the nostril. Magendie 2 found that smell was abolished by section of the fifth nerve. This experiment seemed to show that the in* tegrity of the common sensory nerve of the nostril was a necessary condition of smell proper. In a case reported by Magnan, smell progressively failed with the impairment of common sensibility in the nostril, and disappeared pari passu with it. Even, however, when common sensibility was entirely gone in the nostril, the vapour of acetic acid caused copious .lacrymation ; a fact which showed that certain afferent nerves remained functionally active — presumably the olfactory — which, however, owing to loss of common sensibility, were not of themselves sufficient to convey the impression of odours. In the monkey, above referred to, in which both common and olfactory sensibility were abolished by the cerebral lesions, no lacrymation was caused by acetic acid. In the other. nostril, which had not lost its common sensibility, lacrymation was caused by acetic acid. But lacrymation may be caused by irritation of the nerves of common sensibility alone. Where 1 Brit. Med. Journal, April 1864. See also- three cases reported by Hugh- lings-Jackson, in which, however, it is not stated precisely in which nostril the defect was specially observed (Lond. Hosp. Reports, vol. i. p. 410). 2 Leqons sw lea Fonctions et Us Maladies da Systime Nerveux, tome ii. Lecon 15°. THE TACTILE CENTRE 323 common sensibility is abolished the effect must be attributed to the olfactory nerve. Part IV. — The Centre of Common or Tactile Sensibility. § 23. In my earlier experiments, 1 which I have since abun- dantly confirmed, 2 1 could discover no sign of impairment or loss of tactile sensibility after the most extensive lesions involv- ing the convex aspect of the cerebral hemisphere. And yet, considering the definite localisation of the centres of sight, hear- ing, smell, and probably taste, as well as the respective motor centres, no conclusion seems a priori better warranted than that there must be a definite region for the various forms of sensibility included generally under the sense of touch (contact, pressure, temperature, &c.) For up to the point of radiation into the cerebral cortex the sensory paths have been proved to be entirely differentiated from the motor ; and that the two should become jumbled together indiscriminately in the cortical centres is a hypothesis which prima facie is extremely unlikely. The sensory nerve roots are entirely distinct from the motor, and in the spinal ccrd itself the sensory and motor centres and tracts are clearly differentiated from each other, as evidenced by the facts of anterior poliomyelitis, and by such cases as the remarkable one recorded by Spath-Schiippel. 3 In the pons, and in the crura cerebri, it is rare to find lesions so limited as to affect the sensory tracts apart from the motor, though the occurrence of motor paralysis from lesions in these regions, without paralysis of sensation, shows that the sensory and motor tracts still retain their inde- pendence. But we have ample proof both experimental and patho- logical that the sensory tracts of the internal capsule are quite distinct from the motor, and may be injured or diseased separately, with the result of causing hemianesthesia on the opposite side of the body. It is evident that the cause of the 1 Philosoph. Trans, vol. olxv. Part II. 1875. 1 Ibid. Part II. 1884. 3 Archiv d. Heilkunde, 1874, vol. xv. p. 44. Eeferred to Chap. IV. § 18. y 2 324 THE SENSORY CENTBES hemianesthesia in such case is not due to injury of centres, but merely to interruption of the paths of transmission from the periphery to the cortical centres. What remains, therefore, to he discovered is the cortical destination of these paths of common or tactile sensibility. Anatomically the position of the sensory region of the internal capsule corresponds to the posterior third, or more, of the hinder division of the internal capsule, as seen in hori- zontal section (see fig. 25) lying between the optic thalamus and lenticular nucleus of the corpus striatum. The experiments of Veyssiere ' have shown that when this portion of the internal capsule is divided in the brain of the dog (fig. 102) hemianesthesia is produced on the opposite side of the body. L M /■/ F/G. 102. — Vertical Transverse Section through the Brain of the Po^on a leyel with the Corpora tnammillaria (Carville and Duret). oo, the optic thalami. sa, the nuclei caudati of the corpora striata on each side. LL, the lenticular nuclei of the corpora striata. pj\ the internal capsule, or peduncular expansion, aa, the hippocampi, x, section of the posterior part of the peduncular expansion, oausing hemiancesthesia,. Disease of the same region in man produces precisely similar results. 2 In this condition sensation, general and special, is abolished on the opposite side of the body, but the power of voluntary motion is retained — if the lesion does not also implicate the motor tracts. But though volitional move- ments are. capable of being effected, all sense of movement is lost, nor does the most powerful contraction of the muscles 1 Rccherches Gliniqv.es ct Experimentales sur V Himianesthisie de Cause Ciribrale, 1874. - Charcot, Le Progris MMical, 1S75 ; Reymoncl ibid. ; Rendu, Des Anes- thesias Spontanees. These, Paris, 1875. THE TACTILE CENTRE .325 induced by the electric current rise into consciousness. There is no sense of locality, or of the state of contraction of the muscles, and though the limb may be moved freely by the agency of the motor centres, it can only be used with purpose, and directed under the guidance of the eye, which enables the individual to place the limb in such positions as previous experience has associated with the accomplishment of certain desired effects. The directing agency of the eye being with- drawn, the position of the limb may become altered uncon- sciously, and a weight previously supported will fall to the ground ; a fact of which the individual only becomes aware by other channels of perception. The following description by Demeaux l of a woman affected with cerebral hemian- esthesia is one which graphically represents the condition. ' She moved the limbs voluntarily, but she had no sense of the movements effected.. She did not know in what position her arm was, nor could she tell whether it was flexed or ex- tended. If she were asked to touch her ear, she immediately executed the proper movement, but if my hand were interposed between hers and her ear she was quite unconscious of the fact ; and if I arrested her movement in mid-career she was utterly unaware of it. If I fixed her arm to the bed without her knowledge, and asked her to raise it to her head, she made an effort, and then ceased, believing that she had done what was wanted. If I told her to try again, pointing,. out that her arm had not been moved, she made a greater effort, and only when she had to throw the muscles of the other side into action did she become aware that some obstacle had been interposed.' These facts show clearly that the same condition which abolishes cutaneous sensibility also entirely annihilates the so-called muscular sense. § 24. From such and similar cases, many of which I have myself seen and investigated, and multitudes of which are to be found in medical literature, it is plain that the sensory tracts of the internal capsule are entirely distinct from the motor, and that there is no necessary relation between the power of effecting movement and the sense of movement effected. In other words, the paths of the so-called muscular 1 TMse, Paris, 1843, p. 100 326 THE SENSORY CENTRES sense are quite distinct from the paths of volitional impulse. Whether this holds also in respect to the centres will form the next subject of inquiry. Do the sensory tracts, which, up to the internal capsule, have maintained a separate position, fuse in the cortex with the motor, as some believe ; or are they distributed to a special region of the cortex? Flechsig believes that the tracts which form the posterior or sensory division of the internal capsule are derived, through the tegmentum, from the sensory tracts of the formatio reticularis and lemniscus, and are distributed to that portion of the brain lying between the fissure of Eolando and the occipital lobe. But there is a tract occupying the outer third of the foot of the crus which was regarded by Meynert as the upward continuation of the posterior columns of the spinal cord, and therefore probably the paths of tactile or common sensibility. The posterior . columns of the spinal cord, however, are not the paths of tactile sensibility (see Chapter II. § 7), nor does it appear that any direct eonnec-. tion can be considered as established between the outer third of the foot of the crus and these columns. Flechsig, how- ever, is unable to trace this tract beyond the pons,- but he is of opinion that it consists of fibres which connect the cere- brum with the cerebellum, as it was absent in a case in which the cerebellum was deficient. The same tract was also absent in a case of defective development of the brain reported by Starr. 1 But as in Starr's case the whole foot of the crus was absent also, and the cerebellum showed no defect, it is ob- vious that no relationship is established between the cerebellum and this tract. That the tracts, forming the outer third of the foot of the crus, are centripetal in function is evident from the fact that they are never the seat of descending degeneration, like the inner two thirds ; and, though no one has as yet succeeded in tracing their lower relations satisfactorily, the probability is that they are the more or less direct continuations of the sen- sory tracts of the spinal cord. This conclusion is especially supported by the anatomical distribution of these fibres in 1 ' The Sensory Tract in the Central Nervous System,' Journal of Nervous and Mental Disease, July 1881. TEE TACTILE CENTRE 327 the cortex. The tracts forming the outer third of the foot of the crua diverge from the internal capsule at the base, and radiate outwards and downwards towards the hippocampal region, 1 where, as will be seen, lesions invariably affect tactile sensibility. § 25. In my earlier experiments I had observed that, though tactile sensibility appeared entirely unaffected by lesions invading the convex aspect of the hemisphere, yet in certain experiments where the temporo-sphenoidal lobe was deeply injured (see Section III.) tactile sensibility became very much impaired, or altogether abolished on the opposite side of the body. In all these cases it was found, on post- mortem examination, that the hippocampal region — including the cornu Ammonis and gyrus hippocampi — was more or less extensively invaded. These facts strongly pointed to the hippocampal region as the seat of tactile sensibility, and I therefore devised experiments with a view to destroy this region primarily. To do so without injuring the occipital lobe or the convex aspect of the temporo-sphenoidal lobe is, however, impossible ; but as the effects of lesion of the occi- pital lobe and of the inferior temporo-sphenoidal convolutions are readily capable of determination by themselves, it is a matter of no great difficulty to eliminate these in cases of lesion invading also the hippocampal region. I have effected destruction of the hippocampal region, more or less completely, both by the method of penetration by means of a wire cautery, directed through or underneath the occipital lobe, and by cutting from the outer aspect of the inferior temporo-sphenoidal region inwards towards the hip- pocampal gyrus, so as to destroy or detach it, without injury to the crus cerebri or neighbouring structures. 2 In one case 3 a wire cautery was thrust through the posterior extremity of the left occipital lobe, with a view to 1 Flechsig, Plan des menschlichen Gehirns, 1883, p. 17. 2 See Phil. Trans. Part II. 1884, Section V. figs. 87-181. s Experiment XVII., Phil. Trans. Part II. 1875, figs. 22 and 23. Though in this case there were some indications of basal meningitis, this had nqt occurred to such an extent as to result in any softening or actual lesion beyond that caused by the cautery. 3'28 THE SENSOBY CENTRES traverse the hippocampus. In reality it proved, on post- mortem examination, that the cautery had swerved too far out- wards, and just missed the hippocampus itself. Immediately after the operation, and for two days subsequently, there was no defect of tactile sensibility; but on the third day this became so much impaired that scarcely any reaction was in- duced by a degree of heat which excited most lively signs of sensation on the left side. It was found after death that the track of the cautery, Pigs. 103 and 104. — Fig. 103, Internal Aspect, and fig. 104, External Aspect of the Left Hemisphere, showing the truck of the cautery in the experiment described in the text. which had primarily passed outside the hippocampus (figs. 103, 104), had become the centre of secondary inflammation, which had extended into, and softened, the hippocampal region. In a second experiment ' a wire cautery was similarly pushed through the tip of the right occipital lobe along the 1 Experiment XVIII., fig. 24, I'lul. Trans. Part II. 1875. THE TACTILE CENTBE 329 hippocampal region — this time, as proved after death, with perfect success, and without injury to other structures. The effects of this lesion were very striking. The monkey in question, which was the subject of the present experiment, was found to be, as a rule, left-handed, taking things offered to it preferably with the left hand. For this reason the right hippocampal region was destroyed, with the view of affecting the sense of touch in the limb which the animal usually employed. After recovery from the operation and the narcotic stupor, sight and hearing were found to be unimpaired, and the intel- ligence quick and active as before. But cutaneous stimula- tion by pricking, pinching, or pungent heat sufficient to cause lively manifestations of sensation when applied to the right Pie. 105.— Internal Aspect of Bight Hemisphere of Brain of Monkey. The shading and dotted lines indicate the track of the cautery and position of the lesion, causing loss of tactile sensation on the left side of the body. (Boy. Soc.) side of the body, failed in general to elicit any reaction what- ever on the left side, whether face, hand, or foot. Only occa- sionally, when the stimulus was intense or long continued did reaction at all ensue. This most remarkable absence of response of any kind of itself satisfactorily proved the fact of annihilation of tactile sensibility without further evidence. But the abolition of tactile sensation was further conclusively shown by the condition as to motility of the left limbs. There was no flaccidity of the muscles, and no facial distortion, as is observed in motor hemiplegia ; but the arm was kept motionless by the side, and the leg straddled out- wards, or was placed irregularly, and yet a certain amount of voluntary control was retained over the limbs. This was ex- 330 THE SENSOBY CENTBES emplified by the following incident which occurred in the course of the observations : — On being placed within its cage the animal mounted its perch, gaining its position with some difficulty, on account of its tendency to fall over on the left side. While endeavouring to turn on its perch the left foot slipped off, whereupon, in the struggle to recover its equilibrium, the animal clutched with both hands at the bars of the cage, but grasped only with the right hand, the left being powerless. Aided by its teeth and right hand, it recovered its position, and after grasping the perch firmly with its right foot ultimately dragged up the left leg. This position of steadiness, however, was possible only while the animal kept on the alert. On its dropping off to sleep, which it continually tended to do, the left foot would slip off, and again the same struggle would occur to regain equilibrium. In all these occurrences, though movements of the left limbs were sometimes made, no pre- hensile or other independent action of the left hand or leg was ever manifested. The animal scratched the right side of its body, which seemed to itch considerably, with its right hand, and used its right hand for prehension, instead of the left as before. The paralysis of motion in this case was not true motor paralysis, which, as will be afterwards shown, results from lesion of a totally different part of the brain, but the paralysis of motion which is due to the loss of tactile sensation, by which movements are guided. The animal was killed with chloroform on the same day in order that the position and extent of the primary lesion might be determined before secondary softening could occur. As already stated, the lesion was confined to the hippocampal region, along which the cautery had ploughed its way with great precision. As the position of the lesions in these two cases had been questioned, and a suggestion made that in reality the internal capsule had been injured, I carefully re- examined the brains, which had been carefully preserved n spirit. The accompanying figures (figs. 106, 107), drawn from nature, show the exact appearances presented in the two cases. A series of frontal sections, 1 of which fig. 108 is one 1 See photographs, figs. 87-102, Phil. Trans. Part II. 1884. 831 Pig. 106.— Natural appearance of Brain represented in diagrams 103, 104, the posterior lobe being removed. On the upper aspect of the left lateral lobe of the cerebellum there is a superficial groove where it was grazed by the cautery.— of, ascending frontal convolution, ec, corpus callosum. nit, middle temporo-sphenoidal convo- lution, st, superior temporo-sphenoidal cunvolutiun. t, testes. Fig. 107 (A, B). — Natural Appearance of Posterior Half of Right Hemisphere repre- sented in diagram tig. int.— A, under surface. B, seen from before. The position of the lesion is clearly indicated by the shading, e, crus cerebri, cc, corpus callosum.. ag, angular gyrus. aj>, ascending parietal convolution. fS, fissure of Sylviu-. mt, middle temporo-sphenoidal convolution, st, superior temporo-sphenoidal convolu- tion. Fig-. 108.— Frontal Section of ng_. 107, B, showing the Destruction of the Mippocampal Region, (After a sun-print.) 332 THE SENSOBY CENTBES of the second case, showed that the internal capsule was en- tirely free from lesion, the lesions being in both cases strictly limited to the hippocampal and the inferior temporo-sphenoidal region. § 26. In a second series of experiments l made partly in conjunction with my colleague, Prof. G. P. Yeo, with the object of testing the accuracy of my former results, and also in order to determine the duration of the symptoms, I established lesions in the hippocampal region in ten other monkeys, and in five of these in both hemispheres. The results of this series of experiments confirmed in every par- ticular those I had already arrived ^at, and showed that tactile sensibility was in every case impaired or abolished in proportion to the amount of destruction of the hippocampal and inferior temporo-sphenoidal region. Unfortunately none of the animals in which the destruction was complete, and the anaesthesia absolute, survived many days, so that the question of duration still remained unsolved. But it was established that a very extensive lesion might be made in one or both hippocampal regions without producing permanent anesthesia. The lesions were made either from the occipital lobe, or by incisions from the convex aspect of the temporo- sphenoidal lobe, extending inwards to the hippocampal region. Affections of vision, more or less evanescent, occurred along with anaesthesia when the occipito-angular region was in- vaded, in accordance with the facts stated in Section I., and occasionally some affection of hearing occurred when the superior temporo-sphenoidal convolution was involved. But it was only when the hippocampal region was injured that anaesthesia showed itself. In one experiment 2 the animal had been previously ren- dered partially hemiplegic on the left side by lesion of its right Bolandic zone (see Chapter X. p. 354). Lesion of the left hippocampal gyrus induced profound impairment of the sen- sibility of the whole of the right side of the body, and it waa interesting to note how the slightest touch on the paralysed limbs immediately attracted the animal's attention, whereas 1 Phil. Trans. Part II. 1884. Experiments 24-33, figs. 103-181. * Experiment 24, figs. 103-109, Phil. Trans. Part II. 1884. THE TACTILE CENTBE 333 not the slightest sign of perception was elicited by the same kind of stimulation on the other side. In this case the ansssthesia, which did not amount to insensibility to painful stimulation, gradually disappeared, and ceased to be capable of detection a week after the operation. In a second experiment l a wire cautery was directed through the occipital lobe in the line of the collateral fissure, and following the course of the descending cornu of the lateral ventricle, detaching and destroying a considerable extent of the medullary fibres of the hippocampal gyrus. The result of this lesion was temporary hemiopia to the left side, and a condition of total anesthesia to mere contact. This showed signs of retrogression at the end of a few days, but the im- pairment of tactile sensibility still continued very evident for a fortnight after the operation. At first the fingers and toes of the' left side could be touched or gently scratched without in the least exciting the animal's attention, whereas similar stimulation of the extremities on the right side invariably caused the animal to look and to change its position. A month after the infliction of the injury on the right hippocampal region a similar lesion, but somewhat more ex- tensive, was established on the left side. This operation also severed the portion of the optic tract passing to the corpus geniculatum externum. The animal became absolutely hemiopic to the right side, and continued so till death, nearly a year and a half after the operation. Tactile sensibility was completely abolished in the limbs of the opposite side ; and it was noted that the lesion did not reinduce the anaesthesia on the left side, which had been the result of the lesion of the right hemisphere. Sensibility gradually returned in the right limbs, but some impairment of perception of mere contact was observable for a month after the operation, and particularly in the foot. The defect as regards vision seen in this animal is ex- plained first by the lesion of the right occipito-angular region, and second by the direct lesion of the optic tract on the left, which was the cause of the permanent right hemiopia. But the affection of tactile sensibility, first on the one side and .* Experiment 25, figs. 110-116, op. cit. 334 THE SENSORY CENTBES then on the other, was clearly the result of the injuries in- flicted on the hippocampal region : the ganglia, crura cerebri, and internal capsule being absolutely intact. In a third experiment 1 first the left, and, three weeks sub- sequently, next the right hippocampal region were partially destroyed by heated wires thrust through the occipital lobes. Owing to the injuries of the medullary fibres of the occipito- angular regions vision was impaired. The lesion in the left hemisphere only divided a portion of the medullary fibres of the hippocampal gyrus, and there was only slight and transient impairment of tactile sensibility on the right side. In the right hemisphere the gyrus hippocampi was peeled off, leaving the cornu Ammonis itself and its connections apparently intact. As the result of this there was complete tactile insen- sibility on the left side, which, however, gradually diminished, and could no longer be detected ten days after the operation. In a fourth experiment 2 the whole of the inferior temporo- sphenoidal convolution and portion of the middle tempor*>- sphenoidal convolution of the right hemisphere were cut away, and considerable injury inflicted on the medullary fibres of the hippocampal region. After this lesion there was considerable, but not total, analgesia to severe thermal stimu- lation on the left side, but total insensibility to mere contact, so that the hand or foot could be touched or rubbed without the slightest sign of perception on the part of the animal. Sensibility gradually returned, however, so that at the end of a fortnight it was impossible to detect any difference between the tactile perception of the two sides. At the end of this time a wire cautery was pushed through the convexity of the left occipital lobe, so as to traverse and destroy the cornu Ammonis and medullary fibres of the gyrus hippocampi, as well as those of the inferior and middle temporo-sphenoidal convolutions. The cortex of the gyrus hippocampi formed merely a thin shell enclosing the broken-down debris of the cornu Ammonis and the medullary substance. After this there was almost complete analgesia, as tested by severe thermal stimulation, on the right side, and total anaesthesia 1 Experiment 26, figs. 117-124, op. cit. " Experiment 30, figs. 149-156, op. cit. THE TACTILE CENTRE 335 to mere tactile stimulation, such as touch, rubbing, &c. of the limbs. The permanency of these symptoms, however, could not be determined, as the animal passed into a state of coma on the following day, and was killed with chloroform. In this animal motor power, hearing, and vision were unim- paired from the first. In a fifth experiment * the inferior temporo-sphenoidal and greater portion of the hippocampal region of the left hemi- sphere were destroyed. When the animal had entirely re- covered from the operation it was found that there was almost complete analgesia of the right side and complete tactile anaesthesia. The anaesthesia affected also the cutaneo-mucous surfaces, so that the right nostril could be tickled without causing any reaction, whereas the same stimulation of the left caused grimaces and evident signs of uneasiness. So also the right side of the tongue could be touched and pricked without any signs of reaction ; whereas the same stimulation of the left side caused the animal to rub the part. All the volitional movements of the right side were retained, but the animal tended constantly to fall over on the right side, evidently owing to the loss of the so-called muscular sense. This animal died suddenly on the day following the opera- tion from secondary haemorrhage, so that no further observa- tions as to the permanency of the symptoms were possible. In a sixth experiment 2 a wire cautery was so directed, underneath the left occipital lobe downwards and forwards, as to pass along the dentate fissure, and shear off the fascia dentata and portion of the alveus of the cornu Ammonis, in a most remarkable manner, without injury to the optic tract or other structures. The effect of this limited, and apparently impracticable, lesion was. a well-marked hyperesthesia, instead of anaesthesia, over the whole of the opposite side of the body, so that the signs of sensation to various forms of stimulation, such as plucking the hairs, were very much more energetic than on the left side. This condition had quite disappeared on the day following the operation, and the animal appeared in other respects, with 1 Experiment 31, figs. 157-163. 2 Experiment 32, figs. 164-172, Op. cit. 330 THE SENSOBY CENTRES the exception of slight defect of vision to the right, perfectly normal. On the tenth day.no impairment of vision could be- any longer made out. In this case the lesion seems only to have excited the centres of tactile sensibility, probably by throwing the hippo- campal region, which was only very slightly injured, into a state of active congestion or irritation. A month after the first operation the right temporo-sphenoidal lobe was exposed, and severed in such a manner by incisions as to detach the lower half of the middle and inferior temporo-sphenoidal con- volutions, and break up to a considerable extent the medullary fibres of the corresponding portion of the hippocampal region. Superficially, however, the whole of the gyrus hippocampi was perfectly intact, the incisions not extending inwards beyond the collateral fissure. As the result of this lesion there was a considerable degree of analgesia on the opposite side, and complete insensibility to mere tactile stimulation, so that the limbs could be touched, rubbed, and the hair ruffled without causing the slightest sign of perception ; whereas the same stimulation on the right side caused the animal to put its hand or foot to the place. In doing so, it at first generally fell over on the left side. The left nostril could also be tickled without causing any sign of uneasiness, while on the right the same proceeding caused an active grimace. Vision and hearing, and the motor powers, were altogether unimpaired. On the third day after the operation the tactile anaesthesia was less pronounced, and it gradually diminished, so that at the end of a week it was no longer perceptible. From this time onwards, till its death by chloroform two months subsequently, the animal appeared in perfect health, and without discoverable defect either as regards general or special sensibility or motor powers. In a seventh experiment ' the left cornu Ammonis was disorganised from end to end, in the most precise manner, by means of a wire and porte caustique directed through and beneath the extremity of the occipital lobe, leaving the gyrus hippocampi and its medullary connections intact. The animal was able within an hour to move about, planting its right ' Experiment 33, figs. 173 181. THE TACTILE CENTRE 337 limbs in a very awkward and uncertain manner, but without any appearance of motor paralysis. There was profound, almost complete, analgesia of the limbs on the right side, and total insensibility to mere tactile stimuli. There was also anaesthesia of the right nostril, so that no notice was taken when the interior was tickled. The analgesia had disappeared on the following day, but the anaesthesia to touch, &c. continued. This, however, also gradually disappeared, and was no longer perceptible on the fourth day. There was, however, complete right hemiopia, which was found to be dependent on lesion of the left optic tract, which had been grazed and almost com- pletely severed. A fortnight after this operation the right temporo-sphe- noidal lobe was exposed and incised along the middle temporo- sphenoidal and lower occipital convolution in such a manner as to detach the greater portion of the temporo-sphenoidal region, included between these incisions, from the rest. The incisions were such as to sever the medullary connections of the hippocampal region, especially towards the anterior or lower half. Almost complete analgesia was observed in the limbs of the left side, but the animal died on the following day before further observations could be made. In none of the above-mentioned experiments was the analgesia absolute from the first, and in none of them did the destructive lesion involve the whole of the hippocampal region — hippocampus as well as hippocampal gyrus. In those of them in which the loss of sensibility to painful stimuli was most complete the early death of the animals prevented further observations in regard to the duration of the symptoms. But it was clear that neither destruction of the gyrus hippocampi alone nor of the hippocampus alone was sufficient to induce permanent anaesthesia on the opposite side. In each case, however, whether the lesion involved the gyrus hippocampi, or hippocampus alone or mainly, there was pronounced affection of tactile sensibility, and the degree and duration of the anaesthesia were in proportion to the extent of injury inflicted. In the remarkable case, however, of the sixth animal the slight lesion of the fascia dentata caused an extraordinary hyperaesthesia instead of a diminution of tactile 838 THE SENSOBY CENTRES sensibility; but this, as has been remarked, was an irritative rather than destructive lesion of the hippocampal region, and the true counterpart of the others, and thus quite harmonising with them. In an eighth and ninth experiment greater success was ob- tained in respect to the completeness of the destruction of the Pigs. 100 and 110.— Fig. 100 shows the Lateral Aspect, and Pis. 110 the Under Surface of the Left Hemisphere in a ease of Lesion, causing complete aiuesthcsia of the opposite side of the body. ^From photographs.) hippocampal region and the profoundness of the anaesthesia; but unfortunately the observations as to the duration of the effects were cut short by the sudden death of the animals a few days after the operation in each instance. In the eighth experiment 1 the left hemisphere was exposed, 1 Experiment 27, figs. l25_132, op. tit. THE TACTILE CENTBE 339 and the whole of the inferior temporo-sphenoidal convolution and hippocampal region were severed and scooped out, the lesion being such as to leave only the internal margin of the gyrus hippocampi with the taenia semicircularis and the fimbria of the fornix intact (see figs. 109, 110). Only a portion of the hippocampal gyrus included between the calcarine and collateral fissure (lingual lobule) remained. The result of this experiment was most striking. There was, on the right, complete insensibility to thermal stimulation of such intensity as to cause the most lively sensations of pain on the left side, and total insensibility to every form of mere tactile stimulation, such as touching, gentle pricking, rubbing, &c. The limbs were capable of being freely moved volitionally, but they were planted with great awkwardness and uncertainty as to position. While the animal was resting, with its eyes shut, I drew the right arm away from the side, without its seeming to be aware of the fact, until it fell over. It was keenly sensitive to every form of stimulus, however slight, on the left side. Hearing was unimpaired on both sides. Vision, however, appeared somewhat indistinct, though not abolished, towards the right. There was also anaesthesia of the right nostril. The symptoms remained unchanged on the second day after the operation, the animal being otherwise in apparent perfect health and vigour, but on the third day it died sud- denly from secondary haemorrhage. A series of microscopic sections ' of the brain showed that, with the exception of the injuries above described in the inferior temporo-sphenoidal and hippocampal region, the basal ganglia, crura cerebri, and other structures were perfectly intact. In the ninth experiment 2 a similar lesion was established^ in the left hemisphere, involving almost complete detachment of the hippocampal and lower temporo-sphenoidal region from the rest of the hemisphere. In this animal also there was at first almost if not total analgesia, and absolute anaesthesia to all gentle forms of tactile stimulation, over the whole of the 1 See figs. 127-130, op. cit. * Experiment 28, figs. 133-140. Z 2 340 THE SENSOBY CENTBES right side of the body. Hearing was unimpaired on the right, but vision was somewhat defective towards this side, the animal appearing to have only some degree of uncertainty as to the position of things offered it on the right front. The condition remained practically unchanged on the third day, when the animal had a slight unilateral right-sided fit, lasting a few seconds, indicating some irritation — as was found after death — caused by slight secondary haemorrhage. After this the analgesia became absolute, and no sign of perception could be obtained to any form of tactile stimulation. The animal could move its limbs freely, and lay hold of objects firmly with the right hand, but it continually fell over on the right side, owing to the awkward and uncertain manner in which it planted its limbs. There was also total insensibility to tickling of the right nostril. The same stimulation of the left caused active grimaces and signs of uneasiness. Death occurred on the fourth day from secondary hemor- rhage. The lesion was found accurately limited to the lower » temporo-sphenoidal and hippocampal region of the left hemi- sphere, without the slightest implication of the crus or basal ganglia. In a tenth experiment > a similar lesion of the inferior temporo-sphenoidal and hippocampal region produced exactly similar results, there being almost complete analgesia, and absolute tactile anaesthesia over the whole of the opposite side. In this case also, however, sudden death occurred on the third day, rendering further observations as regards the permanency of the effects impossible. § 27. The foregoing experiments demonstrate the fact that the various forms of sensibility embraced under the term common or tactile sensibility — including cutaneous, muco- cutaneous, and muscular — are capable of being profoundly impaired or altogether abolished, for the time at least, by destructive lesions of the hippocampal region ; and the degree and duration of the anasthesia vary with the completeness of destruction of the region in question. We have seen that lesions of the gyrus hippocampi alone, and of the hippocampus itself alone, do not produce permanent 1 Experiment 29, figs. 141-148. TEE TACTILE CENTBE 341 effects. But whether recovery may ensue after complete removal of both is a point which unfortunately the fatality of the operations in my hands rendered it impossible for me to determine by my own experiments, so far as I had been able to carry them. I have, however, had' the great advantage of witnessing and studying the effects of similar operations care- fully planned and skilfully conducted by Professors Horsley and Schafer, which have succeeded in throwing much addi- tional light on the subject, and deciding certain doubtful points. In these experiments the lesions were established, under strict antiseptic precautions, by excision with the scalpel, so as to obviate all possible risk of diffuse effects. In order to reach and remove the hippocampal region the temporo- sphenoidal lobe was exposed, and the convexity removed in such a manner as that the hippocampus and hippocampa gyrus could be clearly displayed and removed en masse with- out any injury being inflicted on the crus cerebri. In one animal in which this operation was effected there was on the following day partial analgesia, and complete in- sensibility to mere contact, on the opposite side. Death, however, occurred on the second day, so that no further observations as to duration were possible in this case. In a second experiment the hippocampal region was re- moved, and the incisions made so as to detach also the margins of the calcarine fissure and hippocampus minor. This animal was profoundly anaesthetic on the opposite side, but there did not appear to be absolute analgesia. All mere tactile stimuli, however, like touch, scratching, rubbing, gentle pricking, was absolutely unperceived, while similar stimulation on the other side at once attracted attention. The condition of tactile anaesthesia continued for several weeks without appreciable alteration, but a gradual improve- ment occurred, so that examination at the end of six weeks revealed only some degree of impairment, as evidenced by less easily excited attention on gentle pricking, rubbing, &c. of the side opposite the lesion, as compared with the other. Severe pricking, pinching, or pungent heat, however, appeared to be well perceived. The observations on the degree of recovery after apparently 342 THE SENSOBY CENTRES total extirpation of the hippoeampal region led to the idea that probably the sensory region included also the callosal division of the falciform lobe, and to test this hypothesis the following experiment was performed. In an animal in which, some weeks previously, the hippo- campus had been removed, and which had completely recovered from any anaesthesia which might have existed directly after the operation, the same hemisphere was again exposed in the region of the longitudinal fissure, and the gyrus fornicatus excised along the whole length of the corpus callosum. The effect of this second operation was to cause absolute analgesia on the opposite side, continuing for several days after the operation, as well as complete insensibility to all milder forms of tactile stimulation. The analgesia diminished somewhat as time went on, but six weeks after the operation it was still manifest in some degree. The tactile anaesthesia was, however, apparently in nowise improved, all gentle forms of tactile stimulation being absolutely unperceived. The , animal was in perfect health, and exhibited no indications of motor disorder ; though directly after the operation there was slight weakness of the opposite leg, owing to the rather rough handling of the postero-parietal lobule and neighbourhood during the operations necessary to expose the gyrus fornicatus. This experiment completely verified the hypothesis which led to its being made, viz. that the gyrus fornicatus forms part of the tactile sensory centre, and is a physiological demonstration of the accuracy of the anatomical views of Broca that the callosal and hippoeampal regions form part of one great and distinct lobe— the falciform lobe. But at the same time it demonstrates the inaccuracy of his hypothesis, that the falciform lobe is related only to the sense of smell, and varies with the development of the olfactory bulb. It has already (p. 314) been seen that the callosal division of the falciform lobe bears no relation to the development of the olfactory bulb, inasmuch as it is more than usually developed and convoluted in the cetaceans, which have no olfactory bulb, or only a very rudimentary one. The only undoubted rela- tionship is between the development of the olfactory bulb and the hippoeampal lobule, or region of the nucleus amygdala. THE TACTILE CENTBE 343 The rest of the falciform lobe forms the centre of common or tactile sensibility. Therefore, in addition to the hippocampal region proper, we must include the callosal gyrus as forming part of the common sensory centre. This will explain the gradual restitution of tactile sensibility in those cases in which, notwithstanding the extensive, if not complete, destruction of the hippocampal region, the anesthesia, at first pronounced, gradually dis- appeared. For in this case, as in other centres, a portion is capable of carrying on the functions of the whole. The further experiments of Horsley and Schafer have proved that removal of the gyrus fornicatus alone produces effects like those caused by removal of the hippocampal region, viz. a more or less enduring analgesia and anaesthesia of the opposite side of the body. Partial lesions of this gyrus may, however, be made without producing any obvious deficiency. Thus in an animal in which the quadrilateral lobule alone was removed, after removal of the occipital lobe some time pre- viously, we were unable to detect any impairment of tactile sensibility. This is in harmony with the fact, copiously illustrated in the foregoing experiments, that partial lesions only of the hippocampal region, cornu Ammonis or gyrus hippocampi, produce only transient anaesthesia. The whole of the experiments, however, taken together, clearly prove that the centres of common sensibility are situated in the falciform lobe, and that, to produce absolute and permanent anaesthesia, it is necessary to destroy the whole of this lobe, callosal as well as hippocampal division. This is not easily effected, owing to the extreme difficulty of completely exposing and extirpating the falciform lobe without causing serious complications or fatal injuries. But though up to the present the experiments have not furnished a case of absolute and permanent analgesia, as well as anaesthesia, they have furnished abundant evidence that the degree and duration of the anaesthesia are in proportion to the completeness with which this lobe has been removed ; a concomitant variation which establishes beyond all doubt that the falciform lobe is the centre of common and tactile sensation. The symptoms observed in the animals operated on prove that the centres of mere touch proper are precisely the same as 344 THE SENSORY CENTRES those of painful sensation— whether from pressure, heat, or otherwise— the latter being merely an intense degree of the former. In cases in which the lesions have not been sufficient to induce analgesia, they have, however, been sufficient entirely to annihilate mere tactile sensibility. In the same regions are also the centres of cutaneo-mucous and so-called muscular sensibility. In many of the cases the interior of the nostril, and the tongue, were found to be quite as anaesthetic as the skin ; and that the so-called muscular sense was similarly affected was shown by the awkward use of the limbs, and the obvious insensibility to passive movements — so well exemplified in the ninth experiment above recorded. The effects of destruction of the falciform lobe are exactly like those observed in hemianesthesia of cerebral origin in all that relates to common sensibility. For here also there is analgesia or anaesthesia not only of the skin, but of the cutaneo-mucous membranes, together with loss of the so-called muscular sense. The falciform lobe, therefore, is the cortical centre of those fibres of the internal capsule, destruction of which is the cause of hemianesthesia of organic origin. I have not been able to satisfy myself as to the differen- tiation in the falciform lobe of centres of sensation for the different regions of the body, like that which is so character- istic of the motor zone. In general, where anaesthesia has been produced, whether from lesions of the, hippocampal region alone or of the callosal gyrus, it has affected the whole of the opposite side, face, arm, trunk, and leg. Occasionally, however, it has seemed as if one region had been more affected than others, but at other times this has not been noted. Without pronouncing definitely on this point, I am inclined to think that the experimental evidence is against any absolute differentia- tion of centres of tactile sensation for special regions. One of the strongest arguments is the fact that recovery ensues throughout in time, even after the most complete destruction of one portion of the falciform lobe, as in one of Horsley and Schafer's experiments ; and in many of my own experiments, in which very extensive lesions were established in the hippo- campal regions, the recovery was more rapid than could be accounted for on the supposition that the hippocampal region THE TACTILE CENTBE 345 constituted the whole of the sensory centre for any one particu- lar region. All the facts receive the most satisfactory explana- tion, if we regard the falciform lobe as a whole, and in each and every part the centre of tactile sensation for the whole of the opposite side of the body ; though probably the various motor centres are each anatomically related by associating fibres with corresponding regions of the falciform lobe. This association would form the basis of a musculo-sensory localisation. 346 CHAPTEE X. the hemispheres consideeed physiologically. The Motor Centres. § 1. It has been shown (Chapter VII.) that electrical stimulation of the brain of the monkey at certain definite points in the convolutions which, speaking generally, form the boundaries of the fissure of Eolando gives rise to definite and predictable movements of the trunk, legs, feet, arms, hands, facial muscles, tongue, &c, the centres being arranged in the order of enumeration from above downwards. Similar, and in many respects precisely the same, move- ments were shown to result from irritation of the frontal divisions of the external convolutions in the carnivora, and of the anatomically corresponding frontal region of the smooth brain of the rodentia. In the various figures the regions characterised by similar movements ' have been indicated by the same letters of designation. As a basis of topographical homology between the brain of the monkey (and man) and the lower vertebrates these data have an important value. The crucial sulcus (fig. 73, b) has been regarded by some as the homologue of the fissure of Eolando. Others (Meynert, Panseh) regard the coronal fissure or anterior division of the superior external sulcus as the true homologue ; while Broca finds it in the prae- Sylvian sulcus, or sulcus bounding the gyrus formed by the anterior extremities of the lower three external convolutions (fig. 73 in front of (») (9) ). A serious objection to Broca's view is the fact that in this case the centre for the movements of the head and eyes (fig. 73 (12)), would be placed posterior to the fissure of Eolando, whereas in the monkey this centre is situated well in advance THE MOT OH CENTERS 347 of it. For this reason alone the homology of the pras- Sylvian sulcus with the fissure of Kolando is more than doubtful. Nor does the cruciate sulcus, which I was formerly inclined to regard as the homologue of the fissure of Eolando, appear truly to represent this fissure. The crucial sulcus is only the anterior extremity of the subparietal sulcus, which forms the superior boundary of the calioial gyrus in the internal aspect of the hemisphere, and is occasionally absent in the brain of carnivora. If, however, with Meynert and Pansch we take the coronal sulcus as the fissure of Eolando, it is possible to trace a very close correspondence between the position of the various centres in the monkey, cat, dog, and other animals. The differences which are found to exist in the movements excited from anatomically corresponding points are such as would be accounted for by the different habit and modes of activity of the animals. Thus the relatively large area devoted to the facial movements (fig. 73 (7)) in the dog might be looked upon as corresponding with hand movements of the monkey (fig. 70 {a), (b), (c), (d)), as repre- sented in the ascending parietal convolution. And in the cat, in which the paw possesses highly differentiated movements, the centre for the protrusion of the claws and clutching action ( fig. 77 (a) ) corresponds very accurately with the position of the hand centre (fig. 70 (a) ) in the brain of the monkey. § 2. As regards the physiological significance of these regions, we have seen that we cannot conclude from the mere occurrence of movement on' the electrical stimulation that the regions are truly motor ; for the stimulation of a sensory centre may give rise to reflex or associated movement. Thus, stimulation of the superior temporo-sphenoidal convolution, which we have found to be a purely sensory centre — the centre of hearing — almost invariably gives rise to movement of the auricle, as well as of the head and eyes. Whether the centres now under consideration are directly motor, or only give rise to movements in a similar reflex, or indirect manner when stimulated, is a question which has been answered differently by different physiologists. The definite purposive character clearly perceivable in most of the move- ments, however, their correspondence with the ordinary voli- 348 THE MOTOR CENTRES tional activities and individual peculiarities of the animals, and above all their uniformity and predictableness, harmonise best with the hypothesis that they are the signs of the artificial excitation of the functional activity of centres immediately concerned in effecting volitional movements, and as such truly motor. If these centres are part of the mechanism of volitional movements, then paralysis of voluntary motion, and of motion only, ought to result from their destruction, and any apparent exception must be capable of satisfactory explanation in accordance with this view, if it is the correct one. The first experiment I made is illustrative of the effects of irrita- tion, followed by destruction, of the convolutions bounding the fissure of Eolando. The right l hemisphere of a monkey had been exposed and subjected to experimentation with electrical irritation. The part exposed included the ascending parietal, ascending frontal, and posterior extremities of the frontal convolutions. The animal was allowed to recover, for the purpose of watch- ing the effects of exposure of the brain. Next day it was found perfectly well. Towards the close of the day following, on which there were signs of inflammatory irritation and suppuration, it began to suffer from choreic spasms of the left angle of the mouth and left arm, which recurred repeatedly, and rapidly assumed an epileptiform character, affecting the whole of the left side of the body. • Next day left hemiplegia had become established, the angle of the mouth drawn to the right, the left cheek-pouch flaccid and distended with food, which had accumulated outside the dental arch, there being almost total paralysis of the left arm, and partial paralysis of the left leg. On the day following the paralysis of motion was complete over the whole of the left side, and continued so till death, nine days subsequently. Tactile sensation, as well as sight, hearing, smell, and taste, were retained. On post- mortem examination it was found that the exposed convolu- tions were completely softened, but beyond this the rest of the hemisphere and the basal ganglia were free from organic injury (fig. 111). 1 ' Experiments on the Brain of Monkeys,' Philosoph. Trans, vol. olxv. Part II. 1875. PSYCHO-MOTOB PAEALYSIS IN MONKEYS 849 In this we have a case, first, of vital irritation, producing precisely the same effects as the electric current ; and then destruction by inflammatory softening, resulting in complete paralysis of voluntary motion on the opposite side of the body without affection of sensation. In the next experiment the lesion was more limited, and the state of paralysis was limited correspondingly. The left hemisphere of a monkey was exposed, and the cortical sub- stance destroyed by the cautery in the postero-parietal lobule (foot centre), ascending parietal convolution (hand and wrist movements), and superior part of the ascending frontal convolution (movements of arm and leg) (see fig. 70). i, c e Fig. 111.— Lesion of the Grey Matter of the Right Hemisphere, causing complete hemiplegia of the opposite side without affection of sensation. ( Roy. Soe. ) c, tlie fissure of Rolando, d, the postero-parietal lobule, e, the ascending frontal conyolution. The centres of the biceps, facial muscles, and mouth and tongue were not involved. Immediately on this being done the right leg was found to be dragged, the foot and ankle especially hanging flaccid and powerless. The right hand and wrist hung powerless and flaccid, but the animal could flex the forearm and maintain resistance against extension ; a fact easily accounted for by the biceps centre remaining intact. There was no trace of facial para- lvsis or distortion of the angle of the mouth. Cutaneous sensation and the various special senses were unimpaired, and beyond the paralysis mentioned the animal was in good condition, and enjoyed food. In this animal the angular 350 THE MOT OB CEXTEES gyrus was subsequently destroyed, with the effect of causing blindness of the right eye. On post-mortem examination next day the lesion was found to occupy the motor regions specified and the angular gyrus, the rest of the brain and the basal ganglia being intact (fig. 112). In this case the paralysis was confined to the same move- ments as result from electric stimulation of the centres speci- fied. In the following experiment the extent of the lesion was still farther circumscribed, and the effect, as regards voluntary motion, correspondingly limited. The left hemisphere of a monkey was exposed in the region of the ascending frontal convolution sufficiently to display (6) (fig. 113), the centre of bicipital action, or supination and Pig. 112. — Lesion of the Left Hemisphere, causing motor paralysis of the right leg ami right hand and wrist, and of some of the movements of the right arm, and loss of sight in the right eye. (Boy. Soc.) flexion of the forearm. The exact spot being determined by the application of the electrodes, it was then accurately cauterised, just sufficiently to destroy the cortical grey matter. This operation immediately manifested itself in paralysis of the power of flexing the right forearm. All the other move- ments of the limbs were retained, but when the right arm was placed in an extended position the animal was utterly power- less to flex it, and the limb hung in a state of flaccid extension when the animal was lifted. It raised things to its mouth with the left hand, the move- ments of the legs were intact, there was no facial paralysis, and cutaneous and other forms of sensation were unimpaired. PSYCHO-MOTOR PARALYSIS IN MONKEYS 351 § 3. In these earlier experiments the duration of the para- lytic symptoms consequent on lesion of the motor zone was not determined ; but in a subsequent series ' special attention was directed to this question, as also to the sensibility of the paralysed limbs, and the secondary consequences of the cerebral lesions. In the first experiment 2 the cortex was destroyed in the middle third of the ascending parietal convolution and ad- joining margin- of the ascending frontal convolution of the right hemisphere. The result of this lesion was almost complete paralysis of the left hand, and great weakness of the flexor power of the Fig. 113.— Lesion (/) of the Left Hemisphere, causing pnratysis of the action of the biceps on the right side. (Roy. Soc.) forearm. The shoulder movements of the limb were unim- paired. The animal could stretch its arm forwards, but could not grip with its hand what it wanted to lay hold of. Tactile sensibility was absolutely unimpaired in the paralysed limb, the slightest touch on it at once exciting the animal's atten- tion, and a painful stimulus, such as a pinch or a touch with a heated wire, exciting as lively signs of sensation as on the other side. The condition remained essentially unchanged for the two months which the animal survived the operation, death occurring from the intense cold of the winter season. 1 ' The Effects of Lesion of Different Regions of the Cerebral Hemispheres Philosoph. Trans. 1884, Part II. (Ferrier and Yeo). '- Experiment 15*, ibid. fig. 39. 35-2 THE MOTOB CENTRES In this ease those movements were paralysed which are excited by electrical stimulation of the parts destroyed (see (a), (l>), &c. and (6), (fig. 70), the degree of paralysis being in proportion to the extent of destruction of the respective centres. The lesion was accurately limited, and, owing to antiseptic precautions being employed during the surgical operations, no secondary inflammation, meningitis, or en- cephalitis was set up. In the next experiment ' the cortex was destroyed at the upper extremity of the fissure of Bolando in the left herni- FlO. 111.— Lesion of the Left Hemisphere, causing paralj-sls of the right leg. sphere, the lesion invading a considerable extent of the region, irritation of which gives rise to movements of the opposite leg and foot (fig. 70, (l) and (2)). The lesion was purely cortical and did not extend beyond the surface of the medullary fibres, where they radiate into the cortical matter. A slight adhesion of the membranes and erosion of the cortex occurred in ad- vance of the primary lesion, extending into the centre for the forward extension of the arm (fig. 114). The result of this lesion was dragging of the right leg and almost complete immobility of the foot, while the movements 1 Experiment 10*, figs. 40-4-i, Phil Trans. Part II. 18S4. PSYCHO-MOTOR PARALYSIS IN MONKEYS v,:,)\ of the thigh on the pelvis were not perceptibly affected. For a few days, owing to the inflammatory adhesion of the mem- branes over the centre for the forward extension of the arm, there were spasms of the arm at the shoulder. These disap- peared, and the arm movements were retained to all appear- ance intact, but the right leg and foot remained almost com- pletely paralysed. The sensibility of the paralysed parts was in every respect as acute as in the sound limbs, equal re- action being obtained to all the usual tests of cutaneous sen- Fig. 115. — Section of the Sninal Cord in the Cervical Region, showing degeneration of the right pyramidal tract consecutive to the lesion seen in fig. 114. Fig. 11G. — Section of the same Spinal Cord in the lumbar region. sation. Six months after the operation contracture or late rigidity became established in the leg, such as occurs in incur- able paralysis in man, with exaggeration of the patellar tendon reaction. The condition remained unchanged at the death of the animal, eight months after the operation. The cerebral lesion was found accurately limited to the cortex of the upper extremity of the fissure of Eolando. Secondary degeneration was demonstrated by microscopical examination in the medullary fibres of the corona radiata, A A 354 TEE MO TOM CENTRES and in the pyramidal tracts of the opposite side of the spinal cord as far as the lumbar region, whence emerge the motor nerves of the lower extremity (see figs. 115, 116). This case proves conclusively that a lesion of the cortex invading the region, electrical irritation of which causes special movements of the opposite extremity, causes perma- nent paralysis of these movements, and of these alone, and leads to secondary degeneration of those tracts of the internal capsule and spinal cord which connect the cortex with the spinal segment or segments from which spring the motor nerves of the part. In a third experiment ' the cortex was extensively de- stroyed in the region of the upper half of the fissure of Eolando — i.e. ascending parietal and ascending frontal con- volutions — of the right hemisphere, the region for the move- ments of the limbs on the left side. The effect of this lesion was incomplete paralysis of the left arm and leg, the face being unaffected. From immediately after the operation till the death of the animal, nineteen months subsequently, motion was greatly impaired, while sensation was absolutely unim- paired in the left limbs ; and, as in the preceding case, in the course of a few months well-marked contracture, or late rigidity, supervened in the paralysed limbs, with exaggerated tendon reactions. In this animal, two months after the first opera- tion, a lesion was also established in the left hippocampal region, with the effect of causing for a time marked impair- ment of cutaneous sensibility on the right side, without affec- tion of motion. It was instructive to compare the reaction of the paralysed and non-paralysed limbs to tactile stimulation. Whereas in the limbs paralysed as to motion the signs of sensation were active and vigorous, in the non-paralysed limbs various forms of stimulation failed to elicit any signs of per- ception, or, if so, in a much less degree. Microscopical investigation after death revealed well- marked atrophy and degeneration of the pyramidal tracts of the right crus cerebri, right side of the pons, right pyramid, and of the left pyramidal or postero-lateral column of the spinal cord as far as the lumbar region. 2 1 Experiment 17*, figs. 45-51, Phil. Trans. Part II. 1884. 2 See figs. 45-51, op. cit. PSTOHO-MOTOB PARALYSIS IN MONKEYS 855 In a fourth experiment l the cortex was destroyed in the left hemisphere over an area embracing the ascending frontal and ascending parietal convolutions except at their upper and lower extremities, and also the base of the superior frontal convolution. The lesion also trenched somewhat on the an- terior limb of the angular gyrus and supramarginal lobule. There was thus destroyed nearly the whole of the motor area on the convex aspect of the hemisphere, the centres for the leg and foot being only partially invaded, and those for the angle of the mouth and tongue almost entirely escaping (fig. 117). Fig. 117. — Lesion of the Left Hemisphere, causing right hemiplegia. The result of this lesion was almost complete right hemi- plegia with conjugate deviation of the head and eyes to the left side. As in similar cases in man the deviation of the head and eyes was only of comparatively short duration, and the partial facial paralysis at first perceptible also disappeared within a fortnight. But the paralysed condition of the limbs continued very marked. With the exception of slight power of flexion of the thigh and leg the right lower extremity was helpless, and the right arm was utterly incapable of any inde- pendent volitional movement. Occasionally, when the animal struggled, associated movements were observed in the right hand, similar to those initiated by the left, but only under 1 Experiment 18*, figs. 52-55. a a 2 356 THE MOT OB CENTRES such circumstances. The power of prehension was entirely annihilated. Cutaneous sensibility was unimpaired through- out, the slightest touch exciting attention, and a pinch or other painful stimulus causing reaction and signs of sensation quite as vigorous as on the other side. This animal was exhibited before the Physiological Section of the International Medical Congress in London in 1881,' eight months after the operation, when the fact of the right hemiplegia was seen and admitted by all the assembled phy- siologists. At this time well-marked rigidity or contracture had become established in the paralysed limbs with exaggera- tion of the tendon reactions, as in cases of incurable cerebral hemiplegia in man. The investigation of the brain of this animal was entrusted to a committee appointed by the Physiological Section, and the facts of the position of the lesion in the motor zone, and its limitation to the cortex and subjacent medullary fibres, were definitely proved by them. Microscopical investigation also demonstrated the existence of secondary degeneration or sclerosis in the pyramidal tracts of the right side of the spinal cord as far as the lumbar region (figs. 118-120). The experiments of Horsley and Schafer 2 have shown that extirpation of the marginal convolution causes paralysis of those movements which remain more or less unaffected after destruction of the centres on the convex aspect of the hemi- sphere, viz. the movements of the trunk, and those of the limbs on the trunk, effected by the shoulder and hip muscles. In order, however, that these movements should be entirely paralysed it is necessary that the marginal convolution should be destroyed in both hemispheres, as it would seem that the trunk movements are so bilaterally co-ordinated in each mar- ginal convolution that the removal of one alone is not sufficient to cause any very marked effect. When both are removed, however, the most absolute paralysis of the trunk muscles is induced, and the animals remain prone and utterly unable to raise themselves on their limbs. It is unnecessary to multiply further proofs of the fact 1 Trans. Int. Med. Congress, 1881, vol. i. p. 257. 2 Brit. Med. Journ., 1884, vol. ii. p. 735. PSYCHO-MOTOB PABALYSIS IN MONKEYS 357 that in monkeys distinct and permanent paralysis of voluntary motion is induced by destruction of those regions of the cortex, electrical irritation of which gives rise to definite and pre- ■ dictable movements of the opposite side of the body. The paralysis varies in degree with the extent, and is strictly Fig. 118. — Section of the Spinal Cord in the cervical region, showing degeneration of the right pyramidal tract consecutive to the lesion in fig. 115. Fig. 119. — Section of the same Cord in the dorsal region. Fig. 120. — Section of the same Cord in the upper lumbar region. limited according to the position of the lesion. The paralysis affects only that movement or those movements which are thrown into action by irritation of the centre, which is, the seat of the lesion. The paralysis is purely motor, sensation 358: THE MOTOR CENT BE 8 being absolutely unimpaired; and degeneration ensues in those tracts which are developed in relation with the motor centres, and maintain their nutritive integrity through them. § 4. The facts of experiment on monkeys as above described have been abundantly confirmed by clinical and pathological researches in reference to the effects of cortical lesions in man. Within the last ten years clinical research, guided by experi- mental physiology, has accumulated an enormous mass of evidence, which is daily being added to, showing that 'cortical lesions in the region corresponding to the motor zone of the simian brain, as above defined, cause paralysis of voluntary motion without affection of sensation, which varies in degree with the extent of the destruction, and is limited according to the particular region or centre which is implicated. 1 If the destruction invades the whole depth of the cortex the paralysis is of an incurable type, and is accompanied by descending degeneration or sclerosis of the pyramidal tracts of the spinal cord, and contracture of the paralysed limbs, precisely as in monkeys. Though the conditions of nature's experiments in the form of disease are not such as are favour- able to the elimination of cause and effect — hence the long- enduring chaos of cerebral pathology — yet a careful collation and analysis of instances free, as far as possible, from compli- cations and general cerebral disturbances, have, indicated a remarkable concordance between the position of the respective motor centres in the brain of man and those determined by exact experiment in the brain of monkeys. Of themselves, however, the clinical facts at present accumulated would not suffice to establish more than a pro- bability ; but, taken in conjunction with the experimental data, they attain the higher character of sound and stable in- ductions. Crural monoplegia has been found associated with limited ' See the author's Localisation of Cerebral Disease, 1878 ; Charcot and Pitres, Revue Mensuelle, 1877, 1878 ; and Revue de MCdecine, 1883 ; Grasset, De la Localisation dans les Maladies Ciribrales, 1878 ; De Boyer, Sur les Lisions Corticales, 1879 ; Nothnagel, Topische Diagnostik der Gehirnkrank- heiten, 1879 ; Bxner, Localisation der Functionen in der Orosshirnrinde des Menschm, 1881. PSYCHO-MOTOR PARALYSIS IN. MAN 359 lesion at the upper extremity of the fissure of Eolando and paracentral lobule; brachial monoplegia with lesion of the, middle of the ascending frontal and ascending parietal convo- lutions ; brachio-crural paralysis with lesion of the upper third of the ascending convolutions ; brachio-facial paralysis with lesion of the middle and lower third of the same convolutions ; and oro-lingual paralysis or paresis with lesion of the lower extremity of the ascending frontal and parietal convolutions. When the last-mentioned lesion occurs on the left side there is also, with few exceptions, aphasia ; and when, as occasionally has happened, the lesion occurs symmetrically in both hemi- spheres, there is not only aphasia, but complete paralysis of all the volitional movements of the tongue and lips concerned in articulation. 1 This is in accordance with the fact that electrical irritation of the mouth or speech centre (fig. 70 (9) and (10) ) induces action on both sides, and hence in order to cause complete paralysis it is necessary that both centres should be destroyed. The same law obtains in respect of the trunk muscles and other bilaterally associated move- ments. There is not on record 2 a single unequivocal case of destruction involving the motor zone unaccompanied by paralysis of greater or less extent or limitation ; while, on the other hand, there is not another region of the brain which has not been the subject of destructive lesion, times without mention, without any motor paralysis whatever. § 5. What is true of the cortex obtains also of the sub- jacent medullary fibres of the corona radiata. Lesions of the pyramidal tracts of the motor zone which converge to the knee and anterior two-thirds of the posterior division of the internal capsule (fig. 25, i c) invariably cause motor paralysis of the opposite side ; and it has been found that just as stimulation of the respective cones of medullary fibres gives rise to the same movements as stimulation of. the cortical 1 See an important case of this kind reported by Barlow (Brit: Med. Journ. July 28, 1887, p. 103). 2 See on this the excellent tabular and graphic analysis in Exner's work Localisation der Functionen in der Orosshirnrinde des Menschen, 1881 ; also Charcot and Pitres ' Localisations Motrices,' Revue de M&decine, 1883. 360 . THE MOT OB CENTRES centres themselves (Chapter VII. § 5), so destructive lesions cause limited paralysis or monoplegia similarly defined. 1 The differentiation of the pyramidal tracts has further been demonstrated 2 by the fact that the area of secondary degenera- tion in the internal capsule and foot of the crus cerebri varies according to the portion of the cortex which has been destroyed. Apart from the anterior division of the internal capsule, which as will be seen (§ 25) degenerates'in relation with lesions of the prefrontal lobe, the tracts forming the knee and anterior two-thirds of the posterior division are in relation respectively from before backwards with the oro-lingual, facial, brachial, crural, and trunk muscles. Thus destruction of the mouth-centres causes degeneration of the fibres forming the knee of the internal capsule; those of the middle of the ascending convolutions, the fibres posterior to the knee ; and those of the upper extremity of the ascending and marginal convolutions, of the fibres which form the posterior third of the motor division of the internal capsule. These fibres, maintain their relative position in the foot of the crus ; the innermost, or those nearest the median line, corresponding to those in relation with the prefrontal lobes ; and the outermost, or those which he immediately in relation with the sensory tracts of the outer third or of the crus, being in relation with the cortical centres situated at the upper extremity of the fissure of Eolando and paracental lobule. § 6. When, however, we turn from man and the monkey to the animals lower in the scale, such as the cat, the dog, and the rabbit, we meet with facts which to some appear opposed to the doctrine abundantly illustrated by the foregoing ex- periments, that there are special motor centres in the cortex cerebri. Much controversy has taken place on this topic, and owing mainly to a narrowness of view and neglect of com- parative physiology, doctrines have been propounded which, however well according with the results of experiment on one 1 Pitres, Lesions du Centre Ovale, 1877 ; Hughes Bennett, ' Case of Brachial Monoplegia,' Brain, April 1885. 2 Brissaud, Contraction Permanente des Hemipligiques, 1880 ; see also Horsley, 'On Substitution in Eeference to Cerebral Localisation,' Lancet, July 5, 1884. PSYCHO-MOTOR PARALYSIS IN DOGS 8G1 order of animals, are altogether at variance with those on animals higher in the scale. It is, however, inconceivable that brains constructed on the same anatomical type should differ fundamentally in their physiological organisation, and we may assume as certain that, however much the facts of experiment on the motor centres of dogs and rabbits may appear opposed to those of monkeys, they are not so in reality, but are capable of being embraced with them in one comprehensive and harmonious generalisation. § 7. The centres for the movements of the limbs in dogs are, as indicated by the electrical reactions, situated in and around the crucial sulcus. When this region is destroyed in the one hemisphere the movements of the opposite limbs are at once affected in a very striking manner. 1 At first this appears to be absolute paralysis, so that the limbs are powerless to support the animal's weight, and double up under it. Shortly, however, frequently within a few hours, considerable improvement occurs, so that the animal can stand somewhat insecurely, and make attempts to walk. In doing so it generally turns in a circle towards the side of lesion. The limbs, especially the fore limb, tend to double up, and the foot is planted awkwardly, resting frequently on the dorsal instead of on the plantar surface, and the hind leg is dragged, instead of being lifted clear from the ground in the usual manner. Walking, at first impossible, is soon attempted, the animal tending to fall, and frequently actually falling over on the side, especially if the movements are at all hurried. Gradually, however, the power and control of the limbs are regained to such an extent that the animal can stand and walk without exhibiting any very noteworthy abnormality on cur- sory inspection. All this may occur within a few days after the operation. But, though it can stand and walk and run, it still continues for a long time very unsteady, and the limbs tend to slip and diverge outwards if the floor is smooth or if the animal turns round quickly. Even this may become less pronounced after the lapse of months, but no animal ever. 1 Hitzig, TJntersuch il. das Gehirn, 1874 ; Carville and Duret, Sur Us Fonctions des Simisphires Ciribraux, 1875 ; Goltz, Ueber die Verrichtungen, des Grosshirns, 1881. 362 THE MOTOR CENTRES entirely recovers ; ' and, as Tripier 2 has ingeniously shown, the paretic condition of the limbs can always be rendered apparent and intensified by the administration of a dose of morphia, or by conditions causing general prostration of the nerve centres. In the cat the phenomena following destruction of the motor centres are essentially the same as in the dog. In the case of the rabbit the effects are less marked and still more transitory. § 8. There is thus a very remarkable difference between the monkey and the dog in respect to the degree and duration of the powerlessness of the limbs after destruction of the cortical centres, and the question is, how are these differences to be explained on the hypothesis that the cortical centres in these animals are constructed on the same type, and perform homo- logous functions ? The affection with which we have to deal, as will be dis- cussed more at length subsequently, is in both cases a purely motor one, and the centres or regions in question are strictly motor, but motor in a special or limited sense, viz. psycho- motor, or concerned in the execution of consciously discri- minated or volitional movements proper. The differences observable as to the effects of destruction of the cortical centres in different animals depend on the degree or extent in which conscious discrimination, as distinct from automaticity or mere reflex action, is concerned in the ordinary modes of activity manifested by the animals operated on. In order properly to appreciate these differences, it is necessary to revert to certain facts already alluded to in a former chapter (Chapter IV.) It has been shown that entire removal of the cerebral hemispheres operates differently in different classes or orders of animals, in so far as relates to their motor stability and powers of response to external stimulation. In the fish, frog, and pigeon the removal of the hemispheres exercises little or no appreciable effect on the faculties of station and locomotion. Under the influence of stimulation from without these animals swim, jump, or fly with as much vigour, apparently, and 1 Obersteiner, 'Die Motorischen Leistungen der Grosshirnrinde,' Med. Jahrb., Heft II. 1878. z Revue Mensuelle, Sept. 1877, and Jan. 1880. PSYCHO-MOTOR PARALYSIS IN DOGS 3C3 precision as before. In the rabbit the destruction of the hemispheres, while greatly impairing the motility of the fore- limbs, does not render equilibration impossible, or destroy the power of co-ordinated movements of locomotion in response to appropriate external stimuli. In the dog, however, the removal of the hemispheres renders the animal completely prostrate and unable to stand or walk. Whether its powers might be regained, to some ex- tent at least, in course of time is probable, but difficult to determine experimentally, on account of the fatality of the necessary operations. § 9. The independent organisation of the lower centres is thus seen to vary according as we ascend or descend the animal scale. In proportion to the variety and complexity of the forms of motor activity of which the animal is ultimately capable, the longer the period necessary for the acquisition of volitional control over the limbs. Many of the lower animals start from birth with all their powers of movement already fully organised and capable of being exercised ; in most the period of helpless infancy is extremely short, as compared with that of the simian or human young. In these every exact movement is the result of a long and laborious process of education, even though this is rendered comparatively easy by the previous work of the race inherited in their nerve centres. The more machine-like or automatic the movements are at birth, the less the disturbance created by the destruction of the centres concerned in volitional action. Hence in the fish, frog, and pigeon the removal of the cortical centres has comparatively little effect on the motor powers ordinarily exhibited. Where voluntary control is speedily acquired, or automa- ticity inherited or rapidly established, as in the rabbit and dog, the centres of voluntary motor acquisition may be removed without completely or permanently interfering with the powers of locomotion. Locomotion is still possible through the agency of the lower centres, in which this mode of activity is mechani- cally organised, and may be set in action in response to various forms of external or internal impulse. The more the move- 3G4 THE MOTOR CENTRES merits are dependent on conscious discrimination and volitional - impulse, the more marked and enduring is the paralysis resulting from lesion of the centres of volitional action and registration. Hence the complete and lasting character of the paralysis is consequent on destruction of the cortical, motor centres in man and the monkey. The experiments of Soltmann ' on young dogs indicate that at birth the cortical motor centres are not fully developed, and do not respond to electrical stimulation before the tenth day of extra-uterine life. In accordance with these facts he has found that extirpation of the cortical centres before the tenth day causes no perceptible disturbance of the motor powers, such as invariably ensues when the animal has reached a more mature age. The first centres to respond are those for the forelimb, and it is precisely the movements of the forelimb which are most affected by lesion of the motor zone. Up to the tenth day all the movements of the puppy are mere reflex or automatic, and such as are primarily organised in* the lower centres. These are unaffected by removal of the centres of volitional control and acquisition, and it is only when true volition becomes established that destruction of the cortical centres produces the characteristic disorders of move- ment which have been described. And as volition enters more especially into the motor activities of the forelimb, so the forelimb is relatively more affected than -the others. The degree of development and control over the movements which a puppy reaches in ten days or a fortnight are not attained by the human infant under a year or more ; so that if we were to estimate the degree of paralysis resulting from the destruction of the cortical centres simply by the length of time required to reach the same standard of development, it would be at least thirty times more marked in man than in the dog. § 10. Besides these differences in the primary organisation of the nerve centres in different animals, there are certain facts relating to associated and bilateral movements which have an important bearing on the question under considera- 1 ' Experiment. Stud. ii. d. Funct. d. Grosshirns d. Neugebornen,' Jahrb. f. Emderheilkunde, Bd. ix. 1876. BILATERAL ASSOCIATION 365 tion. In hemiplegia or unilateral paralysis of motion from disease of the opposite hemisphere, it is found in man that the individual movements are not all equally affected, and that in the process of recovery some are regained before the others. Thus it is found, that when the arm and hand are perfectly powerless some degree of volitional control over the leg and foot may still be retained. The facial muscles are never entirely paralysed, and in particular the orbicularis oculi remains almost unaffected, so that the eye on the paralysed side can be closed almost as well as the other. In this there is a marked contrast between cerebral facial paralysis and peripheral facial paralysis, depending on direct lesion of the seventh cranial nerve. In the latter case the orbicularis oculi is absolutely paralysed, so that the eye cannot be closed. Generalising from these facts, it may be said that the more independent movements are most affected, while such as are usually associated in action with those of the opposite side — • the eyelids and other facial muscles, and many of the leg muscles — are less paralysed and more speedily recover. The varied and delicate movements of the hand are most of all impaired, and are the last to be re-established. The limbs of quadrupeds are, as regards the general cha- racter of their movements, more like the lower than the upper limbs of man, inasmuch as they are capable of comparatively few independent movements, and, as a general rule, are exer- cised only in alternating or associated action with each other. This fact of bilateral association, added to the greater degree of automaticity in the movements of the lower vertebrates, serves still further to explain the differences between them and the higher animals in respect to the effects of cortical lesions. Some movements are bilaterally represented in each hemisphere, and are thrown into action conjointly by electrical irritation of the cortex. This holds especially of the oro-lingual and trunk movements. Others which are not bilaterally represented in the cortex directly may be, as Broadbent has suggested, so connected by commissural fibres in the lower centres that both may be thrown into action by an impulse initiated by the one hemisphere. That this is the case is supported by many facts. Though moderate irritation of the 306 THE MOTOR CENT RE 8' cortex produces movements of the limbs only on the opposite side, yet under severer irritation, such as gives rise to epilepti- form convulsions, all four limbs may be thrown into action. In hemiplegia also strong energising of the sound hemisphere is apt to act also to some extent on the paralysed side. In one of the experiments above related (p. 355) I noted the f#ct that frequently when the animal used its left hand powerfully the right hand also, otherwise absolutely powerless, tended to close firmly ; and often when scratching movements were made with the left hand the right also scratched purposelessly in mid-air, and sometimes continued to do so for a distinct interval after the other had ceased. A hemiplegic patient when asked to move his paralysed leg is absolutely unable to do so ; but if he is asked first to move the sound leg, and then to try with the paralysed one, he may frequently succeed in moving it with a considerable degree of power. But commis- sural connections between the corresponding spinal nuclei on the two sides would not, as Horsley l has pertinently re ? marked, ensure the associated action of the limbs in locomotion, inasmuch as in locomotion the fore leg and the hind leg act together, and when one leg is flexed the other is extended. But we are not limited to mere commissural fibres between the corresponding spinal nuclei in endeavouring to explain bi- lateral association. Without anatomical commissural connec- tions movements may be so constantly functionally associated with each other, that the initiation of the movement on the one side may call the other into play. The movement need not be the same on the two sides. The closest functional asso- ciate of the fore leg in quadrupeds is the opposite hind leg, and, as we have already seen, since in the lower animals the move- ments concerned in locomotion are organised in the mesen- cephalic and spinal centres, there seems little difficulty in understanding how the centres of locomotion may be thrown into action bilaterally by an impulse proceeding from the one hemisphere alone. There is reason to believe that the initiating impulse of the sound hemisphere is capable of compensating in large measure for the loss of the centres in the other by the development of 1 ' On Substitution, &o.' Lancet, July 5, 1884. FUNCTIONAL COMPENSATION 3G7 freer channels of communication between the bilaterally asso- ciated lower centres. An interesting experiment confirmatory of this hypothesis has been described by Soltmann. The motor' area of the left hemisphere was destroyed in a puppy of four or five days old. No perceptible disorder of movement could be discovered either immediately or some days after the operation. The wound healed, and at the end of eight weeks the animal was perfectly well, though small. At the end of three months the motor zone of the right hemisphere was exposed and stimulated by the electric current, when it was seen that irritation of the centre for the left foreleg caused also similar movement of the right. Isolated action of the left leg could never be obtained, but always the conjoint action of the two. §11. But though from these and other facts it is clear that the sound hemisphere is capable of influencing in greater or less degree the movements of the limbs, and other parts, on both sides of the body, it is impossible to explain the compara- , tively slight impairment of the ordinary motor activities of the dog on destruction of the cortical centres in the one hemisphere merely by the compensatory action of the other. If it were only a matter of compensation by the cortical centres of the other hemisphere, it ought to follow that destruction of these also should cause complete paralysis on both sides. This, however, is not the case. Carville and Duret ' destroyed the motor centres of the limbs in the right hemisphere in a dog. This was followed by the usual paralysis, at first, as usual, very pronounced, but at the end of from six to eight days apparently recovered from. The left hemi- sphere was then similarly operated on, with the result of causing paralysis of the right limbs of the usual type, without reinducing the paralysis of the left side. But what seems still more remarkable, and apparently inconsistent with the specific localisation of motor centres in the cortex, is the fact that even after destruction of the motor centres in both hemi- spheres spontaneous and intentioned movements of consider- able complexity are still capable of being carried out. When 1 ' Fonctions des Hemispheres Cerebraux,' Archives de Physiologie, 2" Serie, tome i. 1875. 3G8 THE MOTOB CENTBES the operation is performed on puppies it would appear, from a successful experiment of this kind related by Soltmann, that, beyond general retardation of development, no special defect as regards motor power is observable. In adult animals, on the other hand, though immediately after extensive bilateral lesion ' there is a condition of general powerlessness, yet this improves to a considerable extent, and station and locomotion, though awkward and unstable, become ultimately possible. But the animals never entirely recover, and the forepaws especially are never capable of being employed for any inde- pendent movements. § 12. It has been assumed by Carville and Duret, and others, that this apparent recovery of volitional control over the limbs, which, however, is more apparent than real, justifies the hypothesis of Flourens and his followers that a process of compensation is effected by other parts of the hemispheres taking up and performing the functions of the centres which have been destroyed. If this hypothesis had any real founda,- tion, however, it ought to apply to monkeys and man. But this is not the case, for the paralysis resulting from destruction of the motor centres in these animals is permanent, and resembles in all its characters incurable cerebral paralysis in man. It is a hypothesis, moreover, altogether inconsistent with the theory of specific localisation of function. If we were to suppose it possible that the functions of the leg centres could be taken up by the neighbouring occipito-angular region, we should have the very remarkable substitution of a motor by a sensory centre ; a region which is at one time a centre of 1 It is questionable whether any experimenter has ever entirely destroyed the whole of the motor area in both hemispheres. In the dog exhibited by Professor Goltz at the International Medical Congress in London, 1881 (see Trans. Int. Med. Congress, 1881, vol. i. p. 218 et seq.) a considerable portion ""afcd of the motor centres of the limbs was perfectly intact in both hemispheres, especially in the left (see figs. 14a and 15a, and reports by Klein and Langley, pp. 242a and 2426. See also the further description of the right hemi- sphere by Langley in the Journal of Physiology, vol. iv. p. 292, and figures 1-3). Yet in this animal, retaining so much of the centres for the limbs, thero was observable an extraordinary t awkwardness of movement. Its legs tended constantly to slip and give way, and, as Goltz remarked, it was unable to use its paws to hold a bone when gnawing it, as dogs ordinarily do. FUNCTIONAL COMPENSATION 36!) visual perception, becoming a centre of voluntary motion, or even a sensory and motor centre at one and the same time, if there is no break in the continuity of function. Such a mode of interpretation is no more justifiable than the supposition that the organ of vision may take up the functions of the organ of hearing, or that a nerve may be at one time a motor nerve, and at another a sensory nerve, or perform both func- tions at once. For the specific localisation of function depends not on accident or indifferentism, but upon structural differ- ences and connections which render each region as distinct from another as the eye from the ear, or the leg from the tongue. The occipito-ahgular region is the cortical expansion of the optic tract in the same sense as the retina iii its peripheral expansion, and destruction of either expansion leads to atrophy of the optic nerves. The cortical motor region is the cerebral origin of the pyramidal tracts, and destruction of this region, and of none other, leads to degeneration of the pyramidal tracts ; and not only so in general, but each cortical centre is in relation with its own particular bundle of pyramidal fibres, and none other, so that limited destruction of the motor zone causes limited degeneration only of those fibres of the pyramidal tracts which are structurally related to the centre in question. The foundation of cerebral localisation resting, as is proved by such facts, on anatomical differences and connections, we may dismiss the hypothesis of substitution of one part by another as involving a contradiction in terms. It is necessary, there- fore, to seek for some other explanation of the apparent retention of voluntary motor power in dogs after removal of the cortical motor centres, consistent with the doctrine of specific localisation so amply demonstrated by the facts of experiment and clinical research in monkeys and man. For it is not to be supposed that animals constructed on the same anatomical type should differ so fundamentally in their cerebral organisation that specific localisation of function should be true of one and absolutely false in respect of another. Though dogs appear to recover from the effects of destruction of the cortical motor centres the recovery is found, on careful examination, to be more apparent than real. As a matter of fact, they never recover those movements which are essentially cortical, B B 370 THE MOT OB CENTRES nor do clogs which have been deprived of their cortical centres at birth «ver acquire them. Though a dog after destruction of its cortical motor centres is able to stand, and walk, and run, it never, even at best, performs these actions as well as the fish, frog, or pigeon without any cerebral hemi- spheres at all. It is obvious that for these modes of activity the cerebral hemispheres are not absolutely indispensable. The independent organisation in the lower centres of all the adjustments involved in station and the movements of trans- lation, appears to be complete and perfect in the lower verte- brates, such as the fish, frog, and pigeon ; but in the higher animals the co-operation of the centres of voluntary motion and registration is necessary, and this in varying degree. In proportion to the extent to which conscious discrimination is involved in the modes of activity displayed by the animal appears to be the time necessary for their acquisition, and in the same proportion are they impaired by destruction of the cortical motor centres. This reaches its extreme in man hi whom the motor capabilities are most complex and varied, and in whom the longest education and experience are neces- sary to develop and establish complete and perfect control over the limbs. In dogs less education is required, and the effects of destruction of the cortical motor centres are much less obvious ; but even in them the mesencephalic and lower centres never attain the same perfection of independent organisation seen in the fish, frog, and pigeon. In order that a dog may be capable of exhibiting a degree of responsive reaction similar to that of a pigeon deprived of its hemispheres, it is necessary that the basal ganglia — the corpora striata and optic thalami — should remain uninjured ; and even in such case the reactions and manifestations are greatly wanting in stability and precision. The so-called recovery which occurs in dogs after destruction of the cortical motor centres extends only to the brute force of the limbs, and to such movements or muscular combinations as are primarily or secondarily organised in the lower centres, and require no conscious discrimination for their accurate performance. Even these are permanently unstable and awkward, and capable of being effected only under favour- able conditions. Equilibrium is easily overthrown, the limbs FUNCTIONAL COMPENSATION 371 slip and double up on a smooth floor, or trip up over com- paratively slight obstacles or inequalities, and are incapable of that quick adaptation which characterises a normal animal under similar conditions. For all purposive actions implying conscious discrimination the limbs are permanently paralysed. The dog can never use its p*aw as a hand. 1 It cannot use the limb to dress its coat, or reach it forth to seize a piece of food lying just beyond its muzzle like a normal dog when tied up. It cannot fix or steady a bone which it wishes to gnaw, or clasp the female in sexual embrace. If it has learnt to ' give a paw ' at the word of command, it looks distressed and sorrowful, and fails to comply with the order. 2 In respect of these and all actions and tricks in which the limb is employed as an instrument of volitional purpose, the dog remains per- manently incapacitated. There is, however, a great difference between the dog deprived of its cortical motor centres and a pigeon deprived of its cerebral hemispheres. The latter is a living mechanism acting only in immediate response to appropriate external stimuli; whereas the dog retains spontaneity, and exhibits a manifold variety of activity under the same external condi- tions. But a dog, deprived only of its cortical motor centres, retains its sensory centres, and is therefore capable of sensa- tion, ideation, and emotion. It is not dependent for its activity on immediate impressions on its organs of sense, but has within itself the springs of action in the mediate form of revived or ideal impressions and emotional states. There is, however, no essential difference as regards causation between actions conditioned by present impressions on the sensory organs and those conditioned by revived or ideal impressions, for the same apparatus is concerned in both. Under the influence of ideational or emotional states, the sequence and causation of which may not be apparent, the dog may walk, run, or give expression to its desires in a manner indistinguish- able from ordinary volition. Only those actions are possible, 1 Goltz, op. cit. p. 30. 2 Goltz says that one or two of his animals have again learnt to ' give a paw,' others not. It may be confidently asserted that the cases of recovery were cases of incomplete destruction of the cortical centres in the first instance. b n 2 372 THE MOTOR CENTRES however, which are primarily or secondarily automatic and organised in the lower centres. All actions not so organised, and still dependent on conscious discrimination and the exer- cise of attentive volition, are effectually and permanently annihilated. § 13. Views have been propounded by other authors with respect to the functions and significance of the cortical motor centres, which appear to me neither justified by the facts of experiment on animals, nor consistent with those of clinical observation in man. Schiff 1 maintains that the movements resulting from irri- tation of the cortex are of a reflex nature, and that the affec- tion of motility following destruction of the cortical centres is essentially only an ataxy, dependent on loss of tactile sensi- bility, and exactly of the same nature as that resulting from section of the posterior columns of the spinal cord. In support of this he argues that those agents which annihilate reflex excitability also annihilate the electrical ex- citability of the cortex. This is true, but the excitability of the cortex does not follow the same laws as those regulating merely reflex actions. Eeflex actions are still readily excitable under conditions which entirely annul the excitability of the cortical centres. Schiff ascribes the movements resulting from electric stimulation to irritation of the fibres of the pos- terior columns, which — altogether without proof and contrary to all recent anatomical investigations — he assumes approach the cortex before turning downwards to reach their true centres at the base. In order to account for the secondary degenera- tion which ensues in the pyramidal tracts after destruction of the cortex, he further assumes that the pyramidal tracts, issuing from the basal centres, ascend near to the surface before turning downwards to pursue their path in the crura cerebri and lateral spinal tracts. The cortex itself, according to this imaginary anatomy, would appear to be altogether indifferent material, merely forming a covering for fibres which come near it, but form no connection with it. The resemblance which Schiff traces between the effects of 1 ArcMv fiir Experiment. Pathol, u. Pharmacol., Bd. iii. 1874; Pfliiger'S Archiv f. Physiologic, Bd. xxx. 1883. VIEWS OF SCHIFF 373 destruction of the cortical motor centres and the ataxy follow- ing section of the posterior columns of the spinal cord is of the most flimsy and superficial character, and disappears entirely on more careful investigation. The term ataxy is altogether inapplicable to the symptoms observed in man and monkeys on destruction of the cortical centres. In these there is a true motor paralysis varying in degree, as has been seen, according to the volitional independence of the movements affected. In dogs and other quadrupeds there is less general powerlessness, but those movements are most affected which are least so in ordinary ataxy. It is the independent and volitional movements of the limbs, suih as the use of the paw as a hand, which are paralysed in dogs ; while associated movements of the limbs, such as are concerned in running, leaping, &c. which are most affected in ataxy, are least impaired after destruction of the cortex. The movements are more or less insecure, but this is attributable to motor weak- ness in general, and not to any ataxic disorder. Schiff, in further support of his theory of the identity between the effects of section of the posterior columns and destruction of the cortex, makes the extraordinary statement that after section of the posterior column on one side the motor area of the opposite hemisphere ceases to be excitable after the lapse of about four days. This he regards as a proof of the continuity of the posterior column with the parts which ordinarily react to the electrical stimulus. He assumes that the section of the posterior column, by severing it from its nutritive centres in the posterior spinal ganglia, leads to ascending degeneration as far as the cortex, so that the fibres are no longer capable of being excited and giving rise to reflex reactions. It is true, as Schiff states, that the operation for section of the posterior column as he performs it leads to abolition of all reactions from the cortex in the parts situated below the sec- tion, but the explanation is a very different one from that which he gives. There is no degeneration up to the cortex, but, as Horsley l has satisfactorily demonstrated, the pyra- 1 Horsley, ' On the Relation between the Posterior Columns of the Spinal Cord and the Exoito-motor Area of the Cortex, &o.,' Brain, April 1886. 374 THE MOT OB CENTRES midal tract, injured by the operation for section of the posterior column owing to secondary inflammatory changes, undergoes degeneration below the section, so that it ceases to be capable of transmitting motor impulses to the parts with which it is in relation. But this result only ensues when the operation is not carried out in such a manner as to prevent .the extension of the primary lesion by secondary inflamma- tion. That the motor area continues excitable, notwithstand- ing the destruction of the posterior column, even in cases where the lateral column becomes implicated, is shown by the occur- rence of the ordinary reactions in the parts deriving then- motor supply from the parts above the lesion. Schiff holds that the posterior columns of the spinal cord are the paths of tactile sensibility or touch proper, as distinct from the other forms of common sensibility, and he attributes the ataxy which results from section or disease of these columns to the loss of tactile sensibility. These questions have already been discussed (Chapter II. § 10), and we ha«ve seen reason to regard Schiff s views as to the functions of the posterior columns and as to the cause of ataxy to be entirely erroneous. § 14. The assertion made by him, as well as by Tripier, 1 Munk 2 and others, that removal of the cortical motor centres causes loss of tactile sensation has no better foundation. Munk, indeed, goes farther than Schiff, and holds that not merely tactile sensibility, but common sensibility in general is abolished by lesion of the cortical motor zone. Munk's state- ments are justly ridiculed by Goltz 3 as being unsupported by any evidence worthy of consideration, and directly contradicted by his own experiments, as well as those of Hitzig, Schiff, and my own. The conclusion that tactile sensibility is lost or diminished after destruction of the cortical motor area is based on defec- tive methods of investigation and erroneous interpretation of the reactions of the lower animals to sensory stimulation. Though an animal does not react so readily to sensory stimula- ' ' De L'Anesthesieproduite par les Lesions des Circonvolutions Cer6brales,' Ecvue Mensuelle de Midecine et Chirurgie, 1880. - Op. cit. 3 ' Verrichtungen des Grosshirns,' Pfliiger's Archiv, Bd. xxxiv. 1884, p. 467. SENSOBY BELATIONS CONSIDERED 375 tion of the paralysed side it does not follow that this is due to diminished or absent perception of the stimulus. An animal may not react, or react less energetically, to a sensory stimulus, not because it does not feel it the less, but because it is un- able, or less able, to do so from motor defect. It is astonishing what apathy or indifference some animals display towards certain forms of stimulation, such as gradually • increasing pressure on the fingers or toes which one would regard as well calculated to elicit reaction or signs of uneasiness. Un- less the stimulus is of a nature to at once excite attention, or to evoke reflex action, it may appear to be altogether un- perceived. All that the experiments of Schiff and Tripier demonstrate is that motor reactions are less readily evoked on the side opposite the cortical lesion. But the same thing occurs in cases of purely motor hemiplegia in man. Cutaneous reflexes are less readily excitable on the paralysed side, though the patients . testify to the fact that they feel and localise the tactile stimulus as readily and acutely on the one side as the other. 1 It is easy by devising methods calculated to evoke signs of true sensation, as distinct from merely reflex reaction, in the lower animals, to prove beyond all question that in them also sensation is entirely unaffected by lesions of the cortical motor zone. In monkeys, attentive to all their surroundings, it is as a rule only necessary to gently touch the paralysed side to elicit the most indubitable signs of attention. In one animal 2 in which for purposes of comparison I established lesion first in the motor area of the right side, and afterwards in the hippocampal region of the left side, there was diminished 1 Why the reflexes should be diminished in pure motor hemiplegia of cerebral origin is not quite clear. It extends not merely to the reactions of the limbs, but also to the cremasteric and other reflexes which are not obviously under volitional control. When the cord is divided the reflexes are more active. It has been supposed by some that the spinal reflexes are inhibited by the cerebral lesion. It appears to me more probable that it is simply a case of greater or less diffusion of the stimulus. Ordinarily the cerebral centres co- operate with the spinal centres, even in the simplest reflex reactions. When the cerebral centres are destroyed the sensory stimulus is diffused upwards and lost. When the cord is divided the sensory stimulus is concentrated in the spinal centres, and more readily calls forth reflex reaction. 2 Experiment 17, Phil. Trans., 1884, Part II. 3 7G THE MOT OB CENTRES reflex reaction in the left limbs, though the signs of sensation were distinct ; whereas on the right side, though the reflex reactions were more readily excitable than on the left, yet the animal bore with perfect indifference stimuli which caused active signs of uneasiness when applied to the paralysed limbs." Goltz ' relates an extremely instructive experiment on a dog, which shows in the clearest possible manner that tactile sensibility is absolutely unimpaired on the side opposite the lesion of the cortical motor zone. Taking advantage of the well-known fact that dogs snarl when touched while engaged in eating any choice morsel, he touched the right side of a dog so occupied, which had had its motor region in the left hemisphere destroyed some time previously. The animal responded on every occasion with the characteristic signs of displeasure to the slightest touch. A similar satisfactory proof of the retention of tactile sensation in a cat after destruction of the opposite cortical motor zone is furnished by Bechterew. 2 It is a familiar^ observation that a cat dislikes having its feet wet, so that if it should accidentally step on a wet place it will stop and shake its paw dry before proceeding further ; or, if while it is indo- lently slumbering, a drop of water falls on it, it will start up and make off hastily. Or it will close its eyes and contract its ears if its paw is gently touched unobserved. After veri- fying these facts in a cat about to be operated on, Bechterew removed the cortex in the region of the sigmoid gyrus of the left hemisphere. On recovery from the chloroform narcosis the animal exhibited the characteristic motor disorders of the right limbs, and was unable to use the right paw for any in- dependent volitional act. But touching the ear or the sole of the foot of the right as well as of the left side induced the same closure of the eyes and drawing in of the ears as before ; and the sprinkling of a few drops of water on its paralysed side caused the animal to start and make off as before. In presence of facts such as these it is useless to contend 1 Pfluger's Archiv, Bd. xxxiv. 1884, p. 465. 2 'Wie sind die Ersoheinungen zu verstehen, die nach Zerstorung des motorischen Kindenfeldes an Thieren auftreten,' Pfluger's Archiv, Bd. xxxv. 1885, p. 137. SENSORY RELATIONS CONSIDERED 377 that tactile sensibility is in any measure impaired by destruc- tion of the cortical motor region. § 15. It is unquestionable that in man paralysis associated with lesion of the cortical motor zone is in the vast majority of instances an essentially motor affection, and is unaccompanied by any defect in the domain of sensation, whether tactile, thermal, or otherwise. In old-standing cases, where the limbs have become rigid, cold, and oedematous, sensation may be found more or less obtuse, but not more so than would be naturally expected from the condition of the tissues of the limb so induced. But, apart from this, sensation is keen and to all tests unimpaired in the limb which is utterly beyond the control of the will. It is, however, true that clinical records furnish in- stances in which sensation has been abolished or impaired in connection with and, as some contend, apparently due to lesions of the cortical motor area. But it is also true that lesions have been found in certain regions — the prefrontal, occipital, and temporal — without any discoverable symptoms whatever ; and on the other hand, as Brown-Sequard ' has shown, there is scarcely a symptom of cerebral disease that has not been found in connection with lesions situated in these regions, as well as in the brain indiscriminately. These facts, instead of establishing causal relationships, serve only to illustrate the comparative impotence of purely clinical research towards the elucidation of the functions of particular regions. Morbid anatomy is not equivalent to pathology, and less so in the case of the brain than elsewhere. The extent of the part visibly diseased is by no means a measure of the extent or position of the functional or organic derangement that actually exists. If the mere visible anatomical lesion were always to be regarded as the true cause of the symptoms, we might find with Exner a centre for almost every function in the most diverse cerebral regions ; or conclude with Brown-Sequard that there is no localisation of function whatever, and that a cerebral lesion, wherever situated, produces symptoms only through some dynamical influence on the true centres situated ' Lectures on the Physiological Pathology of the Brain,' Lancet, 1876 and 1877. 378 THE MOT OB CENT BE S [somewhere unknown. Causation is not established unless an invariable and unconditional relationship has been proved to exist between a particular lesion and a particular symptom. In the case of the motor area it has been satisfactorily demon- strated that a destructive lesion invariably gives rise to motor paralysis, local or general, according to the position and extent of the lesion. That in some instances impairment of sensation has been observed along with paralysis of motion in connection with lesions apparently confined to the cortical motor area does not suffice to establish a causal relationship between the anatomical lesion and the sensory defect ; for a single case of destructive lesion of the motor area without anaesthesia is sufficient to overthrow the apparent causal connection founded on a host of positive instances. But as in reality the cases in which anaesthesia has been observed in connection with destructive lesion of the motor area are quite exceptional in comparison with those in which all sensory impairment has been distinctly disproved, it seems almost inconceivable that they should be seriously adduced as good evidence in support of the sensory functions of the motor zone. 1 Strictly cortical lesions of the motor area do not cause anaesthesia in any form, and it may be laid down as a rule, to which there are no exceptions, that if anaesthesia is found along with motor paralysis, the lesion is not limited to the motor zone, but implicates also organically or functionally the 1 As a type of the evidence and arguments in favour of the sensory function of the motor zone the reader may refer to a paper by Petrina (' Sensibilitiits- storungen bei. Hirnrindenlasionen,' Zeitsch.f. Heilkunde, Bd. ii. p. 375, 1881). The author quotes six cases of what he regards as strictly limited cortical lesions associated with sensory disturbances. In one of these a small hjemorrhagic tubercle, the size of a lentil (!), situated in the right upper parietal lobule, is credited with having been the cause of left hemiplegia and anaesthesia ; and in another a small cheesy tubercle, the size of a hemp-seed (!), situated in Broca's convolution, is regarded as the cause of aphasia, paralysis of the right side of the face and arm, and anassthesia of the right side of the trunk. That such minute morbid specks, which might well have reached three times the size without causing any appreciable disturbance of the parts in which they were situated, should be regarded as the real cause of the wide- spread derangement of cerebral functions observed in these two cases is a truly marvellous phenomenon. VIEWS OF HITZIG AND NOTHNAGEL 379 sensory tracts of the internal capsule or the centres to which they are distributed (the falciform lobe) . § 16. Hitzig 1 and Nothnagel 2 attribute the disorders of motility consequent on destruction of the cortical motor zone to loss of the muscular sense, and assimilate the condition to that of ataxy. Hitzig says of his dogs ' they had apparently only an imperfect consciousness, or inability to form correct notions, of the condition of the limb ' (op. cit. p. 60). The term muscular sense as ordinarily understood, and as employed by these authors, is applied to the assemblage of centripetal impressions generated by the act of muscular contraction in the muscles themselves, as well as in the skin, fasciae, liga- ments, and joints. By the complex impressions so conditioned we judge of the fact and extent of muscular movement, either when we make the movements actively, or when our limbs are moved passively. The motor centres are, according to Hitzig and Nothnagel, the centres of this so-called sense. The de- struction of the motor centres abolishes the perception of those impressions which accompany and guide muscular action, and hence the wavering and uncertain character of the movements actually effected. Even in dogs, however, as has been already indicated, the resemblance to ataxy is only a superficial one. A more careful examination shows that those movements are least affected in which ataxy, when it exists, is most pro- nounced, viz. the movements of locomotion and similar co- ordinated acts 1 ; while those are most affected, or permanently rendered impossible, in which we recognise independence and true volition. Whatever may be said as to the condition in dogs, however, it is most certain that the term ataxy is not applicable to the effects of destruction of the motor zone in monkeys or in man. It is not in these a case of uncertainty or irregularity of movement, but an absolute paralysis and entire withdrawal of the part from the control of the will. It is also certain — and a subject of daily clinical demonstra- tion — that in paralysis from cortical disease the patient though unable to move his arm voluntarily is perfectly aware of every movement passively communicated to it, and can state with exactitude whether his arm is flexed or extended, whether his 1 Untersuchungen, supra cit. 2 Virchow's Archiv, Bd. Ivii. 1873. 380 THE MOT OB CENTBES fist is closed or open, and whether his finger is being flexed or extended gently or with force. His muscular sense, as well as every other form of common sensibility, is absolutely un- impaired. That he cannot move his arm does not arise from an imperfect or absent consciousness of his limb, but from destruction of an essential portion of his motor apparatus. We have further already seen that the total abolition of the so-called muscular sense does not paralyse the power of effecting movements nor render them ataxic (p. 144). Even though the impressions ordinarily generated by muscular contraction are not perceived, yet the person can walk, or move his limbs, with perfect freedom under the guiding sense of vision. Even with the eyes shut the patient can intend his movements with correctness, but he may think that he has performed the intended movement though the limb has been held firmly or checked midway. There is no necessary connection between the power of directing movements and the muscular sense, as has been erroneously assumed by Brown*- Sequard and others. Loss of the muscular sense never occurs without general anaesthesia of the limb. No one has ever furnished the slightest evidence of impairment or loss of the muscular sense apart from profound impairment or total abolition of the common sensibility of the limb. The state- ments to the contrary, sometimes met with, rest only on the foundation of a demonstrably false hypothesis as to the nature of the ataxy which it is invoked to explain. As there is no evidence of impairment of the common sensi- bility of the limbs from destruction of the cortical motor zone, but conclusive evidence to the contrary, so are the views of Hitzig and Nothnagel respecting the abolition of the muscular sense equally without foundation. The existence of the so- called muscular sense does not confer mobility on the limb, for it exists in the limb paralysed as to motion either by spinal or cerebral lesion ; nor does the absence of the muscular sense paralyse the limb as to motion or render its movements ataxic. -§17. Bastian ] assumes that into the composition of the so-called muscular sense in addition to the cutaneous impres- 1 The Brain as an Organ of Mind, 1880, p. 543. VIEWS OF BA8TIAN 381 sions, and those arising in the deep textures of the limbs during the act of muscular contraction, there enter also a ' set of " unfelt " impressions, which guide the motor activity of the brain by automatically bringing it into relation with the dif- ferent degrees of contraction of all muscles that may be in a state of action ' To these unfelt impressions he would give the name kincesthesis, and he is of opinion that the so-called motor centres are in reality sensory, or the seat of this kin- sesthesis, or sense of movement. The stimulation of these kinsesthetic centres acts in a manner reflexly by exciting the activity of the corpora striata or true motor centres. In reference to this hypothesis I would remark that it is undoubtedly true that the due co-ordination of movements is largely conditioned by afferent impressions of an unconscious character, and that a disorganisation of the paths of these centripetal impressions is the main cause of ataxy. But in- asmuch as perfect co-ordination is possible in the entire absence of the cerebral hemispheres, we have no reason for supposing that the cerebral centres are at all concerned in the mechanism of co-ordination. How unfelt impressions can enter into the composition of that which is so essentially a psychical act of discrimination is not very intelligible, nor how ' unfelt ' im- pressions can be ' ideally ' revived, or aid in the formation of a conception of the movement. Why the loss of the sense of movement, which in point of time should come after the movement, should render all movement impossible, as happens when the motor centres are destroyed in monkeys and man, is also incomprehensible. It might explain ataxy, but not paralysis. The theory that the cortical centres act only through the corpora striata is founded on an old and erroneous anatomy of the brain; for it has been conclusively demonstrated that the pyramidal tracts proceeding from the cortical motor centres do not join the corpora striata, but pass directly through, without any interruption in their continuity, to the anterior horns of the spinal cord. As these tracts degenerate centrifugally on destruction of the cortical centres, in precisely the same way as motor nerves on destruction of the anterior cornua, we have as good reason for applying the term motor to the cortical as to the spinal centres. 382 THE MOTOR CENTRES § 18. It is, however, maintained by Bain, 1 Wundt, 2 and others that, apart from the feeling of movement effected, con- ditioned by centripetal impressions of the kind described, we have a feeling of force exerted, conditioned by the energising of the motor centres themselves. Bain says, ' As the nerves supplied to muscles are principally motor nerves, by which muscular movements are stimulated from the brain and nerve centres, our safest assumption is that the sensibility accom- panying muscular movement coincides with the outgoing stream of nervous energy, and does not, as in the case of pure sensation, result from an influence passing inwards, by in- going or sensory nerves' {op. cit. p. 92). There is supposed to intervene between the intended move- ment and the actual carrying it into effect a feeling or sense of the motor innervation requisite for the desired end, which sense of innervation is supposed to be given in the energising of the motor centres themselves. This hypothesis would make us conscious of the molecular processes of our brains. If true, we might have been able to evolve from our consciousness a knowledge of the motor centres which have only recently been discovered after much experi- mental and clinical research. Neither on subjective 3 nor ob- 1 The Senses and the Intellect, 1864. 2 Physiologische Psychologie, 1874. s No one has put this more clearly than Professor W. James (' The Feeling of Effort,' Anniversary Memoirs of the Boston Society of Natural History, Boston, 1880), and his remarks are worthy of quotation in extenso. 'Now what can be gained by the interposition of this second relay of feeling between the idea and the movement? Nothing on the score of economy of nerve tracts ; for it takes just as many of them to associate a million ideas with a million motor feelings, each specific, as to associate the same million ideas with a million insentient motor centres. And nothing on the score of pre- cision ; for the only conceivable way in which they might further precision would be by giving to a mind whose notion of the end was vague a sort of halting stage with sharper imagery on which to collect its wits before uttering its flat. But not only are the conscious discriminations between " ends " much sharper than anyone pretends the shades of difference between feelings of innervation to be, but even were this not the case, it is impossible to see how a mind with its end vaguely conceived could tell out of a lot of Innerva- tionsgefahle, were they never so sharply differentiated, which one fitted that end exactly, and which did not. A sharply conceived end will, on the other hand, directly awaken a distinct movement as easily as it will awaken a distinct feeling of innervation. If feelings can go astray through vagueness, surely the THE SENSE OF EFFOBT 383 jective analysis of cerebral processes does it seem necessary to superadd a sense of innervation to that 'which is contained in the idea of the movement ; and it is certain that the motor centres have no concern in the process, for the idea of the move- ment may be most perfect when the motor centres are entirely destroyed. A dog with its motor centres destroyed has a clear idea of the movement required when asked to give a paw, and exhibits its grief at being unable to do so in an unmistakable manner ; and the patient suffering from cortical motor lesion, after making futile attempts to carry out his ideally realised movement, not uncommonly bursts into tears at his failure. There is no defect in the ideation, but only in the realisa- tion of the movement. § 19. In favour of the existence of a consciousness of effort, apart from afferent impressions conditioned by muscular con- traction, various considerations have been offered, some of which are of little weight. Of this kind are the experiments of W. Arnold : on the roots of the spinal nerves. Arnold cut the posterior roots of the nerves of the frog's fewer steps of feeling there are interposed, the more securely we shall act. We ought, then, on a priori ground alone to regard the Innervationsgefiihl as a pure encumbrance. ' Let us turn now to a posteriori evidence. It is a notorious fact, recognised by all writers on voluntary motion, that the will seems concerned only with results, and not with the muscular details by which they are executed. But when we say " results " what is it exactly that we mean ? We mean, of course, the movements objectively considered, and revealing themselves (as either accomplished or in process of being accomplished) to our sensible perceptions. Our idea, notion, thought, of a movement, what we mean whenever we speak of the movement, is this sensible perception which we get of it when it is taking place or has completely occurred. What, then, is this sensible percep- tion ? What does it introspectively seem to be ? ' I unhesitatingly answer : an aggregate of afferent feelings, coming primarily from the contraction of the muscles, the stretching of tendons, ligaments, and skin, and the rubbing and pressing of joints ; and secondarily, from the eye, the ear, the skin, nose, or palate, any or all of which may be indirectly affected by the movement as it takes place in another part of the body. The only idea of a movement which we can possess is composed of images of these its afferent effects. By these differences alone are movements mentally distin- guished from each other, and these differences are sufficient for all the dis- criminations we can possibly need to make when we intend one movement rather than another ' (p. 6). 1 Die Verrichtungen der Wurzeln der Buckenmarksnerven, Heidelberg, 1844. 384 THE MOT OB CENTBES leg, and observed that when the animal was made to jump it used the leg operated on with apparently as much precision and energy as the sound one. From this the conclusion is drawn that the animal must still have retained the conscious- ness of muscular effort, otherwise it could not have used the limb in the manner described. We know, however, that the precision of the movements of locomotion in a frog is just as great when the cerebral hemispheres are entirely removed, and that bilateral reflex action of the limbs is easily produced in this animal by unilateral cutaneous stimulation. Psychical discrimination — a function which belongs to the hemispheres — forms no essential factor in the co-ordination of the frog's movements of locomotion. Arnold's experiment is nothing more than a very ordinary instance of bilaterally co-ordinated reflex action, and may be demonstrated in a frog deprived of its cerebral hemispheres, and therefore of all truly psychical faculties. To argue from the responsive or reflex actions of the frog to the conditions of psychical discrimination in man is not, I think, likely to lead to trustworthy conclusions. Certain facts observed in cases of hemiplegia in man, alluded to in the following quotation from Wundt, 1 are more to the point : — ' Whether the sensations accompanying the contraction of the muscles arise in the nerve fibres that transmit the motor impulse from the brain to the muscles, or whether special sensory fibres exist in the muscles, cannot be decisively settled. [Bee, however, p. 63.J Certain facts, however, make the first assumption more probable. If special nerve fibres existed they must be connected with special central cells, and thus in all probability the central organs for the apprehension of these sensations would be different; from those which send out the motor impulse ; there would be two independent nerve systems— the one centripetal, the other centrifugal. But in the one, the medium of the sensation, nothing else could be regarded as the stimulus than the changes taking place in the muscle, the contraction, or perhaps the electrical process in nerve and muscle, accompanying the contraction. Now this process is known to keep equal pace with the energy of the ' Menschen- und Thier-Seele, Bd. i. p. 222. THE SENSE OF EFFORT 385 muscular contraction, and we must expect that the muscular sensation would constantly increase and decrease with the amount of internal or external work done by the muscle. But this is not the case, for the strength of the sensation is de- pendent only on the strength of the motive impulse, passing outwards from the centre, which acts on the innervation of the motor nerves.' Wundt then quotes instances of muscular paresis, or partial paralysis, where the patients are capable of feeling that they are putting forth great muscular effort, though the limb is hardly moved. This is a fact also commonly to be observed among hemiplegias, who express themselves con- scious of putting forth great energy when told to move the paralysed limbs, though the limbs remain absolutely motion- less. A still more striking case of sense of effort, apparently conditioned by the outgoing current, is seen in cases of para- lysis or paresis of the external rectus muscle of the eyeball. When, e.g., the right external rectus is paralysed, the patient is unable to rotate the affected eye outwards. Yet, though the act of will has produced absolutely no movement of the eyeball outwards, the patient feels that he has given the proper innervation to the eyeball, and believes that the object flies to the right. When the external rectus is merely in a state of paresis or enfeeblement, and not completely paralysed, the same volitional stimulus which would move the eyeball to the extreme outer angle is able to effect only a very slight rotation outwards — say 20°. Yet though the eyeball has moved only 20° the patient believes that he has moved his eye to the extreme right. Inasmuch as the afferent impres- sions conditioned by a rotation of 20° must be the same in the paretic eye as in a sound one it is argued that the feeling of innervation must be a purely efferent one, varying with the degree of the motive impulse. A little further inquiry, however, into the conditions coincident with the feeling of effort, exemplified in the above instances, speedily disposes of these plausible arguments. It is necessary that all movements whatever should be eliminated before we can admit that the sense of effort is conditioned by c o 386 THE MOT OB CENTRES the central motive impulse. For in the fact of associated muscular action, and the concomitant centripetal impressions, even though not expressly willed, the conditions of the con- sciousness of effort exist, without our being obliged to regard it as dependent on central innervation or outgoing currents. Now though the hemiplegic patient cannot move his paralysed limb, and is nevertheless conscious of putting forth great effort, he will be found to be making powerful muscular exer- tion of some kind. Very often he will be seen to be making with his sound limb the movement which he is desirous to effect with his paralysed limb. Observers of the phenomena associated with the paralysed or paretic external rectus have, as W. James ' has shown, failed to note what is taking place in the associate internal rectus of the sound eye. The conju- gate movements of the eyeballs^the external rectus of the one eye and the internal rectus of the- other — are innervated from a common centre, and we are unable to discriminate between the sensations arising from each individually. Now wljen the patient is unable to move the affected eye outwards at all, or only partially, he is making strong convergent movement of his sound eye, and he estimates the direction of the object precisely in accordance with the degree of contraction of the internal rectus of this eye. The sense of innervation is clearly dependent on the strain on the internal rectus of the sound eye, and not on the central motive impulse. Even when the associated movements are not so obvious as in the cases above alluded to, it is not difficult to discover the basis of the sense of effort in the centripetal impressions generated by some form of active muscular exertion. If the reader will extend his right arm and hold his fore- finger in the position required for pulling the trigger of a pistol, he may, without actually moving his finger, but by simply making believe, experience a consciousness of energy put forth. Here, then, is a clear case of consciousness of energy without actual contraction of the muscles either of the one hand or the other, and without any perceptible bodily strain. If the reader will again perform the experiment, and pay careful attention to the condition of his respiration, he 1 Op. cit. THE SENSE OF EFFOBT 387 •will observe that his consciousness of effort coincides with a fixation of the muscles of his chest, and that, in proportion to the amount of energy he feels he is putting forth, he is keeping his glottis closed and actively contracting his respiratory muscles. Let him place his finger as before, and continue breathing all the time, and he will find that, however much he may direct his attention to his finger, he will experience not the slightest trace of consciousness of effort until he has actually moved the finger itself, and then it is referred locally to the muscles in action. It is only when this essential and ever- present respiratory factor is, as it has been, overlooked that the consciousness of effort can with any degree of plausibility be ascribed to the outgoing current. In the contraction of the respiratory muscles there are the necessary conditions of centripetal impressions, and these are capable of originating the general sense of effort. When these active efforts are withheld no consciousness of effort ever arises, except in so far as it is conditioned by the local contraction of the group of muscles towards which the attention is directed, or by other muscular contractions called unconsciously into play in the attempt. I am unable to find a single case of consciousness of effort which is not explicable in one or other of the ways specified. In all instances the consciousness of effort is conditioned by the actual fact of muscular contraction. That it is dependent on centripetal impressions generated by the act of contraction I have already endeavoured to show. When the paths of the centripetal impressions, or the cerebral centres of the same., are destroyed there is no vestige of a muscular sense. That the central organs, for the apprehension of the impressions originating from muscular contraction, are different from those which send <5ut the motor impulse has already been established. But when Wundt argues that this cannot be so, because then the sensation would always keep pace with the energy of muscular contraction, be overlooks the important factor of the fixation of the respiratory muscles, which is the basis of the general sense of effort in all its varying degrees. In the first instance, our consciousness of the extent and energy of our muscular contractions, and the faculty of c c 2 388 TEE MOT OB CENTBES muscular discrimination, are derived from the centripetal impressions generated by the contraction itself. The associa- tion of the sensory impression with the corresponding move- ment, however, becomes by education so precise, and the nexus so firmly welded, that we can apparently by intuition estimate the exact degree and extent of movement necessary to accomplish any desired end. § 20. It is further possible, by reviving the sensory im- pression, to recall in idea the movement which coincided with it, even though the muscles themselves, to which the move- ment is referred, have been severed from the body. Many remarkable instances of this kind have been given by Weir- MitehelL 1 ' If we faradise the track of the nerves in or above the stump, we may cause the lost fingers and thumb to seem to be flexed or extended, and, what is most remarkable, parts of which the man is conscious, but which he has not tried to stir for years, may thus be made to appear to move, to his utter amazement. In one case I thus acted on the nerves so as to cause a thumb, which for years was constantly and violently bent in on the palm, to straighten out completely. On breaking the circuit, without warning, the patient exclaimed that his thumb was cutting the palm again, and the same result was obtained by shifting the conductors, so as to put the nerves out of the circuit. In a case of amputation of the shoulder-joint, in which all consciousness of the limb had long since vanished, I suddenly faradised the brachial plexus, when the patient said at once, " My hand is there again ; it is bent all up, and hurts me." These impressions are correctly referred by the patient, so that the faradisation of the musculo- spiral or the ulnar gives sensation of movement in the related parts. It is, of course, impossible that* the motor nerves stimulated should convey any impression centrally ; and we must conclude that irritation of sensory trunks may occasion impressions of muscular action in the sensorium' (op. cit. p. 359). The excitation of the sensory nerves calls up, as Wens Mitchell correctly indicates, the correlated movement, i.e. the 1 Injuries of Nerves, 1872. TEE SENSE OF EFFORT 389 movement which in the actuality of past experience had coincided with the sensation now revived by the faradic stimulus. This of itself argues powerfully in favour of the centripetal origin of the impressions constituting the muscular sense. According to the law of contiguity, ' actions, sensations, and states of feeling, occurring together or in close succession, tend to grow together, or cohere, in such a way that when any one of them is afterwards presented to the mind the others are apt to be brought up in idea.' The ideal associated movement is thus made to arise in consciousness, when the corresponding sensation is artificially re-excited. But the register of sensory impressions is anatomically distinct from that of movements, and the two cohere together only by constant functional association. Inasmuch as the idea of a movement is only an idea of the sensory impressions, visual, tactile, and others, which coincide with the particular movement, it seems quite possible that persons who have had a limb amputated may be able to picture a movement of the limb, just as a blind man may recall a scene when he can no longer see. That this in reality occurs is likewise shown by Weir-Mitchell. ' Persons who have had an arm amputated are frequently able to will a movement of the hand, and apparently to execute it to a greater or less extent. A small number have entire and painless freedom of motion as regards all parts of the hand- " My hand is now open, or it is shut," they say. " I touch the thumb with the little finger," " The hand is now in the writing position," &c. Between these cases and such as are conscious of an immobile member every grade of difference as to motion is to be found, with equally wide varieties in the associated pain, which perhaps is most acute in such as will with vigour a motion that they seem to fail in executing ' (p. 357). In some of these cases the muscles which move the hand remain, and, therefore, are excluded from consideration in the present relation. ' In others, as in shoulder-joint cases, or amputa- tions through the humerus, the muscles which act on the hand, are absent altogether ; yet in these there is fully as clear and definite a consciousness of the movements of the fingers, and of their change of positions, as in the former cases.' 390 THE MOT OB CENTRES These facts are supposed by Weir-Mitchell, and also by Hughlings- Jackson, 1 to favour the views of Bain and Wundt as to the dependence of the sense of innervation on the out- going current. They however, in my opinion, only indicate a vivid realisation of sensory impressions associated with a particular movement, and have nothing to do with the motor centres or outgoing currents. A patient suddenly paralysed by embolic softening of his motor centres not unfrequently only discovers his paralysis by being unable to carry out the movement which he has willed, and of which he has formed a distinct conception. The act of volition does not imply move- ment, or the ability to carry it out, nor does the conception of the movement depend on the integrity of the motor centres. Volition is effected when the idea of the movement, formed in the sensory centres, is permitted to operate, even though the active manifestation is rendered impossible by destruction of the motor apparatus necessary for its accomplishment. There is no more reason why we should not be able to revive jn idea past movements through the associated sensations, when the limb by which the experience was gained is amputated, than recall visual impressions after extirpation of the eyeballs. But, as we cannot any longer see when the eyes are destroyed, so we can no longer exercise muscular discrimination, or gain musculo-sensory experience, when the limbs are amputated. We retain what we have already acquired, but make no further advance. But, whether we make the movements in reality or revive them in idea, the consciousness of the extent and energy of the movements is, in my opinion, in all cases dependent on ingoing or centripetal impressions. In the case of actual movements the impressions arise directly in the periphery; in the case of ideal movements the sensory impressions arise by excitation of the centres which form the organic register of impressions primarily originating in the periphery. The centres of centrifugal, or motor, impulses are anato- mically distinct from those of centripetal, or sensory, impres- sions. The one may be destroyed, while the other remains intact. 1 Med. Journal, leading article, Oct. 9, 1875. MUSCULAR DISCRIMINATION 391 The cortical centres, for the movements of the limbs, are concerned purely with centrifugal impulses, and are clearly- differentiated from the paths and terminal centres of the centripetal impressions on which muscular discrimination is based. The destruction of the centripetal centres abolishes muscular sense, or muscle consciousness, though the power of movement remains. The destruction of the centrifugal centres abolishes the power of voluntary motion, and therefore prevents the exercise of muscular discrimination, but the transmission • and perception of centripetal impressions continue unim- paired. § 21. It would be a crucial test of the dependence of the muscular sense on centripetal impressions if it could be shown without fallacy that muscular discrimination can still be exercised when the muscles are made to contract artificially by means of the electric stimulus. Experiments on this point have been made by Bernhardt 1 but, owing to the difficulty of excluding the sense of cutaneous pressure, he came to no positive conclusions. Though Bernhardt himself is inclined to regard the muscular sense as a ' Function der Seele,' only aided by centripetal impressions, his experiments show that differentiation of weights can be made when the muscles are excited to contraction by the electric current alone. ' Normal individuals, however,' says he, ' discriminate equally well when the flexion of the finger, and thereby the raising of the weight, was caused by the electric current.' According to the law of perception of weight by the sense of cutaneous pressure alone, it requires the addition of one- third of the original weight, whatever it may be, to produce a distinctly perceptible difference ; but in Bernhardt's experi- ments on the foot it was found that the addition of from 3 to 5 Loth (1^ to 2£ oz.) to an original weight of from a pound to a pound and a half could be distinctly perceived, which is less than one-half the increment perceptible by cutaneous pressure alone. In regard to the discrimination of weight by the finger the sensibility was found to be much finer. Three drachms could 1 Archivf. Psychiatrie, Bd. iii. 1872. 392 THE MOT OB CENTRES be distinctly differentiated from nothing, and to heavy weights (say 1 lb.) the addition of five drachms was distinctly per- ceived, i.e. a difference of about -± s , a power of discrimination which corresponds pretty nearly with that of the muscular sense, which is capable of detecting an addition of yyth of the original weight. These results, therefore, indicate that the discrimination was much finer tban could be effected by the sense of pressure alone, and that, therefore, it depended on muscular discrimination. Experiments made in reference to this point by myself, with the assistance of Dr. Lauder-Brunton, gave such results as clearly to indicate the retention of muscular discrimination when the muscles were excited to contract by the galvanic current. The method I adopted was to determine, blindfolded, in the first instance, the differences in weight which could be discriminated by my hand held flat on a cushion, and then to test the muscular discrimination of the same weight when the wrist was flexed so as to raise the weight with the fingers. By repeated experiments with weights varying from one to six ounces the average discrimination by the sense of cutaneous pressure was found to be about one-third, while the muscular discrimination accorded pretty nearly with the l-17th, as usually found to be the rule. The same experiments were then made with the same hand as regards cutaneous pressure, and by galvanic excitation of the flexor muscles of the hand, so applied as to cause repeated raising of the weight by the fingers. Again the sense of pressure averaged the normal, and again muscular discrimina- tion was found to be almost as accurate as in the former experiments, when the raising of the fingers depended on voluntary effort. Cutaneous pressure being thus allowed for in both cases, the muscular discrimination by means of the centripetal impressions generated by muscular contraction alone, not depending on voluntary motor impulse, is clearly established. It is also a very important fact, noted by Leyden (Virchow's ' Archiv,' xlvii.) that ataxic patients, who are said to retain muscular discrimination notwithstanding the abolition of cutaneous sensibility, are not able to discriminate weights THE FRONTAL MOTOR CENTRES 393 until they reach a considerable amount. It is supposed that this is due only to a diminution, owing to the absence of the usually associated sensations of pressure. But I am of opinion that the discrimination of heavy weights calls into play the general sense of effort which, as we have seen, is to be more properly ascribed to the region of the respiratory muscles ; and that the discrimination in this case is effected by the amount of bodily strain and fixation of the muscles of the chest necessary to support a heavy weight ; and that it is not a question of the muscular sense of the limb at all, unless general strain is absolutely eliminated by continuous and easy respiration during the trial. When this is eliminated it will be found that the sense of local resistance is the only element in the discrimination of weight. The various considerations above advanced seem to me to prove beyond all doubt that the motor centres are not the centres of the so-called muscular sense, whether we under- stand this as a sense composed of a complex assemblage of centripetal impressions, or as a sense of innervation according to the views of Bain and Wundt. The cortical centres are motor -in precisely the same sense as other motor centres, and are differentiated anatomically from the centres of sensation, general as well as special. The Frontal Motor Centres. § 22. Electrical stimulation of the frontal lobes varies according to the position of the electrodes. Irritation of area (12) comprising the base of the superior and middle frontal convolutions in monkeys, and the corresponding region in other animals, gives rise to lateral movement of the head and eyes to the opposite side, with dilatation of the pupils. The expression assumed by the animal is that of attention or surprise. The same movement occurs, along with other special reactions, also on stimulation of the angular gyrus, and of the superior temporo-sphenoidal convolution more especially. With the latter is associated pricking of the ear, the special sign of stimulation of the auditory centre. The reactions were found to be essentially the same in all the 394 TEE MOT OB CENTRES animals experimented on, varying, however, in degree. If we assume, as will be proved subsequently, that the frontal centre— (12) — is the true motor centre for the lateral move- ment of the head and eyes, and as such the centre for move- ments expressive of attention, it would be natural to expect that the arousal of subjective sensations by stimulation of the visual and auditory centres would excite attention, and induce the same movements of the head and eyes as would result from direct stimulation of the motor centre. In the one case the reaction is the result of stimulation of the motor centre directly, in the other only indirectly or renexly by stimula- tion of a sensory centre proper. As a rule, I have found stimulation of the prefrontal regions and other portions of the frontal lobes to be entirely negative, or so irregular as to render the results very doubtful. In particular the approximation of the electrodes to the anterior extremity of the hemisphere is apt to cause irritation- of the olfactory bulbs, and thus give rise to active reflex reactions which may be erroneously ascribed to the frontal lobes them- selves. Yet in two instances I have noted movements of the eye- balls on irritation of the prefrontal regions under circum- stances entirely precluding diffuse irritation of neighbouring parts. The eyeballs were seen during irritation to move sometimes laterally to the opposite side and sometimes dp- wards. Whether the movements of the eyes in these two cases were only coincidences, or causally related to the irrita- tion of the frontal lobes, is not quite certain, but I am inclined to regard them as of the latter character. § 23. The effects of destructive lesions are not yet sufficiently definite to enable us to speak with certainty regarding the functions of the frontal lobes in all their parts. But there is sufficient evidence to show that the postfrontal regions — area (12) — are the motor centres of the lateral movements of the head and eyes. It has frequently been observed in man that, for a short period after the onset of sudden hemiplegia, the head and eyes are turned away from the paralysed side, looking, therefore, towards the side of lesion. The same thing occurs in the monkey. At the moment of destruction of area (12) in TEE FEONTAL CENTRES 395 the one hemisphere ' there occurs a conjugate deviation of the eyes towards the side of lesion. If the transitory duration of this deviation were due only to the compensatory action of the sound hemisphere it would follow that destruction also of this centre should cause permanent inability to turn the head or eyes in either direction. But this is not the case even when the destruction of area (12) in both hemispheres is very extensive, if not absolutely complete. In two monkeys 2 after extensive bilateral destruction of the base of the superior and, middle frontal convolutions, though for the first day after the operation there was evident inability to turn the head or eyes in either direction, as well as some oscillation of the head (in the one in which the lesion was the more extensive), yet within a few days at most the power of turning the head and eyes in either direction, with- out any appearance of unsteadiness or stiffness, was seen to have been regained. At first the animals did not look round to sounds in proximity to the ear, as usual, or if they did they moved the trunk and head en masse. The complete recovery cannot be accounted for altogether by incomplete destruction of the postfrontal centres, for the lesions were sufficient to have left very visible permanent results if these were the whole of the centres of the movements in question. I had already in my former experiments noted the extra- ordinary absence of any discoverable physiological defect after entire removal of the prefontal lobes or anterior half of the frontal lobes. 3 And in one case 4 also, in which the occipital lobes had been removed some time previously, the removal of both prefrontal lobes was likewise unattended by any evident sensory or motor impairment (see fig. 88). I have again confirmed these observations. In a monkey 5 I destroyed with the galvanic cautery the whole of the pre- frontal region on both sides in advance of area (12), so that, except a minute portion of each frontal lobe overlying the 1 Phil. Trans. Part II. 1884, p. 530. " Experiments 19 and 20, Phil. Trans. Part II. 1884, p. 521 et se%. 3 Experiments I., II., III., Phil. Trans. Part II. 1875. - Experiment XXV., ibid. » Experiment 22, Phil. Trans. 1884, p. 525. 396 THE MOT OB CENTRES olfactory bulbs, all the intervening portion of the superior, middle, and inferior frontal convolutions was obliterated (fig. 121). Notwithstanding this extensive bilateral lesion there was a total absence of symptoms either in the domain of motion or sensation. The animal perceived a touch anywhere on the body, the special senses were intact, and the move- ments of the head and eyes were in all respects unimpaired. A similar total absence of discernible symptoms has been observed also by Horsley and Schafer ' on destruction of the prefrontal regions in two monkeys which survived the opera- tion for many months. There wa.s certainly no affection of the movements of the trunk. § 24. In one case, 2 however, in which the paralysis of the Fig. 121. — Lesion of the Prefrontal Region. lateral movements of the eyes, following lesion of the post- frontal centres, had completely disappeared, the destruction also of the prefrontal regions caused symptoms which, though transient, were of great significance. These were rapid oscil- lations of the head, apparent inability to turn the head, except en masse with the trunk, and drooping of the right eyelid. By the third day, however, all these symptoms had disappeared, and from this time onwards the animal exhibited no defect either as regards its powers of motion or sensation. The lesions in this case were extensive erosion of the cortex at the posterior third of the three frontal convolutions, with complete 1 Private communication. *■ Experiment 23, Phil. Trans. 1884, p. 530, figs. 74-86. THE FBONTAL CENT BE 8 397 removal of the anterior two-thirds of the inferior and middle, and portion of the superior frontal convolution, on the left side ; and complete removal of the middle frontal and anterior two- thirds of the inferior frontal convolution on the right side. These facts indicate that the prefrontal regions belong to the same centres as the postfrontal, just as the occipital lobes belong to the visual centres ; for though the occipital lobes do not react to electrical stimulation, and may be removed with- out any appreciable disturbance of vision, provided the angular gyri remain intact, yet it has been seen that they form an integral portion of the visual centres. So, though the pre- frontal regions do not react, or doubtfully, to electrical stimula- tion, and their removal causes no discoverable symptoms, pro- vided the postfrontal regions are intact, yet as their removal induced effects similar to those resulting from the previous lesion of the postfrontal regions, it may be argued reasonably that they form part of the same centre. The transitory dura- tion of the symptoms, even when the whole frontal region was more or less considerably injured, would be explained by the fact that the postfrontal centres were not entirely destroyed on either side, and less completely on the right than on the left. On the side opposite the more extensive lesion there was a tendency to ptosis of the eyelid as well as inability to turn the eyes laterally. To determine whether the complete removal of the frontal regions— postfrontal as well as prefrontal — induces perma- nent paralysis of the lateral movements of the head and eyes is not an easy matter. A frontal incision through the base of the frontal convolutions, and complete scooping out of the frontal lobes, involves injury to the head of the corpus striatum on each side. The operation is also a serious one. In the only case : in which I performed this experiment the animal died suddenly twenty-four hours after the operation. But the facts are worthy of consideration. Both frontal lobes were severed by a frontal incision imme- diately anterior to the prscentral sulcus. The portions removed included the anterior extremity of the nucleus caudatus, somewhat more on the left side than the right. 1 Experiment 21, Phil., Trans. 1884, p. 524, figs. 58, 59. 398 THE MOTOR CENTRES Notwithstanding the formidable character of the operation,, the animal speedily regained consciousness, and was able to move its facial muscles and the limbs, though the right limbs were used with somewhat less energy than the left. Though it could in some degree extend its head and trunk, it was utterly unable to maintain the upright position or move its head and eyes laterally. The eyes were kept shut except on cutaneous or other sensory stimulation. Sight, hearing, and tactile sensibility were unimpaired. Except the inability to move the head and eyes there was no other defect observable, sensory or motor. Though, as remarked, the injury to the cor- pora striata somewhat complicated the lesion, and the duration / ce Fib. 122— Frontal Section of the Brain (fig. 121), showing degeneration of the mesial fibres of the internal capsule on both sides, consecutive to lesion of the pre- frontal regions. The degenerated fibres are indicated by white patches on each side of the infundibulum and third ventricle. of the period of observation was but short, yet the hypothesis that this portion of the brain is specially concerned in the move- ments of the head and eyes, indicated in the other experiments, is confirmed. For no other movements were paralysed, and there was no affection of vision, hearing, or common sensibility in any part of the body. § 25. In two of the experiments facts were demonstrated of great importance in reference to the anatomical connections of the frontal lobes. In the one of these, 1 in which the pre- frontal regions had been almost completely extirpated (fig. 121), and which survived in perfect health for nearly three months ' Experiment 22, Phil. Trans., Part II., 1884, p. 525, figs. 60-73. ANATOMICAL BELATIONS OF THE FRONTAL CENTRES 399 after the operation, microscopical examination revealed the existence of descending sclerosis in the innermost or mesial bundles of the internal capsule and foot of the crus cerebri on either side (fig. 122). These degenerated tracts could not be traced beyond the upper part of the pons, and therefore their exact destination could not be determined, but they were not traceable in the anterior pyramids of the medulla oblongata. In the other ' the postfrontal centres had first been ex- tensively destroyed, and seven weeks afterwards the prefrontal regions were more or less completely removed. At the end of two months and a half after the first operation degeneration had also occurred in the same mesial bundles of the inter- nal capsule and foot of the crus. The degenerated bundles were from their appearance of different dates. Those situated somewhat external to the most mesially placed bundles were deeply sclerosed, corresponding to the older of the two lesions, viz. of the postfrontal lobes. The most internal bundles, corresponding exactly in position to those of the previous experiment, were of more recent date, and less densely sclerosed, in relation with the later lesions of the pre- frontal centres. We have in these facts a proof of the anatomical relation of the frontal lobes to the motor tracts of the crus cerebri, and inasmuch as no degeneration existed in the anterior pyramids it is clear that the tracts with which they are in connection do not extend below the medulla oblongata. Confirmation is thus given to the conclusion, founded on the symptoma- tology, that the frontal centres are concerned with the move- ments of the head and eyes, the nuclei and motor nerves of which do not extend below the medulla oblongata. Even though in the first experiment the destruction of the prefrontal regions caused no discoverable physiological defect, yet secondary degeneration occurred in the internal capsule. That the functions subserved by these centres and tracts were practically unimpaired would show that the centres for these movements were not entirely destroyed ; and that the prefrontal and postfrontal regions form parts of the same centre, is supported by the facts of degeneration as observed 1 Experiment 23, op. cit. p. 528, figs. 74-86. 400 THE MOT OB CENTRES in the second experiment, as well as by the circumstance that injury to the prefrontal regions reinduced for a time the disturbances which had temporarily manifested themselves after lesion of the postfrontal centres. We have thus good reasons for regarding the frontal lobes as in anatomical relation with motor tracts which do not pass into the spinal cord, but end in the centres of the mesence- phale or bulb. § 26. Munk ! professes to have found that, after destruction of the prefrontal region in dogs and monkeys, paralysis occurs in the muscles of the trunk on the opposite side, so that the animal is unable to turn to this side ; and that bilateral de- struction causes paralysis of the trunk muscles on both sides, so that the animal can turn neither to the right nor to the left. Though he furnishes no evidence of impaired sensibility in the trunk or elsewhere, he nevertheless calls the prefrontal region the sensory sphere (Fiihlsphdre) of the trunk. Munk's assertions as to the effects of lesion of the prefrontal region have as little foundation as many other of his utterances on cerebral physiology. My own experiments, as well as those of Horsley and Schafer, disprove Munk's assertions in the case of monkeys, and clinical observations 2 show that in respect to man they are equally untrue. In regard to dogs Munk is flatly contradicted by Hitzig, 3 Kriworotow, 4 and Goltz. 5 Not one of these physiologists has observed any of the motor disturbances described by Munk, after entire removal of the prefrontal regions. Kriworotow says that in all his dogs the mobility of the trunk, trunk muscles, and lumbar vertebras was absolutely unimpaired, whether one or both prefrontal regions were destroyed. Goltz relates that in one dog he removed the whole of the region lying in front of the crucial sulcus on both sides. Yet 1 Die Functionen der Grosshimrinde, 1881, 4te Mittheilung, und Die Stimlappen des Grosshirns, 1883. z See Localisation of Cerebral Disease, 1878. 3 Neurologisches Centralblatt, July 1883 ; Archiv f. Psychiatrie, Bd. xv, p. 270. 4 Die Functionen des Stirnlappens des Grosshirns, These, 1883. 5 ' Die Verrichtungen des Grosshirns,' Pfliiger's Archiv, Bd. xxxiv. 1884. THE FBONTAL CENT BE S 401 this animal was able to turn its trunk so well as to be able to seize a piece of meat attached to the root of its tail. In numerous other cases in which the prefrontal regions were removed, in addition to extensive lesion of the motor zone proper, there never occurred such affection of the trunk muscles as Munk describes. 1 It is unnecessary to adduce further evi- dence of Munk's untrustworthiness. If the description he gives of his experimental results is correct, they can only be attributed to crude methods and widespread secondary dis- turbances. Horsley and Schafer have shown that the centres for the trunk muscles are in the marginal convolutions. It is only to primary or secondary implication of these marginal centres, and not to lesions strictly limited to the prefrontal regions, that we can ascribe such results as Munk claims to have observed. § 27. Besides the physiological symptoms, such as occur, and the descending degenerations of the motor tracts asso- ciated with lesions of the frontal lobes, I observed and re- corded 2 certain symptoms indicative of mental deterioration which have since been confirmed by other physiologists. In my first series of experiments (carried out without antiseptics) I noted after removal of the prefrontal regions a decided alteration in the animals' character and behaviour, but difficult to describe precisely. After the operation, though they might seem to one who had not compared their present with their past fairly up to the average of monkey intelligence, they had changed considerably. Instead of, as before, being actively interested in their surroundings, and curiously prying into all that came within the field of their observation, they remained apathetic or dull, or dozed off to sleep, responding only to the sensations or impressions of the moment, or vary- ing their listlessness with restless and purposeless wanderings to and fro. While not absolutely demented, they had lost, to all appearance, the faculty of attentive and intelligent obser- vation. In some of my later experiments, 3 in which the lesions were strictly limited (under antiseptic precautions) to the pre- 1 Op. cit. p. 485. 2 Phil. Trans., Part II. 1875. s Phil. Trans., Part II. 1884. D D 402 THE MOT OB CENTBES frontal regions I could not satisfy myself of the existence of any appreciable mental deterioration, but in others the same listlessness and purposeless unrest previously observed were apparent in greater or less degree. Probably the differences were dependent on the degree of implication of the frontal lobes as a whole. In the experiments under antiseptic pre- cautions the area of secondary disturbance would naturally be much less extensive than in those in which no antiseptics were employed. Horsley and Schafer have also noted signs of stupidity in the monkeys in which they had removed the prefrontal regions — for a time at least after the operation. Hitzig 1 observed decided mental deterioration in dogs after destruction of the prefrontal regions. Dogs which before the operation had been in the habit of finding their food on a table, seemed quite unable to do so after bilateral destruction of the prefrontal region. ' They exhibited such a marked weakness of memory (Gedcichtnissschwciche) that they quite forgot the existence of the pieces of meat they had just seen. They, however, ate pieces of meat thrown before them, so long as they saw them ; but they did not search for their food in the accustomed place like normal dogs. Besides these they exhibited other alterations in their behaviour which I will not enter on more fully at present ' (p. 271). Goltz 2 observed that dogs after removal of the frontal regions exhibited, among other symptoms, great irritability and restlessness. They could see, hear, smell, and taste, but reacted in many respects differently from normal animals. All the animals so experimented on had ' a fixed and stupid expression of the eyes, and inability to fix the gaze.' ' They are,' says he, ' able to perceive and recognise persons and things at great distances. They understand also a threatening ges- ture with the hand or with a whip, inasmuch a^s they wince, but they show no inclination to run away, and make no sound indicative of fear. If the finger is thrust towards the eye they only shut the eyelids when the finger actually touches the eyelashes. Yery remarkable is the following experiment 1 Archiv f. Psychiatrie, Bd. xv. p. 271. 2 Pfliiger's Archiv, Bd. xxxiv. 1884. THE FBONTAL CENTBE8 403 which I have made on several dogs. If a bone is thrown down to the animal at some distance, it runs to it with great alacrity, but does not have the sense to stop at the right moment and sink its head, so that it runs beyond the mark. Instead!, however, of turning round and looking for the bone in a methodical way, the animal appears to forget what it was after, and runs on regardlessly, until the bone is lifted and the animal's attention again attracted to it ' (op. cit. p. 481). The observations of Hitzig and Goltz appear to me to illustrate and confirm the occurrence of a mental deteriora- tion from lesion of the prefrontal regions, which I have charac- terised as essentially a defect of the faculty of attention. What relation these symptoms have to the anatomical sub- strata of the frontal regions will be the subject of considera- tion in another chapter (Chapter XII., § 17). D D 2 404 CHAPTER XI. FUNCTIONS OF THE BASAL GANGLIA. § 1. The position and relations of the basal ganglia— the corpora striata and thalami optici— have already been dis- cussed (Chapter I. § 10) , and we have seen that their relations have not yet been in all respects satisfactorily determined. With respect to the corpora striata the most recent investiga- tions are opposed to the view propounded by Meynert that they are ' ganglia of interruption ' intercalated in the projec- tion system between the cortex and the periphery. "We have seen that the pyramidal strands of the internal capsule pass directly from the cortical motor zone to the pyramids of the medulla oblongata without interruption in the grey matter of the corpora striata, either of the lenticular or caudate nuclei. It is doubtful whether any fibres of the corona radiata connect the cortex with the base of the lenticular or caudate nucleus. If so they are relatively much fewer than Meynert supposed. It is much more probable that the ganglia of the corpus striatum are in themselves terminal centres similar to those of the cortex itself. The tracts which proceed from the nucleus caudatus first cross those of the internal capsule and enter the two inner divisions of the lenticular nucleus, and emerge with those derived from the lenticular nucleus itself. These form two main divisions. The one division, the smaller, joins the internal capsule, and lies dor sally to the pyramidal tracts in the foot of the crus. The fibres appear to end in the region of the locus niger or to form connections with the centres of the pons. The other division constitutes a well- marked tract, visible on the internal margin of the crus cerebri in the anterior perforated space, and termed the ANATOMICAL BEL AT ION 8 405 lenticular loop (ansa lenticularis) . This, according to "Flechsig, is connected on the one hand with the red nucleus (fig. 19, b, n) , and thus indirectly with the cerebellum through its superior peduncle ; and on the other hand with the lemniscus derived from the interolivary layer, and thus indirectly with the oli- vary bodies, and perhaps also with the clavate and cuneate nuclei. As the functions of the various tracts and centres with which the corpora striata appear to be related are not in themselves well known, little with respect to the functions of the corpora striata can be founded merely on their anatomical relations. But the fact that the greater portion of the lem- niscus — that portion which is specially connected with the corpus striatum — degenerates in a centrifugal direction is an important indication of motor function. § 2. The connections of the optic thalami are more un- certain than those of the corpora striata. Connections have been traced through the corona radiata with various regions of the cortex, viz. the frontal, parietal, occipito-temporal, region of the insula, and with the hippocampal region by means of the pillars of the fornix, either directly, or indirectly through the corpora mammillaria. The longitudinal tracts of the tegmentum, which by some have been regarded as ending in the optic thalami, are traced by Flechsig past these ganglia into the posterior part of the internal capsule. On this point, however, and on many others, the views of different anatomists are so divergent that it would be unsafe to found any func- tional relationship on anatomical data. Besides the connec- tions with the cortex and the tegmentum others have been traced between the optic thalami and the corpora striata. Luys l describes the optic thalamus as consisting of an agglomeration of centres — an anterior, middle, median, and posterior — connected on the one hand with definite regions of the cortex, and with the olfactory, optic, general sensory, and auditory tracts respectively. The views of Luys have been regarded by most anatomists 2 as purely speculative and devoid of any foundation in demonstrated fact. But Gudden 3 1 ' The Brain and its Functions,' Internat. Scient. Series, vol. xxxvii. 1881. 2 Schwalbe, Neurologie, p. 713. 3 Archiv f. Psychiatrie, Bd. xi. 40G FUNCTIONS OF THE BASAL GANGLIA has shown that after removal of the cortical centres in their entirety the corresponding optic thalamus entirely atrophies, while the corpus striatum remains intact. Ganser ' also dis- tinguishes four separate centres in the optic thalamus of the mole ; and more recently Monakow 2 has differentiated several distinct centres in the optic thalamus of the rabbit,- and con- tends that destruction of certain circumscribed cortical regions leads to atrophy of the correlated nuclei (see further § 9). § 3. The experimental investigation of the functions of the basal ganglia is also surrounded with special difficulties. Owing to their position they can only be reached by exposing the interior of the lateral ventricles, or by inflicting injury on some portion of the cortex and the tracts which surround them or pass tbrough them. Hence the effects of experimental lesions of the basal ganglia are always more or less compli- cated by the injuries necessarily inflicted on other parts, in the attempts to reach them, some of which are incompatible with long survival. We are largely dependent on the data of clinical medicine for what - we know respecting the effects of lesions of the basal ganglia. Owing to the mode of their vascular supply by the lenticulo-striate and lenticulo-optic arteries they are a favourite and frequent seat of embolic softening ; but the lesions so induced are rarely so precise in their limitation to the ganglia proper, apart from the merely transcurrent tracts of the internal capsule, as to afford altogether reliable data for determining their special functions. For purposes of. electrical stimulation it is not difficult to reach the surface of the basal ganglia by division of the corpus callosum and exposure of the interior of the lateral ventricle. But in doing so it is necessary to guard against the occur- rence of hemorrhage and shock, otherwise erroneous conclu-^ sions may be drawn respecting the excitability of these struc- tures. Just as the excitability of the cortex is liable to be annihilated by profound narcosis, shock, and haemorrhage, so the excitability of the basal ganglia is liable to be affected by similar circumstances. The most favourable conditions for 1 Das Gehim des Maulwurfs, 1880. See also fig. 35. 1 Archivf. Psychiatric, Bd. xii. 1882. EFFECTS OF IBBITATION 407 the investigation of the electric excitability of the basal ganglia are furnished by those cases in which after successive exposure and electrical exploration of the different regions of the convexity the corpus callosum is divided, and the hemi- sphere easily everted, so as clearly to expose the interior of the lateral ventricle. Under such circumstances, I have, as before related, found that electrical irritation of the intraventricular nucleus of the corpus striatum causes tonic contraction of the whole of the muscles of the opposite side, resulting in a condi- tion of pleurosthotonus, in which the position assumed is that of equilibrium between the flexors and extensors. In rabbits, however, the tonic spasm was not so rigidly maintained, and during the continuance of the stimulation the jaws were con- stantly ground together. Shifting of the electrodes on to the ventricular aspect of the optic thalamus at once caused cessa- tion of the tonic spasm and an entire absence of all visible results. In only one rabbit was there any sign of irritation, consisting in general shuddering and restlessness, such as might be regarded as indications of general sensory excitation. The experiments of Carville and Duret ' are in entire harmony with mine. They observed general spasm of the muscles of the opposite side on irritation of the caudate nucleus and an entire absence of outward manifestation when the surface of the optic thalamus was similarly irritated by the faradie current. It has, however, been contended by some experimenters z that neither the corpora striata nor the optic thalami are themselves excitable, and that such movements as result from so-called irritation of the nucleus caudatus are in reality due to irritation of the fibres of the internal capsule. It has been shown by Franck and Pitres, and also by Minor, 3 that a current which causes no motor manifestation when applied to the nucleus caudatus causes active spasm when 1 Sur les Fonctwns des H&misph&res Ciribraux. 2 Franck and Pitres, ' Sur les Convulsions Epileptiformes, &e.' Archives de Physiologic, 3me Serie, Bd. ii. ; Gliky, Eckhard's Beitrage, Bd. vii. 1876. This physiologist finds the corpus striatum inexcitable ; but as his experiments were made on sections of the corpora striata they cannot be regarded as appli- cable to the ganglia in their normal condition. 3 'Ueber die Bedeutung des Corpus Striatum,' Abstract in Neurolog. Centralblatt, Bd. ii. 1883, p. 270. 408 FUNCTIONS OF THE BASAL GANGLIA applied direct to the internal capsule. Hence it is attempted to explain away the results of irritation of the nucleus caudatus by diffusion to the internal capsule. Minor further adduces in favour of this explanation the fact that in a dog on which some time previously he had extirpated the motor zone in one hemisphere, and so induced secondary degeneration in the in- ternal capsule, no result was obtained on exposure and irrita- tion of the nucleus caudatus. Irritation of the internal capsule was likewise without result — except closure of the opposite eye. The conclusion drawn from this and other experiments is that all the so-called effects of stimulation of the nucleus caudatus are really due to irritation of the internal capsule. The arguments are an exact repetition of those- which attribute the effects of irritation of the cortical centres to irritation of the subjacent medullary fibres. But though the internal capsule and the pyramidal fibres of the corona radiata are undoubtedly excitable, and continue excitable under conditions which annihilate all manifestations from stimukv tion .applied to the centres, it by no means follows that the centres themselves are inexcitable. We have already seen that the intrinsic excitability of the cortical centres has been clearly established. The explanation of the phenomena of irritation of the nucleus caudatus by mere conduction to the internal capsule is disproved by the negative results of the same stimulus when applied to the optic thalamus. The motor tracts of the internal capsule are in point of fact closer to the optic thalamus than to the nucleus caudatus, and yet irritation of the optic thalamus causes no result. If it were merely a case of conduction to the motor tracts of the internal capsule electric stimulation of the optic thalamus ought to cause at least equal if not greater irritation of these tracts than electrisation of the nucleus caudatus. This, however, is not the case. A mechanical excitability of a certain point in the nucleus caudatus, situated close to the third 'ventricle, has been contended for. by Nothnagel, 1 who finds that in rabbits puncture 1 Virchow's Archiv, Bd. Ivii. 1873 et seq. He terms the spot the nodus cursorius — a term which stands on a par with his 'convulsion-centre,' pre- viously referred to. LESIONS OF THE COBPUS STBIATUM 409 of this spot with a fine needle, or injection of a few drops of chromic acid, causes an apparently irresistible tendency on the part of the animal to run or jump till it becomes exhausted. As the phenomena he describes are merely the expression in the rabbit of some form of irritation, and not peculiar to irritation of the corpus striatum, no conclusions as to the special functions of this ganglion can safely be founded on them. § 4. It is one of the best established facts of human pathology that destructive lesions in the region of the corpus striatum cause hemiplegia of the opposite side of the body — a paralysis in general entirely confined to motion, sensation being in all respects unimpaired. Until recently no exact differentiation was attempted between the effects of lesions involving only the grey matter of the corpus striatum and those involving also, or alone, the anterior division of the internal capsule. Since, however, it has been shown that the pyramidal tracts of the internal capsule have no relation, except that of contiguity, to the caudate or lenticular nucleus, it has become of importance to distinguish, if possible, between the effects of lesions of these parts respectively. As a rule, the lesions of disease are more or less indefinite, but the careful investiga- tions' of Charcot ' and others have established that though lesions of the nucleus caudatus or nucleus lenticularis appear to cause hemiplegia, in all respects similar to that caused by lesion of the anterior two-thirds of the internal capsule, or of the cortical centres themselves, yet the hemiplegia depending on lesions limited to the grey matter of the striate nuclei is of a transitory character, and may entirely disappear even while the lesion remains. On the other hand, hemiplegia dependent on lesion of the fibres of the anterior division of the internal capsule is permanent, and is followed in due course by descending sclerosis of the pyramidal tracts and rigidity of the paralysed limbs. Hence it would appear from the facts of human pathology that, provided the cortical motor centres and their pyramidal 1 Lecons, sur les Localisations dans Us Maladies du Cerveau, 1876 ; Nothnagel, Topische Diagnostic, der Gehirnkrankheiten, 1879. 410 FUNCTIONS OF THE BASAL GANGLIA tracts in the internal capsule remain intact, the ganglionic masses of the corpus striatum may be destroyed, or at least extensively injured, without giving rise to appreciable symptoms. There are some facts which render it probable that lesions of the nucleus caudatus are more transitory in their effects than lesions of the lenticular nucleus. This would be in accordance with the anatomical researches, which seem to show that the fibres proceeding from the nucleus caudatus have to pass into the lenticular nucleus before reaching their peri- pherical destination. The destruction of the nuclei of the corpus striatum, to- gether with the related division of the internal capsule, does not appear to add to the effects of lesion of this division of the internal capsule by itself. § 5. Nothnagel ' describes the results of a series of ex- periments on the basal ganglia of rabbits, in which he pro- fesses to be able to produce localised lesions of these structures by means of injections of chromic acid, or with the aid of a fine needle or trocar. The difficulties of exact localisation, however, are too great to allow of his results being accepted without question. It would appear, however, that, apart from the running or springing movements above referred to, mechanical lesions limited to the caudate nuclei caused little if any interference with volitional movements. Only in cases of unilateral lesion did there appear some impairment of movement and some deviation of the limbs. When both ganglia were extensively broken up no special symptoms were observable, even directly after the operation. 2 Very different were the results of lesion of one or both lenticular nuclei. When one alone was destroyed by the injection of chromic acid, there occurred deviation outwards of the opposite fore limb, and deviation inwards of the hind limb of the same side, together with bending of the vertebral column towards the side of lesion, and some degree of cyphosis or dorsal curvature, due to paralysis of the contralateral trunk muscles. 1 Virchow's Archiv, Bd. lvii., lviii., lx., lxii., 1873-1875. 2 Op. cit. Bd. lx. p. 139. LESIONS OF THE COBPUS STBIATUM 411 "When the lenticular nuclei were destroyed on both sides there was no deviation of the limbs or distortion of the trunk. The animals maintained their normal altitude, but remained quite immovable and apathetic, like animals deprived of their cerebral hemispheres. They allowed their limbs to be with- drawn or placed in any abnormal position without resistance. But if the tail were pinched the animal would make one or two leaps forward, and again relapse into its apathetic im- mobility. Though Nothnagel assimilates the results of destruction of the lenticular nuclei to those observed after removal of the cerebral hemispheres, this is not strictly correct. Animals deprived of their cerebral hemispheres have neither desire nor the power of effecting volitional movements. But destruction of the lenticular nuclei paralyses only the power of carrying desire into effect. In a rabbit in which I had destroyed both corpora striata I observed clear indications of appetite and desire to eat ; but attempts to satisfy them resulted only in vague and ineffectual struggles. Volitional movements only were paralysed, while perception, ideation, and desire continued — faculties which are entirely annihilated by com- plete removal of the hemispheres. It is a question whether the lesions described by Nothnagel were in reality confined to the respective ganglia of the corpus striatum, without impli- cation of the internal capsule, directly or indirectly ; but in any case it is evident that destruction of the ganglionic substance of the corpus striatum produces a much more com- plete and enduring paralysis than destruction of the cortical motor centres alone, or of the pyramidal tracts which proceed from them. The experiments of Carville and Duret ' on dogs are in complete harmony with the results obtained in the case of rabbits. While removal of the cortical motor centres, or section of the pyramidal tracts before they penetrate between the nuclei of the corpus striatum, causes the characteristic paralysis or paresis already described and discussed, destruc- tion of the corpus striatum with section of the pyramidal tracts forming the anterior division of the internal capsule (fig. 123), causes complete hemiplegia of the opposite side, so 1 Sur les Fonctkms des Himisphires Ctribravx. 412 FUNCTIONS OF TEE BASAL GANGLIA that the limbs are entirely useless either for support or pro- gression. Here, too, as in rabbits, the hemiplegia, besides being much more complete than that resulting from destruction of the cortical motor area, appears to be much more enduring, if not permanent. § 6. In connection with lesions affecting the optic thalamus have been observed at one time paralysis of motion of the limbs generally, or of the upper limb in particular ; at another, impairment or abolition of tactile sensibility or of vision ; and in still other cases, considerable in number, no defect what- ever, motor or sensory, has been apparent. It is altogether Fig. 123. — Frontal section of Brain of Dog, five millimetres anterior to the Optic Commissure (CarviUe and Duret). s s, nuclei caudati of the corpora striata. L, the lenticular nucleus. P P, the peduncular expansion. Ch, optic chiasma. x, section of the peduncular expansion causing hemiplegia. B, Veys- siere's stylet for dividing the internal capsule. impossible that lesions accurately restricted to the same region should have such a diverse symptomatology, and the negative cases are so numerous as to render very doubtful, if not absolutely disprove, any causal relationship between lesions of the optic thalamus as such and the sensory or motor symptoms which have been described in connection therewith. It is easy to account for either sensory or motor paralysis in connection with lesions of the optic thalamus without attributing any special share in the causation to the thalamic grey matter, itself. The position of the optic thalamus in LESIONS OF THE OPTIC THALAMUS 413 reference to the internal capsule is such (see fig. 25) that direct or indirect implication of its tracts must necessarily be always considered as possible, and indeed almost inevitable, if the lesion is at all extensive. It has been shown that many of the fibres of the internal capsule pass on to the cerebral cortex without entering into other relations than that of mere contiguity to the basal ganglia ; and it has been found that section of the anterior two-thirds causes paralysis of motion, and lesion or section of the posterior third causes paralysis of sensation on the opposite side, both general and special. It is necessary, therefore, to prove the absolute integrity of these tracts before we can ascribe either motor or sensory paralysis to lesions of the optic thalamus as such. The re- corded cases by no means satisfy the requirements of scientific evidence in this respect, and the fact that not unfrequently lesions have been found in one or both optic thalami without discoverable symptoms goes far to prove that direct or in- direct implication of the internal capsule has been the real cause in all cases where motor or sensory paralysis has been observed. Though Luys l and Fournie 2 consider that the optic thalamus is the ganglion of convergence of all the sensory tracts before they radiate into the cerebral cortex, their views are neither in accordance with recent anatomical researches nor are they supported by well-established clinical or experi- mental data. The clinical cases collected by Luys in support of this theory are exceedingly unsatisfactory, and do not ex- clude implication of the internal capsule. The experiments which Fournie adduces to prove that destruction of the optic thalamus causes loss of sensation on the opposite side are not such as to inspire confidence. Fournie injected strong solu- tions of chloride of zinc into the optic thalami, but his own descriptions of the diffuse lesions, and general cerebral dis- turbance, which his procedure induced, justify the complete distrust with which his results have been received by physio- logists 3 and pathologists in general. 1 The Brain and its Functions. 2 Becherches Expirimentales sur le Fonctionnement du Cerveau, 1873. 8 See Nothnagel's trenchant criticism,' Virehow's Archiv, Bd. lviii. p. 433. 414 FUNCTIONS OF THE BASAL GANGLIA Nothnagel ' detected no paralysis either of motion or sen- sation after destruction of both optic thalami in rabbits, nor anything at first sight capable of distinguishing them from perfectly normal animals. They retained their voluntary motor power and reacted as usual to cutaneous stimulation. The only abnormality was that they allowed the fore limbs to be placed in any position without resistance, and if the one thalamus only were destroyed, the limb opposite the lesion. It is more than probable that this phenomenon depended on loss of sensibility of the limb, due to lesion of the internal cap- sule. For the mere reaction to cutaneous stimulation, which Nothnagel thinks sufficient to indicate the retention of tactile sensibility, is not a satisfactory proof of sensation. But Bechterew 2 did not observe this condition in his experiments, and saw nothing to indicate affection either of sensation or voluntary motor power. This author, however, states that electrical irritation of the optic thalamus in his hands caused the'animals to utter cries such as they employ to express their, feelings or emotions. I have, however, never observed any phenomenon of this nature in my experiments on the optic thalami of various animals, and cannot, therefore, admit the correctness of Bechterew's statements. Bechterew further found that after destruction of the optic thalami in pigeons, fowls, rabbits, and dogs the animals were unable to express their feelings in the usual manner by cries, or to make the mimetic movements characteristic of feeling or emotion. He admits, however, in a subsequent paper 3 that cries may still be elicited even after destruction of the optic thalami. These, however, he regards as merely reflex through the agency of ' elementary ' centres in the pons or medulla, but true signs of feeling and true mimetic movements are only exhibited when the optic thalami are intact. Bechterew's criterion between reflex and true emotional cries and other manifestations of feeling appears to be somewhat arbitrary ; and the experiments of Longet and Vulpian, as well as my 1 Virchow's Archiv, Bd. lxii. 2 ' Die Function der Sehhiigel,' Neurolog. Centralblatt, No. 4, 1883. 8 Neurolog. Centralblatt, No. 4, 1884; LESIONS OF THE OPT 10 THALAMUS 415 own, previously described (Chapter V.), are distinctly contra- dictory in several particulars of the results arrived at by him. Whatever may be the special results of destruction of the optic thalami, it seems fairly well established by the facts of disease, and experiments on the lower animals, that they may be extensively destroyed, if not entirely extirpated, without causing paralysis of voluntary motion or loss of tactile sensa- tion. When these symptoms occur in connection with lesions in the region of the optic thalamus, they may with more reason be ascribed to injury of the internal capsule than to the lesion of the optic thalamus as such. § 7. It is a question, however, whether the optic thalamus has not a special relation to vision. As has been seen, one of the roots of the optic tract is traceable to the external genicu- late body and pulvinar of the optic thalamus, and other fibres have been described as arising from the superficial stratum, as well as from the interior of this ganglion. There are clinical as well as experimental facts to show that lesions invading the posterior region of the optic thalamus cause homonymous hemiopia by paralysis of the corresponding side of both retinae. Thus in a case reported by Hughlings Jackson ' in which there was softening in the region of the pulvinar of the right optic thalamus, and apparently limited to this region, there was observed during life left hemiopia from para- lysis of the right side of both retinas. But as, in addition to the hemiopia, there was also some defect in motor power, as well as some impairment of general sensibility on the left side, there is every reason for believing that the posterior division of the internal capsule was also more or less directly or in- directly implicated. Other similar cases might be alluded to. But, even though we may admit that lesions accurately re- stricted to the pulvinar and corpora geniculata may cause hemi- opia, this may be ascribed merely to interruption of the optic radiations which proceed from this part towards the occipito- angular region of the hemisphere. We have seen that hemi- opia may be induced by cortical and subcortical lesion of the occipito-angular region. The question is whether there is anything to distinguish hemiopia so induced from that caused 1 'A Physician's Notes on Ophthalmology,' Lond. Hosp. Reports, 1875. 416 FUNCTIONS OF THE BASAL GANGLIA by lesion limited to the pulvino-geniculate region of the optic thalamus itself. In an experiment which I made on a monkey, in which the left optic thalamus, along with the medullary fibres external to it, was extensively broken up by penetration from the cortex in the region of the first occipito-angular bridg- ing convolution (fig. 124), there was, in addition to general hemianesthesia, total blindness of the opposite eye— temporary at least, but whether giving place to homonymous hemiopia was not determined — and also dilatation of the opposite pupil. As dilatation of the pupil does not occur in cortical or sub- cortical lesion of the occipito-angular region, this symptom may possibly be a special feature of lesion of the optic tract in the thalamus itself ; indicative of rupture of the centripetal Fig. 124.— The shading indicates the superficial extent of the lesion in the left hemisphere in the operation for destruction of the optic thalamus". The darker centre indicates the sinus leading into the optic thalamus. fibres to the irido-motor nucleus in the floor of the Sylvian aqueduct. § 8. An analysis of the various clinical and experimental data in reference to the effects of lesions of the ganglionic substance of the corpora striata and optic thalami leads to the conclusion that, provided the fibres of the internal capsule are not directly or indirectly injured, neither voluntary motion nor sensation is permanently impaired or abolished. For we cannot consider that Notbnagel's experiments on the lenticular nucleus exclude implication of the internal capsule ; inasmuch as not in every case, but only in those in which the lesion penetrated deeply, as far as the base of the ganglion, was COBPUS STRIATUM— SPECIAL FUNCTIONS 417 voluntary motion paralysed. Lesions of small size and situ- ated well outwards from the internal capsule had no such effect. And the probability is that in all successful cases the internal capsule was really injured directly or indirectly. But it is not difficult to discover, in certain animals at least, a very great difference between the effects of destruction of the cortical motor centres or of the subjacent medullary fibres, and those following destruction of the ganglia of the corpus striatum, together with the tracts of the internal capsule passing through them. The degree of motor paralysis from lesion of the striate-capsular region in different animals appears to bear an inverse ratio to that resulting from purely cortical or subcortical lesion of the motor zone. In man and the monkey there is little if any difference between the effects of complete destruction of the cortical motor centres and those of destruction of the striate-capsular region. There is the same powerlessness of the opposite side of the body, and the same lateral distortion from the unant- agonised action of the muscles on the sound side. The degree of paralysis of the various movements corresponds, those movements being most affected which are the most complex, most volitional, and most independent ; and the duration of the paralysis is, as far as can be judged, as lasting in the one case as in the other, and followed by the same secondary de- generation of the pyramidal tracts of the spinal cord. But while complete hemiplegia of the opposite side can be produced by a very limited lesion in the striate-capsular region, the same effect can only result from a very extensive lesion of the cortex. Hence it is more rare to find complete hemiplegia from cortical lesion than from lesion in the region of the corpus striatum. Only those movements are permanently paralysed the cortical centres of which are thoroughly disorganised ; while others which have their centres only slightly injured, or merely functionally affected, are recovered when the causes of the perturbation have completely subsided. In dogs, however, as the experiments of Carville and Duret prove, destruction of the striate-capsular region produces a much more complete paralysis than lesion of the cortex or subjacent fibres. In the latter case the affection of motility E E 418 FUNCTIONS OF THE BASAL GANGLIA is so slight that it has been described as a paresis rather than a paralysis, and the animal is able to perform many actions apparently as well as before. But in the former case complete hemiplegia is the result. The limbs are entirely powerless, and lateral distortion of the trunk towards the side of lesion occurs. The animal is unable to stand or walk, or if it attempts to move it is impelled to move round in a circle by the action of the unparalysed side. In rabbits, on the other hand, the destruction of the cortical motor centres produces much less marked disturbance of the ordinary motor activities than even in dogs. But when the corpora striata and corresponding division of the internal capsule are destroyed there is complete paralysis of voluntary motion, and only those movements are possible which are capable of being carried out through the cerebellar, mesence- phalic, and spinal centres in the entire absence of the cerebral hemispheres. These differences in the effects of destruction of the cortical motor centres and corpora striata in the different orders of animals, throw considerable light on the special functions of these ganglia. In the rabbit the powers of equilibration and co-ordinated locomotion are not abolished either by destruc- tion of the corpora striata or cortical centres, or both together. In the dog the destruction of the corpora striata (including the corresponding division of the internal capsule) causes complete paralysis (for the time at least) of all the powers of movement which are only partially affected by removal of the cortical centres ; while in the monkey and man the destruction of the corpora striata adds little or nothing to the completeness of the motor paralysis which results from destruction of the cortical motor centres. These differences can only be satisfactorily accounted for on the principles already repeatedly enunciated— that animals differ greatly in respect to the degree of organisation of the ordinary motor activities in the lower centres. This is much greater in the lower than the higher vertebrates, as is shown by the results of complete ablation of the cerebral hemispheres ; and it is evident that the independent organisation of the motor activities in the mesencephalic and lower ganglia is CORPUS STRIATUM— SPECIAL FUNCTIONS 419 much greater in the rabbit than in the dog. For even when the corpora striata and corresponding division of the internal capsules are disorganised in the rabbit, equilibration and co-ordinated locomotion are still possible in response to appropriate external stimuli ; whereas in the dog there is such complete powerlessness that the animal lies perfectly helpless, unable to stand or walk. It appears from these facts that the corpora striata proper are centres of innervation of the same movements as are differentiated in the cortical motor centres, but of a lower grade of specialisation. The innervation of the limbs in all that relates to their employment as instruments of consciously discriminated acts is dependent on the cortical centres, while for all other purposes involving mere strength or automatism, primary or secondary, the corpora striata with the lower ganglia are sufficient. In man almost every movement has to be laboriously acquired by conscious effort through the agency of the cortical centres, and continues to involve the activity of these centres to a greater or less extent throughout. Hence the destruction of the ganglia of the corpora striata adds little if anything to the completeness of the paralysis which results from destruction of the cortical motor centres alone. § 9. As to the special functions of the optic thalami, so far as any definite facts have been ascertained, apart from mere hypotheses more or less plausible, we may still say with Vulpian, ' Nous ne savons rien des fonctions speciales des couches optiques.' * In the absence of any definite symptoms resulting from destruction of these ganglia, apart from such as may with more probability be ascribed to coincident lesions of the internal capsule or optic tracts, we can only speculate as to their proper functions. If the anatomical relations were more satisfactorily deter- mined than they are in reality, we might found more securely on these than we can safely do as yet. But it seems at least certain that they have a closer relation to the sensory tracts and centres than they have to the motor. The cutaneous sensory tracts of the internal capsule are immediately in re- lation to them, and indeed Flechsig, as we have seen, traces 1 Leqons, &c. p. 659. E E 2 420 FUNCTIONS OF THE BASAL GANGLIA them all, though in all probability erroneously, entirely into the tegmentum, with which the optic thalamus is more or less directly continuous. The optic tracts, besides other supposed connections with the optic thalami, are certainly connected with the pulvino-geniculate region of these ganglia. By the pillars of the fornix the optic thalami are in relation with the cortical centres of smell (taste?) and tactile sensibility. Through the fibres of the corona radiata they are in relation with the occipito-temporal regions of the cortex, which, we have seen, are sensory in function. The anterior tracts appear to pass into the frontal regions, but where they end has not been j:rml. A Tcmt. Cam. ex t. Fig. 125.— Horizontal Section of the Optic Tha'ami of Babbit, just above the level of the internal capsule (after Monakow). T. ami., tuberosum anterins. a an- terior, and i, posterior cell group of the same. N. med., median nucleus. lf!ext external nucleus. Jf.pos/., posterior nucleus of the optic thalamus. Gilt can- cellated layer (Gitterschicht). C.gen.ext., corpus geniculatum externum. C.gen.na., corpus geniculatum internum. satisfactorily determined, and it is not improbable that they enter the gyrus fornicatus. Monakow's experiments lead him to conclude that each nucleus of the optic thalamus (fig. 125) is related to a definite cortical region, and undergoes atrophy with its related tracts when this region is extirpated. Thus he concludes that the posterior nucleus (fig. 125, N.post.) is specially related to the basal regions of the hemisphere; the pulvinar and corpus geniculatum externum (fig. 125, C.gen.ext.) to the occipital region or visual sphere ; the corpus geniculatum internum (fig. 125, OPTIC THALAMUS— MONAKOW'S BESEABCHES 421 Cgen.int.) to the temporal region or auditory zone ; the exter- nal nucleus (fig. 125, N.ext.) and neighbouring parts to the upper and lower parietal regions ; and the anterior tubercle and median nucleus (fig. 125, T.ant., N.med.) to the frontal regions of the hemisphere. In addition to the nuclei of the optic thalamus the correlated medullary fibres of the corona radiata, and also the tracts leading to the periphery, undergo atrophy, particularly — apart from the pyramidal tracts related to the motor zone — those of the outer part of the crus and those passing into the tegmentum. The course of these latter fibres is uncertain. But apparently there ensues atrophy to some extent in the formatio reticularis, the middle cerebellar peduncle, the trapezium and lateral portion of the lemnis- cus of the same side, and the opposite half of the spinal /cord. Before these results can be accepted as correct it -will be necessary to repeat the experiments in such a manner as to ensure absolute limitation of the primary lesions, conditions far from being fulfilled by Monakow's researches, and it will be necessary also clearly to differentiate lesions implicating the falciform lobe from those of the convexity. There is reason to believe that the relations which he seeks to establish between lesions of the frontal regions and the anterior tubercle are founded on implication of the gyrus fornicatus. Gudden 1 did not observe any abnormality in the appearance of the optic thalamus after extirpation of the motor zone, which caused degeneration of the pyramidal tracts. Nor did Monakow in his first experiments note any atrophy of the optic thalamus after destruction of the frontal region, though his subsequent researches led him to a different conclusion.. That the optic thalamus is at all related to the true motor zone is extremely doubtful. In a remarkable case reported by myself, 2 in which the whole of the motor zone with the exception of the marginal convolution and portion of the postero-parietal lobule was entirely atrophied— a condition which had existed many years — the optic thalamus with the exception of the anterior tubercle, which was destroyed along 1 Archiv filr Psychiatrie, Bd. ii. 1871. 2 See figs. 64, 65, Chap. VI. p. 216. 422 FUNCTIONS OF THE BASAL GANGLIA with the corpus striatum hy the primary lesion, was perfectly normal in size and appearance as compared with that of the other side. So far as has yet been established beyond doubt the optic thalamus appears to be related to sensory regions and tracts, and more especially has this been demonstrated of the -visual sphere. § 10. It is, however, evident from the results of experiment and disease that the centres of the optic thalamus are not the centres of ' conscious ' sensation, nor are the paths which connect them with the cortex the paths, or at least the only paths, of sensation ; inasmuch as it is only when the posterior portion of the internal capsule is destroyed that anaesthesia results, and this apparently without any evident implication of the ganglionic substance itself. There are no facts or data serving to define whh any degree of definiteness the functions of the respective nuclei and their correlated tracts in the corona radiata. The tracts may be the paths of obscure sensations, some of which may be perhaps related to the organic sensi- bilities, or they may be merely tracts of association between the centres of conscious and subconscious activity. It is probable that the optic thalami, specially related to the sensory tracts, and the corpora striata, specially related to the motor tracts, represent in a subordinate manner all the sensory and motor centres of the cortex, and constitute together a sensori-motor mechanism, subservient to the manifestation of all those forms of activity which do not imply conscious discrimination or true volition. In proportion as the capacities and modes of activity . transcend mere consensual or adaptive automatism, and involve conscious discrimination and special motor acquisition, do the cortical centres become necessary, as in man. In such case the basal ganglia may be more or less completely dispensed with, as would appear from the absence of permanent symptoms in case of lesions confined to the ganglionic substance proper. If, on the other hand, as in rabbits, the modes of activity do not greatly transcend mere automatism, the cortical centres are of less importance, and may be removed without creating much obvious disturbance. GENEBAL CONCLUSIONS 423 In intermediate cases, as in dogs, the degree of disturbance caused by removal of the cortical centres will depend on the relative proportion in their modes of activity between mere automatism, provided for by the basal ganglia, and special acquisitions which have involved the exercise of conscious discrimination. 424 CHAPTEE XII. THE HEMISPHEKES CONSIDERED PSYCHOLOGICALLY. § 1. Hitherto we have considered the brain chiefly in its physiological aspects, and the conclusion has been arrived at that the hemispheres consist of a system of sensory and motor centres. In their subjective aspect the functions of the brain are synonymous with mental operations, the consideration of which belongs to the science of psychology. The phenomena of consciousness cannot be investigated or explained by physio- logical methods only, but anatomical and physiological investi- gation of the substrata of consciousness may serve to elucidate some at least of the correlations between conditions of the brain and psychical manifestations. It is not the object of this chapter to attempt an analysis of mind or the laws of mental operations, but briefly to discuss, in the light of the facts revealed by the physiological and pathological researches recorded in the preceding chapters, some of those relations between the physiological and psychological functions of the brain which present themselves more especially to the physician and medical psychologist. That the brain is the organ of the mind is a universally admitted axiom. We have no proof of subjectivity or modifi- cations of consciousness apart from the action of the cerebral hemispheres. But we have no reason to believe that any- thing is superadded, or that the action of the cortical centres is of a different order from that of the most simple nervous apparatus ; but rather that between the simplest reflex action and the most complex cerebral process there is a continuous unbroken gradation. "Why consciousness should arise only in correlation with the activity of the cerebral hemispheres is a question which has not yet received any satisfactory answer. BBAIN AND MIND 425 It may perhaps be associated with greater complexity or fric- tion than obtains in lower ganglia; but though we should arrive at the true explanation of the conditions of conscious- ness when a sensation is experienced, we are as far as ever from understanding the ultimate nature of that which con- stitutes the sensation. The one is objective and the other subjective, and neither can be expressed in terms of the other. We cannot say that they are identical, or that one passes into, or causes the other ; but only, as Laycock expresses it, that the two are correlated ; or, with Bain, that the physical changes and the psychical modifications are the objective and subjective sides of a ' double-faced unity.' ' We have every reason for believing that there is, in company with all our mental processes, an unbroken material succession. From the ingress of a sensation to the outgoing responses in action the mental succession is not for an instant dissevered from a physical succession. A new prospect bursts upon the view ; there is a mental result of sensation, emotion, thought, termi- nating in outward displays of speech or gesture. Parallel to this mental series is the physical series of facts, the successive agitation of the physical organs. * . . While we go the round of the mental circle of sensation, emotion, and thought there is an unbroken physical circle of effects. It would be incom- patible with everything we know of cerebral action to suppose that the physical chain ends abruptly in a physical void, occupied by an immaterial substance; which immaterial substance, after working alone, imparts its results to the other edge of the physical break, and determines the active response — two shores of the material with an intervening ocean of the immaterial. There is, in fact, no rupture of nervous con- tinuity. The only tenable supposition is that mental and physical proceed together as undivided twins. When, there- fore, we speak of a mental cause, a mental agency, we have always a two-sided cause ; the effect produced is not the effect of mind alone, but of mind in company with body.' ' In accordance with this position it must follow, from the constitution of the cerebral hemispheres, that mental opera- tions in the last analysis must be merely the subjective side 1 Bain, Mind and Body, 1873, p. 131. 426 BBAIN AND MIND of sensory and motor substrata, as has been clearly enunciated by Hughlings Jackson. For the cerebral hemispheres consist only of centres related respectively to the sensory and motor tracts, which connect them with the periphery and with each other. § 2. The physiological and psychological activity of the cerebral hemispheres are not, however, altogether coextensive. While consciousness cannot arise apart from the activity of the hemispheres, many cerebral processes can occur without revealing themselves in consciousness. The brain as an organ of motion and sensation, or pre- sentative consciousness, is a single organ composed of two halves ; the brain as an organ of ideation, or re-presentative consciousness, is a dual organ, each hemisphere complete in itself. When one hemisphere is removed or destroyed by disease, motion and sensation are abolished unilaterally, but mental operations are still capable of being carried on in their completeness through the agency of the one hemisphere. The individual who is paralysed as to sensation and motion by disease of the opposite side of the brain (say the right) is not paralysed mentally, for he can still feel and will and think, and intelligently comprehend with the one hemisphere. If these functions are not carried on with the same vigour as before, they at least do not appear to suffer in respect of com- pleteness. § 3. In order that impressions made on the individual organs of sense shall excite the subjective modification called a sensation, it is necessary that they reach and induce cer- tain molecular changes in the cells of their respective cortical centres. If the visual centre is destroyed or functionally inactive, impressions made on the retina and optical apparatus cause the same physical modifications as usual, but do not affect consciousness. The changes produced have no subjective side. The optical apparatus without the visual centre may be compared to the camera without the sensitised plate. The rays of light are focussed as usual, but produce no chemical action, and leave no trace when the object is withdrawn, or the light from it shut off. The visual centre is like the sensi- CONDITIONS OF PEBCEPTION 427 tive plate. The cells undergo certain molecular modifications which coincide with certain subjective changes constituting the consciousness of the impression or special visual sensation. And as the sensitive plate records, in certain chemical decom- positions, the form of the object presented to the camera, so the visual centre records in cell-modifications the visual cha- racters of the object looked at. We may push the analogy still further. Just as the chemical decomposition effected by the rays of light may be fixed and form a permanent image of the object capable of being looked at, so the cell-modifica- tions which coincided with the presentation of the object to the eye remain permanently, constituting the organic memory of the object itself. When the same cell-modifications are again excited, the object is re-presented or rises up in idea. It is not meant by this analogy that the objects are photo- graphed in the visual centre, as objects are photographed on the plate, but merely that permanent cell-modifications are induced, which are the physiological representatives of the optical characters of the object presented to the eye. The optical characters are purely light vibrations, and few objects are known by these alone. The object appeals to other senses, and perhaps to movements, and the idea of the object as a whole is the revival of the cell-modifications in each of the centres concerned in the act of cognition. For what is true of the visual centre is true, mutatis mutandis, of the other sensory centres. Each is the substratum of consciousness of its own special sensory impressions, and each is the organic basis of the memory of such impressions in the form of certain cell-modifications, the re-induction of which is the representa- tion or revival in idea of the individual sensory characters of the object. The organic cohesion of these elements by asso- ciation renders it possible for the re-excitation of the one set of characters to recall the whole. § 4. The sensory centres, therefore, are to be regarded not merely as the organs of consciousness of immediate sensory impressions, but as the organic register of their own sensory experiences. This organic memory is the physical basis of Eetentiveness, and the property of re-excitability is the organic basis of Kecollection and Ideation. We have thus a physio- 428 BBAIN AND MIND logical foundation of the law arrived at on other grounds by Bain, viz. that ' the renewed feeling occupies the very same parts, and in the same manner as the original feeling.' According to Spencer, the renewal of the feeling is the faint revivification of the same processes which are strongly excited by presentation of the object. The molecular thrill, if we may so term it, of present sensation extending from the peri- pherical organ of sense is in the ideal sensation revived, but, as a rule, not so powerfully as to extend to the periphery ; though, in some instances, the central revivification may be so intense as actually to reinduce the peripherical impression. This occurs in certain morbid states, such as are described under the name of ' fixed ideas,' or in sensory hallucinations from diseased conditions of the brain, as in epilepsy and insanity. The organic memory of sensory impressions is the funda- mental basis of knowledge. If the sense impressions were evanescent, or endured only so long as the object was present, the range of conscious intelligent action would be limited to the present, and we should have no real knowledge. Know- ledge implies the consciousness of agreement or difference. We can only be said to knoiv when we recognise identity, or difference between past and present conscious modifications. We know that a certain colour is green by recognising a simi- larity or identity between the present and a certain past colour sensation, or a difference between this and some other colour in the spectrum. If we had no organic memory of the past capable of re-excitation to serve as the basis of comparison, we should be unable to recognise either agreement or differ- ence. We might be conscious from moment to moment, but there would be no continuation in time, and knowledge would be impossible. The foundation of the consciousness of agree- ment is the re-excitation by the present of the same molecular processes which coincided with a past impression; and of difference, a transition from one physical modification to an- other. The sensory centres, therefore, besides being the organs of sensation or consciousness of immediate impressions, contain, in the persistence and revivability of the coincident physical modifications, the materials and possibilities of simple FEELINGS AND EMOTIONS 429 and complex cognitions, in so far as these are dependent on sensory experience alone. The destruction ' of the visual centre, therefore, not only makes the individual blind presentatively, but blind re-pre- sentatively 2 or ideally, and all cognitions into which visual characters enter in part or whole become mangled or imperfect, or are utterly rooted out of consciousness. The destruction of the eye renders the individual blind only presentatively, but his visual memory and visual ideation remain unaffected ; 3 and it would be of great importance to ascertain whether in an individual born blind, or blind for many years, the visual centres, apart from mere general atrophy, present any special peculiarities in the appearance of the cells or their processes differing from those of the normal brain. § 5. The springs of conscious activity, or the incentives to volition, are present or ideally revived sensations and their accompaniments. Sensations are accompanied in conscious- ness by feelings, which are divisible into two great and opposite classes, pains and pleasures. Just as sensations are the sub- jective side of certain physical modifications of the nerves and nerve centres, so pleasurable or painful feelings may be regarded as the subjective expression of physical harmony or disharmony between the organism and the influences acting on it. A painful sensation is a physiological discord incom- patible with health or comfort, or, it may be, life itself. A pleasurable sensation is a physiological harmony promoting health and comfort, and calculated to prolong existence. 4 1 See further on this subject, § 14. 2 The distinction here drawn between presentative and re-presentative blindness and other states of consciousness, long familiar to English psycholo- gists, has been travestied by Munk under the terms ' cortical blindness ' (Eindenblindheit) and 'psychical blindness' (Seelenblindheit). As all the manifestations of cerebral action, objective and subjective, are at bottom cortical, it. is manifestly absurd to establish an antithesis between ' cortical ' and any other form of blindness. 3 This is not strictly accurate except within certain limits. There is reason to believe that, unless the centres are kept in exercise by the continuous in- coming of new impressions, they tend to degenerate, so that former sensory experience is lost or cannot be revived. It is well known that when total deafness occurs in early life dumbness ensues, even though the child may have learnt to talk with fluency. * As Romanes (Mental Evolution in Animals, p. 107) truly remarks, ' the 430 BBAIN AND MIND As the revived or ideal sensation involves the activity of the same structures as' are concerned in the present sensation, so the revived feelings or emotions are localised in the same regions. Hence the sensory, ideational, and emotional centres are one and the same. The senses differ greatly in respect to the relative preponderance of the intellectual or discrimina- tive, and emotional, or feeling, element in their composition, and in respect to their revivability as ideas or as feelings. In the visual sense the emotional is subordinate to the intel- lectual, or may be almost entirely absent, and in the great majority requires cultivation;, in the sensations of organic life the emotional is at its maximum, and the intellectual or dis- criminative at its minimum. In man vision is the highest intellectual sense, while smell and taste are the highest in point of feeling. In dogs and other animals, however, this rule does not seem to obtain, and smell appears to rank higher than the other senses in an intellectual point of view. The manner in which dogs, with their extraordinary keenness pf smell, are able to investigate with their olfactory organs sub- stances which to man, with his feebly developed sense of smell, would be the cause only of the most unpleasant feelings, shows that the sense of smell in them is largely dissociated from mere feeling, and is the chief organ of intellectual dis- crimination. The feelings accompanying the more intellectual senses, vision and hearing, are the primordial elements of the aesthetic emotions which are founded on harmonies of sight and sound. ■ All the emotions, however complex or difficult of analysis, are founded ultimately on the feelings accompanying the exercise of the centres and organs of sensation. That the sensations of organic life are represented in the cerebral hemispheres, directly or indirectly, is plain from the extraordinary influ- ence which states of the viscera exercise on the emotional tone of the individual. Organic sensations generally, with superficial or apparent objection to the doctrine we are considering, which arises from the fact that feelings of pleasure or pain are not infallible indices of what is respectively beneficial or injurious to the organism, is easily met by the consideration that in all such exceptional cases it is not the doctrine, but its application, which is at fault.' APPETITES AND DESIBES 431 one or two exceptions, are, unless rising to the pitch of pain- ful intensity, obscure and non-localisable, and the healthy or morbid physiological activity is expressed subjectively as the vague and ill-defined feeling of well- or ill-being — euphoria or dysphoria (Laycock). Whether the centres of organic sensation are fused with those of tactile or common sensi- bility in the falciform lobe, or whether they are specially represented in and through the optic thalami or elsewhere are all questions as yet unsolved. But, wherever situated, they seem to be the foundation or universal background of pleasurable or painful emotions in general. As healthy states of the viscera produce pleasurable feelings, and morbid states of the viscera produce painful or depressing feelings, so, con- versely, on the principle that the revived feeling occupies the same parts as the original, pleasurable emotions exalt, and painful emotions depress, the vital functions. Yisceral de- rangements are frequently the cause, and always the accom- paniment, of melancholic depression ; and just as visceral derangements frequently express themselves in localisable sympathetic neuroses, so the melancholic individual, or hypo- chondriac, projects his obscure feelings in some definite objective form. He imagines that his vitals are being gnawed at by some hideous animal, or that his body is the scene of demoniacal revels. The special form of the hallucination varies with the individual and his education, but it always takes some dread or malignant shape. § 6. The physiological needs of the organism in so far as they induce locally discriminable sensations express them- selves subjectively as definite appetites or desires, which are the conscious correlations of physiological wants. The appe- tite of hunger is the desire to satisfy or remove a local sensation, referable to the stomach, in which the physio- logical needs of the organism express themselves. The sub- strata of the feeling of hunger and appetite for food are the stomachic branches of the vagus and their cerebral centres. And as local conditions of the stomach may destroy or increase the feeling of hunger, so central disease may give rise to ravenous appetite or sito-phobia, conditions exemplified in certain forms of insanity. 432 BBAIN AND MIND The bodily need of water expresses itself locally in a dry condition of the fauces, •which is the basis of the feeling of thirst and the appetite for drink. The sexual appetite, though springing from the organic wants of certain glandular structures, centres itself round a certain tactile sensation, which is the reflex key to the grati- fication of the physiological demand for functional exercise on the part of these organs. The sexual appetite appears only with the development of the generative glands. Its appearance induces considerable perturbation of the other organic functions, and expresses itself subjectively at first chiefly in the form of emotional excitability, or in obscure longings, morbid desires, or hysterical outbursts. Long before the link between a definite sensation and a definite action for its realisation has been established in consciousness, the gene- rative glands may gratify themselves reflexly during sleep, the period, par excellence, of reflex excitability. As morbid irrita- tion of the generative organs may excite a morbid sexual appe- tite, so, conversely, the sexual appetite may be morbidly excited by pathological irritation of the cerebral paths and cerebral centres of the sensations connected with the exercise of the generative functions. To the former belong the satyriasis or nymphomania occasionally observed in connection with disease of the middle lobe of the cerebellum ; to the latter the various morbid exhibitions of the sexual appetite in insanity where the centres are functionally or organically diseased. § 7. The various sensations, feelings, and desires, present or revived, singly or in associated combinations, form the incentives to action, the motives to volition. The outward expression of certain physiologically hurtful or beneficial sensory impressions takes place instinctively or independently of individual education; their realisation in consciousness, as painful or pleasurable sensations, merely coinciding with, or, in strict accuracy, more often following, their manifestation externally. Such are the spinal reflex actions, and the reflex expressions of emotion such as we have seen manifested in animals deprived of their cerebral hemi- spheres. All truly volitional action, on the other hand, is the result MOTIVES TO VOLITION 433 01 education, the duration of which varies within extremely wide limits in different classes and orders of animals, and in respect to individual acts of volition in the same animal. At hirth the human and monkey infant have no volition proper, hut only the elements out of which it is evolved. The actions of the infant are at first limited to definite reflex response to definite external or internal stimuli, and to indefinite or general motor activity, conditioned not so much by any definite stimulus as by a natural tendency of the nerve centres to expend their surplus energy in action. To this latter tendency Bain gives the name ' spontaneity.' Though it is impossible to determine how far this expenditure of energy is dependent on central overflow alone, and how far on external and internal sensory impressions in general acting on the nerve centres, the term spontaneity sufficiently well expresses a definite fact of the constitution. Actions determined reflexly, or originating spontaneously, according as they prove physiologically beneficial and subjec- tively pleasurable, tend to continuance and repetition; while actions physiologically hurtful and subjectively painful are checked or avoided. This is the great law of self-conservation, exemplified in the struggle for existence and the survival of the fittest. It is only in accordance with this law that animals have been able to adapt themselves to their environment, and those have succeeded best in which the internal adaptations have best corresponded with its provisions. The conscious discrimination of a sensation as pleasurable, and its ideal persistence and tendency towards repetition as desire, and its association with things seen, smelt, or tasted, are effected long before the sensation, present or revived, is associated with any differentiated motor act for its accom- plishment or realisation. This latter is the result of happy accident, or of repeated trials and error. Though the child possesses in the motor centres 1 of its cerebral hemispheres the potentiality of differentiated motor acts, the individual selection or excitation, of any one of these, in response to a present or revived sensation, requires the establishment, by 1 These, according to the experiments of Soltmann on dogs, already alluded to (p. 234), are not developed so as to be excitable in the earlier days of infancy. F F 434 BBAIN AND MIND education and repetition, of an organic nexus between the special sensory centre or centres, and the special motor centre. Some particular object held before a child recalls by sight a pleasurable sensation, and excites desire; but, instead of inducing, as yet, a definite action for its gratification, excites only vague and undefined movements of arms, legs, and facial muscles, the expression of general excitation of the motor centres. In process of time the centre of the special differentiated movement necessary to the gratification of the desire can be thrown individually into action, and thus a de- finite act of volition is, for the first time, fairly accomplished. Voluntary control is first established over those movements which are also most easily called into play by reflex stimula- tion. A child can voluntarily grasp with its fist long before it can raise its hand to its mouth, or put out its hand to lay hold of anything. Tbis is parallel with the fact that the hand can be made to close reflexly over any object placed in the palm, long before the same action can be performgd voluntarily. And it is curious and interesting to observe in a child, how, in the growth of volition, the first action fairly differentiated in response to any particular sensation or desire is repeated in response to desire in general, however ludi- crously insufficient to accomplish the desired end. The individual activity of the various specially differentiated motor centres having once been fairly established, at first in response to particular sensations and desires,- voluntary acquisition proceeds apace, the centres being free to form new associations and become the means of realisation in action of all the varied simple and complex impulses of the sensory centres. The associating fibres between the one motor centre and the various sensory centres may thus become innumerable. The rate at which the organic nexuses are established between the sensory and motor centres varies according to the degree of complexity and intricacy of the movements. Com- plex and intricate movements are longer in being acquired than those which are simple, and also reflex or already here- ditarily organised. Hence the movements of articulation in combination with those of vocalisation are longer in being acquired than those of the arms or legs. GBOWTH OF VOLITION 435 In the lower animals the control and co-ordination of movements are almost complete at birth, or require little education as compared with the .prolonged helplessness of the human infant. Some birds start from the egg already fully equipped, like Athene from the head of Zeus. They are in great measure mere ' conscious automata.' They are capable of acquiring sensory experience and association of ideas, but of little further motor acquisition beyond that with which they start in life. Their cortical motor centres count for little, and may be removed without causing much disturbance of their ordinary modes of activity. Babbits require but comparatively short education to perfect their powers ; cats and dogs longer ; but cats and dogs are already advanced in life, and have assumed the cares of paternity, or rather maternity, when the human infant can scarcely lift a finger in its own behalf. In proportion as volition predominates over conscious automatism, is education necessary to perfect the powers of movement ; in the same proportion are the cortical motor centres developed ; and in that proportion are the powers of movement paralysed fey destruction of the motor centres of the hemispheres. In the rabbit conscious automatism is more marked than in the dog ; the period of education is shorter ; the faculty of further special motor acquisition is small, the cortical centres are but lowly developed ; and their removal exercises but slight and transient disturbance of their ordinary modes of action. In the dog volition enters more largely into the motor activities ; the period of education is longer ; the faculty of special motor acquisition beyond the mere power of locomotion is greater ; the cortical motor centres are more highly developed, and their removal causes greater disturbance of their motor powers, not however permanently paralysing their conscious-automaticity, but abolishing their special voluntary motor acquisitions. In man volition is predominant ; educa- tion is long and laborious ; the faculty of special motor acquisition is unlimited; the cortical motor centres reach their highest development ; and their removal causes such complete and enduring motor paralysis as to indicate that u2 436 BBAIN AND MIND automatism in and by itself is scarcely detachable from the centres of consciousness and volition. § 8. Man is not merely a passive or receptive organism capable of perceiving and registering impressions made on his organs of sense, but also an active, or executive, organism possessing organs of the most varied and complex motor achievements. In the same manner as the sensory centres are the organs of special sensory perception and the organic basis of the memory of sensory impressions, so the motor cen- tres of the cortex, besides being the organs of differentiated movements, are the organic basis of motor acquisitions. But while the activity of the sensory centres reveals itself subjec- tively in consciousness as ideation or feeling, the activity of the motor centres has no subjective side apart from the func- tioning of the sensory centres, with which they are associated. Modifications of consciousness are correlated exclusively with the functioning of the sensory centres of the cortex. We have therefore in the cortex centres of sensation and centres of motion, centres of sensory and centres of motor ac- quisition or registration, an organic sensory and an organic motor memory ; but whereas we have sensory ideation in and by itself, we have no ideas of movement apart from the sensory centres through which alone the activity of the motor centres is revealed in consciousness. The motor activities called into play by definite feelings and sensations, present or revived, constitute volitional move- ments, and the organic cohesion formed between the sensory and motor centres, persistently enduring in these centres, is the physical basis of our intellectual and volitional acquisitions in all their manifold range and complexity. The motor centres and motor faculties, besides furnishing the conditions and possibilities of multiple and varied voluntary movements, and the organic registration of these as motor or mechanical ac- quisitions, enormously widen the field of sensory experience and complicate its results. By the movements of the head and eyes we greatly extend the scope and complicate the facts of visual sensation, and by the movements of the limbs the range of tactile experience is increased a thousandfold. There are few obiects of cognition known to us only by IDEATION 437 passive sensory characters or impressions. The vast majority- involve the activity both of our sensory and motor faculties, and our ideas are a mixed revival both of movements and sensations in their respective coherent associations. This is exemplified in the acquisition and constitution of ideas of form, shape, weight, resistance, and the like. Our ideas of form are not mere revived optical impressions, which are properly limited to colour (except perhaps in so far as the object viewed does not subtend a visual angle larger than can be included easily within the punctum centrale retinae), but optical impressions combined with ideal ocular movements. Our idea of a circle is a combination of an ideal coloured outline with an ideal circular sweep of the eyeballs, or, it may be, of the tactile impressions coinciding with an ideal circumduction of the arm or hand, or perhaps both these factors combined. The same elements enter into all varieties of form or shape of which we are capable of forming an idea. Our ideas of distance, weight, resistance, all involve not merely sensory factors, but these combined with muscular movements. To revive any of these ideas is to revive both the sensory and motor elements of their composition, and we tend in ideation to repeat the actual movements which were concerned in the primary act of cognition. Ideas, therefore, except in so far as they are simple revivals of definite and uncomplicated sensory impressions, have no circumscribed habitation in the brain, but are the re-excitation of each and every one of the sensory and motor centres which are specially concerned in their acquisition. We know an orange by certain discrimi- nated impressions made on the organs of sight, smell, taste, touch, and by certain muscular movements and sensations- which give the form ; and the re-presentation or idea of an orange is the associated re-excitation of the permanent cell- modifications, in each of the special sensory and motor centres primarily engaged in the act of cognition. There is practically no limit to the number of associated combinations of sensory and motor elements, Sensory centres form organic associations with other sensory centres ; motor centres with motor centres ; sensory centres, simple and in complex association, with simple or complex associations of 438 BBAIN AND MIND motor centres. In this variety and complexity of permanent modifications, and organic cohesions between the sensory and motor centres of the hemispheres, we have the basis of all intellectual and volitional acquisitions. Each motor centre may enter into organic association with each and every sensory centre, each definite association being the representative of some consciously discriminated act. In the variety of asso- ciations between movements and sensations, some are loosely, some more firmly coherent ; while one sensori-motor associa- tion is so constant as to give rise to the notion that the con- nection is indissoluble. This is the association between muscular movement and muscular sense, one in normal con- ditions so constant as to lead Bain to suppose that the latter is the inseparable concomitant of the motor impulse. I have endeavoured to show that the connection, though constant, is not inseparable ; a distinction by no means a matter of hyper- critical refinement, but a fundamental one, and one carrying with it the most important physiological as well as psycho- logical issues. The sensations accompanying muscular action being re- peated as often as the muscular action itself, the organic nexus between the motor and tactile centres becomes so welded that this sensori-motor cohesion enters, like a compound chemical radical, as a simple factor, into every association which motor centres can form with other motor centres, and with sensory centres in general. Hence, in all volitional movements, the tactile sensory centres invariably functionate along with the motor centres, and give the extent and degree of the movement actually or ideally carried out. Bain would make the sensory a proprium of the motor, whereas it is only a contingent ; in normal or physiological conditions an inseparable accident, but separable anatomically and pathologically. § 9. In respect to the development of the volitional control of the movements the conclusion has been reached that this is established when an organic cohesion has been welded between a consciously discriminated sensation or feeling and a definite and differentiated motor act. The volitional control of the individual movements having once been estab- lished, the work of education advances, and the conditions of CONFLICT OF MOTIVES 439 volitional action become more and more complex. The voli- tion of the untutored and inexperienced infant is of a more or less impulsive character, and is conditioned mainly by impres- sions or feelings of the moment. Associations have not yet been found between the painful and pleasurable remote con- sequences of actions. Experientia docet. A child which has acquired the differentiated control of its limbs is impelled to touch and handle whatever strongly attracts its sight. The sight of a brigbt flame, like that of any other bright object, stimulates a desire to touch and handle it. This is followed by severe pain, and an association is formed between touching a certain brilliant object and severe suffering. The vivid memory of pain experienced on a former occasion is sufficient to counteract the impulse to touch when the child is again placed in similar circumstances. Here we have a simple case of the conflict of motives, and the inhibition or neutralisation of one motive by another and stronger. Action, if it results at all, is conditioned by the stronger. Similarly a hungry dog is impelled by the sight of food to seize and eat. Should the present gratification bring with it as a consequence the severe pain of a whipping, when certain articles of food have been seized, an association is formed between eating certain food and severe bodily pain ; so that on a future occasion the memory of pain arises simultaneously with the desire to gratify hunger, and, in proportion to the vividness of the memory of pain, the impulse of appetite is neutralised and counteracted. The dog is said to have learnt to curb its appetite. As experience increases, the associations between acts and consequences increase in complexity. Both by personal expe- rience, as well as by the observed experience and testimony of others, associations are established between actions and their remote consequences as pleasures or pains, and it is found that present gratification may bring a future and greater pain, and actions causing present pain may bring a greater pleasure. As the great law of life is vivere convenienter naturce — to secure pleasure and avoid pain in the highest and most general sense, and not for the moment only (a law which cannot be transgressed with impunity) — actions are conditioned no longer, as in the infant or untutored animal, by present desires 440 BEAIN AND MIND or feelings alone, but by present desires modified by the ideally revived feelings of pleasure or pain near and remote, which experience has associated with definite actions. The motive to action is thus the resultant of a complex system of forces ; the more complex, the wider the experience, and the more numerous the associations formed between actions and their consequences, near and remote. Actions so conditioned are regarded as mature or deliberate, in contradistinction to im- pulsive volitions, but the difference is not in kind but only in degree of complexity ; for in the end, actions conditioned by the resultant of a complex system of associations, are of essen- tially the same character as those conditioned by the simple stimulus of a present feeling or desire, where no other asso- ciations have a3 yet been formed capable of modifying it. But what is normal in the infant or untutored animal may be positive insanity on the part of the educated adult. If in him actions are conditioned merely by present feelings or desires, irrespective of, or in spite of, the associations formed by experience between such acts and their consequences as pains, there is a reversion to the infantile type of volition ; the only difference being that in the one case no opposing associations have as yet been formed, while in the other, though formed, they prove of no avail. An individual who so acts, acts irrationally ; and if in anyone, notwithstanding the opposing influence of past associations, a present feeling or desire reaches such a pitch of intensity as to overbalance these associations, the individual is said to act in spite of himself, or, metaphorically, against his will. Such tendencies occur more or less in all, but they are exemplified more especially in certain forms of insanity, in which the individual becomes the victim of some morbid desire, and is impelled irresistibly, and to his horror, to commit some act fraught with dreadful consequences. In the process of volitional acquisition the cohesions are chiefly formed between sensations and right-sided movements, so that the organic nexuses are established principally between the sensory centres and the motor centres of the left hemi- sphere, by which the movements of the right side are effected and governed. ACQUISITION OF SPEECS 441 § 10. The growth of volition, the formation of permanent motor acquisitions, and the establishment of organic cohesions between the sensory and motor centres of the cerebral hemi- spheres are well illustrated in the acquisition of articulate speech. Commencing with spontaneous vocalisation and spontaneous movements of the articulatory apparatus, and encouraged and aided by imitative repetitions on the part of its teacher, the infant gradually acquires the power of asso- ciating a certain sound with a certain articulation, so that on the given sound the appropriate movements of the articulating and vocalising apparatus are called into play to reproduce it. An organic nexus becomes firmly established between the auditory and the articulating centres, and such nexuses become multiplied indefinitely, each articulate sound being represented by a definite sensori-motor cohesion — sound-arti- culation. A further development of sensori-motor acquisition is the gradual establishment of links of association between certain visible characters and certain articulations, and this in such a manner that a certain visible symbol is recognised as the equivalent of a certain auditory impression, so that either can call up the proper articulation with definiteness and precision. Here the articulatory or motor element is the central ' point of two sensory cohesions — the one auditory, the other visual — which two are regarded as equivalent. In the case of the blind a similar cohesion may be formed between certain tactile impressions and the centres of articu- lation, so that at a definite tactual impression, as well as at a definite auditory impression, a definite articulate combination is called forth ; and in the case of the deaf articulate speech is capable of being taught by means of the aid of vision directed to the movements of articulation. The articulate speech of the deaf fails only in respect of intonation and modulation, owing to the want of the guiding influence of the sense of hearing. A still further stride in complexity is the acquisition of the power to represent, by movements of the fingers, symbols which, when seen, call up by association certain sounds and articulations. 442 BBAIN AND MIND Organic nexuses thus become established between the centres of hearing and articulation, between those of sight and articulation, or between those of touch and articulation ; and complex nexuses between the centres of sight and sound, and the motor centres of articulation and manual movements. These organic nexuses correspond to the acquisitions of spoken and written language, and the art of writing. It is conceivable that all these simple and complex acquisi- tions and cohesions might be formed without any association having been established between certain articulate sounds or written symbols and certain objects or ideas ; or, in other words, both spoken and written language might be acquired altogether apart from things signified. For the connection between words and things signified is nothing more than an association, words in themselves being only symbols. The association of articulate sounds with things signified is, how- ever, generally preceded by, and proceeds pari passu with, the growth of the faculty of speech ; so that the cohesion between the centres of hearing and articulation is rendered complex by the association of definite articulate sounds with certain objects seen, heard, touched, smelt, or tasted, or with objects of cognition in general. Hence the articulation may be called into play not merely by a certain sound, but by the actual presentation or re-presen- tation of the object signified. The centres of articulation become, therefore, the central motor point of an immense number of sensory cohesions, all of which tend to evoke the articulation, and which, in turn, tend to be revived in idea by the actual or ideal articulation itself. The articulation is the essential fact, vocalisation being subordinate, and capable of being dispensed with altogether, as in whisper speech. The primary associations in the acquisition of articulate speech being between sounds and articulations, as in spoken language, or between visible signs and articulations, as in written language, and between both these and things signified —directly in the former, and indirectly in the latter — secondary associations may be formed between visible signs and things signified, the link through articulation becoming subordinate, if not entirely dispensed with. A sound readily ACQUISITION OF SPEECH 443 calls up the thing signified, without the intervention of an articulation. It is, however, less common for a visible symbol to call up the thing signified without the intervention of articulation more or less suppressed. In the great majority of people there is observable a tendency during reading to translate the written symbols into their equivalent articula- tions. The less educated the person, and the less accustomed to reading, the greater is the tendency exhibited ; and some persons cannot read intelligently without actually going through all the process of articulation represented by the written or printed characters. §11. If the motor centres of the cerebral hemispheres are not merely the centres of impulse, but also the centres of registration and reproduction of volitional movements, it must follow that destruction of the motor centres will cause not merely paralysis of volitional movement, but also abolish all previous motor acquisitions. If an individual should by education acquire the faculty of expressing his thoughts by symbolic dextral movements, the destruction of the manual motor centres of the left hemi- sphere will cause not only paralysis of the right hand, but also annihilate in ideation the association between thoughts and dextral movements. Such an individual, like the blind deaf- mute Laura Bridgman, would be rendered not merely hemi- plegic, but aphasic by destruction of the manual motor centres of the left hemisphere. For the registration and revival of volitional movements must take place in the same centres as are primarily engaged and educated. Hence the memory and revivability of volitional movements must, as far as relates to the hand and arm, be principally in the left hemisphere, see- ing that voluntary motor action and motor acquisition are in the great majority of people effected on the right side. The motor centres of articulation present certain pecu- liarities both in their physiological and psychological aspects. Physiologically, as I have experimentally shown, each centre has a bilateral action. Hence destruction of the centre of articulation in the one hemisphere does cause paralysis of the articulatory apparatus, but only, if anything, a slight weak- ness or paresis of the opposite Bide. But while as regards the 444 BBAIN AND MIND mere physiological excitation of the muscles of articulation there seems to be little or no difference between the centres of articulation in the right and left hemisphere respectively, there is a marked difference, as shown by the facts of aphasia, between the two as regards the initiation and registration of the acts of articulation. § 12. In the disorders of speech resulting from cerebral disease classed under the terms aphasia and amnesia many of the principles above laid down in respect to the functions of the sensory and motor centres are strikingly exemplified. The subject of aphasia ' is deprived of the faculty of articu- late speech, and also very generally of the faculty of expressing his thoughts in writing, while he continues intelligently to comprehend the meaning of words spoken to him, or, it may be, to appreciate the meaning of written language. An aphasic individual knows perfectly well — as exhibited by his gestures— if a thing is called by its right name or not, but he cannot utter the word himself or write it when it is suggested to him. In his attempts, only an automatic or interjectional expression or some unintelligible jargon escapes his lips, or unmeaning scrawls are set down on paper as writing. This affection is usually, at first at least, associated with a greater or less degree of right hemiplegia, but the motor' affection of the right side, chiefly of the right arm, is often slight and transient, or may be wanting from the first, the only indication of motor paralysis being a paretic or weak condition of the oral muscles of the right side. The inability to speak is not due to paralysis of the muscles of articulation, for these are set in action and employed for purposes of mastication and deglutition by the aphasic in- dividual. It is only when the centres of articulation are destroyed on both sides that complete paralysis of the articu- latory apparatus occurs as well as aphasia. 2 The cause of this affection was shown by Broca — and his observations have been confirmed by thousands of other cases —to be associated with disease in the region of the posterior 1 By the term in this signification is meant aphasia proper — Broea's or motor aphasia. 2 See case reported by Barlow, Brit. Med. Journ., 1877. APHASIA 445 extremity of the third left frontal convolution, where it abuts on the fissure of Sylvius, and overlaps the island of Eeil ; a region which I have shown corresponds with the situation of the motor centres of articulation in the monkey (see fig. 70, (9) and (io)). 1 1 I do not consider it necessary, in the present state of clinical medicine and pathology, to enter at length into eases and arguments in favour of the definite localisation of the lesion causing aphasia. I take it as established beyond all possibility of doubt that lesions in the region indicated above do in the over- whelming majority of instances cause aphasia, and the problem before us is to explain why such lesions should cause aphasia and leave other faculties intact. It is utterly beside the point to argue that loss of speech is not in all cases due to localised disease of this nature, for naturally whatever causes paralysis of the muscles of articulation will cause inability to speak ; and whatever interrupts the processes of ideation and thought, such as sudden shocks of emotion or the like, will also cause inability to speak. Such states cannot properly be classed under the head of aphasia, where we have a definite condition of loss of speech, while all other faculties— sensation, emotion, thought, and volition— remain practically unimpaired. In reference to the arguments of the opponents of localisation, if such still exist, I would quote with the fullest concurrence the following passage from Dr. Broadbent, written in 1872, which the observations of the intervening years only serve to corroborate and confirm : ' The question being one of primary interest in cerebral physiology, I have examined all the apparently exceptional cases of which I have been able to find the published record ; and it is remarkable how large a proportion of them break down under careful scrutiny. Setting aside the distinction between the conditions to which the terms amnesia and aphasia have been applied, I have found, described under the head of aphasia, cases of labio- glosso-pharyngeal paralysis on the one hand, and of dementia on the other ; and, again, the speechlessness or indistinct articulation of patients who have never fully recovered from the shock of an apoplectic or convulsive attack, or of embolism of a large cerebral artery. Cases are quoted as examples of aphasia without disease of the left third frontal convolution in which the left middle cerebral artery, the nutrient vessel of the part, was blocked up ; in which, therefore, the persistence of speech would have constituted a graver objection to the views in question than its loss; or in which, without apparent dissase of the surface grey matter, the convolution was cut off from the central ganglia and the rest of the cerebrum by lesion of its white fibres ; in some instances again aphasia has been fugitive, and therefore dependent on some temporary condition ; and yet the cases have been considered exceptional because no permanent lesion has been found after death. On the other hand, cases have been described as examples of disease of the left third frontal gyrus without affection of speech, in which the description of the lesion clearly shows that the observer has taken some other convolution for the one named ' (' Mechanism of Thought and Speech,' Medico-Ghirurgical Transactions, vol. Iv. 1872). See also Kussmaul's monograph, ' Die Storungen der Sprache,' Ziemssen's Cyclo- ptzdia, 1877. 446 BBAIN AND MIND One of the most common causes of the affection is soften- ing of this region, consequent on sudden stoppage of the cir- culation by embolic plugging of the arterial channels which convey its blood-supply, by -which the functional activity of the part is temporarily or permanently suspended. Owing to the proximity and common vascular supply of the motor centres of the hand and facial muscles, it is easy to see how they also become implicated in the lesion of the centres of articulation, and why, therefore, dextral and facial motor paralysis should so commonly occur along with aphasia. This may be taken as evidence in proof of the fact that lesions of the cortical motor centres cause motor paralysis on the opposite side. The escape of the articulatory muscles from paralysis in unilateral lesion of the centres of articulation is accounted for by the bilateral influence of each centre which has been experimentally demonstrated. The loss of speech from destruction of the centres of articu- lation is not more difficult of explanation on the principles laid down in this chapter than the loss of sight presentatively or re-presentatively from destruction of the visual centre. That which constitutes the apparent difficulty is the explana- tion of speechlessness without motor paralysis from lesion of the centres of articulation in the left hemisphere. This difficulty is explicable on the principles laid down in reference to motor acquisitions in general. As the right side of the body is more especially concerned in volitional motor acts, so the education is principally in the motor centres of the left hemisphere, and these centres are more especially the organic basis of motor acquisitions. The left articulatory centres, as has been argued by more than one observer, pre- ponderate over the right in the initiation of motor acts of articulation. They are, therefore, more especially the organic basis of the memory of articulations and of their revival. The destruction of the left articulatory centres removes the motor limb of the cohesions which have been formed by long educa- cation between the centres of hearing and sight, and between the centres of ideation in general. Sounds actual or revived fail to excite the appropriate APHASIA 447 articulations. The individual is speechless, the motor part of the sensori-motor cohesion, sound-articulation, being broken. The sight of written symbols also fails to reproduce the equi- valent articulatory action. The individual is speechless because the motor element of the sensori-motor cohesion, sight-articulation, is broken. Ideally revived sights, sounds, touches, tastes, smells, fail to call up the symbolic articulations ; hence the individual can- not express his ideas in language : and in so far as language or internal speech is necessary to complex trains of thought, in that proportion is thought impaired. Thought, however, may be carried on without language, but it is thought in particulars, and is as cumbrous and limited as mathematical calculations without algebraical symbols. Thought, as has been observed by Bain, is in a great measure carried on by internal speech, i.e. through the ideal or faint re-excitation of the articulatory processes which are symbolic of ideas. This is shown by the unconsciously executed movements of the lips and tongue which all persons exhibit more or less, and some so obviously that the unconscious processes rise almost to the point of whispering. So also the blind deaf-mute Laura Bridgman, whose language was symbolic movements of the fingers, during thought or when dreaming, unconsciously executed the same movements as she was accustomed to make in the actual ex- ercise of her manual speech. And just as ideas tend to excite their symbolic representa- tions in articulation or in manual movements, so does the revival of the articulatory or manual movements tend by asso- ciation to call up the other limbs of the cohesions, whether simple sights, sounds, tastes, smells, or their combinations. The importance of this connection between the articulating centres and the centres of ideation in general will be shown more fully in reference to the voluntary revival of ideas and control of ideation. § 13. We have seen that a person aphasic from destruction of his speech centre (as we may for shortness caU the articu- latory motor centres of the left hemisphere) still remains capable of appreciating the meaning of words uttered in his hearing. In this respect he does not (and there is no reason 448 BRAIN AND MIND why he should) differ from a normal individual. His centres of sight, hearing, &c being unimpaired, he is as capable as before of visual, auditory, tactile, gustatory, and olfactory ideation. The difference consists in the fact that in the aphasic individual the word spoken, though it calls up the idea or meaning, cannot evoke the word itself, owing to the centres of word-execution and word-registration being de- stroyed. The appreciation of the meaning of spoken words is readily accounted for by the fact that in the process of educa- tion an association is formed directly between certain sounds and certain objects of sense, simultaneously with, if not ante- cedent to, the formation of the cohesive association between these sounds and certain acts of articulation. The cohesion or association between sound and meaning remains unimpaired in aphasia : it is the cohesion between sound and articulation which is broken by removal of the motor factor of the organic nexus. The association between written symbols and things signi- fied is, however, secondary to the associations formed between sounds and things signified, and between sounds and articula- tions, for speech precedes the art of writing. In the first in- stance, when an individual is learning to read, written symbols are translated into articulations and revived sounds before they call up the things signified. This translation occurs in all at first, and continues apparent in those persons not much accustomed to reading, for they only understand by articu- lating in a more or less suppressed manner all the while. Just as an individual in learning a foreign language is at first obliged to translate the words into his vernacular before he reaches the meaning, but comes by familiarity and practice to associate the new words with their meaning directly without the aid of the vernacular, and even to think in the new lan- guage, so it is possible that, by long experience in reading, a direct association may be established between written symbols and things signified, without the mediation of articulation. In such a case a person who has his speech centre disorganised will still be able to comprehend the meaning of written language. A person, on the other hand, who has not esta- blished the direct association between written symbols and APHASIA 449 things signified, and is still obliged to translate through articulation, will, by destruction of his speech centre, fail to comprehend written language, though he may still understand spoken language. In learning to write a new association has to be grafted on to the association already formed between sounds and articu- lations. The new cohesion is between sounds and certain symbolic manual movements guided by sight, which symbolic tracings are the equivalents of certain acts of articulation. In the first instance this association between sounds, or sounds and things signified, and manual movements, takes place through the mediation of the centres of articulation ; for the sounds or ideas are first reproduced actually or internally by articulations before their equivalence in written symbols is established and recognised. By education, and practice in expressing ideas in written symbols, a direct association becomes established between ideas and symbolic manual movements, without the interven- tion of articulation ; and in proportion as the translation through articulation is dispensed with, in that proportion will an individual continue able to write who is aphasic from disease of his speech centre. In the great majority of cases of aphasia met with in hospitals the direct association be- tween ideas, or articulate sounds, and manual equivalents of articulations has not been established, except for very simple and constantly repeated acts of writing, such as signing one's name ; and hence, as the intervention of articulation is still necessary before ideas can be expressed in writing, destruction of the speech centre causes not merely aphasia, but also agraphia, or loss of written language. To these considerations must be added the fact that in a large proportion of the cases of aphasia the manual motor centres are also more or less damaged, so that agraphia may be in part due to the direct impairment of the associations formed between ideas and certain highly specialised manual movements. Examples of all these different conditions are to be met with among aphasics. Some can neither speak nor write; some can write, but cannot speak ; some can write their names, but cannot write anything else ; all can comprehend spoken G G 450 BEAIN AND MIND language ; many can comprehend written language ; others not at all, or very imperfectly. Between the normal condition of the speech centre and its total destruction many intermediate abnormal conditions occur, which show themselves in partial disorders of speech, inco-ordinate or defective. It is a com- mon observation that persons lose from their vocabulary proper names and substantives more readily than words expressing the relations and qualities of objects and ideas. This leads to more or less cumbrous periphrases in order to express what would otherwise be summed up concisely in a single word. These and other similar defects are readily explicable, as Kussmaul has correctly indicated, 1 on the principle that the more loose the cohesion between objects or ideas and names, the more readily do such words fall out of the vocabulary by any conditions which tend to the impairment or dissolution of the centres of word execution and registration. The more concrete the object, the less do we require a symbol wherewith to remember and think it. We can think of individuals and objects apart from their names, so that, as the association of such objects of ideation with words is but slight, it is the first to give way. The abstract qualities and relations of objects, however, exist only by reason of words, and therefore the association of such ideas with words is a fundamental one, and the last to give way before any dissolving lesion of the word centres. Hence the terms expressing qualities and relations are retained more vividly and persistently than those expressing mere particulars or concretes. Similarly the initial letter of a word is more persistent in memory than the rest of the word, and we can often remember how the wor*d begins, and of how many syllables it is composed, without being able to recall the word itself. So we are able frequently to remember where a passage occurs in a book when we have entirely forgotten and are unable to recall the passage itself or the statements it contains. § 14. The speech centre is, as has been stated, in the great majority of instances situated in the left hemisphere. But there is no reason, beyond education and heredity, 2 why this 1 ' Die Storungen der Spraohe,' p. 164, Ziemssen's Cyclopcedia, 1877. 2 Why dextral pre-eminence should occur in the first instance is not quite APHASIA 451 should necessarily be so. It is quite conceivable that the articulating centres of tbe right hemisphere should be edu- cated in a similar manner. A person who has lost the use of his right hand may by education and practice acquire with his left all the cunning of his right. In such a case the manual motor centres of the right hemisphere become the centres of motor acquisitions similar to those of the left. As regards the articulating centres, the rule seems to be that they are educated, and become the organic seat of volitional acquisitions on the same side as the manual centres. Hence, as most people are right-handed, the education of the centres of voli- tional movements takes place in the left hemisphere. This is borne out in a striking manner by the occurrence of cases of aphasia with left hemiplegia in left-handed people. Several cases of this kind have now been put on record. 1 These cases more than counterbalance any exception to the rule that the articulating centres are educated on the same side as the manual motor centres. The rule need not be regarded as absolute, and we may admit exceptions without invalidating a single conclusion respecting the pathology of aphasia as above laid down. An interesting case has been reported by Wadham 2 of aphasia with left hemiplegia occur- ring in a young man belonging to a family of gauchers. Yet this person had learnt to write with his right hand, so that as regards speech he was right-brained, but as regards writing he was left-brained. Though the left articulatory centre is the one commonly and specially educated in speech, it is quite conceivable that a person who has become aphasic by reason of total and per- manent destruction of the left speech centre may re-acquire the faculty of speech by education of the right articulatory centres. To a certain extent they have undergone education along with those of the left through associated action, regis- satisfactorily made out. See on this W. Ogle, 'On Dextral Pre-eminence,' Med.-Chir. Trans., 1871, p. 279. 1 Vide Mongie, Be I'Aphasie, These, 1866 ; Eussell, Medical Times and Gazette, 1874 ; and other cases by Pye-Smith, Hughlings-Jackson, W. Ogle, quoted by Kussmaul, op. cit. p. 147. Notes of a similar case were also com- municated to me by Dr. Lauder Brunton. 2 St. George's Hosp. Reports, vol. iv. Q G 2 452 BBAIN AND MIND tering automatically, as Hughlings Jackson puts it, the voli- tional acts of the left. This automatic may be educated into volitional power, though at -the age at which aphasia usually occurs, there is less capacity and plasticity in the nerve centres for forming new cohesions and associations. The rapid re- covery which so frequently occurs in cases of aphasia, especi- ally of the kind due to embolic plugging of the nutrient arteries of the left centres, Is not to be regarded as an indication of the education of the right centres, but rather of the re-estab- lishment of the circulation and nutrition in parts only tempo- rarily rendered functionless. But there are other cases which would seem to show that recovery of speech may take place after a lesion which has caused complete and permanent destruction of the left speech centre. A case which seems to me to be of this nature has been reported by Drs. Batty Tuke and Fraser (' Journal of Mental Science,' April 1872), who, however, have adduced it as an instance opposed to the localisation of a speech centre^ which in one sense — i.e. as against absolute unilateral localisa- tion — it certainly is. The case in essentials is that of a female patient who was rendered unconscious by the occurrence of cerebral haemorrhage. On her recovery she was found totally speechless, and she remained so for an indefinite period. In process of time, however, the faculty of speech was restored in great measure, though never quite perfectly. ' During the whole period of her residence two peculiarities in her speech were observed — a thickness of articulation resembling that of general paralysis, and a hesitancy when about to name any- thing, the latter increasing very much some months previous to her death. ' The thickness seemed apparently due 1 to slight immobility of the upper lip when speaking, but there was no paralysis when the lip was voluntarily compressed against its fellow. The inaction of the upper lip was observed by all. ' The hesitancy was most marked when she came to a noun, the hiatus varying in duration according to the un- commonness of the word. Latterly she could not recall even the commonest terms, and periphrases or gestures were used to indicate her meaning. She was always relieved and pleased APHASIA 453 if the words were given her, when she invariably repeated them. For example, she would say, "Give me a glass of " If asked if it was "water?" she said, "No." "Wine?" "No.' "Whisky ? " " Yes, whisky." Never did she hesitate to articu- late the word when she heard it.' Death occurred fifteen years after the seizure, and it was found post mortem that there was total destruction and loss of substance in the cortical region in the left hemisphere corresponding with the position of the centres of articulation. This seems to me one of the clearest cases of reacquisition of the faculty of speech by education of the articulating centres of the right side. That speech was lost in the first instance is in harmony with the usual effect of lesion of the left speech centre. Education of the right side had not become quite perfect even after fifteen years, and that peculiar hesitancy, and the fact, which the authors themselves have specially noted in italics, that speech often required the aid of sugges- tion, is in accordance with the less volitional and greater automatic power of the right hemisphere. § 15. Intimately related with, and very frequently com- plicating, motor aphasia, as above defined, are a series of disorders of speech dependent on lesions of the sensory centres and tracts by and through which impressions are perceived and associated with definite acts of articulation. These dis- orders are classed under the head of amnesia or sensory aphasia. We have seen that a person speechless by reason of destruction of his articulatory centre alone is still capable 1 of comprehending the meaning of spoken language, and also, to a greater or less extent, of written language,, though he cannot name anything, or make any utterance beyond an automatic or interjectional expression altogether irrelevant. With this is usually associated some degree of agraphia, though aphasia and agraphia do not necessarily run parallel to each other. In the class of disorders of language now under considera- tion, of which two chief groups or divisions are recognised, the individuals can both speak and write, often with re- markable fluency. In the one group the individuals cannot comprehend spoken language, or repeat what is said in 454 EBAIN AND MIND their hearing, while they can readily articulate written language ; in the other group they are unahle to interpret written language, or even what they themselves have written, while they readily understand what is said to them, or can write from dictation. Occasionally the two conditions are more or less intermingled, or complicated with aphasia proper. The inability to understand written language has been termed by Kussmaul ' ' word -blindness ' (ccecitas rerbalis), and the inability to understand spoken language, ' word-deafness ' (surditas verbalis) . Word-blindness, which in its different .degrees is an im- pairment or complete interruption of the association formed between written symbols and their equivalent articulations, and with things signified, has been found, in the comparatively few cases as yet investigated post mortem, to be associated with lesion more particularly of the angular gyrus of the left hemisphere. 2 This, as we have seen, is a fundamental portion of the visual centre. • The condition is not dependent on defective vision (though sometimes complicated with hemiopia), for the individuals affected can see minute objects and can copy writing or designs ; nor is it dependent on defective visual ideation in general, for objects and their uses are recognised, though occasionally visual ideation is impaired. Thus mistakes are sometimes made as to the value oi coins, and objects are used for purposes for which they are unfitted ; as, for instance, a fork instead of a spoon to eat soup. The essential, and frequently the only, defect is the in- ability to read, or interpret the meaning of written or printed characters. From the fugacious character of partial and unilateral lesions of the visual centres, as above exemplified, it is easy to account for the absence of any evident impairment of visual perception in the ' word-blind ' ; and the bilateral relations of the eyes, and the associated action of the hemispheres, will 1 Op. cit. See also an excellent memoir, De la CSciti et la Surdity des Mots dans I'Aphasie, by Nadine Skwortzoff. Paris, 1881. 2 See Broadbent's case, Med.-Chir. Trans. 1872. Dejerine's case, reported by Skwortzoff, op. cit. WORD-BLINDNESS 455 suffice to account for the retention of visual ideation in general, even though considerable damage should be inflicted on the visual centre of one hemisphere. The facts relating to word-blindness show that the asso- ciation of written symbols with things signified is a function more particularly of the visual centre of the left hemisphere, the same in which the centre of articulation is developed for purposes of speech. The association of written symbols with things signified is, as has been before remarked, secondary to the association between things signified and acts of articulation, for speech precedes the act of writing. Written symbols are merely, as Hughlings Jackson 1 aptly terms them, ' symbols of symbols of images.' The association between visible symbols and things signified is therefore an indirect and comparatively loose one. Being so, it is an association which gives way sooner before a destructive or dissolving 2 lesion of the centres of vision than the more fundamental functions of visual per- ception and concrete visual ideation. There are degrees of word-blindness, just as there are degrees of aphasia proper. Certain written symbols, like certain words, persist longer than others, or are less readily lost. An individual word-blind to all other words may still recognise his name at sight. His own name is more funda- mentally organised in his visual centres than any other visual symbol. A word-blind may also recognise and pronounce the individual letters of words, while the words themselves are absolutely unintelligible and unpronounceable. Usually the word-blind can neither recognise the meaning of the words directly nor can he make the equivalent articulations, and so reach the meaning indirectly. In one remarkable case on record, 3 however, a patient gifted with unusually vivid powers of visual memory and ideation, suddenly, from some undeter- mined condition, lost his powers in this respect, so that all 1 ' On Affections of Speech from Disease of the Brain,' Brain, vols. i. and ii. 1878-1880. 2 See Hughlings-Jackson's brilliant and suggestive Croonian Lectures on ' Evolution and Dissolution of the Nervous System,' Brit. Med. Joum. 1884. 3 Under the care of Charcot, reported by Bernard, Progress Midical, 1883, p. 568. 456 BRAIN AND MIND things, even his own person, seemed strange and unfamiliar to him. Though visual symbols were of themselves unintel- ligible, he was able to articulate them, and was thus able to comprehend their meaning indirectly through articulation and the revived sounds. A word-blind can speak and express his ideas in writing, or write from dictation; but, though it may seem almost incredible, he cannot read or understand a syllable of what he has just written. But, like the blind man, he may learn to read what he has written, and written characters in general, by the aid of his sense of touch and 'the sensations accompany- ing muscular movements. Several examples of this are on record. Westphal ' relates the case of a word-blind re-acquir- ing the art of reading by passing his fingers over the letters, just as if he were rewriting them, and spelling them out as he went on. In a similar case Magnan 2 taught the patient to recognise and read raised letters by the sense of touch. Considerable progress was made, but at best only one letter — • the letter — was recognised directly by sight alone. In another case, related by Charcot, 3 the individual arrived at the meaning of words which he was unable to read by making symbolic writing movements while fixing his eyes on the page. He could read written characters more readily than printed ones, as he was naturally more familiar with the sensations which would be associated with the act of writing than of drawing printed letters. It is evident, therefore, that in word-blindness we have a defect in visual ideation only, while ideation otherwise is Unaffected ; and this defect is clearly proved to be in relation with lesion of the visual centre and its connections with the centres of articulation. We have reason to believe, from the facts of experiment as well as those of clinical observation, 4 that complete destruction 1 Quoted by Kussmaul, op. cit. p. 180, from Zeitsch.f. Ethnologie, 1874. ° Skwortzoff, op. cit. obs. vii. p. 44. 8 ' Dea differentes Formes de l'Aphasie,' Progris Medical, 1883, p. 441. 1 A case is reported by Shaw (Archives of Medicine, Feb. 1882) in which the angular gyrus and superior temporo- sphenoidal convolution (centres of vision and hearing) were destroyed symmetrically in both hemispheres; The tVOBD-DEAFNESS 457 of the visual centre in both hemispheres would abolish visual perception and visual ideation altogether. This condition would profoundly diminish the scope of human intelligence ; but even in such case, if congenital, and with deaf-mutism superadded, as illustrated by Laura Bridgman, a considerable degree of intelligence might be manifested through the agency of the remaining sensory centres. § 16. ' Word-deafness,' which in its different degrees is a defect or complete interruption in the association of articulate sounds with acts of articulation and things signified, has been found to depend on lesions involving the superior temporo- sphenoidal convolution ' (specially of the left hemisphere) which, as we have seen from the experiments above recorded (Chapter IX. § 15) is the auditory centre. The word-deaf is not deaf to sounds, for he can hear the ticking of a watch ; nor to music, for he can recognise and hum an air ; but articulate sounds, except, perhaps, his own name, or the simplest command which he is accustomed to act on automa- tically, 2 have no meaning, and cannot be repeated. Yet the individual so affected can speak and, it may be, read and write. The s'peech of the word-deaf is, however, though not always, often of a very extraordinary and unintelligible character. Though he may speak fluently, and with lively gesture and intonation, his utterances are frequently mere jargon — words mixed up without regard to grammar or sense — and convey to others none of the meaning which he evidently attaches to them. In all persons except deaf-mutes the centres of articulation patient was both blind and deaf, and at the same time utterly demented and incoherent. 1 Wernicke's case, Der aphatische Symptomencomplex, 1874 ; Broadbent's case, a case of amnesia, Med.-Chir. Trans, vol. lxi. 1878 ; D'Heilly and Chante- messe's case, Progris Medical, No. 2, 1883 ; Seppili (Bevist. Speriment. di Freniat, vol. x. 1884) finds that of seventeen cases in all, in which a post- mortem examination was made, in every one there was lesion of the superior temporo-sphenoidal convolution, and twelve in which also the second or middle convolution was involved. 2 This I observed in a case under my own care. The patient, without any leading gestures, understood and acted on the simple commands, ' Stand up ! ' ' Sit down ! ' and the like, but all complex sentences were apparently utterly unintelligible. 458 BRAIN AND MIND are set in action in response to, and are guided mainly by, articulate sounds. Deaf-mutes articulate and phonate guided by the sense of vision and the sensations which accompany the acts of articulation and phonation. Though, therefore, it is possible that the processes of articulation in connection with ideation may be set in action, and be guided correctly by the sensations accompanying the movements of articulation, altogether apart from the sense of hearing, yet as in all persons not deaf-mutes acts of articula- tion are primarily made in response to, and with a view to reproduce, certain symbolic sounds, it is natural to expect that defect in the registration and ideal revival of the sounds associated with acts of articulation should lead to disorders of utterance. Of these the individual, owing to his defective auditory register, is either not aware at all, or he may have some dim consciousness that he has not used the proper word to express his meaning. It is, however, theoretically possible that such patients might be taught to speak correctly in tr^e same way as deaf-mutes are taught lip-speech, viz. by the aid of vision and the muscular sense. Of those affected with word^deafness some are able to read intelligently, others apparently not at all or very imperfectly. The differences will be found to depend on whether direct associations have been established, or not, between visual symbols and things signified. In the former case the written or printed characters will call up the meaning directly without the mediation of the centres of articulation and sounds. If, however, articulation more or less suppressed and the associated actual or ideal revival of the equivalent symbolic sounds should be necessary, as it undoubtedly is in the large majority, in order to arrive at the thing signified by the written characters, it is obvious that in such cases word-deafness must lead to alexia, or inability to read, according to the degree in which the translation of written symbols into their equivalent sounds is necessary. My own patient, unable to understand spoken language, read and answered simple questions put to him on a slate which he carried for the purpose. But I satisfied myself that he only very imperfectly comprehended the sense of a paragraph in the newspaper which I placed WOBD-DEAFNESS 459 before him. He read and re-read, and after some time, during which he made the remark, ' It loses my head,' he gave me a very imperfect account of the subject matter. It would seem at first sight very unlikely that a word-deaf individual, whose words are a disconnected jumble, should be able nevertheless to write correctly. Yet that such is possible is shown by Magnan's ' case, nor is this difficult to explain. Whereas, owing to the defect of auditory registration, the word spoken vanishes, and if wrong cannot be rectified, litem scripta manet and serves, through the visual sense, as a guide to the appropriate combination and composition. In those cases of word-deafness in which all connected writing, beyond mere letters or scrawls, seems impossible, we may assume that, just as in regard to reading, internal speech and the revival of the symbolic sounds are necessary before images or ideas can be expressed in written symbols. Hence as the ideal revival of the equivalent sounds is impossible or imperfect, so also must be the expression of ideation in writing. Language is associated more particularly with the centres of visual and auditory perception and ideation. Next in importance to these comes the sense of touch, and we can name some things very readily by touch alone without the aid of sight or hearing. The blind man reads by touch. Certain tactile symbols are recognised as the equivalents of certain articulate sounds, and, in time, more or less directly as the equivalents of certain images or objects of ideation. Just as an individual becomes word-blind from lesion of his centres of visual ideation, so a blind man who has learnt to read by touch should become ' word-anaesthetic ' by lesion of his centres of tactile perception and ideation (the falciform lobe). We should thus have an anaesthesia or apselaphesia verbalis, parallel with a ccecitas and surditas verbalis. It is conceivable in like manner that we might have an anosmia verbalis and an ageusia verbalis, an inability to associate things smelt or tasted with their symbolic articulations. Usually 1 See Skwortzoff, op. cit. obs. vii. ' Ne sachant nommer aucun objet, ne ■prononcant que des mots . isolis ou des phrases dicousues, il pouvait oependant bien lire et ecrire facilement sans faire une faute.' 4G0 BBAIN AND MIND things smelt and tasted are objects also of visual perception and ideation, but it is possible that, vision and other senses apart, the mere smell or taste should evoke the symbolic articulation as readily as any of the other sensory characters of the object. It is therefore extremely probable that lesion of the centres of olfactory and gustatory perception and ideation in the left hemisphere may produce verbal anosmia or ageusia. I am not aware that as yet any such cases have been observed. But if so, such facts would indicate lesion of the centres them- selves, rather than of the tracts which convey to them impres- sions conditioned by odorous or sapid stimuli. § 17. It has been assumed by several writers, among others by Hughlings Jackson, 1 that in addition to the sensory and motor substrata, which have been demonstrated and denned by physiological and clinical research, there are other and higher motor as well as sensory centres in which all the motor and sensory functions are again represented, and form the substrata of the higher mental operations. This hypothesis receives no confirmation from the facts of experiment, nor does it appear to me at all necessary to explain the facts either of normal or abnormal ' mentation.' "We have in the sensory and motor centres of the cortex the substrata of the respective forms of sensory perception and ideation, and of the individual acts of volition, simple and compound, as well as of the feelings associated with their activity. It seems more reason- able to suppose that there may be higher and lower degrees of complexity or evolution in the same centres than to assume the separate existence of more highly evolved centres, for which no evidence is obtained by the results of experimental research. In the sensory and motor centres, experimentally denned, we have the elements of the simple and compound cognitions and acts of volition. But while feelings, present or revived, tend to excite action in a purely reflex manner, and ideas excite ideas along the lines of association embraced generally under the heads of contiguity and similarity, there is implied in all the higher mental operations, such as abstraction, deliberation, constructive association, and the 1 'Evolution and Dissolution of the Nervous System,' Brit. Med. Journ. 1884. CONTBOL OF IDEATION 401 like, a power of controlling the current of feeling and ideation, and of concentrating consciousness on one object, or one particular class of ideas or objects, to the exclusion of all others. The control of ideation and the power of attention form the basis of all those intellectual achievements not included in mere receptiveness, ideational or emotional mobility, and the facility of executing delicate and complex motor acts. These powers are in their nature truly voluntary, and depend essentially, as has been clearly recognised by Bain and Wundt, on volitional movements. We have, however, no direct control over the current of ideation, any more than we have the power of calling up a sensation at will. But as we may indirectly call up sensations by adapted voluntary movements, so in- directly we may react upon our ideational centres by making the movements with which certain ideas or feelings cohere. By imitating the physical expression of emotions we may succeed in inducing the corresponding mental states. We cannot feign a painful emotion without making the appropriate facial expression, and still less maintain it if we assume the opposite expression. We cannot feign grief with a smiling countenance. Though there are limits to our powers in this respect, and in some much narrower than in others, yet we can considerably modify the current of ideation and feeling by making volitional movements of an opposite character to those which the feelings we are endeavouring to combat naturally excite, or such movements as will bring us in relation with a new set of impressions, calculated to overwhelm or neutralise the feeling or idea which we seek to banish from our minds. The physical embodiment of emotions, and the special charac- teristics of each, are well known and universally recognised. Less apparent, but none the less real, are the muscular move- ments associated with ideation or thought removed as far as possible from mere feeling. Through these ' thought-reading ' may be, and is, daily accomplished to a greater or less extent by every keen observer of human beings. ' It is not obvious at first sight that the retention of an idea in the mind is operated by voluntary muscles. Which movements are operating when I am cogitating a circle or recollecting St. Paul's ? There can be no answer given to this 462 BBAIN AND MIND unless on the assumption that the mental, or revived, image occupies the same place in the brain and other parts of the system as the original sensation did. .. . . Now, there being a muscular element in our sensations, especially of the higher senses — touch, hearing, and sight — this element must somehow or other have a place in the after remembrance or idea. The ideal circle is a restoring of those currents that would prompt the sweep of the eye round a real circle ; the difference lies in the last stage, or in stopping short of the actual movement performed by the organ. We can direct the currents necessary for keeping an imagined circle in view by the same kind of impetus as is required to look at a diagram in Euclid.' 1 In calling up an idea, therefore, we are in reality making in a more or less suppressed manner the movements with which the ideas are respectively associated in organic cohesion. And just as sensory impressions or ideas tend to call up movements, so the excitation of movements tends to call up by associa- tion the various sensory factors with which these particular movements cohere. The excitation of the motor centres, not sufficient to diffuse itself in actual movement, expends its force internally along the lines of organic cohesion, and the various factors which have become coherent with any particular movement rise into consciousness. As the tugging at a plant with branching roots sends a vibratile thrill to the remotest radicle, so the tension of the motor centre keeps in a state of conscious thrill the ideational centres organically coherent therewith. The intervention of volitional movements in icteation is most apparent in the case of concrete ideation ; such as when we think of a particular object possessing form and extension, our notions of which have been largely gained by the sensations accompany- ing ocular and manual movements. So also when we are recall- ing qualities of taste and smell, in the acquisition of which certain special movements are called into play. The muscular element in the recall of ideas of sound and colour, and of the abstract relations and qualities of objects in general, is at first sight obscure ; but when we remember that thought is in a large measure internal speech, and that the abstract relations and 1 Bain, The Emotions and the Will, 1875, p. 370. ATTENTION 463 qualities of objects are inseparably bound up with words, -we can readily see that we may call up the images symbolised in words, however abstract they may be, by making the articu- latory movements in which we have symbolised them. We recall the image or idea by pronouncing its name in a more or less suppressed manner ; a fact which is plainly evident to all who pay attention to their own ideational processes. § 18. Ideas excited peripherally, arising spontaneously, or recalled voluntarily, tend to flow along the lines of associa- tion by contiguity or similarity. The current may flow on uninterruptedly as in a reverie or a dream, or it may be suddenly checked or diverted by an impression from without, which vividly engages our attention. Attention so excited is purely passive, and the concentration of consciousness is pro- portional to the intensity of the stimulus. But just as we can at will fix our gaze on some one object out of many appealing to our sense of vision, and see this clearly while all others are indistinct or invisible, so we can fix our intellectual gaze, or concentrate our consciousness, on some one idea or class of ideas to the exclusion of all others in the field of intellectual vision. This is a purely volitional act, and its exercise is accompanied by a distinct feeling of exertion, and ultimately fatigue if continued. The physical expression of rapt attention is that of intent gaze, with the eyes accommodated for near or distant objects, and associated with such movements of the head as serve to bring the object on the punctum centrale of the retina. These facts indicate that intellectual attention is essentially ideal vision, and that when we are engaged in attentive ideation we are making precisely the same movements of the head and eyes as are necessary for clear actual vision. Though many individuals when engaged in deep thought close their eyelids in order to keep out distracting images, the eyes themselves maintain the position of actual gaze, near or distant, according to the nature and position of the ideal object. When we think of a large or distant object the eyes are divergent or parallel ; when we think of a small or near object the optic axes converge. Apart from the passive or reflex concentration of conscious- 464 BRAIN AND MIND ness conditioned by the intensity of the spontaneously revived or actual sensation, we cannot voluntarily concentrate attention on any idea which we cannot represent visually, either in its own characters, source, or relations. Thus sounds which have no direct visual characters can — actual reproduction apart — be thought of only indirectly by picturing the source, the in- strument, or the circumstances under which we have actually heard them. When the ideal object is held in the field of clear vision by the appropriate ocular movements, the natural laws of association, combined with our power of controlling the current of ideation through articulatory and other move- ments, enable us to follow the idea in all its relations and ramifications. If intellectual attention is mainly ideal vision it must follow that the faculty of attention, with all that it implies in the sphere of intellectual operations, must be intimately related to the volitional control of the head and eyes in association with the centres of visual perception and ideation. Just #,s the initiation, or partial excitation, of any particular move- ment reacts back upon the sensory cohesions with which it is associated, so the movements of the head and eyes react back on the centres of vision and keep the ideal object in the field of clear consciousness, and through this recall its various sensory and motor associations. It is not essential that the object revived in idea should be so clearly revived in the visual field as the actual object itself. There are great differences in this respect among different individuals, 1 and there is no relation between the vividness of the mental imagery and the faculty of attention and abstract thought. It is, in fact, more conducive to abstract thought that the visual images should not have concrete sharpness, but rather the character of symbols or counters, which are more mobile and manageable than the images themselves with all their details filled in. Expectant attention greatly reduces the time otherwise requisite for the completion of the mental processes intervening 1 See the valuable and interesting observations on this head by Francis Galton, Inquiries into Human Faculty and its Development, 1883 ; Mental Imagery, pp. 83 et seq. SUBSTBATA OF ATTENTION 465 between the reception of an impression and the appropriate act of volition it should call forth. Picturing the situation, we are able to place the organs of sensation in the most favourable position for the reception of the impression, and we already half-perform — by throwing the muscles into a state of tension — the muscular act which is to signalise the completion of the mental process itself. § 19. The reactions consequent on electrical stimulation of the angular gyrus and superior temporo-sphenoidal convolution are evidently of the character of reflex movements, indicative of attention directed towards the supposed origin of the visual and auditory sensations aroused subjectively by the stimulus. That the reactions in question are in this case merely reflex or associated movements is shown by the fact that destruction of these regions, unilaterally or bilaterally, causes no impair- ment of the movements of the head and eyes. 1 The motor centres of the head and eyes are — some certainly, while others are less clearly idefmed — situated in the frontal lobes. Destruction of the frontal lobes, according to the degree of its completeness, impairs or paralyses the lateral movements of the head and eyes. Though some ocular movements may be excited reflexly by retinal impressions, there appears to be loss of the power of looking at, or directing the gaze towards, objects which do not* fall spontaneously within the field of vision. Correlative with this immobility of the head and eyes there is the aspect of uninterest and stupidity, the absence of that active curiosity which is normally manifested by monkeys, and the mental degradation which seems to depend on the loss of the faculty of attention and all that it implies in the sphere of intellectual operations. The symptoms of lesions and disease of the frontal lobes in man, though not sufficient to establish any positive physiological functional relationships, are, however, in accord- ance with the negative character of experimental lesions, 1 Though ptosis has been described by Grasset (Localisations dans Us Maladies C&ribrales, 1880), and by Landouzy (' Blepharoptose Cerebrale,' Archives Gin. de Mid. 1877) apparently in causal relationship with lesions of the angular gyrus in man, we cannot admit any direct causal relationship in face of the total absence of ptosis in cases of experimental destruction of the angular gyrus in monkeys. H H 466 BBAIN AND MIND unilateral or bilateral, so far as relates to the sensory and motor faculties * in general. But several cases have been re- corded in which there has been marked intellectual deficiency and instability of character, not unlike those observed in monkeys and dogs. A comparative study of the relative development of the frontal lobes in different orders of animals renders it abun- dantly evident that they reach their highest development in man. And the investigations of Huschke, 2 Eudolph Wagner, 3 &c, show that in different races, and in different individuals of the same race, there are great differences in the development of the frontal lobes — a greater development characterising those possessed of the highest mental powers. In this relation Wagner remarks : ' Among the convolutions of different individuals there are remarkable differences, so that one may distinguish richly convoluted and poorly convo- luted brains. These relate only to more numerous divisions and to bendings, &c. of the primary convolutions, which retain the same number and essential position in all normal brains of whatever race. The most notable differences occur in the convolution of the frontal lobes. There are to be found brains of adults which in this respect resemble the brain of a seven months' foetus, of which it may truly be said that in their outward configuration at least they have remained in a foetal condition. This slighter development of the frontal convolu- tions occurs more especially in the female brain, so that it may be said that they resemble in this respect the festal brain in its later stages of development before the complete evolution of the frontal lobes. There are to be found also male brains with the same characters, which may therefore be characterised as belonging to the female type ; and female brains which in their richness of convolution approach the male type. As a rule, however, the convolutions and sulci are better developed 1 See the author's Localisation of Cerebral Disease, 1878 ; Charcot et Pitres, 'Localisations dans l'Ecorce des Hemisph.' Revue Mensuelle, 1877-78; De Boyer, Lisions Corticales, 1879. 2 Sch&del, Him, und Seele, 1854. ' Morphologic und Physiologic des menschlichen Gehirns als Seelenorgan, 1860-1862. SUBSTRATA OF ATTENTION 467 in all the lobes when the frontal convolutions are specially complex.' l We have therefore many grounds for believing that the frontal lobes, the cortical centres for the head and ocular movements, with their associated sensory centres, form the substrata of those psychical processes which lie at the founda- tion of the higher intellectual operations. It would, however, be absurd to speak of a special seat of intelligence or intellect in the brain. Intelligence and will have no local habitation distinct from the sensory and motor substrata of the cortex generally. There are centres for special forms of sensation and ideation, and centres for special motor activities and ac- quisitions, in response to and in association with the activity of sensory centres ; and these in their respective cohesions, actions, and interactions form the substrata of mental opera- tions in all their aspects and all their range. We have not yet found, nor are we likely to discover, any simple formula to express the relation between brain and mind. It is not a mere matter of brute weight or quantity, absolute or relative ; though there is no doubt that in animals of the same order a brain below a certain standard of weight is incompatible with normal intelligence. Nor is it merely a matter of quality, by which is meant relative fineness of texture, activity of metabolism, &c. ; though such conditions must have an important influence. There may be highly developed sensory centres and defective sensory apparatus, and highly developed motor centres and defective executive apparatus— conditions which must materially influence men- tal development. But other things being equal— if such a postulate can ever be reasonably made — there are grounds for believing that a high development of certain regions will be found associated with special faculties of which the regions in question are the essential basis. We have seen that in osmatic animals, or those possessed of extraordinary faculties of smell, there is a relatively enormous development of the hippocampal lobule, the cortical centre of smell. There can be little doubt that a relatively high development of the visual centres will 1 Die typischen Verscfoiedenheiten der Windungen der Hemispharen u. d. die Lehre vom Hirngewicht, 1860, p. 89. h h 2 468 BBAIN AND MIND be associated with special faculties in the domain of visual sensation and ideation; and similarly in the case of the centres of hearing, touch, and the other sensory faculties. So we may assume that a high development of special cortical motor centres will be found associated with special motor capacities and powers of acquisition. Special gifts and aptitudes are not, however, incompatible with imbecility or even idiocy. Intelligence and mental power, as a whole, will, however, largely depend on the relative balance or development of one part as compared with another. If, as we have seen reason to conclude, the motor centres are not merely the basis ■of sensori-motor cohesions and acquisitions, but also the basis of the powers of concentration and control of ideation, we should expect a relatively high development of the motor centres as compared with the sensory centres in those animals and individuals capable of the highest intellectual achieve- ments. That such a relation will be found to exist is more than probable, but on this point and many others, in the absence of rigidly determined data, I forbear further to spe- culate. 469 CHAPTEE Xm. CEREBRAL AND CRANIO- CEREBRAL TOPOGRAPHY. § 1. In the foregoing chapters, numerous clinical and pathological facts have been adduced, tending to establish the physiological homology of the brain of man with that of the ape, both generally and in respect to individual anatomically homologous parts. The object of this chapter is to trace these anatomical and physiological homologies in greater detail, and to indicate the relations which subsist between the cerebral convolutions and the surface of the cranium. In addition to the pathological evidence of the existence of differentiated motor centres in the human brain, supplied by the observations of Hughlings Jackson and others, we have experimental confirmation of the same in the investigations of Bartholow ' and Sciamanna. 2 Bartholow found, in the case of a patient whose brain was laid bare by cancerous ulceration, that the insertion of needle electrodes, in connection with an induction coil, into the grey matter of the hemisphere in the region of the postero-parietal lobe (fig. 126, p,), caused convul- sive movements of the opposite arm and leg ; facts which bear out the results of electrical irritation of this region in the brain of the monkey (fig. 69, l), which, as has been shown (Chapter VIII.), causes movements of the opposite leg and foot. The results obtained by Bartholow were, however, somewhat complex, owing to the method and the state of the patient not 1 'Experimental Investigations into the Functions of the Human Brain,' Amer. Journ. Med. Sciences, April 1874. 2 ' Gli Avversari delle Localizzationi cerebrali,' Arch, di Psichiatria e Sciense penali, 1882. 470 CEREBRAL TOPOGRAPHY being consistent with the conditions of exact localisation of the stimulus. Sciamanna, in a case of trephining for fracture of the right parietal bone, applied the electrical stimulus of the faradic, and also the galvanic, current to the surface of the dura mater covering certain regions, denned more accurately post mortem. The results thus obtained, though obviously wanting in accu- racy, were such as to indicate the existence of centres similar to those defined in the brain of the monkey. Irritation about the middle of the ascending frontal convolution caused action of the masseter muscles. Irritation of the lower third of the ascending parietal convolution caused action of the angle of the mouth and elevation of the ala of the nose and upper lip on the opposite side. Irritation somewhat posterior, in the region of the intraparietal sulcus, caused extension of the left hand, specially of the first three fingers, together with flexion of the forearm and elevation of the eyebrows. Irritation above the junction of the supramarginal lobule, with the superior temporo-sphenoidal convolution caused rotation of the head to the left, movements of the orbicularis palpebrarum, elevation of the eyebrows, and slight movements of protrusion and retraction of the tongue. Notwithstanding the unavoidably diffuse character of the irritation, it is not difficult to discover effects very similar to those resulting from stimulation of areas 8, 9, 10, a, n, 13, and 14, in the brain of the monkey (compare fig. 70, Chapter VIII. with description) . We have thus experimental as well as clinical proof that in the human brain electrical irritation of the region corre- sponding to the motor zone of the monkey produces similar motor reactions on the opposite side of the body. § 2. The brain of man is constructed on the same type as that of the monkey, and essentially the same primary fissures and convolutions are recognisable in both : — the chief differences consisting in the greater complexity of the convolu- tional arrangement of the human brain, caused by the develop- ment of numerous secondary and tertiary gyri, which tend to obscure the simple type of the simian brain. These differences are very marked in the adult and highly developed brain, but are less pronounced in that of the foetus. HOMOLOGIES OF HUMAN AND SIMIAN BRAIN 471 The topography, homologies, and nomenclature of the cere- bral convolutions have been investigated by many anatomists. The nomenclature is not altogether uniform. In the following description I have principally followed that of Ecker," which with certain differences, which are indicated, agrees in the main with that of Huxley, Turner, and English anatomists and pathologists. § 3. Of the primary fissures or sulci the fissure of Sylvius (fig. 126, s) is easily recognised, and the corresponding fissure, (fig. 127, a) in the brain of the monkey evident. The fissure of Sylvius divides into two rami, the posterior or horizontal (s') and the ascending or anterior (s"). The portion included between these two branches sometimes receives the name of the operculum (Klappdeckel), and forms the roof of th e island of Beil. The fissure of Rolando (c) or central sulcus~~coTcre~ sponds in position and direction with b (fig. 127) in the brain of the monkey. The parieto-occipital fissure (fig. 126, p o) corresponds to c (fig. 127) in the brain of the monkey. § 4. The frontal lobe (fig. 126, f), including the region situated in advance of the fissure of Eolando (c), is divided by secondary fissures into the following convolutions : — F lf the superior frontal convolution ; f 2 , the middle frontal convolution ; f 3 the inferior or third frontal convolution. The sulci, which separate these convolutions from each other, are termed respectively the supero-frontal (fig. 126, /,) and infero-frontal (/ 2 ) . The sulci sf and if in the brain of the monkey (fig. 127) were considered by Gratiolet to be homo- logous with/,, and/ 2 respectively, and the convolutions f„ f.-, f 3 homologous with the superior, middle, and inferior frontal convolutions of the human brain. But the investigations of Bischoff have rendered this more than doubtful, and shown that with the exception of the anthropoid apes, which possess a more or less distinct ascending ramus of the fissure of Sylvius, and a rudimentary inferior frontal convolution, monkeys in j general cannot be said to have a third or inferior frontal con- volution. Hence f, and f 2 would together form the homo- 1 ' logue of the superior frontal (f,), and f 3 would be homologous ' The Convolutions of the Human Brain (Galton), 1873. 472 CEBEBBAL TOPOGBAPHY really with the second or middle frontal convolution (fig. 126, f 2 ). . The three frontal convolutions terminate posteriorly m a convolution which forms the anterior boundary of the fissure of Rolando, termed the anterior central, ascending frontal Pig. 126. — Lateral View of the Human Brain (Ecker). — F, frontal lobe. P, parietal lobe, o, occipital lobe, t, temporo-sphenoidal lobe, s, fissure of Sylvius, s', hori- zontal ; s", ascending ramus of the same, c, sulcus centralis, or fissure of Rolando. A, anterior central convolution, or ascending frontal. B, posterior central convolu- tion, or ascending parietal. f„ superior ; p a , middle ; F 3 , inferior frontal convolu- tions. /,, superior ; /„, inferior frontal sulcus ; / a , buIcus prtecentralis. P„ superior parietal lobule, or postero-parietal lobule ; P 9 , inferior parietal lobule, viz. p a , gyrus Bupra-marginalis ; P B ', gyrus angularis. ip, sulcus intraparietalis. cm, termination of the calloso-marginal fissure. o„ first ; o = , second ; o s , third occipital convolu- tions, po, parie to-occipital fissure, o, sulcus occipitalis transversus ; o B , sulcus occipitalis longitudinalis inferior. t„ first ; t„ second ; T M third temporo-sphe- noidal convolutions. t u first ; t„ second temporo-sphenoidal fissures (Turner), or antero-parietal convolution (Huxley) (fig. 126, a). The continuity of the three frontal convolutions with the ascending frontal is interrupted by a sulcus termed the antero- HOMOLOGIES OF HUMAN AND SIMIAN BRAIN 473 parietal sulcus (Huxley), or sulcus pracentralis (Ecker) (fig. 126, /j) corresponding to ap (fig. 127) in the brain of the monkey. The ascending ramus of the fissure of Sylvius (s") likewise partially interrupts the continuity of the inferior frontal convolution with the ascending frontal. This ramus is regarded by Turner as the continuation of the antero-parietal sulcus ; but a direct continuity, according to Ecker, is quite an exceptional occurrence. The ascending ramus of the fissure of Sylvius is indicated distinctly only in the anthropoid apes. The inferior aspect of the frontal lobe is sometimes termed TSL Fig. 127. — Left Hemisphere of Brain of Monkey (Macaque). — a, the fissure of Sylvius. B, the fissure of Rolando, c, the parietooccipital fissure. PL, the frontal lobe. PL, the parietal lobe. OL, the occipital lobe, tsl, the temporo-sphenoidal lobe. i'\, the superior frontal convolution. F 9 , the middle frontal convolution. f.„ the inferior frontal convolution, sf, the supero-f rontal sulcus. ir\ the infero- frontal sulcus, op, the antero-parietal sulcus, ap, the ascending frontal convolu- tion, ap, the ascending parietal convolution, ppl, the postero-parietal lobule. AG, the angular gyrus, ip, the inira-parietal sulcus. T„ T a , T 3 , the superior, middle, and inferior temporo-sphenoidal convolutions. ?„ f„, the superior and inferior temporo-sphenoidal sulci, o,, o 9 , and o s , the superior, middle, and inferior occipital convolutions, o, o a , the first and second occipital fissures. the orbital lobule, from its position in reference to the roof of the orbit (see fig. 17, 2', fig. 129, f o). § 5. The parietal lobe (fig. 126, p) is bounded in front by the fissure of Eolando, behind by the parietooccipital fissure (fig. 126, p 0), and is separated from the temporo-sphenoidal lobe by the horizontal ramus of the fissure of Sylvius (fig. 126, s'). In this lobe several convolutions are differentiated. The first, which forms the posterior boundary of the fissure of 474 CEBEBBAL TOPOGBAPHT Bolando, is termed the ascending parietal convolution (Turner), postero-parietal gyrus (Huxley), or posterior central convolution (Ecker) (fig. 126, b), corresponding to a p (fig. 127) in the brain of the monkey. This convolution is bounded posteriorly by a sulcus termed the intra-parietal sulcus (fig. 126, i p, and also fig. 127). The part above the posterior extremity of the intra-parietal sulcus, and between it and the longitudinal fissure, is some- times termed the superior parietal lobule (Ecker) ; by Huxley and Turner it is termed the postero-parietal lobule, and is the superior posterior termination of the ascending parietal con- volution (fig. 126, p,), corresponding to ppl (fig. 127) in the brain of the monkey. This lobule is bounded posteriorly by the parieto-occipital fissure, which separates it from the occipital lobe. Below the intra-parietal fissure are situated a group of convolutions arching over the upper extremities of the Sylvian and superior temporo-sphenoidal fissures (fig. 126, t y ) more complex and less distinctly marked off from each other than in the brain of the monkey. • This region is termed the inferior parietal lobule (Ecker), and consists of an anterior division, arching over the upper end of the fissure of Sylvius, termed the supra-marginal lobule, or lobule du pli courbe- (Gratiolet) (fig. 126, p 2 ) ; and a posterior division, which arches over the upper end of the superior temporo-sphenoidal fissure, and becomes continuous with the middle temporo-sphenoidal con- volution (fig. 126, t 2 ) ; and is termed the pli courbe (Gratiolet), or the angular gyrus (Huxley) (fig. 126, p/). In the monkey — macaque— there is no clear differentiation of this region into a supra-marginal lobule, and an angular gyrus. The two are represented together in fig. 127, a g, the anterior inferior part of which may be regarded as the homologue of the highly developed supra-marginal lobule in the human brain. § 6. The temporo-sphenoidal lobe (fig. 126, t) lies behind and below the fissure of Sylvius, which separates it from the frontal and parietal lobes ; posteriorly it merges with the occi- pital lobe, the anterior boundary of which is formed by the parieto-occipital fissure. The temporo-sphenoidal lobe is divided by two sulci into HOMOLOGIES OF HUMAN AND SIMIAN BBAIN 475 three tiers of convolutions. One fissure which runs parallel to the horizontal ramus of the fissure of Sylvius, is termed the superior temporo-sphenoidalfissure (fig. 126, £,), or parallel fissure (Gratiolet). Between the fissure of Sylvius and the superior temporo- sphenoidal fissure lies the superior temporo-sphenoidal convolution (fig. 126, tJ, or, as it is sometimes termed, the infra-marginal gyrus. Another fissure, running parallel to the superior temporo- sphenoidal fissure, is termed the middle temporo-sphenoidal fissure (fig. 126, y . Between these two is situated the middle temporo-sphenoidal convolution (fig. 126, t 2 ). On the inferior aspect of this lobe is another fissure termed the inferior temporo-sphenoidal fissure, which forms the lower boundary of the inferior temporo-sphenoidal convolution (fig. 126, t 3 ). The corresponding regions in the brain of the monkey are indicated by the same letters (fig. 127) . § 7. The occipital lobe (fig. 126, o) is not defined anteriorly, except at the site of the parieto-occipital fissure. It fuses with the pari£tal and temporo-sphenoidal lobes by means of connecting gyri, termed by Gratiolet 'bridging convolutions,' or ' plis de passage.' Ecker objects to the use of the term 'bridging convo- lutions,' and gives special names to the convolutions on the lateral aspect of the occipital lobe, as follows : — The gyrus oc- cipitalis primus (fig. 126, o,) connects the occipital lobe with the postero-parietal lobule. It is termed by Gratiolet the pli de passage superieur externe, and pli occipital superieur, and by Huxley, the first external annectent gyrus. This convolution is separated from the next by a sulcus termed the sidcus oc- cipitalis transversus (fig. 126, o) corresponding to (o), fig. 125, in the brain of the monkey. The next convolution is termed the second occipital, or gyrus occipitalis secundus (figs. 126, 127, o ? ), or deuxieme pli de passage externe (Gratiolet), or second external annectent gyrus (Huxley). This convolution runs anteriorly into the gyrus angularis. The third occipital con- volution, or gyrus occipitalis tertius (fig. 126, o 3 ), runs parallel with the preceding, and joins the third temporo-sphenoidal convolution anteriorly. It is termed by Gratiolet the troisieme et quatrieme pli de passage externe, or pli occipital inferieur. 476 CEBEBBAL TOPOGRAPHY § 8. On the internal or mesial aspect of the hemisphere the following fissures and convolutions are differentiated. The convolution immediately bounding the corpus callosum is termed the gyrus fornicatus (fig. 128, g/), or callosal gyrus (Huxley). It commences at the frontal extremity of the brain, beneath the genu of the corpus callosum, and moulded on this terminates posteriorly, by a narrow isthmus, in the gyrus hippocampi (fig. 128, h) (Huxley's uncinate gyrus). The. hippocampal gyrus ends inferiorly in a crotchet-like o Fig. 128. — View of Median Aspect of Bight Hemisphere of Human Brain. (Ecker). — cc, corpus callosum, longitudinally divided. G/, gyrus fornicatus. H, gyrus hippocampi, h, sucus hippocampi, u, uncinate gyrus, cm, sulcus calloso- marginalis. F„ median aspect of the first frontal convolution, c, terminal portion of the sulcus centralis, or fissure of Rolando. A, anterior ; B, posterior central convolution, p', prsecuneus. oz, cuneus. po, parietooccipital fissure, o, sulcus occipitalis transversus. oc, calcarine fissure. 0c 7 , superior ; o&', inferior ramus of the same, d, gyrus descendens. r„ gyrus occipito-temporalis lateralis (lobulus fusiformis). T„ gyrus occipito-temporalis medialis (lobulus lingualis). extremity termed the uncus (fig. 128, u), a part which in some of the lower animals is much more largely developed, and termed the hippocampal lobule. The region of the uncus I have previously described specially as the subioulum cornu Ammonis; a term, however, which is sometimes applied to the gyrus hippocampi as a whole. The gyrus fornicatus and gyrus hippocampi together form Broca's falciform lobe or grand lobe limbique. HOMOLOGIES OF HUMAN AND SIMIAN BBAIN 477 Above the gyrus fornicatus, and separated from it by a fissure termed the calloso-marginal fissure (fig. 128, cm), is a convolution which forms the internal margin of the longitu- dinal fissure, and has received the name of the marginal con- volution (fig. 128, F,). It is merely the mesial or internal aspect of the convolutions of the frontal and parietal lobes. That portion which forms the mesial aspect of the ascending .frontal convolution more especially, and bounded posteriorly by the extremity of the calloso-marginal fissure, is often termed the paracentral lobule. Between the posterior extremity of the calloso-marginal salens and the parieto-occipital fissure (fig. 128, p o) is a lobule, c f FO. Fig. 129.— Internal Aspect of Eight Hemisphere of Brain of Monkey (Macaque).— 'cc the corpus callosum divided, c, the internal parietooccipital fissure, cms, the calloso-marginal fissure. Cf, the calcarine fissure, df, the dentate fissure. Gs, the collateral fissure. GF, the gyrus fornicatus. CM, the marginal convolution. Gtr, the uncinate convolution, s, the orochet, or subiculum cornu Ammonis. Q, the quadrilateral lobule, or preecuneus. z, the cuneus. ipo, the orbital lobule. of a quadrilateral form, which is the mesial aspect of the pos- tero-parietal lobule. This is termed the quadrilateral lobule, or preecuneus (fig. 128, v'). Inferiorly, it is continuous with the gyrus fornicatus, though it is to some extent separated bv a shallow fissure termed the subparietal sulcus. A similar •disposition is recognisable in the brain of the monkey (fig. 129, q, and fig. 72, sp). The fissure o c (fig. 128) , termed the calcarine fissure, marks the position internally of the calcar avis, or hippocampus minor in the posterior cornu of the lateral ventricle. The parieto-occipital fissure is seen to fuse with this at an acute 478 CEBEBBAL TOPOGRAPHY angle. The calcarine fissure is not, as in the monkey (fig. 129, Cf), continued anteriorly into the dentate fissure (fig. 128, h), or sulcus hippocampi, and, therefore, does not completely inter- rupt the superficial continuity of the gyrus fornicatus with the gyrus hippocampi. The dentate fissure marks the position of the hippocampus major, or cornu Ammonis, in the descending cornu of the lateral ventricle. In this fissure the fascia den- tata, corps godronne, or dentate gyrus, which forms a border to the hippocampus major, is situated. Fig. 130.- -Lateral View of Human Brain. The circles and letters have the same signification as those in the brain of the monkey, fig. 131. Between the parieto-occipital and calcarine fissures a wedge-shaped lobule is marked off on the mesial aspect of the occipital lobe. This is termed the cuneus (fig. 128, oz), or internal occipital lobule (Huxley) (fig. 129, z). Eunning along the internal or mesial aspect of the occipital and temporo-sphenoidal lobes is a fissure termed the collateral HOMOLOGIES OF HUMAN AND SIMIAN BRAIN 479 fissure (Huxley), or sulcus occipito-temporalis, which -separates two convolutions from each other, which connect the occipital and temporo-sphenoidal lobes with each other, and are, there- fore, termed by Ecker the occipitotemporal convolutions (fig. 129, t 4 and t 5 ). The upper of these is termed the gyrus oc- cipito-temporalis medialis, or lingual lobule (fig. 128, t 5 ). The lower, which frequently merges with the inferior tempore^ sphenoidal convolution, but at other times is marked off by a fissure, is termed the gyrus occipito-temporalis lateralis or lobulus fusiformis (fig. 128, t 4 ). A similar disposition is seen in the brain of the monkey (fig. 129), though the divisions are not so pronounced. Fhj. 131. — Left Hemisphere of Brain of Monkey (see fig. 70 with description). § 9. Within the lips of the fissure of Sylvius, and con- , cealed by the operculum, or region included between the ascend- j ing and horizontal rami of this fissure, lies the central lobe, or island of Eeil, which covers the extra-ventricular nucleus V. of the corpus striatum. Its surface is marked by certain ra- I diating short convolutions, termed the gyri breves (see fig. 7, c).J § 10. In the accompanying figures (figs. 130 — 133) I have indicated approximately the situation of the centres or areas homologous with those experimentally determined in the brain of the monkey. An exact correspondence can scarcely be supposed to exist, inasmuch as the movements of the arm and hand are more complex and differentiated than those of the monkey ; while, on the other hand, there is no- thing in man to correspond with the prehensile movements of the lower limbs and tail in the monkey. 480 CEBEBBAL TOPOGBAPHY In fig. 130 a lateral view of the left hemisphere of the human brain is given, and the same letters placed on regions approximately corresponding to those on fig. 131. In fig. 132 the upper surface of the human brain is dis- played, and the same system followed, to allow of comparison with fig. 133. For the complete details reference is made to Chapter VIII. § 2. Frp. 132.— Upper Surfaoe of Human Brain. The circles and letters have the same signification as those of Brain of Monkey, flg. 133. (1), placed on the postero-parietal lobule, indicates the position of the centres for movements of the opposite leg and foot, such as are concerned in locomotion. (2), (3), (4), placed together on the convolutions bounding the upper extremity of the fissure of Eolando, include centres HOMOLOGIES OF HUMAN AND SIMIAN BBAIN 481 for various complex movements of the arms and legs, such as are concerned in climbing, swimming, &c. (o), situated at the posterior extremity of the superior frontal convolution, at its junction with the ascending frontal, is the centre for the extension forwards of the arm and hand, as in putting forth the hand to touch something in front. (6), situated on the ascending frontal, just behind the upper end of the posterior extremity of the middle frontal* convolution, is the centre for the movements of the hand and Fig. 133. — "Upper Surface of Hemispheres of Monkey. The circles and included numerals are explained in connection with fig. ( forearm, in which the biceps is particularly engaged, viz. supi- nation of the hand and flexion of the forearm. (7) and (8), centres for the elevators and depressors of the angle of the mouth respectively. (9) and (10) , included together in one, mark the centre for the movements of the lips and tongue, as in articulation. This is the region, disease of which on the left side causes aphasia, and is generally known as Broca's convolution. (11), the centre of the platysma, retraction of the angle of the mouth. 1 1 482 CEEEBBAL TOPOGBAPHY (12) , a centre for lateral movements of the head and eyes, with elevation of the eyelids and dilatation of pupil. (a), (b), (c), (d), placed on the ascending parietal convolu- tion, indicate the centres of movement of the fingers and wrist. Circles (13) and (13'), placed on the supra-marginal lobule and angular gyrus, indicate the centre of vision, which includes also the occipital lobe. Circles (u), placed on the superior temporo-sphenoidal convolution, indicate the situation of the centre of hearing. The centre of smell is situated in the uncus gyri hippo- campi or hippocampal lobule (fig. 128, u). In close proximity, but not exactly defined as to limits, is the centre of taste. The centre of touch is situated in the hippocampal region (fig. 128, h), and gyrus fornicatus. Relations of the Convolutions to the Skull. § 11. The determination of the exact relations of the primary fissures and convolutions of the brain to the surface of the cranium is of importance to the physician and surgeon, as a guide to the localisation and estimation of the effects of diseases and injuries of the brain and its coverings, and may prove of great service in anthropological and craniological investigations. Broca's 1 method, followed by Fere, 2 Ecker, 3 &c. consists in driving pegs into the brain at certain fixed points in the sutures of the skull, and estimating the exact distance of the principal fissures from the points so marked. The principal points thus given, the further details can be filled in without great difficulty. Hefftler's 4 method consists in fixing the skull in a determinate position, and taking the projection on a transparent plate successively of the scalp, cranium, and lastly of the exposed surface of the brain. This method requires four different heads in order to obtain a complete view of the whole brain. None of these methods, however accurate — and that of 1 Revue d' Anthropologie, 1876. 2 Bull. Soc. Anat. 1875 ; Revue d' Anthropologie, 2me serie, tome iv 1 Archiv f. Anthropologie, 1878. * Ibid. CBANIO-CEBEBBAL TOPOGBAPHY 488 Hefftler seems in this respect the best — is capable of prac- tical application in the living like that of Turner. 1 Turner divided the skull into certain areas, and made accurate draw- ings of the brain underneath, after removal of the skull and portion of the dura mater corresponding to each area. The following account is founded on Turner's investiga- tions : — . ' In conducting an investigation of this kind it is in the Pig. 134. — Turner's Areas of the Human Skull.^A, the external angular process of the frontal hone, F, the frontal eminence, p, the parietal eminence, 0, the occipital protuberance, c, the coronal suture. I, the lambdoidal suture, s, the squamous suture. ?, the temporal ridge, fs. the fronto-sphenoid suture, ps, the parieto- sphenoid suture, ss, the squamoso-sphenoid suture, pm, the parieto-mastoid suture. 1, frontal line. 2, parietal line, sf, MP, rp, the supero-, mid-, and infero- frontal subdivisions of the frontal area. SAP, the supero-antero-parietal area, iap, the infero-antero-parietal area, spp, the supero-postero-parietal area, rpp, the inf ero-postero-parietal area, o, the occipital area, sq, the squamoso-temporal area. as, the ali-sphenoid area. first instance necessary to have a clear conception of certain ■well-defined landmarks, which can be seen or felt when the outer surface of the skull and head are examined. The exter- nal occipital protuberance (fig. 134, o), the parietal (p), and 1 Journ. Anat. and Phys., vols. xiii. and xiv. 1873-1874. i i 2 484 CRANIO-CEBEBBAL TOPOGBAPHJ frontal (f) eminences, and the external angular process of the frontal bone (a) are easily recognised structures, the position of which can be determined by manipulating the scalp, and still more readily on the surface of the skull itself. The coro- nal (c) and lambdoidal (Z) sutures can also be felt through the scalp in most heads, and on the skull itself, the position of the squamous (s), squamoso-sphenoid (ss), and parieto-sphe- noid sutures (ps), and the curved line of the temporal ridge (t), can also without difficulty be determined ' (Turner, op. cit.) [references inserted]. With these as fixed points the surface of the skull may be divided into ten well-defined areas or regions. The coronal suture (c) forms the posterior boundary of the frontal area. An imaginary line (fig. 134, (•■)) drawn from the squamous suture (s) vertically upwards through the parietal eminence (p) to the sagittal suture or middle line of the skull subdivides the parietal region into an antero-parietal (fig. 134, sap + iap) and a, post-parietal area (fig. 134, spp + ipp). « The occipital region, which lies between the lambdoidal suture (I) and the occipital protuberance (o) , and the superior curved line extending on each side from it, forms the occi- pital area (fig. 134, o). These four primary divisions are further subdivided. The temporal ridge (fig. 134, t), extending backwards from the external process of the frontal bone (a), across the frontal, antero-parietal, and post-parietal areas to the lateral angle of the occipital bone, divides these areas into an upper and a lower division. We have thus an upper and a lower frontal area (sFand if); an upper antero-parietal (s a p) and a lower antero-parietal area (up) ; an upper postero-parietal (spp) and a lower postero- parietal area (ipp). § 12. The boundaries of these areas are as follows : — The inferior frontal area, or, as it may also be called, the fronto- temporal area, is bounded above by the temporal ridge, below by the fronto-sphenoid suture, and behind by the coronal suture. The inferior antero-parietal area is bounded above by the temporal ridge, below by the squamous and parieto-sphe- noid sutures, in front by the coronal suture, and behind by CBANIO-CEBEBBAL TOPOGRAPHY 485 the vertical line through the parietal eminence. The inferior postero-parietal area is bounded above by the temporal ridge, in front by the parietal line above referred to, below by the posterior part of the squamous suture and by the parieto- mastoid suture. The upper frontal area, which includes all the frontal regions above the temporal ridge, is again divided into two, by a line drawn vertically upwards and backwards from above the orbit through the frontal eminence to the coronal suture (fig. 134, (i)) . This divides the upper frontal area into a supero- frontal (sf) and a mid-frontal area (mp). Hence the frontal area has three subdivisions — a supero-, infero-, and mid-frontal division. The upper antero- and postero-parietal areas are bounded below by the temporal ridge, above by the sagittal suture, and are separated from each other by the vertical line through the parietal eminence. Eight areas have thus been marked out. The ninth and tenth are more difficult to define, on account of this region of the skull being concealed by the temporal muscle. The areas alluded to are situated below the squamoso-parietal, sphe- noido-parietal, and fronto-sphenoidal sutures. The lines of the sutures naturally divide this region into a squamoso-temporal (Sq) and an ali-sphenoid area (As). § 13. These different areas being marked off, we can now proceed to consider the relation which the fissures and con- volutions have to them. 1 The fissure of Sylvius (fig. 135, s s) commences behind the posterior border of the lesser wing of the sphenoid, and courses upwards and backwards below the greater wing of the sphe- noid, where it articulates with the anterior inferior angle of the parietal bone, and then appears in the lower part of the inferior antero-parietal region. The fissure of Eolando (fig. 135, e) lies in the antero- parietal region, both in its superior and inferior divisions. It is situated at a variable distance behind the coronal suture, Turner finding its upper extremity sometimes as much as two 1 There are certain variations, as Fere has pointed out, according to sex and age, depending on differences of volume and differences in development respec- tively. These it is not considered necessary to discuss here minutely. J8G CBANIO-CEBEBBAL TOPOGBAPEY inches behind the top of the suture, and its lower end as much as an inch and a half behind the lower extremity of the same. Occasionally its upper and lower extremities are not more than 1-5 and 1-3 inch posterior to the extremities of this suture respectively. 1 It will thus be seen that the coronal suture does not correspond to the boundary between the frontal and Fig. 135. — Diagram showing the Relations of the Convolutions to the Skull (Turner). — k, the fissure of Rolando, which separates the frontal from the parietal lohe. po» the parietooccipital fissure between the parietal and occipital lobes, ss, the fissure of Sylvius, which separates the temporo-sphenoidal from the frontal and parietal lobes, sf, mf, IP, the supero-, mid-, and infero-frontal subdivisions of the frontal area of the skull ; the letters are placed on the superior, middle, and inferior frontal convolutions, sap, the supero-antero-parietal area of the skull : s is placed on the ascending parietal convolution, ap on the ascending frontal convolution, jap, the raf ero-antero-parietal area of the skull : i is placed on the ascending parietal, ap on the ascending frontal convolution, sfp, the supero-postero-parietal area of the skull : the letters are placed on the angular convolution, ipp, the infero-postero- parietal area of the skull : the letters are placed on the mid-temporo-sphenoidal convolution, x, the convolution of the parietal eminence, or supra-marginal gyrus, o, the occipital area of the skull : the letter is placed on the midioccipital convolu- tion. Sq, the squamoso-temporal region of the skull : the letters are placed on the mid-temporo-sphenoidal convolution, as, tbe ali-sphenoid region of the skull : the letters are placed on the tip of the supero-temporo-sphenoidal convolution. 1 Fere found in twenty-eight males the mean distance of the upper extremity from the coronal suture to be 48 millimetres, and of the lower extremity to be 28 millimetres ; while in fifty-four females the distances were 45 and 27 millimetres respectively. CBANIO-CEBEBBAL TOPOGBAPHY 487 parietal lobes of the brain, which, as has been stated, is formed by the fissure of Eolando. The parieto-occipital fissure is situated on the average about 0-7 to 0-8 inch in advance of the apex of the lanibdoidal suture (fig. 135, p o). Fere and Ecker make it almost exactly coincide with the lambda. § 14. Next, as regards the contents of the areas. The frontal area is entirely occupied with the frontal lobe, though it does not cover the whole of what is included under the term, inasmuch as the posterior extremities of the three longitudinal frontal convolutions, and the ascending frontal convolution, lie in the antero-parietal area. The regions included in the frontal area correspond pretty nearly to those which give no external response to electric stimulation. They are, according to the hypothesis advanced (Chapter XII. § 16), the motor substrata of the higher intellectual functions. The subdivisions of the frontal area formed by the temporal ridge, and by the perpendicular drawn from the orbit through the frontal eminence, correspond to the situation of the superior frontal (s f) , mid-frontal (m f) , and inferior frontal (i f) convolutions. § 15. The upper antero-parietal area (s a p) contains the upper two-thirds of the ascending frontal (ap) and ascending parietal (s) convolutions, and the origins of the superior and middle frontal convolutions. The former arises from the ascending frontal about 1*2 or 1-3 inch behind the coronal suture ; the latter about an inch behind the same line. At the upper posterior angle of the area part of the postero-parietal lobule is visible, and below this part of the supramarginal lobule may appear. § 16. The lower antero-parietal area (i a p) contains the lower third of the ascending parietal (i) and ascending frontal (a p) convolutions, and the posterior extremity of the lower frontal convolution (Broca's region). The lower frontal convolution arises from the ascending frontal, somewhat less than an inch behind the lower extremity of the coronal suture. At the upper posterior angle of this area a small portion of the supra- marginal gyrus is visible, and below this a small portion of the superior temporo-sphenoidal convolution comes into view. 488 CBANIO-CEBEBBAL TOPOGBAPHY These two areas contain (with the exception of part of the postero-parietal lobule) all the motor centres of the limbs, facial muscles, and mouth. The antero-parietal area, therefore, is specially the motor area of the skull. § 17. The upper postero-parietal area (fig. 135, spp) con- tains the greater part of the postero-parietal lobule. Below it lies the upper portion of the angular gyrus (s p p) and part of the supra-marginal gyrus (x). Posteriorly, what are generally termed the annectent gyri blend with the occipital lobe. § 18. The lower postero-parietal area (i p p) contains part of the supra-marginal gyrus ; behind it, part of the angular gyrus ; and, below this, the posterior or upper ends of the temporo-sphenoidal convolutions. The postero-parietal area taken as a whole, if we except the postero-parietal lobule, corresponds with sensory regions, and particularly with the centres of vision, which occupy a large extent of this area. It might be of importance, in a phreno- logical sense, to determine whether there is a relation between the development of this region with the next, and those mental faculties of which sight is the basis. § 19. The occipital area (fig. 135, o) indicates the situa- tion of the occipital lobe, though it does not entirely cover it ; inasmuch as part of the occipital lobe generally extends anteriorly beyond the lambdoidal suture into the postero- parietal area. § 20. The squamoso-temporal area (fig. 135, s q) contains the greater portion of the temporo-sphenoidal convolutions, but the superior temporo-sphenoidal convolution (the centre of hearing), though for the most part under cover of the squamoso-temporal and greater wing of the sphenoid, ascends into both the lower antero- and lower postero-parietal areas. § 21. The ali-sphenoid area (fig. 135, a s) contains the lower or anterior extremity of the temporo-sphenoidal lobe, and, therefore, corresponds to the position of the centres of smell and taste. § 22. The central lobe, or island of Eeil, does not come to the surface, but lies concealed within the fissure of Sylvius. It is situated behind the upper part of the greater wing of the CBANIO-CEBEBBAL TOPOGBAPHY 489 sphenoid, and opposite its line of articulation with the anterior inferior angle of the parietal bone and squamous portion of the temporal. The convolutions situated on the internal aspect of the hemisphere are altogether out of relation to the surface of the skull. For the guidance of the surgeon, desirous of trephining over a given cortical region, certain rules of measurement have been laid down by Broca, Pozzi, Lucas Championniere, and others. The superior and inferior extremities of the fissure of Kolando, the principal point of orientation, can be determined as follows. A perpendicular line drawn from the external auditory meatus to the middle line of the vertex indicates the position of the bregma, or point of intersection of the sagittal and biparietal sutures. The upper extremity of the fissure of Eolando lies 47 to 48 millimetres behind this point. To find the inferior extremity a horizontal line, 7 centimetres in length, is to be drawn from the external angular process of the frontal bone. A perpendicular line is to be raised on the extremity of this line 3 centimetres in height, and the extremity will in- dicate the position of the lower end of the fissure of Eolando. Eeid ' has suggested the following rules for determining the position of the principal fissures and convolutions in relation to easily felt landmarks on the skull. These are the glabella or root of the nose, the external occipital protuberance, the superior curved line of the occiput, the parietal eminence, the posterior border of the mastoid process, the depression in front of the external auditory meatus, the external angular process of the frontal bone, the frontal part of the temporal ridge, and the supra-orbital notch (fig. 136 with description). A base line, from which all perpendiculars are drawn, is supposed to run through the middle of the external auditory meatus and the inferior margin of the orbit. The longitudinal fissure between the hemispheres is indicated by a line from the glabella to the external occipital protuberance, and the transverse fissure is indicated by a line - T ~'"The Principal Fissures and Convolutions of the Cerebrum,' Lancet, 1884. 490 CBANIO-CEBEBBAL TOPOGBAPHT from this same protuberance to the external auditory meatus (fig. 136, b c). If a point is taken an inch and a quarter behind the external angular process of the frontal bone, and another three- quarters of an inch below the most prominent part of the parietal eminence, the line joining these two points will indicate the position of the fissure of Sylvius. The first three-quarters of an inch from before backwards will indicate the main fissure. From this point the ascending ramus ascends for Pig. 136.— Diagram of Cranio-Cerebral Relations (Reid).— A, glabella. E, external occipital protuberance, e, a, p y external angular process' of frontal bone, bc, transverse fissure, ab, longitudinal fissure. &y. JLs., Sylvian fissure. Sy.h.jis., horizontal limb of fissure of Sylvius. Sij. a..fi.i., ascending limb of fissure of Sylvius. DE, perpendicular line from depression in front of external auditory meatus to vertex, fg, perpendicular line from posterior margin of base of mastoid process to vertex, fh, fissure of Rolando, p, o, fis., parieto-occipital fissure. + s most prominent part of parietal eminence. about an inch. The rest of the line corresponds with the horizontal ramus (fig. 136, Sy. h.fis.). If two perpendiculars are raised from the base line to the longitudinal fissure — the one from the depression in front of the external auditory meatus, the other from the posterior border of the mastoid process — and a diagonal be drawn from the upper posterior CBANIO-CEBEBBAL TOPOGBAPHY 491 angle to the intersection of the anterior line with the fissure of Sylvius, this diagonal will represent the position of the fissure of Eolando. The parieto-'occipital fissure, somewhat variable, will be indicated approximately by the point where the prolongation of the line of the fissure of Sylvius would intersect the longitudinal fissure (fig. 136, p. o.fis.) The ascending frontal convolution will occupy a space about three-quarters of an inch broad parallel with and in Fig. 137. — Diagram of Cranio-Cerebral Relations (Eeid). +, most prominent part of parietal eminence, a, convex line forming lower boundary of parietal lobe. 1 //•. c, first frontal convolution. 1 fr. /., first frontal fissure. /. E., fissure of Eolando. Sy.f., fissure of Sylvius. Sy. h.f., horizontal limb, and Sy. a.f., ascending limb of Sylvian fissure, p. o. /., parieto-occipital Assure, i. par./., intra-parietal fissure. ang. g., angular gyrus, s. m. c, supra-marginal convolution. 1 t. s. c, first temporo-sphenoidal convolution. 1 t.p. s., first temporo-sphenoidal fissure. 1 o. c, first occipital convolution, p. p. I., postero-parietal lobule. front of the fissure of Eolando (fig. 137, /.e.). The divisions between the three frontal convolutions will be indicated by lines drawn parallel to the longitudinal fissure, from the supra- orbital notch, and along the frontal part of the temporal ridge respectively to the anterior border of the ascending frontal convolution (fig. 137). 492 CBANIfrCEBEBBAL TOPOGBAPHY The boundary between the parietal and the occipital and temporo-sphenoidal lobes is somewhat difficult to define. It may be indicated by a curved line, with the convexity down- wards, drawn between the end of the parietd-occipital fissure and the end of the Sylvian line (fig. 137, a). The intra- parietal fissure is indicated by a line curved in the opposite direction drawn from a point half an inch external to the lower end of the parieto-occipital fissure, and in its anterior third running parallel with the fissure of Eolando, threer quarters of an inch behind it. Above this line, and between it and the fissure of Eolando, lie the postero-parietal lobule (fig. 137, p. p. I.), and the ascending parietal convolution. Below the line lies the supra-marginal lobule and portion of the angular gyrus. The supra-marginal gyrus lies under the most prominent part of the parietal eminence (fig. 137, s. m. c). The temporo-sphenoidal lobe is bounded above by the line of the fissure of Sylvius, below by the upper border of the zygoma, and by its ideal continuation to a point midway between the external occipital protuberance and the posterior border of the mastoid process. The anterior extremity of this lobe extends as far forward as the posterior superior border of the malar bone. The first or superior temporo-sphenoidal fissure is indicated by a line parallel with, and an inch below, the Sylvian line. Between these two lines lies the superior temporo-sphenoidal convolution. The second temporo-sphenoidal fissure is indicated by another line parallel with the last and about three-quarters of an inch below it. The position of the occipital lobe requires no further special definition. INDEX. ACC ACCELEEATOB nerves of heart, 99 Ageusia, 321 Agraphia, 449 • Aladoff, 107 a Alexia, 454 ,Albertoni and Michieli, 214, 231 Amblyopia, 284, 290 Amnesia, 444 Amputated limbs, faradisation of nerves of stumps of, 388 Amygdalae nucleus, 315 . Andral, 222 Angular gyrus, functions of, 276 Anosmatics, 313 Anosmia, 321 Aphasia, 444 Appetites, 431 .Arnold, W., 383 ' .Aronsohn and Sachs, 88 Articulation, centres of, 444 Associated movements, 365 Ataxy, pathology of, 143 Attention, 463 Auditory centre, the, 305 — nerve, effects of section of, 134 — vertigo, 134, 212 Auerbach, 73 Automatism and volition, 435 BAGINSKY, 132 Bain, 382, 447, 461 Balancing experiment, Ooltz's, 109 -Barlow, 359 .-Bartholow, 469 Basal ganglia, electrisation of, 264 functions of, 404 -Bastian, 380 , Bechterew, 134, 157, 164,207, 214, 267, 376, 414 'Beevor, 32, 45 • Bell, Sir Charles, 63, 105 *Bellouard, 293 CEB Bennett, A. Hughes, 360 Bernard, 64, 83, 102, 107 Besiadecki, 154 Bianchi, 295 Bilateral association of movements, 365 Bisehoff, 236 Blaschko, 302 Blood-vessels, tone of, 83 j^ Bochefontaine, 253 Bottcher, 132 Bouillaud, 222 Brain, and mind, 424 — human, electrisation of, 469 — lobes of, 471 Braun, 231 Breuer, 136, 139 Brissaud, 82, 360 Broadbent, 365, 445, 454 Broca, 313, 346, 444, 482 Brondgeest, 81 Brown-Sequard, 53, 62, 65, 206, 222, 301, 377 Bruck and Giinter, 87 Brunton, Lauder, 99, 108, 171, 392 Bubnoff, 232, 233 Budge, 79, 172 Bulbar paralysis, 94 Bulogh, 80 Burdach, columns of, 11 CAPSULE, external, 36 — internal, 35, 323, 360, 411 Carpenter, 119, 140 -Carville and Duret, 227, 229,231, 264, 367, 411 Caudate nucleus, 34 lesions of, 410 Cayrade, 159 Centrum ovale, lesions of, 359 Cerebellar tracts, direct, 9, 91, 218 Cerebellum, anatomy of, 30 494 INDEX CEE Cerebellum, atrophy of, 180, 216 development of, comparative, 200 — disease of, 179 — electrisation of, 187 _ functions of, 174 _ lesions of, general, 175 special, 184 — peduncles of, 31 peduncle inferior, functions of, 207 middle, relations of, 215 section of, 185 superior, degeneration of, 213 lesions of, 214 — relations of, auditory, 208 cerebral, 215 motor, 215 ocular, 213 sensory, 206 . visceral, 217 Cerebral hemispheres, anatomy of, 38 electrisation of, 235 excitability of, 222 excitable areas of, 239, 480 experiments of Fritsch and . Hitzig on, 223 investigation of, method of, 220 removal of in birds, 111 in fishes, 110 in frogs, 109 in mammals, 112 Cerebral topography, 469 " Championniere, L., 489 , Charcot, 61, 85, 145, 288, 456 . Christiani, 114, 172 Cilio-spinal region, 79 Clarke's vesicular column, 7 Clavate nucleus, 14 Commissure anterior, 47, 315 — inferior, 49, 138 — posterior, 34, 158 Compensation, functional, 367 Consciousness, substrata of, 120 Control of ideation, 461 Convolutions, cerebral, of dogs, 246 human and simian, 470 relations of, to skull, 482 Co-ordination of locomotion, 139 Cornu Ammonis, anatomy of, 43 lesions of, 340 Corona radiata, 38 Corpora geniculata, 28, 155, 304 Corpus callosum, 45 Corpus striatum, anatomy of, 34 disease of, 409 electrisation of, 264 experimental lesions of,410 functions of, 417 Couty, 228 ,' FLE Cranial areas, Turner's, 483 — nerves, nuclei of, 19 Cranio-cerebral topography, 483 , Crichton-Browne, Sir J., 147 Croaking experiment, Goltz's, 160 Crum-Brown, 136 Crus cerebri, 25 Cuneate nucleus, 14 Cyon, 81, 105, 107, 127, 129, 210 D ALTON, 177, 295 Danilewsky, 171 Darkschewitsch, 158 Dastre and Morat, 99, 102 Deaf-mutes, sense of dizziness in, 139 Degeneration, secondary, from cortical lesions, 353, 357 Deglutition, centre of, 93 Deiters' nucleus, 20 Dejerine, 454 Demeaux, 325 Depressor nerve, 105 Desires, 431 Dextral pre-eminence, 450 D'Heilly and Chantemesse, 457 ' Diabetes, experimental production of, 107 Dickinson, 176 Dittmar, 100 Dizziness, sense of, 139 Duchenne, 64, 94 Dupuy, 227 Duval, 23, 92 y -•-* r' .' ECKEB, 471, 482 Effort, sense of, 382 Emotion, expression of, 146 — substrata of, 430 Equilibrium, maintenance of, 121 — factors concerned in, 122 Erb, 82, 85 . Eulenburg, 253 Exner, 270, 377 I^ACE, motor centre of, 359 Falciform lobe, functions of, 344 relations of, 314 Fano, 160 Feelings, 429 Fere, 290, 482, 484 Fick, 53 Fillet, the, 27 Flechsig, 2, 18, 26, 36, 44, 326 Fletcher and Bansome, 321 - - INDEX 4-*.. r/ •Tooth, H., 58 ^'» A - ' Tripier, 362, 374 Trophic centres and nerves, 85 Trunk movements, centres of, 356 Tscheschichin, 87 Tsehiriew, 63, 81, 82 Tuke and Praser, 452 Turner, 471, 483 ^^ 7W~-u. kjtj" , Wo.- ,. . T7AGTJS, action on heart, 99 — Y Valentin, 172 -Varigny, 232, 254 Vasomotor centre, 100 — — innervation, 102 Vegas, 21 Vertigo, auditory, 134, 212 — ocular, 126 K K 498 INDEX VEB Vertigo from galvanisation of head, 196 „ Veyssiere, 324 , Vieussens, valve of, 25 Visceral innervation, 88 — nerves, 103 Visual centre, the, 270 — impressions in relation to equili- bration, 125 ^Volekers (seeHensen) Volition, 433 ^Volkmann, 123 Vomiting, mechanism of, 97 _^Vulpian, 84, 94, 95, 108, 111, 120, 129, 164, 176 WADHAM, 451 Wagner, 177,>66 YUN Waller, 79, 82 Ward, 70, 78 Watteville, de, 179 Weber, E., 62 Weir-Mitchell, 177, 204, 388 Wernicke, 45, 457 Westphal, 58, 82, 456 Wilbrand, 293 Wood, H. C, 87 Word-blindness, 454 Word-deafness, 457 Woroschiloff, 54 Writing, relation to speech, 448- -Wundt, 382, 461 -TTEO, G.F., 234, 269 1 Yung, 78