THE ASCENT OF PREHISTORIC MAN

MANS CULTURAL STAGES AND PHYSICAL DEVELOPMENT
TO THE END OF THE OLD STONE AGE

[DJAGONAL LINES INDICATE RACIAL PERIODS,
DCfT SHOWS CONJECTURED DATE OF EXTINCTION]

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PLEISTOCENE

Tht Brain from Ape to Man by Frtderick Tilney
Spff^ /5oA~ . '»4 Copyright igiS by Paul B. Hotter, Inc., N. Y.

i

PLIOCENE

">

THE BRAIN

FROM APE TO MAN

^91. /aft

THE BRAIN

FROM APE TO MAN

A CONTRIBUTION TO THE STUDY OF THE EVOLUTION
AND DEVELOPMENT OF THE HUMAN BRAIN

BY FREDERICK TILNEY, ph.d.,m.d.

Trofesstir of NeuroloRV. Columbia University

With Chapters on the Reconstruction of the Gray
Matter in the Primate Brain Stem by

HENRY ALSOP RILEY, a.m.,m.d.

Associate Professor of Neurology, Columbia University

foreword by
HENRY FAIRFIELD OSBORN, sc.d.,ll.d.

Research Professor of Zoology, Columbia University

557 illustrations, many in color
VOLUME TWO

PAUL B • HOEBER • I^c

NEW YORK ' MCMXXVIII

COPYRIGHT 1928 BY PAUL B. HOEBER, INC.
ALL RIGHTS RESERVED ' PUBLISHED MAY I928
PRINTED IN THE UNITED STATES OF AMERICA

CONTENTS

NOLLMU I

Pace

Preface vii

Foreword xv

List of Illustrations xix

Introduction. The Primates: Lemurs, Monkeys, Apes and Man, Their Place in

Nature i

Pari I. I hi. Lower Primates

Introduction 2i

Chapte k

I. Lemur Mongoz, Its Brain and Bcha%ior 23

II. Reconstruction of the Gray Matter in the Brain Stern of Lemur Mongoz . "3

III. Tarsius Spectrum, Its Brain and Behavior 85

IV. Reconstruction of tiic Gray Matter in the Brain Stem of 'I'arsius Spectrum 135
V. Caliitiirix .laichus, tile Marmoset, Its Brain and BeiKi\ior 153

VT Reconstruction of tiie Cra\ Matter in tlic Brain Stem of Caliitiirix .lacciius 183

VII. Mycetes Scniculus, Its Brain and Beiiavior lyi

VIII. Reconstruction of the Gray Matter in the Br.iin Stem of Mycetes Senicuhis 233
IX. Comparative Summary of Structures IIa\ing E\()iutionaI Significance in tiie

Brain Stems of tiie Low it Primates 243

Pari 1L Ihi. 1mi knu.diate Primates

Introduction 28-

Chaptfr

-X. Papio C>noceijiiaius, tiie CiomiiKin Dofi-I ie.ided Bal)oon, Its Brain and

I5ehavior 289

.X 1 . Reconstruction of the Gray Matter in tiie Brain Stem of Papio Cynocephaius 335

.XII. Pitliecus Rliesus, Macaeus Rhesus, Its Brain and Behavior 349

.XI 11. Riconstruction of tiie Gray Matter in tlie Brain Stem of Pillucus Rhesus 391

\i\'. I l\lolDates I looloclv, tiic Gililson, Its Brain and Behavior 405

W. Recon.struction of the Gray Matter in the Brain Stem of I lyiolxUes I Iooloci< 44-
.X\ 1. Comparative Summary of Structures Having Evolutional Significance in

the Brain Stems of the Intermediate Primates 457

V

3 C 3 3 6

vi CONTENTS

VOLUMI II
Pakt hi. The IIighi.k Amiikopoids

Pace

Introduction 477

CHAPTtK

XVIl. Siniia Satyrus, the Orang-Outang, Its Brain and Behavior 479

Will. Reeonstruction of the Gray Matter in the Brain Stem of Siniia Satyrus. . 533

XI.X. Troglodytes Niger, the Chimpanzee, Its Brain and Behavior 545

XX. Reconstruction of the Gray Matter in tiie Brain Stem of Troglodytes Niger 609

XXI. Troglodytes Gorilla, Its Brain ;md BeJKuior 623

XXII. Reconstruction of tiic Gray Matter in tiic Brain Stem of Troglodytes

Gorilla 685

.\XIII. Comparati\'e Summary of Structures lla\ing lisolutional Signilicance in

the Brain Stems of the I liglu-r Anthropoids 699

Part IV. .Man
Introdlction - 729

Chapter

XXIV. From Primitive to Modern .Man 731

XXV. The Brain of Modern Man '. . 777

XXVI. Reconstruction of the Gra\' Matter in tin- 1 luni.in Brain Stem 837

XXVII. The Brain of Prehistoric Man 861

XW'III. Man — Past, Present and Future • 925

Part V. F\oli tional Modifications of the Primate Cerebrim Cllminating

in the Human Brain

Introduction 939

ClIAPTI K

XXIX. The Significance of the Structur.il Honiogcneitv' and Specilic Modifications
in the Primate Brain. Their Relations to the Progressi\e Adaption of

Behavior 941

XX.X. The Internal Structure of the Brain Stem of the Priiuates. Its E\olutionai
Modification in Relation to tlie Dcxclopmeiit of Beha\ior. Essential
Similarities in Internal l-.lements 993

References FOR Further Reading 1047

Index to Volumes I and 1 1 1077

LIST 01- ILLUSrRATIONS

FiGUBB p^CE

1. Brains of lower vertebrates compared with the luiniaii brain 4

2. Brains of iiiammais compared with tiie human i)ra;n. 5

3. Brains of apes compared with the iuiinan brain 6

4. Comparison of skeletal structures, from iish to man 8, 9

5. Lemur group in Madagascan iiabitat 25

6. 7. Two views of Lemur mongoz 27

8-1 1. Hand and foot of Lenuir mongoz 30, 31

12-15. Hand and foot of Lemur potto 32, 33

16. Dorsal surface of brain, Lenuir mongoz 34

17. Base of brain. Lemur mongoz 35

18. Left lateral surface of brain. Lemur mongoz 36

19. Right lateral surface of brain. Lemur mongoz 37

20. Ventral surface of brain stem, Lemur mongoz 38

21. Dorsal surface of brain stem. Lemur mongoz 39

22. Lemur mongoz. Level of the pyramidal decussation 42

23. Lemur mongoz. Le\el of caudal extremit\' of inferior oli\e 46

24. 25. Lemur mongoz. Level through middle of inferior olive 48, 49

26. Lemur mongoz. Level of the vestibular complex 50

27. Lemur mongoz. Level of the cerebellar nuclei 52

28. Lemur mongoz. Le\ el of emergent fibers of sixth ner\ e 55

29. Lemur mongoz. Le\ el of caudal extremity of pons Varolii 5-^

30. Lemur mongoz. Le\ el of tiie middle of the pons Varolii 60

31. Lemur mongoz. Le\ el of emergence of trochlear ner\e 61

32. Lemur mongoz. Level of the inferior colliculus 62

33. Lemur mongoz. Level of the superior colliculus 66

34. Lemur mongoz. Level of the optic chiasm 69

35. Lemur mongoz. Level of the anterior commissure 70

36. Ventral surface of gray matter of brain stem. Lemur mongoz (color) 75

3''. Dorsal surface of gray matter of brain stem, Lemur mongoz (color) 77

38. Lateral surface of gray matter of brain stem, Lenuir mongoz (co/or) -9

39, 40. Two views of Tarsius spectrum 86

41-44. Hand and foot of Tarsius spectrum 88, 89

45. Dorsal surface of brain of Tarsius S|)cct rum 95

46. Base of brain, Tarsius spectrum 96

47. Right lateral surface of brain, Tarsius spectrum 98

48. Ventral surface of brain stem of Tarsius sjjectrum 100

49. Dorsal surface of brain -Stem of Tarsius spectrum loi

50. Tarsius spectrum. Level of the first cervical segment 102

vii

viii LIST OF ILLUSTRATIONS

Figure Pace

51. Tarsius spectrum. Level of the pyramidal decussation 104

52. Tarsius spectrum. Level of the dorsal sensory nuclei 106

53. Tarsius spectrum. Level of caudal tip of inferior olive 108

54. Tarsius spectrum. Level through middle of inferior olive 11 1

55. Tarsius spectrum. Level of the vestibular complex 114

56. Tarsius spectrum. Level of caudal extremity of trapezoid body 116

5~. Tarsius spectrum. Level of the cerebellar nuclei 118

58. Tarsius spectrum. Level of the trochlear emergence 121

59. Tarsius spectrum. Level of the inferior colliculus 123

60. Tarsius spectrum. Level of the superior colliculus 128

61. Tarsius spectrum. Level of the optic chiasm 131

62. Tarsius spectrum. Level of the anterior commissure 132

63. Ventral surface of the gray matter of the brain stem, tarsius spectrum (color) . . 137

64. Dorsal surface of the gray matter of the brain stem, tarsius spectrum (co/or) . .139

65. 66. Lateral surface of the gray matter of the brain stem, tarsius spectrum (co/or) 141, 143

67, 68. Callithrix jacchus (marmoset) 154

69-72. Hand and foot of marmoset 156, 15"

73. Dorsal surface of brain, Callithrix jacchus (marmoset) 158

74. Base of brain, Callithrix jacchus (marmoset) 159

75. Left lateral surface of brain, Callithrix jacchus (marmoset) 160

76. Right lateral surface of brain, Callithrix jacchus (marmoset) 161

7~. Ventral surface of brain stem, Callithrix jacchus (marmoset) 162

78. Dorsal surface of brain stem, Callithrix jacchus (marmoset) 163

79. Marmoset. Level of the pyramidal decussation 165

80. Marmoset. Level of the dorsal sensory nuclei 166

81. Marmoset. Level of the tip of the inferior oli\e 167

82. Marmoset. Lc\el tlirough the middle of till' inl'ciior oli\-e 169

83. Marmoset. Level of the vestibular niick'I and tiiliorculum acusticum i-o

84. Marmoset. Level of the cerebellar nuclei 171

85. Marmoset. Le\el :it the middle of the j^ons Varolii 173

86. Marmoset. Level of the inferior colliculus 174

87. Marmoset. Level of the superior cerebellar peduncular decussation 176

88. Marmoset. Level of the superior colliculus 178

89. Marmoset. Level of the optic chiasm 180

90. Marmoset. Level of the anterior commissure 181

91. Ventral surface of the gray mattiT of the brain stem, Callithrix jacchus (color). . 185

92. Dorsal surface of the gray matter of the brain stem, Callithrix jacchus (color) .187

93. Liiteral surface of the gray matter of tlu- brain stem, Callithrix jacchus (color) . . 189

94. Habitat group of Mycetes senlculus, the rcti howling monkey 192

95. 96. Two views of Mycetes seniculus, showing prehensile tail I93

97,98. Two views of Mycetes seniculus, the red howling monkey 194

99. Habitat group of Ateles atcr, the spider monkey I95

100. Ateles atcr, the spider monke\, showing prehensile tail. 196

LIST Of II IIJSTRATIONS ix

Figure Paci;

01-104. ll;iiul aiul loot ol Mycctcs scniculus 198, 199

05-108. Hand and loot of s]jidcr monkey 200, 201

09, no. Distal extremities of preliensilc tails, Mycetes seniculus and Ateles ater. . , 203

11. Dorsal surfaee of brain, Mycetcs senieulus 204

12. Base of brain. M\cetes senieulus 205

13. Left lateral surfaee of brain, Mycetcs senieulus 206

14. i^iglit lateral surfaee of brain, Mycetcs senieulus 20~

15. Ventral surface of brain stem, M\cetes senieulus 208

16. Dorsal surface of brain stem, .Mycetcs senieulus 209

i~. Mycetcs senieulus. Level of the pyramidal ticcussation 211

18. Mycetcs scniculus. Le\el ol the caudal c\trcmit\ ol the inferior olive 215

19. Mycetes senieulus. Level through the middle of the inferior olive 2i~

20. iMycctes senieulus. Level of the nucleus ambiguus 218

21. Mycetcs scniculus. Le\ el of the cerebellar nuclei 220

22. Mycetcs scniculus. Lc\cl of the vestibular nuclei 221

23. Mvcetes scniculus. Level ol emergence of sixth nerve 222

24. Mycetcs scniculus. Level through middle of pons X'arolii 224

25. Mycetcs scniculus. Level of the inferior colliculus 226

26. Mycetes scniculus. Lcxel of the superior colliculus 228

2". Mycetes scniculus. Level of the optic chiasm 229

28. Mycetes scniculus. Lcxel of the anterior commissure 230

29. Ventral surfaee of the gray matter of the brain stem, Mycetes scniculus (color) . 235

30. Dorsal surface of the gray matter of the brain stem, Mycetes senieulus (color). . 237

31. Lateral surface of the gray matter of the brain stem, .Mycetes senieulus (color) . 239

32. Habitat group. Baboon at the water hole 290

33. Papio cynoecphalus (baboon) 2yi

34-13-. Hand and loot of Papio cynoceplialus 292, 293

38. Dorsal surface of brain, Papio e\ nocephalus 296

39. Base vi brain, Papio c\noccphalus 29"

40. Right lateral surface of brain, Papio cynoecphalus 298

41. Left lateral surface of brain, Papio cynoecphalus 299

42. Ventral surfaee of brain stem, Papio cynoecphalus 300

43. Dorsal surfaee of brain stem, Papio cynoecphalus 301

44. Baboon. Level of the pyramidal decussation 306

4,-. Baboon. Le\ el of caudal extremitxof nucleus of Burdaeii 309

46. Baboon. Level of the caudal extremity of the inferior olivary nucleus 311

4-. Baboon. Level through the middle of the inferior olive 313

48. Baboon. Le\el of the Ncstibular nuclei 3'6

49. Baboon. Lc\ el of the cerebellar nuclei 3'9

50. Baboon. Level of emergent fibers of sixth nerve and caudal libers of pons. . . . 321
ii. Baboon. Level at midille of pons, showing entering trigcminaMibers 324

52. Baboon. Level of inferior colliculus showing emergence of fourth nerve 326

53. Baboon. Level of the inferior colliculus 327

X LIST Ol ILLUSl RATIONS

Figure Pace

54. Baboon. Level of the superior colliculus 330

55. Baboon. Level of the optic ciiiasm 332

56. Baboon. Level of the anterior commissure 333

5-. Dorsal surface of the gray matter of the brain stem, Papio cynocephalus (color). 33-

58. Lateral surface of the gray matter of the brain stem, Papio cynocephalus (color). 339

59. Ventral surface of the gray matter of the brain stem, Papio cynocephalus (color) . 341

60. Macacus rhesus. Full-grown monkc\ aiui \oung 351

61-164. liand and foot of Macacus riiesus 352, 353

65. Dorsal surface of brain of Macacus rhesus 358

66. Base of brain of Macacus rhesus 359

6". Left lateral surface of brain, Macacus rhesus 360

68. Right lateral surface of brain, ALacacus rhesus 361

69. Ventral surface of brain stem, Macacus rhesus 362

"O. Dorsal surface of brain stem, Macacus rhesus 363

"I. Macacus. Le\el of the pyramidal decussation 366

"2. Macacus. Le\ el of caLidal limit of dorsal sensorx nuclei 36''

73. ALacacus. Le\'el of caudal limit of inferior olivary nucleus 369

"4. ALacacus. Level through middle of inferior olivary nucleus 3-2

-§. ALacacus. Level of the vestibular nuclei - 3~3

~6. Macacus. Level of the cerebellar nuclei 3~6

~7. Macacus. Level of the emergence of the sixth ncr\e 3~8

78. Macacus. Level through the middle of the pons Varolii 381

79. Macacus. Level of the emergence of the trochlear nerve 382

80. Macacus. Level of the inferior colliculus 384

<S[. Macacus. Le\el of the superior colliculus 386

82. Macacus. Level of the optic chiasm 38"

83. Macacus. Level of the anterior commissure 388

84. Ventral surface of gray matter of brain stem, Pithecus rhesus (ro/or) 393

85. Dorsal surface of gray matter of brain stem, Pithecus rhesus (color) 395

86. Lateral surface of gray matter of brain stem, Pithecus riiesus (color) 397

87. 188. Hylobates syndactylus (gibbon) 406, 407

89-192. Hand and foot of Hylobates syndactylus 408,409

93. Dorsal surface of brain, H\lobatcs hoolock 414

94. Base of brain, Hylobates hoolock 415

95. Left lateral surface of brain, Hylobates hoolock 416

96. Right lateral surface of brain, H>lobates hoolock 41:'

97. Ventral surface of brain stem, Hylobates hoolock 418

98. Dorsal surface of brain stem, Hylobates hoolock 419

99. Gibbon. Level of the pyramidal decussation 422

200. Gibbon. Level of the caudal extremity of the inferior olive 425

201,202. Gibbon. Level through the middle of the inferior olive 428,429

203. Gibbon. Level of the vestibular nuclei 431

204. Gibbon. Level of the cerebellar nuclei 433

LIST 01 II 1 L'SIKATIONS

XI

Figure p^^^

205. Gibbon. Le\ci of the cnu-rgcncc of tiic sixth cranial nerve 436

206. Gibbon. Level through the middle of the pons 43-

20". Gibbon. Level of the emergence of the trochlear nerve 438

208. Gibbon. Le\el of the inferior colliculus 440

2og, 210. Gibbon. Level of the superior colliculus 442, 443

211. Gibbon. Le\el of the optic chiasm 444

212. Gibbon. Level of the anterior commissure 44^

213. Ventral surface of gray matter of brain stem, I lylobates hoolock (co/or) 449

214. Dorsal surface of gray matter of brain stem, liylobates hoolock (co/or) 451

215. Lateral surface of gray matter of brain stem, Hylobatcs hoolock (color) .... 453

216. Habitat group, orang-outang, Sadong River, Borneo 481

217. Orang-outang, erect posture, showing disproportion of arms and legs 482

218. Orang-outang, showing anthropomorphous tendencies in head and face 483

219-222. Hand and foot of the orang-outang 484,485

223,\ and b. Dorsal surface of brain, orang-outang 488, 489

224A and B. Base of brain, orang-outang 490, 491

225.\ and b. Left lateral surface of brain, orang-outang 494, 495

22fiA and B. Right lateral surface of brain, orang-outang 496, 497

22-. Ventral surface of brain stem of orang-outang 500

228. Dorsal surface of brain stem, orang-outang 501

229. Orang-outang. Level of the pyramidal decussation 502

230. Orang-outang. Le\el of the caudal extremity of the dorsal sensory nuclei .... 505

231. Orang-outang. Level of the caudal extremity of the inferior olive 508

232. Orang-outang. Level through middle of inferior olive 511

233. Orang-outang. Level of the \estibular nuclei 514

234. Orang-outang. Level of the cerebellar nuclei 516

235. Orang-outang. Level near caudal limits of pons, emergent sixth nerve fibers. . . 518

236. Orang-outang. Level of the middle of the pons Varolii 521

23". Orang-outang. Level of emergence of trochlear ner\e 522

238. Orang-outang. Level of the inferior colliculus 524

239. Orang-outang. Level of the superior colliculus 526

240. Orang-outang. Level of the optic chiasm 530

241. Ventral surface of gray matter of brain stem, Simla satyrus (color) 535

242. Dorsal surface of gray matter of brain stem, Simla satyrus (color) 537

243. Lateral surface of gray matter of brain stem, Simla satyrus (co/or) 539

244. FKabitat group, chimpanzee 547

245. 246. Chimpanzee Susie 548, 549

24~-250. Hand and foot of chimjianzee 532, 553

25 1. \ and B. Dorsal surface of brain, chimpanzee 560, 561

252.^ and B. Base of brain, chimpanzee 562, 563

253.\ and b. Left lateral surface of brain, chimpanzee 568, 569

254. Ventral surface of the brain stem, chimpanzee. . . .' 5~2

255. Dorsal surface of brain stem, chimpanzee 5~3

xii LIST OF ILLUSTRATIONS

TiGURE Pace

256. Chimpanzee. Level of the pyramidal decussation 577

2y~. Chimpanzee. Level of caudal extremity of inferior oIi\e 579'

258. Chimpanzee. Level through the middle of the inferior olive 581

259. Chimpanzee. Level of the vestibular nuclei 584

260-262. Chimpanzee. Level of the cerebellar nuclei 58-^, 588, 589

263. Chimpanzee. Level of caudal limit of pons, showing emergent sixth nerve fibers 593

264. Level through pons, showing emerging sixth nerve fibers 594

265. Chimpanzee. Level through the middle of the pons Varolii 596

266. Chimpanzee. Level of the emergence of the fourth ner\ e 597

267. Chimpanzee. Level of the inferior colliculus 598

268. Chimpanzee. Level of the superior colliculus 602

269. Chimpanzee. Level of the lateral geniculate body 604

270. Chimpanzee. Level of the optic chiasm 606

271. Chimpanzee. Level of the anterior commissure 60""

272. Ventral surface of gray matter of brain stem, Troglodytes niger (co/or) 611

273. Dorsal surface of gray matter of brain stem. Troglodytes niger (color) 613

274. Lateral surface of gray matter of brain stem. Troglodytes niger (color) 615

275. Gorilla group 624

276. Large male gorilla killid in the African Congo 625

277. Gorilla gorilla 62"

278. Bronze statue of gorilla and woman 628

279. John Daniel in an amiable attitude ". . 629

280. Six-year-old gorilla, John Daniel 633

281. Cast of gorilla taken in last hunt of Mr. Carl Akeley 634

282. Young gorilla, John Daniel, showing breast-beating act 636

283. Adult male gorilla 639

284-287. Casts of hand and foot of the gorilla, John Daniel 640, 641

288, 289. Casts of hand and foot of an adult male gorilla 642

290, 291. Casts of the hand and foot of the gorilla, John Daniel 643

292A and B. Dorsal surface of brain, gorilla 646, 647

293A and B. Base of brain, gorilla 648, 649

294A and B. Left hemisphere of brain, gorilla 650, 651

295. Ventral surface of brain stem, gorilla 654

296. Dorsal surface of brain stem, gorilla 655

297. Gorilla. Level of the pyramidal decussation . . 658

298. Gorilla. Level of the dorsal sensory nuclei 659

299. Gorilla. Level of caudal extremity of inferior olive 661

300. Gorilla. Level of the middle of the inferior olive 664

301,302. Gorilla. Level of the vestibular nuclei 668,669

303,304. Gorilla. Level of the cerebellar nuclei 6-0,671

305. Gorilla. Level of the emergence of the sixth cranial nerve 6-3

306. Gorilla. Level through the middle of the pons Varolii 675

30". Gorilla. Level of the emergence of the trochlear ncr\e 6 —

T.TST 01" III rSTRATIONS xiil

Figure Page

308. Gorilla. Lc\cl ol tlic inferior colliculus 6~8

309. Gorilla. Level of the superior colliculus 680

310. Gorilla. Level of the optic chiasm 685

311. Gorilla. Lo\cl of the anterior commissure 684

312. \'entral surface of gray matter of brain stem, Troglodytes gorilla (fo/or) .... 687

313. Dorsal surface of gray matter of brain stem, Troglodytes gorilla (to/or) .... 689

314. Lateral surface of gra\niatter of brain stem. Troglodytes gorilla (co/or) .... 691
315-318. Four extinct races of prehistoric man -32

319. Prof. Osborn's estimates of man's antiquity, industries, arts and races "34

320. Restoration of Pithecanthropus compared with human and anthropoid skulls. . "36

321. Restorations of Heidelberg and Piltdown man by Professor McGregor "39

322. The Neanderthal race -41

323. The Cro-magnon race -42

324. Stone implenu'nts representing the se\eral stages of Paleolithic culture 744

325. "I-.oliths" from Piltdown, Sussex "46

326. Contrasts between implements of the Paleolithic and Neolithic Ages "48

32". Evolution of lance point through se\eral stages of the Old Stone Age 750

328, 329. Manufacturing Hints 752, ■'53

330. I ni|)lenK'nts and ornaments typical of Upper Paleolithic Age 755

331. Australian nati\e -68

332. African pygn:y group irom the Belgian Congo 769

333. African negro 770

334. American Lidian — 2

335. Eskimo ~3

336. Group of British scientists discussing the Piltdown skull 7-4

33-.\ and b. Dorsal surface of brain, Homo sapiens -80, -81

338.\ and b. Base of brain. Homo sapiens ■. . -84, -85

339.\ and B. Left lateral surface of brain. Homo sapiens -92, -93

340. Ventral surface of brain stem. Homo sapiens -96

341. Dorsal surface of brain stem. Homo sapiens 797

342. Man. Le\cl of the p\ ramidal decussation 801

343. .Man. Le\ el of caudal extremity of dorsal sensory nuclei 805

344. .Man. Level of caudal extremity of inferior olivary nucleus 80"

345. .Man. Le\i-1 through middle of inferior oli\ary body 809

346,34-. .Man. Lc\el of the vestibular nuclei 812,813

348. Man. Level of the cerebellar nuclei 816

349. .Man. Level of inferior portion of pons and emergence of sixth nerve 818

350. ALin. Le\el of the middle of the pons Varolii 821

351. Man. Level showing the emergence of the fourth or trochlear nerve 825

352,353. ALin. Level of the inferior colliculus 828, 829

354. Man. Level of the superior colliculus • 831

355. 35^- ^Lin. Level of the optic chiasm 833, 834

3-;-. .\L'in. Level of the anterior commissure 835

xiv LIST OF ILLUSTRATIONS

Figure Pace

35^. 359- Lateral surface of gray matter of brain stem, Homo sapiens (color) . . 839, 841

360. Dorsal surface of gray matter of israin stem, Homo sapiens (color) 843

361. Ventral surface of gray matter of brain stem, Homo sapiens (co/or) 845

362-365. Four views of an endocraniai cast of a modern Iiuman skull 863

366-371. Six views of the endocraniai cast of Pithccanthroi^us crcctus (Javan Ape-
man) 8-0

372-374. Comparison of endocraniai casts ol gorilla. Pithecanthropus and Homo

sapiens 8"3

375. Functional localization of the brain outlined upon the left hemisphere of the

endocraniai cast of Pithecanthropus erectus 880

376-380. Five views of the endocraniai cast of Eoanthropus dawsoni (Dawn man of

Piltdown) 885

381. Functional localization of the brain outlined upon the left hemisphere of the

endocraniai cast of Eoanthropus. (Piltdown.) 890

382-387. Six views of the endocraniai cast of Homo neanderthalcnsis 894

388. Neanderthal Hint workers 896

389-393. Five views of the endocraniai cast of the La Quina skull 900

394-399. Six views of the endocraniai cast of the Gibraltar skull 00.5

400. Functional localization of the brain outlined upon the lelt hemisphere ol Homo

neanderthalcnsis (La Chapelle aux Saints) 907

401-406. Six views of the endocraniai cast of Homo rhodesiensis (Rhodcsian man) . . 910
407. Functional localization outlined on left hemisphere of Homo rhodesiensis . . . 914
408-413. Six views of the endocraniai cast of Homo sapiens of the Prcdmost race 919

414. Functional localization of the brain outlined upon the left hemisphere of the

Prcdmost endocraniai cast 921

415. Cro-magnon artists making fresco in cave of Font-de-Gaume 927

416. Neolithic men 931

417-422. Comparison of the endocraniai casts of Pithecanthropus, Piltdown, Rho-

desian, Neanderthal and Predmost with modern Homo sapiens 934

423-426. Size and configuration of the dorsal and lateral surtaces ol the luinian lirain

compared with those of Lemur mongoz 946

427-430. Size and configuration of the dorsal and lateral surfaces of the human brain

compared with those of Callithrix jacchus, the marmoset 949

431-434. Size and configuration of the dorsal and lateral surfaces of human brain com-
pared with those of Mycetes seniculus ()-;3

435-438. Size and configuration of the dorsal and lateral surfaces of the human brain

compared with that of Papio cynocephalus, the baboon 956

439-442. Size and configuration of the dorsal and lateral surfaces of the human brain

compared with those of Pithecus rhesus, the macacus 1)62

443-446. Size and configuration of the dorsal and lateral surfaces of the human brain

compared with those of h\lobates hoolock, the gibbon 96-

447-450. Size and configuration of the dorsal and lateral surfaces of the human brain

compared with those of Simla satyrus, the orang-outang 9~3

451-454. Size and configuration of the dorsal and lateral surfaces of the human brain

compared with those of Troglodytes niger, the chimpanzee Q^y

455-458. Size and coniiguration of the dorsal and lateral surfaces of the human brain

compared with those of Gorilla gorilla 98"

459. Principal primate horizons, showing evolutional expansion of neopallium (color) 989

LIST 01- ILLUSTRATIONS xv

Figure Pace

460-470. Cross section at Icxcl ol p\ laniidal decussation in tlic comparative primate

series 996, 997

4''i-4iSi. Cross section at the lc\ el ol the caudal extremity of inferior oli\e in the com-
parative primate series 1000, 1001

482 4Q2. Cross section at the le\el of the middle ol the inferior oli\e in the com-
parative primate series 1004, 1005

493. Graphs constructed on the basis of the planimetrie indices 1009

494-504. Cross section at the level ol the \estibular nuclei in the comparative primate

series 1012, 1015

505-5 1 5. Cross section at the le\el of the emerifence of the trochlear ner\e in the com-
parative primate series 10 16, 1017

516. Graph based on planimetnc indices of the pontile nuclei 1018

517-527. Cross section at the le\el of the inferior colliculus in the com|xirati\e primate

series 1022, 1023

528-538. Cross section at the ie\el of tlie superior colliculus m the comparative pri-
mate series 1026, 1027

539. Graph based on planimetrie indices of cerebral petluncle 1028

PARI" III
THE HIGHER ANTHROPOIDS

T

INTRODUCTION TO PART 1 1 1

"^1 1 E <irc'at man-likr ixpcs lia\ t' at(|uirccl an c'spt'cial interest because (j1
w icicsprcaci iiotorirtx aroust'cl b\ thciii as tlu' su])p()st'cl lorehcars or
clirc'tt ancestors of man. i his reputation has crt'ated an attitude
toward the anthro|)()ids which has not always redounded to their credit.
Indeed, it often has inspiretl {\\v eloquence ot sentimental tirades, lor which
tlicy have been the c|uite uiidestaN inti objects. And yet, in such a number of
their structural ieatures and beha\ioral specializations do they resemble
their more exalted iieiuhbors in the human family, that a most unpU'asant
suspicion still lurks in the minds of many. A strani^ely persistent leeling
exists that there ina\ be sonu' fundamental truth in the alleged simian line
of human descent. In some this has produced an almost morbid curiosity
concerning the man-likt' apt's. Otiurs, pt'rhaps more scientilically inclined,
have assiduously followed tlu' matter in order to satisfy themselves concern-
ing the relation which these great apes bear to the races of man.

At \arious times and by \arious authorities, each one ol the three great
anthropoids has been put in close relation to man. Thus, the orang-outang
has been considered tlu' nearest approach to human kind among the anthro-
poid apes. Such a \ie\\ was long suppnrted b\- Sir Richard Owen. Other
equalb important authorities place the chimpanzee in this close relationship
to tlu' human family, while man\, like the present writer, believe that this
j)osition should be assigned to the gorilla becaiise this animal, especiall\ in
the dillerentiation of the central ner\()us system, seems to correspond most
closel\ to the human t\|X'. All of the great man-like apes, however, have so
much in common with their higher coordinate, man, that the c|uestion as to
which of them is most humanoid becomes somewhat academic. It is prob-
able, moreo\er, that each of the higher primates, perhaps with the exception
of man himself, represents a cul-de-sac in the process of progressive speciali-

477

478 THE HIGHER ANTHROPOIDS

zation in which each is, as it were, an c\oiuti(jnaI terminus. This, however,
may not be so strictly the case with man in \\ hom the possibility of further
differentiation may have been retained to a certain extent. His future alone
must reveal his latent capacity lor development, if such there be.

The actual interrelationship between man and the great apes seems much
more likely to be based upon deri\ation from some common or generalized
stock w hich held in it tiie potentialities to specialize along the anthropoid
line in one direction, and through certain subhuman stages to man in another.
There are unquestionable difi'erenees between the anthropoids and man w hich
justify the opinion of extremely remote kinship at best, even in spite of
striking similarities. It would seem most probable that neither modern
man nor any of his extinct paleolithic predecessors who have appeared in
the human drama may trace a direct line of descent to one or other of the
living anthropoid apes. These animals have enlisted so much the attention
of many noted scientists that the summary of their behavior given here gains
considerably by recounting views already expressed by certain distinguished
observers.

The three anthropoid apes are usuallx included in the family Simiidae,
represented by three genera which are arranged according as their species
appear to be nearest to man. In this discussion the orang-outang is placed
lowest in the scale and consequently farthest away from man. The next
position is assigned to the chlmi^anzee, while for the gorilla is reserved the
closest approximation to the human kind. This classification is based
largely u])on morphological consideration of the brain structure which to the
mind of the ])resent writer forms a reliable criterioTi iii assigning to each
of these anthropoids its respeeti\e place.

Chapter W 1 1

SI MIA SATYRUS, THE ORANG-OUTANG, ITS BRAIN

AND BEHAVIOR

lis Pdsilion cimouii ihc Primates; .\[casurcmcnts and Bruin Indices; Surface
Markiniis aj llw Brain and Brain Stem; Structure o/ the Brain Stem in

Cross Sec I ion

IT tlu' orang-outang enjoys a reputation less romantie than cither of his
great congeners, the ehinipan/t't' and the gorilla, this is clue to his insular
habitat which has lelt hini sonu'uhat inaccessible to the attentions of
European curiosity. \\ hate\'er bibulous repute he nia\ have among the
natives ot his island home, he has had less opportunity to tall into the nimble
hands ot the modern table-makei's. It is particularly tortunate that the story
ot his life appears to have had its lirst real introduction to civilization through
the auspices of one of the most celebrated of naturalists, Alfred Russell
W allace.

Appearance and Habiis of the Orang-Outang

The orang is found onl\- in Borneo and Sumatra, and there seems to be
considerable doubt as to whether the animals found in these two localities
constitute distinct species. It is the custom for most systems of classifica-
tion to designate one as the Bornean orang and the other as the Sumatran
orang. The adult animal has a heav^- body, short thick neck, a round head
and somew hat receding forehead, a distinctly protruding muzzle with large
mouth, broad lijjs and face uncovered by hair. The lips arc mobile and
l)rotrusive. The arms are very long, reaching to the ankles in the upright
posture. The hands arc long and narrow and the thumb is short. The
lingers are united by webs at the base of the proximal phalanges. The legs

479

48o THE HIGHER ANTHROPOIDS

arc short in comparison with tlic length ol the b()cl> and considerably bowed.
The feet arc long and narrow. The <i;reat toe is short but opposable. Ischial
callosities are sometimes |)resent in the male adult, bnt tiie tail is absent.
The body is covered w itli a light brownish hair ot considerable length, unlike
tlu' hair of the two other great anthropoids, \\ hieh is darkish. The contrast
makes the orang appear light-colored in coni|)arison with the gorilla and
chimpanzee. Concerning the height of the orang, \\ allace believes that it
seldom exceeds four leet two inches, and is on the average about lour feet
one inch. The outstretched arms measure se\XMi ieet two inches to seven
feet eight inches. Wallace discounts the repi)rt of an orang which approaches
in any way near to the stature ol the gorilla, although statements to the
effect that certain ca])tured specimens haw measured li\e leet three inches
have been made ljy se\eral traxelers. The iigures given b\ \\ allace coincide
\\ith those ol the majority ol observers and may, thcrelore, be accepted
as the most accurate measurements.

The Dyaks, inhabiting the Island of Borneo, believe that the orang
^\hich they call "mias" is possessed of prodigious strength and for this reason
is seldom, if ever, attacked by other animals of the forest. It really seems
to have no enemies because (jf its ow n great olfensive ]iower, and only two
of the great reptiles e\en presume to attack it the crocodile and the python.
The orang always succeeds in killing the crocodile b\- main strength, stand-
ing upon its back and opening its jaws until he is al)le to rip out its throat.
If attacked by the python, tin' orang seizes the reptile with both hands,
squeezing it with such force and biting it so ferociously that the outcome of
the combat is soon decided in laxor of the anthropoid.

w.\ll.\ce's .accounts of the orang-olt.wg

The following abstracts are taken from Wallace's interesting account of
the orang-outang which appears in his famous "Malax Archipelago":

(.ourli^y, ATturuuTi A/umupi oJ .\tiiuTiil lli-tnr]

FIG. 216. HABITAT GHOL l>, OKANG-OUTANG, SADOiNG HI\ ER, BORNEO.

[48.1

Loiirlisw New ^'ork Zoological Conlen

FIG. 217. OKANG-OL lANG, IN llli: HKIXI POSTURE, ILLUSTRATING THE
DISPROPOKIION 01 HIE ARMS AND LEGS.

[482]

SIMIA SAT^RLS. THE ORANC-OITANG

483

"TIk' animal has a wick- distribution, inhabiting many districts along
tlu' coast of the island w htrt' it appears ehielly eonhned to the low swampy
forests. It partleiilaiK aileets a eountr\- which is low and lc\i'l with a few

Courtesy, New York Zoological Garden

FIG. 218. ORANG-OUTANG, SHOWING CERTAIN ANTHROPOMORPHOUS
TENDENCIES I.N THE HEAD AND FACE.

isolated nioiintains on some of which tlu' Dyaks have settled and planted
many i'ruit trees w hieh are a great attraction to the orang as its most desir-
able food seems to be the unripe fruit. The actual habitat of the animal is in
the loftx \ irgin forest in w hich they can roam in every direction w ith as much
facilit\ as the Indian on the prairie, passing from treetop to treetop w ithout
being obliged to descend to the earth. The orang makes his way leisurely
through the forest with remarkable ease. He walks deliberately along the
larger branches in a semi-erect attitude which his great length of arm and the

484

Tllii HIGHER ANTHROPOIDS

shortness of his legs causes him naturally to assume. The disproportion
between his limbs is increased b\ walking on his knuckles and not on the pahn
of liis hand. He chooses those branches ^vhich intermingle with those of the

Courffsy, AmtTnan A/u.st-um oj Salujul History

FIGS. 2iy AND 220. HA.ND A.XD FOOT OF THE ORANG-OUTANG.

Lept. Palmar surface of hand showing long, prehensile ty|jc of liand and sliort, rudiment.iry lluinib. These
features are special adaptations to arboreal life.

RiGnr. Plantar surface of the foot showing the great toe in a position about midway bclwccn the heel and
the other toes. The lesser toes are long, and especially adapted to the clinging grasp necessary to arboreal
life. Attention is called to the position of the great toe and the advance toward the ball of the foot
which progresses in the next higher apes, chimpanzee and gorilla (see Figs. 247, 248, 284 and 285).

adjoining trees. In approaching these, he stretches out his long arms, seiz-
ing the neighboring bough with both hands, and then dehijcrately swings
himself across to the next branch on which he walks along as belore. He
never jumps or springs nor e\cn ajjpears to liurrx hnnsell, yet he manages to
get along almost as quickly as a person can viin through the lorest beneath.
The long powerful arms are of the greatest use to the annnal as thc\- enable
him to climb easily the highest trees, to seize fruits and young lea\es from

SIMIA SAT^RLS, THE ORANG-OUTANG

485

sli'iidcT houghs which will not bear his weight, and to gather leaves and
bi;uu-hes with which to lorni his nest at night. When wounded, he endeavors
to make- a nest in w hieh to remain c|uiet, and siniilarl\-, at night, prepares a

Courtesy, Amencan .Museum of Natural History

FIGS. 221 AND 222. HAND AND FOOT OF ORANG-OUTANG.

Leit^. Dorsum of hand showing hing, tapcrinf; lingers, short thumb, and specialization to arboreal life.
Right. Dorsum of the foot showing many hand-like qualities, with the great toe nearer to the heel than the
ball of the foot.

resting place in the trees to sk'cp. He likes this j)Iace low down In the trees
not oxer twent\ or hftx feet from the ground, probahlx because in this
position it is warm and k'ss exposed to the wind. The orang, it is said,
makes a new nest lor himself t-\ cry night, or, perhaps, remakes an old one.
In rainv weather the- animal co\'ers himself with leaves or large lerns, and
this ma\ ha\e led to the belief that he actually builds huts in the trees. The
animal does not arise from his bed in the morning until the sun is well up and
has dried the dew upon tin- lea\es. His feeding hours extend through the
forenoon, and he seldom returns to the same trees two days in succession.

486 THE HIGHER ANTHROPOIDS

They have no particuhir fear of man and only retreat slowly after a con-
siderable period of scrutinizing inspection. The\ do not manifest so much of
the gregarious tendency as do the other large apes. Two full-grow n animals
are seldom seen together, but males and females are sometimes accompanied
by half-grown young ones. At other limes three or four young animals are
seen together. Their food consists almost e\elusi\ely ot fruits, leaves, buds
and young shoots. They seem to prefer the unrii:)e Iruit even when
very sour or intensely bitter, the red lleshy arillus being a particular favorite.
The orang rarel\- descends to the ground except when pressed by hunger,
when it seeks the succulent shoots at the riverside-. In \ery dry weather it
also comes down from the trees in quest of water of which it generally finds
sufficient In the hollow of the leaves. The\' have been seen upon the ground
playing together, at which times thc\ assume the erect posture and grasp
each other with tluir arms."

Wallace believes that it is safe to say that the orang never stands or
walks erect unless when using its hands to support itseli b\ the branches
overhead or when attacked; and that the representations of its walking with
a stick are c[uite unaginary.

The account given by \\'allace of his expt-rience with a young orang
whose mother had been killed the preceding day is interesting because of the
many human resemblances it records. For example, the great prehensile
strength of this almost helpless orang-outang infant, in hands and feet, was
quickly demonstrated 1)\- the tenaclt\- with which the t'xplorer's beard was
grasped and retained. It was both a prolonged and palnlul ordeal to get away
from the clinging young one. The animal had not a single tooth, but soon Its
milk teeth began to appear much like a human Infant. The lack of milk on
the island served as a great embarrassment In feeding the young ape, but
when the linger was placed in Its mouth it sucked w Ith great \ Igor, draw uig
in Its cheeks with all its mii!;ht In a \aln ellort to extract milk. Only alti'r

SIM I A SATYRUS, THE ORANG-OUTANG 487

persevering a long time would it give uj) in disgust and set up a scream verj'
like that of a baby in similar cireunistanees. \\ lien handled or nursed it was
very cjuiet, and \\ hen laid down by itself, it would invariably er\'. It enjoyed
being rubbed alter its morning bath and was cjuite hap|)\ while its hair was
being combed and bruslu'd. b'or the lirst lew days it clung desperately by all
four hands to w hate\ er it could lay hold ol, and \\ allace remarks that it was
necessary for hnn to ext'rt spt'cial precautions to keep his beard out of the
way. A little hart-lip monkey of the macacus variety was subsequently
obtained as a com]xinion for the young orang, and it was curious to observe
the ditlerent actions of these two young simians, the one the offspring of a
great anthropoid and the other of a much lower form of jjrimate. The two
voung animals were of about the same age, but the orang was very like a
baby lying on its back cpiltc helpless, rolling lazily from side to side, stretch-
ing out all four hands into the air, wishing to grasp something but hardly
able to guide its fingers to an\- object. \\ hen dissatisfied, it opened w ide its
almost toothless mouth, exjjrcssing its wants by a most infantile scream.
The little monkey, on the other hand, was in constant motion, running and
jumping about wherever it pleased, examining every thing about it, taking
hold of objects w ith the greatest precision, balancing itself on the edge of the
box and searching everywhere for something to eat. There could hardl\- be a
greater contrast. The orang beluned in so many ways as a human infant as
to gi\(.' the impression that a long ])criod of slow development was necessary
to it. This appeared essential in order that the j:)otential elements ol its
growth might attain their fullest expression by retarding the period of
maturity to a relati\el\ late jicriod.

YERKES' PSYCHOLOGIC.XL STUDIES

The orang-outang has not been so extensively subjected to exact
psychological study as its more capable fellow anthropoid, the chimpanzee.

488

THE HIGHER ANTHROPOIDS

It is fortunate, however, that at least one of this species has come under the
critical observation of a most astute student of animal behavior. Professor
RoJDcrt M. ^'erkes. In his notable contribution on "The Mental Life of

IIG. -223A. DORSAL SURI'ACE Ol- BRAIN, ORANG-OUTANG.

lAttiial I .CM);!!! 1)4 mm. I

Monkeys and Apes, " Professor "\'erkes has described certain tests devised for
estimating tiie iiitelli<j;ence of lower animals, and ap[)lied to the partly <iro\\ n
orang, known as "Julius." These tests wcrt' designed upon what is known as
the mulli])lc choice hasis. Concerning the results ol^taiiud from the orang-
outang as compared with other lower primates, ^cikts sa\s that Julius,
after many unsuccessful ellorts to sol\c tlu- pi'oblem b\ the nu'thod ol trial

SIMIA SATYRUS, Till- ORANG-OUTANG

489

and cMTor lasting tor a period of owr two weeks, quite unexpectedly one
morning seemed to get the idea of w hat was exjx'eted of him and responded to
llie test withuLit a single mistakt'. lit- had seemed to soKe the problem sud-

MG. 223B. DETAILED DI A(;RAM OF DORSAL SURFACE OF BRAIN,

ORANG-OUTANG.
Key to Diagram, sulc. fr. med.. Sulcus Frontalis Mcdius; suLC. occ, Sulcus Occipitalis (Inferior); sulcus
i>RECENTRALis INF., Sulcus Proccntralis Inferior; suix. retrc. inf.. Sulcus Retroccntralis Inferior; s.R.s.,
Sulcus Retroccntralis Superior.

denlv and in all probal)ilIt\ , ideat ionallx . The eurve of learning plotted irom
the daily wrong ehoicc's of the animal, had it been obtained Irom a human
subject, would undoubtedl\ ha\c- been described as ideational, possibly
even as rational, for its sudden drop from near the maximum to the base
line strongly suggests, if it does not actually prove, the presence of insight.
Never before has a cur\f of learning like this been obtained Irom an inira-

490

THE HIGHER ANTHROPOIDS

human animal. \ crkcs feels justified in concluding from the cxidcncc in liand,
which he has presented in extenso in the work referred to, that the orang-
outang solves problems set before him ideationallx . As a matter ol tact, for

MG. 224A. BASE OF BRAIN, ()KAN(.-()l 1 A.\G.

[Actual Li'[igtli 94 nirn.l

the sohition he required about four times the number of trials of several of
the lower primates, which, if judgi'd b\ the number of these triafs, would
seem to have an intelligence greater than tlu' anthropoids. But other facts
clearly indicate that Julius, the orang, is far supt'rior to the monkeys in his
intelligence, and suggest that in the aniiral, ideational learning tended to
replace the simpler mode of problem solution b\ trial and error. POr Julius,

SIMIA SAlMaS, THE ORANG-OUTANG

491

seemingly incapable of solving ins pn)l)[enis jjy tins lower grade process,
strove persistently and often vainly to gain insight. It is true, lie used ideas
defectively at lirst, but later to much better purpose. Animals tar lower m

FIG. 224B. DETAILED DIAGRAM OF BASE OF BRAIX, ORAXG-OUTAXG.

intelligence, for exami:)le tlie pig, surpassed the orang in their ability to
solve these relational ])rol)lciiis because they used the method of elimination
by trial consistentl\ and ellecti\ely. Julius, in these experiments, made a
poor showing because his substitute for trial and error is only slightly devel-
oped, l)ut, ne\ertheiess, sufTiciently ad\anced to luring al)()ut the final solution
of the |)r(iblem by ideation.

492 THE HIGHER ANTHROPOIDS

Measurements a\d Txdtces of the Oraxg-Oitang

The cranial nicasLUfiiU'iits ol tlic orang-outang arc:

Occipito-nasal diameter 165 mm.

Intertemporal width 88 mm.

Breadth of brain case 98 mm.

The dimensions ol the ijram, inchidmg cercbelhim and brain stem, are:

Longitudinal 96 mm.

Transverse . 84 mm.

The l)ram is markedly gyrencephalic \\ ith its lissural pattern eor-
rcspondmg closely m detail to that ol the human brain.

Total weight of the I)rain 246 gm.

Total water displacement ol the brain 250 e.c.

Weight ol the lorebram 213 gm.

W eight ol the midbrain 4 gm.

\\ i-ight ol the hmdbrain iq gm.

The water displacement ol the sexeral portions ol the brain gave the
following results:

\\'ater displacement ol the forebrain 2 h) e.c.

\\ ater dis]>lacemcnt ol the midbrain 3 e.c.

\\ ater displacenu'iit of the hmdbrain 28 e.c

On the basis ol these ligures, the lollowmg encephalic indices were
computed:

Forebrain index 83 per cent

Midbrain index 5 per cent

Hindbrain index 12 per cent

'^IMIA SATMU'S. TUF ORANG-OUTANG

493

A lorthrain index dI 83 |)c'i" cent alln's the orang-outaiifi w itli the firoup of
aiiiinals reeogmzed as ha\ iiiii \vell-ad\ aneed maiuial thllerentiation, as is the
ease with all ol the primates.

Surface Appeakaxce oi- riii I^kmn i\ ihe Oha\(,-Ol iang

FISSURES AND LOBES

In pattern the brain ot tin- orang-Dutang is riehly <:;> reneephalic, its
lateral, basal and nusial surlaees presentniu many eonxohitions, tlie dis|)()si-
tion 1)1 w Imh almost exaetiv emneides with that nl the human brain. The
hemisplu'ie in its oeeipital portion I'ompletely eoxers the eerel)c-lhim. I he
superior l()n;j;itudinal lissiirt- at tlu' oeeijjital pole ol the hemis|)lu'ri' tends to
diverge slightly in order to aeeommodate t lu' ele\ation eaiisi'd in the superior
vermis of the eerebellum. This di\ergenee at the eaudal e\tremit\ ol the
superior longitudinal lissure is most pronounced in the lower and inti'i-
mediatt' primati-s. It gradualK beeomes less conspicuous in the higher nu-ni-
bers ol the [jrimate group.

The lissiiral [xittern of the- lateral eon\e\it\ of the cerebral hemispiiere is
grouped about three mam lissures, namel\ , i 1 ) the lissure ol S\ l\ lus, (2)
the lissure of I^oiando and 1 3) the semilunar or simian hssurt-. I liese fissures
determine a distinctlx human t\ pe ol lobat ion m the luiiiis|jhcres. Flic lissure
of Rolando, starting about midwa\ between tht- Irontal and oeeipital poles,
at or lu-ar the supt'rior longitudinal lissiiri', extends oblicniel\ downward and
forward toward the S\ K ian lissure. it presents two gemillexions, both less
promiiu'iit than in tlu' human brain. |-5\' means ol this Rolandie lissure, the
Irontal lobe is st'parated from tlu' parietal lobe. Ihe S\l\ian li.ssure, some-
what shorter than in man, presents its usual di\ isions, and up(»n the latt'ral
surface extends oblic|ut-l\ backward and upward to be surrouncktl b\ the
marginal conxolution at its caudal e\tremit\. It constitutes a boundary
Ix'twi'en the temporal lobe and the parietal lobe. The sulcus simiarum is

404

THE HIGHER ANTHROPOIDS

prominent and extends from the superior longitudinal sulcus toward the
base of the temporal lobe. It separates tlie parietal from the oeeii)ital lnl)e
and forms a boundary between tlie oeci|Jital and temporal lobes. The presence

FIG. 225A. LEl-r LATERAL SURFACE OF BRAIN, ORANG-OUTANG.

(AcUial L^ngtli q6 nun.]

of this simian sulcus, so well defined m the orang, adds a feature to the lateral
cispeet ol the hemisphere usually not present in the human bram. It thus
serves as one oi the distmguishmg marks bt'lween man and the anthropoids.
Its developmi'ut in orang has more of the pruiiitive simian character than is
the case in either cinmpan/.ee or gorilla. The convolutional pattern ol the
parietal lobe, as is always the case, shows the greatest richness ot gyration,
and, in accordance with the rule, tlu" ti'inporal lobe is the lU'xt most consjjic-
uous in this particular. 1 he superior tem|)oral sulcus, ho\\e\er. Is not contin-
uous into the parietal lobe as m the higher [)rimates; a deep annectent gyre
interrupts this sulcus near the base of the temporal region so that it is diffi-
cult to identify an angular g\ rus. The coiiMilutional pattern in thi' frontal

SIMIA SAT^RIS, THE ORANG-OUTANG

495

\()\iv IS i\lati\c'l\' rich. The pr()ti>t\ ])r ofcacli lissurc IduiuI in tht- human brain
is iJicsiiit ill orano;. This gixt's the liDiUal lohc a ch'stinctl\ hunianoid appear-
ance. The proportion between the frontal and jxirieto-occipito-temporal

^tRsacv^

FIG. 22j\\. DErAILED DIA(;K\M OF LEFT LATERAL SURFACE OF BRAIN,

OKANOOL TA.NG.

Key to Diagram, ramus post., Ramus Posterior of Sulcus Temporalis Superior; sli.c. fr. oi>.. Sulcus
Fronto-opcrcularis; s. VR. or., Sulcus Fronto-orbitalis; sllc. occip.. Sulcus Occipitalis; sulc. occip. lat..
Sulcus Occipitalis Lateralis; sui.c. precnt. inf.. Sulcus Precentralis Inferior; sulc. prec.nt. sup.. Sulcus
Precentralis Superior; sulc. r. int.. Sulcus Retrocentralis Inferior; sulc. ret. sup.. Sulcus Retrocentralis
Superior; sulc. temp, med.. Sulcus Temporalis Medius; si i.e. ti-mp. sup.. Sulcus Temporalis Superior.

areas appears to he about the same as in man. Actual planlmetric measure-
ments, h()\vc\er, show a dis|)arlty in this regard w hich hixors tlie trontal area
of the human brain. The com nhitions ol the occipital lobe are lairly rich, but
less marked than in an\ othtr region. Upon the mesial surface a deep annec-
tent gyre comes to the surface and thus inti'rrupts the direct continuity of the
sulcus simiarum with the occipital sulcus. This interruption by means of an
annectent ^'\'re in the course' of this lissure is a teature lrec|uently found in
the brain of the yreat anthropoids.

4^6

II IE HIGHER ANTFIROPOIDS

The Basal Surface of the Bkai\

Upon tlu' basal surlacc ol tlu' hrain, the luiiiisplKTc iii the trontal region
shows the two eharaeteristic orbital concavities which are lairlv well marked

f3<%'

FIG. 226a. KK;ni LATERAL SL RFACE OF BRAIN, ORANG-OL TANG.

■|Actii;il length q6 mm.]

altliough gradiiallv losing their lateral boundaries. Mcsially these concavities
are bounded by two marked projections, lorming the inti'rorl)ital keels
N\ hieli ari' more prominent than m the higher anthropoids and less pronounced
than in the lower and intermediate forms. The olfactory bulb and tract are
detachable Ironi the orbital surlace as far back as thi' trigonum ollactorium.
A small ()llact()r\- lissure separates a rudinuntar\ g\ rus rectus from the
ma|or orbital eon\-olutions. The tip of the temporal lobe is sharply separated
from the orbital surfact' 1)\ the horizontal limb of the S\l\ian fissure, and
presents a lairl\- well-dehned uncus on its nu'sial surlace. In the occipital
region the cerebellar conca\it\' is well marked. It is t'speciall\ pronounced in
its median portion where it forms a w ell-de'fiiu-d postspk'iiial fossa.

SIMIA SATVRUS, THE ORANG-OUTANG

497

Tin; CLKI£BI£LLIM

Tlic crrchclluni is rntiri'l\ oNcihun^ b\ the occipital surface of tlu'
lu'inispiu'ics. Its tt'iitonal siirlacc is consiclcrabI\' i;al)lt'(l and sliarplx mcliiiccl

FIG. 226b. detailed di a(;k a\i oi right lateral sl rface of brain,

OKANOOLTANG.

Key to Diagram, ramus post., Ramus PostcriDr of Sulcu.s Ti-mporalis Superior; SULC. fr. op.. Sulcus
Fronto-opcrcularis; sllc. ir. orh.. Sulcus Fronto-orbitalis; sllc. occip.. Sulcus Occipitalis; SLXC. PR. si p..
Sulcus Prcccntralis Superior; sit (\ m r. isi ., Sulcus Ritroccntralis Inlerior; siic. tumi'. med.. Sulcus
Temporalis .\lcclius.

toward a lairl\ dclincd median rid^c-polc wliicli forms the superior ccrclx'llar
\ermis. This ce'iitral portion is more promiiu'iit at its ee[)hahc t'Xtremity
wliich pro|ects into \hv postsplenial h)ssa on the undersurtace ol tlie hemi-
splieres. I hi' posterior ci'ri'bi'lhir notch on the occipital surhici' is clearly
di'hned but li-ss marked than m the ihmipan/.ee, gorilla or man. Thi' inliaior
MMinis, w Inch is easily discerned upon this surlace, does not lie in a depres-
sion so deep as the \allecula ol the human, chimpanzee or gorilla brain.
Ujjon the tentorial surlace the sulcal lines are continued without interruiJtioii

498 THE HIGHER ANTHROPOIDS

from the Miniis to the lateral lobes, w hile two paraniediaii sulei interiLipt the
eoiirse of the folial sulci on the occipital surface. In their hiteral expansion,
the occipital surfaces of the lateral lobes are neither so broad nor so long as in
the case of the still higher j^riinates. There is, however, a decided advance in
all of these respects as compared with tlu' lower and intermediate [jrnnates.
The petroso-ventrieular surface of the cerebellum shows no departure from
the conditions obser\ed in the lower forms. A relatixely small lloeeulus
occupies the cereliello-pontile angle mto relation \\ith which also enters a
large middle cerebellar peduncle.

THE BRAIN STEM

The Medulla Oblongata. The brain stem in its oblongatal portion
shows distinctive leatures along its ventral surlace. The ventromedial! sul-
cus is in relation upon either sidi' with twci elevations lormmg the pyramids
which taper at their caudal extremities to a le\ el where interlacing bundles
ol the decussation cross the sulcus. A well-delmed pre()li\ary sulcus separates
the pyramid Irom a prominent olivary eminence, which latter is in turn
separated from the sj^inocerebellar eminence by tlu' postolivary sulcus.
An intermediate sulcus indicates the boundary between this latter eminence
and the eminentia trigemim. Upon the dorsal surlace both the cuneus and
the elava are prominent and separated Irom each otlu'r by the dorsal para-
median sulcus. As to relatixc Nolume, the ratio ol the cla\a to the euneus is
about one to two, thus indicating Irom surlace markings at least a prej:)onder-
anee ol incoming sensory impulses Irom the upper e\tremit\ antl hand.
This accords with the failuri' on the part of tin- animal to develop a tail and
also w ith the progress which it has made in its maiuial diilerentiation.

The dorsal aspect ol the oblongata comprises its two characteristic
surfaces, the jnlraventricular and the \ (.ntncular. The \entrieular surlace

SIMIA SAT^■RUS, THE ORANG-OUTANG 499

prcscMits the lower aimlc ol' the fourth Ncntriclc whose lloor is IjouikIccI l)y the
ik'xations loniud l)\ the eiiiieus aiul the cla\a. The lloor contains the usual
inarkin<i;s inclieating the trifi;onuni hypogiossi and the fovea vagi. As the
lateral recesses are apj)roachecl tlie two elevations formed by the clava and
euneus decrease in height and linall\- attain the level of the lloor itself.
At this point the enti'ring libi'rs constitutnig the striae acusticac cross the
lloor toward tlu' niidhne, most of tluin with an oblicjuity downward and
inward. .As the\ i-ntir the \entiieular ca\it\' these libers either cross or
become submerged w ithm an t'lexation situated near the lateral recess. This
elevation is the \estibular iinmenee. In the orang its prominence in the lloor
ol the xcntricU' rs relati\ely less pronounced than in the lower and intc'r-
inediate ])runates, but somew hat more conspicuous than in the chnnpan/.i'c,
gorilla and man. A median sulcus s\ inmctricallx di\ides the lloor of the
ventricle into two longitudinal haKis. 1 lu' iijjjx'r angle of the \entricular
chamber is contained m tlu' metcncephalic portion of the stem. Above the
striae acusticac a slight eie\ation marks the position of the nucleus abdu-
centis. In other particulars the markings u[)on the \entricular lloor are rather
indelinite. The lateral walls ot this portion ol the \entricle arc lormed b\ the
converging superior tx'rt'bellar pcdunck's. Ihe \'entricular ea\it\ itself
becomes more attenuated as the caudal orilice oi' the Sylvian aqueduct is
approached.

The Pons \ ahomi. L pon the \entral surface at the cephalic extremity
of the oblongata a marked bulbo|)ontile sulcus draws tln' liiu- ol demarcation
btlwecn the bulb and the pons \ arolii. Ihe latter struct lux- is lairix large
and jjromment. Standing out conspicuously m the base ol the brain, it is
indicative of an animal possessed of a considerable connection between the
cerebral hemispheres and the lateral lobes of the cerebellum. The inference
])erinissible Irom such an ainj:)le i)allio-cerebellar communication is that the
motor organization ol orang represents a relatively wide range of skilled

^00

IllL lllCliER ANlllROPOIDS

pi-rformanccs, while the ncokinctic accjuisitions of the animal all\ it to that
grtjup ol the- pniiiatt's staiuliiig at or near the summit ol this oicKt.

The eephalie l)oiinclai"\- of the jjoiis is inclieatecl by the pontopeduneular

FIG. 227. \ENTRAL SURFACE OF BRAIN STEM OF ORANG-OL TANG.

|Actu;il Length j-t iiiin.|

Kev to Diagram. <:i;ki-.iii<. prdi nci e. Cerebral PidiincU--. I'v. Di ( ., P\ ramiclal Dttiissation; trap. BODy,

Trapezoid Body; Till \KV, Sesentli Nerve.

sulcus which marks the l)e<imninij; of the optico-peduncular space. The latter
is bounded caudall\- l)\ the di\ergeiit cerebral peduncles and cephalically
by till' optic chiasm and optic tracts. This space is proiniiU'iU in theorang's
bram, due to the conspicuous size ol the two cerebral peduncles. The dorsal
.surface ofthe midbrain contains the usual specialization ol the c|uadrigeminal
plates giving rise to the supt'rior and mlerior colliculi. Of tlu-si' the suptMior
colliculus IS somewhat more e\tensi\e, although ha\ing a less wt-ll-marked
surlace elevation. \\ hile tlu' diameters of the inlerior colliculus are less than
those of the superior colliculus, its cKa at ion is somew hat greater. The general

SIMIA SATYRUS, THE ORANG-OUTANG

;oi

cklloixsceiHT 111 tlu'Sf two specializations of the ciuadrigcminai plate in the
orang iiulieates w hat is e\ en niort' e\ iclent in cross section, i.e., a certain degree
ol inxolution incident to a delegation ot the tunctions oi" hearing and vision

FIG. 228. DORSAL SLKKACE OF BRAIN STEM, ORANG-OLTANG.

[Actual Length 54 nini.l
Key to Diagram, d. med. septi m, DorsDniidirin Septum; inf. coll.. Inferior Colliculus; sup. cerebl. ped.,
Superior Cerebellar Peduncle; slp. collicllls, Superior Colliculus; tub. tricem., Tuberculum Trigemini;
8th nkv. Eighth Nerve.

to specialized areas in the ct'rebral hemisphere. L poii the lateral surlacc of
tlu' 111 id!) ram, a small eli'\ at ion mdicatt'S the position ol the mesial geniculate
body, a relav station in the path\\a\ ol aiiditor\ sensibility.

Intfrxai, Stricti re 01 nil Rk ain Stem in the Orang-Oltang

The IcNC'ls selected in the orang-outang correspond closelx to those of
tlu' specirs already described. An\ dilK'rences in the appearance ol the
se\c-ral k'\els is met b\ the addition of su|)|)lementarv sections including
features which ma\ not ha\e ap|)eared in the representatiN'e le\els selected
lor di'sc-ription.

,-02

THE HIGHER ANTHROPOIDS

LEVEL OI- THE F'l KAMIDAL DECUSSATION (FIG. 220))

At the level of tlu' pyramidal decussation the crossing iibers of the
corticospinal tract make their usual im]:)ressi\e alterations. In consequence

FIG. 22g. OKANG-OUTANG. LE\EL OF THE PYKANnOAL DECUSSATION.

en, Coliinm ol Biirdach; cen, C-entr.il Gray M.ittir; cc, (Column of Coll; m, Dcilcrso-spinal Tract; Fi.r.
Dorsal Spinocerebellar Tract; oow. Ventral Spinocerebellar Tract; hel, Spino-oiivary Tract of Helweg;
NR, Nucleus of Rolando; i>v, Pyramid; i>vx. Pyramidal Decussation; Rsr, Rubrospinal Tract; spt. Spino-
thalamic Tract; trd, Descending Trigeminal Tract; ven, Ventral Gray Column; xpv. Crossed Pyramidal
Tract. [Accession No. 199. Section jj. Actual Size 12X11 iiim.|

SIMIA SATYRl'S. THE ORANG-OUTANG 503

of the decussation (Pyx) tlu- \ fiitroiiu-sial sulcus is dcdccted to the left
and the \entral gray column (Ven) is almost entirely separated from
the central gray matter (Ccn). The latter structure has mowd into a
more caudal position m the early stages oi" that migration w hieh e\entuates
m lorming the llo(ir oi the lourth \entricle. In the most ventral portion of
the sectifMi some hbers of the pyramid ( Py ) still keep tluir position
characteristic ol the oblongata. I'he dorsal sensory field is broad and (.'Xijan-
sive. It contains the usual (.■lements: the column of Goll (CG) representing
the leg, the column of Burdach (CB) representing the upper e\tremit\-,
and tlu' descending trigeminal tract (Trd) representing the sensor\- terri-
tories ol the lace. A small detached nuclear mass in the column of GoII
represents the nucleus ol Goll. No such miclcai- structure is present in the
column of Burdach. The nucleus of Rolando (NR), on the other hand, is
ol considerable size, although distinctl\ less in dimensions than is true of the
lower or intermediate primates. The central gray matter (Cen) extends
almost transversely across the section from a small central canal outward
to the nuck'Lisol Rolando. Immediately \entral to it are some of the collected
bundles of the pyramid (XPy) in their course extending into the spinal
cord. On the periphery of the section are the two spinocerebellar tracts
(Fie, Gow), and \ eiitronu'sial to the latter is the spin()-oli\ar\- bundle
of Helweg I H el ). The Deiterso-spinal tracts ( DT ) lie ventral to the \ cntral
gray column (Ven), while the rubrospinal ( Rst ) and spinothalamic iS|:)t )
bundles occupy their usual positions m the intermediate mcdLillar\' substance.
The mterpretation to be gi\en to this level with reference to its major
tLinctional elements concerns tlu' marked increase in the Nolume of the
p\ ramidal decussation, indicative of accessions in the voluntary control
which the animal possesses over tlu' muscles, and the large size of the
column of Burdach as com])ared with the similar sensory columns providing
inllux Irom the lower extremitx and Irom tlu- head. The disparity which

,04 THE HIGHER ANTHROPOIDS

largt'h faxors the column of Biirdach clearly indicates what considerable
gain the upper e.\treniit\ has made as a chscriniinati\ e and locomotor organ,
and thus illustrates the reflection of that process w hich has as its ultimate
goal the most complete dilVerentiation of the upjjcr extremity ada])ted
to the purposes of neokinesis. The hand and ttie arm ol the orang have
not attained that degree of adaptability which is seen in either ot tlie two
other great anthropoids, the chimpanzee and the gorilla. On the other
hand, as an organ for exploring the einironment and lor the prodiiction ol
man\- more complex and learnt'd perlormances, the lorelimb ol the orang
has made decisive advances over that ot the gibbon or an\ ol the inter-
mediate primates.

LEVEL OF JCALDAL E,\^HU.Mn^ Ol DORSAL SENSORY NUCLEI (FIG. 230)

At this U'\cl the most important modilications haxe occurrt'cl m the
dorsal fields where a detached nuclear mass near the dorsomedian septum
has made its api)earanee. This is the nucleus of Coll ( NG) which is invested
by a dense mass ol m\elini/ed ner\e libers, the column ot Goll ( CG ). The
boundai'N liiu- betwi'cn this column and that ol the column of Burdach
(CB) is indicated by the |:)resence ol a poorly detined dorsal paramedian
sulcus, while tin latt'ral boundarx of Burdach's column is nearix li\e times
that of Goll. This coincides with the spi'cializ.ation going forward in the
upper extremitx of the animal, particularl\ the de\elopment of xhv hand and
the long powerful forearm, while tlu' absence ol the tail and the relati\el\
low degree of dexelopment in the short legs account lor a dillerence m
which the column of Goll appears to i)e the smaller of the two. No detached
nuclear mass is seen as yet m the column of Burdach. Near the base ol the
central gray matter (Cen) a small dorsal protrusion marks tlu' beginning
of the caudal extremity of the nucleus of Burdach. Tlu'se two nuclei in the
dorsal column present, throughout the entire series ol primates, a contrast-

SIM I A SAT^RUS. THE ORANG-OUTANG

505

m^ li'aturi' wliieli m;i\ be nu'iitioiu'd lu-iX': The i.-;ukI;i1 r\t rtrnit \ ol the
nucleus ol Goll ni\ ;iiial)l\ has no chiiTt connrrtion with the central firay
matter; such connection as it does ultniiately altani is tenuous and reticular

1 IG. 230. OKAXG-OLTANG. LEVEL Ol- IHL CALUAL FXTREMIT^' OF THE

DORSAL SENSORY NLCLEL

CB, Coluiiin of Burdacli; ciiN, Cintr.il Gray Mattir; CG, Column of Goll; dt, Dcltirso-spinal Tract; 111:,
Dorsal Spinocirilxllar Tract; fjow, \cntral Spin(x:crcbcllar Tract; hel, Spino-olivary Tract of Ik-lwcg;
NC, Nucleus of Goll; NK, Nucleus of Rolando; I'v, Pyramid; i>v.\, Pyramidal Decussation; kst, Rubrospinal
Tract; sit, Spinotlialamic Tract; tkd. Descending Trigeminal Tract; yen. Ventral Gray Column; \f\,
Oosscd Pyramidal Tract. [Accession No. 199. Section 95. Actual Size 14 X 12 mm.]

5o6 THE HIGHER ANTHROPOIDS

in form. The nucleus of Burdach in its caudal c\tiemit\ , on the olliir hand,
appears as a definite extension from a dorsal prolongation of tlie central
gray matter, ll ])resents no detached prolongation into tiie surrounding
medullary substance. Its structural connection with the central gray matter
is much more decisive and appears in the iorm oi a compact, discretely cir-
cumscribed dorsal projection in this region, in this sense it has much the
same appearance of continuity in the gray matter as there is in the nucleus of
Rolando (substantia gelatinosa trigemini) (NR). In connection with the
nucleus of Goll there is no unpaired median nucleus oi Bischoll, which lact
again supports the idea that this median nucleus develops in connection
with the tail.

The central gray matter fCen) is elongated laterally and stretches
as a narrow band along the \entral border of the dorsal sensory fields. It
contains at its center a small central canal, and extends laterally to become
continuous with the expanding dorsal horn now presenting itself in the form
of the substantia gelatinosa trigemini (NR) (the nucleus of Rolando).
This nucleus is in contact by its lateral margin with a collection of libers
constituting the descending trigeminal tract (Trd). Ventral to the
central gray matter are the decussating fibers of the pyramid (Pyx)
which \\n\v the appearance of compact bundles closely interlacing as they
cross from one side to the other. Their decussation separates the \ entral gray
column (Ven) from the central gray (Cen). The separation at this le\el
is not Cjuite complete as there still remain a few strands or bridges of gray
matter connecting the central gray w ith the \ entral gray column. Some idea
of the massiveness of the pyramidal decussation may be obtained m this
section. The mass of fibers affords an opportunity for estimating the xohime
of impulses necessary to the volitional control of the muscles. \ entral to the
substantia gelatinosa and on the ])eripherv of the axis is a dense collection of
fibers which produce a surface prominence, the spinocerebellar eminence

SIM! A SAT^'RIS, THE ORANG-OUTANG 507

separated troin tiu' t'lniiu'iitia lri<:c'iiiiii[ hy llu' sulcus mttTiiU'dius. The
spinocerebellar eminence contains ascending fibers from the proprioceptive
system destined lor the cerebellum, and comprising the dorsal spinocerebellar
tract. This i-inlnence is a well-dehned IV'ature of the brain stem of the
primates, but becomes especially' demarcated as a surface feature m the
anthropoids and man. Its progressive distinction through the higher aiuliro-
l)oids, until It reaches its most clearly delined demarcation m man, gives fur-
ther evidence of tliat process which results in the sharpi'r delinilion ol all
brain stem structures in ascending tlu' primate series.

Lateral to the external limit ol' the pyramid on the circumterence is a
small groove which indicates the caudal e\tremit\' oi the preoli\arv
sulcus. Further along the periphcr\- is the caudal e\tremit\ ol the |)ost-
olivary sulcus. The eminence which is thus demarcated, although ol slight
prominence, occu|)ies the position at which the mierior oli\ar\ nucleus
appears in higher levels, in conseciuence ol whose appearance the olivary
eminence is determined.

At this level the more or less detached Acntral gra\- column is contained
within the limits indicated by the beginning ot the two olivary sulci.
On the outer margin of the ventral gray column, \entrolateral to the central
gray column, are the descending Deiterso-spinal tract ( DT), the rubrospinal
(Rst) and spinothalamic (Spt) tracts. Upon the actual perlphi-r\- of the
circumferi'iit iai /.one are the libers constituting the \entral sj)inocerebellar
tract ( Gow).

This section indicates accessions to the animal's sensor\- sphere, espe-
cially in the held of discriminative sensibility. It also points to a lesser
degree of sensorx inlhix from tlu' lower extremity. The extent of Nolitional
control inlu'reiit in this animal is indicated b\ the \'olume ol the |)\ramidal
decussation (Pyx). The tendenc\ of the central gray matter to move
into a dorsal j^osition in the cross section is show n as a step preparatory to the
ventriculalioii which occurs m tlu' hi<rher KacIs ol tlu' oblongata.

5o8

THE HIGHER ANTHROPOIDS

LEVEL OF IHE CAUDAL EXTREMITY OF THE INFERIOR OLIVE (FIG. 23 l)

At this \v\v\ tlu' princi|)al addition is a small mass of gra,\ matter
constituting the eaudal tip of tiic inferior oh\-ary nucleus (10) situated

FIG. 231.

OKA.NG-OLTANG. LL\ LL 0\ IHL CALUAL LXI KEMITV OF THE
INFERIOR ()LI\ E.

CB, Column of Burdacli; cen. Central Gray Matli'r; c.c. Column of Goll; fle. Dorsal Spinocerebellar Tract;
cow. Ventral Spinocerebellar Tract; iiel. Spino-olivary Tract ol' llelweg; 10, Inferior Olive; Ms, Nucleus of
Burdach; NC, Nucleus of Goll; nk. Nucleus of Rolando; pl, Posterior Longitudinal Fasciculus; I'V, Pyramid;
p\-x. Pyramidal Decussation; kei-. Reticular Formation; rst. Rubrospinal Tract; spt. Spinothalamic Tract;
TKD, Descending Trigeminal Tract. (Accession No. 199. Section do. Actual Size 12X11 mm.)

SIMIA SATYRUS, THE ORANG-OUTANG 509

clDisolatrral to the j^yraniid (Py), sonic ol w I lost' libers arc slill 111
process ol decussation ( P\\). The entn"e section has increased in its
diameters, largclx chie to the expansion occasioned b\ the increment in the
dorsal sensory nuclei, the addition ol the mierior oinary nucleus and the
introduction ot decussatin<i libers Irom the nucleus ol Goll. These inti'rnal
arcuate libers pass vcntrad to the central >i;ra\ matter (Con) into the
median raphe \\ lure the\ undergo decussation, and enter the mesial tillet.
The central pray matter (Cen), somewhat irrei!;ularl\ (|uadrilateral in
outline, IS [)artially detached Irom connection witii tlu' remainin<z jiray
matter by the internal arcuate libers. It has mi<irated dorsad, with the
ellect that the dorsomedian st'plum is be<i:innin<i; to expand and cause the
dixergcnce ol the opposed surlac(.'s ol the two alar plates. In the center ol
the gra\ matter is a small central canal. The dorsal sensory I i elds are occupied
b\ the much increased nuck'i ol'Cioll and Burdach ( N G , N B ), to tlu' latter
ol which are appended scattered nuclear masses lormin<j; the nucleus
of Blumenau. The relatixi' proportions of the nuclei of Goll and Burdach
are cleari\ indicated by the dorsal paramedian sulcus. The substantia
gelatinosa trigemini (NR) occupies its usual position lateral to the nucleus
of Burdach. It is of considerable size and accompanied by a large descend-
ing trigeminal tract ( Trd ). X'cnlral to the substantia gelatinosa is the gray
matter constituting the griseal portion ol the reticular lormation ( Rel ). Its
indefinite and diffuse character is cons|:)icuous at this le\ei. \ his |)ortion of
the ci'iitral axis in the orang contains much ol this ill-deliiietl dilterentiation
which is more characteristic of the lower and intermediate primates than it
is of the great anthropoids.

The ventromcsial area ol tiie cross section is occupied by the pyramid
( Py), some libers of which art' still undergoing decussation in a position
xentral to the accLimulating libers forming tlie mesial lillct. Lateral to the

510 THE HIGHER ANTHROPOIDS

pyramid is the preolivary sulcus and, somewhat further along the pcripherj^
of the section, a faint indenture marks the postoHvary sulcus.

The impression created by this level of the brain stem makes more
clear the accessions in the dorsal sensory field which particularly affect the
column of Burdach. This appears to be related to tlie differentiation of the
forearm and hand. The substantia gelatinosa is relatively small, indicating a
less voluminous sensory contribution from the head and face than is the case
in many of the low er jjrimatcs.

LEVEL THROUGH THE MIDDLE OF THE INFERIOR OLIVE (fIG. 232)

Here the large mass of gray matter occupying the ventrolateral portion
of the field constitutes the most prominent feature. This is the inferior olivary
nucleus (10) which in the orang-outang calls for special comment. In the
fu'St place, the size of the structure in proportion to the rest of the cross
section has obviously increased, thus indicating that the olivary functions
have proportionately acKaneed in their importance to the animal. In addi-
tion, there is distinct progress in the degree of eomolution or festooning
presented by the saccular wall of the nucleus, a feature which is more
particularly in exidence along the dorsolateral and ventromesial portion
than in the olivary fundus. A tliiicl feature is the somewhat clearer definition
of the nucleus as a whole, m contrast with adjacent structures. In this
respect, however, the degree of delinition marking tlu' bouiularii'S of the
inferior oli\e in the orang is less decisive than m chimpanzee, in gorilla or
in man.

In view of tlu' function aseribed to the inferior oli\ar\ nucleus in this
discussion, it would appear that the orang is endowed \\ith a greater degree
of coordination between head, hand and e\ e and of eooixlinat ion of all skilled
learned performances than is the case in the lower primates. This is also
true to some extent m the comparison with the intermediate primates.

SIMIA SATVRUS, THE ORANG-OUTANG 511

\\ lun contrasted w itii the lii<i;lHT nu'iiihrrs ol' tliis order, the morphological
evidence in oranjj; iiulieates an animal less highly organized in this respect.
Thi' motor perloiinances ol" orang, in part at least, hear out this supposi-

FIG. 232. ORANG-OUTANG. LEVEL THROUGH .NHDDLH OF INFERIOR OLI\E.

CTT, Central Tegmental Tract; fle, Dorsal Spinocerebellar Tract; cow, Ventral Spinocerebellar Tract; lo.
Inferior Olive; mf. Mesial Fillet; nd, Dcitcrs' Nucleus; nfs. Nucleus Solitarius; nhv, Hypoglossal Nucleus;
NR, Nucleus of Rolando; XVD, Dorsal Vagal Nucleus; N12, Hypoglossal Nerve; pd, Predorsal Bundle; pl.
Posterior Longitudinal Fasciculus; i>v, Pyramid; ref. Reticular Formation; rst. Rubrospinal Tract; spt.
Spinothalamic Tract; trd. Descending Trigeminal Tract. [Accession No. 199. Section 245. Actual
Size 18 X II mm.)

tion. Tile mock' ol its lile does not rt(|inre so high a degree of specialization
in the iortlmibs as that of the ehiinpanzee, of the gorilla or of man. ^'et
because the animal does assume' a more or less upriglit position, especially
when making its way along the branches of the trees, the forelimb has been

512 THE HIGHER ANTHROPOIDS

emancipated in some measure, and the hand is thus treixl lor jjurposes of
exploration and prehension in functional acti\ities not chrectl\ connected
with locomotion. Such specialization nnplies a greater nvvd ol mtmiate
cooperation between the eye, neck and apjiendicular muscles ol the lorehmb.
This section, being somewhat higher than the corresponding levels ol
the forms pre\iously illustrated, shows a slightl\ dillerent arrangement of
the structures bordering on the lloorol the louith \entricle. The ventricular
lloor is formed by the central gra\ matter m whose most mesial |)ortion
is the nucleus hvpoglossus (Nhy). The nuclcLis is somewhat niore clearl\-
delimited than in tlu' lower primates, although it has by no means the sharj)
demarcation seen in the higher nu'inbers ol the order. The libers ol the
twelfth ner\'e (Nl2) pass forward Irom the nucleus in the direction ol the
inferior olixary body. Tlu' nucleus is se])arated Irom an adiacent aggregation
of gray matter by a delinite grooxe, thi' sulcus limitans. This sulcus marks
the position of the dorsal nucleus ol the vagus nerve (Nvd ). At the lateral
border of this \agal nucleus is an o\al collection ol m\t'linized axons
forming the fasciculus solitarius which is surrounded by a special nuclear
collection, the nucleus ol the lasciculus solitarius (Nts). The caudal
extremity of Deiters' nucleus (ND) occupii's a lateral position beneath
the lloor of the \entricle. Ventral to this nuckuis is the substantia
gelatinosa (NR) whose outer margin is m contact with a large collection
of libers constituting the descending trigeminal tract (Trd). On the
dorsolateral aspect of the section is the compact bundle of libers lorming
the corpus restiforme ( Fie) whose extension cephalad as the mleriiM-
cerebellar peduncle serves to lorm the ultimate connection ol the lower
segmental levels with the cerebellum. The reticular formation (Ret) is
extensive but i)resents no s|X'cialized nuclear aggregations at this le\i'l.
Occupying its characteristic ventromesial position, the pxiamid (Py)
forms a fasciculus of considerable si/e which, however, seems mk'rior m

SIMIA SATYRUS, THE ORANG-OUTANG 513

voluiiH' to this structure ui the still hiyluT primates. This bundle gives
the nnpression that thi' orang is an animal less e\tensi\ily proNicled with
voluntary control o\er the somatic musculature than its higlu'r congeners.
Dorsal to the pvranucl aw the compact bundles constituting the mesial
lillet I Ml) paralleling which the lihers of the twelfth ner\e pass forward,
many ol them to penetiate tlu' mft-rior olisary body.

LE\ EL OF THE \ES'ni5L LAR NLCLEI ( FIG. 233)

At the le\el ol the \estibular nuclei, which is somewhat higher than the
corresponding sections in the otlur forms, the princi]>al feature appears in
the nuclear coniplcx related to the balancing mechanism, as it recei\'es libers
Irom the utricle, saccule and semicircular canals. This complex is torn-
posed ol the \estibular nuclei. The nucleus of Schwalbi' (NSc) lies in
intimate relation with the lloor of the- fourth \entricle. It has its usLial
triangular outline, but is less well delined than the structures lateral to it.
The nucleus ol Deiters (ND) is t\pical in its ajjpearance, consisting of
nuclear substance dispersed throughout which are numerous small bundles
ol myelimzed axons. Lateral to Di'itt'rs' luicleus is tlu' corpLis restiforme
(ICP) which passes cephalad as the interior cerebellar peduncle.
Bordering upon its lateral surface is the mass of gray matter constituting
tlu' tub(.'rculum acusticum iTub), connected with the cochli-ar di\ ision
ol the eighth ner\e (N8), the libers ol which penetrate this eminence.
Ventral to Deiters' nucleus is the substantia gelatinosa (NR) sur-
rounded on Its outer surlace by the t'ompact bundles lorming the descending
trigeminal tract (Trd). Entrant root libers ol the \estibular di\ision of
the eighth nerve pass either through the substantia gelatinosa or between
it and the corpus restiforme on their way to Deiters' nucleus. The prominence
ol the \estibular area as it appears in ri'liel in the lloor ol the lourt h \ en t ride,
as well as the dimensions of these two nuclear structures seen in cross section,

514 THE HIGHER ANTHROPOIDS

convey the impression of a balanciniz; mechanism upon which less demand is
made than in liu' lower, more strictly arl:)()real |)riinates. The orang is
altogether slower in its locomotion, l)oth m its arboreal pursuits and on those

FIG. 233. OKANG-OUTANG. LEVEL OF THE \HST1BLLAK NUCLEI.
CTT, Central Tegmental Tract; cow, Ventral Spinocerebellar Tract; ici', Inferior Cerebellar Peduncle; 10,
Inferior Olive; mf. Mesial Fillet; nar. Nucleus Arciforinis; nd, Deiters' Nucleus; nr. Nucleus of Rolando;
NSC, Nucleus of Schwalbe; n8. Acoustic Nerve; pd, Predorsal Bundle; pl, Posterior Longitudinal Fasciculus;
PY, Pyramid; rep, Reticular Formation; rst, Rubrospinal Tract; spt. Spinothalamic Tract; trd. Descend-
ing Trigeminal Tract; Tuu, Tuberculum Acusticum. [Accession No. 199. Section 285. Actual ,Sizc
20 X 12 mm.]

rarer occasions when it (^oes u|)on the ground. I he dillert lux- in all prol)al)ility
is slight, for the efficacy of the balancing mechanism set'ins to be laiily well
standardized. What one s])ecies requires most m some speciali/ed dux'Ction
is less essential to other loinis. An axcraging ol balancing requirements seems
to equalize the development of eciuilibratory structures.

In the ventrolateral portion ol the section, the ctphalic t'\trt'init\ oi
the inferior olive appears (10), and mesial to it the bundles constituting

SIMIA SATYRUS, THE ORANG-OUTANG 515

tlu' p\raiiiicl ( Py). Extcnclin^^ clircctlx' l)ack\var(l toward the lloor of the
\fiitiick' is tlu' tlc-nse huiKllc of tlir nu'sial lillct (Ml). W-iitroiiU'sial to
tlic ])\raiiiicl IS a larm' (.■oHfction ol gray matter constituting the arcilorni
nucleus (Nar) which, in all probability, is a caudal extension of the
jjontile nuclei. In any east', these two nuclear structures are definitely
continuous, thus creating the impression that e.\|)ansions ol the nuclear
specializations of the pons ha\e rt'sorted to a caudal extension in order to
accommodate their apparently exuberant growth.

LE\"EL OF THE CEREBELIAK NUCLEI (FIG. 234)

At the le\el of the cerebellar nuclei the contour of the section has under-
gone marked alteration chielly beeaust' of the continuitx ot the stem with
the cerebellum b\ means of the middk' cerebellar ])eduncli' i M cp). The
large mass of the niedullarx xcstibule of the cerebellum ap|)ears on the
lateral aspect of the section and contains the somewhat conxoluted and
i:)oorly defined nucleus dentatus (Ndt). Mesial to it in the roof of the
ventricle is tlie nucleus globosus. Both the size and dehnition ol the
dentate nucleus, as compared with tlu' lower jjrimates, indicate an animal
with a greater degree of coordinati\e control over the musculature. Although
the increased dimensions of the dentate nucleus as comparetl with the lower
primates is evident, there is an ec|uall\ striking contrast when this nucleus
is compared w ith that of the higher forms, it then appears less well defined,
less i^romineiit and smaller than in t lu' other great anthropoids, implying
that orang is not so well ])ro\ ided in muscular coordination as those
primates standing above it in tin- scale.

The central gray matter forms the lloor of the ventricle (Ven iv)
without special nuclear dilferentiatioii. Mesially, the posterior longitudinal
fasciculus comes closer to the ventricular lloor than is the case at lower
levels. Some fibers of the cochlear division of the eighth nerve (N 8) enter the

5i6 THE HIGHER ANTHROPOIDS

dorsal cochlear nucleus, and others, either as secondary relay fibers or as
fibers primarily recei\'ed from [hv cochlear di\ision itself", pass uiward and
forward along the \entral portion of the tegmentuni to form the massive

FIG. 234. ORANG-OUTANG. LEVEL OF THE CEREBELL.\R NUCLEI.

CEEJL, Cerebellum; mci', Middle C'erebellar Peduncle; mf. Mesial Fillet; ndt, Cerebellar Nuclei, Lateral
Group; NFG, Cerebellar Nuclei, Mesial Group; n8, Auditory Nerve; pn. Pontile Nuclei; i>v. Pyramid; REF,
Reticular Formation; sci>, Superior Cerebellar Peduncle; so, Superior Olive; \ i;n i\ , Founli \ intricle; ver.
Vermis (x-rebelli. (Accession No. 199. Section 365. Actual Size 45 X 25 nini.|

decussation of the corpus t rape/oidi'um. At the lateral e\tremit\ ot the
corpus trapczoideum is an aggregation of gra\ matter, the caudal extremity
ol the superior oli\ary nucleus i SO). This nucleus, like tlie trapezoid bod\',
is related to the conduction ol auditorx impulsi's receixed by the coch-
lear division of the t'ighth nei\e. \ entrolateial to the entering libiTs ol the
cochlear division of tlie eighth nerxc is tlu' substantia gclatlnosa Rolaiidi
surrounded u|)on its lateral as|:)fet by the desciMulmg trigeminal tract.
Directly ventral to the sui)stantia gi'latmosa is a w ell-dclmed nuclear

SIMIA SATMU'S, THE ORANG-OUTANG 517

mass, till' nucli'Lis facialis. From ihis lacial nucleus many myrlinizccl
libers pass backward ami inward, toward the Moor of the fourth \entricle
where the\ beconu' assi'inbled to lorm the second portion of the emergent
course ol the stAcnth nerw. In tlu'ir usual \entral area are the libers con-
stituting the p\ ramid ( Pv), now surrounded b\ a large nuclear aggrega-
tion, the caudal e\trcmit\ of the pontile nuclei ( PN ). Lying in a
position more trans\erse than in thv lower sections, is a bundle of libers mark-
ing the boundar\ between the tegmentum and the basis, the nu-sial
fillet (Ml ), through w Inch pass the di'cussating libers ol the corjius trapezoid-
vum. 1 hus at this le\el it is possible to make a lairly accurate comparison
ol the \()lumc ol im|)ulses passing o\er the mesial lillet and the pyramid.
Both ol these fasciculi appear more ample than in the lowi-r primates, a
conclusion which would |ustil\ the impression that orang is an animal inort'
highly endowed in discriminatiw sensibilitx' and also m \'ohtional control of
motion.

LEVEL NEAR THE CAUDAL LIMIT OF THE PONS \AROLII SHOWTNC. THE
EMERGENT FIBERS OF THE SL\ IH NER\ E (FIG. 235)

Heri' the section presents those marked changes incident to the appear-
ance ol tlu' t\pical pontile stratification. The pons consists of the stratum
suiK'rficialc; the stratum coinplexum, containing the large mass of jjoiitile
nuclei, trans\erse liln'rs and the scatterttl bundles of the j)\ramidal system,
and thestratum prohmdum compost'd largelx ol tiansxerse libers. The general
size of tht' pons Varolii, especiall\' of tlu' jjontile nuclei, implies an animal
possessed of a high degree of coordinati\e control oxer tlu' more complex
acquired moxemeiits. it indicates an ample communication between several
areas of tin- neopallium and the lati'ral lobes ol the cerebellum. The pallio-
poiito-ccrebellar system, as has alread\ been shown in |>revious discussions,
is characteristic of the mammalian brain alone, its predominant de\elo])-

5.8

THE HIGHER ANTHROPOIDS

mental IVaturc is witnessed in the expansion of the eerebral hemispheres. The
fact that this system, which connects the cerebral cortex with the cortex of
the lateral lobes of the cerebelhim, should manifest itself onl\ m the mammal,

FIG. 235. ORANG-OUTANG. LEVEL NEAR THE CAUDAL LLMITS OF THE PONS,
SHOWING THE EMERGENT FIBERS OF THE SIXTH NER\E.

MCi>, Middle Cerebellar Peduncle; mf, Mesial Fillet; nau, Abducens Nucleus; nr. Nucleus ol Rolando; n6,
Abducens Nerve; N7, Facial Nerve; pn. Pontile Nuclei; pv. Pyramid; rst. Rubrospinal Tract; scp, Superior
Cerebellar Peduncle; so, Superior Olive; trp. Trapezoid Body; trd, Descending Trigeminal Tract; iv.
Fourth Ventricle; ver, Cerebellar Vermis. [Accession No. 199. Section 410. Actual Size 40 X 25 mm.]

denotes the introduction into mammalian organization of a feature, which, it
not morphologicall}' new, is at least product ixc ol new attainments. As such
it calls for comparison with the mtramammalian species to determiiu' what
decisive physiological accession to vertebrate beha\ lor brought this imjjor-
tant svstem into existence.

SIMIA SAT^'RUS, THE ORANG-OUTANG 519

Manx tacts alrevidx exist to prow the essential ix'lation ol the lateral
lobes of the eerebelhini to the arms and the legs. Similar inclieations |)oiiit to
expansions in the lU'opalliuin as a res|)onse to this linil) speeiali/ation. This
evidence seems to put bexond peradxeiiture tlu' C|Liestioii that api)(.'ndicular
speciali/ation sup]:)lK's the (k'\ I'lopmental moti\'e which underlies such far-
reachini; ditlerentiation in the central nerxous system. But limbs are ahnost
as ancient as the \frtcbrate stock itself. Tlu'\ are not characteristic of the
mammalian class alone. Some s])ecialized element intrinsic to the extremities,
and not necessarily apparent m their morpholouical structuri-, therefore,
must be sought to explain this pronounced de\elopment ol the mammalian
hemispheres, cerebral as well as cerebellar. Ho\ve\'er convergent or divergent
the fore- and hindlimbs of rt'ptilcs and birds, anii:)hibia and (ish may be in
structural comparison with those of mammals, there is a lunctional diver-
gence between them which is constant. In inlramammalian orders all mo\e-
ments of the limbs tend to be s\nchronized with the movements of the body
and w ith each other. Thert' appears to be little need of independent motion
on the part of one or the other limb.

In the mammals, on the otiier hand, there is an increasing degree of
independent action in the lore- and hindlimbs and also in one loreiimb
independent of the other. Similarly, oiu- hindlimb may act inde])endentl\-
of all the others. Such iiuk'pendence of action strikes a new note in tlu'
motor organization of the extremities. The appendicular museulalurc liber-
ated itself from that dominating ck-peiuk'iic\ of interaction t'xisting between
the movable parts of tht' body. It gained a freedom which (k'ti'rmined a new
motor objective. Each limb, ha\ing acquired an indi\iduality ol its own,
develops a specilic s{)here of action. In this sense the fore and hind extremities
of mammals ditfer from those of lower xertebrates. Serving as more or k^ss
highly indi\ idualized instruments, the limi)s are capable of expressing what
amounts to a new physiological endowment. At the same time the\ retain

520 THE HIGHER ANTHROPOIDS

many details of their primordial subjugation in that tonimunity ol interests
necessary to cooperation of the entire musculature tor the purposes ol locomo-
tion. In their more recently acc[uned cajxicity, the extremities de\eli)|)ed
numerous performances, ne\v both m design and range, which called lor
expansions in the controlling mechanisms of the central ner\()us system.
The neopallium was the brain's structural response to this demand, simul-
taneously with w hich the cerebellum expanded to atlord a needed increase ot
coordinative control lor these nc\\ activities. It is evident that all ol this
motor adaptation belonged to what may be called ncohintiic or'^ani/.alKin,
which diHers materially Irom those older, more primordial activities which
arc attributed to the jHilcokinclic oriiuni/.ation of lower vertebrates. The j^on-
tile structures denoting this neokmetic expansion in the pallio-ponto-cere-
bellar system are e\ident in the orang; il. not so ])romiiient as m the higher
anthropoids, they are still much more conspicuous than m the lower and
intermediate primates.

The distinction between the basis pontis and tegmentum pontis is
established b\- the transverse ])osition of the nu'sial lillet (Mf) which
occupies the most \entral position m the tegmental portion ol the stem
at this level. The transN'erse fibers ol the basis pontis arc shown m their
collected mass as they constitute the middle cerebellar peduncle (Mcp).
The central gray matter h)rnis the lloor of the fourth \iiitricle (i\) and
is specialized in its median portion as a nucleus giving rise to the sixth
cranial ner\e ( N ab). The libers of this ner\e ( N6) pass from the nucleus in
the direction ol the basis toward their point of emergence in the bulbopontile
sulcus. Latt'ral to this nucleus is a denst' bundle of emergent libers constitut-
ing the tourth jxirt of the intramedullary course of the facial ner\e (N~).
Mesial to the bundles forming this emergent root is the caudal extremity
of the nucleus facialis itself. The roof of tlu' xcntrich' is formed In the

■ - i.i.'i

SIiMIA SAT^ RUS, THE ORANG-OUTANG

521

inferior portion ol the cerebellar \ermis (V'er). The rt'tieular rorniation
nnbraei's tlu- most exteiisixt' |)ortion dI the le^mu'iitum hut shows no spt'-
cialized nuclear collections at this k'X'el, nor are its boundaries well clchiu-cl.

FIG. 236. ORANG-OUTANG. LEVEL OF THE MIDDLE OF THE PONS \ AKOLII.
MCi>, Middle Cerebellar Peduncle; mf. Mesial Fillet; Mst, Nucleus of Bechtcrcw; nr, Nucleus of Rolando;
N5, Trigeminal Nerve; \7, Facial Nerve; I'x, Pontile Nuclei; i>v. Pyramid; Kiu. Reticular Formation; scp,
Superior C^erebcllar Peduncle; tki>, Descending Trigeminal Tract. [Accession No. 199. Section 460.
Actual Size 28 X 19 mm.]

It gives the impression of a clilfuse region of uiulilferentiated gray and white
substance.

LEVEL THROUGH THE MIDDLE OF THE PONS \ AKOLII (FIG. 236)

Here the section shows all of the salient features in the stratified appear-
ance of the pons Varolii. These include the stratunisuperliciale, thccomple.\uni

C22

THE HIGHER ANTHROPOIDS

and the profundum. They aflord again an opportunity for estimating the
relative size of the pontile nuclei ( PN ). The trans^•erse libers of the pons are
collected to form the middle cerebellar peduncle (Mcp). The central

FIG. 237. ORANG-OUTANG. LENEL OF EMERGENCE OF TROCHLEAR NERVE.

CEN, Central Gray Matter; err, Central Tigtnental Tract; i.i , Lateral Fillet; mf. Mesial Fillet; N4, Trochlear
Nerve; pd, Predorsal Bundle; PL, Posterior Longitudinal Fasciculus; PN, Pontile Nuclei; pv. Pyramid; ri;f.
Reticular Formation; scp, Superior Cerebellar Peduncle; SCPX, Decussation of the Superior Cerebellar
Peduncle; sit, Spinothalamic Tract. (Accession No. i(>(). Section 560. Actual Size 19 X 16 mm.]

gray matter, uliiie reduced in size, forms the floor of the \tntiicle whose
general dnnensions are now consicU'rablv h'ss than in thi' lower ie\ els,

SIMIA SAIMUS, THE ORANG-OUTANG 523

clue to tlu' tact that llxv \ mtrifular chatnhcr is approaching the caudal
orifice ol the SvKian aqut'chict. I hi' lloor ol the' \entiich' shows no particular
luich'ai" s|)eciahzation. In It are the transxerse hhers constituting^ the third
portion of the lacial ncr\c m its eiiier<ient course from the l)rain, know n as
the genu facialis (N"). Entering: m rehition to the be<iinnin^ ol the inicldle
cerebellar peduncle are the lihers ol the dorsal root ol tlu' trigeminal ner\'c
(N5). These libers pass inward to come into relation with a somewhat con-
\'oluted mass of gray matter, the ce|jhalic extremity ol the substantia
gclatinosa trigcmini, here torming the com olutiones ciuinti (NR), and
ventral to it a large homogeneous nucleus from w hich arise the fibers forming
the motor root of the trigeminal ner\e, the nucleus masticatorius. The lateral
walls of the fourth \entricle at this le\el arc prockiced b\ tln' massive col-
lection of libers constituting the superior cerebellar peduncle (Sep).

LE\EL OF THE INFERIOR COLLICULLS (FIG. 238)

At this le\el the contour of the section is considerably moditied by the
appearance of two elevations m the roolplate of the midbrain. These are the
inferior colliculi ( ICt directly connected with the auditor\- system, since they
serve as relay stations in that pathway. They were formerly of greater func-
tional importance than in this or other jjrimates. The ventral aspect ot the
section still retaining some of the |)ontile constituents is ol [)articular interest
as it indicatt'S the transition from the pontile level of the stem to the di\erg-
ing cerebral |)cduncles. A dee[) \entral sulcus in the pons indicates the posi-
tion at which the dixarication will occur, while at the junction between the
basis and tegmentum in tlu' midline, a small space marks the position of the
foramen caecum anticum. The central gray matter (Cen) entirely sur-
rounds the Sylvian aqueduct and in its vcntromesial portion is specialized
to form the trochlear nucleus, or nucleus of the fourth cranial ner\e ( N4),
whose emergent fibers are seen collected in a dense bundle occupying a posi-

FIG. 238. ORANG-OUTANG. LEVEL OF IHH LNFEKIOH COLLICULUS.

CEN, Central Gray iMattor; err, Central Tegmental Tract; ic, Interior C^olliculus; Lr, Lateral Fillet; mf,
Mesial Fillet; ntk. Trapezoid Nucleus; N4, Trochlear Nerve; pd, Predorsal Bundle; pl. Posterior Longitudi-
nal Fasciculus; i>n. Pontile Nuclei; i>v. Pyramid; RiiP, Reticular Formation; rst. Rubrospinal Tract; si>T,
Spinothalamic Tract; si>x. Crossing of the Superior Cerebellar Peduncle; tmt, Tractus Mesencephalici
Trigemini. (Accession No. 199. Section 594. Actual Size 19 X 19 mm.j

I524I

SIMIA SAT^RUS, THE ORANG-OUTANG s^5

tion ill the margin of tlu' tt'iitial pray matter. Latcrallv, the central gray
matter contains tlie mcsenceplialic root of the fifth nerve and in a more
\x'ntral ])osition are the- dense l)iiiidles constituting the j^osterior longitudinal
lasciculus ( PL I. The boundary line hetweeii the basis and tegmentum at
this k'\-el is indicated b\ trans\-ersel\ disposed bundles forming the mesial
lillel (iMlj, lateral to which arc' the hbers constituting the large fasciculus
of the lateral lillet (Li ), an important intermediar\ s\sttin of fibers in the
auditory ]xith\\a\-. The most important structure at this le\-el is, however,
represented by the colliculus, as its s|)c'cialization forms a relay station for
the auditory sense. The colliculus is less prominent than in the lower \ crte-
brates and considerably less so than in the lower and intermediate' primates.
It still retains many vestiges of its former histological s]:)ecialization. A
number of strata may still be discerned m it, reminiscent of its stratification
111 the miramammalian \ crti-brate.

LE\EL OF THE SUPERIOR COLLICULUS (FIG. 239)

At this level the section shows those changes peculiar to the appearance
of the cerebral pechmcles m the basal region and the t'lexation caused b\ the
more cephalic i^rommenccs in the C[uadrigeminal plate. The superior colliculi
(SC) a])pear as delimti-lx' specialized structures which inicidsco])i(.ally show
a faint degree ot stratilication. Their cle\ation is less pronounced than is
the case in certain others ot the primate series, irom their general character
the inference seems iustified that the lunction w hich the\ represent, namely,
vision, could at best be but iiu'lli'ctuallx carried on bv them. I heir \fstigial
condition as comparid with the lower vtMtebrates is so jjronounced, both
as to size and histological detail, as to suggest a decrease in tunctional
acti\it\ . The process of \isiial delegation to the occipital lobe of the cerebral
hc-misphere, which in these studies has become so familiar a subject of discus-
sion, is exident in tlu' orang. The continuation ol this telencephahzation is

5^6

THE HIGHER ANTHROPOIDS

carried to a still fiirtluT extent in the higher anthropoids and man. Even in the
|)riinate order, therefori', this sign ol e\olutional progress in the ner\ous sys-
tem is elearU manifest.

FIG. 239. ORANG-OUTANG. LEVEL OF THE SUPERIOR COLLICULUS.

CEN, Central Gray Matter; ci>, Cerebral Peduncle; ctt, Central Tegmental Tract; mf, Mesial Fillet; mgb,
Mesial Geniculate Body; Noc, Nucleus Oculomotorius; nru, Nucleus Ruber; N3, Oculomotor Nerve; pd,
Predorsal Bundle; pl. Posterior Longitudinal Fasciculus; ruf. Reticular Formation; sbn. Substantia Nigra;
SC, SupcriorColliculus;SPT, Spinothalamic Tract ;TMT, Tract us Mesencepl),! I iciTrlfiemini. [Accession No. igg.
Section 636. Actual Size 26 X 13 mni.|

The central gray matter fCen) surrounds tlie S\Ivian aciueduct, and
in its more ventral portion becomes speciahzed to form the oculomotor
nucleus (Noc). This nuclear collection is among the most important of
the cranial nerve groups, not because tfie muscular territory o\ cr which it

SI. MIA SAT\"RUS, THE ORANG-OUTANG 527

pifsidt'S is c'xtcnsnc, hut hccaust' thr imisclc-s tluiustU rs, howt'Ncr delicate
and small, arc capal^lc ot produtin^ the most exactly ad|iistcd ol all move-
ments 111 the body. Ocular moxements are so minutel\- ada|ited to the func-
tion ot \ision, that the slightest de\iation ot the I'xi'ball olOne or both sides
will disturb the process ol \isual lusion, or produce other defects in visual
perce])tion sullicient to disorganize the special sense ol sight. The object of
conjugating the exelxdls so that their \ isual axes shall remain in parallel, or
be convergent to that degree necessary lor the prompt binocular lusion in near
vision, requires the most delicate of muscular mechanisms for its achieve-
ment. This acti\it\, in addition to the immediate read|ustments necessary
to distant vision, exerts a lar-r(,'aching mlluence upon all neokmetic organi-
zation. There can Ix' no question that \ision operates as an essential, sup-
plementary aid both m the acc]uisition and m the control ol a vast number ol
highly skilled motor acti\ities.

So important a musculaturt' as that of the eyeballs requires a compli-
cated nuclear structure for the linal distribution of its innervating impulses.
The visual distance recei)tors of the two eyes are in reality one organ in the
primates; at least, they are dual onl\ in the sense of their morphological
organization. l-*hysiologically their object is to give their possessor a unilied
impression of the world u])on which he gazes, without reduplication, without
distortion, without acUentitious mobilitx. Since the two eyes, serving this
purpose, act as a single organ, the two nuclei b\ which the eye muscles are
moti\ated so operate in unison that they ma\ be rightlx considered a single
nucleus. This unity in structural design of the oculomotor nucleus is deter-
mined b\ a close internuclear communication across the midline pro\ ided by
a great number of crossing libers w Inch |xiss from one side to the other, the
oculomotor, commissural and decus.satmg axons. These libers conjugate
the oculomotor, nuclear groups on the right and left side and so produce
the desired unity.

528 THE HIGHER ANTHROPOIDS

TIk' iiitcnuic'lt'cU" c'omnuinication [x'lwccii the two s\ ninictiical cli\isioiis
of tin- nuclei supplying impulses to the eye muscles depends ujjon the extent
to which the commissural and deeussatmg hhers are de^•eloped. Then- exten-
sive development in the orang denotes a unification ot the \ isual jjroccss
calculated to produce a high degree ol hmocular \ ision. The libers of the
oculomotor nerve ( N 3 ) pass forward to the oculomotor sulcus, whence they
emerge at the base ol the brain in the optico-peduncular space. In their course
they pass, some through and some around, a large nuclear structure which
has diflerentiated in the \cntromesial portion ol the reticular lormation
and constitutes the red nucleus (NRu). Not only the size biit the clear
delmition of this nucleus in the midbrain shows a distinct ad\ance m its
organization as compared with the lower and intermediate primates. It
supplies collateral exidence which, m coniunction with the increased size
of the lateral lobes of the cerebellum, with the increased com[)lexit\ of the
dentatt' nucleus and with the increased size of the superior cerebellar pedun-
cle, indicates that coordination has undergone considerable expansion in
passing upward to this higher lorm of anthropoid. Such must necessarily be
the case m \iew ol the animal's high dillerentiation ol upper extremity and
hand. Com])ared with tlie gibbon, for example, the orang-outang employs
the hand lor man\ pur|)oses much more humanoid in character and rctjuirmg
the organization ol a wider range ol mo\-cmcnt. The greater (k'hnition and
larger size ol the red nucleus in this form signillesan extension ol coordmatixc
control. The reticular lormation is less extensix'c than in the lowt'r lorms and
in its \-entral portion contains the libers of the nu'sial liilct iMf). The
latter separates the rt'ticular lormation 1 Ret I Irom a laigt' nuclear mass
extending oblitjuely across the dorsal aspect of tlu' peduncle, the substantia
nigra fSbn). What the exact physiological signilicanci' ol this structinx-
may be is still 111 doui)t, although the control of certain automatic associated
movements has been attributed to it.

SIM I A SAT\RUS, THE ORANG-OUTANG 529

Till' basis of till' c-iTi'hral pcdLincli' iCP) is (.■ntiiclx nu'cliillai\ . It
contains tlu' bundles of libers which make up the pxramidal tract and
tlu' palllD-ponto-cerebellar liber s\ stems. Nowhere in tlu' brain is the
relative importance of iiln'r systems more clearly indicated than m this
instance. These two s\stems, botli arising in the cert'bral cortex, both
e\pandin<i; in volume, size and capacity as the cerebral cortt'x increases in
the exolutional sense, both concerned with the eUcrent conduction ot ncr\c
imi:)ulses known to be closely associated with the regulation ol motor per-
rormanccs, exceed in size all other similar systems ol the neuraxis. Incre-
ments in the size of the basal portion ol' the cerebral ]X'duncle are in direct
proportion to expansions of areas m the cerebral cortex, j-'roiection libers
arisin<i in the neopallium, as, for exampk-, those constituting tlu' |)\ramidal
system as well as thosi' enterin<i into the formation ol the pallio-ponto-
cerebellar system, denote the ik'o kinetic capacit\ of the animal. 1 he e\ idence
allorded b\ the increased xolume of the cerebral peduncle is suscei)tii)lc of
but a sin>ile interpretation, nanu'l\, that expansion has taken place in
direct proportion to extensions m beha\ loral perlormance, due to the acquisi-
tion of more complex, more numerous and more xaricd motor acti\itics.
This phyletic history of the cerebral peduncle furnishes testimony in tavor
of a progressi\'c cxolution throughout the primate order.

At the lateral extremitx of tlu' ri'ticular formation is a pronounced
elevation, the mesial jicniculate body l^Alf^bj, which recci\es some libers
from the lateral lillet.

From the functional point of \ it'w this lex el signilics certain adxances
in the \isLial sense, which appear in the tendenc\- to accjiiire more capacious
areas for the extension oi' \ ision w ithin its ow 11 s[)heri' as well as its associa-
tion with sensorv impressions in other spheres, such as hearing and body
sense. This midbrain lc\el also dcnotts the |:)rogress in the exact conjugation
of ocular movements for the purpose of binocular and stereoscopic vision.

530

THE HIGHER ANTHROPOIDS

LE\'EL OF THE OPTIC CHIASM (fIG. 240)

At the level of the optic chiasm the brain has passed into its (heneephah'c
portion which contanis xhv thnd xcntricle (V3), hounded upon t'ither

FIG. 240. ORAXG-OLTANG. LEVEL OF THE OPITC CHIASM.
CIN, Internal Capsule; CPii, Corpus 1 lypothalamicuiii; i dp, Deseending Pillar of the Fornix; loK, Fornix;
CLP, Globus Pallidus; nca, Caudate Nucleus; nl, Lateral Nucleus of the Thalamus; nli. Interna! Lateral
Nucleus of the Thalamus; nlv, Ventrolateral Nucleus of the Thalamus; opx, Optic Chiasm; put, Putamcn;
VQ, f'asciculus of Vicq d'Azyr; V3, Third Ventricle. (Accession No. 199. Section 754. Actu.il Size 42 X 29 mm.]

side by the optic thalami and hridiied across by the comniissura molhs. The
optic chiasm (Op\) ap|)ears in the most \t'ntral position ol the st'ction as a

SIMIA SATVRUS, THE ORANG-OUTANG 531

dense huiulK' oi crossinij; lilx'rs fonncctt'd dorsally with the optie tracts and
\entiall\ with tlu- uptic nerves. The optie thalamus is separated from the
most \-entral portion ol the endbram eonstitutmii the globus pallidas ( Glp)
by a dense bundle ol libers many ol which occupied positions in the cerebral
peduncle. This bundle ol libers is the internal capsLile (Cm). Dorsal to
the optic chiasm is a slight bundle oi decussating libers known as the
supraoptic decussation ol Me\nert. Tlu' other structures ol tojjographical
interest in the section are indicated by appropriate letters in the caption
accompanying tlie tigure.

Chapter .Will

RECONSTRUCTION OF THE GRAY MAIIER IN THE
BRAIN STEM OF SLMIA SATVRUS, THE ORANG-OUTANG

Y' I ^1 IE gray niattcT m the hraiii slcni of llu' oranii;-outan<i in many

I respects resembles that m the human. The component structures

II have mati'riall\ uureasecl in size, their complexity is greater and the

entire organization of the central nervous system shows a distinct ad\ance

over the lower primate forms.

In the high cer\ical lexels ot the spinal cord the conliguration ol the gray
matter is idi'iitical with that in the human cord. The central gray matter is
more or less cjuadrilateral in shape, connected at its ventrolateral angle with
the ventral gray column. Extt'iiding Irom its dorsolateral angle is tlu' narrow
eer\i\ ot the dorsal horn which is capped by the substantia geiatinosa
Rohmdi. The dorsal sensorx' nuclei ha\'e already made their aj^pearance m the
dorsal columns, although the distal portion ot the nucleus ot Goll is not yet
connected with the ct'iitral gray matter. It is represented b\ a narrow, com-
pressed strij) ot gra\ matti'r 1\ ing m the \eiitrodorsal plane close to the mid-
line, completel\ surrounded by fibers ot the column ol Goll. I he dorsal horns
are alread\' showing their tt'iideiicx to mo\c into a lateral position. This
tendency is sliow n more 1)\ the lateral inclination ol the e\tremit\ ot the
dorsal horn than b\ the cer\ i\. On tlu' latt'ral sick- of tht' \entral gray column
the ri'ticular lormation appears as a small triangular area.

The Dorsal Sensor^' N'l clei

The nuckais ot Goll appt'ars in the Inst k'\ els ot the reconstruction as an
indepeiuk'nt, com|M-essed band ot gray matter lying among the libers of the
column of Goll. It tiuickly establishes connection with the dorsal surface of

533

534 THE HIGHER ANTHROPOIDS

tlu' M'litral gray matter and continues upward as a Hat strand showing but
littk- inclination to increase in size. Upon the first appearance of the nucleus
of Burdach, the nucleus of Goll shows cielinite and marked expansion in its
dorsal extremity. It increases in size laterally so that its outline presents a
tree-like appearance, the branches of which are directed lateralis from the
dorsal midline. The nucleus st)on occupies almost the entire area of the
column of Coll.

The nucleus of Burdach appears as a small, sessile condensation in the
dorsal surface of the central gray matter, lateral to the base of the nucleus of
Goll. It expands rapidly in size and is displaced laterally by the increasing
bulk of the nucleus of Goll. The entire dorsal nuclear mass begins to show the
ellects of the opening of the fourth ventricle. A marked displacement takes
place in the dorsal sensory nuclei, as is c\idenced by the lateral shiftingof these
nuclear masses. The nucleus of Burdach becomes arborescent in appearance,
Its dorsal surface oxerhangmg the substantia gelatinosa trigemini w Inch lies
ventral and somewhat mesial to it. The nucleus of Goll continues upward
beyond the opening of the fourth ventricle, forming a part of its lateral mass.
.At aboul the caudal level of the fourth \entricle it begins to decrease and it
rapidly is submerged from view by the apj:)roximation of the lateral mass of
the fourth \entricle and the dorsal aspect of the nucleus of Burdach. This
latter nucleus continues upward to a little abo\'e the mid-pomt of the ven-
tricle, where it begins to decrease in size and then disappears to gi\ e place to
the vestibular complex. This complex extends Lipward in approximately the
same topographical relation as that show n successively by the nucleus of Goll
and the nucleus of Burdach.

The substantia gelatinosa trigemini occupies a |)osition w Inch indicates
its continuity with the substantia gelatinosa Rolandi of the spmal cord.
Passing upward into the oblongata, it assumes its lateral position. In the
lower levels the direction of the gelatinous cap is more or less trans\ erse, but

RECONSTRUCTION 01- SIMIA SAT^ RUS

53:

as the structLirc is followed u]3\\arcl into tlu' stiTii the luiclcar mass uncicTgocs
a partial rotation until its dorsal surface isdireettd towards the lateral periph-
ery of the oblongata. The eonstrietion whieh was found to he almost con-

FIG. 241. VENTRAL SL HP ACE OF GRAY MATTER OF BRAIN STE.M, SIMIA SATVRLS.

Key to Diagram, inf. olive. Inferior Olive; i-Ar. f;t;N. body, L.iteral Geniculate Body; meso-g. body.
Mesial Geniculate Body; pontile, Pontile Nuclei; ret. form., Reticular Formation; v. CH. and vent.
COCHL., Ventral Cochlear Nucleus; v. or. col. and ventral gray col., Ventral Gray Column.

stant in the conformation of this nuclear mass is not so well delined in Simia
satyrus as in the other s[)ecies. It is faintly indicated at tlu' mid-ventncular
le\el of the stem. The substantia gelatinosa trigemini continues upon the
surface of the reconstruction to a point \\hich corresponds ap])r().\imately to
the closure of the pontile Ncntrieular ca\Tty. Here it expands to lorm the
caput of the nucleus and at this point comes into relation with the motor
nucleus of the trigeminal ner\e.

The Inferior Oli\ arv Nucleus

Tlu' inlt'iior (>li\ar\ nucleus in the orang-outang assumes considerable
complexitx and bulk. The fundus of the nucleus is broad and disposed toward

536 THE HIGHER ANTHROPOIDS

the wntrolatcral angle of the ncuraxis. It begins just below the le\el ol the
fourth ventricle, extending its two branehes mesiallx' and somewhat ciorsally
toward the median raphe. Both the dorsal and the ventral branehes show
marked reduplieation. The ventral accessory oli\ary nucleus begins at the
level in which the main nucleus arises. It extends upward as a Hat band
applied to the ventral asjX'Ct of the main nuclear mass. It approaches
the cephalic limit of the main nucleus, becoming continuous with
the dorsal extremity of the ventral branch near its summit. The dorsal acces-
sorv olivary nucleus begins below as an mconspicuous mass at about the
same level as the main olivary nucleus. It ra|)idly extends in a ventrodorsal
direction, lying as a Hat band dorsal to the mesial half ol the dorsal branch
of the main nucleus. At the cephalic extremity of the principal nucleus it
becomes conlluent with the dorsal extremity of the dorsal branch. The entire
C()mj)lex extends as far upward as the midventricular level oi the brain
stem, where it disappears by merging with the reticular matrix. Its ventral
surface is in contact with the pyramidal tract and the ventral portion of the
mesial iillet. Its iLindus is covered onlv b\ the external arcuate libers, while
its dorsal surface is in contact with the \entral suriace of the reticular
lormation.

The Reticular FoRMAriox

At a point slightl\ above the lowest sections of the reconstruction, the
ventral gra> column becomes detached from the central gray by the decussat-
ing pyramidal libirs. This gray column is soon replaced by the reticular
formation with which it merges and e\entually disappears. The reticular
formation itself is seen in the lowest lexels of the reconstruction as a small
collection of mixed gray and whitt' matti'i' on the outer suriace ol the \-entral
gray column. This rapidl\ incrt'ases m size as it is lollowed upward. It
extends dorsad to come into contact with the substantia gelatinosa Rolaiidi.

RECONSTRUCTION OF SIMIA SATYRUS

537

\c'ntr;ill\ and latcTall\ it passes toward tlu- Nfiitrolatfral angle of the
tegmentum. I lie dorsal surface of the reticular formation becomes broad
and is intimately connected with the \entral surface of the central gray

FIG. 242. DORSAL SURFACE OF GRAY .MATTER Or BRAl.N STE.M, SI.Ml.A SATYRUS.

Kev to Di.\<,r.\m. dors, coch., Dorsal C^ocliitar Nucleus; .\ieso-gen. body. Mesial Geniculate Body; nucl
oi' BURD.^cii, Nucleus of Burdaeli; N. of o., nuc. of drs. and nucl. of deiters. Nucleus of Deiters; nucl. of
r.oLL, Nucleus of Goll; ret. form., Reticular Formation; subst. gel. rolando. Substantia Gelatinosa of
Rolando; sup. coll., Superior Colliculus; vent, coch.. Ventral Cochlear Nucleus.

matter \vhich is now IJatti-nmg out. Tiie reticular formation gradually
mcreases m bulk, lorming the chiel nuclear mass ot the tegmentum in the
upper oblongatal and pontile regions. It embraces in these le\els the dorsal
surface ol the mlerior oli\ary complex. Dorsal to the retiiular formation lie
the nucleus ol Burdach and the nuch'us ol Goll, together with the increasing
mass of the \estibular com|jle\. The reticular lormation comes into contact
with the \cntral surface of the central gray matter forming the lloor of the
lourth ventricle.

538 THE HIGHER ANTHROPOIDS

The mesial surface of the retieuhir lormatioii throughmit its entire
extent is more or less smooth and separated from its U-llow nl thi' opposite
side h\ the loniritudinal liber traets near the raphe. Abo\e tlie le\el of the
substantia gelatinosa trigemini, and the vestibular and cochlear complexes,
the reticular formation expands and forms almost the entire' mass of the teji-
mcntum ot the upper pons and mesencephalon, it reaches the surlacc and
sends a mim[)er ol prolongations backward, one ol which lorms an iiuest-
ment o\er the suj)erior cerebellar peduncle as this liber tract approaches the
mesencephalic tegmentum. \ entrallx the reticular lormation comes into close
contact with the dorsal portion ol the lateral buttress oi the pontile nucleus.
Latcrall\' and mesiall\- it is in contact w ith the mesial buttress, while between
teshe two points ol a])])osition the \entral surface ol the reticular lormation
and the dorsal suriace ol the jjontile nucleus are separated by the trapezoid
body. In tlu' mesencephalon the reticular lormation is irregular in outline.
It is penetrated from behind forward by the superior cerebellar peduncle
which gradually sinks deeper into the tegmentum, thus allowing more of
the reticular formation to form on its lateral aspect. The diAclopment in the
mesencephalon ol the nucleus ruber presents a massi\e condensation in the
reticular formation. The reticular lormation of the mesencephalon, followed
upward toward the [)oint ot transition into the dienci'phalon, demonstrates
the continuity ol these two structures, the reticular formation of the mesen-
cephalon merging with the indiflercnt zona incerta of tin- intcrbrain. The
lateral surface ol the reticular lormation in the lower mesencephalic area is
crossed from belore backward b\ a di'pression produced by the passage of
the lateral lillet. In the mtercollicular region a continuation of the formatio
reticularis passes dorsalls and mesially to separate the two colliculi. In
the most cephalic j^ortion of the midbrain the retuiilai formation gives
origin to a similar dorsal prolongation which separates the superior colliculus
from contact w ith the nuclear masses of the epithalamus and metathalanuis.

RECONSTRUCTION OF SIM I A SAT^ RUS

539

The Pontile Nuclei

This nuclear mass is very nuicli more eomplieatecl tlian in any of the
lower primates. Although much more mtneate, the arranuenu'nt is identical

l-IG. 243. LATERAL SURFACE OF GRAY MATTER OF BRAIN STEM, SIMIA SATYRUS.
Key to Diagram, dors, cochl.. Dorsal Cochlear Nucleus; gen. body, Geniculate Body; inf. coll.. Inferior
Colliculus; INTERPED. GRAY MAT., Interpeduncular Gray Matter; nucl. of burdach. Nucleus of Burdach;
NUCL. OF D. and nucl. of drs., Nucleus of Deitors; nucl. 01 goll, Nucleus of Goll; pontile. Pontile Nuclei;
RET. FORM., Reticular Formation; subst. gel. of kolan. and si ust. gel. 01 koiando. Substantia Gclatinosa
of Rolando; vent, cochl., Ventral Cochlear Nucleus.

with that loiind m lower lorms. The |)resenee ol the superhcial hiyer corre-
sponds to the general conhguralion and curves of the hram stem. The deep
la\er is in contiguity with tlu' superhcial surlace ol the reticidar lormation
as well as with the two buttresses which serve to connect the superhcial and
llu' del]) layers of the nuclear substance at tliiir extremities. The arciform
nuclei are relatively well dehned, beginning at aijout the mid-olivary region
as strips of gray matter disposed along the mesial and ventral surfaces of
the pyramid. 1 iiese strips continue upward, gradually increasing until a

540 THE HIGHER ANTHROPOIDS

complete sheath is formed around the ])\raiiiid. The pontile nuelei luse at
the midhne. Passin<i; throu^^h the eavity of the nuelear sheath are strands
whieh produce the numerous bridges of gray matter separating the palho-
spinal and palHo-pontile hhers into smaUer groups. Tlie dorsal jjortion of the
hileral buttress is in contact with tlie \entroIateraI angle ol the reticular
formation and a similar arrangement |jresents itsell m regard to the dorsal
part of the mesial buttress. The dorsal surface of the deep la\ er of the |)ontile
nuclei and the ^'entral surfact' of the reticular formation art' not m actual
contact on account of the dcxt'lopment at this point of the \arious longitu-
dinal fibers. The pontik' nuclei begin to diminish as the isthmus is apj)roaclied
and rather rapidly come to a termination. The superhcial layer, together
with tlu' lateral and mesial buttresses, first begin to dmiimsh and then
disajjptar, lca\ing the deep nuclear layer to continue upward and become
conllueiit with the substantia nigra. The latter seems, therefore, to be sup-
ported by the upper extension of the two buttresses and throughout its
extent by tlie deep layer of tiie pontile nuclei.

The Vestibular Complex

The vestibular complex hrst ap|3ears as a small triangular collection of
nuelear material located between the lateral aspect ol the lloor ol the lourtii
ventricle and the upper dorsal j)orti()n of the nucleus of Burdach. It rajjidly
expands in size, acting as a wedge w Inch ser\es to separate the \entricular
floor from the latter nucleus. A prolongation is carried forward vcntrally,
which separates the mlcrior cerebellar peduncle Irom the ]:)()ntik' tegmentum.

At the mid-\'ent iieular lc\'el and dorsal to the nucleus ol Deiters, the
nucleus triangularis of Sehwalbe ap])ears. It lies beneath the lloor of
the ventricle. This nuclear mass continues upward to a j)oint at which the
ventricle begins to close, wlure it rai)idl\ terminates. The triangular nucleus
in the mid-ventricular Icxel is separated Irom the Ncntricular gray matter

RECONSTRUCTION 01- SIMIA SAT^'RUS 541

l)\ tlif dorsal tDclikai- nuclcLis, together with the striae acusticae which
cross It to enter {\iv lateral reeess ol the lourtli \entriele. Tlie nucleus of
Bechterew js eontinuecl dorsallx Irom the vestibular complex into the
lateral wall ol tlu' loiirth \fntriele and is well show 11 in the reconstruction.

The Cochlear Complex

The cochlear complex is relali\ely nisi<inilieant. The ventral cochlear
nucleus is so disposed as to prest'ut a trough which recenes the entering
fibers oi" the cochlear nerxe, which thus is surrounded on its ventral, hiteral
and dorsal aspects. Tlu' mesial aspect of the ner\e is in contact with the
rcstitorm hod\ and the tegmentum ol the metenccphalon.

The dorsal cochlear nucleus is also relati\ c'l\ inconspicuous. It is connected
with the ventral cochlear nucleus by strands of gray matter and also by the
libers which make up the enteruig cochlear root.

The CoLLici LI

The inU'rior eoHieukis appears asa condensation in tht'dorsal mesencepha-
lic reticular formation and is of somew hat greater size than is found in tludowcr
forms. This increase in size, however, is dt'peiulent only uj)on the general
increase in bulk. The eollieulus seems to be ol relatively less extent and sig-
nilieanet' in this form than it is in thosi' already described. It is supported
laterally b\ tlu' lateral extension of the mesencephalic reticular formation,
whereas dorsally it rests on the undilferentiated median gray matter. It is
separated from the sujieiior eollieulus by a lateral extension irom tlu' retic-
ular formation which passes dorsomesially in tlu' intercollicular sulcus.

The superior eollieulus is of moderate size, resting latei"all\ upon the
reticular formation and dorsall\ ujion tlu' dorsal median undillerentiated
gray matter. Its nuclian extremity is disposed similarly to that oi the inferior
eollieulus and is transversed b\ the formation in this region of the intercollic-

lo-
1

542 THE HIGHER ANTHROPOIDS

iilar commissures which join the inrenor conifuli and tlu' superior culheiih'
respectively. The sujx-rior collieuhis is separated Irom the dieneei)halic
structures by another dorsal extension of {\\v nieseneephanc reticular
formation.

The Substantia Nigra

The substantia nigra appears at tiie transition between the meten-
ccphalon and the ineseneephalon. It seems to be a speeiahzation from tiie deep
layer of the jjontile nuclei and is supported by the lateral and mesial but-
tresses. Its ventral surface is in direct relationship with the descending pall
spinal and pallio-pontile systems ol hbers. Mcsiallx' it is eontiiiuous wit
the indilferent interpeduncular gray matter from which it is separated by the
emerging fibers of the oculomotor nerve. It expands laterally as far as the
reticular bed containing the mesial and lateral geniculates. Dorsally it lies
in relationship with the ventral surlace ol the mesencephalic Testicular
formation. As the dicncejjhalon is approached it diminishes m extent and
finally disappears, seeming to gi\ e place to the zona incerta.

The Nucleus Ruber

The nucleus ruber appears at about the le\el ol the oculomotor nucleus
as a roundi'd, well-demarcated speeiali/ntion in the mesial portion of the
mesencephalic reticular tormation. It rapidl\ incri-asi.'s in si/.e to its maximum
and then as rapidly diminishes. It is surrounded at all points and separated
from the rt'tieular formation by the encapsulating libers derived from the
superior cerebellar peduncle.

The Central Grav Matter

The central gray matter has already btin described in conncx'tion with
the upper cervical levels and there presents the ([uadrilateral form which

RECONSTRUCTION OF SIMIA SA IMUS 543

is immcl in tlu- human hram stmi. It presents the usual lour an^K's: the
ventrolateral reeeivni^ the \cntral <ira\' eolunms, and the dorsolateral
rccei\in<i the dorsal gra\ eolunms. As the oljlon^^ata is approaehed the
eentral gray matter gixes rise to the dorsal nu'dullarx iiuelei, the nueU'us of
(m)II appearing shortlx alter the upper leAels ol the et'r\ leal legion are passed,
riu' nueleus ol Burdaeh appears at a eonsick'iahlx higlu-r le\el. As these
nuelei develop tlu' eentral grax' matter heeonies more llattened Irom side
to side and eontinuousl\ approaehes the dorsal surlaee of the stem. This is
very elearly show 11 h\ the diminishing anteroposterior extent ol tlu- dorsal
medullary nuelei. The eentral gra\ matter in the mid-ohlongatal region sends
out a narrow i^dlongation dorsallx which, ri'aehing the surlaee, bilureates
and extends laterally. The remainder ol the eentral gra\ a])parently follows
the li'ad of this extension, passing dorsall\- and llattening out laterally until
the lloor of the fourth \entricie is formed. The lloor of the fourth \entrielc
in the orang begins to show sonu'what more modelling than in the prec'eding
types. The suggestion of the hypoglossal and the \agal trigones ma\' be
diseerned in the lower half of the lourth \i,-ntriele. 1 lu' area aeustiea istairly
well dexeloped, erossed b\ the striae aeustieat'. In the u[jper portion ol the
xentriele the nu'dianix plaeed elexations eorresponding to the de\'elo|)ment
beneath them of the nueleus abdiieentis with the knee of the seventh nerve
are well marked.

Above the mid-\ entrieiilar le\ el of the stem the \c-ntrieli' rather rapidly
narrows by tlu- approximation of its walls. As the juiietion with the mesen-
cephalon is ])assed, the wails ol the aqueduet ol S\ l\ius, tormed by the een-
tral gray matter, beeome progressixely more massi\-e. In the mesencephalon
itself thi' eentral gra\ is continued forward as a fairly well-defined tongue
l\ ing on either side i^\' \\\v nudian rapiie. in this region dexelop the nucleus
trochlearis and the nucleus oculoinotorius. Abo\ e the le\el ol the oculomotor

544 THE HIGHER ANTHROPOIDS

nucleus the ventral prolongation of the central gray matter is continued lor-
ward, indicating the approach of this structure toward the thud \entricle.
When the third ventricle is reached this prolongation becomes contmuous
w ith the subependymal gray matter and the mesial group of the diencephalic
nuclei.

Chaptek X1\

TROGLODYTES NIGER, THE CHIMPANZEE, ITS BRAIN

AND BEHAVIOR

//,s- Posiliu)} umani: the Pnmaics; Mvasurcincnls and Bruin Indices; Surface
Appearance of the Brain; Inter7\al Structure of the Brain Stem in Cross Section

~^11I{ thimpanzff, although usuall\ iftcrrccl to tlu- f^i'iiiis ol l-*an, is
sdim'tinu's clrscribc'cl as Simia, w hicli appears to l)c' an oIcKt clfsigna-
_ tioii. It occiipirs a position amon^ tlu' <j:;rcat antliro[K)icl apes inlcr-
mcduitc bclwecn the gorilla and the orang-outang.

Appearance of the Chimpanzee

In point ol si/e it is somewhat hirger than tlu' orang, hut smaller than the
gorilla. Depending upon its speeies, tiie animal \aries m height Irom some-
thing o\er thrt-e feet to a littk- o\ t'r lour k'ct. In eolor it is a ljlaekish-i)ro\\ n
with rather thiek hair o\er the entire bod\ exeept the laee and brow . In some
species the scalp is bald. Ilu' ehimi)an7.ee i:>ossesses great strength and
agility. In spite of its rc'lati\el\ short stature, it is more than a match e\-en
for the strongest man. Its bod\ is short, usuall\ with a protuberant abdomen.
Tke legs are also short, and compared w ith tin- ii|)per extremity, the\' appear
even shortt-r. The foot is short with a great toe which is thick and opposable.
The otiur toes ari' united b\ a wt'b near tlu'ir basi's. The arms are long, reach-
ing for a considerable distance bilow the kiu't's w hen the animal stands erect.
The hands are broad; the thumb is short and tlu' lingers are united by a web
at their bases, as in the case of the toes. The middle linger is the longest.
Callosities dcxt'lop on the dorsal surkicc' of the lingers in consequence of
"knuckle" walking and running w hich the animal dues mostly upon all lours,

545

546 THE HIGHER ANTHROPOIDS

using tlu' back of the hands for support. The nose is soniew hal depressed,
with nostrils opening downward. The lips are mobile and protrusive, the ears
are large and extend above the skull. The lower jaw protrudes; the eanines
are long and eonieal. In the upper extremities, the humerus nearly equals the
length of the radius. The female is somewhat smaller than the male and bears
one young at a tmie, which she carries in passing through the trees and
over the ground in tlu- manner characteristic of other apes.

Habits of the Chimpanzee

Some nine or ten species have been more or less delinitely identified as
belonging to this genus. The species here described is Pan satyrus (Trog-
lodytes niger). This animal inhabits lower GLiinea, Cenaga to the Ogowe,
Semikaro Desundand near the Cenaga in the Cameroon, ^ ayunch and
Dilundi in the Cameroon and Mayumba.

Concerning the habits of the animal in its native state, little is known of
any of the species of chimpanzee. It is fortunate that man\ of these animals
have been captiuxcl when \erv young and not a few have been made the
subject of careful psychological and behavioral studies. iMobius was appar-
ently the (irst to make systematic obser\ati()n of the behavior of the chim-
panzee, in 1867. Other animals of this genus have been the subject of
psychological investigation b\ W itmer in i<)io, Romanes, 1900, Hirschlall.
1905, Shej)lurd, 1915, and Hobhousc in 1915.

kohi.ek's beha\ ioral research upon the chimpanzee

Undoubtedlx the most carefull\ controlled l)iha\ ioral research yet made
is that of Professor K()hlcr, working at rcncrlllc in tlu' Canary Islands,
under the auspices of the Prussian Acadiinx of Science which had estab-
lished at this place a wc'll-ec|uipped anthropoid station. Nine chimpanzees
were constantly under the obser\ation in ideal conditions for study by

<'nuruy\. AmiTuun Afuvcum oj .\iHurut ilislory

FIG. 244. llAHriAI {;K()1 P, ( IIIMI' WZEE.

154-

548

THE HIGHER ANTHROPOIDS

Kohlcr for a long period of tinic hrtwccn i()i4 and 1916. Kohler's purpose in
this work was to test the inteUigenee of tiie higher apes and tlie methods
applied by him are wliat he called the "roundabout methods" (Umweg),

CoxtrtfiV, New York Zoological Garden

FIG. 24,". CHIMPANZEE SUSIE.

which so complieated ordinar\- situations as to recjuire intelligent solutions
on the part of the animal. Thus oni' of tlu' most gifted animals ot the collec-
tion (it may be noted that ehinipan/A'ts, as well as more highl.x organized
personalities, dilfer in their in(li\ idual abilit\ to a very considerable degree)
was given tlu' following |)robli-m which was not altogether simple, and yet

TROC.IOI)^ lES NIGER, THE CHIMPANZEE

549

was more or less rraclily soKcd l)\ the aj^c w ithout iniiK'cc'ssar\ dclav. Itoiii
the roof Of the animal's plax^rouncl, a basket ol bananas was suspended by
means of a strmij; passed throiigli an iron ring. 1 he end ol tlie string was tied

f-'ouricsA , \tw ^'orti Zoulugittit Ctirdtn

FIG. 246. (HIMI'ANZEE SUSIE.

m a noosi' \\ hieh, m turn, \\ as placed o\ ei' tlu' hmb ot an old \\cv at the height
oi about three meters from tlu' ground. The ehimpanzee. Sultan, was
then atlniittt'd into tlu' pla\ground. He was familiar with tins basket and
associati'd it with feeding time. On entering the eiielosmx', Sultan saw the
basket at onee and soon showed signs of eonsiderable agitation beeause he
was, eontrar\ to custom, alone in the open. Manifesting his feelings in the
usual ehimpanzee st\le, lu' expressed his disapproxal by making a thunder-
ing noise with his feet against the wooden wall of t lu' apt'house, and at the
same tinu' tried to get in touch with the other animals b\- climbing up to
the windows. At length he ceased these inel]ecti\e measures, and seeing the

550 THE HIGHER ANTHROPOIDS

basket again, made lor tlie tree, climbed c|uickl\ up to the noose, paused a
moment Avhilc watching the basket, pulled the string until the I)asket bumped
against the ring in the roof, released tiie string, pulled it a second time e\c'n
more vigorously so that the basket tujiied over and a banana (ell out. The
chimpanzee then came down IVom the tree, but soon ascended once mow now
to pull cjuitc violcntlx until the string broke and the whole basket lell to the
ground. He then clambered down, took the basket and went off to cat the
fruit. Thus Sultan, in a relatively short time, had soKcd this roundabout
problem by obtaining his objective in spite of the obstacles pkiced in his way.
Although many experimental tests w ere made to estimate the degree to
w hich chimpanzees are capable of using implements, in the main such e\i)eri-
ments are not necessary in order to induce the animal to handle objects in
his immediate sm-roundings in a variety of ways. He has large and powcrtul
as well as llc.xible hands which serve as the most natural and uselul link
between him and the world of things outside. Besides this, he obtains the
necessary amount of niuseular strength and coordination at an early age of
development, much earlier than a human child. His feet, although far from
being a second pair of hands, may still be used in emergencies in which the
feet of the human races would bequite useless. Furthermore, the jaw sand teeth
are also ser\iceable, as is the case among man>' African tribes and otiicr primi-
tive people, though it ina\' be to a less extent than w ith the anthropoid apes.
The casual, every-day handling of objects by the chimpanzee comes almost
entirely in the nature of pla\-. In certain instances under the pressure of need,
or compelled by the special circumstances of e\|)erimental tests requiring the
use of objects or impleimnts, it a|)|)e;irs that tlu' new knowledge acciuired for
using objects at play will be utilized to obtain some more ck'finite ol)iective.
Primarily this object nia\ ha\e been einplo\ed without the slightest idea ol
an immediate gain and only to increase the joy ol li\ iiig. Later, however, it
becomes of great j)ractical utility lor purposes serving the needs ol the ani-

TROGLODYTES NIGER, THE CHIMPANZEE 551

rnal. Thus, iunij)iii<i; b\ nuans of a stick or jjoIc, whicli was inwntccl clc novo
by one of tlu' chiinpaiizrfs 111 {\\v ,l,mou|) and soon nnitatt'd by otlicrs as a
nirans of cnUTtainnu'nt, was soon |)ul to a niori,' |:)iac.tKal use in obtammg
lood which had l)ccn suspciuk'd al)o\c them and out ol rracli unless tliey
resorted to some means of eh'xatini,^ (heir fxxlies into closer ]>ro.\miit\- to the
desired goal. So that in the end this improvised mode ol modilied pole \ault-
ing became a regular procedure among the cliimpanzees m the business of
obtaining food put out of their nach o\'er their heads.

The animals also used straws and twigs m the maniu'r ol spoons, at
first more or less in pla\' during nu'al time cspeciallx after their lirst thirst
had i)ecn quenched, and the\ liked to amuse themscK es by dipping the water
u]; with a straw and sucking the straw. On one occasion some red wine was
poured into the drinking water which they shared in common. On tlu' lirst
taste of the new mixture they all paused for a minute, then one of the chim-
panzees began to spoon up this no\el drink w ith a straw , and all of the others
immediately followed his example with twigs and similar straws. In thus
acquiring the use of twigs and straws as spoons there could ha\e been no
possibk' imitation, for noiu' of them had had as yet a chance ol seeing a
human being use a knife, h)rk or si)oon while eating. The tw ig or stalk was
also emploNcd quite deftly in other ways, combining with its usefulness as a
table utt-nsil some of the propertii's ol a weapon ol the chase.

In the summer time, a species of ant intests the portion ol the Canary
Islands where these great ajK'S were housed. These ants passed in a wide
stream, moving along over the beams around tlu' wire netting which I'licircled
the pla\ground. The chimpanzee, ha\ing a special liking for acid fruit,
which he prefers to all others, no doubt for this reason relished the formic
acid of the insect. Usually upon seeing the ants, the chimpanzee simply
rolled his tongue along the beam over which they were crawling and thus
gathered them in h)r himself. If the wire netting intervened between him

55^

THE HIGHER ANTHROPOIDS

and the covctccl delicacy, such a primitive method of capture would not
sullicc. So all ot the chimpanzees soon learned to use sticks and straws
which were thrust throu'di the meshes ol the wire netlmii and lu'ld in such

Cour/fsv-, .Ameruan A/usfum oj Natural History

FIGS. 247 AND 248. HAND AND FOOT OF CHIMPANZEE.
Left. Palmar surface of hand, showing arboreal specialization. 1 lie tluniil] is short, tlic fingers arelong,

thenar and hypothcnar eminences are pronounced.
Right. Plantar smface of the foot showing definite humanoid tendencies, broad heel, distal advance of great

toe, shortening of lesser toes, broadening of sole. The foot in chimpanzee has less of the hand-like

characters observed in the lower primates.

position until they were coNcred by ants. The straws were then withdrawn
and tlic insects j^romptlx licked olT and devoinn-ck This method of capture
proved most satisl'aetor\ and entertaining to the anthropoids. Their atten-
tion was entirely ahsorh^d ni this no\tl method ol o\t'rcoming an obstacle
unintentionall\ placed between them and the delicate morsels which the\
craved, but which would have been out of their reach had it not been for
their recourse to this procedure.

TROGLODYTES NICER. THE CHIMPANZEE

553

II a mouse' or li/.aicl di" small ciawlmij: animal (.■iUcmccI tlu' jjlaNgrouiul
with the chimpan/cTS, it at oiicc Ix't'anu' tlu' obiix't of murh excited interest,
yet the l)i<j; annuals always hesitatitl to make a captuie h\' a sudden snatch

Ctturlvsv, Amtrtcan \tuscuTn of Nalural History

FIGS. 24(.) AND 2j(>. HAND AND FOOT OF CHIMPANZEE.
Left. Dorsum of the li;ind showing di-hnitc .irborcal specializalions.

Right. Dorsum ol loot showing prehensile speciahzation in the region of the great toe and shortening of the
lesser toes.

with the naked hantl. It was almost amusinij; to st'e the apes streteii tlieir
hands out with tlu' intention ol seizing the pre\ , with tlu' hn<i;tTs j^ointed,
and then all at once draw hack a^viin c|uickl\. A lirm, quick <j;ras]) on these
little wriggling animals a|)pcared almost as impossible to tliem as to many
people. Nearly e\er\ mo\iiiunt on tlu' |)ait ol tlu' poor (|iiarr\ was lollowed
by a nerxous gesture, "fhe caution and hesitation ol the apes manifested,
throughout the tiitire perlormance, the repugnance of touching the little
creature with tlu' unaided hand. I'inallx thi' chimpan/.ees k'arned to use
sticks upon these small intruders ol their domain and with such weapons,
if the victim did not escape, at length despatched it, not, it would appear,

554 THE HIGHER ANTHROPOIDS

in any spirit of ctucIix, l)ut more in tiic sheer cxeitement of i:)ursuit and
capture.

Professor Kcililer also had oj^portunitx to observe the rai:)i(hty with
whieli the ehinipanzees resort to the use of stieks whiMi they eneounter a new-
object for the hrst time in their li\es. This was especially apparent upon their
introduction to the electrical cmrent. In the experiment, one pole of an
induction coil was fastened to a wire l)asket Idled with fruit and this sus-
pended from the roof, while the other pole was connected with the wire
netting u|)on the (ground. In a very short time the chimpanzees manifested
a great number and \ariety of entirely human reactions and expressive
movements in res])onse to this new condition. \\ hen contact was made by
one of the great apes w ith the basket and the w ire netting at the same time,
there followed an immediate bounding back as the lirst shock was reeened.
The cry of suri:)rise or dismay, the eautious second attemjjt, the constant
jerking backward before there was an\ possibilit\ of the current passing
through the bod\ , tiie violent shaking of the hand in the air after receiving a
shock, all of these were so exactly similar to the bt'ha\ior of a human Ix'ing
who has inacK t'rtcntly touched a hot stove, as to K'axc no doubt as to the
resemblances in bchaxioral reactions under corresponding cncumstances.
Most of the reactions of the chim|)anzees might easily lind counterparts in
the human being, (|ulte as marked in one as m tlu' other. It seemed almost
astonishing to observe in these apes the number and variety ol automatic
responses to unexpected and e\en painful stimuli, which may be uniNersallN'
observc'd in man as well. Such responses must haxc taken their origin a long
way back in the dark ages wlun the anthropoid and the human kind were
beginning to emerge Irom some common ancestral stock.

In the further manipulat ion of obiects the chimpanzees showed a tenden-
cy to develop additional habits. Tlu'N did not e\xMituall\ eonlinc themselves to
thrusting and hitting w ith sticks alone, but began to throw them. In moments

/-:.

TROGLODYTES NICER, THE CHIMPANZEE

:>■):>

of .urrat |n\, wIumi mtx ;j:i)(kI lood was in-m^^ proNick-cl, onr ol the animals
oltfii sc'i/A'd aiintluT and shonk hini out ol slu'cr pleasure. At lirst one ol the
annuals would taki' a stiek uiidi.'i' sueh proxociition and llnii^ it \ehc-niently
at one ol the ehnnpanzees m his or her pro\iniit\. This also freciuently
hap[)ened ni pla\', part leularlv with the athlelie I em ale Chiea, w ho was in the
habit ol eret'pm^ up hehnid one ol her eompanions as tlu'v sat c|uieti\- at rest
and, Irom lairl\- elose cpiarters, hurhn^ a stiek, and then takmg llight. Prom
throwing stieks it was hut a short step to usiiiiz; handluls ol sand m this
manner, and linall\' stones ol \aried size and weijzht. At lirst the Lhimpanzecs
were not e\[)ert m these ballistie aeti\ities. Bem^ dedeient in the eoordma-
tion ol hand, head and eyes, the\' did not succeed in \'ery accurate aim.
Soon the throwing of stones became such a rulin<i; passion among the chim-
panzees that some ol them became dangerously expert, particularl\ the
gymnastic Chica, who learned to aim e.\cellentl\ and exprt'ssed her skill with
equal satisfaction uj^on her lellow apes as well as lu'r human associates.

These perlormances, whii'h were largel\' in the nature ol play and
amusement, were by no means the only ones by which ihv chimpanzees
showed a strong tendenc\' for manipulating w ith considerable skill objects in
their surroundings. All of the animals made nests, and this was true from the
early periods of infancy onward. V\\v full-grown chimpanzee, as might be
expected, [)articularl\ the lull-gi'own lemale, has the best resLilts m this nest-
building and reall\ does most remarkaliU' work in this line. Usuall\ in the
evening, a heap of straw is carelull\ manipulated while the animal sits
inside and begins to twist the ends of the straw together. This work will
continue all around the edge Lintil an actual nest is lormed which is not
unlike that of the stork. .\ blanket ma\- oftt'ii be interwoxen with the straw,
or used as a co\er over it. The younger animals, in their nest-making, are
less tidy and exact. The\ seldom make so neat a turning down ol the outer
edges. But, on some occasions when the\' apparently take more |)ains with

,-,-6 THE HIGHER ANTHROPOIDS

their handhvork, their movements during the preparation of the nest are
exactly like those of the older females and the results closely approximate
those of the more efTicient workers. The nests are often made during the day
in pure fun, and many different materials, such as string, grass, branches,
rags, ropes and even wire collected for this purpose, not, however, when a
nest is needed to sleep in, but only as a pastime when other objects of interest
are lacking.

Objects of many kinds interested the chimpanzees, and they were not
only intent upon the manipulation of them but seemed ])articularl\ lond of
carr\ ing cjuite a widely different variety of rubbish about on the body in
one way or another. Nearly every day animals could be seen walking about
with a ro[)e, a bit of rag, a blade of grass or twig upon then- shoulders.
Some of them, if gi\en a bit of metal chain, would put it about their necks
c[uite in the manner of a necklace. Bushes and brambles were often carried in
considerable quantities, spread out over the entire back, and twigs and pieces
of grass were commoiilx seen hanging over their shoulders to the ground or
on both sides of the neck. One of the animals contracted the habit of carrying
about em|)ly preserve cans, by taking tlu' side that was open between his
teeth, while one of the more sturdy of the grou|) took a lancv at one time tor
carrying heavy stones about on her back. She began with a stone ot lour
pounds but soon reached a much larger block of lava wx'ighing nine pounds.
Most of this occuj)ation is earned on as play from w Inch they seem to derive a
visible pleasure. \\ lu'ii ornamented in this manner tlu'x Irecjuently dis])lay
an almost impish, self-important audacity, strutting about among their
companions or advancing u])on them in a menacing way. One ot the older
adults, festooned in this maniu'r, trotted around in a circle with several ot
the smaller animals following closely behind at her lux'ls. Sometimes the
entire company j)laying in this fashion would march around in a circle, one
behind the other, the largest animal stamping its loot \ lolently at each stej)

TROGLODYTES NIGER, THE CHIMPANZEE 557

as though gi\ing the- tinu' lor thr ijaracic. Thr other animals followed suit
bv an cxaggeratc'ci accentuation ol the marching mo\ements.

Not only chcl these apes show man\ modes ol employing objects which
they encountered m their eiuironnu'iU, but some ol them, going a step
lurther, manilested a degree ol ingenuity m the construction of implements.
Tlu' results of this constructive activity, it must be admitted, were relatively
simple. On the other hand, it showed a delmite tendency on the part of the
chim])anzec to combine objects m order to deri\e from such combinations
an even greater utilitx . Thus.oiu' of themostgiftedof theseanintalsultimately
learned to lit a smaller j^iece ol bamboo into a ca\ity ol a larger piece, thus
producing lor his special purposes a really long bamboo |)ole which was useful
for procuring desired food which had been sus|)t'ndcd above his head out of
reach. A similar teiidenc\ to constructi\eness was also observed in certain
buildmg propensities ultnnatelx cU'\H'lopt'd b\ these chim|)anzees. W hen the
animal cannot reach an ob|ecti\e hung high abo\t' it, it will utilize a box
which may In- Wtuncl in the enclosure and thus attempt to decrease the
difficulty of space intervening between it and the desired object. There is a
possibility also that tht' chimpanzee ma\ pile two (,r more boxes, one on
top of another, and thus reach his goal. By adequate e\j)enment it was
determined that nearly all the animals eventuall\- developed the ability to
construct this sort of tower arrangement in order to climb up and get the
banana suspended abo\e their heads. 1 he expert ness, as well as the elliciency
with which the chimpanzee learned to perlorm this leat, dillered considerably
in different indi\ iduals. The more alert and quickly reacting members of the
group accomplished the perlormance lirst. Tlie others were slower, aided no
doubt, to some extent, b\ imitation. I lu' (|uicki-r chimpanzees actuall\' j^ut
this procedure into operation eiitirelx ol their own initiatne and thus mani-
fested a definite constructional idea. Often, having constructed the tower,
a long stick was Lised in order to gain a nearer ap]jroach to the suspended

558 THE HIGHER ANTHROPOIDS

fruit and by means of the stick to bring the hint to earth. Here two modes
of reaction were combined, namely, that ot actual building to serve as a
basis from which to employ an implement whose uses were alread\ well
understood.

These building operations soon became a lavorite pastime among the
group, but in spite of the fact that the animals were permitted every opj^oi-
tunity to cooperate in their constructive activities, they ne\er fully developed
any indication of systematic collaboration. However helpful sucii combined
efforts might iiave been toward their ultimate aim, the apes failed to utilize
the adxantages of mutual associations in these transactions. The underlying
reason for this apparent deficiency in cooperation may perhaps become clear
when it is considered that the obtaining of food among a group of animals,
particularly among these chimpanzees, was not in reality a mutual interest.
It was from the beginning and always remained a matter of wholly selfish
indi\ idual acquisition. Whatever division of labor there might be, there never
was a thought of dividing the spoils.

When the chimpanzees were assembled in the presence of an objective
hung over their heads, they gazed about for jjroper materials to use as tools
to approach their goal. One would bring a pole, another a box. These would
be dragged up into position preparatory to constructing a tower. The
building would then begin and when the lirst stages of construction were
completed, several of the animals would manifest an assertive disposition to
ascend at the same time, and each ol them would act as it it alone were the
builder. Often, too, the box already in position would be snatched away by
some competitive group in the building industry and the pilfered object used
in the construction ot another independent tower. This would freqiu-ntly
result in a wrangle among the architects; in tact, the entire company ol
builders might come to blows over this irregularity and mtrmgemeiit ot
property rights. Alter the subsidence of such Babel-like controversies,

TROGLODYTES NIGER, THE CHIMPANZEE 559

huildiii^f was rcsiinu-ci and 1 lu- structure continued to ^n'ow in hciglit until it
hccamc an object ol vwv greater excitt-ineiit to the assi'inhk-d workers, each
manifesting a still keetn'r desire to mount it. As the result of this highly
indi\idualistic competition, the obji-ct ol their mam interest tumbled over
and was destroyed in tiie struggle. In consec|uence, it was necessar\' to begin
the structure all over again and, perhaps, m the continued ellort only the
more diligent and patient ol the grou]) adhert'd to the original purpose. The
others became interested m some less exacting occupations which imposed no
actual strain ol cooperation upon the individual. E\'entuall\, ho\\e\er, the
tower was linished and the more diligent as wfll as the more tenaciously
patient ol the animals, w ithout the obtrusive assistance ot'restlcss companions,
ciUK'tly mounted to the summit ol tin- structure, and either with or without
the aid ol the pole, obtained the co\eted tood. Sometimes, iiowexer, betore
the diligent one had time to reap the rt'ward ol his ellorts, some member
oi the group, endowed w ith more athletic alertness, stealthil\ and w ith great
spi'ed, clambered up to the point ol \antage to seize the prize w ith rapacious
deftness before the rightlul winner had time to |)rotest or retaliate. In all ol
this cooperati\e actnity there seems to l)e something so lundameiitally
human, so reminiscent even ol modern acc|uisiti\e proci'durt-, that it ap]X'ars
inaccurate to restrict it too rigidly within tlu' category of simian beha\ior.

The chimpanzee's register ol emotion is greatc'r than that ol the a\erage
human being lor the reason that his whok' body i)t'comes agitated in such
expression; he shows his kx'Imgs iii other parts ol his b()d\ than merel\ his
facial muscles. It is his custom to jump up and dow n in |oylul anticipation as
well as m impatient annoyance and anger. In e\t ii'ine (U'spair, which seems to
develop as a result of but slight ])ro\ocation, he llings himself upon his back,
rolls \\ildl\ to and fro, swings and waves his arms abo\e his head in a lan-
tastic manner, not. Dr. Ktihler thinks, unlike the reactions among non-
Europtan races as a sign of disappointment and dejection. These anthropoids

56o THE HIGHER ANTHROPOIDS

are not known to weep nor do they laugh in cjLiite the human sense of the
term, Init there is a certain resemblance to human hiugliter in the rhythmic
gasping and grunting when they are tickled. Probably this manifestation is

FIG. 25 1 A. DORSAL SURFACE OF BRAIN, CHIMPANZEE.
lActual Length 06 mni.|

physiological I \ closel\' akin to laughter. During the quiet contemplation ot
objects which si'imu to give them particular |)leasure, and the most conspic-
uous among such objects are little human children, the I'Utire face ol the
chimpanzee, especially the outer corru'rs of the mouth, has an expression
which is not altogether unlike a human smile. W hen perj^lexed, uncertain or

TROGLODYTES NIGER, THE CHIMPANZEE 561

in doubt, the chim])aii/(.'c's ha\r a way of scratchintj; the surlacf nl {\\v body,
especially the aims, breast and the upper ]3ortion ol the thigh. They seem
to ha\e a eertaiu degree ol understanding among lliemsel\es whieli eon\-eys

FIG. 25 IB. DETAILED DIAGRAM OF DORSAL SURFACE OF BRAIN, CHIMPANZEE.

Key to Diagram, obl.. Oblongata; sul. interpar., Sulcus Interparietalis; sulc. i-r. sup.. Sulcus Fron-
talis Superior; SULC. pr. sup.. Sulcus Precentralis Superior; sulc. ret. inf.. Sulcus Retrocentralis Inferior;
s. R. s.. Sulcus Retrocentralis Superior.

the meaning not only ol emotional distaste, but also of delinite desues and
urges whether directed tow ard another of the same species or toward other
creatures or objects.

562

THE HIGHER ANTHROPOIDS

A large proportion of all thfir desires is naturall\' shown by clireet
imitation of the aetions desired. Thus, when one eiiinipanzee wishes to be
accomjxmied by another, it gives the latter a nudge and pulls it by the hand.

FIG. 2j2\. BASE OF BRAIN, CHIMPANZEE.

\\hiie looknig at hun and making the nio\ iMiU'iits ol walLnig ni the diri'it ion
ol the objecti\'e. One wishnig to reeeixe bananas honi another, mutates the
movement of snatehmg or graspmg aeeompamed b\ mtensely pleading
glances. The summoning of another animal from a eonsiderable drstanee is

TROGLOD^TES NICEI^, TIIF CHIMPANZEE

5^)3

oltc'ii accoinpann'cl l)\ a hi'ckoninij: \(.tv liuiiian in chaiattcT. Tlu- iliiiii|Xin/c'C
lias also a way ol In't-konm^ with its loot l)\ thrusting it forward, a little
sideways and seratehiii", with it on the tfround. Another obvious melliud of

FIG. 2-52B. DETAII ED DIAGRAM OF BASE OF BRAIN", CHIMPANZEE.

imitation is for one ape to indieale in his own person w hate\fr mo\enients
he would perform and the aeti\'it\ he w ishes the other to undertake, nuieh the
same as a do<i: in\ ites us to |)la\ In leaping and running about us. The ehiin-
panzees behave in thi.- same way, ineiting others to play with them. In all

564 THE HIGHER ANTHROPOIDS

cases tluir ininiic actions arc characteristic ciioLigh to he distinctly under-
stood l:)y their comrades. The chnnpanzee is especiall\ prone to pay close
attention to the wounds or injuries received by his fellows. The incentive in
this connection can scarcely be considered as mutual aid. They especially
like to remove splinters from each other's hands or feet, employing in tliis
process the methods usually in vogue among the luimau laity. Two finger-
nails are pressed on either side of the splinter w Inch is thus ele\ated until it
may be caught and remo\ed by the teeth. Professor Kcihier, ha\ing sulfercd
from such an accident, ventured to allow one of the chimpanzees to remove
the splinter. On perceiving the condition the chim]Danzee's expression at once
assumed the appearance of eager intensity and his attention was entirely
concentrated in preparation for his surgical undertaking. He examined the
wound, seized the injured hand, forced out the splinter \\ith two skillful,
somewhat po\\crful squeezes of his fingernails, and then examined the hand
closely to be satisfied that his work was well done.

Only a very small portion of Professor Kohler's extensi\e obserxations
and excellent record during his long experience with these interesting anthro-
poids has been given here. Those who may be more interested in this subject
are referred to his admirable thesis which now has appeared in an English
translation entitled "The Mentality of Apes."

The ostensible conclusions as the result of studying this company of
nine ehimjjanzees under the most favorable circumstances may be sum-
marized as lollows: The chimpanzee manilests intelligent behavior of a
general kind familiar in human beings. Not all of their intelligi'iit acts are
externally similar to human acts, but under well-ehoscn ex])enmental con-
ditions the type of intelligent conduct can always be traced. This applies in
spite ol very important differences between one animal and another, vwn
to the least gifted specimens of the species that have been obscrNcd, and
therefore must hold good lor every member of the species as long as it is not

TROGI.OD\TES NIGER, HIE CHIMPANZEE 565

nu-iitally (KlicKMit in llw pathological scnsr ol tin- word. \\ itii this (.'xccption,
which is prcsiimal)l\ raic.', the success ol iiitclliiicncc tests in general will be
more likel\ cnclangerecl by tlu' piTson niaking the experiments than b\' the
animal. Oiu- must know, and it necessary establish by preliminary observa-
tion, within which limits of (lillicult\ and which functions the chimpanzee
cannot possibl\ show mtelligi'iui' and insight. Negati\e or confused results
from complicated and accidentally chosen test material ha\e obviously no
bearing upon tlu' lundamental cjuestion, and in general experimenters
should recognize that e\i'r\ intelligence ti'st is a test not only of the creature
examined but also ol the expermu'iiter hiinst-ll.

In any event, it ri'iiiams true that chimpanzt'cs not only stand out against
the rest ol the animal world by se\eral morphological and, in its narrower
sense, physiological characteristics, biit they also beha\'e in a wa\' which
counts as specilicall\ human. As yet we know little ol their lU'ighbors of ttie
other side among the anthropoids; but according to the little \w do know,
with the resLilts ol this report, it is not impossible that m this rt-gion ot experi-
mental research the anthropoid may be lound nearer to man in intelligence
than to man\' ol the lowx'r species ol apes. So lar obserxations agree well
with the theory ol cNolution, and in particular, the correlation between
intelligence and the de\ elopmeiit of the brain is conlirmed.

StLDIES OxHtK IHAN K.()IILEr's UPON THE Cl 1 1 \!P AXZEE

Other chim[:)anzees have been studied trom time to time with ahnost
similar results and concKisions. Oiu' further detail adding to tlu' intelligence
tests applied to these animals was made some years ago by Romanes upon
the chimpanzee, Sally, which, under his tutelage and instruction, developed
the abilitx to count, in any e\ent, this animal could distinguish a number of
straws to six or seven and upon recjui'st would indicate witii the straws the
e.xact number she had been instructed to show. These lacts, in combination

566 THE HIGHER ANTHROPOIDS

with the many exhibition performances which show a striking human
resemblance in their execution, would seem to indicate a wide range of
teachabihty on the part of the chimpanzee. \\ hether such exhibition per-
formances of the animal as are the result of training may be accounted as
properly within the definition of strict intelligence tests, is a question some-
what aside from the point. All of these feats of learning, however inter-
preted, manifest the degree to which the chimpanzee is able to expand its
behavioral performances. That the execution of such acts requires appro-
priate supervision and urging is certamly true, since the animal tends to
relapse into more primitive modes of reaction, without apparently having
gained any definite advantage for its own purposes of life from the many
additional accomplishments acquued under the tutelage of man.

Brain" Measurements and Indices in Chimpanzee
The dimensions of the brain, including cerebellum and brain stem, are:

Longitudinal loo mm.

Transverse 88 mm.

The following are the dimensions of the brain case:

Total length of the skull igo mm.

Occipito-nasal length 141) mm.

Intertemporal width -2 mm.

W idth of the brain case ()g mm.

The total weight of the brain without the dura niatcr is 350 gm.

Total w aler dis])laccnHnt 369 c.c.

Weight of the forebrain 2C)8 gm.

Weight of the midbrain 5 gm.

Weight of the hindbrain 47 gm.

TROGLODYTES NIGER, THE CHIMPANZEE 567

The indices as computed on this basis arc:

Forcbrain index, displaces 310 c.c 83 per cent

Midbrain index, displaces 4 c.c 5 per cent

Hindbrain index, displaces 55 c.c 12 per cent

A forcbrain index of 83 per cent ibv weight) assigns this animal to the
distinctly manual group, an estimation which accords well with the actual
behavior of the chimpanzee.

Surface Appearance of the Brain in Chimpanzee

The pattern and appearance of the cerebral hemisphere in the chim-
panzee may be said to l)e that of a human brain in miniature. W ith a few
notable exceptions, the convolutional design of this anthropoid corresponds
cIosel\ to that of man, and might easily be mistaken lor the latter were it
not for its diminutive size, actually being about one-quarter the volume
of the human brain. The characterization of the chimpanzee's hemisphere as
a human miniature applies equally to the other two great anthropoid apes.
The chimpanzee, however, does retain marks of its inherent primitiveness
which arc considerably more pronounced than in the case of the gorilla,
although less defined than in the orang. A careful comparison of all the
markings on the surfaces of the endbrain and the brain stem would almost
certainly place the chimpanzee below the gorilla and somewhat above the
orang-outang.

fissures and lobes

The fissural pattern on the lateral surface of the hemisphere is anthro-
poid in type, as determined by the presence of three principal fissures,
namely, the fissure of Sylvius whose long horizontal limb has less of
the usual simian obliquity, the central fissure of Rolando which divides

568

THE HIGHER ANTHROPOIDS

the lateral surface into two nearly I'cjual areas and presents an uj)i)er and a
lower genu, and the marked sulcus suniariini which is continuous on the
mesial surface with the sulcus in the human hrain known as the parieto-

FIG. 253A. LEFT LATERAL SURFACE OF BRAIN, CHLMPANZEE.

(Actual Length 100 mm.)

occipital fissure. These fissures separate the frontal Ironi the parietal,
the parietal from the temporal and the parietal iVom the occipital lobes,
thus establishing definite boundaries lor a distinct lobational design on the
lateral surface of the hemisplu're. As is the case with all ol the great apes,
the richest coinolution ap|)ears in the parietal area, or somesthetic region of
the brain, within which the syntheses of bod\ sensation ari' I'laborated. The
coin'olutional pattern of tiie frontal lobe is also rich, although considerably
less than in man. All of the frontal coiuolutions ol the human brain may be
discerned; some ol them, ho\\f\er, onl\ incompletelx outlined by secondary
frontal fissures. The complexity ol coiuohitional design m the brain ol

TROGLODYTES NIGER, THE CHIMPANZEE 569

chimpanzee compares favorably with human specimens showing a low
degree of organization. The temporal lobe has convolutions and fissures
characteristic of the human bram. These fissures assume their typical posi-

MG. 25315. DETAILED DIA(;KAM OF LEFT LATERAL SLKFACE OF BKAIN,

CHIMPANZEE.
Key to Diagkam. obl., Oblongata; kamis, Ramus Posterior of Sulcus Temporalis Superior; SULC.
occip.. Sulcus Occipitalis; suLC. occip. lat.. Sulcus Occipitalis Lateralis; sulc. pruct. inf.. Sulcus Precen-
tralis Inferior; sulc. prect. sup.. Sulcus Prcccntralis Superior; sulc. ret. inf., Sulcus Retrocentralis
Inferior; s. T. mkd.. Sulcus Temporalis Medius.

tions with a general tendency to extend into the parietal lobe. The sulcus
simiarum is somewhat longer than in gorilla, coming well down behind the
caudal extremity ol the temjjoral lobe.

The eonvoiutional design on the lateral surface of the occi])ital lobe is
notably feeble. Only a few of the secondary fissures make their appearance in
this region. On the mesial surface, however, the cuneus shows somewhat
greater comjjlexity in its coiuolutional pattt'rn even than the human bram.
This is due to the fact that a dee]) annectent gyre in the upper extremity of
the simian fissure comes to the surface and thus interrupts the continuit\- of

--0 THE HIGHER ANTHROPOIDS

this lissurc with the occipito-paric-tal fissuif. In the human brain, this deep
anncctent gyre is sul:)mergecl anti thus [)erniits the (leeij^ito-parietai sulcus to
give the appearanee of continuity in which its parietal portion incises the
lateral surface. This apparent independence of the two di\isions of the parieto-
occipital sulcus in the chinipanzee atlords some ground to doubt the actual
homology with the parieto-occipital lissurc m man. It also secnis to oiler a
reason for questioning whether the sulcus smiiarum has a representative
vestige in the human brain.

THE BASAL SURFACE OF THE HEMISPHERE

Upon the basal surface of the hemisphere, certain characteristic markings
indicate that the brain of the chimpanzee is more primitK'e than that ol the
gorilla. Thus the orbital conca\'ity, into which the orbital portion of the fron-
tal boiu' extends, is a particularly marked feature. This concavity indicates
a faihire on the part of the frontal lobe to expand at the expense of the orbit.
The olfactor\ Inilb and tract are detachable as far back as the trigonum
olfactorium, and a well-delincd gyrus rectus is demarcated by the presence
of an olfactory sulcus. The angulation at the chiasm, Ijoth w ith the optic
nerves and the optic tracts, is characteristic of all other simian forms, tend-
ing to be obtuse rather than acute as it is in most of the lower mammals.
The uncus is present on the mesial surface of the temporal lobe, and, although
well delined, is less prominent than in gorilla. The ccrcbt'llar concavity
in the occi[)ital region is mort' prominent than it is in the gorilla, jjarticu-
larly that portion of it which constitutes the postspleiiial lossa, into which
projects the highly ele\aled cephalic |jortion of the supi'rior \ermis oi the
cerebellum. In all of its features on the basal surlace ol the lu'inisphere the
brain of the chimpanzee approaches more closely that ol the intermediate
primates than of man, and a|)pears to be less acKancecl in this dirt'ction than
the brain of gorilla as judged by these crucial points of basal identilication.

TROGLODYTES NIGER, THE CHIMPANZEE 571

THE CEREBELLUM

The cnt'ljillum presents its usual cli\ isioiis and surlaccs. The tentorial
surface is clist nKtl\ more gabled than is the case ol gorilla, though sonu'w hat
less than ni the baboon or niaeacus. The supt'rior \erniis appears as a definite
ridge-pole and rs partieularl\ pronounced at its cephalic e\treniit\', which
impresses itsell upon the unck-rsurlaci' ol the heniis|)here in the i:)OStsplenial
fossa. The ct'rebellar lolia pass without interruption Ironi the tentorial sur-
face ol the \erniis to the tentorial surlace ol the latt'ral lobes. 1 lu-se lattiT
structures are h'ss extensnc than 111 gorilla. The posterior notch oi tln' cere-
bi'llum IS present but has not attained the depth characteristic ol man.
U|)on the occipital surlace the mlerior \c-rmis is still a notable leature. It
has not been so much submerged by the t-\pansion ol the lateral lobes as m
the case of the human and gorilla brains. It is separated Irom t lu' lateral
cerebellar expansions by two vermolateral sulci which somewhat mti'rrupt
the passage ol the lissLires Irom the median portion to the lateral lobes.
The petroso-Ncntricular surlaix' ol tlu' cerebellum shows little that is dis-
tinctive 111 chimpanzee. The \entriciilar portion occupies a position in rela-
tion to the roof ol tht- fourth \eiitricle. The sui^erior \i'rmis in this region
projects much higher than in the lasi' ol citlu'r man or gorilla. Tlu' petrosal
portion IS occupied b\ the cerebello-pont ile aiigli' m which is lodged a
llocculus which is rt'lativelx small. .As a whole, the cerebellum, both in lorm
and dinu'iisions, apjjcars to be mti-rnu-diatc between that ol man and gorilla
on tlu' one hand, and the intermediate primates on the other.

rHE BRAIN STEM

The OBLONGArA. The markings on the l)rain stem in the chim|3aiizec
arc, if aiuthing, somewhat less delined than might be expected Irom the
prominence of the landmarks of the hemispheres. The oblongata uixm its

572

THE HIGHER ANTHROPOIDS

ventral surface presents two well-defined ])yramids separated by a ventro-
median sulcus. At the caudal extremity ol the pyramid mterlaeing libers ot
the decussation may be discerned upon the surface. Lateral to the pyramid.

FIG. 254. VENTRAL SURFACE OF THE BRAIN STEM, CHIMPANZEE.

lActual Lint;tli 48 mm.]

Ki;v TO Dia(;kam. cercbr. I'edlncle, Cerebellar Peduncle; op- (.miasm, Optic Chiasm; op. ped. space,
0[>tic<)pcdunciiIar Space; vent. med. si i.c:is, Ventrcimedian Sulcus.

and separated from it by the |)reoli\ary sulcus, is a well-defined olixary
eminence, which in turn is separated from the tuberculum tiigcmini b\ the
postolivary sulcus. The dorsal surface ol the ()blon<j;ata presents tlu' two
characteristic divisions, the inlraNcntricular and the \entricular ])ortion.
The inf ravt'iitricular portion is characterized b\ tlu' ap[:)earance of a well-
defined clorsomedian septum, on t-itlu'r side of which may be setn the ele\a-
tions produced l)\' the libers and nucleus const it ut mti; the cla\a. The usual
dorsal paramedian sulcus separates the cla\a from ihe cuiu'us, which latter
appears to be the lari^er ol these two surlace elexalions. i-iom this fact it
may be inferred that the sensory importance of this area has increased, due

TROGLODYTES NIGER, THE CHIMPANZEE

573

1(1 the sprciali/at ion ot t lu' upper r\trriiiit\ and hand. The Inlliix ol sensory
stinudi IS undouhtedl\ greater Irom this part ol the l)od\ tlian Irom the
lower extri'initv. A greater ck'<j;rec oi S|jeeiah/.at ion is manliest in the hand,

FK;. 2jj. DOKSAL SL KIACF. Ol BKAIN STEM, CHIMPANZEE.

lActii.il Lt-ntitli 4H min.l

Key to Diacram. n. m. fis., Dorsonuclian I-issurc; n. m. sept., Dorsomedian St'pnim; sui>. cer. ped.,

Superior CVrcbclI:ir Pi'dunclc; r. t., Tuberculuni Trigcniini.

lorearni and ami tlian in the le^. Takiii<^ into aeeount its relation both to
loeoniotion and to the iiianx feats of manual de\terit\- ol whieh the chim-
panzee is eupablc, the hand seems to lill a more important olliee than the
foot.

In the \ tntrieiilar portion of the dorsal surlaee ol the oblongata, the
eharaeteristit- di\eruenet' occurs in tiie alar plates, tiius disclosing the floor ol
the \-entriele. The lateral walls of this inferior angle of the fourth \entricle
iiiv lormed as elsewhere b\ tlu' iiiiineiices ot the clava and eun(.'us. The ela\a
does not exteiul as far cephalad as does the ciineus. Both ol these eminences

574 THE HIGHER ANTHROPOIDS

decrease in elevation as the lateral reeess is approached and at this point ha\e
reached the jjhiiie ot the \entrieular lloor. It is m this region that the incom-
ing libers of the acoustic ch\ ision ol the eighth ner\e enter the \entricle
whose lloor thcv cross as the striae acusticae. The floor ot the \entricle con-
tains the trigoinini h\poglossi beneath which is located the nucleus ol the
twelfth cranial nerve and latiral to which is the fovea vagi marking the
position ol the dorsal vagal nucleus. Other markings in this region are
e\tremcl\ dillicult to discern. Two hunt elexations appear in the \ (.'ntricular
lloor 111 the region of the lateral recess indicating the position ol the \'estil)ular
nuclei. As compared w ith some of the more delinitely arboreal lorms ol pri-
mates, these elevations are not so [jronounci'd, but still show a degree ol
prominence which indicates a balancing mechanism m chimpanzee charged
with large resjjonsibilities m the general organization ol the animal's motor
activity. The cephalic angle of the fourth \entriclc, aside from the ele\ation
marking the presence of the nucleus abducentis, and the gradual decrease in
its diameters as the ventricle approaches the caudal oriiice of the Sylvian
aqueduct, shows no particularly outstanding feature. The lateral walls are
formed b\ the middle and superior cerebellar [jeduncles. in general, the mark-
ings of the oblongata, lioth u])on its \cntral and dorsal surfaces and m the
region of the xcntricic, are much less striking than is the case m man or even
in the gorilla. The markings are somewhat more clearl\ dclined than m the
intermediate primates.

Tui£ Pons Varolii. At the cephalic limit of the oblongata upon its
N'entral surface appears the bulbopoiitik' sulcus which sej^arates the bulb
from the pons Varolii. This structure is a fairl\ pronounced leaturc ol the
brain stem in chimpanzee. It does not, how c'\-er, attain the proportions which
are characteristic of it in man or in gnrilla. Its latt'ral extremities arc con-
tinued to form the middle cert'bellar pt'tlunclc which approaches and enters
the cerebelluiii to form ultimate connections with tlu- lateral lobes ol this

TROGLODYTES NIGER, THE CHIMPANZEE 5-5

organ. 1 he roots ot the tn^H-iiiinal iH-r\r come into relation w itli tlir pons
Varolii at tlu' point ol transition bttwrcn it and t lu' micklk- ci-rchfllar |)(,-(kin-
clc. Tlicsf libers pciU'tratr the |)ontiU' strata and make their wax to the teg-
mentum ol tin- axis. I hv ix'phalie extremity of the pons is marked by a well
deiiiu'd ponto-pediineular siikus separating the pons Varolii from the eerebral
pedimele. In tlu' midline this point of si'paration is I'urther emphasized b\
till' extt'iision bi'iieath the |)ons ol the blind ending ol the- optieo-peduneular
spiice, the loramen eaeeiim antieum.

The MiDiiKAiN. I lu' midbrain presents upon its dorsal surface the
usual specialization ol the c|uadrigi'minal plate. This consists of two sets of
colliculi corresponding to tlu' structures already obserx cd in all primates in
relation to the sense ol heai'ing and the si'iise of sight. The inferior colliculi
are less prominent than tlu' superior colliculi, and both ha\f uiukagone an
a|:)preciable decrease m their elevation abo\f the roof of the midbrain.
Longitudinall\ , the intercollicular sulcus at its cephalic extrcmit\ becomes
expanded to lorm tlu' pineal lossa, and it is particularl\ m this region that the
superior colliculi show their greatest attenuation. Judgt'd l)\ tlu'se marks of
identilication it seems clear that the chimpan/.t'c is less will i'C|uipped in tlu'
mechanism by means ol whuh it cxecuti's thost' immediate rellex react ions in
response to the stimuli ol hearing, and t hat the process of telenci'phalization
has adxa need much lurtlu'r than in tlu' inti'rmcdiate primates.

The lateral surlaci- ol tlu' midbrain presents the ele\ation of the mesial
geniculate bod\ which ma\ bi' seen connected with tlu' inferior colliculus bv
means ol a iairly w ill-deline<l brachium i'on|iincti\Lim jjosticum. I lie
xcntral surlace ol the midljrain is characteri/.ed bx the ajipearance of the
optico-peduiHular spai'c, upon I'lthcr side ol which tlu' cerebral peduncle is
dixergmg to enter the hemisphcix'. I he ci'phalic boundarx' of this space is
lormed [)\ t lu' dixerging optic tracts and tlu- oj)t ic chiasm. The space contains,
as in all other forms, the point of emergence of the oeulomutor nerxe, the

576 THE HIGHER ANTHROPOIDS

mamniillar\ bodies, the attaclimfiit ol tin- iiilundilnilai' stalk and the tuber
einereuni. There are no espeeially eharaeteristic features in it to distmguisli
this region from that of other primates.

Internal Structire of the Brain Stem in Chlmpanzee
le\el of the pyra.xhdal decussation ( fu;. 256)

At this le\el Xhv section shows as its most conspicuous teature the decus-
sating libers of the p\rainidal system ( P\\ ). Oecup\ ing the usual \entro-
mcsial jjortion of the section are the still uncrossed p\ ramidal libers ( Py ).
The crossing fillers, ho\ve\er, ha\e caused a dellection ol the sulcus, and in
the course of their decussation have gone so far toward occupxing their
ultimate position in tlu' spinal cord as to ha\"e more or less completel\'
di-tached the xentral gray column (V'en) from the central gra\ matter
(Ceil). On the periplu'ry of the section certain indentures indicate the
position ol the major sulci on the surface ol the stem. The ventromedian
sulcus lias alrcad\ been referred to and tin- dellection in it caused b\ the
decussating pyramidal bundles. A laiiitl\ marked internu'diatc sulcus lies
\'cnti"al to the substantia gelatinosa trigemini ( N R ), \\hile dorsal to this
structure is the dorsolateral sulcus and a laintl\ indicated dorsal para-
median sulcus. In tlu' dorsal seiisorx lield, the columns ol CjoII and Burdach
are clearl\ demarcated by a dorsal paraniedian sulcus, the di\isioii between
tlu' two cohimns showing clearly a prepondcranei' in size which favors
Burdach's column ( CB ). In the column of C.oll ( CG ) the caudal extremity
of this nucleus may be discerned ( NG ). It is adjacent to the median septum
but iinested l)y a dense capsule of myelim/A'd libers. E\t("ndiiig dorsolatcrallN
from the central gray matter is the proximal portion of the nucleus of
Burdach passing outwarcf into the surrounding iiu'dullarx substance of
the corresponding column. A tenuous cxtinsion ol the central gray connects
^vith the somewhat expaiuk'd substantia gelatinosa trigemini (NR) upon

TROGLODYTES NIGER, THE GIIIMPANZEE

177

whose outrr margin arc liie collrttcd lilxrs lormin"; tlu' descend ill": triiicni-
inal tract f Trd ).

The impnssion conNcyed In a critical siir\c'\ of this dorsal lield with

FIG. 256. CHIMPANZEE. LEVEL Ol- rHL m KA.MIDAL DECUSSATION.

en, Column of Burdacli; ctN, Central Gray Matter; (<;, Column ol'Goll; dt, Oeitersospinal Tract; im.
Dorsal Spinocerebellar Tract; Gow, Ventral Spinocerebellar Tract; iii;l, Spino-olivary Tract of Hehveg; ng.
Nucleus of Goll; nk, Nucleus of Rolando; py, Pyramid; I'vx, Pyramidal Decussation; kst. Rubrospinal
Tract; spt, Spinothalamic Tract; trd, Descending Trigeminal Tract; ven. Ventral Gray Column; xi>v.
Crossed Pyramidal Tract. [Accessicm No. i 5-. Section 50. Actu;il Size 12X0 mm.)

rclerciice to the discriininatiNC capacity oi the aiiiinal is that oi a seii.sory
organization in which the lorelimb and hand contribute a greater \olunu' of
afTcrent inlhix than either the head or the lower e\treniit\ . This in the main

5-8 THE HIGHER ANTHROPOIDS

is tlu' loniiula tor all ol the great anthropoids incliKling man, in all ol w hich
the column of Burdach is greater than the column of Goll. The tormula
representing this relation in some lower prmiates shows the coUimn ot Goll
to be greater than that of Burdach. The signilicance ot this in\i'rsion ot
sensory rehttion arises from the growing prominence ot manual ditlerentiation
seen in the greater anthropoids as well as from the decline ot the sensory
representation in the caudal portion of the animal, more particularl\ tlu' tail.
The circumferential zotie in the chimpanzee has a considerafjle depth and
contains the two ascending spinocerebellar tracts ( Fie, Go\v ). The inter-
mediate zone contains the rubrospinal and spinothalamic tracts ( Rst, Spt )
and merges insensibly with the reticular loiniation w hose appearance at this
le\-el is somewhat ditfuse. Neither the central gra\ matter (Gen) nor the
ventral gray column (Ven) presents any marked specialization, although
tht' latter stands out conspicuouslx because of its detachment in consequence
of the hca\ydecussationsof pyramidal libers [ Py x ).

LEVEL OF CAUDAL EXTRE^1IT^ OF INFERIOR OLI\ E (FIG. 2,-7)

I iere the appearance of tiie section has undergone some change princi-
pall\ becaust- of a considerable increase in all ot its diameters. This is occa-
sioned both b\ the e\[xinsion of the dorsal st'nsor\ nuclei (NG, NB) and
the appearance of a new gray element, tlu' mtt'iior oli\ar\ nuck'us (10)
whose caudal tip lit's immcdiatcl.x lateral to tin- p\ramid ( Py ). The central
gray matter (Gen) is more conspicuous because ot its dorsal migration
into the [josition which it will occup\ in the lloor ot the tourth \entncle.
Gontained in its center is a small central canal. It dillers in its appt-ar-
ance from all of tlu' lower le\c'ls because ot its complete detachment,
due to the interposition of internal arcuate tibeis arising in the nucleus of
Goll (NG). These libers also detach the central gra\- matti'r from the
nucleus of Burdach (NB) and the substantia gelatinosa trigemini (NR).

TROGLODYTES NIGEK, Mil; CHIMPANZEE

579

The most |)iiin(iuiuctl chan^H's occur in the dorsal held and nia\ he
ascnhed to the expansion ol the dorsal st-nsor\ inieh'i. 'I'he nucleus oi'
Coll (NG) has considcrabl\ increased in size and is still surroLinded by

FIG. 2-

eiiiMi' wziil;. lfn ul oi- cai dal i-.xiKiMin oi i\i i.kiok oi.i\ e.

cii, CdIimiui of Biirclacli; CEN, Q-ntral Gray Matter; co, Column of Goll; dt, Dcitcrso-splnal Tract; fai,
Internal Arcuate Fibers; i le, Dorsal Spinocerebellar Tract; c;o\v, Ventral Spinocerebellar Tract; IIEL, Spino-
olivary Tract of I leKveg; lo, Inferior Olive; \ii, Nucleus of Burdach; ng, Nucleus of Goll; Miv, I lypoglossal
Nucleus; M<, Nucleus of Rolando; i-n, Predorsal Bundle; PL, Posterior Longitudinal Fasciculus; i'\. Pyra-
mid; REi , Reticular Formation; Hsr, Rubrospinal Tract; SPT, Spinothalamic Tract; tkd. Descending
Trigeminal Tract. |Aeeession No. i^r. Section H2. Actual Size 13 X 10 mm.|

58o THE HIGHER ANTHROPOIDS

nu-clullar\- substance constit iitinij; the eoluiiin ol doll (CG). Neither at
tliis level nor at an\ lower le\tl Is there evidence of the unpaned median
nucleus of" Bischoll. This fact adds substantiation to the theory already
acKanced that the nut'lcus of Bischoll is a functional response to the de\elo])-
nient of a tail, jxuticulailx in such forms as specialize this caudal appendage
as a prehensile, support mg or locomotor organ. In general, the nucleus ol Goll
presents a more disseminated and scattered appearance than is the case with
the lower or intermediate primates. In tact the solidarity ol Goll's mick'us
in most of these lower forms is one of its distinguishing characteristics.
The nucleus of Burdach (NB) has not attained its full dimensions, it
does, however, appear as a more compact nucleus than that ol Goll and is
surrounded bv a dense lield of mxclinizcd libers torming the column ol
Burdach (CB). Lateral to the column of Burdach is a large nuck-us of
Rolando, or sul)stantia gelatinosa trigemini ( N R ), whose outer margin
is in contact with a well-marked descending trigeminal tract (Trd). The
substantia gelatinosa trigemini is in continuit\' whh the rc-mnant ol the Neu-
tral gra\- column which now |)rcsents an indelinite outline and appears to
be merging with the reticular lormation ( Re I ).

Dorsal to the pxramid ( Py ), situated along the median ra[:)he, arc the
collected axons arising from the internal arcuate libers ( Fai ) which torm the
mesial fillet. The a])parent increase in densit\ of this lasciculus implies a
certain degree of increment in this central pathway lor the coiucyance ol
impulses of discriminative sensibility.

LEVEL THROIGH THE MIDDLE OF THL IM-EKIOK 01,l\ E (FIG. 258)

At this le\el the most ijronounced change is ck'tcrmiiuci 1)\ the appear-
ance of a large convoluted structure constituting the inU'rior oli\ary nucleus
(10). This structure, situated dorsolateral to the p\ramid iP\ ), has in
association with it the mesial and dorsal accessory oli\es (,D0, \0).

TROGLOD^TES NIGER, THE CHIMPANZEE

581

I lu' siirtacc cK'itiarcat ions ot the ()li\c' arc well shown l)v tlu' prt'smtv of a
marked prt'oli\ arv sulriis. The inlrrior oli\e itscll has nicreasccl ni j^ronu-
ncncc, not only due to increments m its actual cell-eontainrng substance, but

1 IG. 258. CHIMPANZEE. LE\ EL THHOUGll MIL MIUULL Ul MIE IM EKIUK OLI\ E.
CM, Column of Burclrich; 00, Dorsal Accessory Olive; fle, Dorsal Spinocerebellar Tract; cow. Ventral Spino-
cerebellar Tract; Hti., Spino-olivary Tract of Ilelweg; 10, Inferior Olive; mf. Mesial Fillet; N», Nucleus of
Burdacli; Mil., Nucleus of Blunienau; no. Nucleus of Goll; nhv, Hypoglossal Nucleus; nr, Nucleus of Ro-
lando; NVD, Dorsal Vagal Nucleus; si 2, Hypoglossal Nerve; 1>D, Predorsal Bundle; pl, Posterior Longitudinal
Fasciculus; py. Pyramid; ref, Reticular Formation; Ksr, Rubrospinal Tract; spt. Spinothalamic Tract;
1 KD, Descending Trigeminal Tract; vo. Ventral Accessory Olive. (Accession No. 15-. Section 150. Actual
Size 15 X 12 mm.]

■82 THE HIGHER ANTHROPOIDS

by expansion of its funckis which (.'ontuins a greater \-oKiiiu- ot ni\ clini/ecl
(il)ers than in the low it or intermediate primates. The most cons|)ieu()us
features of the olixe in the ehinifxinzee are its cleeisi\e hoLindar\ hne and
definition, to<i;ether with a marked degree of eoinokition into which its
retaining wall of gra\ matter is thrown. These particulars correspond closely
to those of the structure in tlu' human brain, and are in accord with the lunc-
tional interpretation gi\en of the inferior olive in this discussion. The
advances in oli\ary organization signily a dehnitt' increase m the coordina-
tion of simultaneous movements ol hands, head and eyes, in the interest ol
the better perlormanee of skilled acts. The chimpanzee is capable ol a remark-
able range of performances of this kind, notable because ot their great
ra|)idity, precision and force. Animal trainers and scientific ol)servers ha\e
alike been impressed b\' the proficicncx and adaptabilit\- which this animal
manifests in its manual dexterity.

The central gra\' matter, which has nearl\ completed its dorsal migra-
tion, is about to take up its position m the lloor of the fourth ventricle. In
its more ventral portion is a large, w cll-(k'lincd niieU'ar aggregation, the
nucleus hypoglossus ( N ii \' ) from which tlu' emergent fibers of the twelfth
nerve (N12 ) pass toward the inferior oli\t'. The definition of this nucleus is
more prominent than that observed in thclowerand intt'rmcdiate primates.
Lateral to the hxpoglossal nucleus in the central gray matter is another
nuclear collection of lighter color, with less w cll-derined boundaries, the
dorsal nucleus of the \agus ( N\cl ), connet'ted with which are some I'liter-
ing root libers ol t lu' piu-iimogastric ner\ e. i.ateral to the central gra\ mattir
are the three great nuclei of tlie dorsal sensory field, first the nucleus ol
Goll (NG), second, the nucleus of Burdach (NB) and third, the nucleus
of Rolando (NR). The nucleus of Goll ( N G 1 is considerably smalUr than
the nucleus of Burdach ( N B ), w Inch is at least tw ice the size ol cither ol its
sensorv neiulibors. The nucleus of |-5tirdach shows the t\|)ical accessorv

p

TROGLODYTES NIGER, THE CIIIMI^ANZEE 583

nucleus ol Bluincnau ( N B 1 ). Tlir nucleus of Rolando ' N R 1 1 the substantia
gelatmosa tngeninii) is consicleral)l\ less In size than the nucleus ol'Cioll and
also less sharpl\ delined inouthne. It has in contact with its outer margin the
descending trigeminal tract ( Frd) across whose outer surface pass many
ol the libers ol the ascending spinocerebellar sxsti'in 1 bli'l I'litering into
the lormation ol the restiiorm body. The intt'rniediate lissure, together
w ith the postoli\ar\ sulcus, bounds a slight eminence on the latt'ral surface
which corresponds to the |)osition ol the more \i'ntral ol t hi' two spinocere-
bi-llar tracts iGow ) mesial to which are situated the ruljrospmai and
spinothalamic tracts (Rst.Spt). The reticular lormation iRef) forms
tiK' ct'iitt-r ot the section and is pt'iu-t ratc-d by many internal arcuate libers,
eiiiell\ those taking origin in the nucleus ol Burdach. These make their way
inward toward the raphe, w heri' tlu-\ undi'rgo cU'cussation to enter the
mesial hllet 1 M f ). Ventral to the latter is the compact bundle constituting
the pyramid (Py ).

LEVEL 01^ THE \ ESIIBL LAK M CLEI (IIG. 2ji))

Here the chief alti-ration in the section is determiiU'd b\ the wide oj:)en-
ing of the fourth xcntricle and the ajjpi'arance, in the position previously
occupied b\ the dorsal sensory nuclei, of the two \-eslibular nuclei forming
the central primar\ stations of the proprioceptors situated in the semicircular
canals, utricle and saccule. The central gray matter here occupies its typical
position in the lloor of tlu- fourth \i-ntricle and shows certain minor ditlerences
from the arrangement of this structure in pre\"ioiis lexcls. In the lirst |)lace,
it includes the cei)halic t'\trt'mit\ ol' the h\[30glossal nucleus 1 \hy) as its
lil)ers [)ass forward toward tlu' inferior olixc i 10), lateral to which is the
cephalic remnant of the dorsal \agal nucleus ( Nvd ). Interposed between
the Inpoglossal nucleus and the dorsal nucleus ol the vagal nerve is the
well-delined luiclear mass constituting the lower extremitv ol the vestibular

584

THE HIGHER ANTHROPOIDS

nucleus of Sfhwalbc ( NSc). Adjacent anti lateral to this trianmilai' nuelcLis
is an area characterized by the ])rescncc of small scattert'd bundles oi
myclinized libers in a field of gra^' matter, tlu- nucleus of Deiters (ND).

FIG. 2j(.). CHIMPANZEE. LEVEL OF THE \EsilUlLAK NUCLEI.
AMB, Nucleus Ainbifjuus; < rr, Ontral Tegmental Tract; dt, Dcitcrso-spinal Tract; cow. Ventral Spino-
cerebellar Tract; icp. Inferior Cerebellar Peduncle; 10, Inferior Olive; mi-, Mesial Fillet; nar. Nucleus Arci-
forniis; nd, Nucleus of Deiters; MS, Nucleus Solitarius; nhy, I lypoglossal Nucleus; nk. Nucleus of Rolando;
NSC, Nucleus of Sclnvalbi-; n\ i>. Dorsal Vagal Nucleus; pd, Predorsal Bundle; PL, Posterior Longitudinal
Fasciculus; py. Pyramid; mi-. Reticular F'ormation; rst, Rubrospinal Tract; spt. Spinothalamic Tract;
TRD, Descending Trigeminal Tract. [Accession No. 157. Section 221. Actual Size 18 X 0 mni.l

Many libers ol the \-estibiilar di\ ision ot the eiohth ner\ c entei' this nucleus.
Thus, while the central fi;ray matter still presents those specializations

TROGLODYTES NIGER, THE CHIAIPANZEE 585

(.'hnractrnstic dI tlir h\ poulossal aiul \a^'al miile-i, this lf\fl of tlu' hrain
stem illustrates with what ph\ktic constaiiCN the two great mitlci of the
vestibular ineehanisiti niaki- tluir appearaiiee m a topographieal [iosition
eorres|)o[ulnig to that oeeupit-cl hy the uuelei of Goll and Burdaeh at the
lowx'r k'\ els ot the axis.

It rs not possible Ironi this ligure to lucige ol the (Imiensions, and eonse-
(|uentl\ till' lunetional proniiiieiiee ol tlu' ^"estihlllar eomplex in tlu- ehiin-
paiizee. Tlu' appearaiKx- ol it m reeonstruet ion and its surlaee relief in the
lloor ol the tourth \i-iitriele indieate that this eom|)le\, while somewhat less
proiniiu'iit than in the striet l\ arboreal primates, is eonsidi'rabb moreeonsj^ic-
uous than in man or gorilla. This obserxation eoineides with 1 lu' motor
activities upon whieh thi' chimpanzet' dipends lor its great spc-c-d in elimbing
as well as getting about, either U|)on all lours or m its somewhat awkward
upright posture on the ground. Studies of the actions of the chimpanzee in
capti\"it\- reveal the high degree ol balancing specialization which the
animal j:)()ssesses m its man\ intricate and delicati' j^erformances. The
relati\ e lightness ol its body, as compared to man and thi- gorilla, permits of a
facility in climbing possessed b\ neitlu'r ol the other [jrimatcs nu'iitioncd.
The adaptation oi its ieit and arms to locomotion in the trees as well as upon
the ground calls lor special de\ c-lo]:)ments ol balancing, which, combined
with other necessities in this respect, undoubtedly account lor the well-
de\(.loped central nuchanism illustrated In the large size of the vestibular
comi)le\.

Ventral to Deiters' nucleus is the now much r^'duced mass ol tin- sub-
stantia gelatinosa trigemini (NR) whose outt'r margin is in contact with
the ckseendmg trigeminal tract (Trd). The outer surlaee ol Deiters' nucleus
as well as the (k'scending trigeminal tract are co\ered by a massu'c bundle
ol libers constituting the rt'stilorm body ilCP). The intermediate and
postoluary sulci still bound the lateral iiiternu'diale eminence marking the

586 THE HIGHER ANTHROPOIDS

position of the more ventral ol llic two spinocerebellar tracts ( Gow ), mesial
to which are the rubrospinal and spinothalamic fasciculi ( Rst, Spt). The
inferior oli\e apj)ears perhaps even more conspicuous at this level than in the
one pre\iously described. It shows all ol its characteristics m coiuolutions,
definition of outline, size of fundus and richness oi libcr connections. Mesial
to it is the dense bundle constitutin<i the central pathway of discriminati\e
sensibilit\, the nu'sial lillet ( Ml ), while in the ventromesial jjosition ot the
section is tin- massive pyramid ( Py ). A notable addition in connection with
the ventral surface of the pyramid is the appearance ol a relatix fly large mass
of gray matter, the nucleus areiformis ( Nar). This structure aj^pears to be
the caudal extension of the nuclear masses which constitute the pontile
nuclei. One of the most striking IcatLircs of the brain stem in the great
anthropoids is the increase in the pons Varolii, particularly in its nuclear
masses, whose extension below the caudal pontile limits along the \entral
surface of the pyramid is expressive of extreme acti\ity in growth. There
may be obiections to this interpretation of the nucleus areiformis on the
ground of its connections. In reconstruction, however, this nucleus appears
to be in direct continuity with the gray matter constituting the nuclei of the
pons. It appears onl\' in those primates in which the [jons Varolii has show n
that exuberant expansion which dcNcloixs m direct consec|uence of growth in
the cerebral hemisjiheres.

LEVEL OF THE CEREBELLAR NUCLEI (FIGS. 260, 26 1 AND 262)

At this lew I the most prominent lent u re is tlu- appearanct' ol the nucleus
deiitatus 1 NDt) which is situated m tlu' nu'dullar\ \estibule of the cere-
bellum. At this \v\v\ also the cerebellum occupies a ])()sition alio\f the
roof of the fourth \entricle, into theca\'it\ of wliieh projects a [portion of the
inferior \ermis (Ver). The ca\it\ itself Is more s|)acious than in pre\'ious
sections. 1 he lloor of the ventricle is broader than elsewhere because of

TROGLODYTES NIGER, THE CHIMPANZEE

587

tlu' prfscnct.' ol llu- two lariii' hiUial riTcsscs, contu'ctccl with each ol Which
is the dorsolateral iTiiiiu'iKc which foiist itutcs the tubcrniluin acusticum.
Entering inlu these eminences are the iibers of the acoustic cli\ision of

IIG. 260. CHIMPANZEE. LE\EL Ol rilE CEREBELLAR M CLEI.

DT, Dciters' Nucleus; iti', Inferior OrelKlIar Peduncle; mf, Mesial Fillet; ndt. Dentate Nucleus; NT, Facial
Nerve; n8. Auditory Nerve; I'D, Fasciculus Prcdorsalis; pl. Fasciculus Longitudinalis Posterior; pns, Pons;
pv. Pyramidal Tract; ref, Keticular Formation; run, Tubcrculum Acusticum; ver. Vermis. [Accession No.
157. Section 270. Actual Size 32 X 23 mm.) Figures 260, 261 and 262 are introduced to illustrate character
and extent of the cerebellar nuclei.

tile eighth ner\i'. 1 he a|jj)earance ol the dentate nucleus (NDt) is ot partic-
ular nitcrcst. Its general oulhne gives the impression of a definite i'cs-
tooning in the nuclear substance whicii has assumed the ajjpearancc of a
thin ribbon of gray matter di|)pmg dow n m many irregular depressions of
considerable length. Each such depression is characterized by lesser undula-

,-88

THE HIGHER ANTHROPOIDS

tions in the suiraec ol the gra\ mutter. This appearance' of the nucleus is dis-
tinctive and has been olxserved thus far only \n the chimpanzee. The
characteristic features about it are these deep lestoon-like cur\ es w hich are so

FIG. 261. Cm.MPANZtli. LU\ L.L Ol- rilE CEREBELLAR NUCLEL
CJR, Corpus Juxtarcstiluriiu'; i( i>, Inlirior (Aivbillar Prdiiiiclc; mcp, Middle Certbcll.ir Peduncle; mf.
Mesial Fillet; nab, Nucleus Abducentis; ndt. Nucleus Dentatus; nfg. Nucleus Fastigii; n6, Abduccns Nerve;
N7, Facial Nerve; i>n. Pontile Nuclei; I'NS, Pons; i»v. Pyramidal Tract; rf.f. Reticular Formation; SCH, Supe-
rior Cerebellar Peduncle; \ in i\. lourth Ventricle. [Accession No. 157. Section 249. Actual Size 38 X 26 mm.]

extensive as ahiiosl to isolate portions of tlu' nut'leus li'om the mam mass ol
the structure. In its most primiti\c condition the dentati' nucleus has a tar
simpler outline with little or no tcndiMux to conxolution and mipt'ricct
sacculation. In its hi<i;hest morphological ck'\clopment it appears pre-

TROGLODYTES NIGER, HIE CHIMPANZEE

589

rniiiuntl\ as a saccular stnicturc with some roseml^Iaiuc to the inferior
i>h\ar\ body. The degree ol eornohition in the wall ol the dentate nueleus
\aries eonsidi'ral)l\ as the result ol the eoinplixit \ ol its organization. In all

FIG. 262. CHIMP.ANZEE. LEVEL Ol IHL CEREBELLAR NUCLEL

CTT, Ontral Tcijrncntal Tnict; cow. Ventral Spinocerebellar Tract; ici', Inferior Cerebellar Peduncle; mf.
Mesial Fillet; ndt. Cerebellar Nuclei, Lateral Group; ncl, Cerebellar Nuclei, .Mesial Group; fx. Pontile
Nuclei; pv. Pyramid; kst. Rubrospinal Tract; sft. Spinothalamic Tract; yen iv. Fourth Ventricle; ver.
Vermis Cerebclli. (Accession No. i ,— . Section 310. Actual Size 30 X 32 mm.)

of the more highl\ diil(.rentiated species the convolution in the nucleus is
pronounced. The chimpanzee stands intermediate- between the two extremes

390 THE HIGHER ANTHROPOIDS

of dentate difrcrentiation. It presents the undulating and eonNoluted appear-
ance in the outer wail of its structure. It is definitely sacculated in form; and
it has a well-defined fundus. But the degree of the convolution is so niarl<.ed as
to encroach upon the fundus in such a way as to reduce materially its capac-
ity lor myelinized fibers.

What the configuration of the dentate nucleus of the chimpanzee may
actually signify, and how it should be interpreted with reference to the func-
tional capacity of this structure, are problems requiring further investiga-
tion. It is, however, worth noting that such a difTcrence does exist in the
chimi^anzee and is sufficient to distinguish it from both the lower primates and
the higher forms. It is possible that too much emphasis is laid upon this dis-
tinction and that this high degree of convolution in the saccular wall of the
dentate nucleus really implies a far greater degree of specialization than in
other species. On the other hand, the conditions as compared with those in
man lead to the conclusion that specialization in chimpanzee, although
along the lines of greater complexity, is not following the direction prescribed
by the human mode of development which gives rise to a dentate nucleus in
many characteristics quite difl'erent from that of the chimpanzee and much
more in harmony with the gorilla. If any inference is justified with reference
to the functional capacity of the cerebellum, it might properly be that the
chimpanzee is endowed with eoordinativc control which is at least equal to
that of tlu' highest jMimate. The studies of behaxior, already quoted in con-
nection with tlu' animal, emjjhasize the remarkable feats of strength and
dexterity of the fore- and hindlimbs. They demonstrate a capacity for
acquiring jjerformaiices of a skilled nature, some of which surpass in their
complexity those attainable l)y man. All of these facts signify that the chim-
panzee possesses a range and variety of skilled performances which ma\
easily rival those of the highest j)rimates. That it does not apply these eoor-
dinativc capacities in the execution of the many di'licate and precise acts

TROGLOD^TES NIGER, THE CHIMPANZEE 591

which charactenzc man rniu-i'rns another tli-paiinu-nt of its neural organiza-
tion. That it Is ])()tc'ntiall\ ec|uippi'c[ witli and often docs df\rlo|) a surprising
degree ol sueh museuhir regidatioii is a fact concerning whieli tliere ean be
no possible doubt.

The et'iitral gra\ matter lorining the lloor of tln' fourth \ entriele contains
the triangular nucleus of Sehwalbe, lateral to which is Deiters" nucleus.
Manx libi'is of tlu- \estibular di\ision of the eighth ner\e enter the latter
nucleus. X'entral to Deiters" nucleus is the substantia gclatinosa trigeiiiini,
in contact by its outer margin with the compact bundle forming the descend-
ing trigeminal tract. Contiguous w ith tlu' outer margin of this tract and w ith
Deiters' nucleus is a dense mass of mxelinated hbers forming the restiform
bod\-, while u[;on the outi'r edge ol this structure ai)pears the tuln'rculum
acusticum (Tub), into which man\ libers of the acoustic di\ision of the
eightii nerve are entering. Upon the ventral surface of the section some
ot tht' leatures constituting the pons \ arolii ha\e become apparent. These
consist ol transxcrsc libers ot the stratum superliciale surrounding a small
scattered mass ol nuclear substance, the pontile nuclei (PN), together
with the teiuk'ncx' oi the pyramidal tract to become disst'minated l)\ the
inter])osit ion ol nuclear substance and trans\erse j)ontile libers. 1 he boundary
between the basis and the tegmentum is indicated, as at higher levels, by the
tendenc\ of the mesial lilKt 1 Mf ) to dispose itself transversely and thus
serve as the line ol demarcation belwi'cn these two portions of the stem.
Passing through the basis jxmtis, peiu-trating both the pontile nuclei and the
pyramid, are some of the emerging libers of the alxlucens nerve (N6). The
cephalic tip ol the inferior olivary nucleus occupies a position near the center
ol the reticular lormation ( Ref ). The oli\-arv nucleus is in relation to the
dense bundle of fibers along its \entrolateral aspect constituting the central
tegmental tract fCtt) which serves as a connection between the olive and
centers in the midbrain.

592 THE HIGHER ANTHROPOIDS

The reticular lurniatiori I R c I ) is c\U'nsi\c' l)iit presents no marked
specialization at this le\eL It is i^enctratecl l)\ nian\ internal aicuate libers.
Some of these arcuate libers occupying a more dorsal position in the reticular
formation take tht'ir origin in the Dcitersal nucleus and undergo decussation
to form tht' crossed Deiterso-spinal tract. Other decussating libers in a more
ventral position pass inward to iorm the caudal [jortion oi the corpus
trapezoideum. This level is significant as showing the general tendency
()bser\ed in the alferent course of all sensory path\\a\s to undergo decussa-
tion. L'sualK the crossing of such pathways trom one side to the other takes
place in close relation to their nuclear origins. Such is the case with the
pathway serving for alferent im|)ulses from the upper extremity and trunk
and the lower extremity and tail. I^Or the impulses receixed trom the pro-
prioct'ptixe structure of the internal ear, namely, tlu' utricle, saccule and
semicircular canals, a similar decussation takers place immediately alter
relay in the primary receiving stations of Deiters' and Schwalbe's nuclei-

LE\EL THROUGH THE PONS SHOWING THE EMERGENT FIBERS OF THE SI.XTH
NERVE, NER\US ABDUCENS (FIGS. 263, 264)

At this level the contour of the section has undergone a marked change,
due to the presence of the massive structures constituting the pons \ aroiii.
The pons presents its characteristic three layers w hich consist ol tiie stratum
superliciale, the stratum complexum containing trans\-erse pontile libers,
the ponlik' nuclei and the disseminated bundles of the pxramidal tract,
and the stratum profundum consisting iargel\ of trans\t'rst' pontik' libers.
Passing throLigh the st'wral strata of the |)ons are scattered libers making
their way forward to a point of t'lnergence at the iunction ol the pons
Varolii and the oblongata. These are the emergent libers ol the abduceiis
nerve which suppl\ tlu' external rt'ctus muscli's ol the t\ve (N6). The
massive size of the pons, part lcularl\- tlu' large xolume ol the pontili' nuclei

TROGLODYTES NIGER. 11 IF. CIIIMI^ANZEE

51)3

(PN), signifies an animal m wlucli [hvvv is a xohiminous cuniu'c'tioii
bi'twcrn tlu' ccifl)ral cortex and the lati'ial lobes ol the eerebelliim. Such
a eoniieetion, as alreacl\ mentioned in pre\ioiis discussions, is mdieatixc

FK,. 263. CHIMPANZEE. LE\EL OF THE CAUDAL EXIKEMllV OF FHE PO.NS
SHO\VIN(; IHE EMEKGFM FIBERS OF THE SIXTH \EH\E.

CTT, Central TcfjiiK-ntal Trad; ux, Diiterso-spinal Tract; (;ow. Ventral Spinocerebellar Tract; icp, Inferior
Cerebellar Peduncle; lo, Inferior Olive; \ii-. Mesial Fillet; nab, Abdiicens Nucleus; nd, Deiters' Nucleus; nr,
Nuclius (if Rolando; nsc, Nucleus of Scliwalbe; n6, Alxlucens Nerve; nH. Auditory Nerve; i>i). Predorsal
Bundle; i>L, Posterior Longitudinal Fasciculus; pn. Pontile Nuclei; I'v, Pyramid; REr, Reticular Formation;
RST, Rubrospinal Tract; spt. Spinothalamic Tract; trd, Descending Trigeminal Tract; tuh, Tuberculum
Acusticum; vr;\ iv. Fourth N'entriele. (Accession No. i-;^. Section 26,-. Actual Size 24 X 14 mm.]

ol an animal in which skilled peilormanct's are de\elo|)ed to an unusually
high degree. The pontile nuclei in themsi'Kcs are signilicant ol a rich pallio-
ci'rebellar communieal ion. but they also denote the possi'ssion ol an intelli-
genee relati\elv acKanced in its de\ flo|jmeiit. TIk' ck'gree ol this (K'\ elopnu'iit
has l)een carehill\ tested b\ \arious psychological and psychometric experi-
nu'iits. The general conclusion ol \arioiis observers is that tlu' standing ol

594 THE HIGHER ANTHROPOIDS

the chini])anzL'c ani()ii<i- the primates gives this animal a plaee undouljtedly
tar below that of man, but > et sulliciently high to eonsider it capable of
intelligent behaAior.

FIG. 264. CHIMPANZEE. LEVEL THROUGH THE PONS SHOWING THE EMERGENT

FIBERS OF SIXTH NER\E.

CTT, Central Tegmental Tract; MCi', Middle Cerebellar Peduiiele; Mt, Mesial lillel; Mu;, Nucleus of Becli-
tcrew; nab, Abducens Nucleus; ndt. Cerebellar Nuclei, Mesial Group; nfg. Nucleus Fastigii; nr, Nucleus of
Rolando; n$. Trigeminal Nerve; n6, Abducens Nerve; n"'. Facial Nerve; i>N, Pontile Nuclei; py. Pyramid;
RST, Rubrospinal Tract; scp, Superior Cerebellar Peduncle; yen iv. Fourth Ventricle. (Accession No. 15-.
Section 380. Actual Size 36 X 28 mm.]

TROGLODYTES NIGER, THE CHIMPANZEE 595

In iIk' ci'iitial iii"a\' iiiatttT winch htTc forms tin- lloor' ol tiu' louitli
M.'ntrK'lc IS a collection ol niTxc cells forniinti; the nucleus abducentis (Nab).
Into the \ent i'](.-le proiects the nodular portion ol the nilerior \'erinis, while
the \entriCLilar walls are marked b\ the dentate nucleus and its surrounding
cajjsule ol nervt' libers. \ eiitral to the teunientum, and separated Irom it by
the trans\ersel\ disposed libers constitutin<i; the mesial lillet ( \H ), is the
basis jjontis. All ol the ti"ans\-erse libers of the pons become collected to form
a massi\e bundle proceedinir laterally and dorsally to enter the cerebellum as
the micldli' cerebellar pedLincle I Mcp ).

LE\EL THROUGH THE MIDDLE OF THE PONS \AKOLU (fIG. 265)

Here the contour ol the section has undergone considerable modilica-
tion, due to the fact that the ventricle has decreased in size as the caudal
orifice of the Syhian aqueduct is approached. It is bounded dorsally by the
\ermis of the cerebellum (\ er) and laterally by the two superior cerebellar
l^edunclcs (Sep). The central gray matter now lorms the lloor ol the
\entricle and immediatelx' beneath this is a dense bundle oi myehnized
libt'rs which extends ti"ans\ersely and forms the genu facialis (N7), the
third portion ol the enurgent course ol [hv lacial ner\c'. The tegmentum
is bounded Neutrally by tlu' bundles forming xhc nu'sial lillet (,.Mf ) and thus
separated from the basis pontis, which coniprisis the characteristic i)ontiIe
strata already- described in this species. The traiis\'erse fibers of the pons
are collected laterall\ to form t he middle cerebellar peduncle 1 M cp ) through
which the fibers of the trigeminal nerve ( N5 ) make their way. The larger
division of this lu-rve is situated dorsolaterall\ and constitutes the dorsal
root fibers arising in the Gasserian ganglion. The\ represent dermatoinic
sensory areas of the head and face, supplii'd by the fifth cranial ner\e. These
fibers end in an irregular mass of gra\ mattt'r forming the cephalic extremity
of the substantia gelatiiiosa which, because of its c(jn\oluted appearance, is

FIG.

265.

CHIMPANZEE. LE\EI. THROl'GH THE MIDDLE Ol- HIE PONS VAROLII.

CTT, Central Tcgnioiital Tract; i.i , Lateral Fillet; MCi>, Middle Cerebellar Peduncle; mf, Mesial Fillet; \m.
Nucleus Maslicatorius; nbe, Nucleus dI Beclitcrcw; N5, Trigeminal Nerve; n7, Facial Nerve; pn. Pontile
Nuclei; pns. Pons; I'V, Pyramid; Rsr, Rubrospinal Tract; sci', Superior Orebellar Peduncle; spt, Spino-
llialamic Tract; ven iv, Fourth Ventricle; vt£U, Vermis. [Accession No. 157. Section 395. Actual Size
28 X 27 mm. I

l5c/'l

TROGLOD^TES NIGER, THE CHIMPANZEE

597

tcTiiU'd tlu' fDiu iilutioiu's cjuinti. Mesial to the scnsorN root ol tlir lilth tUTNC
arc the hbc-rs ol the motor cli\ ision ol the tri(:;emiiial luaxi' w huh sup|)l\ the
nuiseles of mast leat loii. Tiie ori<im ol these (il)ers is plainK seen m the luieleiis

FIG. 266. CHIMPANZEE. LE\ EL Ol lilE E.MEKGENCE Ol IIIL lOLKlH NEK\E.

CI N, Central Gray Matter; CIT, Central Tegmental Tract; i r. Lateral Fillet; mf. Mesial Fillet; n4. Trochlear
Nerve; I'D, Predorsal Bundle; pl, Posterior Longitudinal Fasciculus; i'n. Pontile Nuclei; i>v. Pyramid; ref.
Reticular Formation; sci', Superior Cerebellar Peduncle; SI'T, Spinothalamic Tract. [Accession No. Ij7
Section yOi. Actual Size 21 X i<) mm.)

FIG. 267. CHIMPANZEE. LEVEL OF THE INFERIOR COLLICULLS.
CEN, Central Gray Matter; ctt. Central Tegmental Tract; \c. Inferior (^ollicukis; u-. Lateral Fillet; mf,
Mesial Fillet; ntr. Nucleus Trochlcaris; pd, Predorsal Bundle; pi., Posterior Longitudinal Fasciculus; p.n.
Pontile Nuclei; pns, Pons; pv, Pyramid; ref. Reticular Formation; hst, Rubrospinal Tract; spt. Spino-
thalamic Tract; spx, Crossing of the Superior Cerebellar Peduncle; tmt, Ascending Mesencephalic Tract ot
the Fifth Nerve. [Accession No. 157. Section lyg. Actual Size kj X >') mm.)

l5y«l

TR0G1.0^^TES NIGER. TIIF CHIMPANZEE 599

situatrd \ cut ronusial to the coinolut lones cjuinti, constituting the nucleus
niasticatonus (NM). The clillusc reticular formation occupies nearly the
entire lield ol the tegmentuni and is not (hllerentiated to form any speciah'zed
nuekar aggregation. This lev(.-l is signihcant as olU'ring some basis f(jr esti-
mating the degree to which tlu- hith cranial nerve contributes to the inlhix
of sensory impulses Irom the bod\, |3articularly as this inner\ation bears
upon the (hrt'ction ol the animal's motor control.

LE\EL OF THE INFERIOR COLLICl LLS (^FIG. 267)

At this le\el, changes incident to the appearance of the two caudal ele-
vations in the c|uadrigeminal phite ha\-e altered the contour of the section.
In this region the \i'ntricular chamber has been reduced in its dimensions to
those characteristic of the SyKian acjueduct w Inch is now entirel\ surroundi'd
by the central gra\ matter (Cen). In the ventromesial [portion of this
substance is a speciahzed region h)rming the nucleus Irochlearis 1 Ntr). A
(k'nse bundle of hbers passing Irom this nucleus constituti'S the lirst portion
ol the emergent course ol this motor ner\'e. At the lateral peripht-ry of
the central gray matter is a band-like collection ol libias, somewhat sepa-
rated into small lasciculi, lorming the ascending mest'iicephalic tract of the
fifth nerve 1 Tint ).

The most outstanding Icatures, howc'\er, art- tlu' two elexations abo\-e
the central gray constituting the interior colliculi 1 IC) to which some
fibers of the lateral fillet are making their way. This colhculus is a way-
station in the pathwax ol auditorx impulses destined lor the temporal lobe
ol the cerebral cortex. It still shows some ol its primiti\e histological details,
especially indicated by the rudimentary stratilication of cell and liber layers.
Comjxuatiw'ly speaking, however, the mierior colliculus is less prominent in
the chim])an/.ee than it is in the mtt'rmediatt' and lower primates, thus indi-

6oo THE HIGHER ANTHROPOIDS

eating that its original and jjrc-clomlnant I'linction with rt-lcTcnce to the sense
of hearing has cleert'ased eoiisiderably in importance. Sueh recession is due to
the fact that \hv aiichtorx activities ha\e been taken o\er !:>>• a higher [portion
of tlie ner\()us system, namely, the temporal area of tlie cerebral hemisphere.
.Mucii emphasis lias been laid u[)on the significance of this portion of the
brain stem in its bearing upon the evolutional process w hieh has operated in
tin' interest of giving to the sense of hearing a more expansible and more
cooperative cerebral region for the elaboration of the auditory sense. The roof
oi' the midbrain was so placed as to be delinitel\ embarrassed by its topog-
rajjhy, since any expansion in the endbrain must necessarily be attended by
corresponding dexelopment of the cerebellum. The mesencephalic roofplate,
from which the inferior collicLdi arise, under such conditions would be caught
between two slowly expanding structures, namelx, the endl^rain in front and
the cerebellum behind. In any case, a delegation of midbrain function to the
hemisj)heres has taken place and the dimensions of the inferior colliculus
have correspondingly decreased.

Considered in terms of functional signilicance, it appears that auditory
sense has become less important as represented in tlu' midbrain ot the chim-
panzee than it is in the lowi'r primatt-s. The inferior colliculi are connected
across tlu' midline l)\ means of medullated commissural libt'rs. The tegmen-
tum in this region of the midbrain is separated Iroin the basis by the inter-
jjosition ol' the mesial lillet (Mf ) and t lu' central portion ol the field is
occLipied b\- the decussation of the superior cerebellar peduncle (Spx)
])re|)arator\ to its entrance into the red nucleus at a somewhat higher le\el.
In the basis of the section are man\ ol' the iharacteristic pontile leatures,
while on the \entral surface a det'pening of the median sulcus is about to
determine the sej)aration of the two haKt's of this region of the stem to torm
the cerebral pitluncles. This section is important because of its bearing upon
the function of hearing, particularly as thai function appears to be undergoing

<■' i- ^- •(. V'-.

■> A A AT: !.! ;....

, ■ /."■'*.

TROGLODYTES NIGER, THE CHIMPANZEE

60 1

delegation to hi<i;hcr and more cHicieiit aix'as of s\ lUhcsIs in tlic cerebral
cortex.

LE\EL Ol- THE SVPEKIOK COLLICULUS (EIG. 268)

At this lc-\c'l two niodilicat lolls Ikinc occurred to dist in<j;uisli tlu' section;
first, tlie separation ol [\\r basal region of the axis to lonii the two cerebral
pechincles (CP) with the proiiuction of an interxal betwrt'ii them the
optico-peduiu'ular space; second, in a dorsal position, the a])pearance of the
two cephalic eliAatioiis ol the ciuatln^cniinal plate constituting tin- supt'rior
colliculi (SC). These striicturi's ari' associated with tln' \isual pathway
and are the \estigial remnants of lormcrlx ]jroniincnt structures lorniina; the
optic IoIk's. I heir luiK'tional si^nilicance, as in all tlu' i^rimates, arises
Ironi xhv lact ol tluir decline m structural promiiu'iicc and the attendant
diniiiuition in lunctional miportanct' with rererence to \ision. The same
process in\ol\cd in the diilerentiation of the inferior colliculus has been in
progress in this portion ol the midbrain. A [)rogressi\e delegation of \isual
lunction to in'w and more expansible art-as of the cerebral cortex has pro-
ceeded, until nearl\ all ol the \ isual acti\ities ha\-e been acKanccd to the
occipital lobes. The su|jerior colliculus, howi'\fr, still bears some e\idence
oi its tornur dominance m \ ision and retains a few of the original fourteen
layers olthis portion of llu' tectal cortex. At best the diilerentiation of these
layers is indelinite and indicati\-e ol an area in j^rocess of decline.

The central gra\ matter (Cen ) cntirel\ surrounds the S\l\ian ac|ueduct
and in its central region is elongated lor the spt'ciali/.ation of the large
oculomotor nucleus ( Noc ) whit'h gi\-es rise to the libers of tlu- oculomotor
nerve (N3). Fibers arising in this nui'leiis make- their wa\ forward to
emerge Irom the brain stem 111 the optico-|jeduncular sjxice from the oculo-
motor sulcus.

6o2 THE HIGHER ANTHROPOIDS

More iiii])()rl;ml than the cnuTgeiit hbcrs ol the oeuloinotor nerve are
the commissural and deeussatm<2; axons w hieh connect the nLiclei of the two
sides. The e.\tensi\ cness ol this mternuclear connection in t'hiinpanzee is

FIG. 268. CHIMPANZEE. LEVEL OF THE SUPERIOR COLLICULUS.
CEN', Central Gray Matter; cp, Cerebral Peduncle; ctf. Central Tegmental Tract; mf, Mesial Fillet; mcb.
Mesial Geniculate Body; NOC, Oculomotor Nucleus; nru, Nucleus Ruber; N'3, Oculomotor Nerve; pd,
Predorsal Bundle; pi., Posterior Longitudinal Fasciculus; rf.f, Reticular Formation; rst, Rubrospinal Tract;
SBN, Substantia Nigra; sc, Superior ('ollicuhis; spt, Spinotlialaniic Tract. [Accession No. 157. Section 530.
Actual Size 26 X 13 nun.)

notable, since this intercommunication is related to hinoeular and stereo-
scopic vision. This animal possesses a iairlx hi^h degree of such vision. The
tests made by most caretul psyclioiogical nuestigalions, particularly in the

TROGLODYTES NIGER, THE CHIMPANZEE 603

hands of Prolt'ssor Kiihlrr, ha\c clclmitclx disclosed the lact that the t'hmi-
panzcc is able to employ stereoscopic lusion elli'etix el\ . In eonjunetion witli
the extensne oeuloinotor eoniieetion hetween the two nuclei, this fact <z;()cs
a long way to substantiate the theory athanced concerning the Innction of
this decussation.

On the boundarx line betwe.Mi tht' basis and tegmentum is a massive
aggregation of gray matter which extends Irom the lateral pt'ripher\ u lu're
it appears to l)c in continuitx with the mesial geniculate body (Mgb)
transversely across the section to the margin ol the optieo-i)eduncular s[)ace.
This is the sul)stantia nigra (Sbn ) the luiu'tional signihcance ot which is
not altogether clcarl\ understood, but to which is attributed the lunction
ol control o\cr automatic associated moxcmcnts. \\ hate\er its functional
capacity ma\' be, it is clear m the ascending series ol the primates, that the
nuclear structure becomes more dehnitely outlined but somewhat smaller
in size. The reticular formation (Ref) contains at this level a highly
specialized nuclear structure situated near the midluu-. This is the nucleus
ruber (NRu), the way-station in the pathwax out of the cerebellum which
serves in the capacity ot eon\eving impulses to the musck's necessary to
coordinative control. Its large size and clear delimtion ol outline in chim-
panzee indicate a strLieture engaged in functional acti\ities ol the greatest
importance. In contrast with the similar nucleus m the lowt'r primates, as
well as in the internudiate group, the red nucleus has increased both in size
and in clearness of dcTmition. 1 his, so lar as the chimpanzee is concerned,
would indicate (K'limte augmentation in the lunction ol muscular coor-
dination. Such interpretation is in keeping with the lact that the dentate
nucleus has similarly increased m this species.

The basal ])ortion of the axis consists of a dense medullar\- structure
constituting the cerebral peduncle (CP) and containing heavil>- mxelinizcd
fibers of the jjallio-ponto-ccrcbcllar and the pyramidal systems. I-rom its

6o4

THE HIGHER ANTHROPOIDS

size may be estimated the degree to wliich the animal lias developed not
only its volitional control, hut that regulation of motion dependent upon
the harmonious cooperation between the severallobes of the cerebral iiemi-

FIG. 26(). CHIMPANZEE. LEVEL OF THE LATERAL GENICULATE BODY.
c.n\, (xntral Gray ALittcr; ctt. Central Tegmental Traet; ci>. Cerebral Peduncle; lgb. Lateral Geniculate
Body; MCI), Mesial Geniculate Body; mf, Mesial Fillet; noc. Oculomotor Nucleus; nru. Nucleus Ruber; pd,
Predorsai Bundle; pi,, Posterior Longitudinal Fasciculus; pul, Pulvinar; kef. Reticular Formation; sc,
Superior Collieulus; siix, Substantia Nigra; spt. Spinothalamic Tract. [Accession No. 157. Section 675.
Actual Size 38 X 15 mm.]

spheres and llu- lateral lobes ol the eerel)elliim. lis ilinn'iisions m ehmii)anzee
thus indicate a high degree ol organization in these particulars.

LENEL OF THL 1_ A I FKAL GENICULATE 1U)^^ ( FIC;. 269)

This section is mlroduced largel\ with the purpose ol showing the

.cons])icuous dimensions and appearand' ol the nuckuis rubi'i" (NRu).

Some fibers in the oculomotor decussation iwv still sct'ii in connection

with the oculomotor nucleus (,Noc). Laterally, Ijoth mesial and lateral

TROGLODYTES NIGER, THE CHIMPANZEE 605

geniculate bodies arc shown (Mgb, Lgl)), the hitter reeei\iii<j; libers making
their way inward through tlie optic tract on their way to the visual area of
the cerebral cortex. The gi-nicuhitc bodies, both mesial and lateral, apparently
have develojjcd in the intiTcst of that delegation of auditory and visual func-
tion to the cerebral cortex which is characteristic of the inaninialian brain
and have become progressivelx more conspicuous in the primate series. The
superior extremity of the colliculi is also seen and lateral to it another
relaj^ station connected with \ Isual biiiction, the pulvinar of the optic
thalamus (Pul). The section is particularl\ important because of the
clear definition of the red nucleus (NRu), thus offering another criterion
l)\ w hich to judge the degree of coordinati\ c specialization in the chimpanzee.

LEVEL OF THE OPTIC CIHASM (pIG. 2-o)

At this level the contour has been changed b\ tin- appearance of the
vertical third ventricle and the extensive lateral masses of tlu' thalami bound-
ing it upon either sich'. The continuit\ of the third \fntricle is interrupted
by the appearance at this level of the large commissura mollis. Tlie optic
thalami here are separated laterall\ from the globus pallidus of the corj)us
striatum (GIp) by the interposition of a dense mass of m\ el inizecl fibers
constituting tlu' internal capsLilc (Cin). This latter structure is the con-
tinuation ccphalad of tlu' cerebral peduncle and serves to establish the
linal connection with the cerebral cortex. In the internal capsule at this
le^•el arc libers of the |:)allio-p()nt()-cerebcllar system, and also ot the
pyramidal system. The most M'litral structure of the section is the optic
chiasm (Opx), along whose dorsal aspect passes a set of less densely
myelinized libers constituting the supra-optic decussation of Meynert.
The optic chiasm serves as the point of partial crossing in the visual
jxithway, receiving at its cephalic angles the two optic ner\es and being
continuous at its caudal border with the optic tracts. These latter together

6o6

THE HIGHER ANTHROPOIDS

with the cerebral peduncles form the lateral hoiindary of the optico-pedun-
cular space. The optic thalanii provide the iinj:)()rtant relay stations in
the patiiway of all types of sensibility w ith the exce|)tion of the olfactory

FIG. 2~0. CHIMPANZEE. LEVEL OF THE OPTIC CHIASM.
riN, Internal CJapsulc; idi', Descending Pillars of Fornix; n>H, Corpus Ilypothalamicum; olp. Globus
Pallidus; nl. Lateral Nucleus of Thalamus; mi. Internal Lateral Nucleus of Thalamus; oi'X, Optic Chiasm;
PUT, Pulamcn; vy, Fasciculus of Vicq D'Azyr. [Accession No. 157. Section 813. Actual Size 45 X 25 mm.)

sense. The specializations withm this poition ol the brain stem are too exten-
sive to jjermit ol discussion at this timr and properly belong to a treatise in
which e\clusi\e attention ina\ be ck'Noted to their structure and e\()lutional
significance. The globus pallidus (Glp), a portion of the corpus stria-
tum, likewise is a structure presenting a highdegreeol s|)ccializat ion. Bcinga
part of the endbrain it should propeilN be considered with other constituents
of this division of the encephalon rather than as related to the brain stem.

TROCI.ODVTES NICER, THF. CHIMPANZEE

607

LEVEL OI-- THE ANILKlOli COMM ISSIKE ( MG. 2-1)

At til is lc-\ t'l \Uv sc'ftion indicatrs the cxtrrnu' cephalic- limit of the brain
stem, in it are shown the eephalie portion of the third \c-ntriele ( V e n iii)

ITG. 2-1. CHLMFANZEE. LE\ EL OF THE WIEKKJK CU.NLMISSLKE.
AC, Anlcrior Comniissiirc; cix, Internal Capsuk-; tdp, Dcsci-ndinfi; Pillar of Fornix; for. Fornix; clp. Globus
Pallidus; nca, Caudate Nucleus; M., Lateral Nucleus of Tlialarnus; I'lr, Putanien; nm. Nucleus Masticato-
rius Trigemini; vem hi. Third Ventricle. |Accession No. I57. Section goo. Actual Size 45 X 17 mm.]

approachinu tlu' lamina termmahs and bounded upon either side by the
eephalie portion ol the optie thalami. 0\'erl\ ing the roof of tiie third
v'entricle is the eonipaet mass ol libers lormnifi the corpus callosum, depend-
ent Irom which are portions ol the anterior pillars of the fornix (Eor)
Beneath the lloor ol the \entricle passes the anterior commissure f AC) con-
neetmg one hemisj^here with the other, the most cephalic link of communi-
cation. Separating the cephalic e\tremit\- ol the oj)tic thalamus from the
globus pallidus ol the corpus striatum is a dense bundle of fibers constitut-
ing the anterior limb of the internal capsule (Cin). The more important
structures in the section are indicated by appropriate letters intlie caption.

Chapter XX

RECONSTRUCTION OF THE GRAY MATTER IN THE
BRAIN STEM OF TROGLODYTES NIGER

IN the rfconstriution ol the high ceTNical lexcl of the spinal eorcl, the
ventral gray column has ahxady het'ii .se])aratecl Irnin the ei'ntral gray
matter h\ the (leeussatmn ol the p\raniiclal traet. The eentral gray
mattt'r itselt is c|uadrilateral in sha])i' with a \'entroinedian prolongation. It
is situated ni its usual eentral position.

The \eiitral gra\ eolunin is irregularly triangular in outline with its
base directed ventronH'siall> , its apex xcntrolatcrally. The dorsal horns are
long, compressed laterallx and situated almost m tlu' transverse meridional
line ol the cross section. Their perijihcral expansion lorming the substantia
gelatinosa trigemini is bulk\, roughly o\al and presents the tendency
towards the rather llame-like conliguration which has been tound to be
characteristic ol this nucK-ar mass.

The sensory nucleus ol Goll has already mack' its appearance, being
elongated from before backward and lying as a more or less laterally
compressed strand of gray matter within the libers of the column of
Goll. It IS surrounded on all sides, except at the base, where it is con-
llueiit with the central gray matter, by the eiu'clopiiig libers of the column
of Goll.

In general, the high le\el of tlu' eer\ical spinal cord is identical in
arrangement with cross sections ol the human brain stem. It becomes appar-
ent m the studu's ol these simian sections that the human pattern is being
more closel\- approached, both in extent and in complexitxof organization.
Many ol the lewis of tlu' chimpanzee and of gorilla are indistinguishable

irom similar sections of the human neuraxis.

6o(j

6io THE HIGHER ANTHROPOIDS

The Dorsal Medullary Nuclei

One of thf dorsal sensory nuelei has already made its appearance. The
nueleus of CjoII is present and oeeupies ahnost tlie entire \entrodorsaI extent
of the eohiniii of Coll. It is narrow, compressed from side to side and con-
nected at its base \\ ith the central gray matter. On all sides, except at its
point of junction with the central gray matter, it is enveloped h\ hbers of the
column of Goll. The sensory nucleus of Burdach first appears at a level
somewhat higher than the caudal e\trcniit\ of the nucleus of Goll. It is dis-
tinguishable as a thickening in the dorsal surlace of the central gray matter
or the junction of the dorsal horn with the central gray matter. This sessile
condensation of nuclear material gradually becomes more promment.

A lateral divergence is characteristic of all of the dorsal gray structures,
being produced by the opening of the fourth \entricle which tends to force
all of the dorsal structures further from the median line. The dorsal extremity
of the tuicleus of Goll becomes expanded laterally and overhangs tln' more
ventral structure at a level below the opening of the expanding lourth
ventricle. Tlu' nuclear material becomes much more extensive near the
dorsal peripher\ of the axis and presents a marked tendency to accumulate
laterally. This arrangement is characteristic also of the nucleus ol Burdach,
the dorsal extremity of w hich becomes hea\ier and shows the same tendency
towards lattwal extension. In some places it is carried so far as to oNX'rhang
the substantia gt'latinosa trigemiiii.

In the caudal region of the xeiitricular opening the lateral walls of tlu'
fourth ventricle on each side are lorined by the nucleus of Goll. Higher up the
nucleus of Goll is gradually separattcl from the lateral borders of the lourth
ventricle by the interposition of the wstibular com]3lex between it and
the ventricular wall.

RECONSTRUCTION OV TROGLODYTES NICER

6ii

Shortly afur Uk- appcarancf ol this midair mass tlu- nucleus of Col!
begins to diminish. 1 lir tliminution ol this nuclear mass contimu's ra])idly
until the I'ntire column with its nucleus disappears.

FIG. 2-2. \ EN rKAL SURFACE OF GRAY MATTER Ol- BRAIN STEM,
TROGLODYTES NIGER.

Key to Diagram, int. oli\ i , InlVrinr Olive; i ai. cin. body, Lateral Geniculate Body; meso-cen. body,
Mesial Geniculate Body; I'ontile, Pontile Nuclei; v. cii. and \e\t. cochi.., Ventral CochUar Nucleus; v.
GR. COL. and vent, gray coi.., Ventral Gray Column.

The nucleus of Burdach reaches its maximum at the le\el of disappear-
ance' of the nucleus ol Coll. It then <^raduall\ diminishes and comes to an end
below the mid-\ entncular \v\v\.

The substantia gelatmosa trigeniini described in connection with the
high cervical le\cl ol the spinal coicl yraduallx passes more Into the latero-
meridianai position, which is charaett'ristic ol this structure. 1 laving reached
this [)osition it continms upward almost unchanged to the upper icxel ol tlie
pontile portion of the stem where it linallN becomes e.xpanded as the convolu-
t lones c|uinti.

6i2 THE HIGHER ANTHROPOIDS

At a point soiiu'w hat below the niicl-vcntricular i^ortion of the sttin the
substantia gelatinosa shows the attenuation which is characteristic ol this
nucleus and which here had been termed the "waist" ot tlie nucleus.
Passing ccphalad, however, it rapidly- expands again and appears as a [prom-
inent feature.' in the cross section ol the pontile region. Its mesial surlace is in
close contact w ith the reticular lormation ol the m\ eleneephalon and meten-
ccphalon, which is hollowed out to receive this trigeminal nucleus. As the
point of transition between the metencephalon and the mesencephalon is
approached the nucleus gradually begins to disappear and it linallx merges
insensibly into the reticular formation of the Lipper metencephalon.

The Inferior Olivary Nucleus

This ULielear mass of gray matter has attained relatively large propor-
tions in the oblongatal sections. It is both extensive in size and complicated
in structure. Its fundus and the two branches which compose it are made up
of a complex series of plications and reduplications which thus greatly
increase the cell-bearing area ol the niuleus. The lundus is deep and directed
toward the ventrolateral angles of the oblongata. It reaches almost to the
periphery and produces a well-marked promiiunee on the surlace ol the
oblongata, the oli\ar\- eminence. It bi'gins below at a point corresponding to
the caudal end of the nucleus of Burdaeh and extends upward through the
metencephalon to a level corresponding with the maximum dexelopmcnt of
the vestibular com]jle\.

Ihe ventral accessory olivary nucleus is ijresent as a well-developed
lamina of gra\' matter arising at almost the lowest \v\v\ ol tlu' duel nucleus
as a small collection of nueUar material in front ol the ventral branch of
the main nucleus. It continues upward closely applu'd to this \-ent ral branch,
to the cephalic extremity of thi' nucleus, where it graduall\ disapi)ears by
becoming conlUu'iit with the dorsal extension ol the \entral branch.

RECONSTRUCTION 01- TROGl OD^ TES NKIER 613

The dorsal acccssorN nucleus presents a somewhat sjniihir arrangement
consisting of a thin lamina olVraN matter ajjpliecl to the surface of the dorsal
branch ol the main nucleus. It extends upward for about the same distance

FIG. l-^. DORS.AL SUKIACE OF GH.W MATTER OF BRAIN STE.M,
TROGLODYTES NIGER.

Key TO Diagram, dorsal cochlear, Dorsal Cochlear Nucleus; inf. coll.. Inferior Colliculus; lat. genicu-
i.AT. BODY, L;iteral Geniculate Body; mlso-gkmcui.ate body. Mesial Geniculate Body; nucl. of durdach.
Nucleus of Burdacli; Nuc. of deitfrs and nucl. of deiters. Nucleus of Deilers; nlcl. of coll. Nucleus of
Goll; ret. ior\l. Reticular Formation; subst. cel. Rolando, Substantia Gclatinosa of Rolando; vent.
cocn.. Ventral Cochlear Nucleus.

as the main nucleus and eephalicall\- comes to an end by becomin_t: conlTuent
with the dorsal Ijranch of the nucK'us. The dorsal surface i)f tlu' main nucleus
as well as the dorsal accessory nucleus arc embedded in tlu' ventral aspect
of the reticular formation and are therefore hidden from view m the reconstruc-
tion. The \'entromesial surface of the nucleus is in contact with the ])yramid,
the hllet and other tracts of the ventral Held of the oblongata.

6i4 THE HIGHER ANTHROPOIDS

The Reticular Formation

The rt'tu'iilar lorination aj^j^cars at a It've-I corrcspondinp; to the hcpiiining
of the pyramidal decussation as an aeeuiiiulatiun ol white and <2;i"a\' matter
lateral to the remnants of the ventral gray column. It lies in the meshes
iaetween the decussating pyramidal fiix-rs. As the pyramidal tracts gradually
fuse in tlu' median line, this formation assumes greater prominence. The
ventral gray columns, as they ascend, are increasingly broken up by the
bundles ol the pyramidal tract and therefore acquire an arrangement charac-
teristic ol the ri'ticular formation, withm w Inch latter they linally disaj)pear.
The reticular lormation becomes more massi\e in the metencephalon in w Inch
segments are lound those \arious condensations lorming important neuraxial
nuclear masses. In outline the reticular lormation is more or less rectangular,
presenting lateral, mesial, ventral and dorsal i)ordcrs. The lateral border
is covered oiil\ b\ white libers and extends almost to the periphery of the
cord, l\ ing l)etween the inferior olixarx nucleus and the substantia gelatinosa
trigcmini. its \cntral aspect is extensive and receives the dorsal surface of
the inferior olivary complex. Its mesial border is located near the raphe
between the dorsal extremities of the mlcrior oli\ary nucleus and the ventral
gray matter, while its dorsal extent is apj^lied to the ventral surface ol the
central gray matter as this structure spreads out to form the lloor ol the lourth
ventricle. This disposition is continued upward, the reticular lormation
forming tlu' mam mass ol the tegmentum ol the brain stt'in. It contains
various fiber tracts and forms the matrix lor tlu' development ol sexeral
nuclear collections. It provides the general support for the entire tegmental
structure. The two mesial surfaces are |)laced opposite one another, each
being separated from its fellow b\ the longitudinal bundles which make u]j
the raphe.

With the de\'elo|:)mciit of the pontiK' nuck'i the ventral surface of the
reticular formation conu's into relationship with these structures.

RECOXSTRl CTIO\ 01- TROGIOD^TES NIGER

(ns

The vi'iitral surlact' ol ihr reticular lorniation enters Into intimate rela-
tionsliip w ith the dorsal extremity ot the lateral and mesial buttresses wliieli
lorm the mam mass ol tlu' pontile nuclei. Between these two areas of con-

I-IG. 274. LATERAL SURFACE OF GRAY MATTER OF BRAIN STEM,
TROGLOD^ TES NIGER.
Key to Diagram, dorsal cochl., Dorsal (^ochk'ar Nucleus; IM-. coll., Inferior Colliculus; inf. olive,
Inferior Olive; lat. gi-.n'. body, Lateral Geniculate Body; meso-gen. body. Mesial Geniculate Body; nucl. of
bukdach. Nucleus of Burdaclt; n. or D. and nucl. of deiters. Nucleus of Deiters; nccl. of goi.l, Nucleus o(
Goll; RET. FORM., Reticular Formation; subs. <;fi . rol. and subst.gel. kolando. Substantia Gelatinosa oi
Rolando; sibsi. nigra, Subst.intia Nigra; sir. coll., Superior (Colliculus; viniral cochlear, \'entr.il
Cochlear Nucleus.

tact tlie dorsal surface of the cK'cp layer of the pontile nucleus does not fuse
with the xx'iitral surface of the reticular lorniation, since m tins area the
trajiczoid bod\ and the other peripheral condensation ol (ihcrs develop.

As the mesencephalon is approached the reticular lorniation replaces
the substantia jiclatinosa tri^H'iuini and the uppt'r jjart of the vestibular
complex as these structures dimmish and linally disappear. In this region
the formation extends backward until it comes into contact witii the central
gray matter. Its lateral |)ortion is tunnelled Irom Ix'hmd lorward and from
without inward by tlu' superior cerebellar |3eduncle as this mass oi libers

6i6 THE HIGHER ANTHROPOIDS

passes deeper into the tegmentum. At the point w here the superior cerebellar
pedunele leaves the superior medullary vehim and approaches the tegmen-
tum a tliin extension of the reticular formation forms on its lateral aspect.
This thin la\er passes further dorsad until the superior cerebellar peduncle
is completely surrounded by mesencephalic reticular formation. From this
point the peduncle sinks deeply into the tegmentum of the pons, tunnelling
the reticular foiniation of the upper part of the metencephalon and the lower
levels of the mesencephalon until it reaches the midline where it decussates.
A termination lor most of its hbers is provided in the nucleus ridjcr.

Just above the termination of the substantia gelatinosa tngemini
the lateral extension of the reticular formation is grooved by the passage of
the lateral lillet. This prolongation of the reticular formation gradually
envelops the lateral lillet as the latter sinks into the tegmentum to vnd in
connectioTi with the niienor colhculus.

The format lo reticularis comes into such close contact with the surface
of the mesencejihalon that its lateral conformation is almost ich-ntical with
the surface of this segment of the neuraxis. It is separated from the lateral
angle of the inferior collicuUis b\ a space in which develops the group of
fibers lorming the inU'iior brachium.

Abo\e this [ioint tlu' reticular formation si'cms to diminish in volume
and becomes conlluent with the indilferent gra\ matter ol the e|)ithalamic
and hypencephalie loiniations. I.aterall\ it merges with the reticular forma-
tion of tlu' dlencephalon.

Between the superior and interior colliculi the reticular formation
gains the surlaci' of the mesencephalon m the mtercollieular furrow. Cephali-
callyit forms the latt-ral and \entral supj^orl tortlu' deep surface of the superior
colllculus. It does not tome into contact with the sujjerlieial layers ol the
colliculus due to the development of the superior brachium which passes
from the lateral aspect of the superior colliculus to the lateral geniculate body.

RECONSTRUCTION OF TROGLODYTES NIGER 617

in the upper If\els ol the iiU'scnccphaloii the reticular formation is to a
great extent rephieed m its \entral portion l)\ the nucleus ruber. Dorsal to
the nucli'us ruber, ho\ve\er, a portion ol the lorniatioii remains and continues
upward to merge with the reticular lormation ol the dieiicephalcMi.

The PoNiiLE Nuclei

The ])ontik' nuclei j^resent an exceedingly c()mj)licaled appearance. They
begin below as thearcilorm nuclei which first appear at about the mid-olivary
level. The arcilorm nu(.k'i lorm a relati\el\ simple la\er of gray matter sur-
rounding the p\ramid. This jjyramidal iiuestment creeps further laterad
until the nuclear material extends completel\' around the pyramidal tract.
The amount ol nuclear material increases, i^rcsenting an extreme com|)lexity
in its deveiopmeiit. It still maintains, howexer, the primitive arrangenu'iit of
a \entral or superhcial layer and a deep or dorsal layer. These two are con-
nected at their extremities by means ol the two buttresses at the mesial and
lateral aspects ol the nuck'ar lormation.

The supcrlicial la\fr corri'sponds closel\ with the surlace ol the pons,
expanding into the lateral buttri'ss and coming into close contact with the
ventrolateral angle of the reticular lormation. Tlu' mesial buttress is an
extensive mass ol gray mattt-r lying in contact with its tellow of the opposite
side and lusing dorsall\ w ith the deep la\i'r ol the pontile nuclei. The union
ol the two nuclear massi's across tlu' mKllme is so extensive as to lorin a
shield-like structure, o\crlapped on either sick- by the ventral prolongation
of the superficial layers ol the pontile nuclei. The internal, lace-like arrange-
ment ol the nuclei is prominent in the chimpan/.ct'. MassiNc strands of
nuclear mattrial ])ass trans\ frsely between tlu' two buttresses and j^resent
branch-like forms which pass to the lateral and mesial buttresses. These
strands of gray matter serve to break up the pallio-spinal and pallio-pontile
tracts into a great number of smaller bundles. The pontile nuclei are continued

6i8 THE HIGHER ANTHROPOIDS

upward into the isthmus mescncephali and hc^in to disappear in their most
lateral and dorsal region. Their disappcaranee from this region results in the
coalescenee of the constituent parts ot the oeeipito-parieto-temporo-j^ontile
fibers. The superlieial layer gradually cHminishes. The mesial buttress then
continues Lipward alone for a short distance, (inall> merging with the indif-
ferent mterpeduncular gray matter. The deep layer ot the pontile nucleus
extends cephalad and at length merges with the substantia nigra. The deep
layer ot the jjontile nuclei is in contact with the ventral surface ot the reticu-
lar tormation niesially and laterally. In the mid-pontile region a separation is
brought about by the development ot tlie trapezoid body.

Large spaces appear on the lateral surface of the superiicial layer ot the
pontile nucknis, from which emerge the bundles of the pontocerebellar fibers.
This breaks up the lateral surface of the pontile nuclei into an irregular
appearing surlace, quite unlike the relativelx smooth surface presented by the
superiicial layer in the lower primates in which the pallial connections with
the cerebellum are relatively meager.

The Vestibl lar Complex

This nuclear mass makes its appearance in the caudal ventricular j)or-
tion of the nu'dulla where it lirst assumes recogni/.able proportions as a small

triangular mass. It is situated betwct-n the ll ■ ot the tourth ^'entriclc and

the dorsomesial aspect of the nucleus of Cioll. in this region the vestibular
complex is represented lj\ the nucleus of Deitcrs. Increasing steadily in
lateral and xcntrodorsal extent this nucleus progressively separates the
nucleus of Goll from the latt'ral wall of the touith ventricle. Above the upper
limit of the nucleus of (ioli tlie lateral suifaee of Di'itt'rs' nucleus comes into
relationship with the upper portion of the nuck'us ol Burdach. Laterall\ the
nucleus of Deiters has a definite xxMilral piolongal ion, triangular in shape,
which extends lorward and lies in contact mesialU with the lateral surtace of

RECONSTRUCTION OF TROGLODVTFS NIGER 619

the descending tract ol tlu' tri<;x'ininal nci\ i-. In rccnnstriictinii tlic substantia
gelatinosa trigcmini is in close relation with, l)Ut separated troin, the nucleus
of Dciters l)y a cicit in which is lodgt'cl the ck-scending root ol tlie trigeminal
nerve.

In the niid-\entricular region Deiters' nucleus gradually begins to
diminish in size and is replaced b\ the triangular nucleus ol Schwalbe situated
somewhat dorsal and slightly mesial to the Deitersal nucleus. This nucleus
continues upward to the mid-])ontile level where it gradually dimimshes in
size and then disappears. The triangular nucleus is covered b\ the dorsal
cochlear nucleus w Inch lies iinnu'diately subjacent to tlie subej)end\ inal gray
matter forming the lloor of the fourth wntricle.

Above the opening ol the lati-ral recess the nucleus of Bechterew
appears in the extreme dorsolateral angle of the tegmentum extending into
the lateral wall of the ventricular ca\ity. The entire vestibular com])K'x
extends cephalically as far as the upper limit of tlu' sul)staiUia gelatinosa
trigemini. Its ventral prolongation passes deepl\' into the tegnn'iituin ol the
metencephaion, approaching closely to the trans\erse plane ot the neuraxis.

The Cochlear Complex

The cochlear complex consists of the ventral and the dorsal nuclei
which are connected by strands of nuclear material. The ventral cochlear
nucleus is relatl\ely massi\e but not augmented in proportion to the abso-
lute increase in the amount of nuclear mali'rial ot the brain stem. By com-
parison the relati\e mass of gray matter would seem to be less than that
found in some of the lower forms such as the Macacus rhesus and the Cyno-
ccphalus babuin. The central tochkar nucleus is arranged in the usual fashion,
more or less trough-like in shape, enveloping the entering cochlear root on
its caudal, lateral and cephalic surfaces. The dorsal nucleus is relativelx
extensive and lies directly in contact with the subependymal gray matter

620 THE HIGHER ANTHROPOIDS

ill the lloor of the fourth xcntriclc. It is travcrst'd Ijv a nuinlxr of the (ibcrs of
thesecoiichuN cochlear tracts w hich ha\ e ah-cacl\- received rehi\ in the ventral
cochlear nucleus and are passing across the lloor ol the toLirth \entricle.

The Colliculi

These masses of gray matter in the tectum ot the mesencephalon repre-
sent a relatively massive accumulation ol nuclear material. The inlerior
colliculus appears as a specialization in the dorsal extension ol the meseii-
ce])halie reticular lormation which supports the colliculi at their lateral
extremities. Dorsally the mierior and superior colliculi are continuous with
the indiilerent gray matter lying in the midline. Each colliculus is connected
across the midline by the decussating libers respectively of the interior and
superior collicular commissures. These decussating hirers support the dorsal
gray matter and j^roduce a defmite elelt between this element and the dorsal
surface of the central gray matter.

Caudallx and laterall\ the t'litrance ol the lateral lillet into the area
immediati'ly sub|aeeiit to tlu' mienor colliculus is elearl\ show n in the recon-
struction. Tlu' inferior colliculus is separated from the superior colliculus by
the intercollicular sulcus which is occupied by a dorsal extension oi the
mesencephalic n-ticular formation and a similar extension serves to se]:)arate
the superior colliculus from the dieiicephalon.

The SlBSTANTIA Nir.i^A

The substantia nigra appears in its usual situation, dexeloping Irom the
dorsal layer of the pontile nucleus Irom which it seems to be (k'rnetl. It is
supported b\ the dorsal la\ cr and, to a U'ss I'xtent than is the case in tlu' lower
forms, by the lateral and mesial buttresses. It is marked \fiitrall\ by the
longitudinal libers of the pallio-s|)inal and pallio-|)ont ilc systems. It merges
mcsially with tlu' interpeduncular gra> matti'r, pierced at this point 1)\ the

RECONSTRUCTION OF TROGLODYTES NIGER 621

I'liuT^mij; IiIhts oI the (Kuliim((t<ir iui\ t'. Latcrallx it pri'Sfiits the nuclear
spc'ciali/at ion w hieli has hccn h)uiKl rc'<j;uhirl\ to {nkv plncv 111 this jxirt ol the
substantia ni^ra in the lower |Miinati' lornis. Laterall\ it eonies into close
relation with tlu' mesial ii;eni(.ailate hocl\, but dot's not make actual contact
with this nuclear mass. Dorsall\ it is separated Irom the reticular formation
by the circumlereiitial libers ol this lormation.

The Nucleus Ruber

The nucleus riibcr is a large nuck'ar mass wliich is lirst encountered at a
point near the mid-nicsence[)halic le\ c'l. Here it appears as a rounded encap-
sulated stiLicture amidst the dccussatinii; libers ol tlu' superior ci'rebcllar
l^edunck'. It rapidix mcri'ases in size, occup\ ing almost the t-ntire mesial
hall of the mesencephalic rc'ticular formation and extending ujjward into
the diencephalon.

The Central Gray Matter

The central gra\ matter in the high cer\ ical le\ tis appears identical in
form with the ci'iitral gra\- matter of the human adult. It is disposed as a
quadrilateral mass surrounding tlu' central canal ol tlu' spinal cord.

As the oblongatal nuclei (k\t'lop and the mlerior e\tremit\ ol tlu' lloor
of tlu' fourth \'entricle is approached tlu' central gra\ matter passes in a dorsal
direction, sending backward a thin lamina toward the dorsal |K'ri|)her\- of
the neuraxis. As this dorsal migrat ion takes place the qua<lrilateral lorm ol the
central gia\ matter undergoes a change. It becomes llattened out and then, as
the fourth \entricle opens, the cut ire extent beconu's disposed in a single layer
extending from side to side. .A thin la\t-r ofgra.\- matter ri'iiiains in the lateral
wall and the roof of the fourth \(.-ntrick' as the sulx'pendx nial gra\ matter.

In the lower part of the fourth \entrick' the [prominence ol the hxpo-
glossal nucleus is easil\ identilud close to the midline. Somewhat abo\e and

622 THE HIGHER ANTHROPOIDS

lateral to this is a triangular depression which corresponds to the underlying
dorsal nucleus of the vagus.

The \entricle as it opens becomes more cxtensi\e from side to side.
In the mid- ventricular portion the markings become more evident, showing
the outline of such underlying nuclear masses as the vestibular and cochlear
complexes. Abo\'c the mid-point of the ventricle as it begins to narrow to\\'ard
theaqueduct of Sylvius a marked median eminence appears on both sides of the
midline, representing the eminentia abducentis and the subventricular course
of the seventh cranial nerve.

Above the lateral recess, the walls of the ventricle rapidly approach each
other and the formation of the acjueduct of Sylvius results m the develop-
ment of a massive central gra}- matter encircling the ventricular cavity.
In the isthmus the nucleus of the fourth cranial nerve appears m this ventral
prolongation of the central gray matter. \\ ith but little distinction between
the nucleus trochlears and the nucleus oculomotorius above it, the latter
nucleus occupies this same ventral prolongation. As the diencephalon is
approached this prolongation becomes more extensive until it is continuous
with the interpeduncular gray matter, thus forming a complete griseal
lamina between the midline and the mesial surface of the red nucleus.

The central gray matter continues upward to the junction of the
mesencephalon and the diencephalon, where it becomes continuous with the
subependymal gray matter of the third ventricle. It merges with the ill-
defined mesial group of the diencephalic nuclei, the epithalamic structures
and the hypencephalic region.

Chapter WI
TROGLODYTES GORILLA, ITS BRAIN AND BEHAVIOR

Its Position, amonti the Primates; Afeasuremenls and Brain Indices; Surface
Anatomy of the Brain; Inter^ial Structure of the Brain Stem in Cross Section

Appearance of the Gorilla

"^HE gorilla, in point of size, when standing upright, is nearly as tall
as the average man. Its recorded measurements give it a height of
live feet two inches to over six feet. Its body is stout and large, its
legs short and its arms long. The tips of its lingers reach to about the middle
of the leg below the knee. Its huge grisly head, Hat, broad nose, prominent
muzzle, large mouth, very large canines, and protruding ears which are
uncovered bj- hair, all contribute to gi\e the animal a terrifying appearance
upon which is based much of its generally accepted reputation for ferocity.
In some instances the full-grown adult attains the great weight of between
three hundred and four hundred pounds. This fact, added to its awe-inspiring
locomotion when it rises upon its hindlegs and stretches forth its tremendous
arms, has made the gorilla known as the most savage of all beasts, and at the
same time one of the most dangerous of all the enemies ol man.

The hands are large and wrinkled, thickl\ covered w ith hair on the back,
but the palmar surfaces are without hair and present cutaneous rugae, no
doubt in the interest of amplifying the areas for sensory receptors. The
thumb is somewhat short for the size of the hand but is thick and bears a
broad nail. The great toe is opposable, large and Hat, and the proximal phal-
anges of the second, third and fourth toes are united by a wob.

The animal's body, as well as the head uj) to the brow-line, is covered

w ith shaggy hair. The skull is massive and the eyes surmounted by protrud-

623

624

THE HIGHER ANTHROPOIDS

ing supra-()rl)ital ridges. A hca\-v sagittal cii'st ot Ijoiic extends Irom tlie
frontal to the oeeipital region, giving attaehnient to an exeeptionally large
temporal nuisele whose presence, together with a sliort, thick neck, imparts

(j>utU\\, AnnTUtm Museum of Natural HisloTV

FIG. 2-5. GORILLA GROUP, FROM THE AMERICAN MUSEUM OF N.-\TURAL
HISTORY. THESE SPECIMENS WERE OBTAINED AND PREPARED RV THE LATE
MR. CARL AKELEV IN HIS LAST GORILLA HUNT.

TROGLODYTES GORILLA

625

so tmicli of the ajipcarancf to the animal upon which its reputation lor pug-
nacity depends. It IS true tliat the hea\ v head, short thick neck and tremeii-
ch)us arms create the imprt'ssion ol a |)eeiiharl\ t-lheient h<j;htm'i; machine,

.nn,;.,i, WTi,M<r,.( Wi;.M.,n ...I •. .,< u : •:! 1 1 i.-Kity

FIG. 2~6. LAKGE MALE GORILLA KILLED IN THE AEKICAN CONGO.

which, howfNcr, has one great inherent weakness in thi- iinperU'ct de\c'lop-
ment ol the legs and feet. Tlu' animal is ahle to assume the u|)right position
and walks thus in an aw kward maiiiu'r, using the great arms to aid in balanc-
ing. In the main, howfxer, it goes upon all lours, partieularl\ when desirous
ol making speed through the underhrush or climbing among the trei's. It
rises upon its hindlegs iargelx for pur|)oses ol inspection, in order to make a
sur\ev ol the surrounding territory through which it may be traveling.
\\ hether it assumes the erect posture when charging to an attack, or sim])ly
stands upright in combat in order to permit tlu' freer ust' of its great
l^owcr in the u|)|)er extremity, is a c|uestion which has not \ ft been dccicK'd.

626 THE HIGHER ANTHROPOIDS

Habits oi the Gorilla

Some six or sc'\en species and subspecies ol gorilla ha\e l)een idenlilied;
although much is still to be desired in the matter ot exact classifrcatiun.
The animal here described is Gorilla gorilla, also known as Troglodytes
gorilla. Its hal:iitat is in the Gaboon of West Africa. This gorilla is also know n
to inhabit regions m the southern and northern Camaroon ol West Airiea,
near the border of the French Congo. It also has been discovered m localities
about the Belgian Congo.

Ancient rumor spread abroad the report that there lived in Africa a huge
ape of most ferocious and savage disposition. Around this rumor fabulous
stories concerning the great strength ol this monster as well as its predatory,
man-like behavior were soon built up. Indeed, gorillas were first spoken
of as w ild, hair\ men. It was Hanno who appears to have been the lirst to
encounter them during his famous voyage to the Pillars of Hercules. Coming
upon a grou]) of these wild people he was able to capture three ol the women
but all of till' men managed to make their escape. The females, however,
fought so sa\agel\- that it was necessary to kill them. Their skins were
preserved and brought to Carthage where they were placed in the temple
of Juno and were still there when that city was destroyed. The noted
ex])lorer, Paul Du Chaillu, in his "Adventiirt's in Equatorial Alrica,"
describes the gorilla as gregarious, going m companies ol eight to ten.
Sometimes when the older males becM)me superannuated, they li\e solitar\-
lives apart from these small communities, and when thus grown old, aj:)pear
to be actually grizzled w ith age, their hair becoming almost w hite.

DU CHAILLU'S DESCRIPTION OE THE GORILLa's HABITS

Du (Chaillu probablx was the lirst European to kill a gorilla in its iiati\-e
forest. His dt'seript ion ol their habits is no doubt more accurate than it was
at lirst belicNC'd to be. It was his opinion that the gorilla tlid not, as olten

l-'rom "A Hevtfw oj tbt; I'rimates," Bv D. ('>. t- tltnt.

FIG. 2~. GORILLA GORILLA.

[62-1

dauTlesy, American Museum of .\'ulural llislory

FIG. 2-8. BRONZE STATUE BY FREMIER.

Based on the legendary ;iccuinu ol the {gorilla's attaeks upon man in vvliieli he is said to have captured native
women and carried them off into the forest. This legend was subsequently proved by Paul l)u ("hallhj and
other explorers to be wholly vmfounded. It is sueii a misrepresentation ol'llie known I'aets that the American
Museum of Natural History will not permit the exhibition of tl

[628J

his bron/i

FIG. 2-(). JOHN DANIEL IN AN AMIABLE A ITITUDE, ENTIRELY CONTROVERT-
ING THE gorilla's REPUTATION I-OK FEROCITY.

[629I

630 THE HIGHER ANTHROPOIDS

claimc'cl, lurk in trees by the roadside to drag up witli its great arms the
unsuspecting passer-by, later to choke him to death. He discredited the
statement that these animals attack the elephant and beat him to death with
sticks, or that they carried oil \\ omen ol the natixe villages to de\'our them m
the depths of the forest. He did not even belle\e that the gorilla built itself a
house of leaves and twigs among the trees, and denied that it ever became
gregarious to the extent attributed to it in many stories. It did not settle in
large communities nor did it assemble in great numbers to make concerted
attacks upon men who established their habitations near the confines of its
forest home. Du Chaillu observed that the animal inhal:)ited the loneliest
]:)()rtions of the dense African jungles and seemed to prefer deep, wooded
valleys and rugged heights. The high plains covered \)\ large boulders were
also its favorite haunts. In general, a plentilul supply ol water is lound m
such territories.

The animal appears to have a roaming tendency which may be induced
by the necessity of obtammg food. It is rarely found in the same place two
days in succession. It wanders from region to region over long ranges in search
of such food as pineapple leaves, berries and other vegetable matter of which
the animal is a large eater. W ild sugar cane has been mentioned among the
things upon which it subsists, as well as nuts whose hard shells are cracked I)y
the powerlul ]aws. The animal slet'j^s sitting upon the ground N\ith its back
against the trunk of the tree, and when full-grown seldom ascends high
among the branches. The young slix'p in the trees and possibly the lemales
may occasionally do so. In spite of tlu'ir reputation for ferocity, the gorillas
are in reality shy, and the female especiallx will run to shelter at the lirst
sound of alarm, carrying her young w ith her il she has one. The male is not so
precipitate in his flight. I le rises upon his hmdU'gs for a moment, show ing his
savage visage in the underbrush. Tlu'ii, glaring at the intruder, he begins to
beat his breast with his closed lists at the same time lifting up his head and

TROCIOD^TFS COR II LA 651

utUTiiifj; an awc-mspirm^^ roar. This sound begins at lirst witii scscral loud
barks hkc those ot a do^j;, and then c'han<iL's to a gLittural roar which is
repeated with redoubled jjowit eausinfi; echoes in the forest which re\er-
berate like distant thunder. Du Chaillu sa\s that tlu' horror of the animal's
appearance at this time is beyond description. It seems as a monster in a
nightmare and so impossii^lc a jjiece ot hideoiisiu'ss that were it not h)r the
danger ot its sa\'age approach the hunti'r might imagine himselt in an ugly
dream.

akeley's experiences with the gorill.\

The gorilla's gait is more of a waddle trom side to side, its hind legs being
short and thus inadequate to support its huge body properl\ . While swinging
his arms to balance himsell, his great trunk mo\es backward and h)rward,
adding to the gruesome horror of his appearance. W hen approaching to the
attack, the features are distorted by hideous \\rinkles, the sharp lips draw n
back to reveal long fangs in a powerful jaw In which a human limb could
easily be crushed. It is not ditiicult to shoot a gorilla. howe\er, and thus
render its savage attack all too easy of restraint. In fact, Akeley, the noted
African explorer, said in ri'terenee to hunting the gorilla that tln're is no
greater ditticulty in shooting this sort ol game than tlu'ri' would be in killing
a defenseless, crippled woman. I-ar trom biing s])ort, it is most distastelul,
indeed an atrocity closel\ akm to murder. It was due to Akeley's good oflices
and etlorts that the king of Belgium set aside a large terrilor\ in the Congo as
a Gorilla Sanctuarx m which all hunting of this animal is prohibited. Here,
Akeley hoped, a biological station might be ultimately established for further
study of the gorilla's beha\ior. lie believed it would be possible to gain
a tooting on close and mtimati' tt'rins with this great anthroijoid which, in
spite of its vaunted reputation for ferocity is, in his opinion, so timid that
It w ill require years of careful cultivation to establish the necessary feeling

632 THE HIGHER ANTHROPOIDS

of tric'n(ll> ix'lations. Akclcy's rt'co^iiitioii ol the i^'onlla as a timid and rt'tiring
anthropoid, with none ol the atrofions characteristics h)r which hi' has so
long been hinied, is ground tor the expectation that in time this fast disap-
pearing ollshoot ol the prehuman stock may lurnish its lull quota oi testi-
mony coiKX'rnmg the e\olutionary j^rocess in its relations to the deri\ation of
man.

JOHN DANIEL 1

In adult life the animal is quite untamable, although if caj^tured young,
as much ma\' be done with it as with any ol the other primates in captivity.
The following account of a gorilla's lite in ci\"ilizati()n, as given by Miss
Alyse Cunningham, ot London, testities to this tact. This record is based on
observations made by Miss Cunningham ot the young gorilla called ".lohn
Daniel." At tirst she had no fancy for this animal. She in fact was allecttxl by
rather a dislike lor an\thmg m the shape ot a monkey or ape. But slie soon
became interested in the Noung gorilla and took his education seriously in
hand. Tlie animal was presented to her by her nephew, Maior Penny, who
was much interested in ])rimates, and bought the gorilla w ith the idea of seeing
how miK'h iiuntalitN could be developed in this highest ot the anthropoids.
John Daniel was captured when \ery xoung, in the French Gaboon country,
and came to England w hen he \vas about three years ol age. At this time he
was sullering from a rachitic condition and had also contracted a severe
inllueiiza through which Miss Cunningham nursed him and so succcsstullx
cared lor him during the next thri'c \ cvirs that he ri-ached the w t'ight ol 112
pounds and tlu' luight of 3 feet 4' _. inclu-s. Meanwhile he acquired much of
the ada]:)tation necessar\ to lit him as an interesting, it rather unusual mem-
ber of the hous<,-hold. To Miss Cunningham wx' are iiuk'btt'd tor excellent
observations which indicate the extent to wliK'h this anthropoid max be
trained and educated. Her imprt'ssions ha\e gixen a new idea as to the dis-
position and teachability of the gorilla.

TROGLODYTES GORILLA

633

Tlu' \()iin,u liorilla inuiu(liatt'l\' showed marked (.'inotiDnal reactions
whii'h caused some ditlicult roiiiplications in the liouseliold. If lie were left
In hiinst'lfat ni!j;ht he would shriek Irom lear and lonehness. Miss Cunning-

Courlcsy, AmcTiiun Museum oj Natural Hislnry

fk;. 2(So. six-year-old gorilla, john damll.

IScc Tf\t p. 632]

ham tht-relorc- treated him as she would a eiiild, and had her nephew ]>laec
his bed e\-er\ ni^lit in the room adioinin<j; the cage of tlie gorilla. As a result,
John I)ecanu' c|uitt' haj)p\ , at once l)e<i;an to grow and put on weight. He was
next taught to he clean in his habits, and by a series of rewards and punish-
ments at the end of six wt'eks was thoroughl\- house-broken. He was then
taken out of his cage and allowid the freedom of the house. Thereafter, he
ran upstairs to the bathroom of his ow n accord, turning the knob of the door

634

THE HIGHER ANTHROPOIDS

of whatc'viM" room he was in, and also oj^rning the door ot the batlirooni. He
showed great fastidiousness in the matter ot chet, although he mueh preferred
stealing his food to ha\ing it given to hnn. lie a[:)peared to tliink himsi'lf

( 'I. '- u -Amiruun A/uvtum of WititTul History

FIG. 281. PLASTER CAST OF AN OLD .NLALE GORILLA TAKEN IN LHE LAST
GORILLA HUNT OF MR. CARL AKELEV.

more cleAer in sueli transactions and was averse to considering himself the
recipient of faxors from others. He showed a strange disposition to axoid all
food whieli had been exposed to the air lor long. He was particularly tond ol
oranges and appk's, hut would not vii\ thest' (tr an\ otiu'r Iruit il tlu'\ liad

TROGI.OD^TF.S GORILLA 635

bc'cn cut a few hours. Hi' had what ahiiost amouiiU'd to a passion lor eating
roses. The more heautilul they were the more he liketl thi-m, although he
never would eat faded msi's. I L- likt-d nibbling at tw igs and also eating green
buds m the sjjrmg. The animal ne\er eared mueh lor nuts ol an\ kind exeept
walnuts. Ills actions with a cocoanut were ratlu'r amusmg. Me knew that it
had to be broken and would trv to break it b\ throwing it upon the lloor.
Lading in this, lu' \\ould bring it to one of llu' memlx'rs ol the lamily and try
to make his desire understood. II gi\fn a hamnu'r he would tr\ to use it on
the nut; and then, being unable to accomplish hi:; puiposi', would present the
hammer and the t'ocoamit to someone to hel]j him out. lie xery wfll under-
stood the use ol hammers and chisels, but was ne\"er I'licouragt'd to attempt
anxthing in the line ol carpentry out ol general respect lor the household
lurmture.

John Danu'l was particularix fond of haxing i)eoi)le come to Aisit him
at his honu'. W hein'\i'r there were \isitors he would show oil liki' a child. It
was his custom to take the visitor b\ the hand and lead hmi round and round
the room. II he saw that a person was at all ner\ous, he en|o\i-d running past
him and gning him a smack on the leg, alter which he would grin at the
visitor's displeasure. His table manners were ratht'r e\ee[)tionall\ good. He
always sat at tlu' table, and w hem'\er the meal was read\ would pull up his
own chair to his place. He did not care to vii{ gri'at c|uantities, but hv t'Si)e-
cially liked to drmk water Irom a tumbler. He always took altt'rnoon tea ol
w Inch he was \ cr\ lond, and then would cat a thin slice ol bread w ith plenty of
m. \\v alwa\s liked collie alter dinner. Inueiieral he was the least greed vol all

t^'

la

animals that had come under the obser\ation ol his owners. He would never
snatch an\ thing and alwa\s ate slowl\. He was accustonied to drink large
Cjuantitii's ol wati'r whii'h he would gi't himsell w hiaiex er hi' wanted it, b\'
turning on a tap. Strange to sa\', he always turned oil the water when he had
finished drinking.

636

THE HIGHER ANTHROPOIDS

John Daniel smiu-d to think thai cxcTNonc was delighted to sec him, and
for this reason he would stand on thi' w nidow sill and throw up the shadt'. In
a short tinu' a large crowd collected to watch hnn m his position at the w in-

(\niru^\, Vt u >(.r/. /i>(>hi:ual Satiety
FIG. 282. VOING GORILLA, JOHN DANIEL, FROM A MOTION PICTL RE TAKEN tO
SHOW THE CHARACTERISTIC BREAST-BEATING ACT OF THE GORILLA.

dow. When it a[)pi'arcd to him that the crowd was of suHieient numbers, lu'
would often pull the shade dcliberalcl\ down in their faces, and run away
shrieking with laughter, seeming to feel that lie had per[)t'trated a huge |oke
upon the curious audience outside.

He was espeeiall\ attached to Miss Cunningham's little three-year-old
niece who often came with her motlu'r to sta\ in the house. .John Daniel and
she played together l)\ the hour. He seemed to understand just what she
wanted him to do. If she cried for an\ rtvison, when her mother came to pick
her up, the gorilla would always lr\ to n'\p the mother and gi\-e lu'r a slap

TROGLODYTES COR 1 1 LA

637

with tlu' fiili w c'i^lit of his hand, apparently thinking that she was thf cause of
the child's tears. One da\ Miss Cunningham was dressed lor going out and
John Daniel wished to sit on her lap. It chanced that her dress was a light
one and she pushed hini away saying she feared that he might soil her gown.
He at once la\ on the lloor and cried like a baby for a moment; then lu' rose,
looked aroLi nd the room, lound a newspaper, spread it out on .Miss Cunning-
ham's lap antl climbed up upon it. This was quite the cleverest thing that he
had e\'er done, and those' who saw it said that they would not havi' bt-lievcd
it had they not thi'msi'Kcs been present.

The gorilla apparently could stand much cold and he often would go on
the root m treezmg weather. I his he did not seem to mind so long as he could
come into a warm room when he wanted to; then he would go straight to
the lire, rub his chest and sit down with his teet on the fender. Exercise was
essential to keep him m lualth and he got much of this by pla\ ing hide-and-
seek with Ma|or Penn\ in the morning before breaklast and in tlu-e\ening
before diniu'r. Tlu' ma|or would run up and down the stairs, in and out ol all
the rooms. The game appeared to delight the gorilla who would giggle and
laugh while being chased, lie was \'cr\ cautious, howexer, ne\er to enter a
dark room without lirst turning on the light. It was his habit to retire I'ach
night at eight o'clock. I le had his ow n little room ad]oming that ol Miss Cun-
ningham's nephew where he had a spring bed ol his own with blankets.
He would get out ol it at night b\' himself, go back to bed and jjull the blan-
kets up over him cpiite neatl\ . 1 he thing he enjoyed most was to stand on
the to]) rail ol his bed and jum|) on the springs, head o\er heels, just like a
child.

John Daniel was ne\er taught an\ tricks. IIcsinipI\ ace|uircd knowledge
himsclt. He was taken in sumnu'r by tram to the family's cottage in the
country, occu|j\ing his seat in the railway coach as an ordinary passenger
without even a chain around his luck. He seemed to be much afraid ol the

638 THE HIGHER ANTHROPOIDS

fields and the open countrx', hut was ha|)p\ ni ihv ^^ardvn and the woods.
FulI-<irown shi'e|), eows and horses he seemed to fear; but eoits, eaKi's or
lambs atlorded him miieh amusement and hi' was (greatly niterested m thiin.
It seemed to those w ho eared for him that hi' recognized youth and was s\ m-
pathetiealU chaw 11 to it. He became so attached to the lamil\ tliat it K'lt
alone he would make a great noise, shrieking and crymg. This tendency
increased so that alter three years it was necessary to make sonu' other
arrangements for him. Due in large nu'asure to a misunderstanding which his
owners have always regretted, John was sold to a circus, transported across
the Atlantic to New ^Ork, where, after a month's separation from liis friends
and j)rotectors, during which time he relused to take food and showed other
signs of real homesickness, he died in the lower ol the old Madison Scjuarc
Garden, in April, i()2i. The skeleton and laxidermic preparation of this
remarkable gorilla which contributed so much to our knowledge and better
understanding of the great troglodyte anthropoids may be seen among the
gorilla collection of the American Museum of Natural History. Most of the
serial sections introduced in this work, illustrating the l)rain stem ol the
gorilla, were obtained from John Daniil the first.

It ma\ be added as a note to this inst ruct i\ e histor\ of what appears
to be the Inst gorilla raised under the conditions ot such intimate domestic
life, that Miss Cunningham has become so much interested m the species as
to secure another young gorilla which she called John Daniel the Second.
John Daniel the first was a little oxer six years old w hen he died. I he present
specimen of this species possessed b\ Miss (Cunningham is ol about the
same age. In man\ respects, these two great apes correspond in their (.'mo-
tional reactions and their suscept ibilit \ to training. John Daniel the Second
is, perhaps, a less likable indi\ idual and has a disposition more in keeping
with the ancient reputation of the great anthropoids.

A

CouTt€sv. AmiTican Mu.wum of Naiurat History

I-IG. 283. ADLLl MALli (iOKILLA.
I639J

640

THE HIGHER ANTHROPOIDS

In anv c'\HMit, the writt-r had the honor about a year ago ot bcinti; nnitecl
to take aftt'inoon tea w ith John Daniel 11 w ho w as then residing in a line suite
of rooms in a I'ashionable New \'ork hoteh On this occasion the host was

CouTlesy, American Musium o) Natural History

FIGS. 284 AND 287. CASTS OF HAND AND FOOT OF THE COKILLA, JOHN DANIEL.

found seated in a eoinloitable and thoi-oughl\ human lashion Lipon a ehau',
surrounded b\ c|uite a gathering of seientilie authorities, interested bom one
point of \iew or another in xhv beha\ ior oi' anthrnpoicLs. \\ ith nuieh gra\ ity
and apparent enio\nient, he drank from a cup ol ti-a. Presently he indicated
a desire for more of this beverage of which lu' would drink large ciuantities
if permitted to do so. During the course of tlu' usual annMiities ot the occasion,
when, for the moment, the gorilla was not the actual center ol attention,
he suddenlv dashed across \hv room with unl)elii'\ able swiltness and
attacked one of his \isilors with repeated, rapid blows ot both lists, m the
neighborhood of the solar plexus; then, w ith ecjual celerity, he liopped over

TROGLOD^TF.S GORILLA

641

the foot ol tlu' Ih'cI Iroiii wIikIi point of \aiita<i;c' \)v watcln'cl tlic cliscomliture
ol liis ^au'st and ])rc|)arfcl tor lurtluT mischu-l. A moment latiT, w lu-n again
less sliarpl\ watclu-cl, he sudclinl\ luiilecl hinisell' with his full weight,

('ouTtcsy, AmtTtcan Mu:s(.um of Xttturul ifislory

FIGS. 286 AND 28". CASTS OF HAND AND FOOT OF IHE GOKII-LA, JOHN DANIEL.

C|uite in the most aeeepti'cl h)()tl)all st\ k', agamst a chst niguishi-cl Pmlessor of
Zoology who in const'CjiK'nec was thrown Ironi his chaii'. In thi' intcr\als
between these |jresnniecll\ pla\ tnl (h\"ersions, the gorilhi sat c|Liietl\ in his
ehair w ith a real seiiihhinee ol propter cleeorum and apparentl\ cpiite mdil-
lerent to the eonipany. But in s[)itt' ol his innoeeiit demeanor, the very
placidity of his manner ga\x' rise to sus|)ieions that he was easting about lor
the next pieee ol misehiet wlueh lie might perpetrate. There was such a
degree of roughness and such sudden de\elopment of strength in the pla\ ful-
ness of this juNenile gorilla, as to allord some idea ol the terrilie |)ower w Inch
these animals must possess when lull-grown. Belore departing tor London,

64:

THE IllGIIFR ANTHROPOIDS

John Danu'l thr Second inllk'ti'd a serious wound with his teeth upon thi-
hand of one of his attendants.

The prospect of Mr. Akek'v's proposed biological station in Africa for

('tniTlcw, Amcncan Museum oj Natural History

I-IC.S. 288 AND 281;. CASTS Ol- HAND AND FOOT OI- AN ADULT MALE GORILLA.
Left. Palmar surface ol tlic liand showing distinct huiu.'inoid tendencies.

Right. Plantar surface of the foot showing l^roadening of the heel, migration of the great toe and shortening
of the lesser toes in adaptation to scmi-tcrrestrial life.

the Study of the massive anthropoid in Iiis natixx' iungh' is nodoubt inspiiing.
yet if one may hazard an ojjnion horn the somewhat superheial and jjassing
acquaintance with iUv hall-grown animal under most la\orable social

TROGIODVTFS (GORILLA

643

inlliu'iicc, it w ill he a long tunc cvv otiurs tliaii the most iiarclx luiiiian a(l\c'n-
turers seek fVatcrnizing communion with tlu' giant anthropoid c\cn in the
safeguarded regions ol'the gorilhi sanetuary.

Ctntrtcsv. ArtifTH un .\tuscum itf S'alural llisiory

FIGS. 2(>() AND 2C)I. CAS rS OF IHE HAND AND FOOT OF THE GORILLA,

JOHN DANTFL.

Top. Cast of the plantar .surface of the foot of the gorilla, John Daniel, showing marked humanoid tendencies

in the distal migration of the great toe, the bro.idcning of the heel and shortening of the toes.
Bottom. Cast of the dorsum of the hand of the gorilla, John Daniel.

644 THE HIGHER ANTHROPOIDS

Measurements and Indices of the Gorilla

Total length of the skull 230 nun.

Occipito-iiasal length 135 mm.

Intertemporal \\ idth g8 . i mm.

Breadth of the brain ease 92 mm.

The dimensions of the brain are:

Longitudinal 123 mm.

Transverse. ? 8~ mm.

Tile average weight of the l:)rain in the lull-grow ti adult enelosed m the
dura mater and pia mater is 450 gms., without the dma mater, 445 gms.

Hie following weight and water displacement \-alues were obtained
from the measurement ol the adult female gorilla. Number 4, ol tlu' Akeley
African expedition nl 1021.

Volume ol the brain :

Forebram 364 c.c.

Midbrain 5 c.c.

Hindl)rain 60 c.c.

Total water displacement 429 c.c.

W eight ol the brain:

Forebrain 359 g'HS-

Midbrain 5 gms.

Hindbrain 5() . 5 Ji'i^s.

Total weight 4-3 5 g'^s.

On the basis of tlii'se liguri's, enet'|)halie nidices wcmx' cornpuli'cl :

lorebrain index 84 per cent

Midbrain index 2 per cent

Hindbrain index 14 per cent

TROGLOD^TES GORILLA 645

Sl Kl ACE Al'I'EAKANCF. OF THE BrAIN OI GoRII.l.A
FISSL RES AND LOBES

The ap[)caraiK-c of the hraiii in (gorilla elosely rcsemljlcs that in man.
Li si/e, li()\\f\cr, its diiiunsions are a little Ii'ss than one-half of the adult
human male. Its general outline' and hssural ]xittt'rns are conspicuously
humanoid. The deslii;n ol' tlu> hteral surface of the hemisphere is distinctly
quadriloliular, with three w ell-delined fissures separatinjjc four i'quallN- well-
delnucl lohes. The fissure ol S\ l\ ius sej^arates the parietal from the ti'mporal
lohe; the hssureot Rolando, tlu' |)arieta! from tlu' frontal lobe; and thesidcus
simiarum, tlu' occipital from the |)ari(.tal lobi'. The latter fissure may be
traced to the mesial surtace ol the hemispheri' where it occupies a pf)siti()n
identical with that ol tlu' paru'to-occipital fissure in tlu' human brain.
The hssurc ol S\l\iiis has all ol the ajjpearance characteristic of the
corresponding sulcus in man; while tiie Rolandic lissure has an e\en closer
correspondence to its human counler[)art. The entire region com|)risecl
within tlu' Rolandic, S\ Kian and simian sulci is richly coiuoluted and in it
arc all of the landmarks ol the similar temjjoro-parietal area in man. As in
most of the ]:)rimate.>, this region is highly convoluted, since it de\elops
in response to specializations in somesthetic sensibility and the special sense
of hearing. \n the occipital lobt' there is a marked degree of convolution, while
the fissural pattern is in man\ respects laid down as though in strict
accordance w ith a human |)rototype. This is true both ol the mesial and the
lateral occipital surfaces.

More striking are the accessions to con\ olutional pattern and riclmessoi
fissural impression which occur in the frontal lobe. This feature distinguishes
the gorilla's lirain from the lower and intermediate primates, and gives it, at
least to superficial inspection, predominance o\ er the corresponding lobe in
the orang and chimpanzee.

646

THE HIGHER ANTHROPOIDS

THE BASAL SURFACE

Certain features on the basal siirfaee are equall\ important m then" elose
corresponclenee to the human bram. The two eharaeterrstie eoneavities of

FIG. 2()2\. DORSAL SLKFACE Ol BRAIN, GORILLA.
[Actual Lcnglli 1 17 111111. |

this surfaee, l)olh snpra-orbita! and ecrel)ellar, show a ni'irkecl cleerease in
prominence as compared with \hv lowt-r and uilcrnu'chatt' lorms. The

TROGLODYTES GORILLA

647

structure often denominated the interorbital keel of the frontal lobe has lost
nuuh of its jjrominence and approaches more closely the conditions observed
in man. The entire orbital surface of the frontal lobe has in fact so altered its

FIG. 292B. DETAILED DIAGKA.M OF DORSAL SURFACE OF BRAIN, GORILLA.
Key to Diacr.\m. inc. s. cin., Incisura Sulci Cinguli; sllc. occip.. Sulcus Occipitalis; s. fr. sup., Sulcus
Frontalis Superior; sllc. prec. slp.. Sulcus Prcccntralis Superior; sllc. ret. slp.. Sulcus Rctroccntralis
Superior.

external configuration as, for the most part, to present a tendency toward
conve.xitv and is thus nearly devoid of the marked indenture so characteristic

648

THE HIGHER ANTHROPOIDS

of lower species. The decrease in the orbital conca\ity is unquestioiialjly due
to progressive expansion ol the frontal lobe. The hssural pattern ol this
orbital surface of tlu' frontal lobe corresponds closely to that of man, while

FIG. 293A. BASU Ol' BRAIN, (JOKILLA.

lAftiiiil I cn-ith I i- mm.]

the boundary betwt'cn it and tlu' lateral surface of the luniispherc is indi-
cated, as in tlu' human bram, by an anterior extension of the S\ Kian fissure.

TROc;i on^TES gorilla

649

Nothing ol thr human (ktail is lacking in this region ol tlic brain, save that
thr Ic-atiirc's arc all U'ss nnj)rcssi\cly drawn and lia\c a greater sniiplicity
ol outhne.

IIG. 2()3B. DEIAILED niA(;RAM Oh BASE OF BRAIN, GOKILLA.

A marked cliaracttMistic ol the primate bram is the dctachability of the
olfactory bulb and tract up to the trigonum ollactoiium, m c()nsec|uence of

650 THE HIGHER ANTHROPOIDS

which these structures appear attenuated as compared with those of ungu-
lates and carnivores. By retracting the olfactory bulb and tract, the gyrus
rectus is brousht to view as well as the medial olfactorv fissure.

FIG. 294A. LEFT HEMISPHERE OF BRAIN. GORILLA.

[Actual Length 123 mm/

A second important character of the basal surface is the relation of the
optic nerves and tracts to the chiasm. Their angulation, as is the casethrough-
out the primate series, approaches the obtuse, the two optic nerves entering
the chiasm at a little less than right angles, while the same angular relation
obtains in the optic tracts. This condition is determined by the shortening
of the nasal cavity and the protrusion forvvard of the frontal lobe into a
position overlying the orbits.

I n the occipital portion of the basal surface, the decrease in the cerebellar
concavity is apparent. This is occasioned by the operation of two factors:

TROGLODYTES GORILLA

651

first, the expansion of the occipital region of the hemispheres in the interest
of further enriching the visual fields and thus visual association; second, by
a conspicuous expansion in the lateral lobes of the cerebellum. The decrease

FIG. 294B. DETAILED DIAGRAM OF LEFT HEMISPHERE OF BRAIX, GORILL.\.
Key to Diagr.\m. sllc. fr. sup.. Sulcus Frontalis Superior; sllc occip. lat.. Sulcus Occipitalis Lateralis;
SULC PR. INF., Sulcus Precentralis Inferior; SLXC PR. sup.. Sulcus Precentralis Superior; SULC ret. inf..
Sulcus Retrocentralis Inferior; suLC sub. post.. Sulcus Subcentralis Posterior; suLC te-MP. med.. Sulcus
Temptoralis Medius.

in the cerebellar concavity is shown particularly on the lateral aspect of the
under surface. In but one region does this indenture bear any of its original
prominence as seen in the lower primates. This is at a point near the midline
just caudal to the splenium of the corpus callosum where a vestige of the
former deep concavity is still apparent, the postsplenial fossa. In the main,
the basal surface of the occipital lobe is assuming a tendency toward con-
vexity and is rounding out its convolutions in such a manner that they pass

6^2 THE HIGHER ANTHROPOIDS

over int(j the lateral surfaee without the sharp clemareation of the limiting
ridge whieh surrouiuls the eerebellar eonca\'ity in lower speeies.

The fissures of this undersurfaee of the oceij^ital lobe are identical with
those of the human brain. The prominence attained by the tip oi the tem-
poral lobe is somewhat greater than that in the intermediate primates. It
approaches more nearly to that of man. The uncus also is more pronounced
both in its elevation and its demarcation.

All things considered, the convolutional and lissural patterns of the
human and gorilla brain coincide so closely that were it not for the great
disparity in size between the organs of these two species, the hemispheres of
the one might be mistaken for those of the other.

THE CEREBELLUM

With regard to the cerebellum, equally striking advances have occurred.
The entire organ has gained particularly in the region of the lateral lobes,
where expansion has produced conspicuous alterations in certain features of
its configuration. The tentorial surface is broader and Hatter. The folial
extension from the vermis to the lateral lobe is more pronounced for the
reason that the superior vermis is less obviously delineated upon this surface.
Its tendency to convexity in the \ermal region has been largely lost due to
expansion of the occij)ital lobes with a corresponding expansion in the lateral
lobes of the cerebellum. Upon the tentorial surface in one place only is any
degree of the former prominence of the \crmis still retained; this is near its
cephalic extremity in close relation to the inferior collieuli of the midbrain.
Here the vermal portitjn of the cerebellum is considerably elevated and
produces a corresponding depression between the occipital lobes, the post-
splenial fossa. The tentorial surface is entirely overhung by the occipital
lobes of the hemisphere, and the occipital notch, which in many lower
forms is quite wide, is now much reduced in size.

TROGLODYTES GORILLA 653

Tlir expansion ol tiic lateral lobes of the cerebellum shows itself even
more conspicuously upon the occipital surface of the organ where the bulging
due to increase in size has produced two elevations. These rise above the
inferior \ermal j;)()rtion ol" the cerebellum and cause it to sink deeply in a
mesial depression, the vallecula. Lying in this positifxi the itiferior vermis
appears relati\cly insignilieant w hen comj)ared with the two massive lateral
lobes upon either side of it. II the lateral lobes are separated, two para-
median sulci may be discerned Interruptnig the eontnuiity of the folial fissures
as they pass Irom the vermis in the direction of either lateral cerebellar
expansion. This sulMiiergence ot the inlerior \ermis in the \ allecular dej)res-
sion is a characteristic seen only in the higher anthrojjoids and man. It is one
of the most significant indications ol the expansion m the lateral lobes of the
cerebellum. Nothing demonstrates more clearly the potential expansibility
of the cerebellum than these lateral extensions. Prom this it appears that the
rapidly increasing functional demand lor augmented cerebellar control is
made, not upon the primordial and more rigidly fixed central portion of the
organ, but upon those plastic extensions of it which constitute the lateral
lobes. The expansion of these cerebellar jiortions, m conjunction with
simultaneous expansion of the cerebral hemispheres, indicates the funda-
mental nature of the Ijond existing between these two structures.

The jK'troso-ventricular surface of the cerebellum shows no great varia-
tion in its adjustment to the petrosal j^ortion of the temporal bone and the
roof of the fourth ventricle. At the cerebello-pontile angli' there is a fairly
vvell-defincd but not conspicuous flocculus. The other markings correspond to
all of the lower forms. This surface, therefore, represents a phyletically more
fixed region than is the case with either the tentorial or occipital surface.

THE BRAIN STE.M

The Oblongata. The external appearance of the brain stem in gorilla
gives the impression of an increasing definition in the outlines of all impor-

654

THE HIGHER ANTHROPOIDS

tant features. Ujjon the \-eiitral aspect of the oblongata are t\\o pronounced
elevations, one on either side of the ventroinesial lissure, the long pyra-
mids, in turn separated from two more laterally placed eminences, the

I K;. 2l)y. \ENTRAL SURFACE OF BRAIN STEM, GORILLA.
[Actual Length 42 nini.)

Key to Diagram, thai-, ihjd^ , Trapezoid Body.

inferior olivar\- bodies, by w (.•11-delined i^reolixary sulci. At the caudal
extremity of the pyramid, large bundles of interlacing fibers interrupt the
ventromesial lissure as the p\ ramidal decussation carries the fibers of this
system from one side to the other across the median line. The interlacing of
these crossing pyramidal libers is more conspicuous than in the lower and
intermediate primates. Upon the lateral surface of the oblongata is the tuber-
culum trigemini which is se|)aratcd from the interior olivary body by the
deep post-olivar\ sulcus. The latter, as it extends cei^halad, becomes
obscured by the dorsal shifting of the dorsal spinocerebellar tract entt'ring

TROGLODYTES GORILLA

655

the restiform body. At the upper extremity of this body is another elevation

upon the hiteral surface, the tubercuKim aeusticum.

The dorsal surface of the oblongata presents the characteristic infra-

FIG. 2()6. DORSAL SURFACE OF BRAIN STEM, GORILLA.

[Actu.il Length 42 mm.|

Key to Diagram, d. m. St., Dorsomcciian Septum; fovea inf.. Fovea Inferior; ink. coll.. Inferior Collicu-
lus; SUP. CEREBL. PED., Superior Cerebellar Peduncle; sup. collicul., Superior Colliculus; tub. trig.,
Tubcrculum Trigemini.

ventricuhir and \entricuhir regions. In the infraventricular region, the
dorsomedian septum in tlie niidhne separates the two alar plates, each of
which is further subdivided by the presence of a dorsal paramedian sulcus.
These sulci demarcate the chiva which represents the column and nucleus of
GoII and the cuneus representing the nucleus and column of Burdach.

In this portion of the oblongata the striking features are the prominence
of the pyramid, indicating a probable increase in the volitional control over

656 THE HIGHER ANTHROPOIDS

the somatic musculature; the cquall\- prominent inferior oli\c", justifying the
inference that coordination of simuhaneous movements in eyes, head and
hands has undergone further extension; and the more clearly marked defini-
tion of the dorsal sensory Held. This augmentation involves both the column
of GoII and the column of Burdach. It more particularly affects the size of the
latter, thus denoting accessions to the inllux of sensory impulses from the
upper extremity and hand. The inferior angle of the ventricular portion of
the oblongata is bounded by the diverging clava and cuneus. In this case the
cuncus extends a greater distance ccphalad than the cia\a. At the lateral
recess the cuneus attains the level of the door of the ventricle, at which point
fibers from the tubercuhnn acusticum enter the ventricle as the strands of
the striae acusticae, while the middle peduncle of the cerebellum forms the
sharp cephalic boundary of this recess. The iloor of the ventricle near the
inferior angle presents the narrow trigonum hypoglossi and, lateral to this,
the fovea vagi. There are also indications of an area plumiformis and an area
postrema, although neither is so marked as in the average human oblon-
gata. A deep median sulcus divides the floor of the ventricle longitudinally
into two symmetrical halves.

In the region of the lateral recess a well-defined prominence makes its
appearance. Its relief is not so conspicuous as in the intermediate or e\ en in
the lower primates. It marks the ])osition of the vestibular complex. The
superior triangle of the fourth \entricle is bounded by the middle cerebellar
peduncles and the libers constituting the superior cerebellar peduncles. Its
lateral walls comerge toward the caudal orilice of the Sylvian ac]ueduct
and pass beneath the inferior colliculi and the superior medullary velum in
the isthmial portion of the stem.

The Pons Varolii. The ventral surface of the oblongata comes to an
abrupt termination at the bulbopontilc sulcus abo\c which the pons X'arolii
rises in strong relief as a massive structure crossing the stem. The pons of the

TROGLODYTES GORILLA 657

gorilla stands next to that ol man in proniini'iUT. \ icwcd as an index of the
differentiation In t lie cerebral heinisphercs, it signiiies an cndbrain organi-
zation highly advanced ni its deveiopnuiit.

Othhk Structures i\ the Midbrain. A deep Ixisilar groove extends
cephalad and grachiallx widens toward the cejjhahc margin of tlie pons
Varohi. At this point the divergence in the basis of tlie midbrain begins, the
cerebral peduncles become apparent, and a huge oi)tico-i)eduncular space is
disclosed. This space contains the mammilhuv bodies, the attacliment of the
mfuncbf)ular stalk and the tuber cmereum. It is bounded at its cephalic
extremity by the optic chiasm and the di\erging optic tracts. Upon the
dorsal surface of the midbrain appear the usual specializations of the
ciuadrigeminal j)lates, lorming the su[)enor and the inferior colliculi. Of
these, the superior colliculi are considerably larger but both sets of eleva-
tions ha\'c lost in the prominence ol their surface relief. The sulci between
them, especiallx the transverse intercollicular sulcus, are less defined than in
the intermediate piimati'S, while the cephalic extremity of the longitudinal
intercollicular sulcus shows a much wider separation to form the j)ineal
fossa. Upon the lateral surface of the midbrain is a fairly well-outlined mesial
geniculate body.

Internal Structure of the Brain Stem in Gorilla

As in all of the primati's, the le\els ujjon which these descriptions are
based show the critical changes in the brain stem.

level of the P'iRAMIDAL DECUSSATION AND THE CAUDAL EXTREMITY OF THE
DORSAL NUCLEI (FIGS. 297 AND 298)

At these liAcIs the sections have the characteristic aj^pearance incident to
the decussation in the motor jjathway with the introduction into the dorsal
field of nuclear masses for the relav of sensorv stinuih to the higher levels

6^8

THE HIGHER ANTHROPOIDS

of the ncuraxis. Tlic p3'ramidal system (Py) appears more massive
than in any of the primates. The decussation (Pyx) shows the fibers
passing from a ventromesial position across the median line to a dorsolateral

FIG. 297. GORILLA. LE\ EL OF THE mUAMlUAL DECUSSATION.
CB, Column of Burdach; CEN, Central Gray Mallir; c;g. Column of Goll; dt. Deiterso-spinal Tract; fi.e.
Dorsal Spinoccrclxllar Tract; cow, Ventral Spinocerebellar Tract; hf;i., Spino-olivary Tract of Hclweg;
NR, Nucleus of Rolando; pv, Pyramid; pvx. Pyramidal Decussation; rst. Rubrospinal Tract; spt, Spino-
thalamic Tract; trd, Descending Trigeminal Tract; \ i-.\, Ventral Gniy Column; xpi. Crossed Pyramidal
Tract. (Accession J. D. Section 100. Actual Size 13X9 mm.|

position on tiie opposite side. Tlie decussating fibers separate the central
gray matter (Cen) from the \entral >j;ra\ niattt'r ( Ven). Passing through
the reticuhir formation are some of thi' emi'rgmg hhers ol the ele\i'iith oi'
spinal accessory ner\e. ScatttTcd through the dorsal portion ol the reticular

TROGLODYTES CORIITA 659

formation are many bundles of myelinated fibers, the descending portion of
tlu' p\ rainidal tract as it is about to enter the sjjinal cord (X.Py). The
central gray matter by means oi a narrow isthmus-like extension is con-

FIG. 298. GORILLA. LE\EL OF TIIF- DORSAL SENSORY NUCLEI.
CB, Column of Burdach; cen, (Central Gray (Jolumn; cc;. t^olumn of Goll; dt, Dt-iterso-spinal Tract; fle.
Dorsal Spinocerebellar Tract", cow, Ventral Spinocerebellar Tract; hel, Spino-olivary Tract of Ilelweg;
MF, Mesial Fillet; nb, Nucleus of Burdach; ng, Nucleus of Goll; nk, Nucleus of Rolando; pv. Pyramid; pvx.
Pyramidal Decussation; rii \ Reticular Formation; rst. Rubrospinal Tract; spt, Spinothalamic Tract; trd.
Descending Trigeminal Tract; xpv, Crossed Pyramidal Tract. [Accession No. J. D. Section 145. Actual Size
14 X 1 1 ram.]

nccted witli ihrtT nuclear masses appearnig ni the dorsal sensory field. The
most mesial of these nuclei, and the most faintly dc\eloped, is the nucleus

66o THE HIGHER ANTHROPOIDS

of GoII (NO) surrounded by an encapsulating mass of medullated fibers,
the column of Goll (CG). Lateral to this is the proximal portion of the
nucleus of Burdach (NB) which projects backward into a massive column
of Burdach (CB). Occupying the most lateral portion of the dorsal sensory
field, and connected bj' a very narrow strip of gray matter with the central
gray, is the substantia gelatinosatrigemini (NR) surrounded on its periphery
bj^ the descending trigeminal tract (Trd).

A comparison of these three nuclear elements in the dorsal field, i.e.,
the nucleus of GoII, the nucleus of Burdach and the nucleus of Rolando (a
term applied to the substantia gelatinosa trigemini), gives an accurate idea
of the sensory influx from the deep proprioceptive organs of the body. The
column of GoII appears to be about one-quarter the size of the column of
Burdach, while the trigeminal area is about one-half the size of the latter
bundle. In terms of functional capacity it appears from these relations that
the influx of sensory impulses from the leg is considerably less than that
from the upper extremity and hand; the influx from the head and face
occupies an intermediate position between these two. \\'hen the great size
of the gorilla's fore extremity, the tremendous forearm and highly developed
hand, is taken into account compared with that of the leg and foot, the reason
underlying the increment in the column of Burdach becomes apparent.
On the other hand, the innervation of the head and face does not vary much
in its relative dimensions as seen in the intermediate primates. It is, however,
considerably less in size than in the lower primates. This fact seems to denote
that the cephalic dermatomic areas play apart of less importance in directing
the animal's locomotion than they do in such forms as depend largely upon
sensory differentiation of the head and face for their guidance.

LEVEL OF THE CAUDAL EXTREMITY OF THE INFERIOR OLIVE (FIG. 299)

Here the lower tip of this structure appears as a circular mass in the
ventrolateral region. The circumference of the section shows even more

TROGLOD^TES GORILLA

66 1

clearly than the external appearance of the brain stem the definition of the
sulci which form the boundary lines of the various functional territories in
the axis. The ventral paramedian sulcus indicates the lower hmit of the pre-

FIG. 299. GORILLA. LEVEL OF CAL DAL EXIKEMITV OF INFERIOR OLI\"E.

CB, Column of Burdach; cen, Central Gray Matter; CG, Column of Goll; nr, Deiterso-spinal Tr.ict; F.\i,
Internal Arcuate Fibers; fle, Dorsal Spinocerebellar Tr.ict; Gow, Ventral Spinocerebellar Tract; H, Spino-
olivary Tract of Hehveg; 10. Inferior Olive; nh. Nucleus of Burdach; nbl. Nucleus of Blumenau; ng. Nucleus
of Goll; NR, Nucleus of Rolando; I'v, Pyramid; pyx, Pyramidal Decussation; kef. Reticular Formation; rst.
Rubrospinal Tract; spt. Spinothalamic Tract; tko, Dcscendini^ Trii;eminal Tract. [Accession No. J. D.
Section ig^. Actual Size i; X n mm.|

662 THE HIGHER ANTHROPOIDS

olivary fissure. A small intermediate suleus in this region demarcates the
position of the bundle of libers constituting the ascending cerebellar tracts,
particularly tlu' dorsal spmocerebellar tract (Fie). These delnniting sulci
separate corresponding ele\ations noted on the external surface. The most
ventral of these elevations is the pyramid ( Py). Lateral to it is the olivary
eminence. The lirst elevation on the dorsal surlace is the tubercuhini
trigemini structurally corresponding to the substantia gelatinosa trigemini
(NR). In the dorsal lields are two other cininences, the cuneus (CB) and
the clava (CG ). Especial attention is called to these elevations and then-
demarcation upon the surface of the axis as this definition of outline appears
increasingly more pronounced in the brain stem of the higher |:)riniates. It
reaches its most marked prominence in man.

The central gray matter (GEN) appt'ars considerably- larger and
more (|uadnlateral m outline than in lower le\els. The entire mass has
migrated into a more dorsal position preparatory to the opening oi the
fourth ventricle. Both tlu' nucleus ol Goll (NG) and the luicleus ol
Burdach (NB) have increased in size and atford an opportunity for
estimating the relative sizes ol the two ma|or nuclei m the dorsal sensory
Held. The inecjuality of the two columns of Cioll and Burdach is still appart-nt,
thus indicating a greater sensory inllux from the arm, lorearm and hand than
from the lower extremity. The substantia gelatinosa of Rolando (, N R )
occupies the most lateral position in the dorsal held and is surrounded by
the descending trigeminal tract (Trd). The rtlative size and importance
of the i^yramidal system may be estimated by tlu' dimensions of the pyramid
(Py). Some of the crossing libers ha\e already assumed their typical
descending position in the dorsolateral area. The caudal extremitx ol the
hypoglossal nucleus is seen located intlu' xi'iilral portion ol the central
gray matter and arising from it sonu' ol its lowermost libers make tht'ir way
outward toward the inferior olivary nucleus. 1 he more caudal sections ol

TROGLODYTES GORILLA 663

tlu' brain stem in gorilla aliorcl a basis for cstiinating the accessions to the
N'oluntary motor control h\ tlu' pidportioiis ol the |j\raniitls. They also dis-
close the relative sizes and hence the relati\e runctional significance of the
three elements t'litermg into the dorsal sensory held, re|)rt'senting collectivelv
the entire inllu.x of sensor\ impulses pertaining to discriminative sensibility.

LEVEL OF THE MIDDLE OF IMF IXI ERIOK OLI\E (IIG. 300)

At this level certain familiar changes have appeared incident to the
alterations in the dorsal held cansed b\ the opening of the fourth \entricle
with the gradual conversion ol the central gray mattt'r into the lloor of
this chamber ol tin- brain. Important also is the a|)pearance of the now
lull\' dcxelopcd inlerior olnarv body ( 10), togctlu'r with its two major
accessory portions, the \eiitral accessory olive (VO) and the dorsal accessory
olive (DO).

The general contour ot the cross section is much altencl by the appear-
ance oi tlu' lourth Ncntricle. Upon either side ol the \ cntricle, the dorsal para-
median sulcus separates the cephalic extremity ol the much atttnuated
nucleus of Goll (NG) from the large adjacent nucleus of Burdach ( NB).
The latter iuicIclis is m turn separated by the dorsolateral sulcus Irom the
tuberculum trigemmi whose prominence ui)on the surlace now has been
bscured by the dorsal migration ol the libers entering into the restiform
)dy. The post- and preoli\7ir\- sulci are well delined, separating on the
one hand the olivary body Irom the corjjus restilorme, and on the other
the pyramid and olive. The central gray matter (Cen) spreads out in a
\-shape, lorming tlu' lowt-r portion ol the lloor ol the lourth \entricle. In
its most mesial portion is the nucleus of the twelfth nerve ( Nhy), from
which pass the liljcrs of the hypoglossal nerve. Immediatclx adjacent to the
nucleus of the tweltth nerve in the central gray matter is a collection of gray
matter which receives incoming libers of the pneumogastric nerve; this is the

o
Ik

664

THE HIGHER ANTHROPOIDS

dorsal nucleus of the vagus (Nvd). A nuich sharper dcniarcatioii exists
between it and the twelfth nerve nueleus than is the case in the lower pri-
mates. Here again, even in these more arehaie and fixed structures such as the

FIG. 300. GORILLA. LEVEL OF THE MIDDLE OF THE INFERIOR OLIVE.

AMB, Nucleus Ambif^uus; cen. Central Gray Matter; do, Dorsal Accessory Olive; fle. Dorsal Spinocerebellar
Tract; cow, Ventral Spinocerebellar Tract; iiilL, Spino-olivary Tract of Helweg; 10, Inferior Olive; mf,
Mesial Fillet; nb, Nucleus of Burclach; NUi., Nucleus of Blunienau; NFS, Fasciculus Solitarius; ng. Nucleus of
GoII; NliY, Hypoglossal Nucleus; nr. Nucleus of Rolando; Nvo, Dorsal Vagal Nucleus; Nio, Tenth Cranial
Nerve; N12, Twelfth Cranial Nerve; i>d, Predorsal Bundle; pl. Posterior Longitudinal Fasciculus; pv,
Pyramid; ref. Reticular Formation; rst. Rubrospinal Tract; spt, Spinothalamic Tract; trd, Descending
Trigeminal Tract; vo. Ventral Accessory Olive; iv. Fourth Ventricle. [Accession No. J. D. Section 330.
Actual Size 18 X u mm.]

cranial nerve nuclei, there is a greater degree of definition in the advanced
species of the primate order. This increasing definition of all the structures of

TROGLODYTES GORILLA 665

the hraiii stem is a characteristic of progressive clillerentiation and is espe-
ciall\ well eni|)hasizecl in the hi<z;her primates.

Ill tlu' lateral wall ol the \'entriclc is a nuclear mass, tlii' most mesial
portion ol which rt'prescnts tlu' attenuated upper extremity of the nucleus
of GoII (NG). Arcuate hhers pass from it forwaixl and inward toward
the median raplu' to enter the mesial fillet (Mf). The adjacent nucleus
of Burdach (NB), as already indicated, is separated by a faintly dis-
cerned dorsal paramedian sulcus, and i)rescnts itself as a more or less scat-
tered a(z;gregation of nuclear substance. The outer portion of the nucleus of
Burdach is the nucleus ol Blunienau (NBI). In the gorilla it is especially
complex in arrangement and large in size. Occupyinga position \entral to the
nucleus ol Burdach is the substantia gelatmosa trigemini ( NR) now some-
^vhat ol)scured by the crowding fibers which lorm the restiform body.

In the lateral extremity of the central gray matter (Cen) is a
dense bundle ol fibers, somewhat oval in outline, the fasciculus solitarius
(Nfs), coming into relation with which are the entering fibers of tlu'
vagus nerve. The reticular formation occupies the central portion of
the section (Ref). It is crossed b\' man\ internal arcuate lii)ers taking
origin in the nucleus of Burdach and following a course which leads to
the ra[)he and the decussation of the mesial fillet (Mf ). Occupying the
most ventromesial portion of the section are the fibers of the pyramidal
system forming the pyramid (Py). The inferior olive (10), showing
not only an increment in \()hime but added complexity in its convolutions,
indicates to what extent there has been an increase in the control of
simultaneous movements of head, eyes and hand, and in the facilitation
of coordination of all skilled learned performances. This observation supports
the idea that the gorilla has made definite advances toward that ultimate
goal In which the hands arc eventually irced from direct participation in
locomotion. Such manual emancipation provides a means for exploring the

666 THE HIGHER ANTHROPOIDS

environment mow extensively, for ereating new modes of action, for augment-
ing the stream of sensory impressions from contacts lieretolore unknown —
in a word, for the discovery and control ol new territories in tlie reahn of
behavior. How much more the hand actLially means to the goriHa than to
any of the lower primates may be inferred from the history of John Daniel
who, in many particulars, approached the human standards ol manual manip-
ulation. In the acquisition of these manipulations, as well as m their execu-
tion, a harmonious interaction is necessary between the muscles of the
eyeballs, of the neck moving the head in the various directions, of the forearms,
arms and hands in order that the object of these movements may be attained.
The structural expansion of the inferior olivary nucleus accords closely
with the increment in function witnessed in the increased capacity of the
gorilla for the simultaneous regulation of eyes, head and hand. The evolu-
tional unfolding of the inferior oli\ary body is one of the most striking
features in the brain stem of the primates.

The features of the brain stem selected for comparative study of their
evolutional relations in the primate order were those which appeared to be
most susceptible to the inlluences of progressive adaptation. Such inlluenees
of evolutional progress do not, however, conline themselves to these more
plastic structures. They also aOect certain archaic elements which represent
the essential h)undations of neural organization upon which the \ital proc-
esses of life depend. Structures, for exam|)le, like the nuclei of the cranial
nerves which regulate the action of the heart, the rate and rhythm ol respira-
tion, the ]ieristaltic movements of the gastrointestinal canal, the rellex
movements of the tongue, lips, nose, soft palate and larynx in acts of swal-
lowing, breathing and emission of vocal sounds come into this category.
All of them represent the biological framework essi'iitial to the actual process
of living. They might for this reason \yv considered to possess an mllexibility
both in design and arrangement because of the unchanging nature of the

TROGI.On^TES GORILLA 667

functions over which they preside". \'ct even such archaic, fixed structures in
tlie brain stem show a degree of modification which is worth\ of noteascmpha-
sizing the fact that they, for all their primitivencss, have felt and responded
to the influences of progress. Thus, in passing from the lowest to the highest
members of the group, these archaic structures, the cranial ner\e nuclei,
show a steadily increasing definition in their outline as they assume more
distincti\e indi\ iduality and greater dimensions in each successive grade of
differentiation in the prnnates.

LEVEL OF THE \ ESTIBULAH AND CEHEBELLAK NL CLEI (hIGS. 301-304)

Here the striking feature is the replacement of the nuclei of Goll and
Binxlach by a large vestibular complex composed of the nucleus of Deiters
(ND) and the triangular nucleus of Schwalbe ( NSc). These two nuclear
masses have gained in definition but are considerably less prominent from
the dimensional standpoint than in some of the lower primates, espe-
cially those whose life is preeminently arboreal. The central gray matter
(Cen) occupies a position under the sube|)end\mal gray in the floor of
the fourth ventricle (Fig. 301). It contains in its most lateral portion the
nucleus of Schwalbe (NSc). Lateral to this is a large-celled nuclear aggre-
gation, the nucleus of Deiters (ND). Ventral to Deiters' nucleus is the
somewhat reduced substantia gelatinosa trigemini (NR) on whose outer
margin descends the trigeminal tract ( Trd). In a position lateral to
Deiters' nucleus lies the massive collection of fibers constituting the resti-
form body (ICP) about to form the inferior cerebellar peduncle and
thus consummate the connection between the cercbelluin, the s|)inal cord and
the oblongata. In their usual ventromesial position are the collected bundles
constituting the p\ramid (Py), and dorsal to it the fasciculus of the
mesial fillet (Mfj. The cephalic extremity of the inferior olive occupies

668

THE HIGHER ANTHROPOIDS

a position hitcnil to the pyramid and still shows its complex convoluted
outline (10).

From the functional standpoint, ttiis section in gorilla takes its signifi-

FIG. 301. GORILLA. LE\ EL OF THE \ESTIBULAK XL CLEI.
CF.N, Central Gray Mailer; Gow, Ventral Spinocerebellar Tract; ici-. Inferior (xrelxllar Peduncle; lo.
Inferior Olive; mf, Mesial Fillet; Ni>, Nucleus of Deiters; nk, Nucleus of Rolando; nsc, Nucleus of Schwalbe;
I'D, Preclorsal Bundle; I'L, Posterior Longitudinal Fasciculus; I'v, Pyramid; ref. Reticular Formation;
RST, Rubrospinal Tract; spt, Spinothalamic Tract; tkd. Descending Trigeminal Tract; iv, Fourth Ventricle.
(Accession No. .1. D. Section 3-6. Actual Size 20 X 13 mm.)

cance from \hv tact that the central balancnif^ mechanism appears to be less
highly sj^ecialized than m inan\ ol the lowei" lorms. This apparent dillereiice
calls for some explanation in the heha\ lor of tfie animal. It may well be that

TROGLODYTES GORILLA

669

the gorilla which, because oi" its great weight, has ceased to live so much in
the trees, and especially in the uiiperniost jjortions ol them where the
branches are too small to bear it, has in consequence changed its modus

FIG. 302. GOKILLA. LE\ IZL OF THE \ESTIBULAK NUCLEI.

CTT, Central Tcfimcntal Tract; (;o\v, Ventral Spinocerebellar Tract; iiel, Spino-olivary Tract of Mclwcg;
icp, Inferior Cerelxliar Peduncle; 10, Inferior Olive; mf, Mesial Fillet; nar, Nucleus Arciforniis; nu, Nucleus
of Deiters; Nsc, Nucleus of Schwalbe; NK, Nucleus of Rolando; n8. Auditory Nerve; pd, Predorsal Bundle;
PL, Posterior Longitudinal Fasciculus; py. Pyramid; rei-. Reticular Formation; rst. Rubrospinal Tract;
SPT, Spinothalamic Tract; trd. Descending Trigeminal Tract; tub, Tuberculum Acusticum. [Accession No.
.1. D. Section 401. Actual Size 22 X 0 mm.]

\-ivendi to a terrestrio-arboreal adaptation. On the other hand, this recourse
to gr()und-li\ ing does not recjuireso much in the way of balancing function as
in those animals which chpend whollx upon the arboreal highways for their
existence. Lidecd, the almost c|uadrupedal locomotion of gorilla would not
in itself call for a highlx de\elo|)ed balancing mechanism. Even if the gorilla
docs stand upright upon its hind legs at times, it is only poorly adjusted to

6-0 THE HIGHER ANTHROPOIDS

this p)o«ti!re. As a matter of fact, this p>osition is so infrequently assumed and
perf':>r _ .r as to require in and of itself but small

.. central axis.

FIG. 303. GORILLA. LEVEL OF THE CEREBELLAR NL CLEL

CBL, Cerefaeliuni; : js; icy. Inferior Cerebellar Peduncle; mcp. Middle Cerebellar Peduncle; ndt.

Dentate Nucleus; s^jl., v. . ^i^; nr, Nudeus of Rolando; n8, Audrtor>- Nerve; obl. Oblongata; Fi", Pj-ramid;
REF. Reticular Fomaation; tkd. Descending Trigeminal Tract; ver. Vermis; rv". Fourth \'entricle. [Accession
No. J. D. Section 515- A ' "-e 45 X 25 mm.]

The cerebellar nuclei and particularly the dentate nucleus (Ndt) show
a most striking advance (Fig. 303). Not only has there been a great increase
in the size of this nucleus which represents the efferent transmission of
cerebellar impulses, but it has also manifested that outstanding feature of
specialization whenever cerebral expansion is necessan,-, namely, a greater
tendency toward convolution. The nucleus dentatus in gorilla is much more
highly organized in this particular than in either the orang-outang or chim-
panzee. TTiis differentiation furnishes another reason for the claim that in
certain details of its encephalic structure the gorilla stands nearer to man

TROGLODYTES GORILLA

671

than the other two great anthropxjid^. The tuncti.r.al significance of the
expansion, increased definition and convolution in the dentate nucleus of
gorilla, as compared with the lower members of the primate group, needs

FIG. 304. GORILLA. LE\ EL OF THE CEREBELLAR NUCLEI.

CBL, Cerebelluin ; icp. Inferior Cerebellar Pedunde; mcp. Middle Cerebellar Peduncie; VF, Mesal Fillet;
NAB, Abducens Nucleus; nut. Dentate Nucleus: nfg. Nucleus Fastigii; n6, .\bducens Nerre; n— , Facial
Ners-e; py. Pyramid; \"ER, N'ermis; iv. Fourth Ventride. [Accession No. J. D. Sectioa 571. .\ctual Size
40 X 22 mm.]

scarcely more than passing mention. TTiis f>oint has been touched u|X)n so
frequently with reference to cerebellar organization, that its bearing must be
clear. In _ :he cerebellum shows notable exp>ansions in the region of its

lateral lobcs CbL. e their efferent representation in the dentate

nuclei. The vermis i \ c r , i; ' :s vested coordinating function for control

of the axial and paraxial musculature of the ; ' - "' ■ ' no such

progressive advance. It' - "act shown : " c variation throughout the
entire vertebrate ' ccause the axiai musculature is rigidly fixed in

6-2 THE HIGHER -\NTHROPOIDS

fii' cfetribution. For this reasc - .ntn.-
tc reas the ities repre-
sented by the prosressh-e!y ex]: _ e cerei ave
eshibr ^e of functional adaptation.

LEX-EL OF EMERGENCE OF SIXTH CR_\XIAI. NERVE, NER\T 5 A? - 505)

.-.- rvel the first pontile elements make their a;

in size of the fourth ventricle. The elements of the Dons constitute
large masses of nuclear substar - 3ying a

pontife nuclei > PN i. Other elements ol the ix>ns \ - is level '

the (fccussating fibers of the oallio-oonto-cerebellar svste:
grav matter here fomv? a th: r

ve 'ntains us (Nab grves rise

to the sixth - aer^-e, the nervui .rns < N6^. 7 -

n€Tve p>roceed forward and toward the basis of the axis. Tihe/
the collected bu : j\TamidaJ s>stem ' Py*. The r

e jxjntile nucleus i PN^ reoresents th
ladofthe nucleiisarciformis. In : ^

abducentis, is a collection of fibers : _- the sc.

gent course of the seventh nerve (N- i. The first p>ort!' _-ent

fiber? of the seventh nerve, arranged in their t-»

api 5 the floor of the ventricle. The fo _'ent

course of the se\'enth nerve extends obliquely : t'^'^'. ard its pwint

of emei^ence in common with the eighth nerve :: -tile sulcus.

The fibers of this part of the emerorent course of the seventh ner\-e pass
between the nucleus fac _ igemini i NR)

whose outer _ vrth the now densely comp>acted

bundle of hea\Tly myeli: xons, ti". _ .ract of the trigeminal

nerve (Trdj.

Tr.e reticular formation constitutes the major f)ortk»n of the teg-
mentum and is sejjarated from the basis by the mesial fillet ' Mf ).
Penetrating the collected bundles of the mesial fillet are a number of trans-

FIG. 305. GORILLA. LE\ EL OF THE EMERGENCE OF THE SIXTH CR.\NIAL NERX'E.

MO>, MidiSe fVnApJI-.r Pedaadez v7. Meszl F3Iet: vas^ Abdacess Nocieiis:: vs. Nocieiss of Hattjaio: >4^

AbdoceES Nerre; v-. Faciil Nervt: ?v, P'Xitiie Naiciei; pns, Pcos; pt. Pyrrniid: 3c=t. Rabcospniil Tract;
scp. Superior CerebelLLr Peduacie; spt. Sob^itslaniic Trsct; tsbx Desceodias T. "-»-,. emI Tract; r>, Fooitk
NeimicJe. lAccesszoo No. J. D. SectJoQ ~y. .VtuaI Ssze 30 X 15 mai."

verse fibers in process of decussation.These fibers belong to the secondarv
cochlear p>athway and constitute the corpus trapezoideum whose collected

674 THE IIK.HER ANTHROPOIDS

ascending axons subst'C|iKntl\- lorm the lateral (auditory) fillet. The out-
standing feature of this level is the size of the pontile luielei. These nuelei
in gorilla, as in all of the great anthropoids and man, are so exuberant in
their development as to rec[uu"e an extension l)eyond tlu' pout ik' segments
of the axis w hieh usually suffice to contain them. Their eaiidal continuation
projects into the ventral surface of the pyramid in the oblongata. The exten-
sion ol the pontile nuelei beyond the actual metencephalie hmits denotes an
increment in the functions of the pons which appears striking when the gorilla
is compared with the l()\\er iorms.

The heavy masses of mcdullated fibers flanking the ventricular walls
are composed of axons of the middle and superior cerebellar peduncles
(Mcp, Sep). They furnish a good index as to the richness of connection
between the cerebellum and other segments of the central nervous svstem.

-e>

LEVEL THROUGH THE AHDDLE OF THE PONS VAROLH (fIG. 306)

Here the contour of the cross section has been materially altered by the
central addition of the massive structures iorming the pons Varolii. The three
characteristic pontile layers dilfer from those encountered in the lower and
intermediate primates in the greater complexity ol their several strata.
There is a marked increased depth in the stratum superficiale, while in
the stratum complexum there are more libers and a greater nuclear
mass constituting the pontile nuelei (PN). The stratum prohmdum
is also of greater depth. The libers of all tlux'i' strata become conlluent
to form a more extensive middle cerebellar |)edunele 1 Mcp). Scattered m
the midst of tlu' stratum complexum iivv the libers of tlu' pyramidal system
(Py) which, however, a|)pear in mueh more disseminated arrangement
because of the greater complexity of the nuclear mass, and the decussat-
ing pallio-ponto-cerebillar libers. The central gray matter (Cen) now sur-
rounds the much reduced apjjroach to the Sylvian aqueduet. It eontains

TRO(;i OD^TFS COR II LA

675

in its lateral cxtriiiiily tlu' mcscnccplialic root ol tlu' tri^H'niiiial lurvc.
Tlu' latc'ial walls arc I'ornuti h\ a diMisi' mass of liht'rs constituting the
suj)cri()r cerebellar peduncle (Sep), lati'ral to which is the tractus uncinatus

FIG. 306. GORILLA. LE\ HL THKOIGH TIIL MIDDLE Ol HIE PONS \AK()Ln.
CEN, Central Gray Matter; li , Lateral I'illet; lix, Lingula; mc:p, Middle Cerebellar Peduncle; mf. Mesial
Fillet; N5, Trigeminal Nerve; I'l), Predorsal Hiindle; i>t , Posterior Longitudinal Fasciculus; pn. Pontile
Nuclei; pns. Pons; py, Pyramid; ref. Reticular Formation; scp, Superior Cerebellar Peduncle. [Accession
No. J. D. Section 580. Actual Size 30 X 19 mni.|

of Russel, and overlying this is a thin stratum of libers, the ventral spino-
cerebellar tract, makin<j; its way toward the \crmis of the cerebellum.

In the lateral portion of the pons Varolii, as its axons become collected
to form the middle cerebellar peduncle, libers Irom the dorsal root of the
trigeminal nerve (N5) penetrate the ])ons. These libers make their way
into the te<i;mentum where they terminate in relation with the cephalic
extremity of the substantia gelatinosa trigemini. The tegmentum pontis

6-6 THE HIGHER ANTHROPOIDS

has as its boundary thr transversely disposed fibers of the mesial fdlet (Mf),
at whose Literal extremity is the bundle of libers forming the Literal lillet
(Lf). In funetional signifieanee, this level takes its importance from the
size and eharaeter of the pons Varolii as well as the dimensions ot the
superior cerebellar peduncle, both indicating the degree to which the cere-
bellum has expanded. It denotes accessions in the development of eoordina-
tive control over the animal's acquired, skilled movements. The impression
conveyed by the pontile nuclei and pallio-pontile system of fibers in gorilla
is that this animal is possessed of a wider range of behavioral reactions
than is the case in the lower or intermediate primates.

LEX'EL OF THE EMERGENCE OF THE TROCHLEAR NERVE (fIG. 3O7)

Here the section is beginning to assume the character ot transition Iroin
the pons Varolii to the midbrain. The central gra\- matter (Cen) entirely
surrounds the beginning of the acjueduet of Sylvius in whose roof the fibers of
the fourth ner\e (nervus trochlearis) (N4) make their emergence from
the stem. The tegmental portion of the axis at this level is separated from the
basis by the characteristic boundary line, the transversely disposed bundle
of the mesial fillet (Mf). The basal jjortion of the section still has the
typical appearance of the pons Varolii, showing the three characteristic
layers, the stratum superliciale, the stratum complexum and the stratum
profundurn. The ventroniedian lurrow along the surtaee ot the pons is now
becoming deeper, preparatory to the final separation ot the two haKes of
the basis which, in the midbrain levels, gives rise to the di\ergence eventu-
ating in the formation of the two cerebral jjeduneles.

LEVEL OF THE INFERIOR COLLICILIS (FIG. 308)

At this level the configuration of the section is changed by the appear-
ance of two dorsal elevations above the roofplatc of the aqueduct of Sylvius.

TROGLODYTES GORILLA

677

These are the inferior eolh'euh fIC). Both in size and in eomplexity of
their stratiheation. the eolheuh in the ^()rl^a show some rechietion as com-
pared with the lower and intermediate primates. This fact is consonant with

MG. 307. GORILLA. LEVEL OF THE E.MERGENCE Oh THE TROCHLEAR NERVE.

CEN, Central Gray Matter; crir. Central Tegmental Tract; lf. Lateral Fillet; mf, Mesial Fillet; N4,TrocliIcar
Nerve; pr>, Prcdorsal Bundle; pl, Posterior LonKituJinal Fasciculus; px, Pontile Nuclei; py, Pyramid; ref.
Reticular Formation; rst. Rubrospinal Tract; scp, Superior Cerebellar Peduncle; spt. Spinothalamic Tract.
(Accession No. J. D. Section 7^4. Actual Size 23 X 20 mm.]

FIG. 308. CORILLA. LE\ EL Ol- THE INFERIOR COLLICULUS.

CEN, Central Gray Matter; err. Central Tegmental Tract; ic. Inferior Colliculus; if. Lateral Fillet; mf,
Mesial Fillet; ntr. Trochlear Nucleus; i>d, Predorsal Bundle; i>l. Posterior Longitudinal Fasciculus; I'N,
Pontile Nuclei; i>Y, Pyramid; ref, Reticular Formation; kst, Rubrospinal Tract; spt. Spinothalamic Tract;
si>x. Crossing of Superior Cerebellar Peduncle. [Accession No. .1. D. Section 815. Actual Size 22 X 22 mm.)

[678]

TROGLODYTES GORILLA 679

tlu' iiKTcast'd expansion in the tenijjoral region especially in the auditory
area of tlie heniis|)liere. Thus, in gorilla, as also in the other higher anthro-
poids, the funetion of hiaring has undergone a marked degree of telenee])h-
alization. The tenij^oral lobe is not only larger, but also more complexly
con\()luted. The central gray matter (Cen) surrounds the much reduced
ventricular space lormmg tlu' Sylvian aqueduct. In the roofjjiate above the
aciucduct are seen decussating libers ol the interior collicular commissure.
In the ventral portion ot the central gray matter near the midline is a well-
defined aggregation ol nerve cells constituting the nucleus trochlearis
(Ntr) from which enurgcnt libers of the fourth nerve take origin. On
the lateral boundary of the central gray matter is a thin zone of heavily
myclinized axons, the tractus mesenccphalici trigemini. Lateral to this
tract is the extensive mass constituting the inferior colliculus which
appears to retain some of its primiti\e stratified arrangement. The stratum
suj)erliciale griseum is clearix defined, but because of its deficiency in his-
tological detail, has a definitely vestigeal appearance. Four other layers
may be discerned. The j)rimordial tendenex' of this portion of the brain to
present delinite stratification is still retained e\'en in this iiigh representative
of the primate ordt'r.

The boundar\ between the tegmentum and basis in this jjortion of the
axis is, as in prect'ding sections, determined by the mesial fillet (Mf).
The tegmentum itself contains a large and somewhat diiluse reticular ior-
mation (Ref'i in the center of which, in process of complete decussation,
arc the fibers of the suj)erior cerebellar ixtluncle (Spx). The basis has
many of the a|)()earances typical of the j)ons \'arolii. The scattered bundles of
the j)yramidal s\stem (Py) are showing a tendency to reassemble as a
single fasciculus. The basilar groove along the ventral surface of the pons has
become deeper as it approaches the point of divergence of the cerebral
peduncles.

68o

THE HIGHER ANTHROPOIDS

LEXEL OF THE SUPERIOR COLLICULUS (PIG. 309)

Here the general contour of the section has undergone marked altera-
tion primarily due to the divergence of the cerebral peduncles (CP).

FIG. 309. GORILLA. LEVEL OF THE SUPERIOR COLLICULUS.

CEN, Central Gray Matter; cp. Cerebral Peduncle; err, Q-ntral Tegmental Tract; mf. Mesial Fillet; mgb.
Mesial Geniculate Body; NOC, Nucleu? Oculomotorius; nrl. Nucleus Ruber; N3, Oculomotor Ner%e; PD,
Predorsal Bundle: pl. Posterior : a! Fasciculus; ref. Reticular Formation; sen. Substantia Nigra;

sc, Superior CoUiculus; spt, Spin^L.„ Tract. [Accession No. J. D. Section 885. Actual Size 30 X ij mm.]

In the dorsal region are the two fairly prominent elevations forming the
superior colliculi (SC). The section is further characterized by the appear-
ance near the center, in the reticular formation, of a large specialized
nuclear mass, the nucleus ruber (NRu). The superior colliculi contain
indications of being the vestige of the once conspicuous optic lobes in the

TROGLODYTES GORILLA 68 1

lower vertebrates. Their reduction is clearly shovNTi in gorilla by a demon-
strable decrease in size and by the vestigeal condit " neir stratification.
A few layers of cells and fibers, rather indiscr; j:ed, may still
be observed up)on high magni: " ajray matter (Cen)
surrounds the aqueduct of Sylvius, and in its ventron a contains
one of the largest of the cranial nuclei, the nucleus oculomotorius ( Noc).
This nucleus is important not only because of the extremely delicate muscu-
lature which it controls, ' :e as much because of the close internuclear
relation which is maintained between the two n ecussating
and commissural fibers. No other structures in y are more cnt
upon mutual cooperatio: - :ghtest deflection in their
adjustment produces gross defects in visual percep" 't only
disorganize the appreciation of objects. -o disturb many ot the reac-
tions of the animal in relation to its exter ations. It is the promi-
nence of these internuclear com _ - which makes
the nucleus oculomotorius in go: picuous.

The emergent fibers of the oculomotor ner\"e pass forward, some of them
p>enetrating the inner margin - NRu), some of them

skirting its margin, to reach the sulcus oculomotor: - c optic - ^""J"

lar space. The nucleus ruber i N R u ) is a large and highly differentiated
structure in the tegmentum, acting as a relay station in the efferent course
of impulses from the cerebellum. The marki :s nucleus,

combined with the increased definition in the size of the dentate nucleus and
the expansion of " oerior cerebellar p>eduncle, indicates to what degree

functional accessions have been made in co ve control in the animal's

muscular system. Such additional coordinati' c muscular activity' of

the gorilla is primarily determined by the develo; if greater adapta-

bilrt\' of the upper extremity and especially ot e feet and

legs have shown relatively less increase of sp>eciaIization over ver

682 THE HIGHER ANTHROPOIDS

primates. Because of the advanced diU'erentiation in the nucleus ruber,
the reticular formation ( Ref) seems to be a less ditluse and more defi-
nitely circumscribed structure. This tendency for the archaic constituents
of the brain to gain an increasingly more precise definition is a feature which
distinguishes gorilla in its evolutionary progress toward the standards
attained by the highest development of the nervous system.

The dense reticular formation passes laterally without a sharp line
of demarcation into the protuberance forming the mesial geniculate body
(Mgb). It appears to become more sharply defined in a ventral direction
as a discrete nuclear mass extending from the midline to the extreme periph-
ery of the section. This is the substantia nigra (Sbn) whose function
in connection with c'crtain automatic associated movements has already been
suggested, although much doubt still exists with regard to its exact physio-
logical significance. Ventral to the substantia nigra is a very dense mass of
fibers constituting the cerebral peduncle (CP) which contains the col-
lected nerve fibers of the pyramidal system as well as all those axons
constituting the pallio-ponto-cerebcllar system. Thus the cerebral peduncle
offers an opjjortunitx to estimate at a glance the size and proportion of those
systems of libers w hich convey the two great concurrent streams necessary to
all skilled motor performances: first, tlu' palliospinal or pyramidal system
which serves for the transmission of impulses necessary for the voluntary
c(jntrol of the movement, and second, tlie pallio-|)onto-cerebellar system,
for the transmission of impulses whicli call into play the simultaneous
cooperation of the eoordinative regulation by the cerebellum.

In the more lateral portion of the reticular formation is an irregular
collection of fibers constituting the mesial fillet ( M f ) which has here
departed somewhat from the jjositioii occupied b\ it throughout tlu' pons
Varolii. This deflection of its course is preparatoi\ to its entrance into the
optic thalamus.

TROGLODYTES GORILLA

683

LE\EL OF THE OPTIC CHIASM (EIG. 3IO)

At this level a marked ehan<i;i' in the outline of the section is determined
by the appearance of tlie third ventricle i \' 3 ) and the two optic thalami.

r-TG. 310. GOKILI.A. LEVEL OF THE OPTIC CHIASM.

ciN, Internal Capsule; cph, Corpus Hypothaiamicuni; rni", Desci-ndin({ Pillars iif tin- Fornix; i ok, Fornix:
GLP, Globus Palliclus; nca, Caudate Nucleus; nl. Lateral Nucleus of the Thalamus; nld, m.i. Internal Liiteral
Nucleus of the Thalamus; nm, Middle Nucleus of the Thalamus; oi'X, Optic Chiasm; PtT, Putamen; vq.
Fasciculus of Vicq D'Azyr; vj, Third Wntricle. [Accession No. J. D. Section toiq. Actual Size 4, X 24 mm.!

In llu' \entriciilar lloor an- the decussating fibers in the optic |xith\va\ form-
ing the optic chiasm (0])\). Superposed abo^•e the optic fibers is a small
specialized bundle of libers constituting tlie narrow sujjia-optic commis-
sure of Meynert. The two optic thalami are separated from the corjius
striatum GIpi by the interposition of the dense mass of myelinated
libers forming the internal capsule (Cin). This secti<jn illustrates the

684

THE fUGHER ANTHROPOIDS

process of di\c'rgcnc't' characteristic ol the upper end ol the brain stem by
which the hbers constitiitiiig the two cerebral pechiiicles cstabhsh ultimate
relations with the two cerebral hemispheres.

FIG. 311. GORILLA. LEVEL OF THE ANTERIOK COMMISSURE.

AC. Aiinriur CJommissiiiv; CAN, Internal Capsule; IDI>, Descending Pillars of the Fornix; lOR, Fornix; glp.
Globus Pallidus; nca, Caudate Nucleus; nl, Lateral Nucleus of the Thalamus; nm. Middle Nucleus of the
Thalamus; put, Putamen; VQ, Fasciculus of V'icci D'Azyr; \3. Third Wntricle. (Accession No. J. D. Section
1 150. Actual Size 47 X 15 mm.)

LE\EL OF THE ANTERIOR COMMISSURE (fIG. 3I1)

liere the cephalic c\tremit\ ol the brain stem presents itsell as the
much reduced cephalic portion ol the optic thalamus. These terminal
structures are separated b\ the internal capsule (Cm) troin the lenticular
nucleus ("Put). The cephalic extremity of the third xcntriclc appears in
the section, beneath which pass the libers of the anterior commissure (AC).
The remainiiifj; ieatures in the cross section are indicated by corresponding
letters in the caption.

■■-•:i*^i--'«A^:^

• s.v

Xi

Chapter XXII

RECONSTRUCTION OF THE GRA^ MATTER IN THE
BRAIN STEM OF TROGLOD\TES GORILLA

The High Cer\ical Level of the Spinal Cord

"^H Ii upper Ic'Nc'l ol tlu' ciTNical (.'ord presents an appearance strik-
intil\ sniiilar to that totiiul ni tlie hiiih cervical le\'el ol the human
spuial cord. In the le\el at which th(.' reconstruction ls l)cgun, the
\entral gray columns are still in contact with the central gray matter of the
cord. Lateral to the \entral gra\ column is the small lateral cell column
behind w hicii is an ari'a alread\' showing indications ol reticular lormation.
The ventral gra\' column is hert' roughly triangular in outline, with its apex
directed ventrally. It i^resents a mesial surlact' which is more or less parallel
w ith the fellow ot" the opjiosite side, a lateral sloping surface and a base w liich
is in contact w ith the central gra\' matter.

The cer\'i\ and base of tlu' dorsal gray column are both directed ven-
trodorsally, while the substantia gelatinosa Rolandi which surmounts the
dorsal horn and Hares somewhat latcrall\ presents a typical |)rimate
appearanct-. As the junction ot the high eer\ical le\'el with the oblongata
is ap|)roached, the \entral gra\- column diminishes in size and linally merges
with the reticular lormation which has incrcasi'd in size pari passu with the
decrease in the \entral gray column.

The substantia gelatinosa Rolandi as it appears to merge with tlu'
substantia gelatinosa trigemini graduall\ assumes the more lateral j^osition
characteristic of it in the oblongata.

The reticular lormation graduall\ increases m size in the oblongata and

spreading laterally establishes contact w ith the ventromesial surface of the

substantia gelatinosa trigemini. It eventually replaces the ventral gray

685

686 THE HIGHER ANTHROPOIDS

column and is fontinuous across the miciliiu' with its Irllow oi the opposite
side.

The Dorsal Medullary Nuclei

The first of the dorsal sensory nuclei to appear is the nucleus of GoII
which comes into view in the hii^hcst cervical sections. It develops as a
narrow prolongation extending backward from the surface ol the central
iirax matter close to the midline. Continuous with the dorsal surface oi the
central gray matter, from which it takes its origin, it rapidly increases in a
veiitrodorsal direction until it occupies almost the entire depth of the column
of Coll. It is compressed from side to side and completely surrounded, e\cei:)t
at its base, by the fibers of the column of Coll. As the lower extremity of the
fourth ventricle is approached the nucleus begins to shorten in its ventro-
dorsal diameter, at the same time showing a marked tendency toward the
formation of a nuclear outgrowth which resembles the overhanging branches
of a tree. As the ventricle opens the nucleus is pressed aside and separated
from its fellow of the opposite side. The nucleus of Coll comes to an end
shortly above the opening of the fourth ventricle. The nucleus of Burdach
appears at a level only slightly above the appearance of Goll's nucleus as a
dorsal prolongation from the base of the dorsal horn. This mass of nuclear
material increases until it occupies a large part of the column of Burdach
with a dorsolateral extension passing laterally and conforming to the surface
configuration of the medulla oblongata. This lateral swing is carried so far
that the nucleus of Burdach overhangs to a considerable extent the sub-
stantia gelatinosa trigemini w hich is separated from it by the descending root
fibers of the trigeminal nerve. The nucleus of Bmclach extends ujiward almost
to the level of entrance ol' tlu' cochlear root, bt'ing separated gradually from
the floor of thi' fourth \entricle by the inler\ention at this point of the
vestibular complex.

RECONSTRUCTION OF TROGLODYTES GORILLA 687

The nuc'lrus ol the substantia (ichitinosa trim'mini, in the lower pontile
levels, presents the eonstrietion lounci m tlu' other primate forms — the
so-eallecl waist ol the tri^t-niiiial nueleiis. I he nuelear mass eontimu-s upward,

FIG. 312. \E.\TRAL SLKKACE OF GRA^MATTER OF BRAIN STEM,
TROGI ODYTES GORILLA.

Key TO Diagram, im-. oi.ive. Inferior Olive; lat. gen. body. Lateral Geniculate Body; meso-gen. body.
Mesial Geniculate Body; pontile, Pontile Nuclei; ret. form.. Reticular Formation; subst. nigra.. Sub-
stantia Nigra; vent, cocml.. Ventral ('oclilear Nucleus; \ i :n. (;i<av col.. Ventral Gray Column.

presenting upon its lateral surfaee the cleseencling root oi the trigeminal
nerve, to tlu' mid-pontile region, at whieh point it t'x[)ancls into its eaput.
It is here in close relation with tlu' nuekus masticatoruis whieh is situated
mesial to the trigeminal eaput. Throughout its entire extent tlu' mesial aspect
of the substantia trigemini rests in a cleej) eonea\ ity formed in the lateral
surtaee ol tlu' retieular lormation.

Thl Inferior Or ivarv Nucleus

1 he interior oli\arv nueleus first apjK'ars somewhat below the le\el of
the opening of the iourth \entriele. Its eaudal extremity consists oi the chief

688 THE HIGHER ANTHROPOIDS

olivary nucleus ( nco-olivi'). The next portion to appear is tlie mesial acces-
sory nucleus which is situated veiitromesial to the mam olivary nucleus. The
chief nucleus shows a considerable advance in the complexity of the convo-
lutions and reduplications which characterized it in the chimpanzee. The
fundus is broad and presents a number of plications. The dorsal and mesial
plates of this nucleus are thrown into extensive folds, while their dorsal
extremities turn somewhat inward to run parallel with the median line.

The mesial accessory nucleus of the olive (mesial paleo-olive) a])pears
as a flat band in apposition to the mesial plate of the chiet olive with which it
is parallel. It becomes continuous with the upper extremit\ ot the mesial
plate near the cephalic extremity of the latter. The dorsal accessory nucleus
(dorsal paleo-olive) extends along the dorsal surface of the main nucleus
embedded in the reticular formation. It forms a narrow band of gray matter
with its mesial extremity turned somewhat in the ventrodorsal plane. As the
chief nucleus extends upward, the dorsal accessory nucleus becomes contin-
uous with its dorsal plate. The cei^halic limit of the oli\ary nucleus is in the
lower pontile region where the nuclear substance gradually disappears by
merging with the reticular matrix.

The Reticllar Fokmahon

71u' reticular formation appears in the upper cer\ical levels situated
between the substantia gelatinosa Rolancli and the \fntral gray column. It
increases in size as it is followed upward, replacing the xfiitral gray column
which merges with it and then extt'iuls to the midline to become contiguous
at various points with its tellow ol the opposite side.

In the lower ventricular le\els it sup|)orts the inlerior olivarx complex
which is embedded in its \t'ntral surface. The leticular lormation is more or
less ciuadrilateral in shape with a veiitromesial, a \ enlrolateral, a dorsal and a

RECONSTRUCTION OF TROGLODYTES GORILLA

689

mesial surlacr. I he nu'sial siirl;uT lace's toward its Icllow ol llu' opposite side
Iroiii winch It IS si'|)arated bv ihv lontiit luhnal hhcr hundles sit uated close to
the raplu'. 1 hese l)Lindlcs are i^arallcl to the median raphe, so that above the

FIG. 313. DOKSAL SURFACE OF CKA'i MATTKK Ol BK\I\ STEM,
TROGLODYTES (iORlLLA.

Kf;\' lo DiA(,HAM. I ()< III .. ("ochliar Nucleus; dors, rociiu. Dorsal Coclili.ir Nucleus; inf. <;oli ., Inferior
Colliculus; LAT. GKN. H()r)^. lateral Geniculate Body; meso-gen. body, .Mesial Geniculate Body; nccl. or
BURDACH, Nucleus ol Burdacli; nucl. oi- d. and nucl. oe t>i:nEi<s; Nucleus of Deilers, nuci.. or goi.l.
Nucleus of GoH; ret. form., Reticular Formation; subst. cei.. rol. and scbst. c;ei.. roi asdo. Substantia
Gclatinosa of Rol.indo; \ent. cocim .. X'entr.il C'oclilear Nucleus.

beuiniiinir ot the oll\ c the ritiht and left sides ol the reticular iormatioii are no
longer coiiti<;iious at tlu' midlme.

The \entrolateral surface of tlu' reticular loriiiatioii ajjpears between the
inlerior oli\ar\ nucleus and the substantia gclatinosa trigeniini which is
I'nibedded in the dorsal portion of this surlact-. In tlu' xeiitrolateral surface
are also the nuclear collections w Inch lorni the lateral nucleus ol the reticular
lormatlon. Ihex mav be followed in an iininterru|)ted continuous chain
almost into t lu' |jontile reij;ion. The dorsal surlace ol thi' reticular iormation

690 THE HIGHER ANTHROPOIDS

is in contact witli tiic central <i;ra\ matter hut cicnuircatcd I'rom It by the
circumferential liher Inindles ot the retieuhir h)rniati()n.

The reticuhir formation is a massive structure in the tegmentum ol tlie
metencephalon. It pro\idcs a matrix m whicli dcNclop the \arious nuclear
specializations characteristic of the metencephalic tegmentum. It also allords
a sup])orti\e medium through w liich pass many longitudinal fasciculi.

In the metencephalon the retiCLilar lormation is in contact with the cK'e])
layer of the pontile nuclei. Here its ventral surface fuses with the dorsal por-
tion of the mesial and lateral buttresses of the pontile nuclei.

Between these two points of contact with the pontile nucleus, the reticu-
lar formation is separated from the basis pontis by longitudinal liber bundles.

In the Lipper ]jontilc levels the reticular formation becomes superlicial-
At the point where the superior cerebellar peduncle begins to sweep forward
in the isthmus mesenccphali a reticular prolongation extends lateral to the
peduncle, between the latter and the surface of the isthmus. This prolongation
gradually extends dorsally, covering the superior cercl)ellar peduncle with a
heavy investment of reticular substance. At length the superior cerebellar
peduncle is completely surrounded by reticular formation. The cerebellar
brachium then passes into a tunnel ol the reticular lormation which extends
toward its jjt'duncular decussation. A similar prolongation ot the nu'sence])h-
alic ri'ticular lormation presents itself at the transition of the trapezoid body
into the lateral lilU't. At (irst the lateral fillet lies superlieially upon the outer
surface of tlu' reticular formation. It then penetrates this structure, to pass
upward toward tlu' lateral extremit\ ol tlu' interior colliculus.

These dorsal extensions of the ri'ticular lormation form a smooth, con-
tinuous layer situated close to the |:)t'riphery ol tlu' brain stem. The \entro-
lateral reticular angk's are continued forward and come into contact w ith the
deep la\i'r of the pontile nucleus. Dorsally these lateral extensions recen e the
lateral extremities of the coUiculi.

RECONSTRICTIOX 01" TROGLODYTES GORILLA 6yi

In gorilla the mesencephalic reticular iorination \ iewecl from above pre-
sents an arranucincnt similar to that loiind in the chimpanzee. It presents a
median luielear mass which extends to the midline, there to become contig-

FIG. 314. LAKEKAL SURFACE OF GRAY MATTER OF BRAIX STEM,

IROGLODYTES GORILLA.
Key to Diagram, im-. coli ., Inl'irior Colliculus; inf. olive. Inferior Olive; ivter-ped. c. Interpeduncular
Gray Matter; lat. gen. body. Lateral Geniculate Body; lat. gray coi.., Lateral Gray Column; meso-cen.
BODY', .Mesial Geniculate Body; nlcl. of bihdach, Nucleus of Burdach; nicl. of deiters, Nucleus of
Deitcrs; n. of g., Nucleus of Goll; ret. form.. Reticular Formation; roof of folrtii yen., Roof of Fourth
Ventricle; slbst. gel. roI-Ando, Substantia Gelatinosa of Rolando; sl'p. coll., Superior Colliculus; ve.st.
cocnL., N'entral Cochlear Nucleus; vent, gray col.. Ventral Gray Column.

nous with its fellow of the opposite side. The lateral surface of this median
mass is serrated and covered In the superior cerebellar peduncle. Lateral to
the superior cerebellar peduncle is the dorsal extension ol the main niiiss of
the reticular formation which, as the peduncle continues in its course toward
Its decussation, becomes more extensive.

From the lateral extremity of the inferior colliculus there arises a mass of
libers which produces a hiatus in the formatio reticularis, separating its more
ventral jjortion from contact with the superior colliculus. This hiatus is lilled

692 THE HIGHER ANrHROPOIDS

by fibers emerging from the inlerior colliculus which collect themselves as a
compact biinclle — the inferior Ijrachium — and groove the surface of the
reticuhir lorniation as the tract passes upward to the mesial genicuhite body.

A similar arrangement appears in the upper part of tlie mesencephalon
where a mass of libers emerges frona the superior eolhculus. These libers
I)roduce a groove on the lateral surlace ot the reticular lormation, passing
Irom the lateral extremity ol the superior colliculus to the lateral geniculate
body. The libers constitute a secondary tract in the visual pathway, the
superior brachiuni.

The mesencephalic reticular formation can, in its upper parts, be divided
into three main masses: (i) a dorsal mass which lies in contact with the
central gray matter, ventral to the colliculi; 1 2) a lateral portion which forms
the most considerable part of the tegmentum of the mesencephalon; and (3)
a central portion which gives rise to the condensation ol the nucleus ruber.
From the mesencephalon the reticLilar formation is continued u]jward to
merge with the zona incerta of the diencephalon and tlu' inditlerent nuclear
masses in the caudal-most part of the inkrlnain.

The Pontile Nuclei

The pontile nuclei lirst appear at le\els marked by the lower extremity
ol the lourth \entricle as the arcijarm nuclei. Here they are disposed along
the mesial and \entral surfaces of llu' p\ rainidal tract. The arcilorm nuclei
gradually become more extensive, pass laterally and mcsiall\- around the
pyramidal tract and linallx produce a complete iinestment of that mass ol
fibers. Proceeding upward they become more extensixe, merging with the
gray masses of tlu' intrinsic pontile nuck'us. The\ then assume a typical
arrangement in a superficial la\'er and a deep layer. A lati'ial accumulation
of nuclear material loiins tlu' so-called lateral buttress, while a similar
mesial accumulation forms the mesial buttress. In addition to these, tlu're

RECONSTRUCTION OF TROGLOD\ TES GORILLA 693

is clc'\rl()|X'cl ;i distinct intcrnu'diatc nuclear layer lyinjj; between the superfi-
cial vi'Utral and the dorsal deep strata. There arc also suhsidiar\ la\'ers of
gray matter which pass more or less as concentric arcs about the common
ceiitt-r from the mesial to the lateral buttrt'ss, separatinii; the pyramidal
tract and the pallio-])ont ile libers into man\ smaller constituent groups of

tract and tlie pallio-])ont ile libers into man\ smaller constituent groups ol
libers. This arrangement produces an intricate lace-like appearance in the
|)ontile nucleus. Thi' lateral surlace ol this nucleus is extrenu'l\ irregular
due to the emergence trom it ol numerous liber buiulli's w hich constitute the
middle cerebellar peduncle. This is especially true in the mid-pontile region
where there appears a well-marked hiatus betw ecu the intermediate and deep
layers ol the nucleus. From this opening a large mass of libers enu-rges to
lorm the mam bulk ol tlu' middle cerebellar peduncle.

Ccphaiicall\ , as the pontili' nucleus becomi's incompk'te along its lateral
margin, tlu' mesial buttress is continued upward in contact w ith the reticular
lorm at ion to the |u net 1011 of the hmd- and midbrain. At this i)oint the pontile
nucleus comes to an vnd. Its deep layer is continued upward to give support
to the substantia nigra. The pontile nucleus is in mlimate contact mesiall\'
and laterall\ with tlu- \entral surlace of the ri'ticular tormation. Between
these two points, however, it is separated by longitudinal bundles m the
jjcriphery ol the tegmental reticular formation. In the mid-pontile region at
the point Irom which the large liber mass t'lnerges Irom tlu' poiitik' nucleus,
the di'cp layer is continued as a delinite structure in the reconstruction and
can be seen to fuse with the ventrolateral angle ot the reticular tormation.

The ViiSTiBUL.A.K Complex

The \estibular com|)Ie\ makes its appearance in the reconstruction as
the nucleus of Deiti'rs, here de\elo])ing in its usual triangular lorm between
the mesial surlace of the upptr extremity of the ulicIcus of Burdach and the
subepend\mal gra\' matter lining the lloor ot the lourth \entricle.

694 THE HIGHER ANTHROPOIDS

The Deittrsal complex rapidly increases in size and separates the upper
])orti()n ol the nucleus of Burdach from the central ^ray matter forming the
lloor oi the lourth ventricle. It also extends rapidly in its ventrodorsal diame-
ter, appearing as a wedge-shaped mass with a triangular extension which
overhangs the substantia gelatinosa trigemini. It is separated from the latter
hy the interposition of the descending root of the trigeminal nerve.

Near the lateral recess of the fourth ventricle the Deitersal complex
begins to diminish in size and is replaced by the triangular nucleus of
Schwalbe.

Above the region of the lateral recess the nucleus of von Bechterew
appears in the lateral wall of the fourth ventricle. The entire vestibular
complex extends upward to the mid-pontile level where it rather abruptly
begins to diminish and then disappears by merging with the metencephalic
reticular formation.

The Cochlear Complex

The cochlear complex consists of the ventral and the dorsal cochlear
nuclei. The ventral nucleus presents the regular appearance of a trough
receiving the entering cochlear root on its mesial surface, surrounding the
nerve upon its caudal, lateral and cej)halic aspects. The dorsal cochlear
nucleus is situated in the lateral vi'iitricular recess. It is superposed upon the
vestibular area and is connected w ith the \i'ntral cochU'ar nuck'us hy strands
of gray matter interspersed between the radicular and secondary cochlear
fibers. The de\ elopnu'iit ol the cochlear comph'x is about the same as that
found 111 the ehimpau/AX' but appears less e\ti'nsl\'e w lu'ii compart-d w ith the
rest of the gray matter of the stem in most of tlu' lowir primates.

The CoLi.ici i.i

These masses occup\ their usual positions in the tei'tuni o| the mesen-
cephalon. The superior colliculus is somewhat larger than tlie uilerior col-

RECONSTRUCTION Ol TROGLODYTES GORILLA 695

liculus. 1 he latter rests niesiall\ upon xUc incliilereiit dorsal !j;ra\ matter w hllc
laterally it Is partially supported by the meseiieepiialie retieular formation.
The Iat(,'ral lillet, as it emerges from the trapezoid body, courses oblic|uel\
backward and u])\\ ard o\ er the surlace oi the meteneephalic and mesenceph-
alic tegmentum. It produces a deep groove m the tegmentum of the mesen-
cephalon as it a])pr()aches its destination in the mferior eolliculus.

Cephalicall\- the inlerior eolliculus is separated from the su[)erior eol-
liculus b>' the dorsal prolongation of the mesencephalic reticular formation
lying in tlie intereollicular furrow. Passing from the lateral surface of the
inferior eolliculus cephahcall\ and ventrally is a groo\-e produced bv the
inferior brachium which connects the inferior eolliculus with the mesial
geniculate body.

The superior eolliculus is supported mesially b\ the indilierent dorsal
gray matter and laterally by the lateral prolongation of the reticular forma-
tion. Mesially the two colliculi arc connected across the midline by the supe-
rior and inicrior collicular commissures. Cephalically the superior eolliculus
is continuous with a thin strip of gray matter, a dorsal reticular prolongation,
which passes forward to merge with the epithalamic gray matter.

The Substantia Nigr.\

The substantia nigra apjjears as a contiiniation of the dorsal laver of the
pontile nuek'us. The supjiort derived from the lateral and mesial buttresses,
which was so conspicuous in the lower primate species, continues in these
higher forms. The substantia nigra presents a ventral surface in contact with
the desctnding pallio-spinal and pallio-pontile libers. .MesialU it is in con-
tinuity w ith the indilierent interpeduncular gray matter. Laterallv it is con-
tinued oLitward into rather close contact with the mesial geniculate body,
|)resenting a Miitral, hook-shaped prolongation. In this lateral portion is
lound the specialization in the substantia nigra from which nerve fibers seem

696 THE HIGHER ANTHROPOIDS

to pass inti) llu' nic'sciUTi:)halic tc<z;iiu'iituni. D()rsall\- it is concaxc and sepa-
rated from the reticular formation bv liber bundles of the tegmentum.
Cephalieally it extends upward to the junction !)et\veen ttie mesenceijhalon
and diencephalon and seems to be continuous with the zona incerta of the
interbrain.

The Nucleus Ruber

The nucleus ruber appears in the lower portion of the mesencephalic
reticular formation as a rounded nuclear mass, separated from the reticular
formation by an encapsulation deri\ed trom the superior cerebellar ]:)tclun-
cle. It is almost spherical in outline and rapidly attains its maximum diam-
eter, occupying the greater portion of the mesencephalic tegmentum. Passing
its level of greatest transverse diameter, the nucleus diminishes and disap-
pears as the mesencephalon begins to assume the characteristics of the dien-
cephalic portion of the brain stem.

The Central Gray M.\tter

The central gray matter in the high cervical sections of the spinal cord
resembles closely that of the human brain stem, being quadrilateral and
meeting at its dorsolateral angles the dorsal cornua and at the ventrolateral
angles the ventral gray columns. It gradualls' is drawn dorsally as has been
found in the lower forms, giving origin to the dorsal sensory nuclei. As the
oblongata is approached the usual narrow |)rolongation ot gray matter passes
dorsally around the mesial surfaces of tht' two tracts of the column of Coll,
seeming, as it were, to draw the central gray matter backward toward the
dorsal surface of the spinal cord. In this way the central gray matter is llat-
tened out and forms the floor of the fourth ventricle. As the lloor opens out-
ward the h\ poglossal eminenct' situated close to its median sulcus and m tin-
most caudal part of the inferior \entricular triangle becomes apparent.

RECOXSTRICTION OF TROGLOD^TES GORILLA r„r

Lateral aiul dorsal to this eminence is a depressed area which indicates the
position of the dorsal vagal nucleus.

The remainder of tlu' lloor of the inferior trianj^le of the fourth ventricU-
does not show any jxirticular modelling, while in the cephalic half of the
\ entricli- a delinitc- marking is found close to the midline. This represents the
position ol the nucleus abducentis and the longitudinal, subependymal por-
tion ol the seventh cranial ncr\c-. This elevation in the floor is the eminentia
teres. It is also know n as the emiiuntia facialis or abducentis.

Lateral to this emmence is a marked prommence in the outer half of the
lloor ol the iourth \i'ntncle. Lying in the lateral recess, it extends for a short
distance both ce|)halad and caudad of the recess. It indicates the position of
the dorsal cochlear nucleus.

As the mesencephalon is a])|)roacht(l the walls of the Iourth ventricle
rapidly contract, the root, lloor and lateral walls thicken and converge until
the gray matter bounding the fourth ventricle lorms a dense mass about the
central canal of the midbrain. In the mesencephalon the gray matter is drawn
forward \cntrall\ toward the rajihe and forms a longitudinal prolongation on
either side of the raphe. In this ventral prolongation appear the trochlear
and oculomotor nuclei. .AI)o\e the upper limit of the nucleus oculomotorius
the ventral prolongation of the central gray matter becomes more extensive.
Proceeding upward this jirocess becomes continuous with the gra\ matter
surrounding the third \eiUricle and w ith the median diencephalic nuclei.

Chai'ti:k .Will

COMPARATIVE SUi\L\lAR^ OF STRUCTURES HAVING

EVOLUTIONAL SIGNIFICANCE IN THE BRAIN STEMS Ol"

THE HIGHER ANTHROPOIDS

A Criliccil C()m])uns(in of ihv Pxramulul Trad, Olivary \iuli'us. Dorsal
Setxsory Suclci, \'cstil)uUn\ Ccrchcllar. Red and Pontilt' \uclci, ll.U' Midhrain
Colliculi and ibt- ()culi)m<>l<ir Dtcussalion: Their Evolutional Sii^nijicancc in

Rclalion Id Behavior

I. The Pyramidal Tract in Relai ion to the VoLLNTAR^ Conirol of
THE Extremities with Especial Reference to the Hand

"^1 IE p\ raniiclal system as an iiuk'x of Noliliona! control allorcls a con-
sistent guide in estimatinji; certain hehaxioral dillereiices among the
]jiimates. This system oi lihers is a distinctlx mammalian acc|iiisi-
tion. It rcjjresents a new acKeiiture in motor organization. In then- progres-
sive dexelopment the primates lia\t' utilized this endowment to greatest
ad\antage. The signilicance of the p\ lamidal system is rt'lati\ely simpli'. It
introduces a new factor into the ancient neural control ol the muscles wliK'h
imparts to their primordial acti\ities a more e\tensi\x' adaptability. In
realitx this new mammalian s\stem remodels tlu' old sj^herc ol \ crtebratc
heha\ lor. The animal possessed of it manifests new combinations m ri'action,
begins to act with some e\ ideiice of a wider selection between man\ possible
courses ot motor response.

the NEOPAI I UM Ol HIE ENDBRAIN

In itseli the p\ ramidal s\stem, however, is but the sublimated repre-
sentation of the most rect'nll\ acquired, most expansible portion ol the

699

700 THE HIGHER ANTHROPOIDS

nervous system. This is the neopallium of the end-brain, whose purpose is to
create more complex sensory associations as a basis for correspondingly more
capable motor reactions. The neopallium is that part of the cerebral cortex
which gave the nerve impulse to and supplied the brain power for the age of
mammals.

Neokinesis. The neural combinations assembled in the neopallium
and projected by the pyramidal system have their externalized expression
in an extensive group of reactions collectively known as neokiitesis. This new
type of activity, characteristic of mammalia, is most important because of its
potential expansibility. Its limits seem to be set only by the degree to which
the neopallium may itself expand. Such extensions as have occurred in this
part of the brain may be followed \\ ith exactness through all the orders of
mammals. They advance step by step through the ultimate transitions
observed in the primates and finally reach their culmination m man whose
multitudinous neokinetic activities are expressed in the history of the human
race. It might be expected that the projection system representing neokinetic
development would be a most outstanding feature by which to differentiate
the primates, one from another. In general, however, efferent conduction sys-
tems in the neuraxis are under the necessity of confining themselves to the
smallest possible space. Their purpose is to convey neural impulses already
synthetized by more or less extensive central areas and thus ready for trans-
mission to the effectors of the body without further modification or
adjustment.

CO.MP.ARISO.N OF THE PYRAMIDAL SYSTEMS IN THE GREAT ANTHROPOIDS

The comparison of the pyramidal systems in the great anthropoids
discloses an essential equality in these three intrahuinan species. The pyram-
idal coefficients of all of the higher anthropoids have relatively the same
value, although the chimpanzee stands somewhat above either the gorilla

SUMMARY OF STRUCTURES 701

or the orang-outang in this regard; so much so that the difference thus
established may require explanation. From the known behavior of Trog-
lodytes niger, based on Professor Kohler's studies, the chimpanzee seems
endowed with a slightly wider range of neokinetic activity than either of the
other great apes. This conclusion might imply a higher degree of intelligence
on the part of the chimpanzee, and consequently place the animal nearer to
man in the primate series. The inference, however, is not so convincing when
the physical limitations of gorilla and orang are taken into account. The
great size of the former and its natural ineptitudes for satisfactory arboreal
and terrestrial living to some extent at least restrict the range of its adapt-
ability as compared to the smaller, better proportioned, somewhat more
active chimpanzee.

The case of the orang is seemingly more difficult to establish, for in
general size and body weight, it is more chimpanzee-like. Its physical handi-
caps, therefore, are not so apparent as those of the gorilla; yet on closer
inspection, the underlying reason for its restriction in the acquisition of
skilled acts may be discerned. The excessive length of Its powerful arm, while
admirably adapted to the purposes of arboreal life, seriously limits its use-
fulness for many other purposes. Thus, although the chimpanzee in its
pyramidal system gives evidence of greater volitional control than either the
orang or the gorilla, this difference may but express certain superior physical
qualities of one form over its closely allied congeners. From this point of
view, the conclusion that, because of "its greater pyramidal coefficient, the
chimpanzee possesses higher intelligence than the orang or the gorilla, seems
somewhat doubtful. The differentiation of the forelimb in all three of these
forms is about on a par, and the manual development can scarcely be said to
give advantages in one or the other. In all three of them the great length of
arm cannot be other than a restricting influence in the more plastic and useful
adaptation of the hand. Furthermore, the dcfrciencics in the feet of all of

702 THE HIGHER ANTHROPOIDS

these great anthropoids unlit tluin tor an circctual ficct posture and thus
impose upon thrni all alike a limitation w hieli prohibits the ultimate eulmina-
tion ol manual diii'erentiation. Neither the hand nor the foot is exclusivclv
sueh in the great anthropoids. Each partakes of characters of the other; the
foot in many respects being hand-like, while tin' hand is much used as a foot.
The plannnetric coefficients of the pyramichil systems in orang, ehim])anzce

and gorilla are given m the tollowing tabulation

Pi_JiNiMETRic Coefficients of the Pyramidal System in Higher Anthropoids

Species

Coefficient

Gorilla
Chimpanzee

.161

.172

Orang-outang

. t6o

COMPARISON OF THE PYRAMIDAL SYSTEM IN THE GREAT ANTHROPOIDS AND

THE INTERMEDIATE PRIMATES

The general relation of the pyramidal system in the higher anthro-
poids to that of the intermediate primates is of even greater interest. W hat-
ever slight differences exist among the great apes in this respect, the variation
between these and the intermediate group is so striking as to ieave no doubt
concerning a dehiiite advance in neokinetic organization. The i)yramidal
system III the higher antliropoids is much greater than in the intermediate
primates. The gibbon stands fow est in the scak'. Reasons lor its more limited
neokinetic activity ha\c' alreadx been ascribed to the restrictions imposed
upon It by its extreme arboreal specialization and its im|)erfect development
of the lower extrt-mity. Macacus, on the other hand, stands nearest to the
higher anthropoids, although the interxal between it and them is impressive.
This approximation may, perhaj^s, be explained b\ tlie fact that the macaque
has developed an ellien-nt manual organ which only lags behind that ol the
higher anthropoids because of tlu' animal's cxtensi\e specialization for an
essentially arl^oreal tyjx' of life. .

SLMMAin OF STRUCTURES 703

COMPARISON OF THE PYRAMIDAL SYSTEM OF THE (iREAT ANTHROPOIDS AND

THE LOWER PRIMATES

Contrasted with tlir lowtr priinatcs, the acKancc ot the |)\raniiclal sys-
ti'in maiiite'stcd by thr <i:ii'at anthropoids puts tiu' qut'stion ol progressive
c'X]jaiisi()n in lU'okinctic function entu'rly Ix-yond the rcahn ot doubt. No more
striking instance of e\'ohitional progress may be found tlian that represented
by the remarkable disparity in pyramidal development between the lower
primates and the higher anthro|)oids. In only one instance, namel\ , mycetcs,
does the pyramidal coellicient e\en approximate that of tiie great apes.
The lemur and the marmoset are so far distant from the chimijanzec, gorilla
and orang in this department of their organization as almost to seem repre-
sentatives of another order. From this lower limit to the higher one, a steady
expansion in neokinesis appears to have exerted an irresistible inlliience in
progressively expanding the sphere ol bt'havioral reaction.

n. The Oli\arv Nucleus in Relation to the Regi lation oi- Simul-
taneous Movements in the Eves, Head and Hand and the
Facilitation of All Skilled Learned Performances

The relation of the inferior oli\-ary body to the control of simultaneous
movements of eye, head and hand and to the tacilitation ol coordination of
all skilled learned performances, ascribed to this structure in this discussion,
should be accepted with certain rcserxations. In any case, the structural
evolution manifested by the nl'wv within the famil\ limits of the Simiidae
is bcNond dispute. The gorilla presents an inlenor olixarv body which is
considerabU' larger in its planimetric coeHicient than that ot either the chim-
panzee or the orang-outang. Combined w ith this adxantage in size accredited
to the gorilla, other structural filatures indicate a further specialization in the
olive. The degree of convolution and the dellnition of outline attained by the
olivary body are features of utmost importance in determining the difleren-
tiation of this structure. In this respect the gorilla approaches most closely

704 THE HIGHER ANTHROPOIDS

to the luiiiiaii slanclard. Its oli\ar\ luick-us is nioiv clearly clcliiird ami more
complexly coinoluted. As compaix'cl with the oranfi-outaiifi, the dillerencc
is strikin<i;, for in this latter species neither oLitline nor convolution shows an
ad\anced degree of diflcrentiation.

In size as well as morphological definition, the chimpanzee occupies an
intermediate position between the orang and the gorilla, w hich latter species,
for this reason, seems better pro\ided with coordination ot simultaneous
movements of head, eye and hand. The physiological expression of these
morjihological conditions may be somewhat diHicult to estal^lish, inasmuch
as bt)th the orang and the chimpanzee are known to possess very accurate
regulation in their oculo-cephalogyric fLinctions. It is probable that the
gorilla has not as yet been sufliciently studied by precise scientilic methods to
justify a statement concerning the relative degree of its development m this
important department oi neural control. Yet, from what is known of this
animal's reactions in captivity, it would seem to possess a high degree of
specialization m those delicately adjusted movements of the eye and head
for the regulation of the hand in movements of extreme precision. \\ hether the
gorilla has actually a greater manual deftness, a more ellectual regulation ol
thosecomplementary movements in theeye, the headand the hand which prac-
tically welds these parts into a single organ ( in the physiological sense at least)
must await still lurther examination bearing upon the comparative behavior
of these three primates. The measurabU' dillerences of the mierior oli\arv
nucleus are show n in the jjlanimetric coellnu'iits ot t he inlenor olivary nucleus
for orang, chimpanzcx" and gorilla as arranged in the follow ing tabulation:
Planimetkic Coefficients of the Infekiok Olive in tficHEK Anthkoi'oids

Species

Coefficient

Gorilla

.186
.174

Cliimpanzee

Orang-outang

• 17^

SUMMARY' OF STRUCTURES 705

COMPARISON' OF THE INFERIOR OLIXARY BODY OF THE GREAT APES AND THE

I NTERM EDI A IT-, PRIM ATES

W hatcxcr signidcaiicc inav \x- attachccl to thrsc clilKTriiccs in the hi<iher
anthropoids Ix'conu'S greatlN increased hy coni|)arin<i ihein with the iiitcr-
mediati' primates. The inlerior oh\ary body ol the great apes has a pro-
nounced ad\anta<,ie in size ()\(.'r the internu'thate group. Nor is size aloin' the
only superioritx in this comparison. 1 he morphological delinition and degree
ol coiudlution m the macacus, Ijaboon ami gi Ijbon are lar mlerior to thes
aspects ol the inkrior oli\t' m the largt'r anthropoids. In one instance only
is there any semblance ol an a|)|)ro\imation to the standard ol tlu' great apes
namely, in the gibbon. Conditions underl\ing the olixary dillerentiation in
gibbon ha\'e pre\Tously been considered. This animal's exacting need ol close
coordination between eye and hand m its llight-hke passage through the
trees has already been noted. E\en with this exception, the dilk'rcnce is so
marked as to dis[X'l any reasonable doubt concerning the I'xolutional unlokl
ing in the olivary adxanci' Irom the intermediate primates to the higher
anthro[:)oids.

COMPARISON OF THE INFERIOR OLI\ARY BODY OF THE GREAT APES AND THE

LOWER PRI.MAIES

The dilVerence between the great anthropoids and the lower ])rimates
in respect to the inferior oli\ar\ body sup|)lies tiie Imal argumeiu, il such
were nei'ded, to maintain that a progressive structural t'X|)ansion has bcx'ii in
process from the lowl\ beginning of the |3rimate kind, through its intermedi-
ate stages up to its higlu-r dillerentiations. The planimetric coellicient of
tarsius, standing at the lowest extremit\ of the ])rimate ordi'r, is represented
by the low \alui' of 4 per cent, while the gorilla's corresponding ])laniinetric
coeiriclent is 18.6 per cent. This dillereiux' bt-twcen the lowest and the highest

7o6 THE HIGHER ANTHROPOIDS

forms is so decisive as to justil\ the supposition oi an evolutionan progress
in tlu' physiological function ot the inferior oh\ar\ body.

111. The Dorsal Sensory Nuclei in Their Relation to

DiSCRlMINATn E SeNSIBILITY IN THE EXTREMITIES
THE NUCLEUS OF COLL

The nucleus ot Goll ui the three great apes diflers in its function from
that of the lower and intermediate forms in the fact that the great anthropoids
do not develop a tail. Hence an important sensory area of the body has
ceased to exist. The absence of this organ should appreciably impress itself
upon the development of the sensory elements in the neuraxis designed to
receive the aOerent inllux from the proprioceptors. As amongthegreat anthro-
poids themselves, the gorilla has developed the nucleus of Goll to a greater
extent than either the chimpanzee or the orang. This may in part be due to
the slight advantage which tht' greatest of these primates has in the develop-
ment of Its foot, which is somewhat better adapted to plantigrade locomotion
than that ol either the chimpanzee or orang-outang. This interpretation
is based upon facts already determined concerning the structural features
of the gorilla foot as compared \\ith his anthropoid associates. It also takes
into account the supposition that the gorilla, because of his great weight, is
iorct'd to go much more upon the ground than the smaller, more agile
members of his family. This position, however, may not be accej)ted without
some reser\atioiis. That locomotion upon the ground has some bearing upon
the expansion of the sensory areas, more particularl\ the tt'iidcncx to assume
the upright posturi', is a \i(.'w \\ huh gams some substantiation from the
know n bt'ha\ ioral reactions ol the Simudae. The |)lani metric and longitudinal
coefficients of the nucleus of (joII, gi\en in the follow ing tabulation, show a
fairly distinct acKantage in the de\ I'lopment ol this structure in the gorilla
over tin- other two forms:

SUMMARY OF STRUCTURES 707

COEFFICIUMS in- THE NlCLllS OF GoLL IN 1111 lllGHFK AnTHKOI'OIDS

SpCC'lfJ

Gorilla

Chimpanzee
Orang-outang

■*lanimctrii'

Longituciinai

.086

.280

.050

.250

048

2-0

CoiisidcTed in rc-Iation witli tlu' nilcrnu'diatc pninati's, tlu' nuclc-us of
Cioll in the great anthropoids chscloscs a rather unexpeeted eqiiahty. It
nii.uht be presumed that with the dellorescenee and final disappearance of the
tail, Xhv nuclear structures in Coil's column would so materiallx fall oil that
there would he a distinct mieriority ol it in the hifj;lu'r iorms. This, however,
does not prove to be the case. The deliciency which the great anthropoids
would naturallx be expected to show because ot the absence of the tail is
surprismgl\ wanting. Therefore, some factors tending to maintain the general
ec[uality ot this nuclear structure among the intermediate primates and the
higher anthropoids must exert a decisive influence. \\ hile it is impossible to
prove conclusively at present what the exact nature of this factor is, it
ajjpears none the less to be embraced in those spt'cializations ot the hindlimb
for locomotion upon the ground as \\v\\ as lor the assumption of the erect
posture. That there is some such modil\ ing iiilliiciice at work is indicated by
a comj^arison ot the gibbon with the" greater anthropoids. In this H\lobatc
form the luicleus of Coll reaches low-water mark, being less in its dimensions
than in any of the other ]:)rimates. The explanation appears to be in tin- fact
that the animal possesses no tail, and has specialized the hindlimbs but little,
either tor [purposes ot locomotion upon the ground or for its arboreal
locomotion.

Compared with thi' lowfr primatt's, the great anthropoids show some-
thing approaching an cc|ualit\ in the size of the nucleus ol Coll, although the
lower forms bring forward one striking instance to illustrate the neural

7o8 THE HIGHER ANTHROPOIDS

results of specialization of the hiiulcr portions of the body. In mycetes, the
coefficient of Coil's nucleus is greater than in all other primates, and as this
is xhv onl\ form of all those considered which possesses a highly developt'd
prehensile tail, the signilicance of sensory specialization in this region ol the
body becomes apparent. The decrease of |:)rehensile lunction ot the tail and
the final disappearance of this organ would of necessity occasion a progres-
sive diminution in the nucleus of Coll. Certain adaptive modifications in the
feet and legs making provision for one kind or another of specialized loco-
motion, either in tree life or upon the ground, would rellect themselves quite
as much upon this nucleus. In those instances in which the tail appears to
play no conspicuous part, the maintenance of the standard dimensions in
GoII's nucleus may be regarded as due to factors operati\e in connection
with specialization in the hindlimb and particularly the toot.

But c|uite apart from the size of this nuclear relay station, emphasis
should be laid upon another feature in the dorsal sensory field. The column ol
Coll, comprising the ascending fibers from proprioceptors in the hind por-
tion of the bod> , inchiding the tail wlu-n pri'sent, shows a progressi\-e tend-
ency to decrease in passing from the lower to the higlu'r primates. The
actual volume of mechillary libers serving tor the purpose ot sensory conduc-
tion In the column of Coll in lemur compared with gorilla is something
slightly less than one-half. This indicates a distinct falling oil in the \olume
of afferent impulses from tlu' lower extremity and caudal portion ot the body
in passing from the lower to the upper end ol the primate order.

THE NUCLEUS OF Bl RDACH

The nucleus of Burdach likewise presiMits not a few diltieulties as evo-
lutional evidence in the great anthropoids. Estimated merelx u])on the
basis of its size, orang has the acKantage over both gorilla and chimpanzee,
thus indicating that the former possesses higher manual ditleri'iit iation. 1 he

SUMMAR\ OF STRUCTURES

709

apparent mcniisistciK'irs ol such a xicw arc cnicIciU at oncx'. In maintain
that the orang-outang- has a niori' highl\ ch'Hrrrntlatrd IkuuI tlian citlirr the
gorilla or the ehnii|janzt'e seems untenable by the criteria of our present
knowledge. Ne\ertheless, the dillerences obtauied by actual measurenu'nts
are sufliciently striking to make this supposition a strong probabilit\. I-Orthc
time, at least, it may be w iser to accept the conclusion forced b\ this relati\'e
mensuration ol the nucleus ol Burdach and seek further light which mav
uphold or disprove it. The planimetric and longitudinal coellicients ol' the
nucleus ol Burdach in the great anthropoids are gi\'en in tlu' following
tabukition :

Coefficients

OF THE Nucleus of Burdach

IN THE IllGUEK

A

NTHKOPOIDS

Species Planimetric

1

i

Loii

gitudinal

Gorilla

.081

.290

Chimpanzee

■ 073

i

.270
.2-0

OraiifT-oiitnng

.093

\\ hen compared with the mtcrmediatt' primates, the nucleus of Burdach
in the great apes again shows a somewhat surprising ec[uality. In fact, the
size of this nucleus in macacus closely approaches that ol the orang, and
actually exceeds the dimensions ol the nucleus in the chim|)anzct' and the
gorilla. The signillcancc to be attached to this comparati\e mensuration
points to the fact that in at least one ol tlu' intermediate primates, inlhu'iices
are ojjerative in the dillerentiation ol tht' upper extremity which iec|uire a
high degree ol |)roprioci-pt i\ t- re|)rescntation in tlu' nucleus ol Burdach.
The |)rincipal mlluence underlying this (k'\ elopmi'iit is tlu' specialization of
the hand. Extreme degrees ol such specialization ma\ oct'ur along sc\eral
divergent !iiu-s. The e\i(k'nct', thcrclore, allordcd by the nucleus of Burdach
as bearing upon manual dillerentiation must be weighed most critically.

710 THE HIGHER ANTHROPOIDS

Such testimony as it docs produce may he particularlx fortunate il it empha-
sizes the need for careful scrutiny and (^reat caution in accepting the evidence
of evolutional structures concerning which there ma\' be any doubts
whatsoever.

When the great apes are contrasted w ith the lower primates, a striking
fact comes to light. Mycetes exceeds in the size of its nucleus of Burdach not
only all of the great anthropoids, but all other primates as well. This feature
has been discussed in the relation of the lower to the intermediate forms.
Emphasis has already been laid upon the probable bearing of the high degree
of manual specialization consecpient upon tlu' animal's jwssession oi an
active prehensile tail.

Conclusions to Be Drawn from .\ Study of the Dorsal Sensory Field

If the conclusions to be drawn trom the relative' proportions of Burdach's
nucleus to the differentiation of the hand in primates are somewhat indeci-
sive, if they leave the tjuestion still in need of further iiuestigation, the
dorsal sensory field as a whole bears witness a\ hich is satisfactory and posi-
tive. It makes clear that in passing from the lower to the higher members
of the primate order there is a delinite increase m the inlliix ol sensory
imjjulses received Irom the proprioceptors ol the upper extremity. In other
words, whatever the size of the receiving nucleus in the column of Burdach,
the impulses which reach it trom the hand and upper extremity progressnely
increase in xolume. \ his progressive expansion m Burdach's column is so
obvious as to leax'c no room tor doubt. A dmieiisional comparison ol the
conduction columns m the dorsal sensor\- lield sutlices to establish this ])oint.
I n the lowt'r prima tt's the column ot (joII is larger than the column ot Burdach.
Gradually' the column ol Goll becomes less than tlu- column ol Burdach,
which may be understood to indicate a lallmg oil in the relatni' importance
of the sensory conduction system Irom tlu' hinder j>ortions ol the body as

SUMMARY' OF STRUCTURES 711

conipai'c'cl with thr Idi (.'limhs In ilu' ^nvit antliropnicls this disparity is so
marked that tin- culuniii dI (h)II is less than hall Of the si/.c of the adjacent
column ol Burdach. Such disproportion in laxorol Burdach's column ma\'
be accepted as \alid e\ ideiice. Its gradations ma\ he traced throu<i;h inter-
mediate stapes Irom a condition in which the column ol Burdach is dis-
tinctly less than that ol Goll in tin- lower primates, to one in w hich it is much
greater, as m the hi<j;her sjjccics. It is |)ossil)le that nuclear structures such as
those ol Coll and Burdach st'r\ iiiu as primarx relaxing stations for sensory
afierents, may, without \ar\ing nuich m size them.seKes, ofliciate in this
capacity e\en when the sensory tracts associated with them become much
increased in xolume.

This discussion may appear to absoKf the dorsal nuclei by oliering
certain extenuations lor their apparent lailure to rellcct the ellects ol adap-
tive ciianges in the extremities. It should m no wise depreciate the evidence
aOorded l)\ the dorsal sensory held itsell. The lact that there is a j)ro<iressive
increment in the- mllux ol sc'iisor\- impulses Irom xUv upper extremit\', as
compared with the lower extremity m ascendin<i the primate series, remains
unassailed. \\hate\cr may be the relative size ol the primary relaying
nuclei of thi-se special seiisor\- systems, tiie conduction paths leading to them
Irom the jjropriocejjtors disclose a relatne \'olumetric change m conduction
capacity. The ratio of the column of Burdach to the column of Coll in lemur
is one to one and a hall. This ratio in the gorilla and all ol the other greater
anthropoids is two to one. It is dillicult to mterj^retthis increase m the volume
of sensory mllux on grounds other than the specialization ol the ujjper extrem-
ity and particularly of the hand. Signilicant also is the relati\e decrease
in the sensory inllux from the head and face as indicated by the substantia
gelatmosa trigeinini in its relation to the nuclei ol Coll and Burdach. It is
apparent from this interrelation that imicii sensor\- responsibility has i^ecn
delegated from the primiti\ (.ly imjjortant areas of the head and face m their

712 THE HIGHER ANTHROPOIDS

capacity as directors of locomotion, to the niorc mobile explorative organ
dctei iniiK'cl by the higher stages ol mamial dillerentiatioii.

i\ . The Vestibi lai^ Nuclei in Their Relation to the
Balancing Mechanism

The problem of maintaining the balance of thi- bod\' appears to be sub-
ject far less to variations according to mode of life than most of the tunction.s
in the i)rain stem which have an exohitional signihcanee. In spite of well-
defined differences in adaptation either to arboreal living or something
approaching terrestrial life, there are many Ihictuating gradients between
these two extremes of specialization. All primates alike develop requirements
w hieh impose upon the balancing mechanism nearly the same burden. \\ hat
one species may lack in one particular, it compensates for by o^•eI■-dc•\ elop-
ment in another direction. This reciprocal rise and fall in equilibratory needs
is fairly elleeti\'e in striking a balance for this function throughout the order.
Among the great anthro[)oids, the chimpanzee presents in its Deitcrsal
nucleus a higher coeflicient than either the gorilla or orang-outang. In this
developmi'iit the gorilla is not far behind its a|)|)arentl\ better balanced
confrere; while the orang shows what a]>]ieais to be a real interiority in the
central control of its balancing mechanism. It seems probable that because ol
its great length of arm, this latter form has de\ t'lii|)rd less of the tendencies
essential to terrestrial locomotion, while both of the uxhcv anthroijoids have
partially adapted themselxes to locomotion upon the ground and in some
degree to the upright posture. The orang's eapabilit\ as a tree-dwi'ller has
none of the remarkable specialization si'eii in the gil)bon, and although it
manages to make t lu' best of its aiboit'al en\ ironmt'iit, its locomotion through
the trees is relatiwiy deliberati' and slow, it has none ol the showy agility
which characterizes many of the lighter apes and e\ en the chimpanzee.

SUMMARY OF STRUCTURES

713

Mensuration ol tlu' t-ntiic xcstilnilar area, including the nucleus of
ncittrs and \hv niulcus ol Schwalln' in tho <z;reat antliropoids, shows the same-
relation between tluin, the ehimpanzec having a slight advantage over both
ol the others, w hile the orang shows a eonsiderabic inferiorit\' in tliis develop-
rnt[it. I he eoellieK'nts of Deiters' nueleus and of the vestibular area in orang-
outang, ehinipanzee and gorilla are gi\i'n in the following tabulation:
Coefficients of Di iieks' Area in the IIighfk Antiikoi'Oids

Gorilla

Species

Planmictric
.072

Lonfiitiiciinai

.140
] .150

I ,-()

Clii]ii|);inzee

1 .077
.0,-4

OraiiK-oiitarif;

Coefficients of VESTiiseLAK Area in the Highek Anthropoids

Species

Pianimetric
.142

Longitudinal
.140

Gorilla

Cliimpanzce
Orang-outang

.157 i

.150

. KM)

.140

COMPARISON OF THE \ESTiBL LAK NLCLEI OF THE GREAT ANTHROPOIDS AND

THE intlk\h;diate 1>RIMATES
Tht' comparison of this portion of the neural organization in the great
anthro|)oids and the interniediate primates shows that they are all about on
the same plane of fli\ tlopnunt. Tlu' balancing nuehanism in the gibbon has
tlu' highest \alue of an\ member of these groups. This applies both to the
size of Deiters' nucleus and the \estibular elements in aggregate. The reason
for the gibbon's suj)eriority is ob\ ious. Its remarkable adaptation to arboreal
life shows to what degree this animal must depend upon a highly organized
ecpiilibratory mechanism. When the contrast is made with the lower iorms,
the great anthropoids appear to be about on a par with these distantly related

714 THE HIGHER ANTHROPOIDS

primates. Notable rxccptions must he taken m llie cases of tarsius and
myeetes whieli exceed all ol the antliropoids m the size ot Deiters' nucleus.
This high specialization results from the lU'W responsibilities imposi'd upon
the Ixilancing mechanism by the addition to the animal's motor organization
of the |)reheiisile tail or its llight-like leaps. Although some variations do
occur in the degree of differentiation manifested by the neural elements of
the balancing mechanism, this functional acti\it\- is in reality a basic and
ancient one which has impressed itsell upon the entire vertebrate phylum. It
has had its chief incentives to exiJansion in tlu' assumption o( those loco-
motor characteristics which become neccssar\ to lift the bod\ and support it
off tlie ground by means of the extremities.

The motor responses determined b\- the essential receptors ol this
activitx l)elong to the most ancient type of mol)ilit\ called paleokinesis.
Although age alone does not necessarily impart inllexibility, it is true that
those elements in the nervous system which ha\e the greatest antiquity
represent functional needs whose proper satisfaction demands a maximum of
structural development. This, for exampk-, applies particularly to such
archaic neural control as that regulating respiration, cardiac acti\ity or the
reactions of the gastrointestinal tract, flence tlu' binction inherent in the
balancing mechanism ol' the body would need to de\elop its full cjuota of
efficienc\- to be of any service w hatsoex'er. In this light it nia\ beclainu'd that
the vestibular compkvx in the central nersous system ol \ertebrates is of
little \alue as indicating the evolutional process. To a certain extent there is
truth in this xiew. On tin- other hand, those pi'diliai' exceptions in which the
fundamental organization manifests marked lluctuations either above the
usual standard or something below it, haxc a spi'cial significance in the prob-
lem of adaptation. They afford illuminating txamples of adaptive radiation
in highly specialized functional departments ol the organism. Par, therelore,
from being insignificant as bearing uijon the e\(ilutionai\ ]:)rocess in the

SUiMMAin' 01- ^TRICTL'RFS

715

primatfs, ihc Ncslihular complrx, althouuh it indicates the gciuTal conserva-
tism inlKTent in the eciuih'hratory elements of motor organization, reveals a
marked susce])tibihty e\ en on x\\c jjart ol'such archaic structures to inlhienccs
developed I)y the irresistible sj^ecializing factors of adapti\ e modification.

V. The Cerebellar Nuclei and Red Nucleus in Relation to the
Coordination of Mo\ ements, EsPECIALL^■ the More Complex

jMo\ E-MENTS OF 1HE UpPER ExTHENH I V

In the matter ol coordinati\e control of the musculature, dillerences in
the ec[uipment of the great anthropoids are not marked. W hatever slight
planimetric advantage may exist is in faxor of the orang-outang, although
the gorilla is close behind it in this sjjccialization. While the basis for
this contrast is allorded b\ the size partlcularix ol the dentate nucleus,
it also includes the conliguratioii of the structure. The coellicients of
the dentate nucleus in the three great anthropoids are given in the follow-
ing tabulation :

Coefficients of the Dentate Nucleus in the IIighkk Anthropoids

Species

Planimetrie Longitudinal

Gorilla

.152

.280

Cli imparl zee

..36

.230

Orang-outang

. 160 1 . 190

IMI'OKIANCE Ol-^ MORPHOLOGICAL APPEARANCES

Conclusions based \vholl\- upon these ligures do not give a comprehen-
sive view of the actual dilferentiat ion in this part of the central nt'r\-oiis
system. Quite as importantas the mensurationof the nuclei is their morpholog-
ical appearance. In two features of the dentate nucleus it is possible to trace

7i6 THE HIGHER ANTPIROPOIDS

a (k'diiitt' Linfolcling which gains siibstaiiliation from the fact tliat actual
expansions arc taknig place in the hitcral cerebellar lobes. The dentate
nucleus ni the orang-outanij; shows a relativclx low degree of dillerentiation
in so far as its boundaries are concerned. It has a diffuse uncircumscribcd
appearaiH'c w hieh relates it niuch more closel\- to the corresponding structure
ni the niterinediate and lower pruiiatcs than it does to those forms standing
abox'c It 111 the scale. The degree ot coiuolution in the dentate nucleus is
consick'rablv inlenor to that oi man, chimpanzee or gorilla. In comparing the
nucleus ol tlu' higher primates it appears at once that the orang is the most
primitixe in morphological organization. This inlerioritx of the dentate
nucleus m the orang corresponds w ith the conditions in the lateral lobes w hich
have not expanded to the extent seen in the primates assigned to higher posi-
tions in this order. The dentate nucleus in the chimpanzee is much more
clearly delmed than in the orang and has a richer coiuolutional pattern. On
the other hand, there is a primit neness about its festooning and foliation
whicii easil\ distinguishes it from t lu' corresponding structure in the human
and gorilla brains. If the dentate nuck'us in man be accepted as the standard
towaicl which the (.■volutional process has been tending, it seems reasonable
to assign to the gorilla a position immediately below the human t\ pe and
distinctly above the chimpanzee. This lact in coiiiunction with the high
degree o I dexelopnient m the latt'ral IoIjcs ol the ccrcbi'llum implit's that the
gorilla stands lirst m the group ol the great anthropoids in so far as the coor-
dmatiNH' control ot its muscles is concerned.

COMl'AHISON OF THE GREAT ANTHROPOIDS AND THE INTERMEDIATE PRIMATES

When compared with the intermediate primates the great anthropoids
show no great adxantage demonstrated b\ mensuration of the (K'litate
nucleus. On the other hand, in morphological particulars it is e\ ideiit that a

SUM \1 A in 01" STRUCTURES 717

great adxaiHx' has Ih'imi madr in the {Iriitatc organization ol tlu' orang, thini-
[janzec and gorilla as coniparcd w itii tlu' intiTinccliate gronp. On the basis of
mcasurt'iiicnts, the baboon has a slight ad\antagc over all the great
anthropoids.

COMPARISON OF THE GREAT ANTHROPOIDS AND IHF LOW I£R PRIMATES

\\ lu-n eomparison is mack' with the lowc'r primates, all of these larger
apes show a distinet advaiux' both in nu'asiirement and in eonlignration ol
the dentatt' nueleiis. The Ijaboon is distinet l\ mierior to tlu' great anthro-
poids in the morphologieal details ol its dentate strLietiire. This portion
ol the eerebelhim whieh ser\-es as an index ol eoordinati\e eontrol alVords a
basis for estmiating the degree to which the extrt'mities haxf been dilleriMi-
tiated. it s lion Id not be ox'er looked that m all |jri mates with tin' exception ol
man the various species are ec|uip|)ed w ith hand-like leet. Their c|uadrumanal
characteristics play an important role in hiNoring the dillerentiation of hand-
like C|ualities. B\ dillusing these c|ualitit's through all four extremities,
however, they rc'tard the more deeisixe specialization which eoncentrates
manual dilKrent lation in the upper extremities. Upon the basis of mensura-
tion the intermediate primates and the great anthropoids ap|)ear to bi' on
about the .--aiiu' plaiu', so lar as manual dillerentiation is concerned. The liner
structural details ol thedc'ii tat e nucK'Us, on 1 he other hand, as well as the expan-
sion ot the latt'ral lobes ol the ceri'bellum, establish a gradation which places
gorilla m the highest ()osition, with chimpanzee, gibbon, macaeusand baboon
succeeding in the order gi\en. Such conclusions are borne out by the size and
morphological delimtion ol another cerebellar index, the re<l nucleus. This
nucleus has a lunctional signilicance essentially similar to the dentate nucleus.
It is largest and best delmed in the gorilla, although its definition and its
size in the orang and chimpanzee indicate the high degree to whieh cx)ordina-
tivc control has been dcNcloped in these animals. The planimetric and

7i8 THE HIGHER ANTHROPOIDS

longitudinal coeflicicnts of tlic- nucleus ruber in gorilla, chimpanzee and orang-
outang are given in the lollowing tahuhition:

Coefficients of the Red Nucleus in the Higher Anthropoids

Species

Planimetric

Longituclinal

Gorilla

.096
.086

.180

Chimpanzee

.210

Orang-outang

.08-

.140

This nucleus is larger in all of the great anthropoids than it is in the
intermediate primates. The dilfcrencc in size becomes even more striking
w hen compared with the lower forms. The evidence, therefore, Ixiscd upon
the cerebellar nuclei and the red nucleus indicates a progressive expansion
which is consonant with increased coordlnative control. Such control is
incident to the acquisition of the complex aetiNities determined i^y the
development of the hand.

VI. The Pontile Nuclei in Their Relation to the Control of Skilled
Movements, Especially Complex Mani al Performances

Few elements in the nervous system allord more convincing evidence ol
the evolutional process than the pontile nuclei. Their status indicates the
degree of expansion in the cerebral cortex, particularly the neopallial portion
of this cortex. Contributions to the fiber constituents which reacii tlie pontile
nuclei are made by tiie Irontal lobe, the parietal lobe, the temporal lobe and
in all probability also from areas of the occipital lobe. The volume ol this
nuclear mass thus beconu's a reliable index of exi)ansion in thecerel)ral cortex.
Like the pyramidal system, the contingents of nerve fibers which comiect the
cortex with the pontili' nuclei are expressive of neokinetie actixities. They
denote the motor potentialities inherent in the mammal as well as the degree

SUMMARY OF STRUCTURES 719

of complexity with which the species is capable of applying its new cflcctor
equipment.

The extension ol neokinetic [jossibihties in the hi}:;her anthropoids is
consicIeral:)le if jiKlgecl by tht' pei tormances ol these animals m captivity.
It was thought at one time, \\ hen the discovery ol the extinct Pak'o|)Jthecus
was made, that this rt-|)resentati\ c- ol the great apes had sullicii'iit intelli-
gence to make use ol Hints. This supposition was probably inaccurate, at
least in so lar as its im|)lieation suggested the purijoselul em|)lo\ment of
implements. On the other hand, there are man\- reliable records to show that
both the chimjxinzee and the gorilla do make use ol implements. In a crude,
inellcctual way, they actually construct accessory means lor accomplishing
their purposes. The manner in which the chimpanzee learns to manipulate
and throw stones as otleusive missiles, its use of sticks and bars lor thrusting
and striking are examples of thi' point in question. Furthermore the state-
ment that the gorilla, John Daniel, so well understood the use of hammer and
chisel that these tools must needs be under concealment to protect the
turniture, are all indications ol the degree to w hich skilled motor perlormanccs
may be dcxeloped in the great anthrojjoids. To (ind this development accom-
panied by a corresponding expansion in the pontile nuclei is not surjjrising.
That the gorilla, on the basis of mcasuri'ment, should apjjcar to be most
favored in this regard seems to have no convincing demonstration in the
com]:)arati\ e behaxior ot these animals. The chimpanzee is but little less
highly specialized in its skilled motor acts than the gorilla, while both of these
species excel the orang-outang, further opportunity for study of the higher
anthropoids may justiix the im[)ressi<)ns conveyed by the comparative
measurements of the pontile nuclei and actually accredit the gorilla with
sui)eriorit\- in its acc|uired motor performances. The planimetrie and longi-
tudinal coefficients of the pontile nuclei in gorilla, chimpanzee and orang
are gix't'ii in the folhiwing tabulation:

720 THE HIGHER ANTHROI^OIDS

Coefficients of the Pontile Nuclei in the Higher Anthropoids

Species

Plaiiinic'tric

Longitudinal

Gorilla

.480

•440

Chimpanzee

.400

300

.440

Orang-outang;

.3-70

CO.MPAKISOX OF THE PONTILE ELEMENTS OF THE GREAT APES WITH THE
INTERMEDIATE AND LOWER PRIMATES

W h;itc\cT small clillerences ma\' he apparent from these figures, tlic
pontile elements (jain added signKieanee when compared with those of the
intermediate primates. In this contrast the degree of pontile expansion
becomes striking. Concernmg the actual neokinetic acces'sions of the great
anthropoids o\ er and above their simian associates in the intermediate
group, there can be no room for question. The de\elopments in this depart-
ment ol bihaxior arc readily recognized. Such contrast ise\c'n more emphatic
when the pontile nuclei of the great anthropoids are compared with those
ol the lower [primates. A superllcial sur\e\ of these structures in the two
groups is sulliclent to disclose pronounced dillerenees betwx'cn tlu'in. Upon
actual measurement these ditferences become conxincing and the value of
the pontile nuclei as e\idenced b\ tlu'ir progressixc expansion stands as one
oi the incontestable indices concerning the process of exoUitional unfolding
in the brain.

\ii. TiiF. Midbrain Collicili in Their Relation to the
EuNCTioNS of Sight and Hearing

Among the higher anthropoids tin- dillerenees in the promineiux' of the
inferior colliculus are relatixely slight. These structures m the orang and
chimpanzee are essentially ec|ual; whik' iu the gorilla the interior colliculus
shows some tendeiu\\- to further dellorescenct'. I nterpii'ted in the light of

SUMMARY' OF STRUCTURES 721

luiutional signilifaiK'c, this (limmutinii 111 tlu' auclitmy cdlliculus ot gorilla
suggests that all motor responses to suclckai soiiiuls ha\c less ol an iinnu-cliatc
ri-lli'\ c|Lialit \ and more ot ack'lihtral ixc element m tluu'exeeution. Such ohser-
\ations as ha\e been made on tlu' annual, partieidarl\ tlu' adult male, would
seem to indieate that \\ Iumi disturhi'd hy tlu' luinttr, it does not take to
niimediati' iliylit. It rist-s up to stand ereet, endea\ ormg to dc'termnu- the
souree whence the sounds arisi', and haxing suHieientl\ miormed itsell eon-
eernmg the nature ot its danger, otten |)reters to attack ratlur than si'ek safety
in retreat. Tlu' planinu-trie and longitudinal eot-llieieiits ol the interior
collieulus m the orang, chimpanzi'e and gorilla are gi\en in the following
tabulation :

COEFIK.IF.NTS OF IMF InFFKIOK CoLI ICL I I 1\ IMI lIlCHEH AnTMKOI'OIDS

Species Pianimetrie Longitudinal

ridrilla ' .III I .070

Chimpanzee ; .132 • .100

Orang-outang 131 0-0

COMPAKISUN Ol- THE I.NFEKIOK COLLICL LI OF THE GKEA 1 APES AND THE

INTERMEDIATE PRIMATES

It is, howe\er, when the comparison is made between the great a|)es and
the intermediate primates that the detloreseent [)roeess m the interior eollie-
Lihis becomes most coiniiicmg. The plammetric coellicients m all ol the
higher anthropoids are less than m the intermediate primates. I he general
signilicance ol the gradual decrease in size ot the interior colhcuhis is not
ditlicult to a|)preciate. It becomes conclusi\c' when the interior collieulus ot
the lower primates is compared with that ol the great anthropoids. I he
meaning ol this decline is not obscure, lor 111 proportion as the interior
collieulus diminishes m size, b\ just so much are com|)ensatory e\|}aiisions
pro\ Ided tor the auditory lunctioii in the temporal lobes of the cerebral

722 THE HIGHER ANTHROPOIDS

hemispheres. This delegation serves the purpose of affording a w ider, more
ample region in the brain for auditory associations. It also firings these
associations into intimate rehition with afferent iinpulses received from many
other types of receptors in the body, and thus makes possible that blending of
sensory impressions w hieh forms the basis of broader experience.

COMPARISON OF THE SUPERIOR COLLICULUS IN THE HIGHER ANTHROPOIDS

The comparison of the superior coilieuhis in the higher anthropoids docs
not turnish as convincing evidence of the telencephahzation of the visual
function as does the interior eolhcuhis with reference to the sense ol hearing.
In lact, the orang-outang and chimpanzee show the greatest amount of
deflioresccnee in this portion of the midbrain and indicate thereby a greater
degree of deh'gation of function to the visual cortex in the cerebral heiiii-
spheres. This places the gorilla at a distinct disadvantage in the comparative
sense. It may be that the mode of life of these three species has some bearing
upon this apparent inconsistency. Both the orang and the chimpanzee live
among the trees, and enjoy a more unrestricted \ iew of their surroundings
than does the gorilla, whose visual outlook is much obstructed by the under-
brush. \\ hether this be regarded as a wiiolly satisfactory explanation for the
distinct retardation which the gorilla shows in tlu' teleneephalization ol its
visual function, it seems advisable to accept the coeilicients of the superior
colliculus as they ha\e been obtained by measurement m the iollowing
tabulation, witli the suggestions ollered in explanation ol them:

Coefficients of the Superior Colliccli

N THE Higher

A

\THROPOIDS

Species

Planinietric

Longitudinal

Gorilla

.140

.110

Chimpanzee
Orang-outang

.125

.130

. oyo

.124

SUMMARY" OF STRUCTURES 723

COMPARISON OF THE SLPEKIOK COI.LICL LI IN THE GREAT ANTHROPOIDS AND

THE INTERMEDIATE PRIMATES

As compared with tlic iiitrrnu'chatc- primates, tln' sLii^enor colliculus in
the great anthropoids is eonsiderahly smaller. This is likewise the case when
comparison is made w itii the lower primates, w ith a single notable exception,
namely, in the lenuir. That animal, in the eot'llleients of its superior collic-
ulus, ec|uals the gorilla. The meaning of this discre]:)ancy must still he leit
in doubt, since the special mlluences which condition \isual expansion can-
not yet be e\aluated as a w hole, and many details of the j:)rocess rec|uirc
further iiuestigation. In the main, the progressive denorescence in the supe-
rior colliculus shows a steady advance m that process which proxides cortical
representation lor \isual lunctions formerly vested in lower midbrain le\els,
and hence denotes evolutional development.

\Tii. The Oculomotor Decussation in Rel.\tion to Binocilar V^ision

The progress in organization of the visual function has also shown a con-
stant achance in the matter of tlu' internuclear decussations and connnissural
connections ol the luicK'us oculoniotorius. The necessity of such close asso-
ciation in the interest of coniugate eye mo\ements, whose ultimate object is
the production and maintenance of binocular vision, has already been dis-
cussed, in the case ol the great anthropoids, there is the additional light shed
upon this held b\ tlu' rtsearches ol Prolessor Kohler in tests made upon
chimpanzee. From tht^se investigations it was concluded that the anthropoid
has developed to a considerable extent the powers of stereoscopic visual
perception. The gorilla shows the greatest internuclear communication, and
appears to be proxided with a more ample means to maintain conjugated eye
movements. The coenicients of the gorilla and the chimpanzee exceed those
of the orang. These coellicients of the oculomotor decussation are given in
the following tabulation :

'24 THE HIGHER ANTHROPOIDS

Coefficients of the Oculomotor Decussation in the Higher Anthropoids

Species

Coeflicient

Gorilla

.880

Chimpanzee

.860

Orang-outang

."lO

COMPARISON OF THE GREAT APES AND THE INTERMEDIATE PRIMATES

Moru inturusting than the comparison ol the great anthropoids among
themselves is the contrast atlorcled between them and the intermediate
])nmates. In this, witli the exception ol' the orang-outang, the man-hke apes
all sho\\' a pronounced advance. The macacus apparently has a dexclopment
in this respect which is equal to that ol tlu' orang-outang; whik' the baboon
exceeds the orang and stands next to the chimpanzee in the tli'\ x'lopmcnt of"
Its oculomotor decussation. The gibbon occupies the lowest i^lace in this
comparison. The high ligurt' re|5rt-sentmg the balloon is undouL)tedl\ due to
the laet that this animal, as it li\cs m more exposed places, is m need of
rapid \isual adiustmeiit to near and distant obiccts. It is contiiuiall\ on the
lookout not only lor the approach ol danger, but in search ol suitable objects
lor Its marauding exploits.

COMPARISON OF THE GREAT APES AND THE LOWER PRIMATES

\\ hen comparison ol the great anthropoids is mack' with the lower
primates, the real strides in the organization ol \Isual lunction beconieappar-
ent. In this particular there exists tlu' striking dillercncc between gorilla and
lemur ol 72 per cent, between gorilla and marmoset, of jo pvv ci'iit, and e\cn
the wily mycctes, with all the additional acKantages of its prehensile tail, is
approximately 20 per cent below the great ant hro[)oids. I hese dillerences arc
too great to leave doubt concerning the expansion which has alleetcd the
progressive de\clopment of coniugated c\ (,■ mo\inunts m t lu' interest ol
binocular \Tsion.

SUMMAin 01 STRUCTURES 725

SlMM AK'i'

Wert' it possible to ^i\t' 111 sumniafv the- iX'latiNc xalucs ol tin- struftural
features eonsiclerecl in this eomparatiN i' re\ lew , the placi' ol Inst importance
would uiuloul)tecll\ lall to the pontile nuelei. Their testimony as prt'sentecl
in the j^reat anthropoids, eonelusi\ c-l\ demonstrates a progressiw (K'\tlop-
nu'iU indieati\e of expansions m lU'okmi'tie organization. I o the i'\ idenee ot
the pontile nuclei and the p\ramidal s\stem should be added that ol the
inferior olivar\ nucknis whose incrcasiniz; Nolume and |)rogrcssi\e gam m
delinition cU'notc lunctional incremt-nts m essential accessories to neokinctic
de\elopmeiit. Likew ist', the oculomotor decussation, indicating as it does the
degree of organization in ocular coiiiugation and binocular \ ision, adds its
increasing acKantages to the sum of those mlhu'iices which ck'\ I'lop m the
interests of lU'okinetic expansion. The indis[)ensable acti\ it\ ol \ isual control
for the acquisition and maintenanei' ol man\ skilli'd mo\ements, contributes
the benelits of stereoscopic xision to tlu' direction of liner manual manipu-
lations. And linall\, the dellorescence of the mesencephalic colliculi, pro-
gressively acKancing through the |)rimate order. t\ pifu-s that unmistakabl\-
evolutional process of telencephalization b\ which functions originallx' \ested
in lower segnu-nts ol the lU'uraxis gam more expansible represt'iitation in
those higher le\ els i-specialls pro\ided In t lu' cortical regions ol the cerebral
hemispheres.

PART IV

MAN

IXTROOrCTlOX TO PART W

"^llE \ast dilU'iTiic'c's bctw (.'cii man aiul all (itluT li\ iii<i c'lX'atLircs arc
inanllrst in tiu' coitipkAit \ ol human allan's. In si/c and lorm of body
lluTc' aw many ncitabk' ri'scmhianci's hclwrt-n man and the a|)os,
particularlv tht' iiri'at apis. Bui Iutc the smiilarit\ ends abrupt l\. Man lias
created a ni-w world whieh \\v stn\t's to control b\' laws ol his own maknig.
The record of man's accomplishments has Invn ti'ni|)i'red b\ (.'xery heat
ofemotion, b\ rabid di-nuncialion, l)\ cc]ually c\trava<j;ant praise. Ob\iously,
theix' IS a lack ol discriminat m<z impartiality arisinii Irom mlu-reiit i-mbarrass-
ments of a situation in w Inch man linds himsi'll at one and the same time the
material and the makir ol his own criticisms. Good reasons exist lor the
dillicultx' of mamtainmij: a detaclu'd at tit ude in lud^ment. bor, according as
the point ol \ lew ma\ be rt'hij;ious, philosophical, historical, scientilic,
artistic oi' et-onomic, tiu' incentiNX' lorce behind tlu' multitude ol human
actixitics is ascribed either to t lu' soul, to the ps\ che, to {hv mind, to the
spii'it ol man or to human <^enius.

In the liiiht of histor\ and contemporaneous acKancenuaits, it is essen-
tial to assunu' the existence ol some specilic powfr which distin<i:uishes man
among all livinii ihini^s. But il this assumption disre<iards the probable
genesis of so remarkable a powx-r, it max omit an important detail in the
process w herebx this striking' dillerent lation has been attained. \\ tii' it
possible to behold man toilm;j; u|>ward oxer the long stages of" his slow
progress during the j^ast hall million xt'ars or so, this genesis might be the
more rtadilx traced. It might be seen in the gradual specialization in those
])arts of his organization, his hands, w ith w Inch he has contimu'd to reach out
and linallx' to lay lirm hold upon t he psx che or soul. I his surpassing endow-
ment, Professor Osborn beliexcs, canu' to man at some critical |X'riod wIumi
he stood up in the dawning glorx ol Ins Cro-Magnon manhood and drew

u|)on tlu' walls ol Ins caxc the lirst imjjcrishable record ol his greatness.

729

Chapter XXIV

FROM PRIMITI\E TO MODERN MAN

Primitive Man — His Times and Personality

"^1 IE length of time during which man lias inhahitrtl the earth olTcrs a
subject for dispute and much (hilerence of opinion. All authorities,
ho\\c\ er, are agreed that se\'eral stages ot human progress must have
required the i)assagc of a reiatnely long period. None ol the modern I'stima-
tions of this period is less than 500,000 years. Many calculations, such as those
of Sir Arthur Keitli, far exceed this iigure and place the origin of man as hir
back as a million years or more. The beginnings of the human species arc
usuall}' attributed to the early part of the Pleistocene, or even the hite |)art
of the Pliocene, keith, however, does not bclie\e that this permits ot siilli-
eient time for the evolutionary process which so evidently has produci'd
all ol the ellects evidenced in the known leatures ot modern man as well as
those of certain extinct \arieties of mankind which have long since passed
Irom the stage. Keith concludes his tamous work on "The Anticjuity ol Man "
with the statement that " there is not a single tact know n to me w hich makes
the existence of the human torm m the Miocene period an impossibility."

the I AMII ^' OI- MAN

Man, in all of his races, both living and extinct, constitutes the sixth
family of the suborder of Anthropoidea, known as the Hominidae. This
family departed from the common stock representing the orthograde stem of
the primates at some time early in the Oligocene. At that critical juncture,
probably twent\-li\e million years ago, two great branches ot the suborder
parted company. Thenceforth they continued their further dilterentiation

731

PITHECANTHROPUS ERECTUS

PILTDOWN" .MAN

NEANDLKTHAL MAN CKC)-M ACNON MAN

FIGS. 315, 316, 317, AND 318. lOLR EXTINCT RACES OF PREHISTORIC
MAN. FROM RECONSTRUCTIONS MADE BV PROFESSOR MCGREGOR. IN THE
HALL OF THE AGE OF MA.N, AMERICAN MUSEU.M OF NATURAL HISIORV.

[732]

FROM PRIMI I l\ E TO MODERN MAN 733

indcpc'iukntK ol'ratli otiur. The lirst ofthcsc branches gave rise to the great
tnocleni anthroi^oltls in tlie iatiiil\ Simiidae, inchiding the orang-outang, the
ehini])an/.ee and the gorilla. With them also were connected at least two
extinct lornis, i.e., Dryopitheciis, a large gibbon-like ape in many ways
resembling the sur\ i\ ing members of this group, and Paleopithecus which
made its appearance at a much latir period. The second branch to leave the
common stem ga\e rise to the human family. It is to-day represented by all
of the modern races of man known collectively as the species Homo sapiens.
This species comprises the African, the Australian, the .Mongolian and the
European \arieties.

Keith has graphically illustrated this conception concerning the deriva-
tion of the human race from a common prehuman stock as shown in figure
i8() in his work, "The Anti(|uit\ of Man." He has also given a like j^ri'sen-
tation with reference to the deri\ation of the great anthropoid apes, showing
their probable relation to the jirehuman stock.

PKIMIIUE RACES WHICH HA\ E DIS.JlPPE.\RED FKOM THE E.\RTH

Paleontological investigations ha\e revealed the former existence of at
least four prehistoric races of men who occupied their places upon the human
stage for a greater or less period and then, in const'ciuence of factors not yet
altogether clear, became extinct. These extinct races appear to vary so con-
siderabU from the modern representative of the species that a question has
been raised concerning the w isdom of creating for each oi them a new genus
within the faml[\ . One reason for this distinction is that none of thecxtinct
races ma\ properly be considered the direct ancestor of living man any more
perhaps than the existing genera of great apes.

PiTiiECANTHKoins Erectls. Tile oldest, most primitive of these
races that ha\e disappeared from the earth is known as Pithecanthropus

FIG. 319. TABLLAllO.N SHOWING PKOIESSOK OSBOKN S LATEST ESTIMATES
OF man's ANTIQUITY, HIS INDUSTRIES, ARTS AND RACES.

The rise of man is attributed to tlic Pliocene Epoch. The beginning of the cave period is indicated at approxi-
mately 300,000 years ago.

[734]

^ •>;?;/.

".-

•'

-'

. . t^ /'•

ti .' J \j.^

■ ^

\

^^^^S^ J^'

y v

^^v

FROM Pl^IMITIVE TO MODERN MAN 735

crt'ctus, the Ja\a man of the Trinil race' (origin, according to Keith, over
one million years ago). This ape-man, ah hough (k'linittlx human in tvjie,
had so many simian (|uahties and so much eharaetenstic ot man as to justily
the view that he represents a transitional stage in human eNolution. Tliat he
possessed a head and a face not unlike that of an ape witii a brain consider-
ably larger than that of an\ known simian, there seems to be no doubt.

Concerning the detailed organization ol this earliest iorerunner ol the
human raet', little can be said since his discoverer. Dr. Eugen Dubois, was
fortunate enough only to recover several teeth, a portion ol the calvarium
and one femur. From these fossil remains, however, Dubois has maintained,
and other authorities unanimously sustain his argument, that Pithecanthro-
pus erectus, by virtue of the size and shape of his femur, must have assumed
the erect j)ostLire. He was thus able to ualk upon both feet much in the man-
ner of his modern successors. It is also probable that m stature this primiti\'c
man was not greatly inferior to the |)reseiit human races. That he employed
his hands in the use of weapons and certain crude implements, that his life
depended mainly u|)on recourse to primitive means for protecting him-
self against the numerous enemies w hich beset his ])ath and lay in wait about
his camping places, seems more than likely, hlis time was doubtless so fully
preempted by the arduous tasks of gaining sustenance for himself, that little
remained for the more leisurely production of ancillary industries or cul-
tural pursuits.

So closely was this human creature related to his contemporaries in the
animal kingdom that he managed to hold his position among them only by
a narrow margin of superiority. This slight ascendancy was derived Irom a
dawning ingenuity w hleh t-nabled him to ecjualize the struggle by the cunning
of his hand. Thus he took advantage of [)rimitive shrewdness and contrivance
to outwit those natural antagonists which in strength and in speed far

' Osburn's chronological estimates arc followed in tliis text.

FIG. 320. RESTOKAIION Ol I'll II HC \\ I 1 1 KOPl S EKECTLS BY PROFESSOR

MCGREGOR COMPAKEH Willi III MAN AND AN 1 1 1 !■;( )!'( )1 1) SKILLS.
I. Homo Sapit-ns (Modt-rn Existing Typi'). 2. Cio-Magnon (I-"ossil Man Equal to the lligiicst Existing
Human Race). 3. Cast of Fossil Skull Found at Taglai, Australia. 4. Neanderthal Man (Lower than Any
Existing Race). ■;. Piltdown .Man (Prehistoric .Man of Sussex, England). 6. Pithecanthropus Erectus (Javan
Ape-man). 7. Skull of Javan Ape-man Restored from Cast of the Fossil by Professor McGregor. H. Skull
of Young Gorilla. 9. Skull of Adult Male Gorilla. 10. Skull of Ailull \l,ile Chimpanzee.
Male Orang-Outang. 12. Skull of Gibbon.

[736]

Skull of .Adult

FROM PRIMITIN F. TO MODERN .\F'\N 737

C'xtitck'd his liniittd |)(i\\crs. lli>\\r\cT lumianoicl Pit luiaiit liropus m;i\ have
ht'i-n m rc's[)t'ct tn thr postuix' nl his body and t hi' <_^'iUTal chaiactcT ol'his loco-
niotiiui. It IS ccTtam that he was iiiin-h l)c'l()\\ an\ nl'thc' known races of man
m the ea|)acit\ ol his l)iain easi'. It has Ih'i'ii estimated that his jjiain did not
much exeerd ()4o um. in Nohime. 'I'his is eonsiderahl\ lowiTlhan thc' human
stanchu'd lor the hrain, i)ut at the same tmu' it is eonsicU'iabK ai)o\A' the
greatest \i>hime olanx of thi- hiuher apes. His hivid and laei' and skull were
also suhhiiman, each ha\ mg a eloser resemblanee to tlu' ape than to man. It
is possil)lr and cwn prol)al)le, aeeordmfj; to tlie eonhguratioii of the brain,
that Pitlu'eant hropus liad aec|nired some mode of spet'eli, primitixc no
doubt and yet suliieient lor purposes ol rudmu'ntar\ lommunieat ion. it is
likewise probabli' that Ins lilr took lorm in tribal oruanizations, and beinti
gregarious he had leariu'd some ol those social and eeonomie ad\antages
accruing Irom li\ ing in eommunit\. He ma\ haw had some crude notion ol
tlu- di\ ision ol labor and its compensations m sharing the results.

PaLEOAN THKOI'L S Hl£IDELBERGENSIS A\I) HoMO N EA\ DEK I II Al.ENSIS.

At sonu' time earl\ in tlu' Pre-Paleolithie, eertainl\ much latt'r than t he origin
ol Pithecanthropus ere ct us, another race ol man math' its appearance and has
come to be know n as Pa li'oant hropus heidelbergensis,or man ol the Heidelberg
Race 1 Homo heidi'Ibergensis). I lis antic|uit\ is \ariously estimated at 3-,"o,o()0
to 450, ()()() years. lie too has bei'ii described as the possibk' ancestor of the
human stock. Although he mamU-sted man\ t raitsdclinitt'l\ more human than
Pithecanthropus, the lU'idelbcrg man still must hn\c been a most primitu'e
creature. It is belie\'ed, howi-\A'r, that he made use ol crude instruments both
of wood and stone Irom the \ariety ol impK'nuaits lound m the neighborhood
ol his fossil rtaiiains. But he, like Pithecanthropus, was doomed to extinction,
and no traces of him are lound which indicate his sur\i\al much beyond
the larlier stages of the Lower Paleolithic (250,000 years ago).

738 MAN

\\ hat inoiiuntous inlluciiccs, what changes in environment destroyed
these two extinct races of man arc not clear. The fate which bclcll them
both reveals phiinlx that, due cither to certain inherent defects or to the
advent of a new and superior race, they were no longer fitted to survive. It
Pithecanthropus, the Java man, was too ape-Hke in jaw and brain to be
considered as the direct ancestor of man. Paleoanthropus, the Heidelberg
man, also had definite simian aflinities both in jaw and teeth, which appear
to exclude him from the ancestral line of modern man.

Although the Heidelberg race became extinct before human progress had
made any great advance, there are many facts wfuch mdicatc that these
primitive men were the forebears of another race called Homo neandertha-
lensis or Homo primigenius which imparted a decisive impetus to the process
of human evolution. Neanderthal man has left many more traces concernnig
his activities in the way of paleolithic implements. By these it is evident that
ill the organization of his life he had made long strides forward m the
chrcction of his more modern successors. The advances of his industry and
his cultural dexclopmcnt laid the foundations for all of the stages which
progressively evoKed as the human race rose in succession through the Old
Stone Age to the Neolithic. Finally, l)y its mastery over the metals, the race
acc[uired that great constructive genius by w hich it has gradually readjusted
the surface of the earth to the greater convenience and comfort of [iian. And
yet Neanderthal man was not, in all probability, the ancestor of the modern
races. His skull was too ape-like to permit of such ancestral relation. The size
of his brain, however, and the general structure of his body were sufficiently
advanced to be in harmony with the requirements of Homo sapiens.

EoANTHROPUS Daw'SOM. 1 11 ])art Contemporaneous with both Pithecan-
thropus erectus and Homo heidelbergensis, and inhabiting the earth w ith
them, perhaps separated by great geographical distances, perhaps from time
to time in conllicl with them, a third race of man made its appearance at some

Z A

FIG. 321. Kl^STOHATlONS Ul HUlDIiLRERG AND PILTDOWN M.^N

liV PROFESSOR MCGREGOR.

,. Homo I Icidclbergensis. . and ... Reconstructions of Piltdo« n Man. 3. Restoration of Piltdo.n Skull.

[-39I

740 MAN

period in tlic lower Paleolithic. In many respects it approached nt'arertothe
type ol the modern race than eitherol t lie other two. This third ract'of the lower
Paleolithic is known as Eoanthropiis dawsoni, the i-'iltdown or dawn man.
His fossil remains w ere found in Sussex, England. By some he is regarded asthe
direct ancestor ot Homo sapiens, In others he is held to be an independent
branch ol the human lamily ol quite unknown relations to all other races.

CHARACTERISTICS ESSENTIAL TO A COMMON PROGENITI\'E STOCK

\\ ith Pithecanthropus, Heidelberg man, Eoanthropus, the Piltdow n and
Neanderthal man thus eliminated as the direct ancestors of the himian race as
it exists to-day, it must be admitted that e\ idcnce of a common progenitive
stock is entirely missing. Such a stock must ha\'e been much more generalized
in t\ [)e, resembling, lor example, some ol the more primitive extant races.
Perhaps it was not unlike the primiti\e Tasmanians, whose last surxiving
representatives passed away within the last hall century. Keith belie\es thatof
all the races ol mankind now alix'c, the aboriginals ot Australia aloiu- could
ser\e in such ancestral capacity. This common ancestor must needs produce
descendants which, on the one hand, might become the typical inhabitant
of central Africa and, on the other, the lair-haired native oi northwestern
Europe. The Australian aborigine has those intermediate and generalized
characters needed lor such an ancestral form. II it be agreed, therelore, that
he or some other primiti\e race ol like kind was the common ancestor ol the
\\ hite and black races, it is apparent that a long period ol exolution would be
necessar\ to product' such divergent descendants as the negro and the Euro-
pean. I'Or this reason, kt'ith beliexes that ihv |n'riod conct'rned in
this differentiation must ha\e \)vcn at least as long as the entire Pleistocene.
Indeed, this liardly seems sullicient lor the purpose. Such an estimation con-
sequently places the more |jrimiti\e forms of man, as Pithecanthropus,
further back than is usually conceded to be the case, it is kiith's opinion

#

4- A

E-IG. 32a. lUli NEANUhKI H Al KACil.
I. Original Tv|X- ol' Ni'anclcrtlial Race Discovered Near Dussc-ldorf in 18,-6. 2. S|)\ Skull n (Neanderthal
Race! Resembles Diisseldorf and la Cliapelle Skulls. 3. Spy Skull 1 (Neanderthal Raeei. Ironi the Collcc-
tioni'of Mr. J. l.eon \\ illiams. 4 and 4A. Reconstructions ol' Neanderthal Man by Professor McGregor.
5. Cast of Neanderthal Skull iLa Chapelle-aux Saintsi Restored by Professor McGregor with Injuries
Corrected and Teeth Replaced. 6. Cast of La Chapelle-aux-Saints Skull Discovered with Mousterian
Flint ln\|)lenu-nls in ]i)oH. -. Restoration of La Qiiina Skull ( Neanderth.il \\ oinan>.

(741)

V— '•'

3

4 A

FIG. 323. THE CRO-MAGNON RACE.
I and 2. Cro-Magnon (^alvaria. 3. Casi of Combe Capilk' Skull (1 lonio Sapiens Aurignaccnsis). The Original
Was Found Near Monlfirrand, France. 4 and 4A. Reconstructions of Cro-Magnon Man by Professor
McGregor. 5 and 6. Homo Sapiens Cro-Magnonensis Found at Les Eyzics in 1868. 7. Calvarium of Cro-
Magnon Race. 8. Restoration of Cro-Magnon Skull from .1 Study of Other Skulls of This Race. (). Replica ol
Cro-Magnon (Woman) Skull and Mandible.

[742]

FROM PRIMITI\E TO MODERN MAN 743

that the Java man maj' represent a Miocene rather than a Pliocene stage in

human evolution.

PKIMITIXE MAX AS REN'EALED in' IllE WORK OF HIS HANDS

However difficult the prohlcms of man's anceslrx , however fragmentary
the skeletal proofs of his anticiuity,one ])hase of his prehistoric existence offers
a fertile iicid for research in the endeavor to discern his lineaments so greatly
dimmed by the past. The use of certain extracoipoix'al agencies must have
been the secret of his fust real successes in the conquest of tlu' earth. Ashedrst
began to manifest the attributes of man through the arts and industries of
manual contrivance, as he passed slowly from one stage to the next, what
record of himself has he left in the way of tlu' implements by means of which
he achieved his ultimate successes?

PKiMnr\ H Man — His Cultural Pjl\ses

Man's obscure beginnings are all but lost in the great geological ages
which lie behind liis recorded history. To eomi^rehcnd this vast extent of
time, whether it be something more or less than a million \ ears, is enough to
baffle the most facile imagination. Little wonder that such insignificant traces
of his remains have yet \x\-n brought to light. Doubtless when the search
becomes more extensive and more thoroughly organized, fiuther signs of his
prmiiti\e structure and activities will be discovered.

Quite as important as the morphological remains of prehistoric man are
those works of his hand, w hich have been slowly accumulating as tiie result
of untiring patience and geological research. It is now possible to classify
this great body of evidence in such a way as to show the existence of certain
industrial and cultural stages through which man has passed prior to his
actual historical period. That he began as a nomadic hunter, slowly acquired
the crude essentials of manufacture, gradually developed the dexterity and

JN^

/

Courlisy, American Museum nf .Wilurtil History

FIG. 324. STONE IMPLEMENTS REPRESENTING THE SE\'EHAL STAGES OF
PALEOLITHIC CULTURE FROM TIIK CRIDEST lO 1IIF MOST REFINED PHASES
OF THE OLD STONE AGE.

[744]

FROM PRIMITI\ F, TO MODFRN MAN 745

csthftic scnsi' ol till' artist, and liiiall\ Icanu'd the ]:)rarticc'.s ol agricultuiv,
inori' or K'ss dilinitilx set tlu- indiistnal torniula accordin"; to wliicli lie
dc'xi'lopc'd inipk'iiU'iits adapted to eaili ol tlu-st' pursuits. His j^ast has tluTi'-
toie been subdixick'd Into periods eliaraeteri/ed b\ the prest'iiee ol imple-
ments mdieatmg these spiciali/A'd aeti\ities. The seNcral periods hear the
names ol f-ri'iieh stations or towns near whieh the diseo\-eries ol the imph--
meiits ha\ e bii'ii niaile. Here tlu' Ireiu'h areheologists ha\'e so sueeesstull\'
dc'N'oted tlu'inseUes to the eilort ol hringinii order out ol ehaos that thev have
established a ehroiiolofiy whieh is aeeepted as a workinij; basis ol the evolu-
tional j:)rogress ol man's aeti\it\ in the lonp j)eriods ol his |)rehistoric
existence.

CL LTLKAL PlRSllTS OF THE MEN BEFORE THE OLD STONE AGE

Man's lirst great ejjoeh on earth was the Paleolithic or the Old Stone
Age. In this era, whieh began at some time m the Fust Interglacial Period,
ins sole impK'iiients we're those (K'xised liom Hint or other kinds ol stones,
wood, ear\ed ixorv and bone. Two subdivisions ol this age are recognized in
the Lowi'r Paleolithic and the I ppt'r Pak'olithic. The Old Stone Age was
lollowed by the ,\c(ililhic which began m postglacial tmu'S, and then eame
the productiN'i' transitional eras which led rapidl\ up to tin- thresholds of
history through the Bronze and Iron Ages.

Pre-Paleolithic .Mi-.\. Long Ix'Tore the beginning of tlu- Old Stone
Age, at sonu' t ime during the First Glacial Period (beginning 1 ,o()(),()(){) years
ago), the oldest known representative ol human kind had li\ed upon the
earth. It was his lossil ix'mams which Dr. Fugt'ii Dubois discoxered in Ja\'a
that led to the recognition ol this I rinil race, now technically known as
Pithecanthropus erectus. Little ma\ be said ol his cultural de\ elo])mcnt,
although some authorities be'lie\'e that he made use ol the \ e'r\ primitu'e
implements called eoliths.

746

MAN

CULTURAL STAGES OF THE OLD STONE AGE

The Upper and Lower Paleolitliie periods are further subdi\ided aecord-
ing as the evohition of manual dexterity makes itseli apparent m the imple-

l-rom QufiTl. J. Gcolog. 5c, Ixix, Plate xvii

FIG. 325. "eoliths" from PILTDOWN, SUSSEX, SUPPOSED TO REPRESENT
THE EARLIEST STONE IMPLEMENTS, SO CRUDE IN APPEARANCE AS TO BE
FREQUENTLY TERMED "ACCIDENTAL FORMS."

ments employed by man. His instrununtal e(|uipnuMit was at first extremely
simple and erude. Biit in tinu' there eame an inereasing eomplexity and mueh
refinement in all of iiis tools. These Implements elearly indicate a
slow but progressive growth in the application of extracorporeal agents which
at length made him master of the inanimate' and li\ing world.

1-ROM I^IUMI ri\n TO MODERN MAN 747

Pkk-Ciifiilan Cii/iLKAL SiAGK. Tlu' carlicst period in liic Lower
I-*ali'olit liK', llu- rn-(.l.)cllvan ( beginning -00,000 years ago), iseharaeterizecl hv
the use ol most simple aiul primiti\e stone implements. The eliase is repre-
sented m this period ahnost e\ehisi\el\- 1)\ the knife (couteau ). War, apparently,
was not among man's then highly organized pastinu-s lor he appears to have
possessed none ol those implements whieh later beeame sueh eonspicuous
produets ol his handiwork and so essential to his existenee. Mis Hint knife was
erudi', but sullieieiit with his other ec|iially erude eombinations of stone and
Stick to I urnish him a slight balanee ol pow er m d<>aling w ith his inlrahuman
com pt-ti tors, to gain his daily lood, ami to establish that footing from whieh he
rose step by step. In this pt'riod he had also uut'iited for his industrial and
domestic purposes a Hint scraper Iracloir), a planing tool igrattoir), a drill
or borer ( percoir) and a stoiu' hammer ( [)t"rcuteur ). Nothing among his [jrim-
iti\e implements appears to ha\e answered llu' purposes of art or artistic
production, nor had he yet learned the practice ol using bone for the pre|)ara-
tion ol instruments applicable eitlu'r m the- t'hase or m domestic industries.

I he lile ol this Pre-Clu'llean man was that ol the \agrant hunter, li\ ing
w ithout the protection ol habitation and thus expost'd to t he devastations of
the great carmxores which sti'althil\ lollowcd his wanderings. There is little
to show that he had acc|uired sulhcieiit construct ixc mgtnuity to protect him-
self against these great i^rt'dacious marauders which stalked him in his
marches by day and lay in wait on the outt'r edges ol his encampments to
find him an eas\ |)i'e\ as he sh'pt b\ night. The less lortunate nu'inbers of his
tribes were easily accessible to tlu' night prow lers waiting only lor the dark-
ness to assist them in the capture ol tluir human c|uarr\. His slow and inelas-
tic imagination recjuired ages to show him that he held within his own hands
the |)owfr to re|)i-l and siibiugati' tlu' beasts ol prey which almost with
impiimt\ made ra\'ages u|)on him 111 his unprotected state. I low long lie
struggled upon this low le\el of intelligence, li\ing a hand-to-mouth existence,

CouTtisy, .American Museum oj .\aHtrtil History

FIG. 326. CONTRASTS BETWEEN IMPLEMENTS OF THE PALEOLITHIC

AND NEOLITHIC AGES.

Upper Row, Paleolithic, i. Hand Ax. 2. Dagger. 3. Scraper.

Lower Row, Neolithic, i. Ax and Hammer with Perforation for Shaft. 2. Partially Polished Ax. 3. Saw.
4. Dagger. 5. Knife. 6. Arrow Point.

[-48I

FROM PRIMITIVE TO MODERN MAN 749

passing his days in a life not unlike other animals of field and forest, with
little recollection of the happenings of yesterday and almost no thought for
the morrow, a creature w hose mental processes shut in so closely behind him
as almost to exclude the experience of the past as a teacher for his future,
cannot be estimated in definite epochs of time. There was little inherent in his
psychological processes that seemed to give promise of further expansive
development in his adaptations. Doubtless some critical incident, like the
discovery of fire and its uses, may have furnished a new incentive for his
advance. A great change in climate with increasing cold may have forced him
into greater physical exertions as a more assiduous hunter of animals for the
warmth to be had from their protecting skins. Long winter seasons when game
was scarce may have taught the wisdom of storing his supply of provisions and
thus aroused in his imagination some conception of the advantages in thought
for the future.

Heidelberg Man iPre-Cbellean). At some time in the Second Inter-
glacial Period (beginning about 700,000 years ago) a type of Paleolithic man
appeared who seemed possessed perhaps of a more progressive spirit and a
definitely increased capacity for adaptation to varying conditions in his
environment. His cultural characteristics during the later stages of his slow-
development merged into those typical of the Pre-Chellean. What relation
this Heidelberg race of men bore to those early apc-Iike humans of the
Pithecanthropus variety is not yet understood. It is probable that both
were offshoots of the same common progenitive stock, and thus only distantly
related. The Heidelberg men were the first human race to inhabit western
Europe. They made their appearance in northern Germany approximately
350,000 jears ago, and lived in the midst of an imposing mammalian fauna,
for the most part of northern aspect. Among these were the lion, the wolf,
the bear, the deer and the w ild boar, w hile on the plains lived the Etruscan
rhinoceros, the Mosbach horse and the ancient elephant. This race, known

750

MAN

as Paleoanthropus hcidclbergensis, although possessed of a low psychic
organization shmvccl a certain ad\ance over its earlier human predecessors.
The Heidelberg man, moreover, appears to have been the precurscr, perhaps

nurifittacian

FIG. 32-

MngcialC'Mi'U.M

CUcllc

EarlxlAclicuUun

Azili

Mou,steriat*

Courtesy, American Museum of Natural History

THE EVOLUTION OF THE LANCE POINT THROl GH THE SEVERAL
STAGES OF THE OLD STONE AGE.

the actual progenitor, ol a race which was later to show pronounced signs of
progress. This was the great Neanderthal race, and because of his pos-
sible ancestral relation to it, Heidelberg man is olten spoken of as
Prc-Neandert haloid.

The actual acKances made b\' Paleoanthr()]:)us are dillicult io trace
in those relics indicating his powers in handicralt. lie j)rol)abIy was a

FROM PRIMITIXE TO MODERN MAN 751

most capable hunter and lairly cIVcctLial in piotcctinji hiniscll I'loni his
natural tMU'niies. 1 liat he- ncNcr rt'arhfcl a hi<i;h staf;:c of intclhgcncc is evident.
In the long period ot his existence he may ha\H' been slowly evoKing until
at length It was possible lor linn to give rise to a more intellectually able race
w hieh has lelt a remarkal)li' record.

Piltdoun \f(n\. \\ hile this slow human acKance was taking place,
there came into western Europe another raw ol Pre-Chcllean men, some time
probably in the First Interglacial Period. This species of mankind is known
as Eoanlbri)})us, the dawn man of Piltdown, whose antic|uit\ is placed by
most authorities at one hundred thousand and more recently (Osborn) at one
million years ago. It is probable that he was contt'mporaiu'ous with the
Heidelberg man, li\ing along with him for a great period ol'timc, perhapsoften
sharing with him nian\ ol'tlu' characteristics of his industry and culture.

There are good reasons to bilicxc that the industries both of Eoanthro-
pus, the Piltdown man, and of the Pre-Neanderthaloid Heidelberg race
became Pre-Chellean in their ultimate period. Both of these races made use
of chance and accidental forms of Hint and stone, retouching them to a
limited extent in such a manner as to give point to the tool or else to fashion
a crude rasping surface. One of the most important of thi'st' prehistoric
implements, the so-called caiij) dc ])()ign, or hand-ax, was de\elo|ied during
these Pre-Chellean times. Additions to the list of the Pre-Chellean equip-
ment lor industrial and domestic purposes were the knife icouteau), the
hammer stone (i)ercuteur) and perhaps the throwing stone (pierre de jet),
in their \erv primitn t'liess these instruments reveal the first experimental
stages in the de\ilopment ol implements.

The daw n man ol Piltdown, like his 1 leidelbcrg contemporary, was still
a nomad. He wandered from station to station, pursuing the track of the
great game upon w hich he depended for his food. I le ii\ed near the course of
the great ri\ X'rs, showing no tendency toward the establishment of i)ermanent

752 MAN

abode. He was a restless migrant following tlic dictates of the seasons almost
as instinctively as did the migratory birds and beasts. As yet he had not
learned those secrets \\ hich later enabled him to stand against tlie \icissitudes

FIG. 328. MANUFACTURING FLINTS, THE RIGHT HAND CLIPPING. I 111 LEFT
HAND HOLDING, ILLUSTRATING AN IMPORTANT INFLUENCE IN THE DE\ELOP-
MENT OF RIGHT HANDEDNESS.

of climate. His aec|insit i\e proclix ities were still m the crude. I he idea which
ga\e hiin the sell-assurance to stake out his elaini, to assert an inalienable
right to his ow n angle olearth was also 111 I'mbrx onic state. Indeed, the ioun-
dations oi that possessive sensedestined to becnnieoncDt thechiel characteris-
tics of the human race, to \)v at length tlu' ruling passion ol humanitx, had
only been laid down in their most simph' instmcti\e rudiments.

Chellean AND AcHEULEAN Stages. The iicxt or Chcllcciu l\rui(l had
an aeti\e dexelopincnt which adapti'd it to tlu' i"o\ing li\es ot the bold hun-
ters \\ ho liNc'tl in the ojicn and w host' t'litn'c mdustr\ was produced m re-

FROM I^RIMI'IINE TO MODERN MAN

753

spouse to tlic needs of the tliasc. As the Pre-Chellean period drew to its close
earl\ in the Second Inter^laeial, e\ idenees of" another race became apjjarent
in westi'in Euroj^e. This new annal was the ScumUrtbul mui} or I lomo pri-

FIG. 32g. MAM FACTL KING I LIMS, THE RIGHT HAND CIJPI'ING, THE LEFT
HOLDING, ILLUSTRATING AN IMPORTANT IM-LUENCE IN THE DE\ ELOPMENT
or H1,GH1 HANDEDNESS.

mliiimus. His race in its first rapid dexclopment passed through a cultural
j)hase somewhat in ad\ anee of the I leick'lherg, for his progress is show n i)y a
great increase and a coiisick'rable rehnement in the small instrunuMits tor-
mcrl\ employed. Such impioNcnient particularly atlected the cou]) dc jxntin
whiih, in addition to its man\ and \aried forms, was now equipj^ed w ith a
sharp cutting blade in the mamier of a chisel or adz-like tool lor fashioning
wooden implements. The flint instruments of the next stage belong to
what is recognized as the Aclwulcan Period. Mint points to form darts and
spearheads were then added to the equipment of the chase.

754 MAN

s\I(}UsU'riun Sta^e. It was not, however, until some time during the
fourth ghieiation (al)()ut i 50,000 years ago) that the Neanderthal raee, pass-
ing through its remarkable Mouslcrian eultural phase, took a decisi\c step
forward, at once so eritieal, so epoch-making that the importance of its lar-
reaching psychological efTccts has scarcely as yet been fidly ap]>reciated.
Tills profitable step — and it may well l)e called such — has made itself felt
with increasing force upon all the subsequent development of the human
race. It actually led the Neanderthal man to the threshold of a new idea.
The ultimate expansion of this new idea was to become one of the kexstoncs
of all social organization, it not ihv fundamental pnncijjie m the upbuilding of
human society. This great step forward gave the Mousterian the first real
conception of jjroperty holding. It implanted in his mind that germ out of
which grew the rights of possession handed down by him as an heirloom to
all the remainder of his race and to other races of mankind.

Development 0/ ibe Ciince])li(in 0/ Pr()])erly I loldu}!^. The jihysical basis
of the conception of property holding de\eloped trom the tact that the
Mousterian Neanderthal became a cave-dweller. He sought shelter from the
elements in the rude dwellings fashioned by nature. W h\ he had not seen
the advantages of such protection long before this late period m his progress
seems c|uite remarkable, and \ ct the explanation ma\ not Ix' tar to seek.
Those caves \\hich he might haxc found to his liking or suited to his con-
venience were already inhal)ited by such dangerous tenants as the ca\e-
lion and leopard, the hyena, the wolf, the great ea\e-bear, and pirhaps
even the dread machacrodus or saber-toothed tiger. All of these were his
nat lira! enemit's tor I lu' most part suecesstLiI ones — with w ho in he could only
at the e\|)ensc of greatest risk dispute the right ol wax, to say nothing of the
right of possession. Through all tlu' long periods of his upward progress, he
had not yet learned the nutans nor had his hands lashioned tlu' implements
by which he could contend w ith these beasts of j)re\ on an\ thing like an cc|ual

FROM PRIMITIX E TO MODERN MAN

loo

footinii. Tlu'V took from him at will and his ri'taliatlon was jjotli IVcblc and
ineflcctiial. They, rather than \\v, were still the masters of the situation. This
condition of ailairs was destimd to eontuuie until some critical discovery,

«.4

Courtesy, Amtrican Museum of Natural History

FIG. 330. IMFLLMEN rS AND ORNAMENTS TYPICAL OF UPPER PALEOLITHIC AGE.
I. Knife Bl;iclc or Spc.-ir-point of Flint. 2. Knife or Etching Tool of Flint. 3. Planing Tool of Flint. 4. I lar-
poon Point of Bone. 5. Lance Point of Bone. 6. Pendants of Elk Teeth. 7. Beads of Shell. 8. Bone Fragment
with Partially Etched I lorse. 9. Bone Fr.igment with Traces of Geometric Design.

some happy chance revealed a new instrument or a new- method w hose dead-
liness at leni^th plaei'd m human hands the means which ga\e man his ulti-
mate supremacy owv tluse crt'atures w ho had so lon^ terrorizt'd and preyed
up(jn him. That this new agent was the work, ol his hands can scarcely I)e
questioned. Some modihcation ol the old Hint weapons or the shaping oi an
implement eapabli' ol destro\ing the marauders provided man with such a
margin ol saiet\' that he no longer came oil second best in his contact with
Ins unrelenting assailants. Whether this new agency was a combination of
the use' ol lire with a more elheient weapon, or some other means, the lact
rt'mams that Ni-andeithal man ultimateK' dro\-e the hostile carni\'ores out ol

756 MAN

the caves. These he C()\etecl for liimsclf and there in lime established his
own d\venin<i places. This slow and hazardous unclertakin<^ undoubtedly
reciuired a hard\ eourai^e and an unfaltering persistency.

But e\'en a hard-louuht contest ol this knid could not lail to have a
signilicant psychological inlhience in the linal outcome. Once he had gained
the right of ownership, this preliminary struggle all the more emphasized his
sense of possession. It doubtless did much also to stimulate those acquisitive
elements in his make-up which laid tln' foundation of the incentives and
desires for conquest. Since Mousterian times, throughout his prehistory and
historx , man has spent much oi his etiort and energy m evi^loitmg, m codi-
fying, in legislating statutes to justify and regulate this last new develop-
ment ol his possessive instinct. Out of such rights and laws of possession
have grow II the inllucnces contnilling all ol his ecDiiomic and political organi-
zation. Much ol his moral code has l)ccn built up around tliesr rights. Just as
they have alforded the justification for the organi/ation of states and empires,
so the right to have and to hold Ix'came the go\crning principle in the life of
the indi\idual. The\- have been the incenti\c' underlying competition and
success, the motive of pillage and plunder, the inducement lor the aggressions
of peace and war. In a word, while this expanded sense of j^ossession has
become the essential element in all the acliie\ cmeiits of mankind, it is no less
the instigator of much of the woe and maiad|ustment m the race.

The Communal Life of Mouslcrian Ncandcrlbal Man. The Neanderthal
of Mousterian times ap|)ears to ha\e li\ed in communities. Such communal
life had its eflects uj^on social organization, upon the ck'\elopment oi lan-
guage, upon the expansKui ol imagination leading to the establishment of
tradition as well as to tribal i'i\alr\ and mdnidual competition. I he self-
assertiveness which must haxc resulted lidin the realization on liic part of
man that he iiad linall\ gained the uppt'r hand in man\ details over the
natural world caused him to change.' his altitude from that ol a lugitne to

FROM PRIMITIX F TO MODERN MAN 757

that of a c'onqiKTor. It was doubtless Ironi this positive scIl-fccling that there
arose most ol his more e\paiisi\e ideas whose imiltipheation easily led on
into the realm ol laney and brought hnn many illusional mterprt'tations
eoncerning the workings of nature. The>- also stimulated the beginnings of
religious beliel and ga\ e him his llrst ineenti\es for the establishment of
customs which mamlested themseKes in such complex ceremonial rites as
those connected witli burial and ])erhaps with sacrifice.

In their remarkably e\hausti\e studies concernmg the mentality of
anthropoids, both Professor riiorndikc and Pn-fessor \ erkes were struck
by the great length of time which is necessary for one of these animals to
grasp a new idea. Tlu' apes in their capacit\ to learn seem vastl\ inferior to
men, although the learning process appears to be essentiall\ similar. There
can be no possible dis|)ute concerning this contrast as between modern man
and e\"en tlu' highest ajjcs. But in the retrospect, does it not seem clear that
])rimiti\(.' man, in his slow e\(>King, reciuired an astoundmgly long time to
grasp a single new idea — great jjcriods of geological time, for example, to
learn how to protect liimsell from the wild beasts or to sharpt'n his Hint
implements? Indeed, are not his modern successors in a general way li\ing
up to this rt'putation lor the slow acquisition of really new ideas?

Implements nj Mnushrian Wandeiihal Man. Mousterian industry in
Hint, however dillerent it may have been m its outward exjjression, still had
all the aj:)pearance of a direct e\-ohition from Acheulean culture'. In some
instances there is a distinct improNcment o\er the ideas of the older culture,
but again a decline or even sujjpression in some of its most eflectne instru-
ments. The same ideas appear to be at work upon the same materials.
-Mousterian aims, howe\'er, were considerablx motlilied b\ the new mode of
living, by the lessened physical resistance w hich a better sheltered life would
aflord. The making of clothing undoubtedly grew out of the conditions of
this more protected type of lili' w Inch jjroduced a people less inured to the

-58 MAN

elements than the hardy races which lived in the open. The eflccts dI this
need lor elothintz; made themselves felt not only in indiistry, but also in
the production of imj:)Ienu'nts necessary to such inchistry. The crowding inci-
dent to the sheltered dwelling in tlie grottoes and eaves also had its deleterious
inlluences upon the ph\sical w ell-l)eing of the Mousterians. Undoubtedly
the ravages of infection and contagion became much more potent, and
disease as well as imperfect hygiene had o]:)portunit\ to go their full length
in j)roducing inroads u]:)on this race.

End of the Lower Paleolithic Period. Little was added to instru-
mental perfection during the Mousterian |)eriod ol culture. The anij) de
poign or liand-a\, so valuable an instrument in earlier cultural ]jeriods, had
fallen somewhat into decadence, although the chopi:)er, the planing tool,
the drill or borer, the knife and scraper were still rt'tained. This last especially
had adapted itself to the new needs of their social conditions for it appears
in many forms, with a cur\ed edge, a saw edge, a double edge, a beaked
edge, or having numerous edges. The hand-stone and the hammer-stone were
still in theii- former Acheulcan state, all of these being adapted to industrial
purposes. No distinctlx new ideas in tlu' implements of war and chase ha\c
yet mack' tluir appearance, the spearlu'ad, tlu' throwing stone and the knile
still being the chief weapons emplo\ ed during this period.

Whatever insidious inlluences might ha\-e been at work, in course of
time tlu- jMousterian culture began to show signs of a steady deterioration.
The predominance which the Neanderthal had exhibited as a race in Lower
Paleolithic limes was distinctl\ on the wane as this ])eriod approached
its end.

The Upper Paleolithic and Cro-NL\gnon Max. A profound change
finally appears to have come over the character of the inhabitants of western
Europe. For some reason the Neanderthal race disa])])eared to bi' leplaced by
another race ol' man, the Cro-Magnon. 'I'his, without c|uestion, was the

FROM PRIMITIX F. TO MODERN MAN 759

rrplacniUMit ol a Iowit rare by owv dI miK'li hi>^r|uT organization. Tlu' Ncan-
cU'i'tlial was (listnu-tl\ on a low rr plane than any now rxistni^^ luinian tyjjc,
w hik' tlu' Cro-i\Ia<inon ranks hi}j;h anionic the races of mankind in intellectual
(k'wlopnient and known capacities ol production, lit' heloiifis to the sjjccie.s
Homo sapiens, the same species ol man that has made modern history.
\\v was dominant throughout the Upper l-'aleolithic and passed through
many interestinii; phases ol cultural dt'\ t'iopmenl, characterized, to he sure,
by the dcNelopmcnt of stone instruments, making him, tlu'refore, still a
man of tlu' Old Stone Age. But he too, like the Mousterian Ni'anderthal,
ultimatel\ bt'gan to decliiu' until his placi' was linall\- usurped l:)\ the new-
comers who niort' probal)l\ wxac the direct ancestors of the modern Euro-
pean. The ad\ t'lit ol the Cro-lMagnon into w estern Europe is usually assigned
to the end ol the lourth glaciation or tlu' beginning ol j)ost-glacial time. The
duration ol this period, as estimated b\ most authorities, is jjlaced between
25,000 and 30,000 years. It ma\ , in this light, be t'oncluded that I lomo sapiens
has been an inhabitant ol the European continent lor about 30,000 years.

The Cro-Magnon race, like its predecessors in Lower Paleolithic times,
iiad its own wt'll-cklined cultural periods. Industrial de\elopment expressed
itself in inno\ations, perlections and impro\ cnn'iits in the Hint instruments
prcNiously t'liiployed in earlu-r periods.

The Cro-Magnon as CfiiKjucrnr (if the Neanderthal Man. Professor Osborn,
who has carclully assembled and anal\zed the evidence concerning the Cro-
Magnon in\asion ol Euro|)e, gives a most illuminating picture ol theevents
which must ha\ e transpiri'd in the re|)lacement ol the old Neanderthal race i)\'
these Cro-Magnon newfonu'rs. Those who would ha\e the details in luli are
referred to j-'rofessor Osborn's chapter on The Main keatures of the UpjXT
l-'aleolithic in his "Men of the Old Stone Age." In substance, the evidence
seems to show that the Cro-Magnons brought with them a t \ pe of industrv
which IS ti-chnicall\ known as Aurignacian. At this time the Neanderthals,

-6o MAN

still in the possession of their country, were practising their waning Mouster-
ian industries. The two types of cultural activity, therefore, came in contact
as these two races met, and consequently show the inlluence of some inter-
mixture. It should be observed, however, that this intermixture was strictly
confined to the industries themselves and did not involve either of the two
races of man. Even in their burial customs the Cro-Magnons followed the
ceremonies of the Neanderthals, choosing the same kind of burial site,
interring the dead with implements of industry and warfare.

The result of the encounter between Neanderthal and Cro-Magnon was
that of a superior people with a much inferior one. Probably possessed of the
bow and arrow, with other advantages for warfare, the Cro-Magnon had
little difficulty in the conquest of a people already reduced in physical resist-
ance both by disease and the severe climatic conditions of the Fourth
Glacial Period (beginning 70,000 years ago). This dispossession of the
Mousterian must have been complete, for in the Cro-Magnon race there is
no sign of such admixture as often occurs when a victorious nation, having
completely annihilated all of its male opponents, still retained man}- of the
women in the households of the conquering warriors. Men and women alike
appear to have shared this extermination of the Neanderthal race. It was
probabl\ the increased brain power of the Cro-Magnon which caused this
great change to sweep over western Europe at the beginning of post-glacial
times. This view is based on the appearance of a large brain case of this race
and the development of an almost modern forehead and forebrain.

Cro-Magnon Periods 0/ Art and Industry. The Cro-Magnons were a
race which developed in Asia but seem to ha\ e had no connection of an
ancestral kind with the Neanderthals. They possessed a brain capable of
more complex ideas, greater comprehension, more reasoning powers, a wider,
more facile imagination. Abo\e all, they were endowed with a highly artistic
sense which had not been present in any of the previous races of man. 1 ndeed.

FROM PR1\1IT1\ F. TO MODERN MAN -6i

they seem to ha\c possessed a cerebral capacity which was nearly if not
quite equal to that of modern man. They were capable of advanced education
and had strongly developed esthetic as well as religious feelings. Their
society was highly different iated along the lines of capacity and talent for
work Their artistic productions as shown in the mural decorations in their
caves were of such excellence as to place them among the truly great achieve-
ments of the human kind. The Aurignacian culture established by the advent
of the Cro-Magnon race in southwestern Europe ultimately succeeded the
Mousterian industry. It introduced the art of f^ngraving and sculpture,
together with a greater refinement in all of the instruments employed during
the previous cultural periods.

A comparison of the Aurignacian period with the stages which had
gone before emphasizes one striking fact. In the pursuits of industry and
domestic life, little in the way of innovation was added by the Cro-Magnon
race. It adapted and perfected what the Mousterians had used with
greater or less advantage. But what it did add, neither the Mousterian nor
any other preceding period possessed, namely, tools and implements for
sculpture and engraving. Chief among these were the drill, engraver, etcher,
carving chisel, mortar, hammer-stone and polisher, all of which were inti-
mately connected with the artistic activities of this new and highly intel-
lectual race of man. The Cro-Magnon also passed through certain cultural
phases which show the same general tendencies observed in previous races.
As in the first flush of any renaissance, so with the awakening of a new race,
the initial period is usually the most fertile in productive ingenuity. Then
comes the gradual culmination as it did m the Solutrean Period which was the
acme of achievement in the Hint industry. Declining greatness followed next
in the Magdalenian Age which brought the closing stage of Cro-Magnon
culture. The same familiar cycle of juvenescence, maturity and decline which
characterized the development of earlier races did not fail to apply its

762 MAN

inevitable fornuila to the Cro-Magnon. For just as Neanderthal and Pre-
Neanderthaloid man passed througli suecessive periods of eulturc which
began with the primiti\e Pre-Chcllean, advanced to the Aeheulean, reached
its climax and began to dechne in Mousterian, so the Cro-Magnon saw the
beginnings of his ascendancy in the Aurignacian period w hen he fnst intro-
duced the art of engraving, drawing and scLilpturnig annual lorms. His
culture and industr\- were still dictated by a hfe devoted to the chase and
conditioned by such pn^tection as might be afforded by grottoes and similar
natural shelters.

Cro-Magnon Industry, Its Rise and Decline. In the next succeeding
period the Cro-Magnon reached the zenith of his industrial supremacy.
The Solutrean was the high noon of his cultural achievement just as the
Middle Mousterian was for the Neanderthal. In this era the Hint industry
attained its culminating stage but its llourishing activities soon began to
wane. Thrt)ugh the Magdalenian all of tiie artistic and industrial develop-
ment sank slowly toward the horizon of its disappearance. At length in the
A/.ilian Period the last survivors of the greatest race in the Old Stone Age,
senescent in their industries, decadent in their art, saw the setting of the Cro-
Magnon sun and the passing of their kind into the darkness.

Charueterislics oj Cro-Magnon Art. Many \icissitudes beset the Cro-
Magnon industries due to inlluences of trade mvasions and new-
inventions. But in their art they revealed one continuous cNolution and
sustained de\elo|)ment. An impressi\e IVviture about Aurignacian art is the
fact that it seems to ha\e escaped that pi'riod of infantilism which is almost
universally observed in the artistic de\elo|)ment of prnnitive races. The Cro-
Magnon first manifests his artistic effort in a period ol virile youth. His art
passed directly into a stage of relatixc maturit\ based upon his keen appre-
ciations of the animate world with which he was in constant contact. The
Aurignacians possessed a true sense ol |)r()portion and of beauty which

FROM l^KIMIl l\ 1£ TO MODERN MAN 763

appears to have been theirs as if l)y instinct. The treasures of their art gal-
leries upon the walls of the ancient caves, their remarkable drawings, sculp-
tures and paintings fully warrant the distinction wliieli has been conferred
u])on tlu'ni in the title oi Paleolithic Greeks.

The paleolithic artist resembled both the Greeks and the Egyptians In
that he was not content w ith plain, uncolored sculpture. Like them, he had
recourse to panituig his relicts whether they were of the bison, the horse, the
deer or the grt-at mammoths. It was his wont to color such sculptures with a
\iok'l tint, w hich may have been a compound ol manganese, or with a red
ochre as well as certain other pigments concerning whose use he already
seemed familiar. \\ hat characterized the Cro-.Magnon's art more than all
else were his close powers of observation and his accuracy of reproducing
w hat he saw in the animal forms w hich he chose to depict. The relative sim-
plicity of his technical execution depended upon the emplo\ment of the
fewest possible lines and the boldest of strokes; these suggested more than
they i)()rtra\ ed. It was this very simplicity which ga\e his art its appearance
of maturity from the first. It enabled him to express his esthetic feelings with
more telling effect than if he had dej)ended upon an infinite amount of detail.
To this accuracy of observation and simplicit\- of execution he imparted a
third great quality which makes his art live in a class well up to the standards
of later and higher periods of artistic dewlopment. This third element wiis
the sense of motion and acti\ity, particularly of locomotion, with which he
endowed the animals car\ed upon the walls of his caverns, upon bone or
ivory, or merely draw n in simplest outline. Perhaps it is safe to say that few,
even with all of the refinements of technical procc"dure, have surpassed him
in that infusion of \italit\ w hich signalizes his art.

Reasons far the Development 0/ Aurijinaeian Art. Although it is clear
that even before the appearance of the Cro-.Magnon race the much simpler
Mousterian man had shown the first teiidencv toward pirmanencv of abode

764 MAN

and the ostahlishnicnt of property rights, it is nc\crthclc'ss true that even
these Upper Paleohthie men for the most part were still nomaclie hunters.
Why, then, cfici they in the dark reeesses of their ea\erns resort to these
artistic activities? W hat meentnes led them to their earvinji upon bone and
ivory? These could scarcely be the meaningless dnersions which helped to
pass unoccupied iiours when not engaged in hunt or combat. Their artistic
efforts and productions assuredly had some more serious and pertinent ob|ect
in their lives than this.

Many h\ |:)oth(.ses have been advanced to exphiin this remarkable
outburst of artistic enthusiasm and devotion in these early times. One \ lew
holds tliat the caxernous art galleries were the schools which contained the
models ol artistic productions, the copies ol which were much desired by
many members oi the race. The caves, therelore, where these mural decora-
tions were made, served as the workshops of copyists who would reproduce
in bone or stone facsimiles of the actual artistic performances of the Cro-
Magnon artists. Such reproductions gave a w ider distribution to their art
among the scattered communities. This \iew, however, has but little to
recommend its acceptance. It seems probable that some much more telling
motive incited the arduous ellorts wIikIi the artistic mural productions
demanded. In the histor\' ol primitnc races whose records are a\ailal)U' lor
study, it has repeatedix occurred that drawing and design Uiwc a spt'cial
signilicance w ith reference to the act ual maintenaiu-e ol hie. The Australians,
for example, draw upon the ground pictures ol the animals the\ use lor
food. Sitting in a sc|uattmg position about thesi- pictures, they j)erlorm
certain incantations which the\' belie\o will insure a pleiitilul supply ol what
they need. The American Indians are in the hal)it of carving images of
animals and also of drawing designs representing ram. In the presence ol
these emblems tlu'\ pi'ilorm religious cxrt'monies and devoutlx belicM' that
they ma\ tiius secure abundant liar\ests and success in tlu'ir hunting expedi-

FROM PRIMITIVE TO MODERN MAN 765

tions. Iina.m'S and ])K'tur(.'s arc (_'ssc'ntial tcaturcs in tlu'sc pii)|)it iator\ vvw-
iiionit's, a sort ot mayic talisman by means ol w hich to exercise an mlluencc
over those annuals whuli ser\(,' lor loocl.

It IS not necessary, ho\\f\t'r, to pass so lar hack as the preiiistory ol the
Old Stone Aij;e, or even to iiucsti^ate tlu' snperstitions ol |)c'0|)le still rt'inain-
inp in the most primitne stage ot ethnical aci\ ancement, to detect the work-
ing ot this superstition. It \\as not so long ago that tlu' j)ictiire ot a man was
believed to be an actual iinanation Irom him and that the possessor of such
a picture must exert powt'r ()\er the person whose prest'iice might thus
mysteriously be coniured u|). Only a tew centuries ago this was a common
jjclu't, and many leariu'd iiidges condemned both men and wonu'ii tockvith on
the evidence ot their having possessed images or |)Ktures of people the\ were
accused ot bewitching. It is not at all unlikt'l\ that there are still to be tound
to-day in Najiles or Sicilx certain sorcerers w ho, tor a stipulated price, will
undertake to destroy an\ undesirabk' indi\idual bv tlu' ri'latively simple
executionarx' method ot sticking pins into the wax image ot the person thus
proscribed, or b\ melting the Image bi'tore a slow lire. In this light it may be
understood wh\- the .Australian nalufs and American Indians set such
store !)\ the pictorial representation ot those elements in nature which con-
tribute to their stock ot loodstulls. It is also to \k- noted that the .Aurignacian
and III tact all ot the Cro-Magnon art tt'iuls to portray those forms ot ani-
mals which were emplo\ ed lor food, while those animals not so emploxed arc
cons|)icuous by their absence trom thest' artistic reproductions. \\ hile this
mav not \k' accepted as the linal solution of that question — why did Paleo-
lithic man resort to art? it ma\ ne\ erthele.ss otler a working hypothesis to
show an essential ulterior moti\c' for his elForts in this direction. To his mind
at least his works ot art assured him peculiar magic control over the animal
lite w Inch was necessary to his maintenance and well-being.

-66 MAN

Man's Progress Following the Decllxe of the Cro-Magnox Race
Cro-Magnon destiny was no exception to w hal liad gone [)efore or wliat
would follow many tniies therealter. It embraced the irresistible tendency
toward racial decline with iinal extinction, and this was the fate which did
at length befall Cro-Magnon man. As the day of his ascendancy waned, a
new race invaded western Europe. Thus the Old Stone Age came to its con-
clusion approxmiately 10,000 years ago, with the advent of the more vigorous
Neolithic man. He developed an innovation in the construction of his miple-
ments in the fact that he now polished the stone. The principal change,
however, was an economic one, namely, the introduction of a rudimentary
knowledge of agriculture with the corresponding use of a variety of plants
and seeds. This naturally was accompanied by a gradual development of
tools and implements for the preparation of the soil and the garnering of
the harvest. As tiller of the soil or as herdsman, there was equal need for a
permanent abode. What, therefore, in earlier Mousterian times gave the
first decisive impulse to the upbuilding of the possessive sense, now found still
more substantial inducements to incite the aecjuisitive tendencies of man.
At this time also ])ottery was introduced and used in the preparation of
food. These two great changes aHecting the food suj^plx ot the race had
far-reaching ellects upon the actual metabolism of the people. Cultivated
crops of various kinds now ga\'e a greater \ariety m carbohydrate nutrition,
whik' cooking produced modilications in tlu' proteins which must have had
tlu'ir elfects upon the pioeesses of digestion. The ad\antages of domesticating
man\ animals for food sup|)ly were realized earl\ in Neolithic times. Domes-
tication also brought to man's aid the scr\ie(.'s of the horse in transportation
and conveyance. Two varieties ol cattle were successlully domesticated, the
Celtic shorthorn and the longhorn. In fact, tlu' New Stone Age witnessed a
domestication of animals which corrt'sponded clost'ly with that of present
times and included cattle, sheep, goats, pigs, horses and dogs.

FROM PRIMITIVE TO MODERN MAN 767

BtioiT the close of Neolithic time all of the direct ancestors of the
modern European races had established themsi-lves in westi'rn Euroj)e.
\\ itii the acKcnt oftlu' l^ronze Age, man was rapidly attaining those manual
capacities wherebx he might transcribe a record ol himsell, and thus enter
U])on an epoch of real historic consciousness. Some authorities set the begin-
ning of this historical |)eriod only as lar back as the commencement ol the
Eg\ptian calendar between lour and live thousand years ago. This dawn ot
history was followed by a procession of great events beginning in the earl\-
prc-dynastic eras ol Egy[)tian ci\'ili/.ation. The sabseciueiit de\-elo|)ments ol
the Pharaonic art and culture, the successive resplendence ol Chaldean, ol
Babylonian, of Grecian and ol Roman achie\ements m the realms ol civil,
artistic and philosoj^hical organization need little lurther comment than to
note in w hat great measure all of the remarkable progress was the work of tlu'
human hand. Each civilization m its turn i-ontributed to the development ol
the race w hich, passing through the long eclipse of the dark ages of medieval
times, emerged again in the brilliant light of the Renaissance and has gone for-
ward with a steady progress in material accomplishments into modern times.

The Birthplace and Mic.katorv Trails of Mankind

The cradling place ol mankind has been a matter ol much sjjcculation.
It is now generally accepted that this was located not m Europe, but rather
in the extensixe central regions ol the Asian continent. From such a birth-
place the race has gone lorth in successive waves of migration to the north,
to the east, to the south and to the west. These successive waves have not
brought forth a uniform product, nor ha\e the results ol the development of
the people thus migrating manifested the same ethnological progress or
specialized differentiation. Indeed, there seem to be certain almost irresist-
ible inlluences at work in consequence of the course and direction w hich the
various migrations have taki'ii.

Courlcsy, American Museum oj Natural History

IK,. 331. AUSTRALIAN NATIVE.

The Australians resemble ll.e negro and nct;r„icl populations in the dark chocolate brown color of the skin.

They have hair which is wavy but never wooly. Average height is 5 It. ," in.

[-681

FROM PRIMITIVE TO MODERN MAN

769

Iiii-. \\ 1 srw AKD Roi n;. 01 all ihv iniyratoiN roLitfs, tin- ucstw arcl
passa<i;t'\vay alone proxccl to \)v llic i^atli ol progress. Those who ha\f pur-
sued this course inexitahK came unckw the spell ol stiniulatmii; lorei's which

IIG. 332. AN AIKICW l*V(.\n (;K()1 I' I HUM THE BEI(;iA.\ CONGO.

seemed to shaj)e their dcNclopnu'iit as li In' some lon<i-]jre(h'stined formula.
The westward trail led to slow hut stt-ad\ rise in specialization with intellec-
tual and cultural acKancement as its lirst phase. I he second sta<z;c was one ol
culmination in which all ol tlu' acti\ ities ol the mind and body rt'aelu'd their
highest point. Then eanu' the third stage characterized by a jirogrcssive
decline with e\ er\ e\ idence of decacK'iice m industry, art and manners. At
length in the last phase, as il at the instigation ot some pursuing Nemesis,
there came a gradual reduction and (inal disappearance of the race. So it
has been w ith every wa\c ol migration w Inch has come Irom Asia into Europe,

770 MAN

lured on by the westward trail, seeking the advantages of the great Mediter-
ranean basin, in some instances pushing onward to the west even as lar as
the seaboard ot the Atlantic.

Couiti'-it .Wfururjn .Mw-iinn iij .\(ittttiil History

FIG. 333. THE AFRICAN NEGRO.

The Southern Route. Something in the migratorN passage to the
west, something in the country which it laid open to the newcomers stimu-
lated them to progress as no other part of the woild has done. The soutinvard
trail leading into Africa had no such successful inllucnct' on the invaders
who infiltrated its terrain. Those who migrated to the south were shut oil
from lh(.' beneficial contacts and competition with progressive peoples and
so have remained in the condition of primitive races. The southeasterly

FROM PRIMITIXT. TO MODERN MAN 771

trail, likewise, allorckd hut littli' stiniulus to advance' hcyoncl the earliest
stages ol liiinian dex (.■iopnu'iit. Tin- inhibitory eflects of migration to the
south and southeast upon raeial cNolution are clearly xisihle m many nati\e
tribes inhabiting tlu'se parts oi the t'arth. In certain localities some ol the
represcntati\cs ol' modern man have scarcely attained the plane ot'Chellean
eulturi'. rin'ir ethnological phase ol di'xelopnu'iit may rightly be considered
as Pre-Paleohthic. 1 his is true, according to Obermaier, of tlu' pygmies of
Central Alrica, the Semangs and Senci ol Malacca, tiu' Negritos of tlie
Philipjjines, the kubus of Sumatra, the Asiatic Pygmy trii)es and the
Andaman Islanders. These last emjjloy only wood, bone and shells in their
industry; they haxe not even acquired the use ot hre.

The Eastern Rchte. The eastern trail, li'ading as it originali\- did
by land connection into North America, although it took the American
Indian to his lanious hunting grounds and put m his ])ossession a land ol
unsurpassed fertilitx, noiu' tlu' less restricti'd him for all the period of his
history and prehistory to the exercise ol a nomadic lilc. Ap[)roacfied from this
direction. North America ollered no further advantages to mankind than did
cither ol the other routes ol migration. Tin- real lertility and productix'cncss
of this continent appear to lia\e rec|uired a prcMoiis period of European
experience in order that its actual richness might be developed and
materialized.

The NoKiiiERX Route. The northern trail led the Eskimo to his
Arctic isolation where he lound an e'lu ironmcnt barel\ habitable and thor-
oughly unijroductixe m its contributions to human progress. All of tliesc
trails alike, the soiitherl\, the southeasterly, the easterly and tlu' northern,
ha\c' pro\c(l to be jjaths ot inhibition. OITshoots of the race which have pur-
sued these routes in\ariabl\ manifist their rt'tardatioii by the retention of
many primiti\ e' characteristics through all the generations of their existence.
Some ol tluni ha\f passed through successive stages of industrial and cul-

FIG. 334. THE AMERICAN INDIAN".

[772]

FROM PRIMITIVE TO MODERN MAN —3

tural ;u'ti\it\ imt unlikt' tliosc of the Old Stone A'^v. It is remarkable, how-
e\ er, that thi' westward tiail alone was the road to protjress. It was the trail
w hieh letl to all the great e\ents of iuiiiuia histor\ . It has taken man lhroiiy;h

riG. 33-,\ THE tSKIMO.

his long prehistoiie era ol i:)rogressi\e aehie\ement and through the briefer
space of his Ijrilliant historical record.

The Dkaw backs oi- the Western Rolte. And \ et the western route
was not without its draw backs. W hatever glories might come of follow ing it
were temporary at best. Man mo\ed along its course in an unfailing cycle,
w hich had a metrical rhythm almost as exact and quite as foreboding as the
chorus of the ancient Greek traged\ . There was that phase which announced
his arrival or awakenmg, that rise which ga\e the lull measure of his worth,

774 MAN

that slow but sure decline, that invaria[)Ie destruction which overtook hini.
The persistent procession of these phases seemed to exert a i)aneful inlluence
on all his ell'orts toward progress, whether the part he phiycd was that of

CourttsVt AmeTictin .Museum oj Natural History

FIG. 336. A GROUP OF BRITISH SCIENTISTS DISCUSSING THE PILTDOWN SKULL.
Standing, Lrrr to Right: Mr. F. O. Barlow, Prof. Elliot Smith, Mr. Charles Dawson, Dr. A. Smith

W oodwarcl.
Sitting, Lilit to Kkhit: Prof. A. S. Uiiderwoud, Sir Arthur Kiith, Mr. \\ . P. P\ craft. Sir F.. Ray Lancaster.

Heidelberg or Pihdown Man, Neanderthal or Cro-Magnon, Egyptian or
Babylonian, Greek or Roman.

Advantages Co.\lmon to the Mediterranean and European Terrain.
What have been the acKantages in the Mediterranean and European
terrain not common to other territories ol the earth? Perhaps some con-
ditions of minuinity, some subtle dictai\ mlhu'nees upon the endoerme sys-
tem, some bacterial or parasitic s\ nibiosis j^cculiar to the temperate zone

FROM PRIMITIVE TO MODERN MAN —5

gave man greater psyeliie zest and more |3h\sieal \igor than liis less ener-
getic brothers of tlie tropics. It may ha\e been an increased fecundit}', a
greater viability ofollspring, which assured rapidly multiplying populations,
keener rualrv and quickened intelligence. Nor should the possibilities of
mutations in cutaneous melanism be overlooked. The lack of black j)igment
m the skm makes troj)ical existence dillicult lor white races and thus
enforces a northern habitat. These problems ol ecology and mutation may
well deserve most extended investigation, not alone to disclose the causes
actiNc in producing the remarkable ])rogress of European races, but, if
possible, to determine what factors have consistently contributed to their
decline. It is not improbable that the tendency toward degeneration, so
notable in European history, has a jjurely sociogenetie explanation.
Oligarchical concentration of political control ine\"itably spreads the con-
taminating efiects of luxurioLis li\ing and relaxation from effort to the mul-
titude so governed. Professor Osborn nisists that mankind in his uncivilized
state is subject to the same orderly laws as those which prevail throughout
the animal kingdom, but the introduction ot civilization interferes with the
natural regulation of things and man himself appears to be upsetting the
order of human progress.

The Great Factor in Human Evolution

From first to last, it has been the achievements of his hands which have
carried man onward from the time when he began to work with the simplest
of stone implements. Some authorities maintain that it was the development
of the brain w hieh led to the attainments distinguishing man from other
animals. Some attribute the distinction to his assumption of the erect pos-
ture. Still others ascribe all of human progress to the de\ elopment of speech.
Unquestionably, each of these factors is inseparably associated with human
evolution. But if one among them were to be selected as the most potent

776 MAN

developmental incentive, first choice would seem to fall most naturalK^ to
the specialized structure of the body best adapted to externalize the neural
energies of the brain. Such a flexible instrument as the human hand seems
preeminently fitted for these purposes. \\ ith the brain to direct its action,
to expand its usefulness, the upright posture to give freer range to its execu-
tion, with speech to make its accompfishments communal, to introduce the
benefits of cooperation, the hand became the master key opening all of the
ways leading through the new and vast domain of human behavior.

Chapter XX\'
THE BRAIN OF MODERN MAN
\\ EIGHT AND Indices of the Human Brain

"^HE weight of the human brain in the full-grown adult is between
1 100 and 1500 gm. In the large proportion of cases the male brain
II weighs between 1304 and 1502 gm., the female brain, 1 134 and 1332
gm. In man the brain seems to show some fluctuation in weight dependent
upon the age of the individual. Its greatest weight according to the time of life
is found in the middle decades, from thirty to fifty years. Before this time the
weight gradually increases until it reaches its middle-age ma.ximum and
thereafter decreases, losing progressively as old age advances. Statistics indi-
cate that the brain weight of distinguished and talented individual members
of the race is somewhat in excess of the average adult brain. Thus, in one
hundred distinguished men, the average weight of the brain was 1469.65 gm.,
about 100 gms. above the average weight of European brains. The usual
senile decrease in weight is apparently delayed about ten years in those
considered distinguished. The brain weight in different races of man shows
some slight differences. Thus, the average Chinese brain weighs 1330 gm.,
that of the Sandwich Islander about 1300 gm., the brain of the Malay and
the American Indian, 1265 gm., the brain of the African Negro, 1245 gm.,
the brain of the native Australian, 1 185 gm., the brain of the Hindu 1 190
gm. The weight of the Latin brain is somewhat less than that of the Teutonic
and Slavonic races.

The following tabulation is based on estimates of the volume of the
cranial cavity in the prehistoric races of man:

Trinil race ( Pithecanthropus erectus) 940 c.c.

Piltdown race ( Eoanthropus) i ^40 c.c.

778 MAN

Neanderthal (Momo priniigcMiius) 1626 c.c.

Grimaldi race 1580 c.c.

Cro-Magnon race 1 590 c.c.

The cnccphahc inchces, calcLilatcd both by weight and xohiincol water
chsphicement ol the human brain in a scries of adult males and lemales, give
the following hgurcs:

Forebrain index 86 to 89 per cent

Midbrain index i to 1^2 per cent

Hindbrain index 93-2 to 13 per cent

These indices of the encephalon place the human brain at the head of
that class characterized by pronounced manual chlKTentiation.

Surface Appearance of the Brain ix Man

Two facts are impressive upon inspection of the cerebral hemisphere
in man when compared with all ol the lower prnnates: lirst, the marked
mcrease m size; second, the great eomplexit\ ot eoUN'olutional nehuess and
intricacy of fissural pattern. A thiicl feature may be mentiont'd; namely,
the fact that the occipital lobe not only entirely covers the cerebelhnn but
protrudes and actually overhangs it.

THE CEREBRAL HEMISPHERE

The lobation of the human i)ram seen u[)on the lateral convexity of the
hemisphere is more dillieult to discern than in an\ of the great anthropoids
or lower prnnatt's. This is due not so much to the laet that the characteristic
boundary lines are less promment, Init because ol the great complexitx ol
convolutional detail. It becomes more dillieult to ideiitilv the typical land-
marks because they are surroundetl by areas which gam so mueh in detail
that their own delinllion is overshadowed b}^ adjacent leatures. In another

THE BRAIN OF MODERN MAN 779

r(.'S|)cx't this latiTal smhu'f clilk'i's li-oin that ot t hi.' ^r'c'at anthropoids and other
priinatcs; nanirlx, the ahnost complete chsappc-araiK'c of thv most char-
acteristic of siiiiiaii hssuri.'s, tlu' sulcus simiaruin. I lius, the actual bouiidar\'
between the parietal and occipital lobes is lor the most part wanting in man.
The occipito-parietal incisurt% whose continuation upon the mesial surface
IS the occipito-parietal lissurt', marks the position ol this boundary. The
extent to which this incisure pro|i'cts laterally upon the coiufxity ol the
heniisplure \arK's 111 dillereiit iiidu iduals and also in the two hemispheres ol
the same brain. Olten it is scarcelx appart'iit bi'voiid tlu' superior longitudinal
lissure, or ma\ extend tor a distance Irom 3 to j cm. upon the lateral aspect.
In no instance, howe\er, doc-s this sulcus ha\e the prominence which tlic
simian hssure presents in the anthropoids.

The Fissure 01^ S^l\ils. Of the primiti\'e anthropoid lissures, only
two may be disceriU'd with certainty upon tlu' lateral sLirlace ol the human
brain. These are the lissure ol SyKius and the hssure ol Rolando. Tiie
Rolandic fissure separates tlu' Irontal from the parietal lobe. The lissure of
SyKius separates thi- Irontal and the parietal lobi's Irom the temporal lobe.
The di\ ision between the i)arieto-temporal area and tin' occipital region is an
indecisive one. These three areas ol the bram become conlluent m a common
nn'cting-ground. Fhe hssure ol SyK'ius is the most ])romiiu'nt iissinx' ol the
human brain, it forms an angle ol something a little more than 45*^ with the
cerebral base line. This portion of it is know n as its posterior ramus. Upon the
basal surlace, between the orbital portion ol the Irontal lobe and the tip ol
the temporal lobe, is the horizontal limb ol the fissure. On the lateral surface
the hssure di\ idi'S into a short anti-rior limb, a longer anterior ascending limb
and the |)osterior limb alread\ mentioned. The ascending limb (ramus
anterior horizontalis I is about 2 cm. in K'ligth; it passes upward and slightly
lorward into the caudal portion of the inferior frontal coiu'olution. The
horizontal branch (^ranuis posterior) is the main lateral contiiuiation of the

-8o

MAN

fissure. It |)assc's biu'kward and sli^htl\ ii|j\\ar(l tor a distance ol approx-
imately 8 eni. This part ol the hssiire lorins the- hoiiiichiry between the Irontal
and parietal lobes aboM' and the temporal lobt' below. It usually ends by

MG. 53~A. UOKSAL SL RF.ACE OV BKAIN, HOMO SAPIENS.

lActiKil Lcnslli I ifi inni.l

di\iding into two short arms, one ol w huh enters tlu' parietal lobe and the
other extends downward into the ti'mj^oral lobe. The three divisions ot the
Sylvian lissure upon the lateral surl'aee of the hemis|:)here demarcate certain
portions of the inferior frontal, [parietal and superior temporal convolutions.
The portion of the inferior frontal convolution lying below the anterior hori-

THE BRAIN OF MODERN AlAN

781

zontal braiK'h lurms tlu' jiurs orhitulis, ov tlic orbital ()|ie'iculuni ; llic poilioii
of the coiuoliilion brtwci-n the anterior and ascciiclm^ branches lornis the
purs triaui^uluris, or intirmediate bontal opercLdnm; eauchil to the ascending

FIG. 337B. DETAILED DIAGKAM Ul UOKSAL SURFACE OF BRAIN, IIUMO SAPIENS.
Key TO Diagram, sllc. intekpar., Sulcus Interparietalis; sulc. occip., Sulcus Occipitalis; i. par. occ.
MD., Fissura Pariito-occipitalis Medialis; suix. precnt. int.. Sulcus Precentralis Inferior; SULC. precnt.
SUP., Sulcus Precentralis Superior; sui.c. ketroc. inf., Sulcus Rctroccntralis Inferior; sulc. ret. sup.. Sulcus
Rctrocentralis Superior.

branch of the SyKian hssure is located the ])urs hasalis. All of these divisions
of the Sylvian hssure and the art-as upon the cerel)ral cortex which are
demarcated by them are poorly delined in the great apes. The chief differ-

-82 MAN

CMicc between the ant hrcjpoids and man in this feature of the l^rain is the
miieh more marked degree of eomplexitx' m the mchx idual eomponents ol the
Sylvian fissure due to greater mtrieae\ ui the eonx olutions surrounding them.
The arrangement ol the \arious sul)di\ isions ot the Sylvian suleus is subjeet
to some variation. For further details m this regard the reader is referred to
standard works on the anatomy of the human brain.

The Fissi re of Rolando. The Rolandie or eentral fissure of the
brain extends obliquely aeross the lateral surfaee of the hemisphere in such
a way as to interrupt the general longitudinal course of the gyri and sulci
of this region. It is bounded by two long oblique convolutions, the j)recentral
and postcentral gyres. The fissure begins near the vertex in relation \\ ith the
superior longitudinal fissure and often incises the mesial surface of the hemi-
sphere. Its point of origin on the vertex is slightly behmd the midpoint of
the superior longitudinal fissure, a little further back in man than in the great
anthropoids. I^rom this ]:)oint it passes outward, downward and forward to end
near the middle of the fissure of Syhius whose posterior limb it sometimes,
though rar(.'l\, joins. At the junction of its upper and middle thirds the fis-
sure of Rolando presents a deep curve with the concavity directed lorward.
The upper and lower limits of this bend in the fissure constitute the su|)erior
and inferior genu respectively. The lower or inlerior genuot the fissure extends
almost verticall\ and terminates in close relation with the fissure of Syl\-ius.
The'angle of inclination of the central fissure with the mesial plane in the
adult brain averages 71."^". This angle is essentially the same as in the great
anthropoids, although in man\ instances in llu' lower primates the angle is
much nearer ()()°. In certain exceptional instances among the great anthro-
poids this angle varies from 75° to 80°.

The Parieto-Occh^it.al Fisslre. The parieto-occipital fissure is best
seen upon the mesial surface and has but slight representation upon the
lateral convexity in man. On this surface, as the parietal incisure, it is con-

THE BRAIN OI- MODERN MAN 783

timud tiansverscly hut a short distance, usually on the average of about \2
nmi. The line connecting this portion of the fissure and ihv prc-occipital
notch establishes an arbitrarx boundary between the occipital lobe bt'hind
and the temporal and |)arii'tal IoIjcs in front. In all of the anthrojjoids this
external portion of the parieto-occipital lissure is concealed in the sulcus
siniiaruni which interxx-nes between tlu' parietal and occipital lobes. It is
doubtful wluther any lissure, e\en as a vestige, in the human brain may be
homologized with the simian sulcus. Some authorities, however, maintain
that it is ])resent in the majoritN of human brains as a cur\ed sulcus, called
the sulcus occipitalis lunatus, situated on the lateral aspect ol the occipital

lobe.

LoBATioN OK THE Bkain. Lobatiou of the brain is not so clearly dcfiiu'd
as in the anthropoids. Tlu' boundary line established l)\ the Rolandic fissure
separates the [xirietal from the frontal lobe, while the Sylvian lissure sepa-
rates the frontal and parietal lobes respectively from the temporal lobe, and
tlu' arbitrar\ line from the parietal portion of the parieto-occipital sulcus
to the ])re-occii)ital notch in <ieneral is presumed to indicate the anterior
limit of the occipital lobe. In all four lolx-s discernible upon the lateral con-
vexit\- of the human brain, the most impressi\e feature is the richness ol
coinolution and of lissural pattern apparent in the frontal lobe. As compared
with this corresponding region in all of the great anthropoids and all otiier
primates, the comph'\it\ in coinolutional design is so striking as to con-
stitute perhaps the chiei" structural dillerencc between man and the upcs.
The greater degree of frontal de\x'lopnu'nt appart'iitls has mo\ed thesujx'-
rior e\trt-mit\ of the- cent ral sulcus further toward the occipital pole. In man
a little less than one-hall' the lateral aspect of the hemisphere is occupied by
the frontal conxolutions. The highest anthropoid fraction is one-third. By
actual planimetric measurement the frontal area in man covers 4" ])i.r cent
of thi' intire lateral surface, in chimpanzee 33 per cent, in gorilla 32 per

784

MAN

cent, in baboon 31 per cent and in Iciiuir 23 per cent. It is, therefore, in
the expansion of the frontal lobe, both in the area covered by it and the
great increase in the complexity of its convolutions, that xhv human brain

FIG. 338A. B.\SE OF BRAIN, HOMO SAPIENS.

Stands in striking contrast to the anthropoids. The c(>n\ olutional com-
plexity is likewise increased in the occipital region, and this is also true,
perhaps to a less extent, in the temporal and parietal areas. These regions.

THE BRAIN OF MODERN MAN

-8^

whirl) in the lower primates are preeminent because of theii' rich convohi-
tional pattern, m man seem to ix- less strikmij; when compared with'the
Irontal and occipital lobes.

FIG. 338B. DETAILED DIAGRAM OF BASE OF BRAIN, HOMO SAPIENS.

The Jraulal Lohc. The lateral surface of the frontal IoIh' presents a
superior, middle and inferior frontal couNolution as well as a precentrai
convolution sometmies spoken ol as the ascending Irontal con\ oiution.
All o( these con\()lutions are exceedingly irregular in outline, and separated

786 MAN

from each other by correspondingly tortuous fissures. The superior frontal
gyrus is situated between the margin ot the hemisphere and the superior
frontal sulcus; it corresponds to the upper part ol the hemisphere and is
mucli longer than any of the other frontal convohitions upon the lateral
surface. It is continued mesially to the marginal gyre on the mesial surface
and joins the central convolution by means of a lateral bridge at the upper
end of the precentral fissure. The middle frontal gyrus is parallel to the
superior frontal eoinolution in a general way, separated from it by the
superior frontal sulcus. The superior and inferior precentral sulci separate
this gyre from the central con\()hition although a well-marked deep annec-
tent gyrus usuallx connects them. The inferior frontal eoinolution, the
smallest of the three gyres in this region, is in some respects the most impor-
tant of them all. It is situated in relation with the horizontal and ascending
branches of the SyKian fissure. These branches di\ide the inferior frontal
convolution into three parts, the anterior frontal operculum (pars orbitalis),
the intermediate frontal operculum (pars triangularis) and the posterior
frontal operculum (pars basalis). The left inferior frontal eoinolution is
often called Broca's convolulion and it is regarded as the motor speech center.
In man it is more dcxcloped upon the left side m right-handed indniduals.
This greater development i:)articularly aflects the triangufar part of the con-
volution which ma\' cntirel\ separate the horizontal and ascending branches
of the Sylvian fissure.

The Parietal I.ohc. The |)arictal lobe presents an extensive and irregular
C|uadrilateral outline. It is bounded b\ the l^olaiidic fissure in front, below
by the fissure of S\l\ius, and behind by the imaginary line connecting the
pre-occipital notch with the external portion of the pancto-occipital fissure.
Upon Its lateral surfai'e the parietal lobe is di\ ided b\ an interruptc'd fissure,
the intraparietal sulcus, into three coinolutions, the post-central, sujicrior
parietal and inferior parit'tal gyres. The intraparii'tal sulcus commences at

THK Bl^AlN 01 MODERN MAN 787

the cephalic angle of the IoIjc a short distance above the Sylvian fissure with
w liieh it is sometimes continuous. It extends for about an inch ])arallel with
the lissure of Rolando and then curves backward and slightly upward, across
the parietal surface into the occipital lobe. This sulcus usually appears in
three distinct parts whicii form tiie superior and inferior postcentral sulci and
tile horizontal intraparietal lissure. The inferior postcentral sulcus, situated
behind and parallel to the lower part of the (issurc of Rolando, is separated
in about ~2 per cent of cases from the superior jiostcentrai sulcus. The
superior postcentral sulcus lies behind and parallel whh the Rolandic sulcus,
ch)rsal to the horizontal liml) of the intraparietal sulcus. The horizontal mtra-
parietal sulcus passes backward and slightly upward. It js often continuous
at its cephalic cxtremit\ w ith the postcentral sulcus. The convolutions on
the lateral surface of the |xirietal lobe are thrt'c in number, the jjosteentral,
the sujx'rior parietal and tlu' inferior parietal, the last being subdi\ided
into certain accessory gyres. The postcentral or ascendmg parietal conxolu-
tion constitutes the caudal wall of the Rolandic fissure. It is bounded cau-
dall\ by the postcentral sulcus in its two subdivisions. The lower extremity
of this gyre is connected with the precentral convolution in front and the
inferior parietal gyre behind b\ means of annectent gyres. The superior
parit'tal gyrus is situated caudal to the superior postcentral sulcus, dorsal to
the horizontal limb of the intraparietal sulcus. The inferior parietal gyrus
is situated between the inferior postct'iUral sulcus, the Sylvian fissure,
and llu' horizontal limlj of tlu' Intraparulal fissure. I his coinolution is more
complex in its configuration than either of the preceding gyres. It is sub-
divided by the upturned end of the Sylvian fissure, also by the caudal ter-
mination of the first and second temporal sulci. The extremities ol tht^sc
fissures determine the position of the supramarginal and angular gyres. The
supramarginal gyrus passes around the upturned end of the Sylxian fissure;
the angular gyrus bears a similar relation to the upturned end of the superior

788 MAN

temporal sulcus, and the postparictal g\rus curves about the extremity of the
middle temporal sulcus.

The Ociipilul Lohc. The occi[)ital lobe is situated at the occipital pole
of each hemisphere. It is ii;enerall\ pxramidal in shape and presents a richly
convoluted lateral surface. la apes this is separated from the parietal lobe by
the sulcus simiaruni. The occipital surface is further subdixided by a
trans\erse furrow, the transverse occipital sulcus, which appears most dis-
tmctly m the Ictus. Subsequently it joins the occipital portion of the intra-
parietal sulcus of which it ap])ears to be the bifuicated caudal extremitx. In
apes it IS concealed b\' the caudal o|:)erculum, but on separatniji the conxolu-
tions bordering upon the sulcus simiarum, it is seen on the anterior wall of
the sulcus. A lateral occipital sulcus extends oblic|uely backward lor a short
distance below the lateral end ol the transverse occipital sulcus toward the
occipital pole of the hemisphere. The calcarine fissure, one of the chief land-
marks on the mesial surlace, olten extends backward upon the mesial sur-
face of the occipital lobe to its pole where it bilurcates to form the li.ssura
extrema ol Seitz, visible when the hemisphere is \iewed from its occipital
aspect.

7^/u' Tcmjxnal Lnhe. The tem|joral lobe presents a lateral surface which
is bounded for two-thirds ol its length by the horizontal portion of the
SyKian lissure. At the caudal extremit\- of this lissure the lobe is contiiuious
with the parietal and occipital lobes. Two \ariable fissures appear on the
lateral surface of tlu' tt-mporal lob(.', the superior and middle temporal sulci.
An inferior t(.'mporal sulcus is seen upon the xentral surface ol the lobe
extending caudally toward the occipital pok'. The coiuolutions upon the
surface of the temporal lobe are three in numlji'r, the superior temporal,
the middle temporal and the inferior temporal g\ res, all ol which may be
easily discerned in this portion of the brain in the great anthropoids, to a
less extent also m some of the still lower primati's. The disposition ol the

' ' ' V ■ I \

* <

THE liRAlN 01 MODERN MAN

789

coinolut loiis in relation with the Liptiiiiu'd t'licl ot the superior and middle
temporal sulci has already been cU'seribed and is important m that it gives
these areas of the cortex a greater coiuolutional rKhness than is true ol any
ol the great anthropoids.

SIGNIFICANCE OF CONXOLUTIONAL COMPLEXITY IN THE HIMAN BRAIN

If a single statement might cover the characteristic leatures ol the
lateral aspect ot the human hemisphere in contrast to all other primates, it is
that the com|)le\ity ol the coiuolutions and the tortuousness ol the lissures
render impossible a unilorm description m man, \\ hile the relatixe simplicit>'
of these leatures in all simian brains discloses the discrete territorial bound-
aries almost at lirst glance.

Although the human brain has made great advance in its relative weight
when compared with the anthro[)oid brain, both absolutely and in relation
to body weight, its chief superiority lies in its intricate compk-xity ofconvolu-
tional arrangement. As applied to the frontal area this obser\ation becomes
l^articularly lorcelul. The frontal lobe, olten spoken of as the silent area, is, as
a matter of fact, now credited with such functions as those cinmected with the
regulation of the higher laculties of the mind, the de\ flopnuMit of pt-rsonahtN ,
the formation ot all those associational memories which enter into and lorm
personal experience and thus bespeak the degree of intellectual de\elopment.
A similar coiu'olutional expansion of tlu' occipital lobe is an indication ol the
extent to w hich \isual lunction has extended its associational significance and
the added degree in which it contributes to the general s\ nthesis of sensory
combinations entering into the ex|)erience of the indi\idual. That the tem-
poral and ])arietal lobes ha\e been somewhat outrun b\ the ex])anding
complexity of the frontal and occipital lobes is perhaps not surjjrising, inas-
much as these two intermediate areas of tlu' brain ha\c' alwa\s presented a
certain predominance because ol tlu' ixpresentation within tlu'ir cortical

790 MAN

areas of somcsthctic sensibility and the sense of hearing. It must not be
inferred from this observation that there are not definite advances in these
types of sensory organizati<MT of man, hut merel\- that the progress mack' in
this department of neural specialization is less conspicuous than that in the
frontal or occipital lobe. Somcsthctic sensiiiility, as well as the sense ol hear-
ing, have always played prominent roles in the organization of the general
sensorium. Undoubtedly the degree of eflicient elaboration in both the
temporal and parietal regions, as far as they concern the sense ol hearing and
general body sense, is in man much more acKanced in its capacity than in any
of the other j)rimates. From the purely structural standpoint this advance
seems less pronounced because it is so greatly overshadowed by the remark-
able expansions which have gone forward in the frontal lobe and to a slightly
less degree in the occipital lobe.

THE BASAL SURFACE OF THE BRA IX

The basal surface of the brain presents features less striking than those
seen upon the lateral con\e.\ity. This surface in its more anterior portion is
in relation with the anterior fossa of the skull and rests upon the orbital
plate of the frontal bone, it is for this reason called the orbital surlacc.

The Orlnlul Surface of ihf Ironlul Rciiion. The general expansion ol the
frontal region of the brain is again indii-ated 1)\ the modifications ot this area.
The orbital conca\it\-, so conspicuous in t lu- low fr and intermediate primates
and gradually becoming less prominent in the great anthropoids, in man has
decreased considerabb . While it is still recognizable, in some human brains
it is often dlllicult to discern an\ such concave disposition in the orbital sur-
face. It is true that the brain makes an impression upon the orbital plate
rather than that this plate indents the orbital surface. It is possible to recog-
nize in the bony structure forming the lloor of the anterior iossa, actual digi-
tations caused b\ im|)ressions of tlu' orbital con\ ulutKuis, known lor this

THE BRAIN OF MODERN MAN 791

reason as digitationes orhilulcs. This entire modification is consonant with
other evidences of expansion in the frontal lobe of the iiunian l^rani. It is
a feature of the utmost miportanee in distinguishing the ence[)halon of man
from ail other species. Inasmuch as the frontal lobe is looketl upon as the
area in which the highest syntheses of neural im[)ulses are composed (the
gallery of human experience), it is evident that its extreme expansion in man
is in direct proportion to his needs in these im|)orlant features of his organi-
zation. The olfactor\ tract and bulb are readil\ dt'tachable as tar back as the
trigonum ollactorunn, and such detachment re\eals the deep, olfactory
sulcus, which in many instances extends forward around the frontal pole of
the brain to become continuous w itli a small extension of the superior frontal
fissure. The increase in size and prominence of this fissure is another instance
of extension in the frontal lobe. In some cases this ollactorv sulcus extends
only as far forward as the frontal pole in one hemisphere, but in the opposite
hemisphere may attain its continuit\ witii the superior frontal sulcus. By
means of the olfactory sulcus, a well-defined gyrus rectus is delimited from
the adjacent orbital coinolutions. In those instances in which the olfactory
sulcus is continuous with the superior frontal fissure, the gyrus rectus then
becomes the orbital expression of the superior frontal convolution. All of the
brain features observed in the great anthropoids and even in lower and inter-
mediate primates, which in these inferior forms prest-nt themselves as incip-
ient landmarks, have in the human brain attained their lull representation.
Thus the process of evolution which had its inception in the more primitive
anthropoid organization finds its ultimate expression in man.

The Chiasm. The chiasm shows an angulation with reference both to
the nerves and the tracts which identifies it with this region of the anthro-
poid brain. Upon the base, however, in the region immediately caudal to the
chiasm, the optico-peduncular space in man appears to be much more con-
spicuous, by the fact that this region is larger and that its contents are more

"9^

easily discerrjcd. It

the st

increa-

cinereum, the area of attachment of

cess and the mammillan*" bodies. The

c cerebral f>eduncles is significant of expansion

-P^s^

FIG. 339A. LEFT LATERAL SURFACE OF BRAIN, HOMO SAPIENS.

[Actual Length 173 mm.]

in those great projection systems connected with the cerebral hemispheres.
The paUio-ponto-cerebellar tracts, as well as the pyramidal tract, are the
constituents of the peduncle. Expansion in these tracts accounts for the
increased size of the peduncle.

Occipital Surface oj Basilar Portion of Hemisphere. The occipital
surface of the basilar portion of the hemisphere shows certain equally striking
modifications in contour. This is especially notable in that the cerebellar con-
cavity, like its cephalic counterpart in the orbital region, has undergone reduc-
tion in size and prominence. Only a slight remnant of this depression appears

THE BR.AIN OF MODERN MAN -93

in the region immediately posterior to the corpus callosum. TTie occipital notch
is much reduced in size, and the degree to which the occipital surface overhangs
the cerebellum has undei^one considerable extension as compared with the

FIG. 339B. DETAILED DIAGR-Jtil OF LEFT LATERAL SLRFACE OF BRAIS.

HOilO SAPIENS-
Ket to Diacrax. scijC tNT-. SoJicus InteipaxiEtafe; stix. ocrrp. lat.., Sakns Ocxaica&Lateia&^sirLjCcs
occrPTTAUs TRA^s~ Salens Occqjttalis Tninsversas; stTLC psecnt. rsT_ Sclcos PrecectnEs Iniexior; scxjC
PBECVT. si-p-. Sulcus Precentrals Superior; sixc- rft. ivf-. Sokes RiKrtjceumEs laiitiicc.

higher anthropoids. All of these facts indicate a simultaneous expansion
both in the occipital region of the hemispheres and in the cerebellum. The
latter, however, is most aflFected in its lateral lobes.

THE CERFBELLL'M

The cerebellum, quite as much as the cerebral hemispheres, afforck
e\Tdence of the expansK-e pHX)cesses which have made such marked advances
in the human brain. Such progress is particularly well shown upon the

794 MAN

tentorial surface of the cerebellum which has lost much of its transverse
convexity. It manifests none of that sharp gabling so prominent in the
lower and intermediate primates. Even the ridge-pole effect produced
by the vermal portion of the cerebellum is almost completely lost, and while
this cerebellar surface is not actually flat, it much more nearly approaches
this condition than in any of the forms already described. The most
cephalic portion of the superior vermis is still somewhat protrusive, extending
slightly above the general plane of the tentorial surface. The interfolial sulci
pass almost without demarcation from vermis to lateral lobes and the folial
delineation is, if anything, slightly more pronounced than in the lower species.
This cerebellar expansion, which appears to have confined itself so largely to
the lateral lobes, accords with the expansion discernible in the cerebral hemi-
spheres. It offers a convincing argument as to the pronounced increment in
the several functional areas of the encephalon. The indications of expansion
evident upon the tentorial surface of the cerebellum become more
pronounced on the occipital surface. The posterior cerebellar notch has
become deep and the vallecula so much depressed below the surface that it
requires a separation of the lateral masses of the cerebellum to reveal the now
almost concealed inferior vermis. The two apposite borders of the lateral
cerebellar lobes arc in contact with the falx cercbclli. The appearance of this
surface gives such outstanding prominence lo the lateral lobes as to make the
vermal portion of the organ seem almost insignificant. \\ hen the lateral lobes
are separated, two deep paramedian sulci are brought to view, which appar-
ently interrupt the continuity of the vermal sulci as they pass into the
lateral lobes. Upon the petroso-vcntricular surface of the cerebellum, all of
the usual landmarks are prominent, including the cerebello-pontile angle, the
great horizontal fissure and the middle peduncle. In every feature, this
portion of the brain, which has its prototype in the brainsof all lower primates,
reaches its greatest definition in man.

THE BRAIN OF MODERN MAN 795

IMPRESSION GAINED FROM A SURVEY OF THE EXTERNAL SURFACE

OF THE BRAIN

The impression gained from a survey of the external surface of the
brain is that of a pronounced expansion in all those parts particularly con-
cerned with the functions over which the neopallium presides. Thes'
tions are all in the interest of neokinesis. Expansions in the pariet lor

the increase of somesthetic sensibility enrich kinesthetic association in the
control of motion. Expansions of the occipital lobe extend the realm of the
visual sphere, not alone for sensory interpretation but equallv for those
contributions which vision makes to the regulation of the more highly
organized skilled movements. Enlargement of the temp>oraI lobe extends the
sphere of auditor\" perception to bring into existence those combinations of
neural impulses advantageous alike to the acquisition " nee

of skilled performances; ; . the most notable expansion ot a

the frontal lobes for the i: lii of neural svntheses essential to the orj^an-

ization of person; ■ .e construction of judgment and of all the higher

faculties of dis. iion and reason governing the conduct of the individual

in adjustment to his complex environment. A similar expansion in the interest
of augmented function appears in the late- of the cerebellum.

SURFACE L.\NDMARKS OF THE BRAIN STEM

As is the case with cerebral hemisphere and cerebellum, all surface land-
marks become better defined in t rain stem. The ventral surface of
the oblongata presents a well-detined ventromedian sulcus which in its
more caudal p>ortions is interr terlacing libers of the
decussation. This decussati' l-s itself apf)arent more in man
than in the lower forms. On either side of the sulcus are two prominent
pyramids, their apices tap>ering toward the pyra \.-cussation. A marked

796

MAN

pre-olivary sulcus separates tin- pyianiicl from a promiiicnl ()li\ai"y eminence.
A distinct postolixary sulcus uiter\enes between the olixary body and the
spinocerebenar t'niinence, tlie expression of which latter is delimited dorsally

?^A^ ' .J

FIG. 340. \'ENTRAL SL KFACE OF B AIN STEM, HOMO SAPIENS.

lActvial Length 82 mm.]

Key to DiM.uwi. op. dr.. Optic Chiasm; o. N., Optic Nerve; opt. ped. sp..\ce, Opticopeduncular Space;
1". H. 1)1 (.., P\ramiclal Dcciis.sation; VENT. .MED. sll., Ventromedial Sulcus.

In- a well-delined intermediate sulcus. The most strikin<i; feature on the ventral
surface of the brain stem in man is the markt'd prominence oi the pons. This
structure lias gained in all dimensions. It is separated from tin- oblongata by
the bulbopont lie sulcus.

The cert'bral peduiules, like the jjons X'arolii, are strikingly j)rominent
in man. The\ are longer and more marked in tlu'ir surface relief. All ol
the features u|)on the xfiitral surface of the brain stem, including more
particularly the prominence of the p\ramld, the pons Varolii and the cere-

THE BRAIN OF MODERN MAN

797

bral prchiiK'Ics, suggest the great acKanees which tlie hiiinan brain lias
made in the organization of nidkinetie eontroL VUv large p\ raniici serves for
the coiueyanei' of motor impulses troni the eorlex which controls somatic

FIG. 341. DOKSAL SLHI-ACE OF BRAIN STEM, HOMO SAPIENS.

lActual Lengtii 82 iniii.]
Key to Diagram, dors. m. fis., Dorsoiiicdian Fissure; ooks. m. sept., Dorsomcdian Septum; fovea inf..
Fovea Inferior; inf. coll., Inferior Colliculiis; middle cerebel. pedunc. Middle ("erebellar Peduncle; sup.
CER. PEIJ., Superior Cerebellar Peclunele; sup. coll., Superior ("ollieiihis; ri li. rule;., luhertulum Trif;einini.

activity. The pons has a somewliat sunilar signiheanee since it represents
those libers which connect the cerebral iiemispheres w ith the lateral lobes of
the cerebellum. 1 he cerebral peduncles express both tlu' connection between
the cerebral hcmisplu'res and the spinal cord in the interest ol voluntary
control, and tlu' pallio-|jonto-cerebellar association m relation to coor-
dination.

The dorsal surface ol tlu- oblongata gi\es lurthe'r em|jhasis to the
advances in the human brain. The ela\al eminence (column and nucleus of
Goll) is separated by the dorsal i^aramedian sulcus Irom the cuneus (cohimn

798 MAN

and nucleus of Burdach). A dorsolateral sulcus separates the cuneus from a
well-defined eminentia trigemini. These three elevations of the dorsal sur-
face constitute the major elements entering into the dorsal sensory field. In
relatrve size the column of Burdach has increased in its diameters as com-
pared with the column of Goll. This expansion indicates an increment in the
influx of sensorj- impressions from the upper extremity and hand as compared
with those making their way brainward from the lower extremity and foot.
At their cephalic extremity the clava and cuneus become reduced in their sur-
face relief. The cuneus extends further cephalad than the clava and at the
level of the lateral recess of the ventricle reaches the general plane of the
ventricular floor. The superior angle of the fourth ventricle is bounded upon
either side by the middle and superior cerebellar peduncles and decreases in
size as it approaches the caudal orifice of the Sylvian aqueduct. The floor
of the fourth ventricle thus outlined consists of two triangles, the inferior
triangle bounded by the cuneus and clava, and the superior triangle bounded
by the middle and superior cerebellar peduncles.

At the caudal angle of the fourth ventricle the divarication of the alar
plates is indicated by a remnant of the gray matter, the obex. The floor is
divided into two symmetrical halves by a median sulcus w hich runs from the
apex of the lower triangle to the apex of the upper triangle. A second sulcus
starts beneath the obex lateral to the median sulcus, and proceeds cephalad.
It is situated about midway between the median sulcus and the lateral wall.
This is the sulcus limilans which divides the floor of the ventricles into a
mesial motor portion derived from the basal plate, and a lateral sensory
portion derived from the alar plate. At the caudal angle of the ventricle
immediately adjacent to the midline is a long narrow elevation, the eminentia
hypoglossi, which indicates the cephalic extremit}- of the hypoglossal nucleus.
Cephalad to the eminentia hypoglossi and upon either side of the median
sulcus is a less prominent elevation, the eminentia fasciculi teretis. In a posi-

THE BR-\IN OF MODERN .\L\N 799

tion lateral to the nucleus fasciculi teretis and the nucleus hNpoglossi is an
elongated and wedge-sh. vation caused by the presence of the nucleus

intercalaris. Many fine grooves cross this nucleus esf)eciaJIy along its mesial
and later rs, the area plumiformis. Lateral to the nucleus intercalaris

and to the sulcus limitans is the inferior fovea vagi, also known as the ala
cinerea. This area presents the middle third of the dorsal vago-glosso-
phar^-ngc js which in large part lies on the floor of the fourth ventricle.

The mesial boundary- of the fovea vagi is formed by the sulcus limitans while
its lateral edge is slightly elevated in a cord-like ridge, the funiculus separans
of Retzius. Dorsolateral to this funiculus is the area postrema. The pwrtion
of the floor of the ventricle lateral to the sulcus limitans forms the area
acustica. This consists of a mesial or vestibular field and a lateral or cochlear
field. The vestibular field forms a pronounced irregular elevation whose
-itords some idea as to the degree of organization in th .ing

mechanism of man. That this apf>ears to be less than in the arboreal pri-
mates is quite evident even u{x>n suj>erficiaJ insp>ecrion.

The floor of the ventricle is traversed by the striae acusticae. Imme-
diately cephalad to the striae acusticae and adjacent to the median sulcus
is a rounded elevation formed by the genu of the facial nerve encircling the
nucleus abducentis. This is the eminentia facialis.

The cephalic extremrtv- of the fourth ventricle becomes continuous with
the Sylvian aqueduct, dorsal to which are situated the quadrigeminal plates,
specialized to form the superior and inferior colliculL Both of these eminences
in man apf>ear relati\"ely insignificant, and their surface relief is much less
than in the lower and intermediate primates. They seem e\-en less prominent
than in the great anthropoids. The sulci sep>arating the two sets of coOiciJi
are broader and more shallow than in the other primates. The longitudinal
intercollicular sulcus is considerably expanded to form the pineal fossa in
which is lodged the epiphysis cerebri. Upwn the lateral surface of the mid-

8oo MAN

brain is a wcll-clc'liiH-tl nu'sial <z;t'niculatr body ccjiinccted witli the inlcrior
colliculus by means ot the braciimni conjimctix Litn posticuni. The decrease
HI proninience of the colliciilar eminences in the rool ol the midbrain is
significant of that general transference of \isual and auditory function w hich
has been in process throughout the primate series. It attains its ultimate
expression in man. Confirmatory evidence of this supersedence of the mid-
brain tectum by the areas in the cerebral hemispheres is easily obtained by a
surve\ of those regions in the cerebral cortex assigned to the functions of
hearing and vision.

Internal Structure of the Brain Stem

It is diflicult to approach the description ol the internal structure of
the human brain without a certain feeling of conviction that the sections
clearly depict the culmination of that evolutionary process w hicli has been
traced from its primate beginnings. What is most impressive about these
sections of the human l)rain is the fact that every feature hitherto seen in
the apes comes at length to its sharp and final focus. The entire brain stem,
like tile hemispheres, manifests an enlargement w hich seems somewhat out
of proportion to the stature ol man. The oblongata, the pons Varolii and the
midbrain lia\c a little less than twice the dimensions of the corresponding
structures in gorilla, an animal which in point of size is considerably larger
than man.

LEVEL OF THE PYRAMIDAL DECUSS.\TION (fiG. 342)

Here the features are those lamiliar througiiDut the entire primate series
incident to the decussation of tlu' jiyramidal libers. The section shows the
ventromedian sulcus, somewhat dellected to one side under the inllucnce
of the crossing fibers. On its dorsal aspect is a long dorsonuxlian se]jtum
extending from the surface into the central gray (Cen). The pyramid,

THE BRAIN OF MODERN MAN

8oi

occupying its usual \ cut roiiU'siai position (P\ ), is uiKlrr^foin<; decussa-
tion, and Its crossin^r lihcrs, passinti; Irom rij^ht to K'lt, lia\'C' separated the
ventral ;ira\ eolumn i\ t' n I IVoiii the eentral <ira\ matter (Cen). Sonic

FIG. 342. MAX. LEVEL OF THE PVKA.MIDAL DECLSSATIO.N.

CD, Column of Burdacli; (:i:n, Cx-ntral Gray Matter; ex., Coluniii olGoll; or, Di-iti-rso-spinal Tract; rm,
Dorsal Spinocerebellar Tract; Gow, Ventral Spinocerebellar Tract; hel, Spino-olivary Tract of Helweg;
NR, Nucleus of Rolando; I'D, Predorsal Bundle; i>y. Pyramid; kkk. Reticular Formation; rst, Rubrospinal
Tract; spt, Spinothalamic Tract; run. Descending Trigeminal Tr.ict; ven. Ventral Gray Column; xpy.
Crossed Pyramidal Tract. [Accession Man Section N 55. Actual Size 10 X ~ mm.|

idea concerning the extensiveness of the pyramidal system ma\ I:)e obtained
from the massi\eiiess of the decussation as the (ibers interpose tlu'iii-
selvcs between the central gray and the ventral gray column. The Jatter

8o2 MAN

seems to retain man\ of the cliaractcristics ol tlie \c'ntra! horn in the
spinal eord, and were it not lor its detaehnient b\- tln' erossing p\ramidal
libers, the general appearanee of the seetion in this respeet would eorrespond
closely to that of the upper eer\ ical region of the eord. The eentral gray
matter is somewhat broader and more massive than in the lower levels
of the axis. It eontains near its eenter the eentral eanal. It has not
manifested as yet any of its tendency toward dorsal migration in preparation
for the opening of the fourth ^•entriele. Dorsolaterally it is connected bj' a
slenck'r cervix with a dorsal gray column, surrounding the periphery of which
is the substantia gelatinosa (NR). This substance has much increased in
size and has moved into a more lateral position as compared with its con-
ditions in the spinal cord. It is beginning to occupy the position \\ hich gives
rise at higher levels to the eminentia trigemini.

The dorsal sensory field exhibits the wide expanse lying between the
two laterall\' denected masses of the substantia gelatinosa. The most strik-
ing featurt' in it, however, is the proportion of the mesial column of Goli
(CG) to the more lati'ral column of Burdach (CB). These two fasciculi
of densely m\clini/cd libers arc separated from each other b\- a well-
dclined dorsal paramedian sulcus. There is thus no diHicultx' in distin-
guishing the lioundaries of the area representing the sensorx inllux Irom the
leg and foot and of that serxing in a similar capacity- for tlu' arm and hand.
The columnar representati\e of the lower extremity, the coKimn ol Goll,
is about one-third the size of the similar represcntatixc of the upper extremity
and hand, the column of Burdach. None of the primates shows with such
decisiveness the delimitation between these two columns, nor is there any
case in which tlu' disparit\' in size between tlu'in is more marked than in
man. This dilference denotes a marked incri'ase in the lunctioiial impor-
tance of those sensory allerents connected w ith the upper extremity and hand.
It is by no means imjilied that the morphological dilferentiation in the hand

THE BRAIN OF MODERN MAN 803

and upper extremity has so progressed over and above the adajjtix e ehangcs
manifest in thele<i;and loot tliat tliis dillerentiation de facto e\])lains the dis-
parit\ in size l)et\veen tlie two sensory cohinins. If the striiet ural chllertMitia-
tion aloni' weie the (k'tt'rnunin>j; ni()ti\'e in tht- expansion w hieh oeeurs ni tlie
eohinm of Burdaeh, it is jjrohable that no siieh chsparit\' wmild he exident.
The greater size of the fascicuhis cuneatus must Ije attributed more to the
funetional expansion arising in eonnt'etion with the wide inerease in range of
mo\<-'ment now possible in the hand. 1 lie total number ol postures and
museular eoml)inatioiis of myotensional states ior liiieness ol moxement 111
the human upper extremit\ has shown a pronouneed inerease as compared
with any of the other primates. This large number of joint and muscle
combinations incident to complex manual manipulation 111 man has called
forth a corresponding increase in the sensory inllux. Although in the great
anthropoids there has been a marked tendency to establish a similar diOer-
ence in the size of the columns of Goll and Burdaeh, thus signifying that the
forelimb was becoming progressively more emphatic in its influence as a
sensory organ, the linal stage is reached in man. The contrast is most con-
vincing on comparing the human conditions with such low forms as the
tarsius or marmoset. The nervous system rellects 111 these particulars the
modifications occurring in the upper extremity and Iiand.

Another feature descrxing emphasis is the fact that the entire sensory
field IS considerably larger than in the lower jarimates. The total sensory
inllux from the i-xtremities, both upper and lower, appears to be of larger
volume in man than m aj^cs.

Lateral to the column of Burdaeh is the substantia gelatinosa trigemini
(NR) on whose outer margin is the descending trigeminal tract (Trd).
The reticular formation ( Ref) is well delined and lies in a j)()sition dorsal
to the \entral gra\' column. In the circumferential and intermediate zones in
the medullary substance are the two ascending spinocerebellar tracts (Fie,

8o4 MAN

Gow), the spinothalamic (Spt), rubrospinal (Rst) and Deiterso-spinal
(DT), tracts together w ith the usual juxtagriseal intersegmental association
fibers. In the ventrohiteral region is the spino-oiivary tract of Helweg (Hel).

LEVEL OF THE CAUDAL EXTREMITY OF THE
DORSAL SENSORY NUCLEI (FIG. 343)

At this level the changes are those incident to the appearance ni the
dorsal sensory field of the nuclei of Goll ( NG) and of Burdach (NB).
The [nramidal decussation is still in process at this level as indicated bj-
the marked dellection of the ventromedian sulcus. The reticular lormation
(Ref ) has increased in size as compared with the lower level, so much so
that the cephalic remnant of the \entral gra\' column ( Ven ) is now connected
by many griseal bridges with the central gray matter (Cen). The latter
structure has migrated somewhat dorsally in the general movement which
takes place in preparation tor the opening oi the fourth \ entricle. The dorsal
sensory columns of Goll and Burdach still show their exact demarcation b\
means of the dorsal paramedian sulcus. The column ol Goll is about one-third
the size of the column of Burdach. In both of these columns there now
appears the corresponding nuclear structure. The nucleus of Burdach is a
l^rotrusion of the central gra\- matter into the in\esting medullary substance
of Burdach's column. The nucleus of Goll occupies a more independent
position almost entiri'l\' surrouiuk'd b\ medullary substance. The substantia
gelatinosa of Rolando ( N R) shows some increase in dimensions as compared
with the last level, and the descendingtrigemiiial tract ( Trd) is also obviously
larger. The central gra\ matter (Cen) is roughly triangular in shape with
its base directed toward the dorsal aspect of the stt'in. Its triangular form is
in part accounted for by tlu' decussating fibers of the pyramidal system
(Py.\). The cervix of the dorsal gray column is rc|)ri-s<.'nted only by a few
gray bridges connecting tlu' substantia gelatinosa trigt'inini with the central

THE BRAIN OF MODERN MAN

805

gray nialtrr. Tlic pyrariiid ocrupics its fuslotnarx Nriitroiiu'sial position
although Its outliiu' IS not clfarl\ di'liiu'cl dur to clillusioii intitli'nt to tlu'
crossinu ol p\ lainidal lii>c'rs. The cart iimlcix'iitial and inttrnu-diatc zones

FIG. 343. MAN. LE\EL Ol- CAUDAL EXIKIAUI^ Ol DOKSAI. SENSOIO NLCLEI.

CB, Column of Burdach; cen, Central Gray Matter; CG, (Joluinn of Goll; dt, Deiterso-spinal Tract; kle.
Dorsal Spinocerebellar Tract; Gow, Ventral Spinocerebellar Tract; hel, Spino-olivary Tract of I lelweg;
NB, Nucleus of Burdach; nbl, Nucleus of Blumcnau; nhy, Hypoglossal Nucleus; NG, Nucleus of Goll; nr,
Nucleus of Rolando; i>Y, Pyramid; PVX, Pyramidal Decussation; ref. Reticular Formation; rst. Rubrospinal
Tract; si>t. Spinothalamic Tract; tkij, Descending Trigeminal Tract; \ en, Ventral Gray Column. (Accession
Man. Section N 175. Actual Size. 13 X 10 mm.]

show tliL- sanif ^ciuaal arrangcnuait as hcTctolorc and contain on tlic
periphery the two spinocerebellar tracts (^Ele.Guwj and in the inter-

8o6 MAN

mediate area, the rubrospinal (Rst), spinothalamic (Spt) and Dciterso-
spinal (DT) tracts.

LEVEL OF THE CAUDAL EXTREMITY OF THE INFERIOR OLINARY

NUCLEUS (FIG. 344)

Here the general configuration of the section has changed considerably
due to expansion incident to the dorsal migration of the central gray matter.
In the ventral position, occupying the usual place on either side of the ventro-
medial sulcus, are the dense bundles <:f the pyramids ( Py). It is possible
at this le\el to obtain some estimation of the relative unportance ol the
pyramidal system in the human neiu-axis. At this Ie\'el the pyramidal libers
occupy at least a ciuarter of the entire cross section. This clearix nulicates
to what extent the function of volitional control over somatic musculature
has expanded to meet new demands Imposed b\ the human race. The.pyrami-
dal system has jirogressively increased from the lowest extremity of the
primate series to this point.

Dorsolateral to the pyramid is a mass of gray matter heretofore not
apparent in the section, the caudal e\trcmit\ ot the interior olivary
nucleus (10). The central gray matter (Cen) has become more circular
in outline, containing the central canal near its center. It is almost entirely
surrounded by arching nu'dullated libers rising for the most part Irom
the nucleus of Coll and sweeping to the ia])lu- to form the lower portion
of the decussation of tlu' mesial lillet (Mfx). These arching axons are the
interna! arcuatt' libers and represt'iit the decussation in thepathwa\' lor the
conduction of impulses from the leg and foot. The dorsal sensory field shows
in this section as in lower IcacIs the disproportion between the column oi
Goll and column of Burdach. These two dorsal columns arc still clearly
demarcated by the dorsal paramedian sulcus. In the most lateral position
of the dorsal sensorv held is the substantia gelatinosa trigemini or nucleus

FIG. 344. MAX. LE\ EL OF CAUDAL F.XTRIl.Ml lAOl I XFEKIOK OLI\ AK^ XL CLEUS.

CB, Column of Biirdatli; cen. Central Gray Mattrr; C(;, Column of Goll; di, Dcitcrso-spinal Tract; ile.
Dorsal SpinoccTfbcll.ir Tract; cow. Ventral Spinocerebellar Tract; mel, Spino-olivary Tract of 1 IcIwck; 10,
Inferior Olive; mfx, Crossing of the Mesial Fillet; m>. Nucleus of Uurdach; n<;, Nucleus of Goll; nhv, I lypo-
fjlossal Nucleus; nr. Nucleus of Rolando; i>D, Predorsal Bundle; I'L, Posterior Longitudinal Fasciculus; i»Y,
Pyramid; ree, Reticular Formation; rst, Rubrospinal Tract; spt. Spinothalamic Tract; rui), Descending
Trigeminal Tract. (Accession M.in. Section N 2;o- Actual size 13X8 mm.]

[80-1

8o8 MAN

of Rolando (NR), upon \\ host' oLitcr margin is tlu- descending trigeminal
tract (Trd). A few scattered collections of gray matter in the column of
Burdach represent the caudal extremity of the accessory nucleus of
Bhinienau, also called tin- lateral nucleus of Monakow.

The circumferential and intermediate zones contain as heretofore the
two ascending spinocerebellar tracts (Fie, Gow) on the periphery, and
mesial to them the rubrospinal, s[jinothalamic and Deitcrso-spinal tracts
(DT, Rst, Spt).

LEVEL THROUGH THE MIDDLE OF THE INFERIOR OLI\ARV BOD'*' (FIG. 345)

At this level the changes in the external conhguration arc those incident
to the o[)ennig of tlu' tourth \cnlricle and the appearance of the inlerior
oh\f in its full development. The dorsal aspect of the section has increased
in Its diameter corresponding to the opening ol the veiitricLilar space. In
a similar manner the \entral diameter has increased due to the appear-
ance of the inferior oli\ary body. Occupying their usual position in the
ventromesial portion ol the section are the two pyramids separated by a
wide ventromedian sukus. Along the \entral margin ol the |:)yramid a nuclear
mass has made its ap|jearance, the nucleus arcilormis. Dorsal to the
pyramids is the collected mass of axons h)rming the mesial lilk't ( M I ),
to which a number of internal arcuate hbers are still making their way from
the cephalic extremitx of tht' nucleus cLineatus. The inferior (liivary nuch'us
has its characteristic human ap|)earance. It is distinctl\ outlined and much
convoluted in form, with its two accessor\- olixarv elemi'iits, the dorsal
accessory obve ( DO) and the mesial accessory oli\e (VO), adjacent to
it. This increase in t hi' xolume, in the delinitioii and in the degree ot con-
volution of the inlerior oli\t' carries this structure to its highest degree of
dilferentiation seen in mammals. Slowly and b\ progressive stages this
structure has advanced through all intermediate lihases from the lowest ol

THE BRAIN OF MODERN MAN

809

the primates until it reaches its euhnination at tliis jjoiiit. It seems fair to
say tliat no strueture in tlie human body shows more elearl\ the expansive
unfolding and progressive specialization indicative oi an cNohitionarx process

MG. 345. MAN. LE\ EL IHKOLGH MIDDLE OF INFERIOR OLI\ AR^ IU)D^ .

AMB, Nucleus Ambiguus; CB, Column of Burdach; ctt. Central Tegmental Tract; do, Dorsal Accessory
Olive; FLE, Dorsal Spinocerebellar Tract; cow. Ventral Spinocerebellar Tract; hel, Spino-olivary Tract of
Helweg; 10, Inferior Olive; mf. Mesial Fillet; nbl. Nucleus of Blumenau; nd. Nucleus of Dcitcrs; nfs.
Solitary Nucleus; Niiv, Hypoglossal Nucleus; nr. Nucleus of Rolando; nvd. Dorsal Vagal Nucleus; NI2,
Twelfth Cranial Nerve; po, Predorsal Bundle: PL, Posterior Longitudinal Fasciculus; pv. Pyramid; REF,
Reticular Formation; rst. Rubrospinal Tract; spr. Spinothalamic Tract; \o, \entral Accessory Olive.
[Accession Man. Section N 433. Actual Size 20 X 1 1 mm.)

than thi' interior olivary nucleus. Starting as an ill-defined aggregation of
gray matter in the ventrolateral quadrant of the oblongata of lemur, this

8 10 MAN

great nucleus of the brain stem has manifested the progressive modifica-
tions seen in the intermechate primates. At length in the great anthropoids
it begins to disclose that outhne familiar both in conliguration and dciinitioti
which finally is expressed in the richly convoluted nucleus of the human
brain. Assuming the correctness of the interpretation already ascribed to
the inferior olivary nucleus in its relation to the simultaneous movements
of the head, eye and hand as well as the facilitating of all skilled move-
ments, it will be clear that a functional expression of this expansion in the
primate order has kept pace with the structural e\olution ol the nucleus.
For example, the skilled performances of man in w liich sinuiltaneous move-
ments of the eyeball, the hand and the head are essential, as compared with
those of the lemur or marmoset, appear to be greatly in advance of such
acts in these lower prnnates.

The bod\ of the central gra\' matter has completed its dorsal migration
and lies in a position forming the floor of the f )urth \entricle. In its \entro-
mesial portion is the clearly dillerentiated hypoglossal nucleus (Nhy),
separated from which b\- the funiculus separans is the dorsal vagal nucleus
(N vd). The emergent fibers from the twelfth nerve (N i 2) make their way
forward from the nucleus toward the inferior olivary body, while the entering
libers of the vagus nerve pass through the lateral aspect of the periphery
and make tluMr way to the dorsal sensory luieleus. They traverse in so doing
the restiform body, the descending trigeminal faseieulus and the sub-
stantia gelatinosa of Rolando (NR). Ventrolateral to the dorsal vagal
nucleus is a colkx'tion of densel\' m\elini/A'd libers surrounded by a nuclear
mass. This comprises the nueU'us solitarlns ( N f s ) and its accompan\ing
fasciculus solitarius. In the most lateral position in the dorsal held is
the cephalic extremity of the nueh'us of BlunuMUiu (NBH surrounded by
a few myelinated libers arising in the column of Bnrdaeh. l-'eri[)heral to
this is the dense myelinized bundle constituting the restiform body (.hie)

THE BRAIN OF MODERN MAN 81 1

and \'(.'ntial to the nucleus ol I^Lirdach is the substantia o;cIatin<)sa trigcmini
( N l-v I ni\ rstc'd on its outer surlace h\- the descenchn<i; tri^n'ininal tract ( T rd ).
Tins le\el represents a critK'al region m xhv bram steni. The nucleus of
Burdach is replact'd b\ another nuclear structure which also receixcs pro-
prioceptive hbcrs but in this case conung Irom the highly specialized
proprioceptors of the vestibular portion of the internal ear. The section is also
critical as showing the approach to the next higher segment of the axis repre-
sented i)v the pons \ arolii. The transition which is about to occur is indi-
cated on the ventral surlace by the appearance of the nucleus arciforniis.
In man this nucleus which appears to be the caudal expression of the exuber-
ant pontile nuclei extends much lurther downward along the axis than is
the case in the other anthropoids. (^See reconstruction of human stem.)

LEVEL OF THE \ESTIBILAR NICLEI (fIGS. 346, 34-)

At this le\el the contour of tiie section shows those changes incident to
the a|)pearance in the dorsal sensor\- field of the large vestibular complex
\\hich now- occupies the position lormerly held by the nuclei of Goll
and Burdach. The reliel ol this vestibular complex has pre\ious!y been
noted upon the lloor of the lourth xeiitricle. Its general proportions and
appearance in man give tiu' impression ol a structure somewhat less exten-
sively develo]X'd than m tlu' lower i^rimates, and particularl\ m those forms
which are highly specialized for arboreal life. It may be diiiicult to maintain
that the \estibular nuclei m man are less extensixe than m other primates.
On the other hand, it would seem likely that the balancing mechanism in
man had less ckmand made upon it than would be the case in those animals
\\ hich lead arboreal li\ fs. Man, w ith his more lirm supporting base upon the
ground, is provided with a surface which aflords him greater security.
There are reasons, however, why the balancing mechanism in man should
not undergo marked reduction. These arise from the fact that, ha\ing

8i

MAN

assiinu'cl the i-rccl ijostiirc, hv walks upon two left without aid or support
from thr upptT cxtrciiiilifs. Such is not the- case m any ol the apes which
c'Mi|)lo\' hotli the hands and the leet m their locomotion. E\'en those which

FIG. 346. M.AN. LEVEL OF THE \ESTIBl LAK NLCLEl.
AMB, Nucleus Ambiguus; err, Central Tegmental Tract; do, Dorsal Accessory Olive; dt, Deiterso-spinal
Tract; cow. Ventral Spinocerebellar Tract; ici'. Inferior Cerebellar Peduncle; 10, Inferior Olive; mf, Mesial
Fillet; NAC, Ventral Cochlear Nucleus; nad. Dorsal Cochlear Nucleus; nd, Deiters' Nucleus; nfs. Solitary
Nucleus; nmi', I ly[>oglossal Nucleus; nr. Nucleus of Rolando; NSC, Schwalbe's Nucleus; mo. Vagal Nerve;
I'D, Predorsal Bundle; I'l., Posterior I ongitudinal Fasciculus; pv. Pyramid; ref. Reticular Formation; rst.
Rubrospinal Tract; si'i, Spinothalamic Tr.ict; trd, Descending Trigeminal Tract: \(i. \entral Accessory
Olive. (Accession Man. Section C 7. Actual Size 23 X 9 mm.|

have acquired something approaching the erect posture do, nevertheless,
supplement tlu'ir locomotor actixities by usin<i- tiu- hands either directlx
in contact with the (i;r()und or as balancinj^ structuix's held outstretched o\'er
the head. An essential dillerenct' also in this connection is that tlu' human
hand has lost its foot-like characters while tlu' leet ha\e correspondin<2;ly
become diflerentiated as locomotor or<;ans de\ oid ol prelu'iisih' specialization.

THE BRAIN OF MODERN MAN

813

I Ins l;ii-ri';iclini<j, modilicat ion must haw expressed itself In nuinx prolound
aitcratiDiis in tin- nu'clianism ol locomotion and produet'd changt's m the
essential substratum ol the balanemii meehanism.

MG. 34-. MAN. LE\EL Ol- lilL \LS11BILAK M CLEl.

err, Ontral I igiiunt;il Fnict; (.ou, \iiitral SpinociTcbcllar Tract; ice, Infcridr (,rrcl)fllar PidiiMtlc; 10,
Infcridr Olive; mi-, Mi-sial Fillt-t; M>, Di-iti-rs' Nuclous; nis, Solitar\ Nucleus; nk, Nucleus of Rolando; nsc,
Scliwalbo's Nucleus; i>D, Prcdorsal Bundle; i>L, Posterior Longitudinal Fasciculus; i-v, Pyramid; ref.
Reticular Formation; kst, Rubrospinal Tract; spt, Spinothalamic Tract; trd. Descending Trigeminal Tract;
TUB, Tubereuluni Acusticum. [Accession Man. Section C 189. Actual Size 22 X 12 mm.]

In man the xestibular eomplex consists of a small-celled tnangtilar
nucleus of Schwalbe (NSc) and a large-celled nucleus of Deiters (ND)
scattered through which are many small bundles of heavily myelinized
libers. Entering fibers from the Nt'stibidar di\ision ol the eighth ner\e make
their way inward and pass through the ventral e\tremit\ ol the restiform

8 14 MAN

body to tlu' mic'k'iis of Dcitcrs. Ventral to Dcitcrs' nucleus is the somcw hat
reduced substantia gclatinosa trigcmini (NR), and latiTal to the nuek-us
is a massive bundle of fil)ers constituting the restiforni hudy (ICP) about
to estabhsh linal connections with the cerebellum. On the outer side of
the restiforni l)ody is a mass of nuclear material penetrated b\ nian\ nerve
fibers. This is the tuberculum acusticiun (Tub) which contains portions
ot the ventral and dorsal cochlear nuclei together with hbers arising in the
cochlear division of the eighth nerve. The body of the central gray matter
spreads across the floor of the ventricle. The specializations in the central
gray substance are particularly concerned with the nuclei of the \estibu-
lar and cochlear divisions of the eighth nerve. The most mesial of these spe-
cializations is the triangular nucleus of Schwalbe ( N Sc).

At this level, the inferior olivary body appears in all its complt'x convolu-
tional arrangement, showing a marked increase in volume as compared with
the lower primates. It is associated w ith the dorsal and mesial accessory olives
(DO, VO). Its fundus contains amass of heavily m\fllnized axons from
w hicli man\ arcuate libers pass across the midline of the raphe and make their
way to the restiforni body. These olivo-ccrcbellar connections are much more
extensive than in anthropoids. They represent the only axons entering the
mierior c(.Tel)ellar ])eduncle and ha\ ing diffuse distribution in tlu' \ermis and
lateral lobes of the cerebelluni. The circumferential zone, in contact \\ ith the
inferior olive, contains the central tegnu'iital tract (Ctt) which affords
connection between the midbrain and the mlenoi- olixe. Whether this tract
also has constituents which establish communication with still higher levels
of the neuraxis, such, for exain|)le, as the interbrain, the corpus striatum and
even the cerebral cortex, is a cjuestion w Inch is yet to be decided. The main
portion of the central tt'gmcntal tract appears to come in dirt'cl communica-
tion with the midbrain in the neighborhood ol the third lurxe nucleus. Some
of its fibers appear to enter and form part of tlu' ])osterior commissure. The

THE BRAIN OF MODERN MAN 815

reticular lurniation ( Ri'f) occupies a lar<ic ])orti()ii of the si'ction but has
less of that (lilTuse appearance so charael eristic of it in tlie apes. Its boundaries
are most clearly drawn in the human bram sti-in.

This Ie\el is of particular signilicance because of its beariny upon the
ixiiancing mechanism, in the apparent decrease in prominence ol the neural
portion ot this apparatus.

LEVEL OF THE CEREBELLAR NUCLEI (fIG. 348)

At this level the chief feature is the nuclear de\elopment in the medullary
substance of the cerebellum. This specialization appears in the extremely
complex dentate nucleus (Ndt) which exceeds in its complicated lorm
all other species. The nearest a[)proach to the dentate nuch-us m man
is that of the gorilla, although both the chimpanzee and orang show a marked
increase in complexity of this nuclear structuri'. In man tln' nucleus dentatus
shows a definite increase m its proportional \'olume, a greater clearness in
definition of its outline, and a much increased richness in its convolutional
arrangement. The nucleus emboliformis is somewhat larger m man than in
the apes, \\hile the nucleus globosus and nucleus lastigii remain about the
same in size as seen in tlu' lower species. Since the dentate- nucleus is the
linal relay station for all neural impulses ])assing irom the cerebellar lu'iiii-
sphercs, its expansion seems to lollow as a natural constciuence ol the
extension in the lateral lobes. These acKances in cerebellar organization
denote the increase of coordinati\e control requin-d by the human mus-
culature in comparison with that of the forms most nearix approaching man
in motor capacity.

Such expansion of the cerebellum does not in any way signify a mere
extension of power in muscular contraction. Some authorities still attribute
to the cerebellum the function of imparting strength to muscular action (the
sthenic element in Luciam's cerebellar triad). The arboreal habits ol the

8i6

MAN

orang-outang, the cliinii)anzee and the gorilla call upon the muscular system
for ihc cIc\cIopiiiciit of great strength. If, as l.uciani hi-lieved, the cerebelluni
served in the canaeitv of aucmentnig the power ol muscular contraction,

FIG. 348. MAX. LEVEL OF THE CEREBELLAR NUCLEL

CBi., OicIkIIihh; sdi, Dintatc Nuck-us; nfg. Nucleus Fastigii; nod. Uvula; obl, Oblongata; I'v, Pyramid;

VEN IV, Fourth Ventricle. |Accession Man. Section N 201. Actual Size 70 X 38 mm.]

then the three great anthro[)oids should far e\ce(.'d the human in cerebt'llar
development. Its function more piobahlx is ri'laled to the delicate and exact
adjustment of tlu' postural att libutt's which permcati' all motor acti\ity.
Motion has been describt-d as a Ihiid sticam ol postures. The ])ostural ele-
ment may be discerned in all xolitional acts. W hen investigated in relation
to movements of the hand and Imgers, tlu- number ol postures entering into
the simplest acts is found to be suiprisingly large. Each of these postures
during the entire movenn'nt is (k'|X'ndent h)r its precision upon impulse's
arising in the cerebellum. This t>pt' of cerebellar control applies chielly to
complex motor actixitics. Disease or injiirx m tlu' lateral lobes ol theccrebel-

THE BRAIN OF MODERN MAN 817

lum leads to a coiulitiDn of ataxia or (lisarrangcnu'nt in tin- |KTlorniancc' of
such mo\ t'liu'iits. 1 lu' act is cmharrassccl i)\ a scries ol irrciiular oscillations.
Flexion in one place is o\H'r-cni|)liasi/.e(l and must he counteracted b\ o\er-
extension, which ni its turn is extri'nie. 1 hus that plastic skeleton ot posture
about which the execution ol each skilk'd act is molded, loses its cohesive
support and has every appearance of thorough disorganization.

The most acti\e agent of skilled |)erlormances in man is the hand.
Without siK'h speciali/.ation as this it would be im|)ossible to de\ flop t he
range and \arii't\ of complex manual moxcmcnts ol which man is capable
and for which the xastlx increased output ol coordmat i\ t' control Ijccomes
necessary. Responding to this demand t he lateral cerebellar lobes ha\e show n
their ex|)ansioii. It is not to be o\ crlooked, ho\w\i'r, that tlu' lower extremit\'
manilests ct'rtain latent potentialities for the de\ elo|jnu'nt ol highl\ complex
acts. Not a lew cases are on record m w huh indi\ iduals ha\e been deprn fd of
both upper extremities b\ amputation at or near the shoulder. Some indi\ id-
uals thus alllicted ha\c so educated the lower extremities and leet as to
accjuirt' the control of moNcnu'iits necessary for painting and writing. These
moxc'iiU'iUs belong to tlu' group ol acc|uired skilU'd perlormanccs to the usual
list of which many others may be added b\ special training as, tor example,
those seen in jugglers. The cerebellum thus appears to contain a certain unde-
veloped jjotcntiality which, under stress of unusual circumstances, may l)e
made available.

LEVEL OF THE INFERIOR PORriOX OFIIIF PONS \ AROl 1 1 ANIVIIlF EMERGENCE
OF THE Sl.MH CKANI Al. NEK\ E, THE NER\T S ABDl CENS (FIG. 34y)

Here the configuration of the section has undergone considerable modili-
cation, due to the addition of massive transverse bundles and other structures
pertaining to tlu' pons \ arohi. By the addition ol the pontili' elements, the
marked distinction l)etween the basis j^ontis and the tegmentum pontis

8i8 MAN

is clearly established. The boLinciarv line- of these two portions is formed
b\- the tiaiisvefsel\ arranged bundles of {\\v mesial hUet (Mt) through
which pass nian\ crossing ner\e hl)ers constituting the trapezoid body,

FIG. 349. M\\. LEX 1:1. OI- THE IMEKIOK POKriON OF THE PONS \AKOLlI
AND THE EMERGENCE OF THE SlXril CKWl Al NEK\E.

err. Central TcK'ncntal Tract; lin, I.ingula; MCi>, Middle Cerebellar Peduncle; mf, Mesial Fillet; nab,
Abducens Nucleus; nbe, Nucleus of Bechterew; n6, Abducens Nerve; n?, Facial Nerve; pd, Predorsal
Bundle; pn. Pontile Nuclei; pv, Pyramid; ref. Reticular Formation; rst, Rubrospinal Tr;ict; scp, Superior
Cerebellar Peduncle; spt, Spinothalamic Tract; so, Superior Olive; tur, Tractus Uncinatusof Russel (Hook
Bundle); iv, Fourth Ventricle. [Accession Man. Section C 109. Actual Size 38 X 31 "iiii.|

THE BRAIN OF MODERN MAN 819

a portion of the sccondarx cochlrar [jatliway. Situated in the lateral extrem-
ity of the trapezoid l)ocl\ is the upper pole of the superior olivary body,
(SO), a relay station in the pathway of auditory conduetion Ironi whieh
some hht'rs arise to take a eourse inward and haekward m the chrec-
tion of the nueleus ahdueentis. These libers form the pedunc'le ol the su|KM-Ior
olivary body. They serve the ])urpose of transmittinii; auditory impulses
from the superior oIi\e to tlu' nueleus of" the sixth ner\e, in order that the
eyes may be directed toward the souree of any sudden sound oeeurring u])on
one side or the other of the indixidual. This pedunek' ol the supt-rior olix'ary
bodv develops in all primatt's, haxinii in man a representation as proiiouneed
as any of the lower forms. Immediate rellex cooperation Ix'tweeii ear and
eyes is as much a human nvcd for ]M-ompt dettxtion ol a|j[:)roaching danger as
it is essential to the protection of the upva.

The body of the central <j:ray matter, a thin layer lormint; the lloor
of the fourth ventricle, is pr()lon<;-ed laterally as a tenuous stratum beneath
the subependymal substance over the walls of the \entricular space which
now are formed by the massive bundles of the superior and middle certbellar
peduncles. The ventricle itself is somewhat more restricted, due to the iact
that it is ap]iroachin<,^ the caudal orifice ol the Sylvian aqueduct. In the
\entromesial |)ortion of the ct-ntral <i;ray matter is the specialized aggregation
ol' ner\e cells forming the nucleus abducentis (Nab). This is the nucleus
of the sixth ner\e which supplu-s the external rectus muscle ol tlu' eye, the
fundamental center of all ocular moxt'ments in lateral gaze. The emergent
fibers of the sixth nerxe make their wa\ forward from the nucleus toward the
pons \ arolii. It is sonuw hat unusLial to observe as in this section three por-
tions of the emergent libers in the intramedullary course of the sexenth nerxe
whieh supplies the i'acial musculaturi'. The microtome was fortunate in
rexealing the second portion passing along the mesial aspect ol the nucleus
abdiici'iitis, the third ixution, the genu facialis, and the lourth portion as

820 MAN

the iH'i\L' libcrs proceed toward tlu' l)iill)()|)()ntilf sulcus. The rt-ticular por-
tion of the section is the most extensive region in the tegnuntuni. The l)asis
contains the elements eharaetenstie ot all pontile IiacIs: the stratum super-
ficiale, the stratum eomplexum in w hieh are the extensive pontik' nuelei, the
transverse pontile libers and the lilxrs of the |)\ ramidal system, and the
stratum profundum. In the dorsal area of this lield are a few scattered
I)undles detached trom the main pyramidal mass lorminii; the aberrant p\ ram-
idal eontingents ol the pons. The large size ol the pontile nuclei is of
particular moment, inasmuch as it indicates the accessions in the reahn oJ
the cortical organization lor skilled acts. These nuclei lorm one ot the mam
contrasting points between man and apes. The ncrxiis abducens, passing
Irom Its nucleus ot origin on the lloor ol tlu' touith \'enti"icle torward to
emerge in the bulbopontile sulcus, is seen in this section as it makes its
\\a\ through the tegmentum pontis and begins to penetrate the stratum
]:)rolundiim.

LE\'EL OF THE MIDDLE OF THE PONS VAROLII (fIG. 350)

At this le\'el a minor alteration has occuirt'd m the contiguration ot the
section which belter illustrates the complexity of the pons Varolii and at
the same time lurmshes means to estimate the size ot the superior cerebellar
peduncle (Sep). The central gia\ matter spreads out as a thin layer
undeilymg the lloor ot the \cntiuli' which is approaching the caudal oritice
of the Sylvian ac|ueduct. At the iunction of the lloor and the lateral wall is a
collection of cells representing tlu' ct'phalic pole ol the nucleus ot Bcchtcrew
(NBe), part of the vestibular complex. Closely associated with this is a
dense bundle ol libers constituting the ascending mesencephalic root ol
the trigeminal nerve (Tmt). The lateral wall of the \enlricular space is
tormed by the superior cerebellar |H'duncle (Sep). This pi'duncle is ol
interest largely because of its size which, as compared with any of the apes.

THE BRAIN Ol MODF.RN MAN

821

indicatt'S tlu' augnu'iitatKin which has ocfurrrd in \hv volunu' of cllrrcnt
inipulsrs Iroin the cx'ix-hrlhim, c'S|xvially Inmi ihc hitcral lobes. In s^eneral
arran<it'niriit the coiuhtions m aiul about the ix'<:I()n ol the superior cerebellar

1 Kj. 350. MAN. l.L\ UL 01 IIIL MIDDLL OF TlIU I'ONS \AKUL1I.

err. Central Tigmt-ntal Tract; (;<)\v. Ventral Spinocerebellar Tract; lin, Lin^ula; MCi', Middle Cerebellar
Peduncle; MI-, Mesial Fillet; MiE, Nucleus ol' Bechterew; N5, Trigeminal Norvc; i>D, Predorsal Bundle;
PL, Posterior Longitudinal Fasciculus; i'\. Pontile Nuclei; I'Y, Pyramid; kst. Rubrospinal Tract; scp,
Superior Cerebellar Peduncle; si't. Spinothalamic Tract; tmt, Tractus Mesencephalici Tri<remini; tuk,
Tractus Uncinalus of Russel (Hook Bundle!; i\. Fourth \'entricle. (Accession Man. Section -15. Actual
Size 30 X 26 mm.]

822 MAN

peduncle corrcsponcl In niiiuile detail In this area in all ol the lower prhiiatcs.
In none of" them, however, is the pro|)ortion ol the superior eerehi'llar
peduncle so great as in man. Judged b\ this index, it is e\KKnt that eoordina-
tive control over the muscles has increased in |)roporti()n to the acquisition
of skilled performances made effective by the human hand. A certain number
of fillers from the sLiperior peduncle extend into the roof of the ti)urlli
\entricU', and man\- of them doubtless assume this position to accommodate
the increasing volume of this pathway. For tin- most part, howe\er, those
filjers seen in the roofplate belong to the cerebellar commissures.

Lateral to the peduncle is a thin la\er of lightly myelinized libers
which constitute the tractus uncinatus of Russel. This fasciculus forms
a part of the juxtarcstiform body and associates the vermal portions of
the eerebelhim with nuclear areas in the region of Deiters' nucleus. L\'ing
upon tlie |X'ripher\' of the narrow zone forming the tractus uncinatus are the
myclinized libers of the ventral spinocerebellar tract (Gow) pursuing its
course to the Ncrmis of tlu- cerebellum. These conditions in the neighborhood
of the superior cerebellar peduncle deserve special comment since they
maintain an invariable arrangement throughout xhv primate series. They
have varied onl\ in their jMd|>()rtions, the lower forms showing a less highly
developed superior cerebellar peduncle and a much more extensive zone
corresponding to the tractus uncinatus of l^ussel. Tlu' fibers composing the
\entral sjiinocerebellar tract follow their latlu'r circuitous route to the
vermis, maintaining about the same proportions throughout the series, it is
dillicult to estimate their actual xohinu', but if anything they ma\ have
decreased in man. 1 he increasing size of the superior cerebellar pedunck' as
contrasted with llu' lelatively decrt'asing size of the tractus uncinatus pro-
duces the x-ariant in the arrangement of this rt'gion. Since the uncinate
tract of Riissi'l is part ol'tlu- iuxtari'stilorm bod\, it represents an acti\ity
connected with the intrinsically primiti\e liinetions of tlu' cerebellum, its

nil- BRAIN OF MODERN MAN 823

proniiiic'iice nia\ well decrease' in comparison \\\{h the more rix'cnt lunctional
accessions ol ihe ccrchelliiin represenlecl h\ the superior ceri'heMar pt'tluncle.
On the one hand, the uncniate tract cK'notes organization in the cerebellum
related to paleokinesis, particularix' concerned in the hahincino; mechanism,
while on the other hand, the superior cia't'ljehar pi'dunck' is an index of
developments in coordinativc control ol precise mo\ements expressing
neokinetic specialization.

The outstanding feature at this level is the great increase in the size
of the pons \ arolil produced by the augmentation ol the pontile nuclei. So
marked is this expansion thai pontile structures ol the basis encroach upon
the tegmentum pontis to such an extent that some ol the pontile nuclei
actually lie dorsal to the mesial lillet ( PN, Mf). Such pontile encroachment
ma\' be looked upon as another e\'i(k'nce ol tlu' exuberant e\[3ansion of these
nuclear masses seeking accommodation in all a\ ailable regions. They appear
to extend caudally as a jirolongation ol the nuclear substance which forms
the nucleus arcilormis, and to some exti-nt mliltrate the mesial lillet. This
invasion ol the tegmentum is j)rimaril\ a human feature. Indications of it
may be lound here and there in the chimpanzee and in the gorilla, but in the
main no such massive extension of nuclear substance into the tegmentum is
witnessed m any other species as in man. 1 he basis pontis takes its character
much more Irom tliese nuclear aggregations than it docs even from the great
mass of transverse pontile libers which lurther increase the actual volume of
the pons N'arolii. 1 he arrangement ol the three layers m the pons is similar
to that noted in other species. All of tlu' pontile layers, the stratum super-
licialc pontis, the stratLim complexum pontis and the stratum prolundum
pontis luu'e their characteristic appearances. The manner in which the
transverse libers accumulate as they approach the lateral aspect of the
section to lorm tlu' middle ci'rebellar pi-duncU' 1 M ep ) is a feature which has
been noted in connection with each form of the primates discussed. In the

824 MAN

ventrolateral jjortion of the section some liht-rs lonninff the dorsal roots of
the tri<ieininal ner\e ( N5) penetrate tlie pons. Man\' of tliese ma\- be traced
inward and backward to a small attenuated mass of ^ray matter, the (.(.'phalic
pole of the substantia m'latmosa of Rolando. The reticidar lormation is
clearly bouiuk'd but is relatively small in its general jjroportions and shows
no nuclear specializations of note.

In general, the significance of this portion of the stem derives importance
from its bearing upon the organization of skilled performances as indicated
bv the size of the pons Varolii. In particular it denotes an extensive expan-
sion of the iH'opallium and a marked increase in the \()luine ol tliost' pallio-
ponto-cerebellar tracts which afford communication between the cerebral
hemispheres and the lateral lolx's of the cerebellum.

LEVEL SHOWING THE EMERGENCE OF THE FOURTH OR TROCHLE.AR

NERVE (fig. 351 )

At this le\el the contour of the section has undergone those changes
incident to the appearance of the caudal orifice of the aqueduct ( Aq) and
the general approach to the next higher segment of the brain stem. The
central gray matter (Cen) entirel\- surroLinds the floor and lateral wall
while its roof is formed by a thin la\er of the posterior medullary \t'liim.
Escaping from \\u- roofplate are tin- libtrs of the trochlear nerve (N4)
which make their way around the lateral aspect of the stem to enter the
cavernous sinus in common with the third and sixth cranial nerves. The
boundary between the central gra\ matter and the subjacent reticular
formation (Ref) is formed l)\ the posterior longitudinal fasciculus (PL)
and the predorsal bundk' ( PD), as well as the scattered bundles of the
fibers constituting the mesencephalic root of tlu' fifth nerve (Tmt). The
lateral portion of the tegmental area at this le\el is occupied by two impor-

FIG. 351. MAX.

LE\EL SHOWING THE EMERGENCE OF THE FOIKTII ()I{
TKOCHLEAR NERVE.

AQ, Aqueduct of Sylvius; ctN, Cintral Gray Matter; CTT, Central Tegmental Tract; u\ Lateral I'illet ; Mr.
Mesial Fillet; N4, Trochlear Nerve; i>i), Pretlorsal Bundle; I'L, Posterior Longitudinal Fasciculus; r>\. Pontile
Nuclei; I'v, Pyramid; hkf. Reticular Formation; kst. Rubrospinal Tract; scp, Superior Cerebellar Peduncle;
SPT, Spinothalamic Tract; r\iT, Tractus Mesencephalic! Trigemini. (Accession Man. Section C' 458. Actual
Size 24 X 24 mm.]

[825I

826 MAN

tant systems of conduction fibers. The mesial and more massive is the su]3erior
cerebellar pechmcle (Sep) in the form of a crescent whose niferior tip
is approaching the median hne. Lateral to the superior cerebellar peduncle
is the lateral (lllet (Lf), the secondary pathway in the conduction of audi-
tory inijiidses. These fibers are approaching a relay station in the inferior
colliculus whose ele\'ations are not as yet present at this level. The relative
size of the superior cerebellar peduncle is readily appreciated and again
affords an opportunity for estimating the volume of efferent impulses pass-
ing out of the cerebelfum in connection with the function of muscular coor-
dination. The significance of its augmentation has already been discussed
and is undoubtedly connected with the vastly increased capacities on the
part of man for the liner adjustment in those highly skilled performances
whicli require the finest eoordinative control.

The boundary line between the tegmentum and basis in this section is
created by the presence of the transversely disposed bundle of fibers of tlie
mesiat fillet (Mf). In the basis are all of the elements characteristic of
the pons Varolii, including its three major strata, the stratum superficiale
pontis, the stratum complexum pontis, containing the large masses of pontile
nuclei, and the stratum profundum pontis. The reticular lormation ( Rel)
at tliis level apj;)ears to be reasserting itself as a more extensive structure.
At the same time it appears somewhat more dill use, due to the tendency
of the superior cerebellar peduncle to undergo decussation. The iormatio
reticularis contains no specialized groups of cells at this level, i^ordering
upon it and perhaps forming a portion of it is a small aggregation of gray
matter, the caudal pole of the substantia nigra. This latter structure has been
variously interpreted as to its functional signilicance. At the present time the
majority of authorities ascribe to it the regulation of certain automatic
associated movements.

THE BRAIN 01 MODERN MAN 827

LE\EL OF THE INFERIOR COLLICL LLS (FIGS. 352, 353)
At this Ic\c'I tlir midbrain is ciitiTrd and sliows ihv (.haracteristic-
modifications occunmii; m xUv roolplalc. Two svmnn-trieal t-lcxations rise
upon cither side fornun^' the inlerior collicuh ( IC). These structures are
more conical in shape than is the case m any ot tlie lower prmiates. From
surface appearances these primar\ way-stations in the |)atln\a\ ot hearing
seem to have undergone considerable reduction m the human hram. The
significance of such rechiction may be gauged l)y Xhv lact that hearing in
man has become much more dehberati\e m its reactions. Au(htor\ stimuli
need and recei\e more coiisidt'iatioii, greater association and mort' exact
evahiation before courses of action are determined in response to them.
The need of immediate rellex response as the rt'sult of auditory impressions
is much less apparent in man than in lower animals. It is probable that such
instantaneous reaction as man\ of the lower a[)es manilest in consequence
of auditory stimuli might proxe in)urioiis to man. The adage, "Look before
you leap," applies ec|iiall\' to the sense ol hearing. Sounds or noises arc usu-
ally submitted to proj)er analysis by higher centers in the neural mechanism.
Although a certain degree of the ancient stratification still is apparent in
the inferior colliculus, reminiscent of its lornu'r functional |:)romineiice among
various parts of the brain, this specialization is but feeble and gi\es a distinct
impression of definite iiuolution. Probably no other single function has
undergone more e\tcnsi\e elaboration than the sense ol hearing. The
evaluation of sounds and the production ol speech and music, as well as the
associations connected with the nian\ \(iiees of natiire, ha\c' formed an
almost inexhaustible material out of which man has constructed his wealth
of auditory perception and understanding. It is little wondi'r, therefore, that
the primitive capitol of lu-aring has \n-vn transferred to a thoroughl\ modern-
ized neural organization callable of meeting all ol the great variety of mocfili-
cation and exiirencN' m the auditor\ realm.

FIG. 352. MAN. LEVEL OF THE IM LKIOK COLLICULUS.
CEN, CiTitral Gray Mattt-r; ctt, Central Tegmental Tract; ic, Inferior C^illieulus; lf, Lateral Fillet; Ml",
Mesial Fillet; ntk, Trochlear Nucleus; I'D, Prcdorsal Bundle; pl. Posterior Longitudinal Fasciculus; i>\.
Pontile Nuclei; i>v. Pyramid; ref. Reticular Formation; rst. Rubrospinal Tract; si>T, Spinothalamic Tract;
SPX, Crossing of the Superior Ccrelnllar Peduncle. [Accession Man. Section C547. Actual Size 22 X 24 mm.)

[ S28I

THE BRAIN OF MODERN MAN

829

Tlu' ci'iitral ^n'ay niattcr (Cen) sunouiuls the Hour and lateral walls
of the SvKian ac]uc'clucl, and upon its \rntral maru'in arc- the extensive
bundles constituting the posterior longitudinal laseieulus ( PL 1, the predorsal

FIG. ^j^. MAX. LEVEL OF THE LNFERIOR COLLICLLUS.
AQ, Aqueduct of Sylvius; CEN, Central Gray Matter; err, Central Tegmental Tract; cp. Cerebral Peduncle;
ic, Inferior (^olliculus; lf, Lateral Fillet; mf. Mesial Fillet; ntr, Trochlear Nucleus; PL, Posterior Longitudi-
nal Fasciculus; ref. Reticular Formation; Ksr, Rubrospinal Tract; sen. Substantia Nigra; spt. Spinothala-
mic Tract; spx. Crossing of the Superior Cerebellar Peduncle; tmt, Tractus Mesencephalici Trigemini.
[Accession Man. Section Nqi8. Actual Size 34 X i<) mm.)

hundle (PD) and some scattered hundli'S of ni\elinlzed libers lorming
the mesencephalic root ol the lilth ner\e (Tmt). The te<imentum itsell
at this level is further conlused b\ the coinergent libers oi the superior

830 MAN

cerebellar peclunck' (Spx) as they approach tlu'ir k'\ el of decHissalioii.
Lateral to the converging peduncle arc (ibcrs ot the lateral fillet ( Lf ) entering
the inferior coiliculus and thus completing tlie lirst stage in thepathway of
liearing. The mesial lillet (Mf) establishes the boundary between the basis
and tegmentum in which iormer may still be discerned the characteristics
of the pons Varolii.

The special feature at this level in all primates is the appearance of the
inferior collieuli. That they show some demonstrable diminution in man is
indicative of the process of telencephalization which has proceeded through-
out the primate series. In man it reaches its termination in that the chief
responsibilitx of the function of hearing has at length been delegated to the
cerebral cortex in the region of the temporal lobe.

LEVEL OF THE SUPERIOR COLLICULUS (FIG. 354)

Here the alterations invariably' associated w ith this region ot the brain
are all apparent. The essential changes are typified by the appearance of
two dorsal elevations in the roofplate of the mesencephalon, the superior
collieuli (SC). These structures have ()b\ lously become much reduced
in size as compared with the other primates. They retain but a vestige of
their former importance, representing as they do the much reduced optic
lobes of the lower \ertebrates. Nothing could demonstrate more eonelusively
the evolutional process which has steadily acKanced m the brain than the
changes affecting this portion of the stem. In man the proct^ss of delegating
function from a lower to a higher, more expansible area ot the brain is carried
to its fullest expression. Although the superior eollieulus doe^s manitest a
certain degree of stratilication in the human brain, although several layers of
cells and libers may \k- detected in this structure, these are so ruchmeiitary
as to lea\e no doubt that the funetion of this lormerix important region has

TIIF I^.RAI\ OI- MODERN MAN

831

diminislR'cl. Tlu' cakIciu'i' oI the iiilcnor and supcrKir cdIIr-uIi 111 tlir midhraiii
ot |jrimatc's, indicated not l)\ expansion hut the re\c'ise, li.irnislies a con-
\'ineing ret'()rd ol an t-\()hit lonal process.

MG. 354. MAN. LE\ EL OF THE SLPEKIOK COLLICILUS.
CEN, Central Gr:iy Matter; ci', Ciribral Peduncle; err, Ontral Tegmental Tract; mf. Mesial Fillet; mob.
Mesial Geniculate Body; noc. Nucleus Oculnmotorius; nru, Nucleus Ruber; n3, Oculomotor Nerve; pd,
Predorsal Bundle; I'l., Posterior Longitudinal Fasciculus; Kii, Reticular Formation; rst, Rubrospinal Tract;
SBN, Substantia Nigra; sc, Superior Colliculus; si>r, Spinothalamic Tract; tmt, Tractus Mescncephalici
Trigemini. [Accession Man. Section (.', 64-. Actual Size 30 X 14 mm.]

The central gray matter (Cen), which .surrounds l[ic aqueduct of
Sylvius, in its ventromesial portion contains a large nuclear aggregation,
the nucleus oculomotonus iNoc). From tins nucleus the ner\e lii^ers
arise which supply all ol the muscles of the t'\e with the exception of the
external rectus and the superior ol)lic[ue. The nucleus is noteworthy because
ol the dense oculomotor decussation and commissural connections. This con-
nection itself is mdicatiNc of close internuclear relationship in the interest of

832 MAN

stereoscopic vision. The reticular lorniation (Ref) is now much reduced
in size. There has emerged Ironi it a large circular nuclear mass, the nucleus
ruber (NRu). This nucleus shows a distinct increase in size compared
with the lower and intermediate primates and is even larger than in
the great anthropoids. Functionally it serves as a rela\ in the transmis-
sion of impulses mainly arising in the lateral lobes of the cerebellum. It may
also be the case that some fibers from the cerebellum are relayed in this
nucleus to pass cephalad into the interbram or e\en the endbrain. The
marked increase of the nucleus in the human brain is important as bearing
upon the increment in coordinative control already indicated in the size
of the lateral lobes of the cerebellum.

Ventral to the reticular formation is a massive aggregation of nuclear
substance, the substantia nigra (Sbn ). Whatever may be the final opinion
concerning the functional significance of this large mass of gray matter in
the midbrain, it unc|uestionabIy manifests a progressive increase in size
and definition in the primates. Ventral to the substantia nigra is the
collection of fibers constituting the cerebral peduncle 1 C P ). These peduncular
fibers provide lor all those intricacies oi motor activity essential to the
life of the hunter m the use and the contrivance ol his weapons and
implements. They serve the expression of man's abilities as agriculturalist,
home-buildi'r, artisan and artist. Without these connections none of the
activities characteristic ol human society and cultural organization would
be possible. It ma\ be ciuestioned, thcrclorc, \\li\ these structures, denoting
such preeminent achit'\t'meiits in man, lia\e an\ representation whatsoever
in aj)es and lowtT mammals. It is, ho\\c\i'r, not the mere presence of these
neokinetic (ibers rejjrcsented m the cerebral pt'duiicK' w Inch gives them their
significance. They have a long mammalian history. In which their linal expan-
sion in the human bram displays this critical surplus over and above their
primitive, fundamental de\elo|)nient.

" " 'J ' J (.,.. ;

THE BRAIN OF MODERN MAN

833

Lateral to t lir ix-ticular lonnation and ap|)arcntl\- c'nK'rjj;inii; Iroin it is a
large pnitubiTanci', {\\v iiicsial gciiKulatc hoclx (Mgh) connfctcd with
tlic pathway ol licarmg. It aj^prars to incn.'asc j)i()gi'f,ssi\t'l\' in si/f through

FIG. 355. MAN. LEVEL OI- IHE OPTIC CHIASM.

CIN, Internal CapsiiU-; <:i'H, Corpus 1 iypotlialaniiciini; 1 ui", Dcscrndins Pillars of the Fornix; i rs, Fields of
Forel; gli>. Globus Pallidus; nlt. Lateral Nucleus of the Thalamus; N.\n, Mesial Nucleus of the Thalamus;
NLi, Internal Lateral Nucleus of the Thalamus; oi't. Optic Tract; opx. Optic (Chiasm; in i. Putamen; V3,
Third Ventricle. [Accession .Man. Section C 79<). Actual Size 64 X 2(j mm.]

the pniiiatc series and in man has hirger chinensions t han m any ol the apes.
Betweiai tlu' two peduneles is a wide opt ico-|)edLineiilai" spaee wiiieli
eontains the mainmillarv bodies, the postinlnndihular eniinenee, the
attaehnienl ol the inhindibular stalk and the tuber einereum. All of these
are more jjroniineiit than thi' lorri'sponding struetures in lower primate

834 MAN

brains. The intcrcoUicular sulcus between the superior colliculi is broader and
deeper than in the anthropoids. It forms a larger pineal fossa for the epiphysis
cerebri. The function attributed to the epiphysis in inhibiting growth and

FIG. 356. MAN. LE\ EL OF THE OPTIC CHIASM.
CEN, Central Gray Matter; cm, Mammillary Body; cp, Cerebral Peduncle; Cph, Corpus Hypothalamicum;
CFT, Central Tegmental Tract; lcb. Lateral Geniculate Body; mgb, Mesial Geniculate Body; nru. Nucleus
Ruber; op.x. Optic C^^hiasm; pul, Pulvinar; ref. Reticular Formation; sbn. Substantia Nigra; sc, Superior
Colliculus; STR, Striatorubral Tract. (Accession Man. Section gSo. Actual Size 65 X 35 mm.)

retarding sexual development is significant in that it delays maturity in man
to a much later period than in other mammals.

LEVEL OF THE OPTIC CHLASM (FIGS. 355, 356)

At this level the contour of the section shows the characteristic modifi-
cations of transition from the midbrain to the inlerhrain. The third ventri-
cle ( V3) appears as a deej:) narrow cleft between the two nuclear structures

THE RRAIX OF MODERN MAN

835

which form thr optic thalami. In the most ventral position and forming
the iloor of the ventricle at this level is the optic chiasm (Opx) into
which enter the optic ner\es and from which th(,' optic tracts depart on

FIG. 35-. -MAN. LE\ EL OF THE ANTERIOR COMMISSURE.

AC, Anterior ("ommissurc; ciN, Intirnal Capsule; fdp. Descending Pillars of the Fornix; for, Fornix; CLP,
Globus Pallidus; .nm. Nucleus Masticatorius; pl"T, Putamen. [Accession Man. Section N 1052. Actual Size
63 X 29 mm.]

their way to the several relay stations before they end in the occipital lobe.
The third ventricle is divided into a dorsal and a ventral division by the
interposition of the commissura mollis. The thalamus is contiguous with
a dense bundle of fibers constituting the internal capsule (Cin) which
represents the cephalic continuation of the cerebral peduncles. The capsule
is placed between the ventrolateral surface of the thalamus and the mesial
surface of the corpus striatum which in this section presents the two major
portions of the lenticular nucleus, the globus pallidus ( Glp) and the putamen

836 MAN

(Put). Other morphological features of this Ie\el are indicated by corre-
sponding markings which appear in the legends accompanying the frgures.

LEVEL OF THE ANTERIOR CO.\LMISSURE (fIG. 357)

Here the brain stem comes to its cephahc termination. The third ven-
tricle, less deep and somewhat broader than in the level of the optic chiasm,
is Hanked upon either side I^y the cephalic extremity of the optic thahimus.
All of the structures in this region of tlie brain in man correspond in detail
with the homologous elements of the lower and intermediate primates as
well as the great anthropoids.

Features of Human Brain Showing Greatest
Evolutional Significance

In concluding the re\'iew of the human brain, it is difficult to decide
which features have the greatest evolutional significance. The neopallium,
pons Varolii, p\ ramid and cerebral peduncle probably should be given the
place of first importance. The lateral lobes of the cerebellum, the dentate
and red nuclei, the superior cerebellar peduncle and inferior olive are but
little less decisive in their evidence. All of these structures are essential
factors in the organization and control of mammalian motor specialization.
Their progressive evolutionary development in the primates denotes to what
degree behavioral capacity has been extended. The history of these structures
is closely interwoven with the differentiation of the extremities and then-
record reveals how that process has advanced through many phases from
apes to man until the human hand made its appearance. This specialization
is the final test which ma\- be employixl to explain the extensive develop-
ments of the human brain.

Chapter XW'I

RECONSTRUCTION OF THE GRA\ MATTER IN THE
HUMAN BRAIN STEM

"^HE reconstruction ol the ij;ra\' matter in tlu- luinian brain stem
re\eals thosi' modllications, expansions and elaborations which
repri'st'nt the cuhnliiation ol the cNolutional process traced throngh
the i:)rimate order. Certam kvitnres made more evident in this nu'thod ol
visualization deser\e particular consideration. In this regard, attenti(ui lirst
directs itsell to the [iontile nuclei, the grc-atest mass formed b\ any one
s|)ecialized structure contributing to the composition of tlu' lU'uraxial gray
matter. This imposing nuclear collection in man contributes a greater pro-
portional amount ol gray matter to the make-up of the brain stem than it
does m any ol the lower members of the primate group. Not only is this
dewiopnieiit easily recognized in the actual amount of nuclear material but
also in the complicated disposition ol {he lil)t'rs which arise within it, and
coursing through the nuclear matrix l)reak it up into a more intricate
nuclear mass than is seen in any of tht' otiur reprcsentatix es of this series.
Another im])ressive mass ol gray matter is the arcilorm nucleus, w hich
re|)resents a marked acKancc' o\er that seen in tiu' lowt'r forms, consisting
ol a layer ol gray matter almost completel\ iiucloping the \entral surface of
the inlrapontiU- portion ol the brain stem. The mlerior olivary complex also
reaches a degree of complication considerabl\ in acKance of that hitherto
oijst'rM'd m the ph\ lum, w hile the colliculi show tlu- hnal steps in the process
which has alread\ been obst-r\'ed to be in progress, the inferior colliculus
continuing to show a steady reduction in size and comple\it\, while the
sujicnor colliculus barely holds its own m comparative and absolute

dillerentiation.

837

838 MAN

OiK' olIuT l(.';iturc' which at once attracts attt'iitioii 111 this (general sur\cy
of the exposed nuclear material is the coinparatixc decrease m the size and
importance of the reticuhir formation, the matrix out of which has de\ eloped
the great majority of the nuclear masses belonging to the gra\ matter of the
brain stem. The reconstruction m general does not give the impression of
massivcncss which might be expected in this the largest brain stem of the
series. The nuclear accumulations, although increased relatnely m size,
dillt-r materially from those which have been observed in the lower members
of the series in an increasing sharpness of definition, a greater degree of deli-
cacy and clearness ol outline, w hich serves more sharplx to dillerentiate them
irom those ol the lower primates than does any material increasein bulkorsize.
The fundamental structures of the brain stem, the reticular formation, the
nuch'i ot the cranial nerves and the specialized masses of gray matter in the
region of the mesencephalon, particularly the nucleus ruber and tiresubstantia
nigra, do not present any material alteration in the a|)pearance of these striic-
tures as they have been observed in the lower orders in this series.

The organized masses w hich ha\ e materially changed in size, complexity
and in contour are those connected with the iunctions which in man have
achieved a greater degree of integration and coordination than that attained
by any of the lower members of the primate group. This |)articularly applies
to the pontile nucleus which develops, pan jjassu, with the expansion of the
cerebral hemispheres and organization of synergy, the contribution of the
cerebellum to animal motion. The olixary nucleus which must be considered
as a comparative newcomer 111 the organization of tlu' lirain stem, as it
presents material comple\it\- only in the upper primates, shows a marked
advance m man oxer that which has bt'cii observed in the other members of
this group. Although its liinction is not tiill\ understootl, its de\ clopnuMit has
been steady, dehnite and continued. The conclusion heri' acKanced ma\- not
yet be entirely supported 1)\ delinite e\ idcnce, iu\ trtlulcss the increase in

RECONSTRICTION OF HUMAN

839

compIc\it\ and si/.c of the nUw has paralleled tlu' emergence of tlu' hand as
an lnd(.'|)t'ndent nuMiiIxT lor the exploration of the cmironnu'iit. 1 his ini|)rove-
nu'iit in nianual de\terit\ in eon jiinet ion with the perleetmn ol hmoeular

ftETlCUL*

FK;. 358. LATERAL SURFACE OF CM \\ \L\TTER OF BRAIN STEM, HOMO SAPIENS.
Key to Diagram, arc. nlc, Arcifoim Nuckus; (eis. gbav matter, Cintrnl Gmy Mattir; <;ociil. com.
Cochlear Compli-x; inf. coll.. Interior Colliculus; inferior olivary nuc, Inferior Olivary Nucleus; ret.
FORM., Reticular Formation; sub. nigra. Substantia Nigra; sup. coll., Superior (!c>lliciilus; vest, comf..
Vestibular C~ompIex; 3rd nerve M'C., Nucleus of the Oculomotor Nerve.

vision mav he explained b\- the critical exercise of the visual Junction in the
guidaiux' of the hand and arm. One other feature w hich deser\i's mention is
the marked increase in the clearness and delmition exinced l)\ the \ari(nis
channels, w hich the lon^^ w hiti' lihi'r tracts ha\x' ])roduccd throui^h tlu' reticu-
lar formation and tln' otlu'r i^iortions of the gray matter ol tlu' stem. These
channels presc-nt a greater sharpness and (U'linition of outline than that seen
in the preceding members ol this group.

The Dorsal Medlllari' Nuclei
In the lowfst |)art of the rc-construction the dorsal medullary nuclei
appear alrcad\ fairly wi-ll diA ciopi'd. l"lu' nucli'us ot the column ol Coll,

840 MAN

situated mt'sially, jx)ssesses the large ()\erhan<2;ing lateral extension wliieli is
characteristie ol the dorsal niielear aeeiinuilations. This lateral extension ol
tlu' nueleus extends outward and almost hides Ironi \ie\\ the more laterally
placed nuek'us ol the eolumn ol Burdach. The nueleus ol Coll eontmues
upward enelosed by a dwnidlmg mantle ol libers and eontaniin<j; witlim its
lateral eonea\it\- a considerable bundle of fibers of the column of Coll. As
it approaches the opening of the fourth \entriele it presents a slight lateral
deviation produced b\ the widening ol the ventricular system in this locality
which has been so characteristic of the beha\ior of these structures in the
forms already described. The nucleus does not, ho\\c'\er, participate in the
formation of the lateral wall of the lourth \ entricle, l)eing at all times excluded
from that cavity by the circumventricular mantle or lining of subepend\ nial
gray matter. The nucleus gradually diminishes in size as the ascending libers
reach their cells of termination, and it linally disappears at a level only
slightly higher than the point ot opening ol the fourth ventricle. In appear-
ance the nucleus is more or less solid and is not broken up into any definite
arborization by the fibers composing the tract \\ hich lie grouped together in
the concax'ity formed by the lateral o\erhang of tiie nucleus.

Tlu' nucleus of tlu' column of l^urdach appears at a slightly higher h'vel
than the ])ri-cedmg nucleus, as a rounded ele\alion on tlu' dorsal surface of
the central gra\ maltt'r at about the ]unction ot the body with the lateral
horn. It rapidly extends dorsallx', the base wicK'ning whik' its dorsal tt'rmina-
tion gradually moves lattaally in con form it \ w it li the de\ lation shown b\ the
preceding nucleus. It also develops a lateral o\ (.'rhanging mass of gray matti'r
enveloped by a steadily diminishing number of fibt'rs, and m tlu' lateral con-
cavity of the overhanging portion ot the nucleus and almost surrounded by
it appears a distmet bundle (d tlu' remaining lil)ers of the ascending tract
of Burdach. The nucleus continues to increase m size until it reaches the
level at which the nucleus of CjoII begins to diminish and then it rather

RECONSTRUCTION OF HUMAN

841

rapidly dfcrrasi's in s\av and iinportancc, its [ilacc iu'iiig takt'ii 1)\ the appear-
ance of tin- mu'lear material appearing in eoniieetion w ith the \estil)ular eoni-
plex. In assoeiation with the u|)|)er half of the iiueleus th(.Te cle\el<)|)s upon

FIG. 359. LATERAL SL Rl- ACE OF GRAY .\L\TTER OF BRAIN STEM, HOMO SAPIENS.

Key to Uiac;ram. arc. nlc, Arcil'orm Nucleus; cen. gray. Central Gray Matter; inf. coll., Inferior
Colliculus; INI-. oi.iv.. Inferior Olivary Nucleus; lateral genic. Lateral Geniculate Body; mes.
Genic, iMesial Geniculate Body: nuc. clneatus, Nucleus Caincatus; RET. form., Reticular Formation;
SUB. GEL., SUBST. GEL. and IRIGEMINI, Substantia Gelatinosa Trigemini; sup. coll., Su])erior
Colliculus; VESTi. co\ii>le.\. Vestibular (Simplex.

its latt'ral aspeet a mass of >j;ra\ matter, the nueU'us of Bliimeiiau, apparently
eonneeieci with the nueleus ol Buidaeh.

The substantia tielatinosa Kolancli is eontinuecl upwarti into tlu'
oblongata as the reee|)ti\ f nuek'us lor the tri^enimal iu'r\c-, beni^ealletl m this
region the substantia gelatinosa tngemnu. I he nueleus is somewhat more
extensivi' both abo\e and below and presents a delinite eonstrietion m the
region of the entr\ of the eoehlear division of the eighth nerve. This has been
mentioned previously and may be ealli'd the waist of the trigeminal nueleus.
It maintains a relati\tl\ uiuhanged position in its course upward through the

842 MAN

brain stem, lying almost in the lateral meridian, and is inllnenced hut little
by the lateral deviation w hieh is so delmitelx |)resent in the ehange oi |)osition
of the dorsal medullary nuelei. The nueleus ]:)resents a few lateral extensions
w hieh proeeed outward between the descending trigeminal libers particularly
in the region where the nucleus of Blumenau appears, and it is diHieult to
determine whether the latter belongs to the trigeminal complex or to the
nucleus of the coluniii of Burdach. At the lexel of the entrance of the cochlear
division of the eighth nerve, the substantia gelatinosa trigemini undergoes
a definite diminution in size, recedes Irom the surface of the stem, then gradu-
ally increasing in size it becomes flattened and applied to the lateral surface
of the reticular formation. As the nucleus continues upward it finally pre-
sents a dorsomesial inclination and disappears within the reticular forma-
tion, being covered on its lateral aspect by a prolongation of this nuclear
matrix which envelops it on its ventral, lateral and finally on its dorsal
as])ect. The disappearance of the substantia gelatinosa trigemini from the
surface of the reconstruction takes place abo\e the upj^er limit of the vesti-
bular nuclei.

The Inferior Oli\akv Nlcleus
The inferior olivary nucleus appears in the lowest portion ol the recon-
struction as a narrow, llattenetl lamina of grax' matter disjjosed m an oblique
direction dorsomesially from the ventrolateral angU' of the reconstruction and
|)ointing toward the central gray matter. As this lamina, which is the \entral
accessory olivary luiekais, is followed upward there begin to appear masses of
gray matter in connection with it, dorsal to its mesial extremity. These repre-
sent the first appeaiaiui.' of the dorsal accessory oli\ar\ nucleus. As the
ventral accessory nucleus is tract'd birther it presents numerous irregularities
in size and shape and proceeds upward in a rc-lati\el\ constant position, con-
nected at its mesial extremit\ by a discontinuous series of nuclear bridges
with the dorsal accessorx nucleus, it comes to an vml at al)oiit the junction

RECONSTRUCTION OF HUMAN

843

oftlK' upper and niKkllc tliircis ol tlu' ()ii\arv complex, sli<z;litl\ caudal to the
first appearance of the pontile nuclei and the termination ol the arcilorni
nucleus. The dorsal accessorx olive seems de(initel\- to <;i\e rise to the mam

FIG. 360. DORSAL SURFACE OF GRAY MATTER OF BRAIN STEM, HOMO SAPIENS.

Key to Diagram, gen. gray M.vriER, Ontral Gray Matter; LAr. gemc. body. Lateral Gcnieulate B<jd\ ;
MESIAL GENic. BODY, Mesial Geniculate Body; Nuc. clav., Nucleus Clava; nuc. gun.. Nucleus Cuneatus;
PONT NUC., Pontile Nucleus; ret. roRvi., Reticular Formation; zona inc.. Zona Incerta.

mass of the ol!\"arv nucleus, this sac-like structure apparently di'xeloping
from the lateral extremity or \entral surlaceol the dorsal accessory nucleus.
The main mass of the inferior olixary nucleus lorms a plicated sac, the
nKjuth of which is directed dorsomesially, while the fundus, w hich is directed
ventrolatcrallx , presents numerous coinolutions producmo; tlu' eminence on
the surface of the stem, called the olivary eminence. Dorsomesially, the
dorsal lamina of the oli\ar\ nucleus and the dorsal accessory nucleus luse
and rest upon the \cntral surface of the reticular formation w hich is hollowed
out to receive this ma.ss of gray material. Tht' inferior oli\ary nucleus proper

844 MAN

appears slightly ahoNc the point ol ojicning ol the iourth \entnele, inereascs
rapidly in size both \-entrocl<)rsall\' and mesiolaterallx , and eontnuies upward
as a prominent mass of gray matter. Above the point at whieh the pontile
luielei are first seen the aeeessory portions of tlu- luieleus disappear and the
luieleus itself eontracts, produeing a dome-shaped strneture which lies within
the more suj)er(ieially placed masses of gray matter representing the caudal
portion of the pontile nuclei. Laterally the mass of the inferior oli\ary nucleus
is separated from the ventral surface of the reticular formation by a con-
siderable space which is occupied by the continuation upward of the lateral
white column of the spinal cord.

The Reticular Formation

This mass of nuclear material representing the matrix from which many
specialized nuclei have differentiated does not bulk so largely nor attain the
apparent importance which it manifests in the lower members of the series.
It appears as a more or less quadrilateral mass of gray matter extending
obliquely from the xentrolateral angle of the oblongata, dorsomesially to its
point of conllueiice w ith the body of the gra\- matter and at a higher level
the floor of the Iourth \entricle. Its \entromesial surface is more or less
irregular, presenting a concavity at the point where the inferior olivary
nucleus comes into close relationship with the reticular formation. In the
lower portion of llu' oblongata it is separated from its fellow of the opposite
side by a consick-iable distance which is occupied b\ the longitudinallx
coursing grou|)s of medlanly disposed libers. As these structures gradually
seek other [positions m t!u' brain stem tlu' reticular lormalion apj^roaches the
midline and its dorsonusial extremity becomes w ider and Hatter as it comes
into contact with tlu' raphe. In tlu' lowest portion ol the reconstruction the
ventrolateral i'xtremit\' of the reticular lormation is continued \entrally and
laterally into two prolongations, the ventral one of which is continuous with

RECONSTRUCTION OF HUMAN

845

the ft'])lialic c\lix'inil\ c if the \ cntial <;ia\ column ol tlu' spina 1 cortl, w hi If the
dorsal (.•xtcnsioii brconus thin and eoncuvc d()rsall\ to rccciw the \fntral
surface ol' the substantia gelatinosa trigemini. As these prolongations arc

FIC;. 361 . \ ENTRAL SURFACE Ol- GKA^' MATTER OF BRAIN STEM, HOMO SAPIENS.

Key to Diagram, cen. gray matter, Central Gr.-iy Matter; hyp. nuc, Hypoglossal Nucleus; N3 nuc.
Oculomotor Nucleus; superior olivary nic, Superior Olivary Nucleus; zon. inc.. Zona Inccrta.

traced upward the \t'ntral I'xtcnsion diminishes m sv/.v and linaliy disap-
pears, leaving only the upward continuation oftlie dorsal prolongation lying
in close contact with the substantia gelatinosa trigcmini. This thickens some-
what, Ijeeomes irregular and then fenestrated by bundles ol white libers.
The reticular formation lliudl\ becomes disposed as an irregular, more or less
transverse mass of gray matter in close contact dorsally w ith the subepen-
dymal gra\ matter of the lloor of the- fourth ventricle in w hieh may be lound
channels produced b\- the longitudinal and transversely crossing i)undlcs of
libers and containing many more or less well-delmed nuclear accumulations,

846 MAN

the rcniainder ol the mass appearing as an indisenmniate, undillerentiated
nuelear matrix.

The dorsal surlaec ol the retieuhir formation eomes into intimate rela-
tionship with, and its eonformation is greatly iniluenced h\ the substantia
gelatinosa trigemmi, the lloor of the fourth ventriele, and the numerous
nuelear eollections which appear in this vieinity in eonneetion with thiM)rigin
and termination ol many of the cranial nerves. In the lower jjart of the pons
the reticular formation is much reduced in thickness, the deep layer of the
pontile nucleus being separated from the floor of the fourth ventricle l)\- only
a small amount of reticular formation. In this region the libers underlying the
lloor of the ventricle form a considerable condensation limiting the dorsal
extent of the reticular formation and reduce the gray reticular formation to a
body of relatively small dimensions. In the mid-portion of the pontile teg-
mentum, however, the reticular formation increases m thickness and is dis-
posed as a more or less transverse quadrilateral mass presenting a smooth
median surface almost m direct contact with tlu' raphe. The development m
this region of the trapezoid body and the lateral fillet serves to differentiate
the more mesial portion of the reticular lormation into a thicker dorsal sub-
di\ision in contact with, or separated by only a small amount of white matter
from, the lloor of tlu' fourth \entricle, and a thin lamina of gray mattt'r which
develops ventrallx in contact with the |)ontile nucleus. Laterally in the mid-
])ortion of the pons, these two sul)di\ isions ol the reticular lormation |om,
the point of junction corresponding to the lateral extri'inity ol the lloor ol
the fourth ventricle.

Still further laterall\ a thm edge ol the reticular lormation works out-
ward and backward, insinuating itself betwA'cn the surlaec ol the brain stem
and the superior cerebellar pedunele, which as it lea\es the roof of the ft)uit li
ventricle turns forward, upward and inward in a spiral course toward the red
nucleus of the opposite side which is situated in the \entral pc)rti()n ol the

RECONSTRUCTION OI HUMAN 847

niesenct-phalic tcgmciUiini. This (.hanin'l loinu'd h\- the suptTior cerebellar
])e(lunele is lar<ie, well delmi'd aiul (lislinet. It is liniilecl iiiesiall\ b\ that
portion ol tlu' reticular loi'iiiation which is 111 contact with the lloor ol the
iourth x'cntncle, and tlu' ac|ucdiK't ol Syl\ lus, while laterally it is hrst uncov-
ered by the reticular formation but as it sinks (kH'|)er and di'cpcr into the
tegmentum it is gradually surrounded b\- the thm lateral txtt-nsions ol the
reticular lormation alread\ mentioned. As the superior cerebellar peduncle
penetrates the tegnu'iitum and mo\ es mesiall\ and \i'ntrall\ it progressively
reduces the amount ol reticular lormation betwc'ii it, the lloor ol the Iourth
ventricle and tlu' nu'dian rai)lu-, until m the upper portion ol the mctenceph-
alon the peduncle reaches ihv midline and completelx obliterates that part of
the reticular lormation which lies mesial to it. In this region the reticular
lormation is divided b\ the superior cerebellar peduncle into two jjortions, a
thm lamina \i,'ntrall\ \\ Inch has already been mentioned as bi'ing m contact
with the deep layer ol the pontiU' nucU'us and a dorsomesial triangular mass
conca\'e latcrall\ which rests mesiallx on the raphe and dorsall\' on the
\entricLilar gray matter. The ventrolatt'ral lamina ol the reticular lormation
luses dorsall\ with the dorsomesial triangular mass at the dorsolateral angle
of the brain stem at the Icn'cI of the ujjpcr port ion of the fourth \ entricK' and
the beginning ol the acjueduct of Sylvius. As the superior cerebellar peduncle
moves ventromesiall\- toward its decussation this area ol lusion between the
ventrolateral lamina and the dorsomesial mass of the reticular formation
becomes more massi\e.

In this vicinity a second tunnelling of this portion of the reticular lorma-
tion takes place by the course of tiie lateral fillet from thi- \ tntrolatcral angle
ol the brain stem as this structure approaches the inlerior colliculus. The
reticular lormation lying immediatelx subiaceiit to the inferior colliculus
assumes considerable proportions and forms a foundation or support for this
colliculus at its \t-ntrolatt'ral c\tremit\. This lateral mass of the reticular

848 MAN

formation contimu's upward and forms a base also for the superior colliculus.
while between ttu' mferior and superior eollieuli a dorsal extension oi the
retieular formation passes around the dorsal surfaee of the brain stem to und
by meeting its fellow of the opposite side at the midline, thus eompletely sur-
rounding the eentral gray matter of the meseneephalon. At the cephalo-
lateral extremity of the inferior eollieulus the retieidar formation is tunnelled
obliquely ventrad, cephalad and somewhat laterad by the course of the
inferior brachium which connects the inferior colliculus with the mesial
geniculate bodx. This channel lies partl\ on the surface but at times it is
bridged by extensions of the reticular formation which pass \entrall\ iiom
the portion lying immediately beneath the superior colliculus, and dorsally
from the part of the reticular formation forming the ventral lip of the
groove.

AboN'e the point at which the superior cerebellar peduncle decussates,
the retieular formation adjacent to the raphe gradually increases in amount
ventrally and laterallx until it completely surrounds the decussated superior
cerebellar ijeduncle w hich is now terminating in the red nucleus and forming
a part of its capsule. This portion of the reticular formation surrounding the
red nucleus and its capsule is continued u])ward through the meseneephalon
and becomes continuous with the zona incerta ot the diencephalon. In the
upper j:)ontile and lower mesencephalic region the reticular tormation lormmg
the ventral lip of the channel containing the inferior brachium is continued
upward as a lateral support for the substantia nigra, in the mesencephalon,
as the lateral portion of the reticular formation is passing upward to luse with
the zona incerta of the (lience])halon, it sends out a lateral extension which
passes dorsal to the substantia nigra and ventral to the mesial geniculate
body, thus separating these two structures. This extension of the reticular
formation is cur\ed \entrall\ into the angle between the mesial geniculate
body and the mesial portion of the diencephalon to a narrow, tapering ])oint.

RECONSTRUCTION OF HUMAN 840

The niori' nu'sial reticular niass continues upward in rather an irrei^ular form
and fuses with the retieuhir lorniatioii ol the diencephalon, gra(hiall\ giving
place to the mesial group ol thalamic nuclei.

The Arciform and Pontile Nuclei

The arciform nucleus consists of a thin lamina of gray matter lying
directU ventral to the p\ ramidal tract and beneath the surface of the brain
stem. It consists of an irregular gra\ lamina which in \an')iis parts ol its
course sends prolongations laterally around the \entrolateral surlace ol the
stem. It increases rather rapidly in width until it reaches the mid-oli\arv
region where it achieves its greatest lateral expansion, the lateral limit of this
extension being the jxisloliiury sulcus. From this point the arcitorm nucleus
rapidU diminishes in size and comes to a termination slightlx' caudal to the
origin of the pontile nucleus. The arcilorm nucleus extends mesially around
the |)\ ramidal tract at some points into the ventromesial sulcus ot the brain
stem, but in the greater jjortion of its extent it stops short of the ventro-
median sulcus. Its dorsal surface corres])oncls accurately with the conlorma-
tioii of the p\ ramidal tract which immediately underlies it, and at its lateral
extremity it a|)proaches the lundLis oi the inferior oli\arv nucleus and also
further dorsally comes into direct relationshi]) with the reticular lormation.

The pontik' nucleus first appears at about the middle of tlu' mam olivary
nuch'us at a le\el slightl\' abo\e the termination oi the arcilorm nucleus, as
a small colk'ction of gra\' matter situated mesial to tlu' |)\raniidal trad. It
contiiUK's upward in this position, steadily extending laterally both \-entral
and dorsal to the pyramidal tract to which it is ch)scly appHcci, until the
uppt'r limit ol the mierior oli\ary nucleus is reached. I-rom this point the
|3ontile nucleus incrt'ases \ery ra])idl\ m size and comple\it\, becoming
complete mesiall\ and surrounding the |)\ ramidal tract \entrall\, mesially
and dorsalU with an unbroken sheath ol nuclear material. The pyramidal

8^0 MAN

tract laterally still remains uncovered and is situated between the ventral
surface of the inferior olivary nucleus and the lateral extremity of the ventral
lamina of the pontile nucleus. The jjontiU' nucleus contnnies to increase in
size and sends a ])rolongation around the uncovered lateral surface oi the
pyramidal tract w lilch, fusin<z; with the already established deep layer ol the
pontile nucleus, now forms a complete in\estment for the pyramidal tract.
The pontile nucleus m this region is divided into a massive structure ventrally
and a somew hat more reticulated collection of gray matter dorsally, which
begins to show channels through which stream the decussating fibers of the
middle cerebellar peduncle. The massive character ot the ventral layer ol the
pontile nucleus gradually loosens and becomes broken up into a vastly retic-
ulated series of laminae of gray matter separated by transversely crossing
pontile libers.

As the nucleus assumes greatei proportions, it may be seen to form three
divisions, a ventral circumferential layer which is cjuite smooth and relatively
unbroken ventrallx , a deep transverse layer in contact with the tegmentum,
and an intermediate lace-like arrangement of nuclear material. The surface
layer of the j^ontih' nucleus, the stratum su])erliciale pontis, conforms to the
contour of the middle cerebellar peduncle, while the deep layer, the stratum
])rofundum jjontis, is in direct contact with the tegmentum. Between these
two rather definite laminae may be seen disposed in a very irregular brandl-
ing maniur maii\ other la\ ers of gray matter, the stratum complexum pontis,
which is disposed traiisx ersel\' between the decussating fibers of the middle
cerebellar peduncle. These laminat- of gray matter continue upward irregu-
larly and as the u|)|)er jjortion of the pons is approached they tend to focus
ventrally and dorsall\, the dorsal grouj) joining the deep layer ol the pontile
nucleus, to form a support for the substantia nigra, while the \entral group
tends to coalesce ventrall\ and forms a thickeni'd mass of gra\ matter into
which the eeri'bral pt-duncle enters as it j^asses from the mesencei)halon into

RECONSTRUCTION OF Hl'M AN 8,-i

thr nu't(,'iUT|)lial()ii. In the region w Iutc the superior cerebellar jjeduncle
enters the brain stt'm, the pontile nucleus arri\'es at its greatest expansion,
lor hvw tlu' (li'cp layer ot the pontik' nut'leus swings dorsally to einbract- the
reticular ionnation almost as lar dorsal as the junction of the dorsal and mid-
dle thirds ol the brain stem. The \arious laminae of the pontile nucleus are
arranged somewhat conci'ntricall\ . all corres])onding to the curve of the
surface c)f the brain stem, and end in irregular, jagged extremities from between
which stream the middle c\'r(.'l)ellar i)eduncular libers as they coiuerge to form
the middle peduncle of the cerebellum on the lateral as])ect of the meten-
cephalic portion ol the brain stem. The delmite condensation of the pontile
nuclei to lorm the buttresses upon which rests the substantia nigra is not so
cU'arl\ exident m this reconstruction ol the human brain stem as it was in
some ol the lower lorms, on account ot the lact that the greater mass of the
peduncular libers ser\ es to break up the lateral buttress into a number of
small laminae and groups of nuclear material.

The transition Iroin tin- pontile nucleus to the substantia nigra is so
gradual and indistinct that it is dillicult to sa\- at which point the deep la\er
of |)ontilc' nucleus and tht- \entral la\ cr ol the reticular formation cease and
the substantia nigra begins. In the ccjihalic portion of the metencephaloii the
pontile nucleus is delicient on its lateral and latt'ro-dorsal aspects, sup])lving
a point ot entrance lor the cerebral |)edunclc as it passes ventrolateral to the
substantia nigra, the pcduncU' being envelo|jed on its dorsal, mesial and
\ciitral surfaces but free on its lateral surface as it enters the meteiicephalon.

The Vestibul.-\r Nuclei

This mass ol gray matter tirst ajjpears at about the level of the opening
ol the lourth \entricle as the nuclc-us ol the descending root, interposed
between the gray matter ot the I loor ot the lourth \entricle and the diminish-
ing nucleus of Burdach and appearing almost as a cephalic continuation of

852 MAN

this nucleus. It is more or less pyramidal in shape, its base being supported
by the gray matter forming the floor of the fourtli ventricle while its apex is
directed outward ventrolaterallx' and is inserted between the substantia
gclatinosa trigemini and the corpus restiforme.

Tlie nucleus of Deiters definitely appears in the vestiljular area at the
lower portion of the fourth ventricle and continues to increase in size until it
reaches the mid-ventricular level of the stem. From this point it diminishes
and rapidly comes to a termination below the level at which the substantia
gclatinosa trigemini disappears within the reticular formation. Prior to its
disappearance the nucleus of von Bechterew appears as a dorsal extension of
the \estibular area in the lateral wall of the fourth ventricle.

The nucleus of Schwalbc or the triangular nucleus of the vestibular
complex appears as a triangular field lying directly subjacent to the gray
matter forming the floor of the fourth \entricle and mesial to the nucleus of
Deiters.lt rapidly increases in size, being quite extensive transversely, and
bulges forward to come into contact with the dorsal surface of the reticular
formation ventrallw Its greatest size corresponds with the maximum devel-
opment of the nucleus of Deiters. It then rapidly diminishes in size and
entirely disap])ears at the level of the nucleus of von Bechterew. At its acme
it occupies the lateral three-fifths of the sube|3endymal portion of the gray
matter ol the lloor of the fourth \i'ntricle in the mid-\entncular portion,
forming a considerable eminence on the \cntricular floor, the acoustic emi-
nence, but its ce|)halo-caudal extent is relati\ely insignificant. Its lowest
extremity corresponds with the ui)per \v\v\ of the cochlear nucleus and its
upper limit with tlu' nucleus of von Bechterew, thus occupx ing the middle
portion of the fourth \entriclc.

The Cochlear Neceei
These nuclei make their appearance at a le\cl slightly below the mid-
point of the incdullai\ portion of the fourth \entricle as a collection of

RECONSTRUCTION OF HUMAN 853

nuclear material acljacrnt to thr latrral aii>;k' of the fourth ventricle. This
mass of gray matter is the dorsal cochlear nucleus. It gradually increases in
thickness and at the same tune extends laterally oxer the acoustic nerve root,
conforming to the surlace contour ol the corjjus restilorme which lies unmc-
diately subjacent to it.

The nuclear material gradually extends more and more laterally and
ventrally and thickening at its distal extremity it becomes a discrete ventral
luicli'ar collection callixl the ventral cochlear nucleus, it occupies the \entro-
lateral angle ot the oblongato-pontile junction, it;: most ventral extent lying
somewhat m front ol the mid-|)oint on the lateral surlace ol the bram stem.
The cochlear nerve root passes through the mesial aspect ol the ventral coch-
lear nucleus, splittmg it into two [portions, a lateral mass which overlies the
root as an o\al collection ot gray matter, and a mesial portion existing as a Hat
lamina ol nuclear tissue aj^jjlied to the mesial aspect ot the entering root.

In the more caudal portion ol the cochlear complex the ventral and
dorsal nuclei arc joined together by a \\ell-delined layer of nuclear material.
This la\c'r becomes thinner and thinner as the corpus restitorme moves dor-
sally toward its entry into the inlt-rior cerebellar peduncle until a delinitc
separation between the two cochlear masses results in the formation of two
discrete nuclei, tlu' dorsal and \'entral. A small portion of the dorsal cochlear
nucleus persists independent l\ in the angle of the lloor and lateral wall of the
lateral \entricle, while the typical o\al-sha])cd mass of nuck'ar material,
the ventral cochlear nucleus, continues cephalad and somewhat \entrad as
a separated mass of gray matter. The nucleus continues upward to tlu' le\ el
ot the delinitne appearanct' of the |)ontile nucleus where it rather abruptly
terminates. I he cochlear complex in the human brain stem is much more
extensive than that found in the lower forms, the nuclear material being
scattered richlx between the libers of the ner\e as that structure aj)|)roaches
the brain stem, producing a continuous and dellnite nuclear connection

854 ^lAN

between the dorsal and ventral aecumulations of gray matter. At its junction
with the fourth ventricle the cochlear nucleus shows its greatest dimensions,
the dorsal nuclear subdivision bemg eontmued mesially under the lloor ol the
fourth ventriek', separating tlie subependymal gray matter of the fourth
ventricle ior a considerable distance from the dorsal surlaee of the vestil)ular
complex.

The CoLLicuLi

These masses of gray matter appear to be relatively insignificant in the
reconstruction oi the gray matter of the human brain stem. In particular
the inlerior colliculus is represented by a relatively small collection ol nuclear
material. It rests upon the cephalic continuation of the deep layer of the
reticular formation in the mesencephalon, this nuclear matrix separating the
colliculus Itself from the gray matter surrounding the aqueduct of Sy!\ ius.
The colliculus itself is made up of a number of layers of gray matter, the most
definite of which is the external layer which is represented in the reconstruc-
tion. The interior ol the colliculus is formed very largely of white fibers and as
these fibers approach each other and coalesce they form a fibrous core for the
colliculus. Arising from the lateral aspect of the colliculus is a bundle of libers,
the inferior brachium, which leaves the eollieulus and passes toward the
mesial geniculate body, producing a deep groove and in some places a tunnel
in the lateral surlaci- of the mesencephalic reticular formation. The inferior
colliculus is supported laterally by the lateral extension of the reticular for-
mation while mesi;ill\' it rests upon the reticular formation forming the dorsal
raphe ol the mesencephalon and a group of libers which emerge from the
colliculus and cross to the opposite side as the commissure of the inferior
colliculus. It is separated cephalicallx from the superior eollieulus 1)\ a dorsal
extension ol the reticular formation. I his dorsal prolongation arises liom the
deep layer of the mesenee|ihalic rt'tieiilar lorination extending dorsally and

RECONSTRICTION OF IlLMAN 855

thrn nu-siall\ to |i)ia its fellow oi the opposite side at the mid-line, thus
separating the superior and nilerior eoHieuli Irom eoutaet w ith one another.
The superior eollieulus is eonsideral)l\ niori- extensive eephalo-caudad
than the ulterior eollieuhis and ajjpears as a nuelear specialization in the
reticular formation whieh surrounds it on all sides and sejjarates it from
the iiilenor eollieulus eaudally, its lellow ot the op|)()site side niesialiy and the
thalamic nuclei ee])halically. Mesiall\ the superior eollieuli are separated
Ironi one another by a continuation ii])\vard ol the indillerent reticular lor-
mation which se|xu"ates the inlerior Irom the superior colliculi. Mesialix the
superior eollieulus rests upon a mass of fibers which arise Irom the interior of
the superior eollieulus, converge toward each other at the midline and cross
to join the superior eollieulus ol the other side, thus lorming the commissure
ol the superior eollieulus. The de\ elo])nient ot this mass ot libers in this region
definitely separates the superior eollieulus Irom the gray matter surrounding
the aqueduct ot Sylvius. Laterally and ventrally the superior eollieulus is
supported by the gradually increa^sing bulk of the reticular formation, which
appears cephalad and dorsad to the intertegmental course of the superior
cerebellar peduncle. Cephalically, the superior eollieulus gradually decreases
in thickness and losing its characteristic appearance, it becomes a part of a
thin lamina ot indillerent gray matter which iuses with the habenular region
ot the dience|)halon.

The SLBsr.\.\Ti.\ Nigka

The substantia nigra appears as a relatively massive collection of gray
matter in the ventral portion of the mesencephalon and seems gradually to
dilTercntiate itself from the fused nuclear matt'rial forming the ventral layer
of the reticular lormation and the dorsal layer ot the pontile nucleus. This
change occurs very gradually and it is diflicult to say at which point the
fused reticuIo-])ontilc gray matter ceases and the distinctixc, characteristic

856 MAN

lU'uial tissue of the substantia nigra appears. It is supported by the pontile
nucleus, the formation of the two buttresses ah-eady mentioned not being
nearly so delinite in man as it is in some of the lower forms. The substantia
nigra rapidly increases in bulk and spreads laterally, its deep surface being
separated from the tegmental reticular formation by the beginning conden-
sation of libers which in the diencephalon will form the fields of Forel.
Laterally the substantia nigra is continued outward into two definite pro-
longations which are producc^d by the appearance of a mass of white fibers
in the lateral jjortion of the substantia nigra, arising from a definite nuclear
condensation. In the interpeduncular region the mesial extremity of the sub-
stantia nigra is separated from its fellow of the opposite side by the indiflerent
gray matter forming the interpeduncular space, w hile the reticular formation
as it gradually becomes reconstituted alter the decussation of the superior
cerebellar |)eduncles moves forward and then swings laterally to parallel the
dorsal surface of the substantia nigra thus completely separating the sub-
stantia nigra from the nucleus ruber.

The Nucleus Ruber

This large mass of gray matter appears in the ventromesial portion of
the mesencephalic tegmentum aboxc the ca\ Ity excavated from the reticular
formation by the decussation of the superior cerebellar peduncles. It is a dis-
tinct globular nuclear mass and ra|3idi\ increases in siz.e, presenting the
spherical a|>ix'arance so typical of it and becoming the most striking structure
in the mesencephalic tegmentum. It is rouiuk'd m form and completely sur-
rounded by a capsule or mantle of w hilt' hbtrs w Inch separates it from the
reticular formation.

The Central Gray Matter

A ihm lannna of gra\ matter is set'ii t'xtt'iuling l)ackward from the
central gray matter as a narrow tongue lining each side of the dorsomedian

RECONSTRUCTION OF HUMAN 857

sulcus. This l;i\cT of tiray niattiT continues to mow dorsally and then rapidly
expands as the fourth \entriclc opens. It is chsposed in an arched fashion
lati'rall\ corresponding w ith thi' opening of the h)urth MMitricle and de\-el()ps
into a layer of gray matter which lorms the lloor oi theh)urth \t'nt rich' and
is interposed between the t'pi'nd\ nial linmg oi the \entrii-le itself and the
dorsal medullarx luiclci. This thin layer of gray matter eoiUiiUH's upward,
increasing considerahlx in lateral extent, fusing with the dorsal cochlear
nucleus and forming a thin layer o\ t'r the triangular nucleus ot the \ estii)ular
complex. In its lower portion it is in direct contact xx'iitrally with the
li\ poglossal nucleus w hich a[jpears as the eminentia hypoglossi on the lloor oi
the \entricle as that structure o])ens. Lateral to this emineiux- ap|)ears
a de])ression which separates theem inentia hypoglossi i'rom another eleva-
tion, the eminentia vagi, which is ])roduced by the underlying dorsal
luick'us oi' the \agus.

I^rom this jjoint uj:)ward tlu' lloor ol the lourth xcntricle is rather smooth
and appears as a thin sheet of gray matter extending from the median sulcus
of the x'entricle to the lateral xentricular wall. At about the mid-portion of
the ventricle another emiiu'nce appears near the midline oi the lloor of the
fourth \ entricle. This ele\ ation is produced b\ thede\elopment in this localitx
of the abducens nucleus and is calK'd the I'lninentia abducent is. These emi-
nentia' are relativelx high, the groo\e between them being c|uite deep. The
area w Inch corresponds w ith the \ t'stibular and dorsal cochlear lUicU'i, know n
as the acoustic area, is relati\c'l\ smooth and is continued laterallx' into the
lateral recess oi the lourth \entricle at the point oi entrance of the cochlear
dix'ision ot the acoustic ner\t'. \hv gray matter oi the lloor ol the fourth
ventricle is continued upward, furnishing a thin covering for the triangular
nucleus of Schwalbe and the nucleus ol von Bechtercw in the lateral wall of
the fourth xciitricle.

The central gray matter i'ormmg the lluor of the fourth ventricle above

858 MAN

the mid-\cntiicular region rapidly contracts in its lateral dimension and,
thickening, it I)egins to assume the characteristic appearance ol the gray
matter surrounding the aqueduct oi" Sylvius. As the mesencephalon is
approached the cavity of the ventricle rapidly diminishes, the walls of the
ventricular system increase considerably in thickness until the region of the
colliculi is approached, w here the lumen of the \entricle rapidly diminishes
in size and the walls of the ventricle become enormously thickened.
This thickening takes place ventral and dorsal to the aqueduct through-
out the lower half of the mesencephalon, the dorsal portion forming the
support for the mesial extremities of the superior and inferior colliculi. This
dorsal layer of gray matter is pierced at various points by the fiber bundles
which are passing across between the two inferior and the two superior
colliculi as the collicular commissures. In the u])per halt ot the mesencepha-
lon the ventral portion of the central gray matter rapidly extends ventrally,
forming a long, tongue-shaped process which passes forward lateral to the
raphe and almost in contact with its fellow of the opposite side, being sepa-
rated onlv by the indifferent material of the raphe. In this ventral extension
of the central gray matter there appears a large nucleus, the nucleus ot the
oculomotor nerve, which is continued cephalad to the junction of the
mesencephalon with the diencephalon.

In the uppermost portion of the reconstruction the dorsal portion ol the
central gray matter is broken up by the appearance ot the posterior commis-
sure w hich passes across from one side to another and di\ ides this part ot the
central gray matter into a ventral lamina lying directly around the cavity of
the aqueduct of Sylvius and a dorsal la\ er w hich lit's between the posterior
commissure and the commissure ol the su])erior colliculi. Laterally the central
gray matter is supported almost throughout its entire extent l)y tlu' reticular
•■.formation of the \arious portions of the stem. In the upper portion ot the
■ mesencephalon the for\vard prolongation of the central gray matter, which

-.■'■/ .■" ' ■■

RECONSTI^l'CTlON 01 HUMAN

850

contains in its subac|iH'cIuctal rci^ion tlu' oculonintor nucleus, is continued
vcntrall\ into thi' nitcrpcduncular space and tluTc becomes contniuous witii
the nilerpeduncular lorniation wIik'Ii is bein^ translonni'd into the zona
incerta. This interpechincular iinw matter is coiitiiuied lorward and merges
with the gra\ matter tormiiiii; the h\ peiicephalon.

CiiAi'TKK x.w'ir

THE BRAIN OF PREHISTORIC MAN

A Survey of I he Psychological Faundalions nf Ihnndn Prniiress

"^111: luinian laiiiilv, atx'orchiifi to most conscrxatiw authorit\, lias
been m cxistfiict' more than a liall million \eais. During' all tiu' vast
cvn of Plc'istoc'ciu' tinu\ w ith its rt'ciirmit glacial ions and mtciAals ol
warmth, man's brain stcadii\' <i;re\v. This t^rowth at lirst was slow and
irregular. Later it became so tlecisive as to makt' ci'rt'bral development one
ot the most strikini;; features m human exoliitioii. The brain slow 1\ increased
in \olume. It acc|uired mueh reliiu'inenl in maii\ structural details. Its
newer parts became more limhl\ specialized. As a result ol tlu- exolutioiial
process tht' brain ol modern man is a lar more eliicient organ than that
possessed b\ the tvirliest ol human kind.

It is i^robable that man\ distinct species ol prehistoric man inhabited
the earth. Several distinct races hiwv already bct'ii identilied by means ol los-
sih/.ed human bones. The racial dillcrentiations established in this manner
have l)een utilized to reconstruct the outward appearance ol these prehistoric
peoples, in tlu- reconstructions ol Prolessor McCregoi', the dilU-ri'iiccs are
Striking (p. 732). The ape-like appearance ol J-'it heeanthropus crectus
aflords some reasons lor calling this earliest known mcmbt'r ol our laniilx"
circle the Ape-man. The old man ol Cro-Magnon, on the other hand, jjossesses
a nobilitx' ol expression which in itsell seems to justilx his characterization
as the "Paleolithic Creek." Bilweeii these two extrt'ines, tiu' iW'andcrt lial
and l-*iltdown nun ari' interiiudiate stages. How these ancient |X'ople felt,
thought and liwd is a matter ol importance, concerning which the bram
has much to reveal. This re\clation is most signilicant, because oi its dis-
closures regarding the cult ural progress and possibilities of mankind.

861

862 MAN

Fossil Evidence in the Stldv of the Brain oi Pki hisioric Man
In order to gain sonu- idea ol what the hrani ot pnniitnc man was hke,
it is necessary to depend upon certain circLinistantial c\idence. This admis-
sion may seem to put the case in its most unhixoraijle hght. The hict remains
that the brain of man shared the same fate as other soft parts ol his body;
but it lias not disappeared without leaving dehnite mipressions of its size
and shape. These impressions ha\t' i)een found upon fossilized cranial bones
datmg [)ack to tfie earliest human races yet recognized. There is, of course,
some question as to the \alue ol such impressions m drawing conclusions
about the brain. Professor Symington, who has investigated the subject
extensively by means of endocranial casts, is e\trcmel\' cautious m the
matter. He prefers to admit frankly the limitations of our knowledge rather
than reconstruct the brain of primitive man upon too slender evidence. This
wise admonition has been borne in mmd throughout the lollowing descrip-
tions ol the prehistoric human brain.

For the purpose of sensing the bill \alue of endocranial evidence, it is
important to recall that the bony capsule enclosing the brain is peculiarly
susceptible to the effects of cerebral growth. Some portions of this capsule
begin to form in cartilage and some m membrane. Four cranial bones lia\e
a membranous origin, i.e., the frontal, the parietal, the occipital, and
the sc|uamous portion ol tlu' tem|)oral bone. Expansion ol the brain appears
to be the dominant factor iii the growth of the head. In consecjuence, the
nu'iiibranous bones ol the skull bear man\ impressions ol the cerebral hemi-
spheres. These impressions would \x- more pronounced il tlu' ci'rebral con-
volutions came into actual contact w ith the iniU'r surface ol the skull. But
the interposition of the dura mater, the pia mater, tlu' arachnoid and the
cerebrospinal lluid in part obsciux's the im|:)rint ol the brain. A number ol
cerebral features, howex'er, art- consistently im|)ressed upon the cndocraiiium.
Schwalbe has shown that there are certain bon\ ridges corresponding

THE I^RAIN OF PREHISTORIC MAN

863

to cerebral lissurcs and a minilxr of dcprcssiOns piocliucd by ccTcbral
coinol lit ions. These he ealled respeetively ju<^a cerehratia and iiiipressiones

digitatae.

FIGS. 362 TO 365. FOLK \IF\\S Ol- AN ENDOCRAMAL CAST Ol A MODI K\

HUMAN SKULL SHOWING THE 1 Ml'KFSSKJN FS DKWIATAE AND Jl GA CEHEBKAI.IA

OF SCHWALBE WHICH INDICAJE THE POSH ION OF SE\ERAL CONA OLl 1 IONS,

FISSURES A.ND ARTERIES OF THE BRAIN.

(a) Vertex or Dorsal Surface of the Brain, (b) Base or Ventral Surface, (c) Right Lateral Surface. (i>) Left
Lateral Surface. Ilhistrating those markings which may be looked for in an indocranial cast.

Ju<i;a and unpressions appear in the separate eranial bones as follows
(Figs. 362-365):

Taiu L A
PRINCIPAL FOSSIL REMAINS OF PREHISTORIC MAN

fPrc-Pa!coIithic and Lower Paleolithic)

Antiq-
uity
(years)

Name

Race

Discoverer

Place and date Parts

Period

500,000

Pithecanthropus
crectus

Trinil

Dubois

Java
1891

Skull cap
Teeth (3)
Femur

Eolithic ?

250,000

Paleoanthropus
heidelbergensis

Heidelberg

Schoetensack

Heidelberg
1907

Lower jaw with
teeth

Eolithic ?

150,000

Eoanthropus
dawsoni

Piltdown

Dawson

Sussex
19U

Parts of skull and
jaw

Early Paleo-
lithic

130,000

Homo rhodesi-
ensis

Rhodeslan

Harris

Rhodesia
1921

Fragments of fe-
mur, tibia, sac-
rum. Skull (no
lower jaw)

7

120,000

Homo neander-
thalensis

Neanderthal

Flint

Gibraltar
1848

Skull

Early Paleo-
lithic (prob-
ably)

120,000

Homo neander-
thalcnsis

Ni'.-indcrthal

Bourret and
Regnault

Malarnaud
iHHH

Jaw (m)

Eady Paleo-
lithic (prob-
ably)

1 20,000

Homo ncander-
thalcnsis

Neanderthal

?

Arcy sur Cure
1859

Jaw (m)

Early Paleo-
lithic (prob-
ably)

120,000

Homo neander-
thalcnsis

Neanderthal

?

Gourdan ?

Fragment of low-
er jaw-

Early Paleo-
lithic (prob-
ably)

120,000

Homo ncander-
thalcnsis

Neanderthal

Dupont

LaNaulette
1866

Lower jaw

Early Paleo-
lithic (prob-
ably)

1 20,000

Homo neander-
thalensis

Neanderthal

Torrent

Banolas
1887

I (iwcr jaw-

Early Paleo-
lithic (prob-
ably)

1 20,000

Homo ncandcr-
thalcnsis

Nennderthal

Fuhlrott

Neanderthal
1856

Top of skull, a
number of skel-
etal fragments

Early Paleo-
lithic (prob-
ably)

120,000

Homo ncandcr-
thalcnsis

Neanderthal

Rzehak

Ochos
1906

Fragment of low-
er jaw-

Early Paleo-
lithic (prob-
ably)

75,000

Homo ncander-

thaicnsis

Neanderthal

N eh ring

Ehringsdorf
and Taubach
1892-1914

Lower jaw, 2
teeth, decidual.
Fragments of
child's skeleton,
3 fragments of
skull-cap, femur

Prc-Mouster-

ian or
Aeheulean ?

[8641

Tahi I A— Continued

PRINCIPAL FOSSll. REMAINS OF PREHISTORIC MAN

I Pre-PaU'olitliic and Lower Paleolithic*

Antiq-
uity Name
(years)

Race Discoverer Place and date ■ Parts

Period

75,000

Homo neander-
thalensis

Neanderthal

Kraniberger

Krapina
1899

Frafjinents of
skulls, skeletons
of II (?) indi-
viduals

Pre-Mouster
lan or
Acheulean ?

75,000

Homo ncander-
thalensis

Neanderthal

Neu-Essing
Klause

I molar

Prc-Mouster-

ian or
Acheulean ?

75,000

Homo neander-
thalensis

Neanderthal

Galilee
1926

Skull

7

75,000

Homo neander-

thalcnsis
Homo neander-

thalensis

Neanderthal

Gibraltar 11
1926

7

50,000

Neanderthal

1 lauscr

Le Moustier
1908

Skull, crushed.
Skeleton. Cere-
monial burial

Mousterian

50,000

1 lomo neander-

thalensis
1 lomo neander-

thalensis

Neanderthal

Kampfe

Ehringsdorf
1914

Jaw. See Tau-
bach

Mousterian

40,000

Neanderthal

Maska

Sipka
1882

Fragment of low-
er jaw

.Mousterian

40,000

1 lomo ncander-
thalcnsis

Neanderthal

Bi'uyssonie
Bardon

La Chapelle
aux Saints
1908

Skull (m) almost
complete. Skele-
ton. Ceremonial
burial

Mousterian

40,000

Homo neandcr-
thalensis

Neanderthal

Martin

La Quina
1911

Skull (f) well-
preserved skele-
t 0 n. C h i 1 d's
skull, skeletal
fragments

Mousterian

30,000

Homo neander-
thalensis

Neanderthal

Peyrony and
Capiton

La Ferravvu
1909 1910

Skeletons (impf.)
2 adults, 4 child-
ren. Ceremonial
burial

Skull of child

Mousterian

30,000

Homo ncander-
thalensis

Neanderthal

Peyrony

Pech de L'Aze
1909

Mousterian

30,000

Homo ncander-

thalensis
I lomo neander-

thalensis

Neanderthal

Peyrony

Petit-Puy-
moycn 1907

Fragments of
jaws (maxillae)

Mousterian

30,000

Neanderthal

Puydt Frai-
pont and
Lohest

Spy
1887

2 skeletons

Mousterian

30,000

Homo neander-
thalensis

Neanderthal

Marett

Jersey
1910

13 teeth

Mousterian

[865

Table B
PRINCIPAL FOSSIL REMAINS OF PRFHISTORIC NL^N

I UppiT Paleolithic)

Antiq-
uity

Name

Race

Discoverer

Place and date

Parts

Period

25,000

Flomo sapiens

Cro-\Lignon

7

Aurignac
1852 ?

Aurignacian

25,000

Homo sapiens

Cro-Magnon

Lartet

Cro-Magnon
1868

4 individuals: i
fetus, 2 men and
I woman, well-
preserved

6 skeletons (2
negroid)

Aurignacian

25,000

Homo sapiens

Cro-Magnon

Verneau

Grotte des
Enfants 1884
(Grimaldi)

Aurignacian

25,000

Homo sapiens

Cro-Magnon

Riviere

Grotte du
Cavillon
1872
(Grimaldi)

I skeleton (6.55
m). Packet of
bones in ochre
at the base

Aurignacian

25,000

Homo sapiens

Cro-Magnon

Abbo

Barma
Grande ?
(Grimaldi)

6 skeletons

Aurignacian

25,000

Homo sapiens

Cro-Magnon

7

Baousso da
Torre

2 skeletons
(adult). Bones
of child

Aurignacian

25,000

Homo sapiens

?

Hauser

Combe Ca-
pelle 1907

I skeleton

Aurignacian

25,000

Homo sapiens

?

Sierra

Camargo ?

Skull fragments

Aurignacian

25,000

Homo sapiens

?

Obermaier

Willcndorf
1908

Fragments of fe-
mur, humerus,
upper and lower
jaws

Aurignacian

25,000

Homo sapiens

Cro-Magnon

Enzheim

I skeleton

Aurignacian

25,000

Homo sapiens

Cro-Magnon

Paviland
1823

I skeleton

Aurignacian

25,000

Homo sapiens

Cro-Magnon

Depcret
A reel in and
Mayct

Ojcovv

I skull-top

Aurignacian

25,000

Homo sapiens

(Sub-brachy-
ccph. Not
Cro-Mag-
non)

Solutre

5 skeletons

Aurignacian

20,000

Homo sapiens

?

Daleau

Pair-non-Pair
1896

Skull fragments
(parietal)

Solutrean

20,000

Homo sapiens

?

Vire

1 ricru'c ?

Frontal skull
tragments

SoUiliean

20,000

Homo sapiens

?

7

Roset ?

Teeth

14 skeletons. Re-
mains of 6 (?)
other individu-
als

Solutrean

20,000

Homo sapiens

Pfedmost or
Briinn ?

Maska Kfiz
Wanki'l

Pfedmost

18K0

Solutrean

20,000

Homo sapiens

Briinn ?

Makowsky

Briinn 1891

I skeleton

Solutrean

20,000

Homo sapiens

Briinn ?

Hillebrand

Ballahohlc

I child's skull i Solutrean

[866]

T\iiif: B — Omlmued

HKINCU-'AL lObblL KliMAINS OF PREHISIOKIC MAN

(Upper Paleolithic)

Antiq-
uity
(years)

Name

Race Discoverer

Place and date

Parts Period

20,000

Homo sapiens

Laugerie-
Haute

I skeleton

Solutrean

20,000

Homo sapiens

Neu-Essing

I skeleton

Solutrean

15,000

Homo sapiens

Cro-Magnon

Cartailhac

La Madeleine
1864

I skeleton

Magdalcnian

15,000

1 lomo sapiens

Cro-Magnon

Massenat

Laugerie-
Basse 1872

I skeleton

Magdalcnian

15,000

Homo sapiens

9

Testut

Chancelade

I88H

r skeleton

.Magdalcnian

15,000

Homo sapiens

Cro-Magnon

CaiJ-HLiric

1 skeleton

Magdalcnian

1 -i.OIH)

Homo sapiens

Cro-Magnon

Duruthy

1 skeleton

.\Ligdalcnian

15,000

Homo sapiens

Cro-Magnon

Tournier

Les Hoteaux

I skeleton

Magdalcnian

15,000

Homo sapiens

Cro-Magnon

Karstcn

Freudenthal

1874

Skeletal and skull
fragments (pari-
etal, mandible,
teeth)

Magdalcnian

15,000

Homo sapiens

Cro-Magnon

Le Placard
1883

I skull (f), 9 cups
made of skull-
to p s. Skeletal
fragments

Magdalcnian

I 5,000

Homo sapiens

Cro-Magnon

Verworn
Bonnet
Steinmann

Obercasscl
1914

2 skeletons

Magdalcnian

15,000

1 lomo sapiens

Cro-Magnon

Bouyssonie

l.imeuil

Skull fragments

.Magdalcnian

15,000

Homo sapiens

Cro-Magnon

Grotte des
Hommes

3 skulls

.Magdalcnian

15,000

Homo sapiens

Cro-Magnon Daleau

Grotte des
Fees

Fragments of up-
per and lower
jaws

.Magdalcnian

15,000

Homo sapiens

Cro-Magnon Breuil

Lussac

Lower jaw

.Magdalcnian

15,000

Homo sapiens

Cro-Magnon [ Pictte

Mas d'Azil

I skull top i .Magdalcnian

15,01111

Hiuiiii sapiens

Cro-Magnon

Nelli

Espelugues or
Lourdcs

Various frag-
ments

Magdalcnian

15,000

Homo sapiens

Cro-Magnon

Castillo

2 skull fragments
worked into
bowls or cups
(child's 1 0 w e r
jaw, I adult
molar. Aurig.)

.Magdalcnian

15,000

Homo sapiens

7

Furfooz

Skull

Uncertain.
Probably
Neolithic

10,000

Homo sapiens

? K. K. NliiMult

OIn. t

33 skulls

Azilian

10,000

Homo sapiens

Cro-Magnon

1 lexenkiielie
Bavaria

I skull

Azilian

1867J

868 MAN

In the Irnnlal Banc:

Pars squamosa, tlic supcTior Iroiital coinolulions
Pars orhitalis, tin- orbital convolutions
Pars tfiiiporalis, the inlcrior Irontal fonxolution.
//! the Parietal Banc:

Postcro-nilVrior triangle (Schwaihe), usually some unpressions ol the

parietal eon\'olutions
The parietal fossa corresponding to the parietal emmenee
The crista S\ Kii, marking the horizontal ramus of theSvKian fissure.
In ibc Tcmjxiral Biinc:

Pars sc|uam()sa with the greater wing of sphenoid, the middle tem-
poral sulcus and the second and third temporal gyres.
//! the ()cci])ital Bone:

The impressiones occi])italis, crista occipitalis, crista margiiTralis and
the iuga cerebellaria.
In the fossilized skull these features become landmarks of utmost impor-
tance as guides in establishing functional localization in the bram of primi-
tive man.

The lumv important fossilized skulls, discovered either in part or largely
intact, are gi\en in the aceompanxing tabulations. To the data arc added
the names of the discoverers, the place and date of the discovery. Further
specifications are included to indicate, is so far as possible, the estimated
antiquity and the race of man to which each fossil specimen has been
accredited (Tables a and b).

The Brain oi Puhfcaxthkopus Erectus, the Ape-Max of Java

According to ])revailing oi^inion, tlu" most ancient human fossil is that
of Pithecanthropus erectus. To it an anticiuity of not less than 500,000 years
is assigned. Although the humanity of this fossil is disputed by some author-

THE BRAIN OF PREHISTORIC MAN 86q

itic's, the testimony it hears iiulieates a primate staiulina: relati\H'lv lii^h in
the scale. The tossih/ecl \):\i\ (il tlie' skull consists ol the caKarium which
incluck's the greater [portion ol the Irontal s(|iiamosa and the parietal hones,
a part ol the occi]jital hone and pt-rhaps a small Iraymeiit ol one temporal
sc|uamosa. The preser\ation is lairl\ sxinmetrical on tlu' two sides ol the
cranium. I'or lurther descriptions ol this lossil, the reader is referred to
Duhois' mono<z;raphs on the suh|ect.

IMPRESSIONS AND ,U GA OF THE CALX ARUM

The caKarium is particularix lortunate hecause it retains many sli^Miili-
cant impressions and luga mdicatmti the conliguration ol the hrain. A cast
made liom the pithecanthropus caKarium rewals a numher ol leatures
which lurnish \aluahle inlormation concerning the hrain of the .)a\'an man.
The j)arietal area shows clearly tlu' distrihution ol the middle meningeal
artery, also the eminence and groo\e corresponding respecti\ cly to the
parietal fossa and crista S\K ii. Reproductions ol the hrain cast ol pithecan-
thro|)us, together with suppleiiu'iitary reconstruction of the cerehral hase
hj' Professor McGregor are shown m I'lgurcs 366 to 3~i. The relic! in
the occijjital region marks the grooves and convolutions corresponding tot hi'
()cci])ital impressions, the crista occipitalis, the crista marginalis and the
juga cerehellaria.

From these data it is possihle to introduce certain houndarK's upon llu'
lateral surlacc ol the cast and thus estahhsh the prohahle position oT several
functional areas in the hrain.

Tun SviA IAN Imssi RE. The horizontal hraiieh of the S\ Kian lissure
extends from the f'rontotem|)oral notch to the lower margin of the parietal
eminence. The lull ixtent and terminal disposition of this lissure cannot he
determined and hence it is not possihle to indicate the character or position
of the supramargmai coii\ulution.

FIGS. 366 TO 371. SIX MEWS OI- THE ENDOCRAMAL CAST OF PITHECAN-
THROPUS ERECTUS (JAVAN APE-.MAN) THE MOST PRIMIIIXF KNOWN REPRE-
SENTATIVE OF THE HUMAN FAMILY. ESTIMATED ANIiyLII'i OF FOSSIL
500,000 YEARS. RESTOKA 1 lONK B'l PROF. J. H. MCGREGOR.

(a) Vertex, (d) Base Restored. ((;/ ItdiUmI Pole. M)) Oeei|)it.il Pole, (e) Riglu Lateral Surfaee. (1) Left Lateral
surface. The frontal convolutions and br.inclies of the middle meningeal artery are especially well
defined. The smoother areas in the cast indicate the regions which h.ive been restored.

[870]

THE BRAIN OF PREHISTORIC MAN 8-i

The Fissurk of Rolando. The lissurr of Rolando (sulcus cintralis)
nia\ in a i^cneral \\a\ \)v placfcl hctwcfn the two inani branches ol the middle
nu'iiiiimvd artciN and in front of the parietal eminence'. Estnnatcd l)\ the
anthropometric criteria of this lissinx' now <j;encrall\ accepted, the upper
extremitx of the lissm-c may be |)laced on or near tlu' superior lon<j;itudmal
groove about 2 cm. posterior to its niidpomt. calculated as one hall the
distanci' iVom the frontal to the occipital vm\ of this yroo\e. The <i;eneral
direction of the Rolandic fissure ma\ likewise be estimated as a descending
line which leaves the superior longitudinal groo\c at an angle ol inclination
forward of somewhere betwct'ii 6"'" and "1.4 . The allocation ol this most
important boundarx is lAtreiiu'ly generalized and must of necessity omit many
essential details of the sulcus. It allords no intimation as to the extent ol the
fissure, or tlu' relations of its upper and lower extremitU's to the superior
longitudinal fissure on the one hand and tlu' lissure ol S\l\ius on the other.
Neither does it denote the presence of the usual geiuillections conspicuous in
the human central sulcus. Idu- position and disposition ol the Rolandic
fissure assigned to the l)rain of pithecanthropus depend more upon deduction
and analog\- than actual indications on the cast. It is dcsirabh', howi'\er, to
establish certain approximations regarding the character and position of
this lissurc.

Thi£ Gkoo\e of the Tka\s\'Erse Si.m s. The third landmark is the
groove of the transverse sinus which indicates the planes ol se])aration
between the occipital lobes of the cerebral hemispheres and the cerebellum.
This groove w ith the sui:)erior longitudinal furrow marks the position ol the
torcula hero|)hili.

These boundary lines determine the general extent of four great lobes
in the brain, namel\, the frontal, parietal, temporal and occipital. It is
possible in the light of this topography to consider tiie characters and sig-
nilicancc ol each lobe separately.

8-2 MAN

TIIF. FRONTAL LOBE OF PITHECANTH KOPUS ERECTUS

The troiital lobe appears as a part leularly eonspieuous portion ol tlie
hemisphere (Fig. 366). It is promiin'iit especially because of its large size and
pronounced comolut ions. Near the middle ol the frontal eoincxity and in
ju\taj)osition with the superior longitudinal hssure is a prominent Pacchion-
ian enlargement. 1 he relief of the frontal coiuolutions is especially note-
worthy as it gives this region of the brain an indi\ idualit\ possessed by no
other area. This observation does not impl\ that the eonvohitional process
is suprt'me m the Irontal lobe of pithecanthropus. It demonstrates, as
Schwa I be has pre\i()usl\' shown, that the frontal sc|uam()sa is more impression-
able to brain growth than other parts ol the skull, it is fortunate, moreo\'er,
that such IS the case, for it is this region of the hemisphere w Inch has most to
reveal regarding the higher psychic development ol the brain. Nor should it
be overlooked that this Irontal lobe represents the latest accessions of
human specialization, w lu'reb\' man has distinguished himself in cremation and
finally acquired all that is implied in the titli', "Ilomo sapiens."

There is a slight asymmetry m the size and shape of" the frontal lobes,
the left being somewhat larger. This also applies to the frontal comolut ions
of the k'lt side. In ri'lati\e size tlu' Irontal area represents upon its latt'ial
surface more than oiu'-third of the entire e\|)osed convexity of the hemi-
sphere. The two frontal lobes togetluT, w luai \ k\\ x'd from aboxc, giNc the
impression ol a t nincated p\ ramid. There is a marked bluntness at the frontal
pole and the outlines extend backward with a gradual widening to the level
of the Rolandic lissure. This general broadtaimg is not consistentl\ main-
tained. In OIK' zone there appears to be a eonsideral)le constriction, hor
purposes of subsec|ueiit identification this zone is calk'tl \\)v coronal conslric-
tion. It begins at either Irontott'iiiporal notch and follows tlu' impression
of the coronal suture to the midline.

Gorilla

Pithecanthropus

lonio sapi> I

FIGS. 372 TO 3-4. A COMPARISON OF THE ENDOCRAXIAL CASTS OF GOKll I A,
PITIIECANTHKOPL S WD HOMO SAPIENS. THE PRINCIPAL FA OLl TION ARV
EXPANSION APPEARS IN HIE FRONTAL LOBE.

I8-3]

874 ^lAN

Frontal Lobe oi- Pithecanthropus as Compared w rm That of
Gorilla and Homo Sapiens. As compared willi the priinalc Irontal lobe
nearest to that of man, i.e., the ironlhi, the brain ot pithecanthropus shows
nianilcst clifFcrcnces (Fig. 372). The frontal lobe as a whole is niLich less con-
spicuous in gorilla. It is actually- and rehitively sniaMer m size. The rchef of
its coiu'olutions is much less pronounced, its sha[)e is more pyrilorm as it
tapers towards its apex at the Irontal pole and it has no coronal constriction.
The left lobe of the Ja\an man is slightly larger than the right, which is
probabl\- indicative of unidexterity. AH of these dilFercnces point to a dis-
tinctly inferior dexclopment in the Irontal lobe oi gorilla as compared with
pithecanthropus. A comparison with the brain of Homo sapiens shows at
once what decisive gains the brain of modern races has made oxer its simple
prototype of primitue man (Fig. 3'"4). In size and general a])pearance the
brain of pithecanthropus resembles that of a three-year-old child.

Fissures in the Frontal Lobe. The fissures in the frontal lobe which
may be idcntilit'd with certainty are the superior and middle frontal sulci.
They are tortuous and bound corrt's|)oiKlingly complex conxolutions. These
fi.ssures are most pronounced m tlu' prelrontal area and cannot be traced
back as far as the frontal region. The com (ilutions determined b\ the frontal
sulci are the superior, middle and inferior frontal g\res. The last of these is
of greatest importance since the mlerior Irontal coiuolution, espt'cially on
the left side, is almost universally regarded as the motor spia'ch center in
man. In connection with this con\-olution some authoritU'S ha\'e idi'iitilied
the anterior and ascending l)ranches of the S\l\ian fissure, if present m
pithecanthropus, howi'xcr, tlu'\ t'xist merel\ as tlu' laintest traces which
aiFord insufficient ground lor their acceptance as delinite cerebral landmarks.
in Ilomo sapiens, these sulci :ivv conspicuous and im|)art nuuh prominence
to the inferior frontal coiuolution. I'here is no indication oi tlu' precentral
fissure and hence no actual guide to tlu' Innits ol the pi'ecentral or motor

THE BRAIN OF PREHISTORIC MAN 875

comolLitidii. How c'\tcnsi\fly tin's region of tlir cortex in jjitlu'tantliropus is
proN iciecl with an iiitcrnu'diate j^reccntral area for skilled nio\-enu-nts eannot
1)1' (Utrrniinrd. Vhv basal surlace ol tlu' Iroiital lobe as show n \n supplemen-
tary reconstruction b\ Professor McGregor indicates the presi'iice of two
orbital conca\ities of considerable depth and well-de\eloped interorbital
keels; in other words, conditions lar more primiti\e and j)ithec()id than those
m mockrn man.

Physiological Dedlctions to Be Dk aw x i kom Frontal Lobe. Esti-
mated from the jjlivsiological standpoint, the Irontal lobe of pithecanthropus
is indicati\e of a beha\ ioral advance lar above the plane of gorilla but
i'c|uall\ below that of Homo sapiens. The Ja\an man must have possessed
increased powers ol adapti\e reasoning. He was capable of more advanta-
geous adjustment than gorilla or other anthropoids. He constructed lor him-
self a greater sphere of experience, created at least an aj>proach to human
personality and dc\clo]3ed the distincti\"c characters of indi\iduality. It is
probable also that in his manual dcxteritx he was right-handed; at least the
greater size of his left Irontal lobe suggests that his brain had singled out one
hand as the chief representati\ c tor externalizing its activities. This in itself
is a distinctly human character. Around it are built many of man's most
productive specializations. In all ol these respects the Javan man was much
below his human successors. There is little in his brain by w hich to judge the
|3i"oricieiic\' ol his manual de\c'lopmcnt, to estimate how much skill he had
ac([uired with his hands. But the prominence ol his mlerior Irontal comolu-
tion (Fig. 375) strongly suggests that he added one supreme advantage to
the motor equipment of animal life. He had learned to speak — to communicate
in \erbal language. The gradual de\elopment of skilled acts had eventually
combined the elfector organs of articulation and phonation into a coordinated
apparatus controlled through the bram, by which he was able to express his
ideas and feelings. The means of communication thus established laid the
foundations of human know ledge.

876 MAN

The degree to whieh pithecanthrf)pus may have developed language can-
not be implied from anything in the external appearance of Wis brain. Doubt-
less his lingiiistie attaimnents were I'xtremely crude. On the other hand, the
fact tliat the cerebrum manifests such pronounced advances over the anthro-
poid brani \n an area so mtunatel\' idcntihed witli spi'cch m Ilomo sapiens
signilics the ch-crsivc step which pithecanthropus liad made m the de\elop-
meiit of Imman kind.

W ith all due allowance for the reservations imposed I)y morpliological
limitations, the frontal lobe of the Javan man clearly indicates that the
brain had progressed in its psychic capacity, that it had expanded in those
portions upon which unide.xterity, reason, language and human personality
depend.

THE PARIETAL LOBE OF PITHECANTHROPUS ERECTUS

The parietal lobe of pithecanthropus also gives evidence of expansion,
although the details of this development are less conspicuous than in the
frontal area. It is impossible to discern the relief of any convolutions, and,
with the exception of the Sjdvian fissure, no critical impressions may be
detected. No discrete boundaries between the frontal and parietal or between
the occipital and parietal lobes may be distinguished. The hypothetical [)osi-
tion of the Rolandic lissure provides the anterior limits of the parietal area.
The increased ])r()minence of the parietal eminence, together with the general
widening of the cerebrum in this region, denotes a considerable extension of
the neopallium. As compared with the corresponding area in gorilla, this
expansion is emphatic. In contrast to the parietal lobe of Homo sapiens, it is
distinctly inferior. The j^arictal lobe as a whole represents the neopallial
area for the elaboration ol somesthetic sensibility. The expansion of this
area must be regarded as incidental not only to the augmentc"d inllux of
sensory impressions, but also to the increased complexity of their association.

THE BRAIN 01- PREHISTORIC MAN 877

Three somatic tactors lia\(.' \)vvn \\v\d especially respmisihlc lor this Increase:
(irst, tlic cle\ elopnieiit ol tlie huiiian or luiiiianoicl loot; second, the assump-
tion ol the erect posture, and thiixl, the emancipation ol the hand Irom loco-
motor lunctions. 01 tliese lactors, [Iw third has perhaps the <i;reatest cogency.
The increase in the jjarietal t'liimence iinoKes a cortical area assigned to
sensory perceptions ol the u|jper extrt'inity.

THE OCCIPITAL LOBIi Ol PITHECANTHROPI S EKECTl'S

The occipital lobe is little more productive ol cerebral landmarks than
the parietal. The occipital pole- ol the brain extends o\-er the cerebt'llum, w hile
the divergence ol the two hemis|)heres is jjronounced in this region. A bilat-
erally' symmetrical groo\e corrt'sponding to the trans\-erse sinus separates
the cerebellum from the cerebrum and thus establislu-s the caudal boundary
ol tile occipital lobe. No other boundar\' ol this lobe is discernible m the cast
nor does any indication appear either of a sulcus simiarum (sulcus lunatiis —
Smith) or parieto-occipital incisure. The demarcation between occipital
and parietal lobes is, therelore, \vholl\- conjectural. This latter indeliniteness,
however, does not impose an embarrassment more serious than is the case
with Homo sapiens, m whom the parieto-occipital dividing line is an arbitrary
one. It is probable that in tlu- human brain there is an intermediate, transi-
tional area between the parietal and occipital lobes where the cortical types
ol these two regions manilest a histological mutualitx'. This area permits
of a physiological blending in the acti\ities of the two /ones. In the apes and
more particularl\- m the great man-like apes, a sharply delined boundary
created by the sulcus simiarum exists between these two regions. No actually
homologous fissure appears in the cerebrum of modern man, although
several authorities maintain that the sulcus lunatus closely resembles the
simian fissure and ma\' be identilied in some human brains.

In the occijjital lobe on the right side a long crescent fissure begins at
the superior longitudinal fissures. It curves downward and forward in the

878 MAN

general direction of the sigmoid sinus, thus appearing both on the occipital
pole and lateral convexity. Above and Ik'Iow it, is the relief of an occipital
con\olution. The markmgs on the lelt occipital lobe are less definite. A
transverse ridge extends transversely outward from the lambda across
either occipital area. This ridge indicates the position ot the lambdoid suture.
In comparison with gorilla the occipital lobe of i)ithecaiithropus shows
considerable expansion in all diameters. As compared w ith the similar region
in modern man this lobe appears much smaller. It seems j)ermissible, how-
ever, to presume that in his visual organization the Javan man had acK aiiced
a long distance abo\e any of the anthropoids. His visual associations must
have been much more e\tensi\'e it it is true, as seems to be the case, that
he had real powers of speech. His visuo-psychic functions must lia\e under-
gone notable expansion as he began to attach verbal names to what he saw
about him, thus la\ ing the foundations of that wide sphere of denomination
and enumeration which mankind has created. The telencephalization of
vision had made great strides in pithecanthropus. He was capable of a more
effective appreciation of his environment and not the least important element
in this increased eifectiveness found its expression in the better control he
gained over his hands through visual super\ision. The man\ and protoLind
innuences arising from such impro\ed visual guidance made themselves felt
in innumerable ways upon his jjsychie organization, upon the makeup of his
personality and experience, upon his capacity to learn. So also was his entire
psychic life affected by the increased facilit\ w ith w hich sensory impressions
of sight, of hearing and of bodN sense entered into more complex associations.

THE TEMPORAL LOBE OF Pill 1 EC AXTHKOIHS EKECTUS

The temporal loi)e in the a|H'-man brain is little, if at all, represented in
the calvarium. Some slight jjortion of the sui)t'rior temporal eoinolution may
be detected, but scarcely enough to pirmit of more than a coniectureas to its

THE BRAIN OF PREHISTORIC MAN 879

cluiracUT. riu' base of this lobe, as seen in the occipito-panetal region, indi-
cates an increase in all diameters. I^rofessor McGregor's supplementary
reconstruction likewise shows decisive expansion in this lobe. I he most
jironounct'd cortical increnu'iit appears to ha\e iinoKed the superior and
middle temporal fi.\ res in the area assigned to auditory function. Although
it seems unwise to be categorical in this matter, all of the axailable evidence
warrants the assumption that the sense of hearing had lollowed the t'xample
of sight and bod\- sense in seeking broader lields lor its actixities in the neo-
palliLim. Such auditory expansion is indispensable to vocal speecii, since
symbolic sounds ari' usually acquired through hearing belore the\ may be
reproduced b\ articulation.

All four of the great neopallial lobes of the pithecanthropus hemispht'rcs
give evidence ot increased si/e and hence augmented hinctioiial capacity
when com|:)ared w ith the great man-like apes. They are all, on the other hand,
inferior to the similar bram regions of li\ ing races.

THE PROBABI L: D'>\AMIC FACTORS 1NDLCIN(; BKAIN Di:\ ELOI'MEN I IX

PI I IIECANTHROPUS ERECTUS

Anv opinion m the endcaxor to estimate w hat d\ namic lactors induced
the acKanced brain de\'elopment in ijitheeanthropus nuist needs be based
upon conjecture. 1 he major somatic \ariants m primate organization express
themselves m the mode and posturt' ol locomotion, in the diilerentiation ot
the foot and the specialization oi the hand. To the reactions and interactions of
these variants tlu' primati' brain has made delinite res|)onses. The cerebral
area most sensitive to and most consistently allected by such modilications
has been the paru'tal lobe. This region rej^rcsents those activities engaged in
sensing the body both in its axial and appendicular parts. In primates the
axial segments ha\X' a greater structural lixity than the limbs whose Junc-
tional adaptations ha\e manilested a lar wider range ol adjustment. In

88o

MAN

this light the expansion of the sensory regions ni the parietal lobe partieu-
larly related to the leg and foot, arm and hand becomes highly significant.
It seems most probable that sensory increment in these areas must be an

FIG. 375. FUNCTIONAL LOCALIZATION OF THE BRAIN OUTLINED UPON THE
LEFT HEMISPHERE OF THE ENDOCRANTAL CAST OF PITHECANTHROPUS ERECTUS.
RESTORATION BY PROF. J. H. MCGREGOR.

A, Auditory Area; F, Hifi;her Faculties Including Personality and Reason; 1 u. Fissure of Rolando; FS, Fissure
of Sylvius; o, Area of Skilled Movements; i>. Sensory Area (Touch and Muselc Joint Sense); s, Speech Area;
V, Visual Area; x. Area of Voluntary Motor ("ontrol.

essential antecedent to any expansion in the reahn ol mori' highly C(jm|)Iex
motor performance. Kinesthetic sensibihty is a limdamental requisite to
all skilled acts. W ithoul it neither the motion lormula nor tlu' motor execu-
tion would be possible. For this reason the de\elopmcnt of new sensory
fields must have been closelx associated with the appearance ol new motor
territories, if they did not actually precede them.

From the femur of i)ithecanthropus it is assumed that he stood and
walked erect much as do his modern successors. The assumption ol such
erect posture entailed an extensi\e sequence of adaptive modihcations, all

THE BRAIN OF PREHISTORIC MAN 88i

of which were reflected in the hrain. Standing u[)riti;ht in itself rec]uires a
complex sensorN' iiieehanisni to reeei\e and adjust the inipidses from the
proprioce])tors. How intricate and esst'iilial this mechanism is ma\ he seen
in those diseases characterized h\ patholouical changes m the sensor\ s\ stem.
Locomiitor ataxia is an oiitstandmii; examjjlc. Here the disease is confined to
the sensory elements hut exprcssi's itself pret'mmeiit l\ in t he motor adjust-
ments of standintj; and walking.

To what extent sensory orientation ol the hody is essential to proper
x'oluntary mo\c'ment is sc'cn m such pat hological condit ions as acragnosis,
in which the patient loses his limh sense to the degree that iu' may not
appreciate the positions ol his extrt-mitics or recognize passixe move-
ments ol them. The adec|uate sensing of the dillerent parts of the hody in
rest and action is essential to kinesthetic sensihility and the mdispensahlc
phj'siological hasis of all xoluiitary movements. Tlu' transactions of this
highlyspeciaiized sense mv thelunction ol the j^arictal lohe. As they hecomc
more extensi\e and complex, the parietal area has expanded to meet the new
demands mack" upon it. Throughout the long history of primate adaptation
and progress, the parietal lohe lias manifested the most consistent expansion.
It has espcciafly seemed to keep pace w ith the progressive tendency to assume
the erect posture, to (k'\elop |)lantigrade locomotion, to acquire himanual
characters. If the [)arietal expansion is a reliahle index to the e\()hition of
kinesthetic seiisihilit \ , then this essential attrihute of \()luntary nioxcment
became more extensive in direct proportion as the u[)per extremity was
emancijjated to perform the duties of the human liand. A sim|)le exam])le
may suffice to elucidate this point. The indi\idual digits m the ])aw of a cat
or dog have not acquiri'd independent mo\ements similar to fingers. Their
sensory representation m the hram is consec|uently much less, and requires
less cortical area. The man\ indi\ idual mo\emeiits of the fingers lia\e nvcd
of much more cortical surlace lor their sensor\- orientation. It would seem to

882 MAN

follow that ihc sensory clcniands of a fool so sjx'cializcd as to supijort the
body on the ground in the upright posture, thus freeing the hand for eon-
strueti\e and aequisitive purposes, called upon the brain for its supreme
de\eIopnient in the ])arietal lobe.

Simultaneous with the expansion in kinesthetic sensibilitx', the motor
areas of the cerebral cortex ha\e enlarged. By their extension the\ have
increased their capacity for the creation of more numirous and xaried
motor patterns. They have gradually dexeloped all of the motor lormulae
essential to the almost innumerable skilled manipulations of human hands.
Much emphasis has been laid upon the expansion of the sensory portion ol
the brain, which may thus seem to pla^' the leading role in dc\clopment.
But motor and sensory expansion have gone hand m hand. These two
factors are inseparably connected. They appear to be but ditlercnt phases ol
the same process, namely, the conversion of energy through the agenc\' of
animal organization. The stream of impulses which Hows m Irom the outer
world by the avenues of the senses is transformed into the specific energy
characteristic of each form of animal life and finally transmitted to the ellec-
lors where it appears again in specilically purposive reactions. The intricacy
of the apjKiratus for the intake and that for the output \ary directl\ w ith the
complexity of reaction. The\ are both, therefore, parts of the same energy-
transforming mechanism. It is impossibk' to consider the sensory organiza-
tion of the brain apart from the motor. This applies to all t\[)es ol sensibilitx'.
The t'\|:)ansi<)n in \ isual capacity indicated by growth in the occipital lobe
supports this view. For as \-oluntary acts became capable ol more etlective
performances, visual functions were increasingly more necessary to their
acquisition and control. Hearing, as the instigator and guide ol new motor
progress, may seem to carry less responsibillt \ than the other senses except
in one transcendent particular. Auditory fuiution made |jossible the recog-
nition and imitation of the inaiu' xoices of nature. It linallv became the guide

THE BRAIN OF PREHISTORIC MAN 883

of motor impulses for the ton<iuc, for tlic larynx, for the lips, cheeks and
tliroat Linlil the aiichhie eiu'r>j;y ol the outer world \\as transformed mto
spoken sounds of the human \i)iee. Sounds ol this kmd e\c'ntuall\' assumed
svmbohe associations with gestures and other movements of tlie body, with
()l)|ects seen or otherw ise pereeixecL The meeption of [luman speech had its
structural basis m the hrst and second temporal convolutions whose expansion
is at least mdieated m pithecanthropus. These gyres represent the funda-
mental sensory elements ol s])eech while the inferior frontal coiiNolution,
constituting Broca's area, exercises motor control over spoken language.
All of these expansions in the sexeral diflerent areas of the bram are ulti-
mati'ly reflected in the dewlopment of the frontal lobe. The cumulatiw efiects
of many factors impress themseKes upon this region. The assumption of
llie erect posture, the freer use of the hands, the fuller sensing of the world,
the acquisition of speech and constructive proclivities, the incentive to
ex|)lore and the ability to migrate, combined to broaden human experience
and to increase the capacit\' to li'arn therefrom. The part the\' pla\ed in
indi\iduahzing human personality, in expanding the powers of selection, in
creating tiie foundations of ]udgment and reason is obvious. All of these
higher psychic faculties are now attributed to the frontal lobe.

In the cNolution of structure and beha\ior indicated by the brain of
Pithecanthropus erectus, man\ factors ha^"e reacted and interacted. It is
doubtless true that no single formula attempting to outline the sequence of
events in this process would be w holly satisfactory or correct. Some working
program of this kind, howi'\'er, is not objectionable and may be helpful if its
hypothetical nature is frankly admitted. The following summary of such a
sequence visualizes pithecanthropus as departing from the pronogradc stem of
the primates and making decisive advances beyond the anthropoid stage by:

1. The development of more extensive kinesthetic and motor capacity

2. The assumption of tlu' erect posture

884 MAN

3. The freeing of the hand for manual perfornuinees and the ineeption
of unidcxterity

4. The expansion of visual and auditory sensibility
j. The development of speech

6. The establishment of human personality and the higher psychic
faculties.

The Bkain of the Dawn Man of Piltdown, Eoanthropus

Dawsom

The fossilized remnants of the Dawn man's skull are more fragmentary
than m the case of the Javan ape-man. It was therefore necessary to give
each fragment its proper place in reconstructing the skull of this long extinct
race of men. These Piltdown cranial fragments include:

1. The left and part of the right parietal bone

2. The left temporal bone in its scjuamous, petrous and mastoid portions

3. A large part of the left half of the frontal squamosa

4. About two-thirds of the occipital bone

5. The right half of the mandible.

The first reconstruction of the Piltdown skull was presented to the
Geological Society in London in Decembti-, M)12, [)y Sir. A. Smith Wood-
ward, of the British Museum and Mr. Charles Dawson, a lawyer, who had
made the original discovery of the fossil. The annoLincement of this remark-
able find deeply stirred the interest of scientific circles. An unknow n ])hase of
early human existence was about to be revealed. The reconstructed skull a.s
pieced together by Dr. Woodward impressed all who saw it as a strange blend
of man and ape. It seemed that the missing link for \\ hich the early followers
of Darwin had arduously searched was at length forthcoming. But whether
this was tlu' long sought missing form or not, the Piltdown strata in the
Wcald of Sussex, not many miles from the English Channel, told ol a race

FIGS. 376 TO 380. 1 1\"E \IE\VS OF THE ENDOCRAMAL CAST OF EOA.NTHKOPUS

DAWSONI (DAWN MAN OF PILTDOWN). C0NSEK\'ATIVE ESTIMATES GIVE THIS

FOSSIL AN ANTIQUITY OF I40,0()0 YEARS. IT IS PROBABLY MLCH MORE ANCIENT.

RESTORATION BY PROF. J. H. MCGREGOR.

(a) Vertex, (b) Base, (c) Left Lateral Surface, (i>) Frontal Pole, li:) Occipital Pole. The smoother areas
in the cast show the regions which have been restored.

I885!

886 MAN

of iuiniaii beings who inhabited England long before history had made its
feeblest beginnings. The stratum in wliich tlie Piitdow ii i'ossil rested indicated
ati antiquity, according to Dr. Woodward, dating back to the early part of
the Pleistocene period. The estimates of this geological period in terms of
years vary considerably. Such authorities as Professor SoIIas and Professor
Pencl:, for example, believe the period comprised between 400,000 and
500,000 years. Professor Rutot is more conservative and sets the ligurc at
140,000 years. Sir Arthur Keith, who made a subsequent reconstruction ol
the Piltdown skull, advocates an antiquity even more remote, dating back
to some portion of the Pliocene. Even if it is impossible to be more exact in
these estimations of geological time, it seems clear that a very primitive
race inhabited England long before Caesar's invasions; in fact, ages before
the ancient Britons chiimed the land which was destined to produce the
most brilliant lights of history.

Endocranial casts of the Piltdown skull have been made by Dr. Wood-
ward and Su" Arthur Keith. These reproductions ^•ar^,■ in eertaui details,
jiarticularly in regard to the archof the\ ertexand theestimated volume of the
brain. Both ol the casts show a distmct superiority w hen com])ared w ith that
of pithecanthropus (Fig. 366). Especially decisive is the gain made by the
Dawn man in the \ault of his skull and the e\|)anse of his forehead. The
general flatness in llu' cranial \ault of the Ja\an ape-man gi\es place to a
degree of arching in the Piltdown skull. This modilication is in ri'sponse to
expansions in the frontal and parietal regions. But increasing proportions are
not limited to these areas. The temporal as well as the occipital lobe ol the
Dawn man have enlarged. By comparison it is e\ident that the brain ol the
ape-man was smaller, less well develo|3ed and less specialized. The volume ol
the pithecanthro]ius brain, as originally estimated by Dubois, was 855 c.c.
Subsequent measurements with corrections by McGregor place this figure
at ij^o c.c. This brain volume, while considerably above the average lor the

THE BRAIN OF PREHISTORIC MAN 887

gorilla, which is between ,■()() and ,45 c.c, is much ht'low {hv average adult
human brain of modern races. Professor Elliot Smith maintams that a brain
must reach the weight of ()5,- gms. (about 1000 c.c.) before it can serve the
ordinary needs of human t'xistence. Woodward eveiituallx t'stimated the
Nohime of tlie Piltdow n brain at i i()5 c.c, but Keith's investigation increased
this figure to approximatt'lx 1400 c.c, or well up to the a\erage ol tlie modern
man. The gorilla's brain xoluiiu' appears to be 5- per cent that ol jiithecan-
thropus, while pithecant hro|)us is about -2 pt'r cent ol the Piltdow n brain
xolume. Tliis difference denoti's more ra|)id brair. expansion in the direction
of the higlu'r human standard, once thi' limits of actual anthropoid conditions
are transcended. The impetus toward hLiman specializations, ex'en in their
earl\' human iiicipienc\, seems to hasten the [progressive development ol the
brain more than an\- of the less acKanced primate stages. Some ol the
increase in the brain ^()lume of most primates might be attributed to general
increase in body structure. Siich, however, can scarcely be the case, since a
gorilla weighing nearly four hundred pounds, or more than tw ice as much as
the axerage man, possessed a brain w hose \oIume was only 545 c.c, approx-
imately one-third that of man. Dubois and ki'ith endeavored to determine
how much of the brain is needed for purely animal contingencies and size
of body. They concluded that these factors are represented by not more than
6 per cent to 8 per cent of the entire cerebrum. Between ()2 per cent and ()4
per cent of the volume of the human brain is therefore determined 1)\ other
factors than the vital functions or the size ol body.

The surfaces of the Piltdow n endocranial cast are shown in I'igures
376-380.

THREE S.\LIENT LANDMARKS OX THE PILTDOWN ENDOCRANIAL CAST

Three salient landmarks on the cast are, all things considered, less
impressive than in pithecanthropLis. The lissure of Sylvius ma\- be discerned

888 MAN

at the frontotcinporal notch where its posterior limh begins to j)ass backward
beneath the parietal eminence. The termination and Liltimate disposition
of this fissure cannot be determined. It presents a faintly nidicated anterior
ascendino; ramus and also a horizontal ramus extending into the frontal lobe.
The position of the Rolandic fissure may be estimated l:)y the general rules
previously applied to this sulcus in the pithecanthropus brain. The groo\-e
of the transverse sinus is well defined but seems open toconsiderablecriticism,
especially concerning its obliciuity as given in the endocranial cast. As a
whole, the occipito-cerebellar area is the least satisfactory region of the
entire cast. Subsequent studies may correct this dcliciency and produce an
()ccij)ital symmetry more in keeping with this portion of the normal skull.

THE FRONTAL LOBE OF THE DAWN ^LAN

The frontal lobe of the Dawn man presents much less m the way oi
frontal impressions and juga than pithecanthropus. It offers no more con-
vincing indications as to the position of the Rolandic fissure. The coronal
constriction is much less marked than m the Ja\an man, thus showing a
real expansion in the frontal lobe. In one feature this area does stand out by
comparison. The inferior frontal convolution of the Piltdown bram is much
more ]3rominent than in pithecanthro[:)us. In it ari' apparent those exten-
sions of the Sylvian fissure so notable in connection w ith the motor speech
area of Homo sapiens (Fig. 381). The increased size of the frontal lobe,
together with the augmented prominence of Broca's speech area, is no doubt
indicative of a human being endowed with better linguistic abilities, broader
capacities for experience and improved reasoning powers. There is little
to denote expansion in the motor area or in the intermediate ])recentral
area for skilled movements. One clue to the i)robable extensions in these
important regions is furnished, however, by the parietal lobe which may
now be considered.

THE BRAIN OF PREHISTORIC MAN 889

THE PARIETAL LOBE OF THE DAWN \L\N

The j)ariftal lobe, although it lacks any impression of lissurcs or con-
\()lutions, lias c'\ickntl\ nicreased in size. This is especially noticeable in
the parietal eminence and m the prommenee ol the arc of the \erte\. Both
of these mcrcments siij;nily accessions to general bocl\ sense and are incident
to specific expansions in the area pertaining to the uppir extremity, more
especiall\ the hand. Such augmentation of the parietal lobe justiiies the
interpretation of further extension in manual attainments. There is reason
to lx'lie\-e that the Dawn man had accjuired increased capacitx in the use of
his hand as a sensory organ. He could emplo\- it to much ad\antage in
exploring the world about him, and in analyzing the objects in his cnviron-
nunt b\ actual contact with them. Thus he learned the consistency, the
shape and the texture of things he touched. The weight and mobilitv of
objects gave him added information concerning their utility and application.
The relative resistance of wood and st(jne, their respective projectile and
penetrating powers, the acKantages of sharp edges as compared with blunt
surlaces, the pliability ol llexible substances, the tensile strength of various
tissues, all came to him as re\elations called forth by these new perceptions
of the world, liut such revelation did not limit itself to inere sensing. The
sensory impressions found externalization in new actions. They doubtless
guided his hand to utilize the serviceable qualities of objects with which
nature surrounded him. In a word, they led him to make use of stick and
stone, Irom which advance it was but a step to fashion his materials into
implements better suited to his purposes.

W hile the increase in the parietal arc and in the parietal eminence
denotes new capacities of sensation, it is quite as insistent concerning the
motor powers added to the human hand. There may be a question whether
the earlier ape-man of Java had learned the secret of making implements
for himself, but it is becoming more clear that the crude flints found in the

890

MAN

same stratum \\ 1th the Piltdown skull were the production of human skill.
These eoliths liavc occasioned much debate concerning tluir "humanity."
If it should at length be decided that they formed no part ol the Dawn

FK;. 381. M NCTIONAL LOCALIZATION OF THE BRAIN OUTLINED UPON IHE

LEFT HE.MISPHEKE OF THE ENDOCHANIAL CAST OF EOANTHROPUS ( PILTDOWN').

RESTORATION BV PROF. J. H. MCGREGOR.

A, Auditory Are.i; F, Iliglicr Faculties; fr. Fissure of" Rohmclo; fs, Fissure of Sylvius; o. Area of Skilled
Movements; p. Sensory Area; s. Speech Area; v. Visual Area; x, Area of Voluntary Motor Control.

man's tT|uipment, the dexelopment of his brain does not gams;i\- his ability
to manufacture or use such miplements. This is all the moic true since the
slightly larger size of his left hemis|)hcre plainly suggests unidexterity. The
chipping of flint instruments, above all other activities, would require such
a modification in his manu;il organization that one hand served to hold and
the other to shape the Hint.

THE BRAIN 01 PREHISTORIC MAN 891

To explain the increased dimensions characteristic of the Piltdow 11 Ijiain,
it seems necessary to presume that this race had made certain adaptations
which called for added neural ca|jacities. In all the \aricd adapti\e radia-
tions seen in otiui- mammals, there is no demand lor complex adjustments
comparable to that anectin<i mankind. Search as one may amongst all of
these variations, no inlluence, no single factor appears so compelling ol
cerebral specialization as the development of the hLiman hand. By this
means an entirely new world iiad been laid oj^cn tor man to concjuer, and a
still newer one waited for him to construct. So it was that a brain sullicient
for the simple living in plain and forest could no longer ser\c this new
mastery of life.

The parietal lobe, although it primarily represents administration
in one of the chief departments of the scnsorium, also expresses the
externalizing capacity of the brain. This is likewise true to a somew hat less
extent of the other cerebral lobes representing the special senses.

THE TE.MPOKAL AND OCCIPITAL LOBES OF THE DAWN MAX

The temporal and the occipital lobes also reveal a marked advance.
The casts of the Piltdown endocranium are fortunate in showing most of
tlu' left temporal lobe. The reconstruction of Dr. Woodward dillers Irom
that of Sir Arthur Keith in disclosing but little of the superior temporal
coinolution. Keith belie\es that his reproduction is in better accord with the
conditions dI human anatomx. His east also obviates the marked dellection
inward of the tip of this lobe and thus gives it a less simian appearance.
Large portions of the middle and inferior temporal convolutions are clearly
delineated, together with a part of the temporo-sphenoidal surface of this
lobe. Both casts show a j)ronounced increase in the auditory eminence Jis
compared with pithecanthropus. This eminence is situated at the base of
the temporal lobe where the latter comes into relation with the occipito-

892 MAN

parietal area. It represents a cortical region engaged in the sense of hearing,
more particuhirly lor complex sounds, such as those of language. In this
capacity it acts as a most important componiMit of the speech mechanism.
Not only does it make possible the learning of language, hut through motor
reprochiction ot what is previously heard it provides a constant auditory
superxision over language as it is vocalized m audible speech. The individual
possessed of articulate expression "listens in," so to speak, while he is talking.
If it is true that thought depends upon unspoken language, the auditory
area of the brain exerts a profound mlluence over the process of thinking.
The Dawn man, on the strength of these facts, must have been capable of
some kind of spoken language just as he was possessed of some capacity
for thought.

Little of the occipital lobe is available for study. It is difficult to deter-
mine whether the Piltdown man had better \isual powers than his lower
antecedents. Impro\ement, if there were such, involved his \isuo-psychic
functions, i.e., the visual powers of association and discrimination.

POSITION OF THE DAWN MAN IN THE HUMAN FAMILY

Thus visualized through the developnunt of his brain, the Daw n man
may appear a somewhat uncertain mem!)er ol the human famil\. Doubtless
he lived m communities ol considerable size, for otherwise his powers of vocal
communication would ha\e had little opportuiiit\' to develop. He seems to
have been capable of man\ skilled acts, but such im[)lt'inents as he did make
were j>robabl\ dictated by the bare essentials of hie, by the nvvd for food and
lor protection. It is [probable that none of his mstrunu'iits ser\ed for cultivat-
ing the soil or for the production ol garments or the construction of ]:)erma-
ncnt duellings. I le was dependent lor his li\ tlihood ii|)on game animals w huh
he followed m their migrations and thus himself became a wandenr. What
powers of thought he had or w hat gifts (jf imagination are matters for conjee-

THE BRAIN OF PREHISTORIC MAN 893

lure. Notliing ix'iiiains Irom \\ liu'h to sui'inist' his at'tual customs or to suggest
his attitudes toward the woi^ld as he chd or chd not undi'istand it. Sir Arthur
keith sa\s that "A sur\e\ ol the eoiuohit i()iiar\' regions ol the brain leads
to the eonelusion that we are deahng here with a sini|)le and primitive
arrangement oi parts; hut not so simple or so primitixe as to make
us wish to place the Pilldown l)rain in a class apart Irom modern
human brains."

The Dawn man, as his brain attests, had come a longdistance from that
parting ol the wavs at which the human and anthropoid stocks separated.
But it is equally certain that then' remained a great distance yet to be
traversed before such a brain coidd attain the development characteristic
ol the modern human cerebrum.

The Brain of Neanderthal Max, Homo Primigexius

Eoanthropus, as his name implies, is i:)resumed to mark the dawn ol man-
kind. But the lull day ol human existence was long m coming. Ages passed
during which it seems certain that se\eral dillerent races of primitive men
made their appearance, only to die out again. It is remarkable what slight
traces of their actual image these earliest inhabitants of Eurojx' have left.
There is, however, reliable c\ idence of at least one such race of ])rehistoric
Europeans, ihc Neaiidcrlbals. I-rom t heir scattered lossil remains they appear
to haw possessed man\ leatures in common. They were of relati\ely short
stature, proi)abl\ not a\eraging much more than live feet three inclu's in
height. Their limbs were powerful, theii' necks short and extremely muscular.
What distinguished them as a race was the shape of their heads and size of
their brains. The Neanderthal cranium shows a low retreating forehead and
a peculiarly low dome. The head seems llattened from abo\e downward,
giving the appearance know n as jjlatycephaly ( Hat head). The occipital as well
as the frontal portion of the skull is afTected by this llattening, so that the

FIGS. 382 TO 387. SIX VIEWS OF THE ENDOCRANIAL CAST OF HOMO NEANDER-

IHALENSIS (la chapelle aux saints), estimated antiquity of fossil,

ACCORDING TO PROFESSOR OSBORN, APPROXIMATELY 300,000 YEARS.
(a) Vertex. (») Base Restored, (c) Fronl.il Pc,k>. (n) Occipital Pole. 11 1 Ri^lit lateral Surlacc. (1) Left

Lateral Surface.

[894]

THE BRAIN OF PREHISTORIC MAN 895

head must have been sup]:)()i"tc'd by a thick powcrlul mxk, cjiiite similar to
the gorilhi.

E\'en more ennspieiiotis is thi' heavy ridge ot bone aboxe the orbits, the
supraorbital torus, whieh prochiees tlie laeial aspect lamihar m l\]v "hght-
iiig mask" of the great apes (cliimpanzee and gorilhi). The orbits themselves
were larger than in modern man and separated by an anterior narial open-
ing which indicates the presence ot a broad Hat nose. The lower jaw was
heavier and broader than in 1 lomo sapiens, although the teeth as a whole
were strikingly human, ha\ing none ol the taiig-hke specialization ol the
great anthropoids. On the mandible in the region ol the chin there is no men-
tal t'lnineiice. All of these cranial characters must have given tlie Neanderthal
man a singularly gorilloid appearance. Tlu' low beetling brow, tlu' llattcncd
vault of the skull, the head set close upon the shoulders, tlu' broad llat
nose, the heavy jaw and rt-cedmg chin could hardly tail to produce a couiite-
nanci' in many respects as brute-like as the great anthrojjoid apes. Envisaged
from his fossil remains. Neanderthal man was indeed a savage-looking
creature. But his brain is not altogether in keejjing with this low estimate of
him. In fact, the \-olume ol' the Neanderthal brain is somewhat greater than
that of modern races. This cerebrum does not denote such low psychic
organization as the ape-like a[)pearancc of the head would seem to suggest.

Neanderthal man had made dclimte advances in liiinian progress.
He laid the foundation of many customs and tendencies which later domi-
nated social organization. I Ii- was a skilled artisan and Hint worker. He had
command ol lire w hich he employed both as an invaluable accessory to his
life and m the upbuilding of distinctive cultural attainments. He buried his
dead w ith ceremonial rites, which shows at once that he believed in a future
existence and possessed some religious conceptions. Far from being a lowly
ape-like creature, he had man\ oi the higher attributes of man. Although
the Neanderthal had a dccick'dly pithecoid cast of countenance, he also

896

MAN

displayed a human ability not to be despised. For this reason he is known as
Homo priiiiigcnius. YvX his aj^e-likt' alliliations, in sj:)ite of his human intelH-
gcnce, make it probal)le tliat he was not the dircet ancestor of mocU'rn man.

IK,. 5JSN.

IIU. M \\I)I 1; 1 HAL FLINT WORKERS.
This group of Mousterian cave dwellers is taken trom a mural painting by Charles R. Knight made
under the direction of Professor Osborn. It is arranged to show the physical characters of Neanderthal
man. The background is the famous cavern of Le Mousticr. From The Hall of the Age of Man,
American Museum of Natural History.

The lossil rt'mams of the Ncanchrthal raee have been found widely
scattered throuji;hout Europe, in France, in Belgium, in Germany, in Mora-
via, in Croatia, and c\cn in the Fsland ol Jerst'v. The earhest disco\'ery ot
this race dates back to 1848, when the (jibraltar skiill was iound b\- Lieu-
tenant Mint. The si<;;nilicanee of this lind, liowe\er, was not fully appreci-
ated ior more- than sixty \ears. NcaiuK'rthal lossils comprise a collection ol
skulls, skeletons, mandibles and tt'cth in total, a remarkablx large number
of fossilized j)arts Irom w Inch the osseous appearance ol the race has been
determined beyond all doubt. 01 the skulls only lour ser\e the purposes of
exact endocranial study, such others as are know n being too fragmentary or
too greatly damaged to permit of more precise deductions.

In the valley of the Dordogne, southwestern France, the Abbes Bouys-
sonic and Bardon (Autumn, 1908) disco\cred in a ca\ ern near the little

THE BRAIN OF PREHISTORIC MAN 897

villagf of La Chapclk' au\ Samts, the skeleton ol a prniiiti\ f man. 1 he body
rested upon its back with its head toward tlie west, its leiis, thighs and lore-
arms llexecL The head had l)een espcciallx protected b\ Hat stones and many
skillliillx workt'd Hints ot the Mousterian period snrrouiuK'd the skehlon.
Thi'ri' was e\erv e\idenee ol interment and burial ceremony about thisdiscov-
ery. Prolessor Boule ol the National Museum ol Natural Historx in Paris
conelutk'd that the skek-ton was that ol a man about middle age, belonging
to the Neanderthal race. In its dimensions the skull exceeds those ol an a\eragc
modern man, ha\ ing tlu' exceptional capacity oi 1600 c.c, which is at least
120 c.c. abo\e the- modern axt'rage. But the skull w as distinetlx low \aulted
and had an apt'-hke supraorbital torus with low receding brow. The t'lido-
cranial cast ol the La Chapi'lk- man scr\es especiall\ well to gi\e us an accur-
ate \iew of the Neanderthal brain (,Figs. 382 to 387).

I-F..\Tl'RES E\IDE\T IX THE CAST OF THE NEANDERTHAL SKILL FROM LA

CHAPELLE AL'X SAINTS

This cast shows those teatures which might i)e presumed from the
Neaiukrthal skull. The shape ol the bram is distinctly Hat. That arching in
the region ol the \'ertt'\ so promuunt m Homo sapiens and at least slightly
foreshadowed in the brain ol |)it hecanthropus, as wt'll as in tiie Dawn man
ol Piltdown, IS remarkably absent, in a portion ol this are which allects the
prefrontal region, the eurxt- actuall\ seems to sink inward. W itli all propcT
allowances lor disere|)anc\ m reconstruction, it is nevertheless certain that
the vertical areas ol this bram ha\e adapted tluinselves to a flattened head.
Ihis observation is j^art leularly pertiiunt from the fact that it is the brain
which m tlu' mam appears to determine the shape of the skull. Doubtless
there is an Interplay of factors in this growth relation, l^ut the cerebrum Is
the essential organ ol the cranium and its developmental demands are of
ehiel moment during the im|)ortant lormative period. It is the shape of the

8()8 MAN

brain rather than the shape- ol'tht' licacl which may be consickrccl a cletcrmin-
ing character in the Neanderthal race. Iti its siiape, this brain is far from ape-
like. It bears all the marks and ieatnres oi the human et-rebriim.

Certain intrnisie factors in cerc'bral dcNelopment may e(ineei\ably be
related to the brain llatness of the Neanderthal. Thus, for exami^le, the
ventral horn and body of the lateral \entriele may be less capacious, the
rhinencephalon (olfactory brain) may be more expansive, the corpus cal-
losum less well developed, or the centrum ovale contam less medullary
substance. Such modifications in the normal process of brain ^rowtii might
contribute to cert'bral llattening or broadenmg. But none ot these purely
conjectural jjossibihties seems so likely to inlluence de\t'lopment as the
salient i'aetor which plainly declares itself on the surface of the Neanderthal
brain.

Compared with tlu' ape-man ol Ja\a, as well as with the Dawn man,
the Neanderthal possessed a brain which siiowed expansion in all its major
divisions. The |)arietal, the occipital, the temporal lobes haxc all increased
in size. So also has the Irontal lobe, but the ratio oi its expansion appears to
I)e less than in the other areas. In this region the real llatness ol the brain is
most pronounced. Not only have the Irontal convolutions on tiie convexity
failed to gl\e the lon-bram those dominant characters which call lorth the
high wide i'orehead of modern man, i)ut the representation ol the Irontal
lobe on the mesial surface appears to have remained in its more primitive
state. Certain secondary cllects leading to tlu' llattened as|)ect ol the brain
would of necessit\- tollow in this comu'ction, and still lurtluT (.'mphasize the
low vaulting of the bram. A lagging dewlopment m tlu' Irontal lobe would
determine a centrum o\ale ot relati\ely small dimensions because oi smaller
fiber contributions from the corpus callosum and from adjacent association
areas. The rostrum and l)od\ ol the corpus callosum would in consequence
be smaller, and thus fail to furnish that fractional increment which gi\es the

THE BRAIN OF PREHISTORIC MAN 899

complftt' fullness to Xhv iiontal aif in Homo sapiens. This apparent failure
of the Neanderthal Irontal li>l)e to attain its iiltnnate proportions not only
charaeterizes theortian Ironi a struetural |)oint ol \ie\\, hut must ha\-e had a
lar-reaehin^ mlluenee upon tlu' ethnical cultures and Imal destiny ol these
prmiit i\ t' Eiiropeans.

1 111 S^'L\ lAX Fissure. The position ol the SyKian hssure is readily
idenlilu'd in its posterior dl\ ision extendinu Irom the tronto-tcniporal notch
beneath and caudal to the [)arietal emun'iiee. The arrangement ot its caudal
e\tremit\ is not discernible but its anterior and horizontal rami are clearly
deliiied.

Tin: r^issL KE 01 Rolando. The lissure of Rolando may be introduced
on the basis ol the usual estimations lor this sulcus. Its exact position, length,
angle ol inclination, and terminations are mainly hypothetical since no actual
groove on the cast indicates the presence ol the (issure.

The Transverse Sinus. The groove of the transxerse sinus is visible
and marks thednision l)t't\\t'en the cerebral hemisplnax's and the cerebellum.

The Fronial Lobe. The frontal lobe as a whole bears i'\ Idence of
much expansion as shown by the broadening ot its pole and a tendency to
round out the arc, which gi\-es the identil\ing prominence to the modern
lorehead. 1 he process, ho\\e\er, iiuoKcs only the polar areas ol the lobe in
which the impi\-ssions ol the superior and middle Irontal comolutions are
apparent. In tin- rt-mainder ol the Irontal area there is no sign of lissures or
con\ olut ions. The exact allocation ol preei'iitral motor area or of the inter-
mediate precentral area for skilled mo\tinents cannot be made. The coronal
constriction is (|uite conspicuous. A large Pacchionian elevation is situated
near the superior longitudinal hssure in the line of the coronal suture. Upon
the right lu'inisphere the position ol the middle nuaiingeal arter\' is faintly
visible, while upon the lelt it is less distinct. The outstanding feature of the
frontal lobe is tlu' prominence ol the inferior frontal couNolution. This

FIGS. 389 TO 3()3. FI\E VIEWS OF THE ENDOCRANIAL CAST OF THE LA yl INA

SKULL. (NEANDERTHAL WOMAN.)
(a) Right Lateral Surface, (n) l.i-lt Lateral Surface, (c) Vertex, (d) Frontal Pole. (1:) Ocei|)ital Pole.

[goo]

THE BRAIN OF PREHISTORIC MAN 901

gvrc on tlu' left sidr is nioif complex in its arraiigcnicnt than \n eitlirr the
Javan or Piltdown man. In it mav he reeognized the pars orhilalis, the pars
triangularis and the pars basalis, all eharacteristic features of Broea's speech
area in Homo sapiens ( Mg. 400).

Sueh iVontal de\elopnu'nt is indieali\e ol psyehie powers m acUaiueot
the still more primitive raees of man and also ol a eaj)acit\ lor speech u hich
seems to be approaching niodi-rn standards. Neanderthal man possessed a
degree of reasoning ability and judgnunt which he doubtless applied with
advantage to the organization of his eiiorts and the rt'gulation ol lile. His
acknowledged capacitx for spec'ch shows that his was not an existence ol iso-
lation but rather that the economic \ ahu' of communal li\ ing had been appre-
ciated and utilized. His acKanccs in the mastery of his en\ ironnuMil may
be understood from the better de\elopnu'nt ol his frontal lobe. He had conu-
to recognize some of the eliineiils ol human superiority as compared with
other living creatures. In his contests with the beasts of pre\ he had gained
a certain degree of ascendancy, enough at li-ast, m his later cultural |jeriods,
to dispossess his carnixorous enemies from their caverns. These shelters he
took over for his ow n abode and thus gave the embryonic sense of ow nership
a new impetus. He buried his dead in a manner showing belief in a life here-
after. In such customs as these he reveak^d not onl\ a fertile imagination,
but that per\asive conception which in time created an egoistic sLiperiority
dei'ined wortin of |)er|:)eluat ion after death. 'Set, even with all these human
acKanct's, his frontal prolieiencies kTt something to be desiicd. lie ll\(.'d and
prospered for \ast jjeriods of time but Uc lailed to de\ clop those C|ualitics
which guaranteed to his kind terrestrial permanency. At length another
race invaded his dominions and the Neanderthal, doubtless not without a
struggle, disappeared before these new people. That he was unable to cope
with the iiuaders bespeaks some serious omission in his frontal develop-
ment, an omission which the newcomers had already overcome. Delensive

902 MAN

cooperation on a large scale, essential to successful niilitar\ puissance, may
well have failed the Neanderthals in their time of need. Their eventual
estabhshment of habits incident to cave dwellinp; eornmitted thi-m to a pro-
gram of simjjle communal hie. They were hunters and nomads (irst ol all,
and tenants only by late acqursitions. Then- clue! interest was the cjuest ot
game. Nothing m then" antiquarian relics shows that they possessed an ec[uip-
nient or organization suited to cflcctive wartare. Thus their dehciencies must
have been m those departments of neural de\elopment upon which higher
social efriciency depends. Failing in these attributes, they at length fell \ic-
tim to those who had, through better brain power especiall\ m the Irontal
lobe, already attanied such advantages.

The Parietal Lobe. The parietal lobe yields little evidence of its
intimate details. There are no signs ol hssures or convolutions. In the cast
this entire lobe indicates much expansion and it seems probable that m this
area the Neanderthal brain has made its greatest advances. The parietal
eminence is particularly prominent and its general [position denotes a region
especially involved in the receipt of sensory impressions from the upper
extremity. The boundaries of the lobe with the exception of the S\ Ivian
fissure are iiulelinite. No actual clue is obtainable w ith reft'reiice to the size
and complexity of the postcentral and prccentral convolutions. The esti-
mated dinu'iisions ol the parietal lobe together with the marki'd prominence
of the parii'tai eminence are, however, significant. The Neanderthal brain
possessed a somesthetic capacitx' nearly ecpial to modern man, and its prin-
cipal specialization iinoKes the area pertaining to the hand. Such increment
in sensibility connotes a corresponding expansion m motor capacity. Per-
haps It is not giving undue stress to this sensory dcvelo[)ment to maintain
that Neanderthal man had made better contacts with his surroundings and
had gained greater mastery over all that his hand could inuch. New combina-
tions and modifications of objects fashioned by his hands began to yield him

THE BRAIN OF PREHISTORIC MAN 903

a ricli harvest o\ new utilitu's. \\v was bcfiinning to take a more tloininant
part ill creation and not tlu' least of the factoi-s contributing to his increasing
power was the parietal lohe ol the hrain.

Tul; Timi^okal and Occipital Lobes. The temporal and occipital
lobes both show t'xpansion. It is ob\Tous that the tenijjoi'al lobe has lost
most oi that highly simian appearance occasioned b\ the Inward delleetion
of its U]). it might in lact ser\'e the needs of modern races. It is (|uite as large
and nearly as well developed. A long palpable groove marking the lissure of
S\ l\ Ilis separates the temporal from tlu' parietal area. A lesser groo\e parallel
to the lirst indicates the position ot the superior temporal hssure, while a
short indenture localizes the middle temporal hssure. The greater portion ol
the temporo-sphenoidal surface is retained in the rejjroduct ion ol both
ti'inporal lobes. TIk' coiuolutions on the lateral and basal aspects are well
marked, gi\ing the impression ol a cerebral territory ol well-de\-eloped lunc-
tional capacity. More convincing is the large size ot the auditory eminence
situated at the conlluence of temporal, parietal and occipital areas. This
eminence is gcnerall\' accepted as part of the speech mechanism, being
especially assigned to those auditory lunctions inherent in spoken language.
Judged by this criterion in relation to Broca's area, the Neanderthal race
possessed linguistic capabilities not lar below the standards ot i iomo sapiens.

The occipital lobe also shows the efiects ot extensive additions. Visual
tunction, and particularl\ \ isuo-|xs\ chic function, has been greatly expanded
as compared with inoit' piimiti\c man. 1 lu' occij)ital pole, as in modern
races, extends considerabl\' beyond the tentorial surface ot the cerebellum.
The impression of the lambdoid suture crosses this lobe transversely near
its iunction with the |)arittal area. At least one fissure, the transverse occi-
pital sulcus, marks this lobe and separates two occii^ital coiuolutions. The
lobt' as a structural entity has assumed much more individuality' than
in the brains of lower races. It denotes a neural organization suited to more

904 MAN

extensive visual perctption and appreciation. I-urtherniore, it signifies the
increment possessed by Neanderthal man tor the visual guidance ol highly
organized manual skill (Fig. 400).

COMPARISON OF TWO OTHER ENDOCR.ANIAL CASTS WITH THE
LA CHAPELLE AUX SAINTS SPECIMEN

Two other endocranial easts of the Neanderthal race should be placed
in comparison with the La Chapelle aux Saints specimen. Both of these
skulls are smaller and attributed to Neanderthal women.

The La Quina Skull. The La Quina skull was discovered by Dr.
Henri iXhirtui m i()ii, together with other |:)ortions ol the skeleton. The
brain capacity, estimated by Professor Anthony to be 1350 c.c., is 250 c.c. less
than that of the Neanderthal man of La Chapelle, but corresponds with
other females of the race found at Gibraltar and Croatia. The cast is remark-
able in two respects: It duplicates all of the cranial characters of the La
Chapelle s|)ecmien with a faithfulness that compels conviction. It is, in
addition, a notable example of endocranial casting. The Neanderthal
peculiarities of cerebral configuration are most |)ronounced, as already
observed, in the frontal region (Figs. 389 to 393). Here the same sharp ele-
vation (at about ()0° with the base) occurs abo\t' the supraorbital torus. It
extends but a short distance and c|uickl\ falls away mto the llattened arc
which adapts itself to tlu' low receding forehead. Nor is this arc consistently
maintained. As in the La Chapelle east, it sinks into an actual concavity
near the j;lane of the coronal constriction. The entire brain seems Hat par-
tially in response to the disposition of the Irontal arc, but also because of
pronounced broadening m the paru'lal region.

The frontal lobe near its pole shows the superior and middle Irontal
convolutions but bcNond this area there are no indications ot sulci or gyres.
The inlenor Irontal convolution is prominent in l)olh hemispheres. In it may

i-i(;s. 3c;4 TO 399. six \ iews of the endockamal cast oi- ihe (;ibraltar

SKULL, (neanderthal WOMAN.)

(a) Vertex, (b) Base, (c) Frontal Pole, (uj Occipital Pole, (e) Right Lateral Surface, (f) Left Lateral Surface.
The smoother areas in the cast indicate the regions which have been restored.

[905I

9o6 MAN

be disccTiU'ci the asccndin<j; and horizontal rami of the Sylvian lissurc espc-
c-ially \w\\ niarkccl on the left side. The parietal and auditor\- eminences are
both [prominent, while the oeeijiital lobt' which oNcrhangs the cerebellum
contains markin<j;s of the trans\erse occi|)ital sulcus and the corresponding
convolutions. The gr()o\e of the posterior ramus ol the Sylvian lissure is
palpal)le beneath the parietal eminence. Some of the temporal lobe may be
defined on tlu' lateral and tcmporo-sphenoidal aspects, but the outlmes are
less clear than in the La Chapelle cast.

The imprints of the coronal, lambdoid and sagittal sutures are particularly
distinct. The course of the middle meningeal artery and its branches ma\ be
easily traced although their relief is not pronounced.

The Gibraltar Skull. The Gibraltar skull, although of greatest
historical importance, does less to lurtlur our know ledge ol the Neanderthal
brain than those discussed in the preceding descriptions (Figs. 394 to 399).
It holds its place as the premier disco\erv related to the existence of
this race of man. A large part of this skull is missing but its reconstruction
declares its Neanderthal characters. The frontal arc manifests its several
typical comjionents, making certain that the brain belonged to an mdi\idual
with a low receding forehead and a marked supraorbital torus. Frontal
convolutions are somewhat imperfectly reproduced because ol erosion in
the inner table of the cranium. The parietal and auditory emmenct's, the
occipital and temporal lobes all present Nt'anderthal appearances. From
the purely structural point of view, the Gibraltar skull has its chief impor-
tance because it has preserved so much of the cranial base. This was a detail
almost wholly missing in the other s|)ecimens. in the frontal region ol the
basal surface the orbital conca\ities are deeji and much more simian than in
modern races. The interorbital kt'cls are prominent. Both of these conspicu-
ously simian features are associated with the large orbits ol the Neanderthal.
The middle fossa contains the large temporal lobes and an ample optico-

THE BRAIN 01- PREHISTORIC iMAN

907

pfcluiu'ular space. 1 lit- mesial surlaee ot tlic temporal li)l)e, near its apex,
shows a \\ell-cle\e[()pecl uncus. The portion ol the l)ram \i\ contact with the
middle fossa and such parts as are preser\ed m rehition to the posterior

FIG. 400. FUNCTION.\L LOC.\LlZA HON OF THE BRAIN OUTLINED UPON THE
LEFT HE.MISPHERE OF HOMO NEANDERTHALENSIS (LA CHAPELLE AUX SAINTS).

A, Auditory Arc.i; f, Higher Faculties; n<. Fissure of Rolando; FS, Fissure of Sylvius; o. Area of Skilled Move-
ments; i>, Sensory Area; s, Speeeli Area; v, \ isual Area; x. Area of Voluntary Motor O)ntrol.

cranial fossa are much mort' liuman m character than tiie hrain areas related
to the anterior fossa. Tins condition ol atlairs is remarkable and \\orth\" of
some comment.

In the Irontal region ol the Neanderthal cranium it is apparent that
certain anthropoid tendencies ha\e had the up|Kr hand. The capacious
orbits, tlu' heavy supraorbital torus, the low recedin<; brow, the broad an-
terior narial openini:; impart a delinitel\ uorilla-like ap]3(,-arance to the head

9o8 MAN

and face. But back of all this is a region of the brain whicli still retains many
resemblances to the great apes. Thus the orbital concavities, the supraorbital
keels and the flattened frontal arc are reminiscent of gorilla and chimpanzee.
In this light it might seem that the Neanderthal brain was not yet highly
human. It has made certain great strides in this direction, but mere increase
in volume, pronounced though it may be, is not sufficient to produce the
cerebral characters of the fully developed human species. One indispensable
item must still be added to complete the stature of man. The frontal lobe
should acquire all of those characters peculiar to Homo sapiens. A brain not
so developed does not attain its full human measure. In such development
cerebral growth is dominant. As the brain grows, the orbital plates flatten
and the supraorbital torus recedes. In the end the pithecoid visage gradually
fades until it loses its brute-like features. It does so because the frontal lobes
of the brain, those last gifts of evolutional progression, have enlarged and
thus compelled the humanity of man to appear in his face and head. Such a
view seems also to reconcile the perplexing discrepancy between the ape-
like head and man-like brain of the Neanderthal. It shows that these parts
of the body arc actually in harmony one with the other. It may even offer
the explanation of why the Neanderthal race progressed so slowly during the
passage of more than 200,000 years and at length was completely replaced
by a more exalted type of man possessed of well-developed frontal lobes.
The cultural phases attributed to the Neanderthals include their feeble
beginnings in the Chellean period, their advances in manual dexterity to the
Acheulean era and their culminating refinements in design and execution
during the Mousterian period. But these people began as nomadic hunters
and so, with very slight and perhaps incidental modifications, they ended.
Succumbing to the invasion of the more effective Cro-Magnons, they left
no trace of themselves among this greater race. Such complete disappearance
with no evidence of that interbreeding common between victors and van-

THE BRAIN OF PREHISTORIC MAN 909

quished may also be due to the Neanderthal's ape-like specializations. Racial
discrimination on the basis of such wide morphological difFerences would tend
more toward the extermination of the inferior race than to its subjugation.

The Brain of Homo Rhodesiensis

Asia and Europe have both produced evidence of prehistoric man, the
latter most abundantly. Until quite recently Africa has been peculiarly
silent in this regard. But at length even the Dark Continent has revealed signs
which show that man of most primitive type had penetrated a long way
into the south during his wanderings over the earth. This important dis-
covery was made in Rhodesia and first publicly reported in 1921 by Mr.
\\ illiam L. Harris iSwiday Times, Johannesburg, Sept. 25).

The conditions under which the discovery was made were peculiar and
significant. Actual remains of two human skeletons were found at Broken
Hill Mine, in northern Rhodesia. These remains differed from similar fossil
discoveries in one essential detail. They were not fossilized in the ordinary
sense. Connected with the Broken Hill Mine there was originally a natural
cave about one hundred and twenty feet long. This was known as the "Bone
Cave" because it contained a vast number of animal bones all of which were
so thoroughly impregnated with salts of zinc and lead as to make smelting
of them worth while. At the bottom of this cave the human remains were
found. Like all of the other bones in this enormous osseous deposit, the sur-
faces of the human skeletons were incrustcd by zinc and lead so that the
action of the earth had failed to mineralize the deeper bony tissue. Paleontol-
ogists accept such remains as "fossils," but unfortunately this surface
incrustation precludes any estimation of the geological age of the bones.
Unfortunate also is the fact that the osseous remains of animals found with
the human skeletons were all of species still extant in Africa. The cave seems
to have been an ancient feasting place for hyenas which dragged thither

^

FIGS. 401 TO 406. SIX VIEWS OF THE EXDOCRANIAL CAST OF HOMO RHODE-
SIENSIS (RHODESIAN MAX). ESTIMATED ANTIQUITY ABOUT EQUAL TO THAT OF
THE NEANDERTHAL RACE, PERHAPS EVEN OLDER.

(a) Vertex, (b) Base, (c) Frontal Pole, (d) Occipital Pole, (t) Riglit Lateral Surface, (f) Left Lateral Surface.
The smoother areas in the cast iudicate the regions which have been restored.

[910I

THE BRAIN Oi PREHISTORIC MAN yj i

tluir |)rc'\ . There is even some remote suspicion that the human remains may
have come to tlieu' last restmg place in the Bone Cave in a snnilai' manner. A
elelt in the rool of tlie cave near its lar end, where a human skull was clis-
eo\erecl, suggests the possibilitx that the men or women whose hones were
found may ha\x' lalh'ii into the ea\'ern m relatively recent times.

Three important details usuall\- liel|)lul in the chronological assignment
of human lossils were wanting in connection with tlu"si' Rhodesian rt-lics:
( i) the actual iossilization ol the bones; (2) the ])resence ol t'\tinct mammals
or otiier ammals; 1:;) tlu' existe'nce o( stratiligraphic identiiieations. No
inh'reiK'i' may \)v draw n concerning the exact natuix' ol this human cU'posi-
tory. It may ha\-e been either accidental or the result ol a buna! ceremony.
I'urt lu'rmore, little exidenci', such as tlu' collateral discovery ol paleolithic
impK'meiits, ma\ be adduced to shi'd light on the antic|uit\ ol tlu' Rhodesian
man. ^ et, certain leatures, especiall\ ot the skull, ha\e convinced eminent
authoritus ol the great age and specilicit\' ol this race. Elliot Smith, lor
example, belie\es that the Rhodesian man is "a long lost and strangelx
exotic cousin" ol tlu' human lamily circle. He bases his opinion on the
striking peculiarities ol the Rhodesian lace w hich lie calls the most primitive in
id I the genus Homo. This lace isalsomorcdjrutal than t hat ol au\ know n human
being, living or extinct. Its enormous exebrow ridges are bigger e\en than
those oi the most archaic human, the Ja\an a|:)e-man, and recall the condi-
tions seen m gorilla. There is no indication ol a groove at the side ol the nose
marking the boundary between it and the lace, such as is constant in all
races ol mockan man, even m the Negro, Mongol and Australian types. The
merging ol the nose with the lace to form what m other animals is called a
snout and regarded as a peculiarly signilicant mark ol the beast is known only
III one otht'r extinct member of the human lamilx, i.e.. Neanderthal man. But
the I^hodesian's nose is e\'en more apt'-like than that ol the Neanderthal.
.Another remarkal)le leature ol the facial skt'leton is the <M"eat size ol the

912 MAN

palate and teeth, although the tanines do not project in the characteristic
simian manner as in the Dawn man of Piltdow n or the fossilized proto-
Australian of Talgai. The form of the brain ease and the chstmctive features
of the brain ahke corroiiorate the inferences drawn from the laee whieli
declare the Rhodesian species the most primiti\e of the entire genus Homo,
older and more primitive in fact than Neanck'rthal man. The shin bone and
fragment of the femur support this estimation of Rhodesian antic[uity. Such
is EUiot Smith's view concerning the age of this last discovered member of
the human race. There is, he admits, much that is tentative aboLit his present
opinion. The Rhodesian fossils were under the charge of Dr. Smith W oodward
in the Natural History Department of the British Museum at South Kensing-
ton. Dr. Woodward has already expressed his view that Homo rhodesiensis
represents a ])hase of exolution later than the Neanderthal type. Doubt-
less in due time a more intensi\ e study of these fossil remains will give a great-
er degree of rinalit\- concerning the antiquity of this race of prunitive men.

FEATURES OF THE ENDOCRAMAL CAST OF THE RHODESIAN SKI LL

The endocranial east of the Rhodesian skull jiresents certain interesting
and at the same time jicrplexing features. At first glance it seems to conlorm
in type with Homo saj)iens. Closer inspection, however, occasions consider-
able doubt in this regard. On the other hand, the Rhodesian brain a|)pears
much superior to that of either the Ja\an or Piltdow n man. It is more primi-
tive in some jjartieulars than the Neanderthal cerebrum. Its volume is slightly
larger than that of the Piltdow n brain, but distinctly smaller than the
Neanderthal. It has much less of the llaltening in the frontal arc than is true
of pithecanthropus, eoanthrojjus or Homo primigenius. In a word, it would
be difficult to associate this brain genetieall\ w ith that of any of the i)rimitive
races already considered. It is, ne\ertheless, too small and too little special-
ized in certain areas to consider it in close relation to Homo sapiens. lor the

THE BRAIN OF PREHISTORIC MAN 913

present it seems desirable lo regard this specimen as representiii<i a distinet
raee whose adinities and aiitic|uit\ iiia\- be estimated in the most general

terms only.

The Sylvian fissure may be loeated without dIfTieuIt\- b\ the deep groove
starting at tlu- temporo-lrontal noteh and extendmij; backward beneath the
parietal eminence. Tlu' lissurc of Rolando has been introduced in the cast
by utilizing the usual formula for this sulcus. The groove of the transverse
sinus is well defined as are also the ridges marking the distribution of the
middle meningeal arteries of the right and left hemispheres. With the recog-
nition of such landmarks it is |)ossible to identify the boundaries of the
major lol)i's u|)on the convexit\- of the hemisphere although no actual limits
ma\ be dcrmcd between tlu' occipital and jxirietal areas (Figs. 401 to
406).

The Frontal Lobe. The frontal lobe shows a notable absence of
con\<)lutional impressions. This is particularlj- true of the prefrontal area
where the polar extremities of the middle and superior Irontal convolutions
are usually well marked. A pronounced ridge indicates the position of the
coronal suture in the immediate \icmity ol which are two i)romincnt Pae-
ehionian elevations, one on either side of the sagittal line. The Irontal are
is higher than in Neanderthal man and suggests a more modern t \ pi' of
fori'head. It does not ]jresent any tendency toward conca\it\ in its entire
extent. The frontal and intermediate prcccntral areas, on the other hand,
show a distinct llalness indicati\e ol a relatnely incomplete de\elopment
in these two regions. Two distinct areas ol compression appear on I'ltherside
of \hv coronal ridge. These are the llatteiied regions rek'rred to as indicating
a lack of fullness in the frctntal contour. They are symnu-trical in the two
hemispheres and for this reason less likely to be in the nature ot arteiacts.
The more anterior of these two depressions is included in a wcll-delined
e(jronal constriction. There is no surface leature to denote any jjarticular

914

MAN

prominence of tlie i^recential convolution nor ol the intermediate precentral
area of skilled mo\ements. The inferior frontal con\()lution, however, is a
conspicuous feature of the frontal lobe. It shows a considerable degree of

FIG. 407. FUNCTIONAL LOCALIZATION OF THE BRAIN OUTLINED UPON THE
LEFT HEMISPHERE OI HOMO RHODESIENSIS.

A, Auditory Area; r. Higher Faculties; FR, Fissure of Rolando; is, Fissure of Sylvius; o, Area of Skilled
-Movements; P, Sensory Area; s, Speech Area; v. Visual Area; x, Area of Voluntary .Motor Control.

specialization on the left side in which the hori/ontal ramus ol theS\Kian
fissure may be discerned. The de\-elopnu'nt of this con\-olution on the right
side is almost as much acNanced. The basal surface of the frontal lobe con-
firms the impression that this is a |)rimiti\c' t\pe of cerebral organization.
The orbital concavities htiw a simian depth and the interorbital keels are
correspondingly pronounced. The imprint of the orbital com olutions is

THE BRAIN 01 PRHIIISTOKIC MAN 915

unusually prominent. In cliaractcr thcv rcscnihlf these structures in the
human l^ram.

B\ all the signs of his frontal lobe. Rhodesian man must have been a
very humble sort of human. Nothing in this region of his brain denotes
an\- approach to the attainments of Homo sapiens. The frontal area bears
man\ marks of his smiian retentions, although it also shows that his cerebral
capacities liad already transcended the anthropoid hmits and were last
carrying him toward broader planes ol human I'xperience. It would be sur-
prising, however, to liiul him capal)l(.' ol an\ advanced handicralt or produc-
tive of any such culture as characterized the Neanderthal, t'\eii in his early
periods ot progress. His must have been a precarious lot, pitted as he was
against the formidable mammals of the African wilds. But even in this
jeopardy his JM-ain had not left him t'lUirely destitute for the exigencies ot
such competition. A more facile association of ideas brought greater wariness
to increase his contrnances and to amplil\ his strategies. He began to have a
real panoramic continuity in his apperceptive \\iv. Past e.\|ierience formed
the conscious background ol his daily existence and entered into his plans
lor the luture. II such adxances as these ma\' reasonably be attributed to his
frontal lobe, there is e\ ideiice of a still greater acKantage j)ossessed by
Rhodesian man by virtue ol de\-elopnu'nt in this region of his brain. His
Broca's area indicates that he had acc|uired the j^owers of speech. Cooperative
preparation and combined ellort w ere thus made possible. The experience not
of one iiidi\ iduai but ol man\ created concentrations of strength which were
more than a match tor tlu' most dangerous of man's adversaries ( I'lg. 407).

The PARiEtAi, TiMPOKAL AM) OcciPiTAL LoBF.s. The ])arietal, tem-
poral and occij)ital lobes indicati- the extremel\ primiti\e status of the
Rhodesian brain. Tlu' marked llatness which characterizes the area of the
supraparietal gyrus is especially striking and significant. This region repre-
sents a functional area in which the higher elaborations of body sense are

oi6 ^L^^

administeredL Sudi comfJex sensory c

St. _ <i? the recogmtion of the f :ter of obiects by .. -

patjon") and acrognosss itb^ propo" sensing of positions rs of

ti»e limbs') are assigned to this part of the cortex. Her. - - ::c sensi-

bility has important nefMTesentation. - - are

essential to the upbuilding of tht . nts.

lial areas not onh :ectK-e sensinff of the environ-

mcEt by contacts with the bodv. : - .

which the naoet oc«afJex ~ > are learr

Judged bv his oarieta. ztesian man had attained no very high

St- -is part . xterity. He

was t not an e^oent artisan. -ess so wide a range of

--pt--j"Ktrrv- as the Xea^ e. The relati\-elv low the

Diirietal eminence is anotr
parietal lobe.

The temptwai lobe ss even nK>re insistent as to the c;
ity of oaebcal developfnent in the Rt<xiesian- In fact, there is t

this re^oa of the brain to suggest the possibiIit\- of p
is growth- This e more particularly the case in regar
spheiKtidal surface, although the tempcwal lobe as a whcJe is
•^Ttmn. The aoditory enaineoce shares in this limited development .
the temporal lobes are not only unusuaDy small, but are s^^
defected mward in a manns" 'Jiiitlar to simian c*"*»KfftK»ns- As ' -

bral c^iacity ths area of the Ixain discloses a

functioc, e^Kcially in those elonents partici|>ating in the spe . :5m.

The spokai language o{ Rhodesian man had at best but a meager stmctural
substratum and was for this reason, no doubt, crude as rth

Neanderthal speech. The CMnposite parieto-temporo-oc.
tiDctIyabbre\^ted — indeed, appears as if oom^M'essed. \Miate\'er

THE BRAIN OF _ . . _ . . . C \L\S 917

binatknis weie depiendent opcm tJiis oeopalEal zocie nuast iiarve Isatf tiuear

f Irmrtatioos-

Tfae occipital Joije, in tiiat portioQ of it lepteseaitiiag- vmao-psTffrir fnnsc-

tioo, is ranartahfy -well deveioped. It is eroded Isy tiiie rar^e oc tiiie laiiELbdiosd

suture and ^-a"=: a wefl-d^med saliciis lunatais erteotfEnis o'ver ^^if^n occapEEal

poie. The coQvoiutaoos above &ad bdiow tfiis saicos itaive a diear ogrdnimf--

0)ctrajy to tte status in all otfcia' parts of tiie Rbodiessaii braiiL tine ocf-npctal

lobe denotes a marked progFesjsive advaiiioe tcward Hosaaio sapaess. Otae

appearanice is tiiis regioo of tiie braia empiiasizes tiie size of tJie occipflial

lobe; naiaely, tiie smallness of tie cerebellar iiesiiispfeeres. Tins fact Mtro-

doces tne dBtnrb'ins oontiissTeiiics' th.st tie cooditJiOE maT be dae ^ conniEeniital

cerebellar smaHness or atrof)fey- Socit a soggestaoa of patitokiffy" im tiiK brami

sboaid be naentsooed oolr wTth. the ob'Tect of iatrodnriring all poi^Eife lactorav

howeva- ranote, b^bre final erahiatioE of" the cereijral co'Efegrarticgi is

FurthenniorE, the occEwtal surface of the cerebeBkiLSSi presejits as.

iinusual obliquitv indjcatrog an angiilariocL of the sopgaocffprtal and! bast-

ocapital portio'ns of the occgjctal faoaae whiich is soaaaewitat m. e^-are<!K m the

human avaage. Thjs sog^estio'ii of a pe«ss9jie pathioilioeacal ■pcDcess as esi:^^js&-

tory oi the general smaJlness <Df the Rhiodiesian bram H!i%ht carry rsiocc wirwfet

were it oot for the remarkable fairi-al skeJetoQ and crasimm 2ss»jcsared with el

The heavy strpfaocbital toctis, tfee capackxns orbffts, the wide antanjor mia-TTal

aperttLre. the bfijiad palate and the Emited cranial capacity are- al S3 thior-

ooshiv ape— Eke as to sDEnifv a stractDral rnieoorrtv aiofsi^ xEthecQad Immift

which oocld not be recooic2ed with a larse braioi of aidvaQced hinaEan type.

The ceTebnim of Homc' liii'xiesienss s «aTt.an, thiaefore. becamse it bekwased

to a man who. althio^ash already htnmaiL, had pnoeressed bet a ^iicjct discaBce

to^iard the ultimate gijai and standartis of humanrrr. EXBdc Sanurth has

estab&hed a str'>r!:g case for the great aptTitjalt* of ths "stm^'geiy esatic

cousin" of OCT £am5v circie. It seems wsest. for the rinme at kast. to accept

9i8 MAN

his iudsment that Rhodesian man occupies a far more primitive place in
an any of the Neanderthals.

Brain of the Predmost Man

It would be particularly illuminating were the brain of the great Cro-
Magnon race available for study. These people occupied an exalted position,
even as the earliest representatives of Homo sapiens, and the record of their
remarkable existence should be corresp)ondingl\- complete. But in lieu of any
survey of the cerebrum of this race, it is necessary- to draw analogies from
certain of their human contemporaries who lived in middle Europe during
Solu" mcs. These others were a remarkable people also. They are

known as the great mammoth hunters of Predmost whose social affiliations
ally them closely to the Briinn race. The remains of these men of the Old
Stone Age were found in .Moravia. Associated with them were the fossilized
bones of nearly nine hundred specimens of mammoths. In addition to these
fr^sils of men and beasts there were manj- highly worked flints including
spearheads of the laurel-Ieaf type, a pattern which marked this industry as
that of the Solutrean era. At Predmost, where .Maika discovered a collective
burial of fourteen human beings, there were also the remains of six others.

In stature these f)eople must have belonged to a large and powerful
race. Their prowess as trackers of great game was exceptional, judged by the
fossils of the huge mammals among which the\- reposed. This fact gave them
the name of "mammoth hunters." But it is the reproduction of their cere-
bral characters which raises them at once to a plane higher than any of the
earlier races of man, in fact, places them definitely in the category of Homo
sapiens. These intrepid hunters had much in common with the Brunn race,
much, indeed, that resembled their splendid contemporaries of western
Europe, the Cro-.Magnons. Of these latter there is ample record, in conse-
quence of which they will always rank among the noblest representatives

FIG^ 408 TO 413. SLX VIEWS OF THE ENDOCRANIAL C^ST OF HOMO SAPIENS
OF THE PftEDMOST RACE. . SOH.-rRE.A.N CONTEMPOR.ARIES OF THE CRO-MAG-
NON'^ > ESTIMATED ANTIQUITY 20,000 YEARS.

(O Vem^ ,Bt Ba«. c Frontal Pole, d OcciphJ Pole. E Rkht l^«ral Surface- f L*ft l^t«J Surface.
The darker >-^ - "- trc c^<t indicate the missmg parts of the cnmum.

[919]

920 MAN

of the human species. Their remarkable artistic contributions denote far
more tlian the executive mastery of plastic reproduction. They signalize
that new spirit which had been breathed mto mankind, that de\'otion to the
beautiful in hfe which created an ai^iding enthusiasm m the race for all its
highest ideals and loftiest purposes.

From earhest Aurignacian times these esthetic tendencies were- domi-
nant. It is e\ident in many indications of the lavish use of personal adorn-
ment, and the important rtMe played b\' coillure. The use ot red and ytllow
ochre was already know n, and it seems lair to assume that these pigments
were sometimes used, much as in modern times, to beautify the body; per-
haps also as tribal symbols and charms against kidnapping, or as tokens of
war and mourning. That the Cro-Magnons had created some form ol music
seems almost certain. Their sketches of dances and masks made it probable
that to vocal expression they had added artihcial accessories in the shape of
very crude musical instruments. Their art took lorm m mobiliary and mural
reproductions. The former included movable objects beaiing ornamentation
on bone, ivory, horn or stone. The latter were decorations upon the w alls and
roofs of caverns, shelters and dills. Among the earliest mobiliaries arc certam
human statuettes and reliefs m'ade in stone which undoubtedly represent
idols. Especially noteworthx is the collection of steatopj-gous feminine
figures carved in limestone of which the "Venus ol Willendorl" has the
greatest artistic merit. In their artistic discrimination these Aurignacian
and Solutrean sculptors showed a decided partiality for portraying women
of extreme corpulence. It was, however, in the carxing of animal forms that
their art reached its real heights. Many living and extinct species ol mam-
mals, birds and fish have thus been immortalized. Conspicuous among the
remains ol the great mammoth hunters of Picdmost is a rare and undecipher-
able engraving on ivory. It represents a much conventionali/A'd female figure
and may have been a phallic symbol, since most of the human designs of

THE BRAIN OF PREHISTORIC MAN

921

Aurignatian tmus maiufist a disposition to exaggerate the sexual eiiar-
acters. Baek of all this \ariecl artistie ereatioii tluri' must have been a
eoinplex and hii^liK dilKrentiated soeial organization. Onl\ a rieh luinian

FIG. 414. FUNCTIONAL LOCALIZATION OF THE BRAIN OL TLINED UPON THE
LEFT HEMISPHERE OF THE PREDMOST ENDOCRANIAL CAST.

A, Auditory Area; i". Higher Faculties; IR, Fissure of Rolando; is, Fissure of Sylvius; o. Area of Skilled
Movements; l>. Sensory Area; s, Speech Area; v. Visual Area; x, Area of Voluntary Motor Control.

experience eould
in art.

provide the soil for sneh \ivid and realistic beauty

FEATURES OF THE PRED.MOST BRAI.N

The Prcdmost brain had made all of those essential ad\anecs which
place it in the class ol Homo sapiens (Figs. 408 to 413). Its volume is
close to the standards for modern men. It had lost the marks of inferiority
which stamp the brains of lower races of man. It had gained that refinement

922 -MAN

of structural detail which proclaims the ultimate ascendency of the human
brain. The fissure of Sylvius may be easily identified and the fissure of
Rolando allocated according to accepted computation. \\ ith these two bound-
aries in place it is obvious at once that the Pfedmost brain has expanded
in all of its neopallial areas. The parietal, the occipital and the temporal
lobes have all alike assumed greater proportions than in any of the earliest
races of mankind. But it is in the frontal lobe that the most remarkable
gains are apparent. Not only are the frontal convolutions more prominent
and better defined, but that flatness so characteristic of the Neanderthal
vertex has disappeared, and there is no sign of that coronal constriction which
seemed to characterize the earliest efforts of the cerebrum in the acquisition
of its frontal areas.

Metric E\ idence of Brain E\olution' in Man

The manner in which evolutional progress of the brain has gone forward
is readily discerned in the accompanying tabulation. From the Javan man
to Homo sapiens there has been a gradual increase in all of the major cerebral
diameters. In one particular only has there been the slightest faltering in
these increments. The Neanderthal brain shows the greatest transverse
diameter. But its superiority in this respect is more than overcome by its
marked flatness. A distinguishing metrical feature in the development of
the human brain is the consistent gain in length and height from Pithe-
canthropus erectus to Homo sapiens. The gain in length is to be ascribed
largely to frontal increments; that in height is dependent in part upon parietal
expansion but also to some extent upon frontal accessions. The bearing of
such pronounced frontal evolution upon the ascent of man is evident in the
progressive development of human intelligence.

THE BRAIN OF PREHISTORIC MAN 923

Measurement and Indices of Hlman Endocranial Casts

Race

Width, I Length, I Height, Encephalic Cephalic Volume,
nun. ' nun. ' mm. ',^A..^ index c.c.

Predmost "9" 141 189

128

Homosapit-- F- :ioan average) ' 143 195 ] 148 "j " i-J'^"

Bi unn race ... ... ... 68. 2 ij

Predmost "4"

140

iS-

131

Homo neanderthalensis
aux Saints)

,1

!Ie

146

181.,-

■23

80.0

-5.0

1

1626

Gibraltar

140

165

112

84.0

77.9

1296

LaQuina

132

171

120

-8.0

1367

Homo rhodesiensis

.36

172

-9.0

' 1300

Eoanthropus dawsoni (,P

ItdowTi)
Java

133

169

120

-90

-So

1240

Pittiecanthropus erectus

126

iJ3

um

80.0

-3-4

940

Chapti:k XW'III
MAN— PAST, PRESENT AND FUTURE

PREHISTORIC man Is ^na(luall\ cnH'iiiinjj: from Iiis lon^s. obscurity.
It is now possihir to discern certain attributes of his which still live
and are as vital to further human progress as they were to iiis own
day on earth. His skeletal form is known from more than 350 speemiens ol his
fossil remains. These re\cal that strikiny harmony of structure which
pervades all human kind. But in them also may be detected manv subhuman
specializations and numerous \ariants representing, no doubt, only a small
portion of the human t'xperimental types discarded by nature belore Homo
sajjiens was at length deri\ed.

All [phases of man's earliest existenct' are singularly pertinent to modern
thought and development. ^ et the past has shut in so closely In-hind us
that our racial consciousness is almost wholly restricted to an historical
world. This scotomatous \ie\\ of human existence loses sight ol the pre-
paratory biological episodes ujjon which our being depends.

E\'OLUTioxAL Significance of the Ape-Like Characteristics of

PKiMirn E Men

\\ ith tlu' appearance oi' prehistoric man the curtain is lilted to reveal
a hinnan |)erspectlve of almost impenetrable depth. Looking through this
long vista of time it is ])ossible to sense, in some measure at least, the vast
distance man has come sinti' his human iourneying began. There are mile-
stones along this course which tell of critical turnings and partings ot the
way. A number of these critical jjoints are indicated by human rtmains.
Certain prominent features of man's skeleton denote that his course did not

lead in ail directness to the standards of ad\anced human organization.

925

926 MAN

Many of his osseous characters were distinctly ape-like — so much so that
these appearances in his earhest known state gave him the name o^ ape-man.
It may not be denied that pithecanthropus had definite pithecoid resem-
blances in his skull. The Dawn man of Piltdown manifested simihir tendencies
less pronounced m the form of Ins cranunn, Ijut still clear m the fang-like
character of his canine teeth. The Heidelberg )a\\ denotes a race in \\ hich
numerous smiian features were stiff retamed, \\ hifc the men of wefl-recognized
Neanderthal type also bore signs of ape-like specializations in head and face.
How otherwise may the massive supraorbital ridge be interpreted, or the
broad flat nose, the receding forehead, the widely separated orbits and the
large palatal process of the liea\\ simian jaw?

Nor had Rhodesian man dixested himself of these marks of the beast.
With the coming of Cro-Magnon times, howe\er, the long experimental
period was drawing to its close. Man in near approach to his final modern
form had at fength arrived. Those many detaifs of simian resemblance were
gone. The heavy characters of head and face essential to the contentious
life of the great ajx's hacf similar reasons for their appearance in the earliest
dex'elopmenl of man. Jucfged by the formidaljle mammals which shared the
earth with him, man's life must have fjeen fiereelv contested. The offensive
equipment of his jaw and head was only feebly supphniented by instru-
mental de\'iccs of his own making. Increasing powers of attack ri'quirecf
simultaneous increments of protection. The great a[)es, gaining in size and
strength as compared with the smaller anthropoids had, in this fact, an
adequate incentive lor the further fortification ol their l)odies, and especially
of their heads. The same incenti\e was operatixc In tlu' earl\ differentiations
of man, perhaps to an even greater extent. IK' at least was more \enturc-
some than the anthropoids in risking encounter with the great game animals.
Some of his success in these pursuits cfe[)eiufe(:f upon eiinning, but brute force
was not a negligible quality. Innumerable dangerous exposures, mollilied

MAN PAST, PRESENT AND FUTURE

927

in time b\ aclaptnx' progress and various eontrivances, demaiicled a resistant
osseous structure in his eraniuiu to protect his brain. Conditions ol Ins lowly
social orgiinization undoubtedly auuniented these traumatic eoiitini;encies.

FIG. 415. CKO-.MAGNON ARTISTS MAKING THE GREAT MAMMOITl FRESCO IN THE
CAVE OF FONT-DE-GAUM E. DORDOGNE, FRANCE.

Mural painting by Charles R. Knight made under the direction of Prof. Henry Fairfield Osborn. From the
Hall of the Age of Man, American Museum of Natural History.

As offensive strength must ha\e been his most ellVctive argument, so a
stout frame was his [)est defense. Is it eiitirelx accurate, therefore, to speak
of his bony facial mask, his heavy jaws and large teeth, his thick skull and
receding forehead as ape-like specializations? Are they not the more general-
ized adaptive modilications shart^I in common b\ the two branches of the
orthograde primate stock, for a life demanding concentrated physical force?
Certain specializing factors in these two great lines of primates clearly oper-
ate in common. Such, for example, were the marked increase in body weight,
the tendency to stand upright, the reduction of speed in escape, the progres-
sive loss of arboreal retreat, the need of augmented offensive powers and a
more capable mechanism for procuring food supply. All of tht^se appear as
vital necessities in the specialization of man and the great apes. If certain

928 MAN

structural features determined by these physiological demands became
progressively less prominent in man, it was because his genius gradually'
devised the means to obviate their need. In fact, it was the potential degree
of cerebral growth and psychic development which kept the human cranium
so plastic.

It is cjuestioiiable, therefore, whether any advantage is gained by the
continued reference to the pithecoid specializations of jjrimitixe man. II
he were ape-like in many aspects of his form and being, the great apes to
offset this have been called man-like on similar grounds. This convenient
uiterchange in terms does no doubt signity a mutuality in dehnite charac-
teristics. On the other hand, it tends to olxscure the common generic factors
which imparted to man and ape alike those distinctive characters described
in the human as pithecoid.

The Five Essential Homimd Characters

That there was a delinite prehuman stock, a stock capable of producing
both anthropoid apes and man, cannot Ik- disputed. But at least five critical
and closel\ interdependent specializations determine the status ot the
human race: the ap])earance (i) of the human brain, (2) of the human loot,
(3) of the human hand, (4) of the erect posture with bipedal locomotion, and
(5) a terrestrial mode of life.

Estimated by these hominid characters, the human l\pe was irrevo-
cably established despite such pithecoid features as it might still retain.
When this status ol man is reached, liowcNcr low and humble it may be,
there is little justification lor the term ape-man. By the lact of his entrance
into the human lamily, man surpassed the more narrow limitations of simian
organization. At the same time he retained within himself a structural plas-
ticity for further development w hich the apes had almost entirely sacrificed
to their definitive specialization.

MAN— PAST, PRESENT AND lUTURE 929

Some Views oi^ Man's Relai ion to the Apes

The human race in this sense hears no ancestral relation to any of the
known apes. cithtT h\Ing or extinct. Man is (listin<i;nisht'cl hi'cause lie was
able to estabhsh his own laniilx m thi.' aiinnal kni^doni by separating hniiself
from the formal restrictions which bound the apes to their simian hai)itat
and structure. In a recent comnuinication. Professor Osborii (Natural
History, xxvi, No. 3, ]). 269) has taken a position in decisi\-e terms whicli
gives tht' liuman race a hiu' ol ancestors entirel\ its own and c|uite distinct
from that ol tlie anthropoid apes. "Man and all ins ancestors," he writes,
"should now bi' embraced within tlu' family hommidae as distinguished
from the family simiidae which embraces all of the anthropoid a|)es. This
family distinction naturally carries with it the appellation 'Dawn .Man'
as distinguished from the appellation 'Ape-man' which will gradually dis-
appear through disuse along with other misleading terms, due to our mis-
conception and ignorance as to the actual ancestors of man."

Over against this view, it is onl\ fair to quote the o|)inion of two other
eminent authorities, I-'rofessor Gregory and Professor MiCiregor. Both take
exception to this interpretation on the ground that it ma\ be misleading.
They are generally agreed that the earliest known races of mankind wt-re
already true hominidae and, therefore, in spite of certain ape-like features,
they hardly deserve the name of "ape-men." They are unwilling, however,
to disclaim all kinship whatsoever of the human race with the anthropoid
apes. Such kinship does not impl\ a direct ancestral relation but indicates
an evolutional process among the primates which places the chim|)anzee
and gorilla closer to man than to any tailed monkey.

In one respect the brain lends unciuestionable support to Professor
Osborn's view. In the lowest known type ol man. Pithecanthropus erectus,
cerebral de\elo])ment had attained human proportions. The critical expan-

930 MAN

sions in the frontal, the parietal and tlu' temporal lobes are deeisively man-
like. The\ seem sullieient to raise the Ja\an man out of the elass olape-men,
even ii sueh a elass should cAcntuallx maintain its \alidity. Furthermore,
the human hrain from its most humble beginning, has, unlike the brain ot
the great apes, manifested advances in specialization of those areas associ-
ated with the produetion oi' s|)oken language, with the regulation of highly
skilled acts and, most probabl\ at least, with unide.\terit\ .

Progressre Development as the Outstanding Feature of

THE Human Brain

Thus from its inception the cerebrum endowed man with the capacity
to develoj), inculcate and transmit certain cultural activities. \\ ith the lirst
rude fashioning of implements from wood or bone, there arose that uninter-
rupted stream ol human achie\ement which has passed on as the main cur-
rent of all culture and knowledge. It was this power of progressive and racial
learning that made the human brain distinctive as compared with all others.
Conditioned reflexes ol the lirst, second and third order de\elop m many
other mammals, but man soon transcended this limited conditional range.
His eventual successes came from his almost unrestricted capacity to utilize
the conditions imposed by his own experience or im])arted to him by tlu'
didactic elforts of others. The kind of brain he possessed is not only apparent
Irom the structure ot this organ, Ijut c|uite as much trom his mode ol hie and
iiandicralt. Viewed in the light ot his man\ cultural phases, man's outstand-
ing attribute has been his pcnver to inipro\e. From age to age, from race to
race, he has shown a steady progress in the control of material conditions
as well as in the de\elopment of sj)iritual understanding. Allow ing for the
not intrequent cultural lluctuations during which human attainments have
waned while the higher human (|ualities were conspicuous by thcirabsence,
man's tendency as a race under fa\orable conditions has been to advance.

MAN— PAST, PRESENT AND I-UTURE 931

Ci LiLKAL Periods as E\ idence of Cekei5kai Development. It is
probable that he had an actual Lolitinc periof/ w hen the stonr implenu-iits he
produet'd had all the eruditx' ol accidental lorins. The many adaptive im-

FIG. 41C). NEOLITHIC MEN.

These men lived along the shores of the Baltic in the early stages of the New Stone Age. They were the
direct forerunners of civilization. They cultivated the soil, domesticated animals, made pottery and woven
textiles, erected sepulchres .and temples of stone (dolmens and megaliths). Painted by Charles R. Knight
under the direction of Prof. 1 Icnrv Fairfield Osborn. From The I lall of the Age of Man, American Museum
of Natural History.

provements in his (lints during; the [)re-CheIIean,Chellean and Acheulean peri-
ods, led by progress i\'e stages to his pronounced Monsterian productiveness.
More striking still was his Aurignacian development with its remarkable out-
burst ol esthetic enthusiasm and artistic creations. II atti'i" the Solutrean era
his industries began to languish, acluall\ sinking to a low le\ fl m the Azilian
period, it seems onl\ m preparation lor the acKcnt ol Neolithic man.

The Cro-Magnon decadence ma\ well ha\ f cleared the way for a transi-
tion which was to pro\ e portentous in its material and psychic acKance. It
ushered in a period ol j^ractical utilities. It substitutc'd tlu' beiielits oi applied
science lor the delusions ol t'xpedient sorcery. Neolithic man ma\' ha\'C
prayed lor his crops, but he also tilled the soil and planted si'cd. He may

932 MAN

have had propitiatory ceremonies lor his liuntin<i; expeditions, hut he domesti-
cated animals to <i;uarantee an assured su[j|)l\ ol food. The efHcienc\ ol repro-
ducing tht' likeness of game animals in dark ea\erns no longer appealed to
his common sense. Unlike his Neolithic successor, the Cro-Magnon was
satisfied, according to his lights, b\ the delusions of his hunting magic and
art sorcery. But Neolithic man had discovered the magic of agriculture and
sought to control nature by the toil of his hands rather than by impractical
incantations. As farmer and herdsman he naturally became a landholder.
This was a long and provocative step in the direction of modern hLimanity.
It enforced upon man the need to defend his claim and assert his right.
Quickly enough this new assertiveness led to the more aggressive Ages of
Bronze and Iron with their harsher organizations for ollense and defense.
Ultimately it extended its inlluenees into historical times, creating all of the
armed carn[)s known as civilization, ancient, medieval and modern.

Mankind's Future Paths of Progress

The Hominidai' have been a truly progressive family, by reason of which
it differs from all others in the animal kingdom. Here and there about the
world it has lagged in its advances. But given its fair opportunity, it has not
failed to go forward. The line of this progress may not be deemed ^\ holly
satisfactory by the standards of enlightened criticism, '^'et in bending the
forces of nature more and more to his w ill and eoinenienee, man has surely
progressicl. \\ here he has stood still, perhaps vwn lallen behind, is in the
manifest lack of control over his own nature.

l-'rofessor l-*avlo\', in his epoch-making work on the Conditioned Reflexes,
has vividly portrayed this situation, Noieing at the same time the hope ol a
possible escape from it. \\ hile tlu' |)all of re\olution still hung owv him m
Soviet Russia, he wrote these inspiring words;

MAN— PAST, PRESENT AND FUTURE 033

"I am cl(.'i'pl\- and iircxocahly ronx-iiici'd that luix- al()n<i; tliis|xith leads
thi' way to the hnal trunnpli of the human mind on er its utmost and SLipreme
prohlcin the know lfd<j;<.' ol the mechanism and laws oi' liuman nature. Only
henee may eome a lull, true and [)ernKuu'nt liuman happiness. Let the mind
rise trom \ietory to victory oxer surroundmij; nature; let it conc|uer for
human life and aeti\ity, not ouIn all the surface of the eartli, hut the water
and surrounding atmosphere; let it transfer for its purjjose prodi<iious
energy from one part of the eartii to tlu' other; k't it annihilate space
for the transference ol its thoughts — \ et the same human and his mind
leadmg hmi mto dark powers, to wars and re\ olutions, with their horrors,
not calcuhiting the material loss and iru-xpressihle pain, reproduces animal
relations. Only science — the exact science about this same human and the
most sincere a|)proach to it Irom the side ol Omnipotent Nature w ill deli\er
man Irom his present gloom and will purge him of his contemporary shame
m the sjihere ol human relations."

The brain of prehistoric man seems to shed new light u])on this jjath.
It seems to give assurance of that delixcrance which ]^a\lo\- conlidently
believes awaits mankind.

THE FI?0\IAL LOBE — ITS POTENTIALITIES FOR HUMAN PROGRESS

IN THE FUTURE

Since his earliest beginning man has grown in humanit\ as his brain
expanded. Such a conclusion appears irresistible. A comparison of the cere-
brum m the stages ol human cNolution ahx-ady known to us is sullicient to
con\ince the most skeptical. Placed side by side (Figs. 41-422), brain casts of
the Javan and the Piltdown man, the Rhodcsian and the Neanderthal, the
Predmost and tlu' modern, demonstrate more efTectually than words the
extent of this progress. The regions in w hich expansion has been most pro-
nounced are easily discerned. Increments in the parietal and temporal areas

Prcdmost Modern

FIGS. 417 TO 422. A COMPARISON OF TIIF ENDOCKANI AL CASTS OF PITHE-
CANTHROPUS, PILTDOWN, RHODESIAN, NEANDERTHAL (lA CHAPELLE AUX

saints) and pkedmost man Willi HOMO sapiens (modern type).

[934]

MAN PAST, PRESENT AND FUTURE 935

ha\(.' been straclil\ maintanu'cl ihrou^^lioul this sltics, but it is in the h'oiital
It)bc' that clrcisiw aclxancc has occurri'cl. 1 his area, so jx)()rl\ rcpri'sciitcd
in man's iR'art'st kni, the ^rcat anthropoid a|5c's, shows (.'MilHTant i^rowth in
pithrcantliropus. Its Icaturcs correspond with thost' of I lonio sajjicns in
iu-arl\ all ck'tails. Its only essential mleriority is its relative sniallness. ^ et
even its size is sullieieiit to iustily admission into the human lainily. Its
specializations in the i^refrontal area, and tlu' di\"elopnuMit of the inferior
frontal convolution denote the aec|iiisition of human si)eech and reason.

l-*erhaps it is ha/.ardous to dehne any single area in the brain as the
region suj^reme in cerebral oi\i:ani/atioii, since the entire neopallium is viv-
tuallx interde[)endent throuiihout all of its special parts. The \ isual, the
auditory and the somesthetic sensory areas contribute so indispensably to
life's reactions, that one part may not be subordinated to another. This is
also true ol \hv motor area, the area regulatiiiij; skilled moxement and the
large intt'iniediate /one w Inch |)artakes of parietal, occii:)ital and temporal
characters. Each ol these art'as has proo;ressi\el\' expanded through the
se\'eral e\olutional stages ot the human bram. ^ et it is reasonable to attri-
bute a certain superiorit\ to that neopallia! region which is charged w ith the
iunctional repri'sentation ol all othc-r cortical territories, which combines
the highly particularized Junctions ot all other areas in broader impressions
ol human existence, which acts as the accumulator of experience, thetlirector
of behavior, and the instigator of ])rogress. Traced through all their inter-
mediate steps upw arc! it is exactly these prefrontal and frontal regions which
manifest the most conspicuous development. The process of this long con-
tinued progressive expansion in tlu' frontal lol)e, reaching back to the earliest
Pleistocene times, and it may be e\en into the Pliocene epoch, conve\s the
impression of a responsi\e plasticity in the human brain. This remarkable
anticiuity and this salutary plasticity ha\H' been largely overlooked. For the
most part the human cerebrum is regarded as a finished product. Itsevolu-

936 MAN

tionary history does not support this point of ^•it■\v, but makes it appear far
more probable that the brain of modern man represents some intermediate
stage in thr ultimate development of the master organ of hfe. And the great-
est possibility tor future progress lies in the further de\elopment of the
frontal lobe. In this sense the brain of prehistoric man is of more than anti-
quarian interest. It has a positive bearing on the future advances ol
mankind.

PART V

EVOLUTIONAL MODIFICATIONS OF THE PRIMATE CEREBRUM
CULMINATING IN THE HUMAN BRAIN

INTRODUCTION TO PART V

"^1 IE ami ot these c'()iu'lu(lin<j; chapters is to eonsKler eertaiii ciii est ions

whose discussion may seem to ]ustil\' tlie deductions chaw n Iroin

the laets as the\ ha\e been presentech

The questions arc pnmarilv designed to gi\'e the e\ idenet' its hnal logical

arrangement, to test, in so hir as ma} be possible, its validity. They have

been lormulated as lollows:

1. Does the appearance ol tlu' bram m prmiati's, including llu' lemurs,
monke\s, apes and man, show such similaritx ol structure as to indicate a
constanc\ which distinguishes them as a distinct and scfxirate order of
mammals? And does this hoiiiogt-iu'it \ ri'cene substantial ];rool in the
essential similarities ot beha\ior within this order?

2. Do the structural pattc'rns ot the brain m these primati's manilest
j)rogressi\e modilications m harmoin with progressive adaptations in the
behavior of these animals?

3. Do these progressi\'e modilications In stiuctuic and l)eha\ lor lustify
the e()nee|)tion ot an CNolutional process in conscciueiicc ot which tiinda-
mentallv simple structures haw become more complex in order that they
might impart to beha\ioral reactions an increasing rangx' ol adaplabihtx ?

4. Does the primate bram indicate that man a\ as dci'i\ed Irom a series
ot preparatory pro-human stages and what relationship dot's it rewal
between man and the apes?

The Position of the Primates among ihi- Mammals

In considering these cjuestions it is lirst lU'ct'ssary to assign the primates
to their proper position among the mammals. They are but one ol many
contemporaneous mammalian orders. II, as is generall\ belicNcd, a period ol
time reaching back to the mci'ption ot the Tertiar\ period was required to

940 EXOLLTIONAL MODIFICATIONS

complete the adaptive modifications of the primates, they were by no means
the only forms undergoing an active process of differentiation. From some
period in the Mesozoic a host of primitive mammals began to pass into the
great habitat zones along many different lines of adaptive radiation. This
process of mammalian differentiation led up to the era of geological time
properly called the age of mammals, more particularly, perhaps, the age of
placental mammals. Even at the beginning of the Tertiary period there had
appeared such diversified forms as the carnivores (creodonts), bats, insecti-
vores, hoofed mammals (protoungulates), rodents, lemuroids and tupaioids.
All of these orders developed a profusion of families, genera and species,
linked together, however, by one mutual bond of heritage in their placental
mode of development. The duration of this great division of time is variously
estimated between ten million^ and one hundred and forty million years. -

' American Museum of Natural History estimate.
- Bv radium emanation method.

C XXIX

THE SIGNIFICANCE OF THE STRLCTL R-\L HOMOGENEITY' AND

SPECIFIC MODIFICATIONS IN THE PRLMATE BR.AIN.

THEIR RELATION TO THE PROGRESSIX E

ADAPTATION OF BEHAMOR

The Primate Bbain as Evie : Closely Int^ d

Primate Order

r

1

^ : . ^ they are in e.\: „_.ce, stand out in

- jle definition as a closely integrated order in consequence

-*" "■" '-a5t one constant mark of identifrcstion, the brain. If in other

It-:

struc " - ::e ordinal association of t ates might be doubted,

this I " of their organizat!*^r! wrviild set .bts aside. Even in the

exter .of the b" iite«. there are featiires which

them tosrether by ^ _ _'\"astG .teat

- e hesitancy in recognizing the essential similarir'.- that

exists between t These similarities constitute a fr>rm: - ogue

of homologous features. Some nine or ten of th*^ ntioned and

discussed.

ESSENTIAL ORDINAL SIMILARITIES OF \IN

The Encephalic Indices. The encep . .dices of these brains,
almost without : •=pec!f!cation, set the primates apart in an order by

themselves. .-MI of thest^ < possess a forebrain ir\6ex above 80 per cent,

both by weight e brain. The . anying table shows

how this index ..ptive process c. .ts especially to the

predominant -ce of the differentiation of the forelimb. Those animals
whose i>ectL. ages are sp>ecialized as wings, fins or |>addles do not

942

EVOLUTIONAL MODIFICATIONS

exceed a forebrain index of 60 per cent. In the main they are all much Ix'Iow
this figure. The forebrain indices in the dogfish, codlish and shark are ail
less than 25 ]>er cent of the total brain \-ohime. A reptihaii form, such as
the soft-shelled turtle, shows the considerable advance to 53 per cent,
while the American ostrich w ith 60 per cent reaches the high level of develop-
Encephalic Indices of Evolitional Significance

Index: 82 and above

Hands Fingers Finger nails

Animal

Volume index

\\ eight index

Forebrain Midbrain
per cent per cent

Hindbrain
per cent

Forebrain
per cent

Midbrain
per cent

Hindbrain
per cent

I Icmo sapiens, modern man

Troglodytes gorilla, gorilla

Simia satyrus, orang-outang. .
Macacus rhesus, Indian monkey

I lylobates hoolock, gibbon

Callithrix jacchus, marmoset.. .

Index: 70 to 80

iilliaris, dog

icstica, cat

ballus, hors

js, cattle

bachtr., camel. .
ndicus, elephant
)phaga jub., g

5 tridact., three-t
Index: 20 to 60

88

83

82

83

14
15

16

87

I

12

84

84

2

14

1 2

2

14

82

2

16

83

2

'5

I liii)fs Claws

Canis familiaris, dog

80 1 7 1 13

80

5 1 '^

Fclis domcstica, cat

' 6

1

1 N .S(i

4 21

Equus caballus, hois

Si > 2

2 iS

Bos taurus, cattle

«.. 2

18 , Sn

2 18

Camelus bachtr., camel

-cj 2

19 -',

^

IQ

Elephas indicus, elephant

-J

2

26

~ 1

73

2

Myrmecophaga jub., giant ant-
eater

75

6

19

5

22

Bradypus tridact., three-toed sloth.

70

10

20

70

10

20

Wings Fins Paddle?

Rhea aiTicnciina, ostrich

58

lO

26

'n 1

1 ',

27

Aspiclonectes fcrox, soft-shellcd
turtle

57

. 15

:^s

53

20

27

Rana svlvatica, frog

4'>

21

3-

42

Gadus morrhua, cod-fish

20

40

20

i"

40

Squalus acanthias, dog-fish

23

27

50

STRUCTURAL CULMINATION 943

nuiit in this type of ^ cTtchratc. Animals developing claws, hoofs and paws
in the forelimf) dilVerentiation ha\e a forebrain index wliich may rise to, but
does not exceed 80 per cent. For tlie most part it is much below this figure.
The sloth, the anteater and e\ en the elepliant all lia\e a \ ahie below 76 per
cent. The camel, thi' horse and the dog reach the upper limit of 79 or 80 per
cent w hich seems characteristic of animals whose forelimbs arc conditioned
by de\eIopment as specified. In that group in which manual diHerentiation
reaches its final stages, the hand presenting fingers and fingernails, the fore-
brain index is always above 80 per cent. It ranges throughout the primates
from 81 per cent m lemur to approximately i)o per cent in man. T he signifi-
cance of these comparati\ e indices takes its importance from the tact that the
forebrain is the most recent accession to the central ner\()us system and
attains its greatest expression m mammalian orders, particularly in the jjri-
mates. It is the structure essential to the most highly organized behavioral
regulation. Animals possessed of the greatest development in this respect
manifest the greatest adaptability in meeting the conditions of their einiron-
meiit. They are better able to adjust themselves and enjoy a greater range
of acti\ity. The primates stand in contrast to all other vertebrates because
they possess the most effective organ for the utilization of their environ-
mental opportunities.

The Diametric Indices of the Primate Brain. The diametric in-
dices of the brain establish an ordinal character which also distinguishes the
primates among mammals. In these animals the ratio of the iiiterj)arietal
diameter to the occipito-frontal diameter varies from .81 to .88. Compared
with carni\()res, ungulates and marsupials, the contrast is striking. It
indicates the type of brain whose longitudinal expansion is concomitantly
followed by a transverse expansion. In other words, the brain is becoming
broad and losing some of that elongated appearance w hich is characteristic
of lower mammalian forms. This condition of broad brainediiess, if such it

944 EVOLUTIONAL MODIFICATIONS

may be termed, is a characteristic of the primates. In effect it is the con-
sequence of expansion taking place in the neopallium which begins to over-
shadow the archipallium (rhinencephalon). The chief increments are at
first evident in the parietal lobe, indicating no doubt the expansions in som-
esthetic sensibility due to quadrumanal differentiation. Corresponding
expansion soon makes itself apparent in the temporal and occipital lobes.
It finally expresses itself, at the upper extremity of the primate series, in
large increments to the frontal lobe. This dimensional modification is expres-
sive of a recession in the rhinencephalon, particuhirly involving the olfactory
sense which is gradually replaced in the jjrimate by an extensive develop-
ment in the distance receptors for sight and hearing. In certain other groups
of mammals there is a marked degree of broad brainedness, for example,
that seen in seals, cetaceans or sirenians. In these instances the brains are
almost as broad as they are long, and thus transcend the upper limit already
prescribed by the diametric indices of the primate brain. In the case of
aquatic mammals, the underlying motive in the transverse expansion of
the hemispheres is different from that in the primates. It particularly
affects the parietal area in relation to expanding the region of somesthetic
sensibility. These animals, by their entire body surface, are in constant
contact with the water. Their somatic sensory surface thus becomes a most
important receptor system and because of its great extensiveness determines
the corresponding expansion of the parietal lobe. Some of the acjuatic
mammals also show a recession in the pruniinenee of the rhinencephalon
and the olfactory sense, which may even exceed that witnessed in apes and
man. They show, however, no such expansion in the frontal or occipital regions
as that seen in the primates.

The Fissural Pattern of the 1 Iemispiiekes in the Primate Brain.
The lissural pattern of the In'misplieres is identical with or lollows a de-
sign similar to the liunuin adult. Fhe eon\e\ity oi the cerebral lurui-

STRUCTURAL CULMIXATIOX Q45

spheres has in general a tri-fissural design in which three chief fissures are
present: first, the fissure of Sylvius, second, the fissure of Rolando and third,
the simian fissure. The position and angulation of these fissures arc charac-
teristic in the primate brain. The SyKian fissure in its lateral portion extends
backward and upward at an angle something less than 45 degrees with the
base line of the brain. The fissure of Rolando extends forward Jrom the
superior longitudinal fissure at an angle varying from 6~.j to 84 degrees.
The sulcus simiarum leaves the superior longitudinal fissure at an angle of
about go degrees. This latter sulcus is believed to have no counterpart in
the human brain. Nevertheless, distinguished authorities such as Elliot
Smith maintain that the sulcus lunatus, on the lateral surface of the occipital
lobe of man, is a vestige of this great simian fissure. In many instances the
human parietal incisure of the occipito-parietal fissure corresponds in striking
degree to the more proximal portion of the sulcus simiarum of the higher
anthropoids.

Nor are the similarities, which link the primates together on the basis
of their fissural patterns, limited to these three major fissures alone. W ith
few exceptions, the identifications may be carried to the secondary fissures.
In many lower primates and also in the intermediate group, these secondary
fissures have no such prominence as they attain in man. If the brains of
such simians be compared with the fetal brain of man in which the secondary
fissures are making their appearance, the correspondence between the anthro-
poid and human brain may be recognized. Further development of the
brain in man adds much complexity both to its convolutions and fissures.
But an essential correspondence of fissural pattern exists in all primates.

The Lobation of the Primate Brain. The lobation in apes and man
is identical throughout the series. As seen upon the lateral convexity of the
hemispheres, this lobation expresses itself in four distinct divisions: the
frontal lobe, the parietal lobe, the temporal lobe and the occipital lobe.

•

FIGS. 423 AND 424. SIZE AND CONFIGURATIOX OF THE DORSAL SI RIACE OF
THE HLMAN BRAIN COMPARED WITH THAT OF LE.Ml R MONC.OZ.

Iiiiilllnliiii

f ■ I • • M II If <} M 13 a I' la la to fi It II n n\

-■■ I.' ,.',.,'.. I .,l,l„,.|l.,J„llll,lll,.„lm,l I .,„Im:,I„„Li,I„,J,m1„J.:iI,.,I„„lJ„.,I..,L|„J„„I„J „„L„I„J.J„J,„,I„„I I

Centiitietstr Seals

0llb

FIGS. 425 AND 426. SIZE AND CONFIGURATION OF THE LATERAL SURFACE OF
THE HUMAN IJRAIN COMPARED WITH 1 HAT OF LEMUR MONGOZ.

[946]

STRUCTURAL CULMINATION 947

This lohation conc'spoiicls so nuich in detail throuf^lioul tin- orckr that tlirre
can he no doubt as to tlu' I'sscntial siinilanty existing m tliese niorpliological
leaturcs ol the central nerxous system.

The CoN\OLUTio\ Ai I^A iTERN 01 Nil Pkim A IF. Bkaix. Thispattciii
coincides with striking consistencx . \\ here\er convolutions de\elop, their
general homologies ma\ be easil\ determined, if not b\ actual comparison
with the adult human brain, at least with some earlier tetal stages.

Okbital and Occipital Conca\ hies ok the Primate Brain. The
two great conca\Tties on the basal surface ol the brain, known respectively
as tlu' orbital and the occii:)ital concavity, ma\- be ideiitilied as corresponding
leatures in all species.

Ceri AiN Characi eristics OF THE Basal SiRFACE. Certain basal char-
acteristics are notablx similar. Ilius the ollactory bulb and its associated
structures ha\"e become much reduced in size as compared with the carni\()rcs
and ungulates. This is especially the case with the ollactor\ tracts which are
readily detachable trom the under surface of the bram as far back as the
trigomim oifactorium. In no instance does either the tract or tiie bulb
contain that ]:)r()Iongation of the xcntricular ca\'it\" common m lower mam-
mals. Another characteristic on the basal surface is the relation of tiie optic
ner\'es and optic tracts to tlu' chiasm m primates. The < ptic nerves approach
the chiasm and the tracts lea\c it at an angle much nearer ()0 degrees than
It is m an\ lower mammalian forms. When retracted the olfactory bulb
and tract usually reveal the beginning of a sniaH sulcus immediately in front
ol the trigonum oifactorium. 1 his is the sulcus olfactorius which more or less
completel\ bounds a gyre situated mesial to it, the gyrus rectus. The sulcus
olfactorius and the gyrus rectus occur in an incipient stage or fully developed
in all of the primates.

Relation of the Cerebellar Hemispheres in the Primate Braix.
The relation of the cerebellum to the cerebral hemisphere is another identify-

948 EVOLUTIONAL MODIFICATIONS

iiifj; characteristic in the primate brain. In all species, with the e\cepti(jn of
the lemur, often nientionecl as a transitional form, the occipital lobe of the
hemisphere has so advanced in its dexelopment as entirel\ to conceal the
tentorial surface ol the cerebellum. Not alone in the relation ol the cere-
bellar to the cerebral hemispheres are the primates distinguished from all
other mammals. There appears another identifying feature on the occipital
surface of the cerebellum, i.e. the vallecula, or vermal notch, w hich is most
characteristic of the order. The depression between the two lateral cerebellar
lobes, w hich lodges the inferior vermis, is also a distinctive mark. The \entral
surface of the bram likewise reveals prommeiit mdices connected with the
de\elopment of neokinetic functions, such as the ])yramid, the inferior oli-
\ary body, the pons Varolii and the cerebral peduncles.

The De\'elopment of the Pineal Fossa in the Primate Brain.
The development of the pineal fossa lying at the cephalic e\tremit\ of tlie
intercollicular sulcus makes ]:)ro\ision lor the epiphysis cereljri. The rela-
tion of this gland to the midbrain is subject to considerable variation among
mammals. In some it occupies a supraeallosal position. In other forms it
IS j)ostcaIIosal, lying bi'hind the splenium ol the corpus callosum l)ut not in
contact with tin- midbrain. In the primates, it lies in a subcallosal position,
resting upon tlu' roofplate in the ])ineal fossa of the midbrain.

Such are the features on the external surface of the bram which consti-
tute an array of similarities sullicieiit to establish the ordinal solidaritx of the
])nmates. Each of these distineti\-c features max not in all instances ha\e the
indul)itable quality of an idi'iitifying character. But the sum total of them
all serves as an entirely reliable guide for the ident ilication of any nu'inberot
the primate group.

INDICAIIO.NS OF ENOLLTIONAI. UL\ ELOPMEN I IN THE PKI.MAIE BKAIN

In connection with such distincti\'e features the question naturall}-
arises whether these charaett'rs are siibiect to such modifications as show

•

FIGS. 42- AND 428. SIZE AND CON IK, I RATION OF IIIF DORSAL SIRFACE OF
THE HIMAN BRAIN (OMRARED Willi ITIAT OF CAMIlllRlX JACCHUS, THE

MARMOSET.

IL I..j..L'„.,Ll.LJ,.j,.J„.,i,„.

,,i.„l,-„i,„,l..„i„J,„.i„,I..,i„i„,i„„L.ii„,l„.i,.,L,

Centunet&r- Scale

.i....J.,...,„.l....lJ....I....I

FIGS. 420 AND 450. SIZE AND CONIIGI RAMON Ol IMF LAIFRAL SIRIACE OF
THE III M \N HK\IN (OMRARID WITH THAT OF CAIIMIIKIX JACCHIS, THE

MARMOSET.

[<H«1

950

EVOLUTIONAL MODIFICATIONS

a progressive evolutional development. In other words, does each one of
these features \\:[\v its sinijilest morphological expression in the lowest of
the primatts, and pass progressi\"ely through graded intermediate stages,
to a euhnination of its greatest complexity in the highest member of the
order?

E\oLi rioNAL Significance of Brain Indices. In the matter of the
brain indices it is certain that the primates show a steady and progressive
advance. There are scune incidental lluctuations, however, which may be
allributi'd to \anations m the degree ol specialization. Thus the lemur, the
tarsier and tlu' marmoset stand at the lower end of the series in so far as
the forebrain index is concerned, each of these genera being slightly above 80
per cent in this respect. The intermediate group is next in position. The
great anthropoids, although they show a dchnite increase m their lorebrain
index, are still considerabl\ below man. The accompanying tabulation indi-
cates the tendency toward expansion as witnessed by this index among the
primates.

Encephalic Indices

Animal

Encephalic index (per cent)

Forebrain ; Midbrain 1 Hindbrain

Lemur

81

5 14

Marmoset

80.5

0.5 i 19

Mycetes

Baboon

Macacus

Gibbon

Oiang-Outaiij:

CInmpaii/ee

Gorilla

I lunian

81.6

83
84

83

_84

86-89

4.8

_i4

J4

_i6

12

la

J4

10-13

STRLC" ' • ^ ~ -: 951

In a similar manner, the diametric indices of the brain reveal a general
tendency toward expansion in p>assing from the lower to the upp>er extremity"
of this order. There are, however, certain notable exceptions in this regard
which need explanation. Thus, marmoset and lemur occupy the lowest
jx>srtions, but, departing from what might be exp>ected, mycetes representing
the majority" of the Cebidae, develojjs the highest figure of all the primates
with a diametric value of 92 p>er cent. This undoubtedly is due to the great
expansion in the parietal lobe incident to the increment in somesthetic
sensibilitA" produced by the sp>eciaIization of the prehensile tail and extreme
quadrumanal differentiation. Among the intermediate primates, the gibbon
stands as high as any of the great anthrop>oids. This again is accounted for
by the extreme sp>eciaIization of its brachiating arms incident to its peculiar
tA"pe of locomotion and exquisitely arboreal life. Ofthe three great anthropwids,
the orang has the highest p>osrtion according to this index, higher even than
that of man. The relatrvely low figure attributed to gorilla and man is explained
by the pronounced expansions in the frontal lobe of both of these species. Thus
while the diametric index may not be considered to furnish the reicord of a stead-
ily progressive evolutionary." process, it indicates certain adaptrse modifications
to which the cerebral axes have resp>onded. in ojnseqtience of specialized
exp>ansions in particular regions of the brain. The condition of broad brained-
ness as contrasted with that of long brainedness is due to the <^>eration
of several factors. In the fir?t place, the general mammalian tendenc>- toward
the development of a long brain depends up>on the degree to which the rhinen-
cephalon dominates the process of growth. The recession in prominence of
this oIfactor\" pwrtion of the brain tends to shorten the long axis and thus
raise the value of the diametric index. Another influence producing the same
result is the combined recession of the rhinencephalon with marked acces-
sions in the pxarietal lobe. A third factor may alter the values of this axial
index. This is the lensrthenini: of the loni: axis of the brain while the trans-

952 E\OLLTIONAL MODIMCATIONS

verse diameter is also increased. Such modification a* thi* rewihs from the
de\-eIopments in the frontal lobe which tend t/j prrxJuce v>mething inter-
mediate between broad bramedness and (ong brained ncs». It is thus ev
in explanation of the . ;.ncies indicated b>' the dfa-

indices of the ne high degree of broad ferainedness

manifested by mycetes is due to expansifwi in the parietal region of tht
incident to accessions in sor .*.y. An additional el-

in mycetes is the apparent - ion in the frontal lobe de^'ek^pment.

In the case of the gibbon, where the axia! index rises to a xdathreiy
high figure, the espFanatron is also i retardatron of the f'

do'elc^ment with - -i the higher

asithiopoidsr both the orang . - refatf*.-e!y hL ^ es

in their diametric indices due tc - bes wrthoat

concomitant development in the : reas in man and

gorilla the tendency" toward increase i .;nence in the frontal reg

the brain makes itself apparent in a diametric fndex which is ojnsrderabFy
below that of their congeners in th- _ _ p. Exp .

the frontal lobe, so important f- r of psychic specializs-

tion, has made itself felt in t ndex of the gorilla and r.

brain more than in any of the anthropoids. This index, which at first glance
seems to be so thoroughly inconsistent in the figures which it produces, does
as a matter of fact indicate a prices? f>f adaptive Sf)ecialization in the primate
order which has great signific . ation to the e\-oIiitionary process.

The developmental conditions which it seems to denote in the adA"ance of
the brain are so well confirmed by other evidence as to leave no doubt con-
cerning the substantial correctness which these values present- A tabula-
tion of the diametric indices provides a most convincing demonstration to
indicate the adapti\'e \-icissitudes through which the brain has pasj?ed.

•

FIGS. 431 AND 432. SIZE AND CONFIGURATION OF THE DORSAL SURFACE OF
THE HUMAN BRAIN COMPARED WITH THAT OF MYCETES SENICULUS, THE RED

HOWLING MONKEY.

ii

...u.— ,■-- -,1-^.11 ■ ■ ■.m«»<n-

Cen t iJB.et,er- Scala

^

<\ f"

^v

FIGS. 433 AND 434. SIZE AND CONFIGURATION OF THE LATERAL SURFACE OF
THE HUMAN' BRAIN COMPARED WITH THAT OF iHCETES SENICULUS, THE RED

HOWLING MONKEY.

[9531

954 EVOLUTIONAL MODIFICATIONS

ExOLLTIOXAL SIGNIFICANCE OF CeHEBRAL FiSSURES. Ill tlu' nuitttr of

fissural patlcTii, tlir pinnate brain presents lew dillieulties in analysis.
As might he expected of a transitional form, the lenuir does not disclose
a pattern entirely harmonious with the primate lormula. The fissures
in lemur ha\c shown a consideral)le specialization of their own. Far
from being a lisseneephalie hemisphere awaiting, as it were, the impress of
adaptive inlluenees, the lemur brain manifests a distineti\e ellort in its
gyrencephalic specialization. Its fissural pattern is, to a degree at least,
rt'iiiiniscent of a carnivore type of brain. In it ma\' be seen some of that tend-
ency, peculiar to fissures m carnnores, to arrange themscKes in circum-
syKian arches. But e\'en if the brain of lemur is slightly suggestive of this
arcade-like arrangenu'iit, it has broken away Irom older influences m this
direction and established certain designs of its own. The anterior and pos-
terior rhinal lissuixs, eharaeleristic of the carnixores in general, haw now^
disap])eared liom the lateral coiut'xitN due to the marked extensions in
the temporal lobe. The lemur thus indicates in its temporal region a distinct
advance o\er anj- possible subprimate prototype, and the Eocene
predecessor ol the lemurs (Adapis) had a brain e\en less developed. The
fissure of SyKius m lemur begins to assume the more oblicjue relations
notable m the ]irimates. The sulcus intraparietalis is well ck'fmed, as is also
the sulcus parallelus (superior temporal). The beginnings of a central sulcus
of Rolando may l)e discerned on the boundary l)et\\ecn the frontal and the
parietal lobes. W hat the lemur brain lacks, howexcr, is any extensive occipital
specialization upon tlu' comcxitx' of tlu' lu'mis[)here.

The phyletic history of the Syl\ ian fissure contributes coinincing
evidence regarding the e\-olutional significance of the fissural j^attern of
the brain. As interpreted by Elliot Smith ( i()03 ), who doubtless has given this
subject the most extensive and aiithoritatn t' consideration, the fissure
of Sylvius is a composite whose elements xary considerably in different

STRUCTURAL CULMINATION 955

mammals. The most coiistaiU of ihcsf compoiU'iits is tlic su|jra-S\ i\ lan
lissurc. The mammah'an sulcus usuall\ liomoloirizcd with llu' fissure ot
S\ Kius in a]ies and man is, aeeorclinii; to Elliot Smith, nowise homolotious.
Ill' calls this subi^rimati' indentation, when it occurs, the ])seud()-Sylvian
sulcus. This sulcus may be absent, as m \ iverra and I l\ rax, or its comjjosi-
tion max include dillerent (.■h-nuMits in dillerent orders. Thus the jjseudo-
Sylvian sulcus of the carnivores may differ from that of tlie unij;ulates, in
which latter the fissure often n-sults from the fusion of two infoldings
analogous to the eeto-Sylvian sulci ot the carnnores. Concerning these latter
lissures, there can be httle doubt but that they are morj^hologicallx unimjjor-
tant, and appear h)r the most part as lurrows compensatory to the imagi-
nation of the pseudo-Syl\ lan lissure. Li Smith's lissural |)attern of the
hypotlu'tical generalized carni\ore this pseudo-S\ Kian element does not
appear. The mammalian generalized ])attern includes the supra-S\l\ian, the
orbital (pre-Sylvian), coronal, lateral, p()St-S\lvian and cruciati- sulci.

The Sj'Ivian fissure in lemurs is formed by the merging of the pseudo-
Sylvian and supra-Sylvian sulci. \n this complex the supra-Syl\ian element
is the most constant in all k'liiurs, just as it is in most mammals. Generally
speaking, this stable and constant sulcus l)v its union with tlu' \ariable
suprarliinal indentation called the ])seudo-SyIvian sulcus gives an ultimate
lixit\ to the latter. The result of this fixation is the jjosterior limb ol the
fissure of Sylvius. Li monkt-\s and apes the onl\ portion ol the lissure which
develops is this ])osterior limb. The I'ulix formed anterior limbs iivv iu'\er
found except in man. Thus the Syl\ ian lissure in its complete lorm occurs
only in the human brain \\ hert' it exists as a combination ol the supra-
Sylvian (superior limiting) sulcus, the pseudo-Sylvian (inferior limiting)
sulcus, and the diagonal (anterior limiting) sulcus. Viewed in this light the
formation of the fissure of Sylvius may be understood to represent a
consistent exolutional process throughout all gyrencephalie mammals.

FIGS. 435 AND 436. SIZE AND CONFIGURATION OF THE DORSAL SURFACE OF
THE HUMAN BRAIN COMPARED WITH THAT OF PAPIO CVNOCEPHALl S, THE

BABOON.

L-....l......I...^..L..l I..^i..li...lJ.xI,.^.Ixl..J.JJ.xi.l.IJJ[J,,IJJxIJ,xIxI,,..I,lJ

Centuneter- Scale

IF

FIGS. 437 AND 438. SIZE AND CONFIGURATION OF THE LATERAL SURFACE OF
THE IIU.MAN BRAIN COMPARED WITH THAT OF PAPIO CVNOCEPHALUS, THE

BABOON.

[956]

.>;■•.

STRUCTURAL CULMINATION 957

In most ol tin- lemurs the post-S\I\ian sulcus is a simjilc Inicar lurrow
representing the parallel or su]:)fn()r teinjjoral sulcus m apes and man.

\\ ith reference to the central (Rolandic) fissure in lemurs, there is some
dilierence of opinion. The slight indentation between the frontal and parietal
areas has been called by Jacobsohn and Flatau the precentral sulcus, a view
which disregards the fact that such a sulcus ne\er occurs in the absence
oi the more stable central hssure. The tendency in all lemuroids is toward
a fusion ol this Irontal indentation with the caudal extremity of the coronal
sulcus which [produces that great transverse fissure, the central (Rolandic)
sulcus of apes and man.

The iissural pattern ol tarsius is simple in the extreme, ])rcsenting as it
does but a single indentation, the fissure of Sylvius. This is undoubtedly
the suj^rarhinal fold corresponding to the mammalian pseudo-Sylvian sulcus.
In this sense the neopallium of tarsius is the most generalized of all the
lower primates. It thus stands closest to some subprimate lissencephalic
brain which was the forerunner of the simian cerebrum. Tarsius at the same
time IS more pithecoid than the lemurs in the development of its visual
cortex and in the appearance ol a posterior cornu in its lateral ventricle.
\\ ith this combination of generalized characters and pithecoid tendencies,
the brain ol tarsius ser\'es particularl\ wi'll as the transition stage which
carru'd upward from sonn' insecti\ ore-like type the basic characters of
mammalian cerebral organization but also felt the decided impetus toward
simian di'\elopment. It has remained dynamically more plastic than the
brain ot lemurs, which latter (however primate in their procli\ ities) have
experienced a specialization quite their own, due, it may be, to secondary
retrogressive modifications.

If, as first suggested by Huxley and subsequently insisted upon with
added emphasis by Osborn, the ancestral type of placental mammal was an
animal resembling the tree shrew (Tupaia), then it is probable that the

958 EVOLUTIONAL MODIFICATIONS

differentiation which led to the \arious orders of mammals started from some
simple lissencephahc condition, showing only the most primiti\e fissures.
It may, therefore, be concluded that the hssural prototype of the j)rimate
order is ah'eady hiid down m the h'lnur hram. Such departures as it makes
from tlu' uhimate design may be ascribed to specific specializations m tlie
U'lnurs themseUes. To whatever extent they experienced the primordial
incentive toward primate dillerentiation, there was that in their organization
which determined characteristics strictlx sui iicncris, yet imparted to their
specialization such tendencies as amply justify their inclusion in a separate
suborder of the primates.

The brain of the marmoset, on the other liaiid, which declares itself in so
many features as inherently primate, allords that more generalized pattern
in its fissural arrangement from which all of the families in the anthropoidea
could take their beginning. The brain of Callithrix jacchus might easily be
descendant from some primiti\e lissenccphalic type. It presents but a single
well-delined sulcus, the lissure of Sylvius, with the faintest inception of a
superior temporal sulcus. Except for these landmarks, the lateral surface
of the hemisphere is quite without sign of fissural inscription. W ilh this as
yet unprejudiced surface of the neo])allium. inlluenced alone by the correct
position of its S\ Kian fissure, the marmoset brain appears to be waiting for
the further Impress of those hssural markings characteristic of the more
advanced ])rimates. This relatively simple condition of the neopallium in
Hapalidae is in harmony w ith what has already been observed in reference
to their simjjle behavioral characters. The departure of this family from tlu'
primitive primate stock was doubtless a retrogressive one, less significant in
what it produced of itself than in its prophetic indications of actual simian
tribes to come. In the lemur brain and in the brain of marmoset two contrast-
ing tendencies in the early ]jrimate differentiation are represented. In the
first instance the lemur, representing the Incipient primate impulses, furnishes

STRUCTURAL CULMINATION (),-()

c'\ icK'iK'c ol rc'spoiisr alonu llirsc lines ami at the same tunc \ iclcls to iiillii-
cnces ol specialization w hu'li (li\'ert it into a |)ath ol its own. In the case ol the
marmoset, the impulse toward anthro|joKl evointion is more strongly active
as a generalized inlluciiee, not \ et specilic enough to ckti'rmine those mdi'lible
cerebral characters which aresullicient to distinguish all ol the other lamilies,
genera and specK's in tlu' suborder anthro])oidea. 1 hat the lull lorce ol the
tendencv toward simian dillen-ntiation is ultimately lelt by all ol the mon-
keys ol the new world is clearly attested by tlie lissural patterns ol these
primates. The Ccljidae re\t'al what was dclinitelx attempted m the diller-
entiation ol the lemur's brain, subject perhaps to some Irustration b\ other
inlluenccs, but again somewhat U-ebl\ aimed at in the marmoset's brain.
Ail of the new world simians present a lissural pattern which marks them as
nu-mbers ol tlu' suborder ant hropoidi'a. The SyKian lissure takes a more
oblicpie course backward and upward, separating the parietal Iroin the
temporal lobe.

The central sulcus, which represents tlu' lissure ol Rolando, is now well
dclincd and forms the boundary between the trontal and jjarietal lobes.
The sulcus ])arallelus i superior tem])oral lissure) is distinct, as arc also the
intermediate tt'inporal and the intraparietal hssures. The greatest degree of
fissural specialization occurs in the temporal and parietal lobes. Only the
slightest indication ol hssures is lound in the Irontal and occijjital regions of
the brum. 1 n I act, neither o I these lobt's shows any marked extent ol expansive
development, thus no doubt accounting lor the high degree of broad brained-
ncss recorded in Mycetes seniculus. In the Irontal region there is a slight
indenture indicating the superior Irontal sulcus, and one somewhat more
pronounced marking the position of the inferior frontal sulcus. In the occip-
ital lobe, which is but slightly developed, there is a faint indication of that
remarkable sulcus which identilies all ol the simian tribe, the sulcus simia-
rum. This lissure appears in mycetes as well as in other Cebidae as a small

96o EVOLUTIONAL MODIFICATIONS

transverse groove, icirntilied l)\ Elliot Smith and utIuTs as the sulcus occip-
italis transversus, which Rctzius nianitanis is the honiologuc ot the sulcus
simiarum ("Affenspalte"). Lateral to this trans\erse occipital fissure is an
equally faint groove indicatnig the position ot the sulcus occipitalis lateralis.
\\ ith reference to the sulcus centralis, or fissure ol Rolando, it nia\' be said
that in the brain of the Ccbidae, particularix in the brain ol niycetes, this
fissure has nuicli that is reminiscent of the hssura cruciata ol the lower
mammals. There is, ho\\e\er, an im]iortant difference. Its angle of inclina-
tion with reference to the superior longitudinal fissure is now considerably less
than ()0 degrees. In mycetes, therefore, as in most of the new-world monkeys,
the lissural fundaments of the primate brain are clearly discermble. Here-
alter, in the further steps of evolutional de\clopment, it is simply a matter ol
increasing complexity, particularly of expansion in the frontal and occipital
lobes, which brings into existence all of the lissural characters of the highest
primates.

In the lower di\ ision of the old-world monkexs, here described as the
intermediate ])rimates, the simian characters in the lissural j)attcrn ol the
brain a])j)ear in their ultimate piominciice. The pattern is now delinitely
trifissural with a fissure of SyK lus, a fissure of Rolando and a simian fissure
constituting easily rec(jgnizetl boundaiN lines between the lour great lobes
appearing on the lateral coii\c'\it\- of the lu'inisphcrc. The hssure ol Sybius
has departed from its jjrimitixe wrtical direction and is tending to approach
closer to the horizontal, characteristic of it in the higher species. The fissure
of Rolando also has reduced the angle ol its inclmat mn in reference to the
superior longitudinal lissure and now runs a courst- of sonu'thing o\'er "j
degrees with the median plane. 1 lu' sulcus simiarum extends outward Irom
the superior longitudinal fissure at an angle of ()o degri'cs and reaches as far
lateral as the latt'ral occipital lissure. In the baboon, \lacacus rhesus and
in the gibbon, these lissural relations are all essentially similar. In none ol

STRUCTURAL CULMINATION (/,i

the three species does the (issure of Rolando show niorr than a siigticstion
ot its two major genulleetions. In all of the tluw tlu' most proniinent and
deep lissuring is seen in the parit-to-temporal area; in the frontal area onl\
the beginnings of the superior frontal lissiire are apparent. The preeentral
fissure is well defined, whik' in the oeeijiital lobe two fissures are elearl\
marked. These are the hssura oeeipitalis and the lateral oeeipital hssure. All
semblance ol the t\pieal eireiims\ l\ian arrangement of the sulci has now
disappeared. In the great anthropoids the lissural pattiMii has increased
consideral)l\- in its com])le\ity, although it retains all of the fundaments
which ha\e Ix'cn traced through the seiial approach to this k'\ el of the pri-
mate ortler. The latt-ral coinexity is still trilissural, tlu' hssure of SyKius,
the fissure ol Rolando and the simian lissure constituting the main
landmarks.

As in all the Jiitcrmediate group, notable expansions are seen in the
occipital and frontal lobes; indeed, it is in tlu'sc regions that the greatest
degree of complcxitN has made itself apparent in the arrangement of the lis-
sures. The central sulcus of Rolando now manifests a delinite tendency to
display its maior genullections so characteristic of tlu- human brain. This
becomes progressi\ely accentuated m passing from the orang, in which the
genuflections are the least pronounced, through the chimpanzee to the
gorilla, w lu're the\ stand out in great prominence. As ni all jjrimatc brains,
the paricto-tem])()ral region shows a degree of lissural richness which is the
most ])ronounced. It is, howe\xr, m much less striking contrast to the
frontal region w ln-re the superior, middle and inlerior Irontal fissures are well
outliiu'd. 'file preeentral hssure has beconu' a di'ip sulcus l\ ing parallel to
the ctntral sulcus. In the occipital lobe the trans\ersc oeeijiital lissure is
deeper and has an inclination to develop several collateral branches. The
lateral occi])ital fissure is also pronounced. This becomes increasingly the
case in passing from the orang to the gorilla, in which latter the occipital

FIGS. 43() AND 440. SIZE AND CONFIGURATION OF THE DORSAL SI RFACE OF
THE HIMAN BRAIN COMPARED WITH THAT OF PITHECUS RHESUS, THE MACACUS.

I a s 4 ft • J B f 10 II It 1} u I) N If ■• ■• » II (r M •• M

I..J,..L.,,Ij.,,,l,,,.l,,,J,J,,.L,ln,,L,l,,,.l,,,.|.,,l ,J,.,l,J„„l„J,.„l„„[j„J., l.„l,.J.„lnJ„„L„L„l„„l I„„I„J ,.,ll,„.ln.L, Ill.lJ

Centimeter Scale

FIGS. 441 AND 442. SIZE AND CONFIGURATION OF THE LATERAL SURFACE OF
THE HUMAN BRAIN COMPARED WFI H THAT OF PITHECl S RHESUS, THE MACACUS.

[962]

STRUCTURAL CULMINATION 963

loht' IS rmu'li mori' piDmiiU'iit l\ lissuri'tl than in cithrr ol x\\c two uix'at ant hro-
|)()i(ls assoc'uilc'd with it. The lissurt' ol S\ Kins tends to l)c' more liorizontal
in Its (lirc'c't ion, while 1 he lissure ol l-\olanclo departs Ironi the superior longi-
tudinal lissnre with an aiif^iilar iiulinat ion of something less than ~j degrees.
I he marked ehanges in the lissiiral pattern of tlie great anthropoids therefore
consists in the eonvolutional riehness seen both in the Irontal and oeei[)ital
lobes, with the presence ot excry lissnre lound in the iuiman brain more
prominentl\ marked than in the intermediate primates, and with marked
accessions in the Innital and occipital regicjns incident to expansion in these
|)ort ions of the brain.

In man the lissural pattern attains its greatest complexitx, so nuieh so
that It bieomes dillienh to identil\ the se\eral eharaeteristie fissures, which
in the lowt'r primate brain stand out in prominence because of tlu' relati\c
sim])licit\ in the siileal markings. The lissure ol Rolando now has an angle
ol inclination with the superior longitudinal lissure of about ~i degrees; the
lissure ol SyKius apjjroaches much nearer to the horizontal than in any olthe
lower species; the sulcus simiarum has jjiactically disappeared and nothing
suggestixe ol it is to be seen in the human brain unless it be the sulcus lunatus
referred to by Elliot Smith as tlu' possible homologue of the sulcus simiarum.
The general position ol this lissure is marked by the parietal incisure ol the
occipito-parietal sulcus. The occi|.)ital lobe itself shows a richness of lissures
generally arranged aljout the occipital and lati'ial occipital sulci, which far
exceeds in compIe.\it\ an\ thing obser\ed in the primates Ik'Iow man.

The evidence, therefore, oHered by the lissural pattern in the primate
brain, especially as it alfects the lateral surface of the hemispheres, points
to a progressive evolution, starting with a pattern in many respects reminis-
cent of the carnivore circumsylvian type, and passing from an almost indif-
lerent intermediate stage of the simplest lissenccphalic neopallium, through

964 EVOLUTIONAL MODIFICATIONS

all gradations to culminate in xhv intricate (issural design of tlie human
brain. There seems to Ix' no single step missing in this gradual transition.

EXOLUTIONAL SIGNIFICANCE OF rilE CeKEBKAL LoBES IN I HI PlilMATE

Brain. Nor is this process of grachial expansion confined tothelissuresalone.
Inasmuch as these landmarks serve to delimit the well-marked physiological
areas of the biain surface and thus produce lohation, as a concomitant of
the increasing richness of fissural pattern, the lolx's themselves become more
complicated. In the transitional form of lemur, the identilication ol the
quadrilobular condition characteristic of the primates is difficult, largely
because the central sulcus of Rolando is onl\- in an incipient state and the
boundaries of llu' frontal lobe must, therefore, be drawn largely by inference.
So also it is dillicult to distinguish I)et\\een the parietal and frontal lobes.
But the boundary between the temporal and parietal lobes is fairly well
defined by the lissure of Sylvius.

Upon the lati'ral coiuexity the e\ idence of an occipital lobe is almost
entirely wanting and such expression as this lobe has is largely confined to
the mesial surface of the hemispheix'. This observation of the occipital lobe
in perhaps its most primitixe condition is borne out by the size ol the
superior colliculi which maintain much of lluir original j^roportion and also
not a little of their ]3rimiti\-e stratilication. In tarsius and marmoset, the
brains of \vhich are so largely lissence])ha!ic, tlu' dilliculty of determining
the lobes is etiuall\ pronounced. In tlu' absence of any sulcus centralis, no
distinct di\iding line between the frontal and i:)arietal lobes exists, and onl>-
in a general way is tlu' dixision between the temporal and parietal lobes
given by the fccblx de\t'lo])ed S\ l\ ian lissure. Nothing resembling the sulcus
simiarum is jjri'sent in these brains, although the dexelopment ol an occip-
ital lobe is much more pronounceti than in the lemur, as show 11 b\ tlu'lact
that the cerebellum is now almost eom|)lctt'l\ co\ered by tin' caudal ])ole
of the hemisphere. Thus, starting in the Tarsiodea with an anthropoid

STRUCTURAL CULMINATION 965

lu'iiiispluial suilacf almost liw ol lissuial insi-ri])ti()n, it hccomc's possible,
at tlu' lU'xt stasia- m thr progrcssi\-c expansion ot the neopallmni, to note in
nixeetes a tlehnite ciuaclrilolKilar eonclition ni the hrani. A w cll-ck'hned (issiire
of Rolando separates the paiutal tioni the liontal lol)e. A ]3roniinent lissurc
of Syl\ nis (h\icles the parutal Ironi the ttinporal, and thi' ineipient suleus
simiarum sets the boLindan bt'tut'eii the oeeipital and the parietal regions.
Of these lour lobi's, the most hi(i;hl\ de\ eloped are tlie parietal and tlu'
temporal, wliile the e\|jansion in the frontal and tiie occipital re<i;ions seems
to be delinitelx' retarded. In tin- intermediate <;roup ot old-world monkeys,
the lobation in the eert'bral hemispheres iijjon the lateral surlaee is so striking
as scarcely to need hirther eomnient. Ihe tri-lissural pattern m allol'these
lorms ])roduees a decisixc c|iiadrilobular lateral surface in \\ hich, how e\er, the
parietal and temporal regions show the greatest degree of e\pansi\ e develop-
ment. This IS true not onl\ of the baboon and macacus, but e\en as much of
the gibbon. The lobular de\ elopment in the frontal region and in the occipital
region in these three lorms is not pronounced as com])ared w ith the temporal
and parit'tal areas, and in none ol these is the frontal lobe beginning to a.ssumc
the prominent proportions which it does in the upper grades of the priniate
series.

In the three great anthropoids, a t|uadriloIjular arrangement on the
lateral surlaee is distinctl\ appart'iit, with t\ idi'ut accessions in the (k'\elo])-
nu'iit of both occipital and frontal lobes. It is not, howe\er, until the human
brain is reached that the full significance in these changing proportions ol the
scleral lobes of the brain becomes a])pareiit. The physiological significance
of that expansion, which has been progressively making itself lelt in the
hemispheres, now becomes more ()b^ ious. While the boundar\ lines between
these several lobes ot the brain are w ith more dilliculty discerned, because
of the greater richiuss ot the lissural j)attern and the high degree of com-
])lexity of the com olutions, such progress as has occurred atlects particu-

966 EVOLUTIONAL MODIFICATIONS

larly the frontal and occipital regions. Not, however, that the temporal and
parietal areas are less characteristic in llieir laiulmarks, but rathtT that in
the process of expansion they iia\e Ix'cn sonicw hat o\ershaclo\vecI In' the rapid
strides of advance made by the frontal and occipital areas of the brain.
This advance mostly involves the prefrontal area, which is regarded by the
physiologists as rejircsenting the seat of such higher faculties as reason,
judgment and discrimination. This is tlu' region of the brain wherein those
syntheses of neural impulses are assembled which constitute the basis ol
human e\]3erience and personality. It is undoubtedI\ the case that diseases
atfccting this ])art of the brain do much to unseat the ]3rocess of reason and
judgment and ha\e far-reaching effects in changing in one direction or
another \hv personalitx' of the individual. Refcrcnct' need only be made to the
great xolume of clinical material already assembled in relation to tumors in
the frontal region of the brain, particularly in the prefrontal region, whose
outstanding clinical manifestations are marked changes in personality with
alterations in the validity of judgment and reason. It is most interesting in
this connection to note the tendency of expansion in the frontal lobes among
the mammals in what may be considered direct ])roportion to the develop-
ment of intelligence. W ithout ]>ausing here to dcline too much in detail the
meaning of intelligence, it may in general be stated that this attribute indi-
cates the capacity presented by an\ brain to select between alternative
courses of action, that is, to reason and linally form a judgment.

If a number of mammals, those low in the ph\ letic scale as well as those
situated in the ui^j^cr lc\els, are contrasted by means of jjlanimetric estima-
tions of the areas on the lateral surface of the brain, and from such measure-
ments planimetric indices are constructed, thi' following interesting facts
are brought to light: The frontal lobe w Iumi compartxl in dilferent mammals
shows that the ant eater has a frontal index of i) per cent, the horse ol 13
per cent, the seal of 16 per cent, the leopard of 20 per cent, the brow n bear of

FIGS. 445 WD 444. SIZE AND COM KJL RATION OF THE DORSAL SURFACE OF
Mil IH\1\N BRAIN C:OMPARFD W IIH IHAT OF H^ LOBATES HOOLOCK, THE

CIBBON.

I ■ ■ 4f« 7 m 9 » II a li t* n m It m 19 to ti It n t* n

Ui.„L..,L„,.Li,,Li,„Ji,.i,.,.Li,„L.iu] ,,J„M,J.j,ij,J,j..J,,,.iMJ,.niiJ,j,,,.l.,,i,,.L,,i,,J,,.i,,,.l,.iiiil,i.J,j,,J,jiiJ,,,,i,,,,l

Contuneter- Scaie

FIGS. 445 AND 44C). SIZE AND CONFKil RATION OF THE LATERAL SURFACE OF
THE HUMAN BRAIN COMPARED WITH THAT OF HVLOBATES HOOLOCK, THE

GIBBON.

I967I

968

EVOLUTIONAL MOOIFICATIONS

2 1 pvv cfiit, the cl()<i; of 2() i^cr cent, tlic Ifimir ol 23 ])ct cent, tlic spider
monkey 31 per cent, the baboon 31 per cent, \\\v ehinipanzee 33 per cent,
the gorilla 32 ])er cent and man 4~ ])er cent. The tabulation Irom which these
indices \\ere computed is gi\en in the appended table. The indices them-
selves dclinitely point to the fact that the expansion of the Irontal lobe is
the goal toward which the entire t'xolutionary process of the primate
brain has been directed.

Planimetric Area Lndices of Neopallu .m

Vernier units

Square

inches

Ind

ices

Anini.il

Frontal
area

T.P.O.*

area

Frontal
area

T.P.O.*
area

Frontal

area,
per cent

T.P.O.*

area,

per cent

Man

832 . 60

965 30

■3 3

15.40

47

53

Gorilla

332.00

713.30

5-3

11.40

32

68

Chimpanzee

2 1 2 . 00

441 .00

3-4

7.00

33

67

HM,.M,„

176.00

394.00

30

6.30

3'

'HJ

hpicicr monkey

106.00

234 00

1.6

3 70

l"l

Lemur

17.60

57.00

0.28

0 91

23

—

Dog

88.60

212.00

1 .40

3 5"
6.10

21

-I

Brown bear

102.60

381.60

1 .64

79

Leopard

30 00

1 1 5 00

0,4R

1.84

20

80

Sea lion

l(,f, in

SS, ;n

1 (ni

14 10

16

84

Horse

173.30

-i(. (.,.

2.77

u 80

13

87

Ant eater

30.00

0.34

3 04

9

91

* Temporo-parieto-occipital.

E\oLi:iio.NAL Significance of Con\ 01 i i ioxai Puierns in the
Brain. This conclusion is further bornt'out In a comparison ot the con^■olu-
tional pattern in the frontal lobe w hich shows the same trend of de\ elopment
from a relatively simple area, through all thelnternu(liatestages,tothe highest
degree of comohition seen in tlu' human heir.:sphere. The obxious purpose of
this con\-olution is to increase the cell-cimtaininij; substance ol the bram and
thus to produce a more ellicient txllular structure lor the tiansaction ol those
functions necessary to the re<rulation of behavior. That the Irontal lobe

STRUCTURAL CULMINATION 969

should show the <ir(.';itcst degree of eomokitional nehness in man is
what might be expeetetl jii \ie\v ol Ins hi'tter powers oi reason and iudg-
ment. hrs greater abilit\' to proht 1)\' experienee and his more ample
eapaeitx' to eonstruet those eomplex neural s\iitheses in the eonslitution ol
liuman ])ersonality.

B\' archious labor and ingenuit\, hieroglx phies ot several dead languages
ha\e been deeiphered and tluir geni'ne relations in linguistie de\elo])ment
established. It requires no sueh ellort to interjiret the signs inseribid upon
the neopallium ot the eerebral hemisplu-res in the primate order. ii-om the
sim]jlest hssural inseriptions, tlirough all degrees of elaboration in their
inereasing struetural eomplexity, tluir translation reveals a progressive
ex]:)ansion m the endbrain. Sueh also is the e\idenee deri\ed Irom tlu' loba-
tion ol the hemis]:)here with its inereasing eomplexity in eon\'oliition.
\\ itliout hiatus or ambiguit\ these faets ])ro\"ide a eomplete reeord of e\()lu-
tionary progress in the brain ol primates.

E\OLUTiONAL Significance oi- ihe Basal Structures. On the base
of the cerebrum, in that portion whieh comes in contact with the orbital
plate ot the Irontal bone, the |)rocess of gradual unlolding is lurther illus-
trated. The orbital plate in the lower primates shows a convexity correspond-
ing 111 ])osition to the orbital socket which produces a conca\it> m tlu' orbital
surlace ol tlie brain. As tlie hemispheri' in its Irontal area beconu's more
expanded this conea\it\ decreases. In consequence the orbital concavity
IS most i^ronoiinccd m tlu' lower primatt's. It is a feature of consicU'rable
prominence m the intermediatt' primates, is conspicuous e\"en m thi' bi'ams
ol the orang and the chimpan/.ee, but shows its first marked decrease in
the gorilla. Although exidence ot it ma\ still be toiind in tlu' human brain,
It IS hert' so inconsiderable that it might tail to attract attention. Associated
with tin- orbital conea\it\' is another notal)le feature, the intcrorhilal kt'cl.
1 his mesial ridge is most prominent in those species with the deepest orbital

970 EVOLUTIONAL MODIFICATIONS

concavities, and becomes gradually less pronounced as this conea\ity is
gradually decreased by the expansion of the frontal lobe. Through graded
stages in the primates the diminution m promiiieiiee ot the mter orbital keel
max be easily traced. It is still a fcatuix' in the brain of the orang, and present
also in tiu' chimpanzee, although less promiiu'nt; it may be discerned. less
well delined, in the gorilla, but almost entirely disappears in man due to
accessions in all portions of the Irontal lobe.

Conditions in the struetm-es related to the olfactory and the optic nerves
denote a similar process of frontal expansion. The ollactorv l)ulb and tract
in tarsius are nuich larger than in other primates. Tluar resemblance to the
more ])riiniti\e rhinencephalic development of carnivores and ungulates is
fairly close. The bull) and the tract appear more as an integral part of the
basal surface of the endbrain. The lateral and mesial olfactory roots follow
their course to their terminations in a manner characteristic ot the lower
mammals. Progressively, howcAcr, in passing upward Irom lemur, the ol-
iactory bulb and tract become relatively smaller. They are both more
easily detached from the overlying orbital surface of the brain, while the
divarication of the lateral and the mesial roots of the olfactory tract becomes
less conspicuous. The entire dcAclopment ol' the rhinencephalon (olfactory
portions of the brain) is less i^iominent and gixcs e\ idence ol a delloreseenee
in its structural elements. Accompan\ ing this ]:)r()cess there is a diminution
in the capacity of olfactory function. In the acKance from the lower to the
upper end of tlu' ]Mimate series a small fissure is found beneath the olfactory
tract. This is the sulcus ollactorius, which determines the existence of the
gyrus rectus. Both of these features beeonu' more conspicuous as the human
stage of developm lilt is approached. The\ are both indicatixe of progressive
difTerenliation in the frontal lobe. These de\ elopmi'Utal changes connected
with the sense of smell are of greatest evolutional moment. Their ob\ ions
connotation is a diminution of olfaetor\ seiisi' which gave to the hunting

STRUCTURAL CULMINATION 971

animal its kern scent and to niaiiy species a jjioteetivc accessory in proxiding
warning of the appioaeli ot enemies. According Id all signs the sense of smell
is on {hv wane in the primates. The archaic rhinencephalon becomes less
|jrominenl, the olfactory hull) and tract grow smaller and lose tluir intimate
incorporation in the orl)ital surface of the brain. Other sense capacities, such
as vision, hearing and the sense of touch, the latter especially as developed
in the hand and hngers, ha\e replaced the sense ol smell by substituting for
it receptors both ol the distant and contact \ariety. Dependence upon these
latter sensor\' organs perha[3s places the animal in more adxantageous rela-
tion to Its eiuironment, in certain respects at least.

The primordial dexclopment ol the olfactory sense is ])reeminentl\ con-
nected with the process ol obtaining food. It is concenable that the constant
influx ol Impulses by this a\enue of sensation might be deterrent, if not
])reiudicial to tlu' further de\elopment of other faculties. In the race of life,
the procuring of food must aKva\s take its place among other obiects of much
importance to the needs of tlu' organism. It ma\ , of course, l)e claimed in this
connection that tlu' u])shot of all action is in the interest of maintaining lifi'.
The olfactory sense, therefore, can no more be said to retard the de\elopment
of such purposes than any other sense. But w ith the possible exct'ption of that
small degree of protectixe insurance and sexual direction which the olfactory
sense proNides, its mam and decisixe mllueiux' is eoniu'cted with the location
and ideiitilication ol lood sup|)l\-. Llence the dellorescence in this department
of sensory organization m the [jrimate max be considered as of adxantage
in developing other and mori' w idel\ productiw courses of reaction.

Again the decrease m the oliactorx portion ot the brain is in direct
proportion to e\j)ansions in the frontal lobe. It thus appears that, howcxer
much the animal max' sulfer bx decreased elliei(>ney in this spluat' of sensi-
bilitx, it gams immeasurablx in tlu- combinations of experience made j:)ossible
through increments to the frontal area.

972 , EVOLUTIONAL MODIFICATIONS

In the case of the optic ncr\c, a similar record of expansion is to he found.
This is seen in the degrees of angulation in the conAergence ol the optic
nerves upon the chiasm and the dixergence ol the optic tracts Irom it.
This angulation gradually increases in passing from the lennir, through the
intermediate ])rimates, to the great anthropoids, and reaches its greatest
prominence in man. It is due to the fact that expansions in the head have
further sej^arated the eyes from each other. The expansions themselves are
due in large measure to the growth of the brain areas abo\e the orbits.
Similar txpaiisions in portions of the brain caudal to the optic chiasm arc in
process and account for the wider angle of divergence in the optic tracts.
This feature w hile far less significant than olfactory dt'xelopnu'nt possesses
a value, which, however slight, should carr\ its due weight in estimating the
evolution of the bram.

Evolutional Significance of Cerebellar Expansion in the Brain.
The inllucnces of expansion may bi' further discerned m the occipital
lobe. This extension likewise affects the lateral lobes of the cerebellum. In
the lowest of the primates the cerebellar conea\ it\ is a deep impression made
upon the basal surface of the occipital lobe In' the cerebellum. It is less pro-
nounced in lenuir than in higher species because the cerelx-llum is onl\ m
part coxered by the occipital lobe. In the marmoset and Hapalidae generally
this concaxity becomes more prominent, due to the lact that the cerebellum
indents the under surface of the brain to a considerable degree, while the
occipital loi)e entirt'ly eo\ers the tentorial surface of the cerebellum. The
cerebellar conca\ity, and more [)art ieularl\ the postsplenial fossa, is a
character obserxed in all primate brains. Tlu' lateral e\])ansions ol it bt'come
progressively less jjronounced in the inti'rmedlate ]:)rnnates. It is well cK'Imed
in the orang and ihimpanzee, but becomes less [jromment m the gnnlla and
almost entirel\ disappears in man where it leaxcs but a small Acstige ol the
postsplenial fossa to accommodate tlu- \Ainiis.

FIGS. 44" AND 448. SIZE AND CONFIGURATION OF THF DORSAL SURFACE OF
THE HUMAN BRAIN COMPARED WITH THAT OF SI.MIA SATVRUS, THE ORANG.

L.I I'!' " " "31

1.iflli,Jli..UllNJlitillmliiilll..J.iiJ.H.I,...|.iiil„lllllll„.tfl,iiiliii.l.ii.L

,.,l„„l,„.l.„.L„!„,,l„„l„„L.,l,.„l„..l,J,..,l,.,ln.,!.,

CaiCuoGtcr- Scale

FIGS.f449 AND 450. SIZE AND CONFIGURATION OF THE LATERAL SURFACE
OF THE HUMAN BRAIN COMPARED WITH THAT OF SIMIA SATVRUS, THE ORANG.

(973]

9-4 E\OLLTIONAL MODIFICATIONS

All of this chanee from i. .nething approaching convexiU"

in t . e is the result of expansions in the

rest of extending the capacit\" of visual function.

In. vHum grves evidence of an expanding

process. In _ martially covered by the caudal p>oIe of

:.e occipital lobe is poorly developed. This
con-^ iracteri; .e more primrtr^e hemispheres in the carniAores

: _ :es. ^ et even in lemur the tentorial surface has a definitely gabled

nee. The superior vermis is a prominent element, while the inferior
vermis app>ears much more as a surface eminence than in the higher species.
In the marmoset, the ultimate primate condition obtains in that the upper
cerebellar surface is entirely concealed by the overlying occipital lobe.
The tentorial surface also shows a marked gabling with an extremely high
p :ts vermal region. A similar condition exists in mycetes, both

on the tentoria. ccrpital surfaces. In all three of the lower primates,

the lateral expansion of the cerebellar hemisphere is relatively slight. The
movement toward development in this p>ortion of the brain first becomes
evident in the intermediate primates, although even in them the vermis
remains a most conspicuous feature of cerebellar organization. It is not until
the great anthropoids are reviewed, that the real changes in cerebellar expan-
sion become apparent. In these instances, while the gabling of the tentorial
surface is still fairly prominent, there is a distinct tendency for the vermal
ridge to lose its high elevation, for the vallecula to become pronounced and
for the 'i.ermi': to fall off in comparison with the lateral lobes. Finally in man,
t rface is almost flat, the vermal ridge inconspicuous and the

vallecula so deepened that the inferior vermis is almost lost to \ iew within
it. The process which has progressively advanced in the development of the
cerebellum is obvious. It is characterized by expansion of the lateral lobes
without proportional increase in the vermal portion of the organ. Since the

STRUCTLR.\L CULMINATION 975

lateral lobes represent coordinative control of the upjjer and lower extrem-
ities, the reason for this expansive srrow-th in the primate order becomes
clear. In prop>ort!on as the hands an^. cct are more capable of precise

and complex ^ is essential to their op>eration that they be

corresp>ondingIy regulated by accessions in coordinative control over the
muscles.

EVOLVTIONAL SIGNIFICANCE OF St.H £5 IN THE BraIN StEM OF

Primates. In many details, the surface of the brainstem reveals aprogressive
differentiation. The features up>on its ventral surface all pertain to the acqui-
sition of that new motor system which makes its first app>earance in mammals.
This system is important from the fact that it introduces the controlling
influences of the nc a. It brings into play a vast series of associational

combinations ^" : ovide motor actr^itA' with a more extensive range of

selective op; ry. The evidence of this progressr\"e expansion is seen in

the presence of three prominent structures on the ventral surface of the
brain stem, the pyramid, the p>ons a; .erebral peduncle. At the lower

extremity- of the series, all three of these structures are feebly marked.
Employed as a key to the combinations of the animal's adaptabilit\', they
indicate to what extent the lemur, for example, is limited in its behavioral
capacrtA". I: respects the cerebral p>eduncle, the f>ons \ arolii and the

pyramid of ~ :t slight advance over the still lower mammals.

Proceeding in the < : ection toward the upf>er extremhy of the primate

group, it is evident almost upon casual insp>ection that these elements become
increasingly more prominent. The marmoset, jjerhaps, adds but little to this
developmen-. cfinite advance is clear in all of the Cebidae. In the

old-worl <eys, such as baboon, macac: gibbon, a still further

advance is demonstrable. The first actually decisr^e change in the prominence
of these structures app>ears in the higher anthrof>oids. In them the pyramid
and pyramidal decussation begin to stand out more conspicuously". The

9-6 E\OLUTIO\AL MODIFICATIONS

pons N'arolii is a more protuberant structure. The cerebral peduncles attain
greater definition and size, while structural differentiation in the base of the
brain stem reaches its full development in man. The increasing size of the
pyramid, of the pons and of the cerebral peduncle seems to indicate the final
development of new motor capabilities made possible by manual specializa-
tion. Man and all his works are epitomized by these structures of the brain.
^^ ithout them there would be neither reason nor opp>ortunity to discuss the
achievements of mankind. Too great importance, therefore, cannot be laid
upon this specialization, which has progressed through certain preparatory-
stages of quadrumanal differentiation, and finally attained its definitive
manual development.

But lest over-much emphasis be attributed to the hand de ipso, it
must be borne in mind that no such development could have occurred had
not an almost equally important specialization affected the lower extremity.
The structural standard of the human upper extremity insists upon certain
proportions in the length of the arm, forearm and hand in relation to the
rest of the body. It also prescribes definite intrabrachial relations of the
arm to the forearm, the forearm to the hand, and the hand to the fingers.
This human standard seems essential to the most perfectly differentiated
upper extremity. "\'et it is a fact that many of the low er apes come nearer to
this standard than do the anthropoids standing nearest to man. This is
notably the case in the orang, in the chimpanzee and in the gorilla. In them
the upper extremity is out of all proportion with the human standard. In
the three great anthropoids, the arm, forearm and even the hand are too
long for the most fiexible adaptability. The limitations of adaptive range of
motion imposed by this excessive length ha\e been noted in recounting the
behavioral activites of the higher anthropoids. The fact that the fingers
almost touch the ground when the animals stand in the erect position shows
in what respect these members are limited in the accomplishment of skilled

STRUCTURAL CUL.MUNATION 97"

performances near to the body. These impediments are also pronounced for
projectile activities, for the wielding of weapons or the manipulation of
instruments. The upper extremity in the great anthropoids is preeminently
specialized in the interest of arboreal life. Its enormous musculature and
great length favor the exigencies of locomotion determined by tree climbing.
Some other factor, therefore, over and above the actual specialization of
the hand, must serve as an important incentrve for the expansion of the
cerebral cortex, which led to its ultimate expression as seen in the human
brain. Were this not the case, it is probable that some of the lower simians
would possess brains more closely in harmony with that of man than the
great anthropoids. It is probable that this primary- factor is to be found in
the foot rather than in the hand.

The lower extremity, which specializes a foot of preeminent hand-
like character, has manifested this differentiation essentially in the
interest of arboreal life. Such life definitely restricts the motor capaci-
ties of the animal by consigning it to a type of locomotion for which the
use of both hands and feet is indispensable. Under the circumstances,
however much the proportions of the arm, forearm, hand and fmgers
may correspond to human standards, complete manual differentiation is
impossible. The hand, to be the freest for the purposes of manual manipula-
tion, must be permitted to operate on a basis far more secure than that offered
by arboreal life. In other words, the animal, to make the most perfect use of
the hand, must, so to speak, stand with both feet upon the ground, and from
this point of vantage, be able to traverse and utilize at will all of the habitat
zones of life. The adequate structure for securing such a basis of operation is
not to be found in the hand-like specialization of the foot. None of the apes,
for example, could in any wise adjust itself to life upon the earth so that it
might effectively take advantage of other habitat zones. It is undoubtedly the
hand-like specialization of the foot in the great anthropoids and in all of the

978 EVOLUTIONAL MODIFICATIONS

lower priinati's that has conimittcd these animals to the relatively low
level of diflerentiatlon attained b\- them, /-or this rtason (l.wy are still a})es.
It seems impossible to eseape the eonelusion that the evolution of a human
foot eventually freed the hand for all the complex purposes to w hieh it has
been applied. The development of this foot doubtless had its inception in
some pedal structure specialized for arboreal life. The main factors producing;
the modidcation were eversion and elongation ot the loot, formation of a
broad supportiufi; plantar surface, loss ol ]:)rehensile lunctions m the threat
toe and distal migration of the hallux. It is generally belie\c'd that such
develo]:>nu'nt of the foot is of primary importance in furthering the assump-
tion ol the erect posture, and thus eventually leading on to all ol the exten-
sne modifications necessary to the dc\"elopmcnt ol the human hand.

The following stages of postural e\'()lution passing from the quadruped to
human bipedal locomotion are based on tlu' critical analysis of Gregory and
Morton. Those gradual changes which linally ga\e rise to the human foot
had their incejjtion in the Eocene. They were lirst manifest in some terrestrial
quadrupeds, which in the course of certain bclia\ioral readjustments began
to live in the trees. This arboreal lilc im|)oscd upon them new necessities in
locomotion, it had mcst ])ronounccd ellccts upon the lore- and hindpaws.
in order to climb and mo\e along the branches, a claw ing grip was necessary
for this clinging t\ pe ol transit. Long, sharp claws de\ eloped in coiisec|uence
ol such ad|ustincnt. The digits of xUv manus were short. The [)alm ol the
hand was well padded. The |)olk-\ was short, but not opposable. 1 here was
as yet no sc|uatting or hall-sittmg p( stiire. The toes were also short and
clawed, tlu' lu'cl t'le\att'd, tlu' plantai' surface of tlu' foot was padded and
the great toe well dcNcloped. These arboreal t|uadrupeds had, howexer,
made but imperfect adaptation to trc'c life. Tiieir moxcments were slow
and tht'ir range of acti\it\' corri'spoiulinglx limited. The tree shrew is a
living representati\e of such subprimate ciuadrupeds, while certain Eocene

^

FIGS. 451 AND 452. SIZE AND CONFIGURATION OF THE DORSAL SURFACE OF
THE HUMAN BRAIN COMPARED WITH THAT OF TROGLODYTES NIGER, THE

CHIMPANZEE.

,■l.,.j,.^^,,,L^lm^Jt,■,^i,.l..l^l.,I■0.,InLJ,...L,J,.J,J.J,iJ,,J..,.l.in■^^^^^^ L„l. J. J„„lu,l„„l

Centimetstr Scale

FIGS. 453 AND 454. SIZE AND CONFIGURATION OF THE LATERAL SURFACE OF
THE HUMAN BHAIN COMPARED WITH THAT OF TROGLODYTES NIGER, THE

CHIMPANZEE.

[9-9I

EN'OLLTIONAL MODIFICATIONS

primates of this ave been described from fossil remains by Professors

Matthews and Grecor\-.

Thenex" - ^ with the advent of light lemuroid

prirr.ates. v. - was stUI of the slow, cautious, climbing type,

__, dutch-like grip. All of the digits of the manus
_er, but the outer two were esp>ecially elongated. Similar modifi-
er ffccted the foot, so that the entire adaptive change established a
?trnr_ >i:manal tendency. Pedal fulcrumation was still of the tarsal
n hallux and p>ollex were well developed. Modern examples
of this s: _ X found in loris and potto.

A more decisive advance made its appearance when arboreal locomotion
combined the advantages of climbing with leaping. Passage through the
trees row became swifter and more effective. A tendency to semi-erectness
S' eloped, and the squatting posture was well established. The digits,

metacarpals, tarsus and metatarsals all elongated, giving the quadrumanal
differentiation still greater prominence. Fulcrumation advanced to the
meta: > ~, thus p>ermrtting of a greater leverage in the take-off for leaping.
The hallux and p>olIex were more powerful and definitely opposable. The
forms most representative of this stage are lepidolemur and notharctus;
with these should be included the leaping tarsioids, and especially the
Indrisinae.

From leaping and climbing it was but a short step to the stage of swing-
ing, cursorial locomotion through the trees. At this time brachiation was first
introduced, and had its far-reaching influence ujxtn all subsequent developn
ment. Swinging by the hands from branch to branch naturally lengthened
and strengthened the arms. The manus developed a suspension grip which
caused the digits to elongate, although the thumb underwent reduction, or
even, as in the spider monkey, did not appear at all. The foot developed a
grasping grip, and all of its elements elongated. Pedal fulcrumation was

STRUCTURAL CULMINATION g8i

metatarsal. The semi-eixtt and sitting postures were still tiirther emphasized
by these ehanges and ischial callosities appeared in consequence of habitual
squatting. The foot maintained digitigrade tendencies, although the heel
touched the supporting surface in locomotion, but did so after the toes made
their contact. The timing formula in this respect was toe-heel, as in the previ-
ous phases. The lower extremity despite its increased length still presented
its pelvic llexion. This stage is represented by the Cebidae and the old-world
monkeys except most of the baboons, whose aberrant cynomorphous spe-
cializations produced a quadrupedal reversion with shortening of the limbs,
fingers and toes in adjustment to li\ing on the ground.

All of these modifications possibly occurred in the earlier portion of
the Oligoccne. Late in this geological era the primate stock took a great stride
forward. Locomotion was still predominantly i)rachiating in type. The
manus retained its suspension grip \\hich produced elongated digits, but a
rudimentary- thumb. The latter, however, was opposable. The tail disap-
peared and the foot developed a grasping grip. The legs became extended on
the pelvis, thus reducing the primitive pelvic thigh-fiexion, and rendering
the ancient type of quadrupedal locomotion impossible. This modification
at once advanced the cause of the erect posture. It did far more, howe\er, by
introducing the first phases of bipedal locomotion which, notwithstanding its
awkward and ineffectual nature at first, created the structural pattern
essential to the culminating diflerentiation of the human foot.

Among living species the beginning of the Hylobate branch (gibbons)
clearly marks this critical departure. The orang-outang is probably an
oflshoot from this stage, while Dryopithecus carries the stage directly upward.
Early in the Miocene there came a great increase in body weight which particu-
larly aflected such primates as possessed this newly acquired orthograde
tendency. The greater weight brought the animals nearer to the ground, and
thus determined certain terrestrial specializations. Arboreal locomotion was

982 E\OLLTIOX.AL MODIFICATIONS

St;.. . .. ... type. T' ' ^ame extremely long and powerful —

longer ...v. ;nore f>o\ver; ...^:. ;nan the legs. Erectness was further

iucr^^ii^rT because the thigh was more extended upon the pelvis. Standing and
wa.fv..,^ -^r^r-fir manifested definite improvements. Under these conditions
the toes a;.,^ ..^^.s touched the ground simultaneously, although the timing
r,.rmii[a was still infrahuman in t\"pe. In arboreal locomotion, the foot still
,\ ;..... cd its grasping grip with shortened digits but opposable hallux. This
is true of all the great apes with the exception of the orang, which developed
a susj>ensr'" L'^ro in the foot due to its more strictly arboreal life. Adult
gorillas, t^f^^^.ci..y the older males, have definitely ground-gripping feet
with broad heels, flat arches and plantar eversion with some distal advance
of the great toe. Their pedal fulcrumation is well forward in the metatarsus.
Arboreal locomotion in all three of the great apes is predominantly br:' '"^^-
ing. This development imparted to the upper extremities those sptx.....z.ci-
tions which maintained the hands as part of the locomotor apparatus
and thus impeded their most effectual manual differentiation. The manus
retained its suspension grip well marked in the orang and chimpanzee, but
showed evident decline in the gorilla whose increasing tendency was to
assume a terrestrial habitat. Thus, however strong the incentr^e toward
terrestrial life may have been in the great apes, that inherent arboreal
commr"^""' "" set upon the primates in early Eocene times still kept them
true to .111 Liicir rigid simian inheritance. To be more than apes it was neces-
sars- for them to shed that stigma which tree fife stamped upon them. This
the modern apes never accomplished. The experimental efforts evident in
their anthropomorphous tendencies at length found a new opening. It was the
foot which led the way, producing a supporting structure having a well-
developed heel, a non-opp>osable hallux, and a heel-toe timing formula in
walking. At some later period in the Miocene the two great branches of the
orthograde primates parted company. The structural decision at this junc-

STRLCTLRAL CULMINATION 983

ture was a critical one. By ■ - accepts rees as their lot, and

man, because of his tAvo they supp>orted above them,

acquired the earth with all it contained. Thus, with arboreal life a thing of
the past, with a true ground-gripping foot ^ntigrade bip>edal locomo-

tion, with longer legs and actual erectness for cdectiAe transportation, the
hands were finally liberated for - . success.

The specialization o: -.e been in process

through great period- " . .<s the decisive parting of the ways be-

tween the apes and the i. :y. For however permissib vbeto

regard the upper extren .itferentiation, as the

most cogent influence affecting the exp., - t the b er,

the hand itself was ultimately depe ierentiation ot human

feet. Nor is rt p>ossible to omit all of those factors in structural organization
which finally made possible the erect . setting the heac the

shoulders so that the eyes might look : the hands

follow the direction of the eyes.

Upon the dorsal si;: rain stem, the record of progressive

expansion may also be discerned. A om the conspicuous evolutional

features in the cerebellum, ex-pressed especi. :he pronounced expansion

of the lateral lobe, this region of the brain contains other elements equally
significant, if less conspicuous. TTie progressive increments in the clava and
cuneus, those structures -orsal sensor\- field representing the sensory

influx from the upp>er and lower extremities, have already been discussed
in their functional aspects. That both of them should enlarge in passing
from the lower primates. _-h the intermediate group, to man, has its

explanation in the augmented stream of afi^erent sensor].- impulses from the
deep proprioceptive structures of the btxly. Fluctuations in the interrela-
tions between the clava and the cuneus are of even greater moment. In
the lower primates it is the clava \\ hich shows more prominence. Recerving

984 EXOLLTIONAL MODIFICATIONS

impulses from the lower extremity and tail, it has an extensive sensory field
to ser^e in its capacity as relay station. The cuneus is concerned with the
influx from the upper extremity. In certain of the lower primates, more partic-
ularly in those which possess a highly developed prehensile tail, this disparity
between the clava and the cuneus is most pronounced. In such species, the
column of Goll is larger than that of Burdach. This augmentation is in fact
signalized by a special element, known as the nucleus of Bischoff. The Bischoff
nucleus makes its appearance only in those animals possessed of a prehensile
tail or one specialized for direct participation in locomotion. The subsequent
disappearance of this median unpaired nucleus, and the gradual loss of the
clava's preponderance over the cuneus, with the involution of the tail, is a
matter of much evolutional significance. The clava actually becomes less
prominent and smaller than the cuneus in the intermediate primates. The
disparity is more marked in the gibbon, which has no tail, and in which the
upright posture is but tentatively and occasionally assumed. The progressive
emphasis of appendicular specialization, imposed by the development of the
hand, completes the supremacy of the cuneus in the sensory field. This final
predominance of sensory areas for the hand has a more far-reaching effect
than its influence upon the sensory sphere alone. The richness of all motor
specialization rests necessarily upon a substratum of sensory apperception,
in order that the kinesthetic associations, built up in connection with each
newly acquired motor performance, may be adequate to direct its execution
and to reconstruct its formula for future repetitions.

Evolutional Significance of the Development of the Special
Senses. If there is much to indicate the waning of olfactory sense, as various
anthropoid stages are traversed in approach to the ultimate conditions in the
human brain, so also there is evidence of a vast change in two other realms of
special sense. In the case of olfactory sensibility, the process is one of actual
involution. With sight and hearing the matter stands otherwise. Here the

STRUCTURAL CULMINATION 985

primitive centers in the midlirain recede i)ut transfer their functional ofTices
to more expansive areas in the cortex of the cndbrain. This telencephalization
favors further enrichment in the realms of sight and hearing. The gradual
diminution in the size of the mesencephalic colliculi furnishes the structural
indication of this process. The transference of functions from an area
formerly prominent as the optic lobe of the midbrain entered upon its initial
stages in the earliest mammals. Even in the lowest of the primates, the
lemur, the marmoset and the tarsius, both sets of colliculi manifest a
degree of prominence which suggests the retention of some primordial func-
tion. Both collicular prominences appear to be still active to a large extent in
the functions of sight and hearing respectively. This is particularly true of
that range of auditory and A'isual activity which concerns itself with imme-
diate rellex reaction, thus oflering the animal a greater margin of safety.
However notably this may apply to the sense of hearing, it is also the case,
perhaps to a less marked degree, with reference to vision. From the lower
primates upward, a definite decrease in the prominence of the colliculi indi-
cates a larger measure of functional participation by the higher auditory and
visual centers. Evidence of their primitive importance may still be elicited
from collicular eminences even in man. This is recognized in the well-known
phenomenon when a sudden, unexpected noise may cause the individual to
start or to come to an abrupt halt. Similarly, a flash of light before the eyes
may produce all of the reactions of primitive defense. But responses such as
these represent vestiges of more extensi^■e reactions formerly administered
through the primordial centers for A'ision and hearing. Sounds and visual
stimuli are in the main treated with deliberation, as the result of cortical
elaboration. The progressive decrease in structural prominence of the
mesencephalic colliculi, taken in conjunction with the expansion in the
occipital portion of the cerebral cortex, supplies the evidence of an evolutional

986 EVOLUTIONAL MODIFICATIONS

process, than which tlicrc is no inoic decisive example in the whole realm
of organized matter.

E\'OLUTioNAL Significance of the Epiphysis Cerebri ix the
Primates. Another side of the collieular deUoresceiice o{ the mesen-
cephalon may perhaps be touched upon somewhat tentatively, l)ut not
without a sense oi growing conlidence as time de\ elops more ample
understanding of the important structures known as the endocrine glands.
The cei^halic extremity of the longitudinal mtercollicular sulcus in the
j:)rimate series tends to become broader and Hatter, forming a comparatively
roomy fo.ssa at the cephalic extremity of the midbrain. In this chpression
rests a specialization of the diencejjhalic roolplate, the c]>ii>hysis
cen'hri. This structure has a long and complicatt'd history Irom the beginning
of vertebrate sjjccialization. In its earliest representation it makes itsell
apparent in a highly specialized form and gi\es rise to a pair ol eyes situated
in the middle of the forehead. This is the primordial condition of the epiphysis
cerebri in the CNclostomes. After man\ lluctiiations in passing through the
selachians, ganoids and teleosts, in \\hicli it manifests a general retrogres-
sion from its sensory specialization, it shows some tendency to develop m a
glandular direction. Then it appears in the amphibians once more as a highly
different iated distance rece])tor, apparentlx for the pi'rception ol light. In
some of the lower rt-[)tiles it becomes even more highly specialized as, lor
example, in the parietal eye ol sphenodon. In the bird it takes lorm as a
complexly organized gland whose special ducts distribute its secretion
directly into the cavity of the third \cntrich'. In the mammals, howe\er, its
development is otherwise. Onl\ in the t'arliest stages ol ontogenesis does it
show tendencies toward glandular dilierent lation, and therealter undergoes
degencratixe changes. In man, in later life, it gixes exidence ol ad\anced
degenerati\'e change characterized In the deposition in it ol a sand-like sub-
stance, know n as aeervulus cerebralis. In early stages ol human de\ elopmeiit,

"«3a52r

FIGS. 455 AND 456. SIZE AND CONFIGURATION OF THE DORSAL SL KFAGE OF
THE HUMAN BRAIN COMPARED WITH THAT OF GORILLA (;ORILLA.

"i-i-l ■...L.i-Liii...L,.im,l I.,i.Ij,,J,,„nmJ,„i,,Ji.j.,J.,,i,,,,I„ii,„L.i,.,J,,,,i.Ji,,.l,Lj,,J,,,,i,,J,,j,J

CantimeCsf Seals

FIGS. 457 AND 458. SIZE AND CONFIGURATION OF THE LATERAL SURFACE OF
THE HUMAN BRAIN COMPARED WITH THAT OF GORILLA GORILLA.

[987

ExPLANAioK-i Note to Figure 459

The several horizons of cerebral development indicated by the figures on the opposite page require some
further comment with reference to their evohitional significance.

I. The Lemuroid Horizon is here considered the basic primate level. It contains many brain features, still
in the crude, which become dominant in later development. It also illustrates such hesitations and indecisions
as might be inherent in a momentous transitional stage. Faintly, at least, it shows the first feeble impressions
imparted to the brain by adaptation to arboreal life and indicates the general lines of cerebral advance
consequent upon tree-living habits. (Tarsius and Lemur.)

II. The Simian Horizon illustrates the dehnite crystallization in cerebral architecture of those structural
features which result from the adaptations to arboreal habitat. It clearly reflects the attainment of quadru-
manous specialization, at the same time disclosing the ellects ol certain restrictive influences, such as prono-
grade locomotion and the as yet partial lilxTation of the forelimbs from locomotory function. (Old and New
World Monkeys.)

III. The Proanthropoid Horizon is epochal in its ellects. A new ty|)e ol adaptation has reorganized the
proportions and postures of the entire body. Brachiation is now substituted for a pronograde locomotion in
which latter the upper surfaces of the branches are grasped by the handlike fore and hind extremities. Swing-
ing from the branches, as do the Gibbons, has produced a marked elongation of the hands, arms and trunk.
It has further caused the body to assume a more [jcrpendicular position in passing through the trees and a
real erect posture upon the ground. The Gibbon can in fact stand, walk and run upright. It has, in addition,
lost its tail, due undoubtedly to its well-established habit of sitting upright in true anthropoid fashion. The
animal is, nevertheless, much inferior in its cerebral organization to the higher anthropoid apes and is hence
regarded as a representative of that proanthropoid stage whose arboreal readjustments laid tlie foundations
for the development of the great a|)es and man.

IV. The Anthropoid Horizon shows a further specialization in the direction of the ultimate erect posture of
man and the final freeing of the hands for purposes other than tho.se of locomotion. Arborealization still
exerts such a potent influence upon all of the three great apes, that their advances in the direction of anthro-
poid specialization are definitely restrained by this factor. While all of the three great apes, Orang-Outang,
Chimpanzee and Gorilla, habitually walk in .'i modified pronograde manner, using the knuckles of the
extended hand for support in walking and running, these animals are capable ol standing, walking and
running upright. The erect posture, under these circumstances, has little of the perlection attained by man.
It is both ineffectual and ungainly. Running and walking are done with a shuffling, waddling gait, with a
tendency to come down upon all fours whenever speed is necessary. The great weight of the anthropoid .apes
has enforced upon them .m arborco-tcrrestri.il niixlc i>f life. This is more particularly true of the Gorilla
which, although it does not resort to anything api>roaching brachiation in its arboreal locomotion, does
employ its massive arms for reaching up to the branches, thus drawing itself upward from the ground. All
three ol the great apes appear to Ik- olfshoots fniin the |)r(>.inthro|)oid stem; while still another <jff shoot gave
rise to the races of men.

V. The Human Horizon demonstrates certain anthropomorphous conclusions which were first suggested
in the proanthropoid stage. Effectual erect posture is at length attained, the hands liberated from purposes
of locomotion, speech acquired, and the frontal area of the brain greatly expanded. The primate tendency
so obviously introduced on the Lemuroid Horizon has, under the influence of arborealization, progressed
to a proanthropoid stage whose essential contribution is the inception of the erect posture. Two major lines
of anthropoid derivation induced the adaptations which led respectively on the one hand to the great apes
and on the other to man. Whetlur tin- .inthropoid stem was a separate offshoot from the proanthropoid level,
or whether several such olfshoots developed, is still a question. The morphological constituents of the brain
strongly suggest that the departure of man from the proanthropoid level was at first by a stem in common
with the Chimpanzee and Gorilla, with subsequent bifurcation leading to the wide divergence between the
human and his neighboring coordinates among the great apes.

[988]

MAN

Human Horizon

ORANG

MVCETES

CHIMPANZEE -««:j^ ^^ GORILLA

Antliiopoicl Horizon

GIBBON

Proanthropoid Horizon

MACACUS BABOi

Simian Horizon

TARSIUS LEMUR

Lemuroicl Horizon

FIG. 45(). PRINCIPAL PRIMATE HORIZONS, SHOWINC THE EXOLLTIONAL
I EXPANSION OF THE NEOPALLIUM.
The original drawiiifj reproduced tlu' actual size of each brain depicted; in this figure each brain is
reduced to two-sevenths actual size. The progressive expansion of the psycliic area (blue) is clearly
demonstrated in ascending from tarsius to man.

Key: Blue, Psycl\ic Region; Red. Motor Region; Green, Sensory Region; \'ello\v, Visual Region; Gray,
Auditory Region; Red and Blue, Speech Area.

I989I

990 E\OLUTIONAL MODIFICATIONS

especially in fetal and infantile life, the pineal body has much the appearance
of a glandular structure. There seems fair probability that it is actually a
gland which contributes its secretion directly to the blood in these periods of
life. It has been maintained that its function is to check the development,
not only of the rigid skeleton, but also of sexual differentiation and maturity.
If destroyed b}' disease, these inhibitory qualities arc lost and precocious
development of body stature with premature differentiation of sexual
activities result. This, in fact, is the clinical syndrome, well recognized for
nearly a quarter of a century and kno\\n as macrogenitosomia praecox.

These and many similar facts would indicate a functional activity on the
part of the pineal gland. Whatever claims may be urged for it in regard to the
specialized inhibitors* function, which it exerts upon the maturation process in
development, should not be accepted without much reservation. There is great
room for improving our understanding both of the structure and the functional
activity of this portion of the nervous system. It is of interest, however,
that the size of the pineal fossa progressively increases from the lowest of
the primates to man. This indicates, no doubt, that the pineal gland itself
correspondingly increases in size, and thus adds to the process of growth a
decisive inhibitory factor which holds in abeyance the development of
maturity in the human race. It is noteworthy in this connection to recall the
pertinent note made by Alfred Russell W ullaee concerning the baby orang-
outang which he once captured and observed. In his efforts to ameliorate
the discomforts of infancy, which this orphaned orang suffered, he placed
with it, as companion, a young macaeus monkey of about equal age. The
great disparity in their reactions was apparent at once. The lower primate,
although an infant, showed almost all of the activities of the adult. It was
constantly in search of food on its own initiati\e and not in any way
embarasscd by the fact that it had been deprived of maternal care. The young
orang, on the other hand, lay continually upon its back as might a human

STRUCTURAL CULMINATION 991

infant, quite as helpless to care for itself and most imperfectly developed
even in its simple motor activities. Here, apparently, in one of the higher
anthropoids, was demonstrated that tendency to retard functional differen-
tiation, in order to obtain the advantages of a long period for maturing.
That this great anthropoid shows a period of latency in development almost
as long as the human infant is most significant. The phylogenesis of the pineal
gland lends weight to the theor\- that it may and does become specialized as
a glandular structure, contributing its secretion to the blood stream. That
it acts in the capacity of holding in abeyance the de\elopment of statural
and sexual differentiation is still somewhat in the conjectural stage. This
theory- is advanced with all the hesitation that should naturally attach to a
h^-pothesis still but imperfectly substantiated and not having as yet
attained universal acceptance.

SL-MMARY

A survey of all these facts concerning the primates amply justifies the
presumption that this group of animals presents a constancy in brain
development b}- which they may be distinguished from all others. E\en more
significant are the progressive modifications affecting the fundamental
design of the primate brain. Nor can there be any doubt that throughout the
entire process of this increasing complexity, the structural pattern of the
brain has shown its progressive modifications in harmony with progressive
adaptations in the behavior of the primates. Many long periods of structural
design, many protracted eras of behavioral trials preceded the final produc-
tion of a brain capable of all the powers which distinguish man.

Chapter X\X

THE INTERNAL STRUCTURE OF THE BRAIN STEM OF THE
PRIMATES. ITS EVOLUTIONAL MODIMCATION IN RELATION
TO THE DEVELOPMENT OF BEHAVIOR

Essential Similurilits in Inttinul LUmcnls'

"^HE external appearance of tiie priniate brain nia\- be sullieiently
conclusive ot the cN'olutional process in tins order of inaniniais. Sur-
face ap[)earances, lio\\e\er, are olten clecepti\c'. The intimate
internal organization of the brani ma\ exen chsqualilV tht' conchisions based
upon superficial sur\e\. II, on the other hand, tlu' e\ ideiice of the tnternal
structure corroborates that ollered by the outer surlace, the testinionx
beconies doublx con\ incmg.

Concernnig the sniulant ies ol organization m the primates, cerebral
architectonics \ield an embarrassment ol riches. The homologous correspond-
ence of each |)articular is pronounced beyond cjuestion of doubt. Onl\ in the
early transitional stages Irom loux'r lorms ol mammals to llu- primate kind,
might there be room for dispute. A review of the brain stem in the lemur, or
even in the marmoset, ma\- seem to justify the objection that the intt-rnal
structure is not sufliciently specific to distinguish it from some relati\elv
lower mammal. E\en under these circumstances, more extended ins])ection
of the chief diagnostic features in the brain could not fail to reveal ellectual
ditTercntial characters. No such objection may be raised in connection with
the intermediate primates or with those constituting the group of higher
anthropoids. In fact, real dillicultii's might be experienced in distinguishing
between the identifying characters of the human brain and the homologous
structures in the brains of gorilla, of chimpanzee or of orang. A close scrutinv,
however, discloses definite structural \ariations u hich differentiate between
man and the great apes.

993

994 EVOLUTIONAL MODIFICATIONS

In their size, position, relative proportion, general disposition and topo-
graphic relations, the following constituents justify the assumption that the
primates represent an organic aggregation, which is harmoniously integrated
by unmistakable ordinal characteristics in the brain: The inferior olivary
nucleus, the pyramid, the pontile nuclei, the cerebral peduncles, the superior
cerebellar peduncles, the dentate and red nuclei, the dorsal sensory nuclei,
the nuclei of Deiters and Schwalbc, the substantia nigra, and the superior
and inferior colliculi of the midbrain.

EVOLUTIONAL MODIFICATIONS IN ARCHAIC STRUCTURES IN THE BRAIN OF

PRIMATES

Although there is some difference in the emphasis with which the archaic
elements of the brain disclose the process of evolution when compared with
more plastic, impressionable structures, the ancient constituents none the less
reveal the effects of adaptive modification. The steadily advancing clearness
of definition, manifested by such archaic elements as the cranial nerve nuclei,
is impressive. There appears to be a progressive sharpening of outline which
determines the locus of these nuclei. Such nuclear aggregations, for example,
as those of the hypoglossal nerve, which innervates the muscles of the
tongue, show increasing distinctness in their boundaries with the assumption
of a more definite nuclear individuality.

Adaptations in Hypoglossal and Facial Nuclei. The hypoglossal
nucleus slowly emerges from the maze of an indefinite cellular collection
until it has all the distinctive characteristics of a circumscribed govern-
ing center. In similar manner, the nucleus facialis shows marked accessions
in nuclear individuality, attaining its sharpest outline in the human brain.
This nucleus is of great interest because it has not in the main all of those
archaic characters inherent in most of the cranial nerve nuclei. The muscles
of facial expression are essentially a mamnuilian de\elopment, and the

INTERNAL STRICTIRE OF THE BRAIN STEM 995

nucleus facialis is therefore, in part at least, a cellular specialization of
relatively late appearance. Since it innervates those structures of the head
and face involved in emotional expression, its greatest functional capacity
occurs in those forms ha\ing the most extensive range of emotion. The
facial musculature is also engaged in the acts of swallowing and mastication.
Not a few (if xhv primates develop large cheek pouches in which they retain
masses of food, awaiting later deglutition. During mastication the vestibule
oi the mouth, between the teeth and the cheeks, is compressed in order to
bring the food between the grinding surfaces of the teeth. The lips during
this process also are drawn together, and thus play an essential role in
mastication. During the act of swallowing, the cheek recesses of the vestibule
are likewise occluded and the lips compressed, so that the bolus of food is
forced backward from the mouth to engage between the pillars of the fauces.
This masticatory and deglutitional element, innervated by the facial nerve,
represents its primitive and basic function. The innervation of the muscles
of expression, for portraying states of emotion, is a newer functional attribute
of the facial nucleus. As a direct effect of the expansion in emotional expres-
sion, the nucleus facialis reaches its highest organization in man.

Adaptations i\ Masticatohv Nucleus and Reticular Fornlation.
A like process of increasing distinctness applies to the nucleus masticatorius
which has an even greater antiquity. Many vicissitudes have affected the
sensory portion of the trigeminal ner\e, init its motor division has remained
constant.

Progressive increase in the definition of the oculomotor nuclei, including
the nucleus abducentis, the nucleus trochlearis and the nucleus oculomotor-
ius, may be observed in passing from the lower primates, through the inter-
mediate stages, to the great anthropoids and man. Nor is this tendency
confined to the cranial nerve nuclei. It is also conspicuous in the reticular
formation of the entire brain stem. The exact degree of progressive dclimita-

Lemur

Tarsius

Marmoset

Myceles

Baboon Macacus

FIGS. 460 TO 470. CROSS SECTION AT LEVEL OF PYRAMIDAL

These comparisons disclose the internal configuration of corresponding levels in the neuraxis. They disregard
several species.

[996]

Chimpanzee Gorilla

DECUSSAl ION IX THE COMPAKATU E PKI.MATE SERIES.

the actual dimensions of the sections. Such measurements are given in the description of each level in the

[997]

998 EVOLUTIONAL MODIFICATIONS

tion of outline in the lornialio reticularis defies estimation b\ means ol men-
suration or other methods of jjrecision. Its comparison in the \arious species
ol" the primates con\evs the impression that this cHHuse mass of (jray and
wliite matter becomes more clearly defined in ascendmjj; the primate series.
This elTect may be the result of increasinp; sharpness in definition ol such
nuclei as constitute the origin of the cranial ner\es, or due to the tact that
certain important nuclear masses, such as the red nucleus and substantia
nigra, gradually emerge from the indiscriminate matrix ol the reticular
formation. Such increasing dehnition within the formatio reticularis is a
morphological tendency clearly demonstrable in the brain stem. It should
not be passed over without due notice of the fact that e\en the diffuse matrix
of this structure does not escape the inlluences of that progressive specializa-
tion aliecting other ancient parts of the central nervous system.

Adaptations in the Vestibular Nuclei. Ecjually archaic are those
centers w hich recei\e impulses from the jjroprioceptors of the semicircular
canals, utricle and saccule. These vestibular luiclei show certain lluctuations
which, however, are entirely proportional to the ecjuilibratory needs of
particular species. In those forms requiring a most effective l)alancing mecha-
nism, the vestibular complex is correspondingly large; while in species less
dependent upnn this function, there is an apparent falling off in the general
dimensions of the vestibular area. In the main, the receiving stations for
this function maintain a minimal standard which is essentially constant
throughout the entire order.

It is also interesting to note that tarsius and mycetes i theSouth American
howling monkey) stand at the head of t lu' list as ha\ ing the highest coefficients
in the vestibular complex. This superiority in the balancing mechanism is
unc]uestionabIy due to the animal's higli degree of s]5eciali/.ation. In mycetes
it is incident to development of the prehensile tail. B\ this organ the animal

INTERNAL STRUCTURE OF THE BRAIN STEM 999

acids to its motor appanitus an cciuipnimt which permits ol suspension in
midair and th lis frees the limd-and torehmhs tor purposes of defense, ollense,
gathering of food and other aelixities m whieh t\\v hancLs and feet may be
simultaneously emplovt'cL A s[)eeit"s tluis sjjeelalized would acquire a more
extensive' funelional power oi bahmemg than animals whose base ol support
and mode ol loenmotion are less jjreearioiis. In other s])eeies, the dimensional
differenees of tlu' central balanciiiij; nu'chanism arc almost negligible. At first
glance it seems inconsistent that the cc|uilibrat'>ry lunctioiis ot the arboreal
animal, which moxcs about upon such uncertain support as the branches ot
trees, should not be greater than that ot a ground-li\ ing Inrm, such as man.
^ et there are undoubtedl\ c(|uali/.ing lactors which ser\e to ollset any tend-
ency toward markctl disparity. In the larger anthropoids, lor c\am|)le, the
attempt to assume the erect posture and to depart from an arboreal mode
of living introduces new equilibratorv factors. This speciali/ation reaches its
highest degree of differentiation in man, who, while no longer m need ot
balancing functions adapted to the conditions of arboreal life, has added to
his equilibratorv responsibilities by dcxclopmg a type ol locomntion in \\ Inch
he must support his body on two feet instead of four. The expansion m the
human balancing mechanism, although not incident to tree-climbing or tree-
dwelling, is, none the less, a direct response to the lactors introduced by
bipedal cc|uilibration. Thus, whiK' the archaic structures, re])resentiiig the
balancing mechanism and know n collectively as tlu' \ cstibular complex, show
certain limitt^d \ariations as more definite terrestrial lile is assumed, they, in
general, maintain a fundamental ccpiality in their coellicient expression. 1 heir
variations, howcxcr limited, all manifest the effects of aclaptni' inlluences and
are signilicant in tlu- sense that tlu'y disclose the exolut lonaix |)redisposition
of neural structures to adjust themselves to \ar\ing demands ol lunctional
specialization.

l.ennir

Tarsius

jMarinosLt

iMycetes

Baboon Nlacaciis

FIGS. 4-1 TO 481. CROSS SECTION AT THE LEVEL OF THE CAIDAL

Tlicsc comparisons arc intended to disclose tlie internal eonllguration of corresponding levels in the neiiraxis.
each level in the several species.

[1000]

iimpanzee Gorilla

EXTREMITY OF INFERIOR OLIVE IX THE COMPARATIVE PRIMATE SERIES.
I hey disrigard tlic actual dimensions of the sections. Such measurements

icnts are given in the descriptions of

1 00 1

1002 EVOLUTIONAL MODIFICATIONS

EVOLUTIONAL MODIUCATIONS IN THE DORSAL SENSORV FIELD

Another scries of structures represents the centers for myo-articular
proprioceptive impulses from the extremities and heacL These comprise
the nuclei of the dorsal sensory field, inchiding the nucleus of Goll, of
Burdach and of Rolando. In their coellicient expressions these sensory
elements maintain a fairly constant equality throughout the primate
order. There arc certain lluctuations in their total rt'presentatinn which
depend upon extreme developments, such, for example, as tiie prehensile tail.
It is claimed that this organ, in many instances, ser\es as a lifth hand. This
is true in most of the South American monkeys whose specialization in this
respect has been described in Mycetes seniculus.

More important than the total volumetric representation of the dorsal
sensory nuclei are those relations between them which indicate variations in
the differentiation oi the extremities. The column and nucleus oi Goll repre-
senting the lower extremity, foot and tail, when compared with the column
of Burdach and its nucleus, the oblongatal representatives of the upper
extremity and hand, show a progressive diminution in M)lume in passing from
the lowest to the highest primate. This transitional disproportion from a
status in w hich the clava (column and nucleus of Goll) is distinctly larger
than the cuneus (column and nucleus of Burdach) to a condition comjjietcly
reversing this relation in which the cuneus is at least twice the size of the
clava, adxances b\- gradient stages.

The two sensory elenu'iits areal)()ut (,'C|ual ui \lacacus rhesus and gorilla,
but in gibbon, orang and chimpanzee, the balanet' begins to turn iii la\'or of
the cuneus. This relation between the two great elements of the dorsal sensory
field indicates the evolutional ])rocess which has c-wntually resulted m the
production ot a bimanal type, ca])able of the t-rect posturi' and l)i]K'dal loco-
motion. Such s]iecialization e\()l\ed out of a common and more generalized

I\TF,K\A1, SI lUCTLRF. OI- TIIF. BK\i\ SIFM 1003

stock whosf inluTt'iU triukiu-ics wcrr not only c|n;Klnmianal but were iLirthcr
conditioned by tlie addition of a tail which augmented tiie stream ot allerent
impulses from the caudal portions ol the body. Ciraduall\ tiie tail became
recessive, lost its prehensile or balancing function, and hiially disappeared.
During this ])rocess the lower extri-mities, and particularly the feet, dilleren-
tiated for the purpose of supporting the bod\ m tlu' upright position. It
was, h()\ve\er. the progressive adaptixe de\clo]:)ment m the u|i|3er extremity
which gave linal ]:)reeminence to the cuneus because this structure rejjre-
sented tlu' i>ro])rioce])ti\e inllux arising from the most ellicieiit organ ol
construction and analwsis yet de\eloped b\ the \t'rtebrate kmd, tlu' human
hand.

The relative proportions of the third element of lln' dorsal sensory
field, the nucleus of Rolando, are al.so significant. It is mteresting to note
that this nucleus has diminished in al! of the primates as compared with the
lower mammalian t\ pes, such as carnivores or ungulates. To some extent a
similar diminution may be observed in contrasting the lowfr jjrimate lorms
u ith those standing nearer to the uppir extremity ol the order. I he decrease,
howex er, is not so impressive as to constitute one of the outstanding features
in the transitional changes incident to e\'olutional adaptation. Such change
as does appear depen<ls upon the fact that the face and head have ])rogres-
sively become less im])ortant as specialized areas for guiding the course ol
locomotion. Their ollices ha\e largely In-vn superseded by the pronounced
development of the hand which has taki'ii upon itself many responsibilities
as the chief explorir in the en\ironment, at least m thos<,- cn-eumstances
demanding actual contact with objects. When com]>aricl with the progres-
sixely expanding cuneus, the nucleus of Rolando, together with the descend-
ing trigeminal tract, stands out all the more conspicuously because it has
not kept pace with the expansion w hich has so strikingly allected its imme-
diate neighbor in the dorsal sensor\- held. For iust as the cuneus, which

Lemur

Marmoset

Tarsius

Mycetes

mc^

Baboon Macacus

FIGS. 482 TO 492. CROSS SECTION" AT THE LEVEL OF THE ^HDDLE

These comparisons disclose the internal configuration of corresponding levels in the neuraxis. Tliey disregard
several species.

[1004]

Gibbon

Orang

Chimpanzee GorUJa

OF THE INFERIOR OLI\E IN THE COMPARATIX E PRIMATE SERIES,
the actual dimensions of the section. Such measurements arc given in the descriptions of each level in the

[1005]

ipt

ioo6 EVOLUTIONAL MODIFICATIONS

represents the arm and hand, has gradually gained preeedenee m size and
conducting capacity (ner xhv elava which represents the leg and foot, so the
dorsal representative of manual dillerentiation gamed ])reemmence ovc^r the
nucleus of Rolando and its accompanying libers, the descending trigeminal
tract.

E\OLLTI()NAL ADVANCES IN NEOKINESIS WITHIN IHE PKIMArEOKDEK

if these elements of the hram, including cranial iuicUm, reticular lorma-
tion and nuclei of the dorsal sensory field, express much that is mherentl\
archaic. If tluA retain in large measure the primordial characters of neural
organization iinoKed in such essential tunctions as respiration, cardiac
acti\Ity and digestion, the control ot deglutition and mastication, the
mechanism of balancing, the transmission of propri()cepti\-e iniijulses
from the head and extremities and the regulation ol the ocular muscles,
there are also elements in the brain which arc much more responsive to the
inlhiences of adaptat ion. The structure of these elements possesses a plasticity
cspcciall\ sensitixe to the exolutional acKances which characterize the new-
sphere ol primate actnity.

Were it ]:>ossible to summanzt' bnell\ the outstanding transitions
through w hich these animals ha\e made their steadx acKance, these features
might l)e said to com])rise those s|)ecilic relinements in motor perlormances
whicli made progressixc adai)tation jjossible. Hu'\ brought to bear upon the
externalizing ca])acity of the animal more complex syntheses ol sensory
combinations and ga\e to the execution of muscular action a grcviter range
of llexibility. Tht'v pro\ ick'd the incenti\efor the constructixc faculties of the
most facile and adaptable |:)ortion of the bod\, the hand, and sublimated in
this facilitx tlie powt'rs of selection betwc-eii alternati\c' courses ol action.
They added the cjuality of judgnu'iit for manual guidance. 1 he\ im|)artedto
deftness those factors of en-atixe imagination w host' culmination is that

INTERNAL STRUCTURF OF THF I^I^MN STFM 1007

vast siipcrstriicturi' representing the ei\ilize(l world with all its rich
content created by the industries and ellorts of man. Delined in a single
term, this new sphere of action has been called ucoliinesis. Its motor possi-
bilities were first revealed by the ad\ent of mammalian forms. They marked
the beginning of that long ])eriod of" cNolutionai progress which constantly
kept in the foreground the de\ elopnuntal potentiality- offering the greatest
ultimate promise. Simple as is the neokinetic specialization in most of the
lower mammals, it may nevertheless be discerned in its incipiency at that
stage of organization w hiii llu' cerebral cortex first began to differentiate
a motor zone for voluntar\ control o\er the muscles. This motor zone of the
cortex acquired connections with the lower st'gnu'nts of the axis through the
projection libers of the jnramidal system, which introduced all of those
advantages accruing from ])rogressi\e expansions in the hemisphere.

Neokinesis and Dexelopmem 01 Mil llwn. A sur\e\ of mammals
clearly indicates that those orders wlmh ha\c manifested the greatest
capacity in de\cl()])ing neokinesis gradually tended to acc[uire ascendancy.
Certain orders among thi- mammals, not distinguished b\ their neokinetic
development, have passed into habitat zones in which tlu\ rexcal no con-
structive prei'mineiice. They have attained only that scant margin of suc-
cess which secured to them a nominal degree of permanenc\ in their organic
differentiation, flow true this is may be set'ii in the history of the carnixores
and ungulates, rodents and insectivores, marsupials and monotremes.
EcjuallN true is it of the pinniped mammals, which bv secondary adaptation
have readjusted their somatic and \ iseeral organization to aquatic lilV-. But
the branch of the mammalian stem which manifested a real tendency toward
manual ditienntiation furnishes a totally diflerent record in the history
of neokinetic expansion. The fust impulses toward this manual differentia-
tion developed certain morphological extremes as, for example, c[uadru-
manal specialization, and thus committt'd the animal to a t\pe of habitat

ioo8

E\OLLTIONAL MODIFICATIONS

in which both the fore and hind extremities were employed in a locomotor
capacity. Yet in all primates the beginning of this manual expansion is
clearly discernible. By means of this differentiation they entered upon a new

Tabllation of Plaximetric Coefficients

Species Pontile nuclei Pyramid

Peduncle

Olive

.Man

550

.183

321

.226

Gorilla

480 . 161

187

.186

Chimpanzee

400

.172

223

.174

Gibbon

200

.138

no

■155

Macacus

150

.147

169

.128

Tarsius

057

.032

OI7

.042

Cat

080

.062

064

.061

Rabbit

054

.029

044

039

Giraffe

063

.030

067

.042

Horse

064

.02-

079

.036

Kangaroo

067

•043

051

•034

Emu

.023

Comparative planimetric indices of four important structures in the brain stem of vertebrates. These
indices show the marked evolutional expansion in all four structures, especially affecting the primates and
emphatically demonstrating the effects of arborealism. Three of the structures are exclusively mammalian.
The fourth, the inferior olivarj" nucleus, is rudimentary in the bird and, when present, in all other lower
vertebrates.

world and in the organization of their brain plainly reveal that the key to
this new realm was already in their possession.

The development of the paw, the hoof, the claw or the swimming paddle
condemned its possessor to the restrictive conditions of a greatly limited
habitat. It would actually' seem, on the other hand, as though the inception
of manual differentiation were an invitation to new freedom, an inspiration
for the exercise of that latent power of supremacy which awaited only the
acquisition of some adequate instrument whereby to express itself.

Even the low organization of the brain in lemur discloses the first signs
of the new impulse to expand the neokinetic portion of the central nervous

INTERNAL STRUCTURE OF THE BRAIN STEM 1009

system. The evidence of its brain indicates to what extent the pyramidal
system has increased in volume oAer and above lower mammalian forms.
Thus begun in lemur, the process of expansion goes steadily forward from

CO.MPARATIX E PLANI.METRIC GRAPHS
A. Oli\ E AND Pyramid

B

K

G

H

R

1

A

1

0

A

R

N

R

R

B

D

C

A

S

B

A

F

E

1

R

F

T

0

E

0

c

A

T

T

M

G

C

A

A

1

H

R

C

B

1

S

A

B

M

1

C

0

P

U

U

N

A

s

s

N

Z
E
E

G
O
R
I

L
L
A

A

N

FIG. 493. GRAPHS CONSTRUCTED ON THE BASIS OF THE PLANI.METRIC INDICES.

This representation clearly indicates the hesitating advances made by subprimate vertebrates in the expan-
sion of important structures connected vrith neoldnetic evolution. The effects of arborealism are plainlv
showTi in the marked advances of the Primate^ o\er other mammals. Such advances are attributed to the
.nous differentiation determin. real habitat. Broken line represents the inferior olr\-e,

• the pj-ramid.

loio EVOLUTIONAL MODIFICATIONS

stage to stage through the prmiati' order until it reaches its highest expression
in the human brain. The acl\ anee as indicated by increments in the pyram-
idal system is clearly seen in tlie lower primates. The marmoset may
express this progress somewhat leebl\ , but the new-world monkeys reassert
the growing imjjortanci' ol ncokmetie organization. Passing upward to the
intermediate primates, the acKanee is more apparent, with the possible
exception of thi- gibbon in w hich there appears to be some hesitation. This
seeming indecision is due no doubt to the lact that this animal has become
largely ckpendent upon its upper extremities lor locomotion and thus has
deprived its manual dillerentiation of a real opportunity to progress. In
olhtM" words, the gibbon has carru'd brachiation to an extreme degree.

In the higher anthropoids the upward progress is resumed with unmis-
takable decisi\eness. The orang, the chimpanzee and the gorilla all show
marked acKanee in the [nramidal system which hnally reaches its highest
pro])ortions m the Ijrain ol man. 1 he progressi\'e expansion allecting this
iieokinetic s\ stem represents a characteristic de\elo])ment in the primates.
It is gra|:)lHcall\ (k'lnonstrated in tabulations ol tlu' planimetric coeflicients
of the pyramid in which man occupies the highest position, while bom him
the line descends through mcasurabk- gradations to the higher anthropoids,
to the intermediate primates, and linall\ reaches its lowest expression in the
tarsier. The tlillerence betwot'ii the latter and man is approximatelx lilteen
hundre'dt hs, which leprtst'iits a remarkable mcix'nicnt in tlu' \olunu' ol the
human pyramid. 1 hat the dillerenee betwoen these two contrasted lorms
does not appear more pronounced is due to the lact that the pxramidal
tract must accommodate itsell to a portion ol the neuraxis through which
many other ec|ually im|:)oi"tanl conduction systems make their wa\. The
pyramidal system, lor (.■xample, represt'iits a conduction ])athwa\ trom the
motor or preeeiitral area ol the hemispheri'. Its axons arise in tlu- giant
cells ol" Bctz, leave the cortex, become cou\ergenl in the internal capsule

INTERNAL STRUCTURE OF THE BRAIN STEM dh

and pass tlirouyli \hv ccic-hral pe'diHK'k- and jjdiis into the nutlulla oblongata.
Each spc'C'iali/c'd aixvi ol the motor forlcx, siuli, lor iwainplc. as the I(.'<j; area,
contributes axons to the |j\ianiidal tract. Accordinfi as such motor area ol
the neopalluim is e\ti'nsi\ c'l\ ii'picsented, tlu' numljtr ol libers arising in it
is c()rres])ondmgly large or small. 1 he progressi\t' expansion ol the pri'ct-ntral
area m all ol the primates is one ol the most noteworthy lealures in the
de\ flopnu-nt ol tlu- brain. The motor area itsell is acti\ated and giiidt-d by
neural mllueiiees Irom man\ other regions ol the neopallium. It is, as it were,
merely tlu' mouthpiece ol the cerebral hemispheres which gi\cs linal expres-
sion to the neural combinations created withm the entire cerebral cortex.
Idlling so important an ollice ol transmission, it is apparent that this
motor area must be in direct communication with adjacent and more distant
portions ol the cerebral hemispheres. Siich communications ma\ be dis-
cerned 111 the many association libers, both ol the long and short Aariety,
\\ hich link the \ arious conxolutioiis together. The important Icature conei'rn-
ing the motor area itsell is its capacity to sublimate into ellecti\'e lormulas
and motor patterns all ol that great stream ol atlereiit impulses which enters
the brain. These motor patterns determining the externalized ex]:)ression ol
the animal's behaxior lind their ultimate con\e\ance b\' way ol the pyram-
idal system. It this system should actuall\ keep pact' with the expansions
of the cerebral lu-misphere by manifesting a corresponding increment in
size, it would soon become too extensixf lor either the bram stem or the
spinal cord. That it does not vary diri-ctl\ with the rate ol exi:)ansion in the
cerebral cortex is evident, although cortical exj^ansion docs exert a delinite
inllueiice in increasing the ]nramidal \<)lume. It is possibk' lor the cerebral
cortex to increase tenlold while the pxramidal system which conxeys the
imj)ulses tor externalizing the actixities ol the entire neopallium, adds but a
small traction ol increment to its size. Thus, the ]:)yramidal tract actuallx'
rellects the ellort toward condensation which is everywhere imposed upon

Lemur

Marmoset

'■^*'W*i

Mycetcs

Baboon Macaciis

FIGS. 4(^4 lO 504. CKOSS SECTION AT THE LEVEL OF

These comparisons disclose the internal configuration of corresponding levels in tlie neuraxis. They disregard
several species.

[1012]

Gibbon

a.-ciiiji

Human

^KJ

Chimpanzee Gorilla

THE VESTIBULAR NUCLEI IX THE COMPARATIVE PRIM ATE SERIES.

the actual dimensions of the secticms. Such measurements arc given in the descriptions of each level of the

[1OI3]

I0I4 EVOLUTIONAL MODIFICATIONS

the neuraxis in the aflerent and eflerent conduction of impidses over its long
projection systems. It is for this reason that e\en the slightest increase in
this system of fibers must be regarded as significant of expansion in the func-
tional capacity which it represents. Upon comparison, the difference between
the planimetric coefTicients of the pyramid in the marmoset and man is
represented only by twelve hundredths increase in fa\or of the human motor
system. Such disparity as this appears relati\ ely small in comparing these
two vastly different primates. But when the pyramidal condensation is
viewed as the functional representative of large areas of cortex, the pyramid
stands out in man in striking contrast to the corresponding system of the
lower primates, and manifests the undoubted influences of an evolutional
process.

The increase of the pyramidal system, however decisi\e it may be in its
bearing upon the development of the neokinetic functions, is relatively less
conspicuous than the expansion of the pons Varolii. This applies most partic-
ularly to the pontile nuclei. Two facts show an intimate connection between
these nuclei and neokinesis: first, they ser\e to relay fibers from several
areas of the neopallium, and second, the axons arising in them terminate
in the lateral lobes of the cerebellum. Interpreted in the light of the function
which the pontile nuclei serve, this linking of the cerebral hemispheres with
the lateral lobes of the cerebellum is in the interest of the coordinative activ-
ities expressed in the appendicular musculature. This conclusion is justified
by the fact that experimental and clinico-pathological evidence points to
the lateral lobes of the cerebellum as an acquisition of the central nervous
system for the distribution of coordinative impulses to the muscles of the
extremities. The lateral lobes differ from the vermis since the latter is partic-
ularly concerned with the distribution of coordinative impulses to the axial
musculature of the trunk, neck and head. From the functional specialization
of the neopallial areas participating in the important communication con-

INTERNAL STRUCTURE OF THE BRAIN STEM 1015

suniinatt'd hv the jjontilc- nuclei, sonu" conception ol tlieir significance may
be gained. Many of the jjallio-pontilc libers take origin in the parietal lobe,
from which region, in lact, they arise in greatest nuniber. This portion of
the neopallium is actixe in tlu' interc-st ol those e\tensi\e sensory syntheses
essential to gciu'ral body sensihilitx. In this broad area of tiie brain, all of
the myoarticular propriocepti\e organs haxe their cortical representation.
Here the impulses arising from such receptors become associated as kines-
thetic memories and guides lor directing all somatic motor acti\ities.
Impulses from other t\|)cs of receptors also find their ultimate area lor
elaboration m the parietal zone. .All \arietics of sensory stimuli arising
from the exteroceptors contribute to the upbuilding of discriminative
sensibilitx in the parietal lobe. The significance of the parieto-ponto-cerebellar
connection in tlu' interest of coordination therefore becomes ob\ious.

In a similar manner, the large contribution of connecting fibers arising
m the temjjoroj^arietal region of the bram seems to have its explanation.
It is probable that in this territory the.' neopallium is acta e in the association
of those impulses \s hich arise in the xestilnilar projjrioccptors of the semi-
circular canals, utricle and saccule. Such impulses arc definitely connected
with the et]uilibratorv sense and, as such, play an important role in the
spatial orientation of the body, more jxirticularly of the head. The close
connection between the conscious fields of equilibratorv sense, of touch and
muscle-joint sense on the one hand, and the cerebellum on the other, serves
to perfect the coordinative control of muscular acti\ity.

It has long been held that a Noluminous bundle of libers establishes
communication between the occipital lobe of the hemisphere and the lateral
lobe of tlu- cirebtllum. This fact has in recent times been called somewhat in
question and the large aggregation ol libers known as the occipito-ponto-
cercbellar fasciculus has been ascribed to origins intt'rmediate between the
parietal, temi^oral and occipital regions of the brain. \\ hether its origin is

Lemur

M.u inosel

iMvcctes

1^- • j^

Baboon

Macaciis

FIGS. 505 K) ,"1 ,-. CROSS SECTION AT TIIU Lt\EL Ol- THE EMERGEN'CE
Thcsi- i-onip:iiis<)Hs disclosi- tin- internal ci)nli';inatii>ii oleorusiinnilinn liviU in the neiiiaxis.l liey disregard
several speeies.

llOlOl

Gibbon

Gvn.la

OF THE TROCHLE.AR NERVE IN THE COMPARATIVE PRIMATE SERIES,
the actual dimensions of the sections. Such measurements are gK en in the descriptions of each level of the

[1017]

ioi8

ENOLLTIONAL MODIFICATIONS

discretely occipital or not, this contingent of the pa>ii/-|^..;\to-cerebeIIar
system •■'-'-f- ■r>+..^ry exists. It arises, p>erhaps, in some common ground in
which tii^ ^MastivicTS of the parietal, of the tempKjral and of the occipital

COMPAR.\TI\ E PLAMMETRIC GRAPHS

B. Pontile Nuclei

B

K

c

H

1?

C

T

M

G

c

G

M

1

A

1

O

A

A

A

A

1

H

O

A

1?

N

R

9

B

T

R

C

B

1

R

N

D

C

A

S

B

S

A

B

M

1

A

F

E

1

1

C

0

P

L

Vt

F

T

u

U

N

A

L

0

E

s

s

N

A

0

Z
E
E

100

/

90

/

80

/

'

70

A

J

60

\

/

V

50

h

s /

40

1

V

30

-'"•"^

^^

,^\

1

2 0

^

" \

/

1 0

/

V

FIG. j\0. GKAPU BASED ON PLAMMETRIC INDICES OI- THE PONTILE NUCLEI.

From this graphic comparison it is apparent that the pons Varolii, like other structures in the brain stem
associated with neokinetic evolution, expands rapidly in passing upward through the several horizons of
the primate order. Prior to this level of vertebrate organization pontile development is relatively insignifi-
cant and the structure is absent in all orders below the class of mammals. The pons Varolii is essential to the
finer coordination of the more highly organized .skilled acts.

INTERNAL STRUCTURE OF THE BRAIN STEM 1019

cortex approach each other in t>pe of specialization. " ding of corti-

cal types as this, implicating as it does three discrete areas of the neopallium,
might well give rise to a contingent of the pallio-ponto-cerebellar system
capable of communicating to the lateral cerebellar lobes cs which

represent a physiological admixture of myoarticular a; ;Iibratorj'

sensibility with visuaI-«ensor\- elements. Such a combination of impressions
received from the muscles and joints, from the semicircular canals and from
the eyes would constitute an invaluable accession in the construction of
those neural combinations necessary- for the coordinative guidance of move-
ments of the extremities, and more particularly the upper extremit>\
W hatevcr function is ultimately ascribed to the occipital contingent of the
pallio-ponto-cerebellar system must depend upon future investigation. In
general, it may be accepted that this system is connected with the functions
of neokinesis, and that its progressive augmentati< c primate series

indicates a definite increment in the sphere of neokinetic organization.

The frontal lobe, especially its intermediate precentral area in close
relation to the origin of the pyramidal system, also establishes communica-
tion with the lateral lobes of the cerebellum through the fronto-ponto-
cerebellar contingent. This bundle of fibers is somewhat less in volume than
cither the occipital or the parieto-temporal contingents of this system.
According to present physiological interpretations of cortical localiza-
tion, the intermediate precentral area has functional control over highly
skilled motor performances. The fronto-ponto-cerebellar fibers in this light
are not difficult to understand. Both the histogenesis and histology" in this
region of the human brain furnish excellent reasons to believe that the
function of this portion of the cortex is intimately associated with motor
activity. Its stratigraphic representation of cells and fibers follows closely
the pattern laid down in much clearer outline in the precentral motor
convolution.

,o2o EVOLUTIONAL MODIFICATIONS

Those who arc opposed to cliseretel\- diagrammatic and somewhat dofj-
matlc allocation of specific functions to circumscribed areas ol the cerebral
cortex may obicct to this interpretation. Their objections must I)e received
and considered w ith respect. Nor should they be lost sight of in the further
exploration of tin- cortex. There already exists, however, so much that is
con\incing with reference to specific localization in the neopallium, that
many authorities hnd no dillicult\ in attributing to the intermediate pre-
cential area a specific function. Whether or not this function ultmiatclx
proves to he the regulation of highly skilled motor perlormancis m no way
affects tlu' \alidity of the large contribution of fibers which the mtt-rmediatc
precentral area makes to the pallio-ponto-cerebellar system. The frontal lobe
of the brain is unc|uestionably connected with the lateral lobes of the cere-
bellum. Its connection represents some phase in the expression of neokinetic
aeti\ ity. W ith certain reservations as to the exact significance of some of its
constituents, the entire i:>aifio-])onto-cerebellar system may be accepted as
an espeeiall\ reliable index of neokinetic expansion. The relation of the pon-
tile nuclei to this system appears in the fact that they are the relay station
for the fibers arising in the several lobes of the neopallium and seeking final
distribution in the lateral lobes of the cerebellum. If these nuclei manifest
augmentation in ]:)assing from tlu' lower to the upper extremity of the order,
the inference seems justifiect that the system with which they are connected
has been corres]:)ondingly augniented. A progressive expansion of this kind
is so ])romiiU'ntl\ demonstrated in the comparison of the primates as to
make the pontile nuclei the most significant indicator of the cN'olutionarv
process in the brain stem. The planimetric cot'llicicnt of these nuclei in the
lemur is j^ 2 hunchx'dths. At the otiu'r e\trcmit\ of the series it is 55 hun-
dredths, a gain of 4()'_» hundredths in passing fronrthc lemur to man. in
no other structure of the brain stem is there such marked expansion. Recon-

INTERNAL STRUCTURE OF TME BRAIN STEM 1021

stnictions ol the poiililc inalci li'iw a still niorc ifalistic idea ol tlicprogrcs-
sivc incTenu'iit which thry ])r(.'srnt m this series.

NeOKIXESIS and DE\ELOiniI£\ I OK THE I^'oOI IN THE AsSlMPTION OF

THE Erect Posit he. W hile ihi' siuniheanee ot manual dillereiitiatiOn may
be easily appreciated m eiHinectioii with t he progrcssivecxtensions in the realm
of neokinesis and esi)eeiall\ in relation to tlie expansions ol tin- pontile nuclei,
it should not be o\erlooked that the highest degree of manual adaptability is
dependent upon an ec|uall\ high specialization ol the loot. Asa matter of hict,
the hand in man is less specialized structurall\ than in man\ of the apes. It is
the extreme specialization of the human loot which imparts to the hand its
real functional opportunit\ to establish manual d 1 11 eren tuition as the supreme
achievement of ncokiiu'tic progrt'ss. The apekmd, clinging persistentlx' to its
quadrumanal type of organization, resisted that decisive mlhunce which
began to shape the human loot. Their conser\atism was epoch-making. It
elTectuallN debarrt-d them Irom an\ connection with tlu' human lamily. It
was the parting of the wa\s which witnessed the beginnings of a new race
ccjuipped to stand upright upon two Icet and use two Iree hands m the strug-
gles of life.

What the pontile nuclei re\ cal ol this ])rocess, the cerebral peduncles
still lurther illuminate. The progressive de\ elopmeiit ol tlu' i)etluncles may
be seen almost without aid of mensuratioiial methods. There is, however,
marked disparity in \ohimetric exi^ression between the cerebral peduncle of
the marmoset, whose ]:)lanimetric cot'lllcieiit has a \alueol 10 hundredths and
that of man, w here its value is a little less than 30 hundredths. Between these
two extremes are all of the intermediate grades indicating progressive incre-
ment. Since the cerebral peduncle comprises all of the libers arising Irom the
motor area and constituting the pyramidal system, as well as all of the fibers
forming the pallio-pontile system, its size accurately rellects the degree of
ex'pansion in the cerebral hemisphere.

Tarsius

M.Hlll,,:,

.Myci'Us

Baboon \lac:icus

FIGS. 517 TO 527. CROSS SECTION AT THE LEVEL OF THE

These comparisons disclose tiic internal configuration of corresponding levels in the neuraxis. Tlicy disregard
several species.

[1022I

Chimpanzii GoiilU

IXFHKIOK COLUCULUS IN THE_COMPAKATI\ E PRIMATE SERIES.

the actual dimensions of the sections. Such measurements .irc f;iven in the descriptions of each level of the

1 1 023]

I024 EVOLUTIONAL MODIFICATIONS

A comparative survey of the Nciitral surface of the [)rain stem discloses
at once progressive extension in the neopallium. The first appearance of the
pyramid, the ])ons Varolii and the eerehral ])eduncles announces the acKent
of the mammalian orders and mtroduces a new epoch ot bram dexelopment.
Along many dillerent hues ol actixity the mammals ha\'e endeavored to make
use of their new cerebral endowments. Manx' diflerent kmds ol extreniity
differentiation have responded to this cerebral specialization in order to
develop new means lor expressing the potentialities ol neokmesis. Hoofs,
claws, paws and e\en paddles in the pinniped carnixores ha\c made their
appearance as the agents tor externalizing these new caj^acities ot bi'hax lor.
Each of thest' In its turn has labored under thost' inherent disad\ antagcs
])eeuliar to appendicular structures w hich are w holl\ dominated by locomotor
function. Tlu' specilicitx' ol locomotor pcrlormance in such forms as the
kangaroo, the rabbit, tlu' giratle, the ckphant. the horse, the whale or the seal
curtailed the opportunities which these animals might possess for the
upbiiifding of a highly comj:)le\ sphere ol bcha\ioial reaction. To some extent
the diflerent Kit Kin of the extremities was ol st-r\K\' in utilizing (.'iiergy ni
combat and in obtaining food supply, liut the motor tornuilas expressed in
locomotor acti\ it\ , in acts of ollense and delense, or in ciuest ot lood, with
the exception ot their distinct mereast' in the complexit\ ol motor pattern,
show little ot real adxancc o\cr such lower xcrtcbrates as the birds and the
reptiles, in most ot the mammalian oixK'is the imj^ression is unavoidable that
all attempts toward de\ eloping the splu're ol lU'okinesis, howe\er ob\iousIy
seeking adecjuatc channels through which to express themselves most etlec-
tively, came lor the most part to naught, or only advanced to indecisive
advantages, until the factors culminating in the primate order made them-
selves felt in a crucial specialization. The fort'- and hmdlinibs, designed pri-
marily as locomotor organs, now attained thosi' powers capable at length of
throwing ofl the yoke which subjugated the extremities to the ser\ice of

INTERNAL STRUCTURE OF THE BRAIN STFAI 1025

locdiiiotion. Tliiis, till' priniatr brain, through its i;am,s 111 nrokiiu'tif expan-
sion, bt'i^an to sliow tliosi' real accessions \sliicli arc sought lor in \ain
throughoLit all other orckas ol nianinials. ^ et the priniati's weri' not without
tlu-ir own serious t'lnbarrassnicnts. The ([uadrunianal cle\ t'lopnient so charac-
teristic ol all simian tribes giNcs neither the hand nor the loot its lull or ample
opportunity lor ultimate dillerentiation. Arboreal hie im]>osed a severe
haiulicap in that it demanded m upper and lowi'r t'\tremit\ alike a high
degree of j^rehcnsilc s])eciali/ation lor locomotor lunction. On tlu'other hand,
tlu' progressi\'e acKance in tlu' neokinetic indices ol the brain, t-speciall\' in
the pyramid, tin- pons \ arolii and the cerebral |:)ed uncles, disclost's the manner
in which an excpiisite arboreal speciali/ation has been slowly superseded,
first by si-mi-arboreal adaptation, then In imperlectl\ organized terri'strial
life, with the gradual assumption of the erect posture and the almost exclu-
sive adoption of the surface of the earth for transportation. DLiring this
process tlu- hand became the su|3reme agent lor externalizing the lull t'xpres-
sion of these ad\ances.

Othek SiKLCTiRES IN Till: Bhain Ste.m Indicaii.ng Necjkinetic
Development in iiil; Phi\iait:s. TIu' insistenci' of neokinesis to iind
adec|uate expression is again and etpiallx well illustrated b> structural extt'ii-
sion of certain t-lemcnts functionally connected with the maintenance ot
coordination. From the standpoint of \olumetric cx])ansion and progressive
adx'ancc in organic delinition, thtae is no structure in the brain w Inch appears
to be moresusct'ptibleto the inlluences of adaptation than thedentate nucleus.
Its plan imetriccocHicient, which in marmoset is "."percent and in man i ".6 per
cent, shows a progressive gain ol about 10 hundredths in \ohime. Even more
proiiouiux'd is its increasing discreteness as a lUuK'ar structure. \\ ith t lu- pos-
sil^Ie exct'])tion ol the inlenor oii\ai"\ nucleus, the nucleus (kaitatus is the most
striking example ol ]jrogressi\e delinition m the entire brain stem. Startingas it
does in a dillusi', irngular nuchar aggregation, it passes tlirough many

M-rceses

Tlrsc

BabKKia Macaccs

FIGS. 528 TO 538. CROSS SECTION AT THE I_E\-EL OF THE

[1026]

Wm

OtftfXlB

Ossjts

X »

Ctxrmta.r^xT

GocSSs.

SUPERIOR OOOJCtXL 5 IX THE COMPARATn-E PROtATE SERIES

tbe actail cEsastacas oc tat secicBs. Srac* isaeass3-e

J iic iiwts ::i t±>e descisiars :£ ^^-r iev^ af ife

fiori

1028 EVOLUTIONAL MODIFICATIONS

developmental gradations until it attains its definitely convoluted stage first
seen in the gibbon, but steadil\ inereasing its nuclear indi\iduality in the
higher anthropoids and num. Not alone does this nucleus acquire decisive

COMPARATIVE PLANIMETRIC GRAPHS
c. Cerebral Peduncle

B

K

C

H

R

C

T

M

c

C

c

M

1

A

1

O

A

A

A

A

1

H

o

A

R

N

R

R

B

T

R

C

B

1

R

N

D

C

A

S

B

S

A

B

M

1

A

F

E

1

1

C

0

P

L

R

F

T

u

u

N

A

L

0

E

s

s

N

A

0

Z
E
E

100

/

/

90

/

80

/

70

/

60

\

r

50

I

40

/

)

30

/

2 0

-^^^

J

1 0

y

^

-

-^^

FIG. 539. GRAPH BASED OX PLANIMETRIC INDICES OF CEREBRAL PEDUNCLE.

This structure is of particular significance in neokinetic evolution. It is a concentrated expression ot the
neokinetic powers of the cerebral cortex, representing as it docs the palliospinal and palliopontile projection
systems. Functionally it provides for the conduction of impulses essential to volitional and coordinated
control of the muscles. It is of an exclusively mammalian character in the brain, showing its greatest expan-
sion under the influence of arboreal life and the consequent development of quadrumanous specialization.

INTERNAL STRUCTURE OF THE BRAIN STEM 1029

specialization in the course of its own evolutionary progress; its advances
in this respect gain c\en more emphasis because of their association with the
simultaneous increase in size of the lateral cerebellar lobes. These lobes, as
well as the dentate nucleus, expand in direct proportion as manual differ-
entiation becomes more definitive.

In a snnilar tnaniier, the red nucleus, serving as the intermediate relay
for impulses from the cerebellum, allords an index of the coordinati\e capac-
ity of the lateral cerebellar lobes. Attention has already been called to the
probable dual nature of the red nucleus as a relaying station. That it serves
other offices than the conduction of coordinati\e control seems likely.
On the other hand, the concomitant expansion of the dentate and red nuclei
in passing from the lowest to the highest of the primates speaks strongly in
favor of its relation to the impulses essential to coordinativc control of the
upper and lower extremities. Ilie red mieleus does not itself disclose an}'
specific participation in the neokinetic ad\ances of the upper extremity.
Its close incorporation in the cerebellar mechanism, however, makes it
probable that it receives its chief incentive toward expansion from the acces-
sion of coordinativc impulses essential to control the muscles in the upper
extremity. The difference in the planimetric coeflicients of the red nucleus
between the lowest of the primates and man is a little over 10 hundredths. In
this respect it coincides closely with the similar difference existing between the
dentate nucleus at the two extremities of the order.

The volumetric comparison of the superior cerebellar peduncle which
connects the dentate with the red nucleus corroborates the conclusions con-
cerning the progressive increment in coordinativc control. This structure also
shows a progressive augmentation in passing from the lower end of the series
to its upper extremity. The significance of all of these elements related to the
cerebellum bears defmitely upon tlie field of neokinesis inasmuch as they are
all alike in\ol\ed in the coordinativc control of the appendicular musculature.

1030 EVOLUTIONAL MODIFICATIONS

In its progressive expansion, the inferior (jlivary nucleus is a distinctive
feature in the brain. Concerning the actual function of this important
structure, much Hght is still needed. The interpretation advanced in this
discussion of the primates, assigns to the nucleus an activity related to the
simultaneous coordination of the hand, liead and eye. Integration of widely
separated muscles so that they act as a single mechanism needs no argument
to defend its physiological necessity in the interest of highly organized motor
performances. A vast range of skilled acts depends upon the harmonious
action of the eye muscles in order to keep the objective m clear \ ision and
focus. The hands which perform the actual execution of the movements are
followed and directed by vision. The underlying motive for the simultaneous
cooperation in the muscles turning the eyes, turning the head, as well as
moving the hands and fingers, is thus ob\ ious. Ocular supervision is essential
both in the acquisition and the direction of a large number of skilled learned
performances. From the known facts concerning the mterior oli\e, this
nucleus stands as an intermediary between the ocular nuclei, lying above it in
the brain stem, and the nuclear centers forming the final common pathway
for motor impulses to the muscles of the neck and the upper extremities.
Equipped to receive proprioceptive impulses from the musculature ot the
eyeball, of the neck and of the upper extremity, the inferior olive is in a
position to transmit these incoming impressions to the cerebellum, not only
to its lateral lobes, but to some extent also to the vermis. It supplies in this
manner the afferent elements to the cerebellum necessary for the organiza-
tion of outgoing syntheses of coordinati\e impLilscs for all highly skilled
acts of the body. This is the control essential in the oculo-cephalo-gyric
movements utilized in the visual direction of many acts, such as handwriting,
painting, drawing and the employment of instruments and implements.

Fundamentally the inferior oli\ e is an ancient structure. Those who have
given attention to its phyletic organization recognize in it at least two parts,

INTERNAL STRUCTURE OF THE BRAIN STEM 1031

i. c, the palco-olive and the nco-olivc. In the lower forms of animals not yet
possessed of anything approaching manual differentiation, the need of an
intimate cooperation betw een muscles of the eyes, of the neck and of the
upper extremity is not pronounced. These animals in consequence depend
upon the associations of a much simpler range of motion. To them the coor-
dination of the neck muscles controlling the movements of the head, and of
the eye muscles regulating the mo\ements of the eyeballs, may be essential
in such acts as browsing or grazing, particularly to animals possessing long
necks, such as the giraffes. These species arc not in need of simultaneous
coordination in the ocular, cer\ical and brachial muscles. In consequence,
although they have developed an inferior olnarv nucleus, this structure
appears in its simplest form. It consists largely of what is properly called
the palco-olive. The paleo-olivary connections with the cerebellum are for
the most part w ith the central portion or vermis. In animals possessing claws,
such as those of the canine and feline families, there is at least some slight
demand for coordinative action between the muscles of the eye, neck and
upper extremities. In such species the inferior oli^ ary nucleus shows consider-
able advance notwithstanding the fact that it still remains, from a structural
standpoint, in a fairly primitive condition. Canine and feline activities in
which the claws are employed, as in digging holes for burying food, require a
certain degree of mutual coordination in oculo-cephalo-gyric and upper
extremity mo\ements. These mo\ ements unquestionably belong to the cate-
gory of performances learned by imitation. In consecjuence there is some
increase in these animals of the inferior olive and the olivo-ccrcbellar
connections.

W hh the advent of the primates, manual differentiation became a
feature of progressive development. The influence of this new impulse was
immediately impressed upon the inferior olivary body. Even in the lemurs,
the nucleus manifests tendencies toward expansion in its neo-olivary portion

I032 EVOLUTIONAL MODIFICATIONS

whose further progress imparts such j^roniinenee to the e\-ohition;uy process
in the' primate brain. Thenceforth, throughout tlie order, this impulse toward
neo-olivary expansion becomes more j^ronouneed. \\ hen, however, the
demands of neokinesis called for greater functional activities in the sphere of
olivary action, no distinctly new element was added to the structure.
Phyletically ancient portions w ere so extended as to create, out of the old,
new and needed material for amplilied functional capacity. This is the
underlying ])rinciple which m the mam characterizes the modifications in
tile \ertebrate brain. The structural substratum ot t^xpansion usually exists
in rudimentary form awaiting only the demand and opjjortunity for further
dcM'lojjment. The inferior olivary body, illustrating this principle, expands
in rt^sponse to increasing demands lor lunctional control in its sphere ol
action. As e\ ideiice of an cvolutionarx unlolding, it is second to no other
element in the entire brain stem. The planimetric coellicients of the olivary
nucleus in jjrimates indicate that in passing from its lowest organization to
that representative ol man, there is a total gain ot almost 20 hundredths.
In the marmoset the planimetric cocflicient oi the mlerior olive is 3.8 per
cent, while In man it is 22.6 per cent. A MiluiiU'tric gain of such proportions
cannot possibly be without great biological sigmlicancc. More conspicuous
even than this increment in Nolunie is the increase in the olive's morpholog-
ical mdi\iduality and delinition. W itli this progressive oli\arv specializa-
tion, the connection of the nucleus with the lateral lobes of the cerebellum
becomes more extensive. This fact strongly suggests that the biological
impulse underlying this olivary diifercntiation is closely related to those
causes which activated the expansion of the lateral cerebellar lobes. It is
well established that the extensions in the lateral portions of the cerebellum
have been induced by the ])rogressi\e s]:)ecializations in the extremities, more
particularly in the upper extremity and hand. The inlerence seems lustilied,
therefore, that the oli\ e itself has also responded to this same incentive.

INTERXAl, STRlCTri^F OF THE BRAIN STEM 1033

Like the lateral lobes ol the eeieln'Muni, it must he lunetioiially associated
with till' (le\ elopnients ol iieokinetie progress. The inferior oli\ar\ inieleus
thus corroborates the exicieiice supplied by the p\ ramid, the pontile nuclei,
thi' cerebral jicduneles, the dentate nucleus, the ri'd luicK'Us and the su])erior
cerebellar pi'duncle. All ol these j^arts of the brain, by reason of their expan-
sion, stand out as prominent signals ol e\'olutionar\ acKance.

Certam constituentsw ith ec|nal I orce denote this process, not by e\])ansi()n
but by progressive (hmnuition m si/e. Among these structures the most
prominent are the superior and the mierior collieuli of the midbram. Their
importanci- ni relation to the special senses of hearing and of sight has been
emphasized, d he dellort'scence \n the inferiorcolliculus isparticularl\ striking
showing, as it does, a decrease in planimetric coefhcients In'twci'ii lemur and
man ot over 1 5 hundredths. W hile m the case of the superior colhculus the
decrease in structural i^romineiice is not so pronounced, it is iu'\erthelcss
clearly evident that a progressive decline proceeds through all of the jjrimate
species from lemur to man, with a total decrease of something mori' than 4
hundredths.

That thi' mesencephalic colliculi are remnants ol prominent features in
lower vertebrates, and that the\ still retain in these classes a pri'dominance in
encephalic organization, has been freciucntly rt'iterated. This is the condition
in birds, ri-ptik's, amphibians and fish, but with the appearance of the
mammals, the introduction of the neopallium concentrated the full force of
development upon the hemispheres. In consequence, this part of the brain
soon gained ])re(.niinence which in large measure was due to the unremitting
attemjjts to capitalize still lurtlur the new endowments of neokinetie behav-
ior. Each of the special senses, w it h the exception of the olfactory sense, partici-
pated in these attempts. These senses sought an advantage in proximity to
each other w Inch representation in the cerebral cortex afforded them together
with more am])le ojiportunities for functional expansion. 1 he optic lobe of

1034 EVOLUTIONAL MODIFICATIONS

the midbrain, compared with the more eosmopoHtan advantages of the
cerebral cortex, became an en\ir()nment too jjrovincial and hmited I'or the
ultimate de\'eIopment of vision. Tlie sense of hearing was similarly alleeted
in its disposition toward its original mesencephalic allocation, once tlu'
neopallium had re\ealed its de\elopmtntal possibilities. Hearing iollowed
tile example of \ ision and together they sought new lields for e.xpansion in
the lu'misj)iieres ol the endbram.

The delegation ot auditory and \ isual hmction Irom the roof of the
mesencephalon to areas in the cerebral cortex is part ol that process of
telencephalization which has pi'ogressed through the mammalian orders.
Its obvious purpose was to procure lor these s|)ccial senses more expansi-
ble areas lor their elaboration with other types ol sensibility. As in all
other instances, the prime object ol such expansion was not mcrel\ the
extension ol the s|)ecial sense iiuolwd, but much rather the multiplication
of its cajjacities lor c\j)ression. 1 hus, increasing the spheres of vision and of
hearing had lar-reaching ellects upon the expansion of neokinesis. The
functional increments to the sense ol hearing, in consec|uence ol its neopallial
opportunities may be clearl\- w itnessed m the expression of articulate speech.
To many other human acti\'itics hearing has bt'conu' essential. The auditory
development that leads to the recognition and combination ol sounds in tlu'
torm ol music and the ultimate externali/.ation ol such auditory syntheses in
the musical |:)rodiictions ol the \()ice or by manipulation ol musical instru-
ments reveal tlu' important role which the sense ol hearing plays in the
extension ol neokinelic aciiievenunls. Its instrumentalit\ m tlu' j)roccsscsof
learning is obxious, for without such auditory assistance it is probable that
many of the highly skilk'd performanci's of which man is capable would fail
of their complete (k'\-clopmcnl and lack one of the chief stimuli which incite,
create and direct them.

INTERNAL STRUCTURE OF THE BRAIN STEM 1035

In similar iiianiuT, tlu- c'\])ansi<)n ol \isual luiU'tiDii wliifli has lakrii
plact' in the ])r()<irc'ssivc augmentation of tlic occipital lobe makes its con-
tribution to the organization and acKaneement ol neokinesis. A large pro-
portion of all skilled motor ptatormanees in man depend primaril\ upon
vision for their aec]uisition. They are ec|uall\ ck'j)t'ndent upon \ isual integrity
lor their execution. This apjjlies ])artieularly to the minute and |)recise skilled
acts of the hand mxoKfd in writing, m drawing, m jjamting, in sculpture.
It must l)e apparent, t hen-lore, t hat t he ])iirposi' ol pro\ iding \ ision and hear-
ing with tlu'ir ultimati- opportunities lor expansion in the cerebral cortex is
especially concerned in the inlliu'iui' which they exert u])on the de\ (.■lopmeiit
and maintenance ol neokinetic acti\ities.

In passing Irom the lower primates to man, the progressn (.• de\ c'lop-
meiit ol the oculomotor decussation is so striking as to lea\'c no doubt con-
cerning Its e\()lutional signilicance. As inter[jreted in this discussion, it makes
pro\ision lor the most complete- con|ugate association of the eyes. The
absence of such mti'rmiclear connection would scarcely permit of that
intimate cooperation between the nioxc-nu'iits ol the excballs essential to
liolding the \isual axes in ])aralK'l or producing those degrees of coinergence
necessary to stereoscopic \ision. In other words, without this connection the
appreciation of objects and their spatial relations, more particularl\ in the
near ranges of \ision, would be incomplete and the more exact a])plication
ol liner manual movements would thus be gri'atly curtailed, i lowessentialsucii
stereoscopic \ ision is to tlu- skilled acts of chirography, painting and sculp-
ture scarcc'lv needs mow than nuntion to establish its claim, l-rom this
\iewpoint It IS again e\ ident that the specific ]:)urp()ses of neokinesis ha\e
been ser\t(l by the de\ clopnunt of t he mternuclear connections of tiie oculo-
motor nerves. By mensuration the disparity between tlu' lemur and man,
in the oculomotor decussation, is the most pronounced of all figures ciuoted.
I^eniur has a re|)resentat ion m its longitudinal coellicient of iC) ])er cent, while

1036 EVOLUTIONAL MODIFICATIONS

in man this ligurf rises to the vahK' ol ()(> piT cent, a total ciiiKTciice oi "4
hundredths between the two extremities of this order, j-roni sueh a ditlerence
in values, it may be inferred that the lunetional importanee of stereoscopic
\ision lias increased most j^artieularly in proportion to tlie degree of apphca-
tion of tlie hand m the execution (j1 the most highly organized motor
perlormanees.

The motive running through this entire j^roeess ol dex'elopment is not
dillieult to appreciate. Some parts ol the brain, essentiall\ progressive in
their tendencies, ha\e reacted by what seems to be an almost enthusiastic
response. They have grown m their proportions and gained preeminence in
their mlluence. This is especially true ol the neopallium, ol the p\raniKl and
pons, ol the cerebral peduncle, ol the lateral lobes ol the cerebellum and the
structures connected with them. Some parts ol the brain ha\'e mamlested
greater conserxatism in their adaptive reactions, as, for example, the centers
of the balancing nu'chanism, or those lor the transmission ol other proprio-
ce]3ti\c' impulses. Still other parts, like most ol the cranial iier\e nuclei,
ha\e been actuallx' resisti\e in their greater ]3hyletic stability, although
even the\ ha\e not escaped the progressu'e inlluences arising from such
acKanced acc|uisitioiis as the development ol articulate speech, ol emotional
expression and ol stereoscojjie vision.

A complete tabulation of the plaiiimetric coellicieiits lor all ol the
structures which ha\e been discussed in their exolutional relations is
appended on page 103". The coellicieiits lia\t' been so arranged as to iiWv
them their sequential order of importance whh relerence to the evolutional
process wiiich they indi\ iduallx rtpresc-nt. It will lie obserxcd that the\ fall
naturall\- into three groups those ]3ri'emineiitl\ concerned witli the ex]:)an-
sion in the neokinetic sphere, those to some extent intimatelx connected
\Mtli this expansion and those representing archaic structurt's which have
ielt m a nuich more remote manner the inlluences ol neokinetic de\elopment.

INTERNAL STRUCTURE 01- THE BRAIN STEM 1037
Plankmetric Coefficients of the Pkimaie Bi<\i\

Man

Gorilla

Cliini-
panzcc

Orang

Gib-
bon

Ba-
boon

Maca-
cus

My-

cctes

.\ 1 a rmo-
sct

Lemur

Tarsius

.183

16.

. J-2

. 160

M38
200

■143

.14-'

•37

064

1 10

.032

Pontile nuclei

.550

4Sn

41 lu

5, M ,

. 164

1 I'l

i.ij

1 H ) T

'I-;-,

"■>"

Cerebral peduncle

.321

.18-

223

.110

. 1 10

. 190

.169

144

o-y

. oH(>

.017

Inferior olive

226

.186

■ 174

172

'55

.125

.128

120

.038

060

.042

Nucleus dentatus

!-<•.

Ii-;

, ,(,

i(h,

134

,65

1 i-i

1 ;.'

1 1

1 1 u

■oiO

Nucleus globosus

023
.128

.0095

.018

OIj

.020

.023

.014

.032

.U5O

.032

.037

Red nucleus

.og6

.086

.087

.051

.060

.057

.081

.044

.012

.034

Superior cerebellar
peduncle

.088

.047

.047

.064

.063

.044

.046

.036

.048

"33

.032

Inferior colliculus.

.070

.III

.132

.131

.130

.155

•175

.182

.2111

^23

337

Superior colliculus

.104

.140

.125

.124

.132

•173

.158

.161

.154

.140

.230

Nucleus of Goll. . .

.064

.086

.050

.048

.034

.086

.076

.131

.068

.041

.026

Nucleus of Bur-
dach

. 100

.081

"-?

.093

.068

.06,-

086

.113

.043

.049
.082

.029

Nucleus of Deiters.

.065

.072

0--

.054

.085

(1^(1

075

,114

.077

.180

Nucleus of
Schwalbc

0-5

. 0-0

080

0,-5

.092

095

.087

. 090

. 060

.04,-

.ofi2

SUMMARY' OF THE E\ IDEXCE OF AN E\'OLl'TIONAL PROCESS AFFORDED BY THE
E.XTERNAL AND IMER.XAL APPEARANCE OF THE PRIMATE BRAIN

In sum total, the evidence atlorded In the external appearance of the
brain m [jrnnatcs, and l)\ its nitcrnal structure, points conclusu cly to an
c\'<)lutioiial process which has run paralk-l with corresponding expansions in
behaxioral de\ elopnunt. Thi.s exohitional process, both in structure and la
function, has made itself apparent most particularl\ in tlu' accessions to the
sphere of neokinesis, which new t\ pe ol' motor expression has been the distin-
guishin<i contribution of the mammals. It was, in this respect, as though
their arri\al had at once opened a lU'w trail which led into realms of more
highly speciali/.ed bchaxioral d(.\ tlopment.

Neokinesis and P\i iokinesis. This new motor specialization intro-
duced b\ tlu' mammals had certain acKantages oxer the ancient type

1038 EVOLUTIONAL MODIFICATIONS

peculiar to ph\ K-ticall\ more ]:>riiniti\ c animals, sucli as birds, reptiles
and fish, which, l)eeause of its \erv ]:)rimiti\ eness, is known as palenkiyiesis.
These two types of motor organization, the new and the old, diller from each
other in certain decisive characteristics, j-'erhaps the one most essential
difTerence between them appears in the insertion of an appreciable ]3eriod of
latency between the receipt of the allerent stimuli and the production
of the corresponding motor response. This ])eriod of latency has resulted
in retarding the immediacy of rellex action. In that mter\al thus created
between the receipt of the allerent stimulus and the dispatch ot the
efferent im])ulse, pro\"ision is made for more ellective sensory associations,
more comjjlcx combinations of neural impulses acti\"ated by the approach
of the afferent stimulus. It also provides for such important conditioning
qualities of jnolor response as rellection, selection and the introduction of the
influences of previous experience as well as the acKantages of higher intelli-
gence. Such a period of latency has in it all of the possibilities of withholding
action for relati^•ely long intervals of time, and thus conferring the far-reach-
ing benefits of that important neural attribute known as inhihition. The real
advances of beha\ lor for which this new clement of motor organization
lays the foundation become obvious at once. For the direct reflex reaction,
it substitutes the deliberately considered act. For the limitt'd rellex motor
pattern, it substitutes the more comple\l\ orgamzt'd motor design. In
general, primltixe paleokinetic acti\it\ is in its nature much mort- mimedi-
ately rellex and has but little rellectixe character. It makes the most achanta-
geous use of automatic and routine precisions in motion, but, on the other
hand, permits of little or no \ariation in its reaction ])atterns. Neither does
it allow of much reconditioning by new mlhuiux's and elements. It is exqui-
sitely objecti\c in its execution which appears to be as rigidly jjrescribed as
it is invariable in production. It possesses all of the characteristics necessary
for generic ada|)tation and but lew of those t|ualities essential lor mcliA idual-

INTERNAL STRUCTURE 01- THE BRAIN STEM 1039

iz(.'(l adiustnu'iits. In contrast to it, tlu- more recent inanimalian ac(|iiisition
ol ncoknicsis, ])y adding tlic acKantaiics ol rcllcction and deliberation,
makes motor reaction more llexihle aiul hehaxior more \\idel\ ada])tal)ie.
Tile ])eiiod ol rellc'ction and latenc\ permits ol ht't ter uiiidanct' of mo\-ement
b\' tlu' diri'ction ol \ ision, ol hearing' and ol ])ro])rioce]5ti\ f organization. It
likewisi' allords all ol those opportunities essential to e\teiisi\e teachal)ilit\'.
Extent to Which M \\im als Utilized Theik New Possession oe
Neokinesis. Although the mammals Irom their beginnings came into pos-
session of this great acKantage owr tlu' more lowly organized \ crtebrates,
they tlid not m all instances utilize it to its full extt'iit. Nor did it become a
sine (jua no)} guaranteeing a lull and tllectn i- di'xclopment of its potentialities
in all cases. Indeed, it setans much more as though tlu' mammals were contin-
ually strixing to lind that ])ath which might prolit tlu'in most in the de\elo])-
ment ol their new possession. But lor all their ellorts, the\ \\ ere surj^risingly
unsiiccesslul m arriving at the desired goal. I low they began to push forward
along this liiu' m their early nionotreme beginnings, how far short lhe\ fell
of an\ ri'al ]:)rogre.ssivc achie\ement, how ihey tried again and again, now in
marsupial specialization, now as rodents, insect noiws, bats, ungulates,
cetaceans or carnivores, but always without approaching nearer to the
desired tnd, is revealed by their several histories. That the\ had made
delimte contributions over and abo\X' the lower forms of \ crtebratt's in the
organization of motion and in the development of beha\ ior is not dillicult
to establish, "^'ct each ordinal specialization, with all its stri\ing in this
direction, seemed clelicu'iit m some essential ecjuipment whereb\' it might
fulfil the promise discernil)le in tlu- new accession to their development.
1 heir motor at 1 1 list men ts \\c'r(.; largely adaj.)ted lor trail sport at ion, for carrying
the body o\er the siirlace ol the earth, under the tarth, m the water or
through the air. These animals progressed but little in their constructive
processes as applied to their environment. Tluy accepted the earth as

1040 EVOLUTIONAL MODIFICATIONS

they IouikI it aiul k-l't little Ix-hiiul to change its appearance as a result ol
their own efl'orts. Their expansions in neokini'sis, Hke their cle\eIopntents in
beha\ior, were strictl.x hmited b>- the handicaps of highly restrictive special-
izations in their instruments of externalization.

The Mosr Profitable Advance in Neokinesis Okiginating w i rii
THE Prim vn;s. With the appearance of the primates, the first really ]:)ront-
able acKances in neokinesis were actually made. It is probable that the
quadrumanal dilferentiation may have led the early prosimia toward the
realm in which the I'liII promise of this motor capacity became possible. I n
any case, the long awaited instrument, the ready servant of neokinesis, had
at length made its appearance. Even with its possession the primates had as
yet a long distance to travel, many experimental trials to experience belore
this new instrument was so adapted as to give its maximum degree ol serx'ice.
The specialization in connection w ith the upper extremity was a real decisive
step forward; but where it extended to the low er extremities and produced
feet w ith many hand-like characters, it immediately imposed serious limita-
tions and creatt'd those disadxantages which result from the possession of
too man\ hands. The c|uadrumanal tendency of the primates positively
prohibited the full dexelopment of manual dilferentiation lor two reasons:
First, it committed the animals to an almost exclusi\el\ arl)ort-al hie. in the
second place, it. created a field of psychological indecision which had a i)ro-
found elfect by causing a c|uandary as to whetlu'r tlu' hand should be used
as a foot or the loot as a hand. It thus left in indeterminate state an instru-
ment which ri'c[uired aboxe all else the most exact discrimination lor its fullest
functional dilferentiation.

Pakmng Ol ruE Ways between An rnROPOiD and Hlm an. In spite ol
their early embarrassment due to over-endow nunt ol hand-like characters,
the primates had come upon tin- right trail. It reciuirttl but one lurther
modification to set them on the track w hich would lead to the ultimate goal.

INTERNA! STRUCTURE OF THE BRAIN STEM 1041

This was indeed a critical niodHKatioii. It established beyond cjuestlon the
great ]:)artlnij; ot the \\a\ s between the antliiDpoid and the lumian, raising an
efTectual barrier betwxx'n the one knul and the other. It was tlu' decisive
inllueiiee w Inch turiied the course ol the a])es to then' o\\ n specilic exohitional
tcrnilnl,]:)uttnig man upon his course which, through \ arlous stages of progress,
has led to his ])resent estate. What the underlying nioti\e ol this critical
modllication may ha\e been is still clouded in obscuritw I In' increasing
weight of the body appears to ha\c jjlayed some role in this alteration. For
it was unquestionabl\ the de\'elopmcnt ol ci-rtain inconx enK'iices and dis-
acKantages in arboreal liti' that cxcntuallx brought someol the primate stock
nearer to the ground and linall\' brought about the change in the lowx'r
cxtremit\' resulting m tlu' inception ot the human loot.

Probable Role of Endoc:ri\e Glands. TIu' lactors \\ ha h ma\ ha\e
increased the bod\" \\eight and so necessitated this change Irom arbort'al to
terrestrial lite are dithcult to estimate. It is possible that the indocrinc
glands had some part in this alteration. Changes in then" acti\'it\ may have
so altered the metabolism ol the body as to jjroduce that degree of maero-
somia which is no longer adapted to tree-dw cllmg. From pathological evi-
dence it is recognized that enlargements m the ])ituitary gland produce the
condition in man termed gigantism. Many ol tlu- more or less monstrous
extravagances m statural growth seen olteii-tmies in (.'\hibit ions and known
the world oxer as giants are the results of h\pertro|)h\ m the glandular
])ortion of the ])itiiitar\- bod\ . That such hypertrophy may well account
for an increased secretion in this gland and thus ])roduce exuberant growth
m the long bones is an accepted clinical lact. So also is the disease known
as acromegaly in which, alter adolescence, certain mdi\ iduals manilest a
tendency toward increased growth in the hands and in the feet, in the face
and other portions ol the bon\- skeleton, due to alterations in the pituitary
gland. Another group of facts pointing in the same direction are those coipo-

1042 EVOLUTIONAL MODIFICATIONS

real changes ascribed to diseases of the pineal gland, particularly in the
early years of adolescence, producing the condition known as macrogenito-
somia praecox or the syndrome of Pellezzi. Under these conditions the
individual grows prematurely tall with precocious sexual differentiation. It
is the belief that the pineal gland normally holds in abeyance the premature
development of the statural and sexual organization by exerting upon the
pituitary body an inhibitory influence. Whether these potent factors in control
of the metabolic mechanism entered into the causes which produced the
critical change in body modification must still be a matter for further investi-
gation. They offer a most enticing suggestiveness. Either they or other similar
factors bore some responsibility in these epoch-making changes. In any case,
it must have been the near approach to the ground and the final necessity of
living upon it which determined the specialization leading to the development
of the human foot. At that juncture the embarrassment of over-endowment
arising from too much in the way of manual specialization began to dissipate
its restrictive influence. With the critical differentiation of the lower extrem-
ity in process, with the upright position guaranteed, with the final
emancipation of the hand a certainty, the ultimate instrument for extending
the boundaries of the neokinetic sphere was at length assured. Too niueh
emphasis cannot be laid upon this decisive change in the two branches of the
orthograde division of the primate stem. In consequence of it, the members
of one branch retained so much of their arboreal specialization that they
continued to be occupants of the forest. Quite the contrary is true of that
branch which finally began to stand upright and go upon two feet. Through
it, the neopallium now proceeded to externalize all of those potential resources
which had so long been held in reserve awaiting the arrival of tliis ultimate
manual equipment. From Pithecantluopus and the Dawn man, from Heidel-
berg man and the Neanderthal, through all of the achievements of Homo
sapiens, the human race has set the full imprint of man's past and contem-

INTERNAL STRUCTURE OF THE BRAIN STEM 1043

poraneous record in the vast sphere of neokinesis which has been created
as the product of his hands.

RELATION OF MAN TO APES

These are the conclusions drawn from the accumulated evidences con-
cerning an evolutionary process in the brain of the primates. They recognize
the development of neokinesis in its several modifications as the keynote of
mammalian difTerentiation. They envision the process of selection and
evolution wherefjy this new type of motor acti\ity, seeking its fullest expres-
sion, at length found in the primates those structures from which to develop
the achievement of human neokinetic expansion. They take full account of
all of the intermediate simian steps in this process, but in no way denote or
imply a direct ancestral descent of man from any of the modern apes. In its
brain each one of the primates below man has, in its turn, borne the impress
of the effort to advance the cause of neokinesis. For this reason, if for no other
reason, each infrahuman primate gradation is important in the evolutionary
picture. It demonstrates the various attempts at progress showing in
what particulars they succeeded and also by just how much they fell
short of attaining the final goal. To consider any of the living apes the
possible ancestor of man is an inconsequential, trilling and incomplete view
of the situation which requires a much more extensive understanding of the
biological process for the complete appreciation of its significance. It does not
seem sufTicient to linger among the modern apes in search of our ancestors.
These animals belong to families totally divergent from man. They have
become most effectually arborealized, have ascended well up into the trees
where doubtless they will remain quite as unconcerned in the origin of man
as they are innocent of participation in it.

\\ e are wise if we turn our attention not to these simians, but rather
to the generalized mammalian ancestors from which both apes and man

1044 EVOLUTIONAL MODIFICATIONS

took origin, to tliat stock w liicli ma\ he traced, as Huxley and others main-
tain, to the organization of some lo\\l\' mammal such as thc' tree-shrew
(tupaia). Nor is there reason to pause at this point in the long hue ol descent.
Looking still furtlier back into the ]3ast, it is possible to recognize those
premammalian reptiles from which tlu' mammals uncjuestionably descended,
as well as their progenitors deri\ed Irom those low Ie\els ol xertebratc
organization which gave rise to the great Mesozoic reptilian orders.
It is indeed the a]i])reciation of this long ancestral line in all the \arious
modifications ol its many geological phases that gives the proper \ahie to
the e\'olutionarv process. Perceived in this way, it is possible to sense the
lull force ol the impetus in that irresistible momentum w hich has carried the
great vertebrate ph\ lum upward and onward through the ages and may still
carry us onward.

This is a conception that should make an urgent appeal for thoughtful
consideration regarding lurther possible readiustment ot human behavior.
It is a ^•Iew■ ol lite which requires lor its acceptance real powers ot vision
combined with an open attitude ot mind. For now, as in the past, intolerance
may resist as rude intrusion any trespass upon its ancient and cherished
delusions, preiudice may reject as worthless what it has not itscll conceixed
as true, conservatism may urge a wai"\ hesitation m the acce]:)tanee ol broad
conclusions ol an\ kind. But these facts, corrt'lated here, perhaps tor the first
time, and standing alone w ithout the aid ol eommentarv or special interpreter,
speak in no uncertain terms of a structural iintoldmg in the brain ol primates
whose e\'olutional signilicance may be seen in the progressne extension ol
their behavioral ca])acities. In this as])ect these factors may appear merely
as a conventional formulation of scieiitilic deductions. They may fail entirely
to create an impression of the actual dxnamii- force which lies behind tlu'in.
It is for this reason and by \ iiiiu' of ha\ ing essa\ ed to aiisw er so maii\ (|u cries,

INTERNAL STRUCTURE OF THE BRAIN STEM 104,-

that the writer \vv\s pvwilv^j^vd to ask at|iu'stii)n ol his own. It touches a
\'itall> iiii]j()rtant ])rohk'm, and nia\' he plirased as hillows:

Is there still a possil)iht\' ol lurther e\()l\]n<i; in the cIe\elopinentaI
process so clearl\- si't-n ni tiu' brani ol prnnates, so ol)\iously reaching its pres-
ent culmination ni the brani ol man -is there still a latent power m the
luiman brain tor the expression ol yet unsuspected j:)otcntialities and benelic-
ial progress?

This is a c|uestion w Inch may not be cjuicklx read or soon lorgotten. There
is an undeniable insistency about it as it calls attention to the palpable
impertections in human organizations. Answered in the negati\e, to what
continuing discouragement does it not commit the race; answered in the
aOirmatne, with what inspiring expectations max we not look to the luture
ol mankind! This greatest problem ol humanitx' is susceptible ol solution.
It awaits onI\ the intelligence, the patience, the persistency and the deter-
mination to sol\ e It.

REFERENCES FOR FURTHER READLNG

I. I^F.FERENCES TO SPECIES

Lemur

Beddard, F. E. Proc. Zoolog. Soc, London, 1894. (Brain of various species of lemur

described.)
Chudzinski, T. Sur Ics plis ccrebraux des icniurienscn general et du loris grcle en particu-

lier. Bull. Soc. d'Arithrop., Paris, 1895, s- 4, vi, 435.
Elliot, D. G. A Review of tlie Primates. N. Y., 1913, i, 130.
Forbes, H. O. A Handbook to the Primates. London, 1894.
Forsyth-NLajor, C. L On some characters of tlic skull in lemurs and monkeys. Proc. Zoolog.

Soc, London, 1901, p. 129. (Deals with os plarnnn and lachrymal in lemurs and

monkeys.)
Geoffrov Saint-Hilaire, E. Annales du Museum d'Histoire Naturclle. Paris, 1812, .\ix.

(Lemur albimanus mentioned.)
Gray, J. E. Catalogue of Monki\s, Lemurs and Fruit-eating Bats in the Collection of the

British Museum. London, i8~o.
Lesson, R. P. Manuel de Mammalogie ou llistoire Naturelle des .\Limmiferes. Paris, 1827.

(Prosimia mongoz.)
Linnaeus, C. Systema Naturae. Stockholm, 1740, 1-66. (Lemur mongoz first described.)
Milne-Edwards, A., and Grandidier, A. Histoire Naturelle des Mammifercs. Paris, i8"'5,

1S9-.
iMivart, St. G. J., and Mlrie, .]. antl M. On the Anatomy of the Lemuroidea. Proc. Zoolog.

Soc, London, 18-2, \-, ~.
MoTT, F. W. Localization of function in the lemur's brain. Proc. Roy. Soc. Lot^d., 1908, s.a.,

Ixxx, 136.
OsBORN, H. F. Dentition of lemurs and the systematic position of tarsius. Science, N. Y.,

1896, n.s. i\', p. "45.
PococK, R. I. On the external characters of lemurs and of tarsius. Proc. Zoolog. Soc, hondon,

1918, p. 19.
Schlegel, H. .Monographie des Singes. Leidc, i8~6.

Tarsius

Cl.\rk, \V. E. LeG. Notes on the living tarsier (tarsius spectrum). Proc. Roy. Zoolog. Soc,

London, 1924, Pt. i, p. 21-.
Cope, E. D. The lemuroidea and the insectivora of the eocene period of North America.

.4m. Naturalist, Phila., 1885, xix, 45".
Earle, C. On the adinities of tarsius. A contribution to the ph\ logeny of the primates.

Ibid., 189", xxxi, 569; 680.
Elliot, D. G. Bull. .Anwr. .Mus. .Mat. Hist., N. Y., 1910, p. 152. (Billiton Island tarsier.)
Ibid. p. I5I.

A Review of tiie Primates. N. Y., 1913, i, 7.

1047

I048 REFERENCES FOR FURTHER READING

Forbes, II. O. A Handbook to tlic Prinialcs. London, 1894, p. 121. (Tarsius luscus.)
Forsyth-Major, C. J. Proc. Zoolog. Soc, London, 1901, p. 138.

Gregory, W. K. The Origin and Evolution of the Human Dentition. Bait., 1922, p. 212.
HuBHECiiT, A. A. \\ . Tlic Deseent of the Primates. Prineeton Lectures, N. Y., 189-, p. 16.
Hunter, J. L The oculomotor nucleus in tarsius and nvctlcebus. Brain, London, 1923,

xlvi, 38.
Lesson, R. P. Species des Maminlieres Binianes ct Quadrumanes. Pans, 184.0.
Lyon, ^L \\'. Proc. U. S. Nal. Mus., Wash., 1911, xl, 136.
Mathew, VV. D., and Granger, W. A revision of the lower eocene Wasatch and \\ ind River

faunas. Bull. Amer. Mus. Nal. Hist., N. "S., 191 5, xxxiv, art. Iv, 446.
Meyer, A. B. Abhamll. u. her'ich. d. konigl. zoo/, u. anthrop.-ethnogr. museum. Dresden, 1894,

no. I, p. r; 1898, no. i, p. 9. (Philippine tarsier.)
Ibid., 1897. (Sanghir tarsier.)
.Miller, G. S. Proc. U. S. Nat. Mus., Wash., 1910, \\\i\, no. ^",7. (Tarsius fraterculus,

from Bohol, Philippine Islands.)
OsBORN, H. F. Dentition of lemurs and the systematic position of tarsius. Science, N. ^ .,

1896, n.s. i\-, p. -45.
Smith, G. E. The relationship of lemurs and apes. Proc. Zooloii. Soc, London, Oct., !()25.
The position of tarsius. Nature, London, 1909, Ixxx, 38.

Contribution to discussion on tarsius. Proc. Zoolog. Soc, London, 1919, p. 46 j.
On examples of tarsius from Sarawak. Ibid., 1921, p. 184.
Son.ntag, C. F. The morphology and evolution of the apes and man. London, 1924, p. 326.
Storr, G. C. C. Prodromus metliodi mammalium. Tubingae, i~8o.
Thomas, O. Trans. Zoolog. Soc, London, 1896, xiv, 381. (Philippine tarsier.)
WooLLARD, H. H. The anatomy of tarsius spectrum. Proc. Zoolog. Soc. London, Oct., 1925.

The cortical lamination of tarsius. J. Anat., London, 1925--26, Ix, 86.
\\ ()()D-Jom:s, F. I he problem (if man's ancestry. London, 1918.

Marmoset

Beevor, C. E. On the course of the fillers of the cingulum and the posterior parts of the

corpus caliosum and fornix in the marmoset monkey. Phil. Trans., Lond., 1891, clxxxii

(b), 135-199-
Elliot, D. G. A Review of the Primates. N. Y., 1913.

Geoffroy Saint-Hilaire, E. Annales du Museum d'llistoire Naturelie. Paris, 1812.
v. Hu.mboldt, a., and Bonpland, A. Recueil d'Observations de Zoologie et d'Anatomie

Comparee, etc. Paris, 181 1-33.
Lesson, R. P. Species dc Mammiferes Bimancs rt Quadrumanes. Paris, 1840.
Linnaeus, C. Systema Naturae. Stockholm, 1-40, i-,-8. (Callithrix jacchus described as

simia jacchus.)
Schlegel, H. Museum d'llistoire Naturelie des Pays-bas. Leyde, 1876, p. 271.

.Mycetes

Demarest, a. G. .Mammalogie ou Description des Especes de Mammiferes. Pans, 1820,
p. 219.

REFERENCES FOR FURTHER READING 1049

Ellioi', D. G. a Rc\ icw of tlic Primates. N. \ ., IQ13, i, 2-7.

Geoffroy Saint-Hilaire, E. Memoires dc Museum d'Histoirc Naturello. Paris, 1829.

(Alouatta scniculus redcscribed as mvcctes clirysurus.)
Geoffroy Saint-Hilaire, I. Catalogue des Primates. 1851, p. ,2.
Gray, J. E. Aniials u)id mai>ay.ine 0/ natural bislory. London, 184,, \vi. (M\cctus villosus

lirst desc rilled.)
Catalogue of Monkeys, Lemurs and Fruit-eating Bats in tiie Coileetion of the British

Museum. London, 18-0, p. 40.
Lesson, R. P. Species des Mamniifcres Bimanes et Quadrumanes. Paris, 1840, p. 1 1~.
ScHLEGEL, H. Museum d'Histoire Naturellc des Pays-i)as. Lcydc, i8~6, p. 156.
Spix, J. B. Simiarum et Vespertilioiiuni Bra/ilensiuni Species Novae, etc. Monachii,

1823, p. 3,-.

CynocL'pbalus Haliu in

Cu\'iEH, F. Memoires du Museum d'Histoire Naturellc. Paris, 181-, i\-, 41Q. (Papio cyno-

cephalus descril)ed as cynocephalus babum.)
Demarest, a. G. Maninialogie ou Description des Especes dc Manunifcres. Paris, 1820,

p. 68.
Elliot, D. G. A Rc\ icw of the Primates. N. ^ ., iyi3, ii, 13".
Gray, .]. E. Catalogue of Monke\s, Lemurs and Fruit-eating Bats in the Collection of the

British Museum. London, i8~o, p. 35.
Major, l\. C. Observations on the brain of the Chacnia baboon. ./. Mcnl. Sc, London, \S~(>,

\xi, 498.
MiNGAZZiNT, G. Beitrag zum Studien des Verlaufes einiger Bahncn des Zentrahier\cnsys-

tems des C\noeephalus Papias. Jabrb. f. Psychiat. u. Neurol., Lcipz., 1921, xii, 71-92.
MiVART, St. G. .1. Prac. Zijolog. Soc, London, 1865, p. 558.
Peters, \\ . II. C. Naturwissenschaftlichc Rcisc nach Mossambique. Berlin, 1852.

Macacus

Anderson, J. Anatomical and Zoological Researches Comprising an Account of the Zoologi-
cal Results of the Two Expeditions to Western Yunnan, etc. London, iS-'S.

Blanford, W. T. Proc. Zoolofi. Soc, London, 1887, p. 625.
Mammalia. (The Fauna of British hidia.) London, 1888-91.

Clarke, R. H., and Henderson, E. E. Atlas of photographs of the frontal sections of the
cranium and brain of the rhesus monkey (macacus rhesus). Johns Hopkins Hosp. Rep.,
i?alt., 1020, spec. vol. liii.

Ut Haan, J. A. B. Experiments on \ision in monkeys. 1. The color sense of the pig-tailed
macaque. J. Compar. Psychol., Bait., 1925, \, 41".

De.marest, a. G. Mammaiogie ou Description des Especes de Mammiferes. Paris, 1820,
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INDEX

- -ootd tba.' page

A:

/CENS nerve, function oU 54, Ji2, 592
in gibboo, 435

in iemur. 54, a, jTt 84

in man, 819, Sao

znarmosrc i~l

mycetes. 222

in orang, 5 1 ~, 520

in taisus, 118, 119
Abdooens nudeus. in chimpanzee, 5~4, 595

in dog-beickd inaiioon, 321, jii, Ji6

function of, 3"t9, 819

in ££i>boEi, 435, 455

in gorilla. 6-2, 697

in man. -99, 819

in marmoset, i~i, 186

in m>xetes, 236, 242

in orang, 499, 520, ;J43

in Prtbecus rhesus, 3-8, 379

in tarsrus, 114-11"
Accessory olri"ary nuclei, in marmoset, 1S4

in mycetes, 2!~— 220

in Prii>ecus rhesus, 3~4
Aijieokan Period, -53, 908, 931
Acoustic area in man, %jr
Acquired reactioas in tardus, 87
Acrognosis. 881, 916
Adapis, 954

Adaptability in marmoset, 1-2
Adaptation, in balancing mechanian, '14, 998, 999

bearing oi, on e^-cJution, -15, 998, 999
AgricoiraTe, introduction of, "45, "66, 932
Akeic>-, 00 gorilla. 631, 632
Ala cinerea. See Inferior foirea t-asi.
Aiar plates, in infraventricular ic^ioa of oiilongata
in chimpanzee, 5^3

in doe-^>eaded baboon, 302

in gibbon, 431

proprioceptive rrJnmn in, 431

in aoiilla, 655

in man, "98

in orang, 509

in Ktbecns riiesas, 361

Alooatta senicalas. See Mycetes seniculus, 196
Ansencan Indian, art of, "64, -65
Amphibia, 260, 2"6

predo€ninance of coQicoli in. 1033
.Anapitomorphos, genus. 92, 93, 94
.Andaman Islanders as pre^jaleoliihic, — i
.Anterior commissure in lemur, -x>. ~i
in man, S36
in marmoset, i8i, 182
in m:.xe:es, 230, 231
in tarsias, 132, 133
function of, (xr

in chimpanzee, fxr
in dog-headed liei»>n, 333, 331
in gii>bon, 446
in gorilla, 684
in Phjjecus rhesus, 388
Anthony, 901

.Anthropokl characters in grh^op, 28-
Anxhroj>5idea, 11-, 153
catarrtiine dri-isaon of, 95
end brain, basal ssartace of. 298
floor of fourth ventricle in, 100
<J£actc»y invtjutjon in, 96
pl£t3~rrhine divisioc 01, 95
suborder, divisoQS in, 21, 8j, -31
variations in hallux and poQes in, 24
.Anthropoids, himer, 2SS
mentalitv" of, -59

vermal ridgepole disappears in, 416
.Anti-huuLan serum, ~
.Anti-sera as test of relatxj«ishn>, ~
-Ape, relation of, to man. —33

dynamic forces involved, 1044
evxiently not that of direct ancestor, 1043, IQ44
long ancestral Enc for both, 1044
.Ape-man of Java, 868; See oiso PithecantJiio|>as

erectas.
.Arachnoid. 862

.Arboreal habits, bearing of, on cerebeOum, 9~5
life of babocm, inireqoent, 31-

fvf gtKhftn ]-

IO-8

INDEX

Arboreal life of gibbon, bearing of, on forclimb
and hand, 424, 425, 430
of gorilla, tcrrestrio-arboreal adaptation of, 669
of lemur, 12, 27, 50, 51
of Pithecus rhesus, 377
purpose of, 14
psychic influences from, 1 5
recession in, significance of, 18
relation of, to quadrunianal characters, 14, 669

to vestibular complex, 66~, 669
significance of, 14, 15
Archaic constituents of brain, evolution in, 682, 714
Archipallium, 944

Arciform nucleus in chimpanzee, 586, 617
in gibbon, 450
in gorilla, 672, 692
in man. 808, 81 1, 823, 83-, 843, 849
in orang, 515, 539
in Pithecus rhesus, 398
Area acustica, definition of, 799
in human brain, 799
in orang, 543
Area plumiformis, in gorilla, 656

in human brain, 799
Area postrema in gorilla, 656

in human brain, 799
Asiatic pygmy as prepaleolithic, ~~l
Ateles, spider monkey, tail of, 191, 203, 208, 210, 213
Auditory eminence in Neanderthal man, 903, 906

relation of, to speech, 903
Auditor^- function, relation of, to speech, 883
Auditory mechanism, in tarsius, 120, 125
Auditory nerve in chimpanzee, 574. 384. 587, jQi
in dog-headed baboon, 316
in gibbon, 418, 419, 431, 432
in gorilla, 672
in Lemur mongoz, 50, 52
in man, 813, 814, 841, 842
in marmoset, 170, 171, 174
in mycetes, 220, 222
in orang, 513, 515, 516
in Pithecus rhesus, 373, 374. 3~6
Auditory sense in chimpanzee, 575> 600
as indexed by inferior colliculi, 602
less important than in lower primates. 600
in dog-headed bab<jon, 328, 46*)
evolutionary changes in, 2-6, 2-7, 2-8, 468
in gibbon, 439, 469

primordial stations in, 439, 469
in gorilla, 679
relation of, to expansion in temporal region, 6-9
Pages I 474 are in Volume I,

Auditory sense in gorilla, telencephalization of, 679
in lemur, 48, 49, 175, 278

in man, relation of, to cerebral cortex, 2~, 278, 881
in marmoset, 164, 175, 178
in orang, 501
in Pithecus rhesus, 373, 379, 469

reflex action in, 379, 383
relation of, to cerebral cortex, 333

to inferior colliculi, 125, 164, 174, 178, 2-7, 328,

383, 469, 470, 525
to lateral fdlet, 525
to reflex action, 278

comparison in lower primates and man, 2-8
to superior olive, 516
to temporal lobe, 277, 383, 790
to trapezoid body, 516
to tuberculum acusticum, 48, 374
Aurignacean Period, art of, 762-765, 920, 931

tools of. See Cro-Magnon, 759-766.
Australian aborigines, 742
natives, art of, 764, 765
Automatic associated control, in marmoset indi-
cated by basal ganglia in forebrain, 1-6, 177,
179.528
movements, modification of, 13

probable relation of, to substantia nigra, 64,
68, 176, 177, 227, 332, 389, 528, 682
relation of, to globus pallidus, -i, i":^, 181
in tarsius, importance of, 113, ii~, I2~
reflexes, in lemur, 278

relation of, to auditor}' organization, 175, 278
to inferior colliculi, 227, 278
to olive, 168, 300

to posterior longitudinal fasciculus, 4~
Avian blood tests, 10
Azilian Period, "62, 931

DABCX)N, dog-headed, 12, i", 287-289, 430,441
^— "^ behavior, 289-294, 317

brain of, 295-298

callosities in, 289

cochlear complex of, 343, 619

color in, 289

digits of, 290, 292, 293

general appearance of, 289-291

habitat of, 290, 292, 293. 294

limbs of, 290

locomotion of. 290, 294, 302

lowest of old-world monkeys, 294

measurements and indices of. 204. 2<h

posture of, 294
pages 475-1120 in Volume II.

INDEX

1079

Baboon, dog-headed, resemblances to dog in, i-,
280
tail of, 289, 302, 303
terrestrial habits of, 17, 289
vision of, 294
Baboon, yellow, habitat of, 294
Balancing in lemur, 48, 50, 53

in man, relation to vestibular nuclei, 261, 799, 815
in marmoset, 170
in mycestes, 219, 263, 264, 714
in tarsius, 114, 115, 120, 714
proprioceptive organization of, 260-262
relation of, to Dciters' nucleus and nucleus of
Schwalbe, 114, l-o, 219, 262, 263, 374
to erect posture, 264
to inferior colliculi, 262
to prehensile tail, 263

to vestibular area, 48, jo, 219, 260, 261, 513
Balancing mechanism, as affected by aquatic,
aerial, and arboreal conditions, 260, 264
in chimpanzee, 574, 712

as indicated by vestibular nuclei, 574, 585
relation of, to light weight of body, 585
in gibbon, in proportion to vestibular area, 432,

713
in gorilla, 668, -12

relation of, to behavior and locomotion, 668,
669, 670
high organization of, and semicircular canals, 260
in intermediate primates and great apes, about

on a par, 464, 713
in man, 799, 811, 812, 813
in orang, 513, 514, 712
paleokinetic organization of, 823
in Pithccus rhesus, 362
preeminence of gibbon in, 464, 465, 713
Basis pontis, 59, 60, 172

in chimpanzee, 591, 595, 600, 603
in dog-headed baboon, 325
in gibbon, 438, 441
in gorilla, 6~3. 690
in man, 819, 820, 823, 826, 830
in marmoset, 179

in orang-outang, 519, 520, 523, -525
in Pithccus rhesus, 3~, 380, 383, 385, 389
Bats, 260, 1039

von Bechterew on inferior olive. 247
nucleus of, in chimpanzee, 619

definition of, 820

in dog-headed baboon, 321. 322, 343

in gibbon, 4j2

Pages 1-474 are in Volume 1,

von Bechterew on inferior olive, nucleus of,
in gorilla, 694
in lemur, 57, 60, 61, 80
in man, 820, 852, 8,8
in marmoset, 188
in mycetes, 222, 236, 238
in orang, 541

in Pithecus rhesus, 381, 400
Behavior, in dog-headed baboon, 458, 459
fundamental comparisons of, 13
in gibbon, 458
in gorilla, 6~6

bearing of, on balancing mechanism, 66g
important factors in, 13, 213, 266, 267, 364, 668
intelligent, in chimpanzee, 594
in Pithecus rhesus, 3~, 458
progressive development of, 13, 18, 266, 364
relation of, to differentiation in the hand, 213, 666

to expansions of the brain, 267
significance of, 13, 18
Behavioral reactions in intermediate primates,

decisive advance shown by, 4-2, 4-3
Bctz, giant cells of, 1010

Binocular and stereoscopic vision, development of,
13, 280, 281
relation of, to oculomotor decussation, 280, 388
to nucleus of Perlia, 281
to oculomotor muscles, 280
to primarj' position of Listing, 280
to skilled acts, 281, 282
Binocular vision, in higher anthropoids, -22--24

in lemur, 27, 67
Bipedal locomotion, 264
Birds, 260, 276
epiglottis of, 41 1

compared with gibbon, 411
optic lobes of, 279
paleokinesis in, 1038
predominance of colliculi in, 1033
Bischoff, nucleus of, absent in chimpanzee, 580
gibbon, 424
orang, 506
tarsius, 105
in mycetes, 213, 215, 259

relation of, to development of tail, 236, 259, j8o
Blood, relation of, to evolution. 7
tests of, in tarsius by Clark, 89
Blumenau, ancillary nucleus of, in chimpanzee, 583
description of, 255
in dog-headed baboon, 310
in gibbon. 424, 42^. 428. 429
pages 475-1120 in Volume IL

io8o

INDEX

cus of, relation of, to fore-

;and, 429
'tion. 420

in gorilla, 66 j
in lemur, i^
in man. -
in marmot-:, i ^
in mycetes. 215

■41, 842

in Pithecus rhesus, 369, 3-0, 3-1, 3-2, 393, 463
in tarsius, : 1 3
Bony capsule enclosing brain, susceptibility' of, to

effects of cerebral growth, 862
Bony sjstem, as witness to evolutionan.- kinship,
in size and shape of skull, in skeleton of limbs, 10
Boule, 89-

Boume method of reconstruction, -3
Bow and arrow, -60

Brachium conjuncti^■um posticum in chimpanzee, 575
in lemur, 64
in man, 800
in marmoset, 177, 1-9
in Prthecus rhesus, 363
Brain, basal structures of, evolutional significance of,
illustrated by deflorescence of rhinen-
cephalon, 9"'0, 971
illustrated by increase in angulation in rela-
tions between optic tract and chiasm, 972
illustrated by orbital concavity, 969
and intcrorbital keel, 969
basal surface of, in gorilla, relation of optic

nerves and tract to optic chiasm, 650
in chimpanzee, measurement and indices of, 566
convolutional and fissural pattern of, in chimpan-
zee, 568
in dog-headed baboon, 295
in gorilla, 647, 652
in orang, 493
in Pithecus rhesus, 357
in dog-headed baboon, 295-298
evolution, metric evidence of, 887, 922-923, 950-

952
of gibbon, 413-456

compared with baboon, 414
measurements and indices of, 412, 41 j
of gorilla, measurements and indices of, 644
gj'rencephalic, of orang, 493

human, advance in, toward neokinetic control, 797
convolutional complexity of, as compared with

simian simplicity, 789
features of, showing greatest evolutional
significance, 886, 954

Pages 1-474 are in Volume I,

Brain, human, lobation of, comparison of, — S-781,
-84, -85
with that of anthropoids, — 8. -Si. -82. -S3.

784, 9+5-94"
motor areas of, extension of, 882
neural specialization in temporal and parietal

lobes, -90
olfactor\' sulcus, prominence of, 94-
orbital concavity in basal surface of, 790
progressive development of, 800, 948-991
surface expansion of, relation to neopallium, 795

two main features of, ; — 8
t\"pe of lobation in hemispheres of orang, 493
ventromedian sulcus in, -95, 800, 804, 806, 808,

849

weight and indices of, in different races and
primates, 7~, "78, 950-952

witness to evolution, 3, 11, 12, i", 18, 791, 800,
948
of lemur, 29-34
of marmoset, fissural pattern in, 15-, 158

lobation in, 158-160
of mycetes, 191-242

measurements and indices of, 201, 202
of orang, 492-544

measurements and indices of, 492
of Pithecus rhesus, compared with that of baboon,
355-357

convolutions and lobation of, 357

surface of, 356

tjTJe of, 355
primate, structural changes in, relation of, to

behavior, 13, 18, 267
simian type of, in dog-headed baboon, 357

in Pithecus rhesus, 357
surface in chimpanzee, resemblance to man, 567
of tarsius, 95-98
vertebrate, structural substratum of, exists in

rudimentarj' form, 1032
volume of, in ape-man, Dawn man, and gorilla, 887
Brain stem, in chimpanzee, 571-607
in dog-headed baboon, 299-334
in gibbon, 417-446

precision in markings on, 417
in gorilla, 653-683

significance of caudal sections of, 662-663
human, comparison of, with that of gorilla, 800

deliniteness of the markings, 795, 796

internal structure of, 800,
in lemur, 34-71
in marmoset, 164, 183 190
pages 475 1 120 in Volume II. ,

INDEX

loSi

Braia arm, ia mycetes, 20^231
inorang, 4W-53»

itstmbizact xa hmnan, 533
■ - -IS, 359

:"- -wTtli krtrer pthmaes, 35^389

^ - n in, c^ dsva aad

e-. -i in, 5I5>3

-TrTf irf stTOCtuies in, 5r"5-9S4
-.... .: ^rsanizatioo in, 993, 9^
-.2 dennitcness in cranial oer-.-e nociei,

BietJcnlar {omiatioo, 995

internal stractare oi^ stdzxKzaoBS in, m v^cstSia-

^ertittiaticici in, in cerebral cietfam-
-- Pjiranoid, 5r5, 5r6
rdztJoQ of, to ne» motor gfsrrm, 9-5, 5r6

to f»'- • ' - .'/--

to - •' fmm^n Swyc, grS

atrranitjes, 5r<5

pr - % ber»eai tie doi5aI

r of erojatioe ia, ia pomSe
in taisos. 99-101

priaiitjve rrx^^mm-str^^n 2S tO rrf-^ nxy^r ■^■■a^ lOI,
IQ2

vEctral soruce c^ a<fvect of manoji^Kjo onfecs,

-^iQr»Ti, 1024

:s in, hov depfTirifTg, 10Z4, lorz^
;^r.,z::::;^3rFe advance ia, in Bfntrwac T^<Tirr».

1025
reiatacic of lacrxmoz/x fnscaoD to, 1124
Bnoca. diifocal ?»r*i-= of. in tsxsiES, 9-
Brocz's ojc-4-ciiraoc in innnan Braia, -SS, S&3, 901
5-i! ilso Motor jOKcii cesxer.
HHI Mrnir, 909
" — - -^se, -45, -^, ^2
BrSnn race, 918

" salens in diimpiiEBee, 5~4

:«{ iiiixoc, 3C1PJ, 322

in somia. 6^ 6-2

in lemnx. 36, J4

in m.-'p, -'06. Sao

in rrtarcaaset. 162

in oran^ 409. 530

in Ktneojs rfcesos, 364

in Taisas spectrEm. 1 24

Btnlbos oHsctonos. See oiw Offacsorr fxalb.
ia mariBoset, j6<>
ia njyoeccs, ir^

prooooQced in tarsus, i^, 9"
Rardsadi, crAamn 'A. in cfaimpenzee, 5"^ 580
in ciog-tieaded belyyjo, 305-313
in gshboQ, 422-431, 4JO
in ^jfSIa, 696, 66», 6^
aagmectaaioe of, 6,6
in great anTrrotxwis and trt^^n, 5*^
in Lesnnr moo^oz, 42-49, ~4
in Itower primates, 5-^
in man, -1^ ^^3, Soi, 840
in mamKftet, 164-1%
in tnycetcs, 205r-2i3, 233, ^59
in caraag-owtaas, J03- jOii, 5ii»
in Pfebecas rfaesas, 366-3-0, 355
proeressr^'e wpersaoci in, -to, —11
rrferirie of^ to devektpeiaesit of >'c>TiMfj 210, 21^ 2j^

^i»,-?63

intaisES. 102, 104, i«>j, ic^ £11—113, 149
BonWf macfess of, in caiaEa&ezee, f-€^3^,6lo-6l8

coeScaesEts of, in LoHner pcisaatjes, ijS, 2^

is feB>^.>T antferooiMGs, ~<J^
oxss&i^yB of ttT-gfrj-r mitn menaaaiigTP- pcoasaSES
as to, -'19

witfe loiier ut?iiii-j'7f^ as to, -i©
in dce-iieaded baboos, 50^315, 33j-Jfl6
is s3)irj«i, 418—4:^ 44-"— 455
in SDrSa, %>-6>i

in imtemecEate pricn^tes. cxteSoemt oC jfe jfit
ia leijsax, .^-49, -4^-83
ia cnan, Soki. Sri, S4&, %r
in mama-jset, 165-169, 183-189
in nrrcetes, 215-2x8, 233-242. 2^9, ~lO
is onn^ 5014-509, 534—543, -»»
m Pfefiecas rfeesus, 360-3-4, 3^^1-403

fC^atioG of. to iai&S!£FV£lieXS of ^-■<"^mnri>n sjbC TiTT-lrFj

43. j6^ loj, 1061. 255-359, .^3, -TBa, 71*
to kcaasQCaoQ- 106. !<)>-, ~i<a
iataraas, loi, 1061, loS, 109, iii— 113, 1^8-1*5

B<srtresses in p:iGt3<e gray nrniriTiT- ee t-imnnF, 82
in 'j.t.raacs^ 18-. i38
is snycetes, 23-. 23S
^fc»<=-*^ asd Ls-teraL nE ^■T!AT,iB..i^>t»ffi^ir_ 1S15— ^fS^ ^C3^
ns dcg-frrrwfed baixniii, 340. 342, 345

BE rihtrwn 451. 4^

OS gjc^i? . 6co— 695

HE oc^us^^ 53^~>a2

in PfefeeCES rioesais. 4<M

I082

INDEX

c

AJAL, on decussation, 421

Calcarine (visual) area in mjxetes, 227

fissure in mycetes, 204
Callithrix jacchus, 12, 153-190. See also Marmoset.
Calvarium, cast of, from ape-man of Java, 869
Candler on the hoolock gibbon, 410, 41 1
Caput of substantia gelatinosa trigemini, in gibbon,
448

in gorilla, 687

in -Macacus rhesus, 304

in orang, ,-34, 535
Carnivores, 7, 128, 6jo, -47, 755, 970, 1007, 1039
Carving chisel, development of, 761
Casts, endocranial, 862, 891, 904
Cat, 7-9, 1 10, 114, 121, 124

digits of, sensory representation of, 881
compared with those of man, 882

experiments upon, 248, 307

increase in, of inferior olive and olivo-cerebcllar
connections, 1031

Pike on, 248
Catarrhine monkey, 22. See also Old-world monkey,

289, 3,-0
Caudal development, etfect of, on sensibility, 212
Caudate nucleus. See also Nucleus caudatus.

in lemur, 70
Cave dwelling, bearing of, on human progress, 902
Cebidae, family of Anthropoidea, 16, 21, 22, 96,

'91. 233. 959. 981
Cebus, type of .Vlycetes seniculus, 197
Central canal of midbrain in chimpanzee, 578, 621
in gorilla, 697
in man, 802, 806
in orang, 509
Central gray matter, in chimpanzee, 576-584, 591-
601, 609-622
in dog-headed baboon, 305-316, 322-330, 340-347
in gibbon, 421-427, 435-456
in gorilla, 658-676, 679-697
in lemur, 42, 44, 46, 56, 57, 60, 61, 62, 64, 66, 75,

80, 81, 82, 83, 84
in man, 800-806, 810-814, 819-824, 829-831, 840,

842, 848, 857-859
in marmoset, 164-167, 173-179, 183-190
in mycetes, 211, 215, 222, 224, 225, 226, 227, 233,

234, 239, 241, 242
in orang, 503-526, 533-544
in Pithecus rhesus, 365-371, 381-392, 402-404
in tarsius, relation to rotation of head, 102-113,
120-123, 126-151

Pages 1-474 are in Volume I,

Central nervous system, 2(>C)

in dog-headed baboon, 299, 310

in gibbon, 28-

in gorilla, 674

in mammals, comparison of, with infra-mam-
malian orders, 519
differentiation in, relation of, to appendicular
specialization, 519

in orang, 533

in Tarsius spectrum, low organization of, i lO-i 13
Central tegmental tract in chimpanzee, 591

in dog-headed baboon, 313, 315, 326, 327, 330

in gibbon, 431, 432

in Lemur mongoz, 50, 52, 55, 60, 61, 62, 66

in man, function of, 814

in marmoset, 170, 171, 173, 176, 178

in mycetes, 220, 224, 226

in Pithecus rhesus, 381, 382, 384, 386

relation of, to olive, 248, 249

in tarsius, 114, ii6, 121, 123, 128-133
Centrum ovale, 898
Ccphalogjric action, predominance in tarsius, 112

relation of, to ventral gray matter and spinal
accessory ncr\'e, 112
Cerebellar brachium in gorilla, 690
(-erebellar commissures in man, 822
Cerebellar concavities of basal surface of brain, in
chimpanzee, 570

in dog-headed baboon, 297

feature of primate brain, 9-2

in gorilla, 646, 650

two factors of decrease in, 650, 65 1

in Hylobates hoolock, 413

in lower species, 652

in man, 972

in orang, 496

in Pithecus rhesus, 3,7
Cerebellar control in gorilla augmented by rapidly

increasing demand, 653
CJerebcllar nuclei. See also Nuclcusdentatus, Nucleus
embolilormis. Nucleus globosus, 264.

control of. over skilled acts, 377, 465-467

in dog-headed baboon, 318, 319

in gibbon, 433

in gorilla, 667, 670

in intermediate primates, 463-465

in lemur, 51, 52

in marmoset, 171, 172

in mycetes, 219

in orang, 51 5

in Pithecus rhesus, 3~5— 377
pages 475 1120 in Volume 11.

INDEX

1083

Cerebellar nuclei, in tarsius, 1 17-120
Cerebellar peduncles, in gibbon, 418
in marmoset, 163, 239
middle. See Middle cerebellar peduncle,
superior. See Superior cerebellar peduncle,
three, as index of power of coordination, jj
Cerebellum, 249-253, 265-2-0, 274, 280, 414-416,

600
in chimpanzee, 5~i, 586, 590

indications of, as to coordinative control, 590
definition of, 318
in dog-headed baboon, 297-302, 312 319, 322, 323

lateral lobes of, 298, 320, 323, 325
in gibbon, 414-416, 430, 433
in gorilla, 652, 653, 667, 671, 674

expansion of, 676
hemispheres of. See lateral lobes of.
latent potentiality of, in human brain, 81-
lateral lobes of. 58, 98, 118, 24-. 248, 26-, 2-5,
814

in chimpanzee, 5-1, 5~4

etfect upon, of disease or injury, 816, 817

function of, 252

in gibbon, 416

in gorilla, 651, 652
expansion of, 653, 6~i

in Lemur mongoz, 51, 52

in marmoset, 161, 163

in mycctes, 206, 207, 221, 223

in orang-outang, 498, 5 1 2

in Pithecus rhesus, 358, 389

relation of, to arms and legs, 53, 320, 519, 817
to coordination, 223, 252, 265
to inferior olivarj' nucleus, 253
to nuclei dentatus and emboliformis, 265, 266

variations in, 320
in Lemur mongoz, 30, 37, 58, 83
of man, function of, 793, 814-816, 822

general superiority of, -94

inferior vermis in, 794

lateral lobes of, 794, -95

posterior cerebellar notch in, 794

progress in surface of, 793, -94
in marmoset, significance of size of, 159-161, 163,

179
in Mycetes seniculus. 204-210, 219, 220
in orang, 493, 49-, 515
in Pithecus rhesus, 35--361, 3-6, 3-9
relation of, to nucleus ruber, 270

to posture, 16
in tarsius, 92, 893, 94, 96, 1 18

Pages 1-474 are in Volume I,

Cerebellum in tarsius, indication of lateral cerebellar
lobes, 1 18

primitive character of, 98, 1 18
Cerebral cortex in chimpanzee, 593, 601

visual area of, 605

voluminous connection of, with cerebellum,
bearing of, on skilled acts, 593
in dog-headed baboon, 301, 304

relation of, to auditory sense, 328
lissencephalic in Tarsius spectrum, 96
in orang, 529

relation of, to behavior, 529

to pallio-ponto-cercbellar fiber systems, 529
as origin of transverse fasciculi of pons, 57
in Pithecus rhesus, 364, 38<>
relation of, to auditory sense, 328, 333

ro cerebellar hemispheres, 266

to pallio-ponto-cercbellar system, 2-4, 304

to pontile nuclei, 272

to skilled acts, 304
Cerebral fissures, in primates, evolutional signifi-
cance of, 964
prototype of, in lemur brain, 954-<>58
two contrasting tendencies in early dltTerentiation
of, 958, 959

in intermediate primates, 960, 961

in large anthropoids, 961-964

in new-world simians, 959
whole series of steps in evolution, (;64
Cerebral hemispheres, 267, 277
in chimpanzee, 56-

connection with cerebellum, 58, 266, 274
in dog-headed babcwn, 322
evolutionary significance of, iS(), 4-0
in gibbon, 412-416

comparison of, with macaque and baboon, 414

fissures and lobation of, 414, 415
in gorilla, 684
human, --8, 793

dis;ippearance of sulcus simiarum in, --9, 783

expansion of, -94, -95
intermediate in lemur, 31
in marmoset, 161, 164
in mycetes, 204
in orang, 493, 494, 501
in Pithecus rhesus, 389
primitive nature of, in tarsius, 95, 96, 125
relation to pallio-ponto-cerebellar fibers, 266, 2-4

to volitional movements. 329
sensory supersedence by, 329
pages 475 1120 in Volume II.

1084

INDEX

Cerebral lobes in primate brain, clilliculties in way of
quadrilobular identification, 964, 965
evolutional significance of, 964
frontal lobe in, indices of, 966-968
Cerebral orjjanization in Tarsius spectrum, a stepping

stone in evolution, I2j
Cerebral peduncles, ,7, 230, 272, 274. 2-5
in chimpanzee, ^~i, 600-606
in dog-headed baboon, 300-304, 325, 330
in gibbon, 418-421, 441
in gorilla, 657, 676-684

bearing of, on skilled acts, 682
structure of, 682
in Lemur mongoz, 36, 38, 62, 63, 66, 68 \

in man, 792, 832, 850, 851
constituents of, 792, 832
function of, 797, 832

prominence of, 792, 796 ,

in marmoset, 162, t64, 176-179
in niycetes 208, 230
in orang, 500, 523-531

relation of, to behavior, 529, 682

size of basal portion of, to size of area in
cerebral cortex, 529
in Pithecus rhesus, 364, 385, 386, 389, 399, 401

bearing of, on behavior, 364, 365
relation of, to skilled acts, 164, 272, 364, 365
in tarsius, feeble development of, 99, 100, 127-131
relation of, to skilled acts, 127
Cerebrospinal fluid, 862

Cerebrum, sensitiveness of, equally to heredity-
chromatin and life environment, 12
susceptibility in, 12
tissue of, its high differentiation, 12
Cetacea, 7, 1039

Chaillu, Paul du, on gorilla, 627-631
Chellcan Period, 752, 931

culture, today, 771
Chimpanzee, 12, 22, 89, 477, 479, 487, 494, 497, 543,
908. See also Troglodytes nigcr.
behavior of, 545-566
Chica, 553

general description of, 545, 546
habitat of, 546

position among primates, 545
research on, 546-566
Sally, 565
species of, 546
Sultan, 547, 548
Susie, 547
Chisel, ^53

Pages 1-474 are in Volume I,

Chopper, 758

Circumferential fiber accumulation in Papio cyno-

ccphalus, 308, 309, 315, 340, 342, 345
Clark, column of, relation of, to dorsal spinocerebellar
tract, 252

to vermis, 253
Clark, Le Gros, on tarsius in captivity, 85, 86, 88

blood tests, 89
Clava, in chimpanzee, 5-2, 573

definition of, 655

in dog-headed baboon, 301, 302

in gibbon, 418, 419

in gorilla, 655, 656, 662

in human, 797, 798

in lemur, 38, 39

in marmoset, 163

in mycetes, 209

in orang, 498, 499

in Pithecus rhesus, 360-363

in tarsius, 99, 101
Cochlear complex in chimpanzee, 619, 622

dorsal nucleus of, in Pithecus rhesus, 400, 401, 403

in gibbon, 452

compared with dog-headed baboon, 452

in gorilla, 694

in man, 853

in marmoset, 188

in Mycetes seniculus, 238

in orang, 538, 541

in tarsius, 135-151

ventral nucleus of, in Pithecus rhesus, 400, 401
Cochlear nerve in lemur, 80, 81

in mycetes, 238, 239

in orang, 541

in Pithecus rhesus, 400, 401
Cochlear nuclei in dog-headed baboon, 316

in lemur, 73, 75, 77, 80

in man, 852

in marmoset, 188, 189

in tarsius, 145-146, 149
Collicular commissures in lemur, 81

in man, 858
Colliculi of midbrain. See also Inferior colliculi;
Superior colliculi.

in chimpanzee, 575, 605, 620

cocfTicients of, 278

delegation of function of, still in process, 277

in dog-headed baboon, 340, 344

in gibbon, 450, 454

in gorilla, 65-, 694
pages 475 1120 in Volume II.

TXDFA'

1085

Colliculi of midbrain in Lemur mongoz, ~3, 81
separation of inferior from superior, 81
in man, decrease of, reason for, 799, 800
in marmoset, bearing of, on vision and hearing, 164
in mycetes. 210
in orang, joo, 501, ,38-542
relation of, to hearing, 277
to optic lobes, 279
to sight, 277
Commissura mollis in chimpanzee, 605
in man, 835
in orang, 530
Conditioned reflexes, Q30

Convolutional patterns in primate brain, evolution-
ary significance of, in frontal lobe, 968
purpose of, 968
Convolutions, in brain of tarsius, 95"
simplicity of, 95-
complcxity of, in human brain, 963
Coordination in chimpanzee, 550, 582, 590

in dog-headed baboon, relation of, to use of fore-
limbs, 466
in gorilla, 6,6, 66;?, 6-6, -16

to inferior olive, 703, 704
in Hylobates hoolock, 435
in lemur, relation of cerebellar peduncles to, j8

relation of nucleus ruber to, 68
in man, 81-

in marmoset, as indicated by cerebello-rubro-
spinal connections, 1-5, 1-6
by inferior olive, 168
by lobes of cerebellum, 163, 171
by restiform body, 171
in mycetes, compared with lemur, marmoset, 216,
219, 220
relation of, to cortical expansion, 223
to semi-erect posture, 224
in orang, 510, 528

relation of, to connections between lateral lobes
of cerebellum and cerebral cortex, 58, 797
to dentate nucleus, 267, 465, 466, 528, 681, 717
to hand, 221, 466, 528, 681
to oculomotor decussation, 280
to olive. III, 512

to pallio-ponto-cerebcllar association, 797
to pons, 51-

to red nucleus, 229, 528, 603, 681, -i-
to rubrospinal tract, 228

to superior cerebellar peduncle, 322, 528,681,822
to vermis, 671
in tarsius, 9(), 1 1 1. 112, 1 18

Pages 1-474 are in Volume I,

Cope, E. D., on tarsius, 92
Corona radiata, 272, 275

Coronal constriction in Ape man of Java, 8-2
in Dawn man, 888
in Neanderthal man, 899, 904
in Rhodesian man, 913
Coronal suture in Ape man of Java, 872
in Neanderthal man, 899, 906
in Rhodesian man, 913
Corpus callosum, 898
in chimpanzee, 607
in dog-headed baboon, 29-
in man, 793

in mycetes, compared with lemur, marmosit, 204
Corpus hypothalamicum in dog-headed baboon, 332
in lemur, 69, 71
in marmoset, 180
Corpus restiforme. See Restiform body.
Corpus striatum in gibbon, 446
in gorilla, 683
in human brain, 835
relation of, to nucleus ruber, 270
Corpus trapezoideum. See Trapezoid body.
Cortex, 413

of cerebellum, 248, 253

of cerebral hemispheres, and motor areas in, 882
sensibility in, 63. 65, 243
in tarsius, markedly lisscncephalic. 9-, 125
expansion of, in cerebral hemispheres of Mycetes
seniculus, 223, 22-
Cortico-spinal connection in dog-headed baboon, 300
function of, 389
in Lemur mongoz, 3,
in orang, 502
in Pithecus rhesus, 389
Coup-de-poign (hand-axi, -51, -53, 758
Cranial bones of membranous origin, 862
Cranial nerves, emergent fibers of, in tarsius, 102
Cro-Magnon art, characteristics of, 759-765
comparison of, with Neolithic, 931, 932
decadence of. 93 1
explanation of, -6i-~65
three important elements of, 763
implements, 759, ~6i, "65
manhood, activities of, -59-763

brain of, 760--65
race, -58--66, 908, 931
decline of, 761-766
"Paleolithic Greek," 86l
periods of, 759, 762
victories of, -59, -60
pages 47S-II20 in Volume II.

i()86

INDEX

Cuneus, 797, 798. See also Coluniii and Nuckus ol
Burdach.

in chimpanzee, 569, 5-2, 573

definition of, 6^

in dog-headed baboon, 301, 302

in lemur, significance of, 38, 39

in gibbon, 4.18, 419

in goriMa, 655, 656, 662

in marmoset, 163

in mycetes, 209

in orang, 498. 499

in Pithecus rhesus, 3f)(i, }6i, 362. 363

relation of, to Idreliml), 38, 39, 302

in tarsius, 99, 101
Cunningham, Alyse, on gorilla, 632-642
Cynocephalous monkeys, 287
Cynoeephalus babuin. See Baboon.

D

ANIIiL, JOHN. .SVe.h.hn Daniel.

Daubentonidae, family of I cniuroidea, 21

Dawn man, 742, 884-893. See also Eoanthropus

Dawsoni, 742
Dawson, Charles, 884

Decussation in allereiU course of all sensory path-
ways, :;92
in impulses from i)r()pnocepU\'e struct urt- ol

internal ear, 592
of oculomotor nuclei in chimpanzee, 602, 604
as index of vision, 602
in dog-headed baboon, 472, 724
function of, 1035
in gibbon, 441, 724
in gorilla, 681

prominence of, 678
in higher anthropoids, coefficients of, 724
as important index of progressive adaptations
in skilled acts, 471, 472, 527
and vision, 832
in intermediate primates, coellicients of, 472
in man, 831
in mycetes, 228
in orang, 724

extension of, 528
in Pithecus rhesus, 387, 388, 724
relation of, to binocular vision, 723, 725
to ditferentiation in hand, 1036
to neokinesis, 1035

to visiim in higher anthropoids, 471-473, 52-
in optic pathway in marmoset, 180
pyramidal. See Pyramidal decussation.

Pages 1-474 are in Volume I,

Decussation of superior cerebellar peduncle, 32-,

343
in chimpanzee, 600, 616, 724
in dog-headed baboon, 32^, 345
in gorilla, 679
in man, 848, 856
in marmoset, 175, 176
in Pithecus rhesus, 384, 385, 402
in Tarsius spectrum, 1 2 1 - 1 27
of trochlear nerve in gibbon, 420
Dcllorescence as signal of evolutionary advance in

inferior and superior colliculi, 1033
Degeneration, sociogenetic explanation of, relation

of, to luxury, 775
Deiters' nucleus, in chimpanzee, 584-592, 618, 6ig,

"12

in dog-headed baboon, 316-318, 336, 33-, 339, 343

first appearance of, in vestibular nuclei, 80

function of, 170

in gibbon, 431, 432, 452

relation of, to bal.incing mechanism, 432

in gorilla, 667, 693

in higher primates, coefficients of, 713

in intermediate primates, coefficients of, 464

in Lemur mongoz, 50-53, 77-83

in lower primates, comparison of, 262
coefficients of, 262, 263

in man, 813, 814, 822, 852

in marmoset, 170, 171, 186-189

in mycetes, 217-221, 236-242

in orang, 512, 513, 540

in Pithecus rhesus, 373. 374, 375, 376, 392, 395,
397, 400, 403

in tarsius, 114-117, 145-149
Deitersal area in Tarsius spectrum, 1 16, 1 18
Deitersal tract in mycetes, 221

in Tarsius spectrum, 118, 119
Deitcrso-spinal tract in chimpanzee, 594

in dog-headed baboon, 306-316 (

function of, 47, 48, 50

in gibbon, 422-429

in lemur, 42, 45, 46, 47

in man, 804, 806, 808

in marmoset, 165, 166, 167, i6<), 170

in mycetes, 2!i, 215, 218, 220

in orang, 503, 507

in Pithecus rhesus, 36f)— 375

in tarsius, 102, 104, 105, 106-108, 1 14-117
Dentate nucleus. See Nucleus dcntatus.
Dermatomic areas, 370, 595, 660
pages 475-1120 in Volume II.

INDEX

1087

Descending trigcminil tract in clilni|)anzcc, 577—
5<ji, 619

in dog-headed baboon, 306 323

in gibbon, 422-432

in gorilla, 660, 662

in lemur, 42, 46, 47, 48, 49, 50, 52, 55, 57, 80

in man, 803-81 1

in marmoset, 164— 171, 184

in mycetes, 211-222

in orang, 503-513, 516

in Pithccus r[iesus, 366-381

in tarsius, 104, 105, 106-108, io(>, iii, ii4-iii>
Diencephalon, 262

in chimpanzee, 616 622

in dog-headed baboon, 345, 347

in gibbon, 450, 455, 456

in gorilla, 6g6

in lemur, 41, 82, 84

in man, 855, 856, 858

in mycetes, 240

in orang, 532, 538, 542

in Pithecus rhesus, 389 404
Differentiation, progressive, evidenced by brain-
stem structures, 664, 665, 666, 667, 682
Digitationes orbitalis in floor of anterior fossa, 790
Digits in chimpanzee, 545, 552

in gibbon, 407-409

in gorilla, 623

in lemur, 258

in marmoset, 153

in mycetes, 193, 198-201, 212. 246

in orang, 479, 480

in Pithecus rhesus, 350-353

variations in, 24
Discriminative sensibility, 256

in chimpanzee, 580

comparison of, in lower primates, 283

in gorilla, 663

indicated in caudal sections of brain stem, 662, 663

in lemur, 44

in marmoset, 166

in mycetes, in hand, 212, 213, 225

in orang, 507, 517

in parietal lobe, 1015

relation of, to behavior, 283

to development in hand, 283, 374

to dorsal sensorj- nuclei, 255, 315, 367, 370, 371

to mesial fillet, 216, 225, 586

to prehensile tail, 283, 374

to volitional control, 284

in tarsius, 1 10, 1 17

Pages I 474 are in Volume I,

Dog, I 14

digits of, compared with those of man, 880
sensory representation of, 879

experiments on, 247

increase in, of inferior olive and olivo-ccrebellar
connections, 1031
Dog-headed baboon. See Baboon.
Domestication of animals, introduction of, 766
Dorsal accessory olive in chimpanzee, 580, 613

in dog-headed baboon, 310-315, 337-339

in gibbon, 427-429, 448

in gorilla, 663, 688

in lemur, 45, 48, 49, 75, ~6

in mycetes, 218, 219, 234, 256

in orang, 536

in Pithecus rhesus, 3-1, 3'"2. 505, 596

in tarsius, 108, i 10
Dorsal cochlear nucleus in chimpanzee, 619

in dog-headed baboon, 337-344

in gibbon, 453

in gorilla, 694, 697

in lemur, 77, 80, 81

in man, 814, 853-857

in mycetes, 239

in orang, 516, 541

in Pithecus rhesus, 395-401
Dors.-il field of sensory discriminatioti in lemur, .^4

relation of, to body jjosture, 44

to dilferentiation in hand, 710, 71 i
to outside contact, 44
to skilled acts, 44, 255
Dorsal gray column in chimpanzee, 620

in gorilla, 685, 695

in man, 802, 804, 854

in marmoset, 183, 190

in mycetes, 233

in orang, 543

in Pithecus rhesus, 391-402

in tarsius, 102, 103, 105
Dorsal horns, cervix of, in orang, 533
in Pithecus rhesus, 366

in chimpanzee, 609

in Papio cynocephalus, 346

in tarsius, separation of, 136
Dorsal nucleus of lateral fillet in lemur, 61
Dorsal paramedian sulcus, in chimpanzee, 572, J76

in gorilla, 655, 663, 665

in man, 802-806

in orang, 498, 504, 509
Dorsal sensory field in chimpanzee, 5-6

in dog-headed baboon, 30-, 308
pages 475-1120 in Volume II.

io88

INDEX

Dorsal sensory field in gibbon, 424, 425

in gorilhi, 656-660

in luiman, 798-81 1

in orang, 503, 506, 507

in Pitlu'cus rhesus, 367-370

relation to discriminative sensibility, 3C7, 371
three major elements of, 370, 371
Dorsiil sensory nuclei, in chimpanzee, 578, 610

in dog-headed baboon, 302, 33-5

in giljbon, 4^0

in gorilla, 657, 686, (k)(>

in intermediate primates, coellieients of, 462-464
comparison of, with lower primates, 463

in lemur, 73

in m.irinoset, 183

in mycetes, 213, 214, 233, 234

in orang, 504, 533, 534, 543

in Pithccus rhesus, 391, 392, 399

relation of, to discriminative sensibility, 2jj, 315

to tarsius, 105-107, 137-139, 149
Dorsal spinocerebellar tract, in chimpanzee, 578, 583

in dog-headed baboon, 306, 309, 31 i

in gibbon, 422, 424, 425, 426, 428

in gorilla, 655, 662

in lemur, 42-46, 48, 49

in man, 803, 805, 808

in marmoset, 165-169

in mycetes, 21 1-21-

in orang, 503, 507

in Pithecus rhesus, 366, 36-', 361), 3-2

relation of, to column of C'lark. 252

in tarsius, 102-T i 1
Dorsal vagal nucleus, in chimpanzee, 574, 582, 583,
585, 622

in dog-headed baboon, 313, 314

in gibbon, 427, 428, 429

in gorilla, 664, 697

in lemur, 49

in man, 810, 857

in marmoset, 169

in mycetes, 218

in orang, 512

in Pithecus rhesus, 372

in tarsius, 108, 1 1 1
Dorsolateral sulcus, in lemur, 39
Dorsoniedian fissure, in dog-headed baboon, 301

in gibbon, 419
Dorsomedullary fissure in tarsius, 101
Drill, 747, 758, 76.

Dryopithecus, extinct gibbon-like ape, 732, 981
Dubois, E., on Java man, 735, 869, 886, 88-

Pages I 474 are in Volume I,

fiura mater, 862
Dyaks, 86, 480, 483

1_,"ARLE, on tarsius, 91

Edentates, pons Varolii in, 271
Eighth nerve. See Auditory nerve.
Embryogenesis, illustrated by spinal cord, 434

portraying a plan of adaptation, i r

witness to evolutionary kinship, 1 1
Eminentia abducentis, in chimpanzee, 622

in dog-headed baboon, 303

in lemur, 40

in man, 799, 857
Eminentia facialis. See Eminentia abducentis.
Eminentia fasciculi tcretis, 798
Eminentia hypoglossi, in gorilla, 645

in human, 798, 857
Eminentia teres, in gorilla, 69-
Eminentia trigemini, in human, "98, 802

in orang, 498, 50-
Encephalon, in chimpanzee, 606

ol man, distinction from other species, 791, 794
End brain, 602

of anthropoid apes, 416

in chimpanzee, 606

effect of expansion of, 600

in dog-headed baboon, 297

in gibbon, 444

in gorilla, 657

in orang, 537

in Pithecus rhesus, 384, 387
Endocranial casts, 912

evidence from, 862
Endocranium, 862, 891
Endocrine glands, 986

possible relation of, to neokinesis, 1041, 1042
Energy, conversion of, through animal organization,

882"
Engraving, art of, development of, -61
Eoanthropus Dawsoni, 738, 751, 884-893

fragmentary fossils of, 742, 884

history of, 738, 742, 75 1 , 886

position of, in human family, 892, 893

skull of, 884-893

casts of, 886

comparison with that of Pithecanthropus, 886, 887
Eocene Period, 978, 982

relatives of tarsius, 92, 93, 94, 95
Rolithie Period, 931
Eoliths, -45, 890
pages 475-ino in Volume II.

INDEX

1089

Epiglottis, in gibbon, 41 i
Epiphysis cerebri. See Pineal gland, 1^48
in clog-headed baboon, 303
function of, 990, 991
history of, 986

in primates, evolutionary significance of, 986-<)9i
Epithalanius in lemur, 81
Equilibrium, 264

in Lemur mongoz, 4'', ■53
in mycetes, 264

relation of, to Dciterso-spinal tracts, 4"
to development of hand, 22 1
to nucleus fastigii, ,3
to proprioceptive organs of vestibule, 49
to vestibular nuclei, 1-0, 262 2f)4. Jl"
Etcher, 7C)i

Etruscan rhinoceros, 74<)

Evolution, brain the supreme witness to, 3, 529, 800
indicated by blood tests, 10
by bony system, 10
by enibryogenesis, i 1
by human brain, 3, 414, 4^0, 800
phylctic history of cerebral peduncles, ,29
progressive, as evidenced by disparity as to

pyramidal development, 703
rel.ition of, to occipital region, 414
to ocular advance, 130
to superior vermis, 414
structures of salient significance in, 13
tetraplastic theory of, 12
unfolding of inferior olive, 666, 705
Evolutional process, bearing of structural clianges

in, on behavior, 13
Evolutional significance of auditory mechanism, 4~o,
600
cerebellar nuclei, 269
colliculi, 2—, 4-0, 4-1, ^25, 601
dentate nucleus, 434
divergence at caudal extremity of superior

longitudinal fissure, 493
midbrain, 276

occipital areas, 498, 526, 601
optic lobes, 276, 605

pallio-ponto-cerebellar fiber system. ^29
pontile nuclei, 46<;, 718, 720
prehensile tail, 264

progressive expansion in liurdach's column, 710
simian fissure, 494
spinocerebellar eminence, 50^
telencephalization, 470, 526
tempor.il area, 600

Pages I 474 are in Volume I,

Evolutional significance of vestibular eminence, 499
Evolutional terminus, possibility of, in higher pri-
mates, 476
Expansion in primate brain, evolutionary signifi-
cance of, as illustrated by cerebellar concavity
and postsplenial fi)ssa, 972
relation of, to coordination in upper and lower
extremities, 975
to expansion of lateral lobes, 974
to vision, 974
External capsule, in Tarsius spectrum, 132
External rectus muscle, 379
function of. 8i()

relation of, to riucKus .ibducentls, -54, 819
Extremities, In intermediate primates, 458
relation of, to behavior, 458

to planimetric coelliclents of pvr.imldal system,
4,-S
Fycb.ill, movements of Importance ol delicacy of
muscular mechanisms lor, 527, 681
bearing of, on neokinetic organization, 527
relation of, to decussation of oculomotor

nuclei, 68 [
to hand, 2jo
muscles of, 38"

innerv.ition of, 38-

FAC'IAl. innervation, relation of, to nucleus of
Rolando, 368
Facial nerve, in chimpanzee, 622

in dog-headed b.iboon, 321, 322

function of. 322

in gibbon, 435

In gorilla, 672, 697

in lemur, j"

In man, 819, 995

in marmoset, 171

in mycetes, 222

in orang, 517, 520, 523

in Pithecus rhesus, 3~9, 381

in t.irsius, 118, 119
Facial nucleus, 994

in dog-headed baboon, 318

In gorilla, 672

In lemur, 50, 52

as mammalian development, 994, 99j

in mycetes, 218, 220

in orang, 517, 520

In Pithecus rhesus, 369, 3-2, 378, 379

In tarsius, 114, 116
Falx cerebelli, ''94
pages 475 1 1 20 in Volume II.

1090

INDEX

Fasciculus cuneatus. See Buidach, culiinin of.
Fasciculus longitudinalis iJDstcrior. See Posterior

longitudinal fasciculus.
Fasciculus mcsenct'phalici trigcniini in Pitliecus, 379
Fasciculus solitarius. See also Nucleus solitarius.
in gibbon, 427
in gorilla, 665
in orang, 512
Fasciculus of Vicq D'Azyr in balloon, 332

in Pithccus rhesus, 387
Felidae, 125

Fifth cranial nerve. See also Descending trigeminal
tract; Trigeminal nerve,
in gibbon, 436
in orang, ,25
First Glacial Period, -45
First Intexglacial Period, 74;;, 751
Fish, 260, 276
optic lobes of, 279
paleokinesis in, 1038
predominance of co!lic\ili in, [033
Fissural development, in gibbon eom|)ared with

baboon and macacus, 41 5
Fissures in human brain, intricacy of, 778, 782, 78()
Flatau, 957
Flint, 896

uses of, 747, 751-757

Acheulean Period in, 753

adaptive improvements in, 931

Cro-Magnon Period of, 759

implements of, in Solutrean Period. -^61, 762,

918
.Mousterian industry in, 757
used by Neanderthal man, 895, 896
Flocculus, in chimpanzee, 571
in gibbon, 417
in gorilla, 653
in mycetcs, 207, 208
in orang, 498
in Pithecus rhesus, 358
Foot, in chimpanzee, 545-553
in gorilla, 625, 706

human, development of, 877, 977, 978, 983, 1041
dilTcrcntiation of, 812, 978, 1041
significance of, 978, 983, 1041
specialization of, 802, 978, 983
in orang, 480
Foramen caecum antieurn in chimpanzee, 575

in orang, 523
Foramen caecum posticum in b.iboon, 300
in lemur, 36

Pages I 474 are in Volume I,

Forel, decussation of, in lemur, (n)
in tarsius, 132

ventral, in dog-headed b.iboon, 332
fields of, in lemur, 71
in man, 856
in marmoset, 180
Forelimb in chimpanzee, 545, 546, 573
strength and dexterity of, 590
in dog-headed baboon, 290, 294
in gibbon, 407, 424, 458, 459
relation of, to arboreal life, 424
.sensory equipment of, 424
in gorilla, sensory influx from, ()^(>, 660. 664
in lemur, 258

innervation of, 38, 39, 43, 44, 46
in man, highest evolution of, 803

lemur, t;irsius, marmosi-t, mycetes, comparison
of, 246
in marmoset, 153, 258
in mycetes, 258, 283
in orang-outang, 479, 483-498

bearing 'of, on coordinative control, 528
decisive advance in, 504
in Pithecus rhesus, 350, 360, 368, 3-0, 3-1
progressive evolution illustrated by orang, 504
relation of, to inferior olive, 253, 254
to locomotion, 254, 258
to nucleus of Blumcnau, 429
to nucleus of Burdach, 43, 46, 255, 258, 504
to posture, 254
in tarsius, 105, 258

capable only of simplest motor patterns, 119
Formatio reticularis. See Reticular formation.
Fornix in chimpanzee, 6o<)
in dog-headed baboon, 332, 333
in lemur, 69, 70
in marmoset, 180, 181
in mycetes, 229

in Pithecus rhesus, 387, 388 ,
in tarsius, 132
Forsyth-.Major on tarsius, 9:
l-'ossilized skulls, features of, 866-868
Fourth cranial nerve. See Trochlear nerve.
Fourth Glacial Period, 754, 759, 760
Fovea pinealis, in dog-headed baboon, 303

in lemur, 40
Fovea vagi, in chimpanzee, 574
in dog-headed baboon, 303
in gibbon, 419
in gorilla, 656
in lemur, 40
pages 47S-II20 in Volume II.

[NDEX

i()()i

Fovea va};i, in man, 7()()
in orang, 499
in Pitlu'ciis rhesus, 361
Franz on new-world monkey, 354
Frontal bone, 790

nieniI)ranoiis orij^in ol, 862
Frontal lobe, in Ape man of Java, 8-2

fissures in, 874

indications in, as to behavior and speech, 875, 876

Pacchionian enlargement in, 8-2

prominence of, 872

significance of, 872, 874
in chimpanzee, 568, 570
in Dawn man, 886, 888
in dog-lieaded baboon, 296, 298
in gibbon, 412, 413, 414, 415
in gorilla, 645-650
in imman brain, 779, 780, 783, 785, 786

expansion of, 783, 790, 791, 795

function of, 769, 791, 795

significance of, 784, 789, 791
last gift of evolutional progression, 908
in man, 783

compared with that of great anthropoids and
all other primates, 783, 784, 789

complexity of convolutions in, "84
in marmoset, 1 58, 1 59
in mycetes, 202-205
in Neanderthal man, 893-904
in orang, 493-495

humanoid appearance of, 495
in Pithccus rhesus, 357, 358
potentialities in, 933-936
pre-frontal convolutions of, ellect ol disease upon

future of, 966
responsive plasticity in, 935
in Rhodesian man, 913-915
in tarsius, 92, 94, 96
Fundus of dentate nucleus in chimpanzee, 590

in gibbon, 434
Fundus of olive in chimpanzee, 582, 586, 612
in dog-headed baboon, 338
in gibbon, 448, 449
in gorilla, 688
in orang, 535, 5.36
in Pithccus rhesus, 395

/^^ALAGO, habits of, similar to those of tarsius, 90

"Gallery of human experience," 791, 883. See also
Frontal lobe.

Pages I 474 are in Volume I,

Ganglion habenulae in lemur, 69, 70
Gasserion ganglia, in chimpanzee, 595

in lemur, 75

in Pithccus rhesus, 394
Geniculate bodies, in lemur, 41, 81

relation of, to auditory and visual functions of
cerebral cortex, 605

in tarsius, 1 35-1 51
Genu facialis, in chimpanzee, 595

in human, 799, 819

in orang-outang, 523, 543

in Pithccus rhesus, 379
Gibbon, 7, 12, 17, 287

arboreal life of, 17, 405, 410

relation of, to balancing mechanism, 715

behavior of, 405-412, 413

bipedal locomotion in, 981

blood relationship of, to tarsius, 89

brain of, 287, 288, 405, 412, 413

compared with baboon and macaeus, 413
cf)nvolutional pattern ol, 415

general description of, 405-412, 413

geographical distribution of, 409

habitat of, 409, 410

locomotion of, 420

measurements and indices ol, 412

olivary expansion in, 458, 705

position of, among primates, 287, 405, 416

posture in, 17

pyramidal system in, 702
Gibraltar skull, 896, 904, 906
Globus pallidus, in chimpanzee, 605-607

definition of, 71, 177

in dog-headed baboon, 333, 334

in gibbon, 445

importance of, 71, 177, 181

in lemur, 69, 70

in man, 835

in marmoset, 177

in mycetes, 229, 230

in orang, 531

in Pithccus rhesus, 38-, 389
Goll, column of, in chimpanzee, 5'"6, 580, 609, 610

definition of, 305

in dog-headed baboon, 305-311

in gibbon, 422-450

in gorilla, 656, 660, 686, 696

in great anthropoids and man, 578, 708, 71 1

in lemur, 42, 43, 45, 46

in lower primates, 578

in man, 798-806, 840
pages 475-1120 in Volume II.

1 09-:

INDEX

Goll in mannosi't, 162-166
in mycctes, 209-215, 233
in ornng, 503, 504, ,-33, 534
in Pithcciis rhesus, 366-369, 392
relation to prehensile t;iil. 209-213, 256, 2", 462
in tarsiiis, 102, 104, 105, 106, 149
Goli, nucleus ol, in eliini|)anzee, 576-583, 609-611,
618
eocfficients of, 7o~

comp.-irison ol", with mtiTnuxliatt' primates,

706, 707
with lower primates, 707, 708
in dog-headed baboon, 305, 306, 30H, 313, 315.

335. 33^). 337, 34^'
in gibbon, 418, 424, 425, 44", 455, 460 462, -07

smaller than in other primates, 707
in gorilla, 659-667, 686, 706
in intermediate primates, 461

coellieients of, 462

comparison of, with lower primates, 462

no nucleus of Bischolf in, 461

relation of, to absence of tail, 461, 462
to discriminative sensibility, 462
to lunetional depreciations in legs, 461, 462
in lemur, 43, 46, 48, 49, 77, 80, 82, 83

relation of, to central gray matter, 73
in lower primates, comparison of, 25-7
in man, 804, 806, 840
in marmoset, 162, 164-169, 183, 18-
in myeetes, 213, 215, 216, 233, 236, 237, 242, 259,

708
in orang, 503-505, 509, 535-537, 543
in Pithecus rhesus, 360, 367-374, 392, 395, 396,

307, 399. 402, 403, 461, 462
relation of, to behavior, 462

to discriminative sensibility, 255, 462

to kinesthetic organization, 255, 256

to leg and tail, 46, 164, 255 259, 460, 462, 707

to mesial fillet, 45

to skilled acts, 255
in tarsius, 111^113, 13-^, 138

relation of, to t.iil, 105
Gorilla, 12, 22, 479, 494, 497, 569, 908
behavior of, 625, 627, 630, 631, 643
brain of, 623

me.isurements and indices of, 644

resemblance to human type, 645-657, 652, 662,

• 670, 682, 685, 696, 704

surface appearance of, 645
close relation of, to man as shown in central

nervous system, 476
i. Pages I 474 are in Volume I,

Gorilla, general description of, 623-643

habitat of, 627, 630
Gregariousness in Pithecus rhesus, 350, 352
Gregory, on primates, 929, 978, 980
Grise.il portion of reticular formation in orang, 509
Groove i)f transverse sinus in ape-man of Java, 871
Guenons, 287
Gyrencephalic brain, in llylobates hooloek, 412

illustrated by cerebrum of lemur, 29, 954

in myeetes, 202, 204

in Papio cynocephalus, 295

in Pithecus rhesus, 355
Gyres, anncctent, in chimpanzee, 569

in dog-headed baboon, 298

in human, 5~o
Gyrus rectus, in chimpanzee, 570

in dog-headed baboon, 297

in gibbon, 413

in gorilla, 650

in man, 791, 947, 9-0

in orang, 496

H

AGGERT^ rm Pitlueus rhesus, 354

Hamilton on Macacus rhesus and irus, 354
Ilammer-stonc, 747, 751, 758, 761
Hand, in chimpanzee, 545, 550-553, 573
development of, 877
differentiation of, in man, 803, 812
in gibbon, 407, 429, 458, 459
in gorilla, 623, 656, 665, 666, 681
human, increase in sensory impressions from,
798, 803
compared with those from foot, 798
relation of, to column of Burdach, 798, 802, 803
specialization in, bearing of, on soul, -30
in marmoset, 166

relation of, to ]3ons, 223
"master key," 776
in myeetes, 194, 214

differentiation in, 212, 213
relation of, to column of Burdach, 210, 213
in orang, 479, 528

in Pithecus rhesus, complex movements ol, their
relation to vision, 350, 560
sensory equipment of, 368, 3^0, 371
progressive adaptation ol, 13, 18, 214, 284, 718
rel.it ion of, to behavior, 214, 284, 718, 776
to dentate nucleus, 718

to human progress, 214, 284, 718, 730, 767, 775,
776, 836, 875, 1042
pages 47s 1 120 in Volume II.

INDEX

1093

Hand, relation of, to movements of eyeball, 250
to nucleus of Burdach, 216
to posture, --6
to speech, 214, -"6
to vision, 2,0
structures essential to, 1042

relation of, to neokinesis, 1042, 1043
Hand-stone, 758
Hapalidac, family of Anthropoidea, 21, 191. 5ee

also Marmoset.
Harris, W'm. L., oo<)

Head, innervation of, relation ol, to nucleus of
Rolando, 256, 257
rotation of, in tarsius, relation to spinal accessory
ncr\'e and ventral gray colutnn, 103. 104. 112
sensory equipment of, in gorilla, 660, -1 1

comparison of, with intermediate and lower

primates, 660
relation of, to locomotion, ^/)o
in Lemur mongoz, 43, 44
in mycetes, 214
in Pithecus rhesus, 370, 371
Hearing. Sec alsa Auditorv sense.

in man, deliberative nature of, Hii). H2-, 830
in tarsius, 125
tclenccphalization of, 1034
Heel-toe timing, ((82

Heidelberg man. See Paleoanthropus I leidelbergensis.
Hclweg, olivary fasciculus of, in lemur, 4"

spino-olivarv tract of, in doe-headed baboon, 306-

3". 31^'
in gibbon, 422, 431
in marmoset, 165-16^
in mycetes, 211, 215, 218

relation of. to olive, 249
in orang, ■503

in Pithecus rhesus, 366, 36-, 3-2
Hemal tests, bearing on theory of evolution, 710
Hemispheres, basal surface of, in chimpanzee, 570
Higher anthropoids, 22, 477--2i
Hindbrain, in Lemur mongoz, 40

in Pithecus rhesus, 381
Ilind-Iimbs, in chimpanzee, 54,

strength and dexterity of, 590
in dog-headed baboon, 302
in gibbon, 429, 430, 458
in gorilla, 625, 681

sensory inpulses from, (>(m
in lemur, 43, 44
in orang, 480

less sensory in(lu\ from, 50-

Pages I 474 are in Volume I,

Hind-limbs, in Pithecus rhesus, 370. 3-71

in tarsius, low specialization of, 105
I lirschleir on chimpanzee, •546
Hobhouse on chimpanzee, 546

on macacus, 354
Hominidae, family of Anthrofjoidea, 21, -51

distinct from Simiidae, 929
evidence of brain, 929, 930

jjrehistoric races of, 733, 861
works of the hand in, -43, 745

time of, 861
Ihiino lieidelbergensis. See Paleoanthropus I leidel-
bergensis.
Homo Rhodesicnsis, 909 <)i8

brain of, 91 2

endocranial casts of, 912

l.ice of, 911, 912

iossils of, 909 91 2

history of, 909

place ol, in evolution, <)i-, 918

Smith on, 91 1
I lomo sapiens, 22, 732

c(minion progenitive stock ol, proof lacking, 742
Keith on, 732
v.irietics of, 732

(Jro-.\l;ignon race of, 759
Hook bundle. ^ceTracIus uncinatus ol Husscl.
I lorse, 1 14. 1024

Howling monkey. South American. See Macacus.
Ilubrecht, A. A. W .. on tarsius, ()i
Hum.in behavior, hand the master key to, — 6

blood, tests for, 7

[jrogress, psychological foundations, of, 861
Humanoid appearance of frontal lobe of orang, 495

attitude in Pithecus rhesus, 3^0

structure and ditferentiation, 259, 42-, 463, 495,
,-28, 5,-2, 645, 739
Hunter, John, on nucleus of Perlia, 281
Huxley, 957, 1044

Hylobates hoolock, 12, 405-456. 5cc also Gibbon.
Ilylobatidae, family of Anthropoidea, 21, 287. See

also Gibbon.
Hypencephalon, in Lemur nmngoz, 82
Hypoglossal nerve in chimpanzee, 574, 582

in dog-headed baboon, 300, 311, 312, 313

in gibbon, 427, 428, 429

in gorilla, 663

in lemur, 48, 49

in man, 810

in marmoset, 169

in mycetes, if, 218
pages 475 1120 in Volume II.

1094

INDEX

Hypoglossal 'nerve in orang, 512, •513

in Pitliccus rhesus, 370, 3~i, 3-2, 403

in tarsius, ()(), 108
Hypoglossal nucleus in chimpanzee, 5^4, 582-585,621

in dog-headed baboon, 303, 312, 313

in gibbon, 427-429

in gorilla, 662, 663, 664

in lemur, 40-48, 49, 84

in man, 798, 810, 857

in marmoset 169, 186

in myccles, 217-220, 236

in orang, 514

in Pitheeus rhesus, 372

in tarsius, 109

not discrete, i oS, 111-115
Hyrax, 955

TMPRESSIONKS digitutae, 863

Indrisinae, 980

Interior brachium in chimpanzee', 616
in dog-headed baboon. 540. 344
in gorilla, 692, 695
in lemur, 78
in man, 848, 854
Inferior collicular commissure, in chimpanzee, (100,
620
in dog-headed baboon, 345
in gorilla, 679, 695
in niycetes, 240
in Pitheeus rhesus, 402
Inferior colliculi, in chimpanzee, 575, 616

index of rellex response to sound, 575, 599, 620
coefTicients of, in higher anthropoids, 721
in intermediate primates, 470

comparison of, with those of lower primates,

470
relation of, to hearing, 470, 525
in dog-headed baboon, 301, 304, 325-328, 337,
339. 340, 344
significance of size in, 328
structure of, 328
function of, 174, 469, 523, 525
in gibbon, 419, 420, 439, 454, 469

superseded by .auditory area of cerebral cortex,
469
in gorilla, 652, 656, 657, 676, 677, 679, 690, 691,

694, 695 720, 721
in great apes, comparison of, with those In
intermediate primates, 721
with those in lower primates, 721

Pages 1-474 are in Volume I,

Inferior colliculi, in higher vertebrates, 328
illustrated by tarsius, 125
in lemur, 39, 62, 63, 77, 78, 79, 81, 83
in lower vertebrates, 328
in man, 800, 827, 830, 837, 847, 848, 854

as index of complete telenccphelization, 830

involution in, 827, 830, 858
in marmoset, 163, 164, 1-3, 174, i"5, 179, 187,

189, 190
in niycetes, 209, 225-22-, 23^, 240, 241
in orang, 523, 525, 541

structure of, 525
in Pitheeus rhesus, 363, 383-386, 398-402

significance of structure in, 383
relation of, to auditory sense, 63, 1-3, 1-4, 225,
227, 277, 327, 469, 523, 525, 599, -21

to balancing, 261

to temporal lobe, 599, 721
in tarsius, 100, tot, 120, 122-12-, 135-151
Inferior fovea vagi, in human, 80
Inferior frontal convolution in human brain, 786, 935
Inferior frontal sulcus, later position indicated in

lemur, 30
Inferior medullary velum in lemur, 83
Inferior olivary eminences, in tarsius, size of, 99
Inferior olivary nucleus in chimpanzee, 583, 591

resemblance to human, 578-582, 586, 612-614
cocllicients of, 254

comparison of, in lemur and great apes, 70;
connections of, 248, 1032
definition of, 510
description ol', 252

in dog-headed baboon, 299, 300, 310-316, 335-341
evolutional unfolding of, 705, 1032
expansion of, as index of neokinetic progress,

725. 1033
function of, 247, 24S, 249, 253, 1030, 1032
in gibbon, 418, 424-432, 447-449

comparison with baboon, macaque, 421, 460

prominence of, 448, 460, 705
in gorilla, 654-665, 687-689

significance as to coordinative control, 703, 704

size and structure of, 656, 665, 66-7
in higher anthropoids, coeHicients of, 704
in lemur, reconstruction of, 34, 38, 45, 46, 4", 48,

49. 73. 75. 79
in man, 806, 808, 814, 837, 842, 843, 844, 849
accessory elements of, 808, 814, 842
compared with lemur, 809, 810
evolution of, 252, 809, 810, 838, 839
fundus of, 814, 843, 849
pages 475 1 120 in Volume II.

INDEX

1005

Inferior olivary nucleus in man, liiuli cliirerenliation
of, 808, 814
in marmoset, low organization ot, 254, 162, 167-

170, 184, 185, 189
in mycetes, 215-221, 234 236, 230
in orang, 507-513. 5'4> 535

index of advance in coordinative control, 510
in Pitl\ecus rhesus, 359, 362, 368-376, 392-394,
395-400
first convolutions of, 375
relation of, to control of simultaneous movements,
312, 582, 656, 703, 1032
to coordination in skilled acts, 312, 5S2, -03,
1030, 1 03 1, 1032
in tarsius, 108-113, 13-, 139, 140, 141
Inferior vermis in chimpanzee, 5-1, 586, 595
in gorilla, 653, 948
in orang, 49-
Infundibular stalk in chimpanzee, 576
in dog-headed baboon, 301
in gibbon, 421
in gorilla, 657
in lemur, 36
in man, -92, 833
in Plthccus rhesus, 364
Inhibition. 1038, 1039

most essential dilference lietween neokinesis and
paleokinesis, 1038
Insectivores, 1007, 1039

Interbrain, 347, 692. See also Dienccphalon.
Intcrcollicular commissure in orang, 542
Intercollicular sulcus, in chimpanzee, 575, 616, 620
in dog-headed baboon, 303, 344
in gorilla, 657, 695
in human, 834, 948
in lemur, 40
in orang, 541
in primate series, 986

relation of, to pineal gland, 986
Intermediate primates, 22, 287-473

vermal ridgepole in, 416
Internal arcuate fibers, in chimpanzee, 578, 580, 583,
592
in gibbon, 426, 428, 430
in gorilla, 665
in lemur, 46
in man, 806, 808
in orang, 509

in Pithecus rhesus, 371, 375, 392
in tarsius, 107, 109

Pages I 474^arejn Volume I,

Internal capsule, in chimpanzee, 605, 607

in dog-headed baboon, 332-334

in gibbon, 445, 446

in gorilla, 683, 684

in lemur, 69, 70, 71

in man, 835, loio

in marmoset, 180, 181, 182

in mycetes, 229, 230

in orang, 531

in Pithecus rhesus, 387, 389

m t;irsius, 1 32
Internuclear commissures, lacking in lemur, 68
Interorbital keel, in ape-man of Java, 875

in dog-headed baboon, 297

in gibbon, 413, 415

in Gibraltar skull, 906

in gorilla, 647

in lemur, 32

in marmoset, 159. 160, 206

in orang, 496

in Pithecus rhesus, 35", 359

in Khodesian skull, 914

in tarsius, 93, 97
Interparietal fissure, in lemur, 29
Interpeduncular gray matter, in chimpanzee, 6 18- 622

in gibbon, 454, 456

in gorilla. 6()5

in marmoset, 188

in mycetes, 240

in orang, 542

in tarsius, 135-1 5 i
Interpeduncular space, in dog-headed baboon, 325,
345, 347

in lemur, 63

in man, 856, 859

in marmoset, 164

in Pithecus rhesus, 364

in tarsius, 97
Iron Age, 745, 932
Isthmus mescncephali, in chimpanzee, O18, 622

in gibbon, 439, 452

in gorilla, 656, 690

in lemur, 81

in orang, 540
Iter, in gibbon, 455

in Pithecus rhesus, 382

J

•XCOBSOllN, 957

Java man of Trinil race, 735, 743, 745. See also
Pithecanthropus ereetus.
pages 475-1 120 in Volume 11.

1096

INDEX

John Daniel 1, 632-63(), 666, 719

John Daniel 11, 639-642

Judgment, relation of, to frontal lobes, 795

Juga ccrcbralia, 863

"Julius," orang, 488-491

Juxtarestiforni Ixxly, 262

in lenuir. ■;2

in man, 822

in marmoset, 171

in mycetes, 219

in Pithecus rhesus, 376

in tarsius, 1 17

K

ANGAROO, if4, 1024

Keith, Sir Arthur, 731, 732, 735, 742, 886, 887, 89 r
Kinesthetie association in human brain, 795

developmeni. in i(.latii)n to t^iil, in lower primates,

258
sensibility, relation of, to skilled aets, 2>t, 258,
880,881
to oculomotor decussation, 284
to parietal lobe, 881
Kinnaman on Pithecus rhesus, 353, 3^4
Knife, use of, "4", ~-;i, "58
Kohler, research of, on chimpanzee, 546-564, 603,

-oi, 723
Kubus of Sumatra as prc-palcolithic, 771

TA CHAPELLE AUX SAINTS, Neanderthal

■^ man of, 8()~

Lagothrix, woolly monkey, tail of, icji, 20H, 210

Langeurs, 287

La Quina skull, history of, 904

Larynx in hooloek gibbon, 41 1

in mycetes, 193, 217
Lasio pygidae, family of inteniiediate monkeys
(Anthropoidea), 21, 287, 294

brain of, resembles gorilla, 288
Lateral lillet, in chimpanzee, 599, 616, 620

in dog-headed baboon, 326-328, 340

function of, 328

in gibbon, 439, 450

in gorilla, 674, 676, 690, 695

in lemur, 52, 60, 61, 64, 76, 77

in man, 826, 830, 846, 847

in marmoset, 173, 174, 175

in mycetes, 224-226

in orang, 52;, 529, 538

in Pithecus rhesus, 380-385

relation of, to auditory sense, 54, 62, 64

in tarsius, 120-123, 142

Pages I 474 are in Volume '.

Lateral geniculate body, in chimpanzee, 604, 616
in dog-headed baboon, 339, 341, 345
in gorilla, 692
in lemur, 75, 77, 79
in macacus, 363, 393, 397
in marmoset, 185, 187
in mycetes, 235, 239
in orang, 542
in Tarsius spectrum, 151
Lateral nucleus of the thalamus in baboon, 332, 333
Lateral reticular nucleus, 68y
in gibbon, 450
in gorilla, 689
I emur, 12, 15, 22, 23, 29-84, 234-238, 242, 423
beliavior of, 24, 26

blood shows no relationship with man, 7
eatta, 24

general deseri|)tion of, 15, 23, 24, 26
geographical distribution ol, 23, 26
mongoz, 12, 26

balancing in, 26

cerebral hemispheres of, 29
evolutionary significance. 31

Chironys, third digit in, 24

g<'neral description and habitat, 23, 24, 26

measurements and indices ol, 28

potto, absence of digit in, 24

pyramids and inferior olives in, 35

signiheant structural modifications of, 31

skilled ai'ts in, 55

\i)!itional control in, 35
minilx'i of genera and species of, 23
posture in, 26
represents transition from arboreal mammal, 12,

15. 23
simultaneous nn)\emenls in, 26, 35
l.emurinae, subfamily, 26

Lemiiroidea. suborder of primates, 21, 23, 85
Lentieiilar ma lens, in dog-headed baboon, 332
in gibbon, 445

in gorilla, 684 '

in man, 835
in marmoset, 181, 1H2
in mycetes, 230
in Pithecus rhesus, 388, 389
in tarsius, 102, i 32
Lepidolemur, ()8o

Limbs, in inframammalian orders, synchronized
moN't-nn'iits ol, 5 i()
III iiiamniaK. independence ol, 519

new plusioiogieal endow niLiit ol, 519
'., pages 475 1 1 20 in Volume II.

INDEX

1 (){j-

Limbs, in mammals, rclatii)ii of, to expansion of
ccTi'licllum, ^20
to neopallium, 520
Lingula, of cerebellum, in Pitliecus rliesus, 378

in tarsius, 120
Linneus, classilication of primates by, 21
Lissencephalic cerebral liemispliercs, in marmoset,
9,-8
in tiirsius, ()i
Listing on primary position of visual a\es, 280
Lobati*>n of brain, in (!!allitiiri\ jaechus, 158
limited. III lemur. 31
in mycetes, 205

in tarsius, its negligilile eharaeter, 96
Locomotion, bipedal, 264
ol chimpanzee, 17, y^i, jS-j

relation of, to vestibular complex, 585
of dog-headed baboon, 290, 465, 466
of gibbon, arboreal character of, 17, 405, 410, 420,

429, 430, 432, 435, 460, 461, 464, 46-;
of lemur, 24, 50, 51
of man-like apes, i~

of mycetes, relation of hand to, 104, 210. 213-215,
21"
of, to coordinat i\i' control, 220, 224
of tail to, 194, 258
of orang, arboreal character ol, 17
plantigrade, 264

in gorilla, 625, 631, 66q, 670
quadrupedal, 669

relation of, to balancing mechanism, 514
to upper and lower extremities, 483, 484
to skilled acts, 276
to tail, 258, 259
to weight, 66g
of tarsius, 1 1 5

directed by sensory innervation of head ,ind f.ice,
87, 105, 107, 109
Locomotor ataxia, 881

specialization, relation of, to balancing mechanism,
465, 669
Loris, 980
Lower extremity, in man, increase in functional

importance of sen.sory alTerents from, 802, 803
Lower Paleolithic Period, 737, 742, 745, 746, -.jS
Luciani, cerebellar triad of, 81^
Lungs and heart, witness to evolutionary kinship,

I I
Luys, corpus of, in macacus, 401

hypothalamic nucleus of, in lemur, 71

Pages I 474 are in Volume I,

M

ACACUS, 7, 89, 441, 619

nearest to great apes, in pyramidal .system, 702

nucleus of Burdach of, larger than in other inter-
mediate primates, 463

playmate of orang, 482

rhesus, 12, 288, 349. See also Pithecus rhesus.
.Macaques, 287, 288, 349, 430. See also Pithecus.
.McGregor, 929

reconstructions of, 861, 869, 875, 879, 886
.Magdalenean Age, 761, 762
.\Lilacca, 771
AL-immaiian characters, 385, 421, 60-;, 699, 700

pallio-spinal connection, 421

pyramidal fibers in orang-outang, and gibbon,
421
dillercnliation, loi, 60-;. 1)40, ()()4
neokinesis keynote of, 1045
Mammals, age of, 940

auditory sense in, 328, 605

contribution of, in new type of motor activity
(neokinesis), 1037

early deficiencies in, 1039

neopallium in, effect of, on colliciili, 1033, 1034

|)inniped, 1007

placental, 940

subprimate, 1 17, 940
Mammillary bodies, in chimpanzee, 576

in dog-headed baboon, 301

in gibbon, 421

in gorilla, 657

in man, 792, 833

in Pithecus rhesus, 364

in tarsius, 150
Mammoth hunters of Predmost, 918
Man, family of, birthplace of, 767

departure from orthognidc stem of primates,
775, 776

migration of, 767-775

primitive races of, 769

relation of, to ape, 929, 1043 ^

not that of direct descent, 929, 1043
.\Lindril, 287

color in, 289
Mangabey, 287
.M.m-like apes, 287, 477. See also Anthropoids.

notoriety as assumed forbears of man, 477

preeminence as to humanoid characters an aca-
demic question, 478

relation to man based on ancestral stock, 478
.Manual complex acts, in man, 8i~
pages 47.S 1 120 in Volume II.

1098

INDEX

Manual development, in eliinipanzcc, 546-566
effect on sensibility, 212
in Pitliecus rhesus, 356

relation of, to column and nucleus of Burdacli,
256, 258
to olive, 219
to pontile nuclei, 276
Manual dexterity in chimpanzee, 582
in dog-headed baboon, 294, 466
in orang, 512
Manual differentiation in gibbon, 413

in intermediate primates and great anthro-
poids, 717
in lemur, 258 \

in marmoset, 16
in mycctes, 212, 463
in new world monkeys, 459
in orang, 498

as indicated by cuncus, 498
Marmoset, 12, 16, 22, 96, 153-190, 234, 235, 236,
237, 238, 242, 803
arboreal life of, 155

brain of, measurements and indices ol, 155-157
cerebral cortex of, lisseiiecphalic condition of,

■57
three lissurcs in, 1 57

in evolution, significance of, 16

general description ol, 16, 153, 155

habitat, 153, 154, 155

position of, among primates, 16, 153, 154, 159
indicated by simplicity of brain, 159, 160, 161

surface marking on brain stem, 161
Marsupials, 128, loo:?, 1039
Martin, Henri, 904
Mathcw and Granger on tarsius, 92
Matthews, 980
Median sulcus, in lemur, 40
Medulla oblongata, 256, 261, 266

in chimpanzee, 571, 574, 592, 612, 613, 618

in dog-headed baboon, 297, 299, 300-317

in gibbon, 415-420, 430, 450, 464

in gorilla, 653-657, 667, 685, 686, 696

in lemur, 84

in man, 795-800, 841, 844

in mycetes, 205-209, 214, 236, 238

in orang, 498, 499, 503, 534. 535. 543

in Pithecus rhesus, 359-361, 364, 374, 391, 392

in tarsius, 135-151
Medullary vestibule, in dog-headed baboon, 318

in lemur, 58
Meningeal artery, middle, 906

Pages 1-474 are in Volume I,

Mesencephalon. See also Midbrain,
in lemur, 41, 65, 78, 81, 82, 84
in marmoset, 190
in mycetes, 2ro, 240, 242

roof-plate in tarsius, prominence of, 100, 1 35-151
Mesial accessory olive (mesial jjaleo-olive), in

chimpanzee, 580
in dog-headed baboon, 312
in gorilla, 663, 68^
in Pithecus rhesus, 371
Mesial fillet in chimpanzee, 580, 583

relation of, to discriminative sensibility, 580
definition of, 586
in dog-headed baboon, 310-314, 316, 321, 324-

327, 330, 332, 334, 340
function of, 47
in gibbon, 425-441

in gorilla, 665, 667, 673, 676, 679, 682
in lemur, 45, 47, 48, 49, 50, 60, 61, 62, 66, 69, 76
in man, 818, 823, 826

decussation of, 806, 808
in marmoset, 167-180
in mycetes, 215-227
in orang, 509-536
in Pithecus rhesus, 36(>, 370, 3-2, 3-3, 375, 376,

378, 380-386, 392, 403
relation of, to basis pontis, 60

to discriminative sensibility, 216, 586

to nucleus of Goll, 45
in tarsius, 106, 110-113, 114, [iS, 1 ii), 121-124,

128-133, 142
Mesial geniculate body in chiin|)anzce, 575, 603,

605, 621
in dog-headed baboon, 304, 330, 333, 339-345
function of, 333, 338, 501
in gibbon, 443, 450
in gorilla, 657, 682, 692, 695
in lemur, 41, 64, 66, 75, 7~~79
in macacus, 363, 386, 388, 398, 401
in man, 800, 833, 848, 854
in marmoset, 177-179
in mycetes, 235, 240
in orang, 501, 529, 542
in Pithecus rhesus, 393
in tarsius, 100, 128-133
Mesozoic period, 940
Metacarpals, 980
Metatarsus, fulcrumation on, 980

effect of, on leaping, 980
Metencephalon in chimpanzee, 612, 614, 616
in dog-headed baboon, 303, 344, 346
pages 475-1120 in Volume II.

INDEX

1099

jMctenceplialon in kniur, 40, ~H, 8}, H4
in man, 847, H^i
in orang, 541, 542
in Pitliccus rhesus, 30", 400, 405
in tarsius, 13^-1 51
Mcynert, dorsal cjcciissation of, in balloon, 332
in lemur, 6<)
in tarsius, 131
supra-optic decussation of, in chinipan/ee, 605

in dog-lieadcd baboon, 334

in gorilla, 685

in lemur, -o

in orans, •)3i
"Mias" of Borneo. See Orang-outang.
Midbrain, 248

in chimpanzee, j",, 600, 612-624
colliculi of, function of, 277, 27<j

index of evolutional modification, 4-1
comparison of, in lower primates and man, 277
delegation of function of, still progressing, 27-7
in dog-headed bal)oon, 303, 304, 31,, 340, 341,

344, 346, 347
early importance of, 2~6
evolutionary changes in, 276, 2j<)
in gibbon, 415, 420, 441, 444, 452, 454
in gorilla, 657, 676, 692, 696
in lemur, 41, 42, 63, 69, 78
in man, 800, 814. 830, 838. 848, 850, 8^4, 8^5, S58,

859, 986
in marmoset, 163, 164, i~~, 190
in mycetcs, 210, 236
optic lobes of, changes in, 276, 2~9

relation of, to vision and hearing, 2-6, 277
in orang, 500, 523, 538, 542, 543
in Pithecus rhesus, 381, 386, 397, 399, 401, 402
roofplate of, rel.ition of, to hearing, 2-6, 2 —
in tarsius, lot, 13-^, 136, 2-7
Middle cerebellar ]X'duncle, in chim|)anzee, 574,

575. 595
in dog-headed baboon, 303, 321-324
function of, 55, 322, 323
in gibbon, 432
in gorilla, 6j6, 674, 6~5, 693

in le

-6t, 83

in man, 794, 798, 819, 823, 851

in marmoset, 172-174

in myeetes, 223, 224

in orange, 498, 515, 523

in Pithecus rhesus, 377-382

size of, significance, 56

in tarsius, 121, 123

Pages I 474 are in Volume I,

Miocene period, 743, 981, 982

possible existence of human form in, 731
Miibius on chimpanzee, 546

Monakow, lateral nucleus of. 5(e Blumenau, .Ancil-
lary nucleus.
Monotremes, i()o~, lojo

pons Varolii in, 2"i
.Mortar, development of, 761
Morton, 978
.Mosbach horse, 749

Motor activity, relation of, to expansion of sensory
portions of brain, 880
to t.iil, 12

.'irea, in hum.m brain. 93^, 101 i
.Motor speech center. See also Broca's convolution.

in ape-man of Java, 881

in Dawn man, 886

in man, 786

in Neanderthal man, 903

in Rhodesian man, 91 j
.Mousterian Period, 908, 931

cultural phase of, 7,4, 758, 759, 763

Hints of, 89,
Muscular .system, witness to evolutionary kinship, 10
Myeetes senieulus, appearance, behavior, 191-201

digits, 193-201

habitat, 192 201

larynx, i<»5

nucleus of Burdaeh in, preeminence of, 710

nucleus of Gol! in, preeminence of, 462, 708
preeminent balancing mechanism, 264, 465

t.iil of. 11)1 211, 203, 2^8, 463, 708

ty|)e of new world monkey, 4.;()
.Myelenccphalon in chimpanzee, 612

in macacus, 403
Myotensional states, in man, 803

|STli.ANDi:RriIAL man, 736, 750, 751 -75«. S61,
•^^ 893-909

ape-like afliliations of, 896

brain of, 738, 895, 897, 898, 904, 908

cave dwelling of, 754, 901

communal life of, 756, 901, 902

description of, 893-895

fossils of, 893, 896

implements of, 738, 753, 755, 758, 895

progression of, 740, 750, 753-757, 861, 895, 901,

902, 908
property rights of, 754, 901
skulls of, 893, 896, 897, 904

casts of, 897, 904
pages 47S-II20 in Volume 11.

I 100

INDEX

Neandtrtluil man, time of, "38, 750, 758
Negritos as pre-paleolithic, 771
Ncokincsis, 520, 527, 795, 1037
definition of, 700

evolution in plastic, sensitive structures, 1006
importance of, 700
incipient stage of, in liist dillereiitlation for

voluntary control, 1007
motor possibilities of, first revealed by .advent of

mammalian forms, 1007
probable connection of, with carl\ quadnuiianal

differentiation, 1040
relation of, to occipital contingent ol pallio-ponto-
ccrcbcllar system, 1015- ioh)
to preccntral area of frontal lobe, loic). 1020
to pyramidal system, 100- 1 1 10
to visual activity, 130, 527
Neokinetic activity greater in chimpanzee than in
other higher anthropoids, 701
limitations in gibbon, 702

explanation of, 702
possibilities of, in higher anthropouls, "!(>
capacity indicated bv great apes over inter-
mediate groups, 702
control in man, 797

indexed by superior cerebellar peduncle, 823
function, progressive expansion in, illustrated by
pontile nuclei, 719
by pyr.amidal system, 703
organization in ehim|)anzee, -01
in man, 797
in mycetes, 230

in orang, joo, 504, 520, 527, 529, 719
in Pithecus rhesus, 377
in tarsius, 99, 125
Neolithic Age, 738, 745, 766

man, 766, 931
Neo-olivc, 250, 688

in gorilla, 688
Neopallial zones, loij
temporoparietal, 1015

relation of, to equilibrium, 1015
Neopallium, 32, 96, 243, 2-5

of endbrain in higher anthropoids, 519, 520
expansions in, 824

in response to limb specialization. ■919
in macacus, 364

in man, interdependence of parts of, 935
relation of, to skilled acts, 272, 275
in tarsius, 127, 132

Pages I 474 are in Volume I,

Nervus abdueens. Scv Abducens nerve.

facialis. See Facial nerve.

hypoglossus. See Hypoglossal nerve.

oculomotorius. See Oculomotor nerve;
Third cranial nerve.
Ncuraxis, 708

in chimpanzee, 609, 616, 619, 621

in gibbon, 450

in gorilla, 658

in orang, 536

in Pithecus rhesus, 377, 381

primordial portions ol, 470

vertebrate, decussation in, 421
New ideas, length of time required to grasp, from

ape to man, 757
New Stone Age, 766
New World monkeys, -, 16, 22, 153, 1 54

behavior of, 459

high specialization in, 4-;9. 1010
Not ha ret us, 980
Nuclear structures, in brain stem ol Pithecus rhesus,

365
■ clarity of definition ol, 365

effect of Bourne method of reconstruction on, -3
Nucleus abduccntis. See Abducens nucleus
Nucleus ambiguus, in gibbon 429
in mycetes, 217, 218
in tarsius, 109
Nucleus .interior thalami, in Pithecus rhesus, 388
Nucleus arciformis. See Arciforni nucleus.
Nucleus caudatus in dog-headed b.iboon, 333
in marmo,set, 177, 181
in mycetes, 230
in tarsius, 132
Nucleus cuneatus, relation of, to ancillary nucleus
of Bliimenau, 2ii
in t.irsius, 139, 141 , [45
Nucleus dentatus in ehimp.inzee, ;86, .;8-, 59^,
716
distinctive appearance of, 588
position of, among primates, 589, 590
coefficients of, 268, 269
in higher primates, 717
description of, 319

in the three primate groups, 466, 717
in intermediate primates, 465, 466

neokinetic development of, 1025-1045
in dog-headed baboon, 318, 319, 323, 717

description of, 319, 320, 465, 466
expansions of, 265, 815
function of, 2ig, 265, 267, 318, 815
pages 475 1120 in Volume II.

INDEX

I I 01

Nucleus dentatus in jjibboEi, 433, 454

coeflicients of, 466
in gorilla, 670, 716

high organization ol, 670
in lemur, 52, 53, 50
in man, 815

comparison of, with gorilla, 81-;
in marmoset, i"!, i~2
in mycctcs, 2iy, 221
in orang, 515, 716

comparison with lower and higher forms, ^i-

index of increase in coordinative control, 515
in Pithccus rhesus, 375
relation of, to arms and legs, 26^, "]-

to behavior, 26-

to coordination, •;2, 1-2, 2ig, 26-, 318, 435,
71,-, 8.,-

to lateral cerebellar lobes, 26,. "ifi, 1024

to red nucleus, 26"
in tarsius, 11^, 118
Nucleus emboliformis. 5ft' iilso ("erebellar nuclei, 264
in man, 81 ^

relation of, to lateral cerebellar lobes, 26>
in tarsius, 1 18
Nucleus facialis. See Facial nucleus.
Nucleus fasciculus solitarius, in gibbon, 42~-429
in lemur, 4<>
in orang, 512
in tarsius, 108, 1 1 1
Nucleus fastigii. See also (Vrebeilar nuclei, 2(14
in dog-headed baboon, 320
function of, 320
in gibbon, 435
in lemur, 52, 53
in man, 815
in mycetes, 2ig-22i
in Pithccus rhesus, 37^
relation of, to balancing, ■53, 210, 320

to equilibrium, 320

to floor of 4th ventricle, 320

to juxtarestiform body, 320
signilicancc of size of, 53
Nucleus funiculus lateralis in tarsius, 1 i 3
Nucleus globosus. Scea/.so Cerebellar nuclei. 2(14, 2<>-)
coellicients of, 268, 2(h)
comparison of, with dentate nucleus, 268
function of, 268
in lemur, coellicients of, 268
in man, 81 ^
in orang, 515
in Piihecus rhesus, i~i

Pages I 474 are in Volume I,

Nucleus globosus, rel.it ion of, to behavior, 2^)8
to coordination, 268
to forelimb, 268
to posture, 268
Nucleus gracilis. Sec Nucleus ol Goll.
Nucleus, habcnular, in marmoset, 180
Nucleus hypoglossus. See Hypoglossal nucleus.
Nucleus hypothalamicus in marmoset, 181
Nucleus intercalaris, 7<w

Nucleus lateralis internus ihalami, in baboon, 332
in lemur, ~o
in Pithccus rhesus, 387
in tarsius, 131
Nucleus lateralis thalami, in lemur, 69

In Pithccus rhesus, 387
Nucleus masticatorius in chimpanzee, 599
in dog-headed b.iboon, 323-333
In gorilla, 687
in lemur, 59
in orang, .525
Nucleus mesialis tli.ilami, in lemur, 69, "o

in Pithccus rhesus, 387
Nucleus oculomotorius. See Oculomotor nucleus.
Nucleus of Pcrlia, relation of, to binocul.ir .ind
stereoscopic vision, 281
to oculomotor decussation, 281
in tarsius, 130
Nucleus ruber. See Ri-d nucleus.
Nucleus solitarius, in dog-headed baboon. 313, 314

in man, 810
Nucleus trochlcaris in tarsius, 123, 126, 127
Nycticebid.ie, family of Lemuroidea, 21
Nycticebus, 89

O'

jerm.iier on ethnology, 771

Obex, in dog-headed baboon, 303

in human brain, 798

in lemur, 40

in macacus, 361

in tarsius, 1 13
Oblongata. See alsn Medulla oblongata.

in lemur, 34, 35, 76

in marmoset, 158, 1,9, ifio, >(>t, 1^)2, i''2

in tarsius, 92, 94
Occipital areas, of cerebral cortex, relation of, to

vision, 277, 329
Occipital bone, membranous origin of, 862
Occipital concavity in lemur, 53

in mycetes, 206, 207

in tarsius, 160. 1*^11
pages 475-1120 in Volume II.

1 I02

INDEX

Occipital lobe, in ape-inan of Java, 877
bearing of, on vision, 878, 882
bearing of, on voluntary acts, 882
in cliimpanzte, 518, 569

relation of, to vision, 601
in Dawn man, 886, 8()2
in dog-licadecl baboon, 206, 298, 330, 471
in Eoanthropus Dawsoni, 891, 892
in gibbon, 412, 413, 414, 420, 470
convolutional pattern in, 415
supervision of vision by, 415, 420
in gorilla, 645, 651, 652

marked convolution of, 647
in human brain, 778, 779, 783, -84, 787, 788, 792,
793. 835, 948
comparison of, witli that of apes, 788
relation of, to association, "89, 795
to vision, 789, 795
in lemur, 30, 32
in marmoset, 158, 159
in mycetes, 202, 204-207, 22"
in Neanderthal man, 893, 898, 905, 906
in orang, 494, 495, 525

relation of, to vision, 525
in Pithecanthropus crectus, .ilisiiKc of sulcus
simiarum in, 877
comparison with gorilla and man, 878
in Pithecus rhesus, 357, 358
in Predmost man, 922
prominence of, in primates, 385, 386
relation of, to optic lobes, 67, 329
in Rhodesian man, 917
in tarsius, 92, 94, 98
Occipital pole, in gibbon, 413
Occipital surface, in gibbon, 416, 4-^0

bearing of, on evolution in vision, 470
in gorilla, 651
in man, 792

relation of, to cerebellum, -93
in orang, 497, 498
Occipito-parietal fissure in ehim|janze<', 568
Occipito-parietal incisure, in luunan variations in

individuals, 570, 779, 945
Oculo-ceplialo-gyric movement in chinipanzee, 704

in gibbon, 460
Oculomotor commissural and decussating axons in

orang-outang, 528
Oculomotor decussation, coellicients of, 283

comparison of great apes and intermediate and
lower primates, 724

Pages 1-474 are in Volume I,

Oculomotor decussation in lower primates, bearing

of, on vision, 279, 280, 282, 283
relation of, to kinesthetic associations, 284

to manual dexterity, 725

to neokinetic expansion, 725

to skilled acts, 284
Oculomotor nerve. See idsi) Third cranial nerve,
in chimpanzee, 575, 601, 621
in dog-headed baboon, 330, 331, 34^;
function of, 227, 228
in gibbon, 421
in gorilla, 68 1
in marmoset, 176, 178
in mycetes, 228
in orang, 528, 542
in Pithecus rhesus, 386, 388
in tarsius, 128-130
Oculomotor nucleus, 248, 249, 262, 279, 280
in chimpanzee, 591, 601, 622
in dog-headed baboon, 329-332, 347
function of, 67, 280
in gibbon, 432, 441
in gorilla, 681, 697
importance of, 527 --

in lemur, 47, 66-69, 84
in man, 831, 858, 859
in marmoset, 176-179, 186
in mycetes, 227, 228, 236, 242
in orang, 526, 542, 543
in Pithecus rhesus, 386-388

relation of, to internuelear connection, 279, 280
in tarsius, 128-130
Oculomotor organization in dog-headed baboon,

329

Old Stone Age, men of, 738, 745, 759, 762, 765, 766,

773. Sec al.sii Paleolithic.
Old world numkeys, 7, 12. See also Catarrhine.

inlluences activating modilications in, 16, 17,
287,981

lowest the dog-headed baboon, 289 (
Olfactory bulb, in chimpanzee, 570

in dog-headed baboon, 297

in gibbon, 413

in gorilla, 649

in lemur, 32

in man, 791

in marmoset, 160

in mycetes, 206

in orang, 496

in tarsius, 92-96
Olfactory nerve in tarsius, 92, 93, 94, 97
pages 475-1120 in Volume 11.

INDEX

1103

Olfactory sulcus in chimpanzee, "2

in gibbon, 413

in man, 791
Olfactory tract in chimpanzee, ,"2

in gibbon, 413

in goriihi, 649

in man, 791, 947

in mycetcs, 206

in orang, 496
Oligocene Period, 981

first bipedal locomotion in, gSi

time of departure of llornini<lae IroTii common
stock, 733
Olivary complex, in Pithecus rhesus, 397
Olivary eminence in chimpanzee, 572, 612

in gibbon, 417

in gorilla, 662

in man, 796, 843

in orang, 498

in Pithecus rhesus, 359
Olivary nucleus, inferior, in gibbon, 4-;(), 460
Olive in mycetcs, 208, 209, 219

inferior coclTicients in intermediate primates, 460

in tarsius, 99, 100
Olivo-cerebcllar pathway, (unction ot, 248
Ontogenesis, 262, 986
Opposable thumb, 981

relation of, to psychic elements, illustrated by
howling monkey, 212
Optic chiasm in chimpanzee, $~o, 5-5, 605

decussation in, in tarsius, 9"

in dog-headed baboon, 297, 300, 301, 332, 534

in gibbon, 415, 418, 444, 445

in gorilla, 652, 659, 685

in lemur, 36, 38, 69, 70

in man, 791, 834, 836, 947

relation to, of optic nerves and tract, 947

in marmoset, 162

in mycetes, 205, 208, 229

in orang, 5O0, 530, 531

in Pithecus rhesus, 359, 362, 364

in tarsius, 9~, 112, 131, 132
Optic decussation in mycetes, 229

in Pithecus rhesus, 387
Optic lobes in dog-headed baboon, 329
strata in, 329

in lemur, superseded by cerebral cortex, 65, 6-

progressive changes in, 276, 2'"7, 329, 385

in tarsius, loi
Optic nerve in chimpanzee, 5~o, 605

in dog-headed baboon, 300

Pages 1-474 are in Volume I,

Optic nerve in gibbon, 418

in gorilla, 650

in man, 835

in marmoset, 162

in mycetes, 208

in orang, 531

in Pithecus rhesus, 362

in tarsius, 100
Optic thalamus, in chimpanzee, 605, 607
function of, 354, f>o6

in dog-headed baboon, 334

in gibbon, 445, 446

in gorilla, 682, 683, 684

in lemur, 70, 71

in man, 835, 836

in marmoset, importance of, 180, 181, 182

in orang, 530, 531

in Pithecus rhesus, 389
Optic tract in chimpanzee, 570, 575, 605

in dog-headed baboon, 332, 334

in gorilla, 650, 657

in lemur, 69

in man, 835

in marmoset, 180

in orang, joo, 531

in Pithecus rhesus, 364

in tarsius, 131
Optico-peduncular space in chimpanzee, 575, 601,
603, 604

in dog-headed baboon, 300

in gibbon, 421, 441, 443

in Gibraltar skull, 907

in gorilla, 657, 681

in lemur, 36, 38

in man, 791, 833

in marmoset, 162

in mycetes, 208

in orang, 500, 528

in Pithecus rhesus, 388

in tarsius, 99, too
Orang-outang, 12, i", 22, 478-544

arboreal life of, 17, 483, 484

behavior of, 480, 483, 491

general appearance of, 479, 480

habitat of, 4-9, 483

measurement and indices of brain of, 492
Orbital concavities, in ape-man of Java, 875

in chimpanzee, 570

in dog-headed baboon, 296, 297

in gibbon, 413, 415

in Gibraltar skull, 906
pages 475 1120 in Volume II.

iioa

INDEX

Orixtal coocavities, in gorilla. 64S
in lemur, 32

in irmn 8^

ia mannoset, i^'j- . ■

in mytxtes, 205, 3o6

lis orang. 4^

in Phhecvis rfaesas, 359

in Rbodesan man, 914

!- -.^rsius, 93, 96

opexcolom. See Pars orbrtalis, -81
...,.:_ sarface of brain, in gorSa, 64-, 648
resemblaiice ot, to that of man, 648

in "»»" "92

in marmoset, 160

in orang. 496
Qsbom. Henr>- FairfieJd, 12, -30, -59, -75. 929. 9>7
Owen, Sir Richard, on orans-ootang, 4—

PACCHIONIAN etikr^mcnt, 872, 899, 9"3

Pakoanthrapos Heidelfaeiaenas, -3-, -38, -49. Tji
characteristics oi, 737. "38, 751
life of, -y, -49
relation erf, to man, TST.'S**
time of, -3-, -49
P-'f-.l-^TM-^a in balancing mechanism, -^14, 823, 1038

rclitioo of, to uncinate tract, 823
Paleokinetic orsanization of lower vertebrates, 520
Paleolithic Age, imiJements of, -45--46
subdivisions erf. "46
Greets, -63, 861. See also Anrignarian Period,
man, art of, rrplanations of, "^
predecessors of, 4"%
P-iJc^Wr-.-e. 249, 1031
F §, ertinct form, -19, -32

F •.• fiijers, bearing of, on behavior, €r6

cocuxct cerebral hemispheres with lateral lobes of

cerebennm, 58, 2^2, 274
fuDctioa of, 2^4, 2-5, 389
path of, 2^2, 2-4

relation of, to cerebral cortex, 2-2, 301
to coordination, j8, 2T2, 1015
to MHetal lobe, 1015
P • system, in chimpanzee. 617, 620

ded baboon, 301, 342, 345
in gibbon, 454
in gorilla, 676, 693, 695
in lemar, 58, 64, 68, 71, 78, ?9
in mycetes, 23-, 238
inTorang, 540, 542
in' Pithecus rhesus. 389, 399

Paces 1-474 >re ia Vohune I,

Pi^ 5\-stem. in tarsius. 12-

P^i ,Lrt.in"3r s>-stem, in chirr. -3,

i- _ ,n, 304,328

: 529.682

i ^ -2.6S2

:". to cerebral p)eduncle, 682
- . jl7

in marmoset, i~7

in mycetes, 22-

in orang, 520, J29

p-"-' '"■-■- nt feature the ;..„_._-. r. of cerebral

res, 518, 529
re;^^; --■! cortex, 529

toe tr, ^2, -^-

tO Coaip.t:JL .iClS. ^"2, 2~J

to coordination, 2-2, "99
to lateral lobes, 266
to z>r.:'lc nuclei, 1020
- 518, 52C1
r^i. --^..™. system, in — ...,,_r^te, 6l~, 620
in d<^-headed baboon, 342, 345
in gibbon, 421, 454
in gorilla, 695
in lemur, -8, ~g
in orang, 540, 542
Pallium- Ste Oirtt
Pan satyrus- See (-

Papio cynocephalus. See Baboon, dog-headed.
Papio, genus, 289

Parietal bone, membranous ori^ of, 862
Parietal lobe. ! nzee, 566, 568

in dc^-heac - . 2<j6. 334

in EoanthropUi DiASoni, 886, 889, 891
benrir-.z of, on hand, 889, 891

n of, with ape-man, 889
ei. :, 568

function of, 876
in gibbon, 412, 414
in gorilla, 645
in Homo Neanderthalensis, 898, 902

reiatioa of, to manual de\-eIopment, 902
somesthetic capacity of, 902
in Homo Rhodesiensis, 916, 922
in human, convolutions of, 779, 780, 783, 784, 786,
78-. 788, 789
function of, 789, 790, 795
comparison with other primates, 790
in marmoset, 158, 159
in mycetes, 202, 204, 205, 206
pages 475— XI 30 in Vohune IL

INDEX

IIO^

Parieral lobe, in oran^ 4£» j, 4^

in Pithecanthrapas erecrus, ovmmrisom virh

HcaiKi sapiens. 8"^ 8 — . 881, 944

expansion, c^tuse ol. ^SSo. 88 1
in Pith«ra5 riiesBS., 3—, 358
rE^tiotn of. to quadrnzBanal <£serenTiaTion sjad

prehensSe ta3. 99I

in TargTtT< #>•» ^

Parietal respon, in Ezbbom. coavaltraosis oC 415
Pari«o-occiprtal fissoit, faoinan, -&2, "83, /S6

compaiisocE ci wiTli amiropoadi. "83
Paj? basalis. -Si. -86, 901
Pais ortitaEs, -81, "SS. 901
Pars trianEoIaris, "8l, ~96, OOI
Pa-4-jo\-. 03Z. 933
Pesck. 886

Penny, dooor of gorSa. 632. 63—
Personalrrr, dc\-eicK>n>eEl of, rf^sTJom <£, to frontal

lobe. ^95
Pes peduocoE of midbrain in hshixeL, 345
Pia mater, 862
Pigment, biack. beaiing of. on ssxtsrsoOcsl &s:jz~

butioei. — 5
Pigs, iol 491
P3tdo»-n man. -42. -51. -52, S61, 8S4. Set ciso

Eoantiirous Da-a-soni, "42
Pineal fossa in cjmapanzee. 5-5

m sc^ula, 65—

in man. -x>9, 834, 918
Pinea] gj-ind, frmraoa of, S34

in Jesnar, 40

in miiTi -xjci. Sji. ciiS
Pitiiecantliropus enscras. ti>e ape-maa, 861
brain of, -35- -3-, 8861. SS"
cah-ariirm of. -35, S60
DoBoss 00, — 3>, -45
dx'naxnjc factors in. 9^

foSsSs of, -3>. ~43

rmpressJioQes ajad jn^ of frcjatral Icibes of. SS3,

comparison oL ■«Tti soiSla, SS"
cannrng rf kaod of. -3^ SS4
frrmtal iabes of. coimpaiied irttii Hoa>o sapaeits.

-3-. 883- SS4
rmpjemeats of, "45
oUest primitivie race, -38. S6S
of^in of. -35. -38. -42, -49. 868
possure of, -35. SSo. SS5
rransTDona] g-^gc of. -3^. S6S
Prrieeus rfaesscs, aoqiiistiMeaess o£ 361
beiavio« of. 3i9-3-;2. 3-;3, 364. 3 —

Rises i-«-i «re ia T:

Rtbems litesus. ccmni&Hson of. trtjt huhntm, 364

digiti of. 3 jo. 352. 353

geaeral descrtyaca of. 349. 390

secjerspbjcal dif^iHbcitiaii of. 349

iifh^f! of. 350

locosDOtion of. 353

Btoisaitsotsns sod rndkif? of. 355

sk^ ol 364. 3 —

tail of. 3-'0
PiaaiiBs tooL -4—. —58
Planti£xade iocxearnxm, 13, 364. 8S1

neiasicai of. 10 jgnfraT kJje. SSi
Pfcstoceasc Period, earfr pait oC is time of besm-

niiiE: of fesrm];- sjeties, -31, S61, 886, 935

Plioceae PeriacL -43. SS6^ 935
l^te part cHL as time of bcfisning of inmus
species. -31
PneiimaCESCric Ben'C. 5oe Vagus.
Poli^aez. devei-^pmeast oL -^1
PoQs X'aixS. in r^^T^pFfiTff 5-4, ~y, 586, 501. 592.

in h£}»xi, aor. 30a. 301, 320, 321-32-, 342

in gibbia. 4 15, 4! -.4:8,43^439.451

in soir3La. sien to tfeat of maa. 65-. 6-2, 6-4, 6-5,

vitri/-\ « iiareffisesice. 2-1. 364

in ksDcr, 35. 36-5S1. 56. 5--614. -8

in mam heziisa^ of. os siaiSed acts. S21

ficactioiE c£. -KT

proasiueacit of. -^06. 800, Sii. 81-, 819, Sao,
S23. 824. S30. S4&. S50
in marmaset 159, 162, i~2. 1-4
in inj-cete&, 2C>5. 3oS^ 2I0l 223-230
ia oranr. 409. 500. 51-. 521. 523

CTTn^j^-xjw of praamsteaice. 499-51—
in PJtnecTts rhesus, 359-364. 3~. 3S0-3&2. 3&i,

prosciaeaoe of. 364. 3S0
tclatioin of. to cooin£natk<m £sd dbiSed .acts, 36,

3-. 223-22-. 2-1. 301. 364. 409. 51-
aae of. to size of cxirbri-\ ooraei. 2—2. joi. 364,

51"
to siSUed acts. 223. 2-1, 2~2. 301, 30a, 364
to vccticcial o^artrci. 22-
sgriacaace of T-iriaticais of siae of. 2~i, 3—2
in tarsus, g^"* >'> size cl. 91. 99, loa. I2i— L25
low dei-^icoanent of. 121
Poctile socieL in cbimptsiaee. 5861, ^t~593. 614-630
agsi&ciaot of. 593
conipariste! oiL in cncit aoes. •^ixk istermesfiate
aad io»iK- prmtsTes. — ac
- -- »T=-iia« is TbIeibs D.

1 1 06

INDEX

Pontile nuclei, di'linition of, 272

in <Jog-hc-;Kii-d baboon, 321-327, 342, 345

I'unction of, 272, 275, 301, 1014

in gibljon, 421, 436, 450, 451-453, 467, 468

in gorilla, increased extension of, 672, 676, 690-

693.695, 719
significance of size of, 674, 676, 725
in higher anthropoids, coellK-ients ol, 719, 720
importance of, 2~3

index of eoordinalinn and skilled acts, 59, 271,
272, 467
of evolutional unfolding, 273, 722, 1020
of expansion of cerebral cortex, 272, 301, 71H
in intermediate primates, cocflicients of, 468
relation to skilled manual movement, 467, 468
superiority of, over lower primates, 468, 469
intimate bearing of, on ncokinesis, 1014
in lemur, 56, 57, 58, 59, 60, 61, 64, 73, 79
reconstruction of, 77, 78
relation of, to metencephalon, 78
in lower primates, coefficients of, 273
in man, 820, 823, 837, 843-853, 856
complexity of, 837

increase in size of, 811, 820, 83-, 838, 850
significance of, 820, 823
in marmoset, 172-175, 186-188
in mycetes, 223-226, 235-240
in orang, 517, 522, 538-542
in Pithecus rhesus, 377-384, 397-401

comparison of, with baboon, 380
relation of, to coordinative control of muscles of
extremities, 10 14
to mammal dillerentiation, 276, 467
size of, to number of fibers, 274, 301
two buttresses and layers of, 399
Pontile tegmentum, in gibbon, 339, 340
Porpoises, 10
Posterior cerebellar notch in chimpanzee, 571

in orang, 49"
Posterior commissure, 249

in man, 814, 858
Posterior longitudinal fasciculus in dog-headed
baboon, 311-316, 327-33". 34". 342
in gibbon, 426-432, 439, 441
in human, 824, 829

in lemur, 47-50, 52, 55, 57, 60, 61, 62, 66, 76
in marmoset, 167, 169, 170, 171, 173, 174, 176, 178
in mycetes, 215-226
in orang, 515, 525
in Pithecus rhesus, 3-2-386, 403
relation of, to regulation of motion, 120

Pages 1-474 are in Volume.I,

Posterior longitudinal fasciculus in tarsius, 108,

109, 111-113, 118-121, 123, 127-130
Posterior medullary velum, in human, 824
Postinfundibular eminence in man, 833
Post-olivary sulcus in human, 796, 849
Postsplenial fossa in chimpanzee, 570, 571
in gorilla, 651, 652
in lemur, 33
in orang, 496, 497
pertains to primate brains, 972
Postural evolution, stages of, 978-983

bearing of, on differentiation in the hand, 983
efi'eet of, on digits, 978-981

importanei' of dillerentiation of foot in, 982
relation of, to arboreal habitat, 978-983
to braehiation, 980, 998
Postural regulation, amplification of, 13
best, 260, 261

relation of, to coordination, 221
to pallio-pontile connections, ^8
Posture, adjustments of, in lemur, 44
relation of, to cerebellum, .Si'i
in tarsius, 87
in baboons, 294, 317
erect, in ape-man of Java, 877, 881

complexity of sensory mechanism in, 881
relation of, to parietal lobe, 881, 882
to cerebral peduncle, 1021
to development of foot, 1021
first shown in gibbon, 1-
in lemurs, 27
in man-like apes, 17
relation of, to balancing, 264
in lemur, relation to pallio-pontile connections, 58
in macaqvies, 349
in mycetes, relation of hand to, 214

relation of, to coordination, 224
in orang, 486

regulation of, by cerebellum, 816
in tarsius, 87
Pottery, introduction of, 766
Pre-C'hellean man, implements of, 747, 751
life of, 747-749, 751, 752
time of, 747, 749, 751, 753
period, 931
Precipitin tests, bearing of, on evolution, 7, lO
Predmost man, brain of, 921, 922

life and art of, 918-921
Predorsal bundle, in dog-headed baboon, 311, 313,
316, 326, 327, 329. 330, 333. 340
in gibbon, 426-441
pages 475-1120 in Volume II.

li\DI£.\

I 107

Predorsal bundle, in man, 824, 829

in marmoset, 167, i6g, 170, fi, 1-3, i-(>, 1-8
in mycetes, 215, 217, 218, 220-222, 224, 226, 228
in Pitlieciis rhesus, 372, 373, 3-6, 3^8, 38 r, 382,

384, 386, 403
relation of, to regulation of motion, 120
in tarsius, 120, 121, 123, 127

relation of size to automatic movements, 117,
1 K)
Prefrontal area, development of, significance of,

<)35

responsive plasticity in, (>3j
Prehensile tail in Cebidae, 16, 230, 2^8, 303

functional capacity of. In new-world monkeys, 459

lacking in old-world m()nkeys, 17

in tarsius and baboon, loj, 106, 303

in mycetes, 191-203, 210, 212, 230, 2iH, 303

relation of, to balancing, 263, 264
to locomotion, 258, 259
to nucleus of Blscliolf, 256, 257
to nucleus of Goll, 209, 212, 256, 258
to skilled hands, 258, 2-59, 263

significance of, 12, 13, 15, 203, 2 in, 256, 258
Prehistoric man, fossil remains of, 925

why called Ape man, 926, 927, 928, 936
Pre-Ncanderthalold man, 750. See also Paleoan-
thropus Heldelbergcnsls
Prc-olivary sulcus, in human, 796
Pre-paleolllhlc culture, today, 771

man, types of, 737, 745, 749
Primate brain, broad brainedness of, 944, 952

concavities in, 947

convolutlonal pattern of, 94"

diametric indices of, 943, 944, 9-;2

encephalic indices of, 941
significance of, 948, 991

fissural pattern In, 944, 945, 954

inferior vermis in, 948

lobation of, 94,

occipital lobe of, 948

olfactory bulb and tract of, 947

optic chiasm and optic nerves of, 947

pineal fossa in, 948

specific modifications of, 992-1045

structural homogeneity of, 944-948

vallecula (vcrmal notch) in, 948
Primates, bonds of kinship between, 14, 423

classification of, 21, 22

comparative study of, 13

first structural modifications fif. In lemurs, 15

four divisions of, 22

Pages 1-474 are in Volume I,

Primates, intermediate, comprise what, 287
nucleus of Goll in, 580
vermal ridgepole in. 416
why thus grouped, 28-
lower, nucleus of Goll in, 580

vermal ridgepole in, 416
pyramidal decussation in, 423
six species of, comparative survey of, 426, 427

unity ol structural design in, 42"
superior collicull in, 385
Primitive man, time of, Keith on, -31--3,-, -42, 886,

88-, 891
Primordial .auditory organization, relation of, to
automatic reactions, in lemur and marmoset, 175
Proprioceptive organs, 249
of forellmb, 256

In gorilla, deep sensory inHux from, 660
of hind limb, and tail, 49, 305, 317, 318,
of internal ear, 262, 431
in lemur, 49-51
Proprioceptors of body, relay of sensory impulses,
374
in tarsius, 1 13

of trunk and extremities in glblx>n, 431
of vestibule of internal ear, in chimpanzee, 583,
592
in dog-headed baboon, 317
in gibbon, 431

in man, high degree of specialization in, 81 1
Pseudo-S\l\'ian sulcus, 955

Pulvinar of optic thalamus in chimpanzee, 605
in dog-headed baboon, 301, 337-341
in gibbon, 419
in lemur, 39, 75, 77, 79
in marmoset, 163, 187, 189
in mycetes, 209, 235-239
in Pithecus rhesus, 363, 395, 397
in tarsius, loi, 139, 141, 143
Putamen, in dog-he.ided baboon, 333
in gibbon, 445
in lemur, 70
in man, 835
in mycetes, 229, 230
in Pithecus rhesus, 38", 389
Pygmies as pre-paleolithlc, "i

Pyramidal decussation in chimpanzee, 572, 576,378
in dilfcrent mammals, 423
in dog-he.ided baboon, 299-J09
effect on detachment of ventral gray column from

central gray matter, 423
on field occupied by decussjited fibers, 423
paf!cs 475-1120 in Volume II.

iio8

INDEX

Pyramidal decussation in gibbon, 418-423
in gorilla, 654-658
in human, 795, 800, 801, 804
in lemur, 35, 38, 41, 42, 44, 76, 80
as mammalian contribution, 423
in marmoset. 162, 164, 165, 166, 184, 185, 188
in mycetcs, bearing of, on voluntary' control, 208,

209, 211, 212, 235
in orang, 498, 502, 509, 536

indicates increase in volunt^iry control, 503-506,
507
in Pithecus rhesus, 359-367, 391-396
in primates, distinct nature of, 423

dynamic significance of, 423
relation of, to cortical control of behaxinr, 423

to ncopallial development, 423
in tarsius, 100, 103-105, 136, 149

Pal-W'eigert preparations of, 103
Pyramidal fasciculi in lenuir, 41, 42, 56, 59, 79

in mycetcs, 238
Pyramidal system in chimpanzee, 603, 605
in dog-headed baboon, 304, 305, 320, 325, 326
in gorilla, 658, 662, 672, 674, 679

function of, 682

massive character of, 658
in higher anthropoids, 699-703

coellicients of, 701

comparison of, with int^Tiiiediatc mid lower
primates, 702, "05
index of volitional control, 212, 2 [6, 22-, 305, 310,

422, 457, 699, 701
in intermediate primates, 457

coefhcients of, 457, 458
in lemur, 34, 35, 38, 41, 42, 46, 56, 58, 50, 64, 68,

71. 79
mammalian acquisition, 421, 699
in man, cxtensiveness of, 801, 806

path of, loio, loi I

relation of, to motor area, 101 1

significance of, 806
in marmoset, insignificance ol, 162, 16-, 172
in mycetes, 223-227
in orang, 529
in Pithecus rhesus, 365, 368, 3-^1, 377, 383, 399,

702
relation of, to cerebral cortex, 422

to cerebral peduncle, 682

to decussation, 421
in tarsius, 1 27

emphasizes low organization of pons Varolii,
124

Pages I 474 are in Volume I,

Pyramidal tract in chimpanzee, 591, 592, 614, 617
comparison of, in lemur, marmoset, mycetcs and

tarsius, 243-246
in gibbon, 448, 450, 451
in gorilla, 659, 692, 693
in man, axons in, loii

condensation of, 101 1, 1014

relation of, to cerebral peduncle, -92, 849, 850,
loio, lOI I
in orang, 529, 536
in Pithecus rhesus, 399
relation of, to behavior, 244

to skilled acts, 244, 245

to voluntary control, 243, 244
in tarsius, 102, 105
Pyramids in chimpanzee, 572, 578, 580, 583, 586,

591, 613, 617
in baboon, 299, 300, 306-321, 324-328, 342
in gibbon, 417-435, 455
in gorilla, 654, 655, 662-674

indications of, as to voluntary control, 655, 656

prominence of, 655
large, in man, 795, 796, 797, 805, 806, 808
in lemur, 45, 48, 49, 50, 52, 53, 55, 57, 60, 61
in marmoset, 162, 165 -175
in mycetcs, 208-217, 218-226
in orang, 498, 517, 539, 540
in Pithecus rhesus, 359-398
relation ot, to volitional control over somatic

musculature, 656, 663
in tarsius, small size of, 99, 100, 104, 106, 108,
III 1 13, 1 1-, 1 18-125

relation ol, to voluntary movement, 117

QIIADRIGF.MINAL plate of midbrain, in chim-
[jaiizee, 5-5, 599, 601
in dog-headed baboon, 303, 325
in gibbon, 439
in gorilla, 657
in lemur, 40, 63
in macacus, 363
in man, 799
in orang, 500, 501, 525
Quadrilobular arrangement, 945, 964, 965
Quadrumanal characters augmented by psychic
influences, 15
developed from arboreal transit, 14, 15
established in Cebidae, 16, 230
in lower primates, 257

as retarding specialization in upper extremi-
ties, 717
pages 475 11 20 in Volume II.

IXDF.X

1 !()()

Ouadrumanal characters in man-like apes, i^, i8
dillercntiation in Pitheciis rliesiis, 14, 1^, 350, 976
in prosimia. lo^o
Oiiaclriiped I\pe in tioii-tu-acied I^aboon, 520

R

ABBIT, 11(1. 114, 121, 1024

Haven, llarrv, on luintinfj tarsius, <X)

Reactions in chimpanzee, resembhince of, to man,

554. 557. 558. 559

illustrated by countin};; ability, 565
emotions, 559-561
progressive readjustments in, 13
Reconstruction by Bourne method, 73
Red nucleus in chimpanzee, 600-605, 616-624

significance of, 603, 60 j, 717
coellicients of, 269, 270
definition of, 68, 603
in dos-headed baboon, 466

coelhcient of, 467
function of, 26-, 269, 68 1
in gibbon, 441, 443, 4,-0, 454

advance as to control over coordination, 441

expansion of, 442

relation of, to arboreal locomotion, 442
to nucleus dentatus, 442
in gorilla, 680, 681, 692

signihcance of size of, 681, 682, 696, 717
in higher anthropoids, coellicients of, 718
index of coordinativc capacity of lateral cere-
bellar lobes, 1029
in intermediate [primates, coelficients of 466, 46-

comparison of, with lower primates, 467
lack of functional parallelism with dentate

nucleus, 270
in lemur, 64, 66, 69

reconstruction of, 73, 82

relation to the mesence]jhalon, 82

significance of size. 68, 82
in man, 832, 838, 846, 848, 856

function of, 832

relation of, to coordinativc control, 832
in marmoset, 175-179, 186
in mycetes, 228, 229, 236, 241
neokinetic development in, 1029
in orang, 528, 538, 542, 717

advance in, 528

bearing of, on coordination, 530
in Pithecus rhesus, 385-388, 398, 402
relation of, to cerebellar expansion, 269, 270

to coordination, 229, 2-0, 603, 605, 1029

Pages 1-474 are in Volume I

Red nucleus, relation of, to nucleus deiitates, 26-,
269
to superior cerebellar peduncle, 1029
in tarsius, 128-132, 143
Rellex actions, limited, in chimpanzee, 5~5
in tarsius, 125
acts in primates, between ear and eye, 435
control in dog-headed baboon, 300
Regulation ol motion in chimpanzee, 604

dependence »(, or cooperation between lobes of
cerebral hemispheres and lateral lobes of
cerebellum, 604
Rcil, island of, in dog-headed baboon, 298
Reptiles, 260, 276, 2-9

blood reactions indicate relationships between, 10
Mesozoic orders of, 1 044
optic lobes of, 279
paleokinesis in, 1038
predominance of colliculi in, 387, 1033
Rcstiform body. See ahu Inferior cerebellarpeduncle.
in chimpanzee, 583, 585, 591

in dog-headed baboon, 304, 312, 313-318, 343
entry of, into inlerior cerebellar peduncle, 853
in gibbon, 417, 418, 429-432, 449
in gorilla, 655, 663, 665, 667
in lemur, 50-52, 55, 76, 83
in man, 810, 813, 814, 852, 853
in marmoset, 170, 171
in mycetes, 217-221, 247
in orang, 512, 513, 540, 541
in Pithecus rhesus, 360, 373-376
relation of, to ancillary nucleus of Blumenau, 255
to coordination, 51, 52, 318
to dillercntiation in hand, 255
size of, as scale of alfercnt inflow, 55, 56, 318
in tarsius, 1 14-116, 117, 118, 119, 146
Reticular formation in chimpanzee, 578, 580, 583,
591, 592, 603, 612, 613, 614-617, 620, 621
in dog-headed baboon, 309, 311-316, 321, 324,

i2(>, 327. 3 JO, 331, 333, 336-342, 344-346
in gibbon, 425-432, 438, 443, 448-450, 451, 455
in gorilla, 658, 665, 673, 679-682, 685 688, 689-

6g6
in lemur, 42, 46, 48, 49, 50, 52, 55, 57, 60, 62,

66, 69, 73, 75, 76, 77, 78, 79, 80, 8r, 82
in man, 803, 804, 815, 820, 824, 826, 832, 833,
838, 842-849, 851, 852, 854, 855, 8,-6, 858
sharpness of outline in channels in, 839
in marmoset, 166, 167, 169-174, 176, 178, 183-190
in mycetes, 215, 217, 218, 220, 222, 224, 226, 228,
234, 235, 236, 23-, 238, 239, 240, 241, 256
pages 475-1120 in Volume 11.

I I lO

INDEX

Reticular formation in orang, ji2, 521, 528, 529,

533-542

in Pithecus rhesus, 366, 36-', 369-373, 375, 376,
378, 379, 381-386, 388, 39-2-403

in tarsius, 102, 104, 106, 109-116, 118, 119, 121,
122, 123, 128, 129, 136-151
Retzius, 960

luiiiciilus sc'parans of, 799
Kliincnci'plialon, 898, 951, 970

Rhonibenceplialon, tegmentum of, in Pithecus, 396
Rights of possession, development of, 752, 754-757,

766, 932
Rodents, 124, I2j, 128, 30-, 100-, 1039
Rolando, fissure of, 945

in .'ipe-man of Java, 871, 8-2, 8-6

in chimpanzee, 567

in Dawn man, 888

in dog-headed balloon, 295

in gibbon, 412, 414

in gorilla, 645

in human, 779, 782, -83, 786, -87

in lemur, 954

in mycetes, 959, 960

in Neanderthal man, 899

in orang, 493

in Pithecus rhesus, 355, 357

in Predmost man, 922

in Rhodcsian man, 913
Rolando, nucleus of.

in chimpanzee, 576—585, 591, 595, 609-619

in dog-headed baboon, 306 324, 336, 338, 339,
346

function of, 306

in gibbon, 418-431, 432-437, 447-452
significance of small size of, 424

in gorilla, 660-667, 672, 675, 685, 686-689, 694

index of sensory influx from head and face, 256,
257> 306, 307, 368, 709, 71 1

in lemur, 42-60, 74, 77, 80

in man, 802-806, 81 1, 814, 841-846, 852

in marmoset, 165-171, 183, 184

in mycetes, 211, 214, 215-222

in orang, 503, 506, 509, 510, 512-513, 523, 534,
535. 538

in Pithecus rhesus, 366-381, 391-400

relation of, to locomotion, 307, 368

in tarsius, 104, 105, 106-109. lit, 116, 118, 119,
121, 137, 138, 139, 141, 143. 145
as evidence of facial innervation, 105
Rolando, substantia gelatinosa of, 234
Romanes on chimpanzee, 546, 565

Pages 1-474 are in Volume I,

Rubrospinal tract, in dog-headed baboon, 306, 308,
309, 311, 313, 315, 316, 324, 326, 327, 333

in gibbon, 422, 424, 425, 426, 428, 429, 431, 432

in lemur, 42, 45, 46, 48-50, 52, 55, 57, 60-62, 69

in man, 804, 806, 808

in marmoset, 166, 167, 169, 170, 175

in mycetes, 211, 215, 217, 218, 220, 221, 224,
228

in Pithecus, 366, 367, 369, 372, 3-3, 382, 384

relation of, to coordination, 228

in tarsius, 102, 104-111, 114, 116, 118, 123, 132
Ruminants, 10
Rutot, 886

SACCULE, 49, 1 70, 261, 262, 315, 320, 513, 583,
592
Schwalbe, 862, 872

nucleus of, in chimpanzee, 584, 591, 592, 619
in dog-headed baboon, Ji6, 343, 344
function of, 170
in gibbon, 431, 432, 452. 453

relation of, to balancing mechanism, 432
in gorilla, 667, 694
in lemur, 50, 52, 53, 80, 83
in lower primates, coefhcients of, 262, 263
in man, 813, 814, 852, 858
in marmoset, 170, 171, 188
in mycetes, 217-220, 221, 236, 238
in orang, 513, 540

in Pithecus rhesus, 373, 376, 400, 403
in tarsius, 114-117, 118, 145, 149
Scraper, 758

Sculpture, art of, development of, 761
Second Interglacial Period, 749, 753
Scmangs as pre-paleolitliic, 771
Semicircular canals, 49, 170, 261, 262, 315, 320, 583,

592
Semilunar fissure. See Sulcus simiarum.
Scnci as pre-palcolithic, 771
Sensory conduction in marmoset, 165
Sensory equipment, in lemur, development of, in
cerebral cortex, 65-67
in man, separation of lower inllux Irom inllux
from upper limb, 802
size of field of, 789, 790
in mycetes' tail, 191, 203, 213
Sensory organization, formula of, for higher anthro-
poids and man, 578
for lower primates, 578
Sensory territories, major, 165
Seventh cranial nerve. See I'aeial nerve,
pages 475 1 1 20 in Volume II.

INDEX

1 1 1 1

Shepherd on ehimpanzec, 546

on Maeaeiis rhesus, 354
Sight. See Vision.
Silent area. See Frontal lobe, ~8ij
Simia Satyrus. See Orang-outang.
Simian characters, introduced by new world

monkeys, 16
SIniian fissure in ciiiinpanzee, 76S, ^(n)
in gibbon, 412
in gorilla, 645
in human brain, 5~o

position of parieto-occipital, 64,
in orang-outang, 493, 494, 495
Simiidac, family of, 2:, 478, 706
modern forms of, 477, 478
origin of, 731, 732
structural evolution of olive in, 703
Simultaneous movements of head, eye and h.ind,
'3. 2'", 35, 112, 168, 216, 2i(). 24Q, 251, 254, 2H4
in chimpanzee, 555, 582
in gibbon, 460, 705

advance in, 430, 459, 705
in gorilla, 656, 665

relation of, to structural expansion of inferior
olivary nucleus, 656, 667, 704
in orang, 512

relation of, to inferior olive, 249, 284, 300
Si\th cranial nerve. See Abducens nerve.
Skilled acts, adjustment of sinuiltancous movements
in, 13, 27, 36, 37, 168
automatic control of, in marmoset, 168
in tarsius, 105

illustrated bj' catching insects on wing, 112
relation of, to absence of retinal macule, 1 12
to decussation of fibers, 1 1 2
of chimpanzee, 582, 590, ^93

comparison of baboon with macacus, 4^8, 460, 466
of gibbon, 430, 460
of gorilla, 665, 666, 676
of lemur, 35, 41, 42, 47, j6, 58, 59
of marmoset, 164, 166, 168
of mycetes, 210, 283
of orang, 499, 510, 511
relation of, to cerebellar nuclei, 377

to connection between cerebral cortex and

lateral lobes of cerebellum, 593
to cortex of cerebrum, 65, 272
to differentiation of hand, 210, 282, 665
to inferior olive, 35, 47, 168, 219, 249, 300, O65
to kinesthetic sensibility, 272
to locomotion, 276, 665

Pages 1-474 are in Volume I,

Skilled acts, relation of, to ocular advance, 130, 250,
281, 282
to oculomotor decussation, 282
to pontile nuclei, 56, 59, 382, 820
to size of cerebral peduncles, 127, 129, 131

of pons Varolii in marmoset, 162
to superior cerebellar peduncle, 822
of tarsius, ro,, 1 10-112, 120, 12"
tw'o simultaneous streams of innervation, 2~I
Skilled manu.'il acts, 282
Skilled movement, relation of, to occipital lobe, 795

to temporal lobe, 795
Sloth, 260
Smith, G. Mlliolt, 90, ()i, 88~, ()ii, 917, 945, 954,

960, 963
Sollas, 886
Solutrean Period, 761, 762

relation of, to Hint industry, 918, 931
Somatic variants in primate organization, 879
Somesthetic sensibility, 790, 797

expansions in, in parietal lobe, relation of, to
quadrunianal dillerentiation, 944, 951
Sonntag on position of tarsius, (>4
Spearhead, 753, 758

Special senses, evolutional significance of, 984-986
Specialization in human race, factors of, 883, 884
in mammals, structures essential to, 1001, 1025,

1039
in primates, common factors of, -25, 994, 1040
Speech, in ape-man of Java, 883
in Dawn man, 888
in Neanderthal man, 903
relation of, to hand, 214
to hearing, 883

to inferior frontal convolution, 883
to prefrontal area, 935
in Rhodesian man, 915, 916
Speech center, motor, position of, in luiman brain,

786, 883
Spider monkey, 203, 213, 303. See also Ateles ater.
Spinal accessorj' nerve in gorilla, 658

in tarsius, 103, 109
Spinal cord, 269

high cervical level of, in chimpanzee, 6o(), 61 1
in gorilla, 685, 696
in orang, 533

in Pithecus rhesus, 391, 402
resemblances to human cord, 533, 609
Spinocerebellar eminence in human, 796
in orang, 498, 506, 507
progressive distinction of, 507
pages 475 1 1 20 in Volume II,

I I 12

INDEX

SpinoccrilxIIar tract, fiinctiiin of, 266

in lemur, 61

in marmoset, 166, 167

in Pithccus rhesus, 381

in tarsius, 105
Spinothalamic tract, in chimpanzee, 578, 583, j86

in clog-headed baboon, 306-316, 324-330

in gibbon, 422-432

in lemur, 42-62

in man, 806-810

in marmoset, 167-178

in mycetes, 2 1 1 -228

in orang, 503, 507

in Pithecus rhesus, 366-373, 382-386

in tarsius, 102-128
Splenium of corpus callosum In l)aboon, 297

in gorilla, 6^1

in man, 048

in mycetes, compared with Icnicir niarninset, 204
Squirrel, 89
Standing on tarsius, 91
Stereognosis, 916

Stereoscopic vision. .SVe Binocular vision.
Stratum complexum pontis, in chimpanzee, 592

in dog-headed baboon, 324, 326

in gibbon, 436, 439

in gorilla, 674, 676

in lemur, 56, 59

in man, 820, 823, 826, 8jo

in marmoset, 172

in mycetes, 223, 224

in orang, 517, 521

in Pithecus rhesus, 380

in tarsius, 124
Stratum profundum pontis, in chimpanzee, 592

in dog-headed baboon, 324, 325

in gibbon, 436, 439

in gorilla, 674, 676

in lemur, 59

in man, 822, 825, 828, 8^2

in marmoset, 172

in mycetes, 223, 225

in orang, 517, 522
Stratum superlicialc griseum in gorilla, 679

in lemur, 65, 67

in marmoset, 172, 177

in mycetes, 223
Stratum superlici.ile pontis in chimpanzee, 591, 592

in dog-headed b.iboon, }2o, 324, 325

in gibbon, 436, 439

in gorilla, 674, 676

Pages I 474 are in Volume I,

Stratum superficiale pontis in lemur, 56, ^9
in man, 820, 823, 826, 850
in Pithecus rhesus, 377, 379, 380
in tarsius, 124
Striae acu.sticae in chimpanzee, 574
in dog-headed baboon, 303, 343
in gibbon, 419
in gorilla, 656
in lemur, 40
in man, 799
in orang, 499, ,-41, ,-43
in Pithecus rhesus, 362
Structural design, dclinite principle of, regulates

series of nuclei in brain stem, 374
features, comparative review of values of, 725
Substantia gelatinosa Rolandi, in baboon, 337-341
in gibbon, 426, 455
in gorilla, 662, 68,-, 688
increase in size in, 43, 46, 47
in lemur, 74, 77, 79
in man, 804, 810, 824, 841
in marmo.set, 183-189
in mycetes, 216, 234-239
in orang, 516, 533-536
in Pithecus rhesus, 379, 393-397
relation o(, to substanti.i gelatinosa trigcmini, 74,

394
in tarsius, 136-149
Substantia gelatinosa trigcmini. See Rolando,

nucleus of.
Substantia nigra in chimpanzee, 603, 618-621
in dog-headed baboon, 328-345
function of, 64, 227, 329, 332, 528, 603, 684
in gibbon, 443, 444, 452
in gorilla, 682, 693, 695
in lemur, 62, 64, 66, 68, 75, 79

approached by reticular formation, 78

as reconstructed, 73, 81, 82

relation to pontile nuclear masses, 81

significance of size of, 64
in man, 826-856
in marmoset, 176-188
in mycetes, 227-240
in orang, 528, 540, 542
in Pithecus rhesus, 386-401
in tarsius, 128-148
Sulcus centralis, 30, 36, 37. See also Rolando, fissure

of.
in dog-headed baboon, 296-299
in gibbon, 414-41^
in lemur, 50, 31, 34, 36
pages 475 1 120 in Volume II.

INDEX

1113

Sulcus contralis, in 111:1 rinosot, 1^8, 1 j()

in mycclcs, 204-207

in Pithccus rhesus, 358-361
Sulcus llmitans in luiiii:in, -(jH, ■^()<)

in orang, 5-2
Sulcus lunatus, 04^
Sulcus olfactorius in man, 1^4-, g^o
Sulcus parallclus. See Superior temporal sulcus.
Sulcus rectus in dog-headed baboon, 296, 298, 299

in gibbon, 414, 416, 417

in Pithecus rhesus, 358, 360, 361
Sulcus simiarum in dog-headed baboon, 296-299

in gibbon, 414-417

in human, disappearance of, --9, 783, 1)4^

in myeetes, 204-207

in Pithecus rhesus, 355, 35-, 3^8, 560, 361
Sulcus temporalis superior. ,S>f Sii|Krinr liiiipi)ral

sulcus.
Superior brachium in ehimpanzee, 616

in dog-headed baboon, 544

in gorilla, 692
Superior cerebellar pediiiKlis in chinip.inzee, ^"4,
595, 61 5 621

in dog-headed baboon, 301, 303, 321 32S, 540, 341

function of, 54, 56, 26-, 322

in gibbon, 419. 420, 43-, 441, 455

as index of coordination, 43-, 439, 450

in gorilla, 656, 674-676, 690-696
significant dimensions of, 676

index of neokinetic specialization, 823, 826

in lemur, 31;, 40, 52, 54, i"^, -jo, 60, 61, 6.j, 68, -8,
82, 83

in man, 798, 819. 820, 823, 826, 830, 846, 851, 855
significant size of, 820-822, 826

in marmoset, 173-175, 186

in myeetes, 209, 219-226, 241

in orang, 499, 523, 538, 542

in Pithecus rhesus, 363, 378 385, 398

relation of, to coordination, 54, 225, 322, 523, 822,
826

size of, as scale of outflow, 56

in tarsius, loi, 120-122, 127-131, T43, 149
Superior cerebellar vermis in lemur, 33, 3"
Superior collieular commissure in chimpanzee, 620

in dog-headed baboon, 345

in gorilla, 695

in marmoset, 177

in myeetes, 241

in Pithecus rhesus, 402
Superior collieuli in chimpanzee, 601, 616, 620

coeflieients of, in lower prim.ites, 2"()

Pages I 474 are in Volume I,

Superior collieuli, delinition and function of, 601
in dog-headed baboon, 301-303, 329-344
evolutionary significance ol, 279, 470, 680, 681
in gibbon, 415, 419, 420, 441, 454, 470
in gorilla, 657, 680, 681, 691-695, 723

vestigeal condition of, 681
in higher anthropoids, 722

coeflieients of, 722

deflorescence of, -22
in intermediate primates, 470, 471

coefficients of, relation of, to sight, 4~o, 4~i
in lemur, 39, 40, 65, 66, 67. 78, 79, 81, 279, 723
in man, 830, 831, 837, 848, 854, 858
in marmoset, 163, 164, I''6 1-9, 18--190, 2~9
in myeetes, 2(kj, 227-240
in orang, 525, 541

bearing of, on vision, 525

vestigeal condition of, 525
in Pithecus rhesus, 363, 385-386, 395-402
relation of, to optic lobes, 279, 385, 680

to vision, 227, 2"9, 4'70, 722
stratification of, in reptile and birds, 38-
in tarsius, 100, 101, 127 129, 135-151

more conspicuous than in lemurs, monkeys
apes, or man, 100, 129
Superior longitudinal fissure in dog-headed baboon,

295, 296
in gibbon, 413, 414
in man, 779, 982
in marmoset, i 58
in orang, 493, 494
Superior medull.irv velum in chimpanzee, 616
in dog-headed baboon, 321, 340

function o(, 516, 819
in gibbon. 420, 439
in gorilla. <tj(t
in lemur, 64, 83
in marmoset, 175

in Pithecus rhesus, 379, 382, 385, 398
111 tarsius, 1 20
Superior olive in dog-headed baboon, 321-324
in gibbon, 435, 450
in lemur, 55, 57, 75, 77
in man, 819

in marmoset, 171, i~2, 186
in myeetes, 222, 223, 236
in orang, 516

peduncle of, function of, 379 435, 819
in Pithecus rhesus, 378, 379, 396
in tarsius, 1 16, 118, 1 19
pages 47S -1120 in Volume 11.

III4

INDEX

Superior temporal sulcus in baboon, 296, 298, 2(j<)

in gibbon, 413, 415

in lemur, 29, 34, 36, 37

in marmoset, 158

in mycetcs, 202-207

in orang, 494
Supra-orbital concavity on basal surface of brain of

gorilla, 646
Supra-orbital torus in Neanclertlial man, 89^, 897,
904, 906, 907, 908

in Rhodesian man, 917
Sylvian sulcus. See Sylvius, fissure of.
Sylvius, aqueduct of, in chimpanzee, 5-4, 595, 599,
601, 622

in gibbon, 420, 439, 44 T, 45 J
griseal investment of, 456

in gorilla, 656, 674, 676, 679, 681

in lemur, 33, 62, 63, 64, 83

in man, 798, 799, 8 [9, 820, 824, 829, 831, 84-,
854-858

in marmoset, 17,, i~~, 1-9, ii)o

in mycetes, 225, 242

in orang, 499, 523, 526, 543

in Papio cynocephalus, 321, 32-;, 329, 346, 347

in Pithecus rhesus, 362, 3~9-383, 38^, 402, 403

in tarsius, 126, 149, 150
Sylvius, fissure of, in Ape man of Java. 869, 874,
876

in chimpanzee, 567

in Dawn man, 887, 888

in dog-headed baboon, 296-299

evolutional significance of, 954, 955

in gibbon, 412-417

in gorilla, 645, 648

in human brain, 779-782, 783, 786, 788

in lemur, position of, 29, 31, 34, 36, 37, 954

in marmoset, 1 58-1 61

in mycetcs, 202-207

in Neanderthal man, 897, 900-904

in new-world simians, 959

in orang, 493, 496

in Pithecus rhesus, 355, 358, 360, 361

in Predmost man, 922

in Rhodesian man, 913, 914

in tarsius, 92-96, 957
Symington on reconstruction, 862
Syncrgia, 838

definition of, 251

relation of, to cerebellum, 251, 252
Synergic units, 251

Pages 1-474 are in Volume I,

' I "AIL, absence of, in gibbon and great anthro-
-'■ poids, 13, 17, 405, 482, 706
in baboon, 289
in cetacea, 213
in kangaroo, 213

in lemur, significance of, 12, 23, 24, 43, 44, 46
in marmoset, 153, 162, 166
in mycetes, 191-201, 203, 209, 213, 258
in Pithecus rhesus, 370
relation of, to clava, 39

to nucleus of BischofT, 213, 257
to nucleus of Goll, 43, 46, 105, 162, 706-708
in tarsius, 105, 106
Tarsiers, 12, 18, 22, 423. See also Tarsius.

below lemurs and new world monkeys in organiza-
tion of visual function, 130
lower primates, begin evolutional advance to
human brain, 18, 85
Tarsiidae, family of Tarsioidea, 21
Tarsioidea, suborder of primates, 21, 85
Tarsius, appearance and behavior of, 85
brain of, 92-151
humanoid, 87

low development of auditory sense in, 125
nail on third toe of, 24
not gregarious, 87
opinions concerning, 85, 9" 94
position of, among primates, 16, 85, 90, 130
posture of, 87
rotation of head of, 85, 90
spectrum, 12, 85-1 ji, 803
blood reactions of, 89
habitat, 8^, go

lisseneephalic cerebral hemispheres in, 95, 96
mammalian organization of brain stem in, 101
measurements of, 95
speed in trees, 85, 87
tail of, 87
Tasmanians, primitive, Keith on, -42
Taste, sense of, in primates, 314
Tectum of midbrain, in chimpanzee, 620
in dog-headed baboon, 344
in gorilla, 694
in Pithecus rhesus, 383
in Tarsius spectrum, 122, 123
Tegmentum pontis, 60, 248

in chimpanzee, 575, 591, 595, 599. f>oo, 603, 616
in dog-headed baboon, 325
in gibbon, 438-444, 450, 454
in gorilla, 673, 6"5

in human, 81-, 820, 823, 826, 829, 830, 846
pages 47S-I120 in Volume II.

INDEX

1115

Tegmentum pontis, in lemur, 76

nuclei of, relation of, to cochlear nuclei, 80
to substantia nigra, 82
in orang, 577-540
in Pithecus rhesus, 377-385, 3<)'"
Telcncephalization, 385
in chimpanzee, 575, ~22
definition of, 63, 66
development of, 277

bearing of, on sight and hearing in intermediate
primates, 277, 470
in gorilla, 679, 722

gradual process as shown by optic lobes of lemur,
65, 66, 6-

of marmoset, 1-9
in man, 830
in orang, 525, -22

in vision and hearing of Pithecus rhesus, 383, 385
of vision, in tarsius, 100, loi

in ape-man of Java, 878
Temporal area, relation of, to hearing, 277, 383

in tarsius, q6
Temporal bone, squamous portion of, in gorilla, 653

membranous origin of, 862
Temporal lobe in ape-man ol Java, 878

expansion in auditory function of, 879

relation of, to speech, 879
auditory eminence in, 891, 892
in chimpanzee, 568-572, 599, 600

relation of, to hearing, 600
in dog-headed baboon, 296-298
in Eoanthropus Dawsoni, 886
in gibbon, 412 415
in gorilla, 645, 652, 679

expansion of, in auditory area, 679
in human, 779, -80, 783, 784, -88

comparison with that of anthropoids, 791

function of, 789, 790, 795, 830
in lemur, 31, 32
in marmoset, 159
in mycetes, 202, 205, 206
in Neanderthal man, 898, 903-907

auditory eminence in, 903
in orang, 495-4<)8

in Pithecanthropus crectus, 878, 879
in Pithecus rhesus, 357> 359
in Predmost man, 922
relation of, to speech and thought, 892
in Rhodesian man, 916
in tarsius, 93, 94, 9-, 125
Temporo-sphenoidal incisure, in Pithecus rhesus, 35-
Pages 1 474 are in Volume I,

Tenth cranial ner%e in gibbon, 429. See also Vagus.

Tertiary Period, 940

Tetraplastic theory, 12

Third cranial nerve. See a/so Oculomotor nerve.

in dog-headed baboon, 329, 332

in gibbon, 418, 456

in Pithecus rhesus, 362

in tarsius, 100
Thorndyke, on behavior of mycetes, 197

on new world monkeys, 354, 355, -57
Toe-heel timing, 981
Tractus mesencephalicus trigemini in gibbon, 437,

in gorilla, 679

in lemur, 61, 62

in Pithecus rhesus, 385
Tractus uncinatus of Russel in baboon, 321-325

in gorilla, 6-5

index of paleokinetic organization in balancing,
823

in lemur, 57, 60

in man, 822, 823

in marmoset, 1-3

in mycetes, 222, 223, 224

in Pithecus rhesus, 380, 381

in tarsius, 120, 121
Transverse sinus in Neanderthal man, 899
Trapezoid body in chimpanzee, 592, 615, 618

in dog-headed baboon, 300, 318-324, 339-342

in gibbf>n, 435, 450, 451
large size of, 453

in gorilla, 673, 690, 695

in lemur, 38, 52, 53, 54, 55, 57, 60, 77

in man. 818, 846

in marmoset, 162, i"i, 1-2, 186

in mycetes, 208, 222, 223

in orang, 516, 517, 538

in Pithecus rhesus, 362, 378, 3-9. 39"

relation of, to auditory sense, 54, 120

in tarsius, 99, 100, 1 16, 1 18, 1 19
Trapezoid nucleus, in lemur, 52, 53

in mycetes, 226, 237

in tarsius, 121, 122
Tree-shrew, 1044

as common stock for ape and man, 1043- 1 044
Trigeminal nerve, 249

in chimpanzee, 575, 595, 59", 599. ^"9

in dog-headed baboon, 323, 329

in gibbon, 432, 448

in gorilla, 6-2, 6-5, 686, 68-, 6<)4
pages 475 1 1 20 in Volume 11.

1 1 16

INDEX

Trigeminal nerve, in lemur, 57, 50, (>$

in man, 820, S24, 829, 841

in mycetes, 224

in orang, 523, 535

in Pitliceus rhesus, 379, 380, 381
motor nucleus of, 394

in tarsius, 120
Trigones, vagal, in orang, 543
Trigonum hypoglossi in chimpanzee, 574

in gibbon, 419

in gorilla, 656

in orang, 501, 545

in Pithecus rhesus, 361
Trigonum olfaetorium, in elilnipanzee, 570 ^

in gibbon, 413

in gorilla, 649

in lemur, 33

in man, 791, 945

in marmoset, 60

in mycetes, 206

in orang, 496
Trinil race, 73;

Trochlear decussation in tarsius, 124
Trochlear nerve, in gibbon, 440, 456

in lemur, 61, 62, 6,

in man, 824

decussation of, 3S2
function of, 382

in marmoset, 173, i''4, i"5

in mycetes, 224, 225

in Pithecus rhesus, 362, 381

in tarsius, 120, i2t

significance of course ol, 126
Trochlear nucleus, in chimpanzee, 599, 622

in dog-headed baboon, 347

in gibbon, 440

in gorilla, 679, 697

in lemur, 84

in marmoset, 186

in mycetes, 236, 242

in orang, 523, 543

in tarsius, significance of size of, 126
Troglodjtes gorilla, 1 2. See Gorilla.
Troglodytes niger, 1 2, 545-622
Troglodytes niger, 1 2, 545-622. Sec (i/so Chimpanzee.

appearance of, 545, 546

behavior of, 545-566, 590

of intelligent type similar to that in human
beings, 564-565

coordinalive control in, 555, 566

constructional ideas in, 557, ?i^. 559-i''6

Pages 1-474 are in Volume I,

Troglodytes niger, habitat of, 546

teachability of, 566,
Tuber cinereum, in chimpanzee, 576

in dog-headed baboon, 301

in gibbon, 421

in gorilla, 657

in lemur, 36

in man, 792, 833

in Pithecus rhesus, 364
Tubcrcuknu aeusticum, in chimpanzee, 587, 591

in dog-headed baboon, 304, 316, 317

function of, 49, 374

in gibbon, 418, 431, 432

in gorilla, 655, 656

in lemur, 48, 50, 51

in man, 814

in marmoset, 169, 170

in mycetes, 220

in orang, 513

in Pithecus rhesus, 360, 373, 374

in tarsius, 1 16-1 18
Tuberculum olfaetorium in tarsius, 97
Tubcrculum trigcmini, in chimpanzee, 572, 654

in dog-headed baboon, 301, 304

in gibbon, 419

in gorilla, 662, 663

in lemur, 39

in marmoset, 163

in mycetes, 209

in Pithecus rhesus, 363

in tarsius, 99
Tupaia, 957, 1044. Sec uho Tree shrew.
Twelfth nerve. See Nervus hypoglossus.

T TN(;iNATE tract of Russel. See Tractus unci-
^""^ natus, Hook bundle.
Uncus, in chimpanzee, 570

in Gibraltar skull, 907

in gorilla, 652

in orang, 496
Ungulates, 7, 650, 970, 1039
Upper Paleolithic, 745, 746, 758, 759, 764
Utricle, 49, 170, 261, 262, 315, 320, 513, 583, 592
Uvula ccrebclli in tarsius, 109, 115

VAGUS nerve in chimpanzee, 582
in gibbon, 419
in gorilla, 663-665
in tarsius, 108, 109
pages 475 1120 in Volume II.

INDEX

I I 17

Vallecula, in gorilla, 653

in man, 974

in orang, 497
Ventral accessory olive, in chimpanzee, 614

in dog-headed baboon, 313, 337

in gibbon, 427-429, 448

in lemur, 75, ~6

in mycetes, 21-, 218, 210, 220, 234

in orang, ^36

in Pithccus rhesus, 372, 394, 39,
Ventral accessory palco-olivc nucleus in lemur, 76
Ventral cochlear nucleus, in chimpanzee, 619, 620

in dog-headed baboon, 337, 339, 341, 344

in gibbon, 452, 453

in gorilla, 694

in lemur, 77, 79, 80, 81

in man, 814, 853

in marmoset, 185, 187

in mycetes, 235, 239

in orang, 541

in Pithccus rhesus, 393-397
Ventral gray column, in chimpanzee, J76-580, 609-
614

in dog-headed baboon, 30J-309, 338, 341

in gibbon, 421-424

in gorilla, 658, 685, 688, 696

in lemur, 42, 44, 75, 77, 79

in man, 801, 802, 803, 804, 84 J, 854

in marmoset, 164, 165, 166, 185, 190

in mycetes, 211, 235, 236, 241

in orang, 503, 506, 507, 533-53^>. 543

in Pithccus rhesus, 365-368, 371, 391-397

in tarsius, 102, 103, 104, 107, 136-151
Ventral paramedian sulcus in gorilla, 661
Ventral spinocereliellar tract, 252, 253

in chimpanzee, 578, 583, 586

in dog-headed baboon, 306, 309, 311, 313, 315,
316, 321, 322, 324, 325

in gibbon, 422-432

in gorilla, 675

in lemur, 42, 45, 46, 48, 49, 50, 57, 60

in man, 803, 805, 808, 822

in marmoset, 165, 166, 167, 169, 170, 173

in mycetes, 211, 215. 218, 220, 221, 222, 223, 224

in orang, 503, 507

in Pithccus rhesus, 366-381

in tarsius, 102, 104, 106-108, ni, 114. 116, 118,
120, 121
Ventricle, fourth, in chimpanzee, 583, 595, 610, 622

in dog-headed baboon, 301-303, 321, 323, 32,,

335. 336-338. 343. 346

Pages 1 -474 are in Volume I,

Ventricle, fourth, floor of, in chimpanzee, 573 -591,
614-621

in dog-headed baboon, 302, 303, 313 322, 336,
344. 346

in gibbon, 419, 427, 432-437, 4,-2, 455, 464

in gorilla, 656, 663, 667, 672, 686, 693, 694, 696

in lemur, 37, 39, 40, 61, 81, 83

in man, 798, 799, 810-814, 819-820, 844-858

in marmoset, 164, 187, 188, 189, 190

in mycetes, 219, 238, 241

in orang, 499, 503, 512, 513, 515, 517, 520-523,
537, 540. 543

in Pithccus, 361, 362, 369, 373-378, 399-404

in tarsius, 100, 107, 113, 116, 119, 135-151
in gibbon, 419, 426, 431, 435, 439, 447, 452, 455
in gorilla, 663, 672, 686, 687, 692, 697
in lemur, 77, 80, 81, 82
lumen of, 860
in man, 798, 804, 808, 840, 844, 851, 853, 854, 857,

858
in marmoset, 163, 169, 183, 189
in mycetes, 209, 218, 236, 23-, 239, 241, 242
in orang, 499, 534, 536, 541
in Pithecus rhesus, 360, 363, 372-379, 391-401
roof of, in chimpanzee, 571, 586, 621

in dog-headed baboon, 321, 337

in gibbon, 417, 435, 439

in gorilla, 653, 697

in lemur, 83

in man, 822, 846

in orang, 513, 520

in Pithecus rhesus, 358, 375, 376, 403

in tarsius, 117, 120, 149
in tarsius, 100, 10 1, 1 15-119, 135-151
Wntricle, third, in chimpanzee, 605, 607, 622
floor of, in chimpanzee, 607

in gorilla, 683
in gibbon, 445, 446, 456
in gorilla, 685, 684, 697
in man, 834 836
in marmoset, 190
in mycetes, 242
in orang, 530, 544
in Pithecus rhesus, 387, 404
roof of, in chimpanzee, 607
in tarsius, 131, 132, 150
Ventricular system of cerebral hemispheres, in

tarsius, 97
Ventrolateral sulci, m lemur, 54
V'entromedian sulcus in chimpanzee, 572, 5-6
in dog-headed baboon, 300, 308
pages 475 1 1 20 in Volume II.

iii8

INDEX

Ventroniedian sulcus in gibbon, 4!~, 418
in gorilla, 676

in human, 795, 800, 804, 806, 808, 849
in lemur, 34, 36, 38
in marmoset, 162
in orang, 498

in Pitliccus rhesus, 359, 362
in tarsius, 100
Vcntromesial accessory olive in lemur, 48, 49
Vermal ridgepole in chimpanzee, 571
in man. 974
in orang, 497
in Pithecus rhesus, 358
Vermis cerebelli, 248, 2^2, 266, 267
in chimpanzee, 595
definition of, 318

in dog-headed baboon, 298, 319-325
function of, 53, 252, 266, 268, 320, 6-1
in gibbon, 416
in gorilla, 652, 671, 677

comparison of, with lateral lobes of cerebellum,

672
no progressive advance in, 6~i, 6-5
in lemur, 51, 52, 53, 5~, 60, 64
in man, 814, 822, 9-2
in marmoset, 161, 163, 169, 170
in mycctcs, 207, 219, 221, 247
in orang, 498, 521
in Pithecus rhesus, 358, 376, 380
relation of, to cerebellar hemispheres, 265
to inferior olivary nucleus, 253
to vestibular nuclei, 262
in tarsius, 98
Vermis, superior, in chimpanzee, 570, 571
in gibbon, 413, 4r4, 435
in gorilla, 652
in man, 794 '

in orang, 493
Vertex, arch of, in Piltdoun skull. 886

absent in Neanderthal man, 897
Vestibular area in chimpanzee, 585, 610-615,618-
622, 712
comparison of, with arboreal primates, gorilla,
man, relation of, to locomotion, 585
coefTicients of, in higher anthropoids, 713
comparison of, in intermediate primates, with

th.it of lower group, 465
components of, 50
definition of, 362
in dog-headed baboon, 339. 343. 344

Pages I 474 are in Volume I,

Vestibular area in gibbon, 420, 464

relation of, to locomotion and balancing, 464
in gorilla, 656, 686, 693, 6tj4
in intermediate primates, 464

coefficients of, 465
in lemur, 50, 78
in mycetes, 238, 239
in orang, 534, 537, 538, 540, 541
in Pithecus rhesus, 373, 375, 393-403

large size of, 374, 375
relation of, to balancing, 362
in tarsius, 103, 1 38-1 51
Vestibular complex. See also Vestibular area,
in lemur, 78

in man, 811, 813, 841, 852, 854, 857
Vestibular eminence in orang, 499

compared with chimpanzee, gorilla, man, 499
in Pithecus rhesus, 362
Vestibular mechanism, phyletic constancy in, 585,

712, 714
Vestibular nuclei in chimpanzee, 574, 583

comparison of, between great anthropoids and

intermediate and lower primates, "13. -14
coefficients of, 262, 263
in dog-headed baboon, 315-317. 322, 343
function of, 219, 260, 261, 262, 316, 317, 3-3, 583
in gibbon, 431, 713
in gorilla, 667
high specialization of, in gibbon, 713

in mycetes, 264

in tarsius, 1 15
in lemur, 73, 78, 80, 81
in man, 811, 842, 851
in marmoset and mycetes, 169, 170, 186-188, 219,

261, 263, 264
in orang, 513

in Pithecus rhesus, 372, 374, 393
relation of, to internal ear, 262, 317, 373

to vermis cerebellum, 262
in tarsius, 1 13-117, 145
Vibrissae, relation of, to nucleus of Rolando, 307
V ision, adjustments in, 472
in ape-man of Java, 878

binocular, development of, 280, 527, 601-603,
"23, -24

relation of, to internuclear connection, 280,
471-473. 603. 681, 723, 725
in chimpanzee, 601, 602, 722, 723

stereoscopic fusion of, 602, 603
comparison of, in lower primates, 280

and man, 282, 283
pages 475 1 1 20 in Volume II.

INDEX

1119

Vision, delicacy of mechanisms for, 527
in dog-headed baboon, 294, 329

as illustrating evolutional progress, 329
only partially binocular, 330
reflex resjxinse in, 4~i
relation of, to habitat, 4~i
evolutionary changes in, 2-6, 2—, 385, 525, 526,

601
in gibbon, 415, 470
in gorilla, 6ji, 681, 722, 723

relation of, to decussation of oculomotor
nuclei, 681
to expansion of occipital region, 65 1
human, relation of, to cerebral cortex, 277

occipital lobe to association, 789
in lemur, 6~
in marmoset, 153, 164, i; — -179

relation of, to suf>erior colliculus, 179
slightly stereoscopic only, 1-9, 282
in mycetes, 227, 228, 282, 283
in Neanderthal man, 903
in orang-outang, 501, 525, 52--529, 722

binocular and stereoscopic, function of, as
revealed in midbrain level, 529
in Pithecus rhesus, 385
relation of, to coordination, 280
to differentiation in hand, 250
to occipital area, 277
to oculomotor decussation, 228, 280, 471-473,

52-, 681
to optic lobes, 385, 601
to pulvinar, 6oj
to skilled acts, 250, 52-

to sufK-rior colliculus, 22-, 385, 525-527, 601
in tarsius, increase in control of, 130
not stereoscopic, 1 1 2, 1 30, 282
prominence of primordial receiving centers,

2-6
relation to central gray column, 112
to inferior olive, 1 1 3
to neck muscles, 1 1 2
to skilled acts, 1 1 2
specialized for nocturnal hunting, 8~, 112
telencephalization of, 1035
Visual axes, positions of, 280

relation of, to intemuclear communication,
281
\'isuo-psychic functions, in ape-man of Java, 878
in Neanderthal man, 903
in Rhodesian man, 917
Volition, relation of, to corticospinal tract, 389

Pages 1-474 are in Volume I,

Volitional movements, importance of pyramidal
system in regulation of, 45, 212, 216, 422, 655,
663, 699
relation of, to dentate nucleus, 220

to diff^erentiation in hand, 212, 216, 284
to discriminative sensibility, 284
Voluntary control in chimpanzee, 604
in dog-headed baboon, 305

relation of, to cerebral hemispheres, 329
in gorilla, 655

relation of, to size of pyramids, 663
to structure of inferior olive, 656, 665
in lemur, 35
in man, 797, 806
in marmoset, 163, 1-7

limited, as indicated bv cerebral 1 ,

164
fay nucleus dentatus, 172
by pons, 162

by pyramidal system, 162, 166, 167
in mycetes, 209, 212, 216, 220, 225
in orang, relation of, to pyramidal decussation,

pyramids and mesial fillet, 503, 506, 507, 517
in tarsius, 99, 1 10, 1 1", 120

'"\AyAIST" of nucleus of Rolando, in chimpanzee,

** 612

in dog-headed baboon, 336

in gorilla, 68"

in lemur, 75

in man, 841

in mycetes, 234

in tarsius, 139
Wallace, A. R., on orang-outang, 479, 480, 990
Watson, J. B., on Macacus rhesus, 354
Weight, increase in, relation to evolution of, 669

of larger anthropoids, I", 981, 1041
Whales, -, 1024
W itraer on chimpanzee, 546

on Pithecus irus, 354
W ood-Jones, on position of tarsius, 94
Woodward, A. S., 884, 88", 891, 912
W'oollard, on tarsius, 91, 92
W ooUy monkey, 303
W risberg, pars intermedia of, in baboon, 314

-\yE}

ERKES, Robert M., on orang-outang, 487—491,

on Pithecus rhesus. 354, 355
pages 475 I :; ^f! n.

1I20 INDEX

VEEHANDELAAR, on nucleus of Bisclioll", 213 Zona incerta of dicnccphalon in lemur, 78

^ in man, 848, 850

Zona incerta of dicnccphalon in baboon, 345 in marmoset, 186, 189

in gibbon, 450, 454 in mycetes, 237

in gorilla, 692, 696 in orang, 538, 542

Pages 1-474 are in Volume I, pages 475-1120 in Volume U.

Paul B. IIoi nFR, Inc., 76 Fifth Avenue, New \'ork

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