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 THE STRUCTURE OF MAN
 
 THE 
 
 STRUCTURE OF MAN 
 
 AN INDEX TO HIS PAST HISTORY 
 
 BY 
 
 DR. R WIEDERSHEIM 
 
 PROFESSOR IN THE UNIVERSITY OF FREIBURG I. BADEN 
 
 TRANSLATED BY 
 
 H. AND M. BERNARD 
 
 THE TRANSLATION EDITED AND ANNOTATED AND 
 A PREFACE WRITTEN BY 
 
 G. B. HOWES, F.L.S. 
 
 PROFESSOR OF ZOOLOGY, ROYAL COLLEGE OF SCIENCE, LONDON 
 
 <Jj>u. - 
 
 WITH 105 FIGURES IN THE TEXT 
 
 ILontion 
 MACMILLAN AND CO. 
 
 AND NEW YORK 
 
 1895 
 
 All rights reserved
 
 PEEFACE 
 
 THE circumstances which led to the production of this work in 
 the original German are sufficiently set forth in the annexed 
 " Introduction," and no one would admit more readily than its 
 author that it is largely supplementary to the classical treatises 
 of Darwin and Huxley, quoted in its pages. Experience of the 
 practical method of scientific education has shown that it is 
 desirable to place in the hands of the student engaged upon a 
 first investigation of individual types of animal structure, some 
 sound treatise of a general character, which he may read while 
 continuing his more systematic studies. Such works awaken the 
 mind to the comparative method of inquiry, and to the higher 
 educational and philosophic issues to which it leads. It was this 
 consideration which prompted me to suggest this translation, in 
 the hope that it might be of use, in the manner indicated, to 
 the medical student while engaged in the study of anatomy. I 
 am further hopeful that an educated public exists to whom a 
 knowledge of the comparative morphology of Man and the 
 Anthropoid Apes as set forth in these pages may be acceptable. 
 
 The truth of Evolution in organic nature is now generally 
 admitted, but its application to man is not perhaps so widely 
 acknowledged. This book, in no sense an exhaustive treatise, 
 is an endeavour to set forth the more salient features in the 
 anatomy of Man which link him with lower forms, and others 
 in that of the lower forms which shed a special light on parts 
 of the human organism. Such comparisons furnish a basis upon 
 which to exercise judgment concerning Man's position in the 
 series of organised beings. 
 
 In dealing with these comparisons, a word of caution is, how-
 
 vi THE STRUCTURE OF MAX j 
 
 ever, needed. Our accepted views as to the inter-relationships 
 between the greater groups of animals are largely based upon the 
 assumption that similarity of gross structure implies community of 
 origin. It is now becoming evident that an essentially similar 
 definitive condition may be independently reached, under advanc- 
 ing modification along parallel lines, by members of independent 
 groups of animals ; and there is reason to suspect that some 
 of our classificatory systems are unnatural and erroneous from 
 want of appreciation of this principle of "convergence." We must, 
 therefore, not lose sight of the possibility that some of the 
 characters which modern Man and the higher Apes have in common 
 may have been independently acquired. A notable instance is fur- 
 nished by the ridges which connect the tubercles of the upper 
 molar teeth, described by Huxley and Topinard. On comparing 
 the little worn upper molars of, say, a female Chimpanzee and 
 Man, one might at first sight be disposed to conclude that modern 
 Man has descended from ancestors hardly differing from the 
 modern Apes. On comparing the entire Man-Ape series, how- 
 ever, it is found that these ridges, and more especially that of 
 Topinard, are extremely variable and not infrequently absent in 
 individuals of both Men and Apes, and it becomes therefore 
 evident that such a conclusion, if not unwarranted, is premature. 
 If for no other reason than this, it will be obvious that consider- 
 able interest attaches to the more precise determination, in the 
 future, of the limits of detailed structural variation in Man 
 and the Anthropoid Apes. With regard to variation in Man 
 some very useful results have been obtained, during the last five 
 years, under the auspices of a "Collective Investigation Com- 
 mittee " of the Anatomical Society of Great Britain and Ireland, 
 of which I have the honour to be a member. Subjects chosen 
 for investigation year by year are taken in hand in the leading 
 dissecting rooms throughout the kingdom. The work of the 
 student, becoming thus a research work, is ennobled; and the 
 reports embody a mine of accurate information which, edited 
 and tabulated, is of great service to both the surgeon and scientific 
 anatomist. 
 
 Our views on some of the topics dealt with in this volume 
 may become very much modified as work of the above-mentioned
 
 PREFACE vii 
 
 order proceeds. There seems, however, no escape from the con- 
 clusion that Man and the Apes must have had a common ancestor 
 in the remote past, and we await with especial interest further 
 discoveries of fossil remains which may throw light upon their 
 inter-relationships and upon the ancestors of Man. 
 
 Kemains of Early Quaternary Man, few and far between, 
 have been unearthed during the last fifty years in England, 
 on the European Continent with Gibraltar, and in North America. 
 The valley of the Meuse is now famous for having yielded the 
 " Naulette " and " Spy " remains, which there is very strong 
 evidence for believing to belong to the Palaeolithic Age. The 
 salient features of these ancient men are a low retreating and 
 contracted forehead and an inwardly shelving occiput (indicative of 
 a primitive type of brain and of powerful neck muscles), a high 
 temporal ridge and an expanded palate (indicative of powerful 
 jaws and jaw muscles); and further, the presence of ape -like 
 brow ridges (for which the famous Neanderthal calvaria is so 
 notorious) appears also to have been a racial character. Dr. 
 Eugene Dubois has recently described some remains from the 
 banks of the Bengawan Eiver in Java, which he believes to be 
 those of a creature structurally intermediate between the types 
 represented by modern Man and the modern Anthropoids. In 
 this he has been proved by Pettit, Cunningham, Turner, and 
 others, to be mistaken. The Bengawan calvaria and the bones 
 associated with it are strictly human. The calvaria shows a 
 cephalic breadth index 1 of 70, as compared with 72 for the 
 Neanderthal, and its smaller capacity and other characters render 
 it perhaps representative of a race more primitive than any 
 1 As mentioned in the body of this work (infra, pp. 51, 52), the cranial capacity 
 of the Caucasian may average 1500 c.cm., and that of the Veddah may be but 950 
 c.cm. Thirty Australian skulls measured by Turner gave a maximum capacity of 
 1514 c.cm. and a minimum of but 930 c.cm., and 100 modern Parisian skulls, worked 
 out by Topinard, varied between 1850 c.cm. and 1150 c.cm., while Testut describes 
 a skull of Quaternary Man from the Dordogne with a capacity of 1730 c.cm. 
 Individual variation being thus extensive, it is clear that far purposes of study 
 of the 'inter-relationships between races of mankind, a method which deals with 
 relative measurements, in such a way as to eliminate differences due to stature, 
 is desirable. The above-named "cephalic breadth index " method has been found 
 to be one of the most serviceable under existing circumstances. It is computed 
 as follows : multiply the maximum transverse diameter by 100 and divide by the 
 maximum long diameter, as determined by a lino drawn between the superciliary 
 ridges and through the most projecting mid-occipital point.
 
 V iii THE STRUCTURE OF MAX 
 
 hitherto discovered. During the passage of these pages through 
 the press, my friend and colleague, Mr. E. T. Newton, has de- 
 scribed 1 from the Thames Terrace-Gravel, at Galley Hill, in 
 Kent, some remains of a human skeleton which there is good 
 reason for believing to belong to the Palaeolithic Age, and to be 
 perhaps slightly older than the Spy example. The Belgian 
 remains were found in caves, those from Galley Hill were em- 
 bedded in a Pleistocene river deposit ; and it is a significant fact 
 that the skull of the latter gives a cephalic breadth index of 
 but 64. 
 
 The posterior molars or " wisdom teeth " of modern Man are 
 exceedingly variable . structures (cf. text, p. 159). Even when 
 most fully developed, their crowns are as a rule less extensive 
 than those of the teeth in front of them. In remains from 
 reputed Palaeolithic deposits hitherto described, in which jaws 
 and teeth have been preserved, the crowns of the " wisdom teeth " 
 are as large as, if not a trifle larger than those of the other 
 molars in front of them. This greater development of the last 
 molar is characteristic of the oldest known human jaws, but is 
 only very rarely met with in those of recent Man. In its most 
 expanded condition the crown of the wisdom tooth of both 
 recent and fossil Man may be beset by numerous tubercles, its 
 posterior and external cusps being subdivided and replaced by 
 a series of smaller ones. The same variation has been observed 
 among the Anthropoid Apes. This is an intensely interesting 
 fact, as it approximates the molar of Man and the higher Apes 
 with that of the multitubercular type, occurring among the 
 oldest fossil and in the young of one of the two lowest living 
 Mammals (e.g. Ornithorhynchus). Concerning the general question 
 of mammalian tooth-genesis, choice to-day lies between the theory 
 of " Trituberculism," originated by Kiitimeyer and Cope, and 
 staunchly upheld by the American Palaeontologists, and that of 
 "Polybuny" or " Multituberculism " founded and recently de- 
 veloped by Forsyth-Major. The advocates of the former would 
 derive the various types of mammalian cheek-teeth from a 
 
 1 Paper read before the Geological Society, London, 22nd May 1895. An 
 admirable critical review of the subject of Fossil Man, by Dr. A. Keith, giving full 
 references to original treatises up to the time of Newton's important work, will 
 be found in Science Progress for July ] 895.
 
 PREFACE ix 
 
 tricuspid prototype, by extension, subdivision, and superaddition 
 of parts, and those of the latter from a multicuspid, by reduction, 
 confluence, and suppression. 1 Osborne has endeavoured to show 2 
 that the human molars may have been evolved out of a tri- 
 tubercular type. I would point out, on the other hand, that 
 during the tooth changes of the human subject of to-day, there 
 is indicated, on the part of the cheek-teeth, a progressive reduc- 
 tion of that type of tooth represented by the first molar. The 
 detailed facts concerning this process (cf. text, p. 160) appear to 
 me to be more in accord with the theory of multituberculism ; 
 and on this basis the suggestion arises whether the first molar may 
 not stand in a similar relationship to the wisdom tooth of the 
 multitubercular order as the deciduous molars do to it, the 
 entire series of modifications being those of advancing reduction 
 of a multitubercular type of tooth. 
 
 No opportunity should be lost of excavating the Quaternary 
 deposits of all parts of the world, especially where mixed with 
 clays likely to be favourable to the preservation of human and 
 other remains. Now that the African continent is being 
 opened up, the scientific mind waits with longing for the 
 careful investigation of its Tertiary Lacustrine deposits. Hugh 
 Falconer long ago predicted that human remains would be 
 forthcoming in the Tertiary deposits of India, and no one con- 
 versant with recent work in Mammalian Palaeontology would 
 doubt that the remains of ancestral Man must be sought thus 
 far back in time. This prediction has been confirmed, by the 
 discovery in 1894, by Noetling, in the Yenangyoung Oil-field, 
 Burma, of flint flakes of early Pliocene date. I could desire 
 no higher reward for the labour expended in placing this 
 book before the English-speaking public than that it might 
 help to awaken the interest necessary to ensure such investiga- 
 tion. It may be added, as an appropriate comment, that the 
 interest in Dwarf Kaces, recently revived through African ex- 
 ploration and the fuller study of the natives of the Andaman 
 
 1 For a fuller account of the history of these theories, and of the leading facts 
 upon which they rest, cf. Osborne, Americ. Naturalist, vol. xxii. p. 1067 ; and 
 Forsyth-Major, Proc. Zool. Soc., Lond., 1893, p. 196. 
 
 - Awit. Anzeiger, Bd. vii. p. 740. Cf., however, the observations of Rose cited in 
 this volume (infra, pp. 158 and 159).
 
 x THE STRUCTURE OF MAN 
 
 Islands, has vastly increased, through the discovery that formerly 
 dwarf races were widely distributed, evidence of their existence 
 having been obtained in North Africa, Sicily, Switzerland, and 
 the Pyrenees in the Old World, and in Central America in the 
 New. 
 
 In editing this work, I have spared no pains to bring it up 
 to the standard of English requirements. In the course of the 
 revision a free rendering, rather than a translation, of the original 
 German has been deemed in many places desirable ; and para- 
 graphs dealing with incidental and controversial topics have 
 been for the most part put into small type. Important altera- 
 tions and intercalations are enclosed in square brackets, and 
 for these I hold myself responsible. My friend Professor 
 Arthur Thomson of Oxford has done me the great service of 
 looking through the proof-sheets, and to him and my friends 
 Dr. Forsyth-Major and Mr. Oldfield Thomas, I tender my sincere 
 thanks for advice upon special topics. 
 
 G. B. HOWES. 
 
 ROYAL COLLEGE OF SCIENCE, LONDON, 
 SOUTH KENSINGTON, S.W., 
 May 1895.
 
 PREFACE TO THE SECOND, REVISED AND 
 ENLARGED, GERMAN EDITION 
 
 THE book " Der Bau der Menschen " made its first appearance in 
 the year 1887 in the form of an academic treatise, intended 
 only for a limited circle of readers. There were no illustrations, 
 and the method of treatment of the material was very brief, 
 indeed, in many parts a mere sketch of the subject was given. 
 Notwithstanding this, I received letters and questions which 
 showed me that my treatise had awakened interest in a circle of 
 readers wider than that for which it was originally intended, and 
 I therefore decided to reissue it in a more complete form. 
 
 The leading ideas are the same, although I think I may 
 claim to have improved upon the manner and form in which 
 they have been carried out. The large number of illustrations 
 which accompany the text, as well as the wider foundation of 
 comparative anatomy and ontogeny on which the subject rests, 
 have, I hope, both made it more intelligible and greatly increased 
 its usefulness. 
 
 An index has been added, giving a review of the material 
 dealt with, and also, for the use of the lay reader, a glossary of 
 the zoological tetms employed. 
 
 I must express my hearty thanks to my publisher for the 
 friendly assistance he has shown me. 
 
 It is my earnest hope that this work in its new form may 
 once more win recognition, since it aims at assisting man to 
 know himself. 
 
 THE AUTHOR. 
 
 FREIBURG, I. BADEN, 
 May 1893.
 
 TABLE OF CONTENTS 
 
 PAGE 
 
 PREFACE ..... . . . . . \ 
 
 PREFACE TO THE SECOND, REVISED AND ENLARGED, GERMAN EDITION xi 
 
 TABLE OF CONTENTS xiii 
 
 LIST OF ILLUSTRATIONS xvii 
 
 INTRODUCTION . . . 1 
 
 THE INTEGUMENT AND THE TEGUMENTAL ORGANS . . . . 3 
 
 Hair 3 
 
 Nails 11 
 
 Cutaneous Glands (Mammary Glands) . . . . .12 
 THE SKELETON 
 
 The Vertebral Column 26 
 
 The Ribs and Sternum . 36 
 
 The Skull 48 
 
 Skeleton of the Limbs .67 
 
 The Pectoral (Shoulder) and Pelvic (Hip) Girdles . . .08 
 
 The Skeleton of the Free Limbs 76 
 
 The Skeleton of the Fore-Limb 77 
 
 The Skeleton of the Hind-Limb 81 
 
 Comparison of the Fore- and Hind-Limbs of Man . . .91 
 
 Changes of Position of the Limbs in relation to the Trunk . . 94 
 
 MUSCULAR SYSTEM . . . . . . . . .97 
 
 Retrogressive Muscles of the Trunk 98 
 
 The Muscles of the Cervical and Cephalic Regions . . .102 
 Muscles of the Limbs . . . .'".'. '. . 109 
 Muscles which appear occasionally, and may be considered Atavistic 112 
 Progressive Muscles . . . . .' . .114 
 
 Retrospect . . . ...;...,. .120 
 
 THE NERVOUS SYSTEM . .{. . . .. . . ... 123 
 
 The Spinal Cord . . ,. , . ., . .123 
 
 Brain . 127
 
 THE STRUCTURE OF MAX 
 
 PAGE 
 
 138 
 
 Peripheral Nervous System 
 
 140 
 
 The Sympathetic System 139 
 
 THE SENSE ORGANS 
 
 Integumental Sense Organ . . . > . 
 
 The Olfactory Organ . . . 
 
 Jacobson's Organ 
 
 The Projectile Nose 
 
 The Eye . / .. , ._ , - - . 147 
 
 The Auditory Organ 
 THE ALIMENTARY CANAL AND ITS APPENDAGES . . . .155 
 
 Palatal Ridges - . . . 155 
 
 Teeth 
 
 156 
 
 The Sublingua 
 
 Thyroid and Thymus .162 
 
 Bursa Pharyngea . . 164 
 
 (Esophagus and Stomach . . .164 
 
 The Vermiform Process .... ... 167 
 
 The Liver and Pancreas . . . .171 
 
 THE RESPIRATORY SYSTEM . . . . .171 
 
 The Larynx .... .172 
 
 The Lungs ... 175 
 
 THE CIRCULATORY SYSTEM . . . . .180 
 
 The Heart ....... 180 
 
 The Arterial System .181 
 
 The Venous System .... . . 184 
 
 The Spleen 186 
 
 THE URINOGENITAL SYSTEM . . . . . .187 
 The Pronephros and the Primitive Kidney . . .187 
 
 Miillerian Duct 189 
 
 Hymen 194 
 
 The Cloaca 194 
 
 External Genital Organs of the Female 195 
 
 Male Genital Glands (Descensus Testiculorum) . . . .196 
 Suprarenal Bodies . . . . . .'.-.. .199 
 
 CONSPECTUS OP THE ORGANS MENTIONED IN THE TEXT, ARRANGED ON 
 
 THE BASIS OF THEIR PHYSIOLOGICAL CONDITION . . . 200 
 
 Organs showing Retrogressive Characters ..... 200 
 
 Organs showing Progressive Characters 204
 
 CONTENTS xv 
 
 PAGE 
 
 LIST OP THE ORGANS AND TOPICS CONSIDERED IN THE TEXT, CLASSED 
 
 ACCORDING TO THE SYSTEMS TO WHICH THEY RELATE . . 206 
 
 Integument and Integumental Organs 206 
 
 Skeletal System 206 
 
 Muscular System 207 
 
 Nervous System ......... 208 
 
 Sense Organs 208 
 
 Alimentary System 208 
 
 Respiratory System 208 
 
 Circulatory System 209 
 
 Urinogenital Apparatus 209 
 
 SOME ORGANS AND VESTIGES OF ORGANS WHICH SHOW REVERSION TO 
 
 THE CONDITION OF VERY PRIMITIVE VERTEBRATE TYPES . . 210 
 CONCLUDING REMARKS . . . . . . . . .212 
 
 GLOSSARY OF TECHNICAL ZOOLOGICAL TERMS OCCURRING IN THE TEXT 219 
 
 INDEX 223
 
 LIST OF ILLUSTRATIONS 
 
 KIG. PACK 
 
 1. FACE OF AX EMBRYO FIVE MONTHS OLD, with the embryonic 
 
 covering of hair. After A. Ecker ..... 4 
 
 2. THE DISPOSITION OF THE HAIR-TRACTS ON THE HUMAN BODY. 
 
 After Eschricht 6 
 
 3. THE VERTEX COCCYGEUS OF THE HUMAN EMBRYO. After A. 
 
 Ecker 7 
 
 4. FOVEOLA COCCYGEA IN A HUMAN EMBRYO. After A. Ecker . 7 
 
 5. AND. JEFTICHJEFF, the " Russian Dog-man " .... 7 
 
 6. A, JULIA PASTRANA. B, HAIRY AINO, from the north-east 
 
 coast of Yesso. After D. Macritchie 8 
 
 7. YOUNG ORANG-UTAN, head from the side 9 
 
 8. YOUNG ORANG-UTAN, head from the front . . . .10 
 
 9. DIAGRAMMATIC REPRESENTATIONS OF THE EARLY DEVELOP- 
 
 MENT OF THE LEADING TYPES OF MAMMARY GLANDS. Modi- 
 fied from Gegenbaur . . . . . . . .12 
 
 10. DISSECTIONS OF A BROODING -FEMALE OF Echidna hystrix. 
 
 A, Ventral aspect ; B, dorsal inner view . . . .13 
 
 11. THE "MAMMARY LINE" IN THE PIG'S EMBRYO, AT DIFFERENT 
 
 STAGES. After O. Schultze 15 
 
 12. THE ARRANGEMENT OF THE TEATS IN A DOG . . .16 
 
 13. EXAMPLE OF POLYMASTY. After D. Hansemann . . .19 
 
 14. CASE OF POLYMASTY IN A YOUNG JAPANESE GIRL NINETEEN 
 
 YEARS OLD . . 21 
 
 15. FRONT VIEW OF THE BODY OF A HOSPITAL ASSISTANT, TWENTY- 
 
 TWO AND A HALF YEARS OLD, showing teats and hair vortices. 
 After 0. Ammon 23 
 
 16. SCHREINER VON ScHONACH, of the 16th Baden Infantry 
 
 Regiment, showing supernumerary teats and teat areas. After 
 
 O. Ammon . . , . . . .24 
 
 17. Two YOUNG HUMAN EMBRYOS, showing freely projecting tail . 27 
 
 18. TAILED HUMAN EMBRYO. After L. Gerlach , 28
 
 xviii THE STRUCTURE OF MAN 
 
 FIO. PAGE 
 
 19. "TAILED" CHILD, Moi, AGED TWELVE 29 
 
 20. DIAGRAMMATIC RECONSTRUCTION OF THE TAIL END OF A 
 
 HUMAN EMBRYO, length of trunk 8 mm. After F. Keibel . 30 
 20A. DIAGRAMMATIC RECONSTRUCTION OF THE TAIL END OF A 
 
 HUMAN EMBRYO, entire length 4 mm. After F. Keibel . 30 
 
 21. THE PELVIS, showing variations in sacrum, promontory, and 
 
 associated parts . . . .... . .35 
 
 22. A, TRANSVERSE SECTION OF THE THORAX OF A LOWER MAMMAL 
 
 (OR OF THE HUMAN EMBRYO) ; B, THE SAME OF A MAN . 36 
 
 23. DIAGRAMS OF THE VERTEBRAL AND COSTAL SKELETON. A, 
 
 IN THE QUADRUPED ; B, IN MAN 37 
 
 24. PART OF THE THORACIC, AND THE WHOLE LUMBAR, SACRAL, 
 
 AND COCCYGEAL SECTIONS OF A YOUNG HUMAN VERTEBRAL 
 
 COLUMN, dorsal aspect ; . 40 
 
 25. DIAGRAM OF A TRANSVERSE SECTION OF THE HIP GIRDLE 
 
 AND SACRUM : A, OF A SALAMANDER ; B, OF MAN, showing 
 detailed constituents . . . . . . . .41 
 
 26. A, FIRST THORACIC SKELETAL SEGMENT, FOR COMPARISON WITH 
 
 B, FIFTH CERVICAL VERTEBRA, OF MAN . . . . 41 
 
 27. A, PORTION OF THE THORACIC SKELETON OF AN ADULT FEMALE 
 
 POSSESSED OF A PAIR OF FREE CERVICAL RlBS. B, EXAMPLE 
 OF THE REDUCTION OF THE FIRST PAIR OF THORACIC RlBS, 
 
 IN AN ADULT MALE . . . . . . . 42 
 
 28. SHOULDER GIRDLE OF ORNITHORHYNCHUS . . . .46 
 
 29. EPISTERNUM OF AN EMBRYO MOLE. After A. Gdtte . . 47 
 
 30. EPISTERNAL VESTIGES IN MAN . . . . . .48 
 
 31. A, SLIGHTLY DIAGRAMMATIC MEDIAN LONGITUDINAL SECTION 
 
 THROUGH THE HEAD AND ANTERIOR PORTION OF THE TRUNK 
 OF A HUMAN EMBRYO, SEVENTEEN TO EIGHTEEN WEEKS OLD. 
 After W. His. B, EMBRYO TORPEDO, as seen by transmitted 
 light. After H. E. and F. Ziegler . . . ' . .49 
 
 32. SKULL OF IMMANUEL KANT. After C. von Kupffer . . 50 
 
 33. SKULL OF A CHILD SEVEN YEARS OLD ... 51 
 
 34. SKULL OF AN AUSTRALIAN FROM THE MURRAY RIVER . .51 
 
 35. SKULL OF A YOUNG ORANG-UTAN .... 52 
 
 36. SKULL OF AN ADULT ORANG-UTAN . . . . . 52 
 
 37. MEDIAN SECTIONS THROUGH THE HEAD OF A DEER, A 'BABOON, 
 
 AND A MAN ...... 54 
 
 38. A to C, VARIOUS FORMS OF THE os INCAE. D, E, DIAGRAMS 
 
 OF THE BONES OF THE OCCIPITAL REGION IN THE EMBRYO. 
 
 Partly after Ficalbi ...... 56
 
 LIST OF ILLUSTRATIONS xix 
 
 PAGE 
 
 39. SKULL OF A GIKL TWO YEARS OLD, showing broad ala magna of 
 
 sphenoid . . . . - . . . ' .i - . . 59 
 
 40. SKULL OF AN ABORIGINAL AUSTRALIAN, showing contracted 
 
 ala magna of the sphenoid . . ..... 59 
 
 41. SKULL OF A NEGRO EUNUCH, showing epipteric bone . . 61 
 
 42. SKULL OF A TURCO, with the temporal bone nearly reaching 
 
 the frontal .......... 62 
 
 43. SKULL OF A TWO-YEAR-OLD CHIMPANZEE, from the side . . 62 
 
 44. HARD PALATE OF A CAUCASIAN, A NEGRO, AND AN ADULT 
 
 ORANG-UTAN ......... 63 
 
 45. HEAD OF A HUMAN EMBRYO OF THE FOURTH MONTH, to show 
 
 the auditory ossicles, tympanic ring, with Meckel's cartilage, 
 
 and the hyoid and thyroid apparatus . . . . .65 
 
 46. SKULL OF A TAILED AMPHIBIAN (Menopoma) . . . . 66 
 
 47. TRANSVERSE SECTION THROUGH THE EMBRYO OF A SHARK 
 
 (Pristiurus melanost&mus), showing limb buds . . .67 
 
 48. DIAGRAM ILLUSTRATING THE DEVELOPMENT OF THE FINS OF 
 
 A FISH .......... 68 
 
 49. DIAGRAMMATIC REPRESENTATION OF THREE SUCCESSIVE STAGES 
 
 IN THE DEVELOPMENT OF THE PELVIC FINS OF A SHARK . 69 
 
 50. AN ATTEMPT TO DEPICT DIAGRAMMATICALLY THE PROCESS BY 
 
 WHICH THE LIMBS OF TERRESTRIAL VERTEBRATES WOULD 
 APPEAR TO HAVE BEEN PROBABLY DERIVED FROM THE FlNS 
 OF FISHES .......... 70 
 
 51. PECTORAL GIRDLE OF A TAILED AMPHIBIAN, ventral aspect . 71 
 
 52. RIGHT BLADE-BONE OF A NEW-BORN CHILD, showing ossifica- 
 
 tion of the coracoid . . . . . . . .72 
 
 53. PELVIS OF A FEMALE CHIMPANZEE, TWO YEARS OLD . . 75 
 
 54. RIGHT HUMERUS OF A NEGRO, showing perforation of the 
 
 olecranon fossa . . . . . . . . .77 
 
 55. DISTAL EXTREMITY OF THE HUMERUS, to show epicondylar 
 
 foramina, in Hatteria, Lacerta, the Cat, and in Man . . 78 
 
 56. SKELETON OF THE HIND- LIMB OF A TAILED AMPHIBIAN 
 
 (Spelerpes fuscus) ........ 79 
 
 57. DIAGRAMS OF THE HUMAN CARPUS. A, EMBRYO ; B, ADULT . 80 
 
 58. PROXIMAL HALF OF A LEFT HUMAN FEMUR POSSESSED OF THREE 
 
 TROCHANTERS . ...... 82 
 
 59. THE ANKLE-JOINT, in a Chimpanzee, an Australian native, and 
 
 a Caucasian . . . . . . . . .84 
 
 60. SKELETON OF THE LEFT PES OF A CHIMPANZEE, dorsal aspect 85 
 
 61. SKELETON OF THE LEFT HAND, dorsal aspect . . . .86 
 
 62. SKELETON OF THE LEFT FOOT, dorsal aspect . . . .87
 
 xx THE STRUCTURE OF MAN 
 
 no. 
 
 63. FORE- AND HIND-LIMBS OF A TWO MONTHS' HUMAN EMBRYO, 
 
 to show the position of the thumb and great toe . . .89 
 
 64. POSTERIOR END OF THE BODY OF TWO HUMAN EMBRYOS, with left 
 
 hind-limb and umbilical cord 90 
 
 65. LARVAL SALAMANDER. After Hatschek. A, with limbs turned 
 
 down ; B, with limbs turned up . . . . . 92 
 
 66. SKELETON OF A YOUNG BEAR, illustrating the positions of the 
 
 limbs. After Hatschek . . . . . . .93 
 
 67. DIAGRAM OF THE DISTRIBUTION OF THE PLATYSMA OVER THE 
 
 HEAD. After Gegenbaur . 104 
 
 68. SUPERFICIAL MUSCULATURE OF THE FACE IN Lepilemur muste- 
 
 linus. After Ruge . . . '. . - ''. .105 
 
 69. FACIAL MUSCLES AND NERVES OF THE LEMUROID Propithecm. 
 
 After Ruge . .... . . " . .106 
 
 70. MUSCLES OF THE EPICRANIAL REGION IN MAN, WITH CERTAIN OF 
 
 THE FACIAL MUSCLES. After Gegenbaur . . _ . '-, . 107 
 
 71. THE PINNA, in Man, a Baboon, an Ox, Macacus and Cerco- 
 
 pithecus. After Schwalbe and Henle . . . -. .108 
 
 72. SUPERFICIAL MUSCLES AND TENDONS OF THE DORSUM OF THE 
 
 FOOT. After Raubev . . . . . . . . Ill 
 
 73. DEEP MUSCLES OF THE FLEXOR SIDE OF THE FOREARM. After 
 
 Rauber . . . . ... . . *. .116 
 
 74. MEDIAN PLANTAR MUSCLES IN THEIR CONNECTION WITH THE 
 
 FLEXOR TENDONS. After Rauber. . . . . .117 
 
 75. DEEP DORSAL MUSCLES OF THE FOREARM. After Rauber . .118 
 
 76. LOWER PORTION OF THE SPINAL CORD, WITH THE GAUD A EQUINA 
 
 AND THE DURA MATER, dorsal aspect. After Schwalbe . . 1 24 
 
 77. BRAIN OF A DOG-FISH (Scyllum canicula), three views . .126 
 
 78. CEREBRUM OF A FEMALE CHIMPANZEE TWO YEARS OLD, showing 
 
 asymmetrical development . . . . . . .128 
 
 79. BRAIN OF A FEMALE CHIMPANZEE TWO YEARS OLD, lateral aspect 1 28 
 
 80. CEREBRUM OF THE GIBBON (Hylobates), lateral aspect . . .129 
 
 81. CEREBRUM OF A SEVEN TO EIGHT MONTHS' HUMAN EMBRYO, 
 
 dorsal aspect . . . '. . , . . .129 
 
 82. CEREBRUM OF A SEVEN TO EIGHT MONTHS' HUMAN EMBRYO, 
 
 lateral aspect . ,1 . .'.','.. . . 130 
 
 83. HYPOTHETICAL MEDIAN-LONGITUDINAL SECTION THROUGH THE 
 
 SKULL AND BRAIN OF A VERTEBRATE EMBRYO. Partly after 
 Huxley 131 
 
 84. BRAIN OF A RABBIT, three views 132 
 
 85. LONGITUDINAL SECTION THROUGH THE PINEAL ORGAN OF A 
 
 REPTILE (Hatteria pundata). After Baldwin Spencer . .133
 
 LIST OF ILLUSTRATIONS xxi 
 
 F10. PAGE 
 
 86. MEDIAN LONGITUDINAL SECTION THROUGH THE HEAD OF A 
 
 NEWLY-HATCHED LARVA OP THE LAMPREY (Petremyzon plaiierf) 136 
 
 87. LATERAL VIEW OP THE NASAL CHAMBER OF A HUMAN EMBRYO . 141 
 
 88. SAGITTAL SECTION THROUGH THE NASAL AND BUCCAL CAVITIES 
 
 OF THE HUMAN HEAD . 142 
 
 89. A-D, STAGES IN THE DEVELOPMENT OP THE SO-CALLED JACOBSON'S 
 
 ORGAN OF THE URODELA. E, THE SAME ORGAN IN A GYMNO- 
 PHIONE. F-H, THE NOSE AND JACOBSON'S ORGAN IN 
 Lacerta, A PLACENTAL MAMMAL, AND Ornithorhynchus. H, 
 after Symington . ....... 144-145 
 
 90. HEADS OF TWO HUMAN EMBRYOS AT SECOND AND THIRD MONTHS 147 
 
 91. HUMAN EYE 148 
 
 92. DIAGRAM TO ILLUSTRATE THE SHIFTING OF THE LACHRYMAL 
 
 GLAND, WHICH HAS TAKEN PLACE IN THE COURSE OF 
 PHYLOGENY 149 
 
 93. EYE OF A MONGOLIAN, WITH THE EPICANTHUS . . . .150 
 
 94. DIAGRAM TO ILLUSTRATE THE METAMORPHOSIS DURING DEVELOP- 
 
 MENT OF THE VISCERAL SKELETAL ARCHES . . . .151 
 
 95. PALATE OF A HUMAN EMBRYO AT THE EIGHTH MONTH . .155 
 
 96. PALATAL FOLDS OP THE RACOON (Procyon lotor) . . . .156 
 .97. HUMAN MOUTH, IN WHICH THE DEVELOPMENT OF THE UPPER 
 
 OUTER INCISORS HAS BEEN SUPPRESSED . . . .158 
 
 98. HUMAN STOMACH 166 
 
 99. THE C^CUM AND PROCESSOS VERMIFORMIS IN A HUMAN 
 
 EMBRYO 167 
 
 100. THE CAECUM AND VERMIFORM PROCESS OF A HUMAN EMBRYO . 168 
 
 101. THE CAECUM AND VERMIFORM PROCESS IN A KANGAROO . .169 
 
 102. HUMAN LARYNX IN FRONTAL SECTION 174 
 
 103. A SERIES OF WHOLLY DIAGRAMMATIC FIGURES TO ILLUSTRATE 
 
 THE COMPARATIVE MORPHOLOGY OF THE URINOGENITAL 
 ORGANS OF THE VERTEBRATA 191 
 
 104. DIAGRAMMATIC REPRESENTATIONS op THE CHIEF TYPES OF 
 
 UTERUS OCCURRING IN THE PLACENTAL MAMMALS . . .193 
 
 105. A, PARTLY DIAGRAMMATIC REPRESENTATION OF THE EMBRYONIC 
 
 URINOGENITAL APPARATUS OF A MALE MAMMAL, showing its 
 relations to the Ventral abdominal wall. B, THE PENIS AND 
 SCROTUM OP A HUMAN EMBRYO, 15 cm. long. Both figures 
 founded on the work of Klaatsch . 197
 
 THE STKUCTUKE OF MAN 
 
 INTRODUCTION 
 
 SOME thirty-four years have elapsed since the publication of 
 Charles Darwin's work On the Origin of Species ly Means of 
 Natural Selection. A short period of time, and yet important 
 enough to throw into the shade all previous centuries, so profound 
 is the significance of the results obtained in it, in the field of 
 Natural Science. 
 
 Darwin's book brought about a reformation not only of 
 Zoology, but of our whole knowledge of surrounding Nature. It 
 marked, in fact, the commencement of a new epoch, and of a new 
 cosmology. This has been said so often and demonstrated so 
 thoroughly, that the topic need not be further enlarged upon 
 here. I cannot, however, refrain from briefly sketching the 
 condition of the natural sciences during the last two centuries, 
 since it is only on such a background that a correct picture of 
 the enormous transformation which has since been effected in the 
 intellectual life of all cultured nations can be obtained. 
 
 In spite of the great discoveries made, in the sixteenth and 
 seventeenth centuries, by such men as Kepler, Newton, Harvey, 
 Schwammerdam, Malpighi, and Leeuwenhoeck, the Aristotelian 
 philosophy, which had been stirred to new life at the period of the 
 Reformation, was universally accepted. Its exegetical principle 
 rested on the assumption of the existence of an intelligent design, 
 to which the phenomena of nature were subordinated. The 
 teleological speculations which arose out of it, and the resulting 
 anthropocentric and anthropomorphic cosmology, outlived the 
 centuries named. Indeed, in spite of all progress in science, they 
 continued to count many of their most brilliant advocates among 
 distinguished scientific men, even into the fifties of the present 
 century. This philosophy was deeply rooted in human vanity, 
 .v B 
 
 I
 
 2 THE STRUCTURE OF MAN 
 
 receiving immense support from the Mosaic cosmogony, which 
 assigned to Man a sovereign position over nature, and especially 
 over the animal kingdom. Every attempt to shake this sover- 
 eignty was regarded as heresy. Even the laity persistently 
 refused to submit Man to the same strict scientific analysis 
 which, with increasing clearness, was being applied to the 
 surrounding forms of life by the existing schools of natural 
 philosophy. 
 
 In spite of this opposition, however, the theory of descent 
 steadily gained ground, and its advance was especially favoured 
 by new and surprising results attained in the three closely 
 allied branches of science Palaeontology, Comparative Anatomy, 
 and Embryology. The proofs of the great changes which must have 
 taken place in both the animal and vegetable kingdoms, during 
 the immeasurable periods consumed in the development of our 
 planet, became more and more convincing. 
 
 The earlier assumption of repeated separate acts of creation 
 gave way to a more satisfactory and strictly scientific conception 
 of the fundamental unity of all organic nature. " Blood relation- 
 ship, and not some unknown plan of creation, forms the invisible 
 band which unites organisms in various degrees of similarity," 
 and in this great family Man must find his place. He forms 
 but a link in the chain, and has no right to consider himself an 
 exception. To claim for himself a special act of creation, in order 
 to account for his appearance in the series of living creatures, would 
 be nothing less than a denial of the unity of physiological science. 
 
 It may be that we have not as yet succeeded in tracing back 
 the primitive history of Man beyond diluvial times by the light 
 of palseontological discoveries, for no certain proof of the actual 
 existence of tertiary Man has been obtained. But this " break 
 in the record " cannot in the least impair the evidence of mor- 
 phology as to the real ancestry of Man. Comparative morpho- 
 logy points not only to the essentially similar plan of organisa- 
 tion of the bodies of all Vertebrates, and to the agreement in 
 their entrance into life, individual existence, and final dissolution, 
 but also to the occurrence in them of certain organs, or parts of 
 organs, now known as " vestigial." 
 
 By such organs are meant those which were formerly of greater 
 physiological significance than at present. In the course of 
 generations, in consequence of the adaptation of the body to special 
 conditions of life, they have been, so to speak, put out of the 
 running, subjected to reduction or degeneration, and now persist as
 
 INTRODUCTION 3 
 
 mere vestiges. Such organs, which remain inexplicable by the 
 doctrine of special creation or upon any teleological hypothesis, can 
 be satisfactorily explained by the theory of selection. They are 
 found alike in the lower animals and in Man ; and it is evident 
 that these relics of a long vanished epoch are of peculiar interest in 
 this latter case, where Palaeontology offers us no help. Their closer 
 study, therefore, has a fascination for us which we cannot resist. 
 
 In the attempt to track the primitive Man, i.e. to follow up 
 the traces of Man's ancestry, we shall find indications here of 
 progression there of retrogression. These will help to throw 
 light on Man's position among the Vertebrata. 
 
 Thirty-one years have passed since Huxley published his 
 Evidence as to Man's Place in Nature. When we remember 
 how much work has been done since, and what results have been 
 attained in physical Anthropology, Anatomy, and Embryology, 
 it will, I think, be evident that the time has come once more to 
 look back, to gather together into a whole the new material which 
 now lies scattered far and wide, and from it to attempt once more 
 to estimate what Man is, what he was, and what he may become. 
 
 THE INTEGUMENT AND THE TEGUMENTAL OEGANS 
 
 In Man, as in all Vertebrata, two of the three germinal 
 layers take part in the formation of the integument, the outer 
 (ectoderm) and the middle (mesoderm). The ectoderm gives rise 
 to the epidermis (cuticle or scarf-skin) and the mesoderm to the 
 corium or dermis. 
 
 The epidermis, again, consists of a superficial and a deep layer, 
 of which the latter is of the greater physiological importance, all 
 the so-called cutaneous or tegumental organs owing their origin 
 to it. To these belong (1) the various corneous structures, such 
 as hair and nails ; (2) many different kinds of glands ; and (3) 
 the terminal apparatus of nearly all the sensory organs. 
 
 HAIR 
 
 Man is the least hairy of all the Primates ; indeed, his skin 
 may be called almost smooth. Apart from the head, the only 
 parts of the body abundantly supplied with hair are, as a rule, 
 the pubic, perineal, and axillary regions, although a careful 
 examination of the skin shows that hair follicles are to be found 
 over its whole surface. In males, in addition to the parts already
 
 4 THE STRUCTURE OF MAN 
 
 mentioned, hair is frequently strongly developed on the ventral 
 and dorsal regions of the trunk, i.e. on the breast and abdomen, 
 and on the buttocks and neck, and on the limbs. 
 
 These facts alone would suffice to render it probable that 
 man was in primitive times far more hairy than at present, but 
 still stronger evidence can be brought forward. 
 
 FIG. 1. FACE OF AN EMBRYO FIVE MONTHS OLD, with the embryonic covering 
 of hair. (After Ecker.) 
 
 The first traces of hair appear, in the human embryo, as early 
 as the twelfth or thirteenth week, the earliest being found about 
 the forehead, the mouth, and the eyebrows, i.e. in those parts of 
 the body where, in the lower Mammals, the so-called " whiskers " 
 (vibrissse) or tactile hairs usually appear. It is evident that, 
 morphologically, the hairs about the mouth and eyebrows in Men 
 belong to this same category. The hairs begin to break through 
 the integument at the end of the fifth month, and they con- 
 tinue to do so till the seventh month, those of the head being the 
 earliest and those of the limbs the latest to appear. 1 In the 
 
 1 The fact of the appearance of hair in different parts of the body in regular 
 order, the lower limbs being the last to become thus clothed, has apparently attained 
 popular recognition in the very old proverb "he has hair on his toes," which may 
 doubtless be referred to a time when boots and shoes did not play the part they now 
 do. From what I have gathered in conversation with inhabitants of Berne (Ober-
 
 TEGUMENTAL ORGANS 5 
 
 sixth month, the whole body of the embryo, except the surface 
 of the hands and feet, the red edges of the lips, the glans penis 
 and clitoridis, and the inner surface of the foreskin, is covered 
 with abundant soft woolly hair (lanugo). 1 
 
 In certain parts of the body the hairs are arranged closely 
 and quite regularly in tracts, just as birds' feathers are arranged 
 in the so-called "pteryloc." These hair- tracts (Fig. 2) are vortex- 
 like in arrangement, diverging over some areas, converging over 
 others. 
 
 In the former (cf. the hair of the head) the hairs point with 
 their free ends outwards, from the vertex as a centre ; in the latter, 
 on the other hand, the direction of the hairs is the reverse of this, 
 their free ends being directed inwards, i.e. towards the centre of 
 the vortex. This latter, converging, disposition is only found, both 
 in the lower Mammals and in Man, at parts where an organ either 
 projects during life, as in the case of horns and antlers, or has pro- 
 jected at some period in ontogenetic or phylogenetic development. 
 
 An excellent example of this is afforded by the radial 
 arrangement of hairs often found in the male sex in the region 
 of the navel, or still better by the "vertex coccygeus" (Fig. 3) 
 described by Ecker. The position of this latter exactly corre- 
 sponds in the embryo with the point at which, before the bending 
 of the os sacrum took place, the extremity of the coccyx pushed 
 against the skin ; i.e. with the point where the coccyx formerly 
 projected as a free tail, the cauda humana (cf, pp. 2*7, 28). 
 
 Just before birth the position of the vertex coccygeus shifts, 
 a hairless area being developed (Glabella coccygea) which may 
 sink in to form a pit (Foveola coccygea, fv, Fig. 4) (Ecker). On 
 the other hand it frequently attains such a degree of development, 
 
 deutsehen) and of Holland (Niederdeutschen), I am convinced that "on his toes" 
 (Zehen) is the light version of the proverb, and not "on his teeth" (Zahnen). 
 
 Many similar perversions of old popular sayings, or of words of which the original 
 meaning has gradually been lost in later generations, are to be found ; for instance, 
 the expression "to have his sheep (Schaffchen) in the dry " originated on the coast, 
 where "to have his ship (Schiffchen) in the dry" is still heard. Again, the 
 Schbnberg near Freiburg was originally called Schynberg, from Schyn, which means 
 a witch, a word which has been retained in the " Witch's Valley " at the foot of this 
 hill, and in the Swabian term of contempt " Schyn- Aas" (literally witch carcase). 
 
 1 In the fourth or fifth month the human embryo has a distinct stratum corneum 
 with an epidermal layer outside it, which corresponds with the epitrichium of Rep- 
 tiles and of many Mammalian embryos (Edentata, Dicotyles, Sus, and others). After 
 the sixth month of embryonic life the latter disappears from most parts of the body. 
 The epitrichial layer covers the hairs and the glands, being able to some extent to 
 keep back the secretions of the latter. In this way it provides for the accumulation 
 of a rich secretory deposit, the so-called "vernix caseosa."
 
 6 THE STRUCTURE OF MAN 
 
 even in the sixth or seventh month, that the hair may be twirled 
 between the fingers like a moustache. 
 
 FIG. 2.-THE DISPOSITION OF THE HAIR-TRACTS ON THE HUMAN BODY 
 
 (After Eschricht.)
 
 TEGUMENTAL ORGANS 7 
 
 Hypertrichosis, or excessive hairiness, which also not in- 
 
 Fio. 3. THE VERTEX COCCTGEUS OF THE FIG. 4. FOVEOLA COCCYGEA IN A HUMAN EMBRYO. 
 HUMAN EMBRYO. (After Ecker.) (After Ecker.) a, anus ; fc, foveola coccygea. 
 
 Fio. 5. AND. JEFTICHJEFF, the "Russian Dog-man." 
 
 frequently occurs in adults of both sexes, is a very interesting 
 phenomenon. By far the greater number of such cases, as
 
 FIG. 6. A, JULIA PASTRANA. B, HAIRY AINO, from the north-east coast of Yesso. 
 ( After Macritchie.)
 
 TEGUMENTAL ORGANS 9 
 
 Ecker has specially pointed out, appear to be due to a temporary 
 arrest in the development of the hairy covering, and the persistence 
 and subsequent growth in post-embryonic life of the foetal woolly 
 covering or lanugo. We can describe this as Pseudohypertrichosis 
 lanuginosa (Bonnet), since normally the greater part of the lanugo 
 is said to be shed, and to be replaced by stronger medullated 
 hairs. 
 
 I I 
 
 FIG. 7. YOUNG ORANG-UTAN. Zeitschri/t far Ethnologic (Anthropolog. 
 Gesellschqft), Bd. viii. 
 
 To this category belong all the well-known cases of " Dog- 
 men," or hairy men, 1 e.g. the Ambraser hairy family, Barbara 
 Uslerin, and Mrs. Lent (commonly known as Zennora Pastrana 
 II.) ; also the Kussian Dog-rnan Jeftichjeff (Fig. 5), his son Fedor, 
 and the Burmese Shwe-Maong and his family. In the cases of 
 Jeftichjeff senior, and Shwe-Maong, the whole face, except the 
 red edges of the lips, was thickly covered with delicate, soft, 
 and partly curly hair, such as also projected from the orifices 
 of the ears and nose. The body of the Russian was somewhat 
 
 1 In these cases defects in the dentition and other traces of arrested development 
 (e.g. retarded puberty) not infrequently occur.
 
 10 THE STRUCTURE OF MAX 
 
 less hairy than that of the Burmese, the whole of whose trunk 
 and limbs was covered with hair from 4-8 inches long. 
 
 The extreme hairiness of the Ainos (Fig. 6, B) may probably 
 also be referred to Pseudohypertrichosis ; but this point requires 
 closer investigation. 
 
 In all the cases mentioned above, the persistence of the 
 vestigial lanugo must undoubtedly be regarded as a return to a 
 
 . - 
 
 FIG. 8. YOONQ ORANG-UTAN. Zeitschrift fur thnologie (Anthropolog. 
 Gesellschaft), Bd. viii. 
 
 primitive hairy condition in Man; whereas true hairiness, or 
 " hypertrichosis vera," is quite a different thing. This, which 
 was well exemplified in the once famous dancer Julia Pastrana I., 
 is due to an excessive development of the secondary covering of 
 hair. In her case (Fig. 6, A) the greater part of the primary 
 hairy covering (the lanugo) must be considered to have been shed 
 during embryonic development. 
 
 Bonnet rightly points out that " in Man and the domestic 
 animals, the accessory structures of the epidermis accurately 
 register the balance of nutrition," and that various circumstances,
 
 TEGUMENTAL ORGANS 11 
 
 such as climate, domestication, natural and artificial selection, 
 influence the hairy covering. Further, the development of this 
 may be in inverse ratio to the thickness of the integument, and 
 particularly of the epidermis (Leydig), the hair and the epidermis 
 supplementing one another in the work of protecting the body. 
 This is illustrated, on the one hand, by animals which have a 
 delicate epidermis and thin skin and a thick covering of wool or 
 fur; and on the other by animals' like the Rhinoceroses, Hippo- 
 potami, some Armadillos, and Scaly Ant-Eaters, in which, while 
 the epidermis is so thickened as to form a hard carapace, the 
 hair is very scanty. 
 
 I cannot leave this subject without touching upon the question of the 
 origin of the Mammalia, especially as this chapter in morphology has recently 
 been ably dealt with by Max Weber, who deduces reasons for taking up the 
 following position. The first Mammals, as descendants from primitive scaly 
 Reptiles, were covered with scales, differing from those of the Reptiles only in 
 minor points. Behind the scales of the primitive Mammals there first 
 appeared a few small hairs, the origin of which it is difficult to explain with 
 certainty. By degrees, as a constant temperature was maintained by the 
 body, the covering of hair attained a greater development and the scales 
 degenerated. Scales, somewhat specialised, are still retained as a covering 
 for the mammalian body in a few cases, e.g. Armadillos and Scaly Ant-Eaters. 
 Among other Mammals they are found, as a rule, only on the tail and limbs. 
 The recurrent arrangement of the hairs, however, due to their original 
 development behind scales, has very generally persisted, and on this basis 
 hairs may be considered to imply the earlier presence of scales. 
 
 NAILS 
 
 The nails of the fourth and fifth fingers (and especially the 
 latter) most nearly suggest the claws of the lower animals, in being 
 decidedly arched from side to side. As the thumb is approached 
 the nails become more and more flat, and the like is true of the 
 great toe as compared with the four lesser toes. This condition 
 commences with the Lemuroidea [although among the lower 
 Mammalia the Squirrels, for example, bear a flattened nail upon 
 the pollex]. 
 
 On the under edge of the nail, between it and the ball of the 
 finger, is found the last vestige of a structure which in the Apes 
 is covered with a thickened layer of epidermis. 1 This structure 
 undergoes considerable degeneration, even during intra- uterine 
 life, through the advancing development of the ball of the finger 
 (Gegenbaur). 
 
 1 This structure is most conspicuous in the Ungulata, and it is there known as the 
 "frog."
 
 THE STRUCTURE OF MAX 
 
 CUTANEOUS GLANDS (MAMMARY GLANDS) 
 
 The cutaneous glands of Man fall into two classes : sweat- 
 glands and sebaceous glands, with their modifications. 
 
 Certain of these glands play an important part in Mammals 
 on account of their odoriferous secretions. In Man the secretion 
 of the axillary and anal glands is well known to have a penetrating 
 odour, but the significance of this we have so far failed to discover. 
 
 FIG. 9. DIAGRAMMATIC REPRESENTATIONS OF THE EARLY DEVELOPMENT OF THE 
 
 LEADING TYPES OF MAMMARY GLANDS. (Modified from Gegenbaur.) 
 A, First or undifferentiated (mammary pit) stage ; B, stage of the false teat ; C, stage 
 of the true teat ; v. v. , rim (or rampart) of the glandular area ; f.g. , glandular area ; 
 gl., mammary glands; d., mammary canal. 
 
 The mammary glands, in all Mammals higher than the Mono- 
 tremata, 1 must be regarded as aggregates of much modified sebace- 
 ous glands. This is attested not only by their whole structure, 
 and by the nature of their secretion, but also by the fact that the 
 sebaceous glands lying immediately around the teat in the female, 
 the so-called Montgomery's glands, grow larger when lactation 
 begins, many of them yielding milk. This functional transition 
 from sebaceous to mammary glands furnishes the best evidence for 
 their homology (Gegenbaur). In rare cases sebaceous glands still 
 farther from the teat may also take part in lactation, instances being 
 known in which such glands extended as far as the axillary region. 
 
 These facts lead us to believe, & priori, that all parts of the 
 skin may be capable of producing mammary glands. 
 
 I 1 The mammary organ of the Monotremata is derived from sweat-glands, so that we 
 have a diphyletic origin for the mammary glands collectively considered (Gegenbaur).
 
 TEGUMENTAL ORGANS 
 
 The development of mammary glands and teats is always 
 initiated by a shallow degression of the integument (f.g., Fig. 9, A), 
 the mammary pit ; the base of this pit is the glandular area, 
 and the surrounding border () the rampart of the gland. The 
 Malpighian stratum of the epidermis at the base of the glandular 
 area, by inward proliferation, gives rise to the glandular tissue. 
 
 The mode of development of the teats is not the same for all 
 
 FIG. 10. DISSECTIONS OF A BROODING FEMALE OF Echidna hystrix. 
 A, Ventral aspect ; B, dorsal inner view, f t. The two tufts of hair, in the lateral folds of 
 the mammary pouch from which the secretion flows. On each side of the pouch 
 (b.m.), which is surrounded by strong muscles, a group of mammary glands (ff.m.) 
 opens ; cl. denotes the cloaca in each figure. (After W. Haacke.) 
 
 Mammals. Either (Fig. 9, B) the rampart which borders the 
 depression rises and forms a tube (the lumen of which is known 
 as the mammary canal), into the base of which the true ducts 
 open, or (Fig. 9, C) the glandular area rises in the shape of a 
 papilla, while the rampart degenerates. The latter, in which the 
 nipple must be considered as a secondary formation, is exemplified 
 in the Marsupials, the Lemuroidea, Apes, and Man ; in the former, 
 which obtains in the Caruivora, Pigs, Horses, and Ruminants, it 
 is a primary formation. The first indications of the primary
 
 14 THE STRUCTURE OF MAN 
 
 formation are found in certain Marsupials (Plialangista vulpina) 
 and among placental Mammals as high as Carnivora (Gegenbaur). 
 
 The question now arises, whether the developmental stages 
 of the mammary glands point to primitive conditions which in 
 any degree persist in the lower Mammals ? An examination of 
 the Monotremata shows that this may be the case ; and to make 
 this clear we must enter somewhat further into detail. 
 
 In the Monotremata, in which as yet there are no teats, the 
 ducts of the mammary organ open in a group on the ventral 
 integument. As the reproductive period approaches, if fertilisation 
 has taken place, a temporary depression of the ventral integument 
 occurs, which gives rise to a pouch (b.m., Fig. 10). The egg is 
 deposited in this pouch, and the mammary fluid is probably 
 carried to the young animal to which the egg gives rise, by 
 means of the pointed tufts of hair which project around the 
 apertures of the glands. Closer examination shows that the ducts 
 open into two cutaneous depressions, which lie near the tufts just 
 mentioned, in the lateral folds of the mammary pouch. These 
 may be called mammary pits, and are of considerable importance, 
 because they are repeated in the development of the various 
 forms of nipples and mammary organs occurring in the higher 
 orders of Mammals. "We have here a glandular area which, like 
 that already described (Fig 9, A), is nothing more than a de- 
 pressed portion of the external integument, with all its character- 
 istic derivatives, such as hairs, glands, and pigment. 
 
 Before passing to the question of the disposition of the 
 mammary glands on the body, an important discovery, for which 
 we have to thank Oskar Schultze, must be mentioned. 
 
 In young embryos of Mammals, e.g. the Pig, a ridge-like 
 prominence (l.m., Fig. 11) is found on each side, running from the 
 base of the anterior limb, which is at this period a mere stump, 
 towards that of the posterior limb and into the inguinal furrow. 
 This is due to a linear thickening of the developing epidermis, 
 and especially of the stratum Malpighi. This lateral epidermal 
 ridge represents the common epithelial rudiment of the mammary 
 glands, and may be called the " Mammary Line." Along this line 
 a row of fusiform thickenings develop (Fig. 11, B and C), the whole 
 presenting the appearance of a regularly varicose fibre. These 
 protruding " primitive teats " flatten out again at a later stage, 
 and in no way represent the teats which form later, although they 
 generally correspond in number with the centres of origin of the 
 future glands.
 
 FIG. 11. THE "MAMMARY LINE" (l.m.) IN THE PIG'S EMBRYO AT DIFFERENT 
 
 STAGES. (After 0. Schultze.) 
 
 A, embryo I, 5 cm. (from head to coccyx) ; B, embryo I, 7 cm. long ; 
 C, embryo I, 9 cm. long.
 
 16 
 
 THE STRUCTUEE OF MAX 
 
 Eesorption of those portions of the mammary line which lie 
 between the primitive teats soon begins to take place, and in such 
 a manner that the originally elongated and fusiform eminences 
 become rounded. At a later stage, as above stated, these flatten 
 out, and extend at the same time into the subjacent tissues. 
 In 'this way they form the well-known button -like epidermal 
 proliferations, which have generally been considered to mark the 
 
 first stage in the develop- 
 ment of the mammary 
 glands, a stage which is 
 immediately followed by 
 the formation of the so- 
 called mammary pits. 
 
 Later on we shall have 
 to refer to the conclusions, 
 with respect to Man, to 
 be drawn from Schultze's 
 observation, but we may 
 now turn to the ques- 
 tion of the disposition of 
 the mammary glands on 
 the body. 
 
 Although the position 
 of these organs may vary 
 greatly, the ventral side of 
 
 the body has the prefer- 
 FIG. 12. SHOWING THE ARRANGEMENT OF THE , 
 
 TEATS IN A DOG, in two longitudinal rows con- ence Oil account of the 
 verging towards the pelvic region. greater facility with which 
 
 the young can reach the teats. The position in the postero- 
 ventral region, i.e. in the region of the groin, may be considered 
 the most primitive. The udder of some Ungulates, as is well 
 known, is found in this position, and the same is also the case 
 in the Cetacea. In the great group of the Carnivora, and in 
 the Pigs, the teats are found on the thoracic and abdominal 
 regions (Fig. 12), arranged in two rows converging towards the 
 pelvic region. In other groups, again, they are confined to the 
 pectoral region (e.g. Elephants, Sirenia, many Lemuroidea, Chirop- 
 tera, Apes, and Man). 
 
 The great range of variation in the position of the teats and 
 mammary glands deserves careful attention, since it enables us to 
 satisfactorily explain the existence of so-called supernumerary 
 mammary glands and teats, which often occur in human beings
 
 TEGUMENTAL ORGANS 17 
 
 of both sexes. The term polymasty is used to denote the former 
 condition, and polythely x the latter. 
 
 During the last three decades an immense number of cases 
 of this kind have been recorded ; and as it is quite impossible to 
 consider them all here, we must limit ourselves to a few of the 
 more characteristic. We may remark at the outset that the 
 increase in number of the mammary glands or teats, in both men 
 and women, may be regarded as a return to a primitive condition 
 in which many glands were developed and many young were 
 produced at a birth. The change from polymasty to bimasty 
 can be observed at the present day in the Lemuroidea. In these 
 animals the teats of the groin and abdomen are functionless and 
 clearly degenerating, whereas the pair which occur in the pectoral 
 region are well developed. In accordance with this most 
 Lemuroids give birth to only two young, which they carry about 
 at the breast. This habit permits of the greatest freedom of 
 movement (for example in climbing), and renders explicable the 
 gradual degeneration of the other teats. 
 
 But how are we to explain the presence of such pronounced 
 vestigial organs as the teats of the male human being ? 
 
 It is usually considered that they are inherited from the 
 female, and it is possible that this explanation is correct. But 
 when we find that in the Monotremata the mammary glands are 
 almost equally well developed in both the male and the female, 
 it seems not improbable that originally both sexes may have 
 taken an equal share in the bringing up of the young. 
 
 It is certain that a functional condition of the mammary 
 glands (gynaekomasty) may occur in men. 2 [Humboldt records 
 a case, to which he bore ocular testimony, of a man who, at the 
 age of thirty-two, was left in charge of a sucking child by the 
 death of his wife. Not knowing how to rear it, he in despair 
 pressed it to his own bosom ; and it is alleged that hypertrophy 
 of his breast, with milk secretion sufficient for the rearing of the 
 infant, was thereby induced.] 3 It is also known that boys, both 
 
 1 Either well-developed or rudimentary supernumerary teats are not infrequently 
 found in various Mammalian orders, for instance two rudimentary teats often occur 
 behind the four normal teats of the cow. 
 
 2 [I can testify to this in person, for, while bathing with friends on the Welsh 
 coast at the age of thirty-six years, milk, sufficient to cover a threepennypiece, issued 
 from my left breast on contact with the towel. This state of affairs continued for 
 three days, the right breast remaining inactive. G. B. H.] 
 
 3 [During the passage of these pages through the press this subject has been 
 comprehensively dealt with by Schaumann (Verhandlg. d. physik. -medic. Gesellsch., 
 Wiirzburg, Bd. xxviii. p. 1)]. 
 
 C
 
 18 THE STRUCTURE OF MAN 
 
 soon after birth and at the time of puberty, may produce milk 
 (so-called " witch's milk ") from more or less swollen breasts. 1 
 Milk has also certainly been obtained from male goats and from 
 castrated rams, and this has been found on chemical analysis to 
 be even richer in caseine than ordinary milk. 
 
 [In this connection it is interesting to note that Dobson has 
 called attention (British Museum Catalogue of the Chiroptera, 
 Lond., 1878, pp. 79 and 83) to the great development of the 
 teats in the males of certain frugivorous Bats. He points out 
 that while many Bats are known to bring forth two young at a 
 birth, he has never found a mother with more than one clinging 
 to her body ; and he inclines to the belief that in such cases the 
 male may relieve the female of the charge of one of the young 
 ones (as the weight of two might render flight difficult or 
 impossible). He suggests that " instances of the male performing 
 the office of nurse are probably not uncommon among Bats."] 
 
 The following results on the subject of supernumerary breasts 
 and teats were obtained by Leichtenstern, from the study of 
 extensive data : 
 
 Cases of polythely, with or without polymasty, were observed 
 with almost equal frequency in the two sexes. On an average, 
 one case may be expected in every 500 individuals. 
 
 In 9 1 per cent the accessory glands and teats were developed 
 on the anterior side of the thorax, and in by far the greater 
 number (94 per cent of these) they were found below (caudad of) 
 the normal teats, in a convergent disposition. 
 
 The following is a table showing the position occupied by 
 the accessory mammillae in the 105 cases recorded by Leichten- 
 stern : 
 
 On the anterior side of the thorax . . 96 cases 
 
 In the axilla . . . . 5 
 
 On the back . . . 2 
 
 Above the acromion . . . . 1 case 
 
 On the outer side of the hip . . * 1 
 
 Eudimentary breasts occurring above (cephalad of) the normal 
 ones are of rare occurrence (3 per cent), and these (Fig. 13, m") 
 always lie outside the normal mammary line in the direction 
 of the axilla. Want of symmetry, especially on the left side, is 
 common in all cases of rudimentary teats or mammary areas, in 
 whatever part of the body they occur. The rarest condition 
 
 1 Decided swelling of the breasts is sometimes found in youths of from twenty to 
 twenty-one years of age, in cases of retarded puberty (Ammon).
 
 TEGUMENTAL ORGANS 19 
 
 (only one case being known) is that in which a supernumerary 
 teat occurs in the same horizontal plane with the normal teats, 
 either at or near the median line. 
 
 Hyrtl put forward the view that the greater development of 
 the left breast is due to the habit of feeding the child from that, 
 in order to leave the right arm free. Leichtenstern opposes this, 
 but does not furnish any satisfactory explanation of the fact. 1 
 
 FIG. 13. EXAMPLE OF POLYMASTY. (After Hansemann.) 
 
 The position of the supernumerary breast (m") is superior and lateral to that of 
 
 the normal (?') The left accessory gland has a second teat (mf"). 
 
 Kudimentary mammary organs were never found by Leichten- 
 stern below the costal ridge or in the inguinal region. 
 
 In the Dog the normal number of teats varies from seven to 
 ten, and Cuvier's dictum that the numerical variation in breasts 
 is greatest where they are most numerous is thus confirmed. 
 
 Towards the end of the last century, Professor Socin of Basel, 
 and subsequently the Medical Faculty of the University of 
 Tubingen, were consulted by a lady with four breasts, as to 
 whether she could marry without incurring the danger of having 
 twins at every birth. The authorities decided that polymasty 
 did not imply predisposition to bear twins, and the result proved 
 the correctness of this opinion. Among seventy women with 
 polymasty, twins are known to have been born in only three cases. 
 
 1 [It may be remarked here that the young " vervet " (Cercopiihecus lalandii) has 
 been recently observed to suck both teats at once (Proc. Zool. Soc., Loud. 1893, 
 p. 615).]
 
 20 THE STRUCTURE OF MAX 
 
 If the supernumerary teat is sufficiently large, it can be used 
 for suckling; but it is generally too small for this purpose, and 
 is merely an encumbrance, since when the child is being fed 
 from the normal breast, milk may dribble from the accessory one. 
 
 Hansemann has recorded the case of a married sempstress, 
 forty-five years old (Fig. 13), who had, above and laterally to 
 the normal breasts, two accessory ones, which possessed teats, but 
 hardly any areolse. Above the supernumerary teat of the left 
 side there was another one showing distinct orifices. Glandular 
 tissue could be discerned below all five teats, and many accessory 
 apertures were found in the areolae of the normal breasts. In 
 the twenty-one years of her married life this woman had given 
 birth to twelve children, twins being born twice, and had had 
 seven advanced miscarriages ; she had thus passed through 
 seventeen pregnancies. All the breasts yielded milk, but a 
 child could only be fed from the normal ones, since these alone 
 were furnished with teats which could be seized by it. 
 
 Hansemann records in his treatise 262 cases in all : 81 males, 
 104 females, and 77 in whom the sex is not stated. The author 
 refers to the goddesses Isis and Diana, who were represented 
 with many breasts as a symbol of fruitfulness ; but he rightly 
 adds that, judging from data of the present day, the myth can 
 have had no foundation in fact. 
 
 I have to thank my pupil Kenkitzi Horiuchi for the record 
 of a case of polymasty, published in the Weekly Medical Journal 
 of Tokio, of 4th July 1891 (No. 692), which may be added to 
 Hansemann's series. It is that of a Japanese girl, aged nineteen, 
 who was examined in the hospital of Fukui. Above the normal 
 well-developed teats, at a distance of 4 cm., there was on each 
 side (Fig. 14 m") an accessory teat of the size of a pea, dark in 
 colour, and in all respects like a true nipple. Above, and at 
 some distance laterally from the normal breast on each side, 
 a second smaller breast (m'"} was found, with a teat. Fig. 14 is 
 taken from a photograph of this case. The girl was in all other 
 respects normal, and menstruation began at the age of fifteen. 
 
 In conclusion, I append some observations for which I am 
 indebted to Otto Ammon, of Karlsruhe, distinguished for his re- 
 searches into the anthropology of Baden. The data were obtained 
 in connection with the recruiting for military service in the 
 year 1890 ; and the manuscript bears the title, " Some Observa- 
 tions on the Occurrence of Supernumerary Teats, and on the 
 Direction of the Hair on the Breasts." Out of 2189 men (of
 
 TEGUMENTAL ORGANS 
 
 21 
 
 the Donaueschingen military district) supernumerary teats were 
 found in sixty-six cases, one extra teat in sixty-two, and two in 
 four, giving a proportion of one case in every thirty -three. 
 Besides these sixty-six cases, forty-eight others showed traces of 
 supernumerary teats, in the form of circumscribed patches of 
 pigment (small areoke). The nature of these patches was indi- 
 cated by the fact that while on one side of the body there was 
 'the pigment patch and the teat, on the other, symmetrically 
 
 YIG. 14. CASE OF POLTMASTY IN A YOUNG JAPANESE GIRL NINKTEEN YEARS OLD. 
 
 m', normal teats ; m", supernumerary teats on the normal breasts ; m'", supernumerary 
 
 teats on accessory breasts. 
 
 placed, there was merely the patch. This condition was so often 
 repeated, that there could be no doubt that these patches, situated 
 as they were along converging lines, were the homologues of 
 teats in an advanced stage of degeneration. 
 
 The above-named sixty-six cases, together with the forty- 
 eight others in which only traces were found, testify to the 
 occurrence of rudimentary mammary organs in various degrees 
 of development in 114 of the 2189 men examined, i.e. in the
 
 22 THE STRUCTURE OF MAN 
 
 proportion of 1 in 19. In every nineteenth man, then, we find 
 the atavistic reappearance of supernumerary mammse. 
 The following is an analysis of these cases : 
 
 On the right. On the left. 
 
 One teat . . . . 24 cases. 36 cases. 
 
 Two teats . ... 3 3 
 
 Other combinations . . . 2 ,, 2 ,, 
 
 One trace .... 8 35 
 
 Two traces ....'. 3 7 
 
 Other combinations . . . 2 ,, 2 
 
 The preponderance of teats on the left side is as 1'4 to 1, 
 and in the case of traces of these organs it is still more striking, 
 viz. as 3 '3 8 to 1. This is no doubt to be associated with 
 the well-known fact that the normal left breast in women is 
 often (always?) more developed than the right (cf. ante, p. 19), 
 and it may be that the right, therefore, degenerates more rapidly 
 than the left. 
 
 In those cases recorded in the literature of the subject in 
 which one of the normal teats is entirely absent (amasty), the 
 right nipple is more frequently wanting than the left. 
 
 In the cases recorded by Ammon (if we reckon together the 
 number of teats and teat traces occurring singly) the proportion 
 of those on the left to those on the right is 71 to 32. These 
 results agree pretty closely with those of Leichtenstern. 
 
 In one of the cases with a pair of supernumerary teats, 
 Ammon found these considerably to the side, quite near the 
 anterior axillary fold formed by the edge of the pectoral muscle ; 
 and in a case described by Leichtenstern they had even entered 
 the axillary area. 
 
 This shifting apart is explained by Ammon as connected 
 with the upright gait of Man, i.e. with the position of the upper 
 extremities, which is secondarily acquired as a result of it. 
 
 The following case, observed by Ammon, is particularly 
 interesting, as a striking example of the extraordinary persistence 
 of certain organs which, after becoming as a rule extinct, 
 occasionally reappear. 
 
 On the upper part of the breast of a very hairy soldier, two 
 diverging hair vortices occurred a few centimetres above the teats, 
 but farther apart than these, and nearer the axillary folds (* Fig. 
 15). At the focal point of each of these vortices there was a 
 light spot from which the hair grew upwards and outwards as
 
 TEGUMENTAL ORGANS 
 
 23 
 
 from the crown of the head. These were evidently the sites of 
 former teats that is, of former orifices ; for, as Ammon rightly 
 remarks, the hair vortices agree with the diverging vortex 
 found at the point where the canalis sacralis finally becomes 
 closed the glabella coccygea, or " sacral dimple," which lies above 
 the coccygeal vortex. This latter, however, is a converging vortex, 
 
 A 
 
 Fio. 15. FRONT VIEW OF THE BODY OF A HOSPITAL ASSISTANT, TWENTY-TWO AND A 
 
 HALF YEARS OLD. (After 0. Ammon.) 
 
 m, normal teats ; *, hair vortices above these, pointing to the former presence of 
 supernumerary teats. 
 
 such as always occurs where a protuberance formerly existed (cf. 
 ante, p. 5) ; but the glandular area of the breast, as Ammon further 
 rightly argues, originally developed not as an elevation, but as a 
 depression, out of which the teat rose up secondarily. According 
 to Ammon there are, on the normal teats also, smaller diverging 
 vortices, in which "the hairs course round and round the areolae . . . 
 but these are soon lost in the general course of the hair tracts." l 
 
 1 I here reprint by permission a letter received from Herr Otto Ammon, on the 
 10th February 1892. 1 have refrained from commenting upon it, as I have not yet 
 been able to confirm the observation recorded : 
 
 " Allow me to draw your attention to another case which I have not yet recorded.
 
 24 
 
 THE STRUCTURE OF MAN 
 
 The most interesting case yet recorded by any author, a 
 case which is in fact unique, is that of a Triberg recruit 
 
 
 FIG. 16. SCHREINERVON ScHONACH, aged twenty-two and a half, serving in 16th Baden 
 
 Infantry Regiment, K. F. HI. No. 114. (After Ammon.) 
 
 m', normal teats ; m", supernumerary teats ; ma! , supernumerary teat areas above 
 the normal breasts ; ma", the same below the normal breasts. 
 
 examined by Ammon. In this man (Fig. 16) there were four 
 pairs of teats and teat traces. Above the normal teats (m') 
 there were two teat areas (bilaterally symmetrical pigment spots, 
 
 As I am not sure of its significance, I simply give the facts, leaving you to decide 
 whether it is anything more than a chance occurrence. In very hairy men there 
 are often found all over the ventral surface small hairs (O'5-l'O cm. long), disposed 
 in the middle line lengthwise and at the sides horizontally, which gradually bend 
 round and converge towards the navel. Above the navel they point downwards, 
 below it upwards. The ordinary course of these hairs is broken at points where 
 longer and stronger hairs grow, and these points occur where in other individuals
 
 TEGUMENTAL ORGANS 25 
 
 ma'} lying in shallow depressions of the axillary folds, and thus 
 still more lateral in position than in the case above described 
 (Fig. 15). In descending order, below the normal teats, came a 
 pair of tolerably distinct though small teats with areolse (m") ; 
 and lowest of all two small rudiments (bilaterally symmetrical 
 pigment spots, ma") lying below tJM ribs. 
 
 This case suggests that the demonstration in the human 
 embryo of a mammary line or ridge like that above described in 
 the quadruped may be only a matter of time. 1 
 
 supernumerary teats appear ; they lie, however, below the normal teats, while in 
 the man in your large photograph (Fig. 15) they lie above these. 
 
 "The greater development of hair at those parts of the body which correspond 
 with the position of supernumerary teats below the normal ones, i.e. on the con- 
 verging lines, has twice been observed by me, and in each case on both sides of 
 the body. The stronger hairs do not form tufts, but lie parallel and close 
 together, and follow the general course of hair, i.e. have the same direction as the 
 rest ; they are merely longer, thicker, and perhaps also darker. The fact that they 
 do not form vortices deterred me from connecting them with rudimentary teats. 
 The facts, however, are worth recording. " 
 
 1 Further information on the subject of supernumerary teats and mammary 
 gland, can be obtained from the works of Mitchell Bruce (Jour. Anat. and Phys., 
 vol. xiii. p. 425) and Karl von Bardeleben (Verhandl. d. Anatom. Gesellsch., Miinchen, 
 1891 ; and Wien, 1892). I would, however, warn inquirers against the danger of 
 seeing a teat in every wart-like prominence !
 
 THE SKELETON 
 THE VERTEBRAL COLUMN 
 
 THE vertebral column of an adult human being consists normally 
 of thirty-three to thirty-four vertebrae, numerical variation being 
 due to the inconstancy of those of the coccygeal or caudal series. 
 As might be expected from the study of other related organs (e.g. 
 the vertex coccygeus, the filiurn terminate, the arteria sacralis 
 media, certain muscles and nerves, and the coccygeal gland), 
 we here meet with evidence of degeneration and variation. This 
 is specially the case during development. It is, above all, the 
 caudal region which, in this respect, has claimed the greatest 
 attention of morphologists : and incidentally to the study of this 
 there arises the old controversy as to whether Man or his 
 ancestors possessed a tail. 
 
 .At an early stage of development the human embryo 
 possesses at the posterior end of the body, clearly in direct 
 continuity with its developing axial skeleton, a free projecting 
 pointed appendage, bearing an undeniable resemblance to the tail 
 of a lower animal. This is delineated in Fig. 17, cd., and will 
 be further discussed as we proceed. At later stages of develop- 
 ment this organ is less conspicuous ; it gradually becomes shorter 
 and blunter, and is slowly, as it were, taken into the trunk. 
 For some time, however, a caudal prominence remains ; but 
 this at last either disappears altogether, or leaves, at the point 
 where its tip abutted against the integument, more or less 
 distinct traces known as the "vertex coccygeus" (cf. ante, 
 pp. 5 and 7). This is the normal course of development, but 
 occasionally a tail-like appendage is found in extra-uterine life. 
 An extensive literature exists on this subject, 1 and to it I 
 
 1 Some of the alleged observations on this subject are not such as to awaken 
 confidence, and others refer to pathological cases or abortions, in which, among 
 other malformations, more or less developed caudal appendages occurred. Other
 
 TEGUMENTAL ORGANS 
 
 27 
 
 must refer the reader, as I can here only call attention to a few 
 cases. 
 
 Fio. 17. Two YOUNG HUMAN EMBRYOS. 
 
 A, ventral ; B, lateral view. (After Ecker.) Both figures are intended to show the 
 freely projecting tail (cd.). cp., head; vs., eye; ap'., fore-limb; ap"., hind-limb; 
 C.M., umbilical cord. 
 
 Gerlach records a very remarkable case of tail formation 
 in an otherwise normal human embryo, in the fourth month 
 of intra-uterine life, an age at which, as a rule, the tail-Uke 
 appendage has disappeared. The length of the trunk was 7'6 
 cm., the total length 10*8 cm.; and as the tail (Fig. 18), which 
 projected freely from the buttocks, measured from root to tip 17 
 mm., it was almost a sixth of the total length of the whole 
 embryo. At its thickest part, where it left the body, it was 2 
 mm. broad, and it thence gradually narrowed towards its middle. 
 Closer examination revealed the following facts: The caudal 
 appendage was not only connected with the last (fourth, and still 
 cartilaginous) coccygeal vertebra, but the chorda dorsalis could 
 be distinctly traced within it. Muscle bundles were also found, 
 which from their whole position could be compared with nothing 
 else than the M. curvator caudse of the lower animals, i.e. with 
 a true tail muscle. The existence of muscles further justifies 
 
 more recent observations, again, have been made on living subjects, where 
 naturally no precise anatomical data could be obtained. One point can be main- 
 tained with certainty, viz. that in some of the observed cases, e.g. in those of de 
 Maillet, a hereditary tendency was evident.
 
 THE STRUCTURE OF MAN 
 
 the assumption of the former presence of "proto- vertebrae" 
 [or mesoblastic somites] in this region, and these, in turn, might 
 indicate the prolongation of the spinal 
 cord into the caudal region in earlier 
 embryonic stages (cf. Fig. 20). 
 
 We must not, however, assume, as 
 Gerlach justly observes, that a true 
 tail, supported by skeletal tissues, 
 would have developed in this embryo 
 had it lived longer ; because the 
 tissues lying in the region of the 
 caudal filament showed no traces of 
 conversion into permanent cartila- 
 ginous or osseous vertebrae. It was 
 further observed, that at the point of 
 junction between the posterior coccy- 
 geal vertebra and the proximal end 
 of the caudal filament, the chorda dor- 
 salis had already disappeared. These 
 FIG. IS.-TAILED^HUMAN EMBRYO. factg indicate an attempt to return 
 
 to the normal. The tail showed every 
 
 sign of degeneration ; but this does not detract from the great 
 morphological interest of the case, which has led me to describe 
 it at some length. 
 
 Three other certified cases of tail formation in human beings 
 may be cited. 
 
 The first is that of an Esthonian recruit, described by Max 
 Braun in vol. iv. of the Zoologischer Anzeiger. The coccyx, in 
 this case, did not recede into the groove of the buttocks under 
 cover of the nates, but ended in an eminence, which, though not 
 long, could be laid hold of and felt by the fingers. Thus exa- 
 mined, it was found to lie in a direct line with the vertebral 
 column and to contain distinct vertebras, the last of which was 
 about the size of a pea. It could not be certainly ascertained 
 in the living subject whether this tail was due to numerical 
 increase in the number of vertebras, or simply to a retention of 
 the embryonic straight condition of the coccyx itself. It is a 
 noteworthy fact, however, that Ecker's glabella and foveola 
 coccygea, or sacral dimple, had persisted. 
 
 The second case is that of a newly-born female child, recorded 
 by Lissner in 1872. Here also hard, irregular bodies, somewhat 
 like the phalanges of a finger, could be distinctly felt in direct
 
 THE SKELETON 
 
 axial continuation of the vertebral column. Twelve years later, 
 when the caudal appendage had reached the length of 12'5 cm., 
 these could still be detected. 1 
 
 I have to thank my friend and colleague, Professor G. B. 
 Howes, for the knowledge of the 
 third case. 2 It is described in the 
 Scientific American of May llth, 
 1889, p. 296, where an engraving 
 taken from a photograph is also 
 given. Fig. 19 is a copy of this, 
 and represents a young Moi, twelve 
 years old, who possessed a tail- 
 like appendage 1 foot in length, 
 and soft and smooth to the touch. 
 As no skeletal elements could be 
 felt, a prolongation of the vertebral 
 column was certainly not present. ' 
 It cannot therefore be considered 
 a true tail, and this conclusion ap- 
 plies to a large number of similar 
 formations which have erroneously 
 been regarded as tails [some of 
 which are purely pathological and 
 due to spina bifida]. 
 
 With regard to the number 
 of caudal vertebrae definitively 
 formed in Man, Steinbach has ar- 
 rived at the following conclusions, 
 after working upon a great ac- 
 cumulation of material. 
 
 The male embryo, from the end of the second month of intra- 
 uterine life, has five post-sacral vertebrae; and indications of com- 
 
 1 It is important also to note that similar reversionary formations have occasion- 
 ally been observed in the Anthropoid Apes (Gorilla and the Orang), and this is the 
 more remarkable, as in the latter the degeneration of the os coccygis, which consists 
 as a rule of only three vertebra, has gone still further than in Man. [It is worthy 
 of remark here that this same maximum reduction of the caudal vertebrae to three 
 occurs also in some Bats, and that the opposite extreme for the mammalian series is 
 reached by a small insectivore from Madagascar (Microgale longicaudala) and the 
 long- tailed Pangolin (Manis macrura) of the old world, in which the caudal vertebrae 
 may be close upon fifty in number. ] 
 
 2 [And I, in turn, have to thank my friend Professor Johnson Symington, of 
 Queen's College, Belfast, in conversation with whom my attention was first drawn 
 to this case. G. B. H.] 
 
 'Fio. 19. "TAILED" CHILD, Moi, 
 
 AGED TWELVE.
 
 30 
 
 THE STRUCTURE OF MAN 
 
 mencing fusion between the last two of these sometimes occur. 
 Six vertebras were once observed in a boy four weeks old ; and 
 
 a I" 
 
 FIG. 20A. DIAGRAMMATIC KECONSTRUCTION OF THE TAIL END OF A 
 
 HUMAN EMBRYO (length of trunk, 8 mm. ) 
 
 ch., notochord ; n., Wolffian tubule ; ., duct of primitive kidney ; al', intestine ; U' , 
 _^ urinary bladder ; m.a., anal membrane ; md, medullary tube ; al", post-anal gut ; 
 bl", neck of allantois ; c.u., umbilical cord. (After Keibel.) 
 
 FIG. 20s. DIAGRAMMATIC RECONSTRUCTION OP THE TAIL END OF A HUMAN EMBRYO 
 YOUNGER THAN FIG. 20A (entire length, 4 mm.). (After Keibel.) 
 
 Lettering as above ; in addition c.c., caudal limit of the ccelom ; a.c., caudal limit of the 
 hind-limb ; i-ii, line drawn through the anterior limit of the tail. 
 
 Leboucq has recorded the same number in an embryo 25 
 mm. long. The opposite extreme is reached where only three
 
 THE SKELETON 31 
 
 vertebrae occur. In the adult man the regular number of caudal 
 vertebrae is five, whereas the number may be either four or five 
 in the adult woman. 1 
 
 In the female embryo four such vertebras are found as early 
 as the end of the third month, and the end of the caudal portion 
 of the vertebral column is in the female at all times more liable 
 to variation than in the male. On the other hand, the whole 
 vertebral column of the female is much more constant, with 
 regard to the limits and detailed characters of its separate 
 sections, than that of the male. 
 
 The complete development of the caudal vertebrae is not 
 concluded at birth, for their ossification has not then commenced ; 
 they are in this condition subject to the most varied influences, 
 which may cause further fusion, reduction, or deviation from the 
 sagittal plane (lateral curvature of the terminal vertebrae) (cf. 
 Fig. 24). 
 
 But what defines the human tail ? In answering this ques- 
 tion we cannot do better than follow Keibel, who rightly points 
 out that the definition of the tail in human anatomy must be 
 in strict harmony with that of Comparative Anatomy, and that 
 therefore so much of the vertebral column as is posterior to that 
 (sacrum) which attaches the pelvic girdle is caudal. Since, 
 however, the relation of the limbs to the axial skeleton is of a 
 secondary nature, Comparative Anatomy cannot help us in the 
 important early stages. We can only deal with this difficulty 
 by dividing up the body of the embryo into regions, each con- 
 taining a certain number of segments, and in so doing we cannot 
 avoid ascribing to the regions the number of segments which 
 are found in the adult. In Man, therefore, whom we are now 
 considering, we refer the first seven vertebras to the cervical 
 region, and the twelve which follow to the thoracic ; the lumbar 
 and " sacral " regions each have five, and the remainder belong to 
 the caudal. 
 
 In all Vertebrates, however, a shifting of the pelvic girdle 
 which occurs during embryonic development has to be taken 
 into account ; and in this case the definitions borrowed from 
 the adult are not altogether applicable. His, Fol, and Keibel, 
 
 1 The most reduced vertebral columns are always those of females. Sexual 
 requirements probably account for this, and for the fact that synostotic union of the 
 first coccygeal with the last sacral vertebra is less frequent in females than in males. 
 In the latter, the connection between the cornua sacralia and coccygea may even 
 give rise to a fifth pair of sacral foramina, and in such cases the sacrum appears to 
 consist of six vertebrae.
 
 32 THE STRUCTURE OF MAN 
 
 agree in attributing to human embryos of 4 to 6 mm. an externally 
 visible and segmented tail, with a nervous axis and a post-anal 
 gut (cf. Fig. 2 OB), in comparison with which the peculiar perma- 
 nent internal tail of the adult is a very degenerate organ. In 
 this early embryonic stage the tail consists of only two or three 
 segments, but at a later period there are six caudal segments, the 
 terminal mesoderrnal mass being reckoned merely as one. At 
 this stage the tail consists of a number of segments, which are 
 but very rarely retained permanently or even for a long time. 
 
 The post-anal gut seems to be constricted off from the cloaca 
 at this stage, but it is continued for the greater part of its course 
 along the whole length of the embryonic tail. It apparently 
 reaches its maximum length at this period (cf. Fig. 20, oT). 
 
 At a later stage of development also, when thirty-six 
 somites or body segments are formed, the post-anal gut can still 
 be traced, but is no longer tubular. The caudal region at this 
 stage possesses four spinal ganglia with three related nerves. At 
 a later stage the post-anal gut degenerates altogether. 
 
 To sum up, we have the following purely anatomical facts 
 which indicate that Man's ancestors possessed a tail : 
 
 (1) The coccyx of the adult consisting of three to six caudal 
 vertebrae. 
 
 (2) The two caudal spinal nerves. 
 
 (3) The caudal musculature, the existence of which, further, 
 
 is a direct proof that the tail was external and func- 
 tional (cf. p. 27). 
 
 (4) The vortex coccygeus and the foveola and glabella 
 
 coccygea (cf. p. 5). 
 
 (5) The variability of the caudal region in general. 
 
 The other divisions of the human vertebral column also 
 furnish many interesting points. One of the most characteristic 
 peculiarities of the human backbone is its typical mode of curva- 
 ture. The lumbar portion (cf. Fig. 23, B), which extends to the 
 promontory of the sacrum and is convex anteriorly, deserves 
 special attention. This lumbar curvature might appear to owe 
 its origin to statical and mechanical causes connected with the 
 upright gait, but while it is less markedly developed in the 
 anthropoid Apes, [it has been shown by Cunningham and Charpy 
 to be at least anticipated in certain quadrupedal Mammals]. 1 
 
 1 [Huxley was the first to appreciate the existence of the lumbar curvature in the 
 anthropoid apes, and Cunningham, Turner, and Symington have more recently drawn
 
 THE SKELETON 33 
 
 Of special interest, however, are the variations of the separate 
 divisions of the vertebral column, in relation to other parts of 
 the skeleton which have become secondarily attached to it, such 
 as the ribs and the pelvic girdle. These variations, though 
 effected ontogenetically, have a phylogenetic significance, and 
 may therefore be described in further detail. 
 
 Although the pre-sacral portion of the column consists normally 
 of twenty-four vertebrae, Embryology and Comparative Anatomy 
 show that this cannot be regarded as a primitive condition, and 
 that the pelvis formerly lay much farther back than at present, 
 that is, that the trunk was originally longer than now. (We 
 shall see later that a more extensive body-cavity or coelom was 
 connected with this greater length of the vertebral column.) 
 
 Eosenberg has demonstrated that in the course of human 
 development the first sacral vertebra becomes incorporated in 
 the sacrum later than the second, and that later than the third, 
 and so on. And further, since a primary relationship between 
 the vertebrae which become the two anterior coccygeal of the 
 adult and the developing sacrum is discoverable, it is evident 
 that while new sacral articulations are formed anteriorly, detach- 
 ment of vertebrae which were formerly sacral takes place 
 posteriorly, the latter being transformed into coccygeal vertebrae. 1 
 A forward shifting of the sacrum and pelvic girdle is thus onto- 
 ' genetically proved. 
 
 attention to the detailed differences in the condition of the lumbar vertebrae of the 
 European and certain dark-skinned races, and the anthropoid Apes.] 
 
 [Cunningham has shown (Mem. B. Irish Acad., No. II. 1886) that Aeby's denial 
 of the existence of a lumbar curvature in the Gorilla is untenable. His own test for 
 a lumbar curvature is a line drawn from the centre of the anterior border of the 
 upper surface of the first lumbar vertebra to the centre of the anterior border of the 
 lower surface of the last lumbar vertebra. The distance of the most prominent 
 point on the ventral surface of the lumbar section of the column from this line, 
 multiplied by one hundred and divided by the length of the line, gives the index 
 of curvature.] Little is known concerning the lumbar curvature of the savage 
 races of mankind ; but the cousins Sarasiu, on the examination of dried" skeletons 
 of the Veddahs of Ceylon, report the lumbar vertebrae to be distinctly concave 
 anteriorly. [From what has been said above, it would appear more than probable 
 that the application of the Cunningham method to the study of the Veddah back- 
 bone, in the fresh or specially prepared state, would reveal a lumbar curvature accord- 
 ing to the above, its most recent and" rigid, definition. And, from what is known of 
 the backbones of other races (ex. the Australian), it would appear probable that 
 the observation of the Sarasins is rather indicative of a greater suppleness of the 
 column during life, induced by habitual resort to certain postures, such as squatting, 
 which lead to a greater compression of the vertebrae, and a corresponding greater 
 tendency towards obliteration of the curvature after death.] 
 
 1 Distinct indications of a shifting of the pelvic girdle are traceable in the lower 
 animals also, such shifting being in some cases in a proximal and in others in a distal 
 
 D
 
 34 THE STRUCTURE OF MAN 
 
 These changes come to an end when the twenty -fifth 
 vertebra, by virtue of its apposition with the hip-girdle, becomes 
 the first sacral, and the promontory attains its full differentiation 
 between it and the last lumbar vertebra, i.e. between the twenty- 
 fourth and twenty-fifth vertebrae of the whole column. This 
 later assimilation anteriorly of sacral vertebrae is further evident 
 in the fact that synostosis between the separate parts of the 
 sacrum always takes place from behind forwards. 
 
 The tendency of the human pelvic girdle to extend even 
 farther forwards is revealed, in cases in which the last or fifth 
 lumbar vertebra enters into the constitution of the sacrum. The 
 number of pre-sacral vertebrae is in such a backbone reduced to 
 twenty-three, and this is the normal condition in the Orang and 
 Chimpanzee, and the general, though not the invariable, condition 
 in the Gorilla. 1 This change is accompanied in Man by the 
 depression of the promontory, which becomes duplicated (Fig. 21, 
 C' C"). The sacrum appears deeply sunk into the pelvis ; 
 although such sinking may also occur, as is shown in Fig. 21, 
 A! A" without any incorporation of the fifth lumbar vertebra in 
 the sacrum. In both cases the iliac crests rise almost to a level 
 with the upper edge of the penultimate lumbar vertebra (l.iv. 
 of Figs.). 
 
 In contrast to this reduction of the lumbar vertebrae to four, 
 the shifting of the pelvic girdle during development may be 
 arrested one vertebra behind the normal ; in such cases, which 
 are rare, we have twenty-five pre-sacral vertebrae. This has 
 become the normal condition in the Gibbon (Hylolates}. 
 
 Similar variations are found in individual Orangs, Gorillas, 
 and Chimpanzees. In the Orang and Gorilla, for instance, the 
 
 direction. Credner, by comparing young with old specimens, has proved that 
 in a fossil Amphibian (Branchiosaurus) a distal shifting of the pelvic arch along six 
 to seven vertebrae took place ontogenetically. 
 
 1 [In this animal, the last lumbar vertebra, although it may take on the relation- 
 ships and detailed structure of a sacral vertebra, always retains its independence 
 (i.e. it does not become co-ossified with the other vertebrae of the sacral series as in 
 the Orang and Chimpanzee). The presence of a highly differentiated articulation 
 between the last lumbar vertebra and the anterior border of the ilium is an invariable 
 characteristic of certain Armadillos. The joint thus formed is a transverse one, which 
 comes into especial use when the animal rolls itself up, and is therefore of a purely 
 adaptive nature. It is well to guard against confusion between this condition and 
 that of incorporation of lumbar with sacral vertebrae under extension or forward 
 translocation of the hip-girdle, in which the extra articulation is a longitudinal 
 one lying on the inner border of the iliac head. (Cf. Symington, Jour. Anat. 
 and Phys. vol. xxiv. p. 42. ; and Paterson. Trans. It. Dublin Soc., vol. v., Ser. 2. 
 p. 123.]
 
 J.iv. 
 
 FIG. 21. THE PELVIS. 
 
 A' A", with depressed ; B, with high standing promontory (A' ventral view ; A" and B, 
 median longitudinal sections). In A" the highest point of the iliac crest almost reaches 
 the level of the upper edge of the penultimate lumbar vertebra (l.iv.). In B, on the 
 contrary (which is the original condition, and that still found in children), the upper 
 edge of the last lumbar vertebra (l.r.) is hardly reached. C' C", pelvis with double 
 promontory, caused by assimilation of the last lumbar vertebra with the sacrum (C', 
 median longitudinal section ; C", ventral view). In the latter the appearances are as 
 if the pelvis had shifted forward along the vertebral column. (After Froriep.)
 
 THE STRUCTURE OF MAN 
 
 lumbo-sacral boundary may be shifted back a vertebra, and in 
 the Chimpanzee even two vertebrae. In the former case the 
 position normal to Man is attained. 
 
 It is evident that shifting of the pelvic girdle (and, as will 
 be seen later, of the pectoral girdle also) cannot take place 
 without concomitant variations in other organs. To this question 
 we shall return. 
 
 THE EIBS AND STERNUM 
 
 Two types of variation of .the thorax are to be distinguished 
 in Mammals, a primary and a secondary type. The former is 
 
 A B 
 
 FIG. 22. A, TRANSVERSE SECTION OF THE THORAX OF A LOWER MAMMAL (OR OF 
 
 THE HUMAN EMBYRO) ; B, THE SAME OF A MAN. 
 
 In the former it is the vertical diameter which is the greater, in the latter 
 it is the transverse, as indicated by arrows. 
 
 far more common than the latter, and is found in most Mammals, 
 including the lower Apes. The thorax of this primary type (Fig. 
 22, A) is elongated, its dorso-ventral greatly exceeding its trans- 
 verse diameter (carinate or keeled type). 
 
 The secondary type (Fig. 22, B) is found in Anthropoid 
 Apes and in Man. The dorso-ventral diameter is here greatly 
 diminished and the transverse is increased in proportion ; the 
 broad thorax is somewhat barrel-shaped, and often compressed 
 antero-posteriorly. This secondary type is preceded, both onto- 
 genetically and phylogenetically, by the primary. 
 
 It is evident that the associated modifications, viz. the
 
 THE SKELETON 
 
 shortening of the thoracic wall, the shifting of the thoraco- 
 abdominal boundary, the changes in the axial skeleton, and the 
 numerical reduction of the thoracic metameres, must have a far- 
 reaching influence on the whole anatomy of the trunk, e.g. on the 
 position of the thoracic viscera (lungs, heart), and on the relation- 
 ships of the pleural cavities. Thus Ruge has shown, in a series 
 of excellent papers, that as the secondary type of thorax begins 
 to develop, the pleural boundary gradually recedes along the 
 anterior and inner wall of the thorax, so that the heart, which in 
 the primitive thorax almost always lies remote from the sternum, 
 approaches nearer the anterior thoracic wall. As a consequence 
 of this, the anterior edges of the pleural sacs, which are primarily 
 apposed behind the sternum, are forced apart, so that in Man, for 
 example, they are often separate as high as the fourth rib. 
 
 A B 
 
 FIG. 23, A AND B. DIAGRAMS OF THE VERTEBRAL AND COSTAL SKELETON. 
 
 A, IN THE QUADRUPED ; B, IN MAN ; the arrows indicate the line of direct pressure 
 
 of the thoracic viscera upon the wall of the thorax. 
 
 Among the various factors recognisable as having played a 
 continuous role in the evolution of the Primates, not the 
 least weighty is the assumption of the upright position. The 
 alteration in the shape of the thorax above described, by shifting 
 back the centre of gravity of the body, favours the upright 
 position ; and the inter -dependence of these two modifications 
 is evident. 
 
 To the same category, it appears to me, belongs the gradual 
 diminution in number and size of the sternal ribs. It is easy 
 to see how, with the shifting of the centre of gravity towards 
 the dorsal side of the body, and a consequent diminution of
 
 38 THE STRUCTURE OF MAN 
 
 pressure on the ventral, the ribs which in the quadrupeds are 
 the more necessary for enclosing and supporting the viscera, 
 might degenerate in the abdominal or lumbar region. The 
 pressure of the viscera is no longer in the ventral, but in the 
 caudal direction (cf. Fig. 23). We find, in consequence, a 
 compensating expansion of the iliac fossse of the bones of the 
 pelvic girdle. The fact that this change is specially pronounced 
 in women is easily explained by functional (sexual) adaptation, 
 and it thus tends to confirm the above theory. 
 
 The shifting of. the centre of gravity towards the dorsal 
 side explains why the vertebral ends of the lowest ribs are so 
 firmly attached, and also why the dorsal portion of the thoracic 
 bony skeleton is much longer than the ventral. In this con- 
 nection we have naturally to take into account the great muscles 
 which are statically and mechanically required by the axial 
 skeleton, and for which these ribs furnish points of origin and 
 insertion. But even supposing that the ribs were not required 
 for this purpose, there are other related structures which, to a 
 certain extent, favour their persistence. The chief of these is 
 the serratus posticus inferior muscle, which is inserted into the 
 four lower ribs, and the latissimus dorsi which partly arises from 
 the last three. 
 
 It may be remarked, however, that the mere presence of 
 these two muscles, as will be seen later on, is insufficient to 
 account for the persistence of the lower ribs. Indeed, the latter 
 might well be degenerating so far as the former are concerned, 
 for not only is the serratus posticus inferior distinctly rudi- 
 mentary, but the parts of the latissimus dorsi attached to 
 these ribs are quite insignificant in comparison with the rest 
 of the muscle. But, notwithstanding this, the action of the 
 serratus to a certain degree favours the retention of these ribs 
 (cf. p. 45). 
 
 Eeturning now to the more important factors which deter- 
 mine the transformation of the thorax, we must, as Huge rightly 
 points out, take into account the influence of the fore-limbs. As 
 the latter developed into seizing organs, their muscles became 
 more powerful and more specialised, and reacted, in turn, on the 
 form of the ribs and the arch of the thorax. Further conse- 
 quences of this are seen in the greater compactness of the internal 
 organs, in the gradual fusion of certain lobes of the liver and 
 lungs, and in the approximation and final union of the peri- 
 cardium and diaphragm, which may also imply the gradual
 
 THE SKELETON 39 
 
 depression of the heart. It is, moreover, evident that the 
 change undergone by the heart and diaphragm, due to the 
 forcing of the former out of the median plane and the shifting 
 of its longitudinal axis towards the ventral and left side of the 
 body, must again react upon the form and limitations of the 
 pleural cavities. 
 
 Slight changes in the limitation of the pleural cavities occur 
 also in the lower Mammals ; but how far these may be related 
 to each other, or in any way to those occurring in the Primates, 
 is not very clear. The original causes of the changes are 
 very various, but their close dependence upon the skeleton is 
 evident. 
 
 The tendency towards a gradual diminution in the number 
 of ribs, previously referred to, requires further consideration. 
 
 The presence of free ribs, as is well known, distinguishes the 
 thoracic vertebrae of the adult from those of the cervical and 
 lumbar regions. The limits of the thoracic region, however, are 
 liable to variation, akin to that already described as occurring in the 
 lumbar and sacral regions. Twelve pairs of free ribs are present 
 normally in Man, as in the Orang, but a comparison with other 
 (and chiefly lower) Vertebrates points to the earlier existence of 
 a larger number. This view is supported by Ontogeny, as well 
 as by the occasional occurrence of so-called supernumerary ribs. 
 These are less frequently found at the upper than at the lower 
 end of the thorax ; and in either case, the thirteenth rib is 
 subject to great variation both in form and size. For example, 
 a thirteenth rib at the lower end of the human thorax may vary 
 'in length from 2 to 14 cm. ; but thirteen is the normal number 
 of ribs in the Gorilla and the Chimpanzee, and Hylobates has 
 thirteen or fourteen. Where a free rib is borne by the seventh 
 cervical vertebra, the number of these vertebrae naturally appears 
 to be reduced to six. Where a thirteenth rib occurs in the 
 thorax, the lumbar vertebrae similarly appear to be reduced to 
 four unless the embryonic forward shifting of the pelvis has 
 been arrested at the twenty-sixth pre-sacral vertebra, as is not 
 unfrequent under these circumstances, for it has been observed 
 that the thirteenth rib, which always appears in the embryo, i 
 jbegins to degenerate as soon as the twenty-fifth pre-sacral vertebra | 
 jis incorporated in the sacrum. 
 
 We have further evidence that Man has inherited more than 
 twelve pairs of free ribs, in the fact that reduced ribs are found 
 in the embryo, not only in connection with the first but with all
 
 40 
 
 THE STRUCTURE OF MAN 
 
 the lumbar vertebrae (Fig. 24, rl), and in the sacral region also 
 (Fig. 25, B r.s.). 1 From this it is clear that the pelvis in Man, 
 
 r.th. I 
 
 FIG. 24. PART OF THE THORACIC, AND THE WHOLE LUMBAR, SACRAL, AND 
 COCCYGEAL SECTIONS OF A YOUNG HUMAN VERTEBRAL COLUMN. (Dorsal aspect.) 
 The lateral processes of the first to the fifth lumbar vertebra are on one side prolonged 
 (by dotted lines) for diagrammatic delineation of the formerly existing lumbar ribs 
 (r.l.), which are present in the embryo. The sacrum is still subdivided into its five 
 component parts, i.e. consists of five distinct vertebrae (v.s.). v.c., caudal (coccygeal) 
 vertebrae ; r.th., the three lower thoracic ribs. 
 
 like that of all terrestrial Vertebrates, is carried by ribs, which, 
 however, become early united with the sacral transverse processes. 
 
 1 In the twenty-first and twenty-second pre-sacral vertebras of the embryo, the 
 ribs are still separated from the vertebral arches by membranous tissue, but in 
 the succeeding vertebrae they are more and more completely united with them. It 
 would thus appear that the reduced ribs are early incorporated in the so-called trans- 
 verse processes of the lumbar vertebrae.
 
 THE SKELETON 
 
 41 
 
 As already stated, the presence of a free rib in connection 
 with the last cervical vertebra (Fig. 27, A) is somewhat rare in 
 
 Fio. 25. DIAGRAM OF A TRANSVERSE SECTION OF THE HIP GIRDLE AND SACRUM : A., OF 
 A SALAMANDER ; B., OF MAN (young stage in which the separate parts of the sacral 
 vertebrae are still distinct). 
 
 b.v., body of sacral vertebrae ; a.n., arch of same ; r.s., sacral rib ; il., ilium ; 
 p., pubis ; c.h., coelom ; ac. , acetabulum. 
 
 adults, but the vestige of such a rib, and even of a second (some- 
 what less attached) near the sixth cervical vertebra, is almost always 
 
 Fia. 26. A, FIRST THORACIC SKELETAL SEGMENT FOR COMPARISON WITH B, FIFTH 
 CERVICAL VERTEBRA (MAN). 
 
 c., first sternal rib ; c', cervical (rib which has become united with the transverse process 
 (tr.)) the two enclosing the costo-transverse foramen (f.c.t.) ; zy., articular process 
 of the arch (zygapophysis) ; b.v., body of vertebra ; st., sternum. 
 
 found in the embryo. The five anterior cervical vertebrae show 
 no such distinct vestiges, although their former presence is clearly
 
 42 THE STRUCTURE OF MAN 
 
 indicated by the detailed characters of the transverse processes 
 (Fig. 26, 6). [In the Platypus (Ornithorkynchus') reduced 
 cervical ribs remain for life distinct on six of the seven neck 
 vertebrae, being absent from the atlas only, and one or more 
 cervical ribs may occasionally retain their independence among 
 the quadrupedal Mammals generally. 1 ] 
 
 r.th.l'. 
 
 FIG. 27. A, PORTION OF THE THORACIC SKELETON OF AN ADULT FEMALE 
 
 POSSESSED OF A FAIR OF FREE CERVICAL RlBS. 
 
 The twelve normal pairs of thoracic ribs were present. Length of the right cervical rib 
 3-5 cm., of the left 6-7 cm. r.c.vii.', vertebral end of the cervical rib ; r.c.vii." , 
 sternal end of the same, fused with the manubrium sterni (the vertebral and sternal 
 ends being in life connected by a ligamentous band, not indicated in the figure), 
 r.th., first and second sternal ribs. 
 
 B, EXAMPLE OF THE REDUCTION OF THE FIRST PAIR OF THORACIC 
 
 RIBS (AN ADULT MALE). 
 
 There were twelve pairs of free ribs present, the first pair being reduced both in 
 length and calibre. The left of these was 9, the right 8, cm. long, r.th.i.' ', vertebral 
 end of the first rib ; r.th.i.", its sternal end, synostotically imited with the 
 manubrium sterni (st.) ; r.L, fibrous band, formed by retrogression of the missing 
 portion of the rib. 
 
 In both figures, I, II denote the first and second thoracic vertebrae, VI, VII the two last 
 cervical vertebrae. (Adapted from Leboucq.) 
 
 The greatest development of the seventh cervical rib would 
 naturally be that of uninterrupted extension round the neck. 
 Such an extraordinary condition has only apparently been once 
 observed (by P. Albrecht). Cases in which the rib in question 
 unites with the first thoracic rib by its cartilaginous extremity, 
 before reaching the manubrium, are far more frequent. Some- 
 times only the sternal and vertebral ends are found (in either 
 a bony or cartilaginous state), the intermediate part being 
 represented by a fibrous band. In spite of the reduced con- 
 
 1 [Mivart has figured and described (for example) what appear to be practically 
 stages in the redevelopment of the last cervical rib on opposite sides of the same 
 vertebra of a Binturong (Arctictis], Proc. Zool. Soc., Lond., 1882, p. 461.]
 
 THE SKELETON 43 
 
 dition, however, the internal and external intercostal muscles 
 between this cervical and the first thoracic rib are well developed 
 in cases like that above figured ; indeed this is so even when 
 (as occasionally happens) the fibrous connecting band is wanting 
 (Leboucq). The sternal portion of the rib is as a rule very 
 weakly developed, sometimes free, sometimes partly fused with 
 the first thoracic rib. The vertebral end varies much in form, 
 size, and articulation upon the vertebral column ; and further, its 
 relations to the first thoracic rib may, as Leboucq has shown, vary 
 greatly. It may either be altogether fused with the latter, merely 
 loosely attached to it by connective tissue, or actually articulated 
 with it. In the first case, the first thoracic rib appears forked 
 at its vertebral end, and this (according to P. J. van Beneden) 
 is the rule in many Cetaceans. 
 
 Apart, however, from such cases as these, a further proof of 
 the former existence of cervical ribs in Mammals is derived from 
 the study of the adult Edentata. Among these, Cholcepus has 
 normally only six cervical vertebrae [defined as those destitute of 
 free ribs]. 1 Bradypus infuscatus and B. tridactylus illustrate 
 the other extreme, possessing normally nine such vertebra? ; 
 while B. cuculliger has either eight or nine. In the latter 
 cases the upper end of the thorax has undergone greater reduction 
 than in any other Mammal. 
 
 The fact that in Man the first thoracic rib is probably 
 beginning to degenerate, 2 and is at the present time in process 
 of atrophy, is established by the not infrequent recurrence of 
 undoubted cases of its abortive development. Such have been 
 recorded by Struthers, Grosse, Hunauld, Gruber, Turner, Leboucq, 
 and others (cf. Fig. 27, B). The description given above of 
 the seventh cervical rib might, in these cases, be applied to the first 
 thoracic. Nevertheless, I believe, for reasons to be given later, 
 that should reduction at the upper end of the thorax advance, 
 it will do so far more slowly than at the lower, or indeed that 
 it may even be arrested for an indefinite period (cf. p. 45). 3 
 
 1 A similar numerical reduction of the cervical vertebra occurs also in the 
 Manatee [but there is reason for believing that it is in that animal due to the 
 excalation of at least the body of one of these, and not to the assumption of thoracic 
 characters by the last of the series.] 
 
 2 I should like here to raise the question whether this tendency to reduction at 
 the upper end of the thorax may not be a determining factor in the degeneration so 
 frequently found to be commencing at the top of the lungs ? (cf. infra). 
 
 3 It is interesting here to note that ventrally to the transverse process of the sixth 
 cervical vertebra, there often arises, on either side, a projection, which might be 
 claimed as a vestigial structure, since in most Mammals it stands out prominently
 
 44 THE STKUCTUKE OF MAN 
 
 From the above facts it is sufficiently evident that the 
 vertebral column was ancestrally furnished with a far greater 
 number of ribs than at present, and that the pleuro-peritoneal 
 cavity or coelom was once more capacious both at its cephalic 
 and caudal ends. Even at the present time, as already shown, 
 its modifications are not permanent. This is manifest, not only 
 from the reappearance of (so-called " supernumerary .") ribs, but 
 also from the decidedly rudimentary character of the eleventh and 
 twelfth ribs, which is rendered evident in several ways, more 
 especially in connection with variation in their size. The twelfth 
 rib, as might be expected, has a much wider range of variation 
 (2 to 27 cm.) than the eleventh (15 to 28 cm.); neither pair of 
 these reaches the sternum, and both show degeneration in their 
 detailed relationship to the vertebral column. These ribs have 
 no tubercle, and, consequently, no costo-transverse articulation ; 
 and the articulation of the head (capitulum) of each of them is 
 vertebral, instead of inter-vertebral, as in the case of those in 
 front of them. Occasionally a tendency to similar conditions 
 appears in the ninth and tenth pairs. Ontogeny shows that the 
 reduction of the eleventh and twelfth ribs is comparatively: 
 recent, since the rudiment of the costo-transverse articulation; 
 (tubercle) of the eleventh rib is still developed in the embryo. 
 
 Turning now to the ensiform (or xiphoid) process of the 
 sternum, the variations in its shape, and more especially the 
 presence of occasional median fissures or foramina in it, show that 
 it arose from paired cartilages. It is, in fact, constricted off from 
 the eighth, and possibly also from the ninth pair of ribs. The 
 cartilages named, undoubtedly, at one time took part in the forma- 
 tion of the " sternal bands " to be described later, and thus the 
 number of ribs reaching the sternum may once have been greater 
 
 as a strong process (Gegenbaur). These lower lateral spinous processes [anapophyses] 
 which are found only in Hylobates, among Anthropoids, arising from the bases of 
 the arches of the last two thoracic and sometimes from the first lumbar vertebrae, 
 according to Broca, occasionally occur in Negroes. It has been observed, further, 
 that the spinous processes of the cervical vertebra, which are, as a rule, forked in 
 Man, are simply pointed in the Hottentots ; and we here encounter a persistence of 
 the original simple condition which is normal among Anthropoids (R. Blanchard). 
 
 Finally, it should be mentioned, that the groove on the dorsal side of the arch 
 of the human atlas for the reception of the vertebral artery is sometimes overarched 
 with bone, and converted into a foramen, such as is always found in most Primates, 
 Carnivora, and various other Mammals (Sappey). [And it is here worthy of remark 
 that the costo-transverse foramen, and its homologue the vertebarterial canal, may 
 in a similar way become completely surrounded by the transverse process 
 (Hippopotamus, Man?}. Cf. Jour. Anat. and Phys., vol. xxvii. p. 545.]
 
 THE SKELETON 45 
 
 than at present. This conclusion is strengthened by the fact 
 that the eighth rib not infrequently reaches the sternum even in 
 adults. 1 
 
 Eight sternal ribs are found in the lower Apes (which may 
 have as many as ten), and may occur in the higher Apes, with 
 the exception of the Orang. It is certain that in all Mammals 
 those ribs which have their ventral ends in any way attached to 
 one another were once connected with the sternum. 
 
 On the other hand, the union of only six ribs with the 
 sternum is not rare in Man ; and the existence of this condition 
 is a clear indication of the gradual degeneration (shortening) of 
 the thoracic skeleton and sternum. In such cases the distal 
 end of the xiphisternum may bear two lateral prongs, which 
 correspond with the sternal ends of the seventh pair of ribs. 
 
 There are certain considerations which confirm the statement 
 above made that the process of degeneration at the upper end of 
 the thorax is slower than that at the lower end, to which latter, 
 indeed, no limits of variation can be foreseen. We have first 
 the rhythmic respiratory mechanism, which is so closely connected 
 anatomically and topographically with the complete ribs ; and, 
 second, the attachment to this part of the thorax of the 
 musculature of the shoulder girdle (I refer especially to the 
 serratus magnus and the pectoralis major). [These muscles 
 under certain conditions play an important part in effecting the 
 movements of respiration], and in order to secure a sufficient 
 range of activity they must necessarily be inserted into a certain 
 number of fixed points. Such points are supplied by the bony 
 framework formed by the seven upper pairs of ribs, the sternum, 
 and the clavicles ; and as long as these muscles remain indis- 
 pensable, the bones named cannot well degenerate further. 
 We have here a striking example of the important reciprocal 
 relation and close interdependence existing between the various 
 organs and systems which, so to speak, hold each other in 
 check. 
 
 We learn both from Ontogeny and Comparative Anatomy 
 that the sternum (which is first formed by the fusion of a couple 
 of sternal bands) consisted, in the ancestors of Man, of a row of 
 
 1 [Cunningham and Robinson have recorded the existence of an eighth sternal 
 rib on one or both sides in 20 per cent of (seventy) subjects examined (Nature, vol. 
 xxxix. p. 248, and Jour. Anat. and Phys., vol. xxiv. p. 127). In the unilateral 
 condition it was found to be dextral in eight out of nine examples ; and Cunningham 
 suggests that this may be a reversionary feature, associated with the greater use of 
 the right fore-limb.]
 
 46 THE STRUCTUEE OF MAN 
 
 successive pieces. Its early condition is now most nearly retained 
 for Mammals among the Edentata [i.e. in the Pangolin (Mams)], 
 and even in the lower Apes extensive remnants of cartilage are 
 occasionally present between the bony parts. In most other 
 Mammals, the ossific nuclei which appear in the course of develop- 
 ment of the sternum are the only indications of its former 
 segmentation. 1 The fully-developed sternum of the Primates is 
 practically a single broad and firm plate, the solidity of which 
 compensates for its decrease in length. 
 
 St. 
 
 FIG. 28. SHOULDER GIRDLE OF ORNITHORHTXCHUS. 
 
 m.s., manubrium sterni ; .,<?.,<?., first, second, third ribs ; st., sternebra ; sc., scapula : 
 m.c., metacoracoid ; 2 e.c., epicoracoid ; d, clavicle ; es'. and es"., interclavicle (episternum). 
 
 The origin of the Mammalian interclavicle (so-called epi- 
 sternum) is still somewhat undetermined ; [but in its position 
 beneath (ventrad of) the sternum proper in the young of the 
 Mole (ed., Fig. 29), in which its development has been most 
 fully worked out, and in its relationships to the clavicles, it agrees 
 with the interclavicle of Eeptiles.] 
 
 In Monotremes (Fig. 28) the episternal apparatus (es f . es".') is 
 triradiate, and disposed altogether cephalad of the sternum proper. 
 
 1 [Approximation of more than one pair of ribs to the posterior end of the 
 sternum is the rule in many of the lower Mammalia ; in the Rabbit, where two pairs 
 of ribs always have this relationship, it may or may not happen that a corre- 
 sponding extra sternal segment is present in the adult. A careful study of the 
 development of that animal's sternum has shown that this segment disappears by 
 absorption where not retained i.e. that a sternal segment may generally, though 
 not invariably, be lost during ontogeny. This fact is of considerable interest in 
 relation to the belief in a tendency towards abbreviation of the mammalian thorax 
 postero-anteriorly (cf. Burne, Proc. Zool. Soc., 1891, p. 159).] 
 
 2 [Until recently known as the "coracoid" ; cf., however, infra, p. 72.]
 
 THE SKELETON 47 
 
 In the adults of the higher quadrupedal Mammals, the episteruum 
 is possibly for the most part represented by a couple of cartilaginous 
 tracts, approximated to the sternal ends 
 of the clavicles (es., Fig. 30); and its 
 body (es!, Fig. 29), so far as is known, 
 appears to become reduced, and either 
 closely apposed to or fused with the 
 anterior end of the sternum. 
 
 The following information concern- 
 ing the human episternum is largely 
 drawn from the admirable work of Euge. 
 
 In an early embryonic stage, when 
 the cartilaginous " sternal bands " have, 
 not yet united along their whole length, 
 two independent masses, which soon be- FIG. 29. EPISTERXUM OF AN 
 come cartilaginous, appear at the upper G^tte. 
 end of the still forked manubrium sterni. *<> sternum; es'., central portion 
 
 , \ce of the episteruum ; es. , lateral 
 
 At a later stage they fuse to form a portion of the same ; d, cia- 
 single cartilaginous tract, which gradu- vicle ; r - c -> costal ribs - ( The 
 
 . , --IPI. .LIP! ti ure was constructed from 
 
 ally interposes itself between the forks two consecutive horizontal 
 of the manubrium, until finally only sections.) 
 the proximal surface of the cartilage projects from that struc- 
 ture. As the two sternal ridges fuse completely, the boundary 
 lines between the episternal cartilages and the manubrium 
 become more and more indistinct, and finally altogether 
 disappear, the former structure becoming incorporated in the 
 latter. The manubrium of Man is thus a compound of two 
 separate structures, one of which is certainly costal and 
 derivative of the first pair of ribs. The homology of the other, 
 i.e. of the suprasternal portion, cannot yet be decided with any 
 certainty. There can be no doubt that we have in it the last 
 vestiges of a skeletal structure, but whether they are those of a 
 seventh pair of cervical ribs which once reached the manubrium, 
 or of the central portion of the episternum of the Monotremes 
 and lower Mammalia, must for the present remain undecided. If 
 the latter supposition should prove correct, it would point to 
 the originally paired nature of the Mammalian episternum, and 
 support Gotte's view of its origin from the median ends of 
 the clavicles. 
 
 Brechet's cartilages, or bones, which occasionally appear at 
 the antero-internal border of the sterno-clavicular articulation, 
 and either become closely applied to the sternum or united with
 
 48 THE STRUCTUEE OF MAN 
 
 it, must not be confounded with the above-described skeletal 
 structures, which are entirely incorporated into the manubrium. 
 These "ossa suprasternalia " (o.s., Fig. 30) may be derivatives of 
 the episternal apparatus, as Gegenbaur has for years insisted, and 
 probably of the central portion of the episternum. The lateral 
 portions of this structure are usually homologised with the inter- 
 articular cartilages that lie between the sternum and the ventral 
 extremities of the clavicles (e.s., Fig. 30). [There is, however, 
 
 r . l". 
 
 FIG. 30. EPISTERNAL VESTIGES IN MAN. 
 
 e.s,, " episternum " (sterno-clavicular cartilage); o.s., ossa suprasternalia ; cL, clavicle, 
 sawn through; I'., inter-clavicular ligament; I"., costo-clavicular ligament; m.s., 
 manubrium sterni ; st., sternum ; r.c., first rib. 
 
 still considerable uncertainty about this ; especially as Carwardine 
 has recently shown x that the ligaments in which the " ossa supra- 
 sternalia " lie embedded when free, may or may not be continuous 
 with an " inter -clavicular ligament" which, by its T-shaped 
 character and detailed relationships, may suggest the inter-clavicle 
 (episternum) of Monotremes and Eeptiles.] 
 
 THE SKULL 
 
 In all Vertebrates the skull may be divided into two 
 principal portions, the cranial and the facial. The cranial 
 portion, or brain case, encloses the anterior part of the central 
 nervous system, and is intimately associated with the higher 
 
 1 Jour. Anat. and Phys., vol. xxvii. p. 232.
 
 THE SKELETON 
 
 49 
 
 sense organs and their investing capsules. In the embryo it 
 is penetrated for some distance at its base by the forerunner of 
 the backbone the chorda dorsalis. For this reason it appears 
 to be in a certain sense a prolongation of the axial skeleton of 
 the trunk. The visceral or facial portion of the skull lies postero- 
 ventrally to the cranial. It is closely connected with the pharyn- 
 geal section of the alimentary canal, the lateral walls of which 
 
 cp. - 
 
 md.* 
 
 IX 
 
 FIG. 31. A, SLIGHTLY DIAGRAMMATIC MEDIAN LONGITUDINAL SECTION THROUGH THE 
 HEAD AND ANTERIOR PORTION OF THE TRUNK OF A HUMAN EMBRYO, SEVENTEEN 
 
 TO EIGHTEEN WEEKS OLD. (After W. His.) 
 
 cp., brain ; op., optic vesicle ; md. , mandibular arch ; pc., pericardium ; cd., heart ; au. , 
 
 auditory vesicle ; I-IV, branchial clefts. 
 
 B, EMBRYO TORPEDO, as seen by transmitted light. (After H. E. and F. Ziegler.) 
 ol., olfactory pit ; hy., hyoid arch ; V., trigeminal nerve ; cd., ventricle ; VII, 
 VIII, facial and auditory nerves ; IX, glosso-pharyngeal nerve. Other references 
 as for A. 
 
 are, in the embryo, perforated by "gill-clefts" (I-IV, Fig. 31, 
 A), so called because their presence points back to a time in which 
 this part of the alimentary canal served not only for taking in 
 food, but for respiration, as is still the case in the lower Verte- 
 brates. That the system of skeletal arches, which alternate with 
 these clefts has, in man, undergone considerable modification and 
 reduction (cf. Fig. 105) will not appear strange, when the 
 biological conditions are taken into account. The only point of 
 
 E
 
 50 THE STRUCTURE OF MAN 
 
 essential importance for us here is the fact that the skull of Man 
 and all Vertebrates is constructed on a common plan (cf. A and 
 B, Fig. 31). 
 
 The fact that this ground plan is not so evident in the skull 
 of the higher Vertebrata and Man as in that of the lower Verte- 
 brates, is due to the progressive modification which the former have 
 
 
 FIG. 32. SKULL OF IMMANUEL KANT. (After C. von Kupffer.) 
 (The great size of the cranium is a noteworthy feature. ) 
 
 undergone ; and the final result has been that the human skull 
 differs markedly not only from that of the lower Vertebrata, but 
 also from that of the Anthropoid Apes, which in the rest of their 
 skeleton agree so closely with Man. It will, therefore, be interest- 
 ing to examine the two latter types of skull, in order to determine 
 and, when possible, explain the differences between them. 
 
 On mere superficial examination, the proportionate difference 
 in size between the cranium and the face of the two is most 
 striking. In Man (Fig. 32) the cranium is a smooth and imposing
 
 THE SKELETON 
 
 51 
 
 FIG. 33. SKULL OF A CHILD SEVEN YEARS OLD. 
 (One-third natural size.) 
 
 rounded or oval bony case, which contrasts strongly with the 
 incomparably smaller one of the Orang (Fig. 36) and Gorilla, with 
 their enormous external 
 ridges and protuberances. 
 These latter animals, like 
 all the Anthropoids, differ 
 from Man in the great 
 development of the face, 
 and especially of the jaws, 
 which in Man are sub- 
 ordinate to the cranium. 
 If, however, young stages 
 of the Anthropoid are com- 
 pared (Fig. 35), this dis- 
 tinction becomes less strik- 
 ing; for, as is well known, 
 not only the whole head 
 but the features of the young Ape bear a decided resemblance to 
 those of the human foetus. Indeed, it is certain that the diverg- 
 ence begins after birth, the characteristics of each type becoming 
 more and more marked as age advances (cf. Figs. 35 and 36). 
 
 The chief cause 
 of the distinction 
 clearly lies in the 
 greater_ development 
 of the human brain. 
 In the higher Verte- 
 brates the brain must 
 be regarded as the 
 dominant organ of 
 the head; and in 
 Man it continues to 
 grow even into the 
 prime of life, the 
 cranial capacity at- 
 tained reaching in 
 the male Caucasian 
 an average of 1500 cubic cm., and the brain a weight of from 
 1375 to 1400 gr. 
 
 With regard to the cranial capacity of the lower races of man- 
 kind, observations made by the cousins Sarasin on the Veddahs 
 of Ceylon are of special interest. In them, not merely the skull 
 
 FIG. 34. SKULL OF AN AUSTRALIAN FROM THE MURRAY 
 RIVER. (One-third natural size.)
 
 52 
 
 THE STRUCTURE OF MAN 
 
 but the whole skeleton is remarkable for its delicacy, a character 
 which, according to Virchow, distinguishes a number of the wild 
 races inhabiting the islands of the East. The skull is on the 
 average 200 gr. lighter than that of the European; it is very 
 small, and the cranial capacity in the pure (unmixed) Yeddah 
 male is at most 1250 cubic cm., and in the female some 140 
 cubic cm. less than that. 
 
 FIG. 35. SKULL OF A YOUNG 
 
 ORANG-UTAN. 
 (One-third natural size.) 
 
 FIG. 36. SKULL OF AN ADULT ORANG-UTAN. 
 (One-third natural size.) 
 
 In cranial capacity the Veddahs are undoubtedly among the 
 lowest of human beings, and this is quite in keeping with their 
 low level of civilisation. The woolly-haired inhabitants of the 
 Andaman islands are on approximately the same level, whereas 
 the Bushmen and Australians rank somewhat higher. 1 
 
 In shape the Veddah's skull is very long and narrow, i.e. 
 strongly dolicocephalic. The cranium of the female is more 
 rounded than that of the male indeed, all the peculiarities 
 which in the European distinguish the skull of the woman from 
 that of the man are present in the Veddahs. 
 
 But while there is a difference of from 250 to more than 
 500 cubic cm. in the cranial capacity of the Veddah and 
 the European, a far greater disparity occurs between the cranial 
 
 1 [In the Akkas (the pygmy race of Central Africa), the cranial capacity of the 
 skull of a male recently described by Sir "W. Flower is 1102 cubic cm., and that of a 
 female 1072 cubic cm. The same writer has,-however, described the skull of a female 
 Veddah, having a capacity of but 950 cubic cm., that being one of the smallest normal 
 adult human skulls on record (cf. Jour, of the Anthropological Instil., vol. xviii. p. 6).]
 
 THE SKELETON 53 
 
 capacity of Man and that of the Anthropoid Apes, the latter 
 ranging from about 427 cubic cm. (Chimpanzee) to 557 (Gorilla), 
 i.e. averaging less than half that of the human races mentioned 
 above. As yet no human skull has been discovered which bridges 
 over this gap. 
 
 The cause of this great difference lies largely in the fact that 
 the brain of the Ape makes no marked progress after birth, and 
 this no doubt applies not only to its size, but also to its micro- 
 scopic anatomy, e.g. to the differentiation of its gray cortex. 
 
 The Anthropoid skull is furnished with massive jaws con- 
 trolled by powerful muscles and armed with formidable teeth. 
 This extraordinary development of the facial portion of the skull 
 which supports the entrance to the alimentary canal, is no doubt 
 of compensatory value in the struggle for existence. We shall 
 return to this subject in considering the dentition as a determin- 
 ing factor in the modification of the jaws. 
 
 The foregoing account of the changes undergone by the 
 cranial skeleton has, I hope, shown that the human skull is 
 subject to the same influences as that of the beasts, and that the 
 two differ as divergent adaptive modifications of one and the 
 same fundamental plan. This is not, however, an altogether 
 satisfactory explanation, since the primary cause of this difference 
 of modification (in Man in the psychic and brain-forming direc- 
 tion, in the Anthropoids in the vegetative direction) remains 
 unknown. 
 
 That these divergent lines of modification from a common 
 starting-point were entered upon very long ago is proved, not only 
 by the sharply differentiated types of skull found both among 
 Anthropoids and Men, but also by the fact that great and un- 
 doubtedly atavistic deviations from the general normal type of 
 human skull are comparatively rare. The type appears complete, 
 well established, and sharply individualised. 
 
 Exception must be made in the case of the dentition, to 
 which the above is not applicable, and also in that of micro- 
 cephalous and teratological conditions, although these are often 
 enough utilised in building up the primitive history of the 
 human skull. It is, however, possible, inasmuch as some of these 
 cases certainly exhibit phenomena due to arrest of development, 
 that an occasional indication of a former primitive condition may 
 be revealed in them ; but the pathological element is, as a rule, so 
 strong that no certain morphological conclusions can be drawn 
 indeed, deceptive appearances may be expected at every step.
 
 54 THE STRUCTURE OF MAN 
 
 Gratiolet has established the fact that the higher races of 
 
 A 
 
 FIG. 37. MEDIAN SECTIONS THROUGH THE HEAD OF A DEER (A), BABOON (B), 
 
 AND MAN (C). 
 
 The relation of the cranium to the nasal cavity should be noted. The former, with gradual 
 enlargement, comes to overlie the latter, thereby altering the facial angle (cf. 
 with these Figs. 32-36). 
 
 men differ from the lower in the order of obliteration of the
 
 THE SKELETON 55 
 
 cranial sutures. In the lower races, as in the Apes, the process 
 always begins anteriorly in the frontal region of the skull, i.e. at 
 the fronto-parietal boundaries, and proceeds backwards. This 
 naturally causes an earlier limitation in growth of the anterior 
 lobes of the brain ; whereas, in the higher (white) races, where 
 the fronto-parietal suture disappears only after the obliteration 
 of the parieto-occipital one, these lobes are capable of further 
 development. This fact may well be closely connected with 
 the intellectual difference between the races. It not infre- 
 quently happens that the frontal suture remains open ; l but 
 whether, as might suggest itself, this is to be regarded as 
 indicative of a further development or, on the other hand, as 
 a reversional feature, cannot yet be decided. On the latter 
 assumption, the fact that fusion of the frontal bones occurs in 
 many Mammals (Apes, Insectivora, Chiroptera, Monotremata, and 
 others) is of interest, especially -as reversion to the condition of 
 the lower Vertebrates is a phenomenon, which, as we have already 
 seen, is by no means unknown in Man. It appears to me that 
 the two views may to a certain extent be harmonised, by con- 
 sidering that the original independence of the ossific centres 
 inherited from lower ancestors may be sometimes retained and 
 utilised in the interest of a progressive development of the 
 anterior lobes of the brain. 
 
 Gegenbaur, in his Lelirbuch der Anatomic des Menschen, calls 
 special attention to the independent ossification of that which 
 becomes the postero-inferior angle of the frontal bone, i.e. that 
 part of it which borders on the alisphenoid. Since, at birth, and 
 even for some time after birth, traces of this division are evident, 
 we are reminded of the post-frontal bone of the lower Vertebrates. 2 
 
 On turning to that part of the skull where the parietals 
 meet the occipital (the lambdoidal suture), an independent mem- 
 brane bone is sometimes found, the so-called " interparietal," 3 
 
 1 According to Welcker, the frontal suture often persists in Caucasians, less 
 often in Malays, and very rarely in Americans, whereas the exact reverse is the case 
 with the transverse occipital suture which divides the interparietal from the occipital 
 bone proper. It often happens that the latter is found together with the frontal 
 suture in one and the same skull. In the child the fusion of the frontal bones begins 
 normally as early as the ninth month, and ends towards the close of the second year. 
 
 2 This must not be confounded with the epipteric bone, which sometimes occupies 
 approximately the same position (cf. infra, pp. 59 and 61). 
 
 3 This is also known as the os transversum, triquetum, epactale, Goetheanum, 
 and most commonly as the os Incae, because of its frequent occurrence in the skulls of 
 the ancient Peruvians (i.e. 5 to 6 per cent, as compared with but 1 to 2 per cent in 
 European skulls). A somewhat similar " prseinterparietal " lying in front of this, 
 and which will be described later, occurs in about 1 per cent of all cases.
 
 56 
 
 THE STRUCTURE OF MAN 
 
 between the parietals, assuming a markedly angular form (i.p. 
 Fig. 38, A). Although this bone persists differently in different 
 races, it is formed in the embryo from two distinct ossific centres, 
 
 FIG. 38. A to C, VARIOUS FORMS OF THE os INCAE (interparietal bone). 
 D, E, DIAGRAM OF THE BONES OF THE OCCIPITAL REGION IN THE EMBRYO. 
 
 (Partly after Ficalbi.) 
 
 i.p., interparietal ; t.j.^>.,praemterparietal ; e.o., exoccipital ; s.o., supra-occipital ; b.o., 
 basioccipital ; f.m., foramen magnum. 
 
 which, at a later stage, normally unite to form one mass with the 
 supra-occipital. This fact testifies to its paired nature, and, as 
 in the new-born child it is still separated by a cleft on each
 
 THE SKELETON 57 
 
 side of the median line from the adjacent and originally cartila- 
 ginous supra-occipital, it may perhaps have existed in the ancestors 
 of man as an independent bone. 1 
 
 The interparietals first appear in Mammals, but among the 
 higher forms they are seen in a state of apparent degeneration, as 
 would appear from their great variability in occurrence, form, and 
 detailed relationships. They may, for example, remain either 
 partly or wholly isolated ; they may be either single, bilaterally 
 symmetrical, or asymmetrical, or may be represented by but one 
 lateral bone. 
 
 Other inconstant ossific nuclei of this region are the prsein- 
 terparietalia. These may remain partly or wholly isolated, and 
 show in form and position variations similar to those above 
 described for the interparietals. The possible combinations 'of 
 these anomalous bones cannot be discussed here (cf. Fig. 38). 
 
 The morphology of the prseinterparietals is not clear, and it 
 is by no means unlikely that, like the ossa Wormiana (o. suturaria), 
 they fall under the category of accessory ossicles. The problem is 
 rendered still more difficult by the fact that, so far as is known, 
 they are constantly present only in the Horses, while in other 
 Mammals they are of mere sporadic occurrence. In Man, as 
 compared with the latter, they appear comparatively frequently 
 (i.e. 1 per cent). Equally uncertain is the morphology of the 
 os fronto-parietale [os antiepilepticum of the ancients], a bone 
 which occurs very rarely in Man, in the neighbourhood of the 
 fronto-parietal suture. This bone, which is more often found in 
 the Cebidse among Monkeys, and less frequently in Eodents, may 
 be sometimes paired. 
 
 An atavistic significance may be probably attached to a 
 bony process which occasionally appears in Man, behind and 
 externally to the jugular foramen, and into which the rectus 
 capitis lateralis muscle is inserted. This corresponds with the 
 par-occipital or paramastoid processus of many Mammals, which 
 attains its strongest development in Ungulates and Eodents. 
 
 There is one more point worth consideration in the occipital 
 region, i.e. the median portion of the linea nuchse superior. 2 
 A bony ridge (torus occipitalis), stretching at times as far as the 
 linea nuchae suprema, occasionally develops here. According to 
 
 1 "Welcker regards all the larger bones which are occasionally intercalated in 
 the lambdoidal suture as fragments of the os Incae. 
 
 2 It is difficult to decide whether the furrow or pit (fossette verraienne, 
 Albrecht), sometimes formed for the reception of the vermis cerebelli, has any 
 phylogenetic significance.
 
 58 THE STRUCTURE OF MAN 
 
 Ecker, this ridge is common in certain races, and it is said to be 
 homologous with the massive occipital crest of the Apes. 1 
 
 In the normal adult skull the sphenoid appears as a 
 single mass, and at a certain age this fuses still further with 
 the basioccipital bone. A comparative study of the Mam- 
 malian skull, as also an examination of the skull of the 
 human embryo, however, shows that the apparently single 
 sphenoid represents a series of fused bones. The basal elements 
 of the skull are segmentally arranged; but comparison 
 with the lower vertebrata shows that this is a secondary 
 feature in no way indicative of original metamerism. The 
 cranial "segments" are no part of a primordial segmentation 
 corresponding with the embryonic somites, as has been clearly 
 shown by Van Wijhe and Froriep from the study of develop- 
 ment (cf. infra). 
 
 Comparative Anatomy shows us that the orbital and temporal 
 fossse were originally one (as they still are even among Lemurs). 
 In the human embryo, and even in the new-born child, this fact is 
 still indicated by the greater width of the spheno-maxillary fissure, 
 the ultimate limitation of which, by extension and the final meet- 
 ing of the alisphenoid and the zygoma (malar), is not then 
 effected. Before this occurs the frontal and the malar have 
 already come into close apposition, and in the double relation of 
 the latter to the frontal bone on the one hand and the sphenoid 
 on the other, we have a distinctive character of the Primates as 
 opposed to all other Mammals. We find, accordingly, that these 
 connections are formed very late in the development of Man, as 
 compared with the relations of the malar to the maxillary and 
 temporal bones, which are established much earlier ontogenetically, 
 as they were phylogenetically. 
 
 Under ordinary circumstances, the upper edge of the ala 
 magna of the sphenoid (alisphenoid) reaches the anterior lower 
 angle of the parietal, but in rare cases (about 1 per cent of 
 European skulls) this junction is prevented by the anterior edge 
 of the temporal bone sending out a process to meet the frontal. 
 
 1 [In the Gorilla the sagittal and lambdoidal crests attain so great a develop- 
 ment in the male as to give the skull a carnivorous aspect. This feature is an 
 accompaniment of the greater development of the temporal jaw-muscles ; and it 
 is not acquired by the female. So marked is this sexual difference between the skulls 
 of these animals that had they been first found in the fossil state, they would in the 
 highest degree of probability have been regarded as at least specifically distinct. We 
 have here a most instructive example of an adaptive and secondarily acquired 
 character.]
 
 THE SKELETON 59 
 
 This so-called processus frontalis is remarkable on account of its 
 more frequent occurrence in the lower races, such as Negroes, 
 Australians, and Veddahs (according to the Sarasins it occurs in 
 
 FIG. 39. SKULL OF A GIRL TWO TEARS OLD, in which the temporal bone (tp.) is 
 separated from the frontal (fr.) by the broad ala magna of the sphenoid (alisphenoid 
 bone, a.s.) ; pa., parietal. 
 
 FIG. 40. SKULL OF AN ABORIGINAL AUSTRALIAN, in which the temporal bone is 
 separated from the frontal merely by a long process of the alisphenoid (a.s.). 
 
 10 per cent of the last named). This process is also often found 
 in the lower Mammals. [The upper edge of the alisphenoid, above 
 alluded to, may be not infrequently replaced by a distinct bone 
 (the epipteric of Flower before mentioned cf. p. 55, footnote, and
 
 60 THE STRUCTURE OF MAN 
 
 Fig. 41, f)- Thomson, from the study of a large series of 
 skulls, has shown good reason for regarding this as one of the 
 series of Wormian bones which so often occur in this region, 
 and for believing it to arise by dismemberment from either the 
 alisphenoid or parietal.] l 
 
 The nasal bones which, as a rule, remain distinct, sometimes 
 fuse to form one bone. This occurs far more frequently in the 
 lower races (Patagonians and tribes of South Africa) than in the 
 higher ; and it is the more probably an atavism, since this fusion 
 is normal in Apes. In the Chimpanzee it takes place as early as 
 the second year. 
 
 The lachrymals are susceptible to not a few variations, and 
 very rarely an abnormal enlargement of the hamular process 
 causes these bones to appear at the surface of the face, as in 
 many lower Mammals (Gegenbaur). 
 
 Many variations are to be found in the bones of the inner 
 orbital wall. For example, the lachrymal bone may be altogether 
 wanting, or only present in a vestigial form, so that the os planum 
 (lamina papyracea) comes into direct contact with the ascending 
 or nasal process of the upper jaw (premaxilla). In other cases 
 the lachrymal bone may be divided into an upper and a lower 
 portion by a suture, and there are other variations to which it 
 and the development of the hamular process are susceptible ; it 
 may be occasionally replaced by a radially disposed series of 
 small bones. 
 
 A similar division of the os planum of the ethmo-turbinal 
 into several pieces has been observed (Turner, Macalister, Arthur 
 Thomson); but it is questionable if any morphological signi- 
 ficance is to be attached to these variations. 
 
 According to the cousins Sarasin, a lower stage of develop- 
 ment is shown in the skulls of the Veddahs and others, in the 
 downward prolongacion of the nasal portion of the frontal bones 
 into the orbits, which lie very close together and are spacious, 
 
 1 [(Jour. Anat. and Phys., vol. xxiv. p. 356). I have elsewhere pointed out (ibid., 
 vol. xxiv. p. xviii.) that the ossa prseinterparietalia lie within the area normal to the 
 parietals, and that therefore these, at least, among the intercalary elements of the 
 cranium, may be similarly referred to an origin from those bones, by dismemberment, 
 under the expansion of the brain case. The phenomenon appears to me akin to that 
 of the well-known double ossification of the supra-occipital in its most expanded 
 form (ex. Cetacea and some Insectivora), and of the occasional duplication of the 
 lachrymal, and of the os planum, itself already intercalated in the orbital wall in 
 the Primates. (My friend Dr. Forsyth Major has lately shown me that the Lemurs 
 do not differ from the higher Primates in the absence of the latter character, as is 
 generally believed). G. B. H.]
 
 THE SKELETON 61 
 
 with strong, over-arching, superciliary ridges. This may be 
 carried so far that the fronto-nasal suture may lie almost on 
 a level with the centre of the orbit, whereas, as a rule, it lies 
 much higher. The arrangement manifestly involves the frontal 
 in a far greater share of the orbital wall than is the case with 
 Europeans ; and, correlatively, the os planum is in this race some- 
 what more than 2 mm. narrower than that of the European. 
 
 The bridge of the nose in the Yeddahs is not nearly so high 
 as in Europeans, i.e. it remains sunk between the orbits. In 
 other words, the two nasal bones do not slope outwards against 
 one another as they do in Europeans (in profile, they together 
 
 FIG. 41. THE SKULL OF A NEGRO EUNUCH, in which the process of the alisphenoid 
 (cf. Figv 40) is represented by a distinct bone the epipteric (f). 
 
 describe a curve slightly concave anteriorly), and this, in life, 
 results in a flat nose. This condition is palingenetically repro- 
 duced in the European child, and finds its expression in the 
 flatness of the nose, the bridge developing only in later years. 
 The choanae of the Veddah's skull are, on an average, half a 
 centimetre lower than in the European. 
 
 Turning now to the facial portion of the skull the upper 
 jaw first claims attention. That portion of it which carries the 
 incisors is particularly interesting, because Ontogeny teaches that 
 it was originally a sejmrate^ bone, homologous with the gre^ or 
 intermaxillary of the lower Vertebrata. This bone is an inherit- 
 ance which reappears with the greatest constancy from the bony 
 Fishes upwards throughout the Vertebrata ; but whereas in by far 
 the greater number of these the premaxillary remains an 
 independent bone, in Primates it early fuses with the adjacent 
 elements of the upper jaw to form one mass. In Man this fusion
 
 62 THE STRUCTURE OF MAN 
 
 usually occurs soon after birth ; in most Apes, on the contrary, 
 much later. In Man the fusion first involves the facial portion 
 
 FIG. 42. SKULL OF A TORCO, in which the temporal bone nearly reaches the 
 frontal. Between the two a narrow process of the parietal is intercalcated. 
 
 FIG. 43. SKULL OF A TWO-YEAR-OLD CHIMPANZEE, in which the temporal bone 
 is to a considerable extent in apposition with the frontal ( fr. ). 
 
 of the bone, its palatal part remaining for a long time, or even 
 permanently, marked off from that of the maxillary by a suture 
 or trace of a suture. The same is the case with the Anthropoids.
 
 THE SKELETON 
 
 68 
 
 Only very rarely and then, as a rule, in the lower races of 
 mankind (Negroes and Australian aborigines) does it remain 
 distinct throughout its whole extent in later years, in otherwise 
 normal skulls. The striking manner in which the original 
 independence of the premaxillary bones is shown in people 
 affected with the deformity known as hare-lip is well known. 
 
 The number of incisors connected with the premaxillary will be con- 
 sidered later in dealing with the buccal cavity. It may here, however, 
 be remarked that Comparative Anatomy affords no explanation of the double 
 nature ascribed by Albrecht to each half of the human intermaxillary bone. 
 
 Quite recently Waldeyer has drawn attention to certain 
 peculiarities of the hard palate, i.e. variations in the posterior 
 
 FIG. 44. THE HARD PALATE, A, OF A CAUCASIAN ; B, OF THE NEGRO ; C, OF AN ADULT 
 ORANG-UTAN. Showing the differences in shape of the bones. The palate of the 
 Negro represents a type transitional between that of the Caucasian and that of the 
 Orang. 
 
 nasal spine, which had previously escaped recognition, and I 
 have confirmed his observations. This spine (Fig. 44) is deriva- 
 tive of the horizontal plates of the palatine bones (pl.\ and is thus 
 morph ologically paired. Not infrequently a more or less marked 
 double spine is found, and where this is most evident the hori- 
 zontal plates of the palatines may sometimes not even meet in 
 the middle line. In the latter case the palatine processes of the 
 maxillae may run back along opposite sides of the middle line, so 
 as to take part in the formation of the posterior edge of the hard 
 palate. These deviations from the normal arrangement have 
 been observed in the skulls of Men and Gorillas. 
 
 There are further interesting variations in the relative 
 positions of the palatine bone and the palatine process of .-the
 
 64 THE STRUCTUEE OF MAN 
 
 maxillary, and also in the relation of the former to the posterior 
 edge of the hard palate. 
 
 As a rule, the transverse palatine suture runs right across 
 the palate, i.e. the two horizontal plates of the palatine bones 
 have a more or less straight anterior edge (Fig. 44, A). Not 
 infrequently, however, the median portions of these plates are 
 more prolonged anteriorly, the course of the transverse palatine 
 suture being correspondingly irregularly oblique on either side, as 
 depicted in Fig. 44, B. 
 
 I find the latter condition to be still more marked in the 
 Orang-Utan (Fig. 44, C), and the same may be true, as Waldeyer 
 has already shown, of other Mammals. [By analogy to the lower 
 vertebrata] we have here an index of a low grade of organisation. 
 
 The proximal end of the first visceral skeletal arch (Meckel's 
 cartilage) (I, mk., Fig. 45), which developmentally precedes the 
 bony lower jaw (md.~), 1 is continued into the middle auditory 
 chamber of the embryo as a cartilaginous enlargement. This 
 becomes twice constricted to form the incus (in.} and the malleus 
 (ml.} Some authorities homologise these with the quadrate 
 and articular elements of the mandible of the lower Yertebrata, 
 [but according to others they are structures sui generis distinct 
 in origin from the embryonic lower jaw. The value of these 
 elements is one of the most vexed problems in comparative 
 morphology. All investigators are, however, agreed that they 
 are the representatives of an apparatus, at least in part functional 
 in lower Vertebrates, in effecting the indirect articulation of the 
 jaw apparatus upon the skull, and that in Man and the Mammals, 
 in which this articulation has become direct, this apparatus, under 
 associated change of function, has entered secondarily into con- 
 nection with the organ of hearing] (cf. Figs. 45 and 46). 
 
 A trace of the embryonic connection between the malleus 
 and Meckel's cartilage is long retained, in the so-called prpcessus 
 gracilis of the malleus, which passes towards the lower jaw 
 
 1 The prognathous type of skull has been assumed to be reversionary to a pithe- 
 coid condition ; but this consideration is by no means a simple one. The cousins 
 Sarasin have pointed out that the lowest forms of human skulls, e.g. those of 
 Veddahs, Andaman Islanders, and Bushmen, are of the orthognathous or (Andaman 
 Islanders) mesognathotis type. The orthoguathous type may thus have been 
 attained by human beings at a very early period, and subsequently lost. If this be 
 the case (but it is doubtful) the prognathous condition of Negroes and Melanesians, 
 and the great projection of the jaw in some woolly and straight-haired races, must 
 be a secondary condition, which has been preceded by orthognathy. In this case 
 the orthognathy once more attained by Europeans must be regarded as a third 
 phylogenetic phase in the evolution of the skull (Sarasin).
 
 THE SKELETON 65 
 
 through [an interspace between the elements of the auditory 
 region of the skull, known as] the Glaserian fissure. 
 
 The second visceral or primitive skeletal arch (II, Fig. 45) 
 becomes, in Man, proximally connected with the auditory capsule ; 
 distally it becomes related to the next arch behind (III of Fig.). 
 Its intervening portion, which at first is cartilaginous, may 
 become partly or altogether ossified, but it is usuall} 7 - transformed 
 
 FIG. 45. HEAD OF A HUMAN EMBRYO OF THE FOURTH MONTH. Dissected to show the 
 auditory ossicles, tympanic ring, and Meckel's cartilage, with the hyoid and thyroid 
 apparatus. All these parts are delineated on a larger scale than the rest of the skull. 
 
 ml., malleus; in., incus; st. , stapes ; an., tympanic ring ; tp., tympanum ; I (mk. ), first 
 skeletal (mandibular) arch (Meckel's cartilage) ; II, second skeletal (hyoid) arch ; 
 III, third (first branchial) arch; IV, V, fourth and fifth arches (thyroid cartilage); 
 b. hy., basihyal element ; tr., trachea ; md., bony mandible. 
 
 along the greater part of its length into a fibrous band. 
 
 In other cases it is replaced by a series of small cartilaginous 
 or osseous bodies which form a chain, recalling the arrangement 
 existing in many lower Mammals. The proximal end of 
 this arch becomes, in Man, the very variable styloid process of 
 the temporal bone ; the distal end, on the other hand, forms the 
 lesser cornu of the hyoid. This latter bone (the hyoid) also con- 
 sists of a central portion or body (&.%.), and a larger or posterior
 
 GG 
 
 THE STRUCTURE OF MAN 
 
 cornu (III), which is paired and projects therefrom backwards. 
 The body may be regarded as the basal element of the second and 
 third embryonic skeletal arches, 1 while the posterior cornua repre- 
 sent the lateral elements of the third (or first branchial) arch 
 alone (cf. Figs. 45, 46, and 107). 
 
 In the earliest stages of the embryo, the ridge which will 
 afterwards develop into the second o hyoid visceral arch, sends 
 a process backwards, which covers a deep groove (the cervical 
 groove) on the postero-lateral edge of the cephalic region. The 
 third and fourth branchial arches lie in the hollow thus 
 formed, and they gradually cease to be externally evident. 
 The entrance to this cervical groove is bounded by the hyoid 
 
 HI 
 
 PT V VI, 
 
 FIG. 46. SKULL OF A TAILED AMPHIBIAN (Menopoma). The skeletal arches are 
 
 lettered serially with those of Man, in Figs. 45 and 105. 
 
 qu., quadrate cartilage ; ar., articular end of ink., Meckel's cartilage ; I, maudibular 
 arch ; II, hyoid arch ; III, IV, V, VI, branchial skeletal arches. 
 
 arch ; and there can be little doubt that we have in the above- 
 mentioned ridge a feeble homologue of the gill-cover of fishes 
 and metamorphosing Amphibia. It at a later stage fuses with 
 the adjacent body wall, the cervical groove (branchial chamber 
 of the Anamnia) becoming thus closed. 
 
 The hyoid apparatus, which is intimately connected with the 
 cervical, lingual, and mandibular musculature, is in fibrous con- 
 nection (thyro- hyoid ligament) with the upper edge of the 
 laryngeal skeleton ; and of this skeleton the thyroid cartilage at 
 least (IV, V, Fig. 45) arises from the fourth and fifth bran- 
 chial arches (cf. Fig. 107 and p. 151). 
 
 1 [It is usually stated to be ossified from a single centre in Mammals, but the 
 fact, to which my friend Mr. M. F. Woodward has drawn my attention, that it may 
 be occasionally subdivided by a transverse suture into two portions (ex. Lepus) 
 indicative of its ossification from two recurrent centres, is of much interest in this 
 connection. G. B. H.]
 
 THE SKELETON 67 
 
 SKELETON OF THE LIMBS 
 
 So far as their skeleton is concerned, the fore and hind limbs 
 of Men and other Vertebrates, notwithstanding their various 
 adaptive modifications, are unmistakably built on the same plan. 
 This fact not only finds its expression in the strictly homologous 
 segmentation of their free portions, but is confirmed by Compara- 
 tive Anatomy and Ontogeny. 
 
 Without entering at length into the old controversy as to 
 the phylogeny of the limbs, I would briefly define my own posi- 
 my. 
 
 FIG. 47. TRANSVERSE SECTION THROUGH THE EMBRYO OF A SHARK (Pristiurus 
 
 mdanostomus), 9 mm. long, showing the mode of origin of the Pectoral Limb Bud (ap. ) 
 
 ch., notochord ; co., ccelom ; ?., myomeres, seen to be growing 
 
 ventrally ; my. , spinal cord. 
 
 tion with regard to this question. I agree with Balfour and 
 Dohrn in regarding the limbs of the Vertebrates as outgrowths 
 of the primitive body segments, and thus believe in their originally 
 segmental nature ; and I see in this an argument for the origin 
 of existing Vertebrates from segmented Invertebrate ancestors. 
 In other words, these limbs, which in origin are polymerous, 
 involve phylogenetically a certain number of body segments with 
 their muscles and nerves ; and these, in consequence of functional 
 adaptation, must necessarily undergo different modifications in 
 the different groups of Vertebrates. Although this subject 
 cannot be further discussed here, it may be remarked, in passing, 
 that the differences between the anterior and posterior limbs, 
 resulting from adaptive modification, become less marked the 
 lower we descend in the vertebrate series ; indeed, a starting-point
 
 68 THE STRUCTURE OF MAN 
 
 of approximate structural uniformity is finally reached among 
 the Fishes. In the higher types, and especially in Birds and 
 Mammals, the limbs have greatly diverged. In the former, the 
 whole weight of the body is thrown on to the posterior limbs, 
 which are thus purely supporting organs; and the anterior 
 limbs, relieved of their original supporting functions, have 
 become transformed into organs of night. 
 f.d. 
 
 FIG. 48. DIAGRAM ILLUSTRATING THE DEVELOPMENT OF THE FINS OP A FISH. 
 A, To show the first formed and originally continuous lateral (/..) and dorsal (f.d.) 
 
 fin-folds ; f.v. indicates the point where the lateral folds are continued ventrally 
 
 behind the anus (a.). 
 B To show the definitive fins [which owe their independence to the absorption of the 
 
 primarily continuous folds throughout the areas indicated by the dotted lines], d'., d"., 
 
 dorsal fins ; pc., pectoral ; pi., ventral or pelvic tins ; v., anal ; and c., caudal fin. 
 
 An almost equally advanced modification is found in many 
 Mammals, e.g. Man, in whom the anterior limbs have been trans- 
 formed from ambulatory into prehensile organs, the " fore-feet " 
 becoming hands. 
 
 A detailed comparison between the upper and lower limbs of 
 Man will be instituted at the close of this section (infra, p. 91). 
 
 THE PECTORAL (SHOULDER) AND PELVIC (Hip) GIRDLES 
 That the limb-girdles were of later origin than the skeleton 
 
 of the free limbs is rendered probable by the Ontogeny of all 
 
 Vertebrates. 
 
 The following is the course of development in the embryo Shark : 
 A number of originally separate skeletogenous rays (rd., Fig. 49, A), de- 
 velop in the dermal fin-folds l ; and, by fusion at their proximal ends, even 
 before they are at all chondrified, they give origin to a basaljalate (bs). The 
 anterior ends of the basal plates of opposite sides next approximate (*Fig. 49, 
 B), and finally fuse in the middle line, leaving passages for their related 
 
 1 [Great interest attaches to the recent discovery, that in the Palaeozoic Selachian 
 Cladoselache, these rays retained their primary independence in the adult pelvic 
 fin. Cf. Dean, Jour. Morph., vol. ix. p. 87.]
 
 THE SKELETON 69 
 
 nerves. Of the cartilaginous arch thus formed, the middle portion becomes 
 in the fore-limb the pectoral, and in the hind the pelvic girdle, and both of 
 these must therefore be regarded as products of the skeletogenous blastema 
 of the free limbs. The segmentation into a central girdle and lateral 
 limb supports is effected by a process of resorption (cf. fFig. 49, C), the 
 points at which this is effected becoming the shoulder and hip-joints. 
 
 FIG. 49. A, B, C, DIAGRAMMATIC REPRESENTATION OF THREE SUCCESSIVE STAGES 
 
 IN THE DEVELOPMENT OF THE PELVIC FINS OF A SHARK. 
 
 rd., primitive skeletogenous rays ; in A these are already commencing to grow together to 
 form a basal plate (bs.) ; in B this fusion has taken place on both sides, and at * 
 the proximal ends of the basal plates are approximating to form the limb girdle ; 
 in C the process is completed, and at t the free limb skeleton is being constricted 
 off. The formation of secondary rays at the periphery is delineated to the left of 
 C ; figure fo., foramen obturatorium ; c/., cloaca! aperture. 
 
 It would appear from the foregoing that not only the girdles, but also 
 the basal limb supports which articulate with them (the later femur or 
 humerus), were primarily the products of fusion of parallel .rays. Inasmuch 
 as this consideration, as will appear later, is of profound importance in 
 dealing with the morphological significance of the limbs, this brief digression 
 into Embryology has been unavoidable. Fig. 50 farther illustrates the same 
 subject, showing the probable manner in which the number of skeletal rays 
 which unite to form the limbs of terrestrial Vertebrates is reduced.
 
 70 
 
 THE STRUCTURE OF MAN 
 
 r.p. 
 
 FIG. 50. AN ATTEMPT TO DEPICT DIAGRAMMATICALLY THE PROCESS BY WHICH, FROM 
 THE STUDY OF COMPARATIVE MORPHOLOGY, THE LIMBS OF TERRESTRIAL VERTE- 
 BRATA WOULD APPEAR TO HAVE BEEN PROBABLY DERIVED, BY MODIFICATION, 
 
 FROM THE FlXS OF FlSHES. 
 
 The shaded parts indicate rays which atrophy ; A, pelvic fin of a Sturgeon ; B, 
 diagram of the posterior limb of a larval Salamander ; C, the hind limb of 
 an adult Urodele Amphibian (Ranodori) ; p., pelvis; bs., basale (femur); rd'., 
 proximal rays (tibia, fibula) ; r.p., peripheral ray segments (tarsal and other 
 elements of the pedal skeleton) ; rd". , rays which atrophy and ultimately 
 disappear.
 
 THE SKELETON 71 
 
 Phylogenetically, the oldest elements of the pectoral girdle 
 are the scapula and coracoid, and of the pelvic girdle the 
 ischium and pubis ; for though in certain Fishes the clavicle and 
 the ilium are indicated, they are only fully developed from 
 the Amphibia upwards. 
 
 Fig. 51 is the ventral view of the pectoral girdle of a 
 tailed Amphibian. It shows that the clavicles (cl.} are directed 
 forwards (i.e. towards the head), and that the coracoids (co.) 
 overlap each other ventrally. The edges of the latter, which 
 are connected by fibrous tissue, only loosely overlie the small 
 so-called " sternum " (s). The connection between the coracoids 
 
 FIG. 51. PECTORAL GIRDLE OF A TAILED AMPHIBIAN, FROM THE 
 
 VENTRAL SIDE. 
 cl., clavicle ; co., coracoid ; ar., shoulder-joint ; st., so-called "sternum." 
 
 and the sternum becomes much closer in Eeptiles and Birds, and 
 persists in the lowest Mammals. The withdrawal from this 
 connection seen in the higher Mammalia is proportionate to the 
 greater development of the antero-ventral element of the pectoral 
 girdle, the clavicle. Through the mediation of this bone the 
 scapula finds a new support upon the sternum, and thus the limb, 
 being the farther removed from the trunk, attains far greater 
 freedom of movement. 
 
 The expanded coracoid of the lower Vertebrata is, in Man, 
 represented by an apparent process of the upper edge of the 
 scapula, called the processus coracoideus (co., Fig. 52). This serves 
 as a point of origin and attachment for certain ligaments and
 
 72 THE STRUCTURE OF MAN 
 
 muscles, but its original independence and greater significance is 
 seen in the fact that it ossifies from two distinct centres, which 
 in Man only completely fuse with one another and with the 
 bony scapula after the sixteenth to the eighteenth year. [This 
 double ossification of the coracoid occurs only in Mammals 
 among living Vertebrates^ The overhanging portion of the 
 coracoidal region of the human blade -bone, which (co., Fig. 
 52) from its suggestiveness of a bird's head has been termed 
 the " coracoid process," answers in 
 every detail of relationship to the 
 epicoracoid of the lowest Mammals 
 (ex., Fig. 28). The basal portion, or 
 second coracoidal element (which 
 does not appear in the human sub^ 
 ject until the fourteenth or fifteenth 
 year), represents, in a highly reduced 
 and vestigial condition, the more 
 robust element of the Ornithorhyn- 
 chus coracoid (m.c., Fig. 28). It was 
 FIG. 52,-RiGHT BLADE-BONE OP A until recently known as the " cora- 
 NEW-BORN CHILD, SEEN FROM THE coid"; but, as it and the epicoracoid 
 INNER OR COSTAL SURFACE. ,-, ,,, , . . n 
 
 co., coracoid process ; the dark spot to g ether *>premt the entire coracoid 
 at os. represents the first of its two of the lower Vertebrata, the term 
 metacoracoid is now applied to it.] 1 
 The scapula is in Man a broad 
 bone, its form being doubtless attained in functional adaptation to 
 a very strongly developed shoulder musculature. In those lower 
 animals, in which the anterior limbs are simple ambulatory organs 
 performing less complicated movements, the scapula is not so broad, 
 especially at its median and hinder border the so-called base. It 
 is therefore very interesting to be able to prove, both by the 
 Anatomy of the lower races (Negroes and aborigines of Australia) 
 and by .human Ontogeny, that the great breadth of the median 
 part of the human scapula, and the sharper differentiation of its 
 spine, may both be considered as secondarily acquired features, 
 which stand in direct relation to the gradually increasing func- 
 tional activity of the fore-limb. 2 
 
 1 [Cf. Lyndekker and Howes, Proc. Zool. Soe., Lond. 1893, pp. 172 and 585.] 
 
 2 [The scapula of the higher Mammalia differs most conspicuously from that of 
 
 the lowest Mammals and all lower Vertebrates, in its expansion, cephalad of its spine, 
 to form the so-called prescapular lamina. This is but feebly formed in Man. It 
 
 with marked specialisation of the 
 purpose. This is readily seen, for 
 
 . n 
 
 attains its highest development in association with marked specialisation of the 
 fore-limb not, however, always for the same purpose. This is readil
 
 THE SKELETON 73 
 
 The close connection between the increased efficiency of 
 the fore-limbs and the stronger development of the clavicle 
 has already been pointed out ; and the great physiological 
 significance of the clavicle is further shown by the fact, that 
 at a certain stage in development it is the strongest por- 
 tion of the whole human skeleton and the first to become 
 ossified. 1 
 
 One distinction between the shoulder and the pelvic 
 girdle, evident even on superficial comparison, lies in the more 
 limited capacity of movement of the latter, which is in turn 
 associated with the more limited movements of the hind-limbs. 
 But although mechanical causes, connected with the upright 
 mode of progression, certainly play a great part in determining 
 the condition of the latter, they do not furnish the complete 
 explanation, as a similar immobility of the pelvis is found 
 in the lowest terrestrial Vertebrates, Eeptiles, and Amphibians. 
 And further, as in both of these, and especially in the tailed 
 Amphibians, no great distinction is found between the mobility 
 of the anterior and the posterior limbs, the first cause of the 
 distinction so marked in Man must therefore be sought elsewhere. 
 It seems to me to lie, on the one hand, in functional adaptation 
 of the pelvis to the requirements of reproduction, and on the 
 other, in the fact that the distal part of the pelvis forms the 
 functional posterior end of the trunk. At this part of the body, 
 where the posterior apertures of the urinogenital and alimentary 
 systems occur, a firm framework is needed for the related con- 
 vergent viscera. Such a framework would be a predisposing 
 factor in the development of the powerful sphincter and limb 
 muscles, furnishing the latter with a more extensive and firmer 
 surface of attachment, which could further be turned to account 
 by the free posterior limbs. 
 
 The relationships of the pectoral and pelvic girdles to the 
 vertebral column are essentially alike in principle. In neither 
 case, among terrestrial Vertebrates, is the connection attained 
 directly, but always through the intervention of ribs. The 
 
 example, on comparison of the Sea Lion (Otaria) and Great Ant-Eater (Myrmcco- 
 phaga), in the former of which the prcscapular lamina far exceeds in area the rest of 
 the blade-bone. The Sea Lion uses its fore-limb as a swimming organ, the Ant-Eater 
 for tearing up Termites' nests and digging.] 
 
 1 In the scapula of the Veddahs, the greater slant of the spine towards the 
 posterior edge, and the consequent greater development of the supiaspinous fossa 
 (prescapular lamina) as compared with that of Europeans, may be indicated as 
 primitive features (Sarasins).
 
 74 THE STRUCTURE OF MAN 
 
 shoulder girdle is loosely attached to its ribs by muscles, the 
 pelvic by firm ligaments and a definite articulation. 1 
 
 In the human embryo, as in all living Eeptiles, Birds, and 
 Mammals, the embryonic pelvis is triradiate, its cellular blastema 
 at first forming one mass with that of the developing femur : this 
 condition I have traced through the whole series of Vertebrates. 2 
 After the pelvic blastema has, at a later stage, become differ- 
 entiated from that of the femur, which is the first to become 
 cartilaginous, the ilium, ischium, and pubis are laid down as 
 distinct chondrifications. The fusion of the acetabular portion 
 of these three pelvic cartilages takes place in the following 
 order : first, the ischium alone unites with the ilium, and later, 
 the ilium with the pubis. The ischium and the pubis do not 
 send out acetabular processes towards one another, and for this 
 reason a space is left at their point of apposition. 
 
 [The bone to which in the adult human subject the term 
 pubis was first applied, is formed by the union of two distinct ele- 
 ments a main one arising in utero, and a lesser, arising during 
 the thirteenth year 3 within the acetabular region, and completely 
 excluding its neighbour from that cavity. The latter element 
 is of regular occurrence among the lower Mammalia, and being 
 in them of considerable proportions has received the name 
 " cotyloid bone " or " os acetabuli." In accordance, however, with 
 its ultimate fate, it may be more appropriately termed the 
 dorso-pubic element, and its neighbour the ventro-pubic. 4 Thus 
 considered, comparison of the pubis with the coracoid (ante, 
 p. 72) shows that in Mammals, and in them alone among living 
 Vertebrates, each consists of two elements, of which one 
 (epicoracoid and pre - pubic element) is excluded from the 
 articular facet (glenoid cavity and acetabulum).] 
 
 In no other Mammals do the iliac bones diverge so greatly 
 
 1 This difference appears less marked, and may altogether vanish, when we 
 compare the [lower vertebrata. Among Chelonians the shoulder girdle very generally 
 articulates upon the anterior thoracic vertebrae ; and in] Fishes a firm connection 
 is established between the shoulder girdle and the skull (Osteichthyes), or even 
 between the former and the vertebral column (Rays), [such as is seen also in many 
 Frogs and Toads, and may, under rare conditions, occur in Man himself.] In 
 certain Salamanders we find, on the rib approximate to the inner border of the 
 suprascapular, a plate-like cartilaginous expansion, which is fastened to the shoulder 
 girdle by means of ligaments ; [this, however, has probably to do with protection of 
 an adjacent pulsatile "lymph-heart."] 
 
 a The author here refers in the original German to his " Gliedmassen Skelet der 
 WirbeWiicrc," Jena, 1892. 
 
 3 [Cf. Krause, Month. Internat. Jour. Anat. and Hist., vol. ii. p. 150.] 
 
 4 [Cf. Howes, Jour. Anat. and Phys., vol. xxvii. p. 550.]
 
 THE SKELETON 
 
 75 
 
 as in the higher races of Men. This feature is not, however, 
 marked during foetal life, when the form of the pelvis recalls 
 that found in the adults of the lower races of Men and in the 
 Apes. 1 The whole embryonic pelvis is comparatively long and 
 narrow ; its angle of inclination is much greater than in the 
 
 *// 
 
 FIG. 53. PELVIS OF A FEMALE CHIMPANZEE, TWO YEARS OLD. 
 
 r.s, sacral ribs ; ac., acetabulum ; f.o., obturator foramen ; is., ischium ; sy., symphysis 
 pubis ; pb., pubis ; il., ilium. 
 
 adult, and the long axis of the symphysis pubis forms anteriorly 
 with the axial line of the body a very acute angle. We herein 
 meet with a form of sacrum resembling that of lower Mammals, 
 and a promontory which only slightly projects (cf. Fig. 53). 
 As a consequence, the entrance to the pelvis is also like that of 
 the lower Mammals, and differs greatly from that of the later 
 adult form. 
 
 1 The pelvis of the Veddah, according to the Sarasins, differs from that of the 
 European in its relative length and narrowness.
 
 76 THE STRUCTURE OF MAN 
 
 The close connection between the great expansion of the 
 iliac bones and the upright gait of Man has already been pointed 
 out (ante, p. 38). 
 
 The sexual dimorphism of the pelvis is more marked in Man- 
 kind than in any other Vertebrate ; indeed, it may be considered 
 as a characteristic of the human species, the rationale of which 
 has still to be discussed. 
 
 If we consider the marked lateral projection of the iliac bones 
 which is met with in both sexes, and has already been described 
 and accounted for, it seems natural enough to regard their in- 
 creased expansion in the female as an adaptation to sexual re- 
 quirements. This increase of breadth is the more necessary, 
 since the human embryo attains a higher development before 
 birth than do the embryos of most Mammals, the skull and brain 
 being incomparably larger in proportion to the size of the mother. 
 So highly differentiated an embryo, again, must influence the pelvic 
 aperture, and, indeed, the whole form of the lower parts, includ- 
 ing the promontory, since the pressure of the pregnant uterus is 
 not exerted ventrally as in Quadrupeds, but, on account of the 
 upright gait, sagittally. The iliac wings thus play the chief part 
 in carrying this weight, and naturally undergo a corresponding 
 lateral plate-like expansion. Further investigation concerning the 
 pelvis in relation to " labour " in the different races of Mankind 
 would be of great interest. All that can now be stated with 
 certainty is, that sexual differentiation of the pelvis, at least so 
 far as the expansion of the iliac bones is concerned, is much 
 less marked in the lower than in the higher races. 
 
 THE SKELETON OF THE FREE LIMBS 
 
 As already indicated, the fore- and hind-limbs of Man con- 
 form to a single type ; and any doubt which might exist as to the 
 differences between the two having been secondarily acquired by 
 functional adaptation, is dispelled by Comparative Anatomy and 
 Ontogeny. As already pointed out (pp. 68, 69), a review of the 
 various groups of Vertebrata shows that the farther we go back 
 in the series the less marked are the differences between the fore- 
 and hind-limbs ; until at length, in the Fishes, we have an undif- 
 ferentiated starting-point for the two. At the top of the scale 
 we have the Birds with their fore-limbs metamorphosed into wings 
 (under conditions by which the pelvis and vertebral column 
 become correlatively modified with the hind-limbs, to support the
 
 THE SKELETON 
 
 77 
 
 weight of the body) ; and Man, with what was originally a fore- 
 foot turned into a hand. 
 
 Before trying to answer the question as to the mode of 
 origin and progress of these important differentiations, let us 
 consider the structural variations to which the free limbs are 
 susceptible. 
 
 The free limbs undergo greater and more numerous modifications than 
 their related girdles ; and the probability that thjs may be perhaps connected 
 with their exposed position and intimate contact with the environment, may 
 be worth consideration. 
 
 THE SKELETON OF THE FORE- LIMB 
 
 The fore-limb of the Anthropoids is relatively longer than 
 that of Man, and it is therefore specially interesting to note that 
 in some of the lower races of Men the arms are relatively much 
 longer than in Europeans. In the Veddahs this difference is 
 even externally obvious, and when the skeleton is examined, is 
 seen to be, as in the Anthropoids, chiefly due to the great 
 length of the forearm (radius and ulna). If 
 the length of the humerus be taken at 100, 
 that of the radius is 73 in the male European, 
 nearly 80 in the male Veddah, and 90 to 94 
 in the Chimpanzee (Sarasins). This great 
 development of the forearm is distinctly a 
 mark of low organisation, and it is a signifi- 
 cant fact that it obtains in the European foetus 
 and child, only giving place to the definitive 
 proportion with advancing age. (Similar 
 variation with age is found in the fore-leg, cf. 
 infra.} 
 
 The occasional perforation of the olecranon 
 fossa of the humerus, to form what is known 
 as the ent-epicondylar (supra-trochlear) foramen 
 (Fig. 55), is undoubtedly to be regarded as 
 atavistic. It is often found in the lower_races 
 
 of mankind, e.g. natives of South Africa, and FIG. 54. RIGHT HUM- 
 , , , -, . ,, i T -.j , ERUS OF A NEC;RO, 
 
 has been observed in the Veddahs in as many SHOWING PERFORA- 
 
 as 58 per cent, in skeletons belonging to the TION OF THE LE - 
 
 ., . , . CRANOX FOSSA. (All- 
 
 stone-age, in the Anthropoids (Gorilla and terior aspect.) 
 Orang), and in the lower Apes. 
 
 On the ulnar side of the lower end of the humerus, a few
 
 78 THE STRUCTURE OF MAN 
 
 centimetres above the internal condyle, a bony process (processus 
 supra-condyloideus) (pr., Fig. 55, D) sometimes projects in a hook- 
 like manner, a fibrous band passing from it to the ent-epicondylar 
 region. The Median Nerve runs through the foramen thus 
 enclosed. This foramen is very common among the lower animals, 
 
 FIG. 55. DISTAL EXTREMITY OP THE HUMERUS TO SHOW EPICONDYLAR FORAMINA. 
 A, in Hatteria; B, in a Lizard (Lacerta ocellata) ; C, in the domestic Cat ; D, in Man ; 
 c.e., external condyle ; c.i., internal condyle. In A the two foramina are developed 
 (at i, the ent-epicondylar ; at ii, the ect-epicondylar). The only canal (t) present 
 in the Lizard (B) is on the external volar side, in the cartilaginous distal extremity. 
 In Man (D) an ent-epirondylar process (pr.) is developed and continued as a fibrous 
 band. 
 
 and is of very great antiquity. It is found not only in very many 
 quadrupedal Mammals, but in Eeptiles (Fig. 55, A and B), in 
 fossil forms which skeletally combine Amphibian with Eeptilian 
 characters (Palceohatteria, Homwosaurus), and in fossil Amphibians 
 (Stegocephala) of the Permian period (Stereorhachis and Bofh- 
 
 1 [Struthers has recorded an interesting case of hereditary development of this 
 supra-condyloid process (Lancet, 15th February 1873), and has specially advocated 
 the view that the completion of the process in Man has a reversionary significance, 
 and not that of mere overgrowth for protection, frequently occurrent in all parts
 
 THE SKELETON 79 
 
 In the great majority of Eeptiles a similar aperture (ect- 
 epicondylar foramen) is found on the outer side of the humerus, 
 (Fig. 55, A ii), and in some both foramina are present. These 
 are in both cases nerve canals, which fact suggests that they may 
 not have arisen either among Amphibians or Eeptiles, but rather 
 among animal forms phylogenetically still older. 
 
 [In consideration of the facts already recapitulated (pp. 68-70) con- 
 cerning the comparative anatomy and development of the vertebrate limb- 
 skeleton, the probability that these condylar foramina may be indicative of 
 a] polymeric origin of the basal segments of the limb-skeleton must not be 
 overlooked, for, in the Ontogeny of the Sharks and Sturgeons, these latter can 
 be traced to an origin by concrescence from parallel cartilaginous rays. If this 
 be the meaning of the foramina, the fact that among living Reptiles they are 
 most marked in the most primitive genus (Hatteria) is the more interesting. 
 
 I have elsewhere l raised the question whether the foramina nutritia, 
 occurring in the long bones of the limbs, may not have had a similar origin. 
 A wide field is here open for research, in which palaeontology should play an 
 important part. 
 
 Special interest attaches to the skeleton of the human hand, 
 and there is still abundant room for 
 further investigation concerning it. 
 
 Taking first the carpus, the re- \\ o j3 
 
 semblance of that of Man to the \ V U JS / 
 carpus and tarsus of the tailed Am- \ A jj S fif 
 phibians is most striking. In its V^ CV ^ I? /> 
 proximal row there are the three w T ell- A y^ U CJ // 
 
 known bones, the radiale (scaphoid = ^<^\^^ 
 
 tibiale in the pes), the intermedium /-^ Q 
 
 (lunar), and the ulnare (cuneiform = V^T 
 
 fibulare in the pes), cf. Figs. 56, 57, 
 59, 60. In the distal row, counting 
 from the inner or radial face, lie the 
 
 first carpale (trapezium = 1st tarsal or 
 
 . . ,, N ,, , FIG. 56. SKELETON OF THE HIND- 
 
 ento-cuneiform in the pes); the 2nd car- LlMB OF A TAILED AMPHIBIAN 
 
 pale (trapezoid = 2nd tarsale or meso- (Spderpesfuscus) 
 
 > ^ . <//., tibia ;/&., fibula; (., tibiale; 
 
 cuneiform in the pes) ; the 3rd carpale /, intermedium ; f, fibulare ; 
 (magnum = 3rd tarsale or ecto-cunei- c,_ceutraie ; 1-5, tarsalia; itov, 
 form in the pes) ; and the 4th carpale 
 
 of the skeleton (cf. Rep. Internal. Medic. Congress, Loud. 1881). A remarkable 
 outcome of the latter tendency has been recently described by Griinbaum, in the 
 discovery of a ligament which, bridging over the posterior condylar foramen, forms a 
 tunnel for a branch of the occipital artery, and, by ossification, may form "a ring of 
 bone projecting downwards from the lower surface of the occiput " (Jour. Anat. and 
 Phys., vol. xxv. p. 428, and Macalister, ibid. p. Hi.).] 
 1 Das Gliedmassen Skelet (see ante, p. 74, footnote).
 
 80 
 
 THE STRUCTURE OF MAN 
 
 ( = cuboid in the pes). The last-named bone (4 and 5, Fig. 57) 
 gives articulation to two metacarpals, viz. the 4th and 5th, and 
 its originally double nature is thus indicated. This is shown 
 (apart from comparison with the carpal skeleton of the lower 
 Vertebrata) by the occasional division of this bone into two, not 
 only in Man, but in the most varied Mammals (Marsupials, 
 Eodents, Cetacea). 
 
 All who are in any degree acquainted with Comparative 
 Osteology, know what a great part is played by the os^centrale as 
 a component of the carpus and tarsus. To Gegenbaur belongs 
 the honour of having first recognised and appreciated this. 
 All investigations made after the year 1864 had to start from 
 
 4+0 
 
 FIG. 57. DIAGRAM OF THE HUMAN CARPUS. A, EMBRYO ; B, ADULT. 
 rd., radius ; ul., ulna ; u, ulnare (cuneiform) ; i, intermedium (lunar); r, radiale (scaphoid); 
 p, pisiforme ; 1, 2, 3, carpalia (trapezium, trapezoid, and magmim) ; 4 + 5 = united 
 4th and 5th carpalia (represented in the adult by a single bone, the uueiform) ; c, 
 centrale, which fuses later with the radiale (scaphoid) ; i to v, digits. 
 
 the broad basis laid down in his extensive researches into the 
 limb-skeleton of representatives of the chief types of terrestrial 
 Vertebrata. In only one of these was Gegenbaur unable to reach 
 a perfectly satisfactory conclusion, and that was in Man himself. 
 It was reserved for Eosenberg, ten years later, to establish the 
 fact, that the centrale in an early stage of development (i.e. at the 
 beginning of the second month of intra-uterine life) is a distinct 
 carpal element. By this discovery the chain was completed, 
 Man forming the last link. 
 
 Eosenberg's discoveries were soon confirmed and extended by 
 other anatomists, among whom may be mentioned Leboucq and 
 von Bardeleben. The former proved that the centrale did not 
 vanish, as Eosenberg believed, i.e. it was not resorbed, but incor- 
 porated into the radiale (scaphoid) in the second half of the third
 
 THE SKELETON 81 
 
 month of fcetal life, giving rise to a prominence which can be 
 recognised in the adult. This prominence is present also in the 
 Chimpanzee, the Gorilla, and Hylobcdes ; and as the centrale is 
 most probably distinct in the embryo of these, it may well be 
 that in them, as in Man, its independent existence has not long 
 been suppressed. Further confirmation of this is afforded by the 
 fact that it is still an independent bone in 0'4 per cent of even 
 adult human beings, and that, normally, it retains its independence 
 in the Orang and in most Monkeys. 
 
 In many Mammals (especially Marsupials, Rodents, and Insectivores) 
 cartilaginous or bony skeletal elements occur on the outer and inner borders 
 of both fore- and hind-limbs, which not only bear a superficial resemblance 
 to the digital skeleton, but may in some cases be clad, like the true digits, in 
 either a claw or a callous horny integument. Similar structures occur in 
 many of the lower Vertebrates (Reptiles and Amphibians). These organs 
 were formerly considered by both von Bardeleben and myself to be vestiges 
 of now vanished digits, and were named by us " praepollex," " prrehallux," 
 and " postminimus." 
 
 I have, however, entirely changed my opinion as to the supposed atavistic 
 nature of these structures, and now agree with others that these "super- 
 numerary rays," whether they occur in the lower or the higher Vertebra ta, 
 are to be regarded rather as progressive structures of convergent and second- 
 arily adaptive significance. Baur has contended, before all others, that the 
 facts of palaeontology favour the view that the terrestrial Vertebrata never 
 possessed more than five rays in the skeleton of either fore- or hind-limb ; 1 
 and my own recent investigations into the development of the limb-skeleton 
 entirely confirm this conclusion. 
 
 From this point of view, the condition of " hyperdactyly," which not ~*j 
 infrequently appears in Man and is often inherited for many generations, 
 loses its supposed atavistic significance. 
 
 THE SKELETON OF THE HIND-LIMB 
 
 The human femur usually bears at its head two processes for 
 muscular attachment, known as the trochanters, inasmuch as 
 they give insertion to the rotator muscles of the limb. Special 
 interest centres in the not infrequent presence of a, third trochanter 
 (&'"., Fig. 58), a development of the roughened area (tuberositas 
 glutealis) which occurs on the external border of the bone 
 
 1 [It is an interesting corollary to this, that the only fossilised limb in which any- 
 thing comparable to a sixth digit has been found, is a fore-limb which, if not actually 
 Mammalian, is that of a Reptile with Mammalian characters (Tlicriodesmus, from the 
 Mesozoic beds of South Africa, cf. von Bardeleben, Proc. Zool. Soc., Lond., 1889, p. 
 259 ; and Seeley, Proc. Roy. Soc., Lond., vol. Iv. p. 227). Nor must it be forgotten 
 that the " prahallux " in its most highly differentiated and digit-like form (Frogs 
 and Toads) is cartilaginous, i.e. so constituted that it would not be preserved in the 
 fossil state.] 
 
 G
 
 S-2 
 
 THE STRUCTURE OF MAN 
 
 in question. This third, or gluteal trochanter, may be ac- 
 companied by a more or less extended ridge (cr., Fig. 58) or by a 
 pitlike depression. It is found in about 30 per cent of European 
 skeletons ; 1 in Negroes its occurrence is less frequent, and in the 
 Anthropoids it is still rarer. 
 
 In the Lemuroidea, on the other 
 hand, the third trochanter is almost 
 always developed. Dollo attributes 
 its gradual disappearance in Man to / 
 certain modifications which, in the 
 course of time, have taken place in 
 the glutens maximus muscle. In the 
 Lemuroids this muscle passes direct 
 to the femur, and the development of 
 a third trochanter is unquestionably 
 an outcome of this association; but 
 in Man, the gluteus maximus is 
 partially inserted into the fascia lata 
 investing the superficial parts of the 
 limb ; and this shifting of its attach- 
 ment would appear to have led to an 
 
 FIG. 58. PROXIMAL HALF OF A accompanying degeneration of the 
 LEFT HUMAN FEMUR POSSESSED , . , . 
 
 OF THREE TROCHANTERS, Pos- third trochanter. 
 TERIOR ASPECT. In the Anthropoid Apes the 
 
 ur, 
 
 into the fascia lata has gone much , 
 farther than in Man, i.e. this muscle has in them deviated I 
 farther from its original condition [in which we find it in many ) 
 quadrupedal types], and the occurrence of the third trochanter 
 is therefore much less frequent. 
 
 The lower part of the leg (fore-leg) has, like the lower part 
 of the arm (forearm), but to a far higher degree, undergone 
 great modifications in length in the races of mankind. The 
 variations of the human tibia, indeed, are greater than those of 
 any other bone in the skeleton. Apart altogether from variation 
 in length, the term platyknemia is applied to a peculiar condition 
 associated with great compression of the tibia. This is found 
 in the lower races, accompanied by a strong development of the 
 tibialis posticus muscle, and in skeletons belonging to prehistoric 
 times. 
 
 1 [Treves has recently called attention to a case in which it could be readily 
 detected in the livin gperson (Jour. Anat. and Phys., vol. xxi. p. 325).]
 
 THE SKELETON 83 
 
 In the lower Mammals both tibia and fibula articulate with 
 the femur, and contribute to the formation of the knee-joint. 
 In Man, under advancing phylogenetic development, the weight 
 of the body has come to rest on the tibia alone, and the proximal 
 end of the fibula has become disconnected from the femur, 1 
 and has shortened and shifted downwards along the postero- 
 external surface of the tibia. 
 
 The human fibula- is now an appendage of the tibia, and the 
 fact that its degeneration has not gone farther 2 is accounted 
 for partly by its important connection with the heads of certain 
 muscles of the leg (especially the peronei), and by the part which 
 it plays in the formation of the ankle (external malleolus). 
 
 The external condyle of the tibia varies very much in different 
 races. In the lower races it is much more convex than in the 
 higher, and this is probably also the case in the oldest prehistoric 
 men. This convexity is evidently connected with the frequent 
 strong flexure of the knee-joint, such as occurs in squatting. 
 
 On the inner border of the distal extremity of the tibia 
 | (malleolus internus) there is, in the lower races, a special facet 
 ' which articulates with the neck of the astragalus ; and the presence 
 I of this may be also connected with the strong " dorsal flexion " 
 consequent on the squatting posture. The astragalo-tibial articula- 
 tion thus formed rarely occurs in the higher races ; but parallel 
 modifications of both the upper and lower ends of the tibia occur 
 in the Anthropoids and among the lower Apes (Arthur 
 Thomson). 
 
 Until approximately the seventh month of fcetal life, the 
 tibial malleolus is larger than the fibular, projecting downwards 
 farther than the latter. In the seventh month the two appear 
 about equal, and then the fibular malleolus begins to take the lead. 
 These phases of development are accompanied by corresponding 
 modifications of the astragalus (Gegenbaur). 
 
 That the earlier condition of these bones is the inherited one 
 seems probable from comparison of those of the Lemuroidea, Apes, 
 and lower human races. Fig. 59 illustrates the manner in 
 which the external or fibular malleolus (c/.) gradually, in adaptation 
 
 1 [The human fibula has been stated by Leboucq, Bernays, and others, to be 
 during early development in contact with the femur, from which it would appear that 
 the loss of connection between the two takes place ontogenetically. Griinbaum, 
 examining the parts with extreme care, has lately shown (Jour. Anal, and Phys., 
 vol. xxvi. p. xx.) that this is not the case from the period of primary differentia- 
 tion of the parts in cartilage onwards.] 
 
 2 In many lower Mammals it has still further degenerated.
 
 84 THE STRUCTURE OF MAN 
 
 to the upright gait, becomes longer than the internal or tibial 
 (c.*.) ; and also how the astragalus (as.} and calcaneum (cZ.) which 
 originally slope laterally outwards, shift inwards, i.e. towards the 
 pre-axial side, so that they come more into a line with the long 
 axis of the tibia. 
 
 The above-described modifications find a parallel in certain 
 most important changes which the foot itself is even now under- 
 going. To understand these rightly we must enter somewhat into 
 detail, in order to gain an insight into the primitive history of 
 the human foot. 
 
 Thanks to Comparative Anatomy and Development, we have 
 
 FIG. 59. THE UPPER ANKLE-JOINT, POSTERIOR ASPECT. 
 
 A, adult Chimpanzee ; B, Australian native ; C, Caucasian, to show the increasing length 
 of the malleolus fibularis (c.f. ), and the difference in the position of the astragalus 
 (as.) and calcaneum (cl. ) in relation to the long axis of the tibia, in passing from 
 the lower to the higher type. 
 
 obtained a sufficiently correct estimate of the skeleton of the 
 limbs in general, to grasp the essential points in the plan of 
 structure common to the hand and foot. The fact that there are 
 obstacles in the way of obtaining a perfectly clear insight into 
 this matter need not surprise us, when we take into account the 
 long series of adaptations which have resulted in the human 
 limbs ; indeed, we can no longer expect to find the primitive condi- 
 tion retained in either the fore- or the hind-limb. If the fore-limb 
 has been transformed from an ambulatory to a prehensile organ, 
 the hind-limb has already reached a third stage in progressive 
 modification as, having first served for support and locomotion, 
 it next became transformed into a grasping organ (as is proved 
 by the musculature of the sole of the foot, and by the Ape-like 
 apposable condition of the great toe during foetal life), and
 
 THE SKELETON 
 
 85 
 
 finally, on the assumption of the upright gait, it has changed 
 back into an ambulatory appendage. 
 
 This ultimate modification has been accompanied by the greater 
 development of the tarsus, and 
 by the concomitant degeneration 
 and decreasing mobility of the 
 phalanges ; and, correlatively, the 
 foot has acquired a disposition at 
 a wider angle to the fore-leg, and 
 has become arched in adaptation 
 to its supporting function. 
 
 These repeated changes of 
 function may well have resulted 
 in great structural changes, 
 which we may now consider in 
 some detail. 
 
 First, comparing the skeleton 
 of the human foot with that of 
 the Anthropoid Apes, we find the 
 former distinguished by the fol- 
 lowing three points (cf. Figs. 60 
 and 62): 
 
 (1) Stronger development of 
 the great toe. 1 
 
 (2) Greater development of 
 the tarsal elements. 
 
 (3) Displacement of the great 
 
 toe into a position of parallelism Fl - ^.-SKELETON OF THE LEFT PES 
 
 x OF A CHIMPANZEE, DORSAL ASPECT. 
 
 With the Other toes. ec>> ec to-cuneiform ; en., ento-cuneiform ; 
 
 If the foot of a second 
 month's human foetus be ex- 
 amined, with special regard to 
 the last point, it will be seen (Fig. 63, B) that the position of 
 the great toe almost entirely agrees with that of the thumb 
 (63, A). When the limbs are laid against the trunk, both point 
 towards the head in the position of abduction. 
 
 Whereas this is the normal lifelong position of the great toe 
 of the Apes, and of the human thumb (cf. Figs. 60 and 61) in 
 the human foot it is merely transitional, and is abandoned 
 
 1 We have herein a noteworthy contrast to most of those lower Mammals in 
 which the great toe is reduced, or has altogether disappeared. A claw may in the 
 former case be found at its distal end (e.g. in the Dog), but even that may disappear. 
 
 ms., meso-cuneiform ; cb., cuboid ; m\, 
 navicular ; as., astragalus ; cl. t cal- 
 caneum ; I-V, digits.
 
 86 THE STRUCTURE OF MAN 
 
 as early as the eighth week of foetal life. The definitive 
 position (Fig 62) is, however, very gradually reached; for it is 
 a well-known fact that the mobility of the great toe is far more 
 marked in children at birth and in the earliest years of life than 
 in adult Europeans. 1 In certain races (e.g. the 
 
 FIG. 61. SKELETON OF THE LEFT HAND, DORSAL ASPECT. 
 
 c/., cuneiform ; lu., lunar ; mg., magnum ; pc., pisiform ; sc., scaphoid ; tp., 
 
 trapezium ; tpz. , trapezoid ; un. , uneiform. I- V, digits. 
 
 a considerable mobility is often retained throughout life ; and 
 the uses to which the great toe can be put fill a European with 
 astonishment. 
 
 Balz, in his work on The Bodily Characteristics of the 
 Japanese, says : " The use made by the Japanese of the great 
 toe as a kind of thumb is very remarkable ; it can be independ-- 
 
 1 The foot of a child which has not yet learnt to stand or walk is a particularly 
 interesting study. Not only are the toes capable of performing complex movements 
 (the great toe being even utilisable for grasping purposes), but the sole or plantar 
 surface of the foot, in its form and in certain of its furrows, resembles the palm of 
 the hand far more than later, when socks and shoes have exercised an influence 
 upon it.
 
 THE SKELETON 
 
 87 
 
 ently moved, and so strongly pressed against the second toe that 
 even small objects can be firmly held between them. A woman, 
 when sewing, may hold the stuff with her toes, stretching it as 
 she pleases; and it is asserted that Japanese women can pinch 
 effectively with their toes. In general, the foot of the Japanese 
 has retained much of its natural mobility. These people seem 
 
 FIG. 62. SKELETON OK LEFT FOOT, DORSAL ASPECT, FOR COMPARISON 
 
 WITH FIGS. 60 AND 61. 
 
 as. (tb. + in.), astragalus (regarded as a product of fusion of the tibiale and intermedium of 
 the lower vertebrata) ; cb., cuboid ; cl. (fb.), calcaneum (tibulare) ; ec., ecto-cuneiform ; 
 en., endo-cuneiform ; ms., meso-cuneiform ; nv. (C), navicular (centrale) ; I-V, digits ; 
 1-5, tarsalia. 
 
 to be able to hold on to the ground with the sole of the foot ; 
 and therefore when they need to stand firmly, as in fighting and 
 wrestling, they are always barefooted. The first time one sees 
 a Japanese man walking about with ease on a steep house-top as 
 if on level ground, it makes one feel quite uncomfortable, but
 
 88 THE STKUCTUEE OF MAN 
 
 no fear of his falling need be entertained, for his foot accurately 
 adapts itself to the surface of the roof ! " 
 
 [Although the great toe of the adult human subject may be 
 thus thumb-like in function, an important difference between 
 the hallux and pollex exists, in the inconstancy in relation 
 to the former of an opponens muscle, such as is present in the 
 manus, and more generally in both manus and pes of the 
 anthropoid Apes. The act of grasping by the human hallux 
 differs from that by the pollex in being one of mere adduction 
 and closer apposition of the first and second digits.] 
 
 The cousins Sarasin have pointed out, that in the Veddah's 
 foot the great toe stands apart from the other toes, and that the 
 last four metatarsals are turned towards the first one more than 
 in a European foot. The whole foot is also flatter, as can be 
 observed in the living state. [In dealing with this comparison 
 allowance must be probably made for the use of the boot.] A more 
 important distinction, from the comparative anatomical point of 
 view, is that the tarsus is markedly shorter and narrower than that 
 of the European. If 100 be taken as the length of the second 
 metatarsal in a European, then 163 would represent the length 
 of the tarsus; in the Veddah it is 152, in the Gorilla 145, and 
 in the Chimpanzee 113, so that the tarsus is found to decrease 
 in length as we descend in the series. A similar diminution in 
 breadth is also recognisable. 
 
 According to Pfitzner, whose accurate observations on the 
 variations in the human pedal skeleton are of special interest, the 
 variations in the proportions of the foot, e.g. in the length of the 
 metatarsals and phalanges, are far greater than those of the 
 hand. This applies especially to the great toe and its 
 metatarsal ; and correlatively, the ento-cuneiform is much more 
 liable to variation than are the meso- and ecto-cuneiform. The 
 so-called Lisfranc's line is also liable to variation in its course, 
 and this especially applies to the third tarso-metatarsal articula- 
 tion. The latter does not as a rule continue the line of the 
 fourth tarso-metatarsal articulation, but makes an angle with it, 
 consequent upon the mode of articulation between the ecto- 
 cuneiform and the fourth metatarsal, which is prolonged back- 
 wards. Here, as well as in the hallux, we have to deal with 
 recent variation (Pfitzner). The great toe is in men not only 
 absolutely but relatively longer than in women, and this is 
 true of the thumb also, a slight confirmation of the well-known 
 saying that women represent the conservative and men the
 
 THE SKELETON 
 
 89 
 
 progressive element in human development in other words, 
 the greater development of the thumb and the great toe of the 
 male must be considered as a recent acquirement. Accom- 
 panying this difference in the first toe, we note also the 
 slighter reduction of the length of the other toes, and especially 
 of the middle phalanges, in Man, as compared with woman. Man 
 has, as a rule, the original elongated type of toe A 
 
 woman the shortened and compressed type. 
 Further interesting results might be 
 obtained by a careful comparison of the tarso- 
 metatarsal joint of the first toe in the various 
 human races and in the Apes. 
 
 While, thus, progressive development takes 
 place on the inner or tibial side of the foot 
 as the result of functional adaptation, the 
 following retrogressive processes take place 
 on the outer or fibular side : 
 
 The little toe is not infrequently two- 
 jointed, the middle and terminal phalanges 
 being synostotically confluent. Pfitzner found 
 this to be the case in thirteen out of forty- 
 seven examples. This fusion, which is, as a 
 rule, found on both feet, is not due to the 
 pressure of shoes or to any other mechanical 
 causes, 1 but to the fact that the little toe 
 and its metatarsus 2 are in process of degene- 
 ration. This process of reduction, which 
 may end in the little toe becoming in a measure like the thumb 
 and great toe, two-jointed, is particularly interesting, as it is 
 taking place, so to speak, under our eyes. All stages from 
 incomplete to complete fusion can be observed. Further, this 
 degeneration of the little toe apparent in these facts can also 
 be gathered from the condition of its muscles; [of these the 
 flexor brevis often sends either but a very weak offshoot to the 
 little toe, or, like the extensor brevis, none at all.] 
 
 1 I find this synostosis also present in the skeletons of Egyptian mummies of 
 various ages, not excluding children. It may here be remarked that, according to 
 Balz, among the Japanese, who do not wear shoes, the little toe appears quite as 
 reduced as in the European foot. 
 
 2 We are at present unable to deal with the question of the significance of the 
 independent origin of the fifth metatarsal tuberosity, which is the more surprising 
 in consideration of the frequency of retrogressive processes on the fibular side of 
 the foot. 
 
 right hind -limb, of a 
 
 uterine life, to show 
 
 thumb and the great toe
 
 90 
 
 THE STRUCTURE OF MAN 
 
 It should, in passing, be noted that the mutual relationships between the 
 muscles and bones are not absolutely similar in every single case, although a 
 general agreement exists. The undeniably close connection between the 
 modifications of two must not be regarded as that of cause and effect, but 
 rather as the joint effect of a common cause. 
 
 Clear signs of degeneration are also to be found in the other 
 toes, and especially their middle phalanges, while the terminal and 
 
 FIG. 64. POSTERIOR END OF THE BODY OP TWO HUMAN EMBRYOS, WITH THE 
 
 LEFT HIND-LIMB AND UMBILICAL CORD. 
 
 A, at the end of the seventh week ; B, in the middle of the eighth week. The position 
 of the great toe (I) is noteworthy, c.u., umbilical cord ; cc., coccygeal eminence. 
 
 basal phalanges may be also affected. The second toe is mostly free 
 from signs of degeneration: its middle phalanx shows a disposition 
 to shorten, but it at the same time tends to become stronger 
 rather than weaker. It might, therefore, be predicted of the 
 human foot that it may end by possessing only two two-jointed 
 toes, the great toe and its neighbour ; l but the possibility of 
 
 1 [It may be questioned whether it would not be more correct to predict, provided 
 there is anything in this argument at all, that all the toes with the exception of the 
 second may ultimately become two-jointed.]
 
 THE SKELETON 91 
 
 development in other directions such as might counteract the 
 present tendency must, however, be allowed for (Pfitzner). 1 
 
 COMPARISON OF THE FORE- AND HIND-LIMBS OF MAN 
 
 In comparing the opposite extremities of the adult two 
 difficulties have to be met, the first being that the knee and elbow- 
 joint bend in exactly opposite directions, and the second that, 
 owing to the inward rotation of the fore-limb, the homologous 
 bones of the fore-arm and fore-leg (radius and tibia, ulna and 
 fibula) are differently disposed. 
 
 Martins and Gegenbaur have endeavoured to explain these 
 difficulties by spiraljrotation of the humerus during development 
 said to be effected by alteration in growth of the epiphysial 
 cartilage, with the addition of bony tissue at some points and its 
 resorption at others. The distal end of this bone has its 
 original ventral surface turned dorsally and vice versd. By 
 comparing the position of the hiunerus in embryos and adults it 
 is found to rotate through an angle of about 35 (Gegenbaur). 
 
 Spiral rotation of the humerus actually takes place, not only 
 in Man, but very commonly in other Vertebrates. It can further 
 be proved that it progressively increases as we pass from 
 the lower to the Caucasian races ; and Broca affirms that an 
 increase is to be found at different epochs within the same race. 
 
 But although the torsio humeri is an undoubted ontogenetic 
 fact, according to more recent authors, it is questionable whether 
 it affords any explanation of the difference between the fore- and 
 hind-limbs. This subject is so important that we must enter 
 into it at some length, referring especially to the works of Hatschek 
 and Holl. The first of these investigators has rightly taken for 
 comparison the lowest terrestrial Vertebrata, the tailed Amphibia, 
 and he lays emphasis upon the fact that in these animals the 
 position of the fore- and hind-limbs in relation to the trunk is 
 almost identical. Both stand out at right angles to the long axis 
 
 1 [It appears to me that the occasional longitudinal subdivision of the human 
 hallux-tarsal (ento-cuneiform) into two distinct bones may be not improbably a 
 phenomenon akin to that of the double ossification of the supra - occipital under 
 expansion (cf. ante, p. 60), if not an actual index of progressive development 
 now at work. My friend Professor Arthur Thomson informs me that, from a study 
 of the articular surfaces of this bone, he believes the tendency towards duplication 
 to be more general than is customarily assumed ; and it would be most interesting 
 to inquire whether among the Seals and Wall-uses, in which the inner and outer 
 digits are one or both similarly dominant over the rest, indications of a correspond- 
 ing variation might not be forthcoming in the foetal state. G. B. H.]
 
 THE STRUCTURE OF MAN 
 
 of the body. The elbow and knee joints are turned slightly 
 outwards, the convexity of the former facing slightly backwards, 
 that of the latter slightly forwards. The supporting portion of 
 the limb looks in both cases outwards, and in each the anterior 
 digit is rightly considered as the first of the series. 
 
 FIG. 65. LARVAL SALAMANDEB. (After Hatschek.) 
 A, with the limbs turned down ; B, with the limbs turned up. 
 
 In the higher Quadrupeds the anterior and posterior limbs 
 undergo characteristic changes of position. First, the supporting 
 segments of the two limbs (i.e. the manus and pes) are rotated 
 inwards, so that their long axes, which were originally transverse 
 to that of the body, come to be parallel with it [and their 
 originally anterior borders become internal] ; as a natural result of 
 this, the first digit (pollex or hallux) becomes the innermost and 
 the fifth the outermost. The rest of the limb, however, differs in 
 its behaviour in the two members. In the fore-limb the humeral 
 and radio-ulnar segments become flexed in such a way that the 
 elbow is no longer directed outwards but backwards (cf. Fig. 65). 
 In the hind -limb, on the contrary, the basal (femoral and 
 tibio-fibular) segments are turned inwards, and so flexed that 
 the knee is directed forwards. According to Hatschek the 
 differences in position of the fore- and hind-limbs involve only 
 their basal segments, their terminal segments (manus and pes) 
 being displaced identically. It would follow from this that the 
 changed position of the fore-limb has little if anything to do with 
 the torsion of the humerus, which is very marked even in the 
 Salamander, and must therefore be referred back to an early 
 process antecedent to the changes under discussion.
 
 THE SKELETON 
 
 93 
 
 Holl also repudiates the torsio humeri as the most important 
 factor in effecting the torsion of the fore-limb. He, unlike 
 others, considers that there is no very great difference between 
 the position of the bones of the 
 forearm and the fore-leg in Man. 
 He rightly points out that the 
 tibia and fibula do not lie parallel, 
 but that the fibula lies external to 
 and behind the tibia, and insists 
 that it thus occupies, in relation 
 to the tibia, a position similar to 
 that of the ulna in relation to the 
 radius. 1 In instituting these com- 
 parisons we ought to start with *&% ^jj&jd. YJ/ tl -'"}[\\ -f 1 - 
 the hind-limb, which is simply 
 so rotated at its base that the 
 whole of its morphologically ven- 
 tral surface becomes posterior in 
 position, and not with the fore- FlG - GG.-SKELETON OF A YOUNG BEAR 
 
 f. ILLUSTRATING THE POSITIONS OF THE 
 
 limb, the torsion of which involves 
 the independent segments individ- 
 ually, and should therefore be 
 excluded in endeavouring to settle the question of homology. 
 This consideration excepted, Holl agrees in the main with 
 Hatschek as to the Quadrupeds ; but he extends his observations 
 to Man, and declares that if he be regarded as a Quadruped, the 
 changes of position in the limbs are such that the homologising 
 of them with those of Quadrupeds is not difficult, i.e. if a man 
 goes on all fours the position of the shoulder girdle and with it 
 that of the humerus is slightly altered. The head of the latter 
 no longer points forwards, but backwards, and its great tuberosity 
 comes to point forwards, just as in the quadrupedal Mammals, 
 the distinction formerly established between them and Man in 
 this particular thus disappearing. 
 
 1 [Holl appears to have insufficiently appreciated the primary disposition of the 
 limb-buds. The postero-internal displacement of the fibula upon which he lays such 
 stress is well marked in the Marsupials, which, with the exception of the Dasyuridse, 
 have an opposable hallux. Detailed examination of the bones of the fore-leg of 
 some of these animals and of the muscles which control their rotatory (so-called 
 " pronator ") movements, proves that the adaptive modification which the hind-limb 
 has at any rate here undergone is of a distinct order from that of the fore-limb above 
 described (cf. Young, Jour. Anat. and Phys., vol. xv. p. 392). And it may be 
 incidentally remarked that an opposable hallux appears independently among 
 Rodents, in the common Dormouse.] 
 
 LIMBS. (After Hatschek.) 
 1-5, digits ; rd., radius ; ul., ulna ; 
 tb., tibia ; fb., fibula.
 
 94 THE STRUCTURE OF MAN 
 
 For the further study of the processes by which the limbs 
 'are displaced during development, I must refer the reader to the 
 works of von Kolliker, Holl, and others. It should, however, be 
 remarked once more that the twisting of the hind-limb occurs 
 at the hip-joint merely, [and affects the limb as a whole, its 
 originally ventral surface becoming posterior and its dorsal 
 anterior in position, and that in the fore-limb the twisting most 
 conspicuously affects the manus and the forearm, the radius under- 
 going a marked inward rotation upon the ulna. The humeral 
 segment more nearly retains in the adult its original position], and 
 the rotation and retroflexion which it ultimately exhibits chiefly 
 result from a twisting of the shoulder girdle, with accompanying 
 modifications of its articular head. 
 
 These changes in position of the shoulder girdle are connected 
 with the development of the thorax. As long as the latter retains 
 the laterally compressed form characteristic of most Mammals, 
 and is not expanded dorsally, the scapula lies at its side. Later, 
 when transverse enlargement and consequent dorsal expansion of 
 the thorax are effected (cf. ante, p. 36), the scapula comes to lie 
 upon (i.e. dorsad of) it. This change in the thorax plays a leading 
 part in altering the position of the shoulder girdle as a whole, 
 and of the limb attached to it. 
 
 If we wish to homologise the two pairs of limbs scientifically, 
 we can only do so by tracing their displacements back towards 
 their embryonic positions. 
 
 CHANGES OF POSITION OF THE LIMBS IN RELATION 
 TO THE TRUNK 
 
 A comparison of the fore-limb of Man with that of the lower 
 Vertebrates, and especially of the Fishes and Amphibians, and a 
 careful analysis of the courses and relationships of its muscles and 
 nerves with respect to the trunk and the spinal cord, lead us to 
 the conclusion that the shoulder girdle and its associated limb 
 originally lay farther forwards, i.e. nearei^the head. The dis- 
 placement backwards most probably took place, as has already 
 been shown (ante, p. 44), simultaneously with the disappearance of 
 the cervical ribs indeed the loss of the latter certainly helped 
 to bring this about, by compelling the scapula and clavicle to 
 find points of attachment farther back on the thorax. 
 
 Whereas this shifting of the fore-limb takes place from before 
 backwards, that undergone by the hind -limb is from behind
 
 THE SKELETON 95 
 
 forwards, i.e. towards the head. Both these alterations in position 
 are most clearly reflected in the variations of the nerve plexuses 
 of the limbs, the origin of which will be discussed later. We 
 must, however, first ascertain what these variations are. 
 
 The lumbo- sacral plexus, as compared with the brachial, 
 is the more subject to variation, and the less definitive. Even 
 if the brachial plexus does show slight inconstancy, no such 
 marked differences in the origin of its component nerve trunks 
 occur as in the lumbo -sacral. In most cases, these varia- 
 tions in the limb plexuses are accompanied by variations in the 
 vertebral column. For example, when the lumbo-sacral plexus has 
 a markedly caudal origin, a supernumerary prsesacral vertebra 
 usually occurs ; here we have an atavism, i.e. an indication of the 
 primitive arrangement under which, as above described (ante, 
 p. 33), the pelvis lay farther back. But we know that, during 
 ontogeny, the pelvis undergoes a forward translocation. Cor- 
 relatively, the lumbar plexus assimilates nerves lying farther 
 forward than those which primarily formed it (the ileo-hypo- 
 gastric, ileo-inguinal, and the genito-crural), while the posterior 
 sacral nerves of the adult show signs of instability and degenera- 
 tion, and may gradually altogether disappear. 
 
 The forward gathering of the nerves for the hind-limb is 
 naturally accompanied by modification in the innervation of 
 those parts of the urino-genital and alimentary systems which 
 lie in the pelvis. These are obviously dependent on the pelvic 
 girdle, and compelled to follow when it shifts along the verte- 
 bral column. The ischiadic and the pudendal plexuses are so 
 closely connected that they could not in any case be separated ; 
 but the relationship between the pudendal and caudal plexuses is 
 less intimate, and if the former shifts forwards with the crural 
 plexus, its distal elements separate from it. These retrogressive 
 nerves of the caudal region would necessarily increase in number 
 in proportion to the forward translocation of the hind-limb, if 
 the caudal region itself did not at the same time shorten 
 (Eisler). 
 
 We thus have transition zones ; and this becomes the more 
 clear the farther the lumbo-sacral plexus shifts in a proximal 
 direction. In extreme cases variation may extend as far 
 forwards as the eleventh thoracic nerve, which then sends a 
 loop to the twelfth. 
 
 Similar phenomena accompany the backward displacement of 
 the fore-limb, but this, as already mentioned, appears to have
 
 96 THE STRUCTURE OF MAN 
 
 nearly attained its definitive position. 1 The brachial transition 
 zone is consequently more restricted and stable than the lumbo- 
 sacral, rarely extending backwards beyond the second thoracic 
 nerve. If, however, the upper limb preserves its original position 
 (the seventh cervical rib persisting), the brachial plexus receives 
 (either no contribution or at best an insignificant one from the 
 I first thoracic nerve (Eisler). 
 
 Even if this conception of the " metameric transformation 
 of nerves," deduced by Fiirbringer, affords a partial explanation 
 of the existence and present condition of the nerve plexuses, the 
 actual causa movens lies deeper, i.e. in the original polymeric 
 origin of the limbs. In the region from which they develop we 
 meet with traces of a gradual fusion of originally distinct segments 
 (somites), with further clear traces of the shifting which they 
 have undergone during phylogeny. An excellent illustration of 
 the commencement of fusion among the body segments is yielded 
 by the transitional zones just defined. Quite apart from the 
 already-mentioned variations of the nerves, the primitive segmenta- 
 tion of the ventro-lateral body muscles is gradually being obliter- 
 ated, and the myocomniata with the ribs are becoming vestigial 
 in fact the whole ventral body-wall is affected by this process 
 of fusion (Eisler). 
 
 1 That a further shifting of the human fore-limb in an antero-posterior direction 
 may be expected is evident, firstly, from the varying relation of the brachial plexus to 
 the anterior thoracic nerves ; and, secondly, from the very rare, yet occasional, retro- 
 gressive condition of the first thoracic rib before mentioned (ante, p. 43).
 
 MUSCULAR SYSTEM 
 
 As might be expected, we find, in the 200 to 250 muscles 
 which form the active motor apparatus of the human body, 
 variations far greater and more numerous than any already 
 described in the different parts of the skeleton. 
 
 It may confidently be asserted that hardly a single human 
 subject has been examined which has not shown some variation 
 or other in the muscular system ; and in a great number of 
 bodies new muscles are discovered which have not before been 
 observed, and of which no mention can be found in text-books. 
 
 Considering this " embarras de richesse," we may be excused 
 for entering in the following pages somewhat into detail ; it is, in 
 fact, absolutely necessary to do so in order to get a general idea 
 of the immense mass of material available. Of the extent of this 
 variation an approximate idea may be obtained from the fact 
 that my French colleague Testut, in his work of 900 pages on 
 the muscular anomalies in Man, has by no means exhausted the 
 subject. 
 
 Examples will be considered in the following order : 
 
 (1) Retrogressive or vestigial muscles. 
 
 (2) Muscles which, appearing only occasionally, are considered 
 
 to be atavistic. 
 
 (3) Progressive muscles. 
 
 This order cannot be rigidly adhered to, inasmuch as both 
 progressive and retrogressive development have been observed to 
 take place, side by side, in one and the same muscular region. 
 It is further to be noted that those muscles which are actually 
 progressive as far as the genus Homo is concerned, are not recog- 
 nisable as such in mere individuals ; their anomalous conditions 
 can only be considered as individual variations until traced 
 through successive generations, i.e. until it is proved that they 
 are inherited. 
 
 An accurate knowledge of Comparative Anatomy and Ontogeny
 
 98 THE STRUCTURE OF MAN 
 
 is necessary, to facilitate judgment and sharpen observation, in 
 dealing with both progressive and retrogressive variations, which 
 latter are the preliminary stages in degeneration. In the critical 
 examination of the muscles, as pointed out by Fiirbringer and 
 Eucre, it is primarily important to ascertain their innervation. 
 The nerve-supply is the safest criterion as to the morphological 
 value of a muscle. 
 
 RETROGRESSIVE MUSCLES 
 
 OF THE TKUNK 
 
 The dorsal upper and lower serratus are, as is well known, 
 connected together by a strong silvery aponeurosis. This is 
 occasionally replaced by muscular tissue, which, in connection 
 with the upper serratus less frequently with the lower 
 may extend down as far as the sixth rib. This clearly points 
 back to a primitive condition in which the two muscles were 
 continuous. In contrast to this variation there occur others in 
 which the two serrati are much less developed than usual, so much 
 so that one or both of them may be entirely wanting. This is 
 very important, as it leads to the conclusion that the serrati, like 
 many other muscles, are being gradually transformed into tendinous 
 tissue. The cause of this must be sought in the modification of 
 the respiratory mechanism of the thorax, and the same would 
 appear to be the rationale of the many variations of these same 
 muscles observed in the Anthropoids (cf. ante, p. 45). 
 
 The degeneration of the caudal region in the human body 
 has naturally been accompanied by a corresponding reduction of 
 the related muscles, i.e. especially of those the homologues of 
 which, in caudate Mammals, are strongly developed for moving 
 the tail. These are serial with the musculature of the trunk, 
 and can be divided into a ventral and a dorsal group. 'To the 
 latter belong the extensor and levator coccygis, which lie along 
 the posterior surface of the coccygeal vertebrae. This extra- 
 ordinarily thin muscle bundle arises either from the great sacro- 
 sciatic ligament or from the lowest end of the sacrum, and sends 
 out tendinous rays towards the apex of the coccyx. 
 
 To the ventral series belongs the coccygeus muscle, which 
 arises from the spine of the ischium, runs along the lesser sacro- 
 sciatic ligament, and is inserted into the lateral edge of the coccyx. 
 This muscle brings about the lateral movement (abduction) of
 
 MUSCULAR SYSTEM 99 
 
 the tail in the lower Mammals, and is therefore termed in them 
 the abductor caudalis. 
 
 The curvator coccygis, which is met with on the anterior 
 surface of the lower sacral and sometimes of the upper caudal 
 vertebrae, belongs to this same category. It corresponds with 
 the depressor caudae of the lower Mammals. 
 
 The vestigial character of all these muscles is in several ways 
 evident. They vary in form and size, and may be partly or 
 wholly replaced by fibrous tissue, or, finally, one or other of 
 them may be altogether wanting. This is also the case in the 
 Anthropoids, where (e.g. in the Orang) their vestigial character is 
 in some ways more pronounced than in Man. 
 
 Another caudal muscle may here be referred to, although 
 morphologically it does not belong to the above-mentioned series. 
 This is the caudo-femoralis (agitator caudae) which, in a large 
 number of Mammals (Monotremata, Marsupialia, most Carnivora, 
 Lemuroidea, and tailed Monkeys) plays a great part, as flexor 
 and abductor of the tail when the thigh is fixed, and which, in 
 exceptional cases, appears in Man also. It lies at the lower edge 
 of the gluteus maximus, being separated from it by only a small 
 space. It arises from the lateral edge of the coccyx or of the last 
 sacral vertebra, and is inserted into the femur below the point of 
 attachment of the lowest bundle of the gluteus. 
 
 Normally, this muscle is wanting in Anthropoids, but it is 
 not improbable that it may occasionally reappear in them as in 
 Man. 
 
 In both the dorsal and ventral trunk muscles we find indica- 
 tions of original segmentation. In the intercostal muscles the 
 segmentation is completely retained, and not infrequently tendons 
 pass from the ends of the lower ribs into the broad abdominal 
 muscles. Cartilaginous tracts are sometimes found persisting in 
 a line with these tendons, but nearer the median plane, and 
 they may be either free or connected with the tendons. Even 
 in cases where all such indications are wanting, the innervation 
 of these muscles points to a primitive metamerism. 
 
 In the same way, the rectus abdominis, by its " inscrip- 
 tiones tendineae," shows a more or less distinct segmentation. 
 
 This muscle in the lower Vertebrates (e.g. tailed Amphibians) 
 extends from the pelvis to the head region ; but in the higher 
 Vertebrates, and particularly in Mammals, in accordance with 
 advancing modification, and especially with the intervention of 
 the sternal apparatus, it has become divided into a posterior and
 
 100 THE STRUCTURE OF MAX 
 
 an anterior tract. The former arises from the pelvis, and is 
 inserted anteriorly, as a rule, on a level with the fifth rib ; the 
 latter is represented by the ventral cervical muscles, viz. the 
 sterno-hyoid and sterno- thyroid, which here and there bear 
 inscriptiones tendineae indicative of their former segmentation. 
 To these must be added the almost constant omo-hyoid, which 
 is provided with an inscriptio, and the thyro-hyoid. Farther 
 forward these are joined by the hyo-glossus, genio-hyoid and 
 genio-glossus, which belong to the same metameric series. 1 
 
 In the lower Primates the rectus abdominis muscle still 
 reaches to near the first rib, and thus recalls the connection 
 with the cervical musculature mentioned above, which was first 
 lost in the Reptiles. Even in Man it may sometimes run beyond 
 the fifth rib and, under cover of the pectoralis major, pass as far 
 up as the second. This is a striking case of atavism. 
 
 In the higher Primates the thoracic head of this muscle 
 shifts back to the lower ribs, and this shifting towards the 
 abdominal region is accompanied by an advancing loss of 
 segmentation in both the Anthropoids and Man. 2 But even 
 where this is most marked the muscle has not quite lost its 
 thoracic character. 
 
 This retreat of the rectus muscle is intimately connected 
 with the development of the great adductor of the fore-limb (the 
 pectoralis major), since it is only when the upper parts of the 
 rectus disappear that the muscular bundle forming the pectoralis 
 major and, indeed, that forming the pectoralis minor as well 
 is able to take possession of the firm anterior thoracic surface 
 furnished by the ribs. Where, as in the lower Apes, the anterior 
 end of the rectus muscle covers the thorax as far as the lateral 
 edges of the sternum, a primitive condition being thus retained, 
 those fasciculi of the pectoral muscles which arise from the 
 skeleton come simply from the sternum. " We here have a con- 
 flict at close quarters between different parts of the organism " 
 (Huge). 3 
 
 In connection with his studies of the abdominal musculature, 
 
 1 [Cf. Albrecht. Beitrag z. Morphologic des M. omo-hyoides u. d. ventr. inneren 
 Interbranchialmusculatur i. d. Reihe d. IVirbelthiere. Inaug. Diss., Kiel., 1876.] 
 
 2 In many cases the muscle withdraws in a distal direction even farther than 
 the fifth rib, and derives its anterior (uppermost) slip from the sixth. A primitive 
 slip from th eighth rib may also be retained (Ruge). 
 
 3 Where, as a rare anomaly, the rectus abdominis is double on one or on both 
 sides, a very low condition is indicated, this arrangement being typical in Amphibia 
 and Saurians.
 
 MUSCULAR SYSTEM 101 
 
 Kuge has called attention to a phylogenetic shifting of the navel. 
 This occurs during the shortening of the thoraco-lumbar portion 
 of the trunk (in relation to the segments of the rectus abdominis), 
 and is accompanied by a gradual elimination of the posterior 
 segments of the rectus. This process may not be yet finished ; 
 if, as has already been argued in dealing with the vertebral column 
 (ante, p. 43), a progressive abbreviation of the thoracic region of 
 the trunk is still taking place. 
 
 In front (ventrad) of the point of origin of the rectus 
 abdominis, at the upper edge of the pelvis, there lies, in Man, 
 the inconstant pyramidalis abdominis muscle. This is sometimes 
 developed only on one side, and sometimes unrepresented, in 
 which case it may be replaced by a tract of fibrous tissue. On 
 the other hand, either one or both halves of this muscle may be 
 double ; and there are variations no less remarkable in its form 
 and size. The pyramidalis usually runs either about half-way from 
 the symphysis pubis to the navel, or only a third of that distance ; 
 it may sometimes, however, reach as far as the navel. In young 
 children it is relatively larger than in adults. These facts rnay 
 all be taken as evidence that the pyramidalis in Man (and the 
 same applies to many Mammals, e.g. the Anthropoids) possesses 
 all the peculiarities of an organ which has long been in a state 
 of degeneration. It claims our attention principally as a striking 
 example of the tenacity with which certain structures remain 
 in the organism and are handed on, through inheritance, long 
 after they have lost their specific significance. The reason for 
 such continuance can only be that, in the course of phylo- 
 genetic development, the muscle has undergone a change of 
 function, and has become associated with or subordinated to 
 other muscles or groups of muscles. In this case the pyramidalis 
 has been overmastered by the rectus abdominis. 
 
 In the non-placental Mammals (Monotremata andMarsupialia) 
 the pyramidalis is powerfully developed in connection with 
 the epipubes (so-called marsupial bones) ; and even in some 
 Placentalia, such as the Insectivora (e.g. Myogale pyrenaica), it may 
 almost reach the ensiform process of the sternum, thus playing 
 an important part in strengthening the abdominal wall. The 
 pyramidalis is undoubtedly an old muscle dating far back to 
 pre-Mammalian times. 
 
 Both the abdominal oblique muscles may be considered as 
 continuations of the intercostal muscles into the abdominal region, 
 and, anteriorly, the scaleni muscles of the neck may be looked
 
 102 THE STRUCTUKE OF MAN 
 
 upon as forward extensions of the same. The neck, as has been 
 seen from the study of the skeletal system (ante, p. 43), was 
 formerly provided with free ribs ; and hence this serial relation- 
 ship of the cervical to the segmental thoracic muscles is easily 
 understood. The degeneration of the cervical ribs has had 
 (among other results) the effect of causing the short-fibred scaleni 
 muscles, which once only stretched across the intercostal spaces, 
 to unite and grow longer, so as finally to reach ribs which lie 
 farther back. Further related modifications may be exemplified 
 in the occurrence of supernumerary scaleni, such as the scalenus 
 minimus (scalene intermediaire, Testut), which is typically present 
 in all Anthropoids, and by the numerous variations in origin and 
 attachment of the three ordinary scaleni. 
 
 The transversus thoracis muscle (triangularis sterni) is clearly 
 degenerating. This muscle, which lies on the inner side of the 
 anterior wall of the thorax, arises from a variable number of slips. 
 It arises, as a rule, from the cartilages of the third to the sixth 
 ribs, and occasionally receives a slip from the seventh rib also. 
 This fact helps us in homologising it as a continuation of the 
 transversalis abdorninis. These two muscles are separated by one 
 of the bundles which give rise to the diaphragm. 
 
 THE MUSCLES OF THE CERVICAL AND CEPHALIC EEGIONS 
 
 In addition to the structural changes going 011 in the scaleni, 
 which have been already mentioned, the following facts are worth 
 recording : 
 
 The original community of the trapezius and the sterno- 
 cleido-mastoid muscles is indicated by their common innervation, 
 and further by the fact that the interval between them is still 
 not infrequently occupied by the cleido-occipitalis which runs 
 from the clavicle to the occipital bone. This muscle thus forms 
 a link between the trapezius and the sterno-cleido-mastoid, 
 and when strongly developed brings about a more or less 
 complete fusion of these two muscles, i.e. reinstates the original 
 condition. 
 
 These facts might have been included in the remarks on 
 muscles which occasionally appear and may be considered atavistic, 
 but they are here dealt with as they indicate a gradual dis- 
 appearance of certain fibrous areas in the region of these muscles, 
 i.e. they point to a retrogressive condition. 
 
 A similar relationship exists between the anterior belly of
 
 MUSCULAR SYSTEM 103 
 
 the biventer maxillae (digastricus) and the mylohyoid (as may be 
 gathered from their innervation), while the posterior belly of the 
 former may sometimes fuse with the stylohyoid. 
 
 Undoubtedly the most interesting of all the retrogressive 
 
 muscles of the cervical region is the so-called platysma myoides 
 
 (subcutaneus colli). This muscle is also related, as will be 
 
 shown later, to certain cephalic muscles, and requires a more 
 
 detailed description (cf. infra, pp. 104 and 114). 
 
 Whereas most muscles are closely connected with the skeleton, 
 there are, in the Vertebrates, certain muscles which both arise 
 from and are inserted into the integument or the subcutaneous 
 tissues. These are the cutaneous muscles (panniculus carnosus 
 of the lower Mammalia). 
 
 These cutaneous muscles are [with rare exceptions] only 
 feebly developed among Fishes and Amphibia, but in Eeptiles 
 and Birds they play a great part in connection with the scutes, 
 scales, and feathers. They are, however, most developed in 
 Mammals, in which they may spread like a mantle over the back, 
 head, neck, and flanks (e.g. Echidna,Dasypus, Pinnipedia, Erinaceus, 
 and others). 
 
 In Man and the Anthropoids only feeble traces of this 
 musculature are found, such as the platysma-myoides already 
 mentioned, which spreads over the upper part of the thorax and 
 the neck and partly over the face (cf. Fig. 67). Other slight 
 traces are found in the shoulders, back, abdomen, axilla, forearm, 
 hand, and buttocks. 
 
 Among the lower Mammalia the panniculus carnosus functions 
 as a protective against injury to the skin. The reaction of the 
 skin of horses when stung by insects may be given as an example 
 of this. 
 
 The mimetic musculature is very closely connected with the 
 cutaneous, and is at least partly to be derived from it phylo- 
 genetically. In a general sense, the differentiation of the 
 mimetic musculature may be said to advance with advancing 
 intelligence ; and we may therefore expect to find it most highly 
 developed in the Primates. 
 
 The phylogenetic development of this system has been 
 studied by Gegenbaur and Ruge. According to Gegenbaur, the 
 human platysma appears to be the remnant of a musculature 
 which was continued on to the head, but which has only retained 
 its primitive undifferentiated condition on the neck. The chief 
 reason of this is that the platysma, even in Man, is sometimes
 
 104 
 
 THE STRUCTURE OF MAX 
 
 directly connected with the zygomaticus minor, the orbicularis 
 palpebrarum, the auricularis anterior, and the transversus nuchse. 
 On the other hand, however, the fact that the mimetic musculature 
 is innervated by the facialis (n.fc., Fig. 69), a nerve which, by 
 location and distribution, is connected with certain muscles of the 
 visceral skeleton, compels us to conclude that this (the mimetic) 
 musculature has to some extent wandered from its original 
 
 FIG. 67. DIAGRAM OF THE DISTRIBUTION OF THE PLATTSMA OVER THE HEAD. (After 
 Gegenbanr.) The larger areas are marked with Roman figures, the smaller with 
 letters (cf. with Fig. 70). 
 
 position. It would appear to have moved up from the region of 
 the lower jaw, 1 and to have entered into close connection with the 
 soft parts surrounding the auditory and buccal apertures, i.e. with 
 the lips and with the pinna, which are themselves of secondary 
 
 1 According to Killian, it is more than doubtful whether Huge is right in 
 assuming a post-auricular upward wandering of the platysma. Killian holds that 
 the pars occipitalis of the platysma had from the beginning a dorsal position, and 
 that it is nothing more than the posterior superficial layer of the dorsal portion of 
 the musculature of the hyoid arch, as it appears not only in most Mammalian 
 groups, but also in many species of Birds, e.g. Owls, in which even external auditory
 
 MUSCULAE SYSTEM 
 
 105 
 
 origin. In time the eyes, forehead, temples, and the parietal 
 region were reached. 
 
 In the Lemuroidea the mimetic muscles, instead of being 
 sharply individualised as in Man, are not anatomically distinct, 
 i.e. they are merely parts of a great muscular tract, in which a 
 superficial and a deeper layer can be distinguished (cf. Figs. 68 
 
 m. orbito-auric. 
 
 m. levator labii 
 
 m. orb. oculi 
 
 m. helicis 
 
 i. auriculo \ sup 
 labial. J it\ 
 
 FIG. 68. SUPERFICIAL MCJSCULATURE OF THE FACE IN Lepilemur mustelinus. 
 (After Euge.) The deeper layer (m. sphincter colli) is visible in the neck. 
 
 and 69). The superficial layer is the platysma, the deeper the 
 so-called sphincter colli. 
 
 In those exceptional cases in Man, in which the cervical 
 portion of the platysma is developed, it is called the transversus 
 nuchse. Schultze found this in eighteen out of twenty-five 
 1 todies, Macalister in 35 per cent; others, however, have been 
 less fortunate. It was always found to be symmetrical, i.e. 
 developed on both sides. This muscle, which is almost always 
 present in the human embryo, corresponds in position with the 
 protuberantia occipitalis ; from this it radiates outwards along 
 the linea semicircularis, towards the tendon of the sterno-cleido- 
 
 muscles split off from it. It is also found in Reptiles (Saurians and Chelonia). In 
 Crocodiles a vestige of it is found in the powerful levator auriculae. Even in 
 Amphibians and Sharks this muscular tract is already developed, and from it can be 
 derived those human muscles which are innervated by the ramus auricularis posterior 
 nervi facialis.
 
 106 
 
 THE STRUCTURE OF MAN 
 
 mastoid, or even as far as the posterior edge of the auricularis 
 posticus. It may even completely fuse with the latter, which 
 thus appears to arise from the protuherantia occipitalis, as seems 
 to be the case with many lower Mammals. 
 
 The second and deeper layer of this cervical muscle, the 
 
 m. orbit, aur. 
 
 i. orb. oculi 
 
 m. auric, sup. m - auric, occipit. 
 
 m. helic. 
 
 FIG. 69. FACIAL MUSCLES AXD NERVES OF THE Lemuroid propithecus. (After Huge.) 
 Superficial muscles with the branchings of the facial nerve (n.fc. ). 
 
 sphincter colli, runs from the occipital region over the edge 
 of the jaw to the regio parotideo-masseterica, the lip and 
 adjacent parts. We shall consider later which of the human 
 facial muscles are derived from this, and which from the 
 platysma ; at present we need only deal with the vestiges, often 
 very slight, of this musculature which was probably incom- 
 parably more developed in the ancestors of Man. Those 
 mimetic muscles which are found partly near the ear and partly
 
 MUSCULAR SYSTEM 
 
 107 
 
 on the cranium, show great individual variation, those on the 
 right sometimes differing from those on the left in one and the 
 same person. By taking their physiological activities into 
 account we can establish three or four stages in their 
 degeneration. 
 
 These muscles may be dealt with in four series, as under : 
 1. Muscles of the cranium, known collectively as the 
 epicranius. Of this the frontal portion (frontalis) is still under 
 
 Fid. 70. MUSCLES OF THE EHICRANIAL REGION IN MAN, WITH CERTAIN OF THE 
 
 FACIAL MUSCLES. (After Gegenbaur.) 
 
 op., epicranial aponeurosis ; a.p. , posterior auricular muscle ; at., attollens auriculam ; 
 fr., frontalis muscle ; g.p., parotid gland ; ms., masseter ; oc., in. occipitalis. 
 
 control of the will, as is seen in frowning ; but the power of 
 throwing the entire epicranius into contraction, as in moving the 
 scalp, is possessed by but few individuals. 
 
 2. Muscles round the pinna : attrahens, retrahens, and 
 attollens auriculam (cf. Figs. 70 and 71). The capacity for 
 moving these muscles varies greatly in individuals. In most people 
 it is entirely wanting ; and the retrogressive character of these 
 muscles is due to the degeneration of the pinna (cf. infra}. 
 
 3. Intrinsic muscles of the pinna (derivatives of the muscles 
 mentioned under 2, which have become exclusively related to the
 
 108 
 
 THE STRUCTURE OF MAN 
 
 pinna, and there again further differentiated). Among these 
 may be mentioned certain bundles which separate off from the 
 
 FIG. 71. A, PINNA OF A PRIMATE DIVIDED INTO ZONES, THE SHADED PORTION BEING 
 
 THAT OF THE AUDITORY EMINENCES OF THE EMBRYO, THE UNSHADED THAT OF THE 
 LATER FORMED AUDITORY FOLD ; b, ITS BASE. 
 
 B, pinna of Man, of a Baboon and of an Ox, drawn to the same scale and superposed, 
 s'., spiua or tip of the ear in Man ; s"., the same of the Baboon ; and s"'., the same 
 of the Ox (homologous points) ; C, pinna of Macacus rhesus, with the tip (s.) 
 pointing upwards ; D, pinna of Cercopithecus, with the tip pointing backwards ; 
 E, pinna of Man, with its muscles ; m.a., attollens auriculam ; m.a'., antitragicus ; 
 m.t., tragicus ; m.t'., inconstant muscle bundle, stretching from the tragicus to 
 the edge of the helix ; m.h'., helicis major ; m.h"., helicis minor ; s., tip of the ear 
 (spina) rolled over ; A-D, after Schwalbe ; E, after Henle. 
 
 retrahens auriculam, chief of which are the transversus and 
 obliquus auriculam (auricularis proprius, Euge) which, belonging 
 to the most folded part of the pinna, are very small.
 
 MUSCULAR SYSTEM 109 
 
 The helicis major (Fig. 71, m.h'.*) and the tragicus (m.t.} 
 (the second of which is often wanting), are to be derived from 
 the scutulo-auriculare (a portion of the depressor helicis, Euge), 
 found in those Mammals which still possess a free and movable 
 scutulum. The helicis minor (m.h".\ antitragicus (m.a'.\ and the 
 incisurse Santorini, which belong to the cartilaginous wall of the 
 external auditory ineatus, are the proper ear muscles (auriculares 
 proprii), and related to the principal cartilages and the pinna 
 alone. 
 
 Taking all the facts into consideration, this intrinsic muscu- 
 lature of the pinna, which is no longer under the control of the 
 will, must be considered as the vestige of a primitive apparatus 
 functional either for the opening and closing, or for the widening 
 and narrowing of the auditory funnel and the external auditory 
 passage (cf. chapter on the auditory organ, infra). 
 
 4. To the fourth class belong those mimetic muscles which 
 have undergone the greatest degeneration, i.e. those which have 
 become transformed into tendinous or membranous structures 
 (fasciae). For example, the auriculo- (temporo-) labialis muscle of 
 the Lemuroids (cf. Figs. 68 and 69) has, in Man, been replaced 
 by the fascia temporalis superficialis, and the sphincter colli 
 muscle by the fascia parotideo-masseterica. A great part of the 
 human epicranial aponeurosis (galea aponeurotica), further, 
 consists of muscle bundles of the occipitalis transformed into 
 tendons. 
 
 [It is interesting to note that the power of contracting the platysma, the 
 ear muscles, and others not normally under the control of the will, has been 
 observed in a few cases to go hand in hand with that of a voluntary con- 
 trol of the heart's action.] * 
 
 MUSCLES OF THE LIMBS 
 
 The palmaris ( = p. longus) and its homologue in the hind- 
 limb, the plantaris, are time honoured (and certainly among the 
 best) examples of the gradual degeneration of a muscle. The 
 degeneration of the former has not yet proceeded as far as that of 
 the latter, as is most evident in the fact that while the palmaris 
 still reaches the palmar fascia of the hand, the plantaris only in 
 exceptional cases becomes connected with the homologous plantar 
 fascia of the foot, and in doing so regains its former significance 
 as a flexor of that organ. 
 
 The plantaris must therefore, as an original flexor, have 
 
 1 [Cf. E. A. Pease, Boston Med. and Surg. Jour., 30th May 1889.]
 
 110 THE STRUCTURE OF MAN 
 
 begun to degenerate from the time that the plantar fascia became 
 secondarily attached to the calcaneum, and helped in the forma- 
 tion of the arch of the foot, as the latter became transformed 
 into a supporting organ. 
 
 But why are the palmaris and plantaris of Anthropoids, 
 in which such transformations do not take place, also in a 
 degenerate condition? It does not appear difficult to answer 
 this question if we consider that these muscles originally 
 extended, as do their homologues in the lower Mammals, 1 
 through the mediation of the palmar or plantar fascia to the 
 phalanges, and acted as common flexors of the fingers and toes. 
 If so, in the course of time to confine our attention to the 
 hand as the flexores digitorum communis superficialis and pro- 
 fundus became more extensively and more subtly differentiated 
 from the primitive " pronato-flexor mass " (Humphry), the fibrous 
 terminal expansions of the palmaris withdrew more and more 
 from the fingers, and found points of attachment in the palm of 
 the hand and in the ligamentum carpi transversum. Thus 
 would the finger flexor appear to have become a hand flexor. 
 As such, however, it could not, on account of its attachments, 
 develop the same strength as the proper hand flexors, 2 which are 
 directly attached to the skeleton, and which, as we see where 
 the palmaris is wanting, are competent alone to bend the hand. 
 The palmaris becoming thus superfluous, is variable and occasion- 
 ally absent. 
 
 A further consequence of the transformation of the hind-limb 
 into a supporting and ambulatory organ, is that some of the 
 flexor muscles which originally ran down without interruption to 
 the sole of the foot have become interrupted at the protuberantia 
 calcanei by the dorsal flexion entailed. Another muscle of this 
 flexor series, e.g. the short flexor, which corresponds with the 
 flexor digitorum communis superficialis of the hand, has shifted 
 its point of origin farther and farther down, till at last, on the 
 acquisition of the upright gait, it has reached the calcaneal 
 tuberosity. In doing so this muscle has become more and more 
 closely connected with the plantar fascia ; and at present it 
 shows in many ways, e.g. in the variation of its terminal tendons 
 
 1 It is said that in Negroes the palmaris is still not infrequently inserted into 
 the metacarpals. 
 
 2 That it is still functional in the hand is shown by its occurrence, which must 
 still be considered normal. It is absent on one or both sides in about one in every 
 ten bodies.
 
 MUSCULAR SYSTEM 
 
 111 
 
 and the frequent absence of that to the fifth toe, evidences of a 
 retrogressive tendency. 
 
 The special extensors of the fingers undergo similar variations, 
 being now as a rule restricted to 
 the thumb, the index, and the 
 little fingers. Occasionally, how- 
 ever, the third and fourth fingers 
 also receive tendons from the ex- 
 tensor minimi digiti,andthe middle 
 finger may receive a tendon from 
 the extensor indicis proprius. 
 
 The changes brought about in 
 the sole of the foot naturally affect 
 the dorsum as well. There can 
 indeed be no doubt that changes 
 have taken place in the extensor 
 brevis digitorum of the foot (e.br., 
 Fig. 72) complementary to those 
 above described in the flexor digi- 
 torum communis brevis. The 
 extensor brevis digitorum must 
 formerly have arisen higher up 
 the fore-leg, and have secondarily 
 shifted downwards to the dorsum 
 pedis. The connection demon- 
 strated by Euge between the short 
 common flexor of the toes and the 
 interossei pedis undoubtedly in- 
 dicates the " extreme limit of the 
 distal wandering of the extensor 
 brevis." 
 
 Euge has further proved the 
 interesting fact that all the seven 
 interossei pedis at a certain stage 
 in the human embryo have a 
 plantar disposition, and that they 
 shift at a later stage to a position 
 between the metatarsals, there to 
 divide into the plantar and dorsal 
 
 series. An exact parallel to this is found in certain Apes (Cebus, 
 Cercopithecus) and in most of the lower Mammals, in which 
 the interossei have a plantar position throughout life. In the 
 
 2. SUPERFICIAL MUSCLES AND 
 TENDONS OF THE DORSUM OF THE 
 RIGHT FOOT. One -third natural 
 size'. (After Rauber.) 
 tibia ; b, fibula ; c, navicular ; t.a'., 
 tibialis anticus muscle ; t.a"., its 
 tendon of insertion ; e.l'., M. extensor 
 hallucis (e.hall. long.) i ; e.d'., 
 extensor communis digitorum 
 (e. digit, longus) ; e.d"., its expan- 
 sion and insertion on the second toe ; 
 p.f., peroneus tertius ; p.t"., its 
 insertion on the fifth metatarsal 
 bone; *., M. soleus ; p.b., M. 
 peroneus brevis ; e.b., M. extensor 
 hallucis brevis ; e.br., extensor brevis 
 digitorum ; Ig. anterior annular 
 ligament ; fc., transverse band of 
 the dorsal fascial of the foot.
 
 112 THE STRUCTURE OF MAN 
 
 Chimpanzee and Gorilla they are not so markedly dorsal in 
 position as in Aides, Inuus, and the Orang ; the latter therefore 
 are, in this respect, the nearest to Man. 
 
 The adductor hallucis with its caput obliquurn and trans- 
 versum [usually described as a distinct muscle, the transversus 
 pedis] originally forms one mass ; this points back to the time 
 when it was more strongly developed, and when the great toe was 
 capable of more extensive movement (cf. ante, p. 85). The fifth 
 toe also once moved more freely, as is indicated by the opponens 
 minimi digiti, which is only secondarily differentiated during 
 embryonic life from the mass of the flexor brevis minimi digiti. 
 The former muscle is, comparatively speaking, much stronger in 
 embryonic life than later, when it may entirely disappear. 1 
 
 MUSCLES WHICH APPEAR OCCASIONALLY, AND MAY BE 
 CONSIDERED ATAVISTIC 
 
 In dealing with this group of muscles, we may confine our- 
 selves to those which point back to lower grades of organisation, 
 through which the ancestors of Man may have passed phylogene- 
 tically. I wish to insist on this, since nothing is gained by 
 simply labelling muscles " theromorphic," and since, in my 
 opinion, in dealing with such muscles, Testut and certain other 
 authors have exceeded the bounds of moderation. 
 
 One of these apparently atavistic muscles, the cleido-occipitalis, 
 which forms a connecting tract between the trapezius and the 
 sterno-cleido-mastoid, has already been mentioned (ante, p. 102). 
 To the same category belong certain muscle bundles which here 
 and there partly fill up the interval between the pectoralis 
 major and the latissimus dorsi. A typical example of these has 
 been lately described by my pupil Endres (Anat. Anzeiger, Bd. 
 viii. p. 387), the morphological significance of the so-called 
 Langer's arch being incidentally discussed. 
 
 A muscle which very rarely occurs in Man is the latis- 
 
 (Isimo-condyloideus (dorso-epitrochlearis of French authors), an 
 appendage of the latissimus dorsi, branching off from the 
 latter shortly before it is inserted into the humerus. From 
 
 1 The opponens minimi digiti seems to attain development only in the Chim- 
 panzee among Anthropoids. [Incidentally to this topic and to that of the reduc- 
 tion and co - ossification of the penultimate and terminal phalanges of the little 
 toe (cf. ante, p. 89), it is interesting to observe that the muscles of the little toe 
 are more reduced in the higher Apes than in Man.]
 
 MUSCULAR SYSTEM 113 
 
 this point the muscle runs perpendicularly along the triceps 
 (radiating out into the surrounding fasciae) .to the condylus 
 internus humeri, into which it is inserted. This muscle is 
 present in all Anthropoids, and is either directly inserted into 
 the olecranon or contributes to the triceps. 
 
 Near the sternal line the so-called " sternalis " muscle is 
 sometimes found. This is a small bundle, which varies in 
 form and in the direction of its fibres, lying ventrad of the 
 pectoralis major. It may either be bilaterally symmetrical or 
 present only on one side. In the former case, the two muscles 
 I may cross one another and be continued direct into the sterno- 
 'cleido-mastoid. 
 
 [Considerable controversy has from time to time arisen con- 
 cerning this sternalis. It occurs in some 3 to 5 per cent of 
 subjects, and is invariably innervated by the anterior thoracic 
 or intercostal nerves. While it has by some been referred to 
 a possible origin from the pectoralis major, the rectus abdominis, 
 and other muscles, it has by others been regarded as a vestige of 
 the panniculus. One interesting variation to which it is liable 
 is that of forming a connection between the external oblique of the 
 abdominal region and the sterno-mastoid. Parsons has recently 
 shown that in Eodents the abdominal panniculus, on reaching 
 the axillary border of the pectoralis, divides into a superficial and 
 a deep stratum ; and from a very careful analysis of the detailed 
 relationships of the panniculus in these animals, he has adduced 
 strong reason for regarding the fascial sheath of the human 
 external oblique as its modified deep abdominal portion. He 
 further gives reasons for believing that the deep part of the 
 cervical panniculus has become incorporated in the sterno-mastoid, 
 and ultimately regards the sternalis as a vestige of that portion 
 of the panniculus which originally connected its deep cervical 
 and deep abdominal sections.] l 
 
 Between the internal condyle of the humerus and the 
 olecranon, in Man, a fibrous band always runs, transversely, 
 below the superficial fascia which bounds posteriorly the deep 
 indentation in which the ulnar nerve lies. This band corre- 
 sponds with the epitrochleo-anconreus muscle, which is constant 
 in many Mammals ; it is only occasionally muscular in Man and 
 the Anthropoids, and then varies greatly in form and size. It 
 
 1 [Parsons has farther simplified matters by suggesting that the pectoralis major 
 may be itself a derivation of the panniculus. Cf. Jour. Anat. and Phys., vol. 
 xxvii. p. 505.] 
 
 I
 
 114 THE STRUCTURE OF MAX 
 
 is always innervated by the ulnar nerve. According to W. Gruber 
 (St. Petersburg), it was found in about 34 per cent, but, accord- 
 ing to Wood (London), in only 8 per cent, of bodies examined 
 a want of agreement which may perhaps be indicative of a racial 
 difference. This muscle must be referred back to a time when 
 a transverse shifting of the ulna was possible in the ancestors of 
 Man, as it now is, to some extent, in many lower animals ; and it 
 would appear that after the movements of this bone had become 
 limited almost entirely to flexion and extension, the muscle 
 gradually degenerated and disappeared. 
 
 Finally must be mentioned the levator claviculse and the 
 ischio-femoralis or glutseus quartus, which occasionally occur in 
 Man. The latter muscle is constantly present in Anthropoids 
 [as the so-called scansorius]. 
 
 3. PROGRESSIVE MUSCLES 
 
 Attention has already been drawn to the fact (ante, p. 97) 
 that in certain regions progressive and retrogressive variations 
 may occur simultaneously ; and this is nowhere so conspicuous 
 as with the facial muscles. Some of these which are in various 
 stages of degeneration have already been referred to (ante, p. 
 109). All the other mimetic muscles (i.e. by far the greater 
 number) appear to be progressively developing, in correlation with 
 the increase of the intellect and the correspondingly advanced 
 functional activity of their associated nerves. This advancing 
 specialisation is indicated in the aberration of certain parts, and 
 the formation of new layers of muscle. These changes have 
 brought about striking differences between these muscles in Man 
 and the homologous tracts in the Lemuroidea, where they are 
 simple and comparatively easy to understand. We are thus able 
 to demonstrate for the mimetic musculature very great variations 
 of form and size in both a progressive and retrogressive direction, 
 as indeed is the case in all organs which are in the act either of 
 suppression or of differentiation, i.e. are not in a definitive 
 state. 
 
 Progressive development is especially shown in the muscles 
 round the eyes, the mouth, and the nose, and also in those of the 
 sub-zygomatic region. 
 
 Euge expresses himself upon the tendency to further develop- 
 ment and completion of the human facial muscles, very aptly, 
 as follows :
 
 MUSCULAR SYSTEM 115 
 
 " A free subcutaneous position, slight relations to the skele- 
 ton, and the absence of definite fasciae, offer most favourable 
 conditions for the initiation of new combinations. The muscular 
 elements can naturally only enter upon new departures in various 
 directions for the attainment of a greater functional activity, as 
 the result of very definite causes. These causes are undoubtedly 
 present in Man, and lie in his mental qualities and in the faculty 
 of speech. The latter calls the muscles around the mouth into 
 activity, and the former seek expression in the play of the 
 features. These causes of the differentiation of new facial muscles 
 hardly exist in the lower animals, which fact accounts, it appears 
 to me, for the absence among them of those signs of progressive 
 variation with which we shall become acquainted in the muscula- 
 ture of the human face. It may be different, however, in the 
 case of variations due to quite other causes. The possibility of 
 great variability in the facial musculature of the lower animals 
 cannot be denied d priori ; nor can we dismiss the objection that 
 the few observations which have been made on animals have by 
 no means settled what must be considered as the normal condi- 
 tion for them. In answer to this, I would, however, emphasise 
 (1) the fact that variation in the muscles of animals is rarer 
 in the wild state than under domestication ; and (2) the con- 
 sideration (to which Dobson has rightly called attention) that 
 variation in that most domesticated of all animals, Man, ought 
 to be far greater than in animals, which, being subject to natural 
 selection, in which the fittest survives, have, in some respects, 
 a narrower field allotted to them for modification." 
 
 " The chief factor in the transformation and diversity of form 
 of the facial muscles in Man, as opposed to the other Primates, 
 is the extensive development of the brain-case. This transforma- 
 tion alone is enough to account for changes in those muscles 
 which lie upon it. But the development of the brain is closely 
 connected with the acquisition of mental powers in Man. The 
 development of language has necessarily determined a correspond- 
 ing development of the muscles round the mouth and nose. If 
 we can only demonstrate some slight progressive development in 
 these parts something will be gained, for we shall be able to say 
 that where the higher development of Man leads us to expect 
 more complicated anatomical arrangements, these are actually 
 found. Vivacity and diversity of expression of the mouth and 
 eye are a peculiarity of Man ; they mirror forth the higher 
 psychical activity, and can only be acquired by the perfecting of
 
 116 
 
 THE STRUCTURE OF MAN 
 
 FIG. 73. DEEP MDSCLES ON THE FLEXOR 
 SIDE OF THE FOREARM. One-fifth natural 
 size. (After Rauber. ) 
 
 The muscles of the upper arm, and the 
 superficial muscles of the forearm and 
 hand, with the lumbricales, are removed. 
 The position of the anterior annular 
 ligament is indicated by two dotted lines. 
 
 hu., humerus ; p.c., processus coronoideus 
 ulnae ; l.o., the orbicular ligament ; p.s'., 
 proc. styloideus radii ; p.s"., proc. sty- 
 loideus ulnae ; e.c., eminentia carpi ul- 
 naris ; I.e., lig. accessorium cubiti mediale; 
 s., M. supinator ; /./., M. flexor longus 
 pollicis ; f.p., M. flexor profundus 
 digitorum ; p.q., M. pronator quadratus ; 
 f.b., deep head of the flexor brevis 
 pollicis ; a.p., M. adductor pollicis; i.p., 
 M. interosseus dorsalis primus ; i.d., Mm. 
 interossei dorsales et volares ; be., 
 bicipital tendon. 
 
 the muscles round these organs. 
 It is, therefore, a fact of the 
 greatest importance that, while 
 many variations are found in 
 the muscles near the mouth 
 and the eyelids of Man, in- 
 dicative of new possibilities of 
 development, in the other Pri- 
 mates these muscles show a 
 monotonous constancy. May 
 it not also be possible that still 
 more subtle differences occur 
 between the various human 
 races in the detailed arrange- 
 ment of the facial muscles ? 
 In such a question, however, a 
 trustworthy decision can of 
 course only be arrived at after 
 extended comparative inquiry." 
 In addition to the facial 
 region, there are three others 
 in which progressive muscular 
 variations are to be found. 
 Taking first the hand, we may 
 select for special consideration 
 the thujmb. We are immedi- 
 ately struck by its apparent 
 superfluity of muscles. 1 Our 
 attention is specially arrested 
 by the long flexor of the thumb 
 
 1 For instance, the abductor pollicis 
 has often a double or even triple 
 tendon, and supernumerary tendons of 
 the most various muscles, as if attracted 
 by a magnet, often become inserted into 
 the thumb (e.g. tendons from the 
 brachio radialis, extensor pollicis longus 
 and brevis, extensor longus radialis and 
 extensor digitorum communis). In all 
 these we probably have to do with the 
 beginnings of secondary processes of 
 differentiation, which have already been 
 indicated in connection with the skeleton 
 of the hand (ante, p. 77).
 
 MUSCULAR SYSTEM 
 
 117 
 
 (fl. longus pollicis) (/./., Fig. 73), the differentiation of which out 
 of the common mass of the flexor profundus digitorum (f.p.} 
 commences in Anthropoids, but is first carried out in Man. 
 Not infrequently, however, more often in the lower than in the 
 higher races, we find reversions to the primitive condition, i.e. 
 a more or less extensive inter-com- 
 munication of fibres of, or even a 
 fusion between, the flexor pollicis and 
 the flexor profundus. 
 
 This differentiation of the flexor 
 longus pollicis, which finds its 
 highest expression in the attain- 
 ment of independent movement and 
 in the greatest possible play of the 
 thumb, has its parallel in that of 
 the flexor longus hallucis (/.&., Fig. 
 74), which is derived from the flexor 
 digitorum communis pedis. 1 The in- 
 terchange between the fibres of these 
 two muscles is so very frequent that 
 it is hardly ever wanting. Further, 
 all the variations observed in them 
 are normally met with in Apes, even 
 to the different radiations from the 
 tendinous anastomosis to the toes. 2 
 
 lb 
 
 1 In the Gorilla the flexor digitorum com- 
 munis profundus is subdivided into two portions. 
 
 FIG. 74. MEDIAN SERIES OF THE 
 PLANTAR MUSCLES, IN THEIR 
 CONNECTION WITH THK FLEXOR 
 TENDONS. One - third natural 
 (After Rauber.) 
 
 The ulnar portion is inserted into the fifth, the c l., tuber calcanei ; Iff., ligam. cal- 
 
 fourth, and the middle fingers, the radial one 
 into the index finger and the pollex. Testut 
 has proved that this condition may rarely 
 occur in Man, and that it sometimes occurs 
 on both sides in the same individual. In the 
 Orang there is only a simple undivided flexor 
 digitorum communis profundus without any 
 tendon for the thumb. This arrangement also 
 has been four times observed in Man in one 
 case in a microcephalous individual. 
 
 2 The frequent variations in the development of the caro quadrate Sylvii, and its 
 occasional entire absence, find a parallel in Anthropoids. In the Chimpanzee, for 
 example, the muscle is often reduced to a single little fleshy bundle, or may be 
 altogether wanting, as appears to be the case in the Orang, Gibbon, and Gorilla. 
 In all cases, however, the numerous variations indicate that the caro quadrata 
 attained its present position secondarily, i.e. that it must formerly have lain higher 
 up on the calcaneus and the fore-leg ; and, indeed, an extension of the muscle in this 
 direction has been observed. 
 
 caneo-cuboideum plantare ; f.l., 
 tendon of flexor longus digitorum ; 
 f.h., tendon of flexor longus hal- 
 lucis ; td., tendinous connection 
 between flexor longus and adjacent 
 tendons ; q.p'., lateral head of 
 the M. quadrati plantae flexor 
 accessorius ; q.p"., its median 
 head ; lb., Mm. lumbricales ; 
 f.V. M. flexor brevis hallucis ; 
 f.b"., M. flexor brevis minimi digiti.
 
 118 
 
 THE STRUCTURE OF MAN 
 
 Fio. 75. DEEP DORSAL MUSCLES OP THE 
 FOREARM. One-fifth natural size. (After 
 Ranber. ) 
 
 hu, huraerus ; ul., olecranon process of ulna ; 
 rd., radius; pr., processus styloideus 
 ulnse ; inc., os metacarpeum secundum. 
 ., M. anconaeus ; f.p., M. flexor pro- 
 fundus digitorum ; f.c., flexor carpi 
 ulnaris, separated from the fascia of the 
 forearm ; e.b., extensor carpi radialis 
 brevior ; e.L, the tendon of the extensor 
 carpi radialis longior ; e.p'., M. ext. 
 metacarpi pollicis ossis ; e.p". M. ext. 
 primi internodii pollicis ; e.p"'. , M. ext. 
 secundi interuodii pollicis ; e.L, M. ext. 
 indicis ; e.m., insertion of the extensor 
 tendon into the middle finger, and its 
 connection with the second and third 
 dorsal interossei. 
 
 of the lower Vertebrates these 
 
 We saw above that a num- 
 ber of muscles and tendons 
 meet in the thumb; and the 
 same applies, though to a lesser 
 degree, to the great toe. To it 
 offshoots of the extensor hallucis 
 longior and the tibialis anticus 
 or their tendons pass; these, 
 however, do not indicate the 
 commencement of a new de- 
 velopment, but rather a rever- 
 sion to a former condition, in 
 which the great toe was capable 
 of freer movement. 
 
 It would be difficult to 
 decide to what extent the 
 variations which occur on the 
 ulnar border of the forearm 
 and hand, in the region of the 
 extensor and flexor carpi ulnaris 
 and the extensor digiti quinti 
 proprius, may be the beginnings 
 of a progressive development. 
 On the other hand, there can 
 be no doubt that the changes 
 at the fibular border of the 
 foot, which have already been 
 mentioned (ante, p. 112), are 
 degenerations. 
 
 The already described dif- 
 ferentiation of a flexor longus 
 pollicis and a flexor longus 
 hallucis out of the original 
 simple flexor masses, finds a 
 parallel in the Ontogeny and 
 Phylogeuy of the superficial 
 and deep common flexors of the 
 fingers. The two latter are 
 connected by an interchange of 
 fibres which may amount to 
 complete fusion ; and in many 
 muscles may not only be con-
 
 MUSCULAR SYSTEM 119 
 
 nected with one another, but also with neighbouring muscles, 
 such as the pronator teres, palmaris longus, flexor carpi radialis 
 and ulnaris. The two flexors originally formed (as in the 
 lower Mammals) one mass ; and in the human embryo they 
 still arise as a single blastema, which is only at a later stage 
 of development split up by ingrowing partition walls of con- 
 nective tissue. 
 
 In Anthropoids these muscles are throughout life connected 
 by anastomosing strands, which clearly indicate their former 
 union, and to this cause, and the lack of a distinct flexor 
 pollicis proprius, is due the less marked specialisation of the 
 Anthropoid hand as compared with that of Man. In Man, the 
 flexores digitorum communes, superficial and deep, are, as a rule, 
 distinct ; but the more or less complete fusion often found 
 between them points to the fact that their separation is (geo- 
 logically speaking) not of long standing, and has not yet become 
 stereotyped. 
 
 The same is the case with the not infrequent fusions 
 involving the two radial extensors of the hand, which must also 
 be regarded as reversionary. Indeed, these two muscles may fuse 
 completely, and, in such a case, we have a realisation of that 
 lower condition in which only one single extensor carpi radialis 
 externus is present. 
 
 A further instance of progressive development in muscles is 
 exemplified by the glutei. These, including the adductors of the 
 thigh, show their original unity by frequent blending ; and 
 very often a more or less complete fusion takes place between 
 them and the pyriformis, or between the latter and the gemellus 
 superior. Further, the frequent absence of the gemellus superior 
 in Man deserves mention, because this muscle is also often 
 wanting in the Anthropoids. 
 
 The special development of the gluteus maximus is a charac- 
 teristic peculiarity of Man. This muscle has a humble origin 
 among the lower Vertebrates, and even in the Anthropoids there 
 is nothing comparable in size and strength with its excessive 
 development in Man, which is a direct accompaniment of the 
 upright gait. The muscle fixes and steadies the pelvis, or rather, 
 the whole trunk, on the heads of the femora, and through them 
 on the lower limbs, as on a support or stand. 
 
 Closely connected with the assumption of the upright gait 
 by Man, which involves the transformation of the former pre- 
 hensile feet into ambulatory and supporting organs, is the
 
 120 THE STKUCTUEE OF MAX 
 
 development of the superficial muscles of the posterior surface 
 of the fore-leg, i.e. of the calf. The gastrocnemius and soleus 
 were formerly as directly connected with the sole of the foot or 
 with its fascia as was the plantaris. The terminal tendons of 
 these muscles have alike shifted back to the calcaneal tuberosity ; 
 but while the plantaris very soon began to degenerate, the soleus 
 and gastrocnemius l have attained an excessive development speci- 
 fically characteristic of Man. We have here another instance of 
 retrogressive and progressive changes taking place side by side 
 in one and the same region. 2 
 
 EETROSPECT 
 
 Gathering together the conclusions which follow from the 
 above review of the musculature, we find first that age seems to 
 have no influence on the frequency of variation and reversionary 
 phenomena. We must, however, except fcetal life, since, during 
 that period, certain muscles may appear which afterwards suffer 
 more or less complete degeneration. 
 
 No definite laws can be framed either as to the disposition 
 or division, the symmetry or asymmetry, of the muscles, or as 
 to the general condition of the body to which they belong, e.g. 
 the strength or weakness of the individual. Correlative changes 
 counteracting those due to variation are not observed. It is the 
 exception to find that anomalies extend to the homologous 
 muscles of the fore- and hind-limbs of the same side. 
 
 Examination of eighteen male and eighteen female bodies by 
 Professor Wood at King's College, London (in 1867-68), led to the 
 conclusion that anomalies are more frequent in the musculature of 
 the limbs than in that of the rest of the body, and that the fore- 
 limb is in particular distinguished by their occurrence (292 varia- 
 tions were found in the fore as against 119 in the hind-limb). 
 It has further been ascertained that variations become more 
 frequent as examination proceeds in a distal direction, i.e. as those 
 peripheral parts of the body are reached which are more directly 
 exposed to the modifying influences of the environment. 
 
 1 A sesamoid bone sometimes occurs near the lateral point of origin of the 
 gastrocnemius. In Anthropoids and many other Mammals several such bones 
 (fabellfe) are found, one, for instance, at the median point of origin of the muscle. 
 
 2 Various circumstances point to the fact that the biceps femoris, semitendinosus 
 and semimembranosus, originally arose higher up than at present, viz. from the 
 ilium, and the sacral, or caudal vertebrae. The fact that they have wandered on to 
 the ischial tuberosity would appear to be connected with the forward tianslocation 
 of the pelvic girdle already discussed (ante, p. 33).
 
 MUSCULAR SYSTEM 121 
 
 In general, the principle holds good that those muscles 
 are most subject to variation which can be dispensed with 
 without disturbance or disadvantage to the organism as a whole, 
 either because they can be easily replaced by other muscles, 
 or because they have only a subordinate part to play. In 
 illustration of this I would merely refer to the pyramidalis, 
 the abortive caudal muscles, the muscles of the pinna, the 
 palmaris and the plantaris, the vestigial character of which 
 clearly points to their ultimate complete suppression. 
 
 Eesearch has shown, however, that it is not only to the 
 retrogressive tendency of the muscles that variation is due, but 
 that variation may in some cases indicate a tendency to 
 progressive development. The best example of this is afforded 
 by certain flexor muscles, and by the flexor longus pollicis, and 
 the gluteus magnus. 
 
 A third kind of variation occurs, in those cases in which a 
 tendon may return to former points of insertion on neighbouring 
 bones, e.g. the rectus abdominis is occasionally inserted on to the 
 more anterior ribs. And to the same category belong the \ 
 splitting off of the abductor hallucis from the tibialis anticus, 
 which occurs in very varying degrees. 
 
 All these cases, which must be denominated reversionary, 
 indicate the extraordinary tenacity with which certain 
 peculiarities persist and are repeatedly passed on from one 
 generation to another. This power of reproduction must, however, 
 necessarily grow weaker, as an organ in course of time loses its 
 original functions in adaptation to new ones. As a consequence 
 of this, attempts at reconstruction necessarily become more and 
 more imperfect. 
 
 The same is the case with many other muscles (e.g. the 
 sternalis, levator claviculse, latissimo-condyloideus, and epitrochleo- 
 anconseus) which now only rarely occur in Man, and which, when 
 they are present, furnish important indications of a long-past 
 period in the development of the human race. 
 
 There is no good ground for doubting the possibility of the 
 hereditary transmission of muscular anomalies, although, as Testut 
 rightly remarks, the difficulty of obtaining material for a direct 
 proof is evident. The difficulty in this case is greater than in 
 that of mere external variation, such as pigmentation, different 
 coloration of the opposite eyes, abnormal hairiness, birth-marking, 
 polydactyly, and others akin to these. 
 
 It is reserved for future investigators to add to our as yet
 
 122 THE STRUCTURE OF MAN 
 
 scanty knowledge on this subject, by using more fully the material 
 which the different human families and races could afford us. 
 It is not impossible that some of the views till now held, e.g. 
 that Negroes and other low races do not differ specifically in their 
 myology from the Caucasians, and do not show more frequent 
 variations, may have to be modified. 
 
 Anthropotomy has here a great field. On the other hand, 
 the mass of recorded observations upon muscular anomalies in 
 general is so great, and the agreement of many of these with 
 the condition normal in Apes is so marked, that the gap which 
 usually separates the muscular system of Man from that of the 
 Anthropoids appears to be completely bridged over (Testut).
 
 THE NERVOUS SYSTEM 
 
 THROUGHOUT the animal kingdom the nervous system is more 
 
 conservative in character than any other, and it thus offers a 
 
 more limited field for the study of vestigial structures. The 
 
 latter, however, as we shall see, are not altogether wanting ; 
 
 indeed, they may be here of special interest, as they afford the 
 
 [ best proof of the extreme tenacity with which an organ, or some 
 
 I part of an organ, may persist and be transmitted through an 
 
 < immense period of time, when its functional activity is to a 
 
 1 marked degree reduced, or even no longer evident. 
 
 The central nervous system of the Vertebrata, as is well 
 known, arises from the so-called medullary folds of the outer 
 germinal layer, and is thus essentially a modified derivative of 
 the epiblast the so-called " sensory layer." The latter, in the 
 lower animals, e.g. certain Coelenterates, in which there is no 
 sharp differentiation into a central and a peripheral nervous 
 system, remains superficial in position and is directly the medium 
 of communication with the external world. This, combined with 
 the fact that, in Vertebrates, the brain and spinal cord are among 
 the first differentiated organs, is a distinct proof of the great age 
 and physiological importance of the nervous system. 
 
 THE SPINAL CORD 
 
 When first differentiated, the nervous axis, as already men- 
 tioned, corresponds in extent with the axial skeleton ; but it 
 soon appears to shorten, partly from inequality of growth, and 
 | partly in consequence of modification taking place in the posterior 
 I portion of the vertebral column. The spinal cord no longer 
 extends throughout the whole length of the vertebral canal, its 
 posterior tapering extremity [i.e. the portion caudad of the spinal 
 nerve -roots, where the filum terminale begins] reaches no 
 farther down [in Man] than to about the boundary between the
 
 124 
 
 Ib.v 
 
 THE STRUCTURE OF MAN 
 
 thoracic and lumbar portions of the column. 
 
 h. This shortening, as above said, is more 
 apparent than real, for the vertebral column 
 [growing the more rapidly] extends farther 
 
 i> and farther back beyond the posterior 
 limit- of the spinal cord. [It is worthy of 
 remark that this inequality of growth, so 
 marked in Man, is still more conspicuous 
 among certain lower Mammals e.g. the 
 Hedgehog, in which the filum terminale 
 commences in the anterior thoracic region.] 
 The filum terminale (f.t., Fig. 76) 
 runs through the lumbar and sacral 
 regions of the vertebral column into the 
 caudal ; and this terminal filament, which 
 grows with the growing vertebral column, 
 is the vestigial homologue of the posterior 
 portion of a spinal cord which, in the 
 ancestors of Man, may have run evenly 
 throughout the whole length of the 
 vertebral column, as it now does in many 
 lower Vertebrates. This process of reduc- 
 tion, which sets in at the posterior end of 
 the spinal cord, is profoundly significant, 
 as we have already had to describe a 
 similar process of reduction going on at 
 the posterior end of the axial skeleton itself 
 (ante, pp. 28 et seq.}. 
 
 I should like to suggest the consideration 
 whether certain pathological conditions may not 
 be traced to this source, if only indirectly ? I 
 refer to those frequent diseases of the spinal cord 
 known as tabetic, which in by far the greater 
 number of cases arise at its posterior end. May 
 not the above described condition of the lumbar 
 
 FIG 76. LOWER PORTION OF THE SPINAL CORD, WITH THE CAUDA EQUINA AND THE 
 ENVELOPING DURA MATER. (Dorsal aspect.) One -half natural size. (After 
 Schwalbe.) 
 
 The dura matral sheath has been opened up from behind and laid back ; on the left side 
 the roots of the nerves are represented entire ; on the right, the lower of these are 
 shown removed above their passage through the sheath, and the bones of the coccyx 
 are delineated in their natural relative positions, in order to show the relations of the 
 filum terminale and the coccygeal nerves. 
 
 cc., coccygeal nerves ; /.., dorsal longitudinal fissure ; f.t., filum terminale, slightly dis- 
 placed to the right side ; Ib. i and v, first and fifth lumbar nerves ; l.d., ligamentum 
 denticulatum ; sc. i and v, first and fifth sacral nerves ; sh., the dura matral sheath ; 
 th. x and xii, tenth and twelfth thoracic nerves.
 
 THE NERVOUS SYSTEM 125 
 
 portion of the rayelon be considered as a predisposing factor in the 
 degenerative processes apparent in such cases ? A parallel to this occurs, 
 it seems to me, in the processes of reduction at the iippejr part of the 
 thorax already mentioned (ante, p. 43), and in the pathological processes 
 which set in at the tips of the lungs, perhaps connected therewith. 
 
 That there are also progressive . processes going on in the 
 human spinal cord is probable, from the following observations 
 made by Lenhossek on Mice, Guinea-pigs, Eabbits, and Cats. In 
 these animals the pyramidal tracts are much more feebly developed 
 than in Man (in whom they attain their highest differentiation), 
 and their position in the spinal cord varies greatly. In the 
 Guinea-pig, Mouse, and Eat, they run in the dorsal columns, in 
 the Eabbit, the Cat, and other Carnivora, in the lateral, and in 
 Man, partly in the lateral and partly in the ventral columns. 
 This may perhaps be indicative of a gradual shifting of these 
 tracts from the dorsal to the ventral columns, as we pass from 
 the lower to the higher Mammalia ; and it would be interesting to 
 investigate this point in the Apes. Even in Man the definitive 
 condition is not reached, for the fact that the pyramidal tracts 
 may run either along the ventral or the lateral columns is 
 evidence that they are still subject to variation. 
 
 Since the pyramidal tracts cross one another completely 
 in all animals which have been examined, it seems likely that 
 their alleged semi-decussation in Man is only apparent, as the 
 elements of the ventral tracts do eventually cross one another. 
 And further, since these ventral tracts are wanting in Man in 
 fifteen cases per cent, it would be necessary, if belief in semi-decus- 
 sation is to be persisted in, to consider that a certain number 
 of individuals were remarkable exceptions in that important 
 character. Inasmuch as this supposed variation is unaccompanied 
 by exceptional conditions of other parts of the organism, it is 
 altogether improbable that it exists. 
 
 I must refer the reader to the works of Waldeyer for an 
 account of the differences to be found between the human spinal 
 cord and that of the Gorilla. 
 
 Before turning to the condition of the brain, attention may 
 be drawn to a small body which lies beneath the last coccygeal 
 vertebra, known as the coccygeal gland. This, on account of its 
 close relation to the arteria sacralis media, is usually, but, it 
 seems to me, incorrectly, relegated in text -books of human 
 anatomy to a connection with the vascular system. Considering 
 the established fact that the caudal end of the spinal cord, at an
 
 126 
 
 THE STRUCTURE OF MAN 
 
 early period of development, reached exactly to that point at 
 which the coccygeal gland is found later, and that, as already 
 
 FIG. 77. BRAIN OF A DOG-FISH (Scyllum caiiicida). 
 
 A, dorsal ; B, ventral ; C, side view ; 6.0., bulbus olfactorius ; ep., pineal gland cut short ; 
 f.b., fore-brain ; f.r., fossa rhomboidalis ; h.b., hind-brain (cerebellum) ; hp., hypo- 
 physis ; i.f., iufuudibulum ; i to x, first to the tenth cranial nerves (the thalamen- 
 cephalon and the fossa rhomboidalis are in life covered by epithelium (plexus 
 chorioidei), not delineated ; the ventral vagus roots are omitted from Fig. B) ; 
 md., medulla oblongata ; m.h., mid-brain (optic lobes) ; sc., saccus vasculosus ; 
 t.o., tractus olfactorius. 
 
 mentioned, all the important variations at the caudal end of the 
 trunk are primarily associated with degeneration of the spinal
 
 THE NERVOUS SYSTEM 127 
 
 cord at that region, I am inclined to think that some connection 
 exists between the latter and tne coccygeal gland. This gland 
 is undeniably a vestigial organ, but we have as yet no certain 
 knowledge of either its significance or its primitive history. 
 
 BKAIN 
 
 The human brain, in the course of its development, passes 
 in regular order through conditions characteristic of certain of 
 the lower Vertebrata (ex. disposition of the cerebral vesicles, 
 smooth surface of the hemispheres), and these lower con- 
 ditions are in rare cases retained, as in many microcephalous 
 individuals, as the probable result of arrested development. 
 There are not infrequent deviations from the normal arrangement 
 of the cerebral furrows and convolutions, which are closely con- 
 nected with the development of the gray matter. These 
 deviations can be best studied by the aid of Comparative 
 Anatomy and Ontogeny, and the same may be said of the 
 posterior cornu of the lateral ventricle, the calcar avis, and 
 the eininentia collateralis Meckelii. Conspicuous among variable 
 cerebral furrows we note the parieto-occipital fissure (f.po., Fig. 78), 
 which is occasionally very pronounced. This fissure runs out 
 laterally, and may probably be a reversion to the pithecoid type 
 (it is called in German the " Affenspalte "). In its normal 
 condition it seems almost to be vanishing, as compared with its 
 supposed homologue in the brain of the Ape. 1 
 
 In spite of difference in detail, there is a closer general 
 resemblance between the human and the Anthropoid brains than 
 between the brains of any other two Vertebrate groups. 
 
 With regard to the weight of the brain in Anthropoids 
 generally, the material as yet examined is not sufficient for the 
 determination of averages and formulation of general conclusions. 
 With the Chimpanzee, however, this is not the case, as a rela- 
 
 1 [The term parieto-occipital fissure insufficiently defines this supposed homologue 
 of the "Affenspalte." Cunningham in a recent elaborate treatise (Cunningham 
 Memoirs, vii. H. Irish Acad., 1892) has devoted much attention to this topic. He 
 and other leading authorities are agreed that, whether the " Affenspalte " of the Ape 
 is present in the human adult or not, the "fissura perpendicularis externa" of the 
 foetus is its homologue. During the passage of these pages througli the press, 
 Beuham, in a very careful study of the Chimpanzee's brain, has shown (Qu. Jour. 
 Micr. Sci., vol. xxxvii. p. 47) that the transverse occipital fissure which replaces this 
 external perpendicular may be genetically related to it, and that therefore Ecker's 
 original view that the "Affenspalte" of the Ape is represented in the adult human 
 brain by that which he termed the ' ' sulcus occipitalis transversus " may be correct. ]
 
 128 THE STRUCTURE OF MAN 
 
 tively large number of specimens have been examined ; and 
 
 FIG. 78. CEREBRUM OF A FEMALE CHIMPANZEE TWO TEARS OLD. (Dorsal 
 
 aspect.) (Showing Asymmetrical Development.) 
 
 c.c'., c.c"., anterior and posterior central convolutions ; f.i., interparietal tissure ; f.l., 
 the longitudinal fissure ; f.p.o., parieto-occipital fissure ; fr., frontal lobes ; oc., 
 occipital lobes ; s.c., sulcus centralis. 
 
 fr. 
 
 FIG. 79. BRAIN OF A FEMALE CHIMPANZEE TWO TEARS OLD. (Lateral aspect.) 
 cb., cerebellum ; c.c'., c.c.", anterior and posterior central convolutions ; fr., frontal lobe ; 
 /.., fissura Sylvii ; is., island of Reil ; md., medulla oblongata ; oc., occipital lobe ; 
 pa., parietal lobe ; s.c., sulcus centralis ; tp., temporal lobe. 
 
 further, a review of the facts known concerning the Gorilla 
 and Orang reveals statistics which may be of use to future
 
 THE NERVOUS SYSTEM 
 
 129 
 
 investigators. For details on this subject I must, however, 
 refer the reader to the works of Moller and others. 1 
 
 c f S ' C - c.c". f.i. 
 
 f.S. tj>. 
 
 FIG. 80. CEREBRUM OF THE GIBBON (HYLOBATES). (Lateral Aspect.) 
 References as for Fig. 79. 
 
 FIG. 81. CEREBRUM OF A HUMAN EMBRYO IN THE SEVENTH TO THE EIGHTH MONTH. 
 
 (Dorsal Aspect) 
 References as for Fig. 78. 
 
 .* Job. Holler, Abhandlg. d. Zool. u. Anthrop. Ethnol. Museums :M Dresden, 
 1890-1891. [Cf. also D. J. Cunningham, Cunningham Memoirs, R. Irish Acad., 
 No. II., 1886 ; No. VII., 1892 ; and Benham, op. tit. In these works the literature 
 of the subject will be found.] 
 
 K
 
 130 THE STRUCTURE OF MAN 
 
 If we take the average weight of the body of a Chimpanzee 
 from two to four years old as 8 J kilogrs., and the average weight 
 of brain as 343 grs., we shall have 1 : 24'7 as the relative 
 weight of the latter. An Orang of the same age appears to 
 possess a rather heavier brain (1 : 22'3 or 340 : 7600). A 
 comparison of these two Anthropoids with Man, the ratio of 
 whose brain weight to his body weight between the second and 
 fourth years ranges from 1:18 to 1:16, shows that the 
 difference at this age is not great, as would seem natural when 
 we recall the greater similarity to human beings shown by 
 young Anthropoids. In older Chimpanzees (90-106,6 cm. long) 
 
 IP. 
 
 FIG. 82. CEREBRUM OF A HUMAN EMBRYO SEVEN TO EIGHT MONTHS OLD. 
 
 (Lateral View.) 
 References as for Fig. 79. 
 
 the relative brain weight is markedly lower, viz. 1 :42,5 (391 : 
 16650) or 1:52 (375,6:19500). It is probable, however, 
 that the average brain weight in older Chimpanzees is con- 
 siderably lower, as in a body weighing 28 kilogrs. it scaled 
 1 : 75. If this is the case, a comparison with an adult human 
 being, in whom the average brain weight is 1:40-35, shows 
 that the brain of Man is relatively at least twice as heavy as 
 that of the Chimpanzee, and absolutely three or four times 
 as heavy. We learn from this that the brain of the Ape, unlike 
 that of Man, develops little with age, and attains its definitive 
 condition far sooner. 
 
 The Chimpanzee and the Orang appear to have approxi- 
 mately the same brain weights, but the Gorilla stands markedly 
 distinct from them, its body being far larger, while its brain 
 does not correspondingly increase in size. The weight of the 
 body of an adult Gorilla being taken at 94-95 kilogrs., and the
 
 THE NERVOUS SYSTEM 131 
 
 brain weight at 425,25 grs., the relative weight of the latter 
 would be 1 : 220 (Moller). 
 
 A comparison of the cerebral surface shows that Man 
 differs from the Anthropoids in the preponderance of the 
 frontal lobe (/>., Figs. 78-82) and, to a lesser degree, of the 
 occipital lobe (pc.\ and in a corresponding backward extension of 
 the temporal lobe (tp.}. The parietal lobe (pa.') is about equally 
 developed in the brains of Man and of Anthropoids (Moller). 
 
 Since this subject has so far been, comparatively speaking, 
 little investigated, and since our knowledge of the functional 
 
 */. c.h. e P-f; b c - p '"f *' cf. A.6. 
 
 . cr - ch- 
 
 op. \ 
 
 id. 
 FIG. 83. HYPOTHETICAL MEDIAN-LONGITUDINAL SECTION THROUGH THE SKULL 
 
 AND BRAIN OF A VERTEBRATE EMBRYO. (Partly after Huxley.) 
 
 cr'., basis cranii ; ch., chorda dorsalis ; cr"., roof of the skull ; na., nasal cavity ; c.h., 
 cerebral hemisphere, with the corpus striatum (c.s.) lying basally, and the olfactory 
 lobe (ol.) anteriorly ; f.b., thalamencephalon (fore-brain), which has been produced 
 dorsally into the pineal gland (ep.\ and basally into the infundibulum (if.), lip., the 
 hypophysis. Anteriorly, the base of the optic nerve (op. ) is seen, and in the lateral 
 wall the position of the optic thalamus is indicated (th. ) ; c.p., posterior commissure ; 
 m.b., mid-brain ; h.b. , hind-brain ; c.c., canalis centralis. 
 
 significance of the different regions of the brain is still far from 
 complete, no general conclusions as to the possible correlation 
 of these differences with mental peculiarities can be drawn. 
 
 The slight projection of the cerebellum from below the 
 edges of the occipital lobes in Anthropoids, is due less to the 
 narrowness of the latter than to the striking breadth of the 
 cerebellum itself (Moller). Even in man the occipital lobes do 
 not always completely cover the cerebellum, but in this matter 
 considerable variation occurs. 1 
 
 Special interest attaches to the pineal gland (epiphysis cerebri) 
 (ep., Figs. 84 and 86) which arises in the region of the roof of 
 the fore-brain. 
 
 In the lower Vertebrates this organ either lies free or is 
 embedded in a depression or foramen (parietal foramen) of the 
 1 It must be left to future investigators to prove whether the topography of the 
 course of the fibres in the optic chiasma given by Joh. Moller for Anthropoids, i.e. 
 the constant occurrence at the surface of certain groups of fibres, has a parallel in 
 Man (perhaps in embryos or the lower races).
 
 132 
 
 THE STRUCTURE OF MAN 
 
 skull roof. In Man and Mammals the pineal gland is pushed 
 away from the free surface of the brain by the growth of the 
 hemispheres, and it is thus shifted back till it comes to lie in a 
 depression between the corpora- quadrigemina (nates). It is in 
 
 Fio. 84. BRAIN OF A BABBIT. 
 
 A, dorsal ; B, ventral ; C, lateral view ; b.o., bulbus olfactorius ; cb'. , median Jobe of the 
 cerebellum (superior vermis) ; cb"., its lateral lobe ; cr., crura cerebri ; ep., glandula 
 pinealis ; /.&., fore-brain ; f.p., fissura pallii ; h.b., hind-brain ; h.p., hypophysis ; 
 i to xii, first to the twelfth cranial nerves ; m.b., mid-brain ; md., medulla oblongata ; 
 p.v., region of the pons. 
 
 this position recognisable, in Man, as the well known dorso-ventrally 
 compressed pine- or cone-shaped organ. Into it the lumen of the 
 third ventricle frequently extends ; and its base divides into two 
 stalks, which pass directly into the taenise medullares and thalami
 
 THE NERVOUS SYSTEM 
 
 133 
 
 optici. The pineal gland of Anthropoids is identical in appear- 
 ance with that of Man. 
 
 The pineal gland in Man is remarkable for its rich vascularity 
 and for its cellular follicles, in which concretions (brain sand) may 
 develop. 
 
 This " gland " has all along claimed the special attention of 
 morphologists ; and as great difficulty has been found in under- 
 
 Fio. 85. LONGITUDINAL SECTION THROUGH THE PINEAL ORGAN OF A REPTILE 
 
 (Hatteria punctata). (Slightly magnified.) (After Baldwin Spencer. ) 
 cp. , connective tissue capsule ; "., " lens " ; cv., cavity of the organ filled with fluid ; '., 
 retina-like portion of the vesicle ; vs., blood-vessels ; c.n., cells in the nerve stalk (s.n.). 
 
 standing it, it has received very different explanations. It is 
 only in recent years that light has been thrown upon it by 
 numerous works devoted to its comparative anatomy and 
 ontogeny. It has been proved that, in close connection with the 
 actual stalk of the gland, there is a second vesicular outgrowth, 
 which, in certain Vertebrates, shows undeniable traces of being 
 a rudimentary unpaired organ of sight. [This organ is now 
 known to arise during development iiTall classes of Vertebrates],
 
 134 THE STRUCTURE OF MAN 
 
 and to have undergone degeneration in the course of Phylogeny, 
 as the roof of the skull became more and more solid. The nerve 
 belonging to it is, so far as is known, most fully retained in 
 certain Eeptiles. In some animals this organ only occurs in the 
 embryo, and altogether disappears at a later stage. 
 
 In examining the finer histological structure of the pineal or 
 parietal organ in the Lizard-like Eeptiles and the Slow- worms, we 
 find the upper wall may in many cases become thickened to 
 form a transparent epithelial plate (?*"., Fig. 85), which is often 
 lens-shaped, while the rest of the epiphysial vesicle (?*'.), which is 
 often flattened, is differentiated into a multilaminar "retina." 
 " Lens " and " retina " thus arise in complete continuity out of one 
 and the same structure ; and it is only at a late stage in develop- 
 ment that a more or less distinct demarcation between them is 
 effected (Be"raneck). The organ is invested by a capsule of 
 connective tissue (cjp.). 
 
 In many cases the skin which overlies the parietal organ, as 
 well as the connective and dural tissues below it, remain free from 
 pigment, indeed they are sometimes so clear and transparent that 
 they might be considered as a kind of cornea. This justifies the 
 assumption that the function of the organ may not be altogether 
 lost even now. 1 Owsiannikow claims to have found traces of a 
 vitreous body within it. 
 
 According to Leydig, Selenka, and others, there is found in 
 the embryos of various Vertebrates (Selachians, Eeptiles, Mar- 
 supials, and probably in others) another unpaired dorsal appendage 
 of the fore-brain, for which Selenka has suggested the name 
 " frontal organ " or " paraphysis." 
 
 Whereas the epiphysis grows forward, the paraphysis, which 
 arises much later ontogenetically, grows backward and, when the 
 epiphysis is once fixed in the epidermis, pushes itself in under 
 that organ, so that the parietal eye comes to rest on the para- 
 physis as on a cushion. Until the embryo is mature, the 
 epithelial tube of the paraphysis remains hollow and in open 
 communication with the cavity of the brain. 
 
 If it be established that the pineal organ and gland are 
 really sui generis, distinct in origin, there is evidence of three out- 
 
 1 [In view of the intimate relationship between birds and reptiles, it is an 
 interesting circumstance that Klinckowstrom has discovered in embryos of certain 
 of the former (Anser. Larus.) a "brow spot," which in its structural differentiation 
 suggests not only the last trace of a pineal organ, but a pineal scale like that of 
 living lizards. Spengel's Zoolog. Jahrb., Anaf. AUh. Bd. v. p. 177.]
 
 THE NERVOUS SYSTEM 135 
 
 growths from the roof of the brain, of which one, the pineal 
 organ, can with certainty be regarded as originally a sense organ. 
 
 [Locy, from the study of young shark embryos, has adduced 
 reason for believing 1 that, at an early stage in development, two 
 pairs of accessory optic vesicles appear, concurrently with those 
 giving rise to the retinae of the paired eyes. The ultimate fate 
 of the former has yet to be fully worked out, and nothing is 
 as yet known concerning the post-embryonic development of the 
 paraphysis. There is, however, reason for thinking that the 
 latter probably takes part in the formation of the choroid plexus ; 
 but whether this is the case or not, Locy's observation seems to 
 indicate that the pineal organ at least may have been originally 
 paired.] 
 
 At the under surface of the thalamencephalon, and connected 
 with the infundibulum, there lies an appendage of the brain called 
 the hypophysis or pituitary body. 
 
 Two distinct structures enter into the formation of this 
 organ, one glandular and the other nervous. The former arises 
 in Man and the higher Vertebrates bylT constriction from the 
 primitive mouth sac (stomodseum) of the embryo, and the latter 
 is, as a rule, assigned genetically to the floor of the thalamen- 
 1 cephalon. Future research must show how far this is the primary 
 origin of at least the glandular portion of the organ, and this is 
 the more desirable since some very interesting results recently 
 obtained by von Kupffer, from the study of Lamprey and Sturgeon 
 embryos, have given new zest to the inquiry into the primitive 
 history of this enigmatical structure. The subject cannot be 
 dealt with in detail here, but mention, may be made of at least 
 a few of the chief points concerning it. 
 
 According to von Kupffer, the hypophysis arises in the 
 above-named Fishes in the manner described by Scott for the 
 Amphibia (Amblystoma). At a very early embryonic stage an 
 ectodermal cell-strand grows in from the anterior region of the 
 head. This cell-strand in the Sturgeon consists of two closely 
 applied epithelial plates which form a fold, and at the point 
 at which it arises the antero- dorsal border of the fore-brain 
 is connected with a thickened portion of the ectoderm by an 
 originally hollow and subsequently solid tract. This ectodermal 
 thickening is termed by von Kupffer the median olfactory 
 plate, and the corresponding cerebral outgrowth the lobus 
 olfactorius impar : in fact, according to this author, the Sturgeon, 
 1 [Anat. Anzeiyer, vol. ix. p. 169.]
 
 136 THE STRUCTURE OF MAN 
 
 during its earliest development, passes through a monorhinal 
 stage, and probably more or less distinct traces of this can be 
 discovered in the embryos of all Vertebrates. 
 
 From this median or unpaired olfactory plate, therefore, 
 which may be homologous with the anterior neuropore of 
 embryologists, and with the " olfactory organ " of Amphioxus, the 
 hypophysial tube arises, prior to the formation of the mouth, and, 
 growing down gradually, approaches the base of the brain till 
 it reaches the neighbourhood of the infundibulum. The epithelial 
 strand later separates off from the ectoderm, and finally to a great 
 
 FIG. 86. MEDIAN LONGITUDINAL SECTION THROUGH THE HEAD OF A NEWLY - 
 
 HATCHED LARVA OK THE SMALL LAMPREY (Petromyzon planeri). 
 
 f.b., fore-brain ; m.b., mid-brain ; h.b., hind-brain ; ep., glandula pinealis ; ol., olfactory 
 organ ; hp. t hypophysis ; st. t buccal sac (stomodaeum) ; al., endodermal cavity 
 (mid-gut) ; ch., chorda dorsalis. 
 
 extent degenerates, so that at last nothing remains of it but its 
 constricted, swollen end the glandular hypophysis of adult 
 anatomy. A somewhat similar arrangement is seen, as has 
 already been said, in Ammocoetes and certain tailed Amphibians. 
 
 The facts appear to me strongly to confirm the view that > ( 
 the hypophysis corresponds with the primitive mouth (archi- ' 
 stoma) of the ancestors of the Vertebrata. 
 
 The present vertebrate mouth (neostoma) is by some considered 
 to have arisen by the running together of a pair of branchial 
 clefts ; but this is by no means definitely proved. 
 
 According to Scott, the close connection between the hypo- 
 physis and the oral invagination (stomodseum) of the higher 
 Vertebrates was developed secondarily in consequence of cephalic 
 flexure, due to the preponderating development of the fore-brain. 
 If so, the hypophysis had originally no relation either to the 
 mouth or the nose, but is to be regarded as an organ (? sensory),
 
 THE NERVOUS SYSTEM 137 
 
 inherited from a supposed invertebrate ancestor, which originally 
 had the form of a blind sac on the free surface of the head, close 
 to the olfactory organ. Scott and von Kupffer thus differ con- 
 siderably in their views ; [but whatever the original significance 
 of the hypophysis, all observers are agreed that it is the vestige 
 of an organ originally distinct from the present vertebrate mouth 
 and from the nose of at least the gnathostomata. With respect 
 to it, the Vertebrata collectively fall into two distinct and diversely 
 modified assemblages, viz. (i.) the Epicraniata (Lampreys and 
 IJags), in which it is carried up with the nose and perforates the 
 basis cranii from above ; and (ii.) the Hypocraniata (Fishes 
 proper, Amphibians, and Amniota), in which it is carried down 
 and inwards with the mouth, and perforates the basis cranii from 
 beneath.] 
 
 We still have to consider those cases in which degeneration 
 of the brain is either beginning or has made some progress. 
 We find an instance of commencing degeneration in the lobus 
 olfactorius, to which we shall have to return when considering 
 the olfactory organs. A case of advanced degeneration is seen 
 in the roof of the fourth ventricle. This, in Man, as in all 
 Vertebrates, becomes almost entirely transformed in the course of 
 Ontogeny into a vascular membrane, overlying a simple epithelium, 
 and continuous laterally and anteriorly with the pia-mater. The 
 lining epithelium is continuous laterally and posteriorly with the 
 delicate structures bordering on the calamus scriptorius known as 
 the obex, ponticulus, and ligula (tsenia). These all consist of 
 nervous tissue, and are to be classed morphologically with the 
 epithelial layer just mentioned. The rudimentary character of 
 the series is evident, and the same applies to the velum medullare 
 posterius. 
 
 In contrast to the degenerate portions of the brain, other 
 parts are found to be in course of progressive development ; these 
 more than compensate for the loss not only of the above 
 mentioned, but of all other degenerating parts. We have only 
 to mention the cerebrum, with its continually developing com- 
 plexity of the nerve tracts, especially the complex components of 
 the gray cortex, which, as the organs of the mental faculties, are 
 kept in constant touch with the surrounding world by means of 
 the centripetal and centrifugal tracts of the peripheral nervous 
 system. 
 
 To this topic we shall have to return. It will here suffice 
 to mention one more portion of the brain in which variation in
 
 138 THE STKUCTURE OF MAN 
 
 form and size are evident to the naked eye, and are, I consider, 
 to be interpreted as progressive. This is the lobus occipitalis 
 of the cerebral hemisphere, in which we find great variation 
 in the extent of the calcar avis, and the posterior cornu of 
 the lateral ventricle. Exact statistics on this subject are a 
 desideratum. 
 
 [In connection with the question of structural degeneration of the brain, 
 certain recent observations of Forsyth-Major are of especial interest. It has 
 been generally assumed that the smooth cerebrum and exposed cerebellum of 
 the Lemurs, which are placed at the root of the order Primates of which Man 
 is the highest member, are primitive characters, indicative of a relationship 
 with and origin from a lowly order of Mammals. Forsyth-Major has discovered 
 evidence of structural simplification and degeneration, during Ontogeny, of 
 the brain of certain Lemurs (apparently in correlation with preponderating 
 development of the face and nose) which points to the conclusion that the 
 supposed primitive characters named may be secondary and retrogressive 
 a welcome suggestion, in view of Cope's discovery that the oldest known 
 Lemurs (Anaptomorphidae) had large and highly - organised brains. The 
 brain of the human foetus, at from three to five months, develops certain 
 convolutions which are early lost and have nothing to do with those of the adult. 
 Kolliker, Beer, Cunningham, and others have investigated them, and the 
 latter, suggesting that they may be the expression of mechanical effects conse- 
 quent on a " quadrupedal growth pause " in development, has proposed to 
 term them " transitory fissures " (microgyri of Beer). Considerable interest 
 attaches to the occasional appearance of convolutions upon the surface of the 
 hemispheres in normally smooth-brained Mammals ; as also to the question 
 whether these are progressive structures, or conversely, whether they, and 
 the convolutions which seem to disappear during Ontogeny among the 
 Lemuroidea, may have anything to do with the "transitory fissures" above- 
 named. A wide field of inquiry is here opened up, which gives promise 
 of most important results.] l 
 
 PERIPHERAL NERVOUS SYSTEM 
 
 But few retrogressive phenomena are here met with ; among 
 these are the present condition of the rami recurrentes of the three 
 branches of the trigeminus and of the vagus, which run to the 
 dura mater, and further, of the ramus auricularis of the latter nerve. 
 
 The fact that in the region of the hypoglossus vestiges of 
 the posterior roots with their ganglia have been found in human 
 embryos, as they were long since in certain lower Mammals, 
 indicates that assimilation of spinal or vertebral elements may 
 be going on in the occipital region of the skull. Certain delicate 
 nerve loops which lie in the region of the trigeminus, facialis 
 
 1 [Cf. Forsyth-Major in Rothschild's Novitates Zoological, vol. i. p. 35 ; and Cun- 
 ningham, Cunningham Memoirs, E. Irish Acad., No. VII. p. 30.]
 
 THE NERVOUS SYSTEM 139 
 
 and glossopharyngeus nerves, or are connected with their ganglia, 
 may possibly be retrogressive in nature ; but we cannot enter 
 further into their study here, as to do so would lead us too far 
 into Comparative Anatomy, and be beyond the purpose of this 
 work. 
 
 The variations which are continually taking place in the 
 brachial and lumbo-sacral nerve plexuses, in connection with the 
 shifting of the limbs and their girdles during development, have 
 been already considered in detail (ante, pp. 95 and 96). 
 
 THE SYMPATHETIC SYSTEM 
 
 Here also extraordinary variations are to be found in the 
 form, number, and size of the ganglia of the main trunks, in the 
 peripheral plexuses, and in the connections between the two chief 
 trunks ; but, except in the caudal portion of this system, we are 
 not justified in assuming that we have to do with retrogressive 
 phenomena.
 
 THE SENSE OKGANS 
 
 THE sense organs have always been classified into lower 
 and higher, and that not without justification. Conspicuous 
 among the lower sense organs are those of the tactile sense lying 
 in the integument ; and by the higher sense organs are under- 
 stood the olfactory, visual, auditory, and gustatory apparatus, 
 which are located in special depressions or cavities of the 
 head. 
 
 It may now be considered as certainly established that all 
 the latter may be traced back phylogenetically to tegumental 
 sense organs, and that their sensory epithelia are to be regarded 
 as modified epidermal derivatives. 
 
 INTEGUMENTAL SENSE OKGANS 
 
 It appears to me not improbable that the tactile bodies which 
 are profusely scattered throughout the integument of man are 
 genetically closely connected with his gradual loss of hair. I am 
 led to this conclusion by the fact that tactile bodies appear 
 in the lower Mammals principally, indeed, perhaps exclusively, 
 in places where there is no hair (proboscis, entrance to the mouth, 
 plantar surface of the paw). They appear unnecessary in hairy 
 parts of the body, because the hairs themselves, being richly 
 provided with nerves, are capable of exercising a delicate tactile 
 function. 
 
 How far certain epithelial structures proved by Maurer to 
 exist in the hair germs are to be deduced from phylogenetically 
 older tegumental sense organs like those of the Anamnia, must 
 be established by further investigation (compare also the already- 
 mentioned temporary appearance of sense organs in the cephalic 
 region in embryos, ante, p. 133).
 
 THE SENSE ORGANS 141 
 
 THE OLFACTORY ORGAN 
 
 The Number and Structure of the Olfactory Ridges 
 and the Turbinals 
 
 Following Broca and Turner, we may divide Mammals, accord- 
 ing to the development of their olfactory apparatus, with especial 
 reference to its cerebral portion [" rhinencephalon," " lobe lim- 
 bique "] into series, viz. : 
 
 [i. Osmatic series, turbinals present and usually five in 
 number.] 
 
 (a) Macrosmatic [organs of smell largely developed], (most 
 Mammals, e.g. Edentata, Ungulata, Carnivora, Eodentia, Mar- 
 supialia, and Lemuroidea). 
 
 (6) Microsmatic [olfactory apparatus relatively feeble] (Pinni- 
 pedia, Whalebone - Whales, 
 Apes, Man, and Monotre- 
 mata). 
 
 [ii. Anosmatic series, or- 
 gans of smell, apparently 
 absent in the adult] (Dol- 
 phins and Toothed - Whales 
 generally, although many of 
 these require further investi- pio> 87 ._ LATERAL VlEW OF THE NASAL 
 gation with regard to this CHAMBER OF A HUMAN EMBRYO. 
 
 point) 1 ^' **' *H' ^ e taree olfactory ridges ; 
 
 f, supernumerary ridge which occurs in 
 The first point to be the embryo ; ., tip of the nose ; pi., 
 
 established is the primitive J-M-ftj - """' '' "" 
 number of the olfactory ridges. 
 
 The investigations of Zuckerkandl lead to the conclusion that 
 the original number of these ridges was comparatively small, and 
 that where, among Mammals, we have a large number or a 
 more complicated form of turbinal, they have been secondarily 
 acquired in the interest of a greater physiological efficiency. 
 
 Most orders of Mammals, e.g. the greater number of Carnivora, 
 Eodentia, Insectivora, Lemuroidea, Marsupialia, with Ornitho- 
 rhynchus (Echidna ?), have five olfactory ridges ; but the Ungulata 
 
 ' 1 [Kiikenthal has recently worked out the development of the olfactory organ in 
 the Delphinid*, and has proved (i) that the union of the external nasal apertures 
 is a secondary process occurring during Ontogeny, and (ii) that in the young embryo 
 well-developed olfactory lobes and bulbs are present which disappear in the adult. 
 Denksch. d. medic. -natur-wiss. Gesellsch., Jena, Bd. iii. pp. 326 ct seq.]
 
 142 
 
 THE STRUCTURE OF MAX 
 
 have, as a ride, more than five, and sometimes as many as eight. 
 The Edentata possess from six to eleven (Orycteropus has eleven, 
 Dasypus nine, Bradypus and Manis seven, Myrmecophaga six), 
 and the Primates from one to three. 
 
 At a late embryonic period three olfactory ridges are often 
 present in Man, inasmuch as between the superior and inferior 
 a third projects into the lumen of the nose (cf. Fig. 87). 
 This last, when present, is more or less distinct at birth, but 
 it becomes reduced later, the superior ethmo-turbinal, as a 
 rule, growing over it like a cover. With this superior ethmo- 
 turbinal, which must be considered as primary, the rudiment 
 of a fourth is found (cf. Fig.) ; but this is further differentiated 
 only in exceptional cases. We thus have at least four ethmo- 
 turbinals represented in the developing human nose, with three 
 olfactory meatuses; and this arrangement recalls those Mammals in 
 which there are four corresponding ridges present in the adult. 
 
 [Concerning variation of 
 the olfactory meatuses of 
 the human adult, on recent 
 examination of 152 indi- 
 viduals, 1 the dominant con- 
 dition presence of three 
 was observed in 56 per 
 cent; four were noted in 
 41 per cent, and five in 
 n1 '- 1'3 per cent. In three 
 r iL instances (i.e. approximately 
 in 2 per cent) only two were 
 found, the superior turbi- 
 nated bone being absent; 
 
 and in one of these " there 
 FIG. 88. SAGITTAL SECTION THROUGH THE i . i i , f 
 
 NASAL AND BUCCAL CAVITIES OF THE was . a horizontal plate of 
 HUMAN HEAD. cartilage projecting into the 
 
 /, II, III, the three olfactory ridges ; sn'., frontal nfle! ol fr,n f f V,o 
 
 sinus ; sn"., .sphenoidal sinus ; os., opening of n&Sal tOSSa r m the se P tlun 
 Eustachian tube ; be., entrance to the mouth ; On a level with the inferior 
 
 >ra ; v.u., axis turbinated bone."] 
 
 When it is further re- 
 membered that the maxillary, frontal, and sphenoidal sinuses 
 (sn'., sn"., Fig. 88) are also lined by olfactory mucous membrane, 
 
 1 [Made under the auspices of the Collective Investigation Committee of the 
 Anatomical Society of Great Britain and Ireland. See Jour. Anat. and Phys 
 vol. xxviii. p. 73.]
 
 THE SENSE ORGANS 143 
 
 and that in the sinus fron tails of the embryo (as Professor 
 Killian, who has paid especial attention to this subject, has 
 kindly informed me) even now ridge-like structures sometimes 
 occur, reminding one in the manner of their origin of the eth- 
 moidal system, it seems probable that there was once a still more 
 highly specialised development of the olfactory organ. 
 
 The above remarks apply to the olfactory region proper, i.e. 
 to the ethmoidal labyrinth with its olfactory ridges. I have 
 so far purposely avoided the term turbinal, and have always used 
 instead the word ethmo-turbinal, or Schwalbe's term " olfactory 
 ridge," in order to exclude any suggestion of parallelism with the 
 " turbinal " of the lower Vertebrata. But we now come to the 
 question of the persistence of the latter among the Mammalia. 
 To these animals it has been handed down as the " inferior 
 turbinal," but it now possesses no olfactory epithelium, having 
 evidently undergone a change of function. In animals in which 
 smell is acute, it is folded or more or less branched, i.e. is much 
 more complicated than in animals with less keen scent, in which 
 it is merely singly or doubly scrolled. The latter must be con- 
 sidered as the more primitive condition, from which the former 
 was secondarily developed. 
 
 The conditions which have led up to reduction of the olfactory 
 organ in the vertebrate series are very various. In Man its 
 degeneration is due to the subordinate part played by it. The 
 olfactory apparatus is here, as Broca has rightly remarked, but a 
 modest vassal of the brain, which does not reach the perfection 
 of the other higher sense organs. 
 
 JACOBSON'S ORGAN 
 
 The first indications of this organ appear to occur among the 
 tailed Amphibia, 1 in the form of a small ventral diverticulum 
 of the nasal cavity (jc., Fig. 89, A, B), which either retains 
 its original position throughout life, or in the course of develop- 
 ment becomes shifted so as to lie in the maxillary sinus (Fig. 
 89, E). 
 
 At exactly the same point near the nasal septum, where, in 
 the Amphibia, this organ arises, in the Amniota Jacobson's organ 
 is found, in the form of a diverticulum of the principal nasal 
 
 1 Apparent indications of this apparatus are forthcoming in certain fishes 
 
 (Polypterus).
 
 144 
 
 THE STRUCTURE OF MAN 
 
 g.m.
 
 THE SENSE ORGANS 145 
 
 H 
 
 FIG. 89. A-D, VARIOUS STAGES OF DEVELOPMENT OP [THE SO-CALLED] JACOBSON'S ORGAN 
 OF THE UKODELIA, illustrated by a series of transverse sections. F, transverse 
 section through the nose and Jacobson's organ of Lacerta agilis ; G, the same of 
 a placental Mammal ; H, the same of Ornithorhynchus, after Symington ; I, diagram- 
 matic side view of G. 
 
 In A the organ commences medially and basally ; in D the lateral position is attained ; 
 E, the Gymnophione, in which separation from the principal cavity is effected ; na., 
 nasal cavity ~ f jc., Jacobson's organ ; c.j., Jacobson's cartilage ; g.tn., inter-maxillary 
 gland ; g.n., nasal gland ; n.o., olfactory nerve ; n.t., trigeminal nerve ; d.n., nasal 
 duct ; mx., upper jaw ; sp., septum nasi ; o.d., dumb-bell-shaped bone, forming a 
 support for Jacobson's organ. 
 
 cavity (jc., Fig. 88, G, H, I). In most Mammals this becomes 
 constricted off and secondarily connected with the buccal cavity. 
 A lateral displacement does not take place, and the organ remains 
 between the floor of the nasal cavity and the roof of the mouth, 
 i.e. in its original position. It is always lined with a pronounced 
 sensory epithelium, innervated by the ventral fasciculus of the 
 olfactory nerve (n.o., Fig. I). 
 
 Eecent investigation has proved, without doubt, that vestiges 
 of a Jacobson's organ are to be found in adult human beings. 
 Before considering these in detail, however, certain structures 
 which attracted the attention of the earlier investigators need 
 to be dealt with. 
 
 Huscke's "plough-share cartilage" in Man was formerly 
 regarded as the vestige of the two cartilaginous tubes lying near 
 the base of the nasal septum, which in many lower Mammals 
 envelop the organ of Jacobson. This is incorrect, since, as 
 Spurgat has shown, the same cartilages are found in the human 
 organs of Jacobson as in those of the lower Mammalia, but in a 
 much reduced condition. These organs, together with the Sten- 
 son's canals, open into the buccal cavity through the ductus
 
 146 THE STRUCTURE OF MAN 
 
 incisivi. The latter are sometimes wide, sometimes constricted, 
 and they communicate with the mouth either independently or 
 by a common orifice. In fresh embryos the passage of the canal 
 is to be found open only in exceptional cases ; there are usually 
 two canals present on both the buccal and nasal surfaces of the 
 palate, the former of these are usually the more prolonged. Both 
 pairs are lined with mucous membrane, and, ending blindly, form 
 together an obtuse angle. Traces of the buccal ends of these canals 
 may still be found in some adults in the form of epithelial 
 strands ; as a rule, however, they disappear without leaving any 
 trace, while the upper or nasal portions persist. 
 
 Between the two canals, or their vestiges, which run up from 
 the buccal cavity just behind the inner incisors, there is on the 
 palate a papilla, the so-called papilla palatina incisiva (p.p., 
 Fig. 95). This has been investigated by Merkel, and found to 
 be a sensory organ, but its physiological significance is not under- 
 stood. 
 
 Returning to the actual organ of Jacobson in Man, the 
 epithelial tubes which form its inner lining agree in every 
 respect morphologically with those of certain lower Mammals 
 (e.g. the Rat). The epithelium of the outer wall somewhat 
 resembles that of the regio respiratoria of the nasal cavity, and 
 that of the inner wall, which is almost four times as thick, that 
 of its regio olfactoria. There are no traces, however, of the 
 characteristic filamentous olfactory sense -cells the cells being 
 much more like the supporting cells of the olfactory epithelium. 
 Between them occur short fusiform elements which do nob reach 
 the surface (and may perhaps be incompletely developed olfactory 
 cells). Numerous acinose glands open into the organ. 
 
 Although no nerves have been as yet discovered in the organ 
 in the human adult, in the embryo, as in the lower Mammals, 
 a well-defined branch of the olfactory nerve (n.o., Fig. 89, 1) runs 
 to it. 
 
 All things considered, the organ of Jacobson in Man has 
 certainly all the characteristics of a vestigial structure. This is 
 seen not only in its inconstant occurrence7 in its frequent one- 
 sided development, and in its degeneration, which commences 
 even during fcetal life, but in its histological structure (Merkel, 
 Schwink, Chiarugi). In Anthropoids it is still further reduced. 
 
 [This organ attains its fullest morphological development 
 in the Monotremes (Ornithorhynchus) (Symington).]
 
 THE SENSE ORGANS 
 
 147 
 
 THE PROJECTILE NOSE 
 
 Whereas the olfactory ridges and Jacobson's organ of Man 
 are to be considered degenerate, the projectile nose and its 
 skeletogenous supports are in a progressive condition ; they may 
 indeed be considered as specifically human structures. It cannot 
 as yet be said with certainty what gave the first impulse to their 
 
 FIG. 90. HEADS OF TWO HUMAN EMBRYOS. 
 
 A, at the end of the second ; B, at the beginning of the third month (after W. His), 
 aw., external auditory involution, with the pinna (p.) seen developing around it. vs., 
 eye ; ol., nose. 
 
 development. 
 inquiry. 1 
 
 This question awaits an extended morphological 
 
 THE EYE 
 
 The human eye itself shows few vestigial structures ; and 
 these, being limited to the embryo, are but transitory. I refer 
 to the arteria hyaloidea which passes through the vitreous body 
 within Cloquet's canal, and which is closely related to the fcetal 
 choroidal fissure! The former plays an important part in the 
 nutrition of the central part of the eye during embryonic life. 
 This is provided for in Fishes and Keptiles by organs known as 
 
 1 This has been undertaken by my pupil F. Spurgat, and a preliminary report on 
 his first series of observations will be found in the Anal. Anzeigcr, Bd. viii. p. 228.
 
 148 THE STRUCTURE OF MAN 
 
 the processus falciformis and the pecten which are permanently 
 retained, but in Man the corresponding structure undergoes com- 
 plete degeneration before birth. 
 
 We meet with indications of atavism in connection with the 
 accessory parts of the eye. In the fissura orbitalis inferior, for 
 instance, there is an accumulation of smooth muscle, which is 
 the last vestige of the well-developed musculus orbitalis of lower 
 Mammals. In these animals the orbital fossa is usually in open 
 communication with the temporal, i.e. the two are not separated 
 by a bony septum (cf. ante, p. 58). This sheet -like muscle 
 forms the boundary between the temporal and the orbital fossae ; 
 it is innervated by nerves arising from the sphenopalatine 
 ganglion, and contracting, under their action, causes the eye to 
 protrude. 1 
 
 The occasional presence of laterally and medially diverted 
 offshoots of the levator palpebrse superioris muscle suggests that 
 it may once have been more extensive than at present. It may 
 be regarded as the vestige of the much more strongly developed 
 palpebralis muscle of certain lower Mammals ; further investiga- 
 tion of this subject, however, is required. 
 
 Great interest attaches to the fold of the conjunctiva which 
 lies at the median angle of the 
 eye, and is known as the plica 
 semilunaris (pi., Fig. 91). This 
 corresponds with the third eye- 
 lid, the so - called nictitating 
 membrane, of the lower animals. 
 In Birds, Anurous Amphibians 
 [some Sharks], and in many 
 
 pi. Eeptiles it is highly developed, 
 
 FIG. 91. HUMAN EYE. and, by means of a special mus- 
 
 cular apparatus, can be drawn 
 across the eyeball. It serves not 
 only to cover, but to keep clean the surface of the eye, the 
 upper lid [which in Man performs that function] being im- 
 movable, and the lower slightly movable or but little developed. 
 In Man, as in the Apes, in association with the absence of a 
 retractor bulbi muscle, this third eyelid has undergone great 
 degeneration, but it may still enclose (more frequently in Negroes 
 than in Caucasians) a cartilaginous support. Among sixteen 
 
 1 Nussbaum has recently announced the discovery in a human orbit of a muscle 
 homologous with the retractor bulbi of lower vertebrata. This awaits confirmation.
 
 THE SENSE ORGANS 
 
 149 
 
 pure Negroes this cartilage was found by Giacomini in twelve 
 individuals. 
 
 The plica semilunaris varies greatly in size at different ages 
 and in different races. In the new-born child, and during the 
 early years of life, it is broader than later, when it does not exceed 
 1 to 2 mm. in breadth. One known exception to this rule is, 
 however, found in the Malay tribe of the Orang-Sakai, in which it 
 reaches a breadth of 5 to 5| mm. It would be worth while to 
 examine other tribes in this respect. 
 
 In the caruncula lachrymalis (c.l., Fig. 91), which lies near the 
 plica semilunaris, glands are to be found, which in their structure 
 
 FIG. 92. DIAGRAM TO ILLUSTRATE THE SHIFTING OF THE LACHRYMAL GLAND, 
 
 WHICH HAS TAKEN PLACE IN THE COURSE OF PHLYOGENY. 
 
 The gland shifts in the direction of the arrows ; a, its position in the Amphibian ; b, in 
 Reptiles and Birds, and in certain human beings, in which case it may be regarded 
 as atavistic ; c, normal position in Man. 
 
 greatly resemble the lachrymal glands. These " nictitating glands " 
 constitute a distinct series and are in no way connected with the 
 sweat and Mollerian glands (Peters). Further, sebaceous glands 
 and fine hairs are, in the Primates, found near the caruncula. 
 
 Finally, a mention may be made of accessory lachrymal glands 
 which, with their ducts, occasionally lie near the conjunctival sac 
 at the lateral angle of the eye (cf. Fig. 92) i.e. in a position 
 approximate to that of the lachrymal glands of Amphibia and 
 Reptiles, and indicative of a gradual shifting of the lachrymal 
 apparatus in the course of Phylogeny. 
 
 Long stiff hairs which occasionally appear in the median
 
 150 THE STRUCTURE OF MAN 
 
 region of the human eyebrow recall from their position the 
 
 feelers [or supra-orbital vibrissae] of the lower Mammals. They 
 
 have been already dealt with (ante, p. 4). 
 
 A well-marked variation of the upper eyelid, apparently due 
 to arrested development during fcetal 
 life, is that resulting in the formation 
 of the so-called epicanthus (ep., Fig. 
 93). This, as its name suggests, is a 
 prolongation of the lid, which extends 
 more especially over the inner angle 
 of the eye. In certain races, such as 
 the Mongolian, this variation is con- 
 spicuous, giving rise to the slit -like 
 appearance and oblique position of the 
 aperture of the eye. The obliquity, 
 however, is only apparent, for it 
 
 FIG. 93. EYE OF A MONGOLIAN, vanishes if the skin above the nose 
 WITH THE EPICANTHUS (ep.). be tightly stretched. The epicanthus, 
 
 (After Merkel.) 
 
 as it appears in the Japanese, has been 
 
 very exactly described by Balz, who points out that it results 
 from the flatness of the bridge of the nose the superfluous skin 
 forming the fold in question. It is a matter of interest that a 
 similar condition has been observed among Caucasian children. 
 According to Kanke, about 6 per cent of these exhibit a markedly 
 Mongolian type of eye during the first six months of their lives. 
 
 THE AUDITORY ORGAN 
 
 In describing the skeleton of the head, mention has been made 
 (ante, p. 49) of the post-oral branchial sacs which characterise 
 a certain embryonic stage, and of the auditory ossicles (p. 64). 
 
 The latter arise partly from the original suspensory apparatus 
 of the lower jaw, i.e. from the visceral skeleton? As to the 
 former, only the anterior sac persists in Mammals ; and from 
 this (the spiraculum l of the lower Fishes) the cavity of the middle 
 ear (Eustachian tube and tympanic cavity) develops. 
 
 1 [Considerable interest attaches to the fact that the only living Vertebrates in 
 which this, the " hyo-branchial cleft " of comparative embryologists, is absent, are the 
 Marsipobranchii (Lampreys and Hags) and the Teleostean or Bony Fishes. Its occur- 
 rence in the embryos of the former group is now well known (Shipley, Qu. Jour. Micr. 
 Sci., vol. xxvii. p. 349), and Sagemehl has described its apparent vestige in certain 
 adult members of the latter (Morpholog. Jahrb., Bd. ix. p. 213). It is, however, in- 
 sufficiently recognised that the painstaking researches of Ramsay Wright have
 
 THE SENSE ORGANS 
 
 151 
 
 We have thus, in each case, a typical example of change of 
 function. 
 
 FIG. 94. DIAGRAM TO ILLUSTRATE THE METAMORPHOSIS DURING DEVELOPMENT OF 
 
 (I-V) THE FIRST TO THE FlFTH VISCERAL SKELETAL ARCHES. 
 
 From the first arch (the so-called Meckel's cartilage) two of the auditory ossicles, the 
 malleus and the incus (mb. and in.}, are represented as arising proximally, but about 
 this there is still considerable doubt (cf. ante, p. 64). p., pinna ; st., stapes ; pr., 
 processus mastoideus of skull. 
 
 From the second (hyoid) arch arise, proximally, the processus styloideus (p.s.), 
 distally the anterior or lesser cornua of the hyoid (CM.), and a portion of the basi- 
 liyoid or copula (bs.}. By far the greater portion of this arch becomes the stylo- 
 hyoid ligament (lg.). It is very doubtful whether the arch of the stapes also arises 
 from the proximal portion of the second arch ; the basal plate of the stapes, at any 
 rate, appears to arise independently of it. 
 
 The third arch gives rise to the greater part of the body (bs.), and the posterior 
 or greater horn, of the hyoid (c.p.). 
 
 The fourth arch gives rise to the upper segment (th'.) of the thyroid cartilage 
 and the fifth to the lower one (th".). The arytenoid cartilage (a.r.) is probably a deri- 
 vative of the fifth arch, tc., the cartilago triticea ; cr., cricoid cartilage ; tr. t trachea. 
 
 proved its regular occurrence, in a modified form, throughout the living Ganoids ; 
 and further, that in these fishes and certain Selachians it gives off a diverticulum 
 (the canalis tubo-tympanicus), which there is reason to regard as the possible homo- 
 logue of the middle auditory chamber of the terrestrial Vertebrata (cf. Ramsay 
 Wright, Jour. Anat. and Phys., vol. xix. p. 476).]
 
 152 THE STRUCTURE OF MAN 
 
 The pinna of the ear deserves special attention. In recent 
 years it has been thoroughly investigated by Schwalbe, the results 
 of whose researches are here incorporated. This pinna (p., Fig. 90) 
 is so elaborately modelled a structure that we can hardly imagine 
 it to be degenerate. It undergoes marked variation and adapta- 
 tion in different races, tribes, and individuals, as well as at 
 different ages. On close examination, variation is found, for the 
 most part, to affect those portions of it which stand out freely 
 from the head in a postero-dorsal direction. Schwalbe calls these 
 parts the " ear-folds," distinguishing the basal region as the zone 
 of the auditory prominence (cf. Fig. 71). 
 
 The pinna of Man arises from six prominences which develop 
 near the anterior visceral cleft (au., Fig. 90), and are called the 
 branchial auricular prominences. In the adult pinna they are 
 still evident as the helix, crus antihelicis inferius, crus helicis, 
 tragus, and antitragus (cf. Fig. 71). The human pinna, as 
 compared with that of Apes, would appear to be a degenerate 
 structure ; and in reality it is much reduced, being rolled over 
 in such a way as greatly to modify the upper edge of the helix 
 and part of the antihelix. 
 
 The variations of the ear -folds are of great interest, and 
 deserve close attention, in connection with the primitive history 
 of Man. 
 
 When we examine the highly movable ear of the Ungulata, 
 we find that the ear-fold gives rise to a very efficient sensitive 
 auditory funnel, which lies parallel to the axis l of the ear, and 
 ends in a free tip (spina). 
 
 In the Primates the pinna is much shortened, and is thrown 
 into folds (helix and antihelix) running at right angles to the 
 axis of the ear. Schwalbe finds two forms of free tip in the 
 Apes. (1) The Macacus or Inuus type (Fig. 71, C) ; and (2) the 
 Cercopithecus type (Fig. 71, D). In the former (C), which some- 
 what resembles in shape the ear-fold in human embryos at from 
 the fourth to the sixth month, there is a freely developed edge of 
 the helix which is not rolled over, and a distinct tip, always in 
 the same place. 
 
 From the eighth month, the human ear-fold enters upon a 
 degenerative process, which essentially consists in the rolling 
 
 1 By the axis of the pinna (regarded as a standard of measurement) is meant 
 a line which connects the true tip of the ear (Woolner's and Darwin's tip [spina]) 
 with the incisura auris anterior (cf. s.',s.",s."', Fig. 71, B). By the breadth of the 
 organ, in both Man and the lower mammals, is understood the measurement of the 
 attached portion (base of the ear).
 
 THE SENSE ORGANS 153 
 
 over of the edgfe of the ear, and in the greater development of 
 the antihelix. The tip, at the same time, shifts down along the 
 posterior edge of the helix, without, however, becoming rolled in ; 
 and there thus arises the so-called Cercopithecus form (cf. Fig. 71, 
 D) of the human embryo. 
 
 If the rolling in of the tip takes place, we have a third type 
 of ear, in which the tip is turned forwards (Darwin's tipped 
 ear). This (Fig. 71, E) is the usual condition of the human 
 adult, but many modifications of it are realised, the tip some- 
 times entirely disappearing as a free projection. 1 
 
 Besides the degeneration which finds its expression in the 
 reduction of the human ear-fold or pinna, 2 its cartilage is also 
 degenerating. The external auditory passage is among the lower 
 Mammalia (Marsupials) beset by three separate cartilages, movable 
 upon each other. The auditory canal of the child still distinctly 
 reveals this structure, although the alleged complete independence 
 of the basal piece affirmed by Burkner has not been fully estab- 
 lished (Schwalbe). The original clefts between the cartilages are 
 incompletely retained as the incisurse Santorini. 
 
 Secondly, the cartilaginous spina helicis (processus spinosus 
 helicis) is completely fused with the other cartilages of the pinna. 
 It corresponds in position with the free tip of the organ, and is 
 the homologue of a cartilage which, in many Mammals (Ungulata, 
 Carnivora, Eodentia), is independent, and is known as the scutulum 
 (clypeus or rotula). This scutulum fuses with the principal cartilage 
 of the ear in the Lemuroidea and the Apes, as well as in Man. 3 
 
 1 One curious variation is the occurrence on only one side of Darwin's process. 
 In a batch of military recruits it was found to be of medium size on the right side in 
 330 men, and on the left only in seventy-nine, and was thus four times as frequent on 
 the former as on the latter. It was found to be remarkably large on the right side 
 in ten individuals, and on the left only in one (Ammon). 
 
 2 The ear-fold may undergo reduction in Mammals which live underground or 
 in water. The rudiment of a pinna has been found in the embryos of some Whales 
 [and a structure which has been similarly interpreted may occasionally appear in the 
 adult Cetacean]. According to this, the ancestors of existing Whales must have 
 possessed an external ear, and since such an organ would occur in land animals, 
 we find in this fact a proof of the descent of the Whales from terrestrial Placentalia 
 (Kiikenthal). 
 
 3 In rare cases the scutulum may remain separate, even in Man. The familiar 
 lobulus auriculie, a non- cartilaginous fatty tegumental fold, first occurs in the 
 Anthropoids. In Man it undergoes many variations of form and size, and is not 
 infrequently entirely absent. It is never found in people of genuine Kyban descent, 
 nor in the Cagots of the Pyrenees (lilanchard). 
 
 I have to thank Herr Otto Ammon of Carlsruhe for the following statistics 
 obtained by him in connection witli the military recruiting in Baden for 1889 : 
 In 4171 ears (of 2086 men) in the military district of Mosbach, the free lobe was
 
 154 THE STRUCTURE OF MAN 
 
 We have every reason for believing that the ancestor of Man 
 could move his pinna to a far greater extent than can his descend- 
 ant of to-day. The pinna, no doubt, formerly took a great 
 part in the play of the features, and served, as it now undoubtedly 
 does in the lower Mammals, as an excellent instrument for 
 appreciating the direction of sound. 
 
 We are justified in this assumption, or rather affirmation, 
 by two facts: (1) the position in which the pinna is still often 
 found with relation to the head ; and (2) the presence of an exten- 
 sive musculature, the primitive history of which has already been 
 given, in describing the platysma myoides (cf. ante, p. 105). 
 
 With regard to the first point, it is well known that in by 
 far the greater number of individuals the pinna of the ear lies 
 more or less closely applied to the temporal surface of the head. 
 When attention has to be concentrated in a special direction, a 
 person may be seen to correct this physiologically bad arrange- 
 ment by applying the hollow of the hand to the back of the 
 ear, and so forming an artificial funnel like an ear trumpet. 
 
 This proceeding is less necessary in individuals whose 
 ears stand out, wing-like, from the head, i.e. are physiologically 
 more correctly disposed. From the modern aesthetic stand- 
 point this is a questionable advantage ; but it is a peculiarity 
 which has a great tendency to be handed on by inheritance. 
 In any case, this position is the original one, and the flattened 
 condition must be considered as secondarily acquired. 
 
 It is difficult to decide what influences brought about the 
 loss of physiological efficiency of the pinna. It may have been 
 due to a gradual alteration of the resting attitude of Man ; and 
 it should be generally known that deformation of the pinna, 
 which often lasts for years, may be produced in children by the 
 same cause. 
 
 wanting 1511 times, i.e. in 36 per cent. It was pi-esent in 2461 ears, i.e. in 64 per 
 cent ; of the median size in 2318, and specially large in 143, i.e. in 3 to 4 per cent. 
 Darwin's point was not to be found in 3106 cases, i.e. in 74 per cent ; it was present 
 in 1066 cases, i.e. in 26 per cent ; in 1027 it was of median size, and in only thirty- 
 nine (i.e. in 9 per cent) unusually large.
 
 THE ALIMENTAKY CANAL AND ITS APPENDAGES 
 
 HUMAN 
 
 PALATAL KIDGES 
 
 THE mucous membrane of the roof of the mouth is thrown into 
 a more or less marked median ridge the raphe, and into a 
 varying number of paired transverse ridges (r.p., Fig. 95), which 
 are especially well developed an- 
 teriorly near the incisors, but pos- 
 teriorly become flattened out. There 
 are five to seven of these transverse 
 palatal ridges on each side, and they 
 are more developed in the embryo 
 and the new-born child than in later 
 life, when their primarily regular 
 arrangement disappears. Those 
 farthest back degenerate, but the FIG. 95. PALATE OF 
 anterior ones increase in size and 
 shift nearer to one another as age 
 advances. In very aged persons 
 the whole system of ridges may almost, 
 disappear. 
 
 In these ridges which, as has been seen, vary to a great extent, 
 we have the representatives of a larger and more numerous series 
 met with in many lower Mammals (cf. Fig. 96) (in Apes there 
 are as many as ten). They are, as a rule, covered with a tough 
 stratified epithelium, and are functional in helping to triturate 
 and crush the food taken into the mouth (Gegenbaur). 
 
 Some years ago I called attention to the fact that in the 
 embryo Cat these ridges develop as rows of papillae, which later 
 unite, and I put forward the suggestion that we may be here 
 dealing with the remains of palatal teeth handed down even to 
 Man. Closer investigation must show whether these papillae are 
 actual vestiges of tooth structures or only horny growths, such 
 
 tina ; al., the later formed alveolar 
 
 even altogether,
 
 156 
 
 THE STRUCTURE OF MAN 
 
 as are still found among the lower Mammals in the form of 
 horny teeth or ridges (Ornithorhynchus, certain Marsupials, and 
 Edentates). 
 
 The extreme anterior border of the palate bears a median 
 eminence, the papilla palatina (p.p., 
 Figs. 95, 96). On either side of 
 this and of the raphe the naso- 
 palatine canal, already described 
 (ante, p. 146), opens. 
 
 TEETH l 
 
 The teeth are among the most 
 important and the most variable 
 organs of the vertebrate body. Long 
 before the appearance of the osseous 
 skeleton i.e. among the lowest Ver- 
 tebrates teeth and tooth-like tegu- 
 mental scutes are found. We cannot 
 be far wrong in asserting that the 
 
 FIG. 96. PALATAL FOLDS OF THE acquisition of teeth by the Vertebra ta 
 RACOON (Procyon lotor}. was a mos t important factor in the 
 
 and form of the teeth are greatly 
 determined by adaptation to the various conditions of life. 
 It is therefore often difficult to decide whether similar tooth 
 forms in fossil animals are cases of analogy or of homology. It 
 is quite possible for different races of animals, in adaptation to 
 similar modes of life, independently to acquire a similar dentition 
 [as for example in the case of the Crocodilian (Gamalis) and the 
 Dolphin (Platanista) living side by side in the Ganges]. If, 
 among the lower Vertebrata, we set aside dental ridges resulting 
 from the fusion of several distinct teeth, and the compound teeth 
 of many Fish, the teeth, as far up as the lower Eeptiles, are, for 
 the most part, simple pointed cones. In these animals they serve 
 only for seizing the prey, the further disintegration of which 
 takes place in the stomach and intestine. In the Mammalia 
 the food is more or less triturated in the mouth, and that chiefly 
 by the cheek teeth. 
 
 The dentition of the Primates is, as compared with that of 
 
 1 In this account of the teeth the researches of Rose have been largely 
 followed. 
 
 , papilla
 
 THE ALIMENTARY CANAL AND ITS APPENDAGES 157 
 
 Mammals generally, but little specialised. The molars in parti- 
 cular are comparatively simple cuspidate teeth, such as are found 
 among the oldest Mammals. Judged from the form of their 
 teeth, the Primates would appear to have branched off very 
 early from the common Mammalian stem. If we can draw 
 conclusions from the fossils as yet found, the Apes were not very 
 widely distributed in earlier periods. They probably lived, as 
 they now do, as climbing animals in tropical climates. In con- 
 sequence partly of their frugivorous manner of life, and partly of 
 the higher development of their intelligence, their teeth, of no 
 great service for warfare in the struggle for existence, appear to 
 have remained comparatively simple. 
 
 The dentition of Man agrees with that of the Old Worjd 
 Apes in number and shape of the teeth. The dental formula is : 
 
 2. 1. 2. 3 
 *-9~c.r- p.m. m. 32. The New World Apes, on the other 
 
 hand, have one more premolar in each set, their formula being 
 
 2. 1. 3. 3 
 
 i o o = 36. If the teeth of Man are compared with those of 
 
 a. 1. O. O 
 
 the nearly related Anthropoids, it is found that their respective 
 milk teeth agree in form and size more nearly than do their 
 permanent or successional dentitions. In the Anthropoids [with 
 the exception of the Gibbon (Hylobates)] the teeth of the second 
 series are larger and stronger than in Man, the contrast being 
 most marked in the size of the canines. The latter serve, in the 
 Ape, as powerful weapons in the struggle for existence, 1 and the 
 prernolars of the Apes are also, in consequence of the greater 
 development of their outer cusps, more caniniform than in Man. 
 The molars, on the contrary, are remarkably similar throughout, 
 although they are larger in Anthropoids than in Man ; and in 
 Hylobates, both in form and size, they can hardly be distinguished 
 from those of the human subject. 
 
 [Since, among Mammals generally], the milk teeth, i.e. those 
 
 1 We have abundant evidence that teeth were once used by Man or by his 
 ancestors as weapons of defence ; traces of such a use have not altogether disappeared 
 in human beings of the present day, and I cannot refrain from quoting in this connec- 
 tion a comment of Darwin which occurs in Ids book on the Origin of Man. 
 
 "He who rejects with scorn the belief that the shape of his own canines, and 
 their occasional great development in other men, are due to our early forefathers 
 having been provided with these formidable weapons, will probably reveal by sneer- 
 ing the line of his descent. For though he no longer intends, nor has the power, to 
 use these teeth as weapons, he will unconsciously retract his ' snarling muscles ' (thus 
 named by Sir C. Bell) so as to expose them ready for action, like a dog prepared 
 to fight."
 
 158 
 
 THE STRUCTURE OF MAN 
 
 of the first series, are as a rule far less modified than the 
 permanent teeth ; and since, in view of this, it is found that 
 the former agree in Anthropoids and Man far more than the 
 latter, we are justified in concluding that the teeth of both 
 Man and the Apes point back to a common origin from some 
 more or less intermediate type. The dental formula of the 
 Anthropoid Apes appears to be comparatively fixed ; but the 
 
 FIG. 97. HUMAN MOUTH, IN WHICH THE DEVELOPMENT OF THE UPPER OUTER 
 
 INCISORS HAS BEEN SUPPRESSED. 
 
 i'., inner incisors ; i"., outer incisors ; p.m., first premolar of the upper jaw ; c., upper 
 canines which, under the special conditions, come next in order to the upper inner 
 incisors. 
 
 teeth of Man show indications of gradual reduction, especially 
 in the variations in the size of the molars and of the upper outer 
 incisors. 
 
 The upper outer incisor shows every transition form between 
 a well-developed typical tooth and a short conical stump. In 
 many individuals, however, this tooth is altogether wanting (cf. 
 Fig. 97), and this dental variation may be hereditarily trans- 
 mitted through several generations. 
 
 The recent researches of Eose have revealed reason for 
 believing that the upper molars of Man have been derived from 
 a four-cusped tooth type, and the lower from a five-cusped type, 
 and that the numerical reduction of these cusps has been due to
 
 THE ALIMENTARY CANAL AND ITS APPENDAGES 159 
 
 Man's adoption of a more delicate diet, those degenerating first 
 which were the last to be added to form the compound tooth, 
 In the upper jaw this is the posterior lingual and in the 
 lower the posterior unpaired cusp. In the third molar, the 
 so-called wisdom tooth, the process of reduction may go so far 
 that finally, instead of a tooth with four or five cusps, a vestigial 
 stump alone appears. In a relatively large number of cases, 
 indeed, no wisdom tooth at all appears, it being either not 
 formed, or, if formed, retained within the gum. 
 
 Repeated investigations on this subject have all tended to 
 show that these signs of degeneration, so marked in Europeans, 
 are found in non-Europeans also, but not at all to the same 
 extent as among the Aryan race. Quite apart from patho- 
 logical cases, upper molars with three cusps, lower molars with 
 four, and reduced wisdom 'teeth, occur more frequently in 
 Europeans than in Negroes, Mongolians, or native Australians. 
 The low race last named, in its dental formula, appears least 
 removed from the hypothetical original type ; for in it are still 
 found complete rows of splendid teeth with powerfully developed 
 canines and molars, the latter being either uniform, or even 
 increasing, in size, as we proceed backwards, in such a way 
 that the wisdom tooth is the largest of the series. This is 
 decidedly a pithecoid character, which is always found in Apes. 
 The upper incisors of the Malay, apart from their prognathous 
 disposition, have occasionally a distinctly pithecoid form, their 
 anterior surface being convex, and their lingual surface slightly 
 concave. The ancestors of the Europeans seem to have had the 
 same form of teeth, for the oldest existing fragments of skulls 
 from the Mammoth age (e.g. the jaws from la Naulette and 
 Schipka) reveal tooth forms which must be classed with those 
 of the lowest races of to-day. 
 
 Apart from those variations in the human dentition, which 
 tend to approximate it to that of Anthropoids, still more 
 startling ones are occasionally found. For example, the 
 appearance of a third premolar is not very rare. In the Freiburg 
 anatomical museum there is an upper jaw with three well- 
 developed premolars on each side, thus showing the dental 
 formula of the New "World Apes. An increase in the number of 
 molars is also not very rare in both Man and the Anthropoids. 
 A fourth molar, in a more or less perfect form, is to be met with 
 in every large collection of skulls. Zuckerkandl has shown that 
 the epithelial germ of a fourth molar is not infrequently present
 
 160 THE STRUCTURE OF MAN 
 
 in Man, and Eose has since proved that this vestige is on each 
 side coincident with the end of the epithelial dental ridge. 
 
 By milk teeth are usually understood the first formed 
 generation of teeth. Eose, however, has recently attempted to 
 show that the milk teeth do not correspond with the first series 
 of teeth of the lower Vertebrates, and that they cannot be 
 homologised with any one special series in Eeptiles and allied 
 forms. Milk teeth, according to him, must rather be considered 
 to have arisen by the concrescence of several consecutive 
 generations of teeth of our ancestors, into one single, more solidly 
 constructed, series, the sum of all the remaining rows which were 
 once present having been in Man, as in all diphyodont Mam- 
 mals, compressed into the second or permanent series. [This 
 is, however, but one of several views put forward during recent 
 years on the subject of the Mammalian tooth genesis. Much 
 more important is the fact that, in Man, while the premolars 
 are comparatively simple teeth, the milk molars which precede 
 them are more complex, and more conformable, in the characters 
 of their fangs and crowns, to the type of the true molars. 
 These facts suggest that the deciduous (milk) molars are of a 
 more primitive (i.e. a less reduced) type than the successional. 1 ] 
 
 Until quite recently, the possibility of Man's developing a 
 third dentition was generally denied, but it is now proved that 
 that may sometimes occur. Baume, Zuckerkandl, and Eose, have 
 discovered a third set of enamelless tooth rudiments on the outer 
 or labial surface of the jaw, [and Schwalbe has lately suggested 2 
 that they may be the vestiges of a distinct pre-milk dentition, 
 of which traces have been found by Kiikenthal in the Seal, by 
 Nawroth in the Pig, and, in a more extensive and calcified form, 
 by Leche in the Banded Ant-Eater (Myrmecobius}. Great 
 interest attaches to further inquiry into these structures.] 
 
 In Fishes, Amphibians, and some Eeptiles, the first formed 
 
 1 [A very interesting allied case is furnished by the common Dog. In the upper 
 jaw of that animal, the characters of the fourth milk (deciduous) molar are almost 
 exactly those of the first true molar, and the characters of the third milk molar those 
 of the fourth premolar. Similarly, the second and first milk molars closely resemble 
 the third and second premolars, allowance being in all cases made for mere differ- 
 ence in size. Indeed, comparison of the premolars with the milk molars and, through 
 these, with the first molar, reveals a marvellous series of progressive stages in 
 simplification and reduction of the type of tooth represented in the adult dentition 
 by the first upper molar. I am hoping shortly to have this most important matter 
 fully worked out in detail. G. B. H.] 
 
 2 [Cf. Schwalbe, Morph. Arbeiten, Bd. iii. p. 531, and Nawroth, "Zur Ontogenese 
 d. Scheweinemolaren," Inaug. Dissert. Basel, Berlin, 1893.]
 
 THE ALIMENTARY CANAL AND ITS APPENDAGES 161 
 
 teeth arise in relation to epithelial papillae, which project above 
 the surface of the mucous membrane of the mouth. A tract of the 
 epithelium of the jaw subsequently sinks down into the meso- 
 dermal tissues to form the so-called dental ridge, from which the 
 actual teeth then develop. The dental ridge of the higher Verte- 
 brates commences to form very early, long before the first appear- 
 ance of the bones. In this early formation of the dental ridge 
 the phylogenetic early appearance of teeth is ontogenetically re- 
 capitulated. The occurrence of freely projecting papillae prior to 
 the formation of the dental ridges seems to have been lost in 
 most Mammals, through abbreviation of the embryonic stages. 
 Eose has, however, lately proved the existence, in Man, of 
 temporary traces of papillae at a period antecedent to the sinking 
 down of the dental ridge. 
 
 THE SUBLINGUA 
 
 Gegenbaur has devoted special attention to a system of folds 
 on the under surface of the tongue (plica fimbriata), which are 
 very distinctly developed in children at and soon after birth, but 
 in adults are found only in various stages of reduction. 
 
 In its general form this organ resembles the sublingua of 
 the Prosimii, in which animals it attains its most independent 
 development in the Slender Loris (Stenops) of Ceylon. It is in 
 this creature supported by cartilaginous, fatty, and connective tissue, 
 its investing epithelium being raised into papillae and showing 
 a tendency to become horny. In the allied Tarsius and in Lemur 
 degeneration has obviously taken place ; since, in the latter, the 
 cartilaginous supporting tissue has altogether disappeared and the 
 organ is no longer independent, so far as its relations with 
 the tongue are concerned. The sublingua would thus appear to 
 have formerly possessed a well-developed supporting skeleton, 
 inherited from the lower classes of animals, and we are, in fact, 
 reminded of the rod-like process of the basihyal which, in Lizards 
 and some Chelonians, passes so conspicuously into the base of the 
 tongue. Thus considered, the sublingua may be regarded as the 
 morphological equivalent of the tongue of the lower Vertebrata, 
 and the actual Mammalian tongue would appear to have been 
 to a certain degree acquired [within the limits of the Mammalian 
 phylum]. The tongue and sublingua thus appear to be organs 
 of very different phylogenetic significance, and there is some 
 reason for thinking that the muscular tongue has probably
 
 162 THE STRUCTURE OF MAN 
 
 been developed out of the posterior part of the degenerating 
 sublingua. 
 
 The study of Ontogeny has up to the present thrown no 
 light on the sublingua. 
 
 Before quitting the tongue the papillee foliatse should be 
 mentioned. These, in Mammals, take the form of localised 
 systems of lamellae, situated on the postero-lateral tongue border, 
 and having their epithelium thrown into a series of flask-shaped 
 depressions. In Man these papillae vary much in form and size, 
 and since they are occasionally represented by but mere traces 
 they are evidently undergoing reduction. 
 
 THYROID AND THYMUS 
 
 These two organs are developmentally related to the pharyn- 
 geal region. 
 
 The thyroid gland, in all Mammals in which it has been 
 examined, arises from two ventral outgrowths, one of which is 
 paired and the other unpaired. 
 
 The unpaired constituent is closely connected ontogenetically 
 with the tongue which, during development, bridges over the 
 floor of the buccal cavity, enclosing a space, the wall of which 
 becomes changed into an epithelial vesicle. This is the unpaired 
 or median thyroid gland, and it for a time remains in com- 
 munication by means of its duct (the ductus thyroglossus) with 
 the posterior surface of the tongue, at its base of attachment. 
 When this duct closes, its orifice may become converted into the 
 so-called foramen ccecum of the adult, and therefore belongs to 
 the class of vestigial structures. The duct itself, as His has 
 shown, may often be retained in the adult for a length of 2^ or 
 more centimetres. Its existence explains the fact that the so-i 
 called middle lobe of the thyroid gland is occasionally prolonged! 
 upwards into a process, which often becomes constricted so asl 
 to form a series of from two to four longitudinally recurrentj 
 vesicles (bursse supra hyoidea and prsehyoidea). 
 
 The paired portions, or the lateral lobes, of the thyroid gland 
 arise at the region of extreme posterior differentiation of the 
 visceral skeleton, by constriction of the primary floor of the 
 pharynx, near the laryngeal orifice. We have thus, here again, a 
 structure of epithelial origin. At a later stage the lateral and 
 median portions of the thyroid gland become approximated.
 
 THE ALIMENTARY CANAL AND ITS APPENDAGES 163 
 
 The whole organ at first has an undoubtedly glandular 
 character, but after the constriction is completed it undergoes a 
 marked structural change. 
 
 The manner in which the thyroid originates justifies us in 
 classing it as a vestigial organ. In the further course of its 
 development, however, it does not degenerate as might be 
 imagined CL priori ; on the contrary, it develops into a large, 
 highly vascular organ, which, according to recent clinical experi- 
 ence, iifoTgreat service in the maintenance of both the bodily 
 and mental health of its possessor. 
 
 It would appear to play some important function in relation 
 to the central^ nervous system, since its removal in animals is 
 attended with the manifestation of an extraordinary number of 
 pathological symptoms, idiocy, muscular twitchings, tetanic, 
 ataxic, apathic, clonic, and epileptic symptoms being conspicuous, 
 with marked disturbances of the organs of deglutition, circulation, 
 and respiration (cachexia strumipriva). It may further be noted 
 that different classes of animals are differently affected by the 
 destruction of this organ. 1 
 
 This gland may be concerned either in the production of a 
 secretion, or in the removal from the blood of substances which 
 would be injurious to the nervous system ; but nothing very 
 definite is known concerning its functions. It is richly supplied 
 with blood, indeed much more so than the brain itself. 
 
 In the thyroid gland, then, we have evidence of change of 
 function, and this is also the case, at least to a certain extent, 
 with the thymus. In Mammals, and especially in Man, this 
 gland is chiefly formed from a hollow epithelial outgrowth of the 
 third_J)ranchial pouch, although the fourth, and to a certain 
 extent the second also, take part in its formation. 
 
 The thymus thus far resembles in its origin a gland ; but it 
 loses this character, and a thorough histological change takes 
 place in consequence of the wandering into it of lymphoid cells. 
 This change renders its physiological significance still more 
 difficult to explain. Towards the end of the second year the 
 thymus (the greater part of which now lies behind the sternum, 
 i.e. ventrad of the heart and of the roots of the larger blood- 
 vessels) reaches its highest development, and after that period it, 
 as a rule, undergoes retrogressive metamorphosis ; in very old 
 
 1 It is difficult to decide whether and to what extent the frequent pathological 
 affections of the thyroid gland (the formation of a "crop" with secondary disorgan- 
 isation of the tissues) may or may not be referred to change of function within it.
 
 164 THE STRUCTURE OF MAN 
 
 people, however, epithelial, lymphoidal, and fatty vestiges of 
 it always occur. 
 
 We cannot at present determine what was the original signi- 
 ficance of the thyroid and thymus glands, and the like is true of 
 an allied body, the so-called carotid-gland (glandula intercarotica), 
 which is found at the bifurcation of the common carotid artery. 
 
 [Concerning the thymus, however, Beard, working chiefly at 
 the lower Fishes, in which it attains its greatest development, has 
 recently been led to the brilliant suggestion 1 that it may be 
 in them primarily protective of the branchial organs of respira- 
 tion, by a process of phagocytosis, in a manner akin to that in 
 which the tonsils and associated cytogenous tissues are protective 
 of the main respiratory passages of the pulmonary organs of the 
 terrestrial Vertebrata.] 
 
 BURSA PHARYNGEA 
 
 The primitive history of this organ cannot at present be 
 certainly determined. In Man it appears at about the third 
 month of foetal life, on the posterior pharyngeal wall, as an 
 epithelial evagination, directed upwards and backwards towards 
 the occipital bone. During embryonic life this structure becomes 
 shifted in the course of its growth ; its canal lengthens, and 
 finally approaches the tonsils ; after this it participates in all the 
 changes which affect these organs. Chief among these is degenera- 
 tion, which normally takes place before the time of puberty. The 
 degenerative processes bring about shrinkings, fusions, the formation 
 of crypts and cysts, and other modifications so diverse that hardly 
 any two cases are alike, and the most different accounts are con- 
 sequently given of them in the literature of the subject. 
 
 The following lower Mammals are known to possess a bursa 
 pharyngea ; the Alpine Marmot (Arctomys marmota), the Pig 
 (Sus scrofa), the Eoebuck (Capreolus), and the Bear (Ursus). In 
 no other Mammals examined has anything of the kind been 
 found, and since no traces of the organ are to be observed in the 
 lower Vertebrata, its primitive history and physiological signifi- 
 cance remains problematical (Killian). 
 
 (ESOPHAGUS AND STOMACH 
 
 In their fully developed condition the cesophagus and 
 stomach show no anatomical peculiarities which need be specially 
 1 [Anat. Anzeiger, Bd. ix. p. 482.]
 
 THE ALIMENTARY CANAL AND ITS APPENDAGES 165 
 
 mentioned here. Attention may, however, be drawn to the saccus 
 csecus, which is, as it were, indicative of the commencement of a 
 process of chambering in the stomach, the antrum pyloricum, and 
 a constriction (c'., Fig. 98) which but very rarely occurs l near the 
 middle of the pyloric region. 
 
 The O3sophageal mucous membrane, which after birth is 
 covered with a dense stratified epithelium, is in the embryo 
 beset by a columnar ciliated epithelium, and thus recalls very 
 primitive conditions. In Amphioxus and the young Lamprey 
 (Ammocoetes), for example, nearly the whole intestine is still 
 lined with a similar ciliated epithelium. In the adult Lamprey 
 it is somewhat more limited, and it is still to be found at various 
 parts at least of the intestine, in a large number of the Anamnia. 
 Ciliated epithelium is also frequent in the resophagus of Eeptiles, 
 and it has even been proved to exist in the intestinal canal of 
 some Mammals, at least over small areas. 
 
 [A similar replacement of ciliated by stratified non-ciliated epithelium 
 may take place over localised areas of the mammalian trachea. In the Dog 
 and Cat, for example, this change is effected over areas of attrition, resulting 
 from a folding over of the tracheal wall ; and this and other allied considera- 
 tions have led to the application of the term "frictional" to stratified 
 squamous epithelium (cf. Haycraft and Carlier, Qu. Jour. Misc. Sci., vol. xxx. 
 p. 519).] 
 
 Muscle bundles often occur between the posterior wall of the t 
 windpipe and the oasophagus, at the point where the left bron- ] 
 chial tube crosses the latter, and at other parts of the intestinal ! 
 canal, e.g. the duodenum. Their significance is undetermined; ' 
 but their inconstancy, variability, and feeble development suggest 
 that they may be among those organs which are being gradually 
 lost by Man. 
 
 The comparative anatomy of the stomach, and of the course 
 and ultimate distribution of the vagus nerve, prove that the 
 former, like some other organs of the viscera (e.g. the heart, the 
 thyroid, and the thymus glands), originally lay farther forward, 
 i.e. nearer the head, and that it has secondarily shiftecf back 
 (cf. ante, p. 38 and Fig. 31). 
 
 It not infrequently happens that a blind diverticulum 
 (diverticulum ilei or diverticulum ofMeckel) arises from the 
 
 1 I noticed this constriction twice during the ordinary dissecting course in this 
 University in the winter of 1892 and 1893 ; and careful dissection showed that there 
 was at the constricted part a ring-like specialisation of the circular musculature.
 
 FIG. 98. HUMAN STOMACH. 
 
 ce., oesophagus ; py., pylorus ; c'.c"., constrictions 
 
 of the pyloric chamber. 
 
 166 THE STRUCTURE OF MAN 
 
 lower part of the small intestine. 1 This diverticulum is connected 
 during the embryonic period, and sometimes still longer, with the 
 navel, by a cord, containing the last vestiges of the ductus 
 omphalo-mesentericus, which connected the yolk-sac with the 
 
 intestine. We have in this 
 a mere vestige of a foetal , 
 organ. 
 
 [On examination of 
 769 bodies, at the insti- 
 gation of the Collective 
 Investigation Committee of 
 the Anatomical Society of 
 Great Britain and Ireland, 2 
 the diverticulum ilei has 
 been encountered in but 
 sixteen cases, or in little 
 more than 2 per cent. 
 Special interest attaches to 
 Eolleston's report upon 
 
 the examination of 337 individuals (nearly 44 per cent of 
 the whole number) which were equally representative of the 
 two sexes, as nine of the ten possessed of the diverticulum 
 were ma^s.] 
 
 [A remarkable case has more recently been put on record by 
 Buchanan, 3 of an adult male subject in whom this appendage had 
 a total length of 9 cm. and a basal circumference of 11 cm., 
 and contained a spacious central cavity having a wide aperture of 
 communication with the ileum. The remaining alimentary 
 viscera were strikingly aberrant, the colic head and the coecum 
 being directed towards the left hypogastric region (instead of the 
 right), the ccecum terminating in an appendix vermiformis which 
 measured 13 J cm. in length.] 
 
 1 According to Sappey, the length of the intestine in white men of middle height 
 is 9600 mm., 8000 of which are to be reckoned to the small intestine, and 1600 to 
 the large one. According to the researches of Chudzinski, who examined nine 
 Negroes, the total average length was 8667 mm., i.e. almost 1000 less. There were, 
 however, great variations in length in different individuals. If the length of the 
 intestine is affected by the height of the individual, it can hardly be so to any great 
 extent. 9 
 
 The fact that the total length of the intestine is less in Negroes is due to the 
 comparative shortness of the small intestine, for the large intestine is longer in the 
 black than in the white races. 
 
 2 [Jour. Anat. and Phys., vol. xxvi. p. 91.] 
 :i [Ibid. vol. xxvii. p. 559.]
 
 THE ALIMENTARY CANAL AND ITS APPENDAGES 167 
 
 THE VERMIFORM PROCESS 
 
 The processus vermiformis (ap., Fig. 99) isr a feebly de- 
 veloped organ which lies at the end of the short ccecum (c?.), 
 and possesses a considerable morphological interest. In Man its 
 average length is 8|- cm., but it may be but 2 cm., or on the 
 other hand, some 20 to 23 cm. long. 
 
 Considerable variation also occurs in its width and disposition 
 
 FIG. 99. THE C<ECUM AND PROCESSUS VERMIFORMIS OF A HUMAN EMBRYO. 
 i.L, large intestine ; i.s., small intestine ; cce., ccecum ; ap., vermiform process. 
 
 (cf. p. 166), and in the folds of mucous membrane which bound 
 its ostium. Indeed, everything ' points to the retrogressive 
 character of this appendage, and justifies us in concluding that 
 the total length of the alimentary tract was formerly greater 
 than it now is. The great variations in the form and size of 
 the coacum (cos.} also support this view. 
 
 According to Kibbert the processus vermiformis at different 
 ages measures as follows :-^-
 
 168 
 
 THE STRUCTURE OF MAN 
 
 At birth 
 
 Up to the 5th year .... 
 From 510 ..... 
 From 10 20 . . 
 
 From 20 30 
 
 From 3040 
 
 From 40 60 
 
 In old people over 60 
 
 In embryos and new-born children on the one hand, and in 
 adults on the other, the vermiform process varies in length in ' 
 
 FIG. 100. THE CascuM AND VERMIFORM PROCESS OP A HUMAN EMBRYO. 
 References as in Fig. 99. 
 
 proportion to that of the rest of the intestinal canal ; and since 
 it is a degenerating organ, it is not surprising to find that it is 
 most strongly developed in foetal times, and does not grow at 
 a rate proportionate to advancing age. In the embryo its 
 length, in proportion to that of the large intestine, is approximately 
 one to ten, and in the adult one to twenty. Further light is 
 thrown on these facts by Eibbert's interesting discovery of the 
 frequent occlusion of the vermiform process. He found it either 
 partially or totally closed in 25 per cent of the cases examined,
 
 THE ALIMENTARY CANAL AND ITS APPENDAGES 169 
 
 with accompanying very decidedly retrogressive changes (patho- 
 logical cases excluded) in the related tissues. 1 
 
 Taking only adults into consideration (i.e. omitting individuals under 
 twenty years of age in whom variations are comparatively rare), out of 100 
 vermiform processes 32 were found partially or wholly closed. Complete 
 occlusion throughout the whole organ was found in a very small number, 
 about 3 1 per cent. Partial occlusion is much more frequent, all degrees 
 being found, from the first narrowing to the complete closing of the lumen. 
 
 FIG. 101. THE CCECCM AND VERMIFORM PROCESS IN A KANGAROO. 
 
 i.l., large intestine ; i.s., small intestine, v.i.c., position of the ileo-colic valve ; cce., 
 
 ccecum. 
 
 In rather more than half of the cases the occlusion affected a quarter of the 
 length ; in nearly half of the remainder its extent varied between one 
 quarter and three quarters, and in only a very small number did it affect 
 more than three quarters, or close up the tube. 
 
 This process of occlusion is equally marked in both sexes, 
 and the statistics concerning its occurrence at different ages are 
 very striking. They make it clear that there is marked increase 
 
 1 Actual pathological obliteration, nevertheless, occasionally occurs at the end of 
 the vermiform process. 
 
 The occlusions which result, and which are probably always due to inflammation, 
 are less frequent than the typical obliteration (Ribbert). 
 
 I cannot again in this connection refrain from referring to the coincidence of the 
 existence of vestigial organs and the tendency to disease caused by them.
 
 170 THE STRUCTUKE OF MAN 
 
 in the frequency of its occurrence in advanced age, as will be 
 seen from the following table : 
 
 From the 1st 10th year occlusion observed in 4 per cent. 
 
 10th 20th ,,H 
 
 20th 30th ,,17 
 
 30th 40th 25 
 
 40th 50th 
 50th 60th 
 60th 70th 
 70th 80th 
 
 27 
 
 30 
 53 
 
 58 
 
 It follows from the foregoing table that in more than 50 per 
 cent of people over sixty years of age there is degeneration of the 
 vermiform process. In new-born children, on the other hand, 
 this phenomenon has never been observed, and the youngest 
 child in whom it has been found commencing was five years old. 
 Total occlusion is also similarly connected with age, though not 
 in nearly so marked a manner as partial closure. It has never 
 been observed before the thirtieth year ; and while it was not 
 found once in individuals between fifty and sixty, it was most 
 frequent in those whose ages ranged from sixty to seventy. Among 
 these, nine out of the twenty-one cases recorded showed complete 
 occlusion ; and since besides them there were seven just on the 
 point of closure, we may conclude that more than 50 per cent 
 were thus affected. 
 
 A relation has further been proved to exist between the 
 length of the appendix and its degeneration. The longest 
 appendices (21 to 15 cm. long) kept their lumen throughout; 
 in those 14 and 13 cm. long, commencing obliteration of the 
 lumen was observed in four cases, and in those 12 and 11 cm. 
 long it was not found. From this point, however, occlusion 
 again increased as the length decreased. If we leave out of 
 account individuals under five years of age, in whom occlusion' 
 has not been observed, we find that it occurs as under, viz. 
 
 Where the length of the appendix is 20 cm. in 34 per cent. 
 
 9 18 
 32 
 
 7 
 
 40 
 30 
 70 
 66 
 
 3 . 100 
 
 Although this connection between length and frequency of 
 occlusion is, as the table shows, somewhat irregular, we may at
 
 THE ALIMENTARY CANAL AND ITS APPENDAGES 171 
 
 least conclude that, as a rule, the shorter appendices show 
 occlusion more frequently than the longer (Eibbert). 
 
 THE LIVER AND THE PANCREAS 
 
 These two organs, which are genetically closely related, ^ 
 occasionally show variations in the manner of their lobation which 
 may amount to constriction, and in the relations of their ducts. 
 
 [Recent investigation at the hands of a number of independent 
 workers has revealed the fact that the pancreas, in all classes of 
 Vertebrates, is a compound organ, derivative of from one to four 
 diverticula of the gut, and in most cases from three, as is said 
 by Felix 1 to be the case in Man himself. One (or more) of 
 these primitive outgrowths gives rise to the chief duct (or ducts) of 
 the adult organ, the rest usually becoming obliterated with advanc- 
 ing development. Pending the working out of further details, 
 considerable interest attaches to the recent discovery by Rolle- 
 ston, 2 that the duodenum of the human adult may sometimes 
 bear a diverticulum (proved to lie distinct from the " ampulla 
 Vateri ") which enters the substance of the pancreas, and which 
 there is reason to suspect may be a persistent vestige of one of 
 the pancreatic outgrowths of the embryo.] 
 
 The average weight of the liver is said to be 1451 grs. in 
 the white races, 1266 grs. in the black. 
 
 THE RESPIRATORY SYSTEM 
 
 The visceral skeletal arches, which lie ventrad of the cranium 
 proper and are intimately related to the cephalic portion of the 
 gut, have been already mentioned in dealing with the head 
 skeleton, and their great phylogenetic importance has been 
 pointed out (cf. ante, pp. 49 and 64, and accompanying Figs.). 
 A few additional remarks, however, are here necessary. 
 
 Whereas certain Fishes (primitive Selachians) have from six 
 to seven pairs of branchial pouches, 3 Vertebrata somewhat higher 
 in the scale (Turtles, Lizards, and Snakes) develop but five pairs, 
 
 1 [Cf. Stbhr, Anat. Anziegcr, Bd. viii. p. 205.] 
 
 2 [Jour. Anat. and Phys., vol. xxviii. p. xii.] 
 
 3 [It is insufficiently recognised that the " Hag Fishes " may bear many more than 
 this, and that in one species of these (Bdellostoma polytrema) from thirteen to four- 
 teen pairs are present (cf. Giinther, Brit. Mus. Cat. of Fishes, vol. viii. p. 512, 
 and Schneider, Archivf. Naturgesch., Bd. xlvi. p. 115.]
 
 172 THE STRUCTURE OF MAN 
 
 which are destitute of branchial organs, and of these (e.g. in the 
 Lizard) only the three anterior, as a rule, break through the outer 
 integument. The fourth, in exceptional cases, may also break 
 through, but this never occurs with the fifth. The same is the 
 case in Birds, except that in them the third pair of sacs open 
 externally only in exceptional cases, and that the fourth and 
 fifth pairs, which are inconstant in their appearance, never break 
 through. In Mammals and Man only four pairs of branchial 
 sacs arise, and here also those which lie most posteriorly are 
 decidedly vestigial in character. For this reduction a parallel 
 is forthcoming in the branchial apparatus of the Anamnia ; 
 and there is thus evidence both in Phylogeny and in Ontogeny 
 of a progressive suppression of the branchial pouches and arches 
 in postero-anterior succession. 
 
 The branchial pouches and the skeletal arches which support 
 them thus belong, in the higher Vertebrata and Man, 1 in which 
 they never bear functional respiratory organs, to the category of 
 typical vestigial structures [inherited and for the most part lost 
 unintelligible, as Gegenbaur long ago insisted, except in the 
 knowledge, furnished by comparative morphology, that in certain 
 lower animals their full development is indispensable to exist- 
 ence]. 
 
 There occasionally occur in the anterior cervical region in 
 Man " fistulae," which may penetrate a greater or lesser distance 
 in from the integument, or may bound canals which even open 
 into the pharynx. These are abnormal structures, due to arrested 
 development, under which branchial clefts have not become com- 
 pletely obliterated. In dealing with the auditory organ details 
 have already been given (ante, p. 150) of the relationship of 
 the cavity of the middle ear (Eustachian tube) to the modified 
 remnant of thejirst visceral cleft, which in the higher Vertebrata 
 has undergone a new development, in adaptation to a change of 
 function. 
 
 THE LARYNX 
 
 The study both of the innervation of the musculature of the 
 larynx, and of the genesis and Comparative Anatomy of its 
 cartilaginous framework, strongly suggest its origin, for the 
 
 1 The branchial sacs, and the external branchial furrows in the outer integument 
 which correspond with them, are most distinctly visible in human embryos of 3-4 
 mm. in length.
 
 THE ALIMENTARY CANAL AND ITS APPENDAGES 173 
 
 greater part, from branchial or visceral structures. 1 It may be 
 considered as certainly proved that the upper part of the thyroid 
 cartilage arises out of the fourth and the lower out of the fifth 
 primitive (i.e. the second and third branchial) visceral arch, and 
 it is probable that the fifth branchial arch gives rise to the 
 arytenoids. 
 
 With regard to the Mammalian epiglottis, it seems now 
 tolerably certain that it does not owe its origin merely to the 
 mucous membrane of the floor of the mouth, but that it repre- 
 sents an originally paired skeletal element which, in the course 
 of phylogeny, has passed from the condition of hyaline- to that 
 of fibro-cartilage. [This view receives support from the investi- 
 gations of Goppert, who has recently given reasons 2 for believing 
 that the cartilages of Wrisberg and the epiglottis, which are 
 frequently in organic continuity among the lower Mammals, are 
 specialised portions of one original structure.] Any attempt, 
 however, to derive the epiglottis from the branchial skeleton 
 seems, in the present state of our knowledge, beset with diffi- 
 culties. 3 
 
 [It is now demonstrated that the upward prolongation of the 
 Mammalian epiglottis involves that organ in a relationship with 
 the velum palatinum (furnishing a raison d'etre for the existence 
 of the latter), for the purpose of restricting the respiratory passage 
 (narial pharynx). Special inquiry has also shown that in both 
 the young and adults of representatives of all orders of Mammals, 
 the epiglottis, when at rest, lies above the velum in an intra- 
 narial position. Man is, however, an exception to this rule, at 
 least in the adult state, and there is reason for believing that 
 the velum and epiglottis have, in him, suffered a loss of connection 
 by the specialisation of the latter more particularly for vocalisa- 
 tion. It is yet uncertain whether the epiglottis of the human 
 embryo does or does not occupy the intra-narial position 4 ]. It 
 
 1 The hyoid and the thyroid skeletal apparatus are still closely connected in Ortiith - 
 orhynchus, and bear distinct traces of their branchial origin, as not only lateral 
 arches, but portions of their median elements or copula can clearly be recognised. 
 In the higher Mammalia the hyoid separates from the thyroid, although the 
 two continue to be related (cf. the cartilago triticea, ante, Fig. 94). In Mammals 
 above the Monotremata the thyroid cartilage appears to consist of a single plate ; 
 but it gives some indications of its primary origin from two consecutive branchial 
 arches which still remain distinct in the Monotremata (Gegenbaur). 
 
 2 [Morph. Jahrb., Bd. xxi. p. 68.] 
 
 3 [Gegenbaur has recently come to the conclusion that the epiglottis is a 
 derivative of the fourth pair of branchial arches, Die Epiglottis, Leipzig, 1892.] 
 
 4 [Cf. Howes, Jmir. Anat. and Phys., vol. xxiii. p. 594.]
 
 174 
 
 THE STRUCTURE OF MAN 
 
 . .th. 
 
 would, therefore, be very interesting to follow closely, in Man's 
 development, the changes of position and inter -relationship 
 between the larynx and the upper part of the pharynx (choanse). 
 I am indebted to my colleague, Professor Killian, for knowledge 
 of the fact that the larynx of the human embryo may occupy 
 a high position, the upper edge of the epiglottis reaching even to 
 the uvula. 
 
 The musculature of the human larynx appears to a great 
 extent to have been derived from the 
 simple sphincter and dilator appa- 
 ratus of lower Vertebrata, of Lizard- 
 like type. Under the more subtle 
 differentiation of the laryngeal 
 skeleton in Man, the musculature 
 has also undergone corresponding 
 changes for example, there is no 
 longer one single muscle for con- 
 stricting the glottis, but a whole 
 system of such muscles. In other 
 words, the reptile - like sphincter 
 laryngis has gained new points of 
 origin and insertion in the cartilage; 
 and Fiirbinger has proved that 
 while this is especially the case 
 with the deeper layers of the 
 sphincter, the superficial do not 
 undergo any such marked differ- 
 a greater extent the original condition, 
 tracts that the greater number of 
 
 FIG. 102. HUMAN LARYNX IN 
 
 FRONTAL SECTION. 
 th., thyroid cartilage ; -., cricoid car- 
 tilage ; tc., first tracheal cartilage ; 
 sn. } sinus of Morgagni. 
 
 entiation, but retain to 
 It is in these superficial 
 variations are to be found. 
 
 The close connection between the laryngeal and the pharyn- 
 geal musculature is evidenced not only by their common relation- 
 ships to the vagus nerve, but by the frequent occurrence of fibres 
 connecting the crico-thyroideus muscle with the constrictor 
 pharyngis inferior, i c^-^- 
 
 Between the true and false vocal cords there arises on each 
 side of the larynx a diverticulum known as the ventriculus or 
 sinus of Morgagni (sn., Fig. 102). This evagination is directed 
 outwards and somewhat forwards ; it also projects upwards more 
 or less, and may even in rare instances reach the upper edge of 
 the thyroid cartilage. 
 
 These Morgagni's pouches are susceptible of marked varia-
 
 THE ALIMENTARY CANAL AND ITS APPENDAGES 175 
 
 tion, and we have little difficulty in recognising in them the 
 homologues of the " yocal___sacs " of the Monkeys. The latter 
 can be filled with air from the larynx, and in certain Anthropoids 
 they may extend far down in the neck, or even to the shoulder 
 or thorax. These sacs, which, when distended, are really 
 immense, may be partly enclosed in an osseus capsule produced 
 by the transformation of the hyoid (Mycetes). It seems to me 
 that they may not only act as resonators when the animal howls, 
 but that, when inflated, they may serve to intimidate enemies. 
 
 Gruber [and Rudinger] have described cases, in Man, in which the sacs 
 broke through the thyroid membrane and came to lie, like those of the Apes, 
 outside the larynx. [In one case of Rudinger's the sac of the right side 
 was alone present The same variation has been observed by Bischoff in 
 the Gorilla ; and it is interesting to note that inequality in growth of the 
 two sacs has been recorded in the Chimpanzee, the Orang, and in Man. 1 ] 
 
 On examination of the larynxes of a number of Negroes, 
 Giacomini asserts that the ventriculus in no way differs from 
 that of Europeans. [This is, however, in strange contradiction 
 to the conclusions of Gibb, 2 that the larynx of the Negro differs 
 from that of the white races in the invariable presence of the 
 cartilages of Wrisberg, the obliquity of the true vocal cords, and 
 the pendent condition of the ventricles, which latter, according 
 to him, are situated below the plane of the true vocal cords, 
 instead of above it as in the whites.] 
 
 Myologically, Giacomini's inquiry is very interesting. The Italian 
 investigator also examined the Anthropoids, and found that while the 
 Chimpanzee's larynx most nearly resembles that of Man, the Orang's is the 
 least akin to it, and that of Macacus and Cercopithecus occupies an inter- 
 mediate position. 
 
 LUNGS 
 
 Aeby, from a careful study of the structure of the lungs and 
 
 of the arrangement of the pulmonary vessels, has concluded that 
 
 M in Man the upper lobe of the left lung is homologous with the 
 
 I middle lobe of the right, and that the upper lobe of the right 
 
 has no^punterpart on the left side. The question therefore arises 
 
 whether this asymmetry is a primitive condition, or whether the 
 
 left lung may not once have possessed a counterpart to the extra 
 
 lobe now borne by the right, i.e. whether the original plan of 
 
 the tractus respiratorius, as judged by the subdivision of the 
 
 trachea, may not have been strictly symmetrical ? This would 
 
 1 [Cf. Ehlers, Abhandlg. K. Gesellsch. d. Wins. Gdttingen, Bd. xxviii. p. 48.] 
 2 [Mem. Anthropolg. Soc. t Lond., vol. ii. p. 1.]
 
 176 THE STRUCTURE OF MAN 
 
 appear at first sight the more likely, from the fact that whereas 
 in man an eparterial bronchus is present only on the right side, 
 in some Mammals it occurs (either bronchial or tracheal in 
 origin) on both right and left. 1 
 
 But all these animals, as Gegenbaur has remarked, in the 
 rest of their organisation do not by any means show primitive 
 conditions which can be considered to bear on the genealogy of 
 Man ; and great care is therefore necessary in dealing with the 
 question in hand. Cases, in Man, like those described by Dalla 
 Kosa and Bohls, in which an eparterial bronchus is present on 
 both sides 2 must not therefore be hastily classed as atavistic. 
 
 It is, further, a very remarkable fact that the Marsupials, 
 Eodents, Insectivora, Lemuroidea, and Apes, show no sign of 
 original bilateral symmetry of the lungs. Further, the ontogeny 
 of Man throws no light on the subject. We therefore at present 
 can neither decide along what line of descent the Mammals 
 above referred to may have inherited their symmetrical eparterial 
 bronchi, nor in what manner the existence of these is to be ex- 
 plained. It is, however, certain that if the human lungs originally 
 bore homologous superior lobes, this symmetry must have been 
 early lost. In face of these facts it is idle to speculate as to 
 probable causes which may perchance have effected a gradual loss 
 of symmetry of the bronchi. 
 
 1 E.g. Bradypus, Equus, Ulephas, Phoca, Phocceiia communis, Delphinus delphis, 
 and Auchenia. 
 
 2 The presence on both sides of an eparterial bronchus has only twice been 
 observed in Man once where the viscera were in the normal position, and once in a 
 case of situs inversus. In both instances there were also marked anomalies of the 
 trunks of the larger arteries in the thorax. On each side three well-defined pulmonary 
 lobes were found, and bilateral symmetry was complete (Dalla Rosa). 
 
 Complete absence of the eparterial bronchus, and the existence of a tracheal near 
 a bronchial eparterial bronchus, have been observed in Man. In the latter case, 
 according to Chiari, it would appear that one of the collateral (dorsal) branches of 
 the normal bronchial eparterial bronchus had become independent, and wandered 
 up to the trachea. This view receives support from the well-known tendency 
 of the lateral bronchus to give up branches to the principal, and from the 
 study of cases in which two eparterial bronchi, one above the other, are found. 
 The upper of these is evidently a branch of the ordinary eparterial bronchus 
 shifted on to the main bronchus, and in this phenomenon we have an intermediate 
 stage between the normal condition and that of the tracheal bronchus. The 
 latter may therefore be regarded as a branch of the ordinary eparterial bronchus 
 which has wandered farther up. I put forward these views with all reserve. 
 
 [His has shown that in Man the first hyparterial bronchus of the left lung divides 
 immediately after its origin, giving off an ascending branch (unrepresented on the 
 right side) which runs forwards to the apex of the lung. Robinson has shown (Jour. 
 Anat. and Phys. , vol. xxiii. p. 240) that the same is true of the Rat, and he suggests 
 that this ascending branch may, as it were, compensate for the absence of a distinct 
 eparterial bronchus. ]
 
 THE ALIMENTARY CANAL AND ITS APPENDAGES 177 
 
 In dealing with the lung of the Primates, considerable 
 importance attaches to the growing together of the pericardium 
 and the diaphragm, for this brings about a constancy, or, if I 
 may be allowed the expression, a certain rigidity in the form of 
 the pleural cavities. As a consequence of this, a stricter limit is 
 placed upon the extension of the lobes of the lungs than in the 
 lower Mammals, in which the lung is able, either constantly or 
 during inspiration, to penetrate between the heart and the 
 diaphragm, into the sinus subpericardiacus. This applies especially 
 to the right lung, at the base of which a special lobe may be 
 more or less distinctly developed. This, the lobus subperi- 
 cardiacus (or azygos impar), is occasionally present in Man, 
 most frequently, it appears, in the lower races and in micro- 
 cephalous individuals. The probability that its presence may 
 be indicative of atavism is not lessened by the fact that indica- 
 tions of it often occur, in the form of a blunt process lying in 
 front of the ligamentum pulmonale, which sinks into a depression 
 in the mediastinum, just as in the Orang. 
 
 Hasse has not only confirmed Aeby's observations in all 
 essential points, but, by the aid of very ample material, has 
 extended and revised them. According to him, the principal 
 bronchi of the human lung run downwards, backwards, and 
 slightly outwards, the direct current of inspired air following the 
 same course. He raises the question whether this has always 
 been the disposition of these bronchi, and inquires into its cause. 
 The first question he answers in the negative, and seeks to prove 
 that a very gradual change took place in the position of the 
 bronchi ; indeed, that the position which has been acquired in 
 the course of Phylogeny is exactly the reverse of the primitive one. 
 The facts discovered by His in the study of the human embryo 
 lend support to this view. In other words, comparison of the 
 embryonic with the adult condition shows most clearly that a 
 depression of the right and an elevation of the left chief bronchus 
 takes place. The condition of the adult, so far as the branching 
 of the bronchi is concerned, is effected as early as the end of the 
 second month of intra-uterine life, the change being in the main 
 due to the twisting of the heart upwards, backwards, and to 
 the left. 
 
 Hasse is, however, unable to prove any more satisfactorily 
 than his predecessors why the right lung-sac is from the first 
 more spacious than the left, and what caused the right eparterial 
 bronchus to appear. He has, however, made an attempt at 
 
 N
 
 178 THE STRUCTURE OF MAN 
 
 explanation which, since it appears to rne to possess a certain 
 degree of probability, may be here recapitulated. He writes : 
 " Since the heart and its immediate connections push the right 
 primary pulmonary sac, which from the first is larger than the 
 left, backwards and upwards, the branches of the fifth aortic arch 
 the arteriae pulmonales (which, as fig. 1 5 in His's work shows, 
 descend quite symmetrically) come to lie somewhat differently 
 on the two sides. The right artery must cut across and overlie 
 the primary lung-sac earlier than the left, and become therefore 
 the sooner connected with it. Herein, perhaps, also lies the 
 explanation of the greater growth of the right sac, and of the 
 fact that this gives rise to a special outgrowth, the foundation of 
 the eparterial bronchial system. I am the more inclined to this 
 belief, and to that in the above-named determining causes, by the 
 fact that in cases of situs inversus and reversal of the heart and 
 great blood-vessels, the relationships of the right and the left 
 main bronchi, and indeed of the two lungs as wholes, are also 
 reversed (Weber, Leboucq, Aeby)." 
 
 This is not the place to consider further either the relationships of the 
 bronchial system, the differences in its distribution in relation to the planes 
 of the body, or the changes which it undergoes after birth. For these 
 details I must refer the reader to the original monograph. In the same 
 work is to be found a discussion of the arrangement of the bronchial system 
 in adult human beings, the explanation of which may be summarised as 
 depending upon the direction of movement of the single points of the 
 thoracic walls lying round the lung. Hasse concludes his interesting account 
 as follows : " If it be admitted that the tendency towards modification 
 conditioned by the mechanism of the walls of the thorax is inherited, then 
 we must allow that the facts point back to the form of lung of the earliest 
 ancestors of Man among the Amniota, and to the changes which the respirat- 
 ing organs have gradually undergone in the course of time in the ancestral 
 series. The principal direction of the bronchi is at first downwards and 
 backwards. From this it follows, it seems to me, that in the ancestors of 
 Man the diaphragm first played the principal part in respiration. Then 
 the system of branches running outwards and downwards is developed in an 
 ascending degree. From this I conclude that thoracic respiration next super- 
 vened in increasing degree, this being most marked in the lower, or better, 
 the posterior part of the thorax, and least marked near its upper and anterior 
 region. By degrees the upper and anterior part of the thorax took an 
 increasing part in respiration, and this led to the mechanism of respiration 
 which is illustrated in Man. This course of the development of respiration 
 and of the respiratory movements, it appears to me, is in exact correspond- 
 ence with the development of the respiratory organs as I have explained 
 them, and with the facts brought to light by Aeby's investigation of the 
 bronchial tree of the lower animals." l 
 
 1 I put forward these views of Hasse with all reserve, and I would draw attention 
 once more to a point already touched upon in dealing with the thoracic skeleton
 
 THE ALIMENTARY CANAL AND ITS APPENDAGES 179 
 
 (ante, p. 43), i.e. the structural variation of the first rib, and the feeble respiratory 
 activity and consequent slight movement of the tips of the lungs. I consider that 
 these phenomena should be regarded as degenerative, on the assumption that the 
 remote ancestors of Man were still provided with cervical ribs, and that their lungs 
 extended farther towards the head than they now do. There must thus, as I think, 
 have been effected in the Phylogeny of Man first a shifting of the respiratory organs 
 in a caudal direction, and next in order the formation of the diaphragm, and, in 
 connection with the latter, a modification of the respiratory mechanism originally 
 restricted to the lungs and the walls of the thorax. The contrast between this 
 theory and that of Hasse is obvious, and although I am as little able as he is to 
 furnish proofs, I believe that my explanation receives support from the facts of 
 development and Comparative Anatomy.
 
 THE CIRCULATORY SYSTEM 
 
 IN no other system of organs does the fundamental law of 
 biogenesis find such wide application as in the circulatory, and 
 to go into details concerning it would be merely to repeat 
 what has been often said before. Attention may therefore be 
 confined to the following facts. 
 
 THE HEAKT 
 
 The heart arises (cd., Fig. 31, A), at an early embryonic 
 stage, far forwards in the cervical and indeed in the cephalic 
 region. This recalls its position in adult Fishes and Amphibians. 
 The comparison with these animals is the more fully justified, 
 in that the heart of the early human embryo, like that of the 
 lowest Ariamnia, has throughout a single lumen, and its further 
 differentiation is gradually undergone in correspondence with the 
 phylogenetic development of the organ. 
 
 The structure of the heart, originally "very simple, soon 
 becomes complicated, but even then certain peculiarities of the 
 right auricle point back to the condition found in the Amphibia. 
 These are, for example, the inconstant vestiges of valves at the 
 opening of the left vena cava superior (Thebesian valve), and 
 the almost constant remains of the valves of the sinus at that of 
 the vena cava inferior (Eustachian valve). The same applies to 
 the traces of the incorporation of the sinus venosus and of the 
 pulmonary veins into the opposite divisions of the atrium 
 (auricles). In short, Comparative Anatomy furnishes not only 
 interesting parallels with, but an explanation of the various stages 
 in the Ontogeny of the heart of the higher Vertebrata. There 
 are, however, some conditions which occur in the Mammalian 
 heart, especially during the early periods of its development, 
 which cannot be explained by inheritance, but which have arisen 
 secondarily through adaptation ; among the chief of these are the
 
 THE CIRCULATORY SYSTEM 181 
 
 secondary perforation of the septum atriorum and the formation 
 of the annulus ovalis or isthmus of Vieussens. 
 
 THE ARTERIAL SYSTEM 
 
 The arterial system of Man bears traces of primitive con- 
 ditions. It is indeed an astonishing fact, for example, that the 
 aortic arch system of the embryos of the higher Vertebrata, up 
 to Man himself, appears in the same manner as in the Anamnia. 
 Six pairs of aortic arches in all are formed in the young 
 Mammalian embryo, but the representatives of the first and 
 second of these and the vestige of the fifth degenerate early, 1 and 
 consequently only three pairs remain to undergo final transfor- 
 mation. 
 
 [Conspicuous among the variations occurring in Man is the 
 occasional presence in the adult of paired aortic arches, the arch 
 of the right side, which usually disappears during development, 
 being retained. Twelve cases of double aortic arch have been 
 recorded in Man, 2 and this variation may be accompanied by the 
 obliteration and reduction to a fibrous band of the ordinarily 
 functional (left) arch, 3 the resulting condition of the parts being 
 essentially that characteristic of Birds.] In a similar manner, 
 many of the variations to which the vessels derivative of the 
 primitive arterial system of the human embyro are liable, can 
 only be explained by the fact that embryonic trunks, which 
 under normal conditions become occluded and vestigial, may 
 remain functional throughout life. In this respect the Anthro- 
 poids altogether agree with Man. 
 
 On the inner surface of the abdominal wall in Man three 
 cord-like structures pass from near the bladder to the navel. 
 These are known as the ligamentum vesicale medium and the 
 ligamenta vesicalia lateralia. The first urachus corresponds with 
 the stalk of the allantois of the embryo ; the latter, however, 
 are the last vestiges of the umbilical or hypogastric arteries, 
 which during intra-uterine life, i.e. from about the time when the 
 posterior limbs are just beginning to appear as buds, convey the 
 
 1 [The recent researches of Boas and others have proved that in all classes of 
 terrestrial Vertebrates the pulmonary artery is a derivative of the sixth aortic arch 
 (the fourth branchial), and that the arch in front of it is suppressed ; and Zim- 
 raermann has shown that Man himself is no exception to this rule (Vcrhandlg. 
 Internal. Medic. Congresses X., Berlin, 1891, Bd. ii., Abth. i. p. 145).] 
 
 2 [Cf. Leboucq, Ann. Sci. Med. Gand., ]894, p. 7.] 
 
 3 [Of. Morrison Watson, Jour. Anat. and Phys., vol. xi. p. 229.]
 
 182 THE STRUCTURE OF MAN 
 
 blood from the aorta to the placenta. The basal portions of these 
 vessels often remain patent throughout life, and function as 
 superior vesical arteries ; the remainder of each, however, i.e. by 
 far its greater portion, loses its lumen altogether and becomes 
 a solid strand of connective tissue. 
 
 [Considerable interest attaches to those veins of the very 
 variable " vesico-prostatic plexus " which, in the adult, in proxi- 
 mity to the above-named arteries, carry back the blood from the 
 urinary bladder to the internal iliac veins. The detailed re- 
 lationships of certain varieties of these would seem to suggest, 
 by analogy to the lower vertebrata, that they may be associ- 
 ated with the " anterior abdominal " venous system regularly 
 present in Birds, Reptiles, and Amphibians, and represented by 
 at least its main trunk, in the Monotreme Echidna 1 among 
 Mammals.] 
 
 The continuation proper of the axis of the human aorta 
 is represented by a weak vestigial vessel, of very variable 
 relationships 2 the arteria sacralis media. In long-tailed 
 animals, in which the posterior end of the body has not 
 undergone reduction, this vessel is represented by the caudal 
 artery, which is a direct, gradually diminishing, continuation of 
 the aorta, originally giving off, like it, segmentally recurrent 
 branches. 
 
 When we consider the polymeric origin of the limbs (cf. ante, 
 p. 67) dating back to an originally segmented condition of the 
 trunk, it is evident that their principal arteries must have arisen 
 in relation to segmental arteries of the body wall, and that 
 originally they in no way differed from these. This assumption 
 finds actual proof in the mode of origin of the arteria subclavia ; 
 but while it is comparatively easy to prove this for the fore- 
 limb, in the hind-limb a difficulty presents itself, since its corre- 
 sponding vessel at a very early period undergoes a great increase 
 in size and marked specialisation in relation to the development 
 of the umbilical artery. 3 In any case it is certain that the 
 
 1 [Cf. Fenwick, Jour. Anal. andPhys., vol. xix. p. 320 ; and Beddard, Proc. Zool. 
 Soc., Lond., 1884, p. 553.] 
 
 2 [These have been recently tabulated for 400 autopsies worked out by collective 
 investigation in medical schools, under the auspices of the Anatomical Society of 
 Great Britain and Ireland. In one instance the vessel appears to have been entirely 
 absent, cf. Jour. Anat. and Phys., vol. xxvii. pp. 184-187.] 
 
 3 I cannot here enter further either into the question of primary origin, direct 
 from the aorta, of the arteria umbilicalis, or into that of the secondary connection 
 between this vessel and the arteries of the limbs. It must suffice to refer the reader
 
 THE CIRCULATORY SYSTEM 183 
 
 artery known as the common iliac is the first formed of the 
 posterior limb, and that it arises as a segmental vessel of the 
 aorta. 
 
 The artery which, in the embryo Mammal, including Man, 
 runs into the developing posterior limb bud, does not directly 
 become the arteria femoralis of the adult. It accompanies the 
 ischiadic [or crural] nerve in its distribution ; on the posterior 
 side of the limb it runs down to the bend of the knee, and from 
 this point is continued into the upper part of the thigh. This 
 artery should be called the ischiadic [or crural] as it corresponds 
 with the vessel of the same name in most Birds, and with the 
 principal vessel of the hind-limb in Eeptiles and Amphibians. 
 
 " The femoral artery develops l^Jgr as a branch of the iliac. 
 At first it spreads only over the inner or ventral portion of the 
 thigh ; it, however, soon grows rapidly in a distal direction, along 
 the inner surface of the cartilaginous femur, to the bend of the knee, 
 where it unites with the ischiadic artery. The femoral artery 
 thus formed rapidly increases in size, while that section of the 
 ischiadic related to the upper leg degenerates. It is thus 
 that the definitive condition is attained ; and but a short vestige 
 of the arteria ischiadica persists in the adult, as the " ischiadic " 
 or " inferior gluteal " (Hochstetter). Mechanical causes may have 
 perhaps brought about this change in the principal artery of the 
 hind-limb in the ancestors of Mammals, but we have no clear 
 knowledge on the subject. 
 
 In no other part of the body are the variations in the arteries 
 so frequent as in the fore-limb, especially in the hand. The 
 arteries of the foot present numerous variations, and, in correla- 
 tion with the variations of the skeleton and musculature, 
 some of these may be classed as progressive and others as 
 retrogressive. 
 
 Where a supracondyloid process of the humerus exists (cf. 
 ante, p. 78) the brachial artery lies behind it. The latter is 
 thus covered by the head of the pronator teres muscle which 
 extends upwards, and the condition resembles that of those 
 Mammals in which the brachial artery and median nerve pass 
 through an invariably developed foramen supracondyloideum. 1 
 
 A comparison of the arteries of the hand with those of the 
 foot shows that there are in the hand two palmar arches, a 
 
 to the recent series of very careful studies by Hochstetter, published in the Morpho- 
 logisches Jahrbuch. 
 
 1 For further details on this point, cf. Huge, Morpholg. Jahrb., Bd. ix. p. 329.
 
 184 THE STRUCTURE OF MAN 
 
 deeper and a superficial, but in the foot ojaly a deep plantar 
 one. It is evident on reflection that a superficial arch cannot 
 exist in the foot on account of its functions as an organ of 
 support, and that the larger pedal arteries, to be free from 
 interference with the circulation, may have had to withdraw 
 into the recesses of the foot. Indications, however, are not infre- 
 quently encountered that the foot formerly possessed a super- 
 ficial arterial arch, and that the arteries for the toes arose from 
 it, in a manner identical with that in which the arteries for 
 the fingers arise from the superficial palmar arch of the hand. 
 
 Finally, as to the intestinal arteries, although our knowledge 
 of the development of these is still very limited, all things point 
 to the fact that originally they were numerous and segmental, 
 and that their final reduction in Man and Mammals to three 
 trunks, the cceliac, omphalo-mesaraic (which later becomes the 
 superior mesenteric), and the inferior mesenteric, is to be con- 
 sidered as secondary. 
 
 THE VEXOTTS SYSTEM 
 
 The developing venous system of Man, like the arterial, 
 shows unmistakable traces of a very primitive condition inherited 
 from the lower Vertebrates. In this connection the anterior 
 and posterior cardinal veins, the ductus Cuvieri, and the sinus 
 venosus cordis, are especially conspicuous. 
 
 The system of the vena cava inferior is a late acquisition, 
 dating [in its fully differentiated form] from the higher Fishes 
 (Dipnoi) and Amphibians. Its phylogenetically recent origin 
 is, even in Man, denoted by the variation and arrested develop- 
 ment which it occasionally exhibits. Several cases of [that which 
 Hochstetter's researches prove to be] the persistence of an early 
 stage in its development have been recorded. I refer to those ] 
 in which the caval vein, from about the level of the superior \l 
 mesenteric, is continued downwards towards the pelvis, owing ' 
 to the retention of the posterior cardinals. 
 
 In these cases we may speak of persistence of the posterior 
 cardinals in the form of a double vena cava inferior. 
 
 In other cases of what we may now regard as arrested develop- 
 ment, the distal portion of the inferior vena cava is formed out 
 of the left instead of the right cardinal vein, there is then a 
 vena cava inferior passing to the left [of the aorta]. 
 
 In very rare cases, where development is arrested at a very
 
 THE CIRCULATORY SYSTEM 185 
 
 early stage (eighteen to twenty-one days after fertilisation), the 
 post-caval vein never develops, and the posterior cardinals take 
 its place. 
 
 In one such case, described by Kollmann, the two posterior cardinal 
 veins persisted to the level of the third lumbar vertebra. At the crura of 
 the diaphragm, within the aortic foramen, the right cardinal vein was con- 
 nected with the left by three branches. The trunk thus related lay to the 
 left of the aorta, and ran on as a persistent portion of the left cardinal. At 
 the level of the tenth thoracic vertebra the vessel turned to the right, and 
 after this it was the right cardinal vein which was continued to its point of 
 entrance into the vena cava superior. The ductus venosus Arantii was absent ; 
 and the circulation in the liver remained entirely embryonic, the hepatic 
 veins still entering the heart separately. This remarkable case was that of 
 a man of twenty-eight, who had committed suicide. 
 
 In Man, and certain Mammals (Apes, Lemurs, Carnivora, 
 Whales, and Edentates), the left vena cava superior early degener- 
 ates and disappears, with the exception of its basal portion, which 
 remains as " the coronary sinus," so-called on account of its 
 receiving the intrinsic cardiac veins. [The great veins of the head, 
 neck, and fore-limb on the left side become connected with those 
 of the right by a transverse trunk, derived from the left innomin- 
 ate vein the two innominate or brachio-cephalic veins uniting 
 to form the single " superior cava."] In this we have to deal 
 with the modification of a condition which in other Mammals 
 (Eodents, Insectivora, Bats, and Ungulates) is retained throughout 
 life ; [and it is an interesting circumstance that among these a 
 transverse connection between the great veins of the neck strongly 
 suggestive of that above described may not infrequently be estab- 
 lished (ex. Lepus), without any accompanying reduction of the 
 left pre-caval.] 
 
 The venous system, so rich in variations, is well known to 
 possess valves which prevent regurgitation, [and thus ensure the 
 maintenance of the single circle of the circulation.] In keeping 
 with this we should expect to find such valves chiefly in the 
 limbs, i.e. where the venous stream I refer especially to the lower 
 limbs already has great difficulties to overcome. This expecta- 
 tion is fulfilled ; but when we reflect that the ancestor of Man 
 himself had a quadrupedal ancestry, it follows that there must 
 have been a time in which his thoracic, and abdominal, and dorsal 
 surfaces, now disposed antero-posteriorly, were turned downwards 
 and upwards and were disposed ventro-dorsally. Circulation within 
 the intercostal and lumbar veins must then have been placed under 
 much less favourable conditions than at present ; it had to be
 
 186 THE STRUCTURE OF MAN 
 
 maintained, as the venous circulation in the lower limbs now has, 
 against the action of gravity. This justifiable assumption has led 
 me to investigate the intercostal veins in Man closely, by way of 
 ascertaining if they possess valves, and my observations in all 
 essentials confirm those of Henle recorded in his Handbuch der 
 Anatomic. That is, I found great variation both in the number 
 and the development of the valves, so that the impression of a 
 retrogressive condition became irresistible. 
 
 It is well known that in other parts of the body, valves of 
 the veins appear in a reduced and evidently degenerating or 
 vestigial form, and also that in the embryo there arise many 
 more valves than attain complete development. [The valves of 
 the portal system are among the number thus suppressed, but 
 they may be occasionally retained. 1 ] 
 
 THE SPLEEN 
 
 Throughout the Mammalian series three lobes of the spleen 
 may be detected, viz. an anterior, a posterior, and a middle, all 
 of which vary greatly in size and form, in the various types. In 
 Marsupials the posterior lobe stretches far down towards the 
 rectum. In the Placental mammals the lobes are increasingly 
 reduced, and finally, in the Primates, the posterior lobe has 
 almost disappeared ; but the anterior and the median are repre- 
 sented even in Man, while the posterior lobe is in him reduced to 
 a projection of its margo obtusus (Klaatsch). 
 
 The average weight of the spleen in the white races is said 
 to be 195, and in the black but 171 grs. 
 
 1 [These valves are typically bicuspid. They are most numerous at birth, in 
 the vessels of the large intestine. After birth they disappear rapidly, and when 
 present in the adult they appear to be most abundant on the small intestine. Cf. 
 Hochstetter, Archiv f. Anat. und Phys., 1887 ; Anat. Abth., p. 137 ; and Bryant, 
 Boston Medical and Surgical Journal, vol. cxix. p. 400. Hyrtl long ago drew 
 attention (Sitzungsb, Wien. Akad., Bd. Ixi. p. 27) to the existence in the Rodentia 
 of a spiral valve-like fold within the portal vein.]
 
 THE UKINOGENITAL SYSTEM 
 THE PRONEPHROS AND THE PRIMITIVE KIDNEY 
 
 IN all classes of Vertebrates the Urinogenital System first appears 
 [in the form of a duct (Wolffian or Segmental duct) which is 
 primarily related to a urinary apparatus confined to the head 
 region. In the Amniota and Selachii the latter is wholly de- 
 generate in character ; among the remaining Anamnia, however, 
 it may for a longer or shorter period persist as a distinct first- 
 formed functional excretory organ. It is accordingly regarded 
 as a possible larval kidney, and termed the pronephros, as it 
 appears to be of very ancient origin]. While the secreting 
 glandular portion of this system never lasts for more than a 
 short period, its duct persists and appears in some cases (cf. 
 infra, p. 190) to give rise to the leading duct of a much more 
 extensive urinary system that develops later and is known as the 
 middle kidney or mesonephros. 
 
 This second nephridial system, which becomes the definitive 
 urinary system of Fishes and Amphibia, consists like the pro- 
 nephros of metamerically recurrent tubes. The two systems 
 are so constituted as to suggest for the Vertebrata of to-day an 
 origin from a lowly segmented ancestor. 1 
 
 The higher Vertebrates pass through an embryonic stage, in 
 which they possess first a pronephros and then a mesonephros, 
 which is an irrefragable proof that in their ancestors, and con- 
 
 3 [This view receives support from the general tendency towards corresponding 
 metamerism of the muscular, skeletal, nervous, and vascular systems of the vertebrate 
 body. There are, however, reasons for thinking that the recurrent symmetry of at least 
 the skeletal and muscular apparatus may be of secondary significance ; and there are 
 not wanting competent investigators who deny in toto the origin of Vertebrates from 
 multi-segmented animals (cf. especially W. K. Brooks "The Genus Salpa, " Mem. 
 Biol. Lab., Johns Hopkins Univ., II. pp. 182-203). The whole question must remain 
 in abeyance, pending further inquiry into the origin of metamerism in general, with 
 a view to the formation of a sounder conception concerning that.]
 
 188 THE STRUCTURE OF MAN 
 
 sequently in the ancestors of Man, each of these organs once 
 constituted in turn a permanent urinary system. 1 
 
 [The definitive kidney and ureter of Mammals arises at a com- 
 paratively later period (eleventh to twelfth day of intra-uterine 
 life) in relation to an outgrowth of the base of the mesonephric 
 duct. 2 This kidney, by extension, reaches to the mesonephridial 
 region. On account of its distinct origin from the rest of the 
 excretory system it is generally termed the metanephros, and its 
 duct the metanephric duct.] 
 
 The definitive adult kidney of Man is, as a rule, a compact 
 organ, with smooth walls; but its surface is not infrequently 
 more or less distinctly furrowed, and thus apparently lobed. 
 Lobation of the kidney is characteristic of certain lower Mammals 
 [e.g. Cetacea and Ungulata]. The regular appearance of furrows 
 in the kidney of the human embryo, giving rise to the so-called 
 " renculi," and the not infrequent occurrence of an increased 
 number of renal arteries, justify the conclusion that the lobate 
 structure may have been typical of the ancestors of Man. 
 
 It is not yet evident what first led to the degeneration of 
 the pronephros and to the loss of a renal function by the 
 mesonephros in the amniota. So far as the mesonephros was 
 concerned, the degeneration did not originally affect the whole 
 organ, but only a part of it. The remainder, undergoing a change 
 of function, became secondarily related to the male reproductive 3 
 apparatus. It gave rise with its duct to the epididymis and 
 vas deferens, and became otherwise transformed into a series of 
 vestigial appendages to the urinogenital organs of both sexes. 
 
 1 This view, so far as it involves the conclusion that the mesonephros of the 
 Amniota is the representative of the excretory organ of their ancestors, receives 
 its chief support from the condition of the excretory apparatus in Reptiles. These 
 animals pass through a period in which the greater part of the mesonephros con- 
 tinues functional, side by side with the later definitive kidney. In the Lizards, for 
 example, it shrivels up after the first hibernation, i.e. in the second year. 
 
 2 [The metanephric tubules of Mammals are stated to arise as outgrowths of this 
 diverticulum itself, but in other animals there is good reason for regarding them as, 
 at any rate in part, distinct in origin i.e. as arising independently of the duct 
 with which they subsequently become connected, in the manner typical of the meso- 
 nephric series. The recent researches of Semon (Jenaische Zeitschrift, Bd. xxvi. 
 p. 89) and Field (Bullet. Mus. Comp. Zool. Harvard, vol. xxi. p. 201) have revealed 
 striking details of similarity in development between the pro- and meso-nephridia, 
 rendering it more difficult than hitherto sharply to discriminate between them. 
 Indeed, recent discovery tends to suggest that the pro-, meso-, and meta-nephridia 
 are portions of one continuous system, and that their apparent independence is due to 
 the assumption of secondary relationships with independently formed ducts.] 
 
 ( 3 The initial stages in this process have been permanently retained as the adult 
 condition by the Elasmobranchs and Amphibia.
 
 THE URINOGENITAL SYSTEM 189 
 
 In the wholly vestigial condition the mesonephros is not infrequently 
 the seat of origin of pathological affections (formation of cysts). 
 
 The vestigial portions of the mesonephros in men are 
 the paradidymis, Giralde"'s organ, and the stalked hydatids of 
 x -Morgagni; in women it gives rise to the greater part of the 
 parovarium and the whole of the paroophoron. Further, in 
 women, the last vestiges of its duct are found, either confined to 
 the region of the parovarium, or, where suppression is least 
 marked, in the form of "Gartner's canal" which reaches the vagina. 
 
 MiJLLERIAN DUCT 
 
 Van Wijhe, believing that the ancestors of the vertebrate were 
 
 hermaphrodite, has argued that the first appearance of the Mullerian 
 
 duct probably dates back to a period in the evolution of the phylum 
 
 when, as a means of preventing self - fertilisation, there were 
 
 distinct ducts for the transmission of the sperm and the ova. Be 
 
 this as it may, the secondary nature of the Miillerian duct is 
 
 shown by its comparatively late development in the individual. 
 
 ' It originates in the Amniota by evagination of the ccelomic 
 
 I epithelium, to form a structure which, becoming constricted off 
 
 \ into a tube, gradually elongates in a caudal direction to reach 
 
 the cloaca. 
 
 In the male, the duct of the mesonephros, and in the female, 
 as is well known, the whole of the Mullerian duct, forms the 
 adult genital duct (cf. Fig. 103). In the male the greater part 
 of the Mullerian duct degenerates or entirely disappears, thus losing 
 nearly all physiological significance. Its proximal vestige becomes 
 in Man the unstalked hydatid of Morgagni, a small appendage of 
 the testis ; its distal end, however, is believed to unite with that 
 of its fellow of the opposite side to form a vesicle, the " uterus 
 masculinus," which becomes embedded in the prostate, and later 
 opensTconjointly with the vasa deferentia, into the urinogenital 
 sinus (urethra). 1 
 
 1 [The term "uterus masculinus" is applied, by analogy, to a somewhat 
 similarly placed median vesicle, opening into the prostatic portion of the urethra 
 in other Mammals. One well-known case is that of the common Rabbit. The 
 so-called " uterus masculinus " of that animal certainly does superficially resemble 
 that of Man, but the two differ fundamentally in their relationships to the vasa 
 differentia, i.e. in Man the bases of these pass behind the vesicle and open at its 
 sides, while in the Kabbit they pass in front of it and open within its anterior lip. 
 Kiilliker from the study of its development, has claimed for the so-called " uterus 
 masculinus" of the Rabbit) (fJiituncklungsf/csch. d. Menschen n. d. Mhern Thicre,
 
 ..d.pn. 
 
 - - -d.pn. 
 
 --d.pn. 
 
 A o ^. 
 
 o + 
 
 taJ.
 
 THE URIXOGENITAL SYSTEM 
 
 191 
 
 FIG. 103. A SERIES OF WHOLLY DIAGRAMMATIC FIGURES TO ILLUSTRATE THE 
 COMPARATIVE MORPHOLOGY OP THE URINOGENITAL ORGANS OF THK VERTEBRATA. 
 A, The pronephros stage of the Auamnia ; B, a later stage of the same ; C, the urinogenital 
 apparatus of the male Amphibian ; D, the same of the female ; E, pronephros 
 stage of the Amniota, the mesonephros as yet rudimentary ; F, urinogenital apparatus 
 of the Amniota, at a stage at which the sexes are not differentiated ; G, urinogenital 
 apparatus of the male Amniota; H, the same of the female; p.n., pronephros; 
 d.pn., duct of the pronephros ; ms., the developing mesonephros ; ms.s., part of 
 the mesonephros, becoming converted into the epididymis and parovarium ; ms.v., 
 vestiges of the mesonephros, the paradidymis and the paroophorou ; t, rete and 
 vasa efferentia testis ; t"t", a network homologous with these structures at the hilus 
 ovarii ; hy.s., stalked hydatid ; nis.r., portion of the mesonephros which in Amphi- 
 bians and Selachians becomes the so-called pelvic kidney; d.ms., duct of the 
 mesonephros, which in male Amphibians and Selachians becomes (Fig. C) the urino- 
 genital, and in females (Fig. D) the urinary duct. In the male Amniota it gives 
 rise to the seminal duct (Fig. G), and in the female to the Gartner's duct (Fig. H). 
 v.a., the seminal vesicle, an outgrowth of the duct of the mesonephros ; d.-m., 
 Mullerian duct, which in Mammals becomes differentiated (Fig. H) into the Fallopian 
 tube (/.), the uterus (ut.\ and the vagina (vg.) ; os., its ostium abdominale tubae ; 
 hy. and u.m. (Fig. G), unstalked hydatids and uterus masculinus (vestiges, in the 
 male, of the Mullerian duct, d.m.) ; mt., the definitive kidney or metanephros of the 
 Amniota, asserted to arise from the ureter (itr.), itself an outgrowth of the mesonephric 
 duct ; of'., allantois (urinary bladder) ; sn. t sinus urogenitalis ; p.g., genital pro- 
 minence ; g.g., genital glands, undifferentiated stage; en:, ovary; ts., testis; cl. t 
 cloaca ; al., hind-gut ; p.a., porus abdominalis ; g.c., Cowper's glands. 
 
 Tabulated Resume of the Facts pictorially illustrated on the 
 opposite Page. 
 
 Anamnia. 
 
 Amniota. 
 
 Pronephros. 
 
 Male and Female. 
 
 Develops in all Auamnia, but in 
 all probability never persists as 
 a permanent excretory organ. 
 
 Still develops in the Amniota, but 
 as an excretory organ undergoes 
 entire degeneration in the embryo. 
 
 U O, x.V-~* ' 
 
 Duct of Pronephros. 
 
 Male and Female. 
 
 In Elasmobranchii, appears to give 
 origin by subdivision to both 
 Mesonephric (Wolffian) and Mul- 
 lerian ducts. In Amphibia, be- 
 comes converted into the Meso- 
 phric duct. Its fate in other 
 Anamnia is not yet fully investi- 
 gated. 
 
 Probably persists as the Mesonephric 
 (Wolffian) duct, and contributes 
 in some to the formation of the 
 Mullerian duct. Great differences 
 of interpretation still exist con- 
 cerning it. 
 
 f 
 
 Male and Female" 
 
 Functions in all Anamuia as a 
 urinary gland. Jn Elasmobranchs, 
 
 Loses its renal function in all 
 Amniota (as a rule in the embryo), 
 and becomes vestigial, except so 
 far as it becomes an accessory 
 portion of the reproductive appar- 
 atus in the male, [and enters into 
 the formation of the suprarenal 
 body.] 
 
 Amphibians, and one or two 
 higher Fishes, its anterior por- 
 tion becomes related to the 
 male genital apparatus, the pos- 
 terior portion persisting as a per- 
 manent kidney.
 
 192 
 
 THE STRUCTURE OF MAX 
 
 
 
 Anamnia. 
 
 Amniota. 
 
 1 
 
 PH 
 < 
 
 I 
 
 The proximal portion becomes in 
 most related to the testis, and 
 functional in the transmission of 
 the semen, the distal functioning 
 as a kidney. 1 
 
 The proximal end becomes the rete 
 and vasa etferentia testis, and the 
 caput epididymis, and perhaps 
 also the stalked hydatid of Mor- 
 gagni : the distal end becomes 
 the paradidymis (Giralde's organ). 2 
 
 1 
 
 Female. 
 
 Persists as the kidney. 
 
 The greater part of the proximal 
 portion becomes the parovarium, 
 the distal the paroophoron. 2 
 
 i 
 
 | 
 
 Functions in most higher Fishes 
 merely as the urinary duct. 
 In Selachians, Amphibians, and 
 some Ganoids, serves as the 
 urinogenital duct. 
 
 The proximal portion becomes the 
 corpus and cauda epididymis, and 
 the distal the seminal duct (vas 
 deferens). 
 
 Duct of Meso 
 
 h 
 
 Functions exclusively as the duct of 
 the mesonephros, i.e. the urinary 
 duct. 
 
 The greater part, as a rule, degener- 
 ates ; the proximal portion may 
 be retained in a vestigial form in 
 the region of the parovarium. In 
 certain cases it may persist as a 
 whole, as Gartner's canal. The 
 distal end becomes the organ of 
 Weber. 
 
 | 
 
 1 
 J. 
 3 
 
 j= r 
 
 CB 
 
 
 
 In Elasmobranchs, for certain, it de- 
 generates in post-embryonic life, 
 vestiges of its proximal portion 
 being retained. (Its fate in most 
 other Fishes is doubtful. ) In Am- 
 phibia it is retained for its whole 
 length, in a functionless and often 
 but little degenerate condition. 
 
 The proximal portion becomes the 
 unstalked hydatid of Morgagni, 
 the distal, in some Mammals, the 
 so-called "uterus masculinus." 
 In exceptional cases the whole is 
 retained as Rathke's duct. In 
 Sauropsida the distal part usually 
 disappears. 
 
 & 
 
 6 
 
 j 
 
 Becomes the whole genital duct. 
 
 Becomes the whole genital duct. 
 
 Metanephros & Ureter. 
 
 | Male and Female. 
 
 Probably unrepresented. 
 
 Development not yet fully worked 
 out. It appears to arise in part 
 (ureter) from the distal end of 
 the mesonephric duct, and in 
 part (secreting elements) as a 
 caudad extension of the meso- 
 nephros. 
 
 1 [The males of the Bony Fishes and of the Marsipobranchii are exceptions to 
 this rule, the mesonephros being in them functional only as a kidney]. 
 
 2 [Allowance being made for its entering into the constitution of the suprarenal 
 body (cf. previous page).]
 
 THE URINOGENITAL SYSTEM 
 
 193 
 
 In Amphibia, Eeptiles, and Birds, the Miillerian ducts in the 
 female remain separate throughout life, and this is also the case 
 in the lowest living Mammals (Monotremata), which are partly 
 on this account called the Ornithodelphia. In all Mammals above 
 the Monotremes, however, they early become to a lesser or greater 
 
 od. 
 
 FIG. 104. A to C, DIAGRAMMATIC REPRESENTATIONS OF THE CHIEF TYPES OF UTERDS 
 
 OCCURRING IN THE PLACENTAL MAMMALS. A, UTERUS DUPLEX ; B, UTERUS 
 
 BIPARTITUS ; C, UTERUS SIMPLEX ; D, URINOGENITAL APPARATUS OF A FEMALE 
 MUSTELINE ; E, THE SAME OF THE HEDGEHOG, THE FORMER WITH EMBRYOS (* *) 
 IN THE UTERUS. 
 
 od., oviduct (Fallopian tube) ; ut., uterus ; ut'., cornua uteri ; ut"., corpus uteri ; vg., 
 vagina; ot. , ostium tubse ; gl. , accessory gland; r., rectum; s.ug., sinus urino- 
 genitalis ; re 1 ., kidney ; re"., suprarenal body ; vr., ureter; bl., bladder. 
 Aufl. II. p. 981) a paired origin from the bases of the mesonephrio ducts, and in 
 respect to this it exactly harmonises with, and would appear to represent in a 
 confluent form, the human vesiculse seminales. The fact that among other Rodents I 
 it is represented (e.g. Guinea-Pig) by a pair of elongated cceca, or (e.g. Muridae) 
 by two folded and more glandular diverticula, having the detailed relationships of the 
 seminal vesicles of the other mammalia, fully bears out this view. G. B."H.] 
 

 
 194 THE STRUCTUKE OF MAN 
 
 extent united, the union being first effected at a middle point, 
 before the ducts themselves open into the urinogenital sinus. 
 [Those portions of the oviducts situated above this point of union 
 become converted into the uteri and Fallopian tubes, and those 
 below into the vaginae.] 
 
 Among the Marsupials there arises at this point a median 
 vaginal sac, and neither the upper (uterine) nor the lower (vaginal) 
 portions unite further. For this reason these animals are fre- 
 quently classified as the Didelphia. In all the higher and truly 
 placental Mammals the union extends backwards to form a 
 single median vagina [as is expressed in the application to them 
 of the term Monodelphia]. It also extends forwards, giving rise 
 to a single median uterus as we ascend in the series (cf. Fig. 
 104). Man and the Primates are among those monodelphous 
 Mammals in which the two uteri as a rule completely unite : 
 but abnormal forms of uterus, known as uterus duplex, bilocularis, 
 subseptus, bipartitus, incudiformis, arcuatus, and bicornis, not 
 infrequently occur, at any rate in Man. These are but the 
 expression of arrested development, arrested, that is, at stages 
 corresponding with those of the gradual fusion of the originally 
 separate Miillerian ducts effected during the course of long 
 geological periods. The uterus simplex is the normal condition 
 in the Primates of the present time. 
 
 In the uterus simplex, traces of the primitive paired condition 
 of the Miillerian duct are still found in the paired Fallopian 
 tubes (pd., Fig. 104, C), and in the longitudinal ridges of the 
 cervix uteri and of the vagina (columnee rugarum). 
 
 HYMEN 
 
 The primitive significance of the fold of mucous membrane 
 termed the hymen, which lies within the entrance of the vagina 
 in the female and more or less completely closes it, is by no means 
 clear. The only thing that can be stated with certainty is that 
 it is coincident in disposition with the elevation of the urethral 
 mucous membrane of the male known as the colliculus seminalis. 
 
 [It is an interesting fact that a similar and complete fold is present within 
 the base of the oviduct in the virgin state of the lower Fishes (Sharks and 
 Rays).] 
 
 THE CLOACA 
 
 At a certain stage in the development of Man the urinogenital 
 ducts and intestine open posteriorly into a common chamber, the 

 
 THE URINOGENITAL SYSTEM 195 
 
 cloaca. This points back to a condition which must have 
 existed in the remote ancestors of Man, for a cloaca persists 
 throughout life in Amphibians, Reptiles, and Birds, as well as in 
 the lowest Mammals, which last are on this account called the 
 Monotremata. 
 
 In the further course of development the cavity of the cloaca 
 becomes divided into two, the posterior chamber serving as a 
 prolongation of the rectum, the anterior forming a sinus 
 urinogenitalis, from the anterior wall of which the genital 
 eminence is developed (cf. Fig. 103, G and H). 
 
 EXTERNAL GENITAL ORGANS OF THE FEMALE 
 
 Concerning the external genital apparatus of the female, the 
 labia majora are probably to be regarded as partially developed 
 homologues of the scrotum of the male. Indications of them are 
 found even in the Lernuroidea and the Apes ; but in most Apes it 
 appears that only the lesser system of folds found in women, the 
 labia minora, form the boundary of the genital aperture. The 
 labia minora, which form a strong praeputium and frenulum 
 clitoridis, belong ontogenetically to the genital eminence, and are 
 developed upon its lower surface. They thus fall under a 
 different morphological category from the labia majora. 
 
 The clitoris in Apes is both relatively and absolutely larger 
 than in human beings, and its under surface is furrowed as far as 
 the urinary aperture. This primitive condition is recalled by the 
 occasional condition, due to arrested development of the genital 
 eminence, known as hypospadias. 
 
 In certain branches of the Ethiopian race the females are 
 distinguished by a very slight development of the labia majora 
 and of the mons veneris, and of hair about these parts. On the 
 other hand, among the female Hottentots, a marked hypertrophy 
 of the labia minora and of the prseputium clitoridis is well 
 known, giving rise to what is known among Bushwomen as the 
 "Hottentot apron." [This, however, is most probably due to 
 manipulation, and to the wearing of a split stick with a weight 
 attached.] The vagina appears (as in Apes) smoother, it being 
 less strongly folded than in unmarried Europeans. In Japanese 
 women the labia majora and the mons veneris are feebly developed 
 and but little hairy, and the labia minora seem also to be but 
 slightly developed (Bischoff).
 
 196 THE STRUCTURE OF MAN 
 
 MALE GENITAL GLANDS (DBSCENSUS TESTICULOKUM) 
 
 Among Mammals the genital glands of the male (testes) 
 agree in their place of origin with those of the female (ovaries). 
 Both are developed out of the germinal epithelium, differentiated 
 near the dorsal wall of the coelom to the right and left of the 
 vertebral column. But while, during further development, the 
 ovaries, as a rule, shift down towards the pelvis, the testes may 
 wander still farther (descensus testiculorum}. This descensus is 
 closely connected not only with the history of the testis, as the 
 result of interaction between the organ and the parts immedi- 
 ately surrounding it, but also with the relations of the testis to 
 other organs more or less remote from it. 
 
 Many variations occur among Mammals in the manner of 
 descent of the testis, and in the changes in the ventral body wall 
 which accompany it. It seems possible, however, as Klaatsch 
 has shown, to reduce these variations to a simple ground plan. 
 The descent of the testes, which is a new_ development peculiar 
 to Mammals, is effected in its most primitive manner in 
 Insectivores and Eodents ; and everything points to the fact 
 that it was originally a periodic^ phenomenon occurring in the 
 adult. For instance, in the Hedgehog the testes retain their ori- 
 ginal intra-abdominal position up to the rutting period ; but as 
 that period approaches they come to lie in evaginable portions of 
 the inguinal body wall. After the rutting season they always 
 return into the abdominal cavity, but the mechanism by which 
 this is accomplished is not yet clearly understood. 
 
 In connection with the shifting of the testis, a structure 
 termed by Klaatsch the " conus inguinalis " is of the greatest 
 significance. This organ is best developed in the Muridse, and 
 consists of a conical invagination of the muscular abdominal wall, 
 at first connected not with the three lateral abdominal muscles, 
 but only with the obliquus internus and transversus. Its 
 internally projecting point, or at least its surrounding tissue, fuses 
 with a cord-like structure called by Klaatsch the ligamentum 
 inguinale (cf. Fig. 105). This ligamentum inguinale (which 
 must not be confused with the gubernaculum or round ligament 
 of earlier writers) is a subperitoneal strand containing smooth 
 muscle, which arises, in both sexes, on each side of the genital 
 ducts, and runs to the inguinal region of the abdominal wall, i.e. 
 to that point which corresponds with the aperture of the canalis 
 inguinalis interna. This " ligament," for which a parallel exists
 
 THE URINOGEXITAL SYSTEM 
 
 197 
 
 in other differentiations of the ccelomic musculature (e.g. the 
 musculus suspensorius duodeni, musculature of the genital ducts), 
 leaves the genital duct at the point where the ligamentum testis 
 or ovarii reaches it. This coincidence of position by no 
 means always obtains ; but the fact that it may do so has led to 
 the erroneous idea that the ligaments of the genital ducts hitherto 
 known as the ligamentum rotundum and the gubernaculuni always 
 and alone connect the ovary and testis with the inguinal 
 region. The study of Ontogeny proves that in origin they are 
 distinct from the ligamentum inguinale. The latter, in the 
 female, becomes the ligamentum rotundum uteri. Besides this, 
 
 FIG. 105. A, A PARTLY DIAGRAMMATIC REPRESENTATION OF THE EMBRYONIC URINO- 
 GENITAL APPARATUS OF A MALE MAMMAL, SHOWING ITS RELATIONS TO THE VENTRAL 
 ABDOMINAL WALL. 
 
 B, THE PENIS AND SCROTUM OF A HUMAN EMBRYO 15 CM. LONG, WITH THE AREJE 
 
 SCROTI (a.S.) MEETING IN THE MIDDLE LINE. 
 
 (BOTH FIGURES FOUNDED ON THE WORK OF KLAATSCH.) 
 
 al., intestine; re'., suprarenal body; re"., kidney ; l.s., suspensory ligament of testis; 
 ff.g., testis ; d.g., genital duct ; l.L, ligamentum inguinale ; pr., processus vagiualis ; 
 c.L, conus inguinalis ; U., urinary bladder. 
 
 the ligamentum inguinale, as well as the conus inguinalis of 
 Klaatsch, were called gubernaculum testis by former authors ; 
 in fact, the term gubernaculum was originally applied to the most 
 heterogeneous structures. 
 
 In the Insectivora and Eodents, the descent of the testis is 
 accompanied by an evagination of the conus due to muscular 
 contraction, so that the ligament may in this case rightly be 
 termed a "gubernaculum." This evagination gives rise to a 
 more or less marked bulging of the integument, to form the 
 " bursa inguinalis " of Klaatsch. This pouch, which represents 
 the point of least resistance in the abdominal wall, is composed 
 of (1) the evaginated abdominal integument (scrotum, sac of the
 
 198 THE STRUCTURE OF MAN 
 
 testis), (2) evaginated derivatives of the internal oblique and 
 trans versus muscles (cremaster), and its cavity is connected with 
 the coeloni by a special canal (canalis vaginalis in the male, 
 canalis Nuckii in the female). 
 
 The differentiation of these parts, which was in all probability 
 originally effected only in the adult, in some cases takes place at 
 an earlier (Mouse) or even embryonic period (Squirrel). 
 
 It is conceivable that next in order to the type represented 
 by Eodents and Insectivores, there may have existed forms 
 in which the descensus occurred periodically in youth, but in 
 which, in more advanced age, in consequence of the loss of the 
 reditus testium at the rutting season, it became fixed. Such 
 forms are not actually known ; but the hypothetical stage is very 
 nearly realised in Man, as in him, by the partial reinvagination 
 of the bursa, and by the consequent formation of a conus 
 inguinalis, we are still reminded, ontogenetically, of the periodical 
 descensus and reditus testium, although it is but a very feeble 
 process. There is thus reason for thinking that, among the 
 Prosimii and Primates, forms corresponding with this hypotheti- 
 cal stage might be found. 
 
 The definitive descensus is due to a further evagination 
 of the conus. The bursa inguinalis, however, which was once 
 (as in the Eodents and Insectivora) the direct product of this 
 very shifting of the testis, in Man first arises independently at 
 some distance from it, forming what is known as the genital 
 ridge or the outer genital fold. 
 
 Among the lower Mammals the development of a permanent 
 scrotum has become established in the Marsupialia, Ungulata, and 
 Carnivora. Among the Edentata only the Orycteropodidse 
 possess a testis sac into which the testes periodically enter. In 
 Dasypus, Bradypus, and Myrmecopliaga, the testes are abdominal : 
 in Manis they are subintegumental, and lie in the inguinal region. 
 In the Monotremes a descensus testiculi is not known to occur. 
 
 In considering the phylogenetic origin of the descensus testiculorum, 
 Klaatsch has formulated the following ingenious argument : The mammary 
 organ, which in the form of a somewhat circular patch of the integument, 
 characterised by glands and smooth musculature, first became differenti- 
 ated in the inguinal region, exercised a great influence on the abdominal 
 wall. He has suggested that among the ancestors of the Mammals there 
 occurred, as he believes is shown by the Monotremata, a transference of the 
 mammary organ from the female to the male ; x and that this may have 
 
 1 In other words, Klaatsch interprets as the homologue of this Mammary area a 
 circumscribed wrinkled portion of the integument, only scantily covered with hair,
 
 THE URINOGEXITAL SYSTEM 199 
 
 exercised a great influence on the lower portion of the abdominal wall. This 
 would appear to have involved the invagination of a more or less circum- 
 scribed portion of the lateral abdominal muscles by the glandular apparatus 
 (which in the Monotremata has already attained large proportions), leading 
 up to the differentiation of a compressor of the mammary organ out of the 
 transversus muscle. He further surmises that this, which represented a 
 primitive conus inguinalis, was retained in the Marsupials to assist in the 
 extra-uterine nourishment of the young, and that it disappeared in the 
 Placentalia owing to the substitution of other methods of providing for the 
 offspring. The invagination of the conus into the ccclom must, like the 
 maturation of the glandular complex, have occurred periodically. The male 
 conus became related to the male genital gland, and the periodic displacement 
 of the latter (towards the point of the least resistance) must thus be associ- 
 ated with its great increase in size at the times of sexual activity. For 
 the ovaries this last factor has not to be taken into account, as they do not 
 undergo such great variations of size ; and further, their power of descent 
 is greatly diminished in consequence of their position in relation to the 
 Miillerian ducts. 
 
 The essential, that is the first, cause of the descensus remains unexplained, 
 and the origin of the ligamentuin inguinale is still a complete enigma. On 
 the other hand, its connection with the uterus, its periodical increase in size 
 during pregnancy, and especially its near relation to the conus inguinalis, and 
 thus to the mammary organ, make it very probable that it originally arose 
 in the female, and was transferred to the male with the other parts belonging 
 to the mammary organ. 
 
 SUPRARENAL BODIES 
 
 These organs are probably to be traced to a double origin, 
 partly from the mesonephros and partly from the syj^athetic 
 nervous_sy_stem. Their physiological significance is as little 
 known as their primitive history, and it is not certain whether, 
 so far as Man is concerned, they are phylogenetically in a pro- 
 gressive or in a retrogressive condition. 
 
 The latter assumption is the more probable when we consider 
 their great development during embryonic life. On the other 
 hand, their rich blood-supply indicates some important physio- 
 logical function performed throughout life. 
 
 which is to be found on the level of the scrotum in the young stage of all 
 Mammals, including Man, and which at a later stage meets the corresponding area 
 of the other side in the middle line. The numerous smooth muscles which 
 constitute the tunica dartos appear to correspond with the smooth muscle layer 
 of the glandular area in the Monotremata. In all Mammals the area scroti is 
 distinguished by the fact that the hair grows on wart -like elevations which 
 are closely crowded together a peculiarity which gives the area a characteristic 
 appearance. The hairs are provided with very small sebaceous glands ; the coiled 
 tubular glands are much larger, and open near hairs disposed singly. In Man 
 the tubular glands are less conspicuous.
 
 CONSPECTUS OF THE OEGANS MENTIONED IN 
 THE TEXT, AEEANGED ON THE BASIS OF 
 THEIE PHYSIOLOGICAL CONDITION 
 
 I. ORGANS SHOWING EETROGRESSIVE CHARACTERS 
 
 A. Retrogressively modified, the Organs still performing 
 clearly recognisable Functions 
 
 Certain muscles of the lower leg and foot. 
 
 Adductor transversus of the foot. 
 
 Opponens of the ball of the little toe. 
 
 Serratus posticus superior and inferior. 
 
 The flexors proper of the fingers. 
 
 M. pyramidalis (when comparatively well developed as 
 accessory to the rectus abdominis). 
 
 M. levator palpebrse superioris. 
 
 Intestinal coecum. 
 
 Eighth sternal rib. 
 
 The eleventh and twelfth ribs. 
 
 Sternum. 
 
 The fifth toes. 
 
 The fibula. 
 
 Olfactory lobe of the brain and (in part) the olfactory organ. 
 
 The canines and upper lateral incisors ; the molars, in so far 
 as there is a decrease in the number of their cusps. 
 
 The pre-maxillary bone. 
 
 B. Retrogressively modified, the Organs having become wholly or 
 in part functionless, some appearing in the Embryo alone, 
 others present during Life constantly or inconstantly. For 
 the greater part Organs which may be rightly termed 
 Vestigial. 
 
 Os coccygis. Cauda humana. 
 
 Superfluous embryonic notochord and associated somites.
 
 CONSPECTUS OF ORGANS MENTIONED IN THE TEXT 201 
 
 Embryonic cervical, lumbar, and sacral ribs. 
 
 The thirteenth rib of the adult. 
 
 The seventh cervical rib in the adult. 
 
 The interarticular cartilage of the sterno-clavicular joint 
 (probable vestige of the episternal apparatus). 
 
 Ossa supra-sternalia. 
 
 Certain centres of ossification in the manubrium sterni. 
 
 The branchial clefts (for the most part) and branchial ridges. 
 
 Processus styloideus ossis temporis, and the ligamentum 
 stylo-hyoideum. 
 
 Anterior cornua of the hyoid, for the greater part. 
 
 Foramen ccecum of the tongue. 
 
 Processus gracilis of the malleus. 
 
 Post-frontal bone (?) 
 
 Ossa interparietalia (and ? prseinterparietalia). 
 
 Processus paramastoideus of exoccipital. 
 
 Torus occipitalis. 
 
 Processus frontalis of the temporal. 
 
 Processus coracoideus [meta- and epi-coracoid bones]. 
 
 Os centrale carpi. 
 
 Processus supracondyloideus humeri. 
 
 Trochanter tertius femoris. 
 
 The phalanges of the fifth toe, and less conspicuously of the 
 third and fourth toes. 
 
 Muscles of the pinna and the Musculus occipitalis. L 
 
 M. transversus nuchse. L. -- 
 
 Facial muscles transformed into tendinous expansions. 
 
 Mm. plantaris and palmaris longus, when completely 
 tendinous. 
 
 M. ischio femoralis. 
 
 The caudal muscles. 
 
 M. epitrochleo-anconseus. - 
 
 M. latissimo-condyloideus. 
 
 M. transversus thoracis (triangularis sterni). 
 
 M. palmaris brevis. 
 
 The transition bundles between the trapezius and the sterno- 
 cleido-mastoideus. 
 
 M. levator claviculse. 
 
 M. rectus thoracis. 
 
 M. ere master. 
 
 The primitive hairy covering or lanugo. 
 
 Vestiges of vibrissse.
 
 202 THE STRUCTURE OF MAN 
 
 The vertex coccygeus, the foveola and glabella coccygea. 
 
 Certain vortices of hair on the breast. 
 
 Nipples in men. 
 
 Supernumerary mammary glands in women. 
 
 Alleged vestiges of mammary pouches [?] 
 
 Supernumerary olfactory ridges. 
 
 Jacobson's organ, and ductus naso-palatinus. 
 
 Papilla palatina and folia ta. 
 
 Plica semilunaris of the eye. 
 
 Vasa hyaloidse (Cloquet's canal) of the embryo the choroidal 
 fissure. 
 
 Lachrymal glands, in part. 
 
 The epicanthus. 
 
 M. orbitalis. 
 
 Certain varieties of the pinna of the ear. 
 
 The filum terminale of the spinal cord. 
 
 Grlandula pinealis and parietal organ. 
 
 The parieto-occipital fissure of the brain [doubtful]. 
 
 The obex, ponticulus, ligula, tseni^e medullares, and velum 
 medullare anterius and posterius, of the brain. 
 
 The hypophysis cerebri (pituitary body). 
 
 The dorsal roots and ganglia of the hypoglossus nerve. 
 
 The rami recurrentes of certain cranial nerves. 
 
 Certain elements of the brachial and lumbo-sacral plexuses. 
 
 The coccygeal nerve. 
 
 The glandula coccygea. 
 
 Palatal ridges. 
 
 The sublingua. 
 
 The formation of rudimentary dental papillae before the 
 sinking of the dental ridge. 
 
 The wisdom teeth. 
 
 The occurrence of a third prsemolar (reversionary). 
 
 The occurrence of a fourth molar (reversionary). 
 
 The vestiges of a third dentition. 
 
 The ciliated epithelium of the embryonic oesophagus. 
 
 Bursa sub- and prsehyoidea (ductus thyroglossus). 
 
 Musculi broncho-cesophagei. 
 
 The appendix vermiformis. 
 
 Ventricle of the larynx (Morgagni's pouch). 
 
 Lobus subpericardiacus of the lung (reversionary). 
 
 Certain valves of the veins. 
 
 Certain structures of a vestigial nature in the heart.
 
 CONSPECTUS OF ORGANS MENTIONED IN THE TEXT 203 
 
 Arteria sacralis media. 
 Arteria ischiadica. 
 
 Superficial plantar arterial arch of the foot. 
 The vena cava superior sinistra. 
 Venae cardinales posteriores, and ductus Cuvieri. 
 Vestiges (in the female) of the mesonephric system, and (in 
 the male) of the Mullerian ducts. 
 
 Conus inguinalis, and ligamentum inguinale. 
 The area scroti. 
 
 C. Modified under Change of Function, though this cannot in 
 all cases be proved 
 
 Suprarenal bodies. 
 
 Glandula thyroidea. 
 
 Glandula thymus. 
 
 Bursa pharyngea. 
 
 Anterior lobe of the hypophysis cerebri (pituitary body). 
 
 Carotid and coccygeal glands. 
 
 D. Characters Indicative of Change of Position or Shifting 
 
 Proximal shifting of the pelvic girdle, and, correlatively, 
 the shortening of the lumbar region of the vertebral column 
 (assimilation of the fifth lumbar vertebra by the sacrum). 
 
 Distal shifting of the shoulder girdle. 
 
 Abbreviation of the ccelom. 
 
 Proximal and distal abbreviation of the osseous thorax. 
 
 Power of abduction in the embryo and at birth of the first 
 metatarsal and great toe. 
 
 Shifting of the eye from the lateral surface of the head to 
 the anterior. 
 
 Wandering of the lachrymal glands. ^ 
 
 [Variations in arrangement] of the platysma myoides muscle. 
 
 [Variations in arrangement] of the sphincter colli. 
 
 Shifting of the navel. 
 
 Shifting of the heart, the stomach, and the thyroid and 
 thymus glands. 
 
 Descent of the genital glands (testes and ovaries). 
 
 Shifting of certain muscles of the lower leg on to the 
 dorsum and plantar surface of the foot. 
 
 Torsion of the humerus, radius, and ulna.
 
 204 THE STRUCTURE OF MAN . 
 
 Disposition of the foot at a sharp angle to the leg. 
 
 Secondary separation of the orbit from the fossa temporalis. 
 
 Shifting of the lachrymal bone on to the surface of the face. 
 
 The disposition of the palatine bones in relation to the 
 palatal processus of the maxilla. 
 
 The fusion of the nasal bones. 
 
 The position of the pinna on the adult head. 
 
 The ultimate positions of the ribs upon the vertebral column. 
 
 (Widening of the thorax, as an accompaniment of an altera- 
 tion in the positions of the organs within the thoracic cavity.) 
 
 II. ORGANS SHOWING PROGRESSIVE CHARACTERS, i.e. TENDING 
 
 TOWARDS MORE PERFECT ADAPTATION 
 
 Higher differentiation and more subtle development of the 
 muscles of the thumb both of those which pass from the fore- 
 arm along the volar and dorsal surfaces to the thumb, and of 
 those of the ball of the thumb. 
 
 Increase in physiological efficiency of the hand in general, 
 especially of the flexors of the hand and of the fingers, the palmaris 
 longus excepted. 
 
 Increased development and strengthening of the arch of the 
 foot, of the tarsus, heel, and great toe. 
 
 Secondary lateral extension of the malleolus fibularis. 
 
 The perfecting of the whole lower limbs for support and 
 ambulation (in adaptation to the upright gait). 
 
 Development of the ilifiLC expansions in the female, with 
 widening of the sacrum and of the aperture of the pelvis. 
 
 Curvature of the lumbar vertebral column. 
 
 Gluteal muscles and muscles of the calf (gastrocnemius and 
 soleus). 
 
 More subtle differentiation of the facial_inuscles proper (as 
 opposed to the muscles of the pinna and of the scalp). 
 
 The projectile nose. 
 
 Certain nerve tracts in the brain and spinal cord. 
 
 The occipital lobes of the brain (posterior cornua of lateral 
 ventricle and calcar avis ?) 
 
 Higher degree of development of the brain cortex (histological 
 differentiation concomitant with increasing intelligence). 
 
 The more subtle differentiation of the muscles of the larynx. 
 Articulate speech.
 
 CONSPECTUS OF ORGANS MENTIONED IN THE TEXT 205 
 
 On glancing through this summary, it will be seen that the 
 arrangement of the subject matter is not altogether a natural 
 one; indeed, in introducing it, I have only sought to give a 
 classified survey of the contents of this book. 
 
 Physiological considerations must determine the ultimate 
 method of grouping the facts, especially because, as was pointed 
 out in the introduction, the term vestigial is, as a rule, 
 only applied to such organs as have lost their original physio- 
 logical significance. Eetrogressive organs, on the contrary, are 
 such as may still remain functional, though, as a rule, only to 
 a limited extent. It has further been seen that both these 
 conditions in the process of degeneration may be, in different 
 individuals, realised in one and the same organ. The palmaris 
 longus and plantaris muscles furnish a case in point ; for while 
 these, and especially the former, are not infrequently so well 
 developed that there can be no doubt of their being functional, 
 cases occur in which one or the other of them has become quite 
 transformed into tendinous tissue and really vestigial. And in 
 yet other cases these muscles may altogether have disappeared. 
 On this subject Osborn makes the following appropriate remark : 
 " Both in the muscular and skeletal systems we find organs so 
 far on the down grade that they are mere pensioners of the body, 
 drawing pay (i.e. nutrition) for past honourable services without 
 performing any corresponding work the plantaris and palmaris 
 muscles for example." l 
 
 Many similar examples might be given. Confining our 
 attention to muscles alone, it may suffice to recall the pyramidalis 
 and certain muscles of the head. 
 
 1 Cf. this author's Cartwright Lectures, Lect. I. "The Contemporary Evolution 
 of Man," Medical Record, Feb. 20, 1892.
 
 LIST OF THE ORGANS AND TOPICS CONSIDERED 
 IN THE TEXT, CLASSED ACCORDING TO THE 
 SYSTEMS TO WHICH THEY RELATE 
 
 I. INTEGUMENT AND INTEGUMENTAL ORGANS 
 
 (a) Horny Structures. 
 
 Vibrisste (tactile hairs). 
 Primitive hairy covering (lanugo). 
 Converging hair vortices, ex. vertex 
 
 coccygeus. 
 
 Glabella and foveola coccygea. 
 Pseudohypertrichosis. 
 Hypertrichosis vera. 
 Nails (the fifth claw -like). 
 
 (6) Glands. 
 
 Montgomery's glands. 
 
 Mammary pouches. 
 
 Mammary line. 
 
 Supernumerary mammary glands 
 and nipples (polymasty, polythely). 
 
 Pectoral hair vortices (probably indi- 
 cating the former position of super- 
 numerary nipples). 
 
 II. SKELETAL SYSTEM 
 
 (a) Vertebral Column. 
 
 Cauda humana. 
 
 Os coccygis. 
 
 Curvature of the lumbar portion of 
 
 the spinal column. 
 Forward shifting of the sacral portion 
 
 of the spinal column (assimilation 
 
 of the last lumbar vertebra). 
 Numerical increase of the lumbar 
 
 vertebrae. 
 Outgrowth of the transverse process 
 
 of the sixth cervical vertebra. 
 
 (6) Thorax. 
 
 Quadrupedal form of the thorax in 
 the child, with greater dorso-sternal 
 diameter. 
 
 Disappearance of the lumbar ribs. 
 
 Disappearance of the cervical ribs. 
 
 Reappearance of cervical, lumbar, and 
 sacral ribs formerly present. 
 
 Variations in development of the 
 upper and lower ribs. 
 
 Former greater extension of the 
 pleuroperitoneal cavity, both an- 
 teriorly and posteriorly. 
 
 The eighth sternal rib. ^ 
 
 Reduction of the sternal ribs to six. 
 
 Reduction of the sternum. 
 
 Vestiges of the episternal apparatus. 
 
 (c) Skull. 
 
 Post-frontal bone. 
 Os interparietale. . 
 Os prseinterparietale. 
 Processus paramastoideus. 
 Torus occipitalis. 
 
 Suppression of the parietal process of 
 the alisphenoid.
 
 LIST OF ORGANS ACCORDING TO SYSTEMS 
 
 207 
 
 Fusion of nasal bones. 
 Participation of the os lachrymale in 
 
 the superficial facial skeleton. 
 Variation of the os lachrymale. 
 Downward prolongation of the nasal 
 
 process of the frontal bone. 
 Lower bridge to the nose. 
 Ductus naso-palatinus. 
 The pre- maxillary and maxillary 
 
 bones. 
 Ossa palatina, in relation to the 
 
 palatine processes of the maxillae. 
 Distinctness of the ossa palatina, and 
 
 the spina nasalis posterior. 
 Vestiges of the branchial skeleton 
 
 (thyro - hyoid apparatus, ossicula 
 
 auditus). 
 
 (rf) Skeleton of the Limbs. 
 
 Processus coracoideus [epi- and meta- 
 coracoid bones]. 
 
 Extension of the basis scapulae. 
 
 Great development (divergence) of the 
 iliac expansions. 
 
 Length of the forearm in the embryo 
 and in the lower races of Man- 
 kind. 
 
 Perforation of the olecranon fossa. 
 
 Processus supracondyloideus (entepi- 
 condyloideus). 
 
 Os centrale carpi. 
 
 Trochanter tertius femoris. 
 
 Variations in the length of the lower 
 leg- 
 
 Platyknemia. 
 
 Exclusion of the fibula from articula- 
 tion with the femur. 
 
 Marked convexity of the condylus 
 externus tibiae. 
 
 Great development of the malleolus 
 tibialis in the embryo, the lower 
 races of Mankind, and Anthro- 
 poids. 
 
 Predominance of the great toe. 
 
 Great development of the tarsal 
 elements. 
 
 Parallel disposition of the great toe 
 with the others, in the adult. 
 
 The great toe in the embryo and the 
 lower races. 
 
 Reduction of the fifth (or fourth and 
 fifth) toes (fusion of their terminal 
 and penultimate phalanges). 
 
 Comparison of the position of the 
 limbs in the human embryo and 
 the lower Vertebrates. 
 
 III. MUSCULAR SYSTEM 
 
 M. serratus posticus superior et 
 inferior. 
 
 Mm. caudse hximanse. 
 
 Traces of metamerism in the ab- 
 dominal muscles. 
 
 M. rectus abdominis. 
 
 M. pyramidalis. 
 
 Mm. scaleni. 
 
 M. triangularis sterni. 
 
 M. cleido-occipitalis. 
 
 M. subcutaneus colli (platysma 
 myoides). 
 
 Mimetic muscles. 
 
 M. sphincter colli. 
 
 M. transversus nuchae. 
 
 M. epicranius. 
 
 Muscles of the pinna. 
 
 M. palmaris longus. 
 
 M. plantaris. 
 
 M. flexor sublimis digitorum. 
 
 M. flexor profundus digitorum. 
 
 M. flexor brevis digitorum pedis. 
 
 M. extensor brevis digitorum pedis. 
 
 Mm. interossei pedis. 
 
 M. adductor hallucis. 
 
 M. opponens minimi digiti. 
 
 M. latissimo-condyloideus. 
 
 M. sternalis. 
 
 M. epitrochleo-anconaeus. 
 
 M. levator claviculae. 
 
 M. ischio-femoralis. 
 
 Muscles of the thumb (especially the 
 
 flexor longus pollicis). 
 Mm. glutei (esp. gluteus maximus). 
 M. gemellus superior. 
 Mm. soleus and gastrocnemius.
 
 208 
 
 THE STRUCTURE OF MAN 
 
 IV. NERVOUS SYSTEM 
 
 (a) Central Nervous System 
 
 Filum terminale. 
 
 Glandula coccygea. 
 
 Pyramidal tracts. 
 
 Parieto - occipital fissure ("Affens- 
 
 palte"). 
 
 Pineal gland (epiphysis cerebri). 
 Pituitary body (hypophysis cerebri). 
 
 Lobus olfactorius. 
 
 Roof of the fourth ventricle. 
 
 Obex, ligula, vela medullaria, tseniae 
 
 medullares. 
 
 Occipital lobe of cerebrum. 
 Posterior cornu of lateral ventricle. 
 Calcar avis. 
 
 (6) Peripheral Nervous System 
 
 Roots and ganglia of hypoglossus. Traces of teguinental sense organs in 
 
 Rami recurrentes of certain cerebral foetal life. 
 
 nerves. Variations in the brachial and lumbo- 
 
 sacral plexuses. 
 
 V. SENSE ORGANS 
 
 Disappearance of an olfactory ridge 
 
 in the embryo. 
 Papilla palatina and foliata. 
 Jacobson's organ. 
 Vasa hyaloidea (Cloquet's canal). 
 The projectile nose. 
 Orbitalis muscle. 
 
 Levator palpebrae superioris muscle. 
 
 Plica semilunaris. 
 
 Supernumerary lachrymal glands. 
 
 Epicanthus. 
 
 Auditory ossicles (relations to the 
 
 visceral skeletal arches). 
 The middle ear (hyoid visceral cleft). 
 
 VI. ALIMENTARY SYSTEM 
 
 Palatal ridges. 
 
 Milk dentition. 
 
 Indications of a third dentition. 
 
 Wisdom teeth. 
 
 Possible indications of free dental 
 
 papillae before the down-growth of 
 
 the dental ridge. 
 Canine teeth. 
 Outer upper incisors. 
 Cheek teeth (reduction of cusps and 
 
 fangs). 
 Appearance of a third premolar and 
 
 a fourth molar. 
 Sublingua. 
 
 Glandula thyroidea. 
 
 Glandula thymus. 
 
 Foramen ccecum and base of the 
 
 tongue. 
 
 Ductus thyroglossus. 
 Bursse supra- and prsehyoidea. 
 Carotid gland. 
 Bursa pharyngea. 
 Constriction of the stomach. 
 Ciliated epithelium in the oesophagus. 
 Diverticulum ilei. 
 Ccecum. 
 Vermiform appendix. 
 
 VII. KESPIRATORY SYSTEM 
 
 Metamorphosis of the aortic arch Sinus Morgagni (laryngeal resonant 
 
 system. chamber). 
 
 Branchial pouches and cervical fistulae. Sinus and Lobus subpericardiacus.
 
 LIST OF ORGANS ACCORDING TO SYSTEMS 
 
 209 
 
 VIII. CIRCULATORY SYSTEM 
 
 Vestiges of valves in the embryonic 
 
 heart. 
 Vestiges of the sinus venosus, in the 
 
 heart. 
 
 Intestinal arteries. 
 Arteria sacralis media. 
 Arteria ischiadica (genesis of femoral 
 
 artery). 
 
 Superficial vascular arch of the foot. 
 Cardinal veins. 
 
 Ductus Cuvieri. 
 
 Sinus venosus cordis. 
 
 Persistence of the post, cardinal veins 
 in the form of a double vena cava, 
 inferior. 
 
 Metamorphosis of superior caval 
 veins. 
 
 Valves of the intercostal and intes- 
 tinal veins. 
 
 IX. URINOGENITAL SYSTEM 
 
 Pronephros and mesonephros. 
 Vestiges of the mesonephros. 
 Uterus duplex, bipartitus, bicornis, 
 
 and simplex. 
 Hypospadias. 
 
 Descensus or reditus testiculi. 
 Conns inguinalis. 
 Ligamentum inguinale. 
 Area scroti. 
 Suprarenal bodies.
 
 SOME ORGANS AND VESTIGES OF ORGANS, WHICH 
 SHOW [STRUCTURAL COMMUNITY WITH] VERY 
 PRIMITIVE VERTEBRATE TYPES 
 
 CONDITIONS DEFINITIVE IN FISHES (ELASMOBRANCHS) AEE 
 INDICATED BY 
 
 (1) The free dental papillae projecting above the surface of 
 the mucous membrane before the sinking of the dental ridge. 
 
 (The appearance ontogenetically of the dental ridges, long- 
 before the first osseous rudiments, points back to the 
 extremely early phylogenetic appearance of teeth, in 
 Vertebrates, before any of the other hard structures of 
 the body.) 
 
 (2) The pineal gland and pineal organ (a parietal foramen 
 in the roof of the skull is found in Fishes as early as the 
 Devonian period, and the organ occurs in the Marsipobranchii). 
 
 (3) The pituitary body (hypophysis cerebri). 
 
 (4) The branchial pouches. 
 
 (5) The vessels of the visceral arch system. 
 
 vj (6) The vasa hyaloidea of the vitreous body (Cloquet's 
 canal). 
 
 (7) The cardinal veins. 
 
 (8) Certain structures, appearing in the development of the 
 heart, vestiges of which are found in the fully developed organ. 
 
 (9) The arteria caudalis (A sacralis media). 
 
 (10) The pro- and naeso-nephric excretory apparatus. 
 
 (11) The possible vestiges of a third set of teeth (pointing 
 back to a probable successive renewal of teeth, such as 
 characterises Fishes, Amphibians, and Reptiles).
 
 INDICATIONS OF DEFINITIVE CONDITIONS 211 
 
 CONDITIONS DEFINITIVE IN AMPHIBIA AND EEPTILES ARE 
 INDICATED BY 
 
 (1) The arteria ischiadica [cruralis]. 
 
 (2) The double rectus abdominis muscle. 
 
 (3) The foramen supracondyloideum (entepicondyloideum) 
 humeri (found in Amphibians and Reptiles as early as the 
 Permian period). 
 
 (4) The presence of (supernumerary) lachrymal glands below 
 the eye.
 
 CONCLUDING REMARKS 
 
 IN the course of Phytogeny the body of Man has undergone a 
 series of modifications which still in part find expression in his 
 Ontogeny. There are indications that changes in his organisa- 
 tion are still continuing, and that the Man of the future will be 
 different from the Man of to-day. It is the more necessary to 
 emphasise this, because it has only recently been asserted by one 
 in authority in the anthropological world, that "since the Neolithic 
 Age Man has been a fixed type." 
 
 I willingly admit that nothing is gained by the mere 
 demonstration of " animal likenesses," and that the final and 
 only satisfactory solution of the great riddle of Man must lie in 
 the demonstration of his genealogy and the line of his inheritance. 
 
 Although small and insignificant in their first appearance, 
 structural changes become more and more distinctly marked 
 from generation to generation, and more and more definitely 
 fixed according to the laws of heredity and selection. There 
 exist different degrees of the degenerative process : first an 
 organ begins to degenerate in the adult body, then this 
 degeneration finds expression in the embryo, then the organ 
 in question only occurs in a certain percentage of the in- 
 dividuals as a reversion, and finally even such occasional 
 occurrence ceases, and all trace of the organ is lost. Osborn 
 calls this process of gradual extinction the " long struggle 
 of the destructive power of degeneration." 
 
 Although these changes are so manifold and follow such 
 different directions (take, for example, those of the musculature), 
 one principle lies at the bottom of them all, viz, the endeavour 
 to shake off, as far as possible, all that is unnecessary and 
 superfluous, in order to make room for further development. 
 Weismann very justly remarks : " If Nature were not able to 
 effect the disappearance of superfluous organs the transformation 
 of species would have been well-nigh impossible, for the existing
 
 CONCLUDING REMARKS 213 
 
 parts which had become superfluous would have been in the way 
 of other active parts, and would have hindered their development. 
 Indeed, had all parts which the ancestors possessed been necessarily 
 retained, an abnormal animal would at last have been produced 
 a monster no longer capable of living. The degeneration of 
 parts which have become superfluous is thus a condition of 
 progress." 
 
 But what is it that actually initiates these various changes ? 
 What is their first cause ? This question cannot be answered off- 
 hand on account of the great number of circumstances which 
 have to be taken into account. First, we have to consider 
 external influences of the most varied kinds which affect the 
 different organs, or systems of organs, in a progressive or 
 retrogressive manner, leading to new acquisitions or to gradual 
 losses. These changes, however, have, as it were, to be intro- 
 duced by the occurrence of slight variations, and then (if I may 
 use a military term) when once a breach has been made in any 
 part, a point of least resistance is formed for pathological affec- 
 tions, as I have tried to prove in the foregoing pages, and a 
 substitute for the gradually degenerating organs has to be found. 
 In other words, as soon as a transformation takes place in any 
 part of the body, correlative alterations in some other part 
 commence, so that, as it were, a wave of modification passes from 
 one system of organs to another. For example, when the 
 dentition of our ancestors degenerated, and the canines became 
 reduced, the important weapons of attack and defence thus lost 
 had to be replaced, if the struggle for existence was to be 
 advantageously maintained. Concurrently with the reduction of 
 powerful jaws the brain was developing, and the intelligence 
 attained a sufficiently high degree of perfection to invent 
 weapons, at first no doubt of a very simple character. Or 
 again, as the foot gradually changed from a seizing organ into 
 one for support of the body, and its musculature consequently 
 changed, then, in adaptation to the new function, great 
 alterations had to be effected not only in the skeleton of the 
 limb, but also in its muscular and nervous system, e.g. the 
 muscles of the calf and buttocks attained a massive development. 
 Such examples might be multiplied, but the above will suffice 
 to show that these modifications are not mere freaks of chance, 
 mere lusus natures, but are the expression of law - abiding 
 processes, even if we cannot always succeed in determining their 
 first cause. At all events, these processes need immense periods
 
 214 THE STRUCTURE OF MAX 
 
 of time for their accomplishment, so that, as a rule, they are 
 removed from direct perception by means of the senses, and can 
 only be inferred from the evidence of Phylogeny, Comparative 
 Anatomy, and Ontogeny. 
 
 This applies not only to Man, but to the whole animal 
 kingdom, which yields us a long series of examples of degenera- 
 tion. Here also we find evidence of the great importance of the 
 external conditions of life to which the organism responds. One 
 of the most striking proofs of this is afforded by the degenerate 
 condition, or even entire absence, of eyes in animals living in 
 the depth of the ocean or in caves. Such animals also illustrate 
 how the loss of one organ is compensated for by the increased 
 development of other organs. From the same point of view are 
 to be considered the limbless Amphibia, and the Slow-worms, 
 and another group of Eeptiles of essentially similar adaptive 
 organisation, the Amphisbsenidee, and finally the more familial- 
 Earthworm itself. 
 
 Whereas, among the above-mentioned cases, it is the organ 
 of sight which atrophies ; in other animals, the olfactory organ 
 disappears, and I may especially refer to those Fishes known, 
 from the characters of their jaws and teeth, as the Plectognathi 
 Gymnodontes. Here, 1 in adaptation to a diet of Crustacea and 
 Molluscs which are very difficult to crush, the musculature of the 
 jaws develops to an extraordinary degree, displacing the olfactory 
 apparatus to such an extent that the olfactory nerve is reduced 
 to a minute thread, which branches either within a mere tegu- 
 mental olfactory process or simply under the surface integument 
 of the olfactory region. 
 
 Until quite recently, the question wherein lay the cause of 
 the degeneration of an organ was thought to be satisfactorily 
 answered as follows : the organ is not used, and the degenerating 
 effect of disuse, passed on from one generation to another, gains 
 in intensity, until it leads to the total removal of the organ in 
 question. This answer presupposes what is often stated, but has 
 never been proved, viz. the inheritance of acquired characteristics. 2 
 
 1 Cf. "Wiedersheim, "Das Geruchsorgan der Tetrodonten." Kolliker Gratula- 
 tionsschrift, 1887. 
 
 2 [This statement requires qualification. It is true that we have no very satisfac- 
 tory concrete instance of a chance structural modification of an individual having been 
 transmitted by inheritance to its own immediate offspring. But, on the other hand, 
 as Herbert Spencer has argued with great force, there seems no way of explaining 
 the phenomena of highly organised life, except on the supposition of some transmis- 
 sion of characters acquired in adaptation to the environment. ]
 
 CONCLUDING EEMARKS 215 
 
 Weismann has recently conclusively proved that this answer is 
 not sufficient, and that it must first of all be shown how it can 
 come to pass that a portion of the body which up to a certain 
 time is indispensable to existence, should disappear as soon as it 
 is not needed. The real cause, according to Weismann, lies in 
 a converse process, that is, the cessation of Natural Selection 
 in Panmixia (general cross-breeding). In other words, as soon 
 as, by change in its external surroundings, an organ is excluded, 
 its condition becomes retrogressive. Then the general inter- 
 breeding between individuals in which the organ in question is 
 well developed and others in which it is but feebly developed, 
 which latter have survived in spite of this, leads to its slow but 
 steady degeneration. 1 
 
 The numerous above-mentioned cases of degeneration in the 
 organs of the human body should also, without doubt, be regarded 
 from this point of view. The fact that the degree of development 
 of this or that organ (e.g. the sense organs, which are incompar- 
 ably more highly developed in savages than in civilised men) is 
 no longer of supreme importance to the individual, i.e. no longer 
 necessary for his prosperity, leads to a degeneration, which, in the 
 struggle for existence, could only be compensated for by a high 
 degree of civilisation. Weismann gives the following striking pv. 
 example of this : " We can at the present day earn our bread 
 quite independently of the acuteness of our hearing and the 
 delicacy of our scent, indeed, even the sharpness of our sight is no 
 longer a decisive factor in our success in the struggle for existence. 
 Since the invention of spectacles, short-sighted men suffer hardly 
 any disadvantage as compared with the long-sighted in their 
 capacity for earning a living, at any rate in the higher circles of 
 society. This is why so many short-sighted people are to be 
 found among us. In ancient times a short-sighted soldier, or 
 still more a short-sighted general, would have been simply an 
 impossibility, as would also a short-sighted huntsman; indeed, 
 in nearly all branches of human society short sight would have 
 been a considerable obstacle, and would have rendered it difficult 
 or impossible for a man to thrive and prosper. This is now no 
 longer the case ; the short-sighted man can make his way like 
 
 1 [This argument is unsatisfactory. Panmixia alone could not lead to the dis- 
 appearance of any organ. Natural selection may effect an increase in an organ, by 
 eliminating those below a certain average ; or the diminution of a structure, by 
 eliminating all above a certain average. But it is not easy to see how Panmixia, or 
 the cessation of Natural Selection, could alter the average in any way.]
 
 216 THE STRUCTURE OF MAX 
 
 every other, and his short sight, so far as it involves hereditary 
 tendency, will be handed on by him and will help to make 
 hereditary shortness of sight a widely-spread characteristic in 
 certain classes of society." 
 
 The above sufficiently illustrates the fact that progressive 
 variations are closely connected with retrogressive variations, 
 indeed that to a great extent the former are rendered possible 
 by the latter. If it be true that the adaptation of a creature 
 to its surroundings depends on the process of Natural Selection, 
 we must also consider that Natural Selection is the determining 
 factor in both retrogressive and progressive processes. We have, 
 then, to fall back on the general law of Selection propounded 
 by Charles Darwin, which may be summed up as follows : survival 
 only of the fittest, transmissibility by inheritance, and the gradual 
 improvement of what is advantageous from generation to genera- 
 tion, till the highest possible degree of perfection is reached. 
 
 But wherein lies Man's special " perfection " ? Does such 
 perfection exist, and if so, is it, in comparison with other living 
 beings, as universal as is generally assumed ? Let us look at 
 this matter a little closer. 
 
 There would appear to have been a time when our ancestors 
 were protected against the inclemencies of the weather by a 
 natural covering of hair, and against insects and other injurious 
 influences by an extensive tegumental musculature, when the 
 pinna of the ear, more advantageously disposed than at present, 
 and moved by numerous and powerful muscles, collected the sounds 
 of approaching danger incomparably better than at the present 
 day, and when the sense of smell, probably intensified by Jacobson's 
 organ, was more highly developed than now. Indeed, at a 
 very low stage of phylogenetic development, when the visual organs 
 were placed laterally on the head, and were furnished with a 
 third eyelid, and regulated by more numerous muscles, there may 
 even have been a " third eye " which could perceive what took 
 place above the head (cf. the pineal organ, p. 133). The intestinal 
 tube may have been longer, and thus better suited than at the 
 present day for vegetable diet, the ancestor of Man enjoying at 
 any rate more favourable conditions of existence as a vegetarian 
 than his successor now does (compare also the former greater 
 number of cheek teeth). He may also have had the further advan- 
 tage of not possessing a vermiform process of the ccecum which 
 predisposes to disease, and causes the destruction of a consider- 
 able percentage of his fellows.
 
 CONCLUDING REMARKS 217 
 
 The herbivorous stage was followed by an omnivorous one, 
 characterised by the development of powerful canines. In this 
 way, as skill in hunting and slaying animals developed, and 
 carnivorous diet became of continually greater importance, the 
 intestinal tube would appear to have begun to shorten and the 
 processus vermiformis to become constricted. 
 
 Laryngeal sinuses may have been developed, which, acting as 
 resonators, lent the voice greater strength and carried it farther, 
 and thus made it a means of frightening or enticing. The 
 lower jaw, the neck and its musculature, were far more powerfully 
 developed than now. 
 
 In the male the genital glands may have remained, as they 
 now normally do in the female, within the abdominal cavity, 
 and been thus better protected from injury than at present. At 
 a later stage even, when they had changed their position, and had 
 reached the pouch-like appendages of the abdominal integument, 
 they could still be withdrawn into the cavum abdominis, at least 
 temporarily, by means of a well-developed muscle (cremaster). 
 This is still indicated by ontogenetic processes. 
 
 There can be no doubt that the ancestors of Man were pro- 
 vided with a more extensive mammary system and more numerous 
 mammae than he to-day possesses, and the significance of this fact 
 is equally clear. It can only be explained by the assumption that 
 a greater number of young were originally produced at a birth. 
 This, of course, was of advantage in the preservation of the species. 
 
 It follows from the above that in the course -of a long 
 geological period, Man has gradually lost a great number of 
 advantages once possessed by his ancestors, and the question 
 arises whether he has acquired any others in exchange for those 
 lost. This certainly is the case, and this indeed must have 
 been so, otherwise the species Homo would have failed in the 
 struggle for existence. We thus have a series of exchanges, based 
 (if we take only the most important organ into consideration) 
 upon the unlimited capacity of development of the human brain. 
 This one acquisition, supported by an increased functional 
 efficiency of the hand and by the development of articulate speech, 
 has entirely compensated for the loss of the great series of ad- 
 vantageous arrangements mentioned above. They had to be 
 sacrificed in order that the brain might successfully develop, and 
 that the Homo sapiens of to-day, with his surprising adaptability 
 to the most varied conditions of life, might be produced. 
 
 This momentous exchange took place slowly and only after
 
 218 THE STRUCTURE OF MAN 
 
 great opposition. It was not accomplished without a struggle, in 
 which every inch of the already occupied territory had to be 
 painfully fought for ; and the extraordinary tenacity with which 
 certain favourable positions once attained are clung to, is seen in 
 the fact that some of them are still taken up by the organism 
 as dim reminiscences of the past, perhaps only during fcetal life. 
 These ancient ancestral pictures, for such indeed they are are 
 eloquent witnesses of a time long since past. They keep our 
 vision clear, when we have, as in this present case, to be impartial 
 judges of ourselves. 
 
 As Testut appropriately says : Let us not unjustly reproach 
 anatomists with lowering Man, with drawing him down from his 
 high position : it is true that Anatomy does rank Man in the 
 class of the Mammalia, but it places him in the highest order 
 of that class, that of the Primates ; and although it cannot 
 entirely separate him from these, it gives him the highest possible 
 position among them. Anatomy not only makes Man the most 
 perfect of Primates, but also proclaims him first of the foremost 
 of all living beings. 1 As Broca has said : " That may well suffice 
 for his ambition and his glory." I cannot do better than 
 conclude with the following words of the last-named author, which 
 are no less worthy of consideration : " Pride, which is one of the 
 most characteristic traits of our nature, has in many minds 
 prevailed over the calm testimony of reason. Like those Eoman 
 Emperors who, intoxicated with their universal power, ended by 
 denying their manhood, and by believing themselves to be 
 demigods, so the king of our planet pleases himself with the 
 thought that the nature of the vile animal which is subject to 
 his caprices cannot have anything in common with his own. 
 The proximity of the monkey is to him inconvenient ; he is no 
 longer satisfied to be the king of animals, he desires that an 
 immense unfathomable abyss should separate him from his 
 subjects ; and, sometimes, turning his back on the earth, he takes 
 refuge, with his endangered majesty, in the nebulous sphere of the 
 Eeign of Man. But Anatomy, like that slave who followed the 
 triumphal car, repeating the words ' Memento te homineru esse,' 
 comes to agitate him in this self-admiration, and reminds him 
 that reality, visible and tangible, links him with the animals." 
 
 1 [Cf., however, Minot, "Is Man the Highest Animal"? Proc. Arncric. Assoc. 
 for flit Advancement of Science, 1881, p. 240.]
 
 GLOSSARY OF TECHNICAL ZOOLOGICAL TERMS 
 OCCURRING IN THE TEXT. 
 
 AMBLYSTOMA. A Tailed Amphibian of the United States and Mexico. 
 
 AMMOCCETES. The sexually immature larva of the Lamprey. 
 
 AMXIOTA. The three higher classes of Vertebrates, i.e. Reptiles, Birds, and 
 Mammals, the embryos of which are enveloped in an amnion. 
 
 AMPHIOXUS. THE LAXCELET. [The lowest animal possessing, in the adult 
 state, a vertebral skeleton (notochord).] 
 
 AMPHISB.ENID^E. Lizards with Snake-like bodies, which live underground. 
 
 AXAMNIA. The two lowest classes of Vertebrates, i.e. Fishes and Amphi- 
 bians, the embryos of which are not enveloped in an amnion (cf. Amniota). 
 
 [AXATOMY. The study of gross structure.] 
 
 ANTHROPOIDS, also ANTHROPOMORPHA. The highest "man-like" Apes 
 (Gibbons, Orangs, Gorillas, and Chimpanzees). 
 
 ANURA. Tailless Amphibians (Frogs and Toads). 
 
 APLACEXTALIA (Mammalia aplacentalia). The lowest Mammals, i.e. the 
 Ornithodelphia (Monotremata) and the Marsupialia. The Monotremata 
 are oviparous. The Marsupials produce immature young, which are in 
 most of them carried about after birth in a pouch (marsupiurn) formed 
 by the abdominal integument. [In neither Monotremata nor Marsupials 
 is an allantoic placenta developed like that of all the higher Mammals 
 (Placentalia).] 
 
 ARCTOMYS MARMOTTA. Marmots ; [terrestrial Rodents inhabiting Europe, 
 North Asia, and North America.] 
 
 [ATAVISM. The reversion to the condition of a lower type.] 
 
 ATELES. The Spider Monkey of South America. 
 
 AUCHEXIA. The Llama. 
 
 [BIOLOGY. In English, the study of all phenomena manifested by living 
 
 organisms. 1 ] 
 BOVINA. Oxen. 
 
 BRADYPTJS. A South American Sloth. 
 BRANCHIOSAURUS. A Tailed Amphibian of the Permian period. 
 
 CAPROMYS. Arboreal Rat-like animals found in Cuba and Jamaica. 
 CARNIVORA. Beasts of prey (flesh -eaters). Especially Felidoe and Canidae. 
 CAVIA. The Guinea-Pig. 
 CEBUS. The " Capuchin," a leading genus of American Monkeys. 
 
 1 [The term " Biologic " of continental observers is usually applied to the study 
 of life itself, i.e. it is more nearly equivalent to our English term Physiology.]
 
 220 THE STRUCTURE OF MAX 
 
 CERCOPITHECDS. A family of African Apes [the "Green Monkeys" of 
 menageries]. 
 
 CEEVUS CAPREOLUS. The Roebuck. 
 
 CETACEA. An order of Aquatic Mammals (Whales, Dolphins, and Porpoises). 
 
 CHELONIA. Turtles and Tortoises. 
 
 [CHIMPANZEES. Anthropoid Apes, readily remarkable for the relative short- 
 ness of the fore-limb. Confined to West and Central Equatorial Africa.] 
 
 CHIROPTERA. Bats. 
 
 CHOLOZPUS. The two-toed Sloth of Northern South America. 
 
 COSLOGENYS. The " Paca," a large Rodent somewhat resembling the Guinea- 
 Pig, inhabiting Central and South America. 
 
 DASYPROCTA. The " Agouti," a near relative of the Ccelogenys. 
 
 DASYPUS. One of the Armadillos. 
 
 DELPHIXUS. The common Dolphin. 
 
 DICOTYLES. The Peccary, or New World Pig. 
 
 DIDELPHIA. Marsupials, Mammalia having two vaginae. 
 
 DIPNOI. Fishes having not a few points of resemblance to the Amphibia. 
 
 [Remarkable among fishes for the conversion of the air-bladder into a 
 
 functional lung] (confined to certain rivers of Queensland, Tropical 
 
 Africa, and South America). 
 DUCKBILL. The "Platypus" of Australia, one of the Monotremata. (Cf. 
 
 Aplacentalia and Ornithodelphia.) 
 
 ECHIDNA. The " Spiny Ant-Eater " of Australia, one of the Monotremata. 
 
 (Cf. Aplacentalia and Ornithodelphia.) 
 EDENTATA. An order of Mammals, comprising the Ant-Eaters, Armadillos, 
 
 and Sloths. 
 [ELASMOBRANCHII. The lowest living order of true Fishes, includes the Sharks, 
 
 Rays, and Herring Kings, with their allies.] 
 [EMBRYOLOGY. The study of the earlier growth stages of living organisms, 
 
 in the higher animals up to the completion of organ formation. A 
 
 department of the wider study of Development] 
 ERINACEUS. The Hedgehog. 
 
 GANOIDEI. A group of living Fishes, [including the Sturgeons, the Bony 
 
 Pikes of North America, and the Polypterus or " Bichir " of the Nile, 
 
 and their allies.] 
 GORILLAS. [The largest of the Anthropoid Apes. Confined to West 
 
 Equatorial Africa.] 
 GYMNOPHIONA. Limbless Amphibians (Coecilians) with Snake-like bodies, 
 
 some of which are known to live a subterranean life. 
 
 HATTERIA. The "Tuatara" of New Zealand. A "Lizard" of very 
 primitive structure. 
 
 [HISTOLOGY. The study of the minute structure of tissues and organs.] 
 
 HoMffiosAURUs. A Fossil Lizard [of the Jurassic of the European Continent]. 
 
 HYLOBATES. The Gibbons ["Long -armed Apes." Anthropoid Apes, con- 
 fined to South-east Asia. The only Apes which habitually walk upright]. 
 
 HYPEROODON. A toothed Whale of the North Atlantic, sometimes called the 
 " Bottlenose." 
 
 HYSTRIX. The Porcupine.
 
 GLOSSARY OF TECHNICAL ZOOLOGICAL TERMS 221 
 
 INUUS. [A genus of Old World Apes, allied to the only European Ape the 
 
 Barbary Ape (Macacus) of Gibraltar.] 
 INSECTIVORA. [A heterogeneous order of Mammals, which includes the 
 
 Hedgehogs, Shrews, and Moles.] 
 
 LEMUROIDEA. Arboreal animals of the Old World, chiefly of Madagascar, 
 with dentition approximate to that of certain Insectivora, and as a rule 
 with Monkey- and Ape -like prehensile (cf. Tarsius) limbs. (The 
 "Tarsier" and "Aye Aye" are of this sub-order.) 
 
 MACACUS. (Cf. Inuus.) 
 
 MANATEE. The " Sea Cow," an aquatic Mammal, famous for having given 
 
 rise to the fable of the Mermaid. 
 MANIS. One of Scaly Ant-Eaters of the Old World. 
 MARSIPOBRANCHII. The Lampreys and Hags. 
 MARSUPIALIA. A sub-class of Mammalia, the females of most of which are 
 
 provided with a inarsupium, or pouch, enclosing the teat-bearing area of 
 
 the body-wall. (Cf. also Didelphia and Aplacentalia.) 
 MONODELPHIA. Mammals possessed of a single vagina, i.e. all those above 
 
 the Marsupials. 
 MONOTREMATA. The lowest sub-class of Mammals. (Cf. Aplacentalia and 
 
 Ornithodelphia.) 
 [MORPHOLOGY. The study of form and arrangement of the parts of the 
 
 body.] 
 
 [MURID.E. A family of Rodents, embracing the Rats and Mice.] 
 MusTELiDiE. A group of Carnivores, including the Weasels, Pole-Cats, and 
 
 Martens. 
 
 MYCETES. The Howling Monkeys of South America. 
 MYOGALE. [The " Desman," an aquatic Insectivore, related to the Moles and 
 
 Shrews, occurring in the Pyrenees and South-East Russia.] 
 MYRMECOPHAGA. [One of the Hairy Ant-Eaters of South America.] (Cf. 
 
 Edentata.) 
 
 [ONTOGENY. The developmental history of the individual.] 
 
 ORANGS. [Anthropoid Apes confined to the Oriental region. The " Red 
 
 Haired Apes " of Sumatra and Borneo.] 
 [ORNITHODELPHIA. The lowest living Mammals (Australian). Oviparous 
 
 Mammals, having non-united oviducts and a cloaca. (Cf. Monotremata, 
 
 Duckbill, and Echidna.)] 
 ORYCTEROPODID^E. The " Aaardvark," or hairy Ant-Eaters of the Old World. 
 
 (The Cape Ant-Eater.) 
 
 PAL^EOHATTERIA. A fossil "Lizard" [of the Permian beds in Saxony] related 
 
 to Hatteria. 
 
 PETROMYZON. The Lamprey (cf. Ammocoetes and Marsipobranchii). 
 PHALANGISTA VULPINA. The Australian "Opossum," or "Vulpine 
 
 Phalanger." A climbing Marsupial. 
 PHOCA. The Seal. 
 PHOC^NA. The Porpoise. 
 
 PHYLLOMYS. An extinct Rodent, from the Brazilian caves. 
 [PHYLOGENY. The developmental history of the race.]
 
 222 THE STRUCTURE OF MAN 
 
 [PHYLUM. A term applied to any great race or assemblage of genetically 
 
 related forms of life, which conform to the same fundamental type.] 
 [PHYSIOLOGY. The study of the functions of living matter, i.e. of the living 
 
 in action.] 
 PINNIPEDIA. Marine Carnivora, having feet transformed into paddles. The 
 
 Seals, Sea-lions, and Walruses. 
 [PLACENTALIA. The highest sub-class of Mammals. Those Mammals which 
 
 develop an allantoic placenta.] 
 PRIMATES. The highest order of Placenta! Mammals, including the Lemur- 
 
 oidea, Monkeys, Apes, and Man. 
 PROSIMII. (Cf. Lemuroidea.) 
 
 REVERSION. (Cf. Atavism.) 
 
 RODEXTIA. An order of gnawing Mammals (Rabbits, Rats, Porcupines, 
 Squirrels, and their allies). 
 
 SADRIANS. Lizards. 
 
 SELACHIANS. Sharks and Dog-fishes. (Cf. Elasmobranchii.) 
 
 SIRENIA. An order of Aquatic Mammals. (Cf. Manatee.) 
 
 SLOW WORMS. A group of Limbless Lizards. 
 
 STEGOCEPHALA. Fossil Amphibians, most abundantly represented in the 
 
 Carboniferous, Permian, and Triassic strata. 
 
 STENOPS. The " Slender Lori " of Ceylon, one of the Lemuroidea. 
 Sus SCKOFA. The Domestic Pig. 
 
 TARSIUS. [The "Tarsier" of Borneo, Sumatra, and the Celebes.] One of 
 
 the Lemuroidea. 
 TELEOSTEI. The Bony Fishes. 
 
 TETRODONTA. Aberrant Bony Fishes, belonging to the family Gymnodontes. 
 TOOTHED WHALES. A group of the Cetacea, including the Cachelots or 
 
 Sperm Whales, Dolphins, and Porpoises. (Cf. Cetacea.) 
 
 UNGULATA. The Hoofed Mammals. 
 
 URODELA. The Tailed Amphibians. Newts, Salamanders, and their allies. 
 
 URSUS. The Bear. 
 
 ZIPHIUS. [A long-snouted Toothed Whale met with in most of the great 
 seas.]
 
 INDEX 
 
 ACETABULUM, 74 
 
 Affenspalte, 127 
 
 Ainos, 10 
 
 Alimentary canal, 155 
 
 Amasty, 22 
 
 Ankle-joint, 84 
 
 Aorta, 181' 
 
 Area? scroti, 197, 199 
 
 Arterial system, 181 
 
 Arteries, intestinal, 184 
 of fore-limb, 182 
 of hind-limb, 183 
 
 Artery, hyaloid, 147 
 hypogastric, 181 
 median sacral, 182 
 
 Astragalus, 84 
 
 Atrium, 180 
 
 Auditory organ, 150 
 
 BONE, alisphenoid, 58 
 
 coracoid, 71, 72 
 
 cotyloid, 74 
 
 epicoracoid, 72 
 
 epipteric, 59 
 
 frontal, 55, 61 
 
 hyoid, 65 
 
 interparietal, 55 
 
 lachrymal, 60 
 
 malar, 58 
 
 metacoracoid, 72 
 
 nasal, 60 
 
 palatine, 63 
 
 post-frontal, 55 
 
 premaxillary, 61 
 
 sphenoid, 58 
 Bones, metatarsal, 88 
 
 turbinal, 60, 141 
 
 "Wormian, 60 
 
 Brain, 127 
 
 fissures of, 127 
 
 growth of, 53 
 
 olfactory lobe of, 137 
 
 transitory fissures of, 138 
 
 weight of, 51, 128 
 Branchial arches, 66, 151 
 
 pouches, 171 
 
 skeleton, 172 
 
 Breasts, supernumerary, 18 
 Bronchus, eparterial, 176 
 Bursa inguinalis, 197, 198 
 
 pharyngea, 164 
 Bursse prse- and supra-hyoid, 162 
 
 | CJECDM, 167 
 j Calcaneum, 84 
 Canalis inguinalis, 196 
 j Canals, naso-palatine, 145, 156 
 Xuckii, 198 
 tubo-tympanicus, 151 
 vaginalis, 198 
 
 Carpus, 79 
 ; Canine ula lachrymalis, 149 
 
 Cauda humana (see Tail) 
 
 Cerebellum, 131 
 
 Cerebrum, lobes of, 131 
 
 Cervical groove, 66 
 
 Choana?, 61 
 
 Chorda dorsalis, 49 
 
 Circulatory system, 180 
 
 Clavicle, 71, 73 
 
 Clitoris, 195 
 
 Cloaca, 194 
 
 Coccyx, 28, 32 
 
 Colliculus seminalis, 194 
 
 Conus inguinalis, 196 
 
 Cranium, capacity of, 51
 
 224 
 
 THE STRUCTURE OF MAX 
 
 DENTAL RIDGE, 161 
 Descensus testiculoruin, 196 
 Diaphragm, 38, 177 
 Diverticulum ilei, 1 65 
 Duct, Miillerian, 189, 193 
 
 Wolffian, 187 
 Ductus Cuvieri, 184 
 
 thyroglossus, 162 
 
 ENSIFORM PROCESS, 44 
 
 Epicanthus, 150 
 Epididymis, 188 
 Epiglottis, 173 
 Epiphysis cerebri, 131 
 Episternum (see Interclavicle) 
 Eustachian tube, 150 
 Eye, 147 
 Eyebrows, 4, 150 
 Eyelids, 148, 150 
 
 FALLOPIAN TUBE, 194 
 Femur, 81 
 Fibula, 83, 93 
 Filum terminale, 124 
 Finger nails, 1 1 
 Fissura orbitalis, 148 
 Fistulae, cervical, 172 
 Foot, skeleton of, 85, 87 
 Foramina, condylar, 78 
 Fore-limb, skeleton of, 77 
 Fossa, olecranon, 77 
 
 orbital, 58, 148 
 
 temporal, 58, 148 
 Foveola coccygea, 5, 23, 28 
 Frog, 11 
 Frontal organ (see Paraphysis) 
 
 GARTNER, canals of, 189 
 
 Genital duct, 189 
 
 Gill clefts, 49 (see also Branchial 
 
 pouches) 
 
 Giralde. organ of, 189 
 Glabella coccygea, 5, 23, 28 
 Gland, coccygeal, 126 
 
 pineal (see Epiphysis cerebri) 
 
 pituitary (see Hypophysis cerebri) 
 
 thymus, 163 
 
 thyroid, 162 
 Glands, genital, 196 
 
 lachrymal, 149 
 
 mammary, 12 
 
 Montgomery's, 12 
 
 Glands, nictitating, 149 
 Glaser, fissure of, 65 
 Great toe, 85 
 Gubernaculum, 196, 197 
 Gynsekomasty, 17 
 
 HAIR, 3 
 
 tracts, 5 
 
 vortices, 5, 23 
 Hairs, tactile (see Vibrissse) 
 Hairy men, 9 
 Hallux (see Great toe) 
 Hand, skeleton of, 79, 86 
 Heart, 39, 180 
 Hind-limb, skeleton of, 80 
 Hip-girdle (see Pelvic girdle) 
 Hottentot apron, 195 
 Hunierus, 77 
 
 torsion of, 91 
 Hymen, 194 
 Hyoid arch, 65, 151 
 Hypertrichosis, 7, 10 
 Hypophysis cerebri, 135 
 
 ILIUM, 74, 76 
 Incus, 64, 151 
 Integument, 3 
 
 sense organs of, 140 
 Interclavicle, 46 
 Intestine, 166 
 Ischium, 71, 74 
 
 JACOBSON, organ of, 143 
 KIDNEY, definitive, 188 
 
 LABIA majora, 195 
 
 minora, 195 
 
 Lamina papyracea (see Os planum) 
 Lanugo, 9 
 Larynx, 172 
 
 musculature of, 174 
 
 skeleton of, 66, 151 
 Ligament, interclavicular, 48 
 Ligamentuin inguinale, 196, 199 
 Ligula, 137 
 
 Limbs, comparison of fore- and hind-, 
 91 
 
 displacement of, during develop- 
 ment, 92 
 
 disposition of, in adult, 9 1 
 
 disposition of, in foetus, 85 
 Limb girdles, 68
 
 INDEX 
 
 225 
 
 Limb skeleton, 67 
 genesis of, 68 
 Little toe, 89 
 Liver, 38, 171 
 Lobus olfactorius, 141 
 Lumbar curvature, 32 
 Lungs, 175 
 
 MALLEOLUS, fibular, 83 
 tibial, 83 
 
 Malleus, 64, 151 
 
 Mammary glands, development of, 13 
 supernumerary, 16 
 
 Mammary line, 14 
 pouch, 14 
 
 Meckel, cartilage of, 64, 151 
 
 Mesonephros, 187 
 
 Metanephros, 188 
 
 Monotremata, mammary organ of, 
 12, 14, 17, 198 
 
 Mouth, development of, 136 
 
 Muscle, adductor hallucis, 112 
 agitator caudse, 99 
 bi venter maxillae, 102 
 cleido-occipitalis, 102, 112 
 coccygeus, 98 
 cremaster, 198 
 curvator caudae, 27 
 curvator coccygis, 99 
 depressor caudse, 99 
 epicranius, 107 
 epitrochleo-ancona?us, 113 
 extensor brevis digitorum, 111 
 extensor carpi radialis, 119 
 flexor brevis minimi digiti, 112 
 flexor digit, communis, 110, 117 
 flexor digit, profundus, 110, 11 7, 119 
 flexor digit, superficialis, 110, 119 
 flexor longus hallucis, 117 
 flexor longus pollicis, 117 
 frontalis, 107 
 gastrocnemius, 120 
 gemellus superior, 119 
 gluteus maximus, 82, 99, 119 
 ischio-femoralis, 114 
 latissimo condyloideus, 112 
 latissimo dorsi, 38 
 levator claviculse, 114 
 levator palpebrae, 148 
 mylohyoid, 102 
 
 opponens hallucis (and o. pollicis), 
 88 
 
 Muscle, opponens minimi digiti, 112 
 
 orbitalis, 148 
 
 palmaris, 109, 110 
 
 panniculosis carnosus, 103, 113 
 
 pectoralis, 45, 113 
 
 plantaris, 109, 110 
 
 platysma, 103, 105 
 
 pyramidalis, 101 
 
 pyriformis, 119 
 
 rectus abdominis, 99 
 
 semimembranosus, 120 
 
 semitendinosus, 120 
 
 serratus magnus, 45 
 
 serratus posticus, 38 
 
 soleus, 120 
 
 sphincter colli, 106 
 
 sternaliSj 113 
 
 subcutaneus colli (see M. platysma) 
 
 transversus abdominis, 198 
 
 transversus nuchte, 105 
 
 triangularis sterni, 102 
 Muscles, caudal, 27, 98 
 
 cervical, 103, 113 
 
 cutaneous, 103 
 
 gluteal, 119 
 
 intercostal, 43, 99 
 
 interossei pedis, 111 
 
 laryngeal, 174 
 
 mimetic, 103, 109, 114 
 
 of head, 103, 107, 115 
 
 of limbs, 109, 116, 120 
 
 of pinna, 107, 154 
 
 progressive, 114, 121 
 
 retrogressive, 98, 121 
 
 scaleni, 102 
 
 serrati, 98 
 Muscular system, 97 
 Myelon (see Spinal cord) 
 
 NAILS, 11 
 
 Nerve, hypoglossus, 138 
 
 trigeminal, 139 
 
 vagus, 138 
 Nerves, caudal, 32 
 
 sympathetic, 139 
 Nervous system, 123 
 Nictitating membrane, 148 
 Nose, bridge of, 61 
 
 the projectile, 147 
 
 OBEX, 137 
 (Esophagus, 164
 
 226 
 
 THE STRUCTURE OF MAX 
 
 Olfactory organ, 141 
 
 Os acetabuli (see Bone, cotyloid) 
 
 antiepilepticum, 57 
 
 centrale carpi, 80 
 
 fronto-parietale, 57 
 
 planum, 60 
 
 prseinterparietale, 57, 60 
 Ossa suprasternalia, 48 
 
 suturaria (see Bones, Wormian) 
 Ossicula auditus, 64, 151 
 Ovary, 196 
 
 PALATE, hard, 63 
 Palate, ridges of soft, 155 
 Pancreas, 171 
 Papilla foliate, 162 
 
 palatina, 146, 156 
 Paradidymis, 189 
 Paraphysis, 134 
 
 Parietal organ (see Pineal organ) 
 Pectoral girdle, 68 
 Pelvic girdle, 68 
 
 development of, 74 
 
 shifting of, 31, 95 
 Pericardium, 38, 177 
 Pineal gland (see Epiphysis cerebri) 
 Pineal organ, 133 
 Pinna, 108 
 
 development of, 152 
 
 muscles of, 107, 154 
 Pituitary body (see Hypophysis cerebri) 
 Platyknemia, 82 
 Pleural cavities, 39 
 Plexus, brachial, 95 
 
 ischiadic, 95 
 
 lumbo-sacral, 95 
 
 pudendal, 95 
 
 vesico-prostatic, 182 
 Plica fimbriata, 161 
 
 semilunaris, 148 
 Polymasty, 17, 19 
 Polythely, 17 
 Ponticulus, 137 
 Post-anal gut, 32 
 Prseputiuin, 195 
 Process, coracoid, 72 
 
 paramastoid, 57 
 
 styloid, 63 
 Processus supra-con dyloideus, 78 
 
 vermiformis, 167 
 Promontory, of sacrum, 32, 34 
 Pronephros, 187 
 
 Pseudohypertrichosis, 9 
 
 Pubis, 71, 74 
 
 Pyramidal nerve tracts, 125 
 
 REDITUS TESTIUM, 198 
 Respiratory system, 171 
 Ribs, cervical, 41, 102 
 
 lumbar, 39 
 
 sacral, 40 
 
 sternal, 45, 46 
 
 supernumerary, 39, 44 
 
 thoracic, 39 
 Round ligament, 196 
 
 SACRAL DIMPLE (see Glabella coccygea) 
 Sacrum, 33, 40 
 Scapula, 71, 72 
 Scrotum, 198 
 Sense organs, 140 
 
 integurnental, 140 
 Shoulder girdle (see Pectoral girdle) 
 Sinus, Morgagni's, 174 
 
 venosus, 180 
 Skeleton, 26 
 Skull, 48 
 Spinal cord, 123 
 Spleen, 186 
 Stenson, canals of (see Canals, naso- 
 
 palatine) 
 Sternum, 44, 46 
 Stomach, 164 
 Sublingua, 161 
 Suprarenal bodies, 199 
 Sutures, cranial, 55 
 
 maxillo-palatine, 63 
 
 premaxillo-maxillary, 62 
 Sympathetic system, 139 
 
 TAIL, human, 5, 26, 31 
 Tarsus, 79 
 
 Teats, development of, 13 
 supernumerary, 18, 20 
 Teeth, genesis of, 156 
 milk, 160 
 pre-milk, 160 
 wisdom, 159 
 Tegumental organs, 3 
 ^Testis, 196 
 
 descent of, 196, 198 
 Third eyelid (see Nictitating mem- 
 brane) 
 I Thorax, types of, 36
 
 INDEX 
 
 227 
 
 Thyroid cartilage, 66, 151 
 
 gland, 162 
 Tibia, 82, 93 
 Tongue, 161 
 Torus occipitalis, 57 
 Trochanter, third, 82 
 Tympanic cavity, 150 
 
 URACHUS,' 181 
 Urinogenital system, 187 
 Uterus, 194 
 Uterus masculinus, 189 
 
 VAOIXA, 194, 195 
 Vas deferens, 188 
 Veins, intercostal, 186 
 
 posterior cardinal, 184 
 
 valves of, 185 
 Velum medullare, 137 
 Vena cava inferior, 1 84 
 
 Vena cava superior, 185 
 Venous system, 184 
 
 anterior abdominal, 182 
 Vertebra, caudal, 31 
 
 coccygeal, 27 
 
 thoracic, 43 
 
 sacral, 33 
 
 Vertebral column, 26 
 Vertex coccygeus, 5, 26 
 Vibrissaj, 4 
 
 supra-orbital, 150 
 Visceral skeletal arches, 49, 64, 
 
 151 
 Visual organ (see Eye) 
 
 WHISKERS (see Vibrissse) 
 
 XlPHISTERNUM, 45 
 
 YOLK SAC, 166 
 
 THE END 
 
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