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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 index1 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.
Viii 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-
scribed1 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.
I1 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 (esf. 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 together *>pre«mt 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-
, , , -, . ,, iT -.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 wTell- 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 ,, 0 , 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 farther2 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>> ecto-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 metatarsus2 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-'"}[\\ -f1-
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 cl., 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) ;
m»d., 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
cf 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. eP-f;bc-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 sePtlun
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 most 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
0 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 suggestion1 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 5—10 .....
From 10 — 20 . .
From 20 — 30
From 30—40
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 Felix1 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 reasons2 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 Echidna1 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 reproductive3
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
0 <
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 ; re1., 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.]
0
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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