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Published by 


DECEMBER 7, 1964 






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Photograph by Waldemar Meisler 


Chicago Zoological Park, September, 1952 



Curator, Division of Vertebrate Anatomy 



Published by 


DECEMBER 7, 1964 

"The field of macrotaxonomy ... is not directly accessible to the geneticist . . . 
Here the paleontologist, the comparative anatomist, and the embryologist 
are supreme." 

Richard Goldschmidt 

Edited by Lillian A. Ross 

Patricia M. Williams 
Edward G. Nash 

Publication costs defrayed in part by National Science Foundation 

Grant GN-116 

Library of Congress Catalog Card Number: 6i-8995 



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This study of the anatomy of the giant panda 
was originally intended to determine the taxo- 
nomic position of this species. As the dissection 
progressed, other questions of rather broader in- 
terest developed, and the scope was widened to 
embrace them. 

In studies of this kind the customary procedure 
is to compare structures with those of supposedly 
related organisms, and estimate relationships of 
organisms from these comparisons. In the back- 
ground are the broader questions of the phylogeny 
and fundamental uniformity of vertebrate struc- 
tures, which have long been the core problems of 
comparative anatomy. But superimposed on the 
underlying pattern of uniformity there is a be- 
wildering array of differences, mostly adaptations 
to special ways of life. Phylogeny continuity of 
ancestry explains the uniformities in vertebrate 
structure. It cannot explain the differences, which 
represent the active creative aspect of evolution. 
Yet we cannot pretend to explain the history of 
vertebrate structure without rational theories to 
account for the differences as well as the uni- 

The existence of an underlying uniformity in 
vertebrate structure is now so well documented 
that it is practically axiomatic, but comparative 
anatomists have scarcely begun to seek similarly 
adequate explanations for the differences in verte- 
brate structure. At this stage I believe it is of 
crucial importance to ask whether comparative 
anatomy can undertake to explain, in causal-ana- 
lytical terms, the structural differences that char- 
acterize taxa among vertebrates. If it cannot, then 
I would agree with the statement once made by 
D. M. S. Watson, that comparative anatomy is a 
term "now obsolescent." 

Such an extension of the goal of comparative 
anatomy assumes that the genetic backgrounds for 
the kind of morphological differences with which 
anatomists are concerned are so simple that they 
can be estimated with reasonable certainty by in- 
ferring causes from results, without resort to breed- 
ing experiments. For some of the primary differ- 
ences at the generic level this appears to be true. 
Evidence is steadily accumulating that, in verte- 

brates, a quite simple change in epigenetic mecha- 
isms may have a profound and extensively different 
end result. Moreover, the result is an integrated 
oi'ganism. This suggests that in favorable cases, 
and at low taxonomic levels, the comparative anat- 
omist may properly seek the mechanisms behind 
the differences he observes. 

In many ways the giant panda seems to be al- 
most ideally suited to a test of this thesis. I do 
not, of course, believe that I have explained com- 
pletely how the morphology of the giant panda 
arose from the morphology of the bears, or that 
everyone will accept my interpretations. I ask 
only that this study be regarded as a first approxi- 
mation, a first attempt to explain the structural 
differences between a derived and an ancestral 
organism in terms of causal mechanisms, an at- 
tempt to identify the raw materials on which 
natural selection acted. 

I am indebted to several institutions and in- 
numerable individuals for assistance in this study. 
On several occasions the United States National 
Museum allowed me to study skeletons housed 
there, and lent embalmed and osteological mate- 
rials for detailed study in Chicago. The American 
Museum of Natural History and Carnegie Mu- 
seum permitted me to study and measure skeletons 
in their collections. Much of the material on 
which the woi-k was based, including all the em- 
balmed giant panda material, originally came from 
the Chicago Zoological Park. Observations on liv- 
ing carnivores were made at both the Chicago Zoo- 
logical Park and the Lincoln Park Zoo. 

Over the years so many individuals have con- 
tributed to this study in various ways that it is 
impossible to thank them individually. I have 
profited particularly from numerous discussions 
with Dr. Harry Sicher, Dr. E. Lloyd DuBrul, Dr. 
Rainer Zangerl, Pi'ofessor Bryan Patterson, and 
Dr. Carl Cans. Dr. Zangerl made many X-ray pho- 
tographs for me. My late colleague. Dr. Karl P. 
Schmidt, repeatedly interrupted his own work to 
help me translate difficult German passages. 

In a work of this kind the artist tends to become 
almost a collaborator. I have been particularly 
fortunate in the several artists who worked with 


me from time to time: the late John C. Hansen, of the finer blood vessels and nerves in addition to 

who made most of the bone drawings; John J. making most of the drawings of the soft anatomy; 

Janacek; Miss H. E. Story, who dissected out most Miss Phyllis Wade; and Mrs. Edward Levin. 

D. D. D. 



List of Tables 9 

Introduction 11 

Goals and Methods of Comparative Anatomy 11 

Material and Methods 13 

History 14 

Distribution 17 

Habits and Behavior 20 

External Characters 28 

Description 28 

Measurements 31 

Growth 31 

Proportions 31 

Conclusions 40 

Skeleton 41 

The Skeleton as a Whole 42 

Measurements 44 

The Skull 46 

The Skull as a Whole 47 

Cranial Sutures and Bones of the Skull 62 

Hyoid 64 

Review of the Skull 65 

Summary of Skull 74 

The Vertebral Column 74 

The Vertebral Column as a Whole 74 

Descriptions of Vertebrae 78 

Review of the Vertebral Column 84 

Conclusions 85 

The Thorax 85 

Ribs 85 

Sternum 87 

Review of the Thorax 88 

The Fore Leg 88 

Bones of the Fore Leg 88 

Review of the Fore Leg 100 

The Hind Leg 102 

Bones of the Hind Leg 102 

Review of the Hind Leg 120 




Discussion of Osteological Characters 122 

Conclusions 124 

Dentition 125 

Description 125 

Discussion of Dentition 127 

Conclusions 130 

Articulations 131 

Articulations of the Head 131 

Articulations of the Fore Leg 132 

Articulations of the Hind Leg 140 

Review of Joints 145 

Muscular System 146 

Muscles of the Head 149 

Muscles of the Body 158 

Muscles of the Fore Leg 172 

Muscles of the Hind Leg 183 

Discussion of Muscular System 196 

Conclusions 198 

Alimentary System 199 

Mouth 199 

Salivary Glands 199 

Tongue 202 

Pharynx and Esophagus 204 

Stomach 207 

Intestines and Mesentery 208 

Liver and Gall Bladder 212 

Pancreas and Spleen 215 

Discussion of Digestive System 216 

Conclusions 218 

Urogenital System 219 

Urinary Organs 219 

Male Reproductive Organs 221 

Female Reproductive Organs 225 

Discussion of Reproductive Organs 225 

Conclusions 228 

Respiratory System 229 

Larynx 229 

Trachea 235 

Lungs 236 

Conclusions 237 

Circulatory System 238 

Heart 238 

Arteries 245 

Veins 280 



Ductless Glands 288 

Hypophysis 288 

Thyroid 288 

Parathyroid Bodies 288 

Thymus 288 

Nervous System 289 

Brain 289 

Discussion of Brain 297 

Cranial Nerves 298 

Cervical Plexus 305 

Nerves of the Fore Limb 306 

Thoracic Nerves 310 

Nerves of the Hind Limb 311 

Sympathetic System 315 

Special Sense Organs 317 

Eye 317 

Middle Ear 318 

Comparative Anatomy and evolution An Evaluation of the Test Problem 

The Relationships of Ailuropoda 322 

Morphogenetic Mechanisms in the Evolution of Ailuropoda 323 

Conclusions 326 

References 328 

Index 335 



1. Limb segment ratios in carnivores 35 

2. Limb proportions in carnivores 36 

3. Weight in grams of dry skeleton 42 

4. Weight ratios in dry postcranial skeleton 43 

5. Surface areas of limb bones 43 

6. Measurements of carnivore skeletons 45 

7. Cranial capacity of carnivores 46 

8. Skull proportions in generalized and specialized carnivores 66 

9. Vertebral counts in carnivores 75 

10. Relative proportions of divisions of the vertebral column in carnivores 75 

11. Measurements and indexes of pelvis in carnivores 103 

12. Relative mass of masticatory musculature 154 



13. Relative weights of masticatory muscles in carnivores 155 

14. Relative weights of muscles of the shoulder and arm in carnivores 183 

15. Relative weights of muscles of the hip and thigh in carnivores 195 

16. Myological characters in arctoid carnivores 197 

17. Intestinal length in arctoid carnivores 210 

18. Liver weight in mammals 214 

19. Percentage differences from control animals in gut measurements of pigs raised on herbivorous 

and carnivorous diets 217 

20. Number of renculi composing kidney in bears 220 

21. Dimensions and proportions of kidneys in arctoid carnivores 220 

22. Kidney weights in mammals 221 

23. Heart structure in arctoid carnivores 243 

24. Branches of aortic arch in arctoid carnivores 277 

25. Composition of lumbosacral plexus in carnivores 315 


It is my intent to make this study a test, based 
on the anatomy of the giant panda, of whether the 
comparative method can yield information that 
goes beyond the customary goals of comparative 
anatomy. It is evident, to me at least, that more 
than fifty years ago comparative anatomy reached 
a stalemate that can be broken only by seeking 
answers to new and different questions. I believe 
it must shift its major emphasis from the conserva- 
tive features of evolution to its radical features, 
from the features that organisms under compari- 
son have in common to those they do not have in 
common. It must seek rational explanations for 
these differences, drawing on data from other fields 
where this is necessary and possible. In this study 
of the giant panda the structural differences be- 
tween it and the bears, and the ways in which these 
differences arose, will be our primary concern. 

The original problem that motivated the work 
the proper taxonomic position of Ailuropoda was 
soon settled; Ailuropoda is a bear and therefore 
belongs in the family Ursidae.' The further prob- 
lem of attempting to infer the causal mechanisms 
involved in the origin of Ailuropoda from its ursid 
ancestors requires some discussion of goals and 


The classical goal of comparative anatomy was 
to demonstrate the existence of an essential and 
permeating uniformity or "ordering" in the struc- 
ture of vertebrates. This goal has been reached. 
Details of the picture remain to be filled in, but 
the unifying concept itself is now so well docu- 
mented that it is no longer open to serious debate. 
Phylogeny, the genetic relatedness of all verte- 
brates, provides an explanation for the uniformity. 
This aspect of the history of vertebrate structure 
cannot be expected to give rise to further concepts. 

> This conclusion is not based on one or a few characters, 
but on a host of similarities, many of them subtle, through- 
out the anatomy. I tried to present the data on the affinities 
of Ailuropoda before going on to other considerations, but 
this became so difficult that I gave it up. Therefore one of 
the primary conclusions is assumed throughout the text. 

We may well ask where comparative anatomy is to 
go from here. 

From the evolutionary standpoint the structural 
differences among vertebrates are just as impor- 
tant as the structural uniformities; these two are, 
in fact, the obverse and reverse of the phylogenetic 
picture of vertebrate structure. Years ago W. K. 
Gregory distinguished them as "habitus" and "her- 
itage" characters. We cannot claim to have ex- 
plained the particular structure of an organism if 
we explain only its heritage characters and offer no 
explanation for its habitus characters. An "expla- 
nation" must account for the differences in terms of 
evolutionary mechanisms, not merely relate them 
to the functional requirements of the organism 
in other words, explain them in the same causal 
sense that common ancestry explains the heritage 

Classical comparative anatomy tended to con- 
centrate on the major features of vertebrate struc- 
ture the differences that characterize orders and 
moi-e often classes. Such, for example, are the 
homologies of the gill arch derivatives, of the ele- 
ments of the mammalian middle ear, of the cranio- 
mandibular muscles. There was practically no in- 
terest in how and why such changes came about, 
and the morphogenetic and selective mechanisms 
involved in these massive alterations are prob- 
ably irretrievably lost in the vast reaches of time 

Structural differences at about the generic level 
are usually far less profound and more recently 
evolved, yet they often represent a level of mor- 
phological differentiation to which the methods of 
comparative anatomy can be applied. In this re- 
spect they differ from the characters with which 
the geneticist customarily deals. At about the 
generic level we may hope to decipher the mech- 
anisms responsible for the observed differences in 
structure between two or more related forms. A 
procedure designed to yield such information is 
followed in this study. The procedure may be 
divided into a series of steps. These are: 

(1) Identification of the structural differences 
between Ailuropoda and its structural ancestor, 
Ursus. At the outset nothing was known of pos- 




sible pleiotropic effects, allometric relationships, 
morphogenetic patterns, or obscure functional re- 
lationships. Therefore all differences were tabu- 
lated uncritically, without attempting to evaluate 
them. For the same reason the entire anatomy 
of the organism was covered so far as practicable. 

(2) Correlation of the observed structural differ- 
ences between Ailuropoda and Ursus with dif- 
ferences in habits or behavior. This is the first 
step in sorting out the adaptive features peculiar 
to the anatomy of Ailuropoda features that pre- 
sumably represent the modifications of the ursid 
morphology resulting from natural selection. This 
step results in two categories: (a) those differences 
that can be correlated with differences in habits or 
behavior, and (6) those that can not. 

The differences in category b may be conspicu- 
ous, and their presence must be accounted for. 
They may be genetically related to an adaptive 
modification but not themselves adaptive. They 
may reflect the results of an inherited differential 
growth rate, whereby the proportions of a mor- 
phological unit may change with the absolute size 
of the unit. A classical example of this effect is 
the antlers of deer. They may merely reflect re- 
laxed selection pressure on certain functions. The 
decision as to whether a condition is or is not adap- 
tive is often very difficult, requiring considerable 
knowledge of mechanics and engineering, as well 
as intimate knowledge of the habits and behavior 
of the animal. 

(3) Separation of the adaptive features that are 
genetically determined from those that are only 
indirectly related to the genetic substrate. Many 
conspicuous features in the skeleton depend only 
on the capacity of bone to respond to extrinsic 
forces. Many soft tissues have a considerable ca- 
pacity to accommodate their form to the molding 
action of extrinsic forces. The caliber of blood 
vessels varies with the demands of the tissues they 
supply, even during the life of the individual; if 
one kidney is removed, the remaining one hyper- 
trophies. Such conditions are adaptive, but they 
are not primary results of selection; they are the ex- 
ogenous adaptations of Waddington (1953). They 
reflect the action of natural selection at second or 
third hand, so to speak. If we are seeking to iso- 
late the structural features on which natural selec- 
tion acted directly, these secondary and tertiary 
effects must be discounted. 

These three steps have presumably isolated the 
morphological features in Ailuropoda that (1) dif- 
fer from those in its structural ancestor, Ursus, 
(2) are functionally correlated with differences in 
habits and behavior, and (3) are genetically deter- 
mined. They are the direct results of natural se- 

lection in the step from bear to giant panda. As 
will appear in the sequel, these features seem to be 
surprisingly few; we are not interested here in 
minor polishing effects, but only in decisive dif- 
ferences. We do not yet know the materials on 
which natural selection acted to effect these 
changes. One final step remains: 

(4) Determination of the morphogenetic mech- 
anisms that were involved in effecting these 
changes. This should be an experimental prob- 
lem, but obviously experimentation is impossible 
in the vast majority of cases, including this one. 
Fotunately, morphogenetic processes appear to be 
remarkably uniform among mammals. By a judi- 
cious combination of the comparative method with 
the known data of mammalian epigenetics I be- 
lieve it is possible to infer, with varying degrees of 
confidence, the true mechanisms behind many of 
the major structural differences that distinguish 
Ailuropoda from the true bears. Many of the 
"unit characters" involved appear to be sizable 
morphological units, although it does not neces- 
sarily follow that the shift from bear condition to 
panda condition was made in one jump, or that 
such morphological units are controlled by simple 
genes. It is clear, however, that they are geneti- 
cally controlled as units. It would be futile to at- 
tempt to reconstruct the history if major adaptive 
differences represent accumulations of numerous 
small mutation effects. 

To the extent that these four steps are carried 
out successfully, the differences between the giant 
panda and the true bears will be explained rather 
than simply described. 

Almost without exception, students of the higher 
taxonomic categories have been reluctant to believe 
that the kinds of morphological differences they 
observe represent accumulations of small muta- 
tion effects such as the geneticist customarily deals 
with. The once-popular solution invoking un- 
known imminent forces to explain systemic differ- 
ences is no longer common. Modern students 
have sought genetic mechanisms capable of pro- 
ducing phenotypic differences of the magnitude 
they believed were involved. Goldschmidt (1940), 
for example, emphasized (among other things) the 
massive co-ordinated differences that can result 
from acceleration and retardation of gene-con- 
trolled developmental processes. Rensch (1960) 
listed pleiotropy, allometric growth rates, and 
compensatory correlations among the agents ac- 
cessible to natural selection as capable of pro- 
ducing extensive generalized effects on the organism 
as a whole. 

It is now generally recognized that gi'owth is es- 
sentially a process of multiplication of cells. Multi- 



plicative rates differ in different parts of the body, 
and in the same part at different times during its 
growth period. Regional growth rates may inter- 
fere with each other, resulting in negative interac- 
tions and in extreme cases even in deformation of 
the entire growth profile of the body. Correlation 
studies show clearly that both regional and gen- 
eral growth rates are genetically controlled as units. 
These insights stem chiefly from Huxley's Prob- 
lems of relative growth, which in turn grew out of 
the earlier On growth and form of D'Arcy Thomp- 
son and Goldschmidt's Physiologische Theorie der 
Vererbung. They provide a mechanism capable of 
producing plastic deformation of a common pat- 
tern, which is what the comparative anatomist 
seems to see when he compares homeomorphic or- 
ganisms. A bridge between genetics and compara- 
tive anatomy was sought in vain during the first 
third of this century; it now seems to have been 

Partly because evolution is a cumulative and 
non-repetitive process, and partly because growth 
fields in vertebrates have proved refractory to ex- 
perimental techniques, their role in the morphosis 
of animal form has been deciphered almost exclu- 
sively by morphological methods. The primary 
tool is demonstration of correlations; the method 
is comparative. Whether subtle correlations are 
sought by sophisticated statistical methods (as in 
recent studies of mammalian teeth) , or more obvi- 
ous correlations by means of coarser but no less 
rigorous comparative methods (as in the present 
study), the goal is the same. It is to identify and 
circumscribe the material bases for differences 
among homeomorphic organisms. This is a proper 
field for the comparative anatomist. 


This study is based largely on the embalmed 
and injected body of a giant panda that lived in 
the Chicago Zoological Park from February, 1937, 
to April, 1938. The panda was popularly known 
as Su Lin. Unless otherwise stated, all statements 
relating to the soft anatomy are based on this 
specimen. Su Lin was a subadult male (teeth fully 
erupted). His age (estimated) was 16 months at 
death. He was in excellent condition and weighed 
132 pounds. Preserved portions of the carcass 
(head, fore and hind limbs, heart, genitalia) and 
the skeleton of an adult male giant panda (known 

as Mei Lan) were available. Mei Lan was esti- 
mated to be 15 years old at death. He was much 
emaciated, and weighed 205 pounds after autopsy. 

The following skeletal material of Ailuropoda 

was available for detailed study: 

CNHM 31128 id' ad.) Szechwan: Yehli. Complete skel- 

CNHM 36758 ( 9 ad.) Szechwan: Dun Shih Goh. Com- 
plete skeleton. 

CNHM 34258 (- ad.) Szechwan: Mouping Dist. Skull, 
lower fore legs, fore and hind feet. 

CNHM 74269 ( (f ad.) (zoo animal: Mei Lan). Complete 

CNHM 39514 (- ad.) Szechwan: Dun Shih Goh. Skull. 

USNM 259076 ( 9 jv.) Szechwan: Wen Chuan. Skull. 

USNM 259027 ( c? ad.) Szechwan: Wen Chuan. Pelvis. 

USNM 259403 ( 9 ad.) Szechwan: Wen Chuan. Pelvis. 

Most of the data on the soft anatomy of bears 
came from the following captive animals that died 
in the Chicago Zoological Park: 

CNHM 48304 (d" ad.) Ursus thibetanus, embalmed and 
injected body. 

CNHM 49061 ( & juv.) Ursus americanus, embalmed and 
injected body. 

CNHM 57267 ( 9 ad.) Ursus americanus, embalmed head, 
fore leg, and hind leg. 

CNHM 57200 ( 9 ad.) Tremarctos ornatus, embalmed head, 
fore leg, and hind leg. 

The following bear skeletons were used for most 
of the detailed osteological data: 
CNHM 43744 (- ad.) Ursus ardos; Iraq. 
CNHM 47419 (- ad.) Ursus arctos; Iraq. 
CNHM 44725 (cf ad.) Ursus americanus; (zoo animal). 

These three skeletons were supplemented with 
numerous skeletons and partial skeletons of bears, 
representing several genera and species, in the col- 
lections of Chicago Natural History Museum. 

Partial dissections were made of several procyo- 
nids, all embalmed zoo animals, representing the 
genera Procyon, Nasua, Bassariscus, Potos, and 
Ailurus. Numerous skeletons of these genera, from 
both wild-killed and zoo animals, were available. 

Linear measurements up to 150 millimeters were 
made with Vernier calipers graduated to 0.1 milli- 
meter. Lengths beyond 150 millimeters were meas- 
ured with large calipers and a meter stick. Weights 
up to 2 kilograms were determined with a small 
Ohaus triple beam balance. Larger objects were 
weighed on a large Ohaus beam balance with a 
capacity of 21 kilograms. In weighing preserved 
soft tissues the usual precautions of removing ex- 
cess surface liquid by blotting were taken. 


The synonymy of Ailuropoda melanoleuca may 
be summarized as follows : 

Ailuropoda melanoleuca (David) 

Ursus melanoleuciis David, 1869, Nouv. Arch. Mus. Hist. 

Nat., Paris, Bull. 5, p. 13. 
Ailuropoda melanoleuca Milne-Edwards, 1870, .\nn. Sci. 

Nat., Paris, (5), Zool., 13, art. 10. 
Pandarctos melanoleucus Gervais, 1870, Nouv. Arch. Mus. 

Hist. Nat., Paris, 5, p. 161, footnote; 1875, Jour. 

Zool., Paris, 6, p. 87. 
Ailuropus melanoleucus Milne-Edwards, 1871, Nouv. 

Arch. Mus. Hist. Nat., Paris, Bull. 7, p. 92. 
Aeluropus melanoleucus Lydekker, 1891, in Flower and 

Lydekker, Mammals living and extinct, pp. 560-561, 

fig. 256. 

During his stay in Mouping on the second of his 
three expeditions to China, the noted French ex- 
plorer and naturalist Pere Armand David learned 
of the existence of a curious black and white "bear." 
This animal, called pei-hsuing ("white bear") by 
the natives, aroused David's interest, and he em- 
ployed hunters to capture specimens of it for him. 
After almost a month of unsuccessful hunting a 
young female was brought to him on March 19, 
1869, and two weeks later he acquired an adult of 
the same sex. Although erroneously believing it 
to be a bear, David immediately recognized the 
animal as a novelty to science. He drew up a con- 
cise but adequate description under the name Ur- 
sus melanoleucus and despatched it to Alphonse 
Milne-Edwards at the Paris Museum with an ex- 
planatory note requesting its publication. David's 
letter, which was duly published in the Nouvelles 
Archives of the Paris Museum, introduced to sci- 
ence the animal now known as the giant panda. 
The subsequent history of the giant panda can best 
be presented in chronological form. 

1870. Milne-Edwards, after e.xamining David's 
material, noted that its osteological characters and 
dentition "clearly distinguish" the giant panda 
from the bears and approach those of the lesser 
panda and raccoons. He erected the genus Ailuro- 
poda to receive it. Gervais, on the other hand, 
concluded from a study of an intracranial cast that 
its brain structure allies it to the bears. Gervais 
considered it worthy of generic distinction, how- 
ever, and proposed the name Pandarctos. 

1871. David published a few brief notes on 
the habits of the giant panda, and even today sur- 
prisingly little can be added to these original ob- 
servations. David recorded that it is restricted to 
high altitudes, that it is herbivorous, and that it 
does not hibernate. Only one of his statements 
has not been substantiated : "It is said that it does 
not refuse meat when the occasion presents itself; 
and I even think that this is its principal nourish- 
ment in winter." 

Milne-Edwards, believing that the generic name 
Ailuropoda was preoccupied by Gray's use of the 
name Aeluropoda for his "Section I. Cat-footed 
Carnivora" in the Catalogue of Carnivorous, Pachy- 
dermatous and Edentate Mammalia in the British 
Museum (1869, p. 3), proposed the name Ailuropus 
for the giant panda. 

1868-74. Milne-Edwards, in the Recherches des 
Mammiferes, gave a detailed description of the 
skin, skull, and dentition. His re-examination led 
him to the conclusion that Ailuropus should be 
placed between the bears and the [lesser] panda. 

1875. Gervais, after an examination of the 
skeleton of David's panda, reasserted his former 
opinion that the giant panda is an aberrant bear. 

1885. Mivart, in his careful review of the clas- 
sification of the arctoid carnivores, concluded that 
Ailurus is a procyonid and that Ailuropus is allied 
to Ailurus and therefore is a procyonid, too. Mi- 
vart thus set the pattern that, with few exceptions, 
has been followed by British and American auth- 
ors to the present day. His conclusion is based on 
the usual agreement of skull architecture and den- 
tal morphology that was to be stressed repeatedly 
by later authors. 

1891. Flower and Lydekker, in their Mammals 
Living and Extinct, placed "Aeluropus" in the Ur- 
sidae and "Aelurus" in the Procyonidae. Their 
emendation of Milne-Edwards' generic name Ailu- 
ropus, appearing in an authoritative work, resulted 
in considerable confusion in subsequent literature. 

1895. Winge regarded the giant panda as a 
very close relative of the extinct Hyaenarctos 
[- Agriotherium of recent authors], these two gen- 
era forming a separate branch of the ursine stem. 




Ailurus, on the other hand, he considered a pro- 
cyonid. Winge's views have been adhered to with- 
out exception by continental European authors. 

1901. Both Lankester and Lydekker, after in- 
. / dependently studying the skull and limb bones, 

concluded that Aeluropus and Aeliirus are closely 
allied, that they are procyonids, and that the Pro- 
cyonidae should be subdivided into two subfam- 
ilies, the Procyoninae and the Ailurinae. ' This, 
of course, is merely a re-affirmation of the earlier 
views of Mivart. They emphasized the procyno- 
nid-like presence of both protocone and hypocone 
on the lingual border of P^ (the protocone is absent 
in the Ursidae), the presence of an entepicondylar 
foramen, and numerous "minute coincidences" in 
the structure of the skull and long bones of the 

Lankester and Lydekker deemed it desirable 
that Aeluropus, which hitherto had been called the 
"parti-coloured bear," should henceforth be called 
the "great panda." This appears to be the first 
published reference to Ailuropoda as a panda.' 

1902. Beddard, in his Mammalia, followed 
Flower and Lydekker in placing "Aeluropus" in 
the Ursidae and "Aelurus" in the Procyonidae. 

1904. Weber, in the first edition of Die Sduge- 
tiere, followed Winge in considering Aeluropus as 
an ursid closely related to Hyaenarctos and refer- 
ring Ailurus to the Procyonidae. 

1913. Bardenfleth made a detailed study of 
the dental and osteological characters of Ailuro- 
poda and concluded that its resemblances to Ailu- 
rus are due to convergent development of the 
molar teeth based on herbivorous diet, and that its 
closest affinities are with the extinct ursids of the 
Hyaenarctos group. 

1915. Woodward described the well-preserved 
skull of a Pleistocene giant panda, which he named 
Aelureidopus baconi, from Burma. This was the 
first proof that the giant panda once had a more 
extensive range than it has at present. 

1921. Pocock, in a review of the classification 
of the Procyonidae, concluded that both Ailuro- 
poda and Ailurus represent distinct and separate 
families. This view he re-affirmed in 1929 and also 
in his article "Carnivores" in the fourteenth edi- 
tion of the Encyclopaedia Britannica, where no 
fewer than 13 families (compared with 7 of other 
authors) and 29 subfamilies (18 of other authors) 
of living fissiped carnivores are recognized. Po- 
cock's "families" correspond roughly to the gen- 
era of other authors. 

' The word "panda," which had been applied to the lesser 
panda (Ailurus) since the time of Cuvier, is "said to be a 
Nepal name." (Oxford Universal English Dictionary.) 

1923. Matthew and Granger described giant 
panda material, under the name Aeluropus fove- 
alis, from Pliocene deposits in eastern Szechwan, 
thus farther extending the former range of the 
giant panda. 

1928. Weber, in the second edition of Die Sdu- 
getiere, retained his views of 1904 as to the ursid 
affinities of Ailuropoda. 

1929. Theodore and Kermit Roosevelt shot a 
giant panda at Yehli, Sikang Province. This in- 
dividual, said to be the first giant panda shot by 
a white man, was mounted, together with a sec- 
ond skin purchased from natives, in a habitat 
group in Chicago Natural History Museum. The 
ensuing publicity started a cycle of "giant panda 
expeditions" that have gi'eatly increased our knowl- 
edge of the distribution, habits, and morphology 
of this animal. 

1936. Gregory examined the skull and denti- 
tion of Ailuropoda, Ailurus, and various fossil and 
recent procyonid and ursid carnivores. He con- 
cluded that Lankester and Lydekker were correct 
in referring Ailuropoda and Ailurus to the Procy- 

Raven, in the same year, studied the viscera of 
a giant panda, which had been preserved in the 
field by an American Museum expedition. He 
listed six points of agreement between Ailuropoda 
and Ailurus, and concluded that resemblances be- 
tween the former and the bears "are an expression 
of convergence in size and food habits." 

1937. Mrs. Ruth Harkness, of New York City, 
succeeded in bringing a living baby giant panda to 
the United States. This individual, named Su Lin, 
lived for 16 months in the Chicago Zoological Park. 
It formed the basis for the present monograph. 
The fanfare that surrounded the life and death 
of Su Lin started a new series of expeditions for 
living pandas. At least a dozen have since been 
exhibited in the United States and Europe. 

1943. Segall made a study of the auditory re- 
gion in the arctoid carnivores. The structure of 
the bony auditory region and auditory ossicles led 
him to associate the Ailuridae (Ailurus and Ailuro- 
poda) with the Ursidae. 

1945. Simpson, in his Classification of Mam- 
mals, adhered to the classical view of Mivart in 
grouping Ailurus and Ailuropoda in the subfamily 
Ailurinae of the family Procyonidae. 

1946. Mettler and Goss, after studying the 
topography of the brain of an adult giant panda, 
concluded that "the configuration of the brain of 
Ailuropoda melanoleuca is identical with that of 
the bear." 

1956. Leone and Wiens reported that compari- 
sons of serum proteins by means of precipitin tests 




"clearly indicate that the giant panda belongs in 
the family Ursidae." 

An examination of this history of research is 
instructive. There can be no doubt that the giant 
panda occupies a more or less isolated position 
among living carnivores, and that the features usu- 
ally relied upon by mammalogists for determining 
affinities are masked by si>ecializing adaptations 
in this form. Two conclusions may be drawn from 
these historical data. 

1. Quite different conclusions have been 
reached by a succession of capable investigators 
on the basis of the same data. This indicates that 
the data employed are not sufficient to form a basis 
for an objective conclusion, and that opinion has 
been an important ingredient in arriving at con- 

2. Opinion as to the affinities of Ailuropoda is 
divided almost perfectly along geographic lines, 
which shows that authoritarianism i-ather than ob- 
jective analysis has really been the determining 

factor in deciding the question. After the pioneer- 
ing work of Milne-Edwards and Gervais, the first 
attempt at determining the affinities of Ailuropoda 
was made by Mivart in England. Mivart's con- 
clusion that both the giant and the lesser panda 
are procyonids has been echoed by every British 
and American author down to 1943, except for the 
short-lived dissenting opinion of Flower and Ly- 
dekker.' In the meantime, on the continent, 
Winge in 1895 relegated Ailuropoda to the Ursi- 
dae and Ailurus to the Procyonidae, and every 
subsequent continental authority has followed in 
his footsteps. Such a cleavage of opinion along 
geogi^aphical and linguistic lines cannot be due to 

It is apparent that the relationships of Ailuro- 
poda will never be decided on the basis of the data 
afforded by the skeleton and dentition. Thus the 
fii-st task of this study was to examine data not 
previously available, with a view to determining 
the much-discussed affinities of this carnivore. 

> Beddard (1902) merely copied Flower and Lydekker. 


The giant panda apparently has a very re- 
stricted distribution in the high mountains of 
western Szechwan and eastern Sikang in western 
China. This is the area of the extremely complex 
mountain escarpment that sharply separates the 
Min River Valley from the Tibetan highland to 
the west. 

Localities where or near which specimens have 
been collected are shown on the accompanying 
map (fig. 1). The localities given on many mu- 
seum specimens obviously represent the city where 
the skin was purchased (e.g., Mouping, Ya-chou) 
rather than the locality from which the specimen 
actually came. Localities given in the literature 
("Moupin," David, 1869; "mountains of Mou- 
ping," Gervais, 1875; "Wassu mountains," "moun- 
tains east of Min valley," Jacobi, 1923a) are often 
very indefinite. Thus the localities that can be 
plotted with any certainty on a map are relatively 
few, although none of the unplottable localities ex- 
tends the known range of this species. The dis- 
tance between the southernmost record (Yehli) 
and the northernmost (25 miles west of Wen- 
chuan) is only about 175 miles. All records, ex- 
cept Yehli are on the slopes of the Chuing-lai 
mountains surrounding the valley of the Min 
River. Yehli, where the Roosevelt brothers shot 
their panda, is on the slopes of the Ta-liang Moun- 
tains south of the Tung River. 

Pen (1943) reported Ailuropoda horn "the up- 
per source of the Yellow [Yangtze] River where it 
connects the two lakes, the Tsaring Nor and the 
Oring Nor, near the central part of Chinghai prov- 
ince" at 34 7' N. Lat. Pen refers, without cita- 
tion, to a record by Berozovski at 34 N. Lat., but 
I have been unable to find such a reference. Pen 
collected no specimens, but there seems to be no 
reason for doubting his identification of the ani- 
mals he saw. Even allowing this provisional ex- 
tension of range, the north-south distribution 
amounts to only about 470 miles. 

Sowerby (1932) has suggested even greater ex- 
tensions of the range of Ailuropoda. He writes: 
"The range of the giant panda is now admitted to 
be much more extensive than formerly supposed. 
. . . We came across indisputable evidence of the 

giant panda in the Tai-pei Shan region of South- 
western Shensi, where the local takin hunters de- 
scribed its appearance to us accurately and also 
showed us its droppings and the places where it 
had torn up the culms of bamboos for food. From 
this region it ranges southward throughout all the 
wilder mountainous areas at least to the Yunnan 
border, eveiywhere being known to the native 
hunters by its native name, pei-hsiung." Sowerby 
(1937a) later defined the range as "more or less 
restricted localities from the Tsing Ling range of 
mountains in southern Shensi and eastern Tibet 
to northern Yunnan." Others have emphasized 
the unreliability of reports by native hunters, how- 
ever, even after being shown pictures of the ani- 
mal, and it seems best to await more positive 
evidence before accepting Sowerby's broad exten- 
sions of range. 

Ailuropoda had a much more extensive distri- 
bution in comparatively recent geological times, 
as is shown by the two fossil records. Smith- 
Woodward (1915) described a Pleistocene panda 
under the name Aelureidopus baconi, from Mogok, 
Northern Shan States, Burma. This is in the Irra- 
waddy River drainage and is more than 500 miles 
southwest of the southern limit of the panda's 
range as now known. Granger (in Matthew and 
Granger, 1923) found giant panda material, which 
was named Aeluropus fovealis, in Pliocene deposits 
near Wan-hsien in eastern Szechwan. Wan-hsien 
is situated on the Yangtze River (of which the 
Min is a tributary), about 250 miles due east of 

Vertical Distribution 

The vertical distribution of Ailuropoda is as 
limited as its geographic distribution. All who 
have studied its habits agree that this animal is 
sharply limited to the bamboo zone, which lies 
between about 5,000 and 10,000 feet. 

Limited to the Si-fan region at altitudes of 1600 to 3300 m., 
consequently to the region of almost impenetrable bamboo 
jungle on the steep slopes. Here it forces tunnels through 
the thickets, which are IJ-^ to 5 m. high and are often 
matted by snow pressure. (Jacobi, 1923b, p. 72.) 

... in the bamboo jungles in altitudes varying between 
six and fourteen thousand feet. We came to the conclusion 
that it could safely be assumed that where there were no 


Fig. 1. Western Szechwan and eastern Sikang provinces, showing locality records for Ailuropoda melanoleuca. 




bamboo jungles, there were no beishung. (Theodore and 
Kermit Roosevelt, 1929, p. 261.) 

The limits of the giant panda's altitudinal range is deter- 
mined largely by the extent of the bamboo growth. Two 
exceptions to this statement were observed, however. In 
one case we found unmistakable panda droppings high on 
the Chen Lliang Shan range, 1000 feet above the rhododen- 
dron forest, and probably 1500 feet above the nearest bam- 
boo. It was interesting to find that on occasion the panda 
must travel above its regular habitat to the bare grasslands 
of the blue sheep country. In another instance I saw where 
a giant panda had climbed a small pine tree just above the 
village of Tsapei on Chengou River. It was located 300 feet 
above the river bottom on an open slope, with the nearest 
bamboo across the valley. (Sheldon, 1937.) 

The vertical distribution of the bamboo bear, which avoids 
the hot arid canyons as well as the high alpine zones, extends 
on the high levels between 1500 and about 4000 m., where it 
is closely confined to the moist, subtropical bamboo zone. 
(Schiifer, 1938.) 

Pen's sight record of a giant panda at the upper 
source of the Yangtze River was on the open steppe 
of the Tibetan plateau. He speculates that these 
animals may have reached the plateau country by 
migrating north and west along the bamboo zone 
of the mountains, and that there is here an annual 
summer migration onto the plateau, with a winter 
retreat into the less rigorous environment of the 


Because of the inaccessible and rugged nature 
of its habitat, there has been httle field observation 
of the giant panda. Various authors have re- 
corded information, beginning with the original 
notes of David, and the observations are in close 
agreement. Details of behavior are known only 
from observations on captive individuals (Schnei- 
der, 1939; Haas, 1963). 


The giant panda appears to be closely confined 
to the moist bamboo zone on the slope of the high 
mountains. The bamboo culms, which are slender 
(up to an inch and a half in diameter) and grow 
to a height of 10 to 12 feet, form dense impene- 
trable thickets that are often matted by snow pres- 
sure. The bamboo jungle is associated with forests 
of fir trees, and at higher altitudes the bamboo 
gives way to rhododendron, into which the panda 
does not wander. The mountain slopes "under 
the influence of the summer-like monsoon rains, 
exhibit a comparatively mild subtropical climate." 
(Schafer, 1938.) 

The panda shares this habitat with such other 
large mammals as the golden monkey (Rhinopithe- 
cus), leopard (Panthera pardus), red dog {Cuon al- 
pinus), black bear (Ursus thibetanus), wild pig 
(Sus cristatus), barking deer (Muntiacus), serow 
(Capricornis), and takin {Budorcas). Only the 
leopard and the red dog would be likely to attack 
the giant panda, and such encounters would be 
uncommon.' Thus the giant panda is practically 
without natural enemies an important point in 
estimating the selection pressures to which this 
species is subjected. 

Wilson (1913) described the vegetation on the 
mountain Wa Shan as follows: 

At one time a dense forest of Silver Fir covered the moun- 
tain. . . . Some of these Firs could not have been less than 
150 feet in height and 20 feet in girth. . . . Besides the Silver 
Fir (Abies Delayayi), the only other conifers are Tsuga yun- 
nanensis, Juniperus formosana, and Picea complanata. Rho- 
dodendrons constitute the conspicuous feature of the vege- 

' Seton (Lives of game animals, 2, 1929) lists the grizzly 
bear and the mountain lion as enemies of the American black 
bear, an animal about the same size as the giant panda. 

tation. . . . They begin at 7500 feet, but are most abundant 
at 10,000 feet and upwards. In the ascent I collected 16 
species. They vary from diminutive plants 4 to 6 inches 
high, to giants 30 feet or more tall. . . . One of the common- 
est species is R. yanthinum. . . . Above this [7200 feet], for 
500 feet, comes a wellnigh impenetrable thicket of Bamboo 
scrub. The species (Arundiruiria nilida) is of remarkably 
dense growth, with thin culms, averaging 6 feet in height. 
Next above this, till the plateau is reached, is a belt of mixed 
shrubs and herbs, conspicuous amongst which are Syringa 
Sargentiana, Hydrangea anomala, H. villosa, Neillia affinis, 
Dipelta ventricosa, Ribes longeracemosum, var. Davidii, Enki- 
anthus deflexus, Styrax roseus, Deutzia (2 spp.), Rubus (5 spp.), 
Viburnum (4 spp.), Spirea (4 spp.), Acer spp., Malus spp., 
Sorbus spp., Meconopsis chelidonifolia, Fragaria filipendulus, 
Lilium giganteum, and the herbs of the lower belt. A few 
Rhododendrons occur chiefly on the cliffs. The plateau 
(8500 feet) is about half a mile across, marshy in places, 
and densely clad with shrubby vegetation and Bamboo 
scrub. . . . From 10,000 feet to the summit of the mountain 
Rhododendron accounts for fully 99 per cent of the ligneous 


All observers (except Pen, see below) agree that 
in its native state the giant panda subsists exclu- 
sively on bamboo. McClure (1943) identified the 
bamboo native to the haunts of the giant panda 
as Sinariindinaria sp. 

"Its food seems to consist exclusively of bamboo shoots, 
but by no means merely the young shoots, which even man 
himself eats with relish, but also those as thick as a finger. 
In winter, in fact, only strongly woody and silicified stalks 
are available. All this can be ascertained from fresh drop- 
pings, which consist almost exclusively of chewed-up stalks, 
often as long as a finger joint, whether in the middle of July 
or in the beginning of January." (Jacobi, 1923a.) 

Not only is the giant panda entirely herbivorous, but it 
is known to live on the dwarf bamboo of the northeastern 
spur of the Himalayas to the exclusion of all other vegetable 
matter. . . . The food supply in the mountains of west 
Szechuan is inexhaustible. . . . We found giant panda eating 
not only the bamboo shoots, but the stalks and leaves of 
fully mature sprouts, often an inch and one-half in diam- 
eter." The author followed a fresh morning trail and found 
"that at an average of every hundred yards there were from 
one to three large droppings (4 to 6 inches long and 2 inches 
thick, tapering at each end). At a conservative estimate 
there were 40 droppings. . . . Below the resting place was a 
pile of at least 30 more droppings, making a total of 70 ex- 
creted between early morning and 9 a.m These droppings 




Fig. 2. Sitting posture and use of fore paws in Ailuropoda. A-C, "Happy" eating bamboo in Leipzig Zoo (from Schneider, 
1939). D, Mei Lan eating green cornstalks in Chicago Zoological Park. 

emerge almost totally undigested. It seems logical to assume 
that an animal of such large proportions must have to eat 
tremendous quantities to secure the nourishment that it 
requires. ... I estimate that they would have to spend 
from 10 to 12 hours a day feeding. (Sheldon, 1937.) 

The bear [Ailuropoda] prefers the young and succulent 
bamboo shoots to the woody stems. For this reason, in the 
main district of bamboo-bears I found no bamboo shoots in 
the spring, since they had been systematically 'browsed' by 
bears. The bulk of its nourishment consists, however, of 
stone-hard bamboo stems thicker than a finger. With 
its powerful molar teeth the bear bites off the 3 to 6 m. 
long stems about 20 to 40 cm. above the ground, lays them 
down and eats the middle part up to the beginning of the 
leaves, while it regularly rejects the lower, hard part and 

lets it lie. Such chewed places are not particularly hard to 
find, although they are always concealed in the middle of 
the jungle. Usually they are not larger than one to two 
square meters. In these places perhaps 15 to 20 stems are 
bitten off, and the rejected parts cover the ground. (Schafer, 

McClure (1943) listed nine species of bamboo 
that are palatable to the giant panda, expressing 
astonishment at the range of its tastes. Sowerby 
(1937a) stated that a half-grown pet giant panda 
that wandered at will on a Chinese farmer's land 
"ate grass and other plants." 

Pen (1943) stated that a giant panda he ob- 
served at a distance of 2000-3000 meters on the 



Fig. 3. Use of fore paws in pandas. A, Ailuropoda (Mei Lan) using both fore paws to manipulate food; Chicago Zoological 
Park, September, 1952. B-D, Lesser panda (Ailurus fulgens) using fore paws to manipulate bamboo; Lincoln Park Zoo. 

Tibetan plateau was eating plants of various kinds, 
"principally gentians, irises, crocus, Lycium chi- 
nense and tufted grasses." Unfortunately it is not 
clear from his description how careful his observa- 
tion was, and this is the only reported field obser- 
vation of the giant panda's eating anything other 
than bamboo. 

Captive specimens of Ailuropoda have eaten 
in addition to various bamboos porridge, green 
corn stalks and ears, stalks of celery, carrots, and 
other vegetables. They refuse meat in captivity. 

Thus in nature the giant panda lives immersed 
in its food supply. It has practically no natural 
enemies, does not pursue prey, and does not need 

to wander in search of food. Demands on loco- 
motor efficiency are absolutely minimal. 


The manner of eating bamboo was well described 
by Schneider (1939), who carefully observed a 
200-pound female temporarily exhibited in the 
Leipzig Zoo. The animal always sat or lay when 
eating bamboo, thus freeing the fore feet (fig. 2). 
Only the stalks were eaten; the leaves were re- 
jected. The bamboo stalks were held in the fore 
foot and carried to the mouth. The tough outer 
layer was quickly and skillfully stripped off with 



the incisors, in which case the stalk was inserted 
transversely into the mouth, or with the canines 
and anterior premolars, in which case it was shoved 
lengthwise between the upper and lower tooth- 
rows. The stripped outer layer was torn off with 
a twisting movement of the fore foot coupled with 
a lateral turning of the head. The peeled stalk 
was then placed crosswise in a corner of the mouth, 
at the level of the large cheek teeth, where it was 
bitten off and chewed up. 

The giant pandas in the Chicago Zoological Park 
manipulated green corn stalks, celery stalks, and 
carrots in a similar manner. The animals invari- 
ably sat down, or stood on their hind legs with 
one fore leg braced against the bars of the cage, 
when eating such food. They often sat with a 
piece of corn stalk or a carrot in each fore paw. 
Items were carried to the mouth in the fore paw, 
inserted transversely between the large cheek teeth, 
and bitten off. Chewing was a succession of ver- 
tical chopping movements. 

Field observers (Weigold in Jacobi, 1923a; Shel- 
don, 1937) have emphasized the poorly chewed 
and undigested condition of pieces of bamboo in 
the droppings of the giant panda. 

The skill and precision with which objects are 
grasped and manipulated by the fore feet is aston- 
ishing. I have observed animals in the Chicago 
Zoological Park pick up small items like single 
straws and handle them with the greatest pre- 
cision. Small disks of candy less than an inch in 
diameter were handled deftly and placed in the 
mouth. Objects are grasped between the radial 
pad and the palmar pad and are held in the shal- 
low furrow that separates these two pads. The 
actions of the fore paw suggest a human hand 
grasping through a thumbless mitten but are less 
clumsy than this comparison would indicate. 

Bears and raccoons, of course, can grasp objects 
with their fore paws. In this action the digits, 
aligned side by side, are closed over the object, 
which is thus held between the digital pads and 
the transverse palmar pad. This is a quite differ- 
ent mechanism from the grasp of the giant panda. 
The lesser panda (Ailurus) grasps objects almost 
as skillfully as the giant panda, and apparently in 
a similar way (fig. 3). 

Diets of Other Carnivores 

It is remarkable that the food habits of none 
of the bears have ever been adequately studied. 
Cottam, Nelson, and Clarke (1939) analyzed the 
contents of 14 stomachs of black bears (Ursus 
americanus) killed in early winter, and found that 
fruits and berries, mast, and foliage accounted 
for 93 per cent of the bulk and vertebrates for 4 

per cent. Brehm (1915, Tierleben, Saugetiere, 3, 
p. 394) states that "more than the rest of the 
carnivores, the bears appear to be omnivorous in 
the fullest sense of the word, to be able to nourish 
themselves for a long time from the plant king- 
dom alone." Seton (Lives of Game Animals, 2, 
(1), 1929) emphasizes the omnivorous nature of 
the diet of each of the species of North Amer- 
ican bears. 

No quantitative study of the diet of Bassariscus 
has been made. Grinnell, Dixon, and Linsdale 
(Fur-bearing Mammals of California, 1, p. 179) 
state that "mice and other small rodents consti- 
tute the largest part of the food eaten by the ring- 
tailed cat. Small birds and berries are the other 
two most important items found in the stomachs 
examined. . . . Their jaws and teeth were so strong 
that they could chew up the leg bones of chicken 
without any trouble." 

The seasonal or annual diets of several other 
American arctoid carnivores have been determined 
quantitatively through large-scale analysis of stom- 
ach contents and scats. These, of course, provide 
the only reliable data on the diet, as opposed to 
what may be eaten under exceptional circum- 
stances, of any animal that is not positively re- 
stricted to a single food item. The diet of Procyon 
is more than 50 per cent (by bulk) vegetable (fruits, 
berries, nuts, and grains). Among the Canidae, 
the fall and winter diet of the red fox (Vulpes) is 
about 20 per cent herbivorous (fruits, grains, 
grasses), the winter diet of the gray fox (Urocyon) 
about 20 per cent herbivorous, and the annual diet 
of the coyote (Canis latrans) only 2 per cent her- 
bivorous. Many mustelids (Mustela vison, Taxi- 
dea, Lutra) are exclusively carnivorous or nearly 
so, but the skunks {Mephitis, Spilogale) may in- 
clude up to 50 per cent of plant material in their 

From these data it is evident that the closest 
living relatives of the giant panda (the Ursidae) 
are, next to Ailuropoda itself, the most herbiv- 
orous of living carnivores.' If the diet of Procyon 
is typical, the Procyonidae are likewise heavily 
herbivorous, though less so than the bears. The 
dogs and foxes are true carnivores, including only 
relatively small amounts of plant material in their 
diets. Thus Ailuropoda is a member of a group 
of carnivores (the procyonid-bear branch) that is 
already heavily herbivorous, and it is most closely 
related to the most herbivorous element of this 
group. The exclusively herbivorous diet of the 

' Unfortunately, no information, beyond vague general 
statements, is available on the diet of the lesser panda 
(Ailurus). Sowerby (1936a) says it feeds largely on bamboo 
leaves, and specimens in the Lincoln Park Zoo in Chicago 
ate green bamboo ravenously. 



Fig. 4. Postures of Ailuropoda: standing (Mei Lan, Chicago Zoological Park) and climbing ("Happy," Leipzig Zoo). 

giant panda is merely an extension, via an inter- 
mediate stage (the Ursidae), of a non-carnivorous 
dietary trend already present in the group from 
which this species was derived. 


The postures of Ailuropoda are similar to, but 
by no means identical with, the corresponding pos- 
tures of Ursus. 

The normal standing posture is similar to that of 
bears. Both fore and hind feet are fully planti- 
grade but are toed in more sharply than in Ursus. 
The prominent shoulder hump of bears is much 
less conspicuous in Ailuropoda, and the hind quar- 
ters are somewhat higher. As in bears, there is 
relatively little angulation at elbow and knee. The 
head is carried low, and the tail is clamped tightly 
against the body. The panda has a stocky appear- 
ance, less dog-like than that of bears. 

The animal often sits on the hind quartei's with 
the fore feet free of the ground. This posture is 
almost invariably assumed during eating, since it 
frees the fore feet for manipulating food (fig. 2). 

The panda does not normally sit erect, as bears 
often do, with the weight resting on the ischial 
surfaces. Instead, the back is curved like the let- 
ter C, and the weight appears to rest on the pos- 
terodorsal surface of the pelvis. In this posture 
the hind legs are thrust forward, their lateral sur- 
faces resting on the ground, with the knees slightly 
bent and the soles of the hind feet turned inward. 
Bears sometimes sit with their hind legs similarly 
extended, although more frequently the legs are 
drawn up in dog fashion. 

Ailuropoda often rests, half sitting and half re- 
clining, in the crotch of a tree. The back is then 
arched sharply, the weight resting on the lower 
part of the back rather than on the ischia. 

Like bears, Ailuropoda readily stands erect on 
its hind legs (fig. 4). This posture is assumed both 
in the open without any support for the fore feet 
and, more frequently, with the fore feet resting 
against the bars of the cage. The hind feet are 
nearly fully plantigrade, the femur and tibia in a 
straight vertical line. The zoo animals show no 






Fig. 5. The eight phases of the slow diagonal walk, with its footfall formula, of AUuropoda and Ursus americanus. 
Tracings from motion picture film taken at 16 f.p.s. Numerals are frame numbers in the sequences. 

more tendency to stand erect than bears do. I 
have never observed a panda walking in the erect 
position. "Bears are able to stand erect on their 
hind legs, and to walk a short distance in an un- 
steady but not particularly awkward movement." 


The normal gait of the giant panda is a "fast 
diagonal walk" (figs. 5, 6) in A. B. Howell's termi- 
nology. Howell (1944) states that this gait is reg- 
ularly employed by nearly all mammals. It is 
used by bears and raccoons. When moving more 
rapidly the panda breaks into a clumsy trot. 
Whether it is capable of galloping at still higher 
speeds is not known. 

The walk of AUuropoda is bear-like, but less 
smooth and graceful. The head is carried well 
below the shoulder line, and the tail is closely ap- 
pressed against the body. The stride is consider- 
ably longer than in bears, and as a result the gait 

is more rolling, with much more lateral rotation of 
the shoulders and hips than in Ursus. This gives 
a pronounced waddling character to the locomo- 
tion. The heavy head is swayed from side to side. 

The sole of the fore foot is fully apposed to the 
ground, but the heel of the hind foot does not 
touch the ground. Indeed, the panda appears to 
be incapable of flexing the ankle joint enough to 
permit plantigrady (p. 144). In this respect AUu- 
ropoda contrasts with Ursus, in which the sole is 
naked to the heel and the foot is fully plantigrade. 

During the recovery phase of the stride the fore 
feet are directed inward much more than in Ursus, 
and this "pigeon-toed" position of the foot is main- 
tained during the support phase. During the re- 
covery phase the hind feet are rotated medially so 
that the soles are directed medially. During the 
support phase, when the hind foot is resting on 
the ground, the toes point inward. At the end of 
the support phase the feet roll off the ground with 
the lateral toes receiving the major thrust. 



Fig. 6. Two types of walking loco- 
motion in the giant panda Mei Mei. The 
top figure is the fast diagonal walk, cor- 
responding approximately to no. 19 in 
figure 5. The bottom figure is a slow 

In captivity the giant panda is a persistent 
climber when young (fig. 4). The movements are 
often astonishingly clumsy but successful. In 
climbing vertical or near vertical tree trunks the 
movements are bear-like. The animal embraces 
the tree, with the soles of all four feet pressed 
against the bark, and progresses by a series of 
"caterpillar" movements. The animal takes ad- 
vantage of branches or other projections to hoist 
itself up. It descends tail first, unless the slope is 
gentle enough to allow it to walk down head first. 

The claws appear to be of less importance in 
climbing than the friction of the soles against the 
bark, although the claws are used, especially if the 
animal slips unexpectedly. In this type of climb- 
ing, called "bracing" or "prop" climbing {Stemm- 
klettern) by Boker (1935), the portion of the body 
not supported by the hind legs is suspended from 
the fore legs. 


Young individuals are active and playful, and 
thousands of zoo visitors have been entertained 
by their clownish antics. As they grow older they 

become much less active. Some individuals, at 
least, become siu'ly and dangerous in captivity. The 
giant panda "Mei-Lan," while in captivity in the 
Chicago Zoological Park, mauled one of his keepers 
so severely that an arm had to be amputated. 

Sheldon (1937), who hunted Atluropoda, wrote: 
"My experience convinced me that the panda is 
an extremely stupid beast. On one occasion at a 
distance of 350 yards I obsei-ved two individuals 
on the edge of a bamboo jungle. Driven out by 
four dogs and warned by several high-powered 
bullets whistling about them, neither animal even 
broke into a run. The gait was a determined and 
leisurely walk. Again, Dean Sage and I observed 
another panda pursued by four dogs. In this in- 
stance he walked to within eight feet of Dean and 
was stopped only by bullets. He gave absolutely 
no evidence that he saw either of us, and seemed 
completely to disregard both the shots and the 
loud talking and shouts of a few minutes previous." 


The giant panda is confined to the moist bam- 
boo zone on high mountain slopes, where the leop- 



ard and the red wolf are its only potential natural 
enemies. Its natural diet consists exclusively of 
bamboo, with which it is always surrounded. Se- 
lection pressure for locomotor efficiency is abso- 
lutely minimal. Bamboo stalks are consumed in 
enormous quantities, but are poorly chewed and 
poorly digested. The fore feet are constantly used 
to manipulate the food. Objects grasped in the 
fore paws are held between the radial pad and the 
palmar pad. This grasping mechanism differs 

from that used by bears and raccoons but is sim- 
ilar to that of the lesser panda {Ailurus). 

Ailuropoda is a member of a group (the bear- 
raccoon line) of carnivores whose diet is more than 
50 per cent herbivorous. Its closest living rela- 
tives (the bears) appear to be more than 90 per 
cent herbivorous. 

Posture and locomotion are similar to those of 
bears. Locomotion is less efficient. Ailuropoda 
climbs clumsily but persistently when young. 


The general habitus of Ailuropoda is ursine. 
The head and fore quarters are heavy and power- 
ful, the hind quarters relatively weak. The build 
is much stockier than that of bears of comparable 



The pelage is thick and woolly, as befits an ani- 
mal frequenting high altitudes. The characteristic 
parti-colored pattern is shown in figui-e 9. This 
pattern is unique among carnivores, although it is 
approached by the ratels {Mellivora}, and by the 
lesser panda (AiluriLs) except that the areas that 
are white in Ailuropoda are for the most part red- 
dish-brown in Ailurus. The coloration of Ailuro- 
poda is certainly a "constitutional" pattern rather 
than a "biological" pattern conditioned by nat- 
ural selection. 

The most unusual feature of the hair arrange- 
ment is found in the nasal region. The short hair 
on the top of the rostrum, from a point just in front 
of the eyes down to the muzzle (a distance of about 
55 mm.), is directed straight forward. Two whorls 
are formed, 35 mm. apart, in front and mesad of 
the eyes, from which the hair radiates. Attention 
was first drawn to this character, which is unique 
among arctoid carnivores, by Kidd (1904). Kidd's 
later suggestion (1920), that this reversal of hair 
stream resulted from rubbing the hair toward the 
muzzle in cleaning it, cannot be taken seriously. 
It is noteworthy that a similar reversal occurs in 
other short-nosed carnivores (e.g.,Fefe). 

The facial vibrissae (fig. 7) are rather feebly de- 
veloped, although not so poorly as Pocock (1929) 
concluded from an examination of prepared skins. 
The superciliary tuft is represented by about three 
moderately long hairs over the eye. There is a 
relatively heavy growth of mystacial bristles along 
the upper lip, extending back almost to the angle 
of the mouth. On the lower lip they extend as far 
as the angle of the mouth. These bristles are much 
worn and broken on the specimen at hand, so that 
their length cannot be determined. They cer- 
tainly do not reach any great length, however. 
Inter-ramal and genal tufts are absent. 

The rhinarium, as pointed out by Pocock, is 
hairy above, with a well-haired infranarial area on 

either side of the midline below. The naked area 
roughly resembles an inverted triangle and is con- 
tinued ventrally into a short, grooved philtrum. 
There is also a V-shaped notch between the nos- 
trils dorsally. The transverse groove below the 
nostrils referred to by Pocock is not evident on the 
fresh animal. The nostrils are transverse. 

The external ear is erect, relatively larger than 
in bears, arising from a curiously constricted base. 
The margin is rounded, as in bears. The ear is 
well haired internally far down into the meatus. 
There is no bursa. The height of the pinna in 
Su Lin is about 85 mm., its breadth about 80 mm. 
The eai-s are set higher on the head and closer to- 
gether than in bears a consequence of the enor- 
mously developed masticatory musculature. 

The fore foot (fig. 8) is short and powerful. The 
digits are enclosed in the common skin of the foot 
up to the base of the digital pads. Examination 
of the fresh animal corrects several errors made by 
Pocock. All the pads are thick and cornified. The 
digital pads are elUptical in outline, those of the 
second, third, and fourth toes approximately equal 
in size. That of the fifth toe is slightly smaller, 
and the pad of the poUex is the smallest of all and 
is joined to the palmar pad by a narrow isthmus 
of naked skin. The palmar pad extends as a nar- 
row strip across the entire foot. There is no evi- 
dence of its breaking up into interdigital pads. 
The outer end of the pad is expanded slightly, 
and its inner end curves proximally to join the 
prominent radial lobe, from which it is separated 
by a transverse furrow. 

The radial lobe is smaller than the outer carpal 
lobe. This lobe is wanting in bears. It is ellip- 
tical in outline, the long axis running anteroposte- 
riorly, and is hemispherical in cross section. It is 
associated with the prominent radial sesamoid 
bone, which hes directly beneath it; Pocock was 
not sure that it represents the missing inner carpal 
lobe. Objects held in the hand lie in the furrow 
between the radial lobe and the inner end of the 
palmar pad and are grasped between these two 

The outer carpal lobe is large and roughly cir- 
cular in outline and is situated somewhat farther 


Fig. 7. Side view of head of Ailuropoda, showing pattern of vibrissae and hair-slope. 


Fig. 8. Ventral surfaces of left fore and hind feet of Ailuropoda melanoleuca (A, B) and Ursus americanus (C, D). Ursus 
after Pocock reversed. 




proximally than the radial lobe, lying about a third 
of its own width behind the palmar pad, much 
closer than in Ursus. 

The remainder of the palmar surface is densely 
covered with long hair. 

The hind foot (fig. 8) is slightly narrower than 
the fore foot and is remarkable for the limited ex- 
tent of the cornified hairless areas. The absence 
of the posterior lobe of the plantar pad is associ- 
ated with the inability of Ailuropoda to flex the 
foot beyond 45 from the vertical (fig. 80). The 
digits are enclosed in the common skin of the foot 
nearly to the bases of the digital pads. The digital 
pads are elliptical in outline, and all are approxi- 
mately the same size. The pad of the hallux is 
joined to the plantar pad by a narrow isthmus of 
naked skin similar to that on the pollex. The 
plantar pad is a narrow transverse cushion, feebly 
convex anteriorly and very faintly divided into 
five lobes (not four as Pocock stated). The pad 
lies beneath the metatarso-phalangeal articulation. 
It is somewhat wider at the outer end than at the 
inner, and the lobe under the hallux is more clearly 
indicated than the others are. Metatarsal pads 
are absent; the remainder of the sole is densely 
covered with long woolly hair. 

The claws on all the digits are strongly com- 
pressed and taper from a wide base to a sharp tip. 
The upper edge of the claw describes almost a per- 
fect quadrant of a circle; the lower edge is sinuous. 

The tail is relatively small but longer and con- 
siderably heavier than that of any of the bears. 
It measures 115 mm. in length in Su Lin (the cau- 
dal vertebrae measure 203 mm. in the skeleton of 
an adult) and tapers abruptly from a heavy base. 
The base of the tail is flattened dorsoventrally; its 
width is about 35 mm. while its depth is only about 
25 mm. (see p. 83). The entire organ is densely 
clothed in long, coarse hairs. 

There are two pairs of nipples, one pair pectoral 
and the other abdominal. The pectoral pair lies 
over the seventh rib, the abdominal pair 200 mm. 
behind the posterior end of the sternum. The 
bears have three pairs of mammae. 

The external structures in the perineal region 
are described on page 221. 


No flesh measurements of an adult giant panda 
are available. The following measurements were 
made on the mounted skeleton of the adult male 
killed by the Roosevelt brothers. Flesh measure- 
ments of an adult female black bear, quoted from 
Seton (1929, Lives of Game Animals, 2 (1), p. 119) 
are given for comparison. 


Ailuropoda americanus 

mm. inches mm. inches 

Snout to tail tip 1422 56 1613 63.5 

(along curve) 

Tail 203 8.5 127 5 

Height at shoulder. .. . 635 25 648 25.5 

Approximate mean pounds pounds 

weight of adult 275 250 

The female "Happy" (weight 223 pounds), meas- 
ured by Schneider (1939), had a shoulder height of 
about 660 mm. 

No actual weight figures for adult giant pandas 
exist. Schafer estimated that an adult male would 
weigh 275 pounds; Ailuropoda is fully grown at 
4-5 years. The adult male Mei Mei weighed 205 
pounds at death but weighed 296 pounds some 
months earlier. The weight of the male Mei Lan 
was estimated by zoo officials at 300 pounds when 
he was six yeai's old. Skeletal measurements (Ta- 
ble 6, p. 45) show that Mei Lan was much the 
largest panda on record. A male at the St. Louis 
Zoo weighed about 280 pounds at eight years of 
age, and a female 240 pounds at five years. Thus 
it appears that the adult weight of the giant panda 
is 250-300 pounds, which is close to the average 
for the American black bear. The giant panda 
Su Lin weighed 132 pounds at death. The snout- 
vent length of this individual was 1195 mm. 


Weight increments for about the first 18 months 
of life are available for three individuals. These 
figures are, of course, for captive animals and do 
not include the first month or two after birth. 
Figures for "Pandah" and "Pandee" were kindly 
supplied by Dr. Leonard J. Goss of the New York 
Zoological Society. Weight figures are shown in 
the accompanying graph (fig. 9). The average 
monthly gain was 9 pounds. 


Measurements of the linear dimensions of ana- 
tomical structures serve two different purposes. 
The simpler of these is as a means of expressing 
relative sizes of homologous parts in two or more 
organisms. Thus, if femur length is 75 mm. in A 
and 60 mm. in B, we say that the femur is longer 
in A, or is 15 mm. longer, or we may express the 
difference as a percentage and say that femur 
length in B is 80 per cent of femur length in A. 
Such simple manipulations are much used in tax- 
onomy and comparative anatomy. They rarely 
present serious difficulties as long as the organisms 
being compared are fairly closely related. 

On the other hand, attempts to compare pro- 
portions between two or more species or genera 



often present serious difficulties. If A and B rep- they are not). This difficulty has plagued corn- 
resent different species, the fact that the femur of parative anatomists from the beginning and has 
A is longer than that of B may reflect the fact never been satisfactorily resolved. 

7 8 9 

Fig. 9. Growth curves of Ailuropoda. 

that A is a larger organism than B, or that the 
femur is relatively longer in A or is relatively 
shorter in B, or a combination of all of these fac- 
tors. The difficulty in determining what is in- 
volved arises from the fact that there is no com- 
mon standard to which the variable (in this case 
femur length) can be related; for practical pur- 
poses all measurements on an organism must be 
treated as independent variables (although in fact 

Many structures in mammals function as lever 
systems. Interpretation of the mechanical advan- 
tage of one lever system over another does not 
depend on knowing how the differences in propor- 
tions were achieved, but a true understanding of 
the morphology of the organism obviously does. 
Index figures, obtained by dividing one dimension 
(e.g., tibia length) by another larger dimension from 
the same individual (e.g., femur length) and multi- 



Fig. 10. Body outlines of representative arctoid carnivores to show posture and proportions. All drawn from photo- 
graphs of living animals (not to scale). Top: Wolverine {Gulo luscus), a generalized mustelid; cacomistl (Bassariscus astutus), 
a generalized procyonid. Middle: Raccoon (Procyon lolor) and les.ser panda (Ailurus fulgens). Bottom: Black bear {Ursus 
americanus) and giant panda (Ailuropoia melanoleuca) . 

plying by a constant (commonly 100), ai-e widely 
used because they are independent of the absolute 
size of the original figures and therefore directly 
comparable between individuals of the most di.s- 
parate sizes. Uncritical comparisons of such index 
figures may, however, lead to grossly ei-roneous 
conclusions. In the present study the femoro- 
length tibia 

tibial index 

X 100 

for a group of 

length femur 

badgers happened to be identical with the corre- 
sponding index for a series of giant pandas, 76 in 
both cases. Analysis of the figures for femur and 
tibia length, using a third dimension (length of 3 
vertebrae) as a common standard, revealed that 
the tibia is abnormally short and the femur about 
normal in the badgers, whereas in the panda the 
reverse is true: the femur is abnormally long and 

the tibia about normal. These relationships may 
be of no importance in comparing the limbs as 
lever systems, but they are of the utmost impor- 
tance in interpreting the morphology, and partic- 
ularly the phylogeny, of the limbs. They could 
not have been detected from the dimensions of 
femur and tibia alone, but required the use of a 
third dimension as a common standard. 

Body Proportions 

Comparative proportions of the body in a series 
of animals may be expressed by equating spine 
length to 100 and expressing the dimensions of 
other body parts as percentages of spine length 
(Hildebrand, 1952). These proportions are shown 
pictorially (fig. 10) and graphically (fig. 11) for a 
series of carnivores. 





Gulo luscus 

Potos flovus 



















Ursus arclos 

Ailuropoda melanoleuca 

Fig. 11. Body proportions in representative carnivores (based on one specimen of each). In each case pre-sacral vertebral 
length was equated to 100, and lengths of other parts were indicated as percentages of vertebral length. Limb length is the 
"functional limb length" of Howell (lengths of propodium + epipodium + metapodium). 

The wolverine {Gulo) represents a generalized 
terrestrial carnivore, in which length of hind limbs 
exceeds that of fore limbs by about 10 per cent, 
the epipodial segments (radius and tibia) are 
slightly shorter than the propodials (humerus and 
femur), and the metapodials (metacarpals and meta- 
tarsals) are long. In an arboreal carnivore (Potos) 
the hind limbs are elongated and the metapodials 
slightly shortened. In canids, which are typically 
cursorial runners, the legs are relatively long, espe- 
cially the epipodial and metapodial segments. 

These all represent rather obvious adaptations 
for locomotor efficiency. Adaptation is less obvi- 
ous in certain other carnivores. The bears, which 
are mediportal ambulatory walkers (p. 38), have 
legs relatively as long as the cursorial canids and 
the proportion between length of front and hind 
limb is about normal for carnivores. The bears 
and the giant panda are remarkable among carni- 
vores in having a long femur associated with a 
short tibia, without corresponding reduction in 
radius length; this condition is characteristic of 
heavy graviportal mammals (A. B. Howell, 1944). 
In Ailuropoda the spine has been shortened by 
elimination of lumbar vertebrae, a condition other- 
wise unknown among carnivores. The trunk in 
Ailuropoda is relatively shorter than in any other 

known carnivore; the index "length thoracics 10- 
12/length thoracolumbar vertebrae X 100" is 18 
and 22 for two pandas, whereas it is 14 (13-15) for 
all other carnivores examined except a specimen 
of Mellivora, for which it is 16. This exaggerates 
apparent leg length, but the legs actually are rela- 
tively long (Table 2). Length of fore and hind 
legs is subequal in Ailuropoda; this condition is 
otherwise encountered among carnivores only in 
the hyenas, although the proportions of the limb 
segments in hyenas are quite different from those 
of Ailuropoda. 

Limb Proportions 

In studies on small rodents, body length (meas- 
ured on the freshly killed animal) is often used as 
the independent variable. This is impractical in 
work on skeletons of large mammals, for which 
measurements of body length are rarely recorded. 
Hildebrand (1952) used length of the vertebral 
column in his work on body proportions of the 
Canidae. Length of vertebrae probably varies as 
little as any convenient linear dimension, but for 
material as heterogeneous as the whole Order Car- 
nivora it is desirable to eliminate the lumbar re- 
gion, which, like the limbs, is intimately involved 
in the mechanics of locomotion and would there- 





Canis lupus 4 

Canis lalrans 3 

Chrysocyon brachyurus 2 

Bassariscus astutus 4 

Bassaricyon 3 

Nasua 3 

Procyon lolor 4 

Potos flavus 3 

Ailurus fulgens 3 

Ursus americanus 2 

Ursus arctos 2 

Ailuropoda 7 

Gulo luscus 3 

Martes pennanti 2 

Taxidea taxus 3 

Mellivora 1 

Lutra canadensis 3 

Enhydra 2 

Viverra tangalunga 5 

Paradoxurus 4 

Herpestes 1 

Felis onca 2 

Felis leo 4 

Felis tigris 1 

Total 71 








































































































































fore be expected to bias the results. A group of 
three thoracic vertebrae is convenient to measure 
and yields a linear dimension of convenient size. 
The combined length of thoracics 10-12 has there- 
fore been used as the independent variable in the 
present study. An obvious disadvantage of using 
this measure as the independent variate is that it 
is the least accurate of all the measures in the set, 
and errors of measurement in the independent 
variate will bias the results, even though the errors 
are random. 

Furthermore, length of centrum is itself a vari- 
able; simple inspection shows that vertebrae are 
relatively longer in Mustela than in Ursus, for ex- 
ample. Therefore, index figures derived from this 
common standard have no absolute value for pur- 
poses of comparison. They are only approxima- 
tions, their reliability depending upon the range 
of variation in relative vertebral length within the 
sample. Reliability is certainly great enough to 
demonstrate gross deviations from the norm. 

A further problem in interpreting these data is 
the selection of a norm against which the index 
figure can be evaluated. Femur length cannot be 
judged "short" or "long" unless it is shorter or 
longer than some standard femur length for the 
Carnivora. Probably the best that can be done 
is to use the index figure for the least specialized 
representative of the Carnivora as a norm. In 
Table 2 the figures for the wolverine (Gulo), whose 
locomotor habits are as generalized as those of any 

living carnivore, are used as a norm, the figures 
being rounded off to the nearest multiple of 5. 

From the table it appears that arm length is the 
most conservative among the four limb segments 
and foi-earm length the most variable. 

These indexes correlate quite well with what is 
known of the locomotor habits of the animals. 
There are puzzling non-conformities (e.g., long 
proximal segments in Ailurus, short arm in Vi- 
verra, long fore arm associated with long thigh in 
Felis leo, etc.) that cannot be explained on the 
basis of existing knowledge. Disregarding these 
exceptions, limb proportions appear to correlate 
with locomotor types as follows in the Carnivora: 

Ambulatory walking norm 

Running all segments long, 

especially forearm 
Arboreal climbing 

Type A hind legs long 

Type B forearm short, 

other segments norm 

Digging di.stal segments short 

Swimming all segments very short, 

especially forearm 

The bears and the giant panda, in which a short 
tibia is associated with length in the other three seg- 
ments, do not fit any of these categories, and this 
combination is difficult to justify on a mechanical 
basis. Elongated limbs are generally associated 
with running, where a long stride is advantageous. 
The limbs are also long in graviportal animals 
(e.g., elephants, titanotheres), although the me- 
chanical factors involved are unknown. The bears 



Canis lupus 4 

Canis latrans 3 

Chrysocyon 1 

Bassariscus 4 

Nasua 1 

Procyon 3 

Polos 3 

Ailurus 2 

Ursus 4 

Ailuropoda 2 

Gulo 2 

Maries pennarUi 1 

Maries flavigularis 1 

Taxidea and Mellivora 4 

Lutra canadensis 3 

Enhydra 2 

Viverra langalunga 5 

Paradoiurus 3 

Herpesles 1 

Croeula 1 

Hyaena 1 

Felis onca 2 

Felis leo 4 

Felis tigris 1 

' V=Iength of thoracics 10 
ifcll to 20. Extremely long or short= 21 or more 

V L. humerus 

V L. radius 

V L. femur 

V L. tibia 

(norm =40) 


(norm = 40) 

(norm = 40) 






verj- long 



all long; forearm very lot 

very long 

extremely long 

ven,- long 

ven.- long 

all very long; forearm 
extremely long 



si. short 



forearm slightly short 




ver>' long 

hind legs long; all distal 
segments long to very 



ver>' long 

ven,- long 

verj- long 

all very long, except 
humerus long 





hind legs long 

slightly long 






proximal segments long 


very long 

very long 


all long-very long, 
except tibia norm 





all long, except tibia 





all norm 






extremely short 



forearm extremely short 







forelegs short 




very short 

distal segments short; 
tibia very short 

very short 

extremely short 

extremely short 

very short 

all very short, forearm 
extremely so 

extremely short 

extremely short ( 

extremely short 


extremely short 

all extremely short, 
especially forearm 





arm short 







slightly short 





forearm slightly short 



very short 



all short-ver>' short, 
except femur 


very long 

very long 


all long; forearm and 
thigh very long 


verj- long 



all long; forearm very 





long thigh 






long forearm and thigh 





long thigh 

2. Norm = 3 from norm. Lor 

ig=-4 to -10. 

Short= +4 to +10. Verj- long or short 



Ambulatory walking . 


Half-bound (cats) . . . 




Mediportal types 







radius short 


90 + 
tibia short 

75 + 
radius shorter 

90 + 
hind legs long 

100 + 

femur longer 

98 + 

90 + 
radius short 

90 + 
hind legs long 

radius short 

85 + 
femur longest 

tibia shorter 

85 + 
radius shorter 

85 + 
hind legs longer 

radius shorter 

femur longer 

95 + 

75 + 
radius shorter 

hind legs longer 

radius shorter 

90 + 
femur long 

tibia shortest 

95 + 

92 + 
hind legs long 

radius shortest 

95 + 

110 + 
tibia longest 

radius shortest 

hind legs longest 

80 + 
radius shorter 

femur much 


tibia very much 


96 + 

hind legs long 

radius much 



tibia much 





? 300 

Ursus omerlcanus 
D " arctos 

A " gyos 




Ailuropoda Y= 37.3 + 0.63 X 
Ursus Y= -6.5 -1- 0.83 X 



Humerus Length 



Fig. 12. Scatter diagram, with fitted regression lines, showing length of radius and length of humerus in panda and bears. 
(Dashed line=slope of 1.) 









Ursus omerlcanus 
o " orctos 

a " gyas 






Femur Length 



Fig. 13. Scatter diagram, with fitted regression lines, showing length of tibia and length of femur in panda and bears. 
(Dashed line=slope of 1.) 

and the panda are relatively slow-moving ambu- 
latory walkers and lack the elongation of the meta- 
podials that characterizes runners. Shortening of 
the distal segments characterizes digging animals, 
in which the mechanical advantage of increasing 
effective power at the distal ends of the limbs is 
obvious. Gregory (in Osborn, 1929) noted that 
among ungulates the tibia shortens with gi-avi- 
portal specialization, whereas relative radius length 
either remains stationary or shortens to a less de- 
gree than tibia length. This is exactly the situa- 
tion in the bears and the giant panda, whose limb 
proportions are those of mediportal or graviportal 

Intramembral Indexes 

Ratios of limb segments with respect to each 
other reflect the same pattern as ratios derived 
from an independent variable. They have the ad- 
vantage over the preceding ratios of greater math- 
ematical reliability and of widespread usage (see 
A. B. Howell, 1944). Limb segment ratios of rep- 
resentative carnivores are given in Table 2. 

These figures are associated with locomotor 
types as shown in the following summary. Several 

forms (e.g., Procyon, Ailurus, Viverra, Herpestes) 
do not fit well into any of the categories, and again 
it must be assumed that unknown factors are in- 
volved in determining the limb proportions of such 

Ratios for the bears agree with those of medi- 
portal or graviportal ungulates. Furthermore, this 
agreement is associated with other mediportal 
adaptations, such as flaring ilia and relatively slight 
angulation of the limbs at elbow and knee. 

The peculiar i-atios in Ailuropoda do not occur 
in any other known mammal, and they often differ 
from the corresponding ratios in Ursus. They are 
most closely approached by those of the burrowing 
mustelids. Functional lengths of humerus and 
femur are equal in a very few scattered forms 
{Tamandua, Icticyon, Dolichotis; A. B. Howell, 
1944). Equality in length of radius and tibia is 
more common but follows no pattern. Equality 
in the intermembral index occurs elsewhere among 
terrestrial mammals only in a few aberrant forms 
(giraffe, hyenas, the extinct forest horse Hippidi- 
um; A. B. Howell, 1944). I conclude that limb 
proportions in Ailuropoda are attributable to fac- 
tors other than mechanical requirements that 



400 -- 

5 300 -- 


Ursus americanus 
D " arctos 

A > 

a gyas 




Ailuropoda Y= -89.1 -i- 1.21 X 
Ursus Y= -58.6+ 1.I6X 






Pelvis Length 

Pig. 14. Scatter diagram, with fitted regression lines, showing breadth and length of pelvis in panda and bears. (Dashed 
line=slope of 1.) 

selection for mechanical efficiency has been over- 
ridden by some other factor or factors. 


Examination of linear measurements of the limb 
bones of Ailuropoda (Table 6, p. 45) shows that 
proportions vary with the absolute size of the 
bones. When pairs of measurements for all indi- 
viduals are plotted on scatter diagrams, clustering 
of observations along a line that deviates from a 
45 angle is evident for nearly all limb proportions. 
This indicates that limb proportions conform to 
the well-known allometric equation y = a + bx, 
where z and y are the two measurements being 
compared, and a and b are constants. Regression 
lines were fitted to the data by the method of least 
squares (Simpson and Roe, 1939). 

For the limb bones of Ailuropoda the plotted 
points are somewhat scattered (figs. 12, 13), indi- 
cating considerable individual variation in pro- 
portions. The slopes of the regression lines diverge 
from unity, indicating an allometric relationship 

between proximal and distal segments of the legs; 
radius and tibia become increasingly short relative 
to the proximal segments as total organism size 

Conditions in Ursus are similar, although allom- 
etry is considerably less for the radius than in 
Ailuropoda. The plotted observations for all pro- 
portions cluster much more closely ai'ound a straight 
line, indicating relatively little individual variation. 

The deviations of the regression lines from unity 
are not statistically significant for either Ailuro- 
poda or Ursus. The close clustering of the values, 
especially for Ursus, suggests that they would be 
significant in a larger sample. 

Similar analyses of data on limb proportions in 
other cai'nivores are available only for the domes- 
tic dog. Lumer (1940) found a close correlation, 
but only a very slight deviation from unity in the 
slopes of regression lines, in both humeroradial 
(6=1.098) and femorotibial (6=1.090) proportions 
in an analysis of data from a wide variety of breeds 
of dogs. 



The limb girdles in the panda and bears are less 
consistent than the limb segments. In the scapula 
of the panda there is little correlation between 
height and breadth (r=0.45, N=9). In Ursus, on 
the contrary, there is a very close correlation be- 
tween height and breadth of scapula (r=0.98, 
N=9), but only a slight indication of allometry 
(6=0.94). The pelvis shows a high correlation in 
total length/breadth across ilia in both Ailuropoda 
and Ursus. There is also a strong allometric rela- 
tionship (6=0.75 in Ailuropoda, 6=0.57 in Ursus), 
the iliac breadth becoming increasingly great as 
size of pelvis increases (fig. 14). 

The "law of allometry' has been tested by many 
workers in a wide variety of cases, and found to be 
a valid empirical representation of ontogenetic 
growth relations. We may therefore postulate 
that the allometric relations demonstrable in Ailu- 
ropoda and Ursus reflect genetically determined 
processes that are as characteristic of the species 
or genus as are any morphological feature, repre- 
senting what Lumer has called "evolutionary al- 
lometry." The intensity of expression of such 
size-dependent relationships is a function of or- 
ganism size. Therefore the proportions at any 
particular phylogenetic stage (strictly, at any par- 
ticular organism size) may not be, and in extreme 
cases certainly are not, directly related to the re- 
quirements of the organism. If selection has fa- 
vored increased organism size, then proportions 
may become increasingly grotesque until a point 
is reached where the disadvantages of mechani- 
cally unfavorable proportions balance the advan- 
tages of further increase in organism size. 


1. The external characters of the giant panda 
are basically similar to those of Ursus. Differences 
from the bears are for the most part conditioned 
by more fundamental differences in underlying 

2. The absolute size of the giant panda is al- 
most identical with that of the American black 

3. Body proportions of the bears and the giant 
panda differ from those of all other living carni- 
vores. They resemble the proportions of medi- 
portal or graviportal animals, although the mass 
of the smaller bears and of the giant panda is less 
than that of mediportal ungulates. It is also less 
than that of the larger cats, which show no medi- 
portal specializations. 

4. The trunk in the giant panda is relatively 
shorter than in any other known carnivore. 

5. Limb proportions in the giant panda resem- 
ble those of bears, but differ in some important 
respects. In neither the panda nor the bears can 
they be explained on the basis of functional re- 

6. Limb proportions in the panda and the bears 
show indications of allometry, the distal segments 
being relatively shorter in larger individuals. Pel- 
vic proportions are also allometric, but scapular 
proportions are not. 

7. Body proportions in the pandas and bears 
are not the result of selection for mechanical effi- 
ciency. Rather they reflect pleiotropic correla- 
tions with other features that have been altered 
through natural selection. 


Most of the literature on the mammalian skele- 
ton is purely descriptive, with no real considera- 
tion of the soft parts to which the bones are 
intimately related in form and function, of the 
functions of the bones themselves, or of the fac- 
tors responsible for observed differences between 
species. Comparisons are often unreal, for bones 
are compared as if they were inanimate geometri- 
cal forms rather than artificially segregated parts 
of living organisms. As a result there has been 
little attempt to evaluate differences in other than 
purely quantitative terms. Even the descriptions 
are often inadequate because the observer described 
only what he saw. The primary objectives have 
been to find "characters" on which a classification 
of mammals can be based, or to reconstruct the 
phylogenies of organisms or of structures. These 
are important but severely limited goals. 

The gross features of the skeleton are deter- 
mined by heredity, conditioned by events in the 
remote past; mammals have one bone in the thigh 
and two in the leg because they inherit this pattern 
from their remote ancestors not because it is par- 
ticularly suited to the needs of mammals. Within 
the limits set by this inherited framework, the pri- 
mary function of the skeleton is support, and the 
form and architecture of bones reflect primarily 
the stresses and strains associated with this func- 
tion. Each bone is also subjected to an assort- 
ment of constantly varying localized stresses and 
strains resulting from the action of muscles and 
ligaments. Besides these mechanical factors, the 
skeleton also serves as a store for calcium salts. 
Consequently the architecture of a bone is far 
more complex than is generally assumed, and at- 
tempts to analyze bones from the engineering 
standpoint have not been entirely successful (see 
Wyss, 1948). 

In the individual the basic features of the skel- 
eton, including accumulated adaptive features 
acquired during phylogeny, are determined genet- 
ically. We cannot go far beyond this obvious gen- 
eral statement, although Stockard (1941) and 
Klatt (1941-43) made a beginning at discovering 
the nature of this genetic control, and Sawin (1945, 
1946) and his co-workers demonstrated gene con- 

trol of morphogenetic fields in the skeleton. Scott 
(1957) concluded that growth and differentiation 
of the skeleton depend on two distinct processes: 
(a) a length-regulating process controlled by con- 
version of cartilage into bone (interstitial growth), 
and (b) a robustness-regulating process that deter- 
mines the thickness of the limb bones, the size of 
the vertebrae, etc., and involves the activity of the 
subperiosteal cellular tissue (appositional growth). 

It is likewise obvious that the inherited features 
of the skeleton are modified, within limits, by the 
activities of the individual. This is seen, if proof 
is needed, in the vertebral column of Slijper's bi- 
pedal goat (Slijper, 1946), in the adaptations to 
pathological conditions described by Weidenreich 
(1926, 1940), and in the experiments of J. A. 
Howell (1917), Washburn (1947), Wolffson (1950), 
Moss (1958), and others. This non-hereditary' 
factor is of unknown, but probably considerable, 
importance in determining the morphology of the 
bones. Howell, for example, found that in the bones 
of the fore leg of the dog most or all growth in 
diameter (appositional growth) is dependent on 
extrinsic mechanical factors, whereas growth in 
length (interstitial growth) is largely independent 
of mechanical factors. 

Finally, it is reasonable to assume that the ca- 
pacity of the individual skeleton to respond adap- 
tively to specific functional demands is inherited, 
and that this capacity varies with the age of the 

The description of the skeleton of the giant 
panda here presented is somewhat unorthodox. 
The customary detailed description of each bone 
has been largely omitted; the illustrations should 
supply such information. The relations between 
bones and muscles, blood vessels, and nerves has 
been emphasized; and mechanical factors, which 
seem to have been of more than usual importance 
in molding the morphology of the giant panda, 
have been treated to the best of my ability. I 
have aimed not merely to describe and compare, 
but so far as possible to interpret. 

' The muscles and other soft parts that act on the bones, 
as well as the psychology that directs the basic activities of 
the animal, are presumably gene-controlled. Thus even this 
factor is hereditary, at second hand, so to speak. 




Fig. 15. Skeleton of Ailuropoda melanoleuca (CNHM no. 31128, adult male). 


The skeleton (fig. 15) resembles in general ap- 
pearance that of a bear of similar size. The massive 
skull and short vertebral column give a somewhat 
non-ursid aspect to the skeleton. As in Ursus, 
surface modeling on the limb bones is prominent. 

The mass of the skeleton is greater than that 
of a black bear of similar size. This is largely but 
not entirely due to the much heavier skull (Table 3). 


Skull as 





Skull of total 




1581 29 





1583 26 


Ursus americanus a' 


818 16 


Ursus americanus 


694 19 


Ursus arctos. . . . 


1923 18 


Ailurus fulgens . 



67.5 25 


Procyon lolor . . . 



67.8 18 


Canis lupus . . . . 



377.5 19 


Hyaena striata . . 


465 22 


Crocuta crocuia. 


864 22 

For the giant panda and black bear these figures 
represent about 4 per cent of total body weight. 

Further analysis of weight figures shows (Ta- 
ble 4) that percentages of total postcranial skele- 

ton weight formed by the trunk, fore limbs, and 
hind limbs are very similar in giant panda and 
bears. These ratios vary considerably among the 
other carnivores. 

It is evident that, except for the skull, the rela- 
tive proportions of total skeleton weight formed 
by each of the major regions of the skeleton in 
Ailuropoda do not differ significantly from those 
of Ursus. This is not true of the skull, which is 
extraordinarily dense in the giant panda. The 
skull-postcranial ratio is quite constant at 16-19 
per cent in other carnivores examined, except Ailu- 
rus and the hyenas, in which the masticatory appa- 
ratus is likewise exceptionally powerful. 

The weight of the bones of the fore limbs is rela- 
tively greater in Ailuropoda, Ursus arctos, and the 
hyenas than in the other carnivores (Table 4). 
Klatt and Oboussier (1951) found this likewise 
true of bulldogs compared with greyhounds, al- 
though the disproportion (bulldog 69 : 31, grey- 
hound 61 : 39, on fresh bones) was greater than in 
any of our material. Klatt and Oboussier found 
a comparable disproportion in total weight (i.e., 
including soft parts) of the limbs, and an even 
greater disproportion for the head. They con- 
cluded that the bulldog proportions result from a 




Percentage of Total Postcrania! 

Fore limbs : Hind limbs 

(incl. pelvis) 

36758 Ailuropoda 44 

31128 Ailuropoda 46 

44725 Ursus americanus 46 

18864 Ursus americanus 42 

47419 Ursus arclos 46 

65803 Ailurus fulgens 47 

49895 Procyon lotor 47 

54015 Canis lupus 40 

46078 Hyaena striata 43 

18855 Crocuta crocuta 45 












































generalized regional effect, centered in the head 
but affecting the whole forequarters. 

Taylor (1935) has shown that the relative mass 
of the skeleton increases, whereas relative bone 
area decreases, with increasing body size in a series 
of mammals. He presented data for a series of 
forms ranging in size from the albino rat to the 
domestic cow. Surface areas of a humerus and a 
femur of an adult male giant panda and an adult 
male black bear were measured according to Tay- 
lor's method. Each bone was carefully covered 
with adhesive tape. The tape was then removed 
and weighed (the number of square centimeters 
per gram of tape having been determined). This 
method yielded highly consistent results on our 
material. The data are given in Table 5. 

In the giant panda the surface area of the hu- 
merus exceeds that of the femur by 6 per cent, 
whereas in the bear the reverse is true and the 
area of the femur is 6 per cent greater than that 
of the humerus. The surface area per gram of 
bone in the bear is exactly the same as the figure 
for man, as computed by Taylor; in the panda it 
is slightly less, because of the greater thickness of 
the walls. Taylor found that this ratio decreases 
with increasing organism size from 10.6 square 
centimeters per gram of bone in the rat to 0.69 
in the domestic cow. The bear falls in about its 

proper place in his table; in the giant panda the 
long bones are heavier than would be expected in 
a mammal of its size. 

Thickness of the walls of long bones was meas- 
ured at the center of the shaft on X-ray photo- 
graphs. The walls are notably thicker in Ailuropoda 
than in a bear of comparable size; the walls of the 
humerus are about 30 per cent thicker, those of 
the femur about 60 per cent thicker (Table 5). 
The diameter of the medullary cavity is corre- 
spondingly decreased in the panda, showing that 
the abnormal cortical thickness results from a 
slowing down of resorption rather than from in- 
creased osteoblastic activity. The ulna is about 
20 per cent thicker in Ailuropoda, and the tibia 
about 27 per cent thicker. Such increased cortical 
thickness cannot be attributed to mechanical re- 
quirements; it must instead reflect a pleiotropic 
effect or important differences in mineral metab- 
olism.. Indeed, it is well known that thickening 
the walls of a tube internally adds very little to 
the strength of the tube, whereas adding the same 
quantity of material to the outer surface does in- 
crease its strength significantly. Increase in mus- 
cle mass leads only to increase in the surface area 
of bone, not to an increase in thickness (Weiden- 
reich, 1922). 


Bone Bone Surface Area per 

weight length area gm. of bone 

gms. cm. cm. 2 cm.' 

Humerus 268.9 27.8 368.1 

Femur 251.3 28.2 344.6 

Total 520.2 712.7 1.36 


Humerus 214.6 26.3 344.6 

Femur 239.8 31.6 364.9 

Total 454.4 709.5 1.56 

Thickness of wall 

at center of shaft 






Fig. 16. Ground sections of compacta from middle of shaft of femur of Ailuropoda (left) and L'rsus gyas (X 100). 

These measurements also indicate the existence 
of regional differences in rate of bone deposition or 
resorption. The walls are significantly thicker in 
the hind leg than in corresponding bones of the 
fore leg, and the proximal segments are relatively 
thicker than the distal. 

The histological structure of the compacta of the 
long bones shows no differences between Ailuro- 
poda and Ursus (fig. 16). The bone is typically 
lamellar, with well-developed Haversian systems. 
Partly destroyed Haversian systems are numer- 
ous, and osteocytes are present in normal numbers. 
There is no evidence of retarded internal reorgani- 
zation of the bone. 

Mineral metabolism involves the skeleton. The 
normal diet of Ailuropoda contains quantities of 
certain minerals (especially silicon) that are ab- 
normal for a carnivore. It therefore seemed desir- 
able to determine the relative amounts of minerals 
in the bone. The following semi-quantitative spec- 
trochemical analysis of bone samples from wild- 
killed animals was made by the Spectrochemical 
Laboratory of the University of Chicago. Obvi- 
ously there is no significant difference between 

In summary, the skeleton of Ailuropoda is more 
dense throughout than that of Ursus, due to 

Ursus americanus Ailuropoda 

CaO --48^^ ^45^c 

MgO 0.9% 0.95% 

SiOj x> .6 X X' 

Sr --1200ppm ^1200 ppm 

Ba -- 300ppm --300ppm 

' Working curve not available, but SiOj is less than 1 %, 
probably about 0.1-0.4%. Ailuropoda has less SiOa than 
Ursus by a factor of 0.6. 

greater thickness of the compacta. This is partic- 
ularly true of the skull. The increase in quantity 
of compacta cannot be attributed to mechanical 
requirements. Regional differences in relative 
thickness of compacta indicate that rate of bone 
deposition or resorption is not uniform throughout 
the skeleton. There appears to be a gradient in 
which relative thickness of compacta decreases 


Most of the bone measurements used in this 
study, except for those of the pelvis, are given in 
Table 6. These include all measurements used in 
calculating ratios and proportions for the most im- 
portant of the species used in this study. 

Lengths of the leg bones are not greatest over- 
all length, but the much more meaningful "func- 
tional length" recommended by Howell. Func- 
tional length is the distance between the termina 


AMNH= American Museum of Natural History; CM=Carnegie Museum; CNHM = Chicago Natural History Museum; 

USNM = United States National Museum 


melanoleuea ^ g m 

CNHM w ^~ 

31128 c? 278 

34258 285 

36758 9 267 

39514 277 

47432' cfj 264 

74269' cf 308 


18390 284 


110451 9 275 

110452 9 265 

110454 280 


258423 274 

259027 d' 295 

259074 cf 282 

259401 cf 266 

259402 cf 290 

259403 9 268 

259076 9 238 

258984 213 

259400 9 243 

132095 234 

259075 cf 273 

258834 cf 273 

259029 cf 304 

258836 d" 276 

258425 d^ 

Ursus arctos 

43744 321 

47419 360 

84467 9j 241 

Ursus ggas 

49882= 9 358 

63802 d' 450 

27268 440 

27270 293 

63803 9 

Ursus americanus 

18864 256 

44725' & 273 

Ailurus fulgens 

65803' 9 112 

57193' d' 

57211' d' 

Procyon lotor 

49895 d' 116 

49227 d' 115 

49057 d" 120 

47386 d' 114 

Gulo luscus 

57196 9 158 

74056 & 

79409 d 167 

Canis lupus 

21207 9 246 

51772 & 263 

51773 9 253 

54015 9 238 



Fore Leg 

Hind Leg 

^ I _ 

C bo 

o c 




252 131 206 




ii be 

O C 



>= o 



M J3 

96 164 184 

92 164 160 

826 105 

ea c 





o 2 
J E 





















254 131 210 154 








145 . 

170 184 266 212 

276 211 





.. 173 180 267 211 

271 206 





160 157 260 199 

260 202 




164 737 

192 186 280 222 

53 290 225 





167 680 

164 164 272 ... 

57.5 280 ... 








159 794 

162 185 256 ... 

52.5 285 215 





159 . 




120 . 










124 . 




113 . 




145 . 




145 . 



149 . 


n 163 273 204 

276 203 




155 92 


93 2( 

)9 192 304 247 

73.5 355 248 





172 9; 


01 2: 

;6 220 312 255 

73.5 377 253 





95 . 

.. n 

!6 117 204 162 

249 179 



.. 2f 

53 222 330 283 

90 402 280 






352 336 415 345 109 519 355 





221 . 


1 301 386 305 105 464 315 





125 . 


)3 230 346 276 


.. 24 

17 221 327 268 

91 390 275 





106 7< 


81 1. 

50 151 244 191 

65.4 276 197 





124 81 


86 1' 

72 157 268 225 

70.5 318 232 





38.5 3' 


40.5 ( 

51 57 107 83.2 

115.5 107 

.. 3( 


40 ( 
40.5 ( 

54 58 105.2 83 

55 59 111 80 

30 115.5 104 
30.5 116.5 104.5 




5 75.5 



38.0 ' 

r5 70 110.8 110.3 

134.7 136.4 






36.5 ' 

12 65 109 112 

.. 130.5 127.5 






33 1 

52.5 59 96 95.5 

113.5 116 




61 32 


35 ( 

59 59.5 99 101 

30 118.5 121 




53.5 ! 

56 80 139 107.5 

.. 145 131.5 




90 5i 


57 ; 

iS 84 139 112 

47 148 134 




5 110 



)2.5 90 141 111 

47.5 151 135 






74 1; 

)7 107 209 213 

94 234 233 





81.6 75 


80 ll 

54 108 228 227 

255 246 





80.5 7f 


76 IE 

)7 110 216 210 

96 241 233 





76 . 

69 U 

)4 100 209 207 

95.5 230 232 


Pelvic measurements on p. 103. 
' Zoo specimen. 




articular surfaces of the bone. In most instances 
the appropriate point on the articular surface is 
either the same as that used for greatest over-all 
length or can be fixed with equal precision. In a 
few instances both ends of the radius, and the 
distal end of the tibia the shape of the articular 
surface makes it impractical to fix exactly the 
proper point from which to measure, and conse- 
quently the corresponding measurements are less 
precise. I have measured from the approximate 
center of such oblique articular surfaces. In a 
study of the present kind the advantages of com- 
paring functional lengths outweigh any disadvan- 
tages resulting from slightly lessened precision. 

For metacarpal and metatarsal length the long- 
est bone was measured, regardless of which one it 
happened to be. For Ailiiropoda this is meta- 
carpal 4 and metatarsal 5; for all other species in 
the table it is metacarpal 4 and metatarsal 4. 

In measuring the scapula, height was measured 
along the spine, from the glenoid cavity to the ver- 
tebral border. Breadth is the distance between 
two lines that are parallel to the spine and intersect 
the anterior and posterior borders of the scapula. 

Length of the vertebral column was measured 
from the anterior border of the ventral arch of the 
atlas to the posterior border of the centrum of the 
last lumbar. The column of the smaller species 
was still articulated by the natural ligaments, and 
length was measured along the cui-ves of the artic- 
ulated spine. For the larger species, in which the 
bones were disarticulated, the vertebrae were laid 
out in proper sequence on a flat surface, following 
the natural curves of the backbone. Length was 
then measured along the cui'ves. 

All measurements are in millimeters. 

Cranial Capacity 

Cranial capacity was measured by filling the 
cranial cavity with dry millet seed and then meas- 
uring the volume of the millet seed in a gi'aduated 
cylinder. Ten trials were made for each skull, and 
the trial that gave the highest reading was re- 
garded as the closest approximation to the true 
cranial capacity. The difference between the low- 
est and highest reading averaged less than 4 per 
cent for all skulls, and in no case was it greater 
than 6 per cent. 

In cranial capacity, as in other basic size charac- 
teristics, the giant panda resembles the American 
black bear very closely. 


The skull of Ailuropoda is characterized by its 
great density and by extreme development of the 
sagittal crest and expansion of the zygomatic 


Ailuropoda melanoleuca 


31128 d" 320 

36758 9 288 

39514 282 

Mean 297 

Ursus americanus 

16027 280 

18146 261 

18151 310 

18152 d' 313 

51641 cf 312 

68178 d' 327 

Mean 300 

Ursus arctos 

25713 412 

81509 335 

arches in comparison with other arctoid carni- 
vores. These features are associated with very 
powerful dentition and masticatory musculature. 
The cranial skeleton and to a lesser extent the 
facial skeleton are profoundly modified by the de- 
mands of mastication. The cranium gives the 
impression of having been subjected to plastic de- 
formation by the temporal muscle, which has at- 
tempted, so to speak, to achieve maximal volume. 
Expanding to the limit in all directions, the tem- 
poral muscle has displaced and compressed sur- 
rounding structures to the mechanical limit on the 
one hand, and to the limits of functional tolerance 
on the other. The face, on the contrary, is rela- 
tively unmodified except where it is hafted to the 
cranium, and in the expansion of the alveolar area 
in association with the enlarged cheek teeth. 

The sutures between bones are almost com- 
pletely obliterated in adult skulls. The bones of 
the cranium are much thickened. In the parietal 
region total thickness is 5 mm. (two individuals), 
whereas in a skull of Ursus arctos the bone in the 
same region measures 2.3 mm. and in a skull of 
Ursus americanus only 1.7. The increased thick- 
ness in the panda involves only the outer lamina 
of the bone; the inner lamina is no thicker than in 
the bears. This is likewise true of the basicranial 
region: in a sectioned skull of Ailuropoda the outer 
lamina of the sphenoid is 2.6 mm. thick below the 
sella, whereas in a skull of Ursus americanus it is 
only 0.9 mm. The difference is similar in the man- 
dible; at the level of the posterior border of M2 the 
body is 12.2 mm. thick from the mandibular canal 
to the external surface of the bone in Ailuropoda 
(3.6 mm. in Ursus americanus), and 5 mm. from 



the mandibular canal to the inner surface (3.4 mm. 
in Ursus americanus) . 

The bones of the face, on the contrary, are little 
if any thicker in Ailuropoda than in Ursus. 

Ailurus agrees more or less closely with the giant 
panda in skull proportions. As was pointed out 
by the earliest investigators, there is also a super- 
ficial resemblance to the hyenas, associated with 
similar masticatory requirements. 

In the following description the skull of the Euro- 
pean brown bear {Ursus arctos) is used as a basis 
for comparison. Four adult skulls of Ailuropoda 
in the collection of Chicago Natural History Mu- 
seum were available for detailed examination. One 
of these (no. 36758) was bisected in the sagittal 
plane and cut frontally through the right auditory 
region. None of these skulls shows the sutures; 
these were determined on a young female skull bor- 
rowed from the U. S. National Museum (USNM 
No. 259076). 

A. The Skull as a Whole 

(1) Dorsal View 

In dorsal view (norma verticalis) the skull of 
Ailuropoda is dominated by the tremendously ex- 
panded zygomatic arches. These form nearly a 
perfect circle, compared with the triangular out- 
line in Ursus and other carnivores. The primary 
result of this expansion is to increase the volume 
of the anterior third of the temporal fossa. 

The muzzle appears to be shortened and has 
often been so described. This is not true, how- 
ever; the pre-optic length is nearly identical in 
Ailuropoda and Ursus. The muzzle is no wider 
anteriorly than in Ursus; its borders divei'ge pos- 
teriorly instead of being nearly parallel as in Ursus, 
but this merely reflects the broader cheek teeth of 
the panda. The postorbital process on the frontal 
is scarcely indicated, and in one skull it is absent. 
The alveolar pocket of the tremendous second up- 
per molar is conspicuous immediately behind the 
floor of the orbit; this is invisible from above in 
Ursus but is equally prominent in Ailurus and 
Procyon. The interorbital diameter is not greater 
in the bears than in the giant panda, but the post- 
orbital constriction is more pronounced in the 
panda, and this increases the volume of the ante- 
rior part of the temporal fossa. This constriction 
is reflected in the form of the brain, which in Ailu- 
ropoda is much narrower anteriorly, in both trans- 
verse and vertical diameters, than in Ursus. The 
maximal cranial diameter is about 10 per cent 
greater in Ailuropoda, and this, together with the 
greater postorbital constriction, gives a character- 
istic hourglass outline to the skull in dorsal view. 

Thus the volume of the anterior part of the tem- 
poral fossa has been increased by expansion both 
laterally and medially, whereas the volume of the 
posterior part of this fossa has been far less affected. 
The skull of Ailurus exhibits a similar increase in 
the volume of the anterior part of the temporal 
fossa. In the hyenas, in which the volume of the 
temporal fossa is also notably increased, it is the 
posterior part of the fossa that is expanded by pos- 
terior extension. The reasons for this difference 
between herbivorous and carnivorous forms are 
discussed later (see p. 155). 

The horizontal shelf formed by the posterior root 
of the zygoma is not wider in Ailuropoda than in 
Ursus, but it is carried farther forward along the 
ventral border of the arch, thus increasing the ar- 
ticular surface of the glenoid cavity on its inferior 
surface and the area of origin of the zygomatico- 
mandibular muscle on its superior surface. There 
are conspicuous muscle rugae, barely indicated in 
Ursus, on the inner face of the posterior half of 
the zygoma. 

The sagittal crest appears to have a conspicuous 
sagittal suture, but the juvenile skull shows that 
this is actually the first suture to close, and that the 
"suture" in the adult results from secondary up- 
growth of the frontals and parietals. The smoothly 
curved outline of the lambdoidal crest contrasts 
with the sinuous crest seen in Ursus, Ailurus, and 
Procyon; it reflects the posterior expansion of the 
temporal fossa. 

(2) Lateral View 

In norma lateralis (fig. 17) the skull of the panda 
contrasts sharply with the bears in the facial angle 
as measured from the Frankfort horizontal. In 
Ursus the toothrow is depressed from the Frank- 
fort horizontal at an angle of about 22, whereas 
in Ailuropoda these two lines are nearly parallel. 
Reference to the ventral axis of the braincase re- 
veals, however, that the angle formed by the tooth- 
row is nearly identical in Ailuropoda and Ursus. 
Actually the position of the orbit is depressed in 
Ailuropoda, as a part of the over-all expansion of 
the temporal fossa, and therefore the Frankfort 
horizontal is misleading in this animal. 

The strongly convex dorsal contour of the skull 
increases the area of the temporal fossa dorsally. 
At the same time the vertical diameter of the mas- 
seteric fossa of the mandible is much greater than 
in Ursus. Thus the whole postorbital part of the 
skull appears expanded, and the skull has a trape- 
zoidal outline when viewed from the side. 

The margin of the nasal aperture in the panda 
curves sharply dorsally, its dorsal third lying at a 
right angle to the long axis of the skull. Behind 



Crista orbitalisi sup. 

For. ethmoideum 

For. aptiaim 

Fissura orbiialis 

M. temporalis 

Prof postorbitalis IfrotUalis] 

Fossa musculans 
Fossa lammalis 

For. injTaorbitalis 

I M pterygoideus int 

M pterygoideus ext 

For. ovale 
Can. palatina posl. mitior 
Crista orbitalis inj. 

For. spkeuopatatinum * 
Can. pterygopalatinum 

Meatus aruxtieus 

Proc. paroccipitalis 

Proc. masloideus 
For. poslgtenoideum 

Fig. 17. Skull of Ailuropoda seen from left side (norma lateralis). 

the nasal aperture the surface of the nasal and 
premaxillary bones shows a pattern of shallow 
grooves, in which lie the terminal ramifications of 
the infraorbital and external nasal vessels, and 
small foramina through which nutrient twigs from 
these vessels entered the bone. The infraorbital 
foramen is small and less elliptical in cross section 
than in Ursus. Below and in front of the orbit the 
anterior root of the zygomatic arch bulges forward 
conspicuously. The postorbital process of the jugal 
is less prominent than in the bears, in which it 
reaches its maximal development among the Arc- 

The temporal fossa in Ailuropoda is relatively 
enormous, in keeping with the size of the temporal 
muscle. Its anteroventral boundary, separating it 
from the orbit, is well marked by the superior or- 
bital ridge. Anteroventrally the fossa is provided 
with about three well-developed muscle ridges, 
paralleling the superior orbital ridge; in Ursus cor- 
responding muscle ridges are present, but scarcely 
more than indicated; in Ailurus there is a single 
ridge in old adults. In the upper posterior part 
of the fossa, near the juncture of the sagittal and 
lambdoidal crests, is a conspicuous nutrient fora- 
men; a similar foramen is present in the bears but 
is lacking in other arctoids. 

In Ailuropoda the infratemporal fossa is sepa- 
rated from the orbit above by the well-marked 
inferior orbital ridge throughout most of its length. 
Behind the orbital fissure it is separated from the 
temporal fossa by an indistinct elevation extend- 
ing from the superior orbital ridge in front of the 
orbital fissure to the anterior lip of the glenoid 
fossa. The infratemporal fossa is relatively small. 
The anterior half of the infratemporal fossa con- 
tains the entrance to the infraorbital foramen, the 
common foramen for the sphenopalatine (spheno- 
palatine artery and nerve; nasal branches of sphen- 
opalatine ganglion) and pterygopalatine (descend- 
ing palatine artery and nerve) canals. These exit 
by separate foramina in Ursus and other carni- 
vores, but are combined in Ailurus; they have 
undoubtedly been crowded together in the two 
pandas by the enlarged maxillary tuberosity. The 
posterior half of the fossa, from which the ptery- 
goid muscles arise, exhibits muscle rugosities. The 
areas of origin of the pterygoid muscles are sharply 
marked on the bone. The area of pterygoid origin 
is much reduced, both vertically and horizontally, 
as compared with Ursus. 

In Ailuropoda the foramen rotundum (maxillary 
branch of trigeminus) is confluent with the orbital 
fissure, although the identity of the two openings 
is usually indicated by a low ridge and on one side 



of one skull there is a paper-thin partition sepa- 
rating them. This is a feature in which Ailuro- 
poda differs from all other canoids; it is associated 
with the general crowding together of non-masti- 
catory structures in the skull. Ailuropoda also 
lacks an alisphenoid canal, which is present in Ur- 
sus. In forms having an alisphenoid canal (Cani- 
dae, Ursidae, Ailurus) the foramen rotundum is 
situated within the canal; in Ailurus it is sepa- 
rated from the orbital fissure only by a thin sep- 
tum, but the two are some distance apart in the 
dogs and bears. In forms lacking an alisphenoid 
canal (Procyonidae, Mustelidae), the foramen and 
the orbital fissure are separated by a thin septum. 
In Ursus the vertical diameter of the infratem- 
poral fossa is much greater than in Ailuropoda. 
This is also true in Cants but not in the procyo- 
nids, in which the relatively much larger orbit 
encroaches on it. Reduction of the infratemporal 
fossa in Ailuropoda is correlated with the more 
ventral position of the eye, and thus secondarily 
with the ventral expansion of the temporal fossa. 
The tremendously enlarged maxillary tuberosity, 
associated with the enlargement of the molar teeth, 
further reduces the volume of the fossa. 

The Orbit. The orbit in Ailuropoda, as in 
other arctoids, is poorly defined on the skull ; only 
the medial wall is entire. The orbit is an elongate 
cone with the base formed by the incomplete bony 
ring of the eye socket (completed by the orbital 
ligament), and the apex by the orbital fissure. On 
its medial wall the dorsal and ventral boundaries, 
separating the orbit from the temporal fossa above 
and the infratemporal fossa below, are well marked 
by the superior and inferior orbital ridges. These 
ridges are less prominent in other arctoids. Else- 
where the boundaries of the orbit are poorly 
marked on the skull; because of the feebly devel- 
oped postorbital processes on both frontal and 
jugal, even the anterior limits are poorly indicated 
in Ailuropoda as compared with those of other 

The orbit is rotated slightly ventrad as com- 
pared with that of Ursus. Its long axis (from the 
orbital fissure to the center of the eye socket) 
forms an angle of about 10 with the long axis of 
the skull in Ursus, whereas in Ailuropoda the axes 
are parallel. At the ventral boundary of the or- 
bital opening there is a prominent crescent-shaped 
depression, which in life lodges a cushion of extra- 
ocular fat. 

The lacrimal fossa, which lodges the lacrimal 
sac, is a large funnel-shaped pit at the antero- 
medial corner of the orbit. The nasolacrimal canal 
opens into the bottom of the fossa. The canal is 

only a millimeter or two long, opening almost at 
once into the nasal cavity, immediately beneath 
the posterior end of the maxilloturbinal crest. Ur- 
sus is unique in having the nasolacrimal canal open 
into the maxillary sinus. Immediately behind the 
lacrimal fossa is a shallow pit, the fossa muscu- 
laris, in which the inferior oblique muscle of the 
eye arises; the thin floor of this pit is usually broken 
through on dry skulls, and then resembles a fora- 
men. In Ursus and other arctoids the lacrimal 
fossa is much smaller than in Ailuropoda, but 
otherwise similar. The fossa muscularis in Ailu- 
rus is very similar to that of Ailuropoda; in Ursus 
it is relatively enormous as large as the lacrimal 
fossa and several millimeters deep. The fossa 
muscularis is completely wanting in the Canidae 
and Procyonidae. 

Three foramina in a row, about equidistant from 
each other, pierce the medial wall of the posterior 
half of the orbit. Each leads into the cranial fossa 
via a short canal directed posteriorly, medially, 
and ventrally. The most anterior is the ethmoi- 
dal foramen, which conducts the external eth- 
moidal nerves and vessels into the anterior cranial 
fossa. Behind this is the optic foramen (optic 
nerve, ophthalmic vessels), and most posteriorly 
and much the largest is the combined orbital 
fissure and foramen rotundum (oculomotor, 
trigeminal, trochlear, and abducens nerves; anas- 
tomotic and accessory meningeal arteries; orbital 
vein). Except for the confiuence of the orbital 
fissure and foramen rotundum, which is peculiar 
to Ailuropoda, the pattern of these three foramina 
is similar in all arctoids. Most variable is the eth- 
moidal foramen, which differs in size among the 
genera and may be characteristically multiple 
(e.g., in Canis). The foramen ovale, in forms in 
which it is separate from the orbital fissure, trans- 
mits the third (mandibular) branch of the tri- 
geminus and the middle meningeal artery. 

The zygomatic arch functions in the origin of 
the temporal fascia from its superior border, the 
temporal and zygomaticomandibular muscles from 
its internal surface, and the masseter from its in- 
ferior surface. Its anterior root lies over the first 
upper molar (over the second molar in Ursus), its 
posterior root over the glenoid fossa; the arch is 
therefore important in resolving the forces gener- 
ated during mastication. As pointed out above, 
the anterior part of the arch is expanded laterally, 
which increases the volume of the anterior third 
of the temporal fossa. In lateral view the arch is 
straighter than in Ursus and other arctoids. Its 
posterior half is much extended dorsally, which 
increases the available area of origin for the zygo- 
maticomandibularis muscle. The whole structure 



For. nuiritium 

For. palatinum ant. med. 

Fossa palatina 

For. palatinum ant. 

Sulcus palatinus 

For. palatinum post. 

For. palatinum post 

For. palatinum 
Spina nasalis post: 

Fotsa nasopharyngea 

Semican. M. tensor- 

Semican. tubae 

, . audilirae 
Can. chordae tympani- 

For. postglenoideum 

For. lacerum post. 

Proc. mastoideus 

M. masseter 

M. z>'gomatico- 


Incisura palatina 

M. pterj'goideus 

For. ovale 

Fossa }nandiimlaris 



Proc. postglenoideus 
-.^featiis acusticus at. 
M. stemomastoideus 

For. slylomasloideum 

Fossa hyoidea 

Proc. paroccipitalis 

M. digastricus 

For. hypoglossum 
For. mastoideum 

Capsula articularis 

M. longus capitis 

M. rectus capitis ventralis 

Fig. 18. Skull of Ailuropoda seen from below {norma ventralis). 

is extraordinarily massive. The anterior i"oot is 
bulky but relatively thin-walled, since it is exten- 
sively excavated internally by the maxillary sinus. 
It bulges forward anteriorly, and posteriorly forms 
the floor of the orbit for a short distance before 
passing into the alveolar pocket of the second 
molar; the infraorbital canal is thus considerably 
lengthened posteriorly. The posterior root of the 
arch is expanded posteriorly to accommodate the 
large mandibular (glenoid) fossa; it has encroached 
considerably on the space between the postglenoid 
and mastoid processes, in which the external audi- 
tory meatus lies, and the meatus is consequently 
much compressed. 

(3) Ventral View 

In ventral view {norma ventralis, fig. 18) the 
facial region is dominated by the massive denti- 
tion, the cranial region by the immense mandib- 
ular fossae. 

It has often been stated that the palate extends 
farther posteriorly in Ursus than in Ailuropoda, 
but this is an illusion created by the enlarged teeth 
of the latter. In relation to the anterior end of the 
braincase, the palate actually extends farther pos- 
teriorly in the panda. The lateral borders of the 
palate are parallel, as in Urstis; in other arctoids 
they diverge posteriorly. The anterior palatine 
foramina, which transmit nerves, vessels, and the 



incisive duct, are situated in the posterior part of 
the large palatine fossa as in other arctoids. There 
is a median nutrient foramen between the fossae 
anteriorly, and a small median anterior pala- 
tine foramen (large in Ursus and procyonids) 
opening into a minute canal that arches back 
through the anterior part of the bony septum, lies 
between the fossae posteriorly. A shallow gi'oove, 
the sulcus palatinus in which the anterior pala- 
tine artery lay, connects each anterior palatine 
foramen with the posterior palatine foramen, 
which is situated at the level of the first molar 
and represents the outlet of the pterygopalatine 
canal. Immediately behind the posterior palatine 
foramen, at the level of the second molar, is a 
much smaller opening, the foramen palatina 
posterior minor. In other arctoid carnivores 
this foramen (often several) connects directly with 
the pterygopalatine canal, but in Ailuropoda, be- 
cause of the immense development of the second 
molar, its canal comes to the surface briefly as a 
groove on the lateral wall of the choana (fig. 20), 
then re-enters the bone and finally emerges several 
millimeters behind the entrance to the pterygo- 
palatine canal (fig. 18). A shallow groove, not 
seen in other arctoids, passes posteriorly from the 
posterior palatine foramen to the palatine notch 
(occasionally closed to form a foramen). As in 
other arctoids, the posterior border of the palate 
bears a prominent median spine. 

The choanae (posterior nasal apertures) are 
separate, the bony septum formed by the vomer 
extending to (dorsally beyond) the posterior bor- 
der of the palate. There is much variation in the 
posterior extent of this septum in arctoids. In 
Ursus, representing the opposite extreme from 
Ailuropoda, the septum ends far anteriorly at 
about the juncture of the middle and posterior 
thirds of the palate, and the posterior third of the 
nasopharyngeal meatus is accordingly undivided. 
Other genera are intermediate between Ailuropoda 
and Ursus in the posterior extent of the septum. 

The nasopharyngeal fossa, situated behind 
the choanae and between the pterygoid processes, 
is absolutely and relatively wider than in Ursus. 
The anterior half of the roof of the fossa bears a 
prominent median keel, the presence and degree 
of development of which varies with the posterior 
extent of the septum. The pterygoid processes 
present nothing unusual. 

The mandibular (glenoid) fossa is the key 
to other modifications of the skull in Ailuropoda. 
The transverse cylindrical mandibular articulation, 
limiting jaw action to a simple hinge movement 
vertically and a very restricted lateral move- 
ment horizontally, is a carnivore heritage that is 
ill-adapted to the feeding habits of this animal. 

In Ailuropoda the transverse diameter of the fossa 
is much greater than in other arctoids. This di- 
mension amounts to 30 per cent of the basal length 
of the skull, while in other arctoids it ranges be- 
tween 15 and 20 per cent, only slightly exceeding 
20 per cent even in Ailurus. The increase in the 
length of the fossa in Ailuropoda has taken place 
wholly in the lateral direction; the medial ends of 
the two mandibular fossae are no closer together 
than in Ursus. 

The articular surfaces of the medial and lateral 
halves of the fossa in Ailuropoda are in quite dif- 
ferent planes. In the medial half the articular 
surface is almost wholly posterior (against the an- 
terior face of the postglenoid process), while 
laterally the articulation is wholly dorsal (against 
the root of the zygomatic arch). Transition be- 
tween these two planes is gradual, producing a 
spiral fossa twisted through 90. The form of the 
fossa is similar, though less extreme, in Ursus and 
other arctoids. The mechanical significance of this 
arrangement is discussed below. 

The Basioccipital Region. The basioccipital 
region in Ailuropoda, like other parts of the skull 
not directly associated with mastication, is com- 
pressed. It is somewhat shorter (about 5 per cent) 
anteroposteriorly than in Ursus, and since in addi- 
tion the postglenoid process is expanded posteri- 
orly and medially, the structures in this region 
(foramina, auditory bulla) are considerably crowded 
together. It is noteworthy that the areas of attach- 
ment of the rectus capitis and longus capitis mus- 
cles have maintained their size, partly at the ex- 
pense of surrounding structures. 

The foramen ovale (mandibular branch of tri- 
geminus; middle meningeal artery) occupies its 
usual position opposite the anterointernal corner 
of the mandibular fossa. There is no foramen 
spinosum, since as in carnivores in general the 
middle meningeal artery passes through the fora- 
men ovale; the foramen spinosum is sometimes 
present in Canis (Ellenberger and Baum, 1943). A 
small foramen situated dorsomedially at the mouth 
of the foramen ovale opens into a canal that runs 
medially and anteriorly through the cancellous 
bone of the basicranium to a point beneath the 
hypophyseal fossa, where it meets its mate from 
the opposite side. This canal apparently contained 
a nutrient vessel; its counterpart was found in 
Ursus, but not in other arctoids. 

A single large opening, the entrance to the ca- 
nalis musculotubarius, is situated at the ante- 
romedial corner of the bulla. The canal is partly 
divided by a prominent ventral ridge into a lateral 
semicanalis M. tensoris tympani and a medial 



semicanalis tubae auditivae. The foramen 
lacerum medium, which normally lies just medial 
to the musculotubular canal, is usually wanting 
in Ailuropoda.^ 

Laterad of the musculotubular canal, at the 
medial border of the postglenoid process, is an 
irregular longitudinal slit, the canalis chordae 
tympani (canal of Hugier), which transmits the 
chorda tympani nerve. The position of this open- 
ing is the same as in Ursus (and arctoids in gen- 
eral), but in Ailuropoda it is somewhat deformed 
by the enlarged postglenoid process. 

The foramen lacerum posterior, which in 
Ailuropoda includes the carotid foramen, is situ- 
ated at the posteromedial corner of the bulla. It 
transmits the ninth, tenth, and eleventh cranial 
nerves, the internal carotid artery, and veins from 
the transverse and inferior petrosal sinuses. The 
posterior carotid foramen, through which the 
internal carotid enters the skull, is situated in the 
anterior part of the lacerated foramen ; this is true 
also of the Ursidae and Ailurus. In other carni- 
vores (Procyonidae, Mustelidae) the carotid fora- 
men is removed from the lacerated foramen, lying 
anterior to the latter along the medial wall of the 
bulla. Segall (1943) found the positional relations 
of the posterior carotid foramen to be consistently 
correlated with recognized family groupings among 
the Arctoidea. 

The postglenoid foramen, in the posterior 
wall of the postglenoid process near the external 
auditory meatus, connects the temporal sinus (in- 
tracranial) with the internal facial vein (extra- 
cranial). The foramen is smaller and more later- 
ally situated than in Ursus. 

Laterad of the posterior lacerated foramen, and 
bounded by the bulla anteriorly and medially, the 
mastoid process laterally, and the paroccipital 
process posteriorly, is a pit. This pit, a conspic- 
uous element of the basicranium, is not present in 
man and does not seem to have been named. I 
propose to call it the hyojugular fossa (fossa 
hyojugularis) . The stylomastoid foramen (fa- 
cial nerve, auricular branch of vagus nerve, stylo- 
mastoid artery) lies at the anterolateral comer of 
the fossa; a conspicuous groove, which lodges the 

' In carnivores the foramen lacerum medium (anterior of 
some authors) transmits chiefly a venous communication 
between the pharyngeal veins extracranially and the caver- 
nous sinus intracranially. It also carries an anastomotic 
twig between the ascending pharyngeal artery (extracranial) 
and the internal carotid; this anastomotic artery is of con- 
siderable size in the cats, but in the pandas, bears, and pro- 
cyonids it is minute or absent. In Ursus the foramen lac- 
erum medium is larger than the canalis musculotubarius, 
and two openings, the outlet of the carotid canal posteriorly 
and the entrance to the cavernous sinus anteriorly, are vis- 
ible within it. 

facial nerve, runs laterad and ventrad from the 
foramen to pass between the postglenoid and mas- 
toid processes. The hyoid fossa, at the bottom 
of which the hyoid articulates with the skull, lies 
in the fossa immediately behind and mesad of the 
stylomastoid foramen, from which it is separated 
by a thin wall. Farther posteriorly (sometimes on 
the crest connecting the paroccipital process with 
the bulla) is a foramen that transmits a branch of 
the internal jugular vein that passes to the infe- 
rior petrosal sinus. 

The hyojugular fossa is almost identical in Ur- 
sus, except that it is deeper and more extensive 
posteriorly. In Ailurv^ it is widely open poste- 
riorly, between the mastoid and paroccipital proc- 
esses. The fossa tends to disappear when the bulla 
is gi-eatly inflated (in procyonids, except Nasua), 
but it is present in Cants. 

The hypoglossal (condyloid) foramen (hypo- 
glossal nerve, posterior meningeal artery) lies be- 
hind and slightly mesad of the foramen lacerum 
posterior. In Ursus it is usually connected with 
the foramen lacerum posterior by a deep groove. 
A similar groove is present in Ailurus but not in 
other arctoids. 

The mastoid process functions in the insertion 
of the lateral flexors of the head on its posterior 
surface, and in the origin of the digastric muscle 
on its medial surface. The process closely resem- 
bles the corresponding structure in Ursus but pro- 
jects much farther ventrally than in the latter. 
It is a powerful tongue-like projection, directed 
ventrally and anteriorly, extending far below the 
auditory meatus. The process is strikingly similar 
in Procyon but is much smaller in other procyo- 
nids. It is also small in Ailurus and Canis. 

The paroccipital process, which functions in 
the origin of the digastric muscle, is much smaller 
than the mastoid. As in Ursus, it is a peg-like 
projection connected by prominent ridges with the 
mastoid process laterally and the bulla antero- 
medially. In forms with inflated bullae (e.g., Pro- 
cyon, Canis) the bulla rests against the anterior 
face of the paroccipital process. 

The bulla is described in connection with the 
auditory region (p. 318). 

(4) Posterior View 

In posterior view (fig. 19) the outline of the skull 
has the form of a smooth arch; the constriction 
above the mastoid process seen in Ursus and other 
arctoids is not evident. To this extent the nuchal 
area is increased in Ailuropoda. The posterior sur- 
face of the skull serves for the insertion of the 
elevators and lateral flexors of the head and bears 
the occipital condyles. 

M. clavotrapezius 
M rhomboideus 
M. splenius 
M. rectus capitis dorsalis medius- 
Crista lamboidi 

Mm. biventer cervicus et complexus 

M rectus capitis dorsalis major 

For. masioideum 

Proe. muloideus 

Proe, paroccxpilalis' 

M. rectus capitis dorsalis minor 

M. cleidomastoideus 

Membrana atlantooccipilalis poelerior 
Capsula articuiaris 

M. obliquus capitis anterior 
M. stemomastoideus 

M. rectus capitis lateralis 
M. longissimus capitis 
'Membrana teclaria \ ^^SIP' fcaput ventralis) 

~^M. stemomastoideus 

'M. digastricus 

Fig. 19. Skull of Ailuropoda seen from rear. 

Sinus 1 
Far. efhmoideum 

Fossa eerebralis 

Sinus 2 

Fossa olfactoria 
iMmina eribrosa 

Sinus I, 

Tentorium otaeum 

Fossa cerebelli 
Sinus sagitUUit 


inus transKTSut 
(pars supj 



For. paUuinum 

For. palalinum 
med. anl. 


(pars tn/J 

Fossa hvpophyseos' 

Dorsum seUae ' 

'iij- alare 

For. condyloideum 
Porus aeusticus int. 

Fig. 20. Sagittal section of skull of Ailuropoda slightly to left of midline. 




In Ailuropoda the peripheral area of muscular 
attachment is sharply set off from the central con- 
dylar area by a ridge that runs dorsad from the 
medial border of the paroccipital process and then 
curves mesad above the condyle. This ridge marks 
the attachment of the atlanto-occipital articular 
membrane; it is not so well marked in other arct- 
oids. A median nuchal line, prominent in most 
arctoids, runs vertically from the foramen mag- 
num to the junction of the lambdoidal and sagittal 
crests, separating the nuchal area into right and 
left halves. 

The area of muscular attachment is rugose, and 
is punctured with numerous nutrient foramina. A 
conspicuous scar near the dorsal midline, seen in 
all except the smallest arctoids, marks the insertion 
of the biventer cervicis and complexus muscles. 
The mastoid foramen (meningeal branch of pos- 
terior auricular artery; vein from transverse sinus) 
lies directly above the paroccipital process. 

The condylar area is relatively smooth, and the 
condyloid fossae present an excavated appearance 
because of the posterior position of the paroccipital 
and mastoid processes. The occipital condyles 
are more obliquely placed than in Ursus, their 
long axis forming an angle of about 45 with the 
vertical compared with about 25 in Ursus. The 
condylar area is interrupted at the ventral border 
of the foramen magnum, as it is in Ailurus. This 
condition is usual, but not invariable, in Ursus. 
In procyonids and canids the condylar area is al- 
ways carried across as a narrow isthmus below the 
foramen magnum. In Ailuropoda the form of 
the foramen magnum varies from a transverse 
oval to almost square. 

(5) Internal View 

A sagittal section through the skull of Ailuro- 
poda (fig. 20) reveals the nasal cavity, the sinuses, 
and the cranial cavity. 

Nasal Cavity. The nasal cavity is high, nar- 
row, and elongate in the arctoid Carnivora. This 
is especially evident in the Ursidae. In Ailuropoda 
the nasal cavity is slightly higher (index .14) than 
in Ursus (index .10-.12), and slightly shorter (in- 
dex .41 vs. .45-.51). In Ailurus the relative height 
is the same as in Ailuropoda, but the cavity is 
shorter (index .37). 

The structures of chief interest in the nasal cav- 
ity are the turbinates, consisting of three elements: 
the maxilloturbinals, the nasoturbinals, and the 
ethmoturbinals. These complex structures were 
described in detail for various Carnivora by Paulli 
(1900), and again by Anthony and Iliesco (1926). 
In some respects, particularly with reference to 
the ethmoturbinals, it is difficult to reconcile these 

two studies. Paulli worked chiefiy from frontal 
sections of the skull, made immediately anterior 
to the cribriform plate, while Anthony and Iliesco 
apparently worked from sagittal sections of the 

The maxilloturbinal (fig. 20) is situated in the 
anterior part of the nasal cavity, which it nearly 
fills. It is kidney-shaped, much higher (45 mm.) 
than long (30 mm.), and its vertical axis is inclined 
posteriorly at an angle of 20. It lies entirely an- 
terior to the ethmoturbinals. The maxilloturbinal 
is attached to the lateral wall of the nasal cavity 
by a single long basal lamella, which runs antero- 
posteriorly in a slightly sinuous line about parallel 
to the long axis of the skull. The line of attach- 
ment extends on the premaxilla and maxilla from 
near the anterior nasal aperture to a point several 
millimeters caudad of the anterior border of the 
maxillary sinus. The basal lamella promptly 
breaks up into an extremely complex mass of rami- 
fying branches that make up the body of the 

In the Ursidae, according to Anthony and Ili- 
esco, the maxilloturbinal is characterized by its 
great dorsoventral diameter and its extremely rich 
ramification; Ailuropoda exceeds Ursus in both. 
According to these authors the Mustelidae resem- 
ble the bears in the height of the maxilloturbinal 
and its degree of ramification, although it may be 
added that in these the upper ethmoturbinals over- 
hang the maxilloturbinal. In the Canidae and 
Procyonidae this element is much longer than 
high, is less complex, and is overhung by the upper 
ethmoturbinals. In Ailurus it is high (height/ 
length ratio 1) as in Ailuropoda and the Ursidae 
but is overhung by the ethmoturbinals; its lamina 
of origin differs from that of all other arctoids in 
curving ventrad at a right angle to the axis of the 
skull, reaching the floor of the nasal cavity at the 
level of PMl 

The nasoturbinal in Ailuropoda (fig. 20) is, as 
in other arctoids, an elongate structure situated 
in the dorsal part of the nasal cavity. It arises 
from the upper part of the anterior face of the crib- 
riform plate and extends forward, above the maxil- 
loturbinal, to within a few millimeters of the ante- 
rior nasal aperture. 

The ethmoturbinal (figs. 20, 21) is very sim- 
ilar to that of Ursus. As in other carnivores it is 
composed of a medial series of plate-like out- 
growths (endoturbinals, internal ethmoturbinals) 
from the anterior face of the cribriform plate, and 
a similar more lateral series (ectoturbinals, exter- 
nal ethmoturbinals), that together fill the posterior 
part of the nasal cavity. The whole structure 
constitutes the ethmoidal labyrinth. The rela- 







Fig. 21. Frontal section through turbinates, just anterior to cribriform plate. Roman numerals refer to endoturbinals, 
Arabic numerals to ectoturbinals. (Diagrams for Ursus and Nasua from Paulli.) 

tions of these elements are best seen on a frontal 
section made immediately in front of the cribri- 
form plate (fig. 21). 

The endoturbinals number four, the typical 
number for all Carnivora except the Procyonidae. 
In the latter, according to Paulli, the fourth endo- 
turbinal has split into three to produce a total of 
six. It is impossible to decide, on the basis of the 
section available to me, how many olfactory scrolls 
the endoturbinals divide into in Ailuropoda. It is 
apparent, however, that the complexity is greater 
than in the Ursidae, in which there are seven. 

The ectoturbinals number nine, as in the Ursi- 
dae and Procyonidae. Except for Meles, in which 
there are 10 (Paulli), this is the largest number 
known for any carnivore. Ailuropoda further re- 
sembles the Ursidae and differs from the Procyoni- 
dae in having the first eight ectoturbinals situated 
between endoturbinals I and II, and in having the 
ectoturbinals arranged in a median and an exter- 
nal series, a long one alternating with a short one 
to produce the two series. 

Anthony and Iliesco state that there are seven 
or eight endoturbinals and that "on peut estimer 
que les Ours possedent plus de 40 ethmoturbinaux 
externes." These figures are obviously based on 
a quite different, and I believe less careful, inter- 
pretation than Paulli 's. 

Paranasal Sinuses. The paranasal sinuses 
are evaginations of the nasal cavity that invade 
and pneumatize the surrounding bones of the 
skull, remaining in communication with the nasal 
cavity through the relatively narrow ostia. The 
cavities lying on either side of the dorsal midline 
are separated by a vertical median septum. The 
occurrence, extent, and relations of the individual 
sinus cavities vary greatly among mammals, often 
even among individuals, and hence topography is 
an unsafe guide to homologies. The cavity in the 
frontal bone of many mammals, for example, is 
not always homologous, and therefore cannot be 
indiscriminately referred to as a "frontal sinus." 
Paulli found that the relations of the ostia to the 
ethmoidal elements are constant, as would be ex- 



pected from the ontogenetic history, and he there- 
fore based his homologies on these. He rejected 
the descriptive terminology of hviman anatomy as 
unusable in comparative studies, and substituted 
a system of numbers for all except the maxillary 
sinus. His terminology has been followed here. 

The dorsal sinuses are enormous in Ailuropoda 
(fig. 20), far exceeding those of any other carnivore. 
At the dorsal midline they separate the relatively 
thin true roof (inner lamina) of the cranial cavity 
from a much heavier false roof (outer lamina) situ- 
ated above it. Intrusion of the sinuses into the 
supracranial area greatly increases the area of the 
temporal fossa. 

The relations of the ostia to the ethmoidal ele- 
ments cannot be determined without cutting the 
latter away. The single bisected skull available 
to me could not be mutilated in this way, but simi- 
larity between the sinuses of Ailuropoda and Ur- 
sus is so close that there can be no doubt as to 
nomenclature. As in Ursus, there is no communi- 
cation between the sinuses. 

Sinus I, which occupies the frontal region, is 
much longer, higher, and wider than in Ursus. 
It is responsible for the characteristic convex fore- 
head of the giant panda. The posterior wall of 
the cavity lies at the level of the postorbital proc- 
ess, as in Ursus, and from here the sinus extends 
forward into the base of the nasals. Its lateral 
wall is formed by the outer wall of the skull. The 
large oval ostium in the floor of the cavity opens 
into the nasal cavity just anterior to the first endo- 
turbinal. None of the ectoturbinals extends into 
this cavity. In Ursus the corresponding cavity 
is narrower, the maxillary sinus lying laterad of 
it, and a leaf of the first ectoturbinal projects 
through the ostium into the cavity. 

Sinus 1 is a small cavity, measuring only about 
15 mm. in length by 20 mm. in height, lying above 
the olfactory fossa some distance behind sinus I. 
It is surrounded by sinus 2 on all sides except ven- 
trally. The small round ostium is situated in the 
floor. In the skull that was dissected this cavity is 
asymmetrical ; it was present on the right side only. 

Sinus 2 is by far the largest of the sinuses. It 
begins at the level of the postorbital process and 
extends back through the frontal and parietal 
bones nearly to the occiput. It is very irregular, 
with numerous out-pocketings and partial septa. 
The long slit-like ostium lies in the extreme ante- 
rior part of the cavity, and as in Ursus a leaf of 
one of the ectoturbinals projects through the os- 
tium into the sinus. 

Sinus IV (sphenoidal sinus of authors) is a large, 
irregular cavity in the presphenoid. The ostium 
is situated in its anterior wall, and as in Ursv^ the 

posterior end of the last ectoturbinal projects 
through the ostium into the cavity. 

The maxillary sinus lies almost entirely in the 
maxillary root of the zygomatic arch, a condition 
that is unique among carnivores. It is situated 
farther laterad than in Ursus and other arctoids. 
This hollowing out of the zygomatic root makes 
possible a considerable increase in bulk without 
adding appreciably to its weight. The sinus is an 
irregular cavity lying directly above the posterior 
end of the fourth premolar, the first molar, and 
the anterior end of the second molar. It opens 
into the nasal cavity, immediately behind and be- 
low the crest of the maxilloturbinal, by a much 
smaller ostium than in Ursus. 

Thus there are five pairs of pneumatic cavities 
in the skull of the giant panda. Although these 
greatly exceed the corresponding cavities of Ursus 
in size, the arrangement and relations are very 
similar. Ursus has an additional small cavity in 
the roof of the skull; in Ailuropoda the area it 
occupies has been taken over by sinus 2, and this 
enormous sinus has almost absorbed sinus 1. 

In other arctoids pneumatization of the skull is 
much less extensive in number of sinuses and in 
the extent of the individual sinuses. In the Mus- 
telidae only the maxillary sinus is present, but 
other arctoids also exhibit at least some pneumati- 
zation in the frontal region. Ailurus has the same 
cavities as Ailuropoda, but sinus 2 is much less 
extensive, extending back only to the level of the 
optic foramen. 

Paulli generalized that the extent of pneuma- 
ticity is dependent on the size of the skull, and 
pointed out that this is borne out in large vs. small 
breeds of dogs. Another over-riding factor obvi- 
ously has operated in the pandas. In Ailurus the 
absolute size of the skull compares with that of 
Procyon, but the sinuses are more extensive. In 
Ailuropoda the skull is about a third smaller than 
that of Ursus arctos, but the dorsal and lateral 
sinuses are much larger. The secondary factor in 
pandas is a mechanical one. 

It is well known that the sinuses develop as 
evaginations of the walls of the nasal cavity, and 
that with increasing age these out-pocketings grad- 
ually invade the surrounding bone. The process 
is called "pneumatic osteolysis," but the nature 
of pneumatic osteolysis is unknown. In Su Lin 
(age 16 months, all permanent teeth in place) 
sinus 2 had not yet invaded the parietal; it termi- 
nated at about the fronto-parietal suture. In this 
animal, sinus I in the nasofrontal region also falls 
short, by about 20 mm., of its adult anterior ex- 
tension. The vertical height of both these cavi- 
ties, on the other hand, is as great as in the adult. 



Thus considerable peripheral growth takes place 
in the larger sinuses after essentially adult skull 
size has been attained. 

Cranial Cavity. The cranial cavity (fig. 20) 
is a mold of the brain, and in the panda it differs 
far less from the typical arctoid condition than do 
other parts of the skull. The cavity is divided 
into the usual three fossae: olfactory, cerebral, 
and cerebellar (anterior, middle, and posterior of 
human anatomy). 

The olfactory fossa is much reduced in diam- 
eter as compared with that of Ursus, but is other- 
wise very similar. It houses the olfactory bulbs. 
The floor of this fossa is on a higher level than the 
remaining cranial floor. In the midline of the floor 
a prominent ridge, the crista galli of human 
anatomy, extends nearly the entire length of the 
fossa. The cribriform plate, forming the ante- 
rior wall, is perforated by numerous foramina for 
filaments of the olfactory nerve. These foramina 
are larger and more numerous at the periphery of 
the plate. In the lateral wall of the fossa is a 
larger opening, the ethmoidal foramen. 

The cerebral fossa, much the largest of the 
cranial fossae, houses the cerebrum. As in the 
bears, a vertical ridge (the site of the sylvian fissure 
of the brain) separates a larger anterior fronto- 
parietal region from a smaller posterior temporal- 
occipital region. This ridge is less obvious in the 
smaller arctoids. The walls of the fossa bear nu- 
merous ridges and furrows that conform to the 
gyri and sulci of the cerebral cortex of the brain. 
A conspicuous groove immediately in front of the 
sylvian ridge lodges the middle meningeal artery; 
a smaller groove, which houses a branch of this ar- 
tery, lies in the posterior region of the fossa (fig. 22). 
In Ursus and other arctoids the groove for the 
middle meningeal artery lies in the posterior re- 
gion of the fossa. 

The cerebellar fossa is largely separated from 
the cerebral fossa by the tentorium osseum, 
which forms most of its anterior wall. The ten- 
torium is exceptionally well developed in the bears 
and pandas. The cerebellar fossa communicates 
with the cerebral fossa via the tentorial notch, a 
large opening that in Ailuropoda is much higher 
than wide; in f7rsMS it is more nearly square. The 
tentorium slopes backward at an angle of only 
about 10 in Ailuropoda, while in Ursus this angle 
is about 25. The slope is much greater in other 
arctoids (about 45). 

The walls of the cerebellar fossa are grooved and 
perforated by various venous sinuses (see p. 281) ; 
otherwise they conform to the shape of the cere- 
bellum. The medial face of the petrosal is visible 

in the wall of this fossa. As in Ursus and Ailurus, 
the tentorium is in contact with the petrosal along 
the entire petrosal crest, and covers the part of the 
petrosal anterior to this line. In Canis and the 
procyonids, in which the tentorium is not so well 
developed, an anterior face of the petrosal is also 
exposed in the cerebral fossa. The enlarged ten- 
torium in the bears and pandas has also crowded 
out the trigeminal foramen the large opening in 
the petrosal near the apex that is so conspicuous 
in canids and procyonids. In the ursids the root 
of the trigeminal nerve passes over, instead of 
through, the apex to enter the trigeminal fossa. 
In Ailuropoda the most conspicuous feature on the 
medial face of the petrosal is the internal acous- 
tic opening, leading into the internal acoustic 
meatus. Immediately behind this opening is a 
smaller foramen, the aquaeductus vestibuli, 
overhung by a prominent scale of bone. Just 
above and behind the acoustic opening is a bulge 
in the surface of the petrosal, the eminentia ar- 
cuata, caused by the superior semicircular canal. 
In all other arctoids examined (except Procyon) 
there is a deep pit, larger than the acoustic meatus 
and situated directly above it, that houses the 
petrosal lobule or "appendicular lobe" of the cere- 
bellum; this pit is wanting in Ailuropoda and Pro- 
cyon. The inferior border of the petrosal is grooved 
for the inferior petrosal sinus, and the superior 
angle is crossed by the groove for the transverse 

The floor of the cerebral and cerebellar fossae 
exhibits several features of interest (fig. 22). The 
dorsum sellae marks the boundary between the 
cerebral and cerebellar spaces. Most anteriorly, 
near the middle of the cerebral fossa, is the open- 
ing for the optic nerve. It leads into a canal, 
nearly 25 mm. long, that opens in the orbit as the 
optic foramen. This canal is of comparable length 
in Ursus but is short in other arctoids. Behind 
the optic opening is a prominent sulcus for the 
optic chiasma, of which the canal itself is a con- 
tinuation. The sella turcica lies in the midline 
at the posterior end of the cerebral fossa. Of the 
components of the sella, the tuberculum sellae 
is wanting anteriorly, but the anterior clinoid 
processes at the anterior corners are well devel- 
oped; these processes, to which the dura is attached, 
are often wanting in arctoids. The posterior 
clinoid processes are plate-like lateral extensions 
of the dorsum sellae, overhanging the cavernous 
sinuses laterally. These processes, to which the 
dura also attaches, are well developed in all arc- 
toids examined except Canis, where they are want- 
ing. The hypophyseal fossa is a well-bounded 
pit in all arctoids except Canis, in which there is 
no anterior boundary. 



A. meningea med. 

For. ovale 

Fossa trigem 

Hiatus canalis facialis 
For. carot.ant. 

Siniis petrosus inf. 

Meatus acusticus interims 

Aquaedudus restibuli 
For. lacerum post. 

Sinus sigmoideiis 

Can. hypoglossi (condyloideum) 

For. mastoideum 
Sinus transversus 

For. opticum 

Fissura orbitalis + 
For. rotuiidum 

Proc. clinoideus ant. 

Sella turcica 
Sinus carer nosus 
T Dorsum sellae 

Proc. clinoideus post. 


Pars basilaris occipitale 

For. magnum 

Fig. 22. Left half of basicranium of Ailuropoda, internal view. 

On either side of the sella turcica is a wide longi- 
tudinal sulcus, extending from the orbital fissure 
anteriorly to the petrosal bone posteriori}', in 
which the cavernous sinus Hes. Anteriorly the 
sulcus opens into the orbit through the large open- 
ing formed by the combined orbital fissure and 
foramen rotundum; fusion of these two foramina 
is peculiar to Ailuropoda. A ridge on the floor of 
the sulcus marks the boundary between the orbital 
fissure (medial) and foramen rotundum (lateral) of 
other arctoids. In the posterior part of the sulcus, 
just in front of the apex of the petrosal, is a deep 
narrow niche, the trigeminal fossa, which lodges 
the semilunar ganglion of the trigeminal nerve. 
The foramen ovale (third and fourth branches of 
trigeminus) opens into the floor of the niche an- 
teriorly; in Ursus, in which the trigeminal fossa 

extends farther anteriorly, both the foramen ro- 
tundum (^second branch of trigeminus) and the 
foramen ovale open directly into it. A small roimd 
opening at the posterior end of the trigeminal fossa 
is the outlet of the hiatus canalis facialis, 
through which the great superficial and deep pe- 
trosal nerves enter the cranial cavity. Imme- 
diately above this is a smaller opening (more 
conspicuous in Ursus), the foramen petrosum 
superior, the anterior outlet of the superior pe- 
trosal sinus. 

The anterior carotid foramen Hes at the an- 
terior corner of the petrosal, directed anteriorly 
and medially. In Ailuropoda, in which there is 
no foramen lacerum medium, the internal carotid 
artery passes from the carotid canal directly into 
the cavernous sinus, and the anterior carotid fora- 



men is thus intracranial. In Ursus, the artery, 
after leaving the carotid canal, passes ventrad into 
the foramen lacerum medium, where it immedi- 
ately doubles back upon itself to pass nearly ver- 

Sinus cavernosus' 

Sinus petrosus iiif/ 

sinus runs nearly vertically, connecting the sagit- 
tal sinus above with the vertebral vein below. It 
is sharply divided into inferior and superior parts. 
The inferior section, much larger in caliber, lies 

Sinus sagillatis sup. 
Sinus rectus 

Sinus transversus (pars sup:) 

Sinus temporalis 
.V mastoidea 
Sinus transversus (pars inf) 

V verlebralis 
Sinus sigmoideus 

To V jugularis int.fvia for. lac. post J 
To V facialis inl.[via for. postglenj 

Sinus petrosus sup. 
Fig. 23. Sinuses and diploic veins. Right half of skull of Ailuropoda, internal view (semi-diagrammatic). 

tically into the cavernous sinus. Thus in Ursus 
the foramen in the floor of the cavernous sinus is 
the internal opening of the foramen lacerum me- 
dium, and the anterior carotid foramen is visible 
only externally within the foramen lacerum me- 
dium. The situation in Ailurus and Procyon is 
similar to that in Ursus. Obliteration of the fora- 
men lacerum medium and of the associated flexure 
in the internal carotid artery in Ailuropoda is un- 
doubtedly correlated with the general crowding of 
non-masticatory structures in this region and is 
therefore without functional or taxonomic signifi- 
cance. Cams, as usual, is quite different from either 
the Ursidae or Procyonidae. 

The inferior petrosal sinus lies just mesad of 
the petrosal, largely roofed over by a lateral wing 
of the clivus. The sinus is continuous anteriorly 
with the cavernous sinus and posteriorly with the 
sigmoid sinus, which name it assumes at the fora- 
men lacerum posterior, at the posterior corner of 
the petrosal. The superior petrosal sinus is re- 
duced to thread-like caliber in Ailuropoda and 
Ursus as a result of the great development of the 
tentorium. It opens into the trigeminal fossa via 
the superior petrosal foramen, at the apex of the 
petrosal. From here the sinus arches posteriorly 
around the petrosal, enclosed in the temporal bone, 
and enters the temporal sinus. The transverse 

in an open groove behind the petrosal, the upper 
part of the groove crossing the petrosal. The 
mastoid foramen and several diploic veins open 
into this part of the sinus. At the dorsal border 
of the petrosal the sinus gives off the large tem- 
poral sinus, which descends as a closed canal to 
open extracranially via the postglenoid foramen. 
The superior section of the transverse sinus con- 
tinues dorsad as a closed canal, much reduced in 
caliber, to open into the sagittal sinus at the dorsal 
midline. The sagittal sinus is visible for a vari- 
able distance as a shallow groove along the midline 
of the roof of the cerebral fossa. The short sig- 
moid sinus runs posteriorly from the foramen 
lacerum posterior, meeting the transverse sinus at 
a right angle about 5 mm. behind the posterior bor- 
der of the petrosal. Beyond the confluence of the 
inferior petrosal and transverse sinuses a groove, 
which houses the vertebral vein, continues caudad 
through the lateral corner of the foramen magnum. 
The vertebral vein lies in a similar groove in Ur- 
sus, while in all other arctoids examined (including 
Ailurus) the groove is roofed over to form a canal. 
From the dorum sellae the floor of the basi- 
cranium slopes backward and downward as the 
clivus. This region is basin-shaped to conform 
to the shape of the pons, and is separated by a 
transverse ridge from the basilar portion of the 



M. pterygoideus 

For. matidibularis 

M. pterygoideus int. 

M. temporalis (prof.) 

Proc. morytnw 
M. digastrii 

M. temporalis superf.+ 

M. zygomaticomandibularis 

Fossa masseterica 

Proc. angutaris 

^_ _ ^, M. masseter 

For. merUaiia 

Fig. 24. Left mandible of Ailuropoda: external surface lower right, internal surface upper left. 

basioccipital bone lying behind it, which supports 
the medulla. The whole plate-like floor of the 
basicranium lying behind the dorsum sellae is 
shorter and wider in Ailuropoda than in Ursus. 
The hypoglossal (condyloid) foramen pierces 
the floor of the basilar portion in a lateral and 
slightly anterior direction, just anterior to the 
foramen magnum. 

Mandible. The mandible of Ailuropoda is no- 
table for its extreme density. Its weight is more 
than twice that of the mandible of a much larger 
bear. The two halves of the mandible are firmly 
fused at the symphysis, with no trace of a suture, 
in all adults examined. This is contrary to the 
condition in Ursus and other arctoids. Fusion 
is nearly complete in a young adult Ailuropoda, 
in which most skull sutures are still open. The 
length of the symphysis is also remarkable. It is 
relatively nearly twice as long as in Ursus, and 
extends to the anterior border of the first molar 
instead of the third premolar. In Ailurus, by 
contrast, the symphysis is short (barely reaching 
the first premolar), and the two halves of the man- 
dible do not fuse. 

The body of the mandible, viewed from the 
side, tapers from the ramus forward, whereas in 
Ursus (but not in other arctoids) the height of the 
body is quite uniform. Among several mandibles 
of Ailuropoda the inferior border is curved in vary- 
ing degrees, reaching its nadir below the second 
molar; in one mandible this border is nearly as 
straight as in Ursus. The body is less high ante- 
riorly than in Ursus, and higher posteriorly, and 
this is probably correlated with the relatively feebly 
developed canines and the large molars. The up- 
per or alveolar border of the body lies about 30 mm. 
below the level of the articular condyle, whereas 
in Ursus these are at very nearly the same level 
(fig. 25). There are typically two mental fora- 
mina, as in arctoids in general. These are sub- 
equal in size. The more anterior foramen is often 
broken up into several smaller foramina. 

Throughout its length the body is more than 
twice as thick as in Ursus, and viewed from below 
the body arches abruptly laterad at the posterior 
end of the symphysis, giving a Y-shape to the ven- 
tral outline of the jaw. 



Ailuropoda 31128. Basal skull length 235 mm. 
Ursus 21859. Basel skull length 303 mm. 

Fig. 25. Outlines of posterior ends of mandible of Ailuropoda (solid line) and Ursus horribilis (broken line) superimposed. 
Note (1) the excavation of the posterior border of the coronoid process, (2) the much deeper masseteric fossa, and (3) the 
depressed occlusal plane in Ailuropoda. 

The ramus, which is that part of the mandible 
lying posterolaterad of the last molar, differs from 
that of Ursus in several important respects. Be- 
sides bearing the mandibular condyle, the ramus 
functions chiefly for the insertion of the muscles 
of mastication. The areas where these muscles 
attach are large, well marked, and rugose in 

The masseteric fossa, in which the zygomatico- 
mandibular muscle inserts, is larger than in Ursus 
in both vertical and transverse diameters. The 
vertical diameter in particular has been increased 
relative to Ursus (and other arctoids) by exten- 
sion ventrad. It is also deeper, for the edges have 
been built out. The surface of the fossa is ex- 
tremely rugose, and is marked by several promi- 
nent transverse ridges (cristae massetericae) for 
the attachment of tendinous sheets in the muscle. 
The coronoid process, into which the masseteric 
fossa grades imperceptibly, functions in the in- 
sertion of the temporal muscle on both its lateral 
and medial surfaces. This process is similar to 
that of Ursus, except that its posterior border is 
eroded away, giving it a scimitar-like form and 
greatly reducing the area available for temporal 
insertion (fig. 25) . The angular process is a small 
but conspicuous prominence on the posteromedial 

border of the ramus, below the condyle. It pro- 
jects medially and posteriorly, instead of posteri- 
orly as in other arctoids. This process characteris- 
tically provides insertion for part of the masseter 
on its outer surface and part of the internal ptery- 
goid on its inner surface; none of the masseter 
fibers reach it in Ailuropoda. In Ursus and other 
arctoids (including Ailuru^) the angular process is 
large and tongue-like, with well-marked muscle 
scars for both the masseter and the internal ptery- 
goid. In Ursus a conspicuous marginal process 
(Toldt's terminology) on the inferior border of the 
ramus, anterior to the angular process, provides 
the main insertion for the digastric muscle. This 
process is wanting in other arctoids. In Ailuro- 
poda the insertion of the digastric is more diffuse 
than in Ursus, and the marginal process, while 
present, is less clearly marked and is situated on 
the medial surface of the mandible immediately 
in front of the internal pterygoid scar. 

Hypertrophy of the jaw-closing muscles in the 
giant panda is reflected in the relatively larger 
areas of attachment on the skull. The total area 
of insertion of the masseter and temporal on the 
lateral surface of the mandible was calculated 
roughly by plotting on millimeter paper. In Ailu- 
ropoda (basal skull length 252 mm.) this area 
amounted to 5368 mm.-, while in a much larger 






Fig. 26. Lateral view of juvenile skull of Ailuropoda (USNM 259076), showing sutures. 

Ursus horribilis (basal skull length 303 mm.) it 
was only 4774 mm.- 

The medial surface of the ramus exhibits con- 
spicuous scars marking the attachment of several 
muscles. A rugose area occupying most of the 
medial surface of the coronoid process marks the 
insertion of the deep layer of the temporal muscle. 
The anterior border of this area sweeps back be- 
hind the last molar, leaving a triangular space 
(about one-fourth of the total medial coronoid 
surface) free of muscle attachment. The ventral 
border of the temporal area is a prominent hori- 
zontal crest at the level of the alveolar border, 
extending back immediately above the mandibular 
foramen; this is the level to which the temporal 
insertion extends in other arctoids. Immediately 
behind this crest, on the dorsal surface of the con- 
dyle, is the extraordinarily conspicuous, pock-like 
pterygoid depression that marks the insertion 
of the external pterygoid muscle. A much larger 
scar, below the condyle and extending back onto 
the angular process, marks the insertion of the in- 
ternal pterygoid. A triangular rugose area in front 
of this, beginning posteriorly at the marginal proc- 
ess, marks the insertion of the digastric. The 
mandibular foramen, for the inferior alveolar 
vessels and nerve, is circular instead of oval in 
cross section. It lies immediately above the mar- 
ginal process. 

The condyloid process has the transverse semi- 
cylindrical form characteristic of the Carnivora, 
but in Ailuropoda this region is an exaggeration 
of the usual arctoid condition. The neck support- 
ing the capitulum is short, flattened, and twisted 
through 90 the typical carnivore arrangement. 

As a result, the medial half of the capitulum is 
buttressed anteriorly but unsupported below, while 
the lateral half is buttressed below but unsup- 
ported anteriorly. In all arctoids the articular sur- 
face tends to conform to this support pattern, the 
medial half facing posteriorly and the lateral half 
more or less dorsally. In Ailuropoda this tendency 
reaches full expression, and the articular surface is 
a spiral track rotated through more than 90, "like 
a riband wound obliquely on a cylinder," as Lydek- 
ker stated. To some extent at least, this spiral 
form is correlated with the large size and dorsal 
position of the pterygoid depression, which in Ailu- 
ropoda occupies a part of the area of the articular 
surface of other carnivores. 

The width of the capitulum much exceeds that 
of any other carnivore. The index basal skull 
length /width capitulum is .27 to .31 for Ailuropoda, 
while for Ursus it is only .15 to .17. Ailurus is 
intermediate, with an index of .22 to .23, while 
all other carnivores examined were below .18 ex- 
cept an old male zoo specimen of Tremarctos or- 
natus, in which it was .21. The long axis of the 
capitulum is oriented at nearly a right angle to 
the axis of the skull in both horizontal and verti- 
cal planes. As in carnivores in general, however, 
the medial end of the axis is tilted slightly caudad 
and ventrad of 90. 

B. Cranial Sutures and Bones of the Skull 

As was mentioned above, the sutures disappear 
early in Ailuropoda, and nearly all are completely 
obliterated on fully adult skulls. The following 
account of the bones of the skull is based on a 
young female skull, with a basal length of 213 mm.. 





CPars mastoidta) 



Fig. 27. Ventral view of juvenile skull of Ailuropoda (USNM 259076), showing sutures. 

on which all but a few of the sutures are still open 
(figs. 26, 27). This skull is intact, so that only 
surface features could be examined. 

For the most part, the relations of the bones 
differ so little from those of Ursus that there is 
no point in a detailed description. The exact po- 
sitions of the sutures are shown in the accompany- 
ing drawings. 

The premaxilla is essentially similar to that of 

The maxilla is modified to accommodate the 
enlarged cheek teeth. The posterior part of the 

bone forms an enormous maxillary tuberosity that 
supports the second molar. The tuberosity carries 
the maxilla back to the level of the optic foramen, 
whereas in Ursus it extends only to the pterygo- 
palatine foramen. In the juvenile skull this pos- 
terior extension of the maxilla has a remarkably 
plastic appearance, as if the bone had flowed back 
over the vertical plate of the palatine, squeezing 
the pterygopalatine and sphenopalatine foramina 
upward against the inferior orbital crest. A sec- 
tion through this region (fig. 21) shows that the 
maxilla lies outside the palatine that the latter 
is not displaced backward. 



As in Ursus, at the anteromedial corner of the 
orbit the maxilla is wedged in between the lacri- 
mal and jugal, forming a part of the anterior, all 
the lateral, and a part of the medial boundaries 
of the lacrimal fossa. 

The anterior zygomatic root contains a lateral 
extension of the maxillary sinus, not seen in any 
other carnivore. 

The nasals, as in Ursus, are short and their 
lateral borders are not prolonged forward as in 
other arctoids. 

The lacrimal closely resembles the correspond- 
ing bone in Ursus, which Gregory characterized 
as "much reduced, sometimes almost vestigial." 
It is a minute plate, about 5 mm. wide and 12 mm. 
high, withdrawn entirely from the anterior rim of 
the orbit, and forming only a small part of the 
medial surface of the lacrimal fossa. The lacrimal 
of Ailurus is essentially similar. It is slightly 
better developed in the procyonids. 

The jugal (malar) does not depart in any essen- 
tial respect from the typical arctoid pattern. 

The palatine, except for the superficial modi- 
fication produced by the posterior prolongation of 
the maxilla over the pars perpendicularis, is sim- 
ilar to that of other arctoids. The pars horizontalis 
extends forward on the palate slightly anterior to 
the first molar. 

The vomer differs from that of Ursus and most 
other arctoids in the great posterior extent of its 
pars sagittalis. Otherwise its relations are similar 
to those of Ursus. 

The frontal, parietal, squamosal, and oc- 
cipital have all suffered more or less change in 
form with the remodeling of the skull to accom- 
modate the enormous masticatory musculature. 
Except for the morphologically insignificant dif- 
ferences resulting from this remodeling, the rela- 
tions of these bones are typical. 

The frontoparietal suture, which is relatively 
straight and about at a right angle to the axis of 
the skull in Ursus and other arctoids, here arches 
forward to the level of the optic foramen. At the 
dorsal midline a narrow tongue of the frontal pro- 
jects posteriorly between the parietals for about 
15 mm., i.e., to about the level of the whole fronto- 
parietal suture in Ursus. This suggests that in 
Ailuropoda the parietal has increased anteriorly 
at the expense of the frontal. 

The interparietal suture is obliterated, and a 
secondary upgrowth of bone is approaching the 
site of the future sagittal crest. 

On the skull examined, the basioccipital-supra- 
occipital suture was still open, but the exoccipital- 
supraoccipital suture was closed. 

The mastoid portion of the periotic is exposed, 
as is usual in arctoids, on the posterior side of the 
mastoid process, where it is wedged in between 
the squamosal and the occipital. The suture be- 
tween the periotic and the tympanic disappears 
early in all arctoids, and was gone in the skull of 
Ailuropoda studied. 

The tympanic, in so far as it is visible exter- 
nally, differs considerably in shape from the cor- 
responding bone in Ursus. It is obvious, however, 
that this bone has merely been crowded by the 
surrounding structures, particularly the postglenoid 
process. The relations of the tympanic are almost 
exactly as in Ursus, and posterior expansion of the 
postglenoid process as seen in Ailuropoda might 
be expected to alter the form of the tympanic pre- 
cisely as it has. (This region is described in detail 
on p. 319). 

The sphenoidal complex has been affected rela- 
tively little by the remodeling of the skull and is 
very similar to the corresponding region in Ursus. 
In the skull examined, the four elements constitut- 
ing the complex (basisphenoid, presphenoid, 
alisphenoid, orbitosphenoid) are still distinct. 
They differ only in the most trivial respects from 
the corresponding elements in a young Ursus skull. 

The pterygoid is completely fused with the 
sphenoid, and this is one of the very few sutures 
of the skull that have been obliterated at this age. 
This condition contrasts sharply with Ursus at a 
comparable age, in which the pterygoid is still en- 
tirely separate. 

The ethmoid is not visible on the surface of 
the skull. 

The following sutures are closed in the young 
skull examined: tympanic-periotic, exoccipital- 
supraoccipital, pterygoid sphenoid, interparietal. 
The first two fusions are characteristic of carni- 
vores at this stage of development. The last two 
are not, and represent departures from the car- 
nivore pattern. 

C. Hyoid 

The hyoid (fig. 28) differs little from that of 
bears and other arctoid carnivores. It is composed 
of the usual nine rodlike bony elements, suspended 
from the basicranium by a pair of cartilaginous 
elements, the thyrohyals. The hyoid fossa, at the 
bottom of which the thyrohyal articulates with 
the skull, lies in the hyojugular fossa. 

The hyoid consists of a transverse body and two 
horns (cornua), an anterior composed of three pairs 
of bones plus the cartilaginous thyrohyals, and a 
posterior composed of a single pair of bones. 

Like all other bones of the skeleton, the hyoid 
bones of Ailuropoda exhibit more pronounced scars 






Cornu anterior 

Cornu posterior 


Cornu posterior 



Fig. 28. Hyoid of Ailuropoda, lateral and ventral views. 

for muscle attachments than they do in Ursus, 
although the bones themselves are no more robust. 
In both the giant panda and the bears the body is 
a transverse rod, less plate-like than in other arc- 
toids. The ceratohyal is also less expanded than in 
other arctoids, and in Ailuropoda it has a distinct 
longitudinal furrow on the dorsal surface. The 
epihyal presents nothing noteworthy. The stylo- 
hyal is flattened and plate-like, with an irregular 
outline, in Ailuropoda. The thyrohyal is slightly 
curved and rodlike. 

D. Review of the Skull 

The skull and teeth of Ailuropoda were described 
in some detail by A. Milne-Edwards (1868-1874), 
Lydekker (1901), Bardenfleth (1913) and Gregory 
(1936). Each of these made point by point com- 
parisons with the Ursidae on the one hand and 
with Ailurus and the Procyonidae on the other, 
in an attempt to determine the affinities of Ailur- 
opoda. Conclusions were conflicting; the only 
legitimate conclusion is that the skull and denti- 
tion of the giant panda are so modified that the 
affinities of this animal cannot be determined from 
these structures alone. I have therefore used 
other characters in deciding the affinities of Ailur- 
opoda, which are unquestionably with the Ursi- 
dae. Here the only important consideration is 
that no skull or dental character shall point un- 
equivocally to relationship with any other group 
of carnivores. 

The demands of the masticatory apparatus in 
Ailuropoda have resulted in such extensive and 
permeating modifications in the skull that many 
elements have been modified beyond the limits of 
inter-generic or even inter-family differences with- 
in the Carnivora. Among those not so affected 
are the pattern (but not the extent) of the para- 
nasal sinuses, the turbinates, and the middle ear 
all intimately associated with primary sense 
organs and not affected by muscle action. Each 
of these structures is very similar to the correspond- 
ing structure in Ursus. Klatt (1912) has shown 
that the extent of the frontal sinus is determined 
by the mass of the temporal muscle, as would be 
expected, because the sinus lies between the outer 
and inner lamina of the cranium. The temporal 
attaches to the outer lamina, whereas the inner 
lamina encapsulates the brain. 

Aside from its function of encapsulating the 
brain and sense organs, the generalized carnivore 
skull is designed primarily for seizing and cutting 
up prey. Skulls of omnivorous or herbivorous 
carnivores are secondary modifications of this pri- 
mary predatory type. Consider the skull of a 
generalized carnivore, such as Canis or Viverra, as 
a construction. How does such a construction 
compare with those of other generalized mammals 
in architecturally or mechanically significant ways? 

1. The skull is elongate and relatively slender 
(see Table 8). Elongation of the head is a primi- 
tive mammalian feature that has been retained in 




N = 

Condylobasal length 
Length thor. vert. 10-12' 


Gnathion-ant. end braincase 
Condylobasal length 

Preoptic length 

Condylobasal length 


Vertex-inf . border mandible 
Condylobasal length 

Zygomatic breadth 
Condylobasal length 

Least diam. braincase 
Condylobasal length 

See page 35. 

Generalized Flesh- 
eating Carnivores 

Canis Viverra 
lupus tangalunga 

Procyon Ailurus 
lotor fulgens 


Extremely Powerful 
Jawed Carnivores 

Ailuropoda Hyaena 


























































































the Carnivora; the skull was elongate in the creo- 
dont ancestors of the carnivores and is characteris- 
tic of generalized mammals. 

As a tool for seizing and cutting up prey an 
elongate skull (particularly an elongate face) has 
certain inherent mechanical advantages and dis- 
advantages. Speed of jaw closure at the level of 
the canines is achieved, though at the cost of 
power. But production of useful force at the sec- 
torial teeth is mechanically very unfavorable, since 
more than twice as much disadvantageous force 
is developed at the mandibular articulation (see 
p. 69). 

Preoptic length is a useful measure of face length 
for our purpose, since it approximately divides the 
tooth-bearing anterior part of the skull from the 
posterior muscle-attachment part. Calculated in 
this way, the face is long in Canis, moderately long 
in Viverra. Both fall within the known range of 
the Paleocene Arctocyonidae, the oldest and most 
primitive of all carnivores: Deltatherium 31 per 
cent, Eoconodon 38 per cent, Loxolophodon 45 per 

Depth and breadth of skull, both intimately as- 
sociated with mechanics of the jaw, are moderate 
in both Canis and Viverra. The civet is more 
slender in both dimensions. 

2. Two areas dominate the dental battery: the 
enlarged dagger-like canines anteriorly, and the en- 

> Calculated from illustrations in Matthew (1937). 

larged scissor-like carnassials (P^ and MO poste- 
riorly. The remainder of the dentition is more or 
less degenerate. These two specialized areas of 
the dentition are the key adaptation of the Car- 
nivora. All other modifications of the skull away 
from the generalized mammalian condition are 
effectors of these seizing and cutting tools. These 
modifications are as follows: 

3. The mandibular articulation is a transverse 
cylinder rotating in a trough-like fossa that is 
strongly buttressed above and behind. This ar- 
rangement permits only a hinge movement of the 
mandible, plus limited lateral shifting of the man- 
dible; the two may be (and probably normally 
are) combined in a spiral screw movement. The 
two halves of the mandible are not fused at the 
symphysis, which indicates that they are capable 
of at least some independent movement. 

4. The mandibular articulation is at the level 
of the occlusal plane, and therefore upper and 
lower toothrows operate against each other like 
the blades of a pair of shears. 

5. The canines interlock and act as a guide for 
the anterior part of the mandible as the jaws ap- 
proach closure (and the carnassials begin to func- 
tion). This is very evident from the wear areas 
on the canines. The interlocking restricts lateral 
movement and guides the two blades of the shear 
very precisely past each other. Xo such arrange- 
ment exists in such generalized marsupials as the 
opossum or in generalized insectivores. 



^\ Z i 4 5 67 89 (0 

Fig. 29. Differences of skull proportions in Ursus horribilis and Ailuropoda melanoleuca shown by deformed coordinates. 

6. The temporal fossa is large, providing space, 
and particularly attachment surface, for the large 
temporal muscle (see p. 150). This fossa is simi- 
larly large in generalized primitive mammals. The 
masseteric fossa does not differ significantly from 
that of primitive mammals. The pterygoid fossa 
is small or wanting. This fossa is well developed 
in primitive mammals; its reduction in the Carni- 
vora is associated with the reduced size and im- 
portance of the pterygoid muscles. 

7. The zygomatic arch is strong and forms a 
smooth uninterrupted curve in both the sagittal 
and frontal planes. The anterior buttress of this 
arch system lies directly over the primary cheek 
teeth, the posterior buttress over the mandibular 
fossa the two sites where pressure is applied dur- 
ing mastication. The zygomatic arch represents 
the "main zygomatic trajectory" of Starck (1935) ; 
it is the principal structure within which are re- 
solved the disintegrating forces generated by the 
powerful jaw muscles. The arch is well constructed 
and extremely powerful in Didelphis. In general- 
ized insectivores, by contrast, the arch is structur- 
ally weak: the curvature is interrupted (Erina- 
ceus), parts of the arch are almost threadlike 
{Echinosorex, Talpidae), or the central part of 
the arch is missing (Soricidae). 

Support for the canines, by contrast, is relatively 
weak in generalized Carnivora. The main element 
of this support system is the "vertex trajectory," 
which in generalized carnivores is weak and often 
interrupted at the glabella. 

What, now, has happened to this basic carnivore 
construction in herbivorous carnivores, and par- 
ticularly in the purely herbivorous giant panda? 

The skull is still elongate, but slightly less so 
than in Canis or Viverra (Table 8). In Ursus the 
skull is even slightly longer than in Canis or Vi- 
verra. There is, in fact, little variation in relative 
skull length among all arctoids examined. 

Face length in the giant panda is only slightly 
less than in Viverra, and in the bears it is prac- 
tically identical with Viverra. Proportions vary 
among other herbivorous carnivores: the face is 
very short in Ailurus, of normal length in Procyon. 
Face length is extremely variable among the Car- 
nivora in general, and the significance of this vari- 
ability has not been explored. The face varies 
independently of the cranium in mammals (p. 72). 

We may conclude that Ailuropoda and Ursus show 
no significant differences from the generalized carni- 
vore condition in longitudinal proportions of the skull. 




Fig. 30. Difference.s of skull proportions in Canis lupus and Ailuropoda melanoleuca shown by deformed coordinates. 

Depth and breadth of skull, on the contrary, in 
all herbivorous carnivores depart significantly from 
the generalized condition (see figs. 29 and 30, and 
Table 8). Among these, depth is least in Ursus, 
in which it scarcely exceeds that of the wolf. 
Depth of skull in Ailuropoda is equaled among 
carnivores only in Hyaena; in both the panda and 
the hyena, depth is achieved largely by develop- 
ment of a high sagittal crest, the inner lamina of 

the skull roof remaining unaffected. The skull is 
typically deep in all arctoids that have forsaken a 
purely carnivorous diet. Increase in depth in- 
volves only the external lamina of the cranium 
and adjoining parts of the mandible not the face 
or the direct housing of the brain. The vertical 
height of the posterior half of the zygomatic arch, 
the area from which the zygomaticomandibularis 
takes origin, is also greatly increased in Ailuropoda. 



Zygomatic breadth is consistently greater than 
in generalized flesh-eaters, and once again this 
is maximal in Ailuropoda and least in Ursus. 
Breadth in the powerful-jawed Hyaena is equal 
to that in most herbivorous carnivores, but is con- 
siderably less than in Ailuropoda. 

We may conclude that breadth and depth of skull 
are increased in all herbivorous carnivores, and that 
these reach a maximum in Ailuropoda. 

Increased breadth and depth of the cranium 
produce increased volume of the temporal fossa. 
In Ailuropoda the volume of this fossa has been 
further increased, especially anteriorly, by crowd- 
ing the orbit downward from its normal position, 
by carrying the temporal fossa anteriorly at the 
expense of the postorbital process and the poste- 
rior part of the frontal table, and by decreasing 
the anterior breadth of the braincase. The vol- 
ume of this fossa probably approaches the maxi- 
mum that is compatible with normal functioning 
of surrounding structures. 

Besides providing space for a greater volume of 
craniomandibular musculature, increased depth of 
skull greatly improves efficiency for production 
of pressure at the level of the cheek teeth. Worth- 
mann (1922) uses a simplified system of vector 
analysis to compare relative masticatory efficiency 
in man and several carnivores. He represents the 
action of the masseter and temporal muscles by 
straight lines connecting the midpoints of origin 
and insertion areas. The axis of the masticatory 
system is represented by a straight line connecting 
the center of rotation of the mandibular articula- 
tion with the last molar tooth. 

From the structural standpoint, greater depth 
of skull increases the magnitude of vertical forces 
that the skull is capable of withstanding. 

Comparison of masticatory efficiency in a gen- 
eralized carnivore iCanis) and in the purely her- 
bivorous Ailuropoda by Worthmann's method re- 
veals a striking improvement in the panda (fig. 31). 
In the wolf the axis of the masseter (m) intersects 
the masticatory axis GK at a point about 30 per 
cent of the distance from G to K. Thus force at 
the joint (G) would be to force at the cheek teeth 
(K) as 7 : 3; in other words joint force is about 
2.5 times as great as useful chewing force. In the 
panda, by contrast, k : fir = 55 : 45 approximately. 
Similarly for the temporalis k:g = 28:12 for 
Canis, whereas k : g = 47 : 53 for Ailuropoda. 

In the cheek-tooth battery emphasis has shifted 
from the sectorial teeth to the molars (p. 128), and 
the anterior buttress of the zygomatic arch now 
lies over the first (Ailuropoda) or second (Ursus) 
upper molar. This shift, by shortening the resist- 

ance arm of the jaw lever, increases the mechanical 
efficiency of the system for production of pressure. 

The form of the mandibular articulation has not 
changed it is still a transverse cylinder rotating in 
a trough. The extensive horizontal movements of 
upper molars against lower that characterize other 
herbivorous mammals are therefore limited to a 
slight lateral displacement in herbivorous carni- 
vores. Because of the interlocking canines at the 
anterior end of the system, no lateral shifting is 
possible with the teeth in full occlusion.' 

In Ursus the mandibular articulation is at the 
level of the occlusal plane as in generalized flesh- 
eating carnivores. In Ailuropoda the articulation 
lies considerably above the occlusal plane. Lebe- 
dinsky (1938) demonstrated that elevating the 
articulation above the occlusal plane imparts an 
anteroposterior grinding movement at the occlusal 
plane, even when the mandible is swinging around 
a fixed transverse axis. 

Lebedinsky's interpretation may be analyzed 
further. Figure 32, A, represents a mandible with 
the mandibular articulation (0) at the level of the 
toothrow. A point x on the lower dentition travels 
through the arc x~x' when the mouth is opened. 
The tangent to this arc at point x is perpendicular 
to the occlusal plane, and therefore there is no 
anteroposterior component in the movement of x 
with respect to the axis AO, and an object placed 
between the upper and lower dentitions would be 
crushed or sheared. This would likewise be true 
at any other point on the axis AO. 

Figure 32, B, represents a mandible with the 
mandibular articulation (0) elevated above the 
level of the toothrow. A point x travels through 
the arc x-x' when the mouth is opened, but in 
this case the tangent to the arc at x forms an acute 
angle with the occlusal plane, A-B, and there is a 
very definite anteroposterior component in the 
movement of x with respect to the axis AB. The 
angles formed by successive tangents along AB 
become increasingly acute as B is approached, 
until at B there is no longer any vertical compo- 
nent at all. Thus, as Lebedinsky pointed out, any 
object placed between the upper and lower denti- 
tions would be subjected to anteroposterior forces 
even with pure hinge movement of the jaw. More- 
over, the anteroposterior force becomes increas- 
ingly great as a point (B) directly beneath the 
articulation is approached. In Ailuropoda, there- 
fore, an anteroposterior grinding action is achieved 
by elevating the articulation, and its effectiveness 
is increased by extending the toothrow posteriorly. 

' In Ailurus fulgens a lateroventral shifting of more than 
2 mm., with the cheek teeth in complete occltision, is possible. 
This is true grinding, otherwise unknown in the Carnivora. 



Fig. 31. Relative masticatory efficiency in a generalized carnivore (Canis) and the giant panda (Ailuropoda). The line 
KG, representing the masticatory axis, connects the center of rotation of the mandibular joint (G) with the midpoint of the 
functional cheektooth area (K) (boundary between P' and Mi in Canis, anterior quarter of M' in Ailuropoda). The line m 
represents the axis of the masseter. The line /, the axis of the temporalis, connects the approximate center of origin (T) of the 
temporalis with the approximate center of insertion (C). The line / may be projected beyond C to K, since a force acting on 
an immovable system may be displaced in its own direction without altering the result. True masticatory force is represented 
by k, articular pressure by g. 
















\ / 


\ / 



Fig. 32. Occlusal relations in a mandible with mandibular articulation at level of toothrow (A), and elevated above level 
of toothrow (B). The lines AO and ABO represent the mandible in occlusion, A'O and A'B'O its position when the mouth 
is opened. The points x and x' represent the positions of a cusp on one of the lower cheekteeth. (C) Occlusal relations in 
AUuropoda in biting down at point x on an object 25 mm. in diameter (see text). 

Stocker (1957) has calculated for the elephant 
the anteroposterior displacement of a point on the 
occlusal surface of a lower molar when the jaw is 
lowered. A similar calculation may be made on a 
panda skull (fig. 32, C). A point x at the anterior 
end of the iirst lower molar is 125 mm. from the 
center of rotation of the mandible, 0. The line xO 
was found to form an angle, X, of 7 with the oc- 
clusal plane, x B. The panda is known to chew 
up bamboo stalks up to 38 mm. in diameter (p. 20) ; 
to be conservative let us assume a bamboo stalk 
25 mm. in diameter. 

An object 25 mm. in diameter placed between 
the upper and lower teeth at the level x displaces 

point X on the lower molar to position x'. The 
two lines x and x' form an angle, a, of 11 30'. 
The horizontal displacement, j M, of x with re- 
spect to the occlusal plane may be calculated as 

a;M=a:OcosX-a:Ocos (X-|-a) 
= xO [cos X -cos (X-|-a)] 

Substituting the values given above, this equation 
gives a value for x M of 5.4 mm., which is the 
horizontal distance through which a point x on 
the lower molar travels as the teeth are brought 
into occlusion. This represents the anteroposte- 
rior grinding component that would be brought 
to bear on the bamboo stalk. 



The mandibular symphysis remains unfused in 
Ursiis and othei- herbivoi'ous carnivores, although 
the two halves interlock so intimately that no 
movement is possible. Its fusion in Atluropoda 
reflects the general increase in bone tissue that 
characterizes the skull as a whole. 

We may conclude that the skull of Ailuropoda 
represents an attempt to adapt the carnivore type 
of skull already highly adapted for seizing and 
cutting to the radically different requirements of 
grinding siliceous plant fibers. Efficient grinding 
requires horizontal movements, but these are al- 
most completely inhibited by the cylindrical man- 
dibular articulation and the interlocking of teeth 
during occlusion, although Ailurus shows that 
effective horizontal grinding can be achieved in a 
carnivore. A compromise solution was to replace 
the unattainable mechanical efficiency seen in true 
herbivores with more power. This attempt to 
achieve maximal power in the masticatory equip- 
ment is the key to the architecture of the panda 

The skulls of other more or less herbivorous car- 
nivores except Ailurus exhibit most of the modi- 
fications seen in Ailuropoda, but to a much less 
extreme degree. Thus the skull of Ailuropoda may 
be considered an ultimate expression of adaptation 
for herbivory within the Carnivora. 

What can be deduced of the morphogenetic 
mechanisms whereby these results were achieved 
in other words, the mechanism through which 
natural selection had to operate? To what extent 
does the skull of Ailuropoda as compared with that 
of Ursus merely reflect extrinsic mechanical fac- 
tors arising from the massive musculature, and to 
what extent intrinsic factors, other than the ability 
of the bone to respond to mechanical stress? 

Some anatomists have recently attempted to re- 
examine the mammalian skull from an analytical 
rather than a purely descriptive standpoint (see 
Biegert, 1957, for a review). In these studies the 
skull is regarded as merely the bony framewoi-k 
of a major functional unit, the head. During on- 
togeny and phylogeny there is a complex interplay 
among the various organs making up the head, 
and the skull adapts itself to the changing spatial, 
mechanical, and static demands. In a given phylo- 
genetic sequence one of the head organs (e.g., 
brain, feeding apparatus, eyes) typically comes to 
dominate the whole and sets the pattern, so to 
speak, for further evolution within the group. 
Changes in the skull are thus not simply additive, 
but are a function of changes in other head organs, 
which in turn may be functionally irreversible and 
therefore in effect "fix" the pattern of further evo- 
lution within the group. The causal factors that 

determine changes in skull form are interpreted as 
an interplay between the inherited basic plan of 
the skull and the demands of other head structures 
extrinsic to the skull itself. This approach iso- 
lates some of the forces modeling the skull, but 
in the end it does little more than describe struc- 
tural correlations. It fails to come to grips with 
the problem of the mechanics of evolution. 

Correlation studies have shown that the facial 
part of the skull varies as if it were genetically 
distinct from the cranium, as it is in fact phylo- 
genetically (Cobb, 1943; and especially Starck, 
1953, for a review). This genetic independence, 
and the further independence of the mandible, 
have been proved in breeding experiments on dogs 
(Stockard, 1941 ; Klatt, 1941^3) . Such independ- 
ence means that a genetic factor affecting the 
ontogenetic growth rate of the cranium (or a com- 
ponent of the cranium) need not affect the face, 
and vice versa. The union between face and cra- 
nium, however disparate these structures may be, 
is maintained by mutual accommodation during 
growth. Genetic control of growth rates in dental 
fields is well known to be distinct from that of any 
other part of the skull. Numerous observations 
(e.g., Cobb, 1943) indicate that the alveolar areas 
of the skull accommodate directly to the space re- 
quirements of the teeth during the gi-owth process. 

The mammalian skull, in short, is a mosaic of 
independent morphogenetic units that are fitted 
into a functional unit partly by natural selection 
acting on their several time-tables of gi'owth and 
differentiation, and partly by accommodation to 
extrinsic forces. The extent of the morphogenetic 
units may vary with time during ontogeny: the 
earlier in ontogeny a genetic effect is manifested, 
the more extensive its target is likely to be. A 
beginning has been made at identifying and iso- 
lating these morphogenetic units (Starck, 1953; 
Landauer, 1962), but they are still inadequately 

Thus, in considering the morphosis of the skull, 
two sets of factors must be kept in mind. These 
are the location and extent at any moment during 
ontogeny of the morphogenetic units of which the 
skull is composed (intrinsic to the skull), and the 
modeling effects on the skull of other head struc- 
tures (extrinsic to the skull as such). 

In the skull of Ailuropoda the increase in quan- 
tity of compacta is clearly limited to two major 
morphogenetic units, the cranium and the man- 
dible, and absent in a third, the face. The hyper- 
trophy of bone substance affects not only the skull, 
but all compacta in the body in a gradient falling 
off from the dorsal body axis, and including struc- 
tures such as the tail and the proximal ends of the 



ribs where hypertrophy can scarcely represent 
structural adaptation. We do not know the time- 
table of mammalian ontogeny in enough detail to 
know whether these effects could have been pre- 
dicted and delimited a priori. The additional bone 
substance certainly strengthens the skull, although 
it is not distributed along trajectory lines of the 
skull as it should be if it were primarily functional. 
We cannot say whether increased bone substance 
in the skull of Ailuropoda was a primary target of 
natural selection, whether it is genetically linked 
with increase in the mass of the masticatory mus- 
cles, or whether it simply reflects disturbed meta- 
bolic or endocrine relations. 

Cephalization in bulldogs is in some respects 
similar to but less extreme than in Ailuropoda. 
Klatt and Oboussier (1951) found that all struc- 
tures of the head (skull, masticatory musculature, 
brain, eyeballs, hypophysis) are heavier in bull- 
dogs than in "normal" dogs. These authors con- 
clude that the bulldog condition results from an 
increase in the growth rate of the anterior end of 
the embryo. More likely it represents a temporary 
intensification of the general growth rate of the 
embryo during the period when the head region 
is undergoing its most rapid growth. The effects 
are less generalized in Ailuropoda; here the brain 
and eyeballs (and the internal ear) are of "nor- 
mal" size, a condition that would result if the 
ontogenetic growth rate were increased after the 
central nervous system and its sensory adnexa had 
experienced their period of most rapid growth. 
The condition in the panda is, in fact, the reverse 
of the condition in man, where the brain is en- 
larged while all other cranial (but not facial) 
structures are of "normal" size. As interpreted 
by Weidenreich (1941), in man the ontogenetic 
growth rate is temporarily intensified during the 
period when the brain is undergoing its most rapid 
growth, and returns to normal before the rapid 
growth period of other cranial structures is reached. 

It is known from comparative studies that sur- 
face relief of the mammalian cranium is deter- 
mined chiefly by the craniomandibular muscles 
(Weidenreich, 1922). The developing cranium is, 
as Anthony (1903) put it, molded between the 
brain and the masticatory musculature. Direct 
evidence of the role of the cranial muscles in de- 
termining skull form in mammals is limited to the 
effects of unilateral paralysis or removal of mus- 
cles in young rats, rabbits, guinea pigs, and dogs. 
Unilateral paralysis of the facial muscles (Wash- 
burn, 1946a), removal of one masseter (Horowitz 
and Shapiro, 1955, and earlier workers), of one 
temporal (Washburn, 1947, and earlier workers), 
or of neck muscles (Neubauer, 1925), all resulted 

in asymmetrical development of the skull, with 
failure of associated bony crests and ridges to form. 
Removal of the temporal was followed by resorp- 
tion of the coronoid process but did not alter the 
internal form of the braincase. No one has re- 
moved simultaneously the temporal, zygomatico- 
mandibularis, and masseter from one side to deter- 
mine the part played by these major muscles in 
determining the form of the zygomatic arch; it is 
very probable that bizygomatic breadth is inti- 
mately related to these muscles. 

These experiments were performed far too late 
in ontogeny to provide the intimate knowledge of 
the factors of embryogenesis we have for the limb 
bones of the chick (Murray, 1936). So far as they 
go, the experiments strongly reinforce the observa- 
tional data of comparative anatomy. Practically 
nothing is known of the development of the form 
of the skull, but from what is known of develop- 
ing limb bones in vertebrates (Murray, 1936; La- 
croix, 1951) the primary form of both dermal and 
cartilage bones of the skull is probably determined 
by intrinsic growth patterns, whereas modeling is 
determined by pressures and tensions extrinsic to 
the bones, created by musculature, brain, sense 
organs, vessels and nerves, and mechanical inter- 
action between the developing bones themselves. 
We may assume that, except for differences result- 
ing from increase in volume of bone tissue, the 
considerable differences in form between the skull 
of the panda and that of the bears are largely, 
perhaps almost entirely, dependent on such ex- 
trinsic factors that of the cranium on the muscu- 
lature, and that of the face on the dentition. 

The only features for which intrinsic factors 
must be postulated appear to be the tremendous 
increase in the bone substance making up the skull 
(by proliferation of connective tissue) and the ele- 
vation of the mandibular articulation (by prolifer- 
ation of cartilage). Elevation of the articulation 
enhances horizontal movements of the mandible. 
It occurs in some degree in all herbivorous mam- 
mals and surely is a direct result of natural selec- 
tion operating on the skull. The morphogenetic 
mechanism whereby it is achieved is unknown, 
but the fundamental similarity to the acromegalic 
mandible suggests that it is simple. 

We may conclude that no more than four, and 
perhaps only three, factors were involved in the 
transformation of the ursid type of skull into that 
of Ailuropoda. Two of these hypertrophy of jaw 
musculature and dentition are extrinsic to the 
skull and therefore involve only the ability of 
the bone to respond to mechanical stress. Two 
general hypertrophy of bone substance and ele- 
vation of the mandibular articulation are intrin- 
sic to the skeleton but involve different growth 



mechanisms. Thus only two factors acting di- 
rectly on the skull itself may distinguish the skull 
of Ailuropoda from that of other ursids. Natural 
selection has no doubt had additional minor polish- 
ing effects, although the whole morphology of the 
giant panda indicates that the morphological in- 
tegration produced by such refined selection is at 
a relatively low level. 

E. Summary of Skull 

1. The skull of Ailuropoda is basically similar 
to that of Ursus. Agreement is particularly close 
in structures relatively unaffected by masticatory 
requirements: the turbinates, the paranasal sinuses, 
the middle ear, and the inner lamina of the cranial 

2. The outer lamina of the cranium and the 
mandible are remarkable for the thickness and 
density of the bone. This greatly exceeds mechan- 
ical requirements, and therefore is not directly 

3. All parts of the skull associated with the 
masticatory apparatus are greatly expanded. The 
volume of the temporal fossa in particular, espe- 
cially its anterior third, has been increased at the 
expense of surrounding structures. Similar adap- 
tive changes appear convergently in Ailurus and, 
in slightly altered form, in hyenas. 

4. From the genetic standpoint these adaptive 
changes are probably extrinsic to the bone itself, 
involving only the ability of the bone to respond 
to mechanical forces during ontogeny. 

5. The only obvious intrinsic factors are the 
great increase in bone tissue in the cranium and 
mandible, and the elevation of the mandibular 
articulation above the occlusal plane. 

6. Thus only two major factors acting directly 
on the skull itself may distinguish the skull of 
Ailuropoda from that of Ursus. 

7. Certain features usually regarded as diag- 
nostic of the Ursidae (e.g., by Flower, 1869) have 
been obliterated in Ailuropoda by the expansion 
of the masticatory apparatus. Among these are 
postorbital processes on frontal bones, presence of 
alisphenoid canal, non-confluence of foramen ro- 
tundum and orbital fissure, and presence of fora- 
men lacerum medium. Such secondary differences 
cannot be used as evidence of non-relationship be- 
tween the panda and the bears. 

A. The Vertebral Column as a Whole 

The vertebral column of the giant panda is in 
many respects the most remarkable among living 
carnivores. Slijper (1946) showed that the archi- 

tecture of the developing column is responsive to 
the mechanical demands of posture and locomo- 
tion. Morphogenetically the mammalian column 
behaves like other homiotic structures (Kiihne, 
1936; Sawin, 1945, 1946). Therefore it is prefer- 
able to consider the column as a whole, rather than 
as a chain of independent units. The analytical 
study of the vertebrae of the Carnivora made by 
Stromer von Reichenbach (1902) showed that the 
morphological details of individual vertebae ex- 
hibit no important features consistently correlated 
with the major categories, and are therefore of 
little systematic importance. For this reason no 
detailed description and comparison of individual 
vertebrae of Ailuropoda is presented here. 

The number of presacral vertebrae is extremely 
constant in carnivores. The normal number of 
thoraco-lumbars in all living Carnivora is twenty, 
and individual variations rarely exceed one above 
or below this figure. The giant panda is conse- 
quently remarkable in having only eighteen trunk 
vertebrae; in one of nine skeletons this number 
was further reduced to seventeen, and in one there 
were nineteen (Table 9). 

The number of lumbar vertebrae in Ailuropoda 
is five in 50 per cent of the cases, and four in the 
remaining 50 per cent; in Ursus it is six in 79 per 
cent, and five in the remaining 21 per cent. (Other 
genera of the Ursidae appear to differ from Ursus, 
but the samples are too small to permit conclu- 
sions.) The modal number of lumbars is either 
four or five in Ailuropoda, and six in Ursus; the 
mean is 4.5 and 5.8, respectively, indicating that 
the lumbar region has been reduced by more than 
one vertebra in Ailuropoda. The thoracics show 
a similar but somewhat more limited tendency 
toward reduction: the mean is 13.5 in Ailuropoda, 
14.2 in Ursus. There was evidence of disturbance 
at the cervico-thoracic boundary in one individual 
(p. 85). Thus in the column as a whole there is 
an anterior displacement of the boundaries of the 
several regions in Ailuropoda, and this displace- 
ment shows a gradient decreasing in intensity from 
the sacrum toward the head. 

A remarkable feature of the column in Ailuro- 
poda is its variability. Of nine skeletons examined, 
the thoraco-lumbar juncture was asymmetrical on 
the two sides of the body in three, and four differ- 
ent vertebral formulae are represented among the 
remaining six individuals (Table 9). This varia- 
bility is greater than was found in any of the nu- 
merous arctoid and ailuroid carnivores examined. 

The proportions of the three main divisions of 
the column in Ailuropoda differ from those in other 
carnivores, as shown below. These proportions 
also show a far greater range of variation than in 




of indi- 

Cants latrans 15 

Canis lupus / 9 

Vulpes fulva / 9 

Uroeyon cinereoargenteus I , 

Bassariscus astutus J j 


Nasua narica 1 

Nasua nasua 5 

Procyon lotor J 2 

I 1 

f ^ 
Bassaricyon alleni J 1 

I i 

Ailurus fulgens^ 5 

Ursus (various species)^ 7 

Ursus^ 2 

C7rsus' 1 

Ailuropoda melanoleuca . 1 3 


' One record from Flower (1885). 
' Three records from Flower (1885). 

any other carnivore examined. The cervical re- 
gion is shorter in Ailuropoda than in Ursus but is 
only slightly shorter than in Ailurus and Nasua 
and no shorter than in Procyon. The thoracic re- 
gion is relatively longer than in any other arctoid 
carnivore, resembling that of burrowing mustelids. 
The lumbar region is short in both Ailuropoda and 
Ursus. The proportions of the vertebral colurnn 



+ lum- 

























































































of the giant panda are similar to those of the an- 
thropoid apes and man, and to those of such bur- 
rowing carnivores as Taxidea, Meles, and Mellivora 
columns designed to withstand anteroposterior 

The vertebrae of Ailuropoda are heavier than in 
Ursus; the weight of thoraco-lumbar vertebrae is 
about 16 per cent greater in a specimen of the 
panda than in a black bear of comparable size. 

The Mechanics of the Vertebral Column 

The vertebral column of mammals, with its as- 
sociated muscles and ligaments, is an extremely 
complex mechanism that has never been satisfac- 
torily analyzed. Yet it is only on the basis of its 
functioning that the differences, often extremely 
subtle, exhibited in this region from animal to ani- 
mal can be intelligently considered. Slijper (1946) 
made a painstaking comparative study of the col- 
umn in mammals in an effort to correlate mor- 
phology and function. Many of his findings are 
relevant in the present connection. 

Slijper rejects former comparisons of the verte- 
bral column with an arched roof, a bridge with 
parallel girders, or a cantilever bridge, and com- 
pares it with a bow flexed by a bow-string (the 
sternum, abdominal muscles, and linea alba). 

Vertebral Bodies. Slijper points out that the 
principal static function of the column is to resist 
bending, chiefly in the sagittal plane, and that 
differences in the size and shape of the vertebral 
bodies reflect the forces acting on them. He used 
as a criterion of the stress to which any part of 
the column is subjected the moment of resistance 
to bending, which he computed for each vertebral 
body by using the formula: breadth of articular 
face of body X square of height of body (bh-). 
Plotting these data for the entire column in a series 
of mammals yields characteristic curves of the 
moments of resistance at successive points along 


N Cervical (%) Thoracic (%) Lumbar (%) 

Canis 2 30 39.5(39-40) 30.5(30-31) 

Vulpes 2 28.8 (28-29.5) 39.8 (39.5-40) 31.5 

Bassariscus 1 24 42 34 

Nasua 1 22 45 33 

Procyon 4 21.4 (21-22) 47.7 (47-48) 30.9 (30-31.5) 

Ailurus 3 22 (21.3-22) 47 (47-47.5) 31 (31.0-31.2) 

Ursus 3 26.2 (25.5-27.4) 45.9 (45.6-46.3) 27.9 (26.3-28.9) 

Ailuropoda 6 22 (21-23.2) 55 (51.7-59) 23 (20-26) 

Taxidea 2 23 50.5 (50-51) 26.5 (26-27) 

Meles 1 25 53 22 

Mellivora 1 25 56 19 

' Ursus and Ailuropoda determined on disarticulated skeletons. 









Fig. 33. Diagrams of moments of resistance in the vertebral columns of various mammals: 

A. Moments of resistance in a beam supported at one end. 

B. Slijper's Type 16 curve of moments of resistance in the vertebral column of mammals with an erect or semi-erect 
posture (compare with A and fig. 34). 

C. Theoretical moments of resistance in quadrupedal mammals, in which the vertebral column is compared to a bow, 
with a beam supported at one end attached to the cranial (left) end of the bow. 

D. Slijper's Type II curve of moments of resistance in the vertebral column, characteristic of carnivores other than bears 
and Ailuropoda (compare with C). 

the column. Slijper divides these curves into three 
major types, each with several subtypes. 

Of the few carnivores examined by Slijper (Ca- 
ms, Vulpes, Ursus, Felis, Panther a), all except 
Ursus yielded curves of Type II, characterized by 
a hump in the posterior cervical region, and a flat 
anterior thoracic region, followed by a rise in the 
posterior thoracic and lumbar regions (fig. 33, D).' 
For Ursus the curve slopes upward gradually from 
the anterior cervical region to about the tenth 
thoracic, then abruptly breaks more steeply up- 
ward, sloping downward again in the posterior 
lumbar region. This is Slijper's Type lb curve, 
characteristic of bipedal animals, including man 
(fig. 33, B). The curve for Slijper's bipedal goat 
was also modified in this direction. This type of 
curve agrees closely with the diagram of the theo- 
retical moments of resistance if the column is re- 
garded as an erect or semi-erect beam supported 
at one end (fig. 33, A). 

The curve of the moments of resistance for Ai- 
luropoda was plotted for two individuals, which 
showed only minor differences (fig. 34) . This curve 
is very similar to that for Ursus, differing chiefly 

' Slijper lists the domestic cat (along with the bear and 
the anthropoid apes and man) as having a Type lb curve. 
This is obviously a mistake. I have measured and plotted 
a disarticulated cat column, and find that it has a typical 
Type II curve. 

in its more even slope without the sharp upward 
break at the level of the diaphragmatic vertebra 
(eleventh thoracic in Ursus, eleventh or twelfth in 
Ailuropoda). In this respect Ailuropoda resem- 
bles the anthropoid apes and man more closely 
than Ursus does. 

It is evident that the vertebral axis in the bears, 
and especially in the giant panda, is constructed 
to withstand anteroposterior thrust. 

Neural Spines. The length and angle of in- 
clination of the neural spines do not depend upon 
the static demands made upon the column, but 
upon the structure and development of the epaxial 
muscles that attach to them (Slijper). Thus the 
structure of the spines is ultimately determined by 
posture and locomotion, plus such secondary fac- 
tors as absolute body size, length of neck, and 
weight of head. Both length and inclination of a 
spine are resultants of the several forces exerted 
by the muscles attaching to it, the spine acting as 
a lever transmitting the muscle force to the ver- 
tebral body. 

Plotting the lengths of neural spines as percent- 
ages of trunk length permits comparison of the 
resulting curves for various animals. These curves 
apparently follow a common pattern in all mam- 
mals, although the relative lengths of the spines 









36759 Ailuropoda melanoleuca 







Fig. 34. Curve showing height (h), breadth (6), and moments of resistance (b/i') in the vertebral column of Ailuropoda. 
D = diaphragmatic vertebra. 

vary greatly from species to species. The spines 
are longest on the anterior thoracic vertebrae (at- 
tachment of cervical muscles and ligaments), de- 
crease in length back to the anticlinal or diaphrag- 
matic vertebra, and are slightly longer again on 
the posterior thoracic and lumbar vertebrae (at- 
tachment of longissimus and spinalis muscles). 
Both Ursus and Ailuropoda exhibit this type of 
curve, although in both forms the spines are rela- 
tively short along the whole length of the column 
(fig. 35). 

The inclination of the spines conforms less closely 
to a common pattern than does the height. Ac- 
cording to Slijper the direction of a given spine 
tends, for mechanical reasons, to be perpendicular 
to the most important muscle inserting into it. 
The spines of the pre-anticlinal (or pre-diaphrag- 
matic) vertebrae are inclined posteriorly in all car- 
nivores, as they are in all mammals. Among the 
arctoid Carnivora the post-diaphragmatic spines 
are inclined anteriorly in the Canidae and Procy- 

onidae, are variable among the Mustelidae (from 
an anterior inclination of 45 in the martens to a 
slight posterior inclination in the skunks and 
badgers), and are posteriorly inclined or at most 
vertical in the Ursidae. In Ailuropoda all the 
post-diaphragmatic vertebrae are posteriorly in- 
clined, the minimum inclination in two skeletons 
being 20 (fig. 36). According to Slijper the direc- 
tion of the post-diaphragmatic spines in Carnivora 
and Primates is determined chiefly by the length 
of the vertebral bodies, because the angle of at- 
tachment of the multifidus muscle depends upon 
this length. The bodies of the lumbar vertebrae 
are short in both giant panda and bears, but they 
are not notably shorter in Ailuropoda than in Ur- 
sus, although the posterior inclination of the spines 
is much greater. Thus, other factors must be in- 
volved in Ailuropoda. It is at least suggestive that 
among the primates and burrowing mustelids a pos- 
terior inclination of the post-diaphragmatic spines 
is associated with anteroposterior thrust along the 



% of length of trunk 



(from Slijper) 


2 3 


K) n 

12 13 

Fig. 33. Curves showing lengths of neural spines in AUnropoda, Ursus arHof, and Canig familiaris. 

B. DE:scRipnoNS of Vertebrae 
1. Cervical Vertebrae 

The cervical vertebrae in Ailuropoda are remark- 
able for their breadth, which gives the cervical 
region a compressed appearance, especially when 
viewed from below. Transverse broadening is evi- 
dent on all vertebrae including the atlas and epi- 
stropheus, and greatly exceeds that in any other 
land carnivore. The vertebrae are shorter antero- 
posteriorly than in the long-necked Ursus, but are 

no shorter than in Proeyon and Ailurus. There 
are seven cervicals in each of the eight skeletons 

Except for the distortion resulting from broad- 
ening, the cervicals differ little from those of other 
carnivores. The atlas is similar to that of Ursus 
in the arrangement of foramina; in both there is 
an alar foramen < vertebral artery and vein>, in- 
stead of a mere notch as in other arctoids, into 
which open the atlantal foramen dntervertebral 
of authors; transmits first spinal nerve and verte- 







I 2 3 4 5 6 7 

Thoraco Lumbar Vertebrae 

20 21 

Fig. 36. Curves showing inclination of neural spines in Ailuropoda, Ursus arctos, and Canis familiaris. 

bral artery) and transverse foramen (vertebral ar- 
tery and vein). The foramina on the atlas are 
crowded together as compared with Ursus (fig. 37). 
The transverse diameter across the wings is greater 
than in Ursus, but the wings are narrower antero- 

The third to sixth cervicals are notable chiefly 
for the conspicuous, backwardly directed hypera- 
pophysis (Mivart) atop each postzygopophysis; 
these are barely indicated in Ursus, and are want- 
ing in other arctoids. The spines are nearly obso- 
lete on the third, fourth, and fifth cervicals, but 
are of normal length on the sixth and seventh. 

2. Thoracic Vertebrae 

The thoracic region in Ailuropoda is notable for 
its length. Since the number of thoracic verte- 

brae averages about one less than in Ursus, the 
gi-oater thoracic' length must be attributed to 
longer centra on individual vertebrae, but I have 
been unable to demonstrate this satisfactorily. 

There is, of course, no anticlinal vertebra in 
Ailuropoda, since the neural spines all slope in the 
same direction. A true anticlinal is also wanting 
in Urstis for the same reason. The diaphragmatic 
vertebra is that transitional vertebra on which the 
prezygapophyseal facets look upward (horizontal), 
while the postzygapophyseal facets look outward 
(vertical or oblique) . The diaphragmatic vertebra 
is the eleventh thoracic in one specimen of Ailu- 

' This length of thorax is approached or even exceeded in 
some burrowing mustelids, e.g., Taxidea, Mephitis, Melli- 
vora. In these forms, however, the thoracic region has taken 
over the anterior lumbars, and the thoracic count is 1 6 or 1 7. 

For. atlantis 

For. alare 

Ala atlantis 

For. Iransversarium 


For. transversarium' 

Corpus epistropheus 


Ursus americanus 

Fig. 37. Cervical vertebrae of Ailuropoda and Ursus. A, atlas from below; B, epistropheus and third cervical from left side. 


Fig. 38. Fifth thoracic vertebra of Ailuropoda. 





ropoda, the twelfth in another. It is the eleventh 
in Ursus. It is uniformly Th. 10 in the Canidae. 
The Procyonidae vary: Bassariscus, Th. 10; Bas- 
saricyon, Th. 10; Ailurus, Th. 11; Procyon and 
Nasua, Th. 12. 

There are fewer lumbar vertebrae (an average 
of 4.5 in the eight skeletons examined) than in any 
other arctoid carnivore. ^ The lumbar spines all 
slope posteriorly; this is not encountered in any 
other arctoid, but is approached in Ursus. 


UrsKs americanus 

Fig. 39. Third lumbar vertebra of Ailuropoda and fourth lumbar of Ursus, seen from the left. 

There are few significant differences in morpho- 
logical details. The intervertebral foramina (spi- 
nal nerves and vessels) are conspicuously larger 
than in Ursus, owing chiefly to the larger size of 
the posterior vertebral notch. The width across 
prezygapophyses and postzygapophyses is much 
greater in Ailuropoda than in Ursus and other 
arctoids, which should contribute to the stability 
of this region. The spines are capitate, especially 
on the anterior vertebrae. Their posterior bor- 
ders are less produced than in Ursus, and their 
lateral surfaces present prominent muscle rugo- 
sities that are lacking in other arctoids. 

3. Lumbar Vertebrae 

The lumbar region is shorter than in any other 
arctoid carnivore examined. It is short in burrow- 
ing mustelids (Meles 22 per cent, Mellivora 19 per 
cent, but Taxidea 26-27 per cent) and hyenas (18- 
20 per cent). The length relative to the total col- 
umn is not much greater in Ursus than in Ailuro- 
poda (see Table 10) , but because of the long neck in 
bears this does not properly reflect the true short- 
ness of the lumbar region in Ailuropoda. The 
absolute length of the lumbar region in Ailuropoda 
is only 165-180 mm. (32-33 per cent of thoraco- 
lumbar length), while in a bear of comparable size 
(Ursus americanus) it measures 233 mm. (38 per 
cent of thoraco-lumbar length). 

The form of the vertebrae is similar to that in 
Ursus. The centra are very short in both. As 
with the thoracics, the intervertebral foramina are 
larger, and the pre- and postzygapophyses are wider 
than in Ursus. 

The lumbar spines in both the giant panda and 
the bears are short and stumpy, and are either ver- 
tical (Ursus) or posteriorly inclined (Ailuropoda). 
Slijper believes that the vertical position of the 
spines in Ursus is correlated with the shortness of 
the lumbar centra, which results in greater me- 
chanical efficiency in the longissimus and multifi- 
dus muscles attaching to them. 

The transverse are not well developed 
in either Ailuropoda or Ursus. In both they are 
relatively short, and directed transversely instead 
of anteriorly as in other arctoids. These processes 
provide attachment for the ilio-costal and quad- 
ratus lumborum muscles, which function in exten- 
sion and flexion of the column and hence are 
important in movements of the back during run- 

Anapophyses (accessory process of Reighard and 
Jennings and Baum and Zietzschmann) are pres- 

' In some of the burrowing mustelids (Arctonyr, Cone- 
paius, Mellivora) four is apparently the normal number of 
lumbars. In these, however, the number of thoracics is cor- 
respondingly increased, and the thoraco-lumbar count is 20 
or 21, the typical carnivore formula. The curve of the 
moments of resistance is also altogether different. 



ent on the first two lumbars, are barely indicated 
on the third, and are obsolete on succeeding verte- 
brae. Ursus is practically identical. These proc- 
esses are present on all lumbars except the last in 
Procyon and Nasua, and on all but the last two in 

Four pelves of Ailuropoda were available for de- 
tailed examination. Three full vertebrae are in- 
volved in the sacro-iliac joint in two, and two and 
a part of the third are involved in two individuals. 
In one sacrum articulating by three full vertebrae. 

Proc. spinosus 

MC Postzygapophysis 


Proc. tramrersus 



Fig. 40. Second lumbar vertebra of Ailuropoda and Ursus americanus, seen from the rear. 

other procyonids and Canis. They provide inser- 
tion for the tendons of the longissimus muscle, 
which functions in extension and flexion move- 
ments of the vertebral column. 

4. Sacral Vertebrae 

The sacrum is composed of five fused vertebrae 
in all eight skeletons of Ailuropoda examined. As 
will be seen from the accompanying table, Ursus 
is remarkably varied in this respect, although the 
most frequent number is likewise five. In all other 
arctoid carnivores the normal number of sacrals is 
three. (Sacrals are reckoned, according to the 
definition of Schultz and Straus, as "the vertebrae 
composing the sacrum and possessing interverte- 
bral and sacral foramina ringed completely by 
bone in the adult.") 

Number of Sacral Vertebrae 

Canis latrans 

Canis lupus 

Vulpes fulva 

Urocyon cinereoargentetis . 

Bassariscus astutus 

Nasua narica 

Nasua nasua 

Procyon lotor 

Bassaricyon alleni 

Ailurus fulgens* 

Ursus sp.** 

Ailuropoda melanoleuca. . 













* One record from Flower. ** Six records from Flower. 

the first sacral has the appearance of a transformed 
lumbar well-formed pre- and postzygapophyses, 
enormous sacral foramina, incomplete fusion of the 
centra ventrally although on the basis of the total 
column it is numerically equivalent to the first sa- 
cral of the second individual. This is of interest in 
connection with the reduced number of thoraco- 
lumbars in Ailuropoda, and the extraordinary in- 
stability of the thoraco-lumbar boundary. It is 
further evidence of the genetic instability of the 
posterior part of the vertebral column in this 

In the primary condition in arctoids, as seen in 
Canis, Bassariscus, and Nasua, the sacro-iliac ar- 
ticulation is restricted almost entirely to a single 
vertebra, the first sacral. In Procyon and Urstts 
the articulation is more extensive, including the 
first two sacrals, while in Ailuropoda it reaches 
its maximum among the arctoid carnivores with 
the third vertebra participating more or less com- 

It is interesting and suggestive that the increase 
in length of sacrum and extent of sacro-iliac artic- 
ulation among the Carnivora is paralleled among 
the Primates. The figures given by Schultz and 
Straus (1945) show that the number of sacrals in- 
creases abruptly in the anthropoid apes and man 
over the number found in other Primates (except 
the aberrant Lorisinae). Examination of a series 
of primate skeletons shows that the extent of the 
sacro-iliac articulation is likewise increased in the 
bipedal apes and man. 




Arnis rertebrae 
Proc: transrersus 


lsl,2nd & 3rd Caudals 

Isl.Znd & 3rd Caudals 

lst,gnd & Srd Caudals 

6th Caudal 

6th Caudal 

6th Caudal 

1st Caudal (anterior) 


1st Caudal (anterior) 


1st Caudal (anterior) 


Fig. 41. Caudal vertebrae of Ailuropoda, Ursus americanus, and Procyon lotor. First three caudals, dorsal view; sixth 
caudal, dorsal view. 

The morphology of the sacrum in Ailuropoda is 
similar to that of Ursus but differs in a number of 
respects. The long axis of the bone is nearly 
straight in the panda, while in the bears it is 
slightly curved ventrad. In the panda the sacrum, 
like the remainder of the vertebral column, ap- 
pears to be expanded laterally and depressed dorso- 
ventrally. The spines are fused to form a contin- 
uous median sacral crest, which forms a peak on 
the first sacral and becomes nearly or quite obso- 
lete on the fifth. The intervertebral foramina are 
minute, irregular, and nearly obliterated. There 
are four pairs of dorsal sacral foramina (dorsal 
divisions of sacral nerves, branches of lateral sa- 
cral arteries). The first two pairs are irregular, 
often small and almost obliterated as a result of 
bone growth in connection with the sacro-iliac an- 
kylosis. The last two pairs are larger and more 
regular. The four pairs of ventral sacral foramina 
(ventral divisions of sacral nerves, branches of 
lateral sacral arteries) are much larger and more 
regular than the dorsal foramina. 

5. Caudal Vertebrae 

The tail is short and almost vestigial, but neither 
as short nor as degenerate as in the bears. 

Nowhere is the shortening and dorso-ventral 
flattening of all the vertebrae of Ailuropoda more 
apparent than in the tail. All the caudals are 
heavy and stocky; even those toward the tip of 
the tail lack the slender rod-like form characteris- 
tic of other carnivores. This is undoubtedly to be 
interpreted as a gratuitous extension of the factors 
influencing the remainder of the column, since in 
Ailuropoda, as in the bears, the tail is functionless. 

The tail is composed of eleven vertebrae in the 
one specimen in which it is complete. This is 
within the range of variation of Ursus, in which 
there are eight to eleven or more vertebrae. Other 
arctoids have much longer tails, with from eighteen 
to twenty or more vertebrae, each of which is rela- 
tively much longer than in Ailuropoda or Ursus. 

The first two caudals are well formed in Ailur- 
opoda, with complete neural arch but no neural 
spine, wide transverse processes, and prezyga- 
pophyses; postzygapophyses, which are present 
in other arctoids except Ursus, are wanting. On 
the first vertebra the transverse processes extend 
the entire length of the centrum, and even ante- 
riorly beyond the centrum onto the prezygapophy- 
sis. There are no chevron bones. In Ursus, in 



contrast, the neural arches are wanting on all 
caudals (U. americanus) or are present on only 
the first vertebra, and the transverse processes are 
almost completely obsolete even on the first cau- 
dal. Chevron bones are wanting in the bears. 

Viewed from the front, the first caudal exhibits 
to a striking degree the dorso-ventral flattening 
of the vertebrae (fig. 41). 

The remaining caudals are short and stocky, ex- 
hibiting less of the typical rod-like form than is 
seen even in Ursus. The broadening effect is evi- 
dent at least back to the seventh vertebra, the 
transverse processes becoming entirely obsolete on 
the eighth. 

C. Review of the Vertebral Column 

The contrast between Gadow's explanation of 
the evolution of the vertebral column (1933) and 
that of Slijper (1946) is a measure of the altered 
point of view with respect to this complex struc- 
ture. To Gadow the column is a series of discrete 
entities, each with its own almost independent 
phylogenetic history. A lumbar vertebra is fun- 
damentally a lumbar, regardless of whether it has 
been "transformed" into a thoracic in one instance 
or a sacral in another. The functioning of the 
column, as well as mechanisms by which observed 
differences could have been achieved, are ignored. 
The goal is to discover the "true homologies" of 
elements a goal that, with respect to the verte- 
brae, we now know is largely a will-o'-the-wisp. 
This is the classical outlook of many of the older 
comparative anatomists. 

Slijper, on the other hand, has regarded the col- 
umn, along with its muscles and ligaments, as an 
architectural construction responsive to the me- 
chanical demands of posture and locomotion. He 
has tried to determine correlations between struc- 
ture and function under varying conditions. Ho- 
mologies are not considered. His work is essentially 
an engineering study. 

Neither Gadow nor Slijper considered the ques- 
tion of how, from the standpoint of evolutionary 
mechanisms, the differences they observed could 
have been brought about. Studies by Kiihne 
(1936) and others on the inheritance of variations 
in the human vertebral column showed that dif- 
ferentiation of the column, like that of other homi- 
otic structures, is genetically controlled as a series 
of fields or gradients of differentiation and growth. 
These fields correspond to the thoracic, lumbar, 
and sacral regions of the column. The anlage of 
a vertebra is indifferent; its differentiated form 
depends on its position in a particular field. There 
is also a general cranio-caudal gradient of differen- 

tiation; so increasing the tempo of development 
would shift the boundaries of all regions cranially, 
and vice versa. Kuhne emphasized that all dis- 
placements were always in the same direction in a 
given individual. Moreover, "besides the trunk 
skeleton, the field of action embraces the periph- 
eral nervous system (limb plexuses), musculature, 
blood vessels, and a large part of the organs of the 
thoracic and abdominal cavities" (Kiihne). Kiihne 
concluded that all the variations he observed could 
be explained by assuming a single pair of alleles, 
"craniad" and "caudad." These deductions were 
verified experimentally by Sawin (1945, 1946), 
who concluded from breeding experiments on rab- 
bits that displacements of the boundaries of verte- 
bral regions are determined primarily by a single 
pair of genes. 

Among the arctoid carnivores the thoracolum- 
bar boundary is shifted caudad in the Procyonidae 
(except the primitive Bassariscus) and Ursidae. 
The functional significance, if any, of this shift is 
unknown. It did not affect the number of thoraco- 
lumbar segments, which remain at the typical 20. 
In Ailuropoda the thoracolumbar boundary is vari- 
able, but obviously has been shifted cranially from 
its position in the Ursidae. The lumbosacral 
boundary has likewise been shifted cranially two 
to three vertebrae from its typical position in arc- 
toid carnivores. Thus in Ailuropoda, as in the 
higher primates, there is a general cranial displace- 
ment in the regional boundaries of the column. 
In both the panda and the higher primates this 
cranial shift is associated with intense differentia- 
tion in the anteriormost part of the body axis 
the head. In both cases this "cephalization" rep- 
resents an increase in the tempo of differentiation 
or growth, although very different tissues are in- 
volved. Because of the axial gradient, the cepha- 
lization is accompanied by a cranial shift in the 
boundaries of the regions of the column. Conse- 
quently, shortening of the column and displace- 
ment of its regional boundaries in Ailuropoda (and 
probably also in the higher primates) are not 
themselves adaptive, but are consequential results 
of a process of cephalization. In bulldogs, which 
are likewise characterized by cephalization, Klatt 
and Oboussier (1951) reported malformations of 
the vertebral column (but no reduction in num- 
ber of vertebrae) in about 80 per cent of their 

The vertebrae are also broadened and depressed 
in Ailuropoda in comparison with Ursus and other 
carnivores. There is no way of determining how 
much this is due to secondary postnatal factors 
extrinsic to the bone itself, although there is no 
evidence that the condition is adaptive. The facts 



that it is markedly evident in the tail, where the 
static influences of posture and locomotion do not 
exist, and that the same effect is evident on the 
proximal ends of the ribs, strongly suggest that 
this is a part of the field effect involving the entire 
axial region of the body. 

Homiotic variability in the column of Ailuro- 
poda is greater than in any other carnivore exam- 
ined. This indicates that the mechanism regulating 
differentiation of the column is not yet stabilized 
around a new norm, which in turn suggests an 
absence of strong selection pressure on this region. 

Thus the vertebral column of Ailuropoda differs 
from that of Ursus in several respects. The dif- 
ferences are not random, but rather form some 
kind of pattern. We must assume as a working 
hypothesis that the differences are adaptive that 
they are a product of natural selection. We then 
seek answers to two questions: (1) what is their 
functional significance, and (2) what morphoge- 
netic mechanism, intrinsic to the bone tissue, lies 
behind them? 

It has been noted repeatedly throughout the 
description that the column of Ailuropoda resem- 
bles columns designed to withstand strong thrust 
forces acting anteroposteriorly in the direction of 
the sacrum. Among terrestrial mammals such 
forces, and correlated modifications of the column, 
occur only in fossorial and bipedal forms. The 
work of Slijper shows that the mammalian column 
responds adaptively to such forces, even non- 
genetically. Ailuropoda is, of course, in no way 
fossorial; and it is no more bipedal than the bears, 
in which the column shows slight almost trivial 
compared with that in Ailuropoda convergence 
toward the column of truly bipedal forms. The 
column of Ailuropoda cannot be explained on the 
basis of mechanical requirements, and therefore 
the differences from Ursus cannot be attributed to 
natural selection acting on the column. The seem- 
ingly adaptive modifications must be "pseudo- 

The data of Sawin and Hull suggest an alterna- 
tive explanation. All those areas of a tissue that 
are in a state of competence at a given moment 
during ontogeny are known to be affected by a 
genetic factor operating at that moment. Thus 
the lumbosacral peculiarities of Ailuropoda may 
reflect an accident of ontogenetic timing rather 
than the action of selection on the lumbar region. 
If the differentiating lumbar region were compe- 
tent at the same moment as some other region on 
which selection was acting strongly (e.g., the skull), 
then in the absence of strong selection against the 
induced lumbar modifications, such modifications 
would be carried as a pleiotropic effect. If they 

were strongly selected against they would presum- 
ably be buffered out. The extraordinary homiotic 
variability of the lumbosacral region in Ailuropoda 
supports this interpretation, as does the otherwise 
unintelligible modification of the pelvis (p. 113). 
On the basis of the available evidence it must 
be concluded that primary differences between the 
column of Ailuropoda and that of Ursus are not 
adaptive, but represent a pleiotropic effect result- 
ing from an accident of ontogenetic timing. The 
genetic basis for such an effect is probably very 

D. Conclusions 

1. The vertebral column of Ailuropoda differs 
from that of Ursus (and other arctoid carnivores) 
in several important respects. 

(a) The regional boundaries are shifted crani- 
ally in a gradient that decreases in intensity 
from the lumbosacral boundary (greatest) 
to the thoracocervical (least). 

(b) All vertebrae are broadened and depressed. 

(c) Homiotic variability exceeds that known 
in any other carnivore. 

2. The differences are not adaptive. 

3. The differences are associated with intensi- 
fied growth at the anterior end of the body axis 
the head. Similar correlations are evident in pri- 
mates and in bulldogs. 

4. The characteristic basic features of the ver- 
tebral column in Ailuropoda are a pleiotropic effect 
resulting from an accident of ontogenetic timing. 


The thoracic region, as pointed out above, is 
relatively longer in Ailuropoda than in any other 
arctoid carnivore. This is true when the extent 
of the thorax is measured dorsally, along the ver- 
tebral column. On the other hand the ventral 
length of the thorax, measured along the sternum, 
is notably less than in any other arctoid carnivore. 

A. Ribs 

The number of ribs varies between 13 and 14 
pairs in the eight skeletons examined, with a high 
proportion of asymmetries on the two sides of the 
same animal (see Table 9, p. 75). On the basis of 
the available material it is impossible to determine 
which is the typical number. 

In one skeleton (31128), which shows other gross 
abnormalities, the first rib on the left side is short, 
not reaching the manubrium, and the tubercular 
head is pathological. The second rib resembles the 
first of the opposite side, but its sternal end is 



bifurcate and attaches to the manubrium by a 
wide bifurcate costal cartilage. 

of the sternum in this animal. In Su Lin two pairs 
of the false ribs are floating. 

Ailurvpoda ^"* 

Fig. 42. Tenth rib, lateral view. Above, posterior views of heads of same ribs. 

In two skeletons there are nine pairs of true ribs, 
which is the normal number for arctoid carnivores. 
The eighth and ninth pairs are not attached to 
sternebrae in Ailuropoda, however; instead, the 
ends of the sternal cartilages of each pair meet at 
the ventral midline, ventral of the xiphoid carti- 
lage. This is obviously a result of the shortening 

The first costal cartilage is about 20 mm. long, 
the ninth about 230 mm., in Su Lin. In an adult 
the costal cartilages are very heavily calcified, with 
coarse granular deposits appearing on the surface. 

The ribs are very similar in length and curvature 
to those of bears of comparable size ( Ursus ameri- 
canus). All the ribs are remarkable, however, for 





\ I ff / 

Fig. 43. Approximate area of maximal increase in thickness of cortical bone in Ailuropoda. 

the immense bulk of their vertebral ends (fig. 42). 
The transverse diameter of the neck of a given rib 
in Ailuropoda is at least twice the diameter in 
Ursus americanus. The disparity becomes in- 
creasingly less toward the sternal end of the rib, 
until the sternal third is no larger in the panda 
than in the bear. It is at least suggestive that the 
maximum broadening is in that part of the rib 
closest to the vertebra, where, as we have seen, a 

pronounced broadening effect is apparent, and 
that the width gradually decreases to normal as 
we move along the rib away from the vertebra. 

B. Sternum 

The sternum is composed of a short body and 
an extremely long xiphoid cartilage. The body is 
about 55 per cent of the length of the thorax in 



Ailuropoda, while in other arctoids it is from 75 
to 100 per cent. 

There are six sternebrae (including the manu- 
brium) in each of three skeletons of Ailuropoda 
examined. In other arctoids there are nine, ex- 
cept in the Canidae, which usually have only eight. 
All the sternebrae are short. 

The manubrium is short, compared with that 
of Ursus and other arctoids, and is relatively wider 
transversely. In other arctoids this bone is pro- 
duced anteriorly into a point, so that the outline 
is similar to a spear head. This point is much less 
evident in Ailuropoda, and in one of three speci- 
mens is totally lacking so that the anterior border 
of the manubrium is truncated. A single pair of 
costal cartilages articulates with the manubrium. 

The remaining sternebrae, five in number, are 
short and spool-shaped, rectangular in cross sec- 
tion. The first four measure about 25 mm. in 
length, the fifth about 20 mm. 

The xiphisternum is a remarkably long (120 
mm.) cartilaginous rod, tapering gradually to a 
point. It provides attachment for the sternal part 
of the diaphragm and the posterior elements of the 
transverse thoracic muscle. Elongation of the 
xiphisternum appears to be a compensation for 
the shortness of the bod^'^ of the sternum, since the 
origin of the sternal part of the diaphragm is thus 
brought into line with the origin of the costal part 
of this muscle. 

In the Canidae and Procyonidae the xiphister- 
num is composed of an ossified rod ending in an 
expanded flattened cartilage. In the Ui*sidae it is 
a cartilaginous rod, with an ossicle of variable size 
embedded in the anterior end. 

In the Procyonidae the last stemebra is only 
about half the thickness of those preceding it, pro- 
ducing a "step" in the sternum. The last costal 
cartilages meet their fellows beneath this bone, in- 
stead of inserting into its lateral edges as they 
normally do. A similar condition is often seen in 
bears, in which this stemebra may be entirelj* un- 
ossified. The posterior end of the sternum seems 
to be undergoing regression in this group. 

C. Review of the Thorax 

Two points are of interest in the bones of the 
thorax: the extraordinary expansion of the prox- 
imal ends of the ribs, and the shortening of the 

No mechanical advantage can be assigned to 
the rib condition. It is most easily explained as 
an extension of the morphogenetic field effect that 
is oi>erating on the adjoining vertebrae, and hence 
without functional significance as far as the ribs 

are concerned. Thus a region of increased bone 
deposition extends the entire length of the head 
and body and extends laterally over the proximal 
two-thirds of the rib cage (fig. 43). Since the cor- 
tex of the long bones is also thickened, the effect 
is general over the entire skeleton though reduced 
peripherally. An astonishingly similar condition 
is seen in the ribs of the Triassic marine nothosaur 
Pachypleurosaurus (1931, Peyer, Abh. Schweiz. 
Paleont. Ges., 51, pi. 25; 1935, Zangerl, op. cit., 
56, fig. 23). In the reptile, enlargement of the 
proximal ends of the ribs is associated with pachy- 
ostosis; there is no evidence of this in Ailuropoda. 

The extreme shortening of the sternum seen in 
Ailuropoda is foreshadowed in the related procyo- 
nids and bears, in which a tendency toward re- 
duction from the rear forward is evident. There 
is no obvious mechanical advantage to this shift, 
which is inversely correlated with elongation of 
the thorax in these animals. The sternum has 
been shortened repeatedly in various mammalian 
lines, but to my knowledge this has never been 
studied from the standpoint of animal mechanics. 

We may conclude, provisionally, that (1) the 
broadening of the vertebral column has extended mor- 
phogenetically to the proximal ends of the ribs in 
Ailuropoda, and (2) the shortening of the sternum is 
the final expression of a trend, of unknown signifi- 
cance, seen in related forms. 


In the giant panda, the bears, and the procyo- 
nids the fore legs are used for manipulating objects, 
especially during feeding, to a far greater extent 
than in other carnivores. This requires a wider 
range of movement, particularly of abduction of 
the humerus and rotation of the fore arm, than in 
tj-pical carnivores. All these forms are also more 
or less arboreal, and in the heavier forms at least 
this has profoundly altered the architecture of the 
shoulder and fore leg (Davis, 1949i. Such uses of 
the fore limb are secondary ; in the primary carni- 
vore condition the fore leg is modified for cursorial 
locomotion, and the structure of the limb in all 
carnivores has been conditioned by this fact. 

A. Bones of the Fore Leg 

The clavicle is vestigial or absent in all Car- 
nivora, never reaching either the acromion or the 
sternum when a clavicle is present. Among the Arc- 
toidea it is normally absent in Canis, exceptionally 
being represented by a small nodule of cartilage 
or bone (Ellenbei-ger and Baum). It is present as 
a small spicule of bone embedded in the cephalo- 
humeral muscle in Bassariscus, Procyon, and Ailu- 
rus. It is completely wanting in the Ursidae, and 

M. rhomboideus 

M. rhomboideus capitis 

M. rhomboideus 

M. infraspinatus 

M. acromiotrap. + 
M. spinotrap. 

M. teres major 

M. subscapularis minor 

M. supraspin. 

M. triceps longus 

M. teres minor/ 

M. spinodeltoideus'' 

M. biceps 

M. atlantoscapularis 

M. acromiodelt. 

Fig. 44. Right scapula of Ailuropoda, lateral view. A, right scapula of Ursus areios. 

M. rhomboideus 

M. subscapularis 

M. coracobrachialis 

M. levator scapulae + 
M. serratus ventralis 

M. teres major 

M. triceps longm 

Fig. 45. Right scapula of Ailuropoda, medial view. 




there is no indication of a clavicle in Ailuropoda. 
The clavicle is less degenerate in the Feloidea. 

1. Scapula 

It has been stated repeatedly that the scapula 
is influenced by muscular action probably to a 
greater degree than any other bone in the body. 
Dependence of scapula shape on muscle function 
has been demonstrated experimentally for rats 
(Wolff son, 1950). The forces involved in molding 
the scapula are extremely complex, no fewer than 
17 muscles arising or inserting on the scapula in 
carnivores, and interpretation of differences in 
scapular form is difficult. No adequate study of 
the I'elation between form and function of the 
mammalian scapula exists, although such a study 
was attempted by Reinhardt (1929). 

The scapula of the giant panda appears at first 
glance to be quite strikingly different from that of 
any other arctoid. This is due to the unorthodox 
outline of the bone (fig. 44). Actually, all the 
features that distinguish the scapula of Ursus from 
other arctoids are also present in Ailuropoda, al- 
though the large postscapular fossa of the bears 
is reduced in the panda. These ursid features 
are: prominent postscapular fossa, large table-like 
acromion with poorly differentiated metacromion, 
breadth of neck exceeding long diameter of glenoid 
fossa, well-defined spiral groove on axillary border, 
and narrow glenoid cavity. There can be no doubt 
that the scapula of the giant panda is basically a 
bear scapula. 

I have tried to show (Davis, 1949) that the 
shoulder architecture of bears, and hence the form 
of the scapula, is adapted to resist pulling forces 
(the opposite of the thrust associated with normal 
locomotion) developed in connection with climb- 
ing, the morphological effects of which are exag- 
gerated because of the size of the animal. The 
tremendous postscapular fossa, from which the 
subscapularis minor muscle arises, is the most con- 
spicuous feature associated with this reversed force 
direction; it is even larger in such powerful diggers 
as the anteaters and armadillos, in which similar 
pulling forces are involved. 

The posterior angle (and thus the scapular in- 
dex) is influenced chiefly by the posterior part of 
the serratus ventralis muscle. This part of the 
serratus is a posterior rotator of the scapula, and 
is used in protraction of the arm (A. B. Howell, 
1926). The posterior part of the serratus is well 
developed in Ailuropoda, and this may account, 
at least in part, for the pulling out of the poste- 
rior angle. 

Morphology. The scapula of Ailuropoda is 
more fan-shaped than the almost rectangular scap- 

ula of Ursus. Of the three borders, the coracoid 
border is produced anteriorly in some individuals 
(fig. 44) to form a sharp angle that marks the an- 
terior limit of the insertion of the rhomboideus, 
which is remarkable for the length of its insertion 
line. In other individuals this angulation is miss- 
ing. The scapular notch, which is at best poorly 
developed in nearly all carnivores, is almost oblit- 
erated in Ailuropoda and Ursus. The vertebral 
border forms a smooth, gentle curve, with no clear 
indication of the juncture of the coracoid and ver- 
tebral borders (the anterior angle; median angle 
of human anatomy). This blurring of the ante- 
rior angle is characteristic of Carnivora. The pos- 
terior extent of the vertebral border is determined 
by the serratus ventralis; the rhomboids appar- 
ently have no influence in determining the position 
of the posterior angle. The axillary border, from 
which the long triceps arises, is relatively straight 
and clearly defined. Its juncture with the verte- 
bral border (the posterior angle; inferior angle of 
human anatomy) marks the juncture of the ser- 
ratus ventralis and teres major muscles, and is 
clearly defined. 

In the Carnivora the ouiline, and hence the major 
indices, of the scapula are determined by two muscle 
groups related to the vertebral border: the rhomboids, 
and the levator scapulae + serratus ventralis. 

The lateral surface is slightly concave, and is 
divided by the spine into the supraspinous and 
infraspinous fossae. The infraspinous fossa con- 
siderably exceeds the supraspinous in area, and 
is relatively much larger than in the bears. This 
increased size is due to an extension posteriorly of 
the axillary border, as is shown by the angle formed 
by the axillary border with the spine; this is 38-40 
in Ailuropoda, 20-30 in Ursus. The floors of both 
fossae are marked by vermiculate rugosities simi- 
lar to those seen in the giant anteater, and there 
is a nutrient foramen in each above the glenoid 
cavity. The coracoid border of the supraspinous 
fossa is sometimes raised and sometimes not, a 
variation also found in bears. In some individuals 
of Ailuropoda it is raised, so that the fossa is con- 
cave in cross section, while in others it is depressed, 
producing a prominent convexity in the fossa. The 
axillary border of the infraspinous fossa is influ- 
enced by the triceps longus, whose origin in the 
bears and giant panda extends nearly or quite to 
the posterior angle. This border is sinuous in Ailu- 
ropoda, straight in the bears. The teres major 
process lies behind the axillary border at the pos- 
terior angle. The teres major muscle arises from 
its posterior border. The lateral surface of this 
process is excavated into the postscapular fossa, 
from which the subscapularis minor muscle arises. 



M. acromiodelt. 

M. biceps 

M. subscapularis minor 

Fig. 46. Ventral view of right scapula of Ailuropoda (left) and Ursus arctos (right). 

In Ailuropoda the postscapular fossa is well 
marked, but has been much reduced by the pos- 
terior extension of the infraspinous fossa so that 
it is much less conspicuous than in Ursus. The 
postscapular fossa is continued toward the glenoid 
cavity as a wide trough that extends the en- 
tire length of the axillary border, separated from 
the medial surface of the blade by a prominent 
ridge, and from the lateral surface by the infe- 
rior scapular spine. This trough (fig. 46), which 
lodges the subscapularis minor muscle, is twisted 
through 180. 

The glenoid cavity is pear-shaped, with the apex 
anteriorly, as it is in other carnivores and in mam- 
mals generally. The notch that appears in the mar- 
gin opposite the spine in certain carnivores {Canis, 
Felis) is wanting in Ailuropoda and most other car- 
nivores. In Ailuropoda the cavity is narrower (in- 


length X 100 

= 645, mean of two specimens) 

than in any other carnivore. It is also narrow in 
bears (index 670, mean of 6 specimens), and gen- 
erally narrower in arctoids than in aeluroids. The 
cavity is shallow in both Ailuropoda and Ursus. 

The neck is notable for its great anteroposterior 
diameter, although this is slightly less than in Ur- 
sus. The supraglenoid tuberosity, for the origin 
of the tendon of the biceps, is a prominent scar 
immediately above the anterior border of the gle- 
noid cavity. Above and mesad of it is a slight 
elevation, the coracoid process, bearing on its me- 
dial surface a scar from which the tendon of the 
coracobrachialis arises. The infraglenoid tuber- 
osity, from which the anteriormost fibers of the 
long triceps take tendinous origin, is much less 
prominent than in Ursus. It is merely a rough- 
ened triangular area above the lip of the glenoid 
cavity that continues without interruption into 
the axillary border. 



M. infraspinatus 

M. brachialis + 
M. triceps lateralis " 

M. triceps medialis 
tcaput longum) 

M. teres minor 

M. acromiodelt 

Crista deltoidea 

M. brachialis 

M. cephalohumer. 
Crista pectoralis 

M. ext. carpi radialis 
longus et brevis 

Crista epicondyltts lat. 
M. anconaeus 

M. ext. dig. comm. ct. lat 
M. ext. carpi ulnaris 

M. supraspin. 
Tuber, majus 

M. stemohumer. prof. 

M. pect. superf. 

M. brachialis 
M. brachioradialis 

M brachialis 

Epicondylus lateralis 

Fig. 47. Lateral view of right humerus of Ailuropoda. 

The spine is slightly twisted, as it is also in bears, 
reflecting the action of the deltoid and trapezius 
muscles. The line formed by the crest of the spine 
is convex posteriorly, in some individuals markedly 
so (reflecting the pull of the acromiotrapezius?) . 
The inferior part of the spine, just above the acro- 
mion, is inclined slightly anteriorly, while the pos- 
terior part is vertical or inclined slightly posteri- 
orly. The lateral (free) border, again as in bears, is 
squared in cross section. The spine is continued 
ventrally into a heavy acromion process, which 
functions in the origin of the acromiodeltoid and 
levator scapulae ventralis muscles. The meta- 
cromion, the process on the posterior border from 

which the levator scapulae ventralis arises in most 
carnivores, is not indicated in Ailuropoda and is 
scarcely more prominent in Ursus. The lateral 
surface of the acromion is flat and table-like in 
both bears and panda. 

In summary, the scapula of Ailuropoda agrees 
with Ursus in all features that distinguish the bear 
scapula from that of other carnivores. The most 
notable difference between the panda and the bears 
is the posterior expansion of the infraspinous fossa 
in Ailuropoda, which seriously encroaches on but 
does not obliterate the typically ursid postscapular 
fossa. The infraspinous fossa is associated with 
the infraspinous and long triceps muscles, which 



Tuber, minus 

M. supi'aspin. j. 

M. subscapularis 

Tuber, majus 

M. triceps medialis 
(caput longum) 

M. coracobrachialis brevis 

M. pect. prof.- 

Crista peclorali 

M. teres major 
M. latissimus dorsi 

M. pect. supei f 

M. triceps medialis 
(caput intermedium) 

M. eoracobrachialib longus 

M. anconaeus 

Fossa olecrani 

M. flexor digitorum prof. (4) 
M. flexor digitorum prof. (2) 

Epicondylus medialis 
M. pronator teres 

M. flexor carpi radialis 
M. flexor digitorum prof. (1) 

M. palmaris longus 
M. flexor carpi ulnaris 

Fig. 48. Medial view of right humerus of Ailuropoda. 

are involved in fixation and flexion of the shoulder 

2. Humerus 

The humerus in the Carnivora serves for the 
origin or insertion of 28 muscles. Of these, 12 be- 
long to the shoulder joint and 16 to the elbow joint 
or lower arm and manus. The form of the humerus 
is determined largely by these muscles. 

In Ailuropoda the humerus is longer than the 
radius, as it is in all arctoid carnivores except Pro- 
cyon and most dogs. The mean ratios (length of 
radius X 100/length of humerus) for various gen- 
era are as follows: 

index * 


Bassaricyon 1 72.7 

Ailurus 3 74.7(72.1-77.8) 

Ailuropoda 7 77.1 (74.7-79.7) 

Bassariscus 4 79.0 (77.9-79.5) 

Ursus (various species) 6 82.3 (78.3-85.8) 

Nasua 2 85.5 (82.7-88.2) 

Canis lupus 4 100.6 (98.1-102.9) 

Procyon 4 100.9 (99.5-102.5) 

* In generalized mammals the radius length is about 85 
per cent of the humerus; this is true in such generalized ter- 
restrial insectivores as Echinosorex, Erinaceus, and Soleno- 
don. A. B. Howell (1944) states that in the generalized 
condition the humerus and radius are about the same length, 
but this is obviously not true for mammals at least. For 
simple mechanical reasons the radius tends to lengthen with 
cursorial locomotion, but reasons for shortening this bone 
are not so clear. In man (European) the index is about 74. 



The humerus of Ailuropoda (figs. 47, 48) does 
not differ notably from that of other arctoid carni- 
vores. It is slightly convex anteriorly. IVIuscle 
scars are extremely prominent, and the area above 
the olecranon fossa, where the anconeus muscle 
arises, is marked by vermiculate rugosities similar 
to those on the scapula. The angulation in the 
profile at the inferior end of the deltoid ridge, char- 
acteristic of bears, is wanting in the giant panda. 

The head is offset posteriorly from the shaft; a 
line drawn through the center of the shaft just 
touches the anterior edge of the head. This is 
similar to other arctoids, except Ursus in which 
the head lies almost on top of the shaft.' The ar- 
ticular surface greatly exceeds the opposing sur- 
face on the scapula in area. The head in transverse 
section forms a perfect arc of about 170, thus 
nearly a semicircle. In frontal section it forms a 
much smaller sector (about 65) of a circle nearly 
twice the diameter, so that the head appears flat- 
tened when viewed from the rear. In Ursus the 
transverse section of the head is nearly identical 
with that of Ailuropoda, but the frontal section 
forms a slightly larger sector (78-93) of a circle 
only slightly larger than that formed by the trans- 
verse section. In other words, in the bears the 
humeral head represents a part of a nearly perfect 
hemisphere, while in Ailuropoda it tends toward 
the almost cylindrical structure seen in such highly 
cursorial forms as the horse. 

The anatomical neck is scarcely indicated, ex- 
cept posteriori}'. The tubercles are low and very 
bear-like. The greater tubercle scarcely rises 
above the level of the head. It is sharply defined 
anteriorly, where it continues into the pectoral 
ridge; its posterior boundary is almost obliterated 
by the infraspinatus impression. The supraspi- 
natus impression extends almost the entire length 
of the dorsal lip of the greater tubercle. There are 
several large nutrient foramina between the greater 
tubercle and the head. The lesser tubercle is 
prominent; the well-marked subscapularis impres- 
sion covers practically its entire medial surface. 
The intertubercular (bicipital) groove between 
the two tubercles is wide and deep. In life it is 
bridged over by the transverse humeral ligament 
to form a canal. The groove lodges the tendon of 
the biceps and transmits a branch of the internal 
circumflex artery. There are a number of nutrient 
foramina in the floor of the groove. 

The shaft is triangular in cross section, because 
of the several prominent crests. The single nutri- 
ent canal that is prominent on the posterior surface 
of the shaft in other arctoids is represented by sev- 

' In other ursids {Thalarcios, Melursus, Helarctos) the 
head is offset. Tremarctos is similar to Ursus. 

eral minute foramina in Ailuropoda. The pec- 
toral ridge (crista tuberculi majoris, BXA), on 
the anteromedial surface, extends from the greater 
tubercle nearly down to the distal end of the shaft. 
It is a very prominent crest that provides inser- 
tion for the superficial and deep pectoral muscles. 
The deltoid ridge begins immediately below the 
posterior end of the greater tubercle, on the pos- 
terolateral surface of the shaft; near the middle of 
the shaft it arches across the anterior surface of 
the shaft and joins the pectoral ridge just below 
the middle of the humerus. The deltoid ridge pro- 
vides origin for the long head of the brachial mus- 
cle and insertion for the cephalohumeral. Midway 
between the pectoral and deltoid ridges there is 
a third ridge, which marks the medial boundary 
of the insertion of the cephalohumeral. Mesad of 
the pectoral ridge, on the flat medial surface of the 
shaft, is a prominent elongate scar 40-50 mm. long 
that marks the insertion of the latissimus dorsi 
and teres major. 

Distally the shaft bears the tremendous wing- 
like expansion of the lateral epicondylar ridge 
on its posterolateral surface. This ridge extends 
proximad nearly to the middle of the shaft. It 
provides origin for the short head of the brachialis, 
the brachioradialis, and the extensor carpi radi- 
alis longus and brevis. These are all forearm flex- 
ors, although the extensor carpi radialis is chiefly 
an extensor of the hand. The lateral part of the 
anconeus arises from its posterior face. This ridge 
is well developed in all procyonids, in some of 
which (e.g., Nasua) it is as prominent as in Ailu- 
ropoda. It is about as well developed in bears as 
in the giant panda. It is likewise present in mus- 
telids, and is extremely well developed in bun'owers 
such as Taxidea and Meles. It is scarcely indicated 
in the cursorial dogs. 

The distal end of the shaft is thinner antero- 
posteriorly but wider than it is farther proximally; 
it is relatively slightly wider and much thinner 
than in bears. The trochlea ( = capitulum -f- troch- 
lea of human anatomy) is almost identical with 
that of Ursus, except that it is somewhat wider. 
The trochlea is divided into lateral and medial 
parts by a faint ridge that runs spirally postero- 
laterally to terminate in the ridge bordering the 
olecranon fossa. The lateral part of the trochlea, 
with which the radius and a small part of the ulna 
articulate, forms a semi-cylinder with only a very 
faint anteroposterior groove. The medial part of 
the trochlea, which forms the major ulnar articu- 
lation, forms a trough-shaped spiral path extend- 
ing posteriorly well into the olecranon fossa. This 
spiral trough forces the ulna to shift medially 
5 mm. or more as the elbow is flexed. The poste- 



rior part of this trough has an extremely prominent 
external lip on which the articular surface faces 
medially. The coronoid fossa, above the troch- 
lea anteriorly, is entirely wanting, as it is also in 
bears. The olecranon fossa, above the trochlea 
posteriorly, is deep and relatively wider than in 

ratio, length pelvis/length radius is 130.3 (126.8- 
132.7) in Ailuropoda, 110.3 (107.3-118.4) in Ursus, 
100.9 (95.5-103.3) in Procyon, 108.2-108.8 in Ailu- 
rus, 110.9 (105.3-113.9) in Bassariscus, and 78.4 
(76.3-80.1) in Canis. The significance of the re- 
duced radius length in Ailuropoda is discussed be- 
low (p. 102). In both panda and bears the radius 





Fig. 49. Distal ends of humeri of Ailuropoda, Ursus americanus, Canis lupus, and Procyon loior. 

The medial epicondyle is more prominent and 
more vertically compi'essed than in Ursus. It pro- 
vides origin for the pronator teres, flexor carpi ra- 
dialis, flexor digitorum profundus, palmaris longus, 
and flexor carpi ulnaris. These are all flexors of the 
hand, except the pronator teres, which pronates 
the forearm. The entepicondylar foramen, 
which transmits the median nerve and median 
artery, was present in all specimens of Ailuropoda 
examined. This foramen is absent in the Ursidae 
(except Tremarctos ornatus) and Canidae, present 
in the Procyonidae, in Ailurus, and in most Mus- 
telidae. Its presence in Ailuropoda and Tremarc- 
tos is probably a secondary condition correlated 
with the large size of the epicondyle in these two 

The lateral epicondyle is less prominent than 
in Ursus, and is considerably narrower. It pro- 
vides origin for the extensor digitorum communis 
and lateralis and the extensor carpi ulnaris. These 
are all extensors of the manus, although the ex- 
tensor carpi ulnaris chiefly abducts the hand ulnar- 
ward. It has no direct genetic basis, and in this 
instance cannot be used as a "character." 

The humerus of Ailuropoda is so similar to that 
of the bears, especially to such forms as Tremarctos 
and Melursus, that Lydekker's statement (1901) 
to the contrary is almost incomprehensible. 

3. Ulna and Radius 

The ulna is slightly heavier than in a bear of 
comparable size, while the radius is slightly more 
slender. The radius is shorter in relation to pelvic 
length than in any other carnivore measured. The 

lies almost entirely laterad of the ulna at the elbow 
joint. The radius is slightly more dorsal in Pro- 
cyon and Ailurus, and in the narrow elbow joint 
of the cursorial dogs it lies almost in front of the 

The form of the ulna is very similar to that of 
Ursus. The olecranon, measured from the center 
of the semilunar notch, averages 14 per cent of the 
length of the humerus;' this is likewise true for 
Ursus, Procyon, and Ailurus, while in Canis it is 
longer (19 per cent). The olecranon, which pro- 
vides insertion for the triceps complex and the 
flexor carpi ulnaris, is a heavy knob-like extension 
of the ulna, bent slightly medially. The medial 
surface is concave and is devoid of muscle attach- 
ments; the lateral surface provides attachment for 
parts of the triceps and anconeus. Anteriorly the 
olecranon forms the prominent anconeal process, 
which interlocks with the olecranon fossa of the 
humerus and forms the posterior part of the semi- 
lunar notch. 

The semilunar notch, bounded anteriorly by 
the coronoid process and posteriorly by the an- 
coneal process, is almost a perfect semicircle in 
profile. It is arched in cross section, lacking the 
median guiding ridge seen in dogs. The anconeal 
process has an extensive external face that rides 
against the external lip on the posterior part of 
the trochlea, and the coronoid process an internal 
face that rides against the inner wall of the troch- 
lear groove. This arrangement effectively locks 
the elbow joint and prevents any medial shifting 

' Calculation as percentage of ulna length gives mislead- 
ing values in forms with elongated fore arm, such as Procyon 
and Canis. 



M. anconaeus 

Incimira seiniliotari 

Proc. coroiioideus. 

M. brachialis 
M. biceps 

M. supinator 

M. flexor digitorum prof. 3 

M. pronator teres 

M. pronator quadratus 

M. triceps 


M. flexor carpi ulnaris 

M. flexor digitorum prof. 5 

M. pronator quadratus 

Proc. .^Iiiloidviis 

Fig. 50. Right ulna and radius of Ailuropoda, posteromedial view. 

of the distal end of the ulna; there is no such pro- 
tection against lateral shifting. 

The radial notch is a shallow depression on the 
lateral side of and immediately below the coronoid 
process, in which the head of the radius rotates. 

The shaft tapers gradually toward the distal 
end. It is slightly bowed, with the convexity out- 
ward. The bone is wider anteroposteriorly than 
it is from side to side. Immediately below the 
coronoid process, on the anterior surface of the 
bone, there is a prominent ovoid depression that 
marks the insertion of the brachialis tendon. In 
most specimens a wide rugose ridge along the mid- 
dle third of the lateral surface of the shaft marks 
the attachment of the interosseous ligament. 

The distal end of the ulna is slightly expanded. 
Dorsally it bears a circular, much-rounded artic- 
ular facet for the radius. Beyond this the shaft 
is continued into the short peg-like styliform 
process, which bears a rounded facet for the cu- 
boid and pisiform on its anteromedial surface. 

The radius is curved in both planes; it is slightly 
convex anteriorly, and forms a long S-curve in the 
lateral plane. This complex curvature of the ra- 
dius is seen to some degree in all Carnivora except 
the cursorial dogs. 

The capitulum of the radius is set off by a very 
distinct neck. It is an elliptical disk, the long 
diameter running from anterolateral to postero- 
medial. The ratio of long to short diameter is 



about 10 : 7, and this ratio is about the same as 
in Ursus. In burrowing forms (Taxidea, Meles) 
the capitulum is even more ovate, whereas in ar- 

M. triceps 

cumference of the head; the medial one-fourth, 
where the capitular eminence is situated, has no 
articular surface. 

M. anconaeus 

M. abductor poll, longus 

M. ext. indicus proprius 

M. ext. dig. lat. 

M. ext. carpi ulnaris 

Emiiieiilia capllulorum 

M. abductor poll, longus 

M. supinator 

M. pronator teres 

M. abductor poll, longus 
M. ext. dig. comm. 

M. ext. carpi radialis longus 
M. ext. carpi radialis brevis 

Fig. 51. Right ulna and radius of Ailuropoda, anterolateral view. 

boreal forms {Procyon, Nasua, Polos) it is more 
nearly circular. 

The capitular depression, which articulates with 
the lateral part of the trochlea of the humerus, is 
very shallow. On its anteromedial circumference 
it bears a low elevation, the capitular eminence, 
that forms the anterior lip of the radiohumeral 
articulation in all positions of the radius, and acts 
as a stop that limits the excursion of rotatory 
movements of the radius. The articular circum- 
ference, which articulates with the radial notch of 
the ulna, is not continuous around the entire cir- 

The shaft of the radius is triangular in cross sec- 
tion, the base of the triangle forming the flat ven- 
tral surface of the bone. The radial tuberosity, for 
the insertion of the biceps tendon, is on the ventro- 
medial surface immediately below the neck. Oppo- 
site this, on the anterior aspect, is a scar marking 
the attachment of the lateral collateral ligament. 
The interosseous crest, for the attachment of the 
interosseous ligament, begins below the radial tu- 
berosity as a wide, roughened scar for the heavy 
proximal part of the ligament. A little above the 
middle of the bone it changes abruptly into a 
ridge-like crest. 

Sesamoid, rad. 



Fig. 52. Right carpus and metacarpus of Ailuropoda, dorsal view. 

Fig. 53. Right carpus and metacarpus of Ailuropoda, ventral view. 




The distal end of the radius is expanded and 
bears two articular surfaces, the large concave car- 
pal surface for articulation with the scapholunar, 
and laterally the small flat ulnar notch for articu- 
lation with the ulna. The carpal surface is nar- 
rower from side to side but wider anteroposteriorly 
than in Ursus, thus providing a less trough-like 
articulation for the carpus. The prominent saddle 
shape of the articular area on the styloid process 
that is seen in Ursus is scarcely indicated in Ailu- 
ropoda. Also the medial end of the articular sur- 
face is in Ailuropoda deflected proximally toward 
the ulnar notch. The styloid process is a blunt 
projection on the medial side; a deep furrow on its 
dorsolateral surface lodges the tendon of the ab- 
ductor poUicis longus. Just laterad of this, on 
the dorsal surface of the styloid process, is a shal- 
low furrow for the tendon of the extensor carpi 
radialis longus, separated by a ridge from the fur- 
row for the extensor carpi radialis brevis. Another 
shallow furrow near the lateral border lodges the 
tendon of the extensor digitorum communis. 

4. Carpus 

The carpus (figs. 52, 53) is very similar to that of 
bears, except for the tremendous development of 
the radial sesamoid and the modifications of the 
scapholunar associated therewith. The carpus-fore- 
arm articulation is largely between the scapholunar 
and the radius, which form an almost ball-and- 
socket joint permitting very extensive excursion. 
The styloid process of the ulna, as in bears and 
procyonids, is lodged in a widely open notch 
formed by the cuneiform and pisiform. 

The carpus is dominated by the scapholunar. 
This bone greatly exceeds any of the other carpals 
in size, and articulates with all the other carpal 
bones except the pisiform, and with the radius and 
the radial sesamoid. The articular surface for the 
radius occupies almost the entire dorsal and poste- 
rior surfaces of the bone, forming an ovate articula- 
tion that in some individuals is in contact anteriorly 
with the articular surface for the trapezium. This 
is more extensive than in any other carnivore, al- 
though in Ailurus and Potos it is closely approached. 
In Ursus the lateral part of this surface has a 
dimple-like depression, to receive the saddle on the 
distal end of the radius; this depression is com- 
pletely wanting in Ailuropoda and in Ailurus and 
Potos. The anteromedial end of the bone is pro- 
duced into a stout hook-like process, directed ven- 
trally, that bears a prominent articular surface for 
the radial sesamoid on its anteromedial surface. 
This articular surface is an elongate oval, its long 
axis vertical, and is convex in both planes. The 
anterior surface of the scapholunar bears three ir- 
regular shallow excavations for the trapezium. 

trapezoid, and magnum, and the lateral surface 
bears articular facets for the magnum and unci- 

The cuneiform is very similar to the corre- 
sponding bone in Ursus, but relatively slightly 
larger. It articulates with the scapholunar, the 
pisiform, and the unciform. 

The pisiform is, next to the scapholunar, the 
largest bone in the carpus, and is very similar to 
the corresponding bone in Ursus. It articulates 
with the cuneiform, forming with it a shallow V- 
shaped notch dorsolaterally, in which the styliform 
process of the ulna articulates. The bone extends 
posteriorly, ventrally, and slightly laterally from 
the carpus, its expanded tip embedded in a large 
fibro-fatty pad that underlies the lateral carpal 
pad. Five muscles and five ligaments attach to 
the bone. The tendon of the flexor carpi ulnaris 
attaches to the posterior surface, the opponens and 
abductor digiti quinti and palmaris brevis to the 
anterior surface, and the flexor digiti quinti to 
the inner border. A prominent scar near the tip 
on the anteromedial surface marks the attachment 
of the transverse carpal ligament, and another scar 
on this surface proximally marks the attachment 
of the pisometacarpal ligament. 

In the distal row the trapezium and trapezoid 
are very small, articulating distally with meta- 
carpals 1 and 2 respectively. The magnum is 
larger, and articulates with metacarpal 3. The 
unciform bears metacarpals 4 and 5. 

The radial sesamoid (fig. 54) is the most ex- 
traordinary bone in the fore foot. It is about 
35 mm. in length, and lies in line with the meta- 
carpals, closely resembling a sixth metacarpal on 
the medial border of the hand. It underlies the 
accessory lobe of the carpal pad. The bone is com- 
pressed from side to side, measuring about 15 mm. 
in height by only 6 or 7 mm. in thickness. The 
distal end hooks sharply inward toward the first 
metacarpal. The radial sesamoid articulates ex- 
tensively with the enlarged medial process of the 
scapholunar, and is in contact with the medial 
border of the first metacarpal. The articular sur- 
face for the scapholunar is ovate with the long 
axis dorsoventral, and is concave both laterally 
and dorsoventrally. The contact surface with the 
first metacarpal is dorsomedial, and is not cartilage 
covered. A large depression on the outer surface 
of the radial sesamoid near the base marks the 
attachment of the tendon of the abductor pollicis 
longus. The abductor pollicis brevis and opponens 
pollicis arise from its medial surface. 

A sizable radial sesamoid articulating with the 
scapholunar is present in all the other arctoid car- 
nivores, and a corresponding bone exists in many 






Ailuropoda Tremarctm Ursus Ailurus Procy<m 

Fig. 54. Relative sizes of (A) right radial sesamoid, and (B) right tibial sesamoid in representative carnivores. 

other mammals. In no other arctoid does it ap- 
proach the proportions seen in Ailuropoda, how- 
ever. In Bassariscus, Procyon, and Nasua it is a 
small bony nodule, and in Procyon at least it lies 
beneath the tendon of the long abductor. The 
radial sesamoid is also relatively small in Ursus 
but provides attachment for a part of the long 
abductor and opponens (fig. 54). The bone is rel- 
atively larger in Ailurus, and the tendon of the 
long abductor inserts into it exclusively, as in Ailu- 
ropoda (see also p. 180). 

Comparison of the relative sizes of the radial ses- 
amoid and the tibial sesamoid, the corresponding 
bone in the hind foot, is very suggestive (fig. 54) . 
The tibial sesamoid has no function corresponding 
to that of the radial sesamoid, yet as is evident 
from the figure it undergoes a corresponding in- 
crease in size. This indicates a genuine serial ho- 
mology between these two bones, with a common 
genetic control of the size factor at least, i.e. that 
the radial and tibial sesamoids represent a morpho- 
genetic field despite their physical remoteness from 
one another. 

5. Manus 

The metacarpals are short and stout, relatively 
considerably shorter than in a bear of comparable 
size. As in other arctoids (except Canis), the fifth 
is heavier than the other four. Length relations 
are the same as in Ursus, although the differences 
are more exaggerated; the fourth is the longest, 
followed in order by the fifth, third, second, and 

first. Ailurus is similar, while in Procyon, Nasua, 
and Bassariscus the third metacarpal is longest. 

The distal articular surface of the metacarpals 
is narrower than in Ursus, especially dorsally, and 
the median ridge is more prominent. A conspicu- 
ous scar on the radial side of the second meta- 
cai-pal, just proximad of the middle, marks the 
insertion on the tendon of the extensor carpi radi- 
alis longus, and a similar scar, situated farther 
proximad on the third metacarpal, the insertion 
of the extensor carpi radialis brevis. 

The phalanges are similar to those of Ursus, 
except that they are somewhat stouter. Those of 
the proximal row are all slightly convex dorsally, 
more so than in Ursus. The bones of the middle 
row are very similar to the corresponding bones in 
bears. On the distal articular surface the median 
furrow is slightly deeper than in Ursus, corre- 
sponding with the more prominent median ridge 
on the terminal phalanges. In the terminal pha- 
langes the core of the claw is higher vertically than 
in Ursus; the dorsal margin is more curved than 
in bears, the ventral margin less so. 

A pair of sesamoid bones is present beneath 
the metacarpophalangeal articulation of each digit 
There are 10 in all. This is typical for all arctoid 
carnivores except the Canidae, in which the first 
digit has only one. 

B. Review of the Fore Leg 
The bones of the fore leg of Ailuropoda agree 
closely with those of Ursus in all essential respects. 

Claenodon corrugatus 

Polos flovus 

Ursus arclos 

Ailuropoda melonoleuco 

Fig. 55. Right manus of representative carnivores, dorsal view. (Claenodon from AMNH 16543.) 




The differences may be examined briefly for evi- 
dence of their significance in interpreting the mor- 
phology of the giant panda. 

All the large bones in the panda exhibit more 
prominent modeling, and this is broadly adaptive. 
Details of modeling, however, are determined by 
surrounding muscles rather than genetically (p. 
147), and this difference therefore merely reflects 
the more powerful musculature of this animal. 

The presence of an entepicondylar foramen in 
Ailuropoda contrasts with its absence in all bears 
except Tremardos. This likewise appears to be 
merely a secondary result of enlarged muscles and 
their bony attachments (see Stromer, 1902). The 
presence or absence of this variable structure, 
which has aroused so much discussion in the litera- 
ture, probably has no direct genetic basis. 

There are considerable differences between the 
giant panda and bears in the form of several ar- 
ticular surfaces. The shoulder articulation allows 
a greater range of lateral movement in bears, which 
cannot be correlated with any known difference in 
habits or behavior. There is no appreciable dif- 
ference in the elbow. The articulation between 
forearm and wi'ist permits notably gi'eater dorso- 
ventral excursion in the giant panda than in bears, 
and this is very obviously coirelated with the 
greater maneuverability of the hand in the giant 
panda. Articulations reflect, rather than deter- 
mine, range of movement in a joint (p. 145), how- 
ever, and here again no genetic control can be 
postulated for adaptive differences in the skeleton. 

As shown by the radiohumeral index, the fore- 
arm is significantly shorter than the upper arm in 
the giant panda, relatively shorter than in Ursus 
where it is near the norm for generalized mammals. 
Little is known of the functional significance of 
shortened forearm, and even less of mechanisms 
controlling the lengths of long bones. It has been 
concluded (p. 38) that the limb proportions in 
Ailuropoda do not reflect mechanical requirements. 

The enlarged, maneuverable radial sesamoid in 
the giant panda is the most notable departure from 
the ursid pattern. This remarkable mechanism is 
unquestionably a direct product of natural selec- 
tion. The correlated enlargement of the tibial 
sesamoid, together with a consideration of the 
muscles and ligaments functionally associated with 
the radial sesamoid (p. 183), clearly indicate that 
simple hypertrophy of the bone was all that was 
required to produce the whole mechanism. The 
genetic mechanism underlying such hypertrophy 
may be, and indeed probably is, quite simple. A 
further, but relatively minor, polishing effect of 
natural selection is evident in the detailed model- 
ing of the bone. 

Thus of the appreciable morphological differ- 
ences in the bones of the fore leg of the giant panda 
and the bears, most are seen to be physiological 
adjustments to primary differences in the muscu- 
lature. Such adjustments are not intrinsic to the 
bones, and therefore not gene controlled. Minor 
details, such as slight differences in individual car- 
pal bones and the shape of the terminal phalanges, 
reflect at most minor polishing effects of natural 
selection. Only two adaptive features, the relative 
shortness of the forearm and the remodeling of the 
radial sesamoid, appear to result directly from nat- 
ural selection on the bones themselves. 


In quadrupeds the hind leg during locomotion 
is more important than the fore leg as an organ of 
propulsion. The mass of the musculature of the 
hind quarters accordingly exceeds that of the fore 
quarters. In most mammals the hind leg has far 
less varied functions than the fore leg; it is pri- 
marily an organ of support and propulsion. The 
forces acting on the pelvis and hind limb are there- 
fore usually less varied and less complex than those 
on the fore leg. In the giant panda the fore leg 
has diverged far more from the normal quadru- 
pedal function than the hind leg, and this is only 
slightly less true of the bears and procyonids. 

Like the fore leg, the hind leg of carnivores is 
basically designed for cursorial locomotion. 

A. Bones of the Hind Leg 

1 . Pelvis 

The pelvis, like the scapula, is molded primarily 
by muscular action. Thrust from the ground is 
transmitted from the femur to the sacrum through 
the body of the ilium, and this, together with the 
acetabulum and the iliosacral union, reflects chiefly 
non-muscular forces. 

The pelvis of the giant panda differs remarkably 
from that of any other arctoid. The ilia lie in the 
frontal, rather than the sagittal plane, the pubis 
is shortened, and the length of the sacroiliac union 
is increased (see p. 82). The pelvis most closely 
resembles that of burrowing forms such as Taxidea 
and especially Mellivora; actually it is most sim- 
ilar to the pelvis of the burrowing marsupial Vom- 
batus. This extraordinary convergence in animals 
with dissimilar habits is understandable when the 
forces operating on the pelvis are analyzed (p. 109). 

Table 11 gives measurements and proportions 
of the pelvis of a number of arctoid carnivores. 
From these figures it is evident that certain pro- 
portions remain relatively constant, regardless of 
the habits of the animal, while others vary con- 





Preace- Width 

Length tabular Iliac iliac 

pelvis length breadth crest 


31128 272 168 230 75 

110452 290 179 268 

110454 280 168 245 

259027 292 193 265 88 

259401 268 166 239 

259403 282 176 257 82 

259402 290 180 260 

258425 266 170 240 


Vrsus amer. 

18864 205 130 194 86 

44725 238 148 206 95 

Ursus arclos 

43744 271 175 255 90 

47419 302 196 282 114 

Ursus gyas 

27268 390 215 401 167 

63803 312 181 320 131 


Ailurus fulgens 

65803 90 57 50 23 

44875 74 47 41 18 

Procyon lotor 

49895 114 69.5 72 29 

49227 107 64 72 26 

49057 98 57 68.5 26 

47386 103 60 77 29 

Canis lupus 

51772 197 114 108 65 

54015 177 112 117 57 

21207 184 112 107 63 


43298 89 53 80 22 


49085 185 119 168 55 

E F G 


Length across Width 

sym- dorsal across 

physis acetab. ischia 


A A A A A A 













46.5 45 
38.5 36.5 

26 58 

26.5 56.5 

26 50 

28.5 59 



91 141 
85.5 123 
88 133 















39.7 37.5 


































































siderably. Using total length of pelvis as a base, 
the position of the acetabulum (indicated by pre- 
acetabular length, B) varies little. This is also 
true of the distance between acetabula (F), which 
is the functional diameter of the pelvis. On the 
other hand, breadth across the ilia (C), breadth 
across the ischia (G), and length of symphysis (E) 
vary greatly with habits. This is also true of the 
slope of the wings of the ilia and of the descending 
ramus of the ischium with respect to the frontal 

The pelvis is very short in Ailuropoda; length 
pelvis/length Th 10-12' =33 and 35 in two indi- 
viduals. The pelvis is also short in Ursus and the 

Morphology. The pelvis is rectangular in dor- 
sal outline (fig. 56), depressed in lateral view (fig. 
57). In posterior view it is U-shaped rather than 

'See page 35. 

V-shaped as in Ursus. In Ailuropoda the greatest 
length of pelvis is about 40 per cent of the length 
of the vertebral column, compared with about 29 
per cent in Ursus americanus and 31 per cent in 
Procyon lotor. This merely reflects the shortened 
column in the panda, however; measured against 
three thoracic vertebrae the pelvic length is com- 
parable to that of Ursus. 

In all specimens examined the sacro-iliac union 
is more or less fused dorsally but open ventrally. 
This is likewise true in Ursus, and contrasts with 
the open articulation in other arctoids. 

The ilium is composed of a remarkably narrow, 
almost parallel-sided ala, and a short heavy corpus. 
The ala is widest across the iliac crest, which is of 
normal width; behind the anterior superior iliac 
spine the inferior border is deeply excised and the 
diameter of the ilium correspondingly narrowed. 

The anterior superior iliac spine, which gives 
origin to the sartorius and tensor fasciae latae 

M. obliquus abdom. intonus 

Ineimira isehiad. major 

M. pyriformis 
M. glutaeus prof. 

M. rectus femoris 

Tuber isehiacl. 

M. gem. post. 
Lig. $acTOluberosum 
M. glutaeus supof. 

M. biceps 

M. semitendinosus 

M. semimembranosus 

Arau ischiad. 

Fig. 56. Male pelvis of Ailuropoda, dorsal view. (Inset, A, pelvis of Ursus arctos.) 





M. pyriformis 
Incisura isrhiad. major 

Incisum iscliiad. minor 
M. gem. post. 

Lig. sfKrotubi^rosu 
M. glutaeus superf. 

Tuber itn-hlad. 

M. semitendinosus 
M. biceps 

M. sartorius 
Spiiio iUaca ant. sup. 
Lima glutaea inf. 
M. glutaeus prof. 

M. adductor 

Ramus descendens 
ossis ischii 

Ramu.t acetabularis ossis pubis 

- M. obturator extemus 
>M. adductor 

sM. gracilis 
M. rectus abdominis 

Fig. 57. Male pelvis of Ailuropoda, lateral view. (Inset, A, pelvis of Ursus arcios.) 

muscles and the anterior end of the inguinal liga- 
ment, is thick and heavy. It lies farther anterior 
than in Ursus, and the iliac crest is correspond- 
ingly shorter and less curved. The posterior supe- 
rior iliac spine is also relatively heavy. The 
anterior and posterior inferior iliac spines are not 
even indicated. The dorsolateral surface of the 
ilium, which provides origin for the middle and 
deep gluteals, is a shallow elongated trough, the 
gluteal fossa. It is devoid of surface modeling ex- 
cept for a faint vermiculation near the iliac crest. 
The area of the gluteal fossa is about 5700 and 
7500 mm." in two specimens of Ailuropoda, 7200 
mm.- in a specimen of Ursus americanus, and 
11,900 mm.- in a specimen of Ursus arctos.' The 
ventro-medial surface of the ilium (fig. 58), which 
provides origin for the iliacus, quadratus lumbo- 
rum, and sacrospinalis muscles, is slightly convex 
along both its axes. A faint longitudinal ridge, 
not always evident, divides the surface into a lat- 
eral iliac area and a medial sacrospinal area; this 
is called the pubic border by Flower, Straus, and 
See p. 43 for method used in measuring areas on bones. 

other anatomists. A low but prominent elevation 
near the middle of the ridge is associated with the 
origin of the sacrospinalis. A large foramen-like 
opening at the posterior end of the ridge, and lying 
in the sacroiliac articulation, is filled with fat and 
connective tissue in life; it is present but is usually 
less foramen-like in Ursus, and apparently repre- 
sents the separation between the dorsal and ven- 
tral elements of the embryonic transverse processes 
of the first sacral. 

The corpus is short and heavy, only slightly lat- 
erally compressed as in Ursus. Its superior border 
bounds the greater sciatic notch, which has been 
crowded posteriorly by the posterior extension 
of the sacroiliac union. The inferior surface is 
rounded, without crests or ridges. The iliopectin- 
eal eminence is a low elevation, much less promi- 
nent than in Ursus, on the inferior surface just 
anterior to the acetabulum. The inferior gluteal 
line, separating the gluteal and iliac surfaces of 
the ilium, is scarcely indicated on the corpus. Im- 
mediately in front of the acetabulum it passes into 
the iliopubic eminence, which is likewise much less 



M. iliocostalis 

. transversus abdominis 

M. sartorius 

M. pectineus 

M. rectus femoris 

Fig. 58. Male pelvis of Ailuropoda, ventral view. 

prominent than in Ursus; it marks the attachment 
of the rectus femoris. 

The articular surface of the ilium (fig. 59), which 
articulates with the auricular surface of the sa- 
crum, resembles that of Ursus but is relatively 
longer and narrower. It is an elongate horseshoe, 
open anteriorly, with a very irregular surface, the 
irregularities interlocking closely with correspond- 
ing irregularities on the sacrum. The narrow space 
enclosed by the horseshoe is filled with fibrocarti- 
lage. The extensive articulation, intimate dove- 
tailing, and partial fusion of the sacroiliac joint 

contrast sharply with the relatively smooth and 
much smaller auricular surface of other arctoids. 
The pubis is the most delicate bone in the pel- 
vis. It is more lightly built than in Ursus, and 
much more so than in the cursorial dogs. The 
corpus, which forms the ventral part of the ace- 
tabulum, is the heaviest part of the bone. The 
acetabular ramus is very slender and elongate; it 
had been fractured bilaterally in one specimen ex- 
amined. The reduction in the length of the sym- 
physis has taken place anteriorly, and the angle 
formed by the acetabular ramus with the symphy- 



Canis lupus lycaon 

Procyon lotor 

Ursus arctos 

AiluropodQ melonoleuca 

Fig. 59. Articular surface of left ilium in representative arctoid carnivores. 

sis in the sagittal plane is about 45 instead of 25- 
35 as in Ursus, and the acetabular ramus is cor- 
respondingly longer. The length of the symphyseal 
ramus cannot be determined, since no available 
specimen is young enough to show the suture be- 
tween the pubis and the ischium. It is obviously 
very short, however, and is relatively much wider 
than in Ursus. The external surface of the sym- 
physeal ramus provides origin for the anterior 
parts of the gracilis, adductor, and external ob- 
turator muscles; the internal surface provides ori- 
gin for the anterior part of the internal obturator. 
The ischium is not directly involved in the sup- 
port function of the pelvis, except during sitting; 
it functions chiefly as anchorage for the posterior 
thigh muscles. The ischium does not differ much 
from that of Ursus or Procyon. It is composed of 
a stout acetabular ramus and a more slender de- 
scending ramus (tabula ischiadica of veterinary 
anatomy), and a heavy symphyseal ramus. The 
acetabular ramus is relatively shorter than in Ur- 
sus, and is ovate in cross section. Its shaft is almost 
free of muscle attachments; only the tiny gemelli 

arise from it. The sciatic spine, which separates 
the greater and lesser sciatic notches, is a short 
prominent transverse ridge as in Ursus. A small 
scar immediately anterior to the spine marks the 
attachment of the anterior gemellus, and immedi- 
ately behind the spine there is a smooth area, cov- 
ered with cartilage in life, over which the internal 
obturator rides. The saddle-shaped area between 
the sciatic spine and the ischial tuberosity is the 
lesser sciatic notch. It is converted into a fora- 
men by the sacrotuberous ligament, and transmits 
the distal end of the internal obturator muscle and 
various vessels and nerves. 

The ischial tuberosity is by far the most promi- 
nent feature of the ischium, and most of the mus- 
cles attaching to the ischium are inserted on or 
near it. The tuberosity is knob-like, about 35 mm. 
in diameter, with a much roughened posterior sur- 
face It has no inferior boundary, but continues 
directly into the roughened swollen posterior edge 
of the descending ramus, which narrows gradually 
as it descends and terminates abruptly about 40 
mm. above the symphysis. The muscle attach- 



ments are around the periphery of the tuberosity; 
the major part of its roughened posterior face Hes 
directly beneath the skin. The tuberosity is simi- 
lar, but more sharply bounded inferiorly, in Ursus. 

The lower third of the descending ramus, below 
the swollen area just described, is much the slen- 
derest part of the ischium ; it is no heavier than the 
acetabular ramus of the pubis. It provides attach- 
ment for the posterior ends of the adductor and 
gracilis externally, and for the internal obturator 
internally. The descending ramus forms an angle 
of about 55 with the sagittal plane. This angle 
is similar in other arctoids examined except in 
Canis, in which it is only about 20 (fig. 61). 

The symphyseal ramus, forming the posterior 
part of the symphysis pelvis, is broad and thick; 
the minimum transverse diameter of the entire 
symphysis (from obturator foramen to obturator 
foramen) is 40-50 mm. in Ailuropoda, whereas in 
a bear of comparable size it is 20-30 mm. In dor- 
sal view the sciatic arch, which is often non-existent 
in bears, is relatively deep. 

The acetabulum, composed of a horseshoe- 
shaped articular portion embracing a non-articu- 
lar fossa, differs little from that of Ursus and other 
arctoids. It looks slightly more laterally, forming 
an angle with the vertical of 11 and 14, respec- 
tively, in two individuals, 15 in three specimens 
of Ursus. The acetabulum looks more ventrally 
in the cursorial wolf, forming an angle of 29 (26- 
31) in three specimens of Canis lupus. 

The acetabulum is situated farther dorsad in 
Ailuropoda than in Ursus, its dorsal border lying 
well above the margin of the greater sciatic notch. 
The entire rim of the acetabulum is extremely 
heavy. The acetabular notch is almost twice as 
wide as in a bear of comparable size; the anterior 
boundary of the notch has been shifted forward 
to produce this increased width. The acetabular 
fossa is also relatively wider, and has increased its 
diameter by encroaching on the anterior arm of 
the articular portion, which accordingly is nar- 
rower than in Ursus. 

The obturator foramen is triangular in out- 
line, rather than ovate as in Ursus. 

Architecture and Mechanics. The mam- 
malian pelvis is an extraordinarily complex struc- 
ture, subject to varied and often subtle forces. 
Moreover, it has had a long history, and treating 
the mammalian pelvis as if it were engineered de 
novo leads to difficulties and often even to absurdi- 
ties. Mijsberg's work (1920) was one of the first 
attempts to analyze the architecture and mechanics 
of the non-human mammalian pelvis. Other such 
studies have been made by Elftman (1929), Rey- 

nolds (1931), Kleinschmidt (1948), and Maynard 
Smith and Savage (1956). 

The mammalian pelvis serves three dissimilar 
purposes: (1) to provide support; to transmit thrust 
from the legs to the vertebral column, and from 
the column to the legs; (2) to provide attachment 
surfaces and lever arms for hip and thigh muscles; 
and (3) to transmit the terminal parts of the diges- 
tive and urogenital canals, especially important 
being the birth canal. Each of these has partici- 
pated in molding the pelvis, but the basic archi- 
tecture was largely determined by the support 
function. Elftman believed that the pelvis is 
"roughly modeled so as to fit the viscera and with 
finer detail so developed as to provide optimum 
support against gravity and leverage for loco- 

As a supporting structure the pelvis is a complex 
system of arches and levers designed to provide 
strength and elasticity. Absorption of shock re- 
sulting from impact between the feet and the 
ground seems to have been a major factor in the 
design of limbs and girdles in mammals. The ar- 
chitecture of the mammalian pelvis, which is far 
less rigid than that of their reptilian ancestors, is 
otherwise unintelligible. 

In the frontal plane (fig. 60, B) the pelvis is com- 
posed of two round arches meeting at the acetab- 
ular a heavy dorsal arch composed of the two ilia 
and the sacrum, and a much lighter ventral ilio- 
pubic arch. Only the dorsal arch is directly in- 
volved in the support function of the pelvis; the 
ventral arch is concerned with the structural sta- 
bility of the pelvis. The dorsal arch is loaded both 
from above (weight of body, W) and from below 
(upward thrust of legs, T). In addition to bend- 
ing and shearing stresses, the loaded arch develops 
horizontal thrust which reaches a maximum at the 
base (the acetabula. A, A) whether loading is from 
above or below. The sole function of the iliopubic 
arch, aside from providing a base for muscle at- 
tachment, appears to be as a bottom tie for the 
dorsal arch, to counteract this horizontal thrust. 

Viewed from the side (fig. 60, D) the pelvis is 
not a simple arch as it is in reptiles. The acetab- 
ulum lies well behind the sacroiliac articulation, 
and upward thrust through the acetabulum is 
translated into a vertical rotational force around 
the sacroiliac articulation as a center; the coxa is 
cantilevered to the sacrum. The sacroiliac articu- 
lation is not normally fused in quadrupeds, but it 
is practically immovably fixed by the sacroiliac 
ligaments, often augmented by interlocking den- 
ticulations on the two articular surfaces. Thus, 
under loading, shearing forces are developed along 
the neck of the ilium the axis connecting acetab- 

A. Alligotor Tronsverse iliosocrol orch 
of quadrupedal mammals CB). 

similar to orch 

Aliigotor Thrust T through acetabulum is transmitted 
directly to socroilioc joint 0^. The iliosocrol orch 
fufKtions OS simple orch , 



B. Conis, Upword thrust T, T' through ocetobulo is resolved 
in transverse iliosocrol orch. This orch is also loaded 
from obove by the weight of the body, Vi_. Horizontal 
thfust, H, H, developed in the tronsverse orch by both T_ 
and W, is counteracted by the ventral iliopubic orch oct- 
ing OS a tie. 

Conis . Thrust T through acetabulum is translated into 
rototionol force R oround socroilioc joint os o cen- 
ter. This produces o shear along the oxts 0-A, as 
indicated by x - xv Horizonol thrust H is developed dur- 
ing locomotion. 

Conis. Upword thrust T is tronsmitted 
directly to vertebral column through ilium 
and sacroiliac joint. A shear is pro- 
duced at ttw socroilioc joint and com- 
pression in the reck of ttw ilium. The 
socroilioc orch functions as o simple 

Fig. 60. Forces acting on the pelvis in quadrupeds. A, transverse arch in a reptile, anterior view; B, transverse arch in 
a mammal, anterior view; C, transverse arch in a reptile, lateral view; D, cantilevered transverse arch of a mammal, lateral 
view; E, forces acting on mammalian pelvis in erect posture, lateral view. 




ulum and sacroiliac articulation and this is by 
far the most destructive force to which this part 
of the arch is subjected. 

The rotational force acting on the sacroacetab- 
ular axis produces a powerful rotational shear or 
torque on the sacroiliac articulation, similar to 
that on a bolt being tightened by a wrench. This 
force would tend to displace the anterior part of 
the articulation downward, the posterior part up- 
ward. The posterior upward force of the couple is 
counteracted by the firm union of the auricular 
surfaces of the sacrum and ilium. The anterior 
downward force is met by the shape of the sacrum, 
which is wedged between the ilia like an inverted 
keystone (fig. 60, B, a). This angle is about 15 
in Canis, and rises to 40 or more in the Bovidae. 
In the bears and Ailuropoda, in which the articu- 
lation is synostotic, the angle approaches zero, and 
this is also true in the giant anteater {Myrmeco- 
phaga), where the joint is fused. 

During locomotion the sacro-iliac articulation is 
also subjected to momentary horizontal thrust 
(fig. 60, D, H) that tends to displace the ilium 
anteriorly on the sacrum. This force results from 
the anterior thrust of the hind legs, and is espe- 
cially evident during galloping or leaping, when 
the femur is nearly or quite in line with the sacro- 
acetabular axis, as is evident in Muybridge's (1957) 
photographs of horses and dogs. This force is 
counteracted by the wedge shape of the sacrum in 
the frontal plane : the bone is wider anteriorly than 
posteriorly. The plane of the auricular surface 
forms an angle with the mid-sagittal plane of 
11-14 in Canis, Ursus, and Ailuropoda, and in a 
specimen of Bison this angle amounts to 34. 

Forces on the Pelvis in the Erect Posture 

If a quadruped stands erect on its hind legs the 
forces acting on the pelvis are approximately dou- 
bled, since the pelvis then bears the entire weight 
of the animal. They are also significantly altered 
in direction. The transverse arch still functions 
as before, but the ilia are no longer cantilevered to 
the sacrum. The thrust is now along the sacro- 
acetabular axis (fig. 60, E, T). Instead of shear- 
ing forces along the sacroacetabular axis there is 
now compression. The rotational shear at the sa- 
croiliac articulation is converted into a simple 
shear, which is largely or entirely counteracted by 
the wedge shape of the sacrum. This is a stronger 
construction than in the quadrupedal posture, but 
most of the elasticity is gone; if the sacroiliac ar- 
ticulation fuses there is virtually no elasticity in 
the pelvis. 

Horizontal forces, i.e., forces approximately par- 
allel to the sacro-acetabular axis, predominate in 

burrowing animals that use their hind legs for brac- 
ing while digging. Thus the dominant forces act- 
ing on the pelvis in such forms are very similar to 
those in the erect posture, and this is reflected in a I 
striking similarity in pelvic architecture. 

Examination shows that seven features charac- 
terize the pelvis in mammals in which forces par- 
allel to the long axis of the pelvis predominate, 
i.e., those that stand erect and those that use their 
hind legs for bracing while digging. These are: 

1. The wings of the ilia tend to shift into the frontal 

2. The pelvis is short anteroposteriorly. 

3. The sacroiliac articulation is strengthened by includ- 
ing additional sacral vertebrae (increased area) and/or 
by strengthening the joint through interlocking bony 
processes, synostoses, etc. 

4. The lateral diameter of the corpus of the ilium is 
increased, and it tends to become circular in cross 

5. The pubo-ischiadic symphysis is greatly shortened. 
This reduction is in the anterior part of the symphysis. 

6. The total number of sacral vertebrae is increased. 

7. The tail is usually, but not always, shortened. 

In marsupials Elftman (1929) attributed the 
shape of the wing of the ilium anterior to the sacro- 
iliac joint chiefly to the "sizes of the three muscle 
masses whose areas of origin form its three borders 
the erector spinae mesially, the gluteus medius 
and gluteus minimus dorso-laterally, and the ili- 
acus ventro-laterally." Waterman (1929) con- 
cluded that the form of the ilium in primates is 
largely determined by muscles. Elftman believed 
that in Vombatus, however, the width of the trunk 
is partly responsible for the lateral flare of the an- 
terior part of the ilium. 

In the bears and Ailuropoda the mass of the 
middle and deep gluteals is relatively no greater 
than in the cursorial dogs and cats (see Table 15). 
Even in man the relative mass of these muscles is 
no greater than in cursorial carnivores. The ilio- 
psoas in Ailuropoda is slightly heavier than in 
bears and dogs but it is smaller than in the lion, 
which has a notably narrow pelvis. In the lion 
the great size of the iliopsoas (almost identical 
with man) is associated with leaping. 

If the relative masses of the large muscles at- 
taching to the wing of the ilium are nearly con- 
stant, then differences in size, shape, and slope of 
the iliac wing must be attributable to other causes.' 
The most consistent character of the iliac wing in 

' The long iliac crest (= broad iliac wing) characteristic 
of bears must be attributable to pecularities, still unknown, 
in the abdominal wall muscles and iliocostalis that attach 
to this crest. Elsewhere among carnivores the crest tends 
to be short in climbing and aquatic forms, "normal" in ter- 
restrial forms. 

Iliac Crest Descending Rannus Ischium 

Cams lupus 

Gulo luscus 

Procyon lotor 

Ursus orctos 



Fig. 61. Anterior views of pelves of carnivores, to show angle of inclination of iliac and ischiadic planes. 




mammals in which forces parallel to the long axis 
of the pelvis predominate is that the wing tends 
to shift into the frontal plane (fig. 61). The iliac 
crest forms an angle with the frontal plane of 20 
21 in Ailuropoda, 22 in a Mellivora, 28 in a 
Meles, and only 12 in a Vombatus. In the bears 
and American badgers the slope of the crest is 
about normal for terrestrial carnivores, 45-50. In 
the cursorial wolf the slope approaches the verti- 
cal, 70-80 (fig. 61). 

The main advantage of a frontal position of the 
wing of the ilium is leverage; in both the erect and 
the burrowing posture the gluteals and iliacus are 
in an increasingly favorable position to stabilize 
the pelvis and vertebral column as these muscles 
approach the frontal plane. Waterman (1929) has 
discussed the relation between erect posture and 
the muscles attaching to the iliac crest in primates. 
The muscles attaching to this crest in Ailuropoda 
are shown in figs. 56-58; the corresponding rela- 
tions in other carnivores are unknown. 

Shortening of the pelvis is symmetrical, affect- 
ing the preacetabular and postacetabular regions 
about equally. The pelvis is almost as short in 
bears (index 36) as in the panda, and is only slightly 
longer in Meles (41) and Taxidea (41). Mellivora 
is a striking exception (index 50). The norm for 
terrestrial carnivores is about 46. The advantage 
of reduction in pelvis length with increased hori- 
zontal forces on the pelvis is not clear to me. 

Strengthening of the sacroiliac articulation with 
increase in horizontal forces on the pelvis is so ob- 
viously functional that it requires no comment. 
It reaches a maximum in the Myrmecophagidae, 
in which the sacroiliac articulation is supplemented 
by a strong sacroischiadic articulation occupying 
the normal site of the sacrotuberous ligament. In- 
creased diameter of the body of the ilium is like- 
wise associated directly with increased horizontal 
thrust; relative diameter of the body reaches a 
maximum in the Old World badgers. 

Shortening of the symphysis is invariably corre- 
lated with increased horizontal thrust on the pel- 
vis. It is seen in the wombat (Marsupialia), the 
extinct ground sloths and the anteaters (Edentata), 
the anthropoids (Primates), and in badgers and 
Ailuropoda among the carnivores. The symphysis 
is also short in aquatic forms: in the otters and 
particularly so in the seals. 

Various attempts, all more or less speculative, 
have been made to explain reduction in length of 
symphysis. All explicitly or implicitly regard sym- 
physis length as proportional to the forces the 
symphysis must withstand. Weidenreich (1913) 
attributed shortening of the symphysis in primates 
to the weight of the viscera and the pull of the 

sacrotuberous and sacrospinous ligaments drawing 
the pubic rami apart. Mijsberg (1920) suggested 
that vertical forces acting on the pelvis in quad- 
rupeds produce exorotation of the coxa around the 
sacrum, and that this exorotation is resisted by 
the symphysis, whose length is proportional to the 
exorotatory force. Mijsberg's interpretation is 
supported by the fact that the seals (Phocidae), 
in which vertical forces acting on the pelvis are 
negligible or absent, have no true symphysis. 
Elftman (1929) accepted Mijsberg's explanation, 
but suggested further that in Vombatus shorten- 
ing of the symphysis posteriorly is necessary to 
provide a proper outlet for the pelvis. Nauck 
(1938) believed he could detect a correlation be- 
tween dorsal shifting of the acetabulum which 
he maintains would reduce the exorotatory forces 
on the pelvis and reduction in symphysis length. 
Nauck's correlation exists only in selected cases, 
and obviously is not a general explanation. 

All investigators' agree that the iliopubic arch 
functions primarily as a tie to counteract horizon- 
tal thrust ("exorotatory forces") developed in the 
dorsal iliosacral arch. All agree further that re- 
duced symphysis length is somehow associated 
with reduced tensile stresses in the iliopubic arch. 
The resolution of vertical vs. horizontal forces 
within the pelvis has not been demonstrated ex- 
perimentally, however, and consequently all expla- 
nations are conjectural. A correlation between 
increased force parallel to the long axis of the pel- 
vis and reduced symphysis length remains as an 
empirical fact. 

Increased sacral length behind the sacroiliac ar- 
ticulation is associated with increased horizontal 
thrust on the pelvis both in forms that stand erect 
and in those that use their hind legs for bracing 
while digging. Extending the sacrum posteriorly 
increases the attachment area for the multifidus 
and sacrospinalis muscles. The main action of 
both of these muscles is to extend the vertebral 
column when acting on the vertebrae, or to extend 
the pelvis when acting on the sacrum. These ac- 
tions are obviously important for spinal fixation 
both in the erect posture and in burrowing. 

It seems likely that reduction in tail length is 
a consequence of increased sacral length, although 
critical data are lacking. If sacral length is in- 
creased to provide additional area for the spinal 
erectors, this area could be provided only at the 
expense of the basal tail muscles. The special 
cases of long sacrum associated with long tail in 
the anteaters and aardvark suggest a fundamental 
difference in either the spinal erectors or the caudal 

' Braus (1929, p. 456) interprets the human pelvis as a 
ring under spring-like internal tension. 



muscles in these forms, but pertinent data are 

The Pelvis of Ailuropoda. The pelvis of the 
giant panda is notably different from that of the 
bears, which it resembles no more closely than it 
does the pelvis of several other arctoid carnivores. 
The bear pelvis, in turn, is unique among arctoids 
in its combination of long iliac crest, very broad 
iliac wing with normal slope in the transverse 
plane, and extremely long symphysis. 

The pelvis of Ailuropoda exhibits, to a far gi-eater 
degree than any other carnivore, the seven features 
that characterize the mammalian pelvis when forces 
parallel to the body axis predominate (p. 110). 
These forces predominate during burrowing, and 
when the animal stands erect on its hind legs. 
Ailuropoda is not a burrower, nor does it stand 
erect to any greater extent than do the bears. 
There is, in fact, no reason for believing that hori- 
zontal forces on the pelvis in Ailuropoda are gr-eater 
or more sustained than in Ursus or other carni- 
vores. This indicates that some other (non-adap- 
tive) factor is responsible for the form of the pelvis 
in Ailuropoda. 

The pelvis adjoins the lumbosacral region of the 
body axis. In this region in Ailuropoda the axial 
skeleton, the urogenital system, and the circula- 
tory system all show non-adaptive deviations from 
the norm. The most plausible explanation for the 
pelvic form in Ailuropoda is that it reflects the 
serious disturbance in the axial gradiant that is 
associated with cephalization (p. 84). 

2. Femur 

The femur in the Carnivora serves for the origin 
or insertion of 22 muscles. Of these, 15 belong to 
the hip joint and 7 to the knee joint or lower leg 
and foot. In the Carnivora the form and archi- 
tecture of the femur are determined largely by the 
static requirements of support, to a far greater 
degree than for the humerus. Except for the tro- 
chanters, the external form of the femur is scarcely 
modified by the muscles that attach to it. 

It was found (Table 2) that if femur length is 
calculated against the length of three thoracic ver- 
tebrae, the femur in Ailuropoda is longer than the 
norm for carnivores but not so long as in Ursus. 
Relative femur length of the panda is similar to 
that of the cats, whereas the bear femur is among 
the longest known for the Carnivora, equal to 
Crocuta and exceeded only by Chrysocyon. 

If the position of the acetabulum remains rela- 
tively constant (as it does among arctoid carni- 
vores; see Table 11), then a long femur would re- 
sult in fast but weak movements of the femur 

around the acetabulum, as compared with a short 
femur.' From the standpoint of locomotor effi- 
ciency, the ratio between femur length and tibia 
length is much more significant than is femur length 
relative to pelvis length. 

The femur of Ailuropoda (fig. 62) is similar in 
form to that of Ursus and the Procyonidae, with 
a low greater trochanter and a straight shaft. As 
in most arctoid carnivores, the bone shows little 
torsion.^ In two wild-killed pandas the torsion 
angle is 1 and 3; in a third, reared in cap- 
tivity, it is 13. The mean of twelve wild-killed 
arctoids is about 1, extremes 3 to +14. Four 
wild-killed Ursus range from 2 to -t-14, mean 
+2. The greatest torsion among arctoids is in 
the Procyonidae: 10 and 14 in two individuals of 
Procyon, 6 in a Nasua. Torsion in two cage- 
reared Ailurus is 3 and 12. 

In Ailuropoda the head of the femur is hemi- 
spherical, about 38 mm. in diameter, slightly 
larger than in a bear of comparable size. The 
fovea, for the ligamentum teres, occupies the same 
position as in Ursv^, but is wider and deeper. 
The neck is distinct, and forms an angle of about 
130 with the shaft; it is slightly more angulated 
than in Z7rsMS (134-138) or Proc|/ow (135). Angu- 
lation of the neck is 125-140 in arctoid carnivores 
in general. The neck is narrower anteroposteri- 
orly but slightly wider dorsoventrally than it is in 

The greater trochanter, which provides at- 
tachment for the middle and deep gluteals and 
the piriformis, does not differ significantly from 
that of Ursus. It is a broad knoblike structure 
scarcely rising above the level of the neck. Its 
anterior border is continued distally as a low crest 
that terminates at the level of the lesser trochanter 
in a prominent scar, the gluteal tuberosity, mark- 
ing the insertion of the superficial gluteal muscle. 
The trochanteric fossa, which receives the ten- 
dons of the obturator muscles, is deep and well 
defined. The lesser trochanter, on which the 
iliacus and psoas major muscles attach, is a low 
conical eminence projecting posteromedially, as in 
other arctoid carnivores. A crescent-shaped trans- 
verse scar extending across the posterior surface 
of the bone, from the lesser trochanter nearly to 
the gluteal tuberosity, marks the attachment of the 
quadratus femoris. 

' Disregarding differences in tension and velocity of con- 
traction of muscles. See Maynard Smith and Savage (1 956) 
for methods of calculating relative mechanical advantages 
in limbs. 

* Torsion was measured by the method given by Schmid 
(1873). My figures do not always agree with his, and I sus- 
pect this is because many of his skeletons were from zoo 



Lig. teres Jeiiioris 

Fossa Irochaiile 

Capauta arlictilaris ^***"^\ " 

TiiH-haiiler minor. 

M. iliacus & psoas major 
M. quadratus femoris 

M. vastus nied. 

M. adductor 

Capsitla articuhiris 

M. gastroc. (cap- nied.'i 

Lig. criic. 

M. pjTiformis 

Trochanter major 

M. glutaeus medius . 
M. obturator int. 

M. glutaeus prof. , 
M. obturator ext. 

M. glutaeus superf. 

M. pjTiformis 

Tuber, glulaea 

M. vastus lateralis 

M. adductor pars post 

M. adductor pars ant 

Epicomlijliis lateralis 

M. plant. & gastroc, 
(cap. lat.) 

Capsula arlicularis 
Colltim femoris 

M. iliacus & psoas major 

M. vastus intermedius 

Lig. coll. fihujare 

Plica synorialii patellaris Lig. cnic. ;)<)S( \M. poplitcus 

M. gastroc.(cap. med.) 
Lig, coll. libiale 
Capsula articttlaris 

M. e.\t. dig. longus 

Fig. 62. Right femur of Ailuropoda, posterior and anterior view. 

The shaft of the femur is nearly or quite straight ; 
it is convex anteriorly to a greater or lesser degree 
in Ursus and other arctoids. The anterior surface 
is faintly reticulated. As in other arctoids the shaft 
is wider transversely than anteroposteriorly: the 
ratio is about 80. The linea aspera on the poste- 
rior surface of the shaft is scarcely indicated, even 
less so than in Ursus. Slight roughenings on the 
proximal two thirds of the shaft mark the attach- 
ments of the pectineus and adductor muscles; 
these are wanting in the distal third of the bone 

where the femoral vessels are in contact with the 
bone. The anterior, medial, and lateral surfaces 
of the shaft are overlain by the vastus muscles, 
and are devoid of any modeling. 

The inferior end of the femur differs in details 
from that of Ursus. The condyles are roller-like, 
rather than ball-like as in Ursus and other arc- 
toids, and the intercondyloid fossa (in which the 
cruciate ligaments attach) is relatively broader. 
The lateral condyle is wider and longer than its 
fellow and its articular surface is more oblique. 



The lateral epicondyle contains a large crater-like 
depression in which the lateral collateral ligament 
attaches; the plantaris and the lateral head of the 
gastrocnemius arise from the prominent superior 
rim of the crater. A dimple-like depression imme- 
diately below the crater marks the attachment of 
the popliteus. The median condyle is much 
narrower than the corresponding condyle in Ur- 
sus, as a result of encroachment by the intercon- 
dylar fossa. The medial epicondyle contains a 
large depression for the medial collateral ligament; 
its anterodorsal rim is elevated into a prominent 
tubercle on which the medial head of the gastro- 
cnemius arises. The patellar surface does not dif- 
fer from the corresponding area in Ursus and 
other arctoids. 

The femur of Ailuropoda thus differs from that 
of Ursus chiefly in details of modeling, torsion, 
and angulation features that certainly represent 
post-natal adaptive adjustments. The only fea- 
ture that cannot be so interpreted is the relative 
length of the femur in Ailuropoda, which probably 
demands a genetic basis. I can find no mechan- 
ical explanation for the shortening of this bone in 
Ailuropoda relative to Ursus; the matter is dis- 
cussed further on p. 38. 

3. Patella 

The patella (fig. 63) is ovate, about 37 mm. long 
by 32 mm. wide. It is relatively wider and more 
disk-shaped than the corresponding bone in Ursus, 
but is otherwise very similar. The anterior sur- 
face bears longitudinal striae. The ai-ticular surface 
is broader than high, and the lateral and medial 
articular facets are not clearly marked. The scar 
for the attachment of the quadratus femoris ten- 
don is prominent on the superior and lateral sur- 
faces, as is the attachment area for the patellar 
ligament on the anterior surface at the apex. 

4. Tibia and Fibula 

The tibia and fibula are very short. These bones 
are also short relative to other limb segments in 
Ursus, and are very short in badgers (Table 2). 
Short distal segments result in relatively powerful 
but slow movements in the distal part of the limb. 
Hence the advantage of a low femorotibial index 
in graviportal animals and in digging forms that 
use the hind legs for bracing. 

The tibia (fig. 63) is basically similar to that of 
Ursus. It differs chiefly in being shorter and more 
compact, and in the greater torsion of the distal 
end. The head, which measures 65-70 mm. in 
transverse diameter, is relatively broader than in 
Ursus. The lateral condyle is about the same 
size as the medial, as in the bears. A crater-like 

depression on its lateral side, for the attachment 
of the lateral collateral ligament, is larger but shal- 
lower than in Ursus. The lateral articular surface 
is ovate, its anteroposterior diameter greatest; it 
encroaches on the anterior intercondyloid fossa 
more than in Ursus. The medial condyle pro- 
jects medially some distance beyond the border 
of the shaft. The articular facet for the head of 
the fibula lies farther posterior than in Ursus, but 
is otherwise similar. The medial articular surface 
is almost circular in outline. Both the anterior 
and the posterior condyloid fossae are wider than 
in the bear. The tibial tuberosity, on which the 
patellar ligament attaches, is prominent in Ursus 
but is scarcely indicated in Ailuropoda. 

The shaft of the tibia is almost straight. It is 
bowed very slightly medially, as in Ursus, and 
this bowing appears to be (but is not) exaggerated 
by the medial extension of the proximal and distal 
ends of the bone. This latter circumstance greatly 
increases the interosseous space between tibia and 
fibula, and the total width across the leg (from 
medial border of tibia to lateral border of fibula). 
The shaft is most slender near the middle, flaring 
somewhat both proximally and distally. The an- 
terior crest, which is associated with the insertions 
of the gracilis, sartorius, biceps, and semitendino- 
sus, is well marked, especially proximally; it con- 
tinues distally into the medial malleolus. The 
interosseous crest on the lateral surface of the 
shaft, on which the interosseous membrane at- 
taches, is a prominent ridge beginning below the 
lateral condyle and extending down to the distal 
fibular articulation. On the posterior surface of 
the shaft several ridges mark the boundaries be- 
tween the flexor hallucis longus, the tibialis poste- 
rior, and the popliteus (fig. 63). 

The distal end of the tibia is very similar to that 
of Ursus, except that it is rotated farther on the 
shaft; the torsion angle of the transverse axis of 
the distal end against the bicondylar axis of the 
proximal end is 35-48 in Ailuropoda, whereas in 
Ursus it is only about 20. The transverse axis 
also is inclined more obliquely with respect to the 
long axis of the bone: about 120 in Ailuropoda, 
about 105 in Ursus. The medial malleolus is 
short and wide anteroposteriorly. A deep groove, 
the sulcus malleolaris, on its posterolateral surface 
lodges the tendon of the posterior tibial muscle; a 
similar groove is present in Ursus. The inferior 
articular surface, which articulates with the as- 
tragalus, is ovate, wider medially and narrower 
laterally than in Ursus. It bears a median ridge, 
bounded on either side by a depression, that fits 
a corresponding surface on the astragalus. At the 
lateral end of the articular surface is a small 



M. vastus lato^is 
M. rectus femoris 

Lig. paleUae 
M. tibialis a(it 
Condylus lot 

M. peronaeus longus 

M. soleus 

Lig. eoll. fibulare 
M. flex, hallucis longus 

M. peronaeus tertius 
M. tibialis ant. 

M. vastus med. 

M. sartorius 
Lig. patellae 

M. semimembranosus 
Condylus med. 

M. peronaeus brevis 

M. ext. hallucis longus 

M. peronaeus longus 

CapstUa artieularis 

M. popliteus 
M. flex, hallucis longus 

M. tibialis post. 
M. gracilis 

Sulcus malleolaris 
Malleolus med 

Capsula artieularis 

M. tibialis post. 

M. flex. dig. longus 

M. soleus 
M. tibialis post. 

M. flex, hallucis 

M. peronaeus bre\TS 

Capsula artieularis 
Malleolus lot. 

M. tibialis post.-/^ 

M. peronaeus brevis' 

vM. peronaeus tertius 
Fig. 63. Right patella, tibia, and fibula of Ailuropoda; anterior and posterior views. 

obliquely situated articular facet for the distal 
end of the fibula. 

The fibula (fig. 63) is slightly heavier than the 
fibula of Ursus, and is bowed slightly laterally, 
which further exaggerates the transverse diameter 
of the leg. It articulates with the tibia by a syno- 
vial joint at each end and therefore, as in Ursus, 
represents the mobile type of fibula. 

The head is an expansion of the proximal end 
differing from that of Ursus only in minor details. 
The articular facet is a flat ovate surface, set 
obliquely and directed medially and posteriorly. 
No scar marks the attachment of the lateral col- 
lateral ligament on the lateral surface immediately 
below the head. The shaft is triangular in cross 

section throughout most of its length, but is con- 
siderably flattened distally. Almost its entire sur- 
face provides attachment for muscles, of which 
seven arise from the shaft, and roughened longi- 
tudinal elevations on the shaft mark the attach- 
ments of aponeuroses and intermuscular septa 
separating many of these muscles. The most con- 
spicuous crest, on the medial surface, is the inter- 
osseous crest to which the interosseous membrane 

The distal end of the fibula is an irregular ex- 
pansion, larger than the proximal expansion, that 
forms the lateral malleolus. It is relatively larger 
and heavier than the lateral malleolus of Ursus, 
but is otherwise comparable. The lateral malle- 

M. tibialis ant- 

Os cuneiforme 1 
Os cuneiforme 2. 

Os naviculare 
Os sesamoid, tib. 

M. flex. dig. quinti brevis 
peronaeus brevis 

Os cuneiforme 3 

M. abductor dig. quinti 
Os cuboideum 

M. tibialis post 
Capsula articularis 


Fig. 64. Right tarsus and metatarsus of Ailuropoda, dorsal view. 

M. flex. dig. quinti brevis 

M. abductor dig. quinti 

M. peronaeus longus 

M. quadratus plant. 

Tendo m. plantaris 
M. soleus & gastrocnemius 

M. peronaeus longus 

M. tibialis ant. 

M. flex, hallucis irevis 

M. abductor dig. quinti 

Tendo m. plantaris 

Fig. 65. Right tarsus and metatarsus of Ailuropoda, plantar view. 




olus does not project so far distad as the medial 
malleolus, and its articular surface is less extensive 
anteroposteriorly. The lateral surface bears a 
prominent elevation, the processus lateralis fibu- 
lae (new name), that separates the peroneal ten- 
dons into two groups; the long peroneal tendon 
lies immediately anterior to the process, while the 
tendons of the brevis and tertius lie immediately 
behind it. In Ursus this process is a sharply pro- 
jecting knob-like structure, and in other carnivores 
(except the Canidae) it forms a hook that arches 
backward over the tendons of the peronaeus brevis 
and tertius. The medial surface of the malleolus 
bears two articular surfaces: a smaller proximal 
one facing proximally and medially that articu- 
lates with the tibia, and a larger distal one facing 
distally and medially that articulates with the 

5. Tarsus 

The tarsus (figs. 64, 65) is in general more con- 
servative than the carpus. The tarsus of living 
procyonids actually differs little from that of the 
more generalized Paleocene creodonts, in which it 
is adapted to arboreal life ( Matthew, 1937, p. 317) ; 
and the tarsus of modem bears is strikingly sim- 
ilar to that of the Middle Paleocene creodont 
Claenodon. In the bears the ankle shows a char- 
acteristic shortening and broadening of all the 
tareal bones; this is also evident, though less pro- 
nounced, in Ailuropoda. 

The tarsus of Ailuropoda is, in fact, moi-phologi- 
cally more "primitive" than that of Ursus. This 
is seen in the less pronounced broadening of all the 
tarsal bones, in the presence of a large astragalar 
foramen, and particularly in the form of the two 
transverse ankle joints the transverse tarsal and 
tarsometatai^sal joints (fig. 65). In Ltsws both of 
these joints are essentially continuous across the 
ankle (as in man), whereas in Ailuropoda and gen- 
eralized carnivores both joints consist of two or 
more transverse segments offset from each other. 
The ursid-human form of these joints is a second- 
ary adaptation to plantigrade walking, whereas 
the interrupted joints seen in more generalized car- 
nivores increase the lateral stability of the tarsus. 

A unique feature of the tarsus of Ailuropoda is 
the extraordinarily loose fit between the astragalus 
and calcaneus. The lateral and medial articular 
surfaces of the two bones cannot be brought into 
congi'uence at the same time, but only alterna- 
tively by sliding the astragalus sideways over the 
calcaneus. In association with this, the diameter 
across the two articular surfaces on the astragalus 
gieatly exceeds the diameter across the correspond- 
ing surfaces on the calcaneus. 

The astragalus (BXA: talus) (fig. 66) is rela- 
tively larger than in Ursus, but differs chiefly in 
its longer neck and narrower head, and in the 
presence of a large astragalar foramen. The troch- 
lea is broader than long, and is characterized by a 
very shallow gi-oove and relatively small malleolar 
surfaces; the upper tarsal joint is less secure and 
permits greater lateral rotation than in Ursus. 
The superior articular surface is not continued 
posteriorly over the posterior process as in pro- 
cyonids. The arc of the trochlea is thereby re- 
duced by about 35; it measures about 165 in 
Ailuropoda and Ursus, and about 200 in procy- 

The medial malleolar surface, which in Ursus 
extends over the neck nearly to the margin of the 
head, reaching as far distad as does the lateral 
malleolar surface, is much shorter in Ailuropoda, 
ending at the base of the neck. The lateral mal- 
leolar surface is similar to that of Ursus except 
that it is flatter. Immediately posterior to the 
trochlear gi-oove there is a large astragalar fora- 
men in all specimens examined. This foramen, 
characteristic of creodonts, occurs sporadically 
among generalized modem procyonids iBassaris- 
cus) and mustelids {Gulo, Taxidea); I also find a 
small astragalar foramen in one specimen of Ursus 
americanus. Behind the trochlea a deep groove 
for the flexor hallucis longus tendon is present in 
Ursus and other carnivores; this groove is want- 
ing in Ailuropoda. 

On the inferior surface the lateral (posterior in 
human anatomy) and medial articular surfaces, 
articulating with con-esponding articular surfaces 
on the calcaneus, resemble those of Ursus. They 
are oblong, relatively shallowly concave areas sep- 
arated by a deep astragalar gi-oove. The lateral 
is more extensive than the medial, and in Ailu- 
ropoda their axes diverge slightly distally. As in 
other camivores, the medial articular surface lies 
mostly beneath the neck of the astragalus. Of the 
accessory facets (Davis, 1958) only the anterior 
marginal facet of the medial articular surface is 
represented. It is a narrow extension of the medial 
surface, continuous anteriorly with the na\-icular 
articular surface, and it rests on the cuboid. 

The head and neck, on the contrary, resemble 
those of procyonids and generalized mustelids and 
viverrids more closely than they do those of Ur- 
sus. The neck is relatively long, nan-ower than in 
Ursus, and deflected toward the medial border of 
the foot, foiTning an angle of about 98 with the 
transverse axis of the trochlea. The head bears 
two articular surfaces, as in other camivores: an 
oval convex area anteriorly and medially for the 
navicular, and a small triangular area inferiorlj' 





Fig. 66. Opposing surfaces of right astragalus and calcaneus of Ailuropoda and Ursus arctos. 

and laterally for the cuboid. On the inferior sur- 
face, immediately behind the navicular articular 
surface, a deep pit marks the attachment of the 
talocalcaneal interosseous ligament. 

The calcaneus (fig. 66) is longer and more slen- 
der than in Ursus. On the superior surface the 
lateral articular surface is an elongate oval, ex- 
tending farther posteriorly than in Ursus. As in 
bears, it describes a continuous spiral track: an- 
teriorly it faces slightly laterally, while its poste- 
rior end is almost vertical, facing medially. This 
articular surface is scarcely curved in cross section, 
and the curvature along the long axis is relatively 
slight; in this flatness the bears and panda differ 
sharply from other carnivores. The medial artic- 

ular surface is a flat discoidal area on the superior 
surface of the sustentaculum. As in Ursus, the 
posterior end of this articular surface is deflected 
sharply downward, forming an angle of almost 90 
with the main articular surface. This arrange- 
ment, which is present in Nasua and indicated in 
Gulo but is wanting in other carnivores, increases 
stability of the lower tarsal joint at the expense of 

The medial articular surface is continued ante- 
riorly into a narrow accessory facet that extends 
forward to the anterior border of the calcaneus, 
articulating with the anterior marginal facet of the 
astragalus. This accessory facet, which increases 
the stability of the lower tarsal joint, is present in 
most, but not all, carnivores. 



Opposite the sustentaculum the lateral surface of 
the calcaneus is produced into a prominent projec- 
tion, the coracoid process (Baum and Zietzschmann, 
1936), from which arise the extensor digitorum 
brevis and quadratus plantae muscles. In Ursus 
the coracoid process is a long shelf-like structure 
extending posteriorly to the posterior border of 
the lateral articular surface, while in other carni- 
vores it is less extensive. 

The cuboid articular surface is more oblique than 
the coiTesponding surface in Ursus but is other- 
wise similar. The posterior end of the calcaneus 
is expanded into a knob-like structure. Almost 
the entire posterior face is occupied by a large de- 
pressed scar that marks the attachment of the 
tendo Achillis and its associated bursa. 

The navicular articulates with the astragalus, 
the cuboid, and the three cuneiforms, as in Ursus 
and other carnivores. The posterior surface is 
composed almost entirely of a large ovate concave 
articular facet that receives the head of the astrag- 
alus (fig. 64). The anterior surface is convex, its 
superior part indistinctly divided into three facets 
for the three cuneiform bones; inferiorly it is 
roughened at the attachment site of the plantar 
naviculari-cuneiform ligaments. On the medial 
surface a smooth prominence marks the articula- 
tion site of the tibial sesamoid. A narrow articu- 
lar facet on the inferolateral surface articulates 
with the cuboid, and immediately mesad of this 
on the inferior surface is a rounded prominence, 
the navicular tuberosity. 

The cuboid resembles that of Ursus in shape, 
but is relatively longer and narrower.' Its poste- 
rior surface presents a rectangular convex articular 
surface for the calcaneus (fig. 64) ; its anterior sur- 
face bears a slightly concave surface for the fourth 
and fifth metatarsals, a faint ridge dividing the 
two areas. Its medial surface presents two artic- 
ular surfaces, a vertical surface posteriorly that 
articulates with the head of the astragalus, and an 
irregularly shaped surface that articulates with the 
navicular and the third cuneiform. The inferior 
surface bears a prominent transverse ridge for the 
attachment of the long plantar ligament. 

The cuneiform bones articulate with the na- 
vicular posteriorly and the first three metatarsals 
anteriorly. The first is the largest ; the tibial sesa- 
moid articulates partly with its posteromedial cor- 

' The tarsus and pes are relatively broader in bears than 
in other carnivores. It is interesting and suggestive that the 
relative breadth of the cuboid increases with absolute size 
in the genus Ursus. The ratio breadth 'length X 100 in a 
series of bears is: Ursus americanus 81, U. arctos 92, U. gyas 
95. The only available specimen of U. spelaeus is a shade 
smaller than my very large U. gyas and has a ratio of 94. 
The corresponding ratio for Ailuropoda is 64. 

ner. The third cuneiform articulates laterally with 
the cuboid. 

The tibial sesamoid is relatively much larger 
than in Ursu^ (fig. 54); it measures 20 mm. in 
length by 13 in breadth. As in other carnivores, 
it articulates with the navicular and first cunei- 
form. The bone is flattened from side to side. 
The tendon of the posterior tibial muscle inserts 
on its posterior border, and a part of the flexor 
hallucis brevis muscle arises from its medial face 
(fig. 102). 

6. Pes 

The metatarsals decrease in length from the 
fifth to the first; in Ursus the fourth is the longest, 
and in procyonids the third and fourth are sub- 
equal. As in Ursus, the metatarsals are short. 
The fifth is relatively heavier than in Ursus, but 
the others are of comparable size. As in other 
carnivores, the proximal end of the fifth metatar- 
sal bears a prominent lateral process to which the 
tendon of the peroneus longus and brevis and the 
abductor digiti quinti attach. j 

As in the manus, the distal articular surfaces of ' 
the metatarsals are narrower than in Ursus, and 
the median ridge is more prominent. 

The phalanges are similar to those of Ursus, 
relativelj- shorter than those of the procyonids. 
In the proximal row a pair of elevations on the 
inferior surface of each bone, near the distal end, 
marks the attachment of the interosseous muscles. 
A conspicuous pit-like excavation on the inferior 
surface of each bone of the middle row, immedi- 
ately behind the trochlea, receives the large plantar 
process of the terminal phalanx. 

A pair of sesamoid bones is present beneath 
the metatarsophalangeal articulation of each digit. 
There are ten in all. 

B. Review of the Hind Leg 

The bones of the hind leg of Ailuropoda, like 
those of the fore leg, agree with the corresponding 
bones of Ursus in all essential respects. As in the 
fore leg, differences in details of modeling, torsion, 
and angulation probably represent postnatal re- 
sponses to stresses extrinsic to the bone tissue itself. 

Relative lengths of limb segments agree with the 
proportions in graviportal animals. This suggests 
that limb proportions in Ailuropoda are broadly 
adaptive, although the animal is much too small 
to be truly graviportal and the adaptive signifi- 
cance, if any. of the limb proportions is not clear. 
Short distal segments result in relatively powerful 
but slow movements in the distal part of the limb. 
Hence the advantage of a low femorotibial index 
to heavy graviportal animals and to digging forms 
that use the hind limbs for bracing. Length of 

Cloenodon cofruqatus 

Potos flavus 

Ursus arctos 

Ailuropodo melonoleuca 

Fig. 67. Right tarsus and pes of representative carnivores. The small inset to the left of Claenodon corrugatus is Claenodon 
montanensis (Bull. U.S. Nat. Mus., 169). 




long bones is certainly gene-controlled, but the 
mechanism of such control is unknown. 

Fuld (1901) demonstrated a slight but signifi- 
cant increase in tibia length in dogs that had been 
bipedal since puppyhood. Colton (1929) found 
that in the rat, on the contrary, bipedalism results 
in a slight increase in femur length. In neither 
the dogs nor the rats was the difference anywhere 
near as great as the difference between the relative 
lengths of these bones in Ailuropoda and Ursus. 

The hypertrophied tibial sesamoid is a product 
of natural selection, but of selection acting on the 
radial sesamoid. The fact that the tibial sesamoid 
has hypertrophied along with the radial sesamoid 
shows that these two bones are homeotic from the 
genetic standpoint as well as serially homologous 
from the morphological standpoint. 

Thus only one (presumably) adaptive feature in 
the bones of the hind leg the relative lengths of 
the long bones appears to result directly from 
natural selection acting on the bones themselves. 
Even this does not appear to be adaptive and may 
be a pleiotropic effect. 


It is evident from the foregoing description that 
the skeleton supplies abundant and convincing 
evidence that Ailuropoda is much closer to the 
Ursidae than to any other group of living carni- 
vores. Missing "ursid characters" have been partly 
responsible for disagreement among mammalogists 
as to the affinities of Ailuropoda (e.g., Mivart, 
1885a; Weber, 1928). It is now obvious that these 
missing characters have been obliterated by phylo- 
genetically recent factors that for the most part 
are extrinsic to the skeleton. The most important 
of these extrinsic factors is hypertrophy of the 
skeletal musculature. Yet, despite close similarity 
in all essential respects, the panda skeleton differs 
from the bear skeleton in a number of very puz- 
zling ways. It is the interpretation of these differ- 
ences that is pertinent to our central problem. 
The panda skeleton resembles the bear skeleton in 
all essential respects. 

The bear skeleton itself differs from the general- 
ized carnivore condition in a number of features 
that cannot be interpreted as adaptive, and I am 
certain that many ursid characters represent what 
Griineberg (1948) has called "subordinated gene 
effects" effects that are genetically, physiologi- 
cally, or even mechanically connected with a pri- 
mary gene effect on which natural selection has 
operated, without themselves being adaptive. Such 
non-adaptive characters might persist indefinitely 

if selection against them is less intense than selec- 
tion for the primary effect. Among the most con- 
spicuous of these in the bears are limb proportions, 
curve of moments of resistance in the vertebral 
column, shortness of lumbar region, shortness of 
tail, length of sacrum, form of pelvis. Ailuro- 
poda shares most of these characters with Ursus, 
and has superimposed additional features, likewise 
mostly non -adaptive, on the ursid pattern. 

Many of the differences between panda and bear 
skeletons are adaptive, but their cause is extrinsic 
to the bone itself; that is, they merely reflect the 
response of the bone tissue to external pressures, 
stresses and strains, and other purely mechanical 
factors. In the absence of the appropriate stimu- 
lus such characters fail to appear. Among such 
features are the surface modeling of bones, tor- 
sions, form and extent of articular areas, and size 
and position of foramina. These are characteristic 
features of the skeleton of Ailuropoda, and they 
may be clearly adaptive in the sense of promoting 
the efficiency of the organism, but they are epi- 
genetic to the bone and therefore are not the result 
of natural selection on the skeleton. 

The most conspicuous way in which the skeleton 
of Ailuropoda differs from that of Ursus is in a 
general increase in the quantity of compact bone 
throughout the entire skeleton. Except for mas- 
ticatory requirements, no differences from the 
habits of bears would demand such increased thick- 
ness of compacta for mechanical reasons. A gen- 
eralized effect of this kind, involving an entire 
tissue and with sharply localized advantage to the 
organism, would almost surely have a single cause. 
Comparable generalized effects, involving the whole 
skeleton and localized in a single genetic factor, 
are well known in laboratory and domestic ani- 
mals (Stockard, 1941; Griineberg, 1952; Klatt and 
Oboussier, 1951). Wherever they have been ana- 
lyzed, it has been found that such effects are me- 
diated through the endocrine system. We may 
postulate that in the panda, because of mastica- 
tory requirements, selection strongly favored in- 
creased thickness of compacta in the skull. This 
increase was actually achieved via a process that 
results in generalized thickening of the compacta 
throughout the skeleton. The functionally un- 
necessary increase of bone tissue in the postcranial 
skeleton is no great disadvantage because of the 
non-predatory habits of this species, which places 
no premium on speed and agility. 

The most significant feature in the panda skeleton 
is a generalized, increase in the quantity of compact 
bone. This probably has an extremely simple genetic 
base. The increased thickness of compacta is advan- 
tageous only in the skull. 



Many proportions in the skeleton of the panda 
and to a lesser extent in the skeleton of bears 
are a mixture of those seen in bipedal, in burrow- 
ing, and in graviportal forms. In part these pro- 
portions are mutually contradictory adaptations 
associated with bipedalism are not the same as 
those associated with graviportalism and in part 
they are not contradictory, since adaptations for 
withstanding anteroposterior thrust are similar in 
bipedal and burrowing forms. Still other propor- 
tions in the panda, particularly in the limbs, cannot 
be reconciled with any mechanical requirements, 
and appear to represent disharmonious relations 
of the "subordinated gene effect" variety. The 
fact is that the panda does not burrow, it is bi- 
pedal only to the extent that, like many other 
mammals, it occasionally stands erect for short 
periods, and it is not heavy enough to qualify as 
graviportal. These facts show that the ill-assorted 
features distinguishing the postcranial skeleton of 
the panda from that of Ursus are not truly adap- 
tive, and that where they agree with conditions 
that presumably are adaptive in other specialized 
forms (bipedal, fossorial, graviportal) such agree- 
ments are either fortuitous or based on something 
other than functional demands. 

Thus we are confronted with a highly modified 
and strongly adaptive skull associated with a con- 
siderably modified postcranial skeleton in which 
the departures from the "ursid norm" appear to 
be completely non-adaptive, even inadaptive to 
the extent of producing a disharmonious organism. 
From what is known of the genetics of acromegaly, 
achondroplasia, and other pathological conditions 
of the skeleton in dogs and mice (Stockard, 1941; 
Griineberg, 1948) the most economical interpreta- 
tion, consistent with all known facts, of the syn- 
drome of non-adaptive features in the skeleton of 
Ailuropoda is that they are associated pleiotropi- 
cally with the one definitely adaptive feature. It 
is even highly probable that the whole complex 
has a very simple genetic base. 

The persistence of such morphological dishar- 
monies in a natural population is unusual but not 
unique, and might in fact be anticipated in highly 
specialized forms whose adaptive niche places a 
low premium on all-around mechanical efficiency. 
Similar disharmonies are clearly evident in the 
hyenas, which like Ailuropoda are highly special- 
ized for masticatory power but do not need speed 
or agility either to escape from enemies or to cap- 
ture prey. 

It is suggestive that bipedal, fossorial, and gravi- 
portal mammals are all characterized by local 
strengthening of the skeleton (i.e., by increase in 
quantity of compacta). The changes in form and 

proportions associated with such local strength- 
ening are presumptively adaptive, and in some 
instances it can be shown unequivocally that they 
are the moments of resistance in the vertebral 
column of bipedal forms, for example. In other 
instances attempts at a functional explanation 
have been unsuccessful; for example, pelvic archi- 
tecture in bipedal and burrowing forms. In many 
instances no functional explanation has even been 
attempted; for example, limb proportions in gravi- 
portal forms. If it can be demonstrated that cer- 
tain features in the skeleton are correlated with 
increased quantity of compacta rather than with 
other functional requirements, then an association 
between such features and a particular functional 
requirement is merely a chance association. At- 
tempts to read adaptive significance into such 
associations are, of course, based on a false as- 
sumption and can only lead to false conclusions. 
The existence in the panda skeleton of numerous 
ill-assorted conditions convergent with conditions 
in bipedal, fossorial, and graviportal forms sug- 
gests that such spurious correlations with func- 
tional requirements may be more common than 
has been assumed. Much more data are required 
to prove this suggestion. 

Numerous ill-assorted disharmonies in the post- 
cranial skeleton of the panda are connected pleiotrop- 
ically, as subordinated gene effects, with the increase 
in quantity of compacta. 

One other feature in the skeleton demands atten- 
tion: the specialized and obviously functional ra- 
dial sesamoid. It was concluded (p. 183) that all 
that would be required to derive this mechanism 
from the radial sesamoid of Ursus is simple hyper- 
trophy of the bone. This symmetrical increase in 
the dimensions of a single bone is quite a different 
thing from the hypertrophy of the compacta seen 
elsewhere in the skeleton. The localized remodeling 
seen in the sesamoid surely has a specific genetic 
base, as is strongly indicated by the "sympathetic" 
hypertrophy of the tibial sesamoid. The parallel 
and non-functional hypertrophy of the tibial sesa- 
moid also indicates that the genetic mechanism is 
a very simple one, perhaps involving no more than 
a single gene. 

The highly specialized and obviously functional 
radial sesamoid has a specific, but probably very 
simple, genetic base. 

Disregarding any minor polishing effects of nat- 
ural selection, aimed at reducing disharmonious 
relations, it appears that the differences between 
the skeleton of Ailuropoda and that of Ursus could 
be based on no more than two gene effects. There 
is, of course, no way of proving that the situation 
actually was so simple, but mechanisms capable 



of producing comparable eflfects on the skeleton 
have been demonstrated experimentally in other 
mammals. The alternative explanation numer- 
ous small gene effects screened by natural selection 
postulates a vastly more complex process, and 
leaves unexplained the many clearly inadaptive 
features in the skeleton. We could, of course, 
assume that these several inadaptive features ap- 
peared one by one during the evolution of Ailuro- 
poda, and persisted simply because there was little 
or no selection against them. But if each of these 
is unconnected with any of the other gene effects, 
then any selection pressure would have eliminated 
them. Obviously there is some selection against 
any inadaptive feature; no feature is truly adap- 
tively neutral. Therefore it seems to me that 
probability strongly favors a single gene effect as 
the causal agent for all the hereditary differences 
between the skeleton of Ailuropoda and Ursus, 
except in the radial sesamoid. 

The major features distinguishing the skeleton of 
Ailuropoda from that of Ursus may depend on as 
few as two gene effects. These are: 

(a) Generalized hypertrophy of compacta. 

(b) Specific hypertrophy of the radial sesamoid. 


1. The skeleton of Ailuropoda resembles the 
skeleton of Ursus in all essential respects. 

2. Many skeletal differences between Ailuro- 
poda and Ursus are epigenetic to the bone tissue, 
and therefore do not result from natural selection 
on the skeleton. 

3. The most significant feature in the panda 
skeleton is a generalized increase in the quantity 
of compact bone. This probably has an extremely 
simple genetic base. 

4. The increased thickness of compacta is ad- 
vantageous only in the skull. 

5. Numerous ill-assorted disharmonies in the 
postcranial skeleton are connected pleiotropically, 
as subordinated gene effects, with the increase in 
quantity of compacta. 

6. The highly specialized and obviously func- 
tional radial sesamoid has a specific, but probably 
very simple, genetic base. 

7. Thus, the major features distinguishing the 
skeleton of Ailuropoda from that of Ursus may 
depend on as few as two genetic factors. These 
are: (a) generalized hypertrophy of compacta; (b) 
specific hypertrophy of the radial sesamoid. 



The classification of mammals has depended 
more on the dentition than on any other single 
feature of morphology. The teeth of the giant 
panda have repeatedly been studied and discussed 
in great detail (Gervais, 1875; Lydekker, 1901; 
Bardenfleth, 1913; Gregory, 1936; McGrew, 1938). 
These studies have led to the most divergent views 
as to the homologies of the various cusps, and in- 
ferences as to the affinities of Ailuropoda based on 
such homologies. I conclude that the cheek teeth 
of Ailuropoda are so modified from those of any 
other known carnivore that interpretations based 
on them have been largely subjective. 

The dental formula of Ailuropoda is 

If CI Pi M=42, 

which is the primitive form for the recent Carni- 
vora. The formula is the same in small species 
of Ursus, but various additional teeth have been 
lost in large species of Ursus and in other genera 
of the Ursidae. In the Procyonidae and Ailurus 
the third lower molar has disappeared, giving the 

U C{ Pi Mt=40. 

The incisors are in no way remarkable in Ailu- 
ropoda. As in carnivores in general, in both jaws 
they increase in size from the first to the third. 
As in Ursus (much less so, if at all, in other arc- 
toids), the third incisor in both jaws is abruptly 
larger than the second, and in the upper jaw is 
less chisel-shaped and more caniniform than the 
two more medial incisors. The third incisor is 
relatively larger in Ailuropoda than in Ursus, and 
is separated from the canines by a very short dia- 
stema. The shortness of the diastema is the only 
evidence of crowding in the anterior dentition. 
The incisors are, of course, single rooted. 

The six incisors in each jaw are closely crowded, 
their combined occlusal surfaces forming an essen- 
tially continuous, slightly arched, scraper or chisel 
edge. The resulting tool, lying between and often 
slightly in front of the canines, is one of the most 
characteristic features of the dentition of the Car- 

The canines are more robust than in Ursus, in 
both long and transverse diameters. Their rela- 
tive length is almost identical in bear and panda, 
however, and this gives the canines of Ailuropoda 
a relatively stumpy appearance. In the unworn 
dentition there is a vertical ridge on both anterior 
and posterior surfaces of the upper canine, and on 
the posterior surface only of the lower. Similar 
ridges are seen in other arctoids (e.g., Procyon), 
but not in Ursus. Ailurus, along with the pro- 
cyonids Bossoncyon and Potos, has vertical grooves 
on its canines. The phylogenetic and functional 
significance, if any, of these surface sculpturings 
is unknown. 

The upper canine in Ailuropoda projects for- 
ward at an angle of about 30. The same tooth 
forms an angle of about 15 in Ursus, while in 
other arctoids examined it does not deviate more 
than a couple of degrees from the vertical. 

The premolars increase in size from the first 
to the fourth, as in all arctoids. The first premolar 
is degenerate and peg-like in both jaws, and is 
often missing. In size and structure it contrasts 
sharply with the remaining premolars. The re- 
maining three teeth are crowded, and in both up- 
per and lower jaws P2 is rotated at an angle of 
about 30 from the axis of the tooth row. 

In the upper series, P'^ is tri-lobed, two-rooted, 
and with no indication of internal (lingual) cusps. 
P ^ is very similar to P \ except in size. The fourth 
upper premolar, the upper carnassial of the Car- 
nivora, has been the chief object of discussion and 
speculation in the dentition of the giant panda. 
It is the largest of the premolars, but is neverthe- 
less considerably smaller than the two upper mo- 
lars. The tooth exhibits five prominent cusps 
arranged in two longitudinal rows. The three on 
the labial side are considerably higher than those 
on the lingual, with the central one the highest of 
all. These have been homologized, from front to 
rear, with the parastyle, paracone, and metacone. 
The two cusps on the lingual side are regarded as 
the protocone (anteriorly) and the hypocone (pos- 
teriorly). There are no cingula. The tooth has 
three powerful roots, arranged in the form of a 
triangle. The anteriormost root supports the para- 






AtUero-uiternal cusp 



Protoconid tii- 


h h I, 



Fig. 68. Occlusal views of unworn right upper and left lower dentitions of Ailuropoda (XI). 

style, the protocone, and the anterior half of the 
paracone. The posteroexternal root supports the 
metacone and the posterior half of the paracone. 
The posterointernal root supports the hypocone. 

Five cusps, occupying similar positions, are found 
on the upper carnassial of Procyon and Ailurus. 
The mode of origin of the Procyon crown pattern 
from the primitive three-cusped shearing carnas- 
sial is well known and documented by fossil mate- 
rial (McGrew, 1938). Morphologically the crown 
pattern of Ailuropoda is very similar to that of 
Procyon, but the relation of the cusps to the roots 
is quite different and essentially nothing is known 
of the history of this tooth in the panda. The 
form of the crown in Ailurus is like that of Pro- 
cyon and Ailuropoda, and the relation of cusps to 
roots is like that of Procyon, not like that of Ailuro- 
poda. It has been assumed by Lydekker, Gregory, 
and McGrew that the morphological similarity in 

cusp arrangement between the raccoon and the 
giant panda denotes homology and hence common 
ancestry. Winge and Bardenfleth, on the con- 
trary, argued that the different cusp-root relations 
show that the similarity in crown pattern is the 
result of convergence. 

In the Ursidae, by contrast, P^ is degenerate by 
normal carnivore standards. It is relatively and 
absolutely small, abruptly smaller than the mo- 
lars, and its crown usually bears only three cusps: 
the paracone, metacone, and protocone; in small 
individuals of Ursus (e.g., U. americanus) there 
may be a minute parastyle. The relation of cusps 
to roots is identical with Ailuropoda. 

The lower premolars are simpler and more uni- 
form than the upper, but otherwise follow the 
trend of the latter closely. As in the upper jaw, 
the first premolar is small and peg-like and con- 
trasts sharply with the following teeth. It is often 



missing. Pj,, like its antagonist, is rotated at an 

angle of about 30 from the axis of the tooth row. 

P , increase in size from front to rear, but P, 

* is much smaller than the following M,. All are 
trilobed, with three conical cusps in series along 
the axis of the tooth. P^ has a small postero- 
internal cusp, sometimes subdivided into several 

f small tubercles. Thus the posteriormost part of 
the lower premolar series is slightly broadened. 
All the lower premolars, except Pj, are two-rooted. 
The upper molars are enormous and richly 
cuspidate, dominating the entire upper tooth row. 
They are abruptly and conspicuously larger than 
the upper premolars, and are closely crowded. 
M ' is almost square, slightly broader than long. 
It bears two prominent conical cusps, the para- 
cone and the metacone, on the labial side. Lin- 
gually and directly opposite these there is a second 
pair of smaller and lower cusps, the protocone and 
hypocone. A third pair of poorly defined cusps is 
situated in the valley between the outer and inner 
rows of cusps; the homology, if any, of these cusps 
is unknown. The internal border of the tooth 
forms a broad shelf-like cingulum whose occlusal 
surface is very regularly serrate. M^ is divided 
into two subequal parts, a trigonid anteriorly and 
a large talonid posteriorly. The anterior part of 
the tooth is very similar to M Mn form and arrange- 
ment of cusps and cingulum. The occlusal surface 
of the talonid is richly tuberculate, with a long 
blade-like cusp medially (immediately behind the 
protocone, and perhaps representing an elongate 
hypocone) and a narrow cingulum. There are 
three roots on M ' , two lateral and one medial, as 
is typical of the Carnivora. The medial root is 
greatly expanded anteroposteriorly, and is partly 
divided by a groove into two pillars that lie be- 
neath the two medial cusps. M'-, in addition to 
the usual three roots, has a fourth large root sup- 
porting the talon. 

The upper molars of Ailuropoda are fundamen- 
tally similar to those of Ursus, but they differ in 
two seemingly important respects: their relatively 
larger size, especially their greater breadth; and 
the rich development of secondary tubercle-like 
elevations. The extinct European cave bear, Ur- 
sus spelaeus, reached a larger size than any other 
known member of the genus Ursus, and hence had 
the largest molars. It is therefore extremely sug- 
gestive that the molars of the cave bear, while 
retaining their ursid outlines, exhibit the same rich 
development of secondary cusps and tubercles as 
is seen in the giant panda. The similarity of the 
molars in these two forms, except for the broaden- 
ing of the crown in Ailuropoda, is quite astonishing. 

The lower molars are simpler and less broadened 
than the upper. M^, the lower carnassial, has 
lost its sectorial character and is quite similar to 
the corresponding tooth in both Ursus and Pro- 
cyon. There are five cusps, which retain the prim- 
itive arrangement (fig. 68). The facing slopes of 
the entoconid and hypoconid exhibit low tubercle- 
like elevations similar to the medial row of cusps 
on M ' , but these are lacking between the proto- 
conid and metaconid. There is a poorly defined 
cingulum externally. M ^ is more tuberculate than 
Mj, and the cusps are less sharply defined. The 
paraconid, which is prominent on Mj, cannot be 
identified with certainty on M ^ . This cusp is often 
almost completely coalesced with the protoconid 
in Ursus. It is also associated with the proto- 
conid in Ailurus, but there is no indication of it 
in Procyon. M., has a rounded triangular outline 
in Ailuropoda, and the cusps are almost completely 
obliterated on its flattened crown. The occlusal 
surface, which opposes the talon of M'^, is thrown 
up into a complex pattern of low tubercles. The 
outline and crown pattern of M 3 in Ailuropoda are 
quite different from the more typically molariform 
Mg of Ursus. It is noteworthy, however, that 
Rode (1935, pi. 7) illustrates, as "abnormal" ex- 
amples, several lower third molars of the gigantic 
Ursus spelaeus and these are almost exactly like 
M., of Ailuropoda. 


It has long been the custom of systematists to 
regard individual teeth, and even individual cusps, 
as the basic units of the dentition. Thus, by im- 
plication, these units are construed as individually 
gene-controlled and therefore subject to individual 
selection. The tooth as a whole, to say nothing 
of the dentition as a whole, would then be a mosaic 
of individually derived elements, each of which 
survives or perishes according to the way in which 
it functions in the dental activities of the animal. 
Similarities between adjacent teeth are ascribed 
to convergence resulting from selection. Such a 
view naturally places great emphasis on "homol- 
ogies" between cusps and similar elements as in- 
dicating affinities between animals. Furthermore, 
the minute structure of each tooth is perforce 
directly correlated with function. 

In practice, the teeth are minutely scrutinized 
and compared, element by element, for similari- 
ties in structure. Identity or near identity in 
architecture is construed as an infallible indicator 
of relationship, and vice versa. Certain teeth (P^ 
in the Carnivora) are often assumed to be better 
indicators of affinities than others. This method 
has worked in the majority of cases because in 



closely related forms the dentitions, like other 
morphological features, usually are closely similar. 
There is a considerable residue of forms with spe- 
cialized dentition, however, whose relationships 
cannot be resolved by any amount of peering at 
the teeth as discrete entities. As Bateson re- 
marked more than half a century ago, "the attri- 
bution of strict individuality to each member of 
a repeated series of repeated parts leads to ab- 
surdity." No better example of the limitations of 
this method could be asked than the giant panda. 

On the basis of a mechanical point-by-point 
comparison, the teeth of Ailuropoda are in some 
respects more similar to the teeth of the Procy- 
onidae than to those of the Ursidae. The whole 
premolar series is strikingly degenerate in the 
bears. Pl-3 are peg-like vestiges, often missing in 
part. Even P* (the carnassial), normally the larg- 
est tooth in the upper battery in carnivores, is 
greatly reduced in all bears. In Ailuropoda, in 
striking contrast, only PI is degenerate and the 
remaining premolars are robust functional teeth. 
P^ is large, with five well-formed cusps occupying 
the same relative positions on the crown as they 
do in Procyon and Ailurus (though they are dif- 
ferently related to the roots). On the other hand, 
the molars of Ailuropoda are far more bear-like 
than procyonid-like, especially in the presence of 
a large talon on M- and in the retention of M.,, 
which is lacking in the Procyonidae. It was the 
opinion of Lydekker, Gregory, and McGrew, how- 
ever, that the premolar features are "more im- 
portant" than the molar. 

Two recent concepts have greatly changed our 
ideas of the evolution of dentitions. Structures 
such as teeth or vertebrae are serially repeated 
(homeotic) elements. It has been found that such 
structures are at least partly controlled by genes 
exerting a generalized effect over a region com- 
prising several adjacent elements, rather than on 
each isolated element. This is the field control 
concept. Sawin (1945, 1946) and Sawin and Hull 
(1946) have so interpreted hereditary variations in 
vertebral formula in rabbits. Butler (1939, 1946) 
has applied the field concept to the teeth of mam- 
mals, arguing that they are homeotic structures 
that have evolved as parts of a continuous mor- 
phogenetic field rather than as isolated units, and 
that a common morphogenetic cause must have 
acted on more than one tooth germ to account for 
the close similarity between adjacent teeth. The 
second concept is that of differential growth, which 
was developed chiefly by Huxley (1932). Accord- 
ing to this theory, now voluminously documented, 
various structures may have a different growth 
rate from that of the organism as a whole. Thus, 

with increase in the size of the organism during 
phylogeny, structures may attain a relative size 
or degree of differentiation that is not directly 
determined by the action of selection on the struc- 
ture itself. The classic examples of the mandibles 
of lucanid beetles and the antlers of deer are well 
known, but it is not so well understood that this 
principle may apply also to the teeth of mammals. 

How do these concepts relate to the dentition 
of Ailuropoda'! In the primitive carnivore den- 
tition, as represented hy Canis, the dental gradient 
of the upper cheek teeth centers in P' and M', 
falling off steeply on either side of this center. 
More specialized carnivore dentitions exhibit a 
shifting of this center anteriorly or posteriorly 
along the tooth row, and expansion or contraction 
of the center to embrace one or several teeth 
(fig. 69). The Ursidae differ from other Carni- 
vora in that the center lies wholly in the molar 
region, falling off abruptly at the boundary be- 
tween molars and premolars. The molar empha- 
sis is further reflected in the conspicuous posterior 
extension of M- in the form of a large talon. In 
Ailuropoda the whole premolar- molar battery has 
been secondarily enlarged, but there is still the 
same molar emphasis as in the bears. The dental 
gradient is quite distinctive and different from 
that of the Procyonidae. 

Enlargement in Ailuropoda begins abruptly at 
the boundary between the first and second pre- 
molars; the teeth anterior to this line (first premo- 
lar, canine, and incisors) are no larger than in 
Ursus, whereas teeth posterior to the line are all 
enlarged to approximately the same degree. These 
correspond almost exactly to the canine and in- 
cisor fields and the molarization field, respectively, 
of Butler. An astonishingly close parallel to this 
condition is seen in the fossil anthropoid Paran- 
thropus robustus (Broom and Robinson, 1949), in 
which the premolar-molar series is so much and 
so abruptly larger than the canine-incisor series 
that it is difficult to believe they belong to the 
same individual. 

The data of Rode (1935) on the dentition of 
fossil and recent bears present a clear picture of 
changes directly correlated with skull size in the 
genus Ursus. Such changes are the result of dif- 
ferential growth rather than of direct selection on 
the dentition, and are only secondarily (if at all) 
related to the functioning of the teeth. The pre- 
molar dentiton is reduced in all members of the 
genus, no doubt as a result of selection, but de- 
terioration becomes progressively more pronounced 
with increased skull size. In small forms ( Ursus 
americanus) the formula is typically Pi; among 
the medium-sized species it is f in U. arctos and 










Fig. 69. Upper cheek teeth of representative carnivores to show varying gradients in the premolar-molar field. 

f in U. horribilis, but in the huge U. spelaeus it 
is { or even ^.' Thus there is an inverse correla- 
tion between skull size and premolar development 
in Ursus, and reduction of the premolars is a fea- 
ture of the growth pattern of this genus, its ex- 
pression becoming increasingly pronounced with 
increased skull size. It is probable, furthermore, 
that the growth pattern was established early in 
bear phylogeny, in animals of relatively small size, 
in adapting the primitive carnivore dentition to 
the requirements of the bear stock. The almost 
total suppression of the premolars in large species 
would then be merely an expression of the gi'owth 
pattern of the bear stock, a direct result of selec- 
tion for larger size, not of selection on the dentition 
itself. If an individual American black bear grew 

' The Alaskan brown bear (Ursus gyas), with a basal skull 
length up to 405 mm., may rival U. spelaeus in size. The 
cheek teeth of gyas are the same absolute size as in the 
grizzly, however, showing that a new and different factor 
(probably resulting from direct selection on the dentition) 
has affected the teeth in gyas. The premolar formula is 
typically f . 

to the size of a cave bear, we should expect its 
pi'emolars to resemble those of a cave bear. 

With respect to the molars, Rode's data show a 
direct correlation between tooth size and elabora- 
tion of the crown sculpture in the form of second- 
ary wrinkles and tubercles. The cingula also 
become wider and better defined with increased 
tooth size. Both reach a peak in Ursus spelaeus. 
Thus, elaboration of the molar crown pattern is 
directly correlated with tooth size, and is an ex- 
pression of the growth pattern of the bear stock. 
The condition seen in U. spelaeus results from the 
absolutely larger teeth, not from selection on the 
teeth themselves. 

The consequences of differential growth thus re- 
veal two significant features of the dentition of 
bears. These probably could not have been de- 
tected, and certainly could not have been verified, 
at the stage when they were under the active in- 
fluence of natural selection. The later effects seen 
on larger individuals, by exhibiting the results of 
the pattern in exaggerated form, leave little doubt. 



The two ursid features are: (1) almost total shift 
of emphasis to the molar region of the cheek-tooth 
field, with the great talon suggesting a tendency 
to carry the center as far posteriorly as possible, 
and (2) elaboration of the crown sculpturing of 
the molars. 

The basal skull length of Ailuropoda is slightly 
less than that of the American black bear. The 
molar teeth are disproportionately large, their ab- 
solute length agreeing with the much larger gizzly. 
But the whole tooth row of Ailuropoda is also 
enormously broadened, and the molars equal (M-) 
or exceed (M') those of the cave bear in width. 
The broadening affects the premolars as well as 
the molars (i.e., it extends over the whole cheek- 
tooth field), and the disparity between premolar 
and molar size is not as obvious as in the bears. 
Nevertheless the molar dominance is still evident 
in Ailuropoda. 

Broadening of the premolars in Ailuropoda is 
associated with the development of an internal 
row of cusps, as it is in Procyon and Ailurus, the 
other two arctoids in which the cheek teeth are 
broadened. These cusps are, of course, conspicu- 
ously wanting in the reduced premolars of Ursus. 
Now, their presence in Ailuropoda may (1) indi- 
cate affinities with the procyonids, or (2) be an 
expression of the common genetic background of 
the arctoid carnivores. As will appear in the se- 
quel, there can be no doubt of the ursid affinities 
of the giant panda, and therefore the second of 
these alternatives is correct. The internal row of 
cusps in Ailuropoda is the result of broadening 
of the premolars. 

The surface sculpturing of the molars is much 
more elaborate in Ailuropoda than in the small 
and medium-sized bears, but it is almost identical 
with that of the gigantic Ursus spelaeus. If, as 
pointed out above, elaboration of sculpturing is a 
function of absolute tooth size in the bear stock, 
then this is exactly what we should expect in the 
huge molars of Ailuropoda. Any relation between 
the "bunodont" character of the molars of Ailu- 
ropoda and its diet is fortuitous. It is only the 
enlargement and broadening of the teeth that are 
so correlated. 

Thus, given the morphogenetic pattern of the 
bear stock, only two (perhaps only one) important 
new factors have appeared in Ailuropoda. In the 
ursid stock the morphogenetic field is concentrated 

in the molar region, with the premolar field essen- 
tially vestigial. In Ailuropoda the ursid pattern 
has been further altered by two' simple morpho- 
genetic factors: (1) secondary enlargement of the 
whole cheek-tooth field, and (2) secondary broad- 
ening of the whole field. Note that both of these 
factors affect the cheek-tooth field as a whole (ex- 
cept PI, which is vestigial), with no indication of 
a gradient that did not already exist in the bears. 
It is these two factors that represent adaptation 
in the dentition of Ailuropoda, and not the de- 
tailed architecture of each individual tooth. 


1. In Ursus the expression of the dentition is 
a function of skull and or tooth size. Elements in 
the premolar field degenerate progi'essively with 
increasing skull size among the species of Ursus, 
whereas the molar crown pattern becomes increas- 
ingly elaborate as absolute tooth size increases. 

2. The dentition of Ailuropoda is an ursid den- 
tition in which all elements in the premolar-molar 
field (except PI) have become uniformly much en- 
larged and broadened. The result is a disharmo- 
nious relation between skull and dentition, which 
is reflected in the displacement of P2. 

3. The molar crown pattern of Ailuropoda 
closely resembles that of the gigantic Ursus spe- 
laeus. The molar crown pattern of Ailuropoda is 
therefore a function of tooth size, not of selection 
for a particular pattern. 

4. Successive disappearance of premolars, which 
accompanied increased skull and or tooth size in 

Ursus, is not evident in Ailuropoda, although the 
ursid proportions between premolar and molar size 
are retained. 

5. In Ailuropoda, selection was for increased 
cheek-tooth size. Selection operated on the mor- 
phogenetic field of the cheek-tooth battery as a 
whole rather than on individual units. The result 
is that all units in this field are enlarged to the 
same relative degree. 

6. The genetic mechanism behind this trans- 
formation is probably very simple and may in- 
volve a single factor. 

' Increased tooth length may, of course, be merely a sec- 
ondary result of broadening, in which case only a single new 
factor would be involved. 


Descriptions of the joints of mammals other 
than man are very few, and are incomplete for 
even the common domestic mammals. This is 
unfortunate, since no mechanism the mastica- 
tory apparatus or the hand, for example can be 
understood unless the structure and functioning 
of the joints are known. Comparative arthrology, 
the comparative anatomy of the joints, cannot be 
said to exist as an organized body of knowledge. 

No attempt is made here to describe all the 
joints of the giant panda. Those forming parts 
of mechanisms that are much modified in Ailu- 
ropoda the mandibular, wrist, and ankle joints 
were studied in detail and compared with the 
corresponding joints in the bears. A few other 
joints, chiefly those important in locomotion, are 
also described. 


Mandibular Joint 

The mandibular joint is a sliding hinge joint, as 
in all carnivores. The two joint surfaces are very 
closely congruent, as they are also in Ursus; they 
are less so in some other carnivores. The joint in 
Ailuropoda is not quite transverse, its axis in the 
frontal plane forming an angle of 5 10 with the 
transverse axis of the skull. This compares with 
a range of 5-20 in a series of Ursus. In the trans- 
verse plane the axis is depressed toward the mid- 
line at an angle of about 10, compared with about 
2 in Ursus. These deviations from the transverse 
axis represent sectors of two circles, one in the 
transverse and one in the frontal plane, whose 
common center lies some distance in front of the 
canines. They reflect the fact that the canines 
interlock as they come into occlusion, checking 
transverse movement at this point and causing 
the canines to act as a point of rotation. Since the 
canines are conical rather than cylindrical, the 
actual point of rotation lies in front of the canines. 

The mandibular joint is remarkable for its mas- 
siveness, its relative size exceeding that of any 
other carnivore. It is also displaced dorsally and 
posteriorly relative to its position in Ursus. This 
displacement increases the mechanical efficiency 

of the jaw apparatus for crushing and grinding 
(p. 69). 

The articular capsule is a close-fitting sac, heavy 
posteriorly but much thinner anteriorly, where it is 
intimately associated with fibers of the temporal 
muscle. The capsule is attached to the margin of 
the mandibular fossa all around, and to the mar- 
gin of the articular surface on the capitulum of the 
mandible. There is no thickening at the lateral 
end corresponding to the temporomandibular liga- 
ment of human anatomy. 

The articular disk is almost paper-thin and is 
imperforate. It increases slightly in thickness from 
anterior to posterior and is not notably thinner 
at the center than at the periphery. The disk is 
firmly attached to the capsule throughout its en- 
tire periphery, and is more tightly attached to the 
fossa than to the condyle. None of the external 
pterygoid fibers insert into it. 

A single ligament is associated with the man- 
dibular joint (fig. 70). This apparently represents 
the stylomandibular ligament combined with the 
posterior end of the sphenomandibular ligament; 
in Ursus these two are separate and distinct and 
attach at the normal sites. The ligament is a band 
about 5 mm. wide, attached anteriorly to the an- 
gular process of the mandible. From this attach- 
ment it runs posteriorly, dorsally, and medially 
beneath the outer end of the postglenoid process. 
Here it bifurcates, one branch going to the inferior 
surface of the bony auditory meatus (the normal 
attachment of the sphenomandibular ligament) 
and the other to the inferior surface of the carti- 
laginous auditory meatus (the normal attachment 
of the stylomandibular ligament). The absence 
of the anterior part of the sphenomandibular liga- 
ment, which normally attaches at the entrance to 
the mandibular foramen, is probably associated 
with the great size of the postglenoid process. 

Movement in the mandibular joint consists, as 
in all carnivores, of two components: hinge move- 
ment around an approximately transverse axis, in 
which the cylindrical head rotates in the trough- 
like fossa; and sliding movement, in which the 
head shifts transversely in the fossa. These two 
movements are combined into a spiral screw move- 




Proe. augularit 

Capsula articularif 

Prof, mastoideuf 

Meatus acusticus ext. 

CorpMS monuHbulat 

M. pter\-goid. int. 

Capsula articularU 

Ljg. stytomandibulare 

Hamulus pterfgoidens 

Proe. posi- glenoid. 

Fig. 70. Right mandibular joint of Ailuropoda, external view. 

ment, as is evident from the wear surfaces on the 
teeth. Measured on the dr>- skull, the lateral com- 
ponent amounts to about 6 mm. after the cheek 
teeth first begin to come into occlusion. The cor- 
resix)nding lateral component is about 3 mm. in 
a specimen of Ursiis aretos. 

In summary-, the mandibixlar joint of Ailuro- 
poda differs from that of I'rsus chiefly in being 
larger and more robust, and in being displaced 
dorsally and posteriorly. These are all directly 
adaptive modifications. They can scarcely be 
attributed to extrinsic factors, but probably rep- 
resent the results of selection operating on intrinsic 
(hereditan.-) factors. It is even plausible that the 
increase in quantity of bone tissue in the skull as 
a whole reflects the generalized working of the 
morphogenetic machiner>- whereby increased size 
of the bony elements of the mandibular joint was 

A. Shoulder Joint 

The shoulder joint is an extremely simple joint, 
as it is in all mammals that lack a clavicle. The 
only ligament is the loose articular capsule, and 
consequently the joint is held in position solely by 
muscles. .\s pointed out by Baum and Zietzsch- 
mann for the dog, the powerful tendon of the in- 
fraspinatus laterally, and that of the subscapularis 
medially, functionally represent collateral liga- 
ments of the shoulder joint. In addition to their 
function of retaining the joint in position, these 
tendons must also tend to limit adduction and 
abduction of the humerus, and thus to i-estrict 
movement to a pendulum-like flexion and extension. 

The glenoid cavity of the scapula is remarkable 
for its narrowness in comparison with other carni- 
vores. The articular surface of the head of the 



humerus, in contrast, is broader than in other car- 
nivores. The fibrous glenoid lip is inconspicuous 
except along the posterior border of the glenoid 
cavity, where it projects a couple of millimeters 
beyond the edge of the bone. 

The articular capsule is a loose sac enclosing 
the shoulder joint on all sides. It extends from 
the prominent rough surface around the margin 
of the glenoid cavity of the scapula, to the head 
of the humerus. On the humerus the capsule is 
attached to the roughened area at the periphery 
of the head. In the intertubercular area it is pro- 
longed distad into the intertubercular sheath 
that encloses the tendon of the biceps. 

The posterior (superficial) fibers of the triceps 
medialis separate from the anterior (deep) fibers 
at their origin, and arise from the inferior surface 
of the capsule instead of from bone. Contraction 
of this muscle would consequently exert traction 
on the capsule. A very few of the posteriormost 
tendon fibers of the triceps lateralis are also at- 
tached to the joint capsule. 

B. Elbow Joint 

The elbow joint (figs. 71, 72) depends for its 
strength and security on bony structures rather 
than on the number, strength, or arrangement of 
its ligaments, as is the case with the knee. In the 
giant panda and bears the elbow joint is a screw 
joint rather than a simple hinge joint as in other 
carnivores. The spiral trough formed by the me- 
dial half of the trochlea (fig. 49) forces the ulna to 
travel medially 5 mm. or more as the elbow is 
flexed. With the foot in the normal position of 
pronation, this would throw the foot medially as 
the elbow is flexed, and would account, at least in 
part, for the rolling motion characteristic of the 
fore feet in bears and the giant panda. 

The capsule is a large and capacious sac to 
which the collateral ligaments are inseparably 
united. The supinator and a small part of the 
abductor pollicis longus muscles arise directly from 
the capsule. The bony attachments of the capsule 
are as follows: (1) on the humerus it encloses the 
vestigial coronoid fossa anteriorly and the ole- 
cranal fossa posteriorly; laterally and medially it 
attaches to the sides of the trochlea and the distal 
ends of the epicondyles; (2) on the ulna it attaches 
to the edges of the semilunar notches; (3) on the 
radius it attaches just distad of the articular facet. 

The lateral collateral ligament arises from 
the lateral epicondyle and runs distad across the 
radiohumeral articulation. At the annular liga- 
ment it is interrupted by the origin of the supi- 
nator muscle, beyond which it continues distad 
to its attachment on the anterolateral surface of 

the radius about 30 mm. below the head. A prom- 
inent scar marks its radial attachment. There are 
two lateral ligaments in the dog (Baum and 
Zietzschmann) and cat (Reighard and Jennings), 
one going to the ulna and the other to the radius. 

The medial collateral ligament is stronger 
and better marked than the lateral ligament. On 
the humerus it is attached to the area in front of 
the medial epicondyle. The nearly parallel fibers 
pass across the joint and attach on the ulna in the 
conspicuously roughened area immediately distad 
of the semilunar notch. In both the dog and the 
cat the medial ligament is double, consisting of 
radial and ulnar heads. 

The oblique ligament is a slender band run- 
ning diagonally across the anterior (flexor) surface 
of the lateral epicondyle. Distally it attaches to the 
distal lip of the semilunar notch. In the dog the 
oblique ligament divides distally to embrace the 
tendons of the biceps and brachialis (Baum and 
Zietzschmann). Parsons (1900) says it is absent 
in Ursus, and Reighard and Jennings do not men- 
tion it in the cat. 

C. Union of the Radius with the Ulna 

The radius and ulna are united at three places: 
a proximal and a distal radioulnar articulation, 
and a mid-radioulnar union via the interosseous 

The proximal articulation is composed of the 
radial notch of the ulna and the smooth circum- 
ference of the head of the radius that rotates in it. 
Two ligaments are special to the joint. The lat- 
eral transverse ligament (fig. 71) is a short diag- 
onal band extending from the annular ligament 
just below the lateral collateral ligament to the 
border of the semilunar notch immediately behind 
the radial notch. This ligament is absent in the 
dog (EUenberger and Baum, 1943) but is present 
in the bears. The annular ligament of the ra- 
dius is a well-defined band of strong fibers about 
15 mm. wide, encircling the head of the radius. 
It forms about 60 per cent of a ring, which is com- 
pleted by the radial notch of the ulna. The an- 
nular ligament is thickest over the notch in the 
head of the radius. It is strongly attached at 
either end to the margins of the radial notch, and 
is much more feebly attached by loose fibers to the 
neck of the radius below the epiphyseal line. 

Since the head of the radius is elliptical in out- 
line, it acts as a cam and imparts an eccentric 
motion to the radius during movements of prona- 
tion and supination. The cam action can easily 
be felt through the annular ligament when the 
radius is rotated on a ligamentary preparation. 
This eccentric motion has the effect of permitting 


Lag. transversum laterale 
Capsula articularis 

Fig. 71. Right elbow joint of Ailuropoda, bent at right angle, lateral \-iew. Foreann halfway between pronation and 


Fig. 72. Right elbow joint of Ailuropoda, bent at right angle, medial view. Forearm halfway between pronation and 





a certain amount of rotation of the radius witiiout 
stretching the interosseous ligament. 

The range of movement in the proximal radio- 
ulnar articulation appears to be severely limited 
in Ailuropoda. The pronation-supination range 
was about 40 (compared with 120-140 in man) 
on a ligamentary preparation when the radius was 

ments lying just distad of the radioulnar articula- 
tion. The dorsal radioulnar ligament (fig. 73) 
is a rope-like band attached at one end to a pit- 
like depression on the neck of the styloid process 
of the ulna, between the radioulnar articulation 
and the head. The other end attaches to the ra- 
dius immediately below and in front of the radio- 

Lig. radioulnaris dors. 

Bursa m. ext. y-<^ -^ 

carpi ulnaris ^^ ~ ^ ^t^ 

Comp;irtment for Radius ^facics artic. carpeae) 

M. ext. dig. com. 

Capsula articularis 

Proc. styloideus ulnae 

Lig. radiocarpi volari 

Septum artic. (cut) 

Fig. 73. Proximal articular surfaces of right antebrachiocarpal joint of Ailuropoda. 

rotated by grasping its distal end and manipulat- 
ing it by hand. Further rotatory movement was 
checked by the capsule of the proximal radioulnar 
articulation, by the interosseous ligament, and by 
the distal radioulnar ligaments. 

The interosseous ligament (figs. 71, 72) is a 
thick tract of glistening fibers extending between 
the ulna and the radius except for the proximal 
quarter of the interosseous space. The ligament 
is heaviest in the middle third of the interosseous 
space, becoming thin and almost membranous in 
the distal third. Most of the fibers run diagonally 
distally from the radius to the ulna, but on the 
anterior surface a large group of proximal fibers 
runs in the opposite direction. The interosseous 
ligament is so heavy that it binds the ulna and 
radius firmly together, permitting very little move- 
ment between them. 

Nothing comparable to the oblique chord of 
human anatomy is present in Ailuropoda. 

The distal radioulnar articulation (fig. 73) op- 
poses a flat, almost circular surface on the radius 
to a slightly convex, almost circular surface of the 
ulna. The surface on the radius is parallel to 
the midline of the radius (which curves toward the 
ulna in its distal quarter), whereas the surface on 
the ulna lies at an angle of about 45 to the long 
axis of the ulna. The articulation is enclosed in a 
capsule. This articulation, which closely resem- 
bles that of Ursus, permits the distal end of the 
radius to roll around the ulna in a limited arc. 

In Ailuropoda the distal ends of ulna and radius 
are held together by two strong transverse liga- 

ulnar articulation. The volar radioulnar liga- 
ment attaches at one end to the neck of the styloid 
process and at the other to the border of the distal 
articular surface of the radius, near the radioulnar 
articulation. It lies mostly deep to the volar radio- 
cai-pal ligament. 

D. Hand and Intercarpal Joints 

The range of movement of the hand as a whole 
is very great in primitive carnivores. All the pos- 
sible angular movements rotation, flexion and 
extension, and abduction and adduction, together 
with combinations of these can be carried out. 
One of the most important and extensive of these 
movements, rotation (inversion and eversion), is 
scarcely a function of the hand joint, but results 
almost entirely from movements of pronation and 
supination of the forearm and rotation in the 
shoulder joint. 

The essential hand joint for movement of the 
hand as a whole is the antebrachiocarpal joint (the 
radiocarpal joint of human anatomy). In all 
the other joints movement is extremely restricted, 
consisting only of a slight gliding of one bone upon 
another, which serves to give elasticity to the 
carpus. In a ligamentary preparation of Ailuro- 
ropoda, movement in the intercarpal and carpo- 
metacarpal joints is almost non-existent, whereas 
in a similar preparation of the bear Tremardos 
there is considerable movement in these joints, 
particularly in the direction of adduction and ex- 






Anterior View (adduction - abduction) 





Lateral View (flexion - extension) 


Fig. 74. Diagrams showing ranges of movement in the left antebrachiocarpal joint in ligamentary preparations of a 
giant panda and a spectacled bear. See text. 




Antebrachiocarpal Joint 

A double joint, consisting of the radius-scapho- 
lunar articulation medially, and the ulna cunei- 
form and pisiform articulation laterally. The joint 
cavity is partly divided into radial and ulnar com- 
partments by an incomplete septum of fibro- 
cartilage (fig. 73). This septum, the "triangular 
fibro-cartilage" of Parsons, is attached proximally 
to the radial side of the neck of the styloid process 
of the ulna; distally it passes into the notch be- 
tween the scapholunar and cuneiform and attaches 
to the scapholunar. Along its volar edge the sep- 
tum is continuous with the joint capsule, thus 
closing off the radial and ulnar compartments, but 
dorsally it stops abruptly at the level of the dorsal 
radioulnar ligament, leaving the radial and ulnar 
compartments in communication with each other. 

The distal articular surface on the radius is 
broader anteroposteriorly than in Ursus, and lacks 
the conspicuous saddle over the styloid process. 
The opposing articular surface on the scapholunar 
is smoothly ovate, lacking the depression into 
which the saddle fits in Ursus, and is about a 
third more extensive than the radial articular sur- 
face. Thus this part of the joint is an almost per- 
fect ellipsoid articulation, capable of extensive 
movements of flexion, extension, abduction, and 
adduction. Of these, only abduction is seriously 
restricted by the styloid process of the ulna and 
the ulnar collateral ligament, which also inhibits 
rotation almost completely. Range of the other 
movements is greatly facilitated by the disposition 
of the antebrachiocarpal ligaments. 

The ulnar-carpal part of the antebrachiocarpal 
joint is notable for the extent and flatness of the 
articular surface on the cuneiform-pisiform com- 
plex. Instead of forming a socket into which the 
styloid process of the ulna fits, as in Ursus, in 
Ailuropoda there is an extensive articular area 
over which the styloid process can wander. This 
articular area faces laterally, and therefore cannot 
transmit thrust from the carpus to the fore arm 
as it does in Ursus. Thus this part of the ante- 
brachiocarpal joint in Ailuropoda has the function 
of steadying the radio-scapholunar part of the joint. 

The following measurements of ranges of move- 
ment in the antebrachiocarpal joint were made on 
an embalmed adult panda and an adult spectacled 
bear. All muscles and tendons crossing the carpus 
were removed, but all ligaments were left intact. 
The fore leg was immobilized and the manus ma- 
nipulated from the distal end, the operator taking 
care not to force the manus beyond its normal 
limits or to induce movements in intercarpal or 
carpometacarpal joints. Angulation was read off 

directly on a protractor, two or mo;e readings be- 
ing made for each position. The long axis of meta- 
carpal 3 was used as the axis of the manus (see 
fig. 74). 

Ailuropoda Tremarctos 

Abduction adduction 29 22 

Abduction (from radial axis=0). . . 4 9 

Adduction (from radial axis=0). . . 25 13 

Flexion-extension 78 55 

Flexion (from radial axis=0) 59 67 

Extension (from radial axis=0) .... 19 12 

These figures indicate that the position of the 
manus in relation to the fore arm in the panda is 
quite different, in both planes, from its position in 
the bear. The axis of the radius is not the true 
axis of the fore arm, but it is close enough to show 
that in the "rest" position the hand of Ailuropoda 
is adducted whereas that of Tremarctos is abducted, 
and that the metacarpus is more strongly flexed in 
Ailuropoda than in Tremarctos. The figures also 
indicate that the range of movement in the ante- 
brachiocarpal joint is greater in the panda than 
in the bear, particularly movements of extension. 
The figures confirm the statement of Lips that the 
bears are incapable of extending the metacarpus 
beyond the long axis of the fore arm. 

Ligaments of the Carpus 

The carpal ligaments have not been described 
for any generalized carnivore. In the present 
study the ligaments of an adult spectacled bear 
{Tremarctos ornatus) were dissected, for compari- 
son, at the same time as those of Ailuropoda. The 
only significant differences were the presence in 
Tremarctos of stout dorsal radiocarpal and radial 
collateral ligaments. The absence of these liga- 
ments in Ailuropoda contributes greatly to the 
mobility of the antebrachiocarpal articulation, par- 
ticularly to the range of dorsal flexion. 

Antebrachiocarpal Ligaments 

The volar radiocarpal ligament (figs. 73, 76) is a 
thick flat band of fibers with a predominantly 
transverse direction. It is attached medially to 
the radius above the styloid process, and laterally 
to the neck and base of the pisiform ; its deep sur- 
face presumably attaches to the scapholunar and 
cuneiform. The proximal border of this ligament 
is thick and sharply defined; distally it continues 
into the transverse carpal ligament. 

The dorsal radiocarpal and radial collateral liga- 
ments of human anatomy are absent in the panda. 
Instead there is a roomy, tough-walled articular 
capsule enclosing the radiocarpal articulation dor- 
sally and laterally (fig. 73). The capsule attaches 
to radius and scapholunar near the margins of their 
articular surfaces. 

Lig. carp)sesam(i 

Tendo m. abd. 
poU. longus 

Lig. basal is 

Fig. 75. Dorsal carpal ligaments of Ailuropoda. 

Os pisijorme 


Lig. pisocuneiform. 

Tuberc. ossis ameift 

Tendo mm. inter ossei 
Tuberc. ossis magmon. 


Lig. radiocarpeum 

Lig. carpi transvereum 

Tendo m. flex, carpi rod. 
Tuberc. ossis scapholunaris 

Tendo m. abd. polUcis 

lig. carposesamoideum 

Os sesamoid, rod. 

\ ^^ Lip. carpo - 

Ligg. basium 
interossea vol. 

Fig. 76. Volar carpal ligaments of Ailuropoda. 




The ulnar collateral ligament of the wrist (fig. 75) 
is a heavy band of fibers extending from the latero- 
dorsal surface of the styloid process of the ulna to 
the distal end of the pisiform, where it attaches 
to a prominent scar on the posterior surface of 
the bone. 

Intercarpal Ligaments 

The transverse carpal ligament (fig. 76) is an ex- 
tensive tract of transverse fibers, continuous proxi- 
mally with the volar radiocarpal ligament. The 
band is cupped to form a trough for the tendon of 
the deep digital flexors. Attachment medially is 
to the ventral process of the scapholunar, laterally 
to the base of the pisiform. Its deep surface pre- 
sumably attaches to the ventral processes of the 
magnum, unciform, and cuneiform. 

The pisohamate ligament is a short band on the 
lateral aspect of the carpus. It attaches to the 
pisiform near the margin of the articular surface 
of the cuneiform, and to the lateral surface of the 
ventral process of the cuneiform. 

A system of short dorsal intercarpal ligaments 
(fig. 75) ties the carpal bones together. These are 
all short bands passing across from one bone to 
its neighbor. 

Ligaments of the Pisiform Bone 

Two ligaments connect the pisiform with the 
cuneiform. A volar pisocuneiform ligament passes 
from the volar surface of the pisiform to the volar 
surface of the cuneiform, median to the tubercle. 
It is inseparable from the pisometacarpal ligament 
throughout most of its length. A short lateral 
pisocuneiform ligament passes from the lateral sur- 
face of the pisiform, directly beneath the articular 
surface, to the tubercle of the cuneiform (fig. 76). 

A strong pisometacarpal ligament (fig. 76) ex- 
tends from the volar surface of the pisiform to 
the base of the fifth metacarpal. 

Carpometacarpal Joints 

The distal surfaces of the distal row of carpals 
present a composite articular surface for the four 
lateral metacarpals. In Ursus and most other 
carnivores the otherwise smooth contour of this 
composite articulation is broken by a wedge-shaped 
projection of metacarpal 2 that thrusts back be- 
tween the trapezium and trapezoid. This wedge 
is absent in Ailuropoda, and the transverse con- 
tour of the composite joint is therefore uninter- 
rupted. Otherwise the joint is similar to that of 
Ursus. The proximal articular surfaces on the 
metacarpals are convex dorso-ventrally, with a 
very slight transverse concavity on metacarpals 
2-4 that produces a modified saddle joint. The 

saddle joint is most pronounced on metacarpal 4, 
and is wanting on metacarpal 5. 

The first metacarpal articulates with the tra- 
pezium by a saddle joint. The transverse curva- 
ture of the saddle is shallow, as in the lateral 
metacarpals. It is relatively deeper in Ursus, in- 
dicating a greater range of adduction-abduction 

Carpometacarpal Ligaments 

Volar carpometacarpal ligaments are associated 
with digits 3, 4, and 5 but are wanting on digits 
1 and 2 (fig. 76). These are short stout bands 
arising from the deep surface of the tendinous 
plate by which the digital adductors take origin 
thus eventually attaching to the magnum and 
unciform and inserting asymmetrically into the 
metacarpals near their bases. The ligament to 
digit 5 attaches to the radial side of the bone, 
those to digits 3 and 4 to the ulnar side. 

A short dorsal carpometacarpal ligament extends 
between the base of each metacarpal and the dor- 
sal surface of the adjoining carpal bone (fig. 75). 

Carposesamoid Joint 

The articulation between the radial sesamoid 
and the scapholunar is a true diarthrosis, capable 
of quite extensive movements of abduction and 
adduction, but probably incapable of dorsal and 
volar flexion. On a ligamentary preparation this 
bone could be manipulated through a range of 
about 20 of abduction-adduction, but was practi- 
cally immobile in the direction of flexion-extension. 

The radial sesamoid in Ursus has no such diar- 
throdial articulation, but the bone occupies the 
same positions relative to the scapholunar. 

Ligaments of the Radial Sesamoid 

Four strong and well-marked ligaments are as- 
sociated with the radial sesamoid bone. A short 
volar carposesamoid ligament (fig. 76) passes from 
the volar surface of the tubercle of the scapholunar 
to the volar surface of the sesamoid bone. A 
broad lateral carposesamoid ligament (fig. 75) passes 
from the lateral surface of the scapholunar tuber- 
cle to the lateral surface of the sesamoid, where it 
attaches proximad of the insertion of the tendon 
of the adductor poUicis longus. A transverse carpo- 
sesamoid ligament (fig. 76) passes from the lateral 
(ulnar) surface of the sesamoid into the transverse 
carpal ligament. On the dorsal side a dorsal basal 
ligament (fig. 75) connects the base of the sesamoid 
with the adjacent base of the first metacarpal. 

In Tremarctos the ligaments of the radial sesa- 
moid are similar to, but smaller than, those in 



Lig. patellae 

Lig. menisci med. ant 

Lig. cruciatum ant.. 

intercondyloid. med.. 

Meniscus med 

Lig. cruciatum post.. 

Lig. menisci 
lat. ant. 

Capsula articularis 
Meniscus lat. 

Lig. menisci lat. post. 

Fig. 77. Joint structures on head of right tibia of Ailuropoda. 

Review of Hand Joint 

Parsons (1900) reviewed very briefly the major 
carpal ligaments of the Carnivora in relation to 
those of other mammals, and concluded that the 
wrist joint in carnivores is modified to permit a 
"moderate amount" of supination. Lips (1930) 
described in great detail the structure and function- 
ing of the hand joint in Ursus arctos in compari- 
son with other arctoid carnivores, unfortunately 
without considering the ligaments. Lips concluded 
that the hand joint of Ursus represents a "univer- 
sal" (we would say unspecialized) type among the 
arctoid carnivores, capable of many-sided move- 

The hand joint of Ailuropoda is very similar to 
that of Ursus, but the panda has gone beyond the 
bear in the range of movement possible in the ante- 
brachiocarpal joint, particularly extension. This 
is accomplished by extending and reshaping artic- 
ular surfaces, and by eliminating or reducing liga- 
ments that would restrict dorsal flexion. Such 
minor remodeling reflects the action of the mus- 
cles that operate these joints (largely the carpal 
extensors and flexors), and demands little or no 
morphogenetic action on the bones and ligaments 
themselves. Even the diarthrodial joint of the 
radial sesamoid requires only the well-known ca- 
pacity of bone to produce true joints wherever 
movement occurs. 


A. Knee Joint 

The knee joint (fig. 77) is an incongruent com- 
pound joint involving the femur, the patella, and 

the tibia. The incongruence between the roller-like 
condyles of the femur and the relatively flat supe- 
rior articular surface of the tibia is compensated 
by the menisci. The internal ligaments of the knee 
joint of the horse, cow, pig, and dog were described 
by Zimmerman (1933). The structure of this joint 
in bears and procyonids is unknown. [ 

The menisci are unequal in size; the medial 
meniscus is larger than the lateral and its struc- 
ture is typical. The lateral meniscus has a promi- 
nent ridge on the femoral side that separates a 
medial articular area from a lateral non-articular 
area. The non-articular part of the meniscus ter- 
minates posteriorly at the entrance to a large 
bursa, which is situated above and immediately 
behind the fibular articulation. Each meniscus 
is attached to the capsule throughout its entire 
circumference, and each is also held in place by 
its own system of ligaments. Each meniscus is 
tightly attached to the head of the tibia at one 
end and more loosely attached at the other, which 
gives to both a certain freedom of movement on 
the tibial head. 

The lateral meniscus is continued into a liga- 
ment at each end. The anterior ligament passes 
mesad beneath the anterior cruciate ligament, to 
attach to the medial wall of the anterior intercon- 
dyloid fossa; the posterior one runs mesad and 
dorsad, to attach to the intercondyloid fossa of 
the femur. The medial meniscus is continued into 
a ligament only at its anterior end; the posterior 
end is tightly attached to the medial lip of the pos- 
terior intercondyloid fossa. The anterior end of 
the medial meniscus has no direct attachment to 



the tibial head; it is continued into a powerful 
ligament that passes across immediately in front 
of the anterior cruciate ligament to attach to the 
anterior intercondyloid fossa in the area in front 
of the lateral condyle, laterad of the attachment 
of the anterior cruciate ligament. There is no 
transverse tract uniting the menisci anteriorly, 
corresponding to the transverse ligament of human 
anatomy; Zimmermann states that this tract was 
demonstrable in 94 per cent of the dogs that he 

The cruciate ligaments are strong and rope- 
like. The anterior cruciate ligament is attached 
to the medial half of the anterior intercondyloid 
fossa of the tibia, near the medial intercondy- 
loid tubercle. It runs upward, backward, and 
slightly laterad to the medial surface of the lateral 
condyle of the femur, where it attaches. The pos- 
terior cruciate ligament is considerably longer than 
the anterior. It attaches to the tibia on a promi- 
nence at the extreme posterior end of the posterior 
intercondyloid fossa. From here it passes upward 
and nearly straight forward, crossing the posterior 
horn of the medial meniscus, and attaches to the 
femur in the medial half of the intercondyloid fossa. 

The only significant difference in the internal 
ligaments of the knee joint between Ailuropoda 
and the mammals described by Zimmermann is 
the less tight fixation of the menisci, especially the 
medial meniscus, in the panda. The resulting 
greater freedom permits more extensive pronation 
and supination in Ailuropoda. 

B. Ankle Joint 

The essential joints for movements of the foot 
as a whole in the primitive carnivore are the upper 
ankle joint, the transverse tarsal joint, and the 
lower tarsal joint. Each of these joints is primarily 
involved in a particular movement. In the upper 
ankle joint, movement is a hinge movement in the 
sagittal plane (flexion and extension of the foot). 
In the transverse tarsal joint, movement is rota- 
tion around the longitudinal axis of the foot (in- 
version and eversion of the foot). In the lower 
ankle joint, movement is an oblique gliding be- 
tween the astragalus and calcaneus (largely ab- 
duction and adduction of the foot) . None of these 
joints acts entirely independently of the others, 
and only the upper tarsal joint is confined to a 
single fixed axis. The resulting combined move- 
ments are extremely subtle and complex. 

The small bones of the distal tarsal row are 
probably mechanically unimportant. They func- 
tion chiefly to break shocks and to increase the 
general flexibility of the foot. 

Upper Ankle Joint (talo-crural) 

A perfect hinge joint between tibia and fibula 
proximally and astragalus distally. Axis runs trans- 
versely through trochlea of astragalus. Movement 
is restricted to dorsiflexion and plantar flexion of 
the foot. 

Lower Ankle Joint (subtalar) 

An incongruent gliding joint between astragalus 
and calcaneus. No definite axis can be fixed; Fick 
called the movement in this joint in man a "com- 
promise" movement consisting of the summation 
of successive rotations around a great number of 
momentary axes. In the bears and giant panda 
the congruence is less than in man, and it seems 
impossible to determine even a "compromise" axis. 
In procyonids the congruence is close and the 
movement is a screw movement. Movement is 
in general oblique: abduction coupled with ever- 
sion and dorsal flexion of the foot, or adduction 
coupled with inversion and plantar flexion (Sivers, 
1931). X-ray photographs (fig. 79) show that 
movement in this joint is relatively slight in Ailu- 
ropoda and Ursus. 

Transverse Tarsal Joint (Chopart's articulation) 

A combination of rotatory and sliding joints, 
between the head of the astragalus and the navic- 
ular (rotatory) and the calcaneus and cuboid (glid- 
ing). The axis of rotation runs longitudinally 
through the head and neck of the astragalus and 
the approximate center of the navicular; the cal- 
caneus glides over the cuboid in an arc. Move- 
ment, which involves compensatory adjustments 
between the astragalus and calcaneus, is inversion 
and eversion and /or abduction and adduction of 
the foot. Dorsiflexion and plantar flexion of the 
foot, which is the main movement of this joint in 
man, is very slight. X-ray photographs (fig. 79) 
show that in Ailuropoda and Ursus rotatory move- 
ments in this joint are extensive, though less ex- 
tensive than between the navicular and the distal 
tarsal row. 

Most students of the comparative anatomy of 
the tarsus in quadrupeds (Tornier, 1888; Sivers, 
1931; Schaeffer, 1947) have emphasized the trans- 
verse tarsal and lower ankle joints, dismissing the 
upper ankle joint as a simple hinge. In the tarsus 
of the generalized carnivores the most conspicuous 
difference is the relation of the axis of the upper 
ankle joint to the remainder of the ankle and foot. 
This difference is not apparent unless the astrag- 
alus is examined in situ, with the foot lying flat 
on the ground (fig. 78, A). Then the position of 
the axis with relation to the surrounding structures 
shows that the relation of the foot to the lower leg 
differs significantly from species to species. Angles 




^y ^ 






\j -'- 





Fig. 78. Dorsal (A) and anterior (B) views of right astragalus and calcaneus of Polos flavus (an arboreal forml and Ursus 
arctos and Ailuropoda (terrestrial forms), to show differences in the angulation of the axis of the upper tarsal joint. In the 
dorsal views the horizontal line is drawn at right angles to the long axis of the foot. The anterior views are drawn with 
the foot flat on the ground, the horizontal line representing the horizon. The diagram associated with each drawing does 
not show the normal position of the foot, but the indicated position of the foot if the tibia were oriented (A) with the trans- 
verse axis of the inferior articular surface of the tibia parallel to the transverse axis of the body, and (B) with the long axis 
of the tibia vertical. C, proximal articular surfaces of navicular and cuboid in the same positions as B. 

were measured with a protractor on dried liga- 
mentary preparations with the foot in normal un- 
strained position. In dorsal view the axis is nearly 
transverse to the long axis of the foot in Ursus and 
Ailuropoda; actually it is rotated slightly counter- 
clockwise ( 6 to 8), so that the foot would 
have a slight tendency to toe out. In Claenodon, 
a primitive Paleocene creodont, the axis is rotated 
counterclockwise about 22. In Potos and other 
procyonids, on the contrary, the axis is rotated 

clockwise (22 in Potos, 15 in Procyon, 15 in Ailu- 
rus), so that the foot would tend to toe in. 

In anterior view (looking at the distal faces of 
astragalus and calcaneus (fig. 78, B), there are 
similar though less extreme differences. In Ursus . 
and Ailuropoda the axis is tilted clockwise 15-20, 
which would tend to produce moderate inversion 
of the foot. This tilting is greater in procyonids 
(50 in Potos) and would tend to produce strong 



Fig. 79. Tracings from X-ray photographs of the right foot of the panda Mei Lan, to show areas in which joint move- 
ment takes place. A, medial view, foot abducted and inverted (solid line), superimposed on tracing of foot adducted and 
everted (shaded) ; the tibia, fibula, and calcaneus were superimposed in tracing. In abduction-eversion the calcaneus is rotated 
mesad on its long axis (note decreased width across sustentacular process trochlear process), in addition to sliding laterad 
and proximad. Note, however, that the major movements of eversion-inversion and abduction-adduction take place in the 
transverse tarsal joint and the more distal parts of the ankle. B, dorsal view, the foot adducted and inverted (solid line), 
superimposed on tracing of foot abducted and everted (shaded). The calcaneus has rotated mesad on its long axis (note 
position of sustentacular process and decreased width across sustentacular process trochlear process), in addition to sliding 
laterad and proximad. Note that the major movements of eversion-inversion and abduction-adduction take place in the 
transverse tarsal joint and the more distal parts of the ankle. 

inversion of the foot. The angle is about 45 in 

Sivers pointed out that the lateral and medial 
facets on the astragalus and calcaneus are more 
convex (or concave) in Mustela and Gulo, and that 
the facets are inclined toward one another. It 
may be added that the articular surface of the 
astragalar head is very extensive, and only part of 
it contacts the concavity of the navicular at any 
one time. This is likewise true of Procyon and 
Potos. These conditions permit a considerable 
range of inversion-eversion movement, wherein 
the astragalus rotates in a screw movement on the 
calcaneus, which remains relatively stationary with 
respect to the cuboid (movement in the intertarsal 
joint), while the astragalar head rotates extensively 
in the concavity of the cuboid (movement in the 
medial half of the transverse tarsal joint) . Exten- 
sive inversion and eversion are obviously associ- 
ated with the arboreal habits of these animals. It 

is functional eversion that permits these animals 
to apply the sole to a flat surface, as in standing 
on the ground. 

In Ursus and Ailuropoda, on the contrary, the 
lateral and medial facets are flatter and are less 
inclined toward one another, and the area of the 
astragalar head exceeds the area of the concavity 
of the navicular only slightly. This signifies a less 
extensive range of movement (particularly of ever- 
sion and inversion) in the ankle. Moreover, as 
Sivers pointed out for Ursus, movement between 
the astragalus and calcaneus (the lower ankle joint) 
is largely horizontal rotation around a vertical 
axis running through astragalus and calcaneus; 
this is affirmed by our x-ray photos (fig. 79). This 
would increase the stability of the ankle, and would 
favor abduction and adduction rather than inver- 
sion and eversion. It also explains the fact that 
in the bears and panda the combined diameter 



across the lateral and medial facets on the astrag- 
alus exceeds the diameter of those on the calcaneus. 

The following measurements of ranges of move- 
ment were made on the fresh unskinned hind leg 
(except Ailuropoda, which was skinned). The 
Ursus americanus was about a quarter grown, the 
other two fully adult. The tibia was placed in a 
vise and the foot manipulated by hand by grasp- 
ing the base of the metatarsals, the operator taking 
care not to force the foot beyond its normal limits. 
Angulation was read off directly on a protractor, 
two or more readings being made for each position. 


Abduction-adduction. . . . 32 
Flexion-extension 130-135 

Flexion (from right/ 0). -40--43'' 


(fromrightZO) -|-90--|-92 

Eversion-inversion 87-89 

Eversion 58-62 

Inversion 27-29 
















Differences in abduction-adduction are negligi- 
ble among these three animals. Otherwise the total 
range of movement is notably greater in Procyon 
than in the bear or panda, and this presumably 
reflects the arboi-eal habits of Procyon. 

In Ailuropoda and Ursus not only is the range 
of flexion-extension more restricted than in Pro- 

cyon, but the pattern is different both from Procyon 
and from each other (fig. 80). In Ursus flexion 
and extension, measured from a line at right angles 
to the tibial axis, are about equal. In Ailuropoda 
the whole range of flexion-extension lies completely 
outside the range in Ursus, and well below the 90 
axis; i.e., the foot in Ailuropoda is permanently 
extended on the tibia. 

The situation is comparable, although less ex- 
treme, for eversion-inversion (fig. 80). In Procyon 
eversion exceeds inversion. The reverse is true of 
Ursus, which also has a much more restricted 
range of movement. In Ailuropoda the range of 
movement is similar to that of Ursus, but is all 
in the direction of inversion; the foot cannot be 
everted on the tibia at all. I can find no differ- 
ences in the transverse tarsal joint of these two 
forms that would account for the differences in 
eversion-inversion. The difference probably lies 
in the torsion angle of the tibia (p. 115) and in- 
clination of the upper ankle joint. 

No detailed dissection of the tarsal ligaments of 
Ailuropoda was made. 

In summary, the ankle joint in the bears is a 
relatively unspecialized structure, combining mod- 
erate flexibility with adequate support (Davis, 
1958) ; it is neither as flexible as the ankle of ar- 
boreal forms, nor as stable as the ankle of cursorial 
forms. The ankle joint of Ailuropoda, so far as 


Fig. 80. Diagrams of ranges of movement in the ankle joint of carnivores. A, eversion-inversion. B, flexion-extension. ^ 
(See figures in adjoining table). ji 



known, is very similar to that of the bears. Cei'- 
tainly the resemblance is closer than in the hand 


In the developing individual the primary gross 
model of a joint is determined by intrinsic (heredi- 
tary) factors, but the further shaping of the joint 
depends almost wholly on extrinsic (non-heredi- 
tary) mechanical factors (Muiray, 1936). The 
importance of mechanical factors in determining 
joint form is heavily underscored by the pseudar- 
throses (joint-like structures in places where nor- 
mally there should be no joint) that have been 
described in the literature. Failure of a fracture 
to heal may, even in the fully mature adult, lead 
to the formation of a "a structure so exactly mim- 
icking a normal joint that the first half of the word 
'pseudarthrosis' does it less than justice" (Mur- 
ray, 1936). Such pseudarthroses may involve 
joint-like expansions of the apposed ends of the 
bones, cartilage-covered articular surfaces, a cap- 
sule, ligaments, and synovial fluid. 

If only the gross model of an articulation is in- 
herited, then natural selection can act directly only 
on the gross model. The articulation is, of course, 
a part of a total functional mechanism that is sub- 

jected to selection. The articulation's response to 
such extrinsic factors as posture and movement 
may therefore, by limiting the range of possible 
functional mechanisms, limit or channel the gene- 
controlled changes in other elements of the total 
mechanism and thus indirectly play an active role 
in natural selection. In seeking a causal explana- 
tion for the differences between two closely related 
organisms, however, we must assign a passive role 
to differences in the articulations. This will not 
be true if we are comparing distantly related or- 
ganisms (perhaps above the family level), where 
differences in the gross model, attributable to in- 
trinsic factors, are likely to be involved. Nor will 
it be true for grossly adaptive differences, such as 
those in the mandibular articulation of the panda, 
if these involve differences in the gross model. The 
chief value of the joints in comparisons between 
closely related forms is, then, as extremely sensi- 
tive indicators of differences in other elements 
that are related mechanically to the joints. 

Except for the mandibular joint, the joints of 
Ailuropoda, so far as they have been studied, differ 
little from those of Ursus. Such differences as 
there are tend to increase the range of movement 
in the joints. None of these differences seems to 
depend on intrinsic factors other than the capacity 
of the joint to respond to extrinsic factors. 


The muscles of the Carnivora are comparatively 
well known, but even for this order our knowledge 
is at a primitive level. Descriptions are incom- 
plete and inaccurate, often doing little more than 
establish the fact that a given muscle is present in 
species dissected. Even for the domestic carni- 
vores the dog and the cat the standard reference 
works are full of inaccuracies and are inadequately 
illustrated. Most of the genera of Carnivora have 
never been dissected at all. 

Within an order as compact as the Carnivora 

there are few differences of the "present" versus 
"absent" variety (see Table 16, p. 197 1, and ques- 
tions of muscle homology' are of no importance. 
There has, however, been a good deal of adaptive 
radiation within the Carnivora, as is obvious if 
the agile predaceous cats are compared with the 
lumbering semi-herbivorous bears, or the cursorial 
cheetah with the burrowing badgers. Such dif- 
ferences in habit are reflected in differences in the 
muscular system. These muscular differences 
their nature, their directions, their limitations 
are important elements of the over-all problem 
of evolutionarj- mechanisms. They show what 
has happened (and what has not happened i to the 
muscle pattern inherited by the Carnivora from 
creodont ancestors. Such empirical data form the 
basis on which the nature of mammalian evolution 
at the sub-ordinal level must be judged. 

How can such differences be detected and eval- 
uated? Certainly not on the basis of existing 
descriptions and illustrations. 


Observation indicates that within a gi-oup of 
related organisms a muscle is responsive, within 
limits, to mechanical demands in (li relative size, 
and (2) position most favorable for the required 
lever action. Limits are set, on the one hand, by 
the heritage of the group; the cephalohumeral of 
the Carnivora, for example, has never reverted to 
the original deltoid and trapezial elements from 
which it arose, no matter how mechanically ad- 
vantageous such a course might be. On the other 
hand, the structures surrounding a muscle defi- 
nitely limit the range of adaptive change of a 
muscle. No alteration can continue to a point 

where it interferes with the vital activities of other 
structures. A remarkable instance of this type of 
limitation is seen in the temf>oral muscle of the 
giant panda (see p. 69). 

A few generalizations as to the mode of phylo- 
genetic alterations of muscles at the sub-ordinal 
level may be listed. These have been derived em- 
pirically from direct observation. 

1. The bony attachments of a muscle may wan- 
der almost at random (within the limits of its area 
of embryonic origin i, provided they do not en- 
croach on some other vital structure. This is seen 
throughout the muscular system. It is particu- 
larly apparent, for example, in the origin of the 
triceps in carnivores (fig. 81). 

2. Phylogenetic decrease in the volume of a 
muscle presents no problem, since surrounding 
structures simply move in and occupy the vacated 
space (e.g., loss of the short head of the biceps in 
carnivores ) . The power of a given muscle is usu- 
ally increased phylogenetically by increasing its 
area of cross section (i.e., increasing the number 
and or diameter of fibers i . In muscles with dif- 
fuse origin this involves increasing the area of 
origin, and this is accomplished in various ways: 

(a) The bone surface may be increased, as in 
the temporal fossa of the giant panda, or 
the postscapular fossa on the scapula of 

(b) Flat muscles may be reflected, like folding 
a sheet of paper, to increase the total length 
of origin without increasing the over-all 
linear extent on the bone. This is seen in 
the deep pectoral of the bears and giant 
panda compared with those of more primi- 
tive carnivores. 

(c) Accessory origin may be gained from super- 
ficial aponeuroses or from a tendon sheet 
embedded in the muscle, as in the temporal 
muscle of carnivores. 

(d ) Surrounding muscles may be displaced from 
their bony attachment, and arise or insert 
instead on the fascia of other muscles. This 
is seen in the deltoids of the giant panda. 

3. It has long been known that muscles may 
become more or less completely transformed into 








Fig. 81. Medial view of humerus of Cant's (after Bradley), Felis (after Reighard and Jennings), and Ailuropoda to show 
variation in the origin of the medial head of the triceps. 

tendons during phylogeny, and Haines (1932) has 
demonstrated that tendons increase at the expense 
of muscle substance during ontogeny in man. He 
suggests that "tendon is lengthened by metamor- 
phosis of muscle tissue in response to a limitation 
of the range of possible contraction determined by 
the nature of the attachment of the muscle." 

Confirmation of this thesis is seen in the zygo- 
maticomandibularis of the dog, where two layers 
cross at an angle and the deeper layer is devoid of 
muscle fibers exactly to the boundary of the more 
superficial layer that partly overlies it. A similar 
situation exists in the trapezius muscles of the 
giant panda; muscle fibers are wanting exactly as 
far as the border of the scapula (fig. 88). In both 
of these examples pressure has limited the range 
of contraction of part of a muscle, and in the areas 
subjected to pressure, muscle tissue is replaced 
by tendon. 

Haines' further suggestion, that "it is no longer 
necessary to postulate complex co-ordinating mech- 
anisms to govern the sizes of the muscles, nor a 
vast series of genes to suit muscles to their work," 
is an over-simplification. In cursorial mammals, 
for example, the limb muscles are concentrated 
near the center of limb rotation, resulting in long 
terminal tendons. This is for the obvious mechan- 

ical reason that such an arrangement reduces the 
moment of inertia of the limb, not because of any 
limitation of the range of possible contraction. 
The tendons are already greatly lengthened in a 
fetal horse. 

Degree of tendinization may be (1) an active 
mechanical adaptation, or (2) a reflection of limi- 
tation of range of contraction resulting from (a) 
pressure from surrounding tissues or (b) simple 
degeneration, as in the short head of the biceps. 
Tendinization of type (2) is probably an individ- 
ual response to local conditions, not dependent 
upon gene action. 

4. The relation between muscle attachment and 
bone relief at the site of attachment was reviewed 
by Weidenreich (1922, 1926) and Dolgo-Saburoff 
(1929, 1935). It is well known that the surface 
relief of bone is attributable almost entirely to the 
muscles and their adnexa, and the ligaments. The 
nature of this relationship is not well understood. 
Weidenreich emphasized that ridges and tuberosi- 
ties represent portions of tendons or ligaments 
that have ossified under tension and are then in- 
corporated into the underlying bone. The extent of 
this ossification tends to be directly proportional 
to the mass of the musculature, and thus to the 
force to which the connective tissue is subjected. 



Where a muscle mass is enlarged beyond the 
available attachment surface on the bone, attach- 
ment is extended onto the adjacent fascia; conse- 
quently the size of a muscle cannot always be 
judged from its mark on the bone (Weidenreich, 
1922). Beautiful examples of this phenomenon 
are seen in the limb musculature of Ailuropoda. 
Transgression onto the fascia may lead to ossifi- 
cation of the fascia and its incorporation into the 
skeleton, as is easily seen in the development of 
the sagittal crest in many mammals. 


We know almost nothing of the genetic basis for 
the differentiation and development of muscles, 
of the relative roles of intrinsic (genetic) vs. ex- 
trinsic (non-genetic ) factors, or of the parts played 
by generalized and localized gene effects. The ex- 
tensive catalog of genes in the laboratoiy mouse 
compiled by Griineberg (1952) does not contain a 
single reference to the muscular system. This al- 
most total ignorance contrasts sharply with the 
considerable body of such knowledge for the skele- 
ton and joints, and makes it almost impossible to 
postulate the nature of the machinery involved in 
producing adaptive differences in the muscular 

The differentiation and growth of muscle in the 
indi\-idual were reviewed by Scott (1957). There 
is an intimate relation between differentiation and 
gi-owth of a skeletal muscle and the neive supply- 
ing it, and the nei-ve seems to be the determining 
agent in this relationship. Initial differentiation 
of muscle fibers and their gi-ouping into individual 
muscles can take place in the absence of any ner\-e 
connection; that is, muscles have a certain capac- 
ity for self-differentiation. But without nen^e- 
muscle connections the muscle fibers do not de- 
velop beyond a certain stage and later undergo 
degeneration. Yet Pogogeff and Mun-ay (1946) 
and others have maintained adult mammalian 
skeletal muscle in vitro for months, without inner- 
vation of any kind, and during this time the tissue 
regenerated and multiplied. The developing mus- 
cles in the individual are at first independent of 
the skeletal elements, to which they gain attach- 
ment only later; a muscle develops normally even 
in the absence of the skeletal elements to which it 
normally gains attachment. Independence of the 
musculature from a factor affecting the skeleton 
was demonstrated in achondroplastic rabbits by 
Crary and Sawin (1952), who found the muscles 
of normal size whereas the bones with which they 
are associated were shorter. The muscles had to 
"readjust their bulk and area of attachment to the 
new bone shapes." During early ontogeny, skele- 
tal muscles grow by di\'ision of developing fibers 

or by differentiation of additional muscle-forming 
cells, but during later ontogeny, gi-owth is believed 
to be exclusivelj' by hj'pertrophy of individual 

Growth of muscles in bulk, even in the adult, 
seems to be controlled at least in part by the nerv- 
ous system. In man, disease of peripheral nerves 
(such as pohTieuritis) may be followed by abnor- 
mal nei-\-e regeneration and associated h\-pertrophy 
of the related muscles, and hypertrophy of the 
masseters is often associated with evidence of dis- 
order of the central nei-\'Ous system (Scott, 1957). 
Such gi-owth is by hypertrophy of individual mus- 
cle fibers. 

Muscular hypertrophy as a hereditan,- condition 
has appeared in various breeds of domestic cattle 
(Kidwell et al., 1952). In this condition the mus- 
cles are enlarged, and most authors (but not Kid- 
well et al. ) describe duplication of muscles. The 
effect is typically localized in the hind quarters 
and loin (Kidwell et al. state that in their stock 
the muscles of the withers and brisket were also 
somewhat hypertrophied ) . All authors describe 
the muscles as coarse-gi-ained, and mention a gen- 
eral reduction in the quantity of fat, both sub- 
cutaneous and intra-abdominal. Kidwell et al. 
concluded from breeding exjjeriments that the con- 
dition "appears to be inherited as an incomplete 
recessive with variable expressivity." In other 
words, a simple genetic mechanism capable of pro- 
ducing a generalized effect on the musculature has 
been demonstrated. 

The data of Fuld (1901) reveal differences from 
his control animals in the relative mass of certain 
muscles of the hind limb in dogs that were bipedal 
from puppyhood. Most of the limb muscles were 
unaffected, but foiu* showed differences of more 
than 5 per cent in their mass relative to the total 
mass of hip and thigh muscles. These were the 
gluteus medius (7.6 per cent heavier), quadriceps 
extensor (6.4 per cent lighter), biceps femoris (8.2 
per cent lighter), and adductors (9.4 per cent 
heavier). Two of these differences (middle glu- 
teal and biceps) are in the direction of the weight 
relations found in man, whereas the other two are 
in the opposite direction. The dogs were said to 
hop rather than to walk on their hind legs, how- 
ever, and the differences from the control animals 
may well have been adaptive, or at least reflected 
differences in the demands made on the muscles. 
Under any circumstances they certainly were not 

These scanty data provide few significant clues 
to the nature of the morphogenetic machinery in- 
volved in the evolution of adaptive differences in 
the musculature. 




Attempts to study muscle mechanics have dealt 
almost wholly with absolute values absolute con- 
tractile force per unit of muscle cross section, lever 
actions of individual muscles or groups of muscles, 
or direct measurements of the power of an organ, 
such as a limb. This approach has yielded indif- 
ferent results because of the complexity of even 
the simplest bodily movement, and the still ob- 
scure relation between nerve impulse and the in- 
tensity of muscle reaction. 

A. B. Howell attempted to determine the rela- 
tions between various locomotor specializations 
(cursorial, saltatorial, aquatic) and musculature by 
comparing various representatives of such locomo- 
tor types regardless of their taxonomic affinities. 
This approach to muscle mechanics is indirect, and 
involves no mechanical analysis or estimate of 
forces. The intent is simply to discover a con- 
sistent correlation between a particular function 
and a particular modification of the muscle pat- 
tern. It may be confidently assumed that any 
such correlation is mechanically significant, even 
though no engineering analysis is made. Howell 
himself repeatedly expressed his disappointment 
at the meager results of this method. It is appar- 
ent that because of the diversity of genetic back- 
ground in so heterogeneous an assemblage of more 
or less remotely related forms, only the crassest 
morphological convergences would be evident. 

The lower the taxonomic level the more homo- 
geneous the genetic background that lies behind 
the muscle pattern. Among representatives of a 
superfamily or family we may focus more sharply 
on divergences from the basic muscle pattern of the 
group, for differences at this taxonomic level are 
not likely to represent the accumulated load of in- 
numerable earlier specializations in different an- 
cestral lines. Here any departure from the norm 
may be assumed to be adaptive, even though the 
mechanics are too complex or too subtle to ana- 
lyze. For example, in a series of carnivores rang- 
ing from most carnivorous to most herbivorous the 
relative masses of the external masseter and zygo- 
maticomandibularis vary reciprocally, whereas all 
other elements of the masticatory musculature re- 
main constant (Davis, 1955). Even without ana- 
lyzing the complex and subtle functioning of the 
masticatory complex we may be sure that in this 
instance the mechanically significant alterations 
are localized in these two muscles. Bringing rep- 
resentatives of other orders, with their different 
heritage, into this comparison would have ob- 
scured this relation, which is valid only within the 

masticatory pattern of the Carnivora. Besides mass 
or area of cross section, the relative values of force 
diagrams and leverage systems may be compared 
among closely related forms in the same way. 
Thus an insight into the functioning of a muscle 
or a group of muscles may be had at second hand, 
without the actual direct mechanical analysis, or 
determination of absolute forces, that has so far 
proved impossible to achieve. 

The possibilities of this method of assessing rela- 
tive muscle mechanics have not been explored. It 
will be used here, so far as existing data permit. 


The nomenclature used here is the BNA, with 
such obvious modifications as are necessary be- 
cause of differences from human anatomy. 

There is, of course, no "proper" sequence in 
which muscles can be arranged, and various sys- 
stems have been advocated. The arrangement 
adopted here is that of Howell's Anatomy of the 
Wood Rat, which is largely topographical. It may 
be suggested that the index is a more satisfactory 
means of locating a given description than at- 
tempting to find it via some system of arrangement. 

Innervation of muscles is given only in special 
cases, since the nerve supply of carnivore muscles 
is given in any standard anatomy of the dog or cat. 

Perhaps the most important consideration in 
evaluating muscle (and skeletal) differences within 
an order or family is an accurate picture of the 
bony attachments. This cannot be obtained from 
verbal descriptions alone; only carefully drawn 
maps will do. The exact areas of attachment of 
all muscles (except axial and a few others) in 
Ailuropoda have therefore been carefully plotted 
on the bones, and appear in the section on the 
skeleton. Unfortunately, comparable data for 
other carnivores exist only for the dog (later edi- 
tions of Bradley) and cat (Reighard and Jennings). 

A. Superficial Facial Musculature 

M. platysma is much reduced. It extends as a 
band of rather uniform width from a point above 
and behind the auditory meatus to the corner of 
the mouth. A few of the dorsal fibers swing up- 
ward in front of the ear, to lose themselves in the 
superficial fascia. Anteriorly a few of the most 
dorsal fibers are separated from the main mass, 
arising over the zygoma. 

M. buccinator (figs. 82, 84) is a heavy flat 
muscle sheet that forms the foundation of the 
cheek. It is not divisible into buccal and molar 



parts as it is in most mammals. Instead, the 
muscle forms a uniform sheet of fibers that con- 
verges partly into the mucosa of the lips near the 
angle of the mouth, and partly into a horizontal 
raphe running back from the angle of the mouth. 

The dorsal fibers arise from the alveolar surface 
of the maxilla just outside the last upper molar, 
beginning at about the level of the middle of this 
tooth. The line of origin runs caudad onto the 
rugose triangular area immediately behind the 
tooth. Ventrad of this area, fibers arise from the 
pterygomandibular ligament, which extends cau- 
dad across the inner face of the internal pterygoid 
muscle. The ventral fibers arise from the alveolar 
surface of the mandible, just outside the molar 
teeth, beginning behind the last lower molar and 
extending as far forward as the middle of the first 
lower molar. 

The remaining superficial facial muscles were 
damaged in removing the skin and were not dis- 

B. Muscles of the Ear 

M. levator auris longus (cervico-auricularis- 
occipitalis of Huber) is a fan-shaped sheet arising 
from the dorsal midline just behind the posterior 
end of the sagittal crest. There is no division into 
two parts. The posterior half of the muscle in- 
serts on the pinna. The anterior half is continued 
forward over the top of the head. 

M. auriculus superior is a narrow band lying 
behind, and partly covered by, the levator auris 
longus. Arising from the midline beneath the 
levator auris longus, it inserts on the pinna just 
caudad of that muscle, and separated from it by 
the insertion of the abductor auris longus. 

M. abductor auris longus lies immediately 
anterior to, and partly above, the auriculus supe- 
rior, and has approximately the same width. Dis- 
tally it emerges from beneath the levator auris 
longus, and inserts on the pinna just behind it. 

M. auriculus inferior lies wholly beneath the 
levator auris longus, and has the same general re- 
lations. It is more powerfully developed than the 
auriculus superior or the abductor auris longus, 
and is more than twice as wide. 

M. abductor auris brevis is the most caudal 
of the auricular muscles. Its origin is beneath 
that of the levator auris longus, but the belly of 
the muscle emerges and inserts low on the posterior 
face of the pinna. 

M. adductor auris superior (auricularis ante- 
rior inferior of Huber) is a narrow band arising 
from the posterior end of the scutiform cartilage. 
It inserts on the anteromesal face of the pinna. 

M. adductor aris medius arises from the ex- 
treme posterior end of the scutiform cartilage, be- 
neath the origin of the superior. It extends as a 
narrow band back to the posterior surface of the 
pinna, where it inserts proximad of the abductors. 

C. Masticatory Musculature 

The masticatory muscles, which are chiefly re- 
sponsible for the characteristic skull form of 
Ailuropoda, are remarkable for their enormous 
development. Otherwise they do not differ much 
from the typical carnivore pattern. In all Carni- 
vora the temporal is the dominant element of the 
masticatory complex, forming at least half of the 
total mass of the masticatory muscles. The in- 
sertion tendon of the temporal extends into the 
substance of the muscle as a tendinous plate, into 
which most of the muscle fibers insert. Thus the 
temporal is a bipennate (or if several such tendi- 
nous plates are present, a multipennate) muscle, 
in which the functional cross section per unit of 
volume is much greater than in a parallel muscle 
such as the masseter (Pfuhl, 1936). In carnivores, 
because of the form of the mandibular articulation, 
fast snapping movements of the jaws depend 
largely on the masseter, whereas slower and more 
powerful cutting and crushing movements depend 
largely on the temporal. 

The masticatory muscles arise ontogenetically 
from the mandibular arch, by condensation about 
the peripheral end of the mandibular nerve. Other 
muscles arising from the mandibular arch, and 
likewise supplied by the third branch of the tri- 
geminal nerve, are the anterior belly of the digas- 
tric, mylohyoid, tensor tympani, and tensor veil 

M. temporalis (figs. 82, 83) is enormously de- 
veloped, filling the greatly expanded temporal fossa 
except for a small area behind the orbit that is 
occupied by fat. In an old, badly emaciated male 
(Mei Lan) this muscle weighed more than twice 
as much as in a black bear of comparable size, and 
the temporal and zygomaticomandibularis together 
nearly three times as much. The muscle is cov- 
ered externally by a tough deep temporal fascia, 
more than half a millimeter thick, that arises from 
the sagittal and lambdoidal crests and postorbital 
ligament and extends to the superior border of the 
zygomatic arch. A few superficial fibers of the 
temporal muscle attach to the zygomatic arch im- 
mediately behind the temporal fascia and insert 
into its inferior edge, thus forming a tensor of the 
temporal fascia. 

The external face of the temporal muscle is cov- 
ered with an extremely heavy tendinous aponeu- 
rosis, the deep temporal fascia, from which the j 


Planum tendineum temporalis 


Lig. postorbitale 

M. temporalis 

M. buccinator; p. buccalis (sup.)' 

M. buccinator; p. buccalis (inf.) 

Raphe tendinosa 

Fig. 82. Masticatory muscles of Ailuropoda, seen from the left side. The temporal and masseteric fasciae have been re- 
moved, and a window cut in the temporal muscle to expose the tendinous plane that separates the superficial and deep 
layers of the temporal muscle. The superficial and deep layers of the masseter are inseparable anteriorly. Note that the in- 
sertion of the superficial masseter does not extend posteriorly onto the angular process of the mandible. 

superficial fibers of the muscle take origin. As is 
usual in carnivores, the muscle is divided into 
superficial and deep parts, separated by a heavy 
tendinous plate, the insertion tendon of the mus- 
cle, that extends between the sagittal crest and 
the superior and posterior borders of the coronoid 
process. Muscle fibers attach to both surfaces of 
this tendinous plate. Additional tendon sheets 
embedded in the substance of the muscle insert 
into the coronoid process (fig. 83), making this 
complex a truly multipennate muscle composed 
of innumerable short fibers. These additional ten- 
don sheets do not occur in Ursus (Sicher, 1944, 
fig. 13; Schumacher, 1961a), and the temporal is 
therefore a simpler and less powerful muscle in 
the bear. 

The superficial part arises from the whole deep 
surface of the tendinous aponeurosis except for a 

small area near the orbit, and, at the periphery of 
the muscle, from the edges of the temporal fossa. 
The fibers converge to insert on the external face 
of the coronoid process of the mandible and into 
the external surface of the tendinous plate. Along 
its inferior border this muscle is incompletely sep- 
arable from the zygomaticomandibularis. 

The deep part of the temporal is much thicker 
than the superficial part and its structure is more 
complex. A tendinous sheet extends between the 
prominent crest running obliquely upward on the 
floor of the temporal fossa, some distance above 
the superior orbital crest, and a crest on the coro- 
noid process above the mandibular foramen. This 
sheet separates the anterior part of the deep tem- 
poral into superficial and deep parts. Additional 
smaller tendon sheets, embedded in the substance 
of the muscle, eventually attach to the inner face 



M. temporalis 

Aponeurosis temporalis 
Fascia temporalis post 

ArcUS ryfjninnJirilft / 1 

M. zygomaticomandibularis 

M. massctericus prof. 

M. massetericus superf L 

Canalis mandibularis 

Sinus I 

Tendo M. temporalis 

Fossa olfactoria 

Crista orbitalis sup. 
Foramen opticum 

Crista orbitalis inf. 

Pars nasalis pharyngis 

A. maxiltaris int. 

Tendo accessorius M. temporalis 
M. pter\'goideus int. 

Gl. sublijigualis 

M. genioglossus 

M. mylohyoideus 

V.Jacialis ex I. 

M. digastricus 
Proc. angularis mandib. 

Fig. 83. Frontal section through head of an old emaciated male Ailuropoda (Mei Lan). The section passes through the 
coronoid process of the mandible (see inset). 

of the coronoid process. Muscle fibers arise from 
tiie whole floor of the temporal fossa, and from the 
deep surfaces of the several tendon sheets. Some 
of the fibers insert into the surface of the coronoid 
process, the insertion area extending ventrad as 
far as the mandibular foramen. Other fibers in- 
sert into the superficial surfaces of the several ten- 
don sheets. 

The temporal is an elevator of the mandible. 
Because of its multipennate structure it produces 
slow but very powerful movements. 

M. zygomaticomandibularis (fig. 83) is rela- 
tively larger than in any other carnivore examined. 
It is completely hidden beneath the masseter and 
zygomatic arch, and fills the masseteric fossa. 
Origin is from the whole internal face of the zygo- 
matic arch. The fibers converge toward the mas- 
seteric fossa, into which they insert by both muscle 

and tendon fibers. Tendon sheets embedded in 
the muscle near its insertion attach to crests on 
the floor of the masseteric fossa, and these tendons 
increase the available insertion area. The flber 
direction of the zygomaticomandibularis is down- 
ward, mesad, and slightly backward. In the sag- 
ittal plane the fibers are almost vertical, forming 
an angle of about 80 with the occlusal plane. In 
the frontal plane the angle is about 75 with the 
transverse axis of the head. In both planes the 
angles become increasingly vertical as the jaw is 

The zygomaticomandibularis is primarily an 
elevator of the mandible. The muscle of one side 
of the head, in conjunction with the pterygoids of 
the opposite side, shifts the mandible transversely 
toward the side of the contracting zygomatico- 
mandibularis. This motion is the grinding com- 



ponent of the jaw movements in Ailuropoda and 
other carnivores. 

M. masseter (figs. 82, 83) is powerfully devel- 
oped. It is more or less divisible into the usual 
two layers, although these are fused and insep- 
arable anteriorly. 

The pars superficialis is a thin sheet covering 
all but the posterior part of the profunda. More 
than the proximal half of the external face of the 
superficialis is covered with a heavy tendinous 
aponeurosis (aponeurosis 1 of Schumacher, 1961a), 
which is continuous posteriorly with the aponeu- 
rosis of the profunda. The muscle arises by this 
aponeurosis and by underlying muscle fibers from 
the anterior half of the inferior border of the zygo- 
matic arch. The fibers run backward and down- 
ward at an angle of about 45 with the occlusal 
plane, to insert non-tendinously into the inferior 
edge of the mandible, immediately below the coro- 
noid fossa, the insertion extending back as far as 
the angular process. At its insertion the muscle 
forms a tendinous intersection with the internal 
pterygoid . The posteriormost fibers do not extend 
beyond the angular process at the posterior end of 
the mandible to insert into the stylomandibular 
ligament, as they do in Ursus and other carnivores. 

The internal face of the superficialis is in veiy 
intimate contact with the underlying profunda, 
the two layers being inseparable anteriorly. 

The pars profunda is covered by the superfcialis, 
except for a narrow area along its posterior edge. 
It arises by fleshy and tendon fibers from the en- 
tire inferior border of the zygomatic arch, back to 
within 10 mm. of the mandibular fossa. The fibers 
have a slightly more vertical direction than do 
those of the superficialis. A tendon sheet em- 
bedded in the posterior part of the profunda, 
attaching to the zygomatic arch, partly divides 
the muscle into superficial and deep layers. The 
external face of the mandibular half of the pro- 
funda is covered with a heavy glistening aponeu- 
rosis (aponeurosis 2 of Schumacher, 1961a). In- 
sertion is made by means of this aponeurosis into 
the mandible along the inferior border of the coro- 
noid fossa. The fibers run backward and down- 
ward at an angle of about 55 with the occlusal 

The masseter is an elevator of the mandible. 
Because it is composed of long parallel fibers it 
produces quick snapping movements, relatively 
less powerful than those of the temporal muscle. 

M. pterygoideus internus (figs. 70, 83, 84; 
lateralis of authors) is a rectangular group of par- 
allel fibers arising from the ventral edge and outer 
side of the perpendicular plate of the palatine, 
pterygoid, and sphenoid bones. The muscle is 

thin and delicate posteriorly, and is relatively 
smaller than in any other known carnivore. It 
shows a tendency to break up into three or more 
subequal elements. Insertion is into the promi- 
nent fossa on the inner side of the lower border 
of the ramus of the mandible, extending onto the 
angular process. A few of the delicate posterior 
fibers insert into the anterior end of the stylo- 
mandibular ligament. 

The internal pterygoids acting together elevate 
the mandible. Unilateral contraction simultane- 
ously elevates the mandible and shifts it toward 
the contralateral side. 

M. pterygoideus externus (figs. 83, 84; medi- 
alis of authors) is much shorter, but considerably 
thicker, than the internal pterygoid muscle. Its 
lateral end lies dorsad of the internal pterygoid, 
and its medial end posterior to it. Origin is by 
two heads, which are separated by the buccinator 
nerve. The more ventral head arises from the 
outer side of the pterygoid plate at its posterior 
end, extending as far back as the combined fora- 
mina ovale and rotundum. The other head con- 
tinues this origin up onto the skull, behind the 
optic foramen. The two heads fuse, and the re- 
sulting muscle extends straight laterad to its in- 
sertion, which is into the prominent pit on the 
anteromedial end of the condyle of the mandible. 

The two external pterygoids are antagonistic. 
Unilateral contraction shifts the mandible toward 
the contralateral side. 

Discussion of Masticatory Muscles 

We have seen (p. 72) that the skull in Ailuro- 
poda, and in herbivorous carnivores in general, is 
designed to promote the production of maximum 
forces at the level of the cheek teeth by (a) im- 
proving lever advantages, (b) increasing the space 
available to muscle tissue, and (c) resisting dis- 
integrating forces. 

The active forces themselves are of course sup- 
plied by the craniomandibular muscles. These 
may further enhance the efficiency of the mastica- 
tory apparatus in three purely morphological ways: 
(a) generalized increase in mass of contractile tis- 
sue, (b) selective increase in mass, involving only 
those elements that produce the forces involved in 
pressure and grinding movements, and (c) increase 
in functional' cross section. Each of these is evi- 
dent in the masticatory musculature of the giant 

1 The functional cross section is a section at right angles 
to the fibers. The anatomical cross section is a section at 
right angles to the long axis of the muscle. In a parallel- 
fibered muscle these two sections may coincide; in a pennate 
muscle they never do. 



Lif. ptervgomandib. {cut & reflected) 

M. ptcrygoideus int. 
M. pterygoideus ext. 

"Hamulus pterygoideue 

Capsula orttcuijris 

Lig. stylomandib. (cut) 
Proe. angukais 

M. mylohyoideus 

Fig. 84. Masticatory muscles of Ailuropoda, medial view. 

Generalized Increase in Mass. I have used 
brain weight as a standard for computing an index 
of the relative mass of the total masticatory mus- 
culature of one side of the head. The data are 
given in the accompanying Table 12. The weights 
are all from zoo animals, and consequently the 
values for the musculature are undoubtedly low, 
although all except the panda were in good flesh 
at time of death. The panda (Mei Lan), in addi- 
tion to his years in captivity, was much emaciated 
at the time of his death. Nevertheless these fig- 
ures show that the relative mass of the masticatory 
musculature in Ailuropoda is at least twice as great 
as in bears of comparable body size. 

That this increase is truly generalized is shown 
by the fact that the mass of the digastric, a muscle 
not involved in jaw closure, equaled 30 per cent 
of brain weight in Ailuropoda, whereas in the bears 
it was less than 10 per cent of brain weight. It is 
impossible to determine whether both bellies of 
the digastric are equally hypertrophied; certainly 
the anterior belly is involved. 

The masticatory musculature, except for the 
posterior belly of the digastric, is derived from the 
mandibular arch of the embryo. Also derived 
from this arch are the mylohyoid, tensor tympani, 
and tensor veli palatini. The mylohyoid is in no 
way involved in jaw closure, yet in Ailuropoda it 
is hypertrophied like the craniomandibular mus- 
cles (p. 157). I was unable to decide from inspec- 
tion whether the tiny tensors were relatively larger 
than in the bears. It is evident, however, that 
what is enlarged in the panda is not a functional 
unit, but a morphological unit the muscular de- 
rivatives of the mandibular arch. The fact that all 
are hypertrophied shows that, in this instance at 
least, the morphological unit is also a genetic unit. 
Indeed, hypertrophy extends in a decreasing gra- 
dient, beyond the derivatives of the mandibular 
arch, to the entire musculature of the anterior 
part of the body (p. 182). The morphogenetic 
mechanism involved in the hypertrophy is prob- 
ably very simple. Selection undoubtedly favored 
an increase in the mass of the jaw-closing muscles 



Musculature Digastric 

(gms.) (gms.) 

Ailuropoda melanoleuca ( d" ad.) 890 92 

Ursus americanus ( 9 ad.) 322 26 

Thalaretos marilimns ( cf ad.) 910 86 

Mean of two brain weights (489 gms., 507 gms.) given by Crile and Quiring (1940). The brain of the polar bear from 
which I dissected the muscles was not weighed. 













in the panda, but the results extend far beyond other mammals, including man) the insertion ten- 

the functional unit. don of the temporal muscle continues into the 

Selective Increase ln Mass. Relative masses muscle substance as a broad tendon sheet. Fibers 

of individual components of the masticatory com- of the temporal muscle insert obliquely into both 

plex may be compared by reducing each to a sides of this tendon sheet, and the temporal is 

percentage of the mass of the total masticatory therefore a pennate muscle. In Ailuropoda the 

complex (Davis, 1955). Data are given in the temporal has been converted into a multipennate 

accompanying table. muscle by tendinization of numerous fascial planes 


(Including data from Davis, 1955) 

Ailuropoda Tremarctos Ursus Procyon Thalarctos Canis Felis 

[Mei Lan| ornatus americanus* lotor maritimus familiaris onca 

Wt.ingms. % % % % % % % 

Masseter superf 44 5 7.5 10 5 1 f 15 21 

Masseter prof 60 7 2.5 2 3 J [ 3 2.5 

Zygomaticomand 188 21 14 11 13 7 6 2.5 

Temporalis 477 54 58 62 63 66 58 59 

Pterygoideus internus 18 2 7 5 6 4 7.5 6.5 

Pterygoideus externus 11 1 1 1 1 1 0.5 0.5 

Digastric 92 10 10 9 9 10 9.5 8 

Totals 890 100 100 100 100 100 99.5 100 

Means of two specimens; data for one individual from Starck (1935). All other figures from one individual each. 

I have pointed out elsewhere (Davis, 1955) that 
in the Carnivora the masses of only two muscles, 
the superficial masseter and the zygomaticoman- 
dibularis, appear to vary significantly with differ- 
ences in food habits, and that these two muscles 
vary reciprocally. A large superficial masseter 
appeared to be associated with carnivorous habits, 
a large zygomaticomandibularis with herbivorous 
habits. The additional data presented here con- 
firm this relation. Moreover, in Ailuropoda the 
superficial masseter is relatively smaller (except 
in Procyon, where it is equally small) and the 
zygomaticomandibularis larger, than in any other 
carnivore examined. 

The masseter, because it is composed of long 
parallel fibers, is particularly effective in producing 
quick snapping movements of the mandible a 
movement obviously important to predaceous car- 
nivores. There is an important horizontal compo- 
nent in the action of the zygomaticomandibularis. 
This muscle, which in bulk far exceeds the more 
horizontally situated but tiny external pterygoid, 
is primarily responsible for lateral shifting of the 
mandible a movement important to herbivorous 
carnivores. Thus, in addition to the generalized 
increase, there is a selective increase in mass among 
the masticatory muscles, and the results conform 
to the requirements of differing dietary habits. 

Increase in Functional Cross Section. In 
the temporal muscle of all carnivores (and of many 

in the substance of the muscle, with muscle fibers 
attaching to both surfaces of these tendon sheets. 

What are the mechanical advantages of penna- 
tion in a muscle? A pennate fiber is the diagonal 
of a parallelogram of which one component repre- 
sents force along the axis of the insertion tendon 
while the other component tends to pull the inser- 
tion tendon toward the origin. Only the first of 
these two components represents useful work. The 
second is waste effort, whose magnitude varies 
with the angle of pennation but in all cases repre- 
sents an important fraction of the total energy of 
the contracting fiber. There is no such waste of 
energy in a parallel-fibered muscle, which is there- 
fore more efficient than a pennate muscle. Some 
advantage must offset the inefficiency of the pen- 
nate structure. 

Eisler (1912) suggested maximum utilization of 
attachment area as a factor in the pennation 
of muscles. He pointed out that powerful mus- 
cles are pennate in situations where available at- 
tachment area is limited, whereas other powerful 
muscles remain parallel-fibered in situations where 
the attachment area can be expanded. Eisler com- 
pared the multipennate human deltoid, with its 
anatomically restricted areas of attachment, with 
the parallel-fibered gluteus maximus, which has 
been able to expand its areas of attachment un- 
hindered. Available attachment area is obviously 
a limiting factor in the temporalis of Ailuropoda. 



The temporal fossa has been expanded in all direc- 
tions, apparently to the limits that are compatible 
with other vital functions of the head (p. 46). The 
mass of the muscle, particularly its area of origin, 
cannot be increased further to achieve additional 

Pfuhl (1936) attempted to work out the mechan- 
ics of pennate muscles. The work (a) of a muscle 
is expressed in two terms: force (F), and the dis- 
tance (rf) through which the force is exerted : 

a=F .d 


The force of a muscle may be expressed by the 

F = k . q (2) 

where q is the functional cross section and A; is a 
constant representing the unit of muscle power.' 
Thus for any value of a in equation (1) the propor- 
tion oiF can be increased by increasing the func- 
tional cross section of the muscle, that of d by 
increasing its length. For a given mass of muscle 
tissue, maximum force would therefore be achieved 
by arranging the muscle as a series of minimally 
short parallel fibers, which would give maximum 
functional cross section. Such an arrangement 
would usually produce architectural difficulties, 
since areas of origin and insertion would become 
unduly large. An alternative is the arrangement 
of the fibers in pennate fashion between more or 
less parallel sheets of bone or tendon. This loses 
a portion of the total energy of the muscle, as 
shown above, but enormously increases the func- 
tional cross section and therefore the power per 
unit of mass. Thus pennation is a device permit- 
ting maximum production of force in a minimum 
of space, and utilizing limited attachment area on 
the skeleton. This effect is multiplied by multi- 

The craniomandibular musculature of Ailuro- 
poda represents an extension of conditions in the 
bears, which in turn are a modification of condi- 
tions in more generalized carnivores. Indeed, in 
Tremarctos, the most herbivorous of the bears, the 
craniomandibular musculature appears to be about 
intermediate between Ursus and Ailuropoda. 

As will appear in the sequel, the generalized in- 
crease in the mass of the craniomandibular mus- 
cles of Ailuropoda is associated with a generalized 
hypertrophy of the skeletal muscles of the shoulder 
region, and probably has a very simple genetic 
basis. The morphogenetic basis underlying the 
other two adaptive modifications increase in rela- 

' The unit of muscle power is the tension produced by a 
muscle with a functional cross section of 1 cm'. For pur- 
poses of calculation it is assumed to be 10 kg. 

tive mass of individual muscles, and increase in 
functional cross section is unknown. 

D. Interramal Musculature 

These three muscles form a topographic, but not 
a morphological, unit. Ontogenetically they are 
derived from two different sources: the anterior 
belly of the digastric and the mylohyoid (from the 
mandibular arch) are supplied by the trigeminal 
nerve; the posterior belly of the digastric and the 
stylohyoid (from the hyoid arch) are supplied by 
the facial nerve. At least the elements derived 
from the mandibular arch are hypertrophied like 
the craniomandibular muscles derived from this 
arch. Of the elements derived from the hyoid arch, 
the stylohyoid is absent in Ailuropoda and there 
is no way of determining whether hypertrophy of 
the digastric involves the fibers of its posterior belly. 

M. digastricus (figs. 82, 83, 85) is a powerfully 
developed muscle, triangular in cross section, with 
the base of the triangle ventrad. The muscle has 
a thickness of 22 mm. The mass of the muscle is 
shot through with powerful longitudinal tendon 
fibers. Origin is from the paroccipital process and 
the ridge connecting this process with the mastoid 
process. The muscle is covered with a tendinous 
aponeurosis at its origin; there is also a small ac- 
cessory tendinous origin from the mastoid process. 
Insertion is into the inner surface of the mandible, 
from a point opposite the second molar tooth back 
as far as the mandibular foramen. 

A fine tendinous inscription runs across the belly 
of the muscle near its middle, marking the juncture 
of the anterior and posterior bellies. 

The digastric is relatively much larger than in 
the bears (Table 12) , but there is no way of deter- 
mining whether both bellies share in this hyper- 
trophy. Certainly the anterior belly is enlarged. 

M. stylohyoideus is absent. This muscle is 
tjT)ically composed of two parts in carnivores, a 
superficial slip external to the digastric and a 
deeper part internal to the digastric. Either may 
be absent, although there seems to be no previous 
record of both being absent simultaneously. Noth- 
ing corresponding to either part could be found in 
the specimens of Ailuropoda dissected. 

M. mylohyoideus (figs. 83, 84, 85) is a thick 
sheet that fills, with its fellow, most of the space 
between the rami of the mandible. Anteriorly a 
small space exposes the end of the genioglossus. 
The muscle arises from the medial surface of the 
mandible just below the alveoli of the teeth, from 
a point opposite the first molar to the angular 
process. The general direction of the fibers is 
transverse, although anteriorly and posteriorly 



M. geniogloesu*' 
M. mylohyoideus' 

/ M' geniogloasus 

M geniohyoideus 


M. styloglossus 

M. pterygoid 
eus int. 

M. pterygoid 
eus ext. 

M. thyreopharyngeua: constr. phar. post 

M. stemothyreoideus 

oc. mastoideus 

Proe. paroceipitalis 
N. hypogU>ssus 

M. constrictor pharyngis medius 

M. hyogloosus 

M. thyreohyoideus 

M. cricothyreoideus pars recta 

M. cricothyreoideus pars obliqua 

Fig. 85. Muscles of the head of Ailuropoda, ventral view. 

they diverge to the mandibular symphysis and the 
hyoid, respectively. Insertion is made in the usual 
way into a median raphe with the opposite muscle, 
and posteriorly into the hyoid bone. Medially the 
inner surface of the mylohyoid is almost insepa- 
rably united to the geniohyoid. 

The mylohyoid is much thicker, particularly 
near its origin (fig. 83), than is the mylohyoid of 

E. Muscles of the Tongue 
The extrinsic muscles of the tongue show none 
of the hypertrophy that characterizes the cranio- 
mandibular muscles. Ontogenetically these tongue 
muscles arise from the ventral portion of the occip- 
ital myotomes. They are innervated by the hypo- 
glossal nerve. 

M. styloglossus (fig. 85) takes extensive origin 
from the stylohyal segment of the hyoid appara- 



tus. The fibers diverge over the ventrolateral sur- 
face of the tongue before they disappear into the 
substance of the tongue itself. 

M. hyoglossus ifig. 85) arises from the inferior 
surface of the body of the hyoid, except for the 
area occupied medially by the origin of the genio- 
hyoideus, and the proximal part of the posterior 
horn. The fibers run straight anteriorly for a short 
distance before they penetrate the tongue, behind 
and laterad of the genioglossus and mesad of the 

M. genioglossus (figs. 83, 85) is a narrow band 
arising from the sjTnphysis just laterad of the mid- 
line. The origin of this muscle is ventral and lat- 
eral to the origin of the geniohyoideus. The 
muscle runs posteriorly, separated from the ven- 
tral midline by the geniohyoideus, and enters the 
tongue partly anterior to and partly medial to the 

A. Muscles of the Neck 

1. Superficial Group 

M. sternomastoideus (fig. 86) is a heavy flat 
band about 40 mm. wide at its widest part (near 
its insertion). It arises, partly tendinously and 
partly fleshily, from the anterior border of the 
manubrium and the proximal end of the first 
costal cartilage. The muscle widens somewhat at 
its insertion, which is made on the lateral and ven- 
tral borders of the mastoid process. There is no 
indication that the sternomastoideus fuses with its 
mate at the midline. 

M. cleidomastoideus (fig. 86) arises from the 
dorsal edge of the stemomastoid, at a point about 
70 mm. anterior to the origin of the latter muscle. 
With a maximum width of only 25 mm., it is con- 
siderably narrower than the sternomastoideus. 
The two muscles run forward side by side, the 
cleidomastoideus inserting on the lower part of the 
lambdoidal crest as a direct continuation of the in- 
sertion of the sternomastoideus, although the two 
muscles remain completely separate. 

2. Supra- and Infrahyoid Group 

M. omohyoideus (figs. 86, 89) is a narrow rib- 
bon, about 16 mm. wide, arising from the coraco- 
vertebral angle of the scapula. It runs forward 
and downward, passing between the scalenus and 
the stemohyoideus. Near its insertion it divides 
into two bellies. The larger of these inserts on the 
hyoid, deep to the insertion of the stemohyoideus. 
The other belly inserts aponeurotically on the ven- 
tral face of the digastric, near its medial border. 

M. stemohyoideus figs. 86, 87, 89, 90) arises 
from the anterodorsal surface of the manubrium, 
a few of the most lateral fibers reaching the costal 
cartilages. It runs craniad as a narrow, flat band, 
in contact with its mate of the opposite side near 
its origin, but diverging from it farther anteriorly. 
Insertion is made on the thyrohj-al element of the 

M. stemothyroideus (figs. 85, 87, 89, 90) is 

inseparable from the sternohyoid at its origin and 
as far forward as a tendinous intersection which 
crosses the common mass of these two muscles 
about 40 mm. in front of the manubrium. Ante- 
rior to this p>oint the sternothyroid lies partly 
above (dorsal ) and partly lateral to the sternohyoid. 
It inserts on the thyroid cartilage, just above the 
insertion of the sternohyoid. 

M. thyrohyoideus (figs. 85, 87, 89) is a wide, 
flat band on the ventrolateral surface of the thy- 
roid cartilage. Arising from the posterior border 
of the thyroid cartilage, just laterad of the mid- 
line, the fibers nm anteriorly to their insertion on 
the posterior border of the thyrohyal and the body 
of the hyoid. 

M. geniohyoideus (fig. 85) is a narrow band 
running from the symphysis mandibuli to the body 
of the hyoid, closely applied to its fellow of the 
opi>osite side. Arising from the s>"mphysis deep 
to and laterad of the genioglossus, it inserts on the 
anteroventral surface of the body of the hyoid, 
just laterad of the midline. 

3. Deep Lateral and Subvertebral Group 

M. scalenus (figs. 86, 89) is divisible into the 
usual longus and breris. The short division Ues 
mostly beneath the much more powerful long divi- 
sion. The scalenus longus arises by short, stout 
tendons from the third to seventh ribs, its origins 
interdigitating with the sraratus anticus. The 
longus is subdivided into a dorsal part, which arises 
from the second to the fifth ribs, and a medial part 
from the sixth and seventh ribs. The bre\Ts arises 
fleshily from the first rib near its junction with the 
costal cartilage. The two divisions unite in the 
cervical region, and the resulting common mass j 
inserts on the transverse processes of the last five 
cervical vertebrae. 

M. longus colli arises from the ventral surfaces 
of the bodies of the first six thoracic vertebrae and 
from the ventral sides of the transverse processes 
of the sixth to third cervical vertebrae. The usual 
simple distinction of the thoracic and cervical parts 
of the muscle because of difference in their fiber 
directions is scarcely possible on the present speci- 
men. The fibers arising from the thoracic verte- 
brae are gathered into a tendinous band that in- 





























serts into the transverse process of the sixth cer- 
vical. The fibers from the cervical vertebrae have 
the customary insertion into the next vertebra 
craniad of the one from which they arise, and into 
the ventral surface of the arch of the atlas. 

M. longus capitis is a prominent subcylindri- 
cal muscle, somewhat flattened dorsoventrally. It 
arises by fleshy fasciculi from the tips of the trans- 
verse processes of the sixth to the second cervical 
vertebrae. Insertion is into the prominent scar 
on the ventral side of the basioccipital. 

M. rectus capitis ventralis is a very slender 
muscle lying mesad of the longus capitis, and in 
contact with its mate of the opposite side at the 
midline. It has the customary origin from the 
ventral surface of the body of the atlas, and in- 
sertion into the basioccipital mesad and caudad 
of the longus capitis. 

B. Muscles of the Trunk 
1. Muscles of the Thorax 

M. panniculus carnosus is rather feebly de- 
veloped; the dorsal division is represented only by 
an almost insignificant vestige. The borders of 
the ventral division do not reach the midline either 
dorsally or ventrally. A few fibers arise on the 
inner surface of the thigh, and the sheet then 
broadens as it passes anteriorly, reaching its great- 
est width over the posterior ribs. At this point it 
is approximately 170 mm. from the dorsal midline 
and 80 mm. from the ventral. The sheet then 
gradually decreases in width as it passes craniad. 
At the point where it passes under the pectoralis 
it is only about 50 mm. wide. The ventral fibers 
insert on the bicipital arch, the dorsal ones on the 
inner face of the pectoralis profundus. 

The dorsal division is represented only by two 
narrow ribbons, lying immediately dorsad of the 
ventral division, that run up onto the shoulder for 
about 50 mm. and insert into the epitrochlearis 
immediately below the latissimus. 

M. pectoralis superficialis (fig. 89). As in the 
bears, the superficial pectoral sheet is a compound 
muscle composed of the pectoralis superficialis an- 
teriorly and the reflected posterior edge of the pro- 
fundus posteriorly. Fusion is so intimate that the 
boundary between superficialis and profundus can- 
not be determined, but as in the bears the posterior 
part of the superficial layer is innervated by the 
medial anterior thoracic nerve. 

Along its posterior border the superficial sheet 
is folded sharply under and continued forward as 
a deeper layer (the profundus) immediately be- 
neath the superficial one. Thus a very deep and 
well-marked pectoral pocket, open anteriorly and 
closed posteriorly, is formed. 

The superficial sheet arises from the entire ma- 
nubrium and from the corpus sterni back to the 
level of the eighth sternal rib. The fibers converge 
toward the humerus, and insert into the pectoral 
ridge in a narrow line along the middle half of the 
bone. In other carnivores (including the bears) 
insertion is into the deltoid ridge. In Ailuropoda 
the proximal end of the insertion line deviates 
slightly from the pectoral ridge toward the del- 
toid ridge, but by no means reaches the latter. 
Probably the tremendous development of the del- 
toid and lateral triceps in the panda has crowded 
the superficial pectoral off the deltoid ridge and 
forward onto the pectoral ridge. 

M. sternohumeralis profundus is a narrow 
band anterior to the superficial sheet. It arises 
from the anterior end of the manubrium, increases 
in width as it passes toward the shoulder along the 
anterior border of the superficial sheet, and inserts 
on the lateral surface of the humerus immediately 
below the greater tuberosity, in a line that con- 
tinues proximad from the insertion of the super- 
ficial sheet. The lateral anterior thoracic nerve and 
its accompanying blood vessels pass through the 
split between this muscle and the supei-ficialis. 

M. pectoralis profundus (figs. 89, 133) lies 
mostly beneath the supei-ficialis, although as stated 
above its posterior edge is folded forward and fused 
with the posterior border of the superficialis. It is 
by far the widest element of the pectoral complex. 
It is not divisible into anterior and posterior parts. 
Origin is from the corpus sterni posteriorly, deeper 
fibers arising from the sternal cartilages, from the 
eighth forward to the third. At the anterior level 
of the third and fourth sternal cartilages the mus- 
cle arises wholly from the cartilages, none of the 
fibers reaching the sternebrae. The most poste- 
rior fibers are joined on their under side by the 
panniculus. Insertion extends almost the entire 
length of the humerus, beginning proximally on 
the greater tuberosity at the edge of the bicipital 
groove, and continuing distad on the pectoral ridge 
to within 60 mm. of the distal end of the humerus. 

M. pectoralis abdominalis (fig. 89) is a nar- 
row thin band lying posterior to the profundus. 
It arises from the rectus sheath at the level of the 
costal arch, passes beneath the posterior edge of 
the profundus, and inserts with the panniculus on 
the deep surface of the profundus, not reaching the 
bicipital arch. The abdominalis is degenerate. 

M. subclavius is entirely wanting. 

M. serratus ventralis (magnus or anterior of 
some authors) and M. levator scapulae (fig. 86) 
form a perfectly continuous sheet, so that the 
boundary between them cannot be determined. 
The common muscle arises from the atlas and all 



succeeding cervical vertebrae, and by fleshy fibers 
from the first nine ribs. The sHp arising from the 
fifth rib lies over the scalenus; those farther for- 
ward lie beneath it. Insertion is made along the 
inner surface of the whole vertebral border of the 

Mm. intercostales externi (figs. 87, 89). The 
fibers of these muscles run craniodorsad as far back 
as the eleventh rib. Between the eleventh and 
fourteenth ribs they run nearly horizontally. The 
muscles reach the costal cartilages of all but the 
first two ribs, although the intercostales interni 
are exposed medially as far back as the seventh 
rib. The part of the muscle between the ribs is 
fleshy anteriorly, becoming quite tendinous poste- 
riorly. Between the costal cartilages this ai'range- 
ment is reversed, the muscles being tendinous an- 
teriorly and fleshy posteriorly. 

A small group of fibers arises from the first costal 
cartilage near the manibrium and inserts on the 
inner face of the tendon of the rectus. The dorsal 
edge of the muscle forms a raphe with the inter- 
costal fibers lying dorsad of it, and the fiber direc- 
tion is more vertical than that of the intercostales. 
It is not known whether this represents a part of 
the intercostalis internus or not. 

Mm. intercostales interni (figs. 87, 90) are, 
as usual, more extensive than the external inter- 
costals. They occupy all the space between the 
ribs and the costal cartilages. The fibers take the 
usual forward and downward direction. 

M. supracostalis (fig. 86) is a narrow band 
arising from the fourth rib. Running anteriorly 
closely applied to the ventral edge of the scalenus, 
it swings ventrad to insert on the costal cartilage 
of the first rib. 

M. transversus thoracis (fig. 90) is a thin 
sheet, more or less divisible into separate bands, 
that occupies the space between the third and 
eighth sternal cartilages on the inner side of the 
thoracic wall. Origin is from all the sternal seg- 
ments except the first two and from the anterior 
third of the xiphoid cartilage, and insertion is 
made on the sternal cartilages and aponeurotically 
on the fascia covering the inner surface of the in- 
ternal intercostals. 

A narrow ribbon of muscle arises from the third 
sternal segment and passes forward to insert apo- 
neurotically into the fascia of the intercostals. It 
is not known whether this represents a part of the 
transversus thoracis or not. 

M. diaphragma (fig. 90). Pars lumbalis is di- 
vided into three crura. Crus laterale, which is the 
largest of the three, has a double origin. The lat- 
eral fibers arise by means of a stout tendon from 

the ventrolateral surface of the third lizmbar ver- 
tebra. Medial fibers arise, at the level of the sec- 
ond lumbar vertebra, from the lateral edge of a 
long tendon that runs cephalad from the ventral 
surface of the fourth lumbar vertebra. This ten- 
don runs forward along the medial border of the 
pars lumbalis as far as the aortic notch, and gives 
rise to all the remaining fibers of this part of the 
diaphragm. On the deep surface of the lateral 
crus some of the fibers also arise directly from the 
second lumbar. Crus intermedium is very narrow. 
It is separated from the lateral crus throughout 
almost its entire length by a branch of the phrenic 
nerve, while its medial border slightly overlaps 
the lateral border of the medial crus. It arises 
from the medial tendon mentioned above, at the 
level of the anterior border of the second lumbar 
vertebra, its origin being continuous with that of 
the lateral crus. Crus mediale arises from the me- 
dial tendon at the level of the posterior border of 
the first lumbar vertebra, its origin being continu- 
ous with that of the intermediate crus. The me- 
dial crus fuses with its fellow of the opposite side 
cephalad of the hiatus aorticus, which is situated 
below the thirteenth thoracic vertebra. 

Pars costalis arises from the ninth to the eleventh 
costal cartilages by a series of interdigitations with 
the transversus abdominis. These interdigitations 
do not correspond perfectly in number with the 
ribs, some costal cartilages receiving more than 
one digitation each; nor do the digitations corre- 
spond exactly on either side of the sternum. 

Pars sternalis arises from the lateral border of 
the posterior part of the elongate xiphoid process. 
It is a narrow band that promptly joins the adja- 
cent medial border of the pars costalis. 

2. Muscles of the Abdomen 

M. rectus abdominis (figs. 86, 87, 89, 91) ex- 
tends as a thin, rather narrow, band from the pel- 
vic symphysis to the first costal cartilage. It 
reaches its greatest width of 100 mm. at about the 
level of the sixth sternal cartilage. Tendinous in- 
scriptions are absent. The muscle arises by fleshy 
fibers, covered by a heavy aponeurosis, from the 
posterior part of the pelvic symphysis, the origin 
extending anteriorly along the ventral midline. A 
few of the fibers nearest the midline insert into the 
linea alba just behind the xiphoid cartilage. Suc- 
cessive slips farther laterad insert on the fifth, sixth 
and seventh costal cartilages, and slightly less than 
the lateral half of the muscle is continued forward, 
to insert by a wide tendon on the first costal carti- 
lage. This tendon begins at the level of the third 
costal cartilage. The rectus does not participate 
in the formation of the inguinal canal. 

M. atiantoscapularis 


M. acromiotiap. (cut) 

M. levator scapulae vent. 

M. cephalohumer. 

M. acromiodclL 

M. brachialis 

M. atiantoscapularis 

M. triceps lateralis 

M. triceps longus 

. dca-so-epitrochlearis 
M. spinodeltoideus 
'M. acromiotrap. 
M. spinotrap. 

M. obliquus abdom. extemus 

M. vastus lateralis 
M. qxiadratus femoris 
M. adductor 

M. semimembranosus 
M. semitendinosus 

M. tenuissimus 

Fascia lumbodorsalis superf. 

M. glutaeus superf. 

M. tensor fasciae latae 

M. semimonbranoeus 
M. biceps femoris 

Fig. 88. Dorsal view of body musculature of Ailuropoda, superficial layer on right, deeper layer on left. 


M. omohyoideus 
M. stemocleidomastoideus ' 

M. cephalohumer. 
M. stemohumer. prof, 

M. pect. superf, 

M. th}rreohyoideus 
M. cricothyreoideus 
M. stemothyreoideus 

M. stemohyoideus 

M. rectus abdominis 


M. vastus med.- 
M. sartorius 
M. adductor 
M. semimembranoeus 

M. gracilis 

M. aemitendinosus 

M. intercost. ext 

M. obliquus intemus 

M. tensor fasciae latae 
M. iliopsoas 

M. adductor 
M. vastus med. 

M. rectus femoris 
v M. adductor 

M. aonimembranoeut 
M. aemitendinosus 

Fig. 89. Ventral view of body musculature of Ailuropoda, superficial layer on right, deeper layer on left. 




M. sternohyoideus + 
M. stemothyreoideus 

M. stemomastoideus 

A. & V. mammaria int. 

M. transv. thoracis 

M. intercost. int, 

M. diaphragma, 
pars sternal is 

Proc. xiphoideus 

M. diaphragma^ 
pars costal is 

M. transversus 

Fig. 90. Ventral wall of thorax of Ailuropoda, internal view. 

M. obliquus abdominis externus (figs. 86, 88, 
89, 91) arises by short tendons from the fourth to 
the ninth ribs, and by fleshy fibers from the tenth 
to the thirteenth. Apparently none of the fibers 
reach the dorsal fascia. Posterior to the serratus 
ventralis the obliquus attaches to the ribs (10-13) 
immediately behind the origins of the latissimus 
dorsi. It is difficult to determine whether the 
fibers dorsal to the origins of the latissimus rep- 
resent continuations of the obliquus or whether 
they are external intercostals, as the fiber direc- 

tion is exactly the same. When the dorsal border 
of the obliquus is lifted, however, the muscle sheet 
dorsal to it is found to be perfectly continuous 
with the intercostals lying beneath the obliquus. 
Insertion: the muscle fibers slightly overlap the 
lateral edge of the rectus before giving way to the 
tendinous aponeurosis that extends over the rectus 
to the linea alba at the ventral midline (the rec- 
tus sheath). In the inguinal region the aponeu- 
rosis expands into a large triangular sheet, the 
abdominal tendon (see below), which inserts into 
the posterior third of the inguinal ligament. 



M. obliquus abdom. ext. 

M. aartoriua 

Vagina m. 
red. abdom. 

M. obLabd. 
int (cut & 


M. obL 
[Tendo abd] 
(cut & rea) 

Aimulus iniuimU int. 

M. adductor 

Tertdo praepubieu* 

Tendo praepubicus 


Fig. 91. The inguinal region of At'/Mropoda. The dotted line shows the position of the internal inguinal ring. The arrows 
pass through the lacuan musculo-vasorum (lateral) and inguinal canal (medial). 

M. obliquus abdominis internus (fig. 87, 89, 
91) is much less extensive than the externus. It 
is rather sharply divided into two parts: an ante- 
rior division (pars costalis) that inserts on the last 
ribs, and a more extensive posterior part (pars 
abdominalis+pars inguinalis) that inserts aponeu- 
rotically into the ventral belly wall. These two 
divisions are separated by a considerable gap ven- 
trally. The anterior division arises from the crest 
of the ilium from the anterior superior iliac spine 
mesad nearly to the middle of the crest, and from 
the iliac end of the inguinal ligament, and inserts 
on the last three ribs. The posterior division arises 
exclusively from the inguinal ligament. Posteri- 
orly the fibers run almost vertically downward, or 
may even run slightly ventrocaudad ; anteriorly 
they run diagonally forward and downward. The 

muscle terminates in a tendinous aponeurosis that 
participates in the formation of the rectus sheath 
(see below). This aponeurosis is more extensive 
anteriorly, where the muscle fibers fail by 40 mm. 
to reach the edge of the rectus. Posteriorly the 
muscle fibers extend to the edge of the rectus. In 
the inguinal region the internal oblique is perforated 
by the inguinal canal. 

M. transversus abdominis (figs. 87, 89, 90, 
91) arises from the cartilages of the last six ribs, 
interdigitating with the origins of the diaphragm. 
Additional origin is taken from the lumbodorsal 
fascia, from the tip of the ilium, and from the an- 
terior end of the inguinal ligament. The muscle 
terminates in a tendinous aponeurosis that fuses 
with the inner layer of the aponeurosis of the in- 
ternal oblique to form the inner sheath of the rec- 



tus. The posteriormost fibers insert into the lateral 
third of the iliac crest. 

M. cremaster (fig. 91) arises as a fine tendon 
from the inguinal ligament 25 mm. anterior to the 
internal inguinal ring. The tendon takes accessory 
origin from the transverse fascia on its way to the 
inguinal canal. As it enters the canal the tendon 
fans out into a band of muscle fibers that passes 
through the canal dorsad of the spermatic cord, 
and expands to form the cremasteric fascia around 
the tunica vaginalis of the testis. 

M. quadra tus lumborum (fig. 100) is a com- 
plex muscle arising from the last three thoracic 
vertebrae and ribs and the transverse processes of 
all the lumbar vertebrae. Insertion is into the 
transverse processes of the lumbars and the in- 
ternal lip of the iliac crest for about its middle 
third and the adjacent inferior surface of the ilium. 

3. The Inguinal Region. Figure 91. 

The structures in the inguinal region are some- 
what modified in Ailuropoda, in comparison with 
related carnivores, because of the extremely short 
pelvic symphysis. 

The abdominal tendon [Bauchsehne+Becken- 
sehne of German veterinary anatomists] is the in- 
sertion aponeurosis of the external oblique muscle. 
Anteriorly the aponeurosis of this muscle passes 
into the outer rectus sheath, while in the inguinal 
region it forms a large triangular sheet that fills 
the angle between the linea alba and the inguinal 
ligament. The aponeurosis is perforated by the 
inguinal canal ; the part anterior to this perforation 
is the "abdominal tendon," the part posterior to 
it the "pelvic tendon" of the German anatomists. 

The aponeurosis inserts into the posterior third 
of the inguinal ligament, from the level where the 
femoral vessels emerge back to the symphysis. 
The lamina femoralis, which in the dog and other 
domestic quadrupeds splits off from the abdominal 
aponeurosis at the lateral border of the inguinal 
ring and runs onto the medial surface of the thigh, 
appears to be wanting in Ailuropoda. 

The prepubic tendon is a heavy, compact liga- 
ment extending from the iliopectineal eminence 
back to the anterior border of the pelvic symphy- 
sis, where it meets its mate of the opposite side. 
The tendon is more or less continuous with the in- 
guinal ligament anteriorly. It lies superficial to 
the pectineus muscle, and arises chiefly from the 
origin tendon of that muscle. Where it passes over 
the origin tendon of the gracilis near the symphy- 
sis, the prepubic tendon is inseparably fused with 
the tendon of that muscle. The tendon provides 
attachment for the linea alba and the posterior- 
most fibers of the internal oblique. 

The inguinal ligament lies at the juncture of 
the medial surface of the thigh and the wall of the 
abdomen. It extends from the anterior iliac spine to 
the iliopectineal eminence. Beyond the eminence 
it is continued posteriorly as the prepubic tendon. 
As in other quadrupeds, the inguinal ligament is 
poorly defined in Ailuropoda. Anteriorly it is little 
more than a fiber tract from which the posterior 
fibers of the internal oblique take origin. Poste- 
riorly, where it bridges over the lacuna musculo- 
vasorum, it is a heavier and more sharply defined 

Between the inguinal ligament and the ventral 
border of the pelvis there is a large gap, the lacuna 
musculovasorum (lacuna musculorum + lacuna 
vasorum of human anatomy; the iliopectineal liga- 
ment, which separates these in man, is wanting in 
quadrupeds). Through this opening the iliopsoas 
muscles and the femoral vessels and nerve pass 
from the abdominal cavity onto the thigh. In 
Ailuropoda (as in the dog) the femoral vessels lie 
ventrad of the iliopsoas, rather than posterior to it, 
and no true femoral ring can be distinguished. 
The lacuna is about 50 mm. long. 

The inguinal canal is very short, its length 
being little more than the thickness of the abdom- 
inal wall. It is about 12 mm. long, and is directed 
posteriorly and slightly medially. It is situated 
about 30 mm. in front of the pelvic symphysis. 
The inlet to the canal, the internal inguinal ring, 
is formed by a hiatus in the internal oblique mus- 
cle; the anterodorsal border, between the limbs of 
the opening in the muscle, is formed by the in- 
guinal ligament. The rectus abdominis does not 
participate in forming the medial border of the 
ring, as it does in the dog. The internal ring meas- 
ures about 30 mm. in long diameter. The outlet, 
the external inguinal ring, is associated with the 
abdominal tendon of the external oblique. In the 
inguinal region this sheet splits to form the lateral 
and medial limbs of the ring. The fibers of the 
lateral limb radiate into the origin tendon of the 
pectineus and the prepubic tendon, while the fibers 
of the medial limb pass into the rectus sheath. 
The ring is completed posterodorsally by the pre- 
pubic tendon; i.e., the two limbs do not re-unite 
posteriorly, but merely form a ventral arch around 
the spermatic cord. 

The sheath of the rectus abdominis is formed 
externally by the aponeurosis of the external 
oblique fused with the ventral layer of the apo- 
neurosis of the internal oblique. Internally the 
sheath is formed by the dorsal layer of the aponeu- 
rosis of the internal oblique fused with the apo- 
neurosis of the transversus abdominis. Thus the 
rectus muscle is embraced between the dorsal and 



ventral layers of the internal oblique aponeurosis. 
In the dog the inner layer of the rectus sheath 
". . . is formed for the most part by the terminal 
aponeurosis of the transversus abdominis . . . and 
in the anterior portion in addition by an inner 
layer of the terminal aponeurosis of the obliquus 
abdominis internus." (Baum and Zietzschmann.) 
The inguinal region of Ailuropoda differs from 
that of the dog (Baum and Zietzschmann; the only 
other carnivore in which this region is known) in 
several respects. The following peculiarities of the 
giant panda may be mentioned: 

(1) The rectus does not participate in the for- 
mation of the inguinal canal. 

(2) The rectus inserts into the posterior part of 
the symphysis. 

(3) The cremaster does not arise from the pos- 
terior border of the internal oblique. 

(4) The abdominal tendon of the external 
oblique does not form the entire circum- 
ference of the external inguinal ring. 

I^. Muscles of the Back 

Superficial Secondary Back Muscles. M. 
cephalohumeralis (= clavodeltoideus +clavotra- 
pezius) (figs. 88, 134) is powerfully developed. Near 
its insertion it has a thickness of about 20 mm. 
Its origin, which is continuous with that of the 
acromiotrapezius, extends on the lambdoidal crest 
from the level of the dorsal border of the zygoma 
to the dorsal midline, then by aponeurosis from 
the ligamentum nuchae for 90 mm. along the mid- 
line of the neck. The anterior border is slightly 
overlapped by the temporalis. The fibers converge 
over the anterior border of the shoulder, and insert 
fleshily into the lower half of the deltoid ridge and 
the area between this ridge and a second ridge 
midway between the deltoid and pectoral ridges. 
At its insertion the muscle forms a partial raphe 
with the acromiodeltoid laterally and with the 
pectoralis superficialis and profundus medially. 

The clavotrapezial part of the cephalohumeral 
is innervated by the spinal accessory, and the 
clavodeltoid part by the axillary nerve. 

Action: Chief extensor of the fore leg. 

M. acromiotrapezius (figs. 88, 134) is a thin, 
rectangular sheet arising from the dorsal midline 
by a long, broad aponeurotic sheet; fleshy fibers 
appear as the muscle crosses the scapular border. 
The muscle is thus sharply divided into two parts, 
a fleshy part lying over the scapula and an aponeu- 
rotic part between the vertebral border of the 
scapula and the dorsal midline. Its origin is con- 
tinuous with the aponeurotic origin of the cephalo- 
humeral anteriorly, and extends a distance of 

110 mm. along the dorsal midline. The fleshy 
part of the muscle has a length of only 70 mm. 
Insertion is made for a distance of 105 mm. into 
the humeral half of the scapular spine. 

M. spinotrapezius (figs. 88, 134) is triangular 
in outline. The anterior border is sharply con- 
cave, so that a portion of the underlying rhom- 
boids and supraspinous fascia is exposed between 
this muscle and the acromiotrapezius. The pos- 
terior edge is concave and thin, but the muscle 
becomes quite heavy anteriorly. Origin is from 
the spinous processes of the thoracic vertebrae for 
a distance of 160 mm. The anterior border is over- 
lapped slightly by the acromiotrapezius near the 
midline. The fleshy part of the muscle stops 
abruptly at the posterior border of the scapula, 
and the muscle continues forward and downward 
across the scapula as a wide, heavy aponeurosis 
that inserts into the superficial fascia of the infra- 
spinatus. Thus the condition in the spinotrapezius 
is the reverse of that in the acromiotrapezius, 
where the part of the muscle lying over the scap- 
ula is fleshy and the part beyond the scapula is 

The relations of fleshy and aponeurotic parts of 
the acromio- and spinotrapezius to the underlying 
scapula in Ailuropoda appear to be pressure phe- 
nomena. Similar conditions are known from human 
anatomy, e.g., the digastric. It is noteworthy, 
however, that the trapezius is almost exactly the 
same in the Ursidae (verified in our specimens of 
Selenarctos and Tremarctos), and is surprisingly 
similar, considering the difference in body size and 
proportions, in Ailurus. The development of these 
extensive aponeurotic sheets is even indicated in 
Bassariscus and Procyon. The dogs, on the other 
hand, show nothing comparable to it, nor do 
other carnivores, including such large forms as 
the hyenas and lion. 

Action: The trapezius muscles elevate the scap- 
ula and rotate it counterclockwise. 

M. latissitnus dorsi (figs. 88, 134) is very pow- 
erfully developed. It has the customary triangu- 
lar form. The anterior border is overlapped by 
the spinotrapezius. It arises mostly by aponeuro- 
sis from the mid-dorsal line, fleshy fibers reaching 
the midline only at a point just behind the spino- 
trapezius. Ventrally and ventro-posteriorly the 
muscle takes origin from the seventh to eleventh 
ribs. Origin from the seventh rib is limited to a 
very few fibers, but the origin from each successive 
rib increases in length until on the eleventh it ex- 
tends over 95 mm. The fibers converge toward the 
axilla, and insertion is made by two heads. The 
smaller head inserts chiefly into the inner face of 



the panniculus carnosus, a few of the most poste- 
rior fibers reaching the epitrochlearis. The main 
mass of the muscle forms a powerful raphe with 
the epitrochlearis, and these two muscles make a 
common insertion into the tendon of the teres 

Action: Chief flexor of the arm. 

M. rhomboideus (figs. 86, 88, 92, 134) is more 
or less divisible into two parts. The muscle is 
elongate triangular in outline, and arises in a con- 
tinuous line from the lambdoidal crest at about the 
level of the dorsal border of the zygoma up to 
the dorsal midline, then back for 270 mm. along the 
midline of the neck. The muscle may be separated, 
particularly near its insertion, into anterior and 
posterior masses, of which the posterior is much 
the more extensive. Insertion is made into the 
dorsal half of the coracoid border and entire ver- 
tebral border of the scapula. The anterior edge 
of the posterior part lies partly over that of the 

Action: Draws the scapula toward the verte- 
bral column. 

M. occipitoscapularis (rhomboideus anterior 
or capitis of authors) (fig. 134) is a narrow band 
arising from the lambdoidal crest. The muscle 
runs backward, separated from the rhomboideus 
by the dorsal branch of the A. and V. transversa 
colli, to insert on the coracovertebral border of 
the scapula, beneath the insertion of the anterior 
part of the rhomboideus. 

Action : Draws the scapula forward. 

M. atlantoscapularis (levator scapulae ven- 
tralis of authors; omo-cleido-transversarius of Carl- 
sson) (figs. 86, 134) is a narrow, heavy band arising 
from the transverse process of the atlas. For a 
short distance it is inseparable from the first digi- 
tation of the levator scapulae, with which it has 
a common origin. Immediately distad of its origin 
it is easily separable into two subequal parts, which 
embrace a branch of the fourth cervical nerve be- 
tween them. This separation loses its identity 
near the insertion, which is made, by means of a 
short fine tendon, into the metacromion of the 
scapula, at the juncture of the acromiodeltoideus, 
the spinodeltoideus, and the acromiotrapezius. 

M. serratus dorsalis anterior (fig. 86) arises 
by fleshy slips from the posterior borders of the 
fifth to tenth ribs. The fibers from these six ori- 
gins more or less unite to form a continuous sheet 
that inserts aponeurotically into the dorsal fascia. 

M. serratus dorsalis posterior (fig. 86) is lim- 
ited to two slips. The more anterior of these 
arises from the twelfth rib; the posterior from the 

thirteenth, with a few fibers coming from the four- 
teenth. The fibers run straight dorsad, to insert 
independently of one another into the dorsolum- 
bar fascia by means of aponeuroses. 

Deep Intrinsic Back Muscles. M. splenius 
(figs. 86, 87, 92) is very powerfully developed, par- 
ticularly along its lateral border, where it attains 
a thickness of 15 mm. Posteriorly the muscle 
arises by a wide tendinous aponeurosis from the 
dorsoliunbar fascia at about the level of the fifth 
thoracic vertebra; this aponeurosis lies beneath the 
origin of the serratus posterior superior. Origin, 
by a similar aponeurosis, is taken along the mid- 
line as far forward as the lambdoidal crest of the 
skull. This medial aponeurosis has a width of 
15-20 mm. Insertion is made on the lambdoidal 
crest, just beneath the insertion of the rhom- 
boideus, and from the mastoid process down to 
its tip. Tendinous intersections are absent. 

The usual undifferentiated muscle mass occu- 
pies the trough formed by the spines and trans- 
verse processes of the lumbar vertebrae. At the 
level of the last rib it divides to form three mus- 
cles: the iliocostalis, the longissimus, and the spi- 
nalis. The medial part of the muscle mass is 
covered with a heavy aponeurosis, which gives 
rise to many of the superficial fibers of all three 

M. iliocostalis (figs. 87, 88, 92) is the most lat- 
eral of the superficial back muscles. It gives off a 
tendinous slip to each of the ribs near its angle 
and to the transverse process of the last cervical 
vertebra. The more posterior tendons pass over 
one rib before inserting, those farther forward over 
two. Slips from all the ribs except the first four 
join the muscle as it runs craniad. 

M. longissimus (figs. 87, 88, 92) is the middle 
one of the three superficial back muscles. There 
is no demarcation between the pars dorsi and pars 
cervicis of human anatomy. On the other hand, 
the muscle is sharply divided into a lumbar part 
(M. ilio-lumbalis [Virchow], Pars lumborum m. 
longissimus dorsi [Winckler], M. longissimus lum- 
borum [Eisler]), arising from the ilium and covered 
by the heavy deep layer of the lumbar fascia; and 
a thoracic part. The thoracic part arises from the 
lumbar fascia, and farther anteriorly from the 
fascia between itself and the spinalis. There is 
the usual double insertion: medially by fasciculi 
into the anapophyses of the lumbar and thoracic 
vertebrae, and laterally by long tendons into all 
but the last four ribs and into the transverse proc- 
esses of the last six cervical vertebrae. 

M. longissimus capitis (fig. 92) arises from the 
transverse processes of the last three cervical ver- 



M. multifidus 

Vertebra thoraaUis I 

Nn. cervicales doraales 

M. splenitis (cut) 

M. rectus capitis 
dorsalis major (cut) 

w ,,. ... . \x -^"- biventer cervicus I M. rhomboideus (cut) 

M. oWiquus capitis post. \\ et complejcus ' 

M. multifidus cervicis \ \\ m. rectus capitis^ 

Axis-Proc. spiMlis\ \ \ dorsalis mediusN 


M. rectus capitis lateralis' 

M. rectus capitis 

dorsalis minor 

M. obliquus capitis ant. 

Fig. 92. Deep muscles of neck and anterior thorax of Ailuropoda, right side. 

tebrae. It is composed of two very slender heads. 
One of these joins the ventral border of the sple- 
nius in the usual way, and thus inserts into the 
mastoid process. The other head, which comes 
from the anterior fibers of the common origin, lies 
deep to the splenius along the ventral border of 
the complexus, inserting with it into the occipi- 
tal bone. 

M. longissimus atlantis (fig. 92) is slightly 
larger than the combined heads of the longissimus 
capitis. It arises from the articular pi-ocesses of 
the third, fourth, and fifth cervicals, and inserts 
into the tip of the wing of the atlas. 

M. spinalis dorsi (figs. 87, 88) is the most me- 
dial and most extensive of the superficial back 
muscles. It is present only in the thoracic region. 
Origin is from the anterior edge of the deep lumbar 
fascia, and farther anteriorly from the fascia be- 
tween itself and the longissimus. The fibers run 
diagonally craniad and mesad, and insert, by ten- 
dons that become progressively longer, anteriorly 
into the tips of the spinous processes of all the 
thoracic and the first cervical vertebrae. 

M. semispinalis is represented only by the 
capitis, which is separable into a dorsal biventer 
cervicis and a ventral complexus. M. biventer 
cervicis (fig. 92) has three diagonal tendinous in- 
tersections. The muscle begins at the level of the 
fifth thoracic vertebra, arising posteriorly from a 
wide aponeurotic fascia that covers the underly- 
ing muscles. Additional origin is taken by means 
of tendinous fasciculi from the tips of the spines 

of the fourth, third, and second thoracics, and an- 
terior to this from the ligamentum nuchae, as well 
as from the transverse processes of the second to 
fifth thoracics. Insertion is fleshily into the occipi- 
tal crest near the dorsal midline. M. complexus 
lies beneath the biventer cervicis posteriorly. It 
begins at the level of the second thoracic vertebra, 
arising posteriorly from an aponeurotic fascia sim- 
ilar to that of the biventer. Additional origin is 
taken from the transverse processes of the first two 
thoracic and last four cervical vertebrae. Inser- 
tion is made, by mingled fleshy and tendon fibers, 
into the medial half of the occipital bone. The 
muscle lies partly deep to the biventer cervicis at 
its insertion. 

M. multifidus (fig. 92) is continued craniad 
from the extensor caudae medialis. In the lum- 
bar region it is deep to the spinalis. The muscle 
is, as usual, best developed in the lumbar region, 
where it is not separable into individual fasciculi; 
at the anterior end of the deep lumbar fascia it is 
fused with the spinalis. In the thoracic region the 
multifidus is more or less separable into fasciculi, 
which arise by mingled tendon and muscle fibers 
from the transverse processes of the vertebrae and 
pass forward over one vertebra to insert on the 
spinous process of the next. M. multifidus cervicis 
is well developed, consisting of three bundles of 
longitudinal fibers extending between the articular 
processes and the spines of the cervical vertebrae. 

M. rectus capitis dorsalis major (fig. 92) is a 
rather thin triangular muscle arising from the an- 



terior two-thirds of the crest of the spine of the 
axis, and inserting into the occipital bone below 
the lambdoidal crest. The muscles from either 
side diverge as they leave the axis, so that a tri- 
angular cavity, bounded ventrally by the atlas 
and filled with fat, remains between their medial 

M. rectus capitis dorsalis medius (fig. 92) 
is apparently represented by a few fibers, super- 
ficial to the medial fibers of the rectus minor and 
with a less oblique fiber direction, that arise from 
the anterior tip of the spine of the atlas and follow 
the border of the triangular cavity described above, 
to insert with the rest of the rectus on the skull. 

M. rectus capitis dorsalis minor (fig. 92) lies 
partly beneath and partly laterad of the medius. 
It is a large muscle with the usual origin from the 
anterior border of the dorsal arch of the axis, and 
inserts into the occipital bone beneath the major 
and medius. 

M. rectus capitis lateralis (fig. 92) is a rela- 
tively small muscle lying along the ventral border 
of the obliquus capitis anterior. Origin is from 
the ventral surface of the tip of the wing of the 
atlas, deep to the origin of the rectus capitis ven- 
tralis. The muscle expands somewhat toward its 
insertion, which is made into the posterior surface 
of the mastoid process near its outer edge. 

M. obliquus capitis anterior (fig. 92) is also 
relatively small. It is triangular in outline, arising 
from the tip of the wing of the atlas and insert- 
ing into the back of the skull just above the mastoid 
process. The dorsal edge of the muscle is overlain 
by the second head of the longissimus capitis. 

M. obliquus capitis posterior (fig. 92) greatly 
exceeds the anterior in size. Origin is from the 
entire spinous process of the atlas. The fiber direc- 
tion is nearly vertical. Insertion is into the wing 
of the atlas. 

5. Muscles of the Tail. Figure 93. 

M. extensor caudae medialis is the posterior 
continuation of the multifidus, and is in contact 
with its mate along the dorsal midline. Origin is 
from the spinous processes of the last two lumbar 
vertebrae and from the spine of the sacnun. Inser- 
tion is into the prezygapophyses (on the anterior 
vertebrae) and dorsal surfaces (posterior vertebrae) 
of the caudals from the second on, by tendons that 
unite with the tendons of the extensor caudae lat- 

M. extensor caudae lateralis arises from the 
deep surface of the deep lumbar fascia, from the 
fused transverse processes of the sacral vertebrae, 
and from the transverse processes (or bodies, where 
these are absent) of the caudal vertebrae. Long 

tendons extend posteromesad over three vertebrae, 
uniting with the tendons of the extensor caudae 

M. abductor caudae externus arises from the 
dorsal surface of the fused transverse processes of 
the sacrum, from the fascia surrounding the base 
of the tail, and from the transverse processes of 
the first four caudals; there is no attachment to the 
ilium. Insertion is into the transverse processes 
(or the sides) of the three following vertebrae. 

M. abductor caudae internus is a relatively 
small fusiform muscle lying ventrad of the exter- 
nal abductor. Origin is by a rather wide, flat 
tendon that splits off from the tendon of the ilio- 
caudalis, thus coming from the medial surface of 
the ilium. Insertion is into the transverse proc- 
esses of the first six caudals, in common with the 
insertions of the external abductor. 

M. iliocaudalis is a thin triangular sheet. Ori- 
gin, by means of a wide tendinous sheet externally 
and fleshy fibers internally, is from the medial sur- 
face of the iliimi caudad of the sacro-iliac articula- 
tion. A long terminal tendon from the fusiform 
part of the muscle joins a tendon of the medial 
division of the flexor caudae longus, to insert into 
the ventral side of the sixth caudal. The remain- 
der of the muscle inserts fleshily into the trans- 
verse processes of the posterior sacral and first two 
caudal vertebrae. 

M. pubocaudalis is a very wide, thin sheet ly- 
ing immediately external to the levator ani. The 
dorsal fibers arise from the tendon of the iliocau- 
dalis, the ventral fibers from the dorsal (inner) 
surface of the symphysis pelvis. Insertion is into 
the ventral surfaces of the fourth and fifth caudals. 

M. flexor caudae longus is composed of two 
sets of fasciculi, which are separated proximally by 
the iliolumbalis. The lateral division consists of 
successive fasciculi arising from the posterior end 
of the sacrum and from the transverse processes 
(or sides) of the caudal vertebrae. The strong ter- 
minal tendons pass over three vertebrae before 
inserting into the transverse process (or side) of 
the fourth succeeding vertebra. The medial divi- 
sion arises just mesad of the lateral division. It 
extends from the anterior end of the sacrum to 
the third caudal vertebra, and its ventral edge is 
partly united to the adjacent edge of the iliocau- 
dalis. It is composed of three successive fasciculi, 
each of which terminates in a tendon. The tendon 
of the most anterior fasciculus joins the much 
stouter tendon of the middle fasciculus; together 
they insert with the pubocaudalis into the ventral 
surface of the fifth caudal. The tendon of the most 
posterior fasciculus joins a tendon of the long flexor, 
and inserts into the ventral side of the sixth caudal. 
















M. flexor caudae brevis consists of short fas- 
ciculi lying along the ventral midline from the fifth 
caudal on. Origin is from the ventral surface of 
the vertebra, and the fibers pass over one vertebra 
to insert into the next. 

6. Muscles of the Perineum 

M. levator ani is a thin triangular sheet of 
muscle lying deep to the coccygeus, and over the 
lateral surfaces of the rectum and urethra. Its 
fiber direction is at right angles to that of the coc- 
cygeus. Origin is chiefly by means of a thin apo- 
neurosis from the medial surface of the ascending 
ramus of the pubis; some of the posterior fibers are 
continued from the retractor penis, and some are 
blended with the sphincter ani externus. Insertion 
is into the centra of the anterior caudal vertebrae. 

M. sphincter ani externus is a narrow ring of 
muscle fibers sun'ounding the anus. The two halves 
of the muscle meet below the anus and immedi- 
ately behind the bulbus urethrae; some of the fibers 
are continued into the suspensory ligament of the 
penis, which attaches to the posterior end of the 
symphysis; others attach to the bulbus urethrae 
and ischiocavernosus. 

M. ischiocavernosus is a very short muscle 
arising from the posterior border of the ischium, 
25 mm. above the symphysis. It is closely applied 
to the posterior wall of the corpus cavernosum 
penis, and terminates by spreading out over this 

M. bulbocavernosus is a thin layer of diag- 
onal muscle fibers surrounding the bulbus iirethrae. 
The two muscles arise from a median raphe on the 
ventral side, and insert into the posterior part of 
the root of the penis. 

M. sphincter urethrae membranaceae is a 

delicate layer of transverse muscle fibers surround- 
ing the urethra proximad of the bulb. It encases 
the urethra for a distance of 30 mm. 

M, retractor penis is a pale muscle arising as 
a continuation of fibers from the levator ani. It 
meets its mate from the opposite side just below 
the rectum, and the two muscles run side by side 
to the base of the glans penis, where they insert. 
A few fibers split off and insert into the side of the 
radix penis. 

M. caudorectalis is a prominent unpaired mus- 
cle lying along the midline in the anal region. It 
is distinctly lighter in color than the surrounding 
musculature. Origin is from the dorsal side of the 
rectum in the midline. The fibers pass backward 
and upward as a fusiform mass, to insert on the 
ventral surface of the sixth caudal vertebra. 


A. Muscles of the Shoulder Girdle 

M, supraspinatus (figs. 88, 95, 96, 133) is cov- 
ered externally by the usual heavy tendon-like 
fascia, which cannot be detached without cutting 
into the muscle substance. This tendinous fascia 
is continued diagonally downward to insert on the 
acromion process, immediately behind the origin 
of the acromiodeltoideus; the fascia over the distal 
end of the muscle is normal. The muscle occupies 
the whole of the supraspinous fossa, overlapping 
the cephalic border. It is powerfully developed, 
having a maximum thickness of 50 mm. Insertion 
is by fleshy fibers into the greater tuberosity of 
the humerus. 

Action: Extends the arm on the scapula. 

M. infraspinatus (fig. 95) arises from the entire 
infraspinatus fossa. It is covered with a tendinous 
aponeurosis down to the origin of the spinodel- 
toideus. The muscle is divisible into two parts, 
the one nearest the glenoid border of the scapula 
being slightly the smaller. The insertion tendons 
of the two parts are more or less distinct, but are 
fused where they are in contact. Insertion is into 
the prominent infraspinatus fossa on the greater 
tuberosity of the humerus. 

Action: Chief lateral rotator of the arm. Its 
tendon acts as a lateral collateral ligament of the 
shoulder joint. 

M. acromiodeltoideus (figs. 88, 95, 134) is 
powerfully developed, having a thickness of 23 mm. 
at its posterior edge. It is covered with tendinous 
fascia superficially. The muscle arises, partly flesh- 
ily and partly tendinously, from the whole tip of 
the acromion. It is bipennate, to two halves of 
approximately equal width. Insertion is by two 
heads, which correspond to the halves of the bi- 
pennate muscle. The anterior half inserts on the 
shaft of the humerus immediately above the in- 
sertion of the cephalohumeral, anterior to the del- 
toid ridge. The posterior part inserts partly on 
the lateral head of the triceps, posteriorly forming 
a strong raphe with the spinodeltoid. 

Action: Chief abductor of the arm. 

M. spinodeltoideus (fig. 88) arises almost 
wholly from the fascia of the infraspinatus; only 
its anterior tip reaches the scapular spine. Most 
of its fibers meet the acromiodeltoideus in a tendi- 
nous raphe, although a few insert on the triceps 

Action: Flexes the arm. 

M. teres minor (fig. 95) is a small muscle, 
closely applied to the inferior border of the infra- 




spinatus, from which it is inseparable at its origin; 
it is not attached to the long head of the triceps. 
It arises by heavy aponeurotic fibers that are 
firmly attached to the underlying infraspinatus on 
the deep surface, from a small area on the axillary 

M. subscapularis (figs. 96, 133) is composed of 
three main divisions. The two anterior subdivi- 
sions are composed of numerous bipennate units, 
whereas the posterior one is made up of units with 
parallel fibers. Insertion is into the proximal end 

Caput humeri 

M. eoracobrachialis brevis 

M. eoracobrachialis longus 

M. biceps (caput longus) 

Epicondylut med 

M. biceps (caput brevis) 

Fig. 94. Right arm of bear (Ursus amerieanus) to show short head of biceps. Medial view. 

border of the scapula just proximad of the middle. 
Insertion is made by a short stout tendon into the 
head of the humerus, immediately distad of the 
insertion of the infraspinatus. 

Action: Flexes the arm and rotates it laterally. 

M. teres major (figs. 95, 96) is powerfully de- 
veloped. It arises from the usual fossa at the distal 
end of the glenoid border of the scapula, and from 
a raphe that it forms with the subscapularis on 
one side and the infraspinatus on the other. In- 
sertion is made, by means of a powerful flat tendon 
30 mm. in width, common to it and the latissimus 
dorsi, on the roughened area on the medial surface 
of the shaft of the humerus, distad of the bicipital 
groove and immediately mesad of the pectoral 
ridge. An extensive bursa (Bursa m. teretis major 
of human anatomy) is inserted between the ten- 
don and the shaft of the humerus. 

Action: Assists the latissimus dorsi in flexing 
the arm, and the subscapularis in medial rotation 
of the arm. 

of the humerus, immediately below and behind the 
lesser tuberosity. The insertion tendon of the first 
(crania) unit is superficial to those of the other two 

Action: Chief medial rotator of the arm. The 
upper part of the muscle acts as an extensor of 
the arm. 

B. Muscles of the Upper Arm 

M. biceps brachii (figs. 96, 97, 133) is a fusi- 
form muscle that, in the position in which the arm 
was fixed, is rather sharply flexed at the site of the 
bicipital arch. The muscle displays a rather curi- 
ous structure. It arises by a single (glenoid) head, 
but in the proximal two-thirds of the muscle a 
narrow anterior group of fibers is more or less sep- 
arable from the main mass of the muscle. These 
fibers, which are particularly conspicuous because 
they lack the glistening tendinous covering of the 
rest of the muscle, arise from the origin tendon of 
the biceps as it passes through the bicipital groove 
and insert extensively into the anterior surface of 



M. supraspinatus 

-Caput humeri 

-M. acromiodelt.(cut) 
M. infraspinatus 
-M. teres minor 

M. triceps longus 

M. triceps lateralis 

M. anconaeus 

M. ext. carpi uln. 

M. ext. dig. lat. 

Caput uln., m. flex dig. prof. 

M. ext. indicis proprius 
M. ext. dig. com. 

Lig. carpi dorsale icuti 

Fig. 95. Muscles of the right fore leg of Ailuropoda, lateral aspect. 

the main mass of the biceps, as far distad as the 
bicipital arch. There was no indication of a short 
head in two specimens dissected. 

The biceps arises from the bicipital tubercle at 
the glenoid border of the scapula, by a long, flat- 
tened tendon that runs through the bicipital 
groove, enclosed in the joint capsule, onto the ante- 
rior surface of the humerus. The tendon is contin- 
ued into an extensive area of tendinous aponeurosis 
on the external surface of the belly of the muscle, 
and a more limited area of similar tissue on the in- 
ternal surface. The most medial (superficial) fibers 
of the biceps terminate in a well-defined lacertus 
fibrosus, which is continued into the fascia over the 
pronator teres. The tendon of insertion begins mid- 
way on the deep surface of the muscle and continues 
distad as a distinct tendinous band on the deep 
surface of the muscle; this band does not form a 
longitudinal furrow as it does in the dog. The mus- 
cle fibers insert into it along its length at a very 
oblique angle, so that the biceps is a pennate mus- 
cle rather than a parallel-fibered one as in man. 
This tendinous band is continued into a short, very 
stout, flattened tendon, 12 mm. in width, that 
passes between the brachioradialis and pronator 

teres to insert into the prominent bicipital tuber- 
cle of the radius. 

Action: Flexes the forearm. 

The biceps is normally, but not invariably, two- 
headed in the bears, a degenerate short head usu- 
ally arising from the coracoid process with the 
brachioradialis (Windle and Parsons, 1897, p. 391). 
I have dissected the biceps in a young black bear, 
with the following results (fig. 94). The long head 
is similar to that of Ailuropoda except that the 
small group of accessory fibers coming from the 
origin tendon lies along the posterior border of the 
muscle, and the tendon of insertion does not begin 
far proximad on the deep surface of the muscle. 
The short head begins as a slender flattened ten- 
don arising from the fascia of the coracobrachialis 
just below the head of the humerus. At about the 
middle of the humerus the tendon begins to form 
a slender muscle belly that lies against the poste- 
rior surface of the long head. A few of the most 
superficial fibers insert via a lacertus fibrosus into 
the fascia over the pronator teres, but most of this 
belly inserts with the long head. The biceps was 
similar in an adult Tremarctos ornatus dissected by 
me. Windle and Parsons found a "very feebly 



M. abd. poll, brevis 

Tendo m. ab<i. poll, longus 

M. triceps longus 
M. triceps medialis 

M. pronator teres 

Tendo m.y^ 
flex dig. prof 

Tfndo m.flex dig. subl 

M. opponeus dig. quinti 

. - ^' flex, carpi rad. 
Ij ilMJ'W _M. flex. dig. prof. 


quinti brevis 
M. abd. dig. quinti 

M. flex, carpi uln. 

Fig. 96. Muscles of the right fore leg of Ailuropoda, medial aspect. 

marked" short head in Procyon, and it was also 
present in Potos. According to Carlsson (verified 
by me) there are two heads in Ailurus. 

M. coracobrachialis (fig. 96) is composed of 
two heads, a brevis and a longus. The two heads 
arise, by a common flattened tendon, from the 
coracoid process of the scapula. The short head 
arises from the tendon deep to the long head ; the 
tendon itself bifurcates and is continued along the 
posterior border of each head. The branch of the 
musculocutaneous nerve that supplies the biceps 
passes between the two heads. 

The short head passes around the end of M. sub- 
scapularis and inserts into the posterior angle of 
the shaft of the humerus immediately proximad of 
the tendon of the latissimus dorsi. 

The long head runs to the elbow behind the bi- 
ceps. Near its insertion it bifurcates, the anterior 
fibers inserting on the bony bridge over the ente- 
picondylar foramen, while the posterior fibers insert 
on the humerus immediately behind the foramen. 
The median nerve and branches of the profunda 
vein pass between these two parts of the muscle. 

Action: Assists the supraspinatus in extending 
the arm on the scapula, and helps return the arm 

to the intermediate position from either medial or 
lateral rotation. 

M. brachialis (figs. 88, 95, 96, 133, 134) is com- 
posed of two heads, a long head arising along the 
deltoid ridge, and a short head arising from the 
lateral condylar ridge of the humerus. The two 
heads unite to make a common insertion. The 
long head is intimately fused with the lateral head 
of the triceps proximally, where the two muscles 
are attached by a common tendon to the surgical 
neck of the humerus immediately behind the del- 
toid ridge. From here the origin of the brachialis 
continues distad in a U-shaped line, one limb fol- 
lowing the deltoid ridge, then the pectoral ridge 
below the juncture of these two ridges, to within 
50 mm. of the distal end of the shaft; the other 
limb extends down the posterior side of the shaft 
to the beginning of the lateral epicondylar ridge 
at about the middle of the humerus. The short 
head arises in a narrow line from the anterior bor- 
der of the lateral epicondylar ridge down to within 
20 mm. of the distal articulation, then across the 
anterior face of the humerus to meet the distal end 
of the origin line of the long head. 

The two heads make a common insertion. Some 
of the fibers insert into the distal two-thirds of a 



tendinous arch that extends from the coronoid 
process of the ulna upward (ectad) and forward 
(distad) to the intermuscular septum between the 
pronator teres and the brachioradialis. The main 
insertion is by a stout tendon into the prominent 
depression on the anterior surface of the ulna, im- 
mediately below the coronoid process. 

Innervation: The long head is supplied by the 
radial nerve, the short head by the musculocuta- 
neous nerve. 

Action: Flexes the forearm. 

Windle and Parsons (1897, p. 393), in their re- 
view of the musculature of the Carnivora, state 
that they did not find the short head in any carni- 
vore, and that they encountered only radial inner- 
vation, although "further observation is necessary 
before a definite statement can be made." They 
regarded two heads, with radial and musculocuta- 
neous innervation, respectively, as the "typical 
arrangement" for the Mammalia. Carlsson (1925) 
describes a single muscle, with both radial and 
musculocutaneous innervation, in Ailurus. 

M. epitrochlearis (fig. 88) is an extremely 
powerful muscle embracing the whole posterior 
part of the upper arm. The internal border is 
carried well around onto the medial border of the 
arm. The main mass of the muscle arises, by 
means of a stout tendinous raphe, from the latis- 
simus dorsi. A few of the fibers on the medial 
border, representing the medial head of the mus- 
cle, arise from a raphe that is fonned with the 
ventral fibers of the panniculus carnosus. Inser- 
tion is by means of a tendinoxis aponeurosis into 
the posterior and medial parts of the olecranon. 

Action : Extends the forearm. 

M. triceps longus (figs. 88, 95, 96, 133, 134) is 
a complex and extremely powerful muscle, com- 
posed of incompletely separable lateral and medial 
heads. The lateral head is triangular in form, and 
proximally shows an incipient division into a super- 
ficial posterior part and a slightly deeper anterior 
part. It arises, by muscle fibers covered externally 
by tendon fibers, from the proximal two-thirds of 
the axillary border of the scapula. The medial 
head takes a short tendinous origin, deep to that 
of the lateral head, from the axillary border of the 
scapula near the neck. 

The two heads fuse distally, the external fibers 
of the lateral head forming a powerful tendon that 
receives fibers from the triceps lateralis. Insertion 
is into the tip of the olecranon. 

M. triceps lateralis (figs. 88, 95, 134) is a pow- 
erful prismatic muscle running diagonally across 
the external surface of the upper arm and extend- 
ing medially behind the humerus. It has a maxi- 

mum width (near the humero-ulnar articulation) 
of 45 mm.; medially it is continuous with the long 
head of the triceps medialis, except near its origin. 
The muscle arises chiefly from the surface of the 
brachialis lying immediately beneath it. These 
two muscles are covered by a heavy common ten- 
don layer proximally. The common origin begins 
on the surgical neck of the humerus in the area 
immediately behind the deltoid ridge, a few of the 
fibers coming from the articular capsule. The lat- 
eral triceps immediately becomes superficial to the 
brachialis, and takes further extensive origin from 
the surface of the latter, until the two are sepa- 
rated by the brachioradialis. Insertion of the lat- 
eral triceps is made chiefly into the posterolateral 
border of the olecranon, although the distal part 
of the anterior edge of the muscle makes a power- 
ful insertion into the fascia of the forearm and 
posteriorly there is some insertion into the lateral 
head of the triceps longus. 

M. triceps medialis (figs. 96, 133, 134) is the 
smallest of the three heads of the triceps. It is 
composed of two very poorly defined heads, the 
posterior of which is separable from the triceps 
lateralis only for a short distance after its origin. 
The muscle is visible only on the medial surface 
of the arm, where the posterior head appears as a 
narrow muscle lying between the triceps longus 
and the coracobrachialis longus. 

The posterior ( long) head arises from a triangu- 
lar area on the posterior surface of the neck of the 
humerus, the base of the triangle lying against the 
lip of the articular surface. The most superficial 
fibers arise from the joint capsule. It is independ- 
ent of the intermediate head only for about its 
proximal third, the main branch of the radial nerve 
and branches of the profunda brachialis artery and 
vein passing through the interval between them. 
Immediately distad of its origin the lateral (deep) 
edge of this head fuses with the adjacent edge of 
the triceps lateralis, and from this point on, the 
two muscles are completely inseparable. 

The intermediate head of the triceps medialis 
takes an extensive tendinous origin along the pos- 
teromedial side of the shaft of the humerus. Its 
origin extends from a point above the scar for the 
teres major distad almost as far as the end of the 
pectoral ridge. This head has little independence 
from the other head of the triceps medialis. 

Insertion of the fibers coming from the triceps 
medialis is made, without intervention of a ten- 
don, into the medial and dorsomedial surface of 
the olecranon. 

Action: The triceps is the chief extensor of the 
forearm; it also acts (especially the lateralis) as a 
tensor of the forearm fascia. 



M. anconaeus (figs. 95, 134) is a powerful tri- 
angular muscle extending more than one-third the 
distance up the shaft of the humerus. Medially 
it is inseparable from the triceps. It arises from 
the well-marked triangular area on the posterior 
side of the distal end of the shaft of the humerus, 
the origin extending down over the posterior side 
of the lateral epicondyle. Insertion is on the pos- 
terior side of the olecranon, immediately above the 
insertion of the triceps. 

Action: Assists the triceps in extending the 

M. epitrochleo-anconaeus (anconaeus inter- 
nus) is not present as an independent muscle. The 
most medial fibers of the distal part of the triceps 
medialis partly overlie the ulnar nerve and are in- 
nervated by a branch of it, however, and appar- 
ently represent the epitrochleo-anconaeus. These 
fibers insert on the inner side of the olecranon, but 
they arise from the shaft of the humerus some dis- 
tance above the epicondyle. 

C. Muscles of the Forearm 

M. palmaris longus (fig. 96) is single. It is 
square in cross section, and fusiform when viewed 
from the medial side of the forearm. The muscle 
takes a very restricted origin from the medial epi- 
condyle immediately proximad of the origin of the 
humeral part of the flexor carpi ulnaris, from which 
its fibers are incompletely separable near the origin. 
Near the carpus the muscle separates into a stout 
superficial tendon and an entirely separate deeper 
fleshy part. The tendon expands into the palmar 
aponeurosis, while the fleshy part inserts into the 
proximal edge of the transverse fibers of the pal- 
mar aponeurosis (see below), which here form a 
sheath for the tendon. The fleshy part does not 
represent the "palmaris longus internus" of Windle 
and Parsons. 

Action: Flexes the manus and tenses the palmar 

The Aponeurosis palmaris (fig. 96) consists 
chiefly of fibers that arise from the tendon of the 
long palmar muscle and radiate toward the digits. 
The fibers extend about equally to all five digits, 
lying on the palmar surface as far distad as the 
metacarpophalangeal joint. Here the palmar apo- 
neurosis gives way to the vaginal ligaments on the 
volar surface of the digit, although fibers of the 
aponeurosis are continued distad for some distance 
along the sides of the digit. A powerful group of 
fibers arises from the palmar aponeurosis over meta- 
carpal 5 and sweeps transversely across the palm, 
to insert on the distal end of the radial sesamoid. 
The fasciculi transversi of human anatomy could 
not be demonstrated. 

Transverse fibers in the antebrachial fascia cor- 
responding to the Lig. carpi volare are present 
chiefly on the radial side, where they form a wide 
band running across the wrist as far as the tendon 
of the long palmar muscle. 

M. pronator teres (figs. 96, 97, 133) is a flat 
muscle lying partly beneath the brachioradialis. 
It arises from the anterior side of the proximal end 
of the medial epicondyle of the himierus. It is 
inseparable from the adjacent border of the flexor 
carpi radialis for about half the length of the fore- 
arm. The fibers run distad and radial ward, partly 
beneath the brachialis. Insertion is made, mostly 
beneath the insertion of the brachialis, by means 
of a wide aponeurotic tendon into the radial side 
of the distal two-thirds of the radius. 

Action : Pronates the forearm, turning the palm 
upward; flexes the forearm. 

M. flexor carpi radialis (figs. 96, 133) is so in- 
timately united to the pronator teres at its origin 
that the two appear as a single muscle. It arises 
from about the center of the anterior side of the 
medial epicondyle, its origin being continuous with 
that of the pronator teres. The muscle tapers 
gradually toward its insertion, becoming tendi- 
nous on its ulnar side at about the middle of the 
forearm but remaining fleshy down to the carpus 
on its radial side. The stout terminal tendon en- 
ters the hand through an osteofibrous canal lying 
partly beneath the tubercle of the scapholunar, 
and inserts into the base of the second metacarpal 
(fig. 99; Wood-Jones says the second and third 

Action: Flexes the wrist. 

M. flexor carpi ulnaris (figs. 96, 133) consists 
of two completely independent parts, which are 
separated by the ulnar nerve. The pars ulnaris 
is the more superficial, and forms the ulnar con- 
tour of the forearm. It arises, chiefly by fleshy 
fibers, from the posteromedial part of the olecra- 
non. Additional origin is taken medially from the 
fascia of the upper arm; and the lateral border, 
which is tendinous, is continued with the ante- 
brachial fascia for about 70 mm. distad of the 
elbow. The fibers converge to a narrow terminal 
tendon, which inserts on the proximal side of the 
pisiform dorsad of the insertion of the pars humer- 
alis. The pars humeralis lies mostly internal to 
the pars ulnaris. It arises from the distal side of 
the medial epicondyle, where it is inseparable from 
the palmaris longus for a short distance, and ter- 
minates in a wide, flat tendon that inserts on the 
proximal side of the pisiform (fig. 98). 

Action: Flexes the wrist and abducts the hand 
ulna ward. 



M. flexor digitorum sublimis (figs. 97, 98) is 
represented by three small fleshy heads arising from 
the volar surface of the flexor digitorum profundus. 
Proximally their fibers interdigitate inextricably 
with the most superficial head (1) of the profundus. 
The sublimis extends only about the distal third 

quadratus, so that its proximal end extends onto 
the volar surface of the radius. This head lies 
deep to the pronator teres and flexor carpi radi- 
alis, and most of its fibers insert into the tendinous 
part of head L 

(4) A narrow, deep head arises from the medial 

Mm. luitibrieales 

M. brachialis 
M. biceps brachii 

Tendo m. flex dig. prof. 

Tendo m. flex dig. sublimis 

Mm. lumbricales 

M. flex. dig. prof. 
Fig. 97. Deep muscles of right forearm of Ailuropoda, medial view. 

of the forearm. Each of the three parts of the 
sublimis forms a slender terminal tendon beneath 
the transverse carpal ligament. These are distrib- 
uted to digits 2, 3, and 4, and are perforated at 
the metacarpophalangeal joints by the tendons of 
the profundus. Insertion is into the base of the 
second phalanx of the digit. 

Action : Flexes the middle phalanx on the proxi- 
mal phalanx of digits 2-4. 

M. flexor digitorum profundus (figs. 97, 98, 
133, 134) is very powerfully developed. It is com- 
posed of five heads, and terminates in five strong 
perforating tendons that are distributed to the 
digits. Insertion is into the base of the terminal 
phalanx. The structure of the parts of the muscle 
is as follows: 

(1) The most superficial head arises from the 
middle part of the medial epicondyle. It lies along 
the ulnar border of the flexor carpi radialis. Most 
of the tendon fibers arising from this head are con- 
tinued into the tendon of digit 1, but it does not 
form a separate tendon as Wood-Jones (1939a) 

(2) A head arises from the lower part of the 
medial epicondyle, deep to the origins of the pal- 
maris longus and humeral head of the flexor carpi 
ulnaris. Distally this head attaches to the under- 
lying ulnar head (5), in addition to giving rise to 
the three heads of the flexor digitorum sublimis. 

(3) A head arises from the proximal two-thirds 
of the volar surface of the radius; the medial bor- 
der of the origin follows the border of the pronator 

border of the condyle of the humerus, just in front 
of the epicondyle. Its fibers insert on the ulnar 
head (5). 

(5) The ulnar head is by far the largest element 
of the muscle. It arises from the entire volar sur- 
face of the ulna, including the olecranon. The 
distal three-fourths of its volar surface is covered 
with a heavy tendinous aponeurosis, and it is 
chiefly from this aponeurosis that the terminal 
tendons of the flexor digitorum profundus arise. 

Wood-Jones mentions a deep head arising from 
the olecranon ; judging from its position he referred 
to the head arising from the condyle (4). 

Action: Flexes all the digits, especially the ter- 
minal phalanx on the middle phalanx. 

M. pronator quadratus (figs. 96, 133) is an 
extensive, thick fleshy mass, trapezoidal in outline. 
The origin is somewhat narrower than the inser- 
tion, and is taken from the distal third of the volar 
surface of the ulna. The muscle fans out some- 
what to its insertion, which is made into the distal 
half of the volar surface of the radius. 

Action: Pronates the forearm and hand, turn- 
ing the palm upward. 

M. brachioradialis (supinator longus of auth- 
ors) (figs. 95, 96, 133, 134) is very powerfully de- 
veloped, with a width of about 50 mm. on the fore- 
arm. It arises by two heads, which are separated 
by a branch of the radial nerve. One head arises 
from the lateral epicondylar ridge, from a point 
60 mm. proximad of the epicondyle up past the 




middle of the humeral shaft, some of its fibers be- 
ing joined to adjacent parts of the extensor carpi 
radialis longus. The other head arises from the 
deep surface of the triceps lateralis. The two heads 
promptly fuse, and the resulting common mass in- 
serts into the prominence on the radial side of the 
distal end of the radius. 

Action: Flexes the forearm; supinates the fore- 
arm and hand, turning the palm downward. 

M. extensor carpi radialis longus (figs. 95, 
134) arises from the anterior face of the lateral 
epicondylar ridge. Its ulnar border is inseparable 
from the adjacent border of the extensor carpi 
radialis brevis. At about the middle of the fore- 
arm the muscle ends in a relatively slender tendon 
that passes across the carpus, deep to the extensor 
brevis poUicis, to insert into the radial side of the 
second metacarpal, just proximad of the center of 
the bone. 

Action: Extends the hand and abducts it ra- 
dial ward. 

M. extensor carpi radialis brevis (figs. 95, 134) 
IS somewhat more slender than the longus. It is 
more or less inseparable from the longus laterally, 
and is even more closely united to the extensor 
digitorum communis medially, where a tendinous 
septum is formed. It arises from the distal part 
of the lateral epicondylar ridge. It remains fleshy 
somewhat farther distad than the longus, termi- 
nating in a tendon that inserts near the base of the 
third metacarpal, on the radial side of the bone. 

Action: Extends the hand and adducts it ra- 

M. extensor digitorum communis (figs. 95, 
134) is inseparable proximally from the adjacent 
muscles on either side. It arises from the distal 
part of the lateral epicondylar ridge. The muscle 
tapers gradually toward the wrist, becoming very 
narrow at the proximal border of the dorsal carpal 
ligament. It terminates in four tendons, which go 
to the basal phalanges of the second, third, fourth, 
and fifth digits. 

The tendon going to the second digit comes off 
first, about 20 mm. proximad of the others; the 
muscle fibers going to this tendon are quite sep- 
arate from those going to the other three for most 
of the length of the muscle. The tendon to the 
third digit comes off independently at the proxi- 
mal border of the dorsal carpal ligament. The 
tendon to the fourth and fifth digits is common at 
first, dividing after ten or twelve millimeters. The 
tendons go chiefly to the radial sides of the re- 
spective digits. 

Action: Extends digits 2-5. 

M. extensor digitorum lateralis (BNA: ex- 
tensor digiti quinti proprius) (figs. 95, 134) is a 
rather slender muscle arising from the middle part 
of the lateral epicondyle and from the condyle 
itself. At its origin it is more or less inseparable 
from the adjacent borders of the extensor carpi 
ulnaris and the extensor digitorum communis. Be- 
neath the dorsal carpal ligament the muscle forms 
two terminal tendons, which go to the ulnar sides 
of the basal phalanges of digits 4 and 5. 

Action: Assists the common extensor in extend- 
ing digits 4-5. 

M. extensor carpi ulnaris (figs. 95, 134) arises 
by mingled fleshy and tendinous fibers from the 
distal end of the lateral epicondyle and from the 
condyle. At its origin its fibers are more or less 
inseparable from those of the adjacent borders of 
the anconeus and extensor digitoi-um lateralis. The 
flat insertion tendon, which can be separated from 
the dorsal carpal ligament only with difficulty, 
attaches to the tubercle on the ulnar side of the 
base of the fifth metacarpal. 

Action: Extends the hand and abducts it ulna- 

M. supinator (figs. 95, 134) arises from the liga- 
ments surrounding the radiohumeral articulation; 
there is no origin from the lateral condyle of the 
humerus described by Wood-Jones. Insertion is 
into the lateral and dorsal surfaces of the radius, 
from below the head down to the junction of the 
middle and distal thirds. The proximal two-thirds 
of the outer surface of the muscle is covered with a 
heavy tendinous aponeurosis. 

Action: Supinates the forearm and hand, turn- 
ing the palm downward. 

M. abductor pollicis longus (figs. 95, 96, 98, 
134) includes the extensor and long abductor mus- 
cles of the thumb in hiunan anatomy. It is a power- 
ful muscle arising from the anterior (radial) half of 
the dorsal surface of the ulna, from the semilunar 
notch to the head ; from the posterior (ulnar) half 
of the medial surface of the shaft of the radius, 
from the bicipital tubercle to a point just distad 
of the center of the shaft; from the interosseous 
membrane between these areas; and from the cap- 
sule of the elbow joint immediately below the ra- 
dial collateral ligament. At the distal end of the 
radius the muscle fibers converge to a powerful 
compound flat tendon, which passes through the 
deep notch on the medial (thumb) side of the head 
of the radius, to insert into the proximal end of the 
outer surface of the radial sesamoid. The tendon 
is divisible throughout its length into two elements, 
and the more lateral of these shows a tendency to 
subdivide further. There is no attachment to the 



Tendo m. flex, carpi rad, 
M. flex, carpi rad 

Lig. radiocarp. rol. 

Tendo m. abductor poll, longus 

Lig. carpi trans, (cut) 

Os sesamoid, rad. 

M. interosseus 1 
M. oppwnens pollicis 
M. abductor poll, brevis 
M. flex. poll, brevis 

M. flex, carpi uln. 
(pars humeralis) 

R. prof, ro/arw . ubi. 
Os pisiforme 

M. palmaris brevis (cut) 

M. abductor dig. quinti 

Mm. adductores digitorum 

M. interosseus 4 

M. opponens dig. quinti 

Tendo com. m. flex. dig. prof, 

Fig. 98. Deep muscles of palm of Ailuropoda. 

pollex, and the "fascial insertion" of the medial 
slip between the radial sesamoid and the first meta- 
carpal described by Wood-Jones could not be dem- 

Action : Abducts the radial sesamoid bone. 

In a specimen of Procyon lotor the terminal ten- 
don of the abductor longus was separated from the 
scapholunar by the radial sesamoid bone, which 
was closely bound by fascia to the deep surface of 
the tendon. The tendon inserted into the radial 
side of the base of metacarpal 1. In a specimen 
of Ursiis americanus and one of Tremarctos ornatus 
the abductor longus terminated in two tendons 
that passed side by side onto the carpus. The 
larger of these had the normal insertion into the 
base of metacarpal 1, whereas the smaller inserted 
into the radial sesamoid. 

M. extensor indicus proprius (figs. 95, 134) 
is a thin and rather slender muscle arising from 

the middle third of the doi^sal border of the ulna 
and extensively from the underlying surface of the 
abductor pollicis longus. Just before reaching the 
base of the carpus the muscle forms two terminal 
tendons, which pass diagonally across the carpus 
and metacarpus to insert into the base of the first 
phalanges of digits 1 and 2. The tendon to digit 2 
is considerably the larger, and fibrous bands are 
carried across from it to digit 1. 

Action : Assists the common extensor in extend- 
ing digits 1-2. 

D. Muscles of the Hand 

M. palmaris brevis (figs. 96, 98) does not seem 
to have been described hitherto in a carnivore. In 
Ailuropoda a small group of muscle fibers arising 
from the anterior face of the pisiform and inserting 
partly into the palmar aponeurosis and partly into 
the skin in front of the outer carpal pad can only 



represent this muscle. The fibers going to the 
palmar aponeurosis extend part way across the 
flexor digiti quinti brevis, while those going to the 
skin arch laterad. Innervation is by a twig from 
the palmar division of the deep branch of the ulnar 
nerve, and the blood supply is by a short twig from 
the branch of the mediana propria that supplies 
the outer side of digit 5. 

Action: Helps to cup the palm of the hand. 

M. abductor pollicis brevis (fig. 98) is incom- 
pletely separable from the opponens and short 
flexor. It is represented by a group of fibers ly- 
ing at the distal border of the interspace between 
the radial sesamoid and the pollex. Origin is from 
the inner face of the radial sesamoid, and insertion 
into the radial side of the base of the first phalanx 
of the pollex. 

Action : Adducts the radial sesamoid bone. 

M. flexor pollicis brevis (fig. 98) is a slender 
muscle incompletely separable from the abductor 
pollicis brevis. Origin is from the transverse car- 
pal ligament and the scapholunar near the base 
of the first metacarpal. The muscle inserts into 
the radial side of the base of the pollex, close to the 
insertion of the abductor. 

Action: Flexes and abducts the pollex. 

M. opponens pollicis (fig. 98) is a large muscle 
occupying most of the interspace between the ra- 
dial sesamoid and the pollex. It arises extensively 
from the inner face of the radial sesamoid, and in- 
serts with the short abductor into the radial side 
of the first phalanx of the pollex. 

Action: Adducts the radial sesamoid bone. 

In a specimen of Procyon lotor the short muscles 
of the pollex were represented by a superficial and 
a deep element, which arose from the transverse 
carpal ligament and the scapholunar (no relation 
with the radial sesamoid), and inserted into the 
radial side of the base of the first phalanx. In a 
specimen of Ursus americanus and one of Tre- 
marctos ornatus these short muscles of the pollex 
were represented by a single muscle mass, which 
arose extensively from the radial sesamoid in addi- 
tion to the origin from the carpal ligament and 

M. abductor digiti quinti (figs. 96, 98) is a 
large muscle arising extensively from the anterior 
and dorsal surfaces of the pisiform. The fibers 
converge to a tendon that inserts partly into the 
underlying surface of the opponens digiti quinti, 
and partly continues on to the ulnar side of the 
base of the first phalanx of digit 5. 

Action: Abducts and flexes the fifth digit. 

M. flexor digiti quinti brevis (figs. 96, 133) is 
composed of two heads, one deep to the other, that 
insert by a common tendon. The superficial head 
arises exclusively from the connective tissue pad 
over the pisiform, whereas the deep head arises 
partly from the inner border of the pisiform and 
partly from the superficial layer of the transverse 
carpal ligament. The common tendon gives off a 
slip to the base of the first phalanx of digit 5, but 
most of its substance is continued to the base of 
the second phalanx. 

Action : Flexes the proximal phalanges of digit 5. 

M. opponens digiti quinti (figs. 96, 98) is a 
powerful fleshy muscle arising by two heads. One 
head takes origin from the tip of the unciform and 
the adjoining part of the deep layer of the carpal 
ligament. The other head arises from the anterior 
surface of the pisiform, deep to the origin of the 
abductor. Insertion, as Wood-Jones pointed out, 
is into the sesamoid on the ulnar side of the meta- 
carpophalangeal joint of digit 5. 

Action: Flexes and adducts the fifth metacarpal. 

Mm, lumbricales (fig. 97) occupy the usual 
position between the tendons of the flexor digi- 
torum profundus. Origin is from the wide com- 
mon tendon of the flexor digitorum profundus, 
from which four bellies radiate into the interten- 
dinous spaces. Insertions are made by means of 
flat tendons into the radial sides of the bases of the 
second phalanges of digits 2 to 5. 

Action: Flex the basal phalanges of digits 2-5 
and draw them toward the thumb. 

Mm. adductores digitorum (superficial pal- 
mar muscles, Wood-Jones) (fig. 98). The most 
superficial layer of palmar muscles cannot be ho- 
mologized with the interossei of human anatomy; 
the belly going to the thumb represents the ad- 
ductor pollicis of man. Three bellies arise together 
from the transverse carpal ligament and the fascia 
covering the underlying carpal bones. The largest 
belly goes to the radial side of the base of the first 
phalanx of the fifth digit. Another belly goes to 
the ulnar side of the first phalanx of the pollex. 
The middle, and by far the smallest, belly goes to 
the ulnar side of the second digit. Wood-Jones 
described a fourth very slender belly to the third 
digit; this slip was absent in our specimen. 

Action: Flex the digits; draw digits 1 and 5 
toward the midline of the hand. 

In a specimen of Ursus americanus the arrange- 
ment of these muscles was identical with our speci- 
men of Ailuropoda. 

Mm. interossei (fig. 99) are composed of four 
groups of muscles, made up of ten separate slips. 
The first group arises from the base of the first 



metacarpal, and is made up of two slips: these go 
to the ulnar side of the pollex and the radial side 
of digit 2, respectively. The second gi'oup arises 
from the third metacarpal, and is made up of three 

any importance to its absence in the panda. Ailu- 
ropoda differs from the bears, and apparently from 
all other carnivores, in the distinctness of the two 
heads of the brachialis. 

Os scapJwlunare Os magnum 

O.s trapezoid \ I Os unciforme 

Os cuneijorme 

Tendo m. flex, carpi rad. 
Os trapezium 
Lig. carpi trans, {cut)-^^ 

Os sesamoid, rad. 
M. interosseus 1 

Os pisiforme 
Lig. carpi trans, (cut) 

M. interosseus 4 
M. opponens dig. quinti 

Fig. 99. Interosseous muscles of manus of Ailuropoda. 

slips; two of these go to either side of digit 2, while 
the third, which is very slender, goes to the radial 
side of digit 3. The third group arises from the 
fourth metacarpal, and is made up of three heads ; 
two of these go to either side of digit 3, the third 
going to the ulnar side of digit 4 ; a few of the fibers 
are also contributed to the ulnar side of digit 4. 
The fourth group arises from the fifth metacarpal, 
and is made up of two heads; one goes to the ulnar 
side of digit 4, the other to the radial side of digit 5. 

Action : Flex the phalanges on the metacarpals. 

M. flexor brevis digitorum manus is absent. 
This muscle is also absent in bears, but is present 
in all procyonids. It inserts into the vaginal sheath 
of digit 5. 

E. Review of Muscles of the Fore Limb 

In general the muscles of the fore limb in Ailu- 
ropoda agree closely with those in Ursus. Often 
correspondence extends down to minor details of 
muscle structure and attachment sites. In the 
tabulation of myological characters (p. 197) the 
panda and the bears disagree in only one point: 
the short head of the biceps, usually present in 
Ursus, is absent in Ailuropoda. Since this head 
is known to be variable in Ursus, I do not attach 

There is a generalized increase in the mass of the 
musculature in the anterior part of the body, par- 
ticularly in the neck, shoulder, and upper arm. 
This is evident in a direct comparison of individual 
muscles with those of Ursus and in the heavy sur- 
face modeling on the scapula and humerus, and it 
is indicated in the relative weights of the muscula- 
ture of the fore and hind limbs (Table 15, p. 195). 
I can find no functional reason for this heavy mus- 
culature. This is the region of the body closest 
to the head, and furthermore there is a gradient 
away from the head: the neck and shoulder mus- 
culature is most affected, the upper arm less so, 
and the lower arm and hand least. This strongly 
suggests a generalized regional effect, centered in 
the head and decreasing in a gradient away from 
the head, similar to that seen in the skeleton. 

The most distinctive feature of the fore limb in 
Ailuropoda is the enlarged and mobile radial sesa- 
moid bone. The muscles associated with this bone 
in the panda are the palmaris longus, the opponens 
pollicis, and the abductor pollicis longus and brevis. 
Normally in carnivores these muscles insert into 
the base of the thumb, and the radial sesamoid is 
a typical sesamoid bone developed in the tendon 
of the long abductor where it glides over the scapho- j 
lunar. In bears, however, the radial sesamoid isj 





Wt. in 
gms. % 

Supraspinatus 122 

Infraspinatus 1 19 

Acromiodelt. +Spinodelt 85 

Teres major 72 

Subscapularis +Teres minor 168 

Biceps 75 

Coracobrachialis 16 

Brachialis 52 

Epitrochlearis 58 

Triceps longus 189 

Triceps lateralis 95 

Triceps medius 55 

Anconaeus 26 



Totals 1132 100.0 

* Half-grown individual (Su Lin). 
** Data from Haughton. 


Wt. in 
gms. % 

















1309 100.2 



amerieanus** familiaris* 

% % 








Leo Uo** 









enlarged and the basic panda condition of the mus- 
cles already exists: the terminal tendon of the long 
abductor ends partly in the radial sesamoid (p. 179), 
and the short muscles (brevis and opponens) at- 
tach extensively to the radial sesamoid. In other 
words, all elements attaching to the radial sesa- 
moid in Ailuropoda already have some attachment 
to this bone in Ursus, apparently simply as a me- 
chanical result of the enlargement of the sesamoid 
in bears. The step from the bear condition to the 
panda condition involves only a further shift of 
muscle attachments in favor of the sesamoid, and 
such a shift would probably result automatically 
from the further enlargement of the sesamoid bone: 
the size of the bone simply blocks off the tendon of 
the long abductor from the poUex, and the short 
muscles from their original attachment sites on the 
transverse carpal ligament and the scapholunar. 
Thus, the musculature for operating this remark- 
able new mechanism functionally a new digit- re- 
quired no intrinsic change from conditions already 
present in the panda's closest relatives, the bears. 
Furthermore, it appears that the whole sequence 
of events in the musculature follows automatically 
from simple hypertrophy of the sesamoid bone. 

Other subtle differences in the musculature, im- 
portant from the functional standpoint, are revealed 
by comparing the relative masses of individual 
muscles. Such data are available for the shoul- 
der and arm in a series of carnivores (Table 14). 
These figures reveal that in the panda and the 
bears the medial rotator of the arm (subscapu- 
laris), the abductor of the arm (deltoid), and the 
flexors of the elbow (biceps, brachialis) are rela- 
tively large, whereas in the dog (the horse is very 
similar) the extensors (supraspinatus, triceps) are 
dominant. The lion tends to be intermediate be- 

tween the panda-bear condition and the dog-horse 
condition. These muscle-mass relations are obvi- 
ously correlated with the differing mechanical re- 
quirements in a limb used for ambulatory walking 
and prehension versus one used for cursorial run- 
ning. The morphogenetic mechanisms through 
which such anatomical differences are expressed, 
and thus the basis on which natural selection could 
operate, are unknown. Indeed, in view of Fuld's 
data on bipedal dogs (p. 148), it is not even 
certain that differences in muscle-mass relations 
among related forms are intrinsic to the muscu- 

A. Muscles of the Hip 

1. Iliopsoas Group 

M. psoas major (fig. 100) lies ventrad of the 
medial part of the quadratus lumborum. It arises, 
by successive digitations, from the bodies and 
transverse processes of all the lumbar vertebrae. 
Each slip has a double origin: medial fibers arise 
from the side of the body of the vertebra, and lat- 
eral fibers from the transverse process; a part of 
the quadratus lumborum is embraced between. 
The muscle is joined posteriorly by the iliacus, 
and inserts by a wide common tendon with it into 
the lesser trochanter. 

M. iliacus (fig. 100) is a small muscle arising 
from the ventral face of the ilium. It is more or 
less inseparable from the psoas major medially, 
and inserts by a common tendon with it into the 
anterior border of the lesser trochanter. The fibers 
of the iliacus insert into the ventral part of the 



M. quadratus lumborum 

M. iliocostalis 
M. psoas minor. 

M. psoas major. 
M. iliacus 

M. iliopsoas 

M. obturator extemus 

M. quadratus femoris 

Fig. 100. Deep muscles of back and hip of Ailuropoda, ventral view. 

M. psoas minor (fig. 100) lies deep to (ventrad 
of) the psoas major, from which it is entirely free. 
It arises from the bodies of the last thoracic and 
first three lumbar vertebrae, and inserts by a stout 
flat tendon into the ilium just above the iliopec- 
tineal eminence. 

Action: The iliopsoas flexes the thigh and ro- 
tates the femur laterally. When the thigh is fixed, 
it flexes the pelvis on the thigh. 

2. Gluteal Group 

The gluteal muscles arise chiefly from the ilium, 
and in Ailuropoda they have been affected by the 



reduction in the area of the wing of the ilium. This 
reduction in attachment area is not reflected in 
their mass, which is relatively greater than in any 
other carnivore examined. As often happens when 
the area available for muscle attachment is re- 
stricted, the muscles of the gluteal group tend to 
fuse and to extend their areas of origin to fascia. 
The insertions of these muscles do not differ much 
from those of Ursus. 

M. glutaeus superficialis (figs. 88, 138) is a 
broad, thin, fan-shaped sheet completely covering 
the middle and deep gluteals. It arises, by a wide 
aponeurosis tightly adherent to the underlying 
fascia of the middle gluteal, from the iliac crest, 
the lumbodorsal fascia over the last lumbar ver- 
tebra, the entire sacral fascia, the fascia over the 
first caudal, and, by fleshy fibers, from the ante- 
rior border of the ischial tuberosity directly above 
the attachment of the sacrotuberous ligament. It 
has no attachment to the transverse processes of 
the sacrals or caudals, or to the sacrotuberous liga- 
ment. In addition, the anteriormost fibers are 
reflected around the anterior border of the middle 
gluteal onto the deep surface of the middle gluteal, 
to insert with these middle gluteal fibers into the 
fascia covering the dorsal surface of the iliopsoas. 

Anteriorly the superficial gluteal borders on the 
sartorius and tensor fasciae latae, posteriorly on 
the semimembranosus and biceps. It is not com- 
pletely separable from the tensor. Its fibers con- 
verge rapidly to a stout tendon, which inserts into 
the prominent scar below the great trochanter. 
There is a large gluteofemoral bursa beneath the 
muscle at its insertion. 

Action : Flexes the thigh and rotates the femur 

M. glutaeus medius (figs. 88, 138) is the most 
powerful element of the gluteal complex, although 
it exceeds the mass of the superficial gluteal much 
less than in other carnivores. It consists of a sin- 
gle heavy fan-shaped layer, 85 mm. wide, com- 
pletely hidden beneath the superficial gluteal. It 
is not completely separable from the underlying 
deep gluteal. Anterior to the greater sciatic notch, 
origin is from the lumbodorsal fascia and from the 
gluteal surface of the ilium; posterior to the notch, 
origin is from the lateral edge of the crest formed 
by the fused transverse processes of the sacral ver- 
tebrae. Insertion is by mingled muscle and tendon 
fibers into the dorsal and anterior borders of the 
great trochanter. 

Action: Extends and abducts the thigh. 

M. glutaeus profundus (fig. 138) is the small- 
est of the gluteal muscles. It lies entirely beneath 
the middle gluteal, from which it is separated by a 

large trunk of the superior gluteal nerve; its bor- 
ders conform rather closely to those of the medius. 
The profundus consists of a single wide layer, 
somewhat thinner than the medius. Origin is from 
almost the entire inferior gluteal line, beginning a 
short distance behind the anterior superior iliac 
spine and continuing posteriorly onto the body of 
the ilium in front of the acetabulum. Insertion is 
by a wide tendon into the anterior border of the 
great trochanter, deep to the insertion of the mid- 
dle gluteal. 

Action: Abducts the thigh and rotates the fe- 
mur medially. 

M. tensor fasciae latae (figs. 88, 137, 138) is 
not completely separable from the adjacent bor- 
der of the superficial gluteal. It arises from the 
lateroventral edge of the ilium, along a line run- 
ning caudad from the crest. It inserts into the 
fascia lata in a curved line, convex distally, that 
begins at the prominence for the insertion of the 
superficial gluteal and ends at about the middle 
of the thigh. 

Action: Tenses the fascia lata and assists the 
superficial gluteal in flexing the thigh and rotating 
it medially. 

3. Obturator Group 

M. gemellus anterior (figs. 88, 138) is com- 
pletely free from the obturator internus. It is a 
small muscle arising from the ischium along the 
lesser sciatic notch anterior to the ischial spine. 
The fibers converge to insert into the anterior part 
of the internal obturator tendon for a distance of 
20 mm. 

M. piriformis (figs. 88, 138) is completely dis- 
tinct from the middle gluteal, its anterior third 
being overlapped by the posterior part of the mid- 
dle gluteal. Origin is from the antero-inferior bor- 
der of the sciatic notch (as in Ursu^) and from the 
lateral edge of the fused transverse processes of 
the sacral vertebrae. Insertion is made by min- 
gled muscle and tendon fibers into the dorsal (prox- 
imal) border of the great trochanter, deep to the 
insertion of the middle gluteal. 

Action: Abducts the femur. 

M. obturator internus (fig. 138) is much 
smaller than the external obturator, as in the 
Ursidae. It has the usual origin from the pelvic 
surfaces of the pubis and ischium where they form 
the margin of the obturator foramen. The fibers 
converge to a long flat tendon that passes out over 
the lesser sciatic notch, to insert into the trochan- 
teric fossa of the femur. There is a large mucous 
bursa beneath the obturator tendon where it passes 
over the ischium. 



Action: Abducts the femur and rotates it lat- 

M. gemellus posterior (fig. 138) is larger than 
the anterior gemellus, and, like it, is free from the 
internal obturator. It arises from the ischium im- 
mediately in front of the tuberosity and beneath 
the sacrotuberous ligament. Insertion is narrow 
and by means of tendon fibers, into the posterior 
edge of the tendon of the internal obturator. In- 
sertion of the posterior gemellus is distad of the 
insertion of the anterior gemellus. 

Action: Abducts the femur and rotates it lat- 

M. quadratus femoris (figs. 88, 100, 138) is a 
stout quadrilateral muscle arising from the dorsal 
third of the lateral surface of the ramus of the 
ischium, directly below the ischial tuberosity. In- 
sertion is by means of a short tendinous aponeu- 
rosis into the crescentic inter-trochanteric line. 

Action: Extends the thigh and rotates the fe- 
mur laterally. 

M. obturator externus (figs. 100, 138) is of 
the usual triangular form. It arises from the lat- 
eral surface of the ascending ramus of the pubis, 
from the pubis and ischium along the symphysis, 
from the descending ramus of the ischium caudad 
of the obturator foramen, and from the external 
surface of the obturator membrane. The fibers 
converge strongly to a powerful tendon, which is 
inserted into the proximal part of the trochanteric 

Action : A powerful lateral rotator of the thigh 
and a weak extensor and adductor. 

B. Muscles of the Thigh 

M. semimembranosus (figs. 88, 89, 137, 138, 
140) is divided, as in other carnivores, into two 
subequal parts: an anterior belly that inserts into 
the femur, and a posterior belly that inserts into 
the tibia. These arise together from the postero- 
lateral surface of the descending ramus of the 
ischiimi immediately below the origin of the bi- 
ceps and semitendinosus. They promptly divide 
and run distad, diverging slightly in their course. 

The anterior belly lies at first mostly mesad of 
the posterior belly. It inserts, by fleshy fibers, 
chiefiy into the medial epicondyle of the femur 
just anterior to the origin of the medial head of 
the gastrocnemius. The line of origin continues 
distad onto the tibial collateral ligament. The 
posterior belly inserts, by mingled fleshy and ten- 
don fibers, into the infraglenoid margin of the 
median condyle of the tibia. 

Action: (1) extends the thigh; (2) flexes the leg. 

M. semitendinosus (figs. 88, 89, 138) arises 
from the ischial tuberosity only; there is no extra 
head from the caudal vertebrae. Origin is by short 
tendon fibers, above and partly behind the origin 
of the biceps. Insertion is made for the most part 
by a short flat tendon, 50 mm. in width, into the 
anterior crest of the tibia, beneath the insertion of 
the sartorius. The posterior fibers are continued 
distad into the fascia of the lower leg. 

Action: (1) extends the thigh; (2) flexes the leg. 

M. sartorius (figs. 88, 89, 137, 139) is a single 
fiat band lying superficially on the median and an- 
terior sides of the thigh. It arises, by mixed fieshy 
and tendon fibers that are continuous with those 
of the middle gluteal dorsally, from the anterior 
superior iliac spine and the inguinal ligament. In- 
sertion is made in a long sinuous line running along 
the medial border of the patella, across the liga- 
ments of the knee joint, and down along the me- 
dial side of the anterior crest of the tibia for about 
half its length. 

Action: (1) flexes the thigh; (2) flexes the leg. 

M. rectus femoris (figs. 88, 89, 103, 137) is a 
fusiform muscle wedged in between the vastus lat- 
eralis and vastus medialis; it is intimately associ- 
ated with both these muscles distally. The rectus 
arises by two short stout tendons that attach close 
together, one above the other, to a prominent 
roughened scar on the anterior lip of the acetab- 
ulum. Almost the entire deep surface of the mus- 
cle is covered with a glistening tendinous aponeu- 
rosis, but this does not form a terminal tendon. 
Insertion is into the proximal border of the patella, 
partly by fleshy fibers and partly by fibers of the 
tendinous aponeurosis. 

Action : Extends the leg and flexes the thigh. 

M. vastus lateralis (figs. 88, 102, 103, 138-140) 
is, as usual, the largest component of the quadri- 
ceps extensor group. It is completely inseparable 
from the vastus intermedius throughout its entire 
length. Origin is from the posterolateral surface 
of the great trochanter and the shaft of the femur 
in a narrow line along the lateral lip of the linea 
aspera nearly down to the lateral epicondyle. At 
its distal end it fuses with the rectus femoris and 
inserts in connection with it into the dorsal and 
lateral borders of the patella. 

Action: Extends the leg, assisted by the other 
muscles of the quadriceps femoris. 

M. pectineus (figs. 89, 137) is a wedge-shaped 
muscle lying between the adductor and the vastus 
medialis. It may with difficulty be separated into 
two layers: an anterior ("superficial") and a pos- 
terior ("deep"). It is easily separable from the 
adductor except at its insertion. Origin is by a 



thin flat tendon from the crest on the anterior 
border of the ascending ramus of the pubis, from 
the iHopectineal eminence nearly to the symphy- 
sis. The tendon of origin is intimately united, on 
its superficial surface, with the prepubic tendon 
(p. 166). Insertion is by a flat tendon, which be- 
comes increasingly heavy distally, into the middle 
third of the medial lip of the linea aspera. The 
insertion line terminates inferiorly at the level 
where it meets the femoral vessels emerging from 
the hiatus adductorius. The anterior layer is in- 
nervated by N. femoralis, the posterior by N. ob- 

Action: Adducts and flexes the thigh and ro- 
tates the femur laterally. 

M. gracilis (figs. 89, 137) arises by mingled ten- 
don and fleshy fibers from the entire length of the 
short symphysis and for some distance up the an- 
terior border of the descending ramus of the pubis 
anteriorly, and about half way up the posterior 
edge of the descending ramus of the ischium pos- 
teriorly. It is a flat muscle about 70 mm. in width, 
covering the posteromedial surface of the thigh. 
It inserts by means of a short tendinous aponeu- 
rosis into the medial side of the proximal end of the 
tibia, immediately behind the insertion of the sar- 
torius. The posterior fibers are continued distad 
into the fascia of the lower leg. 

Action: (1) adducts the thigh; (2) flexes the leg. 

M. adductor (figs. 88, 89, 102, 137, 138) can- 
not be separated with any certainty into a magnus, 
longus, and brevis. As in Ursus (original obser- 
vation), it is composed of a continuous sheet that 
is reflected back on itself at its distal (posterior) 
edge to form a double-layered muscle with a deep 
pocket separating the two layers; the pocket is 
open proximally and posteriorly. This is strikingly 
similar to the structure of the pectoralis major of 
man as described by Zuckerkandl (1910). 

The anterior layer of the adductor arises in a 
long narrow U-shaped line that descends along the 
ventral half of the external surface of the acetab- 
ular ramus of the pubis, crosses the entire length 
of the symphysis pelvis, and ascends nearly half 
way up the descending ramus of the ischium. The 
posterior layer arises from a relatively small area 
on the external face of the descending ramus of 
the ischium, deep to the anterior layer and directly 
adjoining the area of origin of the external obtu- 
rator. The anterior layer of the adductor is very 
wide and thin at its origin, the posterior layer nar- 
row and relatively thick. 

The two layers insert side by side into the linea 
aspera (which is very poorly defined in Ailuropoda 
and the bears), on the posterolateral side of the 

shaft of the femur. Insertion begins proximally 
just below the level of the third trochanter. The 
posterior layer is intimately associated with the 
pectineus at its insertion. Distally, at the distal 
sixth of the shaft of the femur, both layers leave 
an opening, the hiatus adductorius, for the passage 
of the femoral vessels. Distad of the hiatus, inser- 
tion is by muscle fibers into the medial side of the 
posterior surface of the femur, including the medial 
epicondyle and the adjacent popliteal surface. 

Action: Adducts and extends the thigh. 

M. biceps femoris (figs. 88, 138) is completely 
differentiated from the glutaeus superficialis and 
tensor fasciae latae. It is composed of a single 
head; the small posterior head, which is partly dif- 
ferentiated in Ursus and completely separate prox-. 
imally in Canis, is indistinguishable in Ailuropoda. 
The muscle arises, by a short stout tendon, from 
the lateral part of the ischial tuberosity; no fibers 
come from the caudal vertebrae or the sacrotuber- 
ous ligament. The muscle expands rapidly into a 
fan-shaped sheet, reaching a width of 185 mm. at 
its distal end. Near its insertion the muscle ter- 
minates abruptly in a continuous wide aponeuro- 
sis that passes into the fascia lata proximally and 
the crural fascia below the knee. Insertion is thus 
indirectly into the lateral side of the patella, the 
patellar ligament, and the anterior crest of the 
tibia. The most distal part of the aponeurotic 
sheet turns abruptly distad and caudad to the 
tuber calcis. Insertion of the biceps thus extends 
from immediately above the knee to the heel, the 
most distal extension of the biceps insertion known 
to me for any carnivore. 

Action: The muscle is chiefly a flexor of the leg; 
the anteriormost fibers extend the thigh. 

M. abductor cruris posterior (abductor cruris 
caudalis; Ziegler, 1931; Baum and Zietzschmann, 
1936). This muscle was present on the left limb 
only, as a narrow, rope-like tract of fibers. Origin 
was from the ischial tuberosity immediately be- 
neath the biceps, wedged in between the biceps 
and the quadratus femoris. The muscle ran distad 
deep to the biceps and inserted into the posterior 
surface of the femur a few millimeters above the 
condyles. Innervation was by a branch of the 
sciatic nerve. 

This muscle is well known in the dog, where it 
forms a ribbon-like band arising from the sacro- 
tuberous ligament and inserting into the crural 
fascia. It is described by Shepherd (1883) for Ur- 
sus americanus under the name "lesser portion of 
the adductor," and by Carlsson (1925) for Ursus 
arctos under the name "caudo-femoralis,"' as aris- 

' Carlsson's "femoro-coccygeus" is the caudofemoralis of 
Windle and Parsons and the abductor cruris cranialis of 



ing from the ischial tuberosity and inserting into 
the distal part of the femur, as here described for 
Ailuropoda. The muscle is unknown from other 

M. tenuissimus (fig. 88) arises from the fascia 
over the posterior border of the gluteus superfici- 
ahs, immediately anterior to the origin of the bi- 
ceps femoris. The muscle, which is a narrow 
ribbon only about 12 mm. wide throughout most 
of its length, lies wholly beneath the posterior bor- 
der of the biceps femoris. At the distal end of the 
biceps the tenuissimus is continued into the same 
fascia as that by which the biceps inserts. 

Action: Assists the biceps in flexing the leg. 

M. vastus intermedius lies beneath the vastus 
lateralis, and the two muscles are inseparable. Ex- 
tensive origin is taken from the shaft of the femur 
between the origins of the vastus lateralis and the 
vastus medialis, from the greater trochanter distad 
nearly to the patellar surface. Insertion is into 
the capsule of the knee joint. 

M. vastus medialis (figs. 89, 139) is triangular 
in cross section. It arises by a heavy aponeurosis 
along nearly the entire length of the posteromedial 
border of the femur. Origin begins on the neck 
just below the articular capsule and extends along 
the linea aspera to within a few millimeters of the 
medial epicondyle. Insertion is into the proximal 
and medial borders of the patella. 

Action : Assists the other quadriceps muscles in 
extending the leg. 

C. Muscles of the Leg 

M. gastrocnemius (figs. 101, 138, 140) consists 
of the usual lateral and medial heads, the edge of 
the plantaris appearing on the surface between 
them. The medial head is slightly smaller than 
the lateral. It arises, by mingled tendon and fleshy 
fibers, from the medial condyle of the femur. At 
the junction of the middle and lower thirds of the 
leg it forms a flat tendon that joins the tendon of 
the lateral head. The lateral head is fused insep- 
arably with the plantaris proximally, although a 
cross section of the two muscles shows a fibrous 
septum between them; distally, where the gastro- 
cnemius becomes tendinous, they are easily sep- 
arable. The common origin of the two muscles is 
from the lateral condyle of the femur. The termi- 
nal tendon of the lateral head of the gastrocnemius 
is smaller than that of the medial head. The two 
unite and insert into the outer side of the calca- 
neus. There is no sesamoid in the origin of either 

Action: Extends the foot; flexes the knee. 

M. plantaris (fig. 101) is inseparable from the 
lateral head of the gastrocnemius proximally, and 
arises with it from the lateral condyle of the femur 
(fig. 102). It forms a stout tendon distally, which 
twists around that of the gastrocnemius so that it 
comes to lie externally, and spreads out over the 
calcaneus. The aponeurosis-like tendon, which 
attaches to the distal end of the calcaneus on either 
side, is continuous with the plantar aponeurosis. 

Action : Assists the gastrocnemius in extending 
the foot and flexing the knee. 

M. soleus (figs. 101, 140) is enormously devel- 
oped, greatly exceeding the combined heads of the 
gastrocnemius in size. It is a flattened fusiform 
muscle, 57 mm. in greatest width. Origin is by 
fleshy fibers from the posterior side of the head of 
the fibula and the lateral condyle of the tibia, from 
the distal end of the fibular collateral ligament, 
and extensively from the intermuscular septum 
between it and the peroneus brevis. Insertion is 
into the calcaneus, with considerable attachment 
also to the deep surface of the common tendon 
formed by the plantaris and the lateral head of the 

Action: Extends the foot. 

M. popliteus (figs. 102, 140) is an extensive 
and rather heavy triangular sheet arising by a 
powerful flat tendon from the outer side of the 
lateral condyle of the femur. Insertion is into a 
long triangular area mesad of the popliteal line on 
the posteromedial surface of the tibia, for its proxi- 
mal two thirds. 

Action: Flexes the leg and rotates it medially. 

M. flexor digitorum longus (flgs. 102, 140) 
arises almost entirely from the underlying surface 
of the tibialis posterior; its origin reaches the tibia 
only behind and below the lateral condyle, where 
a few of the fibers gain a tendinous attachment. 
The exposed posterior surfaces of the flexor digi- 
torum longus and the tibialis posterior are covered 
by a common continuous layer of tendinous fascia 
where they lie beneath the popliteus. The tendon 
of the flexor digitorum longus, which is smaller 
than that of either the flexor hallucis longus or the 
tibialis posterior, lies in a groove behind the me- 
dial malleolus in company with the tendon of the 
tibialis posterior. It joins that of the flexor hallu- 
cis longus from the medial and deep sides to form 
the conjoined tendon. 

Action: Flexes the phalanges of all the toes. 

M. flexor hallucis longus (figs. 102, 140) is the 
largest of the deep flexor muscles, as is usual in 
carnivores. Origin is from the posterior surface of 
the shaft of the fibula throughout nearly its entire 
length, from the interosseous membrane between 

Lig. coll. fibulare 

M. plantaris 

M. gastrocnemius (cap. lat.). 

M. soleus 

Tendo m. gastrocnemius (cap. med.V 

Tendo m. plantaris 

Tendo m. biceps femoris icut) 
Lig. trans, cruris 

Tuber calcanei 

Lig. cruciatum crurii 

M. abductor dig. quinti 

Aponeurosis platitar is icul) 

M. flex. dig. quinli brevis 

M. tibialis ant. 
.M. ext. dig. longua 

M. peronaeus Jongui 
M. peronaem tertius 

M. peronaeus brevia 

Tendo m. peronaei tertii 

M. ext. dig. brevis 

Fig. 101. Muscles of the right leg of Ailuropoda, lateral view. 


M. ftddoctor magnus. 

M. gastTocDcmini (cap. iiied.\ 

M. semimemfaraQosQS, 

M. flex, haltucis brevis 

Lin. ^- Jtbuian 

M. \-astus lateralis 

gastroc (cap. iat.) 

M. flex, balhins kwgas 

M. peronaevE tolitB 
M. perooaeiK brevis 

Tuber cakaei 
.Tendo peronaeus kngiB 
Aportemnsis plamtariM (otf) 

M. ^xiuctcr dig. quinti 

M. Hex. dip. bmis 

Accessor>- slips of flex. d;g. brevis 

M. flex. dig. quinti brevis 
Mm. lumbrica^es 

flex dig. longus 

Fig. 102. Muscles of the right leg of AUuropodOt posterior view. 




the fibula and tibia, from the adjacent lateral sur- 
face of the tibia, and from the septum between the 
muscle itself and the peroneal muscles. Proxi- 
mally a very definite group of fibers arises from 
the fibular collateral ligament. The muscle is bi- 
pennate, the tendon beginning at the juncture of 
the proximal and middle thirds. The tendon, 
which is very powerful, is joined by that of the 
flexor digitorum longus. The resulting conjoined 
tendon breaks up at the proximal end of the meta- 
tarsals into five slips, which are distributed to the 
digits. Each perforates the tendon of the flexor 
digitorum brevis at the metatarsophalangeal joint, 
and inserts into the terminal phalanx. 

Action: Flexes the phalanges of all the toes. 

M. tibialis posterior (fig. 102) is hidden be- 
neath the popliteus proximally, and partly beneath 
the flexor digitorum longus distally. Origin, from 
the posterior surface of the shaft of the tibia lat- 
eral to the popliteal line, extends nearly the entire 
length of the shaft. The stout terminal tendon, 
after passing through the malleolar groove behind 
the medial malleolus, passes across the neck of the 
astragalus to its insertion on the tibial sesamoid. 

Action: Inverts and extends the foot. 

M. tibialis anterior (figs. 101, 103, 139) is in- 
completely separable into two parts; this is true 
even of the proximal part of the terminal tendon. 
The separation involves only the superficial fibers, 
the deeper fibers refusing to separate. Origin is 
from the anterior surface of the lateral condyle of 
the tibia and the proximal third of the lateral sur- 
face of the shaft of the tibia, with a delicate origin 
from the proximal half of the fibula. At the distal 
end of the tibia the muscle forms a powerful flat 
tendon, which inserts into the outer side of the 
base of the first metatarsal. 

Action : Inverts and flexes the foot. 

M. extensor digitorum longus (figs. 101, 103, 
139) arises by a long narrow tendon from a pit on 
the external condyle of the femur. The muscle 
expands gradually as it passes distad, reaching a 
maximum over the distal end of the tibia. The 
muscle becomes tendinous at the tarsus. The four 
terminal tendons go to the phalanges of digits 2-5; 
that to digit 2 is extremely slender and arises as a 
slip from the tendon to digit 3. 

Action: Flexes the ankle joint; extends the four 
lateral toes, with eversion of the foot. 

M. extensor hallucis longus (figs. 103, 139) is 
a rather slender muscle arising from the distal half 
of the medial surface of the fibula; it forms a raphe 
with the peroneus brevis throughout the length of 
of its origin. The terminal tendon, which compares 
with those of the extensor digitorum longus in size, 

inserts into the terminal phalanx of the hallux, 
with considerable fibrous attachment to the basal 
phalanx. There is no attachment to the tibial 

Action: Flexes the ankle joint; extends the hal- 
lux, with eversion of the foot. 

M. peronaeus longus (figs. 101-103, 139) arises 
by mingled fleshy and tendon fibers from a small 
area on the anterolateral surface of the head of the 
fibula and an adjacent area on the lateral condyle 
of the tibia. The muscle becomes tendinous near 
the distal end of the fibula. The tendon passes 
over the tendons of the other peroneal muscles, 
to insert into the base of the fifth metatarsal just 
posterior to the insertion of the peroneus brevis. 

Action: Everts and abducts the foot. 

M. peronaeus brevis (figs. 101, 102, 139, 140) 
arises from the lateral surface of the shaft of the 
fibula throughout its distal three fourths. The 
muscle becomes tendinous after passing through 
its groove in the lateral malleolus of the fibula. 
The tendon exceeds those of either of the other two 
peroneal muscles in size, and inserts into the dorsal 
surface of the base of the fifth metatarsal. 

Action : Everts and abducts the foot. 

M. peronaeus tertius (figs. 101-103, 139, 140) 
is a very slender muscle lying on top of the much 
larger peroneus brevis. It reaches the fibula only 
at its extreme proximal end. The muscle forms its 
terminal tendon at the distal end of the fibular mal- 
leolus, beneath the transverse tarsal ligament. The 
tendon is somewhat smaller than that of the pero- 
neus brevis, immediately in front of which it lies; 
it extends to the base of the basal phalanx of 
digit 5, gradually coming to lie dorsad instead of 
laterad, and joining the tendon of the extensor 
digitorum longus. 

Action: Everts and abducts the foot. 

D. Muscles of the Foot 

M. extensor digitorum brevis (figs. 101, 103) 
has the usual origin from the coracoid process of 
the calcaneus. Its structure is complex, but it 
forms four more or less distinct digitations that 
go to digits 14. That to the lateral side of digit 4 
is the most distinct, and is the only one that forms 
a well-defined tendon. Each of the others bifur- 
cates at the metatarso-phalangeal articulation, to 
supply adjacent sides of two digits by means of a 
tendinous expansion. There is some insertion of 
muscle fibers into the deep surface of the tendons 
of the extensor digitorum longus, but the tendons 
of the two muscles remain distinct. 

Action : Aids the long extensor in extending the 

Fig. 103. Muscles of the right leg of Ailuropoda, anterior view. 




Lig. plant arum prof. 

M. flex, hallucis brevis 

Tuber calcanei 

Mm. adductores digitorum 

M. flex. dig. quinti brevis 
(pars med.) 

M. flex. dig. quinti brevis 
(pars lat.) 

Fig. 104. Muscles of the plantar surface of the right foot of Ailuropoda. 

M. flexor hallucis brevis (figs. 102, 104) is a 
powerful, complex muscle. It is composed of a 
very small internal part, and a large bipennate ex- 
ternal part. The internal part arises from the 
plantar ligament in common with the external part, 
and extends as a very short muscle belly to its in- 
sertion on the inner side of the base of the first 
phalanx. The external part arises from the tibial 
sesamoid, from the navicular and cuneiform bones, 
and from the plantar ligament. It inserts into 
the outer side of the base of the first phalanx of the 

Action: Flexes the hallux. 

M. abductor digiti quinti (figs. 101, 102, 140) 
is a slender fleshy band of muscle arising from the 
lateral and ventral sides of the distal end of the 
calcaneus. Insertion is into the tuberosity of the 

fifth metatarsal, just proximal to the insertion of 
the peroneus brevis. 

Action: Abducts the fifth toe. 

M. flexor digiti quinti brevis (figs. 102, 104) 
is a powerful muscle occupying the entire plantar 
surface of the fifth metatarsal. It is partly sep- 
arable into a small medial part and a much larger 
lateral part. The lateral part, in turn, has a bi- 
pennate structure. The fibers of the median part 
arise from a small area on the ventral surface of 
the cuboid, and this part of the muscle inserts into 
the medial metatarso-phalangeal sesamoid. The 
lateral part of the muscle arises from the cuboid, 
and from the sheath of the peroneus longus along 
nearly the entire length of the metatarsal. This 
part inserts into the lateral sesamoid. 

Action : Flexes the basal phalanx of the fifth toe. 




Os sesamoid, tib 

Os metatarsal 1 


Os metatarsal 5 

Phalanx 5 

Fig. 105. Interosseous muscles of right foot of Ailuropoda. 

M. flexor digitorum brevis (figs. 102, 140) 
arises as a continuation of the aponeurosis of the 
plantaris and from the deep surface of the plantar 
aponeurosis. It consists of a fleshy belly that di- 
vides into four digitations distally, that going to 
the fifth toe being the largest. At the proximal ends 
of the metatarsals the digitations form slender ten- 
dons, which are distributed to digits 2-4. These 
tendons are perforated by the tendons of the fiexor 
digitorum longus at the metatarso-phalangeal ar- 
ticulations. Insertion is into the second phalanx. 

Accessory slips, four in number, pass from the 
superficial surface of the conjoined long flexor ten- 
don to the tendons of the flexor brevis; a few of 
the most superficial fibers come from the quadratus 
plantae. These slips decrease in size from the fifth 
to the second, and each inserts into the medial side 

of the corresponding tendon of the flexor digito- 
rum brevis. 

Action : Flexes the middle and basal phalanges 
of digits 2-5. 

M. quadratus plantae is a wide band arising 
from the lateral surface of the shaft of the calca- 
neus, and extending obliquely across the sole to 
its insertion on the superficial surface of the con- 
joined long flexor tendon. The muscle is shot 
through with tendon fibers, which unite toward 
the insertion into a central tendon into which the 
muscle fibers insert in bipennate fashion. 

Action: Assists the long flexor in flexing the toes. 

Mm. lumbricales(fig. 102), fourin number, arise 
from contiguous sides of the digital slips of the 
conjoined long flexor tendon. They insert on the 



medial sides of the bases of the fii-st phalanges of 
digits 2-5, that to the fifth digit being the largest. 

Action: Flex the basal phalanges of digits 2-5. 

Mm. adductores (fig. 102) are three bellies on 
the sole, arising together from the deep plantar 
ligament and the underlying tarsal bones. The 
largest and most medial belly is double, and goes 
to the inner side of the base of the first phalanx 
of digit 1. The middle belly goes to the lateral 
side of digit 2. The lateral belly goes to the lat- 
eral side of digit 4. 

Action: Flex the basal phalanges of digits 1, 2, 
and 4 and draw them toward the midline of the 

Mm. interossei (fig. 105) are made up of three 
groups of muscles arising from the plantar liga- 
ment and the bases of the metatarsal bones, and 
inserting into the bases of the proximal phalanges. 
The first and most medial is a single large inde- 
pendent slip arising between the first and second 
metatarsals at their bases and going to the medial 
side of digit 2. The second arises beneath the 
second metatarsal, slips going to both sides of 
digit 2 and to the medial side of digit 3. The third 
arises beneath the fourth metatarsal, and goes to 
both sides of digits 3 and 4. 

Action: Flex the phalanges on the metatarsals. 

E. Review of Muscles of Hind Limb 

The muscles of the hind limb in Ailuropoda, like 
those of the fore limb, agree closely with the corre- 
sponding muscles of the bears in gross structure. 
As in the fore limb, correspondence often extends 
down to minor details. In the tabulation of myo- 
logical characters (p. 197), the giant panda and 
the bears are in complete agreement. 

As in the fore limb, comparison of the relative 
masses of individual muscles reveals subtle differ- 
ences among representative carnivores (Table 15). 
These differences are less obviously correlated with 
functional requirements than was the case in the 
foi'e leg, and agreement between Ailuropoda and 
the bears is less close than in the muscles of the 
fore leg. In the cursorial dog the extensors of 
the thigh (adductors) and flexors of the leg (biceps) 
are dominant, whereas in the bears and the giant 
panda no single muscle stands out, and muscles 
that adduct, abduct, and rotate are more impor- 
tant than in the dog. As in the fore limb, the lion 
tends to be intermediate. 

The weight relations between fore and hind 
quarters are significantly different in Ailuropoda 
from those in other arc told carnivores (Table p. 196; 
data as in Tables 14 and 15). In the panda the 
hind quarters are relatively lighter (or the fore 



Wt. in 

gms. % 

Iliacus and psoas 121 7.2 

Glutaeus superficialis 123 7.3 

Glutaeus medius 136 8.1 

Glutaeus profundus 21 1.2 

Tensor fasciae latae 21 1.2 

Obturator internus 14 .8 

Gemellus anterior 1 .1 

Gemellus posterior 3 .2 

Piriformis 15 .9 

Quadratus femoris 20 1.2 

Obturator externus 42 2.5 

Semimembranosus 148 8.8 

Semitendinosus 91 o.4 

Sartorius 114 6.8 

Rectus femoris 76 4.5 

Vastus lateralis \ 1-7 qs 

Vastus intermedius J 

Vastus medialis 91 5.4 

Pectineus 33 2.0 

Gracilis 115 6.8 

Adductor 146 8.7 

Biceps 199 11.8 


Totals 1687 100.2 

* Half-grown individual. 
'* Data from Haughton. 




Wt. in 



Leo leo' 












































































I 50 









































gms. % 

gms. % 

gms. % 



Shoulder and arm 

1132 40 

1309 35 

1607 36 



Hip and thigh 

1687 60 

2382 65 

2891 64 



' Half-grown individual (Su Lin). 
* Data from Haughton. 

quarters heavier) and there is no obvious func- 
tional reason for this altered relationship, which 
agi-ees with the relationships found in the skeleton. 
It probably reflects a generalized increase in the 
mass of muscle tissue in the anterior part of the 
body (p. 182). 


The data on the muscular system may be con- 
veniently considered under two heads: taxonomic 
characters, and evidence for the operation of evo- 
lutionary mechanisms. It is not intended to im- 
ply that these two kinds of data are unrelated to 
each other. 

Taxonomic Characters 

The musculature of the Carnivora fissipeda was 
reviewed in detail by Windle and Parsons (1897, 
1898). The viewpoint of these authors was purely 
morphological. They summarized the literature, 
supplemented it with many original dissections, 
and critically analyzed the resulting mass of data 
for features that characterize the order Canivora, 
or that characterize families within the Carnivora. 
They had data on 55 individuals, representing 25 
species, of arctoid carnivores. 

The accompanying table (Table 16), expanded 
from the summary table of Windle and Parsons, 
summarizes the musculature of the arctoid carni- 
vores from the morphological and taxonomic stand- 
points. Consideration of the facts in Table 16 
yields the following conclusions: 

1. The Canidae appear to differ from all other 
arctoids more than any of the latter do among 
themselves. But the features peculiar to the Cani- 
dae are, apparently without exception, adaptations 
to cursorial locomotion and therefore do not repre- 
sent deep-seated primary differences. Practically 
every one of the canid characters is shared with 
the likewise highly cursorial Hyaenidae, to which 
the dogs are only remotely related. 

2. The Mustelidae differ among themselves more 
than do the members of any other family. Never- 
theless two features appear to characterize all mus- 
telids: the presence of the deep rhomboid as a 
distinct muscle,' and the presence of an extra head 

' This is present in Potos, which shares many other ana- 
tomical features with the Mustelidae. 

of the triceps, arising from the angle of the scap- 
ula. Both of these appear to be deep-seated, long- 
standing features. 

3. The Ursidae and Procyonidae resemble each 
other more than either resembles the Canidae or 
Mustelidae. For the most part this resemblance 
is merely the absence in both of specializations 
such as characterize the dogs and mustelids; in 
other words, the bears and procyonids share gen- 
eralized carnivore features. 

4. The Ursidae and Procyonidae differ in a 
number of minor characters. These are not obvi- 
ously correlated with functional differences, nor is 
the pattern of the musculature notably more spe- 
cialized in one family than in the other. 

5. Ailuropoda does not differ from the Ursidae 
in a single myological character (see above for a 
discussion of the biceps). Indeed, the resemblance 
is much closer than the table implies. The pattern 
of the musculature strongly supports the conclu- 
sion that the giant panda is closely related to 
the bears. 

Myological Evolution 

Although the pattern of the musculature in the 
giant panda is practically identical with that of 
the bears, the musculature differs in other impor- 
tant ways. These differences must be accounted 
for before we can claim to understand the anatomy 
of the giant panda. They are: 

1. Regional hypertrophy of the musculature. 

2. Differences in the relative mass of the individual muscles. 

3. Differences in internal muscle structure. 

4. Differences in attachment sites 

1. Available data show significant size differ- 
ences between Ailuropoda and the bears in whole 
regional muscle masses. These regional masses 
appear to be moi-phological units rather than func- 
tional units: in the head all muscles derived from 
the mandibular ai-ch are hypertrophied, regardless 
of function, whereas muscles of other embryonic 
origin are unaffected, even though they lie in the 
same general area of the head. Thus in this in- 
stance the morphological unit is also a develop- 
mental and genetic unit. 

The case for the limb musculature is less clear. 
The ratio between fore quarter weight and hind 






































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quarter weight in Ailuropoda clearly differs from 
that in other carnivores examined, and this seems 
to involve the total musculature rather than indi- 
vidual elements. The difference is far less than for 
the craniomandibular musculature, but is never- 
theless considerable. It is impossible, from our 
data, to determine what, if anything, is involved 

2. It is well known that in the individual a 
muscle hypertrophies as a result of continuous 
exercise and atrophies with disuse. It has been 
shown experimentally that the relative sizes of 
muscle elements depart significantly from the norm 
when the forces to which they are habitually sub- 
jected are changed (e.g., Fuld, 1901). Therefore 
observed differences in the relative size of a given 
muscle, even when consistent in all individuals of a 
species, may simply reflect the response of that 
muscle to extrinsic mechanical forces rather than 
the action of factors intrinsic to the musculature. 
No morphogenetic mechanism capable of produc- 
ing selective hypertrophy of individual muscles 
has so far been demonstrated. 

Differences of this kind occur in the musculature 
of Ailuropoda as compared with that of the bears. 
Involved are both craniomandibular and limb ele- 
ments. The observed differences are no greater 
than those distinguishing Fuld's bipedal dogs from 
his normal controls, and may therefore represent 
factors extrinsic to the musculature. There is at 
present no known way of determining whether 
such differences depend on factors intrinsic or ex- 
trinsic to the musculature. 

3. Differences in internal muscle structure in- 
volve arrangement of fibers, form and extent of 
tendons and tendinous aponeuroses, length and di- 
ameter of fibers, etc. Obviously, profound changes 
of this kind must have occurred during the phy- 
logeny of vertebrates. The only such difference 
of any importance observed in the present study 
was the tendinization of fascial planes in the tem- 
poral muscle of Ailuropoda. The extent to which 
such a difference reflects changes in the genetic 
substrate is unknown. 

4. There is considerable variation in the attach- 
ment sites of muscles among the carnivores, and 
these differences usually shift lever advantages in 
the direction of either speed or power and so are 
broadly adaptive. Such differences must surely 
result from the action of selection on genetic sys- 
tems, but they scarcely exist between Ailuropoda 
and the bears and therefore need not concern us 
here. The only notable differences in attachment 
sites between these two groups failure of the ab- 
ductor pollicis longus and tibialis posterior to reach 
the first metapodials have a purely mechanical 
cause. The tendons of these muscles already at- 
tach partly to the radial and tibial sesamoids, re- 
spectively, in bears. Further enlargement of the 
sesamoids in Ailuropoda has simply blocked the 
tendons off from the metapodials. 


1. The musculature of Ailuropoda is almost 
identical with that of the Ursidae. 

2. Only two significant differences are evident: 
hypertrophy of the craniomandibular musculature, 
and failure of the abductor pollicis longus and tibi- 
alis posterior to reach their normal attachment sites 
on the first metapodials. 

3. Hypertrophy of the jaw muscles is associ- 
ated with hypertrophy of all muscles derived from 
the mandibular arch, and extends in a decreasing 
gradient to the musculature of the neck, shoulders, 
and upper arm. This condition has a direct, and 
probably very simple, genetic base. 

4. The abductor pollicis longus and tibialis pos- 
terior are prevented mechanically from reaching 
their respective metapodials. The cause for the 
condition in the panda is therefore extrinsic to the 
muscular system. 

5. Differences in the relative sizes of individual 
jaw and limb muscles are evident. Some, prob- 
ably all, are adaptive, but whether the causes for 
these differences are intrinsic or extrinsic to the 
muscular system cannot be determined from our 



The hard palate (fig. 106) is narrow and elon- 
gate. Its lateral borders are nearly straight, al- 
though there is a slight expansion opposite the 
fourth premolar and first molar. There are 10 pairs 
of low palatal ridges, rounded rather than V-shaped 
in cross section, which meet a faint longitudinal 
ridge running down the midline. Only the first 
pair of ridges is transverse; successive pairs are 
progressively more obliquely displaced, and less 
and less sharply set off from the surrounding tis- 
sue. The last ridge is at the level of the posterior 
border of the first molar. There is a prominent 
incisive pad between the incisor teeth and the first 
pair of palatal ridges. The palate of a second indi- 
vidual (Mei Lan) is similar except that the ridges 
are even less prominent. 

The soft palate has a length of 105 mm., end- 
ing posteriorly in a square free border, the velum 
palatinum. Numerous punctures, representing the 
openings of the palatine glands, are distributed 
over the anterior part of the soft palate and the 
extreme posterior part of the hard palate. 

The entire palate is unpigmented. 

In specimens of Ursus tibetanus, Tremarctos or- 
natus, Ailurus fulgens, and Procyon lotor the pala- 
tal sculpturing is much more prominent than in 
Ailuropoda, which looks almost degenerate in com- 
parison. The palatal ridges number 8-10, and are 
V-shaped in cross section and much larger and 
sharper than in the giant panda. They are also 
more transversely situated. 


The parotid gland (figs. 107, 108) is roughly 
rectangular in form, its height considerably ex- 
ceeding its width. It is quite extensive, the main 
part of the gland measuring approximately 90 mm. 
by 50 mm. The entire gland, with its duct, weighs 
57 grams. The gland fills the area between the 
posterior border of the head posteriorly, a line pro- 
jected along the upper teeth ventrally, and the 
posterior border of the masse ter muscle anteriorly; 
dorsally it extends well up onto the ear cartilage. 

The dorsal border of the gland is concave, with 
moderately well-marked pre-meatal and post- 
meatal processes. The posterior border is nearly 

straight, but is produced slightly backward at its 
ventral angle by the underlying internal facial 
vein. The ventral border is somewhat irregular; 
it is molded around the submaxillary gland to give 
a general concave contour. The anterior border 
is convex. 

The gland is much flattened. It is divided into 
rather small leaf-like lobulations. The parotid duct 
emerges below the center of the gland, by a dorsal 
and a ventral root that promptly unite. The sub- 
stance of the gland is carried forward along the 
duct on the right side of the head, and small acces- 
sory lobules are distributed along the length of the 
duct on both sides of the head as far as the labial 
commissure. These lobules open separately into 
the parotid duct by short ducts of their own. The 
main parotid duct runs horizontally across the 
outer face of the masseter, passes internal to the 
external facial vein at the anterior border of the 
masseter, to terminate in the cheek near the gum 
line, opposite the posterior part of the fourth pre- 
molar (carnassial). 

The submaxillary gland (figs. 107, 108) is reni- 
form, with the concavity directed caudad. It meas- 
ures approximately 50 mm. in height and 35 mm. 
in width. The entire gland, with its duct, weighs 
19 grams. Its surface is nearly smooth, the lobu- 
lations being much shallower and more regular 
than are those of the parotid. 

The gland is in contact with the parotid dor- 
sally. Its medial border rests on the sternohyoid 
muscle. Immediately in front of it is a pair of 
lymph glands, one on either side of the external 
facial vein. 

The submaxillary duct leaves the deep surface 
of the gland slightly above its center. It passes 
forward between the digastric and masseter mus- 
cles, then deep to the mylohyoid where it runs 
along the medial border of the sublingual gland. 
Beyond the anterior end of this gland it parallels 
the sublingual duct to the caruncula sublingualis, 
where the two ducts open side by side. The sub- 
lingual carunculae are a pair of very prominent 
papillae, 4 mm. in diameter, situated on the floor 
of the mouth. They are located 10 mm. anterior 
to the frenulum of the tongue, and the two carun- 
culae are 9 mm. apart. 




Papilla incisiva 

Opening of Ductus nasopalatlnus 

Palatum durum < 

Palatum molle < 

.Raphe palati 

Rugae palati 

Openings of Gl. palatini 

Ostium pharyngeae tubae 

Ostium bursae pharyngae 

Fig. 106. The hard and soft palates of Ailuropoda. 
expose the entrances to the pharyngeal bursae. 

A window has been cut in the posterior part of the soft palate to 

The greater sublingual gland (figs. 107, 108) 
is elongate and irregular in outline, triangular in 
cross section posteriorly, and much flattened an- 
teriorly. It is wider posteriorly than anteriorly. 
An irregular vertical arm is continued up along the 
submaxillary duct, around the digastric muscle, to 
the anterior border of the submaxillary gland, with 
which it is in contact. The main part of the gland 
(exclusive of the vertical arm) measures 92 mm. in 

length, with a maximum width of only about 10 
mm. It occupies the lateral sublingual space, and 
is in intimate contact with the mylohyoideus ven- 
trally. It extends from the level of the angular 
process of the mandible forward to the posterior 
border of the first lower molar. 

The duct may be traced through the substance 
of the gland, occasionally appearing on its lateral 
surface. It leaves the gland at its anterior tip, 




A. & N. supraorbital is 

.V. lacrimalis 

A. & v. auric, ant. 
R. auric, aiit. N. facialis 

M. auric, ant. inf. 
M. lev. auris long. 
VII: N. zj/gomaticoteoiporalis 

A. & N*. frontalis 

V. ophthalmica superior 
.V. supratroch. 
N. infratroch. 

V. nasofrontalis 

A. & V. annularis 

Orificium ducti parotidei 
A. & N. infraorbital is 
A. & V. labialis su(>erf. 
y. nasal is 

Ductus parotideiis 

Gl. parotis 

IN. auric, magnum 
N. buccali^ inferior^ 
Gl. subling. major ' 
Gl. submaxillaris. 
Ductus submazillaris 
X. cutatteus colli 

V. facialis interna 

V. jugularis externa 

V. facialis prof. 
R. m. platysma 
V. anast. V. labialis inf. 
A. maxillarU externa ^- * ^- '"'"'^''^ '"^ 

Fig. 107. Superficial dissection of the head of Ailuropoda. 

and parallels the submaxillary duct to the sublin- 
gual caruncle, where it opens. 

The lesser sublingual glands (fig. 108) are 
represented by glandular masses situated just deep 
to the greater sublingual gland, and extending from 
the posterior border of the greater sublingual gland 
to the base of the tongue, a distance of 43 mm. 
Dorsally they are continuous with the palatine 
glands, and ventrally there is no boundary sepa- 
rating them from the inferior alveobuccal glands. 

The palatine glands consist of a layer of lob- 
ulated glandular tissue under the mucous mem- 
brane of the soft palate and the posterior end of 
the hard palate. Laterally they are continuous 
with the lesser sublingual glands. Numerous dots, 
distributed like pin-pricks over the mucous mem- 
brane of the soft palate and the posterior part of 
the hard palate (fig. 106), represent the outlets 
of these glands. 

The inferior alveobuccal glands (molar gland) 
(figs. 107, 108) are well developed. They may be 
traced on the medial side of the mandible from the 
symphysis (at the posterior border of the third pre- 
molar) back to a point beyond the last molar ; the 
gland mass gi'adually increases in size posteriorly. 
Behind the last molar it crosses over to the outside 
of the mandible, where it is continued forward on 
the buccinator muscle and deep to the masseter to 
the labial commissure. Each of the glandular ele- 
ments opens by an independent duct. There are 
numerous outlets, hardly visible under a magnify- 
ing glass, in the mucous membrane below the teeth 
on the inner side of the mandible. A double row 
of 24 or more prominent papilla-like projections, 
ranging up to a millimeter in diameter, in the 
mucous membrane of the cheek near the lower 
molar teeth, mark the outlets of the extra-man- 
dibular part of the gland mass. 

The orbital glands (fig. 108) form a compact 
ovate mass of 12-14 independent but closely asso- 




Sublingualis minor 

Ductus submaxillaris 

Fig. 108. Salivary glands of Ailuropoda, semi-diagrammatic. 

dated elements situated in the suborbital space 
immediately above the last upper molar. The 
much-flattened gland mass lies between the bone 
and the temporal muscle. It measures 37 mm. in 
length by about 18 mm. in height. The dozen or 
more ducts open on low, inconspicuous projections 
that are scattered over a fold of the oral mucous 
membrane laterad of the posterior half of the last 
upper molar. 

The orbitoparotid gland (fig. 108) is a small 
structure situated at the inferior corner of the an- 
terior root of the zygoma. It is bounded, as usual, 
by the anterior border of the masseter posteriorly, 
the parotid duct dorsally, and the buccinator mus- 
cle and oral mucous membrane internally. The 
gland measures about 10 mm. in diameter. The 
duct parallels the parotid duct to a point opposite 
the middle of the second upper molar, where it 
opens on a minute papilla near the lateral border 
of the tooth. 

Carmalt (1913) described and compared the gi-oss 
structure of the salivary glands in eight species of 
fissiped carnivore: Canis familiar is, Procyon lotor, 
Ursus tihetanus, Taxidea taxus,Gulo luscus, Mephi- 
tis mephitica,Felis domestica, andF. leo. The liter- 
ature on these glands was reviewed extensively by 
Fahrenholz ( 1937). In general the salivary glands 
are relatively small in cai-nivores, particularly the 
serous ( parotid) glands, which may be smaller than 
the submaxillary gland in predominantly flesh-eat- 

ing forms. Carmalt concluded that the form of 
the salivary glands in carnivores is determined 
largely by the molding effect of surrounding tis- 
sues, and therefore that differences in shape are of 
no great significance. The parotid gland tends to 
be large in herbivorous mammals. Among the 
Carnivora it is large in the bears, immense in Pro- 
cyon (Fahrenholz), "considerably larger than the 
submaxillary gland" in Ailurus (Carlsson, 1925). 
These are among the most herbivorous of the car- 
nivores. It is small in the Canidae. 

Ailuropoda resembles other herbivorous carni- 
vores in its large parotid gland. The relative size 
of this gland (twice the size of the submaxillary) is 
comparable to the condition in bears, but is far 
short of the relative size in Procyon, in which the 
parotid is six times the size of the submaxillary. 


The tongue (fig. 109) is of moderate length and 
narrow, and is devoid of pigmentation. It meas- 
ures 210 mm. from tip to base, and 55 mm. in 
greatest width. The lateral margins of the oral 
part are nearly parallel, although the organ tapers 
slightly toward the tip. There is a prominent 
frenultun on the inferior surface, situated 75 mm. 
from the tip. There is a small but distinct median 
notch at the tip, but no indication of a median fur- 
row on the dorsum. The glosso-epiglottic furrow, 
on the other hand, is very well marked. 

M. cricoaryt. post. 

M. constrictor pharyngis med 
Recessus pyriformis 

Plica vocalis 
M. constrictor pharyngis ant. 

Os tympanohyale 

Papillae vallatae 

N. laryngeus inf., R. ant. 

Rima glottidis 


Sulcus glosso-epiglotticus 
Tonsilla palatina 

Gl. sublingualis 

Fig. 109. Upper surface of tongue of Ailuropoda. 




Conical papillae cover the entire dorsum from 
the tip back to the epiglottis. They are quite uni- 
form in size except near the tip, where they are 
sHghtly larger, and in the pharyngeal region where 
they are much larger and sparser. Large conical 
papillae are also present on the under surface at 
the tip and for 65 mm. along the lateral margins. 

Fungiform papillae are distributed over the 
entire dorsum of the oral part of the tongue, ex- 
cept for a small area along the midline 30 mm. long 
and about 5 mm. wide, and situated about 20 mm. 
back from the tip, where they appear to be absent. 
They are very conspicuous and are evenly spaced 
at intervals of 2 to 3 mm., posteriorly showing a 
tendency to form diagonal rows running from the 
midline outward and backward. They are not ab- 
sent over the entire middle of the dorsum, as Raven 
found in the tongue he examined. 

The vallate papillae are arranged in a semi- 
circle, and not in V formation as Raven suggested. 
There are thirteen papillae; in some cases a small 
secondary papilla is closely approximated to a 
larger one and enclosed in the same fossa (these 
were not counted in arriving at the total) . In addi- 
tion there are three papillae situated irregularly 
behind the row on the right side, making a total 
of sixteen. Raven postulated seventeen as the 
number originally present on the incomplete tongue 
he examined. 

Foliate papillae are absent. Raven identified 
as foliate papillae two longitudinal slits, asym- 
metrically placed on the anterior dorsum of the 
tongue. A single such slit is present on the dor- 
sum near the tongue tip in our specimen. This 
slit is not glandular and quite evidently represents 
a mechanical injury. 

The lyssa is a small structure, 33 mm. long by 
about 2 mm. in diameter, situated in the anterior 
part of the tongue. Its length is thus about 16 
per cent of that of the tongue as a whole. The 
structure, which is oval in cross section, is attached 
to the mucous membrane at the tip of the tongue 
anteriorly. Posteriorly it is continued into a thin 
cord that is lost in the lingual septum. 

The gross structure of the tongue in the Carni- 
vora was reviewed by Sonntag (1923), and again 
by Stadtmiiller (1938). Among the Procyonidae 
and Ursidae, differences appear to involve prima- 
rily the number and distribution of the papillae. 
The fungiform and conical papillae diflFer little from 
conditions described here for Ailuropoda. In the 
procyonids and bears the number of vallate papil- 
lae ranges from six to twenty, the larger numbers 
occurring in the bears. They are more numerous 
in bears than in any other carnivore. The vallate 
papillae are arranged in a V, except in certain bears 

( Ursus americanus, Helarctos malayanus) in which 
they are described as forming a semicircle. The 
Ursidae and Ailuropoda agree in the large number 
of vallate papillae, and only in these forms do they 
ever form a semicircle. 

According to Stadtmiiller the number of vallate 
papillae in mammals is not correlated either with 
diet or with degree of development of the sense of 
taste, but tends to be larger in less primitive forms. 
Nimiber and arrangement are consistent at or be- 
low the family level. 

Statements on the foliate papillae are very con- 
tradictory. Sonntag found no trace of them in 
Procyon cancrivora, Nasua narica, Polos, or Ailu- 
rus, but observed "some small foliate clefts" in 
Procyon lotor. Stadtmiiller failed to find them 
in Nasua rufa and Potos. Carlsson says they 
"stand out prominently" in Ailurus. I could find 
no trace of foliate papillae in Procyon lotor. 

Among the Ursidae, Sonntag observed "small 
foliate clefts" in Thalarctos and Melursus, and 
Tuckerman described foliate papillae for Ursus 
americanus and Helarctos. Stadtmiiller, on the 
contrary, could find no foliate papillae in Ursus 
tibetanu^, Helarctos, and Thalarctos. I failed to 
find them in Ursus tibetanu^. 

The lyssa, which is large in the Canidae, is pres- 
ent but small in all ursids and procyonids except 
Potos, in which it is said to be large. 

The tongue appears to differ little among the 
Procyonidae and Ursidae. The tongue of Ailu- 
ropoda most closely resembles that of Ursus. 


A. Pharynx 

The pharynx is relatively capacious. The naso- 
pharynx and pharynx proper together have a total 
length of about 135 mm., and the width just back 
of the velum palatinum is about 40 mm. (with the 
walls flattened out). The pharynx is fusiform in 
shape, tapering gradually toward the choanae an- 
teriorly and the esophagus posteriorly. The pars 
nasalis pharyngis is 115 mm. long, thus greatly 
exceeding the pharyngis propria, which measures 
only about 20 mm. 

A pair of openings, the outlets of the bursae 
pharyngeae, is situated in the dorsal wall of the 
nasopharynx (fig. 106). These openings are lo- 
cated 12 mm. anterior to the ventral border of 
the foramen magnum and 35 mm. anterior to the 
posterior border of the velum palatinimi; they lie 
immediately in front of the anterior border of the 
pterygopharyngeal division of the anterior con- 
strictor muscle of the pharynx. They are a pair 
of crescent-shaped slits, 7 mm. in length, separated 



by a prominent isthmus 5 mm. in width. The 
right slit is more prominent and opens into a ca- 
pacious thin-walled sac, 130 mm. long by 30 mm. 
in greatest width (flattened out), situated between 
the esophagus ventrally and the longus colli mus- 
cle and centra of the cervical vertebrae dorsally 
(fig. 110). The bursa, lying in the trough bounded 
laterally by the prominent longus capitis muscles, 
extends caudad to the disk between the fifth and 
sixth cervical vertebrae. The bursa begins with a 
narrow neck, which expands into an extensive 
blind sac. A very short septum divides the pos- 
terior end of the bursa into right and left halves. 
The left bursa, into which the left slit opens, is 
much smaller, measuring only 15 mm. in length. 

Proximally the lining of the large right bursa 
is thrown up into prominent longitudinal ridges, 
which on the lateral wall are interrupted by two 
small pocket-like sinuses open anteriorly, and 
slightly farther caudad by a small oval perforation 
in the lining of the bursa that opens into a small 
sinus. An additional pocket-like sinus is present 
near the extreme posterior end of the bursa. 

Killian (1888) failed to find a pharyngeal bursa 
in the following carnivores: Cams familiaris, Nasua 
Tufa, Mephitis mephitica, Lutra vulgaris, Herpestes 
griseus, Viverra civetta, Paradoxurus trivirgatus, Felis 
domestica. I have examined specimens of Procyon 
lotor and Ailurus fulgens and find they have no 
pharyngeal bursa. 

On the other hand, the existence of pharyngeal 
bursae in bears has long been known (literature 
reviewed by Killian). These are described by vari- 
ous authors as paired structures, always unequal 
in size, with relations very similar to those de- 
scribed here for Ailuropoda. Such paired bursae 
have not been described for any other mammal. 
Pharyngeal bursae have been described for Ursus 
arctos, U. americanus, U. horribilis, Melursus ur- 
sinus, and Helardos malayanus. The function of 
these structures is unknown. 

The openings of the auditory tubes are a pair 
of longitudinal slits in the lateral walls of the naso- 
pharynx at about its posterior third, 15 mm. ante- 
rior to the openings of the pharyngeal bursae 
(fig. 106). They are much less prominent than 
the latter. 

B. Muscles of the Soft Palate and 


M. levator veli palatini is a rather narrow 
band of muscle fibers arising from the petrosal im- 
mediately laterad and caudad of the orifice of the 
auditory tube and from the adjacent lateral wall 
of the auditory tube. The muscle extends ventrad 
and caudad, passing internal to the pterygopha- 

ryngeus, to insert into the palate. The fibers ex- 
tend to within a few millimeters of the caudal 
border of the velum palatinum. 

M. tensor veli palatini is shghtly smaller than 
the levator. It arises, as a rounded mass of min- 
gled tendon and fieshy fibers, from a groove and 
ridge in the floor of the middle ear, from the scaph- 
oid fossa of the sphenoid, and from the adjacent 
lateral wall of the auditory tube. From its origin 
the muscle passes ventrad and craniad, across the 
hamular process of the pterygoid. Mesad of the 
hamular process the muscle becomes tendinous, 
forming a thin tendinous sheet that runs craniad 
in the soft palate just inside the pterygoid process. 
The tendon fibers can be traced craniad nearly to 
the posterior border of the hard palate. 

M. uvulae is composed of a pair of narrow bands 
of muscle extending along the midline of the soft 
palate and the velum palatinum. Origin is by 
tendon fibers from the posterior border of the bony 
palate at the midline, with accessory tendinous 
slips coming from the soft palate in its anterior 
quarter. The paired muscle extends caudad to 
the posterior border of the velum palatimun, where 
it inserts. 

M. pharyngopalatinus is a thin layer of fibers 
lying deep to the constrictor muscles of the phar- 
ynx. It is situated at the posterior end of the 
velum palatinum, where it arises from the aponeu- 
rosis of the palate. From this origin the fibers fan 
out over the lateral and dorsal walls of the phar- 
ynx, beneath the middle constrictor and the ante- 
rior part of the posterior constrictor. 

M. constrictor pharyngis anterior, the small- 
est of the three constrictors, is composed of three 
elements, which maintain their identity through- 
out. The most anterior {Pterygopharyngeus of 
human anatomy) is a narrow band of fibers aris- 
ing from the hamular process of the pterygoid bone. 
It runs caudad to the neck of the pharyngeal bursa 
and arches sharply around this structure, its most 
anterior fibers forming the bulk of the isthmus that 
separates the ostii bursae. The posterior part of 
the muscle is overlain by the anterior border of 
the middle constrictor. All the fibers of the mus- 
cle pass to the dorsal midline of the pharynx, where 
the muscle forms a raphe with its fellow of the 
opposite side. A posterior muscle {buccopharyn- 
geus of human anatomy) lies at first deep to and 
co-extensive with the pterygopharyngeus. It arises 
from the medial surface of the pterygoid process 
and the soft palate mesad of the pterygoid process. 
As the muscle passes beyond the pterygopharyn- 
geus it splits into subequal parts which arch dor- 
sad, embracing the pharyngopalatinus between 
them, to their insertion on the dorsal midline of 



Os palatinum 

Pars nasalis pharyngis 

Os sphenoidale 

Os basioccipitale 

Ostium pharyngeae tubae 

Ostium bursae pharyngae 

Mm.constrictores pharynges 
Velum palatinum 

Bursa pharyngea 

Pharynx propria 


Cart, thyreoid. 

Plica vocalis 

Cart, cricoid. 


Fig. 110. Sagittal section through larynx of Ailuropoda. 

the pharynx. The glossopharyngeal division is a 
narrow band arising from the side of the root of 
the tongue at the level of the tonsils. It runs 
caudad and slightly dorsad to its insertion, which 
is into the lateral wall of the pharynx at the level 
of the thyrohyal arm of the hyoid. Throughout 
its length it lies ventrad of the other two parts of 
the anterior constrictor. 

M. constrictor pharyngis medius (fig. 85) is 
composed of a superficial and a deep layer. The 
superficial layer, which is more or less rectangular 
in form, arises from the lateral surface of the thy- 
rohyal. Near its insertion, where it is overlapped 
by the anterior border of the posterior constrictor, 
it fuses with the underlying deep layer. The deep 
layer, which is considerably smaller, arises from 
the posterior surface of the epihyal. Both layers 
insert along the dorsal midline of the pharynx. 

M. constrictor pharyngis posterior (fig. 85) 
is the largest and heaviest of the pharyngeal con- 
strictors. It is partially separable into an anterior 
superficial part, which partly overlaps a deeper 
and more caudal posterior part. The anterior 
part {thyreopharyngeus of human anatomy) arises 
from the oblique line of the thyroid cartilage be- 

tween the superior and inferior thyroid tubercles. 
The posterior part {cricopharyngeus of human 
anatomy) arises from a tendinous arch extending 
from the thyroid cartilage to the dorsolateral bor- 
der of the cricoid cartilage, and from the entire 
dorsal surface of the inferior cornu of the thyroid 
cartilage. The fibers of the two parts soon become 
inseparable, and the resulting common mass fans 
out to its insertion, which is into the median raphe 
on the dorsal side of the pharynx. 

C. Esophagus 

The esophagus is 35 cm. long and about 20 mm. 
wide when flattened out dorsoventrally. As it 
passes posteriorly from the pharynx, the esopha- 
gus gi-adually moves to the left of the midline. 
This deflection is greatest at the level of the third 
rib, posterior to which it moves back toward the 
midline, to be deflected to the left again as the 
diaphragm is approached. It joins the stomach at 
the level of the tenth thoracic vertebra, immedi- 
ately after passing through the diaphragm. The 
inner surface of the esophagus is thrown into longi- 
tudinal folds which terminate abruptly at the level 
of the stomach, as Raven (1936) noticed. Raven 
describes the smooth epithelium lining the stom- 




Fundus ventrieuli 


Curvatura minor 

Lig. hepatogastricum 

(omentum minor) 


Sphincter pylori 

Rirs pylorica. 

Lig. lienorenalis 


Duodenum (pars anterior) 

Pancreas (cervix) 

Ductus choledochus 

Lig. gastrolienalis 

Lig. duodenorenalis 

Fig. 111. Stomach, spleen, and pancreas of Ailuropoda, dorsal view. 

ach as "almost horny"; such a texture is not evi- 
dent in the specimen at hand. 


The stomach, as Raven observed, is elongate 
and slender (fig. 111). The fundus is only mod- 
erately dilated, and the whole cardiac region tapers 
gradually toward the pylorus. The pylorus is elon- 
gate and tubular, with extremely muscular walls. 
The stomach was empty in the specimen dissected; 
its length along the greater curvature, from the 
esophagus to the pyloric sphincter, was 400 mm. 
This compares with a length of 80 cm. given by 
Raven for a fully adult individual. There is a 
very sharp flexure in the stomach near the begin- 
ning of the pylorus, so that the pylorus is doubled 
back against the cardia with its distal end near the 
esophagus. The strong gastrohepatic ligament 
holds the stomach in this position. 

The lining of the stomach displays rather prom- 
inent plicae mucosae throughout. These diff'er 
considerably in diff'erent regions. In the region 

of the fundus they are low and irregular, forming 
an irregular reticulation. They became much 
more prominent in the middle region of the stom- 
ach, and show a tendency toward a longitudinal 
arrangement. In the pylorus they take the form 
of four elevated longitudinal folds. The mucosa 
is similar over the whole stomach ; there is no corni- 
fication anywhere. The wall of the pylorus is 8- 
9 mm. thick. Most of this (about 6 mm.) is ac- 
counted for by the tunica muscularis. Raven states 
that the muscularis was only 2 mm. thick in his 

The stomach is simple in all fissiped carnivores, 
with a more or less spherical fundus and a cylin- 
drical, thick-walled pylorus (fig 112). The py- 
lorus is characteristically doubled back against the 
minor curvature. Among the arctoid carnivores 
there are minor variations in form, but these have 
no obvious relation to differences in diet. In Ailu- 
ropoda the stomach is more elongate, particularly 
the long tubular pylorus, than in any other carni- 
vore examined. In bears ( Ursus americanus and 



Canis familiaris 

Ailurus fulgens 

Bassariseus astutus 

Procyon lotor 

Helarctos malayanus 

Ailuropoda melanoleiica 

Fig. 112. Form of the stomach in representative arctoid carnivores, not to scale. (Canis from Ellenberger and Baum, 
Ailurus from Flower 1870, others original). 

Helarctos malayanus examined) the pylorus is 
rather globular in form. In an adult Helarctos 
the wall of the pylorus is about 6.5 mm. thick, 
almost as thick as in Ailuropoda, but the pyloric 
region is far shorter than in the panda. 


The intestines of Ailuropoda are remarkable for 
their shortness and the slight differentiation of the 

various regions. The fixed and preserved intesti- 
nal tract, measured with the mesentery still at- 
tached, was only 4780 mm. in length from pyloric 
valve to anus in Su Lin. This is only four times 
head and body length. In the fully adult individ- 
ual studied by Raven intestinal length was 5.5 
times head and body length. The gut in Ailu- 
ropoda appears to be as short as in any known 



Jejuno- ileum 


A. mesenterica ant. 

A. colica ant. 

A. colica med. 


-A. mesenterica post. 
~-A. colica post. 
\. hemorrhoidalis ant. 

Fig. 113. Intestinal tract and mesentery of Ailuropoda, spread out. Dorsal view. 

The duodenum begins a few millimeters to the 
right of the midline of the body. It turns caudad 
rather abruptly at the pyloric sphincter, and I'uns 
almost straight back to its juncture with the jeju- 
num. There is thus scarcely any indication of the 
U-shaped duodenal loop that characterizes the 
arctoid carnivores. The duodenum has a length of 
only 130 mm. and a diameter of about 25 mm. 
The duodenorenal ligament is well developed. Its 
anterior end is heavier and attaches to the tip of 
the caudate lobe of the liver. 

The heavy wall of the pylorus gives way abruptly 
to the very much thinner wall of the duodenum at 
the pyloric sphincter. Raven describes the mu- 
cosa of the duodenum as thrown up into numerous 
longitudinal folds. These are not evident in my 
specimen; the few folds that are present corre- 
spond to folds involving the entire wall of the 
duodenum, and may be considered a post-mortem 

effect. The lumen is lined with close-set villi, each 
about 2 mm. long, which gives the lining a velvety 

The jejuno-ileum is suspended from a short 
mesentery that is nearly circular in outline (fig. 
113). This part of the intestine is comparatively 
short, measuring only 3890 mm. in length. It is 
not sharply separated from the duodenum. It 
is arranged around the circumference of the mes- 
entery in a series of about a dozen U-shaped loops. 
The villi lining the jejuno-ileum do not differ in 
appearance from those lining the duodenum. There 
are no Peyer's patches, in which this specimen 
agrees with the one examined by Raven. 

The internal diameter of this part of the intes- 
tine varies. It is about 60 mm. near the duodenum, 
decreasing gradually to about 20 mm. a meter and 
a half beyond the duodenum. The rest of the tract 
is about 20 mm. in diameter. The mean internal 



diameter of the jejuno-ileum is 28.6 mm., based 
on circumference measurements made at 500 mm. 
intervals on the opened and flattened-out intestine. 

The internal surface area of the entire small in- 
testine, calculated from the measured length of 
4020 mm. and a mean internal circumference fig- 
ure of 90 mm., is 361,800 mm-'. 

There is no caecum, and no external indication 
of the ileo-colic junction. Internally there is no 
indication of a valve at the juncture between the 
ileum and colon. 

The colon (fig. 113) measures 580 mm. in length. 
The internal diameter is about 31.5 mm., which 
slightly exceeds the diameter of the lower part of 
the small intestine. The colon is arranged in a 
short but well-defined colic loop, which is supplied 
by a separate branch of the anterior mesenteric 
artery and vein, and which passes without a sharp 
boundary into a short straight rectum. The rec- 
tum is suspended from a narrow mesocolon, and 
has approximately the same diameter as the rest 
of the intestine. It has a length of 180 mm. The 
lining of the rectum does not differ in appearance 
from that of the colon. 

The internal surface area of the colon-rectum, 
calculated from the measured length of 760 mm. 
and a mean internal circumference of 99 mm., is 
75,240 mm-. 

The mesentery from which the small intestine 
is suspended arises from the dorsal midline at the 
level of the last thoracic vertebra. It is nearly 
circular in outline, as is characteristic of carnivores. 

and is comparatively limited in extent (fig. 113). 
The anterior mesenteric artery and vein cross it in 
the form of a short, gently curved arc. The mesen- 
teric vein gives off only four main branches in its 
course across the mesentery; each of these bifur- 
cates, however, about 15 mm. from its origin. The 
mesenteric artery gives off seven branches; like 
the veins, these bifurcate a short distance from 
their origins. The anterior mesenteiic artery and 
vein each give rise to a well-defined colic branch. 
The colic vein arises a short distance distad of the 
origin of the inferior mesenteric vein. 

The pattern of the intestinal tract is simple 
and extremely uniform in the fissiped carnivores 
(Mitchell, 1905, 1916). Among the Arctoidea, a 
caecum is present in the Canidae but absent in the 
Mustelidae, Procyonidae, and Ursidae. A definite 
colic loop is present in the Ursidae but absent in 
other arctoids (Mitchell); a bear-like colic loop is 
present in Ailuropoda. 

An ileocolic valve is said to be absent in the 
Procyonidae and Ursidae (Jacobshagen, 1937), but 
I find a conspicuous sphincter-like ileocolic valve 
in Procyon. No indication of a valve could be 
found in a specimen of Ursus americanus, and 
there is no valve in Ailuropoda. 

The relative length of the intestinal tract varies 
among arctoid carnivores (Table 17). The gut is 
4-4.5 times head and body length in most arctoids. 
It is longer than this in some procyonids (up to 6 
times body length in Potos, 6-9 times in Procyon), 
but is only 4-4.5 times in Bassariscus and Nasua. 



and Body 


f 1217 
Canis lupus < j^qqA 

Canis familiaris 

Bassariscus astutus [385] 

Nasua socialis 

Nasua sp 460 

Potos flavus ( ^30 

[ 594 

Procyon lotor \ 490 

I [530) 

Ailurus fulgens < ^25 

Thalarclos maritimus 1244 

Ursus arctos 1352 

Ursus gyas 1720 

TT ! 900 

Ursus amencanus ( /., - 

( olo 

Ailuropoda melanoleuca I ,<gg 

* Evidently an error. 






Colon and 


Head and 










Landois (1884) 






Landois (1884) 
Beddard (1898) 
Carlsson (1925) 
Raven (1936) 






Carlsson (1925) 
Raven (1936) 








Raven (1936) 





Flower (1870) 
Carlsson (1925) 








Raven (1936) 





Raven (1936) 

_Vena cava post. 

Lobus centralis dexter 

Lig. falciforme hepatis 

Lobus lateralis dexter. 

Lig. triang. dext. 

F*rocessus caudatus 

Lobus centralis sinister 

Incisura umbilicalis 

Lig. teres 

Lobus lateralis sinister 
Lobus caudatus 

Lig. triang. sin. 

Lobus lateralis sinister 

Lig. triang. dext. 

Ix)bus centralis sinister 

Lobus quadratu.s 

Vesica fellea 

Lobu.s centralis dexter 

A. hepatica 

Ductus choledochus 

Lobus lateralis dexter 


Fig. 114. Liver of Ailuropoda. A, ventral, B, visceral view. 




The gut is longest in the bears (6-10, average 7.7 
times head and body length). Thus there is a 
broad correlation with diet, the herbivorous forms 
tending to have a longer gut (as is general among 
mammals), but this is by no means a clear-cut cor- 
relation in the Carnivora. In no carnivore does 
gut length approach the proportions (up to 25 
times head and body length in artiodactyls) found 
among mammals that are primarily, rather than 
secondarily, herbivorous. 

The most striking lack of correlation between 
diet and gut length is in Ailurus and Ailuropoda. 
Ailuropoda is exclusively herbivorous and Ailurus 
seems to be highly so, and yet gut length in these 
is among the shortest known for the Carnivora. 


The liver is small. Fixed in situ, it is a dome- 
shaped organ, very narrow dorsoventrally and with 
rather sharply arched diaphragmatic and visceral 
surfaces (fig. 114). It measures 270 mm. in breadth, 
and weighs 1564 grams. The liver is divided into 
six distinct lobes, of which the right lateral lobe is 
the largest. These are not arranged in the echelon 
formation characteristic of bears and other carni- 
vores. The size relations of the four principal 
lobes are RL>RC>LC>LL. These relations 
confirm Raven's findings. 

The left lateral lobe is roughly circular in out- 
line when viewed from the visceral surface. It is 
more or less triangular in cross section. The free 
margin is devoid of notches, which are often pres- 
ent in other carnivores. A small accessory lobule 
on the visceral surface near the transverse fissure 
has been described in both Ailuropoda and Ailu- 
rus. This structure is also present in my speci- 
men, although it is hidden behind the quadrate 
lobe. A heavy suspensory ligament, the left tri- 
angular ligament, attaches to the dorsal margin of 
the lobe and passes to the corresponding portion 
of the diaphragm. 

The left central lobe is approximately the same 
size as the left lateral lobe, but it is more flattened 
and lies mostly anterior to it; only a small triangu- 
lar section of the central lobe is visible from the 
visceral surface. Far below the surface of the liver 
the contact surfaces of these two lobes are joined 
by a prominent ligament, about 40 mm. in length, 
that extends laterad from the transverse fissure. 

The right central lobe is larger than either of the 
left lobes, but not so large as the right lateral lobe. 
When the liver is viewed from the ventral surface, 
this lobe is trapezoidal in form. There is a shallow 
fissure along its visceral margin near the falciform 
ligament, which terminates at a short accessory 
branch of the falciform ligament, extending diag- 

onally across the lower left corner of the lobe. This 
fissure is continued on the visceral surface of the 
lobe to a point where the small ligament support- 
ing the fundus of the gall bladder arises. On the 
diaphragmatic surface of the liver a wide isthmus 
connects the right central and right lateral lobes. 

The quadrate lobe is remarkable for its small 
size. It is visible only on the visceral surface of 
the liver, and lies largely in a depression on the 
visceral surface of the right central lobe. When 
the gall bladder is inflated it hides much of the 
quadrate lobe. 

The right lateral lobe is the largest lobe in the 
liver, exceeding the right central lobe slightly in 
size. Its free margin is rounded and shows a slight 
notch at the site of the triangular ligament. The 
right triangular ligament, broader than the left, 
connects the dorsal border of this lobe with the 

The caudate lobe is small but well marked, with 
a poorly defined papillary process. The basal part 
of the lobe lies to the left of the portal fissure as a 
tongue-shaped structure, reaching to approximately 
the center of the left lateral lobe. The papillary 
process is separated from the basal part of the 
caudate lobe by a shallow fissure to the left, from 
the caudate process by a notch to the right. It is a 
low, inconspicuous eminence scarcely rising above 
the level of the caudate lobe. 

The caudate process is continuous with the cau- 
date lobe except for the notch separating it from 
the papillary process. The caudate process is 
sharply defined but short, extending to the right 
only to about the middle of the right lateral lobe. 
It embraces the vena cava as in Ursus, but lacks 
the keel-shaped form characteristic of the bears 
and other carnivores. 

The gall bladder is an ovoid sac 55 mm. in 
length. The gall bladder occupies a prominent 
fossa, approximately half of which is in the right 
central lobe and half in the quadrate lobe. It is 
crossed diagonally by a ligament-like fold of peri- 
toneum. The gall bladder is entirely visible when 
the liver is viewed from the visceral surface, and 
when it is distended is partially visible from the 
ventral side of the liver. It is not visible from the 
diaphragmatic surface, as it is in most carnivores. 
The wall of the gall bladder is tough and heavy. 
Internally the mucosa is thrown up into low, inter- 
connected ridges, which give it a reticulated or 
honeycomb appearance. 

The cystic duct is arranged in a series of S- 
shaped curves. A small accessory duct emerging 
from the connective tissue deep to the gall bladder 
but not traceable to the gall bladder itself, enters 
the cystic duct 10 mm. before the latter joins the 





Bassariscus astutus 

Procyon lotor 

Ursus americanus 
Fig. 115. Livers of representative arctoid carnivores. Not to scale. 

hepatic duct. This accessory duct apparently is 
homologous with the atypical "cyst-hepatic ducts" 
that have been described in human anatomy. The 
cystic duct joins the hepatic duct at an acute angle. 
The collecting branches of the hepatic duct unite 
to form the hepatic duct proper about 15 mm. from 

the juncture of the latter with the cystic duct to 
form the ductus choledochus. 

The ductus choledochus is 95 mm. in length. 
It passes through the vertical arm (caput) of the 
pancreas to open obliquely into the duodenum, in- 
dependently of the pancreatic duct, about 115 mm. 



from the pylorus, i.e., close to the distal end of the 
duodenum. The lining of the ductus choledochus 
is smooth to a point about 15 mm. from its termi- 
nation, that is, to its entrance into the wall of the 
duodenum. Then it expands slightly to form an 
ampulla (ampulla of Vater), whose lining is raised 
into a series of lamelliform rings (fig. 116). The 
papilla in the lining of the duodenum at the ter- 
mination of the ductus choledochus is small but 

The comparative anatomy of the liver in mam- 
mals was reviewed by Renvall (1903), Meyer (1911), 
and Siwe (1937), in carnivores by Carlsson (1925). 
It is evident that the mammalian liver shows con- 
sistent and meaningful structural patterns, although 
there is no agreement as to the causes of these pat- 
terns. In all carnivores the liver is divided by 
deep fissures into four principal lobes, subequal in 
size: right and left lateral and right and left cen- 
tral. The quadrate lobe is typically large, and lies 
between the two central lobes. On the visceral 
surface of the liver there is always a sixth lobe, 
the caudate lobe, with a well-developed papillary 
process projecting posteriorly into the omental 
bursa. A large boat-shaped caudate process ex- 
tends to the right of the portal fissure. The lobes 
are typically arranged in echelon in carnivores, 
with the two central lobes lying most anteriorly 
and partly overlapping the quadrate and lateral 
lobes, and the caudate lobe and its appendages 
lying behind all the others. The caudate may or 
may not embrace the postcaval vein. 

Consistent variations on the basic carnivore pat- 
tern have been described (see fig. 115). In the 
Canidae the accessory lobes are large, the post- 
caval vein is not embraced by the caudate lobe, 
and the gall bladder is not visible from the dia- 
phragmatic surface of the liver. In the Procyoni- 
dae (two Procyon lotor, one Bassariscus astutus ex- 
amined) the accessory lobes are as large as the 
principal lobes, completely excluding the central 

lobes from the visceral surface of the liver. The 
quadrate is not overlapped by the central lobes on 
the diaphragmatic surface. Indeed, in the Pro- 
cyonidae the cystic fissure is no more than a deep 
notch, leaving the right central and quadrate lobes 
broadly confluent on the diaphragmatic surface of 
the liver. The fundus of the gall bladder reaches 
the diaphragmatic surface. The caudate lobe con- 
sists almost entirely of a large papillary process. 
Renvall's descriptions of the liver of Procyon lotor 
and Nasua sp. agree with my observations in all 
essential respects. Apparently the liver of Ailurus 
is very similar to that of the Procyonidae (Carlsson, 
1925, figs. 13-14). 

In the Ursidae ( Ursus americanus and Helarctos 
malayanus examined) the accessory lobes are rela- 
tively small, the postcava is embedded in the cau- 
date lobe, and the gall bladder is not visible from 
the diaphragmatic surface. Renvall's description 
and figure of the liver of Ursus arctos agree closely 
with my observations. The liver of Ailuropoda 
resembles in general that of the bears, but the ac- 
cessory lobes are much reduced. The quadrate 
lobe is a mere appendage of the right central lobe 
and is visible only on the visceral surface. The 
caudate lobe is smaller than in the bears, but still 
partly embraces the postcava, and the papillary 
and caudate processes are much reduced. The 
gall bladder is invisible from the diaphragmatic 
surface. In both bears and panda the liver is high- 
domed and much flattened dorsoventrally, although 
this merely reflects the shape of the cavity into 
which the liver is molded. 

Among vertebrates the liver is larger in carni- 
vores and omnivores than in herbivores (Siwe, 
1937; see also Table 18), and is relatively larger 
in small mammals. Reliable data available to me 
indicate that the weight of the liver in carnivores 
is about 3-4 per cent of body weight (Table 18). 
Unfortunately no reliable figures are available for 
bears. The relative liver weight in Ailuropoda is 



Canis familiaris 9 4 

Canis lupu; cT 1 

Potos flavus 9 1 

Ailuropoda melanoleuca cf 1 

Felis domestiea cf 52 

Felis domestiea 9 52 

Felis leo cf 2 

Homo sapiens cf 

Equiis caballus cf 5 

Equus caballus 9 10 

Bos taurus 9 218 

Sus scrofa cf 53 

Sus scrofa 9 36 

Body weight 

Liver weight 

Liver weight 



Body weight 





Crile and Quiring (1940) 




Crile and Quiring (1940) 




Crile and Quiring (1940) 








Latimer (1942) 




Latimer (1942) 




Crile and Quiring (1940) 




Morris, Human anatomy 




Crile and Quiring (1940) 




Crile and Quiring (1940) 




Crile and Quiring (1940) 




Crile and Quiring (1940) 




Crile and Quiring (1940) 



Sphincter pylori 

Duodenum (pars superior) 

Valvula pylori 

Ductus pancreaticus ace. 

Papilla minor 



Papilla major. 

Ductus pancreaticus major 

Fig. 116. Pancreatic and common bile ducts of Ailuropoda. 

slightly less than in any other carnivore in Table 18, 
but is much greater than in any of the herbivores. 


The pancreas (figs. Ill, 116) is a compact, V- 
shaped structure embracing the stem of the com- 
mon mesentery and the mesenteric blood vessels 
between its arms. The lateral edge of the vertical 
arm (caput pancreaticus) is in intimate contact 
with the duodenum, while the other (corpus pan- 
creaticus) is related to the greater omentum near 
the pylorus. The two arms are nearly equal in 
length, each measuring approximately 85 mm. 
There is a well-defined processus uncinatus, which 
is hooked around the anterior mesenteric blood 

The pancreas is drained by two ducts (fig. 116). 
The more posterior of these appears to be homolo- 
gous with the main pancreatic duct (Wirsung) be- 
cause of its position and relation to the ductus 
choledochus, although it is much less extensive and 
of smaller caliber than the accessory duct (Santo- 
rini). The main duct drains the lower end of the 
head and the uncinate process. It arises in the 
uncinate process, turns craniad into the head, and 

then caudad at an acute angle, to enter the wall 
of the duodenum; its course is thus more or less 
S-shaped. It opens on the papilla major by an 
independent outlet that is immediately caudad of 
the outlet of the ductus choledochus. The acces- 
sory duct arises in the tail of the pancreas and runs 
along the corpus and into the anterior end of the 
head. It opens into the duodenum about 18 mm. 
craniad of the papilla major. There is no connec- 
tion between the main and accessory ducts. 

No taxonomically significant variation in the 
gross structure of the pancreas has been demon- 
strated for the Carnivora. In all it is a compact 
organ, V-shaped or L-shaped (even circular, Carls- 
son, 1925). Typically there are two ducts, al- 
though one is suppressed in occasional individuals. 
The main duct opens with the ductus choledochus, 
the other farther caudad. 

The spleen (lien) is a long narrow structure, 
340 mm. in length and about 40 mm. in width, 
that lies mostly along the caudal part of the greater 
curvature of the stomach (fig. 111). It is slightly 
wider anteriorly than posteriorly. It is also much 
flattened, its thickness averaging only about 10 
mm., so that it has only two surfaces, a gastric 



and a diaphragmatic. The anterior end of the 
spleen is bent to the right almost at a right angle, 
so that it lies dorsad of the fundus of the stomach. 
The posterior end is also bent to the right to follow 
the sharp flexure of the stomach at the beginning 
of the pylorus, which gives the whole spleen the 
general form of a letter C. The organ is bound 
rather closely to the stomach throughout its entire 
length by the gastrolienal ligament, which attaches 
to the gastric surface at the hilus and does not ex- 
ceed 30 mm. in width. A narrow lienorenal liga- 
ment, attaching to the edge of the spleen near its 
middle, binds the spleen to the left kidney. 

The spleen appears to vary little among the Car- 
nivora. In all forms in which it has been described 
or in which I have examined it (Canis,Bassariscus, 
Procyon, Ursus, Felis) the spleen is a tongue-shaped 
organ with an elongate hilus on the gastric surface. 
It was relatively broader in the procyonids than 
in the others. 


If the operation of evolutionary mechanisms on 
the skeleton and musculature is sometimes difficult 
to interpret, the difficulty is multiplied when we 
come to the digestive system. The masticatory 
apparatus usually shows the most exquisite adap- 
tive relations to diet, but the rest of the digestive 
apparatus may or may not show differences corre- 
lated with food habits. A horse, with a simple 
stomach and intestine only 10 times body length, 
does as well on a diet of grass as does a cow with 
its complex stomach and intestine 25 times body 
length. Yet among mammals there is in fact a 
broad correlaton between diet and the structure 
of the digestive system ; this correlation is with the 
mechanical, rather than the chemical, properties 
of the food (Flower, 1872; Pernkopf, 1937). 

Since a higher taxonomic category is usually 
characterized by a major adaptation, often to a 
particular diet, we would expect the gut in the vast 
majority of cases to be no more variable than other 
taxonomic characters. The fact is that within the 
family or order the gut tends to remain conserva- 
tive even in the face of the most extreme changes 
in diet. No better example of this conservatism 
could be asked than the herbivorous carnivores. 
For most features of the digestive system the clos- 
est and most consistent correlation is with the 
taxonomic unit, which exists even where no other 
correlation can be demonstrated. It is strikingly 
evident in the liver, where form is tremendously 
varied but has no conceivable relation to function. 
All attempts to correlate lobation of the mammal- 
ian liver with ramification of the hepatic vessels 

or bile ducts, or with posture or other mechanical 
factors, have failed (Siwe, 1937). Yet lobes and 
fissures are clearly homologous throughout the 
Mammalia, and patterns characteristic of orders, 
families, and genera are evident everywhere (Meyer, 

Variation in the digestive system, then, is not 
random, even where there is no obvious way that 
selection can determine form. But it is evident that 
evolution of the gut involves factors more subtle 
than the mechanical and architectural require- 
ments that largely determine the evolution of the 
skeleton and skeletal musculature. 

Among the arctoid carnivores, diet ranges from 
practically exclusively carnivorous in such canids 
as the coyote, through heavily herbivorous in the 
bears, to exclusive foliage-eating in the giant panda. 
These differences in diet are accompanied by cor- 
responding modifications of the masticatory appa- 
ratus, but the structure of the remainder of the 
digestive system is astonishingly uniform through- 
out this group. 

The digestive system of the bears differs from 
the more generalized carnivore condition in sev- 
eral points, mostly relatively minor and adaptive 
to a heavily herbivorous diet (but not necessarily 
one composed of foliage) . Such adaptive features 
are the large parotid gland, the numerous vallate 
papillae, and the length of the intestine. Other 
ursid features, not overtly adaptive, are the fre- 
quently semicircular arrangement of the vallate 
papillae, the paired pharyngeal bursae, the small 
size of the accessory lobes of the liver, the presence 
of a colic loop in the intestine, the absence of an 
ileocolic valve, and the globular form of the py- 
loric region of the stomach. 

The digestive system of Ailuropoda agrees closely 
with that of the Ursidae in most of these features. 
Strikingly different is length of intestine; less ex- 
treme are differences in the form of the stomach 
and liver. The intestine is typically elongate in 
herbivorous mammals, but there are many excep- 
tions to this rule (Weber, 1928; Jacobshagen, 1937). 
The exceptions can be only partly explained by 
large caeca, expanded intestinal diameter, or the 
tendency for primitive forms to have a short in- 
testine regardless of diet. Secondary reduction of 
intestinal length in connection with secondary her- 
bivory, such as must have taken place in Ailuro- 
poda and apparently in Ailurus, is something else. 
A. B. Howell (1925) observed a similar relation in 
comparing the digestive tract of a nut- and fruit- 
eating tree squirrel (Sciurus carolinensis) with that 
of a grass-eating ground squirrel {Citellus beldingi). 
The small intestine was nearly twice as long in the 
Sciurus as in the Citellus. Howell says "the sig- 



nificance of this discrepancy in length is not un- 
derstood. It is at variance with what might be 

Reduced intestinal length has been shown to be 
correlated with a herbivorous diet in experimental 
animals. Haesler (1930) divided a litter of nine 
pigs into three groups, one of which was raised on 
an exclusively carnivorous diet, one on an exclu- 
sively herbivorous diet, and one on a mixed (nor- 
mal) diet. At the end of the experiment, in the 
animals on a herbivorous diet the stomach was 
largest, the small intestine shortest and with the 
smallest internal surface area, the caecum largest, 
and the colon shortest but with the greatest inter- 
nal surface area (Table 19). In the pigs on a car- 
nivorous diet the stomach was smallest, the small 
intestine longest but intermediate in surface area, 
the caecum and colon were smallest. The length 
differences in Table 19 are far smaller than the 
differences of hundreds, even thousands, of per- 
centage points in normally herbivorous versus nor- 
mally carnivorous species of mammals. Wetzel 
(1928) had earlier had similar results in a less care- 
fully planned experiment on rats. 

The data in Table 17 show that the total intes- 
tine is relatively about half as long in Ailuropoda 
as in the bears. The difference is due to a shorter 
small intestine, since relative length of colon is 
the same in the two groups. In both groups the 
colon is longer than in any other for which we 
have data. But whereas colon circumference in 
our Ursus americanus is identical with mean small 
intestine circumference (27.6 mm.), in Ailuropoda 
the colon circumference (99) exceeds mean small 
intestine circumference (90) by about 10 per cent. 
Therefore the relative surface area of the colon is 
about 10 per cent greater in Ailuropoda. Conse- 
quently, both in Haesler's experimental animals 
and in our Ailuropoda compared with Ursus, length 
and surface area of small intestine are reduced, and 
surface area of colon is increased, with an exclu- 
sively herbivorous diet. The slight reduction in 
colon length reported by Haesler was not evident 
in our carnivore material. 

Haesler concluded that the efficient factor deter- 
mining differences in gut proportions in mammals 
is the volume of the residue of ingesta that remains 
insoluble after it has passed through the stomach 
and small intestine. The more voluminous this is, 
the larger are the caecum and colon, and vice 
versa. Where the ingesta is soluble only after be- 
ing acted upon by bacteria and protozoa in the 
caecum and/or colon, the small intestine functions 
largely to transmit the ingesta from stomach to 
caecum colon. This is the case in Ailuropoda and 
in Haesler's pigs reared on a herbivorous diet. In 

(Data from Haesler, 1930) 

Diet Length Volume Surface 

% % 

cfu /Herbivorous ... + 6.9 .... 

^'^'^h (carnivorous ... -10.3 

^"J^',' ;. /Herbivorous -6.2 -17.6 -13.6 
^"'^^^""^- \ Carnivorous +1.4 -8.1 -4.0 

/-o, /Herbivorous ... +50.0 .... 

C^^'^"'" (carnivorous ... -14.3 

r^u^ /Herbivorous -2.4 +35.5 +17.3 

^'" \ Carnivorous -12.4 -43.0 -28.0 

T, J 1 n ,f /Herbivorous 5.3 + 7.0 4.0 

^'^'''^"'^-- /Carnivorous -1.5 -19.3 -9.6 

such cases the small intestine has little digestive 
function, and reduced length is advantageous. In 
ruminants, on the contrary, cellulose solution oc- 
curs mainly in the rumen (Dukes, 1935), and the 
small intestine can therefore function in digestion 
and absorption, and length is advantageous. 

In mammals that habitually ingest large quan- 
tities of cellulose, either the stomach is complex or 
there is a large caecum. Ailuropoda has neither, 
and in this animal the normal ingesta must be 
practically insoluble until it reaches the colon. 
With no caecum, and a short and relatively nar- 
row colon, digestion must be remarkably ineffi- 
cient. Observers have commented on the high 
proportion of undigested material in the feces of 
Ailuropoda (p. 27). 

The stomach of Ailuropoda differs from that of 
Ursus chiefly in the extensive development of the 
pyloric region. In the panda this region is almost 
gizzard-like. The stomach in Howell's squirrels 
agreed with conditions in the panda; in the grass- 
eating Citellus the pylorus was more tubular and 
more muscular than in Sciurus. Kneading, mix- 
ing, and soaking are prerequisite to cellulose di- 
gestion (Dukes, 1935), and in simple stomachs the 
pylorus is the site of true motor activity (Pern- 
kopf, 1937). Thus the modified pyloric region in 
Ailuropoda appears to perform the kneading func- 
tion and therefore to be directly adaptive. 

The liver is consistently smaller in typically her- 
bivorous than in typically carnivorous mammals, 
and it appears to be slightly smaller in Ailuropoda 
than in other carnivores. Since protein break- 
down and the emulsification, digestion, and ab- 
sorption of fats are the primary digestive functions 
of the liver, it is scarcely surprising that this organ 
is smaller in herbivorous mammals whose diet has 
a high foliage content. In the Carnivora the ac- 
cessory lobes appear to be affected first when there 



is phylogenetic reduction of liver size, and this may 
explain the much reduced accessory lobes in Ailu- 
ropoda as compared with the bears and other arc- 
toid carnivores. Since the liver is a passive organ, 
molded by surrounding organs, we would expect 
the form of the liver in Ailuropoda to reflect the 
somewhat modified stomach form. 

Nothing is known of the morphogenetic mech- 
anisms controlling growth and differentiation of 
the digestive system. Experiments such as those 
of Haesler indicate a certain capacity for individ- 
ual adaptation in the proportions of the gut, but 
the differences fall far short of those seen in species 
adapted to extremes of herbivorous or carnivorous 
diet. Thus selection, operating through genetic 
mechanisms, must be at least partly responsible 
for differences in the digestive system such as those 
seen in Ailuropoda as compared with the bears. 


1. The gross morphology of the digestive sys- 
tem of the Ursidae differs in details from that of 
other arctoid carnivores. Most of these differ- 
ences represent adaptations to a heavily herbivo- 
rous diet, but a few conspicuous differences are not 
overtly adaptive. 

2. The digestive system of Ailuropoda agrees 
closely with that of the Ursidae in nearly all de- 
tails. It differs in the pyloric region of the stom- 
ach, in liver form, and in intestinal proportions. 

3. The pylorus is almost gizzard-like in Ailu- 
ropoda, an adaptation for kneading and mixing 
the ingesta. 

4. The liver is small and the accessory lobes 
are much reduced. In mammals a small liver is 
correlated with a herbivorous diet. 

5. Length and internal surface area of the small 
intestine are much reduced in Ailuropoda as com- 
pared with the bears. The normal ingesta of Ailu- 
ropoda is probably still insoluble in this part of 
the gut. 

6. Surface area of the colon, the gut region 
where solubility of fibrous ingesta would be great- 
est, is greater in Ailuropoda than in the bears. 

7. Thus all significant differences in gross struc- 
ture between the gut of Ailuropoda and the gut of 
the Ursidae are directly adaptive to the bulky 
fibrous diet of the panda. 

8. The genetic mechanisms controlling growth 
and differentiation of the elements of the digestive 
system are unknown. Consequently nothing is 
known of the morphogenetic mechanisms whereby 
adaptive changes in the gut can be effected. 


A. Kidneys 

The kidneys are situated with their anterior bor- 
ders about on a level with the anterior border of 
the first lumbar vertebra; their long axes converge 
slightly anteriorly. The anterior border of the 
right kidney is 15 mm. farther craniad than that 
of the left. The kidneys weigh 93 and 87 gi-ams, 
together 180 grams. This represents a ratio to 
body weight of 1 : 333. The dimensions in milli- 
meters are as follows (measurements in parenthe- 
ses are from an adult female as given by Raven) : 


Right 105(112) 

Left 100(108) 

Width Thickness 
51 (62) 33 (26) 
55 (55) 31 (25) 

Each kidney (fig. 135) is composed of several in- 
dependent lobes or "renculi." The renculi are 
packed closely together, and the organ as a whole 
has the usual kidney form. The entire kidney is 
enclosed in a thin tight-fitting capsule whose walls 
contain a quantity of fat, and each renculus in turn 
has an individual capsule of its own. The right 
kidney is composed of 10 renculi, 5 of which are 
double, giving a total of 15. The left kidney is 
made up of 10 renculi, 8 of which are double, for 
a total of 18. A single layer of the capsular mem- 
brane separates the halves of the double renculi. 
The renculi are arranged around a prominent renal 

The renculi average about 20 mm. in diameter. 
Each is composed of a heavy cortex, about 6 mm. 
thick, surrounding a small medulla averaging 7.1 
mm. thick. The difference between cortex and 
medulla is not well marked macroscopically, and 
the inner and outer zones of the medulla cannot 
be distinguished. The medulla is composed of 
from one to three pyramids, each of whose apices 
forms a very long (4 mm.) and prominent papilla. 
Many renculi have three papillae. There is a total 
of 23 papillae in the right kidney. Under a hand 
lens the numerous foramina papillaris, the termi- 
nations of the papillary ducts, can be seen on the 

All the papillae of a single renculus lie together 
in a common minor calyx. The minor calyces of 

the several renculi unite, within the renal fossa, 
into two major calyces, an anterior and a poste- 
rior. The two major calyces unite outside the 
fossa to form the slightly expanded proximal end 
of the ureter. There is no renal pelvis. 

The literature on the structure of the carnivore 
kidney has been reviewed by Gerhardt (1914), 
Sperber (1944), and Schiebler (1959). The com- 
parative anatomy of the ursid kidney was described 
by Guzsal (1960). In all fissiped carnivores, ex- 
cept the Ursidae and Lutrinae, the kidney is sim- 
ple, with a single papilla or a crest. The simple 
kidney with a single papilla is the most primitive 
type of mammalian kidney, and a crest is a slightly 
modified papilla (Sperber). In the Ursidae (and 
Lutrinae) the kidney is renculate, the most highly 
modified kidney type known among the Mam- 
malia. In the Ursidae each kidney is composed 
of 23 34 renculi, except Thalarctos, in which there 
are twice as many (Table 20). Usually a few ren- 
culi are double, in one case even triple. Each 
renculus has a papilla; when a renculus is double 
there are two papillae, so the number of papillae 
is probably an index of the number of units com- 
posing the kidney. 

Since many of the renculi have three papillae in 
Ailuropoda, the total number of papillae is about 
the same as in the bears, although the number of 
renculi is considerably less. From what is known 
of the ontogeny and comparative anatomy of the 
mammalian kidney, it is evident that the multi- 
papillate renculus type of the panda represents a 
partial consolidation of the unipapillate renculus 
type of the ursids, a partial "reversion," so to speak, 
to the simple kidney type from which the renculate 
kidney was originally derived. 

Among mammals renculate kidneys are associ- 
ated with large organism size and, /or aquatic habits. 
Factors in addition to organism size must be in- 
volved among terrestrial mammals, for the kidneys 
are simple (although modified in other ways) in as 
large a mammal as the horse, and among terres- 
trial carnivores they are renculate in all bears re- 
gardless of size, but simple even in the largest of 
the cats. Dividing the kidney up into renculi re- 
duces nephron length. The factor limiting nephron 
length is the pressure required to force fluid through 







Ursus arctos 34 

Ursus arctos 33 

Ursus americanus 28 

Ursus tibelanus 22-25 

Thalarctos 62-65 

Melursus 23 

Melursus 26-30 

Helarclos 23 

Ailuropoda 10 







Sperber (1944) 

(1 triple) 


Guzsal (1960) 



Guzsal (1960) 



Guzsal (1960) 


65 + 

Guzsal (1960) 



Gerhardt (1914) 



Guzsal (1960) 







the nephron (Sperber). Relative thickness of cor- 
tex and medulla, particularly of the medulla, is 
reduced in renculate kidneys. Table 21, based on 
Sperber, gives the absolute and relative dimen- 
sions of cortex and medulla in representative arc- 
toid carnivores. Sperber's data show that relative 
thickness of cortex and medulla (particularly me- 
dulla) is greatest in the most primitive kidney 
types, least in the most highly modified. The fig- 
ures for carnivores given in Table 21 conform to 
Sperber's general figures for each kidney type in 
the Mammalia. 

Relative kidney size varies with organism size, 
the kidneys being relatively larger in small mam- 
mals than in large mammals. Beyond this, how- 
ever, the kidneys are relatively heavier in flesh- 
eating than in plant-eating mammals (Table 22). 
In the bears and giant panda the ratio is like that 
of herbivores rather than like that of other car- 

Thus it appears that in Ailuropoda the kidney is 
basically of the ursid type, but that it has begun 
to revert to a simpler type. The significance of 
this reversion is not apparent, although there are 
indications of "fetalization" in other structures in 
this region the postcava and external genitalia, for 
example. It is probably a part of the general dis- 

turbance in the lumbosacral region of Ailuropoda. 

B. Ureters 

The right ureter is 195 mm. in length and 4 mm. 
in diameter; the left is slightly shorter. The ure- 
ters are separated by a distance of 95 mm. at their 
origins, and converge toward the bladder across 
the psoas muscles. Near the bladder they pass 
between the external iliac and hypogastric vessels. 

The ureters enter the dorsal wall of the bladder 
at an oblique angle near the neck. The two ure- 
ters penetrate the bladder 20 mm. apart. 

C. Bladder 

The empty bladder (fig. 118) is an elongate pear- 
shaped sac, much flattened dorsoventrally. The 
entire organ lies anterior to the very short symphy- 
sis pelvis. The bladder measures 105 mm. in length 
and 55 mm. in width. The walls are 9 mm. thick. 

The lining of the bladder is thrown up into irreg- 
ular longitudinal folds, except for the area occu- 
pied by the trigone. The openings of the ureters 
appear as a pair of dimple-like depressions, 25 mm. 
apart. The trigonum vesicae is a prominent 
elongated triangle; the uvula vesicae is present 
as a faint longitudinal elevation along its mid line 



(in mm.) of Layer thickness X 10 

kidney layers kidney size 

Kidney Cortex + 

size* Cortex Medulla medulla Cortex Medulla Source 

... , [57 ... ... ... ... ... Raven (1936) 

Ailuropoda .^ -g g^ ^j 2.3 1.0 1.3 Original 

Ursus arctos 65 4.0-4.5 8.5 1.9 .6 1.3 Sperber (1944) 

Helarctos malayanus 60 5.2 6.9 2.0 .9 1.1 Original 

D ,, / 30 6.3 12.5 6.2 2.1 4.1 Original 

Procyonlolor | gS 5.5 10.5 5.7 1.9 3.8 Sperber (1944) 

Nasuanarica 26 5.5 10.0 6.0 2.1 3.9 Sperber (1944) 

Canis familiaris 40 7.0 17.0 6.0 1.7 4.3 Sperber (1944) 

Canislupus 51 7.0 23.0 5.9 1.4 4.5 Sperber (1944) 

* The cube root of the product of the three dimensions of the kidney. 

Cants familiaris 9 

Canis lupus cf 

Ailuropoda cf 

Ursus horribilis 9 

Procyon lotor 9 

Felis domeslica < ^ 

Felis leo cf 

Homo sapiens cf 

Equus caballus I ^ 

Bos taurus 9 

Sus scrofa < g 



Body weight 

Kidney weight 

Kidney weight 




Body weight 





Crile and Quiring (1940) 




Crile and Quiring (1940) 








Crile and Quiring (1940) 




Crile and Quiring (1940) 





Latimer (1939) 
Latimer (1939) 





Crile and Quiring (1940) 



Morris, Human Anatomy 





Crile and Quiring (1940) 
Crile and Quiring (1940) 





Crile and Quiring (1940) 





Crile and Quiring (1940) 
Crile and Quiring (1940) 

Ligaments of the Bladder 

The bladder is supported by the usual two sets 
of ligaments, the "false" ligaments and the "true" 

The false ligaments are composed of dorsal and 
ventral elements. A long continuous fold of peri- 
toneum is attached to the dorsum of the bladder. 
Medially it forms a deep triangular cul-de-sac, 
roofed over with peritoneum through which the 
ductus deferentes run. From this fold of perito- 
neum dorsal and lateral ligaments run to the walls 
of the pelvic cavity. A single ventral fold of peri- 
toneum runs from the venter of the bladder to the 
ventral abdominal wall. The urachus arises be- 
hind the ventral ligament and runs craniad on the 
belly wall to the umbilicus. 

There are three true ligaments from the poste- 
rior part of the bladder: the unpaired puboprostatic 
ligament running from the ventral midline of the 
neck of the bladder to the pubis, and the pair of 
lateral ligaments running from the lower part of 
the bladder to the walls of the pelvis. 

A. Male Perineal Region 

The perineal region (fig. 117) comprises the anus, 
the prepuce, and the naked glandular region lying 
between them. The testes lie immediately caudad 
of the inguinal canal, which places their caudal 
borders about on a line with the caudal end of the 
symphysis pelvis. This means that the caudal end 
of the testis lies about 35 mm. in front of the penis 
and 50 mm. laterad of the midline, which places 
them at a considerable distance from the perineum. 
In addition, there is no scrotum or other external 
evidence of the site of the testes in the juvenile 
individual dissected. At sexual maturity the tes- 
ticles are very evident. 

The anus is a transverse aperture, somewhat 
U-shaped, with the concavity directed ventrally. 

It is 30 mm. wide in the contracted condition, and 
is surrounded by an extensive area of light-colored 
naked skin. This hairless area is triangular in out- 
line, with the base of the triangle at the root of the 
tail and the apex continued ventrad to the prepuce. 
It is granular in texture, the granulations becom- 
ing less pronounced ventrally as the prepuce is 
approached. The dorsal wall of the anus forms a 
prominent cushion, underlain by fat, which is tra- 
versed by deep furrows radiating from the anus. 
Typical anal glands are absent. 

Ventrad of the anus is a narrow vertical median 
prominence bounded laterally by a deep furrow on 
each side, which extends from the anus to the dor- 
sal root of the prepuce. It widens slightly toward 
the anus, into which it is continued, and shows a 
faint median raphe. 

The structure of the external genitalia is remark- 
able. The penis is entirely withdrawn within a 
prominent heart-shaped elevation. This eleva- 
tion, which represents the prepuce, measures about 
40 mm. in both transverse and longitudinal diam- 
eters. It is sharply constricted off from the sur- 
rounding skin by a shallow furrow laterally and a 
deep excavation dorsally, which gives it a button- 
like appearance. There is an additional concen- 
tric furrow on its surface on either side. Its outer 
surface is rather well haired, except dorsally, where 
the naked area is continuous with the naked area 
of the perineum. An aperture, around which the 
skin is puckered, occupies the center of the promi- 
nence. A faint median raphe extends dorsad from 
the aperture. 

The lining of the prepuce is heavily pigmented 
and has a puckered, honeycomb appearance. It 
is reflected to form the covering of the pars intra- 
praeputialis of the penis. Thus the pars intraprae- 
putialis appears to be enclosed in a thick-walled 
pocket, the lining of which would form the outer 
covering of the body of the penis during erection. 



Fig. 117. Perineal region of subadult male Ailuropoda (Su Lin). 

Dorsally (posteriorly) the lining of the prepuce is 
attached to the pars intrapraeputialis by a small 
but conspicuous frenulum. 

B. Testis and Its Appendages 

The testes lie just outside the external inguinal 
ring, and hence are prepenial in position (fig. 135). 
The two organs are separated by a distance of 
70 mm. There is no true scrotum, and at least in 
the subadult animal dissected the testes and their 

wrappings are so embedded in fat that they do not 
even produce a swelling in the contom- of the body. 

The testis is an ovate structure, 28 mm. in 
length, and wider posteriorly than anteriorly. It 
is considerably flattened dorsoventrally. 

The epididymis is relatively large, and is di- 
vided into three well-marked regions: caput, cor- 
pus, and Cauda. The caput is a relatively small 
expansion occupjnng the usual i>osition over the 
anterior end of the testis. The corpus is a flat 


Vesica urinaria 

Gl. ductus deferenti 

M. ischiocavernosus 

Papilla ductus deferenti 

M. bulbocavemosus 

Fascia penis 

M. retractor penis 


Fig. 118. Male reproductive organs of Ailuropoda. 




M. ischiocav 

M. bulbocavernosus 

M. sphincter 

Caput penis 


M. sphincter urethrae 

M. bulbocavernosus 

Bulbus urethrae W/W'^/^ 



Corpus ca%'ernosui 

Praeputium (cut) 

M. sphincter urethrae 

. ^.., '-J,--- P^f^ membranaceae 


Corpus spongiosum-^ W 

Corpus fibrosum 
Tunica albuginea 

Pars cavernosa urethrae 


Praeputium (cut) 

Fig. 119. Penis of Ailuropoda. A, lateral aspect, B, longitudinal section. 

band, 8 mm. wide, closely applied to the lateral 
border of the testis. The cauda is by far the larg- 
est region of the epididymis. It is a conical caplike 
structure over the posterior end of the testis. 

The ductus deferens (fig. 118) is continued 
from the tail of the epididymis along the medial 
border of the testis, entering the funiculus sper- 
maticus at the anterior end of the testis. The 
funicular part of the ductus is about 80 mm. long. 
At the entrance to the inguinal canal it leaves the 
spermatic vessels and loops back, ventrad of the 
terminal vessels of the aorta and the ureter, to the 
dorsiun of the bladder. The last 45 mm. of the 
ductus, Ijnng on the neck of the bladder, is en- 
larged and encased in a thick layer of glandular 
tissue. The ducts from each side, which are con- 
siderably enlarged by their glandular investment, 
approach each other on the neck of the bladder. 
They unite, 5 mm. before reaching the wall of the 
urethra, into a common duct, which passes through 
the wall of the urethra at a very oblique angle. 
The duct opens into the urethral canal on a small, 
elongate papilla. 

There is no indication of vesicular, prostate, or 
bulbo-urethral (Cowper's) glands. 

The urethra is divisible into pars membranacea 
and pars cavernosa. The pars membranacea is 
60 mm. in length, with heavy muscular walls about 
4 mm. thick. The lining of the lumen is thrown 
up into prominent longitudinal ridges at its prox- 
imal end. The pars cavernosa is 43 mm. in length. 
The lining of its lumen is elevated into numerous 
small longitudinal mucous folds, and the lining of 
the distal half, except near the external orifice, is 
irregularly pigmented. There is a prominent longi- 
tudinal fold along the dorsal wall of the fossa nav- 

C. Penis 

The penis (figs. 118, 119, 135) is remarkable for 
its small size. It measures only 36 mm. in length 
(measured from the posterior border of the ischio- 
cavernosus muscle) by 13 mm. in diameter. The 
corresponding measurements on the penis of a fully 
adult male (Mei Lan) are 70 mm. by 25 mm. The 
organ is divided into a button-like pars intraprae- 
putialis and a cylindrical body. The penis is S- 
shaped, its tip directed posteriorly. The prepuce 
was described on page 221. 

In addition to its crural attachment to the ischia, 
the penis is supported by a pair of suspensory liga- 
ments arising from the ischiadic part of the sym- 
physis pelvis. These ligaments attach to the sides 
of the penis at its base, where the ischiocavernosus, 
sphincter ani externus, and suspensory ligament 
have a common attachment. There is also a paired 
M. retractor penis (p. 172) inserting into the base 
of the pars intrapraeputialis. 

The body or shaft of the penis is composed prin- 
cipally of three cavernous elements, the two cor- 
pora fibrosa and the corpus spongiosum. These 
are enclosed within a common sheath of tough 
connective tissue, the fascia penis. 

The two corpora fibrosa (BNA: corpora caver- 
nosa penis) are remarkably small, each scarcely 
exceeding the corpus spongiosimi in size. The 
corpus fibrosum arises, as the crus penis, from the 
descending ramus of the ischium, covered by the 
ischiocavernosus muscle. The two corpora con- 
verge to form the body of the penis. Anteriorly 
they are continued as the baculum, which is lodged 
in the distal part of the penis but does not extend 
into the pars intrapraeputialis. Each corpus is 
enclosed in a tough tunica albuginea, and between 



the two corpora these are united into a median 
septum penis. 

The corpus fibrosum is composed of dense spongy 
tissue, divided into two regions differing sharply in 
structure (fig. 119). The basal part (correspond- 
ing to the unossified part of the corpus fibrosum 
in bears and procyonids) is a firm meshwork with 
coarse interspaces, resembling the corpus fibrosum 
of other arctoid carnivores. Between this basal 
part and the baculum (corresponding to the prox- 
imal part of the baculum in bears and procyonids), 
the meshwork contains an immense number of 
glistening white fibers, straight and radially ar- 
ranged. The medial ends of these fibers are deeply 
embedded in the tunica albuginea. To judge from 
its position, this part of the corpus fibrosum repre- 
sents the degenerate proximal part of a formerly 
much longer baculum. 

The corpus spongiosum (BNA: corpus caver- 
nosum urethrae) surrounds the pars cavernosa ure- 
thrae, except distally where it is replaced by the 
corpus cavernosum. It begins proximally as a rela- 
tively small bulbus urethrae, which tapers gradu- 
ally into the corpus. The bulbus is surrounded by 
a small M. bulbocavernosus. 

The pars intrapraeputialis is the hemispher- 
ical tip of the penis lying within the preputial cav- 
ity. It is broader transversely than dorsoventrally, 
and is composed of a caput and a collum marked 
off from the head by a faint constriction. The in- 
tegument covering the head is continuous with the 
integument lining the preputial cavity. It is faintly 
pitted, and is pigmented peripherally, unpigmented 
centrally. A very small frenulum connects the 
urethral border of the head with the prepuce. The 
meatus of the urethra is a vertical slit in the center 
of the head. 

The interior of the pars intrapraeputialis and 
the distal part of the body of the penis are filled 
with erectile tissue, the corpus cavernosum. 
This is exceedingly fine-meshed cavernous tissue, 
clearly distinguishable from the coarser tissue of 
the corpus spongiosum. 

D. Baculum' 

The baculum is a small, remarkably shaped 
structure, completely different from that of any 
other carnivore for which this bone has been de- 
scribed (fig. 120). It is only 24 mm. in length. 
There is a short, rod-like body from which rounded 
winglike expansions, deflected downward at an an- 
gle of about 45, arise. These wings occupy more 
than the distal half of the bone. They are heavy, 
with slightly irregular rounded edges, and the max- 

Description from an adult male (CNHM 31128). The 
baculum of the specimen dissected was incompletely ossified. 

imum width across them is 12 mm. The tip of the 
bone is a short, rounded, papilla-like projection. 

The dorsal border of the baculum forms a rounded 
keel. It is slightly sinuous in profile, convex over 
the rodlike base and concave over the winglike 
processes. The tip is directed slightly downward. 
The wings form a deep inverted trough for the 
urethra ventrally. 


The female reproductive organs are known only 
from the description, based on the viscera of an 
adult individual, given by Raven (1936). The fol- 
lowing account is taken from his report (fig. 121). 

The ovary is slightly flattened, rounded, and its 
surface is fissured and pitted, thus having some- 
what the appearance on the surface of a highly 
convoluted brain. It measures 30 mm. in length 
by 23 mm. in width and 11 mm. in thickness. 

The uterine tube is very much contorted but 
when straightened out measures 95 mm. 

The corpus uterus is less than half the length 
of the cornua and is slightly depressed. The cor- 
nua are rounded on the free edge and diminish in 
thickness toward the broad ligament. The surface 
of the uterine mucosa is arranged in a mosaic with 
distinct clefts separating the smooth areas making 
up its surface. The mucosa has the same appear- 
ance over its entire surface from the extremities of 
the cornua to the cervix. The cervix is strong, 
with comparatively muscular walls. 

The vagina, which has a total length of 85 mm., 
is narrow, with firm muscular walls. Its mucosa 
forms a series of closely set, transverse circular 
folds. Caudally the vagina is bounded ventrally 
by the tubercle, on the center of which is the ure- 
thral opening, laterally and dorsally by the hymen, 
which is a fold 8 mm. long. 

The urogenital sinus, like the vagina and cor- 
pus uterus, is flattened so that, though not wide, it 
is more extensive transversely than dorsoventrally. 

Of the specimen under consideration there is 
preserved only a very little of the skin surround- 
ing the genital and anal openings. It is bare, ex- 
cept for a few hairs. On this skin are the openings 
of numerous glands, which when squeezed express 
an oily substance. 

Lateral to the dorsal limit of the genital opening 
on each side is a rather large crypt, which contains 
the minute openings of many of these glands. 


The female reproductive organs in the arctoid 
Carnivora show little variation in gross structure 



Ailuropoda melanoleuca 


Ailunis fulgens 

Bassarisctis astutus 

t\?X'iir-^.~yyt''7,'j^.: ;^^ ... ^-^ . 

Procyon lotor 

Ursus atnericanus 

Fig. 120. Baculum of Ailuropoda and other arctoid carnivores. A, dorsal, B, ventral, C, anterior views. Ailuropoda 
X 2, others XI). 

and therefore need not concern us further here. 
The male organs, on the contrary, show extensive 
and fundamental differences, both in the accessory 
sex glands and in the copulatory organ. 

The accessory sex glands of the Mammalia were 
reviewed by Oudemans (1892), who recognized four 
kinds of glands, and by Disselhorst (1904). With- 
in the Carnivora there are pronounced differences 
in the degree of development of these several kinds 
of glands, and these differences are strictly corre- 

lated with taxonomic units. No recent or detailed 
studies exist for the accessory sex glands of the 
Ursidae or Procyonidae. Owen says: "In the Bear 
the sperm-ducts are enlarged and in close contact 
at their terminations, with thick follicular walls" 
[= glands of ductus deferens]; "beyond this gland- 
ular part they retain their width, but contract to 
open upon the verumontanum. A thin layer of 
prostatic substance surrounds the beginning of the 
urethra." He further states that in the Procyoni- 



dae and Mustelidae "the prostate is better devel- 
oped than in the Ursines, especially in the Racoon, 
in which it is in advance of the neck of the blad- 
der." In Nasua sp. "the walls of the vasa defer- 

Ailurus fulgens differs somewhat from Procyon 
and Nasua, and is considerably different from Ur- 
sus and Ailuropoda. In an adult male dissected 
by me the distal ends of the ductus deferentes 

Lig. ovarii proprium 
Ovarium dext. 


Vestibulum vaginae 


FiG. 121. Female reproductive organs of Ailuropoda. Dorsal view, vestibule and vagina opened along mid-dorsal line 
and spread out. (From Raven, redrawn). 

entia are swollen immediately before these vessels were not dilated, there were neither glands of the 

enter the urethra, and the prostate has a more ductus deferens nor ampullae, and the prostate 

sudden projection at its upper end than I have ob- was present but much smaller and less sharply set 

served in the musteline animals that I have dis- off from the urethra than in Procyon. This agrees 

sected." (Turner, 1849.) essentially with Flower (1870). 

In a specimen of Procyon lotor dissected by me The differences in the male accessory sex glands 

the prostate was a large and prominent globular among the Carnivora, are: 

structure surrounding the urethra at the base of vesicular glands absent all Carnivora 

the bladder. The distal ends of the ductus defer- ^.^^^^^.^ ^1^^^^ ^^^^^^ Arctoidea 

entes were dilated as in Ailuropoda, but these dila- Prostate large, glands of ductus deferens absent. 

tions contained no glandular tissue. Instead this Ampulla ductus deferens small or ab.sent Canidae 

portion of the ductus formed an ampulla with Ampulla ductus deferens large Procyonidae 

thick cavernous walls, somewhat similar to the Prostate vestigial, glands of ductus deferens present, 

, , ,oN 1 i i. fillmg ampulla Ursidae 

ampulla of man. Weber (1928) erroneously states ^ , , ^ . > 

^, f . . _, ., ^, ... i.- 1 Cowper s glands present I 

that m the Procyonidae the prostate is vestigial Prostate present 1- Aeluroidea 

and glands of the ductus deferens are present. Glands of ductus deferens absent J 



This table is based largely on the data compiled 
by Oudemans. 

It is evident that Ailuropoda agrees closely with 
the Ursidae in the structure of the male accessory 
sex glands, and therefore these structures need not 
be considered further here. Ailurus most closely 
resembles the Procyonidae, but does not agree fully 
with any other arctoid carnivore. 

For the external genitalia the picture is not so 
clear. The morphology of the penis was reviewed 
by Gerhardt (1909, 1933), Pohl (1928), and Slijper 
(1938). In the arctoid carnivores the penis is char- 
acterized by the abdominal position of the prepuce 
with the shaft long and enclosed in the belly skin 
(Pocock, 1921), and by the great length of the 
baculum and sparsity of erectile tissue (Gerhardt, 
1933). In the Ursidae and Procyonidae the bacu- 
lum extends proximally through the entire corpus 
nearly to the root of the penis, and the corpus fibro- 
sum, which continues proximally from the bacu- 
lum, is correspondingly short. Except for the 
intrapreputial part, the bone is clothed only in a 
thin layer of fascia. The erectile tissue the cor- 
pus cavernosum surrounding the intrepreputial 
part of the baculum, and the corpus spongiosum 
surrounding the urethra is remarkable for its 
flabbiness, with delicate trabeculae enclosing huge 

The ursid-procyonid-mustelid penis type is a 
highly specialized derivative of the more primitive 
vascular type, with the originally vascular corpora 
fibrosa almost completely replaced by bone. This 
might be called the "osseous type." As in the 
likewise highly specialized fibro-elastic type of the 
artiodactyls, temporary stiffening by engorgement 
of the corpora fibrosa with blood has been re- 
placed by permanent stiffening through special 
supporting tissue. 

The penis of Ailuropoda and Ailurus contrasts 
sharply with the osseous type so characteristic of 
all other arctoid carnivores. In the two pandas 
this organ closely resembles the much more prim- 
itive penis of the cats and certain viverrids: it is 
small, posteriorly directed, sub-anal in position, 
the corpus consisting largely of cavernous tissue, 
the baculum absolutely and relatively small. From 
the ontogenetic standpoint this approaches the fetal 
condition, and represents a state of arrested develop- 
ment, of "fetalization." 

' It is remarkable that there are no descriptions of the 
penis of any bear or any procyonid. I have dissected this 
structure in a specimen of Procyon lotor, but no bear material 
was available to me. 

Since Ailuropoda is an ursid, it must originally 
have had the highly specialized osseous penis type 
of the bears. The remarkable structure of the 
corpus fibrosum strongly supports this conclusion. 
The antecedents of Ailurus are unknown, but cer- 
tainly they were not ursids, and therefore fetaliza- 
tion of its male external genitalia was independent 
of the corresponding process in Ailuropoda. Fetali- 
zation of the genitalia can scarcely be interpreted 
as adaptive, and if not adaptive it must be associ- 
ated morphogenetically with some other feature 
that is adaptive. In Ailuropoda there is abundant 
evidence of disturbance in the whole lumbosacral- 
pelvic region, apparently associated with strong 
cephalization of the body axis, and the modified 
external genitalia may simply reflect this general 
disturbance. There is no overt indication of 
such disturbance in Ailurus. The only obvious 
adaptive feature the two pandas have in common 
is hypertrophy of the masticatory apparatus, and 
it is difficult (though not impossible) to associate 
this with fetalization of the male genitalia. 


1. The kidney of Ailuropoda is renculate as in 
the Ursidae, but the renculi are fewer in number 
and are multipapillate. 

2. The total number of renal papillae is about 
the same as in bears. This suggests that each ren- 
culus in Ailuropoda represents a consolidation of 
several unipapillate renculi of the ursid type. 

3. The male reproductive organs of Ailuropoda 
may be divided into two parts: 

(a) The accessory sex glands, which agree closely 
with the distinctive pattern of the Ursidae. 

(b) The external genitalia, which differ from 
those of all other arctoid carnivores except 

4. The Arctoidea (except the Canidae) are char- 
acterized by a highly specialized osseous penis, in 
which erectile tissue has been almost completely 
replaced by bone, and during erection the organ 
increases only insignificantly in length and diam- 
eter. The penis of the Canidae is unique among 

5. In Ailuropoda and Ailurus the penis has 
been arrested at a much more primitive state of 
development than in other arctoids. The signifi- 
cance of this convergent "fetalization" of the ex- 
ternal genitalia in two remotely related forms is 
unknown. In Ailuropoda it may be associated 
with cephalization of the body axis. 



The epiglottis(figs.l09,122) is triangular, with a 
pointed apex and moderately large rounded wings. 
The structure is nearly as broad as long. The epi- 
glottis is subpalatal, not retrovelar, in position, 
the tip lying below and well forward of the poste- 
rior margin of the soft palate. A median glosso- 
epiglottic fold connects the epiglottis with the base 
of the tongue, and a very high and narrow pharyn- 
goepiglottic fold runs laterally and slightly ante- 
riorly from the side of the epiglottis to the wall of 
the pharynx. The pharyngoepiglottic fold sepa- 
rates a shallow epiglottic depression anteriorly 
from an extremely deep and roomy pyriform re- 
cess posteriorly. The pyriform recess abuts pos- 
teriorly against the arytenoid and the arch of the 
cricoid. Its floor is far below the inferior wall of 
the esophagus. 

A. Cavity of the Larynx 

The laryngeal cavity is characterized by a very 
deep vestibulum, the portion of the cavity lying 
above the vocal folds (fig. 110). The superior 
laryngeal aperture (fig. 122) is bounded by the 
epiglottis anteriorly, followed by a short ary-epi- 
glottic fold extending between the epiglottis and 
the cuneiform cartilage. Behind the cuneiform 
tubercle the aperture is bounded by the cuneiform 
and arytenoid cartilages. The outlines of the cu- 
neiform cartilage lying beneath the mucous mem- 
brane are clearly visible. The cuneiform tubercle 
is a conspicuous knob-like elevation formed by the 
protruding upper end of the cuneiform cartilage. 
The corniculate tubercle, lying behind the cunei- 
form tubercle, is a less prominent elevation formed 
by the corniculate process of the arytenoid. 

The ventricular folds lie deep within the cavity 
of the larynx. Each fold is a heavy, smoothly 
rounded elevation in the laryngeal wall, broader 
posteriorly than anteriorly and extending diago- 
nally forward and downward from the cuneiform 
cartilage to the anterior end of the laryngeal cav- 
ity. The vocal lips lie several millimeters below 
the ventricular folds and are much more promi- 
nent. They stand nearer the median line than the 
ventricular folds. The vocal lip is triangular in 

cross section. Its thin free border is the vocal fold, 
or true vocal cord. Between the ventricular and 
the vocal fold is a shallow recess, the laryngeal ven- 
tricle, running the length of the folds and broadly 
open to the laryngeal cavity. There are no laryn- 
geal sacs. The true cavity of the larynx, the space 
below the vocal folds, is shallow and scarcely wider 
than the rima glottidis anteriorly, gradually broad- 
ening to the diameter of the larynx posteriorly. 

B. Cartilages of the Larynx 
Figure 123 

The laryngeal skeleton is boxy. The margins of 
the thyroid and cricoid cartilages are only slightly 
excised, and the thyrohyoid and thyrocricoid mem- 
branes correspondingly limited. The result is that 
almost the entire laryngeal cavity is encased in 

The thyroid cartilage is characterized by broad 
lamina. The anterior thyroid notch is scarcely 
indicated, but the posterior thyroid notch is deep, 
extending more than half way to the anterior mar- 
gin of the cartilage. The dorsal outline of the 
cartilage is nearly straight. The anterior and pos- 
terior cornua are relatively short and stout, and 
about equal in length. There is a poorly defined 
muscular process near the middle of the posterior 
margin, and from this a faint linea obliqua extends 
anteriorly and dorsally across the lamina. Above 
the muscular process, the posterior margin is deeply 
excavated to form a pit for muscle attachment. 

The cricoid cartilage is completely divided at 
the ventral midline, the two halves of the arch 
separated by an interval of about 2 mm. There 
is in addition a deep U-shaped notch in the poste- 
rior margin at the ventral midline and a shallower 
notch in the anterior margin. The arch is concave 
in cross section, and is otherwise practically de- 
void of surface relief. The lamina is about twice 
as broad anteroposteriorly as the arch, and is quad- 
rangular in outline, somewhat longer than broad. 
Its anterior margin has a shallow U-shaped notch 
at the midline. There is a prominent median keel 
separating the areas of origin of the two posterior 
cricoarytenoid muscles. The cricothyroid articu- 
lation is at the juncture between arch and lamina. 





Ventriculus laryngis 

Tuberculum cuneiforme .' 

Vallecula epiglottica 

Plica pharyngoepiglottica 

V Plica ventricularis 
Plica vocalis 

Plica aryepiglottica 

Tuberculum corniculatum 

Recessus pyriformis 

Incisura interarytaenoidea 

Fig. 122. Laryngeal cavity of Ailuropoda from above. 

The arytenoid cartilage is massive and irreg- 
ular in form, with well-developed processes. The 
median processes of the two arytenoids are in con- 
tact at the midline. The apex is short and blunt, 
the muscular process moderate in length but very 
broad and heavy. The corniculate process is a 
very short cylindrical projection on the medial 
margin of the cartilage. The vocal process is a 
keel-like projection on the ventral surface of the 

The cuneiform cartilage is a very large L-shaped 
structure attached to the apex of the arytenoid. 
A small unpaired interarytenoid cartilage lies im- 
mediately anterior to the two median processes of 
the arytenoid, and marks the posterior limit of the 
interarytenoid notch. 

C. Muscles of the Larynx 

M. aryepiglotticus (fig. 125) arises from the 
interarytenoid cartilage, beneath the oblique ary- 
tenoid, and extends almost directly ventrad along 
the aryepiglottic fold, lying lateral to the ventric- 
ular fold, to insert on the base of the epiglottis. 
A few of the posterior fibers insert on the antero- 
lateral margin of the arytenoid cartilage. 

M. cricothyreoideus (fig. 124) is partially di- 
visible into straight and oblique portions. The 

more superficial pars recta arises from the medial 
ventral border of the arch of the cricoid cartilage, 
separated by a small interval from its mate of the 
opposite side, and passes straight dorsad to its in- 
sertion along the dorsal half of the posterior border 
of the thyroid cartilage from the level of the infe- 
rior tubercle to the inferior cornu. A few of the 
superficial fibers are continuous with some of the 
posterior fibers of the thyropharyngeal division of 
the posterior constrictor of the pharynx. The 
deeper pars obliqua arises from the posteroventral 
border of the cricoid, and inserts into the posterior 
cornu and inner surface of the thyroid cartilage. 
A few fibers continue into the cricopharyngeal di- 
vision of the posterior pharyngeal constrictor. 

M. cricoarytaenoideus posterior (fig. 125) is 
a fan-shaped muscle lying on the dorsal surface of 
the lamina of the cricoid cartilage. Origin is from 
the middle and posterior thirds of the dorsal sur- 
face of the cricoid lamina, where it is separated 
from its mate by a median keel on the cricoid lam- 
ina. The fibers converge anterolaterally, to insert 
on the posterior margin of the muscular process of 
the arytenoid cartilage. 

M. cricoarytaenoideus lateralis arises from 
the dorsolateral margin of the cricoid caitilage and 
inserts on the anterolateral border of the muscular 

Proc. medianus 


Linea obliqua 

Cart, interarytenoid 
Cornu ant.v. 

Cornu post, os hyoid 

Cornu post. 

Cart, tracheales 
Fossa muscularis 

Cart, thyreoidea 


Cart, cricoidea 
Tub. thyreoideum post. 

Cart, interarytenoid^ p^ comiculatus 
Cart, arytenoid. _/-! l'f<[ ^ p^^ medianus 

Proc. muscularis 

Incisura thyreoidea post. 

Arcus cart, cricoideae 

Cart, tracheales 

Cornu ant. 

Lamina cart, cricoidea 


Cart, thyreoidea 

Tub. thyreoideum post. 

Cornu post. 


Cart, postarytenoid 

Cart, cuneiform is 

I*roc. medianus 

Cart, arytenoid. 
FVoc. vocalis 

Lig. vocalis 


Fig. 123. Laryngeal cartilages of Ailuropoda. 

process of the arytenoid cartilage. The anterior 
fibers insert into a narrow raphe shared by the 
transverse arytenoid. 

M. vocalis arises from the thyroid lamina at the 
ventral midline, and inserts on the muscular proc- 
ess of the arytenoid cartilage. The muscle lies 
lateral to the vocal ligament. 

M. hyoepiglotticus (fig. 125) is a slender paired 
muscle extending from the ceratohyal to the lin- 

gual surface of the epiglottis. The fibers overlap 
and unite with those of the muscle of the opposite 
side at the insertion. 

M. thyreoarytaenoideus (fig. 125) arises from 
the midventral border of the thyroid cartilage, 
passes around the lateral dorsal aspect of the ary- 
tenoid cartilage, and inserts on the interarytenoid 
cartilage. It is not entirely separable from the 
vocal muscle lying deep to it. 



Os ceratohyale 
Os epihyale 

M. ceratohyoideus 
Corpus ossis hyoidei 

Os thyreohyale 

M. hyoglossus (cut) 

Insertion m. mylohyoid. 
M. constr. phar. med. 

M. thyreohyoid. 

M. thyreopharyng 

M. styloglossus (cut) 

constr. phar. med. 

m. hyoglossus 


m. thyreohyoid. 



Os stylohyale 

Cart, thyreoidea 

Insertion m. thyreohyoid. 

Origin m. cricothyreoid. 
Cart, cricoidea 
Insertion m. cricothyreoid. 

Origin m. cricopharyngeus 

Insertion m. sternothyreoid. 

Lig. cricothyreoid. med. 
M. cricothyreoideus 

M. cricopharyngeus 

Fig. 124. External laryngeal musculature of Ailuropoda, ventral view. Superficial dissection to left, deeper dissection to right. 

M. arytaenoideus obliquus (fig. 125) is a thin 
strand of muscle fibers arising from the interary- 
tenoid cartilage at the dorsal midline, crossing the 
origin of its fellow, and running obliquely anteri- 
orly along the aryepiglottic fold to insert on the 
epiglottis at the pharyngo-epiglottic fold. 

M. arytaenoideus transversus (fig. 125) is a 
well-developed paired muscle arising from the mus- 
cular process of the arytenoid cartilage and insert- 
ing at the midline on the interarytenoid cartilage. 
It is overlapped at its insertion by fibers of the 
oblique arytenoid, aryepiglottic, and external thy- 
roarvtenoid muscles. 

D. Discussion of Larynx 
Larynxes of Canis latrans, Procyon lotor, Xasna 
narica, AiluTus julgens, Ursus tibetanus, U.ameri- 
canus (juvenile), and Melursus ursinus were dis- 
sected for comparison with Ailuropoda (fig. 126). 
Among arctoid carnivores, only the larynx of Cams 
familiaris has been well described in the literature. 
Albrecht ( 1896) described and compared the mucous 
membrane folds of the larynx in several arctoids: 
Canis, Vulpes, Otocyon, Procyon, Potos, Ursus, and 
several mustelids. Goppert (1894) described the 
cartilage of the epiglottis and the cuneiform carti- 
lage of Ursus arctos and several mustelids. Owen 

Os ceratohyale 

Corpus ossis hyoidei 

M. genioglossus 


M. ceratohyoideus 

Os epihyale 

M. hyoepiglotticus 

Os thyreohyale 
Os stylohyale 

Membrana hyothyreoidea 


Os tympanohyale 

Cart, thyreoid.' 

Proc. muse, cart, aryt 

Cart, interarytenoid 

Proc. medianus, cart, aryt- 

M. arytenoid, obliquus 
M. thyreoarytenoid. extemiis 

M. arytenoid, transversus 

M. cricoarytenoid, posterior 


Fig. 125. Intrinsic laryngeal musculature of Ailuropoda dorsal view. 

(1868) described and figured the laryngeal carti- 
lages of Ursus. Fiirbringer (1875) studied the in- 
trinsic laryngeal musculature of seventeen species 
of Carnivora, including Canis, Procyon, Nasua, 
and Ursus. 

In general, the larynx is most primitive in the 
Ursidae among the arctoids. This is emphasized 
by Goppert (1894) for the epiglottal and cuneiform 
cartilages, and (1937) for the arytenoids. It is 
confirmed in the present study. The larynx is 

generally primitive in the Canidae, but with dis- 
tinct and characteristic specializations. In the 
Procyonidae the larynx is much reduced, in some 
respects almost degenerate. 

The epiglottis is lanceolate in all arctoids in 
which it has been examined. In the Canidae the 
angles of the epiglottis are very sharp and the ary- 
epiglottic folds are narrow and transverse, giving 
a characteristic triangular shape to the anterior 
part of the entrance to the larynx. Cuneiform 

Cants familiaris 


Ailurus fulgens 

Nasua nariea 

MduTSus UTsinug 

Ailuropoda melanoUuca 

Fig. 126. LarjTigeal cartilages of representative arctoid carnivores, right lateral view. The arj-tenoid and cuneiform 
cartilages are shown separately above the main cartilages. 




and corniculate tubercles are present, both pairs 
lying close to the midline. In the Procyonidae the 
epiglottis is reduced, especially its lateral wings. 
The aryepiglottic folds are heavy and run obliquely. 
A cuneiform tubercle is present, although unsup- 
ported by cartilage, but the corniculate tubercle 
is completely absent. In the Ursidae and Ailu- 
ropoda the aryepiglottic fold is heavy and runs 
obliquely, but the line is interrupted at the cunei- 
form tubercle. Both cuneiform and corniculate 
tubercles are prominent. The ventricular and 
vocal folds show little significant variation among 
the arctoids examined. They are oriented very 
steeply, and the ventriculus is very deep, in the 

The thyroid and cricoid cartilages are only 
slightly excised at their margins in the Ursidae 
and Ailuropoda, and the posterior thyroid notch, 
while deep, is very narrow, giving a boxy appear- 
ance to the laryngeal skeleton. The hyothyroid, 
cricothyroid, and cricotracheal membranes are 
correspondingly reduced. The thyroid cornua are 
moderately long and subequal. There is a sharply 
defined muscular fossa below the posterior cornu. 
The posterior thyroid tubercle is large but low. 
The cricoid arch is intact but deeply incised at the 
ventral midline (Melursus), almost divided ( Ursus 
malayanus, Owen), or completely divided {Ailu- 
ropoda and our specimen of Ursus americanus) . 

In the Canidae the margins of the cartilages are 
somewhat more excised than in the Ursidae. The 
posterior thyroid notch is very shallow. The an- 
terior thyroid cornu is normal, but the posterior 
cornu is extremely short, scarcely differentiated 
from the thyroid lamina. There is no muscular 
fossa, and the posterior thyroid tubercle is small. 
The cricoid arch is intact, and its anterior margin 
is broadly excised. 

In the Procyonidae (including Ailurus) the mar- 
gins of the thyroid lamina are deeply excised, in 
addition to a very deep posterior thyroid notch. 
The laryngeal membranes are very extensive. The 
thyroid cornua are approximately normal. Mus- 
cular fossa are absent. The posterior thyroid tu- 
bercle is enormous and projecting in Nasua and 
Ailurus, absent in Procyon. The anterior margin 
of the cricoid arch is broadly excised (except Ailu- 
rus), and the posterior margin is reflected in lip- 
like formation. 

The arytenoid is massive and with well-devel- 
oped processes in the Ursidae and Ailuropoda. 
The median processes of the two arytenoids meet 
at the midline. The vocal process is large and 
wing-like. The cuneiform cartilage is large and 
L-shaped. A rod-like interarytenoid cartilage is 
lodged between corniculate and median processes. 

In the Canidae the arytenoid resembles that of the 
Ursidae but is less massive. The median process 
is much reduced. It is notable for the great length 
of the corniculate process, which extends back as a 
curved finger-like structure beyond the interaryte- 
noid incisure. The cuneiform is very large and 
irregular in outline, with a long dorsal process. 

In the Procyonidae (including Ailurus) the ary- 
tenoid is reduced to a triangular flake of cartilage, 
the apexes of the triangle representing the apex, 
and the muscular and median processes, respec- 
tively. The median processes are well separated 
at the midline. The corniculate process is entirely 
absent {Procyon, Nasua) or represented by a small 
elevation {Ailurus). The cuneiform cartilage is en- 
tirely absent, but the interarytenoid is present as 
a nodule of cartilage. 

There do not appear to be any significant differ- 
ences in the laryngeal muscles of the Canidae and 
Ursidae. These muscles were not dissected in the 

E. Summary of Larynx 

1. The larynx of the Ursidae is the least spe- 
cialized among the arctoid carnivores. 

2. The larynx of Ailuropoda closely resembles 
that of the Ursidae. 

3. In the Canidae the larynx shows numerous 
characteristic modifications. 

4. In the Procyonidae the larynx has under- 
gone degenerative modifications. Thyroid and 
cricoid are reduced, and the arytenoid and its asso- 
ciated cartilages are degenerate. 

5. The functional significance of these differ- 
ences is unknown. 


The trachea (fig. 127) has a length of 270 mm., 
from the base of the cricoid cartilage to the poste- 
rior base of the bifurcation of the bronchi. It is 
composed of 27 cartilaginous rings, which is the 
number estimated by Raven (1936). Several pairs 
of rings are partly united, and this gives them a 
bifurcated appearance. The diameter of the tra- 
chea is 35 mm. (36 mm. in Raven's specimen). 
The dorsal membranous part of the rings has a 
maximum width of 6 mm. 

The bronchi are extremely short, dividing al- 
most immediately into eparterial and hyparterial 
rami. The base of the bifurcation of the right 
bronchus is scarcely farther ectad than the border 
of the trachea, but the left bronchus has a length 
of 30 mm. before it bifurcates. The right bronchus 
has a diameter of 41 mm.; that of the left is only 
23 mm. 



Lobus ant. sin. 

Lobus ant. dex 

Vv. pulmonales 

Lobus med. de.x. 

Lobus post. dex. 

Ramus A. pulmonalis 

Bronchus sin. 

Lobus azygos 

Lobus post. sin. 

Ligg. pulmonales 

Fig. 127. Trachea, bronchi, and lungs of Ailuropoda, ventral view. 

in. LUNGS 

The lungs (fig. 127) are elongate wedge-shaped 
structures. They are made up of completely sep- 
arate lobes, the lobes of either side being joined 
only by the bronchi and a small isthmus of the 
serous coat. The left lung consists of two sub- 
equal lobes, both larger than any of the lobes of 
the right lung. The anterior lobe measures 175 
mm. in length, the posterior 165 mm. The ante- 
rior and posterior lobes of the right lung are ap- 
proximately equal in size, each measuring about 
135 mm. in length. The very small right median 
lobe is wedged in between the anterior and poste- 
rior lobes. The small pointed azygous lobe lies 
ventral to the median edge of the right posterior 
lobe. It is deeply molded by the posterior vena 
cava, which it embraces from the dorsal side. As 
in the specimen studied by Raven, the right epar- 
terial bronchus supplies only the anterior lobe. 
There is a prominent posterior pulmonary liga- 

ment at the posterior end of each lung, which 
attaches to the diaphragm. 

Discussion of Lungs 

The form of the lungs is molded by the shape of 
the thoracic cavity, the heart, and the diaphragm. 
Differences in form attributable to these agents 
are evident among carnivores, but scarcely seem 
worth discussing here. The most dramatic char- 
acter of the lungs among the Carnivora is the dif- 
ference in the number of lobes. In the Canidae 
(and all Aeluroidea that have been examined) the 
left lung is divided into three lobes, whereas in 
the Procyonidae (including Ailurus; Carlsson, 
1925), Ursidae, and Mustelidae the left lung is di- 
vided into only two lobes (Goppert, 1937). Ailu- 
ropoda agrees with the second group. The right 
lung is divided into four lobes (including the azy- 
gous) in all fissiped carnivores. 

Secondary reduction of lobation appears to be 
correlated primarily with broadening of the thorax 



(Marcus, 1937). No figures are available for the 
thoracic index in the Procyonidae, Ursidae, and 
Mustelidae, but it is evident from inspection that 
the thorax is relatively broader in these than in 
the dogs, cats, and civets. 


1 . The respiratory system of Ailuropoda closely 
resembles that of the Ursidae. 

2. The larynx of the bears and Ailuropoda is 
the most primitive among the arctoid Carnivora. 
The larynx is specialized, in different directions, 
in the Canidae and Procyonidae. 

3. Lung lobation is similar in the Procyonidae, 
Ursidae, and Mustelidae. The Canidae and all 
aeluroid carnivores have one more lobe in the left 



Two hearts were available for study: the sub- 
adult heart, fixed in situ, of Su Lin, and the fully 
adult heart, preserved in formalin after removal 
from the body, of Mei Lan. The description is 
based largely on the heart of Su Lin; the adult 
heart was not in suitable condition for detailed 

The heart, fixed in situ in moderate contraction, 
has the form of a slender cone. The longitudinal 
diameter gi'eatly exceeds the transverse diameter, 
and the apex is pointed. The proportions of the 
heart resemble those in the Ursidae, except that 
the organ is more slender in Aihiropoda. In the 
Canidae the heart is markedly globular. 

The heart of Su Lin (empty, without the peri- 
cardium, and with the great vessels cut short) 
weighs 302 gi-ams, which is 0.5 per cent of total 
body weight. This heart measures 92 mm. from 
base to apex (apex= coronary sulcus at the origin 
of the left longitudinal sulcus),' 79 mm. in trans- 
verse diameter (gi-eatest distance between the two 
longitudinal sulci), 77 mm. in sagittal diameter 
(greatest distance between points intermediate be- 
tween the two longitudinal sulci), and 252 mm. 
in circumference (maximum circumference around 
ventricles). The heart of Mei Lan weighs 530 gi-ams 
and measures about 115 mm. from base to apex. 

In an old male Tremarctos ornatus, which died 
in the Chicago Zoological Park and which weighed 
175 pounds at death, the heart formed 0.5 per cent 
of body weight. Heart weights given by Crile and 
Quiring (1940) represent 0.8 per cent of total body 
weight for a fresh specimen of Ursus horribilis 
that weighed 310 pounds, 0.6 per cent for a fresh 
specimen of Thalarctos maritimus that weighed 440 
pounds, and 0.4 per cent for another Thalarctos 
that weighed 700 pounds. In the domestic dog 
the heart forms about 1.1 per cent of adult body 
weight (Ellenberger and Baum, 1943), in the do- 
mestic cat about 0.4 per cent (Latimer, 1942). 

A. Exterior of the Heart. (Figure 128.) 

The left surface (anterior of human anatomy) of 
the heart is almost flat, and the right surface is 

' For heart measurements I have used the method de- 
scribed by Gschwend (1931, Anat. Anz., 72, p. 56). 

divided into two planes that meet at an acute an- 
gle opposite the left surface. Thus the cross sec- 
tion of the heart is triangular. The auricles are 
relatively small; the left auricle, much smaller than 
the right, measures 35 mm. in diameter, the right 
52 mm. The auricles are broadly separated from 
one another by the great vessels. The right auri- 
cle lies much higher than the left, almost entirely 
above the coronary groove. It is wi-apped around 
the base of the aorta. The left auricle lies below 
the pulmonary artery, mostly below the coronary 
gi'oove. Its distal two thirds is appressed against 
the left ventricle. 

The longitudinal gi'ooves are well marked. The 
left is more prominent than the right. The left 
longitudinal gi'oove begins near the base of the 
pulmonary artery, beneath the left auricle, and 
runs diagonally toward the tip of the heart. It 
crosses over onto the right surface at the incisura 
cordis, well above the apex of the heart. The po- 
sition of the incisura cordis is about 20 per cent of 
the distance between the apex and base of the heart. 
The right longitudinal groove begins at the root of 
the posterior vena cava and runs almost straight 
toward the tip of the heart. Some distance above 
the tip it unites with the left longitudinal groove. 
Thus the right ventricle does not reach the tip of 
the heart, which is formed entirely by the left ven- 
tricle. The conus arteriosus is moderately inflated. 
The right atrium is much inflated and almost glob- 
ular. The sulcus terminalis appears as a faint 
gi'oove beginning between the anterior vena cava 
and the wall of the atriiun and running toward the 
base of the postcava. The left atrium is much 
smaller than the right. Externally the two atria 
meet only posteriorly, above the postcava, and 
here the boundary between them is very indistinct. 
Anteriorly they are broadly separated by the aorta 
and pulmonary artery. 

B. Interior of the Heart 


Right Atrium. The cavity of the distended 
right atrium is much larger than that of the left, 
and is much broader than high. The atrium proper 
measures about 60 mm. in breadth. Except in the 
auricular region the external wall is thin, only 


V. cava ant. 


Aorta ascendens 

Auricula dext. 

A. pulmonalis 

Conus arteriosus / 

Ventriculus dext. [' 


^ V. pulmonalis 

Auricula sin. 


Sulcus longitud. sin. 

Incisura cordis 

Ventriculus sin. 

Fig. 128. Heart of Ailuropoda from the left side. 

about a millimeter in thickness. The anterior vena 
cava enters the atrium from above, the posterior 
vena cava from behind. The crista terminalis, 
corresponding in position to the sulcus terminalis, 
is a ridge running from the right (anti-septal) side 
of the anterior caval orifice toward the postcaval 
orifice. It is prominent at first, but quickly fades 
out. Pectinate muscles are prominently developed 
in the auricle, and are faintly evident on the exter- 
nal wall of the atrium nearly to the entrance of the 
postcava. The septal wall is smooth. 

The tuberculum intervenosum is indistinguish- 
able from the crista intervenosa, into which it nor- 
mally continues. The tuberculum intervenosum 
has the form of a conspicuous ridge on the septal 
wall, running apically and to the right between the 
orifice of the anterior vena cava and the fossa ovalis. 
The fossa ovalis is an inconspicuous shallow and 
poorly defined depression, only about 7 mm. in 
diameter, bounded anteriorly by the ridge-like tu- 
berculum intervenosum. The orifice of the coro- 
nary sinus, which is about 7 mm. in diameter, lies 



Cuspis ant. 

Conus arteriosus 

Valv. semilunares 

A. pulmonalis 


Trabeculae transversae 

M. papillaris subart. 
Sulcus longitud. sin. 
Trabeculae cameae 

Incisura cordis 

Moderator band" 

Fig. 129. Right ventricle of Ailuropoda. 

directly below (apicalward of) the entrance of the 

Left Atrium. The cavity of the atrium proper 
is ovate, with the long diameter transverse to the 
long axis of the heart. The long diameter meas- 
ures about 40 mm. The wall is about 6 mm. thick, 
and thus is much heavier than the wall of the right 
atrium. The walls of the auricle are almost paper- 
thin. The pulmonary veins enter the atrium from 
above. The lining of the atrium is completely 
smooth and practically devoid of relief. The pe- 
ripheral part of the auricle contains a meshwork 

of coarse pectinate muscles, some of them free- 
standing cylindrical strands. On the internal wall 
of the auricle, near its entrance into the atrium, 
there is a large pillar-like pectinate muscle, 7 mm. 
in diameter, from which smaller strands pass to 
the auricular wall. On the septal wall the site of 
the foramen ovale is marked by an inconspicuous, 
very shallow depression. 


Right Ventricle. The right ventricle (fig. 129) 
has a triangular cavity, somewhat broader than 
high, terminating posteriorly in a long funnel- 



shaped conus arteriosus. The crista supraven- 
tricuiaris is short and extends nearly vertically 
downward. The ventricular cavity measures about 
70 mm. in breadth (measured to base of semilunar 
valve, and 58 mm. in height (base to apex). The 
conus accounts for about 37 per cent of the total 
breadth of the chamber. The external wall has a 
maximum thickness (near the base of the conus) 
of about 9 mm.; it is thinnest near the apex. The 
septal wall is firm, and arches prominently into 
the cavity. It is smooth and free of trabeculae 
except near the basal groove. The external wall, 
on the contrary, is covered with a coarse mesh- 
work of ridges, the trabeculae carneae, except in 
the conus region. A system of free cord-like tra- 
beculae is present on the external wall. There are 
four well-developed papillary muscles, situated 
near the center of the septal wall. There evidently 
was considerable disturbance of the normal devel- 
opmental pattern in the right ventricle of Mei Lan, 
although the arrangement and proportions of struc- 
tures are generally similar to Su Lin and the 

The papillaris subarterialis can scarcely be 
said to exist. At its customary site, on the septal 
wall near the beginning of the conus, a single 
chorda tendinea arises directly from the septum 
and passes to the cusp of the septal valve. Imme- 
diately behind this chorda, but completely sepa- 
rate from it, lies the base of the arteriormost chorda 
tendinea propria. In the heart of Mei Lan not 
only the papilla, but also the chorda normally aris- 
ing therefrom, are completely absent. 

Of the four papillary muscles, the first three rep- 
resent anterior papillary muscles; the fourth, situ- 
ated most posteriorly in the posterior niche of the 
ventricle, is the posterior papillary muscle. 

The three anterior papillary muscles are sit- 
uated in a line, the first two close together, the 
posteriormost one somewhat isolated. All arise 
from the septum, but the base of each is con- 
nected with the external wall by a transverse tra- 
becula. The anteriormost papilla, the largest, is 
cylindrical, 11 mm. in height by 7.5 mm. in diam- 
eter, and terminates in three chordae tendineae 
that pass to the anterior cusp. The base of this 
papilla is connected to the external wall by two 
large plate-like transvei'se trabeculae, the larger of 
these 3.5 mm. in diameter. A short but conspic- 
uous ridge-like elevation of the septal wall (repre- 
senting the moderator band of human anatomy) 
passes downward and posteriorly to the base of 
the anteriormost papilla. It fuses with the base 
of the papilla, where it continues directly into the 
uppermost of the two plate-like transverse tra- 
beculae. The second papilla stands free of the 

septum except at its base. It terminates in a sin- 
gle chorda that subdivides and passes to the ante- 
rior and posterior cusps. The base of this papilla 
is connected to the base of the first papilla and to 
the external wall by a stout cylindrical transverse 
trabecula, 1.5 mm. in diameter. The third papilla 
is slightly smaller than the second, and terminates 
in a single chorda that passes to the posterior cusp. 
Its is connected with the external wall by a 
short cylindrical transverse trabecula. 

A single posterior papillary muscle is situ- 
ated in the posterior niche of the ventricle. It is 
stout, but shorter than any of the anterior papil- 
lae, and has the shape of a flattened cylinder. It 
is septal in position, but its base is connected to 
the external wall by a short stout transverse tra- 
becula. This papilla is two-tipped. A group of 
2-3 chordae tendineae arising from each tip rami- 
fies to the posterior and septal cusps. 

There are no accessory papillary muscles. A 
row of 8 direct chordae tendineae arises from 
the middle part of the septum, the anteriormost 
lying directly behind (septalward of) the subarte- 
rial papilla. These are fairly regularly spaced at 
intervals of about 7 mm. Each ramifies to the 
cusp of the septal valve. 

Transverse trabeculae. Ackerknecht (1919) 
defines these as more or less cylindrical strands 
that (1) are related to the papillae, and (2) cross 
the ventricular cavity transversely or obliquely. 
Thus he distinguishes the transverse trabeculae, 
which contain a part of the conducting system, 
from other trabecular structures that often extend 
across between septum and external wall. Acker- 
knecht interprets these latter structures as modi- 
fied trabeculae carneae. In Ailuropoda these two 
trabecular systems are topogi'aphically closely re- 
lated at the base of the anteriormost papilla. Two 
heavy, flattened-cylindrical transverse trabeculae 
arise from the base of this papilla and run horizon- 
tally to the external wall, where they terminate in 
the trabecular meshwork situated there. The up- 
permost of these is continuous at its origin with 
the moderator band ; these two structures together 
form the "trabecula septomarginalis" of Acker- 
knecht. Near its origin the upper trabecula gives 
off a slender trabecular strand that runs independ- 
ently to the meshwork on the external wall. In 
addition, the first and second papillae are inter- 
connected at their base by a flattened-cylindrical 
free trabecula; one slender transverse trabecula 
arises from the middle of this and a larger trans- 
verse trabecula comes from its attachment to the 
second papilla. Both go to the meshwork on the 
external wall. Thus four transverse trabeculae, 
all inserting into the meshwork, arise from the 
anterior papillae. 



From the base of the posterior papilla a short, 
stout transverse trabecula passes to the external 
wall in the niche region of the ventricle. 

Trabeculae carneae. The inner surface of 
the whole external wall is covered with very prom- 
inent, coarse trabeculae carneae. These are ridges 
in high relief, about 3 mm. in diameter, surround- 
ing shallow sinuses. Fleshy trabeculae are least 
prominent, but still present, on the external wall 
in the conus region. The general direction of the 
trabecular ridges is horizontal. The septal wall is 
smooth and free of trabeculae, except for short, 
heavy, pillar-like structures in the basal groove. 

Two powerful muscular bands, 14 mm. in diam- 
eter, arise from the septum near the base of the 
anteriormost papilla and run horizontally to the 
external wall, where they insert on the trabecular 
ridges. These resemble transverse trabeculae, but 
are not connected either with papillae or with the 
trabecular meshwork on the external wall, and 
therefore are interpreted as trabeculae carneae. 
A similar arrangement, except that the trabeculae 
were much more slender, was present in one speci- 
men of Helarctos. 

The trabecular meshwork of cord-like free strands 
lies on the external wall at the level of the papillae, 
i.e., at about the middle of the external wall. This 
system consists of two or three strands, all paral- 
leling the transverse axis of the ventricle, with 
numerous short thread-like roots arising from the 
external wall. There are a few interconnections 
between the main strands. The transverse tra- 
beculae from the papillae insert into this trabecu- 
lar meshwork. 

Tricuspid valve. The atrioventricular orifice 
is 42 mm. in length. The anterior and septal 
(medial) cusps are subequal in size, and the bound- 
ary between them is clearly marked. The ante- 
rior cusp measures about 40 mm. in breadth. The 
posterior cusp, much smaller than the other two, 
is clearly bounded from the septal cusp, less dis- 
tinctly so from the posterior cusp. No accessory 
cusps are evident, but the free margin of each pri- 
mary cusp is deeply notched between the attach- 
ments of the chordae tendineae, giving it a scalloped 

The three semilunar valves occupy the usual 
position at the base of the pulmonary artery. 
Each forms a deep pocket. In the middle of the 
free margin of each there is a conspicuous nodulus 
of Aranti. 

Left Ventricle. The cavity has the form of 
an inverted cone, and is smaller than the cavity 
of the right ventricle. The external wall has a 
maximum thickness of about 16 mm., and thus is 
nearly twice as thick as the wall of the right ven- 

tricle; it is thinnest at the apex, where it measures 
about 9 mm. Except in the conus region, the lin- 
ing is thrown up into prominent longitudinal ridges, 
much more regular and slightly more prominent 
than the trabeculae carneae of the right ventricle. 
There is a simple system of free trabecular strands. 
Two large and well-formed papillae are present, 
nearly equal in size, close together on the exter- 
nal wall. 

The anterior papillary muscle is pillar-like, 
about 11 mm. in diameter, and fused to the ex- 
ternal wall except at its tip. The tip is truncated, 
and from it arise two very unequal conical struc- 
tures from the tips of which the chordae tendineae 
are given off. The smaller of these conical struc- 
tures, on the medial side of the papilla tip, termi- 
nates in five chordae tendineae that ramify to the 
external cusp of the bicuspid valve. The larger 
conical structure is a long cylinder, 10 mm. long, 
terminating in four chordae that ramify to both 
valves, but mostly to the septal valve. A single 
heavy chorda arises from the base of this cylinder 
and ramifies to the septal valve. This gives a total 
of ten chordae tendineae. A stout chorda-like 
strand arises from the septal side of the tip of the 
papilla and runs upward toward the base of the 
ventricle, near which it fuses with the septal wall. 
At several points along its course this strand is 
united to the meshwork of the fleshy trabecular 

The posterior papillary muscle is slightly 
larger than the anterior papilla, and resembles it 
in foi'm except that the tip of the posterior papilla 
is more conical. Five chordae tendineae arising 
from the tip ramify to the cusps of both valves. 
A sixth chorda, arising partly from the papilla 
and partly from the external wall, ramifies to both 
the septal cusp and the external wall. A large 
transverse trabecula arises by several roots from 
the septal side of the body of the papilla and runs 
up toward the septum, to which it attaches near 
the entrance to the conus. 

The system of transverse trabeculae consists, 
in addition to the strands associated with the pa- 
pillae, largely of a single strand running freely and 
more or less horizontally over the septal wall near 
its middle. Along its course this parent strand is 
joined by about six smaller lateral roots arising 
from the septal wall, and at each end by a root 
from each of the papillary transverse trabeculae. 
There is also a loose, coarse meshwork of slightly 
smaller strands in the region between the anterior 
papilla and the septal wall. Finally, there are a 
few very short slender trabeculae in the apical 




Canis* Bassariscus Procyon Ursidae 

Form of heart globular subglobular subglobular conical 

Right ventricle 

Length of conus long very short very short short 

Papillaris subart well developed small slightly larger small 

Typical no. of anterior 

papillae 1 3 3 3 

Typical no. of posterior 

papillae 3 0? 1 1 

Transverse trabeculae moderately stout slender absent slender 

Trabecular carneae well developed poorly developed well developed poorly developed 

Free trabeculae on external 

wall none feeble very feeble yes 

Left ventricle 

Apical cones on anterior 
papillae no no no yes 

Trabecular strand on septum . . no yes no yes 

Data largely from Ackerknecht (1919). 






well developed 



The trabeculae carneae form a pattern of 
prominent longitudinal ridges covering all the in- 
ner surface of the ventricle except the conus. They 
tend to converge toward the apex. The ridges 
vary in width; the broadest are about 5 mm. wide. 
Adjacent ridges are interconnected in many places 
by short threadlike strands more or less horizontal 
in direction. 

The bicuspid valve is much shorter than the 
tricuspid, measuring about 20 mm. in length. The 
cusps are heavier than those of the tricuspid, and 
the two primary cusps are divided by deep inci- 
sions into five accessory cusps. 

The aortic ostium is situated in the usual place 
between the septal valve and the septum, at the 
base of a funnel-shaped conus arteriosus. The 
semilunar valves guarding the ostium are typical. 
There is a nodulus of Aranti in the middle of the 
free margin of each valve. 

C. Discussion of Heart 

The comparative anatomy of the heart in the 
Carnivora has been studied by Ackerknecht (1919) 
and Simic (1938). Ackerknecht's description of 
the papillary muscles and their adnexa was based 
on 30 hearts of the domestic dog, one heart of a 
European fox, and 15 hearts of the domestic cat. 
He was interested primarily in the range of varia- 
tion. Simi5 compared the general structure of the 
heart in Canis lupus, Vulpes vulpes, Lycaon pictus, 
Procyon lotor, Meles meles, Zorilla striata, Felis leo, 
Felis tigris, Felis pardus, and Crocuta crocuta. She 
listed several characteristic differences between the 
Arctoidea and Aeluroidea, but did not attempt to 
characterize heart structure at the family level. 
It is extraordinary that no one has described the 
heart of any species of bear. 

I have supplemented the data in the literature 
with dissections of the following hearts: 

Height in mm. Weight 

(base apex) ingms. 

Bassariscus astutus (cf ad.) 26 7 

Procyon lotor ( cf ad.) 33 19 

Procyon lotor (unsexed ad.) 44 42 

Helarclos malayanus (d' ad.) 94 345 

Helarctos malayanus ( 9 ad.) 98 362 

Tremarctos ornatus (cf ad.) 113 397 

Ursus americanus (d" juv.) 43 35 

Ursus americanus (cf ad.) 127 833 

Canis lupus ( cT ad.) 91 265 

Felis uncia ( cf) 68 132 

Even from this limited material it is evident that 
there are characteristic differences among the arc- 
toid carnivores. Some of these are listed in the 
accompanying table (Table 23). Most relate to 
the right ventricle; Ackerknecht found that indi- 
vidual variation is also greatest in this ventricle, 
which is phylogenetically the most recent part of 
the mammalian heart. 

At present there is no sure way of deciding what 
is primitive and what is specialized in the heart ar- 
chitecture of placental mammals, or indeed whether 
such terms can be used in comparing heart struc- 
ture within the Carnivora.' I shall therefore avoid 
such terms here. Whether there is any significant 
relationship between structural differences and per- 
formance of the heart is likewise unknown. 

The heart of the Canidae differs from the heart 
of other arctoid carnivores in practically every fea- 
ture examined. Some of these differences appear 
to be fundamental. 

' Ackerknecht "gained the general impression" that the 
heart is more primitive in Felis than in Canis, but he does 
not give the basis for this opinion. 



There are consistent differences in heart form 
among the several families. These reflect the de- 
gree of acuteness of the apex, and therefore do not 
show up in ratios based on measurements of length 
and diameter of the organ. The globular form of 
the heart in the Canidae is unlike that of any other 
known carnivore. The subglobular form in the 
Procyonidae resembles that of the cats. The po- 
sition of the incisura cordis seems to be related to 
the relative sizes of the two ventricles: where it is 
high the relative height of the right ventricle is 
less, and vice versa. The incisura is very high in 
the Canidae. It is near the apex in the Procyoni- 
dae, actually almost at the apex in Bassariscus. 
Its position varies among ursid genera; in none is 
it as high as in canids or as low as in procyonids. 
In Ailuropoda it is as high as in any ursid exam- 
ined. It appears to be very high in felids. 

The conus arteriosus tends to be short in bears, 
although there is considerable variation among 
genera. It is longest in Helarctos. The conus is 
longer in Canis than in the Ursidae; it is very short 
in the Procyonidae. 

The papillary muscles of the right ventricle are 
situated on the septum in all arctoid carnivores, 
whereas in the Aeluroidea the anterior papilla 
arises from the external wall. The subarterial 
papilla varies in size and position. In the Canidae 
and Procyonidae it is well developed (although not 
as large as in the cats) and situated directly below 
the supraventricular crest. In the Ursidae and 
Ailuropoda it is small and situated in the conus 
region. Among the arctoids examined there is a 
reciprocal relationship between the anterior and 
posterior papillae: in the Canidae the anterior pa- 
pilla is typically single and shows little variation 
in number whereas the posterior is multiple and 
extremely variable (modal number 3). In the Pro- 
cyonidae and Ursidae, on the contrary, the ante- 
rior papilla is multiple and variable (especially in 
the Ursidae), and the posterior single and only 
slightly variable. Among the five bears exam- 
ined, the number of anterior papillae varied be- 
tween 2-4 (modal number 3). The number of 
direct chordae tendineae is also very high in bears 
(8-15). These conditions suggest that the region 
of the right ventricle nearest the niche is broad- 
ened and least stable in canids, whereas in procyo- 
nids and ursids the region toward the conus is 
broadened and least stable. The anterior and pos- 
terior papillae are situated much higher (near the 
center of the septal wall) in the Procyonidae, Ur- 
sidae, and Ailuropoda than in the Canidae. 

Trabeculae carneae were poorly developed in the 
right ventricle of all bear hearts examined, whereas 
they were at least moderately prominent in all pro- 

cyonids and are described by Ackerknecht as vari- 
able but typically well developed in Canis. Typ- 
ically absent in the Canidae but very characteristic 
of the Procyonidae, Ursidae, and Ailuropoda is a 
system of free trabecular strands on the external 
wall. These are restricted to a narrow zone more 
or less paralleling the transverse axis of the ven- 
tricle. Where best developed ( Helarctos) the strands 
may form a loose meshwork. The transverse tra- 
beculae of the anterior papillary muscle gi-oup in- 
sert into this system. 

There is much less variation in the left ventricle 
than in the right. There were two massive papil- 
lae, arising from the external wall, in all speci- 
mens examined. The posterior papilla is tj^jically 
slightly the larger. In the Ursidae and Ailuropoda 
one or more small conical structures, from the tips 
of which groups of chordae arise, sit atop the pa- 
pillae. These accessory structures are absent in 
Canis and the Procyonidae. A transverse trabec- 
ula, at its origin looking like a chorda tendinea, 
arises from the septal side of the tip of each papilla 
and runs up to insert near the base of the ventricle 
in all hearts examined. In Bassariscus, the Ursi- 
dae, and Ailuropoda a free trabecular strand ex- 
tends more or less horizontally over the septal wall. 
This strand was usually, but not always, connected 
with the transverse trabeculae. It was absent in 
the Canidae and in Procyon. 

D. Conclusions 

1. Most differences in heart structure among 
arctoid carnivores involve the right ventricle. The 
most characteristic feature of this ventricle is the 
increased number of cardinal papillary muscles. 

2. The structure of the heart in the Canidae 
differs in several respects from that of the Procyon- 
idae and Ursidae. 

(a) The canid heart has a characteristic form. 

(b) In the right ventricle the region nearest the 
conus is stable and the niche region is broad- 
ened and variable, whereas in the Procyoni- 
dae and Ursidae the reverse is true. 

(c) In the right ventricle the cardinal papillae 
are situated much nearer the basal groove 
than in the Procyonidae and Ursidae. 

3. The structure of the heart in the Ursidae re- 
sembles that of the Procyonidae, but differs in 
several respects. 

(a) The ui'sid heart has a characteristic form. 

(b) In the right ventricle the subarterial papilla 
is situated in the conus region. 

(c) In the right ventricle there is a well-devel- 
oped system of free trabeculae carneae on 
the external wall. 



Truncus thyreocervicalis 
A. carotis communis dext 
A. vertebralis 

A. truncus costocervicalis 

N. vagus dext. 
A. subclavia dext. 
A. mammalia int. dext, 

Ductus lymphaticus dext. 
A. anonyma 


V. intercostalis ant. dext. 

Vena azygos 
N. recurrens dext. 

N. vagus sin. 
A. carotis communis sin. 

R. cardiacus ant. 
A. mammaria int. sin. 

A. subclavia sin. 

Ductus thoracicus 
R. cardiacus post. 

N. recurrens sin. 

V. intercostalis 
A. intercostalis 

A. intercostalis V I 

Aorta thoracalis 

Fig. 130. Great vessels of the thorax of Ailuropoda. 

(d) In the left ventricle the anterior papilla is 
furnished! with apical cones. 

4. The heart of Ailuropoda resembles that of 
the Ursidae in all essential respects. 

5. The basis for these differences in heart ar- 
chitecture is unknown. 



The aorta is 45 cm. in length, from the origin of 
the subclavian artery to the bifurcation that forms 

the common iliacs. Its diameter at the top of the 
arch is 26 mm., at the middle of the thorax about 
13 mm., and midway between the diaphragm and 
the terminal bifurcation (below the origin of the 
renal arteries) about 9 mm. The aorta arises from 
the left ventricle at the level of the fourth thoracic 
vertebra, and extends upward and to the left to 
form the aortic arch. The aorta then runs poste- 
riorly below the vertebral column, lying just to the 
left of the midline until it emerges from between 
the crura of the diaphragm, where it moves over 
to the midline. The vessel terminates at the level 



of the last lumbar vertebra by breaking up to foi'm 
the external iliac, hypogastric, and middle sacral 

The arch of the aorta gives rise to two branches 
in typical carnivore fashion: the innominate and 
the much smaller left subclavian. These leave the 
top of the arch in close proximity to one another; 
they are separated by an interval of less than 5 
mm. The smaller visceral branches of the thoracic 
aorta were not traced. In the abdomen (fig. 135) 
the celiac artery arises at the level of the fourteenth 
thoracic vertebra, followed a few millimeters far- 
ther posteriorly by the anterior mesenteric. The 
renal arteries arise at the level of the first lumbar, 
and the posterior mesenteric at the level of the 
third lumbar. 

Innominate and Common Carotid Arteries 

A. anonyma (fig. 130) arises at the level of the 
fourth rib, and has a length of 30 mm. before the 
left common carotid is given off. The carotids 
arise from the innominate independently, the right 
coming off 20 mm. farther anterior than the left. 
This is contrary to what Raven (1936) found, and 
places Ailuropoda in Parson's (1902) class A in- 
stead of class B. 

Each A. carotis communis (figs. 130, 131) 
passes forward alongside the trachea to the level 
of the anterior border of the thyroid cartilage. 
A. thyreoidea ima arises from the common caro- 
tid just anterior to the manubrium sterni and 
passes anteriorly on the ventral surface of the 
trachea. It supplies the posterior part of the thy- 
roid gland and gives off small branches to the tra- 
chea. A. thyreoidea anterior (fig. 131) arises at 
the level of the third tracheal ring. On the right 
side of the neck the anterior thyroid arises as a 
large, very short trunk that promptly breaks up 
into a number of branches. These supply the an- 
terior end of the thyroid gland, the trachea, the 
esophagus, and the laryngeal and hyoid muscula- 
ture. On the left side the anterior thyroid proper 
supplies only the thyroid gland and the intrinsic 
laryngeal musculature. A separate branch arising 
independently from the carotid 20 mm. farther an- 
terior supplies the rest of the laryngeal and hyoid 
muscles, the trachea, and the esophagus. At the 
anterior border of the larynx the common carotid 
divides into the external and internal carotids. As 
in other carnivores the internal carotid is smaller 
than the external, but in the panda the internal 
carotid is relatively large, more than half the diam- 
eter of the external carotid, as in bears. 

External Carotid Artery 

A. carotis externa (fig. 132) curves laterad 
around the medial and anterior borders of the di- 

gastric muscle. The external maxillary is given 
off at the posterior wall of the mandibular fossa, 
and beyond this the trunk is continued as the in- 
ternal maxillary. The internal maxillary immedi- 
ately curves mesad, so that the entire external 
carotid trunk describes a pronounced S-curve in 
the basicranial region. The external carotid gives 
rise to the following branches: 

1. A good-sized branch arises from the lateral 
wall at the bifurcation into external and internal 
carotids. It breaks up at once into twigs for the 
large cervical lymph gland and twigs that supply 
the anterior end of the sternomastoid muscle and 
the posterior end of the digastric. 

A. pharyngea ascendens^ (fig. 131) arises as 
one of the branches of this trunk. It runs anteri- 
orly and mesad to the anterior pharyngeal con- 
strictor muscle, then anteriorly along this muscle. 
At the posterior border of the levator veli palatini 
muscle the trunk bifurcates into palatine and pha- 
ryngeal branches of subequal caliber. R. pala- 
tinus supplies the anterior pharyngeal and palatine 
musculature, ramifies in the glands of the soft pal- 
ate, and anastomoses with a descending twig from 
the internal maxillary and with the ascending and 
descending palatine arteries. A fine muscle twig, 
R. m. tensoris tympani, arising from the pala- 
tine branch, passes into the middle ear beside the 
tendon of the tensor veli palatini, which it sup- 
plies, and runs to the tensor tympani muscle, where 
it anastomoses with the other tympanic arteries. 

R. pharyngeus runs anteriorly beneath the rec- 
tus capitis ventralis, continuing in the medial wall 
of the eustachian tube to its anterior border, where 
it divides into a branch to the pharyngeal tonsil 
and another to the dorsal wall of the nasopharynx. 
The pharyngeal ramus supplies several minute 
Rr. eustachii that ramify in the tubal mucosa. 
A. pharyngeotympanica is given off at the level 
of the foramen lacerum medium and lies against 
the eustachian tube in the musculotubarian canal, 
on its way to the middle ear. Near the tympanic 
orifice of the eustachian tube the pharyngeotym- 
panic sends a fine anastomotic twig that pierces 
the wall of the foramen lacerum medium to reach 
the internal carotid artery. The pharyngeotym- 
panic artery terminates in the tympanic arterial 

2. A branch arises from the bifurcation of the 
carotids and immediately divides into lateral and 
medial twigs. The lateral twig accompanies the 
external branch of the spinal accessory nerve to 

' This vessel is only partly homologous with the ascending 
pharyngeal of human anatomy. The posterior meningeal 
artery comes from the internal carotid in the panda; the 
inferior tympanic arises from the external carotid. 



Nrt. pakUini tnaj 
V. palatiiia major 
V. palatina minor 
V. annularis 
V. labialis inf 

R. pharyiigeiif! 
V. ptcn-R. int 
V. facialis externa icut) 

V. & X. buccinator. 
N. tcmjiprof. ant 
N. mnssetericu.' 
\. lingtialis 
-V. picryg. i,il ^ 
N, alieolaris inf. 
N. nmndibuhri 

iV. mylohyoiil 
X. chorda tymp 

V. for. lac. n 

A'', auriculoletiiporalis 

H. articiilarif 
v. for. postglenoid 
V. ma.xilluris inti*rna 
V. stylomiLstoidea 
R. kI. submaxil!aii.s 
-V. facialis 
N. glossopfiaryiigeus 
N. kypoglossus _ 
Ganglion cerricalui sup. 

X. vagus 
V. facialis interna 
V. lingualis 
N. accessoritts 

V. facialis externa (cut) 
R. anast. w. v. vertebral, 

R. anast. a. pal. major dextra 
Foramen incisimm 

U. anast. a. sphenopalatina 
Sulcus palatitius 
A. palatina major 

R. anast. 

A. palatina minor 

. anast. a. pal. asc. 
R. m. pteryg. int. 
A. temp. prof. 
.A. alv. inf, 
A. maxillaris interna 

R. tons. phar. 

A. pharj-ngeotympanica 
A. maxillaris ext. 
R. m. pieryg. int. 

A. temp, superf. 

Rr. parotidei 

R. auric, prof. 

A. trans, faciei 

__ R. gl. submaxillaris 

Tr. auric, post. & occip. 

K. m. pter>-g. int. 

A. submentalis 
A. lingualis 
A. palatina asc. 
R. m. trapezius 
A. lymph glanduia 
carotis externa 
A. carotis interna 
\. carotis communis 
Rr. mm. sternomast. & cleidomast. 

V. jugularis externa 

v. jugularis interna 

A. thyreoidea ant. 

Fig. 131. Vessels and nerves of the head of Ailuropoda, inferior view. 

the trapezius. The medial branch, A. tympanica 
inferior, runs to the lateral border of the foramen 
lacerum posterior and accompanies the tympanic 
branch of the glossopharyngeal nerve in the mid- 
dle ear. The inferior tympanic terminates by 
anastomosing with the other tympanic arteries on 
the promontorium. 

3. A. palatina ascendens (fig. 131) is a slen- 
der vessel arising from the medial wall and run- 
ning anteriorly and mesad to the pharynx and 

posterior part of the palate. It ramifies in the 
palatine glands and anastomoses with twigs from 
the ascending pharyngeal and posterior palatine 

4. A, lingualis (fig. 131) is the largest branch 
of the external carotid. It arises from the ventral 
wall at the level of the hyoid bone, and accom- 
panies the hypoglossal nerve anteriorly and me- 
sad, deep to the mylohyoid muscle, to the lateral 
border of the hyoglossal muscle. Here the artery 



A. temp. prof. ant. 

.V. frotitalis 

Phxus pliriigoiJeus 
V. sinus transversus 
.V. mamlibularis \\ 

A. temp, superf. 
\'. transv. facei 
. temp, superior 

.Y. al 
A. meningea access}ria 
.V. maxillaris \'. 
A. temp. prof. post. 
A. masseter. 
A. temp. prof. post. 

\. frontalis 

R. anast.V. ophthalm. inf. 
-V. supratroch. 
.\.dorsaIis nasi 
Gi- lat-ritnalis 
V. nasofrontalis 

Vv. parotidei 

V. gl. subma.\illaris 
Tr. auric, post. & occip. 
A. auric, post. & occip. 
V. facialis interna 
R. muse. 


Saccus larrimalis 
Lig. orbitalis 
Rr. temp. ant. 

R. auric, anl. 
A. carotis externa ^ 
A. gl. submaxillaris' 
v. maxillaris interna' 
A. maxUlaris externa 

A. maxillaris interna 

\'. sphenopalatina (Vv. pal. desc.) 
A. infraorbitalis 
Tr. splienopalatina & pal. desc. 
* . alv. sup. ant. 
facialis prof. 
GL orbitoparotidea 

,,^- buccinatoria 
O/. orbitalis 
M. buccinator 
alv. sup. post. 
A. canal. pter>'g. 

A. & v. alveolaris inf. 

V. pterj'g. int. 

\. anast V. lab. inf. 
ab. inf. 
V. facialis externa 

Fig. 132. Deep vessels and nerves of the head of Ailuropoda, side view. 

gives rise to a good-sized R. symphyseus, which 
accompanies the hypoglossal nerve along the me- 
dial border of the styloglossal muscle, then along 
the lateral border of the genioglossus, to the sym- 
physeal foramen. Numerous twigs from this branch 
supply the sublingual muscles and the floor of the 
mouth anterior to the tongue. The main trunk of 
the lingual runs beneath the lateral border of the 
hyoglossus, into the body of the tongue, where it 

Just before passing beneath the mylohyoid, the 
lingual gives rise to the small A. submentalis, 
which runs forward on the mylohyoideus at its 
juncture with the digastric. 

5. A slender branch arising from the ventral 
wall just anterior to the lingual runs forward to 
the pterygoid muscles, which it supplies. 

6. A. auricularis posterior + A. occipitalis 

(fig. 132) arise by a common trunk at the anterior 
border of the mastoid process. The trunk runs 
laterad beneath the digastric and parotid gland to 
the posterior border of the base of the pinna. Here 
the A. sternocleidomastoidea is given off to the 
sternomastoid and cleidomastoid muscles. 

A. stylomastoidea arises from the posterior 
side of the auriculo-occipital trunk at its base. It 
runs mesad over the digastric, dividing into a mus- 
cular twig to the digastric and the stylomastoid 
artery proper. The latter runs beside the facial 
nerve to the stylomastoid foramen. A. tympan- 
ica posterior is given off in the facial canal, and 
accompanies the chorda t\Tnpani nerve into the 
middle ear, where it sends a twig to the malleus 
and anastomoses with the other tympanic arteries. 

A. occipitalis, which is considerably smaller 
than the posterior auricular, appears to arise as a 
branch of the latter at the boundary between the 
sternomastoid and cleidomastoid muscles. The 
occipital gves rise to the following branches: Rr. 
musculares, arising near the base of the artery, 
supply the adjacent muscles and the atlanto-occip- 
ital capsule, and send fine nutrient branches into 
the back of the skull. R. occipitalis, the termi- 
nal part of the artery, runs dorsad beneath the 
splenius. At the ventral border of the rectus ca- 
pitis posterior major it divides into a superficial 
and a deep branch. These ramify to the muscula- 
ture in the occipital region and to the nutrient 
foramina in the back of the skull, none of the 



twigs extending beyond the lambdoidal crest. The 
deep branch also supplies the atlanto-occipital cap- 
sule. A slender cutaneous branch runs through to 
the skin at the back of the head. 

A. auricularis is the continuation of the auric- 
ular-occipital trunk after the occipital is given off. 
It divides immediately into muscular and auricu- 
lar branches. The muscular branch ramifies in the 
posterior part of the temporal muscle, also giving 
off a twig that supplies the cartilage of the pinna. 
A branch, R. mastoideus, arises from the base 
of the muscular branch and passes to the mastoid 
foramen, which it enters. The auricular branch 
then divides into anterior and posterior branches. 
A. auricularis posterior is distributed over the 
posterior surface of the pinna and to the muscula- 
ture of the ear. A. auricularis anterior (fig. 107) 
passes around the medial side of the pinna to sup- 
ply structures on its anterior side; a large cutane- 
ous twig from this branch runs across the top of 
the head toward the midline. 

7. A. glandularis is a good-sized vessel arising 
from the lateral wall of the external carotid oppo- 
site and slightly anterior to the preceding trunk. 
It passes into the submaxillary gland, where it 

8. A. temporalis superficialis (fig. 132) arises, 
as a single vessel on the left side of the head and 
as two independent but closely associated vessels 
on the right, just behind the angular process of the 
mandible. Aside from the several small parotid 
twigs and the small anterior auricular branch, 
which come off near its base, the superficial tem- 
poral may be said to divide, after a short trunk, 
into two subequal systems : a transverse facial sys- 
tem that ramifies below the zygoma, and a tem- 
poral system that ramifies above it. 

The superficial temporal gives rise to the follow- 
ing branches: (a) R. auricularis profundus is the 
first branch given off. It is a small twig that runs 
to the base of the pinna, (b) Rr. parotidei are 
small twigs that arise near the base of the artery 
and pass into the parotid gland, (c) A. transversa 
facei breaks up into two large branches that ram- 
ify over and into the masseter muscle, and a slender 
transverse facial branch. The transverse facial 
branch is an extremely delicate twig running across 
the masseter a short distance below the zygoma; 
it accompanies the infraorbital branches of the 
facial nerve, and lies above the parotid duct. Twigs 
are given off to the masseter, the zygomatic rete, 
and cutaneous structures over the masseter; the 
vessel terminates by anastomosing with the supe- 
rior labial artery, (d) A. zygomaticoorbitalis 
(fig. 107) arises from the temporal branch of the 
superficial temporal. It runs across the posterior 

end of the zygoma and the lower part of the tem- 
poral muscle to the orbit, where it anastomoses 
with the frontal, supraorbital, and lacrimal arteries. 
(e) A. temporalis media is the main continuation 
of the temporal trunk after the zygomatico-orbital 
branch is given off. It runs up vertically across 
the posterior part of the zygoma, dividing into 
anterior and posterior branches as it passes over 
the upper edge of the zygoma. Both of these 
branches ramify through the substance of the tem- 
poral muscle, (f) R. temporalis superficialis 
(fig. 107) is a slender twig arising from the zygo- 
matico-orbital artery midway between the eye and 
the ear. It passes up onto the top of the head just 
superficial to the temporal aponeurosis, where it 
ramifies into an extremely delicate rete in the pari- 
etal and posterior frontal regions. 

At the angular process of the mandible the ex- 
ternal carotid gives off the very small external 
maxillary, beyond which the trunk continues on 
the medial side of the mandible as the internal 

A. maxillaris externa (fig. 107), which has none 
of the cervical branches that arise from it in man, 
is a slender vessel running across the ventral part 
of the masseter. Beyond the edge of the digastric 
it is accompanied by the anterior facial vein. Nu- 
merous fine twigs are given off to the masseter, and 
at the posterior end of the exposed part of the in- 
ferior alveobuccal (molar) gland the vessel divides 
into the superior and inferior labial arteries. A. 
labialis inferior (fig. 107) runs anteriorly along 
the inferior border of the molar gland, to which it 
gives off twigs, anastomosing anteriorly with the 
mental branch of the inferior alveolar artery. A. 
labialis superior (fig. 107) is larger than the in- 
ferior labial. It passes anteriorly along the supe- 
rior border of the molar gland, into which it sends 
twigs, and along the base of the upper lip. Ante- 
riorly it anastomoses with branches of the infra- 
orbital artery. A. angularis is a slender branch 
arising from the superior labial directly below the 
eye, and passing up across the anterior root of the 
zygoma into the orbit. 

The Internal Maxillary Artery 

A. maxillaris interna (figs. 131, 132) is so much 
larger than the external maxillary artery that it 
appears to be the continuation of the external caro- 
tid trunk, with the external maxillary only one of 
the lesser lateral branches. It arises at the poste- 
rior border of the mandible, just above the angular 
process, and arches forward and upward around 
the condyle, lying between the external and inter- 
nal pterygoid muscles. The vessel continues into 
the space between the coronoid process and the 



skull, terminating near the sphenopalatine fora- 
men by dividing into the infraorbital artery and a 
trunk for the sphenopalatine and descending pala- 
tine arteries. There is no alisphenoid canal. 

The internal maxillary gives rise to the following 
branches (fig. 132): 

L A. alveolaris inferior arises at the inferior 
border of the temporal muscle and passes forward 
and slightly downward to the mandibular foramen. 
The artery lies below the inferior alveolar nerve 
as they enter the foramen. The mental branches 
emerge from the mandible through the mental fora- 
mina, accompanying the corresponding branches 
of the nerve. 

2. A. temporalis profunda posterior comes 
off at the neck of the mandible, passing to the tem- 
poral fossa between the internal and external ptery- 
goid muscles. Here it divides into posterior and 
anterior branches. 

The posterior branch gives off a slender R. ar- 
ticularis near its base, which passes to the mandib- 
ular articulation. Posterior deep temporal vessels 
pass back over the root of the zygoma, one of them 
entering a nutrient foramen in the temporal bone 
at the root of the zygoma, while another anasto- 
moses with a twig of the occipital artery near the 
lambdoidal crest. A. masseterica, arising as one 
of the branches of the posterior branch, arches 
around behind the coronoid process, to enter the 
masseter muscle, where it ramifies. 

The anterior branch of the posterior deep tem- 
poral ramifies in the anterior part of the temporal 
fossa, beneath the temporal muscle. 

3. A. tympanica anterior is a slender vessel 
arising at the same level as the deep temporal. It 
passes caudad across the external pterygoid mus- 
cle, joining the chorda tympani nerve and passing 
with it into the petrotympanic fissure. A twig, 
given off from the anterior tympanic before it 
reaches the fissure, anastomoses with the ascend- 
ing pharyngeal artery. 

4. A. meningea media is a small twig, con- 
siderably smaller than the accessory meningeal, 
arising from the internal maxillary just beyond 
the temporalis profunda posterior. In the panda 
it is not the main source of the meningeal circula- 
tion. It joins the trunk of the mandibular nerve 
and passes beside it into the foramen ovale. With- 
in the cranial cavity the vessel anastomoses with 
the accessory meningeal. 

5. Rr. pterygoidei, arising from the internal 
maxillary along its course, supply the external and 
internal pterygoid muscles. A twig associated 
with these goes to the orbital gland. 

6. A. meningea accessoria is a slender vessel 
that enters the orbital fissure, where it lies beside 
the maxillary nerve. Within the cranial cavity it 
receives the middle meningeal artery, then runs 
posteriorly beside the semilunar ganglion to the 
tip of the temporal lobe of the brain, where it 
breaks up into three branches. These form the 
main blood supply to the dura ( fig. 143) ; this was 
verified on two specimens. The first branch is dis- 
tributed over the frontal lobe; the second passes 
up in the lateral cerebral fissure, and is distributed 
to the adjacent parts of the frontal and temporal 
lobes and to the parietal lobe; the third supplies 
the dura over the ventral and posterior parts of the 
temporal lobe. 

7. .\. orbitalis fophthalmica of authors) is a 
good-sized vessel, only a little smaller than the 
deep temporal, arising from the internal maxillary 
at the anterior end of the internal pterygoid mus- 
cle, about 10 mm. beyond the origin of the poste- 
rior deep temporal artery. It passes forward and 
upward, lying external to the maxillary nerve, to 
pierce the ventral wall of the periorbita at about 
its posterior third. 

Before entering the orbit, the orbital artery gives 
rise to an anterior deep temporal branch, which 
passes across the periorbita to the anterior part of 
the temporal fossa, where it ramifies. The termi- 
nal twigs of this vessel pass out of the temporal 
fossa onto the frontal area of the head. 

As it pierces the periorbita, the orbital artery 
gives rise to a posterior and an anterior branch of 
approximately equal size, which arise from oppo- 
site sides of the parent tiunk. The posterior branch 
turns posteriorly, passing beneath the ophthalmic 
nerve and through the wall of the superior oph- 
thalmic vein. It passes inside the vein through 
the orbital fissui-e into the cranial cavity. The 
anterior branch, A. lacrimalis, accompanies the 
lacrimal nerve forward along the lateral rectus 
muscle of the eye. At about the middle of the mus- 
cle the artery bifurcates into a muscular and a lac- 
rimal ramus. The muscular ramus supplies the 
lateral and inferior recti and the inferior oblique, 
and supplies an anastomotic twig to one of the 
ciliary arteries, while the lacrimal ramus continues 
forward to the lacrimal gland. 

Immediately after entering the orbit the orbital 
artery divides into two equal-sized trunks. The 
more supei-ficial trunk, which lies external to the 
ocular muscles, supplies structures outside the or- 
bit, terminating as the ethmoidal artery. The 
deeper trunk arches around the optic nerve, sup- 
pljing all the structures within the orbit and anas- 
tomosing with the ophthalmic artery. 



A. zygoma tica arises from the superficial trunk 
of the orbital artery as the latter crosses beneath 
the ophthalmic nerve. Accompanying the paired 
zygomatic nerve along the lateral border of M. rec- 
tus superior, it pierces the orbital ligament and 
emerges near the posterior corner of the eye. The 
terminal twigs of the vessel ramify in the super- 
ficial area immediately behind the eye. 

After giving off the zygomatic branch, the super- 
ficial trunk passes across the proximal parts of the 
ocular muscles to the ethmoidal foramen. Just 
before entering the foramen it gives rise to A. 
frontalis, which pierces the dorsal wall of the 
periorbita along with the frontal nerve and the 
superior ophthalmic vein (fig. 107) ; all three struc- 
tures emerge above the eye, where the artery gives 
off a small anterior A. dorsalis nasi, then arches 
posteriorly to anastomose with a twig of the zygo- 
matico-orbital artery. Beyond the origin of the 
frontal artery the main trunk is continued into the 
ethmoidal foramen as R. ethmoidalis, which 
unites with the ethmoidal artery below the olfac- 
tory bulbs (p. 253). 

The deeper trunk of the orbital artery passes 
between M. rectus superior and M. retractor oculi, 
arches around to the deep side of the optic nerve, 
and anastomoses with the ophthalmic artery to 
form the minute central retinal artery. A. cen- 
tralis retinae enters the optic nerve 4 mm. behind 
the eyeball, and passes to the eye within the nerve. 
Numerous muscular twigs arising from the deeper 
trunk of the orbital artery supply M. rectus supe- 
rior, M. levator palpebrae superior, M. retractor 
oculi, M. rectus medialis, and M. rectus inferior. 
Two of these twigs terminate by anastomosing 
with the muscular ramus of the lacrimal artery. 
Aa. ciliares arise from one or more of the muscu- 
lar twigs and pass forward alongside the optic nerve 
to the eye. 

8. A. temporalis profunda anterior (fig. 132) 
arises from the internal maxillary directly opposite 
the origin of the orbital artery. It ramifies in the 
most anterior part of the temporal muscle, one or 
more of its delicate terminal branches emerging on 
the face below the eye and ramifying over the an- 
terior part of the zygoma. A. buccinatoria arises 
from the trunk of the anterior deep temporal. It 
joins the buccinator nerve and passes with it to the 
buccinator muscle. 

Beyond the point where the orbital and ante- 
rior deep temporal arteries arise, the internal max- 
illary corresponds to the "third part of the internal 
maxillary" of human anatomy. The vessel passes 
upward and forward toward the sphenopalatine 
foramen, giving rise to the following branches: 

9. A. palatina minor (fig. 131) arises at the 
posterior border of the alveolar prominence of 
the last molar tooth. It immediately arches me- 
sad and ventrad, accompanying the posterior pala- 
tine nerve along the anterior border of the internal 
pterygoid muscle down to the prominent notch in 
the outer border of the vertical pterygoid plate 
immediately behind the last molar. After leaving 
the notch the vessel bifurcates ; an anterior branch 
runs forward along the medial border of the last 
molar tooth, to anastomose with the major pala- 
tine artery; and a posterior branch runs caudad 
along the soft palate to anastomose with the major 
palatine. Twigs from the posterior branch ramify 
to the palatine glands and other structures in the 
roof of the pharynx, and a twig from the anastomo- 
sis with the major palatine goes to the auditory 

10. A. infraorbitalis (fig. 132), the more lat- 
eral of the two terminal branches of the internal 
maxillary, accompanies the infraorbital nerve to 
the infraorbital foramen. On emerging from the 
foramen it ramifies over the lateral side of the nose 
(fig. 107). Alveolar branches (Aa. alveolares su- 
periores) from this part of the vessel supply the 
premolars, canine, and incisors. A. alveolaris 
superior posterior arises from the base of the 
infraorbital and pursues a tortuous course back 
over the alveolar prominence of the last molar, 
giving off niunerous twigs that enter the minute 
foramina in this region. A. alveolaris superior 
media arises a few millimeters farther forward. 
It runs forward, ramifying twigs to the area over 
the anterior part of the last molar and the next 
tooth forward (M'). A. malaris (Bradley) arises 
from the infraorbital just before the latter enters 
the foramen. It runs out at the anteroventral 
corner of the orbit, lying between the periorbita 
and the preorbital fat. Branches supply the lower 
eyelid and the lacrimal sac, after which the trunk 
continues onto the face in front of the eye. 

The medial terminal branch of the internal max- 
illary is a short trunk that divides just before 
reaching the closely juxtaposed sphenopalatine fo- 
ramen and pterygopalatine canal to form the sphe- 
nopalatine and descending palatine arteries. A. 
sphenopalatina passes into the nose through the 
sphenopalatine foramen A. palatina descend- 
ens reaches the posterior part of the hard palate 
through the pterygopalatine canal. Upon emerg- 
ing onto the palate through the posterior palatine 
foramen, the vessel divides into anterior palatine 
and posterior anastomotic branches. A. palatina 
anterior (palatina major) considerably exceeds the 
posterior anastomotic in caliber. It runs forward 



in the mucoperiosteum of the hard palate to the in- 
cisive foramen, where it anastomoses with the 
sphenopalatine artery. The groove for this artery 
can be seen on the skull, running forward not far 
from the alveolar border. The posterior, anasto- 
motic branch passes backward along the border of 
the last molar tooth, to anastomose with the minor 
palatine artery at the notch in the outer border of 
the pterygoid plate. 

Internal Carotid Artery 

The internal carotid runs forward and mesad 
from the bifurcation of the common carotid, arch- 
ing dorsad around the medial border of the origin 
of the digastric muscle, to enter the foramen lac- 
erum posterior. At the level of the paroccipital 
process it gives off the posterior meningeal artery. 
A. tneningea posterior sends a minute R. sinus 
transversus into the foramen lacerum posterior, 
supplies a twig to the adjacent cranial nerves, and 
then enters the hypoglossal canal. Within the skull 
the posterior meningeal ramifies to the dura of the 
posterior cranial fossa, and anastomoses with the 
basilar artery. 

As it enters the foramen lacerum posterior, the 
internal carotid is situated anterior to the cranial 
nerves passing out of the foramen, and laterad of 
the internal carotid (sympathetic) nerves. Just 
inside the foramen the artery enters the carotid 
canal, within which it passes through the middle 
ear. In the middle ear the carotid canal runs for- 
ward and slightly mesad, and is situated below 
and at first in contact with the petrosal, lying ven- 
trad and slightly mesad of the cochlea (fig. 159). 
A fine anastomotic twig from the ascending pha- 
ryngeal artery joins the internal carotid at the 
juncture of the foramen lacerum medium with the 
anteromedial part of the carotid canal. The in- 
ternal carotid gives off nutrient twigs to the walls 
of its canal. Emerging from the carotid canal, the 
artery enters the cavernous sinus. Immediately 
after entering the sinus it forms a tight knot by 
arching first posteriorly, then anteriorly upon it- 
self. This is followed in the vicinity of the sella 
turcica by a tight S-loop, all of which gi-eatly in- 
creases the length of the vessel ; while the distance 
traversed within the sinus (from the carotid fora- 
men to the anterior border of the sella) is only 
22 mm., the length of the vessel is 68 mm.' The 
internal carotid emerges from the sinus in the vi- 
cinity of the tuberculum sellae, and terminates 
several millimeters anterior to the optic chiasma 
by dividing into the anterior and middle cerebral 

' Tandler (1899) gives the corresponding length of this 
vessel in a polar bear as 160 mm. (see also p. 257). 

The internal carotid gives rise to the following 
branches : 

1. A. communicans posterior arises from 
the internal carotid as soon as it emerges from the 
sinus. It is a good-sized vessel, exceeding the pos- 
terior cerebral in caliber, that nms backward across 
the base of the brain to join the posterior cerebral. 
Near its origin, the posterior communicating ar- 
tery gives rise to the A. chorioidea, which is 
joined by a twig from the internal carotid before 
ramifying to the choroid plexus. Farther poste- 
riorly it gives off a good-sized hippocampal twig to 
the hippocampal gyrus. 

2. R. chorioidea, which joins the choroid ar- 
tery as described above, arises about midway be- 
tween the origin of the communicans posterior and 
the terminal bifurcation of the internal carotid. 

3. A. ophthalmica is present on the right side 
only ; the origin of the corresponding blood supply 
on the left side was not traced. The vessel arises 
from the internal carotid just before its terminal 
bifurcation, and enters the orbit through the optic 
foramen. During its course it makes a spiral revo- 
lution of 180 around the optic nerve. Situated at 
first laterad of the nerve, it enters the optic fora- 
men lying dorsad of it, finally emerging from the 
foramen into the orbit on the medial side of the 
nerve. In the orbit the vessel terminates by anas- 
tomosing with the deep trunk of the orbital artery 
to form the central retinal artery. - 

4. A. cerebri media, the larger of the two 

terminal branches of the internal carotid, arches 
laterad around the temporal pole into the lateral 
fissure where it ramifies to the outer surfaces of 
the frontal, parietal, and occipital lobes. Near its 
origin the middle cerebral divides into a pair of 
parallel vessels (these arise separately on the left 
side), which reunite into a common trunk as they 
enter the lateral fissure. 

5. A. cerebri anterior, the smaller of the ter- 
minal vessels, runs toward the midline above the 
optic nerve. At the midline it unites with its mate 
from the opposite side to form a common trunk 
(there is consequently no A. communicans an- 
terior), which immediately arches dorsad into the 
longitudinal fissure. At the juncture of the two 
anterior cerebral arteries the large median eth- 
moidal artery, which equals the common anterior 
cerebral trunk in caliber, is also given off. 

6. A. ethmoidalis interna appears to be some- 
what anomalous. The ethmoidal circulation arises 
from the anterior cerebrals in the form of three 
vessels: a very large median artery flanked on 

- Most of the ophthalmic circulation of man has been 
taken over by the orbital artery in the panda and related 




either side by a much smaller artery. The median 
artery is tied in with the orbital circulation via the 
ethmoidal foramen, while the lateral arteries run 
directly to the cribriform plate. 

J The median ethmoidal artery runs foi-wai-d in 
the dura immediately below the longitudinal fis- 
sure. Just proximad of the olfactory bulbs it is 
joined by a large branch that represents the com- 
bined ethmoidal rami of the two orbital circulations. 
The vessel then continues forward, breaking up 
below and between the olfactory bulbs into numer- 
ous terminal branches that pass into the cribriform 
plate. A. meningea anterior arises as a fine 
twig from the orbital division of the ethmoidal, and 
ramifies to the dura of the anterior fossa. 

The lateral ethmoidal arteries arch toward the 
midline at the posterior border of the olfactory 
bulbs, continuing between the bulbs into the crib- 
riform plate. 

The Subclavian Artery 

The left subclavian arises from the convex side 
of the arch of the aorta, immediately beyond the 
origin of the innominate; the bases of these two 
arteries are almost in contact. The right subcla- 
vian begins much farther craniad, as the continua- 
tion of the innominate after the right common 
carotid is given off. Both subclavians have the 
same relations beyond the origin of the right sub- 
clavian (about from the posterior border of the 
first rib). Beyond the origin of the thyi-ocervical 
axis the subclavian is continued as the axillary 
artery. The subclavian gives off the following 
branches: (1) the vertebral; (2) the internal mam- 
mary; (3) the thyrocervical trunk; and (4) the 
costocervical trunk. 

1. A. vertebralis (fig. 130) arises from the dor- 
sal side of the subclavian just anterior to the costo- 
cervical trunk, to which it corresponds in size. It 
passes forward and upward around the M. longus 
colli, to enter the transverse foramen of the sixth 
cervical vertebra. Passing craniad thi'ough the 
transverse foramina of succeeding cervical verte- 
brae from the sixth to the first, it reaches the alar 
foramen in the atlas greatly reduced in caliber be- 
cause of the large muscle branches to which it has 
given rise. Turning mesad through the atlantal 
foramen, the vessel reaches the spinal canal of the 
atlas, where it turns forward again and passes into 
the skull through the foramen magnum, lying im- 
mediately above the atlanto-occipital articulation. 
Within the skull the artery lies at first beside the 
medulla, then, between the origins of the first spi- 
nal and twelfth cranial nerves, it turns toward the 
midline, terminating on the pyramid about 15 mm. 
caudad of the pons by uniting with the vertebral 

artery of the opposite side to form the unpaired 
A. basilaris. On the left side the basilar also re- 
ceives an anastomotic twig from the internal caro- 
tid; this twig arose outside the skull, entering the 
cranial cavity through the condylar foramen. The 
basilar artery runs forward in the ventral median 
fissure and across the ventral surface of the pons 
to the anterior border of the pons, where it termi- 
nates by dividing into the two superior cerebellar 
arteries (not into the posterior cerebrals, as it does 
in man). For a short distance beyond its origin 
the basilar is composed of two trunks lying side by 
side, but these soon fuse; this condition is probably 
an individual anomaly. 

The vertebral artery gives rise to the following 

(a) Rr. musculares arise at the intervertebral 
spaces, one to each space. These are very large 
vessels that pass upward between adjacent trans- 
verse processes to ramify in the dorsal axial mus- 
culatui'e. Near its base each vessel gives off a slen- 
der twig (R. spinalis) that passes through the in- 
tervertebral foramen into the spinal canal. 

(b) A. spinalis posterior' is a threadlike vessel 
that winds caudad along the side of the medulla 
to the dorsum of the cord. The paired vessel may 
be seen lying in the dorsal lateral sulci of the cord 
in a section through the neck made at the fourth 
cervical vertebra. 

(c) A. spinalis anterior is unpaired in the ani- 
mal dissected, and considerably exceeds the pos- 
terior spinal in caliber. It arises from the left 
vertebral artery at the midline, and runs caudad 
on the ventral surface of the medulla and cord. 

The branches from the basilar artery are: 

(d) A. cerebelli inferior posterior arises from 
the basilar (vertebral?) at about the middle of the 
olive, and (e) A. cerebelli inferior anterior at 

about the posterior third of the pons. These two 
vessels form a very loose rete on the inferior sur- 
face of the cerebellum, to which they send numer- 
ous twigs, eventually uniting at the postero-infer- 
ior part of the cerebellum to form a common tmnk 
that plunges into the substance of the cerebellum. 

(f) A. auditiva interna arises as a delicate 
twig from the anterior inferior cerebellar artery. 
It accompanies the auditory and facial nerves into 
the internal acousticomeatus. 

(g) Rr. ad ponteni are given off from the basi- 
lar as it the pons. 

(h) A. cerebelli superior, paired to form the 
terminal branches of the basilar artery, arises at 
the anterior border of the pons and runs laterad 

' No structure corresponding to the R. meningeus of 
human anatomy could be found. 



to the anterior surface of the cerebellum. It is 
separated from the posterior cerebral artery by the 
oculomotor nerve, as in man. 

Near its origin the superior cerebellar artery re- 
ceives the posterior communicating branch, which 
runs caudad from the internal carotid. At this 
juncture a good-sized middle thalamic twig is given 
off, on the left side only, to the thalamus; no cor- 
responding structure is present on the right side. 

(\) A. cerebri posterior arises from the poste- 
rior communicating branch (at about its posterior 
third), and hence actually belongs to the internal 
carotid circulation rather than to the vertebral. 
It is a slender vessel, considerably smaller than the 
superior cerebellar, that runs laterad, caudad, and 
dorsad into the notch between the cerebrum and 
the cerebellum, eventually supplying the posterior 
part of the cerebrum. 

2. A. mammaria interna (fig. 130) takes ori- 
gin from the ventral wall of the subclavian, imme- 
diately opposite the origin of the vertebral artery 
and costocervical trunk. Extending obliquely ven- 
trad, caudad, and mesad, it meets the internal 
mammary vein which descends on the opposite 
side of the vena cava, in the space between the 
second and third costal cartilages. The artery and 
vein pass beneath the transverse thoracic muscle 
side by side, about 10 mm. laterad of the sternum. 
They pass straight caudad as far as the fifth costal 
cartilage, then gi-adually curve toward the midline. 
The artery is almost in contact with the tip of the 
xiphoid cartilage. 

In each intercostal space the internal mammary 
artery gives off the usual R. perforans medially 
and a R. intercostalis laterally. A. thymica 
arises in the first intercostal space and runs trans- 
versely to the thjTTius. Beyond the last rib carti- 
lage the internal mammary is continued as the 
anterior epigastric artery. 

3. Truncus thyreocervicalis (fig. 130) arises 
from the medial wall of the subclavian about 15 
mm. beyond the origin of the internal mammary 
artery. It runs forward and outward, ventrad of 
the brachial plexus and closely applied to the ex- 
ternal jugular vein. The thyrocervical trunk gives 
off three branches. The first and smallest (cervi- 
calis ascendens of Reighard and Jennings) gives off 
a twig that supplies the sternomastoideus, sterno- 
hyoideus, and adjacent muscles; the rest of this 
branch supplies the posterior cervical lymph gland 
and a part of the clavotrapezius. The second 
branch supplies the proximal part of the clavo- 
trapezius and adjacent muscles. 

The third branch, A. transversa colli, is the 
largest and appears to be the direct continuation 
of the thyrocervical trunk. It passes up around 

the shoulder to emerge at the scapulohumeral ar- 
ticulation, where it lies between the acromiotra- 
pezius and the supraspinatus. The transverse 
cervical divides just above the scapulohumeral ar- 
ticulation to form anterior and posterior rami. A 
third branch, only slightly smaller in size, runs 
forward into the clavotrapezius. 

R. niedialis (descendens, BNA) runs dorso- 
caudad between the rhomboideus and the sub- 
scapularis, then turns caudad just before the 
coracovertebral border of the scapula is reached, 
passing deep to the rhomboids and levator scap- 
ulae. Opposite the infraspinous fossa a branch is 
sent outward and over the vertebral border of the 
scapula into the infraspinous fossa, where it anas- 
tomoses with the termini of the circumflex scap- 
ular and the thoracodorsalis. Other branches 
supply the rhomboids, the latissimus, the spino- 
trapezius, the serratus, and the subscapularis. The 
branch to the latissimus descends along the ante- 
rior border of this muscle, sending off short lateral 
twigs into the muscle, and eventually anastomos- 
ing with an ascending branch of the thoraco- 
dorsalis. The main trunk of the medial ramus 
continues beyond the border of the scapula, to 
anastomose with the sixth intercostal artery. 

R. lateralis (ascendens, BNA) passes across the 
supraspinatus caudad of the occipitoscapularis. 
Numerous twigs are sent to the occipitoscapularis 
and spinotrapezius, other twigs entering the supra- 
spinatus fossa to participate in the supraspinatus 
anastomosis. Near the coracovertebral angle of 
the scapula it sends a terminal twig down into the 
supraspinous fossa, which anastomoses with the 
terminus of the transverse scapular. 

Twigs from the lateral ramus pass across M. 
supraspinatus to the proximal part of M. acromio- 
trapezius. The most dorsal of these sends a twig 
down along the scapular spine, which receives twigs 
from the circumflex scapular, transverse scapular, 
and external circumflex humeral arteries before it 
reaches the acromial process of the scapula. This 
branch is the main source of the Rete acromiale. 
Other branches from the external circumflex hu- 
meral and transverse scapular arteries pass across 
the neck of the scapula, and form the other roots 
of the rete. 

Since the posterior thyroid artery is absent, the 
thyrocervical trunk has no relation with the thy- 
roid gland. 

4. Truncus costocervicalis dextra (fig. 130) 
is the first branch given off from the right subcla- 
vian. It arises from the dorsal side of the artery, 
immediately caudad of the origin of the vertebral 
artery, i.e. at the anterior border of the first rib. 
Arching upward just outside the pleura, it bifur- 



cates near the articulation of the fiist rib. One 
branch, A. intercostalis suprema, passes back- 
ward just inside the ribs, giving oflF the usual 
branches to the intercostal spaces. The other 
branch, A. cervicalis profunda, immediately 
passes dorsad between the eighth cervical and first 
thoracic nerves, then between the necks of the 
first and second ribs. The vessel emerges on the 
back of the neck between the longissimus dorsi and 
multifidus cervicus muscles, where it divides into 
anterior and posterior branches. The anterior 
branch ramifies in the biventer cervicis; the pos- 
terior branch supplies the longissimus dorsi and 
multifidus cervicis. 

The left costocervical trunk arises from the left 
vertebral artery. It passes dorsad between the 
seventh and eighth cervical nerves, giving off a 
small intercostalis suprema to the first intercostal 
space. The remainder of the vessel continues dor- 
sad as the cervicalis profunda, passing between 
the seventh cervical vertebra and the neck of the 
first rib, beyond which it parallels the course of its 
fellow on the opposite side. 

Axillary Artery 

A. axillaris (figs. 133, 134) is the distal continu- 
ation of the subclavian beyond the origin of the 
thyrocervical axis. The proximal part of the ar- 
tery lies between the brachial plexus (dorsad), 
where it is situated between the seventh cervical 
and first thoracic nerves and immediately ventrad 
of the eighth cervical nerve, and the axillary vein 
(ventrad). With the foreleg in an extended posi- 
tion the artery curves outward and slightly back- 
ward into the leg, where it becomes the brachial 
artery beyond the origin of the subscapular trunk. 
The axillary artery gives rise to the following 
branches: (1) the transverse scapular; (2) the an- 
terior thoracic; (3) the thoracoacromial; (4) the 
lateral thoracic; (5) the subscapular; (6) the in- 
ternal humeral circumflex; and (7) the external 
humeral circumflex. 

1. A. transversa scapulae (fig. 133) is the first 
branch given off by the axillary. It is a good-sized 
branch arising from the convex side of the curve of 
the axillary as the latter arches back from the first 
rib. Running forward, outward and upward, par- 
allel with the transverse cervical artery, it gives 
off a twig to the anterior division of the superficial 
pectoral as it passes around the shoulder joint to 
enter the space between M. suprascapularis and 
M. infraspinatus. At this point the vessel breaks 
up into a number of smaller branches. Of these, 
superficial rami supply the adjacent parts of the 
supraspinatus and subscapularis, while the largest 
branch, which appears to be the direct continua- 

tion of the transverse scapular, passes through the 
scapular notch onto the supraspinous fossa of the 
scapula. Here the larger of two branches ramifies 
in the supraspinous fossa, eventually anastomosing 
with the posterior branch of the transverse cervical 
artery near the vertebral border of the scapula; 
twigs from this branch pass toward the scapular 
spine, where they participate in the acromial rete. 
A smaller branch passes across the neck of the 
scapula, at the base of the scapular spine, into the 
infraspinous fossa, where it ramifies and anasto- 
moses with branches of the circumflex humeral 
scapular artery near the glenoid border and with 
the descending branch of the transverse cervical 
artery near the vertebral border. This branch also 
contributes a twig to the acromial rete. 

2. A. thoracalis anterior (fig. 133) is a small 
vessel arising from the posterior wall of the axillary 
artery immediately beyond the border of the first 
rib. It runs caudad across the ventral part of the 
first intercostal space, which it supplies. It is ac- 
companied by a corresponding vein. 

3. A. thoracoacromialis arises from the ante- 
rior wall of the axillary immediately beside and 
internal to the origin of the transverse scapular, 
which it slightly exceeds in caliber. Passing dis- 
tad between the anterior and posterior divisions of 
the pectoral muscle, the thoracoacromialis gives 
off numerous twigs to both layers of the pectoral 
musculature, the humeral end of the clavotrape- 
zius and the acromiodelteus. 

The main trunk, greatly reduced in caliber, 
pierces the tendon of the pectoral profundus below 
the head of the humerus and divides to form as- 
cending and descending rami that run along the 
pectoral ridge of the humerus. The ascending ra- 
mus passes up along the pectoral ridge, pierces the 
anterior superficial pectoral muscle near the greater 
tuberosity, and so emerges onto the bicipital groove. 
The main part of the branch enters a nutrient fora- 
men in the bicipital groove, while a smaller twig 
continues beneath the tendon of the biceps, where 
it anastomoses with a branch of the internal hu- 
meral circumflex. The descending ramus runs dis- 
tad along the ridge, to anastomose with a twig 
from the profunda brachii at the distal border of 
the tendon of the teres major. 

4. A. thoracalis lateralis (fig. 133) arises from 
the posterior wall of the axillary, 17 mm. distad of 
the origin of the thoracoacromial artery. It passes 
caudad, giving off branches to the pectoralis pro- 
fundus, the panniculus, and the serratus. Inter- 
costal branches to the second to fourth intercostal 
spaces anastomose with the aortic intercostals. 
Twigs are also sent to the axillary lymph glands. 












5. A. subscapularis (fig. 133) takes origin from 
a trunk that gives rise also to the two circumflex 
humeral arteries and a large vessel that furnishes 
the main blood supply to the latissimus, subscap- 
ular, and adjacent muscles. This trunk arises from 
the anterior wall of the axillary about 35 mm. dis- 
tad of the origin of the thoracoacromial (i.e., oppo- 
site the ventral border of the teres minor), and 
beneath the pectoral musculature. The trunk 
passes laterally (externally) through the interval 
between the teres major and the teres minor, emerg- 
ing at the level of the external surface of the scap- 
ula. Here, at the antero-internal border of the 
triceps longus and 10 mm. beyond its origin from 
the axillary, the trunk bifurcates to form two 
branches of approximately equal size: one of these, 
the subscapular proper, passes caudad beneath the 
triceps longus; the other, the external humeral cir- 
cumflex, runs outward in the interval between the 
triceps longus and the triceps medialis. The small 
internal humeral circumflex arises from the com- 
mon trunk about 5 mm. beyond the origin of the 
trunk from the axillary, at the level of the internal 
border of the scapula; immediately proximal to it, 
and from the opposite side of the trunk, arises the 
large branch supplying the latissimus, subscapu- 
laris, teres major and teres minor. 

The subscapular artery proper runs along the 
glenoid border of the scapula for a short distance, 
then divides to form two terminal branches. The 
infrascapular branch of the circumflex scapular ar- 
tery (cf. human anatomy) does not arise from the 
circumflex scapular, but takes origin independently 
from the subscapular opposite the scapular notch. 
The terminal bi'anches of the subscapular are (a) a 
circumflex scapular, and (b) a slightly smaller dor- 
sal thoracic. 

(a) A. circumflexa scapulae (fig. 134) passes 
into the infraspinous fossa, where the main part of 
the vessel passes aci'oss the fossa parallel to the 
scapulai' spine, eventually anastomosing with the 
descending branch of the transverse cervical and 
the dorsal thoracic branch of the subscapular near 
the gleno-vertebral angle of the scapula. A twig 
from this artery enters the large infraspinous nutri- 
ent foramen of the scapula; and a second twig 
passes toward the spine, where it participates in 
the acromial rete by anastomosing with a branch 
of the transverse cervical. Immediately opposite 
its origin from the subscapular, the circumflex 
scapular gives off a small anastomotic branch that 
passes toward the supraglenoid groove, where it 
anastomoses with the infraspinous branch of the 
transverse scapular. 

(b) A. thoracodorsalis (fig. 134), lying between 
the teres major and the triceps longus, continues 

the subscapular artery along the glenoid boi'der of 
the scapula nearly to the gleno-vertebral angle. 
Numerous short twigs pass into the triceps longus, 
and a branch arising at the ventral end of the teres 
major fossa passes into the latissimus dorsi. The 
vessel terminates by anastomosing with the cir- 
cumflex scapular and the descending branch of the 
transverse cervical near the gleno-vertebral angle. 

6. A. circumflexa humeri interna [BNA: 
anterior] (figs. 133, 134) is a slender vessel that 
arises from the subscapular trunk just before its 
terminal bifurcation. The internal circumflex di- 
vides a few millimeters beyond its origin (on the 
left leg these two vessels arise independently side 
by side). The deeper of the two branches passes 
along the ventral border of the teres minor, then 
beneath the coracobrachialis, onto the head of 
the humerus. Passing up across the lesser tuber- 
osity and beneath the tendon of the biceps, it 
anastomoses with an ascending branch of the tho- 
racoacromial in the bicipital groove. The more 
superficial branch of the internal humeral circum- 
flex passes forward external to the coracobrachi- 
alis to the proximal end of the biceps, which it 
supplies; a twig supplies the coracobrachialis. 

7. A. circumflexa humeri externa [BNA: 

posterior] (fig. 133) is a large vessel that arises by 
bifurcation of the trunk that gives rise to it and 
the subscapular. The external humeral circumflex 
passes ectad between the subscapularis and teres 
major, emerging between the triceps medialis and 
the triceps lateralis and breaking up into a number 
of branches beneath the spinodeltoideus. Branches 
go to both divisions of the deltoid, to the infra- 
spinatus, and to the integument in the shoulder 
region. Twigs from the deltoid branch enter the 
acromial rete. A large descending branch supplies 
the triceps medialis and the triceps longus; this 
descending branch anastomoses with a branch of 
the profunda brachii beneath the triceps medialis, 
then bifurcates. One of the resulting twigs passes 
to the olecranal rete; the other runs distad with 
the lateral ramus of the superficial radial nerve, to 
anastomose with an ascending twig from the dorsal 
terminal branch of the volar interosseous. There 
is also an anastomosis with the dorsal interosseous. 
Nutrient branches enter the foramen in the head 
of the humerus immediately behind the deltoid 

Brachial Artery 

A. brachialis (fig. 133) is the continuation of 
the axillary beyond the origin of the subscapular 
trunk. There is no sharp boundary between the 
brachial and median arteries, but the brachial may 
be considered as terminating at the level of the 












entepicondylar foramen, beyond which the trunk 
is continued as the median. The brachial artery 
runs distad along the posterior border of the bi- 
ceps, and has the following relations with the 
median nerve: Immediately after passing through 
the loop of the median nerve, the nerve lies pos- 
terior to the artery. Between this point and the 
elbow the nerve makes a complete spiral revolu- 
tion around the artery, so that just proximad of 
the elbow it again occupies a posterior position. 
The nerve and artery now diverge, the nerve con- 
tinuing straight distad through the entepicondylar 
foramen, while the artery follows the crease of the 
elbow, lying craniad of the nerve. The artery re- 
joins the nerve below the foramen, and passes 
distad with it. 

The brachial artery gives rise to the following 
branches in addition to numerous twigs to the 
flexor musculature of the upper arm: (1) the pro- 
funda; (2) the superior ulnar collateral; (3) the 
inferior ulnar collateral; (4) the superficial radial. 

1. A. profunda brachii (fig. 133) is a small 
branch arising from the posterior wall of the bra- 
chial artery at the level of the bicipital arch. Im- 
mediately beyond its oiigin the vessel gives off a 
slender twig that follows the lower border of the 
tendon of the teres major, thus lying deep to the 
biceps and brachialis, to the pectoral ridge of the 
humerus. Here it divides to form ascending and 
descending rami that run along the pectoral ridge. 
The ascending ramus anastomoses with the de- 
scending ramus of the thoracoacromialis, while the 
descending ramus passes down along the pectoral 
ridge to anastomose with a branch of the radial 
recurrent. A ramus from this twig also supplies 
the coracobrachialis longus. 

The main part of the pi-ofunda brachii bifurcates 
about 5 mm. beyond its origin, one branch enter- 
ing the medial side of the triceps longus, where it 
ramifies, while the other entei-s the medial side of 
the triceps medialis. A twig from the branch to 
the triceps medialis accompanies the radial nerve 
through the space between the triceps medialis 
and triceps longus to the posterior side of the hu- 
merus, where it anastomoses with the descending 
ramus of the circumflexa humeri externa. 

2. A. collateralis ulnaris superior (fig. 133) 
arises, on the right foreleg, from the posteiior side 
of the brachial about 25 mm. proximad of the in- 
ternal condyle of the humerus. On the left fore 
leg the two ulnar collateral arteries arise by a short 
common trunk. The superior collateral crosses the 
ulnar nerve, lying external to it, then accompanies 
the nerve downward for a short distance before 
plunging into the triceps medialis. One branch 
ramifies in the distal end of the triceps medialis, 

while a second passes through this muscle and into 
the triceps longus, where it ramifies. 

3. A. collateralis ulnaris inferior arises, on 
the right leg, about 12 mm. distad of the superior 
collateral. It accompanies the ulnar nerve, lying 
distad of it, to the region immediately above the 
internal condyle. Here the vessel breaks up to 
form four main branches: (1) A slender branch runs 
forward, accompanying the median nerve through 
the entepicondylar foramen. (2) A branch enters 
the triceps medialis, where it ramifies. (3) The 
largest branch winds back behind the median epi- 
condyle to the posterior side of the humerus. (4) A 
slender branch accompanies N. cutaneus ante- 
brachii medianus across the median epicondyle. 

4. A. radialis superficialis (collateralis radi- 
alis superior of veterinary anatomy) (fig. 133) arises 
from the anterior side of the brachial 10 mm. be- 
yond the origin of the collateralis ulnaris inferior. 
At its origin it divides into a dorsal branch and a 
smaller volar branch. The volar branch ramifies 
extensively to the forearm flexors. The dorsal 
branch runs across the distal end of the biceps, 
immediately above the origin of the lacertus fibro- 
sus, dividing into a pair of collateral branches at 
the anterior border of the biceps; these branches 
reunite at the carpus after pursuing their separate 
ways down the fore arm. One of them passes 
through the brachioradialis to the dorsum of the 
forearm, where it joins the medial ramus of the su- 
perficial radial nerve and accompanies it to the 
carpus; numerous branches to the brachioradialis 
considerably reduce the caliber of this vessel. The 
second collateral branch joins N. cutaneus ante- 
brachii lateralis and V. brachialis superficialis at 
the crease of the elbow, and runs distad with them 
in the groove between the pronator teres and bra- 
chioradialis. The vessel winds along the distal 
border of the brachioradialis onto the dorsum of 
the forearm, where it receives the dorsal collateral 
branch, then terminates by dividing into subequal 
terminal twigs. One of these terminal twigs anas- 
tomoses with the dorsal branch of the interossea 
volaris, while the other opens into the anastomotic 
branch of the medianoradialis, the resulting com- 
mon trunk forming the radial end of the superficial 
dorsal arch. 

Recurrent twigs to the biceps, with a larger re- 
current branch running back in the furrow between 
the biceps and brachioradialis to ramify to the 
latter muscle and the distal end of the clavotra- 
pezius, arise from the dorsal branch before it di- 
vides into its collateral branches. 

The arcus dorsalis superficialis is a very deli- 
cate double arch with three vessels contributing to 
its formation. The first arch, which extends across 



metacarpals 1 and 2, is formed by the common 
trunk of the radialis superficialis and the anasto- 
motic branch of the medianoradiaHs radially, and 
the dorsal branch of the interossea volaris ulnar- 
ward. Aa. digitales dorsales communes 12 
arise from this loop. The second arch extends 
across metacarpals 3 and 4, and is formed by the 
dorsal branch of the interossea volaris and the ul- 
naris dorsalis. It gives rise to digitales dorsales 
communes 3-4. Each of these digital arteries is 
joined by a delicate anastomotic branch from the 
corresponding metacarpea dorsalis at the distal 
ends of the metacarpal bones. 

Median Artery 

A. mediana communis' (fig. 133) is the con- 
tinuation of the brachial beyond the level of the 
entepicondylar foramen. It passes just medial of 
the tendon of the biceps onto the forearm. Imme- 
diately proximad of the biceps tendon it is joined 
by X. medianus, which has passed through the 
entepicondylar foramen. The artery and nerve 
pass beneath the proximal ends of the flexor carpi 
radialis and pronator teres, coming to lie in the 
space between the flexor carpi radialis and the 
flexor digitorum profundus. The artery lies on 
the radial side of the nerve. Just proximad of the 
carpus the artery divides to form two branches of 
nearly equal size: the median proper and the me- 
dianoradial. The first of these passes to the palm, 
while the other passes around the radial border of 
the wrist, deep to the tendon of the extensor pol- 
licis brevis, onto the dorsum of the hand. 

The common median artery gives off the follow- 
ing branches on the forearm. 

1. A. recurrens radialis (Davis, 1941, p. 176) 
is a small branch arising from the lateral side of 
the median artery at the level of the entepicondy- 
lar foramen. It ascends along the humeromedial 
border of the brachialis, dividing after about 15 
millimeters to form two branches. 

One of these branches passes back around the 
distal end of the insertion tendon of the deltoid, 
sending twigs to the tendon and to adjacent parts 
of the brachialis; a twig passes proximad along the 
medial border of the deltoid tendon, to anasto- 
mose with the descending branch of the profunda 
brachii. Another small twig passes from the main 
trunk to the distal end of the humerus. 

The other branch passes around in front of the 
distal end of the humerus, beneath the brachialis. 
Twigs are given off to the distal end of the bra- 

> I follow the German anatomists in regarding the main 
artery in the forearm as the median rather than as the 
radial. Conditions found in lower mammals show that it is 
erroneous to designate this vessel the radial, as Reighard 
and Jennings (1935) have done. 

chialis. After emerging on the opposite side of the 
brachialis the vessel breaks up to form numerous 
terminal twigs, which pass, in contact with the 
radial nerve, to the extensor carpi radialis longus 
and brevis. 

2. Aa. recurrentes ulnares (fig. 133) are three 
small branches arising from the medial side of the 
median artery a few millimeters below the origin 
of the brachialis anterior. The first of these passes 
through the pronator teres, emerging on the me- 
dial surface of the forearm. In addition to supply- 
ing the pronator teres, it sends twigs to the flexor 
carpi ulnaris, the flexor digitorum profundus, and 
the palmaris longus. The second branch runs back 
into the entepicondylar foramen, where it anasto- 
moses with a branch of the collateralis ulnaris in- 
ferior. The third branch gi-eatly exceeds the other 
two in caliber, and arises 20 mm. farther distad. 
Its origin is adjacent to the origin of the ulnar 
artery. The vessel forms three main twigs. The 
smallest passes distad to supply the condylar heads 
of the flexor digitonim profundus. A second twig 
passes back to the ulnar articulation, giving off 
twigs to the proximal ends of the flexor muscles on 
the ulnar side of the forearm. A third twig passes 
to the ulnar articulation, giving off twigs to the 
ulnar head of the flexor digitorum profundus, and 
terminates in the olecranal region. 

3. A. collateralis radialis (fig. 133) arises from 
the radial side of the median opposite the origin 
of the ulnar artery. It bifurcates just beyond its 
origin. One twig supplies M. pronator teres. The 
other passes around in front of the brachialis, to 
anastomose with the recuiTent interosseous; twigs 
are given off along its course to the brachialis and 
the extensor carpi radialis longus. 

4. Rr. musculares. Numerous short branches 
pass from the median artery along its course to 
contiguous muscles on the flexor side of the forearm. 

5. A. ulnaris (fig. 133) is a fair-sized branch, 
approximately the same diameter as the interossea 
volaris, that arises from the ulnar side of the me- 
dian at the level of the insertion of the biceps, i.e., 
at the proximal fifth of the forearm. It runs to 
the ulnar side of the forearm, and then toward the 
carpus, but remains hidden by the flexor muscula- 
ture throughout its course. It gives off twigs to 
the flexor muscles situated on the ulnar side of the 
forearm, and thus its caliber is considerably re- 
duced. Several millimeters before reaching the 
pisiform, at about the distal quarter of the fore- 
arm, it divides into a very slender ulnaris volaris 
and a larger ulnaris doi-salis. The volaris passes 
onto the palm, where it anastomoses with the 
branch of the mediana propria that goes to the 
outer border of digit 5; the ulnar artery has no 




connection with the superficial volar arch proper. 
The ulnaris dorsalis accompanies the dorsal ramus 
of the ulnar nerve onto the dorsum of the manus 
just proximad of the pisiform. On the dorsum it 
anastomoses with the much larger medianoradialis 
to form the deep dorsal arch, and sends twigs into 
the dorsal carpal rete; an additional fine twig forms 
the ulnar half of the delicate superficial dorsal arch 
with the dorsal branch of the interossea volaris. 
The branch of the ulnaris dorsalis that goes to the 
outer side of digit 5 (metacarpea dorsalis 5) gives 
off an anastomotic loop that passes around the 
border of the hand to anastomose with metacarpea 
volaris 5. 

6. Aa. interosseae. There is no interossea 
communis, the volar and dorsal branches arising 
together, but without the intervention of a com- 
mon trunk; they come off immediately distad of 
the ulnaris. A. interossea volaris (fig. 133) 
slightly exceeds the dorsalis in caliber. It passes 
distad on the intei'osseous membrane, accompa- 
nied by its vein, to the radiocarpal articulation. 
Numerous twigs are given off to the deep fiexor 
muscles of the forearm, and nutrient twigs to the 
ulna and radius. At the radiocarpal articulation 
it divides into a large dorsal terminal branch and 
a slender volar terminal branch. The volar ter- 
minal branch passes between the heads of the 
ulna and radius onto the carpus, where it divides; 
the larger branch passes toward the pisifoi'm, where 
it anastomoses with the volar branch of the ulnar 
artery; the smaller branch passes toward the base 
of the radial sesamoid, to anastomose with a twig 
from the R. carpeus volaris of the medianoradialis. 
The dorsal terminal branch perforates the in- 
terosseous membrane near the base of the carpus. 
On the dorsal side of the forearm it first gives off a 
twig that runs proximad between the extensor digi- 
torum communis and the extensor digitorum lat- 
eralis, to anastomose with a descending branch of 
the interossea dorsalis. The main trunk bifurcates 
after giving off this twig. The more superficial 
of the resulting branches runs distad external to 
the dorsal carpal ligament. At the proximal bor- 
der of the ligament it gives off a recurrent twig 
that runs back toward the elbow beside the lateral 
branch of the superficial radial nerve, to anasto- 
mose with a descending branch of the external cir- 
cumfiex humeral. The superficial branch divides 
on the carpal ligament, one twig passing toward 
the pollex to anastomose with the anastomotic 
ramus of the medianoradialis to form the radial 
half of the superficial dorsal arch, while the other 
forms the ulnar half of this arch with a twig from 
the ulnar. The deeper twig of the dorsal terminal 
branch passes beneath the dorsal carpal ligament, 
where it enters the dorsal carpal rete. 

A. interossea dorsalis (figs. 133, 134) emerges 
onto the dorsal side of the forearm by perforating 
M. abductor pollicis longus. It divides immedi- 
ately into two branches of approximately equal 
caliber. One of these, A. interossea recurrens, 
runs back toward the olecranon, giving off twigs 
to the proximal ends of the extensor muscles of the 
forearm and continuing into the olecranal rete. 
The second branch, the main continuation of the 
dorsal interosseous, runs distad beneath the ex- 
tensor digitorum. It supplies twigs to the exten- 
sor muscles, the largest of these anastomosing with 
the descending branch of the external circumflex 
humeral. The vessel terminates by emptying into 
the dorsal terminal branch of the interossea volaris. 

7. A. medianoradialis (figs. 133, 134) arises, 
as usual in carnivores, from the bifurcation of the 
common median artery, just proximad of the car- 
pus. The medianoradialis is the larger of the two 
resulting branches, and passes diagonally radial- 
ward with N. cutaneus antibrachii lateralis. 

About 25 mm. beyond its origin the mediano- 
radialis gives rise to a branch, R. carpeus volaris 
(fig. 133), from its medial wall. This branch runs 
distad beneath the tendons of the fiexor muscles 
and enters the volar carpal rete. A few milli- 
meters farther distad the medianoradialis gives off 
a long anastomotic ramus that accompanies N. cu- 
taneus antibrachii lateralis around the radial sesa- 
moid, superficial to the tendon of the abductor 
pollicis longus, to the dorsum, where it receives a 
delicate anastomotic twig from the brachialis super- 
ficialis, then anastomoses with the dorsal branch 
of the interossea volaris to form a part of the 
superficial dorsal arch. 

Winding up around the base of the radial sesa- 
moid, deep to the tendon of M. abductor pollicis 
longus, the trunk of the medianoradialis reaches 
the dorsum manus, where it terminates by anasto- 
mosing with the ulnaris dorsalis to form the deep 
dorsal arch. Upon reaching the dorsum the me- 
dianoradialis first gives off (a) a slender perforating 
twig that passes between the base of the first meta- 
carpal and the radial sesamoid to the vola, where 
it participates in the formation of the radial end 
of the deep volar arch. This is followed immedi- 
ately by (b) a somewhat larger twig that passes 
distad between the radial sesamoid and digit 1. 
This twig divides into subequal terminal twigs, 
one of which supplies the outer border of digit 1, 
and the other goes to the radial sesamoid. A per- 
forating twig from the latter passes to the vola 
between the radial sesamoid and the first meta- 
carpal, to participate in the formation of the radial 
end of the deep volar arch. A second twig passes 
around the outer border of the radial sesamoid. 



accompanying the nerve that supplies the radial 
sesamoid, and empties into the anastomotic loop 
of the medianoradialis on the vola. At the distal 
border of the carpus the medianoradialis gives off 
(c) a twig that passes transversely across the carpo- 
metacarpal articulation to anastomose with a cor- 
responding twig from the ulnaris dorsalis. This 
anastomotic loop gives off several twigs to the 
dorsal carpal rete. 

The arcus dorsalis profundus (fig. 134) is 
formed by the union of the medianoradialis and 
the ulnaris dorsalis. It lies deep to the extensor 
tendons of the digits. From it are radiated Aa. 
metacarpeae dorsales 1-4, which run to the cor- 
responding intermetacarpal spaces. The second 
and third dorsal metacarpals are the largest. Near 
the middle of the first phalanx each dorsal meta- 
carpal divides into two Aa. digitales volares 
propriae, and at the bifurcation each dorsal meta- 
carpal receives the perforating branches of the cor- 
responding volar common digital. 

In addition to the dorsal metacarpal arteries, 
the deep dorsal arch gives rise to a perforating 
branch that pierces the interstitium between the 
second and third metacarpal bones. On the palm 
it enters the middle of the deep volar arch. 

The arcus volaris profundus (fig. 133) is 
slightly smaller in caliber than the superficial volar 
arch, and is a compound arch with contributory 
vessels entering it at three points. The main source 
of the arch is the large perforating branch of the 
medianoradialis that passes through the second in- 
termetacarpal space. On the vola this vessel di- 
vides, one anastomotic loop passing across the 
base of the first metacarpal to inosculate with a 
common trunk formed by the union of the two 
perforating twigs that pass between the radial ses- 
amoid and the first metacarpal. This part of the 
arch gives lise only to A. metacarpea volaris 1. 
The second and larger anastomotic loop from the 
perforating branch passes toward the ulnar side of 
the palm, anastomosing with terminal twigs of the 
mediana propria to complete the arch. This part 
of the arch gives rise to Aa. metacarpeae volares 
2-4. Each volar metacarpal opens into the corre- 
sponding common digital artery at the distal end 
of a metacarpal bone. 

8. A. mediana propria (fig. 133) accompanies 
the median nerve to the palm. In the wrist it gives 
off a large branch to the outer side of digit 5 ; this 
branch gives off a transverse anastomotic loop to 
the parent vessel in the palm; it also receives the 
terminus of the ulnaris volaris, and beyond the 
pisiform a slender anastomotic twig from the ul- 
naris dorsalis. The main trunk of the mediana 
continues onto the palm, where it curves in a gen- 

tle arc (arcus volaris superficialis) toward the 
ulnar side. A branch to the outer side of the pollex, 
which also supplies a twig to the radial sesamoid, 
and Aa. digitales volares communes 1-3 arise 
from the arch, while the trunk itself is continued 
as the digitalis volaris communis 4. Each com- 
mon digital bifurcates at the distal end of the 
metacarpal bone to form two Rr. perforantes, 
which pass through the interosseous spaces to anas- 
tomose with the corresponding dorsal metacarpal 
artery. The second, third, and fourth common 
digitals receive the corresponding volar metacarpals 
from the deep volar arch. 

Abdominal Aorta 

Parietal Rami 

A. phrenica anterior (fig. 135) arises from the 
left ventral wall of the aorta as the latter passes 
between the medial crura of the diaphragm. Its 
origin is 12 mm. anterior to the origin of the celiac 
axis. The vessel divides into right and left branches 
25 mm. beyond its origin; the right branch is some- 
what smaller than the left (see below under Renal 
Arteries). A small left posterior phrenic arises 
from the base of the anterior phrenic. The right 
posterior phrenic comes from the right renal artery. 

Celiac Artery 

A. coeliaca (fig. 135) arises from the ventral 
wall of the aorta immediately after the latter 
emerges from the diaphragm, i.e., ventrad of the 
last thoracic vertebra. The celiac artery is a short 
vessel which passes forward and slightly to the left 
for about 12 mm., then breaks up to form three 
branches: the hepatic, the splenic, and the left 
gastric arteries. 

1. A. hepatica arises independently from the 
ventral wall of the celiac artery. It is only slightly 
smaller than the splenic artery, but much larger 
than the left gastric. It passes forward alongside 
the portal vein to the liver, giving off a single large 
branch (the gastroduodenal). Near the liver the 
hepatic artery divides into the customary right 
and left branches, which supply the liver and gall 

A. gastroduodenalis is very short, dividing 
about 5 mm. beyond its oi'igin from the hepatic 
artery to form two branches of nearly equal size. 
The larger of these is a short trunk which forks 
after 9 mm. to form the right gastroepiploic and 
anterior pancreaticoduodenal arteries. A. gas- 
troepiploica dextra runs beneath the duodenum, 
turns to the left and runs along the pylorus (in the 
omentum), to anastomose with the left gastroepi- 
ploic branch of the splenic near the proximal end 
of the pylorus. The usual twigs are given off to 

Hiatus aorticiis 
A. hepatica 
Gl. sttprarenales 


\ phrenica '\nt 

A,o?t I ihdominalis 
\ plirenita p(t. 
\ dastrua sin. 

Vena cava post 
V. phrenica access. ^ 
A. phrenica post. 

\AVrenaIis dext, 

"^alyx ren. maj 
Ren dext. 

Rennilu.< ^ 

Hilus _m<M 

Cortex ^^^5^ 
Medulla ^""^^S 


Pelris renalia 
Tunica fibrosa 
Calyces ren. min 

M.quad. lum^'^'M 
V. lumbalis con ^^ 

Ri (K'sopliajjei 

ii,..^. lienalis 

.\. eoeliaca 

Tendo diaphr. 

M. psoas maj- 

A. mesenterica 

M. iliacus 

A. & V. lumbalis 

rA.&V. spormatica 




intern us 

( 'refer 

M. psoas mm 

A.&V.circ. ilium pr fV 
R. iliacus lat ^ 
R. m. sartonui. 
R. lumbalis 

A. hypogast. panetalis 

V. hypogastrica 
A. & V. iliolumbalis'^ 
A. sacral is lateralis 
A. & V. femoris 
A. & V. Klutea ant. 
A. & V. haemorrhoid. med 
A. & v. circ. ilium superf. 
A. & \'. profunda femoris 

I'reler (cut)- 

M. cremast. 
Tunica raffinalis com. 
Tun. rag. prop., lamina parietalis 
Ductus deferens {cut 
Caput epididymis 
Tun. rag. prop., lamina rviceralis 
Corpus epididymis 
Fascia cremasteric a 
Septtda testis 
Cauda epididifmis 

Fascia m. red. abdom 

.\. & V. iliaca externa 

A. hypogast. vi.sceralis 
Peritonaeum {cut) 
Textus adiposus 
Ductus deferens 

A. umbilicalis 

Funiculus spermaticus 

A. & y. sacralis media 
A. pudenda int. 
A. & V. epigastrica post. 

R. pubicus 
-Tr. pudcndo-epigast. (cut) 

A. & V. haemorrhoid. ant. 

.\. & V. epigastrica superf. 
A. & \'. spermatica ext. 
M. rectus abdominis (cut) 

Cutis (cui_ 


Fig. 135. Vessels and nerves of the abdomen of Ailuropoda 


Tunica vaginalis com. 

Gubernaculum testis 
R. anast. a. pudenda ext. 

Corpus penis 
Clans penis 
Orificuim urethrae ext. 



the pylorus and omentum. A, pancreaticoduo- 
denalis anterior runs through the substance of 

the head of the pancreas, giving off twigs to the 
pancreas and duodenum, and anastomosing with 
the posterior pancreaticoduodenal artery near the 
caudal end of the duodenum. 

The smaller branch of the gastroduodenal artery, 
A. gastrica dextra, is more important as a blood 
supply to the corpus of the pancreas than to the 
stomach. A branch (the right gastric proper) runs 
through the lesser omentum, giving off twigs to the 
pylorus and eventually anastomosing with the left 
gastric in the lesser curvature of the stomach. 

2. A. lienalis is the largest branch of the celiac 
artery. After giving off the hepatic artery, the 
celiac continues for 3 or 4 mm. and then divides 
to form the splenic and left gastric arteries. A. lien- 
alis follows the curvature of the gastrolienal liga- 
ment. Two pancreatic branches arise from the 
proximal end of the artery and supply the cauda 
and coi-pus of the pancreas, also giving off epiploic 
twigs to the omentum. Large splenic branches, 
which become progressively smaller and shorter 
toward the posterior end of the spleen, are given 
off from the main trunk of the artery at more or 
less regular intervals. In the region of the fundus 
of the stomach each splenic branch divides into at 
least two twigs near its terminus, one of which goes 
to the spleen while the other (the vasa brevia of 
human anatomy) passes in the omentum to the 
wall of the stomach. Near the posterior end of the 
spleen the gastric and splenic twigs are independ- 
ent, coming off from opposite sides of the main 
trunk. The main trunk is continued as the A. gas- 
troepiploica sinistra, which lams in the omentum 
along the pylorus to anastomose with the right 
gastroepiploic artery. 

3. A. gastrica sinistra is the smallest branch 
of the celiac artery. It follows the lesser curvature 
of the stomach, giving off numerous twigs to the 
cardia. A separate anastomotic branch arises high 
on the cardia and runs through the lesser omentimi 
to join the right gastric which runs along the py- 
lorus from the opposite direction. At its base the 
left gastric gives rise to two small branches, the 
Rr. oesophagi. The more medial of these runs 
craniad just to the left of the midline, dividing into 
right and left branches at the level of the eso- 
phageal opening in the diaphragm. The other 
ramus runs craniad, supplying the posterior end 
of the esophagus. 

Anterior Mesenteric Artery 

A. mesenterica anterior arises from the ven- 
tral wall of the aorta about 15 mm. caudad of the 
celiac artery (fig. 135). It slightly exceeds the 

celiac in size. It runs through the mesentery in a 
short, sharp arc, giving off the following branches: 
(1) the posterior pancreaticoduodenal; (2) the intes- 
tinal arteries; and (3) the ileocolic trunk (fig. 113). 

1. A. pancreaticoduodenalis posterior arises 
from the anterior wall of the anterior mesenteric 
about 25 mm. beyond the origin of the latter from 
the aorta, i.e., as the anterior mesenteric passes the 
edge of the pancreas. Running into the head of 
the pancreas, it supplies that region and the poste- 
rior end of the duodenum, anastomosing with the 
anterior pancreaticoduodenal within the substance 
of the pancreas. 

2. Aa. intestinales arise from the convex side 
of the arch of the anterior mesenteric and radiate 
into the mesentery in the usual way. Nine main 
branches come off from the arch, and each of these 
bifurcates a few millimeters beyond its origin. The 
primary loops so formed are further subdivided 
down to quinary divisions. Near the intestinal 
border of the mesentery the usual inosculations 
join the separate branches to one another. The 
termination of the arch of the anterior mesenteric 
forms a strong anastomosis with a branch of the 
ileocolic artery. Twigs from the main branches 
before their bifurcation supply the large lymph 
gland (pancreas of Asellus) which lies dorsad of 
the arch of the anterior mesenteric. 

3. The Truncus ileocolicus is the first artery 
that arises from the anterior mesenteric; it comes 
off several millimeters before the posterior pancre- 
aticoduodenal, and from the opposite side of the 
mesenteric artery. The Aa. ileocolicae and col- 
icae take origin from this trunk. Two ileocolic 
arteries arise from the ileocolic trunk, and the 
trunk itself is continued as a third. The latter, 
which is the largest ileocolic branch, anastomoses 
with the termination of the anterior mesenteric 

The anterior and middle colic arteries arise from 
the ileocolic trunk near its origin from the mesen- 
teric artery. A. colica anterior [BNA: colica 
dextra] comes off first, followed a millimeter or 
two farther distad by the A. colica media. The 
anterior colic divides into anterior and posterior 
branches near the intestinal wall. The anterior 
branch supplies the proximal end of the colon by 
means of numerous short intestinal twigs and con- 
tinues craniad to anastomose with the first branch 
of the ileocolic artery; the posterior branch like- 
wise gives off intestinal twigs and continues caudad 
to anastomose with the anterior branch of the mid- 
dle colic. The middle colic divides into anterior 
and posterior branches, each of which sends nu- 
merous short branches to the colon. The anterior 
branch, as noted above, anastomoses with the an- 



terior colic; the posterior branch runs caudad and 
anastomoses with the posterior coHc. 

Renal Arteries 

Aa. renales (fig. 135) arise symmetrically from 
the lateral walls of the aorta, 20 mm. caudad of the 
anterior mesenteric, i.e., at the level of the first 
lumbar vertebra. Each passes almost straight lat- 
erad across the crus of the diaphragm to the hilus 
of the kidney. In the hilus it breaks up into three 
branches, which in turn ramify to the individual 
lobules. The renal artery gives off the following 
branches in addition to the main trunk supplying 
the kidney: 

1. A. lumboabdominalis is a large vessel aris- 
ing from the anterior wall of the renal immediately 
beyond the origin of the latter from the aorta. The 
right lumboabdominal passes dorsad of the corre- 
sponding vein, whereas the left passes ventrad. 
On the left side the A. suprarenalis posterior 
arises as the vessel passes the suprarenal body, and 
runs forward to the posterior end of that organ ; on 
the right side the lumboabdominal gives rise to the 
right posterior phrenic, and the right posterior 
suprarenal comes from this. The lumboabdom- 
inal runs diagonally backward and outward along 
the dorsal body wall. 

2. A. suprarenalis anterior arises on the left 
side of the body from the anterior wall of the renal 
beyond the origin of the lumboabdominal. On the 
right side it is a short lateral branch from the ac- 
cessory phrenic as the latter vessel passes the supra- 
renal body. 

3. A. phrenica accessoria. An accessory 
phrenic branch arises from the anterior wall of the 
right renal artery slightly laterad of the middle of 
the renal. It passes forward and outward, ventrad 
of the suprarenal body, across the crus of the dia- 
phragm, supplying the dorsal part of the right half 
of the diaphragm. A similar, but much smaller 
vessel arising from the left renal does not reach the 
diaphragm, but loses itself in the fat surrounding 
the kidney. 

Internal Spermatic Arteries 

Aa. spermatica internae (fig. 135) arise from 
the lateral wall of the aorta 20 mm. caudad of the 
renal artery. The two arteries are given off sym- 
metrically. Each passes diagonally backward and 
outward to the abdominal inguinal ring, where it 
is joined by the ductus deferens. At about one- 
third the distance between its origin and the in- 
guinal ring each spermatic gives rise to a lateral 
branch that passes to a prominent mass of post- 
renal fat. Beyond this point the spermatic artery 
breaks up to form a rete mirabile, which is main- 
tained distad into the epididymus. 

Posterior Mesenteric Artery 

A. mesenterica posterior (figs. 113, 135) arises 
from the ventral wall of the aorta at the level of 
the third lumbar vertebra, 40 mm. behind the ori- 
gin of the internal spermatics and 45 mm. in front 
of the posterior end of the aorta. The vessel passes 
caudad and toward the colon within the mesocolon. 
Near the colon it gives rise to the small A. colica 
posterior, which passes craniad, giving off numer- 
ous twigs to the posterior part of the colon, to 
anastomose with the middle colic. The main part 
of the posterior mesenteric is continued caudad as 
A. haemorrhoidalis anterior, which ramifies 
over the anterior part of the rectum, anastomos- 
ing posteriorly with the middle hemorrhoidal. 

Terminal Branches of the Aorta 

The aorta terminates abruptly at the level of the 
posterior border of the fourth lumbar vertebra by 
breaking up to form two paired vessels and one 
unpaired vessel. The first and largest of the paired 
vessels are the external iliacs. The much smaller 
hypogastrics diverge symmetrically from the mid- 
line immediately behind the external iliacs. Thus 
the continuation of the aorta as a common trunk 
before the hypogastrics are given off (the so-called 
hypogastric trunk) is scarcely represented in Ailu- 
ropoda. Dorsad of the origin of the hypogastrics 
the much reduced aorta is continued into the tail 
as the middle sacral artery. 

Hypogastric Artery and Its Branches 

Aa. hypogastricae arise from the bifurcation 
of the external iliacs with scarcely an indication of 
a hypogastric trunk (fig. 136). Each divides al- 
most immediately to form a parietal and a visceral 
ramus, and these pass caudad, the parietal ramus ly- 
ing above and a little to the outside of the visceral. 

The parietal branch divides at the level of the 
second sacral foramen into the anterior gluteal ar- 
tery and the very slender lateral sacral. 

1. A. glutaea anterior (figs. 136, 138) emerges 
from the pelvis at the anterior border of M. piri- 
formis (i.e., at the extreme anterior end of the gi-eat 
sciatic foramen), accompanied by the anterior glu- 
teal nerve. It then breaks up into several terminal 
branches, which ramify to the gluteal muscles and 
the piriformis. A branch descends toward the tro- 
chanteric rete, sending an anastomotic twig to the 
posterior gluteal artery and participating in the for- 
mation of the rete. 

2. A. caudae sacralis lateralis passes into the 
tail, where it lies in the groove between the dorsal 
and ventral sacro-coccygeal muscles. 

The visceral branch of the hypogastric gives rise 
to the following vessels: 



A. fern 
A. epigasthca post. 
R. deferentialis, 
A. sacralisjat 
A. spcnnatica externa 
Ir.ctsura ischiadica major 

Spina ischiadica 
Incisura iachiadica minor 

Lig. ingiiinalis (cut) 
A. glutea ant. 
A. prof. fem. 

Ductus deferens 

A. sacralis media 

A. iliaca ext- (cut) 
Aa. lumbales 

.A. spermatica int 


Vesica urinaria 
Urachus ' lig. umb. med.) 
A. haemorrhoid. med. 
A. vesica post. 

Fig. 136. Terminal branches of the abdominal aorta in Ailuropoda. 

1. A. umbilicalis (fig. 136) is given off from 
its lateral wall 20 mm. beyond the origin of the 
artery itself, and passes back to the bladder. As 
it nears the bladder the vessel gives off A. vesi- 
calis anterior, which ramifies over the anterior 
part of the bladder. The umbilical artery then 
ceases to be pervious, and passes around onto the 
ventral side of the bladder, from where it continues 
craniad in the lateral lunbilical fold as the lateral 
umbilical ligament. 

2. A. vesicalis posterior (fig. 136) arises from 
a tnmk common to it and the middle hemor- 
rhoidal. It passes onto the posterior part of the 
dorsum of the bladder, where it ramifies. A fine 
twig runs caudad on the ureter, and a posterior 
twig anastomoses with a twig from the middle 

3. A. haemorrhoidalis media (figs. 135, 136) 
passes caudad and ventrad to the middle part of 
the rectum, over which it ramifies. Branches go 
to the urethra, to the ampulla of the ductus def- 
erens, and to the muscles surrounding the rectum. 
Anteriorly it anastomoses with the anterior hemor- 
rhoidal, and posteriorly with the posterior hem- 
orrhoidal arteries. 

4. A. glutaea posterior (fig. 138) is of the same 
caliber as the internal pudendal, so that the tnmk 
appears to bifurcate to form these two terminal 
vessels. The posterior gluteal emerges from the 
pelvis just behind the sciatic nerve, at the poste- 
rior border of M. piriformis, and immediately 
breaks up into terminal branches. These supply 
the posterior part of the gluteus superficialis, the 
obturator internus, and the gemelli, and partici- 
pate in the formation of the trochanteric rete. The 
branch ninning to the rete anastomoses with the 
circumflexa femoris medialis. A posterior branch 
anastomoses with a terminal branch of the pro- 
funda at the ischial tuberosity. A. comitans n. 
ischiadici is absent. 

5. A. pudenda interna is the second of the 
terminal vessels of the visceral division of the hj^po- 
gastric. It nms caudad beside the rectiun, divid- 
ing near the posterior border of the ischium into 
the artery of the penis and a trunk for the posterior 
hemorrhoidal and perineal arteries, (a) A. peri- 
naei bifurcates at its origin. One branch descends 
vertically, external to M. levator ani and in front of 
M. sphincter ani externus, to the base of the penis. 



giving twigs to the ventral part of the anus and 
to Mm. ischiocavernosus, bulbocavernosus, and 
levator penis. The other branch runs caudad, sup- 
plying the skin around the dorsal and lateral parts 
of the anus, (b) A. haemorrhoidalis posterior 
runs to the anal region, where it ramifies richly in 
the skin surrounding the anus. A single twig goes 
to the terminal part of the rectum, (c) A. penis 
arises from the ventral wall of the internal puden- 
dal 20 mm. before its termination. It descends 
vertically to the base of the penis, where it breaks 
up to form three vessels: the artery of the bulb, 
and the deep and dorsal arteries of the penis. A. 
bulbi urethrae is a slender branch that runs cra- 
niad to ramify over the bulbus urethrae, anasto- 
mosing anteriorly with a twig from the middle 
hemorrhoidal. A. profunda penis is a short 
branch that enters the crus penis. A. dorsalis 
penis passes onto the dorsum of the penis, first 
giving off a delicate twig to the bulbus urethrae; 
the main trunk runs along the penis to the glans, 
where it anastomoses with twigs from the external 
pudendal and with its mate from the opposite side. 

External Iliac Artery and Its Branches 

A. iliaca externa (fig. 135) passes diagonally 
caudad from the aorta across the ventral surface 
of M. psoas minor, to the femoral ring. Passing 
through the ring onto the medial surface of the 
thigh, it lies in the femoral triangle and takes the 
name of femoral artery. The external iliac artery 
lies ventrad of the corresponding vein, and has a 
length of 100 mm. It gives rise to the following 
branches: (1) the deep circumflex iliac, (2) the ilio- 
lumbar, and (3) the deep femoral. 

1. A. circumflexa ilium profunda (fig. 135) 
arises asymmetrically on the two sides of the body. 
On the left side it comes off at the very base of the 
external iliac, while on the right it arises from 
the external iliac 20 mm. beyond the origin of the 
latter. The vessel passes deep to the common iliac 
vein, running laterad and slightly caudad across 
the dorsal body wall. Twigs from its posterior 
wall pass into the iliacus and psoas, supplying 
these muscles and anastomosing with a branch 
from the iliolumbalis within the muscle tissue. 
Just before reaching the iliac crest it gives off a 
branch that pierces the body wall to supply the 
proximal end of M. sartorius. At the level of the 
iliac crest the main vessel pierces M. transversus, 
bifurcating immediately to form anterior and pos- 
terior branches that ramify between this muscle 
and M. obliquus internus. The anterior branch 
anastomoses with a muscular branch of the lum- 
bar arteries; the posterior branch anastomoses with 
the superficial circumflex iliac. 

2. A. iliolumbalis (fig. 135) arises from the 
dorsomedial wall just proximad of the deep fe- 
moral. It passes dorsad around the external iliac 
vein and the tendon of the psoas minor, giving off 
the following branches: (1) A twig arises from its 
posterior wall 10 mm. beyond its origin and runs 
back into the pelvic cavity, where it anastomoses 
with the obturator twig of the profunda femoris. 
(2) R. lumbalis is a small twig given off from the 
opposite side and just distad of the preceding. It 
breaks up in the psoas minor. The main vessel 
continues as the (3) R. iliacus, which passes lat- 
erad across iliopsoas muscles. It gives off several 
nutrient branches to the body of the ilium and 
muscular twigs to the iliopsoas muscles. About 
midway across the psoas major the vessel breaks 
up to form terminal branches. In addition to mus- 
cular branches that supply the gluteus medius 
and minimus, anastomotic branches run forward 
to the deep circumflex iliac and the last lumbar. 

3. A. profunda femoris' (figs. 135-137) arises 
from the medial wall 40 mm. before the external 
iliac reaches the femoral ring. It diverges from 
the external iliac, running almost parallel with the 
longitudinal axis of the body. It passes through 
the femoral ring onto the medial side of the thigh, 
where it lies beneath M. pectineus and in contact 
with the ventral surface of the ilium just caudad of 
the iliopectineal eminence. Continuing caudad 
beneath M. adductor femoris and adductor longus, 
i.e., across the juncture between the ilium and 
pubis and across the articular capsule of the hip 
joint, it reaches the posterior side of the thigh. 
Here, between the adductor femoris and the quad- 
ratus femoris, it breaks up to supply the posterior 
thigh musculature. 

The deep femoral artery gives rise to the follow- 
ing branches: 

(a) Truncus pudendo-epigastricus (fig. 135) 
arises from the ventral wall of the deep femoral at 
the internal inguinal ring. It divides 10 mm. be- 
yond its origin into the posterior epigastric and 
external spermatic arteries. A. epigastrica pos- 
terior is the larger of the two branches and runs 
craniad. It gives off' a fine twig that supplies the 
extreme posterior end of M. rectus abdominis, then 
continues through the suspensory ligament of the 
bladder to the neck of the bladder. The main 
trunk of the posterior epigastric gives off a branch 
to the rectus abdominis, then enters the space be- 

' The origin of the deep femoral has migrated up inside 
the inguinal ligament in carnivores, so that in these animals 
it corresponds to A. obturatoria+A. profunda femoris 
of human anatomy. The origin of A. circumflexa femoris 
lateralis has been transferred from the deep femoral (as 
it is in man) to the femoral. The deep femoral is absent in 
Procyon loior and some bears (Zuckerkandl, 1907). 



tween M. transversus and M. obliquus internus, 
sending off a fine anastomotic branch to the super- 
ficial epigast!-ic; branches ramify over both these 
muscles and to the rectus. The anterior ends of the 
vessel anastomose with the superficial and anterior 
epigastrics. A. spermatica externa runs along 
the medial border of the spermatic cord to the 
testis, where it divides. The smaller of the two 
resulting branches sends twigs into the tissues sur- 
rounding the testis and into the skin of the scrotal 
region, in addition to a twig that enters the prepuce, 
where it anastomoses with the external pudendal. 
The other branch of the external spermatic repre- 
sents A. epigastrica superficialis. It divides in 
the subcutanea of the inguinal region, the smaller 
branch running distad on the medial surface of the 
thigh, while the other runs craniad in the subcuta- 
neous fat over the rectus abdominis, to anastomose 
with a branch of the posterior epigastric. 

(b) R. nutritius is a slender branch arising 
from its anterior wall just outside the abdominal 
wall. It passes to the region of the ilium just 
craniad of the acetabulum. 

(c) Rr. musculares pass to the posterior thigh 
muscles. The first of two large muscular rami aris- 
ing from the posterior wall of the profunda near its 
proximal end sends a twig through the obturator 
foramen. This twig, which apparently represents 
the obturator artery of human anatomy, gives off 
pubic, anterior, posterior, and acetabular branches. 

(d) A. circumflexa femoris medialis is repre- 
sented by two branches. A slender branch arising 
from the medial wall of the profunda at the level 
of the first muscular ramus apparently represents 
R. superficialis; it supplies the pectineus and ad- 
ductor brevis and sends a fine twig to the gracilis. 
R. profunda arises from the anterior wall of the 
profunda near the posterior border of the pec- 
tineus, passes between the adductor magnus and 
the obturator externus, and divides into ascending 
and descending branches on the external surface 
of the thigh. The ascending branch participates 
in the trochanteric rete and anastomoses with the 
posterior gluteal; the descending branch passes 
down along the posterior border of the vastus lat- 
eralis, anastomosing with the ascending perforat- 
ing branch of the femoral. 

(e) One of the terminal branches of the pro- 
funda passes ectad between the quadratus femoris 
and semimembranosus and divides into ascend- 
ing and descending rami on the external surface 
of the thigh. The ascending branch breaks up at 
the ischial tuberosity to form muscular twigs and 
an anastomotic twig that joins the posterior glu- 
teal; the descending branch runs distad behind the 

sciatic nerve, giving off twigs to the posterior thigh 

(f) A. pudenda externa (fig. 137) is a slender 
twig from the medial terminal branch of the pro- 
funda. It runs mesad to the posterior border of 
the ascending ramus of the pubis, along which it 
descends to the penis. Entering the ventral wall 
of the prepuce, it ramifies in the prepuce, anasto- 
mosing with its mate from the opposite side and 
with the pudendal branch of the external spermatic. 

Femoral Artery 

A. femoralis (figs. 136, 137) is the continuation 
of the external iliac beyond the femoral ring. It lies 
anterior to the femoral vein, passing first through 
the femoral triangle, then deep to the adductor fe- 
moris and semimembranosus. Finally it emerges 
into the popliteal space through the interval be- 
tween the anterior and posterior parts of the ad- 
ductor longus and magnus (there is no tendinous 
opening), where it becomes the popliteal artery. 
It gives rise to the following branches. 

(1) A. circumfiexa ilium superficialis (fig. 137) 
arises from the posterior wall of the femoral just 
beyond the inguinal ligament. It passes back 
through the femoral ring, then runs craniad on 
the internal abdominal wall, to anastomose with 
a descending branch of the deep circumflex iliac. 
Rr. inguinales arise from the superficial circum- 
flex iliac near its base. They run back toward the 
inguinal ring, to ramify in the transverse and in- 
ternal oblique muscles in the inguinal region. The 
most anterior twig anastomoses with a descending 
twig of the anterior epigastric. 

(2) A. circumflexa femoris lateralis' (fig. 137) 
is by far the largest branch of the femoral. It is a 
short trunk arising from the anterior wall of the 
femoral 25 mm. beyond the inguinal ligament. 
The trunk runs toward the anterior side of the 
thigh, bifurcating 10 mm. beyond its origin to form 
two branches of approximately equal size. R. an- 
terior promptly bifurcates again. One resulting 
branch runs craniad and distad beneath the sar- 
torius and tensor fasciae latae, passing between the 
branches of the femoral nerve, and giving off twigs 
to both these muscles. The other branch runs dis- 
tad in the rectus femoris almost to the knee, giv- 
ing off numerous twigs to that muscle and a twig 
to the tensor fasciae latae. R. posterior also bi- 
furcates immediately. One bi'anch passes ectad 
between the rectus femoris and the vastus medialis 
to the external surface of the thigh, where it gives 
off twigs to the gluteal muscles and sends a de- 
scending twig down along the boundary between 

> See note, p. 267. 

R. ciro. ilium priif. 

M. obliquus iiil. 

M. teiixur fasriae liifae 

X. fi'mi>ralis. 

R. cutaneus latonilis 
R. asc'.. a. circ. fern. lat. 
A. I'irc. fern, lat. 

R. desc. a. circ. fern, lat 
A. perforana fr. prof.fom. 

A. feinoral 

M.traHSversalis abd. 

M. iliopsoas 

Rr. inKuinalfS 

M. ms7((.v Idteralii 

A. circ. ilium .sup. 
.M. pectineus 

A. profunda fcmoris 
Ox pubU 

miYH -W. aiMiirlor 

X. obturatorius 

M. luhluctor 

^^^^^_.V/. pectineus 



M. mlthietor 

M. rertuH frmnri^. - . 

A. genu supr 
R. muscularii 

R. articular 

\. pudenda e.\t. 
.V. (inadratus Jtmoritt 

R. tuber, isch. 
M. scininienihratioKiis 

A. genu sup. 

, A. saphena, r. dorsalis 
_A. saphena, r. plantaris 

Rr. cutanei cruris medialis 
N. cutaneus 

Fig. 137. Vessels and nerves of thigh of Ailuropoda, medial view. 




the rectus femoris and the vastus laterahs that 
supplies these muscles; the twig to the vastus lat- 
eralis anastomoses with an ascending twig of the 
superior lateral genicular. The other branch of 
the posterior- ramus runs toward the knee between 
the rectus femoris and the vastus lateralis, supply- 
ing twigs to these muscles and to the vastus inter- 

(3) Rr. musculares arise from both sides of the 
femoral in its course along the thigh. These supply 
the sartorius, the gracilis, the rectus, the pectineus, 
the vastus medialis, the vastus intermedius, and 
the adductors. A posterior branch arising at about 
the middle of the thigh and an anterior branch aris- 
ing a few millimeters farther distad are much larger 
and more elaborate than the others. The anterior 
branch sends a twig to the arterial rete at the knee. 

(4) A. genu suprema (fig. 137) arises from the 
posteromedial wall of the femoral just before the 
latter passes beneath the adductor femoris. It 
breaks up after a few millimeters to form the usual 
terminal branches, (a) R. articularis is the small- 
est branch. It passes to the articular rete at the 
knee, (b) A. saphena accompanies the saphenous 
nerve distad. At the level of the medial epicon- 
dyle of the femur it divides to form dorsal and 
plantar branches. The larger dorsal branch ac- 
companies the saphenous nerve to the dorsum of 
the foot, where it anastomoses with the superficial 
branch of the anterior tibial artery to form the 
delicate superficial dorsal arch. From this, the 
Arcus dorsalis superficialis, four fine superficial 
dorsal metatarsal arteries radiate. These anasto- 
mose with the corresponding deep dorsal meta- 
tarsal arteries at the metatarso-phalangeal ai'ticu- 
lations, to form the common digital arteries. The 
plantar branch passes down the back of the leg in 
the fascia; below the ventral border of the semi- 
membranosus it lies in the groove for the tibial 
nerve. At the bifurcation of the tibial nerve, at 
the distal quarter of the leg, it anastomoses with 
the superficial branch of the posterior tibial artery. 
Both the dorsal and plantar branches give off nu- 
merous muscular rami to the muscles along their 
courses, (c) R. muscularis is the largest branch 
of the genu suprema. It passes caudad across the 
adductor longus, to supply the posterior thigh 

(5) A. perforans is a small vessel arising from 
the femoral just before it reaches the popliteal 
space. It passes back through M. adductor mag- 
nus, along the posterior border of M. vastus later- 
alis and beneath M. biceps, to the region of the 
great trochanter. Here it anastomoses with the 
descending twig of the deep branch of the circum- 
flexa femoris medialis, and participates in the tro- 
chanteric rete. 

(6) A. poplitea (fig. 138) is the continuation of 
the femoral artery in the popliteal space. It is a 
very short trunk, dividing near the upper border 
of the femoral condyles, some distance above the 
popliteal muscle, into the anterior and posterior 
tibial arteries.' The only branch arising from the 
popliteal is a muscular ramus to the biceps femoris 
and tenuissimus. 

Anterior Tibial Artery 

A. tibialis anterior (figs. 138, 139) is much the 
larger of the two tibial arteries. It passes deep to 
the popliteal muscle, then between the tibia and 
fibula at the extreme proximal end of the interos- 
seous space, and runs distad on the anterolateral 
aspect of the leg, lying between the anterior mus- 
cles, as far as the ankle. Beyond the tibio-tarsal 
articulation it continues as the dorsalis pedis artery. 

The anterior tibial gives rise to the following 

(1) A. genu superior lateralis (fig. 138), the 
larger of the two superior genicular branches, arises 
from the anterior tibial at its base. It passes lat- 
erad above the lateral condyle of the femur. An 
ascending branch enters the vastus latei'alis, within 
which it anastomoses with a descending branch of 
the lateral circumfiex. A descending branch en- 
ters into the deep articular rete. 

(2) A very large muscular branch to the biceps 
and tenuissimus comes off behind and slightly be- 
low the superior lateral genicular. A subfascial 
twig descends across the biceps, to anastomose with 
the sural artery at the lower border of the biceps. 

(3) A. genu inferior lateralis (fig. 138) arises 
13 mm. beyond the origin of the superior lateral 
genicular. It runs laterad across the lateral con- 
dyle of the femur and the tendon of the lateral 
head of the gastrocnemius. Only one of the four 
main branches into which the vessel breaks up 
passes beneath the fibular collateral ligament; the 
other three pass superficial to it. Twigs from the 
vessel participate in the deep articular rete, and a 
descending twig runs down beneath the peroneus 
longus, to anastomose with the tibial recurrent 

(4) A. recurrens tibialis is represented by two 
small branches arising from the anterior tibial im- 
mediately after it has passed through the interos- 
seous space. They run back toward the knee, lying 

' The term "popliteal" for the distal end of the femoral 
artery is retained here only for convenience. Because of its 
division into the tibial arteries in the proximal part of the 
popliteal space, the popliteal artery gives rise to none of 
the branches that characterize this artery in man. Many 
anatomists have attempted to circumvent this difficulty by 
calling the proximal ends of the anterior and posterior tibials 
the "deep" and "superficial" popliteals. 

Fa>via lumhiidorsalis isufH'Tf.)_ 

Fascia titmlnxlursalis ifirof.). 

A. & N'. glutaeus ant. 

A/. giulaei4s Kuperf. icut) 

M. piriformis icul 

Ftiscia glulaea 

Spina iliaea aul. sup. 

M. glutaam nifditts inU) 

M. tensor Jascuxe lata* [cut) 
M. glulaeus sitperf. {aU^ 

A. & N.gluUeus post. 

N. to m. quadralus 

N. cutaneus femuris [xist. 
-W. gritirllt 
M. oUunilor til 

Br. of A. circ. fern, lat.? 

^f. gliitaeus sufterf. tcul) 
.\t. qiuitiratus femoris 

A. perf(rana ascendens (A. femoralis) 

N. tibialis 
\. peroneus communis 

,A. poplitea 

A prof. fern. .r. ttTtniMal; 

genu superior lat. 

A. genu inf. lat. 

M. biceps fe maris (eul) 

Rr. n. cutaneus 
surae lateralis) 

N. articularis 

M. gai^lrocnemiuj! 

i caput lateralt) 

.V. tenuissimn.'? tcul) 

Fig. 138. Vessels and nerves of thigh of Ailuropoda. lateral view. 




close to the bone beneath the leg muscles, and sup- 
ply structures in that region. Nutrient twigs to 
the proximal ends of the tibia and fibula are in- 

(5) A. peronaea (fig. 139) is a slender branch, 
no larger than the several muscle branches with 
which it is associated, that arises from the anterior 
tibial at its proximal third. It passes immediately 
into M. peroneus brevis, running in the substance 
of this muscle down to the distal third of the leg, 
and winding around with the muscle to the poste- 
rior side of the fibula. Here it joins the perforating 
branch (8) of the anterior tibial, and the trunk so 
formed runs distally between the flexor hallucis 
longus and the peroneus brevis, receiving the sural 
artery at the tip of the calcaneum, to form the 
external end of the deep plantar arch. 

(6) Rr. musculares arise from both sides of the 
anterior tibial as it passes toward the foot, and 
supply the surrounding musculatui-e. 

(7) A. tibialis anterior superficialis (A. n. 
peronei superficialis, Zuckerkandl) (fig. 139) is an 
extremely slender vessel arising at about the junc- 
tion of the middle and lower thirds of the leg. It 
joins the superficial peroneal nerve and runs with 
it between the peroneus longus and extensor digi- 
torum longus onto the dorsum of the foot. Here 
it anastomoses with the dorsal branch of the saphe- 
nous artery to form the superficial dorsal arch. 

(8) R. perforans (fig. 139) is a stout branch 
coming from the posterior wall of the anterior tib- 
ial just above the tibiofibular syndesmosis. It 
winds around the extensor hallucis longus, per- 
forates the distal end of the interosseous mem- 
brane, and is joined by the peroneal artery. The 
resulting trunk anastomoses with the suralis at 
the tip of the calcaneum. The perforating ramus 
represents the perforating section of the primitive 
interosseous artery. 

Just before entering the interosseous membrane 
the perforating branch gives rise to a short trunk 
that divides to form the medial and lateral ante- 
rior malleolar arteries. A. malleolaris anterior 
medialis (fig. 139) is the larger of the two malleo- 
lar arteries. It runs across the medial malleolus, 
giving off a nutrient twig to the tibia, to the medial 
malleolar rete. The rete is formed by a twig from 
the deep plantar branch of the posterior tibial and 
twigs from the medial tarsal artery, in addition to 
the malleolar branch. A. malleolaris anterior 
lateralis (fig. 139) runs around the lateral malleo- 
lus to the lateral malleolar rete. This rete is formed 
by interanastomosis between this vessel and twigs 
from the lateral tarsal artery. 

Immediately after passing through the interos- 
seous membrane, the perforating branch gives off 
a nutrient twig to the distal end of the fibula. One 
of the terminal twigs of the perforating branch 
forms the lateral end of the superficial plantar arch 
by anastomosing with the terminus of the super- 
ficial branch of the posterior tibial. 

Dorsal Artery of the Foot 

A. dorsalis pedis (fig. 139) is the direct continu- 
ation of the anterior tibial. It divides at the sec- 
ond interosseous space into a branch forming the 
deep dorsal arch and a much larger perforating 
branch that joins the lateral tarsal artery to form 
the deep plantar arch. The dorsalis pedis gives 
rise to the following branches: 

(1) A. tarsea medialis (fig. 139), the larger of 
the two tarsal branches, arises at the same level as 
the lateral tarsal, at the tibio-tarsal articulation. 
It ramifies over the medial side of the tarsus, par- 
ticipates in the medial malleolar rete, and sends a 
twig around onto the sole to anastomose with a 
twig from the first deep plantar metatarsal artery. 
The main trunk of the artery runs around the me- 
dial border of the tarsus, to anastomose with the 
deep branch of the posterior tibial artery. 

(2) A. tarsea lateralis (fig. 139) runs across the 
tarsus to its lateral side, where it ramifies. It par- 
ticipates in the lateral malleolar rete and the dorsal 
pedal rete, anastomoses with a descending branch 
of the sural artery, with the arcuate artery to form 
the deep dorsal arch, and forms the lateral end of 
the plantar arch. A twig arising from the lateral 
tarsal near its base runs into the tarsus between 
the astragalus and the calcaneum, ramifying as a 
nutrient artery of the tarsus. 

(3) A. metatarsea dorsalis 1 arises from the 
dorsalis pedis just proximad of the tarso-metatar- 
sal articulation. At the base of the first meta- 
tarsal it breaks up into a perforating branch that 
passes through the first intermetatarsal space to 
join the first deep plantar metatarsal artery; a 
branch that supplies adjacent sides of the first and 
second digits; and a branch that supplies the out- 
side of the first digit with one twig, and sends 
another around the first metatarsal to the deep 
plantar arch, and gives off an anastomotic twig to 
the medial tarsal artery. 

(4) A. arcuata (fig. 139) is the dorsal terminal 
branch of the dorsalis pedis. It arches laterad from 
the second interosseous space, forming the deep 
dorsal arch by anastomosing with a descending 
branch from the lateral tarsal artery. Aa. meta- 
tarseae dorsales profundae 2-5 are radiated 
from this arch. Each receives its corresponding 
superficial dorsal metatarsal near the middle of 

M. rectus femoris 
M. vafitus taterali 

.U. vastus mediatis 

Lig. coll. fib 

R. articularis. 

M. ext. dig. long. (cut). 

M. peromeus longus (cut) 

Aa. tibiales recurrentes 

N. peronaeus superf 

X. peronaeus prof. - _,^, 

M. peronaeus tertius 
M. solew 

R. nutritia fib. 
A. peronaea 

R. superficialis 
M. peronaeus brei'is- 

Rr. nutritia fib. 

A. sural is 

A. malleolaris ant. iat. 

Rete malleolare Iat, 

A. tarsea Iat. 
R. nutritius tarsi 

A. suralis. 

R. anast. w. r. superficialis (A. tib. ant.) 
Reto dorsale pedis. 

A. arcuata 

Aa. metatarseae plantares prof. I V 
Aa. metatarseae dorsales prof. II-V 

M. sartor itis (cut) 

M. ext. hallucis longus 
R. pcrforans 

A. malleolaris ant. med. 
Rr. nutritia tib. 

Rete malleolare med. 

A. tarsea med. 
R. anast. w. r. plant, prof., A, tib. post. 

A. dorsalis pedis 

A. metatarseae dorsales prof. I 

R. perforans 
R. plantaris prof, 
cus plantaris prof. 

Aa. metatarseae dorsales superf. 
"\^Rr. perforantes, to Aa. met. plant, sup. 

Aa. digitales propreae 
Aa. digitales communes 

Fig. 139. Arteries and nerves of lower hind leg of Ailuropoda, anterior view. 




the metatarsus, and the anterior perforating branch 
from the plantar metatarsal at the metatarso- 
phalangeal articulation. The resulting dorsal digi- 
tals divide immediately into digitales propriae. 

(5) R. plantaris profundus (fig. 139) is the 
plantar terminal branch of the dorsalis pedis. It 
perforates the second intermetatai-sal space to reach 
the planta, where it joins a branch of the lateral 
tarsal artery to form the deep plantar arch. This, 
the Arcus plantaris profundus (fig. 139), arches 
across the bases of the metatarsals, radiating the 
deep plantar metatarsal arteries. Each A. meta- 
tarsea plantaris profundus receives its corre- 
sponding superficial plantar metatarsal near the 
head of the metatarsal bone, and each resulting 
common vessel gives off an anterior perforating 
branch at the metatarso-phalangeal articulation, 
beyond which it continues distad as the plantar 
digital artery. The anterior perforating branches 
join the dorsal digital arteries at the metatarso- 
phalangeal articulations. 

Posterior Tibial Artery 

A. tibialis posterior (fig. 140), the smaller of 
the two tibial arteries, accompanies the tibial nerve 
superficial to the popliteal muscle. At the lower- 
most quarter of the leg it divides into superficial 
and deep plantar branches. The superficial plantar 
branch forms the superficial plantar arch, while 
the deep plantar branch terminates in the tarsus. 

The posterior tibial gives rise to the following 

(1) A. genu superior medialis (fig. 140) runs 
medially just above the medial head of the gastro- 
cnemius and beneath the femoral head of the semi- 
membranosus. It emerges on the medial side of 
the thigh between the femoral head of the semi- 
membranosus and the adductor longus, and anas- 
tomoses with the articular branch of the genu 
suprema and with the doi-sal branch of the saphena. 

(2) A. genu inferior medialis (fig. 140) runs 
medially beneath the medial head of the gastro- 
cnemius and between the two heads of the semi- 
membranosus. On the medial side of the knee it 
anastomoses with the superior medial genicular 
and the dorsal branch of the saphena. 

(3) A. genu media (fig. 140) arises from the 
posterior tibial beside the origin of the superior 
medial genicular. It passes directly into the knee 

(4) A. suralis (fig. 140) is the largest branch 
given off by the posterior tibial in the popliteal 
space. It runs distad over the gastrocnemius and 
plantar muscles, in which it exhausts itself. A 
slender cutaneous branch runs subfascially with 
N. cutaneus surae medialis, perforating the fascia 

at the distal border of the biceps, where it receives 
the descending branch of the large muscular ramus 
of the anterior tibial. The sural terminates by 
anastomosing with the much larger perforating 
branch of the anterior tibial at the distal end of 
the fibula. 

(5) Rr. musculares arise from the posterior 
tibial in its course along the leg, and pass to the 
muscles of this region. The largest of these are 
two vessels arising opposite one another at the 
lower border of the popliteal muscle. The medial 
of these two branches follows the lower border of 
M. popliteus, giving off twigs to that muscle, the 
flexor digitorum longus, and the posterior tibial. 
It terminates at the distal quarter of the tibia as 
a tibial nutrient branch. The lateral of the mus- 
cular branches passes into the soleus, where it 

(6) R. plantaris superficialis (fig. 140), the 
larger of the two terminal branches of the posterior 
tibial, receives the plantar branch of the saphena 
near its origin, and then continues across the sole 
with the medial plantar branch of the tibial nerve, 
to terminate as the superficial plantar ai-ch. The 
first of the superficial plantar metatarsals arising 
from this arch supplies the outer side of digit 1, 
and the remaining four anastomose with the corre- 
sponding deep plantar metatarsals at the meta- 
tarso-phalangeal joints. 

(7) R. plantaris profundus (fig. 140) gives off 
a slender anastomotic branch at the tibio-tarsal 
articulation that passes around the medial border 
of the ankle to anastomose with the descending 
branch of the medial tarsal artery. The plantaris 
profundus itself terminates as a nutrient artery of 
the ankle joint. 

Interosseous Artery 

A. interossea, the third primary branch of the 
popliteal artery, is gi'eatly modified and represented 
only in part in Ailuropoda (fig. 142). The most 
proximal part of this vessel, which typically arises 
from the popliteal and runs distally through the 
popliteal space, is missing. The middle section is 
represented by the peroneal artery, which here is 
a branch of the anterior tibial that anastomoses 
distally with the perforating branch of the ante- 
rior tibial. The perforating section of the interos- 
seous is represented by the perforating branch of 
the anterior tibial, and the distal section, which 
typically continues into the dorsal pedal artery, is 
represented by the distal part of the anterior tibial. 

Discussion of Arteries 

During ontogenetic development the anlagen of 
the systemic vessels first appear as elaborate capil- 

A/, adductor magnus 
A. poplitea 

A. genu sup<>rii)r nil. 

,, , A. genu med 

jVf. gastrocnemius caput medial, i{cul), 
A. genu inf. med 

M. semimembranosus {cut) 

N. to mm. popliteus & 
flexor digitorum longl 

M. fiei. dig. lougus. 

Arcus planLaris superf. 

M. castas taleralis 

A. genu sup lat. 

Kr. mm. biceps fem. & tenuiasimui 

N'. tibialis 
'A. genu inf. lat. 
,A. tibialis ant. 

N'. cutan. surae med. 
.V. liuralis (cut) 
,U. gaslrociiemiu.1 icapnl lalrrale) {cut) 

\t. solfits fcut) 

\. tibialis post. 

N". intensseus cruris 

M. peroiiaeus tcrtius 

V. ftejc. httllucis loiigus 
A. suralis 

Rr. nutritia tib. 
R. plantaris, A. saplicna 

R. plant, prof., A. tib. post.^^' 

R. plant, sup., A. tib. post.C]^ 

N'. plantaris med 

R. anast. w. A tarsea med. 

.U. peroiiaeus hrecis 

N". plantaris lat. 
R. nutritia fib. 
R. perforans A. tibialis ant. 
Tul)er calcaiiei 

Teiido m. peroiiaeus toiig. 
A/xmeurosis plantaris {nil) 

r^a ,M. abd. <iiji. quinti 

M . flex. dig. hrecis 

R. anast. w. A. tarsea lat. 

Fig. 140. Arteries and nerves of lower hind leg of Ailnropoda, posterior view. 




lary netwoi-ks, the patterns formed by these net- 
works becoming increasingly irregular away from 
the heart. The arteries and veins arise by enlarge- 
ment and differentiation of pathways through the 
networks i^Copenhaver, 1955). The only function 
of the vessels is to transport fluids to and from the 
tissues, and obviously this can be accomplished via 
an almost infinite variety of potential vessel pat- 
terns. Individual variations in patterns occur, but 
the choice among the multiple potential pathways 
through the primary netwoi-k is not random; the 
vessels form definite patterns that are faithfully 
replicated in individual after individual. Definite 
vessel patterns also tend strongly to be character- 
istic for taxa of mammals. Several factors are 
known to contribute to determining the particular 
pathways that are followed, but the relative roles 
of these factors are poorly understood. Experi- 
mental studies (e.g., Clark, 1918, Am. Jour. Anat., 
23, p. 37; Clark et al., 1931, Anat. Rec, 50, p. 129), 
and comparative studies of adult vessel patterns, 
both show that heredity somehow plays an impor- 
tant part, although it is not clear to what extent 
vessel patterns reflect genetic factors acting directly 
on the forming vessels (intrinsic factors) and to 
what extent genetic factors acting on surrounding 
tissues (extrinsic factors) are involved. The studies 
of Sawin and Nace (1948) and Sawin and Edmonds 
(1949) indicate that extrinsic factors (genetic fac- 
tors at second hand, so to speak) are almost wholly 
responsible. Chemical and mechanical factors as- 
sociated with blood flow also play a part after 
circulation is established (Copenhaver, 1955). 

Comparative studies show that basic patterns 
can be identified throughout the systemic circula- 
tion in the Carnivora (Davis, 1941; Story, 1951), 
and somewhat more broadly throughout the Mam- 
malia (Tandler, 1899; Zuckerkandl, 1907; Hafferl, 
1933). Variations in a particular basic pattern 
occur in several different ways: (1) the site at 
which a vessel ai'ises from a parent trunk may shift 
proximally or distally; (2) the relative calibers of 
collateral vessels or vessel systems may vary re- 
ciprocally; (3) embryonic trunks may drop out in 
whole or in part, their terminal ramifications hav- 
ing been captured by another vessel; and (4) the 
calibers of vessels vary with the physiological de- 
mands of the tissues they supply. 

Within the Carnivora, at least, the basic pat- 
terns vary in characteristic ways among the sev- 
eral families, subfamilies, and genera. Patterns 
that are "primitive" in the sense that they resem- 
ble those found in the most primitive placentals 
tend to occur in those carnivores that display gen- 
erally pi-imitive morphological features. Special- 
ized vessel patterns are found in more advanced 

carnivores. A hierarchy of patterns, increasingly 
refined from ordinal down to generic level, is evi- 
dent in all parts of the carnivore arterial system 
wherever adequate samples have been studied. 
Thus the arteries appear to supply trustworthy 
data, which may be used to support data from 
other sources, on inter-relationships among the 

On the other hand, the circulatory system is per- 
haps unique among the organ systems in being a 
passive distribution system. We can scarcely imag- 
ine vessel pattern as a factor limiting adaptive 
radiation within the Mammalia, nor can we visu- 
alize natural selection acting directly on blood 
vessels as it does on bones, muscles, nerve tissue, 
etc. Thus vessel patterns are of no help in under- 
standing the evolution of functional mechanisms. 
At best they may reflect function; they can scarcely 
direct or channel function. Within the Mammalia 
the circulatory system is useful to the comparative 
anatomist only as one of several sources of data 
from which relationships may be inferred. 

I have not tried to compare in detail all parts of 
the circulatory system of Ailuropoda with other 
carnivores. In general, only those parts for which 
comparative data already exist will be considered. 

Branches of Aortic Arch 

The manner in which the carotids and subcla- 
vians arise from the arch in mammals may be 
gi'ouped into five types (Hafferl, 1933). All terres- 
trial carnivores fall into his type II, in which both 
common carotids and the right subclavian arise 
from a common trunk, the left subclavian arising 
independently. Parsons (1902) found that two fur- 
ther subtypes of branching are represented among 
terrestrial carnivores: type A, in which the two 
carotids arise from the innominate independently, 
and type B, in which there is a short common caro- 
tid trunk after the right subclavian is given off. 
Raven (1936) added several observations to those 
tabulated by Parsons. I have added 11 observa- 
tions on arctoids, making a total of 33 individual 
arctoid carnivores for which data are available 
(Table 24). 

All of the 14 canids so far examined represent 
type A. The Procyonidae and Ursidae are more 
variable but are predominantly type B, except 
Procyon lolor, which appears to favor type A. Of 
the two specimens of Ailuropoda that have been 
checked, one represents type A and the other 
type B. 

It has been commonly assumed that the type of 
arch pattern in mammals depends on mechanical 
factors, such as are reflected in body build, rather 
than genetic factors. This opinion was confirmed 



by Sawin and Edmonds (1949), who concluded from 
extensive breeding experiments on rabbits that 
there is "little indication of dominance and segre- 
gation characteristic of mendeiian inheritance," 
and that variations in the aortic arch pattern are 
determined by hereditary differences in regional 
growth centers in which the vessels are located. 


Type A Type B 

Cants familiaris 4/4 

Canis lupus 3/3 

Cants latrans 1/1 

Lycaon pictus 2/2 

Vulpes fulva 1/1 

Vulpes vulpes 3/3 

Procyon lotor 3/4 1/4 

Nasua sp 1/3 2/3 

Polos flavus 1/1 

Ailurus fidgens 1/1 

Ailuropoda melanoleuca 1/2 1/2 

Helarctos malayanus 1/1 

Ursus americanus 3/3 

Ursus gyas 1/4 3/4 

Carotid Circulation 

The pattern of the carotid circulation in the 
Garni vora has been reviewed by Tandler (1899), 
Davis and Story (1943), and Story (1951). Tand- 
ler showed that any pattern of carotid circulation 
found among mammals can easily be derived from 
a single basic type (fig. 141, A). In this basic pat- 
tern the common carotid terminates in three main 
trunks, which apparently are always laid down 
during ontogeny: the external carotid, which pri- 
marily supplies extra-cranial structures except the 
upper jaw and primary sense organs; the internal 
carotid, which supplies the brain, eyeball, and ear; 
and the stapedial, which is the primary vessel for 
the upper jaw, the adnexa of the eye, and the nose. 
These three trunks are interconnected by anasto- 
motic vessels, through which one trunk can cap- 
ture the terminal branches of another. The proxi- 
mal part of a trunk disappears after its terminal 
part has been captured. The carotid pattern of 
any mammal can easily be derived by dropping out 
sections of this basic pattern. 

In adult Garnivora the stapedial artery has dis- 
appeared, its terminal branches having been taken 
over by the external carotid (fig. 141, B). In the 
Aeluroidea the external carotid tends to take over 
the internal carotid circulation as well; in the do- 
mestic cat the internal carotid is completely sup- 

pressed, and of the three primary trunks only the 
external carotid remains. Among the Arctoidea 
there are minor variations of the basic arctoid pat- 
tern (Story, 1951), but these are almost wholly 
associated with differences in head proportions, 
muscular development, and sense organs. In gen- 
eral, Ailuropoda shares more characters with the 
Ursidae than with the Procyonidae or Ganidae 
(Story, 1951). 

A striking example of the close agreement be- 
tween Ailuropoda and the Ursidae is the elongation 
and looped arrangement of the subdural part of 
the internal carotid. In all other carnivores the 
carotid passes straight through the sinus caverno- 
sus, but in a specimen of Thalarctos described by 
Tandler the vessel immediately arched caudad in 
the sinus, forming a long U-shaped loop twisted 
around its own long axis, along the medial border 
of the petrosal. I found an identical situation in 
a specimen of Ursus americanus, in which the sub- 
dural part of the carotid measured 60 mm. while 
the linear distance traversed by this part of the 
vessel was only 12 mm., a ratio of 1 : 5. Exactly 
the same condition was present in Ailuropoda 
(p. 252), except that the posterior prolongation 
was not as extensive, with a ratio of only 1 : 3. 

Branches of the Abdominal Aorta 

This part of the circulatory system has received 
little detailed comparative study, probably be- 
cause few significant variations have been found 
among mammals (Hafferl, 1933). In the dog and 
cat there are no common iliacs; there is a common 
hypogastric trunk, but it is very short. The pat- 
tern in Ailuropoda differs little from that in the 
domestic dog and cat, and resembles even more 
closely the pattern in a specimen of Ursus ameri- 
canus dissected by me. The only notable differ- 
ence between Ailuropoda and other carnivores is 
that the iliolumbalis arises from the external iliac 
trunk instead of from the hypogastric trunk. This 
general agreement is somewhat unexpected in view 
of the shortening of the lumbar region and indica- 
tions of other profound disturbances in the poste- 
rior part of the axial skeleton in Ailuropoda. Sawin 
and Nace (1948) concluded that variations in the 
posterior aortic region in inbred races of rabbits 
resulted from the interaction of regional growth 
centers, which were genetically different in each 
race. In other words, as in the branches of the 
aortic arch, variations were determined by extrin- 
sic factors. 

Arteries of the Fore Limb 

These vessels have been reviewed most recently 
by Zuckerkandl (1907) and Hafferl (1933) for mam- 
mals in general, and by Davis (1941) for the Garni- 



R. anastomoticus 

A. comm. post. 

/ R. circ. Willisi 

A. stapedia r. sup. 

A. ophthalmica 

A. carotis int. 

A. ethmoid, ext. 

^ A. ciliaris 

A. stapedia 

k. infraorbitalis 

A. carotis ext 

emp. superf 

.V. mandibularis 
.4. 'stapedia r. inf. 
. maxillaris int. 

R. anastomoticus 

A. stapedia r. 

A. stapedia r. inf. 

Fig. 141. Basic pattern of the carotid circulation in mammals (A), and in arctoid carnivores (B). Embrj'onic vessels 
that have disappeared are indicated by broken lines. Note particularly the anastomotic ramus, through which the external 
carotid captures the internal carotid circulation in cats. 

vora. The primary artery of the forearm, both 
phylogenetically and ontogenetically, is the interos- 
sea, which primitively is the direct continuation of 
the brachial artery. Two collateral deep vessels, 
the median and ulnar arteries, provide alternative 
pathways. Three types, based on which of these 
vessels is dominant, may be recognized : the interos- 
sea type, the mediana type, and the ulnaris type. 
Most arctoid carnivores belong to the mediana 
type, although in some (Canidae, Procyon, Ailii- 
rus) the median and interosseous arteries are sub- 
equal in caliber. 

The pattern of the arteries of the fore limb is 
generally primitive in the Carnivora, and distinc- 
tive patterns tend to be associated with the various 
taxa. Among the arctoid carnivores the pattern 
in the Canidae is very primitive and uniform with- 
in the family. The Procyonidae and Ursidae (in- 

cluding Ailuropoda) have a common pattern, which 
is more specialized than in any other gi"Oup of car- 
nivores; Procyon is somewhat aben-ant. These 
arctoids are unique in that the brachial artery does 
not pass through the entepicondylar foramen (al- 
though the median nerve does). The bifurcation 
of the common median artery into subequal me- 
diana propria and medianoradial arteries tends to 
be shifted distally toward the carpus; in the bears 
and panda it is near the carpus. The Procyonidae 
and Ursidae also share other less conspicuous fea- 
tures in the arterial pattern of the fore limb. The 
bears and panda agree with each other particularly 

Arteries of the Hind Limb 

Comparative studies of these vessels in the Mam- 
malia were made by Bluntschli (1906) and Zucker- 



A. poplitea 

A. saphena 

R. plantaris 

A. tibialis post. 


R. perforans 

A. tibialis ant. 

R. superf. 

Arcus plantaris superf. 

Arcus plantaris prof. 

Arcus dors, superf. 
Arcus dors. prof. 

Fig. 142. Diagram of chief arteries of the hind leg in the Carnivora. The remains of the primitive interossea is repre- 
sented by the peroneal, the perforating branch of the anterior tibial, and that part of the anterior tibial distal to the perfor- 
ating branch. 

kandl (1907). Our knowledge of the patterns in 
the Carnivora is much less satisfactory than for the 
fore limb, although Zuckerkandl's material included 
18 carnivores, and valid generalizations as to pat- 
terns within the order are not yet possible. 

In the thigh region the deep femoral is often ab- 
sent in bears. Zuckerkandl refers specifically to 
its absence in one (Helarctos) of three bears dis- 
sected by him; in the second case (Melursus) he 
describes a profunda, but in the third (Thalardos) 
he does not state whether the profunda was pres- 
ent or absent. It was absent in a specimen of 
Ursus americanus dissected by me. It was also 
absent in one specimen each of Procyon, Mustela, 
Viverra, and Lutra dissected by Zuckerkandl. Ab- 
sence of the profunda is otherwise unknown as a 
normal condition in placental mammals. 

The primary vessel of the lower leg and foot is 
the interossea, which is laid down in the embryos 
of all mammals that have been studied (Bluntschli, 
1906). Three collateral vessels that develop later 
the saphena, tibialis anterior, and tibialis pos- 
terior provide alternative pathways to the lower 

leg and foot. Each of these four vessels may be 
enlarged or reduced to produce a variety of pat- 
terns. Bluntschli called three of these the inter- 
ossea type, the saphena type, and the [anterior] 
tibial type. The fourth could be called the poste- 
rior tibial type. In all Carnivora so far examined, 
the anterior tibial is the main trunk of the lower 
leg and foot (fig. 142). The saphena and posterior 
tibial persist as relatively minor vessels, and the 
interossea is partly suppressed, partly represented 
by the threadlike peroneal, and distally has been 
captured by the anterior tibial. 

In my specimen of Ursus americanus the sa- 
phena was nearly as large as the anterior tibial, 
making this specimen intermediate between the 
saphena and anterior tibial types. 

The arteries of the hind limb in Ailuropoda do 
not differ in any important respect from the carni- 
vore pattern as now known. 


1. Arterial patterns are elements of a passive 
distribution system, and therefore reflect function 



rather than directing function. Vessel pattern can- 
not be a factor that limits or channels adaptive 
radiation, and therefore is not directly subject to 
natural selection. 

2. \'essel patterns are not themselves inherited. 
Differences are apparently produced almost exclu- 
sively by differences in mechanical forces in the 
vessel environment during ontogeny, and these are 
hereditary. Therefore vessel patterns have a cer- 
tain taxonomic value. 

3. Vessel patterns characteristic of taxa are 
evident throughout the arterial system in the Car- 

4. Where comparative data are available, arte- 
rial patterns in Ailiiropoda resemble those of the 
Ursidae more closely than those of any other fam- 
ily or genus of Carnivora. 

in. VEINS 
Vena Cava Anterior and Its Tributaries 

The anterior vena cava has an external diameter 
of 20 mm., and a length of 90 mm. before it bifur- 
cates to form the innominates. It receives the 
following tributaries: (1) the azygos; (2) the inter- 
nal mammaries; (3) the costocervical axis; and (4) 
the innominates. 

1. V. azygos enters the dorsal side of the vena 
cava at a point about midway between the right 
aiu-icle and the junction of the innominate veins, 
i.e., at the level of the fifth thoracic vertebra. At 
its origin the azygos lies well to the right of the 
midline, but it gi-adually moves mesad until at 
the level of the ninth thoracic vertebra it lies along 
the midline. Immediately after its origin it gives 
off a branch from its left wall that runs cephalad 
to the second and third intercostal spaces. Bi- 
lateral branches begin at the level of the sixth 
vertebra, a large left branch supplying the fourth 
right intercostal space and the third, fourth, and 
fifth left intercostal spaces; the con-esponding right 
branch supplies the sixth right intercostal space. 
Successive intercostal branches are more or less 
symmetrically arranged back to the diaphragm, 
where the azygos terminates by bifurcating into 
branches that supply the fourteenth intercostal 

2. Vv. mammariae internae enter the ventral 
wall of the vena cava independenth^ just caudad 
of the origin of the innominates. The right inter- 
nal mammary enters about 15 mm. directly behind 
the left. Extending obliquely ventrad, caudad, 
and mesad, each joins the artery of the same name 
and passes with it beneath the transverse thoracic 
muscle, where it supplies the ventral intercostal 

3. Truncus costocervicalis enters the right 
dorsolateral wall of the anterior vena cava at about 
the same level as the right internal mammary vein. 
The costocei-vical trunk runs craniad and slightly 
laterad, dividing to form three branches: ( 1) V. in- 
tercostalis I arises opposite the first intercostal 
space, which it supplies; (2) V. vertebralis and (3) 
V. cervicalis profunda arise opposite the first rib 
by bifurcation of the trvmk. The vertebral vein 
joins the artery of the same name, and together 
they pass into the transverse foramen of the sixth 
cervical vertebra. The deep cervical vein slightly 
exceeds the vertebral vein in caliber. It runs cra- 
niad with the deep cervical artery. 

4. Vv. anonymae arise by bifurcation of the 
anterior vena cava at the level of the posterior bor- 
der of the firet rib. Each innominate is very short, 
breaking up to form the axillary and jugulars im- 
mediately in front of the rib. V. jugularis ante- 
rior is an unpaired vessel arising from the medial 
wall of the left innominate, about midway in the 
course of the latter. Running craniad along the 
ventral midline of the trachea, the anterior jugular 
gives off the V. thyreoidea posterior at the level 
of the hyoid. Here it bifurcates, each branch run- 
ning laterad and craniad to anastomose with the 
lingual vein. 

Internal Jugular Vein 

V. jugularis interna arises from the medial 
wall of the innominate, thus from the convex side 
of the curve of the latter vein as it arches around 
the first rib. The left internal jugular arises some- 
what farther distad than the right, probably be- 
cause of the origin of the anterior jugular from the 
left innominate. Each internal jugular nins cran- 
iad beside the corresponding common carotid ar- 
tery, the vein lying toward the outside. The 
diameter of the internal jugular is 4 mm. V. thy- 
reoidea anterior dextra arises at the level of the 
artery of the same name. A smaller branch open- 
ing independently into the internal jugular immed- 
iately caudad of the anterior thjToid apparently 
corresponds to the occasional V. thyreoidea me- 
dia of human anatomy. V. thyreoidea anterior 
sinistra opens into the left jugular 25 mm.caudad 
of the corresponding arteiy. 

At the level of the cricoid cartilage the inter- 
nal jugular receives the large R. anastomotica, 
which lies mesad of the vagus nerve. The anasto- 
motic branch gives off two large vessels to the ver- 
tebral vein, as well as smaller twigs to the pha- 
ryngeal plexus. Much diminished in caliber, the 
anastomotic ramus enters the foramen lacenun 
posterior where it empties into the inferior petro- 
sal sinus. 



The internal jugular accompanies the carotid ar- 
tery as far craniad as the origin of the digastric 
muscle, where the vein and artery diverge. As the 
vein approaches this point it crosses over the ar- 
tery, passing ventrad of it. The internal jugular 
continues anteriorly beside the glossopharyngeal 
nerve to the base of the postglenoid process, where 
it receives numerous pharyngeal branches from the 
pharyngeal plexus and terminates by uniting with 
the medial branch of the internal facial vein. The 
pharyngeal plexus is a network of veins draining 
the walls of the pharynx, from the level of the fora- 
men magnum to the posterior nares. One of the 
pharyngeal rami communicates with the sinus cav- 
ernosus through the foramen lacerum medium. 

Venous Sinuses of the Dura Mater 

The combined veins of the vertebral canal pass 
through the foramen magnum into a deep exoccip- 
ital groove that opens at the hypoglossal canal into 
the sigmoid groove for the transverse sinus. The 
sinus transversus extends from the opening of the 
superior petrosal sinus, laterally, to the posterior 
lacerated foramen, medially. The sinus petrosus 
superior is entirely surrounded by bone, beginning 
at the posterosuperior angle of the petrosal bone 
and running along its superolateral margin. The 
superior petrosal sinus is large posteriorly, where 
it drains into the lateral branch of the internal 
branch of the internal facial vein through the post- 
glenoid foramen. Anterior to this foramen the 
superior petrosal sinus is a narrow canal opening 
from the sinus cavernosus at the lateral wall of 
the foramen ovale. The sinus petrosus inferior 
is the direct continuation of the transverse sinus 
from the foramen lacerum posterior to the dor- 
sum sellae, where it becomes the cavernous sinus. 
The sinus cavernosus fills the sella turcica and 
opens anteriorly into the ophthalmic vein. 

External Jugular Vein 

V. jugularis externa (figs. 107, 131), with a 
diameter of 9 mm., is considerably larger than the 
internal jugular. The external jugular enters the 
innominate vein between the internal jugular and 
axillary veins, and runs forward immediately lat- 
erad of the sternomastoid muscle, dividing at the 
posterior border of the submaxillary gland to form 
the external and internal facial veins. Only one 
branch, the thyrocervical trunk,' is received in the 
cervical region. 

' This designation is used for this trunk because the 
branches that it receives are practically identical with 
the branches of the thyrocervical artery. This condition 
is quite different from the usual arrangement in man, the 
domestic cat, etc. 

The transverse scapular arises from the jugular on the 
right side of the body (cf. p. 283), but this does not seem to 
be the normal condition. 

V. thyreocervicalis is a large vessel entering 
the external wall of the external jugular about 
50 mm. craniad of the origin of the latter. It 
curves away from the jugular to join the thyro- 
cervical artery, which it accompanies toward the 
scapulo-humeral articulation. The vein receives 
the following tributaries: (1) The large V. trans- 
versa colli enters the thyrocervical 40 mm. beyond 
the origin of the latter. It joins the corresponding 
artery, accompanying it around the shoulder joint 
to the lateral shoulder region. About 10 mm. far- 
ther distad the thyrocervical bifurcates to form 
two branches of approximately equal size: (2) a 
large muscular ramus that accompanies the corre- 
sponding artery to the proximal part of the clavo- 
trapezius and adjacent muscles, and (3) the cephalic 
vein (p. 284). 

Internal Facial Vein 

V. facialis interna (posterior) (figs. 107, 131, 
132) arches dorsad and craniad to the base of the 
ear, in front of which it terminates by entering the 
postglenoid foramen, to be continued within the 
skull as the transverse sinus. V. sternocleido- 
mastoidea arises from the internal facial near its 
base; it accompanies the artery of the same name. 
V. auricularis and V. occipitalis arise by a com- 
mon trunk, as was the case with the correspond- 
ing arteries; the ramifications of both veins agree 
closely with those of the arteries, except that the 
main auricular veins do not come from this trunk. 
The occipital vein gives off the large Vv. mas- 
toideae, which communicate with the sinus trans- 

V. temporalis superficialis (fig. 132) is a pow- 
erful vein given off over the base of the ear carti- 
lage. It gives off a stout branch at its base that 
runs across the root of the zygoma to anastomose 
with the transverse facial; twigs from this branch 
go to the masseter and to the postglenoid rete. 
V. transversa facei arises higher. It receives the 
anastomotic branch described above, then joins a 
masseteric branch of the artery of the same name 
and runs anteriorly with it. V. auricularis an- 
terior (fig. 107), the larger of the two accompany- 
ing veins of the anterior auricular artery, arises 
opposite and a little above the transverse facial. 
It joins the corresponding artery, and passes with 
it onto the front of the ear. V. auricularis pos- 
terior comes off at the upper third of the root of 
the zygoma. It gives off twigs to the base of the 
pinna, receives an anastomotic twig from the oc- 
cipital-auricular trunk, gives off a slender accom- 
panying branch of the anterior auricular artery, 
and then joins the posterior auricular artery at the 
level of the dorsal border of the zygoma. Its fur- 



ther ramifications agree with those of the corre- 
sponding artery. Beyond the origin of the posterior 
auricular, the temporal trunk is continued as V. 
temporalis media. The ramifications of this vein 
agree with those of the artery of the same name. 

Immediately beyond the origin of the superficial 
temporal the internal facial vein arches sharply 
mesad around the mastoid process. Twigs are 
given off in this region to the parotid and submax- 
illar}^ glands. In front of the mastoid process arises 
the small V. stylomastoidea, which passes into 
the stylomastoid foramen. Opposite this a slender 
vessel arises and passes across the medial part of 
the mandibular condyle, laterad of the postglenoid 
process, to join the pterygoid rete farther anteri- 
orly. Twigs arising from this vessel near its base 
form a delicate postglenoid rete on the postglenoid 

The internal facial appears to bifurcate in front 
of the mastoid process to form two vessels of ap- 
proximately equal size. One of these, which may 
be regarded as the continuation of the internal 
facial trunk, soon enters the postglenoid foramen. 
The postglenoid foramen leads into a bony canal 
that passes dorsad in front of the auditory meatus, 
to open into the cerebellar cavity of the skull. Be- 
yond this canal the vein continues as the trans- 
verse sinus. 

The other terminal branch of the internal facial 
is V. maxillaris interna (figs. 131, 132). This 
vessel arches around the base of the postglenoid 
process, to be joined by the terminus of the inter- 
nal jugular at the medial border of that process. 
The resulting common trunk passes forward be- 
tween the medial border of the postglenoid process 
and M. levator veli palatini, to break up into the 
pterygoid plexus at the posterior border of the 
temporal fossa. 

The Plexus pterygoideus gives rise to the fol- 
lowing branches: 

1. Vv. alveolaris inferior (paired accompanying 

2. V. temporalis profunda posterior. 

3. V. masseterica. 

4. V. tympanica anterior. 

5. V. foramina ovalis (accompanies A. meningea 

6. Vv. pterygoidei. 

7. V. meningea media. 

These vessels, with the exceptions noted, accom- 
pany the corresponding arteries. 

Anteriorly the pterygoid plexus drains into a 
powerful anastomotic branch, which passes along 
the ventral border of the buccinator muscle to 

empty into the inferior labial vein near the juncture 
of the latter with the external facial. Numerous 
small Vv. buccinatoria and a large V. alveolaris 
superior posterior empty into the anastomotic 
branch in its course along the muscle. 

External Facial Vein 

V. facialis externa (anterior) (figs. 107, 131, 
132) follows the anterior border of the masseter 
forward and upward to a point in front of the an- 
terior root of the zygoma. Continuing upward in 
front of this root of the zygoma, it divides in front 
of the orbit into the external nasal and nasofrontal 
veins. The external facial receives the following 
tributaries along its course: 

1. A transverse communicating branch passes 
from the external facial near the posterior end of 
the digastric, to the sublingual branch of the ante- 
rior jugular. A twig from this communicating 
branch passes forward between the mylohyoid and 
hyoglossus, to anastomose with the lingual vein. 

2. V. submentalis enters the external facial 
directly opposite the preceding branch. It receives 
a twig from the submaxillary gland, then passes 
across the digastric and between the digastric and 
masseter to the superficial surface of the mylo- 
hyoid. Here it joins the submental artery, and 
the further course of the two vessels agrees closely. 

3. V. labialis inferior (figs. 107, 131) is re- 
ceived at the posterior end of the exposed part of 
the inferior alveobuccal gland. The vein passes 
forward with the artery on the mandible, the rami- 
fications of the two vessels agi-eeing. 

4. A muscular twig from the platysma enters 
the external facial a few millimeters farther distad. 

5. V. facialis profunda (figs. 107, 132) enters 
the deep surface of the external facial at the dorsal 
border of the inferior alveobuccal gland. It lies 
directly beneath the external facial as far as the 
lower border of the zygoma, then passes behind the 
anterior root of the zygoma to the common outlet 
of the sphenopalatine foramen and pterygopala- 
tine canal. Just before reaching the foramina the 
trunk divides into a V. sphenopalatina and a 
pair of small Vv. palatina descendens. These 
vessels enter the foramina with the corresponding 

V. alveolaris superior anterior enters the deep 
facial at its base, and numerous smaller alveolar 
twigs from the minute foramina below the orbit 
open into the deep facial along its course. There 
are also muscle twigs from the temporal muscle. 
Below the orbit the deep facial gives off a large 
communicating branch, which pierces the ventral 
wall of the periorbita to anastomose with the infe- 



rior ophthalmic; a twig from this branch passes 
out of the ventral side of the orbit, to anastomose 
with the angular vein on the face. 

Just beyond the deep facial, the external facial 
receives a common trunk formed by (6) a muscular 
branch from the masseter and (7) V. labia lis supe- 
rior (fig. 107). 

8. A communicating branch arising in front of 
the anterior root of the zygoma arches upward and 
backward across the temporal muscle, to anasto- 
mose with the anterior auricular vein. 

9. V. angularis (fig. 107), which enters the ex- 
ternal facial just above the foregoing, follows the 
angular artery. 

10. Several nutrient twigs from the jugal enter 
below and in front of the orbit. 

11. V. nasofrontalis (fig. 107), the more pos- 
terior of the two terminal vessels, arches around to 
the dorsal side of the orbit. Just above the orbit 
it receives V. frontalis, which follows the corre- 
sponding artery. The nasofrontal then anasto- 
moses with the superior ophthalmic vein, which it 
meets immediately above the eye but outside the 

12. V. nasalis externa (fig. 107), the anterior 
of the terminal vessels, passes forward on the side 
of the nose. Several communicating branches pass 
up over the bridge of the nose, to anastomose with 
corresponding vessels from the opposite side. At 
the nasal aperture the trunk of the external nasal 
vein bifurcates, a dorsal and a ventral branch anas- 
tomosing with corresponding vessels from the oppo- 
site side to encircle the nasal cartilages immediately 
in front of the premaxillary and nasal bones. 

Ophthalmic Vein 

V. ophthalmica arises from the sinus caverno- 
sus, from which it passes into the orbit through 
the orbital fissure. The vessel runs forward in the 
orbit, to be perforated by the orbital artery at 
about the posterior third of the orbit. At this 
point the ophthalmic breaks up into its terminal 

1. V. ophthalmica superior, by far the larg- 
est of the terminal branches, accompanies the fron- 
tal artery through the dorsal wall of the periorbita. 
V. ethmoidalis, which accompanies the corre- 
sponding artery through the ethmoidal foramen, 
enters the vessel near the posterior end of the orbit. 
As it passes anteriorly the superior ophthalmic re- 
ceives a muscle twig that perforates the periorbita 
independently. Directly above the eye, and just 
before passing out of the orbit, it receives a vein 
that emerges from the frontal sinus through a 
small foramen in the dorsomedial wall of the or- 

bit. Upon emerging from the orbit the superior 
ophthalmic becomes the nasofrontal vein, and 
this communicates openly with the external facial 

2. V. centralis retinae is a thread-like vessel 
that comes off immediately below the superior oph- 
thalmic. It joins the deep branch of the orbital 
artery and follows it (and the central retinal artery 
in which the orbital artery terminates) into the 
optic nerve and thence into the eye ball. 

3. V. lacrimalis follows the corresponding ar- 
tery to the lacrimal gland, where it anastomoses 
with a twig from the angular vein. 

4. Vv. musculares, two in number, supply the 
ocular muscles. 

5. V. ophthalmica inferior, the most ventral 
branch of the ophthalmic, runs toward the eye 
between M. rectus inferior and the periorbita. It 
terminates by anastomosing with the communi- 
cating branch of the deep facial vein immediately 
below the eye. 

Axillary Vein 

V. axillaria is the largest and most posterior of 
the triad of branches in which the innominate ter- 
minates.' The left axillary (14 mm. in diameter) 
is considerably larger than the right (11 mm.). 
The axillary arches around the anterior border of 
the first rib, becoming the brachial vein beyond the 
point where it receives the subscapular trunk. It 
has a length of about 70 mm. The axillary receives 
the following tributaries: (1) A small branch enters 
the anterior wall of the axillary 20 mm. beyond the 
origin of the external jugular. It bi'eaks up into a 
number of branches that drain the longus colli and 
the anterior end of the scalenus; the largest branch 
passes ectad beside the axillary artery, to anasto- 
mose with a branch from the internal circumflex 
humeral. (2) V. thoracoacromialis enters im- 
mediately distad of the preceding vein. It accom- 
panies the corresponding artery. (3) A muscular 
ramus, nearly as large as the thoracoacromialis 
and entering immediately behind and ventrad of 
it, drains the anterior parts of the superficial and 
deep pectoral muscles. (4) V. transversa scap- 
ulae on the right side of the body enters the exter- 
nal wall of the external jugular 45 mm. beyond the 
origin of the latter. On the left side it empties into 
the axillary a few mm. distad of the thoracoacrom- 
ialis. The vein accompanies the corresponding 
artery into the space between M. suprascapularis 
and M. infraspinatus; its branches correspond 

' The arrangement of the vessels in this region, particu- 
larly the origin of the transverse cervical and transverse 
scapular veins from the external jugular, makes it impos- 
sible to distinguish a deflnitive subclavian vein. 



closely with those of the artery. (5) V. thora- 
calis anterior enters the posterior wall of the 
axillary slightly distad of the preceding branches. 
It accompanies the corresponding artery. (6) V. 
thoracalis lateralis enters the posterior wall of 
the axillary immediately before the latter divides 
to form the subscapular and brachial veins. It 
accompanies the corresponding artery to the deep 
pectoral and panniculus muscles, but does not re- 
ceive the intercostal branches. About 70 mm. be- 
yond its origin the axillary vein of the left fore leg 
bifurcates to form two branches of nearly equal 
size: (7) V. subscapularis, into which both cir- 
cumflex humerals empty, and (8) V. brachialis. 
On the right leg the subscapular enters the axillary 
at the same level as it does on the left leg, but does 
not receive the circumflex humerals and conse- 
quently is much smaller. The circumflex humerals 
of this leg empty into a common trunk 20 mm. in 
length, which enters the axillary independently 
immediately distad of the subscapular. 

The subscapular vein accompanies the subscap- 
ular artery, receiving branches that with a few 
exceptions conform closely to the branches of the 
artery. The large arterial ramus to the latissimus 
and subscapular muscles is accompanied by two 
veins whose ramifications do not correspond ex- 
actly with those of the artery. The more proximal 
of the two veins receives the intercostal branches 
(which in the arterial system come from the lateral 
thoracic) and the branch draining the latissimus; 
the distal branch drains the subscapular, teres 
major, and teres minor. 

The two circumflex humerals, whose ramifications 
conform closely with those of the corresponding 
arteries, enter the subscapular vein independently. 
V. circumflexa humeri interna is composed of 
a pair of collateral vessels (a single vessel on the 
right leg) that enter the anterior wall of the sub- 
scapular 15 mm. beyond the origin of the latter 
vein. The two collateral trunks embrace the sub- 
scapular artery between them, immediately be- 
yond which they are connected by a transverse 
communicating anastomosis. V. circumflexa 
humeri externa accompanies the corresponding 
artery through the septum between the long and 
lateral heads of the triceps onto the lateral side of 
the shoulder. It then runs along the ventral bor- 
ders of the spinodeltoid and acromiodeltoid to the 
cephalic vein, into which it opens. 

Brachial Vein and Its Tributaries 

V. brachialis is the continuation of the axillary 
beyond the origin of the subscapular trunk. It lies 
mesad and slightly caudad of the corresponding 
artery, to which its course and branchings conform 

very closely as far as the elbow. Here, anterior to 
and slightly proximad of the entepicondylar fora- 
men, the brachial bifurcates to form two vessels of 
approximately equal size: the superficial brachial 
and a trunk from which the ulnar and interosseous 
veins arise. This trunk receives Vv. collateralis 
radialis, recurrens radialis, and recurrens ul- 
naris before its bifurcation. 

V. brachialis superficialis accompanies its ar- 
tery distad on the forearm, receiving a large com- 
municating branch from the cephalic in the lower 
third of the forearm, to the radiocarpal articula- 
tion. Here it divides into volai- and dorsal branches. 
The volar branch forms an arch with the ulnar vein 
which conforms closely to the superficial arterial 
arch. The dorsal branch passes around the base 
of the radial sesamoid onto the dorsum, where it 
forms an anastomotic arch with the cephalic; the 
digital veins from digits 1, 2, and 3 open into this 
arch, and a perforating branch pierces the inter- 
stitium between the second and third metacarpals 
to form the deep volar arch with a branch from 
the ulnar. 

Vv. ulnaris, interosseus dorsalis, and inter- 
osseus volaris arise together at the level of the 
corresponding arteries, accompanying them distad 
and conforming closely to their ramifications. 

Cephalic Vein 

V. cephalica (fig. 134) arises as one of the ter- 
minal branches of the thyrocervical vein. Passing 
around in front of the head of the humerus, be- 
neath M. clavotrapezius, it emerges on the lateral 
side of the shoulder. Here it receives the external 
circumflex humeral, and then runs distad over the 
biceps and brachioradialis to the hollow of the 
elbow. Joining the lateral ramus of the superficial 
branch of the radial nerve on the flexor side of the 
forearm, it runs distad with it to the carpus. Here 
it divides into radial and ulnar branches. The 
radial branch forms an arch with the anterior bra- 
chial on the radial side of the dorsum, while the 
ulnar branch forms a similar arch with a branch of 
the ulnar vein on the ulnar side of the dorsum. 
The dorsal digital veins open into the resulting 
compound arch, the veins from the first, second, 
third, and radial side of the fourth into the radial 
arch, and the veins from the ulnar side of the fourth 
and from the fifth digits into the ulnar arch. There 
is a slender accessory vein from the ulnar side of 
the fifth digit. 

Vena Cava Posterior and Its Tributaries 

The vena cava posterior (fig. 135) is double up 
to the level of the renal veins; the undivided ante- 



rior part of the postcava is only 55 mm. long.' The 
undivided part receives the following tributaries: 

1. Vv. phrenicae posterior enter the vena 
cava on either side, just anterior to the renal veins. 
Thus the right is considerably farther forward than 
the left. Each posterior phrenic receives a short 
V. suprarenalis as it passes across the suprarenal 

2. Each V. renalis enters by a short trunk 
common to it and the lumboabdominal. The right 
is 25 mm. farther anterior than the left. As it 
approaches the kidney, the renal first receives a 
branch from the posterior part of the kidney, then 
two branches from the middle and anterior parts 
of the kidney, respectively. 

3. V. lumboabdominalis joins the renal pos- 
teriorly on the right side and anteriorly on the left. 
Each joins its corresponding artery, which it fol- 
lows closely. 

Hypogastric Veins 

V. hypogastrica (fig. 135) unites with the ex- 
ternal iliac to form the common iliac. The junc- 
tion takes place slightly anterior to the junction 
of the corresponding arteries. As usual, the vein 
differs from the artery in not having separate pari- 
etal and visceral divisions. The vein lies lateral 
to, and between, the parietal and visceral rami of 
the artery. 

V. sacralis media enters the right hypogastric 
immediately before the latter enters the common 
iliac. From here the middle sacral runs diagonally 
caudad and mesad to the midline, where it joins the 
middle sacral artery and runs with it into the tail. 

V. glutaea anterior, one of the two main trib- 
utaries of the hypogastric, enters its medial wall 
20 mm. before its termination. Beyond this point 
the hypogastric continues posteriorly as a common 
trunk formed by the union of the middle and pos- 
terior hemorrhoidal, posterior gluteal, perineal, and 
penial veins. The courses of these veins corre- 
spond with those of the arteries of the same names. 

' Raven found a similar condition in his specimen of Ailu- 
ropoda, so a double postcava may be normal for this species. 
Among the bears, the postcava divides at the normal level 
in a specimen of Ursiis atnericanus figured by Raven, and 
in a specimen of Ursiis americanus dissected by me. Raven 
described and figured a double postcava for Ailurus fulgens; 
this vessel was normal, but the precava was double in a 
specimen of Ailurus described by Sonntag (1921), and the 
postcava divides normally, at the same level as the abdom- 
inal aorta, in a specimen of Ailurus dissected by me. Accord- 
ing to Beddard (1909) a double postcava occurs frequently 
in the Mustelidae. McClure and Huntington (1929) showed 
that the occurrence of a double postcava in placental marn- 
mals represents the persistence of parts of the embryonic 
system of cardinal veins. In view of other indications of 
disturbance in the lumbosacral region in Ailuropoda, the 
occurrence of a double postcava is interesting. 

Portal System 

The portal vein arises in the porta of the liver 
by the union of short right and left branches com- 
ing from the liver substance. Running caudad 
across the caudal lobe, it gives off (1) the splenic 
vein dorsad of the cervix of the pancreas, and im- 
mediately posterior to this (2) the pyloric vein. 
V. coronaria ventriculi is absent, the pyloric 
vein supplying the parts normally supplied by it. 
A few millimeters caudad of the pyloric vein the 
portal vein divides to form (3) the large anterior 
mesenteric vein and (4) the smaller posterior mesen- 
teric vein. The total length of the portal vein is 
about 60 mm. 

1. V. lienalis conforms closely to the artery of 
the same name, following the curvature of the gas- 
trolienal ligament and radiating branches to the 
spleen which correspond to the splenic branches of 
the splenic artery. 

2. V. pylorica is slightly smaller than the 
splenic vein, and arises from the portal vein just 
caudad of it. The pyloric vein immediately curves 
sharply cephalad, passes ventrad of the splenic vein, 
and accompanies the right gastric artery around 
the lesser curvature of the stomach. Branches are 
given off to the pancreas, to the duodenum, to the 
stomach along the whole lesser curvature, and to 
the esophagus. 

3. V. mesenterica anterior may be described 
as the posterior continuation of the portal vein. 
It arises near the anterior mesenteric artery, and 
its course and branchings follow the arrangement 
of that artery very closely. The termination of 
the vein anastomoses with the termination of the 
ileocolic vein in the region of the ileum. 

4. V. mesenterica posterior arises from the 
portal vein caudad of the origin of the pyloric vein. 
It promptly breaks up into a number of veins 
that supply the ileocolic region. The anterior 
and middle colic veins come off by a very short 
common trunk near the origin of the posterior 
mesenteric; the vein then continues as the ileo- 
colic vein, dividing farther distad to form two 
main branches. 

Vv. colica anterior and media conform closely 
to the arteries of the same names. The anterior colic 
vein divides into anterior and posterior branches 
near the intestine. The anterior branch anasto- 
moses with the posterior branch of the ileocolic, 
giving off short twigs to the colon; the posterior 
branch anastomoses with a small anastomotic 
branch given off by the middle colic. The middle 
colic supplies the entire posterior half of the 



Common Iliac Veins 

The conunon iliac veins (V. iliaca communis, 
fig. 135) run craniad as far as the middle of the 
kidneys before they unite to form the posterior 
vena cava. The confluence of the common iliacs 
takes place slightly to the right of the midline, and 
ventrad of the aorta, at the level of the first lum- 
bar vertebra. The common iliacs receive the fol- 
lowing tributaries: d) Vv. spermatica internae 
enter symmetrically, 20 mm. anterior to the origin 
of the internal spermatic arteries, at the confluence 
of the common iliacs. Each accompanies its con-e- 
sponding artery to the testis, with a branch coming 
from the posterior renal fat. (2j Vv. lumbales 
consist of two vessels entering the mediodorsal wall 
of the right common iliac. The first of these is a 
large vessel entering 20 mm. behind the confluence 
of the two common iliacs. Branches are distrib- 
uted from this trunk to the first three lumbar ver- 
tebrae. The second lumbar vein enters the common 
iliac at the junction of the third and fourth lumbar 
vertebrae; it is distributed to the fourth and fifth 
lumbars. (3) V. circumflex ilium profunda en- 
ters the lateral wall of each common iliac at the 
level of the coiTesponding artery. Its bi-anches are 
the same as those of the artery. At the level of 
the articulation between the first and second sacral 
vertebrae the common iliac divides to form the 
h\T)ogastric and external iliac veins. 

External Iuac Vein 

V. iliaca externa (fig. 135) is much the larger 
of the two roots of the common iliac. Running 
across the iliimi in front of the iliopectineal emi- 
nence, it passes through the femoral ring posterior 
to the corresponding artery, and becomes the fe- 
moral vein. The external iliac receives the follow- 
ing branches: ( 1) V. iliolumbalis enters the medial 
wall at the level of the corresponding artery-, whose 
branches it follows. (2) V. epigastrica posterior 
enters its medial wall at the iliopectineal eminence, 
i.e., at the level of the corresponding artery. The 
course of the vein agrees closely with that of the 
artery, branching to form V. spermatica externa 
and the posterior epigastric proper. (3) V. pro- 
funda femoris enters the external iliac at the fe- 
moral ring. It joins the deep femoral artery, and 
the course of the two vessels is similar. The main 
trunk of the vein consists of an anastomotic branch 
with the popliteal vein. 

V. femoralis lies posterior to the femoral artery 
in the upper part of the thigh, but just below the 
middle of the thigh it becomes superficial to ime- 
sad ofi the artery. It receives two branches, V. 
circumflexa femoris lateralis and V. muscu- 
laris posterior, which agree closely with the cor- 

responding arteries. At almost exactly the middle 
of the thigh the femoral vein di\'ides to form the 
great saphenous and popliteal veins. The pop- 
liteal considerably exceeds the great saphenous in 

V. saphena magna runs distad with the corre- 
sponding artery and the saphenous ner\'e. In the 
thigh its branchings correspond closely with those 
of A. genu suprema, in addition to a large muscle 
branch that runs forward to the knee. Between 
the distal ends of the heads of the semimembrano- 
sus it receives a slender branch that accompanies 
the plantar branch of the saphenous arter\' to near 
the distal end of the tibia, where it anastomoses 
with the tibialis posterior. Just beyond the distal 
end of the tibia the saphena magna receives an 
anastomotic branch, chiefly from the tibialis pos- 
terior, that runs around the tibial border of the 
tai-sus. At the distal end of the tai-sus it receives 
a smaller anastomotic branch from the tibialis an- 
terior. The dorsal venous arch is formed chiefly 
by the saphena magna, supplemented by two small 
terminal twigs of the saphena parva and the super- 
ficial branch of the anterior tibial. Five dorsal 
metatarsal veins arise from the arch, and accom- 
pany the corresponding arteries to the toes. 

V. poplitea accompanies the popliteal artery 
into the popliteal space, where it breaks up into 
a number of terminal branches. As the vein enters 
the popliteal space it receives a perforating branch 
that corresponds to the perforating bi-anch of the 
femoral artery. The popliteal vein receives the 
following tributaries in the popliteal space, in addi- 
tion to various muscle branches: 

1. An anastomotic bi^anch with the profunda 
femoris, which does not accompany an arten.', 
runs proximad between the heads of the semi- 

2. A genicular trunk is formed by veins whose 
ramifications agree with those of the genicular 

3. V. saphena parva enters the posterior wall 
of the popliteal at about the center of the popliteal 
space. It runs distad on the back of the leg be- 
neath the biceps, hing successively across the lat- 
eral head of the gastrocnemius and the soleus. At 
the distal end of the fibula it receives a strong anas- 
tomotic branch from the tibialis posterior, then 
continues along the lateral border of the tarsus 
and foot. 

A twig arising from the saphena parva at the 
distal end of the fibula passes onto the tarsus, 
where it is joined by the distal end of the super- 
ficial anterior tibial vein; the resulting common 
trunk joins the much larger saphena magna to 
form the superficial dorsal arch. At the tarso- 



metatarsal articulation the saphena parva gives 
off a branch that passes across the dorsum of the 
foot to the space between digits 4 and 5, where it 
is joined by a branch from the superficial arch to 
form the digital vein to the outer side of digit 5. 
The saphena parva continues along the lateral 
border of the foot, anastomosing at the metatarso- 
phalangeal articulation with the vein that supplies 
the outer side of digit 5. 

4. V. suralis enters the popliteal where that 
vessel bifurcates into the anterior and posterior 
tibial veins. In addition to muscle branches to 
the plantaris and both heads of the gastrocnemius, 
it receives an anastomotic twig arising from the 
saphena parva near the distal end of the soleus. 

5. V. tibialis anterior is slightly larger than 
the posterior tibial vein. It accompanies the ar- 
tery of the same name through the proximal end 
of the interosseous space and distad along the an- 
terolateral aspect of the leg, its branches cori'e- 
sponding closely to those of the artery. At the 
middle of the leg it divides into a larger lateral and 
a smaller medial branch, which flank the artery. 

V. tibialis anterior superficialis arises from 
the lateral branch at the lower third of the leg and 
accompanies the superficial branch of the anterior 
tibial artery onto the dorsum of the foot. Here it 
joins a branch from the saphena parva, the result- 
ing common trunk forming one end of the super- 
ficial dorsal arch. 

The medial accompanying vein gives off V. tar- 
sea medialis at the tibio-tarsal articulation, an 
anastomotic branch to the saphena magna in the 
proximal part of the tarsus, and an anastomotic 
branch with the lateral accompanying vein in the 
proximal metatarsal region, and terminates by 
opening into the second superficial dorsal meta- 
tarsal vein. 

The lateral accompanying vein gives off the large 
V. tarsea lateralis at the tibio-tarsal articulation. 
The lateral tarsal supplies a nutrient vein to the 
tarsus. At the second inter-metatarsal space the 
lateral accompanying vein gives rise to two per- 
forating branches that pass through to the deep 

plantar arch. The deep dorsal arch is composed 
of two parallel vessels that flank the corresponding 
artery. The more distal of these, in which the lat- 
eral accompanying vein terminates, gives off Vv. 
metatarseae dorsales profundae 3 5, which en- 
ter the corresponding superficial veins near the 
heads of the metatarsals. 

6. V. tibialis posterior accompanies the pos- 
terior tibial artery along the back of the leg. Near 
the distal end of the tibia it gives off a strong anas- 
tomotic branch, which passes across the leg deep 
to the tendon of Achilles and M. soleus, to the 
saphena parva. The tibialis posterior is continued 
beyond the anastomotic branch, considerably re- 
duced in caliber, to the tibio-tarsal articulation. 
Here it divides into a superficial branch that runs 
around the medial side of the tarsus to anastomose 
with the saphena magna, and a deep branch that 
anastomoses with the nutrient branch of the prox- 
imal part of the tarsus. 

A powerful trunk arises from the transverse anas- 
tomotic branch that passes between the saphena 
parva and the posterior tibial. This trunk runs 
distad beneath the shaft of the calcaneum, break- 
ing up at the posterior border of the astragalus into 
a leash of three vessels that form both plantar 
arches. The medial of the three supplies the me- 
dial side of digit 1. The middle one forms the arch 
proper by anastomosing with a twig from the sa- 
phena parva. Branches to the lateral side of digit 1, 
to adjacent sides of digits 2, 3, and 4, and to the 
medial side of digit 5 arise from the arch; each is 
joined by the corresponding deep plantar meta- 
tarsal vein. The lateral branch runs to the lateral 
side of the tarsus, where it receives the terminal 
branches of the lateral tarsal vein. At the middle 
of the tarsus the vessel divides into medial and 
lateral branches. The medial branch arches across 
the sole, giving off an anastomotic branch to the 
saphena magna and terminating by entering the 
perforating branch of the anterior tibial. The lat- 
eral branch runs down the lateral border of the 
ankle, then arches across the sole to form the prox- 
imal of the two deep plantar arches. It terminates 
by entering the perforating branch of the anterior 
tibial vein. 



The hypophysis (fig. 144) is a flattened pear- 
shaped structure situated posterior and slightly 
ventral to the optic chiasma. It is connected to 
the floor of the third ventricle by a short infundib- 
ulum. The hypophysis lies almost horizontally in 
the sella, which in Ailuropoda is deep, with promi- 
nent anterior and posterior processes. The hy- 
pophysis measures 10.5 mm. in length, about 9 mm. 
in transverse diameter (measured after bisection), 
and 5.5 mm. in vertical diameter. The organ was 
not weighed. 

In sagittal section the hypophysis is seen to be 
composed of a smaller anterior lobe lying anteri- 
orly and ventrally, and a larger neural lobe lying 
posteriorly and dorsally. The pars intermedia could 
not be differentiated macroscopically from the pars 
posterior. A dark-colored pars tuberalis embraces 
the infundibular stalk as far forward as the optic 
chiasma. As in the Ursidae, a well-developed re- 
cessus hypophysis extends from the bottom of the 
third ventricle through the infundibular stalk and 
into the posterior lobe nearly to its posterior end. 
Below the recessus hypophysis a hypophyseal cleft 
separates the anterior lobe from the posterior lobe, 
as it does in the bears; there is no cleft above the 

In an adult female Ursus americanus the hy- 
pophysis is similar in size and topography to that 
of Ailuropoda but is less broadened and flattened. 
In this bear it measures 12.2 mm. in length, 6.6 
mm. in transverse diameter, and 6.5 mm. in ver- 
tical diameter. 

The hypophysis of Thalarctos and Ursus arctos 
were described by Hanstrom (1947), and that of 
Ailurus fulgens by Oboussier (1955). The topog- 
raphy of the hypophysis in Ailuropoda closely 
resembles that of the bears and lesser panda (es- 
pecially the bears) and differs considerably from 
that of the Canidae. Except for a very brief de- 
scription of the hypophysis of Potos by Oboussier, 
the structure of this organ in the Procyonidae is 


The thyroid is composed of the customary pair 
of lateral lobes that lie on either side of the tra- 
chea, and are connected by a narrow isthmus. The 
lobes are somewhat asymmetrically situated in the 
specimen dissected, the left being more posterior 
than the right. This condition is reflected in the 
direction of the isthmus, which runs diagonally in- 
stead of transversely. 

Each lobe has a length of about 55 mm. and a 
width of about 20 mm. The right lobe extends 
from the cricoid cartilage back to the sixth tra- 
cheal ring; the left from the second tracheal ring 
to the tenth. The isthmus crosses the seventh 
tracheal ring. 

The thyroid is supplied by anterior and poste- 
rior vessels, which come from the thyrocervical 
trunks and the internal jugular veins. 


The parathyroids appear as a pair of small oval 
whitish structures on the dorsal surface of the thy- 
roid gland. They are symmetrically placed, one 
being located on each lateral lobe about 20 mm. 
from its anterior tip. Each body measures about 
12 mm. in length and 4 mm. in width. The left 
body is partly buried in the substance of the thy- 
roid, while the right lies wholly on the surface. 


The thymus is an elongate bilobed gland, pale 
chocolate brown in color. It is rather well devel- 
oped, with a length of 117 mm. The gland lies 
wholly within the mediastinum, its anterior end 
reaching only slightly beyond the middle of the 
first costal cartilage. The left lobe considerably 
exceeds the right in size. Both lobes lie to the left 
of the left innominate vein, and are crossed ven- 
trally by the left mammary artery and vein. 

A quantity of fat at either end of the thymus 
indicates that regression of this structure was well 
under way. 

The thymus is supplied by branches from the 
mammary vessels. 




The brain of the adult female giant panda Pan 
Dee was described briefly by Mettler and Goss 
(1946). The description given here is based on 
the brain of the subadult male Su Lin. It was 
embalmed in situ and later removed by sectioning 
the skull. The brain was undamaged. 

The brain of Su Lin weighed 238 grams, minus 
the dura but including the pia mater and arach- 
noid. This gives a ratio to body weight of 1 : 252. 
It measured 115 mm. in total length and 85 mm. 
in breadth. The brain of the adult male Mei Lan 
weighed 277 gi'ams, giving a ratio to body weight 
of about 1 : 496. This brain was partly decom- 
posed and not suitable for study. 

In dorsal view the brain is almost circular in out- 
line, but is somewhat acuminate anteriorly. The 
olfactory bulbs project prominently beyond the 
cerebrum. Posteriorly the cerebrum covers a little 
less than half of the cerebellum. In lateral view 
the brain is almost fiat inferiorly. The superior 
outline is arched, acuminate anteriorly and trun- 
cated at the posterior margin of the cerebellum. 
An endocranial cast of an adult skull (fig. 143) is 
much depressed in the frontal region, giving the 
brain an almost triangular outline in profile view. 
This reflects the degree of expansion of the dorsal 
sinus system in the skull of this individual. 


Medulla oblongata 

This region is short and broad, and conical in 
form, tapering posteriorly. The distance from the 
rear margin of the pons to the decussation of 
the pyramids is 12.5 mm. The pyramids stand 
out prominently, and the median ventral fissure 
is correspondingly deep. The olive region is broad 
and flat. Cranial nerves I X X 1 1 arise at the usual 
sites. The roots of the glossopharyngeal, vagus, 
and accessorius cannot be separated from one an- 
other. The corpus trapezoides, lying immediately 
behind the pons, is not clearly defined. From it 
arise the facial and auditory nerves (VII and VIII). 
The abducens (VI) arises in the angle between the 
lateral border of the pyramid and the posterior 
border of the corpus trapezoides. 


The pons is a flattened eminence, 27 mm. in 
transverse diameter. It is broadest at its poste- 
rior margin and therefore somewhat trapezoidal in 
outline. The basilar sulcus is very shallow. The 
root of the trigeminal nerve (V) arises from the 
posterolateral angle of the pons. 


The cerebellum is spindle-shaped in dorsal view, 
almost circular in sagittal section. It measures 
59 mm. in breadth by 36 mm. in length, and weighs 
about 35 grams, about 15 per cent of total brain 
weight. On a mid-sagittal section (fig. 146) the 
cortex is extensive and richly foliated, the medulla 
correspondingly small. The central gray substance 
is small and stellate, the limbs of the arbor vitae 
slender. A narrow, deep fastigium extends nearly 
vertically from the roof of the fourth ventricle to 
the central gray substance. Directly opposite the 
fastigium the primary fissure divides the cerebel- 
lum into anterior and posterior parts. The ante- 
rior part is slightly the larger. The relations of 
the remaining lobes and fissures are shown in the 

In dorsal view the anterior lobe is broad, with a 
U-shaped posterior boundary marked by the pri- 
mary fissure. The lunate lobule (simplex of Bolk, 
1906, and Haller, 1934) is narrow and crescent- 
shaped, embracing the anterior lobe from behind. 
The posterior boundary is easily distinguished be- 
cause the folia of the lunate are continuous across 
the paramedian sulcus, whereas those of the me- 
dian lobe are not. The limbs of the lunate lobule 
exclude the ansiform lobule from contact with the 
anterior lobe, except at the extreme anterior end 
of the cerebellum. The unpaired lobulus medianus 
posterior of Bolk (1906), separated from the paired 
lateral lobes by the paramedian sulcus, is divided 
by transverse fissures into a short median lobe 
(tuber vermis), a longer pyramis, a uvula, and a 
nodulus. The tuber vermis is straight as in other 

The ansiform lobule is large and very similar to 
that of the Ursidae, composed of two crura sepa- 
rated by a deep and slightly S-shaped intercrural 
sulcus. It hides the paraflocculus almost com- 
pletely in dorsal view. The pteroid area (crus I 




Fig. 143. Endocranial east of adult female Ailuropoda (CNHM 36758). Lateral view (X 1). 

of the ansiform lobule") is broad and triangular, 
and continues without interruption into eras IL 
Crus II is worm-like, with regular transvei-se folia, 
and is faintly S-shaped. Bolk describes a second- 
ary, ventrally concave loop (the "ansula") in crus II 
in Ursus arctos, Thalarctos maritimus, and Felis 
leo, and I found this loop well developed in two 
specimens of Ursus americanus. It is absent in 
the brain of Ailuropoda. Medially crus II con- 
tinues without interruption into the paramedian 
lobule, which descends vertically on the posterior 

surface of the cerebellum, lying between the py- 
ramis and the medial end of the paraflocculus. 

The paraflocculus closely resembles that of the 
Ursidae. It is a large U-shaped lobe composed of 
regular transverse folia, giving it a worm-like ap- 
pearance. The larger superior limb abuts against 
the inferior end of the paramedian lobule, the 
smaller and shorter inferior limb terminates against 
the flocculus. The petrosal lobule, at the convex- 
itj' of the U, does not protrude beyond the re- 
mainder of the paraflocculus. The flocculus is a 

Sulcus CTudatus 
A. cerebri ant. 

Fissura primaria 


Medulla oblongata 

C<Hpus callosum 

Chiasma opticum 

Ventriculus tatius 

Thalamus . . 

Hypophysis Cwpus mamillans 

Aquaeductus cerebri 
CoUiculus ant. 

Pedunculus cCTebri 

Fig. 144. Brain of Ailuropoda, mid-sagittal section (X 1). 



A. ethmoidalis 

A. cerebri ant. 

A. cerebri med. ...^ f 

A. communicans ant 

A. chorioidea 
A. carotis int. 

A. communicans post 

A. cerebri post. 
A. cerebelli sup.- 

Tractus olfactorius 
N. opticus (II) 

A. cerebelli inf. ant 

N. facialis (VII) 

N. acusticus (VIII) 

A. basilaris 

A. cerebelli inf. 

lasma opticum 

N. oculomotorius (III 

N. trochlearis (IV) 

N. trigeminus (V) 

. abducens (VI) 

_N. glossopharyngeus (IX) 

N. vagus (X) 
N. hypoglossus (XII) 

N. accessorius (XI) 
A. vertebralis 

Fig. 145. Brain of Ailuropoda, inferior view (X 1). 

small lamella wedged in between the inferior limb 
of the paraflocculus and the cerebellar peduncle. 

Fourth ventricle 

On sagittal section this appears as a roomy 
chamber, narrowing rather abruptly anteriorly and 
posteriorly. Its floor is distinctly concave. 

Midbrain and Thalamus 

These structures were studied only on a mid- 
sagittal section through the brain (fig, 144). 


The aquaeductus cerebri (sylvii) is of almost uni- 
form diameter in sagittal section, only a little larger 

posteriorly than anteriorly. It lies only slightly 
above the level of the fourth ventricle. The cor- 
pora quadrigemina (colliculi anteriores and poste- 
riores) roof over the anterior part of the aqueduct. 
Each anterior quadrigeminate body is a low rounded 
hillock, much broader than long. The posterior 
body, on the contrary, scarcely forms an elevation. 
The optic tract emerges from beneath the pyri- 
form lobe of the cerebrum, closely applied to the 
cerebral peduncle. In front of the tuber cinereum 
the optic tract leaves the optic chiasma, from 
which the optic nerves (II) arise. Mettler and 
Goss commented on the small diameter of the optic 

Fissura primaria 

Fiss. praecentralis 

Fiss. praepyramidalis 

Fig. 146. Cerebellum of Ailuropoda, mid-sagittal section. 

Fiss. secunda 

Fiss. primaria 

Lob. ant. 

Lob. lunatus 

S. paramed. 

Lob. med. 

Lob. paramed, 

S. intercruralis 

Lob. ansiformis 

Fiss. paraflocculus 


Fig. 147. Cerebellum of Ailuropoda, lateral view. 




nerves, but I find them relatively no smaller than 
in a specimen of Ursus americanus. 

A sagittal section through the cerebral peduncles 
at the interpeduncular fossa is nearly rectangular 
in outline. In inferior view the peduncles appear 
as broad tracts emerging from beneath the optic 
tracts and converging to disappear into the pons. 
The mammillary bodies form a low rounded emi- 
nence, scarcely subdivided into a paired structure, 
lying in the angle between the limbs of the cere- 
bral peduncles. The oculomotor nerve (III) arises 
as usual from the interpeduncular fossa. 


In mid-sagittal section the thalamus is circular, 
surrounded by a rather narrow third ventricle. 


In mid-sagittal section the corpus callosum ap- 
pears as the usual U-shaped structure, 31 mm. in 
length, with a nearly straight body, a sharply bent 
knee, and a slightly arched splenium. A deep sul- 
cus corporis callosi separates it from the cerebral 
convolutions lying directly above it. 

Gyri and sulci 

These were mapped by Mettler and Goss on the 
brain of the panda Pan Dee. The configuration in 
our specimen differs from theirs only in unimpor- 
tant details. The nomenclature used here is largely 
that of Papez (1929). 

As in carnivores in general, the pattern of gyri 
and sulci in Ailuropoda is characterized by a con- 
centric series of vertical arches (the arcuate convo- 
lutions) arranged around a central sylvian fissure, 
with vertical furrows predominating over horizon- 
tal on the whole cerebral cortex. There is a deep 
sylvian fossa, with the sylvian fissure and sylvian 
gyri (first arcuate convolution) hidden from view 
within the fossa, as in the Ursidae (HoU, 1899; 
Smith, W. K., 1933a), Procyon (Papez, 1929), and 
Mustelidae (Holl, 1899). The lips of the sylvian 
fossa are formed by the second arcuate convolu- 
tion, composed of the anterior and posterior ecto- 
sylvian gyri. The anterior ectosylvian gyrus is 
more slender and lies slightly deeper than the pos- 
terior. The third arcuate convolution is composed 
of the anterior and posterior suprasylvian gyri. 

The coronal sulcus is conspicuous, sinuous, and 
oriented at an angle of about 45 to the basal plane 
of the brain. It is continuous dorsally with the 
lateral sulcus, as in the Ursidae. The inferior tem- 
poral gyrus is represented by the inferior loop con- 
necting the posterior ectosylvian and posterior 
suprasylvian gyri, and is continuous with both of 
these gyri. The temporal lobe of the cortex, repre- 
sented by the sylvian, posterior ectosylvian, poste- 

rior suprasylvian, and inferior temporal gyri (Papez, 
1929), is only moderately developed as compared 
with that of the dog or cat, resembling that of 
the bears. 

The coronal gyrus is very large and bifid inferi- 
orly (this cleft was absent in the brain of Pan Dee). 
In Ursus and other arctoids the inferior end of the 
coronal gyrus extends forward beneath the poste- 
rior sigmoid gyrus to meet the inferior end of the 
anterior sigmoid gyrus. In Ailuropoda, however, 
the coronal gyrus is separated from the anterior 
sigmoid gyrus by the downward expansion of the 
posterior sigmoid gyrus. 

The postcruciate gyrus is continuous anteriorly 
with the posterior sigmoid gyrus. It is well devel- 
oped and subdivided by short shallow furrows, and 
is considerably more extensive than the correspond- 
ing gyrus in our specimen of Ursus americanus 
(fig. 149). The postcruciate gyrus, together with 
the coronal gyrus, represents somatic afferent area I. 

The ansate sulcus, separating the postcruciate 
from the posterior sigmoid area, is a short sagittal 
furrow unconnected with any other furrow. In 
bears the ansate may be similarly isolated (Haller, 
1934, fig. 195), or it may be connected with the 
lateral sulcus (fig. 148). 

The sigmoid gyri, surrounding the cruciate sul- 
cus, are extensive. The posterior sigmoid gyrus 
(motor area I) is much expanded ventrally. The 
inferior, expanded part of this gyrus corresponds 
to the facial-masticatory motor area in Ursus 
(Smith, W. K., 1933b). The cruciate sulcus, sep- 
arating the frontal from the sigmoidal area, ex- 
tends only a short distance onto the medial surface 
of the hemisphere, and is not connected with any 
other sulcus. 

Anteriorly there is a well-developed frontal area. 
It is divided into three well-marked frontal gyri: 
a superior, separated from the posterior sigmoid by 
the cruciate sulcus, a middle frontal, and an infe- 
rior frontal (proreal). The superior frontal gyrus, 
the "ursine lozenge," is about as well developed 
as in the bears. The short sagittally directed pro- 
real sulcus extends forward from the presylvian sul- 
cus, separating the middle and inferior frontal gyri. 

The lateral gyrus is broad, and is subdivided in- 
to two parts by a parietal sulcus, as in Ursus. The 
lateral sulcus is continuous with the postlateral 
sulcus, which separates the posterior suprasylvian 
gyrus from the ectolateral gyrus. The postlateral 
sulcus terminates at about the level of the lower 
third of the cerebrum, on both sides of the brain; 
in the brain of Pan Dee it continued down into the 
temporal pole, as in Ursus. In the brain of Su Lin 
the ectolateral gyrus is interrupted by a short 

S. lateralis 

Ailuropoda melanoleuca 

S. postlata^is 

S. entolateralis 

S. coronalis 

S. postcruciatus 

S. ansatus 
G. frontalis sup. 

S. proreus 

S. suprasylvius post. 

S. praesylvius 
S. cruciatus 

S. suprasylvius ant. 
Fossa Sylvia 




S. entolateralis 

Ursus americanus 

ll ! I I 1 11 FACE 

S. lateralis 


S. ansatus 

G. frontalis sup. 

S. cruciatus 

S. proreus 

S. postlateralis 
S. suprasylvius post 

S. praesylvius 

S. coronalis 
S. suprasylvius ant. 
Fossa Sylvia 

Fig. 148. Right cerebral hemisphere of Ailuropoda and Ursus to show patterns of gyri and sulci. Lateral view. Motor 
area I in Ursus mapped from Smith (1933b). Note particularly the expanded masticatory motor area in Ailuropoda. 




S. praesylvius 
S. praecruciatus 
S. cruciatus a\1 

S. praesylvius 

S. cruciatus 

S. ansatus 
S. coronalis 

S. suprasylvius ant. 
Fossa sylvia 
S. suprasylvius post, 

suprasylvius ant. 

suprasylvius post. 

S. postlateralis 

S. lateraUs g. parietalis 

S. lateralis 
S. parietalis 

1. postlateralis 



Fig. 149. Right cerebral hemisphere of Ailuropoda and left cerebral hemisphere of Ursus americanus to show patterns 
of gyri and sulci. Dorsal view. 

transverse furrow in the temporal region; this sec- 
ondary furrow is only indicated by a notch in the 
brain of Pan Dee, and is completely absent in 

On the medial surface of the cerebrum (fig. 150) 
the cortex is divided by a deep and nearly contin- 
uous furrow, paralleling the corpus callosum, into 
a dorsal and a ventral system of gyri. The furrow 
begins posteriorly with a very deep and nearly 
vertical calcarine sulcus, which above terminates 
abruptly in a short transverse furrow. Behind the 
calcarine sulcus lies the broad lingual gyrus, cleft 
by a postcalcarine sulcus and behind this by a para- 
calcarine sulcus, both of which parallel the cal- 
carine sulcus. A short intercalary sulcus connects 
anteriorly with a long cingular sulcus, from which 
three short lateral furrows go off at right angles. 
Anteriorly, the cruciate sulcus is continued into a 

U-shaped rostral sulcus. T:ie genual sulcus is a 
short diagonal fissure behind the rostral sulcus. 
The system of sulci on the medial surface of the 
rostral region is much simpler than in Ursus (see 
also Smith, W. K., 1933a, fig. 6). 

The inferior end of the calcarine sulcus is con- 
tinuous with a well-developed sulcus on the infe- 
rior surface of the brain, running laterad behind 
the rhinal fissure. According to Elliot Smith (1902) 
this sulcus is fully developed only in bears (see also 
Smith, W. F., 1933a, fig. 8), and was called by him 
the "ursine sulcus." It is as well developed in 
Ailuropoda as in the bears. 

The parasplenial gyrus is remarkably broad. It 
is bounded inferiorly by the corpus callosum, pos- 
teriorly by the calcarine sulcus, and superiorly by 
the intercalary and cingular sulci. Anteriorly it 
continues without interruption into the cingular 


AUuropoda melanoleuca 

S. verticalis 

S. cingularis 

S. intercalaris 

S. suprasplenialis 

S. cniciatus 

S. rostralis 

S. postcalcarinus 

S. paracalcarinus 

S. calcarinus 

S. genualis 

S. lu^nus 

Ursus americantis 

S. verticalis 

S. intercalaris 


S. rostralis 

S. calcarinus 


S. ursinus 
Fig. 150. Medial surface of right cerberal hemisphere of AUuropoda and Ursus to show patterns of gyri and sulci. 

gyrus, which is also notably broad. The straight 
and subcallosal gyri are poorly marked. The supra- 
splenial gyrus bears a short, nearly vertical su- 
prasplenial sulcus instead of the longitudinal one 
usually present in carnivores. The middle parietal 
gyrus is much longer than in Ursus. Because of 
the short distance that the cruciate sulcus extends 
onto the medial surface of the hemisphere, the 
middle parietal gyrus is continuous with the supe- 
rior frontal gyrus. 

Central Olfactory Structures 

The olfactory brain of AUuropoda is much re- 
duced compared with the corresponding structures 

in a brain of Ursus americanus. The bulbs are 
relatively smaller, and the olfactory stalks slender. 

The olfactory bulbs are ovate structures, about 
16 mm. in length, lying anterior to the cerebrum. 
The olfactory tracts are prominent but slender. 
Each divides posteriorly into lateral and medial 
parts. The lateral olfactory tract is much the 
larger. It is a rope-like structure that diverges 
from the midline as it runs posteriorly; it termi- 
nates in the pyriform lobe. The medial olfactory 
tract is a short flat band that separates from the 
lateral tract and runs posteriorly and medially to 
the olfactory tubercle. The olfactory tubercle is 




a low eminence, perforated by numerous holes for 
blood vessels, lying just anterior and medial to the 
tip of the pyriform lobe. Between the olfactory 
tubercle and the optic tract is a rather broad diag- 
onal band of Broca, the lateral end of which dis- 
appears beneath the pyriform lobe. 

Discussion of Brain 

Comparative studies of the brain in the Carni- 
vora have dealt almost entirely with the pattern 
of the gyri and sulci in the cerebral cortex. The 
morphology of these structures was compared by 
Krueg (1880), Mivart (1885b), Holl (1889), Klatt 
(1928), Papez (1929) and Haller (1934). Motor 
areas in the cortex of Ursus were mapped by W. K. 
Smith (1933b), and both motor and sensory areas 
in Procyon by Welker and Seidenstein (1959) and 
in Canis most recently by Pinto Hamuy, Bromiley 
and Woolsey (1956). 

The brain of Procyon has been figured by Klatt, 
Papez, and Welker and Seidenstein, that of Nasua 
by Klatt, and of Ailurus by Flower (1870) and 
Klatt. Bear brains have been figured by Mivart, 
Papez, W. K. Smith (1933a), Haller, and others. 
I had the following arctoid brains available for 
comparison: Bassariscus astutus (1), Procyon lotor 
(3), Nasua narica (1), Ailurus fulgens (1), Ursus 
americanus (2). 

The question of whether the sulci demarcate 
physiological subdivisions of the cortex or are mere 
artifacts resulting from expansion of the cortex is 
of considerable importance, since it is unlikely that 
the brains of more than a few species will ever be 
studied experimentally in the living state. This 
question has been much disputed (Haller, 1934). 
The work of Welker and Seidenstein indicates that 
at least in the Carnivora the sulci do delimit true 
physiological subdivisions, the correspondence in 
Procyon extending down to such small anatomical 
units as the individual digits. They found a faith- 
ful relation maintained despite individual varia- 
tions in the location and orientation of the sulci. 

Of similar interest is the question of whether 
there is a correlation between degree of receptor 
specialization and degree of cortical elaboration. 
Such a correlation has been found for every exam- 
ple of a highly specialized function that has been 
checked experimentally (reviewed by Welker and 
Seidenstein, 1959), and we may therefore assume 
with some confidence that similar correlations exist 
in animals where experimental verification is im- 

The pattern of gyri and sulci is remarkably uni- 
form in all canids (Mivart, 1885b; Klatt, 1928), 
and more primitive than that of the Procyonidae 
and Ursidae. The Procyonidae and Ursidae, in 

turn, have a common pattern. The pattern in 
Ailurus is more primitive than in Procyon and 
Nasua, but definitely represents the procyonid- 
ursid type (Klatt). 

In the procyonids and bears the sigmoidal (mo- 
tor I) and coronal and postcruciate (somatic affer- 
ent) areas of the cortex are greatly expanded, and 
elaboration of these areas is associated with a cor- 
responding elaboration of the motor and sensory 
functions (Smith, W. K., 1933b; Welker and Sei- 
denstein, 1959). The morphological result of this 
expansion is that (1) the superior end of the sylvian 
fossa tends to be crowded posteriorly, (2) the syl- 
vian gyri (first arcuate convolution) are crowded 
into the sylvian fossa, where they are hidden from 
view, and (3) the postcruciate area is considerably 
divided up by secondary fissures, especially in the 
Procyonidae. On the medial surface of the hemi- 
sphere the cruciate sulcus fails to meet the cingular 
sulcus, at least in Procyon, Ailurus, and the Ursi- 
dae. These two sulci meet in all canids. 

The bears and procyonids differ in a few impor- 
tant respects, and in several minor details sum- 
marized briefly by Mettler and Goss. The frontal 
area of the cortex is relatively larger in bears, and 
the superior frontal gyrus appears on the surface 
as a well-developed "ursine lozenge," a structure 
that is rudimentary in procyonids and absent in 
other carnivores. The procyonid brain is notable 
for the great expansion of the postcruciate area 
(the central part of somatic afferent area I). As 
a result of this expansion the continuity of the 
coronal-lateral sulcus is broadly interrupted, where- 
as in the Ursidae these two sulci are continuous as 
in other arctoids. Welker and Seidenstein (1959) 
have showti that this expanded part of somatic 
afferent area I is devoted to the hand in Procyon. 
In the bears the lateral gyrus is divided longitudi- 
nally by a parietal sulcus (often indicated in dogs), 
whereas in procyonids this gyrus is narrower and 
lacks the parietal sulcus. 

Gross differences in the cerebral cortex between 
the Canidae on the one hand, and the Procyonidae 
and Ursidae on the other, are attributable almost 
entirely to expansion of three areas in the procy- 
onid-bear brain. These are (1) the postcruciate- 
coronal area, (2) the sigmoidal area, and (3) the 
frontal area. These cannot be attributed to dif- 
ferences in brain size, since the procyonids are con- 
siderably smaller than large dogs. Experimental 
studies have shown, on the contrary, that elabora- 
tion of the first two of these areas is associated with 
elaboration of manual and prehensile functions in 
procyonids and bears. 

In Ailuropoda the pattern of gyri and sulci agrees 
closely with that of the Ursidae. Mettler and Goss 



state that the arrangement in Ailuropoda "is so 
similar to what is seen in the bears that one is 
forced to rely on small variations from the ursine 
pattern to detect any differences in the brain." 
The brain of Su Lin differs in minor details from 
the brain of Pan Dee as described and figured by 
Mettler and Goss, but confirms the close similarity 
in gross brain structure between the giant panda 
and the bears. The cortex of Ailuropoda differs 
in two points that seem to be of importance: (1) 
The postcruciate area is considerably larger than 
in Ursus. A similar, though even more extensive 
elaboration of this area is associated with elabo- 
ration of sensory functions of the hand in Procyon 
(Welker and Seidenstein). It is reasonable to as- 
sume a similar correlation in Ailuropoda. (2) The 
inferior end of the posterior sigmoid gyrus is con- 
siderably larger than in Ursus. This is the facial- 
masticatory motor area in Ursus (Smith, W. K., 
1933b), and its elaboration in Ailuropoda is asso- 
ciated with elaboration of the masticatory func- 
tion. The motor area for the fore limb does not 
appear to be any larger than in Ursus. 

Thus the two elements of major adaptive speciali- 
zation in Ailuropoda (the hand and the masticatory 
apparatus) are both associated with elaboration of the 
corresponding areas of the cerebral cortex. 

The gross structure of the cerebellum offers little 
of interest within the Carnivora. Eight carnivores, 
including three arctoids (Canis familiaris, Ursus 
arctos, Thalarctos maritimus) were included in the 
material used by Bolk (1906). In general, the cere- 
bellum is better developed in bears than in Canis. 
This is particularly evident in crus II of the ansi- 
form lobule, in which a secondary loop (the an- 
sula) is present in bears. The ansula is absent in 
Ailuropoda and the Procyonidae. 

Among the Carnivora, the cerebellum is largest 
in the Ursidae (15.8-16.3 per cent of total brain 
weight in three individuals), smallest in the Cani- 
dae (average 9.5 per cent in 16 domestic dogs) 
(Putnam, 1928). No values are available for any 
procyonid. My figure for Ailuropoda (15 per cent) 
is very similar to that for the bears. 


1. Gross differences in brain structure among arc- 
toid carnivores involve chiefly the cerebral cortex. 

2. In the Canidae the cerebral cortex is less spe- 
cialized than in the Procyonidae and Ursidae. 

3. In the Procyonidae and Ursidae the cerebral 
cortex has been modified by expansion of three 
areas: the sigmoidal, coronal and postcruciate, and 
frontal. The first two are associated with enhanced 
prehensile and tactile functions of the fore limb in 
raccoons and bears. 

4. In gross structure the brain of Ailuropoda 
agrees closely with the brain of the Ursidae in all 

5. The postcruciate gyrus (somatic afferent area 
for the fore limb) and the inferior end of the pos- 
terior sigmoid gyrus (masticatory motor area) are 
larger in Ailuropoda than in Ursus. 


A^. Opticus (II) (fig. 151) 

The optic nerve emerges from the optic foramen, 
to pursue a faintly S-shaped course to the eye ball. 
It has a diameter of about 2.5 mm., and its length 
from the optic foramen to the back of the eye ball 
is 50 mm. 

A'^. Oculomotorius (III) (fig. 151) 

The oculomotor nerve is the most medial of the 
nerves passing out of the orbital fissure. Just be- 
fore reaching the base of the rectus superior muscle 
it divides into superior and inferior branches. The 
smaller superior branch passes along the lateral 
border of the rectus superior, supplying that mus- 
cle and giving off a fine twig to the levator palpe- 
brae superioris. 

The inferior branch passes forward between the 
rectus superior and the retractor oculi, then be- 
neath the optic nerve. At about the middle of the 
optic nerve it gives off a branch to the rectus me- 
dialis, a branch to the rectus inferior, then the 
Radix brevis ganglii ciliaris, and is itself continued 
as a branch to the oblique inferior. 

N. Trochlearis (IV) (fig. 151) 

The trochlear nerve is the most dorsal of the 
nerves passing out of the orbital fissure. It passes 
forward above the rectus superior and levator pal- 
pebrae superior to the dorsal border of the superior 
oblique. The nerve enters the latter muscle at 
about its middle. 

A^. Trigeminus (V) 
N. Ophthalmicus (Trigeminus 1) 

The ophthalmic nerve emerges from the skull 
through the orbital fissure, situated within the 
ophthalmic vein. It emerges from the vein at the 
posterior third of the orbit, where the vein breaks 
up into its terminal branches. The ophthalmic 
nerve has only two main branches, the frontal and 
the nasociliary.' The nerve separates into these 
branches at the semilunar ganglion. 

1. N. frontalis (fig. 152) is slightly smaller than 
the nasociliary. It accompanies the frontal artery 
and superior orbital vein over the dorsal surface of 

' The lacrimal branch of the human ophthalmic forms a 
part of the maxillary nerve in carnivores (see p. 30). 



Biilbus oculi 
R. palpebralis iiif 
R. palpebralis sup. 

N. infratrochlearis 


N. m. levator palpebrae sup 

Nn. ciliares longi